Phase transitions in cuprous sulphide evaporated thin films

The films of Cu_xS(1x2), prepared by evaporation in vacuum and condensation of stoichiometric sulphides of copper, change their phases by heat treatment in vacuum. Cu₂S chalcocite appears as the most stable phase in the range 270 to 450° C and the other sulphur rich phases transform into chalcocite presumably by a loss of sulphur. By electron diffraction we have confirmed the low temperature monoclinic chalcocite phase, the high temperature hexagonal chalcocite phase, the monoclinic djurleite phase, the cubic digenite low and high temperature forms and the hexagonal covellite phase. The low temperature digenite phase presents a superstructure which is similar to that observed by Kazinetset al. on digenite prepared by evaporation in vacuum on a single crystal substrate of NaCl at temperatures of 350 to 400° C. Electron diffraction data of chalcocite (Cu₂S), djurleite (Cu_1.93S), digenite (Cu_1,8S) are presented.     

International conference on thin and thick film technology,Augsburg, F.R.G., 28–30 September, 1977

Cu₂S thin films of well-controlled thickness and stoichiometry were prepared by a solid state reaction between CdS and CuCl films in the temperature range 200–250°C. The Cu₂S films exist in the orthorhombic chalcocite phase. The growth of Cu₂S on CdS is topotactial, and the chalcocite phase is obtained on reaction with both wurtzite and sphalerite structures of CdS. The electrical and optical properties of the Cu₂S films are consistent with the Cu₂S composition. These films were utilized to fabricate Cu₂S/CdS solar cells.     

Effect of reduction potential and post-deposition annealing on the structural,compositional and optical properties of electrodeposited copper(I) sulfide thin films

In the present work it is reported on the deposition of cuprous sulfide (Cu₂S) by the electrodeposition technique and its characterization followed by a heat treatment. Cu₂S films were deposited using reduction potentials in a range of ??600 to ??555 mV (vs. SCE) with a deposition time of 1000 s. The annealing process was performed varying the atmosphere (inert or with sulfur) and temperature (250 and 350 °C). The properties of deposited Cu₂S films were analyzed using UV–Vis spectroscopy, X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The deposited films had a hexagonal structure in the chalcocite phase and showed a band gap in the range of 1.61 and 1.8 eV. Characterization techniques demonstrated modifications in the properties of the material due to the presence or deficiency of sulfur in the films.     

Synthesis of copper nanoparticles from refractory sulfides using a semi-industrial mechanochemical approach

The large-scale mechanochemical reduction of binary sulfides chalcocite (Cu₂S) and covellite (CuS) by elemental iron was investigated in this work. The reduction of Cu₂S was almost complete after 360 min of milling, whereas in the case of CuS, a significant amount of non-reacted elemental iron could still be identified after 480 min. Upon application of more effective laboratory-scale planetary ball milling, it was possible to reach almost complete reduction of CuS. Longer milling leads to the formation of ternary sulfides and oxidation product, namely cuprospinel CuFe₂O₄. The rate constant calculated from the magnetometry measurements using a diffusion model for Cu₂S and CuS reduction by iron in a large-scale mill is 0.056 min^−0.5 and 0.037 min^−0.5, respectively, whereas for the CuS reduction in a laboratory-scale mill, it is 0.1477 min⁻¹. The nanocrystalline character of the samples was confirmed by TEM and XRD, as the produced Cu exhibited sizes up to 16 nm in all cases. The process can be easily scaled up and thus copper can be obtained much easier from refractory minerals than in traditional metallurgical approaches.     

Growth and properties of Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> thin films prepared by multiple metallic layer stacks as a function of sulfurization time

In this paper, we report the two stage growth of Cu₂ZnSnS₄ (CZTS) thin films as a function of sulfurization time. First, magnetron sputtered metallic precursors were deposited sequentially (Zn/Cu/Sn/Cu) over rotating glass substrates held at 230?°C. Later, the sputtered precursors were heat treated at 500?°C in the ambiance of sulfur for various time durations in the range, 10–120 min. The sulfur treated samples were examined using various analytical tools to understand the role of sulfurization time on the CZTS growth and properties. From composition and structural analysis, Zn/Cu/Sn/Cu precursors sulfurized for shorter duration (10 and 20 min) revealed severe deficiency of sulfur that resulted in several metallic, bi-metallic and metal sulfide phases. With the increase of sulfurization time to 30 min, sulfur incorporation was enhanced and reached stoichiometric ratio (~50% S) for CZTS growth, however, samples were poorly crystalline in nature and consisted of prominent Cu_2?xS phase as well. The Zn/Cu/Sn/Cu precursors sulfurized for 60 min exhibited prominent CZTS phase without Cu_2?xS phase. Further, rise in sulfurization time to 120 min enabled drastic improvement in crystallinity of CZTS phase. Raman mapping over 60 µm × 60 µm for these films confirmed the homogeneous phase growth of CZTS. XPS study revealed the oxidation states of Cu¹⁺, Zn²⁺, Sn⁴⁺ and S^2? in CZTS films. The optimized films showed high absorption coefficient of 10⁵ cm^?1 with an optical band gap of 1.51 eV. These films showed leaf like grain morphology with high mobility and low resistivity of 18.2 cm²/V-s and 0.7 Ω-cm, respectively.     

Copper sulfides obtained by spray pyrolysis — Possible absorbers in solid-state solar cells

Copper sulfide (Cu_xS, x = 1.8-2) thin films were deposited at 285 °C by spray pyrolysis from aqueous and alcoholic solutions of copper (II) chloride and thiourea with different Cu:S molar ratio. The XRD analysis showed that deposited films are chemically close to chalcocite (Cu₂S) or to mixtures of copper-rich phases (Cu₂S, Cu_1.8S, Cu_1.9375S) in which chalcocite or digenite (Cu_1.8S) is predominant. The films containing the single phase Cu₂S are denser and more homogenous than the films formed by two or more phases. The current-voltage (I-V) dark curves showed the diode behavior of the films, depending on the film thickness.     

The influence of annealing atmosphere on the phase formation of Cu–Sn–S ternary compound by SILAR method

The influence of annealing atmosphere on the phase formation of Cu–Sn–S ternary compound by SILAR method was studied. Structural, optical and electrical properties of the compound were studied for the samples annealed at 420 °C for 1 h in different atmosphere. X-ray diffraction and Raman spectra showed that Cu₂SnS₃ cubic phase was obtained in an atmosphere of nitrogen and sulfur vapor mixture, while Cu₄SnS₄ orthorhombic phase was obtained in H₂S atmosphere. An optical band-gap of 0.98 eV was obtained for Cu₂SnS₃ and 0.93 eV for Cu₄SnS₄ phase. The activation energies are about 0.1 eV for Cu₂SnS₃ phase and 0.06 eV for the Cu₄SnS₄ phase in high temperature region, but those are about 0.007 and 0.009 eV for them in low temperature region respectively.     

Formation of Cu2SnS3 thin film by the heat treatment of electrodeposited SnS–Cu layers

Thin films of copper tin sulfide (Cu₂SnS₃) were obtained by sulfurizing a stack of thin layers of Cu and SnS in nitrogen atmosphere. The film stack was obtained by the sequential electrodeposition of SnS and Cu. The Cu₂SnS₃ film was characterized for structural, morphological, composition, optical, spectroscopic, and electrical properties. The optimum condition for the formation of Cu₂SnS₃ was developed after testing different sulfurization temperatures. The films were polycrystalline with monoclinic structure which was confirmed by Raman and transmission electron microscopy analysis. The interplanar spacings estimated from the high resolution transmission electron microscopy images are 2.74, 2.19, and 2.06 Å. The average crystallite size is 13 nm, and the band gap of the film is in the range of 1 eV. The surface chemical composition determined by X-ray photoelectron spectroscopy showed the Cu:Sn:S ratio as 1.9:1:2.85 which is close to the stoichiometric Cu₂SnS₃. The films are p-type, photosensitive, and the conductivity measured in dark was in the range of 4 × 10^?3 Ω^?1 cm^?1. The comprehensive characterization presented in this paper will update the knowledge on this material.     

Liquid-state and solid-state interfacial reactions between Sn–Ag–Cu–Fe composite solders and Cu substrate

The growth kinetics and morphology of the interfacial intermetallic compound (IMC) between Sn–3Ag–0.5Cu–xFe (x = 0, 0.5 wt%, 1 wt%) composite solders and Cu substrate were investigated in the present work. The Sn–Ag–Cu–Fe/Cu solder joint were prepared by reflowing for various durations at 250 °C and then aged at 150 °C. During soldering process, Fe particles quickly deposited in the vicinity of IMC, resulting in the formation of Fe-rich area. Isothermal equation of chemical reaction and phase diagrams were used to explain the effect of Fe on the growth kinetics of IMC during liquid-state interfacial reaction. It was shown that Fe could effectively retard the growth of interfacial Cu₆Sn₅ and Cu₃Sn layers during liquid-state reaction and reduce the size of Cu₆Sn₅ grains. Small cracks were observed in the Cu₆Sn₅ grains after reflowing for 2 min while they were found in the other composite solders reflowing for about 30 min. The Fe tended to suppress the growth of the Cu₃Sn layer during solid-state aging. However, the total thickness of IMCs (Cu₆Sn₅ + Cu₃Sn) for the composite solders with Fe particles was similar to that for SnAgCu without Fe particles.     

Sulfurization time effects on the growth of Cu2ZnSnS4 thin films by solution method

Cu₂ZnSnS₄ (CZTS) films were obtained by sulfurizing (Cu, Sn) S/ZnS structured precursors prepared by a combination of the successive ionic layer absorption and reaction method and the chemical bath deposition method, respectively. The effect of sulfurization time on structure, composition and optical properties of these CZTS thin films was studied. The results of energy dispersive spectroscopy indicate that the annealed CZTS thin films are of Cu-poor and Zn-rich states. The X-ray diffraction studies reveal that Cu_2?x S phase exists in the annealed CZTS thin film prepared by sulfurization for 20 min, while the Raman spectroscopy analysis shows that there is a small Cu₂SnS₃ phase existing in those by sulfurization for 20 and 40 min. The band gap (E _g ) of the annealed CZTS thin films, which are determined by reflection spectroscopy, varies from 1.49 to 1.56 eV depending on sulfurization time. The best CZTS thin film is the one prepared by sulfurization for 80 min, exhibiting a single kesterite structure, dense morphology, ideal band gap (E _g  = 1.55 eV) and high optical absorption coefficient (>10⁴ cm^?1).     

Hydrogen sorption enhancement in cold-rolled and ball-milled CaNi<Subscript>5</Subscript>

The effect of cold rolling and ball milling on the hydrogen sorption properties of CaNi₅ was investigated with a special emphasis on the first hydrogenation. We compared cold rolling for 5, 12, and 25 rolling passes in the air with ball milling in argon for 30 and 60 min. Results show that 15 min of ball milling had a positive effect on the first hydrogen absorption, but further milling to 60 min made the sample almost impermeable to hydrogen. Cold rolling had a positive effect on first hydrogenation. We found that cold rolling greatly reduces the particle size as well as the crystallite size. We also found that dehydrogenation under 5 kPa of hydrogen at 323 K was not complete. Two partially hydride phases remained: CaNi₅H and Ca₂Ni₇H _x .     

Synthesis and Characterization of CuNi Magnetic Nanoparticles by Mechano-Thermal Route

In the present investigation, Cu_0.5Ni_0.5 nanoparticles were synthesized using high energy ball milling of a mixture of Cu₂O, NiO, and graphite powders. The mixture of powders was milled up to 50 h. The 30 h milled sample was heat treated at various temperatures for 1 h in a vacuum tube furnace. The effects of milling time and heat treatment temperature on the powder particle characteristics were studied employing X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), differential thermal analysis (DTA), and vibrating sample magnetometer (VSM) techniques. XRD results indicated incomplete formation of Cu_0.5Ni_0.5 after 30 h of milling. Further heat treatment at 500 ^°C led to the formation of a single phase Cu_0.5Ni_0.5 powder. FESEM and TEM images of the heat treated sample showed spherical Cu_0.5Ni_0.5 nanoparticles with a mean particle size of 15 nm. Magnetic properties data measured by VSM of the above sample are correlated well with the XRD results. Coercivity and saturation magnetization have been approximately achieved at 25 Oe and 18 emu/g, respectively.     

Metallothermic reduction of zinc sulfide induced by ball milling

Stoichiometric mixtures of ZnS + Al and ZnS + Mg were milled for different times in a planetary ball mill. The XRD traces of the as-milled samples showed the presence of zinc, MgZn₂, and MgS after 30-min milling in the ZnS–Mg system. The traces of MgZn₂ disappeared after 1-h milling and the reduction reaction seemed to have been completed after 5-h milling. The ZnS–Al system was somewhat different with only slight reduction to zinc after 1 h and ZnS peaks still present after 10 h of milling. Isothermal heating under argon atmosphere of 3-h-milled samples showed the presence of hexagonal ZnAl₂S₄ and mixtures of MgS and Zn_0.68Mg_0.32S in the ZnS–Al and ZnS–Mg systems, respectively. These results show that the reaction in the ZnS–Al system progressed gradually during milling. The decrease in the crystallite size of reactants materials (especially ZnS) during milling operation led to decrease in the formation temperature of hexagonal ZnAl₂S₄ phase and decrease in the transformation temperature of sphalerite (ZnS) to hexagonal wurtzite.     

Synthesis of Cu2ZnSnS4 films from sequentially electrodeposited Cu–Sn–Zn precursors and their structural and optical properties

The Cu₂ZnSnS₄ (CZTS) films are successfully prepared using a process of sequentially electrodeposited Cu–Sn–Zn precursors by a novel electrolyte formula and optimized parameters on Mo substrate, succeeded by annealing in saturated sulfur atmosphere. The results show that the Cu/Sn/Zn precursor sequence is strict, and optimized electro-deposition parameters are as follows: ?0.6 V, 5 min for Cu, ?1.2 V, 2 min for Sn, and ?1.35 V, 10 min for Zn. Layered precursors firstly alloy into Cu₆Sn₅ and CuZn binary phases under low annealing temperature. Then Cu₆Sn₅ and CuZn alloys decompose in sulfur atmosphere, and form CuS, SnS and ZnS binary phases. Cu₂SnS₃ ternary phase forms through reaction between CuS and SnS with increasing the temperature. Finally, the CZTS film is synthesized through reaction among binary and ternary sulfides. The photoluminescence peak from the CZTS films synthesized at 550 °C for 1 h is about at 1.49 eV.     

Structural evolution of B2-NiAl synthesized by high-energy ball milling

Structural evolution during the synthesis of B2–NiAl intermetallic compound by mechanical alloying of equiatomic elemental mixtures was studied by Rietveld analysis, DSC and HTXRD. The lattice parameter, crystallite size, microstrain, amount of phase and ordering of the B2 phase were monitored as a function of milling time. Formation of the B2–NiAl phase shows a sigmoidal behavior, which suggests that Johnson–Mehl–Avrami nucleation and interface-controlled growth are the responsible mechanisms in the transformation. Almost complete transformation (~ 97 mol%) was obtained after 25 h of milling. A specific phase transformation sequence during milling was not absolutely determined, however, the sequence Ni + Al → NiAl₃ → Ni₂Al₃ → B2–NiAl was identified by HTXRD. This sequence was confirmed by DSC. The transformation temperature of the B2–NiAl phase and the presence of additional intermetallic compounds show a direct dependence on the Ni–Al layer spacing. Using a production-scale Simoloyer horizontal Attritor Mill, the presence of Ni₂Al₃ phase was observed prior to the full synthesis of B2-NiAl.     

Mechanochemically driven amorphization of nanostructurized arsenicals,the case of β-As<Subscript>4</Subscript>S<Subscript>4</Subscript>

The amorphization is studied in mechanically activated β-As₄S₄ using high-energy ball milling in a dry mode with 100–600 min^?1 rotational speeds, employing complementary methods of X-ray powder diffraction (XRPD) related to the first sharp diffraction peak, positron annihilation lifetime (PAL) spectroscopy, and ab initio quantum-chemical simulation within cation-interlinking network cluster approach (CINCA). The amorphous substance appeared under milling in addition to nanostructurized β-As₄S₄ shows character XRPD halos parameterized as extrapolation of the FSDPs, proper to near-stoichiometric amorphous As–S alloys. The structural network of amorphized arsenicals is assumed as built of randomly packed multifold cycle-type entities proper to As₄S₄ network. The depressing and time-enhancing tendency in the PAL spectrum peak is direct indicative of milling-driven amorphization, associated with free-volume evolution of interrelated positron- and Ps-trapping sites. At lower speeds (200–500 min^?1), these changes include Ps-to-positron trapping conversion, but they attain an opposite direction at higher speed (600 min^?1) due to consolidation of β-As₄S₄ crystallites. In respect of CINCA modeling, the effect of high-energy milling is identified as destruction–polymerization action on monomer cage-type As₄S₄ molecules and existing amorphous phase, transforming them to amorphous network of triple-broken As₄S₄ derivatives. These findings testify in a favor of “shell” kinetic model of solid-state amorphization, the amorphous phase continuously generated under speed-increased milling being identified as compositionally authentic to arsenic monosulfide, different in medium range ordering from stoichiometric As₂S₃.     

X-ray powder diffraction line profile analysis of mechanically alloyed Cu–Cr powder

Abstract

Four different compositions of Cu–Cr system (Cu_0·90Cr_0·10, Cu_0·75Cr_0·25, Cu_0·60Cr_0·40 and Cu_0·50Cr_0·50) were mechanically alloyed using different milling parameters. Samples collected from the milled powder of 24 batches after different time intervals were studied by X-ray diffraction. The diffraction data were analysed by three different line profile analysis methods, namely, Williamson–Hall method, integral breadth method and peak fitting method to calculate the crystallite size and microstrain in the materials. Peak fitting and integral breadth methods were found to be more suitable for the systems under study. Logarithmic relationships between the milling time and crystallite size or microstrain are proposed. The model was further validated by time interpolated data from two of the present batches and two composition extrapolated batches (Cu_0·25Cr_0·75 and Cu_0·10Cr_0·90).     

Band gap tailoring,structural and morphological behavior of Zn0.96−x Co0.04Cu x O (0 ≤ x ≤ 0.10) alloys by sol–gel method

Zn_0.96?x Co_0.04Cu _x O (0 ≤ x ≤ 0.1) nanopowders were successfully synthesized by sol–gel method. Hexagonal structure was confirmed by X-ray diffraction spectra. A new phase around 38.4° corresponding to CuO was noticed after Cu = 4 %. The reduced crystal size up to Cu = 4 % is due to the substitution of Cu²⁺ and the increasing crystal size after Cu = 4 % is due to the interference between Co and Cu metal ions. The higher absorption of Cu doped Zn_0.96Co_0.04O than undoped was due to the created charge carries. The tuning of energy gap from 3.18 to 3.69 eV by Cu-doping was discussed in terms of crystal size, the created charge carriers and the interstitial zinc atoms and oxygen deficiencies. Presence of chemical bonding and purity of the nanopowders were confirmed by Fourier transform infrared spectra.     

Phase transformation and fracture behavior of Cu/In/Cu joints formed by solid–liquid interdiffusion bonding

In this paper, microstructure evolution and phase transformation of Cu–In intermetallic compounds in Cu/In/Cu joints formed by solid–liquid interdiffusion bonding at 260 and 360 °C were investigated respectively. The shearing properties and fracture behaviors of the Cu/In/Cu joints formed under different bonding conditions were also studied. For Cu/In/Cu joints bonded at 260 °C, Cu₁₁In₉ phase firstly generated and then Cu₂In phase formed between Cu₁₁In₉ layer and Cu substrate. For Cu/In/Cu joints bonded at 360 °C, Cu₂In phase firstly formed and then parts of Cu₂In grains transformed to Cu₇In₃ phase, and this transition from incomplete to complete coverage of Cu₂In/Cu₂In grain boundaries by Cu₇In₃ phases was observed with the bonding time increasing. The shear test results show that Cu₂In was high-quality phase which could improve the mechanical properties of Cu/In/Cu joints. After shear test, the fractures in Cu/In/Cu joints bonded at 260 °C were found at Cu₁₁In₉ layers and the fracture mode was cleavage fracture. In the case of the joints bonded at 360 °C, the intergranular fractures were found at the interface between Cu₂In layer and Cu₇In₃ layer while the cleavage fractures were found at Cu₇In₃ layer.     

Fabrication of Cu<Subscript>2</Subscript>SnS<Subscript>3</Subscript> thin-film solar cells with oxide precursor by pulsed laser deposition

In this paper, Cu₂SnS₃ (CTS) thin film is fabricated through sulfurization of oxide precursor which is deposited by pulsed laser deposition with a mixed CuO/SnO₂ target. XRD and Raman analyses indicate a pure monoclinic Cu₂SnS₃ phase has been obtained by sulfurization at temperature from 500 to 600 °C. A compact and smooth film with polycrystalline structure is observed through SEM result. In addition, the CTS films show excellent absorbance with the band gap around 0.91 eV estimated by UV–Vis, which is suitable for the absorption layer of solar cells. Final devices were fabricated with a SLG/Mo/CTS/CdS/i-ZnO/AZO/Al structure. Device performance is improved with the temperature increasing. The best efficiency of CTS-based solar cells is 0.69% with an open-circuit voltage of 144 mV and a short-circuit current density of 18.30 mA/cm^?2.