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EPR study of paramagnetic centers in and on host crystal matrices ; Application to silicon thin films, single molecular magnets and alanine/ESR dosimetry

From the broad area of the possible application of EPR spectroscopy the three typical examples will be presented which involves three different types of paramagnetic probes. Implantation of He, Kr, Au, Si, ions into silicon produced dominant paramagnetic defects characterized by singlet at g=2.0055 in an EPR spectrum. This singlet is often found in amorphous silicon and it is attributed to neutral charge state of dangling bond in the vacancy cluster. On the other side, implantation H2+ and D2+ ions under the similar condition as heavier ions produce S1 type of paramagnetic defects and defects with corresponding singlet at g=2.0066 which was earlier denoted as S2 defect. The microscopic structure of S2 defect has been studied and involvement of hydrogen and oxygen atoms in this center has been discussed. In the second case the paramagnetic probe NMP-TCNQ containing very narrow linewidth (~0.2G) is only deposited to surface of the single molecule magnet Mn12-Ac crystal. The possibility of EPR investigation of magnetic field and magnetic field gradient near the surface of the crystal will be discussed. Stability of paramagnetic centers in gamma-irradiated L-alanine and its linear dependence on the concentration in the wide range of irradiation dose are the most important properties of ESR/alanine dosimeter. Besides of such stability the radical exhibit a very complex relaxation rates. The mechanism of the relaxation rates of the first stable alanine radical has been investigated in the low temperature region (4K-20K). The evidence for the presence of the low-frequency modes in the L-alanine crystal lattice detected by Pulse EPR and supported by specific heat measurements will be presented.

EPR; Silicon films; Molecular magnets; Alanine/ESR dosimetry

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