Near-edge X-ray absorption fine structure spectra of three pyrimidine (viz., cytosine, uracil, and thymine) and two purine (viz., adenine and guanine) nucleobases, which are the key constituents of DNA and RNA, were measured at the C, N, and O K-edges using the self-absorption-free partial electron yield mode. The nucleobase samples were prepared as highly pure native polycrystalline powder films. The spectra are analyzed in terms of the electronic structure of the nucleobases. Subtle chemical effects related to the molecular structures of these heterocyclic compounds with extended pi-electron systems are considered and discussed.

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The paper considers the physical basis for the technique of controllable defect formation at heterointerfaces and in the bulk of epitaxial GaAs layers in the process of isovalent doping. Results of studying crystal defects and their rearrangement depending on the isovalent doping modes in the process of epitaxial growth are presented. The main aspects of the defect influence on the charge carrier lifetime as well as on the diode structure blocking voltage are analyzed. Particular cases of the developed technique application for controllable defect formation in fabricating such GaAs-based devices as Hyper Fast Recovery Epitaxial Diodes and Drift Step Recovery Diodes are considered.Keywords-gallium arsenide, liquid phase epitaxy, crystal defects, charge carrier lifetime, isovalent doping, turn-off time, fast recovery epitaxial diode, rise time, step recovery diode.

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