We have developed a new laser ablation and plasma hybrid technique for depositing thin diamond-like carbon (DLC) films on Si〈100〉 substrates at room temperature and at 110 °C with improved optical and mechanical properties. The technique involves coupling of laser energy (λ=0.308 μm, pulse duration=40 ns, and power 125 MW/cm2) to a graphite target and superimposing capacitively stored energy (2–3 J at 3 kV) to the laser ablated spot. The laser- and plasma-deposited diamond-like carbon films were analyzed by spectroscopic ellipsometry and microhardness measurements. These films showed considerable improvements in both uniformity and homogeneity. Optical properties and hardness of the films deposited by this technique closely match the DLC films. We discuss possible causes of improvements in the above properties of these films.

We show that there is no correlation between the blue shift of the visible photoluminescence band and red shift of the Raman phonon line in porous silicon, in contrast to the recently reported results. We also report a drastic red shift of the photoluminescence peak position with pressure up to 6 GPa and show that this is much larger than that of the crystalline silicon. These observations cast doubt on the suggested mechanism of quantum size effects in porous silicon.

We report Rainan and Photoliiinincscciice (PI,) st udics of porous silicoit (PS) as a. function of isochronal thermal ariiiealiiig from ruuin teiri~~er.atnre to Y0O"C:. 'l'lic PI, peak position atid intensity show Iiuriinotiotoiiic-variiitioii with incrcming terriperature. The PL intensity first increases upto 100°C, tlicn decreases till 550°C: and recovers its intensity at 700°C before it corripletely disappears at 800°C. ' I' hta red shifted asymmetric Ranian line shape can be fitted by phonon confinement model along with the disordered silicoti componeitt. O u r rcsiilLs clearly indicate thitl. the origin of visible PL can be better explained by i l iiew hybrid rnodel which inrorporates both nariostructures for quantuiii cmifiiicrnetit arid silicoii ~:oniplc:xes (sucli as SiH, and siloxerie) aiid d e f d s at Si/Si02 iiit(~II'iir~.~s as I i i i i i i i i (~~: t : i i t ceiitrcs.

We report the formation of excellent quality epitaxial YBa2Cu3O7 films on (100) SrTiO3 and (100) ZrO2 (yttria stabilized) substrates in the temperature range of 500–650 °C by XECl excimer laser ablation in a 0.2 Torr oxygen ambient. By applying a dc bias voltage of +300 V to an interposing ring, we were able to reduce the substrate temperatures from 650 to 500 °C for obtaining epitaxial films. The quality of the epitaxial films was found to decrease with temperature, particularly below 550 °C. The thickness of the superconducting films was varied from 500 to 5000 Å with superconducting transition temperatures Tc (zero resistance) varying from 87 to 90 K for 650 °C deposits. The critical current density Jc of films was found to vary linearly with temperature with values of (zero magnetic field at 77 K) 5.0×106 and 1.0×106 for films deposited at 650 °C on (100) SrTiO3 and (100) yttria-stabilized zirconia substrates, respectively. X-ray diffraction, transmission electron microscopy, electron channeling patterns, and Rutherford backscattering (RBS)/channeling showed excellent epitaxial quality of films on both substrates with best values of minimum ion channeling yield of 3.5% on (100) SrTiO3 substrates.

Raman investigations of C7o films in the 14 -370-K range show significant changes across the orientational phase transitions around 270 and 330 K. Seven of the Raman modes of C70 soften smoothly across the transitions, the magnitude of the decrease in frequencies being in the range of 2 -5 cm . Linewidths of the bands increase in the transition region over and above the anharmonic contributions.The fullerene C6Q exhibits many fascinating properties, the specially noteworthy ones being superconductivity in the alkali-metal fullerides and ferromagnetism in C6Qt etrakis dimethylaminoethylene.' In addition, pristine C6Q solid, being composed of nearly spherical molecules, undergoes a phase transition involving orientational ordering. In the ordered state, electron-rich double bonds between two hexagons (6-6 double bonds) are adjacent to the electron-deficient pentagonal faces on nearestneighbor molecules. X-ray diffraction and calorimetric experiments show that solid C6Q undergoes a first-order phase transition from the high-temperature free-rotor fcc phase (Em 3) to the orientationally ordered simple cubic phase (P2, /a3) around 250 K. Spectroscopic investigations of the orientational-ordering transition in C6Q include Raman and infrared studies. In going from the orientationally disordered to the orientationally ordered phase, frequencies of the Raman modes increase abruptly, accompanied by a steplike decrease in the linewidths.The abrupt hardening of the modes, first attributed to the decrease in unit-cell volume (-2.S%%uo) near the transition, was later ascribed to be partly due to laser-induced electronic excitations into the metastable triplet state. Raman experiments of Matus, Kuzmany, and Kratschmer do not, however, reveal discontinuities in the peak position and linewidth of the strongest C6Q mode at 1468 cm ' at the transition temperature. Hadjiev and Thomson have observed that the abrupt changes in frequencies could be due to possible contamination of C6Q by a small amount of C7Q. C7Q being nearly spherical, would also be expected to undergo phase transitions involving orientational ordering and such transitions have been identified by x-ray and calorimetric measurements by Vaughan et al. ' at 337 and 276 K. These workers have shown that the hightemperature phase is essentially fcc, but could not unambiguously decide on the structures formed on cooling.Verheijen et al. , " based on single-crystal x-ray studies, have obtained the structure of the minority hcp phase since the fcc crystals are twinned. Constant-pressure molecular-dynamics simulation' predicts that cooling the high-temperature free-rotor phase I gives rise to a partially ordered trigonal phase II where the free rotation only occurs around the fivefold axis. On cooling II, a fully ordered monoclinic phase (phase III) is predicted. A recent infrared spectroscopic study' of the phase transitions of C7Q has shown changes in the absorbance and linewidths of the 674-, 643-, and 577-cm ' modes across the phase transitions. There was no clear evidence...