Papers by Dumitru Dumcenco
Data for resonator behavior in the paper "Self-sensing, tunable monolayer MoS2<br> nan... more Data for resonator behavior in the paper "Self-sensing, tunable monolayer MoS2<br> nanoelectromechanical resonators", <em>Nat. Commun.</em> 10, 4831 (2019); DOI:10.1038/s41467-019-12795-1.
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Conference on Lasers and Electro-Optics, 2019
Broadband transient absorption with sub-20fs temporal resolution, supported by ab-initio calculat... more Broadband transient absorption with sub-20fs temporal resolution, supported by ab-initio calculations, quantitatively provides the strength of exciton-coherent phonon coupling in 1L-MoS2, showing a resonant profile around the C exciton.
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Conference on Lasers and Electro-Optics, 2019
We exploit two-dimensional electron spectroscopy to coherently excite the A and $\mathrm{B}$ exci... more We exploit two-dimensional electron spectroscopy to coherently excite the A and $\mathrm{B}$ excitons in monolayer Mos2. Combined with simulations, our data distinguish ultrafast bright excitons decoherence and sub-ps scattering decays to dark excitons. OCIS codes 300.6530. © 2019 The Author(s)
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Nature Communications, 2019
Excellent mechanical properties and the presence of piezoresistivity make single layers of transi... more Excellent mechanical properties and the presence of piezoresistivity make single layers of transition metal dichalcogenides (TMDCs) viable candidates for integration in nanoelectromechanical systems (NEMS). We report on the realization of electromechanical resonators based on single-layer MoS2 with both piezoresistive and capacitive transduction schemes. Operating in the ultimate limit of membrane thickness, the resonant frequency of MoS2 resonators is primarily defined by the built-in mechanical tension and is in the very high frequency range. Using electrostatic interaction with a gate electrode, we tune the resonant frequency, allowing for the extraction of resonator parameters such as mass density and built-in strain. Furthermore, we study the origins of nonlinear dynamic response at high driving force. The results shed light on the potential of TMDC-based NEMS for the investigation of nanoscale mechanical effects at the limits of vertical downscaling and applications such as re...
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Applied Physics Letters, 2018
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Advanced Electronic Materials, 2018
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Nano letters, Jun 13, 2018
Degenerate extrema in the energy dispersion of charge carriers in solids, also referred to as val... more Degenerate extrema in the energy dispersion of charge carriers in solids, also referred to as valleys, can be regarded as a binary quantum degree of freedom, which can potentially be used to implement valleytronic concepts in van der Waals heterostructures based on transition metal dichalcogenides. Using magneto-photoluminescence spectroscopy, we achieve a deeper insight into the valley polarization and depolarization mechanisms of interlayer excitons formed across a MoS/MoSe/MoS heterostructure. We account for the nontrivial behavior of the valley polarization as a function of the magnetic field by considering the interplay between exchange interaction and phonon-mediated intervalley scattering in a system consisting of Zeeman-split energy levels. Our results represent a crucial step toward the understanding of the properties of interlayer excitons with strong implications for the implementation of atomically thin valleytronic devices.
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2D Materials, 2017
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Nano letters, Jan 12, 2017
A long-standing problem in the application of solid-state nanopores is the lack of the precise co... more A long-standing problem in the application of solid-state nanopores is the lack of the precise control over the geometry of artificially formed pores compared to the well-defined geometry in their biological counterpart, that is, protein nanopores. To date, experimentally investigated solid-state nanopores have been shown to adopt an approximately circular shape. In this Letter, we investigate the geometrical effect of the nanopore shape on ionic blockage induced by DNA translocation using triangular h-BN nanopores and approximately circular molybdenum disulfide (MoS2) nanopores. We observe a striking geometry-dependent ion scattering effect, which is further corroborated by a modified ionic blockage model. The well-acknowledged ionic blockage model is derived from uniform ion permeability through the 2D nanopore plane and hemisphere like access region in the nanopore vicinity. On the basis of our experimental results, we propose a modified ionic blockage model, which is highly rela...
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Nano letters, Jan 12, 2017
Monolayer transition metal dichalcogenides (TMDCs) grown by chemical vapor deposition (CVD) are p... more Monolayer transition metal dichalcogenides (TMDCs) grown by chemical vapor deposition (CVD) are plagued by a significantly lower optical quality compared to exfoliated TMDCs. In this work, we show that the optical quality of CVD-grown MoSe2 is completely recovered if the material is sandwiched in MoS2/MoSe2/MoS2 trilayer van der Waals heterostructures. We show by means of density functional theory that this remarkable and unexpected result is due to defect healing: S atoms of the more reactive MoS2 layers are donated to heal Se vacancy defects in the middle MoSe2 layer. In addition, the trilayer structure exhibits a considerable charge-transfer mediated valley polarization of MoSe2 without the need for resonant excitation. Our fabrication approach, relying solely on simple flake transfer technique, paves the way for the scalable production of large-area TMDC materials with excellent optical quality.
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Electronics, 2017
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Physical Review B, 2016
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Nature, 2016
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Nature Communications, 2016
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Nano letters, Aug 30, 2016
Layered transition metal chalcogenides with large spin orbit coupling have recently sparked much ... more Layered transition metal chalcogenides with large spin orbit coupling have recently sparked much interest due to their potential applications for electronic, optoelectronic, spintronics and valleytronics. However, most current understanding of the electronic structure near band valleys in momentum space is based on either theoretical investigations or optical measurements, leaving the detailed band structure elusive. For example, the exact position of the conduction band valley of bulk MoS2 remains controversial. Here, using angle-resolved photoemission spectroscopy with submicron spatial resolution (micro-ARPES), we systematically imaged the conduction/valence band structure evolution across representative chalcogenides MoS2, WS2 and WSe2, as well as the thickness dependent electronic structure from bulk to the monolayer limit. These results establish a solid basis to understand the underlying valley physics of these materials, and also provide a link between chalcogenide electroni...
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ACS nano, Jan 6, 2015
Two-dimensional semiconductors such as MoS2 are an emerging material family with wide-ranging pot... more Two-dimensional semiconductors such as MoS2 are an emerging material family with wide-ranging potential applications in electronics, optoelectronics, and energy harvesting. Large-area growth methods are needed to open the way to applications. Control over lattice orientation during growth remains a challenge. This is needed to minimize or even avoid the formation of grain boundaries, detrimental to electrical, optical, and mechanical properties of MoS2 and other 2D semiconductors. Here, we report on the growth of high-quality monolayer MoS2 with control over lattice orientation. We show that the monolayer film is composed of coalescing single islands with limited numbers of lattice orientation due to an epitaxial growth mechanism. Optical absorbance spectra acquired over large areas show significant absorbance in the high-energy part of the spectrum, indicating that MoS2 could also be interesting for harvesting this region of the solar spectrum and fabrication of UV-sensitive photod...
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ACS Nano, 2014
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Physica Status Solidi (C) Current Topics in Solid State Physics, 2012
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Solid State Phenomena, 2012
Single crystals of Cu2ZnSn(SxSe1-x)4(CZTSSe) solid solutions have deen grown by chemical vapor tr... more Single crystals of Cu2ZnSn(SxSe1-x)4(CZTSSe) solid solutions have deen grown by chemical vapor transport technique using ICl3as a transport agent. Analyzing the X-ray diffraction patterns reveal that the as-grown CZTSSe solid solutions are crystallized in kesterite structure and the lattice parameters are determined. The S contents of the obtained crystals are estimated by Vegard’s law. The composition dependent band gaps of CZTSSe solid solutions are studied by electrolyte electroreflectance (EER) techniques. The band gaps of CZTSSe are evaluated by a lineshape fit of the EER spectra and are found to increase almost linearly with the increase of S content.
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Optical Materials, 2011
In this study, the near band edge anisotropic optical properties of wurtz-stannite (WS) Cu2ZnGeS4... more In this study, the near band edge anisotropic optical properties of wurtz-stannite (WS) Cu2ZnGeS4 single crystals were characterized using polarization-dependent transmittance and electrolyte electroreflectance (EER) techniques. Single crystals of Cu2ZnGeS4 were grown by chemical vapor transport method using iodine as a transport agent. Analysis of absorption spectra revealed indirect allowed transitions for Cu2ZnGeS4 with the band gaps of 2.02 (2.07) and 2.08 (2.14) eV for E‖b and Е‖a polarization configurations at 300 (10) K. The room-temperature EER spectra in the vicinity of the direct band edge showed anisotropic transitions at around 2.38, 2.44 and 2.45eV for E‖b, Е‖a and Е‖c polarizations, respectively. Based on the experimental observations and recent band-structure calculations a plausible band diagram near band edge of WS-Cu2ZnGeS4 was constructed.
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Papers by Dumitru Dumcenco