Deposition of alumina films by inverted cylindrical magnetron sputtering assisted by optical emission spectroscopy

Alumina coatings have been deposited on glass substrates by reactive ac (41 kHz) magnetron sputtering of two hollow aluminum targets in argon-oxygen plasma at 5 kW sputtering power in the poisoned mode and in the unstable region of hysteresis loop of reactive sputtering. The poisoned mode produces nanocrystalline films of and alumina at a low deposition rate of 0.06 nm·s-1. Amorphous alumina films have been grown at a higher deposition rate of 0.2 nm·s-1 with the aid of optical emission spectroscopy in which the feedback signal of Al emission spectral line at 396 nm monitored Al concentration in the plasma discharge and accomplished the controlled oxidation of targets during reactive sputtering. Dynamic secondary ion mass spectroscopy studies confirm that alumina films grown in the unstable region of the hysteresis loop of reactive sputtering are highly stoichiometric and of uniform composition with film thickness. Our study demonstrates the successful coupling of optical emission spectroscopy with hollow cylindrical magnetrons for deposition of alumina films

Short-range structure and thermal properties of barium tellurite glasses

BaO-TeO2 glasses containing 10 to 20 BaO mol% were prepared and characterized by X-ray diffraction, density measurements, differential scanning calorimetry and Raman spectroscopy. Glass density decreases with increase in BaO concentration from 10 to 20 mol%, due to replacement of heavier TeO2 by lighter BaO, however glass transition temperature (Tg) increases significantly from a value of 318°C to 327°C due to increase in average single bond enthalpy of the tellurite network. Raman studies found that glass short-range structure consists of TeO4 and TeO3 structural units and BaO modifies the network by producing the structural transformation: TeO4→ TeO3

DSC and Raman studies of silver borotellurite glasses

Silver borotellurite glasses of composition: xAg2O-yB2O3-(100-x-y)TeO2 (x=20-mol%, y = 0, 10, 20 and 30-mol%) were prepared and characterized by density, X-ray diffraction (XRD), differential scanning calorimetry, and Raman spectroscopy. XRD confirmed the amorphous structure of all samples. Density of glasses decreases while the glass transition temperature increases with increase in B2O3 content from 10 to 30-mol%. Raman study shows that coordination number of Te with oxygen decreases steadily from 3.42 to 3.18 on adding B2O3 due to the transformation of TeO4 into TeO3 units

Thermal characteristics, Raman spectra, optical and structural properties of TiO2-Bi2O3-B2O3-TeO2 glasses

Tellurite and borotellurite glasses containing Bi2O3 and TiO2 were prepared and structure-property correlations were carried out by density measurements, X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC), Raman and UV-visible spectroscopy. Titanium tellurite glasses require high melt-cooling rates and were fabricated by splat quenching. On adding B2O3, the glass forming ability (GFA) enhances, and glasses could be synthesized at lower quenching rates. The density of glasses shows a direct correlation with molecular mass of the constituents. UV-visible studies were used to determine the optical band gap and refractive index. Raman studies found that the co-ordination number of tellurium ions with oxygen (NTe-O) decreases with the increase in B2O3 as well as Bi2O3 content while, TiO2 produce only a small decrease in NTe-O, which explains the lower GFA of titanium tellurite glasses that do not contain Bi2O3 and B2O3. DSC studies show that the glass transition temperature (Tg) increases with B2O3and TiO2 concentrations and that Tg correlates well with bond enthalpy of the metal oxides

Optical properties of borotellurite glasses containing metal oxides

Glass samples of the system: 5MxOy-20B2O3-75TeO2 : MxOy = WO3, Nb 2O5, PbO, Nd2O3, Y2O3, Eu2O3 were prepared by melt quenching and characterized by X-ray diffraction, density, Differential Scanning Calorimetry, UV-visible and FTIR spectroscopy. XRD patterns confirmed the amorphous structure of all samples. Glass transition temperature was maximum in borotellurite glass containing Y2O3. Refractive index, atomic polarizability and basicity increased in the following order of ions: Y3+ < Eu3+ < Pb2+ < Nd3+ < Nb 3+ < W6+. FTIR studies showed that PbO is outstanding in enhancing the concentration of tetrahedral borons in the borotellurite network

Structural and thermal properties of vanadium tellurite glasses

V2O5-TeO2 glasses containing 10 to 50 mol% V2O5 were prepared by melt quenching and characterized by X-ray diffraction (XRD), density, Differential Scanning Calorimetry (DSC) and Raman studies.XRD confirmed the amorphous nature of vanadium tellurite samples. The density of the glasses decreases and the molar volume increases on increasing the concentration of V2O5. The thermal properties, such as glass transition temperature Tg, crystallization temperature Tc, and the melting temperature Tm were measured. Tg decreases from a value of 288°C to 232°C. The changes in Tg were correlated with the number of bonds per unit volume, and the average stretching force constant. Raman spectra were used to elucidate the short-range structure of vanadium tellurite glasses

Structural transitions in alumina nanoparticles by heat treatment

γ-alumina nanoparticles were annealed sequentially at 800°C, 950°C and 1100°C and structural transitions as a function of heat treatment were studied by X-ray diffraction (XRD), Differential Scanning Calorimetry (DSC) and 27Al Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) methods.. XRD studies found that γ-Al2O3 is stable upto a temperature of at least 950°C and transforms to the thermodynamically stable α-phase after annealing at 1100°C. MAS-NMR revealed that γ-alumina contains AlO4 and AlO6 structural units in the ratio 1: 2, while α-phase contains only AlO6 units. DSC confirmed that γ → α transition initiates at 1060°C

Short-range structure and thermal properties of lead tellurite glasses

PbO-TeO2 glasses having composition: xPbO–(100 - x)TeO2 (x = 10, 15 and 20 mol%) were prepared by melt quenching and characterized by X-ray diffraction,density measurements, differential scanning calorimetry and Raman spectroscopy. Glass density increases from 5.89 to 6.22 g cm-3 with increase in PbO concentration from 10 to 20 mol%, due to the replacement of TeO2 by heavier PbO. DSC studies found that glass transition temperature (Tg) decreases from a value of 295°C to 281°C. Raman studies found that glass short-range structure consists of TeO4 and TeO3 structural units and that PbO modifies the network by the structural transformation: TeO4 to TeO3

Structural characterization of PbO–B2O3–SiO2 glasses

The effects of silica on the density, boron–oxygen speciation and thermal properties of glasses from the system: PbO–B2O3–SiO2 (PbO concentration: 30, 40, 50 and 60 mol% and silica concentration: 5, 10, 20 and 30 mol%) was studied by 11 B MAS NMR and DSC techniques. The incorporation of silica in the borate network steadily increases glass density, decreases the glass transition temperature and increases the thermal stability of glasses against crystallization. SiO2 at low concentrations of up to 20 mol% increases the three dimensional network connectivity by promoting the conversion of BO3 into [BO4]– units, however at higher silica contents of 30 mol%, the formation of [BO4]– was suppressed and nonbridging oxygens were rapidly generated in SiO4 and BO3 units. The average number of NBOs per BO3 unit increases with silica concentration and this was indicated in the NMR spectra of glass series with 60 mol% PbO which exhibited a shift in the centre of gravity of the BO3resonance peak towards more positive ppm values (de-shielding) at a silica concentration of 30 mol%. DSC studies indicated phase separation in the glasses which suggested that the mixing of Pb2+ ions, BO3, [BO4]– and SiO4 units was not completely random

Structure of copper tellurite and borotellurite glasses by neutron diffraction, Raman, 11B MAS-NMR and FTIR spectroscopy

The structure of copper tellurite and borotellurite glasses is studied by x-ray and neutron diffraction, reverse Monte Carlo (RMC) simulations, FTIR, Raman and 11B MAS-NMR spectroscopy. Copper tellurite sample with 15 mol% CuO forms precipitates of tetragonal TeO2 within the glass matrix on melt quenching. The glass forming ability of the xCuO-(100-x)TeO2 system enhances with increase in CuO concentration from 15 to 20 mol% and also with the addition of B2O3. RMC simulations on the neutron diffraction data found that the Cu-O and Te-O bond lengths are approximately at equal distances in the range: 1·96 to 1·98±0·02 Å, while the nearest O-O distance is at 2·71±0·02 Å. Neutron and Raman results on the Te-O speciation are in agreement and confirmed that the Te-O coordination decreases with an increase in CuO and B2O3 molar concentrations in the tellurite and borotellurite glasses, respectively. RMC studies found that Cu2+ has tetrahedral coordination with oxygen, as predicted by Jahn-Teller distortion and that Cu-O and Te-O structural units have very similar size and geometry. The copper tellurite glass-ceramic sample with 15 mol% CuO was heat treated and it formed crystalline precipitates of TeO2 and CuTe2O5 upon devitrification; the average Te-O coordination was significantly smaller in the glass as compared to that in the crystalline sample