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Transition-metal high-entropy oxides (HEOs) are promising electrode materials for lithium-ion batteries (LIBs) due to their superior electrochemical properties and excellent long-term cycling stability. The performance of HEOs for LIBs is highly correlated with their microstructures, especially their evolution during charging/discharging. However, there is limited information regarding this topic in the literature. In this study, the unique transition behavior of a spinel HEO, (CrMnFeCoNi)3O4, at various states of charge and cycle numbers is examined in detail for the first time. Although the elemental segregation of lithiated HEO particles is observed, the crystal structure remains spinel, leading to great cyclability. Mn nanocrystals form at 0.5 V lithiation and metallic Cr, Fe, Ni, and Co particles form at 0.01 V lithiation. The spinel CrxFe3-xO4 and LiNixCo1-xO2 phases act as seeds that grow by devouring surrounding metal nanoparticles during delithiation. The Mn can reversibly move at least dozens of nanometers across the oxide during lithiation/delithiation. The detailed cycling mechanism is examined using electron energy-loss spectroscopy. The reversible valence state variations of the constituent elements are observed. The results provide an in-depth understanding of the fundamental lithiation/delithiation mechanism of HEO, which will facilitate the development of better multi-element HEOs for Li+ storage applications.

In this work, we present our study of suspended graphene with low-energy electrons based on a point projection microscopic/diffractive imaging technique. Both exfoliated and chemical vapor deposition (CVD) graphene samples were studied in an ultra-high vacuum chamber. This method allows imaging of individual adsorbates at the nanometer scale and characterizing graphene layers, graphene lattice orientations, ripples on graphene membranes, etc. We found that long-duration exposure to low-energy electron beams induced aggregation of adsorbates on graphene when the electron dose rate was above a certain level. We also discuss the potential of this technique to conduct coherent diffractive imaging for determining the atomic structures of biological molecules adsorbed on suspended graphene.

One-dimensional polycrystallineTa2O5nanostructures are synthesized by the annealing of theSiO2nanowires at 950°C in a reductive Ta vapor ambiance. The formation mechanism ofTa2O5nanostructures is discussed and illustrated in detail. The nucleation and grain growth ofTa2O5crystals were investigated during the formation of theSiO2/Ta2O5core-shelled structures. The diffusion-controlled growth is suggested to be the rate-determining step for the diffusion of the Ta atoms through the ash layer to react with O atoms and substitute Si atoms.

Recently, monolayers of layered transition metal dichalcogenides (LTMD), such as MX2 (M = Mo, W and X = S, Se), have been reported to exhibit significant spin-valley coupling and optoelectronic performances because of the unique structural symmetry and band structures. Monolayers in this class of materials offered a burgeoning field in fundamental physics, energy harvesting, electronics, and optoelectronics. However, most studies to date are hindered by great challenges on the synthesis and transfer of high-quality LTMD monolayers. Hence, a feasible synthetic process to overcome the challenges is essential. Here, we demonstrate the growth of high-quality MS2 (M = Mo, W) monolayers using ambient-pressure chemical vapor deposition (APCVD) with the seeding of perylene-3,4,9,10-tetracarboxylic acid tetrapotassium salt (PTAS). The growth of a MS2 monolayer is achieved on various surfaces with a significant flexibility to surface corrugation. Electronic transport and optical performances of the as-grown MS2 monolayers are comparable to those of exfoliated MS2 monolayers. We also demonstrate a robust technique in transferring the MS2 monolayer samples to diverse surfaces, which may stimulate the progress on the class of materials and open a new route toward the synthesis of various novel hybrid structures with LTMD monolayer and functional materials.

Large-area MoS2 atomic layers are synthesized on SiO2 substrates by chemical vapor deposition using MoO3 and S powders as the reactants. Optical, microscopic and electrical measurements suggest that the synthetic process leads to the growth of MoS2 monolayer. The TEM images verify that the synthesized MoS2 sheets are highly crystalline., Comment: First submitted on 12-Dec-2011. Accepted in Adv. Mater

The effect of twisting on the electrical resistance of a raw single-walled carbon nanotube (SWCNT) rope was investigated and found to increase with increasing number of twists, varying from 28.7 Ω initially to 35.2 Ω after 12 twists. There are two reasons for this. One is that the twisting generated more contact points between the SWCNTs and catalytic nanoparticles, resulting in a high density of high local resistance points. The other is that the protrusion of SWCNTs in a rope twisted a large number of times (12–15 twists) partially interrupted the conducting path. By using a 9-V battery, ignition of the rope could be produced at a threshold resistance between 17.5 and 21.1 Ω, and this could be used to ignite ferrocene with the process lasting for several minutes.

Chromium silicide nanostructures are fabricated inside silicon nanopillars grown by the vapor-liquid-solid mechanism. The remarkable field-emission behavior of these nanostructures results from extensive improvement of carrier transport due to the reduced energy barrier between the metal and semiconductor layers. The results warrant consideration of chromium silicide as a potentially important contact material in future nanosystems.

Coaxial metal-oxide-semiconductor (MOS) Au-Ga2O3-GaN heterostructure nanowires were successfully fabricated by an in situ two-step process. The Au-Ga2O3 core-shell nanowires were first synthesized by the reaction of Ga powder, a mediated Au thin layer, and a SiO2 substrate at 800 degrees C. Subsequently, these core-shell nanowires were nitridized in ambient ammonia to form a GaN coating layer at 600 degrees C. The GaN shell is a single crystal, an atomic flat interface between the oxide and semiconductor that ensures that the high quality of the MOS device is achieved. These novel 1D nitride-based MOS nanowires may have promise as building blocks to the future nitride-based vertical nanodevices.

1-D tungsten oxide nanowires exhibiting distinctive electrochromic, gaschromic properties; in this study, we demonstrate an innovative way to fabricate the tungsten oxide nanowires on silicon substrate. The suggested growth mechanism is Vapor-Solid (VS) growth, while, the nitrogen-doping tungsten oxide nanowires were fabricated via the ammonia decomposition during the formation process. Their nano-devices were successful fabricated and the variety devices characteristics were reported.

Half-metallic materials, such as CrO2, La0.7Sr0.3MnO3 (LSMO), and Fe3O4 are highly attractive for spintronics applications because of their high spin polarization. Among these materials, magnetite (Fe3O4) is superior to others because of its high Curie temperature (Tc) of 858 K, which is crucial for thermal stability in device applications. In addition, magnetite has proven to be a ferromagnetic material with a high spin polarization (ca. 100 %) at the Fermi level, which results in a metallic minority spin channel and a semiconductor majority spin channel. Besides the utilization of spin electronics, magnetite can also be used as catalyst and in tunneling magnetoresistance (TMR) and giant magnetoresistive (GMR) devices. Previously, various studies in electron transport and magnetoresistance (MR) of magnetite have mainly focused on 2D structures, such as epitaxial thin films, polycrystalline films, and nanoclusters. Recently, the electronic characteristics of 1D magnetite nanostructures have received much attention because of their unique electron-transport behaviors, which may be different from those of the bulk. In addition, low-dimensional Fe3O4 nanoparticles are particularly promising in biomedical applications, such as drug transport/delivery, cell separation and imaging, and therapeutic in vivo technologies. In this study, a simple vapor–solid growth method was applied to grow a-Fe2O3 NWs in an oxygen-deficient environment; magnetite NWs were then formed by converting the vertically aligned a-Fe2O3 NWs template in a reductive atmosphere. An extensive investigation on the mechanism of transforming a-Fe2O3 NWs to Fe3O4 NWs has been published elsewhere. Electrical measurements were performed by fabricating nanodevices in which the NWs were laid on top of the designed Si chips. The Verwey temperature-transition phenomenon was observed in low-temperature measurements of the nanodevices. The magnetic behavior of the NWs was investigated by superconducting quantum interference device (SQUID) measurements. In addition, a magnetic flux map was acquired by electron holography, which revealed the magnetic microstructure of the 1D magnetite nanowires. Figure 1A and B shows a top-view morphology image of a-Fe2O3 and Fe3O4 NWs, respectively. After the reduction process, the morphology of the Fe3O4 NWs was very similar to that of the a-Fe2O3 template. Figure 1C shows a transmission electron microscopy (TEM) image of the magnetite NWs; the high-resolution TEM (HRTEM) image of the modulated a-Fe2O3 NW due to the oxygen deficiency and the magnetite diffraction pattern (DP) are shown in the insets of the image. The HRTEM image in Figure 1D reveals the single-crystalline structure of the NWs, without linear or planar defects. The two d-spacings of 0.29 nm were identified as Fe3O4 {022} planes. The diffraction pattern, shown in the inset in Figure 1D, also illustrates the single-crystal nature of the NWs at the [111] zone axis. Figure 2A shows a scanning electron microscopy (SEM) image of the nanodevices; an enlarged image of one of the devices in Figure 2A is shown in Figure 2B. The two-point I–V measurements were performed at room temperature in a LabView controlled measurement system under ambient conditions. The linear I–V curves (shown in Fig. 2C) indicate that the characteristics fit well to Ohm’s law. The zero-field resistivities of the nanodevices were estimated by the following equation: R = qL/A (R: resistance, q: resistivity, A: cross-section area, L: NW length). The diameter and length of the measured NWs were 25 nm and 0.7526 lm, respectively. Assuming that the Fe3O4 NWs were of a circular cross-section, the obtained resistivity was 10.30 X cm; approximately three orders of magnitude larger than that of bulk magnetite crystal (19 000 lX cm). The large measured difference between the NWs and the single crystal may be due to contact resistance and surface scattering, resulting from the high surface ratio. However, the surface-scattering mechanism, based on the Fuchs–Sonderheimer (FS) theory, indicates that the aspect ratio is an important factor to the total resistance of nanostructures. According to FS theory, when surface scattering is the dominant mechanism the resistivity of a nanowire deC O M M U N IC A TI O N

Very dense and uniformly distributed nitrogen-doped tungsten oxide (WO(3)) nanowires were synthesized successfully on a 4-inch Si(100) wafer at low temperature. The nanowires were of lengths extending up to 5 mum and diameters ranging from 25 to 35 nm. The highest aspect ratio was estimated to be about 200. An emission peak at 470 nm was found by photoluminescence measurement at room temperature. The suggested growth mechanism of the nanowires is vapor-solid growth, in which gaseous ammonia plays a significant role to reduce the formation temperature. The approach has proved to be a reliable way to produce nitrogen-doped WO(3) nanowires on Si in large quantities. The direct fabrication of WO(3)-based nanodevices on Si has been demonstrated.

Functional 1D metal oxides have attracted much attention because of their unique applications in electronic, optoelectronic, and spintronic devices. For semiconducting oxide nanowires (NWs) (e.g., ZnO, In2O3, and SnO2 NWs), field-effect transistors and light-emitting diodes have been demonstrated. Metallic oxide nanoscale materials, such as nanoscale RuO2, can be good candidates as interconnects in electronic applications. RuO2 nanomaterials have been produced by chemical vapor deposition (CVD) and through chemical reaction. Recently, RuO2 NWs have been synthesized using pure Ru as metal target under different flux ratios of O2/Ar in a reactive sputtering system. [5]

Magnetic patterning, with designed spatial profile of the desired magnetic properties, has been a rising challenge for developing magnetic devices at nanoscale. Most existing methods rely on locally modifying magnetic anisotropy energy or saturation magnetization and thus post stringent constraints on the adaptability in diverse applications. We propose an alternative route for magnetic patterning: by manipulating the local intergranular exchange coupling to tune lateral magnetic properties. As demonstration, the grain boundary structure of Co/Pt multilayers is engineered by thermal treatment, where the stress state of the multilayers and thus the intergranular exchange coupling can be modified. With Ag passivation layers on top of the Co/Pt multilayers, we can hinder the stress relaxation and grain boundary modification. Combining the pre-patterned Ag passivation layer with thermal treatment, we can design spatial variations of the magnetic properties by tuning the intergranular exchange coupling, which diversifies the magnetic patterning process and extends its feasibility for varieties of new devices.

Low-temperature synthesis of GaN nanowires is successfully achieved by silica-enhanced processes. GaN nanowires were synthesized by reaction of metal gallium vapor with ammonia and hydrogen gases at the temperature of 700 °C on the amorphous SiO2 substrate. From scanning electron microscopy images, the morphologies of GaN nanowires are wirelike with a length up to 5μm and the average diameter of GaN nanowires measured by transmission electron microscopy (TEM) is about 25 nm. The x-ray diffraction analysis of as-synthesized products indicates that the nanowires have the hexagonal wurtzite structure of GaN crystal. The corresponding electron diffraction pattern also indicates that the as-synthesized GaN nanowires exhibited a single-crystal feature with uniform oxygen doping characterized by electron energy loss spectroscopy. The compositional line profile of TEM analysis reveals that GaN nanowires are terminated by Au nanoparticles, which infer an evidence that the vapor-liquid-solid model is the major grow...

CuOx nanowires were synthesized by a low-cost and large-scale electrochemical process with AAO membranes at room temperature and its resistive switching has been demonstrated. The switching characteristic exhibits forming-free and low electric-field switching operation due to coexistence of significant amount of defects and Cu nanocrystals in the partially oxidized nanowires. The detailed resistive switching characteristics of CuOx nanowire systems have been investigated and possible switching mechanisms are systematically proposed based on the microstructural and chemical analysis via transmission electron microscopy.

We demonstrate a new and simple process to fabricate tungsten tips with good control of the tip profile. In this process, we use a commercial function generator without any electronic cutoff circuit or complex mechanical setup. The tip length can be varied from 160 μm to 10 mm, corresponding to an aspect ratio of 1.6–100. The radius of curvature of the tip apex can be controlled to a size

The two-dimensional layer of molybdenum disulfide (MoS2) has recently attracted much interest due to its direct-gap property and potential applications in optoelectronics and energy harvesting. However, the synthetic approach to obtain high quality and large-area MoS2 atomic thin layers is still rare. Here we report that the high temperature annealing of a thermally decomposed ammonium thiomolybdate layer in the presence of sulfur can produce large-area MoS2 thin layers with superior electrical performance on insulating substrates. Spectroscopic and microscopic results reveal that the synthesized MoS2 sheets are highly crystalline. The electron mobility of the bottom-gate transistor devices made of the synthesized MoS2 layer is comparable with those of the micromechanically exfoliated thin sheets from MoS2 crystals. This synthetic approach is simple, scalable and applicable to other transition metal dichalcogenides. Meanwhile, the obtained MoS2 films are transferable to arbitrary substrates, providing great opportunities to make layered composites by stacking various atomically thin layers., manuscript submitted on 11-Dec-2011, revision submitted on 16-Feb-2012

To realize graphene-based electronics, bandgap opening of graphene has become one of the most important issues that urgently need to be addressed. Recent theoretical and experimental studies show that intentional doping of graphene with boron and nitrogen atoms is a promising route to open the bandgap, and the doped graphene might exhibit properties complementary to those of graphene and hexagonal boron nitride (h-BN), largely extending the applications of these materials in the areas of electronics and optics. This work demonstrates the conversion of graphene oxide nanosheets into boron carbonitride (BCN) nanosheets by reacting them with B(2) O(3) and ammonia at 900 to 1100 °C, by which the boron and nitrogen atoms are incorporated into the graphene lattice in randomly distributed BN nanodomains. The content of BN in BN-doped graphene nanosheets can be tuned by changing the reaction temperature, which in turn affects the optical bandgap of these nanosheets. Electrical measurements show that the BN-doped graphene nanosheet exhibits an ambipolar semiconductor behavior and the electrical bandgap is estimated to be ≈25.8 meV. This study provides a novel and simple route to synthesize BN-doped graphene nanosheets that may be useful for various optoelectronic applications.

One-dimensional metal oxide nanomaterials have attracted much attention due to their semiconducting behavior and applications in nanodevices such as gas sensors, photoA field-effect transistors (FETs), and light-emitting diodes. [1] The control of electrons and holes, that is, n- or ptype nature, inside the functional metal oxide is of vital importance in the application of nanodevices. In general, ntype metal oxide nanomaterials are easily formed due to oxygen deficiencies (vacancies), which result in a donor level below but close to the conduction band. By contrast, p-type behavior is hard to achieve except in cases where the material is naturally p type. The common way to form the p type is through diffusion during the growth process or implantation into an as-grown sample, followed by post-annealing at high temperatures in order to eliminate defects. [2] By contrast, by using a reductive ambient, the direct transition between the n and p types of a metal oxide can be A through a change of dominant carriers on the surface, namely, those of electrons or holes. This n–p switch was first found in Cr2O3 under a treatment of ethanol vapor. [3] In addition, the n–p switch was found in other functional metal oxides, such as SnO2, MoO3, and In2O3, under certain kinds of reductive ambient. [4] However, the details of the n–p transition are still under investigation.

Combination of EBSD and EDS are known as a powerful strategy to investigate the relationship between crystalline characteristics and chemical composition of metal-based materials [1]. In present study, combining EBSD and EDS was applied to analyse a chloride induced stress corrosion crack on a stainless steel cladding which is applied on protecting the reactors for carrying out petrochemical reactions. The results of the crack initiation from EDS and EBSD analysis are shown in figure (a) and (b), in which sigma phase is found forming at the grain boundary. It is also noticed that the corrosion type at the crack initiation is intergranular corrosion. Figure (c) and (d) display the EDS/EBSD results of the propagation part of the crack, showing that the chemical composition at this part are mainly Cr and Mo, and the corrosion type of the crack turns into transgranular corrosion. A detailed discussion of this work will be present in the conference.

Formation of Pt nanoparticles or nanoisland films as a function of annealing temperature, initial thickness, underlying substrates, and annealing process is investigated. Using microphotoluminescence (PL) measurement, we find great enhancement of self-emission in visible spectrum from Pt nanoparticles. The integral intensity of the micro-PL of the 49.38nm Pt nanoparticles is 38 times of that of the Pt thin film. In addition, the peak wavelength varies from 554to615nm as the surface morphology of Pt changes due to different annealing parameters. Spectral analyses suggest that this enhancement of micro-PL from Pt is due to the local field enhancement mechanism analogous to that of PL from noble metals.

An approach to investigate the electric field distribution and field-emission property of a single crystal tungsten oxide (WO3) nanowire by electron holography technique is presented, which solves the problems encountered in the traditional reconstruction of the holograms, the so-called perturbed reference wave. We proposed this unique method to meticulously illustrate the status of the surroundings of a single crystal nanowire under biased conditions. This paves the way to precisely quantifying the electric and magnetic field distributions for nanostructures as well as nanodevices.

GaN nanowires were synthesized by reaction of metal gallium vapor with ammonia and hydrogen gases at the temperature of 700 °C on the amorphous SiO2 substrate. The morphologies of GaN nanowires are wirelike with a length up to 5 μm and the average diameter of GaN nanowires measured by transmission electron microscopy (TEM) is about 25 nm. The x-ray diffraction analysis of as-synthesized products indicates that the nanowires have the hexagonal wurtzite structure of GaN crystal. The corresponding electron diffraction pattern also indicates that the as-synthesized GaN nanowires exhibited a single-crystal feature with uniform oxygen doping characterized by electron energy loss spectroscopy.

A 15-nm-thick GdO x membrane in an electrolyte-insulator-semiconductor (EIS) structure shows a higher pH sensitivity of 54.2 mV/pH and enzyme-free hydrogen peroxide (H2O2) detection than those of the bare SiO2 and 3-nm-thick GdO x membranes for the first time. Polycrystalline grain and higher Gd content of the thicker GdO x films are confirmed by transmission electron microscopy (TEM) and X-ray photo-electron spectroscopy (XPS), respectively. In a thicker GdO x membrane, polycrystalline grain has lower energy gap and Gd2+ oxidation states lead to change Gd3+ states in the presence of H2O2, which are confirmed by electron energy loss spectroscopy (EELS). The oxidation/reduction (redox) properties of thicker GdO x membrane with higher Gd content are responsible for detecting H2O2 whereas both bare SiO2 and thinner GdO x membranes do not show sensing. A low detection limit of 1 μM is obtained due to strong catalytic activity of Gd. The reference voltage shift increases with increase of the H2O2 concentration from 1 to 200 μM owing to more generation of Gd3+ ions, and the H2O2 sensing mechanism has been explained as well.