Improvement in growth yield of single-walled carbon nanotubes with narrow chirality distribution by pulse plasma CVD

A pulse plasma chemical vapor deposition (CVD) technique was developed for improving the growth yield of single-walled carbon nanotubes (SWNTs) with a narrow chirality distribution. The growth yield of the SWNTs could be improved by repetitive short duration pulse plasma CVD, while maintaining the initial narrow chirality distribution. Detailed growth dynamics is discussed based on a systematic investigation by changing the pulse parameters. The growth of SWNTs with a narrow chirality distribution could be controlled by the difference in the nucleation time required using catalysts comprising relatively small or large particles as the key factor. The nucleation can be controlled by adjusting the pulse on/ofF time ratio and the total processing time.     

Diamond nucleation suppression in chemical vapor deposition process

A systematic study of the effect of different pre-treatments of the Si substrate surface in suppressing diamond nucleation was performed to investigate the nature of the nucleation centers in chemical vapor deposition (CVD) of diamond. The Si substrates were initially scratched with diamond powder and then submitted to one of the following pre-treatments: thermal annealing in high vacuum and in air, deposition of an amorphous silicon film, and ⁸⁴Kr⁺ ion implantation. The pre-treated substrates were used in a hot filament CVD diamond process, and the diamond films obtained were analyzed by different techniques. The results suggest that the observed nucleation reduction under certain pre-treatment conditions is related to modifications induced on the original topographical features of the scratched substrate surface, which would be responsible for the CVD diamond nucleation. The dimensions of these surface features are estimated to be of the order of 5 nm.     

NUCLEATION REACTIONS AND FILM GROWTH OF COPPER ON TiN USING HEXAFLUOROACETYLACETONATE COPPER(I) TRIMETHYLVINYLSILANE

In this work, the nucleation and film growth of copper on TiN chemically treated with WF₆ and air-exposed TiN by chemical vapor deposition(CVD) from hexafluoroacetylacetonate copper¹ trimethyl-vinylsilane, (HFA)Cu(TMVS), was studied. Copper grows as islands of poorly connected grains on air-exposed TiN. In contrast, copper grows as a continuous film with well-connected grains on the surface of WF₆-treated TiN. The effect of TiN surface condition has been examined using Auger electron spectros-copy(AES), X-ray photoelectron spectroscopy(XPS) and scanning electron microscopy(SEM). On the basis of our experimental observation, and information in the literature, nucleation reaction mechanisms are proposed for the chemical vapor deposition of copper on the two different TiN samples.     

纳米线的制备方法以及研究进展

综述纳米线的主要制备方法：激光烧蚀法、化学气相沉积法、热气相沉积法、横板法、水热法等,以及目前纳米线的研究进展。     

An atomic force microscopy study of the effects of surface treatments of diamond films produced by chemical vapor deposition

Diamond films produced by chemical vapor deposition (CVD) technique must be polished and machined in order to be used for many applications (windows, heat spreaders, surface acoustic wave devices, etc). We present an Atomic Force Microscopy study of the effects of mechanical polishing, hydrogen plasma etching, and ion implantation followed by annealing and chemical etching, on the morphology of Microwave Plasma CVD polycrystalline diamond films. Both growth and nucleation sides of 0.3–0.5 mm thick free-standing films were characterized. We found that grain boundaries and anisotropy of mechanical properties (hardness and wear rate) mostly contribute to the overall roughness of Microwave Plasma CVD diamond films, which is below 0.2 nm at the single-grain scale. The further deposition of a diamond overlayer, even of small thickness, on highly polished polycrystalline diamond, results in a variety of growth modes and different growth rates depending on the grain orientation, leading to the roughness increase. Hydrogen plasma etching proved to be effective for inducing morphological and chemical changes on the surface, while an ion implantation/annealing/etching can be used for precise removal of thin diamond layers. The latter approach is promising for diamond lithography.     

Pre-treatment for diamond coatings on free-shape WC–Co tools

A new multiple chemical pre-treatment including microwave oxidation, reaction in alkaline solution and cleaning by ultrasonic treatment in acid solution has been performed for free shape cemented WC–Co tools in order to increase the diamond nucleation and to enhance the coating adhesion. High quality diamond films were deposited on such pre-treated substrates by a hot filament chemical vapor deposition (CVD) method using a mixture of acetone and hydrogen gases. After pre-treatment, the surface of the WC–Co substrate becomes slightly rough, but its composition or structure shows no changes identified by X-ray diffraction (XRD). Scanning electron microscopy (SEM) indicates a distribution of uniform micro-roughness WC grains on substrate surface. The results show that the multiple chemical pre-treatment effectively increases the diamond nucleation as well as greatly enhancing the coating adhesion. Especially, it is suitable for free-shape substrates, which may open the way to the use of diamond coatings for coated tool applications.     

Experimental study of nucleation and quality of CVD diamond adopting two-step deposition approach using MPECVD

Effects of the deposition conditions on quality and nucleation density of CVD diamond were investigated using a microwave plasma enhanced chemical vapor deposition (MPECVD) method with methane-hydrogen gas mixtures. Diamond films were deposited at pressures of 665–4000 Pa, temperatures of 660–950 °C, and methane concentrations of 0.5–5 vol.%. Deposited diamond films were characterized by scanning electron microscopy, field emission scanning electron microscopy, micro-Raman spectroscopy, and X-ray diffraction. Diamond quality and nucleation density significantly affected by the deposition pressure, substrate temperature, and methane concentration. The findings of this work were discussed in terms of the effects of deposition conditions on the plasma composition. A two-step deposition approach was applied to improve nucleation density and quality of CVD diamond films. Polycrystalline diamond films were grown using the two-step deposition process changing a combination of parameters in the two steps. Growth and quality of the deposited diamond films were improved altering the deposition pressure and substrate temperature in the two steps.     

Nucleation stability of diamond nanowires inside carbon nanotubes: A thermodynamic approach

Aiming at synthesis diamond nanowires, a simple thermodynamic approach was performed with respect to the effect of nanosize-induced additional pressure on the Gibbs free energy of critical nuclei to elucidate diamond nucleation inside carbon nanotubes upon chemical vapor deposition, based on the carbon thermodynamic equilibrium phase diagram. Notably, these analysis showed that the diamond nucleation would be preferable inside a carbon nanotube due to the effect of surface tension induced by the nanosize curvature of the carbon nanotube and diamond critical nuclei, compared with diamond nucleation on the flat surface of a silicon substrate. Meanwhile, the metastable phase region of diamond nucleation would be driven into a new stable phase region in the carbon thermodynamic equilibrium phase diagram by the effect of nanosize-induced additional pressure. Eventually, we predicted that carbon nanotubes would be an effective path to grow diamond nanowires by chemical vapor deposition.     

Porous graphene networks as high performance anode materials for lithium ion batteries

Porous graphene obtained by chemical vapor deposition (CVD) using porous MgO sheets as template is demonstrated to exhibit a high reversible capacity (1723 mAh g^-1), excellent high-rate capability and cycling stability for Li-ion batteries. The simple CVD approach offers a new way for large-scale production of porous graphene materials for energy storage.     

Synthesis of oriented nanotube films by chemical vapor deposition

Oriented nanotube films (20-35 μm thick) were synthesised on flat silicon substrates by chemical vapor deposition (CVD) of a gas mixture of acetylene and nitrogen. For the CVD we used metal oxide clusters formed by spin coating an iron(III) nitrate ethanol solution onto a silicon substrate and subsequent heating. The cluster density and its effects on the nanotube density were investigated as a function of the iron(III) nitrate concentration and the synthesis temperature. A high nanotube density was achieved with a high density of iron oxide clusters as nucleation centres for the growth of nanotubes. The cluster density was controlled by the iron(III) concentration of the ethanolic coating solution and by the synthesis temperature. The perpendicular orientation of the nanotubes with respect to the substrate surface is attributed to a high density of nanotubes.     

Surface Pretreatments of Silicon Nitride for CVD Diamond Deposition

The efficiency of different surface pretreatments (four standard chemical etchings and four diamond powder abrasive procedures) on silicon nitride (Si₃N₄) substrates for chemical vapor deposition (CVD) of diamond has been systematically investigated. Blank Si₃N₄ samples were polished with colloidal silica (∼0.25 μm). Diamond nucleation and growth runs were conducted in a microwave plasma chemical vapor deposition apparatus for 10 min and 6 h, respectively. Superior results concerning nucleation density ( N _d∼ 10¹⁰ cm⁻² after 10 min), film uniformity, and grain size (below 2 μm after 6 h) were obtained for the mechanically microflawed samples, revealing that chemical etchings (hot and cold strong acids, molten base or CF₄ plasma) are not crucial for good CVD diamond quality on Si₃N₄.     

Chemical Vapor Deposition of CuOx Films by Cul and O2: Role of Cluster Formation on Film Morphology

CuO _x films were deposited on silica substrates by the chemical vapor deposition (CVD) method, using CuI and O₂ as source gases at low pressure in a tubular reactor. The growth mechanism to obtain a dense and uniformly distributed (in the axial direction in a tubular reactor) film was investigated. It was found that the occurrence of homogenous nucleation caused an abrupt increase of deposition rate and made the film porous. Homogeneous nucleation can be prevented by properly selecting reactant concentration, reactor temperature, and reactor diameter. Based on an aerosol diffusion theory from laminar pipe flow, a method of predicting cluster size in this CVD reaction system was proposed. The result showed that the clusters formed by homogeneous nucleation had an average size of about 1 nm in diameter.     

Highly self-oriented growth of (020) and (002) monoclinic HfO2 thick films using laser chemical vapor deposition

Monoclinic hafnia (m-HfO₂) films were prepared on polycrystalline AlN substrates via thermal and laser chemical vapor deposition (thermal CVD and laser CVD). Highly self-oriented growth of (020) and (002) m-HfO₂ films was demonstrated at a high deposition rate. Films prepared using thermal CVD exhibited a porous microstructure and no preferred orientation, whereas those prepared using laser CVD exhibited significant proportions of (020) and (002)-oriented m-HfO₂. The (020) and (002) orientations were observed to be as high as 90% and 98%, respectively. The (002)-oriented m-HfO₂ film exhibited a columnar structure with a feather-like texture in cross-section, and with a pyramidal faceted surface. Deposition rates of the (002)-oriented m-HfO₂ films reached 67 μm h⁻¹, approximately 40 times greater than previously reported, thermal-CVD-grown m-HfO₂ films.     

Evaluation research of polishing methods for large area diamond films produced by chemical vapor deposition

The current study compared several polishing techniques of chemical vapor deposition (CVD) diamond films. Although research on various diamond polishing techniques has been carried for years, some issues still need to be examined in order to facilitate application on large areas in a cost-efficient manner. In the present work, microwave plasma enhanced chemical vapor deposition (CVD) was used to obtain diamond films with full width half magnitude (FWHM) less than 10 wavenumbers at 1332 cm^− 1 Raman peak. The diamond films were processed through mechanical polishing, chemical-assisted mechanical polishing, thermo-chemical polishing, excimer laser ablation, and catalytic reaction assisted grinding. A profilometer, an atomic force microscope, and a scanning electron microscope have been used to evaluate the surface morphology of diamond films before and after polishing. The results obtained by using the above mentioned techniques were analyzed and compared.     

Nucleation and Initial Growth Stages of Chemical Vapor Deposition (CVD) Diamond

Nucleation of diamond on non-diamond virgin substrates is characterized by low nucleation densities and long incubation times. Various methods have been developed to enhance nucleation densities and reduce the duration of incubation. This report describes a number of different but related studies of diamond nucleation on silicon and chemically modified silicon surfaces. The effect on the initial stages of deposition of mechanical abrasion with slurries and in-situ sample biasing are especially discussed. Substrate abrasion with diamond results in the embeddying of diamond debris into its surface. Destructive ion implantation into this diamond debris is found to prevent subsequent diamond growth, therefore leading to the conclusion that the diamond debris serves as growth centers. Abrasion of the substrate with mixed metal/diamond slurries is reported to further enhance nucleation relative solely to diamond abrasion. It is suggested that during the chemical vapor deposition (CVD) process some metals alter the composition of the gas phase above the growing surface. Also, the role of surface reactions is emphasized. We also introduce the dc-glow discharge process as a novel, in situ surface pretreatment method for the formation of a precursor for diamond nucleation. Our results show that the promotion of diamond growth by this method is primarily due to formation of nano-size diamond particles during the pretreatment process. It is suggested that, to some extent, graphitic carbon with a high degree of defects may serve as a diamond nucleation center as well.     

Characterization of Lead Oxide Thin Films Produced by Chemical Vapor Deposition

As a step toward creating a chemical vapor deposition (CVD) process for PbTiO₃ thin films, lead oxide films were deposited and then examined. The reaction was oxidation controlled, with an apparent activation energy of 97 kJ/mol in this low-temperature, low-pressure metalorganic CVD (MOCVD) process. Across the deposition parameters examined, several distinct types of morphology were observed. Growth occurred as a combination of layer-on-layer and island formation. The structural and chemical properties of the lead oxide were examined by Auger electron spectroscopy, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and electron diffraction. Various forms of lead oxide were produced (litharge, massicot, and scrutinyite, singly or in combination with each other). The deposition parameters used in this work showed a tendency to maintain the same crystalline form from the initial nucleation stages through post-deposition annealing. Lead oxide formed readily on SiO₂ surfaces (contrary to studies by other researchers) and, indeed, reacted with the underlying SiO₂ layer.     

Diamond Growth on a Si Substrate With Ceramic Interlayers

Deposition of diamond films on Si substrates precoated with a series of ceramic intermediate layers was examined. The interlayers containing SiC, SiN _x , SiCN, TiSiN, and TiAlSiN were prepared by a liquid injection plasma-enhanced chemical vapor deposition (PECVD) method using alkoxide solution precursors. The subsequent diamond synthesis on these coatings was carried out by microwave plasma-assisted CVD (MPCVD) using a H₂–1%CH₄ mixture. A higher nucleation density of diamond was obtained on these intermediate layers than on the as-polished Si wafer, along with a nonuniform surface distribution of diamond. Diamond powder scratching pretreatment of these interlayers enhanced the nucleation density and promoted the formation of fully uniform diamond films. Particularly, nanocrystalline diamond films were directly generated on TiSiN and TiAlSiN layers under an identical deposition condition that had favored the formation of microcrystalline diamond films on Si wafers and the Si(C,N) interlayers. The mechanism for this difference is attributed primarily to a higher amount of residual amorphous carbon in TiSiN and TiAlSiN layers than that inside Si(C,N) layers.     

Diamond Coating of Porous Silicon

Diamond coatings on porous silicon (PS) samples have been obtained by the hot-filament chemical vapor deposition(CVD) technique. We focused our attention on the coating morphology, showing experimentally that high quality diamond coatings may be produced with the PS sample kept at 710°C. The deposited patterns consist of polycrystalline grains with a plane interface with the PS layer.At 790°C, the quality of the coating is improved but the PS layer becomes damaged, and at 650°C the coating consists of diamond-like carbon particles. Besides the temperature, other factors such as the porosity, roughness and chemical activity of the PS layer deserve attention. We observed that one of the limiting factors of the deposition process was the high nucleation time. Two nucleation mechanisms are involved in the growth process. The first nucleation mechanism occurs on the top of the sharp PS features, subsequently to the nucleation a superficial film, and then a second nucleation mechanism occurs over this surface, which allows the growth process to continue. We also observed the presence of ablue-shift in the luminescence spectra following the coating.     

Fine-grained 3C-SiC thick films prepared via hybrid laser chemical vapor deposition

An ultraviolet laser (λ = 266 nm) operated in pulsed mode and a diode laser (λ = 1060 nm) operated in continuous mode were simultaneously applied to create a hybrid laser chemical vapor deposition (CVD) approach. Fine-grained 3C-SiC thick films were prepared via hybrid laser CVD by using SiCl₄, CH₄ and H₂ as precursors. The effects of the ultraviolet laser on the preferred orientations, microstructures, microhardness values and deposition rates of 3C-SiC thick films were investigated. The 3C-SiC thick films that were prepared at 4 kPa via diode laser CVD exhibited <110>-orientations and 5-100 µm grain sizes, whereas those prepared via hybrid laser CVD were randomly oriented with 0.5-5 µm grain sizes. Compared to diode laser CVD, the additional irradiation of the ultraviolet laser in the hybrid laser CVD improved the Vickers microhardness values of the 3C-SiC thick films from 30 to 35 GPa, and the maximum deposition rate was also increased from 935 to 1230 µm/h.     

Prospects of novel hybrid methods for the activated chemical vapor deposition of diamond

High-intensity activation of the vapor phase is a necessary condition for diamond synthesis in the customary chemical vapor deposition (CVD) of diamond. In this paper a novel approach to activated CVD (ACVD) of diamond based on the combined or hybrid ACVD techniques will be discussed.By hybrid diamond ACVD we mean a technique that employs more than one way of activating the crystallization medium. Together with the basic activation mode, the hybrid method includes different supplementary activation modes that influence the physical and physico-chemical processes in the vapor phase and also on the diamond crystal surface. The role of added activation in changing the growth kinetics of diamond film (DF) and microcrystals has been considered. The published research works and our own data are indicative of the remarkable influence of added activation in such hybrid ACVD techniques as chemical transport reaction, HF (Hot Filament) or DC arcjet in combination with electrical activation, and also in MW ACVD with the addition of ultraviolet-irradiation. Along with the increase in the DF growth rate there also may be changes in the constitution and crystalline perfection of DF and microcrystals grown by hybrid methods. Depending on the combination of the methods used as well as the ratio of the activation levels and crystallization temperature the linear growth rate of diamond can be raised by 1.2–6 times as compared to the rate gained via the single-activation technique. It is a striking fact that the added power of the secondary activation may amount from several to several tens of percent of the main activation power. In conclusion the possible reasons for the growth gain obtained in the novel hybrid ACVD of diamond will be considered.