ESCA studies of Cu,Cu2O and CuO

Cu 2p, Cu 3d and O 1s electron spectra and Cu L₃M_4,5M_4,5 Auger electron spectra from Cu, Cu₂O and CuO have been studied at 25°C and at 400°C. The height of the Cu 2p satellite peaks from copper oxides was lowered when the temperature was raised. The intensity of the satellites also decreased if the sample stayed in vacuum for prolonged periods.Two commercial cuprous oxides were different with respect to the behaviour of the satellite peaks. One produced very weak satellites, while the other produced strong ones as previously reported in the literature for cuprous oxide. The colour of the oxides was slightly different, indicating that the stoichiometry was not the same.The change in satellite intensity is accompanied by changes in oxygen spectra, Cu L₃M_4,5 M_4,5 Auger spectra and valence band spectra.It is useful to study Auger electrons in addition to the direct electron spectrum, since Auger signals can be more sensitive to surface conditions than direct electron spectra.     

Valence band photoemission study of the copper chalcogenide compounds, Cu2S, Cu2Se and Cu2Te

The electronic structures of the copper chalcogenide compounds, Cu₂S, Cu₂Se and Cu₂Te have been investigated by taking photoemission data with synchrotron photon sources. The band calculations are done using the full-potential linear-muffin-tin-orbital method. Since the crystal structures are not clarified well, several simplified structure models are used. The calculated densities of states are compared with the observed spectra. The analysis shows that a sharp peak at −3.5 eV is due to the Cu 3d states, and that the tails at the high and low energy sides of the Cu 3d peak are due to the chalcogen p states.     

Investigations on co-evaporated Cu2SnSe3 and Cu2SnSe3-ZnSe thin films

Cu₂SnSe₃ is an important precursor material for the growth of Cu₂ZnSnSe₄, an emerging solar cell absorber layer via solid state reaction of Cu₂SnSe₃ and ZnSe. In this study, we have grown Cu₂SnSe₃ (CTSe) and Cu₂SnSe₃-ZnSe (20%) films onto soda-lime glass substrates held at 573 K by co-evaporation technique. The effect of annealing of these films at 723 K for an hour in selenium atmosphere is also investigated. XRD studies of as-deposited Cu₂SnSe₃ and Cu₂SnSe₃-ZnSe films indicated SnSe as secondary phase which disappeared on annealing. The direct optical band gap of annealed Cu₂SnSe₃ and Cu₂SnSe₃-ZnSe films were found to be 0.90 eV and 0.94 eV respectively. Raman spectroscopy studies were used to understand the effect of ZnSe on the properties of Cu₂SnSe₃.     

Strain imaging of a Cu2S switching device

Strain imaging of electrochemical behavior of a solid electrolyte Cu₂S in switching devices for nonvolatile memories is presented. The precipitation and dissolution of Cu, and the nonstoichiometry changes cause changes in volume. Strain imaging we have proposed detects the volume changes through the surface displacements using scanning probe microscopy and provides high resolution images. We observed the distributions of the electrochemical reactions in Cu₂S and located the Cu bridges causing switching.     

POSITRON ANNIHILATION STUDY OF YBa2(Cu1-xSnx)3Oy SUPERCONDUCTORS

The positron annihilation lifetime spectra and their temperature dependence for the YBa₂Cu₃O_y superconducting ceramics doped with Sn have been studied. The resutts of analyses indicate that the element Sn is substituted for Cu(1) sites, and this leads to the ordering of the oxygen atoms as well as the increase of local electronic density in the Cu(1)-O layer where Cu(1) is substituted by Sn.     

Synthesis of earth-abundant Cu2SnS3 powder using solid state reaction

Cu₂SnS₃ (CTS) powder has been synthesized at 200 °C by solid state reaction of pastes consisting of Cu and Sn salts and different sulphur compounds in air. The compositions of the products is elucidated from XRD and only thiourea is found to yield CTS without any unwanted CuS_x or SnS_y. Rietveld analysis of Cu₂SnS₃ is carried out to determine the structure parameters. XPS shows that Cu and Sn are in oxidation states +1 and +4, respectively. Morphology of powder as revealed by SEM shows the powder to be polycrystalline with porous structure. The band gap of CTS powder is found to be 1.1 eV from diffuse reflectance spectroscopy. Cu₂SnS₃ pellets are p-type with electrical conductivity of 10⁻² S/cm. The thermal degradation and metal–ligand coordination in CTS precursor are studied with TGA/DSC and FT-IR, respectively, and a probable mechanism of formation of CTS has been suggested.     

Electronic structure and surface structure of Cu2S nanorods from polarization dependent X-ray absorption spectroscopy

Highly aligned Cu₂S nanorods have been studied by polarization dependent X-ray absorption spectroscopy. In contrast to bulk Cu₂S, strong s, p, and d hybridization is found in the nanorods. The polarization dependence shows a predominant d_z2${\text{d}}_{z^2}$ character of Cu 3d states. Ab initio multiple-scattering calculations confirm the strong hybridization, and reveal that Cu₂S nanorods are grown along the z-axis of chalcocite structure with Cu₇ and Cu₁₀ sites being the main building blocks. The hybridized absorption peak in the nanorods is shifted towards lower energies for smaller diameter of nanorods, which is attributed to surface reconstruction due to strong Cu–Cu interactions on the Cu-rich surface of the nanorods.     

三元合金Cu76Ni15Sn9的离子溅射研究

在２７ｋｅＶ Ａｒ⁺离子轰击时,用收集膜技术结合俄歇谱仪（ＡＥＳ）,研究了三元合金Cu₇₆Ni₁₅Sn₉系统的择优溅射行为。同时使用扫描电子显微镜（ＳＥＭ）与电子探针微分析（ＥＰＭＡ）．观察了靶点表面形貌变化并测定了形貌特征微区的合金组份原子的相对百分浓度。结果表明,Ｃｕ原子较Ｎｉ原子、Ｎｉ原子较Ｓｎ原子,在所测定范围（０─６０°）内择优发射。最后讨论了靶点表面形貌特征和“元素局域富集”现象对择优溅射过程的影响。 关键词：     

Low energy sputtering of neutral Cu2 molecules

The ratios of relative yields of neutral sputtered Cu₂ molecules to neutral sputtered Cu atoms were found to be linearly proportional to the sputtering yield of Cu, from a Cu target under bombardment by Ar⁺ ions (energy 50–90 eV), as determined by secondary neutral mass spectrometry.     

YBa2(Cu0.95M0.05)3O7-δ的代换效应及其中子衍射研究

X射线衍射实验表明YBa₂(Cu_0.95M_0.05)₃O_7-δ(M=Ti,V,Cr,Mn,Fe,Co,Ni,Cu和Zn)均为单相结构。Fe,Co,Ni和Zn对Cu的替代使超导临界温度T_c显著下降,而同样含量的Ti,V,Cr,Mn对Cu的替代并未对超导性能产生显著影响。并利用中子衍射分析了Ti,Mn,Fe和Co对Cu原子的取代,发现代换原子对Cu的两个晶位各自存在不同的择优占据 关键词：     

Structure and composition of the segregated Cu in V2O5/Cu system

We have investigated segregation of copper at the surface of V₂O₅ films deposited onto Cu substrate by employing surface analysis techniques. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) confirmed that the Cu is segregated at the surface and its chemical state is Cu₂O. According to secondary ion mass spectroscopy (SIMS) and glow discharge spectroscopy (GDS), the Cu concentration inside the deposited V₂O₅ layer is low. Ultraviolet photoelectron spectroscopy (UPS) and scanning tunneling spectroscopy (STS) revealed the segregation alters the surface local density of states. Surface analysis of deposited samples in ultra high vacuum (UHV) condition verified that the segregation occurs during the deposition. We have extended kinetic tight binding Ising model (KTBIM) to explain the surface segregation during the deposition. Simulation data approve the possibility of surface segregation during room temperature deposition. These results point out that on pure Cu substrate, oxidation occurs during the segregation and low surface energy of Cu₂O is the original cause of the segregation.     

Room temperature synthesis of Cu2O nanocubes and nanoboxes

Monodisperse Cu₂O nanocubes are synthesized by reducing freshly prepared Cu(OH)₂ with N₂H₄·H₂O in water at room temperature. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations show that most of these nanocubes are uniform in size, with the average edge length of ∼500 nm. Selected area electron diffraction (SAED) investigation reveals that these nanocubes are single crystalline. Further, Cu₂O nanoboxes are obtained by etching Cu₂O nanocubes with acetic acid solution at room temperature. The nanoboxes retain the size and external morphology of the nanocubes.     

A STUDY OF THE CRYSTALLIZATION OF AMORPHOUS Cu60Zr40 ALLOY

The crystallization of the amorphous Cu₆₀Zr₄₀ alloy has been studied by differential scanning calorimetry (DSC), scanning Auger microprobe (SAM) and transmission electron microscopy (TEM). The DSC trace showed that the sample exhibited a glass transition at 750 K and a strong exothermic effect beginning from 782 K. An enrichment of the element Zr and significant oxygen contamination in a zone near the surface to a depth of about 10 nm were revealed by SAM in the analysis of surface competition and depth profiles of the Cu₆₀Zr₄₀ sample. Also, the change of concentration ratio of Ca to Zr in amorphous matrix at the clean Cu₆₀Zr₄₀ surface as a function of annealing temperature was examined in detail, and it was found that the concentration of Zr at the surface is slightly higher than that in the bulk until 780K and that the concentration ratio of Cu to Zr in matrix has an abrupt increase in the temperature range of 780-800K. The observations by high resolution TEM revealed the appearance of cluster-like regions of approximately 1.5-2.0 nm in size just before crystallization and they distributed randomly throughout the sample. This phenomenon is analogous to the results obtained using field ion microscopy (FIM) by the present authors. The microstructural changes of the sample daring heating show the gradual crystallization of the amorphous matrix.     

Magnetic properties for the Cu2MnSnSe4 and Cu2FeSnSe4 compounds

Magnetic susceptibility χ measurements in the range from 2 to 300 K were carried out on samples of the Cu₂FeSnSe₄ and Cu₂MnSnSe₄ compounds. It was found that Cu₂FeSnSe₄ was antiferromagnetic showing ideal Curie-Weiss behavior with a Néel temperature T_N of about 19 K and Curie-Weiss temperature θ=−200 K, while for Cu₂MnSnSe₄ the behavior was spin-glass with a freezing temperature T_f of about 22 K and Curie-Weiss temperature θ=−25 K. The spin-glass order parameter q(T), determined from the susceptibility data, was found to be in agreement with the prediction of conventional spin-glass theory.     

Effects of Cu2−xS phase removal on surface potential of Cu2ZnSnS4 thin-films grown by electroplating

Cu₂ZnSnS₄ (CZTS) has an optical band gap of 1.4–1.5 eV, which is similar to that of Cu(In,Ga)Se₂ (CIGS), and a high absorption coefficient (>10⁴ cm⁻¹) in the visible light region. In previous reports, CIGS thin-film solar cells have been shown to improve the performance of the device since the secondary phase is removed by Potassium cyanide (KCN) etching treatment. Therefore, in this study we applied a KCN etching treatment on CZTS and measured the effects. We confirmed the removal of Cu_2−xS via Kelvin probe force microscopy (KPFM) and Raman scattering spectroscopy. The effects of the experiment indicate that we can define with precision the location of the secondary phases, and therefore the control of the secondary phases will be easier and more efficient. Such capabilities could improve the solar cell performance of CZTS thin-films.     

Electronic structure and optical properties of wurtzite-kesterite Cu2ZnSnS4

As promising light-absorber material for solar cells, Cu₂ZnSnS₄ was found to have another crystal structure (wurtzite-kesterite) in addition to the conventional zinc blende-kesterite structure. Structural flexibility of Cu₂ZnSnS₄ opens up an avenue to develop light-absorber material with novel exciting properties and applications. However, its electronic and optical properties have not been comprehensively studied yet. For this purpose, the method of density functional theory within hybrid functional of PBE0 was adopted to study the structural, electronic, and optical properties of wurtzite-kesterite Cu₂ZnSnS₄ in this Letter. The calculated results suggested that the energy of its band gap is about 1.372 eV and it has obvious optical anisotropy. Furthermore, its crystal structure leads local internal fields that are especially beneficial to suppress the recombination of photoexcited electron–hole pairs.     

Synthesis of Cu2ZnSnSe4 compound powders by solid state reaction using elemental powders

The solid state reaction method was used to synthesize single phase and near stoichiometric Cu₂ZnSnSe₄ compound from elemental Cu, Zn, Sn and Se powders in a quartz tube furnace under an Ar flow at atmospheric pressure. These elemental powders were initially milled using zirconia balls. The α-CuSe phase was present in all of the milled powders because of the mechanical alloying effect between the Cu and Se powders. The solid state reaction mechanism was examined for the synthesis process. The phase analysis suggested that the Cu₂ZnSnSe₄ powder crystallized into the stannite phase with a high degree of crystallinity after near stoichiometric molar ratios of the powders was reacted at 500 °C for 6 h. This study showed that the solid state reaction method was a straightforward technique for the synthesis of the Cu₂ZnSnSe₄ compound powders from the elemental powders.     

Optical absorption spectrum of Cu2O-CaO-P2O5 glasses

Homogeneous CaO-P₂O₅ and Cu₂O-CaO-P₂O₅ glasses were prepared using a melt-quenched method under controlled conditions. The binary glasses were found to be colourless and transparent while the ternary glasses changed from light green to dark green as the Cu₂O content increased. From the absorption edge studies, the values of the optical band gap, E_opt and Urbach energy, ΔE were evaluated. The position of the absorption edge and hence the optical band gap were found to depend on the glass composition. Analysis of the optical band gap shows that for the binary glasses, the value increases as the content of CaO decreases, while for the ternary glasses, the value of the optical band gap increases as the content of the Cu₂O decreases. The density of the glasses was also measured and was found to increase with the increase in CaO and Cu₂O contents.     

First-principles calculation of defect formation energy in chalcopyrite-type CuInSe2, CuGaSe2 and CuAlSe2

In order to quantitatively evaluate the formation energies of Cu, In/Ga/Al and Se vacancies in chalcopyrite-type CuInSe₂ (CIS), CuGaSe₂ (CGS) and CuAlSe₂ (CAS), first-principles pseudopotential calculations using plane-wave basis functions were performed. All calculations were performed using a supercell with 64 atoms, which was eight times greater than the number of atoms in a primitive cell with eight atoms. The formation energies of point defects were calculated as a function of the atomic chemical potentials of constituent elements. Atomic arrangements around the vacancy were optimized allowing relaxation of the first- and second-nearest-neighbor atoms of the vacancy. The obtained results were as follows: (1) the formation energy of Cu vacancy was smaller than those of the other vacancies in CIS, CGS and CAS. Under the Cu-poor condition, the formation energy of Cu vacancy in CIS was lowest among those in them; (2) the formation energy of Se vacancy in CIS was relatively lower than those in CGS and CAS; (3) the formation energy of (2V_Cu+In_Cu) pair in CIS was greatly dependent on the chemical potential of the constituent elements, i.e. Cu, In and Se. On the other hand, the formation energies of (2V_Cu+Ga_Cu) in CGS and (2V_Cu+Al_Cu) in CAS were not largely dependent on the chemical potential of the constituent elements. Under the Cu-poor condition, the formation energy of (2V_Cu+In_Cu) pair in CIS was much lower than those of (2V_Cu+Ga_Cu) in CGS and (2V_Cu+Al_Cu) in CAS.     

Shape-controlled synthesis of Cu2O microcrystals by electrochemical method

Cuprous oxide (Cu₂O) microcrystals have been successfully synthesized via a facile electrochemical method in alkaline NaCl solution with copper plate and graphite slice as electrodes and Na₂Cr₂O₇ as additive. The as-synthesized products have been systematically studied by X-ray powder diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), selected area electron diffraction (SAED) and ultraviolet-visible spectrum (UV-vis). The results indicate that the pH value, temperature and potential play important roles in the morphology control besides the crystal habits of Cu₂O. The possible mechanism has been explored in the article.