铜铁镁三掺铌酸锂晶体的第一性原理研究

利用基于密度泛函理论的第一性原理,研究了Cu:Fe:Mg:LiNbO3晶体及对比组的电子结构和光学特性.研究显示,单掺铜或铁铌酸锂晶体的杂质能级分别由Cu 3d轨道或Fe 3d轨道贡献,禁带宽度分别为3.45和3.42 eV;铜、铁共掺铌酸锂晶体杂质能级由Cu和Fe的3d轨道共同贡献,禁带宽度为3.24 eV,吸收峰分别在3.01,2.53和1.36 eV处;Cu:Fe:Mg:LiNbO3晶体中Mg^2+浓度低于阈值或高于阈值(阈值约为6.0 mol%)的禁带宽度分别为2.89 eV或3.30 eV,吸收峰分别位于2.45 eV,1.89 eV或2.89 eV,2.59 eV,2.24 eV.Mg^2+浓度高于阈值,会使吸收边较低于阈值情况红移;并使得部分Fe^3+占Nb位,引起晶体场改变,从而改变吸收峰位置和强度.双光存储应用中可选取2.9 eV作为擦除光,2.5 eV作为读取和写入光,选取Mg^2+浓度达到阈值的三掺晶体在增加动态范围和灵敏度等参量以及优化再现图像的质量等方面更具优势.     

Prediction of band gap reduction and magnetism in (Cu,S)-codoped ZnO

By employing a density functional theory plane-wave pseudopotential method, we investigated band gap reduction and magnetism as well as electronic structures of (Cu, S)-codoped ZnO. Our calculations indicated that Cu and/or S-doped ZnO can reduce the band gap of ZnO. The (Cu, S)-codoped ZnO has a large band gap reduction of 0.37 eV, two times larger than that in Cu-doped ZnO. S atom has no contribution for the total magnetic moment of (Cu, S)-codoped ZnO, whereas it plays a central role in spin-polarizing of both Cu and S dopants due to strong coupling between Cu 3d and S 3p states. This would offer a new strategy for designing narrow band gap devices with magnetism.     

The interaction of Cu and S2 with aluminum and alumina surfaces: a comparative study

The bonding interactions between Cu and Al are much stronger than those between Cu and Al₂O₃. Cu atoms supported on alumina show a narrow 3d band with a centroid shifted 0.35 eV with respect to that of the 3d band in bulk metallic Cu. In contrast, Cu atoms deposited on aluminum exhibit shifts of 1.3–1.6 eV in the centroid of the 3d band. Similar differences are observed when comparing the behavior of Ag and Pt overlayers on alumina and aluminum. The d band shifts on the oxide substrate are in the order of 0.3–0.4 eV, whereas on the metal substrate they vary from 0.8 to 2.0 eV. These trends are explained in terms of a simple model that takes into account changes in the energy of the Al(3s, 3p) bands when going from metallic aluminum to alumina. The sticking coefficient of S₂ on alumina surfaces is at least one order of magnitude smaller than on aluminum, a difference that also reflects variations in the position of the Al(3s,3p) bands. Submonolayer coverages of Cu do not produce significant changes in the electronic properties of Al₂O₃. In contrast, the deposition of small amounts of sulfur (0.1 ML) induces a substantial reduction (0.4–0.5 eV) in the binding energies of the O KVV, O 1s and Al 2p features of alumina. This is consistent with a transfer of electrons from alumina into the S atoms that produces a transformation similar to a change from n-type to p-type semiconductors. The reactivity of Cu/Al₂O₃ surfaces toward sulfur is much larger than that of pure Al₂O₃ surfaces. Cu clusters supported on alumina react with S₂ to form CuS_x compounds that decompose at temperatures between 850 and 1100 K.     

低能单个Cu原子与Cu13团簇沉积到Fe（001）表面的比较

本文利用分子动力学模拟方法对相同初始沉积条件下的单个Cu原子和Cu13团簇与Fe(001)表面的相互作用分别进行了模拟研究, 并将两者的模拟结果进行了比较分析. 单个Cu原子和Cu13团簇的初始入射能量范围均为1eV/atom、3eV/atom、5eV/atom和10eV/atom, 初始入射角度均为0o、10o、30o和45o, 衬底温度分别为100K、300K和800K. 对单个Cu原子和Cu13团簇的原子动能、质心高度、迁移距离和最终沉积形貌进行了分析, 对比研究了相同初始沉积条件下单个Cu原子和Cu13团簇在沉积过程中和沉积效果上的具体差异. 模拟结果表明: 单个Cu原子和Cu13团簇与Fe(001)表面的相互作用机制存在差异, Cu13团簇表现出显著的集体效应. 在特定沉积条件下, 由于Cu13团簇的集体效应, 导致Cu13团簇与Fe(001)表面的结合能力和在Fe(001)表面上的扩散能力均强于单个Cu原子.     

Electronic structure of the Cu(111) surface

Self-consistent electronic structure calculations are reported on bulk Cu, and 3- and 5-layer Cu films. These yield a size insensitive work function, φ = 5.0±.1 eV, and a surface energy of 0.75 eV, in agreement with experiment. Good size convergence of the film potential permits the construction of a self-consistent potential for an 11-layer Cu(111) film, whose spectral properties we studied. A prominent p-like surface band was found within 0.1 eV of experiment, serving as a check on the surface potential.     

氯原子在Cu(111)表面的吸附结构和电子态

密度泛函理论(DFT)总能计算研究了不同覆盖度下氯原子在Cu(111)表面的吸附结构和表面电子态。计算结果表明,清洁Cu(111)表面自由能 为15.72 ,表面功函数φ为4.753eV。在1/4ML和1/3ML覆盖度下,每个氯原子在Cu(111)表面fcc谷位的吸附能分别等于3.278eV/atom和3.284eV/atom。在1/2ML覆盖度下,两个紧邻氯原子分别吸附于fcc和hcp谷位,氯原子的平均吸附能为2.631eV/atom。在1/3ML覆盖度下,fcc和hcp两个位置每个氯原子吸附能的差值约为2meV/atom,与正入射X光驻波实验结合蒙特卡罗方法得到结果(<10meV/atom)基本一致。在1/4ML、1/3ML和1/2ML覆盖度下,吸附后Cu(111)表面的功函数依次为5.263eV、5.275eV和5.851eV。吸附原子和衬底价轨道杂化形成的局域表面电子态位于费米能级以下约1.2eV、3.6eV和4.5eV等处。吸附能和电子结构的计算结果表明,氯原子间的直接作用和表面铜原子紧邻氯原子数目是决定表面结构的两个重要因素。     

Electronic and optical properties of Cu, CuO and Cu2O studied by electron spectroscopy

The electronic and optical properties of Cu, CuO and Cu(2)O were studied by x-ray photoelectron spectroscopy (XPS) and reflection electron energy-loss spectroscopy (REELS). We report detailed Cu 2p, Cu LVV, O 1s and O KLL spectra which are in good agreement with previous results. REELS spectra, recorded for primary energies in the range from 150 to 2000 eV, were corrected for multiple inelastically scattered electrons to determine the effective inelastic scattering cross section. The dielectric functions and optical properties were determined by comparing the experimental inelastic electron scattering cross section with a simulated cross section calculated within the semi-classical dielectric response model in which the only input is Im(-1/ε) by using the QUEELS-ε(k,ω)-REELS software package. By Kramers-Kronig transformation of the determined Im(-1/ε), the real and imaginary parts (ε(1) and ε(2)) of the dielectric function, and the refractive index n and extinction coefficient k were determined for Cu, CuO, and Cu(2)O in the 0-100 eV energy range. Observed differences between Cu, CuO and Cu(2)O are mainly due to modifications of the 3d and O 2p electron configurations.     

Atomic adsorption of oxygen on Cu(111) and Cu(110)

We have studied angle-resolved inverse photoemission ( = 9.7 eV) after room temperature adsorption of oxygen on Cu(111) and Cu(110). On Cu(111) exposure to 500 L induces a band (3.0 eV aboveE _F at) which shows clear dispersion (1.0 eV) to higher energies for off normal incidence. Since no LEED superstructure is seen for that system, our results present strong evidence for the presence of short-range surface order. Two adsorbate bands are identified (2.8 eV and 6.3 eV at) on Cu(110)p(2×1)-O. Our results are in good agreement with a long-bridge adsorption site.     

An angle-resolved photoemission study of the chemisorption of chalcogens on Cu(100) III. Cu(100) + p(2 x 2)S

Normal emission ARPES data for Cu(100) with a p(2x2)S overlayer were obtained in the photon energy range hv=11 to 34 eV. These spectra have been compared, within a framework proposed previously, with spectra from clean Cu(100). Changes were found in the Cu emission features, which could be explained by the relaxation of momentum conservation perpendicular to the surface in the optical excitation step and by the relaxation of momentum conservation parallel to the surface in the escape step. These changes include a broadening of the d-band peak and the strong attenuation of the sp-band peak. In addition, a prominent feature appears at about ?4.0 eV at normal emission upon sulfur chemisorption. We tentatively attribute its appearance at normal emission to a new surface umklapp process induced by the overlayer. Changes in the spectrum of scattered electrons were related to modifications of evanescent final states. The sulfur 3p_z^? and 3p_x.y-components could be separated at normal emission and are located at ?4.7 and ?5.4 eV, respectively. No dispersion of the sulfur 3p-bands was detected when the $\text{Γ}\text{X}$ and $\text{Γ}\text{M}$ symmetry lines of the surface Brillouin zone were probed. Sulfur-induced emission above the Cu d-bands was observed and attributed to antibonding states. This emission was directed towards the bulk [011] directions.     

第一性原理下铜锰共掺铌酸锂晶体的电子结构和吸收光谱

采用基于密度泛函理论的第一性原理研究了Cu、Mn单掺及共掺LiNbO3晶体的电子结构和光学性质.结果显示,Cu、Mn掺杂LiNbO_3晶体禁带中的杂质能级分别由Cu 3d轨道、Mn 3d轨道贡献;各掺杂体系的带隙均较纯LiNbO_3晶体变窄.共掺晶体中Cu离子形成了较单掺时更浅的能级中心,并在2.87eV处有较强的吸收峰;Mn离子在1.73eV附近的吸收较单掺时减弱且中心略有偏移,在2.24eV处的非光折变峰与Mn~(3+)相关,这对吸收峰的变化被认为与Cu、Mn间电子转移相联系.相对Cu、Fe共掺LiNbO_3晶体,Cu、Mn共掺LiNbO_3晶体可以通过适当提高Cu离子浓度,来改善存储参量中的动态范围和记录灵敏度.由于同一深能级掺杂离子伴以不同浅能级掺离子将呈现出不同的吸收特征并影响存储性能,在共掺离子的配搭选择时对各待选配搭的模拟计算非常必要.     

Cs3Cu2I5晶体薄膜吸收谱的研究

本文测定了Ｃｓ３Ｃｕ２ Ｉ５ 晶体薄膜在室温及液氮温度下的吸收谱,并依此计算出该材料的激子参数,即激子束缚能ΔＥ（１）ｅｘ ＝ （０．５３±０．０７）ｅＶ,激子半径ａｅｘ ＝ ０．３２６ ｎｍ ,禁带宽度Ｅｇ ＝ （５．００±０．０７）ｅＶ。在谱分析的基础上,论证了Ｃｓ３Ｃｕ２Ｉ５ 的电子和激子激发定域在该晶体的ＣｕＩ亚晶格之中,同时,揭示了在低温下Ｃｓｘ Ｃｕ１－ ｘ Ｉ系列化合物的第一激子峰位置随其摩尔组分变化的规律。     

Doctor-bladed Cu2ZnSnS4 light absorption layer for low-cost solar cell application

The doctor-blade method is investigated for the preparation of Cu2ZnSnS4 films for low-cost solar cell application.Cu2ZnSnS4 precursor powder,the main raw material for the doctor-blade paste,is synthesized by a simple ball-milling process.The doctor-bladed Cu2ZnSnS4 films are annealed in N2 ambient under various conditions and characterized by X-ray diffraction,ultraviolent/vis spectrophotometry,scanning electron microscopy,and current-voltage(J-V) meansurement.Our experimental results indicate that(i) the X-ray diffraction peaks of the Cu2ZnSnS4 precursor powder each show a red shift of about 0.4°;(ii) the high-temperature annealing process can effectively improve the crystallinity of the doctor-bladed Cu 2 ZnSnS 4,whereas an overlong annealing introduces defects;(iii) the band gap value of the doctor-bladed Cu 2 ZnSnS 4 is around 1.41 eV;(iv) the short-circuit current density,the open-circuit voltage,the fill factor,and the efficiency of the best Cu2ZnSnS4 solar cell obtained with the superstrate structure of fluorine-doped tin oxide glass/TiO2/In2S3/Cu2ZnSnS4/Mo are 7.82 mA/cm2,240 mV,0.29,and 0.55%,respectively.     

Electronic structure of the corrugated Cu3N network on Cu(110): Tunneling spectroscopy investigations

The local electronic structure of a submonolayer-thick corrugated Cu₃N–Cu(110) network is investigated by low temperature scanning tunneling spectroscopy (LT-STS). The corrugation present in the Cu₃N network plays a vital role by causing the surface electronic features to vary locally due to different N–Cu bonding. Our studies indicate a work function larger by 0.9 eV for Cu₃N compared to bare Cu(110), suggesting the formation of a significant surface dipole. Theoretically predicted various N 2p, Cu 3d hybridized states have been shown and explicitly verified by a combination of constant height and constant current tunneling spectroscopy measurements, thereby providing information about the chemical composition of the N–Cu(110) network.     

CdTe太阳电池中起因于Cu的深能级

在CdTe太阳电池中,易引入并形成Cu深能级中心. 本文采用深能级瞬态谱测试法研究了ZnTe背接触和石墨背接触CdTe太阳电池的部分深能级中心. 研究中运用密度泛函相关理论,分析闪锌矿结构CdTe,Cd空位体系和掺Cu体系的电子态密度,计算得出T_d场和C_3v场下Cu²⁺ d轨道的分裂情况. 计算结果表明,CdTe太阳电池中的E_v+0206 eV和E_v+0122 eV两个深中心来源于Cu替代Cd原子. 计算结果还表明,掺入Cu可降低CdTe体系能量. 关键词： 深能级瞬态谱 第一性原理 CdTe Cu杂质     

Low-temperature measurements of the fraction of re-emitted positronium from a Cu(111)+S surface

A positron beam has been utilized to measure the positronium (Ps) fraction re-emitted from a Cu(111)+S sample from 40 K to 350 K for incident energies ranging from 0.5 to 5 keV. Our results at 525 eV incident energy are compared with two recent theories from 40 K to 850 K. The Ps fraction shows only a slight positive temperature dependence below room temperature and we conclude that the positron trapping rate and probability of Ps formation at the surface are largely independent of sample temperature for Cu(111)+S. In addition we present evidence that positrons in the bulk material are not localized in shallow traps at low temperatures for well-annealed high-purity single crystals of Cu and Al.     

c(2×2)O吸附Cu(001)表面结构、电子态与STM图像的研究

用投影子缀加波和CP分子动力学方法研究了贵金属Cu(001)面的表面结构、弛豫以及O原子的c(2×2)吸附状态. 研究结果得出在这种吸附结构中，O原子与衬底Cu原子之间的垂 直距离约为0069nm，Cu—O键长为0.194nm，功函数约为5.29 eV；吸附O原子形成金属性能带结构，由于Cu—O的杂化作用,在费米能以下约6.7 eV处出现了局域的表面态.用Tersoff-Hamann途径计算了该表面的扫描隧道显微镜图像，并讨论了与实验结果之 间的关系. 关键词： Cu(001)-c(2×2)/O 电子态 STM图像     

LEED and Auger investigations of Cu (111) surface

After ultrahigh vacuum bake-out, electropolished Cu (111) surfaces were shown by Auger analysis to be contaminated by C, N, O, S and Cl. Other than C and S, which were contained in the bulk, the impurities were introduced by surface preparation; but all were easily removed by light Ar ion bombardment. Heating to ≈ 750°C caused diffusion of C and S from the bulk to the extent that a clear diffraction pattern corresponding to a √7 × √7 structure was produced by S on the surface. At ≈ b 900°C evaporation of Cu occurred to an observable degree, and S and C could no longer be detected on the surface. Auger analysis of clean Cu surfaces showed many details of the LMM and MMM types of transitions. Kinetic energies of all observed Auger electrons were in excellent agreement with calculated values. Also, the ≈ 62 eV MMM peak was resolved into two components related to the small differences in the M₂ and M₃ energy levels. The LMM transitions were classified according to their intensities, which could be rationalized on the basis of Coster-Kronig transitions and transition probabilities, as L₃MM > L₂MM > L₁MM.     

Quantitative Auger electron spectroscopy analysis with co-evaporated AuCu films

A method for the quantitative Auger electron spectroscopy (AES) analysis by using a co-evaporation technique is extended to the AuCu system following the previous work. The calibration curves for lower Auger energy have peaks at 60 eV for Cu and at 69 eV for Au, and for higher Auger energy peaks at 239 eV for Au and at 920 eV for Cu. It is found that a simple linear relation does not exist in the results for AES measurements and the bulk analysis by atomic absorption spectroscopy (AAS) because of the back-scattering effect and the overlap of the spectra at lower energies in the Au-Cu system. It is also found that the adsorption of oxygen caused by electron beam bombardment has a significant influence on the AES results. The calibration curves obtained after a correction for oxygen adsorption are successfully applied to the determination of the composition at the surface of a sputtered AuCu alloy.     

The adsorption of CO on Cu surfaces studied by electron energy loss spectroscopy

Electron energy loss spectroscopy (ELS) in the energy range of electronic transitions (primary energy 30 < E₀ < 50 eV, resolution ΔE ≈ 0.3 eV) has been used to study the adsorption of CO on polycrystalline surfaces and on the low index faces (100), (110), (111) of Cu at 80 K. Also LEED patterns were investigated and thermal desorption was analyzed by means of the temperature dependence of three losses near 9, 12 and 14 eV characteristic for adsorbed CO. The 12 and 14 eV losses occur on all Cu surfaces in the whole coverage range; they are interpreted in terms of intramolecular transitions of the CO. The 9 eV loss is sensitive to the crystallographic type of Cu surface and to the coverage with CO. The interpretation in terms of d(Cu) → 2π¹(CO) charge transfer transitions allows conclusions concerning the adsorption site geometry. The ELS results are consistent with information obtained from LEED. On the (100) surface CO adsorption enhances the intensity of a bulk electronic transition near 4 eV at E₀ < 50 eV. This effect is interpreted within the framework of dielectric theory for surface scattering on the basis of the Cu electron energy band scheme.     

Photoelectron spectroscopy from CO adsorbed on a Cu(111) surface

He II-ultraviolet photoelectron spectra (hv = 40.8 eV) from a carbon monoxide layer adsorbed on a Cu(111) surface exhibit two peaks at 8.5 and 11.6 eV below the Fermi level and a weaker maximum centered at about 13.5 eV. The emission from the Cu d-band is markedly suppressed after adsorption. The results are discussed in terms of the recent models for assigning the UPS peaks observed after adsorption of CO on transtion metals