Diffusion Of Oxygen Species Research Articles

Self-assembled Gd0.1Ce0.9O1.95-BaGd0.8La0.2Co2O6‒δ nanocomposite cathode for efficient protonic ceramic fuel cells

Protonic ceramic fuel cells (PCFCs) are characterized by a low activation energy for proton conduction and a high fuel utilization efficiency at low-to-intermediate temperatures. However, the sluggish oxygen reduction reaction kinetics on the cathodes drastically limit the power output performance of PCFCs. Herein, multiphase Gd0.1Ce0.9O1.95-BaGd0.8La0.2Co2O6‒δ (GDC-BGLC) nanocomposite cathodes are prepared by coupling self-assembly and sintering-free electrode construction methods. The nanocomposite cathode comprises mixed H+/e– conducting BGLC and O2− conducting GDC and BaCoO3 nanoparticles, and these phases are homogeneously mixed with coherent heterointerfaces. The nanocomposite cathode exhibits a significant increase in surface oxygen vacancies and three-phase boundaries, enhanced catalytic activity, and reduced activation energy for the oxygen reduction and water formation reactions. The results imply that the oxygen reduction and water formation reactions on the multiphase GDC-BGLC nanocomposite electrodes are most likely the dissociation, reduction and diffusion of oxygen species, which in turn is affected by the water vapor formed. An anode-supported single cell with the GDC-BGLC cathode exhibits a peak power density of 810 mW cm−2 at 700 °C with excellent operating stability at 650 °C for 110 h. This study provides a new strategy for the preparation of a high-performance and durable nanocomposite cathode for PCFCs.

Oxygen Adsorption and Desorption Kinetics in CuO Nanowire Bundle Networks: Implications for MOx-Based Gas Sensors

Copper oxide (CuO) nanostructures have demonstrated a good chemiresistive response for the sensing of various gases. The precise sensing mechanisms of this material and, in particular, the kinetics of the response to gases and the sensor recovery remain much less investigated. For metal oxide (MOx) chemiresistive gas sensors, oxygen adsorption and desorption reactions on a material surface play a major role in the sensor kinetics, as most other gases react with oxygen on the sensor surface in order to provide the sensing signal, and nanoscale materials are known to achieve faster response. Here we investigate the oxygen adsorption and desorption kinetics on CuO nanowire bundle (NWB) networks by analyzing the electrical response and recovery curves of sensing devices exposed to oxygen. The observation of multiple time constants for the response and recovery curves led us to discuss the various potential mechanisms related to surface reaction kinetics and diffusion of oxygen species. By comparing the reaction rate constants and diffusion constants extracted from the obtained time constants, we conclude that the diffusion of oxygen defects into the material might be the main reason for the observed large time constants. Surprisingly, we observe that the sensor devices based on as-deposited materials show 4–16 times faster response and recovery as compared to devices after being annealed, depending on the temperature. By comparing this result with detailed characterization using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, we discuss the role of the junctions between nanostructures in the network and of the hydroxylated CuO surface to explain this result. Our investigation on the kinetics of adsorption and desorption of oxygen of CuO NWB provides a direct understanding of the general response of the sensor and will be useful in order to further understand and optimize these materials for the sensing of various gases.

Spinel Co3O4 oxides-support synergistic effect on catalytic oxidation of toluene

Bulk spinel Co3O4 oxide and supported Co3O4 catalysts (Co3O4/YSZ and Co3O4/TiO2) were synthesized by one-step hydrothermal method. Their physicochemical properties were characterized by inductively coupled plasma optical emission spectroscopy, N2-sorption, powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, hydrogen-temperature programmed reduction and X-ray photoelectron spectroscopy.These characterization strategies were applied to corroborate and better understand the interaction between Co3O4 and the supports induced by the synergistic effect of support and the subsequent catalytic performance in toluene oxidation. The catalytic stability was evaluated by three consecutive runs and a long-term test. A highest toluene catalytic activity was achieved over Co3O4/YSZ supported catalyst comparing to that of the bulk Co3O4 and Co3O4/TiO2 catalysts, which could be attributed to its better low-temperature reducibility, oxygen activation and mobility induced by the intrinsic support properties. Thus, the positive interaction between spinel Co3O4 phase and YSZ support promoted the intrinsic catalytic properties for toluene oxidation, which was verify by testing a dual catalyst bed system consisting of bulk Co3O4 catalyst and YSZ support beds. These results were further confirmed by temperature-programmed oxygen isotopic exchange experiments, which indicated that the activation and diffusion of oxygen species on the YSZ oxygen vacancy sites were promoted by Co3O4, resulting in a significant increase of the reaction rate for toluene oxidation.

Self-assembled cubic-hexagonal perovskite nanocomposite as intermediate-temperature solid oxide fuel cell cathode

Self-assembly is an emerging strategy for preparing composite cathodes with good oxygen electrochemical reduction activity and congenital chemical compatibility for intermediate-temperature solid oxide fuel cell (IT-SOFC). Here we report that a self-assembled BaCo0.6Zr0.4O3-δ (BZC-BC) nanocomposite is prepared through one-pot glycine-nitrate process and exhibits high cathode performance. The BZC-BC nanocomposite is composed of 62 mol% cubic perovskite BaZr0.82Co0.18O3-δ (BZC) as an ionic conductor and 38 mol% hexagonal perovskite BaCo0.96Zr0.04O2.6+δ (12H-BC) as a mixed ionic and electronic conductor. The BZC-BC nanocomposite has the pomegranate-like particles aggregated with a larger number of nanoparticles (50-100 nm) which greatly enlarge the three-phase boundary sites. The BZC-BC nanocomposite exhibits a thermal expansion coefficient of 12.89 × 10−6 K−1 well-matched with that of Ce0.8Gd0.2O3-δ (12.84 × 10−6 K−1) electrolyte. The high electro-catalytic activity of BZC-BC nanocomposite cathode for oxygen reduction is reflected by the low polarization resistances of oxygen ions incorporation at cathode/electrolyte interface (0.02823 Ω cm2), oxygen species diffusion (0.03702 Ω cm2) and oxygen adsorptive dissociation (0.07609 Ω cm2) at 700 °C. The single cell with BZC-BC nanocomposite cathode achieves the maximum power density of 1094 mW cm−2 at 650 °C and shows good stability under 25 h run.

ZnO/AAO photocatalytic membranes for efficient water disinfection: Synthesis, characterization and antibacterial assay

Novel type of ZnO/AAO photocatalytic membranes were fabricated by growing highly dense and porous network of ZnO nanosheets on nanoporous anodic aluminum oxide (AAO) using the facile hydrothermal approach. The structural properties of the membranes were investigated by field emission gun scanning electron microscopy (FEG-SEM) and X-ray diffraction spectroscopy (XRD). The ZnO nanosheet networks were found polycrystalline, showing mainly (100) and (002) ZnO reflections. The XRD results suggested that the ZnO-AAO interface promotes lattice disorder mainly along the polar-axis while the nonpolar plane remains less defective. The energy dispersive X-ray spectrometry (EDX) confirmed the formation of pure ZnO. In addition, Fourier transform infrared spectroscopy (FTIR) indicated an intense absorption band in the range of 661–780 cm−1 for stretching vibrations of Zn–O bond and also specified the presence of intrinsic crystal defects. The diffuse reflectance spectroscopy (DRS) revealed an optical absorption edge of 401 nm and a band gap of 3.09 eV for grown ZnO nanosheet mesh. Moreover, the DRS studies also substantiated the existence of crystal defects by recognizing a red shift in the band gap, and a trail of low energy absorptions in the reflectance spectrum in the range of 400–800 nm. Due to the corrugated surface morphology and hierarchical porosity of ZnO scaffolds on porous AAO substrates, the membranes possess a great deal of catalytic surface and demonstrated a strong antibacterial activity against water-borne bacteria Escherichia coli (E. coli) under dark and UV light conditions. Our results showed that fabricated ZnO/AAO membranes have great potency for photocatalytic disinfection of contaminated water on account of their large catalytic surface and inherent porosity which can facilitate the mass transfer and diffusion of oxygen species and Zn+2 ions during the disinfection process. This morphology-function relationship is highly effective for designing cost effective, efficient, environment-friendly, and self-antifouling photocatalytic disinfectants.

Surface topography evolution of TiO2/SnO2 coatings during thermal oxidation of Ti/Sn composite coatings

Abstract Mechanical coating followed by thermal oxidation in the atmosphere was used to prepare TiO 2 /SnO 2 composite coatings. The coatings were characterized by X-ray diffraction (XRD), scanning electronic spectroscopy (SEM), energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and so on. Results show that continuous rutile TiO 2 coatings decorated with discrete SnO 2 particles were formed during thermal oxidation at the temperature range of 873–1073 K. Through the temperature range, a small quantity of SnO was formed. However, tiny amount of Ti 2 O 3 was formed only when oxidation temperature was 1073 K. The surface topography evolution of rutile TiO 2 crystals during the thermal oxidation and relevant mechanism was also examined. Equiaxed, rod, columnar and needle TiO 2 crystals with nanoscale were formed at temperatures from 873–1073 K. The topography evolution indicates that the diffusion of oxygen species into the formed rutile TiO 2 layer was predominant at 873 K. It favored the growth of equiaxed crystals in the tangent plane rather than radial direction of Al 2 O 3 ball substrate at the early stage of the thermal oxidation. However, the diffusion of Ti cations became prevailing compared with oxygen species at 1073 K. The reaction of Ti and oxygen species occurred at the external surface of the formed TiO 2 layer where rutile TiO 2 needles were formed. During thermal oxidation at 973 K, both the Ti cations and oxygen species were involved in the diffusion process and clusters of paired/parallel rutile TiO 2 nanorods were formed. The addition of metallic Sn remarkably affected the surface topography and the grain size of rutile TiO 2 crystals through regulating the diffusion of Ti cations and changing the local oxygen concentration surrounding Ti coatings. A proper additive amount refined the grains of rutile TiO 2 .

The reduction and oxidation of ceria: A natural abundance triple oxygen isotope perspective

Ceria (CeO2) is a heavily studied material in catalytic chemistry for use as an oxygen storage medium, oxygen partial pressure regulator, fuel additive, and for the production of syngas, among other applications. Ceria powders are readily reduced and lose structural oxygen when subjected to low pO2 and/or high temperature conditions. Such dis-stoichiometric ceria can then re-oxidize under higher pO2 and/or lower temperature by incorporating new oxygen into the previously formed oxygen site vacancies. Despite extensive studies on ceria, the mechanisms for oxygen adsorption–desorption, dissociation–association, and diffusion of oxygen species on ceria surface and within the crystal structure are not well known. We predict that a large kinetic oxygen isotope effect should accompany the release and incorporation of ceria oxygen. As the first attempt to determine the existence and the degree of the isotope effect, this study focuses on a set of simple room-temperature re-oxidation experiments that are also relevant to a laboratory procedure using ceria to measure the triple oxygen isotope composition of CO2.Triple-oxygen-isotope labeled ceria powders are heated at 700°C and cooled under vacuum prior to exposure to air. By combining results from independent experimental sets with different initial oxygen isotope labels and using a combined mass-balance and triangulation approach, we have determined the isotope fractionation factors for both high temperature reduction in vacuum (⩽10−4mbar) and room temperature re-oxidation in air. Results indicate that there is a 1.5‰±0.8‰ increase in the δ18O value of ceria after being heated in vacuum at 700°C for 1h. When the vacuum is broken at room temperature, the previously heated ceria incorporates 3–19% of its final structural oxygen from air, with a δ18O value of 2.1-4.1+7.7‰ for the incorporated oxygen. The substantial incorporation of oxygen from air supports that oxygen mobility is high in vacancy-rich ceria during re-oxidation at room temperature. The quantified oxygen isotope fractionation factors are consistent with the direct involvement of O2 in the rate limiting step for ceria reoxidation in air at room temperature. While additional parameters may reduce some of the uncertainties in our approach, this study demonstrates that isotope effects can be an encouraging tool for studying oxygen transport kinetics in ceria and other oxides. In addition, our finding warns of the special cares and limits in using ceria as an exchange medium for laboratory triple oxygen isotope analysis of CO2 or other oxygen-bearing gases.

Oxygen incorporation at the three-phase boundary of LSCF–SDC composite

Oxygen reduction at LSCF–SDC (La0.6Sr0.4Co0.2Fe0.8O3 − δ–Sm0.2Ce0.8O1.9) composite cathode might take place at the LSCF-gas two-phase interface (2 PB) and the LSCF–SDC-gas three-phase boundary (3 PB). A method is developed to determine the oxygen incorporation rate and the amount of incorporated oxygen at 3 PB using the electrical conductivity relaxation technique. The obtained results are powerful supports to the viewpoint that oxygen incorporation at 3 PB is much more facile than that at 2 PB. The amount of oxygen incorporated absolutely at 3 PB plays a dominating role in the total process, which actually contributes an average of more than 70% when only 4.5 vol. % SDC is added to LSCF. The incorporation rate at 3 PB is found to be affected not only by the 3 PB length but also the diffusion of oxygen species on the LSCF surface. An effective surface diffusion length of about 1.5 μm is suggested by the relation between the rate, 3 PB length and LSCF surface area.

Development of Ternary Cathodes Using MyCe1–x–yMnxO2–δ (M = La, Gd) as Catalysts for Oxygen Reduction Reactions

AbstractMyCe1–x–yMnxO2–δ (M = La, Gd) oxides have been investigated as oxygen reduction catalysts for LSM–YSZ based ternary cathodes. MyCe1–x–yMnxO2–δ samples are characterized by X‐ray diffraction (XRD), temperature programmed reduction of H2 (H2‐TPR), and temperature programmed desorption of O2 (O2‐TPD). The results show that the incorporation of M (M = La, Gd) ions increases the solution limit of Mn in the solid solutions, which increases the amount of oxygen vacancies and promotes oxygen adsorption and dissociation processes. The ternary cathodes show much higher electrochemical performance than LSM–YSZ binary cathode, and greatly accelerate oxygen dissociative adsorption and diffusion of oxygen species. The MyCe1–x–yMnxO2–δ catalysts exhibit greatly high activity for oxygen reduction at intermediate temperature. The ternary cathodes have high stability and high resistance to CO2 at 600 °C.

Increased Power Density of Solid Oxide Fuel Cells Using LaGaO3 Film Prepared by Screen Printing Method with (Ba,La)CoO3-δ and Pr1.9(Ni,Cu,Ga)O4+δ Composite Oxide Cathode

Effects of microstructure and phase compatibility in a composite of Ba0.5La0.5CoO3–δ (BLC) and Pr1.9(Ni,Cu,Ga)O4+δ (PNCG) with a mass ratio of 5:1 (BP51) on electrochemical properties were investigated with varying firing temperature of the composite as cathode (973–1373 K). Grain growth was observed with increasing firing temperature while single phase was maintained below 1173 K in the composite. Area specific resistance (ASR) of BP51 cathode fired at 1073 K was decreased due to fine particles, intimate contact, and phase purity, leading to enhancement of reactivity on oxygen exchange and diffusion of oxygen species. Moreover, BP51 cathode with small grains revealed improved electrochemical performance compared with that of coarse particles. Accordingly, increased maximum power density of ca. 1.3 and 0.2 Wcm−2 at 973 and 773 K was achieved in an anode supported single cell of Sr- and Mg-doped LaGaO3 (LSGM) electrolyte film with fine BP51 cathode owing to decrease in both electrode polarization and interfacial contact resistance. Furthermore, cell performance was stable under an applied current density of 1.7 Acm−2 at 973 K. This study reveals that fine BP51 composite is a promising cathode for high performance intermediate temperature SOFCs.

Synthesis of Co3O4 nanotubes and their catalytic applications in CO oxidation

Co3O4 nanotubes with the inner of about 8nm and the length of 200–500nm were synthesized by oxidizing Co nanowires. Analyses on the structural evolution of the intermediates at different intervals identified that the formation of Co3O4 nanotubes followed a nanoscale Kirkendall effect. The outward diffusion of cobalt species was faster than the inward diffusion of oxygen species, resulting in the formation of nanovoids at the initial stage and subsequently the tubular structure. The Co3O4 nanotubes showed a higher activity and stability than the spherical nanoparticles in CO oxidation, primarily due of the facile redox feature.

Catalytic abatement of trichloroethylene over Mo and/or W-based bronzes

In this paper we present the results of the synthesis, characterization and catalytic behaviour of Mo(W)–Nb–V–O mixed metal oxides bronzes for the catalytic oxidation of trichloroethylene. The catalysts were prepared hydrothermally with different Mo/W/Nb/V/P atomic ratio and heat-treated at 500 and 700°C. They were characterized by several techniques as N2-adsorption, X-ray diffraction, FTIR, SEM-EDS, temperature programmed desorption, temperature programmed reduction, UV–vis, Fourier transformed infrared spectroscopy of adsorbed pyridine and 18O/16O isotope exchange. X-ray diffraction patterns (XRD) of samples heat-treated at 500°C suggest the presence of a semi-crystalline material with a diffraction peak at ca. 2θ=22.2°, while XRD patterns of samples heat-treated at 700°C show the formation of a tetragonal tungsten bronze (TTB) structure. The activity for the catalytic abatement of trichloroethylene strongly depends on the heat-treatment temperature and the catalyst composition. Thus, samples with W/(Mo+W) atomic ratios of 0.25-0.75 and heat-treated at 500°C are the most active ones. The enhanced activity has been related to the remarkable higher surface area of the catalyst and to the catalyst composition which influences the acid characteristics as well as the reducibility and reoxidation of the catalysts. The importance of the oxygen dissociation on the catalyst surface and the diffusion of oxygen species through the catalyst are also discussed.

Enhanced storage/operation stability of small molecule organic photovoltaics using graphene oxide interfacial layer

Graphene and graphene oxide (GO) have been applied in flexible organic electronic devices with enhanced efficiency of polymeric photovoltaic (OPV) devices. In this work, we demonstrate that storage/operation stability of OPV can be substantially enhanced by spin-coating a GO buffer layer on ITO without any further treatment. With a 2nm GO buffer layer, the power conversion efficiency (PCE) of a standard copper phthalocyanine (CuPc)/fullerene (C60) based OPV device shows about 30% enhancement from 1.5% to 1.9%. More importantly, while the PCE of the standard device drop to 1/1000 of its original value after 60-days of operation-storage cycles; those of GO-buffered device maintained 84% of initial PCE even after 132-days. Atomic force microscopy studies show that CuPc forms larger crystallites on the GO-buffered ITO substrate leading to better optical absorption and thus photon utilization. Stability enhancement is attributed to the diffusion barrier of the GO layer which slow down diffusion of oxygen species from ITO to the active layers.

A mechanistic study on the activation process of (La, Sr)MnO 3 electrodes of solid oxide fuel cells

The mechanism of the activation process for the O 2 reduction on (La 0.8Sr 0.2) 0.9MnO 3 (LSM) electrodes is investigated by examining the electrochemical behavior of LSM under cathodic and anodic polarization conditions and the relaxation behavior of LSM under open circuit. A comparative study is also performed on a LSM electrode after dilute acid etching treatment. It has been shown that the segregated SrO has a significant inhibiting effect on the surface exchange process such as dissociative adsorption, incorporation and diffusion of oxygen species on the LSM surface, resulting in the initially very high impedance for the O 2 reduction on LSM electrodes. A mechanism involving the incorporation of SrO into LSM lattice with the concomitant removal of cation vacancies is proposed for the activation effect of cathodic current passage/polarization in solid oxide fuel cells.

Charge transfer at oxygen/zirconia interface at elevated temperatures: Part 9: Room temperature

The present paper reports the reactivity between the surface of zirconia and oxygen at room temperature. The experimental studies, performed with polycrystalline yttria-stabilised zirconia (YSZ), include in situ monitoring of charge transfer at the oxygen/zirconia interface using work function measurements and determination of mass transport at the oxygen/zirconia interface using the incorporation of oxygen isotope 18O and its analysis using secondary ion mass spectrometry. Oxidation of YSZ at room temperature is found to result in oxygen chemisorption, leading to the formation of singly ionised molecular oxygen species, and subsequent oxygen incorporation into the lattice. Oxygen incorporation takes place by lattice diffusion from the entire surface exposed to the gas phase, resulting in oxygen penetration of depths of the order of 2 nm over 60 days, and diffusion of oxygen species along the surface from the adsorption sites towards grain boundaries with subsequent rapid diffusion of oxygen into the bulk along grain boundaries. These processes take place in the absence of an electronic conductor. The present findings contradict the widely held perceptions that YSZ at room temperature is quenched and not reactive, and that oxygen incorporation into YSZ requires the presence of a triphase boundary (TPB) formed by the gas phase (oxygen), electronic conductor and oxygen ionic conductor (zirconia).

Dynamics of oxygen species on reducedTiO2(110)rutile

Using density functional theory calculations, we have investigated the adsorption and diffusion of oxygen species on the reduced ${\mathrm{TiO}}_{2}(110)$ surface. We have found that molecular ${\mathrm{O}}_{2}$ strongly binds not only to O vacancies, but also to $\mathrm{Ti}(5c)$ neighbors, due to delocalization of unpaired electrons arising from removal of neutral bridging oxygen. Our results show that molecular ${\mathrm{O}}_{2}$ can jump across an oxygen vacancy and diffuse along a $\mathrm{Ti}(5c)$ row with moderate barriers. On the other hand, atomic O diffusion along a $\mathrm{Ti}(5c)$ row is rather unlikely at low temperatures $(l300\phantom{\rule{0.3em}{0ex}}\mathrm{K})$, because of the relatively higher probability of O-O formation from interaction with an adjacent bridging $\mathrm{O}(2c)$ atom. Based on our calculation results, we discuss the diffusion and healing of O vacancies associated with ${\mathrm{O}}_{2}$ adsorption.

Oxygen Transport in the SOFC Cathode

The impedance of the La0.75Sr0.2MnO3-cathode/electrolyte interface for cathodes with different porosity is measured. The impedance spectra are fitted using a developed model of the oxygen transport at this interface. After the measurements, the cathode is removed from the electrolyte. The contact area and the three-phase boundary length (TPBL) at the interface are estimated from SEM images of the electrolyte surface. The dependence of the interfacial electrical resistance on the microstructure is discussed. It is shown that the bulk diffusion of oxygen vacancies at the interface at 950°C is high enough to use the whole La0.75Sr0.2MnO3/YSZ contact area F for the oxygen transport into the electrolyte for microstructures with 2F/TPBL ≤ 2 μm. The impact of the surface diffusion of oxygen species on polarization resistance at operation temperatures <900°C is discussed. The polarization resistance and the morphology of composite cathodes made from La0.75Sr0.2MnO3/YSZ and yttria- or scandia-stabilized zirconia powders (3YSZ, 8YSZ, 10ScSZ) are investigated by impedance spectroscopy at 800–950°C. The polarization (interfacial) resistance decreases gradually with addition of electrolyte powder in the uLSM cathode material independent of the electrolyte powder used. The interfacial resistance of the uLSM/3YSZ, uLSM/8YSZ, and uLSM/10ScSZ composite cathodes is almost the same. The interaction between uLSM and doped zirconia particles is discussed on the basis of the interfacial resistance, activation energies, and high-frequency impedance.

Formation and Desorption of Oxygen Species in Nanoporous Crystal 12CaO×7Al2O3.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Formation and Desorption of Oxygen Species in Nanoporous Crystal 12CaO·7Al2O3

The formation and desorption mechanisms of oxygen species in nanoporous crystal 12CaO·7Al2O3 (C12A7) are studied by temperature-programmed desorption (TPD), electron-spin resonance (ESR), and Raman spectroscopy. Various oxygen ion species, including O-, O2-, and O22-, are observed to exist in C12A7 at high concentrations (∼1020 cm-3). The desorption of these oxygen species in C12A7 is proposed to proceed in three steps: (1) diffusion of oxygen species from bulk to the surface (rate-limiting step), (2) decomposition of oxygen species into oxygen molecules, and (3) release of molecular oxygen into the gas phase. Oxygen species in C12A7 can be regenerated by heating in an O2 atmosphere at higher than 400 °C, and the concentrations of O- and O2- increase with temperature. More O2- is formed than O- at low activation temperatures, whereas nearly equal amounts of O- and O2- are formed at high temperatures around 1350 °C. At 400−700 °C, a considerable amount of molecular oxygen, O2, is suggested to be present t...

Resistless patterning of quantum nanostructures by local anodization with an atomic force microscope

Abstract We report here two processes for fabricating quantum devices based on local anodization induced by Atomic Force Microscope (AFM). The first process involves ultra-thin films of doped silicon-on-insulator (SOI) passivated with hydrogen. AFM-drawn oxide lines create a chemical contrast that is used as a mask for silicon wet etch. Etching is performed down to the buried silicon oxide layer, thus leading to silicon nanowires supported on insulator. We show that this process appears well suited to obtain SOI nanostructures and investigate electrical transport though silicon wires with sub-1000 nm 2 cross-section. In the second process, diffusion of oxygen species is performed through the whole layer of metallic ultra-thin films, which provides a technique for direct writing of insulating regions. This technique was applied to ultra-thin niobium films for fabricating mesoscopic structures. A superconducting quantum interferometer useful for nanomagnetism is demonstrated.