Electrochemical effects manifest as nonlinear responses to an applied electric field in electrochemical devices, and are linked intimately to the molecular orientation of ions in the electric double layer (EDL). Herein, we probe the origin of the electrochemical effect using a double-gate graphene field effect transistor (GFET) of ionic liquid N,N-diethyl-N-(2-methoxyethyl)-N-methylammonium bis(trifluoromethylsulfonyl)imide (DEME-TFSI) top-gate, paired with a ferroelectric Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) back-gate of compatible gating efficiency. The orientation of the interfacial molecular ions can be extracted by measuring the GFET Dirac point shift, and their dynamic response to ultraviolet–visible light and a gate electric field was quantified. We have observed that the strong electrochemical effect is due to the TFSI anions self-organizing on a treated GFET surface. Moreover, a reversible order–disorder transition of TFSI anions self-organized on the GFET surface can be triggered by illuminating the interface with ultraviolet–visible light, revealing that it is a useful method to control the surface ion configuration and the overall performance of the device.Keywords: electrochemical effect; graphene field effect transistor; interface; ionic liquid; self-organization;

Inorganic/biomolecule nanohybrids can combine superior electronic and optical properties of inorganic nanostructures and biomolecules for optoelectronics with performance far surpassing that achievable in conventional materials. The key toward a high-performance inorganic/biomolecule nanohybrid is to design their interface based on the electronic structures of the constituents. A major challenge is the lack of knowledge of most biomolecules due to their complex structures and composition. Here, we first calculated the electronic structure and optical properties of one of the cytochrome c (Cyt c) macromolecules (PDB ID: 1HRC) using ab initio OLCAO method, which was followed by experimental confirmation using ultraviolet photoemission spectroscopy. For the first time, the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels of Cyt c, a well-known electron transport chain in biological systems, were obtained. On the basis of the result, pairing the Cyt c with semiconductor single-wall carbon nanotubes (s-SWCNT) was predicted to have a favorable band alignment and built-in electrical field for exciton dissociation and charge transfer across the s-SWCNT/Cyt c heterojunction interface. Excitingly, photodetectors based on the s-SWCNT/Cyt c heterojunction nanohybrids demonstrated extraordinary ultra-broadband (visible light to infrared) responsivity (46–188 A W–1) and figure-of-merit detectivity D* (1–6 × 1010 cm Hz1/2 W–1). Moreover, these devices can be fabricated on transparent flexible substrates by a low-lost nonvacuum method and are stable in air. These results suggest that the s-SWCNT/biomolecule nanohybrids may be promising for the development of CNT-based ultra-broadband photodetectors.Keywords: ab initio calculation; broadband photodetectors; cytochrome c; exciton dissociation; s-SWCNTs;

Colloidal nanocrystals are attractive materials for optoelectronics applications because they offer a compelling combination of low-cost solution processing, printability, and spectral tunability through the quantum dot size effect. Here we explore a novel nanocomposite photosensitizer consisting of colloidal nanocrystals of FeS2 and PbS with complementary optical and microstructural properties for broadband photodetection. Using a newly developed ligand exchange to achieve high-efficiency charge transfer across the nanocomposite FeS2–PbS sensitizer and graphene on the FeS2–PbS/graphene photoconductors, an extraordinary photoresponsivity in exceeding ∼106 A/W was obtained in an ultrabroad spectrum of ultraviolet (UV)-visible-near-infrared (NIR). This is in contrast to the nearly 3 orders of magnitude reduction of the photoresponsivity from ∼106 A/W at UV to 103 A/W at NIR on their counterpart of FeS2/graphene detectors. This illustrates the combined advantages of the nanocomposite sensitizers and the high charge mobility in FeS2–PbS/graphene van der Waals heterostructures for nanohybrid optoelectronics with high performance, low cost, and scalability for commercialization.Keywords: FeS2−PbS; graphene; nanohybrids; printable broadband photodetector; van der Waals heterostructures;

In ZnO quantum dot/graphene heterojunction photodetectors, fabricated by printing quantum dots (QDs) directly on the graphene field-effect transistor (GFET) channel, the combination of the strong quantum confinement in ZnO QDs and the high charge mobility in graphene allows extraordinary quantum efficiency (or photoconductive gain) in visible-blind ultraviolet (UV) detection. Key to the high performance is a clean van der Waals interface to facilitate an efficient charge transfer from ZnO QDs to graphene upon UV illumination. Here, we report a robust ZnO QD surface activation process and demonstrate that a transition from zero to extraordinarily high photoresponsivity of 9.9 × 108 A/W and a photoconductive gain of 3.6 × 109 can be obtained in ZnO QDs/GFET heterojunction photodetectors, as the ZnO QDs surface is systematically engineered using this process. The high figure-of-merit UV detectivity D* in exceeding 1 × 1014 Jones represents more than 1 order of magnitude improvement over the best reported previously on ZnO nanostructure-based UV detectors. This result not only sheds light on the critical role of the van der Waals interface in affecting the optoelectronic process in ZnO QDs/GFET heterojunction photodetectors but also demonstrates the viability of printing quantum devices of high performance and low cost.Keywords: graphene; interface; nanohybrids; printable ultraviolet photodetectors; van der Waals heterostructures; zinc oxide quantum dots;

Two-dimensional (2D) MoS2/graphene van der Waals heterostructures integrate the superior light–solid interaction in MoS2 and charge mobility in graphene for high-performance optoelectronic devices. Key to the device performance lies in a clean MoS2/graphene interface to facilitate efficient transfer of photogenerated charges. Here, we report a printable and transfer-free process for fabrication of wafer-size MoS2/graphene van der Waals heterostructures obtained using a metal-free-grown graphene, followed by low-temperature growth of MoS2 from the printed thin film of ammonium thiomolybdate on graphene. The photodetectors based on the transfer-free MoS2/graphene heterostructures exhibit extraordinary short photoresponse rise/decay times of 20/30 ms, which are significantly faster than those of the previously reported MoS2/transferred-graphene photodetectors (0.28–1.5 s). In addition, a high photoresponsivity of up to 835 mA/W was observed in the visible spectrum on such transfer-free MoS2/graphene heterostructures, which is much higher than that of the reported photodetectors based on the exfoliated layered MoS2 (0.42 mA/W), the graphene (6.1 mA/W), and transfer-free MoS2/graphene/SiC heterostructures (∼40 mA/W). The enhanced performance is attributed to the clean interface on the transfer-free MoS2/graphene heterostructures. This printable and transfer-free process paves the way for large-scale commercial applications of the emerging 2D heterostructures in optoelectronics and sensors.Keywords: graphene; heterostructures; MoS2; photodetectors; printable; transfer-free;

A novel type of substrate for quantitative surface enhanced Raman spectroscopy (SERS) composed of chemical vapor deposition (CVD) graphene and in-situ fabricated rounded gold nanoparticles (AuNPs) was designed. SERS was measured on samples of different concentrations of Rhodamine 6G (R6G) on the AuNPs/graphene substrates using a low power 632.8 nm laser. Finite element simulations were carried out for a system of two gold hemiellipsoids under various conditions such as with R6G analyte covering the surface and with graphene underneath the nanoparticles. Graphene or R6G being present between the two nanoparticles caused a redshift in the plasmonic resonance frequency, and the graphene dampened the electric field of the surface. Regardless of the weakened electric field, the synergy of the AuNPs and graphene still enhanced the Raman signature of R6G to a greater extent than the nanoparticles or graphene alone could, which is attributed to the charge transferring mechanism effect of graphene on SERS. The lowest concentration of solid phase R6G deposited in this manner that could be detected was 8 × 10−7 M. Higher analyte concentrations and the characteristic peak intensities of the analyte showed a logarithmic relation as anticipated from the plasmonically enhanced Raman scattering.

Zinc oxide nanoparticles (ZnO-NPs) with radius of the Debye length have the optimal electron depletion effect for high-performance optoelectronic devices. However, a major challenge remains in assembling ZnO-NPs into 3D interlinked networks for high-efficiency electron transport. Here an ultrafast thermal annealing process has been developed by exposing the ZnO-NPs to excessive heat for a short period of 2 s. This enables the formation of NP–NP interface nanojunctions, resulting in nearly two orders of magnitude decrease of the dark current IDark and more than an order of magnitude increase of the photocurrent IPh under ultraviolet (UV) illumination. Moreover, the UV photodetectors based on such 3D interlinked ZnO-NP networks exhibit extraordinary performance with high IPh/IDark ratio of 3.1 × 105, responsivity of up to 95.4 A W−1 at 340 nm UV power of 0.1 mW cm−2 (and up to 430 A W−1 at 0.003 mW cm−2), detectivity of 1.4 × 1013 Jones, and rise/decay time of 9.4 s/13.5 s. These results illustrate the critical importance of the NP–NP interface nanojunctions and provide a low-cost pathway for high-performance ZnO-NP optoelectronics.

Vertically aligned zinc oxide nanowires on graphene (ZnO-NW/graphene) heterojunction nanohybrids combine the superior sensitivity of crystalline ZnO-NWs with high charge mobility of graphene to provide an ideal platform for high-performance detectors and sensors. Controlling the ZnO-NW microstructure and ZnO-NW/graphene interface is of primary importance for the device performance. This work explores floating hydrothermal growth of ZnO-NWs on seedless and ZnO seeded graphene, and investigates the effects of the microstructure and interface on the performance of ZnO-NW/graphene ultraviolet (UV) detectors. It has been found that the ZnO seed layer facilitates the growth of a dense ZnO-NW array with a NW radius approaching the Debye length. In contrast, the seedless process results in a lower NW areal density and a larger NW diameter on the order of sub-to-few micrometers. Consequently, higher UV responsivity up to 728 A W−1 was obtained in the former. However, a strong charge trapping effect was also observed, which is attributed to the poorer crystallinity of the ZnO-NWs originating from the ZnO seed layer. These results shed light on the importance of controlling the microstructure and interface towards high-performance ZnO-NW/graphene nanohybrid optoelectronics.

Combining the high mobility of graphene and surface electron depletion effect of zinc oxide nanoparticles (ZnO-NPs), graphene/ZnO-NP nanohybrids can be anticipated for significantly enhanced photoresponsivity and photoconductive gain in optoelectronics. Herein, a transfer-free and printable method was developed for the fabrication of wafer-size graphene/ZnO-NP nanohybrids for high-performance UV photodetectors. These photodetectors achieved the extraordinary photoresponsivity of up to 1000 A W−1 V−1 and high gain of 1.8 × 104, representing more than an order of magnitude improvement compared to that of previously reported UV photodetectors based on various ZnO nanostructures and transferred-graphene/ZnO nanohybrids. Our method provides a low-cost pathway for the run-to-run wafer-size fabrication of high-performance graphene/ZnO optoelectronics.

Graphene was inserted into the interface between electric dipole layers from DEME-TFSI ionic liquid (top-gate) and ferroelectric Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT, back-gate) to probe the interface dipole–dipole interaction in response to DC and pulsed gate voltages. A highly complicated behavior of the interface dipole–dipole interaction has been revealed as a combination of electrostatic and electrochemical effects. The interfacial polar molecules in the DEME-TFSI electrical double layer are pinned with assistance from the PLZT back-gate in response to a DC top-gate pump, leading to strong nonlinear electrochemical behavior. In contrast, depinning of these molecules can be facilitated by a faster pulsed top-gate pump, which results in a characteristic linear electrostatic behavior. This result not only sheds light on the dynamic dipole–dipole interactions on the interface between functional materials but also prototypes a unique pump and probe approach using graphene field effect transistors to detect the interface dipole–dipole interaction.Keywords: dipole interaction; electrochemical effect; ferroelectric thin film; graphene; ionic liquid;

AbstractGraphene field effect transistor sensitized by a layer of semiconductor (sensitizer/GFET) is a device structure that is investigated extensively for ultrasensitive photodetection. Among others, organometallic perovskite semiconductor sensitizer has the advantages of long carrier lifetime and solution processable. A further step to improve the responsivity is to design a structure that can promote electron–hole separation and selective carrier trapping in the sensitizer. Here, the use of a hybrid perovskite–organic bulk heterojunction (BHJ) as the light sensitizer to achieve this goal is demonstrated. Our spectroscopy and device measurements show that the CH3NH3PbI3–PCBM BHJ/GFET device has improved charge separation yield and carrier lifetime as compared to a reference device with a CH3NH3PbI3 sensitizer only. The key to these enhancement is the presence of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), which acts as charge separation and electron trapping sites, resulting in a 30-fold increase in the photoresponsivity. This work shows that the use of a small amount of electron or hole acceptors in the sensitizer layer can be an effective strategy for improving and tuning the photoresponsivity of sensitizer/GFET photodetectors.

A systematic study shows that continuous graphene with controllable number of layers and stacking structure can be directly grown on SiO2/Si without any metal catalysts by chemical vapor deposition. Raman spectroscopy and mapping confirm the monolayer, bilayer and few-layer nature of the graphene with a high coverage over ∼95%. Ultraviolet photoemission spectroscopy verifies that the monolayer graphene and AB-stacked bilayer graphene have a work function of 4.46 eV and 4.50 eV, respectively, which are close to that of the intrinsic graphene. This is in contrast to the much lower work function of 4.26 eV observed on Cu-catalyzed graphene probably due to contaminants produced during the transfer process. Field-effect transistors were directly fabricated on graphene/SiO2/Si for evaluating their electric properties. Importantly, we reveal a crucial role of SiO2 layer thickness in controlling the graphene structure: (1) monolayer graphene preferably grown on thick SiO2 layer (∼300 nm or higher) by a surface-catalyzed process, and (2) AB-stacked bilayer or few-layer graphene favorably formed on thin SiO2 layer by a surface-adsorption/precipitation process. This study sheds light on the graphene growth mechanism on SiO2/Si and this insightful understanding is important to large-scale, controllable CVD growth of graphene in absence of metal catalysts.

•Interfacial effect is prominent in ferroelectric thin film capacitors (≪ 500 nm).•Relaxor ferroelectric contribution persists up to 200 °C for 500 nm film.•Thicker films allow optimal dielectric and relaxor ferroelectric contributions.•Energy storage efficiency ~ 70% achieved for 500 nm film up to 200 °C.The influence of temperature on the energy storage behavior of relaxor-ferroelectric epitaxial Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) thin film capacitors fabricated using pulsed laser deposition was evaluated using cyclic current-voltage measurements from 25 °C to 225 °C in order to elucidate ferroelectric and dielectric contributions across the Curie temperature (Tc). In the film thickness range of 125 nm to 500 nm, it has been found that the leakage current through the capacitors increases monotonically with increasing temperature and the effect is more prominent at smaller film thickness, primarily due to a more efficient movement of ferroelectric domains. While these effects prevent thinner PLZT films from maintaining adequate energy storage efficiencies at temperatures above ~ 100 °C, thicker films show promising energy storage properties in a wide temperature range. Specifically, the 500 nm thick PLZT film capacitors have a nearly constant energy storage efficiency above ~ 70% in the temperature range of 25 °C to 175 °C, with a peak efficiency of 78% at 175 °C due to the large dielectric constant exceeding ~ 2000 as the temperature approaches the PLZT Tc of 200 °C. By quantifying the three contributions of the electric conductivity, dielectric capacitance, and relaxor-ferroelectric domain switching polarization to temperature dependent energy storage properties of relaxor-ferroelectric capacitors, this study reveals that the dielectric contribution dominates in the PLZT capacitors with smaller thickness, while even contributions from all three components are present in films of larger thickness. These results suggest that the PLZT relaxor-ferroelectric thin film capacitors are promising for energy storage applications and further improvement of performance may be achieved by optimization of the film/electrode interface.

A transition in source–drain current vs. back gate voltage (ID–VBG) characteristics from extrinsic polar molecule dominant hysteresis to anti-hysteresis induced by an oxygen deficient surface layer that is intrinsic to the ferroelectric thin films has been observed on graphene field-effect transistors on Pb0.92La0.08Zr0.52Ti0.48O3 gates (GFET/PLZT-Gate) during a vacuum annealing process developed to systematically remove the polar molecules adsorbed on the GFET channel surface. This allows the extrinsic and intrinsic hysteresis on GFET/PLZT-gate devices to detangle and the detection of the dynamic switch of electric dipoles using GFETs, taking advantage of their high gating efficiency on ferroelectric gate. A model of the charge trapping and pinning mechanism is proposed to successfully explain the transition. In response to pulsed VBG trains of positive, negative, as well as alternating polarities, respectively, the source–drain current ID variation is instantaneous with the response amplitude following the ID–VBG loops measured by DC VBG with consideration of the remnant polarization after a given VBG pulse when the gate electric field exceeds the coercive field of the PLZT. A detection sensitivity of around 212 dipole per μm2 has been demonstrated at room temperature, suggesting the GFET/ferroelectric-gate devices provide a promising high-sensitivity scheme for uncooled detection of electrical dipole dynamic switch.

Transparent nanostructured glass coatings, fabricated on glass substrates, with a unique three-dimensional (3D) architecture were utilized as the foundation for designing plasmonic 3D transparent conductors. Transformation of the nonconducting 3D structure to a conducting porous surface network was accomplished through atomic layer deposition of aluminum-doped zinc oxide (AZO). After AZO growth, gold nanoparticles (AuNPs) were deposited by electron-beam evaporation to enhance light trapping and decrease the overall sheet resistance. Field emission scanning electron microscopy and atomic force microcopy images revealed the highly porous, nanostructured morphology of the AZO-coated glass surface along with the in-plane dimensions of the deposited AuNPs. Sheet resistance measurements conducted on the coated samples verified that the electrical properties of the 3D network are comparable to those of untextured two-dimensional AZO-coated glass substrates. In addition, transmittance measurements of the glass samples coated at various AZO thicknesses showed preservation of the transparent nature of each sample, and the AuNPs demonstrated enhanced light scattering as well as light-trapping capabilities.Keywords: aluminum-doped zinc oxide; atomic layer deposition; nanostructured glass; plasmonic effect; three-dimensional electrode; transparent conductor;

This work explores nucleation and epitaxy of graphene on crystalline Cu2O templates formed via self-assembly and surface reduction of Cu2O nanocrystallites on the cubic textured (100) orientation Cu (CTO-Cu) and polycrystalline Cu (poly-Cu) substrates, respectively. It has been found that the presence of sub-surface oxygen causes the reconstruction of Cu surface due to the formation of oriented Cu2O nanocrystallites at a low H2 gas flow. Self-assembly of the Cu2O nanocrystallites into a textured surface template provides direct nucleation sites for graphene growth after the oxygen-sublattice on the template surface is reduced. The atomic Cu surface layer provides advantages of high graphene growth rate due to the catalytic role of Cu and in-plane alignment of graphene nuclei. It is particularly important that the Cu2O crystallites have predominantly (111) orientation aligned to each other in the plane of the (100) CTO-Cu substrates, which allows epitaxy of graphene with much lower defect density as compared to that in the poly-Cu case. Since Cu2O (111) templates may be developed on lattice matched (100) surfaces of other dielectric materials, this self-assembly approach provides a promising pathway for large-scale, transfer free graphene epitaxy on nonmetallic surfaces.

AB-stacked bilayer graphene has attracted considerable attention due to its feasibility of band gap tuning. Although synthesis of bilayer graphene on Cu has been reported using chemical vapor deposition (CVD) through a layer-by-layer growth mechanism, the process is long and complicated due to lack of catalytic assistance of Cu to the second graphene layer growth. Here we show that theoretical modeling demonstrates an alternative synchronous growth of bilayer graphene on Cu is possible by passivating the top graphene nuclei edges with hydrogen to allow carbon diffusion underneath the top graphene nuclei for bottom graphene layer formation. Moreover, such a growth mechanism has been achieved experimentally in a facile CVD method by simply controlling the H2 pressure. Bilayer graphene with high coverage of over ∼95% and a high AB stacking ratio of up to ∼90% has been obtained within a short growth time of 30 min. Also, graphene with single, double and multiple layers can be obtained by simply controlling the hydrogen pressure. This result represents the demonstration of the fast synchronous AB-stacked bilayer graphene growth, which is important to scalable manufacture of graphene with controllable layer number and stacking required for practical applications.

Plasmonic gold nanoparticles (AuNP) with controllable dimensions have been fabricated in situ on graphene at moderately elevated temperature for high sensitivity surface enhanced Raman spectroscopy (SERS) of Rhodamine 6G (R6G) dye molecules. Significantly enhanced Raman signature of R6G dyes were observed on AuNP/graphene substrates as compared to the case without graphene with an improvement factor of 400%, which is remarkably greater than previous results obtained in ex situ fabricated SERS substrate. Simulation of localized electromagnetic field around AuNPs with and without the underneath graphene layer reveals an enhanced local electromagnetic field due to the plasmonic effect of AuNPs, while additional Ohmic loss occurs when graphene is present. The enhanced local electromagnetic field by plasmonic AuNPs is unlikely the dominant factor contributing to the observed high SERS sensitivity on R6G/AuNP/graphene substrate. Instead, the p-doped graphene, which is supported by the large positive Dirac point shift away from “zero” observed in AuNP/graphene field effect transistors, promotes SERS signals through enhanced molecule adsorption and non-resonance molecular–substrate chemical interaction.

The energy storage properties of Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) films grown via pulsed laser deposition were evaluated at variable film thickness of 125, 250, 500, and 1000 nm. These films show high dielectric permittivity up to ∼1200. Cyclic I–V measurements were used to evaluate the dielectric properties of these thin films, which not only provide the total electric displacement, but also separate contributions from each of the relevant components including electric conductivity (D1), dielectric capacitance (D2), and relaxor-ferroelectric domain switching polarization (P). The results show that, as the film thickness increases, the material transits from a linear dielectric to nonlinear relaxor-ferroelectric. While the energy storage per volume increases with the film thickness, the energy storage efficiency drops from ∼80% to ∼30%. The PLZT films can be optimized for different energy storage applications by tuning the film thickness to optimize between the linear and nonlinear dielectric properties and energy storage efficiency.Keywords: energy storage; PLZT film; relaxor ferroelectrics; solid-state dielectric capacitors

High-aspect-ratio, vertically aligned carbon nanofibers (VACNFs) were conformally coated with aluminum oxide (Al2O3) and aluminum-doped zinc oxide (AZO) using atomic layer deposition (ALD) in order to produce a three-dimensional array of metal–insulator–metal core–shell nanostructures. Prefunctionalization before ALD, as required for initiating covalent bonding on a carbon nanotube surface, was eliminated on VACNFs due to the graphitic edges along the surface of each CNF. The graphitic edges provided ideal nucleation sites under sequential exposures of H2O and trimethylaluminum to form an Al2O3 coating up to 20 nm in thickness. High-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy images confirmed the conformal core–shell AZO/Al2O3/CNF structures while energy-dispersive X-ray spectroscopy verified the elemental composition of the different layers. HRTEM selected area electron diffraction revealed that the as-made Al2O3 by ALD at 200 °C was amorphous, and then, after annealing in air at 450 °C for 30 min, was converted to polycrystalline form. Nevertheless, comparable dielectric constants of 9.3 were obtained in both cases by cyclic voltammetry at a scan rate of 1000 V/s. The conformal core–shell AZO/Al2O3/VACNF array structure demonstrated in this work provides a promising three-dimensional architecture toward applications of solid-state capacitors with large surface area having a thin, leak-free dielectric.Keywords: 3D electrode; atomic layer deposition; conformal coating; core−shell nanostructure; vertically aligned carbon nanofiber array;

Chemical vapor deposition of graphene on copper foil is an attractive method of producing large-area graphene films, but the electronic performance is limited by defects such as creases from the film transfer process, wrinkles due to the thermal expansion coefficient mismatch, and grain boundaries from the growth process. Here we present an all-optical technique to correlate defect structure with electronic properties using spatially resolved Raman spectroscopy and transient absorption microscopy. This technique is especially attractive since it does not require any lithographic steps to probe the electronic properties of the graphene film. As a first demonstration, we focus on the effects of both wrinkles and creases while averaging over many small grains. It was found that wrinkles and creases may decrease the charge carrier diffusion coefficient by over 50% due to increased defect scattering. This technique may easily be extended to large grain graphene films in order to study the effect of different types of grain boundaries.Keywords: chemical vapor deposition; defects; grain boundaries; graphene; Raman spectroscopy; transient absorption microscopy;

Efficient exciton dissociation is crucial to obtaining high photonic response in photodetectors. This work explores implementation of a novel exciton dissociation mechanism through heterojunctions self-assembled at the graphene/MWCNT (multiwall carbon nanotube) interfaces in graphene/MWCNT nanohybrids. Significantly enhanced near-infrared photoresponsivity by nearly an order of magnitude has been achieved on the graphene/MWCNT nanohybrids as compared to the best achieved so far on carbon nanotube (CNT) only infrared (IR) detectors. This leads to a high detectivity up to 1.5 × 107 cm·Hz1/2·W–1 in the graphene/MWCNT nanohybrid, which represents a 500% improvement over the best D* achieved on MWCNT film IR detectors and may be further improved with optimization on the interfacial heterojunctions. This approach of the self-assembly of graphene/CNT nanohybrids provides a pathway toward high-performance and low-cost carbon nanostructure IR detectors.Keywords: carbon nanotube; graphene; infrared detector; photoresponse;

Despite the potentials and the efforts put in the development of uncooled carbon nanotube infrared detectors during the past two decades, their figure-of-merit detectivity remains orders of magnitude lower than that of conventional semiconductor counterparts due to the lack of efficient exciton dissociation schemes. In this paper, we report an extraordinary photocurrent harvesting configuration at a semiconducting single-walled carbon nanotube (s-SWCNT)/polymer type-II heterojunction interface, which provides highly efficient exciton dissociation through the intrinsic energy offset by designing the s-SWCNT/polymer interface band alignment. This results in significantly enhanced near-infrared detectivity of 2.3 × 108 cm·Hz1/2/W, comparable to that of the many conventional uncooled infrared detectors. With further optimization, the s-SWCNT/polymer nanohybrid uncooled infrared detectors could be highly competitive for practical applications.

Transparent conductors (TCs) are an important component of optoelectronic devices and nanoscale engineering of TCs is important for optimization of the device performance through improved light trapping. In this work, patterned periodic arrays of nanopillars and nanolines of pitch size of ∼700 nm were created on fluorine-doped tin oxide (FTO) using nanoimprint lithography and reactive ion etching using environmentally friendly gases. The patterned FTO exhibits enhanced light trapping as compared to the unpatterned FTO, which agrees well with simulations based on Finite-Difference Time-Domain method for up to a distance of 4 μm. Dye sensitized solar cells (DSSCs) fabricated on the patterned FTO exhibited improved performance (fill factor and power conversion efficiency), which can be attributed to enhanced light absorption in the range 400–650 nm. Further, electrochemical impedance measurements revealed lower recombination resistance for the patterned FTO/TiO2 electrode compared to the unpatterned FTO electrode/TiO2 electrode as a result of better light capturing properties of patterned FTO. The direct fabrication of nanopatterns on TCs developed in the present study is expected to be a viable scheme for achieving improved performance in many other optoelectronic devices.Keywords: dye sensitized solar cells; fluorine-doped tin oxide; light scattering; nanoimprint lithography; nanopatterned transparent conductors; photovoltaic;

A thermal vapor transport process has been employed for fabrication of boron-related (boron, boron–silicon alloys, and MgB2) nanowire films on Au-coated Si and MgO substrates. Tangled polycrystalline as well as aligned single-crystalline boron nanowires (BNWs) have been obtained and their growth mechanism investigated at different growth temperatures, cooling rates, and vapor sources. The growth temperature was found critical to the nucleation of the BNWs and different growth modes were observed in different temperature ranges. The temperature ramping rate in the cooling process after the high-temperature growth of the BNWs was found crucial for the formation of crystalline structures and for controlling the alignment of BNWs. We have observed that slow cooling at 1–5 °C/min resulted in non-textured BNWs, while fast cooling at ∼90 °C/min induced crystallization of the non-textured BNWs. We have also found that the alignment of the BNWs depended on the cooling rate. At a slow cooling rate the BNWs were heavily tangled while at a higher cooling rate they aligned well with the normal of the substrate. By manipulating the growth parameters, we have obtained two types of nanowire junctions. One was via fusing two nanowires together and the other, via joining them with another material.

Hg-based high-temperature superconductors (Hg-HTSs) have a similar layered structure to that in most other superconducting cuprates. The weakly attached Hg cations can be swapped with Tl ones in a cation exchange process, which allows exploration of the physical properties associated closely to the charge reservoir block change as a consequence of the Hg–Tl cation exchange. This paper intends to provide an overview of over a decade long investigation of Hg(Tl)-HTSs thin films processed in forward and reverse cation exchange, and from which to elucidate the interesting aspects that are related to the superconductivity of these fascinating materials.

Combining the high mobility of graphene and surface electron depletion effect of zinc oxide nanoparticles (ZnO-NPs), graphene/ZnO-NP nanohybrids can be anticipated for significantly enhanced photoresponsivity and photoconductive gain in optoelectronics. Herein, a transfer-free and printable method was developed for the fabrication of wafer-size graphene/ZnO-NP nanohybrids for high-performance UV photodetectors. These photodetectors achieved the extraordinary photoresponsivity of up to 1000 A W−1 V−1 and high gain of 1.8 × 104, representing more than an order of magnitude improvement compared to that of previously reported UV photodetectors based on various ZnO nanostructures and transferred-graphene/ZnO nanohybrids. Our method provides a low-cost pathway for the run-to-run wafer-size fabrication of high-performance graphene/ZnO optoelectronics.