Fast-ion channeling in fullerene crystals

The motion of H⁺ and He⁺ ions with energies of 230 and 2000 keV in C₆₀ and K₃C₆₀ crystals was calculated by the Monte Carlo method. Ion channeling was shown to occur in the 〈100〉 and 〈111〉 directions. The main parameters characterizing channeling were determined. Medium-energy ions were found to be preferable in the detection of channeling in C₆₀ films.     

Magnetoresistance measurements concerning the conduction band structure of cubic SrTiO3

The longitudinal and transverse magnetoresistance of cubic n-SrTiO₃ was measured with current in 〈001〉 and 〈111〉 directions at 120 K. The results support a model with a warped constant energy surface and are not consistent with a 〈100〉 many model of the lowest conduction band.     

Dependence of high electric-field-induced strain on the composition and orientation of Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals

Electric-field-induced strain behavior of (1−x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMNT) crystals with different orientations and compositions was investigated for use as electromechanical actuators. Crystallographically, high strains with low hysteresis were achieved for 〈001〉 oriented rhombohedral crystals (29%≤x≤31%) near a morphotropic phase boundary, rather than 〈110〉 and 〈111〉. Domain instability could explain inferior strain levels and large hysteresis for 〈110〉 and 〈111〉 oriented crystals. Ultrahigh strain levels up to 1.8% could be achieved for 〈001〉 oriented PMNT crystals, being related to an E-field induced phase transition. −2 kV/cm negative E-field can be applied to PMNT ferroelectric material with low hysteresis. High strain with low hysteresis makes PMNT crystals promising candidates for high performance solid-state actuators.     

Channeling and axial to planar channeling transition of protons in magnesium oxide

The channeling of 1.7 MeV protons along 〈100〉 axial direction, (100), (110) and (111) planar directions in magnesium oxide single crystals and axial to planar channeling transitions from 〈100〉 to (100), (110) and (210) have been studied experimentally. The experimental data and preliminary analysis of results are presented.     

High field magnetization of NdAl2 single crystals interpreted with crystal field theory

The magnetization of NdAl₂ single crystals was measured at 4.2, 20.3 and 77 K, in magnetic fields up to 35 tesla applied in the 〈100〉, 〈110〉 and 〈111〉 directions. The magnetization in these directions may be described theoretically, without any fitting, in terms of two cubic crystalline electric field parameters and one molecular field constant which have been taken from inelastic neutron scattering data.⁵     

Defect agglomeration in wüstite at high temperatures—I: The defect arrangement

Measurements are reported of the diffuse scattering (in absolute units) from a single crystal of Fe_0.93O, in a volume of reciprocal space and in equilibrium at 1173 K. These data were separated into the scattering due to ionic displacements and that due to the defect arrangement. The resulting local order parameters indicate clustering similar to that reported for quenched crystals. Some degree of order exists between clusters even at the high temperature, which is similar to that for the P″ phase. The clusters are distributed along 〈100〉 directions with a spacing of ∼ 2.5 a₀ (where a₀ is the lattice parameter). The cluster consists (on the average) of two incomplete corner-sharing vacancy tetrahedra aligned along 〈110〉 type directions, each containing an interstitial iron ion so that the ratio of vacancies to tetrahedral ions is 5.2.     

Combined channeling study of α-LiIO3 crystal in an electrostatic field

The combined channeling backscattering and channeling nuclear reaction analysis of the α-LiIO₃ monocrystal in an electrostatic field has been performed by proton beam at different energies to identify the behaviour of Li and I ions in the crystal. The thickness of the crystal was about 2 mm and has been cut perpendicular to C-direction. The channeling parameters like half angular width and minimum yield of 〈001〉 axial channeling have been measured precisely and the channeling behaviour of different ions in the crystal has been observed and measured quantitatively first time. The ionic d.c. conductivity can be calculated from the surface peak of the aligned channeling spectrum directly.     

ESR study of color centers in yttria stabilized zirconia

The ESR of single crystals of yttria stabilized zirconia (YSZ), containing color centers due to reduction in a flowing H₂ atmosphere, has been measured at room temperature. The spin density is about 3 × 10¹⁷ cm^?3 and the strong ESR line displays axial symmetry with principal values g₆ = 1.989, g_⊥ = 1.860.The behaviour of the ESR spectra when the magnetic field is rotated about the 〈1 0 0〉 and 〈1 1 0〉 directions shows that the centers have axial symmetry, the symmetry axis being along the 〈111〉 and equivalent directions. The derivative peak to peak envelope width is g-dependent and varies from 18 Gauss at g = 1.989 to 65 Gauss at g = 1.860. The results are interpretable in terms of an electron trapped at an oxygen vacancy adjacent to an yttrium ion.     

Properties of the oxygen sublattice structure of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">x</Emphasis></Subscript> crystal studied by ion channeling

Properties of the oxygen sublattice structure of the YBa₂Cu₃O_{7 ?x} crystal are studied using the diffusion model of ion channeling. The angular dependence of the elastic resonance scattering of helium ions on oxygen nuclei along the 〈001〉 direction is measured at an ion energy of 3.055 MeV. Steps are observed in the scattering yield at an angle of about 0.4°. The best fit of the calculated angular dependence of elastic resonance scattering to the experimental data is attained under the assumption that the oxygen rows contain vacancies corresponding to a fraction (not exceeding 20%) of the disordered oxygen atoms, which are randomly distributed in the plane normal to the 〈001〉 direction, and that the oxygen atoms in the rows are displaced from their equilibrium positions in a direction normal to the 〈001〉 axis.     

A theory of the surface reconstruction in gold

A phenomenological theory of the unidirectional contraction of the (111) surface layer of gold at low temperatures and the isotropic contraction of it at high temperatures is presented. It is shown that the state contracted unidirectionally in one of the 〈1$\text{1}$0〉 directions is of lowest energy in an intermediate range of the magnitude of the misfit energy, being stabilized mainly by the elastic energy λe_xxe_yy of the two dimensional continuum model. The reconstruction of the (100) surface is also discussed.     

Stopping power of fast channeled protons in Hartree-Fock approximation

The electronic energy loss of MeV-protons in crystals is investigated in the Hartree-Fock approximation for the core electrons of the target. It turns out that each core electron can be regarded as stopping the proton independent of all other electrons without restriction by the Pauli principle. For the channeling stopping power the impact parameter dependent energy loss of a proton moving rectilinearly past a crystal ion is calculated in first Born approximation. Low excitations of the core electrons lead to a long range impact parameter dependence, whereas high excitations contribute to the energy loss proportional to the electron density sampled along the proton trajectory. The results are applied to 4 MeV proton channeling along the main channels of Si using Clementi wave functions for the core electrons and a free electron approximation for the valence electrons. The comparison with the experimental results of Clarket al. yields good agreement. In the high velocity limit a reduction of the channeling stopping power to 0.64(0.83) of the random value is predicted for Si(C).     

The voigt-type magneto-kerr effect in cubic semiconductors having ellipsoidal constant energy surfaces

A plane-wave analysis is given for the Voigt orientation of an applied static magnetic field ?B in cubic semiconductors having ellipsoidal constant energy surfaces. The effect is shown to be highly anisotropic with respect to the orientation of ?B (magneto-anisotropy) as well as to the initial polarization direction of the incident wave with respect to ?B (polarization anisotropy). The character and extent of the magneto-anisotropy depends not only on the location of the energy extrema, but on the anisotropy of the energy surfaces and on the energy dependence and anisotropy of the scattering processes.Calculations are given for the cases of propagation along 〈100〉 and 〈110〉 crystallographic directions in n-type germanium. High-field effects and infrared (IR) behavior are considered; however, the low-field quadratic range for microwaves in high-loss material is emphasized. A useful approximation for the high-loss case is given. Particular attention is given to the potential diagnostic applications of the effect.Room-temperature measurements of the Voigt-type Kerr effect for the TE₁₁ circular-waveguide mode at 35 GHz in n-type Ge are presented and compared with plane-wave calculations for propagation along 〈100〉 and 〈110〉 directions. Good quantitative agreement is obtained when the plane-wave calculations are reduced by the same mode-reduction factor as is applicable for the Faraday orientation.     

Calibration of CR-39 with atomic force microscope for the measurement of short range tracks from proton-induced target fragmentation reactions

We studied the track response of CR-39 plastic nuclear track detectors (PNTD) for low (<6 MeV/n) and high (>100 MeV/n) energy heavy ions using the atomic force microscope (AFM). CR-39 PNTD was exposed to several heavy ion beams of different energy at HIMAC (Heavy Ion Medical Accelerator in Chiba). For AFM measurement, the amount of bulk etch was controlled to be ∼2 μm in order to avoid etching away of short range tracks. The response data obtained by AFM for ∼2 μm bulk etch was in good agreement with data obtained by the conventional optical microscope analysis for larger bulk etch. The response data from low energy beams (stopping near the surface) was also consistent with the data from high energy beams (penetrating the detector) as a function of REL (restricted energy loss) with the δ-ray cut off energy of ω₀ = 200 eV. We experimentally verified that REL (ω₀ = 200 eV) gives a universal function for wide energy range in CR-39 PNTD. This work has been done as part of a basic study in the measurement of secondary short range tracks produced by target fragmentation reactions in proton cancer therapy fields.     

Hysteresis phenomena in the course of polarization evolution in a sinusoidal electric field in lead magnesium niobate crystals

The processes of polarization evolution in single crystals of the PbMg_1/3Nb_2/3O₃ model ferroelectric relaxor in a sinusoidal electric field are investigated at temperatures near and above the temperature T _d 0 of destruction of the induced ferroelectric state upon heating in zero electric field. The polarization switching current loops are measured in the ac electric field applied along the 〈111〉 and 〈110〉 pseudocubic directions. The electroluminescence intensity loops are obtained under the combined action of ac and dc electric fields applied along the 〈100〉 direction. In a certain temperature range above T _d 0 and the freezing temperature T _f in lead magnesium niobate, there are electric current anomalies, that correspond to the dynamic formation and subsequent destruction of the ferroelectric macroregions throughout each half-cycle of the ac electric field. The measurements of electroluminescence hysteresis loops demonstrate that the observed depolarization delay (related to the ac electric field amplitude) increases with an increase in the dc electric field and decreases as the ac field amplitude increases. The nature of the observed phenomena is discussed.     

Bias field effects on the dielectric properties of 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 single crystals with different orientations

The domain states and phase transitions in 0.67Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ single crystals were investigated by studying their relative permittivity under various dc bias at constant heating and cooling rates. The orientation dependence of the bias field effect was revealed by examining the temperature dependence of relative permittivity as a function of crystal orientation (the 〈111〉, 〈011〉 and 〈001〉 directions) and dc bias field. The crystals basically have a macrodomain rhombohedral ferroelectric state in the ferroelectric phase under zero dc bias. External bias field could modulate the domain state and induce a stable macrodomain state in the crystals. Also, it is proposed that the dc bias applied along the 〈001〉 or 〈011〉 direction could induce a tetragonal ferroelectric phase or an orthorhombic ferroelectric phase, respectively, in an intermediate temperature range.     

Preferential ejection pattern of sputtered KC1

The sputtering of KCl crystals in an argon plasma has produced well defined spot patterns when surface accumulation of potassium was minimal. 〈112〉 and 〈100〉 spots have resulted from the photon and low energy ion irradiation of the (100) surface.     

Low temperature magnetization of TbAl2 single crystals

Magnetization measurements on TbAl₂ single crystals are reported for 4.2 K in magnetic fields up to 50 kOe applied in the three symmetry directions. We find 〈111〉 as the easy and 〈100〉 as the hard direction of magnetization. No quenching of the magnetic moment is observed. The results are interpreted in terms of the crystalline electric field.     

Ion implantation of sulphur into GaAs,GaP and ge monocrystals

The possibility of using ion implantation to form high concentration junctions in semiconductors has been explored for the specific case of sulphur in GaAs, GaP and Ge. The effects of ion dose, ion energy, crystal orientation and target temperature have been investigated by means of radiotracers and sectioning techniques.

It is shown that high concentration junctions can be formed using an incident ion having high electronic stopping cross-section and implanted along the <110< channeling directions of the crystals. A large increase in junction concentration may be obtained when the GaAs and GaP crystals are maintained at 150 °C during the implantation process, but this is not the case with Ge. Rutherford back-scattering of 1 MeV He⁺ ions has been used to measure the ion-bombardment induced damage in the crystals and to show how this damage can be annealed by heating the crystal during the implantation. The annealing, at temperatures up to 150 °C, is most effective in GaAs and least effective in Ge.     

Simulation of radiation energy losses by channeled relativistic electrons in a crystal

A computer code is developed to calculate the radiation energy losses (RELs) of electrons during both 〈100〉 axis and (100) plane channeling in a thin Si crystal. A computer simulation of these losses is carried out by taking the initial angular divergence of the beam into account, and the REL dependences on the angle of electron entry into the crystal are obtained for both axial and planar channeling (orientational dependences). The calculations are carried out in connection with experiments on the interaction of 20–255 MeV electrons with crystals conducted at the SAGA Light Source linear accelerator (Tosu, Saga, Japan). The simulation results show the possibility of using the orientational dependence of the RELs of channeled electrons in thin crystals to diagnose the initial angular divergence of the electron beam and to orient crystals.