Abstract : Scanning tunneling microscopy (STM) has been used to image and modify the surfaces of III-V, II-VI and group IV semiconductors. A tip-simulator based on a photocode was developed. The simulator allows the development of ultra- sensitive electronics for controlling STM tip movement. Various forms of 'nano- machining,' including chiselling, sanding, and sweeping of atoms on a surface, were developed. An STM design was modified to allow bending of long thin samples of Si(100) in UHV to permit the study of surface strain. A variety of studies were conducted on Au (in air) CdTe (in air), Hg(sub 1-x)Mn(sub x)Te (under glycerin), and Hg(sub 1-x)Cd(sub x)Te (in air and under glycerin).