M. Balooch

Pulsed laser deposition of ZnO nanocluster films by Cu-vapor laser

The dependence of stoichiometry, grain size, cathodoluminescence colors, adhesion, and surface morphology of zinc oxide films, deposited by a Cu-vapor laser at room temperature, as a function of oxygen ambient pressure during synthesis were investigated. Auger electron spectroscopy showed that ZnO films with a Zn/O ratio close to 1 were obtained at oxygen pressures >10−1 Torr. X-ray diffraction revealed that pulsed laser deposited zinc oxide films were composed mainly of nanocrystals, the average grain size of which grew from 5 to 17.5 nm as the oxygen pressure was increased from 10−5 to 1 Torr. The surface morphology of the films, as determined by secondary electron microscopy, also exhibited increasing roughness as the grain size increased. Films grown in an oxygen pressure >1.5×10−1 Torr glowed blue under electron bombardment, while slightly substoichiometric films glowed white under similar excitation. Films deposited in an oxygen background pressure up to 1.5×10−1 Torr exhibited good adhesion to subs...

The nature and effects of the thermal stability of lithium hydroxide

Temperature programmed decomposition and complimentary microscopy/spectroscopy techniques were performed on lithium hydroxide with micron-sized grains. The lithium hydroxide grains thermally decomposed into Li2O, releasing H2O, following a three dimensional phase boundary moving from the surface inward. The energy barriers measured for the decomposition of surface and near-surface lithium hydroxide are noticeably smaller than those of bulk counterpart. The conversion of Li2O grains back to lithium hydroxide during moisture exposure was also found to proceed from the surface inward such that surface states are filled before bulk states. In a different set of experiments, nanometer-scale composite grains composed of LiD inner cores and LiOH outer layers were observed to form on top of pressed polycrystalline LiD upon moisture exposure. A diffusion coefficient on the order of 10−23 m2/s was measured for the diffusion controlled reaction of LiOH with LiD in the nanopowder at room temperature in a dry environment. The measured kinetics were used to model the evolution of the LiD/LiOH composite system in a dry environment.

Properties of GaAs nanoclusters deposited by a femtosecond laser

The properties of femtosecond pulsed laser deposited GaAs nanoclusters were investigated. Nanoclusters of GaAs were produced by laser ablating a single crystal GaAs target in vacuum or Ar gas. Atomic force and transmission electron microscopies showed that most of the clusters were spherical and ranged in diameter from 1 nm to 50 nm, with a peak size distribution between 5 nm and 9 nm, depending on the Ar gas pressure or laser fluence. X-ray diffraction, solid-state nuclear magnetic resonance, Auger electron spectroscopy, electron energy loss spectroscopy, and high-resolution transmission electron microscopy revealed that these nanoclusters were randomly oriented GaAs crystallites. An oxide outer shell of ∼2 nm developed subsequently on the surfaces of the nanocrystals as a result of transportation in air. Unpassivated GaAs nanoclusters exhibited no detectable photoluminescence. After surface passivation, these nanoclusters displayed photoluminescence energies less than that of bulk GaAs from which they were made. Our photoluminescence experiments suggest an abundance of sub-band gap surface states in these GaAs nanocrystals.

Nanometer-Scale Pulsed Laser Modification of the Basal Plane of Graphite Observed with Stm

Scanning tunneling microscopy has been used to document changes in the nanometer-scale morphology of the basal plane of highly oriented pyrolytic graphite after exposure to 7 ns, 1064 nm laser pulses in air. Surface modification was visible at fluences far below those that produce melting. Damage appears first on step edges and consists of exfoliation of graphite layers and recession of steps through removal of mono- or multilayer patches. 13 refs., 3 figs.