Solution-phase synthesis of Cu2O cubes using CuO as a precursor

We describe a facile route for the synthesis of Cu₂O cubes using CuO as the precursor and hydrazine hydrate as the reducing agent. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations indicate that the Cu₂O products are composed of cubes with an edge length of 0.7-1.2 μm. This method is surfactant-free, and well-dispersed Cu₂O cubes can be obtained through this route. The presence of small amounts of ions in reaction solution has a great influence on the morphology of Cu₂O products.     

Self-generation of three-dimensional hierarchical Cu2S architectures at room temperature

A simple approach is proposed to realize the three dimensional (3D) hierarchical Cu₂S architectures at room temperature in this letter. The 3D Cu₂S architectures are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectrum (XPS). The effects of synthetic conditions, such as reaction time and the amount of reagents, on the morphology of the product are investigated. The growth mechanism of the product is proposed, based on the evolution of the morphologies with the increasing of reaction time. Our work provides a facile and easy method on designing for the fabrication of 3D hierarchical architecture materials.     

Optoelectronic properties of sputter-deposited Cu2O-Ag-Cu2O treated with rapid thermal annealing

Cu₂O and two types of Cu₂O-Ag-Cu₂O (CAC) multilayered thin films were deposited on glass substrates using DC-magnetron sputtering. For CAC films, the mass thickness of Ag layer was controlled at 3 nm. After deposition, some of these films were annealed using a rapid thermal annealing (RTA) system at 650 °C, in order to create embedded Ag particles. AC films were used to study the clustering effect of Ag in Ar atmosphere, as well as for forming the 2nd type of CAC film by covering another Cu₂O layer on the annealed AC structure. A UV-VIS-NIR photometer, a Hall measurement system, and a I-V measurement system were used to characterize the optical and electrical properties of these films with and without RTA. The results show that 2-dimensional Ag layer can transform into many individual particles due to its high surface tension at annealing temperature, no matter when the annealing was carried out. For CAC films, without annealing, the optical transmission and the resistivity are decreased with the inserted Ag layer. After annealing, both the transmission and resistivity are increased, possibly due to the clustering effect of Ag layer. Most importantly, it is found that the embedded Ag particles can increase the light absorption in the NIR-IR region, which can increase photo-induced current.     

Mechanisms of carrier generation and transport in Ni-doped Cu2O

The density and mobility of hole carriers in Ni-doped and undoped cuprous oxide (Cu₂O) films prepared by pulsed laser deposition (PLD) from Ni-doped and undoped CuO targets, respectively, were measured in order to examine the mechanisms of carrier generation and transport in doped films. The temperature dependence of the carrier density of the films revealed that regardless of the Ni content, the activation energies of the acceptor level of the films are 0.22-0.25 eV. The temperature dependence of the mobility of the films changed from −0.58 to ∼0 by doping with Ni. These results evidenced that hole carriers in Ni-doped Cu₂O as well as in undoped Cu₂O were generated by Cu vacancies and were primarily scattered by neutral impurity scattering centers. X-ray diffraction (XRD) measurements of the films showed that the mass fraction of Cu₂O in the films decreased with increasing Ni content, while that of CuO increased. It was also found that the reduction process of CuO to Cu₂O was suppressed by the Ni doping.     

Synthesis of Cu2O crystals by galvanic deposition technique

A simple galvanic deposition technique has been developed to demonstrate the deposition of cuprous oxide (Cu₂O) on transparent conducting oxide substrate for the first time. The result shows that the morphologies of galvanically obtained Cu₂O crystals are mainly dependent on the nature of anions in aqueous solution. The presence of NO₃⁻ ions tends to increase the stability of (111) planes of Cu₂O cubes and makes the crystals develop a fraction of (111) planes at the corners of the Cu₂O cubes, thus resulting in the formation of truncated octahedral Cu₂O crystals.     

Effect of annealing on the electrodeposited Cu2O films for photoelectrochemical hydrogen generation

Cu₂O films were electrodeposited on stainless steel substrates followed by Ar annealing for photoelectrochemical hydrogen generation. Plating variables including time and pH for the plating bath were explored to obtain desirable film qualities. X-ray diffraction (XRD) patterns indicated that the as-deposited Cu₂O films exhibited preferred orientations in (200) and (111) planes from the plating bath of pH 9 and pH 11, respectively. Images from scanning electron microscope (SEM) revealed pyramid-like grains in 1 µm size for the Cu₂O films from pH 9 plating bath and large plate-like grains in 3-8 µm size from pH 11 plating bath. Identical results from SEM and XRD were obtained from the Cu₂O films at longer plating time. After annealing at 350 °C for 30 and 60 min, the Cu₂O phase was nicely maintained but SEM images demonstrated coarser grains. Photoelectrochemical activity for H₂ generation was obtained on the Cu₂O films before and after annealing by recording relevant photoelectrochemical currents at − 0.3 V in 0.5 M aqueous Na₂SO₄ solution. For the Cu₂O films from both baths, substantial increments in photoelectrochemical current were observed for the annealed samples as opposed to as-deposited ones. The largest photoelectrochemical current was obtained at 0.143 mA/cm² from the Cu₂O film of pH 9 plating bath with 60 min annealing, which exhibited a 560% increase over the as-deposited sample. We attributed the enhanced photoelectrochemical current to the improved crystallinity and reduced defects for the annealed Cu₂O films.     

Fabrication and photocatalytic property of ZnO nanorod arrays on Cu2O thin film

ZnO nanorod arrays were fabricated on Cu₂O thin film by a simple low-temperature liquid-phase-deposition method. The samples were characterized by X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FESEM). The UV-Vis spectroscopy showed that the obtained sample was able to absorb a large part of visible light (up to 650 nm). Their photocatalytic activities were investigated by degradation of dye methylene blue (MB) under UV-Vis and visible light irradiation. It was found that the photocatalytic activity of the ZnO/Cu₂O NRs was higher than the ZnO/ZnO NRs under UV-Vis light. In a word, Cu₂O played an important role in enhancing the photocatalytic activity of the ZnO/Cu₂O NRs.     

Repeatable synthesis of Cu2O nanorods by a simple and novel reduction route

Cu₂O nanorods were synthesized by reducing bamboo leaf-shaped Cu(OH)₂ with sodium hypophosphite (NaH₂PO₂) in an H₂O/ethylene glycol (EG) mixing solution. The Cu(OH)₂ was prepared by adding an alkaline solution to an aqueous solution containing CuSO₄ and NaH₂PO₂ at room temperature. The optimum temperature range for the reduction of the Cu(OH)₂ to Cu₂O nanorods was 55-70 °C. The products were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and high-resolution transmission electron microscopy. The result showed the prepared Cu₂O nanorods were uniform and had diameters of 10-20 nm and lengths of 150-200 nm. The synthesis is simple, inexpensive, and highly repeatable.     

Shape controlled synthesis and characterization of Cu2O nanostructures assisted by composite surfactants system

A simple methodology has been demonstrated to synthesize various nanocrystalline Cu₂O materials assisted by composite surfactant system, SDS and Tween 80 using the polyol method. Glycolaldehyde prepared in situ by heating ethylene glycol solvent at 160 °C for 2 h, was utilized as the reducing agent. The relative ratio of the two surfactants was manipulated to achieve different Cu₂O morphologies, e.g. nanocrystalline Cu₂O flowers, hollow spheres consisting of holes and ring type structure. The FT-IR spectroscopy confirmed that the SDS and Tween 80 moieties were indeed present on the surface as capping agents in order to stabilize the surface nanocrystallites by the co-ordinative interactions between the oxygen atoms of Tween 80 and SDS and the Cu atoms at the surface of the synthesized Cu₂O particles. These oxygen atoms eventually encourage the oxidation of the surface Cu atoms to form a thin CuO layer, presence of which on the surface was corroborated by the XPS measurements. Sputtering of the samples was also carried out to remove the surface CuO thin layer and expose the inner Cu₂O. These nanomaterials were then investigated for their potential applications in photocatalytic degradation of Rhodamine B dye.     

Tuning the electronic structure of the transparent conducting oxide Cu2O

The electronic structure of Cu₂O is important for its application as a p-type transparent conducting oxide (TCO). To be useful as a TCO, a material needs to show enhanced transparency in the visible range (band gap > 3 eV) as well as good conduction properties. While Cu₂O has too small a band gap, alloys of Cu₂O and Al₂O₃ or Cu₂O and alkaline earth oxides are known to display enhanced transparency, with little degradation of electrical properties. It is of interest to consider how to dope Cu₂O p-type, e.g. Cu vacancies (oxidation) or cationic dopants. We present a study of the electronic structure and effective hole masses of stoichiometric and oxidised Cu₂O and study metal cation doping, using density functional theory (DFT), to analyse p-type doping scenarios. We show that formation of a Cu vacancy is relatively facile, introducing delocalised hole states, with a light hole present. Substitutional cation doping with Al and Au/Ag is found to decrease the band gap but maintains a light hole effective mass necessary for p-type conduction.     

Influence of Cu2O surface treatment on the photovoltaic properties of Al-doped ZnO/Cu2O solar cells

Low cost Al-doped ZnO (AZO)/Cu₂O Schottky barrier solar cells with a high conversion efficiency of 2.19% were fabricated by depositing a transparent conducting AZO thin film on high quality Cu₂O sheets prepared by thermally oxidizing copper sheets. To achieve efficiencies higher than 2%, it is necessary to form the AZO thin film at a low deposition temperature using a low-damage deposition method, i.e., at room temperature by a pulsed laser deposition. In addition, the obtained efficiency could be enhanced with a surface treatment of the Cu₂O sheets, such as by applying a Pd-Sn catalyst layer as a coating or a rapid thermal annealing treatment at approximately 500 °C in air.     

Electrochemical reduction of CO2 by Cu2O-catalyzed carbon clothes

Cu₂O cubes with average edge lengths of 640 nm were prepared by a chemical reduction approach. The as-synthesized Cu₂O particles were deposited on carbon clothes for electrochemical characterizations in cyclic voltammetry (CV) and potentiostatic measurements. In 0.5 M NaOH electrolytes saturated with N₂ or CO₂, both the Cu₂O and carbon clothes were stable at the potential range of 0 to − 1.7 V. Comparisons in the current responses from the CV and potentiostatic measurements suggested the Cu₂O with notable catalytic abilities for the CO₂ reduction. The mass activity was estimated at 0.94 mA/mg. Chemical analysis from gas chromatography confirmed the methanol to be the predominant product.     

Controlled reduction of Cu to Cu with an N,O-type chelate under hydrothermal conditions to produce Cu2O nanoparticles

N,O-type organic chelates reduced coordinated Cu²⁺ ions under hydrothermal reaction conditions to produce Cu₂O/CuO nanoparticles. Chelates in which the N and O atoms are closely spaced produced smaller amounts of CuO nanoparticles, indicating their higher ability to reduce Cu²⁺ ions to Cu⁺ ions. [Cu(Gly)₂]² with the shortest ligand chain length produced only Cu₂O nanoparticles and, therefore, can be used as a single molecule precursor for the synthesis of Cu₂O nanoparticles.     

Single-step sputtered Cu2SnSe3 films using the targets composed of Cu2Se and SnSe2

Cu₂SnSe₃ thin films were prepared by single-step D.C. sputtering at 100-400 °C for 3 h using targets composed of Cu₂Se and SnSe₂ in three different ratios of 2/1 (target A), 1.8/1 (target B), and 1.6/1 (target C). The advantages of self-synthesized SnSe₂ instead of commercially available SnSe for depositing Cu₂SnSe₃ thin films were demonstrated. Effects of target composition and substrate temperature on the properties of Cu₂SnSe₃ thin films were investigated. Structure, surface morphology, composition, electrical and optical properties at different process conditions were measured. The 400 °C-sputtered films obtained from target B display with direct band gap of 0.76 eV, electrical resistivity of 0.12 Ω cm, absorption coefficient of 10⁴-10⁵ cm^− 1, carrier concentration of ∼ 1.8 × 10¹⁹ cm^− 3, and electrical mobility of 2.9 cm²/V s.     

Synthesis of hexagonal prisms and hexagonal plates of Na2SiF6 microcrystals

Hexagonal Na₂SiF₆ prisms and hexagonal or dodecagonal Na₂SiF₆ plates were prepared using Na₂CO₃, SiO₂, and HF under microwave irradiation for the large-scale production of ice-analog materials. The morphology of the Na₂SiF₆ crystals changed from long thin hexagonal prisms to flat hexagonal or dodecagonal plates with pyramidal faces as the Na₂CO₃ concentration was increased. X-ray diffraction studies confirmed that the axes of the hexagonal Na₂SiF₆ prisms were aligned along the c axis. The microwave irradiation time played an important role in controlling the morphology and aspect ratio of the Na₂SiF₆ microcrystals. The mechanisms of formation of the various Na₂SiF₆ microcrystalline morphologies are discussed.     

Growth behavior of Cu6Sn5 grains formed at an Sn3.5Ag/Cu interface

The growth behavior of Cu₆Sn₅ grains formed at an Sn3.5Ag/Cu interface was investigated. During soldering, Cu₆Sn₅ grains formed at the interface, showing a flattened ovoid shape. During solidification, Cu precipitated from molten solder in the form of Cu₆Sn₅, forming faceted surfaces on existing interfacial grains. The interfacial Cu₆Sn₅ morphology was unrelated to its crystal orientation, which was primarily dependent on reaction temperature. A reaction temperature of 240 °C led to an increase in (002) growth and a decrease in (101) growth with time. However, the (002) plane peak was not detected in the interfacial grains formed at a higher reaction temperature (280 °C).     

Multi-stage evaporation of Cu2ZnSnS4 thin films

Multi-stage evaporation is a well-established method for the controlled growth of chalcopyrite thin films. To apply this technique to the deposition of Cu₂ZnSnS₄ thin films we investigated two different stage sequences: (A) using Cu₂SnS₃ as precursor to react with Zn-S and (B) using ZnS as precursor to react with Cu-Sn-S. Both Cu₂SnS₃ and ZnS are structurally related to Cu₂ZnSnS₄. In case (A) the formation of copper tin sulphide in the first stage was realized by depositing Mo/SnS_x/CuS (1 < x < 2) and subsequent annealing. In the second stage ZnS was evaporated in excess at different substrate temperatures. We assign a significant drop of ZnS incorporation at elevated temperatures to a decrease of ZnS surface adhesion, which indicates a self-limited process with solely reactive adsorption of ZnS at high temperatures. In case (B) firstly ZnS was deposited at a substrate temperature of 150 °C. In the second stage Cu, Sn and S were evaporated simultaneously at varying substrate temperatures. At temperatures above 400 °C we find a strong decrease of Sn-incorporation and also a Zn-loss in the layers. The re-evaporation of elemental Zn has to be assumed. XRD measurements after KCN-etch on the layers prepared at 380 °C show for both sample types clearly kesterite, though an additional share of ZnS and Cu₂SnS₃ can not be excluded. SEM micrographs reveal that films of sample type B are denser and have larger crystallites than for sample type A, where the porous morphology of the tin sulphide precursor is still observable. Solar cells of these absorbers reached conversion efficiencies of 1.1% and open circuit voltages of up to 500 mV.     

Morphology-dependent photocatalytic activities of hierarchical microstructures of ZnO

A range of hierarchical microstructures of ZnO were prepared using a hydrothermal method with Zn(NO₃)₂ and N,N-dimethyl ethylenediamine (DMEDA) in the presence of sodium 1-undecanesulfonate. The resulting ZnO products exhibited rod-, peanut-, dumbbell-, and notched spherical-like shapes. With increasing sodium 1-undecanesulfonate concentration, the morphology of the ZnO products evolved from rod-like, through to peanut- and dumbbell-like, then to notched spheres with higher hierarchy. The photocatalytic activities of the ZnO products for the decomposition of Rhodamine 6G were examined. The morphology of ZnO products had a significant effect on the photocatalytic activity. The mechanism of the morphology-controlled synthesis of ZnO and their morphology-dependent photocatalytic activity are discussed.     

Textured growth of Cu6Sn5 grains formed at a Sn3.5Ag/Cu interface

The growth orientations of Cu₆Sn₅ grains formed at a Sn3.5Ag/polycrystalline Cu interface were investigated. Similar as reported on Cu single crystals, strong textures in Cu₆Sn₅ layers can also form on polycrystalline Cu, but the texture formation mechanisms differ. The texture formation on polycrystalline Cu occurs during the ripening growth and results from the differences in stability of the interfacial grains with various orientations at different temperatures. A reaction temperature of 240 °C causes the Cu₆Sn₅ layer to form [0001] texture in the direction normal to the substrate, and a special morphology of interfacial Cu₆Sn₅ grains can be formed on this layer to reinforce joint properties.     

Cu2S nanostructures prepared by Cu-cysteine precursor templated route

A facile Cu-cysteine precursor templated route for the synthesis of Cu₂S nanowires, dendritic-like and flowerlike nanostructures is reported. The Cu-cysteine precursors are prepared through the reaction between Cu²⁺, l-cysteine and ethanolamine at room temperature, and the morphologies of Cu-cysteine precursors can be controlled by adjusting the molar ratio of l-cysteine to Cu²⁺. The Cu-cysteine precursors are used as both templates and source materials for the subsequent preparation of polycrystalline Cu₂S nanostructures by thermal treatment, and the morphologies of the precursors can be well preserved after the thermal transformation to Cu₂S nanostructures. The samples are characterized using X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopy.