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1.
A.S. Leal D. Kröner L. González 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(2):185-190
The selective preparation of an enantiomer starting from a pure state of H2POSH representing a 50%:50% mixture of two enantiomers with opposite chiralities is extended to its deuterated counterpart,
H2POSD. A one-dimensional model involving the torsional angle of S-H/D around a pre-oriented P-S axis is used. The design of
an appropriate sequence of ultrashort infrared laser pulses to achieve molecular handedness for H2POSH/D is based on the characteristic level splitting and tunneling times of both molecules. A simple scheme of two linearly
polarized laser pulses involving a three level system serves to convert the different isotopomers to opposite enantiomers,
for any given mixture of H2POSH and H2POSD molecules.
Received 31 August 2000 and Received in final form 23 November 2000 相似文献
2.
K. Elihn F. Otten M. Boman P. Heszler F.E. Kruis H. Fissan J.-O. Carlsson 《Applied Physics A: Materials Science & Processing》2001,72(1):29-34
Iron-containing nanoparticles were made by laser-assisted (ArF excimer laser, λ=193 nm) photolytic dissociation of ferrocene
(Fe(C5H5)2 or FeCp2) in argon and an oxygen/argon gas mixture. The particle-size distributions were obtained on-line by using differential mobility
analysers (DMAs) and were found to be log-normal with a geometric standard deviation of 1.85. In argon, particle sizes between
3 and 100 nm were generated. The volumes of these particles were found to increase linearly with the increased repetition
rate, fluence and beam size of the laser. These observations are explained on the basis of the residence-time approach model.
Received: 23 November 1999 / Accepted: 19 September 2000 / Published online: 22 November 2000 相似文献
3.
Carbon nitride nanocrystals were prepared using a pulsed laser induced liquid–solid interfacial reaction and transmission
electron microscopy, while high resolution electron microscopy characterized their morphology and structure. It is important
that the cubic-C3N4 phase was observed. The formation mechanism of the carbon nitride nanocrystals is also discussed.
Received: 23 May 2000 / Accepted: 26 May 2000 / Published online: 2 August 2000 相似文献
4.
Gab‐Yong Lee 《Journal of Physical Organic Chemistry》2010,23(2):91-95
The substituent effect of electron‐withdrawing groups on electron affinity and gas‐phase basicity has been investigated for substituted propargyl radicals and their corresponding anions. It is shown that when a hydrogen of the α‐CH2 group or acetylenic CH in the propargyl system is substituted by an electron‐withdrawing substituent, electron affinity increases, whereas gas‐phase basicity decreases. The calculated electron affinities are 0.95 eV (CH?C? CH2?), 1.15 eV (CH?C? CHF?), 1.38 eV (CH?C? CHCl?), 1.48 eV (CH?C? CHBr?) for the isomers with terminal CH and 1.66 eV (CF?C? CH2?), 1.70 eV (CCl?C? CH2?), 1.86 eV (CBr?C? CH2?) for the isomers with terminal CX at B3LYP level. The calculated gas‐phase basicities for their anions are 378.4 kcal/mol (CH?C? CH2:?), 371.6 kcal/mol (CH?C? CHF:?), 365.1 kcal/mol (CH?C? CHCl:?), 363.5 kcal/mol (CH?C? CHBr:?) for the isomers with terminal CH and 362.6 kcal/mol (CF?C? CH2:?), 360.4 kcal/mol (CCl?C? CH2:?), 356.3 kcal/mol (CBr?C? CH2:?) for the isomers with terminal CX at B3LYP level. It is concluded that the larger the magnitude of electron‐withdrawing, the greater is the electron affinity of radical and the smaller is the gas‐phase basicity of its anion. This tendency of the electron affinities and gas‐phase bacisities is greater in isomers with the terminal CX than isomers with the terminal CH. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
5.
OES study of the gas phase during diamond films deposition in high power DC arc plasma jet CVD system 下载免费PDF全文
This paper used optical emission spectroscopy (OES) to study the gas
phase in high
power DC arc plasma jet chemical vapour deposition (CVD) during diamond films growth processes. The
results show that all the deposition parameters (methane concentration,
substrate temperature, gas flow rate and ratio of H2/Ar) could strongly
influence the gas phase. C2 is found to be the most sensitive radical
to deposition parameters among the radicals in gas phase. Spatially resolved
OES implies that a relative high concentration of atomic H exists near the
substrate surface, which is beneficial for diamond film growth. The
relatively high concentrations of C2 and CH are correlated with high
deposition rate of diamond. In our high deposition rate system, C2 is
presumed to be the main growth radical, and CH is also believed to
contribute the diamond deposition. 相似文献
6.
T. Kamiya A. Suemasu T. Watanabe T. Sameshima I. Shimizu 《Applied Physics A: Materials Science & Processing》2001,73(2):151-159
The carrier transport property of polycrystalline silicon (poly-Si:H:F) thin films was studied in relation to film microstructure,
impurity, in situ or post-annealing treatments to obtain better carrier transport properties. Poly-Si:H:F films were prepared
from SiF4 and H2 gas mixtures at temperatures <300 °C. Dark conductivity of the films prepared at high SiF4/H2 gas flow ratio (e.g., 60/3 sccm) exhibits a high value for intrinsic silicon and its Fermi level is located near the conduction
band edge. The carrier incorporation is suppressed well, either by in situ hydrogen plasma treatment or by post-annealing
with high-pressure hot-H2O vapor. It is confirmed that weak-bonded hydrogen atoms are removed by the hot-H2O vapor annealing. In addition, evident correlation between impurity concentrations and dark conductivity is not found for
these films. It is thought that the carrier incorporation in the films prepared at high SiF4/H2 gas flow ratios is related to grain-boundary defects such as weak-bonded hydrogen. By applying hot-H2O vapor annealing at 310 °C to a 1-μm-thick p-doped (400)-oriented poly-Si:H:F film, Hall mobility was improved from 10 cm2/Vs to 17 cm2/Vs.
Received: 7 August 2000 / Accepted: 2 March 2001 / Published online: 20 June 2001 相似文献
7.
For the deposition of cubic boron nitride thin films in Ar–N2–BF3–H2 system by dc jet plasma chemical vapor deposition, the role of dc substrate bias ranging from -70 V to -150 V was investigated.
A critical bias voltage was observed for the formation of cBN phase. The cBN content in the film increased with bias voltage
and reached a maximum at the bias voltage of -85 V. Increasing the bias voltage further caused a decrease in cBN content and
peeling of the films from the substrate. By combining the results of infrared spectroscopy, Raman spectroscopy and X-ray diffraction,
the bias voltage was also found to strongly affect the crystal size, crystal quality and residual stress of the deposited
films. A bias voltage a little higher than the critical value was demonstrated to be favorable for the deposition of a high-quality
cBN film with large crystal size and low residual stress.
Received: 13 June 2000 / Accepted: 21 June 2000 / Published online: 23 August 2000 相似文献
8.
CO2 laser-induced plasma CVD synthesis of diamond 总被引:1,自引:0,他引:1
V.I. Konov A.M. Prokhorov S.A. Uglov A.P. Bolshakov I.A. Leontiev F. Dausinger H. Hügel B. Angstenberger G. Sepold S. Metev 《Applied Physics A: Materials Science & Processing》1998,66(5):575-578
2 laser maintenance of a stationary optical discharge in a gas stream, exhausting over a substrate into the air (laser plasmatron).
Nano- and polycrystalline-diamond films were deposited on tungsten substrates from atmospheric-pressure Xe(Ar):H2:CH4 gas mixtures at flow rates of 2 ?/min. A 2.5-kW CO2 laser focused beam produced plasma. The deposition area was about 1 cm2 and growth rates were up to 30–50 μm/h. Peculiarities and advantages of laser plasmatrons are discussed.
Received: 15 January 1998/Accepted: 16 January 1998 相似文献
9.
This paper presents experimental evidence that using the KrF excimer laser for quantitative laser-induced fluorescence (LIF)
studies of the OH A-X (3,0) system is highly problematic if the effects of both photobleaching and photochemistry are not included for laser spectral irradiances greater than 20 MW/cm2 cm-1. Pump-probe and time-resolved measurements of the OH LIF signal in an atmospheric pressure, premixed CH4-air flame at low- and high-laser-spectral-irradiance conditions show that a significant amount of OH is produced from photofragments
resulting from the simultaneous 2-photon predissociation of H2O molecules in the C-X system. A 5+2-level rate-equation model that includes the effects of both photobleaching and photochemical
OH production is shown to satisfactorily predict the data using a single adjustable parameter given by the effective, spectrally
integrated 2-photon cross-section of H2O near 248 nm. The time-integrated OH LIF signal was found to depend on both the laser spectral irradiance and the local concentration of H2O. Additionally, use of the KrF excimer laser for 2-line rotational thermometry can produce temperature errors as great as
+550 K at high laser-pulse energies.
Received: 21 August 2000 / Revised version: 30 October 2000 / Published online: 21 February 2001 相似文献
10.
S.T. Sanders 《Applied physics. B, Lasers and optics》2002,75(6-7):799-802
A swept-wavelength source is created by connecting four elements in series: a femtosecond fiber laser at 1.56 μm, a non-linear
fiber, a dispersive fiber and a tunable spectral bandpass filter. The 1.56-μm pulses are converted to super-continuum (1.1–2.2 μm)
pulses by the non-linear fiber, and these broadband pulses are stretched and arranged into wavelength scans by the dispersive
fiber. The tunable bandpass filter is used to select a portion of the super-continuum as a scan-wavelength output. A variety
of scan characteristics are possible using this approach. As an example, an output with an effective linewidth of approximately
1 cm-1 is scanned from 1350–1550 nm every 20 ns. Compared to previous scanning benchmarks of approximately 1 nm/μs, such broad,
rapid scans offer new capabilities: a gas sensing application is demonstrated by monitoring absorption bands of H2O, CO2, C2H2 and C2H6O at a pressure of 10 bar.
Received: 5 August 2002 / Revised version: 23 September 2002 / Published online: 22 November 2002
RID="*"
ID="*"Corresponding author. Fax: +1-608/265-2316, E-mail: ssanders@engr.wisc.edu 相似文献
11.
U. Beierlein C. Hess C. Schlenker J. Dumas R. Buder D. Groult E. Steep D. Vignolles G. Bonfait 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(2):215-226
Resistivity, thermoelectric power and magnetotransport measurements have been performed on single crystals of the quasi two-dimensional
monophosphate tungsten bronzes (PO2)4(WO3)2m for m
=5 with alternate structure, between 0.4 K and 500 K, in magnetic fields of up to 36 T. These compounds show one charge density
instability (CDW) at 160 K and a possible second one at 30 K. Large positive magnetoresistance in the CDW state is observed. The anisotropic Shubnikov-de Haas and de Haas-van Alphen
oscillations detected at low temperatures are attributed to the existence of small electron and hole pockets left by the CDW
gap openings. Angular dependent magnetoresistance oscillations (AMRO) have been found at temperatures below 30 K. The results are discussed in terms of a weakly corrugated cylindrical Fermi surface. They are shown to be consistent
with a change of the Fermi surface below 30 K.
Received 23 November 1999 and Received in final form 23 March 2000 相似文献
12.
Materials science of Mg-Ni-based new hydrides 总被引:20,自引:0,他引:20
One of the advantageous functional properties of Mg alloys (or compounds) is to exhibit the reversible hydriding reaction.
In this paper, we present our systematic studies regarding the relationship between nanometer- or atomistic-scale structures
and the specific hydriding properties of the Mg-Ni binary system, such as(1) nanostructured (n)-Mg2Ni, (2) a mixture of n-Mg2Ni and amorphous (a)-MgNi,(3) pure a-MgNi, and(4) n-MgNi2. Further studies on(5) an a-MgNi-based system for clarifying the effect of the short-range ordering on the structural and
hydriding properties and(6) a MgNi2-based system for synthesizing the new Laves phase structure are also presented. The materials science of Mg-Ni-based new
hydrides will provide indispensable knowledge for practically developing the Mg alloys as hydrogen-storage materials.
Received: 14 August 2000 / Accepted: 6 November 2000 / Published online: 9 February 2001 相似文献
13.
Wen-Pin Wang Sheng-Rui Jian Jenh-Yih Juang Yi-Shao Lai Wen-Fa Wu Chang-Pin Chou 《Applied Surface Science》2007,253(23):9248-9253
The effects of H2 plasma pretreatment on the growth of vertically aligned carbon nanotubes (CNTs) by varying the flow rate of the precursor gas mixture during microwave plasma chemical vapor deposition (MPCVD) have been investigated in this study. Gas mixture of H2 and CH4 with a ratio of 9:1 was used as the precursor for synthesizing CNTs on Ni-coated TiN/Si(1 0 0) substrates. The structure and composition of Ni catalyst nanoparticles were investigated by using scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (XTEM). Results indicated that, by manipulating the morphology and density of the Ni catalyst nanoparticles via changing the flow rate of the precursor gas mixture, the vertically aligned CNTs could be effectively controlled. The Raman results also indicated that the intensity ratio of the G and D bands (ID/IG) is decreased with increasing gas flow rate. TEM results suggest H2 plasma pretreatment can effectively reduce the amorphous carbon and carbonaceous particles and, thus, is playing a crucial role in modifying the obtained CNTs structures. 相似文献
14.
Honeycomb-like alignments of carbon nanotubes were prepared by pyrolysis of a metal phthalocyanine at 950 °C in an Ar/H2 flow. A simple synthetic method has been developed for a large-scale synthesis of aligned carbon nanotubes normal to a substrate
surface.
Received: 15 June 2000 / Accepted: 21 June 2000 / Published online: 2 August 2000 相似文献
15.
The possible construction of a self-contained and compact pulsed chemical HF-laser based on an auto-wave photon-branched chain
reaction initiated in a gaseous disperse medium composed of H2-F2-O2-He and Al particles by focused external IR radiation is theoretically substantiated. It is shown that an autonomous system
and minimization of the parameters of the main pulsed HF-laser units are achievable due to both the effect of ignition of
the laser-chemical reaction in an auto-wave regime under the condition of external beam focusing and the effect of a huge
laser energy gain of 1011. These effects provide strong reduction of the input pulse energy necessary for initiation up to ∼10-8 J, and make it possible to construct a self-contained laser with kilojoule output energy, which can be initiated by a small
submicrojoule master oscillator powered by an accumulator. Due to an increase in the general pressure of working gases up
to P=2.3 bar and optimization of the parameters of the dispersed component (Al particles with radius r0=0.09 μm and concentration N0=1.4×109 cm-3) and the composition of the working mixture, the HF-laser system will ensure an output energy up to ∼1.5 kJ in a pulse from
the rather small volume of ∼2 L of the active medium.
Received: 18 April 2000 / Revised version: 21 August 2000 / Published online: 8 November 2000 相似文献
16.
We demonstrate monitoring of H2O and CO2 emitted in a volcanic area, using a spectrometer equipped with two distributed feedback (DFB) semiconductor diode lasers.
Each laser is resonant with a molecular species and is fiber-coupled to allow remote operation of the spectrometer. Recordings
of H2O and CO2 lines made at the Solfatara volcano, in southern Italy, are shown, and the application of such a spectrometer as a new tool
for the continuous monitoring and surveillance of volcanoes is discussed.
Received: 28 June 1999 / Revised version: 20 December 1999 / Published online: 23 February 2000 相似文献
17.
R. Kullmer 《Applied physics. B, Lasers and optics》1996,62(2):191-196
The transfer of heat from tungsten spheres into an ambient H2 atmosphere was investigated. The spheres had a radius between 35 and 100 µm and were heated to 1400–2000 K by a laser beam. The H2 pressure ranged from 35 to 1000 mbar. Heat transfer by convection is effective with large spheres and high H2 pressures. With small spheres and low H2 pressures, a pronounced temperature discontinuity at the interface between the tungsten sphere and the ambient gas was observed. The results are relevant to the modelling of gas-phase transport phenomena in laser processing. 相似文献
18.
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
19.
We propose an experimental method for the determination of the electro-optic coefficients of photorefractive crystals. Using
anisotropic properties of the crystal and using the response of the crystal to different polarization states of the incident
light, it is possible to determine the ratio between various electro-optic coefficients by measuring the gain in a two-wave
mixing set-up. The accuracy of the measurements is estimated and the obtained electro-optic coefficients for a Ba0.77Ca0.23TiO3 crystal show good agreement with corresponding values already known from the literature.
Received: 24 January 2000 / Revised version: 23 May 2000 / Published online: 16 August 2000 相似文献
20.
J. Hayoz M. Bovet T. Pillo L. Schlapbach P. Aebi 《Applied Physics A: Materials Science & Processing》2000,71(6):615-618
We demonstrate a very simple and reliable method of manufacturing clean, single-crystalline Y2O3 films on Nb(110) substrates in situ. The method exploits the oxygen bulk contamination of Nb as a source of clean oxygen.
For substrate temperatures above 800 K oxygen segregation to the Nb surface is so efficient, that yttrium becomes oxidized
during deposition without any background oxygen pressure required in the ultrahigh vacuum system. The crystallinity and stoichiometry
of these films can be tuned by the deposition temperature. For Y deposition at 1300 K the formation of well-ordered (111)-oriented
Y2O3 films is achieved.
Received: 19 April 2000 / Accepted: 20 April 2000 / Published online: 23 August 2000 相似文献