A precisely selected elastic strain can be introduced in submicron-thick single-crystal SrTiO3 sheets using a silicon nitride stressor layer. A conformal stressor layer deposited using plasma-enhanced chemical vapor deposition produces an elastic strain in the sheet consistent with the magnitude of the nitride residual stress. Synchrotron x-ray nanodiffraction reveals that the strain introduced in the SrTiO3 sheets is on the order of 10 4, matching the predictions of an elastic model. This approach to elastic strain sharing in complex oxides allows the strain to be selected within a wide and continuous range of values, an effect not achievable in heteroepitaxy on rigid substrates.
We have investigated the effect of ambient gas pressure (Argon) used during thermal exfoliation of graphite oxide on the number of graphene sheets in the resulting graphene. The ambience gas Ar pressures used are 80, 25, 1 atmosphere and 10-3 as well as 10-5 torr. We have found curious result that the number of graphene sheets in exfoliated graphene stack is dependent on the applied pressure for exfoliation of graphite oxide (GO). By lowering the exfoliation pressure, the numbers of sheets get reduced. The numbers of sheets in exfoliated graphene stack have been determined by Lorentzian fit of…
Cubic spinel lithium manganese oxide (LiMn2O4) has been able to attract a great deal of attention over the years as a promising cathode material for large scale lithium ion batteries. Here a facile hydrothermal route followed by solid state reaction is developed using as grown ultrafine alpha-MnO2 nanorods to prepare one dimensional LiMn2O4 with 10-50nm diameters. To enhance the cathodic property of these nanorods, a unique synthesis technique of heat treatment is developed to grow 2D graphene oxide sheet enveloping 1D LiMn2O4 as interconnected framework. This nanocomposite 3D porous cathode e…
Graphene is an intriguing material with properties that are distinct from those of other graphitic systems. The first samples of pristine graphene were obtained by peeling off and epitaxial growth. Recently, the chemical reduction of graphite oxide was used to produce covalently functionalized single-layer graphene oxide. However, chemical approaches for the large-scale production of highly conducting graphene sheets remain elusive. Here, we report that the exfoliation-reintercalation-expansion of graphite can produce high-quality single-layer graphene sheets stably suspended in organic solven…
Through direct nanoparticle nucleation and growth on nitrogen doped, reduced graphene oxide sheets and cation substitution of spinel Co3O4 nanoparticles, a manganese-cobalt spinel MnCo2O4/graphene hybrid was developed as a highly efficient electrocatalyst for oxygen reduction reaction (ORR) in alkaline conditions. Electrochemical and X-ray near edge structure (XANES) investigations revealed that the nucleation and growth method for forming inorganic-nanocarbon hybrid results in covalent coupling between spinel oxide nanoparticles and N-doped reduced graphene oxide (N-rmGO) sheets. Carbon K-edg…
Two-dimensional graphene offers interesting electronic, thermal and mechanical properties that are currently explored for advanced electronics, membranes and composites. Here we synthesize and explore the biological application of nano-graphene oxide NGO, single-layer graphene oxide sheets down to a few nanometers in lateral width. We develop functionalization chemistry to impart solubility and compatibility of NGO in biological environments. We obtain size separated pegylated NGO sheets that are soluble in buffers and serum without agglomeration. The NGO sheets are found to be photoluminescen…
Recently, two-dimensional boron sheets have attracted a lot of attentions owing to their structural polymorphs and outstanding properties. And, due to chemical complexity and electron deficiency of B atoms, the 2D boron sheets are easy affected by the environment. So, exploring novel 2D boron oxides gets highly needed. In this study, we theoretically explored 2D boron oxides structures and their basic properties. We found 2D boron oxides are metals or semimetals, when oxygen concentration is low. More interesting, the B6O1 exhibits Dirac Loop near the Fermi level and the maximum Fermi velocity…
Graphene oxide (GO) is one of chemically modified graphenes and has been extensively investigated worldwide. A monolayer sheet of GO can be chemically produced in solution and it has been expected to be adaptable to a wide variety of applications. Most of works have focused on fabrication and reduction processes of GO, while its intrinsic property has not been explored in detail. We have succeeded in fabricating large scale GO nanosheets reproducibly. In the present work, we observed GO nanosheets by conductive atomic force microscopy. The current image is useful to monitor the GO thickness as…
In the paper, high temperature induced phase transformation in chemically grown CdO thin films has been demonstrated whereas their corresponding electronic origin is further investigated by density functional theory. In particular, cubic rocksalt to hexagonal wurtzite PT in 900 degree centigrade annealed CdO thin films is confirmed by Xray diffraction , consistent with High Resolution Transmission Electron Microscopy. Such high temperature treatment also leads to significant enhancement in optical band gap from 2.2 to 3.2 eV as manifested by UV-Visible spectroscopy. Moreover, atomic force micr…
Copper oxide thin films are deposited on quartz substrates by DC magnetron sputtering and the effect of deposition temperature on their optoelectronic properties is examined in detail. Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) analysis, Raman spectroscopy, UV-Vis spectroscopy, and four-probe sheet resistance measurements are used to characterize the surface morphology, structural, optical, and electrical properties respectively. Deposition is carried out at room temperature and between 200 and 300 °C. XRD analysis indicates that the oxide formed is primarily Cu$_2$O and the a…
Graphene based sheets have stimulated great interest due to their superior mechanical, electrical and thermal properties. A general visualization method that allows quick observation of these single atomic layers would be highly desirable as it can greatly facilitate sample evaluation and manipulation, and provide immediate feedback to improve synthesis and processing strategies. Here we report that graphene based sheets can be made highly visible under a fluorescence microscope by quenching the emission from a dye coating, which can be conveniently removed afterwards by rinsing without disrup…
Graphene oxide (GO) is one of chemically modified graphenes and has been extensively studied worldwide. A monolayer sheet of GO which is chemically produced in solution can be deposited on various substrates. We have proved that use of graphite powder with a large grain size enables preparation of a single layer GO film that is larger than 100 micrometers easily and reproducibly. If it is possible to reduce the GO film completely, one can obtain graphene without mechanical exfoliation. However, the reduction methods employed so far have been insufficient to remove oxygen or to restore the long…
Recent experimental reports on in-plane proton conduction in reduced graphene oxide (rGO) films open a new way for the design of proton exchange membrane essential in fuel cells and chemical filters. At high humidity condition, water molecules attached on the rGO sheet are expected to play a critical role, but theoretical works for such phenomena have been scarcely found in the literature. In this study, we investigate the proton migration on water-adsorbed monolayer and bilayer rGO sheets using first-principles calculations in order to reveal the mechanism. We devise a series of models for th…
In the present work we demonstrate the self-organized formation of anodic Mo-oxide nanotube arrays grown on a Mo sheet under suitable electrochemical conditions in glycerol/NH4F electrolytes. The resulting amorphous tubes can be crystallized by annealing to MoO2 or MoO3. The tube walls then can be further sulfurized fully or partially to Mo-sulfide to form well-ordered arrays of vertically aligned MoOx/MoS2 nanotubes. Under optimized conditions, defined MoS2 sheets form on the oxide walls in a layer by layer low angle zig-zag arrangement that provide a high density of reactive stacking faults.…
We develop a simple chemical method to obtain bulk quantities of N-doped, reduced graphene oxide (GO) sheets through thermal annealing of GO in ammonia. X-ray photoelectron spectroscopy (XPS) study of GO sheets annealed at various reaction temperatures reveals that N-doping occurs at a temperature as low as 300C, while the highest doping level of ~5% N is achieved at 500C. N-doping is accompanied by the reduction of GO with decreases in oxygen levels from ~28% in as-made GO down to ~2% in 1100C NH3 reacted GO. XPS analysis of the N binding configurations of doped GO finds pyridinic N in the do…
The layers of graphene oxide (GO) are found to be good for permeation of water but not for helium (Science 2012 335 (6067): 442-444) suggesting that the GO layers are dynamic in the formation of permeation route depending on the environment they are in (i.e, water or helium). To probe the microscopic origin of this observation we calculate the potential of mean force (PMF) of GO sheets (oxidized and reduced parts), with inter-planar distance as reaction coordinate in helium and water. Our PMF calculation shows that equilibrium interlayer distance between oxidized part of GO sheets in helium is…
A commercially available membrane filter paper composed of mixed cellulose esters bearing typically an interconnected pore structure was transformed into a stimuli-responsive bilayer actuator by depositing a thin film of poly(ionic liquid)-modified graphene oxide sheets (GO-PIL) onto the filter paper. In acetone vapor, the as-synthesized bilayer actuator bent readily into multiple loops at a fast speed with the GO-PIL top film inwards. Upon pulling back into air the actuator recovered their original shape. The asymmetric swelling of the top GO-PIL film and the bottom porous filter paper toward…
Oxide superlattices and microstructures hold the promise for creating a new class of devices with unprecedented functionalities. Density-functional studies of the recently fabricated superlattices of lattice-matched perovskite titanates (SrTiO3)n/(LaTiO3)m reveal a classic wedge-shaped potential originating from the Coulomb potential of a charged sheet of La atoms. The potential in turn confines the electrons in the vicinity of the sheet, leading to an Airy-function localization of the electron states. Magnetism is suppressed for structures with a single LaTiO3 monolayer, while the bulk antife…
A simple optical method is presented for identifying and measuring the effective optical properties of nanometer-thick, graphene-based materials, based on the use of substrates consisting of a thin dielectric layer on silicon. High contrast between the graphene-based materials and the substrate is obtained by choosing appropriate optical properties and thickness of the dielectric layer. The effective refractive index and optical absorption coefficient of graphene oxide, thermally reduced graphene oxide, and graphene are obtained by comparing the predicted and measured contrasts.
Water dispersed graphene oxide sheets were used to prepare graphene-polyethylenglycol diacrylate resin composites by photopolymerization. It was found that graphene sheets undergo excellent morphological distribution within the resin system, giving rise to transparent composites with unaltered thermal properties with respect to the neat resin, that are electrically conductive at loading ratios as low as 0.02 %wt of graphene oxide . The proposed strategy based on photopolymerization provides an easy, energy-saving and environmental friendly technique that can find a wide application in coating …
The interface between LaAlO3 and SrTiO3 hosts a two-dimensional electron system of itinerant carriers, although both oxides are band insulators. Interface ferromagnetism coexisting with superconductivity has been found and attributed to local moments. Experimentally, it has been established that Ti 3d electrons are confined to the interface. Using soft x-ray angle-resolved resonant photoelectron spectroscopy we have directly mapped the interface states in k-space. Our data demonstrate a charge dichotomy. A mobile fraction contributes to Fermi surface sheets, whereas a localized portion at high…
In this work we report results of step-by-step modeling of the oxidation of free-standing boron monolayers of different types. Results of the calculations demonstrate that the process of the oxidation is always exothermic and lead toward the formation of foam-like boron oxide films with incorporated non-oxidized small boron clusters. Some of these boron-oxide films demonstrate the presence of chemically stable magnetic centers. Evaluation of the physical properties of oxidized boprophene sheets (OBS) demonstrate it possible application in solar energy, as sensors and coating against leakage of…
We reconsider the long-explored problem that the magnitude of the measured Casimir force between an Au sphere and an indium tin oxide (ITO) film decreases significantly with no respective changes in the ITO dielectric permittivity required by the Lifshitz theory. Two plausible resolutions of this conundrum are discussed: the phase transition of an ITO film from metallic to dielectric state and the modification of a film surface under the action of UV light. To exclude the latter option, we propose an improvement in the experimental scheme by adding a graphene sheet on top of an ITO film. The f…
We report on an extensive structural and electrical characterization of under-gate dielectric oxide insulators Al2O3 and HfO2 grown by Atomic Layer Deposition (ALD). We elaborate the ALD growth window for these oxides, finding that the 40-100 nm thick layers of both oxides exhibit fine surface flatness and required amorphous structure. These layers constitute a base for further metallic gate evaporation to complete the Metal-Insulator-Semiconductor structure. Our best devices survive energizing up to ~3 MV/cm at 77 K with the leakage current staying below the state-of-the-art level of 1 nA. At…
The electronic reconstruction at the interface between two insulating oxides can give rise to a highly-conductive interface. In analogy to this remarkable interface-induced conductivity we show how, additionally, magnetism can be induced at the interface between the otherwise nonmagnetic insulating perovskites SrTiO3 and LaAlO3. A large negative magnetoresistance of the interface is found, together with a logarithmic temperature dependence of the sheet resistance. At low temperatures, the sheet resistance reveals magnetic hysteresis. Magnetic ordering is a key issue in solid-state science and …
Low Work Function Tethers (LWT) is long conductors with a segment coated with a material that has loosely-bounded electrons. Unlike a standard bare tether equipped with an active electron emitter, LWTs close the electrical circuit (cathodic contact) with the ambient plasma in a passive manner thanks to the thermionic and photoelectric effects. This work presents experimental results on a novel procedure for manufacturing LWT samples. Conductive substrates (aluminum and copper) have been coated with graphene oxide doped with Cesium by using a scalable, simple and cost-effective coating method w…
Based on first-principles calculations we performed a systematic study of the energetic stability, structural characterization, and electronic properties of the fully oxidized $A_{2}B$, electrenes, with the following combinations, (i) $A$=Ca, Sr, and Ba for $B$=N; (ii) $A$=Sr and Ba for $B$=P; and Y$_{2}$C, and Ba$_{2}$As. We have considered one side oxidation of single layer electrenes $(O/A_{2}B)$, and two side oxidation of bilayer electrenes $(O/(A_{2}B)_{2}/O)$. We show that the hexagonal lattice of the pristine host is no longer the ground state structure in the oxidized systems. Our tota…
Rapid Atmospheric Vapor Deposition of H:In2O3 Transparent Conducting Oxide Thin Films
University of Oxford（牛津大学）；University of Surrey（萨里大学）；National Taiwan University（台湾大学）；University of Cambridge（剑桥大学）；University of Manchester（曼彻斯特大学）；Sungkyunkwan University（成均馆大学）；Univ. Toulouse, CNRS, Toulouse INP, LGC（图卢兹大学，法国国家科学研究中心，图卢兹第三工业大学，化学实验室）
Because they may provide ultrathin, high-flux, and energy-efficient membranes for precise ionic and molecular sieving in aqueous solution, GO membranes (partially oxidized, stacked sheets of graphene) have shown great potential in water desalination and purification, gas and ion separation, biosensors, proton conductors, lithium-based batteries and super-capacitors. Unlike carbon nanotube (CNT) membranes, in which the nanotube pores have fixed sizes, the pores of GO membranes - the interlayer spacing between GO sheets - are of variable size. This presents a challenge for using GO membranes for…
Quasi all water soluble composites use graphene oxide (GO) or reduced graphene oxide (rGO) as graphene based additives despite the long and harsh conditions required for their preparation. Herein, polyvinyl alcohol (PVA) films containing few layer graphene (FLG) are prepared by the co-mixing of aqueous colloids and casting, where the FLG colloid is first obtained via an effcient, rapid, simple, and bio-compatible exfoliation method providing access to relatively large FLG flakes. The enhanced mechanical, electrical conductivity, and O2 barrier properties of the films are investigated and discu…
Non-monotonic hydration dependence of ionic transport in atomically-thin MnO2 sheets
Institute of Materials Science and Nanotechnology, Bilkent University（比尔肯特大学材料科学与纳米技术研究所）；Bilkent National Nanotechnology Research Center - UNAM（比尔肯特国家纳米技术研究中心）；Department of Physics, Middle East Technical University（中东理工大学物理系）
The structure of a new member of the AxCoO2 x nH2O family (A=Li,Na,K) was determined by high-resolution synchrotron X-ray powder diffraction. Layered lithium cobalt oxide hydrate LixCoO2 x 2H2O crystallizes in a disordered monoclinic structure (space group C2/m) with lattice parameters a = 4.8915(2) A, b = 2.8239(1) A, c = 10.7033(9) A, beta = 112.386(4)deg. Unlike the superconducting sodium cobalt oxide hydrate, this material possesses a structure with lithium-water layers intercalated between disordered octahedral sheets of cobalt oxide. The interlayer spacing is slightly larger (~0.9%) due …
We show that the growth of the heterostructure LaGaO3/SrTiO3 yields the formation of a highly conductive interface. Our samples were carefully analyzed by high resolution electron microscopy, in order to assess their crystal perfection and to evaluate the abruptness of the interface. Their carrier density and sheet resistance are compared to the case of LaAlO3/SrTiO3 and a superconducting transition is found. The results open the route to widening the field of polar-non polar interfaces, pose some phenomenological constrains to their underlying physics and highlight the chance of tailoring the…
We report on the transport characterization in dark and under light irradiation of three different interfaces: LaAlO3/SrTiO3, LaGaO3/SrTiO3, and the novel NdGaO3/SrTiO3 heterostructure. All of them share a perovskite structure, an insulating nature of the single building blocks, a polar/non- polar character and a critical thickness of four unit cells for the onset of conductivity. The interface structure and charge confinement in NdGaO3/SrTiO3 are probed by atomic-scale- resolved electron energy loss spectroscopy showing that, similarly to LaAlO3/SrTiO3, extra electronic charge confined in a s…
The current family of experimentally realized two-dimensional magnetic materials consist of 3$d$ transition metals with very weak spin-orbit coupling. In contrast, we report a new platform in a chemically bonded and layered 4$d$ oxide, with strong electron correlations and competing spin-orbit coupling. We synthesize ultra-thin sheets of SrRu$_2$O$_6$ using scalable liquid exfoliation. These exfoliated sheets are characterized by complementary experimental and theoretical techniques. The thickness of the nano-sheets varies between three to five monolayers, and within the first-principles calcu…
Epitaxial strain imposed in complex oxide thin films by heteroepitaxy is recognized as a powerful tool for identifying new properties and exploring the vast potential of materials performance. A particular example is LaCoO3, a zero spin, nonmagnetic material in the bulk, whose strong ferromagnetism in a thin film remains enigmatic despite a decade of intense research. Here, we use scanning transmission electron microscopy complemented by X-ray and optical spectroscopy to study LaCoO3 epitaxial thin films under different strain states. We observed an unconventional strain relaxation behavior re…
Similar to silicon that is the basis of conventional electronics, strontium titanate (SrTiO3) is the bedrock of the emerging field of oxide electronics. SrTiO3 is the preferred template to create exotic two-dimensional (2D) phases of electron matter at oxide interfaces, exhibiting metal-insulator transitions, superconductivity, or large negative magnetoresistance. However, the physical nature of the electronic structure underlying these 2D electron gases (2DEGs) remains elusive, although its determination is crucial to understand their remarkable properties. Here we show, using angle-resolved …
