Papers by Keyword: Vibrational Mode

Abstract: We report an initial experimental exploration of engineering very thin, suspended amorphous silicon carbide (a-SiC) membranes into vibrating micromechanical devices. We show that micromachined a-SiC thin square membranes can make interesting multiple-mode flexural resonators, with frequency spectra exhibiting many measurable resonant modes over a wide frequency range (100kHz–10MHz) in the low radio frequency (RF) bands. Initial demonstration and preliminary data suggest interesting and rich dynamical, nonlinear, and dissipative properties in these micromechanical resonances. Specifically, for instance, at room temperature (T≈300K) and in moderate vacuum (e.g., ~20mTorr), resonant modes of an a-SiC square membrane (thickness: t≈1.5µm, size: 1mm×1mm) are observed in the ~100kHz–5MHz range, with measured quality factors (Q’s) in the range of ~2,500–9,000.

Abstract: The temperature and particle size dependence of the holewidths for the 7F0 → 5D0 transition of Eu3+ ions in Eu2O3 are calculated and compared with experiment. The calculation is able to describe the effect of nanocrystal vibrational modes on the dephasing of the electronic states of probe ions. The nanocrystal was treated as an elastically isotropic sphere from which the acoustic phonon displacements and phonon spectrum were calculated. Then we applied this to the temperature and size dependencies of the electron-phonon interaction. Also the vibrational modes in nanocrystals are discussed.

Abstract: Fourier transform infrared absorption spectroscopy was used to study the evolution of multivacancy-oxygen-related defects in the temperature range 200-300 °C in Czochralski-grown Si samples irradiated with MeV electrons or neutrons. A clear correlation between disappearance of the divacancy (V2) related absorption band at 2767 cm-1 and appearance of two absorption bands positioned at 833.4 and 842.4 cm-1 at 20 K (at 825.7 and 839.1 cm-1 at room temperature) has been found. Both these two emerging bands have previously been assigned to a divacancy-oxygen defect formed via interaction of mobile V2 with interstitial oxygen (Oi) atoms. The present study shows, however, that the two bands arise from different defects since the ratio of their intensities depends on the type of irradiation. The 842.4 cm-1 band is much more pronounced in neutron irradiated samples and we argue that it is related to a trivacancy-oxygen defect (V3O) formed via interaction of mobile V3 with Oi atoms or/and interaction of mobile V2 with VO defects.

Abstract: Local vibrational mode (LVM) spectroscopy has been used to study the evolution of vacancy-oxygen-related defects (VOn) in the temperature range 300-700°C in carbon-lean Cz-Si samples irradiated with MeV electrons or neutrons. New experimental data confirming an attribution of the absorption bands at 910, 976 and 1105 cm-1 to the VO3 complex are obtained. In particular, a correlated generation of VO3 and the oxygen trimer is observed upon irradiation of Cz- Si crystals in the temperature range 300-400°C. Strong evidence for the assignment of the bands at 991 and 1014 cm-1 to a VO4 defect is presented. The lines are found to develop very efficiently in the VO2 containing materials enriched with the oxygen dimer. In such materials the formation of VO4 is enhanced due to occurrence of the reaction O2i+VO2 ⇒ VO4. Annealing of the VO3 and VO4 defects at T ≥ 550C °C is found to result in the appearance of new defects giving rise to a number of O-related LVM bands in the range 990-1110 cm-1. These bands are suggested to arise from VO5 and/or VO6 defects. Similar bands also appear upon the annihilation of oxygen-related thermal double donors at 650°C in Cz-Si crystals pre-annealed at 450°C.

Abstract: We report on a combined experimental and theoretical study of the metastable form of the vacancy-dioxygen defect in Si labeled VO∗ 2. Important new experimental observations are the detection of mixed local vibrational modes of VO∗ 2 in 16O,18O co-doped samples, the determination of the position of LVM bands for the negatively charged defect, and an assignment of an acceptor level at about Ec − 0.05 eV. Defect energetics, electrical levels and LVM frequencies of the VO∗ 2 complex are also investigated by ab-initio density-functional modeling.We find it to be a bistable defect which accounts well for the experimental data. The metastable form produces an acceptor state at 0.05 eV below Ec, and can be thought of as a VO defect perturbed by interstitial oxygen.