G. Sáfrán

Influence of high power impulse magnetron sputtering plasma ionization on the microstructure of TiN thin films

HIPIMS (High Power Impulse Magnetron Sputtering) discharge is a new PVD technology for the deposition of high-quality thin films. The deposition flux contains a high degree of metal ionization and nitrogen dissociation. The microstructure of HIPIMS-deposited nitride films is denser compared to conventional sputter technologies. However, the mechanisms acting on the microstructure, texture and properties have not been discussed in detail so far. In this study, the growth of TiN by HIPIMS of Ti in mixed Ar and N2 atmosphere has been investigated. Varying degrees of metal ionization and nitrogen dissociation were produced by increasing the peak discharge current (Id) from 5 to 30 A. The average power was maintained constant by adjusting the frequency. Mass spectrometry measurements of the deposition flux revealed a high content of ionized film-forming species, such as Ti1+, Ti2+ and atomic nitrogen N1+. Ti1+ ions with energies up to 50 eV were detected during the pulse with reducing energy in the pulse-off t...

Epitaxial growth and characterization of Ni films grown on MgO(001) by biased direct‐current sputter deposition

Ni films thinner than 180 nm are deposited on MgO(001) substrates at a temperature Ts of 190 or 280 °C by dc sputtering at 2.5 kV in Ar gas. A dc bias voltage Vs between 0 and ‐140 V is applied to the substrate during the deposition. A study of structural and physical properties of the Ni film is made by the use of reflection high‐energy electron diffraction (RHEED), cross‐sectional transmission electron microscopy (XTEM), x‐ray reflection diffraction (XRD), Rutherford backscattering spectroscopy (RBS), and by measuring (TCR) in the temperature range from 35 to 135 °C. When Ts=190 °C the Ni film retains a polycrystalline structure at any Vs. When Ts=280 °C, as Vs increases from 0 to −140 V the film transforms from the polycrystal to the single crystal with the orientation as Ni(001)∥MgO(001) and Ni〈010〉∥MgO〈010〉, indicating that an optimal value of Vs for the epitaxial growth ranges from −80 to −110 V. Besides, an analysis of RBS spectra in comparison with XTEM images explains that the atomic density of t...

Silica-Supported Au Nanoparticles Decorated by CeO2: Formation, Morphology, and CO Oxidation Activity

Silica-Supported Au Nanoparticles Decorated by CeO2: Formation, Morphology, and CO Oxidation Activity Anita Horv ath,* Andrea Beck, Gy€orgyi Stefler, Tímea Benk o, Gy€orgy S afr an, Zsolt Varga, Jen 00 o Gubicza, and L aszl o Guczi Department of Surface Chemistry and Catalysis and Department of Radiation Safety, Institute of Isotopes of HAS, P.O. Box 77, H-1525 Budapest, Hungary Research Institute for Technical Physics and Materials Science of HAS, P.O. Box 49, H-1525 Budapest, Hungary Department of Materials Physics, E€otv€os Lor and University, Budapest, P.O. Box 32, H-1518, Hungary

Low-temperature synthesis of indium tin oxide nanowires as the transparent electrodes for organic light emitting devices

Low-temperature growth of indium tin oxide (ITO) nanowires (NWs) was obtained on catalyst-free amorphous glass substrates at 250 °C by Nd:YAG pulsed-laser deposition. These ITO NWs have branching morphology as grown in Ar ambient. As suggested by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM), our ITO NWs have the tendency to grow vertically outward from the substrate surface, with the (400) plane parallel to the longitudinal axis of the nanowires. These NWs are low in electrical resistivity (1.6×10⁻⁴ Ω cm) and high in visible transmittance (~90–96%), and were tested as the electrode for organic light emitting devices (OLEDs). An enhanced current density of ~30 mA cm⁻² was detected at bias voltages of ~19–21 V with uniform and bright emission. We found that the Hall mobility of these NWs is 2.2–2.7 times higher than that of ITO film, which can be explained by the reduction of Coulomb scattering loss. These results suggested that ITO nanowires are promising for applications in optoelectronic devices including OLED, touch screen displays, and photovoltaic solar cells.

RBS and XHRTEM characterization of epitaxial Ni films prepared by biased d.c. sputter deposition on MgO(001)

Abstract Rutherford backscattering spectrometry (RBS) channelling and cross-sectional high-resolution transmission electron microscopy (XHRTEM) have been applied to characterize the structure of Ni films grown epitaxially on MgO(001) by biased d.c. sputter deposition. The RBS spectra indicate that the Ni films have a high density of lattice imperfections near to the MgO surface. The XHRTEM investigations revealed a lattice expansion in the [010]direction confirming the existence of the slightly distorted cubic lattice of Ni in the vicinity of the substrate surface which was detected by RBS channelling measurements. Regularly distributed edge dislocations due to the mismatch of Ni and MgO lattices have been clearly demonstrated by XHRTEM.

Microstructure and magnetic properties of Co/Pd multilayered thin films with C or Si seedlayer

Microstructure and magnetic properties of sputter deposited Co/Pd multilayered perpendicular magnetization films with amorphous C or Si seedlayer were investigated. The angstrom scale surface roughness of the seedlayer causes fine crystal grains to form in the Co/Pd multilayer and to decrease the extent of intergranular exchange coupling, while it obstructs the formation of a regular interface between Co and Pd layers. The Si seedlayer, which exhibits a surface roughness lower than the C seedlayer, yields Co/Pd multilayered films with the lowest intergranular exchange coupling and the highest coercivity. The improvement in magnetic properties of the Co/Pd film with Si seedlayer is attributable mainly to the formation of Pd2Si at the interface between the Co/Pd layer and the Si seedlayer. The Pd2Si provides suitable nucleation sites for the grain growth of Co/Pd multilayered film that can be utilized as a perpendicular magnetic recording medium.

Epitaxial growth, structure and properties of Ni films grown on MgO(100) by d.c. bias sputter deposition

Abstract Ni films of 70–240 nm thickness were deposited on an MgO(100) substrate at temperatures T s ⩾190°C by d.c. sputtering at 2.5 kV in pure Ar gas. A negative bias voltage V s between zero and −110 V was applied to the substrate during the deposition. Reflection high energy electron diffraction, X-ray diffraction, cross-sectional transmission electron microscopy. Auger electron spectroscopy, ferromagnetic resonance and the measurement of the temperature coefficient of resistance were used to determine the structure and properties of the films. The degree of epitaxy of Ni increases with increasing T s as well as increasing V s . The optimum conditions for epitaxial growth of Ni are T s ⩾280°C and V s ⩾80 V. In this range epitaxial films with Ni(100) ∥ MgO(100) and Ni〈100〉 ∥ MgO〈100〉 can be prepared. A magnetic anisotropy is induced in the film plane. This anisotropy may be a result of superposition of a magnetocrystalline anisotropy originating from the epitaxial Ni film and of a uniaxial magnetic anisotropy induced during the film formation. In conclusion, as V s ranges −80 to −110 V the bombarding effect of both energetic ions and fast neutrals of Ar will rule the epitaxial growth of the Ni film by increasing the mobility of Ni adatoms and by resputtering the impurities. This effect is pronounced at T s ⩾280°C.

Microstructure and magnetic properties of a Co/Pd multilayer on a controlled Pd/Si seed layer for double-layered perpendicular magnetic recording media

A 10 nm Pd/Si dual thin film was developed as a seed layer for a Co/Pd multilayer in double-layered perpendicular magnetic recording media. The Pd/Si seed layer, sputter deposited under Ar sputtering gas containing N2 and postannealed at 400 °C, markedly reduced intergranular exchange coupling of the Co/Pd multilayered film, resulting in a decrease in both the slope parameter, defined as 4π(dM/dH)H=Hc, and the magnetic cluster size. Consequently, medium noise was essentially reduced, thereby improving the signal-to-noise ratio of the Co/Pd recording media on a CoZrNb soft magnetic underlayer. The addition of N2 gas effectively decreased the grain size of Pd in the seed layer. A Pd/Si seed layer prepared with both processes exhibited a granular structure of fine Pd-rich grains surrounded by a Si-rich amorphous region, which provided nucleation sites for the growth of well-separated Co/Pd multilayered grains.

Hysteresis of the phase transformation detected by galvanomagnetic measurements of Ag2Se layers

Temperature dependence of the resistivity, carrier concentration, and carrier mobility have been investigated in vacuum deposited Ag2Se thin layers. Properties of silver selenide layers developed by the reaction of poly‐ and monocrystalline parent Ag films and selenium on NaCl substrates in identical circumstances have been described and compared with one another. Experimental evidences of the hysteresis of the electrical properties due to the reversible first order transformation have been found during heating and cooling cycles. Irreversible changes of these properties in the semiconductor phase were detected.

TEM study of Ag2Se developed by the reaction of polycrystalline silver films and selenium

The formation of Ag 2 Se phase has been studied in the case of high-temperature successive deposition of polycrystalline silver thin films and selenium. It is the first time that the formation of very large Ag 2 Se single crystals of (001) orientation on polycrystalline Ag films are observed and discussed. Continuous 35 nm thick silver films prepared on amorphous substrates have been reacted with various amounts of selenium at different substrate temperatures above and below the bulk polymorphic phase transition temperature of Ag 2 Se (T c = 133°C). All structural investigations were carried out on films transformed to or formed directly in the low temperature orthorhombic phase. TEM investigations revealed that the continuous Ag 2 Se layers undergoing phase transformation during cooling to room temperature consisted of large (100-300 μm) (001) oriented orthorhombic crystals of various azimuthal orientations. No preferred orientation was found in discontinuous Ag 2 Se films. Without phase transformation the orientation remained random with grain sizes below 1 μm. Strong thickness fluctuations showing up in the form of island-channel-like morphology within the Ag 2 Se crystallites has been observed in all continuous layers. The formation of large (001) oriented single crystals is proposed to be related to the polymorphic phase transition from body-centred cubic to orthorhombic phase taking place during the cooling of the film after sample preparation.