The development of a scanning tunnelling microscope
A simple stand-alone Scanning Tunnelling Microscope has been designed and constructed with the aim of providing first stage toward an in-situ instrument for study of thin-film growth. It is functionally capable of STM operation (constant current, constant height, line test) and STS operation (I - V and dI/dv - V). This thesis describes mechanical design, electronic design, computer interfacing in hardware and software, and computer graphics, and presents the results of testing and some applications. The STM head mechanical design features a helical spring/diaphragm coarse approach assembly and a concentric tube scanner. An analysis of the control system indicates that an integrator and single-pole low-pass filter provides near optimal behaviour of the control loop and deals with mechanical resonance in a particularly satisfactory manner. A discussion of hardware/software tradeoff and analog/digital tradeoff leads to a stand-alone design based on a PC, giving good performance with maximum use of standard commercial components and relatively simple special-purpose interface. Commercial graphical software package UNIRAS PC-DOS is employed for image display and hardcopy output. Results show excellent repeatability and stability of STM operation, with atomic resolution.