Results

With the described approach, we could perform simple measurements. In all the measurements, we used a Platinum-Iridium wire as tip and a HOPG sample. As the work on the scanning electronics is not completed yet, we could only measure a current-distance characteristic. In the paper, there is a section about the interpretation of the measurements. At this place, it should be enough to say that the results show a large discrepancy from theory. This is due to a condensate which inevitably forms a thin layer on the sample when operating in air. Thus the calculated workfunction can be lower by a few orders of magnitude when compared to operation in vacuum.¹

The two graphs below show a current-position diagram. In the lower graph, the current is logarithmised, which illustrates the exponential relationship between current and distance.

Fig. 1: The current-position graph of one of our best measurements. The current is in nanoampères, the position in nanometers.

Fig. 2: The same graph but the current is logarithmised.

Not all the measurements returned useful results. The tunneling current often made sudden jumps, especially when we had already been measuring for a while. This can also be explained by the condensate forming on the sample. When the tip moves into the condensate, the current immensely increases. A new sample had to be prepared in order to solve the problem.

Fig. 3: The current suddenly jumps. Here being shown as the output voltage of the amplifier over the voltage at the z-piezo.

¹ Yusipovich, A. I.; Vassiliev S. Yu.
Voltage-Height Spectroscopy in the Ex Situ Configuration of a Scanning Tunneling Microscope.
In: Russian Journal of Electrochemistry, Vol. 41, No. 5, 2005, pp. 510–521.