Showing papers on "Chemical vapor deposition published in 2006"

New Benchmark for Water Photooxidation by Nanostructured α-Fe2O3 Films

Abstract: Thin films of silicon-doped Fe2O3 were deposited by APCVD (atmospheric pressure chemical vapor deposition) from Fe(CO)5 and TEOS (tetraethoxysilane) on SnO2-coated glass at 415 °C. HRSEM reveals a highly developed dendritic nanostructure of 500 nm thickness having a feature size of only 10−20 nm at the surface. Real surface area determination by dye adsorption yields a roughness factor of 21. XRD shows the films to be pure hematite with strong preferential orientation of the [110] axis vertical to the substrate, induced by silicon doping. Under illumination in 1 M NaOH, water is oxidized at the Fe2O3 electrode with higher efficiency (IPCE = 42% at 370 nm and 2.2 mA/cm2 in AM 1.5 G sunlight of 1000 W/m2 at 1.23 VRHE) than at the best reported single crystalline Fe2O3 electrodes. This unprecedented efficiency is in part attributed to the dendritic nanostructure which minimizes the distance photogenerated holes have to diffuse to reach the Fe2O3/electrolyte interface while still allowing efficient light abso...

Translucent thin film Fe2O3 photoanodes for efficient water splitting by sunlight: nanostructure-directing effect of Si-doping.

Abstract: Thin, silicon-doped nanocrystalline α-Fe2O3 films have been deposited on F-doped SnO2 substrates by ultrasonic spray pyrolysis and chemical vapor deposition at atmospheric pressure. The photocatalytic activity of these films with regard to photoelectrochemical water oxidation was measured at pH 13.6 under simulated AM 1.5 global sunlight. The photoanodes prepared by USP and APCVD gave 1.17 and 1.45 mA/cm2, respectively, at 1.23 V vs RHE. The morphology of the α-Fe2O3 was strongly influenced by the silicon doping, decreasing the feature size of the mesoscopic film. The silicon-doped α-Fe2O3 nano-leaflets show a preferred orientation with the (001) basal plane normal to the substrate. The best performing photoanode would yield a solar-to-chemical conversion efficiency of 2.1% in a tandem device using two dye-sensitized solar cells in series.

Ultralow surface recombination of c-Si substrates passivated by plasma-assisted atomic layer deposited Al2O3

Abstract: Excellent surface passivation of c-Si has been achieved by Al2O3 films prepared by plasma-assisted atomic layer deposition, yielding effective surface recombination velocities of 2 and 13cm∕s on low resistivity n- and p-type c-Si, respectively. These results obtained for ∼30nm thick Al2O3 films are comparable to state-of-the-art results when employing thermal oxide as used in record-efficiency c-Si solar cells. A 7nm thin Al2O3 film still yields an effective surface recombination velocity of 5cm∕s on n-type silicon.

Gas sensor array based on metal-decorated carbon nanotubes.

Abstract: Here we demonstrate design, fabrication, and testing of electronic sensor array based on single-walled carbon nanotubes (SWNTs). Multiple sensor elements consisting of isolated networks of SWNTs were integrated into Si chips by chemical vapor deposition (CVD) and photolithography processes. For chemical selectivity, SWNTs were decorated with metal nanoparticles. The differences in catalytic activity of 18 catalytic metals for detection of H2, CH4, CO, and H2S gases were observed. Furthermore, a sensor array was fabricated by site-selective electroplating of Pd, Pt, Rh, and Au metals on isolated SWNT networks located on a single chip. The resulting electronic sensor array, which was comprised of several functional SWNT network sensors, was exposed to a randomized series of toxic/combustible gases. Electronic responses of all sensor elements were recorded and the sensor array data was analyzed using pattern-recognition analysis tools. Applications of these small-size, low-power, electronic sensor arrays are...

Fabrication and microwave absorption of carbon nanotubes/CoFe2O4 spinel nanocomposite

Abstract: A large-scale carbon nanotube∕CoFe2O4 (CNTs∕CoFe2O4) spinel nanocomposite has been fabricated by a chemical vapor deposition method using CoFe2O4 nanoparticles as catalysts. A uniform mixture of CNTs and CoFe2O4 nanoparticles was obtained simultaneously. The structure and chemical composition of the product were investigated using various techniques, such as x-ray diffraction, high-resolution transmission electron microscopy, and electron energy loss spectroscopy. It was found that the particles functionalized on CNTs were cubic phase CoFe2O4. Microwave absorption of the CNT∕CoFe2O4 nanocomposites at 2–18 GHz is evidently enhanced, as compared with that of both pure CNTs and CoFe2O4 nanoparticles. The enhancement mechanism is discussed based on magnetization hysteresis loop measurement and electromagnetic theory.

Single-walled carbon nanotube growth from highly activated metal nanoparticles.

Abstract: We demonstrate that any metal, even gold, silver, and copper, can act as a catalyst for SWCNT synthesis in chemical vapor deposition (CVD). Metal nanoparticles 3 nm or less in diameter, introduced into CVD ambience immediately after heat treatment at 800-950 degrees C in air, produce SWCNTs. The activation method is effective for copper and various noble metals as well as for iron-family elements. This implies that any metal particle may produce SWCNTs when its size becomes 1-3 nm. In other words, carbon atoms can form SWCNTs in a self-assembling fashion on nanoparticles without the specific functions of iron-family elements.

Gas diffusion barriers on polymers using Al2O3 atomic layer deposition

Abstract: Thin films of Al2O3 grown by atomic layer deposition (ALD) were investigated as gas diffusion barriers on flexible polyethylene naphthalate and Kapton® polyimide substrates Al2O3 ALD films with thicknesses of 1–26nm were grown at 100–175°C For Al2O3 ALD films with thicknesses ⩾5nm, oxygen transmission rates were below the MOCON instrument test limit of ∼5×10−3cc∕m2∕day Applying a more sensitive radioactive tracer method, H2O-vapor transmission rates of ∼1×10−3g∕m2∕day were measured for single-sided Al2O3 ALD films with thicknesses of 26nm on the polymers Ultrathin gas diffusion barriers grown by Al2O3 ALD may enable organic displays and electronics on permeable, flexible polymer substrates

Iron oxide particles are the active sites for hydrogen peroxide sensing at multiwalled carbon nanotube modified electrodes.

Abstract: We demonstrate that the "electrocatalytic" hydrogen peroxide detection reported at multiwalled carbon nanotube modified electrodes is due to iron oxide particles arising from the chemical vapor deposition nanotube fabrication process rather than due to intrinsic catalysis attributable to the carbon nanotubes arising, for example, from edge plane-like sites/defects.

Initiated Chemical Vapor Deposition (iCVD) of Poly(alkyl acrylates): An Experimental Study

Abstract: In a two-part investigation, an experimental study and a kinetic model analysis of the initiated chemical vapor deposition (iCVD) of alkyl acrylate polymers are described. In this first part, an experimental study was performed to look at the effect of process parameters on iCVD polymerization. A homologous series of alkyl acrylates, from ethyl up to hexyl acrylate, were iCVD polymerized. The resulting polymers matched well spectroscopically with those from liquid-phase polymerization, demonstrating that stoichiometric polymers with no observable cross-linking can be achieved in a chemical vapor deposition environment. Deposition rate and molecular weight increased by a factor of over 300 and 60, respectively, when monomer saturated vapor pressure, Psat, was reduced from 42.6 to 0.584 Torr at equal gas pressures, PM. Over three times increase in deposition rate was observed for ethyl acrylate when substrate temperature was reduced from 29 to 17 °C. These trends are attributed to an increase in PM/Psat or,...

ZnO light-emitting diode grown by plasma-assisted metal organic chemical vapor deposition

Abstract: We report a breakthrough in fabricating ZnO homojunction light-emitting diode by metal organic chemical vapor deposition. Using NO plasma, we are able to grow p-type ZnO thin films on n-type bulk ZnO substrates. The as-grown films on glass substrates show hole concentration of 1016–1017cm−3 and mobility of 1–10cm2V−1s−1. Room-temperature photoluminescence spectra reveal nitrogen-related emissions. A typical ZnO homojunction shows rectifying behavior with a turn-on voltage of about 2.3V. Electroluminescence at room temperature has been demonstrated with band-to-band emission at I=40mA and defect-related emissions in the blue-yellow spectrum range.

Treatment processes for a batch ald reactor

Abstract: Embodiments of the invention provide treatment processes to reduce substrate contamination during a fabrication process within a vapor deposition chamber. A treatment process may be conducted before, during, or after a vapor deposition process, such as an atomic layer deposition (ALD) process. In one example of an ALD process, a process cycle, containing an intermediate treatment step and a predetermined number of ALD cycles, is repeated until the deposited material has a desired thickness. The chamber and substrates may be exposed to an inert gas, an oxidizing gas, a nitriding gas, a reducing gas, or plasmas thereof during the treatment processes. In some examples, the treatment gas may contain ozone, water, ammonia, nitrogen, argon, or hydrogen. In one example, a process for depositing a hafnium oxide material within a batch process chamber includes a pretreatment step, an intermediate step during an ALD process, and a post-treatment step.

Quantum confinement effect in crystalline silicon quantum dots in silicon nitride grown using SiH4 and NH3

Abstract: Crystalline silicon quantum dots (Si QDs) were spontaneously grown in the silicon nitride films by plasma-enhanced chemical vapor deposition using SiH4 and NH3 as precursors. When the size of the Si QDs was reduced from 4.9 to 2.9nm, the photoluminescence peak energy was shifted from 1.73 to 2.77eV. The photoluminescence peak energy was fitted to the relationship, E(eV)=1.13+13.9∕d2, where d is the diameter of the Si QD in nanometers. The measured band-gap energies of the Si QDs were in good agreement with the quantum confinement model for crystalline Si QDs. These results suggest that the hydrogen dissociated from NH3 plays an important role in improving the crystallinity and surface passivation of Si QDs.

Effect of Nd dopant on magnetic and electric properties of BiFeO3 thin films prepared by metal organic deposition method

Abstract: Polycrystalline Bi1−xNdxFeO3 (x=0–0.15) thin films were prepared on (111) Pt∕Ti∕SiO2∕Si substrates via metal organic deposition method. The effect of Nd dopant on the structural, electric, and magnetic properties was studied. It was found that the ferroelectric polarization and saturation magnetization of the films were enhanced by appropriate Nd doping due to the structural distortion and the suppressed cycloidal spin structure. Meanwhile, Nd-doped BiFeO3 thin films exhibited magnetic anisotropy because of the magnetocrystalline anisotropy.

Oxidative Chemical Vapor Deposition of Electrically Conducting Poly(3,4-ethylenedioxythiophene) Films

Abstract: An oxidative chemical vapor deposition (CVD) process is presented as an alternative to conventional solution-based processing of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films. This solventless technique yields PEDOT with higher conductivities and conformally coats fibers and other high area morphologies, important for enhancing efficiencies in some organic electronic devices. The CVD method eliminates corrosive poly(styrenesulfonate) that is used to disperse PEDOT in an aqueous suspension for solution-based processing. A mechanistic approach is presented that favors the deposition of the conjugated, conducting form of PEDOT. We achieved conductivities as high as 105 S/cm and demonstrated films about 100 nm thick that do not crack upon bending and are more than 84% transparent to visible light. The compatibility of oxidative CVD deposition of PEDOT is demonstrated on silicon, glass, plastic, and paper substrates.

Processing and Applications of Aerosol‐Assisted Chemical Vapor Deposition

Abstract: The aerosol-assisted (AA) CVD method involves the atomization of a precursor solution into fine, sub-micrometer-sized aerosol droplets which are delivered to a heated reaction zone and undergo evaporation, decomposition, and homogeneous and/or heterogeneous chemical reactions to form the desired products. As a variant of conventional CVD processes, AACVD addresses the availability and delivery problems of the chemical precursors. A wide range of precursors can be used since volatility is no longer crucial, offering more possibilities to produce high-quality CVD products at low cost. Some variants of AACVD have also been developed, such as AA combustion (C) CVD, electrostatic spray-assisted vapor deposition (ESAVD), and electrostatic-assisted aerosol jet deposition (EAAJD). These variants provide additional flexibility and capability to the AACVD-based processes. AACVD-based processes have attracted increasing interest in most of the CVD-related areas, and have been widely used to synthesize various films, coatings, powders, composites, nanotubes and nanowires, etc. This review highlights the principles, applications, and recent progress of AACVD-based processes.

Nanoscopic wire-based devices and arrays

Abstract: Electrical devices comprised of nanoscopic wires are described, along with methods of their manufacture and use. The nanoscopic wires can be nanotubes, preferably single-walled carbon nanotubes. They can be arranged in crossbar arrays using chemically patterned surfaces for direction, via chemical vapor deposition. Chemical vapor deposition also can be used to form nanotubes in arrays in the presence of directing electric fields, optionally in combination with self-assembled monolayer patterns. Bistable devices are described.

Principles and applications of CVD powder technology

Abstract: Chemical vapor deposition (CVD) is an important technique for surface modification of powders through either grafting or deposition of films and coatings. The efficiency of this complex process primarily depends on appropriate contact between the reactive gas phase and the solid particles to be treated. Based on this requirement, the first part of this review focuses on the ways to ensure such contact and particularly on the formation of fluidized beds. Combination of constraints due to both fluidization and chemical vapor deposition leads to the definition of different types of reactors as an alternative to classical fluidized beds, such as spouted beds, circulating beds operating in turbulent and fast-transport regimes or vibro-fluidized beds. They operate under thermal but also plasma activation of the reactive gas and their design mainly depends on the type of powders to be treated. Modeling of both reactors and operating conditions is a valuable tool for understanding and optimizing these complex processes and materials. In the second part of the review, the state of the art on materials produced by fluidized bed chemical vapor deposition is presented. Beyond pioneering applications in the nuclear power industry, application domains, such as heterogeneous catalysis, microelectronics, photovoltaics and protection against wear, oxidation and heat are potentially concerned by processes involving chemical vapor deposition on powders. Moreover, simple and reduced cost FBCVD processes where the material to coat is immersed in the FB, allow the production of coatings for metals with different wear, oxidation and corrosion resistance. Finally, large-scale production of advanced nanomaterials is a promising area for the future extension and development of this technique.

The role of nitrogen doping on the development of visible light-induced photocatalytic activity in thin TiO2 films grown on glass by chemical vapour deposition

Abstract: A brief review of the findings of a range of studies aimed at describing the influence of the N-doping of TiO2 thin films and particles on possible visible light induced photoactivity is presented. By way of a new approach to the direct growth of N-doped TiO2 thin films, the physical and photochemical effects of the addition of ammonia during atmospheric chemical vapour deposition (CVD) growth of TiO2 are described. It is found that the addition of ammonia to the CVD reactive gas mixture causes a dramatic change in film morphology and a reduction in growth rates. In addition, it is found that although we have clear evidence for the incorporation of ?O-substitutional N atoms within the growing film, there is no evidence of any appreciable photocatalytic activity of the doped TiO2 films when irradiated with visible light. In fact the degradation in film morphology results in a decrease in conventional uv-induced photoactivity as compared to that for an undoped film. These findings are discussed in terms of the findings of other studies of N-doped TiO2 films that have been reported.

Influence of the Al distribution on the structure, elastic properties, and phase stability of supersaturated Ti1- xAlxN

Abstract: Ti1−xAlxN films and/or their alloys are employed in many industrial applications due to their excellent mechanical and thermal properties. Synthesized by plasma-assisted vapor deposition, Ti1−xAlxN is reported to crystallize in the cubic NaCl (c) structure for AlN mole fractions below 0.4–0.91, whereas at larger Al contents the hexagonal ZnS-wurtzite (w) structure is observed. Here we use ab initio calculations to analyze the effect of composition and Al distribution on the metal sublattice on phase stability, structure, and elastic properties of c-Ti1−xAlxN and w-Ti1−xAlxN. We show that the phase stability of supersaturated c-Ti1−xAlxN not only depends on the chemical composition but also on the Al distribution of the metal sublattice. An increase of the metastable solubility limit of AlN in c-Ti1−xAlxN from 0.64 to 0.74 is obtained by decreasing the number of Ti–Al bonds. This can be understood by considering the Al distribution induced changes of the electronic structure, bond energy, and configuration...

Effect of Graphitization on the Wettability and Electrical Conductivity of CVD-Carbon Nanotubes and Films

Abstract: The use of carbon nanomaterials in various applications requires precise control of their surface and bulk properties. In this paper, we present a strategy for modifying the surface chemistry, wettability, and electrical conductivity of carbon tubes and films through annealing in a vacuum. Experiments were conducted with 60−300 nm nanotubes (nanopipes), produced by noncatalytic chemical vapor deposition (CVD) in a porous alumina template, and with thin films deposited by the same technique on a glassy carbon substrate having the same structure and chemistry of the CNTs. The surface of the as-produced CVD-carbon, treated with sodium hydroxide to remove the alumina template, is hydrophilic, and the bulk electrical conductivity is lower by a factor of 20 than that of fully graphitic multiwalled nanotubes (MWNT) or bulk graphite. The bulk electrical conductivity increases to the conductivity of graphite after annealing at 2000 °C in a high vacuum. The analysis of CNTs by transmission electron microscopy (TEM)...

Vapor deposition of metal carbide films

Abstract: Methods of forming metal carbide thin films are provided. According to preferred embodiments, metal carbide thin films are formed in an atomic layer deposition (ALD) process by alternately and sequentially contacting a substrate in a reaction space with spatially and temporally separated vapor phase pulses of a metal source chemical, a reducing agent and a carbon source chemical. The reducing agent is preferably selected from the group consisting of excited species of hydrogen and silicon-containing compounds.

Method for fabricating an ultralow dielectric constant material as an intralevel or interlevel dielectric in a semiconductor device and electronic device made

Abstract: A method for fabricating a thermally stable ultralow dielectric constant film comprising Si, C, O and H atoms in a parallel plate chemical vapor deposition process utilizing a plasma enhanced chemical vapor deposition (“PECVD”) process is disclosed. Electronic devices containing insulating layers of thermally stable ultralow dielectric constant materials that are prepared by the method are further disclosed. To enable the fabrication of a thermally stable ultralow dielectric constant film, specific precursor materials are used, such as, silane derivatives, for instance, diethoxymethylsilane (DEMS) and organic molecules, for instance, bicycloheptadiene and cyclopentene oxide.

Zinc oxide thin films prepared by thermal evaporation deposition and its photocatalytic activity

Abstract: Thin zinc oxide (ZnO) films have been grown on silicon substrates by thermal physical vapor deposition approach. X-ray diffraction (XRD) analyses reveal that the deposited films are polycrystalline ZnO phase. Atomic force microscopy images (AFM) show needle-like shape highly oriented ZnO crystals. Thin film thickness ranges from 10 to 80 nm. X-ray photoelectron spectroscopy (XPS) results declare that the films compose mainly of Zn and O. Nevertheless, Si is not detected in the films and consequently no possibility of any silicide formation as is confirmed by XRD analysis. Photocatalytic decomposition of azo-reactive dye on ZnO films is tested. The results show that the dye decomposition efficiency increases with decreasing pH. Maximum photodecomposition, 99.6% is obtained at pH 2 with 10 mg/l dye concentration.

Low zirconium, hafnium-containing compositions, processes for the preparation thereof and methods of use thereof

Abstract: This invention relates to hafnium-containing compositions having a zirconium concentration of less than about 500 parts per million, a process for producing the hafnium-containing compositions, organometallic precursor compositions containing a hafnium-containing compound and having a zirconium concentration of less than about 500 parts per million, a process for producing the organometallic precursor compositions, and a method for producing a film or coating from the organometallic precursor compositions. The organometallic precursor compositions are useful in semiconductor applications as chemical vapor deposition (CVD) or atomic layer deposition (ALD) precursors for film depositions.

Piezoelectric properties of polycrystalline AlN thin films for MEMS application

Abstract: The piezoelectric coefficient d 33eff of aluminium nitride thin films was measured using both, the piezoresponse force microscopy and an interferometric technique. Wurtzite AlN thin films were prepared on Si (1 1 1) substrates by reactive dc-sputtering and by metal organic chemical vapor deposition (MOCVD). Direct measurements of the inverse piezoelectric effect in the picometer range showed that the acceptable tolerance in the crystal orientation is much larger for MEMS applications than expected previously. The value of the effective piezoelectric coefficient d 33 for the prepared AlN thin films remained as high as 5.1 pm/V even for lower degrees of texture.