Thin GaAs photovoltaic heterostructures are grown by MOCVD with various p-GaAs base thicknesses. The total n/p absorbing thickness is varied systematically. Output voltages up to ∼1.155V were obtained for individual n/p junctions at an average illumination intensity of ∼8W/cm2. Novel phototransducer devices are then achieved with a vertical epitaxial heterostructure architecture, monolithically integrating 5 or more such thin n/p junctions. Around the design wavelength, the stacked heterostructure design is yielding an optimal external quantum efficiency approaching unity divided by the number of junctions. The modeled and measured conversion efficiencies are exceeding 60%. The photocarrier extraction properties are simulated for different junction thicknesses using a model based on a 3-dimensional (3D) radially-symmetric TCAD implementation of the heterostructures. The study clearly demonstrates that for such thin n/p junctions the photocarrier extraction can still be efficient due to the operation at reduced current densities and higher voltages in heterostructures enhancing electrical power extraction. With the supplementary add-on of a window layer with a reduced sheet resistance for the stacked structure, we demonstrate the possible efficient operation of phototransducers for optical inputs exceeding 150 W/cm2, even for the case of devices designed without gridlines.

In-situ grown CuO and ZnO nanowire (NW) arrays were evaluated for their gas sensing performance. The metal structures were fabricated by standard e-beam lithography, thermal evaporation and lift-off process onto a silicon substrate with gold electrodes. After integration onto a test structure with resistive heater and thermocouple for temperature control, the samples were thermally oxidized at 400°C. During thermal oxidation, nanowires were grown between the oxidized metal structures. The gas sensing performance of the NW array was tested for carbon monoxide, - and a hydrocarbon-mixture (acetylene, ethane, ethene, and propene) at three relative humidity levels.

Tough and responsive hydrogels have recently attracted great research interestsfor potential applications in artifical muscles, soft robotics, and actuators,etc. This paper overviews our recent progresses in the design and synthesis ofhydrogels with very high strength and toughness, and actuators based on thesehydrogels. Inorganic nanospheres, nanorods, and nanosheets are exploited asmulti-functional crosslinkers to adsorb or bond with hydrophilic chains, leadingto hydrogels with very high strength, toughness, fatigue resistance, and/orself-healing. Introduction of functional groups including ionic monomers andamino groups results in hydrogels reponsive to pH, ionic strength and electricfield. Besides, ionoprinting has been used to change local crosslink densitybased on reversible chelating/decomposition of metal ions with functionalgroups. This process is rapid and thus enables reversible and rapid actuation ofhydrogel devices. Our studies will further aim to develop sophiscated devices byassembling hydrogel actuators.

World-record solar-to-electricity energy conversion efficiency has been previously achieved by photovoltaic devices that maximize the use of the solar spectrum, such as multi-junction tandem solar cells. These cells are made of III-V materials whose high cost is a strong limitation on their widespread commercial application. One solution to suppress the cost of these types of devices is to grow III-V solar cells on low-cost carrier materials such as silicon. We will discuss the material, structure and analysis of GaAsP/SiGe-on-silicon multi-junction tandem solar cells. A low threading dislocation density is realized by effective lattice-matching of the top and bottom cells which demonstrate a device that achieves high open-circuit voltage in the top solar cell. The GaAsP/SiGe solar cells have reached a measured efficiency of 20.6% under one sun concentration. Analysis of these results based on the product of the best parameters shows efficiency potential of 26% under one sun, 30.8% at 20× and 35.1% at 400×.

Activated carbon materials are integrated into functionalization of graphene nano-sheets to serve as a high-power lithium cathode. The electrochemical performance shows that the composite displays the highest reversible capacity (c. 170 mAh g-1) comparing with functionalized graphene and activated carbon. Also, approximately 92% of its capacity can be retained after 4,000 cycles at a current of 1 A g-1. Moreover, the composite exhibits an excellent rate performance, a reversible capacity of 90 mAh g-1 even at 6 A g-1, which corresponds to the power density of 15.2 kW kg-1 and energy density of 227 Wh kg-1, respectively. The high performance of this composite can be attributed to the fact that the activated carbon particles not only reduce the graphene sheet stacking thus making it easier for ions to diffuse, but also act as an ion storage buffer against accelerating electron transfer.

We discuss recent literature data on the relaxation times (the primary tα), viscosity, and self-diffusion in water-glycerol and water-methanol mixtures across a wide temperature range from the stable water phase to the deep supercooled regime (373–147K). In particular, to clarify the role of hydrophilicity interactions (the hydrogen bonds) and hydrophobic interactions we study the mixture in terms of the water molar fraction (XW) with fixed temperatures at 5K steps across the entire composition range, and we find a marked deviation from the ideal thermodynamic behavior of the transport functions. This deviation is strongly T and XW dependent and spans values that range from two orders of magnitude at the highest temperature to more than five in the deeply supercooled regime (more precisely, at ≃200K). We analyze these deviations in terms of how the measured values differ from ideal values and find that the hydrogen-bonding water network dominates system properties up to XW = 0.3. We also examine an Arrhenius plot of the maximum excess value (Δtα(T) vs. 1/T) and find two significant changes due to water: one at the dynamical crossover temperature (TL ≃ 225K, i.e., the locus of the Widom line), and one at T ≃ 315K (the water isothermal compressibility χT minimum).

The damage evolution and structural failure in trees and other plants are mainly originated from the plastic yielding in the wood cell wall at the microstructural level, which consists of cellulose fibrils embedded in a polymer matrix of hemicellulose and either lignin or pectin. Understanding the mechanical behavior of wood cell wall at the plastic regime is critical to the investigation of the fracture characteristics of trees at macro-scale. In this research work, the wood cell wall, which consists of cellulose fibrils, hemicellulose chains and lignin macromolecules, is modeled at the mesoscale to investigate the mechanical responses under deformation. By examining the force-strain relationship, the mechanical behaviors of the wood cell wall at the plastic yielding range are obtained, which are initiated from the slippage between the fibrils and polymer matrix. The simulation results are compared with experimental measurements and theoretical predictions to provide a bottom-up description of micromechanics of the wood cell wall, and to explain the damage evolution and structural failure occurred at the larger scales. The wood cell wall investigated here can be applied to the construction of wood hierarchical structure as a basic unit and adapted to the studies of different natural materials.

The adsorption 2-anthroic acid on titania has been shown to result in an interfacial charge transfer band, which makes this a promising interface for dye-sensitized solar cells with direct injection. Here, we model the adsorption of 2-anthroic acid on a TiO2 nanocluster exhibiting a (101)-like interface and compute light absorption properties of this system using for the first time a hybrid functional. The band alignment and the formation of interfacial charge transfer bands proposed in previous experimental and lower-level computational works are confirmed.

Despite having an npn epitaxial structure resembling a Si BJT, the switching performance of the SiC Junction Transistor or SJT is purely controlled by its terminal capacitances, similar to a SiC MOSFET or JFET. Further, the absence of a “high-resistance” SiC MOS channel in the SJT means that the SJT’s RON,sp is solely limited by the resistance of the n- drift region. Recently released SJTs feature RON,sp as low as 2 mΩ-cm2 for a breakdown voltage (BV) of 1600 V, and a RON,sp of 2.4 mΩ-cm2, for a breakdown voltage of 2000 V. Current gains > 100 are achieved, even on the highest current SJTs. Unlike Si BJTs, SJTs do not suffer from second breakdown, and can perform under unclamped inductive switching (UIS) conditions, even at full rated collector currents. Near-∞ Early voltage and a negative temperature co-efficient of current gain in a SJT ensure low collector currents under short-circuited load conditions, resulting in short-circuit withstand time as high as 14 µs, even at > 80% of the maximum rated BV. Recent technological developments have significantly improved the stability of the SJT current gain (β) under high-current stress conditions. A 1000-hour long, 200 A/cm2 DC current stress results in only 10% reduction of the current gain (β) during the early stages of the stress test, while the β is perfectly stable for the remainder (>90%) of the stress duration. Similar β compression is observed, whether the collector current stress is applied at DC, or at a high switching frequency ≥ 200 kHz.

Three II-VI wide bandgap compound semiconductors have been investigated for surface passivation of various photovoltaic devices. First part of this work focuses on the surface passivation of HgCdTe IR detectors using CdTe. A new metalorganic chemical vapor deposition (MOCVD) process has been developed that involves depositing CdTe films at much lower temperature (< 175°C) than the conventional processes used till now. Deposition rate as high as 420nm/h was obtained using this novel experimental setup. Favorable conformal coverage on high aspect ratio HgCdTe devices along with a significant minority carrier lifetime improvement was obtained. Another II-VI semiconductor, namely, CdS was investigated as a surface passivant for HgCdTe IR detectors. It was deposited by MOCVD as well as atomic layer deposition (ALD) and was studied for optimal conformal coverage on high aspect ratio structures. Surface passivation of p-type Si wafer has also been demonstrated using p-ZnTe grown by MOCVD, for possible application in solar cells. Preliminary work showed a remarkable improvement in the minority carrier lifetime of Si light absorbing layer after passivation with a thin layer of ZnTe.

Soft conducting elastomers have been prepared from polydimethylsiloxane-polyethyleneglycol (PDMS-PEG) copolymer and surfactant-stabilized multi-walled carbon nanotubes (MWCNTs). The copolymer was chain-extended with PDMS of molecular weight 17.2 kg mol-1 in order to obtain a crosslinkable PDMS with molecular weight around 20 – 30 kg mol-1. MWCNTs were treated with surfactant and sonicated for better dispersion in the polymer matrix. The conductivity and mechanical properties of conducting elastomers were thoroughly investigated including stress and strain at break. The developed conducting elastomers showed high conductivity combined with inherent softness. The high conductivity and softness, PDMS-PEG copolymers with incorporated MWCNTs hold great promises as compliant and highly stretchable electrodes for stretchable devices such as electro-mechanical transducers.

Nanodiamonds (NDs) represent a novel nanomaterial applicable from biomedicine to spintronics. Here we study ability of air annealing to further decrease the typical 5 nm NDs produced by detonation synthesis. We use atomic force microscopy (AFM) with sub-nm resolution to directly measure individual detonation nanodiamonds (DNDs) on a flat Si substrate. By means of particle analysis we obtain their accurate and statistically relevant size distributions. Using this approach, we characterize evolution of the size distribution as a function of time and annealing temperature: i) at constant time (25 min) with changing temperature (480, 490, 500°C) and ii) at constant temperature (490°C) with changing time (10, 25, 50 min). We show that the mean size of DNDs can be controllably reduced from 4.5 nm to 1.8 nm without noticeable particle loss and down to 1.3 nm with 36% yield. By air annealing the size distribution changes from Gaussian to lognormal with a steep edge around 1 nm, indicating instability of DNDs below 1 nm.

The clean-up of the Fukushima Daiichi site, after the March 2011 earthquake and tsunami, continues to generate large amounts of spent adsorbents. These adsorbents need to be disposed of permanently in a low temperature immobilisation process to avoid volatilising radioactive Cs and Sr species. To this end an immobilisation process with a maximum temperature of 600 °C was developed by sintering model waste with glass frit to form a dense Glass Composite Material (GCM) wasteform. A zeolitic model wasteform, chabazite, was sintered with a lead borosilicate glass composition at a maximum temperature of 600 °C. The sintering process was optimised with various thermal treatment steps to ensure that volatile species, aqueous or otherwise, were released before full sintering to yield a dense final wasteform. With this process dense wasteforms of up to 40 wt. % chabazite have been achieved.

We report a study of direct laser fabrication that produces quantum dots with their density higher than the critical density without appearance of large clumps. Atomic force microscopy is used to image GaAs(001) surfaces that are irradiated by high power laser pulses interferentially. The analysis suggests that high density quantum dots be fabricated directly on semiconductor surfaces during epitaxial growth processes.

This paper provides an overview of the U.S. Department of Energy’s (DOE) hydrogen and fuel cell activities within the Office of Energy Efficiency and Renewable Energy (EERE), focusing on key targets, progress towards meeting those targets, and materials-related issues that need to be addressed. The most recent, state-of-the-art data on metrics such as cost, durability, and performance of fuel cell and hydrogen technologies are presented. Key technical accomplishments to date include a 50% reduction in the modeled high volume cost of fuel cells since 2006, and an 80% cost reduction for electrolyzers since 2002. The statuses of various hydrogen production, delivery, and storage technologies are also presented along with a summary of materials-related challenges for hydrogen infrastructure technologies such as compression, dispensing, seals, pipeline materials/embrittlement, and storage materials. Specific examples and areas requiring more research are discussed. Finally, future plans including EERE’s lab consortium approach such as HyMARC (Hydrogen Storage Materials Advanced Research Consortium) and FC-PAD (Fuel Cell Performance and Durability) Consortia, are summarized.

Nanoparticles are used in chemical mechanical planarization for semiconductor manufacturing as well as in other precision manufacturing operations. Particles used in processing need to be removed from surfaces in order to enhance yields. Nanoparticles are difficult to remove from surfaces during cleaning due to the high van der Waals attractive forces between particles and surfaces relative to the low fluid drag forces that are used for typical removal methods. Ionic surfactant molecules can adsorb on particles and surfaces to create an electrostatic repulsion between particles and surfaces as well as provide a steric barrier to mitigate adsorption and adhesion. The effectiveness of the surfactant in enhancing particle removal is related to surfactant properties, and it can be correlated with and modeled relative to the critical micelle concentration of the surfactant. The general approach for modeling will be discussed, and the model will be compared with particle removal data.

In this paper, a facile and novel method was developed to fabricate high toughness and stiffness double network hydrogels made of ionical-linked natural hydrogel and synthetic hydrogel. The synthetic hydrogel network is formed firstly, and then the gel is soaked in the ionic solution to build second network to form double network hydrogel with high toughness and stiffness. Two different natural polymers, alginate and chitosan, are employed to build rigid and brittle network and poly(acrylamide) is used as soft network in double network hydrogel. The compressive strength of Calcium alginate/poly(acrylamide) double network hydrogels is increased twice than that of poly(acrylamide) single network hydrogels, and the Ca2+ ionically cross-linked alginate is the key to improve the compressive property of double network hydrogels as a sacrificial bond. However, the chitosan/poly(acrylamide) double network hydrogels exhibit no enhancement of compressive strength comparing to poly(acrylamide) single network hydrogels.

Fabricated stainless steel structures are susceptible to stress corrosion cracking (SCC), despite being placed in chloride-containing natural water or humid atmospheres. The present paper describes a model that can define the conditions under which SCC is initiated and propagated, based on analyses of actual SCC incidents induced at welded flanges of cylindrical stainless steel structures.

Whenever the vitrified radioactive waste canister storage conditions deviate from normal and appropriate conditions due to earthquakes or tsunamis, the exposed canisters are expected to suffer SCC within 400 hours to 7 years, according to the analytical results obtained such as degree of sensitization, residual stress distribution, chloride ion concentration, and temperature.

The unique planar structures and high surface area of graphene oxide (GO) and reduced graphene oxide (rGO) has induced great interest as drug delivery platforms. Silver and platinum nanoparticles are used in medicine, biotechnology and cosmetics and have electrocatalytic properties. However, GO has been found to be toxic to a variety of cells; pure graphene is insoluble; and nanoparticles aggregate, diminishing their activity. This research functionalized GO and rGO with silver or platinum nanoparticles (Ag/PtNPs) and experimental solutions were then tested on bacteria, dermal fibroblasts (DFBC’s), and cancerous (SCC13’s) and non-cancerous (DO33’s) epidermal cells to determine toxicity and/or cell viability.

GO was functionalized with Ag or Pt salts, forming metalized-GO; then reduced with NaBH4. Ag-rGO, depending on nanoparticle size, killed either S. Aureus or K. Pneumoniae, while Pt-rGO and rGO had no effect. 1mM Ag-prGO concentrations diluted 1:100 with DMEM was toxic to SCC13 cancerous keratinocytes but showed reduced toxicity to DO33 non-cancerous keratinocytes; whereas Pt-rGO and rGO exerted little effect on SCC13’s and DO33’s at all concentrations. All test solutions adhered to DFBC’s and influenced the orientation of their growth, suggesting potential use in wound dressings to aid healing.

In this study, we have investigated a behavior of particle with diameter several ten nanometers size at the time of heating on an atomic scale by numerical analysis using the molecular dynamics (MD) simulation. On solving the equation of motion, the Langevin equation was adopted. The Finnis-Sinclair potential, which can well reproduce the mechanical properties of a BCC-metal, was used as the interatomic force. We determined the relationship between the melting point (Tm) of the nano-sized particles and its diameter by MD simulations. We have also investigated the self-diffusion coefficient of each atom-forming at a temperature larger or less than Tm of the submicron-size metal particles . As a result, even in case of heating at a temperature larger than Tm, the mean self-diffusion coefficient at the center of a particle was 10-7–10-6 cm2/sec. On the other hand, at the surface layer of the particle was two to three orders of magnitude larger than that at the center. Those particles were in a quasi-molten state. It is conceivable that the thickness of the surface layer can explain a phenomenon that sintering progresses as the heating temperature increases.