Correlation of sp and sp fraction of carbon with electrical, optical and nano-mechanical properties of argon-diluted diamond-like carbon films

In the present work the correlation of electrical, optical and nano-mechanical properties of argon-diluted diamond-like carbon (Ar-DLC) thin films with sp³ and sp² fractions of carbon have been explored. These Ar-DLC thin films have been deposited, under varying C₂H₂ gas pressures from 25 to 75 mTorr, by radio frequency-plasma enhanced chemical vapor deposition technique. X-ray photoelectron spectroscopy studies are performed to estimate the sp³ and sp² fractions of carbon by deconvoluting C 1s core level spectra. Various electrical, optical and nano-mechanical parameters such as conductivity, I-V characteristics, optical band gap, stress, hardness, elastic modulus, plastic resistance parameter, elastic recovery and plastic deformation energy have been estimated and then correlated with calculated sp³ and sp² fractions of carbon and sp³/sp² ratios. Observed tremendous electrical, optical and nano-mechanical properties in Ar-DLC films deposited under high base pressure conditions made it a cost effective material for not only hard and protective coating applications but also for electronic and optoelectronic applications.     

Piezoelectric effect in graphene-like 2D supracrystals with a periodic perforation breaking the central symmetry

Components of the piezoelectric modulus tensor in graphene-like carbon 2D supracrystals with a periodic perforation breaking the centrosymmetry of the structure have been calculated. It has been shown that the piezoelectric moduli of the supracrystals with sp ² hybridization are one order of magnitude lower and those of the supracrystals with sp ³ hybridization are several time higher than in lithium niobate.     

Stiffness matrix and debye temperature of ReO3 from ultrasonic measurements

We have measured the propagation velocities of bulk acoustic waves in the simple cubic transition-metal oxide ReO₃ by ultrasonic pulse propagation. The elastic stiffness constants at 300 K are: C₁₁ = (47.9 ± 1.4) × 10¹¹ dyne/cm²; C₄₄ = (6.1 ± 0.2) × 10¹¹ dyne/cm²; C₁₂ = (?0.7 ± 2.8) × 10¹¹ dyne/cm². These elastic constants indicate a crystal with highly anisotropic shear propagation. The Debye temperature of the compound from these measurements is 528 K. This value is somewhat higher than previous results from specific heat and resistivity determinations.     

Carbon phases from <Emphasis Type="Italic">sp</Emphasis><Superscript>2</Superscript> hybridized atoms with three-dimensional rigidly bound structure

Methods of molecular mechanics are used to calculate cluster structures of new carbon phases of 3D graphite. It is established that 3D graphite polytypes differ by the structure of layers and order of their alternation, consist of sp ² hybridized atoms, and have hexagonal unit cells. New carbon phases can be synthesized by polymerization and carbonization of hydrocarbon molecules.     

Ion-beam analysis of the structure and composition of nanocomposite nc-TiC/a-C:H coatings

The structure and composition of nanocomposite nc-TiC/a-C:H thin films prepared by closed-field unbalanced reactive magnetron sputtering in an argon-acetylene atmosphere have been investigated. The concentrations of carbon and heavier elements have been obtained by Rutherford backscattering and nuclear backscattering. The hydrogen concentration in the films has been determined by elastic recoil detection analysis. Based on the data obtained, a scheme has been proposed to evaluate the C:H matrix mass density and the sp ³ and sp ² fractions in the matrix.     

Cluster-Type Structure of Amorphous Smooth Hydrocarbon CD<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Films (<Emphasis Type="Italic">x</Emphasis> ~ 0.5) from T-10 Tokamak

Structure of smooth hydrocarbon CD _x films with a high deuterium ratio x ~ 0.5 redeposited from T-10 tokamak D-plasma discharges (NRC Kurchatov Institute, Moscow) has been studied. For the first time, small and wide angle X-ray scattering technique using synchrotron radiation and neutron diffraction have been employed. A fractal structure of CD _x films is found to consist of mass-fractals with rough border, surface fractals (with rough surface), plane scatterers and linear chains forming a branched and highly cross-linked 3D carbon network. The found fractals, including sp² clusters, are of typical size ~1.60 nm. They include a C₁₃ fragment consisting of three interconnected aromatic rings forming a minimal fractal sp² aggregate 9 × C₁₃. These graphene-like sp² clusters are interconnected and form a 3D lattice which can be alternatively interpreted as a highly defective graphene layer with a large concentration of vacancies. The unsaturated chemical bonds are filled with D, H atoms, linear sp² C=C, C=O, and sp³ structural elements like C-C, C-H(D), C-D_2,3, C-O, O-H, COOH, C _x D(H) _y found earlier from the infrared spectra of CD _x films, which are binding linear elements of a carbon network. The amorphous structure of CD _x films has been confirmed by the results of earlier fractal structure modeling, as well as by researches with X-ray photoelectron spectroscopy which allow finding a definite similarity with the electron structure of their model analogues — polymeric a-C:H and a-C:D films with a disordered carbon network consisting of atoms in sp³ + sp² states.     

Raman spectroscopy of graphene and carbon nanotubes

This paper reviews progress that has been made in the use of Raman spectroscopy to study graphene and carbon nanotubes. These are two nanostructured forms of sp² carbon materials that are of major current interest. These nanostructured materials have attracted particular attention because of their simplicity, small physical size and the exciting new science they have introduced. This review focuses on each of these materials systems individually and comparatively as prototype examples of nanostructured materials. In particular, this paper discusses the power of Raman spectroscopy as a probe and a characterization tool for sp² carbon materials, with particular emphasis given to the field of photophysics. Some coverage is also given to the close relatives of these sp² carbon materials, namely graphite, a three-dimensional (3D) material based on the AB stacking of individual graphene layers, and carbon nanoribbons, which are one-dimensional (1D) planar structures, where the width of the ribbon is on the nanometer length scale. Carbon nanoribbons differ from carbon nanotubes is that nanoribbons have edges, whereas nanotubes have terminations only at their two ends.     

Studies of EPES REELS spectra of polyethylenes aided by line shape analysis—Effect of electron irradiation

Polyethylenes of different density, branching structure, crystallographic order, and their degradation due to electron beam were studied using elastic peak electron spectroscopy (EPES) and reflection electron energy loss spectroscopy (REELS) aided with line shape analysis by the pattern recognition (PR) method. This approach offers an algorithm of classification derived from a reference set, i.e. set of spectra recorded from standards exposed to low electron dose (about few C m⁻²), i.e. polyethylene (100% of C sp³ bonds) and polystyrene (75% of C sp² bonds). Then, the obtained classifier is applied for identification of spectra recorded from polyethylenes exposed to electron beam (doses from 40 to 60 C m⁻²). The EPES REELS spectra are analyzed in the vicinity of electron quasi-elastic and inelastic losses. Due to electrons undergoing a quasi-elastic scattering from atoms of different atomic numbers, i.e. carbon and hydrogen, for undamaged polymers the surface hydrogen content can be evaluated.Changes due to electron irradiation in polyethylenes are indicated by decreasing content of hydrogen, increasing C sp² content and changes in the π loss peak in the REELS spectra. Results of PR method are consistent with results obtained from the C 1s XPS spectra fitting and the width of C KLL XAES spectra (parameter D). Highest stability under electron irradiation was shown by polyethylene of largest molecular weight and most linear branching structure. Application of the PR method to EPES REELS spectra allows to distinguish different polyethylenes and quantify the C sp² content.     

Density-functional study of Si<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>C<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 10–15) clusters

Density-functional theory with generalized gradient approximation for the exchange-correlation potential has been used to calculate the structural and electronic properties of Si _n C _n (n = 10–15) clusters. We find that the Si _n C _n clusters prefer cagelike structures. An extensive isomer search shows that the lowest-energy arrangements are those in which the silicon atoms and the carbon atoms form two distinct subunits. It is found that the carbon atoms favor to form fullerene-like structure due to the sp ²-like bond. The silicon atoms are trying to cope with an unfavorable sp ² environment, but distorted tetrahedra still show up somewhere of the cagelike structures. On the basis of the lowest-energy geometries obtained, the binding energy, HOMO–LUMO gap, Mulliken charge, ionization potential and electron affinity of the clusters have been computed and analyzed. An electronic charge transfer from the Si-populated to the C-populated regions is observed.     

Decorated graphyne and its boron nitride analogue as versatile nanomaterials for CO detection

The sensitivity of a new two-dimensional (2D) carbon allotrope built from sp- and sp²-hybridised carbon atoms, graphyne (GY), as well as its boron nitride analogue (BN-yne) towards CO molecule has been theoretically investigated. Indeed, a theoretical understanding of the interaction between gas molecules and extended carbon-based network structures is crucial for developing new materials that could have a wide range of applications. Here, we report our first-principles calculations to explore the impact of metal decoration on the GY and BN-yne upon the CO adsorption. We predict that Ca and Li decorations significantly enhance the CO-sensing ability of the GY and BN-yne compared to that of their pristine sheets. Owing to strong interactions between CO and the decorated GY and BN-yne, dramatic changes in the electronic properties of the sheets together with large band gap variations were observed. The present study sheds a deep insight into the sensing properties of the novel carbon-based 2D structures beyond the graphene sheet.     

类金刚石薄膜力学特性的分子动力学模拟

基于Brenner的REBO势函数,利用分子动力学方法模拟了含氢量不同的类金刚石薄膜的纳米压痕过程,依据得到的加载卸载曲线,计算了薄膜的刚度、硬度以及弹性模量.结果表明:类金刚石薄膜的硬度由氢含量和sp³键含量两个因素共同决定;当薄膜中氢含量小于39% 时,薄膜硬度主要取决于sp³键含量,sp³键越多,硬度越高;当薄膜中氢含量达到52%,薄膜硬度则显著下降,此时氢的作用占据主导地位. 关键词： 类金刚石薄膜 分子动力学模拟 纳米压痕 硬度     

Time-Dependent Resonant Tunneling in a Double-Barrier Diode Structure

The elastic moduli of bilayer graphene nanomeshes, i.e., nanomeshes of bilayer graphene, where layers at the edges of “closed” holes are coupled to each other by a continuous network of sp²-hybridized atoms, have been calculated by ab initio methods. Structures with different configurations of holes in layers with AA, AB, and 30° stackings have been studied. It has been shown that the ultimate tensile strength of the nanomeshes under consideration is higher than that of graphene nanostructures and is comparable with the ultimate tensile strength of bilayer graphene and single-layer carbon nanotubes. A possible application of such strong nanomeshes as nanocontainers for hydrogen storage and other compressed gases has been also discussed.

     

Correlations between the physical properties of the carbon phases obtained at a high pressure from C<Subscript>60</Subscript> fullerite

Correlations between the density, elastic properties, and hardness of the carbon phases prepared from C₆₀ at a high pressure are studied. By varying the high pressure and temperature properly, one can obtain from C₆₀ a broad class of ordered polymerized and disordered phases, for which the fraction of the sp² and sp³ states, the characteristic dimensionality of the structure, the degree of covalent bonding, etc. can be varied successfully. 3D-bonded carbon structures are shown to exhibit a clearly pronounced correlation between the hardness or bulk modulus and the density, with these correlations also apparently applying to the carbon phases in a general case. At the same time, the mechanical characteristics of structures with a lower dimension covalent bonding are worse than those of 3D-bonded phases with similar values of the density.     

含氮氟化类金刚石(FN-DLC)薄膜的研究：(Ⅰ) sp结构与化学键分析

以CF₄，CH₄和N₂为源气体，利用射频等离子体增强化学气相沉积法，在不同功率下制备了含氮氟化类金刚石膜.用俄歇电子能谱、拉曼光谱、X射线光电子能谱和傅里叶变换红外光谱对薄膜的电子结构和化学键进行了表征，并结合高斯分峰拟合方法分析了薄膜中sp²，sp³结构比率.结果表明，制备的薄膜属于类金刚石结构，不同沉积功率下，薄膜内的sp²/sp³值在2.0—9.0之间，随着沉积功率的增加薄膜内sp²的相对含量增加.膜内主要有C—F_x(x=1，2)，C—C，C=C和C≡N等化学键.沉积功率增加，C—C基团增加，膜内F的浓度降低，C—F基团减少，薄膜的关联加强，稳定性提高. 关键词： 含氮氟化类金刚石膜 sp结构 化学键结构 射频功率     

Crossed graphene: Stability and electronic structure

Carbon has always attracted attention due to its rich chemistry and the almost complementary properties of the natural phases graphite and diamond. While graphite is a highly anisotropic semi‐metal, diamond shows high hardness and thermal conductivity and is a wide‐gap insulator. With the discovery of graphene, fullerenes, and carbon nanotubes which resemble properties of the two crystalline phases, research on those and novel carbon materials emerged. Since carbon is forming different covalent bonds, there is a multitude of possibilities to create new structures by just combining sp, sp², and sp³ bonded carbon. Here we report on the discovery of a new sp² and sp³ bonded carbon structure which can be seen as a crossed graphene structure providing hybrid properties of graphene and diamond by means of an evolutionary algorithm.

     

Properties of diamondlike films obtained in a barrier discharge at atmospheric pressure

Diamondlike films are synthesized from gaseous hydrocarbons in a barrier discharge at atmospheric pressure. The films were investigated using transmission electron microscopy, electron diffraction, and infrared spectroscopy. A technique for determining the quantitative characteristics of the films (hydrogen content, ratio of different types of carbon-carbon bonds and hydrocarbon groups) using standard samples is described. The highest-quality films were obtained from methane (ratio of hydrogen to carbon atoms H/C=1.04, fraction of diamondlike to graphitelike bonds sp ³: sp ²=100%: 0%) and from a mixture of acetylene and hydrogen in the ratio 1:19 (H/C=0.73, sp ³: sp ²=68%: 32%). Zh. Tekh. Fiz. 67, 100–104 (August 1997)     

Nitrogen 1s electron binding energy assignment in carbon nitride thin films with different structures

Carbon nitride thin films deposited by dc unbalanced magnetron sputtering have been analyzed by high-resolution X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The XPS data show that N 1s binding states depend on substrate temperature (T_s). By comparison with the Raman spectra, N 1s binding states are assigned in which nitrogen atoms are mainly bound to sp² and sp³ carbon atoms at T_s = 100°C, whereas at T_s = 500°C nitrogen atoms are mainly bonded to sp², sp³ and sp¹ carbon atoms.     

Nonlinear elastic properties of a model one-dimensional granular unconsolidated structure

The characteristic features of the propagation of finite-amplitude elastic waves in a model one-dimensional unconsolidated granular medium are investigated. The model medium is represented by a linear chain of 80 steel balls with a diameter of 6.5 mm each, this chain being preliminarily loaded with an external static force F. The elastic properties of the model are analyzed. The theoretical dependences of the coefficients of elasticity of the second, third, and fourth orders on the force F are obtained. The experimental setup is described. The results of studying the nonlinear effects, namely, the higher harmonic generation and the wave generation at combination frequencies, which accompany the acoustic wave propagation in the chain, are presented. For the chain of balls under study, a structural phase transition from the 1D structure to a 2D one is observed with an increase in the external compression force F applied to the balls. The results of the study are analyzed using the Hertz theory of contact interactions.     

Effect of pulsed ion irradiation on the electronic structure of multi-walled carbon nanotubes

The effect of pulsed ion irradiation and vacuum annealing on the ratio of sp ²- and sp ³-hybridized orbitals of carbon atoms in the layers of oriented multi-walled carbon nanotubes has been studied by analyzing the photoemission spectra of the C1s core level and the valence band of carbon, which were obtained using the equipment of the BESSY II Russian-German beamline of synchrotron radiation and a Riber analytical system. It has been shown that the ion irradiation leads to a significant decrease in the fraction of atoms with the sp ³ hybridization of electrons. On the contrary, the annealing reduces the fraction of the sp ³-component in the spectra of carbon. Typical features of the valence band of multi-walled carbon nanotubes in the annealed and irradiated states have been established.