Development of an ultralow current amplifier for scanning tunneling microscopy

A transimpedance amplifier for ultralow current scanning tunneling microscopy has been developed. Conditions for maximum signal-to-noise ratio have been explored, showing that best results can be obtained with a simple circuital arrangement. The amplifier associates a very high amplification factor (0.5 V/pA) to a sufficiently wide bandwith (1.6 kHz) and very low noise current (49 fA). Those features enable microscopy studies on an almost insulating surface, such as a freshly cleaved mica surface.