Influence of alkali metal superoxides on structure,electronic,and optical properties of Be_(12)O_(12) nanocage:Density functional theory study

The effect of alkali metal superoxides M_3O(M = Li,Na,K) on the electronic and optical properties of a Be_(12)O_(12) nanocage was studied by density functional theory(DFT) and time-dependent density functional theory(TD-DFT).The energy gaps(Eg) of all configurations were calculated.Generally,the adsorption of alkali metal superoxides on the Be_(12)O_(12) nanocage causes a decrease of Eg.Electric dipole moment μ,polarizability α,and static first hyperpolarizability β were calculated and it was shown that the adsorption of alkali metal superoxides on Be_(12)O_(12) increases its polarizability.It was found that the absorption of M_3 O on Be_(12)O_(12) nanocluster improves its nonlinear optical properties.The highest first hyperpolarizability(β≈ 214000 a.u.) is obtained in the K_3O–Be_(12)O_(12)nanocluster.The TD-DFT calculations were performed to investigate the origin of the first hyperpolarizabilities and it was shown that a higher first hyperpolarizability belongs to the structure that has a lower transition energy.     

Effect of separation on second-order hyperpolarizability of two silver nanoclusters

We present a study on dielectric response of Ag₁₄ nanocluster dimer using first principles methods. The interaction energy, (hyper)polarizability of dimer are predicted under various separations of the two identical Ag₁₄ nanoclusters. The appropriate separation makes the second-order hyperpolarizability of Ag₁₄ dimer is about 70 times larger than the Ag₁₄ monomer. The increase of polarizability and hyperpolarizability is ascribed to reconfiguration of molecular electronic state from Ag cluster monomer to dimer. Nonlinear response is more susceptible to the steady intermediate state compared to linear response. The crucial transitions contributed to hyperpolarizability are assigned to be from highest occupied molecular orbitals to the lowest unoccupied molecular orbital (HOMOs-LUMO) of nanocluster dimer. Binding character of LUMO plays an important role in determining nonlinear optical properties.     

内嵌复合物M@C60（M=Li,Na,K,Rb,Cs）的分子力学研究

利用分子力学方法计算了碱金属内嵌复合物Ｍ＠Ｃ６０中Ｍ与Ｃ６０之间的相互作用，考察了Ｍ在Ｃ６０笼内的平衡位置。研究表明Ｌｉ和Ｎａ的平衡位置偏离Ｃ６０分子的中心，Ｋ、Ｒｂ和ＣＳ的平衡位置在Ｃ６０分子的中心。平衡位置的确定取决于色散作用和排斥作用的大小。最后，讨论了碱金属原子进入笼内的可能机制。     

Phase diagram of Ge:(C,Sn)

We present the self-assembling conditions of 1C4Sn tetrahedral nanoclusters with carbon atoms in their centers in Ge:(C, Sn) in the wide temperature range as a function of the impurity contents and temperature. These conditions are the phase diagram of Ge:(C, Sn) since nanocluster occurrence and completion of self-assembling when all carbon atoms are in nanoclusters are results of the continuous phase transitions. The significant decrease of the strain energy after formation of nanoclusters is a cause of self-assembling. It is shown that the nanocluster occurrence temperature depends only on the Sn content. The impurity content conditions when all carbon atoms are in 1C4Sn nanoclusters are obtained for the temperatures up to 855 ^°C.     

M@C_(20)H_(20)(M=Sc,V,Cr,Mn,Fe,Co,Ni)几何结构和电子性质的理论研究

采用密度泛函理论(DFT)中的广义梯度近似(GGA)方法对M@C_(20)H_(20)(M=Sc,V,Cr,Mn,Fe,Co,Ni)几何结构和电子性质进行了计算研究.几何结构优化发现,过渡金属原子M内掺到C_(20)H_(20)笼时,都稳定于碳笼中心.能隙和内掺能计算发现,M@C_(20)H_(20)的热力学稳定性随着M原子序数的增大而逐渐减弱,内掺M原子使得其动力学稳定性大幅度下降,但是其中Ni@C_(20)H_(20)结构仍然具有良好的热力学和动力学稳定性,其有望在实验中被成功合成出来.电子性质研究发现,随着M原子序数的逐渐增大,M原子对M@C_(20)H_(20)前线轨道的贡献也越来越大,M@C_(20)H_(20)(M=Sc,V,Cr,Mn,Fe,Co)都具有一定的磁矩,而Ni@C_(20)H_(20)为闭壳层结构,磁矩为零.     

A density functional theory (DFT) study of the doping effect on 2-cyano-3- [4 (diphenylamino) phenyl] acrylic acid

In this work, the DFT method (B3LYP) with the base 6-31+G** was used to study the influence of doping on the molecule 2-cyano-3- [4- (diphenylamino) phenyl] acrylic. To do this, the dipole moment (μ), the polarizability (α0), the anisotropy of the polarizability (Δα), the hyperpolarizability (β0), the gap HOMO-LOMO (HL gap), the dielectric constant (ε), the electric susceptibility (χ), the refractive index (η) and the thermodynamic properties of the different molecules have been calculated. The polarizability, the first hyperpolarizability and the HL gap enable us to conclude that the doping with titanium dioxide leads to new interesting molecules for applications in the design of new nonlinear and optoelectronic materials.     

内嵌富勒烯[M@C70] (M=Li, Na, K, Be, Mg, Ca)与[Mg(H2O)6]2+相互作用的密度泛函理论研究

使用密度泛函理论方法, 对内嵌多种碱金属及碱土金属原子(M=Li, Na, K, Be, Mg, Ca)的富勒烯C70与水合Mg(II)离子之间的相互作用进行了理论研究. 首先对各原子(M=Li, Na, K, Be, Mg, Ca)嵌入C70后的形成能进行了讨论, 之后计算了[M@C70]各体系与[Mg(H2O)6]2+的相互作用能, 并采用自然键轨道理论(NBO)研究了电荷转移的情况, 最后进行了电子密度拓扑分析. 结果表明, 内嵌原子半径越大, [M@C70]各体系的热力学稳定性就越高, 转移至[Mg(H2O)6]2+的电荷也随之增加, 二者之间的相互作用属于闭壳层相互作用及共价作用.     

内嵌富勒烯[M@C_(70)](M=Li,Na,K,Be,Mg,Ca)与[Mg(H_2O)_6]~(2+)相互作用的密度泛函理论研究

使用密度泛函理论方法,对内嵌多种碱金属及碱土金属原子(M=Li,Na,K,Be,Mg,Ca)的富勒烯C70与水合Mg(II)离子之间的相互作用进行了理论研究.首先对各原子(M=Li,Na,K,Be,Mg,Ca)嵌入C70后的形成能进行了讨论,之后计算了[M@C70]各体系与[Mg(H_2O)6]2~+的相互作用能,并采用自然键轨道理论(NBO)研究了电荷转移的情况,最后进行了电子密度拓扑分析.结果表明,内嵌原子半径越大,[M@C70]各体系的热力学稳定性就越高,转移至[Mg(H_2O)6]2~+的电荷也随之增加,二者之间的相互作用属于闭壳层相互作用及共价作用.     

Au-Cu nanoparticles in silica glass as composite material for photonic applications

In the framework of metal nanocluster composite glasses for photonic application, (gold + copper)-containing silica films were synthesized by radiofrequency co-sputtering deposition technique by varying the Au/Cu ratio. To obtain the formation of metallic (alloy) nanoclusters, the deposited samples were annealed in reducing atmosphere at 900 °C. The linear and nonlinear optical properties of the composite glasses were investigated. In particular, the nonlinear ultrafast optical response was measured by means of the Z-scan technique at a wavelength of 527 nm with single 6 ps pulse configuration. Significant refractive and absorptive effects were observed in all the annealed samples. The two main figures of merit related to the performance of materials for optical switching device application were evaluated for all samples, showing interesting values for the Cu-rich composites.     

Anomalous changes in electron emission during adsorption of alkali metals on a carbon film

An anomalous change was discovered in the field of electron emission during the adsorption of alkali metal atoms on the surface of an amorphous carbon film. The phenomenon involves the disappearance of electron emission from graphite nanoclusters that were local emission sources before the deposition of cesium. The observed effect is explained on the basis of surface diffusion processes of cesium atoms in a nonuniform electric field and intercalation graphite nanostructures by cesium.     

Diffusion behavior of transition metals in field-assisted ion-exchanged glasses

The use of ion-exchange techniques for doping silicate glasses with transition metals has attracted much attention in the last decades for its potential in several applications, namely, light waveguides technology, luminescent materials, and for the possibility to realize systems in which metal nanocluster formation is controlled by suitable post-exchange techniques. In this framework, the control of metal distribution inside the glass is a central issue for both the understanding of the incorporation process and for the definition of effective preparation protocols. In this experiment, metallic films (Ag, Cu, Au, Co) were deposited onto the substrates by the rf-sputtering technique. Metal ions then penetrate to substitute glass alkali by means of field-assisted ion-exchange, realized at different temperature and electric field values. In particular, we present in this paper the Au doping of silicate glasses, successfully realized for the first time with this method. The gold diffusion profiles, as measured by Secondary Ion Mass Spectrometry (SIMS), indicate that the migration depends on the experimental parameters (temperature and electric field), but also on the local structure, as well as on chemical phenomena occurring at the metal/glass interface.     

Electrical Properties of C 70 Intercalation Compounds

While the behavior of solid C 60 upon doping has been extensively investigated, very little is known about the compounds based on C 70 , the next stable fullerene. The aim of this paper is to compare the potential capacities of both fullerenes to form intercalation compounds and to refer the recent achievements in the C 70 intercalation, both spontaneous (oxygen diffusion from the atmosphere) and induced (by pressure of alkali metal vapors or the applied electric field).     

Self-assembling conditions of 1O4Ca nanoclusters in ZnTe:(Ca,O)

Self-assembling conditions for 1O4Ca tetrahedral nanoclusters in ZnTe:(Ca, O) with Ca content up to 0.02 and with the ultradilute limit of oxygen are represented. The causes of self-assembling are a CaO and ZnTe bonding preferential over a CaTe and ZnO one and decrease of the strain energy after nanocluster formation. Self-assembling conditions were studied in the temperature range from 200 ^°C to 1305 ^°C. The occurrence of nanoclusters depends only on the Ca content and temperature. The temperature of self-assembling completion when all oxygen atoms are in 1O4Ca nanoclusters is determined by the Ca and oxygen contents.     

Structure and dynamics of graphite-supported bimetallic nanoclusters

Molecular dynamics simulations are used to analyze the structure and dynamics of isolated bimetallic nanoclusters of 343 (Cu-Ni) and 1000 atoms (Cu-Ni and Pt-Au) deposited on a graphite substrate. The metal-metal interactions are modeled with the many-body Sutton-Chen potential, and a Lennard-Jones potential is used to describe the metal-carbon interactions. The nanocluster melting temperature is determined from caloric and heat capacity curves, and the atomic distribution is studied layer-by-layer as a function of temperature in a direction perpendicular to the substrate plane. Changes in the nanocluster shape as temperature increases are monitored through deformation parameters that show clear evidence of structural and melting transitions as well as of atomic surface diffusion in the cluster. Dynamic properties such as atomic and whole-cluster diffusion, and the motion of the metal atoms at the interface metal/graphite are characterized as a function of temperature.     

Time-resolved electric-field-induced second harmonic: simultaneous measurement of first and second molecular hyperpolarizabilities

The standard electric-field-induced second-harmonic (EFISH) technique for measurement of the first hyperpolarizability (beta) of nonlinear optical molecules is limited by the fact that the second hyperpolarizability (gamma) also contributes to the second-harmonic signal from which beta is deduced. We present a modified time-resolved EFISH in which the first and the second hyperpolarizabilities can be determined separately and accurately in the same experiment. We studied para-nitro aniline dissolved in a highly viscous solvent, glycerol, under conditions whereby the electric field was applied faster than the characteristic time for molecular rotation. This technique enabled the gamma contribution to the signal to be resolved separately from the beta contribution. The results confirm that for this molecule gamma contributes only ~10% of the total EFISH hyperpolarizability.     

硼掺杂双层石墨烯吸附钠的第一性原理研究

采用密度泛函理论(DFT)的第一性原理方法,对Na在本征双层石墨烯(PBLG)和不同掺杂浓度的B掺杂石墨烯(BBLG)表面的吸附性质进行了研究.确定了不同B掺杂浓度时BBLG的最稳定B分布结构,计算了Na在PBLG和不同掺杂浓度的BBLG表面的吸附能.计算结果表明,B原子掺杂倾向于占据上层中对位或次临近位置,并与下层中六边形碳环中心相对,B_4C_(32)的形成能最小;B掺杂浓度的增加使BBLG中上层石墨烯片层结构起伏增大,而对下层影响较小;Na在BBLG表面吸附高度和平均层间距受上层结构起伏影响显著;Na倾向于吸附在B_9C_(27)表面B原子的上方,使原始平面结构产生起伏,Na与B_9C_(27)表面的结合最稳定.     

Ab initio study of structural, electronic, optical, and vibrational properties of ZnxSy (x?+?y?=?2 to 5) nanoclusters

An ab initio study of the stability, structural, electronic. and optical properties has been performed for 46 zinc sulfide nanoclusters Zn _x S _y (x + y = n = 2 to 5). Five out of them are seen to be unstable as their vibrational frequencies are found to be imaginary. A B3LYP-DFT/6-311G(3df) method is employed to optimize the geometries and a TDDFT method is used for the study of the optical properties. The binding energies (BE), HOMO-LUMO gaps and the bond lengths have been obtained for all the clusters. For the ZnS₂, ZnS₃, and ZnS₄ nanoclusters, our stable structures are seen to be different from those obtained earlier by using the effective core potentials. We have also considered the zero point energy (ZPE) corrections ignored by the earlier workers. For a fixed value of n, we designate the most stable structure the one, which has maximum final binding energy per atom. The adiabatic and vertical ionization potentials (IP) and electron affinities (EA), charges on the atoms, dipole moments, optical properties, vibrational frequencies, infrared intensities, relative infrared intensities, and Raman scattering activities have been investigated for the most stable structures. The nanoclusters containing large number of S atoms for each n is found to be most stable. The HOMO-LUMO gap decreases from n = 2–3 and then increases above n = 3. The IP and EA both fluctuate with the cluster size n. The optical absorption is quite weak in visible region but strong in the ultraviolet region in most of the nanoclusters except a few. The optical absorption spectrum or electron energy loss spectrum (EELS) is unique for every nanocluster and may be used to characterize a specific nanocluster. The growth of most stable nanoclusters may be possible in the experiments.     

Investigation on Third-order Optical Nonlinearity of Ni-Azo Metal Complex by the Z-scan Technique

Third-order optical nonlinearity of Ni-azo metal complex in solution was investigated by the Z-scan technique with 38 ps laser pulse excitation at 1.064 μm. Self-defocusing was observed, and third-order nonlinear susceptibility χ(3)pure and the second hyperpolarizability <γ> were measured to be 1.8×10-11 esu and 1.0×10-32 esu, respectively.     

Investigation on Third-order Optical Nonlinearity of Ni-Azo Metal Complex by the Z-scan Technique

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