A NEW SURFACE SCIENCE IN-SITU TRANSMISSION AND REFLECTION ELECTRON-MICROSCOPE

We describe an ultrahigh vacuum instrument for transmission electron m icroscopy and reflection electron microscopy for the study of surfaces and thin him growth. The focus of previous experiments was on the hig h spatial resolution (<3 Angstrom) generally associated with microscop y, at the cost of controlled growth and characterization. We have take n a different approach. It has been shown that most experiments using diffraction and diffraction contrast imaging can be performed well at poorer resolution (similar to 20 Angstrom), including the imaging of m onatomic steps and monolayer coverages. The instrument is designed for best control of growth and vacuum, with sacrifices in optical resolut ion, which is theoretically similar to 2 nm. The instrument is called SHEBA (surface high-energy electron beam apparatus). We can examine a similar to 1 cm(2) sample in both transmission electron microscopy and reflection electron microscopy, in situ with well-controlled molecula r beam epitaxy (MBE) growth capabilities, well characterized vacuum, a nd surface characterization by Auger spectroscopy and low-energy elect ron diffraction. Preliminary experiments of cobalt on silicon have sho wn MBE growth rates ranging from 1.5 monolayers per hour to 18.3 monol ayers per hour depending on the temperature of the evaporation source. Using SHEBA for a reactive MBE experiment has provided the first dire ct evidence of the formation of aluminum nitride by nitridation of bas al plane sapphire. The most serious design problems were stray magneti c fields and mechanical vibrations. These have been overcome and allow a spatial resolution of <10 nm. The instrument is expected to be very valuable in studies of film growth. (C) 1998 American Institute of Ph ysics.