Impact of Mo and Ce on growth of single-walled carbon nanotubes by chemical vapour deposition using MgO-supported Fe catalysts

A series of nine catalysts containing Ce/Fe and Mo/Fe at various loadings on MgO supports have been studied as catalysts for chemical vapour deposition (CVD) of single-walled carbon nanotubes (SWCNTs) using a methane carbon source. Our results show that the Ce/Fe system is very suitable as a catalyst that favours SWCNT growth, and we question the special importance that has been attributed to Mo as an additive to Fe-based catalysts for SWCNT growth, as it appears that Ce is equally effective. Our results indicate that dehydroaromatization (DHA) is not a defining step for the growth mechanism, as has been suggested for Mo/Fe systems previously, and show that Ce and Mo do not seriously perturb the well-known Fe/MgO system for growth of high quality SWCNT. Using Raman spectroscopy, we have shown that the Ce/Fe/MgO catalyst system favours growth of SWCNTs with a different distribution of chiralities compared to the analogous Mo/Fe/MgO system.     

The influence of Ga source and substrate position on the growth of low dimensional GaN wires by chemical vapour deposition

This paper presents the investigation of low dimensional GaN structures synthesized from Ni-catalyzed chemical vapour deposition (CVD) method under two different conditions, i.e. Ga source and substrate position. Comparative studies based on the morphological, structural and optical characteristics of synthesized GaN wires were carried out in this work. The variations of morphological and dimensional aspects of the GaN wires were attributed to the position of Ga precursor and substrates. These factors were found to be able to influence the degree of supersaturation of gaseous reactants, which is essential in the growth of GaN wires by vapour-liquid-solid (VLS) mechanism. The synthesized GaN wires typically were found to have diameters ranging 35-80 nm (nanowires) and 0.4-1.3 μm (microwires), respectively, with length up to several ten of microns. X-ray diffraction (XRD) results indicated that the grown GaN wires were hexagonal wurzite phase. Ultraviolet (UV) and blue emissions were observed from photoluminescence (PL) measurements. Raman spectra displayed asymmetrical and broadened bands which could be ascribed to the size effect, surface disorder and internal strain of the synthesized GaN wires.     

A theoretical analysis of epitaxial growth of CuInS2 by chemical vapour deposition

Summary A theoretical analysis has been carried out to investigate the kinetics involved in the CVD growth of CuInS₂. A stagnant-layer model is assumed for the numerical, simulation. Computational results for the growth rate as a function of the substrate temperature, mean, gas velocity and partial pressures in the reaction tube are obtained. This analysis indicates that the substrate temperature plays a dominant role in the growth rate, which is consistent with our experimental data. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Influence of ignition condition on the growth of silicon thin films using plasma enhanced chemical vapour deposition

The influences of the plasma ignition condition in plasma enhanced chemical vapour deposition (PECVD) on the interfaces and the microstructures of hydrogenated microcrystalline Si (μc-Si:H) thin films are investigated.The plasma ignition condition is modified by varying the ratio of SiH 4 to H 2 (R H).For plasma ignited with a constant gas ratio,the time-resolved optical emission spectroscopy presents a low value of the emission intensity ratio of Hα to SiH (I Hα /I SiH) at the initial stage,which leads to a thick amorphous incubation layer.For the ignition condition with a profiling R H,the higher I Hα /I SiH values are realized.By optimizing the R H modulation,a uniform crystallinity along the growth direction and a denser μc-Si:H film can be obtained.However,an excessively high I Hα /I SiH may damage the interface properties,which is indicated by capacitance-voltage (C-V) measurements.Well controlling the ignition condition is critically important for the applications of Si thin films.     

Atmospheric pressure chemical vapour deposition of vanadium diselenide thin films

Atmospheric pressure chemical vapour deposition (APCVD) of vanadium diselenide thin films on glass substrates was achieved by reaction of [V(NMe₂)₄] and ^tBu₂Se. X-ray diffraction showed that the VSe₂ films were crystalline with preferential growth either along the (1 0 1) or the (1 1 0) direction. Energy-dispersive analysis by X-rays (EDAX) gave a V:Se ratio close to 1:2 for all films. The films were matt black in appearance, were adhesive, passed the Scotch tape test but could be scratched with a steel scalpel. SEM showed that the films were composed of plate-like crystallites orientated parallel to the substrate which become longer and thicker with increasing deposition temperature. Attempts to produce vanadium selenide films were also performed using ^tBu₂Se and two different vanadium precursors: VCl₄ and VOCl₃. Both were found to be unsuitable for producing VSe₂ from the APCVD reaction with ^tBu₂Se. The VSe₂ showed charge density wave transition at 110-115 K.     

The properties of GaMnN films grown by metalorganic chemical vapour deposition using Raman spectroscopy

An investigation of room-temperature Raman scattering is carried out on ferromagnetic semiconductor GaMnN films grown by metalorganic chemical vapour deposition with different Mn content values. New bands around 300 and 669 cm-1, that are not observed in undoped GaN, are found. They are assigned to disorder-activated mode and local vibration mode (LVM), respectively. After annealing, the intensity ratio between the LVM and E2 (high) mode, i.e., ILVM /IE2 (high) , increases. The LO phonon-plasmon coupled (LOPC) mode is found in GaMnN, and the frequency of the LOPC mode of GaMnN shifting toward higher side is observed with the increase in the Mn doping in GaN. The ferromagnetic character and the carrier density of our GaMnN sample are discussed.     

Exclusion zone surrounding silicon nanoclusters formed by rapid thermal chemical vapour deposition on SiO2

We present results of an experimental investigation on the nearest-neighbour distance of silicon nanoclusters obtained by chemical vapour deposition of silane on silicon oxide substrates. Structural characterization has been performed by means of energy filtered transmission electron microscopy, which allowed us to observe dot sizes down to 0.5 nm in radius. We have found that silicon nanodots after deposition are separated by a minimum distance of about 4 nm. This effect has also been observed on samples deposited in the same conditions on substrates which have been subjected to different chemical treatments. The phenomenon is attributed to the existence of a capture zone, within which new deposited Si monomers preferentially contribute to the growth of a previously nucleated seed rather than aggregate to form a new nucleus. As a confirmation of this hypothesis, the average dot radius has been observed to be proportional to the capture region size, thus indicating a scaling behaviour for this process. Moreover when the inter-dot distance distribution is scaled to its average value, it collapses into a universal curve.     

Growth of aligned single-walled carbon nanotubes under ac electric fields through floating catalyst chemical vapour deposition

Through floating catalyst chemical vapour deposition(CVD) method,well-aligned isolated single-walled carbon nanotubes (SWCNTs) and their bundles were deposited on the metal electrodes patterned on the SiO₂/Si surface under ac electric fields at relatively low temperature(280℃). It was indicated that SWCNTs were effectively aligned under ac electric fields after they had just grown in the furnace.The time for a SWCNT to be aligned in the electric field and the effect of gas flow were estimated. Polarized Raman scattering was performed to characterize the aligned structure of SWCNTs. This method would be very useful for the controlled fabrication and preparation of SWCNTs in practical applications.     

Laser assisted chemical vapour deposition of silicon oxide layers

This paper focuses on the deposition of silicon oxide thin films, using laser assisted CVD based on a CO₂ laser, and on the feasibility of the process for coating porous silicon samples. Scanning electron and atomic force microscopy were used to analyse the morphology and microstructure of the films, while structure and chemical composition were determined by Fourier transform infrared and Rutherford backscattering spectroscopy. Two-wavelength ellipsometry was used for thickness and refractive index evaluation. The photoluminescence of SiO₂/PS was measured and compared with that of uncoated samples.     

Nanoparticulate cerium dioxide and cerium dioxide-titanium dioxide composite thin films on glass by aerosol assisted chemical vapour deposition

Two series of composite thin films were deposited on glass by aerosol assisted chemical vapour deposition (AACVD)—nanoparticulate cerium dioxide and nanoparticulate cerium dioxide embedded in a titanium dioxide matrix. The films were analysed by a range of techniques including UV-visible absorption spectroscopy, X-ray diffraction, scanning electron microscopy and energy dispersive analysis by X-rays. The AACVD prepared films showed the functional properties of photocatalysis and super-hydrophilicity. The CeO₂ nanoparticle thin films displaying photocatalysis and photo-induced hydrophilicity almost comparable to that of anatase titania.     

Effect of diffusion length on the nucleation of chemical vapour deposition diamond

Atomic steps have been suggested as preferential sites for nucleation. However, evidence from recent experiments on diamond growth using faceted sapphire as well as reconstructed silicon substrates shows that atomic steps alone do not always enhance nucleation in the chemical vapour deposition environment. The comparison of the diffusion length of the nucleation precursors and the width of the terraces between the surface steps provides further insights into this nucleation mechanism.     

Electron field emission characteristics of nano-catkin carbon films deposited by electron cyclotron resonance microwave plasma chemical vapour deposition

This paper reported that the nano-catkin carbon films were prepared on Si substrates by means of electron cyclotron resonance microwave plasma chemical vapour deposition in a hydrogen and methane mixture. The surface morphology and the structure of the fabricated films were characterized by using scanning electron microscopes and Raman spectroscopy, respectively. The stable field emission properties with a low threshold field of 5V/μm corresponding to a current density of about 1μA/cm^2 and a current density of 3.2mA/cm^2 at an electric field of 10V/μm were obtained from the carbon film deposited at CH4 concentration of 8%. The mechanism that the threshold field decreased with the increase of the CH4 concentration and the high emission current appeared at the high CH4 concentration was explained by using the Fowler-Nordheim theory.     

Catalyst-free growth of well-aligned arsenic-doped ZnO nanowires by chemical vapor deposition method

ZnO nanowires with different arsenic concentration were grown on Si (1 0 0) substrates by chemical vapor deposition method without using catalyst. Zn/GaAs mixed powders were used as Zn and As source, respectively. Oxygen was used as oxidant. The images of scanning electron microscope show that the arsenic-doped ZnO nanowires with preferred c-axial orientation were obtained, which is in well accordance with the X-ray diffraction analysis. The arsenic related acceptor emission was observed in the photoluminescence spectra at 11 K for all arsenic-doped ZnO samples. This method for the preparation of arsenic-doped ZnO nanowires may open the way to realize the ZnO nanowires based light-emitting diode and laser diode.     

Influence of double A1N buffer layers on the qualities of GaN films prepared by metal-organic chemical vapour deposition

<正>In this paper we report that the GaN thin film is grown by metal-organic chemical vapour deposition on a sapphire (0001) substrate with double AlN buffer layers.The buffer layer consists of a low-temperature(LT) AlN layer and a high-temperature(HT) AlN layer that are grown at 600℃and 1000℃,respectively.It is observed that the thickness of the LT-AlN layer drastically influences the quality of GaN thin film,and that the optimized 4.25-min-LT-AlN layer minimizes the dislocation density of GaN thin film.The reason for the improved properties is discussed in this paper.     

Generation of a stable surface concentration of amino groups on silica coated onto titanium substrates by the plasma enhanced chemical vapour deposition method

This report describes the amino functionalisation of the surface of plasma enhanced chemically vapour deposited silica films (PECVD-SiO₂), which were coated onto titanium substrates. Amino groups were linked to PECVD-SiO₂ via 3-aminpropyl triethoxysilane (APTES). We showed that the APTES functionalised PECVD-SiO₂ surfaces contained a high packing density of amino groups (67-92 NH₂ groups per nm²), indicative of a multilayered and highly cross-linked APTES film. 65-66% of the original surface concentration of APTES was retained on the PECVD-SiO₂ surface after incubation under physiological conditions, indicating that APTES films are relatively stable on PECVD-SiO₂ in these environments. The stability of the amino groups obtained on PECVD-SiO₂ in this study is much higher compared to other hydroxyl-bearing materials, such as titanium. Therefore, PECVD-SiO₂ films may find use as functional biomaterial coatings and as intermediate adhesion layers in silanisation processes.     

Morphology of carbon nanotubes prepared via chemical vapour deposition technique using acetylene: A small angle neutron scattering investigation

Small angle neutron scattering (SANS) has been utilized to study the morphology of the multi-walled carbon nanotubes prepared by chemical vapour deposition of acetylene. The effects of various synthesis parameters like temperature, catalyst concentration and catalyst support on the size distribution of the nanotubes are investigated. Distribution of nanotube radii in two length scales has been observed. The number density of the smaller diameter tubes was found more in number compared to the bigger one for all the cases studied. No prominent scaling of the structure factor was observed for the different synthesis conditions.      

Nanofabrication of tungsten supertip by electron-beam-induced deposition

Two methods were used to fabricate tungsten supertips by electron-beam-induced deposition using 200 keV electrons. The first method is stationary deposition of self-standing tips. The smallest lateral size is less than 10 nm with a rather low aspect ratio of tip. High aspect ratio (up to 30) can only be obtained at a big lateral size with a saturated root diameter of 60–65 nm. The other method is scan deposition of self-supporting tip, with a root width of 7–10 nm and a sharp apex in size of 3 nm. Using this method a higher aspect ratio (more than 72) can be achieved at a smaller lateral size, which is better to fabricate fine supertips for usage.     

Morphological control of copper phthalocyanine films by protonation-electrophoretic deposition

Films composed of various nanostructured copper phthalocyanine are controllably prepared by the method of protonation-electrophoretic deposition. The ultralong nanowires of copper phthalocyanine are grown at the deposition temperature of 70 °C. And the results of films UV-vis absorption spectra and X-ray diffraction indicate that copper phthalocyanine possesses the transformation tendency from α-phase to thermostable β-phase under the higher deposition temperature. The formation process of the ultralong nanowires illustrates that the nanowires grow in longitudinal orientation much faster than in lateral direction. And the time dependence of the films morphology, from another point of view, proves that copper phthalocyanine is dissolved in the precursor solutions, and the formation of the nanostructured copper phthalocyanine contains the process of crystal growth, which is different from the traditional electrophoretic deposition. So the films morphology is flexible to be controlled by varying the deposition conditions. These diverse nanostructured films have potential applications in the electrochemical and optoelectrical equipments.     

First nucleation steps during deposition of SiO2 thin films by plasma enhanced chemical vapour deposition

The initial nucleation stages during deposition of SiO₂ by remote plasma enhanced chemical vapour deposition (PECVD) have been monitored by XPS inelastic peak shape analysis. Experiments have been carried out on two substrates, a flat ZrO₂ thin film and a silicon wafer with a native silicon oxide layer on its surface. For the two substrates it is found that PECVD SiO₂ grows in the form of islands. When the SiO₂ particles reach heights close to 10 nm they coalesce and cover completely the substrate surface. The particle formation mechanism has been confirmed by TEM observation of the particles grown on silicon substrates. The kinetic Monte Carlo simulation of the nucleation and growth of the SiO₂ particles has shown that formation of islands is favoured under PECVD conditions because the plasma species may reach the substrate surface according to off-perpendicular directions. The average energy of these species is the main parameter used to describe their angular distribution function, while the reactivity of the surface is another key parameter used in the simulations.     

Structure evolution and stoichiometry control of Pb(Zr, Ti)O3 thick films fabricated by electrospray assisted vapour deposition

Well-crystallized and stoichiometric Pb(Zr, Ti)O₃ (PZT) films, typically ∼5 μm thick, with pure perovskite-type rhombohedral structures have been successfully prepared via an electrospray assisted vapour deposition (ESAVD) method. Control of the deposition temperature within a narrow range of 300-400 °C resulted in films with the most desirable phases. PZT films with close stoichiometric match with the expected composition ratio and uniform element distribution were obtained by adding the appropriate levels of excess Pb in the precursor solutions. The annealed films were uniform, dense, compact and adherent to the substrates. The dielectric constant, ?_r, and loss tangent, tan δ, of the fabricated PZT films measured at 10 kHz were 442 and 0.09, respectively. The ESAVD deposited PZT films showed a remanent polarization, P_r, of 15.3 μC/cm² and coercive field, E_c, of 86.7 kV/cm. These results demonstrate the clear potential of the ESAVD method as a promising technique for the fabrication of thick PZT films.