The electronic emission spectrum of SiB

The gas phase spectrum of the silicon boride radical has been observed for the first time. Two electronic transitions were observed in emission from a corona excited supersonic expansion source. The D⁴Σ⁻-X⁴Σ⁻ system consists of emission from v′ = 0 to v″ = 0-3, while the A⁴Π-X⁴Σ⁻ system consists of numerous bands with v′ = 0-5 and v″ = 0-11, although only the strong 0-0 and 0-1 bands have been analyzed so far.     

不同气体组分的PS-PVD射流光谱诊断

采用发射光谱分析不同气体组分的等离子喷涂-物理气相沉积(PS-PVD)射流,通过Abel转换得出射流径向各点处的光谱强度,比较和分析射流中不同气体的成分分布。采用多谱线斜率法研究不同气体组分的射流在径向距离上电子温度的变化,通过H_β谱线的stark展宽计算径向上电子密度的分布。结果表明：Ar/H₂气体中,H₂在焰流中心区域(0～30 mm)分布较为均匀,但在焰流中心稍靠外的区域(30～60 mm)随着径向距离的增加而增加;加入He后,Ar和H₂在焰流中心处浓度较低并在一定范围内随着径向距离的增加而增加,He往焰流中心聚集;不同气体组分的电子温度和电子密度随着径向距离的增加而降低,同时受到H₂和He的影响。     

Structural,elastic and thermodynamic properties of the tetragonal structure of germanium carbonitride

The structural, mechanical, electronic and thermodynamic properties of the tetragonal structure germanium carbonitride (t-GeCN) were first investigated using the density function theory with the ultrasoft psedopotential scheme in the frame of the generalized gradient approximation and the local density approximation. The elastic constants have confirmed that the t-GeCN is mechanically stable and phonon spectra have confirmed that the t-GeCN is dynamically stable. The anisotropy studies show that t-GeCN exhibits a larger anisotropy in its Poisson's ratio, Young's modulus, shear modulus, sound velocities and universal elastic anisotropy index. Electronic structure study shows that t-GeCN is an indirect semiconductor with band gap of 0.628 eV. The thermodynamic properties of t-GeCN, including Debye temperature, heat capacity, Grüneisen parameter and thermal expansion coefficient are investigated utilizing the quasi-harmonic Debye model.     

Fourier-transform spectroscopic study of the rotational intensity distribution in the first positive BΠg-AΣu band system of the nitrogen molecule

In the present work we have studied the rotational intensity distribution in the 0-0, 0-1 and 1-3 bands of the B³Π_g-A³Σ_u⁺ system of N₂ recorded on a Fourier transform spectrometer. The effective Hamiltonian used by Roux et al. (J. Mol. Spectrosc. 97 (1983) 253) for reduction of the experimental line position data to molecular parameters, is found to be adequate in reproducing the observed line intensities. To enhance the accuracy of the theoretical line intensity calculations, it proved necessary to use rotation-dependent Frank-Condon factor. Using the calculated intensities, it was possible to identify certain rotational lines belonging to the weakest branches Q₁₃ and Q₃₁, not reported before.     

低气压长间隙介质阻挡放电的光谱诊断

设计了一种电极间隔为10 cm的介质阻挡放电装置,以氩气为工作气体,在低气压下产生等离子体。采用发射光谱法,研究了放电空腔内等离子体电子温度和电子密度随空间位置的变化规律。等离子体电子温度的变化通过使用Corona模型计算获得,等离子体电子密度的变化通过分析Ar原子750.4 nm谱线强度变化得到。实验发现空腔内不同位置的等离子体电子温度和电子密度是不同的。当测量位置从阴极向阳极移动时,电子温度先略上升而后迅速下降,再缓慢上升;电子密度先缓慢而后迅速地增大。     

发射光谱法研究无极灯等离子体参数分布

使用电感耦合放电装置和拍型明泡,以氩-汞混合气体作为工作气体,在低气压下点亮了无极灯.利用发射光谱法,研究了无极灯点灯5s时的电子温度和电子密度随轴向和径向位置的变化规律.等离子体电子温度变化通过分析Ar原子425.9和750.4nm谱线强度比值获得,等离子体电子密度的变化通过分析Ar原子750.4nm谱线强度变化得到...     

Electronic structure and elastic properties of scandium carbide and yttrium carbide: A first principles study

We have studied the electronic, structural, and elastic properties of scandium carbide and yttrium carbide by means of accurate first principles total energy calculations using the full-potential linearized plane wave method (FP-LAPW). We have used the generalized gradient approximation (GGA) for the exchange and correlation potential. Volume optimization, energy band structure, and density of states (DOS) of the systems are presented. The second order elastic constants have been calculated and other related quantities such as the Zener anisotropy factor, Poisson's ratio, Young's modulus, Kleinman parameter, Debye temperature, and sound velocities have been determined. The band gap calculation shows that YC is relatively more ionic than ScC.     

Nature of the band gap of silicon and germanium nanowires

Nanowires of both Si and Ge have been predicted to have band gaps that are either direct or indirect depending upon the crystallographic direction along which the nanowire is oriented. We use a sp³d⁵s^* tight binding model to calculate the band structures for both Ge and Si nanowires oriented along the (1 0 0), (1 1 0) and (1 1 1) directions. We show that the nature of the band gap and the variation of the zone centre band gap with nanowire width depends upon the nanowire stacking direction for both Si and Ge nanowires. We then show, by considering bulk unit cells along the (1 0 0), (1 1 0) and (1 1 1) directions, that it is possible to accurately predict whether a nanowire stacked in the same direction as one of these bulk unit cells has a direct or indirect band structure.     

The electronic spectrum of the SiC radical: A theoretical study

Electronic structure and spectroscopic properties of the low-lying electronic states of the SiC radical have been determined from the ab initio based configuration interaction calculations. Potential energy curves of 32 Λ-S states of singlet, triplet, and quintet spin multiplicities have been constructed. Spectroscopic constants (r_e, T_e, and ω_e) of 23 states within 6 eV are reported and compared with the existing data. The dipole moments (μ_e) of most of these states at their respective equilibrium bond lengths have been computed. Effects of the spin-orbit coupling on the spectroscopic properties of SiC have been studied. The E³Π state is found to be an important one which has not been studied before. A transition of the type E³Π-X³Π is predicted to take place in the range 25 000-26 000 cm⁻¹. The partial radiative lifetimes for several electric dipole allowed transitions such as A³Σ⁺-X³Π, B³Σ⁺-X³Π, C³Π-X³Π, D³Δ-X³Π, E³Π-X³Π etc. have been reported.     

The surface modified composite layer formation with boron carbide particles on magnesium alloy surfaces through pulse gas tungsten arc treatment

A novel fabrication process of surface modified composite layer by pulse current gas tungsten arc (GTA) surface modification process was used to deposit B₄C particles on the surface of magnesium alloy AZ31. This method is an effective technique in producing a high performance surface modified composite layer. During the pulse current GTA surface modification process, considerable convection can exist in the molten pool due to various driving forces and the pulse current could cause violent stirring in the molten pool, and the large temperature gradient across the boundary between the GTA modified surface and matrix metal resulted in rapid resolidification with high cooling rates in the molten pool, so that the process result notable grain refinement in the GTA surface modified composite layer. The hardness and wear resistance of the GTA surface modified composite layer are superior to that of as-received magnesium alloy AZ31. The hardness values and wear resistance of GTA surface modified composite layer depend on the GTA process parameters and the B₄C particles powder concentration and distribution. The optimum processing parameters for the formation of a homogeneous crack/defect-free and grain refinement microstructure were established.     

液相隔膜辉光放电发射光谱法检测水中钾和钠离子

研究了液相隔膜辉光放电发射光谱法对水中钾离子和钠离子的检测性能,考察了外加电压和有机添加剂甲醇对检测灵敏度和检出限的影响。结果表明提高外加电压和添加甲醇能提高检测灵敏度和降低检出限。在电压850 V,添加0.6%～0.8%甲醇时钾和钠的检出限分别为0.007和0.001 mg·L-1。液相隔膜辉光放电发射光谱法检测水中金属离子具有背景光谱干扰小和灵敏度高的特点。     

Interaction of germanium with silicon dioxide

The interaction of germanium (Ge) adatoms with SiO₂ (silica) plays an important role in selective, heteroepitaxial growth of Ge(100) through windows created in silica on Si(100) and in the selective growth of Ge nanoparticles on hafnia, located at the bottom of pores etched through silica. Both processes rely on the inability of Ge to accumulate on silica. In hot wire chemical vapor deposition of Ge nanoparticles from GeH₄, etching of the silica has been invoked as one path to prevent accumulation of Ge on silica; whereas dense silica is not etched when Ge atoms are incident on the surface in molecular beam processes. Surface studies were conducted to determine the nature of oxidized Ge on SiO₂, to reconcile the etching claim with GeH₄, and to look for the additional etching product that must accompany GeO, namely SiO. Etching of silica is not found with GeH₄ or GeH_x fragments. A more complete examination of the Ge isotopes reveals instead the m/e 90 signal, previously attributed to GeO, originates from interactions between iron oxide impurities in the molybdenum holder, and hydrogen and GeH_x fragments. Coating the Mo with gold eliminates m/e 90 from Ge TPD spectra. The high temperature m/e 74 and m/e 2 peaks observed from 800 to 900 K are attributed to GeH_x decomposition to Ge and H followed by their desorption, while the appearance of GeO_x is attributed to possible reactions between GeH_x species with hydroxyl groups and/or oxidation of Ge clusters by background oxidants.     

气相CBr2 自由基的产生及激光诱导荧光色散谱研究

利用双层流动反应管作为束源 ,研究了F与CH2 Br2 反应生成的CBr2 和Br2 的气相激光诱导荧光色散谱 ,将得到的谱线分别指定为CBr2 的 A(0 ,13,0 )→ X(0 ,v2 ″,0 ) (v2 ″ =1～ 6 )跃迁和Br2 的 B3 Π+ u → X1Σ+ g 跃迁 ,从光谱中首次得到气相CBr2 自由基基态弯曲振动频率ν2 ″ =2 15cm-1,实验确认了CBr2 自由基和Br2 是F +CH2 Br2 过程多步反应的产物     

The electronic spectrum of silicon monotelluride radical

In the electronic spectrum of silicon monotelluride which has been produced in microwave discharges through sealed tubes, a large number of new bands belonging to theA ¹Π-X ¹Σ⁺ system (3100–3900 Å) and theE ¹Σ⁺-X ¹Σ⁺ system (2800–3100 Å) of Si¹³⁰Te has been observed. The vibrational structure analyses of these band systems have resulted in the determination of improved vibrational constants in all the three electronic states involved in these transitions. An error in the previous determination of the vibrational constants of theE ¹Σ⁺ state has been corrected. An upper limit for the dissociation energy of the silicon monotelluride has been determined to be 40,000 cm^?1.     

Electronic and magnetic properties of single-wall GeC nanotubes filled with iron nanowires

Under GGA, the structural, electronic and magnetic properties of single-wall (8, 8) GeC nanotubes filled with iron Fe_n nanowires (n = 5, 9, 13 and 21) have been investigated systematically using the first-principles PAW potential within DFT. We find that the initial shapes of the Fe₅@(8, 8), Fe₉@(8, 8) and Fe₁₃@(8, 8) systems are preserved without any visible changes after optimization. But for the Fe₂₁@(8, 8) system, the initial shapes are distorted largely for both nanowire and nanotube. The binding processes of Fe_n@(8, 8) systems are exothermic, and Fe₅@(8, 8) system is the most stable structure. The pristine (8, 8) GeCNT is nonmagnetic and direct semiconductor with a wide band gap of about 2.65 eV. Projected densities of states onto different shell Fe atoms show that the separation between the bonding and antibonding d states is reduced as going from the core Fe atom to the outermost shell Fe atom. The spin polarization of the Fe_n@(8, 8) systems and free-standing nanowires are higher than that in bulk Fe. And the spin polarization generally decreases with the number n of the Fe atoms increasing for both the Fe_n@(8, 8) systems and free-standing nanowires. Both the largest spin polarization value itself and not more decrease with respect to value of free-standing Fe₅ nanowire suggest the Fe₅@(8, 8) system could be of interest for the use in electron spin injection. The magnetism is mainly confined within the inner Fe nanowire for these combined systems. More importantly, the Fe₅ nanowire encapsulated inside (8, 8) GeCNT is under the protection of the GeCNT to prevent from oxidation, thus may stably exist in atmosphere for long time and can be expected to have potential applications in building nanodevices.     

New Insights in the Interpretation of Tryptophan Fluorescence

Origin of tryptophan fluorescence is still up to these days a quiz which is not completely solved. Fluorescence emission properties of tryptophan within proteins are in general considered as the result of fluorophore interaction within its environment. For example, a low fluorescence quantum yield is supposed to be the consequence of an important fluorophore–environment interaction. However, are we sure that the fluorophore has been excited upon light absorption? What if fluorophore excitation did not occur as the result of internal conformation specific to the fluorophore environment? Are we sure that all absorbed energy is used for the excitation process? Fluorescence lifetimes of Trp residues are considered to originate from rotamers or conformers resulting from the rotation of the indole ring within the peptide bonds. However, how can we explain the fact that in most of the proteins, the two lifetimes 0.5 and 3 ns, attributed to the conformers, are also observed for free tryptophan in solution? The present work, performed on free tryptophan and tyrosine in solution and on different proteins, shows that absorption and excitation spectra overlap but their intensities at the different excitation wavelengths are not necessarily equal. Also, we found that fluorescence emission intensities recorded at different excitation wavelengths depend on the intensities at these excitation wavelengths and not on the optical densities. Thus, excitation is not equal to absorption. In our interpretation of the data, we consider that absorbed photons are not necessary used only for the excitation, part of them are used to reorganize fluorophore molecules in a new state (excited structure) and another part is used for the excitation process. A new parameter that characterizes the ratio of the number of emitted photons over the real number of photons used to excite the fluorophore can be defined. We call this parameter, the emission to excitation ratio. Since our results were observed for fluorophores free in solution and present within proteins, structural reorganization does not depend on the protein backbone. Thus, fluorescence lifetimes (0.5 and 3 ns) observed for tryptophan molecules result from the new structures obtained in the excited state. Our theory allows opening a new way in the understanding of the origin of protein fluorescence and fluorescence of aromatic amino acids.     

Dependence of electronic and optical properties of multilayer SiC and GeC on stacking sequence and external electric field

The electronic and optical properties of different stacked multilayer SiC and GeC are investigated with and without external electric field (EEF). The band gaps of multilayer SiC and GeC are found smaller than that of monolayer SiC and GeC due to the interlayer coupling effect. When EEF is applied, the direct band gaps (ΔK–M) of multilayer SiC and direct band gaps (ΔK–K) of multilayer GeC all turn to indirect band gaps (ΔK–G) as the band at the G point drops dramatically toward zero. The imaginary part ε₂(ω)s of multilayer SiC and GeC show that new absorption peaks between 2–5 eV appear when the polarized direction is perpendicular to the layer plane, and new absorption peaks in infrared region appear as the EEF is higher than a certain point when the polarized direction is parallel to the layer plane. Our calculations reveal that different stacking sequences and EEF can provide a wide tunable band structures and optical properties for multilayer SiC and GeC.     

Automated laser fabrication of cemented carbide components

Automated Laser Fabrication (ALFa) is one of the most rapidly growing rapid-manufacturing technologies. It is similar to laser cladding at process level with different end applications. In general, laser cladding technique is used to deposit materials on the substrate either to improve the surface properties or to refurbish the worn-out parts, while ALFa is capable of near net shaping the components by layer-by-layer deposition of the material directly from CAD model. This manufacturing method is very attractive for low volume manufacturing of hard materials, as near net shaping minimizes machining of hard material and subsequently brings significant savings in time and costly material. To date, many researchers have used this technology to fabricate components using various alloy steels, nickel-based alloys and cobalt-based alloys. In the present study, the work is extended to tungsten carbide cobalt (WC–Co) composites. A set of comprehensive experiments was carried out to study the effect of processing parameters during multi-layer fabrication. The process parameters were optimized for the component-level fabrication. Fabricated components were subjected to dye-penetrant testing, three-point flexural testing, hardness measurement, optical and scanning electron microscopy and X-ray diffraction analysis. The test results revealed that the laser-fabricated material was defect free and more ductile in nature. Thus, ALFa technology, not only produced the quality components, but also minimized machining of hard material and brought significant saving of time and costly WC–Co material.