Volume 87, Issue 2, 15 January 2000
- lasers, optics, and optoelectronics (pacs 42)
- structural, mechanical thermodynamic, and optical properties of condensed matter (pacs 61-68, 78)
- electronic structure and transport (pacs 71-73)
- magnetism and superconductivity (pacs 74-76)
- dielectrics and ferroelectricity (pacs 77)
- device physics (pacs 85)
- applied biophysics (pacs 87)
- interdisciplinary and general physics (pacs 1-41, 43-47, 79, 81-84, 89-99)
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
Photorefractive holographic contrast enhancement via increased birefringence in polymer composites containing electro-optic chromophores with different alkyl substituents87(2000); http://dx.doi.org/10.1063/1.371917View Description Hide Description
The birefringence of a photorefractive polymer composite in response to an applied electric field is used to predict the holographic index contrast attainable. Predictions have been obtained for three different polymer composites based on the charge transfer complex matrix poly(N-vinyl carbazole)/2,4,7-trinitro-9-fluorenone, doped with electro-optic azo chromophores differing only in their alkyl substitutions. A comparison with experimental data indicates that unexpected large variations in the holographic contrast obtainable from different chromophores are, in most cases, accounted for by a corresponding variation in electric field-induced birefringence. This variation may be due to a combination of the chromophore number density and the composite viscosity. Where the birefringence does not correlate with holographic index contrast, a prediction based on a trap density limited space-charge field fits the data well.
87(2000); http://dx.doi.org/10.1063/1.371918View Description Hide Description
A new Mueller matrix approach is developed for the design of optical modes for all nematic liquid crystal displays (LCD). In particular, for linearly polarized light going into the LC cell, conditions for linear polarization and circular polarization outputs are obtained. By considering the switching between different polarization modes, new transmittive and reflective bistable twisted nematic (BTN) LCD operating conditions with optimized contrast and brightness are discovered. A passive matrix driven single polarizer reflective BTN display was fabricated with reasonably good measured optical performance and fast selection time.
87(2000); http://dx.doi.org/10.1063/1.371919View Description Hide Description
We demonstrate that a photochemical reaction can create various distributions of refractive index in polymer. When the polymer containing a photochemically active material is irradiated by UV light, the photochemical reaction which breaks the π-conjugated system in the material and decreases its linear polarizability can reduce refractive index of the polymer. We prepared a PMMA film added DMAPN ((4-N,N-dimethylaminophenyl)--phenylnitrone) with a rate of 23 wt % by use of spin coating. Electronic structural change of DMAPN and refractive indices of the film before and after UVirradiation were evaluated by UVabsorption spectra and m-line method, respectively. The UVirradiation decreased at 380 nm in the absorption spectra, which is attributed to nitrone, and the refractive indices exponentially with irradiation time. The change of refractive indices reached 0.028. The refractive index profile upon depth of the film was investigated by measuring refractive indices of stacked DMAPN/PMMA films. When UV with a power of irradiated upon three stacked DMAPN/PMMA films for 35 s, variation of the refractive index change showed a quadratic profile. The refractive index profile with various irradiation time can be accounted with the combination of the chemical kinetics with the steady state approximation and Lambert–Beer's law. Thus, the photochemical reaction can be used to control the refractive index distribution in polymer.
87(2000); http://dx.doi.org/10.1063/1.371920View Description Hide Description
The self-enhanced diffraction with oscillatory behavior for unfixed holograms is observed and investigated in new photorefractive crystals. The recorded diffraction efficiency can be increased 10 times during the readout process. The maximum peak diffraction efficiency obtained is close to unity. A closed solution of dynamic two-wave mixing equations and a coupling coefficient expression obtained from the standard band transport model are used to fit the observed results. The observed self-enhancement is caused by the interference between a new grating, formed by the reading beam and the diffracted signal, and the existing grating. The fitted results show that the internal space-charge field originating from the photovoltaiceffect and the pyroelectric effect can reduce the phase shift.
Approximate description of the three dimensional director and electric field in a liquid crystal display at a high voltage87(2000); http://dx.doi.org/10.1063/1.371921View Description Hide Description
An approximate analytical approach for describing properties of a liquid crystal display associated with a homeotropic to multidomainlike transition for a liquid crystal with a positive dielectricanisotropy was developed. The electrode and surface coating of the display are prepared in such a way that in the absence of an electric field (dark state) the liquid crystal alignment is homeotropic. The bright state corresponds to a situation when a high voltage is applied to the interdigitated electrodes located on both substrates, which causes a director deformation of a multidomain type. Approximate solutions for the three dimensional electric field and director configuration in the case of strong homeotropic anchoring were obtained to describe the bright state. It was found that two different defect structures are possible for the director configuration: one corresponds to a wall defect and the other to two disclination lines. A first order phase transition between the two structures is predicted at a particular value of the voltage. An estimate of this critical voltage is obtained.
- STRUCTURAL, MECHANICAL THERMODYNAMIC, AND OPTICAL PROPERTIES OF CONDENSED MATTER (PACS 61-68, 78)
87(2000); http://dx.doi.org/10.1063/1.371922View Description Hide Description
The reverse annealing phenomena and the nature of the As clusters were studied on silicon on insulator samples uniformly doped with As at concentrations up to Carrier concentration and electron mobility were determined by Hall and resistivity measurements after annealing at temperatures in the range 550–800 °C. The amplitude of transient reactivation, which can involve up to 20% of the clustered As, depends on dopant concentration and on the annealing temperatures and times. The results of a detailed study of the influence of these parameters are reported. The occurrence of reverse annealing confirms the existence of different types of As clusters, whose distribution and features depend on the experimental conditions. The effect of clustered As on the electron mobility was measured and a quantitative relationship for this phenomenon is reported. The amplitude of this effect is in agreement with the view that at room temperature As clusters are electrically neutral.
Comparison of the annealing characteristics of resistivity and vacancy defects for implant isolated n-type GaAs87(2000); http://dx.doi.org/10.1063/1.371923View Description Hide Description
Gallium arsenide layers, Si-doped at concentrations of and grown on SI substrates were implanted using multiple-energy regimes, with and respectively, to produce resistive structures. Sample resistivity was measured following annealing in the temperature range 400–800 °C. Maximum resistivity values were achieved after annealing at 600 °C for the and and 500 °C for the implanted sample. Equivalently implanted and annealed semi-insulating GaAs samples were analyzed using positron annihilation spectroscopy in the gamma-ray Doppler-broadening mode, a technique which is predominantly sensitive to negatively charged, or neutral, vacancy-type defects. The annealing behavior of the resistivity is in good agreement with previous reports. Vacancy defects to which the positron is sensitive are found to be removed from all semi-insulating samples at a temperature which is 100 °C below that at which maximum resistivity is achieved. Therefore, such vacancy types can be eliminated as the defect responsible for optimum electrical isolation of GaAs following implantation, and the source of vacancies necessary to annihilate such defects.
Effect of annealing and replacement of vanadium by Cr(III) and Mn(IV) ions in glass on its magnetic susceptibility, electrical conductivity, and dielectric constant87(2000); http://dx.doi.org/10.1063/1.371924View Description Hide Description
The effect of heat treatment and substitution of vanadium by other transition metal ions, such as or in glass on the electrical conductivity,dielectric constant,dielectric loss, and magnetic susceptibility has been studied over a temperature range of 80–400 K and frequencies of The ac conductivity, was found to be increased by annealing and decreased by the replacement of vanadium with or ions. The value increased with the measuring frequency ω according to where s has a value in the range of 0.33–0.48. Dielectric loss ε showed maxima at temperatures depending on the sample composition and the measuring frequency. The magnetic susceptibility χ was found to increase by annealing and by introducing or into glass materials. The results obtained were explained on the basis of a mutual interaction, which is exclusively occurring between double redox pairs during the sample preparation or during the annealing process, to produce a shift in redox ratios. The experimental results were correlated together and discussed.
Residual lattice strain in thin silicon-on-insulator bonded wafers: Thermal behavior and formation mechanisms87(2000); http://dx.doi.org/10.1063/1.371925View Description Hide Description
The residual lattice strain in annealed bonded silicon-on-insulator (SOI) wafers was investigated as a function of the temperature and duration of the heat treatment. Measurements were made in a temperature range from 900 to 1050 °C and annealing times were from 6 to 30 h. In as-received SOI wafers, a tensile strain parallel to the surface of the order of was observed. For specimens annealed at greater than 950 °C, an abrupt change from tensile to compressive strain was observed after 12–15 h annealing, and then the strain approached a saturation value with increasing annealing time. However, at 900 °C no such change to compressive strain was observed even after long annealing times. In view of this, the onset of this strain behavior is consistent with viscous flow of the Although it might be expected that the strain in the SOI layer would be greater for thinner layers, the observed strain was found to decrease with decreasing SOI layer thickness. There was no significant variation in the radius of curvature of samples with different SOI layer thicknesses. The radius of curvature is determined mainly by the Si substrate and the buried oxide, and the thermal behavior of these two layers depends upon the heat treatment conditions, particularly the time and the temperature. Taking into account the strain formation mechanism, these results suggest the possibility of plastic deformation of the at the and the substrate interfaces during heat treatment.
87(2000); http://dx.doi.org/10.1063/1.371926View Description Hide Description
The thermal expansion coefficient of precipitates embedded in an Al–Cu thin film matrix is determined by in situx-ray diffraction measurements on free films. The phases present and the thermal expansion or contraction are simultaneously observed during a temperature ramp. The precipitate has a tetragonal structure. The thermal expansion coefficient of the phase in the a direction is significantly smaller than that of the surrounding Al matrix while the thermal expansion in the c direction is comparable to that of the Al matrix. Upon cooling from 500 °C, the mismatch of the thermal expansion between the precipitate and the Al matrix results in compressive and tensile stresses in the aluminum matrix near the precipitates and in compressive stresses in the precipitates. Those stresses are estimated to be on the order of 100 MPa.
Analysis of the coupling between shear horizontal plate waves and liquids: Application to the measurement of the shear rigidity modulus of glycerol solutions87(2000); http://dx.doi.org/10.1063/1.371927View Description Hide Description
This article presents an acoustic wave viscometer based on the shear horizontal acoustic plate mode excited by interdigital transducers on a ST-cut quartz substrate. A theoretical model, which is an extension of the plate effective permittivity function taking into account the presence of liquids, is developed in order to predict the phase and attenuation variations versus the viscosity of liquid. These results are discussed and compared to those of models from the literature such as variational or perturbation methods. The measured results for aqueous solutions of glycerol show linear dependence between the phase and attenuation variations and the square root of liquid viscosity, and are consistent with the theoretical results. The device can be used for viscosity measurements up to 1000 mPa s. For higher viscosities, the viscoelastic behavior of the solution appears and the shear rigidity modulus must be taken into account. The value of has been obtained for glycerol by fitting the theoretical curves to the experimental points.
87(2000); http://dx.doi.org/10.1063/1.371928View Description Hide Description
We present a detailed numerical study of the electromigration-induced shape evolution of quasi-two-dimensional (cylindrical) voids in metallic thin films. The problem is treated within a continuum formulation which takes into account mass transport along surfaces, current crowding, and crystal anisotropy in the surface mobility. Finite strips with periodic boundary conditions in the current direction are treated as well as voids in infinite or semi-infinite films. For the strip geometry, it is shown that the linear instability of the strip edge can induce the release of voids into the interior of the film, while edge voids develop into fatal slits only in the presence of moderate (not too strong) crystalline anisotropy. Distorted voids in an infinite film typically disintegrate, but the breakup scenario is qualitatively different in isotropic and anisotropic media. A rigid boundary attracts voids and may also induce void breakup.
87(2000); http://dx.doi.org/10.1063/1.371929View Description Hide Description
For investigating arsenic self-diffusion, phosphorus (P) and antimony(Sb) were used. New P and Sb in-diffusion experiments show the same behavior as P and Sbinterdiffusion experiments. This is in contradiction to results from the literature. By means of transmission electron microscopy we observed a phase transformation to polycrystalline at the surface under experimental conditions similar to those described in the literature. This leads to a penetration depth much higher than for the P in-diffusion without this phase transformation. The new diffusion coefficients of the P and Sb in-diffusion above 900 °C are in the same range as the interdiffusion coefficients and self-diffusion coefficients from As-tracer diffusion. From this result we conclude that P and Sb have tracer properties for arsenic self-diffusion in GaAs. Measurements of the diffusion coefficients at different As-vapor pressures revealed that As self-diffusion is dominated by As self-interstitials. Furthermore, we performed annealing experiments on differently doped samples. There is no indication of a Fermi-level effect. Hence, As self-diffusion is governed mainly by neutral defects. Between 900 and 1100 °C, we obtain an Arrhenius expression which describes As self-diffusion. The P in-diffusion values below 900 °C show a weaker temperature dependence, which indicates a changeover to a different diffusion mechanism.
87(2000); http://dx.doi.org/10.1063/1.371930View Description Hide Description
A series of reconstructed high-index Si surfaces, with angle β from the  to [11̄0] direction varying between 10° and 35° (in increments of 5°) were systematically studied by ultrahigh vacuum scanning tunneling microscopy. The reconstruction of the (12, 2, 7) surface with as a typical example of the series was described in detail. Fourier transforms revealed a structure of the terrace, the splitting lattice on the step wall, and diffuse streaks from the kinks. The results were compared with other high-index surfaces of the β series. The reconstructed terrace structures were separated into two groups by the boundary between and 25°. With regard to the reconstructed step wall structures, a remarkable characteristic pattern of these high-index surfaces was clarified, namely that they are composed of several splitting lattices. The degree of splitting proved to be closely proportional to the effective dangling bond density. The diffuse streaks from the kinks were also observed as a common phenomenon of this series.
87(2000); http://dx.doi.org/10.1063/1.371931View Description Hide Description
We report on accurate structural investigations of sputtered Nb/Pd multilayers by means of high-resolution secondary ion mass spectrometry and x-rayreflectivity. The combined use of secondary ion mass spectrometry and x-ray specular reflectivity techniques allows us to study the chemical configuration of the interfaces and to relate it to the observed superconductingproperties.Secondary ion mass spectrometryanalyses reveal a distinct Nb and Pd modulation and very sharp profiles with abrupt interfaces indicating a negligible interdiffusion of Nb and Pd at the interfaces. Moreover, analyzing the features in the Nb and Pd profiles and correlating them to the oxygen distribution in the multilayers and to the low-angle x-ray patterns, thin layers (3–4 nm thick) of niobium oxide were noticed at the Nb/Pd interfaces, while no oxide layers at the Pd/Nb interfaces could be detected. The role of this oxide layer in the determination of the crossover between three- and two-dimensional superconducting behavior in parallel external magnetic field, is discussed.
87(2000); http://dx.doi.org/10.1063/1.371932View Description Hide Description
Heteroepitaxialgrowth of InSb was performed on and surface phases over a wide temperature range, by optimizing the growth rate and substrate temperature. When the heteroepitaxy was performed on the surface, the reconstruction modified the growth process depending on the growth temperature. At low temperatures, the reconstruction contributes mildly to the growth, and as the growth temperature increases, it starts degrading the quality of the films. For temperatures above the reconstruction virtually destroys the growth. In the present article, we illustrate this behavior using the growth of InSb on both and surfaces at 210, 250, and Based on reflection high-energy electron diffraction observations, we discuss the initial stages of growth. A model for the interface formation is proposed based on our earlier results suggesting the temperature-dependent modification of In-induced surface phases on Si(001) and Si(111) surfaces during Sb deposition.
87(2000); http://dx.doi.org/10.1063/1.371933View Description Hide Description
The influence of initial growth conditions and lattice matching on the deep level spectrum of grown on GaAs by molecular-beam epitaxy is investigated by means of deep level optical spectroscopy. A detailed study of both the steady-state and transient photocapacitance allows us to measure optical threshold energies, concentrations, and emission rates of electronically active defects in the ZnSe layer. Several deep levels are found in the ZnSe layer at 1.46, 1.90, and 2.25 eV with concentrations in the range. When a 2-nm-thick composition controlled interface layer is grown at different beam pressure ratios prior to the ZnSe growth, a distinct decrease in the 1.46 eV level concentration with increasing Se content is found. Deposition of a lattice-matched buffer layer prior to the ZnSe growth reduces the concentration of both the 1.15 and 1.46 eV levels by over an order of magnitude, indicating the role of lattice matching in the ZnSe overlayer. We also perform depth profiling of the defect distributions within the ZnSe overlayer to see the effect of the ZnSe thickness on the concentration of these levels as well as their possible association to the ZnSe/GaAs interface. We find that only the 2.25 eV level concentration shows a dependence on depth, increasing as the II–VI/III–V interface is approached.
87(2000); http://dx.doi.org/10.1063/1.371934View Description Hide Description
The thin film growth at the level of a single molecular layer can be achieved via laser molecular beam epitaxy approach. Such a growth can be monitored not only via the reflection high-energy electron diffraction technique, but also with the use of relative reflectivity change between - and -polarized light. The epitaxygrowth of thin film is modeled as a microscopic two-dimensional (2D) gratings on the surface of the substrate with a period over two orders of magnitude less than the wavelength of probe light. The solution of Maxwell’sequations for such a 2D gratings leads to an effective multilayer medium model, from which the reflectance-difference (RD) signal in the process of epitaxygrowth can be calculated in the framework of general optics. The simulation results demonstrate that the growth of thin film at the atomic level can be detected by such an optical RD technique. The theoretical calculations of RD signal are in agreement with the experimental measurements both in the order of magnitude and variation character of RD signal curve.
Effect of growth interruption time and growth temperature on the natural formation of InGaAs/AlGaAs quantum disk structures on GaAs (311)B substrates87(2000); http://dx.doi.org/10.1063/1.371935View Description Hide Description
We studied the effect of growth interruption time and growth temperature on the natural formation of InGaAs/AlGaAs quantum disk structures grown on high-index GaAs (311)B substrates by metalorganic vapor phase epitaxy at about 800 °C. The InGaAs/AlGaAs quantum disks were uniformly grown only with growth interruption time of 0 s. With increasing growth interruption time, the self-organizedgrowth mode disappeared with the growth interruption time of 20 s. During growth interruption, strain for the natural formation of quantum disks was released by intermixing between In and Al. With decreasing growth temperature, the quantum disk did not show a hexagonal shape with clear facets. The quantum disks were formed at temperature range between 700 and 830 °C. The self-organization appeared through strain-driven mass transport. The strain-driven mass transport seems to have two characteristic lengths such as the amplitude and the periodicity determined by In composition and the InGaAs layer thickness from electron-beam induced mass transport phenomena.
Electron microscopy study of interfacial reaction between eutectic SnPb and Cu/Ni(V)/Al thin film metallization87(2000); http://dx.doi.org/10.1063/1.371967View Description Hide Description
The wettingreaction between molten eutectic SnPb solder and a sputteredtrilayer Cu/Ni(V)/Al thin filmmetallization was studied using cross-sectional transmission electron microscopy and scanning electron microscopy.Reaction temperatures were from 200 to 240 °C and reaction times ranged from 1 to 40 min. The initial reaction products were and The latter transforms to the former after an annealing greater than 1 min at 220 °C. The grains adhere well to the Ni(V) surface and no spalling of them was observed, even after 40 min at 220 °C. This surprising result indicates that the Cu/Ni(V)/Al or is a stable thin filmmetallization for low temperature eutectic SnPb solder direct chip attachment to organic substrates. Additionally, Kirkendall voids accompanied formation, yet the voids disappear when the transforms to