Electrical and optical studies of metal organic chemical vapor deposition grown N-doped ZnO films ZnO synthesis by high vacuum plasma-assisted chemical vapor deposition using dimethylzinc and atomic oxygen J.A high-vacuum plasma-assisted chemical-vapor deposition system was used to systematically study ZnO:N thin film synthesis. Nitrogen doping was achieved by mixing either N 2 O or N 2 with O 2 in a high-density inductively coupled plasma (ICP) source. In situ diagnostics showed that the ICP composition was predominantly a function of the elemental oxygen to nitrogen ratio, and relatively insensitive to the choice of N 2 or N 2 O as the molecular precursor. Nitrogen incorporation was measured by both x-ray photoelectron spectroscopy and secondary ion mass spectrometry and was found to increase monotonically with both N 2 O and N 2 addition. Nitrogen doping was correlated with systematic shifts in the lattice spacing, electrical conductivity, and optical absorption. Quantitative comparisons between film properties and gas composition suggest that atomic nitrogen is the primary precursor for doping in this system.
The tetra-anionic form of ATP (ATP 4-) is known to induce monovalent and divalent ion fluxes in cells that express purinergic P2X 7 receptors (Steinberg et al., 1987;Sung et al., 1985), and with sustained application of ATP it has been shown that dyes as large as 831 daltons can permeate the cell membrane (Steinberg et al, 1987). The current study explores the kinetics of loading α,α-trehalose (342 daltons) into ATP stimulated J774.A1 cells, which are known to express the purinergic P2X 7 receptor (Steinberg et al., 1987). Cells that were incubated at 37˚C in a 50 mM phosphate buffer (pH 7.0) contailing 225 mM trehalose and 5 mM ATP, were shown to load trehalose linearly over time. Concentrations of ~50 mM were reached within 90 min of incubation. Cells incubated in the same solution at 4 ˚C loaded minimally, consistent with the inactivity of the receptor at low temperatures. However, extended incubation at 37 ºC (>60 min) resulted in zero next-day survival, with adverse effects appearing even with incubation periods as short as 30 min. By using a two-step protocol with a short time period at 37 ºC to allow pore formation, followed by an extended loading period on ice, cells could be loaded with up to 50 mM trehalose while maintaining good next day recovery (49% ± 12 % by Trypan Blue exclusion, 56 ± 20% by Alamar Blue TM assay). Cells porated by this method and allowed an overnight recovery period exhibited improved dehydration tolerance suggesting a role for ATP poration in the anhydrous preservation of cells.3
Zinc oxide thin films were produced by high vacuum plasma-assisted chemical vapor deposition (HVP-CVD) from dimethylzinc (DMZn) and atomic oxygen. HVP-CVD is differentiated from conventional remote plasma-enhanced CVD in that the operating pressures of the inductively coupled plasma (ICP) source and the deposition chamber are decoupled. Both DMZn and atomic oxygen effuse into the deposition chamber under near collisionless conditions. The deposition rate was measured as a function of DMZn and atomic oxygen flux on glass and silicon substrates. Optical emission spectroscopy and quadrupole mass spectrometry (QMS) were used to provide real time analysis of the ICP source and the deposition chamber. The deposition rate was found to be first order in DMZn pressure and zero order in atomic oxygen density. All films demonstrated excellent transparency and were preferentially orientated along the c-axis. The deposition chemistry occurs exclusively through surface-mediated reactions, since the collisionless transport environment eliminates gas-phase chemistry. QMS analysis revealed that DMZn was almost completely consumed, and desorption of unreacted methyl radicals was greatly accelerated in the presence of atomic oxygen. Negligible zinc was detected in the gas phase, suggesting that Zn was efficiently consumed on the substrate and walls of the reactor.
Recently there has been much interest in using sugars such as trehalose to preserve mammalian cells in a dry state as an alternative to cryopreservation (1–5). However, some studies indicate that sugars alone may not be sufficient to prevent cell injury during drying. Other factors like sodium toxicity, ionic imbalance and pH excursions during dehydration are a few of the mechanisms that have been hypothesized to decrease the viability of mammalian cells. In the present study, we investigated whether or not substituting sodium chloride with choline chloride (2-hydroxy-N, N,N-trimethylethanaminium chloride) in the preservation medium improves desiccation tolerance of Chinese Hamster Ovary (CHO) cells.
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