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1.
Zhen Hua Ni Hao Min Wang Zhi Qiang Luo Ying Ying Wang Ting Yu Yi Hong Wu Ze Xiang Shen 《Journal of Raman spectroscopy : JRS》2010,41(5):479-483
The effect of vacuum annealing on the properties of graphene is investigated by using Raman spectroscopy and electrical measurement. Heavy hole doping on graphene with concentration as high as 1.5 × 1013 cm−2 is observed after vacuum annealing and exposed to an air ambient. This doping is due to the H2O and O2 adsorption on graphene, and graphene is believed to be more active to molecular adsorption after annealing. Such observation calls for special attention in the process of fabricating graphene‐based electronic devices and gas sensors. On the other hand, because the quality of graphene remains high after the doping process, this would be an efficient and controllable method to introduce heavy doping in graphene, which would greatly help on its application in future electronic devices. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
2.
Xiaohua Jia Huiqing Fan Xiangdong Lou Jiaqiang Xu 《Applied Physics A: Materials Science & Processing》2009,94(4):837-841
The CdSnO3 semiconducting oxide that can be used as a gas-sensitive material for detecting ethanol gas is reported in this paper. CdSnO3 nanoparticles were prepared by a chemical co-precipitation synthesis method, in which the preparation conditions were carefully
controlled. The n-type gas-sensing semiconductors were obtained from the as-synthesized powders calcined at 600°C for 1 h.
The phase and microstructure of the obtained nanoparticles were characterized by X-ray diffraction (XRD), transmission electron
microscopy (TEM), and Brunauer–Emmett–Teller (BET) method with a gas adsorption analyzer. CdSnO3 has a small particle size range of 30–50 nm and a high surface area of 9.12 m2/g, and a uniformity global shape. The gas sensitivity and operating temperature, and selectivity of CdSnO3-based sensors were measured in detail. The gas sensors fabricated by CdSnO3 nanoparticles had good sensitivity and selectivity to vapor of C2H5OH when working temperature at 267°C, the value of gas sensitivity at 100 ppm of C2H5OH gas can reach 11.2 times. Furthermore, gas-sensing mechanism was studied by using chromatographic analysis. 相似文献
3.
Plasma enhanced chemical vapor deposition (PECVD) is one effective method to prepare graphene at low temperature in a short time. However, the low temperature in PECVD could not provide substrate a proper state for large area and few layer graphene preparation. Herein, we propose a two-step method to grow graphene on Cu foils. In the first step, in order to acquire a smooth and oxide-free surface state, methanol was used as a reductant to pretreat Cu. In the second step, graphene films were prepared on Cu foils by PECVD using CH4 as carbon source with H2-free. Few-layer graphene sheets with diameter about 1 μm under low temperature (700 °C) and at a short time (10 min) on well pretreated Cu foils were successfully gotten. The effect of methanol pretreatment on graphene synthesis and the graphene growth mechanism on Cu substrate by PECVD are analyzed comprehensively. 相似文献
4.
A. D. Bass J. H. Bredehöft E. Böhler L. Sanche P. Swiderek 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2012,66(2):53
Thermal desorption spectrometry (TDS) and electron stimulated desorption (ESD) are
employed to investigate mechanisms responsible for the formation of
C2H6 in electron irradiated multilayer films of acetonitrile
(CH3CN) at 30 K. Using a high sensitivity time-of-flight mass spectrometer,
we observe the ESD of anionic fragments H−,
CH2
−,
CH3
−
and CN−. Desorption occurs following dissociative electron attachment (DEA) via
several negative ion resonances in the 6 to 14 eV energy range and correlates well with a
“resonant” structure seen in the TDS yield of C2H6 (i.e., at mass
30 amu). It is proposed that C2H6 is formed by the reactions of
CH3 radicals generated following DEA to CH3CN which also yields
CN−. Between 2 and 5 eV, a second resonant feature is seen in the
C2H6 signal. While DEA is observed in the gas phase at these
energies, no anion desorption occurs since anionic fragments likely have insufficient
kinetic energy to desorb. Since the CH2
−
ion has not been observed in gas-phase measurements, we propose that it is formed, along
with HCN (that is detected in TDS) when dissociation into
CH3
−
and CN is hindered by adjacent molecules. 相似文献
5.
B. Milton Boaz R. Samuel Selvaraj K. Senthil Kumar S. Jerome Das 《Indian Journal of Physics》2009,83(12):1647-1657
Sodium p-nitrophenolate dihydrate (NPNa.2H2O) is a highly polarisable non linear optical material. It has a deff about 1.45 times than that of potassium titanyl phosphate. Single crystals of (NPNa.2H2O) have been grown successfully by slow solvent evaporation having water and methanol as solvent. The structure of the crystal
is verified by single X-ray analysis. Optical absorption shows that the crystal is highly transparent between 1500 and 300
nm. Microhardness of the crystal is found to increases with increase in load and the hardness number is found to be high for
methanol grown crystal as compared to the water grown crystal. Electrical conductivity as evaluated from the cole-cole plot
is found to be 1.26 × 10−5 mho m−1. The dielectric constant of the crystal is low and independent at higher frequencies. The crystal has prominent photoconduction
in the presence of trap energy levels formed by the Na+ ions. The SHG efficiency of the crystal is studied by performing Kurtz powder test and the results of scanning electron microscope
analysis indicate that the major part of the crystal surface is free from inclusion and dislocation. 相似文献
6.
A. S. Zubkov V. I. Artyukhov L. A. Chernozatonskii O. S. Nedelina 《Russian Journal of Physical Chemistry B, Focus on Physics》2011,5(5):748-764
Electron transfer is an elementary chemical event involved in many biochemical reactions. Experiments have shown that some
oxyacids participating in electron transport are capable of dissociative capture of low-energy electrons, a process indicative
of the formation of a metastable anion. The present work reports the results of quantum-chemical simulations of the dissociative
electron attachment to a number of oxyacids (H3PO4, H2SO4−, HPO42−, H2SO4, HSO4−, B(OH)4−, HCOOH) with formation of a hydrogen atom in vacuum and in the aqueous medium. Phosphate is one of the most important building
units of biological molecules, whereas formic acid can serve as a model of the −COOH group in amino acids, carboxylic acids,
functional sites of enzymes, etc. The electron affinity of these oxyacids in the aquatic environment is positive and exceeds
the energy of hydrogen atom abstraction. The proton of the OH group captures the electron, while the aquatic environment stabilizes
it in the trapped state due to its polarizability. The data obtained provide a fresh look at the phenomenon of proton-assisted
electron transfer and at the use of oxyacid buffers. 相似文献
7.
2 +O2→H2 O in the pressure range 0.2 Torr≤ptot≤10 Torr on Pt(111) surface. At a catalyst temperature of T=700 K the equilibrium oxygen coverage θo is determined as a function of hydrogen partial pressure α. The experimentally obtained θo is modelled in a two step process considering the mass transport in the gas phase as well as the catalytic reaction on the
surface. In this pressure range the mass transport in the gas phase changes from molecular flow conditions to laminar flow,
inducing a strong modification of the gas phase present at the catalyst through different diffusivities of the reactants as
well as through desorbing reaction products from the catalyst. It is shown that these gas phase alterations have to be taken
into account for a proper modelling of the surface mechanism.
Simulation calculations allow one to identify the sequential hydrogen addition reaction as the main reaction path for water
production in this parameter range. Excellent agreement with previous investigations is obtained for the determined activation
energies of the water-producing reaction steps equal to Ef
H2O≥0.7 eV.
Received: 20 September 1998 / Revised version: 15 December 1998 相似文献
8.
R. Riahi Ph. Teulet Z. Ben Lakhdar A. Gleizes 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(2):223-230
The weighted total cross-section (WTCS) theory is used to
calculate electron impact excitation, ionisation and dissociation cross-sections and rate coefficients of OH, H2, OH+, H2
+,
OH- and H2
- diatomic molecules in the temperature range 1500–15000 K. Calculations are performed for H2(X, B, C), OH(X, A, B),
H2
+(X), OH+(X, a, A, b, c), H2
-(X) and OH-(X)
electronic states for which Dunham coefficients are available. Rate
coefficients are calculated from WTCS assuming Maxwellian energy
distribution functions for electrons and heavy particles. One and two
temperature (θe and θg respectively for electron
and heavy particles kinetic temperatures) results are presented and fitting
parameters (a, b and c) are given for each reaction rate coefficient:
k(θ) = a (θb)exp (-c/θ). 相似文献
9.
L. Tian J. L. Zhu L. Chen B. An Q. Q. Liu K. L. Huang 《Journal of nanoparticle research》2011,13(8):3483-3488
α-Cobalt hydroxide was synthesized by a facile hydrothermal process from Co(Ac)2 and NH3·H2O in the presence of 1,3-propanediol. The large-scale-prepared cobalt hydroxide has a uniform nanobelt morphology with a considerably
high aspect-ratio more than 20 which may be advantageous for exploration of their physicochemical properties. This synthetic
method is convenient, economical, and controllable. The samples were characterized by powder X-ray diffraction, energy dispersive
spectrum, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, CHN element
analysis, thermogravimetric and differential-thermogravimetric analysis, which revealed the compound is lamellar structural
cobalt organic–inorganic hybrid with the chemical formula of Co(OH)1.49(NH3)0.01(CO3
2−)0.22(Ac−)0.07(H2O)0.11 and single-crystalline. 相似文献
10.
L. G. Romanova A. N. Zavilopulo O. B. Shpenik A. V. Kukhto A. S. Agafonova 《Journal of Applied Spectroscopy》2008,75(4):506-513
Single and dissociative ionizations of the POPOP molecule by electron impact in the gas phase are studied using mass spectroscopy.
Fragmentation pathways of the molecule are proposed taking into account the common system of conjugated π-electrons and heteroatoms
in the POPOP molecule. The appearance thresholds for certain fragments of the molecule are determined based on experimentally
measured ionization cross sections as functions of the ionizing electron energy. An ion with m/z = 144 [C9H6ON]+ that is complementary to a fragment with m/z = 220 [C13H10ON]+ (present in the NIST mass spectrum database) is found for the first time in the mass spectrum of POPOP. Its appearance threshold
is determined (Eap = 9.48 eV).
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 4, pp. 482–489, July–August, 2008. 相似文献
11.
A. M. Orlov I. O. Yavtushenko M. V. Churilov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2010,4(5):831-835
The adsorption and kinetic processes of the formation of gas bubbles passivating the surface during polarization of copper
and graphite electrodes in 1% aqueous solution of sulfuric acid have been investigated. Three stages of the process related
to the recharging of the double electric layer—adsorption accumulation of the gas escaping from the surface, the critical
nucleation of the gas bubbles, and their subsequent growth—have been revealed, distinguished, and quantitatively estimated.
It has been shown that potential leveling at the steady-state value specified by the Tafel equation is unambiguously associated
with achievement of the limiting surface area screened by the gas bubbles for each particular current density. The surface
diffusion constants D
H = (1.5–4.4) × 10−4 and (0.1–3.8) × 10−5 cm2/s of hydrogen on copper and graphite, respectively, and D
O = (1.8–4.5) × 10−7 cm2/s of oxygen on graphite during the motion toward the drain (the gas bubbles) have been calculated. 相似文献
12.
S. Kataria Avinash Patsha S. Dhara A. K. Tyagi Harish C. Barshilia 《Journal of Raman spectroscopy : JRS》2012,43(12):1864-1867
We report the synthesis of high‐quality graphene on Cu foils using hot‐filament chemical vapor deposition technique and demonstrate that by suitably varying the CH4 and H2 flow rates, one can also obtain hydrogenated graphene. Micro‐Raman spectroscopy studies confirm the growth of monolayer graphene as inferred from the intensity ratio of 2D to G peak which is nearly four in unhydrogenated samples. Detailed Raman area mapping confirms the uniform coverage of monolayer graphene. The grown layer is also transferred onto a Si substrate over ~10 × 10 mm sq. area. The present results provide a leap in synthesis technology of high‐quality graphene and pave way for scaling up the process. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
13.
V. Vizcaino S. E. Huber P. Sulzer M. Probst S. Denifl P. Scheier 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2012,66(1):27
A detailed study on dissociative electron attachment (DEA) to
2,3-dimethyl-2,3-dinitrobutane (DMNB) in the gas phase is presented. Ion yields as a
function of the incident electron energy from about 0 to 14 eV have been measured for the
most dominant fragments including anions such as NO2
−,
[M-NO2]− or N2O4
−. To help
identifying which anion and neutral fragments are formed upon electron attachment we
calculated the thermodynamic thresholds using the G4(MP2) method. 相似文献
14.
A simple, economic diode laser based cavity ringdown system for trace-gas applications in the petrochemical industry is presented. As acetylene (C2H2) is sometimes present as an interfering contaminant in the gas flow of ethylene (ethene, C2H4) in a polyethylene production process, an on-line monitoring of such traces is essential. We investigated C2H2–C2H4 mixtures in a gas-flow configuration in real time. The experimental setup consists of a near-infrared external cavity diode laser with an output power of a few mW, standard telecommunication fibers and a home-made gas cell providing a user-friendly cavity alignment. A noise-equivalent detection sensitivity of 4.5×10-8 cm-1 Hz-1/2 was achieved, corresponding to a detection limit of 20 ppbV C2H2 in synthetic air at 100 mbar. In an actual C2H2–C2H4 gas-flow measurement the minimum detectable concentration of C2H2 added to the C2H4 gas stream (which may already contain an unknown C2H2 contamination) increased to 160 ppbV. Moreover, stepwise C2H2 concentration increments of 500 ppbV were resolved with a 1-min time resolution and an excellent linear relationship between the absorption coefficient and the concentration was found. PACS 07.07.Df; 42.62.Fi; 82.80.Gk 相似文献
15.
D. Selbmann B. Bendjemil A. Leonhardt T. Pichler C. Täschner M. Ritschel 《Applied Physics A: Materials Science & Processing》2008,90(4):637-643
Single-walled carbon nanotubes (SWCNTs) were synthesized using the high-pressure carbon monoxide disproportionation process.
The SWCNT diameter, diameter distribution and yield can be varied depending on the process parameters. Important parameters
are the temperature, the pressure, the CO gas flow rate and the nozzle injection velocity and geometry for the injection of
reactant gas into the reaction zone. Carbon nanotubes as small as 1.0 nm in diameter have been produced. The purity and yield
of the deposited material were increased with increasing CO gas flow by means of rapid heating of the gas mixture and using
an optimum injection profile. Highly pure SWCNTs were produced at 1250 K, pressures between 5 and 10 bar and gas in the turbulent
flow regime in the cold line of 2000–2500 sccm CO. The raw materials were purified by oxidation in high vacuum at 523 K in
wet Ar/20 vol. % O2 to remove SWCNT carbon-like impurities and to oxidize the iron catalyst nanoparticles. The iron oxides were removed by chemical
treatment in concentrated HCl/C2H5OH mixture solution. The SWCNTs were analyzed by scanning electron microscopy, high-resolution transmission electron microscopy,
atomic absorption spectroscopy and optical absorption spectroscopy to determine the purity, the diameter and diameter distribution,
the chemical composition and the catalyst morphology, as well as the optical properties of deposited SWCNTs in dependence
on the synthesis parameters.
PACS 29.30.-h 相似文献
16.
T. Suzuki Y. Guo S. Inoue X. Zhao M. Ohkohchi Y. Ando 《Journal of nanoparticle research》2006,8(2):279-285
Uniform cathode deposits (longer than 15 mm), containing multiwalled carbon nanotubes (MWNTs) inside, were produced by dc arc discharge evaporation with a computer-controlled feeder of a pure-carbon electrode without a metal catalyst in a He–H2 gas mixture. The purification of MWNTs was carried out to remove amorphous carbon and carbon nanoparticles. High-resolution transmission electron microscopy observations and Raman scattering studies show that the MWNTs possess a high crystallinity and a mean outermost diameter of ∼
∼10 nm. It has been confirmed that the current density in the electron field emission from a purified MWNT mat can reach 77.92 mA/cm2, indicating that the purified MWNTs are a promising candidate electron source in a super high-luminance light-source tube or a miniature X-ray source. 相似文献
17.
A facile and green synthesis of 1,4-disubstituted-1H-1,2,3-triazoles is reported. The reaction of α-azido ketones and terminal alkynes in the presence of [CuSO4 (H2O)5/sodium ascorbate] in a mixture of H2O/polyethylene glycol 400 as solvent afforded the corresponding 1,4-disubstituted triazoles at ambient temperature with short
reaction times and at high yields. The corresponding α-azido ketones were directly prepared in situ from various substituted styrenes using the oxidant cerium ammonium nitrate
and sodium azide in oxygen-saturated methanol. 相似文献
18.
S. Schilt 《Applied physics. B, Lasers and optics》2010,100(2):349-359
Water-vapor-induced pressure broadening is reported for two NH3 absorption features at 6612.7 and 6596.4 cm−1 that are exploitable for gas sensing applications at atmospheric pressure. Absorption spectra of different NH3–H2O–N2 mixtures were measured at an elevated temperature of 70°C to enable high H2O concentrations to be reached. Line parameters were determined from a fitting procedure. The significantly greater values
obtained for the H2O-broadening coefficients of the two lines compared to N2-broadening leads to cross-sensitivity effects in NH3 trace gas sensors based on spectroscopic techniques that are sensitive to the width of the analyzed absorption line, as is
the case in a simple implementation of wavelength modulation spectroscopy or in photoacoustic spectroscopy. In such a case,
cross-sensitivity results in inaccurate gas concentration retrieval when the composition of the diluting gas changes. H2O represents a potentially significant cross-sensitivity source as its concentration may be subject to large variations, especially
in high-temperature applications where concentrations up to a couple of tens of percent may be encountered. In contrast to
interference which can be minimized by an appropriate choice of the analyzed transitions, cross-sensitivity affects the entire
spectrum of the analyte and is thus unavoidable in the mentioned type of gas sensors. 相似文献
19.
Suthari Prashanthi P. Hemant Kumar Li Wang Arun Kumar Perepogu Prakriti Ranjan Bangal 《Journal of fluorescence》2010,20(2):571-580
Steady state and time resolved fluorescence quenching behaviors of meso-Tetrakis (pentafluorophenyl) porphyrin (H2F20TPP) in presence of different aliphatic and aromatic amines have been executed in homogeneous dichloromethane (DCM) solution.
At room temperature in DCM, free base (H2F20TPP) shows fluorescence with two distinct peaks at 640 and 711 nm and natural lifetime τ
f = 9.8 ns which are very similar to that of meso-tetraphenyl porphyrin (TPP). Unlike TPP, addition of both aliphatic and aromatic
amines to a solution containing H2F20TPP results in an efficient decrease in fluorescence intensity without altering the shape and peak position of fluorescence
emission. Upon addition of amines there was no change in optical absorption spectra of H2F20TPP. The fluorescence quenching rate constants ranged from 1 × 109 to 4 × 109 s−1, which are one order below to the diffusion control limit, and temperature dependent quenching rate constants yield the activation
energies which are found to be order of 0.1 eV. Femto second transient absorption studies reveal the existence of amine cation
radical and porphyrin anion radicals with very short decay time (15 ps). The fluorescence quenching reaction follows Stern–Volmer
kinetics. Steady state and time-resolved data are interpreted within general kinetic scheme of Marcus semi-classical model
which attributes bimolecular electron transfer process between amines and the lowest excited singlet state of H2F20TPP. Calculated internal reorganization energies are found to be in between 0.04 and 0.22 ev. Variation of electron transfer
rate as function of free energy change (∆G0) points the ET reactions in the present systems are in Marcus normal region. This is the first example of reductive fluorescence
quenching of free base neutral porphyrins in homogeneous organic solvent ever known. 相似文献
20.
Based on density functional calculations, boron-adsorbed graphene has been found to be a kind of hydrogen-storage medium. B-adsorbed graphene has excellent hydrogen-storage capacity: when the B atoms are adsorbed on one side, the hydrogen-storage capacity is up to 10.10 wt% and when the adsorption is on both sides the capacity is up to 16.95 wt%. In each of these two cases, the hydrogen-storage capacity exceeds 6 wt%, surpassing the target of US Department of Energy (DOE). The calculated adsorption energy of H2 molecules is ?0.209 eV/H2 and ?0.208 eV/H2 for single-side and both-sides B-adsorbed graphene, respectively, which is within the range ?0.2 to ?0.6 eV/H2 and indicates that hydrogenous storage can be recycled in near ambient conditions. By analyzing the electron density distribution of the adsorbed system, we have found that the high hydrogen-storage capacity was due to the change of electron distribution of H2 molecules and graphene by adsorbed B atoms. 相似文献