Optimization of etching parameters for STM tips and an STM study of SiC (0001) [square root]3 x [square root]3 reconstruction

by Ng, Yee-fai

(Uncorrected OCR) Abstract of thesis entitled OPTIMIZATION OF ETCHING PARAMETERS FOR STM TIPS AND AN STM STUDY OF SiC (0001) V3 ?V3 RECONSTRUCTION submitted by Ng, Yee Fai for the degree of Master of Philosophy at The University of Hong Kong in October 1998 This empirical study systematically investigated how the changes in etching parameters would affect the shape and the sharpness of scanning tunneling microscope (STM) tips fabricated. The tip etched with optimum values of the parameters was then employed to scan the SiC (0001) V3 ?V3 reconstructed surface. A tip-etching package was constructed for direct-current (d.c.) electrochemical etching of tungsten wires, in which a mechanical rise-up method was adopted. By using this package and a scanning electron microscope (SEM), we examined the influence of the etching parameters (e.g., length of wire, etching current and so forth) on the aspect ratios and the radii of curvature at the apexes of the tips. The current-time curves were analyzed, and an optimum setting of the etching parameters was obtained by trial and error. From this, tips with aspect ratio of about 0.9 and radius of curvature of about 30 nm were obtained. A beam model and a bar model, basing on Rayleigh? energy method, for vibrations of an STM tip are presented. Finally, we acquired STM images of the 3 ?V3 reconstruction of the Si-terminated 6H-SiC (0001) surface after annealing at around 1000?C under a Si flux, and the measured side length of the unit cell was about 7 ?