JPH0518742A - Atomic probe microscope - Google Patents

Abstract

PURPOSE:To provide an atomic probe microscope capable of performing further accurate measurement. CONSTITUTION:A probe 12 is provided at the free end of a cantilever 14, and supported close enough to let interatomic force act between a sample 16 And the probe 12. The cantilever 14 is fixed to a Pyrex glass substrate 20 having parts of thickness d1 and d2 (d1>d2) by anode jointing, and an electrode 22 is formed on the upper face of the Pyrex glass substrate 20. The cantilever 14 for adjusting the distance between the probe 12 and the sample 16 is supported by a piezoelectric element 24 for performing the scanning of the probe 12. The sample 16 is stably fixed on a conductive sample substrate 18 using a method such as chemisorption. The electrode 22 and the sample substrate 18 are connected to the power supply V1 for applying the specified voltage.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an atomic probe microscope.

[0002]

2. Description of the Related Art A typical example of an atomic probe microscope is a scanning tunneling microscope (STM; Sca).
nning Tunneling Microscope) and atomic force microscope (AF)
M; Atomic Force Microscope) is known.

The STM is a surface shape measuring apparatus that utilizes a tunnel current that flows when a sharp conductive probe is brought close to a conductive sample by about several Å and a bias voltage is applied between them. Generally, in the STM, the probe-sample distance is servo-controlled so that the distance between the probe and the sample is kept constant while the probe scans the surface of the sample. A piezoelectric element driven by a high voltage is mainly used for scanning and servo control of the probe.

The tunnel current is detected from the probe electrode attached to the piezoelectric element via the insulating member. A servo voltage corresponding to the unevenness of the sample surface is supplied to the piezoelectric element so that the probe scans the sample surface at a constant interval. An insulating member is interposed between the drive electrode and the probe electrode of the piezoelectric element to which the servo voltage is supplied, and a capacitance is formed between the drive electrode and the probe electrode. Therefore, when a time-varying servo voltage is applied to the drive electrodes of the piezoelectric element,
As when an AC voltage is supplied to the capacitance electrode, a current flows through the probe electrode, and accurate measurement cannot be performed.

On the other hand, the AFM is an elastic body of 100 μm.
A sharply pointed probe is provided at the free end of the cantilever with a length of m to 2000 μm, and this probe is brought close to the sample to exert attraction force such as adsorption or van der Waals force between the atoms at the tip of the probe and the sample surface. , The local shape and physical properties of the sample are measured from the resulting displacement of the cantilever.

In the AFM, in addition to the above-described attractive force mode mainly composed of attractive force, the probe is brought closer to the sample, and the interatomic distance between one atom of the probe and one atom of the sample according to the Pauli law is calculated. There is a force-based repulsive mode measurement. The former is 10
The force of ⁻⁷ to 10 ⁻¹² N and the latter force of 10 ⁻⁷ N or higher are detected by the displacement of the cantilever.

In the repulsive force mode among the objects to be measured by the AFM, the force between only the atoms closest to the atoms at the tip of the probe and the atoms of the sample is dominant. That is, an attractive force acts on atoms other than the closest atom, but this force is a minute force compared to the repulsive force and can be ignored.

On the other hand, in the attractive mode, a force that affects the displacement of the cantilever occurs in addition to the atomic force. One of them is the meniscus force generated by the accumulation of water molecules between the probe and the sample.

In general, for a non-polar liquid such as water, a method of immersing a probe and a cantilever in water so that the meniscus force does not act on them is measured by S. of the University of California, Berkeley. Manne, PKHamsma (App
l. Phy. lett. 56 (18), 30 April 1990) and has been effective.

However, in an environment in which a polarizable polarizable insulating material surrounds the probe and the cantilever, AF
Due to the presence of an object having anomalous potential energy inside and outside the M device, the insulating material is polarized, and the electrostatic force of the charge generated on the surface of the probe or the cantilever acts to prevent normal measurement.

An object of the present invention is to provide an atomic probe microscope capable of making accurate measurements.

[0012]

Atomic probe microscope of the present invention is provided with a probe having a sharp tip and a probe at its free end, and acts between the probe tip and the sample surface. Lever body that is elastically displaced by a force that acts on the lever body, a support means that fixes and supports the other end of the lever body, an electrode that is integrally provided with the support means so as to face the lever body, and a conductive material that supports the sample. And a power source for applying a voltage between the electrode and the sample substrate.

A predetermined voltage is applied between the electrodes and the sample substrate by a power source, and an electric field is generated between the electrodes. On the other hand, the electric field generated by an external potential object is
The line of electric force is incident on the electrode and is terminated, and does not enter the space sandwiched between the electrode and the sample substrate. Thus, the electric field of the external potential is blocked by the electrodes.

Another atomic probe microscope of the present invention is
A conductive probe, a probe electrode electrically connected to the probe for extracting a tunnel current, two plate-shaped piezoelectric bodies, and a plate-shaped common sandwiched between two piezoelectric bodies A cantilever for scanning the probe, which includes an electrode and two strip-shaped drive electrodes provided on each piezoelectric body, and is insulated from the drive electrode of the cantilever and the probe electrode between these electrodes. And a guard ring electrode having a ground potential provided therein.

Since the guard ring electrode provided between the drive electrode of the cantilever and the probe electrode is grounded,
The fluctuation component of the voltage applied to the drive electrode, that is, the AC component is absorbed by the guard ring electrode and does not flow into the probe electrode. Therefore, the drive voltage applied to the drive electrode for scanning does not affect the tunnel current.

[0016]

1 is a sectional view of a first embodiment of the present invention.
The bottom view is shown in FIG. The probe 12 is provided at the free end of the cantilever 14 and is supported so as to be close to the extent that an atomic force acts on the sample 16. Cantilever 14
Is fixed by anodic bonding to a Pyrex glass substrate 20 having portions of thickness d ₁ and d ₂ (d ₁ <d ₂ ). The upper surface of the Pyrex glass substrate 20 is
An electrode 22 is formed by depositing u. Such a cantilever 14 is supported by a piezoelectric element 24 for scanning the probe 12 while adjusting the distance between the probe and the sample. Further, means for detecting the displacement of the free end of the cantilever 14 due to the atomic force / adsorption force is omitted. Further, the sample 16 is stably fixed on the conductive sample substrate 18 such as Au by using a method such as chemical adsorption. The electrode 22 and the sample substrate 18 are connected to a power source V ₁ that applies a predetermined voltage.

In this embodiment, a predetermined voltage is applied between the electrode 22 and the sample substrate 18 by the power source V _1, and an electric field E is formed between both electrodes. On the other hand, the electric field E _ext generated from an external potential object is
A part of the light is vertically incident on the upper surface of the electrode 22 and is terminated. Whether other electric lines of force are incident on the sample substrate 18 and terminated,
The light enters the space other than the electrode 22 and does not enter the space sandwiched between the electrode 22 and the sample substrate 18. In this way, the electrode 22 blocks the electric field E _{ext of the} external potential,
The electric field E _ext does not affect the probe 12.

The Pyrex glass substrate is polarized by the electric field E, and + charges and − charges of an amount corresponding to the dielectric constant ε and the thicknesses d ₁ and d _{2 of the} Pyrex glass substrate are distributed on the upper surface and the lower surface, respectively. In addition, the cantilever 14 and the probe 12 are made of Si ₃ N ₄ or SiO _2.
If it is made of an insulator such as
The probe 12 is also polarized, and charges are distributed on the surface. Further, when the sample 16 is a polarized substance, the sample is also polarized.
Each electric field due to these charge distributions is affected by the dielectric constant, but when the potential V applied to the electrode 22 and the sample substrate 18 is set to a predetermined value, the electric charge (the tip has a high density) of the probe 12 is generated. The acting electrostatic force is determined by its value and can be controlled. At this time, the electric charge of the probe 12 interacts with the polarized local electric charge of the sample 16, and an attractive force acts to displace the cantilever 14.

That is, since the electric field controlled to a constant value is generated only by the power source V _{1 in} the vicinity of the probe 12, it is possible to perform the measurement without being influenced by the electric field E _ext of the external potential object.

A second embodiment of the present invention is shown in FIG. The same members as those in the above-described embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

In this embodiment, the electrode 22, that is, the upper electrode is provided on the side surface as well as the upper surface of the Pyrex glass substrate. An electrode 26, that is, a lower electrode, is provided on the lower surface of the thin portion (thickness d ₂ portion) of the Pyrex glass substrate 20. The electrode 26 is electrically connected to the sample substrate 18 via the variable power source v ₁ . In addition, the probe 12 and the cantilever 14 have S
i is made strongly doped with P to a, through the variable power supply v ₂ is electrically connected to the sample substrate 18 is connected to a variable power supply v ₂ for applying a voltage to the sample 16 and the probe 12, the tunnel An AFM that can detect the current i is configured.

A voltage having a predetermined constant value is applied to the electrode 22 by the power source V ₁ . As a result, the electric field E _{ext of} the disturbance is blocked and the influence on the probe 22 is removed, as in the above-described embodiment. A predetermined variable voltage is applied to the electrode 26. The variable input at this time is amplitude v, as shown in FIG.
Assuming that the pulse voltage has pulse time intervals T ₁ and T ₂ and the output of the AFM or the output of the tunnel current i has a waveform synchronized with FIG. 4A, as shown in FIG. It is possible to obtain the relaxation times t ₁ and t ₂ of the orientation characteristics and the polarization characteristics of.

Since it is easy to make the Pyrex glass substrate 20, the electrode 22, and the electrode 26 light-transmissive, it is possible to measure the polarization of the sample 16 at the same time by sandwiching this device with a polarizer / analyzer. it can.

A third embodiment of the present invention is shown in FIG. In this embodiment, a polarizable insulating thin film 28 is laminated on the sample substrate 18, a predetermined voltage is applied to the electrode 22 and the sample substrate 18 to shield the external potential E _ext, and at the same time, the Pyrex glass substrate 20 and the insulating thin film 28. To polarize.
Due to the polarization of the insulating thin film 28, the molecular layer of the sample 16 is immobilized by obtaining chemical adsorption. If the sample 16 is colloidal molecules and is suspended in the solution 30, it is possible to form a molecular film and measure the result while controlling the orientation of the molecular layer.

A fourth embodiment of the present invention is shown in FIG. In this embodiment, as an element for scanning a probe, Stanford University Albricht, C.I. F. Cantilever 5 incorporating two sets of piezoelectric bimorphs developed by Kuwait and others
0 is used. The cantilever 50 has a common electrode 5 in the center.
2, and ZnO thin films 54 and 56 are provided on the upper and lower surfaces thereof, and four drive electrodes 58a to 58d extending in the longitudinal direction are further provided on the upper and lower surfaces thereof. By controlling the voltage applied to the four drive electrodes 58a to 58d, the cantilever 50 as described above can move its tip in three-dimensional directions. The operating principle is "USP 4,91
2,822 ". In this embodiment, the insulating film 62 is formed on the drive electrodes 58a and 58c of the cantilever 50.
The guard ring electrode 60 is laminated via the. An insulating film 64 is formed on the guard ring electrode 60, a probe electrode 66 extending in the longitudinal direction at the center thereof is provided, and the probe 12 is provided thereon.

In this embodiment, the guard ring electrode 60 is grounded and kept at the ground potential.

As a result, by applying a variable drive voltage to the drive electrodes 58a to 58d, the drive electrodes 58a
The AC component that tends to flow between the electrodes 58c and the probe electrode 66 is blocked by the guard ring electrode 60. Therefore, this AC component does not flow into the probe electrode 66, and the drive voltage applied to the drive electrode does not affect the tunnel current. As a result, the position of the probe 12 is obtained more accurately, which is effective in improving the measurement accuracy.

[0028]

According to the present invention, the electric field generated from the external potential object is blocked by the electrode and does not enter the space sandwiched between the electrode and the sample substrate, so that more accurate measurement can be performed.

Further, the AC component of the voltage applied to the drive voltage is blocked by the guard ring electrode and does not flow into the probe, so that the measurement accuracy is improved.

[Brief description of drawings]

FIG. 1 is a side sectional view of a first embodiment of the present invention.

FIG. 2 is a bottom view of the cantilever shown in FIG.

FIG. 3 shows a second embodiment of the present invention.

4 is a pulse voltage applied to the lower electrode of FIG.
It is a time chart of the output of FM or tunnel current.

FIG. 5 shows a third embodiment of the present invention.

FIG. 6 shows a fourth embodiment of the present invention.

[Explanation of symbols]

12 ... probe, 14 ... cantilever, 18 ... sample substrate, 2
0 ... Pyrex glass substrate, 22 ... electrode, V ₁ ... power.

Claims (2)

[Claims] 1. A probe having a sharp tip, a lever body having the probe at its free end portion, which is elastically displaced by a force acting between the tip of the probe and the sample surface, and the lever body. Means for fixing and supporting the other end of the electrode, an electrode integrally provided with the supporting means so as to face the lever body, a conductive sample substrate for supporting the sample, and a voltage between the electrode and the sample substrate. Atomic probe microscope equipped with a power supply for applying. 2. A conductive probe, a probe electrode electrically connected to the probe for extracting a tunnel current, two plate-shaped piezoelectric bodies, and a piezoelectric body sandwiched between the two piezoelectric bodies. Plate-shaped common electrode and two strip-shaped drive electrodes provided on each piezoelectric body, and a cantilever for scanning the probe, and between the drive electrode of the cantilever and the probe electrode, An atomic probe microscope comprising a grounding guard ring electrode which is provided so as to be insulated from these electrodes.