JPH0543241B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a scanning tunneling microscope for detecting the atomic structure of an extremely surface layer.

(Prior Art) In recent years, a scanning tunneling microscope has been proposed that can examine the arrangement of atoms on a surface by measuring the tunneling current flowing between the surface and a detector.

For example, Applied Physics Letters (Appl.Phys.Lett.40, 178 (1982)) volume 40, page 178,
The device described in 1982 uses a tungsten needle placed about 10 angstroms away from the sample surface to detect the tunneling current flowing between the surface and the needle, and adjusts the tunneling current so that it remains constant. The needle is moved perpendicularly to the surface using a piezoelectric element, and at the same time the needle is moved (scanned) parallel to the surface, and the arrangement of surface atoms is detected from the amount of movement in directions perpendicular and parallel to the surface.

(Problems to be Solved by the Invention) However, the device shown in the report has no choice but to judge the contact between the sample surface and the needle from the contact current flowing between the surface and the needle; This often damages the tip of the needle, damages the sample, and is very difficult to adjust its position. Additionally, extremely large-scale vibration isolation equipment is required to reduce the effects of vibration on the equipment.

The object of the present invention is to provide a scanning tunneling microscope that can extremely sensitively sense the contact between the sample surface and the needle, extend the life of the needle, facilitate initial settings, and reduce the effects of vibrations on the device to enable highly sensitive measurements. The goal is to propose the following.

(Means for Solving the Problems) The scanning tunneling microscope according to the first embodiment of the present invention is equipped with a load transducer to which a sample is attached and a probe that approaches the sample. It has means for preventing destruction of the probe by detecting a tunnel current between the needles and at the same time detecting contact between the sample and the probe using the load converter and then returning the probe to a non-contact state. It is characterized by

The second embodiment further includes a displacement measuring device between the load transducer and the probe, and a signal from the displacement measuring device is transmitted through a servo mechanism to attenuate vibrations of the load transducer. It is a type tunneling microscope.

(Example) Next, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing a first embodiment, in which a sample 1 is placed on a sample pan 3 of an electronic balance 2 used as a load converter. A tungsten needle 4 having a protrusion with a radius of 10 angstroms at the tip is produced by electrolytic polishing, and brought close to the sample surface using a piezoelectric actuator 5. After the needle 4 stops moving when it comes into contact with the sample surface and a load is detected, the actuator 5 moves the needle approximately 10 angstroms away from the sample surface. The piezoelectric actuator 7 scans the needle 4 parallel to the sample surface while measuring the tunnel current flowing between the sample surface and the needle using the ammeter 6, and drives the piezoelectric actuator 5 using the personal computer 8 so that the tunnel current is constant. Control voltage. At this time, the scanning movement causes the mirror 20 to reflect the light that has passed through the optical fiber 21 from the optical fiber displacement measuring device 22, and is monitored by the displacement measuring device 22. By writing the drive voltage of the piezoelectric actuator 5 and the drive voltage of the piezoelectric actuator 7 on the recorder 9, the arrangement structure of the surface atoms of the sample can be known. In addition to the piezoelectric actuator 7, other piezoelectric actuators may be used to operate the piezoelectric actuator 7.
By driving the needle in the in-plane direction at 90 degrees perpendicular to the driving direction, it is possible to determine not only the one-dimensional but also the two-dimensional arrangement structure of surface atoms.

FIG. 2 is a diagram showing the second embodiment, and the sample 1, electronic balance 2, sample dish 3, tungsten needle 4, piezoelectric actuators 5, 7, ammeter 6, personal computer 8, and recorder 9 are the same as in FIG. In Although,
Apart from this, the following mechanism is provided to prevent displacement and vibration of the sample plate 3. That is, an optical fiber displacement measuring device 11 is attached to a mirror 10 placed on a sample plate 3.
The light passing through the optical fiber 13 is reflected, the displacement of the sample plate 3 is measured by the displacement measuring device 11, and a current is applied to the electromagnetic coil in the electronic balance 2 to apply a servo to cancel the displacement. Dampen vibrations. The accuracy of the electronic balance 2 used as a load converter in the above example can be up to 0.1 μg. Also, fiber optic displacement meters 11 and 22 used as displacement meters.
If mirrors 10 and 20 are made of gold or silver coated on a glass plate by sputtering or vapor deposition, displacements up to 100 pm can be detected. Note that interfaces 15, 14, 16, 17,
24 and 12 are provided.

In addition to the above-mentioned electronic balance, a balanced chemical balance, a dynamic strain type load transducer (strain gauge), etc. can also be used as the load transducer used in the present invention, but considering accuracy and ease of handling, electronic A scale is most suitable. Displacement meters used in the present invention include displacement meters that use changes in capacitance, changes in electromagnetic induction (reactance), changes in magnetic fields, etc., displacement meters that use optical interference or X-ray interference, and Doppler sensors that use laser light. A displacement meter using the effect can also be used.

Next, a measurement example will be described.

First, 100% of cobalt was placed on a 10 mm square chrome plate.
A nanometer-sized coating was applied by sputtering, and the surface structure of cobalt atoms was measured using the scanning tunneling microscope shown in FIG.

Next, the surface structure of cobalt atoms on the surface of a cobalt film prepared in the same manner as in the previous example was measured using a scanning tunneling microscope shown in FIG. As a comparative example, a sample was placed on an immovable table and measured in the same manner as above, but without using an electronic balance as a load converter.

In the measurements of the two examples above, it was found that the cobalt atoms were composed of a mixture of hexagonal and cubic crystals, but in the comparative example, there was a lot of noise due to vibration, and the needle was deformed in one measurement, making measurement impossible. Summer. Measurements made with the device shown in FIG. 2 had 20% less noise than measurements made with the device shown in FIG. 1, and in both cases no deformation of the needle was observed even after more than 30 measurements. Also, the measurement using the device shown in Figure 1 has less noise than the comparative example.
30% less.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the structure of a scanning tunneling microscope according to a first embodiment of the invention, and FIG. 2 is a diagram showing a scanning tunneling microscope according to a second embodiment of the invention. In the figure, 1...sample, 2...electronic balance, 3
... Sample dish, 4 ... Tungsten needle, 5 ... Piezoelectric actuator, 6 ... Ammeter, 7 ... Piezoelectric actuator, 8 ... Personal computer, 9
...Recorder, 10,20...Mirror, 11,22...
...Optical fiber displacement measuring device, 13, 21...Optical fiber, 24, 12, 23, 14, 15, 1
6,17...Interface, 18,19...
It's an amplifier.

Claims (1)

[Claims] 1. A device comprising a load transducer to which a sample is attached and a probe that approaches the sample, detects a tunnel current between the sample and the probe, and simultaneously detects contact between the sample and the probe. A scanning tunneling microscope characterized in that the scanning tunneling microscope has means for preventing destruction of the probe by returning the probe to a non-contact state after detecting it with the load converter. 2 Equipped with a displacement measuring device between the load converter and the probe,
2. The scanning tunneling microscope according to claim 1, wherein the signal from the displacement measuring device is transmitted through a servo mechanism to attenuate vibrations of the load transducer.