This PDF file contains the front matter associated with SPIE Proceedings Volume 10349, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Monolayer two-dimensional transition metal dichalcogenides (2D-TMDCs) have gained immense attention for their desirable transport properties and direct bandgap that have led to a plethora of studies on modern nanoelectronic and optoelectronic applications. These properties are known to occur exclusively in TMDCs when thinned down to one or few monolayers. However reduced dimensionality poses a significant challenge for photonics and optoelectronics applications due to poor light absorption and emission dictated by the volume of semiconductor material. Plasmonic nanostructures have been widely studied for enhancing light-matter interactions in wide variety of material systems resulting in increased emission and absorption properties. 2D Materials provide the ultimate lower limit in terms of material thickness, therefore investigation of plasmon/2D Material hybrid material systems with a specific aim to enhance light-matter interactions is essential for practical optoelectronic applications. In this talk, I will discuss increased photoluminescence emission from MoS2 using both periodic plasmonic nanodisc arrays as well as a single plasmonic optical antenna. I will also describe a method for understanding and identifying the contributions of excitation and emission field enhancements to the overall photoluminescence enhancement using a tapered gold antenna. Additionally, I will describe a systematic study in which we have demonstrated increased light absorption in a monolayer WS2 film.

This paper presents the design and fabrication of inkjet printed graphene field-effect transistors (GFETs). The inkjet printed GFET is fabricated on a DuPont Kapton FPC Polyimide film with a thickness of 5 mill and dielectric constant of 3.9 by using a Fujifilm Dimatix DMP-2831 materials deposition system. A layer by layer 3D printing technique is deployed with an initial printing of source and drain by silver nanoparticle ink. Then graphene active layer doped with molybdenum disulfide (MoS₂) monolayer/multilayer dispersion, is printed onto the surface of substrate covering the source and drain electrodes. High capacitance ion gel is adopted as the dielectric material due to the high dielectric constant. Then the dielectric layer is then covered with silver nanoparticle gate electrode. Characterization of GFET has been done at room temperature (25°C) using HP-4145B semiconductor parameter analyzer (Hewlett-Packard). The characterization result shows for a voltage sweep from -2 volts to 2 volts, the drain current changes from 949 nA to 32.3 μA and the GFET achieved an on/off ratio of 38:1, which is a milestone for inkjet printed flexible graphene transistor.

The structural polymorphism intrinsic to select transition metal dichalcogenides provides exciting opportunities for engineering novel devices. Of special interest are memory technologies that rely upon controlled changes in crystal phase, collectively known as phase change memories (PCMs). MoTe$_2$ is ideal for PCMs as the ground state energy difference between the hexagonal (2H, semiconducting) and monoclinic (1T’, metallic) phases is minimal. This energy difference can be made arbitrarily small by substituting W for Mo on the metal sublattice, thus improving PCM performance. Therefore, understanding the properties of Mo$_{1-x}$W$_x$Te$_2$ alloys across the entire compositional range is vital for the technological application of these versatile materials. We combine Raman spectroscopy with aberration-corrected scanning transmission electron microscopy and x-ray diffraction to explore the MoTe$_2$-WTe$_2$ alloy system. The results of these studies enable the construction of the complete alloy phase diagram, while polarization-resolved Raman measurements provide phonon mode and symmetry assignments for all compositions. Temperature-dependent Raman measurements indicate a transition from 1T’-MoTe$_2$ to a distorted orthorhombic phase (T$_d$) below 250 K and facilitate identification of the anharmonic contributions to the optical phonon modes in bulk MoTe$_2$ and Mo$_{1-x}W$_x$Te$_2$ alloys. We also identify a Raman-forbidden MoTe$_2$ mode that is activated by compositional disorder and find that the main WTe$_2$ Raman peak is asymmetric for x<1. This asymmetry is well-fit by the phonon confinement model and allows the determination of the phonon correlation length. Our work is foundational for future studies of Mo$_x$W${1-x}$Te$_2$ alloys and provides new insights into the impact of disorder in transition metal dichalcogenides.

Transition Metals Dichalcogenide (TMDC) materials have attracted the scientific community due to their unique optical, mechanical, and electronic properties. Molybdenum disulfide (MoS2), an emerging 2D material, exhibit a tunable band gap that strongly depends on the numbers of layers, which makes MoS2 an attractive candidate for optoelectronic applications. However, recent reports have shown that engineering a monolayer using laser thinning can be an effective method without oxide formation, which can be a promising technique for various applications. Here, we investigate this laser thinning process using Raman spectroscopy, µ-XPS, and AFM measurements. Our results show that laser thinned multilayer MoS2 exhibit a large oxide on the surface of the nanosheet, contrary to previous reports. This oxide cannot be detected using µ-Raman spectroscopy. We also show that monolayer and bilayer MoS2 nanosheets exhibit distinctive phonon behavior compared to multilayer MoS2 nanosheets after prolonged laser treatments. This behavior is reflected on the steep intensity decrease for E2g mode, while the intensity of A1g mode slightly changes. This behavior can be interpreted as localized non-equilibrium temperature change due to the formation of anomalous particles on the surface of monolayer and bilayer MoS2 nanosheets. We show that these anomalous particles have a significant effect on the measured Raman properties of pristine monolayer and bilayer MoS2 nanosheets, unlike multilayer MoS2 nanosheets. Our results shed some light on the behavior of MoS2 nanosheets when laser treated for future photodetector applications.

Two-dimensional van der Waals (2D vdWs) materials are a class of new materials that can provide important resources for future electronics and materials sciences due to their unique physical properties. Molybdenum disulfide (MoS2) is one of the most promising n-type TMD semiconductors. Several research groups reported on MoS2 nanosheet based transistors that exhibit satisfactory carrier mobility values with high on/off current ratios. On the other hand, a newly discovered 2D vdWs material, called black phosphorous (BP), has generated considerable scientific and technological interest in the research community. 2D BP also has considerable potential for electronic and optoelectronic applications. This is evidenced by recent research on FETs, diodes, and photodetectors involving few-layered BP flakes. Here, we report on a high performance MoS2 and BP nanosheet based nonvolatile memory transistors with a poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) ferroelectric top gate insulator. The MoS2 ferroelectric field-effect transistor (FeFET) shows a highest linear electron mobility value of 175 cm2/Vs with a high on/off current ratio more than 107, and a very clear memory window over 15 V. The program and erase dynamics and static retention properties are also well demonstrated. Our BP ferroelectric FETs (FeFETs) also exhibit a clear memory window of 15 V and a highest linear mobility value of 1159 cm2V-1s-1 with a 103 on/off current ratio at room temperature in ambient air. In order to explore advanced memory applications beyond unit memory devices, we implement two kinds of memory inverter circuits: a resistive-load inverter circuit and a CMOS inverter circuit combined with n-type MoS2.

Interfacing mismatched low-dimensional materials is an important step in development of hybrid and complex heterostructures. At nanoscale size regimes, interfacial bonding strength and strain energy can very well define the structural integrity and physiochemical properties of semiconductor junctions changing fundamental properties such as distribution of electron-hole wave functions, carrier charge density, etc. Here, we present some of our results on structural behavior of 2D membranes and their overgrowth with laterally grown 1D nanocrystals. Based on the surface energy of 2D layered materials, we hypothesize different bonding scenarios between 1D and 2D nanocrystals. Using experimental results such as structural changes at the interfaces as well as electro-optical properties, we identify some of the interfacial forces involved, and discuss their significance in controlling the properties of the heterojunctions. We use the metal-catalyzed Surface-directed Vapor-Liquid-Solid (SVLS) process for the lateral growth of 1D nanocrystals

Two manganese oxides built from MnO₆ octahedra arranged in layered (Mg-BUS) and tunnel (Mg-TOD) crystal structures are tested for their performance in Li-ion and Na-ion batteries. The layered Mg-BUS consists of an open layered structure with 2D diffusion pathways for charge-carrying ions, while the Mg-TOD is built from structural tunnels (1D diffusion pathways) with the same height as the interlayer spacing in Mg-BUS. Benefiting from the similar chemical composition and crystal structure dimensions of these two materials, we study the role of diffusion channel geometry in reversible ion intercalation/deintercalation. It was found that in both Li-ion and Na-ion batteries, the two materials have similar initial capacities of ~120-130 mAh g^-1. The Mg-TOD demonstrated superior cycling stability in both battery systems, indicating the tunnel structure is advantageous for extended cycling. Rate performance experiments show that in Na-ion batteries, Mg-BUS maintains a higher capacity at higher current rates, suggesting the layered structure allows for more facile diffusion of the larger and heavier Na+ ions. Thus, these results indicate that the tunnel walls, while impeding ion diffusion for the larger Na⁺ ions, provide structural stability during electrochemical cycling, a finding which can help guide the design of electrode materials for intercalation-based batteries.

Chemical pre-intercalation is a soft chemistry synthesis approach that allows for the insertion of inorganic ions into the interlayer space of layered battery electrode materials prior to electrochemical cycling. Previously, we have demonstrated that chemical pre-intercalation of Na⁺ ions into the structure of bilayered vanadium oxide (δ-V₂O₅) results in record high initial capacities above 350 mAh g^-1 in Na-ion cells. This performance is attributed to the expanded interlayer spacing and predefined diffusion pathways achieved by the insertion of charge-carrying ions. However, the effect of chemical pre-intercalation of δ-V₂O₅ has not been studied for other ion-based systems beyond sodium. In this work, we report the effect of the chemically preintercalated alkali ion size on the mechanism of charge storage of δ- M_xV₂O₅ (M = Li, Na, K) in Li-ion, Na-ion, and K-ion batteries, respectively. The interlayer spacing of the δ-M_xV₂O₅ varied depending on inserted ion, with 11.1 Å achieved for Li-preintercalated δ-V₂O₅, 11.4 Å for Na-preintercalated δ- V₂O₅, and 9.6 Å for K-preintercalated δ-V₂O₅. Electrochemical performance of each material has been studied in its respective ion-based system (δ-Li_xV₂O₅ in Li-ion cells, δ-Na_xV₂O₅ in Na-ion cells, and δ-K_xV₂O₅ in K-ion cells). All materials demonstrated high initial capacities above 200 mAh g^-1. However, the mechanism of charge storage differed depending on the charge-carrying ion, with Li-ion cells demonstrating predominantly pseudocapacitive behavior and Naion and K-ion cells demonstrating a significant portion of capacity from diffusion-limited intercalation processes. In this study, the combination of increased ionic radii of the charge-carrying ions and decreased synthesized interlayer spacing of the bilayered vanadium oxide phase correlates to an increase in the portion of capacity attributed diffusion-limited charge-storage processes.

We have recently developed a novel III-V integration scheme, where III-V material is grown directly on top of Si within oxide nanotubes or microcavities which control the geometry of nanostructures. This allows us to grow III-V material non-lattice matched on any crystalline orientation of Si, to grow arbitrary shapes as well as abrupt heterojunctions, and to gain more flexibility in tuning of composition. In this talk, applications for electronic devices such as heterojunction tunnel FETs and microcavity III-V lasers monolithically integrated on Si will be discussed along with an outlook for the future.

Nanoscale process integration demands novel nanopatterning techniques in compliance with the requirements of next generation devices. Conventionally, top-down subtractive (etch) or additive (deposition/lift-off) processes in conjunction with various lithography techniques is employed to achieve film patterning, which become increasingly challenging due to the ever-shrinking alignment requirements. To reduce the complexity burden of lithographic alignment in critical fabrication steps, self-aligned processes such as selective deposition and selective etching might provide attractive solutions. Selective atomic layer deposition (SALD) has attracted immense attention in recent years for self-aligned accurate pattern placement with sub-nanometer thickness control. During the atomic layer deposition (ALD) process, film nucleation is critically dependent on the surface chemistry of the substrate which makes it possible to achieve selective-ALD (SALD) by chemically modifying the substrate surface. Local modification of substrate surface opens up possibilities to achieve lateral control over film growth in addition to robust thickness control during ALD process. SALD offers numerous advantages in nanoscale device fabrication such as reduction of the lithography steps required, elimination of complicated etching processes, and minimization of expensive reagent use. In this work, we review our recent SALD efforts using various inhibition layers resulting in promising self-aligned deposition solutions for metaloxide, metal, and III-nitride thin films. We report a comprehensive investigation to select the most compatible inhibition layer among poly(methylmethacrylate) (PMMA), polyvinylpyrrolidone (PVP), and ICP-polymerized fluorocarbon layers for SALD of metal-oxide and metallic thin films. In addition, single-layer and multi-layered graphene layers are explored as plasma-compatible inhibition layers for selective deposition of III-nitride materials. Extensive materials characterization efforts are carried out to correlate the ALD recipe parameters with the selective deposition performance. The materials and deposition recipes developed in this work overcome various challenges associated with previous methods of SALD and provide alternative routes towards nano-patterning particularly for the sub-10 nm CMOS technology nodes as well as for sensors, photovoltaics, materials for energy storage, catalysis, etc.

GaN nanocolumns are extensively studied as promising nano-materials for high-performance visible emitters because of their dislocation filtering and strain relaxation effects. The size and position of nanocolumns were precisely controlled using Ti-mask selective-area growth (SAG) by RF-MBE, fabricating uniform arrays of pn-junction InGaN/GaN nanocolumns. The periodic arrangement in the nanocolumn arrays led to nanocolumn photonic crystal (PhC) effect. It is however, necessary to integrate a wave-guiding scheme in the nanocolumn system to activate efficiently the PhCs. In the experiment, triangle-lattice GaN nanocolumn arrays with the lattice constant from 280 to 350 nm were grown, followed by the growth of InGaN/GaN superlattice buffer, MQW, and p-type GaN cladding layers. In the upper region of pn-junction nanocolumns from SL to p-GaN, the nanocolumn diameter increased and introduced the increase in the equivalent refractive index, which acts to confine the optical field there. Thus, the optical mode propagated laterally, interacting with the nanocolumn PhC. The diffraction at the photonic band edge resulted in high-directional beam radiations from the nanocolumn system. The photonic band edge was systematically investigated for various nanocolumn arrays with L=280–250 nm. The experimental photonic band diagram for the triangular-lattice pn-junction InGaN/GaN nanocolumn array exhibited a clear photonic band edge.

The colloidal semiconductor quantum dots (QDs) have the potentials to be used in white light-emitting diode (WLED) as a down-converting component to replace incandescent lamps, because the traditional WLED composed of Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce) phosphor lack of red color emissions and shows low color quality. Among various QDs, CdSe has been extensively studied because it possesses attractive characteristics such as high quantum yields (QYs), narrow emission spectral bandwidth, as well as size-tunable optical characteristics. However, in order to enhance the color rendering index (CRI) of WLED, blending materials with different emission wavelengths has been used frequently. Unfortunately, these procedures are complex and time-consuming, and the emission energy of smaller QDs can be reabsorbed by larger QDs, resulting in decreasing the excitation intensity in yellowish-green region. Therefore, in this study, in order to decrease the reabsorption effect and to simplify the procedures, we have demonstrated a facile thermal pyrolyzed route to prepare bicolor CdSe QDs with dual-wavelengths. The emission wavelengths, particle sizes, and QYs of QDs can be tuned from 537/595 to 537/602 nm, 2.59/3.92 to 2.59/4.01 nm, and 27 to 40 %, for GR1 to 3 samples, respectively when the amount of Se precursor is decreased from 1.5 to 0.75 mmol. Meanwhile, the area ratio of green to red (A_g/A_r) in fluorescence spectra is gradually increased, due to the increase in growth rate, and decrease in nuclei formation in red emission. The GR1, GR2, and GR3 QDs are then encapsulated by convert types to form the LED, in which the QDs are deposited on the blue-emitting InGaN LED chip (λem = 450 nm). After encapsulation, the devices properties of Commission International d’Eclairage (CIE) chromaticity and A_g/A_r area ratio are (0.40, 0.24), 0.28/1, (0.40, 0.31), 0.52/1, and (0.40, 0.38), 1.02/1, respectively for GR1, GR2, and GR3. The results show that the green emission intensity are strongly reabsorbed by red emission, as the A_g/A_r area ratios are gradually increased and the CIEs are dramatically shift to white light region, suggesting that the Se amount not only can tune the red emission intensity but also can decrease the reabsorption effect. Based on the above results, the GR3 is suitable to be applied for WLED against the reabsorption effect. Besides, when the GR3 is blended with UV resin of 30 wt. % to prepare the WLED, the CIE located at (0.35, 0.34) is applied as backlight source, providing 126 % color gamut in sRGB standard. As a result, by simply adjusting the concentration of Se precursor, QDs with dual-wavelengths can be prepared and the reabsorption effect can be avoided to show promising lighting properties for the application in WLED.

Micro chevron laser beam annealing (μCLBA) of Si film and Ge film were introduced. Single crystal stripe with a dimension of several tens to hundreds μm in length and 3-8μm in width was formed in Si film or Ge film by scanning μCLBA over the film. Main boundaries in the c-Si stripe were Σ3 CSL twin boundary. Scanning speed of micro linear laser beam annealing (μLLBA) was varied from 0.05 m/s to 8m/s to investigate its influence to crystallinity. Even at 8m/s lateral growth taken place, however, crystal quality was better for slower lateral growth. Crystallization area per energy (APE) of μLLBA was evaluated and compared with other methods. It was found APE of μLLBA was larger than other method, especially for a display with low fill factor of TFT, APE can be several orders of magnitude larger.

We present a CMOS compatible fabrication technique to create micro/nanostructures on silicon and germanium surfaces for effective photon trapping and enhanced absorption. We achieved many times of absorption enhancement enabled by these photon trapping micro/nanostructures compared to bulk silicon and germanium counterparts. This method can lead to designing both highly efficient photovoltaics, ultra-fast photodetectors and highly sensitive photon counting devices with dramatically reduced device thickness. We also demonstrate that different fabrication techniques (dry etch, wet etch, and their combination) and different geometries of these micro/nanostructures can affect the ability and extent of the photon trapping and light manipulation in semiconductor.

Nanostructures allow broad spectrum and near-unity optical absorption and contributed to high performance low-cost Si photovoltaic devices. However, the efficiency is only a few percent higher than a conventional Si solar cell with thicker absorption layers. For high speed surface illuminated photodiodes, the thickness of the absorption layer is critical for short transit time and RC time. Recently a CMOS-compatible micro/nanohole silicon (Si) photodiode (PD) with more than 20 Gb/s data rate and with 52 % quantum efficiency (QE) at 850 nm was demonstrated. The achieved QE is over 400% higher than a similar Si PD with the same thickness but without absorption enhancement microstructure holes. The micro/nanoholes increases the QE by photon trapping, slow wave effects and generate a collective assemble of modes that radiate laterally, resulting in absorption enhancement and therefore increase in QE. Such Si PDs can be further designed to enhance the bandwidth (BW) of the PDs by reducing the device capacitance with etched holes in the pin junction. Here we present the BW and QE of Si PDs achievable with micro/nanoholes based on a combination of empirical evidence and device modeling. Higher than 50 Gb/s data rate with greater than 40% QE at 850 nm is conceivable in transceivers designed with such Si PDs that are integrated with photon trapping micro and nanostructures. By monolithic integration with CMOS/BiCMOS integrated circuits such as transimpedance amplifiers, equalizers, limiting amplifiers and other application specific integrated circuits (ASIC), the data rate can be increased to more than 50 Gb/s.

Telescope mirrors based on highly reflective silver films must be protected from atmospheric corrosion with dielectric overlayers. Reflectivity is optimized when the silver surface is extremely smooth and uniform prior to dielectric overlayer deposition. Silver thin films were deposited on glass slides by electron beam evaporation using a custom deposition system at the University of California Observatories Astronomical Coatings Lab. The silver thin films were subsequently covered with a stack of dielectric films utilizing silicon nitride and titanium dioxide deposited by ion assisted electron beam evaporation to fabricate protected mirrors. In-situ argon ion bombardment was introduced after silver deposition prior to the deposition of dielectric films to assess its effects on the performance of the mirrors. Effectiveness of the ion bombardment was systematically studied for different holding time in vacuum, the time between the end of the silver thin film deposition and the start of the ion bombardment, related to the changes in the surface morphology of silver films and resulting reflectivity spectra. Reflectivity at wavelengths in the range of 350nm – 800nm was found to improve due to ion bombardment, which was qualitatively interpreted to result from decreased surface plasmon resonance coupling. The decrease in the coupling is explained by asserting that the ion bombardment slows down silver surface diffusion and pins grain boundaries, preventing post-deposition grain growth, forming smoother silver-dielectric interfaces.

Self-assembled niobium dioxide (NbO2 ) thin-film selectors self-aligned to tantalum dioxide (TaO2) memristive memory cells are studied by a multi-physics simulation of the mass transport equation coupled to the current continuity equation and heat equation. While a compact circuit model can resolve quasi-static negative differential resistance (NDR), a self-consistent coupled transport formulation provides a non-equilibrium picture of NbO2-TaO2 selector-memristor operation ab initio. By employing the drift-diffusion transport approximation, a finite element method is used to study dynamic electrothermal behavior of our experimentally obtained selector-memristor devices, showing bulk conditions exist favorable for electroformation of NbO2 selector thin-films. Simulation results suggest Poole-Frenkel defects introduce negative differential resistance, in agreement with our measured results.

Understanding thin film oxidation is fundamental from a scientific point of view. There are many processes that benefit from oxidation, such as passivation or memristor formation. On the other hand, oxidation can be a burden, such as in metallic interconnects. Oxidation thermodynamics have been studied for a long time; however, oxidation kinetics in different time scales, oxidation environments and temperatures have yet to be fully understood. In this work we use a combination of simulations and nanoscale characterization to further investigate and understand oxidation kinetics. Results include self-aligned electroforming of selector/memristor structures and ways to control copper oxide formation.

This research examines the influence of lighting on the electrical properties of graphene on different substrates, including PET, glass and SiO2, which are the most widely used substrate materials representing the flexible and rigid applications. The graphene sheets were prepared by CVD and subsequently transferred to three substrates. The resistances of graphene under periodic visible light irradiation were measured inside a vacuum chamber. Results show that the resistances for graphene samples on all substrates increased slowly under lighting, while decreased slowly as well after the light was switched off. The change degree and speed were different for graphene on different substrates, which were influenced as well by the illumination time, environment atmosphere and irradiation power. Graphene on flexible PET substrate is more stable than that on other substrates.

Recently, the investigation of quantum dots (QDs) as a color converter for white light-emitting diodes (WLEDs) application has attracted a great deal of attention. Because the narrow emission wavelength of QDs can be controlled by their particle sizes and compositions, which is facilitated to improve the color gamut of display as well as color rendering index (CRI) and the correlated color temperature (CCT) of WLEDs. In a typical commercially available LCD display, the color gamut is approximately to 75 % which is defined by the National Television System Committee (NTSC). In order to enhance NTSC, the full width at half-maximum (FWHM) of color converter should be less than 30 nm. Therefore, the QDs are the best choice for display application due to the FWHM of QDs is meet the demand of display application. In this study, the hot injection method with one-pot process is used to synthesis of colloidal ternary ZnCdSe green (G-) and red-emission (R-) QDs with a narrow emission wavelength around 537 and 610 nm. By controlling the complex reagents-stearic acid (SA) and lauric acid (LA), high performance of G- and R-QDs can be prepared. The quantum yields (QYs), particle sizes and FWHM for G- and R-QDs are 70, 30 %, 3.2 ± 0.5, 4.1 ± 0.5 nm and 25, 26 nm, respectively. In order to explore the performance of QDs-based WLEDs, mixing ratios effect between G-QD and R-QD are studied and the WLED is packed as conformal-type. Different ratios of R-QD and G-QD (1:10, 1:20 and 1:30) are mixed and fill up the 3020 SMD blue-InGaN LED, and named as LED-10, LED-20 and LED-30. After that, UV curable gel is deposited on the top of QD layer to form WLED and named as LED-10*, LED-20* and LED-30*. The results show that the Commission International d’Eclairage (CIE) chromaticity coordinates, color rendering index (CRI), luminous efficacy of LED-10*, LED-20* and LED-30* are (0.27, 0.21), 53, 1.9 lm/W, (0.29, 0.30), 72, 3.3 lm/W and (0.25, 0.34), 45, 6.8 lm/W, respectively. We can find that the positions of CIE can be controlled simply by adjusting the ratios of G- and R-QDs. Besides, the LED-10 and LED-20* device shows the high CRI, implying that it has great potential for application on backlight of display technology and solid-state lighting.

In the field of science, there is a significant interest in graphene due to its extraordinary properties such as high electrical conductivity, good electrochemical stability and excellent mechanical behavior. This paper presents the direct graphene growth on interdigital electrodes by plasma enhanced chemical vapor deposition (PECVD) using Ni catalyst and methane (CH4) as the carbon source. The 100 nm of Ni was deposited on the top of SiO² substrate functional as catalyst and electrode of MEMS supercapacitor. The growth of graphene was investigated at temperature 1000°C at 10 minutes and at fix power of 40 Watt. The morphology and structure of as- grown graphene were characterized by Raman spectroscopy, Field Emission Scanning Electron Microscope (FESEM) and Atomic Force Microscopy (AFM). From Raman spectra, it is observed that the intensity ratio of the 2D band to G band produced a good quality bilayer graphene.

Recently, flexible organic optoelectronics have got great attention because of their light weight, mechanical flexibility and cost effective fabrication process. Conjugated polymers like PEDOT: PSS are widely used for the transparent electrode applications due to its chemical stability, high conductivity, flexibility and optical transparency in the visible region. Conductivity of the PEDOT: PSS polymer can be enhanced by adding organic solvents or conducting nano fillers like CNT, graphene, etc. Carbon nanotubes are good nano fillers to enhance the conductivity and mechanical strength of PEDOT: PSS composite film. Inthe present work, the effect of gold nano particles in PEDOT: PSS/CNT composite is studied. The conductivity enhancement in PEDOT: PSS/CNT thin films can be attributed to the formation of CNT network in the polymer matrix and conformational change of the PEDOT from benzoid to quinoid structure. Even though the conductivity was enhanced, the transparency of the composite thin films decreased with increase in CNT concentration. To overcome this problem, gold nano particles were attached to CNT walls via chemical route. AuMWCNT/PEDOT: PSS composite films were prepared by spin coating method. TEM images confirmed the decoration of gold nano particles on CNT walls. Electrical and optical properties of the composite films were studied. This simple solution processed conducting films are suitable for optoelectronic applications

Photodetectors (PDs) in datacom and computer networks where the link length is up to 300 m, need to handle higher than typical input power used in other communication links. Also, to reduce power consumption due to equalization at high speed (>25Gb/s), the datacom links will use PAM-4 signaling instead of NRZ with stringent receiver linearity requirements. Si PDs with photon-trapping micro/nanostructures are shown to have high linearity in output current verses input optical power. Though there is less silicon material due to the holes, the micro-/nanostructured holes collectively reradiate the light to an in-plane direction of the PD surface and can avoid current crowding in the PD. Consequently, the photocurrent per unit volume remains at a low level contributing to high linearity in the photocurrent. We present the effect of design and lattice patterns of micro/nanostructures on the linearity of ultra-fast silicon PDs designed for high speed multi gigabit data networks.

Crystalline silicon (c-Si) remains the most commonly used material for photovoltaic (PV) cells in the current commercial solar cells market. However, current technology requires “thick” silicon due to the relative weak absorption of Si in the solar spectrum. We demonstrate several CMOS compatible fabrication techniques including dry etch, wet etch and their combination to create different photon trapping micro/nanostructures on very thin c-silicon surface for light harvesting of PVs. Both, the simulation and experimental results show that these photon trapping structures are responsible for the enhancement of the visible light absorption which leads to improved efficiency of the PVs. Different designs of micro/nanostructures via different fabrication techniques are correlated with the efficiencies of the PVs. Our method can also drastically reduce the thickness of the c-Si PVs, and has great potential to reduce the cost, and lead to highly efficient and flexible PVs.