This proposal requests a new-generation, variable-vacuum (pressure) scanning electron microscope (SEM), for the central Bessey Microscopy Facility (BMF) at Iowa State University, with a digital image enhancement system for observing details more clearly with simple operation using automated functions, and capable of providing high resolution (@ 3.5nm at 30 kV). This instrument can be retrofitted with a cryopreservation system and a x-ray energy dispersive detector already in use in the BMF. Certain modern-day SEMs are able to provide both high-resolution, bright images at high vacuum over a range of kVs and magnifications, and at low vacuums and kVs to reduce specimen radiation damage and charging, but also with good resolution. Need for a high performance, high resolution SEM has become a basic requirement in biological sciences, and in other diverse areas of scientific research. In addition, interest of using SEM at a kV below SkV is also recognized in such applications as studying intracellular ultrastructure, detection and identification of 5-10 nm colloidal gold markers for immunocytochemical labeling with a backscattered detector, and particularly viewing beam sensitive and/or unstable specimens such as food products and other delicate biological samples which cannot withstand high accelerating voltages and beam currents. These latter specimens can be preserved by using quick freezing capabilities such as with a cryopreservation unit and a propane jet freezer already available in the BMF. It is also important to observe with increased resolution surface structures and fracture faces of specimens and, at the same time, to provide x-ray elemental analysis of localized substances within these surfaces. Compositional information and corresponding surface ultrastructure can also be determined and analyzed with a backscattered electron detector. Six specific research projects have been identified on the Iowa State University campus which would directly benefit from a new-generation, high-resolution, and variable-vacuum SEM with the above capabilities. There are a number of other projects that would also benefit from this new-generation SEM by a wide variety of other users of the BMF.
