Effect of temperature on crystallite sizes of copper sulfide nanocrystals prepared from copper(II) dithiocarbamate single source precursor

We report the synthesis of CuS nanoparticles using [Cu(butdtc)₂] as single source precursor thermolysed at two different temperatures. The products were characterized by UV–vis absorption spectroscopy, X-ray diffraction, Transmission electron microscopy, scanning electron microscopy, energy dispersive X-ray analysis and atomic force microscopy. The absorption spectra of the CuS nanocrystals are blue shifted and the XRD were indexed to the hexagonal phase of CuS with nanoparticles obtained at 120 °C showing well defined crystalline structure compared to those obtained at 180 °C. Transmission electron microscopy images showed particles that are almost spherical in shapes with average crystallite sizes of 21–38 nm for CuS1 prepared at 180 °C and 3–7 nm for CuS2 prepared at 120 °C and confirms that the chosen reaction temperature determine the crystallite sizes of the nanoparticles.     

Effect of preheating and annealing temperature on the microstructure and optoelectronic properties of CZTS films prepared by sol-gel method

The effects of different preheating and annealing temperatures on the surface morphology, microstructure, and optical properties of Cu2ZnSnS4 (CZTS) thin films are investigated by controlling the preheating and annealing temperatures. The prepared thin films were characterized using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and ultra-violet-visible (UV-Vis) spectroscopy techniques. XRD and Raman spectroscopy showed that a Kesterite structure with a selective orientation along the (112) peak was generated, and the thin films produced at a preheating temperature of 300 °C and annealing temperature of 570 °C had fewer secondary phases, which was beneficial for improving the performance of the solar cells. SEM confirms that the crystallite size increases and then decreases as the temperature increases, and the largest and most uniform crystallite size with the smoothest surface is generated at the above preheating and annealing temperatures. UV-Vis measurements show that the thin films generated at the above temperature have the lowest transmittance and the lowest optical band gap value of 1.46 eV, which is close to the optimal band gap value for solar cells and is suitable as an absorber layer material.     

Effect of calcination temperature on Cu doped NiO nanoparticles prepared via wet-chemical method: Structural,optical and morphological studies

In the present study, NiO and Cu-doped NiO nanoparticles were successfully synthesized by wet chemical method at room temperature using sodium hydroxide (NaOH) as precipitating agent. The as-prepared Cu-doped NiO powder samples were subjected to three different calcination temperatures such as, 350 °C, 450 °C and 550 °C in order to investigate the impact of calcined temperatures on the phase formation, particle size and band gap evolution. The phase formation and crystal structure information of the prepared nanomaterials were examined by X-ray powder diffraction (XRD). XRD revealed the face-centered cubic (FCC) structure. Average crystalline size of pure and doped samples estimated using Scherer formula was found to be 15 nm and 9 nm respectively. With increase in the calcination temperature from 350 °C to 550 °C for the Cu doped NiO samples the particle size of the nanoparticles was found to increase from 4 nm to 9 nm respectively. The optical study for both pure and doped NiO nanoparticles was performed using an UV–Vis spectrophotometer in the wavelength range of 200–800 nm. The strong absorption in the UV region confirms the band gap absorption in NiO and was estimated from the UV–Vis diffuse reflectance spectra via Tauc plot. Systematic studies were also carried out to study the effect of calcination on the optical transmittance. Samples were also investigated using Raman and Fourier Transform Infrared Spectroscopy (FTIR). Furthermore, morphology of the pure NiO and Cu-doped NiO Nanoparticles were examined by scanning electron microscope (SEM).     

Quantum confinement and size effects in Cu2ZnSnS4 thin films produced using solution processed ultrafine nanoparticles

Copper–zinc–tin-sulfide (Cu₂ZnSnS₄, abbreviated as CZTS) is a direct band gap p-type semiconductor material with high absorption coefficient. Using oleylamine as solvent/stabilizing agent and metal chlorides and sulfur particles as chemical precursors, CZTS based nanoparticles were produced and subsequently deposited as thin films on glass substrates via spin coating of the nanoinks. The effect of temperature on crystallite size and phase composition was assessed after the solution mixture was undercooled by 30, 70 or 90 °C. Upon cooling the solution from 230 to 140 °C i.e. by 90 °C, maximum refinement in the nanoparticles size was noticed with average size on the order of few nanometers. The morphological and compositional studies of the nanoparticles were performed by means of scanning electron microscope, X-ray diffraction and Fourier transform infrared spectroscopy techniques. Phase-pure CZTS formation was confirmed from fast Fourier transform (FFT) patterns and lattice fringes observed during HR-TEM examination. Characterization of the annealed spin coated films, made from nanoink containing ultrafine nanoparticles, indicated morphological changes in the film surface during air annealing at 350°C that can be attributed to depression of CZTS phase decomposition temperature. Spectrophotometric studies of the annealed films suggested quantum confinement effect through an associated increase in the band gap value from 1.34 to 2.04 eV upon reduction in the nanoparticle size caused by increasing the degree of undercooling to 90 °C.     

Effect of deposition temperature on structural,optical properties and configuration of CdSe nanocrystalline thin films deposited by chemical bath deposition

CdSe nanoparticle thin films were deposited on glass substrates by the chemical bath deposition (CBD) method at low deposition temperature ranging from room temperature up to 50 °C while the pH of the bath was kept constant at 12.1. The structural and morphological variation were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) technique. The energy band gap and optical properties were characterized by the absorbance spectra. Rutherford backscattering spectroscopy (RBS) analysis reveals the excess of Cd rather than Se in depth profile along the thin film thickness. The prepared CdSe nanoparticles have cubic structure and by increasing the temperature the deposited films become continues, homogeneous and tightly adherent. The results also revealed that by increasing the deposition temperature from room temperature up to 50 °C, the band gap decreases from 3.52 eV up to 1.84 eV.     

Synthesis,characterization and optical band gap of La2CuO4 nanoparticles

Pure La₂CuO₄ nanoparticles were synthesized via sol–gel process using stearic acid as complexing reagent. This method consists of the formation of an organic precursor, with metallic cations homogeneously distributed throughout the matrix. The gel was calcined at 700 °C, 800 °C and 900 °C for 4 h. The as-prepared La₂CuO₄ nanoparticles were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy and diffuse reflectance spectroscopy. Results show that the purity of La₂CuO₄ crystallites increases with the increase of heat treatment temperature from 700 °C to 900 °C. Optical properties show that La₂CuO₄ crystallites have broad absorption in the UV–vis region and the corresponding band gap is 1.24 eV.     

<Emphasis Type="Italic">In Situ</Emphasis> Study of Reduction Process of CuO Paste and Its Effect on Bondability of Cu-to-Cu Joints

A bonding method utilizing redox reactions of metallic oxide microparticles achieves metal-to-metal bonding in air, which can be alternative to lead-rich high-melting point solder. However, it is known that the degree of the reduction of metallic oxide microparticles have an influence on the joint strength using this bonding method. In this paper, the reduction behavior of CuO paste and its effect on Cu-to-Cu joints were investigated through simultaneous microstructure-related x-ray diffraction and differential scanning calorimetry measurements. The CuO microparticles in the paste were gradually reduced to submicron Cu₂O particles at 210–250°C. Subsequently, Cu nanoparticles were generated instantaneously at 300–315°C. There was a marked difference in the strengths of the joints formed at 300°C and 350°C. Thus, the Cu nanoparticles play a critical role in sintering-based bonding using CuO paste. Furthermore, once the Cu nanoparticles have formed, the joint strength increases with higher bonding temperature (from 350°C to 500°C) and pressure (5–15 MPa), which can exceed the strength of Pb-5Sn solder at higher temperature and pressure.     

Low temperature synthesis of PbS and CdS nanoparticles in olive oil

Heterocyclic dithiocarbamate complexes; bis(dipiperidinyldithiocarbamato)M(II) and bis(ditetrahydroquinolinyldithio-carbamato)M(II), M= Pb and Cd, were used as precursors for the synthesis of PbS and CdS in olive oil. The precursors were thermolysed at a relatively low temperature of 180 °C. Distinct cube shaped PbS nanoparticles were obtained with the X-ray diffraction peaks assigned to the cubic rock salt phase. The optical properties of the olive-oil capped CdS particles synthesized at 180 °C showed evidence of quantum confinement. The CdS particles obtained from both precursors were spherical in shape with evidence of agglomeration in the transmission electron microscopy images.     

Interfacial Reactions Between Pb-Free Solders and In/Ni/Cu Multilayer Substrates

This study investigates the interfacial reactions between Sn-3.0wt.% Ag-0.5wt.%Cu (SAC) and Sn-0.7wt.%Cu (SC) on In/Ni/Cu multilayer substrates using the solid–liquid interdiffusion bonding technique. Samples were reflowed first at 160°C, 180°C, and 200°C for various periods, and then aged at 100°C for 100 h to 500 h. The scalloped Cu₆Sn₅ phase was formed at the SAC/In/Ni/Cu and SC/In/Ni/Cu interfaces. When the reflowing temperatures were 160°C and 180°C, a ternary Ni-In-Sn intermetallic compound (IMC) was formed when the samples were further aged at 100°C. This ternary Ni-In-Sn IMC could be the binary Ni₃Sn₄ phase with extensive Cu and In solubilities, or the ternary Sn-In-Ni compound with Cu solubility, or even a quaternary compound. As the reflow temperature was increased to 200°C, only one Cu₆Sn₅ phase was formed at the solder/substrate interface with the heat treatment at 100°C for 500 h. Mechanical test results indicated that the formation of the Ni-In-Sn ternary IMC weakened the mechanical strength of the solder joints. Furthermore, the solid–liquid interdiffusion (SLID) technique in this work effectively reduced the reflow temperature.     

Optical and electrical properties of crystalline indium tin oxide thin film deposited by vacuum evaporation technique

Indium tin oxide (ITO) thin film was deposited on glass substrate by means of vacuum evaporation technique and annealed at 200 °C, 300 °C and 400 °C in air for 1 h. The characterization and properties of the deposited film samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-VIS-NIR spectroscopy techniques. From the XRD patterns, it was found that the deposited thin film was of crystalline at an annealing temperature of 400 °C. The crystalline phase was indexed as cubic structure with lattice constant and crystallite size of 0.511 nm and 40 nm, respectively. The SEM images showed that the films exhibited uniform surface morphology with well-defined spherical grains. The optical transmittance of ITO thin film annealed at 400 °C was improved from 44% to 84% in the wavelength range from 250 nm to 2 100 nm and an optical band gap was measured as 3.86 eV. Hall effect measurement was used to measure the resistivity and conductivity of the prepared film.     

Synthesis and characterization of Cu2ZnSnS4 from Cu2SnS3 and ZnS compounds

The Cu2ZnSnS4 (CZTS) powders are successfully synthesized by using ZnS and Cu2SnS3 as raw materials directly without any intermediate phase at 450 °C for 3 h in Ar atmosphere. The crystalline structure, morphology and optical properties of the CZTS powders are characterized by X-ray diffraction (XRD), Raman spectrum, field emission scanning electron microscopy (FESEM) and ultraviolet-visible (UV-vis) spectrophotometer, respectively. The results show that the band gap of the obtained CZTS is 1.53 eV. The CZTS film is fabricated by spin coating a mixture of CZTS powders and novolac resin with a weight percentage of 30%. The photoelectrical properties of such CZTS films are measured, and the results show an incident light density of 100 mW.cm-2 with the bias voltage of 0.40 V, and the photocurrent density can approach 9.80×10-5 A.cm2within 50 s, giving an on/off switching ratio of 1.64.     

Annealing effects on physical properties of doped CdTe thin films for photovoltaic applications

Polycrystalline Cadmium Telluride (CdTe) thin films were prepared on glass substrates by thermal evaporation at the chamber ambient temperature and then annealed for an hour in vacuum ~1×10⁻⁵ mbar at 400 °C. These annealed thin films were doped with copper (Cu) via ion exchange by immersing these films in Cu (NO₃)₂ solution (1 g/1000 ml) for 20 min. Further these films were again annealed at different temperatures for better diffusion of dopant species. The physical properties of an as doped sample and samples annealed at different temperatures after doping were determined by using energy dispersive x-ray analysis (EDX), x-ray diffraction (XRD), Raman spectroscopy, transmission spectra analysis, photoconductivity response and hot probe for conductivity type. The optical band gap of these thermally evaporated Cu doped CdTe thin films was determined from the transmission spectra and was found to be in the range 1.42–1.75 eV. The direct energy band gap was found annealing temperatures dependent. The absorption coefficient was >10⁴ cm⁻¹ for incident photons having energy greater than the band gap energy. Optical density was observed also dependent on postdoping annealing temperature. All samples were found having p-type conductivity. These films are strong potential candidates for photovoltaic applications like solar cells.     

Preparation and Characterization of CdTe for Solar Cells,Detectors, and Related Thin-Film Materials

Cadmium telluride (CdTe) thin films were prepared by the close-space sublimation (CSS) technique, using 99.99% pure CdTe powder as the evaporant. Films were then annealed at 400°C for 30 min and were later dipped in Cu(NO₃)₂-H₂O solution at 80 ± 2°C. After immersion these films were again annealed at 400°C for 1 h to ensure the Cu diffusion into the films. X-ray diffraction (XRD) results confirmed the formation of a new compound copper telluride and a change in the morphology was observed by scanning electron microscopy (SEM). The DC electrical resistivity reduced from 10⁶ Ω-cm for as-deposited to 10⁻³ Ω-cm for 15 h immersed film. As the wt.% of Cu increased, the mobility increased to some extent, while the carrier concentration showed a systematic increase. The film thickness and optical parameter such as refractive index, absorption coefficient, and the optical band gap were deduced by fitting the optical transmittance in the wavelength range 300 to 3000 nm. The transmission decreased with increasing immersion time of films in the␣solution. The Cu concentration was recorded as 0.9 wt.% for 3 min to 56.6 wt.% for 15 h immersed samples using an electron microprobe analyzer (EMPA). In the next step, ITO/CdS/CdTe heterojunctions with 10.9% solar cell efficiency were fabricated on glass slides.     

Effects of Cu/In ratio and annealing temperature on physical properties of dip-coated CuInS2 thin films

CuInS₂ thin films were prepared by sol–gel dip-coating method on glass substrates using 0.75, 1 and 1.25 ratios of Cu/In in the solution. The prepared films were annealed at 380 °C, 420 °C and 460 °C for 30 min under argon environment. The structural, optical, morphological and composition properties of those were investigated by X-ray diffraction (XRD), UV–vis transmittance spectroscopy and scanning electron microscopy with an energy dispersive X-ray spectrometer. The XRD results showed that the films exhibit polycrystalline tetragonal CuInS₂ phase with (112) orientation. According to the EDX results the Cu/In ratios of the films were respectively 0.65, 0.92 and 1.35 for the Cu/In ratios of 0.75, 1 and 1.25 in the solutions. The optical band gap was found to be between 1.30 eV and 1.43 eV, depending on Cu/In ratio.     

Temperature-Dependent Phase Segregation in Cu/42Sn-58Bi/Cu Reaction Couples under High Current Density

The effects of current stressing at 10⁴ A/cm² on Cu/42Sn-58Bi/Cu reaction couples with a one-dimensional structure at 23°C, 50°C, and 114°C were investigated. The microstructural evolution during electromigration was examined using scanning electron microscopy. The temperature dependence of the coarsening of the Bi-rich phase, the dominant migrating entity, and hillock/whisker formation in eutectic Sn-Bi were investigated under high current density. During current stressing at 10⁴ A/cm², the average size of the Bi-rich phase remained the same at 23°C, increased at 50°C, and shrank at 140°C. Bi accumulated near the anode side at both high (50°C, 140°C) and low temperature (23°C). At high temperatures, both Sn and Bi diffused towards the anode side, but Bi moved ahead of Sn during current stressing. However, at low temperatures, Sn reversed its direction of migration to the cathode side. Pure Bi hillocks/whiskers and a mixed structure of Sn and Bi hillocks were extruded as a consequence of compressive stress from electromigration- induced mass flow towards the anode side.     

Study of Structural,Electrical and Optical Properties of (200)-Oriented CdTe Thin Films Depending on the Post-deposition Low Temperature

Cadmium telluride nanoparticles (CdTe NPs) have been synthesized by a sonochemical technique, deposited on glass and quartz glass at 100°C and 2.7?×?10^?6 kPa and then studied by analyzing the x-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV–Vis), current–voltage test (I–V) and scanning electron microscopy (SEM). The XRD results indicated the formation of a strong preferential (200) orientation of CdTe with a cubic zinc-blende structure on both substrates. In order to show the effect of heating on the structure and optical properties of the prepared thin films, they were annealed at temperatures of 50°C, 70°C and 100°C for 1 h. It was found that the grain size in this orientation increases with the increase of the temperature. In addition, the obtained optical band gap energies by UV–Vis measurements were in the range of 1.46–1.53 eV. The electrical properties of the prepared films were observed to increase with annealing using I–V measurements. The thin films were also found to be uniform with a small particle size, as revealed by SEM.

     

The Effects of Solid-State Aging on the Intermetallic Compounds of Sn-Ag-Bi-In Solders on Cu Substrates

The growth behavior of the intermetallic compounds that formed at the interfaces between Sn-Ag-Bi-In solders and Cu substrates during solid-state aging is investigated. The compositions of the intermetallic compounds are Cu₃(Sn,In) near the Cu substrates and Cu₆(Sn,In)₅ near the solders; very little Bi or Ag was dissolved in the compounds. The aging temperatures were 120°C, 150°C, and 180°C for 5 days, 10 days, 20 days, and 40 days. The change in the morphology of Cu₆(Sn,In)₅ from scallop type to layer type was prominent at the aging temperature of 180°C. The thickness of the compound layers did not vary much at the lower aging temperatures but followed the diffusion- controlled mechanism at 180°C. Massive Kirkendall voids were observed in Cu₃(Sn,In) layers at the aging temperature of 180°C.     

The optical band gap of hydrogenated amorphous boron thin films: The effect of substrate temperature

Hydrogenated amorphous boron thin films have been produced on quartz substrates heated to 150, 250, and 350°C by the glow discharge decomposition of a gas mixture of 5 v/o BoHg and 95 v/o H₂. Doped films have also been prepared by the addition of 1 a/o C₂H₄ or 0.5 a/o SiH₄. The absorp-tion coefficients as a function of wavelength across the visible spectrum and the concomitant optical band gaps of all films were measured. The optical band gaps of the films produced at 150 and 250°C were approximately 2.1 eV while those films produced at 350°C showed band gaps between 1.6 and 1.4 eV. These results indicate that it is possible to optimize theroretical photovoltaic conversion efficiencies of solar cells based on hydrogenated amorphous boron thin films produced by glow discharge methods through the tailor-ing of the optical band gap by control of substrate temper-ature.     

The formation of Cu2O nanoparticles in polyimide using Cu electrodes via chemical curing,and their application in flexible polymer memory devices

Flexible polymer memory devices were fabricated based on 4,4′-(hexafluoroisopropylidene)diphthalic anhydride-4,4′-oxydianiline (6FDA-ODA) polyimide (PI)/Cu₂O nanocomposite via chemical curing, heat treatment, and post-heat treatment at low temperature (<200 °C). Following the deposition of a Cu bottom electrode on a commercial PI film substrate, a PI precursor, polyamic acid (PAA) was spin-coated onto the Cu bottom electrode, and Cu was dissolved into the PAA, providing Cu ions for particle formation. The 6FDA-ODA PAA–Cu complex was imidized via chemical curing using acetic anhydride and triethylamine at 50 °C, and thermal treatment was performed at 200 °C in a reducing atmosphere to remove the solvent completely and precipitate Cu nanoparticles. Post-heat treatment was sequentially carried out at 150 °C in an oxidizing atmosphere to oxidize Cu to Cu₂O. The Al top electrode was deposited onto the 6FDA-ODA PI/Cu₂O nanocomposite film, and the flexible memory device with a crossbar array showed an ON/OFF ratio of ∼10⁴, endurance of 60 cycles, retention time of 10⁴ s, and device yield of 86% (31 cells out of total 36 cells) under flat and bending conditions (bending radius ∼1.5 mm) when the electrical measurements were performed in air at room temperature.     

Tuning the Properties of CZTS Films by Controlling the Process Parameters in Cost-Effective Non-vacuum Technique

Highly dispersive Cu₂ZnSnS₄ (CZTS) nanoparticles were successfully synthesized by a simple solvothermal route. A low cost, non-vacuum method was used to deposit CZTS nanoparticle ink on glass substrates by a doctor blade process followed by selenization in a tube furnace to form Cu₂ZnSn (S,Se)₄ (CZTSSe) layers. Different selenization conditions and particle concentrations were considered in order to improve the crystallinity and surface morphology; the annealing temperature was varied between 400°C and 550°C and the annealing time was varied between 5 min and 20 min in a selenium-nitrogen atmosphere. The influence of annealing conditions on structural, compositional, optical and electrical properties of CZTSSe thin films was studied. An improvement in the structural and surface morphology was observed with increasing of annealing temperature (up to 500°C). An enhancement in the crystallinity and surface morphology were observed for thin films annealed for 10–15 min. Absorption study revealed that the band gap energy of as-deposited CZTS thin film was approximately 1.43 eV, while for CZTSSe thin films it ranged from 1.15 eV to 1.34 eV at different annealing temperatures, and from 1.33 eV to 1.38 eV for different annealing times.