Characteristics of Vertical Ga2O3 Schottky Junctions with the Interfacial Hexagonal Boron Nitride Film.

We present the device properties of a nickel (Ni)-gallium oxide (Ga2O3) Schottky junction with an interfacial hexagonal boron nitride (hBN) layer. A vertical Schottky junction with the configuration Ni/hBN/Ga2O3/In was created using a chemical vapor-deposited hBN film on a Ga2O3 substrate. The current-voltage characteristics of the Schottky junction were investigated with and without the hBN interfacial layer. We observed that the turn-on voltage for the forward current of the Schottky junction was significantly enhanced with the hBN interfacial film. Furthermore, the Schottky junction was analyzed under the illumination of deep ultraviolet light (254 nm), obtaining a photoresponsivity of 95.11 mA/W under an applied bias voltage (-7.2 V). The hBN interfacial layer for the Ga2O3-based Schottky junction can serve as a barrier layer to control the turn-on voltage and optimize the device properties for deep-UV photosensor applications. Furthermore, the demonstrated vertical heterojunction with an hBN layer has the potential to be significant for temperature management at the junction interface to develop reliable Ga2O3-based Schottky junction devices.

Recent Development in Vanadium Pentoxide and Carbon Hybrid Active Materials for Energy Storage Devices.

With the increasing energy demand for portable electronics, electric vehicles, and green energy storage solutions, the development of high-performance supercapacitors has been at the forefront of energy storage and conversion research. In the past decade, many scientific publications have been dedicated to designing hybrid electrode materials composed of vanadium pentoxide (V2O5) and carbon nanomaterials to bridge the gap in energy and power of traditional batteries and capacitors. V2O5 is a promising electrode material owing to its natural abundance, nontoxicity, and high capacitive potential. However, bulk V2O5 is limited by poor conductivity, low porosity, and dissolution during charge/discharge cycles. To overcome the limitations of V2O5, many researchers have incorporated common carbon nanostructures such as reduced graphene oxides, carbon nanotubes, carbon nanofibers, and other carbon moieties into V2O5. The carbon components facilitate electron mobility and act as porous templates for V2O5 nucleation with an enhanced surface area as well as interconnected surface morphology and structural stability. This review discusses the development of various V2O5/carbon hybrid materials, focusing on the effects of different synthesis methods, V2O5/carbon compositions, and physical treatment strategies on the structure and electrochemical performance of the composite material as promising supercapacitor electrodes.

Biological Synthesis of PbS, As3S4, HgS, CdS Nanoparticles using Pseudomonas aeruginosa and their Structural, Morphological, Photoluminescence as well as Whole Cell Protein Profiling Studies.

Metal sulfide nanoparticles are semi-conductors that possess many applications in optics, optoelectronics and magnetic devices. There are physical and chemical methods for their synthesis but such methods involve toxic precursors as well as many obnoxious by-products. Hence, biological synthesis of metal sulfide nanoparticles are efficient enough to transform toxic metals to non-toxic ones. Pseudomonas aeruginosa, isolated from textile effluent and tolerant of high levels of heavy metals, was used for the green synthesis of metal sulfide (HgS, As3S4, CdS and PbS) nanoparticles. The optical, structural and morphological nature of metal sulfide nanoparticles was also determined. FTIR (Fourier Transform Infra-red) analysis showed spectral changes when P. aeruginosa was grown in medium containing heavy metals viz. Hg, As, Pb and Cd indicating that there are functional groups viz. carboxyl, hydroxyl, phosphate, amino and amide, that exists on the surface of the bacteria, thus facilitating binding of metals on its surface. The bacterial samples which were treated with different metals at different concentrations, were subjected to whole cell protein analysis using SDS-PAGE (Sodium dodecyl Sulphate- Polyacrylamide gel electrophoresis) and protein profiling. The total protein estimation revealed that there was an increase in the protein concentration in the presence of heavy metals and a significant change in the banding pattern was observed which showed induction of a set of proteins under heavy metal stress especially mercury.

Bimetallic Au-Pd nanoparticles supported on silica with a tunable core@shell structure: enhanced catalytic activity of Pd(core)-Au(shell) over Au(core)-Pd(shell).

A facile ligand-assisted approach of synthesizing bimetallic Au-Pd nanoparticles supported on silica with a tunable core@shell structure is presented. Maneuvering the addition sequence of metal salts, both Aucore-Pdshell (Au@Pd-SiO2) and Pdcore-Aushell (Pd@Au-SiO2) nanoparticles were synthesized. The structures and compositions of the core-shell materials were confirmed by probe-corrected HRTEM, TEM-EDX mapping, EDS line scanning, XPS, PXRD, BET, FE-SEM-EDX and ICP analysis. The synergistic potentials of the core-shell materials were evaluated for two important reactions viz. hydrogenation of nitroarenes to anilines and hydration of nitriles to amides. In fact, in both the reactions, the Au-Pd materials exhibited superior performance over monometallic Au or Pd counterparts. Notably, among the two bimetallic materials, the one with Pdcore-Aushell structure displayed superior activity over the Aucore-Pdshell structure which could be attributed to the higher stability and uniform Au-Pd bimetallic interfaces in the former compared to the latter. Apart from enhanced synergism, high chemoselectivity in hydrogenation, wide functional group tolerance, high recyclability, etc. are other advantages of our system. A kinetic study has also been performed for the nitrile hydration reaction which demonstrates first order kinetics. Evaluation of rate constants along with a brief investigation on the Hammett parameters has also been presented.

Synthesis and Characterization of Li-C Nanocomposite for Easy and Safe Handling.

Metallic lithium (Li) anode batteries have attracted considerable attention due to their high energy density value. However, metallic Li is highly reactive and flammable, which makes Li anode batteries difficult to develop. In this work, for the first time, we report the synthesis of metallic Li-embedded carbon nanocomposites for easy and safe handling by a scalable ion beam-based method. We found that vertically standing conical Li-C nanocomposite (Li-C NC), sometimes with a nanofiber on top, can be grown on a graphite foil commonly used for the anodes of lithium-ion batteries. Metallic Li embedded inside the carbon matrix was found to be highly stable under ambient conditions, making transmission electron microscopy (TEM) characterization possible without any sophisticated inert gas-based sample fabrication apparatus. The developed ion beam-based fabrication technique was also extendable to the synthesis of stable Li-C NC films under ambient conditions. In fact, no significant loss of crystallinity or change in morphology of the Li-C film was observed when subjected to heating at 300 °C for 10 min. Thus, these ion-induced Li-C nanocomposites are concluded to be interesting as electrode materials for future Li-air batteries.

Room-temperature graphitization in a solid-phase reaction.

Graphitized carbon including graphene has recently become one of the most investigated advanced materials for future device applications, but a prerequisite for broadening its range of applications is to lower its growth temperature. Here we report a great decrease in graphitization temperature using the well-known catalyst Ni. Amorphous carbon films with Ni nanoparticles (NPs) were deposited, using a simple one-step magnetron sputtering method, onto microgrids and a SiO2/Si substrate for transmission electron microscopy (TEM) and Raman spectroscopy analyses, respectively. The amorphous carbon surroundings and locations between the Ni NPs started to become graphitized during the film deposition even at room temperature (RT) and 50 °C. The graphitization was confirmed by both high-resolution TEM (HR-TEM) and Raman 2D peak analyses. The increase in the relative amount of Ni in the amorphous carbon film led to the partial oxidation of the larger Ni NPs, resulting in less graphitization even at an elevated deposition temperature. Based on the detailed HR-TEM analyses, a decreased oxidation of NPs and enhanced solubility of carbon into Ni NPs were believed to be key for achieving low-temperature graphitization.

The Mo catalyzed graphitization of amorphous carbon: an in situ TEM study.

For the fabrication of graphene-based nano-scale interconnects, precise control over their position and proper nanoscale soldering are essential. In this work, we report the Joule heat-induced conversion of amorphous carbon to graphene in an in situ TEM setup, using Mo as a catalyst. The catalytic role of Mo during graphene formation has been less explored compared to other metals like Cu or Ni. Compared to metals like Cu, Mo is less subject to electromigration and brittleness, making it suitable for high-temperature electronics. We found that during the electromigration of Mo, amorphous carbon nanofibers (CNFs) can be converted to highly crystalline few-layered graphene. It was also found that during the graphene formation process, agglomerated Mo particles can be effectively channeled to the end of graphene by voltage-driven electromigration. An agglomerated Mo particle between the probe and graphene acted as a soldering agent, providing the prospect of the further exploration of Mo as a nanoscale soldering material. This work explores the double role of Mo: as a catalyst for graphene synthesis and as a soldering material.

Transfer free graphene growth on SiO2 substrate at 250 °C.

Low-temperature growth, as well as the transfer free growth on substrates, is the major concern of graphene research for its practical applications. Here we propose a simple method to achieve the transfer free graphene growth on SiO2 covered Si (SiO2/Si) substrate at 250 °C based on a solid-liquid-solid reaction. The key to this approach is the catalyst metal, which is not popular for graphene growth by chemical vapor deposition. A catalyst metal film of 500 nm thick was deposited onto an amorphous C (50 nm thick) coated SiO2/Si substrate. The sample was then annealed at 250 °C under vacuum condition. Raman spectra measured after the removal of the catalyst by chemical etching showed intense G and 2D peaks together with a small D and intense SiO2 related peaks, confirming the transfer free growth of multilayer graphene on SiO2/Si. The domain size of the graphene confirmed by optical microscope and atomic force microscope was about 5 µm in an average. Thus, this approach will open up a new route for transfer free graphene growth at low temperatures.

An immobilized symmetrical bis-(NHC) palladium complex as a highly efficient and recyclable Suzuki-Miyaura catalyst in aerobic aqueous media.

A bis-N-heterocyclic carbene (NHC) functionalized with chloropropyltriethoxysilane over silica was used to synthesize a well-defined immobilized palladium complex. This complex is a suitable and easily retrievable catalyst for Suzuki-Miyaura cross-coupling reactions under mild aqueous conditions. Excellent yields and conversions were obtained with low palladium loadings (down to 0.03 mol% Pd). The catalyst can be reused up to six cycles without the loss of its activity. The catalytic role of the NHC complex of palladium during coupling between bromobenzene and phenylboronic acid was investigated theoretically. The oxidative addition step is predicted to be endothermic in agreement with the experimental conditions.

Visualization of silver-decorated poly (DL-lactide-co-glycolide) nanoparticles and their efficacy against Staphylococcus epidermidis.

Understanding of self-protection activity of the bacteria and interaction with drug substances has significant importance for designing of effective drug delivery system for treatment of biofilm infections. Recently silver nanoparticle has attracted attention as antibacterial substance for drug delivery system because of its high antibacterial activity. Here, efflux of silver nanoparticles obtained from within the prepared silver-decorated poly (DL-lactide-co-glycolide) (Ag PLGA) nanoparticles derived from Staphylococcus epidermidis bacterial cell was successfully visualized using scanning transmission electron microscopy (STEM). We also revealed the interaction between prepared Ag PLGA nanoparticles and the bacterial cells at the nanoscale level using field emission scanning electron microscopy and STEM, after a pretreatment process by an ionic liquid. This finding is significant to understand a fundamental function of S. epidermidis bacterial cells, which is not explored previously. The results suggest that Ag PLGA nanoparticles could demonstrate high efficacy against biofilm infections.

Influence of oxygen on nitrogen-doped carbon nanofiber growth directly on nichrome foil.

The synthesis of various nitrogen-doped (N-doped) carbon nanostructures has been significantly explored as an alternative material for energy storage and metal-free catalytic applications. Here, we reveal a direct growth technique of N-doped carbon nanofibers (CNFs) on flexible nichrome (NiCr) foil using melamine as a solid precursor. Highly reactive Cr plays a critical role in the nanofiber growth process on the metal alloy foil in an atmospheric pressure chemical vapor deposition (APCVD) process. Oxidation of Cr occurs in the presence of oxygen impurities, where Ni nanoparticles are formed on the surface and assist the growth of nanofibers. Energy-dispersive x-ray spectroscopy (EDXS) and x-ray photoelectron spectroscopy (XPS) clearly show the transformation process of the NiCr foil surface with annealing in the presence of oxygen impurities. The structural change of NiCr foil assists one-dimensional (1D) CNF growth, rather than the lateral two-dimensional (2D) growth. The incorporation of distinctive graphitic and pyridinic nitrogen in the graphene lattice are observed in the synthesized nanofiber, owing to better nitrogen solubility. Our finding shows an effective approach for the synthesis of highly N-doped carbon nanostructures directly on Cr-based metal alloys for various applications.

Opening of triangular hole in triangular-shaped chemical vapor deposited hexagonal boron nitride crystal.

In-plane heterostructure of monolayer hexagonal boron nitride (h-BN) and graphene is of great interest for its tunable bandgap and other unique properties. Here, we reveal a H2-induced etching process to introduce triangular hole in triangular-shaped chemical vapor deposited individual h-BN crystal. In this study, we synthesized regular triangular-shaped h-BN crystals with the sizes around 2-10 µm on Cu foil by chemical vapor deposition (CVD). The etching behavior of individual h-BN crystal was investigated by annealing at different temperature in an H2:Ar atmosphere. Annealing at 900 °C, etching of h-BN was observed from crystal edges with no visible etching at the center of individual crystals. While, annealing at a temperature ≥ 950 °C, highly anisotropic etching was observed, where the etched areas were equilateral triangle-shaped with same orientation as that of original h-BN crystal. The etching process and well-defined triangular hole formation can be significant platform to fabricate planar heterostructure with graphene or other two-dimensional (2D) materials.

Electron microscopy of Staphylococcus epidermidis fibril and biofilm formation using image-enhancing ionic liquid.

We established an optimized biofilm observation method using a hydrophilic ionic liquid (IL), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]). In the present study, a biofilm was formed by Staphylococcus epidermidis. Using field emission (FE) scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the colonization of assemblages formed by microbial cells was observed as a function of the cultivation time. FE-TEM analysis revealed that the fibril comprises three types of protein. In addition, the ultrastructure of each protein monomer was visualized. It was expected that the curly-structured protein plays an important role in extension during fibril formation. Compared to the conventional sample preparation method for electron microscopy, a fine structure was easily obtained by the present method using IL. This observation technique can provide valuable information to characterize the ultrastructure of the fibril and biofilm that has not been revealed till date. Furthermore, these findings of the molecular architecture of the fibril and the colonization behavior of microbial cells during biofilm formation are useful for the development of antibacterial drugs and microbial utilization.

Visualizing copper assisted graphene growth in nanoscale.

Control synthesis of high quality large-area graphene on transition metals (TMs) by chemical vapor deposition (CVD) is the most fascinating approach for practical device applications. Interaction of carbon atoms and TMs is quite critical to obtain graphene with precise layer number, crystal size and structure. Here, we reveal a solid phase reaction process to achieve Cu assisted graphene growth in nanoscale by in-situ transmission electron microscope (TEM). Significant structural transformation of amorphous carbon nanofiber (CNF) coated with Cu is observed with an applied potential in a two probe system. The coated Cu particle recrystallize and agglomerate toward the cathode with applied potential due to joule heating and large thermal gradient. Consequently, the amorphous carbon start crystallizing and forming sp(2) hybridized carbon to form graphene sheet from the tip of Cu surface. We observed structural deformation and breaking of the graphene nanoribbon with a higher applied potential, attributing to saturated current flow and induced Joule heating. The observed graphene formation in nanoscale by the in-situ TEM process can be significant to understand carbon atoms and Cu interaction.

Synthesis of carbon fibers with branched nanographene sheets for electrochemical double layer capacitor application.

We demonstrate a one step technique to synthesis the carbon fibers (CNFs) with branched nanographene sheets by the pulsed discharge (PD) plasma chemical vapor deposition (CVD) process. Highly crystalline branched nanographene sheets were directly grown from the surface of the carbon fibers to obtain a three dimensional (3D) nanostructure. The growth process can be explained from the catalyst support growth of the CNFs, and subsequently nucleation and growth of the nanographene sheets from the crystalline surface of the CNF. The deposited nanostructured films with different pulse discharge were used as an electrode for electrochemical double-layer capacitors (EDLC). It is observed that the capacitance is dependent on the morphology of the electrode materials and an optimum capacitance is obtained with the branched nanographene on CNFs.

A photoinduced charge transfer composite of graphene oxide and ferrocene.

We demonstrate the formation of a photoinduced charge transfer composite with graphene oxide (GO) and ferrocene (Fc) molecules. Derived insulating GO was partially reduced to improve the conductivity and modified with the Fc molecules. Transmission electron microscopy (TEM), elemental mapping, X-ray photoelectron and UV-visible spectroscopy studies confirm that the Fc molecules were well grafted to the surface of a GO sheet. Photoresponsivity of the prepared GO-Fc composite was investigated by fabricating a metal/GO-Fc/metal device. The fabricated device shows enhanced current density under light illumination, suggesting a photo-induced charge transfer process in the developed GO-Fc composite.

Synthesis of transfer-free graphene on an insulating substrate using a solid phase reaction.

We demonstrate a solid phase reaction approach to synthesise transfer-free graphene on an insulating substrate by controlling the C diffusion process. Metal assisted crystallization by annealing of a C thin film was carried out to synthesise transfer-free graphene, in the presence of a top metal oxide and metal layer. Without the metal oxide layer, a large amount of C atoms diffused to the top of the metal surface and hence the formation of only small graphene domains was observed on the underneath of the metal layer. Introducing the metal oxide layer at the top surface, C diffusion was reduced and consequently the thin C film was crystallized to form large area graphene at the metal-insulating substrate interface. The metal oxide or metal catalyst layer was removed after graphene formation and transfer-free graphene was obtained directly on the base substrate. This finding shows that the thin metal oxide layer is critical to synthesise graphene with better quality and continuous domain structures.

In situ TEM observation of Fe-included carbon nanofiber: evolution of structural and electrical properties in field emission process.

In situ transmission electron microscopy (TEM) of single Fe-included carbon nanofibers (CNFs) revealed that the fine polycrystalline structure in the shank region of CNFs transformed to graphitic, hollow structures during a field emission (FE) process. The iron metal platelets agglomerated during the FE process and perceptibly were emitted from the shank, which featured bamboo-like carbon nanotube (CNT) structures. The structural evolution also improved the electrical properties, and the FE current was remarkably increased, that is, 1000 times higher than the initial value (from 10(-9) to 10(-6) A). The structural transformations were effectuated by Joule heating that generated simultaneously during the FE process. The in situ TEM study of room-temperature-synthesized CNFs could provide essential information regarding CNFs' structural transformation for their possible application in future electron emitter sources.

High temperature in-situ observations of multi-segmented metal nanowires encapsulated within carbon nanotubes by in-situ filling technique.

Multi-segmented one-dimensional metal nanowires were encapsulated within carbon nanotubes (CNTs) through in-situ filling technique during plasma-enhanced chemical vapor deposition process. Transmission electron microscopy (TEM) and environmental TEM were employed to characterize the as-prepared sample at room temperature and high temperature. The selected area electron diffractions revealed that the Pd4Si nanowire and face-centered-cubic Co nanowire on top of the Pd nanowire were encapsulated within the bottom and tip parts of the multiwall CNT, respectively. Although the strain-induced deformation of graphite walls was observed, the solid-state phases of Pd4Si and Co-Pd remain even at above their expected melting temperatures and up to 1,550 ± 50°C. Finally, the encapsulated metals were melted and flowed out from the tip of the CNT after 2 h at the same temperature due to the increase of internal pressure of the CNT.

Poly(3-octylthiophene)/fullerene heterojunction solar cell incorporating carbon nanotubes.

Here, we report incorporation of multiwalled carbon nanotubes (MWNTs) in Poly(3-octylthiophene)/fullerene heterojunction solar cells. Multi-walled carbon nanotubes (MWNTs) were functionalized by oxygen plasma treatment. Photoelectron spectroscopy study of oxygen plasma treated MWNTs shows surface modification with hydroxyl and carboxyl groups. Plasma treated MWNTs were combined with Poly(3-octylthiophene) and solar cell was fabricated with the structure Au/P3OT + MWNTs/C60/FTO. Fabricated device shows short circuit current density (Jsc) open circuit voltage (Voc), fill factor and conversion efficacy as 0.04 mA/cm2, 0.355 V, 21% and 0.003%. Solar cell fabricated with incorporation of MWNTs shows much better device performance, then that of the device without MWNTs. MWNTs in the polymer composite act as exciton dissociation site and provide efficient hole transportation, and thereby improving device performance.