Showing papers on "Chemical vapor deposition published in 2005"
TL;DR: By controlling various aspects of nanowire growth, these methods will enable their efficient and economical incorporation into devices to enable their practical integration into devices.
Abstract: Silicon nanowires were synthesized, in a controlled manner, for their practical integration into devices. Gold colloids were used for nanowire synthesis by the vapor−liquid−solid growth mechanism. Using SiCl4 as the precursor gas in a chemical vapor deposition system, nanowire arrays were grown vertically aligned with respect to the substrate. By manipulating the colloid deposition on the substrate, highly controlled growth of aligned silicon nanowires was achieved. Nanowire arrays were synthesized with narrow size distributions dictated by the seeding colloids and with average diameters down to 39 nm. The density of wire growth was successfully varied from ∼0.1−1.8 wires/μm2. Patterned deposition of the colloids led to confinement of the vertical nanowire growth to selected regions. In addition, Si nanowires were grown directly into microchannels to demonstrate the flexibility of the deposition technique. By controlling various aspects of nanowire growth, these methods will enable their efficient and eco...
674 citations
TL;DR: The optical band gap of ZnO thin films deposited on fused quartz by metal-organic chemical-vapor deposition was studied in this article, where X-ray diffraction measurements showed that samples deposited at low temperatures (<450°C) consisted of amorphous and crystalline phases.
Abstract: The optical band gap of ZnO thin films deposited on fused quartz by metal-organic chemical-vapor deposition was studied. The optical band gap of as-grown ZnO blueshifted from 3.13to4.06eV as the growth temperature decreased from 500to200°C. After annealing, the optical band gap shifted back to the single-crystal value. All the ZnO thin films studied show strong band-edge photoluminescence. X-ray diffraction measurements showed that samples deposited at low temperatures (<450°C) consisted of amorphous and crystalline phases. The redshift of the optical band gap back to the original position after annealing was strong evidence that the blueshift was due to an amorphous phase. The unshifted photoluminescence spectra indicated that the luminescence was due to the crystalline phase of ZnO, which was in the form of nanocrystals embedded in the amorphous phase.
662 citations
607 citations
TL;DR: The temperature dependence of the growth rate of carbon nanofibers by plasma-enhanced chemical vapor deposition with Ni, Co, and Fe catalysts is presented and a low activation energy of 0.4 eV is extrapolated, much lower than for thermal deposition.
Abstract: We present the temperature dependence of the growth rate of carbon nanofibers by plasma-enhanced chemical vapor deposition with Ni, Co, and Fe catalysts. We extrapolate a common low activation energy of 0.23-0.4 eV, much lower than for thermal deposition. The carbon diffusion on the catalyst surface and the stability of the precursor molecules, C2H2 or CH4, are investigated by ab initio plane wave density functional calculations. We find a low activation energy of 0.4 eV for carbon surface diffusion on Ni and Co (111) planes, much lower than for bulk diffusion. The energy barrier for C2H2 and CH4 dissociation is at least 1.3 eV and 0.9 eV, respectively, on Ni(111) planes or step edges. Hence, the rate-limiting step for plasma-enhanced growth is carbon diffusion on the catalyst surface, while an extra barrier is present for thermal growth due to gas decomposition.
405 citations
TL;DR: High-throughput growth of highly aligned single-walled carbon nanotubes arrays on a-plane and r-plane sapphire substrates using chemical vapor deposition with ferritin as the catalyst may enable the construction of integrable and scalable nanotube devices and systems.
Abstract: We report high-throughput growth of highly aligned single-walled carbon nanotube arrays on a-plane and r-plane sapphire substrates. This is achieved using chemical vapor deposition with ferritin as the catalyst. The nanotubes are aligned normal to the [0001] direction for growth on the a-plane sapphire. They are typically tens of micrometers long, with a narrow diameter distribution of 1.34 ± 0.30 nm. In contrast, no orientation was achieved for growth on the c-plane and m-plane sapphire, or when Fe films, instead of ferritin, were used as the catalyst. Such orientation control is likely related to the interaction between carbon nanotubes and the sapphire substrate, which is supported by the observation that when a second layer of nanotubes was grown, they followed the gas flow direction. These aligned nanotube arrays may enable the construction of integrable and scalable nanotube devices and systems.
343 citations
TL;DR: In this article, the authors used time-resolved reflectivity (TRR) of a HeNe laser beam from vertically aligned nanotube arrays (VANTAs) as they grow during chemical vapor deposition (CVD), and developed a rate-equation model to describe the measured kinetics in terms of activation energies and rate constants for surface carbon formation and diffusion on the catalyst nanoparticle.
Abstract: Direct measurements of carbon nanotube growth kinetics are described based upon time-resolved reflectivity (TRR) of a HeNe laser beam from vertically aligned nanotube arrays (VANTAs) as they grow during chemical vapor deposition (CVD). Growth rates and terminal lengths were measured in situ for VANTAs growing during CVD between 535 °C and 900 °C on Si substrates with evaporated Al/Fe/Mo multi-layered catalysts and acetylene feedstock at different feedstock partial pressures. Methods of analysis of the TRR signals are presented to interpret catalyst particle formation and oxidation, as well as the porosity of the VANTAs. A rate-equation model is developed to describe the measured kinetics in terms of activation energies and rate constants for surface carbon formation and diffusion on the catalyst nanoparticle, nanotube growth, and catalyst over-coating. Taken together with the TRR data, this model enables basic understanding and optimization of growth conditions for any catalyst/feedstock combination. The model lends insight into the main processes responsible for the growth of VANTAs, the measured number of walls in the nanotubes at different temperatures, conditions for growth of single-wall carbon nanotube arrays, and likely catalyst poisoning mechanisms responsible for the sharp decline in growth rates observed at high temperatures.
341 citations
TL;DR: The formation of a stable superhydrophobic surface via aligned carbon nanotubes (CNTs) coated with a zinc oxide (ZnO) thin film is reported and the wettability of the surface can be reversibly changed from superhydrophic to hydrophilicity by alternation of ultraviolet (UV) irradiation and dark storage.
Abstract: We report the formation of a stable superhydrophobic surface via aligned carbon nanotubes (CNTs) coated with a zinc oxide (ZnO) thin film. The CNT template was synthesized by chemical vapor deposition on an Fe-N catalyst layer. The ZnO film, with a low surface energy, was deposited on the CNT template by the filtered cathodic vacuum arc technique. Contact angle measurement reveals that the surface of the ZnO-coated CNTs is superhydrophobic with water contact angle of 159 degrees . Unlike the uncoated CNTs surface, the ZnO-coated CNTs surface shows no sign of water seepage even after a prolonged period of time. The wettability of the surface can be reversibly changed from superhydrophobicity to hydrophilicity by alternation of ultraviolet (UV) irradiation and dark storage.
338 citations
TL;DR: In this article, the authors report the technical progress that has occurred in the last decade in the development of Cd-free buffer layers for Cu(In,Ga)Se2-based thin-film solar cells and modules.
329 citations
TL;DR: In this article, a study of ZnO material deposited by the low-pressure chemical vapour deposition technique, in a pressure range below the pressures usually applied for the deposition of this kind of material, is presented.
304 citations
TL;DR: In this paper, the chemical structure of SiO (silicon monoxide) anodes has been analyzed using X-ray photoelectron spectroscopy (XPS), and it has been found that some Si remains oxidized in the full charge state and that lithium silicates are formed.
Abstract: The chemical structure of SiO (silicon monoxide) anodes has been analyzed using X-ray photoelectron spectroscopy (XPS). Vapor deposition was used to form SiO anodes on Cu film. XPS analysis was performed on anodes at eachof three stages: after deposition, after initial charge, and after discharge. The results of this analysis were then evaluated in terms of the anode's respective electrochemical characteristics. It has been found that some Si remains oxidized in the full charge state and that lithium silicates are formed. The lithium silicates serve as a buffer with respect to changes in anode volume.
286 citations
TL;DR: In this article, Nitrogen-doped films of ZnO grown by two methods, metalorganic chemical vapor deposition (MOCVD) and reactive sputtering, were studied with x-ray and ultraviolet photoelectron spectroscopy (XPS and UPS).
Abstract: Nitrogen-doped films of ZnO grown by two methods, metalorganic chemical vapor deposition (MOCVD) and reactive sputtering, were studied with x-ray and ultraviolet photoelectron spectroscopy (XPS and UPS). Systematic differences in the N chemical states were observed between films grown by sputtering and MOCVD: only two N chemical states were observed in films grown by reactive sputtering, whereas four N chemical states were observed in MOCVD films. To aid in the assignment of the N chemical states, photoemission data from the polycrystalline films were compared with data taken on N2+-implanted Zn metal and N2+-implanted ZnO. High-resolution core level spectra of the N1s region indicated that nitrogen can occupy at least four different chemical environments in ZnO; these include the NO acceptor, the double donor (N2)O, and two carbon–nitrogen species. Valence band spectra indicate that the Fermi energy of all films studied was near the conduction band minimum, implying that the films remained n-type after n...
TL;DR: Flexible transistors were fabricated by sputter deposition of zinc tin oxide (ZTO) onto plasma-enhanced chemical vapor deposition gate dielectrics formed on flexible polyimide substrates with a blanket aluminum gate electrode, and they exhibited high on-currents of 1mA, on/off ratios of 106, subthreshold voltage slopes of 1.6V/decade, turn-on voltages of −17V, and mobilities of 14cm2V−1s−1.
Abstract: Flexible transistors were fabricated by sputter deposition of zinc tin oxide (ZTO) onto plasma-enhanced chemical vapor deposition gate dielectrics formed on flexible polyimide substrates with a blanket aluminum gate electrode. The flexible transistors exhibited high on-currents of 1mA, on/off ratios of 106, subthreshold voltage slopes of 1.6V/decade, turn-on voltages of −17V, and mobilities of 14cm2V−1s−1. Capacitance measurements indicate that the threshold voltage and subthreshold slope are primarily influenced by residual doping in the ZTO rather than by defects at the semiconductor/dielectric interface, and are useful for assessing contact resistance.
TL;DR: This approach provided detail on the nucleation and growth mechanisms of Ag and Pt on SWNTs under electrochemical control, and Ag growth was found to be rapid and progressive with an increasing nanoparticle density with time, whereas Pt deposition was characterized by lower nucleation densities and slower growth rates with a tendency for larger particles to be produced over long times.
Abstract: The use of single-walled carbon nanotube (SWNT) networks as templates for the electrodeposition of metal (Ag and Pt) nanostructures is described. Pristine SWNTs, grown on insulating SiO2 surfaces using catalyzed chemical vapor deposition, served as the working electrode. In the simplest case, electrical contact was made by depositing a gold strip on the SWNT substrate (device 1). Deposition of Ag and Pt over extensive periods (30 s) resulted in a high density of particles on the SWNTs, with almost contiguous nanowire formation from the Au/SWNT boundary moving to isolated nanoparticles at further distances from the contact. For direct electrochemical studies of Ag and Pt nucleation, the assembly was coated in a resist layer and a small window opened up to expose only the electrically connected SWNTs to solution (device 2). In this case, the electrochemical signature in voltammetric and amperometric studies of metal deposition was due solely to processes at the SWNTs. Coupled with high-resolution microscopy...
TL;DR: Carbon-coated LiFePO4 electrodes were prepared by a vapor deposition process as discussed by the authors, which led not only to the formation of few monolayers of carbon film at the surface of olivine particles but also allowed for carbon to be deposited inside the pores of the particles.
TL;DR: In this paper, an epitaxial single perovskite phase thin film was obtained by growing BiFeO3 thin films on SrRuO3∕SrTiO3 and SrinO3 ∕Si using liquid delivery metalorganic chemical vapor deposition.
Abstract: We have grown BiFeO3 thin films on SrRuO3∕SrTiO3 and SrRuO3∕SrTiO3∕Si using liquid delivery metalorganic chemical vapor deposition. Epitaxial BiFeO3 films were successfully prepared through the systematic control of the chemical reaction and deposition process. We found that the film composition and phase equilibrium are sensitive to the Bi:Fe ratio in the precursor. Fe-rich mixtures show the existence of α-Fe2O3, while Bi-rich mixtures show the presence of β-Bi2O3 as a second phase at the surface. In the optimized films, we were able to obtain an epitaxial single perovskite phase thin film. Electrical measurements using both quasistatic hysteresis and pulsed polarization measurements confirm the existence of ferroelectricity with a switched polarization of 110–120μC∕cm2, ΔP(=P*−P). Out-of plane piezoelectric (d33) measurements using an atomic force microscope yield a value of 50–60pm∕V.
TL;DR: In this paper, the Raman spectra of carbon nanowalls (CNWs) grown using dc plasma-enhanced chemical vapor deposition were analyzed, and it was shown that CNWs are composed of small crystallites with a high degree of graphitization.
Abstract: Raman spectra of carbon nanowalls (CNWs) grown using dc plasma-enhanced chemical vapor deposition were analyzed. The Raman spectra of CNWs exhibited G and D bands at ∼1580 and ∼1350cm−1, respectively. It is found that the bandwidth of the G band is relatively narrow, even when the peak intensity ratio of D band to G band is significantly high. This spectral feature of CNWs is distinguished from those of typical graphitelike carbons reported so far. From the comparison of these spectral features, it is shown that CNWs are composed of small crystallites with a high degree of graphitization.
TL;DR: In this article, the authors investigated the transition from a micro-crystalline to a nanocrystalline diamond morphology by using transmission electron microscopy (TEM) and Raman spectroscopy.
TL;DR: The behavior of nitrogen in ZnO thin films grown by high-vacuum plasma-assisted chemical vapor deposition is examined in this paper, where it is observed that hole conduction decreases and films revert to n-type conductivity in a period of several days.
Abstract: The behavior of nitrogen in ZnO thin films grown by high-vacuum plasma-assisted chemical vapor deposition is examined. Highly oriented (002) films doped with 0–2at.% N were characterized by x-ray photoelectron spectroscopy, x-ray diffraction (XRD), Seebeck, and Hall measurements. XRD measurements revealed that the zinc oxide lattice constant decreased systematically with nitrogen doping. The as-deposited films were p-type at high doping levels, as confirmed by both Seebeck and Hall measurements. However, it was observed that hole conduction decreased and films reverted to n-type conductivity in a period of several days. This change was accompanied by a simultaneous increase in the lattice constant. The transient electrical behavior may be explained by compensation caused either by hydrogen donors or through defect formation processes common to analogous II-VI semiconductors.
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12 May 2005TL;DR: In this paper, a method for depositing dielectric materials on substrates during vapor deposition processes, such as atomic layer deposition (ALD), is described, which includes sequentially exposing a substrate to a hafnium precursor and an oxidizing gas to deposit the material thereon.
Abstract: Embodiments of the invention provide methods for depositing dielectric materials on substrates during vapor deposition processes, such as atomic layer deposition (ALD). In one example, a method includes sequentially exposing a substrate to a hafnium precursor and an oxidizing gas to deposit a hafnium oxide material thereon. In another example, a hafnium silicate material is deposited by sequentially exposing a substrate to the oxidizing gas and a process gas containing a hafnium precursor and a silicon precursor. The oxidizing gas contains water vapor formed by flowing a hydrogen source gas and an oxygen source gas through a water vapor generator.
TL;DR: In this paper, the structure and electrochemical properties of arrayed nitrogen-containing carbon nanotube (CNx NT)−platinum nanoparticle (Pt NP) composites directly grown on Si substrates have been investigated.
Abstract: The structure and electrochemical properties of arrayed nitrogen-containing carbon nanotube (CNx NT)−platinum nanoparticle (Pt NP) composites directly grown on Si substrates have been investigated The CNx nanotube arrays were grown by microwave-plasma-enhanced chemical vapor deposition first and then acted as the template and support for Pt dispersion in the following sputtering process Under the same sputtering conditions, it was found that well-separated Pt NPs would form with an average diameter of 2 nm on the arrayed NTs while a continuous Pt thin film was observed on the bare Si substrate X-ray photoelectron spectroscopy (XPS), X-ray diffraction, and electron microscopy were employed to study bonding and structure changes with increasing deposition time Implications of the C1s and N1s bonding changes in XPS and their possible relation to the NT−Pt composite structures with self-limited size distribution are discussed Cyclic voltammograms show well-behaved curves in methanol oxidation, suggesting
TL;DR: In this paper, the limits of magnetism in thin, electronic grade, hafnium oxide, and HFO silicate films deposited onto silicon wafers by chemical vapor deposition and atomic layer deposition were established.
Abstract: We establish the limits of magnetism in thin, electronic grade, hafnium oxide, and hafnium silicate films deposited onto silicon wafers by chemical vapor deposition and atomic layer deposition. To the limits of sensitivity of our measurement techniques, no ferromagnetism occurs in these samples. Contamination by handling with stainless-steel tweezers leads to a measurable magnetic signal. The magnetic properties of this contamination are similar to those attributed to ferromagnetic HfO2 in a recent report, including the magnitude of moment, magnetization field dependence, and spatial asymmetry.
TL;DR: The spectroscopic results, the contact-angle results, and the swelling analysis altogether prove the retention of the hydrophilic pendant groups in the iCVD process.
Abstract: Initiated chemical vapor deposition (iCVD) is able to synthesize linear and cross-linked poly(2-hydroxyethyl methacrylate) (PHEMA) thin films, in one step, from vapors of 2-hydroxyethyl methacrylate (HEMA), ethylene glycol diacrylate (EGDA), and tert-butyl peroxide (TBPO) without using any solvents. This all-dry technique also allows control of the cross-link density by adjusting the partial pressure of the cross-linking agent EGDA in the vapor phase. Films with specific cross-link densities and hence thermal, wetting, and swelling properties can be created in one single vacuum processing step. Through selective thermal decomposition of the initiator TBPO, films with well-defined chemical structures and full functionality retention can be deposited, which is evident in the Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses. These spectroscopic methods also facilitate determination of EGDA incorporation in the cross-linked films based on the fact that HEMA contains a hydr...
Patent•
08 Aug 2005TL;DR: In this paper, the same mixture of metal amides and alkylphosphates is used to produce a uniform stochastic mixture with a uniform distribution of thickness and excellent step coverage.
Abstract: Metal silicates or phosphates are deposited on a heated substrate by the reaction of vapors of alkoxysilanols or alkylphosphates along with reactive metal amides, alkyls or alkoxides. For example, vapors of tris(tert-butoxy)silanol react with vapors of tetrakis(ethylmethylamido)hafnium to deposit hafnium silicate on surfaces heated to 300° C. The product film has a very uniform stoichiometry throughout the reactor. Similarly, vapors of diisopropylphosphate react with vapors of lithium bis(ethyldimethylsilyl)amide to deposit lithium phosphate films on substrates heated to 250° C. Supplying the vapors in alternating pulses produces these same compositions with a very uniform distribution of thickness and excellent step coverage.
TL;DR: In this article, the surface morphology with different grain structures has been used to characterize the green photoluminescence of ZnO thin films grown by metal-organic chemical vapor deposition (MOCVD) at varied growth pressures.
Abstract: Photoluminescence and atomic force microscopy have been used to characterize ZnO thin films grown by metal-organic chemical vapor deposition (MOCVD) at varied growth pressures. The surface morphology with different grain structures has strong influence on the green photoluminescence of ZnO. When large discrete islands or structureless overgrowth cover the rough surface, broad green emissions around 500 nm go beyond the ultraviolet (UV) emission band; whereas, when the surface is packed closely with small grains, only weak green emission is observed with a red-shift to 528 nm. This variation of green emissions is ascribed to changes in the charge states of oxygen vacancies, which is strongly dependent on the surface morphology and grain structures. Based on the grain boundary defect model, two possible recombination processes for the green emission are proposed and discussed in detail.
TL;DR: The results showed that preparing closely packed self-assembled films and fabricating surface nanometer-scale and micrometer-scale binary roughness can achieve superhydrophobic films with a water contact angle larger than 156 degrees.
Abstract: The self-assembled films of methyloctyldimethoxysilane (MODMS) and fluorooctylmethyldimethoxysilane (FODMS) were prepared on silicon surfaces and evaluated with AFM, water contact angle measurement, and X-ray photoelectron spectroscopy. Superhydrophobic surfaces were obtained by cooperation of MODMS and FODMS self-assembly with surface roughening. The results showed that preparing closely packed self-assembled films and fabricating surface nanometer-scale and micrometer-scale binary roughness can achieve superhydrophobic films with a water contact angle larger than 156°. The difference between solution deposition and chemical vapor deposition is also investigated. Moreover, superhydrophobic surfaces created with MODMS and FODMS show the different water-adhesion effects, which could have great significance on liquid microtransport in microfluid devices.
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26 Aug 2005TL;DR: In this article, a chemical vapor deposition method for forming a dielectric material in a trench formed on a substrate is described, which includes flowing a silicon-containing precursor into a process chamber housing the substrate, flowing an oxidizing gas into the chamber, and providing a hydroxylcontaining precursor in the process chamber.
Abstract: A chemical vapor deposition method for forming a dielectric material in a trench formed on a substrate. The method includes flowing a silicon-containing precursor into a process chamber housing the substrate, flowing an oxidizing gas into the chamber, and providing a hydroxyl-containing precursor in the process chamber. The method also includes reacting the silicon-containing precursor, oxidizing gas and hydroxyl-containing precursor to form the dielectric material in the trench. The ratio of the silicon-containing precursor to the oxidizing gas flowed into the chamber is increased over time to alter a rate of deposition of the dielectric material.
TL;DR: In this article, hydrogenated nanocrystalline silicon (nc-Si:H) films were deposited by using 13.56MHz plasma-enhanced chemical vapor deposition at 260°C by means of a silane (SiH4) plasma heavily diluted with hydrogen (H2).
Abstract: Hydrogenated nanocrystalline silicon (nc-Si:H) films were deposited by using 13.56MHz plasma-enhanced chemical vapor deposition at 260°C by means of a silane (SiH4) plasma heavily diluted with hydrogen (H2). The high-quality nc-Si:H film showed an oxygen concentration (CO) of ∼1.5×1017at.∕cm3 and a dark conductivity (σd) of ∼10−6S∕cm, while the Raman crystalline volume fraction (Xc) was over 80%. Top-gate nc-Si:H thin-film transistors employing an optimized ∼100nm nc-Si:H channel layer exhibited a field-effect mobility (μFE) of ∼150cm2∕Vs, a threshold voltage (VT) of ∼2V, a subthreshold slope (S) of ∼0.25V∕dec, and an ON∕OFF current ratio of ∼106.
TL;DR: In this paper, the emission properties of nonpolar a-plane GaN layers grown on r -plane sapphire were investigated and temperature-, excitation-density-, and polarization-dependent photoluminescences and spatially resolvable spatial resolvability was obtained.
Abstract: We report on the emission properties of nonpolar a -plane GaN layers grown on r -plane sapphire. Temperature-, excitation-density-, and polarization-dependent photoluminescences and spatially resol ...
Patent•
06 May 2005TL;DR: In this paper, a method for the fabrication of nonpolar indium gallium nitride (InGaN) films as well as non-polar InGaN-containing device structures using metalorganic chemical vapor deposition (MOVCD) is presented.
Abstract: A method for the fabrication of nonpolar indium gallium nitride (InGaN) films as well as nonpolar InGaN-containing device structures using metalorganic chemical vapor deposition (MOVCD). The method is used to fabricate nonpolar InGaN/GaN violet and near-ultraviolet light emitting diodes and laser diodes.