Showing papers on "Evaporation (deposition) published in 2009"

A comparative analysis of deep level emission in ZnO layers deposited by various methods

Abstract: This study examined the origin of visible luminescence from ZnO layers deposited on p-Si substrates by various growth methods using temperature dependent photoluminescence measurements. The deep level emissions of ZnO layers are found to be strongly dependent on the growth conditions and growth methods used. For the samples grown by sputtering, the visible emission consisted of violet, green, and orange-red regions, which corresponded to zinc interstitial (Zni), oxygen vacancy (VO), and oxygen interstitial (Oi) defect levels, respectively. In contrast, the deep level emissions of metal organic chemical vapor deposition grown samples consisted of blue and green emissions and blue and orange-red emissions at low and high oxygen flow rates, respectively. The ZnO nanorods synthesized by thermal evaporation showed a dominant deep level emission at the green region, which is associated with oxygen vacancies (VO).

Large-area single- and few-layer graphene on arbitrary substrates

Abstract: A film of single-layer to few-layer graphene is formed by depositing a graphene film via chemical vapor deposition on a surface of a growth substrate. The surface on which the graphene is deposited can be a polycrystalline nickel film, which is deposited by evaporation on a SiO 2 /Si substrate. A protective support layer is then coated on the graphene film to provide support for the graphene film and to maintain its integrity when it is removed from the growth substrate. The surface of the growth substrate is then etched to release the graphene film and the protective support layer from the growth substrate, wherein the protective support layer maintains the integrity of the graphene film during and after its release from the growth substrate. After being released from the growth substrate, the graphene film and protective support layer can be applied onto an arbitrary target substrate for evaluation or use in any of a wide variety of applications.

BiVO4 as a Visible-Light Photocatalyst Prepared by Ultrasonic Spray Pyrolysis

Abstract: BiVO4 powders with unique particle architectures have been synthesized using ultrasonic spray pyrolysis (USP). Gases created from the evaporation of solvent and the decomposition of precursor materials shape the morphology of the particles as the solids are formed in the heated aerosol. The BiVO4 powder was tested as oxygen evolving photocatalysts by monitoring the kinetics of O2 formation from a AgNO3 solution irradiated with λ > 400 nm light. USP prepared BiVO4 was found to have significantly superior photocatalytic activity compared to commercial BiVO4 and WO3, likely due to differences in particle morphology.

Enhanced toluene sensing characteristics of TiO2-doped flowerlike ZnO nanostructures

Abstract: The large-scale flowerlike ZnO nanostructures, consisting of many aggregative nanorods with the diameter of about 60 nm, were prepared by a simple and facile hydrothermal route. The toluene sensing properties of the pure ZnO and TiO 2 -doped ZnO nanostructures were tested at different operating temperatures from 160 to 390 °C and toluene concentrations ranging from 1 to 3000 ppm. The results indicate that the response of the ZnO nanostructures towards toluene was enhanced significantly by TiO 2 doping, which was deposited onto the ZnO products by evaporation. It is found that the TiO 2 -doped ZnO sensor exhibits remarkably enhanced response of 17.1 at the optimal operating temperature of 290 °C to 100 ppm toluene, which has been improved up from 7.4 at 390 °C from pure ZnO nanostructures.

Vapor−Solid Growth of One-Dimensional Layer-Structured Gallium Sulfide Nanostructures

Abstract: Gallium sulfide (GaS) is a wide direct bandgap semiconductor with uniform layered structure used in photoelectric devices, electrical sensors, and nonlinear optical applications. We report here the controlled synthesis of various high-quality one-dimensional GaS nanostructures (thin nanowires, nanobelts, and zigzag nanobelts) as well as other kinds of GaS products (microbelts, hexagonal microplates, and GaS/Ga(2)O(3) heterostructured nanobelts) via a simple vapor-solid method. The morphology and structures of the products can be easily controlled by substrate temperature and evaporation source. Optical properties of GaS thin nanowires and nanobelts were investigated and both show an emission band centered at 580 nm.

Study of molecular spin-crossover complex Fe(phen)2(NCS)2 thin films

Abstract: We report on the growth by evaporation under high vacuum of high-quality thin films of Fe(phen)2(NCS)2 (phen=1,10-phenanthroline) that maintain the expected electronic structure down to a thickness of 10 nm and that exhibit a temperature-driven spin transition. We have investigated the current-voltage characteristics of a device based on such films. From the space charge-limited current regime, we deduce a mobility of 6.5×10−6 cm2/V s that is similar to the low-range mobility measured on the widely studied tris(8-hydroxyquinoline)aluminum organic semiconductor. This work paves the way for multifunctional molecular devices based on spin-crossover complexes.

Thin-film fabrication method for organic light-emitting diodes using electrospray deposition.

Abstract: A new method for fabricating micropatterns of MEH-PPV thin films with surface roughnesses below 1nm is proposed, using electrospray deposition and a dual-solvent technique. The basic concept is that nanoparticles are deposited on the target substrate just before they become completely dry, by adding a solvent that has an evaporation speed relatively lower than that of the original solution.

Ultra-fast Microwave Synthesis of ZnO Nanowires and their Dynamic Response Toward Hydrogen Gas

Abstract: Ultra-fast and large-quantity (grams) synthesis of one-dimensional ZnO nanowires has been carried out by a novel microwave-assisted method. High purity Zinc (Zn) metal was used as source material and placed on microwave absorber. The evaporation/oxidation process occurs under exposure to microwave in less than 100 s. Field effect scanning electron microscopy analysis reveals the formation of high aspect-ratio and high density ZnO nanowires with diameter ranging from 70 to 80 nm. Comprehensive structural analysis showed that these ZnO nanowires are single crystal in nature with excellent crystal quality. The gas sensor made of these ZnO nanowires exhibited excellent sensitivity, fast response, and good reproducibility. Furthermore, the method can be extended for the synthesis of other oxide nanowires that will be the building block of future nanoscale devices.

Thick C60:ZnPc bulk heterojunction solar cells with improved performance by film deposition on heated substrates

Abstract: We study the influence of different substrate temperatures during the deposition of the ZnPc:C60 blend layer in bulk heterojunction organic solar cells. It is shown that substrate heating during evaporation leads to a significant improvement in the solar cell performance mainly due to an increase in photocurrent and fill factor (FF). This is attributed to improved morphology resulting in better charge carrier percolation pathways within the ZnPc:C60 blend, leading to reduced transport losses. Using this method, blend layer thicknesses of 150 nm are possible without loss in FF, which requires a three-dimensional interpenetrating network without isolated clusters. When heating the substrate up to 110 °C, an efficiency of 2.56% is achieved compared to 1.59% for an identical device prepared at room temperature.

In situ monitoring the drying kinetics of knife coated polymer-fullerene films for organic solar cells

Abstract: The efficiency of polymer based bulk heterojunction (BHJ) solar cells mainly depends on the film morphology of the absorption layer and the interface properties between the stacked layers. A comparative study using atomic force microscopy(AFM) and optical in situthin film drying measurements is performed. The strong impact of distinct drying scenarios on the polymer:fullerene BHJ layer morphology is investigated by AFM. The AFM images show a systematic dependency of structure sizes at the surface on drying kinetics. In addition thin film optical measurements for the determination of thin film drying kinetics and parameters are performed using a dedicated experimental setup. The data are used as the input for a quantitative simulation of the drying process. The film thickness decreases linearly during drying while the solvent mass fraction decreases moderately over a wide range until it drops rapidly. Subsequently the remaining solvent fraction evaporates considerably slower. Our work gives a fundamental understanding of the film formation kinetics and prerequisites for the systematic optimization of the film morphology in solution processed organic photovoltaic devices.

Influence of transient environmental photothermal effects on optical scattering by gold nanoparticles.

Abstract: Transient photothermal phenomena in the environment of light-absorbing plasmonic nanoparticles, heating and evaporation, were shown to influence the optical scattering efficacy of such nanoparticles, when they absorb and scatter the light. The heating of the environment suppresses the optical scattering, while the evaporation enhances the scattering by the nanoparticles. These opposite effects have transient, local, and thermal nature and significantly (more than 10 times) influence the optical contrast of the nanoparticles as shown for gold spheres in water.

Photonic metamaterials by direct laser writing

Abstract: We present a planar magnetic metamaterial fabricated using 3D direct laser writing and silver chemical vapor deposition as well as a negative-index bi-anisotropic metamaterial metallized via silver shadow evaporation. Calculations and experiments show good agreement.

Self-Assembled Organic Functional Nanotubes and Nanorods and Their Sensory Properties

Abstract: Self-assembled, one-dimensional nanostructures of N,N′-bis(2-(trimethylammonium iodide)ethylene)perylene-3,4,9,10-tetracarboxyldiimide (PTCDI-I) with tunable morphologies were successfully prepared by a facile evaporation method. PTCDI-I nanotubes with diameters of approximately 100−300 nm were obtained by the evaporation of the aqueous solution of PTCDI-I, while long nanorods with diameters of approximately 200−300 nm were produced by slow evaporation of the methanolic solution of PTCDI-I. Studies of the nanostructures formed at different stages suggested that the formation of nanotubes and nanorods could be ascribed to different crystallization processes from different solutions. The PTCDI-I nanostructures were redox-active, and four-probe measurements based on a single nanotube or nanorod exhibited resistance decreased by 2 to 3 orders of magnitude after being exposed to reducing agents such as hydrazine or phenylhydrazine. Such high resistance modulations indicate that these nanostructures will be use...

Structure of Reduced Ultrathin TiOx Polar Films on Pt(111)

Abstract: The structure of well-ordered reduced TiOx nanolayers (NLs) on Pt(111), prepared by reactive evaporation of Ti in an oxygen background and postannealed in different conditions, is discussed on the ...

Interaction of Au with CeO2(111): A photoemission study.

Abstract: We have studied the adsorption of low dimensional gold on ceria, produced by evaporation onto the surface. The interaction of gold with CeO2(111) layers was investigated with x-ray photoemission spectroscopy, ultraviolet photoemission spectroscopy, and resonant photoelectron spectroscopy (RPES). Gold was deposited in steps onto a 1.5 nm thick CeO2(111) layer epitaxially grown on a Cu(111) substrate. The RPES showed a partial Ce4+→Ce3+ reduction, observed as a resonant enhancement of the 4f level of the Ce3+ species. This can be explained by possible creation of a new Au+ ionic state. The observed effects are stronger for Au deposition at room temperature than at 250 °C. The obtained results are in agreement with already published density functional theory calculations reporting weakening of bond between the oxygen and the Ce atoms in ceria caused by the presence of gold.

Spray pyrolysis synthesis of ZnS nanoparticles from a single-source precursor

Abstract: ZnS, a II-VI semiconductor with a relatively high direct bandgap (approximately 3.6 eV) in the near-UV region, has potential applications in areas such as solar cells, lasers and displays. In addition, ZnS nanoparticles can be applied as phosphors, probes for bioimaging, emitters in light emitting diodes and photocatalysts. Here, we report synthesis of cubic ZnS nanoparticles from a low-cost single-source precursor in a continuous spray pyrolysis reactor. In this approach, the evaporation and decomposition of precursor and nucleation of particles occur sequentially. Product particles were characterized by HRTEM, XRD, and EDX. Particles with diameters ranging from 2 to 7 nm were produced. HF was used to remove ZnO impurities and other surface contamination. As-synthesized ZnS nanoparticles exhibit blue photoluminescence near 440 nm under UV excitation and have quantum yields up to 15% after HF treatment. This demonstrates a potentially general approach for continuous low-cost synthesis of semiconductor quantum dots for applications where tight control of the size distribution is less important than scalable, economical production.

Dense spinel MnCo2O4 film coating by aerosol deposition on ferritic steel alloy for protection of chromic evaporation and low-conductivity scale formation

Abstract: Conducting ceramic layers with a spinel structure of MnCo2O4 and a thickness of ~3 μm were deposited on ferritic stainless steel (SS) by aerosol deposition (AD), for use as an oxidation-resistant coating layer on the metallic interconnects of a solid oxide fuel cell (SOFC). The microstructural changes in the interface between the MnCo2O4 and SS were analyzed, as were the subsequent electrical conductivity changes at an SOFC operating temperature of 800 °C in air. The coated spinel layers were dense without pores or cracks, and maintained good adhesion even after oxidation at 800 °C for 1,000 h in air atmosphere. Close observation of the interface between the coated spinel oxide and SS substrate indicated the presence of ~1-μm thick, Cr-rich scale formation; however no MnCrCoO4 or MnCr2O4 spinel phase was detected. The area specific resistance (ASR) of the MnCo2O4-coated alloy after heat treatment at 800 °C for 1,000 h was 13.4 mΩ cm2.