Showing papers on "Crystal published in 1984"

A parameterization of the particle size spectrum of ice clouds in terms of the ambient temperature and the ice water content

Abstract: A data set obtained in cirrus clouds has been examined to deduce any dependencies of the particle size spectral form or the crystal habit on the temperature. It was found that both form of the spectra and crystal habit changed systematically with temperature, the largest change occurring between −l40 and −50°C. These findings are consistent with previously found dependencies between linear backscatter measurements and temperature. A preliminary scheme for parameterizing the cirrus particle size spectra for crystal dimensions greater than 20 μm in terms of the temperature and the ice water content is described. The visible extinction in cirrus is estimated.

Kinetics of non-isothermal crystallization process and activation energy for crystal growth in amorphous materials

Abstract: An equation expressing the volume fraction,x, of crystals precipitating in a glass heated at a constant rate, α, was derived. When crystal particles grow m-dimensionally,x is expressed as In [- ln(1 -x)] = -n (nα - 1.052mE/RT + Constant whereE is the activation energy for crystal growth andn is a numerical factor depending on the nucleation process. When the nuclei formed during the heating at the constant rate,α, are dominant,n is equal tom + 1, and when the nuclei formed in the previous heat-treatment before thermal analysis run are dominant,n is equal tom. The validity and usefulness of this equation was ascertained by applying it to a Li2O·2SiO2 glass. A method for determining the values ofn andm from DSC curves was proposed and it was concluded that the modified Ozawa-type plot is very useful and convenient to obtain the activation energy for crystal growth.

Hole diffusion length in n‐TiO2 single crystals and sintered electrodes: Photoelectrochemical determination and comparative analysis

Abstract: The photoelectrochemical behavior of an n‐TiO2 (rutile) single crystal under different treatments (mechanical polishing and chemical and photoelectrochemical etching) is analyzed and the conditions under which Gartner’s model can be applied are determined. The hole diffusion length Lp obtained from the photoelectrochemical data is about 10−6 cm for the etched single crystal and seems to be governed by electron‐hole recombination at centers associated to impurities introduced in the lattice during the manufacturing process. This value of the hole diffusion length determines the minimum value of the donor concentration Nd for an efficient separation of carriers within the semiconductor depletion layer. This explains the existence of a maximum of the quantum efficiency for Nd∼6×1018 cm−3, which has been found to be a value common to n‐TiO2 single crystals of different origin. Lattice deffects introduced near the crystal surface by mechanical polishing behave as recombination centers which reduce Lp to values...

Improved quartz crystal microbalance technique

Abstract: The importance of using the most pertinent mathematical description of the mass load versus frequency relation for quartz crystal thin‐film thickness monitors is reviewed. The different usable crystal load ranges of the so‐called frequency‐ and period‐measurement techniques in comparison with the Z‐Match technique are calculated for most of the commonly used deposition materials. A new thin‐film thickness monitoring procedure is described, which takes the influence of the acoustic film properties on the mass load versus frequency slope into consideration without need for the explicit knowledge of the acoustic impedance ratio z of the deposited film and the quartz crystal. It is shown how the effective z value in the composite resonator built by the quartz crystal and the deposited foreign layer can be derived from a measurement of a quasiharmonic overtone resonance frequency in addition to the commonly practiced exclusive measurement of the fundamental resonance frequency. The presently established relati...

The Crystal Structures of Sodalite-Group Minerals

Abstract: Sodalite, Nas(A16Si6024)CI2, is cubic, P43n, M, = 969-2, F(000) = 476, a = 8.882(1)~, Dx = 2 . 3 0 M g m -3, Z = I , R = 0 . 0 1 7 for 157 unique observed reflections measured on an automated fourcircle X-ray diffractometer using Mo Ka radiation. The 1:1 aluminosilicate framework is completely ordered. A geometrical sodalite model has been developed, which, when calibrated with the parameters from the refined structure, enables: (1) the accurate prediction of the atomic coordinates of all members of the sodalite-group minerals at both room and elevated temperatures; (2) the prediction of the chemical limits of structural stability of all such materials; (3) thermal-expansion data and substitution of interframework ions to be rationalized and predicted in terms of the rotation of the (A1, Si)O4 tetrahedra.

Size quantization of the electron energy spectrum in a microscopic semiconductor crystal

Abstract: The interband absorption spectrum of microscopic CdS crystals ranging in size from ∼ 30 to 800 A and dispersed in a transparent insulating matrix has been studied. There is a significant (∼0.8-eV) shift of the fundamental absorption edge in the short-wavelength direction, and there are oscillations in the interband absorption spectrum caused by quantum size effect.

Liquid crystal element

Abstract: PURPOSE: To improve initial orientability by providing plural structural members having side walls to one substrate into a stripe shape, subjecting the other substrate to an orientation treatment in the direction parallel with or perpendicular to the extension direction of said members and using a specific liquid crystal compsn. CONSTITUTION: The structural members 104 having the stripe-shaped side walls 106, 107 are disposed to one substrate 101 of a pair of the electrode substrates 101, 110. The other substrate 110 is subjected to a uniaxial orientation treatment and the treatment direction thereof is controlled to the direction parallel or orthogonal with the extension direction of the members 104. The liquid crystal compsn. incorporated therein with one kind of a liquid crystal of which the phase transfers from a Ch phase to an SmA phase and Sm* phase in the course of a temp. fall and at lest one kind of a liquid crystal of which the phase transfers from an isotropic phase to the Ch phase and liquid crystal phase or from the isotropic phase to the Ch phase, Sm phase and crystal phase in the course of the temp. fall is used. The liquid crystal element made into the construction in which the operation of the element based on the bistability of the ferroelectric liquid crystal and the mono-domain characteristic of the liquid crystal layer are compatible is obtd. by such constitution and the defect at the spacer edge is eliminated even in the storage state in which the defect is particularly liable to appear. COPYRIGHT: (C)1986,JPO&Japio

AgGaS2 infrared parametric oscillator

Abstract: A report is presented of the first operation of an optical parametric oscillator in a chalcopyrite crystal, AgGaS2. Tuning from 1.4 to 4.0 microns is demonstrated for 1.06-micron Nd:yttrium aluminum garnet pumping. The potential tuning range extends to the 12-micron transparency limit of the crystal.

Si-III (BC-8) crystal phase of Si and C: Structural properties, phase stabilities, and phase transitions

Abstract: With use of the pseudopotential local-density-functional approach, the lattice constant, the $x$ parameter for atomic coordinates, and the phonon frequency of the mode ${\ensuremath{\Gamma}}_{1}^{+}$ are calculated for the Si-III (BC-8) crystal phases of Si and Ci. The results agree well with available experimental data for the BC-8 phases of Si. From the total-energy curves of the diamond and the BC-8 phases of Si, we find that the BC-8 phase of Si is not stable at ambient pressure or at high pressure. The diamond---BC-8 (I-III) transition of Si will not occur quasistatically. Comparing the diamond, the BC-8, and the simple-cubic phases of C, we find that diamond will first transform to the BC-8 phase at 12 Mbar and then to the simple-cubic phase at 27 Mbar under quasistatic conditions.

Alloy phase diagrams

Abstract: These proceedings collect papers presented at a symposium on alloy phase diagrams. Topics include: Crystal phase transformations; order-disorder transformations; crystal lattices; metallic glasses; metastable states; solubility; binary alloy systems; and alloys of iron, tantalum, silicon, aluminum, germanium, palladium, copper, and nickel.

Surface Studies by Optical Second-Harmonic Generation: The Adsorption of O 2 , CO, and Sodium on the Rh(111) Surface

Abstract: Optical second-harmonic generation is used to study the adsorption of atomic and diatomic species on a well characterized Rh(111) crystal surface in ultrahigh vacuum. The results correlate well with those obtained by other surface probes.

Shear-induced partial translational ordering of a colloidal solid

Abstract: Highly charged submicrometer plastic spheres suspended in water at low ionic strength will order spontaneously into bcc crystals or polycrystals. A simple linear shear orients and disorders these crystals by forcing (110) planes to stack normal to the shear gradient and to slide relative to each other with a 111g direction parallel to the solvent flow. In this paper we analyze in detail the disordering and flow processes occurring beyond the intrinsic elastic limit of the bcc crystal. We are led to a model in which the flow of a colloidal crystal is interpreted as a fundamentally different process from that found in atomic crystals. In the colloidal crystal the coupling of particle motion to the background fluid forces a homogeneous flow, where every layer is in motion relative to its neighboring layers. In contrast, the plastic flow in an atomic solid is defect mediated flow. At the lowest applied stress, the local bcc order in the colloidal crystal exhibits shear strains both parallel and perpendicular to the direction of the applied stress. The magnitude of these deformations is estimated using the configurational energy for bcc and distorted bcc crystals, assuming a screened Coulomb pair interaction between colloidal particles. As the applied stress is increased, the intrinsic elastic limit of the crystal is exceeded and the crystal begins to flow with adjacent layers executing an oscillatory path governed by the balance of viscous and screened Coulomb forces. The path takes the structure from the ${\mathrm{bcc}}_{1}$ and ${\mathrm{bcc}}_{2}$ twins observed at zero shear to a distorted two-dimensional hcp structure at moderate shear rates, with a loss of interlayer registration as the shear is increased. This theoretical model is consistent with other experimental observations, as well.

A molecular dynamics simulation of nitrogen adsorbed on graphite

Abstract: The adsorption of N2 molecules on a structured graphite surface has been studied using the molecular dynamics technique. N2 is modelled using two Lennard-Jones centres and partial charges to represent the quadrupole moment. The surface, which is represented by a rigid external field, has longitudinal structure and the adsorbate molecules form a √3 × √3 commensurate solid with herringbone orientational ordering in two sublattices. The model exhibits a rotational transition to plastic crystal at 33 K (experiment 27 K). The simulated transition temperature does not vary markedly with coverage. The adsorbate shows little residual herringbone ordering above the phase transition, but a six-fold ordering due to the crystal field of the adsorbate appears.

Sensor having piezoelectric crystal for microgravimetric immunoassays

Abstract: A sensor and method for performing immunoassays using surface acoustic waves on a piezoelectric crystal is provided. A specific antigen or antibody is bonded to the surface of the piezoelectric crystal and its resonant frequency in a blank solution is determined. The sensor is then exposed to a test solution containing an antigen or antibody corresponding to the substance bonded to the surface of the crystal. As the antigen and antibody react, the resonant frequency of the crystal is altered. This change can be correlated to determine the amount of antigen or antibody in the test solution. A nonreactive reference sensor can also be used to compensate for any nonselective adsorption.

Mechanical strength of silicon crystals as a function of the oxygen concentration

Abstract: Mechanical strengths of silicon crystals involving oxygen at various concentrations up to 1018 atoms/cm3 are investigated with the use of crystals grown by the Czochralski technique in magnetic field. Oxygen atoms dispersed on interstitial sites at any concentration have almost no influence on the dislocation processes that control the mechanical behavior of a dislocation‐free crystal. Oxygen atoms in a dislocated crystal lock dislocations effectively and result in the strengthening of the crystal. Locking of dislocations becomes more effective as the concentration of oxygen in the crystal increases. Softening of crystals due to precipitation of oxygen at elevated temperature occurs rapidly in highly concentrated crystals with oxygen, but is almost absent or takes place slowly in crystals of oxygen concentrations lower than about 5×1017 atoms/cm3.

Crystallization of reaction center from Rhodopseudomonas sphaeroides: preliminary characterization.

Abstract: Reaction centers (RCs), integral membrane proteins that mediate the conversion of light into chemical energy, were crystallized by two different vapor diffusion techniques. In one method, small amphipathic molecules (1,2,3-heptanetriol and triethylammonium phosphate) were added to the RCs that had been solubilized in detergent. In the second method, crystallization occurred near the phase boundaries of a two-phase system created by the addition of polyethylene glycol and NaCl to RCs in octyl beta-D-glucoside. Several different crystal forms were obtained; two were analyzed by x-ray diffraction. One was monoclinic (space group P2) with beta = 105 degrees, and a = 70 A, b = 105 A, and c = 85 A, two RCs per unit cell, and one RC per asymmetric unit; the crystal diffracted to 3.5 A at 17 degrees C. The other crystal form was orthorhombic (space group C222) with a = 185 A, b = 170 A, and c = 105 A, with eight RCs per unit cell and one RC per asymmetric unit. Reversible light-induced EPR signals of the primary donor (bacteriochlorophyll dimer) showed that the RCs in the crystal were fully active. From the angular dependence of the EPR signal the molecular g anisotropy of the bacteriochlorophyll dimer was deduced to be g perpendicular - g parallel = (64 +/- 3) X 10(-5). Linear dichroism measurements were performed on the monoclinic crystal. The two bands at 535 and 544 nm assigned to the Qx transitions of the bacteriopheophytins were resolved and preliminary orientations of some of the pigments were obtained.

Thermal evolution of crystal shapes: The fcc crystal

Abstract: The thermal evolution of the equilibrium shape of an fcc crystal with both first- and second-nearest-neighbor interatomic interactions is studied Exact zero-temperature calculations are extended to nonzero temperatures by use of solid-on-solid models appropriate to 001g and 110g directions in the crystal, yielding a reasonably complete global description of the thermal evolution Universal features of the shape associated with second-order phase transitions are described, as are first-order phase transitions which appear as sharp edges between facets Some new results for the six-vertex model appear as by-products Contact is made with experiment, including a discussion of practical limitations on measurements of universal features of crystal shapes