Interfacial study of cubic boron nitride films deposited on diamond

We have studied the nucleation and growth of cubic boron nitride (cBN) films deposited on silicon and diamond-coated silicon substrates using fluorine-assisted chemical vapor deposition (CVD). These comparative studies substantiate that the incubation amorphous/turbostratic BN layers, essential for the cBN nucleation on silicon, are not vital precursors for cBN nucleation on diamond, and they are inherently eliminated. At vastly reduced critical bias voltage, down to -10 V, cBN growth is still maintained on diamond surfaces, and cBN and underlying diamond crystallites exhibit an epitaxial relationship. However, the epitaxial growth is associated with stress in the cBN-diamond interfacial region. In addition, some twinning of crystallites and small-angle grain boundaries are observed between the cBN and diamond crystallites because of the slight lattice mismatch of 1.36%. The small-angle grain boundaries could be eliminated by imposing a little higher bias voltage during the initial growth stage. The heteroepitaxial growth of cBN films on different substrate materials are discussed in the view of lattice matching, surface-energy compatibility, and stability of the substrate against ion irradiation.     

Process study of thermal plasma chemical vapor deposition of diamond,part I: Substrate material,temperature, and methane concentration

Effects of process parameters on diamond film synthesis in DC thermal plasma jet reactors are discussed including substrate material, methane concentration and substrate temperature. Diamond has been deposited on silicon, molybdenum, tungsten, tantalum, copper, nickel, titanium, and stainless steel. The adhesion of diamond film to the substrate is greatly affected by the type of substrate used. It has been found that the methane concentration strongly affects the grain size of the diamond films. Increased methane concentrations result in smaller grain sizes due to the increased number of secondary nucleations on the existing facets of diamond crystals. Substrate temperature has a strong effect on the morphology of diamond films. With increasing substrate temperature, the predominant orientation of the crystal growth planes changes from the (111) to the (100) planes. Studies of the variation of the film quality across the substrate due to the nonuniformity of thermal plasma jets indicate that microcrystalline graphite formation starts at the corners and edges of diamond crystals when the conditions become unfavorable for diamond deposition.     

金刚石膜生长过程原位光发射谱研究

近年来由于化学气相沉积（CVD）金刚石膜具有优异的物理、化学性能及广阔的应用前景而引起人们的普遍关注．现在人们越来越多地把注意力移向金刚石膜生长过程的研究，即生长机理的实验和理论研究·这些研究致力于探讨反应过挥中存在的基团种类、作用及气相如何转变为固态的金刚     

Development of the electrocrystallization theory

The problems of nucleation at electrocrystallization of metals and alloys are considered. The thermodynamics and kinetics of nucleation in stationary and nonstationary modes, the atomistic approach to the formation of nuclei and their growth (isolated and overlapped), the dependence of the nucleation rate on the adsorption of surfactants, the deposit grain size as a function of overpotential, and the grain size of eutectic alloys are discussed. Conclusions are drawn on the most important factors which should be taken into account during the analysis of processes of electrochemical nucleation and cluster growth.     

Imaging SIMS for the investigation of substrate surfaces for CVD diamond deposition

The influence of substrate surface preparation on diamond nucleation is a major topic in the investigation of CVD-diamond deposition. The substrate, polishing material, its grain size, and the resulting surface roughness all influence diamond nucleation. Diamond can nucleate at scratches or residues of the polishing process which are providing nucleation sites. In this paper the surface of molybdenum and substrates polished with SiC and diamond powder was studied by imaging (2- and 3-dimensional) secondary ion mass spectrometry. The distribution and grain size of polishing residues (SiC, diamond) were determined and the reaction of diamond with the substrate during heating to deposition temperature was investigated. In this case a laterally inhomogeneous system of carbon containing species had to be characterized. Therefore compound-specific secondary ion mass spectrometry had to be performed. The results suggested that diamond residues on molybdenum substrates are partly dissolved during the heat treatment. The measurements indicate that a fraction of the diamond residues is still present after heat treatment and can provide nucleation sites for diamond deposition.     

Synthetic Semiconductor Diamond Electrodes: Comparison of Electrochemical Behavior of the Growth and Nucleation Surfaces of Thin Polycrystalline Films

A comparative study of electrochemical kinetics in ferro- and ferricyanide solutions is performed. Electrochemical impedance spectra for the growth and nucleation sides of relatively thin films of boron-doped polycrystalline diamond synthesized by hot-filament CVD technology are taken. Concentrations of noncompensated acceptor near the growth and nucleation surfaces are estimated. It is shown that the growth and nucleation surfaces differ little in their electrochemical behavior, which is attributed to the absence of significant difference in the concentration of electrochemically active structural defects or the boron-acceptor impurity between the two sides of thin diamond films.     

Compacts of Boron-Doped Synthetic Diamond: Lowering of Synthesis Temperature and Its Effect on the Doping Level and Electrochemical Behavior

Substituting of metal (Co, Ni) borides for boron carbide in the boron carbide–graphite growth system for the process of diamond growth in the region of diamond thermodynamic stability allowed lowering the synthesis temperature for the electrodes of this new electrode material―boron-doped diamond compacts―significantly (by ~1000°C) without any deterioration of their electrochemical properties. On the other hand, using of amorphous boron with finer grain as compared with the boron carbide, mixed with graphite, results in a marked increase of the electrodes’ electrochemical efficiency, due to increase in their roughness after the chemical removing of boron-containing inclusions from their surfaces. Thus obtained compact electrodes have wide potential window and low background current in supporting electrolytes, they are well reproducible. Special features of their electrochemical impedance spectroscopy are similar to those of the recently studied compacts synthesized on the basis of boron carbide.     

Electrical bias dependent photochemical functionalization of diamond surfaces

Diamond is an excellent substrate for many sensing and electronic applications because of its outstanding stability in biological and aqueous environments. When the diamond surface is H-terminated, it can be covalently modified with organic alkenes using wet photochemical methods that are surface-mediated and initiated by the ejection of electrons from the diamond. To develop a better understanding of the photochemical reaction mechanism, we examine the effect of applying an electrical bias to the diamond samples during the photochemical reaction. Applying a 1 V potential between two diamond electrodes significantly increases the rate of functionalization of the negative electrode. Cyclic voltammetry and electrochemical impedance measurements show that the 1 V potential induces strong downward band-bending within the diamond film of the negative electrode. At higher voltages a Faradaic current is observed, with no further acceleration of the functionalization rate. We attribute the bias-dependent changes in rate to a field effect, in which the applied potential induces a strong downward band-bending on the negative electrode and facilitates the ejection of electrons into the adjacent fluid of reactant organic alkenes. We also demonstrate the ability to directly photopattern the surface with reactant molecules on length scales of <25 microm, the smallest we have measured, using simple photomasking techniques.     

直流偏压对于在玻碳电极上双层类脂膜成膜过程的影响

应用循环伏安法和电化学阻抗谱研究了直流偏压对卵磷脂在玻碳电极表面自组装成膜过程及其结构的影响.实验发现:无论在正偏压还是负偏压条件下,卵磷脂在玻碳电极上均可组装成膜.施加正偏压时,由于玻碳电极表面所带的正电荷与卵磷脂端基之间的静电作用,使得卵磷脂在电极表面倾向于形成双层的类脂膜,并在0.4V偏压下电极阻抗达到最大值.继续增大电极正向偏压,s-BLM缺陷增加,以至趋于被击穿.提出了适宜的等效电路,并据此非线性拟合电极过程,求得部分阻抗的模型参数.研究发现:膜电容和电荷传递电阻呈现良好的互补效应.     

Nanodiamond Thin Film Electrodes: Metal Electro‐Deposition and Stripping Processes

The properties of a nanodiamond thin film deposit formed on titanium substrates in a microwave‐plasma enhanced CVD process, are investigated for applications in electroanalysis. The nanodiamond deposit consists of intergrown nano‐sized platelets of diamond with a high sp² carbon content giving it high electrical conductivity and electrochemical reactivity. Nanodiamond thin film electrodes (of approximately 2 μm thickness) are characterized by electron microscopy and electrochemical methods. First, for a reversible one electron redox system, Ru(NH₃)₆^3+/2+, nanodiamond is shown to give well‐defined diffusion controlled voltammetric responses. Next, metal deposition processes are shown to proceed on nanodiamond with high reversibility and high efficiency compared to processes reported on boron‐doped diamond. The nucleation of gold is shown to be facile at edge sites, which are abundant on the nanodiamond surface. For the deposition and stripping of both gold and copper, a stripping efficiency (the ratio of electro‐dissolution charge to electro‐deposition charge) of close to unity is detected even at low concentrations of analyte. The effect of thermal annealing in air is shown to drastically modify the electrode characteristics probably due to interfacial oxidation, loss of active sp² sites, and loss of conductivity.     

Progress in electrochemistry of hybrid diamond/sp2-C nanostructures

Hybrid diamond/sp²-C nanostructures have aroused growing interests in electrochemistry currently owing to the good chemical/physical properties, including high electrical conductivity, mechanical robustness, and high specific surface area, as well as the unique electrochemical properties, namely, an enhanced electrochemical activity while retaining a wide potential window and low background currents when properly engineering the microstructure. This mini-review presents the recent electrochemistry process of diamond/sp²-C nanostructures. In particular, the synthetic methods, microstructures, and possible growth mechanism of diamond/sp²-C nanostructures are briefly summarized. Then, the electrochemical property tailoring is addressed in detail, and subsequently, their potential applications in electrochemistry including electrochemical sensors, supercapacitors, electrocatalysis, and other applications are discussed. The future perspectives of diamond/sp²-C nanostructures in electrochemistry finally conclude this review.     

Electrocrystallization of Phase I, CuTCNQ (TCNQ = 7,7,8,8-Tetracyanoquinodimethane), on indium tin oxide and boron-doped diamond electrodes

The electrochemical reduction of TCNQ to TCNQ*- in acetonitrile in the presence of [Cu(MeCN)4]+ has been undertaken at boron-doped diamond (BDD) and indium tin oxide (ITO) electrodes. The nucleation and growth process at BDD is similar to that reported previously at metal electrodes. At an ITO electrode, the electrocrystallization of more strongly adhered, larger, branched, needle-shaped phase I CuTCNQ crystals is detected under potential step conditions and also when the potential is cycled over the potential range of 0.7 to -0.1 V versus Ag/AgCl (3 M KCl). Video imaging can be used at optically transparent ITO electrodes to monitor the growth stage of the very large branched crystals formed during the course of electrochemical experiments. Both in situ video imaging and ex situ X-ray diffraction and scanning electron microscopy (SEM) data are consistent with the nucleation of CuTCNQ taking place at a discrete number of preferred sites on the ITO surface. At BDD electrodes, ex situ optical images show that the preferential growth of CuTCNQ occurs at the more highly conducting boron-rich areas of the electrode, within which there are preferred sites for CuTCNQ formation.     

In-situ voltage tunneling spectroscopy at electrochemical interfaces

Nanophysics at electrochemical interfaces, probing the physical properties of nanostructures, requires laterally resolved in-situ spectroscopy, in particular voltage tunneling spectroscopy (VTS), which is at present not yet established. In-situ spectroscopy is required to achieve reliable and reproducible measurements of the intrinsic properties of nanostructures in an electrochemical environment, which are mainly determined in small nanostructures by surface atoms rather than bulk atoms. In contrast to tunneling spectroscopy in ultrahigh vacuum, tip and substrate double-layer capacitances as well as Faradaic currents play an important role in voltage tunneling spectroscopy at electrochemical interfaces. Deoxygenation of the electrolyte, fast measurements using appropriate instrumentation, and minimization of the unisolated tip apex and substrate surface areas exposed to the electrolyte are the key parameters to achieve reliable in-situ voltage tunneling spectroscopy data at electrochemical interfaces. The presented data show that bias voltage intervals of more than 1000 mV can be utilized for spectroscopic investigations in aqueous electrolytes, which allow the in-situ study of discrete electronic levels in nanostructures.     

温度对PbO2电沉积形核生长过程的影响研究

为了探讨温度对PbO₂电沉积形核生长过程的影响,在25℃、35℃、45℃、55℃、65℃使用电化学工作站测试了PbO₂在玻碳电极上沉积过程的循环伏安曲线、计时电位曲线及计时电流曲线,并对不同温度下电沉积的PbO₂镀层进行了SEM和XRD分析. 结果表明,在不同温度下PbO₂都经历了成核和核生长过程. 温度的升高没有改变PbO₂电沉积三维连续成核的模式,降低了沉积过程溶液阻力,对成核和晶体生长速率均有促进作用,在晶核密度达到饱和晶核密度以前,是以促进成核速率为主,减小PbO₂颗粒尺寸. 达到饱和晶核密度后,电沉积后期以促进晶体生长速率为主,不利于形成细小PbO₂颗粒.高温使得析氧速率提高,能耗增大.由实验结果得出,在55℃时得到的PbO₂镀层粒径最小.     

Composite electrochemical coatings with a carbon-containing dispersed phase or polytetrafluoroethylene

Composite electrochemical coatings based on nickel, zinc, and chromium were studied. The dispersed phase of these coatings is constituted by graphite, diamond, and polytetrafluoroethylene produced from wastes formed in manufacture of fluoroplastic and ultradispersed diamond produced from industrial waste. The conditions in which high-quality coatings with best characteristics, such as microhardness and corrosion resistance, were determined. The wear resistance was additionally found for the chromium-diamond coating.     

基于超微电极的原位电化学拉曼光谱

原位电化学拉曼光谱是一种重要的光谱电化学技术.基于超微电极的原位电化学拉曼光谱将拉曼光谱反映的结构信息与电极表面的电化学过程从实验上严格对应和关联,为深刻理解电化学反应机理提供依据.本文综述了采用超微电极作为工作电极的原位电化学拉曼光谱的研究方法和应用进展,总结了应用超微电极作为工作电极开展电化学拉曼光谱实验的方法和具有表面增强拉曼活性的超微电极制备方法,展示了如何利用在超微电极表面获得的拉曼光谱与界面电化学过程的严格关联研究单个锌颗粒电化学氧化过程、吡啶分子在Au电极表面的电化学吸附过程,以及如何利用该技术能以高的信噪比和灵敏度同时测量光电流与分子反应这一特性研究对巯基苯胺选择性光氧化反应.采用超微电极作为工作电极的原位电化学拉曼光谱技术极大拓展了拉曼光谱技术的研究范围,有望成为探索(光)电化学反应的有力工具.     

Electrodeposition of coatings from sulfite gold-plating electrolyte and their properties

Mechanism of the electrolytic gold-plating and some properties of coatings deposited from a sulfite gold-plating electrolyte were studied. It was shown that soft coatings with low internal stresses can be produced from sulfite electrolytes. The mechanism of the electrolytic gold-plating process was described in terms of the nucleation–growth model in which the metal is deposited at growth points via a single-electron reaction in which sulfite complexes of gold(I) are reduced.     

Hydrogenated polycrystalline diamond films: Elastic and inelastic electron reflectivity

The microstructure and properties of carbon-based thin films depend on the deposition process and conditions used, including pressure, gas phase composition, and substrate temperature, as well as the energy of the reactive species (atoms or ions). For instance concerning diamond films, each method results in different type of films which may differ in terms of diamond grain size (from nano to micro), grain boundary nature, hydrogen content, defect density, amorphous or graphitic components, morphological properties and different chemical and physical properties. Among them, the well-known negative electron affinity, very attractive for the detection and emission of electrons, and high conductivity of diamond surfaces are properties of fully hydrogenated diamond surfaces. Similarly, diamond grain size may influence the electronic and optical properties of the films. More generally the chemical and physical characterization of the uppermost surface atomic layer of diamond films presents a great challenge.In this review we present results on hydrogen bonding configuration in hydrogenated polycrystalline diamond films of varying size (few nanometers up to micrometers) obtained by high resolution electron energy loss spectroscopy (HREELS). More precisely we will present energy loss spectra extended up to 800 meV, as well as elastic and inelastic reflectivity curves (associated to different vibrational modes of hydrogenated diamond surfaces), measured over the 3–18 eV electron energy range. We will show in particular that due to the specific features of diamond bulk electronic band structure, which is maintained up to the surface in the case of fully hydrogenated diamond, it is possible to extract from these data valuable information about the surface properties and composition such as diamond or graphitic like nature of the films, surface versus lattice nature of the vibrational modes.     

Voltage gated carbon nanotube membranes

Membranes composed of an array of aligned carbon nanotubes, functionalized with charged molecular tethers, show voltage gated control of ionic transport through the cores of carbon nanotubes. The functional density of tethered charge molecules is substantially increased by the use of electrochemical grafting of diazonium salts. Functionality can be forced to occur at the CNT tip entrances by fast fluid flow of an inert solvent through the core during electrochemical functionalization. The selectivity between Ru(bi-pyridine)(3)2+ and methyl viologen2+ flux is found to be as high as 23 with -130 mV bias applied to the membrane as the working electrode. Changes in the flux and selectivity support a model where charged tethered molecules at the tips are drawn into the CNT core at positive bias. For molecules grafted along the CNT core, negative bias extends the tethered molecules into the core. Electrostatically actuated tethers induce steric hindrance in the CNT core to mimic voltage gated ion channels in a robust large area platform.     

Evaluation of bias voltage effect on diamond‐like carbon coating properties deposited on tungsten carbide cobalt

Diamond‐like carbon (DLC) coatings are getting new trends for cutting tool applications. In this research work, the DLC coatings were deposited on 15 × 15 × 5‐mm tungsten carbide cobalt substrates with variation of bias voltage from 0 to 500 V. The DLC films of 400 nm were deposited using filter cathode vacuum arc system, and 100‐nm chromium interlayer was deposited by sputtering. The optimized conditions for plasma pretreatment at different argon flow rates and deposition rates with bias variation were found. The effect of bias voltage on microstructure, tribology, adhesion, and mechanical properties were evaluated. The characterization techniques employed were field emission electron microscopy, Raman spectroscopy, wear test, SEM, scratch test, and nano‐indentation. The effect of substrate pretreatment on film adhesion was also evaluated. It was observed that etching rate increased with the increase in Ar flow rate while DLC deposition and sputtering rates decreased with increase in the bias voltage. The characterization suggests the DLC coatings deposited at 0 V bias as optimum condition because of showing the best results among all other conditions. Copyright © 2014 John Wiley & Sons, Ltd.