Direction Of Crystal Axis Research Articles

Asymmetry of photostimulated exoemission in ferroelectrics

Abstract It is shown that photostimulated exoemission in ferroelectrics is substantially asymmetric. Asymmetry is exhibited in the dependence of emission current on the direction of the crystal polar axis. Consideration is given to the nature of the phenomenon of emission asymmetry which is determined by two factors: a) bending of zones having opposite signs arising near the polar cuts as a result of the screening of the spontaneous induction field; b) existence of asymmetric periodic potential in an acentric polar crystal. The asymmetry parameters have been measured by registering the orientational and spectral dependences of the photoemission quantum yield. The possibility is shown of studying the asymmetry of elementary electronic processes in ferroelectric LiNbO3:Fe excited by light which does not produce an extrinsic photoeffect, but induces on the crystal surface a photovoltaic field with an intensity of 106 V.cm−1. The emission current proceeding from the cut perpendicular to the positive direction...

The theory of the electron loss by a multiply-charged ion moving at a small angle to crystal planes

Abstract The theory of ionization of atomic particles channeled by an interplanar crystal potential is developed. Taking account of nuclei thermal vibrations the effect of the diminution of electron loss probability of an ion by elastic interaction with the lattice atoms during channeling as well as in a crystal with random orientation is investigated. The anomalous dependence is predicted of the ionization probability on the angle between the direction of ion momentum and crystal axes (planes). It is shown that, unlike the ionization of fast atomic particles in an amorphous substance, this process in the crystal can proceed owing to inelastic interaction with the electron subsystem of the crystal.

Spin density and manganese electronic structure in phthalocyaninatomanganese(II)

The collection of polarised neutron diffraction data for ferromagnetic (Tc= 8.6 K)β-phthalocyaninatomanganese(II), [Mn(pc)](MnII, S=), is described. Flipping ratios for 552 unique Bragg reflections were observed at 4.2 K and at a magnetic field strength of 1.49 T applied along the b crystal axis direction. These were used, together with the 5.8 K neutron diffraction nuclear structural data, to refine by a least-squares procedure a model of the spin-density distribution in the [Mn(pc)] crystal. The magnetic moments on the two [Mn(pc)] molecules in the monoclinic cell lie approximately perpendicular to the planes of the molecules. The molecules pack in a ‘herringbone’ fashion, with each molecular plane inclined at ca. 45° to the monoclinic b axis. The orientation of the magnetic moments has been described in terms of two refineable angles ρ and ψ. The angle that the magnetic moment makes with the b axis, ρ, is 37.3(7)° and ψ, the angle the projection of the moment onto the ac plane makes with the a axis, is –40.3(11)° measured in a clockwise sense towards the c axis. The model of the spin-density distribution also employed the 3d and diffuse 4s-type orbitals of manganese, and orbitals of the inner-ring nitrogen and carbon atoms of the macrocyclic ligand. The manganese spin populations 3dxy0.74(6), 3dxz, yz1.17(6), 3dz20.83(6), 3dx2–y2–0.15(6), ‘4s’–0.44(6) were found, together with a total population of –0.31 (3) spin on the macrocycle N and C atoms. The manganese orbital electronic populations deduced are thus 3dxy1.26, 3dxy1.0, 3dyz1.0, 3dz20.83,3dx2–y20.15, ‘4s’1.56. These orbital populations are shwon to be in reasonable agreement with the predictions of an angular overlap ligand-field model treatment, and with those populations determined from an X-ray diffraction analysis of [Mn(pc)] at 116 K. The observed negative ligand spin densities, which must arise through spin polarisation effects, are in concordance with the results of a polarised neutron diffraction analysis of [Co(pc)].

The influence of transverse magnetoresistance on Hall-effect measurements on n-type germanium and other semiconductors

The conditions under which magnetic field reversal and voltage averaging can be used to eliminate the contributions of transverse magnetoresistance to Hall voltage measurements have been generalized. The conditions are shown to be satisfied for three specific orientations of the magnetic field to the crystallographic axes of n-type germanium. In general, the conditions are demonstrated to be met in any crystal material with a cubic structure if the magnetic field is applied in a direction parallel to a crystallographic axis of threefold or fourfold rotational symmetry. At sufficiently high fields it is shown that magnetoresistance contributions can be made negligibly small regardless of the B-field orientation to the sample’s crystal structure. Experimental data on n-type germanium at 77 °K verifies the validity of the theory by demonstrating that magnetoresistance contributions are cancelled by averaging when the magnetic field is parallel to a highest-symmetry 〈100〉 crystal axis direction as well as parallel to a lower-symmetry 〈110〉 direction.

Computer Indexing of Electron Diffraction Patterns Including the Effects of Lattice Symmetry

In the 50 year period since the discovery of electron diffraction from crystals there has been much theoretical effort devoted to the calculation of diffracted intensities as a function of crystal thickness, orientation, and structure. However, in many applications of electron diffraction what is required is a simple identification of an unknown structure when some of the shape and orientation parameters required for intensity calculations are not known. In these circumstances an automated method is needed to solve diffraction patterns obtained near crystal zone axis directions that includes the effects of systematic absences of reflections due to lattice symmetry effects and additional reflections due to double diffraction processes.Two programs have been developed to enable relatively inexperienced microscopists to identify unknown crystals from diffraction patterns. Before indexing any given electron diffraction pattern, a set of possible crystal structures must be selected for comparison against the unknown.

Low-temperature viscoelasticity of poly-oxymethylene by radiation-induced solid-state polymerization of trioxane single crystal

The polymerizate is a porous, white cylinder of polyoxymethylene, whose direction of crystal axis is unique. The dynamic viscoelasticity was measured by the vibrating-reed-method at −180° ∼ +10 °C. The existence of the γ-dispersion is doubtful in this sample. Therefore we can conclude that (i) the amorphous part is negligibly small both on the surface and inside of this sample, and (ii) the vibration of molecular chains is prohibited even on the surface of a single crystal.

The Energy Loss by Charged Particles in Silicon as a Function of Track Orientation

It is important to know the orientation of the crystal axis of silicon semiconductor detectors when they are used for the detection of energetic charged particles in stacked arrays and the particles are expected to traverse all of the detectors. It has been observed that particles that pass through the crystal along the directions of crystal planes or axes lose less energy than those in other directions. This anomalous energy loss spoils the response characteristics of the detector. Various experiments have demonstrated that the penetrating particles tend to move along crystal planes or axes by a process of correlated multiple-coulomb scattering. The experimental evidence for these anomalous characteristics will be reviewed and the degrading effects on the discrimination ability of mass-discrimination detector-systems will be shown. Mass distribution curves were taken for protons, deuterons, tritons, as well as He3 and alpha particles in the 20 to 40 MeV region with a thin silicon?E detector oriented with the (111), (110) and other axis parallel to the penetrating particle direction. The mass separation is appreciably improved when the crystal is oriented so that the direction of the penetrating particles is well away from any of the major crystal planes or axes.

半導体用スライシング機の試作について

In this paper is reported a newly designed slicing machine for semiconductor wafers. The distinctive designes of the machine are as follows:(a) A safety device for power stoppage is attached on the machine to prevent the diamond wheel from damage.(b) An optical measuring device for the direction of crystal axis of the workpiece mounted on the machine to avoid the deviation resulting from resetting of the workpiece.(c) A forced lubrication system is employed to the cutting spindle to ensure long running.(d) A hydraulic device is applied to eliminate the backlash of the feeding screw.The performance of the machine has been pursued experimentally in comparison with the similar machines now in popular service and has been concluded as follows.(a) The deviation of the direction of the wafer's crystal axis is within one (1) degree both in X axis and Y axis.(b) The uniformity of thickness among a lot of wafers is within 0.010 mm through 0.015 mm. while it is 0.015 mm through 0.020 mm for the machine now in popular use.(c) The minimum thickness of the wafers which can be sliced by the machine is about 0.200 mm. while it is 0.25 mm for the machines now in popular use.(d) The surface roughness of the wafers is 1.2, 1.8, and 1.4 micron Hmax respectively for the thickness of the wafer of 0.2, 0.25, and 0.3 mm, while it is 2, 2.4, and 2.8 micron Hmax for the machine now in popular use.(e) The parallelism of the wafer expressed by the thickness unifomity of the individual wafer is within 0.010 mm for the machines in popular service.