研究目的
Investigating the use of a cooled junction field effect transistor in open gate operation to reduce the DC-current to less than 10?19 A for almost ideal measurements of the local electrochemical potential on a surface.
研究成果
The experiments show that an open gate circuit using a cooled JFET enables scanning probe microscopy at very low tunneling conductance, making it suitable for samples with low conductivity and for scanning tunneling potentiometry. The method provides a direct measurement of the local electrochemical potential at the sample surface and could be combined with dynamic force microscopy.
研究不足
The bandwidth of the feedback is reduced compared to the standard STM feedback due to the more complicated feedback scheme using a lock in amplifier. The resolution is limited by the noise of the JFET.
1：Experimental Design and Method Selection:
The experiment uses a cooled junction field effect transistor (JFET) in open gate operation to reduce the DC-current to less than 10?19 A. An AC-bias is applied to the sample, and a lock-in amplifier connected to the preamplifier evaluates the conductance of the tunneling gap.
2：Sample Selection and Data Sources:
A Cu(111) surface was prepared by repeated cycles of sputtering with Ar+ ions followed by annealing at 870 K.
3：List of Experimental Equipment and Materials:
JFET (BF545 B), ultra-high vacuum low temperature STM, lock-in amplifier, current voltage converter.
4：Experimental Procedures and Operational Workflow:
The JFET is operated in an open-gate configuration, with the tip of the STM connected to the gate. The output of the JFET is connected to a current voltage converter. The drain voltage is adjusted, and the second op amp subtracts the drain voltage.
5：Data Analysis Methods:
The ratio of output voltage to AC sample bias as a function of tunneling conductance is analyzed.
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