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Figure 2: Comparison of experimental and simulated strain profiles obtained from GPA, NBED, and FEA.  The two simulated strain profiles demonstrate how the revised chemistries seen in the inset improved the FEA model.
Nanoscale Stress State Characterization of InAlN/GaN Nanoribbon HEMT Structures
  • Due to its high band gap energy and superb electronic-carrier mobilities, GaN is fast becoming the material of choice for…


Figure 2: (a) J–V characteristics of the graphene-based PbS QD devices with different polymer interlayers, demonstrating performance comparable to that of an ITO reference cell. (b) J–V characteristics of representative graphene-based P3HT devices with different polymer interlayers, compared with an ITO reference device. Insets in (a) and (b) show SEM cross-section images of the complete devices.
Graphene Cathode-based ZnO Nanowire Hybrid Solar Cells
  • Semiconducting nanowire-based solar cells have gained interest because of their potential to achieve one-dimensional charge transport pathways and large interfacial…


Towards Highly Scaled Gate Length Asymmetrically Strained Ge Nanowire p-MOSFETs
  • Ge nanowires are of interest for future sub-10-nm gate length p-MOSFETs because of the excellent electrostatic control afforded by the…


Figure 2: J-V characteristics under AM1.5G illumination for representative planar (black) and nanowire-based (red) QDPV devices. Incorporating ZnO nanowires boosts the short-circuit current density (JSC) and the power conversion efficiency (PCE) by 50% and 35%, respectively. Black crosses indicate the maximum power point.
ZnO Nanowire Arrays for Enhanced Photocurrent in PbS Quantum Dot Solar Cells
  • Here we demonstrate a solution-processed ordered bulk heterojunction quantum dot (QD) solar cell with AM1.5G power conversion efficiencies of up…


Figure 1: Electrical double-layer transistor (EDLT) implemented using monolayer MoS2. MoS2 can be grown on a variety of substrates through chemical vapor deposition using S8 and MoO3 at 650°C. MoS2 channel regions are isolated via oxygen plasma etch. Ti/Au source-drain contacts are subsequently deposited using electron beam evaporation.
Flexible High-Density MoS2 Sensor Arrays for Monitoring Action Potentials
  • Monolayer MoS2, a transition metal dichalcogenide, is a novel flexible semiconducting material with a 1.8 eV direct band gap.  Recent…


Figure 1: Brightfield image showing the patterned structure on a silicon substrate. The patterns were defined using ebeam lithography on SU8 resist followed by sputtering of 100 nm of silicon dioxide.
Nano-patterning of J-aggregate Thin Films
  • We show patterning of thin J-aggregate[1] films using nano-imprinting. Unlike the conventional microfabrication techniques, such as direct-write or lift-off processes,…


Figure 1. Large-area (1.5- x 1.5-cm Si/SiO2 substrate) binary nanocrystal superlattices (BNSLs) assembled from 8-nm CdSe/ZnS and 4-nm PbS/CdS core-shell QDs. (a) Fluorescence microscope image (1000x, 595-nm band filter) of BNSLs showing an average grain size of 3.2 um. (b) False color high-resolution transmission microscope (HRTEM) image and small-angle electron diffraction (CL 200 cm) pattern obtained from a single BNSL domain showing a formation of a cub-AB13 structure.
Binary Nanoparticle Superlattices Formed from Highly Luminescent Core-Shell Quantum Dots and Their Photoluminescence Properties
  • Colloidal semiconductor nanocrystals or quantum dots (QDs) offer size-tunable absorption and luminescence spectra, permitting a broad range of applications in…


Figure 2: A plot of external quantum efficiency versus current density, demonstrating the ~50- to 100-fold enhancement in QD-LED performance achieved by replacing core-only PbS QDs (black) with core-shell PbS-CdS QDs (green). The inset is a photograph of an array of five QD-LEDs taken with an infrared camera, with the middle device turned on and emitting at a center wavelength of λ=1242 nm .
High-performance Near-infrared Light-emitting Devices using Core-shell (PbS-CdS) Colloidal Quantum-dots
  • Near-infrared light sources integrated at room temperature with any planar surface could be realized by harnessing the broad spectral tunability,…


Figure 1: Breakdown voltage measurement using the drain current injection technique (ID = 1 mA/mm). The inset shows the circuit diagram of this technique. As the device is turned off, we observe the onset of channel breakdown before gate breakdown. This phenomenon is typical for short-channel devices.
Breakdown Voltage of High-voltage GaN FETs
  • GaN FETs offer superior advantages in high-voltage and high-temperature operation due to its large bandgap (3.4 eV) and high breakdown…


Figure 1: Schematics of nanostructured PV architectures studied in this work.  Left to right: QD PbS:ZnO pn-heterojunction (inset shows cartoon of QD passivated by organic ligand on ZnO), ClAlPc:C60 planar heterojunction with ClAlPc molecular structure, DBP:C60 planar heterojunction with DBP molecular structure, and DBP:( DBP/C60):C60 planar mixed heterojunction. All devices are sandwiched between an electron and hole transporting layer such as bathocuproine and molybdenum oxide  and ITO and Au as electrodes.
Recombination Dynamics of Charge Carriers in Nanostructured Solar Cells
  • Nanostructured solar cells attract increasing attention as a promising photovoltaic (PV) technology[1]. Generation of free charge carriers in nanostructured PV…


Figure 1: (a) Optical image of CVD-grown WSe2 flakes directly grown on SiO2/Si substrate and the back-gated devices on the flake. The triangular shape is consistent with the lattice crystal structure of WSe2 and indicates the high quality of the synthesized sample. (b) Photoluminescence signal mapping of WSe2 flakes. The darker triangle in the center demonstrates thicker islands. (c) Transfer properties of CVD WSe2 back gate devices in linear scale (left) and similog scale (right). Electrons conduct at the high positive back gate voltage region, and holes conduct at the negative bias region. (d) Output performance of WSe2 FET with different back gate bias.
Electronics on MoS2 and Other 2D Semiconductors
  • After enabling much of the modern world for more than 60 years, in the near future electronics will develop in…


Figure 1:  A 30-nm InGaAs nanowire fabricated by our reactive ion etching process.
Towards a Superlattice-source Nanowire FET with Steep Subthreshold Characteristics
  • Achieving a sharp subthreshold swing (S) is crucial to enable the supply voltage scaling that is necessary to reducing power…


Electronic Transport Studies of Thin Film Bi and Bi1-xSbx
  • Currently bulk Bi and BixSb1-x­ have the best known thermoelectric (TE) properties at cryogenic temperatures. These properties can be further…


Micron- and Submicron-thick Parylene Substrates for Transfer Printing and Solar Applications
  • Transfer printing of thin metal films enables the fabrication of both planar and suspended membrane electrodes for microelectromechanical (MEMS) sensors…


Figure 1: a) TEM image of highly monodisperse lead sulfide QDs capped with oleic acid ligands. The dots have a mean diameter of 6.3 nm (σ=6.0%) and show self-assembly into a hexagonal closely packed lattice system. An ideal hexagonally close packed lattice is shown in the top inset, with color used to indicate different shells of dots. The bottom inset is high-resolution TEM on a single QD to highlight its crystallinity. b) Center-to-center distance distribution of the main TEM image in Figure 1a, confirming the high degree of ordering in the film. The first major peak indicates an average center-to-center distance between nearest neighbors of 9.6 ± 0.5 nm.
Effect of Morphology in Quantum Dot Electronics
  • Quantum dots (QDs) are exciting materials because their bandgap is dependent on the dot size. The use of QDs allows…


Ionic Conduction Studies in TlBr Radiation Detector Materials
  • Detection of high-energy radiation (e.g., γ-rays) is key in nuclear non-proliferation strategies.  When a wide-band gap semiconductor detector intercepts a…


Figure 2. All-dry deposited PEDOT is shown to conformally coat a nanoscale feature. This uniform thickness over sharp features is a substantial improvement over the non-conformal coating properties of spun-coat PEDOT:PSS on features of the same scale.
Applications of Nanoimprinted Structures In Organic Photovoltaics
  • Small-molecule organic photovoltaic cells (OPVs) have the potential to be a low-cost, flexible power conversion solution to many energy problems[1]….


Figure 1: Time-resolved anti-Stokes Raman imaging schematic. A) A high-energy pulsed laser excites and locally heats the sample with a Gaussian excitation profile. B) After a variable delay time Δt, the Raman probe laser measures the anti-Stokes scattered signal at a known distance from the excitation source. By varying the position and time between the laser pulses, we will map the thermal properties of our samples.
Heat Transport in Nanostructured Materials
  • Thermal management in nanoscale materials dramatically affects the efficiency of novel energy generation technologies, and engineering devices with appropriate heat…


Figure 1: ESEM fixture and micrograph.  (a) Experimental apparatus within an ESEM chamber. A water droplet is held against a vertically oriented superhydrophobic micropillar surface by a copper wire. Water drop is cooled by a Peltier device and can be swept across the surface (x-direction) by rotating the ESEM stage about the y-axis. (b) Illustration of electron beam imaging area with respect to droplet contact line. (c) Single micrograph from video of water droplet receding along superhydrophobic micropillars in positive x-direction.
Self-similarity of Contact Line Depinning from Textured Superhydrophobic Surfaces
  • We report a technique for observing the dynamic behavior of a liquid contact line on superhydrophobic surfaces at high magnification…


Figure 1: SEM of electrode surface after removal of CNTs, showing a CNT density of approximately 9 x 1010 cm-2.
Improved Carbon Nanotube Ultracapacitor Electrodes for Storage
  • Due to their mechanical, thermal, and electrical properties and their natural ability to grow on a variety of metallic and…


Figure 1: Scanning electron micrographs of fabricated pillar geometries. (a) Electrodeposited Au nanopillars defined by an anodic alumina template. (b) Si nanopillars fabricated using interference lithography and metal-assisted wet etching. (c) Si nanopillars fabricated using e-beam written mask and DRIE. (d) Si micropillars fabricated using optical lithography and DRIE.
Condensation on Micro/Nanostructured Superhydrophobic Surfaces
  • Water condensation on surfaces is a ubiquitous phase-change process that plays a crucial role in nature and across a range…


Figure 1: Artist’s impression of a tip-enhanced microscopy setup.
Spatially Resolved Exciton Dynamics in Quantum Dot Thin Films
  • The diffusion of excitonic energy from within the photosensitive layer of a photovoltaic cell towards the charge separation interface is…


Figure 1: Plot comparing variation of surface area fraction covered by condensed water droplets versus time on surfaces impregnated with Krytox (Sow > 0, solid squares) and BMIm (Sow < 0, open diamonds). The ESEM experiments were conducted under identical conditions (pressure 800 Pa, substrate temperature ~3.6 oC, beam voltage 25 kV, and beam current 1.7 nA). In the analysis, t = 0 s is defined as the first frame in which water drops can be identified
Lubricant-Impregnated Nanotextured Surfaces for Efficient Heat Transfer during Condensation
  • Despite years of advancement in making energy systems more efficient, the predominant mode of condensation seen in large-scale industrial processes…


Figure 1: Schematic of the planar STPV experimental layout. Incoming solar radiation is converted to heat at the absorber (MWCNT/W); heat is selectively radiated by the emitter (1D PhC) and converted to electrical power at the PV (InGaAsSb – 0.55 eV).
Optimizing Emitter-to-Absorber Area Ratio for Improved Efficiency in Planar Solar Thermophotovoltaics
  • Solar thermophotovoltaic (STPV) devices have the potential to overcome the Shockley-Queisser limit by converting solar radiation to a narrow-band thermal…


Figure 1: (a) Schematic of the droplet jumping mechanism showing two droplets with radii R, prior to (state 1) and immediately after (state 2) coalescence. (b) Side view field emission scanning electron microscopy FESEM image of a nanostructured CuO surface. The sharp, knife-like CuO structures have characteristic heights, h ≈ 1 μm, solid fraction, φ ≈ 0.023, and roughness factor, r ≈ 10. (c) Jumping-droplet superhydrophobic condensation on a nanostructured CuO tube (Inset: magnified view of the jumping phenomena). The tube sample has outer diameter DOD = 6.35 mm, inner diameter, DID = 3.56 mm, and length L = 131 mm.
Scalable Superhydrophobic Copper Oxide Surfaces for Enhanced Heat Transfer
  • Vapor condensation is observed in everyday life and routinely utilized in industry as an effective means of transferring heat. In…


Figure 1: Energetics of Beta and Gamma C2S surfaces. The least energetic surface structures are indicated.
Properties of Polymorphs of Belite
  • Portland cement clinker contains four major phases; alite (C3S) is the most dominant (50-70% by mass) and highly reactive with…


Figure 2: Energy of the plasmon peak (Ep) extracted from low-loss EELS data plotted as a function of scan position. The compositional variation corresponding to the observed changes in Ep is < 5.4%, which suggests that there are no large-scale In-rich clusters present.
Understanding the Light Emission Mechanisms in InGaN by Correlating its Structural and Optical Properties
  • Solid state light-emitting diodes (LEDs) containing InxGa1-xN (0 ≤ x ≤ 1)/GaN hetrostructures as active components are of particular importance…


Figure 1: (a) Top-view SEM image of GaAs nanowire array showing nanowire density and uniformity. (b) 45° tilted nanowire array reveals average height of nanowires as 4.6 μm.  (c) Nanowires have a tapered morphology due to consumption of Ga seed particle.
Self-assisted GaAs Nanowire Growth by MOCVD
  • Nanowires combine the intrinsic properties of semiconductors with low dimensionality, which makes them potential building blocks for optoelectronic applications. GaAs…


Investigation of Fuel Cell Cathode Performance in Solid Oxide Fuel Cells – Application of Model Thin Film Structures
  • Understanding the oxygen reduction reaction (ORR) kinetics at solid oxide fuel cell (SOFC) cathodes is considered critical for enhanced performance,…


Catalytic Oxygen Storage Materials
  • Combustion of fossil fuels, essential for electricity generation and vehicular propulsion, is generally incomplete, leading to harmful NOx, CO, and…


Figure 2: Fitting experimental results of PS;DCM(II) peak energy shift as function of changed molecular packing density or dielectric susceptibility. Red dashed line indicate the OLM theory of DCM(II) with initial dielectric constant of 2.44 (x0 = 1.44) in polystyrene, and blue points indicate the fitted peak wavelength from the pressure experiment using elastic modulus as a fitting parameter. The plot shows good agreement for a PS elastic modulus of 1.2 0.6GPa.
Mechanical Pressure-induced Solid State Solvation in Organics Thin Films
  • Significant technological progress of organic semiconducting structures has led to their commercialization in the form of organic LED displays, solid…


Figure 1: Simulated extraction efficiency as a function of the QW placement for m-directional and c-directional axial heterostructures, with the solid line indicating the extraction efficiency for a 
c-directional radial heterostructure with the QW placed at 0.9 the distance from the center to the surface.
Efficiency Comparison of m- and c-directional GaN Nanowire-based LEDs on Si
  • III-nitride nanowire-based light-emitting diodes (LEDs) are promising alternatives to thin-film LEDs for solid-state lighting[1]. Facile strain relaxation in nanowires allows…


Figure 2: Plot of the change in voltage drop across one half of the sensor versus the change in voltage drop across the other half of sensor for application of pressure and two directions of shear. The appearance of points for each type of deformation in different quadrants of the plot demonstrates that the sensor can separate pressure and shear. Note that this preliminary data was generated under specific conditions on a single sensor.
Stretchable Pressure- and Shear-sensing Skin Printed from PDMS
  • In the fields of robotics and prosthesis design, there is need for inexpensive, wide-area pressure- and shear-sensing arrays that can…


Figure 1: Neural recordings obtained from the medial prefrontal. (A) Activity in absence of stimulation. (B) Spike shapes isolated from data in (A). (C) Response to 20-Hz optical stimulation. (D) The multi-unit spikes in response to optical pulses across 20 trials identical to the one shown in (C). (E) Firing rate averaged across 20 trials shown in (D). (F) Response to 100-Hz optical stimulation. (G) The multi-unit spikes in response to optical pulses across 20 trials identical to one shown in (F). (H) Firing rate averaged across 20 trials shown in (G).
Flexible Probes for in vivo Recording and Stimulation of Neural Tissue
  • Probing and stimulating neural tissue is important to understand fundamentals of information processing and pathologies of the nervous system such…


Figure 2: Confocal microscopic setup for quantum dot emission measurement.
Tunable Surface Plasmonics on Electric-gated Nanostructures and its Coupling with Quantum Dot Emission
  • The main goal of this work is to introduce functional natural materials into the design of surface plasmonic structures and…


Figure 2: Normalized integrated intensities of the 3.59-eV and 3.35- eV CL luminescence along the length of the nanorod shown in Figure 2(h). The positions of the nanorod coalescence in the n-GaN section and metallurgical junction are indicated. The squares and circles are experimental data and the dashed lines are fits based on an exponential decay model.
Correlation of Doping, Structure and Carrier Dynamics in a Single GaN Nanorod
  • GaN-based nanowires and nanorods are promising materials systems for optoelectronic applications such as high efficiency light emitting diodes[1],[2] or low…


Figure 2: Simulation and experimental demonstration of tilting pillars. a) Finite element (Abaqus) simulation of tilt angle when h=80μm d=26μm, field is 0.7 Tesla at 60°. Legend represents the strain. b) Simulation result of tilt angle as a function of field. Square symbol shows experimentally demonstrated result. c) Time-lapse side view image of a sample with field of ~0.5 Tesla at ~60°. d) Time-lapse top view image of a sample with field of~0.5 Tesla at ~60°.
Design and Fabrication of Magnetically Tunable Microstructured Surfaces
  • Micro- and nanostructured surfaces have broad applications ranging from liquid transport in microfluidics and cell manipulation in biological systems to…


Figure 1: Raman spectroscopy and TEM characterization of bilayer graphene. (a) Two representative Raman spectra taken from suspended bilayer graphene on a SiN TEM grid. The insets show the stacking orientation.  (b) The SAED patterns for (a) and the corresponding intensities profile along the yellow lines. Inset in upper-left corner of (b) is TEM image, which indicates the number of layers.
Rapid Identification of Stacking Orientation in Isotopically Labeled Chemical-vapor Grown Bilayer Graphene by Raman Spectroscopy
  • The growth of large-area bilayer graphene has been of technological importance for graphene electronics. The successful application of graphene bilayers…


Figure 1
Quantitative Analysis and Modeling of Templated Solid-state Dewetting of Thin Single-crystal Ni Films
  • Thin films are generally metastable in the as-deposited state and will dewet (agglomerate) when heated.  Nanometer scale films (<100 nm…


Figure 2: Scanning-Electron Micrographs of ZnO NWs grown through EBL-defined PMMA masks with a 1-µm pitch.  a) The growth of the NWs was not perpendicular to the substrate.  (inset) PMMA hole mask before NW growth. b) The growth of the NWs was more perpendicular to the surface than in a) with a reduction of growth-solution molarity and addition of PEI.
Lithographically-defined ZnO Nanowire Growth
  • Photovoltaics (PVs) with inorganic zinc oxide nanowire (ZnO NW) active layers are possible for future generations of technology due to…


Organic Light Emitting Devices on Plastic and Paper Substrates
  • The successful fabrication of optoelectronics on economical, flexible, and lightweight substrates such as plastic and paper could pave the way…


Figure 1: (a) Schematic of graphene supported on a chemically patterned substrate. (b) Schematic of reaction pattern in graphene induced by substrate. (c) Raman map of reaction intensity.
Understanding and Controlling the Substrate Effect on Graphene Electron-transfer Chemistry via Reactivity Imprint Lithography
  • Graphene has exceptional electronic, optical, mechanical, and thermal properties, which provide it with great potential for use in electronic, optoelectronic…


Figure 1. Co-crystals growing on SAMs at increasing magnification.
Concomitant Co-crystallization on Engineered Surfaces
  • A co-crystal is a crystalline material made up of two or more components. In pharmaceutical systems, co-crystallization is frequently used…


Figure 1: Schematic of absorption and fluorescence enhancement using the J-aggregate excitonic antenna.
Absorption and Fluorescence Enhancement of Single Molecules and Quantum Dots Using an Excitonic Antenna
  • Nature presents us with a fundamental mismatch between the “size” of visible light (~250 nm in free space) and the…