Application of Ion Implantation for Synthesis of Copper Nanoparticles in a Zinc Oxide Matrix for Obtaining New Nonlinear Optical Materials

We have obtained a layered composite material by implantation of single crystal zinc oxide (ZnO) substrates with 160-keV Cu+ ions to a dose of 10(16) or 10(17) cm(-2). The composite was studied by linear optical absorption spectroscopy; the nonlinear optical characteristics were determined by means of Z-scanning at a laser radiation wavelength of 532 nm. The appearance of the optical plasmon resonance bands in the spectra indicated that ion implantation to the higher dose provides for the formation of copper nanoparticles in a subsurface layer of ZnO. The new nonlinear optical material comprising metal nanoparticles in a ZnO matrix exhibits the phenomenon of self-defocusing and possesses a high nonlinear absorption coefficient (beta = 2.07 x 10(-3) cm/W). (C) 2004 MAIK "Nauka / Interperiodica"

Theory of Interplay of Nuclear Magnetism and Superconductivity in AuIn2

The recently reported coexistence of a magnetic order, with the critical temperature T_M=35 \mu*K, and superconductivity, with the critical temperature T_S=207 m*K, in AuIn_2 is studied theoretically. It is shown that superconducting (S) electrons and localized nuclear magnetic moments (LM's) interact dominantly via the contact hyperfine (EX) interaction, giving rise to a spiral (or domain-like) magnetic order in superconducting phase. The electromagnetic interaction between LM's and S electrons is small compared to the EX one giving minor contribution to the formation of the oscillatory magnetic order. In clean samples (l>\xi_0) of AuIn$_2$ the oscillatory magnetic order should produce a line of nodes in the quasiparticle spectrum of S electrons giving rise to the power law behavior. The critical field H_c(T=0) in the coexistence phase is reduced by factor two with respect to its bare value.Comment: 4 pages with 2 PS figures, RevTeX, submitted to Physical Review B - Rapid Communication

Structural and electrical transport properties of superconducting Au{0.7}In{0.3} films: A random array of superconductor-normal metal-superconductor (SNS) Josephson junctions

The structural and superconducting properties of Au{0.7}In{0.3} films, grown by interdiffusion of alternating Au and In layers, have been studied. The films were found to consist of a uniform solid solution of Au{0.9}In{0.1}, with excess In precipitated in the form of In-rich grains of various Au-In phases (with distinct atomic compositions), including intermetallic compounds. As the temperature was lowered, these individual grains became superconducting at a particular transition temperature (Tc), determined primarily by the atomic composition of the grain, before a fully superconducting state of zero resistance was established. From the observed onset Tc, it was inferred that up to three different superconducting phases could have formed in these Au{0.7}In{0.3} films, all of which were embedded in a uniform Au{0.9}In{0.1} matrix. Among these phases, the Tc of a particular one, 0.8 K, is higher than any previously reported for the Au-In system. The electrical transport properties were studied down to low temperatures. The transport results were found to be well correlated with those of the structural studies. The present work suggests that Au{0.7}In{0.3} can be modeled as a random array of superconductor-normal metal-superconductor (SNS) Josephson junctions. The effect of disorder and the nature of the superconducting transition in these Au{0.7}In{0.3} films are discussed.Comment: 8 text pages, 10 figures in one separate PDF file, submitted to PR

Ferroelectric properties of epitaxial BaTiO3 thin films and heterostructures on different substrates

Ferroelectric thin films of BaTiO3 and BaTiO3/SrRuO3 epitaxial heterostructures on different single-crystalline substrates were fabricated by pulsed laser deposition. The BaTiO3 films of 100-400 nm thickness show high structural perfection and c-axis-oriented growth. For the electrical characterization of the BaTiO3 in a thin-film capacitor structure, Pt top electrodes were deposited by e-beam evaporation. The results are compared to the current experimental and theoretical models. Special consideration is given to the model of charge injection from the electrodes

Ferroelectric BaTiO3 thin-film optical waveguide modulators

High-quality BaTiO3 epitaxial thin films on MgO substrates have been grown by pulsed-laser deposition. Both, c-axis and a-axis BaTiO3 orientations were studied. Mach-Zehnder optical waveguide modulators with a fork angle of 1.7degrees have been fabricated by ion-beam etching. The waveguides are of the ridge type, the BaTiO3 thickness is 1 mum, the ridge step 50 nm, and the width 2 mum. Light was coupled into the waveguides from optical fibers. The BaTiO3 waveguide propagation losses are 2-3 dB/cm. Electrodes of 3 mm length were deposited besides the waveguides. Electro-optic modulation has been demonstrated with V-pi=6.3 V at 632 nm wavelength and V-pi=9.5 V at 1550 nm wavelength for the a-axis samples, and with V-pi=8 V at 632 nm wavelength and V-pi=15 V at 1550 nm for the c-axis samples. Theoretical modelling of the Mach-Zehnder modulators for both crystalline orientations of the BaTiO3 films gave the Pockels coefficients r(51)=80 pm/V for the c-axis film and an effective Pockels coefficient r(eff)=734 pm/V for the a-axis films at 632 nm wavelength. (C) 2002 American Institute of Physics

Metal-germanium-metal ultrafast infrared detectors

We demonstrate silicon-based ultrafast metal-semiconductor-metal (MSM) photodetectors for near infrared optocommunication wavelengths. They show a response time of 12.5 ps full width at half maximum (FWHM) at both 1300 and 1550 nm wavelengths. The overall external quantum efficiencies are 13% at 1320 nm and 7.5% at 1550 nm. The sensitive volumes are 270 nm thick Ge films, grown on Si(111) by molecular beam epitaxy. Interdigitated Cr metal top electrodes with 1.5-5 mum spacing and identical finger width form Schottky contacts to the Ge film. A Ti-sapphire femtosecond laser with an optical parametric oscillator and an electro-optic sampling system are used to evaluate the temporal response, which is limited by the transit time of the carriers between electrodes. In addition, results on Si-Ge MSM heterostructure detectors with plate capacitor geometry are presented. At 1550 nm an ultrafast response of 9.4 ps FWHM and an overall quantum efficiency of 0.9% are measured. (C) 2002 American Institute of Physics

Fabrication of ZnO nanoparticles in SiO2 by ion implantation combined with thermal oxidation

Zinc-oxide (ZnO) nanoparticles (NPs) are fabricated in silica glasses (SiO2) by implantation of Zn+ ions of 60 keV up to 1.0x10(17) ions/cm(2) and following thermal oxidation. After the oxidation at 700 degrees C for 1 h, the absorption in the visible region due to Zn metallic NPs disappears and a new absorption edge due to ZnO appears at similar to 3.25 eV. Cross-sectional transmission electron microscopy confirms the formation of ZnO NPs of 5-10 nm in diameter within the near-surface region of similar to 80 nm thick and larger ZnO NPs on the surface. Under He-Cd laser excitation at lambda=325 nm, an exciton luminescence peak centered at 375 nm with FWHM of 113 meV was observed at room temperature. (c) 2005 American Institute of Physics

Photoluminescence of Er3+-implanted amorphous hydrogenated silicon suboxides

Erbium ions incorporated into amorphous hydrogenated silicon suboxides (a-SiOx:H) allow to overcome the disadvantages of Er3+ in c-Si such as the limited solubility, the strong quenching of the luminescence at room temperature, and the need for co-doping with electronegative atoms. a-SiOx:H alloys have an enhanced Er solubility and easily variable oxygen content, thereby providing favorable atomic environments for an efficient Er luminescence and reduced excitation backtransfer due to deeper localized band-tail states. In the present study, Er3+ doses up to 7x10(14) cm(-2) were implanted into a-SiOx:H with oxygen content between 0 and 44 at. %. Optical properties such as the absorption coefficients and the photoluminescence (PL) spectra of the Er3+ ions and of the SiOx host were investigated as a function of erbium implantation dose, oxygen content, defect density, temperature, and annealing treatment. It was found that annealing is a requirement for activating the characteristic Er PL at 1.54 mum mainly due to a reduction of implantation induced defects. The intensity of both the intrinsic SiOx and the Er PL was found to be inversely proportional to the defect density as measured by electron spin resonance or subgap absorption. The Er PL is additionally enhanced upon annealing, probably as a result of better structural arrangements of the Er ions. The Er PL intensity increases approximately linearly with the implantation dose. An increase of the oxygen content (and correspondingly of the optical band gap) of a-SiOx:H causes no drastic changes in the erbium luminescence energy and intensity, whereas the intrinsic PL shifts to higher photon energies according to the larger band gap. Already low O concentrations of a few percent provide favorable Er environments. The main advantage of a-SiOx:H as a host matrix is revealed by temperature-dependent PL measurements. For high oxygen contents, the thermal quenching of both the Er3+ and the intrinsic PL is strongly reduced. In an a-SiOx sample with 44 at. % oxygen, the Er PL is only quenched by 20% between 77 and 300 K. In contrast, the quenching of the intrinsic PL for all [O] is roughly one order of magnitude stronger than that of the Er PL. These PL measurements were complemented by PL excitation experiments over a wide spectral range. We have observed that the Er3+ PL is excited about one order of magnitude more efficiently when pumped with sub-band-gap light compared to band-to-band excitation. The experimental results are discussed with regard to the two currently proposed Er3+ excitation models, the defect-related Auger effect and the Forster transfer mechanism

Fast time response from Si-SiGe undulating layer superlattices

We have grown Si-Si1-xGex undulating layer superlattices with x=0.39 and 0.45 by molecular-beam epitaxy on top of epitaxial implanted CoSi2 layers and fabricated vertical metal-semiconductor-metal detectors. The detectors show a quantum efficiency of 5% for the wavelength of 1320 nm and 0.9% for 1550 nm. We performed temporal response measurements, using a Ti:sapphire laser and an optical parametric oscillator which generates ultrafast pulses at infrared wavelengths. An electrical response time of 16 ps full width at half maximum was obtained at a wavelength of 1300 nm. (C) 2002 American Institute of Physics

Crack-free BaTiO3 films on Si with SiO2, MgO, or Al2O3 buffer layers

Crack-free polycrystalline BaTiO3 films Of UP to 1-mu m thickness were grown on silicon and on silicon-on-sapphire (SOS) substrates by pulsed laser deposition. The quality of films of different thickness was studied, particularly the onset of the formation of cracks. The crystallinity of the films was confirmed by x-ray diffraction measurements. The thickness and composition of the films were examined by Rutherford back-scattering spectrometry. The optical properties (index of refraction and damping) of planar BaTiO3 waveguides were determined with a prism coupling setup. The films showed an optical attenuation of less than 2 dB/cm and a birefringence of up to 0.01. (c) 2005 Optical Society of America