Picosecond nonlinear optical properties of cuprous oxide with different nano-morphologies

Cuprous oxide nanoclusters, microcubes and microparticles were successfully synthesized by a simple co-precipitation method. Phase purity and crystallinity of the samples were studied by using X-ray powder diffraction. Transmission electron microscopy (TEM) images show different morphologies like nanoclusters, microcubes and microparticles. For linear and nonlinear optical measurements, the as-synthesized Cu₂O with different morphologies were dispersed in isopropanol solution. The absorption spectrum recorded in the visible regions shows peaks that depend on the morphology of the particles and the peak shifts towards red region as one goes from nanoclusters to microparticles. Simple open-aperture Z-scan technique is used to measure nonlinear optical properties of cuprous oxide at 532 nm, 30 ps excitation at 10 Hz repetition rate. Cuprous oxide nanoclusters show reverse saturable absorption (RSA) behaviour, the microcubes and microparticles at a similar concentration exhibit saturable absorption (SA) type of behaviour at lower peak intensities and exhibit RSA within SA at higher peak intensities. The results show that the transition from SA to RSA can be ascribed to the two-photon absorption (TPA) process.     

Electrical conductivity of Co doped cuprous oxide

The solubility limit of metals in cuprous oxide is very low and it is therefore difficult to form solid solutions of metal oxides with cuprous oxide. In an on going research looking for such solid solutions and their properties we have prepared Co doped Cu₂O. We report here on measurements of the electrical conductivity of Co doped Cu₂O as a function of the oxygen partial pressure. It is found that Co doped material is an n-type semiconductor in the low oxygen partial pressure regime and p-type at higher oxygen pressures (while undoped Cu₂O is a p-type material throughout the whole existence regime). A point defect model is discussed. The ionic transference number is also measured and is found to be less than 2⋅10⁻⁴. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995     

Phase contrast imaging of preclinical portal vein embolization with CO2 microbubbles

Preoperative portal vein embolization (PVE) is employed clinically to avoid postoperative liver insufficiency. Animal models are usually used to study PVE in terms of mechanisms and pathophysiological changes. PVE is formerly monitored by conventional absorption contrast imaging (ACI) with iodine contrast agent. However, the side effects induced by iodine can give rise to animal damage and death. In this study, the feasibility of using phase contrast imaging (PCI) to show PVE using homemade CO₂ microbubbles in living rats has been investigated. CO₂ gas was first formed from the reaction between citric acid and sodium bicarbonate. The CO₂ gas was then encapsulated by egg white to fabricate CO₂ microbubbles. ACI and PCI of CO₂ microbubbles were performed and compared in vitro. An additional increase in contrast was detected in PCI. PCI showed that CO₂ microbubbles gradually dissolved over time, and the remaining CO₂ microbubbles became larger. By PCI, the CO₂ microbubbles were found to have certain stability, suggesting their potential use as embolic agents. CO₂ microbubbles were injected into the main portal trunk to perform PVE in living rats. PCI exploited the differences in the refractive index and facilitated clear visualization of the PVE after the injection of CO₂ microbubbles. Findings from this study suggest that homemade CO₂ microbubbles‐based PCI is a novel modality for preclinical PVE research.     

Fabrication of cuprous and cupric oxide thin films by heat treatment

Cuprous oxide (Cu₂O) and cupric oxide (CuO) thin films were prepared by thermal oxidation of copper films coated on indium tin oxide (ITO) glass and non-alkaline glass substrates. The formation of Cu₂O and CuO was controlled by varying oxidation conditions such as, oxygen partial pressure, heat treatment temperature, and oxidation time. The microstructure, crystal direction, and optical properties of copper oxide films were measured with X-ray diffraction, atomic force microscopy, and optical spectroscopy. The results indicated that the phase-pure Cu₂O and CuO films were produced in the oxidation process. Optical transmittance and reflectance spectra of Cu₂O and CuO clearly exhibited distinct characteristics related to their phases. The electrical properties indicated that these films formed ohmic contacts with Cu and ITO electrode materials. Multilayers of Cu₂O/CuO were fabricated by choosing the oxidation sequence. The experimental results in this paper suggest that the thermal oxidation method can be employed to fabricate device quality Cu₂O and CuO films that are up to 200–300 nm thick.     

Optical constants of thin oxide films on titanium

Thin oxide films on titanium formed by heating were studied by the ellipsometric method. To obtain the complex refractive index and film thicknesses, the ellipsometric measurements were performed by means of the immersing method: each sample was measured first in air and then in a liquid of known refractive index (in our case CCl₄). The optical constants and the oxide film thickness were computed by means of a computer from two pairs of ellipsometric values. To state the optical constants of clean titanium surface the graphic-computational method was proposed and applied. The measurements were carried out at two wavelengths on oxide films grown in air and dry oxygen by thermal oxidation at temperatures from 150 to 700 °C. It has been shown that when increasing the film thickness the refractive index of the film decreases, whereas the absorption coefficient is independent on the film thickness. Optical constants of oxide films growing in dry oxygen are smaller than those growing in air.     

Homogeneity range of cubic high temperature cuprous sulfide (digenite)

Within the homogeneity range of the cubic cuprous sulfide Cu_2?δS the sulphur fugacity was measured as a function of composition and temperature using direct (silica gauges) and indirect (H₂S/H₂) methods. The experiments were performed between 789 and 1321 K and in the whole field of compositions from copper-rich to the sulphur-rich boundary of the homogeneity range.The experimental data are interpreted by a combination of the thermodynamics of mixed phases and the point defect theory. The results show that Cu_2?δS is essentially a mixture of Cu₂S and CuS. Other defects than CuS dissolved in Cu₂S, e.g. copper interstitials, are present in small amounts at high temperatures and low sulphur fugacities. These results are in close agreement with data from the literature, derived from metallurgical, DTA, thermobalance and electrical conductivity measurements.     

Tunable diode laser measurements of the band strength and collision halfwidths of nitric oxide

The strength of the fundamental absorption band of nitric oxide at 5.3 μm and collision halfwidths of nitric oxide lines broadened by nitrogen, argon, and combustion gases were measured in absorption cell, flat flame and shock tube experiments using a tunable diode laser. Room temperature absorption measurements were made in an absorption cell filled with NO/N₂ or NO/Ar mixtures or with probe-extracted combustion gases. High temperature (to 2500 K) absorption measurements were performed for NO in N₂ and NO in Ar using a shock tube, and for NO in combustion gases using a flat flame burner.Absorption measurements were made on lines from 1860–1925 cm^?1, ($\text{Ω=}\text{1}\text{2}$ and $\text{3}\text{2}$,P($\text{5}\text{2}$-R ($\text{29}\text{2}$)) resulting in a band strength of 123±8 cm^-2 atm^?1 at 273.2 K. Collision halfwidth dependencies for each broadening species were examined as a function of rotational quantum number and temperature.     

Characteristic of natural rubber composites absorbing X-radiation

Radiopaque polymers can be used in medicine. Conventional protective shields against radiation X contain harmful lead compounds that are heavy and fragile. The aim of this work was to study the check the properties of selected fillers as X-radiation absorbing substance and them use in natural rubber (NR) composites. Fillers and simultaneously active substances were bismuth (III) oxide (Bi₂O₃), gadolinium (III) oxide (Gd₂O₃), tungsten (III) oxide (WO₃) and antimony (III) oxide (Sb₂O₃). The polymeric matrix consisted of NR and sulfuric cross-linking system was applied. The properties of the fillers were determined from zeta potential and particle size measurements. X-ray absorption measurements were carried out using isotopic source ⁵⁷Co (122?keV). The mechanical properties of the thin 1?mm composite plates were examined.     

Microwave absorption investigation on the formation of YBa2Cu3O7−σ by a binary metal oxide route involving interaction of BaCuO2 and Y2Cu2O5

Low-field microwave absorption has been used to discriminate between the YBa₂Cu₃O_7?σ high temperature superconductor synthesized by reacting the binary metal oxides, BaCuO₂ and Y₂Cu₂O₅, versus synthesis with a single metal oxide route. This discrimination is more clearly seen by microwave absorption than by resistance measurements. Supplementary data was obtained by electron spin resonance in the g=2 region, scanning electron microscopy, thermal analysis and x-ray diffraction techniques. The scanning electron micrographs indicate a more separated granular structure for the material synthesized from the binary oxides. The low field non-resonant microwave absorption, which is characteristic of the superconducting phase, is twice as intense for the binary metal oxide preparation as compared to the single metal oxide preparation. Also, the superconducting transition temperature seems to be several degrees higher for the binary oxide preparation.     

Cu_2O室温电调制反射激子光谱

本文用电解液电调制反射谱方法;研究了室温下Cu_2O的青系蓝系激子谱.实验结果用最小二乘法对Aspens的理论进行了曲线拟合.将拟合结果与低温和室温下的反射、吸收谱数据进行比较,得到在电解液电反射谱中,不仅有青系.系n=1的激子效应,而且也包含n=2的激子效应.文中也做了不同抛光表面样品的电反射谱;发现它们有显著不同的光谱特征.     

Optical properties of cuprous telluride films

The structure of vacuum-deposited cuprous telluride Cu₂Te films deposited on carbon substrates was observed by means of an electron microscope. Films on glass substrates were also investigated by X-ray diffraction. The optical constants (the refractive index n and the extinction coefficient k) of Cu₂Te thin films were determined from the measured transmittance and reflectance at normal incidence of light in the wavelength range 0.4 m to 2.5 m. The variation of the optical constants with thickness for different evaporated films have been determined.     

Energy bands and soft x-ray absorption and emission in cuprous chloride

The observed X-ray (Cl^-L₂₃) absorption and emission spectra are compared with spectral intensities calculated with the help of energy bands in CuCl. The interpretation of the absorption spectrum puts in evidence the formation of the core excitons in addition to the usual band to band transitions. In the case of emission spectrum, the effect of correlation on the core levels seems to be an important contribution.     

Optical band-edge absorption of oxide compound SnO2

Tin oxide (SnO₂) is an important oxide for efficient dielectrics, catalysis, sensor devices, electrodes and transparent conducting coating oxide technologies. SnO₂ thin film is widely used in glass applications due to its low infra-red heat emissivity. In this work, the SnO₂ electronic band-edge structure and optical properties are studied employing a first-principle and fully relativistic full-potential linearized augmented plane wave (FPLAPW) method within the local density approximation (LDA). The optical band-edge absorption α(ω) of intrinsic SnO₂ is investigated experimentally by transmission spectroscopy measurements and their roughness in the light of the atomic force microscopy (AFM) measurements. The sample films were prepared by spray pyrolysis deposition method onto glass substrate considering different thickness layers. We found for SnO₂ qualitatively good agreement of the calculated optical band-gap energy as well as the optical absorption with the experimental results.     

Potential dependence of cuprous/cupric duplex film growth on copper electrode in alkaline media

The duplex oxide film potentiostatically formed on copper in concentrated alkaline media has been investigated by XRD, XPS, negative-going voltammetry and cathodic chronopotentiometry. The interfacial capacity was also measured using fast triangular voltage method under quasi-stationary condition. The obvious differences in the thickness, composition, passivation degree and capacitance behavior were observed between the duplex film formed in lower potential region (−0.13 to 0.18 V versus Hg|HgO electrode with the same solution as the electrolyte) and that formed in higher potential region (0.18-0.60 V). Cuprous oxides could be formed and exist stably in the inner layer in the both potential regions, and three cupric species, soluble ions and Cu(OH)₂ and CuO, could be independently produced from the direct oxidation of metal copper, as indicated by three pairs of redox voltammetric peaks. One of the oxidation peaks appeared only after the scan was reversed from high potential and could be attributed to CuO formation upon the pre-accumulation of O²⁻ ions within the film under high anodic potentials. A new mechanism for the film growth on the investigated time scale from 1 to 30 min is proposed, that is, the growth of the duplex film in the lower potential region takes place at the film|solution interface to form a thick Cu(OH)₂ outer layer by field-assisted transfer of Cu²⁺ ions through the film to solution, whereas the film in the higher potential region grows depressingly and slowly at the metal|film interface to form Cu₂O and less CuO by the transfer of O²⁻ ions through the film to electrode.     

An optical system for measuring nitric oxide using spectral separation techniques

An optical sensor based on differential absorption spectroscopy for real-time monitoring of industrial nitric oxide (NO) gas emission is described. The influence of gas absorption interference from sulfur dioxide (SO₂) in the environment was considered and a spectral separation technique was developed in order to eliminate this interference effect. The absorption spectrum of SO₂ around 226 nm was evaluated by the SO₂ concentration obtained using the experimentally recorded absorption spectrum around 300 nm. The absorption spectrum of NO around 226 nm was obtained by subtracting the absorption of SO₂ from the integral absorption spectrum of SO₂ and NO. The concentration measurements were performed at atmospheric pressure. The technique was found to have a lower detection limit of 0.8 ppm for NO per meter path length (SNR=2) and be immune from the influence from SO₂ on the NO measurement. The sensor based on this technique was successfully employed for in situ measurement of SO₂ and NO concentrations in the flue gas emitted from an industrial coal-fired boiler.     

Optimization of cuprous oxide nanocrystals deposition on multiwalled carbon nanotubes

Cu (I) phenyl acetylide was used as a source of copper to achieve a homogeneous distribution of Cu₂O nanocrystals (10–80 nm) decorated on multiwalled carbon nanotubes (MWCNTs) having an average diameter of 10 nm. Pristine MWCNTs were first oxygen-functionalized by treating them with a mixture of concentrated (H₂SO₄/HNO₃ : 3/1) acids and the products were characterized by X-ray powder diffraction, transmission and scanning electron microscopy, energy dispersive X-ray analysis, X-ray photoelectron spectroscopy and thermogravimetric analysis. An easy, efficient and one-step impregnation method was followed to produce copper-containing nanoparticles on the MWCNTs. The copper-treated MWCNTs dried at room temperature were seen to be well decorated by copper-containing nanoparticles on their outer surface. The MWCNTs were then heat-treated at 400 °C in a nitrogen atmosphere to produce a homogeneous distribution of cuprous oxide nanocrystals on their surface. By varying the ratio of copper to oxygen-functionalized MWCNTs, Cu₂O nanocrystals decorated on MWCNTs with different copper content can be obtained.     

Optical characterization of thin thermal oxide films on copper by ellipsometry

A complete optical characterization in the visible region of thin copper oxide films has been performed by ellipsometry. Copper oxide films of various thicknesses were grown on thick copper films by low temperature thermal oxidation at 125 °C in air for different time intervals. The thickness and optical constants of the copper oxide films were determined in the visible region by ellipsometric measurements. It was found that a linear time law is valid for the oxide growth in air at 125 °C. The spectral behaviour of the optical constants and the value of the band gap in the oxide films determined by ellipsometry in this study are in agreement with the behaviour of those of Cu₂O, which have been obtained elsewhere through reflectance and transmittance methods. The band gap of copper oxide, determined from the spectral behaviour of the absorption coefficient was about 2 eV, which is the generally accepted value for Cu₂O. It was therefore concluded that the oxide composition of the surface film grown on copper is in the form of Cu₂O (cuprous oxide). It was also shown that the reflectance spectra of the copper oxide–copper structures exhibit behaviour expected from a single layer antireflection coating of Cu₂O on Cu. Received: 19 July 2001 / Accepted: 27 July 2001 / Published online: 17 October 2001     

Absorption electronic spectrum of gaseous FeO: in situ detection with intracavity laser absorption spectroscopy in a nanoparticle-generating flame reactor

Absorption measurement of a gas-phase iron oxide (FeO) electronic spectrum is reported for the first time. FeO was obtained in a methane/oxygen/nitrogen flame doped with iron pentacarbonyl and monitored via the 611-nm band of the orange system with intracavity laser absorption spectroscopy. The measured spectral range extends from 16,250 to 16,450 cm^?1 for the appropriate intracavity tuning element position. The presented measurements demonstrate sensitive detection of the gas-phase precursor, playing a key role in flame synthesis of iron oxide nanoparticles. The sensitivity of the intracavity technique does not depend on broadband cavity losses and allows conducting measurements in a highly scattering, particle-laden flame environment.     

Methane steam reforming in an annular microchannel with Rh/Al2O3 catalyst

Regularities of methane conversion in the presence of water steam were obtained experimentally while activating chemical conversions on the inner convex wall of an annular microchannel. The steam methane reforming was done on the Rh/Al₂O₃ nanocatalyst with the heat applied through the microchannel gap from the outer wall. Concentrations of the products of chemical reactions in the outlet gas mixture are measured at different temperatures of the outer microchannel wall. The range of channel wall temperatures at which the ratio of hydrogen and carbon oxide in the outlet mixture grows substantially is determined. Data on the composition of methane conversion products for the ratio H₂O/CH₄ = 1.77 and the activation energy of methane steam reforming at reactor outer wall temperatures of up to 880°C are obtained. The effect of the radiation heat exchange and the external diffuse limitation on the rate of chemical conversions in methane steam reforming in an annular microchannel with external heat supply is determined.     

Theory of enhanced dynamical photo-thermal bi-stability effects in cuprous oxide/organic hybrid heterostructure

We theoretically demonstrate the formation of multiple bi-stability regions in the temperature pattern on the interface between a cuprous oxide quantum well and DCM2:CA:PS organic compound. The Frenkel molecular exciton of the DCM2 is brought into resonance with the 1S quadrupole Wannier-Mott exciton in the cuprous oxide by “solvatochromism” with CA. The resulting hybrid is thermalized with the surrounding helium bath. This leads to strongly non-linear temperature dependence of the laser field detuning from the quadrupole exciton energy band which is associated with the temperature-induced red shift of the Wannier exciton energy. A numerical up- and down-scan for the detuning reveals hysteresis-like temperature distribution. The obtained multiple bi-stability regions are at least three orders of magnitude bigger (meV) than the experimentally observed bi-stability in bulk cuprous oxide (μeV ). The effective absorption curve exhibits highly asymmetrical behavior for the Frenkel-like (above the 1S energy) and Wannier-like (below the 1S energy) branches of the hybrid.