Showing papers on "Chemical vapor deposition published in 2009"

Large-Area Synthesis of High-Quality and Uniform Graphene Films on Copper Foils

Abstract: Graphene has been attracting great interest because of its distinctive band structure and physical properties. Today, graphene is limited to small sizes because it is produced mostly by exfoliating graphite. We grew large-area graphene films of the order of centimeters on copper substrates by chemical vapor deposition using methane. The films are predominantly single-layer graphene, with a small percentage (less than 5%) of the area having few layers, and are continuous across copper surface steps and grain boundaries. The low solubility of carbon in copper appears to help make this growth process self-limiting. We also developed graphene film transfer processes to arbitrary substrates, and dual-gated field-effect transistors fabricated on silicon/silicon dioxide substrates showed electron mobilities as high as 4050 square centimeters per volt per second at room temperature.

Large Area, Few-Layer Graphene Films on Arbitrary Substrates by Chemical Vapor Deposition

Abstract: In this work we present a low cost and scalable technique, via ambient pressure chemical vapor deposition (CVD) on polycrystalline Ni films, to fabricate large area (∼cm2) films of single- to few-layer graphene and to transfer the films to nonspecific substrates. These films consist of regions of 1 to ∼12 graphene layers. Single- or bilayer regions can be up to 20 μm in lateral size. The films are continuous over the entire area and can be patterned lithographically or by prepatterning the underlying Ni film. The transparency, conductivity, and ambipolar transfer characteristics of the films suggest their potential as another materials candidate for electronics and opto-electronic applications.

Evolution of Graphene Growth on Ni and Cu by Carbon Isotope Labeling

Abstract: Large-area graphene growth is required for the development and production of electronic devices. Recently, chemical vapor deposition (CVD) of hydrocarbons has shown some promise in growing large-area graphene or few-layer graphene films on metal substrates such as Ni and Cu. It has been proposed that CVD growth of graphene on Ni occurs by a C segregation or precipitation process whereas graphene on Cu grows by a surface adsorption process. Here we used carbon isotope labeling in conjunction with Raman spectroscopic mapping to track carbon during the growth process. The data clearly show that at high temperatures sequentially introduced isotopic carbon diffuses into the Ni first, mixes, and then segregates and precipitates at the surface of Ni forming graphene and/or graphite with a uniform mixture of 12C and 13C as determined by the peak position of the Raman G-band peak. On the other hand, graphene growth on Cu is clearly by surface adsorption where the spatial distribution of 12C and 13C follows the pre...

Growth of large-area single- and Bi-layer graphene by controlled carbon precipitation on polycrystalline Ni surfaces

Abstract: We report graphene films composed mostly of one or two layers of graphene grown by controlled carbon precipitation on the surface of polycrystalline Ni thin films during atmospheric chemical vapor deposition (CVD). Controlling both the methane concentration during CVD and the substrate cooling rate during graphene growth can significantly improve the thickness uniformity. As a result, one- or two- layer graphene regions occupy up to 87% of the film area. Single layer coverage accounts for 5%–11% of the overall film. These regions expand across multiple grain boundaries of the underlying polycrystalline Ni film. The number density of sites with multilayer graphene/graphite (>2 layers) is reduced as the cooling rate decreases. These films can also be transferred to other substrates and their sizes are only limited by the sizes of the Ni film and the CVD chamber. Here, we demonstrate the formation of films as large as 1 in2. These findings represent an important step towards the fabrication of large-scale high-quality graphene samples.

Growth of graphene on Ir(111)

Abstract: Catalytic decomposition of hydrocarbons on transition metals attracts a renewed interest as a route toward high-quality graphene prepared in a reproducible manner. Here we employ two growth methods for graphene on Ir(111), namely room temperature adsorption and thermal decomposition at 870–1470 K (temperature programmed growth (TPG)) as well as direct exposure of the hot substrate at 870–1320 K (chemical vapor deposition (CVD)). The temperature- and exposure-dependent growth of graphene is investigated in detail by scanning tunneling microscopy. TPG is found to yield compact graphene islands bounded by C zigzag edges. The island size may be tuned from a few to a couple of tens of nanometers through Smoluchowski ripening. In the CVD growth, the carbon in ethene molecules arriving on the Ir surface is found to convert with probability near unity to graphene. The temperature-dependent nucleation, interaction with steps and coalescence of graphene islands are analyzed and a consistent model for CVD growth is developed.

Long term operation of high quantum efficiency GaAs(Cs,O) photocathodes using multiple recleaning by atomic hydrogen

Abstract: Atomic hydrogen, produced by thermal dissociation of H2 molecules inside a hot tungsten capillary, is shown to be an efficient tool for multiple recleaning of degraded surfaces of high quantum efficiency transmission-mode GaAs photocathodes within an ultrahigh vacuum (UHV) multichamber photoelectron gun. Ultraviolet quantum yield photoemission spectroscopy has been used to study the removal of surface pollutants and the degraded (Cs,O)-activation layer during the cleaning procedure. For photocathodes grown by the liquid-phase epitaxy technique, the quantum efficiency is found to be stable at about 20% over a large number of atomic hydrogen cleaning cycles. A slow degradation of the quantum efficiency is observed for photocathodes grown by metal-organic chemical vapor deposition, although they reached a higher initial quantum efficiency of about 30%–35%. Study of the spatial distributions of photoluminescence intensity on these photocathodes proved that this overall degradation is likely due to insertion o...

Boron-doped diamond electrode: synthesis, characterization, functionalization and analytical applications.

Abstract: In recent years, conductive diamond electrodes for electrochemical applications have been a major focus of research and development. The impetus behind such endeavors could be attributed to their wide potential window, low background current, chemical inertness, and mechanical durability. Several analytes can be oxidized by conducting diamond compared to other carbon-based materials before the breakdown of water in aqueous electrolytes. This is important for detecting and/or identifying species in solution since oxygen and hydrogen evolution do not interfere with the analysis. Thus, conductive diamond electrodes take electrochemical detection into new areas and extend their usefulness to analytes which are not feasible with conventional electrode materials. Different types of diamond electrodes, polycrystalline, microcrystalline, nanocrystalline and ultrananocrystalline, have been synthesized and characterized. Of particular interest is the synthesis of boron-doped diamond (BDD) films by chemical vapor deposition on various substrates. In the tetrahedral diamond lattice, each carbon atom is covalently bonded to its neighbors forming an extremely robust crystalline structure. Some carbon atoms in the lattice are substituted with boron to provide electrical conductivity. Modification strategies of doped diamond electrodes with metallic nanoparticles and/or electropolymerized films are of importance to impart novel characteristics or to improve the performance of diamond electrodes. Biofunctionalization of diamond films is also feasible to foster several useful bioanalytical applications. A plethora of opportunities for nanoscale analytical devices based on conducting diamond is anticipated in the very near future

Large area few-layer graphene/graphite films as transparent thin conducting electrodes

Abstract: By dissolving carbon atoms decomposed from methane in a metal substrate at high temperatures, large area uniform few-layer graphene (FLG)/graphite films were precipitated on metal surfaces upon cooling. The thickness could be controlled by varying the amount of carbon atoms in the metal. Such films were transferred to glass slides after dissolving the metal substrate in an aqueous solution of Fe(NO3)3. Sheet resistances as low as 200 Ω/◻ with a transmittance of 85% were obtained from FLG films. The resistance and transmittance can be changed over one order of magnitude, making such films potentially useful for transparent thin conducting electrodes.

Chemical Vapor Deposition of Conformal, Functional, and Responsive Polymer Films

Abstract: Chemical vapor deposition (CVD) polymerization utilizes the delivery of vapor-phase monomers to form chemically well-defined polymeric films directly on the surface of a substrate. CVD polymers are desirable as conformal surface modification layers exhibiting strong retention of organic functional groups, and, in some cases, are responsive to external stimuli. Traditional wet-chemical chain- and step-growth mechanisms guide the development of new heterogeneous CVD polymerization techniques. Commonality with inorganic CVD methods facilitates the fabrication of hybrid devices. CVD polymers bridge microfabrication technology with chemical, biological, and nanoparticle systems and assembly. Robust interfaces can be achieved through covalent grafting enabling high-resolution (60 nm) patterning, even on flexible substrates. Utilizing only low-energy input to drive selective chemistry, modest vacuum, and room-temperature substrates, CVD polymerization is compatible with thermally sensitive substrates, such as paper, textiles, and plastics. CVD methods are particularly valuable for insoluble and infusible films, including fluoropolymers, electrically conductive polymers, and controllably crosslinked networks and for the potential to reduce environmental, health, and safety impacts associated with solvents. Quantitative models aid the development of large-area and roll-to-roll CVD polymer reactors. Relevant background, fundamental principles, and selected applications are reviewed.

Surface chemistry for molecular layer deposition of organic and hybrid organic-inorganic polymers.

Abstract: The fabrication of many devices in modern technology requires techniques for growing thin films. As devices miniaturize, manufacturers will need to control thin film growth at the atomic level. Because many devices have challenging morphologies, thin films must be able to coat conformally on structures with high aspect ratios. Techniques based on atomic layer deposition (ALD), a special type of chemical vapor deposition, allow for the growth of ultra-thin and conformal films of inorganic materials using sequential, self-limiting reactions. Molecular layer deposition (MLD) methods extend this strategy to include organic and hybrid organic−inorganic polymeric materials. In this Account, we provide an overview of the surface chemistry for the MLD of organic and hybrid organic−inorganic polymers and examine a variety of surface chemistry strategies for growing polymer thin films. Previously, surface chemistry for the MLD of organic polymers such as polyamides and polyimides has used two-step AB reaction cycle...

Chemical vapour deposition: Making graphene on a large scale

Abstract: Graphene samples with areas of several square centimetres and excellent electrical and optical properties have been fabricated using chemical vapour deposition.

Nanostructured α-Fe2O3 Thin Films for Photoelectrochemical Hydrogen Generation

Abstract: α-Fe2O3 thin film photoelectrodes were fabricated by aerosol-assisted chemical vapor deposition (AACVD) using a new hexanuclear iron precursor [Fe6(PhCOO)10(acac)2(O)2(OH)2]·3C7H8 (1) (where PhCOO = benzoate and acac = 2,4-pentanedionate). The precursor (1) designed for AACVD has a low decomposition temperature and sufficient solubility in organic solvents and was synthesized by simple chemical techniques in high yield. It was characterized by melting point, FT-IR, X-ray crystallography, and thermogravimetry (TGA). The TGA analysis proved that complex (1) undergoes facile thermal decomposition at 475 °C to give iron oxide residue. In-house designed AACVD equipment was used to deposit highly crystalline thin films of α-Fe2O3 on fluorine-doped SnO2 coated glass substrates at 475 °C in a single step. The material properties were characterized by XRD, XPS, and Raman spectroscopy, and the results confirmed that films were highly crystalline α-Fe2O3 and free from other phases of iron oxide. Further analysis of ...

Al2O3/ZrO2 Nanolaminates as Ultrahigh Gas-Diffusion Barriers—A Strategy for Reliable Encapsulation of Organic Electronics

Abstract: Adv Mater 2009, 21, 1845–1849 2009 WILEY-VCH Verlag G Gas-diffusion barriers play an important role in many applications today, such as flat-panel displays or solar cells grown on plastic substrates In particular, organic light-emitting diodes (OLEDs) need efficient encapsulation because of the high sensitivity of many organic or electrode materials to moisture and oxygen, which has been demonstrated to cause device degradation and limited lifetime Maximum allowable permeation rates for a viable encapsulant to be used in organic optoelectronics are still under debate, but it is common sense that the requirements are far more demanding than those for typical barrier films used in food or pharmacy packaging A very commonly quoted figure for the upper limit of the water-vaportransmission rate (WVTR) in order to reach a minimum OLED lifetime of 10000 h is 10 6 gm 2 day This value originated from an estimate of the amount of water needed to degrade the reactive cathode material For the oxygen-transmission rate (OTR), maximum values for similar OLED lifetimes have been reported in the region of 10 –10 3 cmm 2 day Nowadays, a very common technique is the encapsulation of organic devices with a glass or metal lid, which is applied under nitrogen atmosphere using, for example, an epoxy resin as glue In addition, the residual moisture in the cavity between the organic device and lid is further minimized by an opaque getter material For large-area, flexible, or transparent applications, glass-lid encapsulation is not suitable A promising alternative is thin-film barriers of metal oxides or nitrides, such as Al2O3, SiO2, TiO2, or SiN These materials can be deposited by several techniques Plasma-assisted processes, such as sputtering or plasma-enhanced chemical vapor deposition (PECVD), provide high quality films, but their typically reported OTR and WVTR values of about 05 cmm 2 day 1 and 03 gm 2 day , respectively, limited by imperfections in the films, are not sufficient for OLED applications Moreover, efficient step coverage and conformal coating are not straightforward with these techniques As a workaround, hybrid organic/inorganic multilayer structures have been introduced In these, the polymeric intermediate layer levels the inorganic layer so that diffusion pathways through the entire stack of the barrier can be reduced However, the combination of alternating nonvacuum-based polymer deposition processes and vacuum-based deposition processes is timeconsuming and costly, and therefore not really practical for production An alternative technique that promises highly uniform thin-film coatings is atomic-layer deposition (ALD) ALD relies on the sequential exposure of the surface to be coated to a metal–organic precursor and a reactant (H2O, O3, NH3, etc) The sequential dosing of precursors leads to a self-limiting process with concomitant precise control over thickness and homogeneity The technique is well-established in the processing of insulating films for gate dielectrics and capacitors ALD has the advantage of allowing the deposition of very dense films at low temperatures (<100 8C), and thus appears to be a promising technique suitable for preparing encapsulation layers on top of organic electronic devices There are a few reports dealing with ALD-grown thin films for OLED encapsulation Very-low permeation rates of 65 10 5 gm 2 day 1 at 60 8C have been reported for Al2O3 films that were grown at 120 8C [13] However, deposition temperatures above 100 8C might be critical, because glass-transition temperatures for many functional OLED materials have been reported in this very temperature range In this Communication, we report on thin encapsulation layers prepared by ALD at a temperature of 80 8C Specifically, we study neat Al2O3 films as a reference, and introduce novel highly efficient permeation barriers based on so-called nanolaminate structures A nanolaminate, in this case, is a composite film consisting of repetitively deposited ultrathin (a few nanometers thick) alternating layers of Al2O3 and ZrO2 The alternating nanolayer structure suppresses the formation of both microscopic voids and nanocrystals As a result, the probability of the occurrence of statistical defects in the barrier structure related to permeation paths along connected voids or grain boundaries is significantly reducedWe demonstrate that nanolaminates render pinhole-free thin-film encapsulation layers suitable for large-area organic devices possible First, the quantitative assessment of permeation rates on the order of 10 6 gm 2 day 1 for water and 10 3 cmm 2 day 1 for oxygen is very challenging and, as yet, no commercially available method can be applied in this range Therefore, we used a very sensitive permeation-measurement technique that was introduced by Paetzold et al The method allows the measurement

Synthesis, Transfer, and Devices of Single- and Few-Layer Graphene by Chemical Vapor Deposition

Abstract: The advance of graphene-based nanoelectronics has been hampered due to the difficulty in producing single- or few-layer graphene over large areas. We report a simple, scalable, and cost-efficient method to prepare graphene using methane-based CVD on nickel films deposited over complete Si/SiO2 wafers. By using highly diluted methane, single- and few-layer graphene were obtained, as confirmed by micro-Raman spectroscopy. In addition, a transfer technique has been applied to transfer the graphene film to target substrates via nickel etching. FETs based on the graphene films transferred to Si/SiO2 substrates revealed a weak p-type gate dependence, while transferring of the graphene films to glass substrate allowed its characterization as transparent conductive films, exhibiting transmittance of 80% in the visible wavelength range.

High-Density Through Silicon Vias for 3-D LSIs

Abstract: High density through silicon via (TSV) is a key in fabricating three-dimensional (3-D) large-scale integration (LSI). We have developed polycrystalline silicon (poly-Si) TSV technology and tungsten (W)/poly-Si TSV technology for 3-D integration. In the poly-Si TSV formation, low-pressure chemical vapor deposition poly-Si heavily doped with phosphorus was conformally deposited into the narrow and deep trench formed in a Si substrate after the surface of Si trench was thermally oxidized. In the W/poly-Si TSV formation, tungsten was deposited into the Si trench by atomic layer deposition method after the poly-Si deposition, where poly-Si was used as a liner layer for W deposition. The 3-D microprocessor test chip, 3-D memory test chip, 3-D image sensor chip, and 3-D artificial retina chip were successfully fabricated by using poly-Si TSV.

Silicon Inverse-Opal-Based Macroporous Materials as Negative Electrodes for Lithium Ion Batteries

Abstract: Several types of silicon-based inverse-opal films are synthesized, characterized by a range of experimental techniques, and studied in terms of electrochemical performance. Amorphous silicon inverse opals are fabricated via chemical vapor deposition. Galvanostatic cycling demonstrates that these materials possess high capacities and reasonable capacity retentions. Amorphous silicon inverse opals perform unsatisfactorily at high rates due to the low conductivity of silicon. The conductivity of silicon inverse opals can be improved by their crystallization. Nanocrystalline silicon inverse opals demonstrate much better rate capabilities but the capacities fade to zero after several cycles. Silicon–carbon composite inverse-opal materials are synthesized by depositing a thin layer of carbon via pyrolysis of a sucrose-based precursor onto the silicon inverse opals. The amount of carbon deposited proves to be insufficient to stabilize the structures and silicon–carbon composites demonstrate unsatisfactory electrochemical behavior. Carbon inverse opals are coated with amorphous silicon producing another type of macroporous composite. These electrodes demonstrate significant improvement both in capacity retentions and in rate capabilities. The inner carbon matrix not only increases the material conductivity but also results in lower silicon pulverization during cycling.

High-Density Through Silicon Vias for 3-D LSIs : Silicon stacked chips that perform highly-parallel data transfer have been successfully fabricated for image processing, artificial retinas, and for microprocessor and memory testing

Abstract: High density through silicon via (TSV) is a key in fabricating three-dimensional (3-D) large-scale integration (LSI). We have developed polycrystalline silicon (poly-Si) TSV technology and tungsten (W)/poly-Si TSV technology for 3-D integration. In the poly-Si TSV formation, low-pressure chem- ical vapor deposition poly-Si heavily doped with phosphorus was conformally deposited into the narrow and deep trench formed in a Si substrate after the surface of Si trench was thermally oxidized. In the W/poly-Si TSV formation, tungsten was deposited into the Si trench by atomic layer deposition method after the poly-Si deposition, where poly-Si was used as a liner layer for W deposition. The 3-D microprocessor test chip, 3-D memory test chip, 3-D image sensor chip, and 3-D artificial retina chip were successfully fabricated by using poly-Si TSV.

Very low surface recombination velocity on p-type c-Si by high-rate plasma-deposited aluminum oxide

Abstract: Aluminum oxide layers can provide excellent passivation for lowly and highly doped p-type silicon surfaces. Fixed negative charges induce an accumulation layer at the p-type silicon interface, resulting in very effective field-effect passivation. This paper presents highly negatively charged (Qox=−2.1×1012 cm−2) aluminum oxide layers produced using an inline plasma-enhanced chemical vapor deposition system, leading to very low effective recombination velocities (∼10 cm s−1) on low-resistivity p-type substrates. A minimum static deposition rate (100 nm min−1) at least one order of magnitude higher than atomic layer deposition was achieved on a large carrier surfaces (∼1 m2) without significantly reducing the resultant passivation quality.

Electronic and optical properties of boron-doped nanocrystalline diamond films

Abstract: We report on the electronic and optical properties of boron-doped nanocrystalline diamond (NCD) thin films grown on quartz substrates by CH4/H2 plasma chemical vapor deposition. Diamond thin films with a thickness below 350 nm and with boron concentration ranging from 1017 to 1021 cm−3 have been investigated. UV Raman spectroscopy and atomic force microscopy have been used to assess the quality and morphology of the diamond films. Hall-effect measurements confirmed the expected p-type conductivity. At room temperature, the conductivity varies from 1.5×10−8 Ω−1 cm−1 for a nonintentionally doped film up to 76 Ω−1 cm−1 for a heavily B-doped film. Increasing the doping level results in a higher carrier concentration while the mobility decreases from 1.8 down to 0.2 cm2 V−1 s−1. For NCD films with low boron concentration, the conductivity strongly depends on temperature. However, the conductivity and the carrier concentration are no longer temperature dependent for films with the highest boron doping and the NCD films exhibit metallic properties. Highly doped films show superconducting properties with critical temperatures up to 2 K. The critical boron concentration for the metal-insulator transition is in the range from 2×1020 up to 3×1020 cm−3. We discuss different transport mechanisms to explain the influence of the grain boundaries and boron doping on the electronic properties of NCD films. Valence-band transport dominates at low boron concentration and high temperatures, whereas hopping between boron acceptors is the dominant transport mechanism for boron-doping concentration close to the Mott transition. Grain boundaries strongly reduce the mobility for low and very high doping levels. However, at intermediate doping levels where hopping transport is important, grain boundaries have a less pronounced effect on the mobility. The influence of boron and the effect of grain boundaries on the optoelectronic properties of the NCD films are examined using spectrally resolved photocurrent measurements and photothermal deflection spectroscopy. Major differences occur in the low energy range, between 0.5 and 1.0 eV, where both boron impurities and the sp2 carbon phase in the grain boundaries govern the optical absorption.

Gas diffusion ultrabarriers on polymer substrates using Al2O3 atomic layer deposition and SiN plasma-enhanced chemical vapor deposition

Abstract: Thin films grown by Al2O3 atomic layer deposition (ALD) and SiN plasma-enhanced chemical vapor deposition (PECVD) have been tested as gas diffusion barriers either individually or as bilayers on polymer substrates. Single films of Al2O3 ALD with thicknesses of ≥10 nm had a water vapor transmission rate (WVTR) of ≤5×10−5 g/m2 day at 38 °C/85% relative humidity (RH), as measured by the Ca test. This WVTR value was limited by H2O permeability through the epoxy seal, as determined by the Ca test for the glass lid control. In comparison, SiN PECVD films with a thickness of 100 nm had a WVTR of ∼7×10−3 g/m2 day at 38 °C/85% RH. Significant improvements resulted when the SiN PECVD film was coated with an Al2O3 ALD film. An Al2O3 ALD film with a thickness of only 5 nm on a SiN PECVD film with a thickness of 100 nm reduced the WVTR from ∼7×10−3 to ≤5×10−5 g/m2 day at 38 °C/85% RH. The reduction in the permeability for Al2O3 ALD on the SiN PECVD films was attributed to either Al2O3 ALD sealing defects in the SiN PE...

Vapor deposition method for ternary compounds

Abstract: Embodiments provide a method for depositing or forming titanium aluminum nitride materials during a vapor deposition process, such as atomic layer deposition (ALD) or plasma-enhanced ALD (PE-ALD). In some embodiments, a titanium aluminum nitride material is formed by sequentially exposing a substrate to a titanium precursor and a nitrogen plasma to form a titanium nitride layer, exposing the titanium nitride layer to a plasma treatment process, and exposing the titanium nitride layer to an aluminum precursor while depositing an aluminum layer thereon. The process may be repeated multiple times to deposit a plurality of titanium nitride and aluminum layers. Subsequently, the substrate may be annealed to form the titanium aluminum nitride material from the plurality of layers. In other embodiments, the titanium aluminum nitride material may be formed by sequentially exposing the substrate to the nitrogen plasma and a deposition gas which contains the titanium and aluminum precursors.

Understanding the chemical vapor deposition of diamond: recent progress.

Abstract: In this paper we review and provide an overview to the understanding of the chemical vapor deposition (CVD) of diamond materials with a particular focus on the commonly used microwave plasma-activated chemical vapor deposition (MPCVD). The major topics covered are experimental measurements in situ to diamond CVD reactors, and MPCVD in particular, coupled with models of the gas phase chemical and plasma kinetics to provide insight into the distribution of critical chemical species throughout the reactor, followed by a discussion of the surface chemical process involved in diamond growth.

Gate-bias stress in amorphous oxide semiconductors thin-film transistors

Abstract: A quantitative study of the dynamics of threshold-voltage shifts with time in gallium-indium zinc oxide amorphous thin-film transistors is presented using standard analysis based on the stretched exponential relaxation. For devices using thermal silicon oxide as gate dielectric, the relaxation time is 3×105 s at room temperature with activation energy of 0.68 eV. These transistors approach the stability of the amorphous silicon transistors. The threshold voltage shift is faster after water vapor exposure suggesting that the origin of this instability is charge trapping at residual-water-related trap sites.

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.

Closed loop mocvd deposition control

Abstract: A method and apparatus are provided for monitoring and controlling substrate processing parameters for a cluster tool that utilizes chemical vapor deposition and/or hydride vapor phase epitaxial (HVPE) deposition. In one embodiment, a metal organic chemical vapor deposition (MOCVD) process is used to deposit a Group III-nitride film on a plurality of substrates within a processing chamber. A closed-loop control system performs in-situ monitoring of the Group III-nitride film growth rate and adjusts film growth parameters as required to maintain a target growth rate. In another embodiment, a closed-loop control system performs in-situ monitoring of film growth parameters for multiple processing chambers for one or more film deposition systems.

Effective surface passivation of crystalline silicon using ultrathin Al2O3 films and Al2O3/SiNx stacks

Abstract: We measure surface recombination velocities (SRVs) below 10 cm/s on p-type crystalline silicon wafers passivated by atomic–layer–deposited (ALD) aluminium oxide (Al2O3) films of thickness ≥10 nm. For films thinner than 10 nm the SRV increases with decreasing Al2O3 thickness. For ultrathin Al2O3 layers of 3.6 nm we still attain a SRV < 22 cm/s on 1.5 Ω cm p-Si and an exceptionally low SRV of 1.8 cm/s on high-resistivity (200 Ω cm) p-Si. Ultrathin Al2O3 films are particularly relevant for the implementation into solar cells, as the deposition rate of the ALD process is extremely low compared to the frequently used plasma-enhanced chemical vapour deposition of silicon nitride (SiNx). Our experiments on silicon wafers passivated with stacks composed of ultrathin Al2O3 and SiNx show that a substantially improved thermal stability during high-temperature firing at 830 °C is obtained for the Al2O3/SiNx stacks compared to the single-layer Al2O3 passivation. Al2O3/SiNx stacks are hence ideally suited for the implementation into industrial-type silicon solar cells where the metal contacts are made by screen-printing and high-temperature firing of metal pastes. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Stable and transparent superhydrophobic nanoparticle films.

Abstract: A superhydrophobic surface with a static water contact angle (θw) > 150° was created by a simple “dip-coating” method of 60-nm SiO2 nanoparticles onto an amine-terminated (NH2) self-assembled monolayer (SAM) glass/silicon oxide substrate, followed by chemical vapor deposition of a fluorinated adsorbate. For comparison, a close-packed nanoparticle film, formed by convective assembly, gave θw ~120°. The stability of the superhydrophobic coating was enhanced by sintering of the nanoparticles in an O2 environment at high temperature (1100 °C). A sliding angle of <5° indicated the self-cleaning properties of the surface. The dip-coating method can be applied to glass substrates to prepare surfaces that are superhydrophobic and transparent.

High-Yield Synthesis of Boron Nitride Nanosheets with Strong Ultraviolet Cathodoluminescence Emission

Abstract: Bulk quantities of hexagonal boron nitride (h-BN) nanosheets have been synthesized via a simple template- and catalyst-free chemical vapor deposition process at 1100−1300 °C. Adjusting the synthesis and chemical reaction parameters, the thickness of the BN nanosheets can be tuned in a range of 25−50 nm. Fourier transform infrared spectra and electron energy loss spectra reveal the typical nature of sp2-hybridization for the BN nanosheets. It shows an onset oxidation temperature of 850 °C for BN nanosheets compared with only about 400 °C for that of carbon nanotubes under the same conditions. It reveals a strong and narrow cathodoluminescence emission in the ultraviolet range from the h-BN nanosheets, displaying strong ultraviolet lasing behavior. The fact that this luminescence response would be rather insensitive to size makes the BN nanosheets ideal candidates for lasing optical devices in the UV regime. The h-BN nanosheets are also better candidates for composite materials in high-temperature and hazar...