Nanocrystalline growth and diagnostics of TiC and TiB2 hard coatings by pulsed laser deposition

Nanocrystalline coatings of TiC and TiB₂ were grown by pulsed laser deposition on Si(100) and on X155 steel at low substrate temperatures ranging from 40 °C to 650 °C. A pulsed KrF excimer laser was used with the deposition chamber at a base pressure of 10^-6 mbar. The morphology and structure of the films, studied with SEM, XRD, and TEM, showed that nanocrystalline films with a fine morphology of TiC and TiB₂ were deposited with a grain size of 10 nm-70 nm at all substrate temperatures. The growth of the polycrystalline coatings possessed a columnar morphology with a 𘜄¢ preferred orientation. The hardness of the coatings was determined to be 40 GPa and the elastic modulus, 240 GPa. The composition and the kinetics of the plume produced during the pulsed laser deposition of TiC and TiB₂ was studied under film growth conditions. The mass analysis of ions of the ejected material was performed by time-of-flight mass spectroscopy (TOF-MS) and showed the presence of Ti⁺ and C⁺ during TiC ablation and B⁺, B₂⁺, and Ti⁺ during TiB₂ ablation. The kinetic energies (KE) of the ions depended on the laser fluence which was between 0.5 eV and 340 eV. The kinetic energy and the evolution of the plasma was studied with a streak camera. The velocity of the plasma was of the order of 10⁶ cm/sec and was linearly dependent on the energy fluence of the laser. The emission spectroscopy of the plasma plume confirmed the atomic neutral and single excited species of Ti. These results show that coating growth basically occurs by the recombination of the ionic species at the surface of the substrate.     

激光光解NO2产物—NO分子NO（X2П）与氧原子O(3PJ″)的REMPI离子谱研究

利用激光光解NO₂分子,通过共振增强多光子电离(REMPI resonance enhanced multiphoto ionization)及飞行时间（TOF time of flight）质谱技术,获得了振转态分辨的NO（Ｘ^２Π,υ″,Ｊ″）与自旋-轨道分辨的氧原子O（２Ｐ^３Ｐ_{Ｊ″＝２,１,０})离子谱.NO分子与O原子的离子信号强度与ＵＶ电离激光能量之间的关系分别能用二次方和三次方曲线很好拟合,它表明:光解产物NO分子和氧原子是分别通过（1+1）和（2+1）多光子吸收过程而被电离的.由氧离子信号得到的氧原子基态三个自旋-轨道支能级布居比f_１与f_０分别为0.54±0.09和 0.20±0.04,这一比值与统计分布计算的值为0.6和0.2一致.     

The influence of Exciting Frequency on N2 and N2+ Vibrational Temperature of Nitrogen Capacitively Coupled Plasma

By using optical emission spectroscopy （OES）, N2 and N2^＋ vibrational temperatures in capacitively coupled plasma discharges with different exciting frequencies are investigated. The vibrational temperatures are acquired by comparing the measured and calculated spectra of selected transitions with a least-square procedure. It is found that N2 and N2^＋ vibrational temperatures almost increase linearly with increasing exciting frequency up to 23 MHz, then increase slowly or even decrease. The pressure corresponding to the maximum point of N2 vibrational temperature decreases with the increasing exciting frequency. These experimental phenomena are attributed to the increasing electron density, whereas the electron temperature decreases with exciting frequency rising.     

Positron lifetime spectroscopic studies of as-grown 6H-silicon carbide

Positron lifetime spectroscopy has been employed to study the as-grown n-type 1.2᎒¹⁸ cm^-3 N-doped and p-type 1.8᎒¹⁸ cm^-3 Al-doped 6H-silicon carbide in the temperature range 10 K-300 K. For the p-type material, a positron trapping site, which has a lifetime of 225ᆟ ps, was found and is attributed to positron annihilating from the V_SiV_C divacancy-related defect having a neutral charge. For the case of the n-type material, a positron trapping centre having a lifetime of 200Nj ps, attributed to a V_Si-related defect, and a shallow trap were observed. The shallow trap, having binding energy of l8 meV was attributed to Rydberg-like states resulting from positron binding with a negative ion.     

Rare decays B0s,d→l+l－ in a top quark two-Higgs-doublet model

In the framework of T2HDM, we calculated the new physics contributions involving neutral Higgs bosons to the branching ratios of B⁰_s,d→l⁺l^－ (l=e, μ) decays. Comparing the theoretical predictions with the experimental upper-limits, we found that (a) The data of Br(B⁰_d→l⁺l^－) give the upper bound on tanβ: tanβ≤22, while Br(B⁰_s→l⁺l^－) give tanβ≤12 for fixed δ=0°, m_H+=350 GeV, m_H0=160 GeV, m_h0=115 GeV and m_A0=120 GeV; (b) A light neutral Higgs boson mass m_h0 (m_A0) less than 50 GeV (120 GeV) is excluded by the data of branching ratios for B⁰_s,d→l⁺l^－(l=μ) decays with tanβ=10; (c) The bounds on m_h0 and tanβ, or m_A0 and tanβ are strongly correlated: a smaller (larger) tanβ means a lighter (heavier) neutral Higgs boson.

     

Distinct orientation of AlN thin films deposited on sapphire substrates by laser ablation

We report the experimental characterization of the charged species produced in excimer laser ablation of a superconducting intermetallic compound (YNi₂B₂C). By using energy-selective time-of-flight mass spectrometry, we have obtained direct measurements of both mass spectra and kinetic energy distributions of ions. The investigation has been carried out in the laser fluence range 1-5 J cm^-2, which is typical of laser ablation thin film deposition. High kinetic energies of the charged component (up to 0.4 keV) have been observed even at moderate laser fluences.     

Laser-induced positive ion and neutral atom/molecule emission from single-crystal CaHPO4·2 H2O: The role of electron-beam-induced defects

We examine laser-induced ion and neutral emissions from single-crystal CaHPO₄·2 H₂O (brushite), a wide-band-gap, hydrated inorganic single crystal, with 248-nm excimer laser radiation. Both laser-induced ion and neutral emissions are several orders of magnitude higher following exposure to 2 keV electrons at current densities of 200 7A/cm² and doses of 1 C/cm². In addition to intense Ca⁺ signals, electron-irradiated surfaces yield substantial CaO⁺, PO⁺, and P⁺ signals. As-grown and as-cleaved brushite show only weak neutral O₂ and Ca emissions, whereas electron-irradiated surfaces yield enhanced O₂, Ca, PO, PO₂, and P emissions. Electron irradiation (i) significantly heats the sample, leading to thermal dehydration (CaHPO₄ formation) and pyrolysis (Ca₂P₂O₇ formation) and (ii) chemically reduces the surface via electron stimulated desorption. The thermal effects are accompanied by morphological changes, including recrystallization. Although complex, these changes lead to high defect densities, which are responsible for the dramatic enhancements in the observed laser desorption.     

The Study of Primary Cosmic Ray Mass Composition Around the

The lg N_e-N_μ relationship has been studied from 4.4×10⁴ events (total observation time is 2.9×10⁶s)collected from Mt. Liang Wang Array (24.5°N, 102.9°E, 2720m above sea level). In order to study the mass composition at the knee, Monte-Carlo simulations for the EAS development and detection under same event selection criteria as used in the experimental data have been performed. The result shows that the mass composition of primary cosmic rays has no obvious change and the dominant component is light nuclei around the knee.     

Quark Condensate in Two-Dimensional SU(NC) Lattice Gauge Theory with Massive Wilson Quarks

Using the improved lattice Hamiltonian with massive Wilson quark and the variational method, we study the quark mass m_q and the Wilson parameter r dependences of the quark condensate 〈ψψ〉in the two-dimensional SU(N_C) lattice gauge theory. The numerical results show that when r is given, for N_C=2,3,4,5,6,7, the value of 〈ψψ〉_suba/(gN_C^3/2) decreases as m_q increases. For N_C>3, when m_q is small, 〈ψψ〉_suba/(gN_C^3/2) is almost independent of r; when m_q is large, 〈ψψ〉_suba/(gN_C^3/2)increases with increasing r. Particularly, when m_q→0, our numerical results agree very well with Zhitnitsky's analytical weak coupling result in the continuum, which implys that our numerical results in the case of m_q≠0 are reliable.     

STRATO-GLUON MECHANISM FOR HADRONIC MULTIPLE PRODUCTION AND AVERAGE CHARGED MULTIPLICITY

By assuming that in a high energy hadronic collision process,N pairs of stratonsare produced together with gluons,the number of which is supposed to be propor-tional to the number of“bonds”between any two stratons,we are able to get a rela-tion between the Q-value and the number of pairs N:N=（α²+βQ）^1/2-α.The average charged multiplicity〈n_ch〉_theo is calculated,and is compared withthe experiments.The data of pp、π^±p、K^±p collisions all coincide with the theoreticalcurve in a wide range of energies.The deviation between the energy vs.chargedmultiplicity relations for meson-proton and proton-proton collision processes are ex-plained quantitatively.The average straton mass estimated from the theory is ingood agreement with that.given by other authors.     

Neutral Higgs Effects on Rare Decay B→Xsl+l－ in the T2HDM

We calculate the new physics contributions to the branching ratios of the rare decays B→X_sl⁺l^－(l=e,μ) induced by neutral Higgs bosons loop diagrams in the top quark two-Higgs-doublet model (T2HDM). From the numerical calculations, we find that (a) the neutral Higgs boson's correction to B→X_sl⁺l^－ decays interferes constructively with its standard model counterpart, but small in magnitude; (b) the neutral Higgs contributions to the branching ratio of B→X_sl⁺l^－ decay can be neglected safely if their masses are larger than 100GeV and tanβ≤40.     

多模叠加态|Ψe4,Ⅲ〉q中广义电场分量的N次方H压缩

利用多模压缩态理论,详细研究了由多模偶相干态和多模虚偶相干态的线性叠加所组成的一种新型的四态叠加多模叠加态光场|Ψ_e⁴,Ⅲ〉_q中广义电场分量的等幂次N次方H压缩特性结果表明:1)在腔模总数q与压缩次数N的乘积q·N=4m(m=1,2,3,…)的条件下,态|Ψ_e⁴,Ⅲ〉_q的广义电场分量可恒处于等幂次NH最小测不准态2)在q·N=4m’+2(m’=0,1,2,…)的条件下,当态间的初始相位差(θ₁-θ₂)、各模的初始相位和 φ_j,以及各模平均光子数之总和 R_j²等分别满足一定的取值条件时,态|Ψ_e⁴,Ⅲ〉_q的广义电场分量总可呈现出周期性变化的偶数次的等幂次N次方H压缩效应.     

Formation Mechanisms of Electrical Conductivity and Optical Properties of ZnO:N Film Produced by Annealing Treatment

The effects of annealing on the chemical states of N dopant, electrical, and optical properties of N-doped ZnO film grown by molecular beam epitaxy (MBE) are investigated. Both the as-grown ZnO:N film and the film annealed in N₂ are of n-type conductivity, whereas the conductivity converts into p-type conductivity for the film annealed in O₂. We suggest that the transformation of conductivity is ascribed to the change in ratio of the N molecular number on O site (N₂)_O to the N atom number on O site (N_O) in ZnO:N films under the various annealed atmosphere. For the ZnO:N film annealed in N₂, the percentage content of (N₂)_O is larger than that of N_O, i.e.the ratio >1, resulting in the n-type conductivity. However, in the case of the ZnO:N film annealed in O₂, the percentage content of (N₂)_O is fewer than that of N_O, i.e., the ratio <1, giving rise to the p-type conductivity. There is an obvious difference between low-temperature (80K) PL spectra of ZnO:N film annealed in N₂ and that of ZnO:N film annealed in O₂. An emission band located at 3.358eV is observed in the spectra of the ZnO:N film after annealed in N₂, this emission band is due to donor-bound exciton (D⁰X). After annealed in O₂, the PL of the donor-bound exciton disappeared, an emission band located at 3.348eV is observed, this emission band is assigned to acceptor-bound exciton (A⁰X).     

Blue-to-Orange Tunable Luminescence from Europium Doped Yttrium--Silicon--Oxide--Nitride Phosphors

Europium-doped yttrium-silicon-oxide-nitride phosphors are synthesized by carbothermal reduction and nitridation method. The crystal structure of the phosphors changed gradually from oxide Y2Si2O7 to nitride YSi3N5 state with increasing dosage of Si3N4 and carbon powder. The Y2Si2O7：Eu phosphor shows a blue emission at 465 nm with 300 nm excitation and a characteristic red emission of Eu^3＋ at 612 nm with 230 nm excitation. The YSi3N5：EU phosphor shows a broad emission band centred at 595nm with some sharp peaks of Eu^3＋ with 325nm excitation. The absorption of the studied phosphors increases from 450 to 700hm with an increment in nitrogen content. Blue-to-orange tunable luminescence is observed with 390 nm excitation.     

Phenomenological Scaling of Rapidity Dependence for Anisotropic Flows in 25 MeV/nucleon Ca＋Ca by Quantum Molecular Dynamics Model

Anisotropic flows （v1, v2, v3 and v4） of light fragments up to the mass number 4 as a function of rapidity are studied for 25 MeV/nucleon ^40Ca ＋ ^40Ca at large impact parameters by a quantum molecular dynamics model. A phenomenological scaling behaviour of rapidity dependent flow parameters vn （n = 1, 2, 3 and 4） is found as a function of mass number plus a constant term, which may arise from the interplay of collective and random motions. In addition, v4/v2^2 keeps to be almost independent of rapidity and remains a rough constant of 1/2 for all light fragments.     

Measurement of Reaction Cross Section for 17C and Finite-Range Glauber Model Analysis

We have measured the reaction cross section σ_R of ¹⁷C on the carbon target at the intermediate energy of 97A MeV by using transmission method.finite-range Glauber model has been employed to investigate the density distribution of ¹⁷C by fitting the present result and the previous result of interaction cross section σ_I.By contrast with the result from the analysis of σ_I,a tail in the neutron density distribution of ¹⁷C is found necessary to interpret the present result.Considering the configuration of the valence neutron,a dominant 1d_5/2(77±21%)occupancy is found,which is in agreement with results of momentum distribution measurements.     

态|ψ3(3)〉q广义电场分量的等幂次N次方H压缩

构造了由多模复共轭相干态|{iZ_j^*}〉_q、多模复共轭虚相干态|{iZ_j^*}〉_q(j=1,2,…q)和多模真空态|{0_j}〉_q线性叠加所组成的第Ⅲ类三态叠加多模叠加态光场|ψ₃⁽³⁾〉_q.利用多模压缩态理论,研究了态|ψ₃⁽³⁾〉_q中广义电场分量(即第二正交相位分量)的广义非线性等幂次N次方H压缩特性.发现:态|ψ₃⁽³⁾〉_q是一种典型的三态叠加多模非经典光场;当腔模总数q与压缩次数N之积q·N为偶数时,在一定条件下,态|ψ₃⁽³⁾〉_q的广义电场分量可分别呈现出周期性变化的广义非线性等幂次奇数模-偶数次、偶数模-奇数次、偶数模-偶数次N次方H压缩效应.     

Diagnostics of laser-produced plume under carbon nanotube growth conditions

This paper presents diagnostic data obtained from the plume of a graphite composite target during carbon nanotube production by the double-pulse laser oven method. The in situ emission spectrum (300 to 650 nm) is recorded at different locations upstream of the target and at different delay times from the lasers (IR and green). Spectral features are identified as emissions from C₂ (Swan System: d³@_g-a³@_u) and C₃ (Comet Head System: A¹@_u-X¹D_u⁺). Experimental spectra are compared with computed spectra to estimate vibrational temperatures of excited state C₂ in the range of 2500 to 4000 K. The temporal evolution of the 510-nm band of C₂ is monitored for two target positions in various locations, which shows confinement of the plume in the inner tube and increase in plume velocity with temperature. The excitation spectra of C₂ are obtained by using a dye laser to pump the (0,1) transition of the Swan System and collecting the laser-induced fluorescence signal from C₂. These are used to obtain "ground-state" rotational and vibrational temperatures which are close to the oven temperature. Images of the plume are also collected and are compared with the spectral measurements.     

Large Storage Window in a-SiNx/nc-Si/a-SiNx Sandwiched Structure for Nanocrystalline Silicon Floating Gate Memory Application

An a-SiNx/nanocrystalline silicon [（nc-Si）/a-SiNx] sandwiched structure is fabricated in a plasma enhanced chemical vapour deposition （PECVD） system at low temperature （250℃）. The nc-Si layer is fabricated from a hydrogen-diluted silane mixture gas by using a layer-by-layer deposition technique. Atom force microscopy measurement shows that the density of nc-Si is about 2 ×10^11 cm^-2. By the pretreatment of plasma nitridation, low density of interface states and high-quality interface between the Si substrate and a-SiNs insulator layer are obtained. The density of interface state at the midgap is calculated to be 1 ×10^10 cm^-2eV^-1 from the quasistatic and high frequency C - V data. The charging and discharging property of nc-Si quantum dots is studied by capacitance-voltage （C- V） measurement at room temperature. An ultra-large hysteresis is observed in the C - V characteristics, which is attributed to storage of the electrons and holes into the nc-Si dots. The long-term charge-loss process is studied and ascribed to low density of interface states at SiNx/Si substrate.     

A Time-Dependent Wavepacket Method for Photodissociation Dynamics of Triatomic Molecule

We report a time-dependent quantum wavepacket theory employed to interpret the photoabsorption spectrum of the N20 molecule in terms of the nuclear motion on the upper 21A＇ and 11A＂ potential energy surfaces. The N2-O bond breaks upon excitation leading to dissociation. The total angular momentum is treated correctly taking into account the vector property of the electric field of the exciting radiation.