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1.
Combined Hall effect and low-temperature photoluminescence measurements have been used to perform a thorough evaluation of the growth temperature dependence of Ge incorporation in GaAs during molecular beam epitaxy (MBE) over the entire substrate temperature range (400°≦T s ≦600[°C]) practicable forn-type layer growth. Using a constant As4 to Ga flux ratio of two, growth below 500°C yieldsn-GaAs: Ge films having electrical and optical properties rapidly deteriorating with decreasingT s . Growth at 500° ≦T s ≦600[°C] produces high-qualityn-GaAs: Ge films (N D /N A ≈4) with C as well as Ge residual acceptors competing on the available As sites. The amount of Ge atoms on As sites [GeAs] increases with substrate temperature, whereas simultaneously the amount of C atoms on As sites [CAs] decreases thus leading to the well-establishednonlinear behaviour of the (N A /N D vs. 1/T s plot. Counting the incorporated Ge impurities separately, however, yields alinear behaviour of the ([GeAs]/[GeGa]) vs. 1/T s plot which has exactly the same slope as the (P As 2/P Ga) vs. 1/T s plot derived from vapour pressure data of As2 and Ga over solid GaAs surfaces. The important result is, therefore, that the incorporation behaviour of Ge in GaAs during molecular beam epitaxy is directly correlated with theevaporation behaviour of the growing GaAs surface.  相似文献   

2.
The ferroelectric and switching properties of spray deposited cesium nitrate: poly (vinyl alcohol) composite films at different substrate temperatures (T s ) have been studied. The optimum value of remanent polarization was obtained in the film deposited at T s =200°C, which may be due to larger structural distortion (c/a ratio) and less porosity as revealed by x-ray diffraction and field emission scanning electron microscope (FESEM) analysis. The switching current transients have been analyzed by nucleation limited switching model (NLS) with the Lorentzian distribution function. This model gives excellent agreement with the experimental polarization current throughout the whole time range. The switching parameters were determined in the composite films deposited at different T s and found to be optimum at T s =200°C. The effect of pulse amplitude on the domain switching properties has also been studied and analyzed. The peak value of polarization current exhibits an exponential dependence on the external applied field.  相似文献   

3.
Crystallographic phase transitions in perovskite-like LaSrMnO metallic oxides are studied. The transitions are induced when internal stresses generated during film synthesis (at temperatures between 450 and 730°C) vary (decrease or increase) upon subsequent irradiation by a KrF laser emitting in the UV range. As the synthesis temperature T s grows, the rhombohedral-to-orthorhombic phase transition occurs at 650–670°C. The resistivity is shown to be either temperature-independent, ρ(T)=const, at T<T crit, or varies and reaches a maximum, ρ(T)=ρmax, at the Curie temperature T c. Optical transmission spectra taken at photon energies ℏω=0.5–2.5 eV exhibit both a high (0.8–0.9) and low (0.1–0.3) transmission coefficient t, depending on the synthesis temperature. As follows from X-ray diffraction data, the laser irradiation causes a phase transition only in LaSrMnO films grown at T s<650°C. Phases of different size scales appear: the long-range-order orthorhombic matrix and mesoscopic-range-order rhombohedral clusters are observed in the films grown at T s=450–550°C and the rhombohedral matrix with orthorhombic clusters, in the films grown at T s=550–650°C.  相似文献   

4.
The structures of amorphous CNx-Co films grown at different temperatures (T s = 200–365°C) are studied by X-ray diffraction. As the growth temperature increases above T s = 200°C, a concentration phase transition is found to occur in the amorphous state; this transition is related to a change in the major portion of carbon or cobalt in the structure of the cluster films. At T s = 365°C, a disorder-order phase transition, which is accompanied by the transition from the amorphous to crystalline state, occurs in the films.  相似文献   

5.
The optical properties of thick sputtered films (~30μ) of amorphous Ge, grown with different substrate temperatures (0ˇ-T sˇ-350°C), were obtained between 0·05 and 4·5 eV by a combination of reflectance, transmittance and ellipsometric measurements. The refractive index at 0·15 eV decreases monotonically with increasing T s, or equivalently, with increasing density, and is 4·13±0·05 eV in the highest density films. The absorption edge is approximately exponential (102?α?104 cm?1) but shifts monotonically to higher energy and increases in slope with increasing T s. Similarly, the peak in ε2 grows by about 10% and shifts by about 0·15 eV to higher energies, reaching a maximum of about 23 at 2·90±0·05 eV in the high density films. The peak in the transition strength ω2ε2 occurs at 4·2±0·2 eV in all films, but increases in magnitude with increasing T s. The sum rules for n eff(ω) and ε0,eff(ω) are evaluated for ▄ω?5 eV and vary monotonically with T s. These trends are neither compatible with Galeener's void resonance theory nor with changes in the oxygen content of the films, determined by the examination of absorption peaks at 0·053 eV and 0·09 eV. An explanation, suggested here and expanded in I, is based on the observed changes in the structure of the network and voids.  相似文献   

6.
Identified π±,K ±, p and -p transverse momentum spectra at mid-rapidity in √sNN = 130 GeV Au-Au collisions were measured by the PHENIX experiment at RHIC as a function of collision centrality. Average transverse momenta increase with the number of participating nucleonsN part similarly for all particle species. The multiplicity densities scale faster thanN part. TheK ± andp ±yields per participant increase faster than the π± yields. We combine the PHENIX neutral and charged pion measurement and find that in central collisions forp T >-2 GeV/c,-p andp yields are comparable to or even exceed the pion yields.  相似文献   

7.
We have studied the low-temperature annealing effect on the physical properties of Bi2Sr2CaCu2O y thin films deposited on a MgO(100) substrate by rf magnetron sputtering. It is found that the characteristics of the films depend strongly on the oxygen partial pressure during re-annealing at 470°C after high-temperature annealing at 770°C in air. Tc and ρ at 300 K abruptly change for less than 20% oxygen partial pressure. A peak shift of the Bi4f core level spectrum is also observed at 0% oxygen partial pressure in an XPS measurement, which is due to the change in the ligand of the Bi atom.  相似文献   

8.
In the compound MnBi, a first-order transition from the paramagnetic to the ferromagnetic state can be triggered by an applied magnetic field and the Curie temperature increases nearly linearly with an increase in magnetic field by ∼2 K/T. Under a field of 10 T, TC increases by 20 and 22 K during heating and cooling, respectively. Under certain conditions a reversible magnetic field or temperature induced transition between the paramagnetic and ferromagnetic states can occur. A magnetic and crystallographic H-T phase diagram for MnBi is given. Magnetic properties of MnBi compound aligned in a Bi matrix have been investigated. In the low temperature phase MnBi, a spin-reorientation takes place during which the magnetic moments rotate from being parallel to the c-axis towards the basal plane at ∼90 K. A measuring Dc magnetic field applied parallel to the c-axis of MnBi suppresses partly the spin-reorientation transition. Interestingly, the fabricated magnetic field increases the temperature of spin-reorientation transition Ts and the change in magnetization for MnBi. For the sample solidified under 0.5 T, the change in magnetization is ∼70% and Ts is ∼91 K.  相似文献   

9.
The coherent X-ray scattering for momentum transfer, k, between 0·025 and 15·0 Å?1 has been measured for a series of sputtered amorphous Ge films prepared at various substrate temperatures, T s, between 0 and 350°C. Differences in the radial distribution function (RDF) of films of different T s have been determined by an accurate differential scattering technique. The small angle scattering (SAS) of the films is less than 100 electron units for k < 1 Å?1. From a combination of SAS, RDF and scanning electron microscope studies, it is concluded that an observed increase in film density with increasing T s occurs through a reduction in the number of voids about 7 Å or less in diameter. No variation of bond length with T s is found. With increasing T s, there is an increase in first and second-neighbour coordination and a reduction in bond angle distortion.

The rate of change of coordination, C, with density, ρ0, is found to be d ln C/d ln ρ0 = 0·6±0·2. Using a new, general theory of the dependence of the RDF on the dihedral angle distribution, P(θ), it is shown that with increasing T s there is an increased probability of dihedral angles corresponding to the staggered configuration. For all films, the experimental RDF between r = 4·5 and 6·2 Å agrees with a nearly random P(θ) distribution. Comparison of experimental RDF's of crystalline and amorphous Ge indicates the static distortion of the first-neighbour bond length has a standard deviation of only about 0·04 Å.  相似文献   

10.
Nanocrystalline ZnO thin films were deposited at different temperatures (Ts = 325 °C–500 °C) by intermittent spray pyrolysis technique. The thickness (300 ± 10 nm) independent effect of Ts on physical properties was explored. X-Ray diffraction analysis revealed the growth of wurtzite type polycrystalline ZnO films with dominant c-axis orientation along [002] direction. The crystallite size increased (31 nm–60 nm) and optical band-gap energy decreased (3.272 eV–3.242 eV) due to rise in Ts. Scanning electron microscopic analysis of films deposited at 450 °C confirmed uniform growth of vertically aligned ZnO nanorods. The films deposited at higher Ts demonstrated increased hydrophobic behavior. These films exhibited high transmittance (>91%), low dark resistivity (~10?2 Ω-cm), superior figure of merit (~10?3 Ω?1) and low sheet resistance (~102 Ω/□). The charge carrier concentration (η -/cm3) and mobility (μ – cm2V?1s?1) are primarily governed by crystallinity, grain boundary passivation and oxygen desorption effects.  相似文献   

11.
A study is reported of the structural, magnetic, and magneto-optic properties of Mn/Dy/Bi films obtained by multilayer technology. The maximum Kerr rotation angle in such films is shown to be θ k =2.25°. Possible reasons for such a large Kerr effect enhancement are considered, namely, an increase in the 6p–3d transition probability caused by symmetry distortion, polarization of the Bi6p band, and a change in the density of states near the Fermi level. The latter reason has been analyzed by simulating the electronic structure of Mn/Dy/Bi through superposition of Dy levels on the MnBi band structure. This approach has revealed possible additional transitions which may be induced by the presence of a Dy buffer and could contribute to the Kerr magneto-optic effect. Fiz. Tverd. Tela (St. Petersburg) 41, 91–97 (January 1999)  相似文献   

12.
Iron films have been grown on (1 1 0) GaAs substrates by atmospheric pressure metalorganic chemical vapor deposition at substrate temperatures (Ts) between 135°C and 400°C. X-ray diffraction (XRD) analysis showed that the Fe films grown at Ts between 200°C and 330°C were single crystals. Amorphous films were observed at Ts below 200°C and it was not possible to deposit films at Ts above 330°C. The full-width at half-maximum of the rocking curves showed that crystalline qualities were improved at Ts above 270°C. Single crystalline Fe films grown at different substrate temperature showed different structural behaviors in XRD measurements. Iron films grown at Ts between 200°C and 300°C showed bulk α-Fe like behavior regardless of film thickness (100–6400 Å). Meanwhile, Fe films grown at 330°C (144 and 300 Å) showed a biaxially compressed strain between substrate and epilayer, resulting in an expanded inter-planar spacing along the growth direction. Magnetization measurements showed that Fe films (>200 Å) grown at 280°C and 330°C were ferromagnetic with the in-plane easy axis along the [1 1 0] direction. For the thinner Fe films (⩽200 Å) regardless of growth temperature, square loops along the [1 0 0] easy axis were very weak and broad.  相似文献   

13.
《Current Applied Physics》2015,15(5):588-598
Thin films of tin sulphide (SnS) have been grown by sulphurization of sputtered tin precursor layers in a closed chamber. The effect of sulphurization temperature (Ts) that varied in the range of 150–450 °C for a fixed sulphurization time of 120 min on SnS film was studied through various characterization techniques. X-ray photoelectron spectroscopy analysis demonstrated the transformation of metallic tin layers into SnS single phase for Ts between 300 °C and 350 °C. The X-ray diffraction measurements indicated that all the grown films had the (111) crystal plane as the preferred orientation and exhibited orthorhombic crystal structure. Raman analysis showed modes at 95 cm−1, 189 cm−1 and 218 cm−1 are related to the Ag mode of SnS. AFM images revealed a granular change in the grain growth with the increase of Ts. The optical energy band gap values were estimated using the transmittance spectra and found to be varied from 1.2 eV to 1.6 eV with Ts. The Hall effect measurements showed that all the films were p-type conducting nature and the layers grown at 350 °C showed a low electrical resistivity of 64 Ω-cm, a net carrier concentration of 2 × 1016 cm−3 and mobility of 41 cm2 V−1 s−1. With the use of sprayed Zn0.76Mg0.24O as a buffer layer and the sputtered ZnO:Al as window layer, the SnS based thin film solar cell was developed that showed a conversion efficiency of 2.02%.  相似文献   

14.

It has been found that the resistance of the (Bi0.3Sb0.7)2Te3 porous polycrystalline film fabricated by thermal vacuum evaporation at substrate temperature T s ≤ 363 K drastically decreases near the threshold AC frequency ω0 ≈ 105 Hz as low as the resistance of dense films with T s ≈ 423 K. After the action of N ≈ 105 cycles of mechanical deformation with amplitude ε = ±1 × 10–3 a.u., the film resistance increases by 1.5 times and the threshold frequency decreases in almost 102 times, which can qualitatively be accounted for by the model of microcontacting blocks.

  相似文献   

15.
The gain saturation in the 46.9 nm line of the Ar+8 laser is analyzed using an atomic kinetics code. The dependence of the gain (G) on the electron kinetic temperature (Te) in the region (50 ‐150 eV) is calculated in the quasi steady‐state approximation for the different values of the electron density (Ne) and the plasma radius (rpl). The influence of radiat on trapping, ion random and mean velocities, Stark line broadening and refraction losses on the gain saturation is taken into consideration. For rpl = 150‐600 μm, the amplplication (G > 0 cm‐1) exists in the large temperature/density domain (Te = 60‐150 eV, Ne = 0.5‐10 × 1018 cm‐3). However, the value Gs ∼ 1.4 cm‐1 required for the gain saturation at the typical plasma length Lpl ∼ 15 cm is reached in the extremely narrow density regions at the high temperatures. The saturation is reached for rpl = 600 μm at Tse = 150 eV in the region Nse = 1.8‐2 × 1018 cm ‐3, for rpl = 300 μm at Tse = 125 eV and Nse = 2.5‐3 × 1018 cm‐3, and for rpl = 150 μm at Tse = 110 eV and Nse = 3‐4 × 1018 cm‐3. The broadest density region (Nse = 2 ‐8 × 1018 cm‐3) is predicted for the narrowest column (rpl = 150 μm) at the highest temperature (Tse = 150 eV). The operation in the broadest density region Nse, should make easier achievement of the gain saturation in the experiments.  相似文献   

16.
The N‐(3‐ammoniumpropyl)‐1,3 diammoniumpropane hexabromobismuthate (III) monohydrate exhibits a structural phase transition at T = 330 °K, which has been characterized by differential scanning calorimetric. The alternating current electrical conductivity and the dielectric relaxation properties of the (C6H20N3)BiBr6.H2O compound have been investigated by means of impedance spectroscopy measurements over a wide range of frequencies and temperatures, 100 Hz–1 MHz and 290–355 °K, respectively. The Z′ and Z″ versus frequency plots are well fitted to an equivalent circuit consisting of series of combination of grains and grain boundary elements. The frequency dependent alternating current conductivity is well described by Jonscher's universal power law: σ(ω,T) = σDC(T) + A(T)ωs(T). The nature of direct current conductivity variation suggests the Arrhenius type of electrical conductivity. Furthermore, the modulus plots can be characterized by full width at half height or in terms of a non‐experiential decay function φ(t) = exp(?t/τ)β. The variation of the value of these elements with temperatures confirmed the result detected by differential scanning calorimetry measurements. Thus, the near values of activation energies obtained from the impedance and modulus spectra confirm that the transport is through an ion hopping mechanism. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

17.
Carbon nitride thin films deposited by dc unbalanced magnetron sputtering have been analyzed by high-resolution X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The XPS data show that N 1s binding states depend on substrate temperature (Ts). By comparison with the Raman spectra, N 1s binding states are assigned in which nitrogen atoms are mainly bound to sp2 and sp3 carbon atoms at Ts = 100°C, whereas at Ts = 500°C nitrogen atoms are mainly bonded to sp2, sp3 and sp1 carbon atoms.  相似文献   

18.
The structure and magnetic properties of Fe-N and Fe-Ti-N films have been studied as a function of annealing temperature Ta with a transmission electron microscope and a vibrating sample magnetometer. The as-prepared Fe-N films consist of the γ-Fe4N and α′′-Fe16N2 phases, and the Fe-Ti-N films are composed of the γ-Fe4N, α′′-Fe16N2, and TiN phases. The structural changes with annealing temperature in the Fe-N films are distinct. The α′′-Fe16N2 decomposes into α+γ phases in the Fe-N film annealed at about 300 °C, and it disappears in the film annealed at 350 °C. Annealing of the Fe-Ti-N films shows no structural changes between room temperature (RT) and 500 °C. The saturation magnetization 4πMS and coercivity Hc of the Fe-N films change drastically with the annealing temperature Ta, whereas those of the Fe-Ti-N films do not change with Ta up to 500 °C. These results indicate that the additon of Ti may improve the thermal stability of Fe-N films. Recieved: 6 Juli 1998 / Accepted: 19 Oktober 1998 / Published online: 10 March 1999  相似文献   

19.
Time differential perturbed angular correlation measurements of the 133–482 keVγ-γ cascade of181Ta in Hf-doped YBa2Cu3O7−x are presented. The181Hf precurser nuclei are incorporated into the sample by thermal neutron irradiation. Two quadrupole interaction frequencies are observed in the as-irradiated sample:v Q1=161±10 MHz with intensityf 1=75%, asymmetry parameterη 1=0.32 and damping parameter Λ1=0.42, andv Q2=1108±40 MHz withf 2=25%,η 2=0.62, and Λ2=0.60. On annealing the sample in air at various temperaturesT a and quenching to room temperature,f 1 remained nearly constant forT a<600°C andv Q1 for all annealing temperatures indicating that these are insensitive to oxygen stoichiometry. This frequency is interpreted to be due to181Hf substitutingY sites. BeyondT a=600°C,f 1 increased and reached a constant value of 90% forT a=800°C. The value ofv Q2 showed a slight variation between 1086 and 1160 MHz, whilef 2 remained nearly constant at 25% forT a<600°C. This component is identified to be due to181Hf substituting Cu 1 sites in the Cu-O chains of YBCO. Above 600°Cv Q2 decreased and reached a value of 808 MHz beyond 750°C.  相似文献   

20.
Novel polyurethane (PU) adhesive was prepared and coated on poly(methyl methacrylate) (PMMA) and poly(methyl methacrylate)/fullerene (PMMA/Full-C60) composite. Dip-coating technique was employed as facile and cost-effective procedure to coat polyurethane on film substrate. The properties of PU/PMMA and PU/PMMA/Full-C60 composite were studied using Fourier transform infrared spectroscopy, Field Emission Scanning Electron Microscopy, tensile, adhesion, thermal and flammability measurement. Testing polyurethane-coated PMMA exhibited crumpled surface while fullerene addition formed unique pattern of dispersed spherical structures. Fullerene nanofiller loading improved the adhesion and mechanical properties of composite films due to polymer–carbon interaction. In PU/PMMA/Full-C60 0.5 composite with 0.5 wt.% nanofiller, tensile strength (71.4 MPa) was increased by 18.6% while tensile modulus was increased by 143.85% compared with PU/PMMA. In PU/PMMA/Full-C60 0.5, T0 of 473 °C and Tmax of 655 °C were observed. Increasing the fullerene content up to 0.5 wt.% decreased the peak heat release rate to 131 kW/m2. Novel polyurethane-coated PMMA/Full-C60 composite have potential applications as adhesive coatings in electronic and automotive appliances.  相似文献   

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