2015 Vol. 28, No. 1

Content
2015, 28(1): 0-0.
Chinese Abstracts
2015, 28(1): 123-123.
Article
ZnO nanosheets with thickness of a few nanometers are prepared by vapor transport and condensation method, and their structure and optical properties are well characterized. Field effect transistor (FET) and ultraviolet (UV) sensors are fabricated based on the ZnO nanosheets. Due to the peculiar structure of nanosheet, the FET shows n-type enhanced mode behavior and high electrical performance, and its field-effect mobility and on/off cur-rent ratio can reach 256 cm2/(V·s) and ~108, respectively. Moreover, the response of UV sensors can also be remarkably improved to ~3×108. The results make the ZnO nanosheets be a good material for the applications in nanoelectronic and optoelectronic devices.
Moisture measurement is of great needs in semiconductor industry, combustion diagnosis, meteorology, and atmospheric studies. We present an optical hygrometer based on cavity ring-down spectroscopy (CRDS). By using different absorption lines of H2O in the 1.56 and 1.36 μm regions, we are able to determine the relative concentration (mole fraction) of water vapor from a few percent down to the 10-12 level. The quantitative accuracy is examined by comparing the CRDS hygrometer with a commercial chilled-mirror dew-point meter. The high sensitivity of the CRDS instrument allows a water detection limit of 8 pptv.
A broadband infrared surface sum frequency generation vibrational spectroscopy (SFG-VS) and an in situ UV excitation setup devoted to studying surface photocatalysis have been constructed. With a home-made compact high vacuum cell, organic contaminants on TiO2 thin lm surface prepared by RF magnetron sputtering were in situ removed under 266 nm irradiation in 10 kPa O2 atmosphere. We obtained the methanol spectrum in the CH3 stretching vibration region on TiO2 surface with changing the methanol pressure at room temperature. Features of both molecular and dissociative methanol, methoxy, adsorbed on this surface were resolved. The CH3 symmetric stretching vibration frequency and Fermi resonance of molecular methanol is red-shifted by about 6?8 cm-1 from low to high coverage. Moreover, the recombination of dissociative methanol and H on surfaces in vacuum was also observed. Our results suggest two equilibria exist: between molecular methanol in the gas phase and that on surfaces, and between molecular methanol and dissociative methanol on surfaces.
The Raman depolarization ratios of gaseous CO2 in the spectral range of 1240-1430 cm-1 are determined with a sensitive photoacoustic Raman spectroscopy, and more accurate data compared to the literature results are presented. The precision of the obtained depolarization ratio is achieved by measuring and fitting the dependence of the PARS signal intensity on the cross angle between the polarizations of two incident laser beams.
A promising method to improve the attosecond pulse intensity has been theoretically presented by properly adding an ultraviolet pulse into the orthogonal two-color field. The results show that by properly adding a 125 nm ultraviolet pulse to the orthogonal two-color field, not only the harmonic yield is enhanced by 2 orders of magnitude compared with the original orthogonal two-color field case, but also the single short quantum path, which is selected to contribute to the harmonic spectrum, results in an ultrabroad 152 eV bandwidth. Moreover, by optimizing the laser parameters, we find that the harmonic enhancement is not very sensitive to the pulse duration and the polarized angle of the assisted ultraviolet pulse, which is much better for experimental realization. As a result, an isolated pulse with duration of 38 as can be obtained, which is 2 orders of magnitude improvement in comparison with the original two-color orthogonal field case.
The decay dynamics of N,N-dimethylthioacetamide after excitation to the S3(ππ*) state was studied by using the resonance Raman spectroscopy and complete active space selfconsistent field method calculations. The UV-absorption and vibrational spectra were assigned. The A-band resonance Raman spectra were obtained in acetonitrile, methanol and water with the laser excitation wavelengths in resonance with the first intense absorption band to probe the Franck-Condon region structural dynamics. The CASSCF calculations were carried out to determine the excitation energies and optimized structures of the lowerlying singlet states and conical intersection point. The A-band structural dynamics and the corresponding decay mechanism were obtained by the analysis of the resonance Raman intensity pattern and the CASSCF calculated structural parameters. The major decay channel of 3,FC(ππ*)→S3(ππ*)/S1(nπ*)→1(nπ*) is proposed.
The binding energy spectra and electron momentum distributions for the outer valence molecular orbitals of gaseous 2-fluoroethanol have been measured by the non-coplanar asymmetric (e, 2e) spectrometer at impact energy of 2.5 keV plus binding energy. The quantitative calculations of the ionization energies and the relevant molecular orbitals have been carried out by using the outer-valence Green’s function method and the density functional theory with B3LYP hybrid functional. The observed ionization bands in binding energy spectra, as well as the previous photoelectron spectrum which was not assigned, have been assigned for the first time through the comparison between experiment and theory. In general, the theoretical electron momentum distributions calculated by B3LYP method with aug-cc-pVTZbasis set are in line with the experimental ones when taking into account the Boltzmannweighted thermo-statistical abundances of five conformers of 2-fluoroethanol.
The vibrational state-selected population transfer from a highly vibrationally excited level to the ground level is of great importance in the preparation of ultra-cold molecules. By using the time-dependent quantum-wave-packet method, the population transfer dynamics is investigated theoretically for the HF molecule. A double-Σ-type laser scheme is proposed to transfer the population from the |v=16> level to the ground vibrational level |v=0> on the ground electronic state. The scheme consists of two steps: The first step is to transfer the population from |v=16> to |v=7> via an intermediate level |v=11>, and the second one is to transfer the population from |v=7> to |v=0> via |v=3>. In each step, three vibrational levels form a Σ-type population transfer path under the action of two temporally overlapped laser pulses. The maximal population-transfer efficiency is obtained by optimizing the laser inten-sities, frequencies, and relative delays. Cases for the pulses in intuitive and counterintuitive sequences are both calculated and compared. It is found that for both cases the population can be efficiently (over 90%) transferred from the |v=16> level to the |v=0> level.
Investigation on vibrational excitation and relaxation process will provide important in-formation for a better understanding of ultrafast dynamic response of energetic materials. Using sub-ps time-resolved coherent anti-Stokes Raman scattering (CARS) experiments, we directly observe excitation of vibrational mode νs(NO2) and its relaxation process of ground state HNS (2,2',4,4',6,6'-hexanitrostillbenein) in solution. The results show that νs(NO2) at 1385 cm-1 has been excited and relaxation time of 0.38 and 8.5 ps is obtained. The possible quantum beat frequencies are also discussed via fs-CARS experiments. The original results provide an insight into ultrafast process of energetic materials.
The exciton relaxation kinetics of ZnCuInS/ZnSe/ZnS quantum dots (QDs) is investigated by time-resolved spectroscopy techniques in detail. Based on the rate distribution model, the wavelength-dependent emission dynamics shows that the intrinsic exciton, the exciton in the interface defect state and that in donor-acceptor pair state (DAPS) together participate in the photoluminescence process of QDs, and the whole emission process is mainly dependent on the DAPS emission. Transient absorption data show that the intrinsic exciton and the interface defect species maybe together appear after excitation and the intensity-dependentAuger recombination process also exists in QDs at high excitation intensity.
Based on the location of bromine substituents and conjugation matrix, a new substituent po-sition index 0X not only was defined, but also molecular shape indexes Km and electronega-tivity distance vectors Mm of diphenylamine and 209 kinds of polybrominated diphenylamine (PBDPA) molecules were calculated. Then the quantitative structure-property relationships (QSPR) among the thermodynamic properties of 210 organic pollutants and 0X、K3、M29、M36 were founded by Leaps-and-Bounds regression. Using the four structural parameters as input neurons of the artificial neural network, three satisfactory QSPR models with network structures of 4:21:1, 4:24:1, and 4:24:1 respectively, were achieved by the back-propagation algorithm. The total correlation coefficients R were 0.9999, 0.9997, and 0.9995 respectively and the standard errors S were 1.036, 1.469, and 1.510 respectively. The relative mean deviation between the predicted value and the experimental value of S?,ΔfH? and ΔfG? were 0.11%, 0.34% and 0.24% respectively, which indicated that the QSPR models had good stability and superior predictive ability. The results showed that there were good nonlinear correlations between the thermodynamic properties of PBDPAs and the four structural pa-rameters. Thus, it was concluded that the ANN models established by the new substituent position index were fully applicable to predict properties of PBDPAs.
Besides carbon solubility, the carbide formation possibility is another important factor to differentiate various substrate materials in graphene growth. A recent experiment indicates that the formation of transition metal carbides (TMCs) can suppress carbon precipitation. In this study, Mo2C, a representative of TMCs, is used to study the effects of carbide formation in graphene growth from first principles. Carbon diffusion in Mo2C bulk turns out to be very difficult and it becomes much easier on the Mo2C(001) surface. Therefore, carbon precipitation suppression and graphene growth can be realized simultaneously. A direction depended diffusion behavior is observed on the Mo2C(101) surface, which makes it less favorable for graphene growth compared to the (001) surface.
We demonstrate a home-built electrochemical scanning tunneling microscope (ECSTM). The ECSTM exhibits highly stable performance. The drifting rates in XY and Z directions of the ECSTM are about 67 and 55.6 pm/min, respectively. Moreover, a specially designed scanner unit successfully solves the well-known problem of large leakage current in high humidity atmosphere. The mechanical structure of the ECSTM is described in detail. The excellent performances of the system are demonstrated by the measured STM images (in copper sulfate solution), including clean and well-ordered large area morphology of Au(111) and the atomically resolved image of highly oriented pyrolytic graphite.
Downconversion (DC) with emission of two near-infrared photons about 1000 nm for each blue photon absorbed was obtained in thulium (Tm3+) and ytterbium (Yb3 ) codoped yt-trium lithium fluoride (LiYF4) single crystals grown by an improved Bridgman method. The luminescent properties of the crystals were measured through photoluminescence excitation, emission spectra and decay curves. Luminescence between 960 and 1050 nm from Yb3 : 2F5/22F7/2 transition, which was originated from the DC from Tm3 ions to Yb3 ions, was observed under the excitation of blue photon at 465 nm. Moreover, the energy transfer processes were studied based on the Inokuti-Hirayama model, and the results indicated that the energy transfer from Tm3 to Yb3 was an electric dipole-dipole interaction. The max-imum quantum cutting effciency approached up to 167.5% in LiYF4 single crystal codoped with 0.49mol% Tm3 and 5.99mol% Yb3 . Application of this crystal has prospects for increasing the energy e ciency of crystalline Si solar cells by photon doubling of the high energy part of the solar spectrum
The single crystal bismuth nanowire arrays grown along [0112] with the diameter of 30 nm was synthesized in the pore of anodic aluminum oxide templates through electrodeposi-tion process. The temperature dependent electric conductance of Bi nanowire arrays was measured from 78 K to 320 K. We found that the semimetal-to-semiconductor transition happened around 230 K for 30 nm Bi nanowires oriented along [01112] and the electric con-ductance of the nanowires had a strong temperature dependence.
Hierarchically porous CaFe2O4/carbon ber hybrids with enhanced microwave induced cat-alytic activity for the degradation of methyl violet (MV) from water were synthesized from kapok by a novel two-step process coupling pore-fabricating and nanoparticles assembling. The as-prepared samples exhibited characteristic hollow ber morphology, CaFe2O4 nanopar-ticles dispersed uniformly on the surface of hollow carbon fibers (HCF). The effects of various factors such as CaFe2O4 loading, microwave power, catalyst doses, initial concen-tration of MV solution and pH value on the microwave induced degradation of MV over CaFe2O4/HCF were evaluated. It was found that the microwave induced degradation of MV over CaFe2O4/HCF had high reaction rate and short process time. The kinetic study indicated that the degradation of MV over CaFe2O4/HCF followed pseudo-first-order kinet-ics model. The high catalytic activity of CaFe2O4/HCF was facilitated by the synergistic relationship between microwave induced catalytic reaction and adsorption characteristics.
Two organic dyes XS51 and XS52 derivated from triarylamine and indoline are synthesized for dye-sensitized solar cells (DSCs) employing cobalt and iodine redox shuttles. The effects of dye structure upon the photophysical, electro-chemical characteristics and cell performance are investigated. XS51 with four hexyloxyl groups on triarylamine performs better steric hindrance and an improvement of photovoltage. XS52 provides higher short-circuit photocurrent density due to the strong electron-donating capability of indoline unit. The results from the redox electrolyte on cell performances indicate that the synthesized dyes are more suitable for tris(1,10-phenanthroline)cobalt(II/III) redox couple than I?/I3? redox couple in assembling DSCs. Application of XS52 in the cobalt electrolyte yields a DSC with an overall power conversion efficiency of 6.58% under AM 1.5 (100 mW/cm2) irradiation.
The rules on regulating aromatic compounds production was investigated by aqueous cat-alytic reforming of sorbitol. It was found that aromatics, ketones, furans, organic acids were main compounds in organic phase. The obvious e ect of metal content showed that the highest carbon selectivity of aromatics was 34.36% when 3wt% Ni content was loaded on HZSM-5 zeolite modi ed by MCM-41. However, it was decreased only to 4.82% when Ni content was improved to 20wt%. Meanwhile, di erent reaction parameters also displayed important impacts on carbon selectivity. It was improved with the increase of temperature, while it was decreased as liquid hourly space velocity and hydrogen pressure was increased. The results showed that appropriate higher temperature, longer contact time and lower hy-drogen pressure were in favor of aromatics information, which suggested a feasible process to solve energy crisis.
The simultaneous γ-ray-radiation-induced grafting polymerization of acrylic acid on ex-panded polytetra fluoroethylene (ePTFE) lm was investigated. It was found that the degree of grafting (DG) of poly(acrylic acid) (PAA) can be controlled by the monomer concentration, absorbed dose, and dose rate under an optimal inhibitor concentration of [Fe2+]=18 mmol/L. SEM observation showed that the macroporous structure in ePTFE films would be covered gradually with the increase of the DG of PAA. The prepared ePTFE-g-PAA film was im-mersed in a neutral silver nitrate solution to fabricate an ePTFE-g-PAA/Ag hybrid film afterthe addition of NaBH4 as a reduction agent of Ag to Ag atom. SEM, XRD, and XPS results proved that Ag nanoparticles with a size of several tens of nanometers to 100 nanometers were in situ immobilized on ePTFE film. The loading capacity of Ag nanoparticles could be tuned by the DG of PAA, and determined by thermal gravimetric analysis. The quan-titative antibacterial activity of the obtained ePTFE-g-PAA/Ag hybrid lms was measured using counting plate method. It can kill all the Escherichia coli in the suspension in 1 h. Moreover, this excellent antibacterial activity can last at least for 4 h. This work provides a facile and practical way to make ePTFE meet the demanding antimicrobial requirement in more and more practical application areas.
Optical transmission characteristics of water between quartz glass under shock compression are in situ observed by using the technique of missile-borne light source. Through these transmission properties, the phase transition of liquid water is studied. The experimental results show that liquid water exhibits transparency decline phenomenon when the pressure is lower than 2 GPa under shock compression process, and the transparency variation is related to the existence of quartz glass. So, the transparency decline is attributed to a quartz-induced freezing phenomenon of water.
Measurements of atmospheric benzene and toluene were carried out continuously using dif-ferential optical absorption spectroscopy from August 7 to August 28 in Beijing during the period of vehicular restrictions. The correlations between traffic flows and totals of benzene and toluene were studied during the period of vehicular traffic restrictions from August 17 to August 20 and non-traffic restrictions on August 16 and August 21. The correlation coef-ficient was 0.8 between benzene and toluene. And the calculated daily mean value ratios of benzene to toluene were 0.43-0.50. During the period of vehicular restrictions, traffic flows were reduced about 11.8% and the levels of benzene and toluene were reduced by 11.4% and 12.8%, respectively. The vehicle emissions were recognized as the major sources for atmospheric benzene and toluene in Beijing.