Multiple source and detection frequencies in detecting threshold

Abstract

Multiple frequency sources are used to apply a time varying signal to a scanning tunneling microscope and a current or voltage passing between the electrodes of the microscope is measured by a microwave spectrum/network analyzer which detects simultaneously at the multiple input frequencies and combinations thereof. This permits multiple substances to be monitored simultaneously. By choosing appropriate frequencies of input signals to be mixed or combined before application to the sample, it is possible to measure at a difference frequency which may improve signal to noise ratio and possible to match generating and reaction potentials and relaxation times to render detection possible. When applied to an array of Coulomb blockade devices used as a current standard, accuracy of the standard can be tested and the signal-to-noise ratio can be improved in the measurements, or the thresholds of the devices can be detected. Multiple frequency sources of light are used to apply a light signal to a scanning near-field optical microscope. After being modulated by the sample, the signal is detected and a spectrometer which detects simultaneously at the multiple input frequencies and combinations thereof. This permits multiple substances to be monitored simultaneously.