Showing papers in "Chemical Vapor Deposition in 2008"

The CVD of Nanodiamond Materials

Abstract: The growth and characteristics of nanocrystalline diamond thin films with thicknesses from 20 nm to less than 5 µm are reviewed. These materials contain between 95% and >99.9% diamond crystallites, the balance being made up from other forms of carbon. Within this class of materials there is a continuous range of composition, characteristics, and properties which depend on the nucleation and growth conditions. It is convenient to classify these films as either ultra-nanocrystalline-diamond (UNCD) or nanocrystalline-diamond (NCD) based on their microstructure, properties, and growth environment. In general, UNCD materials are composed of small particles of diamond ca. 2–5 nm in size with sp2-carbon bonding between the particles. UNCD is usually grown in argon-rich, hydrogen-poor CVD environments, and may contain up to 95–98% sp3-bonded carbon. NCD materials start with high density nucleation, initiating nanometer-sized diamond domains which grow in a columnar manner with the grain size coarsening with thickness. NCD is generally grown in carbon-lean and hydrogen-rich environments. NCD and UNCD exhibit an interesting range of physical properties which find use in X-ray windows and lithography, micro- and nanomechanical and optical resonators, tribological shaft seals and atomic force microscopy (AFM) probes, electron field emitters, platforms for chemical and DNA sensing, and many other applications.

Thin Polymer Films with High Step Coverage in Microtrenches by Initiated CVD

Abstract: Initiated (i)CVD is used to deposit thin films of poly(cyclohexylmethacrylate) (pCHMA) in microtrenches of depth 7 µm and widths 1-5 µm. By changing the fractional saturation of the monomer vapor, step coverage of 0.85 is achieved for the highest aspect ratio trench studied while maintaining a deposition rate of 15 nm min−1. An analytical model for determining the sticking probability of the initiating radical (CH3)3CO· is developed, and is experimentally shown to be a function of the fractional saturation of the monomer vapor. For the conditions studied, the sticking probability is in the range 1.1 × 10−2–5.0 × 10−2. These results suggest that iCVD proceeds via the reaction of a vapor-phase initiating radical with a surface-adsorbed monomer.

Atomic Layer Deposition of Iron Oxide Thin Films and Nanotubes using Ferrocene and Oxygen as Precursors

Abstract: Thin films and nanotubes of iron oxide are deposited using atomic layer deposition (ALD) on Si(100) and anodic aluminum oxide (AAO), respectively. Ferrocene, Fe(Cp)(2), and oxygen are used as pre ...

Formation of Continuous Nanocrystalline Diamond Layers on Glass and Silicon at Low Temperatures

Abstract: Nanocrystalline diamond thin films are grown on silicon and glass substrates by microwave plasma (MP)CVD from a gas mixture of methane and hydrogen at low substrate temperatures. The initial stages of diamond growth, i.e., i) the growth of individual nanometer-sized crystals and clusters, and ii) coalescence into a continuous layer, are investigated by diverse analytic techniques. Atomic force microscopy (AFM) measurements reveal nearly unchanging surface roughness up to 40 min. X-ray photoelectron spectroscopy (XPS) measurements detect changing of the surface composition from the very beginning of the growth process. The rapid carbon increase is assigned to the enlarging of the grown crystals and clusters. Scanning electron microscopy (SEM) images indicate a possible lateral growth type. The found dependences indicate that a two-dimensional growth mode takes place at low substrate temperatures. Grown nanocrystalline diamond films are optically transparent in a wide spectral range, and exhibit a high refractive index of 2.34.

Zinc Oxide Thin Films Grown by Aerosol Assisted CVD

Abstract: Zinc oxide (ZnO) thin films are deposited at 400-650 degrees C onto glass substrates by aerosol assisted (AA)CVD of a zinc acetate [Zn(C2H3O2)(2)] solution in methanol. The thin films show high transparency over the visible and infrared regions (80-95%) and a 001 (c-axis) preferred orientation. The surface morphology and crystallographic orientation are dependent on the substrate temperature. The photocatalytic activity of the films is determined using the destruction of stearic acid (SA) by UV irradiation. The rate is monitored via infrared spectroscopy (IRS) and shows appreciable activity, close to that seen for anatase titania, in the films deposited at 650 degrees C. Water droplet contact angles on both ambient and UV-irradiated ZnO surfaces are determined, and there is seen to be an increase in photoinduced hydrophillicity for all films, with a reduction in contact angle of around 50 degrees.

Hybrid Aerosol Assisted and Atmospheric Pressure CVD of Gold‐Doped Vanadium Dioxide

Abstract: Hybrid aerosol-assisted (AA) and atmospheric pressure (AP) CVD methodology is utilized, for the first time, to produce thin films of gold nanoparticle-doped vanadium dioxide. Good surface coverage, comparable to that of APCVD processes, is observed, and a variety of different film thicknesses and dopant levels are easily produced. The films are analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Their optical and thermochromic behaviors are also determined. Incorporation of gold nanoparticles in the films leads to significant changes in the color of the film due to the presence of a surface plasmon resonance (SPR) band.

Tribenzyltin(IV)chloride Thiosemicarbazones: Novel Single Source Precursors for Growth of SnS Thin Films

Abstract: Tin sulfide (SnS) thin films are deposited using simple tin thiosemicarbazone complexes of the type Bz(3)SnCl(L) (L = thiosemicarbazones of salicylaldehye and 4-chlorobenzaldehyde). Thin films are deposited using aerosol-assisted (AA) CVD in the range 375-475 degrees C. X-ray diffraction (XRD) shows the formation of SnS regardless of growth temperature and precursor type. Scanning electron microscope (SEM) images show that the films have wafer-like morphology, and the growth temperatures do not have a profound effect on morphology.

The Atomic Layer Deposition of HfO2 and ZrO2 using Advanced Metallocene Precursors and H2O as the Oxygen Source

Abstract: The atomic layer deposition (ALD) of HfO2 and ZrO2 thin films is investigated using (MeCp)(2)HfMe2, (MCp)(2)Hf(OMe)(Me), (MeCp)(2)ZrMe2, and (MeCp)(2)Zr(OMe)(Me) as the precursors at deposition temperatures between 300 and 500 degrees C, with water vapor as the oxygen Source. A self-limiting growth mechanism is confirmed at 350 degrees C for all the metal precursors examined. The processes provide nearly stoichiometric HfO2 and ZrO2 films with carbon and hydrogen concentrations below 0.5 and 1.0 at.-%, respectively, for representative samples. All films are polycrystalline as deposited, and possess a thin interfacial SiO2 layer. The capacitance-voltage (C-V) and Current density-voltage (I-V) behavior is reported and discussed for capacitor structures containing films from this study.

Coating of Highly Porous Fiber Matrices by Atomic Layer Deposition

Abstract: The potential of atomic layer deposition (ALD) in the coating of highly porous, 0.5 mm thick, metal fiber matrices is explored. Three different reactor types are compared for ALD of Al2O3 thin films from trimethylaluminum and water. Both an evacuation-type and a flow-type process are successful in forming conformal Al2O3 coatings on the fibers. The coatings are able to protect the fibers against electrochemical corrosion and thermal oxidation. In addition, a metallic Ir thin film is deposited by ALD on one of the Al2O3-coated fiber matrices. This kind of a structure could be used, for example, as a catalytic filter.

An Analysis of the Deposition Mechanisms involved during Self-Limiting Growth of Aluminum Oxide by Pulsed PECVD†

Abstract: Self-limiting growth of Al2O3 is accomplished using both pulsed plasma-enhanced (PE) CVD and plasma-enhanced atomic layer deposition (PEALD). In pulsed PECVD the two reactants (Al(CH3)3/TMA and O2) are supplied continuously, while in PEALD the TMA is delivered in pulses separated by purge steps. For both processes the rate per cycle saturates with ∼200 L of TMA exposure. At 165 °C a rate of 1.37 A per cycle is obtained using PEALD. For pulsed PECVD the rate scales linearly with the TMA partial pressure, and its extrapolation is in good agreement with PEALD. The results suggest that deposition in pulsed PECVD involves an ALD component which is supplemented by PECVD growth, and that the contribution of the latter may be tuned using the TMA partial pressure. Experiments using patterned wafers support this hypothesis. Conformal coatings are observed within 10:1 aspect ratio trenches using pulsed PECVD; however the deposition rate on the surface of these substrates is greater than within the trench. The ratio between the two corresponds well to the ratio of rates obtained from pulsed PECVD and PEALD on planar substrates. With cycle times <1 s, net rates up to 20 nm min−1 are obtained by pulsed PECVD while retaining high quality and digital control.

Molecular dynamics simulations of the sticking and etch behavior of various growth species of (ultra)nanocrystalline diamond films

Abstract: The reaction behavior of species that may affect the growth of ultrananocrystalline and nanocrystalline diamond ((U)NCD) films is investigated by means of molecular dynamics simulations. Impacts of CHx (x ¼ 0 � 4), C2Hx (x ¼ 0 – 6), C3Hx (x ¼ 0 – 2), C4Hx (x ¼ 0 – 2), H, and H2 on clean and hydrogenated diamond (100)2T 1 and (111)1T 1 surfaces at two different substrate temperatures are simulated. We find that the different bonding structures of the two surfaces cause different temperature effects on the sticking efficiency. These results predict a temperature-dependent ratio of diamond (100) and (111) growth. Furthermore, predictions of which are the most important hydrocarbon species for (U)NCD growth are made.

Atomic Layer Deposition of LaF3 Thin Films using La(thd)3 and TiF4 as Precursors

Abstract: Lanthanum fluoride is a vacuum ultraviolet (VUV) transparent material which is widely used in optical applications. An atomic layer deposition (ALD) process is developed for depositing lanthanum fluoride thin films for the first time. LaF3 films are grown at 225–350 °C using La(thd)3 and TiF4 as precursors. The crystallinity, morphology, composition, thicknesses, and refractive indices of the films are analyzed by X-ray diffraction/reflection (XRD/XRR), atomic force microscopy (AFM), scanning electron microscopy (SEM), time-of-flight elastic recoil detection analysis (TOF-ERDA), and UV-vis spectrophotometry. Electrical properties, such as permittivity and leakage current density, are also studied. An exceptionally high growth rate of about 5 A per cycle is achieved at 225–250 °C. The films are polycrystalline, the refractive indices vary between 1.57 and 1.61, and the permittivity is 12.3. The impurities detected in the LaF3 film are Ti, C, O, and H. The level of all of these tends to decrease with increase in the deposition temperature, and is only 3.5 at.-% at 350 °C.

Bis(tert‐butylimido)‐bis(dialkylamido) Complexes of Molybdenum as Atomic Layer Deposition (ALD) Precursors for Molybdenum Nitride: the Effect of the Alkyl Group

Abstract: Bis(tert-butylimido)-bis(diethylamido)molybdenum [(tBuN)2Mo(NEt2)2] and bis(tert-butylimido)-bis(di-isopropylamido)molybdenum [(tBuN)2Mo(NiPr2)2], possible precursors for atomic layer deposition (ALD) of molybdenum nitride, are synthesized and characterized. Calorimetric studies are carried out to examine the thermal stability of the new precursor candidates. For the diethylamido complex, sufficient thermal stability is found, ALD tests are performed, and satisfactory parameters for controlled growth are identified. Films grown from bis(tert-butylimido)-bis(diethylamido)molybdenum and ammonia are amorphous, smooth, and conformal. The di-isopropylamido complex shows thermal instability and a very low synthetic yield, hence it is not tested in ALD. Possible decomposition reactions of the precursors are studied by density functional theory (DFT) calculations. The computational results support the low thermal stability of di-isopropylamido complex found through calorimetric studies.

Formation of Tantalum Carbide and Nitride Phases in Atomic Layer Deposition Using Hydrogen Plasma and tert‐Butylimido‐tris(diethylamido)‐tantalum (TBTDET), and its Effect on Material Properties

Abstract: TaCN films are deposited with plasma-enhanced atomic layer deposition (PEALD) using tert-butylimido-tris(diethylamido)-tantalum and hydrogen. It is confirmed that the film is a homogeneous mixture of TaC, TaN, Ta3N5, and Ta2O5 with the oxide phase formed from the post-deposition uptake of oxygen from the air. It is shown that the electrical properties of TaCN film are affected by the phase composition in the film. The effects of process parameters, such as deposition temperature, plasma power, and cycle time, on the film composition and electronic properties are evaluated. With the increase of the TaC and TaN phases over the Ta3N5 phase, the resistivity of the film is decreased. As the deposition temperature, plasma power, and plasma cycle time are increased, the carbide and TaN phases in the film are increased and the film resistivity is decreased. The uptake of oxygen after deposition is up to 10 at.-%, and the resistivity of TaCN film deposited using PEALD is as low as 350 µΩ · cm.

Growth of diamond nanoplatelets by CVD

Abstract: Hexagonal, single-crystalline, diamond nanoplatelets synthesized by microwave plasma (MP)CVD on Au-Ge alloy and nanocrystalline diamond (nc-diamond) film substrates, respectively, are reported. On the nc-diamond matrix, hexagonal diamond nanoplatelets can grow to a thickness of as little as approximately 10 nm. The effects of various processing parameters, such as methane concentration, microwave power, and gas pressure, on the growth of diamond nanoplatelets are explored. High-resolution transmission electron microscopy (HRTEM) reveals that the diamond nanoplatelets contain multi-parallel twins, and the side faces of the platelets exhibit {100}/{111} ridge-and-trough structure. Anisotropic growth of diamond nanoplatelet is believed to result from the side face structure of the twinned platelets and intensive plasma reaction.

A Theoretical Study of Nitrogen‐Induced Effects on Initial Steps of Diamond CVD Growth

Abstract: Diamond is an important material in many industrial applications (e.g., machining of hard materials, bio-electronics, optics, electronics, etc.) because of its exceptional properties such as hardness, tolerance to aggressive environments, compatibility with human tissues, and high carrier mobility. However, a highly controlled method for growing artificial high-purity diamond on a range of different substrates is needed to exploit these exceptional properties. The Chemical Vapour Deposition (CVD) method is a useful tool for this purpose, but the process still needs to be developed further to achieve better control of growth. In this context, the introduction of dopant species into the gas phase has been shown to strongly influence growth rate and surface morphology. Density Functional Theory (DFT) methods are used to deepen our atomic-level understanding of the effect of dopants on the mechanism for CVD growth on diamond. More specifically, the effect of four dopants (N, P, B and S) has been studied on the important reaction steps in the growth mechanism of diamond. Substitution of N into the diamond lattice has generally been found to disfavour critical reaction steps in the growth of the 100-face in diamond. This negative effect has been related to electron transfer from the N dopant into an empty surface state, e.g., a surface carbon radical. In addition, strong surface stabilization is observed for N substitution in certain sites via a beta-scission reconstruction, with the formation of sp2 carbon. These observations correlate well with observed surface degradation and decrease in growth rate when a high concentration of nitrogen gas is introduced into the CVD growth process. The effect of co-adsorbed P, S and B onto the diamond surface has also been investigated for two reaction steps: CH3 adsorption and H abstraction. While P and B are observed to influence these reaction steps, the effect of S is rather limited.

Atomic Vapor Deposition of Titanium Nitride as Metal Electrodes for Gate-last CMOS and MIM Devices

Abstract: Pure and diluted Ti[N(Et)2]4 precursors are used to grow TiN layers at 400–600 °C by using atomic vapor deposition (AVD®). The composition, microstructure, and electrical properties of TiN films with various thicknesses are investigated. The determined work function of 4.7 eV indicates the possibility of using AVD®-grown TiN as a metal gate electrode for PMOSFET and metal-insulator-metal (MIM) devices. TiN/HfO2/SiO2 stacks are integrated into gate-last PMOS transistors, and the extracted parameters are compared to poly-Si/SiO2 reference transistors. The optimized films grown at 400 °C with a thickness of 20 nm exhibit a resistivity of 400 µΩ cm.

Growth of ZnO Nanostructures Produced by MOCVD: A Study of the Effect of the Substrate

Abstract: A study of the influence of the substrate mismatch on the growth of ZnO nanostructures is reported. ZnO nanostructures are deposited, by a simple catalyst-free metal-organic (MO)CVD approach, onto various substrates, such as SrTiO3(100), Si(100), and Al2O3(0001), using a novel diamine adduct of zinc bis-2 thenoyl-trifluoroacetonate (Zn(tta)2 · tmeda, Htta = CF3COCH2COC4H3S, tmeda = N,N,N′,N′-tetramethylethylenediamine). Structural characterizations indicate that both morphology and crystalline structure of the obtained ZnO nanostructured systems strongly depend upon the crystalline mismatch with the substrate. Room-temperature cathodoluminescence (CL) spectroscopy is used to characterize the optical properties of the various nanostructures. The resulting cathodoluminescence spectra of all the samples show the presence of a strong and broad green band around 2.4 eV.

Controlled Nanostructured Silver Coated Surfaces by Atmospheric Pressure Chemical Vapour Deposition

Abstract: Thin film silver has been widely reported for its interesting properties. In this paper we describe a route to produce controlled nanostructured silver layers. A combination of Flame Assisted Chemical Vapour Deposition at atmospheric pressure, with low cost and a low toxicity silver precursor, was used to generate coatings of structured silver surfaces on glass. This approach gives a high degree of control of surface structure, density and topography. These layers have potential applications in areas such as catalysis, photo-activity and for biocidal surfaces. Our results indicate very high biocidal activity where the nano-structure is proposed as playing a significant role

Surface Science Contribution to the BEN Control on Si(100) and 3C-SiC(100): Towards Ultrathin Nanocrystalline Diamond Films†

Abstract: Deposition of thin and smooth nanocrystalline diamond films requires a high degree of control of the nucleation stage. The nature of the interface between diamond film and substrate is also important for some applications. The successive steps of the bias-enhanced nucleation (BEN) process are studied in-situ on Si(100) and 3C-SiC(100) using electron spectroscopies. Thin nanodiamond films (80-900 nm) have been achieved on Si(100). The formation of a thin covering SiC layer (2-3 nm) during the plasma exposure for parameters stabilization (PEPS) step leads us to study the plasma/surface interactions on 3C-SiC(100) surfaces. The C-terminated 3C-SiC(100) demonstrates a large inertia under microwave plasma (MP)CVD conditions. An enhancement of diamond nucleation on this surface is observed. Moreover, surface analysis reveals very little damage after BEN on 3C-SiC surfaces. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.

Study of Atmospheric MOCVD of TiO2 Thin Films by Means of Computational Fluid Dynamics Simulations

Abstract: This paper presents the computational study of the metal-organic (MO) CVD of titanium dioxide (TiO2) films grown using titanium tetraisopropoxide (TTIP) as a precursor and nitrogen as a carrier gas. The TiO2 films are deposited under atmospheric pressure. The effects of the precursor concentration, the substrate temperature, and the hydrolysis reaction on the deposition process are investigated. It is found that hydrolysis of the TTIP decreases the onset temperature of the gas-phase thermal decomposition, and that the deposition rate increases with the precursor concentration and with the decrease of substrate temperature. Concerning the mechanism responsible for the film growth, the model shows that at the lowest precursor concentration, the direct adsorption of the precursor is dominant, while at higher precursor concentrations, the monomer deposition becomes more important.

The Impact of Diamond Grain Size on Hydrogen Concentration, Bonding Configuration, and Electron Emission Properties of Polycrystalline-Diamond Films

Abstract: In the present work we review our recent studies of the incorporation of hydrogen and its bonding configuration in diamond films composed of diamond grains of varying size. Polycrystalline-diamond films are deposited by three different methods; hot filament (HF), microwave (MW) and direct current glow discharge (DCGD)CVD. The size of the diamond grains which constitute the films varies in the following way; hundreds of nanometers in the case of HFCVD (“sub-micrometer size”, ∼300 nm), tens of nanometers in the case of MWCVD (3–30 nm), and a few nanometers in the case of DCGDCVD (“ultra nanocrystalline diamond”, ∼5 nm). Raman spectroscopy (RS), secondary ion mass spectroscopy (SIMS), and high-resolution electron energy loss spectroscopy (HREELS) are applied to investigate the hydrogen trapping in the films. The hydrogen retention of the diamond films increases with decreasing grain size, indicating the likelihood that hydrogen is bonded and trapped in grain boundaries, as well as on the internal grain surfaces. RS and HREELS analyses show that at least part of this hydrogen is bonded to sp2- and sp3-hybridized carbon, thus giving rise to typical CH vibration modes. Both vibrational spectroscopies show the increase of sp2 CH modes in transition from sub-micrometer to ultra nanocrystalline grain size. The impact of diamond grain size on the shape of the RS and HREELS hydrogenated diamond spectra is discussed. In addition, the dependence of electron emission properties on film thickness and diamond grain size is reported.

Nanodiamond-Coated Carbon Nanotubes: Early Stage of the CVD Growth Process†

Abstract: A series of deposits formed by single-walled carbon nanotube (SWNT) bundles coated by nanocrystalline diamond (NCD) are produced using a modified CVD reactor. The nanocylindrical structures are deposited on Si substrates using carbon nanopowders and atomic H as reactants. The nanocrystalline coating obtained from short-time runs lasting up to 6 min are analyzed by micro-Raman and cathodoluminescence (CL) techniques, in order to obtain information on the structural evolution of the material during the first steps of the growth process. The morphological investigation performed by field emission scanning electron microscopy (FESEM) indicates that the nanocrystalline coating generated by a process lasting 4– 6 min is formed by protruding embryo diamond crystallites with a needle-like shape. Thereafter the shape of the diamond phase evolves giving rise to elongated and better faceted diamond grains well anchored on the nanotube bundle surfaces.

An Investigation of Titanium‐Vanadium Nitride Phase Space, Conducted Using Combinatorial Atmospheric Pressure CVD

Abstract: The technique of combinatorial atmospheric pressure (AP)CVD, a recent addition to the growing number of combinatorial materials methods, is used to form twelve members of the TixV1-xN alloy series with 0.29 < x < 0.94. This series of compounds has a rock-salt structure with TiN and VN as the end members. The twelve phases, which have potential use as heat mirror coatings, are all synthesized in a single experiment. The structure and properties of the materials are investigated using powder X-ray diffraction (XRD) and electron probe microanalysis (EPMA). The optical properties are considered using visible-IR spectroscopy (IRS), which allows the suitability of the films as solar control coatings to be investigated and optimized as a function of composition.

PECVD Siloxane and Fluorine‐Based Copolymer Thin Films

Abstract: Plasma copolymerization is utilized to fabricate thin photonic films based on hexamethyldisiloxane (HMDSO, C6H18Si2O) and octafluorocyclobutane (OFCB, C4F8). The structure of the plasma copolymerized films is examined by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR), and the optical properties including refractive index, n, and extinction coefficient, k, are determined by spectroscopic ellipsometry. The refractive indices, which range from 1.38 to 1.54, can be manipulated by adjusting the volume ratio of the two monomers, HMDSO and OFCB, during the polymerization. A nonlinear relationship between the refractive index and extinction coefficient with comonomer feed ratio is observed. A strong initial increase in both n and k as the amount of HMDSO is increased is attributed to significant defluorination of the resultant polymer films coupled with the formation of a C-C rich crosslinked network. Once the network incorporates substantial amounts of Si-C and Si-O bonds, the refractive index starts to decrease slowly due to a lowering of the density. XPS and FTIR results confirm the changes in internal structure consistent with this mechanism.

The Preparation and CVD Densification of Multi‐walled Carbon Nanotube Felt Synthesized by a Catalytic CVD Method

Abstract: Silica-nickel binary aerogels are used as catalysts for the synthesis of multi-walled carbon nanotube (MWCNT) felts. The MWCNT felts are prepared by the catalytic decomposition of methane at 680 °C over durations ranging from 30 to 120 min. After purification by a graphitization heat-treatment in argon, the MWCNT felts have a bulk density of about 0.4 g cm–3. The graphitized MWCNT felts are densified in a CVD furnace under a mixed atmosphere of propene and nitrogen at 1000 °C. The morphology and the structure of the MWCNT felt and its CVD-densified product are investigated by SEM, TEM, XRD, and Raman spectroscopy. The results reveal that the carbon nanotubes in the primary MWCNT felt have a diameter of between 15 and 40 nm, with a high aspect ratio. High-resolution TEM imaging reveals that the walls of the carbon nanotubes show little amorphous carbon covering. After the graphitization treatment, the surface of the carbon nanotubes becomes rough and some “stacked cups” and triangular structures are formed in the core of some of the nanotubes. The graphitization treatment effectively promotes crystal growth and layer orientation of the carbon nanotubes. This high temperature-treated MWCNT felt has a high purity and a low bulk density, as well as low thermal conductivity. Pyrolytic carbon formed by CVD is deposited in between carbon nanotubes and on the walls of the carbon nanotubes, leading to the densification of the MWCNT felt. The CVD-densified MWCNT felt has a higher bulk density and thermal conductivity than that of the corresponding high temperature-treated MWCNT felt. It is suggested that the MWCNT felt could be used as a precursor in the production of carbon nanotube/carbon or carbon nanotube/polymer composites.

Nanodiamond Tipped and Coated Conical Carbon Tubular Structures

Abstract: Studies of diamond nucleation and growth on conical carbon tubular structures show that the nucleation preferentially occurs at the tips, but only occurs on the sidewalls when they are pretreated with diamond or other powder dispersions, forming a nanodiamond coating. The high-resolution transmission electron microscopy (HRTEM) studies reveal that the diamond nucleation on the sidewalls may proceed through the formation of diamond nuclei within the walls at subsurface damage sites caused during pretreatment. In the case of experiments with low atomic hydrogen conditions, carbon onion structures are observed on the sidewalls but only with pretreatments.

Growth of SmNiO3 Thin Films on LaAlO3 Single Crystals

Abstract: We present experimental results on the growth of SmNiO3 epitaxial thin films, successfully deposited by a liquid source metal-organic (MO) CVD technique. X-ray diffraction (XRD) characterizations and wavelength dispersive spectroscopy (WDS) are performed in order to optimize the composition and the purity of the films. Depositions on Si (001) and LaAlO3 (001) substrates show that the SmNiO3 phase needs a perovskite substrate with a good lattice match in order to be epitaxially stabilized. Texture analysis performed on asymmetric diffraction lines reveals the epitaxial character of the growth; in-plane and out-of plane mosaicity are determined on a 1000 A thick film.

Heteroepitaxial YAlO3 Films on (100)SrTiO3 Substrates: The Use of Pole Figures as a Non‐invasive Tool to Assess the Direction of Growth

Abstract: YAlO3 films are grown on (100)SrTiO3 substrates through an in-situ novel metal-organic (MO)CVD strategy involving a molten source consisting of the second-generation Y(hfa)3·diglyme (Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione, diglyme = bis(2-methoxyethyl)ether) precursor which acts as a solvent for the Al(acac)3 (Hacac = acetylacetone). The X-ray diffraction (XRD) patterns show that the films are crystalline and highly oriented, while compositional analysis indicates that the films possess the correct 1:1 ratio. Pole figures are applied as a simple, economic, non-invasive tool to assess the growth direction of YAlO3 films.

Spectroscopic Diagnostics of Pulsed Microwave Plasmas used for Nanocrystalline Diamond Growth

Abstract: In this paper, we report emission and broadband absorption spectroscopy measurements carried out in order to characterize the pulsed process used for nanocrystalline diamond (NCD) film deposition using an Ar/H2/CH4 gas mixture. Both the gas temperature and C2 total density are determined from the C2 (D1Σu+ − X1Σg+) Mulliken system. Time-resolved and time-averaged measurements are performed in order to probe the influence of the pulse repetition rate for a duty cycle of 50%, keeping a constant time-averaged microwave power. Time-resolved fast imaging enables the two-dimensional examination of plasma ignition and expansion during the microwave pulses. The time-averaged gas temperature and C2 density depend weakly on the pulse repetition rate, with values always in the range 3600–4000 K, and around 1 × 1014 cm−3, respectively. These values are close to those measured for a continuous discharge, which suggests that the changes of the NCD growth process should be linked to the time evolution of the gas temperature and key-species density. The time evolution of the gas temperature is characteristic of a heating rate of approximately 100 K ms−1, which is very long compared to conventional H2/CH4 microwave discharges. Variation of 1000 K is thus obtained during the microwave pulse at 50 Hz, which implies important changes in the plasma composition during the microwave period. Also, the time-resolved fast imaging of the plasma discharge for a 50 Hz pulse repetition rate shows that the plasma volume and intensity evolve almost all over the microwave pulse. A considerable time evolution of some plasma characteristics such as absorbed microwave power or species density and gas temperature radial profiles is then expected. Finally, since the C2H2 C2 C conversion channels are mainly driven by the gas temperature, the increase of the gas temperature during the microwave pulse seems to lead first to the production of the C2 molecule, while C atoms are produced at the end of the microwave pulse when the gas temperature is high enough. Such time evolution of the plasma chemistry should influence the NCD deposition process in pulsed mode.