Method of making probes with carbon nanotubes

FIELD: physics.

SUBSTANCE: invention relates to vacuum technology and the technology of making carbon nanotubes, such as carbon nanotubes at ends of probes, which are used in probe microscopy for precision scanning. The method of making probes with carbon nanotubes is realised by depositing carbon films with nanotubes through magnetron sputtering in a vacuum at direct current of 100-140 mA using a carbon target with a nanotube growth catalyst. Work pieces of the probes are put into a vacuum installation. A carbon film with nanotubes is then sputtered in a residual atmosphere of inert gas.

EFFECT: invention allows for obtaining probes with carbon nanotubes, lying perpendicular the surface of the probe, in required amounts without using explosive substances and complex devices.

6 dwg

 

The invention relates to the field of vacuum equipment and technologies for production of carbon nanostructures such as carbon nanotubes at the tip of the probe. They can be used in probe microscopy as a scanning probe for precision scanning, a noticeable improvement in the quality control samples and for nanolithography.

A method of obtaining a particularly sharp probes, based on the method of field emission [1], which is that tungsten nanofibres grown on the silicon tip of the probe when exposed to field emission in a high vacuum chamber, combined with an electronic microscope. Two preparations of electrochemically etched tungsten probes were placed on two of the micromanipulator. The flow of the working gas - tungsten exurbanite at a temperature of 35°C and the inclusion of a constant field emission induced growth of tungsten nanofibers on one of the blanks probes serving as the cathode. The length of the resulting nanofibers depends on the duration of the exposure field. However, the known method is poorly monitored and involves the formation of a strong tip of the probe with a small number of defects.

Of the known methods, the closest to the technical essence is a method of producing carbon nanotubes at the tip of the probe by khimicheskogo the vapour deposition [2], adopted for the prototype. In this way offers pre electrochemically sharpened tungsten probe heated to a temperature of 700°C, first in argon, and then in the environment of ethylene. Thus, the entire surface of the probe is covered with a lot of nanotubes, which are then mostly travliata the electron beam in the electron microscope. Although this method ensures the formation of nanotubes at the tip of the probe, however, it is poorly controlled and characterized by complexity and multi-stage.

The technical result aimed at reducing mnogostadiinost and reproducibility, is the deposition of nanotubes directly on the tip of the probe. This is achieved by the fact that the carbon film is applied by magnetron sputtering in a vacuum at a constant current of 100-140 mA using the carbon target with a catalyst for the growth of nanotubes.

Magnetron sputtering is optimal for the application of nanotubes at the tip of the probe, as it ensures the locality of spraying and growth of nanotubes. A necessary condition for sputtering is a high vacuum, which provides defectless formed nanotubes. When the supply current less than 100 mA spraying weak and nanotubes are not formed, and when the coil is energized more than 140 mA intense sputtering, the quality of carbon laid down is, and accordingly nanotubes, falling.

This method was implemented using research vacuum installation MRH-3 [3].

Figure 1 shows a diagram of the experimental setup, consisting of a vacuum chamber 1, the magnetron node with the target 2, the sample holder 3 and the plate with the probe 4. As a target, we used a disk of pure graphite for cores of reactors with metal catalysts Y, Ni (sometimes Co, Fe). The square surfaces of the component parts of the target was mapped as C:Y:Ni=94:5:1. After the preliminary pumping into the chamber was snarled working gas is argon. As preparations probes were used platinum-iridium, tungsten and gold-kovarova wire. The wire is cut into pieces with a length of 2-3 cm, were fixed in the sample holder at a distance of 3-5 cm above the target.

These billet probes were placed in the vacuum installation. It was further held deposition of carbon in the residual atmosphere of inert gas. Electrical discharge: constant current power targets 100-140 mA, the discharge voltage 150-400 C.

The resulting probes with nanotubes were investigated by scanning electron microscope (SEM), and conducted comparative testing with probes without nanotubes by scanning tunneling microscope (STM).

Method REM investigated the tips of the probes on most probes b is detected whether nanotubes with a diameter of 10 nm, arranged perpendicularly to the surface of the probe. Figure 2 presents the SEM image of the tip of a platinum-iridium tip with the increase in 170 times. Under higher magnification of 30,000 times (figure 3) at the tip of the probe were detected nanotubes with a diameter of ~30 nm.

According to the results of comparative testing of the received probes and probes without nanotubes was confirmed by high resolution probes with nanotubes up to atomic resolution. 4 shows the STM image of the crystal lattice vysokoorientirovannogo pyrolytic graphite, received platinum-iridium tip-nanotube.

So using the STM method was shown the suitability of the probes with the nanotubes to conduct nanolithography (figa) - the diameter of the formed channels 20 nm or less (figb).

Figure 6 shows the results of scanning a conventional platinum-iridium electrode (figa) and platinum-iridium tip-nanotube (figb) of the test sample from the DVD. It is well visible that figb spelled out all fields with high resolution, since the small diameter of the nanotubes allows you to penetrate even in the area between the tracks of the DVD, and a small amount of rounding of the tip of the nanotube provides high resolution at each point of the scan. Therefore, the tip-nanotube provides significantly better control the quality of the VA samples compared to conventional probes.

Thus, the proposed method allows to obtain probes with carbon nanotubes with a diameter of 10 nm and positioned perpendicular to the surface of the probe in the required quantities without the use of hazardous substances (hydrocarbons, etc.) and complex installations. In addition, the resulting probes are sturdy, multitechnology and durability.

References:

[1] AVN. Tau, J. T. L. Thong "Fabrication of super-sharp nanowire atomic force microscope probes using a field emission induced growth techniques". // Review of scientific instruments, v. 75, No. 10 (2004), 3248-3255.

[2] Y. Shingaya, T. Nakayama, M. Aono "Carbon nanotube tip for scanning tunneling microscopy". // Physica B 323 (2002), 153 to 155.

[3] Antonenko S. C., S. Maltsev., EN 2218299 C1, 17.07.2002.

The way to obtain probes with carbon nanotubes, consisting in the application of carbon films with nanotubes at the tip of the probe, wherein the carbon film is applied by magnetron sputtering in a vacuum at a constant current of 100-140 mA using the carbon target with a catalyst for the growth of nanotubes.



 

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