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The potential use of down-sized BFO-xSTO systems (x ≤ 25%) as highly efficient photoanodes for photocatalytic water splitting is investigated. BFO-xSTO is prepared by a solid-state method and subsequently deposited by spray coating. The compounds possess rhombohedral symmetry for x ≤ 15% and phase coexistence for x > 15%, as demonstrated by Raman spectroscopy and transmission electron microscopy. Our findings revealed a drastic grain size decrease with increasing STO content, namely 260 nm for BFO to 50 nm for BFO with 25% STO. Moreover, BFO-xSTO, x > 10% exhibited high optical absorption (> 80%) in the full spectrum and interestingly a very promising band alignment with water redox potentials. Moreover, the photochemical measurements revealed a photocurrent density of ~0.17 μA cm−2 achieved for x = 15% at 0 bias. Using DFT calculations, the substitution effects on the electronic, optical, and photocatalytic performances of the BFO system were investigated and quantified. Surprisingly, a high hydrogen yield (~191 μmol g−1) was achieved by BFO-12.5%STO compared to 1 μmol g−1 and 57 μmol g−1 for BFO and STO, respectively. This result highlights the beneficial effects of both the downsizing and substitution of BFO on the photocatalytic water splitting and hydrogen production performances of Bi1−xSrxFe1−xTixO3 systems.

Chemical vapor transport synthesis of SnTiS3 yields a self-assembled heterostructure of two distinct constituent materials, the semiconductor SnS and the semimetal TiS2. The misfit layer compound, although thermodynamically stable, is structurally complex, and precise understanding of the structure is necessary for designing nanoengineered heterojunction compound devices or for theoretical studies. In our work, we reveal the unique complexity of the quasi-periodic structure of this heterostructure by systematically investigating the misfit compound using a set of advanced electron microscopy techniques. X-ray and electron diffraction patterns along with high-resolution scanning/transmission electron microscopy images obtained from different crystallographic orientations resolve the complexity of the sublattice component layer structure and reveal the uniquely bonded alignment among interlayers and a quasi-periodic arrangement of the sublayers. Density functional theory calculations embedded with the extracted structural information provide quantitative insights into the formation of self-assembled heterojunction structures where the nonpolar van der Waals interaction is found to play a dominant role in the structural alignment over the polar interlayer interaction.

Holey or porous graphene, a structural derivative of graphene, has attracted immense attention due to its unique properties and potential applications in different branches of science and technology. In this review, the synthesis methods of holey or porous graphene/graphene oxide are systematically summarized and their potential applications in different areas are discussed. The process-structure-applications are explained, which helps relate the synthesis approaches to their corresponding key applications. The review paper is anticipated to benefit the readers in understanding the different synthesis methods of holey graphene, their key parameters to control the pore size distribution, advantages and limitations, and their potential applications in various fields.

MnO1.88/MnO2/Ti3C2Tx composites on Ti3C2Tx (MXenes) were synthesized for potential applications as supercapacitor electrodes. A composite with a cotton candy-like morphology was formed on nanometer-sized Ti3C2Tx flakes by redox reaction using KMnO4 at room temperature, where Ti3C2Tx acts both as a molecular template and as a reducing agent. MnO1.88/MnO2/Ti3C2Tx has a high specific capacity of 312 F g−1 at 1 A g−1, and the capacity retention was over 91% after 5000 charge–discharge cycles. As such, the facile preparation of MnO1.88/MnO2/Ti3C2Tx composites promotes the highly specific pseudo-capacitance of MXenes, which have emerged as highly promising electrode materials.

Currently, a wide range of materials are being used as barrier coatings for different applications. Among them, polymers and graphene have been the focus of many studies. Polymers are used in numerous industries due to their remarkable properties, including resistance to thermal degradation, resistance to chemical permeation, and good mechanical properties. On the other hand, graphene, a one-atom-thick and two-dimensional material, does not allow the permeation of gases or liquid molecules through its plane; thus, it has been considered one of the promising nanomaterials used in gas and liquid barrier applications and corrosion inhibition coatings.

Recent theoretical studies proposed that two-dimensional (2D) GaGeTe crystals have promising high detection sensitivity at infrared wavelengths and can offer ultra-fast operation. This can be attributed to their small optical bandgap and high carrier mobility. However, experimental studies on GaGeTe in the infrared region are lacking and this exciting property has not been explored yet. In this work, we demonstrate a short-wavelength infrared (SWIR) photodetector based on a multilayer (ML) GaGeTe field-effect transistor (FET). Fabricated devices show a p-type behavior at room temperature with a hole field-effect mobility of 8.6 - 20 cm2 V-1s-1. Notably, under 1310 nm illumination, the photo responsivities and noise equivalent power of the detectors with 65 nm flake thickness can reach up to 57 A/W and 0.1 nW/Hz1/2, respectively, at a drain-source bias (Vds) = 2 V. The frequency responses of the photodetectors were also measured with a 1310 nm intensity-modulated light. Devices exhibit a response up to 100 MHz with a 3dB cut-off frequency of 0.9 MHz. Furthermore, we also tested the dependence of the device frequency response on the applied bias and gate voltages. These early experimental findings stimulate the potential use of multilayer GaGeTe for highly sensitive and ultrafast photodetection applications.

In this letter, we demonstrate a recessed-gate p-channel MISFET using a p-GaN (70 nm)/Al 0.2Ga0.8N (15 nm)/GaN heterostructure grown by metalorganic chemical vapor deposition (MOCVD) on a Si substrate. A major benefit of such epi-structure is that it contains both a 2-dimensional electron gas (2-DEG) and a 2-dimensional hole gas (2-DHG), hence making it suitable for the GaN-based complementary circuit implementation. In addition, the 2-DEG at the interface of the AlGaN/GaN heterostructure is depleted due to the p-GaN layer on top giving rise to normally- OFF operation for the n-channel transistors. A contact resistivity of $\textsf {4.9}\times \textsf {10}^{-\textsf {6}}\Omega \cdot \textsf {cm}^{\textsf {2}}$ is obtained for the ohmic contact to the hole channel for a p-GaN Mg concentration of $\textsf {2}\times \textsf {10}^{\textsf {20}}\, \textsf {cm}^{-\textsf {3}}$ . Long channel ( ${L} _{\textsf {g}}=\textsf {3}\,\,{\boldsymbol \mu } \text{m}$ and ${L} _{\textsf {sd}}=\textsf {9}\,\,{\boldsymbol \mu } \text{m}$ ) p-type transistors show an ON–OFF current ratio of ~105 and ON resistance of $\sim 2.3~\text{k}{\Omega } \cdot \textsf {mm}$ at ${V} _{\textsf {GS}}=-\textsf {11}$ V.

This work demonstrates a p-MOSFET with a GaNM.l 0.2 Ga 0.8 N (20 nm)/GaN heterostructure grown by metal-organic-chemical vapor deposition (MOCVD) on 6-inch Si substrate with optimized self-aligned process. Devices with source-to-drain distance, L SD , varying from 1 µm down to 200 nm were fabricated. Significant field-induced acceptor ionization was found in these devices at high drain voltages. The device with L SD =200 nm shows a record combination of I ON of ~45 mA/mm and ON-OFF ratio of ~104 when compared with other p-channel transistor demonstrations. The device also exhibits Enhancement-mode operation with threshold voltage of -0.5V. The best device shows an ON-current of 100 mA/mm but at the expense of lower on-off ratio of ~102.

Plan-view transmission electron microscopy (TEM) or electron diffraction imaging of a bulk or 2D material can provide detailed information about the structural or atomic arrangement in the material. A systematic and easily implementable approach to preparing site-specific plan-view TEM samples for 2D thin film materials using FIB is discussed that could be routinely used. The methodology has been successfully applied to prepare samples from 2D materials such as, MoS

Plasmonic nanostructures have played a key role in extending the activity of photocatalysts to the visible light spectrum, preventing the electron–hole combination and providing with hot electrons to the photocatalysts, a crucial step towards efficient broadband photocatalysis. One plasmonic photocatalyst, Au/TiO2, is of a particular interest because it combines chemical stability, suitable electronic structure, and photoactivity for a wide range of catalytic reactions such as water splitting. In this review, we describe key mechanisms involving plasmonics to enhance photocatalytic properties leading to efficient water splitting such as production and transport of hot electrons through advanced analytical techniques used to probe the photoactivity of plasmonics in engineered Au/TiO2 devices. This work also discusses the emerging strategies to better design plasmonic photocatalysts and understand the underlying mechanisms behind the enhanced photoactivity of plasmon-assisted catalysts.

We report a study on the nonlinear optical properties of cobalt- ($\mathrm{Co}$) doped $\mathrm{Zn}\mathrm{O}$ nanorods (NRs) using the single-beam $Z$-scan technique. In the open-aperture measurements, the undoped sample shows two-photon absorption (TPA) characteristics, whereas the doped samples exhibit a saturable absorption (SA) signature. In the closed-aperture measurements, all the samples show a self-defocusing behavior. We correlate the nonlinear absorption coefficient with the exponential reduction of the optical band gap and explain it in terms of electronic-band-structure modification because of doping. Density-functional-theory calculation is also used to understand the observed nonlinear absorption and band-gap variation. The present study can help to understand the origin of SA in $\mathrm{Zn}\mathrm{O}$. Doped $\mathrm{Zn}\mathrm{O}$ nanorods can illustrate high SA and nonlinear refraction by appropriate $\mathrm{Co}$ doping, which can drive the technology for $Q$ switching and mode locking in solid-state and fiber lasers.

Two-dimensional metal dichalcogenide/monochalcogenide thin flakes have attracted much attention owing to their remarkable electronic and electrochemical properties; however, chemical instability limits their applications. Chemical vapor transport (CVT)-synthesized SnTiS3 thin flakes exhibit misfit heterojunction structure and are highly stable in ambient conditions, offering a great opportunity to exploit the properties of two distinct constituent materials: semiconductor SnS and semi-metal TiS2. We demonstrated that in addition to a metal-like electrical conductivity of 921 S/cm, the SnTiS3 thin flakes exhibit a strong bandgap emission at 1.9 eV, owing to the weak van der Waals interaction within the misfit-layer stackings. Our work shows that the misfit heterojunction structure preserves the electronic properties and lattice vibrations of the individual constituent monolayers and thus holds the promise to bridge the bandgap and carrier mobility discrepancy between graphene and recently established 2D transition metal dichalcogenide materials. Moreover, we also present a way to identify the top layer of SnTiS3 misfit compound layers and their related work function, which is essential for deployment of van der Waals misfit layers in future optoelectronic devices.

We demonstrate that surfaces presenting heterogeneous and atomically flat domains can be directly and rapidly discriminated via robust intensive quantifiables by exploiting one-pass noninvasive methods in standard atomic force microscopy (AFM), single ∼2 min passes, or direct force reconstruction, i.e., ∼103 force profiles (∼10 min collection time), allowing data collection, interpretation, and presentation in under 20 min, including experimental AFM preparation and excluding only sample fabrication, in situ and without extra experimental or time load. We employ a misfit SnTiS3 compound as a model system. Such heterostructures can be exploited as multifunctional surface systems and provide multiple support sites with distinguishable chemical, mechanical, or opto-electronic distinct properties. In short, they provide an ideal model system to exemplify how current AFM methods can significantly support material discovery across fields.

Non-monotonic behavior has been observed in the optoelectronic properties of ZnO thin films as doped with Hf (HZO). Here we propose that two competing mechanisms are responsible for such behaviour. Specifically, we propose that provided two crystal orientations dominate film growth, only one of them might be responsible for direct Hf substitution. Nonmonotonic behaviour is expected at once by considering that preferential growth of the crystal that allows for direct Hf substitution is inhibited by Hf concentration in the manufacturing process. This inhibition would also be a thermodynamic consequence of Hf substitution. Maxima in Hf substitution is thus reached at a point where enough crystals exhibit the preferential orientation, and where enough Hf is present on the surface for substitution. Outside this optimum scenario, Hf substitution can only decrease. We interpret the surface phenomena by discussing surface energy and the van der Waals forces as measured experimentally by means of atomic force microscopy.

© 2019 IEEE. In this work, we demonstrate a self-aligned p-FET with a GaN/Al0 2Ga0 8N (20 nm)/GaN heterostructure grown by metal-organic-chemical vapor deposition (MOCVD) on Si substrate. Our 100 nm channel length device with recess depth of 70 nm exhibits a record ON-resistance of 400 Ωmm and ON-current over 5 mA/mm with ON-OFF ratio of 6×105 when compared with other p-FET demonstrations based on GaN/AlGaN heterostructure. The device shows E-mode operation with a threshold voltage of -1 V, making it a promising candidate for GaN-based complementary circuit that can be integrated on a Silicon platform. A monolithically integrated n-channel transistor with p-GaN gate is also demonstrated. The potential of the reported p-FET for complementary logic application is evaluated through industry-standard compact modeling and inverter circuit simulation.

The surface plasmon resonance of dewetted Au structures on TiO2 substrate using physical vapor deposition and post-annealing is investigated. In this work, we employ an aperture-probe scanning near-field optical microscope (SNOM) to study the plasmonic properties of dewetted Au structures and the influence of the size, shape, and interdistance of the dewetted structures on their plasmonic behavior. This investigation is corroborated by numerical calculations performed using finite-difference time-domain (FDTD) and atomic force microscopy (AFM) to provide a realistic and direct comparison with SNOM experiments. The near-field images obtained by both experiments and simulations reveal surface plasmon resonance around Au structures which are correlated to the broadband activity in the visible light region observed by UV-Vis spectrophotometry and photoluminescence. In addition, near-field enhancement is associated with the external quantum efficiency (EQE), which shows a multi-peak response after 570 nm due higher-order modes of plasmon resonance. This broadband improvement in the visible region obtained by controlled dewetting has potential use in large-scale solar energy applications.

We attempt to evaluate Black Silicon (BSi) substrate loaded with water splitting (WS) semiconductor and Au particles as an efficient WS composite material. Further, thermal annealing was performed to study the effect of the WS photocatalyst microstructure evolution on optical properties, crystallinity, photo-response and the hydrophilicity. The thermal annealing was carried out at 450–850 °C range in ambient environment. The WS crystal structure analysis by X-ray Diffraction, shows that TiO 2 turns after annealing at 450 °C to anatase phase known for high photocatalytic behavior. This transformation increases the optical reflection (%R) of the WS material in UV–Vis–Near IR region for both substrates (Si and BSi), however this increase about 1–5% is insignificant for the BSi due its morphology consisting of needles and wells. Nevertheless, this transformation decreases the hydrophilicity of the material surface of BSi due to its inherent structure. In addition, we showed that the photo-response after annealing is associated with lower resistance and higher photocurrent emission compared to non-annealed sample. This result suggests that BSi used as a substrate to receive WS semi-conductor has a great potential to be used as an efficient WS materials compared to Si.

We report on the effect of thermal annealing on the microstructure, optical properties and wettability of TiO 2 -based water-splitting (WS) composite using full solar spectrum as source of energy. The WS material used in this study is composed of three layers (SiO 2 , Al 2 O 3 and TiO 2 ) on top of which a distribution of Localized Surface Plasmon Resonance structures such as gold are formed to obtain a multilayer composite material. The fabricated samples are then annealed at 450−1100 °C temperatures range under atmospheric conditions. The crystal structure and chemical composition are determined using X-ray Diffractometer, Scanning Electron Microscope, Energy Dispersive Spectroscopy, High Resolution Scanning and Transmission Electron Microscope. UV–Vis spectroscopy is used to study the influence of thermal annealing on optical absorption. Besides, wettability alteration is assessed using both in-situ (Environmental Scanning Electron Microscope) and ex-situ (sessile drop technique). Our findings reveal that thermal annealing leads to the transformation of amorphous TiO 2 to its more stable phase anatase. This transformation enhances significantly the optical properties and increases the hydrophilicity of the material surface making it suitable for WS activity. More importantly, the presence of plasmonic nanostructures allow the material to extend its photoactivity from UV region to full solar spectrum. The gold nanocrystals were also found to prefer the orientation during their evolving and growth after thermal annealing. This specific compact orientation is also reported to increase the efficiency of WS.

In this work, we report for the first time a unique configuration of N-doped and Cu-doped TiO 2 bilayer. The activity of TiO 2 was improved by combining Cu- and N-doping in a layered thin-film structure. The impact of the stacking order was studied, pointing out how the best arrangement is by far the one with Cu-TiO 2 as the top layer. The results reveal a unique and simple way to enhance the photocatalytic response of TiO 2 in the visible domain.

Vertically aligned MoS2 nanosheets (NSs) with exposed edges were successfully synthesized over a large area (∼2 cm2). The NSs were grown using an ambient pressure chemical vapor deposition technique via rapid sulfurization of sputter deposited thick molybdenum films. Extensive characterization of the grown MoS2 NSs has been carried out using high resolution scanning and transmission electron microscopy (SEM & TEM). A special care was given to the TEM lamella preparation process by means of a focused ion beam to preserve the NS growth direction. The cross-section TEM measurements revealed the growth of densely packed, vertically aligned and straight MoS2 NSs. Additional characterization techniques such as atomic force microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and photoluminescence (PL) were used to evaluate the MoS2 NSs. These studies revealed the high crystallinity and quality of the synthesized NSs. The MoS2 NSs show visible light emission similar to mechanically exfoliated monolayer MoS2 NSs. The striking PL signal comes from the exposed edges as shown by experimental and theoretical calculations. The vertical MoS2 NSs also exhibit a hydrophobic character with a contact angle of 114°. The as-grown MoS2 NSs would be highly useful in the development of catalysis, nano-optoelectronics, gas-sensing and bio-sensing device applications.

This work demonstrates the viability of direct fabrication utilizing a single (deposition/anneal) process for polycrystalline silicon germanium sub-micro particles. The process combines plasma chemical vapor deposition enhanced with inductively coupled radio frequency plasma at intermediate pressure and high temperature for deposition and rapid thermal annealing as a final step to tune the particles' growth. The deposition process utilizes high plasma density at low kinetic ion energy providing a relatively high deposition rate, favorable for industrial fabrication requirements. Our characterization was performed at two points in the process, post-deposition and post-annealing. Raman spectroscopy and X-ray diffraction were combined to determine the value of stoichiometry x and hence the nature of the obtained compound. Post-annealing, the samples were analyzed by atomic force microscopy, and scanning and transmission electron microscopy to investigate the crystallization, growth kinetics and the strain relaxation of the particles. Our findings show that optimized coarsening of the crystals occurred after annealing at 600 °C for 30 minutes which resulted in internal strain minimization while the composition stoichiometry is kept constant. In addition, the presence of well-defined geometrical facets observed on the surface of SiGe particles, as revealed by atomic force microscopy analyses, suggests that the SiGe particles seem to grow along a preferred crystallographic orientation.

Vertically aligned graphene nanosheet arrays (VAGNAs) exhibit large surface area, excellent electron transport properties, outstanding mechanical strength, high chemical stability, and enhanced electrochemical activity, which makes them highly promising for application in supercapacitors, batteries, fuel cell catalysts, etc. It is shown that VAGNAs terminated with a high-quality single-layer graphene sheet, can be directly grown on germanium by plasma-enhanced chemical vapor deposition without an additional catalyst at low temperature, which is confirmed by high-resolution transmission electron microscopy and large-scale Raman mapping. The uniform, centimeter-scale VAGNAs can be used as a surface-enhanced Raman spectroscopy substrate providing evidence of enhanced sensitivity for rhodamine detection down to 1 × 10−6 mol L−1 due to the existed abundant single-layer graphene edges.

Background: Nanoimprinting lithography technique uses a very simple concept of transferring pattern of nanoscale features from a mold to a target substrate. In the past two decades, this technique has successfully broken through the barrier of laboratory scale production and become an industrial scale production technique. The aim of this paper is to introduce to readers to the basic working principle, applications, analysis the technological limitations. It will also point out future research direction of this useful nanofabrication technique. Methods: We adopted a systematic approach to give a comprehensive review of the work principle, hardware and analysis of advantaged and disadvantages of major nanoimprint lithography techniques. Moreover, a technical comparison of these methods is carried out to provide future research direction. Results: 87 papers were reviewed. Four techniques including thermal NIL, ultraviolet light NIL, laser-assisted direct imprint and nanoelectrode lithography have been identified as main stream of NIL techniques. These techniques possess certain advantages and disadvantages in terms of cost, throughput, attainable resolution. Lack of flexibility is the common limitation of current NIL techniques. NIL has gained wide applications in the fabrication of optoelectronics devices, solar cells, memory devices, nanoscale cells, hydrophobic surfaces and bio-sensors. The potential applications of NIL in biochips, artificial organs, diagnostic system, and fundamental research in cell biology will demand large scale 3D fabrication capability with resolution towards 10nm or less. Conclusions: The findings of this review confirm that NIL is one of the most employed commercial platforms for nanofabrication which offers high throughput and cost-effectiveness. One of the disadvantages of NIL over other nanofabrication techniques is the flexibility of patterning. Integrating NIL with other existing nanofabrication techniques can be helpful to overcome such issue. The potential applications of NIL in biochips, artificial organs, diagnostic system, and fundamental research in cell biology will attract researchers to push nanoimprint lithography forward at a resolution of 10 nm or less in the future.

Titanium dioxide (TiO[subscript 2]) loaded with gold (Au) as noble metal, acts as an efficient photocatalyst that has been extensively investigated for water splitting processes. In this paper, we report on the microstructure of atomic layer deposited titanium dioxide and the crystallinity modification of the material using energetic electron beam irradiation. A rapid high-energy electron beam induced crystallization of the nanostructures has been observed in-situ inside a High-Resolution Transmission Electron Microscope (HRTEM). The systematic crystallization of the nanomaterial occurring under the electron beam irradiation (300 KV) indicates the transformation of the near amorphous material into a mixture of two nuances of TiO[subscript 2] polymorphs, namely rutile and anatase. We believe that this transformation will enhance the efficiency of water splitting process, as the mixed phases of rutile and anatase are known to possess better optical properties than the individual polymorphs of TiO[subscript 2]. This finding may be of particular interest in developing appropriate heat treatment methods for these nanostructures dedicated to water splitting to increase their efficiency., MIT Masdar Program (02/MI/MI/CP/11/07633/GEN/G/00)

Plasmonic nanostructures have played a key role in extending the activity of photocatalysts to the visible light spectrum, preventing the electron–hole combination and providing with hot electrons to the photocatalysts, a crucial step towards efficient broadband photocatalysis. One plasmonic photocatalyst, Au/TiO2, is of a particular interest because it combines chemical stability, suitable electronic structure, and photoactivity for a wide range of catalytic reactions such as water splitting. In this review, we describe key mechanisms involving plasmonics to enhance photocatalytic properties leading to efficient water splitting such as production and transport of hot electrons through advanced analytical techniques used to probe the photoactivity of plasmonics in engineered Au/TiO2 devices. This work also discusses the emerging strategies to better design plasmonic photocatalysts and understand the underlying mechanisms behind the enhanced photoactivity of plasmon-assisted catalysts.

Generation of hydrogen using photoelectrochemical (PEC) water splitting has attracted researchers for the last two decades. Several materials have been utilized as a photoanode in a water splitting cell, including ZnO due to its abundance, low production cost and suitable electronic structure. Most research attempts focused on doping ZnO to tailor its properties for a specific application. In this work, atomic layer deposition (ALD) was used to precisely dope ZnO with hafnium (Hf) in order to enhance its PEC performance. The resultant doped materials showed a significant improvement in PEC efficiency compared to pristine ZnO, which is linked directly to Hf introduction revealed by detailed optical, structural and electrical analyses. The photocurrent obtained in the best performing Hf-doped sample (0.75 wt% Hf) was roughly threefold higher compared to the undoped ZnO. Electrochemical impedance spectroscopy (EIS) and open-circuit potential-decay (OCPD) measurements confirmed suppression in photocarriers' surface recombination in the doped films, which led to a more efficient PEC water oxidation. The enhanced PEC performance of Hf-doped ZnO and effectiveness of the used metal dopant are credited to the synergistic optimization of chemical composition, which enhanced the electrical, structural including morphological, and optical properties of the final material, making Hf-doping an attractive candidate for novel PEC electrodes.

Pristine, few-layer graphene (FLG)/Si nanopillar assemblies are introduced as gas sensitive chemiresistors showing unprecedented sensitivity towards NO2 when operated at room temperature (25 °C) and in humid air. To achieve this, we first developed wafer-scale (∼50 cm2) FLG growth using sub-micrometer thick films of thermally evaporated Cu/Ni on a SiO2/Si substrate. The Ni film was deposited and annealed to induce the formation of a Cu-rich binary alloy. This alloy formation limited the inter-diffusion of Cu and SiO2, a phenomenon known to take place during the CVD growth of graphene on Cu/SiO2/Si. The as-grown high structural quality FLG was transferred, using a conventional wet chemical method, to lithographically patterned arrays of Si nanopillars (non-flat substrate). Testing of the FLG/Si assembly revealed a NO2 sensitivity that outperforms what is reported in the literature for pristine graphene. Overall, our growth and device fabrication work-flow demonstrate a way to design graphene-based gas sensing systems without incurring inconvenient processing steps such as metal foil etching, surface functionalization or particle loading.

Densely populated edge-terminated vertically aligned two-dimensional MoS2 nanosheets (NSs) with thicknesses ranging from 5 to 20 nm were directly synthesized on Mo films deposited on SiO2 by sulfurization. The quality of the obtained NSs was analyzed by scanning electron and transmission electron microscopy, and Raman and X-ray photoelectron spectroscopy. The as-grown NSs were then successfully transferred to the substrates using a wet chemical etching method. The transferred NSs sample showed excellent field-emission properties. A low turn-on field of 3.1 V/μm at a current density of 10 µA/cm2 was measured. The low turn-on field is attributed to the morphology of the NSs exhibiting vertically aligned sheets of MoS2 with sharp and exposed edges. Our findings show that the fabricated MoS2 NSs could have a great potential as robust high-performance electron-emitter material for various applications such as microelectronics and nanoelectronics, flat-panel displays and electron-microscopy emitter tips.

Densely populated edge-terminated vertically aligned two-dimensional MoS2 nanosheets (NSs) with thicknesses ranging from 5 to 20 nm were directly synthesized on Mo films deposited on SiO2 by sulfurization. The quality of the obtained NSs was analyzed by scanning electron and transmission electron microscopy, and Raman and X-ray photoelectron spectroscopy. The as-grown NSs were then successfully transferred to the substrates using a wet chemical etching method. The transferred NSs sample showed excellent field-emission properties. A low turn-on field of 3.1 V/μm at a current density of 10 µA/cm2 was measured. The low turn-on field is attributed to the morphology of the NSs exhibiting vertically aligned sheets of MoS2 with sharp and exposed edges. Our findings show that the fabricated MoS2 NSs could have a great potential as robust high-performance electron-emitter material for various applications such as microelectronics and nanoelectronics, flat-panel displays and electron-microscopy emitter tips.

Photocatalytic nanostructures loaded with metallic nanoparticles are being considered as a potential candidate for designing efficient water splitting devices. Here, we aim to unveil the plasmonic behavior of a device made of Au–TiO2 nanostructures through in-depth investigations combining electron energy loss spectroscopy (EELS) and cathodoluminescence (CL). The experiments confirm the existence of Au bulk plasmon excitation, intrinsic interband transitions, and plasmon losses over a wide range of energies (0.6–2.4 eV). Depending on the size and the shape of the obtained nanostructures, such as fishing hook (FH), asymmetric nanorod (AR), and a/symmetric nanoparticles, in our devices, the dephasing times and the quality factors of the modes vary. Finite difference time domain simulations were then carried out on FH and AR structures. These simulations indicate good agreement between the electric field enhancement and the obtained plasmon excitation as observed in EELS. Moreover, the plasmonic activity obtained by CL and EELS was correlated with the photocurrent measurements recorded with the device, which confirmed that the localized plasmons in Au generate hot electrons and enhance the photoresponse of the device. This study confirms the functionality of the metal dielectric photocatalyst device over a wide range of wavelengths ranging from UV to near IR.

Summary Locating and profiling porosity or cavities in materials science has been of great interest and importance. However, it has been a great challenge to detect and analyze these hidden cracks because of lack of efficient measurement technique. Artificial voids are created and covered by self-supporting thin films in order to replicate a hidden crack situation. Subsequently, these hidden voids are located in the scanning electron microscope images and the backscattered electrons, which emerge from a deeper part of a material and depend on the material property (such as atomic number, atomic density, etc.), are shown to play the key role in locating these hidden voids. Detection has been done by collecting the backscattered electrons as well as the secondary electrons (produced by the backscattered electrons). The efficacy of the detection technique is presented in terms of variation in the grayscale intensity values of the scanning electron microscope images. The role of the primary beam energy and the beam dwell time in the detection efficiency is discussed. The successful demonstration of the imaging technique in profiling hidden voids shows a promising and efficient analytical technique in detecting and analyzing invisible cracks in materials. SCANNING 36:430–436, 2014. © 2014 Wiley Periodicals, Inc.

In order to fabricate a nanostructure precisely, the effect of different parameters involved in the fabrication processes should be extensively studied. We have studied the effect of beam parameters such as beam dwell time, mode of deposition as well as pattern size, on focused-ion-beam-induced deposition of nanopillars. While fabricating the nanopillars in the circular and serpentine mode deposition, long tails of the deposited material are observed. The amount deposited in the tails is found to be a function of the beam dwell time as well as the diameter of the pillar. The tail disappears at higher beam dual time and pillar diameter. The elemental composition of the tail is found to be same as that of the pillar.