碳纳米管向金刚石纳米晶粒的转变

在碳60（C60）[1]和碳纳米管(CNTs)[2]发现之前,人们知道碳通常显示石墨和金刚石两种晶体结构.自从C60和碳纳米管发现后,由于其独特的纳米结构而具有广泛的应用前景,国内外许多学者致力于研究它们的物理和化学特性,而C60、巴基葱（多层碳纳米球）、碳纳米管和金刚石之间的转变是所研究的焦点之一.目前,由碳的其他形式向金刚石转变的主要方法有：Meilunas等人[3]以C60和C70薄膜为基底气相生长多晶金刚石,C60和C70的稳定性和微平面结构在外界条件下,有利于金刚石成核和外延生长;Banhart[4]小组研究了在电子束辐射作用下巴基葱转变…     

NIR- and VIS-raman spectroscopy of CVD diamond films

Raman spectroscopy is a widely used method for the analysis of CVD diamond layers, because it enables to distinguish between different carbon phases, such as diamond, graphite, amorphous carbon and nanocrystalline carbon, which are all commonly present in CVD diamond films. A comparison of visible Raman spectroscopy and near-infrared Raman spectroscopy applied to CVD diamond layers on various substrates (Si, SiAlON, Au, Pd, Mo, W and cemented carbides) has been carried out with the result that visible Raman spectroscopy can be preferably used for characterizing the diamond quality, but for the detection of non-diamond carbon phases NIR-Raman spectroscopy exhibits certain advantages. The NIR-Raman spectra of diamond on silicon substrates are interfered by thermal activation of the Si.Dedicated to Professor Dr. Dr. h.c. mult. J.F.K. Huber on the occasion of his 70th birthday     

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.     

Kinetics of small ion evaporation from the charge and mass distribution of multiply charged clusters in electrosprays

The distribution of charge z and radii R in clusters electrosprayed from formamide solutions of tetraheptylammonium bromide was investigated by selecting those within a narrow range of electrical mobilities Z(1) in a first differential mobility analyzer (DMA), reducing their charge to unity by passage through a neutralizing chamber containing a radioactive (alpha) source, and measuring the mobilities Z(z) of the resulting discrete set of singly charged clusters in a second DMA. After correcting for the polarization contribution to cluster drag, the tandem DMA data yield the range of radii present at detectable levels for each charge state up to z = 9. Because small ion evaporation from electrospray drops leads to charge loss when a drop reaches a certain critical radius R(crit)(z), the measured maximum and minimum cluster radii associated with a given z can be used to infer the activation energy Delta for ion evaporation as a function of drop charge and curvature. These results confirm the Iribarne-Thomson ion-evaporation mechanism, and support earlier theoretical expressions for the functional form of Delta(z,R). The different phenomenon of ion evaporation from metastable multiply charged dry clusters is also observed at characteristic times of 1 s. Its activation energy is estimated as approximately 0.3 eV larger than for ion evaporation from the drops. This new process complicates the interpretation of the present measurements in terms of ion evaporation from liquid surfaces, but introduces no radical change in the picture. It helps understand why salt clusters with more than two or three charges are harder to see in mass spectrometers than in mobility studies under ambient conditions. Copyright 2000 John Wiley & Sons, Ltd.     

Selective growth of SWNTs on partially reduced monometallic cobalt catalyst

SiO(2) supported cobalt (Co) catalyst could be partially reduced and anchored by unreduced Co ions during a carbon monoxide (CO) chemical vapor deposition (CVD) process. This resulted in the formation of sub-nanometre metallic Co clusters catalyzing the growth of single-walled carbon nanotubes (SWNTs) with a narrow diameter distribution.     

CVD Growth of Carbon Nanotubes and Nanofibers: Big Length and Constant Diameter

Summary: We report mass production of carbon nanotubes (CNTs) and carbon nanofibers (CNFs) with relatively high length and aspect ratio. We synthesized carbon nanomaterials by chemical vapor deposition (CVD) of methane as the feeding gas on Fe/Mo nanoparticles that use alumina-aerogel support. Alumina-aerogel-supported Fe/Mo catalyst was prepared using sol-gel. Drying step performed using rotary evaporation and freeze-drying. CVD was performed using a quartz tube furnace. Samples were analyzed using scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Raman spectroscopy.     

Determination of evaporation rates and vapor pressures of very low volatility compounds: a study of the C4-C10 and C12 dicarboxylic acids

A method for the measurement of evaporation rates and vapor pressures of low volatility compounds was developed and applied to the homologous series of C4-C10 and C12 dicarboxylic acids. Proton-transfer chemical ionization mass spectrometry was used to follow directly the temperature-dependent evaporation rates of aerosol samples collected on a cold plate that could be heated at a known rate. The vapor pressures of the deposited compounds were derived from observed evaporation rates through application of the Hertz-Knudsen equation. Temperature programmed desorption allowed for quantification of the enthalpy (DeltaHsub) and entropy (DeltaSsub) of sublimation of the diacids and is described. A strong odd-even dependence with respect to the total carbon number was observed in the derived diacid vapor pressures, consistent with previous measurements. However, the vapor pressures from this method were systematically lower than previous measurements. Though seen in the vapor pressure, no odd-even carbon chain length dependence was readily discernible in the measured values of DeltaHsub and DeltaSsub. Perhaps most importantly, these experimental results also suggest that residual solvent molecules (from the aerosol generation process) trapped in the diacid samples can have a considerable influence on the measured thermodynamic parameters and, if not properly accounted for, may give erroneous results.     

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.     

神木半焦粉末萃取物的组成特征

依次用石油醚、CS₂、CH₂Cl₂、丙酮和甲醇在索氏萃取器中萃取了神木半焦粉末,得到了五级萃取物(E_1-5)和最终的萃余物,总萃取率为1.76%。分别用气相色谱/质谱联用仪(GC/MS)、大气压固体探针/飞行时间质谱仪(ASAP/TOF-MS)和电喷雾电离/飞行时间质谱仪(ESI/TOF-MS)分析了各级萃取物。用GC/MS分析的结果表明,在E₁中C_15-24的直链烷烃和E₂中3与4环的芳烃比较丰富,在E_3-5中含杂原子有机化合物较丰富,特别是E₄和E₅中含氧有机化合物的含量最高。与用GC/MS分析的结果相比,用ASAP/TOF-MS和ESI/TOF-MS从E_3-5中检测出更多的含杂原子有机化合物。     

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.     

Growth of Aligned Carbon Nanotubes on Large Scale by Methane Decomposition with Deactivation Inhibitor

The effects of additives containing iron or nickel during chemical vapor deposition(CVD)on the growth of carbon nanotubes(CNTs)by methane decomposition on Mo/MgO catalyst were investigated. Ferrocene and nickel nitrate were introduced as deactivation inhibitors by in-situ evaporation during CVD. The precisely controlled in-situ introduction of these inhibitors increased the surface renewal of catalyst, and therefore prevented the catalyst from deactivation.Using this method,aligned multi-walled CNTs with parallel mesopores can be produced on a large scale.     

Ideal velocity focusing in a reflectron time-of-flight mass spectrometer

A single-stage ion mirror in a time-of-flight (TOF) mass spectrometer (MS) can perform first order velocity focusing of ions initially located at a start focal plane while second order velocity focusing can be achieved using a double-stage reflectron. The situation is quite different when an ion source extraction field is taken into account. In this case which is common in any practical matrix-assisted laser desorption/ionization (MALDI) TOF-MS a single-stage reflectron, for example, cannot perform velocity focusing at all. In this paper an exact, analytic solution for an electric field inside a one-dimensional reflectron has been found to achieve universal temporal focusing of ions having an initial velocity distribution. The general solution is valid for arbitrary electric field distributions in the upstream (from the ion source to the reflectron) and downstream (from the reflectron to an ion detector) regions and in a decelerating part of the reflectron of a reflectron TOF mass spectrometer. The results obtained are especially useful for designing MALDI reflectron TOF mass spectrometers in which the initial velocity distribution of MALDI ions is the major limiting factor for achieving high mass resolution. Using analytical expressions obtained for an arbitrary case, convenient working formulas are derived for the case of a reflectron TOF-MS with a dual-stage extraction ion source. The special case of a MALDI reflectron TOF-MS with an ion source having a low acceleration voltage (or large extraction region) is considered. The formulas derived correct the effect of the acceleration regions in a MALDI ion source and after the reflectron before detecting ions.     

Kinetic methods for quantifying magic

Two methods are described for obtaining activation energies for evaporation from isolated clusters. They involve measurements of (1) kinetic energy distributions during evaporation and (2) metastable decay probabilities. The two methods supplement each other and can be applied to data garnered in the same apparatus. The methods are illustrated with applications to data in the literature on copper and carbon clusters. An even/odd alternation in evaporation energies from the copper clusters is consistent with a similar alternation in electron affinities, but not with elementary theory. Thermodynamic properties of carbon clusters are also deduced and discussed.     

Quantitative investigation of boron incorporation in polycrystalline CVD diamond films by SIMS

Polycrystalline diamond films have been produced on pre-treated silicon substrate by CVD hot filament method, with B(C₂H₅)₃ added to the gas phase. However, under identical surface conditions, boron incorporation is not homogeneous. In {111} growth sectors, the boron concentration is found to be about 5 times higher than in {100} growth sectors. Moreover, a marked increase in contaminating elements such as aluminium and sodium in regions with higher boron concentrations is detected. Under SIMS fine focus conditions it can be shown that the interface between these two different facet regions is smaller than 0.5 μm. With 3D-depth profile images it can also be shown that the carbon distribution in the diamond layer is not totally homogeneous.     

Structural investigation of zeolite-templated, ordered microporous carbon by scanning tunneling microscopy and Raman spectroscopy

Scanning tunneling microscopy (STM) and Raman spectroscopy have been employed for a detailed structural characterization of an ordered microporous carbon synthesized in the nanochannels of zeolite Y by a templating approach. The carbon exhibited an exceptionally high adsorption capacity together with a long-range structural organization on the nanometer scale. As revealed by STM, this material exhibited both terrace-like and periodic (approximately 1.4 nm) stripe-like nanostructures. The vertical separation between contiguous terraces was measured to be also about 1.4 nm and was thus coincident with the structural periodicity deduced by X-ray diffraction. The terraces of the carbon material were shown to consist of arrays of approximately 1 nm wide carbon clusters. The carbon clusters displayed only a limited degree of local order within the terraces but not long-range periodicity. Likewise, STM indicated that the micropore structure of this carbon originated from the large number of voids that separate adjacent clusters, being morphologically very different from that commonly found in activated carbons. The range of void sizes measured by STM (0.8-2.3 nm) was in complete agreement with the pore size distribution determined from nitrogen adsorption measurements. The origin of the nanostructural features observed for this microporous carbon was discussed on the basis of the surface structure of the zeolite Y template. Finally, Raman spectroscopy provided evidence that the carbon clusters were made up of nanographenes with a curved topology.     

Quantitative investigation of boron incorporation in polycrystalline CVD diamond films by SIMS

Polycrystalline diamond films have been produced on pre-treated silicon substrate by CVD hot filament method, with B(C₂H₅)₃ added to the gas phase. However, under identical surface conditions, boron incorporation is not homogeneous. In {111} growth sectors, the boron concentration is found to be about 5 times higher than in {100} growth sectors. Moreover, a marked increase in contaminating elements such as aluminium and sodium in regions with higher boron concentrations is detected. Under SIMS fine focus conditions it can be shown that the interface between these two different facet regions is smaller than 0.5?μm. With 3D-depth profile images it can also be shown that the carbon distribution in the diamond layer is not totally homogeneous.     

Photodissociation of (SO2)m(H2O)n clusters employing femtosecond pump-probe spectroscopy

A femtosecond pump-probe technique was employed to study the photodissociation dynamics of (SO2)m(H2O)n clusters in real time for clusters, where m=1, 2 and n as large as 11. The pump (excitation) step occurs through a multiphoton process which populates the dissociative E state as well as a lower-lying bound state of the sulfur dioxide (SO2) chromophore. Dissociation of the SO2 monomer occurs through the E state and the decay is fit to a lifetime of 230 fs. The present study is in agreement with our previous investigations of homogeneous (SO2)m clusters that have shown that cluster formation inhibits the dissociation process owing to a steric effect induced by the cluster environment [K. L. Knappenberger, Jr. and A. W. Castleman, Jr., J. Chem. Phys. 121, 3540 (2004)]. The E state lifetime increases sequentially as a function of cluster size to as much as 668 fs when 11 water molecules solvate the chromophore. We have employed a method to compare the ratio of amplitude coefficients, which reflect a respective component of the mathematical fit, to determine the nature of the wave packet evolution in binary clusters. An increase of this ratio by as much as 440% was observed for large cluster sizes. A preferential ion state charge transfer, rather than dissociation, was observed in binary clusters. The significance of cluster size on evaporation processes has been investigated.     

Study of CVD diamond C(100) by X-ray absorption spectroscopies

Surface sensitive x-ray absorption fine structure measurements were carried out near the carbon K-edge on chemical vapor deposited (CVD) diamond and natural diamond. Utilizing different methods, namely near edge and extended x-ray absorption fine structure measurements (NEXAFS and EXAFS), features were found in the spectra which were attributed to non-diamond coordination fractions, such as bulk C-H bonds, graphite-like and more diamond-like coordinated amorphous carbon domains. Both techniques show that the non-diamond fractions consist mainly of diamond-like amorphous carbon.     

Evaporation rates of hot sodium clusters

A scheme based in density functional theory with pseudopotentials is used to obtain the normal modes of vibration of Na _n clusters (4 ≤n ≤ 22). The monomer and dimer evaporation rates from thermally excited clusters are obtained in this harmonic approximation. The time evolution of the abundance spectra from an initial uniform mass distribution of hot clusters is studied and its influence in the experimentally observed spectra is discussed.     

Development of a supercritical fluid extractor coupled with a time-of-flight mass spectrometer for online detection of extracts.

A combined apparatus of a supercritical CO2 extractor (SFE) and a time-of-flight mass spectrometer (TOF-MS) was developed aiming at the direct analysis of extracts. A fused-silica capillary acts as both a pressure restrictor and an effluent injection nozzle into the TOF-MS. The tip of the nozzle was narrowed by melting and abrasion so that a greater pressure drop occurred at the tip. In the TOF-MS chamber, differential pumping between the main and ionization chamber kept the pressure in the ionization chamber at around 10(-3) Pa when the SFE pressure was at 9.7 to 29.4 MPa. The TOF-MS performance, a mass resolution of 263 at m/z = 146, and a sensitivity of 1.6 ng (p-dichlorobenzene) were certified by direct injection of a standard organic solution. Online detection of SFE effluent containing naphthalene, p-dichlorobenzene, phenanthrene and pyrene were successfully performed by the TOF-MS only for 48000 ionization cycles corresponding to 7.5 s.