Cuprous Oxide Layer Research Articles

Synthesis of copper nanorods for non-enzymatic amperometric sensing of glucose

An electrochemical non-enzymatic glucose sensor based on copper nanorods (CuNRs) was developed. The CuNRs were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction spectroscopy, and X-ray photoelectron spectroscopy. The results display a layer of rough cuprous oxide that is formed on the surface of CuNRs. The CuNR- modified glassy carbon electrode exhibits an outstanding capability in terms of nonenzymatic sensing of glucose. The sensor displays high sensitivity (1490 μA•mM−1•cm−2), fast response time (less than 5 s), a low detection limit of 8 nM (S/N = 3), long term stability, and excellent anti-fouling ability. The sensor was applied to the detection of glucose in (spiked) human serum and in black ice tea, with relative standard deviations (for n = 6) of 1.7 % and 1.9 %, respectively.

Investigation of significantly high barrier height in Cu/GaN Schottky diode

Current-voltage (I-V) measurements combined with analytical calculations have been used to explain mechanisms for forward-bias current flow in Copper (Cu) Schottky diodes fabricated on Gallium Nitride (GaN) epitaxial films. An ideality factor of 1.7 was found at room temperature (RT), which indicated deviation from thermionic emission (TE) mechanism for current flow in the Schottky diode. Instead the current transport was better explained using the thermionic field-emission (TFE) mechanism. A high barrier height of 1.19 eV was obtained at room temperature. X-ray photoelectron spectroscopy (XPS) was used to investigate the plausible reason for observing Schottky barrier height (SBH) that is significantly higher than as predicted by the Schottky-Mott model for Cu/GaN diodes. XPS measurements revealed the presence of an ultrathin cuprous oxide (Cu2O) layer at the interface between Cu and GaN. With Cu2O acting as a degenerate p-type semiconductor with high work function of 5.36 eV, a high barrier height of 1.19 eV is obtained for the Cu/Cu2O/GaN Schottky diode. Moreover, the ideality factor and barrier height were found to be temperature dependent, implying spatial inhomogeneity of barrier height at the metal semiconductor interface.

Influence of temperature and inhibitor content on the lifetime of copper nanoparticles in a propylene glycol‐based nanofluid

The present paper investigated the lifetime of copper nanoparticles in a propylene glycol‐based nanofluid. The corrosion behavior of nanoparticles was observed by means of linear polarization resistance, resistometry, transmission electron microscopy, and X‐ray photoelectron spectroscopy. Copper nanoparticles were tested in pure propylene glycol with the addition of the inhibitors benztriazole, benzimidazole, and tolyltriazole. The best performance was found with tolyltriazole as it provided some inhibiting efficiency even at higher temperatures, i.e., up to 120 °C. A layer of cuprous oxide was observed on the surface after exposure to propylene glycol, but this oxide was defective on the curved surface of nanoparticles. The corrosion rate of nanoparticles was at least two orders of magnitude greater than the corrosion rate of the compact sample. The lifetime of bare copper nanoparticles was not sufficient for practical purposes even when an inhibitor was used.

Novel affinity monolithic column modified with cuprous sulfide nanoparticles for the selective enrichment of low-molecular-weight electron-rich analytes.

A novel monolithic column modified with cuprous sulfide nanoparticles was developed and its affinity characteristics towards low-molecular-weight electron-rich analytes were investigated. In the synthesis process, home-made cuprous oxide nanocubes were immobilized on the surface of monolithic skeleton with the moderate thickness based on the strong interaction between imidazole groups and cuprous oxide, then the cuprous oxide layer was transformed into the more stable cuprous sulfide layer through the treatment by sodium sulfide. The resulting cuprous sulfide modified monolithic column presented good permeability and stability in a wide pH range from 2 to 10. Two kinds of typical electron-rich analytes, kanamycin A and purine, were chosen to assess its affinity characteristics. Compared with the commercial Cu(2+) - and Ni(2+) -based affinity sorbents, a larger binding capacity of cuprous sulfide modified column toward kanamycin A was obtained under basic condition and the recovery of kanamycin A in a milk sample was over 70%. Moreover, the binding capacity of cuprous sulfide modified column for purine was up to 5.57 mg/mL in frontal elution mode. These results suggested that the Cu2 S column has a promising application for the enrichment of electron-rich analytes.

Atomic layer deposition of tin oxide and zinc tin oxide using tetraethyltin and ozone

Silicon or glass substrates exposed to sequential pulses of tetraethyltin (TET) and ozone (O3) were coated with thin films of SnO2. Self-limiting deposition was found using 8 s pulse times, and a uniform thickness per cycle (TPC) of 0.2 nm/cycle was observed in a small, yet reproducible, temperature window from 290 to 320 °C. The as-deposited, stoichiometric SnO2 films were amorphous and transparent above 400 nm. Interspersing pulses of diethylzinc and O3 among the TET:O3 pulses resulted in deposition of zinc tin oxide films, where the fraction of tin, defined as [at. % Sn/(at. % Sn + at. % Zn)], was controlled by the ratio of TET pulses, specifically nTET:(nTET + nDEZ) where nTET and nDEZ are the number of precursor/O3 subcycles within each atomic layer deposition (ALD) supercycle. Based on film thickness and composition measurements, the TET pulse time required to reach saturation in the TPC of SnO2 on ZnO surfaces was increased to >30 s. Under these conditions, film stoichiometry as a function of the TET pulse ratio was consistent with the model devised by Elliott and Nilsen. The as-deposited zinc tin oxide (ZTO) films were amorphous and remained so even after annealing at 450 °C in air for 1 h. The optical bandgap of the transparent ZTO films increased as the tin concentration increased. Hall measurements established that the n-type ZTO carrier concentration was 3 × 1017 and 4 × 1018 cm−3 for fractional tin concentrations of 0.28 and 0.63, respectively. The carrier mobility decreased as the concentration of tin increased. A broken gap pn junction was fabricated using ALD-deposited ZTO and a sputtered layer of cuprous oxide. The junction demonstrated ohmic behavior and low resistance consistent with similar junctions prepared using sputter-deposited ZTO.

Electrodeposition of p-type cuprous oxide layers on n-type zinc oxide layers with different electrical resistivities

The development of metal oxide semiconductor-based absorber layers consisting of earth abundant elements is currently in the early stages of research. Cuprous oxide (Cu2O) is a representative p-type oxide material with an appropriate band gap for this application. To produce all-oxide photovoltaic cells, the authors grew Cu2O films on top of n-type Zinc oxide (ZnO) layers by electrodeposition. Prior to the electrodeposition of Cu2O, the underlying ZnO layers were deposited by atomic layer deposition at different temperatures. The resulting films had different electrical conductivities. For the low conductivity ZnO grown at 100 °C, the Cu2O layer was coated with a highly (111) preferred orientation leading to low electrical resistivity. Consequently, these Cu2O/ZnO heterojunction solar cells showed relatively high conversion efficiencies despite the low conductivity of the ZnO. Conversely, the Cu2O deposited on the highly conductive ZnO film (grown at 150 °C) exhibited extremely low photocurrent, which was attributed to low crystallinity and poor electrical properties.

Double oxide shell layer formed on a metal nanoparticle as revealed by aberration corrected (scanning) transmission electron microscopy

Determining the extent of oxidation in batches of metal nanoparticles is essential to predict the behaviour of the material. Using aberration corrected transmission electron microscopy (TEM) it was possible to detect the formation of an oxide shell, of thickness 3 nm, on the surface of copper nanoparticles. Further analysis showed that this shell actually consists of two layers, both of which were polycrystalline in nature with domains in the size range of 1–2 nm, and having a thickness of 1.5 nm each. Energy dispersive x-ray spectroscopy confirms that the layers arise due to the formation of oxides, but it was not possible to determine their exact nature. Analysis of the intensity variation within images obtained via probe corrected scanning TEM combined with a high angle annular dark field detector indicates that the shell consists of an inner layer of cuprous oxide (Cu2O) and an outer layer of cupric oxide (CuO). This work was complemented by conventional TEM which provided size distribution and revealed that the majority of particles have a core consisting of a single crystal of copper. This demonstrates the ability of TEM to help to determine the oxidation state of nanoparticles and its potential to be applied to a wide range of homogenous and heterogeneous nanoparticles.

Plasmon-enhanced terahertz emission from a semiconductor/metal interface

Terahertz emission by ultrafast optical excitation of semiconductor/metal interfaces strongly depends on the strength of the depletion-field. Here, we report on the strong enhancement of the emission after optical excitation of surface plasmons at these interfaces. The enhancement is caused by the plasmonic localization of the pump light near the metal surface, where the depletion-field is the strongest. Compared to the case where no surface plasmons are excited, a terahertz field enhancement of more than an order of magnitude is obtained for a particular thickness of cuprous oxide layer on gold, where localized surface plasmons are excited at the interface.

Low-potential amperometric determination of purine derivatives through surface oxide regeneration method

This article described a novel amperometry which can be used for determination of purine derivatives including uric acid, xanthine, hypoxanthine, guanine, and adenine without surface contamination. By applying a constant potential of −0.125V (vs. Ag/AgCl) in a flow injection system, the chelating capability of these purine derivatives converts the cuprous oxide layer into a soluble complex. This behavior would dissolve the passive oxide layer and expose the bottom copper layer to the solution, subsequently; an oxidation current which attributed to the regeneration of the original cuprous oxide layer is used to reflect the concentration of these purine derivatives. In a 50mM phosphate buffer, pH 7.0, this approach provides a high sensitivity with LOQ of sub-micro molar level of five purines and high stability with a RSD of 2.5% for 10μM xanthine (N=12). This method does not suffer from most biological species including ascorbic acid, acetaminophen, creatine, dopamine, sarcosine, ammonium ion, chloride ion, and urea at equal or higher than its physiological concentration.

Enhanced terahertz emission by coherent optical absorption in ultrathin semiconductor films on metals

We report on the surprisingly strong, broadband emission of coherent terahertz pulses from ultrathin layers of semiconductors such as amorphous silicon, germanium and polycrystalline cuprous oxide deposited on gold, upon illumination with femtosecond laser pulses. The strength of the emission is surprising because the materials are considered to be bad (amorphous silicon and polycrystalline cuprous oxide) or fair (amorphous germanium) terahertz emitters at best. We show that the strength of the emission is partly explained by cavity-enhanced optical absorption. This forces most of the light to be absorbed in the depletion region of the semiconductor/metal interface where terahertz generation occurs. For an excitation wavelength of 800 nm, the strongest terahertz emission is found for a 25 nm thick layer of amorphous germanium, a 40 nm thick layer of amorphous silicon and a 420 nm thick layer of cuprous oxide, all on gold. The emission from cuprous oxide is similar in strength to that obtained with optical rectification from a 300 μm thick gallium phosphide crystal. As an application of our findings we demonstrate how such thin films can be used to turn standard optical components, such as paraboloidal mirrors, into self-focusing terahertz emitters.

Growth and characterization of p-Cu2O/n-ZnO nanorod heterojunctions prepared by a two-step potentiostatic method

p-Cu2O/n-ZnO nanorod heterojunctions were fabricated by a two-step process. The process was performed with potentiostatic deposition of n-ZnO nanorods on conductive indium-tin-oxide (ITO) glasses followed by potentiostatic deposition of p-Cu2O to form p-Cu2O/n-ZnO nanorod heterojunctions. The deposition condition required to form the cuprous oxide layer affected significantly the formation and microstructure of the p-Cu2O/n-ZnO nanorod heterojunctions. In particular, the high-quality p-Cu2O/n-ZnO nanorod heterojunctions were obtained only at relatively high temperatures of 90 and 100°C. The p-Cu2O/n-ZnO nanorod heterojunctions exhibited a well-defined p–n diode characteristic with an ideality factor of about 4.3.

New strategy for amperometric determination of nabam pesticide by using potential assisted surface oxide regeneration method

Abstract This project demonstrates a novel amperometric method to measure the concentration of nabam through a process of potential assisted surface oxide on the copper based electrode. Based on the strong cuprous ion chelating capability of nabam, the cuprous oxide layer is dissolved away from the electrode surface. A subsequent oxidative current induced from regeneration of the oxide layer was used to reflect the concentration of the nabam. Under a set of optimal conditions with operating potential at −125 mV in the 50 mM phosphate buffer, pH 5.75, a suitable dynamic range of nabam from 0.2 μM to 10 μM (or 0.051–2.56 ppm) was achieved, which meets the requirement of the Joint FAO/WHO Meeting on Pesticide Residues. This method is free from the environmental interferences. However, most of all metal ions show a negative deviation due to the formation of other metal–nabam complexes. Here, a simple cation exchange column was used to release the chelated nabam molecule. Finally, two successful real applications were demonstrated by using a standard addition procedure after this cation exchange pretreatment.

Oxidation kinetics of nanoscale copper films studied by terahertz transmission spectroscopy

Terahertz (THz) transmission spectroscopy is used to measure the oxidation kinetics of copper thin films evaporated on silicon substrates. The transmission of broadband THz pulses from 1 to 7 THz through the copper film is measured while it gets oxidized at an elevated temperature in ambient air. The change in the transmitted THz electric field is correlated with the growth of the cuprous oxide layer and the decrease in thickness of the copper layer. Oxidation curves were obtained for heating temperatures of 120–150 °C and were found to follow a parabolic rate law. Using the Arrhenius equation, we calculate an activation energy for diffusion of 0.55 eV. By measuring the THz transmission through unoxidized copper layers of several thicknesses, we also measured the optical properties of thin copper films around the percolation threshold thickness of 7 nm. Around the percolation transition, the optical properties of freshly deposited copper thin films are very different from that of copper layers of the same thickness remaining after partial oxidation of thick copper films.

High-Efficiency Ferroelectric-Film Solar Cells with an n-type Cu2O Cathode Buffer Layer

Because of the existence of interface Schottky barriers and depolarization electric field, ferroelectric films sandwiched between top and bottom electrodes are strongly expected to be used as a new kind of solar cells. However, the photocurrent with a typical order of μA/cm(2) is too low to be practical. Here we demonstrate that the insertion of an n-type cuprous oxide (Cu(2)O) layer between the Pb(Zr,Ti)O(3) (PZT) film and the cathode Pt contact in a ITO/PZT/Pt cell leads to the short-circuit photocurrent increasing 120-fold to 4.80 mA/cm(2) and power conversion efficiency increasing of 72-fold to 0.57% under AM1.5G (100 mW/cm(2)) illumination. Ultraviolet photoemission spectroscopy and dark J-V characteristic show an ohmic contact on Pt/Cu(2)O, an n(+)-n heterojunction on Cu(2)O/PZT and a Schottky barrier on PZT/ITO, which provide a favorable energy level alignment for efficient electron-extraction on the cathode. Our work opens up a promising new method that has the potential for fulfilling cost-effective ferroelectric-film photovoltaic.

Corrosion inhibition of copper by sodium phytate in NaOH solution: Cyclic voltabsorptometry for in situ monitoring of soluble corrosion products

The ability to in situ monitor the formation and transition of soluble corrosion products generated during metal electrochemical processes is important for elucidating the corrosion mechanism. The combination of cyclic voltammetry and cyclic voltabsorptometry allows simultaneous measurements of the potential-dependent current and absorbance, the latter of which corresponds to the characteristic wavelength of each light-absorbing species. For this purpose, a long-optical-path thin-layer electrochemical cell (LTE-cell) was fabricated to study the corrosion inhibition of copper by phytate in alkaline media. A conventional electrochemical cell was also used for common cyclic voltammetry and impedance spectroscopy. The morphology of the corroded copper surfaces was characterized using field-emission scanning electron microscopy. A high corrosion inhibition efficiency (ca. 90%) of phytate on copper was achieved in 0.1moldm−3 NaOH solution. Phytate was shown to promote the formation of the soluble intermediate cuprous ions and hinder the generation of the cupric ions from pitting corrosion of the initially deposited cuprous oxide layer. The integrity of the cuprous passive layer was therefore maintained, which strongly suppressed further formation of various cupric corrosion products. The results of this study indicate that cyclic voltabsorptometry based on a LTE-cell is an effective method for studying metal corrosion processes that involve light-absorbing ions.

Void-Free Cuprous Oxide Tube Prepared by Thermal Oxidation on Outside of Copper Tube

A new setup in an oxidation system was proposed to remove voids from cuprous oxide during the oxidation of copper. The key is the formation of a single cuprous oxide layer. To form the layer on the outside surface of a copper tube, argon gas was introduced into the tube. In the cuprous oxide wall oxidized at 920–950 °C in air for 8 h, no voids were found. The diameter of the tube indicated that the voids were swept out from the inner unoxidized surface. This knowledge contributes to the development of the growth of high-quality cuprous oxide crystals.

Copper Nanoparticles Prepared from Oxalic Precursors

The synthesis of nanoparticles of copper metal via a soft chemistry route is presented in this paper. The method is based on the thermal decomposition under nitrogen or hydrogen of oxalic precursors with a well-controlled morphology and particle size. The precipitation of the copper oxalates in a water-alcohol medium allows the submicron size of the precursor grains to be controlled and, consequently, the nanometric size of the metallic copper particles to be determined, as required, between 3.5 and 40 nm. The majority of the final particles are made of pure copper metal although some present a superficial layer of cuprous oxide (Cu2O).

Formation of cuprous oxide layers in Cu(II) solutions containing gluconic acid

In accordance with thermodynamic analysis, cuprous oxide layers are formed spontaneously in the Cu|Cu(II), gluconic acid system at pH > 3.7 under open-circuit conditions. A current peak of Cu2O reduction is observed on cathodic voltammograms at ca −0.7 V, its height being dependent on the exposure time. The analysis of the charge transferred in this region yields the rate of Cu2O formation equal to 1.25 × 10−10 mol cm−2 s−1. The light perturbation of Cu electrode under open-circuit conditions results in the generation of a negative photopotential, which is indicative of n-type conductivity. The threshold wavelength is equal to ∼590 nm and is consistent with a band gap of ∼2.1 eV. Anodic photocurrents, which are observed near the open-circuit potential, decrease with cathodic polarization and change their sign at ∼0.05 V. Analysis of impedance data was performed, invoking the equivalent circuit that accounts for the two-step charge transfer. In the presence of Cu2O, some retardation of Cu(II) reduction was found to occur with a slight increase in the admittance of the double layer. The suggestion has been made that oxide layers formed in Cu(II) gluconate solutions cannot be compact and uniformly distributed over the entire electrode surface. Relevant investigations of surface morphology support this conclusion.

Corrosion of Cu under Highly Corrosive Environments

Cu corrosion in mixed flowing gases (MFG) has been widely studied. However, most of these studies have been carried out using conditions which were designed for accelerated tests simulating North America and Western Europe. More and more equipment are being deployed to emerging markets such as Asia Pacific and China, Eastern Europe, and the Middle East, where they are subjected to much more corrosive environments than those typically seen in North America and Western Europe. There is a need to understand the corrosive conditions in the emerging markets and come up with an accelerated test for products to be deployed in those conditions. In this work, we investigated the corrosion products on test Cu coupons exposed to harsh conditions by a combination of several analytical techniques. This work allowed us to establish a procedure for quantifying corrosion products and led to insights about corrosion mechanisms for copper in highly corrosive environments. Results showed that the corrosion of copper in the highly corrosive MFG testing condition (containing , , , and ) leads mainly to the formation of copper sulfide at the exposed surface, with the presence of a thin, buried cuprous oxide layer sandwiched between and copper substrate. The thickness of the corrosion products increases linearly with the exposure time.

Erosion–corrosion of heat exchanger tubes

The shell and tube heat exchanger failed before 5 years of operation. The failure was caused by pits on the tube outside surface developing until its perforation. Inside the Cu-DHP tubes in soft temper a cooling agent circulated to cool down industrial water at the shell side from 16 to 4 °C. The cooled water was hard, rich in chloride ions with relatively low sulphate ions concentration and pH ranging from 4 to 7. The leaking tubes were subject to standard metallographic examination, hardness measurement, scanning electron microscopy and X-ray energy dispersion analysis. It was found that the tube damage was caused by erosion–corrosion induced by two factors: disturbed flow of water containing suspended solid particles and chemical composition of water rich in chlorides that resulted in loss of stability of protective cuprous oxide layer.