Design and development of an in-house scanning tunneling microscope system

The invention of Scanning Tunneling Microscope (STM) by Binnig and Rohrer in 1982 eliminated the use of optical lenses and replaced the conventional optical microscopes with a new class of microscopes called the Scanning Probe Microscopes (SPM). Because of their unique characteristics such as higher resolution and acquisition of nano level images without affecting the physical properties of the sample, they have found wide applications in a variety of scientific disciplines such as biology, material science and electrochemistry. After considerable advancements in instrumentation, the STM has evolved as a nanomanipulation and nanofabrication tool. It operates in two modes: constant current mode and constant height mode. In constant current mode, the feedback parameter is the tunneling current based on which the voltage applied to the piezoelectric actuator is varied. Hence, the tip height is varied in accordance with this tunneling current. In the constant height mode, however, the height is maintained at a constant value and hence the voltage applied to the piezoelectric actuator is adjusted (PZT). Unlike constant current mode, it is the tunneling current which changes according to the surface profile and the local electronic structure of the tip and the sample.