Weakening of the Cu/Cu3Sn(100) Interface by Bi Impurities

We have performed density functional theory calculations to examine the role of Bi impurities in modifying the structure and properties of the Cu/Cu₃Sn(100) interface. Analysis of the heat of supercell formation reveals that Bi atoms preferentially replace Cu atom in the Cu slab. Substitution of Cu by Bi reduces the adhesion energy of the interface from 1.5 J/m² to 1.1 J/m², primarily due to the atomic size effect. The size effect leads to expansion of the interface, because surrounding Cu and Sn atoms are pushed away from the misfit Bi atoms. Analysis of electronic density indicates that the local charge density is dispersed around Bi atoms. The presence of a Bi atom makes surrounding atoms less active, which is attributed to the reduction of hybridizations.     

Effects of Bi segregation on the tensile properties of Cu/Cu3Sn(1 0 0) interface

The relaxed-type tensile processes of the clean and Bi segregated Cu/Cu₃Sn(1 0 0) interfaces were investigated by the ab initio calculations based on the density functional theory. Fracture occurs at the Cu/Cu₃Sn interface which has the lowest adhesion energy and tensile strength compared to the Cu/Cu and Cu₃Sn/Cu₃Sn interlayers. The theoretical tensile strength of the clean interface is 8.04 GPa, while that of 10% Bi segregated interface drops to 4.72 GPa. According to the atomic and electronic analyzes during tensile test, failure originates from the break of interfacial bonding and the extension of charge depletion region through the interface, when the supercell stretching exceeds the critical tensile strain of 12% for clean interface and 9.5% for Bi segregated interface. Large Bi atom not only introduces interfacial distortion but also reduces the hybridization of surrounding Cu and Sn atoms, which cause the weakening of interfacial mechanical strength of SnBi solder joints.     

Sensor effect in YBa2 Cu3 Oy

The high-T_c superconducting material YBa₂ Cu₃ O_y, well known as a 1–2–3 compound, shows other very interesting properties. One of them is very strong conductivity-oxygen content dependence. On the basis of our previous measurements, an investigation of dilatation synthesis, X-ray diffraction (XRD) analysis and conductivity measurements were performed. The results on quenched and slowly cooled samples show a phase transition region and an obvious interdependence between conductivity, unit cell volume and oxygen content.     

Quench Behavior of YBa2 Cu3O7 Coated Conductor With AC Transport Current

Alternating current (ac) loss and quench behavior measurements were performed on a YBa₂Cu₃O_x coated conductor at 45 K. The minimum quench energies (MQEs) and the quench propagation velocities were measured as a function of transport current and frequency. AC losses were measured at the corresponding temperature and frequencies to quantify the internal thermal load during ac quench measurements. It was found that the direct current (dc) and ac quench behavior are similar, but that the MQE for dc experiments is higher than the corresponding ac cases. This difference is not seen in the normal zone propagation velocity data, indicating that the difference in MQE is minimal if the ac losses are included in the energy calculation. The ac experiments show that the MQE and propagation velocity varies weakly with frequency.     

Experimental study of the current redistribution in pulsedoperation inside the Nb3Sn CICC of an ITER relevant magnet

It is believed that critical current reduction in multistrand superconducting cables at nonsteady state conditions is caused by a nonuniform current distribution among strands. This was experimentally proven for small model cables, but is still not verified for large cables. In the ENEA Frascati Laboratory, an ITER relevant, large superconducting magnet has been tested at different field ramp rates. By means of numerous local miniature field sensors (Hall probes and pickup coils) located in a few positions along the conductor, current redistribution phenomena inside the cable have been studied. Fast and slow local field changes have been studied to quantify the current nonuniformity. It has been shown that severe current nonuniformity does exist in the cable and that induced current loops are generated, which decay with very long time constants (up to 10⁴-10⁵ s)     

Preparation and characterization of sphere-like Cu2SnS3 nanoparticles and their dropcasted thin films

Ternary sphere-like Cu₂SnS₃(CTS) semiconductor and 2D hexagonal sheets were synthesized via a simple solvothermal method using PVP as the surface ligand at two temperatures of 180 and 220℃. The structural, morphological, and chemical compositions as well as optical properties of as-synthesized CTS particles were characterized using X-ray diffraction (XRD), Raman spectroscopy, energy dispersive X-ray spectrometry (EDS), field emission scanning electron microscopy (FESEM), and UV-Vis spectroscopy. The size of sphere-like particles and the side length of hexagonal sheets were within the range of 120-140 nm and 500 nm-2 μm, respectively. FESEM, XRD, and EDS were analyzed to investigate the mechanism of the morphological evolution of CTS particles. CTS particles showed proliferation of Sn atomic ratio, which is strongly sensitive to reaction temperature and, highly affects the increase of band gap energy from 1.36 to 1.53 eV due to generation metal defects and formation SnS₂. The optical analysis via the transmittance and reflectance reveals that the band-gap energy of dropcasted CTS thin films decreases after annealing due to grain growth and change of chemical compositions. Photo-responses of CTS nanocrystal thin films indicated a considerable increase in the conductivity of the films under light illumination. All these results showed the potential of these films for solar cell applications.     

The electron-voltaic effect in CdS/Cu2S heterojunctions

An investigation of energy conversion in CdS/Cu₂S thin film heterojunctions has shown that the devices appear to operate differently in the photovoltaic and electron-voltaic modes, the response in the latter mode occurring mainly on the CdS side of the junction. With a view to the manufacture of compact long-life reliable microgenerators the electron-voltaic mode has been studied using 6–15 keV electrons, 75–400 keV electrons and β-emitting radioactive sources such as tritium, promethium and thallium. Greater efficiencies for electron-voltaic energy conversion were obtained when the cells were fabricated by a ‘dry’ barrier method rather than by a conventional ‘wet’ barrier technique. Tritium was found to be an ideal source for electron—voltaic energy conversion in the particular CdS/Cu₂S heterojunctions studied.     

Colloidal synthesis and characterization of Cu2ZnSnS4 nanoplates

Synthesis of copper zinc tin sulphide (Cu₂ZnSnS₄) with nanoplate morphology was achieved through colloidal method using oleic acid as capping agent and solvent with 1-octadecene (1-ODE) at 240℃. X-ray diffraction (XRD) analysis shows that the synthesized nanoplates possessed pure kesterite phase. SEM analysis clearly shows the formation of nanoplates having the size of about 50-100 nm. Electron spin resonance (ESR) spectrum analysis of the prepared nanoplates shows that the valence state of copper (Ⅱ) which indicates the strong coupling with other metal ions. Thermo gravimetric/differential thermal analysis (TG/DTA) analysis shows the weight loss of sample at 450℃ predicting the loss of capping ligands on the surface of the nanoparticles. The possible mechanism for the conversion of nanoplate-like structures during synthesis was discussed. The results are discussed in detail.     

Cu2O-based solar cells using oxide semiconductors

We describe significant improvements of the photovoltaic properties that were achieved in Al-doped ZnO (AZO)/n-type oxide semiconductor/p-type Cu₂O heterojunction solar cells fabricated using p-type Cu₂O sheets prepared by thermally oxidizing Cu sheets. The multicomponent oxide thin film used as the n-type semiconductor layer was prepared with various chemical compositions on non-intentionally heated Cu₂O sheets under various deposition conditions using a pulsed laser deposition method. In Cu₂O-based heterojunction solar cells fabricated using various ternary compounds as the n-type oxide thin-film layer, the best photovoltaic performance was obtained with an n-ZnGa₂O₄ thin-film layer. In most of the Cu₂O-based heterojunction solar cells using multicomponent oxides composed of combinations of various binary compounds, the obtained photovoltaic properties changed gradually as the chemical composition was varied. However, with the ZnO-MgO and Ga₂O₃-Al₂O₃ systems, higher conversion efficiencies (η) as well as a high open circuit voltage (V_oc) were obtained by using a relatively small amount of MgO or Al₂O₃, e.g., (ZnO)_0.91-(MgO)_0.09 and (Ga₂O₃)_0.975-(Al₂O₃)_0.025, respectively. When Cu₂O-based heterojunction solar cells were fabricated using Al₂O₃-Ga₂O₃-MgO-ZnO (AGMZO) multicomponent oxide thin films deposited with metal atomic ratios of 10, 60, 10 and 20 at.% for the Al, Ga, Mg and Zn, respectively, a high V_oc of 0.98 V and an η of 4.82% were obtained. In addition, an enhanced η and an improved fill factor could be achieved in AZO/n-type multicomponent oxide/p-type Cu₂O heterojunction solar cells fabricated using Na-doped Cu₂O (Cu₂O:Na) sheets that featured a resistivity controlled by optimizing the post-annealing temperature and duration. Consequently, an η of 6.25% and a V_oc of 0.84 V were obtained in a MgF₂/AZO/n-(Ga₂O₃-Al₂O₃)/p-Cu₂O:Na heterojunction solar cell fabricated using a Cu₂O:Na sheet with a resistivity of approximately 10 Ω·cm and a (Ga_0.975Al_0.025)₂O₃ thin film with a thickness of approximately 60 nm. In addition, a V_oc of 0.96 V and an η of 5.4% were obtained in a MgF₂/AZO/n-AGMZO/p-Cu₂O:Na heterojunction solar cell.     

Cu_2O不同形貌的研究进展

近年来,Cu2O形貌控制合成的研究受到了广泛关注。首先,介绍了Cu2O一维、二维、三维结构中不同形貌的最新研究成果,分析了不同形貌的合成机理,并对各形貌的进一步研究趋势进行了探讨。然后,着重评述了Cu2O纳米笼、纳米骨架结构的研究进展,指出此类形貌的合成中主要涉及到氧化刻蚀作用和奥斯特瓦尔德熟化机理。最后,总结了Cu2O不同形貌研究的现状,指出了今后研究的方向,并提出了未来关于Cu2O形貌研究中主要的两大类趋势,即具有更多晶面的非传统型多面体结构以及具有更大比表面积、更高开放程度的纳米笼和纳米骨架结构。     

Humidity sensing properties of Cu2O-PEPC nanocomposite films

In this study, the blend of copper oxide nanopowder (Cu2O), 3 wt.% and poly-N-epoxypropylcarbazole (PEPC), 2 wt.% in benzol were drop-casted on glass substrates with pre-deposited surface-type silver electrodes for the fabrication of Cu2O-PEPC nanocomposite thin films. The thicknesses of the Cu2O-PEPC films were in the range of 10-13 μm. The effect of humidity on the electrical properties of the nanocomposite films was investigated by measurement of the capacitance and dissipation of the samples at two different frequencies of the applied voltage: 120 Hz and 1 kHz. The AC resistance of the samples was determined from values of dissipation. The DC resistance was measured directly. The effect of ageing on the humidity sensing properties of the nanocomposite was observed. After the ageing it was observed that at 120 Hz and 1 kHz, under humidity of up to 86% RH , the capacitance of the cell increased by 85 and 8 times and resistance decreased by 345 and 157 times, accordingly, with respect to 30% RH conditions. It was found that with increase of the frequency, the capacitance and resistance of the samples decreased. It is assumed that the humidity response of the cell is associated with diffusion of water vapors and doping of the semiconductor nanocomposite by water molecules.     

铜锌锡硫带边电子结构及缺陷态的光学表征

利用吸收、光电流和光致发光等光谱表征并结合理论报道,分析了缺陷态丰富的铜锌锡硫半导体材料的光学带隙、带尾态和深浅杂质能级,揭示了Sn_Zn相关的缺陷态是影响铜锌锡硫带边电子结构的关键因素,其中高浓度的中性缺陷簇[2Cu_Zn+Sn_Zn]能导致带隙明显窄化,而离子性缺陷簇[Cu_Zn+Sn_Zn]是主要的深施主缺陷态,同时存在的大量带尾态引起带边相关的光致发光峰明显红移。贫铜富锌条件下,适当减少锡含量,可有效抑制与Sn_Zn相关的缺陷簇,并避免带隙的窄化。     

Cu2ZnSnS4薄膜及其太阳电池的研究进展

Cu2ZnSnS4（CZTS）薄膜材料成本低廉且无毒,其电学性能主要由自身所含的缺陷决定,一般呈P型导电性。CZTS的禁带宽度为1．5eV左右,在可见光范围内的光学吸收系数一般都大于10^4cm^-1,所以其非常适合作为太阳电池的吸收层。经过国内外学者10余年的努力,CZTS太阳电池光电转换效率提升明显。相信不久的将来,CZTS薄膜电池必将得到广泛的应用。主要介绍了CZTS材料的制备方法、CZTS材料性能和CZTS太阳电池的研究进展。     

Analysis of “on” and “off” times for thermally driven VO2 metal-insulator transition nanoscale switching devices

Vanadium oxide undergoes a sharp metal-insulator transition in the vicinity of room temperature and there is considerable interest in exploring novel device applications that utilize this phase transition. Using experimentally determined values of the thermal conductivity across the metal-insulator transition in VO₂ thin films, we estimate the switching characteristics of two-terminal VO₂ devices. The minimum switching time for both heating (“on” state) and cooling (“off” state) processes is explored using a simple resistance-capacitance thermal circuit model. The estimated minimum switching time is on the order of ∼1 ns for 20 nm VO₂ films which is comparable to experimentally observed switching times. Optimal operating temperatures to maximize switching times are estimated. Methods to further enhance the switching kinetics by device thickness, carrier doping/strain, interfacial thermal resistance and input thermal energy are discussed. The simulations are compared with a 3-D model for VO₂ devices on Si substrates utilizing COMSOL. The results are of potential relevance to the emerging field of correlated oxide electronics with fast phase transitions.     

用溶胶-凝胶法制备的Cu2Bi2Cr2O8薄膜 及其光学和铁磁性能研究

以硝酸铜Cu(NO₃)₂·3H₂O、硝酸铬Cr(NO₃)₃·9H₂O、硝酸铋Bi(NO₃)₃·3H₂O和乙二醇为原料,利用溶胶-凝胶工艺在石英衬底上制备了纳米Cu₂Bi₂Cr₂O₈薄膜。通过X射线衍射(X-Ray Diffraction, XRD)和拉曼测试对样品进行了表征。结果表明,Cu₂Bi₂Cr₂O₈薄膜具有良好的光学特性,其禁带宽度为1.49 eV;在磁性测试方面,Cu₂Bi₂Cr₂O₈薄膜呈现出了良好的铁磁性。     

用热蒸发法制备的Cu2ZnSnS4 薄膜的光电性能

在室温下用真空热蒸发法在玻璃基片上制备Sn/Cu/ZnS 前躯体膜层,然后对其在550C 下在硫气氛中硫化3小时以制得Cu₂ZnSnS₄ (CZTS) 多晶薄膜。对该薄膜进行X射线衍射（XRD）、能量色散X射线光谱（EDX）、紫外可见近红外分光光度计、霍尔测量系统和3D光学显微镜等分析测试。实验结果表明,当[Cu]/([Zn] [Sn]) =0.83和[Zn]/[Sn] =1.15时,该CZTS薄膜在光子能量范围在1.5 - 3.5 eV 时其吸收系数大于4.010₄cm_-1 ,直接带隙为1.47 eV。其载流子浓度、电阻率和迁移率分别为7.9710₁₆ cm_-3, 6.06 Ω.cm, 12.9 cm₂/(V.s), 导电类型为p型。因此,所制备出的CZTS 薄膜适合作为太阳电池的吸收层材料。     

“Gated-diode” in SOI MOSFETs: a sensitive tool forcharacterizing the buried Si/SiO2 interface

A “gated diode” technique is described for the measurement of the interface state density of the silicon film/buried oxide interface of SOI MOSFETs. This approach becomes possible by taking advantage of the front gate, which is biased to inversion (NMOSFET) or accumulation (BC-PMOSFET) during the measurement, while scanning the back interface through depletion. Using this technique the estimated value of the buried interface state density of typical low dose SIMOX MOSFETs was slightly over 10¹¹/cm²     

Electrical properties of Cu4ZnSnS2/ZnS heterojunction prepared by ultrasonic spray pyrolysis

Cu₂ZnSnS₄ (CZTS)/ZnS heterojunctions have been prepared by a successive deposition of ZnS and CZTS thin films by ultrasonic spray pyrolysis technique on glass substrates. The cupric chloride concentration has been varied in the starting solution in order to investigate its influence on device properties. CZTS/ZnS heterojunctions were characterized by recording their current-voltage characteristics at different temperatures. The obtained results exhibit a good rectifying behavior of the realized heterojunction. Analysis of these results yields saturation current, series resistance and ideality factor determination. From the activation energy of saturation current we inferred that the thermal emission through the barrier height is the dominant mechanism of the reverse current rather than the defects contribution.     

A simple chemical route to synthesize the umangite phase of copper selenide (Cu3Se2) thin film at room temperature

Copper selenide (Cu₃Se₂)thin films have been synthesized with Se as the precursor in aqueous solution by chemical bath deposition technique at room temperature. We have investigated the influence of the growth time ranging from 30 to 90 min on structural, optical and electrical properties of Cu₃Se₂ thin films. The as-grown film at 60 min exhibits a tetragonal structure and is (101) oriented. The maximum value of crystal size D= 55 nm is attained for Cu₃Se₂ films grown at 60 min. The Raman spectrum reveals a pronounced peak at 259 cm^-1, which is assigned to vibrational (stretching) modes from the covalent Se-Se bonds. The optical band gap energy is 1.91 to 2.01 eV with growth time increased from 30 to 90 min. The scanning electron microscopy (SEM) study reveals that the grains are uniform and spread over the entire surface of the substrate of the film at 60 min. The Hall effect study reveals that the film exhibits p-type conductivity. The synthesized film showed good absorbance in the visible region which signifies that synthesized Cu₃Se₂ films can be suitable as a sensitized material in semiconductor sensitized solar cells.