A proposal of a semiconductor-integrated self-complementary bow-tie antenna towards a terahertz transmitter

H. Yamakura, Y. Ishiguro, Y. Kato, M. Suhara
2016 2016 41st International Conference on Infrared, Millimeter, and Terahertz waves (IRMMW-THz)  
We propose a self-complementary bow-tie antenna-integrated resonant-tunneling-diode relaxation oscillator and investigate its oscillation/radiation characteristics. In the investigation, we establish a physics-based equivalent circuit model of the oscillator for taking the all physical phenomena related to the diode and the antenna into consideration simultaneously. In this paper, we report the equivalent circuit modeling and the large-signal oscillation/ radiation analysis of the oscillator.
more » ... gure 1 Schematics of a proposed oscillator. Figure 2 Block expressions of an equivalent circuit for the oscillator shown in Figure 1. Abstract The transient simulation of semiconductor devices using a deterministic Boltzmann equations solver is presented. In order to avoid the numerical difficulties originated from the conventional H-transformation, the kinetic-energy-based scheme is adopted. Within the kinetic-energy-based scheme, the transport parameters become time-independent, therefore, implementing the transient simulation capability can be done easily. Preliminary results for a device are shown. Figure1 (a) DC IV characteristics of various N + NN + devices, which are obtained from the deterministic Boltzmann equation solver. (b) Transient results of an N + NN + device whose total length is 1200 nm. The DC bias voltage is 0.8 V. AC voltages of 1 THz with various amplitudes are applied to the anode terminal. The first two periods are simulated. Abstract Photocatalysis of hydrogen from water is limited by incomplete absorption of solar radiation and by uncontrolled disposition of generated carriers. Nanoantenna (NA)-induced coupling of photons to excitons could enhance photocatalytic solar fuel generation by increasing broadband optical absorption and by injecting energetic electrons where NA interfaces with semiconductor catalyst. This work examined catalysis of hydrogen evolution reaction (HER) by monolayer (1L) transition metal dichalcogenide (TMD) with and without decoration by optical NA. Spectroscopic and microscopic characterization of heterostructures of 1L-TMD and NA self-assembled via exfoliation and redox chemistry was compared with discrete dipole simulation. Electrodes inked with 1L tungsten disulfide (WS 2 ) onto which NA was electrochemically reduced exhibited higher HER relative to 1L-WS 2 in neat or physically NA-decorated forms as measured by linear sweep and cyclic voltammetry. Coordinated simulation and measurement of supports improved design of 1L-TMD-NA photocatalysts and their implementation in chemical, biological, energy and water systems. Abstract View Online References [1] X.-Y. Pen; J.-H. Teng; X.-H. Zhang; Y.-L. Foo, Distortion analysis of pulsed terahertz signal measured with spectral-encoding technique. Abstract Broadband terahertz (THz) radiation from laser-plasma interaction and a corresponding broadband THz time domain spectroscopy based on optically-air-biased-coherent-detection technique are presented. One of the singleshot detection techniques for THz time domain spectroscopy, the spectral-encoding technique, is also reviewed [1]. Distortions of the signals measured by this technique and the corresponding strategies to reduce them are demonstrated [2]. Figure 1. (a) Attenuated and corrected THz waveforms using 10 Si wafers as attenuators vs. the original strong THz signal. (b) THz spectrum of the corrected THz signal with 10 Si wafers vs. that of the original one. Abstract View Online References [1] Yamamoto T.; Notomi M.; Taniyama H.; Kuramochi E.; Yoshikawa Y.; Torii Y.; Kuga T, Design of a high-Q air-slot cavity based on a width modulated line-defect in a photonic crystal slab. Optics Abstract Based on the air-slot line-defected photonic crystal nano-cavity [1], here we develop a monolithic integration of photonic crystal optomechanical oscillators and on-chip high speed Ge detectors (see Figure 1 ) by using the silicon CMOS platform. With the generations of both high harmonics (up to 59th order) and subharmonics (down to 1/4), due to strong mutual couplings between optomechanical self-sustained oscillation and self-pulsation oscillation, our chipset provides multiple low phase noise frequency tones [2] for applications in both frequency multipliers and dividers. The synchronization between two mechanical modes [3] and dynamical chaos [4] in the optomechanical cavity are reported as well. These characteristics enable optomechanical oscillators as a frequency reference platform for radio-frequency-photonic information processing. Abstract Terahertz technology promises unique applications in high speed communication, high accuracy imaging and so on [1]. However, one major bottleneck for developing Terahertz application systems is the lack of high-performance dynamic devices for effectively manipulating the Terahertz wave. In recent years, the rapid development of twodimensional electron gas (2DEG) devices provides a promising way to develop dynamic terahertz devices [2]. Here, we combined a stagger-netlike metamaterial array with high-electron-mobility transistor (HEMT) structure to form a electronic grid-controlled THz modulator. By controlling the carrier concentration of 2DEG, the mode conversion between two kinds of dipolar resonances has been realized. Modulation depth of this device can reach up to 94%. More importantly, in the dynamic test, 600 MHz sinusoidal signals was received by a THz detector. It may provide a way to achieve effective active devices in THz wireless communication system. Figure 1. (a) 3-D structure of a GaN HEMT metamaterial unit cell. (b) Schematic of the THz modulator. (c)Simulation transmission spectrum results with different carrier density. (d) Image of packaged THz modulator. (e)The received sinusoidal modulating signals. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License. Abstract Nano-Micro Conference Published by Nature Research Society http://nrs.org Abstract Terahertz (THz) wave, bridging electronics and photonics in the electromagnetic spectrum, features many exotic properties and promising applications. However, because of low THz emission efficiency, less sensitive detectors, and few manipulating devices, THz wave is still on the horizon for practical applications since 1980s. With the application of femtosecond laser, THz surface emission spectroscopy has also been developed to serve as a sensitive and contactless tool for the optoelectronic measurement of semiconductor surfaces and interfaces. When a femtosecond laser beam impinges on the semiconductor surface, photocarriers or photodipoles are excited, which then induce THz radiation with the mechanism of photoconductivity or optical rectification. As the THz surface emission is sensitive to the surfaces and interfaces, the modification of the semiconductor surface provides a significant strategy for the design and performance evaluation of many electronic and optoelectronic devices for THz applications. In this talk, we will discuss the THz radiation mechanism for traditional semiconductors by changing the crystal orientation, exciting laser intensity, surface condition, and so on [1][2][3][4]. We will also discuss THz radiation from two-dimensional layered semiconductors under linearly polarized femtosecond laser excitation. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License. Abstract Here we present our recent work on tuning the polarization of terahertz waves via subwavelength metallic gratings. Firstly, we have experimentally demonstrated a linear polarization rotator that is a three-layer metallic grating structure for manipulating the polarization of broadband terahertz waves. By mechanical rotations of the composite grating layers, this freely tunable device can rotate the polarization of a linearly polarized THz wave to any desired direction with high conversion efficiency [1]. Then we theoretically investigate the propagation of terahertz waves through a graphene-loaded metal grating under external magnetic field. It is found that resonant modes in the system can be converted between transverse-electric and transverse-magnetic polarizations due to Hall conductivity of grapheme, as a consequence, asymmetric transmission of terahertz waves through this graphene-loaded metal grating is achieved, and it can be tuned by adjusting either the external magnetic field or the Fermi level of grapheme [2]. These tunable terahertz devices have potential applications in various areas, such as material analysis, wireless communication, and terahertz imaging. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License. Abstract Nano-Micro Conference Abstract View Online Abstract Since terahertz provides a wide frequency band, terahertz communication realizes a data rate exceeding 100 Gbps approaching fibre-optic speed. The frequency band from 252 to 275 GHz has already been allocated for communication. Further discussion is being made to use the frequency band exceeding 275 GHz, which has not been assigned yet, for communication use. On the other hand, since terahertz has large atmospheric attenuation and strong directivity, it is limited to short-distance fixed radio communication. However, it is long-distance and mobile application that is intrinsically expected for wireless communication. In this talk, even in terahertz, it is shown that kilometre communication is potentially possible by selecting the frequency appropriately. It is also shown that terahertz communication can be performed using CMOS process, which was said to have inferior high frequency characteristics to compound semiconductors. How will the world change when technologies beyond such conventional common sense are established? The impact of terahertz communication and the contribution of CMOS transceivers are discussed. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License. Abstract By supporting tens or hundreds GHz bandwidths, Terahertz (THz)-band (0.1-10 THz) communication is envisioned as a key wireless technology of the next decade. The THz band will help overcome the spectrum scarcity problems and capacity limitations of current wireless networks, by providing an unprecedentedly large bandwidth. In addition, THz-band communication will enable a plethora of long-awaited applications, both at the nano-scale and at the macro-scale, ranging from wireless massive-core computing architectures and instantaneous data transfer among non-invasive nano-devices, to ultra-high-definition content streaming among mobile devices and wireless highbandwidth secure communications. In this invited speech, an overview of THz-band communications will be provided. First, the current progress and open research directions in terms of THz-band channel modeling will be presented. The main phenomena affecting the propagation of THz signals will be explained and their impact on the channel capacity will be assessed. Second, novel communication mechanisms such as the modulation techniques, resource allocation, timing acquisition schemes, and Ultra-Massive Multiple-Input Multiple-Output (UM-MIMO) will be presented. Finally, the state of the art and open challenges in the network layer design and other relevant research directions will be stated. This presentation is expected to provide the audience with the necessary knowledge to work in a cutting-edge research field, at the intersection of antennas and propagation, and information and communication technologies. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License. Abstract Advanced optical fiber communication technologies enable low-loss and broad-bandwidth transmission in the millimeter-wave and terahertz-wave bands via an optical fiber network. Precise optical modulation techniques can directly generate the millimeter-wave signals, and finally, an optical frequency comb signal generated by the modulation also provides the terahertz-wave signals by optical heterodyning systems. These technologies on the signal generation could be utilized for realization of distributed antenna system in the millimeter-and terahertz-wave bands based on the optical fiber network for some specific applications: foreign object debris detection systems for airport runway surveillance and high-speed railway radiocommunication systems between train and trackside. In the talk, we briefly introduce the R&D activities on the millimeter-and terahertz-wave for both wireless communication and radar/non-destructive imaging systems based on photonics. Abstract Metamaterials with many unique optical properties are made of periodically arranged sub-wavelength metallic structures that are able to couple to external electromagnetic (EM) waves. One of such structures is the commonly used split-ring-resonators (SRR). In this talk, I will discuss and demonstrate some new progress we made on SRRbased terahertz metamaterials. By looking into the coupling between SRRs and the effect of incident polarization, we proposed a way to continuously modulate their resonances, changing the transmission intensity at resonant frequency from 20% to 80% [1]. We also designed a SRR-based polarization-insensitive broadband filter in THz range and discovered its effect in eliminating asymmetric characteristics in device structure [2]. A stop band with bandwidth of as large as 1.40 THz was achieved. To improve the fabrication process, a facile metal transfer method was employed to create SRR patterns on PDMS surface, planar and otherwise, as well as PDMS-coated surfaces, such as paper, fabric and leaf [3]. Lastly, a design of 3D THz metamaterial device was proposed to be used in biomedical field for cancer cell studies, exploiting its structural similarities with the single-cell-capturing microfluidic devices. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License. Abstract In recent years, more and more attention has been paid on the research and development of terahertz (THz) technologies all over the world. Biosensing in one of the most important applications of THz waves. Metasurface is an artificial two-dimensional material with flexible structures and good electromagnetic wave control capability, which is very suitable for THz wave control and sensing. In this work, a L-shape metasurface THz biosensor was designed, simulated, optimized, micro-fabricated, and finally tested by the time-domain spectroscopy (TDS) system. Abstract Graphene and carbon nanotube present unique structure and excellent properties, such as high specific surface area, high conductivity, high thermal conductivity, etc., and play an increasingly important role in the electrochemical energy storage and conversion. The doping of nano-carbon with nitrogen and boron can modulate the electron and energy band structure, and further improve its physical and chemical properties. The pore structure, pore size distribution and wall thickness of the electroactive material display important effect on the electrolyte infiltration, the ion transport and adsorption, and the overall performance of the battery. The use of doped nano-carbon and porous composite structure can improve the conductivity and the electrochemical surface area and reaction sites of the electroactive materials, and significantly increase the efficiency of energy storage and conversion. This presentation focuses on some progresses of the doped nano-carbon and porous composite structures, including the following three aspects: (1) The controllable synthesis and electrochemical lithium insertion characteristics of the porous electrode materials. Porous materials have been widely used in a variety of fields, but their large-scale controllable synthesis is still a considerable challenge. We have designed a novel templated freeze-drying method to conveniently control the porous properties of materials, which has been successfully applied to the synthesis of various porous phosphates, oxides and composites, and the electrochemical lithium storage properties have been explored. (2) The porous lithium iron phosphate and nitrogen-doped graphene composite. Three-dimensional porous microspheres composed of LiFePO 4 and nitrogen-doped graphene have been synthesized by a solvothermal method. The effect of graphene doping on the nucleation and growth of LiFePO 4 and the influence of the unique selfassembled porous microsphere structure on the electrochemical lithium insertion performance have been studied. (3) Supercapacitance properties of doped graphene. A series of dopant graphene materials have been facilely synthesized by a thermal solid state reaction. The regulation of doping configuration on the electronic structure of graphene and the influence on the supercapacitance have been systematically studied. The relevant mechanisms have been proposed and some phenomena in the literature have been reasonably explained. Abstract Recently nano-structural carbons have become the most widely used electrode materials in supercapacitor community, because of their high specific surface area, good electrical conductivity, chemical stability in a variety of electrolytes, and relatively low cost. In particular, graphene-based carbons are emerging as an auspicious candidate due to the unique feature of grphane. Among electrolytes used for supercapacitors, ionic liquids (ILs) have been becoming a promising class of them, owing to their exceptionally wide electrochemical stability window, excellent thermal stability, non-volatility and relatively inert nature. Despite considerable work on supercapacitor with graphene-based carbon as electrodes, the details of what happens under nano-confinement, including pores, still require in-depth exploration especially for IL electrolytes. We studied the interfacial phenomena occurring between ILs and graphene-based electrodes in supercapacitors, using the combined molecular dynamics (MD) simulation by modeling ILs-based EDLs at planar, cylindrical, spherical electrode surfaces and inside electrode pores at nano/micro-scale. This talk would include: 1) MD modeling on ILs-based EDLs at open surfaces (e.g., planar, cylindrical, spherical, with defects, etc.) [1][2] and the integration with experiments (e.g., atomic force microscopy, AFM) [3][4], which would focus on the EDL structure and its influence from ion size, ion type, applied potential, electrode curvature, etc. 2) MD modeling on ILs-based porous carbon supercapacitors [5][6][7], which would embody the pore size effects on capacitance, the ion dynamics under porous confinement, and pore expansion during charging. 3) The anatomy of electrosorption for water in ionic liquids at electrified interfaces [8], which would show, for the first time, the work on the adsorption of water on electrode surfaces in contact with humid ILs. Situ Study of Anion and Cation Insertion into Porous Carbon Electrodes with Different Pore Sizes. Abstract Mesoporous carbon materials are being in vogue because of their intriguing properties and wide potentials. Doping of heteroatoms, especially N, in carbons have attracted enormous interests owing to its capability in enhancing or expanding their applicability in separation, energy conversion and catalysis. In addition, N-doping can further boost dually doped carbons, such as with S and metal as the second dopant. Such a dual doping could possibly optimize material property and maximize performance through synergistic effects. In this talk, several synthetic methods, such as post modification [1-2], one-step solvent-free nano-confining synthesis [3][4] and spray-drying-assisted assembly [5], for the synthesis of heteroatom (singly or dually) porous carbon materials with different porosities and structures will be introduced and discussed. Furthermore, the controllable synthesis of metal/heteroatom dually doped mesoporous carbons with desirable fascinating properties will be introduced. The demo-applications of these materials in typical adsorption, such as arsenic removal and CO 2 capture, and typical catalysis, such as oxygen reduction, biodiesel production and dehydrogenation/hydrogenation coupling reactions, will be presented and their structure-performance correlations will be discussed. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License. Abstract Chemical vapor deposition (CVD) is a simple but powerful technique to synthesize thin films of various materials. It can also be used to synthesize nano-structured materials if it is used with nano-structured templates or catalysts. We have developed separate flow CVD system to make multilayered transition metal dichalcogenides (TMDCs) or doped layers [1,2]. We used the apparatus to make nanocomposite between carbon nanotube and MoS 2 that was applied to photovoltaic applications (Figure 1) [3]. We also describe the search for the catalysts to make TMDC nanostructures. Abstract Advanced materials for electrocatalytic andphotoelectrochemical water splitting are central to the area of renewable energy. Recently, two dimensional layered materials of MX 2 (M: Mo, W; X:S, Se, etc.) have emerged as a new kind of catalysts for such applications. Our group have reported the direct synthesis of high-quality, domain size tunable, strictly monolayer MoS 2 flakes on commercially available Au foils by a chemical vapor deposition (CVD) method. The nano-sized triangular MoS 2 flakes on Au foils are proven to be excellent electrocatalysts for hydrogen evolution reaction (HER), featured by a rather low Tafel slope (61 mV/dec) and a relative high exchange current density (38.1 μA/cm 2 ). The excellent electron coupling between MoS 2 and Au foils is considered to account for the extraordinary HER activity [1]. Furthermore, via a facile all-CVD approach, we have also demonstrated the direct growth of monolayer MoS 2 on graphene (MoS 2 /Gr) over Au foils [2,3]. A dramatic decrease of the bandgap from ~2.20 to ~0.30 eV was detected at the domain edge of MoS 2 within a lateral distance of ~6 nm, as evidenced by STM/STS observations. The edges of monolayer MoS 2 nano-sheets were thus served as narrow-gapquantum wires, which can greatly facilitate the electrocatalytic property of MoS 2 in HER [4]. Meanwhile, we also synthesized either MoS 2 /WS 2 or WS 2 /MoS 2 vertical heterostructures on Au foils by a growth-temperature-mediated, selective two-step CVD strategy. Relative enhancement or reduction in the photocatalytic activities were observed for MoS 2 /WS 2 and WS 2 /MoS 2 in HER under illumination, respectively. This is explained from the type-II band alignment of the MoS 2 / WS 2 stack that enables effective electron-hole separation and fast electron transfer kinetics, as well as directional electron flow from electrode to catalytically active sites [5]. The abovementioned efforts are expected to establish the internal relationship between the metallic edge states of MoS 2 and its HER performances, as well as the advantage of MX 2 /MX 2 vertical stacks in photocatalytic HER applications. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License. Abstract Transition-metal dichalcogenides (TMDs) are novel layered materials for various kind of application. In particular, those formed in hexagonal prismatic structure (Figure 1a) with group-VIB transition-metal are semiconductors in nature and show good transistor performance and strong light-matter interaction. However, the potential application of group-VIB TMDs is not only limited to such general electronics and optics, but also covers next-generation electronics of spintronics and valleytronics including the coupling to the optical polarization (Figure 1b) [1]. Owing to the lack of the inversion centre in the individual layer, the six conduction band minima and valence band maxima at the edge of the hexagonal Brillouin zone split into two groups, creating a valley degree of freedom. Optical interband transition at these high symmetry points are further coupled to the helicity of light. In addition, the heavy transition-metal elements leads to a large spin-orbit interaction and a consequent spin splitting. Here, I will report our recent research aiming at next-generation electronics, including optoelectronic device utilizing valley degree of freedom [2,3] and the fundamental investigation of the spin relaxation in TMDs [4]. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License. © The Author(s) 2017 Figure 1. Crystal structure (a) and band structure (b) of group-VIB transition-metal dichalcogenides. Abstract Freestanding flexible Si nanoparticles-multi-walled carbon nanotubes (SiNPs-MWNTs) composite paper anodes for Li-ion batteries (LIBs) have been prepared using a combination of ultra-sonication and pressure filtration. No conductive additive, binder or metal current collector is used. The SiNPs-MWNTs composite electrode material achieves first cycle specific discharge and charge capacities of 2298 and 1492 mAh/g, respectively. To address the first cycle irreversibility, stabilized Li metal powder (SLMP) has been utilized to pre-lithiate the composite anodes. As a result, the first cycle irreversible capacity loss is reduced from 806 to 28 mAh/g and the first cycle coulombic efficiency is increased from 65% to 98%. The relationship between different SLMP loadings and cell performance has been established to understand the pre-lithiation process of SLMP and to optimize the construction of Si-based cells. A cell containing the pre-lithiated anode is able to deliver charge capacity over 800 mAh/g without undergoing the initial discharge process, which enables the exploration of novel cathode materials. It was also found out the SiNPs-MWNTs electrode with 3:2 Si/MWNT ratio exhibits the optimal balance between the high capacity of SiNPs and the high electrical conductivity and structural stabilization quality of MWNTs, leading to a high rate capability, high specific capacity, and cycle life surpassing the conventional slurry-cast SiNPs electrode using binder and Cu current collector. The reversible capacity is 1866 mAh/g (based on the total composite weight, the same below) at current density of 100 mA/g. After 100 cycles, the electrode retains capacity of 1170 mAh/g at 100 mA/g and 750 mAh/g at 500 mA/g. The superior performance is believed to be due to the cooperative or even synergistic effect achieved by the optimal combination. Furthermore, the freestanding feature of our electrode eliminates the non-active mass, which is promising for enhanced capacity and energy density of Li-ion cells. Abstract Open Access This article is licensed under a Creative Commons Attribution 4.0 International License. Abstract Use of energy storage devices such as lithium ion batteries (LIBs) can help to mitigate the problem of intermittent photovoltaic (PV) power to achieve higher PV penetration into the electric grid. Also, the benefit of deployment of electric vehicles for energy sustainable future seems rather irrelevant unless they are charged using electricity generated from renewables. In addition, large scale practical applications of battery based electric vehicles is still challenging because of the inflexibility it has with the charging stations. All these issues can be addressed by use of solar cells as a viable energy source to charge lithium ion batteries. Here we demonstrate simple, efficient and cost effective photo-charging design approach where the use of promising low cost solar cells such as perovskite solar cell or dye sensitized solar cell with the help of DC-DC power conversion can efficiently charge a Li 4 Ti 5 O 12 -LiCoO 2 LIB. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License. Abstract In this work, the flexible fiber-shaped supercapacitors have been fabricated by using the conductive polymers and graphene as the electrodes. The prepared fiber-shaped electrodes show good mechanical properties and excellent electrochemical performances. They can be easily knoted, twisted and woven into different shapes without sacrificing their electrochemical properties [1][2]. Abstract Open Access This article is licensed under a Creative Commons Attribution 4.0 International License. Abstract Published by Nature Research Society http://nrs.org Abstract In fuel cells and metal-air batteries, there are critical chemical reactions: oxygen reduction reaction (ORR), and oxygen evolution reaction (OER), respectively. These reactions, however, are sluggish and require noble metals (e.g., platinum) or their oxides as catalysts. The scarcity and high cost of noble metals have hampered the commercial applications of these technologies [1]. Therefore, it is necessary to search for alternative materials to replace Pt. Carbon nanomaterials, such as carbon nanotubes (CNTs) and graphene, are appealing as an alternative for metal-free catalytic applications because of their structures and excellent properties. Although the superior catalytic capabilities of heteroatom-doped carbon nanomaterials for ORR have been demonstrated, trial-and-error approaches are still used to date for the development of highly-efficient catalysts. To rationally design a catalyst, it is critical to correlate intrinsic material characteristics with catalytic activities. Through first-principles calculations, we have identified a material property that serves as the activity descriptor for both ORR and OER, and established a volcano relationship between the descriptor and the catalytic activities of the carbon-based nanomaterials [2]. The design principles can be used as a guidance to develop various new carbon-based materials for clean energy conversion and storage. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License. © The Author(s) 2017 Figure 1. Volcano relationships between the descriptor and the catalytic activities of the carbon-based nanomaterials. High performance NiO microsphere anode assembled from porous nanosheets for lithium-ion batteries. Abstract Carbon-based supercapacitor is also called electric double-layer capacitor that store energy via physical adsorption and desorption of ions from the electrolyte. Pseudocapacitors based on metal oxides or conductive polymers store energy via a redox process and generally have higher specific capacitance compared to the EDL type. Graphene has been regarded as an ideal candidate for supercapacitor applications, while the specific capacitance achieved so far in the lab, normally 200-300 F/g, is much lower than its theoretical value of 550 F/g. In order to enhance the charge storage capacity of graphene, we functionalized reduced graphene oxide by N-doping and adsorption of small molecules of hydrolysized polyimide (PI). In N-doped graphene, the N-O bonds are responsible for the enhanced capacitance owing to their pseudo capacitive property [1]. Further, we found that the hydrolysis of PI can release small molecules into water solution, and these aromatic molecules adsorbed onto graphene via π-π interaction have a significant effect in increasing the capacitance. With merely 3% weight increase after adsorption, the specific capacitance is about 40% increased. High capacitance over 420 F/g can be easily achieved from the functionalized graphene electrode in H 2 SO 4 aqueous electrolyte, even the electrode has high mass loading around 5 mg/cm 2 . In Li 2 SO 4 aqueous electrolyte that can extend the operation voltage window to 1.6 V, the specific capacitance also remains high around 400 F. References [1] T. . Nitrogen-doped mesoporous carbon of extraordinary capacitance for electrochemical energy storage. Science. 350, 1508Science. 350, -1513Science. 350, (2015. Figure 1. (a) Comparison to the electrochemical performance of N-doped graphene electrode before and after adsorption of hydrolysized PI molecules. (a) CV curves. (b) Capacitance Vs. discharging current density in galvanostatic CD measurement. Abstract Open Access This article is licensed under a Creative Commons Attribution 4.0 International License. Abstract The world's population is growing continuously and in close proportionality to thedemand on fossil fuels, which may lead to its depletion in the coming decades. Theability to harness energy from renewable resources is highly desirable for sustainableenergy economy. In recent years, photoelectrochemical (PEC) water splitting processbased on Earth-abundant semiconductor photocatalysts has gained considerable research interests for resolving energy and environmental issues. The PEC watersplitting that mimics the natural photosynthesis process can convert solar energy intostorable form of hydrogen (H 2 ) energy, which is a good energy vector to meet theescalating energy demand. To date, however, almost all singular semiconductor photocatalysts used demonstrated poor PEC performance for solarto-H 2 energy conversion. In this study, two different novel ternary nanostructured hematite-based photocatalysts of eRGO/C60/α-Fe 2 O 3 and eRGO/NiO/α-Fe 2 O 3 were synthesized, characterised and tested as photoanodes toward PEC water splitting application. Theternary nanostructured hematite-based photoanodes were characterised using FE-SEM, EDX, XRD, XPS, as well as Raman, UV-Vis and EIS spectroscopic methods. It wasfound that the ternary nanostructured photoanodes of eRGO/C60/α-Fe 2 O 3 andeRGO/NiO/α-Fe 2 O 3 showed 5-fold and 9-fold enhancement in current density andsignificant reduction in charge transfer resistance when compared to the pristinehematite photoanode. In this instance, the enhancement in PEC performance of ternary nanostructured eRGO/C60/α-Fe 2 O 3 photoanode was attributed to the electrons cavenging property of C60 as well as the highly conducting eRGO property that have mitigated the high interfacial recombination rate of photogenerated electron-hole pairs. Whilst for the ternary nanostructured eRGO/NiO/α-Fe 2 O 3 photoanode, eRGO transferred the electrons efficiently in the p-n heterojunction without causing substantial bulk recombination. Additionally, the internal electrostatic field in eRGO/ NiO/α-Fe 2 O 3 could facilitate the effective separation of photogenerated electron-hole pairs so that more holes could participate in the water oxidation reaction instead of recombination process. It is anticipated that the fundamental understanding gained through this study is helpful to design and construct high-performance photoelectrodes for the application in PEC water splitting in the near future. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License. Abstract In the diligent pursuit of low-power consumption, multifunctional, and environmentally friendly electronics, more sophisticated requirements on functional materials are on demand. For example, flexible electronics represents a fastdeveloping field and has a great potential to impact our daily life. In building up flexible electronics, the materials with controllable conduction, transparency, and good flexibility are required. Recently, the discovery of free-standing 2D materials has created a revolution to this field. Pioneered by graphene, these new 2D materials exhibit aboundant unusual physical phenomena that is undiscovered in bulk forms. In the meantime, it also possesses very high transparency to the visible light. However, the extensively studied pristine graphene naturally has no bandgap and become restricted in many field-effect based applications. Hence, looking for various types of new 2D materials has been a focal research direction nowadays. In this talk, we intend to take the same concept, but to integrate a family of functional materials in order to open new avenue to flexible electronics. Due to the interplay of lattice, charge, orbital, and spin degrees of freedom, correlated electrons in oxides generate a rich spectrum of competing phases and physical properties. However, a generic approach to build up flexible electronics based on functional oxides is yet to be developed. In this study, we use a 2D material as the substrate. And we take several functional oxides as model systems, including transparent conducting oxides, VO 2 , NiO, Fe 3 O 4 , Pb(Zr,Ti)O 3 , and oxide nanocomposites, to demonstrate a pathway to build up functional oxides for transparent and flexible electronics. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License. Abstract Optical absorption enhancement using plasmonic structures enables a wide range of applications such as solar energy harvesting devices, light emitting devices and photothermal management. For example, in plasmonic photocatalysis, it has recently attracted great interest in enhancing photocatalytic efficiency not only by the plasmonenhanced near field but also by the plasmon-enhanced hot-carrier injection, which could boost the visible response of wide bandgap photocatalysts [1]. Here we report measurements and simulations of the efficient sunlight-driven and visible-active photocatalysts composed of plasmonic metals and ZnO nanowire (NW) arrays fabricated via an all-wetchemical route ( Figure 1a ) [2]. Another application of plasmon-enhanced light absorption is the perfect absorber and thermal emitter [3]. It is found that with proper designs supported by the electromagnetic simulation, the plasmonic structures could exhibit near perfect absorption at desired resonant wavelengths, making them promising for a number of potential application such as thermal emitters (Figure 1b) [4], molecular sensors [5] and IR sensors [6]. Abstract Water splitting and CO 2 fixation on heterogeneous photocatalysts are importance reactions from the viewpoint of solar-to-fuel energy conversion. To achieve these reactions, it is important to improve both bulk and surface properties of a photocatalyst so as to suppress electron-hole recombination and promote surface redox catalysis. In this presentation, recent progress on the development of new photocatalysts that are active for such artificial photosynthetic reactions will be given. In particular, surface modification techniques developed by our group to construct active sites and light-absorbing centers will be presented. For example, we developed a new powdered photocatalyst consisting of Co(OH) 2 and TiO 2 [1]. It is well known that TiO 2 is an active photocatalyst, but only works under UV irradiation. By contrast, the Co(OH) 2 /TiO 2 hybrid photocatalyst is capable of absorbing visible light with wavelengths of up to 850 nm and oxidizing water into oxygen gas, even though it consists of only earthabundant elements only. To our knowledge, this system provides the first demonstration of a photocatalytic material capable of water oxidation upon excitation by visible light up to such a long wavelength.
doi:10.1109/irmmw-thz.2016.7758647 fatcat:knvsrtqm6nhx3jbvhhw4drwn5m