Fabrication of nanometer-to-micron sized Cu2O single crystals by electrodeposition

Nanometer-to-micron sized cuprous oxide (Cu₂O) single crystals were fabricated on Au/Pd sputter-coated silicon wafer and stainless steel cathode substrates by electrodeposition in CuSO₄ at pH 4.0 at room temperature (25 °C) with no additives. The Cu₂O crystals were generally of an octahedral shape with sizes ranging from 100 nm to 400 nm on Si wafer, and 1 μm to 3 μm on stainless steel substrates respectively. Very small crystals of a spherical shape were also observed under low applied voltage. Transient crystal shapes observed on the cathode near the electrolyte surface suggest that growth slows down once {1 1 1} free surfaces are formed, and this explains the robust observation of the octahedral crystal shape. The effect of electrodeposition parameters such as deposition voltage and deposition time on the size of the crystals and their coverage on the substrates was investigated. Apart from the cathode, similar octahedral Cu₂O nanocrystals were also found to deposit on the Cu anode used. This work provides a method to fabricate Cu₂O crystals on both electrodes in a single step.     

Preparation and shape evolution of cuprous oxide in the solution phases of copper (II) dodecyl sulfate

In this paper, the functionalized surfactant of copper dodecyl sulfate [Cu(DS)₂] was used both as the metal ion source and as the modifier to investigate the preparation and shape evolution of cuprous oxide (Cu₂O). The increase of Cu(DS)₂ concentration from 0.27 to 6.82 mM caused the morphological change of Cu₂O crystals from the truncated cubic to the cuboctahedral, then to the coexistence of the cubic and the truncated octahedral, and finally to the truncated octahedrons. As an experimental control, the inorganic salt of copper (II) chloride was also used as the metal ion source to conduct the precipitation of Cu₂O. These results indicate that the special adsorption of organic counterions (i.e., dodecyl sulfate ions) exerted a great influence on the shape control of Cu₂O crystals, especially at a relatively low concentration. Meanwhile, the d-glucose concentration and the incubation time of crystals were also considered. In conclusion, the competitive adsorption of surfactant ions and d-glucose molecules onto crystalline faces, as well as the aging time, accounted jointly for the shape control of Cu₂O crystals.     

Green sonochemical synthesis of cupric and cuprous oxides nanoparticles and their optical properties

Nanoparticles of cupric oxide (CuO) and cuprous oxide (Cu₂O) with various morphologies were synthesized by a green sonochemical process without any surfactants and templates. The Cu₂O nanoparticles with the truncated cubic, cubic octahedral and octahedral morphologies were prepared via the deoxidation of the CuO nanoparticles. The Cu₂O and CuO samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet visible absorption spectroscopy (UV–vis). The experimental results indicate that the molar ratio of sodium hydroxide to copper sulfate affects the morphology and size of the CuO and Cu₂O nanoparticles produced by the sonication. The band gap energy of CuO nanoparticles was 1.45–1.75 eV, the morphology had a great effect on the optical properties of CuO. The Cu₂O nanoparticles had broad emission peaks at the visible region, and the band gap energy was estimated to be 1.95–2.09 eV. The growth mechanisms of the CuO and Cu₂O nanoparticles are discussed.     

Potentiostatic electrodeposition of cuprous oxide thin films for photovoltaic applications

Potentiostatic deposition of Cu₂O thin films on glass substrates coated with F-doped SnO₂ from an alkaline electrolyte solution (pH 12.5) containing copper (II) sulfate and lactic acid was studied for fabrication of a Cu₂O/Al-doped ZnO (AZO) heterojunction solar cell. The band gap of the electrodeposited Cu₂O films was determined by photoelectrochemical measurements to be around 1.9 eV irrespective of the applied potentials. The solar cells with a glass/FTO/Cu₂O/AZO structure were fabricated by sputtering an AZO film onto the Cu₂O film followed by deposition of an Al contact by vacuum evaporation. The highest efficiency of 0.603% was obtained with a Cu₂O film deposited at −0.6 V (vs. Ag/AgCl). This was attributed to better compactness and purity of the Cu₂O film than those of the Cu₂O films deposited at other potentials.     

Facile preparation of Cu2O microcrystals with morphologies of octahedron, half circular and rectangular plates by anodic dissolution of bulk Cu in alkaline aqueous solutions

In this work, a facile electrochemical route i.e., anodic dissolution of bulk Cu at 2.0 V or more (vs. SCE) in a NaOH solution containing NH₂OH·HCl, was introduced for the synthesis of clean Cu₂O microcrystals (Cu₂O MCs) with morphologies of octahedron, half circular plate, etc. The bulk Cu electrode can be facilely dispersed into Cu(OH)₄²⁻ in alkaline solutions with the help of intense O₂ releasing. In the presence of reductive NH₂OH·HCl, Cu(II) was quickly reduced to Cu(I). Due to the concentration gradient of Cu(I) and OH⁻ resulting from the electrochemical reaction and the selective adsorption of OH⁻ on different crystal facets, half circular plate Cu₂O MCs were for the first time, synthesized. By changing the NaOH concentration or applied potential, octahedron and rectangular plate Cu₂O MCs could also be obtained. Scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) techniques, etc. were used to characterize the oxides. The Cu₂O MCs were phase-pure cubic Cu₂O. This electrochemical route is simple, basically green and can be used to synthesize Cu₂O MCs with different morphologies.     

Effect of electrodeposition and annealing of ZnO on optical and photovoltaic properties of the p-Cu2O/n-ZnO solar cells

Cu₂O/ZnO p–n heterojunction solar cells were fabricated by rf sputtering deposition of n-ZnO layer, followed by electrodeposition of p-Cu₂O layer. The different electrodeposition potentials were applied to deposit Cu₂O on ZnO. The particle size, crystal faces, crystallinity of Cu₂O is important factor which determine the p–n junction interface and consequently their effect on the performance of the heterojunction solar cell. It is observed that at −0.6 V, p-Cu₂O film generates fewer surface states in the interband region due to the termination of [1 1 0] resulting in higher efficiency (0.24%) with maximum particle size (53 nm). The bandgap of Cu₂O at this potential is found to be 2.17 eV. Furthermore, annealing of ZnO film was performed to get rid of deteriorating one and two dimensional defects, which always reduce the performance of solar cell significantly. We found that the solar cell performance efficiency is nearly doubled by increasing the annealing temperature of ZnO thin films due to increasing electrical conductance and electron mobility. Doping studies and fine tuning of the junction morphology will be necessary to further improve the performance of Cu₂O/ZnO heterojunction solar cells.     

Zn2 +-assisted synthesis of concave Cu2O crystals and enhanced photocatalytic properties

The effects of Zn^2 + on the structure Cu₂O crystals and photocatalytic decoloration of methylene orange (MO) were studied. Samples were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM), and Ultraviolet–Visible Spectroscopic (UV–VIS). The results indicated that Zn^2 + ions can transform the surface curvature of Cu₂O microcrystals from convex to concave. Tests of photodecoloration showed that the concave trisoctahedron Cu₂O microcrystals exhibited higher catalytic activity than those of octahedra Cu₂O and convex Cu₂O for MO under visible light.     

Synthesis and magnetic properties of Cu-doped ZnO nanowire arrays

Arrays of Cu-doped ZnO nanowires were successfully fabricated by electrodeposition of Zn²⁺ and Cu²⁺ into anodic aluminum oxide template and post-oxidation annealing in air atmosphere. The transmission electron microscopy result shows that the nanowires are uniform, about 100 nm in diameter and with the aspect ratio of up to 40. Selected area electron diffraction and X-ray diffraction results indicate that the nanowires are in hexagonal wurtzite structure. Magnetization measurements show that the Zn_1−xCu_xO (x = 0.07 and 0.11) nanowires exhibit room-temperature ferromagnetism and the enhancement of the ferromagnetism is revealed for the Zn_0.93Cu_0.07O nanowires annealed in vacuum.     

Simple synthesis of Cu2O/Na-bentonite composites and their excellent photocatalytic properties in treating methyl orange solution

Cu₂O/Na-bentonite (Cu₂O/NB) composites were firstly synthesized by a simple deposition method. The morphology and composition of the prepared catalysts were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR) spectroscopy, Brunauer–Emmett–Teller (BET) specific surface area. The results show that the Cu₂O microparticles can be immobilized on the surface of the NB. Visible-light photocatalytic properties of the Cu₂O/NB composites were evaluated using methyl orange (MO) as a model pollutant and the effects of various experimental factors on MO decolorization were investigated. Cu₂O/NB composites demonstrated a much higher photocatalytic activity than the pure Cu₂O particles under similar experimental conditions.     

Characterization of electrodeposited CuInSe2 (CIS) film

CuInSe₂ thin film was grown by one-step cathodic electrodeposition on Pt-coated glass using amperometry mode (fixed potential), in a three-electrode potentiostatic system containing the precursor solutions, 10 mM CuSO₄, 50 mM InSO₄, 30 mM SeO₂, and 0.1 M K₂SO₄ as a supporting electrolyte, at a pH of 1.5 (±0.1) adjusted with 0.1 M H₂SO₄. The structure, chemical composition, morphology, optical properties, and uniformity of the electrodeposited CuInSe₂ film were characterized by X-ray diffraction (XRD), electron probe micro analysis (EPMA), UV-vis-NIR spectrophotometry, field-emission scanning electron microscopy (FE-SEM), and Auger electron spectroscopy (AES), respectively. Several experiments were conducted in which the deposition voltage and post-annealing conditions were varied. As the applied deposition voltage was increased from −0.6 V to −0.7 V versus Ag/AgCl, a CuInSe₂ thin film with a chalcopyrite structure came to be predominantly formed, in accordance with the chemical composition, while the formation of the binary compounds (CuO and Cu_xSe) which influence the degradation of the performance in the application of CIS-based solar cells, rapidly decreased. The optimum conditions consisted of an annealing temperature of about 350 °C for 30 min under nitrogen ambient. At this temperature, a CuInSe₂ thin film, in the form of ternary compound, is formed with the required conditions, namely good crystallinity, good stoichiometry, a suitable bandgap, and depth uniformity.     

Enhanced high rate properties of ordered porous Cu2O film as anode for lithium ion batteries

Highly ordered porous Cu₂O film is electrodeposited on copper foil through a self-assembled polystyrene sphere template. Compared with the dense Cu₂O film and the octahedral Cu₂O powder, the ordered porous Cu₂O film exhibits an improved electrochemical cycling stability. The capacity of the porous Cu₂O film can maintain 336 mAh g⁻¹ and 213 mAh g⁻¹ after 50 cycles at the rate of 0.1 C and 5 C, respectively. The reversible capacity holds 63.4% as the discharge-charge rate even increases by 50 times. The enhanced high rate properties of the ordered porous film should be attributed to the sufficient contact surface of Cu₂O/electrolyte and the short diffusion length of Li⁺. Moreover, the direct contact between Cu₂O and current collector and the decreasing inactive interfaces of Cu₂O/polymer binder are also suggested as being responsible for the enhanced high rate property.     

Electrochemical properties of Cu2O/Cu composite particles prepared by a novel and facile method

Cu₂O/Cu composite particles were synthesized by a novel and facile chemical reduction method without any template or surfactant. X-ray diffraction (XRD) results showed that the product mainly consisted of the Cu₂O phase coexisting with a few Cu phases. Typical FE-SEM images indicated that the particles with an octahedral shape were Cu₂O. In addition, the electrochemical performance of the Cu₂O/Cu particles as the working electrode material in alkaline solution was systematically investigated. The particles showed a maximum discharge capacity of 222.9 mAh g⁻¹ at a discharge current density of 60 mA g⁻¹ and a high value of 109.1 mAh g⁻¹ after 50 charge–discharge cycles. The results of cyclic voltammetry demonstrated that the reaction between Cu₂O and Cu is the major electrochemical reaction during the charging and discharging process. The results of electrochemical impedance spectroscopy indicated that the formation of Cu₂O on the surface of Cu particles significantly increased the contact resistance and the charge transfer resistance of the electrode during the discharging process.     

Development of growth cycle for antimony telluride film on Au (1 1 1) disk by electrochemical atomic layer epitaxy

Electrochemical deposition of Sb₂Te₃ thin film on Au (1 1 1) disk via the route of electrochemical atomic layer epitaxy (ECALE) is described in this paper. Electrochemical aspects of Te and Sb on Au, Te on Sb-covered Au, and Sb on Te-covered Au were studied by means of cyclic voltammetry and coulometry. The apparent variation of coverage for Te or Sb on hetero-covered substrate is explained by considering the thermodynamic process of compound formation. A steady ECALE deposition for Sb₂Te₃ compound could be attained after negatively adjusting the underpotential deposition (UPD) potentials of Sb and Te on Au in steps over the initial 40 cycles, and the potentials could be kept constant for the following deposition. A 200-cycle deposit, which was grown with the steady deposition potentials, was proved to be a single phase Sb₂Te₃ compound by X-ray diffraction analysis. The 2:3 stoichiometric ratio of the deposit was further verified by energy dispersive X-ray (EDX) quantitative analysis. The p-type semiconductive property was demonstrated by measurements of the Seebeck coefficient and the electrical resistivity with a value of 145 μV/K and 9.37 μΩm, respectively. The morphologies of deposits with various growth cycle numbers were observed with FE-SEM. The evolvement mechanism of the morphology was investigated. The results show that the morphology of deposit has changed after initial potential adjustment and numberless thin sheets appeared and grew uprightly during the continuous cycle process. Fourier transform infrared spectroscopy (FTIR) absorption measurements suggested a band gap of 0.26 eV in very good agreement with literature reports for Sb₂Te₃ single crystals.     

Experimental determination of the eutectic temperature in air of the CuO-TiO2 pseudobinary system

Eutectic temperature and composition in the CuO-TiO₂ pseudobinary system have been experimentally determined in air by means differential thermal analysis (DTA), thermogravimetry (TG) and hot-stage microscopy (HSM). Samples of the new eutectic composition treated at different temperatures have been characterized by X-ray diffraction (XRD) and X-ray absorption near-edge structural spectroscopy (XANES) to identify phases and to determine the Cu valence state, respectively. The results show that the eutectic temperature in air is higher by 100 °C (∼1000 °C) for a Ti-richer composition (XTiO₂=25 mol%) than the one calculated in the literature. The reduction of Cu²⁺ to Cu⁺ takes places at about 1030 °C. The existence of Cu₂TiO₃ and Cu₃TiO₄ has been confirmed by XRD in the temperature range between 1045 and 1200 °C.     

Suppression of 3D mobility of carrier and superconductivity by Y substitution in Cu0.5Tl0.5Ba2(Ca2−xYx)Cu3O10−δ samples

Bulk Cu_0.5Tl_0.5Ba₂(Ca_2−xY_x)Cu₃O_10−δ superconductor ceramic samples were synthesized by the conventional solid-state method and characterized by X-ray diffraction, dc-resistivity, ac-susceptibility and Fourier Transform Infrared spectroscopy. The main purpose of this study was to investigate the role of charge carriers and the effect of Y substitution at Ca sites in between the CuO₂ planes on superconductivity. The superconducting properties are suppressed by Y substitution at Ca sites in between the CuO₂ planes of Cu_0.5Tl_0.5Ba₂(Ca_2−xY_x)Cu₃O_10−δ samples. It is most likely that Y³⁺ may create correlated domains in between the CuO₂ planes and localizes the carriers, which lowers the diamagnetic screening and suppresses the superconductivity. Therefore, cationic substitution reduces the three dimensional (3D) mobility of carriers, resulting in the reduction of the Fermi vector and velocity of the carriers, which in turn suppresses the superconducting properties of the material.     

Parametric Study on Dimensional Control of ZnO Nanowalls and Nanowires by Electrochemical Deposition

A simple electrochemical deposition technique is used to synthesize both two-dimensional (nanowall) and one-dimensional (nanowire) ZnO nanostructures on indium-tin-oxide-coated glass substrates at 70°C. By fine-tuning the deposition conditions, particularly the initial Zn(NO₃)₂·6H₂O electrolyte concentration, the mean ledge thickness of the nanowalls (50–100 nm) and the average diameter of the nanowires (50–120 nm) can be easily varied. The KCl supporting electrolyte used in the electrodeposition also has a pronounced effect on the formation of the nanowalls, due to the adsorption of Cl⁻ ions on the preferred (0001) growth plane of ZnO and thereby redirecting growth on the (10[`1] \bar{1} 0) and (2[`1] \bar{1} [`1] \bar{1} 0) planes. Furthermore, evolution from the formation of ZnO nanowalls to formation of nanowires is observed as the KCl concentration is reduced in the electrolyte. The crystalline properties and growth directions of the as-synthesized ZnO nanostructures are studied in details by glancing-incidence X-ray diffraction and transmission electron microscopy.     

Formation of LiNi0.5Co0.5VO4 nano-crystals by solvothermal reaction

LiNi_0.5Co_0.5VO₄ nano-crystals were solvothermally prepared using a mixture of LiOH·H₂O, Ni(NO₃)₂·6H₂O, Co(NO₃)₂·6H₂O and NH₄VO₃ in isopropanol at 150–200 °C followed by 300–600 °C calcination to form powders. TGA curves of the solvothermal products show weight losses due to evaporation and decomposition processes. The purified products seem to form at 500 °C and above. The products analyzed by XRD, selected area electron diffraction (SAED), energy dispersive X-ray (EDX) and atomic absorption spectrophotometer (AAS) correspond to LiNi_0.5Co_0.5VO₄. V–O stretching vibrations of VO₄ tetrahedrons analyzed using FTIR and Raman spectrometer are in the range of 620–900 cm⁻¹. A solvothermal reaction at 150 °C for 10 h followed by calcination at 600 °C for 6 h yields crystals with lattice parameter of 0.8252 ± 0.0008 nm. Transmission electron microscope (TEM) images clearly show that the solvothermal temperatures play a more important role in the size formation than the reaction times.     

Current oscillations during chronoamperometric and cyclic voltammetric measurements in alkaline Cu(II)-citrate solutions

It is demonstrated that current oscillations can be observed during chronoamperometric and cyclic voltammetric experiments in solutions containing 0.4 M CuSO₄ and 1.2 M citrate at pH 11 and 50 °C. The oscillations, which are shown to originate from local variations in the pH, result in the deposition of nanostructured Cu and Cu₂O materials. It is concluded that the current oscillations are analogous to the previously described potential oscillations obtained under controlled current conditions in alkaline Cu(II)-lactate, -tartrate and -citrate solutions. Rotating disk electrode results clearly show that the reduction of the Cu(II)-complexes is kinetically controlled and that the rate of the reduction increases with increasing pH and temperature. It is also shown that the presence of a cathodic peak on the anodic scan in the cyclic voltammograms can be used to identify the experimental conditions leading to the spontaneous current (or potential) oscillations. Electrochemical quartz crystal microbalance results indicate that the cathodic peak stems from an increased rate of the reduction of the Cu(II)-citrate complexes due to a rapid increase in the local pH. This causes Cu₂O rather than Cu to be deposited which, however, results in a decrease in the local pH and a decreasing current. In situ ellipsometry data confirm that Cu₂O deposition replaces that of Cu in the potential region of the cathodic peak. The present findings should facilitate syntheses of nanolayered materials based on spontaneous potential or current oscillations.     

Adsorption of gaseous SO2 and structural changes of montmorillonite

Several montmorillonite samples after adsorption of gaseous SO₂ were analyzed to evaluate structural and textural changes. The equilibrium adsorption of the SO₂ gas was measured at 25 °C and 0.1 MPa. The samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), swelling index (SI), pH measurements, and N₂ adsorption–desorption isotherms. SO₂ adsorption increased with the specific surface area of montmorillonite. SO₂ retention decreased pH of the dispersed samples from 6 to 1 and released interlayer and octahedral cations from the structure, which increased the specific BET surface area and specific micropore surface similar to that of acid-activated montmorillonite.     

Surface-initiated growth of copper using isonicotinic acid-functionalized aluminum oxide surfaces

Isonicotinate self-assembled monolayers (SAM) were prepared on alumina surfaces (A) using isonicotinic acid (iNA). These functionalized layers (iNA-A) were used for the seeded growth of copper films (Cu-iNA-A) by hydrazine hydrate-initiated electroless deposition. The films were characterized by scanning electron microscopy (SEM), electron-dispersive X-ray spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and advancing contact angle measurements. The films are Cu⁰ but with surface oxidation, and show a faceted morphology, which is more textured (R _q = 460 ± 90 nm) compared to the SAM (R _q = 2.8 ± 0.5 nm). In contrast, growth of copper films by SnCl₂/PdCl₂ catalyzed electroless deposition, using formaldehyde (CH₂O) as the reducing agent, shows a nodular morphology on top of a relatively smooth surface. No copper films are observed in the absence of the isonicotinate SAM. The binding of Cu²⁺ to the iNA is proposed to facilitate reduction to Cu⁰ and create the seed for subsequent growth. The films show good adhesion to the functionalized surface.