摘要:

The bistable cholesteric twist cell (BCTC) described here is a liquid‐crystal device which can be in either of two stable laminar configurations while a particular holding voltage is applied. The major shortcoming of previous implementations of this device was the narrow thickness tolerance required for proper bistable operation. In order to ascertain the effect which material parameters might have on increasing this thickness tolerance an adequate method is needed for characterizing the behavior of the cell. In this paper we describe a wedge cell method for characterizing the behavior of a given BCTC system. The characterization can be conveniently done within a single cell. The data obtained include both the thickness to pitch range for pratical bistable operation and the switching properties. All of these features can be interpreted in terms of static free energy curves calculated for the system. We have also used this wedge cell method to determine the effect of the bend to splay elastic constant ratio on the thickness range of bistable operation in the BCTC. The range is observed to increase with increasing ratio of bend to splay elastic constant. A material has been identified with a bistable thickness range in excess of 10%.

ISSN:0021-8979    

DOI:10.1063/1.335349

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

2‐K photoluminescence was used to determine the amount of nonuniformity present in undoped semi‐insulating GaAs bulk substrate materials grown by the liquid‐encapsulated Czochralski method. The relative photoluminescence intensities of the intracenter (5T2−5E) transition of the Fe2+state, the near‐band‐edge transitions, and the Zn peaks, measured across the wafer diameter, show almost the same ‘‘W’’ pattern. The deep‐center bands at 0.63 and 0.77 eV were also measured. Possible mechanisms of the photoluminescence intensity variation are discussed. In the materials used, a predominant shallow acceptor was observed to be Zn.

ISSN:0021-8979    

DOI:10.1063/1.335350

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A systematic study of channeling of aluminum in the silicon crystal is reported. Depth distributions measured by secondary ion mass spectrometry are reported for 40‐, 75‐, and 150‐keV aluminum channeled in the ⟨100⟩ and ⟨110⟩ directions of silicon. The profile dependence on alignment angle is shown for 150‐keV aluminum in the ⟨110⟩ of silicon. Aluminum has low electronic stopping in silicon and corresponding deep channeled profiles are observed for aligned implants and deep channeling tails are observed on random implants. The maximum channeling range for 150‐keV Al in ⟨100⟩ silicon is about 2.8 &mgr;m and is about 6.4 &mgr;m in ⟨110⟩ silicon. Some ions will reach the maximum channeling range even for 2° misalignment. Many of the deep channeling tails and ‘‘supertails’’ reported in earlier literature can be explained by the normal channeling of aluminum in silicon.

ISSN:0021-8979    

DOI:10.1063/1.335351

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We show that the anchoring energy function, i.e., the anisotropic part of the interfacial free energy, at a nematic liquid crystal‐wall interface can be determined uniquely without a numerical fitting procedure, when the integrated birefringence of a liquid crystal cell with a thickness much larger than the extrapolation length is measured as a function of an electric or magnetic field well above the Freedericksz threshold. The precision of the present method is closely argued, showing that the resulting anchoring energy function is reasonably insensitive to the uncertainties in the material parameters and in the cell thickness. As an example, the anchoring energy function at the interface between 5CB(pentylcyanobiphenyl) and an obliquely evaporated SiO was determined for the first time, by measuring the birefringence and the capacitance of a 56‐&mgr;m‐thick cell up to 150 V rms at 0.23 °C below the clearing temperature. A saturation of the field‐induced distortion was clearly observed at about 100 V rms. The anchoring energy function was found to be well fitted by a function of the form (1)/(2)Ea sin2 &thgr;+ (1)/(4)E1 sin4 &thgr;, where &thgr; is the angle between the boundary director and the substrate, withEa∼4.0×10−5J/m2andE1∼−1.8×10−5J/m2.

ISSN:0021-8979    

DOI:10.1063/1.335352

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The kinetics of the supersaturation of self‐interstitials and the enhancement of impurity diffusivity in short‐time/low‐temperature oxidation of silicon is investigated analytically. It is found that, whereas in long‐time/high‐temperature oxidation the interstitial supersaturation and the diffusivity enhancement decrease with time ast−n(n&bartil;0.2–0.3), in short‐time low‐temperature oxidation they start from zero and increase with time, until some characteristic time determined by the linear‐parabolic oxide growth. This characteristic time increases rapidly with the decrease of temperature. This kinetic behavior has not been expected previously, mainly because there is no available data on stacking fault growth and on diffusion enhancement under the short‐time/low‐temperature condition which has become common in modern IC processings. The more general case of linear‐parabolic oxidation and the effect of bulk recombination have also been analyzed.

ISSN:0021-8979    

DOI:10.1063/1.335353

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The possibility of using x‐ray diffuse scattering experiments to investigate the atomic arrangement within the substituted sublattice in III‐V solid solutions has been demonstrated. TheIcwscattering by static composition waves has been separated from Compton and phonon scattering along the 100 direction in reciprocal space for a thick Ga1−xAlxAs (x=0.32) layer grown by liquid‐phase epitaxy. The dependence ofIcwon the scattering angle has given a detailed experimental proof that the Ga and Al atoms are distributed in a random way within the cation sublattice. An exception to this behavior, which is related to a slight (13%) increase ofIcwat the 100 point, is discussed in the light of the pseudochalcopyrite model for the local bonding in III‐V alloys.

ISSN:0021-8979    

DOI:10.1063/1.335354

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Expressions for the threshold and saturation voltages are derived for twisted chiral nematic layers with weak boundary coupling and arbitrary elastic constant ratios. A general discussion is given of the stability of the various states which may occur in such layers.

ISSN:0021-8979    

DOI:10.1063/1.335355

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The six independent elastic constants of a single crystal of tetragonal MgF2with rutile structure were measured ultrasonically at room temperature from ambient conditions to 10 kbar. The values at 1 bar and 10 kbar are (in 1011dyn/cm2)C11: 14.081 (1 bar), 14.597 (10 kbar);C12: 9.003 (1 bar), 9.569 (10 kbar);C13: 6.417 (1 bar), 6.543 (10 kbar);C22: 20.490 (1 bar), 21.094 (10 kbar);C44: 5.664 (1 bar), 5.768 (10 kbar);C66: 9.560 (1 bar), 9.964 (10 kbar).CS=(C11−C12)/2 softens with pressure, whileC44shows a weak pressure dependence. Similar behavior has been observed in NiF2, ZnF2, TiO2, and in the distorted rutile crystal TeO2. The reported pressure induced transition from tetragonal MgF2to distorted fluorite type observed at 250 kbar using x‐ray scattering is not anticipated by the softening ofCSwhich would lead to an orthorhombic distortion.

ISSN:0021-8979    

DOI:10.1063/1.335356

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The low‐temperature (<210 °C) crystallographic structure, electrical conductivity, and thermal stability of Mg2NiH4powders compacted under isostatic pressures of up to 10 kbar were studied. A comparison is made with the corresponding properties of the noncompressed material. It has been concluded that under stress‐free hydriding conditions performed below 210 °C, a two‐phase hydride mixture is formed. Each of the hydride particles consists of an inner core composed of an hydrogen‐deficient monoclinic phase coated by a layer of a stoichiometric orthorhombic phase. The monoclinic phase has a metalliclike electrical conductivity while the orthorhombic phase is insulating. High compaction pressures cause the transformation of the orthorhombic structure into the monoclinic one, thereby resulting in a pressure‐induced insulator‐to‐conductor transition. Reduced decomposition temperatures are obtained for the compressed hydrides. This reduction is attributed to kinetic factors rather than to a reduced thermodynamic stability.

ISSN:0021-8979    

DOI:10.1063/1.335357

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The thermal conductivity of Tl3AsSe3in the temperature range 1.5–100 K is reported. The measured thermal conductivity can be fitted using defect scatteringonlydue to isotopes and using normal process scattering.

ISSN:0021-8979    

DOI:10.1063/1.335358

出版商:AIP    

年代:1985

数据来源: AIP