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With the increasing importance of power storage devices, demand for the development of supercapacitors possessing both rapid reversible chargeability and high energy density is accelerating. Here we propose a simple process for the room temperature fabrication of pseudocapacitor electrodes consisting of a faradaic redox reaction layer on a metallic electrode with an enhanced surface area. As a model metallic electrode, an Au foil was irradiated with Ar

Novel glass-ceramic composites with optical bandgap tunability were synthesised. Zinc silicate powder (ZS) was mixed with multi-walled carbon nanotubes (MWCNTs) at various mass fractions (0, 1, 2, and 3 wt %), followed by argon sintering. X-ray diffraction (XRD) analysis revealed the structural change from an amorphous ZS phase to a crystalline willemite phase (Zn2SiO4) by adding MWCNTs, and the largest crystallite size was obtained for ZS with 2.0 wt% MWCNTs. Although the agglomeration of ZS and MWCNTs was observed by field emission scanning electron microscopy (FESEM), there was no chemical interaction between ZS and MWCNTs as confirmed by Fourier transform infrared spectroscopy (FTIR). MWCNTs enhanced the crystallisation, which led to the green emission of Zn2SiO4 blue-shifting from 572 nm to 557 nm. The narrowed optical bandgap of Zn2SiO4 was attributed to the MWCNT-induced exciton localised between the valence band and conduction band of Zn2SiO4. The bandgap tuning effect of MWCNTs potentially paved new ways to mass fabricate zinc silicate-based semiconductors with desirable optical bandgap energy Eg, which significantly benefits the sensor and laser-related industry.

Underwater Sensor Networks (UWSNs) are deployed to monitor various phenomena in marine environment such as pollution control, fuel exploration and underwater seismic activities. Various challenges such as, limited and non-replaceable batteries in sensor nodes, high path loss and high propagation delay exist for UWSNs, to name a few. Successful design deployment of an energy efficient routing scheme is an intense need of the day for successful operation of UWSNs. In this paper we have presented an energy efficient routing protocol by the name of Energy Harvesting Intelligent Relay Selection Protocol (EH-IRSP). The scheme uses task-specific energy harvested relay nodes using piezoelectric technique utilizing dynamic transmission radius incorporated in all sensor nodes. EH-IRSP protocol is compared with existing UWSNs protocols Cooperative UWSN (Co-UWSN) and Energy Harvested Analytical approach towards Reliability with Cooperation for Underwater WSNs (EH-ARCUN). The Co-UWSN focuses on strengthening the sound-to-noise ratio on the minimum distance communication channel in order to reduce the path loss. The EH-ARCUN scheme selects relay nodes based on energy harvesting level in combination with Amplify and Forward (AF) technique. The proposed scheme employs a Euclidean distance between the source-destination and source-relay nodes pairs. Each source node selects the most feasible energy harvested relay node by computing cosine of the angles between itself, relay node, and destination nodes and sends the data using cooperative communication. Based on these computed parameters, each source node adjusts its transmission radius hence conserving energy. Performance parameters for this comparison are based on stability period, packet delivery ratio, end-to-end delay and path loss. Simulation results show enhanced performance of proposed scheme EH-IRSP in contrast to Co-UWSN and EH-ARCUN.

This paper presents the modelling of the specific heat capacity (SHC) of CuO/water nanofluids using a support vector regression (SVR) and artificial neural network models (ANN). The models presented were developed from the experimental data of SCH of CuO nanoparticles, the volume fractions of CuO nanoparticles and fluid temperature. The volume fraction of CuO nanoparticles considered ranges from 0.4 to 2% while the temperature range includes 293–338 K. The results obtained revealed that the SVR model exhibits slightly higher accuracy compared to the ANN model. However, both the SVR and ANN models clearly demonstrate better prediction performance for the SHC of CuO/water nanofluids compared to the existing theoretical models. The results obtained in this study proves that machine learning models provide a more accurate estimation of SHC of CuO/water nanofluids and they are recommended for heat transfer calculations due to their superior accuracy.

Eu3+-doped Zn2SiO4/ZnO phosphor-based composites were prepared using a simple thermal treatment method. The effect of Eu3+ content on the morphological and photoluminescence performance was examined using XRD, FTIR, FESEM, UV–Vis, and PL measurement. The existence of two crystal phases by the XRD measurement confirmed the development of zincite (ZnO) and zinc silicate (Zn2SiO4) crystal phases. Besides, the FTIR spectra and FESEM micrograph support the XRD result by verifying ZnO and Zn2SiO4 phase formation through the existence of their characteristic Zn–O–Si and Zn–O vibration modes with the decrement of SiO4 broad absorption band as the Eu3+ concentration increased. Also, UV–Vis absorption spectra presented by the composite samples displayed a broad absorbance that confirmed the addition of Eu3+ ions in the ZnO/Zn2SiO4 has caused the absorption edge of the curve having red shift. The photoluminescence spectrum showed red shift light emissions at 485 and 615 nm, associating with the Zn2SiO4 crystal phase, in addition to the ZnO crystal phase. From the interesting results achieved, this ZnO/Zn2SiO4 phosphor-based composite material can be a potent candidate in optoelectronic applications.

Natural rubber (NR) glove disposal is not environmentally appropriate and a range of approaches have been suggested to overcome the problem. Herein we indicate a simple method for producing high-value nanotubes from waste NR glove as a partial solution to the environmental problem. The laboratory-based waste NR glove was selected as a carbon precursor. Carbon nanotubes (CNTs) were synthesized using chemical vapor deposition (CVD) method comprising ferrocene over SiO2 substrate, which acted as a catalyst and surface for the carbon conversion process. The growth temperature was varied using 500, 600 and 700°C. The carbon precursor was analyzed using thermogravimetric analysis (TGA) to determine the optimum thermal decomposition of the waste. The CNTs collected after CVD process were analyzed using Raman spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM). Optimization studies to determine the effect of temperature showed that the highest yield of CNTs was produced under a reaction temperature of 700°C (yield % = 5.47%, Raman ID/IG ratio = 0.82). The nanomaterials formed confirmed as CNTs and amorphous carbon under TEM images of the tubular structure of the products with a diameter range of 13 – 16 nm.

In this study, the authors attempted to propose the very first study on fabrication and characterization of zinc-boro-silicate (ZBS) glass-ceramics derived from the ternary zinc-boro-silicate (ZnO)0.65(B2O3)0.15(RHA)0.2 glass system through a conventional melt-quenching method by incorporating rice husk ash (RHA) as the silica (SiO2) source, followed by a sintering process. Optimization of sintering condition has densified the sintered samples while embedded beta willemite (β-Zn2SiO4) and alpha willemite (α-Zn2SiO4) were proven in X-ray diffraction (XRD) analysis. Field emission scanning electron microscopy (FESEM) has shown the distribution of willemite crystals in rhombohedral shape crystals and successfully form closely-packed grains due to intense crystallization. The photoluminescence (PL) spectra of all sintered ZBS glasses presented various emission peaks at 425, 463, 487, 531, and 643 nm corresponded to violet, blue, green, and red emission, respectively. The correlation between the densification, phase transformation, microstructure, and photoluminescence of Zn2SiO4 glass-ceramic phosphor is discussed in detail.

Hard anodizing has proven to be a helpful surface treatment for aluminium alloy and typically accompanied by the growth of a porous and highly flawed oxide layer. The presence of pores on the oxide surface can be taken as an advantage in improving the surface properties. Fly-ash particles are high in SiO2 and Al2O3 content and can be utilized as inexpensive strengthening particles, which can increase the wear resistance and microhardness of composite material. It was noticed that limited research had been carried out in utilizing fly-ash as reinforcement on composite oxide coating as a wear resistance candidate. Thus, this study focused on reinforcing fly-ash on oxide coating and investigating its tribological performance. The composite oxide coating was grown on AA2017 aluminium alloy through anodizing process. To understand the effect of anodizing time and fly-ash content, the parameters were varied from 5–60 min and 0–50 g/L, respectively. The findings suggested that 60 min of anodizing time provides the highest thickness and surface roughness at 35 µm and 6.5 µm, respectively. Interestingly, composite oxide coating with 50 g/L fly-ash provides the highest coating thickness but has the lowest roughness at 52 μm and 8.2 μm, respectively. The composite oxide coatings are observed to reduce friction only for a limited time, despite their potential in significantly reducing the wear rate. The wear mechanism observed was adhesion, micro-crack, and delamination. The findings of this study are believed to provide insight on the potential of fly-ash to be a reinforcement for wear-reduction materials.

Willemite is an inorganic semiconductor material used for optoelectronic applications. The present study purposes a new polymer thermal treatment method involving calcination temperature to fabricate the willemite nanoparticles. The effects of polyvinylpyrrolidone (PVP) on the structural and optical properties of the material were thoroughly investigated. Thermogravimetric and its derivative confirmed the decomposition behavior of PVP. The minimum calcination temperature to decompose PVP was appraised at 740 °C. The FTIR and the Raman analyses confirmed the presence of organic source before the calcination process and the formation of the crystalline structure of the willemite nanoparticles after the heat treatment. The optimum PVP concentration in this study based on the FTIR results was found to be 40 g L−1. This is the minimum concentration at which the willemite nanoparticles remained pure with homogenous distribution. X-ray diffraction analysis of the PVP samples before calcination was confirmed to be amorphous, and upon calcination between 800 and 1000 °C, an α-willemite phase was obtained. The morphology and the average particle size were determined with FESEM and HR-TEM analysis. The average particle size is between 23.8 and 36.7 nm. The optical energy band was found to be increasing from 5.24 to 5.32 eV with the corresponding increase in PVP concentration from 20 to 50 g L−1. The findings in this study provides a new pathway to understand the effects of PVP concentrations on the structural and optical properties of willemite semiconductor nanoparticles as it may have key potential applications for future optoelectronic devices. The primary task of polyvinylpyrrolidone (PVP) is to serve as a capping agent and to stabilize the metallic salts. The interaction between the PVP and the metallic salts (zinc acetate dihydrate and silicon tetraacetate) is through the strong ionic bonds between the metallic ions and the amide group via oxygen in the PVP chain. The PVP stabilizes the dissolved metallic precursor by amide group steric and electrostatic stabilization. In the drying process at the temperature about 80 °C, the PVP decompose to the shorter polymer chains which they cap the metallic ions. In the step of calcination at the range of 900 °C for 1–4 h, the polymer content and unwanted anions are entirely removed and the nucleation of willemite nanoparticles achieved.

In this work, we utilize Joule heating to convert Pt-embedded amorphous carbon nanofiber (CNF) to multiwall carbon nanotube (CNT) in a transmission electron microscope (TEM). The transformation process of Pt-embedded amorphous CNF to multiwall CNT and nano-soldering process using Pt encapsulated CNT was investigated in TEM in detail. Molten Pt-encapsulated inside CNF and CNT always flowed towards the anode, proving electromigration to be the dominant force over thermal migration. Controllable electromigration of Pt was utilized to connect the Pt-included CNT to another CNT, thus forming a seamlessly welded CNT structure. Further, two separate CNF were brought together to form Y-contact which was transformed into Y-junction CNT structure by controlled electromigration of Pt. Changes in morphology and electrical property during CNT formation and nano-soldering were probed in real time with high resolution TEM. Our method provides a procedure for the position control synthesis of CNT and its nano-soldering which can be an important step for future development of a CNT based nanoelectrical circuit.

We performed single-walled carbon nanotube (SWCNT) growth on flexible stainless-steel foils by applying alcohol catalytic chemical vapor deposition (CVD) using an Ir catalyst with an alumina buffer layer. When the alumina thickness was 90 nm, vertically aligned SWCNTs with a thickness of 4.6 μm were grown. In addition, Raman and transmission electron microscope results showed that the diameters of most SWCNTs were distributed below 1.1 nm. Compared with conventional CVD growth where Si wafers are used as substrates, this method is more cost effective and easier to extend for mass production of small-diameter SWCNTs.

This study focuses on developing a new simple and low cost environmentally friendly synthesis technique for producing α-Zn2SiO4 nanoparticles. To study the crystal growth, nanostructure and optical properties of the nanoparticles, further analysis was conducted using XRD, FESEM, EDX, FTIR, RAMAN, HRTEM, UV–vis and PL spectroscopy. The analysis confirmed the progress of α-Zn2SiO4 with the increase of calcination temperature. Additionally, calcination at higher temperatures improved the crystallinity and revealed a uniform spherical morphology and better nanoparticle distribution. These findings were found to be in good agreement with XRD and FESEM results. The optical absorption spectra showed a reduction of the absorption intensity due to an improved crystallinity. Several broad emission peaks were observed at wavelengths of 423, 447, 484, and 530 nm with the increase in calcination temperature. The findings of this study are anticipated to result in finding a potential application for phosphor materials in optoelectronic applications.

The electrochemical processes in current fuel cell is still relying on high-loading of scarce and expensive precious metals such as Pt as electrocatalysts for device operation which hinder their commercialization Thus, there is a critical need in search of non-precious metal-based electrocatalysts to replace these precious metals. In view of its corrosion resistant advantage and low production cost, non-precious metal oxides have been recognized as the potential candidates for electrocatalysts in fuel cell. In this study, the aim was to develop a stable catalyst based on transition metal oxides using a simple and cheap modified precipitation technique. Three types of transition metal oxides, namely the cobalt oxides, nickel oxides and iron oxides, were synthesized and a systematic study on the physicochemical properties of the materials are carried out using X-ray diffraction (XRD), Raman spectroscopy and field emission scanning electron microscopy (FESEM). It was observed that cobalt oxide was grown as porous hexagonal platelets while iron oxides and nickel oxides were grown as nanosized particles. The role of the microstructural properties of these transition metals in enhancing their catalytic performance is discussed.

NBR is one of the common rubber used in oil and gas sector, automotive sector and gloves manufacturing. Conversion of solid waste Nitrile Butadiene Rubber (NBR) latex sludge into liquid can be done by using fractional distillation method. The solid waste NBR was heat above its decompose temperature to evaporate the polymer in form of vapor and will be condensed by condenser column into liquid form. The decomposed temperature of waste NBR was determined by Thermogravimetric (TGA) analyzer which is at 450 °C. The processed hydrocarbon liquid was characterized by using Carbon Nitrogen Sulphur (CNS) analyzer, and Gas Chromatography Mass Spectroscopy (GCMS) analyzer. Sulfur is the main compound exist in the waste NBR latex sludge which is 0.73670 % as it being added for vulcanization process. The carbon and nitrogen percentage are 0.17419 % and 0.16479 %.

Ceramic matrix composites (CMCs) are well-established composites applied on commercial, laboratory, and even industrial scales, including pottery for decoration, glass–ceramics-based light-emitting diodes (LEDs), commercial cooking utensils, high-temperature laboratory instruments, industrial catalytic reactors, and engine turbine blades. Despite the extensive applications of CMCs, researchers had to deal with their brittleness, low electrical conductivity, and low thermal properties. The use of carbon nanotubes (CNTs) as reinforcement is an effective and efficient method to tailor the ceramic structure at the nanoscale, which provides considerable practicability in the fabrication of highly functional CMC materials. This article provides a comprehensive review of CNTs-reinforced CMC materials (CNTs-CMCs). We critically examined the notable challenges during the synthesis of CNTs-CMCs. Five CNT dispersion processes were elucidated with a comparative study of the established research for the homogeneity distribution in the CMCs and the enhanced properties. We also discussed the effect of densification techniques on the properties of CNTs-CMCs. Additionally, we synopsized the outstanding microstructural and functional properties of CNTs in the CNTs-CMCs, namely stimulated ceramic crystallization, high thermal conductivity, bandgap reduction, and improved mechanical toughness. We also addressed the fundamental insights for the future technological maturation and advancement of CNTs-CMCs.

A technology for converting waste materials to high quality large-area monolayer graphene film can be significant and thereby obtaining high value-added product. Here, we revealed the transformation of waste chicken fat into uniform monolayer graphene film on re-solidified Cu by a low pressure chemical vapor deposition (LPCVD) technique. The evolve gas analyzer-gas chromatography⿿mass spectrometry (EGA-GC⿿MS) analysis of chicken fat oil showed that the free fatty acid in chicken oil decomposed into a short hydrocarbon chains which makes it favorable to use as a carbon precursor for graphene synthesis. Growth of uniform monolayer graphene film on the re-solidified Cu was confirmed by Raman mapping, where 2D to G peak intensity ratio (I2D/IG) is 3.0 at most of the area. Thus, the use of waste from poultry industry as a carbon source instead of commonly used hydrocarbon gas sources for graphene synthesis can be an approach for green nanotechnology.

Synthesis of hexagonal boron nitride (hBN) crystals with a controlled morphology is a major challenge due to various kinetic and thermodynamic factors at the edge. Supplying BN building blocks by heating precursor ammonia borane at a temperature of 90 °C produced triangular crystals, whereas, at higher heating (130 °C), hBN crystals with a hexagonal morphology were observed. The shape of crystals could also be modulated from hexagonal to triangular under a continuous reduced supply of BN building blocks. We attributed these phenomena to a different growth mechanism dependent on the concentration of BN radicals in the growth region. With a low supply of BN building blocks, crystal growth is the edge attachment limited, producing triangles, whereas, under higher concentration of BN building blocks, crystal growth is limited by diffusion producing hexagons. The presence of alternating B and N terminated vertices in hexagonal hBN crystals offers the possibility of hBN/graphene in-plane heterostructure synthes...

Here, we demonstrate the synthesis of nitrogen-doped (N-doped) graphene using imidazole and melamine as two different nitrogen containing aromatic rings carbon precursors. Structure of N-doped graphene was investigated at different temperature (800–1020 °C) without changing the precursor quantity. It is observed that higher crystalline N-doped graphene can be obtained from the solid precursors at 1020 °C on Cu foil. X-ray photoelectron spectroscopy (XPS) analysis shows interesting features for the N-doped graphene synthesized from mixture of imidazole and melamine. Overall graphitic nitrogen content is enhanced in the graphene layers using the mixture of precursors, attributing better coordination of carbon and nitrogen atoms on Cu catalyst. Our finding shows that the graphitic and pyridinic nitrogen content in graphene lattice can be tuned by combination of two different nitrogen containing organic molecules.

Herein, we present a direct observation of the formation of graphene from a single copper–carbon nanoneedle (Cu–CNN) during the measurement of current–voltage (I–V) and direct heating via in situ transmission electron microscopy (TEM). Significant structural transformation of Cu–CNN was observed with an applied potential in a two probe system. Under a high current flow between 4.9 μA to 49.0 μA, the Cu nanoparticles melted and evaporated due to Joule heating. The amorphous carbon began crystallizing and transformed into sp2 hybridized hollow graphitic carbon, which was catalyzed by the dispersed Cu nanoparticles. The temperature generated during the current flow was estimated to be 1073 K, as revealed by an in situ TEM heating experiment. The graphene nanoneedle formed exhibited a high current density of 106 A cm−2, which is comparable to Cu in normal interconnect applications. Thus, the graphene nanoneedle formed will be promising for future alternative interconnect materials.

This work focused on the influence of carbon nanotubes (CNT) to the microstructural properties of Zn2SiO4/CNT (ZSO/CNT) composite. CNT was synthesized via alcohol catalytic chemical vapor deposition (ACCVD) using cobalt oxide as catalyst and ethanol as carbon source. Zinc silicate (ZSO) glass was prepared from quenching the melted commercial waste glass bottle with zinc oxide powder. ZSO/CNT-x composites with various CNT concentration (0, 1, 2 and 3 wt%) was prepared through introducing CNT into ZSO glass via dry processing technique followed by sintering process in Argon gas (Ar) environment and atmospheric (atm) environment, respectively. FESEM, XRD and EDS were employed to determine the surface morphology, phase composition and elemental distribution of sintered sample. Crystallite trigonal willemite (Zn2SiO4) phase was observed from argon sintered sample and the crystallite size of willemite phase in ZSO/CNT-3/Ar showed the most reduced lattice strain of 22.85% compared to ZSO/CNT-0/Ar. In contrast, semi-crystalline phase exhibited in atmospheric sintered sample resulted in high lattice strain. It is concluded that dry powder processing and inert gas thermal treatment can be an effective technique in fabricating strain-reduced ceramics/CNT composite without alternating the domain phase. Least internal strain in crystal lattice have potential on enhancing the luminescence properties of phosphor material and lattice thermal conductivity of thermoelectric material.

This study demonstrates graphitization directly through the amorphous carbon under the catalysis of a low-melting-point metal, gallium (Ga), by heating in a vacuum heater as well as by Joule heating during in situ transmission electron microscopy (TEM) operation. For the material system of the mixture of Ga nanoparticles (NPs) and amorphous carbon matrix, the graphitization temperature is determined to be about 600 °C for the first time. With increasing the temperature, evaporation and agglomeration of small Ga NPs start to occur together with the graphitization at around the places where Ga NPs would have been located at the surface region. In situ TEM experiment reveals the accelerated increase in electrical conductivity with structural change from amorphous to graphitization. Thus, the combination of the in situ and ex situ TEM observations is believed to be a lead step to understand deeper the graphitization process and provide information in nanoscale.

A new transparent zinc silicate glass-ceramic was derived from the 55ZnO&ndash, 5B2O3&ndash, 40SLS glass system via a controlled heat-treatment method. The precursor glass sample was placed through the heat-treatment process at different temperatures to study the progress in phase transformation, optical performance and emission intensity of the zinc silicate glass-ceramics. For this project, material characterization was measured through several tests using densimeter and linear shrinkage measurement, X-ray diffraction (XRD), Fourier transform infrared reflection (FTIR), ultraviolet&ndash, visible (UV&ndash, Vis) and photoluminescence (PL) spectroscopy. The density and linear shrinkage measurements show that the density of the particular glass-ceramic samples increases with the progression of heating temperature. The XRD analysis displays the result in which the zinc silicate crystal starts to grow after the sample was treated at 700 &deg, C. In addition, the FTIR spectra indicated that the crystallization of the zinc silicate phase occurred with the appearance of SiO4, ZnO4 and Si-O-Zn bands. UV&ndash, visible exhibited the small changes when the value for the optical band gap decreased from 3.867 to 3.423 eV, influenced by the temperature applied to the sample. Furthermore, the PL spectroscopy showed an enhancement of broad green emission at 534 nm upon the increased heat-treatment temperature. Thus, it can be concluded there is the progression of crystal growth as the heat-treatment temperature increased, three emission peaks appeared at 529, 570 and 682 nm for the green, yellow and red emissions, respectively.

In this work, manganese (II, III) oxide, (Mn3O4) doped zinc soda lime silica glasses have been synthesized using a conventional melt-quenching process and followed by control heat treatment process. The crystal phase composition and optical properties of α-Zn2SiO4:Mn3O4 based glass-ceramics are comprehensively studied. The physical properties and crystal growth of α-Zn2SiO4 phase were measured by density analysis, linear shrinkage, X-ray diffraction (XRD) and Fourier transform infrared reflection (FTIR) spectroscopy. From the measurement, the average density and linear shrinkage of α-Zn2SiO4:Mn3O4 based glass-ceramics increased with increasing heat treatment temperature. Besides, the presence of Zn–O–Si bands indicates the formation of α-Zn2SiO4 crystal phase and causing the decrement of energy band gap. The photoluminescence spectra of Mn2+ ions exhibit emission transitions of 4T1(G)–6A1(S) and show a prominent green emission colors of α-Zn2SiO4 phase at 524 nm. Keywords: α-Zn2SiO4, Glass-ceramic, Phosphor, Crystal growth, Optical properties

We have demonstrated the fabrication of Si- and Ge-incorporated carbon nanofibers (CNFs) at room temperature. Graphite foil surfaces were irradiated by Ar+ and Ne+ ions with simultaneous Si and Ge supply, and the dependences of the ion-induced composite CNFs surface morphology on the ion species and type of incorporated materials were investigated. The sample surfaces were characterized by various kinds of densely distributed nanostructures, such as conical protrusions, nanoneedles, nanocones, and CNF-tipped cones, depending on the Si and Ge supply rates during ion irradiation. In addition, Ne+ irradiation yielded longer CNFs compared to Ar+-irradiated CNFs. Thus, the nanostructures growth was controllable by adjusting the ion and material species. Surface morphology of ion-induced Ge-incorporated CNFs.

We have studied graphene formation from a single Ag-incorporated carbon nanofiber (CNF) during electron emission using in situ transmission electron microscopy. The formation of graphene from the Ag-incorporated CNF structure was observed under a high current of between 900 nA to 2.03 μA during field and thermal electron emission. Joule heating during the process generated an increased temperature, estimated at approximately 440 K to 1030 K, leading to the transformation of a significant amount of the amorphous carbon surrounding Ag particles to a graphene structure, and to the nearly simultaneous evaporation of Ag particles. This evaporation interrupted the thermal electron emission process, thus leading to a decrease of the emission current to ∼300 nA. Also, graphene stopped forming after the Ag particles had evaporated. In this paper, the effect of Ag particle size on its ability to catalyze the fabrication of high-quality graphene are discussed.

We present a direct observation of structural change in Au-incorporated carbon nanofiber (CNF) during a field emission (FE) process using an in situ transmission electron microscopy (TEM). The TEM images and their electron diffraction pattern together with electron energy loss spectroscopy (EELS) indicated that the amorphous carbon structure of CNF was transformed to hollow graphitic structure catalyzed by dispersed Au particles before FE. Thus, the in situ TEM study will be promising to reveal the formation process of nanocarbon materials by solid phase reaction depending on the catalyst metal element for metal-incorporated CNFs.

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.

In this paper, we investigate the structural, electronic and transport properties of graphene/silicene substrate system, Si 2 C 6 in top stacking configuration using density functional theory and semi-classical Boltzmann transport equation. From electronic band structure, the Si 2 C 6 substrate system exhibits semi-metallic properties and charge transfer due to multiple band crossings at K-point, H-point, along H–A-line, A–G-line and G–K-line. Dirac cone is preserved in the band structure of Si 2 C 6 due to the weak band interaction between graphene substrate and silicene layer. Using BoltzTraP, the study on electronic transport properties revealed electrical conductivity and Seebeck coefficient of Si 2 C 6 have a higher thermoelectric response in the p-type doping concentration. Major peaks are found in p-type region of Seebeck coefficient, suggesting that major charge carrier in Si 2 C 6 is hole.

Pd is a unique substrate to explore graphene growth. Pd is a well-known “carbon sponge” which have potential to grow graphene with semiconducting properties in nature. Here, we reveal a solid phase reaction process to achieve Pd assisted graphene growth in nanoscale by in-situ transmission electron microscope (TEM). Significant structural transformation of amorphous carbon nanofiber (CNF) incorporated with Pd is observed with an applied potential in a two probe system. The Pd particle recrystallize and agglomerate starting from the middle part of CNF toward the end part of CNF with applied potential due to joule heating and large thermal gradient. Consequently, the amorphous carbon start crystallizing and forming sp2 hybridized carbon to form graphene sheet from the tip of Pd surface. The observed graphene formation in nanoscale by the in-situ TEM process can be significant to understand carbon atoms and Pd interaction.

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.

Willemite is a wide band gap semiconductor used in modern day technology for optoelectronics application. In this study, a new simple technique with less energy consumption is proposed. Willemite nanoparticles (NPs) were produced via a water–based solution consisting of a metallic precursor, polyvinylpyrrolidone (PVP), and underwent a calcination process at 900 °C for several holding times between 1–4 h. The FT–IR and Raman spectra indicated the presence of metal oxide bands as well as the effective removal of PVP. The degree of the crystallization and formation of the NPs were determined by XRD. The mean crystallite size of the NPs was between 18.23–27.40 nm. The morphology, particle shape and size distribution were viewed with HR-TEM and FESEM analysis. The willemite NPs aggregate from the smaller to larger particles with an increase in calcination holding time from 1–4 h with the sizes ranging between 19.74–29.71 nm. The energy values obtained from the experimental band gap decreased with increasing the holding time over the range of 5.39 eV at 1 h to at 5.27 at 4 h. These values match well with band gap obtained from the Mott and Davis model for direct transition. The findings in this study are very promising and can justify the use of these novel materials as a potential candidate for green luminescent optoelectronic applications.

In situ transmission electron microscopy (TEM) observation of the graphene synthesis by solid phase reaction is dealt with. For this purpose, metal-included and pristine (metal free) amorphous carbon nanofibers (CNFs) were fabricated on an edge of a graphite foil by Ar ion irradiation (Ar ion irradiation method) with and without a supply of metals at room temperature, respectively. In Ar ion irradiation method, any kinds of metals could be included in CNFs. Cu-coated pristine CNFs were also prepared. The graphite foils thus prepared were cut into small pieces to be mounted directly on a TEM sample holder equipped with a piezo-controlled nanoprobe to, measure their current-voltage characteristics in direct current (DC) and field emission (FE) modes. Depending on the included metal element in the CNFs, different types of nanocarbons, such as graphene, ring-shaped graphene, and carbon nanotubes (CNTs), were formed from amorphous CNF during the electron current flow by solid phase reaction. Here, dependence of included metal on the nanocarbon formation is reviewed, together with the visualization of graphene sheet formation in nanoscale during the electron current flow for the Cu-coated pristine CNFs. It is believed that the graphene formation by solid phase reaction is essential also for the growth area (position) control of graphene nano-ribbon.

This paper demonstrates a carbon-copper (C-Cu) composite nanostructure directly fabricated on a copper (Cu) substrate using the Ar+ ion irradiation method at room temperature. The morphology of C-Cu composite was controlled by a simultaneous carbon supply during ion irradiation. Conical protrusions formed on the surface of the Cu substrate with the low carbon supply rate (RC), whereas high RC area prominently produced nanoneedle structures. The field electron emission (FEE) tests demonstrated significant improvement between conical protrusions and nanoneedle structures, where the emission current increase from 5.70 μAcm−2 to 4.37 mAcm-2, while the turn-on field reduced from 5.90 to 2.00 Vμm−1.

Here, we report field emission (FE) properties of a chemical vapor deposited individual graphene investigated by in-situ transmission electron microscopy. Free-standing bilayer graphene is mounted on a cathode microprobe and FE processes are investigated varying the vacuum gap of cathode and anode. The threshold field for 10 nA current were found to be 515, 610, and 870 V/μm for vacuum gap of 400, 300, and 200 nm, respectively. It is observed that the structural stability of a high quality bilayer graphene is considerably stable during emission process. By contacting the nanoprobe with graphene and applying a bias voltage, structural deformation and buckling are observed with significant rise in temperature owing to Joule heating effect. The finding can be significant for practical application of graphene related materials in emitter based devices as well as understanding the contact resistance influence and heating effect.

We have demonstrated the growth of Au- and Ag-incorporated carbon nanofibers (CNFs) at room temperature by Ar+ bombardment on graphite surfaces with simultaneous Au and Ag supply. The evolution of their morphology and its effects on field emission properties were investigated. The structure and density of the grown CNFs depended on the metal supply rate. The ion-irradiated surfaces with excess metal supply featured sparsely distributed conical protrusions and a wall-like structure, while the surfaces irradiated with appropriate metal supply produced densely distributed CNF-tipped cones and a needlelike structure. Compared with Ag supply, Au supply yielded fewer CNFs in terms of number density. Thus, the CNF number density was controllable by adjusting the metal supply rate and metal species. A lower threshold field and a higher emission current density were achieved in the field emission of both metal-incorporated CNFs than of pristine CNFs (without metal incorporation). Thus, it is believed that metal-incorporated CNFs are promising for practical field emission device applications.

Over a past few decades, carbon nanotubes (CNTs) have attracted much attention for their unique properties, although their formation mechanism is not well understood. Recent advances in in situ techniques now open up the new possibility of studying solid phase interaction at atomic level. Here, we report the direct observation of bamboo-like CNTs formation by in situ transmission electron microscopy (TEM) [1]. In our approach, nickel incorporated carbon nanofiber (Ni-CNF) was grown on the edge of graphite foil by ion irradiation of Ar+ at room temperature [2]. Ni-CNF then was mounted on cathode microprobe and bamboo-like CNTs formation was investigated during current-voltage (I-V) measurement. TEM images revealed that the Ni-CNF was amorphous and polycrystalline in nature initially, and the current flow in I-V process induced the dramatic change in the crystalline structure of CNF; formed bamboo-like CNTs. The nickel metal platelets agglomerated during the I-V process and disappeared to leave the crystalline bamboo-like CNTs structure. The structural transformation resulted in improvement of electrical properties where the current produced was remarkably increased, which is 30μA.