Showing papers on "Evaporation (deposition) published in 2013"

Molten-salt-mediated synthesis of SiC nanowires for microwave absorption applications

Abstract: Silicon carbide (SiC) nanowires were synthesized by a reaction of multiwall carbon nanotubes (MWCNTs) and silicon vapor from molten salt medium at 1250 °C. The phase, morphology, and microstructure of the nanowires were systemically characterized by X-ray diffraction, field emission scanning electron microscopy, and high resolution transmission electron microscopy. The results revealed that the nanowires were of single-crystalline β-SiC phase with the growth direction along [111] and had diameters of 20–80 nm and lengths up to several tens of micrometers. The molten salt introduced facilitated the evaporation of Si (vapor) onto MWCNTs (solid) and the growth of SiC nanowires followed the vapor–solid process. The investigation of microwave absorbability indicated that a minimum reflection loss of −17.4 dB at 11.2 GHz could be achieved with 30 wt% SiC nanowires as the filler in the silicone matrix. The attenuation of microwave could be attributed to the dielectric loss and a possible absorption mechanism was also discussed.

Plasma‐Enhanced Atomic Layer Deposition of Ultrathin Oxide Coatings for Stabilized Lithium–Sulfur Batteries

Abstract: One of the most challenging problems in the development of lithium–sulfur batteries is polysulfide dissolution, which leads to cell overcharge and low columbic efficiency. Here, we propose the formation of a thin conformal Li-ion permeable oxide layer on the sulfur-carbon composite electrode surface by rapid plasma enhanced atomic layer deposition (PEALD) in order to prevent this dissolution, while preserving electrical connectivity within the individual electrode particles. PEALD synthesis offers a fast deposition rate combined with a low operating temperature, which allows sulfur evaporation during deposition to be avoided. After PEALD of a thin layer of aluminium oxide on the surface of electrode composed of large (ca. 10 μm in diameter) S-infiltrated activated carbon fibers (S-ACF), significantly enhanced cycle life is observed, with a capacity in excess of 600 mA·h·g−1 after 300 charge–discharge cycles. Scanning electron microscopy (SEM) shows a significant amount of redeposited lithium sulfides on the external surface of regular S-ACF electrodes. However, the PEALD alumina-coated electrodes show no lithium sulfide deposits on the fiber surface. Energy dispersive spectroscopy (EDS) studies of the electrodes’ chemical composition further confirms that PEALD alumina coatings dramatically reduce S dissolution from the cathodes by confining the polysulfides inside the alumina barrier.

Synthesis of the catalytically active Mn3O4 spinel and its thermal properties

Abstract: Tetragonal hausmannite (Mn3O4) was synthesized by pulsed-spray evaporation chemical vapor deposition (PSE-CVD) at moderate temperatures. The thermal properties of the obtained Mn3O4 thin films were evaluated with a newly developed in situ emission FTIR method. The performance of Mn3O4 grown on flexible stainless steel mesh substrates was investigated toward the oxidation of CO and C3H6. X-ray diffraction (XRD) patterns, FTIR, and Raman spectroscopy reveal that only the single-phase tetragonal Mn3O4 spinel structure was obtained within the temperature range of 350–500 °C. The as-deposited Mn3O4 is thermally stable up to 800 °C, and its reduction plays a determinant role in the catalytic process. Compared to conventional powder catalysts, the combination of PSE-CVD, in situ emission FTIR, and the flexible substrate provides a novel tool for catalyst synthesis and the evaluation of the thermal properties and catalytic performance.

Controlled production of patterns in iridescent solid films of cellulose nanocrystals

Abstract: A method to produce predefined patterns in solid iridescent films of cellulose nanocrystals (CNCs) by differential heating of aqueous CNC suspensions during film casting has been discovered. Placing materials of different temperatures beneath an evaporating CNC suspension results in watermark-like patterns of different reflection wavelength incorporated within the final film structure. The patterned areas are of different thickness and different chiral nematic pitch than the surrounding film; heating results in thicker areas of longer pitch. Thermal pattern creation in CNC films is proposed to be caused by differences in evaporation rates and thermal motion in the areas of the CNC suspension corresponding to the pattern-producing object and the surrounding, unperturbed suspension. Pattern formation was found to occur during the final stages of drying during film casting, once the chiral nematic structure is kinetically trapped in the gel state. It is thus possible to control the reflection wavelength of CNC films by an external process in the absence of additives.

Investigation of Cu(In,Ga)Se2 thin‐film formation during the multi‐stage co‐evaporation process

Abstract: In order to transfer the potential for the high efficiencies seen for Cu(In,Ga)Se2 (CIGSe) thin films from co-evaporation processes to cheaper large-scale deposition techniques, a more intricate understanding of the CIGSe growth process for high-quality material is required. Hence, the growth mechanism for chalcopyrite-type thin films when varying the Cu content during a multi-stage deposition process is studied. Break-off experiments help to understand the intermediate growth stages of the thin-film formation. The film structure and morphology are studied by X-ray diffraction and scanning electron microscopy. The different phases at the film surface are identified by Raman spectroscopy. Depth-resolved compositional analysis is carried out via glow discharge optical emission spectrometry. The experimental results imply an affinity of Na for material phases with a Cu-poor composition, affirming a possible interaction of sodium with Cu vacancies mainly via In(Ga)Cu antisite defects. An efficiency of 12.7% for vacancy compound-based devices is obtained. Copyright © 2011 John Wiley & Sons, Ltd.

Inch-Size Solution-Processed Single-Crystalline Films of High-Mobility Organic Semiconductors

Abstract: A method for continuously growing large-domain organic semiconductor crystals is developed to fabricate multi-array high-mobility organic transistors. An organic semiconductor solution is held at the edge of a moving blade to grow a large-area crystalline thin film. The continuous evaporation of the solvent at around 100 °C, while the solution is supplied at the same rate, allows the organic crystals to grow steadily on the substrate to several inches in size. The performance of the arrays of field-effect transistors based on the large-domain crystal films is excellent, with mobility of 5–10 cm2 V-1 s-1.

In situ monitoring of a flash light sintering process using silver nano-ink for producing flexible electronics

Abstract: In this work, a flash light sintering process using silver nano-inks is investigated A silver nano-ink pattern was printed on a flexible PET (polyethylene terephthalate) substrate using a gravure-offset printing system The printed silver nano-ink was sintered at room temperature and under ambient conditions using a flash of light from a xenon lamp using an in-house flash light sintering system In order to monitor the light sintering process, a Wheatstone bridge electrical circuit was devised and changes in the voltage difference of the silver nano-ink were recorded during the sintering process using an oscilloscope The sheet resistance changes during the sintering process were monitored using the in situ monitoring system devised, under various light conditions (eg light energy, on-time and off-time duration, and pulse numbers) The microstructure of the sintered silver film and the interface between the silver film and the PET substrate were observed using a scanning electron microscope, a focused ion beam and an optical microscope The electrical sheet resistances of the sintered silver films were measured using a four-point probe method Using the in situ monitoring system devised, the flash light sintering mechanism was studied for each type of light pulse (eg evaporation of organic binder followed by the forming of a neck-like junction and its growth, etc)The optimal flash light sintering condition is suggested on the basis of the in situ monitoring results The optimized flash light sintering process produces a silver film with a lower sheet resistance (095 Ω/sq) compared with that of the thermally sintered silver film (203 Ω/sq) without damaging the PET substrate or allowing interfacial delamination between the silver film and the PET substrate

PS-PVD deposition of thermal barrier coatings

Abstract: In this study, the influence of the deposition parameters on the coating structure during the ‘quasi-PVD’ process was investigated. This type of coating could be deposited at powder feed rates between 10 and 20 g/min using He/Ar plasma gasses. The microstructure of the ceramic coating obtained using these parameters is unique because the evaporation of the ceramic powder was not complete. The deposition was conducted by the LPPS-Hybrid system produced by Sulzer Metco. Rene 80 nickel superalloy was used as a base material. A Zr-modified aluminide coating deposited by the CVD (Chemical Deposition) method, and a MeCrAlY coating deposited by the APS (Air Plasma Spraying) method were used as bond coats. Metco 6700 yttria-stabilized zirconia powder was used as a coating material. An increase in the coating thickness was triggered by increasing the powder feed rate. The pressure inside the working chamber exercised a strong influence on the structure and thickness of the coatings. In coatings deposited under a pressure of 200 Pa, unevaporated powder particles were observed along with a significantly lower thickness. The same effect was rendered by decreasing the power current of the plasma gun to 1800 A. The PS-PVD method provides an alternative process to APS and EB-PVD (Electron Beam Physical Vapor Deposition) technologies.

Multi-layered mesoporous TiO2 thin films with large pores and highly crystalline frameworks for efficient photoelectrochemical conversion

Abstract: Mesoporous thin films with various compositions are unique architectures for photoelectrochemical (PEC) solar cells. In this paper, we report the synthesis of highly ordered, multi-layered, continuous mesoporous TiO2 thin films with uniform large pores, crystalline walls and tunable film thickness, via a ligand-assisted evaporation induced self assembly (EISA) method. A Ti(acetylacetone) precursor and a diblock copolymer PEO-b-PS are employed for the controlled assembly of the TiO2/template mesostructure, followed by a two-step pyrolysis that generates carbon residue as an intermediate protection layer to support the TiO2 framework and mesostructures during the crystallization. Other transition metal ion dopants (such as Cr, Ni and Co) can be facilely incorporated into the TiO2 frameworks by co-assembly of these metal acetylacetone precursors during the EISA process. The obtained TiO2 thin film possesses an ordered monoclinic mesostructure distorted from a (110)-oriented primitive cubic structure, uniform and tunable large pores of 10–30 nm, a large surface area of ∼100 m2 g−1 and a high crystallinity anatase wall. The film thickness can be well controlled from 150 nm to several microns to tune the absorption, with the capability of generating free-standing film morphologies. Furthermore, this designed architecture allows for effective post-deposition of other small-bandgap semiconductor nanomaterials inside the large, open and interconnecting mesopores, leading to significantly improved solar absorption and photoconversion. As a proof-of-concept, we demonstrate that the photoanodes made of 4.75 μm thick mesoporous TiO2 film with deposited cadmium sulfide quantum dots exhibit excellent performance in PEC water splitting, with an optimized photocurrent density of 6.03 mA cm−2 and a photoconversion efficiency of 3.9%. These multi-layered mesoporous TiO2-based thin films can serve as a unique architecture for PEC and other solar energy conversion and utilization.

Solid-State Thermal Dewetting of Just-Percolated Gold Films Evaporated on Glass: Development of the Morphology and Optical Properties

Abstract: Solid-state thermal dewetting of just-percolated gold films of nominal thicknesses in the range 10–16 nm, prepared by evaporation on glass slides and annealing, was systematically studied. The kinetics of thermal dewetting and transition from a percolated film to isolated islands were monitored using in situ transmission localized surface plasmon resonance (LSPR) spectroscopy combined with ex situ high-resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and selected-area electron diffraction (SAED) to correlate between evolution of the film morphology and development of the optical properties. Annealing at 550 °C results in transformation of the as-evaporated, percolated polycrystalline films, with mean crystallite dimensions close to the film nominal thickness, to (111) textured films comprising large separated single-crystalline islands. The dewetting scenario depends on the initial morphology of the unannealed,...

Large Area Films of Alternating Graphene–Carbon Nanotube Layers Processed in Water

Abstract: We report the preparation of hybrid paperlike films consisting of alternating layers of graphene (or graphene oxide) and different types of multiwalled carbon nanotubes (N-doped MWNTs, B-doped MWNTs, and pristine MWNTs). We used an efficient self-assembly method in which nanotubes were functionalized with cationic polyelectrolytes in order to make them dispersible in water, and subsequently these suspensions were mixed with graphene oxide (GO) suspensions, and the films were formed by casting/evaporation processes. The electronic properties of these films (as produced and thermally reduced) were characterized, and we found electrical resistivities as low as 3 × 10–4 Ω cm. Furthermore, we observed that these films could be used as electron field emission sources with extraordinary efficiencies; threshold electric field of ca. 0.55 V/μm, β factor as high as of 15.19 × 103, and operating currents up to 220 μA. These values are significantly enhanced when compared to previous reports in the literature for oth...

Toward indium-free optoelectronic devices: Dielectric/metal/dielectric alternative transparent conductive electrode in organic photovoltaic cells

Abstract: Depending on their resistivity and their transmittance, the thin films of transparent conductive oxide (TCO) are widely used in optoelectronic devices In2O3:Sn (ITO) is the most widely used TCO in optoelectronic devices As indium is scarce and ITO is limited in flexibility due to its ceramic structure, many studies have been dedicated to new transparent conductive electrodes This review article presents the state-of-the-art concerning the dielectric/metal/dielectric structures and their application as transparent electrodes in organic photovoltaic cells (OPVCs) First, TCO/Ag/TCO structures were created to achieve higher conductivity than ITO films Then others dielectrics have been used such as transition-metal oxides (WO3, MoO3, V2O5, etc), ZnS, etc Such structures exhibit excellent flexibility, high conductivity, and good transparency They can be deposited onto substrates at room temperature by simple evaporation under vacuum Moreover, it is possible to manage the anode work function through the choice of the dielectric, which can allow them to be used as cathodes or anodes and as intermediate electrodes in tandem solar cells The properties of the dielectric/metal/dielectric (D/M/D) structures depend on the thickness of the different layers The threshold thickness value of the metal film is usually around 10 nm, where the structures change from an insulating state to a highly conductive state This is attributed to the percolation of conducting metal paths The transmittance of the films increases when the metal thickness increases up to the percolation thickness, while further increase induces a decrease in transmittance Finally, the nature and the thickness of the dielectric layers can be chosen as a function of the device properties requested, which is illustrated through different examples of OPVCs

Large‐Area, Electronically Monodisperse, Aligned Single‐Walled Carbon Nanotube Thin Films Fabricated by Evaporation‐Driven Self‐Assembly

Abstract: By varying the evaporation conditions and the nanotube and surfactant concentrations, large-area, aligned single-walled carbon nanotube (SWCNT) thin films are fabricated from electronically monodisperse SWCNT solutions by evaporation-driven self-assembly with precise control over the thin film growth geometry. Tunability is possible from 0.5 μm stripes to continuous thin films. The resulting SWCNT thin films possess highly anisotropic electrical and optical properties that are well suited for transparent conductor applications.

Hydrogen gas sensor with self temperature compensation based on β-Ga2O3 thin film

Abstract: Field-effect hydrogen gas sensor devices with self-temperature compensation based on β-Ga 2 O 3 thin films were fabricated. A β-Ga 2 O 3 thin film was deposited on a sapphire substrate by gallium evaporation in oxygen plasma. The resistance between two ohmic electrodes on a β-Ga 2 O 3 thin film with a Pt gate was decreased in H 2 atmosphere. The sensor could detect 100 ppm H 2 in 20% O 2 /N 2 at 400 °C. The resistance of the device without the Pt gate electrode did not change significantly with variation in the atmospheric composition. A sensor device with self temperature compensation was constructed by the in-series connection of devices with and without gate electrodes. The output of the sensor device remained stable, even for temperature fluctuations over 100 °C in the region of approximately 400–550 °C.

Inkjet Printing of Back Electrodes for Inverted Polymer Solar Cells

Abstract: Evaporation is the most commonly used deposition method in the processing of back electrodes in polymer solar cells used in scientifi c studies. However, vacuum-based methods such as evaporation are uneconomical in the upscaling of polymer solar cells as they are throughput limiting steps in an otherwise fast roll-to-roll production line. In this paper, the applicability of inkjet printing in the ambient processing of back electrodes in inverted polymer solar cells with the structure ITO/ZnO/P3HT:PCBM/PEDOT:PSS/Ag is investigated. Furthermore, the limitation of screen printing, the commonly employed method in the ambient processing of back electrode, is demonstrated and discussed. Both inkjet printing and screen printing of back electrodes are studied for their impact on the photovoltaic properties of the polymer solar cells measured under 1000 Wm − 2 AM1.5. Each ambient processing technique is compared with evaporation in the processing of back electrode. Laser beam induced current (LBIC) imaging is used to investigate the impact of the processing techniques on the current collection in the devices. We report that inkjet printing of back electrode delivers devices having photovoltaic performance comparable to devices with evaporated back electrodes. We further confi rm that inkjet printing represent an efficient alternative to screen printing.

Oxidation of Co- and Ce-nanocoated FeCr steels: A microstructural investigation

Abstract: The effect of novel Co and Ce nanocoatings on oxidation behaviour and chromium volatilization from a commercial Fe-22Cr steel (Sanergy HT) developed for solid oxide fuel cell interconnect applications is investigated. Three different coatings (10 nm Ce, 640 nm Co and 10 nm Ce + 640 nm Co) are studied. Uncoated and nanocoated samples are exposed isothermally at 850 C in the air with 3% H2O for 168 h. The detailed microstructure of the different coatings is investigated. The surface morphology and microstructure of the oxide scales are characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and energy dispersive X-ray analysis (EDX). Cross-section TEM thin foils are prepared by using a combined FIB/SEM (focused ion beam/scanning electron microscope) instrument. A 640 nm cobalt coating strongly inhibits Cr volatilization but has only minor effects on oxidation rate. In contrast, a 10 nm Ce coating decreases the oxidation rate but has no significant effects on chromium volatilization. Combining the two coatings, i.e., applying a 640 nm Co coating on top of the 10 nm Ce, effectively reduces Cr evaporation and slows down the rate of alloy oxidation.

Temperature dependence of electrical characteristics of Pt/GaN Schottky diode fabricated by UHV e-beam evaporation

Abstract: Temperature-dependent electrical characterization of Pt/n-GaN Schottky barrier diodes prepared by ultra high vacuum evaporation has been done. Analysis has been made to determine the origin of the anomalous temperature dependence of the Schottky barrier height, the ideality factor, and the Richardson constant calculated from the I-V-T characteristics. Variable-temperature Hall effect measurements have been carried out to understand charge transport at low temperature. The modified activation energy plot from the barrier inhomogeneity model has given the value of 32.2 A/(cm2 K2) for the Richardson constant A** in the temperature range 200 to 380 K which is close to the known value of 26.4A/(cm2 K2) for n-type GaN.

High-resolution inkjet printing of electrically conducting lines of silver nanoparticles by edge-enhanced twin-line deposition

Abstract: We report a process for inkjet printing electrically continuous micron-wide lines of silver nanoparticles by exploiting edge-enhanced evaporation commonly associated with the coffee-stain effect. In situ and real-time flow observation confirmed preferential nanoparticle deposition at the contact line of printed rivulets. The resulting twin-pair of parallel continuous lines showed characteristic width (2–8 μm), height (100–300 nm), and pair spacing (100–600 μm) that depended on substrate and printing conditions in a theoretically predictable way. Thermally sintered lines were used to form rectilinear grids showing ∼5 Ω/◻ effective sheet resistance. The robustness of the deposition process was investigated, and line pathologies were found to depend on substrate surface wettability.

Enhanced visible-light-driven photocatalytic activity of mesoporous TiO2−xNx derived from the ethylenediamine-based complex

Abstract: A facile solvent evaporation induced self-assembly (SEISA) strategy was developed to synthesize mesoporous N-doped anatase TiO2 (SE-meso-TON) using a single organic complex precursor derived in situ from titanium butoxide and ethylenediamine in ethanol solution. After the evaporation of ethanol in a fume hood and subsequent calcinations at 450 °C, the obtained N-doped TiO2 (meso-TON) anatase was of finite crystallite size, developed porosity, large surface area (101 m2 g−1) and extended light absorption in the visible region. This SE-meso-TON also showed superior photocatalytic activity to the SG-meso-TON anatase prepared via sol–gel synthesis. On the basis of characterization results from XRD, XPS, N2 adsorption–desorption and ESR, the enhanced visible-light-responsive photocatalytic activity of SE-meso-TON was assigned to its developed mesoporosity and reduced oxygen vacancies.

Evaporation-induced synthesis of carbon-supported Fe3O4 nanocomposites as anode material for lithium-ion batteries

Abstract: We report the high-yield preparation of carbon-supported superparamagnetic Fe3O4 nanocomposites (C–Fe3O4-NCs) using a simple evaporation-induced method. The Fe3O4 products consist of ∼3–10 nm nanocrystals uniformly embedded in a carbon matrix to assemble nanoparticles with a size range from 40 to 80 nm. It is shown that lithium-ion batteries (LIB) assembled from heat-treated C–Fe3O4-NCs present attractive characteristics including a high specific capacity of 752 mA h g−1 at a current rate of 0.2 C for the second discharge cycle as well as good cycling performances with ∼87% retained capacity after 100 cycles.

Structural Stoichiometry and Phase Transitions of MoO 3 Thin Films for Solid State Microbatteries

Abstract: MoO 3 is a potential material because of its wide range of stoichiometry with interesting behaviour, which includes chromogenic and catalytic properties. This leads to the applications in electrochromic display devices, optical memories, gas sensors and lithium batteries. The substochiometric films MoO 3-x with oxygen deficient contain excess metal atoms which act as doping centers; these centers control the electrical and optical film properties. The orthorhombic phase ( �-MoO 3) has a layered structure, which consists of double layers of MoO 6 octahedra held together by covalent forces in the (100) and (001) directions but by Van der Waals forces in the (010) direction. There are several approaches to prepare MoO 3 thin films including sputtering, chemical vapor deposition, electro-deposition and evaporation. In particular, chemical vapor deposition has been regarded as a suitable technique which could induce a homogeneous thin film using vaporized phases. Crystalline molybdenum oxide presents either an orthorhombic structure ( �-phase) or a monoclinic structure ( �-phase) of the perovskite-like type; both structures are essentially built up of corner-sharing MoO 6 octahedra. A layered oxygen deficient orthorhombic MoO 3 (�-phase) and monoclinic MoO 3 (�-phase) are found to exhibit optical switching upon thermal, photo or electric excitations. This optical modulation (colouration/bleaching) is effectively used in many applications like smart windows, anti dazzling coatings and display devices. Thus the synthesis of large area Mo-oxide thin films by an economical route and the structure tailoring of deposited material for the end application seems to be of prime importance. This paper deals with the detailed technological aspects of properties, different structures of MoO 3for the fabrication of all solid state lithium ion batteries with wide applications of MoO 3films as electrochromic display devices and gas sensors.