Individual and center-of-mass resonances in the motional spectrum of an electron cloud in a Penning trap

We have examined experimentally the motional spectrum of an electron cloud confined in a Penning trap. When the axial oscillation is excited by a radio frequency field the resonance exhibits a double structure. Both components depend differently on the number of trapped electrons and have different shape and width. We conclude that one of them corresponds to the excitation of the individual electrons while the other is the center-of-mass mode of the cloud. The threshold behaviour of the center-of-mass resonance suggests that it is a parametric instability of a Mathieu type equation of motion. Received 11 July 2001 and Received in final form 12 November 2001     

Mechanisms of ion-beam-enhanced diffusion in amorphous silicon

We have investigated ion-beam-enhanced diffusion of Au in undoped and B doped amorphous Si. The diffusion coefficients depend linearly on ion flux and exibit an Arrhenius-like temperature dependence with an activation energy of 0.37 eV in the temperature range 200–350° C. Moreover the diffusivity is enhanced by a factor of 5 by B-doping at a concentration of 1×10²⁰ atoms/cm³. A similar enhancement is observed in thermal diffusion of Au which has an activation energy of 1.5 eV. On the basis of these results a model for the ion-beam-enhanced diffusion of Au is proposed where the high density of defects present in amorphous Si act as traps for the fast moving interstitial Au atoms. The effectiveness of this trapping process can be changed by the high concentration of mobile defects generated by the beam and also by a change in the charge state of the traps induced by the presence of B.     

Eliashberg theory for disordered superconductors. II. Tunneling into disordered two-dimensional Pb films

A series ofc-axis oriented YBa₂Cu₃O _x -films with different oxygen content were prepared by laser deposition. The oxygen contentx was determined by X-ray diffraction and by resonant Rutherford-back-scattering (RRBS) measurements. Thec-axis length in these films of YBa₂Cu₃O _x is about 0.5% larger compared to bulk values. We describe transport measurements in magnetic fields up to 7 Tesla between room temperature andT _c in samples with an oxygen content between the orthorhombic-to-tetragonal transition (x6.4) and full oxygenation (x7). The ratio /R _H was investigated with respect to the two-dimensional Luttinger liquid theory and the model of the two-dimensional ionic metal. We report on deviations from the expected quadratic temperature behaviour of /R _H , especially in films with high oxygen content.     

Temperature dependent preferential sputtering in CoSi2 and NbSi2

Sputtering of CoSi₂ and NbSi₂ has been carried out by Xe ion bombardment at room temperature, as well as at elevated temperatures putting these systems in their radiation-enhanced diffusion regimes. The range of the Xe ions (at 200–260 keV) was appreciably less than the thickness of the silicides. The samples were analyzed by 2 MeV He⁺ backscattering spectrometry, x-ray diffraction and optical microscopy. The ratio of the sputtering yield of Si to that of the metal (i.e., Co or Nb) always exceeds the stoichiometric ratio 21, leading to Si depleted surface layers. The amount of the sputtered species increases almost linearly with dose until intermixing of the silicide with the underlying Si becomes appreciable. This happens at lower doses in the radiation-enhanced diffusion regime than at room temperature. Irradiation of CoSi₂ samples at high temperature leads to a broadening of the implanted Xe profile compared to the room temperature profile. No such phenomenon has been found in NbSi₂. The effect of Xe broadening on the sputtering yields is discussed.     

Combinatorial investigation of nanostructures formed in a titanium dioxide based nanocomposite film on top of fluor‐doped tin oxide layers

Nanostructures formed in a titanium dioxide (TiO₂)–poly(styrene)‐block‐poly(ethyleneoxide) nanocomposite film on top of fluor‐doped tin oxide (FTO) layers are investigated. The combinatorial approach is based on probing a wedge‐shaped FTO‐gradient with grazing incidence small angle X‐ray scattering (GISAXS) in combination with a moderate micro‐focus X‐ray beam. The characteristic lateral length is given by adjacent nanowire‐shaped TiO₂ regions. It decreases from 200 nm on the thick FTO layer to 90 nm on the bare glass surface.

     

Efficiency Enhancement of Dye-Sensitized Solar Cells： Using Salt CuI as an Additive in an Ionic Liquid

Energy conversion efficiency of the dye-sensitized solar cell is improved from 3.5% to 4.5% by adding a small amount of CuI into an ionic liquid electrolyte. It is found that other copper-I salts, for example, CuBr, have the same effect for the dye-sensitized solar cell. Experimental results show that no Cu^2＋ ions exist in this electrolyte. It is suggested that this improvement is caused by the adsorption of Cu^＋ onto the TiO2 porous film.     

Investigation of organic impurities adsorbed on and incorporated into electroplated copper layers

At room temperature electroplated copper layers exhibit changes in resistivity, residual stress, and microstructure. This process, known as self-annealing, is intimately linked to the release of organic impurities, which stem from the incorporation of organic additives into the Cu layer in the course of the electroplating process. The behavior of these impurities during self-annealing, represented by the carbon content, could be detected by analytical radio frequency glow discharge optical emission spectrometry (GD-OES) and carrier gas hot extraction (CGHE). The precondition of a quantitative determination is a surface cleaning procedure to remove adsorbed organics from the copper surface. It was observed that at first almost all impurities have to leave the Cu metallization before an accelerated abnormal grain growth can start. The small amount of remaining organic species after self-annealing could be quantified by both examination techniques, GD-OES and CGHE.     

Space-Selective Precipitation of Ba2TiSi2O8 Crystals in Sm3^＋-Doped BaO-TiO2-SiO2 Glass by Femtosecond Laser Irradiation

The ferroelectric crystal Ba2TiSi2O8 with high second-order optical nonlinearity is precipitated in Sm^3＋-doped BaO-TiO2-SiO2 glass by a focused 800hm, 250 kHz and 150fs femtosecond laser irradiation. No apparent blue and red emissions are observed at the beginning, while strong blue emission due to second harmonic generation and red emission due to the f-f transitions of Sm^3＋ are observed near the focal point of the laser beam after irradiation for 25s. Micro-Raman spectra confirm that Ba2 TiSi2O8 crystalline dots and lines are formed after laser irradiation. The mechanism of the phenomenon is discussed.     

Preparation of Cu（In,Ga）Se2 Thin Film Solar Cells by Selenization of Metallic Precursors in an Ar Atmosphere

Cu（In, Ga）Se2 thin films are deposited on Mo-coated glass substrates by Se vapour selenization of sputtered metallic precursors in the atmosphere of Ar gas flow under a pressure of about 10 Pa. The in situ heat treatment of as-grown precursor leads to the formation of a better alloy. During selenization, the growth of CuInSe2 phase preferably proceeds through Se-poor phases as CuSe and InSe at relatively low substrate temperature of 250℃, due to the absence of In2Se3 at intermediate stage at low reactor pressure. Subsequently, the Cu（In,Ga）Se2 phase is produced by the reactive diffusion of CuInSe2 with a Se-poor GaSe phase at high temperature of up to 560℃. The final film exhibits smooth surface and large grain size. The absorber is used to fabricate a glass/Mo/Cu（In, Ga）Se2/CdS/ZnO cell with the total-area efficiency of about 7%. The low open-circuit voltage value of the cell fabricated should result from the nonuniform distribution of In and Ga in the absorber, due to the diffusion-controlled reaction during the phase formation. The films, as well as devices, are characterized.     

Influence of Yb-Doped Nanoporous TiO2 Films on Photovoltaic Performance of Dye-Sensitized Solar Cells

Yb-doped TiO2 pastes with different Yb/TiO2 weight ratios are prepared in the sol-gel process to obtain dyesensitized solar cells （DSCs）. The nanocrystalline size of Yb-TiO2 becomes smaller and the lattice parameters change. Lattice distortion is observed and dark current is detected. It is found that a part of Yb existing as insulating oxide Yb2O3 state acts as barrier layers at the electrode-electrolyte interface to suppress charge recombination. A Yb-doped TiO2 electrode applied in DSCs leads to a higher open-circuit voltage and a higher fill factor. How the Yb-doped TiO2 films affect the photovoltaic response of DSCs is discussed.