Photo-luminescence and growth defects in ZnS: Cu monocrystals

The paper describes microscopic investigation into the spectral distribution of photo-luminescence and its polarization on hexagonal ZnS monocrystals in relation to the structural defects of such crystals. These observations, as well as birefringent observations, show that the values of the birefringence and the degree of polarization in different stripes of the same crystal are the same within the limits of observational errors.

---

ZnS: Cu

ZnS . , , , .

---

---

In conclusion the author would like to thank K. Pátek, L. Souková and M. Mokonová for providing the monocrystals and for fruitful discussions.     

Anisotropic properties of volume holograms in Bi12SiO20 monocrystals

A theoretical and experimental study is made on light diffraction from holographic diffraction gratings, recorded in cubic photorefractive crystals Bi₁₂SiO₂₀ with (110) cut, for two orientation of the grating wave vector,K [001] andK [110], when an external electric field is applied.     

Oxygen induced surface segregation of Cu on the Au0.7Cu0.3(100) surface

The oxygen induced surface segregation of Cu on the Au_0.7Cu_0.3(100) surface was investigated by means of LEED and AES techniques. The dissociative adsorption of O₂ did not take place on this clean surface for a long time exposure at least up to 10⁴ L, and so the oxygen was forcibly introduced onto the surface through a pre-deposition of few a layers of Cu and its successive oxidation. The oxygen coverage was controlled by a heat treatment, which leads the system to a thermal equilibrium state. For the clean surface, the segregation of Au was clearly observed and the surface concentration of Au was estimated to be about 86%, greater than the bulk concentration of 70%. At low coverages below 0.16 ML, no remarkable oxygen induced segregation of Cu was observed. But, above 0.2 ML, the surface concentration of Cu was proportional to the oxygen coverage. The (2 × 4) LEED pattern was observed in a wide range of oxygen coverage. The maximum intensity of the (2 × 4) was observed at about 0.45 ML.     

Polarization of photo-luminescence of ZnS: Cu monocrystals

Different models of luminescence centres are discussed on the basis of measurements of the composition of ZnS monocrystal photo-luminescence in different polarizations and temperature dependence of the degree of polarization. Those of the models submitted by Birman, which assume the polarization to be due to the different force of the oscillators for transitions withEc andEc, or models assuming luminescence polarization to be due to the orientation of the luminescence centres, agree with the results of experiments, i.e. the temperature independence of the degree of polarization and the conformable spectral composition of both polarizations. It is also shown that measurements made up to now of the degree of polarization must be taken as orientational as a consequence of the depolarizing influence of the diffused rays of luminescence on its value.

---

ZnS: Cu

ZnS , . , . . , , , E E, , . , , - .

     

Di-jet correlation in Au+Au and Cu+Cu Collisions from PHENIX

PHENIX has measured the two-particle azimuth correlation in Au+Au at √s=200 GeV. Jet shape and yield at the away side are found to be strongly modified at intermediate and low p _T, and the modifications vary dramatically with p _T and centrality. At high p _T, away side jet peak reappears but the yield is suppressed. Similar jet strength is found for Au+Au and Cu+Cu collisions with similar number of participant nucleons.     

Fermi surface of ordered Cu3Au by positron annihilation

The Fermi surface of ordered Cu₃Au has been studied by positron annihilation. The results suggest that the Fermi surface is complicated by splitting of the zone.     

在RHIC-PHENIX中观测到的AuAu和CuCu碰撞中已鉴别强子产物的标度率特性

Particle type dependences of hadron yield and emission patterns, especially its difference between mesons and baryons, at intermediate p_{T(2—5GeV/c) is one of the findings in heavy ion collisions at RHIC. A systematic study of identified hadron production was performed in Au+Au/Cu+Cu collisions at sNN=62.4/200GeV, to investigate the possible origins of this difference. In this paper, we show particle ratios, elliptic flow strengths, and their scaling properties.}     

A surface analysis of CuAu alloy by leed and Auger electron spectroscopy

Surface structures and compositions of the CuAu alloys have been investigated, which were prepared by depositing gold on (110) and (111) surfaces of copper and by subsequent heating. By this method the structure of alloy surfaces corresponding to different compositions can be observed by LEED. A series of the LEED patterns, streak, (1 × 2), (1 × 1)I, complex, c(3 × 1), (1 × 1)II, (2 × 2) and (1 × 1) have been observed on the (110) surface with decreasing gold composition. On the (111) surface (1 × 1) pattern, weak (2/√3 × 2/√3)R30° and (2 × 2) patterns are observed. The mean surface composition is determined by analysing the data of Auger electron spectroscopy. Most surface periodicities observed are different from those expected if one passes a mathematical plane through the crystal (unreconstructed surface).     

Chemically shifted surface core-levels and surface segregation in EuAu and YbAu alloys

Chemically shifted surface core-level binding energies are observed for the rare-earth alloy component in Eu_1?xAu_x and Yb_1?xAu_x. Furthermore, these shifts are different from the chemical shifts of the bulk 4f levels. The surface core-levels are used to identify surface segregation of the lanthanide metal in the present alloys.     

Anisotropic diffusion of Cu adatoms on strained Cu (1 1 1) surface

Diffusion of Cu atoms on a strained Cu (1 1 1) surface was studied by molecular dynamic simulation using an EAM potential. The anisotropic diffusion behaviour is found when the uniaxial strain is imposed on the surface, which does not exist under the biaxial strain. The migration of the adatom is suppressed along the tensile strain direction. The results suggest that different island morphology can be obtained by controlling anisotropic diffusion of adatoms on the strained surfaces during film growth.     

Diffusion of gold in Cu3Au

The diffusion coefficient of Au¹⁹⁵ in the disordered Cu₃Au alloy is found to obey an Arrhenius equation, the activation energy of the process being 1.66 ± 0.04 eV. This result is discussed in connexion with data concerning the ordering kinetics of Cu₃Au below the critical temperature and indications of the existence of a partially ordered structure above the critical temperature.     

Anisotropic effects in surface acoustic wave propagation from a point source in a crystal

Strong anisotropic effects in the propagation of surface acoustic waves (SAWs) from a point-like source are studied experimentally and theoretically. Nanosecond SAW pulses are generated by focused laser pulses and detected with a cw probe laser beam at a large distance from the source compared to the SAW wavelength, which allows us to resolve fine intricate features in SAW wavefronts. In our theoretical model, we represent the laser excitation by a localized impulsive force acting on the sample surface and calculate the far-field surface response of an elastically anisotropic solid to such a force. The model simulates the measured SAW waveforms very well and accounts for all experimentally observed features. Using the data obtained for the (111) and (001) surfaces of GaAs, we describe a variety of effects encountered in the SAW propagation from a point source in crystals. The most interesting phenomenon is the existence of cuspidal structures in SAW wavefronts resulting in multiple SAW arrivals for certain ranges of the observation angle. Cuspidal edges correspond to the phonon focusing directions yielding sharp peaks in the SAW amplitude. A finite SAW wavelength results in internal diffraction whereby the SAW wavefront spreads beyond the group velocity cusps. Degeneration of a SAW into a transverse bulk wave is another strong effect influencing the anisotropy of the SAW amplitude and making whole sections of the SAW wavefront including some phonon focusing directions unobservable in the experiment. The propagation of a leaky SAW mode (pseudo-SAW) is affected by a specific additional effect i.e. anisotropic attenuation. We also demonstrate that many of the discussed features are reproduced in powder patterns, a simple technique developed by us earlier for visualization of SAW amplitude anisotropy.Received: 17 June 2003, Published online: 15 October 2003PACS: 43.35.+d Ultrasonics, quantum acoustics, and physical effects of sound - 68.35.Gy Mechanical properties; surface strains - 62.65.+k Acoustical properties of solidsA.M. Lomonosov: On leave from the General Physics Institute, 117942 Moscow, Russia     

NeXSPheRIO results on elliptic flow and directed flow for Au+Au and Cu+Cu collisions at RHIC

Hydrodynamics has been rather successful at describing results obtained in relativistic nuclear collisions at RHIC. Here we show results obtained with NeXSPheRIO on Au+Au collisions and the less studied Cu+Cu collisions. We study elliptic flow and its connection with eccentricity suggested by PHOBOS, as well as present elliptic flow fluctuations. We also show results for directed flow and compare with PHOBOS and STAR data.     

Bonding in Cu,Ag, and Au clusters: relativistic effects,trends, and surprises

Electronic structure and bonding in anionic coinage metal clusters are investigated via density-functional calculations, focusing on an extensive set of isomers of Cu(-)(7), Ag(-)(7), and Au(-)(7). While the ground states of Cu(-)(7) and Ag(-)(7) are three dimensional (3D), that of Au(-)(7) is planar, separated from the optimal 3D isomer by 0.5 eV. The simulated thermally weighted photoabsorption spectrum of Au(-)(7) is dominated by planar structures, and it agrees well with the measured one. The propensity of Au(-)(N) clusters to favor planar structures (with N as large as 13) is correlated with strong hybridization of the atomic 5d and 6s orbitals due to relativistic effects.     

Anisotropy of photoconductivity and nonlinear effects in GaSe monocrystals at high optical excitation

In this work, the photoelectric properties of gallium selenide (GaSe) monocrystals in the edge absorption region, with various configurations of current contacts, at low and high optical excitation levels are investigated. The photoconductivity spectrum behavior is determined by localized electronic and excitonic states along c-axis. It is shown that the localization of electronic and excitonic states in one-dimensional fluctuation potential along c-axis results to an anisotropy in photoconductivity spectrum at various current contacts configurations. At E⊥c the photoconductivity is observed in the hν < E_g and hν > E_g regions. In the case of hv < E_g, the maximum photoconductivity, in the impurity and exciton absorption region are observed at 1.975 eV and 2.102 eV, respectively. With rising of excitation energy level, suppression of photoconductivity in the exciton absorption region and increases in impurity absorption region is observed. At E||c contact configuration, the considerable photoconductivity is observed only in the impurity absorption region, which also increases with rising of excitation level. It is supposed that, suppression of photoconductivity in the exciton absorption region at high excitation levels is connected with exciton-exciton interaction, which results to a nonlinear light absorption. The results are compared with the absorption and photoluminescence measurements.