Nano Tungsten Probe Preparation Method

Scanning Tunneling Microscope (STM) is an instrument for detecting various surface information with atomic spatial resolution. The structure of the probe tip is one of the main factors determining the performance of the instrument. For example, the size, shape and chemical purity of the tip will affect the electron density of states of the atoms on the surface of the material under test, and the image of the STM. It has important influence on the resolution and quality.

According to the use characteristics of micro-operating system, nano tungsten probe should not only have a large aspect ratio, but also have a high mechanical strength to avoid bending and fracture during the use of the probe. The length to diameter ratio of the probe determines the ability of STM to measure the depth and width of the probe. High quality STM probes should have high resonance frequency, only one stable atom instead of multiple tip tip, combined length-diameter ratio, high chemical purity and stable chemical properties. Some scholars have improved the electrochemical etching method and prepared nano-metal probes by controlling the parameters of the electrochemical etching process to meet the needs of different applications.

1.Tungsten wire (99.99% purity, 0.5mm diameter) was used as anode, copper rod as cathode, and placed in NaOH solution (2mol/L). The immersion depth was 5mm for the anode and 40mm for the cathode, respectively. Then the alternating current of 10V is used to corrode 60s and remove the oxide layer on the surface of tungsten wire.

2.Clean the tungsten wire after the first step with deionized water.

3.Turn on the power supply of the axial displacement system of the stepper motor and set the lifting speed in the single chip computer control system to 2.78 um/s. The cleaned tungsten wire is used as the anode and the copper rod as the cathode, which are placed in NaOH solution (2mol/L). The immersion depth is 4.5mm and the cathode is 40mm respectively. When the power supply is connected, the tungsten wire begins to corrode. At the same time, the switch of single chip computer is pressed and the tungsten wire is lifted. After 540S is stopped, it will be stopped and 830s will continue to be etch.

Tungsten nanoprobes with different length-diameter ratios can be fabricated by controlling the immersion depth, lifting speed and time. The tip curvature radius of tungsten nanoprobes can reach 30 nm. The probe was used in the MM3A nano-manipulation system produced by Kleindiek Nanotechnik Company. A new nano-scale displacement, positioning and control measurement of carbon nanotubes (8nm in diameter) was carried out. In addition, the method of preparing tungsten nanoprobes is simple, efficient, easy to realize, good controllability and low cost.

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