The design of electronic circuitry is described that has the capability of measuring independently the bias dependence of the first derivativesdIsol;dV(dynamic conductance) anddVsol;dI(dynamic resistance) and the second derivativesd2Isol;dV2andd2Vsol;dI2of a tunneling currenthyphen;voltage (Ihyphen;V) characteristic over a wide range of junction impedances (less than 1 OHgr; to greater than 104OHgr;). Connections to the sample are four terminal so that problems with lead resistance are eliminated. Resolution in the measurement of the first derivatives is better than one part in 104, and problems with longhyphen;term drift are obviated by the use of feedback. Modulation levels at the sample junction, both at constant current and constant voltage, are conveniently monitored with a calibrated lockhyphen;in amplifier and can be easily changed. The circuitry has been operated successfully with voltage modulation levels across the junction ranging from 1.0 mgr;V to 2.5 mV rms. Data are presented on Alsngbnd;Isngbnd;Pb and Alsngbnd;Isngbnd;AuPb3tunnelhyphen;junction samples to illustrate the capabilities of the system.
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