Amorphisation and Growth Mechanisms of Carbon Films under Ion Beam Irradiation

Amorphisation mechanisms during Physical Vapour Deposition of diamond-like carbon films are presented and illustrate the role of ion bombardment on the microstructure and disorder of the deposited films. It is shown that, at low energy, densification of the carbon film is produced by an ion pinning effect, leading to cross-bonding between graphitic planes present in the layers. Increase of the sp³ concentration is observed as ion energy is increased until an optimum value at which irradiation induced defect migration leads to graphitisation of the layers. The effect of amorphisation–recystallisation depends strongly on the ion mass, ion energy and ion flux per deposited atom. A simple model of the ion beam assisted deposition mechanism is proposed and is in good qualitative agreement with experimental results.     

Mathematical modeling and interpretation of reactive plasma chemistry

A problem of much recent technological interest is the analysis and interpretation of the chemistry of audiofrequency plasma enhanced chemical vapor deposition of thin films. In this process, low pressure methane gas is input into a reactor chamber and a low-current, high-voltage audiofrequency electric discharge applied. The energetic electrons thus produced bombard the methane molecules, fragmenting them, and causing radical and ion formation. These new species go on to form a range of products under various operating conditions from soot-like amorphous carbon, to diamond-like carbon. Despite the increasing experimental understanding of reactive organic plasma dynamics, the chemical kinetics of the reactions in the gas phase is still not completely understood: quite different species densities are found in different regions of the discharge system implying spatially inhomogeneous physiochemical processes. The experimental problem is first outlined, and a simple physiochemically-motivated reaction-advection-diffusion model of the reactive plasma chemistry described. Results of the kinetics models are presented and discussed in terms of the input model parameters and related to surface deposition.     

Plasma environment during hot cathode direct current discharge plasma chemical vapor deposition of diamond films

The plasma characteristics have been investigatedin situ by using optical emission spectroscopy (OES) and the Langmuir probe during hot cathode direct current discharge plasma chemical vapor deposition of diamond films. The changes of atomic H and CH radical in the ground state have been calculated quantitatively according to the results of OES and the Langmuir probe measurement as discharge current density varied. It is shown that atomic H and CH radicals both in the ground state and in the excited state increase with the enhancement of the discharge current density in the plasma. The electron density and CH emission intensity increase linearly with the enhancement of discharge current densities. The generation of different carbon-containing radicals is related to the elevation of electron temperature. Combining the growth process of diamond films and the diagnostic results, it is shown that atomic H in the excited state may improve the diamond growth efficiently, and the increase of electron temperature and density plays an important role in the increase of the deposition rate of diamond films. Project supported by the National Natural Science Foundation of China (Grant Nos. 69493505, 19475039, 19835002).     

Structure and Some Electrical Properties of Amorphous Diamond-like Carbon Films

Diamond-like carbon (DLC) layers deposited at room temperature in 27.12 MHz radiofrequency methane plasma have been studied. The results of structural identification and roughness characterization of the DLC films are reported. AFM images and Raman spectra analysis of investigated samples revealed that, in the RF PCVD technique, amorphous hard carbon film are produced. Trap levels in DLC films are investigated by using the thermally stimulated current (TSC) technique. The open-circuit technique was applied for the drift mobility measurements. Thermally activated hopping is a predominant mechanism of charge carrier transport in the considered range of temperature for amorphous diamond-like carbon films.     

Epitaxial growth and electrical transport properties of La0.5Sr0.5Co03 thin films prepared by pulsed laser deposition

Epitaxial growth of the La_0.5Sr_{0.5 3}(LO) thin films has been realized on Lin3, SrTiC₃ and MgO substrates by pulsed laser deposition. The epitaxial growth behavior and the electrical transport properties of these films were studied systematically. The temperature dependencies of the resistivity of the film have been determined. Studies indicate that close dependencies exist between the crystal structures and the electrical transport properties of the epitaxial LSCO films, and that the epitaxial thin films are of low resistivity and metallic conductive features. The epitaxial films deposited on the LaA10₃ substrates at about 700 °C possess the optimal properties compared with the others. Discussions of the dependencies and the mechanisms of the epitaxial structures on the electrical transport properties of the LSCO films have been made. Project supported by the National Natural Science Foundation of China (Grant No. 19574003 and No. 19674001).     

Comparison of Mechanical Properties and Effects in Micro- and Nanocomposites with Carbon Fillers (Carbon Microfibers,Graphite Microwhiskers,and Carbon Nanotubes)

The mechanical properties and effects in fibrous composite materials are compared. The materials are based on the same matrix (EPON-828 epoxy resin) and differ in the type of fibers: Thornel-300 carbon microfibers, graphite microwhiskers, carbon zigzag nanotubes, and carbon chiral nanotubes. Two material models are considered: a model of elastic medium (macrolevel model) and a model of elastic mixture (micro-nanolevel model). Mechanical constants of 40 materials (4 types + 10 modifications) are calculated and compared. The theoretical ultimate compression strength along the fibers is discussed. The effects accompanying the propagation of longitudinal waves in the fiber direction are investigated.     

Change in the Surface Properties of Carbon Fibers as a Result of Plasmochemical Modification

The influence of plasmochemical modification of carbon fibers on their surface properties and compatibility with the PTFE matrix is investigated. It is shown that the thin PTFE coating formed on the carbon fiber surface improves the wetting of the fibers by PTFE. As a result, the mechanical characteristics of PTFE-based composites are improved.     

A data-driven surrogate model to rapidly predict microstructure morphology during physical vapor deposition

Here, we present a surrogate model that rapidly predicts the microstructures of a binary-alloy thin film during physical vapor deposition. This surrogate model is constructed and trained from a data set produced by phase-field simulations of physical vapor deposition. It relies on a statistical representation of the microstructure, principal component analysis, polynomial chaos expansion, and a microstructure-reconstruction algorithm to estimate the microstructure as a function of the deposition parameters and properties of the materials being deposited. This protocol, exercised on a simplified physical vapor deposition model, demonstrates the efficacy of the surrogate model to rapidly predict a broad class of microstructures as a function of deposition conditions with good accuracy relative to high-fidelity models. The considerable computational gain from the surrogate model compared to the detailed phase-field approach highlights the importance of pursuing such approaches, especially when used for producing parameter-microstructure maps for rapid and accurate predictions of the microstructure. As such, this surrogate model can be used to guide the choice of deposition conditions and materials being deposited to fabricate functional thin films with targeted microstructures.     

Morphology, structure and Raman scattering of carbon nanotubes produced by using mesoporous materials

Carbon nanotubes were prepared by chemical vapor deposition (CVD) of hydrocarbon gas on various substrates. The effect of substrates on the growth, morphology and structure of carbon nanotubes were investigated. Aligned carbon nanotubes with high density and purity were achieved by CVD on mesoporous silica substrate. The Raman scattering of aligned carbon nanotubes was carried out, and the dependence of the phonon properties on the microstructure of the nanotubes has been discussed.     

Nanocrystalline Diamond Coatings

Carbon—in the form of diamond coatings (nanocrystalline diamond—NCD) on suitable substrates—has attractive properties for biomedical applications. The excellent chemical inertness of NCD films makes them a promising material for medical implants, cardiovascular surgery and for coating of certain components of artificial heart valves.

The medical applications of carbon films impose some special requirements on their quality, purity, phase content and the state of the surface. Of particular importance is the smoothness of the surface and good adhesion of the coatings to the substrate. We have investigated carbon films which were synthesized by Radio Frequency Plasma Chemical Vapour Deposition (RF–PCVD).

The specimens obtained have been tested to show their structure and their biological, mechanical and chemical resistance. Additional investigations of the NCD films were carried out by micro-X-ray spectroscopy, Raman spectroscopy, AFM, Auger spectroscopy, corrosion tests, breakdown tests and clinical investigations. Nanocrystalline diamond (NCD) layers obtained by a new method of RF dense plasma CVD onto AISI-316L steel used in surgery were investigated to determine their suitability as biomaterials.     

Nanomechanics of Carbon Nanotubes

We discuss the mechanical properties of carbon nanotubes, in particular the pressure-dependence of the Raman modes and the collapse pressure, and their relation to the corresponding mechanical properties of graphite and graphene. The frequencies of the Raman G-mode and radial breathing mode (RBM), as well as the pressure dependence of the RBM can be largely-explained in the existing framework of C–C stretching modes and envirionmental effects induced by the pressure medium. The pressure dependence of the G-mode is still missing such an explanation. The collapse pressure can be understood in terms of the continuum theory for thin-walled tubes. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bounds for the Elastic Properties of Pyrolytic Carbon

The elastic properties of heterogeneous materials without defects depend on both the constitutive properties of the constituents and the microstructural characteristics. In this paper the first-order bounds of aggregates of domains with hexagonal material symmetry are determined in terms of tensorial texture coefficients. The predictive capability of these bounds is compared to higher-order bounds for pyrolytic carbon. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

含非均匀界面相碳／碳纤维复合材料等效热传导性质的研究

本文研究含非均匀界面相碳／碳纤维复合材料的热传导性质．将非均匀界面相近似模拟为由许多性质均匀的薄层构成的层状结构，并应用Mori-Tanaka平均场概念得到了该复合材料等效热传导系数封闭形式的解析解．     

A comparative study on the mechanical and barrier characteristics of polyimide nanocomposite films filled with nanoparticles of planar and tubular morphology

Polyimide (PI) films based on poly(pyromellitic dianhydride-co-4,4′-oxydianiline) (PI-PM) were filled with different nanoparticles, such as organically modified montmorillonite (MMT), vapor-grown carbon nanofibers (VGCF), and silicate nanotubes (SNT) of different concentration.. Rheological measurements and structural investigations showed a relatively good dispersion of the nanoparticles in the PI matrix to an extent that depended on the type and morphology of the nanoparticles used. The mechanical (tensile modulus, strength, and deformation at break) and the barrier (oxygen permeability) properties of PI-PM nanocomposite films were investigated. The polyimide nanocomposites filled with SNT and tubular VGCF nanoparticles showed an increased tensile modulus with increasing volume concentration of the nanoparticles without a catastrophic decrease in the elongation at break. In addition, the MMT particles, chemically modified with 4,4'-bis-(4′′-aminophenoxy)diphenylsulfone, significantly improved the barrier properties of the PI-PM films, which exceeded those of the nanocomposites filled with VGCF or SNT. The relative poor oxygen barrier and mechanical properties of the PI-PM/VGCF nanocomposite films are ascribed to the relative weak adhesion between the VGCF and the polyimide matrix, which was confirmed by scanning electron microscopy of the fracture surface of these films.     

基于随机电阻网络碳毡复合层力阻建模

基于碳纤维单丝力阻效应影响因素的统计规律,揭示了碳毡复合层力阻传感特性的导电网络定量化模型．对碳纤维单丝相互搭接后的长度进行了讨论,得到关于纤维均长、纤维密度、纤维根数等多参量间的统计关系;在假设毡内纤维随机均匀分布且搭接点正态分布的情况下,分别对4种不同尺寸的碳纤维毡复合层的电阻进行了估测,并通过箱线图分析表明实测值在相应的估测范围内,说明本模型可较好地对碳纤维随机乱相分布的碳毡复合层电阻进行估测;最后,基于碳毡电阻网络的统计模型,对碳毡复合层的力阻特性进行了研究,通过比较理论电阻变化率与实测电阻变化率发现模型给出的复合层力阻效应灵敏系数较为稳定,从而表明随机电阻网络模型可较好的模拟碳毡受载荷时的力阻行为．     

基于金属型碳纳米管在电场中变形的柱壳理论

提出了关于金属型碳纳米管在电场中变形的柱壳理论．借助于半球模型,得到了金属型碳纳米管在电场中的电荷与电场分布的解析解．将带电碳原子所受的电场力看作是碳纳米管的内力,根据柱壳理论碳纳米管在电场中的变形被解析地给出．结果表明:碳纳米管的长径比对碳纳米管在电场中的变形有重大影响,长径比越大,碳纳米管的变形越明显;碳纳米管的径向变形沿轴向是不均匀的,最大的径向变形出现于碳纳米管的端部;更为有意义的是,即使外加电场不够大,对于长径比很大的碳纳米管仍然可以表现出明显的变形．     

基于碳关税和配额的再制造决策研究

在跨国闭环供应链中考虑碳关税、碳配额和碳税三种政策的影响,分别建立了出口国制造商(OEM)再制造模型和OEM授权进口国零售商进行再制造模型,得到不同模型中OEM和零售商的最优价格、最优销售量、最优利润,进一步分析了产品碳排放总量是否超过配额的不同情形下新产品碳排放量对新产品和再制造品价格、销售量的影响以及其中碳关税和碳税发挥的作用.结果表明,在配额限制下,存在碳关税、碳税以及两种政策共同约束的取值区间,当税率水平在不同区间时,新产品碳排放量对两种产品的价格、销售量有不同的影响.     

Facility Location on a Sphere

In this paper, we consider a modification of the Weber problem which consists of locating a new facility on a sphere so that the weighted sum of distances to given demand points is minimized. Two ways of measuring distance are used. One is simply the length of shortest arc on the sphere. The other norm, first suggested by Katz and Cooper, may be used to approximate squared arc distance on a hemisphere and also as a rough approximation for arc distance. Several properties of the problem are established. An iterative heuristic method for solving the problem with shortest arc distances is presented.     

Single wall carbon nanotubes and their electrical properties

Single-wall carbon nanotubes (SWCNTs) were synthesized and purified. A water colloid of SWCNTs was prepared and used to assemble SWCNTs onto a gold film surface. Scanning tunneling microscopy (STM) images showed that short SWCNTs stood on gold film surfaces. Using STM tips made of SWCNTs, a crystal grain image of a gold thin film and an atomic resolution image of highly oriented pyrolytic graphite were successfully obtained. The electrical properties of short SWCNTs, which stood on the surface of gold film, were measured using STM. That SWCNTs stand on gold thin films is a promising technique for studying structures and properties of carbon nanotubes, as well as assembling and fabricating high-intensity coherent electron sources, field emission flat panel display, tips for scanning probe microscopes, new nanoelectronic devices, etc.     

辛体系下THz波在碳纳米管阵列中的传播

对于一个被周期性平行有限长碳纳米管阵列填充的平面波导,本文基于平行碳纳米管阵列的等效介质模型,忽略其空间色散,考虑了电磁波的损耗,从而得到填充介质的介电特性,并将电磁波在波导中的传播导入到Hamilton体系,同时考虑两侧边界条件均为理想导电边界条件,从而在辛理论框架下求解本征值方程,得到了电磁波传播色散关系.分析可知,存在一个窄的频段,电磁波基模无法传播,然而在频段外,电磁波基模传播具有极其低的损耗,这使得碳纳米管阵列具有宽频带传播的特性,这些特性使得碳纳米管阵列相比于传统材料具有更优的传播特性.