摘要:

Optical absorption over a large dynamic range obtained by two different experimental techniques is reported for an undoped &agr;‐Al2O3single crystal. Absorption data are presented in two energy ranges: 0.94–3.5 eV and 4.5–8.6 eV. Vacuum ultraviolet (vuv) absorption measurements were performed on three boules of Czochralski‐grown single‐crystal Al2O3with differing starting material purities. The initial powder purities were 99.99%, 99.999%, and 99.999999%. In addition to the vuv measurements, calorimetric absorption results obtained in the visible and near‐infrared (ir) are presented. An empirical formula is obtained that provides an estimate of the absorption coefficient from the near‐ir to the vuv for undoped Al2O3. Detailed impurity analyses and sample histories are given for the optical‐quality &agr;‐Al2O3utilized herein.

ISSN:0021-8979    

DOI:10.1063/1.345817

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Detailed and practical expressions are given for the magneto‐optical Kerr effect (MOKE) for various configurations of two media. One is a magneto‐optic (MO) one, and the other is a nonmagnetic (NM) medium. For a system of two thick media with a single interface, with a first‐order approximation in MOKE termQ, the Kerr function is determined by the product of a MOKE termQand an optical term &eegr;. A second type of system includes a thin MO (or NM) layer deposited on a thick NM (or MO) substrate. For a MO/(NM‐substrate) configuration, the Kerr function is related to the Kerr effects from the air/MO and MO/NM interfaces, and to the Faraday effects of the MO layer, as well as to interference effects. The enhancement factor can be expected to be large by proper choice of materials. For a NM/(MO‐substrate) configuration, the total Kerr function is related to the Kerr effect from the NM/MO interface and can be enhanced by interference. The enhancement factor is expected to be less than one if the NM layer is strongly absorbing. Calculations of Kerr effects for examples of the PtMnSb/AuAl2and Fe/Cu configurations are given. These indicate that the peaks shown in the onset region of the interband transitions of Cu can be attributed to a dramatic change of the refractive index in that region. The merits of a MO/(NM‐metallic) structure have been evaluated, and indicate that a better Kerr enhancement effect can be achieved if the refractive index of the MO layer is larger than one and is much larger than that of the metallic material. A drawback to this configuration comes from the fact that a MO material with a large refractive index value usually is not expected to have a large intrinsic Kerr effect.

ISSN:0021-8979    

DOI:10.1063/1.345818

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Ion emission has been obtained from a LiF‐coated tungsten field‐emitter tip. Ion formation is thought to be caused by the high electric field experienced by the LiF. At the time of emission the electric field at the surface of the LiF is calculated to be on the order of 100 MV/cm. Inside the LiF the field is on the order of 10 MV/cm. These fields exceed the value needed to produce bulk dielectric breakdown in LiF. The surface field is of sufficient magnitude to produce ion emission by field evaporation from the crystal surface. Even prior to dielectric breakdown, precursor processes can lead to ion formation. Electric‐field‐stress fragmentation of the LiF layer is thought to occur, followed by ionization of the fragments.

ISSN:0021-8979    

DOI:10.1063/1.345819

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A new Monte Carlo simulation including secondary electron generation has been performed to study energy dissipation in electron beam lithography. The simulation of inelastic scattering is calculated from the model of the generalized oscillator strength density distribution determined by a set of resonance energies and oscillator strengths. Varying the polymethylmethacrylate film thickness, the energy dissipation profiles for various electron beam energies are evaluated. The effects of backscattered electrons from the silicon substrate and secondary electrons are studied with respect to film thicknesses and electron beam energies. The backscattered electrons from the Si substrate broaden the profile, especially near the bottom layer, and the secondary electrons broaden the profiles over the whole film.

ISSN:0021-8979    

DOI:10.1063/1.345820

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

When left in air, as‐grown anodic oxides grown under optimized conditions described in the literature have been found to age. It is shown that this is caused by a hygroscopic component in the outer indium‐rich layer of the oxide film. When oxalic acid is present in the forming electrolyte, this phenomenon is not observed: As‐grown oxides are stable and have a constant composition throughout their thickness. This paper discusses some of the properties of the oxide films, both as‐grown and annealed, and some aspects of the chemistry of their formation. This distinct behavior of oxalic acid can be attributed to the fact that it forms soluble complexes with In(III) in the relevantpH range.

ISSN:0021-8979    

DOI:10.1063/1.345821

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The possible factors which can determine the localized anisotropic photoetching ofn‐GaAs are analyzed. Mass transport to and from the reaction zone is considered. It is shown that diffusion of the oxidizing agent can become limiting when photoetching is performed by illumination of a masked pattern. Photogalvanic effects, leading to a delocalized dissolution mechanism, play a vital role under almost all practical conditions. Heating effects and local photostimulation of the dissolution reaction are of minor importance.

ISSN:0021-8979    

DOI:10.1063/1.345822

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The prevention of disastrous leakage of AsH3is a requirement for metalorganic vapor phase epitaxy systems. Less hazardous organoarsine has been investigated as an alternative to AsH3, and recently, tertiarybutylarsine (tBAs) has been used as an arsenic source. So far the use of tBAs has been restricted to fundamental experiments. The growth of GaAs, AlGaAs, and selectively doped AlGaAs/GaAs heterostructures has been studied using tBAs and AsH3, and the properties of the epilayers grown using both sources have been compared. From the PL spectra at 4.2 K, it was determined that GaAs films using tBAs were of high purity and equivalent to those using AsH3. The properties of AlGaAs grown using tBAs are as good as those using AsH3. A higher V/III ratio results in high‐quality AlGaAs layers. The epitaxial uniformity of growth rate and AlAs mole fraction along a wafer using tBAs was poorer than those using AsH3due to vapor phase reactions in the trimethylgallium‐tBAs mixture. However, the increase of total gas flow rate in the reactor has the effect of improving uniformity. The activation efficiency of Si in AlGaAs is the same for both sources. The properties of heterostructures grown using tBAs are similar to those using AsH3. The sheet carrier concentration and electron mobility at 77 K with a spacer layer thickness of 35 A˚ were 9.5×1011cm−2and 48 000 cm2 V−1 s−1, respectively. This suggests that tBAs can be used as an alternative to AsH3, for growing device‐quality GaAs and AlGaAs.

ISSN:0021-8979    

DOI:10.1063/1.345823

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The slips on a silicon wafer edge which normally occur during rapid thermal process have been eliminated by forming an oxide ring on the wafer‐back surface, thereby reducing the light reflectance from the silicon wafer edge. A simple model which gives the optimum ring oxide thickness and width has been proposed. From the model, it has been found that about 3000 A˚ thickness of ring oxide gives the best thermal compensation effect. The effect of nonuniform irradiation on the wafer has been incorporated in the model by introducing light power uniformity (LU) factor. In case of 3300‐A˚‐thick, 7‐mm‐wide ring oxide and 0.86–0.88 of LU, the temperature variation on a 3‐in. wafer is within ±4 °C at 1137 °C, and the slip is completely eliminated.

ISSN:0021-8979    

DOI:10.1063/1.345824

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We report on long‐term creep experiments on dilute tantalum tritides at room temperature. Significant deviations of the recorded strain rates from isotropic swelling are found above approximately 30 MPa. We attribute this room‐temperature creep to a stress‐induced preferential dislocation loop punching by bubbles in crystallographic directions close the stress axis. Quantitative estimates show that this mechanism can indeed account for the observed creep rates.

ISSN:0021-8979    

DOI:10.1063/1.345825

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Recent experimental work has shown that foams having a negative Poisson’s ratio may be fabricated by inverting the usual energetically preferred tetrahedral structure to form a reentrant structure. It is shown here that a linear elastic analysis of a two‐dimensional reentrant honeycomb provides a theoretical prediction of the negative Poisson’s ratio in the plane for a transversely isotropic material. The value of Poisson’s ratio depends upon the reticulation angle, which is related to the permanent volumetric compression ratio required to form the reentrant structure.

ISSN:0021-8979    

DOI:10.1063/1.345826

出版商:AIP    

年代:1990

数据来源: AIP