Charged particle beams can be used to initiate chemical reactions in precursor gases adsorbed onto substrates. Metallorganic precursors, for example, can be used to deposit metals. Other molecules can be used to etch and remove material. This approach therefore offers the possibility of direct-write fabrication of nanometer-scale structures, including three dimensional architectures. However, currently very little is understood about the relevant physics of the electron-precursor molecule interactions, nor are the kinetics of the processes well known. Our group examines the effects of deposition conditions on the structure, composition, and physical properties of the deposit, as well as considering the role of different precursor chemistries.