JPH06331309A - Cathode using carbon nano-tube - Google Patents

Abstract

PURPOSE:To obtain a cathode having excellent resolving power as the probe of an electron microscope and having high electron discharge efficiency by finely closing the tip part of a carbon nano-tube in a conical shape and providing a voltage terminal at the other end of the nano-tube. CONSTITUTION:A carbon nano-tube cathode 12 used as the probe of an electron microscope has a thick part with a diameter of 30mm and a tip part with a diameter of 2mm and a voltage terminal is provided at the other end of the cathode 12. When a sample 11 and the cathode 12 are allowed to sufficiently approach each other and voltage is applied to the cathode 12, an electron is discharged from the tip part of the cathode 12 and a tunnel current flows across the cathode 12 and the sample 11. X- and Y-control shafts 14, 15 are moved using a piezoelectric element to scan the sample 11 by the cathode 12. At this time, the voltage of the piezoelectric element driving a Z-control shaft 16 is controlled so as to make the tunnel current constant. The fluctuations of the voltage of the piezoelectric element driving the Z-control shaft 16 reflect the surface shape of the sample with extremely high accuracy. The fluctuations of this voltage are plotted as a position function to accurately detect the surface shape of the sample 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an extremely fine cathode used for scanning tunneling electron microscopes, transistors and the like.

[0002]

[Prior Art] Physical Review Letter No. 4
Volume 9, No. 1, p. 57, Scanning Tunneling Microscopy;
It is written as STM. ) Is an extremely high resolution observation means,
Observation at the atomic level is possible. FIG. 2 is a schematic configuration diagram of the STM. When the probe 22 negatively applied to the conductive sample 21 approaches a certain distance or less, a tunnel current flows between the probe 22 and the sample 21. Since the tunnel current changes exponentially with respect to the distance between the probe 22 and the sample 21, it is very sensitive to this distance. Probe 2
The X-, Y-, and Z-direction control shafts 23, 24, and 25 are attached to 2 and each control shaft is driven by a piezoelectric element. A piezoelectric element is an element that changes its length depending on the voltage, and by applying a voltage to the piezoelectric element,
The position of the probe 22 in the X, Y and Z directions can be controlled respectively. In the observation, a constant current is made to flow between the sample 21 and the probe 22 under a constant voltage, and the probe 22 is scanned by applying a voltage to the X and Y direction control shafts 23 and 24. Let At this time, the distance between the sample 21 and the probe 22 changes according to the unevenness of the surface of the sample 21, and the tunnel current tends to change. However, voltage is applied to the piezoelectric element that drives the Z-direction control shaft 25 so as to keep this tunnel current constant. Is applied to keep the distance between the sample 21 and the probe 22 constant. By monitoring the voltage applied to the piezoelectric element that drives the Z-direction control shaft 25 as a function of position, the shape of the surface of the sample 21 can be known. The STM is an extremely high-sensitivity observation means because the tunnel current is extremely sensitive to the distance between the sample 21 and the probe 22 and the position can be controlled in Angstrom units by using a piezoelectric element.

[0003]

In order to increase the STM resolution and obtain a clearer image, it is desirable that the tip of the probe 22 be as sharp as possible. The STM probe 22 is obtained by scraping a metal such as a platinum-iridium alloy or tungsten by electropolishing. However, the diameter of the tip is about 50 nm at the minimum, which is disadvantageous in that it is too large compared to the observed object such as an atom. This ST
As can be seen from the example of the M probe, an atom level electron source (cathode) has not been obtained in the past. The present invention is
It is an object of the present invention to provide an extremely fine cathode which can greatly improve the conventional performance by using it for the probe of the STM.

[0004]

DISCLOSURE OF THE INVENTION The present invention is a cathode using carbon nanotubes, characterized in that the tip of carbon nanotube is narrowly conically closed and the other end is provided with a voltage terminal. is there.

[0005]

[Function] Carbon nanotube is a solid physics volume 27,
As described in No. 6, page 441, it is a nanometer-sized graphite ultrafine tube, which is a conductor having the properties of metal or semiconductor. When part of the carbon six-membered ring constituting the carbon nanotube is replaced with a five-membered ring, the carbon nanotube becomes conical and the tip is closed. The diameter of this tip is about 1 nm to several nm, and can be extremely thin. Therefore, an extremely fine cathode can be obtained by closing the tip of the carbon nanotube and providing the electrode at the other end.

[0006]

EXAMPLES Next, examples of the present invention will be described. In this embodiment, the cathode using the carbon nanotube is STM.
Described below is the case of using it for the probe. FIG. 1 is a schematic configuration diagram of an STM for observing a sample 11 which is an object to be observed. There is a carbon nanotube cathode 12 as a probe. The carbon nanotube cathode 12 has a thick portion with a diameter of 30.
It has a tip diameter of 2 nm in nm and is a metallic conductor. The carbon nanotube cathode 12 is attached to a probe base 13 made of metal, and electrons are supplied through the probe base 13. In this embodiment, copper is used for the probe base 13. The position of the probe base 13 is defined by the X, Y, Z direction control axes 14,
It is controlled by 15, 16. The X, Y and Z direction control shafts 14, 15 and 16 are driven by piezoelectric elements, respectively.

Sample 11 and carbon nanotube cathode 12
When a voltage is sufficiently applied to the carbon nanotube cathode 12 via the probe base 13, electrons are emitted from the tip of the carbon nanotube cathode 12, and a tunnel current flows between the carbon nanotube cathode 12 and the sample 11. The carbon nanotube cathode 1 is moved by moving the X and Y direction control shafts 14 and 15 using a piezoelectric element.
2 is scanned on the sample 11. At this time, the voltage of the piezoelectric element that drives the Z-direction control shaft 16 is controlled so that the tunnel current becomes constant. Since this tunnel current is determined by the distance between the sample 11 and the carbon nanotube cathode 12, the fluctuation of the voltage of the piezoelectric element that drives the Z-direction control shaft 16 reflects the shape of the sample surface with extremely high accuracy, and this voltage By plotting as a function of
1 The shape of the surface can be known accurately.

In this embodiment, since the tip of the STM probe is made of carbon nanotube, it is extremely thin. ST
Since M is usually aimed at observing the structure at the atomic level, it is extremely important that the tip of the probe is of the same size as the atom in order to improve the resolution and obtain a clear image. From the above, an extremely fine cathode can be obtained by using this embodiment, and by using it for an STM probe, it is possible to observe a sharp image with high resolution at the atomic level. In this embodiment, the cathode using the carbon nanotube is used as the probe of the STM, but it can be used as the cathode of the transistor. In this case, a large effect can be expected not only from the size but also from the ease of emitting electrons due to the thin tip.

[0009]

As described above, according to the present invention, the carbon nanotube can be used to realize a cathode having a sharp tip up to the atomic size. This carbon nanotube cathode can be used, for example, as an STM probe, and has the effect of achieving a resolution far exceeding that of the conventional one. Further, when it is used as a cathode of a transistor, there is an effect that a transistor which operates at a smaller voltage than that of the conventional one can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an STM using a cathode according to the present invention as a probe.

FIG. 2 is a schematic configuration diagram of an STM using a probe according to a conventional example.

[Explanation of symbols]

 11 sample 12 carbon nanotube cathode 13 probe base 14 X-direction control axis 15 Y-direction control axis 16 Z-direction control axis 21 sample 22 probe 23 X-direction control axis 24 Y-direction control axis 25 Z-direction control axis

Claims (1)

[Claims] 1. A cathode using carbon nanotubes, characterized in that the tip of the carbon nanotube is narrowly conically closed and the other end is provided with a voltage terminal.