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• Gautham Radhakrishnan -
EMAIL: gradhakr [at] yahoo.com
Atomic Force Microscope (AFM) created a sensation in the scientific world after its invention as it was the first technology to make atomic-scale imaging a routine procedure. An essential requirement for the practical application of an AFM is some means for the reproducible fabrication of super sharp, atomic-scale needle tips for use as probes. There are several techniques of preparing sharp efficient tips. From various different tip materials and preparation methods, chemical etching exhibits the advantage of easy and cost effective fabrication technique.
Therefore the technique in use in our lab involves electrochemical etching of micro-diametric commercial tungsten wire to form sharp pointy tips. This particular technique fall under the category of wet-tip etching procedures. The technique involves the use of these short thin tungsten wires dipped in potassium chloride electrolyte baths. The dipped tungsten wire acts as anode while another dipped iron rod acts as the opposite electrode. Applying a D.C. current source between the electrodes causes the proper current flow through the electrochemical cell leading to the etching of the oxidizing anode, which in the mean time erodes, acquiring a sharp pointy tip. This reaction etches the tungsten, causing the wire to neck down and eventually break into two pieces. If the etching current turns off milliseconds of the wire?s breaking, then the point of separation remains super-sharp.
Therefore a mechanism, by which the current flow leading to the etching process is terminated, is an essential and prominent factor affecting the sharpness of the tip. This project aims at designing and implementing such a circuit that effectively executes precision etching. The circuit achieves precision etch-termination by using certain circuit components accompanied by interface programs which monitor changes in the etching current and thus trigger the automated shut down of current flow to cause the etching process to stop.
The implementation of basic circuitry components like relay switches and transistor are used to direct current away from the etching circuit. National Instruments LabView is used as interface program to control the working of the relay switches and other components. The continuous monitor of etch current by the circuit components in feed to the interface program where the data is simultaneously analyzed in order to execute current termination.
The extensive use of Labview and simple relays and circuitry components help in creating a design set up that aims at precision etch termination.