Design and characteristics of quantum cascade laser-based CO detection system

National High Technology Research and Development Program of China 2007AA03Z112；Program of Ministry of Education of China 20060183030；Program of Jilin Provincial Science and Technology Department of China 20070709；Program of Bureau of Science and Technology of Changchun City 2007107

Origin of flat-band voltage sharp roll-off in metal gate/high-k/ultrathin- SiO2/Si p-channel metal-oxide-semiconductor stacks

The origin of the flat band voltage roll-off (V-FB roll-off) in metal gate/high-k/ultrathin-SiO2/Si metal-oxide-semiconductor stacks is analyzed and a model describing the role of the dipoles at the SiO2/Si interface on the V-FB sharp roll-off is proposed. The V-FB sharp roll-off appears when the thickness of the SiO2 interlayer diminishes to below the oxygen diffusion depth. The results derived using our model agree well with experimental data and provide insights to the mechanism of the V-FB sharp roll-off.

Fermi-Level Pinning at Metal/High-k Interface Influenced by Electron State Density of Metal Gate

The Fermi-level pinning (FLP) at the metal/high-k interface and its dependence on the electron state density of the metal gate are investigated. It is found that the FLP is largely determined by the distortion of the vacuum level of the metal which is quantitatively ruled by the electron state density of the metal. The physical origin of the vacuum level distortion of the metal is attributed to an image charge of the interface charge in the metal. Such results indicate that the effective work function of the metal/high-k stack is also governed by the electron state density of the metal.

Dynamic behaviors of mode III interfacial crack under a constant loading rate

In an earlier study on intersonic crack propagation, Gao et al. (J. Mech. Phys. Solids 49: 2113-2132, 2001) described molecular dynamics simulations and continuum analysis of the dynamic behaviors of a mode II dominated crack moving along a weak plane under a constant loading rate. The crack was observed to initiate its motion at a critical time after the onset of loading, at which it is rapidly accelerated to the Rayleigh wave speed and propagates at this speed for a finite time interval until an intersonic daughter crack is nucleated at a peak stress at a finite distance ahead of the original crack tip. The present article aims to analyze this behavior for a mode III crack moving along a bi-material interface subject to a constant loading rate. We begin with a crack in an initially stress-free bi-material subject to a steadily increasing stress. The crack initiates its motion at a critical time governed by the Griffith criterion. After crack initiation, two scenarios of crack propagation are investigated: the first one is that the crack moves at a constant subsonic velocity; the second one is that the crack moves at the lower shear wave speed of the two materials. In the first scenario, the shear stress ahead of the crack tip is singular with exponent -1/2, as expected; in the second scenario, the stress singularity vanishes but a peak stress is found to emerge at a distance ahead of the moving crack tip. In the latter case, a daughter crack supersonic with respect to the softer medium can be expected to emerge ahead of the initial crack once the peak stress reaches the cohesive strength of the interface.

Relativistic Distorted-Wave Collision Strengths of Ni-, Cu- and Zn-like Au Ions

Excitation energies and electron impact excitation strengths from the ground states of Ni-, Cu- and Zn-like Au ions are calculated. The collision strengths are computed by a 213-levels expansion for the Ni- like Au ion, 405-levels expansion for the Cu-like Au ion and 229-levels expansion for the Zn-like Au ion. Configuration interactions are taken into account for all levels included. The target state wavefunctions are calculated by using the Grasp92 code. The continuum orbits are computed in the distorted-wave approximation, in which the direct and exchange potentials among all the electrons are included. Excellent agreement is found when the results are compared with previous calculations and recent measurements.

Theoretical Study on Inner Shell Electron Impact Excitation of Lithium

Cross sections for electron impact excitation of lithium from the ground state 1s(2)2s to the excited states 1s2s(2), 1s2p(2), 1s2snp (n = 2-5), 1s2sns (n = 3-5), 1s2pns (n = 3-5), and 1s2pnp (n = 3-5) are calculated by using a full relativistic distorted wave method. The latest experimental electron energy loss spectra for inner-shell electron excitations of lithium at a given incident electron energy of 2500 eV [Chin. Phys. Lett. 25 (2008) 3649] have been reproduced by the present theoretical investigation excellently. At the same time, the structures of electron energy loss spectra of lithium at low incident electron energy are also predicted theoretically, it is found that the electron energy loss spectra in the energy region of 55-57 eV show two-peak structures.

Hyperfine quenching of the 3s3p P-3(0) level in Mg-like ions

Hyperfine quenching rates of the 3s3p P-3(0) level in Mg-like ions were calculated using the GRASP2K package based on the multi-configuration Dirac-Hartree-Fock method. Valence and core-valence correlation effects were accounted for in a systematic way. Breit interactions and QED effects were included in the subsequent relativistic CI calculations. Calculated rates were compared with other theoretical values and with experiment, and a good agreement with the latest experimental value for the Al-27(+) ion (Rosenband et al 2007 Phys. Rev. Lett. 98 220801) was found. Furthermore, we showed in detail the contributions from Breit interaction and QED effects to concerned physical properties. Finally, electronic data were presented in terms of a general scaling law in Z that, given isotopic nuclear spin and magnetic moment, allows hyperfine-induced decay rates to be estimated for any isotope along the isoelectronic sequence.

Analysis of the xuv photoabsorption spectrum of Au2+, Au3+, and Au4+

The photoabsorption processes of Au2+, Au3+, and Au4+ have been investigated experimentally and theoretically in the 70-127 eV region. Using the dual laser-produced plasma technique, the 4f and 5p photoabsorption spectrum has been recorded at 50 ns time delay and was found to be dominated by a great number of lines from 4f-5d, 6d and 5p-5d, 6s transitions, which have been identified by comparison with the aid of Hartree-Fock with configuration interaction calculations. The characteristic feature of the spectrum is that satellite lines from excited configurations containing one or two 6s electrons are more important than resonance lines, and with increasing ionization, satellite contributions from states with one 6s spectator electron gradually become more important than those with two 6s spectator electrons. Based on the assumption of a normalized Boltzmann distribution among the excited states and a steady-state collisional-radiative model, we succeeded in reproducing a spectrum which is in good agreement with experiment.

Shell effect and capture cross sections in the synthesis of superheavy nuclei

The shell effect is included in the improved isospin dependent quantum molecular dynamics model in which the shell correction energy of the system is calculated by using the deformed two-center shell model. A switch function is introduced to connect the shell correction energy of the projectile and the target with that of the compound nucleus during the dynamical fusion process. It is found that the calculated capture cross sections reproduce the experimental data quantitatively at the energy near the Coulomb barrier. The capture cross sections for reaction (35) (80) Br + (82) (208) Pb -> (117) (288) X are also calculated and discussed.

Doubly excited 2s2p P-1,3(1) resonances in photoionization of helium

The multi-configuration Dirac Fock (MCDF) method is implemented to study doubly excited 2s2p P-1,3(1) resonances of the helium atom and the interference between photoionization and photo excitation autoionization processes. In order to reproduce the total photoionization sprectra, the excited energies from the ground 1s(2) S-1(0) state to the doubly excited 2s2p P-1,3(1) states and the relevant Auger decay rates and widths are calculated in detail. Further more, the interference profile determined by the so-called Fano parameters q and rho(2) is also reproduced. Good agreement is found between the present results and other available theoretical and experimental results. This indeed shows a promising way to investigate the Fano resonances in photoionization of atoms within the MCDF scheme, although there are some discrepancies in the present calculations of the 2s2p P-3(1) state.

Photoionization of 1s electron and corresponding shake-up process in ground and excited lithium atoms

The cross sections of the 18 electron photoionization and corresponding shake-up processes for Li atoms in the ground state 1s(2)2s and excited states 1s(2)2p, 1s(2)3p, 1s(2)3p and 1s(2)3d are calculated using the multi-configuration Dirac-Fock method. The latest experimental photoelectron spectrum at hv = 100 eV [Cubaynes D et al. Phys. Rev. Lett. 99 (2007) 213004] has been reproduced by the present theoretical investigation excellently. The relative intensity of the shake-up satellites shows that the effects of correlation and relaxation become more important for the higher excited states of the lithium atom, which are explained very well by the spatial overlap of the initial and final state wavefunctions. In addition, strong dependence of the cross section on the atomic orbitals of the valence electrons are found, especially near the threshold.

Electron impact excitation of xenon from the metastable state to the excited states

The electron impact excitation cross sections from the lowest metastable state 5p(5)6sJ = 2 to the six lowest excited states of the 5p(5)6p configuration of xenon are calculated systematically by using the fully relativistic distorted wave method. In order to discuss the effects of target state descriptions on the electron impact excitation cross sections, two correlation models are used to describe the target states based on the multiconfiguration Dirac-Fock (MCDF) method. It is found that the correlation effects play a very important role in low energy impact. For high energy impact, however, the cross sections are not sensitive to the description of the target states, but many more partial waves must be included.

Theoretical analysis of xuv photoabsorption spectra of laser-produced iodine plasmas

The 4d photoabsorption spectra of I2+, I3+, and I4+ have been obtained in the 70-127 eV region with the dual laser-produced plasma technique at time delays ranging from 400 to 520 ns. With decreasing time delay, the dominant contribution to the spectra evolves from the I2+ to the I4+ ions, and each spectrum contains discrete 4d-nf transitions and a broad 4d-epsilon f shape resonance, which are identified with the aid of multiconfiguration Hartree-Fock calculations. The excited states decay by direct autoionization involving 5s or 5p electrons, and rates for the different processes and resulting linewidths were calculated. With increasing ionization, the 4d-epsilon f shape resonance become intense and broader in going from I2+ to I3+, and then vanishes at I5+. In addition, the discrete structure of the calculated spectrum of each ion gradually approaches the corresponding shape resonance position. Based on the assumption of a normalized Boltzmann distribution among the excited states and a steady-state collisional-radiative model, we reproduced spectra which are in good agreement with experiment.

Application of rough set-based analysis to extract spatial relationship indicator rules: An example of land use in Pearl River Delta

Spatial relations, reflecting the complex association between geographical phenomena and environments, are very important in the solution of geographical issues. Different spatial relations can be expressed by indicators which are useful for the analysis of geographical issues. Urbanization, an important geographical issue, is considered in this paper. The spatial relationship indicators concerning urbanization are expressed with a decision table. Thereafter, the spatial relationship indicator rules are extracted based on the application of rough set theory. The extraction process of spatial relationship indicator rules is illustrated with data from the urban and rural areas of Shenzhen and Hong Kong, located in the Pearl River Delta. Land use vector data of 1995 and 2000 are used. The extracted spatial relationship indicator rules of 1995 are used to identify the urban and rural areas in Zhongshan, Zhuhai and Macao. The identification accuracy is approximately 96.3%. Similar procedures are used to extract the spatial relationship indicator rules of 2000 for the urban and rural areas in Zhongshan, Zhuhai and Macao. An identification accuracy of about 83.6% is obtained.

Broadband near-infrared emission in Er3+-Tm3+ codoped chalcohalide glasses

The near-IR emission spectra of Er3+-Tm3+ codoped 70GeS(2)-20In(2)S(3)-10CsI chalcohalide glasses were studied with an 808 nm laser as an excitation source. A broad emission extending from 1.35 to 1.7 mu m with a FWHM of similar to 160 nm was recorded in a 0.1 mol.% Er2S3, 0.5 mol.% Tm2S3 codoped chalcohalide glass. The fluorescence decay curves of glasses were measured by monitoring the emissions of Tm3+ at 1460 nm and Er3+ at 1540 nm, and the lifetimes were obtained from the first-order exponential fit. The luminescence mechanism and the possible energy-transfer processes are discussed with respect to the energy-level diagram of Er3+ and Tm3+ ions. (C) 2008 Optical Society of America