Implementation of Scanning Tunneling Microscope/Atomic Force Microscope utilizing Length Extension Resonator

Abstract

Atomic structure of materials can be resolved with scanning probe microscopy. Atomic Force Microscope (AFM) has been used to observe the geometric structure of microscopic sized sample, i.e. biological specimen, chemical compounds. Meanwhile, Scanning Tunneling Microscope (STM) is widely used to study the electronic structure of conducting materials. However, AFM cannot investigate the electronic structures, and STM forbid non-conducting materials. AFM integrated STM surmounts these shortcomings, by operating different functions of them at the same time. For AFM integrated STM, quartz resonator based AFM can be adopted to implement the system. In this thesis, the Length Extension Resonator (LER), a tiny quartz resonator, is mounted on STM head with an Ir-tip for non-contact mode AFM. Having high stiffness, LER can prevent jump to contact effect, and acquire high resolution. For frequency modulation mode AFM operation, Phase Locked Loop (PLL) is used to detect frequency variations. Also, to avoid interference from parasitic capacitances and amplify tiny output signal of LER effectively, home-built low temperature pre-amplifier was fabricated.