摘要:

The relative effect of atomic and ionic oxygen for the oxidation of YBa2Cu3O7−δthin films is investigated. To this goal, the characteristics of an oxygen plasma produced by a small, compact, permanent magnet electron cyclotron resonance plasma source were investigated as a function of a bias applied to the plasma. With no bias, a plasma potential of 23 eV was measured by an energy analysis of the ions. With increasing positive plasma bias voltage, the ion current decreases and its energy increases above the 23 eV by the amount of applied bias voltage. When a negative voltage is applied to the plasma, both electron and ion current drastically decrease, while the atomic flux remains high. The atomic oxygen flux was measured by the oxidation rate of Ag and the etching rate of a standard photoresist as a function of distance from the source and the bias voltage. We find that the resistivity of a YBa2Cu3O7−δfilm in the plasma is well characterized by the flux of atomic oxygen and that there is no significant effect of oxygen ions.

ISSN:0734-2101    

DOI:10.1116/1.577210

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Films of silicon nitride have been grown in an ultrahigh vacuum system by the reaction of silane with nitrogen remotely excited in a microwave plasma at pressures in the range 0.1–0.9 Torr with substrate temperatures in the range 70–350 °C. Growth rates have been determined as a function of silane–nitrogen flow ratio, pressure, microwave power, and substrate temperature in order to give some insight into the growth mechanism. Results indicate that the rate of film deposition is governed by the arrival rate of active nitrogen species at the surface. The films have been characterized by15N nuclear reaction profiling and Rutherford backscattering analysis to determine the hydrogen, silicon, and nitrogen contents. Hydrogen contents are comparable to those obtained with parallel‐plate plasma enhanced chemical vapor deposition reactors while near stoichiometric, nitrogen rich films can be obtained over a wide range of deposition parameters. Floating double probe measurements used to obtain the electron temperatures and ion densities verify that substrate bombardment by charged or energetic particles is not a factor in the growth of these films.

ISSN:0734-2101    

DOI:10.1116/1.577211

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Diethylsilane was used to prepare SiO2films on Si wafers by a low pressure chemical vapor deposition technique at low temperatures (≤400 °C). The deposited films have good conformality (83%), a low residual carbon concentration (<1 at. %) and a low residual stress (<109dyn/cm2); which compare favorably with films prepared by other processes. We also correlated the growth rates with the processing parameters to show that the deposition process follows the heterogeneous bimolecular reaction kinetics. Infrared spectroscopy was used to detect the presence of HSi–O3bending band (880 cm−1) in SiO2films prepared under certain processing conditions. Based on the reaction kinetic model, we optimize the processing conditions to reduce the SiH incorporation and mobile charge carrier concentration in SiO2films.

ISSN:0734-2101    

DOI:10.1116/1.577212

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

X‐ray photoelectron spectroscopy spectra were recorded after sequential deposition of submonolayer amounts of copper on an organized molecular assembly (OMA) of HS(CH2)10COOH 11‐mercaptoundecanoic acid (MUA) on 80‐nm‐thick gold films on silicon substrates. The self‐assembly process results in stable monolayers with the thiol group attached to the gold film and the COOH group as the outer monolayer. Copper deposited in vacuum interacts with the surface of the MUA OMA to produce a unidentate copper complex with the single bonded oxygen atom of the acid monolayer. The data do not support forming a bidentate copper complex or chemical interaction of the double bonded oxygen atom of the acid group with copper. The maximum charge residing on the copper atom of the complex is +1 with one charged copper atom on the surface per MUA molecule of the OMA.

ISSN:0734-2101    

DOI:10.1116/1.577213

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The interface between ZnSe and GaAs (100) has been studied as a function of annealing temperature by high‐resolution photoemission spectroscopy using synchrotron radiation. From an analysis of chemical shifts and relative intensities of the atomic core levels, we find an interfacial Ga2Se3layer forms with loss of Zn and As at the interface. The valence band offset between ZnSe and GaAs is found to be 1.25±0.07 eV, from photoemission measurements of the top of the valence band.

ISSN:0734-2101    

DOI:10.1116/1.577214

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

A new ion‐plating system has been devised through a simple and cost‐effective modification of the ordinary thermal evaporator. We characterized the system itself through evaporation of the various metallic elements such as Zn, Al, and Ti, first of all. The ionization efficiency for the evaporants was so enhanced without any introduction of inert gases that the bias voltage for, and temperature of substrate were reduced in the preparation of the films. The practical performance of the system was recognized in terms of the preparation of the TiN and TiC films which are widely employed for decoration and tools. The overall and layer‐by‐layer compositions, surface and cross‐sectional morphology, and textures of the films have been analyzed by scanning Auger multiprobe (including inert‐gas depth profiling), X‐ray photoelectron spectroscopy, secondary ion mass spectroscopy, and x‐ray diffraction. The process parameters such as nitrogen pressure have been established for five typical groups of colors of TiNx. In case of gold color, the atomic ratio of N to Ti was 0.95 and the main texture was developed along the (200) direction. The surface of film was smooth and dense. The relationship between microhardness, stoichiometry, and texture was investigated for the TiC films which were prepared with the various combination of the process parameters. Higher atomic ratio of C to Ti and Vicker’s hardness number were obtained at higher C2H2pressure with two distinct preferred orientations, (111) and (200).

ISSN:0734-2101    

DOI:10.1116/1.577215

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The microstructural analysis of a chemically converted black copper solar selective coating using transmission electron microscopy technique has been presented. The phases present in the as‐deposited surfaces are predominantly CuO along with a strong ring pattern of Cu2S and traces of CuCO3, Cu(OH)2, and Cu2O. No noticeable changes in the microstructural and optical properties have been observed up to 300 °C under ambient conditions and up to 250 °C in vacuum conditions. On air annealing above 350 °C, phase transformations occur resulting in change in the microstructural and the optical properties of the coating. No significant microstructural changes have been observed in case of vacuum annealed surfaces above 300 °C. However, a decrease in the optical properties have been observed. Studies with steam and external environment exposed surfaces reveal no significant microstructural and optical changes in the coating.

ISSN:0734-2101    

DOI:10.1116/1.577216

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

An ultrahigh vacuum coevaporator equipped with three sources for preparation of Y–BaF2–Cu–O thin films is described. Evaporation rates of Y, BaF2, and Cu were controlled using a quadrupole mass spectrometer operating in a multiplexed mode. To evaluate the method depositions have been performed using different source configurations and evaporation rates. Utilizing Rutherford backscattering spectrometry absolute values of the actual evaporation rates were determined. It was observed that the mass‐spectrometer sensitivity is highest for Y, followed by BaF2(BaF+is the measured ion) and Cu. A partial pressure of oxygen during evaporation of Y, BaF2, and Cu affected mainly the rate of Y. It is shown that the mass spectrometer can be utilized to precisely control the film composition.

ISSN:0734-2101    

DOI:10.1116/1.577217

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Ge(100) single‐crystal films, up to 30 μm thick, have been obtained by molecular‐beam epitaxy (MBE) on a CaF2(100) or BaF2(100) single‐crystal film substrate, 2000 Å thick, grown in turn by MBE on a sapphire (11̄02) single‐crystal wafer. By dissolving the CaF2or BaF2in water, this double epitaxy procedure allowed the recovery and the subsequent reuse of the expensive sapphire substrate. This is of interest for large area devices, such as solar cells. The Ge single‐crystal films served as substrates for the growth of GaAs single‐crystals by metalorganic chemical vapor deposition (MOCVD). Furthermore, by doping during growth, tandem double energy gap photovoltaic junctions, which may be suitable for high‐efficiency solar cells, may be obtained. The growth conditions, orientation relationship, crystalline quality and microstructure of these films was examined byinsitureflection high‐energy electron diffraction (RHEED) and by transmission electron diffraction and microscopy and by scanning electron microscopy. The Ge films grew in a parallel orientation to that of the CaF2or BaF2substrate and were composed of three‐dimensional nuclei. The sharp Kikuchi lines in the RHEED patterns demonstrated their high perfection. The final film of 3–30 μm thickness had a mirror like appearance and was free of cracks due to thermal stresses. The intrinsicp‐type carrier concentration was 2.2×1015cm−3and the mobility 1300 cm2 V−1 s−1, at room temperature.

ISSN:0734-2101    

DOI:10.1116/1.577218

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

A new ultrahigh vacuum system has been specially designed and built to deposit high temperature superconducting thin films over a large area with great uniformity in both thickness and composition. The sources are in close proximity and a large distance (460 mm) separates the substrate holder and the sources. We will describe the design and the capabilities of the system including the design rationale. We have preparedinsituYBa2Cu3O7−xfilms to demonstrate the feasibility of the system. As configured, the reactive coevaporation system can deposit up to 35 mm diam YBa2Cu3O7−xfilms. Evaporant uniformity is expected up to 60 mm diam with the present limit in area set by the heater size, the size of the appropriate substrates, and the difficulty in attachment of substrates to the holder with uniform thermal contact. Films are prepared by coevaporation of yttrium, barium, and copper from three different evaporation sources with the substrate holder temperature measured at 680 °C in a PO2=5×10−4Torr ambient. Because the substrate holder is 460 mm above the sources, debris from the sources cannot travel upward and stick to the film surface. Films less than 250 nm thick on (001) SrTiO3and (001) LaAlO3exhibit a sharp transition width (ΔT=0.5 K) andTc(R=0)=90 K by resistivity measurements. In addition, alternating‐current (ac) magnetic susceptibility characterization shows sharp transitions (<1 K) at a slightly lower temperature implying that the induced screening current is uniform over the area of the detection coil. These films are structurally very close to single crystals as characterized by both x‐ray diffraction and Raman scattering.

ISSN:0734-2101    

DOI:10.1116/1.577219

出版商:American Vacuum Society    

年代:1991

数据来源: AIP