Showing papers on "Evaporation (deposition) published in 2010"

Growth, thermodynamics, and electrical properties of silicon nanowires.

Abstract: 2.4. Molecular Beam Epitaxy 366 2.5. Laser Ablation 367 2.6. Silicon Monoxide Evaporation 367 3. Catalyst Materials 368 3.1. Gold as Catalyst 368 3.2. Alternative Catalyst Materials 369 3.2.1. Type-A, Au-like Catalysts 370 3.2.2. Type-B, Low Si Solubility Catalysts 371 3.2.3. Type-C, Silicide Forming Catalysts 371 4. Crystallography 372 5. Heterostructures 373 6. Surface Induced Lowering of the Eutectic Temperature 375

Buffer layers and transparent conducting oxides for chalcopyrite Cu(In,Ga)(S,Se)(2) based thin film photovoltaics : Present status and current developments

Abstract: The aim of the present contribution is to give a review on the recent work concerning Cd-free buffer and window layers in chalcopyrite solar cells using various deposition techniques as well as on their adaptation to chalcopyrite-type absorbers such as Cu(In,Ga)Se-2, CuInS2, or Cu(In,Ga)(S,Se)(2). The corresponding solar-cell performances, the expected technological problems, and current attempts for their commercialization will be discussed. The most important deposition techniques developed in this paper are chemical bath deposition, atomic layer deposition, ILGAR deposition, evaporation, and spray deposition. These deposition methods were employed essentially for buffers based on the following three materials: In2S3, ZnS, Zn1-xMgxO.

A Controllable Self-Assembly Method for Large-Scale Synthesis of Graphene Sponges and Free-Standing Graphene Films

Abstract: A simple method to prepare large-scale graphene sponges and free-standing graphene films using a speed vacuum concentrator is presented. During the centrifugal evaporation process, the graphene oxide (GO) sheets in the aqueous suspension are assembled to generate network-linked GO sponges or a series of multilayer GO films, depending on the temperature of a centrifugal vacuum chamber. While sponge-like bulk GO materials (GO sponges) are produced at 40°C, uniform free-standing GO films of size up to 9 cm 2 are generated at 80°C. The thickness of GO films can be controlled from 200 nm to 1 μm based on the concentration of the GO colloidal suspension and evaporation temperature. The synthesized GO films exhibit excellent transparency, typical fluorescent emission signal, and high flexibility with a smooth surface and condensed density. Reduced GO sponges and films with less than 5 wt% oxygen are produced through a thermal annealing process at 800 °C with H 2 /Ar flow. The structural flexibility ofthe reduced GO sponges, which have a highly porous, interconnected, 3D network, as well as excellent electrochemical properties of the reduced GO film with respect to electrode kinetics for the [Fe(CN) 6 ] 3―/4― redox system, are demonstrated.

Ultra-thin ultra-smooth and low-loss silver films on a germanium wetting layer

Abstract: We demonstrate a method to fabricate ultra-thin, ultra-smooth and low-loss silver (Ag) films using a very thin germanium (Ge) layer as a wetting material and a rapid post-annealing treatment. The addition of a Ge wetting layer greatly reduces the surface roughness of Ag films deposited on a glass substrate by electron-beam evaporation. The percolation threshold of Ag films and the minimal thickness of a uniformly continuous Ag film were significantly reduced using a Ge wetting layer in the fabrication. A rapid post-annealing treatment is demonstrated to reduce the loss of the ultra-thin Ag film to the ideal values allowed by the quantum size effect in smaller grains. Using the same wetting method, we have also extended our studies to ultra-smooth silver-silica lamellar composite films with ultra-thin Ag sublayers.

Oxide Surface Science

Abstract: Most metals are oxidized under ambient conditions, and metal oxides show interesting and technologically promising properties. This has motivated much recent research on oxide surfaces. The combination of scanning tunneling microscopy with first-principles density functional theory–based computational techniques provides an atomic-scale view of the properties of metal-oxide materials. Surface polarity is a key concept for predicting the stability of oxide surfaces and is discussed using ZnO as an example. This review also highlights the role of surface defects for surface reactivity, and their interplay with defects in the bulk, for the case of TiO2. Ultrathin metal-oxide films, grown either through reactive evaporation on metal single crystals or through oxidation of metal alloys (such as Al2O3/NiAl), have gained popularity as supports for planar model catalysts. The surface oxides that form upon oxidation on Pt-group metals (e.g., Ru, Rh, Pd, and Pt) are considered as model systems for CO oxidation.

Highly Efficient p‐i‐n and Tandem Organic Light‐Emitting Devices Using an Air‐Stable and Low‐Temperature‐Evaporable Metal Azide as an n‐Dopant

Abstract: Cesium azide (CsN3) is employed as a novel n-dopant because of its air stability and low deposition temperature. CsN3 is easily co-deposited with the electron transporting materials in an organic molecular beam deposition chamber so that it works well as an n-dopant in the electron transport layer because its evaporation temperature is similar to that of common organic materials. The driving voltage of the p-i-n device with the CsN3-doped n-type layer and a MoO3-doped p-type layer is greatly reduced, and this device exhibits a very high power efficiency (57 lm W−1). Additionally, an n-doping mechanism study reveals that CsN3 was decomposed into Cs and N2 during the evaporation. The charge injection mechanism was investigated using transient electroluminescence and capacitance–voltage measurements. A very highly efficient tandem organic light-emitting diodes (OLED; 84 cd A−1) is also created using an n–p junction that is composed of the CsN3-doped n-type organic layer/MoO3 p-type inorganic layer as the interconnecting unit. This work demonstrates that an air-stable and low-temperature-evaporable inorganic n-dopant can very effectively enhance the device performance in p-i-n and tandem OLEDs, as well as simplify the material handling for the vacuum deposition process.

Stress in Evaporated and Sputtered Thin Films – A Comparison

Abstract: Stress in thin films and heterostructures is often the cause for malfunction of respective applications, but enables also the controlled engineering of novel materials properties. In the last years considerable progress has been achieved in understanding the mechanisms for stress evolution and relaxation. Whereas originally the stress generation appeared to be strongly dependent on the chosen deposition technique, it turned out that many of the involved stress mechanisms apply independently of the deposition technique and are intrinsically determined by the growth process. A comparative review of recent results on the stress of polycrystalline and epitaxial thin films prepared by evaporation and sputtering techniques will be given. The review focuses on stress results measured in situ during the film deposition.

Multi-walled carbon nanotube-doped tungsten oxide thin films for hydrogen gas sensing.

Abstract: In this work we have fabricated hydrogen gas sensors based on undoped and 1 wt% multi-walled carbon nanotube (MWCNT)-doped tungsten oxide (WO3) thin films by means of the powder mixing and electron beam (E-beam) evaporation technique. Hydrogen sensing properties of the thin films have been investigated at different operating temperatures and gas concentrations ranging from 100 ppm to 50,000 ppm. The results indicate that the MWCNT-doped WO3 thin film exhibits high sensitivity and selectivity to hydrogen. Thus, MWCNT doping based on E-beam co-evaporation was shown to be an effective means of preparing hydrogen gas sensors with enhanced sensing and reduced operating temperatures. Creation of nanochannels and formation of p-n heterojunctions were proposed as the sensing mechanism underlying the enhanced hydrogen sensitivity of this hybridized gas sensor. To our best knowledge, this is the first report on a MWCNT-doped WO3 hydrogen sensor prepared by the E-beam method.

Thermally enhanced mechanical properties of arc evaporated Ti0.34Al0.66N/TiN multilayer coatings

Abstract: Cubic metastable Ti0.34Al0.66N/TiN multilayer coatings of three different periods, 25+50, 12+25, and 6+12 nm, and monoliths of Ti0.34Al0.66N and TiN where grown by reactive arc evaporation. Differe ...

The physical properties of SnS films grown on lattice‐matched and amorphous substrates

Abstract: The development of high-quality tin monosulphide (SnS) layers is one of the crucial tasks in the fabrication of efficient SnS-based optoelectronic devices. Reduction of strain between film and the substrate by using an appropriate lattice-matched (LM) substrate is a new attempt for the growth of high-quality layers. In this view, the SnS films were deposited on LM Al substrate using the thermal evaporation technique with a low rate of evaporation. The as-grown SnS films were characterized using appropriate techniques and the obtained results are discussed by comparing them with the properties of SnS films grown on amorphous substrate under the same conditions. From structural analysis of the films, it is noticed that the SnS films deposited on amorphous substrate have crystallites that were oriented along different directions. However, the SnS crystallites grown on Al substrate exhibited epitaxial growth along the 101] direction. Photoluminescence (PL) and Raman studies reveal that the films grown on Al substrate have better optical properties than those of the films grown on amorphous substrates. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Performance and Stability Improvement of P3HT:PCBM-Based Solar Cells by Thermally Evaporated Chromium Oxide (CrOx) Interfacial Layer

Abstract: We report on thermally evaporated chromium oxide (CrOx) as cathode interfacial layer to improve the efficiency and stability in air for the bulk heterojunction solar cells of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM). Devices with CrOx interfacial layers show higher power conversion efficiency (PCE) and stability than those without interfacial layer. Devices with CrOx show improved stability more than 100 times that of devices without interfacial layer or with LiF interfacial layer. We tentatively attributed the CrOx interfacial layer as an electronic tunneling layer for electron collection and a protective layer of Al assumably by minimizing the organic−Al interfacial areas caused by the evaporation of Al and blocking diffusion of oxygen and water.

The effect of size and size distribution on the oxidation kinetics and plasmonics of nanoscale Ag particles

Abstract: We employed a simple and effective electroless (EL) plating approach to produce silver nanoparticles (NPs) on bare silicon, on dielectric ZnO nanowires (NWs) and on Si NWs, respectively. The surface stability of the homogeneous Ag NPs formed on the ZnO NW surfaces was investigated by surface enhanced Raman spectroscopy (SERS), which show that the attachment of thiol to the Ag surface can slow down the oxidation process, and the SERS signal remains strong for more than ten days. To further examine the Ag NP oxidation process in air, the oxygen content in the silicon nanowire core/Ag sheath composites was monitored by the energy dispersive x-ray (EDX) method. The amount of oxygen in the system increases with time, indicating the silver NPs were continuously oxidized, and it is not clear if saturation is reached in this time period. To investigate the influence of the Ag NPs size distribution on the oxidation process, the oxygen amount in the NPs formed by EL deposition and e-beam (EB) evaporation on a bare silicon surface was compared. Results indicate a faster oxidation process in the EL formed Ag NPs than those produced by EB evaporation. We attribute this observation to the small diameter of the EL produced silver particles, which results in a higher surface energy.

Multiple nozzle evaporator for vacuum thermal evaporation

Abstract: Disclosed is a multiple nozzle evaporator in which a material to be evaporated in the evaporator can be deposited on a substrate with an improved efficiency of use of the material, thereby forming a large-area uniform thin film The evaporator includes a rectangular post-shaped crucible with an open top face; and a nozzle having a body portion having a rectangular post-like shape with a height smaller than that of the crucible and assembled to an upper portion of the crucible, and a plurality of evaporation tubes penetrating through the body portion between top and bottom faces of the body portion The evaporation tubes are divided into four groups of which evaporation tubes are inclined toward respective four corners of a top face of the nozzle unit An evaporated material spouts toward peripheral areas of a substrate due to the inclined evaporation tubes, thereby improving the uniformity of a thin film to be deposited and the efficiency of use of the evaporated material, and preventing condensation of the evaporated material at a spouting portion

Evaporation-Induced Crystallization of Pluronic F127 Studied in Situ by Time-Resolved Infrared Spectroscopy

Abstract: Rapid scan time-resolved infrared spectroscopy has been used to study in situ the crystallization induced by evaporation in an aqueous solution of a triblock copolymer, Pluronic F127 A droplet of the solution was cast on a silicon substrate and the evaporation followed by an infrared microscope in transmission mode The evaporation rate of water, in the last stage of the process, has been shown to be correlated to the changes in the block copolymer; four different stages can be distinguished The block copolymer passes from an amorphous micellar state in water to a partially crystallized phase in well-defined stages of the evaporation; the complete change from amorphous to crystalline state of Pluronic F127 is observed only after all water is evaporated

Growth and characterization of organometallic l-alanine cadmium chloride single crystal by slow evaporation technique

Abstract: Single crystals of l -alanine cadmium chloride (LACC), an organometallic nonlinear optical material, have been grown by the slow evaporation technique. The grown crystals were subjected to various characterization techniques, such as single crystal and powder XRD, FTIR, UV–vis and TGA-DTA. The mechanical properties of the crystals show that this material belongs to the category of hard materials. Second harmonic generation was confirmed by the Kurtz and Perry powder technique. Electrical parameters, such as dielectric constant, dielectric loss, ac and dc conductivity and their corresponding activation energies have been studied. The low dielectric constant and dielectric loss suggest that this material is a good candidate for micro-electronic applications.

Evaporation mask, method of fabricating organic electroluminescent device using the same, and organic electroluminescent device

Abstract: An evaporation mask, a method of manufacturing an organic electroluminescent device using the evaporation mask, and an organic electroluminescent device manufactured by the method are provided. The evaporation mask is formed of a thin film and is drawn taut by application of tension. The evaporation mask includes at least one mask unit, the mask unit including a plurality of main apertures, and a plurality of first dummy apertures formed adjacent to outermost ones of the main apertures in a direction in which tension is applied to the evaporation mask.

Decomposition controlled by surface morphology during langmuir evaporation of GaAs.

Abstract: When GaAs is heated in vacuum, it decomposes into Ga and As as it evaporates. Real-time in situ surface electron microscopy reveals striking bursts of “daughter” droplet nucleation and growth when coalescence of large “parent” droplets exposes nonplanar surface regions. We analyze the behavior, predicting a morphology-dependent congruent evaporation temperature. Based on this we propose a new approach for the self-assembly and positioning of quantum structures via droplet epitaxy, which we demonstrate at the proof-of-concept level.

Thermal Evaporation Synthesis and Properties of ZnO Nano/Microstructures Using Carbon Group Elements as the Reducing Agents

Abstract: ZnO nano/microstructures have been formed by thermal evaporation method using ZnO powders mixed with carbon group elements (C, Si, Ge, Sn, or Pb) as the reducing agent. For cases of mixed precursors of ZnO/C, ZnO/Si, and ZnO/Ge, the pure ZnO nano/microstructures are realized, while for ZnO/Sn (ZnO/Pb) systems, the phase of Pb2O3(Zn2SnO4) generally are represented in the ZnO products. The appearance of Pb2O3(Zn2SnO4) is attributed to the lower melting point and higher vapor pressure of Sn (Pb) in the heating and evaporation processes. The morphologies and sizes of the products are controlled by adjusting the growth regions and/or introducing gaseous argon. Room temperature (RT) photoluminescence spectra indicate that the intensity (peak position) of the ultraviolet emission is increased (redshift) due to the existence of Zn2SnO4 phase in the ZnO products. The Pb2O3(Zn2SnO4) phase in ZnO nano/microstructures plays a important role in enhancing the saturation magnetizations of RT ferromagnetism with respect to the case of pure ZnO products fabricated by the precursor of mixed ZnO and graphite.

Correlation between target surface and layer nucleation in the synthesis of Al–Cr–O coatings deposited by reactive cathodic arc evaporation

Abstract: The deposition parameters of reactive cathodic arc are correlated with processes at the surface of the composite Al–Cr targets and the nucleation and phase formation of the synthesized Al–Cr–O layers. The oxygen pressure and the pulsed operation of the arc current influence the formation of intermetallic phases and solid solutions at the target surface. The nucleation of the ternary oxide coatings at the substrate site appears to be, to some extent, controllable by the intermetallics or solid solutions formed at the target surface. A specific nucleation process at the substrate site can therefore be induced by the free choice of target composition in combination with the oxygen pressure and a pulsed arc operation. It also allows the control over the oxide island growth at the target surface which occurs occasionally at higher oxygen pressure. This hypothesis is supported by the X-ray diffraction analysis of the layers as well as of the target surface, and the layer analysis by cross-sectional scanning electron microscopy and Rutherford backscattering spectroscopy.

Thin films of polymer blends for controlled drug delivery deposited by matrix-assisted pulsed laser evaporation

Abstract: We demonstrate the use of matrix-assisted pulsed laser evaporation technique for incorporating drugs (indomethacin) within thin films of polymer blends, to be used as biodegradable implants that deliver drugs in a controlled manner. For irradiation at fluences up to 1 J/cm2, the films show excellent surface morphology and the chemical structure of all constituent polymers within the blend is well preserved. The optical characteristics of the films are assessed by spectroscopic ellipsometry. The presence of the drug within the polymeric films is confirmed by its specific absorption at 319 nm.

Electrochromic properties of nanocrystalline WO 3 thin films grown on flexible substrates by plasma-assisted evaporation technique

Abstract: Thin films of Tungsten trioxide (WO3) were deposited on ITO-coated flexible Kapton substrates by plasma-assisted activated reactive evaporation (ARE) technique. The influence of growth and microstructure on optoelectrochromic properties of WO3 thin films was studied. The nanocrystalline WO3 films grown at substrate temperature of 250°C were composed of vertically elongated cone-shaped grains of size 65 nm with relative density of 0.71. These WO3 films demonstrated higher optical transmittance of 85% in the visible region with estimated optical band gap of 3.39 eV and exhibited better optical modulation of 66% and coloration efficiency of 52.8 cm2/C at the wavelength of 550 nm.

Growth of zinc oxide nanoflowers by thermal evaporation method

Abstract: An alternative method for site-selective growth of ZnO nanostructures that does not use an Au catalyst or a ZnO thin-film seed layer is presented. Well-aligned ZnO nanoflower structure arrays were directly fabricated on silicon substrates through zinc powder evaporation, which uses a simple thermal evaporation method without a catalyst. The collected ZnO nanoflowers were then characterized through X-ray diffraction (XRD) and scanning electron microscopy (SEM). The optical properties of these nanostructured materials are also discussed.