category » Energy

Figure 1: Circuit diagram of a 1-2 unipolar stacked switching capacitor energy buffer.
Efficient, Reliable Energy Buffer for Grid-interface Power Conversion with Switched Capacitor Architecture
  • A buffering strategy that utilizes the ability of a capacitor to efficiently operate over a wide voltage range allows increasing…


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Device-level Thermal Analysis of GaN-based Electronics
  • Gallium nitride (GaN)-based electronics are one of the most exciting areas of innovation for high-frequency and high-voltage semiconductor devices. Although…


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…


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: (a) Chip block diagram. (b) Measured EOP under different read operation to write operation ratios and temperatures. EOP changes by more than 2× across different conditions.
Low-power Memory Circuits
  • Transistor scaling has resulted in integration of more functionality on a single die. On-chip memories are responsible for a large…


Figure 1: (A) Multi-flow microfluidic device, showing the fluidic layer (blue) where the cells are grown and the pneumatic layer (red) containing microvalves. (B) Approach to quantify shear stress using our sensor. (C) Correlation of fluorescence induction to shear stress intensity.
Cell-based Sensors for Measuring Impact of Microsystems on Cell Physiology
  • The use of microsystems to manipulate and study cells in microenvironments is continually increasing.  However, along with such increase in…


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: The three dimensions of research development for a universal village.
Universal Village: Our Desired Living Conditions
  • Due to the growing populations in cities, resources for city and village residents have become scare while costs for public…


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…


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…


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 2: Field ionization of N2: ion current vs. tip-to-gate voltage, VIG, at 10 Torr. Inset shows the experimental setup.
Self-aligned Gated Tip Arrays for Low-voltage, High-pressure Field Ionization of Gases
  • Field ion sources operate based on field ionization (FI) phenomena in which an electron tunnels out of a molecule under…


Figure 1: A PEV public charging system configuration with two distribution voltage levels. This configuration has two charging locations and three possible locations for the renewable DG and storage units.
Methodology for the Optimal Design of PEV Charging Systems with Multiple Chargers and Distributed Resources
  • Increased penetration of plug-in electric vehicles (PEVs) will necessitate deployment of a large number of PEV chargers[1],[2], but chargers can…


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…


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Materials and Structures for Li-air Batteries
  • Lithium-air batteries hold promise for the next generation of electric vehicles and other applications. By reacting oxygen directly with lithium…


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 2: I-V characteristics of a Si cell with emitter thickness of 1 μm and doping level of 6x1018 cm-3 at AM1.5.
Design and Fabrication of a Si Sub-cell for Multi-junction GaAsP/Si Solar Cells
  • This work is part of a collaborative program aimed at ultimately achieving photovoltaic conversion with more than 40% efficiency at…


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 Fabricated nonlinear resonance based energy harvester.
Wide-bandwidth, Low-frequency, Low-g Piezoelectric MEMS Energy Harvesters
  • Our group proposes the piezoelectric energy harvester based on a nonlinear resonator to address the narrow bandwidth issue of conventional…


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: Photographs of the sintered rare-earth oxide pellets (cerium oxide through lutetium oxide). All the pellets are hydrophobic: water contact angles range between 100° and 115°. The image at the center is a goniometer snapshot of a water droplet beading up on a smooth neodymium oxide surface, as a model sample of the entire REO series; scale bar is 1 mm.
Hydrophobic Rare-earth Oxide Ceramics with Applications to Sustained Dropwise Condensation
  • Hydrophobic materials that are robust to harsh environments are needed in a broad range of applications[1][2][3]. Although durable materials such…


Figure 2: Dimensionless thickness of EC vortex zone dec/w plotted against the scaling factor (φ2/ UHP)1/3 at various applied voltages and flow rates for both experiment (V = 4-20 V and Q= 5-50 µL/min (UHP =0.42-4.17 mm/s)) and simulation (V=21V0-41V0 and UHP=60U0-120U0, where V0 =25 mV and U0 =29.66 µm/s). Dotted lines are the best fitting straight lines for two different sets of experiment data on CEM and AEM, and one set of simulation data.
Sheared Electroconvective Vortices in Electrodialysis
  • We consider electroconvective fluid flows initiated by ion concentration polarization (ICP) under pressure-driven shear flow, a scenario found in many…


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 2: Effect of ALD encapsulation on time-resolved power conversion efficiency of polymer cells stored in air or in an inert environment.  The cells last
Nano-thin Encapsulation of Photovoltaics via Atomic Layer Deposition
  • Device lifetime is a key figure of merit for solar cells and impacts the levelized energy cost ( $/(kW*hr) )…


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) Schematic depiction of oleic-acid-coated lead sulfide QDs (PbsS QDs); the oleic acid ligands are exchanged for 1,3-benzenedithiol (1,3-BDT), 1,2-benzenedithiol (1,2-BDT), or ethanedithiol (EDT). (b) Valence band, Fermi level, and conduction band energies determined from ultraviolet photoelectron spectroscopy and absorption spectroscopy for PbS QDs treated with different ligands. (c) Current-voltage curve of PbS QD/C60 donor-acceptor heterojunction photovoltaics, where the PbS QDs are ligand-exchanged with 1,3-BDT (blue curve) or 1,2-BDT (red curve). The insets depict the expected mode of device operation.
Engineering Energy Level Alignment in Lead Sulfide Quantum- Dot Photovoltaics through Ligand Exchange
  • Solar cells based on lead sulfide colloidal quantum dots (PbS QDs) have made dramatic improvements in efficiency in recent years,…


Utilization of Doped-ZnO and Related Materials Systems for Transparent Conducting Electrodes
  • Efficient transparent electrode materials are vital for applications in smart window, LED display, and solar cell technologies.  These materials must…


Direct Solar to Hydrogen Conversion: Low Cost Photoelectrodes
  • With continuously growing energy demands, alternative emission-free solar-energy solutions become ever more attractive. However, to achieve sustainability, efficient conversion and…


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…


Chemomechanics of Fuel-cell-related Materials
  • Solid oxide fuel cells (SOFCs) convert chemical energy directly into electrical energy with higher efficiency and lower emission than conventional…


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,…


Figure 1: Porous amorphous silicon on glass using MCE. This structure is able to accommodate the volume expansion that occurs during lithiation.
Structured Silicon for Energy Storage in Microsystems
  • Micro-batteries provide a critical component for self-powered autonomous microsystems. Lithium-ion batteries provide relatively high energy storage capacities.  Improvement in energy…