Showing papers on "Evaporation (deposition) published in 2004"

Different origins of visible luminescence in ZnO nanostructures fabricated by the chemical and evaporation methods

Abstract: We prepared ZnO nanostructures using chemical and thermal evaporation methods. The properties of the fabricated nanostructures were studied using scanning electron microscopy, x-ray diffraction, photoluminescence, and electron paramagnetic resonance (EPR) spectroscopy. It was found that the luminescence in the visible region has different peak positions in samples prepared by chemical and evaporation methods. The samples fabricated by evaporation exhibited green luminescence due to surface centers, while the samples fabricated by chemical methods exhibited yellow luminescence which was not affected by the surface modification. No relationship was found between green emission and g∼1.96 EPR signal, while the sample with yellow emission exhibited strong EPR signal.

Ultrathin Gold Island Films on Silanized Glass. Morphology and Optical Properties

Abstract: Evaporated gold island films have been the subject of studies dealing with a variety of spectroscopic and sensing applications. Development of these and other applications requires film stability as well as tunability of the morphology and optical properties of the island films. In the present work, ultrathin, island-type gold films were prepared by evaporation of 1.0−15.0 nm (nominal thickness) gold at a rate of 0.005−0.012 nm s-1 onto glass substrates modified with 3-mercaptopropyl trimethoxysilane (MPTS), the latter used to improve the Au adhesion to the glass. The morphology of the films, either unannealed or annealed (20 h at 200 °C), was studied using atomic force microscopy (AFM) and high-resolution scanning electron microscopy (HR-SEM). The information provided by the two imaging techniques is complementary, giving a good estimate of the shape of the islands and its variation with film thickness and annealing. The optical properties of the films were examined using transmission UV−vis spectroscopy...

Room-temperature hydrogen storage characteristics of ZnO nanowires

Abstract: Massive ZnO nanowires with the mean diameter of 20 nm have been rapid synthesized by evaporation of metal zinc at 900 °C in the quartz tube. Metal catalyst, graphite additive, and vacuum are not necessary, and, more importantly, it is very convenient and effective for large-scale industrialization. The hydrogen storage characteristics of the synthesized ZnO nanowires are investigated at room temperature. The highest storage capacity of 0.83 wt% is achieved under the pressure of about 3.03 Mpa, and about 71% of the stored hydrogen can be released under ambient pressure at room temperature.

Template-induced growth of close-packed and non-close-packed colloidal crystals during solvent evaporation

Abstract: Template-induced colloidal deposition during solvent evaporation is a promising technique for extending the possibilities of nanosphere lithography and the creation of photonic band gap materials. We investigated the influence of the parameters that determine the surface topography of templates on colloidal crystal structure. On pillar-shaped templates, large defect-free square symmetric monolayers, ordered vacancy arrays, and body-centered cubic (bcc) and simple cubic (sc) colloidal crystals could be grown. Close-packed crystals displayed defects and large defect grains. Our results indicate that this may be avoided when the direction of gravity with respect to the substrate is changed.

Studies on optical and dielectric properties of Al2O3 thin films prepared by electron beam evaporation and spray pyrolysis method

Abstract: Al2O3 thin films find a number of applications in optoelectronics, sensors and tribology. In this paper, we report the preparation and characterization of alumina films prepared by both electron beam evaporation and spray pyrolysis method. The electrical properties of alumina films were determined by measuring (C–V) and (I–V) characteristics in a metal oxide semiconductor (MOS) structure. A relative dielectric constant (er) of 9.6 for spray pyrolysed films and 8.3 for evaporated films was obtained. The breakdown electric field was found to be around 5 and 1 MV/cm, respectively for spray pyrolysed and evaporated films. The refractive index of alumina films by evaporation was found to be 1.71 and 1.61 at 275 and 500 nm, respectively. The optical band gap of spray pyrolysed films deposited at 300 °C was found to be in the range of 5.40–5.55 eV. Structural, elemental analysis and stoichiometry of the films was studied by scanning electron microscope (SEM), energy dispersive X-ray analysis (EDAX), Auger electron spectroscopy (AES) and Rutherford back scattering (RBS) spectra.

Direct synthesis of single crystalline In2O3 nanopyramids and nanocolumns and their photoluminescence properties

Abstract: Single crystalline indium oxide pyramid and column structures were synthesized by a simple physical evaporation technique. The pyramid structure was obtained without any catalytic action while the column structure was produced using gold as the catalyst. The nanostructures were characterized by x-ray diffraction, scanning electron microscopy and transmission electron microscopy. A blue-green photoluminescence band in the visible region was observed in the In2O3 structures which could be ascribed to the existence of a large amount of singly ionized oxygen vacancies, confirmed by electron paramagnetic resonance.

A novel process from cobalt nanowire to Co3O4 nanotube

Abstract: Cobalt oxide (Co3O4) nanotubes were synthesized by calcining cobalt nanowires embedded in an anodic alumina template (AAT) in air. The morphologies and phases of the nanowires/nanotubes were studied by transmission electron microscope (TEM) and x-ray diffraction (XRD) respectively. A hypothesis of the tube formation process is presented and illustrated by experimental results. According to the experimental results, it is concluded that competition between the oxidation and the evaporation of cobalt nanocrystals plays a crucial role in the formation of such tube-like nanostructures of Co3O4.

Bulk synthesis of single-crystalline magnesium oxide nanotubes.

Abstract: Crystalline tubular magnesium oxide nanostructures were obtained through carbon-thermal evaporation of a MgO powder. Gallium oxide was added into the mixture of MgO and carbon. The reduction of gallium oxide by carbon resulted in gallium vapor at high temperatures. Condensed gallium droplets catalyzed the anisotropic growth of tubular MgO nanostructures in situ. The products were characterized by X-ray powder diffraction technique, scanning electron microscopy, and high-resolution microscopy. All the analyses indicated that the prepared tubular MgO nanostructures are, in fact, single crystals.

Analysis of Silicon Nanowires Grown by Combining SiO Evaporation with the VLS Mechanism

Abstract: Silicon nanowires have received increasing attention as potential building blocks for nanoscale devices. We report the growth and analysis of silicon nanowires consisting of a crystalline silicon core and a thick oxide shell, which were grown by evaporation of silicon monoxide (SiO) in an inert gas atmosphere using a gold-coated silicon wafer as a substrate. This method combines SiO evaporation with the vapor-liquid-solid (VLS) nanowire growth mechanism. The resulting nanowires were analyzed using scanning electron microscopy, transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDXS). The thick oxide shell was determined to be the product of the SiO evaporation and subsequent phase separation into Si and SiO 2 . The EDXS measurements confirmed the silicon core/oxide shell structure of the nanowires and the existence of a gold dot on the nanowire tip as required by the VLS mechanism. An explanation is proposed for growth of the nanowires by combination of the VLS mechanism and SiO disproportionation. High-resolution TEM micrographs show the crystalline structure of the nanowire silicon core. Some of the nanowires were found to show an oscillation in diameter.

Evaporation of Y-Si-O films for medium-K dielectrics

Abstract: A gate oxide and method of fabricating a gate oxide that produces a more reliable and thinner equivalent oxide thickness than conventional SiO 2 gate oxides are provided. Gate oxides formed from yttrium, silicon, and oxygen are thermodynamically stable such that the gate oxides formed will have minimal reactions with a silicon substrate or other structures during any later high temperature processing stages. The process shown is performed at lower temperatures than the prior art, which inhibits unwanted species migration and unwanted reactions with the silicon substrate or other structures. Using a thermal evaporation technique to deposit the layer to be oxidized, the underlying substrate surface smoothness is preserved, thus providing improved and more consistent electrical properties in the resulting gate oxide.

Large-scale growth of In2O3 nanowires and their optical properties

Abstract: Large-scale single-crystalline In2O3 nanowires were successfully synthesized by a simple physical evaporation method at 950 °C. The as-synthesized products, characterized by XRD, SEM and TEM, are pure, structurally uniform and single crystalline with typical diameters of 10–100 nm and lengths of up to a few hundreds of micrometres. Two strong and wide violet emission bands centred at 388 and 401 nm are observed in the room-temperature photoluminescence measurements and their mechanism is discussed.

Synthesis and luminescent property of single-crystal ZnO nanobelts by a simple low temperature evaporation route

Abstract: Large-scale ZnO nanobelts in aligned fashion have been prepared via a simply conducted low temperature evaporation route using the oxidization of metallic zinc plates at 450±10 °C under ambient pressure. The produced nanobelt array has been structurally characterized by powder X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy (TEM). The microscope images show that the nanobelts are about 120-micron long, ranging on average from 80 to 160 micron, with about 30 nm in thickness. In addition to XRD, high-resolution TEM images and electron-diffraction patterns show that the nanobelts are single crystalline with wurtzite structure and mostly grow along the [0001] direction. The photoluminescence spectra of the single nanobelts show that the nanobelts have a dominant near-band-edge emission at about 388 nm with a very weak defect emission band centered at about 514 nm.

Charged clusters in thin film growth

Abstract: A cauliflower structure is a granular film composed of spherical particles similar in size, each with numerous nanoscale nodules on its surface. The structure is produced during certain chemical vapour deposition (CVD) processes for diamond and silicon thin film growth. A classical account in terms of atomic unit deposition fails to explain the growth of such a cauliflower structure, as it requires a gas phase of much higher supersaturation than for onset of diffusion controlled growth. Another interesting and somewhat puzzling phenomenon encountered during a diamond CVD process is that while diamond is depositing on a graphite substrate, carbon atoms in the graphite itself are etched away into the vapour phase; that is, experience evaporation. Again, an elementary kinetic barrier mechanism fails to explain such CVD deposition of a less stable diamond phase combined with simultaneous evaporation of a stable graphite phase. In order to account for such puzzling CVD phenomena and others, a theory o...

Growth of Ternary Oxide Nanowires by Gold-Catalyzed Vapor-Phase Evaporation

Abstract: Zn2SnO4 nanowires and Zn2SnO4 diameter-modulated (DM) nanowires were successfully synthesized, accompanied by the formation of ZnO nanowires, via the thermal evaporation of a mixture of ZnO and SnO2 powders, using gold as a catalyst. Their morphologies and structures were characterized by scanning electron microscopy, X-ray spectroscopy, and high-resolution transmission electron microscopy. The ZnO nanowires were single crystalline, with an axis of [0110], which is different from the conventional [0001] orientation and might be determined by the vapor components involved in the reaction. Zn2SnO4 nanowires and Zn2SnO4 DM nanowires were single crystalline, with [302] and [111] growth directions, respectively. A vapor−liquid−solid (VLS) growth mechanism is proposed, to interpret the growth of nanowires in the experiment. In regard to the formation of Zn2SnO4 DM nanowires, we suggest that the disturbance of vapor concentration is a major factor that changes the size of the catalyst alloy droplets and the gro...

Thin films of synthetic melanin

Abstract: We have developed a new synthetic route to melanin, using different organic solvents, namely dimethyl sulfoxide and N , N -dimethyl formamide. Contrary to conventional water based melanin thin films can be made with organic solvents. Thin films were made either by room temperature solvent evaporation (casting) or using spin coating. X-ray diffraction, thermogravimetry, infrared transmission spectroscopy, UV–VIS transmission spectroscopy, electron spin resonance, atomic force microscopy (AFM) and temperature dependent conductivity have been used to characterize the material obtained. The new synthetic material is found to be similar to melanin made in water, however with an increase in thermal stability. AFM results shows that the thin films are made of graphitic-like planar structures, with root mean square roughness of ∼0.3 nm, separated by steps ranging from 1 to 3 nm in height. These sheets have lateral extensions of several microns, which make this new material potentially interesting as a 2D organic polymer.

Deposition of biopolymer thin films by matrix assisted pulsed laser evaporation

Abstract: We report on the successful deposition of high quality type I fibrilar collagen thin films by Matrix assisted pulsed laser evaporation (MAPLE). Thin films deposition was performed in a N2 ambient (20 Pa) using a KrF* laser source (λ=248 nm,τ≥20 ns) operated at a repetition rate of 3 Hz, the incident laser energy at a value within the range (20-35) mJ , and the laser spot area was (3.5-18.5)±0.1 mm2. The collagen films were deposited on double face polished 〈100〉 single crystalline Si wafers and characterized by Fourier transform infrared spectroscopy, atomic force microscopy and high-resolution transmission electron microscopy. We demonstrate that our thin films are composed of collagen, with no impurities and the roughness can be controlled by the deposition conditions.

Cathodic arc evaporation of (Ti,Al)N coatings and (Ti,Al)N/TiN multilayer-coatings—correlation between lifetime of coated cutting tools, structural and mechanical film properties

Abstract: (Ti,Al)N and (Ti,Al)N/TiN multi-layer coatings were deposited by cathodic arc evaporation with a large area TiAl and/or Ti cathode. The ratio of Ti/Al varied between 50/50, 40/60 and 33/67. The goal was to determine the influence of the bias voltage, which varied between −30 and −125 V, on the lifetime of coated cutting tools under drilling conditions. Film orientation and compressive stress were determined by X-ray diffraction. The chemical composition of the coatings was investigated by secondary-neutral-mass spectrometry (SNMS). It was found, that in the multi-layer coatings, there is a transition in the texture from 〈2 0 0〉 to 〈1 0 0〉 with increasing negative bias voltage, beginning at approximately −75 V, while the monolayer retained 〈2 0 0〉 orientation. The stress in the monolayers reached a maximum at a bias voltage approximately −100 V. Rockwell and Scratch tests show excellent adhesion on carbide and steel materials. Multilayer tool lifetime reached a maximum at −100 V, while the monolayer coated tool life increased monotonically with negative bias.

Development of novel coating technology by vacuum arc with rotating cathodes for industrial production of nc-(Al1-xTix)N/a-Si3N4 superhard nanocomposite coatings for dry, hard machining

Abstract: The development of novel superhard nanocomposite, nano-layered coatings and of the coating technology based on vacuum arc evaporation from rotating electrodes is summarized The nc-Al1-xTi x N/a-Si3N4 coatings in which the nanocrystals of the Al-rich solid solution with the fcc crystal structure of TiN are imbedded into a thin matrix of amorphous silicon nitride show high thermal stability, oxidation resistance and excellent performance in dry, fast machining that is superior to the state-of-the-art (Ti1-xAl x )N coatings

Indium-assisted synthesis on GaN nanotubes

Abstract: Gallium nitride (GaN) nanotubes in a high yield were synthesized by a simple indium-assisted thermal evaporation method in the presence of NH3 gas flowing. A vapor–liquid–solid process was proposed for formation of the GaN nanotubes. The synthesized GaN nanotubes were amorphous and partially filled with indium, several micrometers in length, 40–50 nm in outer diameter, and 7 nm for the tube wall thickness. The representative photoluminescence spectrum at room temperature exhibits a great shift from the band gap of 3.40 eV (365 nm) of bulk GaN to high energy of 3.63 eV (342 nm). The synthetic route for the GaN nanotubes is simple and effective, and could provide great opportunities for both fundamental and technological applications.