R.F. Huang

X-ray photoelectron spectroscopy and auger electron spectroscopy studies of Al-doped ZnO films

The chemical state of oxygen, aluminum and zinc in Al-doped ZnO (ZAO) films was investigated by X-ray photoelectron spectroscopy (XPS), as well as the transition zone of the film-to-substrate, by auger electron spectroscopy (AES). The results show that zinc remains mostly in the formal valence states of Zn2+. A distinct asymmetry in Al 2p(3/2) photoelectron peaks has been resolved into two components, one is metallic Al and the other is oxidized Al. The depth profile of the two components revealed that metallic Al mainly exists in the thin surface layer. The close inspection of Ols shows that Ols is composed of three components, centered at 530.15 +/- 0.15, 531.25 +/- 0.20 and 532.40 +/- 0.15 eV, respectively. AES reveals an abrupt transition zone between the ZAO and quartz substrate

Optical and electrical properties of direct-current magnetron sputtered ZnO:Al films

In this study, high-quality ZnO:Al (ZAO) films were prepared by using dc reaction magnetron sputtering technology. The effect of Al doped in ZnO films on electrical and optical properties and its scattering mechanism were discussed in detail. The results showed that Al2O3 could be effectively removed by controlling oxygen flow and Al-doped concentration during deposition of ZnO:Al films. Zn, Al, and oxygen elements were well distributed through the films. For highly degenerated ZnO:Al semiconductor thin films, it was revealed that ionized impurity scattering dominated the Hall mobility of the films in the low-temperature range; while the lattice vibration became a major scattering mechanism in the high-temperature range. The grain-boundary scattering only played a major role in the ZAO films with small grain size (as compared to the electron mean-free path). The photoelectric properties of ZAO films showed that the lower resistivity (similar to 5x10(-4) Omega cm) was obtained, and transmittance in the visible range and reflectance in the IR region were above 80% and 60%, respectively

Oxidation behaviour of NiCrAlY coatings on Ni-based superalloy

NiCrAlY coatings were prepared on cast Ni-based IN100 superalloy using are ion plating, leading to a dense structure. The surface became smoother after vacuum heat treatment. The oxidation kinetic curves of the IN100 alloy and the coating were obtained. The results indicate that NiCrAlY coating gains more weight after cyclic than after isothermal oxidation and no oxide spallation was evident. The oxidation resistance of IN100 superalloy when exposed to either isothermal or cyclic oxidation was markedly improved by coating with NiCrAlY. The oxide scales mainly consisted of alpha-Al2O3 and Cr2O3, at 900degreesC. In the initial oxidation stage at 1000degreesC, three kinds of oxides, NiO, Cr2O3 and alpha-Al2O3, formed simultaneously. With further oxidation, not only is the thickness of the oxide scale increased, but complex reactions also occurred

Oxidation behaviour of the alloy IC-6 and protective coatings

Abstract In this work, NiCoCrAlY coatings were deposited on a new Ni-base alloy, IC-6. The oxidation kinetic curves of alloy IC-6, K17 and NiCoCrAlY coatings on alloy IC-6 at 900–1100 °C were obtained. The results indicated that the oxide scales consisted of α-Al2O3, NiAl2O4, NiO, as well as a small amount of NiMoO4 and MoO2. These scales occurred after alloy IC-6 exposure at 900 °C for 100 h. The weight loss occurred when alloy IC-6 were exposed at 1050 and 1100 °C due to the formation of volatile MoO3. After the NiCoCrAlY coating was deposited, the scales mainly contained α-Al2O3, when the specimens were oxidized at 900 °C, and α-Al2O3and Cr2O3 at 1050 °C. The formation of α-Al2O3 and Cr2O3 scales on NiCoCrAlY coating was directly responsible for improving oxidation resistance of the alloy IC-6.

Influence of hot filaments arranging on substrate temperature during HFCVD of diamond films

The substrate temperature distribution during hot filaments chemical vapor deposition (HFCVD) of diamond films was stimulated. Results showed that the substrate temperature varied with the space position. A temperature distribution with the periodic fluctuation that is in accordance with the filaments arranging occurred. An optimum homogeneous temperature substrate position available for the growth of diamond films over a large area existed in the space with 6-8 nun away from the filaments arranging plane. The substrate temperature was influenced by filaments diameter and distance between filaments. The substrate temperature increased with the filaments diameter, but the temperature distribution was not changed. The parallel arranging of the filaments with a 10-min distance between filaments has a lower temperature fluctuation and larger uniform temperature areas for diamond film growth. A more effective way to enlarge the growth areas of the diamond films was to increase the quantity of the arranged filaments with a proper distance between them

Interdiffusion Behavior of Ni–Cr–Al–Y Coatings Deposited by Arc-Ion Plating

Ni–Cr–Al–Y coatings were deposited on the Ni3Al–base superalloys IC-6 and K17 by arc-ion plating. The results indicated that a small amount of substrate atoms, such as Co, Ti, Mo, etc., existed in the Ni–Cr–Al–Y coatings near the substrates, probably due to “sputter” and “antisputter.” For the alloy K17, the impeding effect of Al was not obvious, because the temperatures of the substrate and the coating were high (420–480°C) during the deposition process and interdiffusion was accelerated. However, for alloy IC-6 which contains Al, as well as a high concentration of Mo, the diffusion of Cr was impeded. Vacuum heat treatment at 1050°C drastically increased diffusivities and the presence of Al and Mo was not enough to prevent some Cr diffusion. Thus, the coating became more uniform and close to the desired composition.

Two-dimensional simulations of temperature fields of the reactor wall during hot-filament CVD diamond film growth over a large area

In order to study the growth of diamond films over a large area in a traditional hot-filament chemical vapour deposition (HFCVD) reactor, two-dimensional mathematical models were first developed to investigate the temperature fields of the reactor walls, which made significant contributions to thermal round-flow of the reactant gases under different energy transfer systems. The set of partial differential equations involved in the thermal conduction system was solved with different boundary conditions by the finite control volume method. Numerical simulations showed that the temperature space distributions were heterogeneous when thermal radiation was assumed to be the only mechanism in heat transfer from the filaments to the reactor walls. However, taking into account the effects of thermal conduction under adiabatic and different isothermal temperature boundary conditions, the temperature uniformities improved greatly. In addition, thermal convection did not affect the temperature distributions but only increased the total temperature of the reactor wall. These results not only give insight into the dominant reasons resulting in low nucleation density and low growth rate of diamond films, but also provide a basis for the design of industrial HFCVD reactors to obtain high-quality diamond films over a large area.

Influence of quantity and energy of the particles in gas phase on nucleation of the HFCVD of diamond films

In this paper, the nucleation of diamond films was studied with the varied bias value and mass current density by adjusting the gas flow rate through the chamber. Results showed that the two parameters above greatly influenced the nucleation density and the morphology of diamond films. Both bias value and mass current density had an optimum value in which the nucleation density reached the maximum. The nucleation of diamond films by hot filament chemical vapor deposition (HFCVD) is a competitive process of deposition and etches (sputtered) due to particle impact on the substrate. The magnitude of the particle energy in gas plasma and mass current density of gas controlled the competitive process and determined whose process was primary. The deposition process was gradually strengthened and the nucleation density increased due to the increment of the energy and quantity of the adatoms and reached a maximum at optimization with the increment of the two parameters mentioned above. The deposition process is suppressed by strengthened particle impact on substrate and the etch (sputtered) process was primary with the further increment of the two parameters above.