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Multi-Dimensional Direct-Write Nanofabrication...
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Multi-Dimensional Direct-Write Nanofabrication

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "D：Materials and Processing".

Deadline for manuscript submissions: closed (31 October 2019) | Viewed by 58836

Special Issue Editor

Dr. Harald Plank

E-Mail Website
Guest Editor
Institute of Electron Microscopy and Nanoanalysis, Graz University of Technology, Steyrergasse 17, 8010 Graz, Austria
Interests: direct-write nanofabrication; focused electron beam-induced deposition; focused ion beam processing; atomic force microscopy; functional nano-probes

Special Issue Information

Dear Colleagues,

During the last decade, additive direct-write manufacturing has attracted considerable attention in research and development. The main advantage of such a method is the ability to fabricate complex structures in a single-step, which expands accessibility to non-flat surfaces, morphologically exposed areas, already finished device architectures, or encapsulated packages; accordingly, such direct-write technologies complement situations in which alternative methods approach their intrinsic limitations. While applications on the micro- and meso-scale below are already well established in industrial productions such as roll-to-roll processes, laser sintering, inkjet printing, or imprint lithography, the extension to the real nanoscale is still an ongoing and highly challenging task. Promising candidates with the potential to meet these dimensional requirements are photons, ions, or electrons, as demonstrated by numerous proof-of-principle studies during the last decade. Aside from their technical nature, direct-write approaches enable controlled fabrication of complex, freestanding 3D nano-architectures in a single step, which paves the way for novel applications. Accordingly, this Special Issue seeks to showcase research papers, short communications, and review articles that focus on (1) additive and/or subtractive direct-write technologies for (2) fabrication of 1D–3D nanostructures including their combination to larger structures, (3) modelling fundamental process mechanisms, and (4) applications and/or material properties of such structures that strongly benefit from direct-write fabrication approaches.

Prof. Dr. Harald Plank
Guest Editor

Manuscript Submission Information

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Keywords

  • Additive direct-write nanofabrication
  • Subtractive direct-write nanofabrication
  • Process modelling
  • Applications and material properties.

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Published Papers (8 papers)

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Research

Jump to: Review

9 pages, 10729 KiB  
Article
Temperature-Dependent Growth Characteristics of Nb- and CoFe-Based Nanostructures by Direct-Write Using Focused Electron Beam-Induced Deposition
by Michael Huth, Fabrizio Porrati, Peter Gruszka and Sven Barth
Micromachines 2020, 11(1), 28; https://doi.org/10.3390/mi11010028 - 25 Dec 2019
Cited by 8 | Viewed by 3297
Abstract
Focused electron and ion beam-induced deposition (FEBID/FIBID) are direct-write techniques with particular advantages in three-dimensional (3D) fabrication of ferromagnetic or superconducting nanostructures. Recently, two novel precursors, HCo 3 Fe(CO) 12 and Nb(NMe 3 ) 2 (N-t-Bu), were introduced, resulting in fully [...] Read more.
Focused electron and ion beam-induced deposition (FEBID/FIBID) are direct-write techniques with particular advantages in three-dimensional (3D) fabrication of ferromagnetic or superconducting nanostructures. Recently, two novel precursors, HCo 3 Fe(CO) 12 and Nb(NMe 3 ) 2 (N-t-Bu), were introduced, resulting in fully metallic CoFe ferromagnetic alloys by FEBID and superconducting NbC by FIBID, respectively. In order to properly define the writing strategy for the fabrication of 3D structures using these precursors, their temperature-dependent average residence time on the substrate and growing deposit needs to be known. This is a prerequisite for employing the simulation-guided 3D computer aided design (CAD) approach to FEBID/FIBID, which was introduced recently. We fabricated a series of rectangular-shaped deposits by FEBID at different substrate temperatures between 5 ° C and 24 ° C using the precursors and extracted the activation energy for precursor desorption and the pre-exponential factor from the measured heights of the deposits using the continuum growth model of FEBID based on the reaction-diffusion equation for the adsorbed precursor. Full article
(This article belongs to the Special Issue Multi-Dimensional Direct-Write Nanofabrication )
►▼ Show Figures

Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Thickness vs. temperature of samples grown at 5 keV and 1.6 nA beam current (experiment <span class="html-italic">a</span>). Green points: samples fabricated with the CoFe-precursor. Blue squares: samples grown using the Nb-precursor. Red stars: deposits grown with the Pt-precursor. Distributed about the main panel, a selection of scanning electron microscope (SEM) images is shown for samples fabricated at the substrate temperatures as indicated.</p> Full article ">Figure 2
<p>Thickness vs. temperature of samples grown at 5 keV and 30 pA beam current (experiment <span class="html-italic">b</span>). Green points, blue squares, and red stars refer to samples grown using the CoFe-, Nb-, and Pt-precursor, respectively. Distributed about the main panel, a selection of SEM images is shown for samples fabricated at the substrate temperatures as indicated.</p> Full article ">Figure 3
<p>Topography (upper row) and line scans (middle and lower row) from atomic force microscope (AFM) measurements carried out on samples prepared at 15 <math display="inline"><semantics> <msup> <mrow/> <mo>°</mo> </msup> </semantics></math>C using the precursors as indicated: For each sample, a scan in the vertical direction (in blue) and horizontal direction (in red) is shown. The last two column of pictures, labeled <span class="html-italic">CoFe (b)</span> and <span class="html-italic">CoFe (a)</span>, refer to samples prepared in experiments <span class="html-italic">b</span> and <span class="html-italic">a</span>, respectively.</p> Full article ">Figure 4
<p>Logarithm of <math display="inline"><semantics> <mrow> <mi>F</mi> <mo>(</mo> <mi>h</mi> <mo>)</mo> </mrow> </semantics></math>, as defined in Equation (<a href="#FD5-micromachines-11-00028" class="html-disp-formula">5</a>), plotted vs. <math display="inline"><semantics> <mrow> <mn>1</mn> <mo>/</mo> <mi>T</mi> </mrow> </semantics></math> for the CoFe-, Nb-, and Pt-precursor as indicated. The dashed lines represent linear fits of the data excluding the lowest temperature data point for the CoFe and Nb deposits and the two low-temperature data points for Pt deposits.</p> Full article ">
15 pages, 2098 KiB  
Communication
Simulation Informed CAD for 3D Nanoprinting
by Jason D. Fowlkes, Robert Winkler, Eva Mutunga, Philip D. Rack and Harald Plank
Micromachines 2020, 11(1), 8; https://doi.org/10.3390/mi11010008 - 18 Dec 2019
Cited by 13 | Viewed by 3254
Abstract
A promising 3D nanoprinting method, used to deposit nanoscale mesh style objects, is prone to non-linear distortions which limits the complexity and variety of deposit geometries. The method, focused electron beam-induced deposition (FEBID), uses a nanoscale electron probe for continuous dissociation of surface [...] Read more.
A promising 3D nanoprinting method, used to deposit nanoscale mesh style objects, is prone to non-linear distortions which limits the complexity and variety of deposit geometries. The method, focused electron beam-induced deposition (FEBID), uses a nanoscale electron probe for continuous dissociation of surface adsorbed precursor molecules which drives highly localized deposition. Three dimensional objects are deposited using a 2D digital scanning pattern—the digital beam speed controls deposition into the third, or out-of-plane dimension. Multiple computer-aided design (CAD) programs exist for FEBID mesh object definition but rely on the definition of nodes and interconnecting linear nanowires. Thus, a method is needed to prevent non-linear/bending nanowires for accurate geometric synthesis. An analytical model is derived based on simulation results, calibrated using real experiments, to ensure linear nanowire deposition to compensate for implicit beam heating that takes place during FEBID. The model subsequently compensates and informs the exposure file containing the pixel-by-pixel scanning instructions, ensuring nanowire linearity by appropriately adjusting the patterning beam speeds. The derivation of the model is presented, based on a critical mass balance revealed by simulations and the strategy used to integrate the physics-based analytical model into an existing 3D nanoprinting CAD program is overviewed. Full article
(This article belongs to the Special Issue Multi-Dimensional Direct-Write Nanofabrication )
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Figure 1

Figure 1
<p>(<b>a</b>) A 3D-FEBID computer simulation of a so-called ‘calibration structure’ exhibiting a non-linear downward deflection/distortion causing the experimental final deposit to deviate from the CAD design (grey sphere-stick model). The precursor surface concentration is color-coded and presented as a fraction of monolayer coverage. The distance measured from the substrate along the deposit is given by (s), the total deposit length is (S<sub>T</sub>); (<b>b</b>) The proposed distortion correction scheme is based on (Step 1) a computer simulation that mimics experiments. In Step 2, the most important physics governing deposition is revealed which is incorporated into an analytical model. Ideally, the analytical mathematical model, called the ‘dwell time compensation method’, can be derived based on physical/chemical principles to ultimately correct for geometric distortions; (<b>c</b>) 3D-FEBID of the calibration structure following implementation of the analytical correction model described conceptually in the Discussion section.</p> Full article ">Figure 2
<p>(<b>a</b>) The precursor surface concentration (<span class="html-italic">C</span>) along the deposit axis (<span class="html-italic">s</span>) at four different stages of deposition. The solid lines represent deposition without segment deflection compensation while the dashed lines represent deposition with compensation. Results are shown for a total deposit length (S<sub>T</sub>) ≅ 650 (<b>red</b>), 890 (<b>yellow</b>), 1120 (<b>green</b>) and 1300 nm (<b>blue</b>). The hatched grey line shows the boundary between the pillar (s &lt; 500 nm) and segment (s &gt; 500 nm) exposure elements.; (<b>b</b>) The complementary surface temperature (<span class="html-italic">T</span>) profile for the four stages of deposition shown in panel (a).</p> Full article ">Figure 3
<p>(<b>a</b>) 3D-FEBID simulation calibration structure cross-section for the uncorrected, as-deposited non-linear case. The dwell time per pixel τ<sub>d</sub> = 8.19 ms for segment deposition, E<sub>o</sub> = 30 keV, i<sub>b</sub> = 32 pA and P = 0.5 mTorr; (<b>b</b>) The distortion corrected, complementary 3D-FEBID simulation cross-section demonstrating the deposition of the intended linear segment. In this case, the dwell time per pixel spanned the range τ<sub>d</sub> = 8.19–12.23 ms. CAD specified a pillar length of 500 nm, a segment length of 1000 nm and a segment angle of ζ = 30°.</p> Full article ">Figure 4
<p>(<b>a</b>) A 3D-FEBID simulation demonstrating the uncorrected deposition of a calibration structure with a CAD specified segment angle of ζ = 54°, a pillar length of 400 nm, a segment length of 800 nm. The dwell time per pixel for segment deposition was τ<sub>d</sub> = 15 ms, E<sub>o</sub> = 30 keV, i<sub>b</sub> = 32 pA and P = 0.25 mTorr; (<b>b</b>) The complementary 3D-FEBID simulation for the corrected situation. The dwell time per pixel spanned the range τ<sub>d</sub> = 15–26.86 ms.</p> Full article ">Figure 5
<p>(<b>a</b>) A 3D-FEBID simulation of a calibration structure deposited at E<sub>o</sub> = 5 keV and i<sub>b</sub> = 25 pA. The CAD specified segment angle was ζ = 54°, the pillar element is 400 nm long and the segment element is 800 nm in length. The dwell time per pixel for the segment element was τ<sub>d</sub> = 15 ms; (<b>b</b>) The distortion corrected, complementary 3D-FEBID simulation cross-section where the dwell time per pixel spanned the range τ<sub>d</sub> = 15–21.94 ms during segment deposition.</p> Full article ">Figure 6
<p>(<b>a</b>) A 3D-FEBID simulation of a multi-level deposit exposure without dwell time compensation using E<sub>o</sub> = 5 keV, i<sub>b</sub> = 25 pA, P = 0.5 mTorr and T<sub>o</sub> = 294 K. The initial segment angle at take-off is ζ = 54° and the segment element length is 800 nm. A second segment element was deposited with an in-plane/substrate plane rotation of (π) to simultaneously simulate (i) a doubling of segment length and (ii) the incorporation of a ‘kink’ in the 3D geometry. Thus, the segment angle specified in the CAD file for the second segment is also ζ = 54°. (b) Dwell time compensation results in the desired linearization of the exposure elements. The dwell time range calculated for the first segment was τ<sub>d</sub> = 15–21.94 ms. The second segment required the dwell time range of τ<sub>d</sub> = 15–41.26 ms.</p> Full article ">Figure A1
<p>(<b>a</b>) The normalized precursor surface concentration (<span class="html-italic">C</span>/<span class="html-italic">C<sub>eq</sub></span>) profile along the calibration element centerline (s) for each profile previously shown in <a href="#micromachines-11-00008-f002" class="html-fig">Figure 2</a>a. In addition, only simulations without distortion correction are shown (<a href="#micromachines-11-00008-f002" class="html-fig">Figure 2</a>a, <b>-</b> for all colors). The concentration is normalized to the equilibrium concentration (<span class="html-italic">C<sub>eq</sub></span>) (<a href="#app2-micromachines-11-00008" class="html-app">Appendix B</a>). The position origin has been shifted to the total deposit length (s-S<sub>T</sub>) for each normalized concentration profile. The hatched line indicates that the characteristic region defining the relatively steep concentration gradient (∆s = 80 nm), feeding precursor to the BIR, is nearly constant, regardless of the total calibration structure length (S<sub>T</sub>). The total deposit length for each case is S<sub>T</sub> ≅ 650 (red), 890 (yellow), 1120 (green) and 1300 nm (blue).</p> Full article ">
14 pages, 6528 KiB  
Article
Additive Manufacturing of Sub-Micron to Sub-mm Metal Structures with Hollow AFM Cantilevers
by Giorgio Ercolano, Cathelijn van Nisselroy, Thibaut Merle, János Vörös, Dmitry Momotenko, Wabe W. Koelmans and Tomaso Zambelli
Micromachines 2020, 11(1), 6; https://doi.org/10.3390/mi11010006 - 18 Dec 2019
Cited by 38 | Viewed by 22113
Abstract
We describe our force-controlled 3D printing method for layer-by-layer additive micromanufacturing (µAM) of metal microstructures. Hollow atomic force microscopy cantilevers are utilized to locally dispense metal ions in a standard 3-electrode electrochemical cell, enabling a confined electroplating reaction. The deflection feedback signal enables [...] Read more.
We describe our force-controlled 3D printing method for layer-by-layer additive micromanufacturing (µAM) of metal microstructures. Hollow atomic force microscopy cantilevers are utilized to locally dispense metal ions in a standard 3-electrode electrochemical cell, enabling a confined electroplating reaction. The deflection feedback signal enables the live monitoring of the voxel growth and the consequent automation of the printing protocol in a layer-by-layer fashion for the fabrication of arbitrary-shaped geometries. In a second step, we investigated the effect of the free parameters (aperture diameter, applied pressure, and applied plating potential) on the voxel size, which enabled us to tune the voxel dimensions on-the-fly, as well as to produce objects spanning at least two orders of magnitude in each direction. As a concrete example, we printed two different replicas of Michelangelo’s David. Copper was used as metal, but the process can in principle be extended to all metals that are macroscopically electroplated in a standard way. Full article
(This article belongs to the Special Issue Multi-Dimensional Direct-Write Nanofabrication )
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Figure 1

Figure 1
<p>Automated force-controlled electrochemical (ec) 3D printing process schematized [<a href="#B36-micromachines-11-00006" class="html-bibr">36</a>] the simple case of two pillars side-by-side: we emphasize the layer-by-layer fabrication (layers I-III are labeled), i.e., the pillars are printed in parallel and not in series. (<b>a</b>) The ion tip filled with CuSO<sub>4</sub> solution is positioned over the first pillar at a set separation (e.g., 500 nm) where the metal voxel is to be deposited. Local electroplating is switched on at a given overpressure, leading to local pillar growth (voxel III). (<b>b</b>) When the growing voxel touches the pyramidal apex, a cantilever deflection is detected on the photodiode via the moving laser beam. The inset graph shows the temporal evolution of the deflection signal (defl.) for a voxel touching event (yellow segment). (<b>c</b>) As soon as this touching event is recognized by the software, the probe is moved to the next position, i.e., on top of the second pillar again with a typical separation of 500 nm, and the voxel ec deposition is started. Reprinted with permission from Ref. [<a href="#B36-micromachines-11-00006" class="html-bibr">36</a>]. Copyright 2017 John Wiley &amp; Sons Inc.</p> Full article ">Figure 2
<p>Scanning electron microscope (SEM) micrographs of the apertures at the apex of the pyramid of the ion tips. Top view of a (<b>a</b>) 300 nm and a (<b>b</b>) 500 nm diameter aperture, obtained by contact lithography. Top view of a (<b>c</b>) 100 nm, a (<b>d</b>) 1 µm and a (<b>e</b>) 2 µm side square aperture, obtained by focused ion beam (FIB) milling of closed pyramidal probes. The choice of the smallest aperture dimension of 100 nm was conditioned to avoid potential complications in filling the probes with electrolyte [<a href="#B54-micromachines-11-00006" class="html-bibr">54</a>], whereas 2 µm was the maximum size possible due to the limit set by the presence of the apex of the inner pyramid (discernable in (<b>e</b>)). Reprinted with permission from Ref. [<a href="#B51-micromachines-11-00006" class="html-bibr">51</a>]. Copyright 2019 John Wiley &amp; Sons Inc.</p> Full article ">Figure 3
<p>Schematic of the force-controlled ec µAM system. On the left, a system computer sends commands to the system control unit on the right. The system control unit governs the printing process using an embedded controller. The ion tip is mounted on the z-stage in the printing head and is moved inside the ec deposition cell by the z-and x-y stages. A microfluidics control system with 1 mbar precision regulates the electrolyte flow through the cantilever aperture. Adapted with permission from Ref. [<a href="#B51-micromachines-11-00006" class="html-bibr">51</a>]. Copyright 2019 John Wiley &amp; Sons Inc.</p> Full article ">Figure 4
<p>(<b>a</b>) SEM image of a field of pillars printed at different pressure and deposition potential values with a 300 nm aperture ion tip, while a SEM image of a single pillar with overlaid the results of the diameter d analysis is shown in the inset. (<b>b</b>) Pillar diameters d obtained as a function of the pressure applied during printing and, (<b>c</b>) volumetric deposition speed <math display="inline"><semantics> <mover accent="true"> <mi>z</mi> <mo>˙</mo> </mover> </semantics></math> as a function of the pressure. Panels (<b>b</b>) and (<b>c</b>) reprinted with permission from Ref. [<a href="#B51-micromachines-11-00006" class="html-bibr">51</a>]. Copyright 2019 John Wiley &amp; Sons Inc.</p> Full article ">Figure 5
<p>SEM images of pillars deposited with a nozzle aperture of 300 nm with 10, 50, 100, 150 and 200 mbar applied pressure and −0.42, −0.44, −0.46, −0.48 and −0.50 V deposition potential. All the images are taken at the same magnification (the scale bar corresponds to 2 µm).</p> Full article ">Figure 6
<p>(<b>a</b>) Vertical plating speeds (dots), (<b>b</b>) pillar diameters and, (<b>c</b>) volumetric deposition speeds as a function of the pressure applied during printing at different deposition potentials. Dots are the experimental data, whereas lines the fitted data. Because of the semi-empirical fitting, the lines have a characteristic shape.</p> Full article ">Figure 7
<p>SEM images of a 1:10,000 and a 1:70,000 replica of the David (Michelangelo). (<b>a</b>), (<b>b</b>) and (<b>c</b>) are the 1:10,000 scaled, 700 µm-tall replica imaged from different angles, the insets in (<b>a</b>) and (<b>b</b>), and the panel (<b>d</b>) are the 1:70,000 scaled, 100 µm-tall replicas.</p> Full article ">Figure 8
<p>SEM images (colored) of four intertwined coils printed with a 500 nm nozzle, each coil printed at a different pressure to highlight the flexibility and the ability to change and control the voxel size within the same structure during the printing process; 3056 voxels were printed in 25 min to obtain the 180 µm tall structures. (<b>a</b>) and (<b>b</b>) are two different views of the same object. Reprinted with permission from Ref. [<a href="#B51-micromachines-11-00006" class="html-bibr">51</a>]. Copyright 2019 John Wiley &amp; Sons Inc.</p> Full article ">

Review

Jump to: Research

47 pages, 14363 KiB  
Review
Mechanical Properties of 3D Nanostructures Obtained by Focused Electron/Ion Beam-Induced Deposition: A Review
by Ivo Utke, Johann Michler, Robert Winkler and Harald Plank
Micromachines 2020, 11(4), 397; https://doi.org/10.3390/mi11040397 - 10 Apr 2020
Cited by 49 | Viewed by 5958
Abstract
This article reviews the state-of-the -art of mechanical material properties and measurement methods of nanostructures obtained by two nanoscale additive manufacturing methods: gas-assisted focused electron and focused ion beam-induced deposition using volatile organic and organometallic precursors. Gas-assisted focused electron and ion beam-induced deposition-based [...] Read more.
This article reviews the state-of-the -art of mechanical material properties and measurement methods of nanostructures obtained by two nanoscale additive manufacturing methods: gas-assisted focused electron and focused ion beam-induced deposition using volatile organic and organometallic precursors. Gas-assisted focused electron and ion beam-induced deposition-based additive manufacturing technologies enable the direct-write fabrication of complex 3D nanostructures with feature dimensions below 50 nm, pore-free and nanometer-smooth high-fidelity surfaces, and an increasing flexibility in choice of materials via novel precursors. We discuss the principles, possibilities, and literature proven examples related to the mechanical properties of such 3D nanoobjects. Most materials fabricated via these approaches reveal a metal matrix composition with metallic nanograins embedded in a carbonaceous matrix. By that, specific material functionalities, such as magnetic, electrical, or optical can be largely independently tuned with respect to mechanical properties governed mostly by the matrix. The carbonaceous matrix can be precisely tuned via electron and/or ion beam irradiation with respect to the carbon network, carbon hybridization, and volatile element content and thus take mechanical properties ranging from polymeric-like over amorphous-like toward diamond-like behavior. Such metal matrix nanostructures open up entirely new applications, which exploit their full potential in combination with the unique 3D additive manufacturing capabilities at the nanoscale. Full article
(This article belongs to the Special Issue Multi-Dimensional Direct-Write Nanofabrication )
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>(<b>a</b>) Comparison of 3D nanoprinting via focused electron beam-induced deposition (FEBID) and focused ion beam-induced deposition (FIBID) to other sub-10-μm metal additive manufacturing methods within the speed-size parameter space. The acronyms stand for direct ink writing (DIW), electrohydrodynamic printing (EHD), laser-induced forward transfer (LIFT), the electroplating of locally dispensed ions in liquid–atomic force microscopy (AFM), and cantilever-based (FluidFM) and glass capillary-based scanning ion conductance microscope (SICM). The potential of multi-beam versus single beam FEBID/FIBID is indicated. Modified from Hirt et al. [<a href="#B1-micromachines-11-00397" class="html-bibr">1</a>]. (<b>b</b>,<b>c</b>) Examples of 3D FEBID. (<b>b</b>) Reprinted from Winkler et al. [<a href="#B7-micromachines-11-00397" class="html-bibr">7</a>], with the permission of AIP Publishing. (<b>d</b>) Example of 3D FIBID structure. Modified from Matsui et al. [<a href="#B8-micromachines-11-00397" class="html-bibr">8</a>].</p> Full article ">Figure 2
<p>(<b>a</b>) SRIM (stopping and ranges of ion in matter) [<a href="#B15-micromachines-11-00397" class="html-bibr">15</a>] simulation of a zero-diameter gallium ion beam and 100 trajectories (red) with the adjacent collision cascade (green) in a 100 nm wide and 400 nm tall pillar of carbon (density 2 g/cm<sup>3</sup>) illustrating the inevitable implantation of Ga (shaded red) and its redistribution via the collision cascade for primary energies of 30 kV (left) and 5 kV (right). Blue arrows signify secondary electrons (SEs), leading to deposition events if generated in close proximity to the surface. (<b>b</b>) TEM image of a core–shell structure of an as-grown Ga-based, FIBID carbon pillar using phenanthrene. Modified from Matsui et al. [<a href="#B69-micromachines-11-00397" class="html-bibr">69</a>]. (<b>c</b>) CASINO [<a href="#B66-micromachines-11-00397" class="html-bibr">66</a>] simulation of a zero-diameter electron beam and 20 trajectories (red) in a 100 nm wide and 1 μm tall carbon pillar for primary electron energies of 5 keV (left) and 20 keV (right). The electron trajectories were truncated once they exit the pillar volume for the sake of clarity. Blue arrows again indicate SEs generated along the electron paths. (<b>d</b>) SEM side view images of a carbonaceous FEBID pillar deposited from residual vacuum pump oil molecules on an AFM tip before (left) and after oxygen plasma treatment (right). The much narrower core that remains indicates a different chemical bonding, which is closely related to different mechanical properties. Modified from Wendel et al. [<a href="#B68-micromachines-11-00397" class="html-bibr">68</a>]. Note that (<b>a</b>) and (<b>c</b>) have the same scale for easy comparison and that the pillar diameters will also depend on the charged particle beam intensity profile (focus), which was omitted for the sake of clarity.</p> Full article ">Figure 3
<p>Approaches to measure the elastic modulus of FEBID/FIBID materials using simple high/low aspect ratio pillar or spring geometries. (<b>a</b>) Bending (one end pinned), (<b>b</b>) buckling, (<b>c</b>) nanocompression, (<b>d</b>) bending (two ends pinned), (<b>e</b>) thermal noise vibrations, and (<b>f</b>) spring tension (or compression). Circular cross-sections enable simple mathematics (see text), yet complex 3D architectures can be measured according to (<b>a</b>)–(<b>f</b>) as well.</p> Full article ">Figure 4
<p>Selected examples of published deposit shapes and methods to determine the elastic modulus. The force <span class="html-italic">F</span> acting on the structure is indicated in all images. (<b>a</b>) Bulk FEBID square deposit for nanoindentation, modified from Ding et al. [<a href="#B45-micromachines-11-00397" class="html-bibr">45</a>]. (<b>b</b>) FEBID pillar bending by commercial silicon cantilever, modified from Okada et al. [<a href="#B36-micromachines-11-00397" class="html-bibr">36</a>]. (<b>c</b>) FIB pillar bending by another FIB pillar with known spring constant, modified from Guo et al. [<a href="#B37-micromachines-11-00397" class="html-bibr">37</a>]. (<b>d</b>) FIB pillar vibration method combined with density determination, modified from Kometani et al. [<a href="#B38-micromachines-11-00397" class="html-bibr">38</a>]. (<b>e</b>) Tensile strain experiment with horizontal FIB rods on a comb drive stage, modified from Kiuchi et al. [<a href="#B39-micromachines-11-00397" class="html-bibr">39</a>]. (<b>f</b>) Compression of a thick FIB cube with 3.5 μm × 3.5 μm base area, modified from Kim et al. [<a href="#B41-micromachines-11-00397" class="html-bibr">41</a>]. (<b>g</b>) Thermal noise vibration method at the very end of a 21.7 μm long FIB pillar. The inset shows the related fuzzy secondary electron signal, modified from Nonaka et al. [<a href="#B42-micromachines-11-00397" class="html-bibr">42</a>]. (<b>h</b>) Tensile strain experiment with FIB helix fixed between a cantilever and gold glass capillary, modified from Nakamatsu et al. [<a href="#B43-micromachines-11-00397" class="html-bibr">43</a>]. The organic precursors used were paraffin (<b>a</b>) and phenanthrene (<b>b</b>) to (<b>h</b>).</p> Full article ">Figure 5
<p>Typical nanoindentation curve for a load–unload cycle. The elastic modulus and hardness derive from the unloading part. The inset schematically shows the indenter tip pushed into the sample.</p> Full article ">Figure 6
<p>Approaches to measure the yield strength (plasticity) and the fracture strength of FEBID and FIBID materials. (<b>a</b>) Bending (one end pinned), (<b>b</b>) tensile straining, and (<b>c</b>) nanocompression with a flat blunt indenter. An example of a stress–strain diagram obtained from a nanocompression experiment with an FEBID pillar is shown in (<b>d</b>). Plasticity and fracture onsets are indicated by arrows; see also the crack propagating into the pillar. Circular cross-sections enable simple mathematics (see text); yet more complex 3D architectures can be also measured according to (<b>a</b>)–(<b>c</b>).</p> Full article ">Figure 7
<p>Bending fracture experiment with silicon nanowires inside an SEM. A cantilever (shaded red) bends a pillar (shaded green) laterally (<b>a</b>) until it finally breaks off (<b>b</b>). (<b>c</b>) Finite element simulations of the curved foot base of a pillar. Geometry of bending experiment and foot base with a curvature <span class="html-italic">κ</span> = 10<sup>−2</sup>nm<sup>−1</sup>. Largest tensile (red) and compressive (blue) stresses occur above the substrate–pillar interface. (<b>d</b>) Deviations due to curved foot base with respect to Equation (12), which assumes idealized uniform cylinder geometry. Modified from Hoffmann et al. [<a href="#B89-micromachines-11-00397" class="html-bibr">89</a>].</p> Full article ">Figure 8
<p>Density determination of FEBID/FIBID nanostructures. (<b>a</b>) Resonant vibration mode of single clamped pillars. The alternating excitation force can be applied via the pillar substrate through piezoactuators or via electrostatic forces surrounding the pillar. (<b>b</b>) Frequency sweeps of vibration amplitude (upper) and phase shift (lower) for a FEBID pillar across its fundamental vibration. The frequency inset shows the total 1 MHz scan and a single excitation, which is due to the uniformity of the deposited pillar. The SEM observation insets show the top view of the pillar in static and resonant mode. Modified from Friedli et al. [<a href="#B53-micromachines-11-00397" class="html-bibr">53</a>]. (<b>c</b>) Mass measurement in the femtogram region via the frequency change of cantilevers during FEB or FIB deposition. The inset shows the shift in frequency during an FEBID deposition. Modified from Friedli et al. [<a href="#B46-micromachines-11-00397" class="html-bibr">46</a>].</p> Full article ">Figure 9
<p>Selected overview of published methods for the density determination of nanostructures grown by FEBID and FIBID. (<b>a</b>–<b>c</b>) Pt-C FEBID pillar vibration with electric AC excitation inside a TEM. The first (a and b) and second fundamental resonances (c) can be seen. Note the large amplitude that the pillar can withstand as well as the diameter Ø variations. Modified from Hao et al. [<a href="#B90-micromachines-11-00397" class="html-bibr">90</a>]. (<b>d</b>) SEM tilt view of an electrostatically AC excited Pt-C FEBID pillar vibration with integrated electrode design, modified from Arnold et al. [<a href="#B47-micromachines-11-00397" class="html-bibr">47</a>]. (<b>e</b>) FEBID Pt-C bridge, which monitors vibrations in situ via the current read out shown in (<b>f</b>) modified from Arnold et al. [<a href="#B47-micromachines-11-00397" class="html-bibr">47</a>]. (<b>g</b>) SEM tilt view of a laterally FIB grown pillar from W(CO)<sub>6</sub> with integrated electrode. The inset shows the fundamental resonance. Modified from Cordoba et al. [<a href="#B51-micromachines-11-00397" class="html-bibr">51</a>]. (<b>h</b>) Destructive mass measurements of FEBID pillars grown on a cantilever. Modified from Utke et al. [<a href="#B55-micromachines-11-00397" class="html-bibr">55</a>]. <b>(</b><b>i)</b> <span class="html-italic">In situ</span> mass measurement of a Pt-FIBID deposit deposited on an SEM integrated cantilever with piezoresistive frequency readout. Modified from Friedli et al. [<a href="#B46-micromachines-11-00397" class="html-bibr">46</a>]. (<b>j</b>) Mass measurement of Ga-FIB grown carbon structure. The cantilever frequency was measured before and after the deposition. Modified from Kometani et al. [<a href="#B38-micromachines-11-00397" class="html-bibr">38</a>].</p> Full article ">Figure 10
<p>The ternary phase diagram of carbon materials with varying sp<sup>2</sup>, sp<sup>3</sup>, and hydrogen contents. Modified from Robertson [<a href="#B92-micromachines-11-00397" class="html-bibr">92</a>]. The acronyms are amorphous carbon (a-C), tetrahedrally coordinated amorphous carbon (ta-C), amorphous hydrogenated carbon (a-C:H), and tetrahedrally coordinated amorphous hydrogenated carbon (ta-C:H). HC stands for hydrocarbon. Structural formulae are given for polyethylene and polyacetylene, sum formulae are given for paraffin and phenanthrene FEBID/FIBID precursors. Trends in mechanical properties are indicated by arrows as well as changes in composition during electron beam curing (EBC). The as-grown CH<sub>x</sub>-FEBID material space according to measurements from Bret et al. [<a href="#B93-micromachines-11-00397" class="html-bibr">93</a>] and Ding et al. [<a href="#B45-micromachines-11-00397" class="html-bibr">45</a>] is indicated (yellow shade) as well as the anticipated space for C:(H,O,F) FEBID (and FIBID) matrix material (green shade). No data are available for FIBID material.</p> Full article ">Figure 11
<p>Summary of elastic moduli derived from as-grown FEBID and Ga-FIBID grown carbon materials; all using either paraffin (C<sub>22</sub>H<sub>46</sub> and C<sub>48</sub>H<sub>50</sub>) or phenanthrene (C<sub>14</sub>H<sub>10</sub>). The vertical axis lists the precursor molecule used to grow the structure and the author reference. The measurement, deposition parameters (acceleration voltage, beam current), and the Ga implantation contents in at.% (when reported) for FIB deposits are indicated. On the top values and ranges of elastic moduli for polymers, various carbon types, diamond (<math display="inline"><semantics> <mi>E</mi> </semantics></math> = 1143 GPa), gallium, and gallium oxide are shown for orientation. The trend in hydrogen content is indicated. Maximum and minimum values have specific legends when parameter studies were performed; otherwise, they show the experimental scatter. Note the logarithmic horizontal scale. Green colored bars represent measurements on homogeneous material, red-gray colored bars represent core–shell structures, and blue-orange bars made no core–shell distinction.</p> Full article ">Figure 12
<p>Core–shell pillar elastic modulus <span class="html-italic">E<sub>C.S</sub></span> vs. shell thickness normalized to the core–shell pillar radius <span class="html-italic">r<sub>C.S</sub></span> according to Equation (12) for the case of (i) stiff core/compliant shell (<span class="html-italic">E<sub>C</sub></span> = 300 GPa/<span class="html-italic">E<sub>S</sub></span> = 30 GPa) (blue line) as for pillar FEBID and FIBID, and (ii) compliant core/stiff shell (<span class="html-italic">E<sub>C</sub></span> = 30 GPa/<span class="html-italic">E<sub>S</sub></span> = 300 GPa) (orange dotted line) as may happen for e-beam curing. The total diameter 2<span class="html-italic">r<sub>C.S</sub></span> was kept constant. The inset shows the cross-section geometry related to Equation (12). Furthermore, three core–shell cross-sections were visualized for indicated shell thicknesses to pillar radii. For discussion, see text.</p> Full article ">Figure 13
<p>Overview of published metal–carbon deposit shapes and methods to determine their elastic moduli. The force <span class="html-italic">F</span> acting on the structure is indicated as well as the initial shape of the structure (dashed line). (<b>a</b>) Pt-C FEBID pillar bent within an electrostatic field toward the electrode, modified from Arnold et al. [<a href="#B47-micromachines-11-00397" class="html-bibr">47</a>]. (<b>b</b>) Buckled Pt-C pillar between an actuator (top) and substrate (bottom). The initial shape was straight as indicated, modified from Hao et al. [<a href="#B90-micromachines-11-00397" class="html-bibr">90</a>]. (<b>c</b>) Pt-C FEBID pillar nanocompression by a flat diamond punch (not shown), modified from Lewis et al. [<a href="#B48-micromachines-11-00397" class="html-bibr">48</a>]. (<b>d</b>) FEBID Co-C pillar with Ga–FIB milled flat top for compression experiments. (<b>e</b>) Cu–C pillar bending with cantilever and pillar base image tracing, modified from Friedli et al. [<a href="#B53-micromachines-11-00397" class="html-bibr">53</a>]. (<b>f</b>) FIB pillar from W(CO)<sub>6</sub> giving large lateral spike shapes (left), which were FIB-milled for better shape assignment in bending experiments, modified from Ishida et al. [<a href="#B100-micromachines-11-00397" class="html-bibr">100</a>]. (<b>g</b>) FIB grown helix with W(CO)<sub>6</sub> and C<sub>14</sub>H<sub>10</sub> for tensile strain experiments, modified from Nakamatsu et al. [<a href="#B43-micromachines-11-00397" class="html-bibr">43</a>]. (<b>h</b>) Tensile strain experiment with Fe-C FIB helix fixed between a cantilever and substrate, modified from Nakai et al. [<a href="#B59-micromachines-11-00397" class="html-bibr">59</a>]. (<b>i</b>) FIB W-C horizontal rod three-point bending experiments, modified from Córdoba et al. [<a href="#B51-micromachines-11-00397" class="html-bibr">51</a>]. (<b>j</b>) FIB grown silicon oxide structure with FIB-milled hinge geometry for bending experiments, modified from Reyntjens et al. [<a href="#B62-micromachines-11-00397" class="html-bibr">62</a>].</p> Full article ">Figure 14
<p>TEM images of FEBID nanopillars using differing precursors and post-treatments. (<b>a</b>) Amorphous dielectric Si-O-C tip from tetraethoxysilane (TEOS), fabricated at 25 keV/100 pA. (<b>b</b>) shows an Au-C nanopillar shaft fabricated at 30 keV/21 pA using Me<sub>2</sub>Au(acac) precursor, revealing 3–5 nm Au nanograins (dark), which are embedded in a carbon matrix (bright). (<b>c</b>) shows the same pillar after full purification using 5 keV/1.2 nA in 10 Pa H<sub>2</sub>O environments, where the highly crystalline Au character becomes evident. Of particular relevance is the widely maintained morphology, although diameters are strongly reduced (see scale bars). The remaining surface contamination by carbon due to the imaging is only about 1 nm, which becomes essential for plasmonic applications [<a href="#B75-micromachines-11-00397" class="html-bibr">75</a>].</p> Full article ">Figure 15
<p>(<b>a</b>) The average nanoparticle distance <span class="html-italic">s</span> normalized to their size <span class="html-italic">d</span> versus the metal content for five metals. For <math display="inline"><semantics> <mrow> <mi>s</mi> <mo>/</mo> <mi>d</mi> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math>, the full percolation metal threshold is reached. The inset shows the corresponding idealized close packed geometry of metal nanoparticles (purple) with a carbon shell (gray, dotted line). The carbon matrix density was set to 2 g/cm<sup>3</sup>. (<b>b</b>) and (<b>c</b>) show 3D reconstructions from Pt-C nanopillars, which were derived from high-resolution TEM tomography. (<b>b</b>) shows the as-grown FEBID with 30 keV/21 pA, with large Pt nanocrystals becoming evident and revealing slightly percolated characteristics, as indicated by the different colors. After high-dose e-beam curing at 30 keV/150 pA, the grain growth (average by 25 rel.%) is clearly evident, while the partial percolation characteristics remain, as shown by the different colors in (<b>c</b>). Images have been adapted from reference [<a href="#B102-micromachines-11-00397" class="html-bibr">102</a>].</p> Full article ">Figure 16
<p>Summary of elastic moduli measurements of FEBID and FIBID-grown metal–carbon materials. The vertical axis lists the precursor molecule employed to grow the structure together with the first author. Bulk elastic moduli for metals, gallium, gallium oxide, and diamond are shown for orientation. The data point entries give the corresponding elastic modulus ratios of deposit to bulk metal. Metal contents are in at.% (parenthesized values were inferred from separate literature). The measurement methods and deposition conditions (acceleration voltage, beam current) are shown inside the bars. Maximum and minimum values have specific legends when parameter studies were performed; otherwise, they show the experimental scatter. Green shades signify measurements on uniform material that has no potential core–shell structure hidden. <b>(a)</b> Deposits with metal content below percolation threshold and <b>(b)</b> deposit material with metal content &gt;50 at.% and percolation threshold. Note the logarithmic horizontal scale.</p> Full article ">Figure 17
<p>Elastic moduli of FEBID and FIBID material vs. reported metal content. (<b>a</b>) For Pt–carbon deposits. Composite elastic moduli according to the Hashin–Shtrikman upper and lower bounds are shown as lines. The corresponding numerical values represent fits to the data points. (<b>b</b>) Normalized elastic moduli of metal carbon materials from references indicated in the data legend. Stiffening due to e-beam curing is indicated by an orange dashed arrow. The additional gallium metal content for FIB deposits was not considered.</p> Full article ">Figure 18
<p>Reported nanoindentation hardness values for FEBID and FIBID material. The characterization method, beam acceleration voltage, and beam current are reported together with the metal content. Metal contents are given in at.%. Hardness ranges for the metals and amorphous hydrogenated carbon are also indicated.</p> Full article ">Figure 19
<p>Reported quality factors for FEBID and FIBID pillars from vacuum, room temperature vibration experiments in the range of 0.1 to 1 MHz.</p> Full article ">Figure 20
<p>Compilation of pillar nanocompression experiments of varying materials: single crystal diamond [<a href="#B120-micromachines-11-00397" class="html-bibr">120</a>], pyrolytic graphite (PyC) [<a href="#B118-micromachines-11-00397" class="html-bibr">118</a>,<a href="#B119-micromachines-11-00397" class="html-bibr">119</a>], nanocrystalline nickel (nc-NI) [<a href="#B122-micromachines-11-00397" class="html-bibr">122</a>], nanocrystalline gold (nc-Au) [<a href="#B121-micromachines-11-00397" class="html-bibr">121</a>], FEBID Au-C pillar (this work), and an FIB carbon cube of amorphous hydrogenated carbon [<a href="#B41-micromachines-11-00397" class="html-bibr">41</a>]. The crosses signify the appearance of cracks or catastrophic fracture. Note the ductility of all pillars in contrast to the stiff and brittle diamond pillars.</p> Full article ">Figure 21
<p>Fracture strengths of as grown FEBID and FIBID structures. The methods are indicated as well as the metal content whenever available from the reference. The precursor molecules and the first authors are listed on the vertical axis. Green colors highlight measurements on large volume structures; other colors indicate measurements on high aspect ratio pillars with potential core–shell internal structure. The purple bars indicate the measured stress at 7% strain and not the fracture stress, which is higher.</p> Full article ">Figure 22
<p>Summary of density measurements of FEBID and FIBID (noted as FEB and FIB) grown materials. The vertical axis lists the precursor molecule used to grow the structure and the author reference; if not noted otherwise, the density is reported for as-grown material. Maximum and minimum densities as far as accessible, the metal contents, and the measurement methods are indicated. Metal contents given in parentheses were interpolated in the respective reference but not explicitly measured. The measurement methods are pillar vibration (PV), cantilever-based (Cant.), and thermal noise (Th. Noise). Bulk density values of pure compounds and elements are also indicated. The density ratios of deposit to bulk are noted in green for the maximum deposit density.</p> Full article ">Figure 23
<p>Normalized density of FEBID and FIBID material vs. reported metal content. The lines were obtained from Equation (18) normalizing to the metal density (see inset). Numerical values refer to the corresponding <math display="inline"><semantics> <mrow> <msub> <mi>ρ</mi> <mrow> <mi>M</mi> <mi>a</mi> <mi>t</mi> </mrow> </msub> <mo>/</mo> <msub> <mi>ρ</mi> <mrow> <mi>M</mi> <mi>e</mi> <mi>t</mi> </mrow> </msub> </mrow> </semantics></math> ratios; the metal is shown in the data point legends.</p> Full article ">Figure 24
<p>Compression along the vertical axis of a 3D FEBID tower truss lattice structure. (<b>a</b>) Initial lattice dimensions. Note the different dimension of the zigzag units in front view (red arrows) and projected view (purple arrows). (<b>b</b>) Dimensions after 500 nm compression along the long lattice axis. Note the plastic deformation of 194 nm. (<b>c</b>) Monitored force–displacement curve during a tower truss compression experiment with 400 nm plastic deformation. Modified from Lewis et al. [<a href="#B48-micromachines-11-00397" class="html-bibr">48</a>].</p> Full article ">Figure 25
<p>Strength–density scatter plot. The open asterisk denotes the FEBID Pt–C lattice tower structure from Lewis et al. [<a href="#B48-micromachines-11-00397" class="html-bibr">48</a>] shown in <a href="#micromachines-11-00397-f024" class="html-fig">Figure 24</a> and the full asterisk denotes the Ga–FIBID carbon material from Kim et al. [<a href="#B41-micromachines-11-00397" class="html-bibr">41</a>] shown in <a href="#micromachines-11-00397-f004" class="html-fig">Figure 4</a>f. Modified from Bauer et al. [<a href="#B127-micromachines-11-00397" class="html-bibr">127</a>].</p> Full article ">Figure 26
<p>Nanofabrication-related implications on mechanical properties. (<b>a</b>) shows an SEM side-view of a Pt-C tetrapod fabricated via 3D FEBID on SiO<sub>2</sub>. The upper part is a truncated AFM tip, which allows dynamic compression of such nanoarchitectures. The latter is shown in (<b>b</b>), where unexpected twisting effects were stochastically found. The SEM top view image in (<b>c</b>) reveals slight mismatches in the merging zone by left/right-handed displacements in the sub-10 nm regime (see arrows). (<b>d</b>) shows a finite-element simulation during vertical compression, including the aforementioned displacement as shown in the red-framed inset. This mismatch, although small, induce the twisting effect, which clearly shows the high demands on spatial precision during 3D nanofabrication. (<b>e</b>) shows another tetrapod structure in an SEM side view, in which the non-straight branches become evident. For further studies, Δα was defined as indicated in blue. Then, this parameter was varied in finite-element simulations, while vertical stiffnesses were calculated as shown in (<b>f</b>) and further validated by experiments (see ref [<a href="#B128-micromachines-11-00397" class="html-bibr">128</a>]). As evident, even a small Δα of 5° implies a four-fold decrease in stiffness, which decays quickly with larger Δα. As for the upper row, these experiments reveal the high demands on nanofabrication to fully exploit the intended mechanical properties. Images were reproduced with permission from reference [<a href="#B128-micromachines-11-00397" class="html-bibr">128</a>].</p> Full article ">
31 pages, 8516 KiB  
Review
Focused Electron Beam-Based 3D Nanoprinting for Scanning Probe Microscopy: A Review
by Harald Plank, Robert Winkler, Christian H. Schwalb, Johanna Hütner, Jason D. Fowlkes, Philip D. Rack, Ivo Utke and Michael Huth
Micromachines 2020, 11(1), 48; https://doi.org/10.3390/mi11010048 - 30 Dec 2019
Cited by 77 | Viewed by 7724
Abstract
Scanning probe microscopy (SPM) has become an essential surface characterization technique in research and development. By concept, SPM performance crucially depends on the quality of the nano-probe element, in particular, the apex radius. Now, with the development of advanced SPM modes beyond morphology [...] Read more.
Scanning probe microscopy (SPM) has become an essential surface characterization technique in research and development. By concept, SPM performance crucially depends on the quality of the nano-probe element, in particular, the apex radius. Now, with the development of advanced SPM modes beyond morphology mapping, new challenges have emerged regarding the design, morphology, function, and reliability of nano-probes. To tackle these challenges, versatile fabrication methods for precise nano-fabrication are needed. Aside from well-established technologies for SPM nano-probe fabrication, focused electron beam-induced deposition (FEBID) has become increasingly relevant in recent years, with the demonstration of controlled 3D nanoscale deposition and tailored deposit chemistry. Moreover, FEBID is compatible with practically any given surface morphology. In this review article, we introduce the technology, with a focus on the most relevant demands (shapes, feature size, materials and functionalities, substrate demands, and scalability), discuss the opportunities and challenges, and rationalize how those can be useful for advanced SPM applications. As will be shown, FEBID is an ideal tool for fabrication/modification and rapid prototyping of SPM-tipswith the potential to scale up industrially relevant manufacturing. Full article
(This article belongs to the Special Issue Multi-Dimensional Direct-Write Nanofabrication )
►▼ Show Figures

Figure 1

Figure 1
<p>Aspects of 3D nano-printing via focused electron beam-induced deposition (FEBID): (<b>a</b>) Feature sizes of a Pt–C multi-pod structure in 52° tilted view. The diameter of individual nanowires is routinely well below 100 nm, while 20 nm can be achieved for special FEBID conditions; (<b>b</b>) Materials: a large number of precursors allow the deposition of materials containing different chemical elements [<a href="#B43-micromachines-11-00048" class="html-bibr">43</a>]. While for some, the fabrication of freestanding 3D objects has been demonstrated (green) in various studies (numbers in the left corners correspond to the number of articles for the respective element) [<a href="#B34-micromachines-11-00048" class="html-bibr">34</a>], the suitability for 3D-FEBID of other (2D)-FEBID precursors (yellow) is still pending; (<b>c</b>) Pt–C based FEBID 3D nano-towers fabricated on top of mineral wires, which is extremely challenging via alternative techniques. Adapted and reprinted from Winkler et al., ACS Appl. Mater. Interfaces 2017 [<a href="#B44-micromachines-11-00048" class="html-bibr">44</a>]; (<b>d</b>) In addition to straight segments, arbitrarily curved nano-wires are possible; (<b>e</b>) Fabrication of multiple 3D geometries with 640 elements over several µm² in a single process step.</p> Full article ">Figure 2
<p>FEBID nano-pillar characteristics. The tilted scanning electron microscope (SEM) image at the left shows the typical nano-pillar morphology, which can be categorized into three vertical sections: a slightly broader base section close to the substrate, a cylindrical shaft region, and the topmost cone, terminated by the apex. The latter can exhibit tip radii down to 5 nm, as shown by the transmission electron microscopy (TEM) inset top left. While the shaft length is proportional to the growth time, the vertical expansion of the conical region scales with the primary electron energy due to the varying mean free paths of electrons, statistically described by the interaction volume. The vertical expansion of the latter decreases with lower primary energies, which explains the higher curvature of the tip region (compare 5 keV/squares with 30 keV/inverted triangles). The insets show representative SEM images of the tip region in a titled view.</p> Full article ">Figure 3
<p>Feature sizes, 3D shape flexibility, and scanning probe microscopy (SPM) advantages: (<b>a</b>) shows a horizontally grown Pt–C FEBID tip, where the beam moves across the original tip edge (top-down in this image) with scan speeds around 30 nm/s. The resulting nanowires reveal constant widths in the sub-20 nm regime along the entire tip; (<b>b</b>) vertically grown 3D tip, composed of a four-legged base, which then converges to a tall single pillar. While the latter enables high aspect ratio measurements, the former increases the mechanical stability and the adhesion to the surface; (<b>c</b>) shows a FEBID modification (green arrow) of a Pt–Ir coated conductive-atomic force microscopy (C-AFM) tip (red arrow). The tip was also fully purified, revealing a tip radius below 10 nm, which strongly improves the lateral resolution capabilities, as shown in (<b>d</b>) by a direct comparison of FEBID (top) and the original Pt–Ir tip (bottom), performed on a nanogranular gold sample. The scan width is 1 µm, while both Z scales span across 14 nm, as indicated.</p> Full article ">Figure 4
<p>Atomic force microscopy (AFM) imaging with FEBID nano-pillars. (<b>a</b>) and (<b>b</b>) show tapping mode height images of SiN after 0.5 h and 7 h continuous operation, respectively, where the maintained image quality reflects the tip robustness. The Z-range is 3 nm in both high-resolution images. (<b>c</b>) shows a commercially available AFM tip, modified by a Pt–C nanopillar, revealing an end radius of ∼4 nm, as shown by a circle in the inset (scale bar is 200 nm). (<b>d</b>) shows a direct comparison of close-packed polystyrene spheres obtained with the aforementioned standard tip and the FEBID tip at the left and right, respectively (scale bar is 400 nm). Selected line scans along the white lines are shown below and clearly demonstrate the advantage of deeper profiling abilities via FEBID tips. (<b>a</b>) and (<b>b</b>) were adapted and reprinted from Chen et al., Nanotechnology 2006 [<a href="#B64-micromachines-11-00048" class="html-bibr">64</a>], (<b>c</b>) and (<b>d</b>) were adapted and reprinted from Brown et al., Ultramicroscopy 2013 [<a href="#B28-micromachines-11-00048" class="html-bibr">28</a>].</p> Full article ">Figure 5
<p>High-speed AFM imaging of biological systems using FEBID modified Si tips. (<b>a</b>) Formation process of cartwheels and centrioles by the assembly of CrSAS-6 homodimers, which arrange due to their coiled-coil/globular head domains. (<b>b</b>) High-speed, high-resolution imaging using FEBID tips, which make it possible to follow the formation of a cartwheel. Scale bar is 50 nm; Z range, 6.3 nm. Adapted and reprinted from Nievergelt et al., Nat. Nanotechnol. 2018 [<a href="#B65-micromachines-11-00048" class="html-bibr">65</a>].</p> Full article ">Figure 6
<p>FEBID-based electric AFM modes. (<b>a</b>–<b>d</b>) show height (left) and Kelvin force microscopy (KFM) (right) images of SiGe quantum ring, performed with commercial, Pt–Ir coated AFM tips (upper row) and Pt–C nano-pillar modified tips (lower row). While the resolution improvement is evident by the more circular feature shapes, the KFM images reveal many more details, as representatively indicated by the blue and white rings. Adapted and reprinted from Chen et al., IEEE 2012 [<a href="#B94-micromachines-11-00048" class="html-bibr">94</a>]. (<b>e</b>,<b>f</b>) show TEM micrographs of the tip region of a Pt-based FEBID nano-pillar after deposition (<b>e</b>) and after full purification using e-beam assisted carbon removal in H<sub>2</sub>O atmospheres at room temperature [<a href="#B44-micromachines-11-00048" class="html-bibr">44</a>,<a href="#B90-micromachines-11-00048" class="html-bibr">90</a>]. As evident, the pillar gets smaller in width, which entails a slight reduction of the apex radius in the sub-10 nm regime. The larger Pt crystals and the dense packing are evident, while the carbon-free character was confirmed by scanning transmission electron microscopy-based electron energy loss spectroscopy (STEM-EELS) measurements. Such highly conductive tips are then used for C-AFM measurements, as representatively shown in (<b>g</b>) and (<b>h</b>). The scheme below shows the layer setup, consisting of Au paths separated by Al<sub>2</sub>O<sub>3</sub> lines on Si. The advantage of the high aspect ratio pillar is an accurate edge profiling in the height image (<b>g</b>), while the current signal (skin overlay in (<b>h</b>)) allows for the identification of non-conductive regions of thick (red circles) and nanometer thin (purple rings) impurity layers. Image copyright GETec Microscopy 2019 [<a href="#B95-micromachines-11-00048" class="html-bibr">95</a>].</p> Full article ">Figure 7
<p>Sub-10 nm resolution magnetic force microscopy (MFM) imaging via FEBID super-tips. (<b>a</b>) shows a Co-based, FEBID super-tip with a metal content of ~60 at.% and end radii below 10 nm. Such tips are then used for imaging bit patterned media, as shown by the height and lift-mode phase images in (<b>b</b>) and (<b>c</b>), respectively. As evident, the MFM image (<b>c</b>) clearly reveals the written bits with lateral resolution in the sub-10 nm regime. Adapted and reprinted from Belova et al., Rev. Sci. Instrum. 2012 [<a href="#B111-micromachines-11-00048" class="html-bibr">111</a>].</p> Full article ">Figure 8
<p>FEBID-based, high-performance MFM tips. (<b>a</b>) shows a tilted SEM side view of a pre-structured, self-sensing cantilever, modified by a magnetic Co<sub>3</sub>Fe tip via 3D-FEBID at 20 keV/13 pA. Such tips reveal typical diameters and apex radii well below 100 nm and 10 nm, respectively. (<b>b</b>) shows a 3D height image with the MFM signal as overlay, taken from a Co/Pt multilayer structure with perpendicular magnetic anisotropy. (<b>c</b>) and (<b>d</b>) show MFM phase images from the same sample, however, acquired via Fe and Co<sub>3</sub>Fe FEBID tips, with similar morphologies. A closer look reveals that MFM tips from Co<sub>3</sub>Fe reveal much stronger phase contrasts by a factor of more than three, while lateral resolution is also improved to the sub-20 nm regime. Images are courtesy of GETec Microscopy [<a href="#B95-micromachines-11-00048" class="html-bibr">95</a>] (<b>a</b>–<b>c</b>) and Michael Huth (<b>d</b>). Copyright 2019.</p> Full article ">Figure 9
<p>FEBID-based ferromagnetic resonance force microscopy (FMRFM). (<b>a</b>) and (<b>b</b>) show differently sized Co nano-spheres (top down), fabricated on top of a high-resolution AFM cantilever in the top (<b>a</b>) and side views (<b>b</b>), revealing a close to spherical morphology. (<b>c</b>) shows the cobalt content of the beads as a function of the diameter, which has to be correlated with its magnetic properties. Additional measurements revealed a minimum diameter of 150 nm to exploit the full performance. (<b>d</b>) and (<b>e</b>) show FMRFM and MFM measurements, respectively, using a Co-AFM cantilever modified via FEBID. These measurements use an in-plane magnetic field, which aligns the sample magnetization. A microwave-frequency current is then introduced perpendicular to the magnetic field, but also in-plane. The latter decreases the quasi-static component of the magnetization, which impacts the magneto-static force between the sample and tip. Once the magnetic resonance is found, FMRFM reveals defects induced by chemistry or morphology, as provoked in this example by a different shape of the central element in the 3 × 3 array. This explains why that part is dark in FMRFM mode (<b>d</b>). In contrast, classical MFM measurements are unable to detect such defects, as shown in (<b>e</b>). Although powerful in its analytical capabilities, the lateral resolution is currently limited to about 90 nm, as that depends on the bead diameter. (<b>a</b>–<b>c</b>) were adapted and reprinted from Sangiao et al., Beilstein J. Nanotechnol. 2017 [<a href="#B117-micromachines-11-00048" class="html-bibr">117</a>]. (<b>d</b>) and (<b>e</b>) were adapted and reprinted from Chia et al., Appl. Phys. Lett. 2012 [<a href="#B118-micromachines-11-00048" class="html-bibr">118</a>].</p> Full article ">Figure 10
<p>FEBID-based 3D nano-probes for localized thermal sensing. (<b>a</b>) shows the self-sensing cantilever platform (copyright GETec Microscopy, Austria [<a href="#B95-micromachines-11-00048" class="html-bibr">95</a>]), where sensing elements and pre-structured Au electrodes are indicated blue and yellow, respectively. (<b>b</b>) shows an SEM image of the tip region, in which the truncated, pre-existing tip, the split electrodes, and the 3D nano-bridge are evident. The latter is shown in higher magnification in a side (<b>c</b>) and top view (<b>d</b>), where the 3D nano-bridge is shown in red. Once in contact with the sample surface, the small active volumes of the 3D structure allow a fast response, as shown in a dynamic response test in (<b>e</b>) by the red curve in comparison to the reference temperature (blue). A sensing rate better than 30 ms/K with a noise level below ±0.5 K could be demonstrated, which exhibits the advantages of 3D-FEBID nano-structures for advanced AFM concepts, applicable on even pre-finished micro-cantilever. Adapted and reprinted from Sattelkow et al., Appl. Mater. Interfaces 2019 [<a href="#B66-micromachines-11-00048" class="html-bibr">66</a>].</p> Full article ">Figure 11
<p>FEBID/ focused ion beam (FIB) assisted, photonic/plasmonic tip-enhanced Raman scattering (TERS) nano-probe. (<b>a</b>) Overview of a 100 nm thick Si<sub>3</sub>N<sub>4</sub> AFM cantilever, equipped with the photonic and plasmonic element, based on FIB and FEBID, respectively. (<b>b</b>) shows a close up in which the FIB holes (160 nm diameter and 250 nm distance) are evident. The central element uses a Pt-based 3D-FEBID pillar as scaffold, further coated with pure Ag and milled down via FIB to apex radii of 5 nm and below (<b>c</b>). Such TERS nano-probes are then used in AFM-based configuration, as shown in (<b>d</b>), where the laser couples in from the backside via the photonic element, launching surface plasmons. After propagation along the cone structures, they induce a localized plasmon resonance at the tip apex in a nanometer-sized volume. (<b>e</b>) shows an AFM height image in 3D representation of a sub-micrometer Si nanocrystal/SiO<sub>x</sub> trench. The Raman intensity along the red line is shown in (<b>f</b>) in a spectrally resolved diagram, where the intensity variation reflects the crystallinity degree. As evident, the applied step size of 7 nm allows for sharp intensity edges, which confirms a sub-10 nm resolution in TERS operation. Adapted and reprinted from De Angelis et al., Nat. Nanotechnol. 2010 [<a href="#B128-micromachines-11-00048" class="html-bibr">128</a>].</p> Full article ">Figure 12
<p>FEBID-based AFM-IR. (<b>a</b>) and (<b>b</b>) show two examples of Pt- and W-modified cantilevers, respectively, which were further treated via e-beam curing (EBC) to increase the electric conductivity for the required electric field enhancement during IR operation. (<b>c</b>) shows a comparison of localized nano-IR spectra on thin poly-vinylidine-fluoride (PVDF) films, performed via commercial SiN (black) and FEBID modified tips (red), where the enhancement in chemical sensitivity is clearly evident. The insets show 1.5 µm wide height scans (same frame color as the spectra), which reveals the improved lateral resolution. (<b>d</b>,<b>e</b>) show the 2 µm wide correlated height and chemical mapping image of PVDF, respectively, acquired at a constant wavenumber of 1078 cm<sup>−1</sup>, which indicates the asymmetric C–C stretching mode in the β-phase and allows morphology to chemistry studies. Adapted and reprinted from Qian et al., Nanotechnology 2018 [<a href="#B129-micromachines-11-00048" class="html-bibr">129</a>].</p> Full article ">Figure 13
<p>Non-conical apex design. (<b>a</b>) shows a truncated standard AFM tip, which was modified via Helium ion beam-induced Pt–C deposition, consisting of a 14 nm wide pillar, equipped with a hammerhead feature at the end (see upper inset). Please note, the pillar was laterally grown to reduce the width to a minimum, as shown for FEBID in <a href="#micromachines-11-00048-f003" class="html-fig">Figure 3</a>a. Such fine tips are then used for imaging shark fin structures, as shown by a 3D height scan in the lower part of (<b>b</b>). A corresponding cross-sectional profile is shown above, which reveals a measured opening angle of 33° over a height of more than 200 nm, which is very close to the real opening angle of 30°. To produce azimuthally equally distributed features at the apex, vertical growth modes are preferred, as representatively shown by the tilted SEM image of a 3D-FEBID structure in (<b>c</b>). This vertically grown tip consists of a 65 nm wide pillar, which is equipped with six radially symmetrical distributed blades with lateral expansions around 90 nm and widths of about 25 nm. At the top, a fine cone is protruding for localized detection of vertical sample interactions. (<b>a</b>) and (<b>b</b>) were adapted and reprinted from Nanda et al., J. Vac. Sci. Technol. B 2015 [<a href="#B137-micromachines-11-00048" class="html-bibr">137</a>].</p> Full article ">Figure 14
<p>FEBID nano-scalpel. (<b>a</b>) and (<b>b</b>) are the top and side view SEM images of laterally grown 3D carbon structures, which evolve into blade like structures along the Z axis. Such blades have very sharp end regions with knife-like morphologies, which allow operation as nano-scalpel by modulating the exerted force. (<b>c</b>) shows the fabrication of a sub-25 nm wide gap across an Au electrode system by 3D height images, while (<b>d</b>) shows an example of a “nano-surgery” in smooth rat aortic muscle cells with constant cut widths of 50 nm, as shown by the cross-section inset at the bottom. Adapted and reprinted from Beard et al., Nanotechnology 2009 [<a href="#B141-micromachines-11-00048" class="html-bibr">141</a>].</p> Full article ">Figure 15
<p>Application possibilities of Au/Co/SiO<sub>X</sub> multi-material, nanoactuated magnetomechanical systems (NAMMS). (<b>a</b>) Basic design of a Co/SiO<sub>X</sub> NAMMS device, equipped with a small Au sphere at the end of the moving Co cantilever. (<b>b</b>) and (<b>c</b>) show an SEM image and the correlated energy dispersive X-Ray analysis (EDXS) based elemental map, respectively, which demonstrate FEBID multi-material fabrication capabilities within a single 3D structure. (<b>d</b>–<b>f</b>) show potential application examples for correlated analyses concerning magnetic, mechanical, optical, and electrical properties at the nano-scale. Adapted and reprinted from Vavassori et al., Small 2016 [<a href="#B144-micromachines-11-00048" class="html-bibr">144</a>].</p> Full article ">
19 pages, 3230 KiB  
Review
Additive Nano-Lithography with Focused Soft X-rays: Basics, Challenges, and Opportunities
by Andreas Späth
Micromachines 2019, 10(12), 834; https://doi.org/10.3390/mi10120834 - 30 Nov 2019
Cited by 4 | Viewed by 4762
Abstract
Focused soft X-ray beam induced deposition (FXBID) is a novel technique for direct-write nanofabrication of metallic nanostructures from metal organic precursor gases. It combines the established concepts of focused electron beam induced processing (FEBIP) and X-ray lithography (XRL). The present setup is based [...] Read more.
Focused soft X-ray beam induced deposition (FXBID) is a novel technique for direct-write nanofabrication of metallic nanostructures from metal organic precursor gases. It combines the established concepts of focused electron beam induced processing (FEBIP) and X-ray lithography (XRL). The present setup is based on a scanning transmission X-ray microscope (STXM) equipped with a gas flow cell to provide metal organic precursor molecules towards the intended deposition zone. Fundamentals of X-ray microscopy instrumentation and X-ray radiation chemistry relevant for FXBID development are presented in a comprehensive form. Recently published proof-of-concept studies on initial experiments on FXBID nanolithography are reviewed for an overview on current progress and proposed advances of nanofabrication performance. Potential applications and advantages of FXBID are discussed with respect to competing electron/ion based techniques. Full article
(This article belongs to the Special Issue Multi-Dimensional Direct-Write Nanofabrication )
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<p>Scheme of main scanning transmission X-ray microscope (STXM) components and their typical degrees of freedom. The monochromatic X-ray beam is focused by a Fresnel zone plate. A proper alignment of central stop and order sorting aperture (OSA) filters undesired diffraction orders. The specimen is raster-scanned through the focal spot of the Fresnel zone plate. Signals are detected in transmission either in form of directly transmitted photons (black) or as undirected secondary radiation (gray arrows).</p> Full article ">Figure 2
<p>Schematic depiction of electron excitation induced by X-ray absorption and the generation of near-edge X-ray absorption fine structure (NEXAFS) spectra. Resonant soft X-ray illumination induces excitation of core level electrons into unoccupied states. The resulting absorption spectrum exhibits discrete resonant peaks that are a probe of the density and energy levels of respective unoccupied states and, thus, of the chemical state of the excited atom.</p> Full article ">Figure 3
<p>Scheme of the current focused soft X-ray beam induced deposition (FXBID) setup implemented at the PolLux-STXM. The precursor gas is provided within a gas flow cell mainly consisting of two sealed Si<sub>3</sub>N<sub>4</sub>-membranes. The incident X-ray beam is focused onto one of the two membranes for spatially confined deposition of metallic nanostructures.</p> Full article ">Figure 4
<p>Exemplary data from FXBID with Co(CO)<sub>3</sub>NO and subsequent characterization. (<b>a</b>) STXM micrograph (optical density) of FXBID nanostructures deposited with three different incident photon energies around the Co <span class="html-italic">L</span><sub>3</sub>-edge (pre-edge, resonant, and post-edge) and varied illumination time per pixel (100 × 50 pixel per deposit). (<b>b</b>) Comparison of Co <span class="html-italic">L</span><sub>3</sub>-edge NEXAFS spectra from an exemplary FXBID deposit with the reference spectrum from a clean Co film. Pink and blue curves represent two individual chemical states and their relative intensities required for fitting of the deposit spectrum. (<b>c</b>) Growth rates of FXBID deposits at various photon energies (normalized to energy dependent variations of the incident photon flux). (<b>a</b>,<b>b</b>) reproduced in revised form from [<a href="#B21-micromachines-10-00834" class="html-bibr">21</a>] with permission by Royal Society of Chemistry. (<b>c</b>) Reprinted from [<a href="#B47-micromachines-10-00834" class="html-bibr">47</a>] with permission by Cambridge University Press.</p> Full article ">Figure 5
<p>Mn <span class="html-italic">L</span><sub>3</sub>-edge NEXAFS spectrum of an exemplary FXBID deposit from MeCpMn(CO)<sub>3</sub> (on-resonance deposition). According to reference data at least three individual oxidation states from Mn<sup>2+</sup> to Mn<sup>4+</sup> are detected [<a href="#B22-micromachines-10-00834" class="html-bibr">22</a>].</p> Full article ">Figure 6
<p>C <span class="html-italic">K</span>-edge NEXAFS spectra from Co FXBID deposits (Co(CO)<sub>3</sub>NO precursor) before (black) and after dosing and photo-induced reaction with H<sub>2</sub>O (red). Green arrows highlight the prominent changes in the spectrum. While a post-edge decrease of optical density indicates an overall removal of carbonaceous material, the rise of a peak at ~290 eV is a sign of oxidation.</p> Full article ">Figure 7
<p>Scheme on the respective contributions of substrate and precursor excitation to overall precursor splitting. (<b>a</b>) Excitation of precursor molecules is dominant. FXBID growth rate has a strong dependence on excitation photon energy at the respective absorption edge. (<b>b</b>) Excitation of the substrate is dominant. Excitation photon energy has little impact on deposition rate.</p> Full article ">Figure 8
<p>Comparison of penetration depths of X-rays and electrons/ions. In terms of functionalization of porous substrates FXBID allows for depositions zones several µm below the surface of the substrate and might outperform FEBIP/FIBIP.</p> Full article ">
17 pages, 31229 KiB  
Review
Functional Metallic Microcomponents via Liquid-Phase Multiphoton Direct Laser Writing: A Review
by Erik Hagen Waller, Stefan Dix, Jonas Gutsche, Artur Widera and Georg von Freymann
Micromachines 2019, 10(12), 827; https://doi.org/10.3390/mi10120827 - 28 Nov 2019
Cited by 21 | Viewed by 5405
Abstract
We present an overview of functional metallic microstructures fabricated via direct laser writing out of the liquid phase. Metallic microstructures often are key components in diverse applications such as, e.g., microelectromechanical systems (MEMS). Since the metallic component’s functionality mostly depends on other components, [...] Read more.
We present an overview of functional metallic microstructures fabricated via direct laser writing out of the liquid phase. Metallic microstructures often are key components in diverse applications such as, e.g., microelectromechanical systems (MEMS). Since the metallic component’s functionality mostly depends on other components, a technology that enables on-chip fabrication of these metal structures is highly desirable. Direct laser writing via multiphoton absorption is such a fabrication method. In the past, it has mostly been used to fabricate multidimensional polymeric structures. However, during the last few years different groups have put effort into the development of novel photosensitive materials that enable fabrication of metallic—especially gold and silver—microstructures. The results of these efforts are summarized in this review and show that direct laser fabrication of metallic microstructures has reached the level of applicability. Full article
(This article belongs to the Special Issue Multi-Dimensional Direct-Write Nanofabrication )
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<p>(<b>a</b>) Scheme of direct laser writing (DLW) setup: A femtosecond pulsed laser is power modulated by an acousto-optical modulator (AOM). Galvanometer scanning mirrors introduce a tip and tilt and are imaged onto the entrance pupil of a high numerical aperture objective. The objective focuses the beam into a photosensitive material which—in the vicinity of the focal point—selectively hardens (negative-tone resists). The tip and tilt translates the focal point laterally while a stage moves the focal point axially. (<b>b</b>) Scheme of the voxel size dependence on incident laser power. Due to the fixed intensity threshold, reducing incident laser power leads to a reduction in voxel size. (<b>c</b>) Fabrication process: after direct laser writing, samples are placed in a developer bath for a few minutes to reveal the final structure. (<b>d</b>) Principle of metal direct laser writing: in step I, a photoreducing agent (R) is excited by multiphoton absorption. The excited agent donates an electron to metal ions (M<math display="inline"><semantics> <msup> <mrow/> <mo>+</mo> </msup> </semantics></math>) that are thus reduced (II). The neutral metal atoms nucleate, the seeds grow, and finally aggregate to yield the voxel of a metallic microstructure (III).</p> Full article ">Figure 2
<p>(<b>a</b>) Scanning electron micrograph of a planar silver microstructure fabricated by metal direct laser writing (MDLW) (left) and corresponding atomic force microscopy topography measurement (center). The black line indicates the line along which the height plot on the right is taken. The surface roughness of the structure is determined to be around 25 nm peak to valley. (<b>b</b>) Scanning electron micrograph of silver lines separated by 600 nm. Scale bars in (<b>a</b>) and (<b>b</b>) correspond to 1 µm and structures were fabricated with a speed of 1 µm/s. (<b>c</b>) Energy-dispersive X-ray spectroscopy (EDX) imaging of silver: the pink color indicates positions at which silver is detected. (<b>d</b>) Scanning electron micrograph of a 3D silver monopole with a diameter of 10 µm and a height of 20 µm. The scale bar corresponds to 5 µm.</p> Full article ">Figure 3
<p>(<b>a</b>) Close-up scanning electron micrograph of a helical microswimmer. Scale bar is 10 µm. Below: Schematic of transport capabilities of the swimmer: a rotating magnetic field induces a rotary motion and translation of the swimmer. (<b>b</b>) Time-lapse image of the controlled motion as well as cargo pick-up and drop-off of a microswimmer. The scalebar corresponds to 50 µm. Reproduced with permission [<a href="#B28-micromachines-10-00827" class="html-bibr">28</a>].</p> Full article ">Figure 4
<p>Electric components fabricated by MDLW. (<b>a</b>) Scanning electron microscopy (SEM) image of silver wires fabricated on a flexible sheet (top), measurement setup (bottom left), and results (bottom right): resistance versus bending radius and resistance versus bending times. Modified with permission [<a href="#B46-micromachines-10-00827" class="html-bibr">46</a>]. (<b>b</b>) Microscope image of silver source and drain electrodes fabricated by MDLW (top left), scheme of integration in an OFET (bottom left) and measurement of the resulting on-off values (right). Modified with permission [<a href="#B47-micromachines-10-00827" class="html-bibr">47</a>]. (<b>c</b>) SEM image of a silver heating device fabricated inside a microchannel (left) and temperature versus heating time measurement (right). Modified with permission [<a href="#B48-micromachines-10-00827" class="html-bibr">48</a>]. (<b>d</b>) Transmission microscope image of a silver microwave antenna (left) that couples spin-transitions of nitrogen vacancies in nanodiamonds and optical detection of magnetic resonances (right).</p> Full article ">Figure 5
<p>Sensor components fabricated by MDLW. (<b>a</b>) PVP-functionalized gold structures fabricated inside a microchannel that enable detection of gaseous 4-MBT, ethanol, acetone, and other gaseous species via surface enhanced Raman scattering: scheme of measurement setup (top), SERS detection of 4-MBT (bottom left), and ethanol as well as acetone (bottom right). Reproduced with permission [<a href="#B52-micromachines-10-00827" class="html-bibr">52</a>]. (<b>b</b>) Scheme of setup (top) to demonstrate the functionality of silver wires for the detection of mechanical forces and measurement of the relative resistance change when applying a small force to the wire (bottom). Reproduced with permission [<a href="#B53-micromachines-10-00827" class="html-bibr">53</a>].</p> Full article ">Figure 6
<p>Metamaterials fabricated by MDLW. (<b>a</b>) SEM image of a parallel silver rod-based metamaterial (left). Inclined angle transmittance measurement (right): for increasing angle, the magnetic mode of a TE-polarized field at 18 THz increasingly couples to the structure. Reproduced with permission [<a href="#B54-micromachines-10-00827" class="html-bibr">54</a>]. (<b>b</b>) SEM image of gold u-type split-ring-resonators (left) and their transmittance and reflectance spectra (right). A clear resonance is observed at 63 THz. Modified with permission [<a href="#B55-micromachines-10-00827" class="html-bibr">55</a>]. (<b>c</b>) SEM image of a silver c-type split-ring-resonator array (left) and its transmittance spectrum (right). The electric and magnetic resonances are observed. Reproduced with permission [<a href="#B56-micromachines-10-00827" class="html-bibr">56</a>]. (<b>d</b>) U-type silver split-ring-resonator arrays with different leg lengths (left and right) and their corresponding reflectance (center) showing a shift of the resonance towards lower wavelength with lower leg length.</p> Full article ">Figure 7
<p>3D components fabricated by MDLW. (<b>a</b>) SEM image of two perpendicular gold-composite wires with one of the wires bridging the second one. Reproduced with permission [<a href="#B58-micromachines-10-00827" class="html-bibr">58</a>]. (<b>b</b>) Calculated focal intensity distribution (left) that is obtained by shaping the incident field using a spatial-light-modulator. The shaped focal intensity distribution is used to fabricate the double helix unit cell of a metamaterial in a single shot. An inclined view of the metamaterial is shown in the SEM image in the middle. The chiral metamaterial acts as a polarizer for circularly polarized light with the measured transmittance shown in the right graph. Reproduced with permission [<a href="#B59-micromachines-10-00827" class="html-bibr">59</a>].</p> Full article ">Figure 8
<p>(<b>a</b>) SEM image of a nickel microarchitecture after pyrolysis (top left) and close-up (top center). The scale bars correspond to 2 µm and 500 nm, respectively. Bottom left: SEM images during compression test. Scale bars correspond to 5 µm. Right: Diagram of measured specific strength versus structure beam size. Reproduced with permission [<a href="#B60-micromachines-10-00827" class="html-bibr">60</a>]. (<b>b</b>) Photographs of diverse large-scale 3D silver-composite structures fabricated by projection lithography instead of a laser scanning procedure (left images). Right table: Residues measured via thermogravimetric analysis (TGA), T<math display="inline"><semantics> <msub> <mrow/> <mi>g</mi> </msub> </semantics></math> values from differential scanning calorimetry (DSC) experiments and resistivity for different photoresist compositions. Reproduced with permission [<a href="#B61-micromachines-10-00827" class="html-bibr">61</a>].</p> Full article ">
14 pages, 4690 KiB  
Review
Comparison between Focused Electron/Ion Beam-Induced Deposition at Room Temperature and under Cryogenic Conditions
by José María De Teresa, Pablo Orús, Rosa Córdoba and Patrick Philipp
Micromachines 2019, 10(12), 799; https://doi.org/10.3390/mi10120799 - 21 Nov 2019
Cited by 32 | Viewed by 5509
Abstract
In this contribution, we compare the performance of Focused Electron Beam-induced Deposition (FEBID) and Focused Ion Beam-induced Deposition (FIBID) at room temperature and under cryogenic conditions (the prefix “Cryo” is used here for cryogenic). Under cryogenic conditions, the precursor material condensates on the [...] Read more.
In this contribution, we compare the performance of Focused Electron Beam-induced Deposition (FEBID) and Focused Ion Beam-induced Deposition (FIBID) at room temperature and under cryogenic conditions (the prefix “Cryo” is used here for cryogenic). Under cryogenic conditions, the precursor material condensates on the substrate, forming a layer that is several nm thick. Its subsequent exposure to a focused electron or ion beam and posterior heating to 50 °C reveals the deposit. Due to the extremely low charge dose required, Cryo-FEBID and Cryo-FIBID are found to excel in terms of growth rate, which is typically a few hundred/thousand times higher than room-temperature deposition. Cryo-FIBID using the W(CO)6 precursor has demonstrated the growth of metallic deposits, with resistivity not far from the corresponding deposits grown at room temperature. This paves the way for its application in circuit edit and the fast and direct growth of micro/nano-electrical contacts with decreased ion damage. The last part of the contribution is dedicated to the comparison of these techniques with other charge-based lithography techniques in terms of the charge dose required and process complexity. The comparison indicates that Cryo-FIBID is very competitive and shows great potential for future lithography developments. Full article
(This article belongs to the Special Issue Multi-Dimensional Direct-Write Nanofabrication )
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<p>Three different applications of Focused Electron Beam-Induced Deposition (FEBID) and Focused Ion Beam-induced Deposition (FIBID) growth are sketched: (<b>a</b>) In-plane nanowires on flat substrates; (<b>b</b>) Three-dimensional nanostructures; (<b>c</b>) Nanowire growth on tips and cantilevers. RT stands for room temperature.</p> Full article ">Figure 2
<p>The three main steps of FEBID and FIBID under cryogenic conditions are sketched: (<b>a</b>) The precursor is dosed for a given time on a cooled substrate, giving rise to a condensed layer of precursor; (<b>b</b>) The focused electron or ion beam irradiates the precursor condensed layer with the wanted pattern; (<b>c</b>) The substrate is heated to above room temperature, which produces the sublimation of the unirradiated precursor and the emergence of the desired deposit.</p> Full article ">Figure 3
<p>Growth rate enhancement of Pt-C deposits grown by Cryo-FEBID compared to those grown using RT FEBID. The inset shows SEM micrographs of the obtained deposits. Adapted and reprinted from Bresin et al., Nanotechnology 2013 [<a href="#B54-micromachines-10-00799" class="html-bibr">54</a>].</p> Full article ">Figure 4
<p>(<b>a</b>) SEM micrograph of a W-C 30-nm thick Cryo-deposit irradiated with a 4.21 μC/cm<sup>2</sup> dose (unoptimized dose); (<b>b</b>) SEM micrograph of a W-C 30-nm thick Cryo-deposit irradiated with a 35.7 μC/cm<sup>2</sup> dose (optimized dose); (<b>c</b>) SEM micrograph of a W-C Cryo-deposit array, composed of 100 rectangles of 4 μm<sup>2</sup> x 3.85 μm<sup>2</sup> in size, grown in a single Ga<sup>+</sup> irradiation exposure using an irradiation dose of 50 μC/cm<sup>2</sup>, amounting to a total irradiation time of 85 s (compared with 14 h using RT FIBID). Adapted and reprinted from Córdoba et al., Scientific Reports 2019 [<a href="#B55-micromachines-10-00799" class="html-bibr">55</a>].</p> Full article ">Figure 5
<p>(<b>a</b>) Theoretical composition as a function of depth for Cryo-FIBID W-C deposits according to the calculations reported in the main text for a fluence of 4 × 10<sup>14</sup> ions/cm<sup>2</sup>; (<b>b</b>) Surface composition as a function of fluence for the same modelling conditions as for (<b>a</b>).</p> Full article ">Figure 6
<p>Electrical resistance as a function of the Ga<sup>+</sup> irradiation dose in W-C deposits grown by Cryo-FIBID, suggesting that an optimized dose to achieve the lowest resistance value occurs in the 45 to 60 μC/cm<sup>2</sup> range. The current-versus-voltage measurements shown in the inset are compatible with metallic behavior. Adapted and reprinted from Córdoba et al., Scientific Reports 2019 [<a href="#B55-micromachines-10-00799" class="html-bibr">55</a>].</p> Full article ">Figure 7
<p>Comparison of charge-particle-based lithography techniques in terms of the required charge dose per area and the process complexity. The single-step or multi-step character of the technique is considered a means to classify it as a process with less or more complexity, respectively. Cryo-FIBID requires the lowest charge dose amongst the single-step techniques.</p> Full article ">Figure A1
<p>(<b>a</b>) Theoretical composition as a function of depth for Cryo-FIBID W-C deposits according to the calculations reported in the main text for a fluence of 1 × 10<sup>16</sup> ions/cm<sup>2</sup>; (<b>b</b>) Surface composition as a function of fluence for the same modelling conditions than for (<b>a</b>).</p> Full article ">
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