Optimization of Parameters of Graphene Synthesis on Copper Foil at Low Methan Pressure

Graphene films on copper foils were synthesized using low-pressure (2200-2800 Pa) chemical vapor deposition (CVD) from methane/hydrogen mixtures. The number of graphene layers is shown to be dependent on the composition of gas mixture and synthesis parameters. The annealing procedure of copper foils used as substrates was optimized to obtain high quality graphene. Atomic and electronic structures of graphene on copper and SiO₂/Si substrates were studied by Raman, X-ray photoelectron, and near-edge X-ray absorption fine structure spectroscopy methods.     

Raman spectroscopy of C-, BN-, SiC-layers deposited on multifilament substrates

The analytic characterisation of various layers and layer systems on fibrous materials are presented. The layers, deposited by an isothermal CVD process, consisting mainly of pyrolytic carbon, hexagonal boron nitride and silicon carbide were characterised by different analytical methods, especially by Raman spectroscopy [1]. The surface enhanced Raman spectroscopy (SERS) was used first time for the investigation of boron nitride (BN) coatings on fibres.     

Study of the Interface Microstructures of CVD Diamond Films by TEM

 The characteristics of the interface microstructures between a CVD diamond film and the silicon substrate have been studied by transmission electron microscopy and electron energy loss spectroscopy. The investigations are performed on plan-view TEM specimens which were intentionally thinned only from the film surface side allowing the overall microstructural features of the interface to be studied. A prominent interfacial layer with amorphous-like features has been directly observed for CVD diamond films that shows a highly twinned defective diamond surface morphology. Similar interfacial layers have also been observed on films with a <100> growth texture but having the {100} crystal faces randomly oriented on the silicon substrate. These interfacial layers have been unambiguously identified as diamond phase carbon by both electron diffraction and electron energy loss spectroscopy. For the CVD diamond films that exhibit heteroepitaxial growth features, with the {100} crystal faces aligned crystallographically on the silicon substrate, such an interfacial layer was not observed. This is consistent with the expectation that the epitaxial growth of CVD diamond films requires diamond crystals to directly nucleate and grow on the substrate surface or on an epitaxial interface layer that has a small lattice misfit to both the substrate and the thin film material.     

Etude par spectrométrie Raman de l'interaction entre un substrat de graphite et un mélange MCl4---H2 (M = Si, Ti)

Raman spectroscopy has been used in order to optimize the reactive CVD conditions for silicium carbide or titanium carbide deposits on carbon fibers. With this technique 50-nm-thick carbide coatings could be characterized at the surface of the individual filament constituting the carbon fibers. In bulk carbon substrates evidence of degraphitization near the carbon/carbide interface was observed.     

Superhard coatings — Production and analysis

In the development of diamond and c-BN products the analytical methods for characterizing the surface, bulk and interface of the diamond coatings are very important. SEM, Raman, XRD and IR are the methods used for characterization and SIMS, TEM, AES, NRA, RBS, XPS, STM, etc. are used for the investigation of special problems. The techniques for diamond and c-BN production are briefly summarized to give an idea of the complex interactions between production, application and analytical characterization. The analytical methods for diamond characterization and many relevant results are summarized in this paper; some physical properties (e.g. thermal conductivity, transparency, etc.) and their interaction with applications are also discussed.Abbreviations AES Auger electron spectroscopy - AFM atomic force microscopy - c-BN cubic boron nitride - CL cathodoluminescence - CVD chemical vapour deposition - EELS electron energy loss spectroscopy - EPMA electron probe microanalysis - ERDA elastic recoil detection analysis - h-BN hexagonal boron nitride - HP-HT high-pressure high-temperature - HF hot-filament - IR infra-red - LEED low energy electron diffraction - MW microwave - NAA neutron activation analysis - NRA nuclear reaction analysis - PL photoluminescence - PVD physical vapour deposition - RBS Rutherford backscattering spectrometry - RHEED reeflected high energy electron diffraction - SAD selected area diffraction - SEM scanning electron microscopy - SIMS secondary ion mass spectrometry - STM secondary ion mass spectrometry - TEM transmission electron microscopy - TMB trimethylborate - XPS X-ray photoelectron spectroscopy - XRD X-ray diffraction Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Free-standing boron doped CVD diamond films grown on partially stabilized zirconia substrates

Boron doped diamond films have been grown adhered to silicon substrates by chemical vapor deposition using boron containing gases. In this work it was shown that it is possible to grow free-standing boron doped CVD diamond films on partially stabilized zirconia substrates using boron powder as the source for doping. Results from Raman spectroscopy confirmed the boron incorporation with concentration up to ∼10²⁰ cm⁻³. X-ray diffraction and scanning electron microscopy showed that the effect of boron incorporation in the microstructure of the diamond film is negligible. The measurement of the resistivity as a function of temperature confirmed the semiconductor behavior, as expected for p-type diamond.     

Production and characterization of nitrided CVD-SiC films

Silicon Carbide (SiC) and SiC with free silicon [SiC(Si)] thin films were prepared by chemical vapor deposition (CVD) using a CH₃SiCl₃-H₂-Ar gas mixture at a temperature of 1223 K. Afterwards these layers were gas nitrided in an ammonia-hydrogen-argon mixture at 1273 K. The solid product is an extremely thin film of silicon nitride on SiC or SiC(Si)-basic layers. These ultra thin silicon nitride films were investigated by glow discharge optical spectroscopy (GDOS) and x-ray photoelectron spectroscopy (XPS). The thickness of the layers was determined to a maximum value of 30 nm.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Diamond/porous titanium three-dimensional hybrid electrodes

Hybrid three-dimensional electrodes produced from microcrystalline boron-doped diamond (BDD) and/or nanocrystalline diamond films were grown on porous titanium (Ti) substrate by hot filament chemical vapor deposition (HFCVD) technique. Powder metallurgy technique was used to obtain the Ti substrates provided by interconnected and open pores among its volume. Diamond growth parameters were optimized in order to provide the entire substrate surface covering including the deeper surfaces, pore bottoms, and walls. The morphology and structure of these electrodes were studied by scanning electron microscopy (SEM) and visible Raman spectroscopy techniques, respectively. Electrochemical response was characterized by cyclic voltammetry measurements. Results showed a wide working potential window and low background current characteristic of the diamond electrodes. The kinetic parameters also pointed out to a quasi-reversible behavior for these hybrid three-dimensional diamond/Ti electrodes.     

Selective matching of catalyst element and carbon source in single-walled carbon nanotube synthesis on silicon substrates

We have studied the compatibility of various catalysts for ethylene and ethanol chemical vapor deposition (CVD) syntheses of single-walled carbon nanotubes (SWNTs) on Si substrates. A strong selectivity between the catalyst elemental species and carbon source was found; SWNT yield for Fe (Co) catalysts was much higher for ethylene (ethanol) CVD than for ethanol (ethylene) CVD. This strong and completely opposite selectivity implies significantly different SWNT growth mechanisms for ethanol and ethylene CVD on Si substrates.     

Growth and characterization of ultrathin carbon films on electrodeposited Cu and Ni

Ultrathin carbon films were grown on different types of metallic substrates. Free‐standing foils of Cu and Ni were prepared by electroforming, and a pure Ni film was obtained by galvanic displacement on a Si wafer. Commercial foil of Ni 99.95% was used as a reference substrate. Carbon films were grown on these substrates by chemical vapour deposition in a CH₄‐H₂ atmosphere. Obtained films were characterized by Raman spectroscopy, X‐ray photoelectron spectroscopy (XPS), Auger electron spectroscopy, and ultraviolet photoemission spectroscopy. The XPS at grazing collection angle was used to determine the thickness of carbon films. Depending on the deposition parameters, the films of graphene or graphite were obtained on the different substrates. The uniformity of graphene and its distribution over the sample area were investigated from Raman data, optical images, and XPS chemical maps. The presence of graphene or graphite in the films was determined from the Raman spectra and Auger peak of C KVV. For this purpose, the D parameter, which is a fingerprint of carbon allotropes, was determined from C KVV spectra acquired by using X‐rays and electron beam. A formation of an intermediate layer of metal hydroxide was revealed in the samples with graphene overlayer.     

Characterisation of diamond coatings with different morphologies by Raman spectroscopy using various laser wavelengths

Since the beginning of low-pressure diamond synthesis, Raman spectroscopy has been widely used to identify and characterise the quality of diamonds. The diamond crystal is characterised by a Raman peak at about 1,332 cm^-1. Other peaks are associated with miscellaneous carbon structures, e.g. graphite and amorphous phases. In recent years, both well-faceted crystalline diamonds and nanocrystalline and ultrananocrystalline diamonds have been investigated. For these fine-grained materials, the diamond peak at 1,332 cm^-1 disappears and the intensities of peaks at other wavelengths increase. To study the influence of the Raman laser wavelength, three lasers were used (472.681 nm, blue; 532.1 nm, green; 632.81 nm, red). For well-faceted diamonds, the Raman spectra with blue and green laser light were similar. A shift of the peak maxima and different intensities were observed. With use of the red laser, a strong luminescence peak and low peak intensities for the various carbon-related peaks occurred. When the diamond morphology changes from well-faceted to fine-grained ballas diamond, the spectra are similar for all three lasers.     

Micro-Raman and Tip-Enhanced Raman Spectroscopy of Carbon Allotropes

Summary: Raman spectroscopic data are obtained on various carbon allotropes like diamond, amorphous carbon, graphite, graphene and single wall carbon nanotubes by micro-Raman spectroscopy, tip-enhanced Raman spectroscopy and tip-enhanced Raman spectroscopy imaging, and the potentials of these techniques for advanced analysis of carbon structures are discussed. Depending on the local organisation of carbon the characteristic Raman bands can be found at different wavenumber positions, and e.g. quality or dimensions of structures of the samples quantitatively can be calculated. In particular tip-enhanced Raman spectroscopy allows the investigation of individual single wall carbon nanotubes and graphene sheets and imaging of e.g. local defects with nanometer lateral resolution. Raman spectra of all carbon allotropes are presented and discussed.     

A rapid synthesis of iron phosphate nanoparticles via surface-mediated spontaneous reaction for the growth of high-yield, single-walled carbon nanotubes

The direct formation of iron phosphate nanoparticles on hydroxyl-terminated SiO(2)/Si substrates with a narrow size distribution (average diameter = 2.2 nm) is achieved by a simple room temperature spontaneous reaction of ferric chloride and phosphoric acid. Single-walled carbon nanotubes (SWNTs) are grown in high yield from the synthesized iron phosphate nanoparticles by the thermal chemical vapor deposition (CVD) method, as confirmed by atomic force microscopy (AFM) and Raman spectroscopy. Furthermore, three-terminal, p-type, nanotube network field effect transistor (FET) devices are successfully fabricated using the synthesized SWNTs via the photolithography technique. The reduced solubility of Fe(III) ions when they form iron phosphate salts in aqueous media is the main driving force for the nanoparticle formation. Systematic control experiments reveal that the surface property, concentration, and pH of the reaction solution play equally important roles in the formation of nanoparticles.     

Cathodoluminescence (CL) and CL spectra of microwave plasma-enhanced CVD diamond

Recent research work is reported on cold cathode luminescence (CL) microscopy and CL microspectrophotometry of diamond produced by means of plasma-activated mixtures of hydrogen and methane gases. Diamond layers of octahedral, cubooctahedral or cubic habit on SiAlON substrates as well as ballas-type layers were investigated. Diamond was also deposited on sheet substrates of titanium, niobium, tantalum, chromium, molybdenum, tungsten, iron (spheroidal and lamellar cast iron), cobalt and nickel. Studying CL colors together with CL spectra has proved to be a reliable diagnostic method for differentiating between the morphological properties of CVD diamond on SiAlON substrates. It is however not possible with this method to clearly differentiate all diamond layers on any one of the sample substrates investigated. These findings could justify a future application of both CL microscopy and CL microspectrophotometry in production control.     

Growth rate studies of CVD diamond in an RF plasma torch

This paper addresses the complex chemistry in the boundary later over a substrate in a chemical vapor deposition rector at atmospheric pressure. In this study, a highspeed plasma (140m/s) was created using a radio-frequency inductively coupled plasma torch for the deposition of diamond thin films. Growth rates on the order of 50 m/ h were obtained for well-faceted continuous films grown on molybdenum substrates positioned normal to the plasma flow. The highest growth rates were obtained at substrate temperatures of 1370 K and a feed gas ratio of 2.5% CH₄ in H₂. Growth rates are compared to predicted results obtained from numerical simulations, based on a one-dimensional stagnation-point flow, and are/mend to be in good agreement. Several other surface analysis techniques were used to characterize the deposited films, inchaling SEA/, Raman spectroscopy, transmission electron microscopy. Rutherfard backscattering spectroscopy, and hydrogen-forward recoil spectroscopy. Optical emission spectroscopy was used to characterize the RF plasma during the deposition process. Results from these studies form an important database for the validation and improvement of current models of the atmospheric-pressure diamond CVD environment.     

Chemical nucleation for CVD diamond growth.

A new nucleation method to form diamond by chemically pretreating silicon (111) surfaces is reported. The nucleation consists of binding covalently 2,2-divinyladamantane molecules on the silicon substrate. Then low-pressure diamond growth was performed for 2 h via microwave plasma CVD in a tubular deposition system. The resulting diamond layers presented a good cristallinity and the Raman spectra showed a single very sharp peak at 1331 cm(-1), indicating high-quality diamonds.     

小尺寸金石墨纳米颗粒的合成与表征

在表面增强拉曼光谱(SERS)的研究领域中,基于局域表面等离子体共振效应的等离子体SERS基底的制备成为过去几十年的研究热点。然而,通常开发的等离子体金属基底具有较差的稳定性和重现性。对于SERS而言,石墨烯类材料具有拉曼化学增强效应,除此之外,还具有分子富集、强的稳定性与荧光猝灭能力等优点,因此基于石墨金属复合纳米材料的SERS基底受到了研究人员的重视。我们利用化学气相沉积(CVD)法制备了小尺寸的金石墨核壳纳米颗粒(Au@G),其粒径约为17 nm。我们通过在Au NP上包覆介孔二氧化硅来控制Au@G的尺寸,同时还研究了包覆二氧化硅过程中,正硅酸乙酯(TEOS)的浓度对于石墨壳层形成的影响。结果表明当TEOS在一定浓度范围内,其浓度的降低有利于得到石墨化程度高的Au@G。进一步利用Au@G对结晶紫分子进行拉曼检测,也表明了Au@G具有较好的拉曼增强效果。这种小尺寸的Au@G在分子检测与细胞成像分析领域中具有广泛的应用潜力。     

High Resistive ZnO／Diamond／Si Films Grown via Metal-organic Chemical Vapour Deposition

Piezoelectric ZnO layers with high resistivity for surface acoustic wave applications were prepared on polycrystalline diamond/Si substrates with(Ill) orientation via metal-organic chemical vapour deposition.The characteristics of the films were optimized through different growth methods. The comparative study of the X-ray diffraction spectra and scanning electron microscopic images showed that the final-prepared ZnO films were dominantly c-axis oriented. Zn and O elements in the final prepared ZnO films were investigated through X-ray photoelectron spectroscopy. According to the statistical results, the n(Zn)/n(O) ratio is near 1. The Raman scattering was also performed in back scattering configuration. E2 mode was observed for the final films, which indicated that the better quality ZnO films had been obtained. The resistivity of the films was also enhanced via the modification of the growth methods.     

Two-dimensional Raman Imaging Analysis of Microcrystal Diamond Film

Two-dimensional distributions of the impurity carbon (sp²-bonded carbon), crystallinity, and tensile stresses in a(Ⅲ) oriented diamond crystal of a diamond thin film were studied by using Raman imaging microscopy. The amount of the impurity carbon was more in the center of (Ⅲ) plane than in the circumference of the plane. The crystallinity and tensile stress were also higher in the center than in the circumference. Based on those two-dimesional distributions, we discuss the boundary structure between diamond carbon and sp²-bonded carbon in CVD diamond.     

不锈钢上液相电沉积类金刚石薄膜

以甲醇有机溶液作碳源,应用直流脉冲电化学沉积方法,在不锈钢表面制备了类金刚石碳薄膜.用原子力显微镜、扫描电镜、拉曼光谱仪和傅立叶红外吸收光谱表征该薄膜的表面形貌和结构.结果表明:经电化学沉积的含氢类金刚石碳薄膜均匀、致密,表面粗糙度小;Raman光谱在1 332.51cm-1处有一强的谱峰,与金刚石的特征谱峰相重合.加入活性添加剂,增加了电流密度,使沉积速率提高到0.5μm/h.