Unstable Oxide Research Articles

Fluorinated Graphene in Interface Engineering of Ge‐Based Nanoelectronics

Germanium is a promising candidate to replace silicon in nanoelectronics due to its significantly higher electron and hole mobilities. However, the unstable germanium oxide formed at the interface between the channel and dielectric layer has impeded the progress of Ge‐based nanoelectronics. By taking advantage of the impermeability of graphene, it is discovered that the insulating fluorinated graphene is able to act as an efficient diffusion barrier layer to suppress the formation of the unstable interfacial oxide in Ge‐based devices. The Ge‐based device with the fluorinated graphene exhibits negligible capacitance versus voltage hysteresis, extremely low leakage, and superior equivalent oxide thickness. First‐principles calculations reveal that interfacial diffusion, which would otherwise be unmanageable, is sufficiently obstructed by the fluorinated graphene. This new structure is expected to expedite the implementation of germanium as a channel material in next‐generation nanoelectronic devices.

Rock magnetism of tiny exsolved magnetite in plagioclase from a Paleoarchean granitoid in the Pilbara craton

AbstractGranitoids are widespread in Precambrian terranes as well as the Phanerozoic orogenic belts, but they have garnered little attention in paleomagnetic studies, because granitoids often contain abundant coarse‐grained, magnetically unstable oxides. In this study, the first example of tiny, needle‐shaped, exsolved oxides in plagioclase in a Paleoarchean granitoid is reported. The magnetic properties of single plagioclase crystals with the exsolved oxide inclusions have been studied to determine their paleomagnetic recording fidelity. Demagnetization experiments and hysteresis parameters indicate that the oxide inclusions are near stoichiometric magnetite and magnetically very stable. First‐order reversal curve (FORC) diagrams reveal negligible magnetostatic interactions. Minimal interactions are also reflected by very efficient acquisition of anhysteretic remanent magnetization. Single plagioclase crystals exhibit strong magnetic remanence anisotropies, which require corrections to their paleodirectional and paleointensity data. Nonetheless, quantitative consideration of anisotropy tensors of the single plagioclase crystals indicates that the bias can be mitigated by properly averaging data from a few tens of single crystals. From the nonlinear thermoremanence acquisition of the plagioclase crystals, we estimate that the plagioclase crystals can reconstruct paleointensity up to 50 μT. Local metamorphic condition suggests that those magnetite may carry remanence of ∼3.2 to 3.3 Ga. We suggest that exsolved magnetite in granitoids is potentially a suitable target for the study of the early history of the geomagnetic field, and prompt detailed microscopic investigations as well as paleomagnetic tests to constrain the age of remanence.

Effects of Miscut Substrates on Electrical Conductivity Across InP and GaAs Wafer-Bonded Structures

Direct wafer bonding of III-V materials is of great interest for the fabrication of next generation high efficiency solar cells. Traditional wafer bonding methods of III-V materials lead to highly unstable oxide interfaces and poor electrical properties. To resolve these issues, elevated annealing temperatures (>600 °C), long times, and large compressive forces are employed to break up this interfacial oxide layer, so that there is better contact between the III-V bonding interfaces. These harsh processing conditions ultimately limit the achievable efficiencies, due to dopant diffusion and residual thermal strains in processed devices. Sulfur surface treatment prior to bonding was found to reduce the inclusion unfavorable oxides at the interface, reducing the post-bonding thermal and compressive force requirements, and promoting the ability to bond large (100 mm diameter) wafers.. Various combinations of sulfur treated n-GaAs and n-InP directed bonded structures were measured to investigate the effects of offcut angles on the electrical conductivity. The impact of the relative offcut angle on the electrical properties is an new unexplored area which is of important issuece, as misorientated substrates are typically used for the growth of III-V epitaxial layers in the solar industry to avoid anti-phase boundaries. It is observed in both the GaAs and InP bonded structures, that out-of-plane relative surface orientations between the (001) planes that are greater than 4° exhibit non-ohmic behavior. A theoretical model that describes the electron tunneling across a grain boundary between semiconductor bicrystals is used to represent the bonded interface and estimate the barrier conduction height. Fitting the zero-bias conductance over a range of temperatures reveals an increase in barrier heights for samples with greater than 4° misoriented bonded pairs, correspondingly the interface resistance at room temperature increases. These results demonstrate that the out-of-plane relative surface misorientation is the critical parameter to be monitored in order to achieve superior electrical conductivity in direct-bonded multijunction solar applications. In addition, differences between GaAs-GaAs bonded structures and InP-InP bonded structures indicate that the barrier for GaAs-GaAs is significantly greater than for InP-InP. The impact of the miscut itself, however, is similar in both cases, showing that both the chemical nature and the structural interface properties play roles in trans-interface electrical conduction.

Evolution of novel bioresorbable iron-manganese implant surfaces and their degradation behaviors in vitro

The purpose of this study is to advance understanding of surface degradation kinetics for Fe-Mn bioresorbable alloys (specifically Fe-20%Mn) and target degradable fracture fixation implants for hard tissues. This study addresses how arc melted Fe-20%Mn discs degrade in a static, osteogenic medium for up to a 3 month time span. Degradation behavior of these bulk alloys was investigated using both mass loss tests for measuring long-term corrosion rates and potentiostatic tests for following the instantaneous rate of degradation. It was discovered that cold-rolling Fe-20%Mn to 77% cold work (CW) suppressed the instantaneous corrosion rate compared with the cast structure. It was also found that an unstable iron-rich oxide layer forms on the entire surface of these bulk samples and the act of machining the bulk metal into a defined shape may affect the morphology of the oxide layer on the outer edge of the samples during degradation. The mechanisms behind the surface evolution of these potential orthopedic implants are investigated in detail.

Sub-Tg enthalpy relaxation in an extremely unstable oxide glass and its implication for structural heterogeneity

We study the sub-Tg relaxation in an extremely unstable glass former, i.e., 65SiO2–35Al2O3, and its relation to structural heterogeneity (e.g., structurally ordered domains in glass matrix). This is done by hyperquenching (~106K/s) the liquid, then annealing the hyperquenched (HQ) glass below Tg and subsequently scanning the annealed HQ glass in a differential scanning calorimeter (DSC). The results show that structural ordering can take place even below Tg. An endothermic pre-peak is observed when the HQ sample is annealed at 0.75Tg for sufficiently long time, which is, however, much weaker compared to that of stable glass formers subjected to same annealing conditions. We also investigate the effect of the sub-Tg annealing on crystallization above Tg. The results imply that some structurally ordered domains exist already in the liquid state. The ordered domains lower the activation energy for further structural ordering during the sub-Tg annealing, and thereby lowers the activation energy for crystal growth above Tg.

Stabilizing Nanostructured Solid Oxide Fuel Cell Cathode with Atomic Layer Deposition

We demonstrate that the highly active but unstable nanostructured intermediate-temperature solid oxide fuel cell cathode, La0.6Sr0.4CoO3-δ (LSCo), can retain its high oxygen reduction reaction (ORR) activity with exceptional stability for 4000 h at 700 °C by overcoating its surfaces with a conformal layer of nanoscale ZrO2 films through atomic layer deposition (ALD). The benefits from the presence of the nanoscale ALD-ZrO2 overcoats are remarkable: a factor of 19 and 18 reduction in polarization area-specific resistance and degradation rate over the pristine sample, respectively. The unique multifunctionality of the ALD-derived nanoscaled ZrO2 overcoats, that is, possessing porosity for O2 access to LSCo, conducting both electrons and oxide-ions, confining thermal growth of LSCo nanoparticles, and suppressing surface Sr-segregation is deemed the key enabler for the observed stable and active nanostructured cathode.

Electrografting of in situ generated pyrrole derivative diazonium salt for the surface modification of nickel

This work reports for the first time on the modification of nickel surfaces by cathodic electrografting of in situ generated diazonium. An original diazonium salt (the 4-pyrrolylphenyldiazonium called Py-PD hereafter) was electrografted on nickel after its generation from 4-(1H-pyrrol-1-yl)aniline (Py-A) in presence of three acidic conditions (1, 2 and 10equiv. of HClO4/Py-A) has been investigated by UV–vis spectroscopy. Results show that the potentiostatic electrografting of Py-PD is concomitant with nickel and proton reduction. This electrografting leads to the formation of multilayered films in each of the studied in situ generation conditions. The use of 1equiv. of HClO4/Py-A for the in situ generation results in the formation of inhomogeneous and irreproducible coatings while 2 and 10equiv. lead to the formation of highly covering, homogeneous and reproducible films. These films present good electrochemical barrier properties toward the ferri/ferrocyanide couple. The use of gentle stoichiometric acidic conditions for in situ diazonium generation widens the application field of this one-step procedure to the surface modification of oxidizable materials presenting an unstable oxide layer.

Expression of Fusion Proteins of Aspergillus terreus Reveals a Novel Allene Oxide Synthase

Aspergilli oxidize C18 unsaturated fatty acids by dioxygenase-cytochrome P450 fusion proteins to signal molecules involved in reproduction and host-pathogen interactions. Aspergillus terreus expresses linoleate 9R-dioxygenase (9R-DOX) and allene oxide synthase (AOS) activities in membrane fractions. The genome contains five genes (ATEG), which may code for a 9R-DOX-AOS fusion protein. The genes were cloned and expressed, but none of them oxidized 18:2n-6 to 9R-hydroperoxy-10(E),12(Z)-octadecadienoic acid (9R-HPODE). ATEG_02036 transformed 9R-HPODE to an unstable allene oxide, 9(R),10-epoxy-10,12(Z)-octadecadienoic acid. A substitution in the P450 domain (C1073S) abolished AOS activity. The N964V and N964D mutants both showed markedly reduced AOS activity, suggesting that Asn(964) may facilitate homolytic cleavage of the dioxygen bond of 9R-HPODE with formation of compound II in analogy with plant AOS (CYP74) and prostacyclin synthase (CYP8A1). ATEG_03992 was identified as 5,8-linoleate diol synthase (5,8-LDS). Replacement of Asn(878) in 5,8-LDS with leucine (N878L) mainly shifted ferryl oxygen insertion from C-5 toward C-6, but replacements of Gln(881) markedly affected catalysis. The Q881L mutant virtually abolished the diol synthase activity. Replacement of Gln(881) with Asn, Glu, Asp, or Lys residues augmented the homolytic cleavage of 8R-HPODE with formation of 10-hydroxy-8(9)-epoxy-12(Z)-octadecenoic acid (erythro/threo, 1-4:1) and/or shifted ferryl oxygen insertion from C-5 toward C-11. We conclude that homolysis and heterolysis of the dioxygen bond with formation of compound II in AOS and compound I in 5,8-LDS are influenced by Asn and Gln residues, respectively, of the I-helices. AOS of A. terreus appears to have evolved independently of CYP74 but with an analogous reaction mechanism.

Surface characterisation of fine inert gas and water atomised stainless steel 316L powders: formation of thermodynamically unstable surface oxide phases

New insights are presented on the speciation of surface oxide phases on fine inert gas atomised (GA, <45 and <4 μm) and water atomised (WA, <45 μm) stainless steel AISI 316L powders. X-ray photoelectron and Auger electron spectroscopy, scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry were applied for the characterisation. Oxidised manganese was strongly enriched in the outermost surface oxide of the GA powders (13 and 47 wt-%), an effect increasing with reduced particle size. Manganese and sulphur were enriched in oxide nanoparticles on the surface. Oxidised silicon (59 wt-%) was enriched on the WA powder surface. Tri- or tetravalent manganese oxides were observed on the GA particles in addition to α-Fe2O3, and Cr2O3. The oxide of the WA powder revealed in addition the likely presence of a silicate rich phase, mainly consisting of tetravalent Si, di- and/or trivalent Fe, and hexavalent Cr, which was confirmed not present as chromate.

Surface modifications on InAs decrease indium and arsenic leaching under physiological conditions

Devices containing III–V semiconductors such as InAs are increasingly being used in the electronic industry for a variety of optoelectronic applications. Furthermore, the attractive chemical, material, electronic properties make such materials appealing for use in devices designed for biological applications, such as biosensors. However, in biological applications the leaching of toxic materials from these devices could cause harm to cells or tissue. Additionally, after disposal, toxic inorganic materials can leach from devices and buildup in the environment, causing long-term ecological harm. Therefore, the toxicity of these materials along with their stability in physiological conditions are important factors to consider. Surface modifications are one common method of stabilizing semiconductor materials in order to chemically and electronically passivate them. Such surface modifications could also prevent the leaching of toxic materials by preventing the regrowth of the unstable surface oxide layer and by creating an effective barrier between the semiconductor surface and the surrounding environment. In this study, various surface modifications on InAs are developed with the goal of decreasing the leaching of indium and arsenic. The leaching of indium and arsenic from modified substrates was assessed in physiological conditions using inductively coupled plasma mass spectrometry (ICP-MS). Substrates modified with 11-mercapto-1-undecanol (MU) and graft polymerized with poly(ethylene) glycol (PEG) were most effective at preventing indium and arsenic leaching. These surfaces were characterized using contact angle analysis, ellipsometry, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). Substrates modified with collagen and synthetic polyelectrolytes were least effective, due to the destructive nature of acidic environments on InAs. The toxicity of modified and unmodified InAs, along with raw indium, arsenic, and PEG components was assessed using zebrafish embryos.

Wet-Chemical Passivation of InAs: Toward Surfaces with High Stability and Low Toxicity

In a variety of applications where the electronic and optical characteristics of traditional, siliconbased materials are inadequate, recently researchers have employed semiconductors made from combinations of group III and V elements such as InAs. InAs has a narrow band gap and very high electron mobility in the near-surface region, which makes it an attractive material for high performance transistors, optical applications, and chemical sensing. However, silicon-based materials remain the top semiconductors of choice for biological applications, in part because of their relatively low toxicity. In contrast to silicon, InAs forms an unstable oxide layer under ambient conditions, which can corrode over time and leach toxic indium and arsenic components. To make InAs more attractive for biological applications, researchers have investigated passivation, chemical and electronic stabilization, of the surface by adlayer adsorption. Because of the simplicity, low cost, and flexibility in the type of passivating molecule used, many researchers are currently exploring wet-chemical methods of passivation. This Account summarizes much of the recent work on the chemical passivation of InAs with a particular focus on the chemical stability of the surface and prevention of oxide regrowth. We review the various methods of surface preparation and discuss how crystal orientation affects the chemical properties of the surface. The correct etching of InAs is critical as researchers prepare the surface for subsequent adlayer adsorption. HCl etchants combined with a postetch annealing step allow the tuning of the chemical properties in the near-surface region to either arsenic- or indium-rich environments. Bromine etchants create indium-rich surfaces and do not require annealing after etching; however, bromine etchants are harsh and potentially destructive to the surface. The simultaneous use of NH(4)OH etchants with passivating molecules prevents contact with ambient air that can occur during sample transfer between solutions. The passivation of InAs is dominated by sulfur-based molecules, which form stable In-S bonds on the InAs surface. Both sulfides and alkanethiols form well-defined monolayers on InAs and are dominated by In-S interactions. Sulfur-passivated InAs surfaces prevent regrowth of the surface oxide layer and are more stable in air than unpassivated surfaces. Although functionalization of InAs with sulfur-based molecules effectively passivates the surface, future sensing applications may require the adsorption of functional biomolecules onto the InAs surface. Current research in this area focuses on the passivation abilities of biomolecules such as collagen binding peptides and amino acids. These biomolecules can physically adsorb onto InAs, and they demonstrate some passivation ability but not to the extent of sulfur-based molecules. Because these adsorbents do not form covalent bonds with the InAs surface, they do not effectively block oxide regrowth. A mixed adlayer containing a biomolecule and a thiol on the InAs surface provides one possible solution: these hybrid surfaces enhance passivation but also maintain the presence of a biomolecule on the surface. Such surface functionalization strategies on InAs could provide long-term stability and make these surfaces suitable for biological applications.

Plasma Oxidation Kinetics of Gold Nanoparticles and Their Encapsulation in Graphene Shells by Chemical Vapor Deposition Growth

High-throughput chemical vapor deposition (CVD) growth of carbon or graphene shells encapsulating gold nanoparticles (AuNPs) is a challenge due to limited solubility of carbon in AuNPs. Such a growth is only possible by utilizing surface-oxidized AuNPs. There is a lack of fundamental understanding regarding the role of morphology and surface oxidation of AuNPs in the formation of graphene shells. Here, we studied a simple wet-chemical synthesis of AuNPs with hexadecyltrimethylammonium bromide as a surfactant and the effect of postsynthesis quenching on size, shape, and defect density of AuNPs. In the next step, plasma oxidation kinetics of AuNPs to form surface gold oxide (AuOx) was studied. The surface gold oxide shell thickness was found to be independent of stoichiometry of AuOx and followed the Cabrera–Mott model for oxidation kinetics. The surface-oxidized AuNPs were further utilized as catalysts for the growth of graphene shell encapsulated AuNPs (GNPs) in a xylene CVD process. The unstable surface gold oxide played a major role in the CVD process by accepting electrons from the incoming carbon feed, resulting in graphene shells around AuNPs. On the other hand, surface oxidized AuNPs with lattice defects, in a similar xylene CVD process, resulted in amorphous carbon and distorted graphene shells encapsulating AuNPs. Overall, this study reveals the mechanisms and critical factors relevant to the growth of GNPs. Such an approach for hybridizing graphene shells with AuNPs is promising for nanoelectronics and sensing.

1,3-Dipolar Cycloaddition Reaction in Porphyrin Systems with Functionalized Alkyl Nitrile Oxides — Synthesis of Isoxazoline-Fused Chlorins

meso-Tetraphenylporphyrin reacts at higher temperature with unstable alkyl nitrile oxides (R-CNO) affording isoxazoline-fused chlorins according to dipolar (3+2)-cycloaddition pathway. The respective nitrile oxides were in situ generated from the corresponding functionalized nitroalkanes in the presence of base (NEt3, DABCO) and dehydrating agent (PhNCO, (Boc)2O). Substituent R bearing diverse of functionality allows synthesis of very attractive moieties which may be of potential use as sensitizers in photodynamic therapy. The products obtained are also suitable intermediates for further derivatization of porphyrins. In the past decade numerous investigations oriented towards the synthesis and utilization of chlorins and bacteriochlorins have been undertaken. These compounds may be considered as second generation photosensitizers in antitumor photodynamic therapy (PDT) 1 due to their characteristic strong absorption bands shifted to the red region of visible spectrum (630-780 nm). The attractive chlorin systems can be synthesized by various methods. 2 One of the approaches involves 1,3-dipolar cycloaddition reaction of peripheral β,β-double bonds of porphyrin moiety with some 1,3- dipoles. Among others, nitrile oxides could be used for this purpose. In the recent past we reported our preliminary results concerning this type of cycloaddition with the use of alkyl nitrile oxides, 3 generation of which is relatively difficult, and which are generally less stable 4 as compared to the aryl ones. It was one of the first three published works in which synthesis of fused porphyrin-isoxazoline derivatives was described. 3,5a,b Herein we report our further investigations oriented towards the synthesis of diversely functionalized chlorins. Studies on the scope and limitations of this derivatization method and exploring other possibilities of generation this type of alkyl nitrile oxides (and their applications in the above cycloaddition) were attempted. The previous reactions of meso-tetraphenylporphyrin (1) with an excess of alkyl nitrocompounds 2a-c, carried out in the presence of NEt3 and PhNCO in refluxing benzene (Mukaiyama's method 4a ), gave the expected isoxazoline-fused chlorins (3a-c) 3 (Scheme 1).

Toluene dioxygenase-catalyzed cis-dihydroxylation of benzo[b]thiophenes and benzo[b]furans: synthesis of benzo[b]thiophene 2,3-oxide

Enzymatic cis-dihydroxylation of benzo[b]thiophene, benzo[b]furan and several methyl substituted derivatives was found to occur in both the carbocyclic and heterocyclic rings. Relative and absolute configurations and enantiopurities of the resulting dihydrodiols were determined. Hydrogenation of the alkene bond in carbocyclic cis-dihydrodiols and ring-opening epimerization/reduction reactions of heterocyclic cis/trans-dihydrodiols were also studied. The relatively stable heterocyclic dihydrodiols of benzo[b]thiophene and benzo[b]furan showed a strong preference for the trans configuration in aqueous solutions. The 2,3-dihydrodiol metabolite of benzo[b]thiophene was utilized as a precursor in the chemoenzymatic synthesis of the unstable arene oxide, benzo[b]thiophene 2,3-oxide.

In situ thermal reduction of graphene oxide for high electrical conductivity and low percolation threshold in polyamide 6 nanocomposites

Electrically conductive and thermally stable polyamide 6 (PA 6) nanocomposites were prepared through one-step in situ polymerization of ε-caprolactam monomer in the presence of electrically insulating and thermally unstable graphene oxide (GO) nanosheets. These nanocomposites show a low percolation threshold of ∼0.41 vol.% and high electrical conductivity of ∼0.028 S/m with only ∼1.64 vol.% of GO. Thermogravimetric analysis and X-ray photoelectron spectroscopy results of GO before and after thermal treatment at the polymerization temperature indicate that GO was reduced in situ during the polymerization process. X-ray diffraction patterns and scanning electron microscopy observation confirm the exfoliation of the reduced graphene oxide (RGO) in the PA 6 matrix. The low percolation threshold and high electrical conductivity are attributed to the large aspect ratio, high specific surface area and uniform dispersion of the RGO nanosheets in the matrix. In addition, although GO has a poor thermal stability, its PA 6 nanocomposite is thermally stable with a satisfactory thermal stability similar to those of neat PA 6 and PA 6/graphene nanocomposite. Such a one-step in situ polymerization and thermal reduction method shows significant potential for the mass production of electrically conductive polymer/RGO nanocomposites.

Thalidomide Analogues Suppress Lipopolysaccharide-Induced Synthesis of TNF-α and Nitrite, an Intermediate of Nitric Oxide, in a Cellular Model of Inflammation

An unregulated neuroinflammation accompanies numerous chronic and acute neurodegenerative disorders and it is postulated that such a neuroinflammatory component likely exacerbates disease progression. A key player in brain inflammation is the microglial cell; a vital soluble factor synthesized by activated microglial cells is the key cytokine, tumor necrosis factor–alpha (TNF-α). Additionally, microglial cells release IL-1α/β, reactive oxygen species (ROS), such as superoxide (O2-) and reactive nitrogen species (RNS) like nitric oxide (NO). Nitric oxide reactive oxygen species can undergo various forms of interactions in cells whereby the synthesis of RNS / ROS intermediates are generated that can damage cell membranes. The presence of oxidative damaged cells is implicated with the abnormal cellular activity in brain or in the spinal cord, and is a classical feature of neurodegenerative disorders. To aid characterize this process, a quantitative analysis of nitrite generation was undertaken on agents developed to lower TNF-α levels in cell culture. Nitrite is a stable end product of nitric oxide metabolism and, thereby, acts as a surrogate measure of the highly unstable nitric oxide. Utilizing a RAW 264.7 cellular model of lipopolysaccharide-induced inflammation that induces high levels of TNF-α protein accompanied by a robust generation of nitrite, the properties of a series of thalidomide-based TNF-α synthesis inhibitors were evaluated to reduce the levels of both. Specific analogues of thalidomide effectively suppressed the generation of both TNF-α and nitrite at well-tolerated doses.

Investigation on sliding wear performance of WC10Co2Ni cladding developed through microwave irradiation

Abstract Present work reports on the investigation of sliding wear of cladding developed through a novel processing technique. Wear resistant WC10Co2Ni cladding was developed using microwave irradiation on austenitic stainless steel (SS-316). The microwave claddings were characterized through field emission scanning electron microscope (FESEM), X-ray elemental analysis, X-ray diffraction (XRD) and measurement of Vicker′s microhardness. The FESEM study showed good metallurgical bond with substrate and the clads are free of cracks. Clads were formed with partial dilution of a thin layer of the substrate. The clad is composed of relatively soft metallic matrix and uniformly distributed hard carbide phase with ‘skeleton’ likes structure. The developed clads exhibit an average microhardness of 1064 ± 99 Hv. The porosity of developed clad has been significantly less at approximately 0.89%. Tribological properties of cladding have been analyzed through pin on disc sliding method against an EN-31 (HRC-70) counter surface. The clads show significant resistance to sliding wear. Wear resistance was observed to be the better at lower sliding speeds. An unstable metallic oxide layer is formed during rubbing of clad surface. The loss of material from the mating surfaces is mainly due to spalling, growth of microcracks, and smearing of the unstable oxide layer.

Interactions of Copper and Iron in Conversion Reactions of Nanosized Oxides with Large Variations in Iron-Copper Ratio

A representative investigation of the interaction of two elements, here Cu2+/Cu0 and Fe3+/Fe0, as electrochemically reacting neighbors in the 3d transition metal oxide system Cu-Fe-O (CFO) was carried out. Oxide materials with a large variation of Cu and Fe from 4:1 to 1:4 were synthesized by the self-combustion method to achieve a homogeneous elemental distribution on a nanoscopic scale. The redox behavior of the conversion reaction of the ternary system was characterized qualitatively and quantitatively by cyclic voltammetry and galvanostatic cycling. The element-specific stability was found to be different in the single copper (stable) and iron (unstable) oxide under the same conditions and was consigned in the various CFO materials. The instability of the iron oxide electrode could be improved in the presence of copper, probably due to the in situ formed Cu metal particles as neighborhood of the iron ions before the Fe3+/Fe0 redox couple becomes active.

Controllable low energy ion assistance as a tool for tailoring properties of gold oxide and gold–silver oxide thin films

In the present study, gold oxide (AuOx) and gold–silver oxide (AuAgOx) thin films are deposited by reactive sputtering in a magnetron with unbalanced ratio continuously controlled by the current Is trough an external solenoid. Two film characteristics: the specific electric resistivity ρo of as deposited films and their life-times τ are systematically investigated in dependence of the oxygen gas pressure pO2, magnetron discharge power Pm and solenoid current Is.It is demonstrated that employing optimal regime of ion assistance and gradient sublayers, AuOx and AuAgOx films with a high electric resistivity and long life-times (up to 3years) can be deposited.Incorporation of the more reactive silver atoms into the film structure significantly changes the behavior of AuAgOx films as compared to that of AuOx films. While the initial electric resistivity and the life-time of AuAgOx films monotonously increase with the combined parameter IspO2/Pm, tending to saturation at higher values of this parameter, films of thermodynamically unstable gold oxide with long life-times can be produced within a narrow range of deposition parameters, only.

Interfacial reactions in Ru metal-electrode/HfSiON gate stack structures studied by synchrotron-radiation photoelectron spectroscopy

We have investigated the thermal stability and interfacial reactions of a Ru/HfSiON gate stack structure, annealed in a nitrogen ambient, using synchrotron-radiation photoelectron spectroscopy. We find that in HfSiON films with Ru metal, competition between catalyst-induced oxidation and oxygen or SiO desorption arises upon high-temperature annealing, unlike in the same films without Ru. The desorption reaction during high-temperature annealing at 1050 °C could be caused by the decomposition of an unstable Si oxide component, formed by catalytic oxidation at the interface between the HfSiON layer and the Si substrate after annealing below 850 °C.