Design and Construction of a Low Temperature Scanning Tunneling Microscope
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A low temperature scanning tunneling microscope (LTSTM) was built that we could use in an ultra high vacuum (UHV) system. The scanning tunneling microscope (STM) was tested on an existing 3He cryostat and calibrated at room, liquid nitrogen and helium temperatures. We analyzed the operational electronic and vibration noises and made some effective improvements. To demonstrate the capabilities of the STM, we obtained atomically resolved images of the Au (111) and graphite surfaces. In addition, we showed that the stable tunneling junctions can be formed between the Pt/Ir tip and a superconducting thin film PbBi. We observed the atomic corrugation on Au (111) and measured the height of the atomic steps to be approximately2.53?, which agrees with published values. In our images of the graphite surface, we found both the ? atoms triangular structure, as well as the complete ?-? hexagonal unit cell, using the same tip and the same bias voltage of 0.2V. The successful observation of the hidden ? atoms of graphite is encouraging in regards to the possibility of imaging other materials with atomic resolution using our STM. We also demonstrated that stable tunneling junctions can be formed at various temperatures. To demonstrate this, the superconducting current-voltage and differential conductance-voltage characteristics of a PbBi film were measured from 1.1K to 9K From this data, the temperature dependent energy gap of the superconductor was shown to be consistent with the predictions of the Bardeen, Cooper, and Schrieffer (BCS) theory.