有机阳离子对卤素钙钛矿太阳能电池性能的影响

采用第一性原理计算了CH_3NH_3PbI_3中有机部分CH_3NH_3~+和CH_3NH_3的静电特性.结果表明:CH_3NH_3~+具有强的亲电特性,CH_3NH_3的CH_3~-端具有弱亲电性,而NH_3~-端具有弱亲核性.发现在CH_3NH_3PbI_3中CH_3NH_3~+之间强静电排斥作用在相变中起着重要的作用,且在室温条件下CH_3NH_3~+在无机笼中具备活性和无序的特性,使得TiO_2/CH_3NH_3PbI_3异质结中n型TiO_2的电子通过界面扩散到CH_3NH_3PbI_3材料,并与CH_3NH_3~+结合形成CH_3NH_3,CH_3NH_3的静电特性导致在内建电场作用下更容易取向,取向的CH_3NH_3周围形成的静电场会变得更弱和更加均匀.这对无机框架上载流子的产生和传输更加有利,这样的异质结比传统的pn结具有更大优势.这是CH_3NH_3PbI_3太阳能电池高的光电转换效率的重要原因.     

大气压甲烷针-板放电等离子体中粒子密度和反应路径的数值模拟

甲烷针-板放电与重油加氢耦合形成甲烷转化重油加氢,可实现重油高效加氢并增产高附加值低碳烯烃,有实践应用前景和科学研究意义.建立二维流体模型,对大气压甲烷针-板放电等离子体进行数值模拟,得到电场强度、电子温度和粒子密度的空间与轴向分布,总结反应产额并提炼生成各种带电和中性粒子的关键路径.模拟结果表明,CH_3~+和CH_4~+密度与电场强度和电子温度的轴向演化接近且密切相关;CH_5~+和C_2H_5~+密度沿轴向先增大后减小;CH_3与H密度的空间和轴向分布几乎相同;CH_2,C_2H_4与C_2H_5的粒子密度分布在靠近阴极的区域内明显不同而在正柱区内较为相像;电子与CH_4发生电子碰撞电离生成的CH_3~+和CH_4~+,CH_3~+和CH_4~+分别与CH_4发生分子碰撞解离生成C_2H_5~+和CH_5~+;电子与CH_4间的电子碰撞分解是生成CH_3,CH_2,CH和H的主导反应;CH_2与CH_4和电子与C_2H_4发生的反应分别是生成C_2H_4和C_2H_2的关键路径;电子与CH_4间的电子碰撞分解反应和CH_2与CH_4发生的反应的产额各占H_2总产额的52.15%和47.85%.     

甲胺分子的紫外光解离动力学实验研究

在280—287.5 nm区域内,通过实验测定共振增强多光子电离-时间飞行质谱、碎片离子的分质量激发谱以及光强指数等对甲胺分子的光解离通道进行了研究.实验结果证实甲胺分子在单光子能量范围内存在一个电子排斥态,主要的光解离过程为甲胺分子共振吸收1个光子到达该电子排斥态后解离成中性碎片,然后是中性碎片经多光子共振电离形成碎片离子和碎片离子的进一步解离.     

CH_3I~(2+)的二体、三体解离过程的理论研究

采用密度泛函和耦合簇理论从过渡态的观点对CH_3I~(2+)离子的解离过程进行了计算和分析.优化得到了CH_3I,CH_3I+和CH_3I~(2+)的稳定结构及解离过渡态的几何构型并给出了相应能量,计算的第一、二电离能与实验结果符合.基于母体离子、过渡态和解离碎片的几何结构和能量,对CH_3I~(2+)的两体解离过程和三体解离过程进行了详细分析和讨论.给出了二体、三体解离的可能解离通道,并分析了实验上观测到的解离碎片离子的产生机制.计算结果表明,三重和单重绝热势能面上的一些解离过程表现出明显的差异.     

Computer simulation of a carbon-deposition plasma in CH4

A transport and reaction model of a low-pressure, high-frequency (13.56 MHz) CH₄ plasma used for diamondlike carbon (a-C:H) deposition was developed. The model includes reactions among four molecular species (CH₄, C₂ H₆, C₂H₄, and H₂), five radicals and atom (CH₃, CH₂, CH, C₂H₅, and H), and four ions (CH₄⁺ , CH₃⁺, CH₅⁺, and C ₂H₅⁺). It also accounts for the influence of the sticking coefficient of species at the walls. Calculated values of the dissociation degree for several flow rates are in good agreement with experimental measurements made by quadrupole mass spectroscopy. A simple surface-model based on the hydrogen coverage of surface and ion flux and energy at the substrate surface was established. This model permitted the calculation of the deposition rate on the powered electrode as a function of the power applied to this electrode. Good agreement between experimental and calculated growth rates was obtained when CH₃, C₂H₅, and CH₂ were assumed to participate in film formation, and when hydrogen removal by ion bombardment with variable energy as a function of the power was included in the model     

中性和阳离子丁酮团簇的结构及稳定性的理论研究

使用密度泛函B3LYP方法,在6-31G*和6-311+G**基组水平上计算中性和阳离子丁酮团簇(CH_3COC_2H_5)_n和(CH_3COC_2H_5)_n~+(n 7)的稳定结构,并比较不同尺寸团簇之间的相对稳定性.中性和阳离子丁酮团簇的结构具有相似性:n=3—7时,组成团簇的丁酮的平均几何参数基本相同,单环结构最稳定;随着团簇尺寸的增加,双环结构的稳定性逐渐上升.通过平均结合能、一阶差分能、HOMO-LUMO能隙等计算分析可知:在所研究的各种尺寸团簇中,(CH_3COC_2H_5)_3是最稳定的中性团簇,与实验中的最强峰对应;(CH_3COC_2H_5)_4~+是最稳定的阳离子团簇.通过电离能计算得到丁酮分子的垂直电离能为9.535 eV与实验值相符,同时证明中性和阳离子丁酮二元团簇的结构变化较大.研究结果为实验中丁酮团簇碎片离子的形成机理提供一定的理论依据,并且为进一步研究酮类分子团簇的生长规律提供有价值的信息.     

First-principles study of structural and opto-electronic characteristics of ultra-thin amorphous carbon films

Most amorphous carbon(a-C)applications require films with ultra-thin thicknesses;however,the electronic structure and opto-electronic characteristics of such films remain unclear so far.To address this issue,we developed a theoretical model based on the density functional theory and molecular dynamic simulations,in order to calculate the electronic structure and opto-electronic characteristics of the ultra-thin a-C films at different densities and temperatures.Temperature was found to have a weak influence over the resulting electronic structure and opto-electronic characteristics,whereas density had a significant influence on these aspects.The volume fraction of sp3 bonding increased with density,whereas that of sp2 bonding initially increased,reached a peak value of 2.52 g/cm³,and then decreased rapidly.Moreover,the extinction coefficients of the ultra-thin a-C films were found to be density-sensitive in the long-wavelength regime.This implies that switching the volume ratio of sp2 to sp3 bonding can effectively alter the transmittances of ultra-thin a-C films,and this can serve as a novel approach toward photonic memory applications.Nevertheless,the electrical resistivity of the ultra-thin a-C films appeared independent of temperature.This implicitly indicates that the electrical switching behavior of a-C films previously utilized for non-volatile storage applications is likely due to an electrically induced effect and not a purely thermal consequence.     

NH+4，F-对萤石浮选的影响机理及红外光谱分析

萤石浮选过程中矿浆中的NH+₄,F-对萤石的可浮性有重要影响,而目前关于难免离子对浮选影响的研究主要集中在稳定的阳离子对浮选的活化或抑制作用机理,而关于不稳定阳离子（NH+₄）、阴离子（F-）影响油酸钠吸附萤石作用机制的研究较少。因此借助于红外光谱分析,结合纯矿物浮选、Zeta电位和溶液化学计算等手段,研究难免离子（NH+₄,F-）对油酸钠浮选萤石的作用机理。实验结果表明,在酸性条件下,NH+₄对萤石有较强的活化作用,提高了萤石的回收率, 在pH值为6时,不同NH+₄浓度下,萤石的回收率均提高到94%左右,而在碱性条件下,NH+₄对萤石的浮选的有一定的抑制作用,且随着pH值增加,抑制作用增强,回收率逐渐下降;但F-对萤石浮选有一定的抑制作用,且在pH值为6时,不同F-浓度的抑制作用均明显增强,导致萤石回收率降低;而在碱性条件下,F-对萤石的可浮性影响不大。其作用机理为阳离子（NH+₄）与萤石表面解离到溶液中的F-生成NH₄F,在酸性条件下提高了萤石表面的正电性,增强萤石表面与油酸的一聚物、二聚物和分子-离子缔合物的吸附作用,而在碱性条件下NH+₄的水解生成NH₃·H₂O,正电性降低,导致油酸钠在萤石表面的吸附作用减弱;F-抑制萤石表面F-的解离,从而抑制了油酸根在萤石表面的化学吸附。红外分析结果表明,油酸钠在萤石表面发生了化学吸附;NH+₄的加入,在酸性条件下对萤石有很强的活化作用,-CH₃,-CH₂-和-COO-的特征峰峰位红移,峰强度加强,显现出较强的化学吸附作用;而在碱性条件下,仅出现了-CH₂-的特征峰的峰位红移,且特征峰强度减弱,说明NH+₄在弱碱条件在萤石表面的化学吸附较弱,起抑制作用;当加入F-后只出现了-CH₃的反对称伸缩振动峰,峰位并未发生偏移,故F-加入后油酸钠在萤石表面并未发生任何基团的化学吸附,从而抑制了萤石的可浮性。     

利用速度成像技术研究碘乙烷多光子电离解离动力学

卤代烷烃会破坏臭氧层,而碘乙烷（C₂H₅I）是卤代烷烃中重要代表物质之一.采用离子速度成像技术、飞秒激光技术和飞行时间质谱技术,探究了C₂H₅I的多光子电离解离动力学.通过分析C₂H₅I在强场作用下多光子电离解离得到的解离通道、碎片的动能、角度分布和各向异性参数等信息来研究碘乙烷离子（C₂H₅I⁺）C–I键裂解机理.根据飞行时间质谱实验,C₂H₅I在飞秒激光脉冲作用下发生多光子电离解离得到的碎片有C₂H₅⁺,I⁺,CH₂I⁺,C₂H₂⁺,C₂H₃⁺,C₂H₄⁺等.与C–I键相关的碎片为C₂H₅⁺和I⁺,解离机制分别对应于C₂H₅I⁺→C₂H₅⁺+I和C₂H₅I⁺→C₂H₅+I⁺.同时,采用离子速度成像技术研究C₂H₅I⁺的C–I键裂解产生的C₂H₅⁺和I⁺的速度影像,得出两者的速度分布和动能分布,分析结果表明C–I键裂解产生C₂H₅⁺和I⁺的过程都存在高能通道和低能通道.进一步分析解离碎片离子的角度分布发现C₂H₅⁺解离时各向异性参数接近于0,可能对应于慢速的振动预解离过程.I⁺在解离时各向异性参数较高,可能源于排斥势能面上的快速解离过程.最后采用密度泛函理论计算了C₂H₅I分子电离前后构型变化、离子态的能级强度及谐振强度,对C₂H₅I⁺的解离机制做了更进一步的分析和讨论.     

Interprétation de la susceptibilité magnétique de l'oxysulfure de samarium par un modèle de champ cristallin

The paramagnetic susceptibility of polycrystalline samarium oxysulfide has been measured between 3° and 300°K. The data are interpreted with an approximation to the crystal potential of the form

V_c = _JV₂⁰O₂⁰ + β_JV₄⁰O₄⁰ + β_JV₄³O₄³

and correction taking into account exchange is made. The energy levels and crystal fields parameters have been calculated. Fluorescence studies of Gd₂O₂S: Sm³⁺ and Y₂O₂S: Sm³⁺ have confirmed these results.     

Field emission properties and surface structure of nickel containing amorphous carbon

Nickel containing amorphous carbon (a-C:Ni) films have been deposited by filtered cathodic vacuum arc (FCVA) technique by introducing pure nickel into the graphite target. The field electron emission property of a-C:Ni was improved when compared to that of pure tetrahedral amorphous carbon (ta-C) by FCVA. The emission threshold field of a-C:Ni film is about 5 V μm⁻¹, whilst the threshold field of the ta-C film is about 13 V μm⁻¹. Raman spectroscopy suggests that the sp² clusters in the carbon film increase both in size and number when Ni is introduced. However, the emission was found to degrade to threshold fields beyond 20 V μm⁻¹ after the a-C:Ni film was left in ambient for a week. This observation is attributed to surface absorption of oxygen on the a-C:Ni film, as determined by X-ray Photoelectron Spectroscopy.     

An XPS study of SO2 ON A CaO surface derived from Ca(OH)2

The adsorption of SO₂ on a CaO surface derived from Ca(OH)₂ has been studied by X-ray photoelectron Spectroscopy. It is shown that SO₂ adsorbs molecularly on the CaO surface forming SO₃²⁻ and SO₄²⁻. The adsorbate SO₃²⁻ species shift the Ca2p core levels about 2 eV toward higher binding energy. However, the formation of SO₄²⁻ species does not induce any further observable changes in the Ca core line spectra. These results are explained and discussed in terms of an electronic charge transfer from the substrate metal atoms to the adsorbed molecules and vice versa.     

Absorption spectra and isotope shifts of the(2, 0),(3, 1), and(8, 5) bands of the A~2Π_u-X~2Σ_g~+ system of ~(15)N_2~+ in near infrared

The high-resolution absorption spectra of the(2, 0),(3, 1), and(8, 5) bands of the A~2Π_u–X~2Σ_g~+system of~(15) N_2~+ have been recorded by using velocity modulation spectroscopy technique in the near infrared region. The rotational constants of the X~2Σ_g~+and A~2Π_u states of~(15) N_2~+ were derived from the spectroscopic data. The isotope shifts of these bands of the A~2Π_u–X~2Σ_g~+system of~(14) N_2~+ and~(15) N_2~+ were also analyzed and discussed.     

Experimental study of the time-dependent rate of K → πππ

The time-dependence of the decay rate of initially pure K⁰ into the final state (π⁺π⁻π⁰) has been studied in search for the decay k_S⁰→π⁺π⁻π⁰. No evidence is found in a sample of 384 observed events. The ratio of the CP -violating K_S⁰ amplitude and the K_L⁰ amplitude is η₊₋₀ = (0.13_−0.20^+0.17) + i(0.17_−0.26^+0.27); the ratio of the CP-conserving K_S⁰ amplitude and the K_L⁰ amplitude is < 0.4. The energy dependence of the K⁰→π⁺π⁻π⁰ matrix element is found to be a₊₋₀ = −0.31 ± 0.03.     

Effect of substrate bias on SE, XPS and XAES studies of diamond-like carbon films deposited by saddle field fast atom beam source

This paper reports the effect of positive substrate bias (V_s) varying from 0 to 180 V on the spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy (XPS) and X-ray Auger electron spectroscopy (XAES) studies of diamond-like carbon (DLC) films deposited using CH₄ gas as a feedstock into a saddle field fast atom beam (FAB) source. The values of optical constants like refractive index (n) and extinction coefficient (k) of the deposited DLC films were determined using a two phase model. The values of ‘n’ were found to fall in the range from 1.505 to 1.720 and ‘k’ from 0.03 to 0.125 by application of different values of V_s. Value of these optical constants were found to decrease with the increase of substrate bias up to 90 V and then increase beyond this value. Position of C 1s peak evaluated from XPS data was found to occur at 286.09±0.18 eV in DLC films deposited by application of different values of V_s. Observation of full width at half maximum (FWHM) (τ) value (1.928 eV at V_s=0 V, 2.0 eV at V_s=90 V and 1.89 eV at V_s=180 V) clearly hinted the existence of a point of inflection in the properties of DLC films deposited using FAB source this way. A parameter ‘D’ defined as the distance between the maximum of positive going excursion and the minimum of negative going excursion was calculated in the derivative XAES spectra. The values of ‘D’ evaluated from XAES data for DLC films were found to be 14.8, 14.5 and 15.2 at V_s=0, 90 and 180 V, respectively. The sp² percentage was calculated for samples deposited this way and was found to be low and lie approximately at 5.6, 2.8, 2.3, 5.7 and 11.5 for different values of V_s=0, 50, 90, 150 and 180 V. The sp³ content percentage and sp³/sp² ratio was found to be 94.4 and 16.7, 97.7 and 42.5 at V_s=0 and 90 V, respectively. Beyond V_s=90 V these values started decreasing. Mainly, a point of inflection in all the properties of DLC films studied over here at around 90 V of applied substrate bias has been observed, which has been explained on the basis of existing theories in the literature.     

CaMoO4：Eu3+,Bi3+,Li+红色荧光粉的共沉淀制备与表征

采用共沉淀法合成了红色荧光粉Ca_0.75MoO₄：Eu_0.25³⁺、Ca_0.75MoO₄：Eu_0.25-x³⁺,Bi_x³⁺及Ca_0.5MoO₄：Eu_0.25-2x³⁺, Bi_x³⁺,Li_0.25+x⁺,并采用X射线衍射(XRD)、拉曼光谱,扫描电镜(SEM)和荧光光谱(PL)测定分析了其结构形貌特征及发光性能。结果表明：制备的CaMoO₄：Eu³⁺,Bi³⁺,Li⁺红色荧光粉为白钨矿结构,颗粒尺寸约为0.5~1 μm。掺杂Bi³⁺的Ca_0.75MoO₄：Eu_0.25-x³⁺,Bi_x³⁺的相对发光强度明显高于未掺Bi³⁺的Ca_0.75MoO₄：Eu_0.25³⁺荧光粉。Bi³⁺离子的掺杂将吸收来的能量传递给激活离子Eu³⁺,起到了能量传递的作用。当Bi³⁺掺杂量为x=0.005时,在395 nm激发下,主发射峰在616 nm处的相对发光强度最大,但掺杂浓度过高时会出现浓度猝灭现象。另外,电荷补偿剂的掺入能够解决材料中因同晶取代引起的电荷不平衡的问题,以Li⁺作电荷补偿剂、Eu³⁺和 Bi³⁺共掺合成的Ca_0.5MoO₄：Eu³⁺_0.23,Bi_0.01³⁺,Li⁺_0.26红色荧光粉的发光性能强于Ca_0.75MoO₄：Eu_0.25³⁺、Ca_0.5MoO₄：Eu_0.25³⁺, Li_0.25⁺及Ca_0.75MoO₄：Eu_0.24³⁺,Bi_0.01³⁺。     

三联吡啶钌超分子包合物及其SiO2复合纳米粒的电化学发光信号放大

利用环糊精类物质能够形成超分子包合物的性质,研究了电中性的β-环糊精（β-CD）和负电性的羧甲基-β-环糊精（CM-β-CD）与电化学发光（ECL）活性物质三联吡啶钌（Ru（bpy）₃²⁺）形成超分子包合物的能力及其对ECL的增强作用。结果表明：形成的超分子包合物能够增强Ru（bpy）₃²⁺的ECL,其中CM-β-CD具有更强的增强作用。相对于Ru（bpy）₃²⁺,CM-β-CD增强了1.42倍,而β-CD仅为1.28倍。以制备的表面电荷为负的SiO₂纳米粒为载体,考察了其对Ru（bpy）₃²⁺超分子包合物的吸附能力。结果表明,与Ru（bpy）₃²⁺的CM-β-CD超分子包合物相比,SiO₂纳米粒载体对Ru（bpy）₃²⁺的β-CD 超分子包合物表现出了更强的吸附能力。制备了ECL信号放大能力最强的β-CD-Ru（bpy）₃²⁺超分子包合物的SiO₂复合纳米粒。     

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开发了氢气甚高频(60MHz)容性耦合放电的PIC/MC模型.在模型中考虑了带电粒子(e,H+,H2+,H3+)与H2的21种碰撞反应过程,模拟了氢气甚高频放电射频电场和电势分布以及电子和氢离子(H+,H2+,H3+)粒子密度和平均能量分布,并与频率为13.56MHz的放电结果进行了比较.结果表明,相对于频率13.56MHz的放电,氢气甚高频放电等离子体电势增高,导致两电极附近的电场增强;另外,两鞘层厚度变窄并且电子和H3+离子平均能量减小,其总密度却增加.H3+离子为氢气甚高频放电空间的主要离子,H2+离子密度比H3+离子小约2～3个数量级.     

The nature of 0 excitations in Er

Lifetimes of excited 0⁺ states in ¹⁶⁶Er have been measured with the (n,n′γ) reaction. The first and second excited 0⁺ states have no significant collective enhancements of their decays, and their properties are suggestive of pair-type excitations rather than those of a β vibration or phonon excitation built on the γ vibration. The third excited 0⁺ state at 1934 keV has an enhanced decay to the ground state band with B(E2; 0₄⁺ → 2_gsb⁺) = 8.8 ± 0.9 W.u., consistent with that expected for a β vibration.     

Deposition and characterization of carbon nitride films from hexamethylenetetramine/N2 by microwave plasma-enhanced chemical vapor deposition

Carbon nitride thin films were deposited on Si(1 0 0) substrate by microwave plasma-enhanced chemical vapor deposition (PECVD). Hexamethylenetetramine (HMTA) was used as carbon and nitrogen source while N₂ gas was used as both nitrogen source and carrier gas. The sp³-bonded C---N structure in HMTA was considered significantly in the precursor selection. X-ray diffraction analysis indicated that the film was a mixture of crystalline - and β-C₃N₄ as well as graphitic-C₃N₄ and β-Si₃N₄ which were not easily distinguished. Raman spectroscopy also suggested the existence of - and β-C₃N₄ in the films. X-ray photoelectron spectroscopy study indicated the presence of sp²- and sp³-bonded C---N structures in the films while sp³C---N bonding structure predominated to the sp² C---N bonding structure in the bulk composition of the films. N was also found to be bound to Si atoms in the films. The product was, therefore, described as CN_x:Si, where x depends on the film depth, with some evidences of crystalline C₃N₄ formation.