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Along with the rapid development of technology and industry, the need for energy storage has become fundamental. One promising energy storage devices is the supercapacitor. Several type supercapacitors are available, one of which is the electrical double-layer capacitor made from carbon graphite and multiwalled carbon nanotubes (MWCNTs). In this study, we combined these two materials into a working electrode in a three-electrode system. In the morphological analysis using scanning electron microscope, transmission electron microscope, and X-ray diffraction, the two materials were found to have formed a composite on the surface. In the electrochemical analysis, two types of testing were conducted using cyclic voltammetry and electrochemical impedance spectroscopy. Electrochemical analysis was carried out on five electrolyte concentrations of Na2SO4 from 1 to 6 M. The capacitance produced at concentrations of 1, 2, 3, 4, and 5 M were 34.395, 35.808, 46.284, 49.502, and 76.815 F/g, respectively. At an electrolyte concentration of 5 M Na2SO4, an energy density of 27.312 Wh/Kg and a power density of 343.786 W/Kg were produced. Meanwhile on concentration of 6 M, the surface of the electrode was damaged.

By using angle-resolved photoemission spectroscopy (ARPES), we study the electronic structure of highly oriented pyrolytic graphite (HOPG). In contrast to the pristine HOPG, band gap opening of approximately 100 meV is directly observed at the surface of nano-scale HOPG square pattern. Our Raman data and density functional theory calculations suggest that the bandgap opening is likely caused by tensile strain induced from the patterning. We believe that this surface engineering of HOPG will not only be useful for enhancing terahertz devices but also provides a route for modifying other materials/metasurfaces for optoelectronics applications.

Water electrolysis has received much attention in recent years as a means of sustainable H2 production. However, many challenges remain in obtaining high-purity H2 and making large-scale production cost-effective. This study provides a strategy for integrating a two-cell water electrolysis system with solar energy storage. In our proposed system, CuO-Cu(OH)2/Cu2O was used as a redox mediator between oxygen and hydrogen evolution components. The system not only overcame the gas-mixing issue but also showed high gas generation performance. The redox reaction (charge/discharge) of CuO-Cu(OH)2/Cu2O led to a significant increase (51%) in the initial rate of H2 production from 111.7 μmol h-1 cm-2 in the dark to 168.9 μmol h-1 cm-2 under solar irradiation. The effects of light on the redox reaction of CuO-Cu(OH)2/Cu2O during water electrolysis were investigated by in situ X-ray absorption and photoemission spectroscopy. These results suggest that surface oxygen vacancies are created under irradiation and play an important role in increased capacitance and gas generation. These findings provide a new path to direct storage of abundant solar energy and low-cost sustainable hydrogen production.

In this letter, we report on the simple process of preparing perovskite oxide SrMnO3 and the studying of the size effect on electrochemical properties for high-performance supercapacitor electrode. The high-crystalline micro-sized and nano-sized perovskite oxide SrMnO3 particles were successfully synthesized by a simple solid-state reaction, followed by a simple size reduction using high-energy ball milling. The electrochemical properties of the SrMnO3 had intriguing results on both sizes of particle, especially when comparing between before and after cycles. After a size reduction, the specific capacitance of the particles increased approximately twofold. Interestingly, the micro-sized SrMnO3 gained ∼500% its initial specific capacitance after 3000 successive cycles due to electrochemical nano-feature activation and oxygen-vacancy production, while the specific capacitance for the nano-sized SrMnO3 remained almost unchanged. Our work suggested a cost-effective and simple technique for high-performance perovskite-based supercapacitor electrodes by achieving the desired performance.

Exploring new materials and structures and optimizing integrated photosupercapacitors systems are extensively developed. In this work, we report the study of the influence of light intensity on the performance of photosupercapacitors. The photosupercapacitors was constructed from active materials TiO2-ZnO-natural dye-DSSC and BaTiO3 based supercapacitors. The photoelectric current and open current voltage at various light intensity. The photo-charging was measured under various light intensity illumination 30400, 60800, 91200, 144500, and 170,800 Lux. It is shown that intensity significantly influences the charging rate on the supercapacitor section. The higher the intensity, the quicker the charging occurs.

Ni-Co MOF-based systems have been proposed as supercapacitor electrode materials due to their high energy capacitance. This study aims to determine the effect of Ni-Co MOF addition in the ZnO-FC-NiCo MOF as supercapacitor electrode. ZnO and functionalized carbon (FC) materials are mixed with the addition of Ni-Co MOF mass of 10% and 20% of the total mass then deposited onto the Al foil substrate. The supercapacitors were arranged symmetrically using 0.5 M H3PO4 electrolytes. The sample characterizations were carried out using XRD, SEM, TEM and Cyclic Voltammetry. It is shown that specific capacitance is increasing, ranging from 1.15 to 6.62F/g.

The electrical transport properties of a thin film of the diamondoid adamantane, deposited on an Au/W substrate, were investigated experimentally. The current I, in applied potential V, from the admantane-thiol/metal heterstructure to a wire lead on its surface exhibited non-symmetric (diode-like) characteristics and a signature of resistive switching (RS), an effect that is valuable to non-volatile memory applications. I(V) follows a hysteresis curve that passes twice through $$I(0)=0$$ I ( 0 ) = 0 linearly, indicating RS between two states with significantly different conductances, possibly due to an exotic mechanism.

Photosupercapacitor is an integrated device for harvesting and storing solar energy into electrical energy. Photosupercapacitor is constructed by solar cell and supercapacitor. In the solar cell with DSSC type, one of the influential variables is photoanode performance. The photoanode with ZnO layer plays a role in light absorption, charge mobility, and electrical properties, which are influenced by crystal structure and nanoscale morphology. One of nanoscale morphology of ZnO that widely used is nanorods. This work is focussed to investigate the effect of annealing temperature on seed layer ZnO to growth nanorods shape in photoanode of photosupercapacitor and its performance. The seed layer ZnO nanoparticle was deposited onto FTO substrate by a screen printing method. The ZnO nanorod was grown by dippin FTO/ZnO in solution (Zinc nitrate, HMT, and DI water) under 100 °C. The photosupercapacitor was constructed by DSSC and ZnO symmetric supercapacitor which integrated by using aluminum foil substrate. The annealing temperature on ZnO nanoparticles affected on increasing crystal size of ZnO seed. All of the samples show ZnO wurtzite phase with the highest peak located on the hkl plane (101), but ZnO nanorod growth to hkl plane (100). The DSSC part efficiency produced around 0.874%. The resulting efficiency of photosupercapacitor is around 0.549%. The annealing temperature causes the value of specific capacitance to decrease, because of decreasing DSSC performance.

In this work, we study and compare the photo-induced conductivity of a two-dimensional electron gas (2DEG) at the bare surface of SrTiO3 (STO) and in the heterostructure of BiFeO3 (BFO) and STO, where BFO was deposited by radio frequency magnetron sputtering. The photo-induced conductance of the BFO/STO interface shows a large increase which is 20.62 times more than the sum of photo-induced conductance from each individual BFO thin film and STO crystal. Since this photo-induced conductance of the BFO/STO heterostructure can be adjusted to become higher and lower by applying an electric field to the top surface, we attribute this large increase to the strong photo-induced electrical polarization of BFO. With the two-point setup of positive bias and negative bias, the conductivity also exhibits diode-like behavior where the forward and backward resistances are different. This work provides methods to interplay between light irradiation, electric field, and conductivity in all-oxide electronics.

Photo-supercapacitor (PSc) was an integration of photovoltaic as a device for harvesting light energy and supercapacitor as an energy storage device. Multifunctional harvesting device has increasing demand in the green energy industry sector. In this study, we demonstrate the integrated array of photovoltaic type dye-sensitized solar cells and carbon-based supercapacitors. The photo-supercapacitor integration will be arranged in a different arrangement, called series and parallel arrangement. DSSC photoanode was used TiO2material that deposited using screen printing method on FTO substrate. Activated Carbon/Carbon Black/SBR as a material composite of the electrode was deposited on the aluminium foil substrate using dr. blade technique. XRD characterization has identified the TiO2anatase. The morphology of mesoporous TiO2 and Ti element has been identified by SEM characterization and EDX of 64.30 wt%. The UV-Vis spectroscopy curve has identified the absorbance in the wavelength range of 200 – 900 nm and the absorbance area of 914.58. The J-V characterization shows that TiO2 photoanode has a efficiency of 2.15 %. The Charge-Discharge shows that AC/CB/SBR performance has capacitance specific of 61.33 F/g. The l–-V characterization of photo-supercapacitor performance was arranged by series has voltage higher than parallel arrangement, because it produces a larger voltage (Vop ).

A supercapacitor (SC) is an energy storage device with high energy density, high power density, long life cycle and a bundant material in nature.. Activated carbon based on coconut shell waste (ACCS) is one of the most promising supercapacitor base materials due to its abundance in nature, environmentally friendly, and high surface area. Activated carbon based on coconut shell (ACCS) waste is a potential material as a supercapacitor base material. This is because ACCS has undergone chemical and physical activation, has a high surface area, is abundant in nature, and is environmentally friendly. However, ACCS has common ionic transport diffusion, resulting in inefficient utilization of activated carbon surface area. Therefore, ACCS composite with TiO2 material is needed. TiO2 material with a small particle size can be used to reduce the aggregation so it can increase the electrolyte to an active redox site. Therefore, this research was conducted to obtain information about the most optimum activation method for ACCS biomass and the supercapacitors enhancement with ACCS-TiO2 composite to obtain great ionic diffusion performance and an effective surface area utilization. In brief, the experiment was started by preparing the composite solutions with various compositions of TiO2 (0%, 10%, 15%, and 20%). The deposition was carried out using the doctor blade technique on the aluminum foil based substrate and the liquid electrolyte of 1 M Et4NBF4 was injected between the electrodes. The crystal structure, morphology, and elemental analysis of the composite were identified using X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray (EDX), respectively. Charge Discharge was applied to measure the electrical performance of the device. The highest performance of symmetric supercapacitor was performed by TiO2 15% that able to show its cyclic reversibility at the voltage range of 0-2 V, generated a specific capacitance of 53.10 F g-1 with the power density and maximum energy density of 367.05 W kg-1 and 26.15 Wh kg-1, respectively. Over 50 cycles, its maximum energy density was decreased to 24.83 Wh kg-1 with the capacity retention of 94.64 %.

The discovery of a two-dimensional electron gas (2DEG) at the $$\hbox {LaAlO}_3/\hbox {SrTiO}_3$$ LaAlO 3 / SrTiO 3 interface has set a new platform for all-oxide electronics which could potentially exhibit the interplay among charge, spin, orbital, superconductivity, ferromagnetism and ferroelectricity. In this work, by using angle-resolved photoemission spectroscopy and conductivity measurement, we found the reduction of 2DEGs and the changes of the conductivity nature of some ferroelectric oxides including insulating Nb-lightly-substituted $$\hbox {KTaO}_3$$ KTaO 3 , $$\hbox {BaTiO}_3$$ BaTiO 3 (BTO) and (Ca,Zr)-doped BTO across paraelectric-ferroelectric transition. We propose that these behaviours could be due to the increase of space-charge screening potential at the 2DEG/ferroelectric regions which is a result of the realignment of ferroelectric polarisation upon light irradiation. This finding suggests an opportunity for controlling the 2DEG at a bare oxide surface (instead of interfacial system) by using both light and ferroelectricity.

Light-sensitive capacitance variation of Bi0.95La0.05FeO3 (BLFO) ceramics has been studied under violet to UV irradiation. The reversible capacitance enhancement up to 21% under 405 nm violet laser irradiation has been observed, suggesting a possible degree of freedom to dynamically control this in high dielectric materials for light-sensitive capacitance applications. By using ultraviolet photoemission spectroscopy (UPS), we show here that exposure of BLFO surfaces to UV light induces a counterintuitive shift of the O2p valence state to lower binding energy of up to 243 meV which is a direct signature of negative electronic compressibility (NEC). A decrease of BLFO electrical resistance agrees strongly with the UPS data suggesting the creation of a thin conductive layer on its insulating bulk under light irradiation. By exploiting the quantum capacitance model, we find that the negative quantum capacitance due to this NEC effect plays an important role in this capacitance enhancement

Bismuth Ferrite (BiFeO 3 ) is a multiferroic material with high dielectric properties which can be improved by various doping such as lanthanum, and yttrium. In this research, Bi 1-x Ba x FeO 3 ceramics (x = 0 and 0.05) were prepared using simple co-precipitation method with calcining temperature at 600 °C. Here, we report the two steps of capacitance enhancement by doping and violet-light irradiation. Firstly, the dielectric constant of BiFeO 3 is observed to increase approximately 60% (from 230 pF to 360 pF at 10 kHz) by doping with barium (x= 0.05); one main cause of this increase is attributed to the larger grain size. Moreover, the capacitance in this Ba-doped sample can be enhanced by approximately 9% at 1 kHz under violet light exposure (comparing to 2% increase in pure BiFeO 3 ). This indicates that Ba doping can help improving the dielectric property of BiFeO 3 not only in the conventional way but at the same time in another property, such as optoelectronic aspect presented in this work.

s The preparation and electronic properties of Cs1−xAxAl0.33Te1.67O6 (A = K, Rb, and Cs) are reported. Replacing Cs with smaller Rb and K reduces cell parameters of the compounds but does not affect the overall structure. Electronic conductivities of all samples were measured and explained based on the band conduction model. Although XPS Te3d5/2 spectra indicate that all samples contain similar amount of Te4+/Te6+ mixed valency, their conductivities are varied from about 0.1 S cm in CsAl0.33Te1.67O6 to 3 × 10−5 S cm in RbAl0.33Te1.67O6 and 3 × 10−7 S cm in KAl0.33Te1.67O6 at 300 K. To explain such large differences, the band structure diagrams are proposed based on the UV–Vis spectra and XPS spectra at valence band region. When the obtained activation energies of conduction and the proposed band diagram are considered, it is concluded that AAl0.33Te1.67O6 (A = K, Rb, and Cs) are n-type semiconductors. The defect levels in these samples originate from Te4+ whose energy level relative to the conduction band minimum is different from samples to samples. Such differences are affected by Cs content in the structure as Cs seems to lower the band gap energy and increase the valence band maximum. It is the position of these defect levels that determines the electronic conductivity of the compounds.

In this work, the magnetic carbon sand (MCS) have been successfully prepared by the chemical vapor deposition (CVD) on sands using adamantane (C10H16) as a precursor. The MCS was obtained by the deposition of adamantane precursor on sand at 1050 °C. The magnetization of MCS has been measured by the vibrating sample magnetometer (VSM) with applied magnetic field in the range between -15 and 15 kOe. From VSM results, the magnetic hysteresis loop is observed in MCSs indicating the ferromagnetic behavior without the presence of magnetic elements. The saturated magnetization has been observed as high as 72 m-emu/g at room temperature. From the Raman-spectroscopy measurement, the observed ferromagnetism in MCS may come from the unpaired electrons in carbon (i.e. dangling bond) resulted by calcining adamantane at high temperature. This finding suggests an inexpensive method for preparing magnetic particles which can be applied in broad applications such as bio-compatible drug delivery and large-scale magnetic shielding.

In this work, electronic structure variations of MoS2 under violet laser irradiation and potassium evaporation have been studied by angle-resolved photoemission spectroscopy (ARPES). By exposing violet laser on the fresh MoS2 surface, we found the shift of valence band to the higher binding energy of 140±10 meV. This behavior can be described by the optical excitation where electrons in the valence band are temporary pumped to the conduction band edge. By using potassium evaporation, the shift of valence band of 280±20 meV to higher binding energy as well as the emerging of conduction pockets at K point which are a result of electron donation from alkali metals. Another shift of valence band up to 40±10 meV have been observed after irradiating violet laser on the doped sample. The schematic band diagram which can be described the chemical shifts based on experimental ARPES data has been proposed. By using transport measurement, a variation of MoS2 electrical resistance under light irradiation supports the nonequilibrium electron donation induced by optical excitation.

Funding: The experimental work has been supported by the European Research Council (ERC), the Scottish Funding Council, the UK EPSRC and the Swiss National Science Foundation (SNSF). Theoretical work was supported by the ERC grant ERC-319286-QMAC and by the SNSF (NCCR MARVEL).

Two-dimensional transition metal carbides, carbonitrides, and nitrides, called MXenes, exhibit high metallic conductivity, ion intercalation capability, and reversible redox activity, prompting their applications in energy storage and conversion, electromagnetic interference (EMI) shielding, and electronics, among many other fields. It has been shown that replacement of ∼50% of carbon atoms in the most popular MXene family member, titanium carbide (Ti3C2Tx), by nitrogen atoms, forming titanium carbonitride (Ti3CNTx), leads to drastically different properties. Such properties include very high negative charge in solution and extreme EMI shielding effectiveness, exceeding all known materials, even metals at comparable thicknesses. Here, by using ultraviolet photoemission spectroscopy (UPS), the electronic structures of Ti3CNTx and Ti3C2Tx are systematically investigated and compared as a function of charge carrier density. We observe that, in contrast to Ti3C2Tx, the Ti 3p core-level of Ti3CNTx exhibits a counterintuitive shift to a lower binding energy of up to ∼250 meV upon increasing the electron density, which is a spectroscopic signature of negative electronic compressibility (NEC). These experimentally measured chemical potential shifts are well captured by the density functional theory (DFT) calculation. The DFT results also further suggest that the hybridization of titanium–nitrogen bonding in Ti3CNTx helps to promote the available states of Ti atoms for receiving more electrons above the fermi level and leads to the observed NEC. Our findings explain the differences in electronic properties between the two very important and widely studied MXenes and also suggest a new strategy to apply the NEC effect of Ti3CNTx in energy and charge storage applications.

The influence of ultraviolet (UV)-induced oxygen vacancies on dynamic changes of electrical conductance in a random-oriented SrTiO3 polycrystalline and SrTiO3 single crystals with (100), (110), and (111) surfaces is reported in this study. It was discovered that a large fraction of ultraviolet-induced oxygen vacancies in the SrTiO3 polycrystalline are primarily contributed from grain boundaries, but these oxygen vacancies are less influenced to the reversible conductance changes due to UV irradiation. The dynamic change of electrical conductance in the polycrystalline is similar to what has been observed for the polar (110) and (111) oriented single crystals, offering a potential alternative for multifunctional electronic devices.

Indium oxide (In2O3) based heterojunction thin films with enhanced visible light photoelectrochemical (PEC) performance were successfully grown on c-Si substrate by plasma assisted in-situ thermal annealing at three different filament temperatures, Tf. The in-situ thermal annealing has significantly changed the grainy morphology of InN/In2O3 heterojunctions to sharp crystallites of W2N/In2O3 with increase in Tf from 1300 to 1700 °C, respectively. It is shown that the formation InN, WO3, and W2N on In2O3 nanostructures has significantly improved the photocurrent to 0.966, 0.429, and 1.84 mA/cm2 at 1 VAg/AgCl which are 4.2, 1.86, and 8 times higher than the photocurrent density measured for intrinsic In2O3 (0.23 mA/cm2), respectively. The effects of the band alignments in charge separation and thus improving the photoelectrochemical properties of the heterojunction films are discussed.

We explore the utility of controlled low-doses (0.2–100 Gy) of photon irradiation as initiators of structural alteration in carbon-rich materials. To-date our work on carbon has focused on β-, x- and γ-irradiations and the monitoring of radiotherapeutic doses (from a few Gy up to some tens of Gy) on the basis of the thermoluminescence (TL) signal, also via Raman and X-ray photo-spectroscopy (XPS), providing analysis of the dose dependence of single-walled carbon nanotubes (SWCNT). The work has been extended herein to investigate possibilities for analysis of structural alterations in graphite-rich mixtures, use being made of two grades of graphite-rich pencil lead, 8H and 2B, both being in the form produced for mechanical pencils (propelling or clutch pencils). 2B has the greater graphite content (approaching 98 wt %), 8H being a mixture of C, O, Al and Si (with respective weight percentages 39.2, 38.2, 9.8 and 12.8). Working on media pre-annealed at 400 °C, both have subsequently been irradiated to penetrating photon-mediated doses. Raman spectroscopy analysis has been carried out using a 532 nm laser Raman spectrometer, while for samples irradiated to doses from 1 to 40 Gy, XPS spectra were acquired using Al Kα sources (hv ∼1400 eV); carbon KLL Auger peaks were acquired using 50 eV Pass Energy. At these relatively low doses, alterations in order-disorder are clearly observed, defect generation and internal annealing competing as dominating effects across the dose range.

By using angle-resolved photoemission spectroscopy (ARPES), the variation of the electronic structure of HfSe$_2$ has been studied as a function of sodium intercalation. We observe how this drives a band splitting of the p-orbital valence bands and a simultaneous reduction of the indirect band gap by values of up to 400 and 280 meV respectively. Our calculations indicate that such behaviour is driven by the band deformation potential, which is a result of our observed anisotropic strain induced by sodium intercalation. The applied uniaxial strain calculations based on density functional theory (DFT) agree strongly with the experimental ARPES data. These findings should assist in studying the physical relationship between doping and strain, as well as for large-scale two-dimensional straintronics., Comment: 6 pages, 4 figures

Tunable bandgaps, extraordinarily large exciton-binding energies, strong light-matter coupling and a locking of the electron spin with layer and valley pseudospins have established transition-metal dichalcogenides (TMDs) as a unique class of two-dimensional (2D) semiconductors with wide-ranging practical applications. Using angle-resolved photoemission (ARPES), we show here that doping electrons at the surface of the prototypical strong spin-orbit TMD WSe2, akin to applying a gate voltage in a transistor-type device, induces a counterintuitive lowering of the surface chemical potential concomitant with the formation of a multivalley 2D electron gas (2DEG). These measurements provide a direct spectroscopic signature of negative electronic compressibility (NEC), a result of electron-electron interactions, which we find persists to carrier densities approximately three orders of magnitude higher than in typical semiconductor 2DEGs that exhibit this effect. An accompanying tunable spin splitting of the valence bands further reveals a complex interplay between single-particle band-structure evolution and many-body interactions in electrostatically doped TMDs. Understanding and exploiting this will open up new opportunities for advanced electronic and quantum-logic devices.

(Ba0.7Ca0.3)1–1.5xLaxTiO3 ceramics with x=0–0.03 were prepared using a solid state sintering method. All ceramics exhibit ferroelectric state at maximum temperatures, Tm, between 340 and 383 K. Upon increasing La3+ content, although the maximum temperature of permittivity becomes lower (well correlated with the decrease of tetragonallity), the dielectric response is significantly higher near room temperature for the x=0.03 sample. Furthermore, the conductivity shows clear enhancement under ultra-violet (UV) irradiation. This enhancement becomes larger upon increasing La content, which correlates with the decrease in activation energy extracted from the temperature-dependent conductivity. The results here suggest that BCT properties may be largely tunable by La doping, which could be applied with much potential use with ferroelectric devices and in optoelectronics.

We study the low-energy surface electronic structure of the transition-metal dichalcogenide superconductor PdTe$_2$ by spin- and angle-resolved photoemission, scanning tunneling microscopy, and density-functional theory-based supercell calculations. Comparing PdTe$_2$ with its sister compound PtSe$_2$, we demonstrate how enhanced inter-layer hopping in the Te-based material drives a band inversion within the anti-bonding p-orbital manifold well above the Fermi level. We show how this mediates spin-polarised topological surface states which form rich multi-valley Fermi surfaces with complex spin textures. Scanning tunneling spectroscopy reveals type-II superconductivity at the surface, and moreover shows no evidence for an unconventional component of its superconducting order parameter, despite the presence of topological surface states., 6 pages, 3 figures

Transition-metal dichalcogenides (TMDs) are renowned for their rich and varied properties. They range from metals and superconductors to strongly spin-orbit-coupled semiconductors and charge-density-wave systems, with their single-layer variants one of the most prominent current examples of two-dimensional materials beyond graphene. Their varied ground states largely depend on the transition metal d-electron-derived electronic states, on which the vast majority of attention has been concentrated to date. Here, we focus on the chalcogen-derived states. From density-functional theory calculations together with spin- and angle- resolved photoemission, we find that these generically host type-II three-dimensional bulk Dirac fermions as well as ladders of topological surface states and surface resonances. We demonstrate how these naturally arise within a single p-orbital manifold as a general consequence of a trigonal crystal field, and as such can be expected across a large number of compounds. Already, we demonstrate their existence in six separate TMDs, opening routes to tune, and ultimately exploit, their topological physics., 10 pages, 4 figures

Although silver nanostructures have been widely used for H2O2 detection, the development of silver based nanomaterials with higher performance toward H2O2 detection is still needed. In this work, metallic silver nanodendrite (AgND) modified reduced graphene oxide (rGO) electrode with open pore structure was prepared by an electrodeposition method and used for H2O2 detection. The rotating disk electrode (RDE) was used to study the convective diffusion effect of H2O2 to the electrode. The performance of the AgND/rGO electrode toward H2O2 detection significantly depends on the rotation rate of the electrode. At the rotation rates of 0 and 100 rpm, the as-fabricated electrode could not detect H2O2. At higher rotation rates, wide linear ranges of detected H2O2 concentrations with a determination coefficient R2 of over 0.99 are found to be 1–100, 0.5–100, 0.1–100, and 0.05–30 mM at the electrode rotation rates of 500, 1000, 2000, and 6000 rpm, respectively. The LOD values determined at a signal-to-noise ratio of ca. 3 are about 100, 50, 30, and 10 μM at 500, 1000, 2000, and 6000 rpm, respectively. The as-fabricated electrode can detect diluted H2O2 in milk demonstrating its potential sensing application.

The electronic structure of a single Na monolayer on the surface of single-crystal HfSe$_2$ is investigated using angle-resolved photoemission spectroscopy. We find that this system exhibits an almost perfect "nearly-free-electron" behavior with an extracted effective mass of $\sim\!1m_e$, in contrast to heavier masses found previously for alkali metal monolayers on other substrates. Our density-functional-theory calculations indicate that this is due to the large lattice constant, causing both exchange and correlation interactions to be suppressed, and to the weak hybridization between the overlayer and the substrate. This is therefore an ideal model system for understanding the properties of two-dimensional materials., Comment: 5 pages, 3 figures

The unique properties of graphene can vary greatly depending on the number of graphene layers; therefore, spatial control of graphene thickness is desired to fully exploit these properties in promising new devices. Using low energy electron microscopy (LEEM), we investigate how scratches on the surface of 6H–SiC(0 0 0 1) affect the epitaxial growth of graphene. Oscillations in the LEEM-image intensity as a function of electron energy (I–V LEEM analysis) show that the number of graphene layers clearly differs between regions of scratched and smooth substrate. The extent of the thicker graphene layers formed above scratches is found to be significantly larger than the width of the scratch itself. This finding can be implemented as an additional technique for spatially modulating graphene thickness.

Many-body interactions in transition-metal oxides give rise to a wide range of functional properties, such as high-temperature superconductivity, colossal magnetoresistance, or multiferroicity. The seminal recent discovery of a two-dimensional electron gas (2DEG) at the interface of the insulating oxides LaAlO3 and SrTiO3 represents an important milestone towards exploiting such properties in all-oxide devices. This conducting interface shows a number of appealing properties, including a high electron mobility, superconductivity, and large magnetoresistance and can be patterned on the few-nanometer length scale. However, the microscopic origin of the interface 2DEG is poorly understood. Here, we show that a similar 2DEG, with an electron density as large as 8x10^13 cm^-2, can be formed at the bare SrTiO3 surface. Furthermore, we find that the 2DEG density can be controlled through exposure of the surface to intense ultraviolet (UV) light. Subsequent angle-resolved photoemission spectroscopy (ARPES) measurements reveal an unusual coexistence of a light quasiparticle mass and signatures of strong many-body interactions., 14 pages, 4 figures, supplementary information (see other files)

In this work, room-temperature ferromagnetism, which is not caused by conventional magnetic elements (e.g., Fe, Co, and Ni), is observed in carbon films prepared by using adamantane (C10H16): the smallest member of the so called diamondoid series (nano-diamond structures). These chemical-vapor-deposition films exhibit a moderately strong ferromagnetism which can be further enhanced by mechanically exfoliating the top layers of the films off; the saturated magnetization can be as large as 4.4 emu/cm3 at room temperature. Magnetic force microscopy measurements show a clear contrast in magnetization between the original and exfoliated regions, indicating that the magnetic origin likely comes from the broken “dangling” bonds at the exfoliated surface. This work suggests an inexpensive method for creating carbon films whose magnetization can be activated from mechanical exfoliation.

In conventional superconductors, a gap exists in the energy absorption spectrum only below the transition temperature (Tc), corresponding to the energy price to pay for breaking a Cooper pair of electrons. In high-Tc cuprate superconductors above Tc, an energy gap called the pseudogap exists, and is controversially attributed either to pre-formed superconducting pairs, which would exhibit particle-hole symmetry, or to competing phases which would typically break it. Scanning tunnelling microscopy (STM) studies suggest that the pseudogap stems from lattice translational symmetry breaking and is associated with a different characteristic spectrum for adding or removing electrons (particle-hole asymmetry). However, no signature of either spatial or energy symmetry breaking of the pseudogap has previously been observed by angle-resolved photoemission spectroscopy (ARPES). Here we report ARPES data from Bi2201 which reveals both particle-hole symmetry breaking and dramatic spectral broadening indicative of spatial symmetry breaking without long range order, upon crossing through T* into the pseudogap state. This symmetry breaking is found in the dominant region of the momentum space for the pseudogap, around the so-called anti-node near the Brillouin zone boundary. Our finding supports the STM conclusion that the pseudogap state is a broken-symmetry state that is distinct from homogeneous superconductivity., Comment: Nature Physics advance online publication, 04/04/2010 (doi:10.1038/nphys1632) Author's version of the paper.

Exposure of a clean Zn metal to oxygen in ultra high vacuum provides a mean to gradually form ZnO. With in situ synchrotron photoelectron measurement, the progressive change in the spectra with the oxygen exposure time is observed. The analysis of the spectra allows the determination of ZnO formation. It was found that the oxidation process takes place until reaching the critical thickness, at which the oxidation rate reduces greatly to nearly zero. The critical thickness was determined to be about 2 monolayers.

Surfaces and interfaces offer new possibilities for tailoring the many-body interactions that dominate the electrical and thermal properties of transition metal oxides1–4. Here, we use the prototypical two-dimensional electron liquid (2DEL) at the SrTiO3(001) surface5–7 to reveal a remarkably complex evolution of electron–phonon coupling with the tunable carrier density of this system. At low density, where superconductivity is found in the analogous 2DEL at the LaAlO3/SrTiO3 interface8–13, our angle-resolved photoemission data show replica bands separated by 100 meV from the main bands. This is a hallmark of a coherent polaronic liquid and implies long-range coupling to a single longitudinal optical phonon branch. In the overdoped regime the preferential coupling to this branch decreases and the 2DEL undergoes a crossover to a more conventional metallic state with weaker short-range electron–phonon interaction. These results place constraints on the theoretical description of superconductivity and allow a unified understanding of the transport properties in SrTiO3-based 2DELs. Postprint

Thermal oxidation of polycrystalline Zn foils at 5 × 10 −7 Torr oxygen pressure and at room temperature, 50 °C, 70 °C, 90 °C and 110 °C was studied. In situ photoemission spectroscopy using synchrotron light with photon energy of 57 eV was used to monitor the formation of ZnO and to determine the thickness of the oxide overlayer. At the initial oxidation, the oxidation rate follows a two-stage logarithmic equation and later trends to saturate at a certain thickness depending on the oxidation temperature. The saturated thickness was found to increase with the oxidation temperature. The two-stage oxidation process may be governed by two kinds of space charge presumably formed in the thin oxide overlayer.

We have used angle-resolved photoemission spectroscopy to investigate the band structure of ${\mathrm{ReS}}_{2}$, a transition-metal dichalcogenide semiconductor with a distorted 1T crystal structure. We find a large number of narrow valence bands, which we attribute to the combined influence of structural distortion and spin-orbit coupling. We further show how this leads to a strong in-plane anisotropy of the electronic structure, with quasi-one-dimensional bands reflecting predominant hopping along zigzag Re chains. We find that this does not persist up to the top of the valence band, where a more three-dimensional character is recovered with the fundamental band gap located away from the Brillouin zone center along ${k}_{z}$. These experiments are in good agreement with our density-functional theory calculations, shedding light on the bulk electronic structure of ${\mathrm{ReS}}_{2}$, and how it can be expected to evolve when thinned to a single layer.

Methods to generate spin-polarised electronic states in non-magnetic solids are strongly desired to enable all-electrical manipulation of electron spins for new quantum devices. This is generally accepted to require breaking global structural inversion symmetry. In contrast, here we present direct evidence from spin- and angle-resolved photoemission spectroscopy for a strong spin polarisation of bulk states in the centrosymmetric transition-metal dichalcogenide WSe$_2$. We show how this arises due to a lack of inversion symmetry in constituent structural units of the bulk crystal where the electronic states are localised, leading to enormous spin splittings up to $\sim\!0.5$ eV, with a spin texture that is strongly modulated in both real and momentum space. As well as providing the first experimental evidence for a recently-predicted `hidden' spin polarisation in inversion-symmetric materials, our study sheds new light on a putative spin-valley coupling in transition-metal dichalcogenides, of key importance for using these compounds in proposed valleytronic devices., Comment: 6 pages, 4 figures