摘要:

Considering nucleation of dislocation half‐loops from the crystal growth surface as a mechanism of generation of misfit dislocations between an epitaxial film and a substrate, critical thicknesses can be determined by calculating the zero of free energy of the system according to van de Leuretal.’s model [J. Appl. Phys.64, 3043(1988)]. On estimating the free energy, two analytical methods are adopted; one is the whole‐space approximation and another treats surface half‐loops in the half‐space by the image stress construction. In both of the methods, interaction between the two dislocation glide loops either lying in the identical slip plane or lying in the parallel slip planes are incorporated into the analysis. It is shown that half‐loop correction reduces critical thickness, the former interaction reduces and the latter interaction increases it, and the interaction effects become smaller by the half‐space correction. Finally, it is also shown that the effect of anisotropy in the whole‐space approximation tends to increase critical thickness. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359729

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have carried out a systematic investigation of the achievable accuracy in the determination of the independent elastic constantsc11andc12and the related constantc44of thin isotropic films from the phase velocity dispersion of surface acoustic waves (SAWs). As a model system SiO2and Au films deposited on Y‐cut LiNbO3were considered. The phase velocity dispersion was calculated for real elastic constants in dependence on the film thickness. These input data were used to determine the least‐squares fits of the input dispersion and the phase velocity obtained by modifyingc11andc12. The minimum of this error field describes the solution of the inverse wave propagation problem. Error fields of the least‐squares fits were calculated with ±5% variation forc11and ±30% forc12. Different functional behavior and various magnitudes of the dispersion were compared. When simulating a small measuring uncertainty for the phase velocity the solution of the inverse problem becomes unstable which results in an insufficient accuracy of the interesting elastic constants. By superposition of two SAW modes the inaccuracy was significantly reduced. For the model system each independent SAW mode offers the ability to determine one elastic constant or one relation between different elastic parameters. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360738

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The effects of Al as an isoelectronic dopant have been investigated on the deep level defects in GaAs grown by molecular‐beam epitaxy (MBE), using deep level transient spectroscopy. Two different compositions containing 0.1% Al (Al0.001Ga0.999As) and 1% Al (Al0.01Ga0.99As) have been studied. At least nine different deep levels have been detected. Their detailed characteristics consisting of emission rate signatures, capture cross sections, concentrations, and junction depth profiles have been determined. The deep levels observed have been compared with the M levels normally found in MBEn‐GaAs. The emission rates of deep levels have been found to shift to higher values with decrease in Al concentration. This fact has been attributed to lattice strain and random alloy effects. The relative concentrations of deep levels are seen to undergo large changes as the Al concentration is increased from 0.1% to 1%. Al doping upto 0.1% does not seem to reduce the deep level concentration, unlike the case of other isovalent dopants such as In and Sb in MBE GaAs. Further increase in the Al doping to 1% is found to lead to a pronounced increase in the overall deep level concentration. These data along with the other measured characteristics are interpreted in terms of the possible models for the various defects. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359730

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The thermopower &eegr; of Sr1−xLaxTiO3ceramics was investigated up tox=0.5 and in the temperature range between 150 K and 1200 K. In addition, the carrier concentrationnwas determined by Hall measurements and by a chemical Ti3+‐analysis. For low temperatures and highn, &eegr; depends linearly on temperature and onn−2/3, as expected from a degenerate quasi free electron gas. In the case of high temperatures and lown, the absolute value of &eegr; rises with 1.5⋅ln10⋅k/eper decade of temperature and with ln10⋅k/eper decade of carrier concentration, as expected from a classical broad‐band semiconductor obeying the Boltzmann statistics. In the range of degeneration an effective massmeffof 4.2 electron masses can be deduced without the assumption of a transport factorAe. In the classical rangeAe=3 can be evaluated, requiring only a temperature and lanthanum independentmeff. Thus, the thermopower of Sr1−xLaxTiO3ceramics can be described by a constant effective mass and a constant transport factor within a wide range of temperature and lanthanum content. Furthermore, the transition from degeneration to classical behavior can be described as a function of temperature and electron density, e.g., at room temperature it takes place at aboutx≊0.2 (i.e.,n≊3.4⋅1021/cm3). ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359731

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The detailed monolayer terracelike topography of nominal on‐axis and misoriented vicinal (100) InP surfaces was systematically investigated by ‘‘exsitu’’ atomic force microscopy. Vicinal (100) InP reconstructs into steps around 550 °C in either argon or phosphine/hydrogen. Widths of observed monoatomic terraces are measured to be in close agreement with misorientation angles. Homoepitaxial growth by metalorganic chemical vapor deposition preserves the terracelike structure. Growth acts through a monoatomic step flow mode following the classical Burton–Cabrera–Frank theory. Surface diffusion length is estimated up to 350 nm in our standard growth conditions at 630 °C and 2.5 &mgr;m/h. Spiral growth is also observed and takes its origin from a screw dislocation emerging on the surface of the substrate. The critical misorientation angle below which the spiral growth mechanism occurs and competes with the vicinal steps is in the range of 0.05°–0.1°. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359732

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We study the performances of a type of single‐phase shift register based on flux‐quanta dynamics. The system employs as a clock signal a spatially localized sinusoidal current injection in a discrete Josephson transmission line. This drive generates fluxon–antifluxon pairs which, traveling along the transmission line, move the single flux quanta stored in attractive potential wells. These wells are obtained by inserting inductive discontinuities in the transmission line. The simulations show that the device could operate in real Josephson systems with clock frequencies in the range 10–100 GHz. Good margins are found for the most critical parameters of operation. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359733

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We communicate a detailed study of the epitaxial growth of CeO2on MgO. The key feature of the growth is the dependence of the in‐plane orientation of the CeO2epitaxial layer on the MgO surface morphology. Atomic force microscopic (AFM) measurements, x‐ray analyses, as well as high‐resolution transmission electron microscopy (HRTEM) investigations reveal that on rough substrates a cube‐on‐cube growth of CeO2on MgO occurs while on smooth substrates the CeO2unit cell is rotated around the surface normal by 45° with respect to the MgO unit cell when the deposition rate is low (∼0.3 A˚/s) during the first stages of growth. This growth mechanism can be used for a defined fabrication of 45° grain boundaries in the CeO2layer by controlling the surface roughness of the MgO substrate. This report demonstrates that these 45° grain boundaries may be used to fabricate YBa2Cu3O7−xJosephson junctions. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359734

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The direct‐current (dc) joule heating technique was exploited to fabricate giant magnetoresistance (GMR) Co10Cu90granular alloys. The Co cluster precipitation process was investigated by calorimetric and x‐ray diffraction measurements. AtT=10 K, the largest MR change of 25.0% has been observed for the melt‐spun Co10Cu90ribbon annealed atI=5 A. The magnetoresistance scales approximately as the inverse Co particle size. At room temperature, it was found that the dc joule‐heated samples show relatively high GMR in comparison with furnace‐annealed samples. Based on the phenomenological GMR model, we assumed that it is a consequence of smaller Co particles formed in dc joule‐heated samples. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359735

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Ti and TiN layers implanted with57Fe ions were studied by conversion electron Mo¨ssbauer spectroscopy at 295 and 80 K. In as‐implanted Ti samples the local states of iron implants were assigned to &agr;‐Ti(Fe) and &bgr;‐Ti(Fe). In TiN, about 68% of iron implants replace Ti atoms forming Fe2N and nonstoichiometric Fe–N complexes. The remaining Fe ions replace N atoms exhibiting &agr;‐Ti(Fe) and &bgr;‐Ti(Fe) states. The protective properties of the TiN cover layer are discussed in terms of changes of the these states after subsequent annealing in air. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359736

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The degradation (fatigue) of dielectric properties of ferroelectric Pb(ZrxTi1−x)O3(PZT) and SrBi2Ta2O9thin films during cycling was investigated. PZT and SrBi2Ta2O9thin films were fabricated by metalorganic decomposition and pulsed laser deposition, respectively. Samples with electrodes of platinum (Pt) and ruthenium oxide (RuO2) were studied. The interfacial capacitance (if any) at the Pt/PZT, RuO2/PZT, and Pt/SrBi2Ta2O9interfaces was determined from the thickness dependence of low‐field dielectric permittivity (&egr;r) measurements. It was observed that a low &egr;rlayer existed at the Pt/PZT interface but not at the RuO2/PZT and Pt/SrBi2Ta2O9interfaces. In the case of Pt/PZT, the capacitance of this interfacial layer decreases with increasing fatigue while the &egr;rof the bulk PZT film remains constant. This indicates that fatigue increases the interfacial layer thickness and/or decreases interfacial layer permittivity, but does not change the bulk properties. For the capacitors with RuO2/PZT/RuO2and Pt/SrBi2Ta2O9/Pt structures, however, the &egr;rdoes not change with ferroelectric film thickness or fatigue cycling. This implies no interfacial layer exists at the interfaces and which can be correlated to the observed nonfatigue effect. Additionally, the equivalent energy‐band diagrams of these different capacitor structures were proposed to complement the proposed fatigue mechanism. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359737

出版商:AIP    

年代:1995

数据来源: AIP