CiteULike: Tag oxide

Surface Oxidation and Reduction of CuO and Cu2O Studied Using XPS and XAES

S Poulston — 2007-02-14T09:43:25-00:00

Surface and Interface Analysis, Vol. 24, No. 12. (1996), pp. 811-820.

Using XPS and x-ray-excited Auger electron spectroscopy (XAES), we have studied the variation in surface composition of CuO and Cu2O with a variety of high-vacuum treatments, including vacuum annealing, oxidation and hydrogen reduction. Prolonged annealing of CuO results in the formation of a thick layer of Cu2O at the surface whilst vacuum annealing of Cu2O produces a thin (possibly one monolayer) film of Cu metal. Both bulk Cu2O and the thick Cu2O film generated from vacuum-annealed CuO were oxidized to CuO by heating at 800 K in 1×10-4 mbar O2, the original surface being regenerated with vacuum annealing at the same temperature. Both CuO and Cu2O are reduced to metal at the surface by heating in 1×10-4 mbar hydrogen at 400 K. In the case of CuO, the extent of reduction varies with the thermal history of the sample, with prolonged vacuum annealing producing a more reducible surface. Hydrogen-reduced CuO and Cu2O were both reoxidized on vacuum annealing, demonstrating the diffusion of lattice oxygen to the surface.

Chemical and thermal reduction of thin films of copper (II) oxide and copper (I) oxide

PD Kirsch — 2007-02-14T09:33:11-00:00

Journal of Applied Physics, Vol. 90, No. 8. (2001), pp. 4256-4264.

Chemical and thermal reduction of copper oxide thin films (~20 Å) has been studied with x-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) for application in microelectronic device interconnects. XPS showed that copper (I) oxide (Cu2O) and copper (II) oxide (CuO) were reduced to copper metal at 400 K within a 30 min exposure to deuterium atoms (D*) and molecules at 1×10–4 Torr. Similarly, XPS showed that Cu2O was reduced to copper metal at 400 K within a 30 min exposure to methyl radicals (CH3*" align="middle">) and acetone molecules at 1×10–4 Torr. After D* exposure, TPD showed O leaves the Cu2O surface as D2O from 400 K to 700 K with a peak desorption temperature of 510 K. After CH3*" align="middle"> exposure, TPD showed O leaves the Cu2O surface as CO2 over a range from 400 to 700 K with a peak temperature at 590 K. With carbon impurity below the XPS detection limit, thermal reduction of CuO to Cu2O was verified by XPS near 890 K. TPD experiments showed that O leaves the CuO surface as O2 at 890 K. Without surface C, thermal reduction of Cu2O was not observed up to 1073 K. Reduction of Cu2O without reactive radical species (D* or CH3*" align="middle">) was negligible. These results suggest that thin films of copper oxide can be reduced at 400 K with D* and CH3*" align="middle">. ©2001 American Institute of Physics.

Reduction of copper oxides by UV radiation and atomic hydrogen studied by XPS

TH Fleisch — 2007-02-14T08:47:35-00:00

Applications of Surface Science, Vol. 10, No. 1. (1982), pp. 51-62.

The reduction of polycrystalline cupric oxide (CuO) and cuprous oxide (Cu2O) by UV irradiation and by atomic hydrogen was investigated with X-ray photoelectron spectroscopy (XPS or ESCA). UV photons from a low pressure mercury lamp ([lambda]=2537 A, HV=4.8 cV) slowly reduce both CuO and Cu2O at room temperature. After approximately 10 h of irradiation the sample surfaces appear completely reduced to metallic Cu. This indicates that after that time the top 30 A of the sample pellets, the approximate sampling depth of XPS, have been reduced. Further irradiation causes the reduction to progress through the pellet interior and bulk phase. The sample color changes from dark to metallic copper. Photochemically generated hydrogen atoms reduce copper oxides at ambient temperatures. The reduction rate is about 10 times faster than the one caused by UV light alone. The reduction of Cu2O is in both cases slightly slower than the one of CuO. The degree of reduction has been calculated from XPS data in different ways involving the atomic ratio of O/Cu, the relative intensity of the shake-up structure of CuO, and changes in the structure of the Cu L3M45M45 Auger line. Freshly reduced Cu surfaces are sensitive to air exposure. They oxidize easily to Cu2O.

Characterization of Cu surface cleaning by hydrogen plasma

MR Baklanov — 2007-02-14T08:02:02-00:00

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, Vol. 19, No. 4. (2001), pp. 1201-1211.

When a Cu surface is exposed to a clean room ambient, a surface layer containing Cu2O, CuO, Cu(OH)2, and CuCO3 is formed. Thermal treatment in a vacuum combined with hydrogen plasma can remove this layer. Water and carbon dioxide desorb during the thermal treatment and the hydrogen plasma reduces the remaining Cu oxide. Ellipsometric, x-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectroscopy analyses indicate that the mechanism of interaction of the H2 plasma with this layer depends on temperature. When the temperature is below 150 °C, H2 plasma cannot completely reduce Cu oxide. Hydrogen diffuses through the oxide and hydrogenation of the Cu layer is observed. The hydrogenated Cu surface has a higher resistance than a nontreated Cu layer. The hydrogen plasma efficiently cleans the Cu surface when the substrate temperature is higher than 150 °C. In this case, hydrogen atoms have enough activation energy to reduce Cu oxide and adsorbed water forms as a byproduct of Cu oxide reduction. When the wafer temperature is higher than 350 °C, the interaction of the Cu film with hydrogen and residual oxygen is observed. ©2001 American Vacuum Society.

The Removal of Copper Oxides by Ethyl Alcohol Monitored In Situ by Spectroscopic Ellipsometry

Alessandra Satta — 2007-02-14T07:53:32-00:00

Journal of The Electrochemical Society, Vol. 150, No. 5. (2003), pp. G300-G306.

As an interconnect material, copper has the disadvantage of not forming self-limiting oxides, which can negatively affect device performance and reliability. Undesired oxide layers need to be removed by in situ cleaning, before the copper is subjected to subsequent depositions. We have used ethyl alcohol (C2H5OH) as a vapor phase reducing agent to remove copper oxides formed on electroplated copper films upon exposure to the ambient. Spectroscopic ellipsometry has been used to monitor the reduction process in situ. Ex situ characterization using X-ray photoelectron spectroscopy and atomic force microscopy support in situ measurements. While oxide removal can be achieved at temperatures as low as 130°C, independent of oxide layer thickness and composition, it occurred more efficiently at 200°C, showing compatibility with the low temperature (<400°C) processing requirements of low dielectric constant materials. The initial reaction involves the reduction of Cu2+ to Cu+ species followed by a second phase consisting of Cu+ conversion to elemental copper, producing a clean metal surface. Reduction of Cu2+ to Cu+ species is the rate-limiting step as evidenced by enhanced sensitivity to the reaction temperature. ©2003 The Electrochemical Society. All rights reserved.

The reduction of copper oxide thin films with hydrogen plasma generated by an atmospheric-pressure glow discharge

Yasushi Sawada — 2007-02-14T07:47:03-00:00

Journal of Physics D: Applied Physics, Vol. 29, No. 10. (1996), pp. 2539-2544.

The reduction of copper oxide thin films by a hydrogen plasma generated by an atmospheric-pressure glow (APG) discharge was investigated. The copper oxide films were prepared by heating the sputtered copper films to IMGC in the air (heat-formed copper oxide) or by sputtering (sputtered copper oxide). Both films were composed of IMG. The reduction occurs first on the surface, then the IMG interface gradually shifts from the surface into the inner region and finally the whole layer is reduced to metallic copper. This process is approximately explained by assuming that the diffusion of the atomic hydrogen in the reduced layer is the rate-deyermining step. By transmission electron microscopic (TEM) observation, a layer of 3 - 5 nm thickness composed of many IMG microcrystals was observed along the surface of the heat-formed copper oxide. After the APG hydrogen plasma treatment, the crystal IMG layer disappeared and the crystalline lattice was re-arranged to form large crystal Cu grains.

Atomic layer deposition of Ta-based thin films: Reactions of alkylamide precursor with various reactants

WJ Maeng — 2007-02-14T13:43:17-00:00

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, Vol. 24, No. 5. (2006), pp. 2276-2281.

The growth mechanisms and film properties of atomic layer deposition (ALD) Ta-based thin films were investigated from alkylamide precursor [Ta(NMe2)5, (PDMAT)]. The reactions of PDMAT with various reactants including water, NH3, oxygen, and hydrogen plasma were studied and the resulting film properties were investigated by various analysis techniques. For TaN ALD from NH3 and H plasma, the films were contaminated by considerable amount of carbon, while the Ta2O5 deposited from water and O plasma were quite pure. Also, nitrogen was incorporated for ALD from PDMAT and H plasma, while no nitrogen incorporation was observed for O-plasma based plasma enhanced-ALD of Ta2O5 except at high deposition temperature over 300 °C. The results were comparatively discussed focusing on the differences in growth mechanism depending on reactants. ©2006 American Vacuum Society

The new field of nanopiezotronics

Zhong Wang — 2007-05-03T12:43:49-00:00

Materials Today, Vol. 10, No. 5. (May 2007), pp. 20-28.

Semiconducting and piezoelectric nanowires and nanobelts have exciting applications in electronics, optoelectronics, sensors, and the biological sciences. We review the use of ZnO nanowires and nanobelts in electromechanical coupled devices. A nanogenerator that uses aligned ZnO nanowires for converting nanoscale mechanical energy into electric energy is described. The mechanism of the nanogenerator relies on the unique coupling of ZnO's piezoelectric and semiconducting properties. The approach has the potential to convert biological mechanical energy, acoustic/ultrasonic vibration energy, and biofluid hydraulic energy into electricity, demonstrating a new pathway for harvesting energy for self-powered wireless nanodevices and nanosystems. Based on the nanogenerator mechanism, we also describe piezoelectric field-effect transistors, diodes, force/pressure sensors, and resonators. These devices form the fundamental components of nanopiezotronics, a new field in nanotechnology.

Cu2O/n-ZnO nanowire solar cells on ZnO:Ga/glass templates

Ting-Jen Hsueh — 2007-05-03T12:41:19-00:00

Scripta Materialia, Vol. 57, No. 1. (July 2007), pp. 53-56.

We report the deposition of p-Cu2O onto vertical n-ZnO nanowires prepared on ZnO:Ga/glass templates. With the sputtered Cu2O, the nanowires became club0like (nanowire with a head). Experimental results indicate that sputtered Cu2O also formed nano-shells surrounding the ZnO cores. The p-Cu2O/n-ZnO nanowire heterostructure exhibits rectifying behavior with a sharp turn on at ~0.46 V. Furthermore, the short-circuit photocurrent density, open circuit voltage, fill factor and conversion efficiency of the fabricated solar cell were 2.35 mA cm-2, 0.13 V, 0.29 and around 0.1%, respectively.

Ellipsometry characterization of oxidized copper layers for chemical mechanical polishing process

H Nishizawa — 2007-02-15T14:41:48-00:00

Thin Solid Films, Vol. 455-456 (1 May 2004), pp. 491-494.

Oxidized copper layers prepared in hydrogen peroxide for chemical mechanical polishing (CMP) have been characterized using spectroscopic ellipsometry. In the spectral analysis of the oxidized copper layers, Lorentz oscillator model is used. Lorentz model was assumed a graded layer based on glow discharge spectroscopy analysis, the precise optical constants and thickness of oxidized copper layers was determined. Its optical constants and FT-IR analysis indicate that the oxidized copper layers consist of CuO and voids. The proportion of void was increases with growth of the oxidized layers. These analyses are useful to investigate an advanced CMP process using organic acid.

Optical properties and highly efficient laser oscillation of Nd:YAG ceramics

J Lu — 2007-05-02T00:12:12-00:00

Applied Physics B: Lasers and Optics, Vol. 71, No. 4. (1 October 2000), pp. 469-473.

Diode-pumped Yb:Y[sub 2]O[sub 3] ceramic laser

J Kong — 2007-06-28T22:25:16-00:00

Applied Physics Letters, Vol. 82, No. 16. (2003), pp. 2556-2558.

We report on a diode-pumped polycrystalline Yb:Y2O3 ceramic laser. We demonstrate that, with a pump power of 11 W at 937 nm, 0.75-W cw laser output at 1078 nm can be obtained from the laser. The laser had a threshold of 4.7 W and a slope efficiency of 12.6% when an output coupler of R = 98% was used. ©2003 American Institute of Physics.

Fabrication of Transparent Yttria Ceramics at Low Temperature Using Carbonate-Derived Powder

Noriko Saito — 2007-05-02T20:24:30-00:00

Journal of the American Ceramic Society, Vol. 81, No. 8. (August 1998), pp. 2023-2028.

A new preparation method for a highly sinterable yttria powder has been developed, the resultant powder characterized, and its sinterability studied. As a precursor of the yttria powder, a fine and needle-shaped yttrium carbonate was prepared by a precipitation and aging method. A fine and low-agglomeration yttria powder was obtained by calcining the carbonate precursor at 1100°C. The primary crystallites measured ~0.1 µm and weakly agglomerated to a size of ~0.3 µm. The powder had a very high sinterability, so that the powder compact could be sintered to transparency by normal sintering under vacuum without additives at low temperatures, over 1600°C. The sintered transparent ceramics exhibited a homogeneous microstructure with no abnormal grain growth.

Sintering Crystalline Solids. II. Experimental Test of Diffusion Models in Powder Compacts

RL Coble — 2007-05-03T17:30:08-00:00

Journal of Applied Physics, Vol. 32, No. 5. (1961), pp. 793-799.

During sintering in alumina powder compacts, the density has been found to increase linearly with the logarithm of time, and the grain size increases with the one-third power of time. Incorporation of the time dependence of grain size increase into latestage bulk diffusion sintering models (from Part I) [R. L. Coble, J. Appl. Phys. 32, 787 (1961)] leads to corrected models by which a semilogarithmic behavior is predicted. The presence of density gradients in normally fabricated pellets makes impossible the deduction of whether theoretical density will be achieved from the early stages of the course of densification. Diffusion coefficients calculated from the intermediate and later stages of sintering bear order-of-magnitude agreement with those calculated from the initial-stage sintering measurements in alumina. All diffusion coefficients from sintering data are higher than Kingery's measured diffusion coefficients for oxygen. It is hypothesized that the sintering process must then be controlled by bulk diffusion of aluminum ions while the oxygen transport takes place along the grain boundaries. In controlling the sinterability of alumina to theoretical density, it appears that magnesia does not “inhibit” discontinuous grain growth, but instead increases the sintering rate such that discontinuous growth nuclei do not have time to form. ©1961 The American Institute of Physics

Fail-safe light transmitting SiC fiber-reinforced spinel matrix optomechanical composite

AF Dericioglu — 2007-05-18T02:34:31-00:00

Journal of Materials Science, Vol. 37, No. 3. (1 February 2002), pp. 523-530.

A light transmitting “Optomechanical Composite” was fabricated by incorporating SiC (SCS-6) fibers into optically transparent MgAl2O4 ceramics. The fibers were aligned unidirectionally in the matrix with a spacing of 1 to 4 mm to allow light transmittance between the fibers: resulting fiber volume content was from 0.75 to 0.19 vol%. The total and in-line light transmittance of the matrix and the composite was measured in the visible/near-IR wavelength region. The light transmittance of the composite was found to be decreasing with increasing fiber volume fraction, however, even the composite with the highest fiber volume fraction has a light transmittance of 25–50% in the visible wavelength region. Although the optical transparency of the matrix becomes slightly lower by the incorporation of the opaque fibers, its catastrophic failure is prevented by the bridging effect of the intact fibers, introducing the fail-safe nature to the brittle ceramic material. To obtain this fail-safe mechanism, the minimum fiber volume fraction was ~0.37 vol% in the present material system.

The fabrication of the translucent ZnO by sintering

Yusuke Moriyoshi — 2007-05-08T23:02:07-00:00

Journal of Materials Science, Vol. 12, No. 11. (1 November 1977), pp. 2347-2349.

Nd[sup 3+]-doped lead lanthanum zirconate titanate transparent ferroelectric ceramic as a laser material: Energy transfer and stimulated emission

ASS de Camargo — 2007-05-17T21:11:12-00:00

Applied Physics Letters, Vol. 86, No. 15. (2005), pp. 152905-152907.

An investigation of the spectroscopic characteristics of high optical quality Nd3+-doped lead lanthanum zirconate titanate transparent ferroelectric ceramics was done to evaluate its potentiality as a near-infrared laser active host. Nonradiative losses that could compromise laser action were quantified in terms of the Judd-Ofelt theory, the Dexter model for ion–ion energy transfer and by measuring excited state absorptions. It was verified that under low power 0.8 µm diode pumping, ion–ion energy transfers are negligible and the system presents =0.87. Stimulated emission was observed at 1.06 µm (SE=3.5×10–20 cm2) with no influence of ESA transitions. ©2005 American Institute of Physics

Origin of Metallic States at the Heterointerface between the Band Insulators LaAlO[sub 3] and SrTiO[sub 3]

K Yoshimatsu — 2008-07-15T07:17:35-00:00

Physical Review Letters, Vol. 101, No. 2. (2008)

We have studied the electronic structure at the heterointerface between the band insulators LaAlO3 and SrTiO3 using in situ photoemission spectroscopy. Our experimental results clearly reveal the formation of a notched structure on the SrTiO3 side due to band bending at the metallic LaAlO3/TiO2-SrTiO3 interface. The structure, however, is absent at the insulating LaAlO3/SrO-SrTiO3 interface. The present results indicate that the metallic states originate not from the charge transfer through the interface on a short-range scale but from the accumulation of carriers on a long-range scale.

Electrical characterization of ZnO, including analysis of surface conductivity

Schmidt — 2007-07-05T13:16:49-00:00

Applied Physics A, Vol. 88, No. 1. (July 2007), pp. 71-75.

Ab initio density-functional study of NO on close-packed transition and noble metal surfaces: I. Molecular adsorption

Marek Gajdo[scaron] — 2007-09-20T19:25:31-00:00

Journal of Physics: Condensed Matter, Vol. 18, No. 1. (2006), pp. 13-40.

Ab initio density-functional calculations have been used to investigate the molecular adsorption of NO on the close-packed surfaces of late transition metals (Co, Ni, Ru, Rh, Pd, Ir, Pt) and noble metals (Cu, Ag, Au). The energetics, geometry, and vibrational properties of the adsorbate-substrate complex have been calculated. With the exception of Ir and Au, adsorption in a hollow-site is always preferred. On Ir(111) the potential-energy surface for NO adsorption is very flat, with a slight preference for a linear on-top geometry. On Au(111), where NO adsorption is only very weak, bridge-adsorption with a strong tilting of the NO molecule relative to the surface normal is predicted. Among the different hollows on a (111) surface preference changes from hcp on Co, Ni, Ru, Rh to fcc on Cu, Pd, Pt, and Ag. However, not only on Ir, but also on Co, Ru, Rh and Pt are the site-dependent differences in the adsorption energies small enough to allow a coexistence of NO adsorbed on different sites. A careful comparison of the calculated vibrational eigenmodes with the available experimental data leads to full agreement between the predicted site preference and the observed NO stretching frequencies. This leads to a redefinition of the characteristic frequency intervals to be used for the site assignment. The trends in the adsorption energies and in the vibrational spectra are compared to those derived from studies of CO adsorption on the same surfaces and discussed in terms of the filling of the d-band of the substrate. In a forthcoming publication, these studies will be extended to NO dissociation on these substrates.

Ab initio density-functional study of NO adsorption on close-packed transition and noble metal surfaces: II. Dissociative adsorption

Marek Gajdo[scaron] — 2007-09-20T19:19:05-00:00

Journal of Physics: Condensed Matter, Vol. 18, No. 1. (2006), pp. 41-54.

Following our investigation of molecular NO adsorption (Gajdos et al 2006 J. Phys.: Condens. Matter 18 13), the dissociation of NO molecules on the close-packed surfaces of late transition (Co, Ni, Ru, Rh, Pd, Ir, Pt) and noble (Cu, Ag, Au) metals has been studied using first-principles density functional calculations. The nudged-elastic-band method has been used for the determination of the transition states. Our results demonstrate that the transition-state energies show a linear dependence on the dissociative chemisorption energies according to the Brønsted-Evans-Polanyi rule. The validity of this linear relationship is shown to arise from the geometrical similarity of the transition states on all metals, which are very close to the final state geometries.

Ratiometric and fluorescence-lifetime-based biosensors incorporating cytochrome c' and the detection of extra- and intracellular macrophage nitric oxide

SLR Barker — 2007-08-07T19:16:22-00:00

Anal. Chem., Vol. 71, No. 9. (1999), pp. 1767-1772.

Ratiometric and lifetime-based sensors have been designed for cellular detection of nitric oxide. These sensors incorporate cytochrome c', a hemoprotein known to bind nitric oxide selectively. The cytochrome c' is labeled with a fluorescent reporter dye, and changes in this dye's intensity or fluorescence lifetime are observed as the protein binds nitric oxide. The ratiometric sensors are composed of dye-labeled cytochrome c' attached to the optical fiber via colloidal gold, along with fluorescent microspheres as intensity standards. These ratiometric sensors exhibit linear response, have fast response times (? 0.25 s), and are completely reversible. The sensors are selective over numerous common interferents such as nitrite, nitrate, and oxygen species, and the limit of detection is 8 ?M nitric oxide. The lifetime-based measurements are made using free, dye-labeled cytochrome c' in solution and have a limit of detection of 30 ?M nitric oxide. The use of these two techniques has allowed measurement of intra- and extracellular macrophage nitric oxide. Employing the ratiometric fiber sensors gave a multicell culture average extracellular nitric oxide concentration of 210 + 90 ?M for activated macrophages, while an average intracellular concentration of 160 ± 10 ?M was determined from the lifetime-based measurements of dye-labeled cytochrome c' in the macrophage cytosol. Microscopic adaptation of the lifetime-based methods described here would allow direct correlation of intracellular nitric oxide levels with specific cellular activities, such as phagocytosis.

Nanostructured Zinc Oxide Particles in Chemically Modified Electrodes for Biosensor Applications

Ashok Kumar — 2008-03-05T10:21:09-00:00

Analytical Letters, Vol. 41, No. 2. (2008), pp. 141-158.

Zinc oxide (ZnO) has received considerable attention because of its unique optical, semiconducting, piezoelectric, and magnetic properties. ZnO nanostructures exhibit interesting properties including high catalytic efficiency and strong adsorption ability. Recently, the interest has been focused toward the application of ZnO in biosensing because of its high isoelectric point (9.5), biocompatibility, and fast electron transfer kinetics. Such features advocate the use of this exciting material as a biomimic membrane to immobilize and modify biomolecules. This review highlights the potential use of ZnO in modified electrodes and biosensing.

Electrocatalysis and Amperometric Detection of the Reduced Form of Nicotinamide Adenine Dinucleotide at Toluidine Blue/Zinc Oxide Coated Electrodes

Ashok Kumar — 2008-03-05T10:56:53-00:00

Electroanalysis, Vol. 19, No. 18. (2007), pp. 1952-1958.

Thin toluidine blue (TBO) and zinc oxide (ZnO) hybrid films have been grown on glassy carbon electrode (GCE) and indium tin oxide coated (SnO2) glass electrodes by using cyclic voltammetry (CV). Scanning electron microscopy (SEM) images revealed spherical and beads-like shape of highly oriented TBO/ZnO hybrid films. Energy dispersive spectrometry (EDS) results declared that the films composed mainly of Zn and O. Moreover, TBO/ZnO hybrid films modified electrode is electrochemically active, dye molecules were not easily leached out from the ZnO matrix and the hybrid films can be considered for potential applications as sensor for amperometric determination of reduced nicotinamide adenine dinucleotide (NADH) at 0.0 V. A linear correlation between electrocatalytic current and NADH concentration was found to be in the range between 25

Rotational diffusion constant of microcrystals of Wolfram oxide (WO3) in suspension

Hitoshi Suda — 2007-10-09T22:47:14-00:00

Journal of Colloid and Interface Science, Vol. 104, No. 1. (March 1985), pp. 204-208.

Rotational Brownian motion of Wolfram oxide (WO3) colloids having rectangular-platelike shapes has been analyzed by means of a direct microscopic observation. By using a video-recording system and a time averaging method on the trace of each colloid in its polydispersed suspension, the rotational diffusion constants have been obtained as a function of its particle size. The rotational diffusion constants thus obtained have been compared with Perrin's expression for rotational diffusion of general ellipsoidal particles, by assuming that a WO3 colloid has approximately an ellipsoidal shape with three different axes. The order of the magnitude of rotational diffusion constant, Dr, about the longest axis, c, has been found to be about 10-3/sec for c around 5 [mu]m. The agreement with the theory has been numerically satisfactory, and the linear dependence of --log Dr on c seen in the theory in this c range has been nearly established in the experiment.

Kinetics of dissolution of ZnO, MgO and their solid solutions in aqueous sulphuric acid solutions

J Guspiel — 2008-07-27T23:22:41-00:00

Hydrometallurgy, Vol. 34, No. 2. (November 1993), pp. 203-220.

The dissolution kinetics of polycrystalline preparations of ZnO, MgO and their solid solutions was studied in H2SO4 aqueous solutions using the rotating disc technique. For each of these oxides, ranges of experimental parameters were established within which the rate of dissolution was diffusional, activation- diffusional or activation-controlled. For ZnO the limits of these ranges were shifted towards higher acid concentrations and lower temperatures than for MgO. In the diffusional regime the dissolution rate was controlled by the protons transporting ions (H3O+ and HSO4-). At concentrations of 0.01-0.1 M H2SO4, MgO dissolution occurred under activation-diffusional and activation-control; the reaction order with respect to the concentration of H3O+ ions was 0.5. At those H2SO4 concentrations, the dissolution rate of ZnO remained diffusionally controlled. In solutions of CH2SO4 >= 0.1 M H2SO4, the reaction order with respect to H3O+ concentration was close to 0.1 for each preparation. The rate of chemical reaction found for ZnO and Zn0.93Mg0.07O was about ten times higher than for MgO and MgyZn1-yO, the reduction of y within the range 1 >=y>=0.65 led to an increase of the dissolution rate. An attempt has been made to give an explanation for the results obtained.

Etching of MgO crystals in acids: surface micromorphology

K Sangwal — 2008-07-27T23:17:35-00:00

Journal of Materials Science, Vol. 11, No. 12. (1 December 1976), pp. 2271-2282.

Several etchants based on simple acids are proposed for revealing dislocations on 100, 110 and 111 faces of MgO single crystals. Some acids under different etching conditions are shown to produce etch pyramids at decorated dislocations, while etch hillocks, spherulites and dendrites are formed under different conditions. With increasing concentration of H2SO4, pits, circular pits, pits, pyramids as well as pits, dendrites and spherulites, and hillocks are formed in that order. Etching characteristics of other acids also showed a more or less identical trend. The observations are interpreted with the assumption that with increasing concentration of acid, an effective undersaturation and later supersaturation is developed very close to the dissolving crystal face. The chemistry of the dissolution process is also discussed.

Etchant for revealing dislocations in magnesium oxide single crystals

Toshio Harada — 2008-07-27T23:16:11-00:00

Journal of Crystal Growth, Vol. 44, No. 5. (December 1978), pp. 635-637.

A newly developed etchant is proposed for revealing dislocations on the (100) surface of MgO. The reliability and usefulness of this etchant have been established by the matching of pits on the separated faces of a cleaved crystal and by the pit arrays obtained by etching of a plastically deformed crystal. The size and shape of etch pits are temperature- as well as concentration- dependent. With increasing concentration of the etchant, the etch pits changed their shape from square with the edges oriented in the <110> directions, to circular.

Vacuum ultraviolet thin films. 1: Optical constants of BaF2, CaF2, LaF3, MgF2, Al2O3, HfO2, and SiO2 thin films

Muamer Zukic — 2008-07-27T21:07:19-00:00

Appl. Opt., Vol. 29, No. 28. (1 October 1990), pp. 4284-4292.

The optical constants of MgF 2 (bulk) and BaF 2 , CaF 2 , LaF 3 , MgF 2 , Al 2 O 3 , HfO 2 , and SiO 2 films deposited on MgF 2 substrates are determined from photometric measurements through an iteration process of matching calculated and measured values of the reflectance and transmittance in the 120–230-nm vacuum ultraviolet wavelength region. The potential use of the listed fluorides and oxides as vacuum ultraviolet coating materials is discussed in part 2 of this paper.

Pump-probe imaging of femtosecond pulsed laser ablation of silicon with thermally grown oxide films

Joel Mcdonald — 2008-02-12T00:25:35-00:00

Journal of Applied Physics, Vol. 102, No. 6. (2007)

Transparent Nano-Composites Ceramics by Annealing of Amorphous Phase in the HfO2-Al2O3-GdAlO3 System

Shunji Araki — 2007-05-18T03:40:03-00:00

International Journal of Applied Ceramic Technology, Vol. 1, No. 2. (2004), pp. 155-160.

We have succeeded in fabricating transparent nano-structured ceramics by annealing of the amorphous phase obtained by the solidification of the eutectic melt in the ternary system HfO2- Al2O3- GdAlO3. The ceramics annealed at 1273 K for 6 hr contained 5-10-nm cubic hafnia grains, and those annealed at 1273 K for 72 hr contained both cubic hafnia and gadolinium aluminum garnet grains 5-10 nm in size. They showed high transparency. Annealing at 1473 K, however, resulted in grain growths that brought about non-transparency.

Fabrication of Polycrystalline, Transparent YAG Ceramics by a Solid-State Reaction Method

Akio Ikesue — 2007-05-02T00:17:49-00:00

Journal of the American Ceramic Society, Vol. 78, No. 1. (1995), pp. 225-228.

Polycrystalline, transparent YAG (Y3AI5O12) ceramics were fabricated by a solid-state reaction method using high-purity Al2O3 and Y2O3 powders. The mixed powder compacts were sintered at 1600o to 1850oC for 5 h under vacuum. Optical transmittance in the region between the ultraviolet and infrared wavelengths for YAG ceramics (1 mm thick) sintered at 1800oC was similar to that for a YAG single crystal.

72 W Nd:Y[sub 3]Al[sub 5]O[sub 12] ceramic laser

Jianren Lu — 2007-05-02T00:08:52-00:00

Applied Physics Letters, Vol. 78, No. 23. (2001), pp. 3586-3588.

A high-power continuous-wave polycrystalline 1% Nd:Y3Al5O12 (Nd:YAG) ceramic rod laser was demonstrated. With 290 W/808 nm laser diode pumping, cw laser output of 72 W was obtained at 1064 nm. The optical-to-optical conversion efficiency is 24.8%. Thermally induced birefringence properties of Nd:YAG ceramic was also investigated. ©2001 American Institute of Physics.

Transparent ceramic lamp envelope materials

GC Wei — 2007-05-03T17:35:52-00:00

Journal of Physics D: Applied Physics, Vol. 38, No. 17. (2005), pp. 3057-3065.

Transparent ceramic materials with optical qualities comparable to single crystals of similar compositions have been developed in recent years, as a result of the improved understanding of powder-processing-fabrication- sintering-property inter-relationships. These high-temperature materials with a range of thermal and mechanical properties are candidate envelopes for focused-beam, short-arc lamps containing various fills operating at temperatures higher than quartz. This paper reviews the composition, structure and properties of transparent ceramic lamp envelope materials including sapphire, small-grained polycrystalline alumina, aluminium oxynitride, yttrium aluminate garnet, magnesium aluminate spinel and yttria–lanthana. A satisfactory thermal shock resistance is required for the ceramic tube to withstand the rapid heating and cooling cycles encountered in lamps. Thermophysical properties, along with the geometry, size and thickness of a transparent ceramic tube, are important parameters in the assessment of its resistance to fracture arising from thermal stresses in lamps during service. The corrosive nature of lamp-fill liquid and vapour at high temperatures requires that all lamp components be carefully chosen to meet the target life. The wide range of new transparent ceramics represents flexibility in pushing the limit of envelope materials for improved beamer lamps.

Polycrystalline Nd:YAG ceramics lasers

Akio Ikesue — 2007-05-02T22:41:13-00:00

Optical Materials, Vol. 19, No. 1. ( 2002), pp. 183-187.

Optical spectra of undoped and rare-earth-(=Pr, Nd, Eu, and Er) doped transparent ceramic Y[sub 3]Al[sub 5]O[sub 12]

Masami Sekita — 2007-05-02T19:32:14-00:00

Journal of Applied Physics, Vol. 69, No. 6. (1991), pp. 3709-3718.

Undoped and rare-earth- (Pr, Nd, Eu, and Er) doped transparent Y3Al5O12 ceramics have been prepared, and their optical spectra have been measured. It is found that absorption coefficient of the undoped ceramic Y3Al5O12 is almost independent of wavelength with 0.258 cm−1, which gives transmittance of the undoped ceramic Y3Al5O12 to be, for example, 95% for a 2-mm height. Peaks in the absorption and emission spectra of Pr:Y3Al5O12 are assigned to the transitions in 4f2 configuration. The transitions from the multiplets with total angular momentum J=0 to multiplets with even J momentum are strong as predicted by Judd–Ofelt theory. The overall and detail structure of the absorption and emission spectra of Nd:Y3Al5O12 is the same as those in a previous publication. However, the absorption coefficient at nonabsorbing wavelengths by Nd3+ is reduced from more than 1.7 to 0.25 cm−1. A simple estimation of the population inversion threshold of the Nd:Y3Al5O12 ceramic reveals that the threshold is still about 25 times larger than that of single-crystal Nd:Y3Al5O12. Peaks in the absorption and emission spectra of Er:Y3Al5O12 ceramic are assigned to the transitions in 4f11 configuration. The transition energies agree well with those reported for single-crystal Er:Y3Al5O12 and the other hosts within 30 cm−1. A Stark splitting scheme for some multiplets has been constructed. Peaks in the emission, absorption, and excitation spectra of Eu:Y3Al5O12 ceramic are assigned to the transitions in 4f6 configuration. The transition energies are in very good agreement with those of single-crystal Eu:Y3Al5O12 within 8 cm−1 for the emission peaks and 3 cm−1 for the absorption and excitation peaks. Spectral characteristics and derivation of a broad peak in the absorption spectrum at around 280 nm are discussed in some detail. Journal of Applied Physics is copyrighted by The American Institute of Physics.

Induced emission cross section of Nd:Y[sub 3]Al[sub 5]O[sub 12] ceramics

M Sekita — 2007-05-03T19:44:27-00:00

Journal of Applied Physics, Vol. 67, No. 1. (1990), pp. 453-458.

Optical absorption and emission spectra have been measured for Nd-doped Y3Al5O12 ceramics obtained by a urea precipitation method. The optical properties of the ceramics are almost the same as those of single crystals grown by the Czochralski method and floating-zone method, except for a higher background absorption of 2.5–3 cm–1. The energy-level structure for Nd3 + in the Y3Al5O12 ceramics is determined for a 1-at. % Nd concentration. The induced emission cross section for the 1-at. %-Nd-doped ceramic is calculated to be 4.9×10–19 cm2, which falls in the range reported for the Nd:Y3Al5O12 single crystals. The Nd concentration dependence of the emission decay time at the 1064-nm laser wavelength was also measured, and typical concentration quenching was observed. The decay time of the 1-at. %-Nd-doped ceramic is 219 µs, which is slightly smaller than the reported values for single crystals. Journal of Applied Physics is copyrighted by The American Institute of Physics.

The NosX and NirX proteins of Paracoccus denitrificans are functional homologues: their role in maturation of nitrous oxide reductase.

NF Saunders — 2008-05-11T09:23:21-00:00

Journal of bacteriology, Vol. 182, No. 18. (September 2000), pp. 5211-5217.

The nos (nitrous oxide reductase) operon of Paracoccus denitrificans contains a nosX gene homologous to those found in the nos operons of other denitrifiers. NosX is also homologous to NirX, which is so far unique to P. denitrificans. Single mutations of these genes did not result in any apparent phenotype, but a double nosX nirX mutant was unable to reduce nitrous oxide. Promoter-lacZ assays and immunoblotting against nitrous oxide reductase showed that the defect was not due to failure of expression of nosZ, the structural gene for nitrous oxide reductase. Electron paramagnetic resonance spectroscopy showed that nitrous oxide reductase in cells of the double mutant lacked the Cu(A) center. A twin-arginine motif in both NosX and NirX suggests that the NosX proteins are exported to the periplasm via the TAT translocon.

Nitric oxide is a signal for NNR-mediated transcription activation in Paracoccus denitrificans.

RJ Van Spanning — 2008-05-11T09:20:07-00:00

Journal of bacteriology, Vol. 181, No. 13. (July 1999), pp. 4129-4132.

By using the 'lacZ gene, the activities of the nirI, nirS, and norC promoters were assayed in the wild type and in NNR-deficient mutants of Paracoccus denitrificans grown under various growth conditions. In addition, induction profiles of the three promoters in response to the presence of various nitrogenous oxides were determined. Transcription from the three promoters required the absence of oxygen and the presence both of the transcriptional activator NNR and of nitric oxide. The activity of the nnr promoter itself was halved after the cells had been switched from aerobic respiration to denitrification. This response was apparently not a result of autoregulation or of regulation by FnrP, since the nnr promoter was as active in the wild-type strain as it was in NNR- or FnrP-deficient mutants.

Field-driven hysteretic and reversible resistive switch at the Ag--Pr[sub 0.7]Ca[sub 0.3]MnO[sub 3] interface

A Baikalov — 2008-04-09T19:25:40-00:00

Applied Physics Letters, Vol. 83, No. 5. (2003), pp. 957-959.

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Reversible resistive switching of SrTiO[sub x] thin films for nonvolatile memory applications

Dooho Choi — 2008-04-02T18:21:55-00:00

Applied Physics Letters, Vol. 88, No. 8. (2006)

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New Conduction and Reversible Memory Phenomena in Thin Insulating Films

JG Simmons — 2008-04-08T22:02:49-00:00

Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences (1934-1990), Vol. 301, No. 1464. (3 October 1967), pp. 77-102.

It has been observed that when thin (200 to 3000 $overset\circ \mathrm A$) film insulators have been formed by the electrolytic introduction of gold ions from one of the electrodes they can draw appreciable currents. They then show temperature-independent conductivity, voltage-controlled negative resistance and reversible voltage and thermal-voltage memory effects. It is postulated that the injected ions introduce a broad band of localized impurity levels within the normally forbidden band of the insulator. The electrons are assumed to move through the insulator by tunnelling between adjacent sites within the impurity band; it is also assumed that the electrons can, under certain conditions, be trapped within the impurity band. A model based on these ideas accounts in a self-consistent manner for all the experimental observations, and calculations of current-voltage characteristics based on the model are in fact in agreement with them.

Hysteretic current--voltage characteristics and resistance switching at a rectifying Ti/Pr[sub 0.7]Ca[sub 0.3]MnO[sub 3] interface

A Sawa — 2008-04-09T19:24:07-00:00

Applied Physics Letters, Vol. 85, No. 18. (2004), pp. 4073-4075.

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Colossal electroresistance of a Pr0.7Ca0.3MnO 3 thin film at room temperature

A Odagawa — 2008-04-09T19:21:55-00:00

Phys. Rev. B Condens. Matter Mater. Phys., Vol. 70, No. 22. (2004)

The electronic conduction through a Pr0.7Ca 0.3MnO3 thin film is investigated by measurements using dc and pulsed biases. Semiconducting Pr0.7Ca0.3MnO 3 films sandwiched by electrodes show both hysteretic and asymmetric behaviors in current-voltage characteristics. The observed conduction characteristics exhibit the space-charge-limited-current effect, and the hysteretic behavior can be ascribed to a carrier trapping and detrapping of the trap sites in the manganite. The hysteresis induces a colossal electroresistance (CER) of more than 5000% at room temperature. The CER ratio is independent of the duration time of pulses from an infinite (dc) down to 150 ns, indicating that the carrier filling of all the traps can be completed within a short time.

Giant resistance switching in metal-insulator-manganite junctions: Evidence for Mott transition

Rickard Fors — 2008-04-09T19:12:43-00:00

Physical Review B (Condensed Matter and Materials Physics), Vol. 71, No. 4. (2005)

Heteroepitaxial CeO2(80 nm)/L0.67Ca0.33MnO3(400 nm) film structures have been pulsed laser deposited on LaAlO3(001) single crystals to fabricate two terminal resistance switching devices. Ag/CeO2/L0.67Ca0.33MnO3 junctions exhibit reproducible switching between a high resistance state (HRS) with insulating properties and a semiconducting or metallic low resistance state (LRS) with resistance ratios up to 105. Reversible electrical switching is a polar effect achievable both in continuous sweeping mode and in the pulse regime. Successive temperature crossover of electronic transport from the thermal activation of the deep levels (Ea = 320 meV) at high temperatures to thermal activation of the shallow levels (Ea = 40 meV) and finally at low temperatures to the regime of temperature independent resistance, usually associated with quantum tunneling, has been found for the insulating HRS. The temperature dependence of the LRS reveals a para-to-ferromagnetic phase transition in the L0.67Ca0.33MnO3 (LCMO) electrode at Tc = 260 K and an anomaly at lower temperatures ~200 K corresponding to the Curie temperature of the Mn4+ depleted part of the LCMO film. Current-voltage characteristics in the LRS are highly nonlinear, and show negative differential conductivity (NDC). We suggest that the reversible resistance switching ocurrs due to the electric field induced nucleation of filament-type conducting valence-shifted CeOx domains inside the insulating CeO2 matrix. The abrupt insulator-to-metal transition is the result of localization of 4f electronic states in Ce3+ ions and the subsequent appearance of hole conductivity in the oxygen p-bands. NDC at low temperatures is relied upon the interband scattering of CeOx carriers from a low energy, high mobility valley into a high energy valley with low mobility.

Electroforming and Switching in Oxides of Transition Metals: The Role of Metal-Insulator Transition in the Switching Mechanism

FA Chudnovskii — 2008-04-02T18:04:25-00:00

Journal of Solid State Chemistry, Vol. 122, No. 1. (15 February 1996), pp. 95-99.

Electroforming and switching effects in sandwich structures based on anodic films of transition metal oxides (V, Nb, Ti, Fe, Ta, W, Zr, Hf, Mo) have been studied. After being electroformed, some materials exhibited current-controlled negative resistance with S-shapedV-Icharacteristics. For V, Fe, Ti, and Nb oxides, the temperature dependences of the threshold voltage have been measured. As the temperature increased,Vthdecreased to zero at a critical temperatureT0, which depended on the film material. Comparison of theT0values with the temperatures of metal-insulator phase transition for some compounds (Tt= 120 K for Fe3O4, 340 K for VO2, ~500 K for Ti2O3, and 1070 K for NbO2) showed that switching was related to the transition in the applied electric field. Channels consisting of the above-mentioned lower oxides were formed in the initial anodic films during the electroforming. The possibility of formation of these oxides with a metal-insulator transition was confirmed by thermodynamic calculations.

Switching the electrical resistance of individual dislocations in single-crystalline SrTiO3

K Szot — 2008-04-09T19:10:09-00:00

Nat. Mater., Vol. 5, No. 4. (2006), pp. 312-320.

The great variability in the electrical properties of multinary oxide materials, ranging from insulating, through semiconducting to metallic behaviour, has given rise to the idea of modulating the electronic properties on a nanometre scale for high-density electronic memory devices. A particularly promising aspect seems to be the ability of perovskites to provide bistable switching of the conductance between non-metallic and metallic behaviour by the application of an appropriate electric field. Here we demonstrate that the switching behaviour is an intrinsic feature of naturally occurring dislocations in single crystals of a prototypical ternary oxide, SrTiO"3. The phenomenon is shown to originate from local modulations of the oxygen content and to be related to the self-doping capability of the early transition metal oxides. Our results show that extended defects, such as dislocations, can act as bistable nanowires and hold technological promise for terabit memory devices. © 2006 Nature Publishing Group.

Conductivity switching characteristics and reset currents in NiO films

S Seo — 2008-04-09T19:00:37-00:00

Applied Physics Letters, Vol. 86, No. 9. (2005)

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Molecule-Independent Electrical Switching in Pt/Organic Monolayer/Ti Devices

DR Stewart — 2008-04-02T17:55:13-00:00

Nano Lett., Vol. 4, No. 1. (14 January 2004), pp. 133-136.

Abstract: Electronic devices comprising a Langmuir-Blodgett molecular monolayer sandwiched between planar platinum and titanium metal electrodes functioned as switches and tunable resistors over a 102-105 range under current or voltage control. Reversible hysteretic switching and resistance tuning was qualitatively similar for three very different molecular species, indicating a generic switching mechanism dominated by electrode properties or electrode/molecule interfaces, rather than molecule-specific behavior.

Bistable switching in Zr---ZrO2---Au junctions

KC Park — 2008-04-08T21:45:38-00:00

Journal of Non-Crystalline Solids, Vol. 2 (January 1970), pp. 284-291.

Bistable switching has been observed in Zr---ZrO2---Au junctions. The resistance ratio is as high as 104. Significant physical changes have occurred during forming and subsequent switching of these junctions. The physical changes were observed by optical microscope, scanning electron microscope, and electron microprobe techniques. The temperature changes and profiles were observed by the liquid crystal technique during forming and switching. These studies indicate that in the low resistance state the current is carried by a single filament centered around one of the spots formed while switching from the high resistance state to the low resistance state. A voltage controlled negative resistance was observed for the junction in the low resistance state.