Carbine formation as a result of graphite sample surface heating by laser radiation at atmospheric pressure to a temperature not exceeding 4000 K

Raman spectra from various areas of a laser crater resulted from carbon melting at a temperature not exceeding 4000 K and a pressure of the order of atmospheric were studied. The spectra were excited by the second harmonic of the Nd:YAG laser at a wavelength of 503 nm. Graphite and carbine peaks were observed in the Raman spectra, which suggests that small amounts of carbine in addition to graphite are formed during liquid carbon crystallization.     

PAN基碳纤维在表面处理中的拉曼光谱研究

采用激光拉曼光谱研究了PAN基碳纤维在表面处理中的微结构变化,分析了表面处理前后碳纤维的一级拉曼光谱特性。结果表明：拉曼光谱中主要的D峰和G峰的拉曼频移、半高宽以及各个不同拉曼频移位置对应肩峰的积分面积比是表征碳纤维物相结构变化的重要参数。经过不同的表面处理,PAN基碳纤维的一级拉曼光谱参数发生了一定程度变化,D峰和G峰的拉曼峰位向高波数偏移,表征石墨微晶尺寸的R值有所提高,这说明在表面处理后碳纤维的石墨微结构受到刻蚀,微晶尺寸有所减小,石墨微晶的边界活性增大;此外,表征碳纤维结构有序程度和缺陷多少的D峰和G峰的半高宽均有减小,表征无定型碳结构或某种有机官能团的A峰和D″峰的相对积分面积减小,这说明与乱层石墨结构相比,碳纤维中存在的无定型碳结构更容易被刻蚀,经过表面处理之后无定型碳的物相比例减小,这与碳纤维XRD图谱中表观结晶度提高的规律相一致。因此,利用激光拉曼光谱可研究碳纤维物相结构的变化规律。     

FOURIER ANALYSIS OF TEMPORAL AND SPATIAL OSCILLATIONS OF TUNNELING CURRENT IN SCANNING TUNNELING MICROSCOPY

Partially oxidized Si(111) surfaces and surfaces of highly oriented pyrolytic graphite (HOPG) were studied by two different ultrahigh vacuum scanning tunneling microscope (UHV-STM) systems and by an STM system working under ambient conditions, respectively. The STM current images of partially oxidized Si(111) surfaces and HOPG surfaces were analyzed by one/two-dimensional fast Fourier transformation (1D-FFT/2D-FFT). The phenomenon of temporal oscillations of tunneling current on the partially oxidized Si(111) surfaces was detected with both UHV-STM systems. Temporal as well as spatial oscillations of tunneling current appeared in highly resolved STM current images of the Si(111) surfaces simultaneously, but both kinds of oscillations could be discriminated according to their different influence on the 2D-FFT spectra of the current images, while varying the scanning range and rate. On clean HOPG surfaces only spatial oscillations of tunneling current induced by the surface structure were observed.     

Graphite at high pressures: Pseudomelting at 44 GPa

Abstract

The Raman spectra comparative study of graphite-like modifications of carbon: monocrystalline graphite, pyrolytic graphite and amorphous (glassy) carbon was performed at high pressures and room temperature. At P = 44 GPa an abrupt broadening of Raman bands of pyrolytic graphite and glassy carbon was observed. The same process in monocrystalline graphite occures continuously from 23 to 44 GPa and for higher pressures the Raman spectra of all three substances under study become practically indistinguishable from one another and from that of amorphous carbon (a-C) at the same pressure. This result is ascribed to the formation at these pressures of the dence amorphous carbon modification.     

Tunneling-current-induced light emission from individual carbon nanotubes

Tunneling electrons from a scanning tunneling microscope were used to excite light emission from individual multiwalled carbon nanotubes adsorbed on a highly ordered pyrolytic graphite surface. In the integral photon-intensity map, spatially uniform emission in the visible region was observed along the identical multiwalled carbon nanotubes. The emission spectra for the individual nanotubes showed unique profiles which differed with each nanotube, and were classified into two types. Our results indicate that the light emission is due to not the localized electronic states at the tube ends or defects but radiative transitions of electrons between the one-dimensional van Hove singularities, indicating that the two types of spectra are attributed to metallic and semiconducting nanotubes.     

Insight into STM image contrast of n-tetradecane and n-hexadecane molecules on highly oriented pyrolytic graphite

Two-dimensional ordered patterns of n-tetradecane (n-C₁₄H₃₀) and n-hexadecane (n-C₁₆H₃₄) molecules at liquid/graphite interface have been directly imaged using scanning tunneling microscope (STM) under ambient conditions. STM images reveal that the two different kinds of molecules self-organize into ordered lamellar structures in which alkane chains of the molecules extend along one of three equivalent lattice axes of highly oriented pyrolytic graphite (HOPG) basal plane. For n-C₁₄H₃₀ molecules, the molecular axes are observed to tilt by 60° with respect to inter-lamellar trough lines and the carbon backbones of the alkane chains are perpendicular to the HOPG basal plane in an all-trans conformation. However, for n-C₁₆H₃₄ molecules, the molecular axes are perpendicular to lamellar borders (90°) and the planes of the all-trans carbon skeletons are parallel to the graphite basal plane. The results clearly indicate that outmost hydrogen atoms of the alkane chains dominate atom-scaled features of the STM images. That is, in the case of long-chain alkane molecules, topographic effects dominantly determine STM image contrast of the methylene regions of the alkane chains that are adsorbed on HOPG.     

Direct observation of an ordered step surface reconstruction on Au(111) by scanning tunneling microscopy

Experiments with a scanning tunneling microscope (STM) are reported which include the first surface topographic images of Au(111), cleaned and annealed in ultrahigh vacuum. The STM system used for this work includes in situ sample manipulation for sample cleaning, annealing and characterization. Topographs with very large atomically flat (111) regions are obtained and no corrugation on the scale of about 0.1 Å is observed. Some single atomic steps are observed. Surprisingly, ordered arrays of single steps are observed over a large region. These represent a type of surface reconstruction whose repeat period agrees with values derived from previous LEED, TEM and ion scattering measurements. These results represent the first critical information about the surface topography of the Au(111) surface.     

STM investigation of the adsorption and temperature dependent reactions of ethylene on Pt(111)

The adsorption and reactions of ethylene adsorbed in UHV on Pt(111) have been studied as a function of temperature by STM. The STM images taken at 160K show an ordered structure of adsorbed ethylene. Annealing to 300 K produces ethylidyne (C-CH₃) irreversibly, as has been demonstrated by a wide variety of surface science techniques. The ethylidyne on Pt(111) is not visible to the STM at room temperature. Cooling the sample allows direct observation of the ethylidyne ordered structure by STM. Annealing above 430 K results in further dehydrogenation, eventually leaving only carbon on the surface. The decomposition products appear as small clusters which are localized and uniformly distributed over the surface. Further annealing to temperatures >800 K results in the growth of graphite islands on the Pt(111) surface. The annealed graphite islands exhibit several supersturctures with lattice parameters of up to 22 Å, which are thought to result from the higher order commensurability with the Pt(111) substrate at different relative rotations.     

Graphene growth on h-BN by molecular beam epitaxy

The growth of single layer graphene nanometer size domains by solid carbon source molecular beam epitaxy on hexagonal boron nitride (h-BN) flakes is demonstrated. Formation of single-layer graphene is clearly apparent in Raman spectra which display sharp optical phonon bands. Atomic-force microscope images and Raman maps reveal that the graphene grown depends on the surface morphology of the h-BN substrates. The growth is governed by the high mobility of the carbon atoms on the h-BN surface, in a manner that is consistent with van der Waals epitaxy. The successful growth of graphene layers depends on the substrate temperature, but is independent of the incident flux of carbon atoms.     

Au(111)表面单个钴酞菁分子的去氢过程

利用低温超高真空扫描隧道显微镜对单个钴酞菁分子实现了选键化学反应.通过对吸附于Au(111)表面的单个钴酞菁分子外围H原子的"剪裁",并用实验图像和谱学方法,结合第一性原理理论计算研究了逐步去除钴酞菁分子8个外围H原子的过程.理论计算结果再现了实验中所观测到的分子空间构型的变化,并阐明了吸附体系中局域自旋的恢复和变化过程.     

材料动力损伤的相似性

 从理论上推导了材料中空洞分布函数，阐明两种材料，Fe和Ta样品，受不同飞片速度冲击后，其空洞分布的相似性。从文献[5]中又发现，脆性材料的裂纹分布也具有同样的相似性，这说明理论分布函数可能具有普遍性。最后提出了这种性质的广阔应用前景。     

Calculation of scanning tunnelling microscopy images for Kr/graphite system

The scanning-tunnelling-microscopy (STM) images of Kr atoms adsorbed on a monolayer graphite sheet (Kr/graphite system) are calculated using the first-principle total-energy electronic structure calculations within the density functional theory in the local density approximation. The results obtained agree well with the observations. It is found that the optimal site of the adsorbed Kr atom is at the top of the centre of the carbon hexagon, and its equilibrium distance from monolayer graphite surface is about 0.335nm. It is shown that the hybridization of C 2p electronic states (π-electronic states) and Kr 4p and 5s electronic states is the main origin of the Fermi-level local density of state.     

Structure and vibrational properties of carbon tubules

The structure of multilayered carbon tubules has been investigated by electron microscopy and X-ray diffraction. The structure of tubules is characterized by disorder in the stacking of cylindrical graphene sheets. Raman scattering measurements have been carried out in tubules and compared with graphite. The observed features in the Raman spectra in tubules can be understood in terms of the influence of disorder. The additional Raman modes predicted for single layer carbon tubules have not been observed.     

Folding and cracking of graphene oxide sheets upon deposition

Graphene Oxide (GO) sheets, suspended in an aqueous solution, were deposited on freshly cleaved highly oriented pyrolytic graphite (HOPG) and studied using Raman spectroscopy, atomic force microscopy (AFM) and scanning tunneling microscopy (STM). AFM phase imaging shows a distinct contrast between GO and the underlying HOPG substrate. Raman spectroscopy clearly showed the presence of GO sheets on the top of HOPG substrate. The AFM and STM images also reveal wrinkling, folding, and tearing of individual GO sheets after depositing onto an HOPG substrate. We have also observed a distinct cracking of a GO sheet after folding. We attribute this new cracking phenomenon to a weakening of C–C bonds during the oxidation of a graphene sheet.     

Raman and X‐ray diffraction analysis on unburned carbon powder refined from fly ash

The bonding and crystalline structures of oil‐fried fly ash collected from a power plant were analyzed by using Raman spectroscopy and X‐ray diffraction (XRD), respectively. These carbon powders underwent a series of annealing treatment for graphitization and crystallization. In Raman spectra, the refined, unburned carbon contains clearly the D, G and D′ peaks under 2000 or 2700 °C treatment. The Raman spectral line shape of refined, unburned carbon heated at 2700 °C is similar to that of commercial graphite made from graphitization process. In the XRD spectra, the refined, unburned carbon contains (002), (100) and (004) diffraction peaks under heating at 2000 or 2700 °C. The XRD spectral line shape of refined, unburned carbon heated at 2700 °C is similar to that of a commercial graphite bar. The quantitative graphitization level from Raman spectra and crystallization degree from XRD spectra on refined, unburned carbon powders serve as preliminary guide for the qualitative evaluation of these unburned carbon powders. Copyright © 2009 John Wiley & Sons, Ltd.     

Tip-enhanced Raman spectroscopy and microscopy on single dye molecules with 15 nm resolution

Our recently developed approach of UHV-tip-enhanced Raman spectroscopy permits us to acquire Raman spectra of a few single brilliant cresyl blue (BCB) molecules and even a single one adsorbed on a Au(111) surface. This is substantiated by simultaneously recorded STM images. Furthermore, because of the reduced photobleaching in UHV, the time frame for spectral acquisition is sufficiently extended to allow tip-enhanced Raman imaging of a single BCB molecule with a lateral resolution of 15 nm.     

Dissociation reactions of CO Gas on Fe and Fe3O4 surfaces observed by Raman-ellipsometry spectroscopy

A combined system of Raman spectroscopy and ellipsometry is developed for the study of catalyst surfaces on which a chemical reaction is taking place. The dielectric function and the thickness of a surface layer or a surface compound produced in the reaction are analyzed by ellipsometry; vibrational modes of the compound and surface species are analyzed by Raman spectroscopy, and the products in the gas phase by mass spectrometry. The system is applied to the study of the Boudouard and dissociation reactions of CO molecules on Fe and Fe₃O₄ catalysts. A surface layer produced by diffused C and O atoms, a thin oxide layer produced on the Fe by the CO dissociation reaction, and graphite layers produced by the Boudouard reaction are analyzed. Raman spectra reveal the existence of several kinds of carbon species such as defective graphite and an Fe carbide formed on the Fe and Fe₃O₄ surfaces. Specific Raman bands at 1121 and 1147 cm^-1 are tentatively concluded to be produced from microscopic clusters of surface graphite. The reaction of the defective graphite with H₂ gas is found to be stepwise on a time scale of seconds.     

碳纳米管和高取向热解石墨的拉曼光谱对比研究

同时测量了碳纳米管（Ｄ－ＣＮＴ）和高取向热解石墨（ＨＯＰＧ）的拉曼光谱，第一次分别在ＨＯＰＧ和Ｄ－ＣＮＴ中观察到了位于４２６５ｃｍ－１和４２４８ｃｍ－１的（Ｇ＋Ｄ＊）三级模的拉曼散射；拉曼谱的研究显示，Ｄ－ＣＮＴ的结构比ＨＯＰＧ的无序，同时也进一步表明此无序程度主要来源于结构的缺陷，而非石墨层卷曲成筒状之故     

Imaging of ferroelectric vinylidene fluoride and trifluoroethylene copolymer films by scanning tunneling microscopy

In this paper, we reported the possibility to image non-conducting P(VDF-TrFE) copolymer films by STM. The films had the thickness of ∼25.0 nm and were spin-coated onto Au or graphite substrates. For films deposited on Au substrates, STM images showed grain structures of ∼100 nm, much larger than the grains of bare Au substrate. With increased scan rate, the film surface was damaged by STM tip and extreme protrusions and holes were observed. For films deposited on graphite substrates, we only obtained an image of very flat plane and could not observe the topography of the film surface. It seemed that the tip had pierced through the uppermost P(VDF-TrFE) layers and only imaged the layers nearest to the substrate. Asymmetrical current-voltage curves were observed from copolymer films deposited on HOPG. Experimental results were discussed.     

THE RAMAN SCATTERING OF CARBON NANOTUBES PRODUCED IN DIFFERENT INERT GASES AND THEIR PRESSURES BY ARC DISCHARGE

First- and second-order Raman spectra of carbon nanotubes produced in helium and argon atmospheres at a pressure ranging from 11 to 92 kPa by arc discharge have been measured and compared with each other. The position and bandwidth of the spectral lines depend on the kind of inert gases and their pressure. The Raman spectra of the nanotubes produced in argon gas atmosphere are much more similar to that of polycrystalline graphite than those of the nanotubes produced in helium gas atmosphere. The position and bandwidth of nanotube Raman peaks change with gas pressure in arc discharge because different diameter distribution of nanotubes is produced at different inert gas pressure. The Raman spectra of nanotubes produced at high pressure is much more like that of graphite than those produced in lower pressure