We are studying carbon thin films by using a pulsed excimer laser to ablate pyrolytic graphite targets to form highly tetrahedral coordinated amorphous carbon (at-C) films. These films have been grown on room temperature p-type Si (100) substrates without the intentional incorporation of hydrogen. In order to understand and optimize the growth of at-C films, parametric studies of the growth parameters have been performed. We have also introduced various background gases (H 2 , N 2 and Ar) and varied the background gas pressure during deposition. The residual compressive stress levels in the films have been measured and correlated to changes in the Raman spectra of the at-C band near 1565 cm-1 . The residual compressive stress falls with gas pressure, indicating a decreasing atomic sp 3 -bonded carbon fraction. We find that reactive gases such as hydrogen and nitrogen significantly alter the Raman spectra at higher pressures. These effects are due to a combination of chemical incorporation of nitrogen and hydrogen into the film as well as collisional cooling of the ablation plume. In contrast, films grown in non-reactive Ar background gases show much less dramatic changes in the Raman spectra at similar pressures.

The superconducting properties of TlBa2CaCu2O7+δ(Tl-1212) films are greatly enhanced by annealing in unreactive ambients such as nitrogen at temperatures ranging from Ta=250–600 °C. The transition temperature, Tc, of these Tl-1212 films as-grown in oxygen is 70 K. Annealing for 1 h at 250 °C elevates Tc above 90 K. Tc further increases and sharpens for Ta=600 °C. In addition, subtle changes occur in the microstructure correlating with improved critical current density. These results indicate that Tl-1212 films may be of greater relevance for electronics applications than previously believed.

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Highly tetrahedral-coordinated-amorphous-carbon (a-tC) films deposited by pulsed-laser deposition (PLD) on silicon substrates are studied. These films are grown at room-temperatures in a high-vacuum ambient. a-tC films grown in this manner have demonstrated stability to temperatures in excess of T = 1000'C, more than sufficient for any post-processing treatment or application. Film surfaces are optically smooth as determined both visually and by atomic-force microscopy. PLD growth parameters can be controlled to produce films with a range of sp 2 -sp 3 carbon-carbon bond ratios. Films with the highest yield of sp 3 C-C bonds have high resistivity, with a dielectric permittivity constant s -4, measured capacitively at low frequencies (1 -100 kHz). These a-tC films are p-type semiconductors as grown. Schottky barrier diode structures have been fabricated.

TlBa2CaCu2O7 (Tl-1212) superconducting films 5000–6000 Å thick have been grown on LaAlO3 (100) substrates using oxide precursors in a closed two-zone thallination furnace. Tl-1212 films can be grown with transition temperatures ∼100 K, and critical current densities measured by magnetization of Jcm(5 K)≳107 A/cm2 and Jcm(77 K)≳105 A/cm2. Processing conditions, substrate temperatures and Tl-oxide source temperatures are found which result in smooth, nearly phase-pure Tl-1212 films. Variations in the respective temperature ramps of the Tl-oxide zone and the substrate zone can greatly influence resulting film properties such as microstructure, morphology, superconducting transition temperature, and critical current density.