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1.
Thin films of different molybdenum carbides ( δ-MoC 1−x, γ′-MoC 1−x and Mo 2C) have been deposited from a gas mixture of MoCl 5/H 2/C 2H 4 at 800°C by CVD. The H 2 content in the vapour has a strong influence on the phase composition and microstructure. Typically, high H 2 contents lead to the formation of nanocrystalline δ-MoC 1−x films while coarse-grained γ′-MoC 1−x is formed with an H 2-free gas mixture. This phase has previously only been synthesized by carburization of Mo in a CO atmosphere and it has therefore been considered as an oxycarbide phase stabilized by the presence of oxygen in the lattice. Our results, however, show that γ′-MoC 1−x films containing only trace amounts of oxygen can be deposited by CVD. Stability calculations using a FP-LMTO method confirmed that the γ′-MoC 1−x phase is stabilized by oxygen but that the difference in energy between e.g. δ-MoC 0.75 and oxygen-free γ′-MoC 0.75 is small enough to allow the synthesis of the latter phase in the absence of kinetic constraints. Annealing experiments of metastable δ-MoC 1−x and γ′-MoC 1−x films showed two different reaction products suggesting that kinetic effects play an important role in the decomposition of these phases. 相似文献
2.
AgInSn xS 2−x ( x = 0–0.2) polycrystalline thin films were prepared by the spray pyrolysis technique. The samples were deposited on glass substrates at temperatures of 375 and 400 °C from alcoholic solutions comprising silver acetate, indium chloride, thiourea and tin chloride. All deposited films crystallized in the chalcopyrite structure of AgInS 2. A p-type conductivity was detected in the Sn-doped samples deposited at 375 °C, otherwise they are n-type. The optical properties of AgInSn xS 2−x ( x < 0.2) resemble those of chalcopyrite AgInS 2. Low-temperature PL measurements revealed that Sn occupying an S-site could be the responsible defect for the p-type conductivity observed in AgInSn xS 2−x ( x < 2) thin films. 相似文献
3.
Microcrystalline silicon carbide (μc-Si 1−xC x) films were successfully deposited by the hot wire cell method using a gas mixture of SiH 4, H 2 and C 2H 2. It was confirmed by Fourier transform infrared and X-ray diffraction analyses that the films consisted of μc-Si grains embedded in a-Si 1−xC x tissue. The p-type μc-Si 1−xC x films were deposited using B 2H 6 as a doping gas. A dark conductivity of 0.2 S/cm and an activation energy of 0.067 eV were obtained. The p-type μc-Si 1−xC x was used as a window layer of a-Si solar cells, in which the intrinsic layer was deposited by photo-chemical vapor deposition, and an initial conversion efficiency of 10.2% was obtained. 相似文献
4.
The Ba xSr 1−xTiO 3 (BST)/Pb 1−xLa xTiO 3 (PLT) composite thick films (20 μm) with 12 mol% amount of xPbO–(1 − x)B 2O 3 glass additives ( x = 0.2, 0.35, 0.5, 0.65 and 0.8) have been prepared by screen-printing the paste onto the alumina substrates with silver bottom electrode. X-ray diffraction (XRD), scanning electron microscope (SEM) and an impedance analyzer and an electrometer were used to analyze the phase structures, morphologies and dielectric and pyroelectric properties of the composite thick films, respectively. The wetting and infiltration of the liquid phase on the particles results in the densification of the composite thick films sintered at 750 °C. Nice porous structure formed in the composite thick films with xPbO–(1 − x)B 2O 3 glass as the PbO content ( x) is 0.5 ≥ x ≥ 0.35, while dense structure formed in these thick films as the PbO content ( x) is 0.8 ≥ x ≥ 0.65. The volatilization of the PbO in PLT and the interdiffusion between the PLT and the glass lead to the reduction of the c-axis of the PLT phase. The operating temperature range of our composite thick films is 0–200 °C. At room temperature (20 °C), the BST/PLT composite thick films with 0.35PbO–0.65B 2O 3 glass additives provided low heat capacity and good pyroelectric figure-of-merit because of their porous structure. The pyroelectric coefficient and figure-of-merit FD are 364 μC/(m 2 K) and 14.3 μPa −1/2, respectively. These good pyroelectric properties as well as being able to produce low-cost devices make this kind of thick films a promising candidate for high-performance pyroelectric applications. 相似文献
5.
Transmission electron microscopy (TEM) studies of epitaxial YBa 2Cu 3O 7−x thin films and YBa 2Cu 3O 7/PrBa 2Cu 3O 7 superlattices are summarized. High-resolution imaging of cross-sections and plan views and energy-dispersive X-ray microanalysis and electron energy loss spectroscopy in the transmission electron microscope were the methods applied. In the first section results on YBa 2Cu 3O 7−x thin films With varying oxygen stoichiometry deposited onto SrTiO 3 are discussed. Then, YBa 2Cu 3O 7/PrBa 2Cu 3O 7 superlattices deposited onto SrTiO 3 and MgO are investigated. Finally, an interface analysis of high-quality YBa 2Cu 3O 7−x thin films deposited onto sapphire with yttrium-stabilized zirconia buffer layers is presented. 相似文献
6.
B-doped a-Si 1−xC x:H films for a window layer of Si thin film solar cells have been prepared by the Cat-CVD method. It is found that C is effectively incorporated into the films by using C 2H 2 as a C source gas, where an only little C incorporation is observed from CH 4 and C 2H 6 under similar deposition conditions. Using a-Si 1−xC x:H films grown from C 2H 2, heterojunction p–i–n solar cells have been prepared by the Cat-CVD method. The cell structure is (SnO 2 Asahi-U)/ZnO/a-Si 1−xC x:H(p)/a-Si:H(i)/μc-Si:H(n)/Al. The obtained conversion efficiency was 5.4%. 相似文献
7.
We propose a new approach to fabrication of hydrogenated amorphous silicon carbide (a-Si 1−xC x:H) thin films for solar cells by the catalytic chemical vapor deposition (Cat-CVD) method using a carbon catalyzer, which is more stable than tungsten or tantalum. It was found that by using the carbon catalyzer, undoped and boron-doped a-Si 1−xC x:H films were easily obtained from a SiH 4, CH 4 and B 2H 6 mixture without any change in the catalyzer surface, even after deposition for longer than 30 h. 相似文献
8.
Excimer laser ablation has been used to produce thin films of lanthanum-modified lead zirconate titanate (PLZT), or Pb1−xLax( Zr1−yTiy) 1−x/4O3. PLZT is an interesting class of materials since it has a wide range of compositionally dependent electro-optical properties and strong non-linear optical characteristics. PLZT thin films of 7/0/100, 28/0/100 and 0/0/100 compositions have been deposited onto crystalline Si100 and amorphous fused silica substrates. Effects of oxygen backfill pressure on the Pb:(Ti + La) ratios were investigated. The results indicate that controlling the oxygen backfill pressure during laser deposition strongly influences the stoichiometry and crystal structure of PLZT thin films. 相似文献
9.
Doping and electrical characteristics of in-situ heavily B-doped Si 1−x−yGe xC y (0.22< x<0.6, 0< y<0.02) films epitaxially grown on Si(100) were investigated. The epitaxial growth was carried out at 550°C in a SiH 4–GeH 4–CH 3SiH 3–B 2H 6–H 2 gas mixture using an ultraclean hot-wall low-pressure chemical vapor deposition (LPCVD) system. It was found that the deposition rate increased with increasing GeH 4 partial pressure, and only at high GeH 4 partial pressure did it decrease with increasing B 2H 6 as well as CH 3SiH 3 partial pressures. With the B 2H 6 addition, the Ge and C fractions scarcely changed and the B concentration ( CB) increased proportionally. The C fraction increased proportionally with increasing CH 3SiH 3 partial pressures. These results can be explained by the modified Langmuir-type adsorption and reaction scheme. In B-doped Si 1−x−yGe xC y with y=0.0054 or below, the carrier concentration was nearly equal to CB up to approximately 2×10 20 cm −3 and was saturated at approximately 5×10 20 cm −3, regardless of the Ge fraction. The B-doped Si 1−x−yGe xC y with high Ge and C fractions contained some electrically inactive B even at the lower CB region. Resistivity measurements show that the existence of C in the film enhances alloy scattering. The discrepancy between the observed lattice constant and the calculated value at the higher Ge and C fraction suggests that the B and C atoms exist at the interstitial site more preferentially. 相似文献
10.
We present the results of ab initio calculations of the spin-polarized electronic structure of disordered bcc and fcc Fe 1 − xSi x alloys from dilute solid solutions of Si on iron up to FeSi intermetallic compound composition ( x=0.01..0.5) and ordered intermetallic phases FeSi in B20 structure and Fe 3Si in DO 3 structure. The self-consistent calculations were performed with the coherent potential approximation within the Korringa–Kohn–Rostoker method (KKR–CPA) for disordered case and by using the tight-binding linear muffin–tin orbital (TB LMTO) method for intermetallic compounds. In the last case the supercell approach has been utilized in order to take into account the structural defects for this ordered phase. In particular, we have performed a series of calculations in the BCC Fe 1 − xSi x alloys with x=0.01, 0.015, 0.1, 0.15, 0.25. 相似文献
11.
(Ti, Al)N films have drawn much attention as alternatives for TiN coatings, which are oxidized easily in air above 500 °C. We have investigated the effect of Al content on the oxidation resistance of (Ti 1 − xAl x)N films prepared by r.f. reactive sputtering. (Ti1 − xAlxN films (O ≤ x ≤ 0.55) were deposited onto fused quartz substrates by r.f. reactive sputtering. Composite targets with five kinds of Al-to-Ti area ratio were used. The sputtering gas was Ar (purity, 5 N) and N2 (5 N). The flow rate of Ar and N2 gas was kept constant at 0.8 and 1.2 sccm, respectively, resulting in a sputtering pressure of 0.4 Pa. The r.f. power was 300 W for all experiments. Substrates were not intentionally heated during deposition. The deposited films (thickness, 300 nm) were annealed in air at 600 900 °C and then subjected to X-ray diffractometer and Auger depth profiling. The as-deposited (Ti1 − xAlx)N films had the same crystal structure as TiN (NaCl type). Al atoms seemed to substitute for Ti in lattice sites. The preferential orientation of the films changed with the Al content of the film, x. Oxide layers of the films grew during annealing and became thicker as the annealing temperature increased. The thickness of the oxide layer grown on the film surface decreased with increasing Al content in the film. For high Al content films an Al-rich oxide layer was grown on the surface, which seemed to prevent further oxidation. All of the films, however, were oxidized by 900 °C annealing, even if the Al content was increased up to 0.55. 相似文献
12.
Many perovskites and perovskite related materials exhibit electronic phase separation phenomena at nanometer scales, which are thought to concur to important electric and magnetic properties, like high- Tc superconductivity or colossal magnetoresistence (CMR). Recent and new anelastic spectroscopy experiments are presented, which supply information on the dynamics of such inhomogeneities in the superconductors of the La 2−xSr xCuO 4 (LSCO) family and on the magnetic perovskite La 1−xCa xMnO 3. In La 2−xSr xCuO 4, a relaxation process at liquid He temperatures is identified as due to the motion of the hole stripes, acting as walls between antiferromagnetic (AF) domains. Another process is identified as the depinning of these stripes from defects in the disordered phase. In La 1−xCa xMnO 3 a glassy dynamic response below the ferromagnetic (FM) transition is attributed to the insulating nanodomains coexisting with the ferromagnetic background. 相似文献
13.
Thin films of Cd xSe 1−x (0< x<1) have been deposited by the vacuum evaporation technique onto ultra clean substrates maintained at 300°C. The optical properties (specially transmission spectra) of these films were studied. The wavelength dependence of refractive index and extinction coefficient of the films along with the variation of these constants with composition was studied. 相似文献
14.
Nanocrystalline Ba 1−xSr xTiO 3 ( x=0, 0.2, 0.4, 0.6, 0.8 and 1.0) precursors were synthesized using the stearic acid gel method. After the precursors had been calcined at 600–950°C for 0.5–1 h, nanocrystalline powders with the cubic perovskite structure were obtained and these were made into thick films. The powder samples were characterized by differential thermal analysis, X-ray diffraction and transmission electron microscopy, and the thick film samples were characterized by scanning electron microscopy and X-ray diffraction. The humidity-sensitive properties of the nanocrystalline Ba 1−xSr xTiO 3 thick films were investigated. The results show that these nanocrystalline thick films possess higher humidity sensitivity and lower resistance than those of conventional materials. 相似文献
15.
(Ti 1−xAl x)N films were prepared on a Si wafer at 700°C from toluene solution of alkoxides (titanium tetraetoxide and aluminum tri-butoxide) in an Ar/N 2/H 2 plasma by the thermal plasma chemical vapor deposition (CVD) method. The films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, electrical resistivity, and Vickers micro-hardness. Single phase TiN formed at an Al atomic fraction of 0–0.2, with a mixed TiN and AlN phase occurring up to 0.6 and single phase AlN forming above 0.8. The films had relatively sooth surfaces, 0.4 μm thick at an Al atomic fraction of 0.2, and thickened with increasing Al fraction. The atomic concentration of Ti, Al, N, O, and C determined from their respective XPS areas showed that the Ti and Al contents of the films changes with the solution composition in a complementary way. The impurities were about 10 at.% oxygen and carbon. The electrical resistivity was almost unchanged from the value of 10 3 μΩ cm at 0–0.6 Al but then suddenly increased to 10 4 μΩ cm at higher Al contents. The hardness showed a synergic maximum of about 20 GPa at an Al fraction of 0.6–0.8. 相似文献
16.
The optical and magneto-optical properties of Mn(Sb 1−xBi x) films were investigated for incident photons within the energy range from 1.3 to 4.0 eV. The diagonal and off-diagonal optical conductivities were determined from the results of spectroscopic ellipsometry and the polar Kerr effect measurements. A large Kerr rotation angle of about 0.57° was observed at photon energy ω≈2.65 eV for the Mn 55Sb 36Bi 9 film with an average grain size of 30 nm. The changes of the exchange splitting and the spin–orbit interaction strength are responsible for the strong spectral dependence of the Kerr effect in Mn(Sb 1−xBi x) nanocrystalline films. 相似文献
17.
High quality GaN epitaxial layers were obtained with Al xGa 1−xN buffer layers on 6H–SiC substrates. The low-pressure metalorganic chemical vapor deposition (LP-MOCVD) method was used. The 500 Å thick buffer layers of Al xGa 1−xN (0≤ x≤1) were deposited on SiC substrates at 1025°C. The FWHM of GaN (0004) X-ray curves are 2–3 arcmin, which vary with the Al content in Al xGa 1−xN buffer layers. An optimum Al content is found to be 0.18. The best GaN epitaxial film has the mobility and carrier concentration about 564 cm 2 V −1 s −1 and 1.6×10 17 cm −3 at 300 K. The splitting diffraction angle between GaN and Al xGa 1−xN were also analyzed from X-ray diffraction curves. 相似文献
18.
In 2O 3 thin films have been prepared from commercially available pure In 2O 3 powders by high vacuum thermal evaporation (HVTE) and from indium iso-propoxide solutions by sol-gel techniques (SG). The films have been deposited on sapphire substrates provided with platinum interdigital sputtered electrodes. The as-deposited HVTE and SG films have been annealed at 500°C for 24 and 1 h, respectively. The film morphology, crystalline phase and chemical composition have been characterised by SEM, glancing angle XRD and XPS techniques. After annealing at 500°C the films’ microstructure turns from amorphous to crystalline with the development of highly crystalline cubic In 2O 3−x (JCPDS card 6-0416). XPS characterisation has revealed the formation of stoichiometric In 2O 3 (HVTE) and nearly stoichiometric In 2O 3−x (SG) after annealing. SEM characterisation has highlighted substantial morphological differences between the SG (highly porous microstructure) and HVTE (denser) films. All the films show the highest sensitivity to NO 2 gas (0.7–7 ppm concentration range), at 250°C working temperature. At this temperature and 0.7 ppm NO 2 the calculated sensitivities ( S= Rg/ Ra) yield S=10 and S=7 for SG and HVTE, respectively. No cross sensitivity have been found by exposing the In 2O 3 films to CO and CH 4. Negligible H 2O cross has resulted in the 40–80% relative humidity range, as well as to 1 ppm Cl 2 and 10 ppm NO. Only 1000 ppm C 2H 5OH has resulted to have a significant cross to the NO 2 response. 相似文献
19.
We report on epitaxial {1 0 0} K 1−xRb xTiOPO 4 waveguide films for the visible spectral range grown on KTiOPO 4 substrates by liquid phase epitaxy. Using the m-line technique a refractive index increase of Δ nx≈0.007 and Δ nz≈0.004 for TM and TE polarisation has been determined for a K 0.78Rb 0.22TiOPO 4 film. Optical transmission and nearfield distribution are comparable to conventional ion-exchanged waveguides. Typical attenuation of about 1 dB/cm for both TM and TE polarisation was obtained at λ=532 and 1064 nm. Energy-dispersive X-ray spectrometry reveals solid-solution films with graded rubidium composition profiles. X-ray rocking curve analyses confirm the epitaxial growth process and indicate perfect and relaxed K 1−xRb xTiOPO 4 films. Atomic force microscopy investigations reveal regular step structures with step heights Δ h<1.3 nm resulting in rms-roughness values of ≈0.4 nm. 相似文献
20.
Solid solutions of Bi 3(Nb 1−xTa x)O 7 ( x = 0.0, 0.3, 0.7, 1) were synthesized using solid state reaction method and their microwave dielectric properties were first reported. Pure phase of fluorite-type could be obtained after calcined at 700 °C (2 h) −1 between 0 ≤ x ≤ 1 and Bi 3(Nb 1−xTa x)O 7 ceramics could be well densified below 990 °C. As x increased from 0.0 to 1.0, saturated density of Bi 3(Nb 1−xTa x)O 7 ceramics increased from 8.2 to 9.1 g cm −3, microwave permittivity decreased from 95 to 65 while Qf values increasing from 230 to 560 GHz. Substitution of Ta for Nb modified temperature coefficient of resonant frequency τf from −113 ppm °C −1 of Bi 3NbO 7 to −70 ppm °C −1 of Bi 3TaO 7. Microwave permittivity, Qf values and τf values were found to correlate strongly with the structure parameters of fluorite solid solutions and the correlation between them was discussed in detail. Considering the low densified temperature and good microwave dielectric proprieties, solid solutions of Bi 3(Nb 1−xTa x)O 7 ceramics could be a good candidate for low temperature co-fired ceramics application. 相似文献
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