Filled skutterudites are one of the most promising materials for thermoelectric (TE) power generation applications at intermediate temperatures due to their superior TE and thermomechanical performance as compared to other materials. In the past, we have demonstrated that n-type skutterudites can be optimized so that their maximum TE figure of merit reaches 1.7 at 850 K. TE performance of the p-type, however, is lagging behind, which hinders the optimization of skutterudites-based TE module development. In this paper we reveal that the underlying reasons for inferior TE properties of the p-type root in their electronic band structures, which result in higher thermal conductivity at elevated temperatures due to bipolar lattice thermal conduction and lower power factor because of heavy valance bands induced strong electron-phonon interactions. We also identify means of improving the power factor and reducing bipolar effect.

We have studied the electrochemical reduction of CO2 to produce short chain hydrocarbons and alcohols using supported Cu2O electrocatalysts. The catalysts are prepared using Cu2O nanoparticles formed by chemical reduction of aqueous CuCl2 mixed with polyethylene glycol surfactant, followed by addition of NaOH and L-ascorbic acid (sodium). The nanoparticles are then added to a Nafion/ethanol solution and coated onto a carbon fiber support. When tested used for CO2 electroreduction at −1.5 V(NHE), the Cu2O particles are reduced to metallic Cu, but the hydrocarbon product distribution remains different from that reported for conventional metallic Cu electrodes. Ethylene is the major hydrocarbon produced, with a Faradaic efficiency around 25%, while the efficiency for CH4 formation is reduced to around 1%. The major alcohol product is ethanol, with a Faradaic efficiency around 6%. The relative formation rates of the individual products are discussed in terms of the relevant branch points in recent computational models for the overall reaction mechanism.

Sodium plays an important role in the development of device quality CIGS (Cu-In-Ga-Se) and CIGSeS (Cu-In-Ga-Se-S) chalcopyrite thin film solar cells. In this study the effect of location of sodium precursor on the device properties of CIGS solar cells was studied. Reduction in the surface roughness and improvement in the crystallinity and morphology of the absorber films was observed with increase in sodium quantity from 0 Å to 40 Å and to 80 Å NaF. It was found that absorber films with 40 Å and 80 Å NaF in the front of the metallic precursors formed better devices compared to those with sodium at the back. Higher open circuit voltages and short circuit current values were achieved for devices made with these absorber films as well.

We have developed a novel class of colloidal particles capable of shape and size recognition as well as specific binding to the target cells. These colloid particles were fabricated using a nanoimprinting technology which yields inorganic imprints of the chosen target microorganisms. The products of the templating process are partially fragmented inorganic shells which can selectively bind to their biological counterparts, therefore impairing microbial cell growth, replication and infection. We have named this class of particles, which are capable of selectively recognizing bacterial shape and size, “nanoantibiotics”, which can be further functionalized to kill the target cells. The selective binding is driven by the increased area of contact upon recognition of the cell shape and size between the cells and their matching inorganic shell fragments. Here, we demonstrate the cell recognition and binding action of such particles using two different microbial test organisms.

Papers in the Appendix were published in electronic format as Volume 1534

Pulsed d.c Magnetron Sputtering (PdcMS) has been investigated for the first time to study the deposition of copper indium gallium diselenide (CIGS) thin films for photovoltaic applications. Pulsing the d.c. in the mid frequency region enhances the ion intensity and enables long term arc-free operation for the deposition of high resistivity materials such as CIGS. It has the potential to produce films with good crystallinity, even at low substrate temperatures. However, the technique has not generally been applied to the absorber layers for photovoltaic applications. The growth of stoichiometric p-type CIGS with the desired electro-optical properties has always been a challenge, particularly over large areas, and has involved multiple steps often including a dangerous selenization process to compensate for selenium vacancies. The films deposited by PdcMS had a nearly ideal composition (Cu0.75In0.88Ga0.12Se2) as deposited at substrate temperatures ranging from no intentional heating to 400 °C. The films were found to be very dense and pin-hole free. The stoichiometry was independent of heating during the deposition, but the grain size increased with substrate temperature, reaching about ∼ 150 nm at 400 °C. Hot probe analysis showed that the layers were p-type. The physical, structural and optical properties of these films were analyzed using SEM, EDX, XRD, and UV-VIS-NIR spectroscopy. The material characteristics suggest that these films can be used for solar cell applications. This novel ion enhanced single step low temperature deposition technique may have a critical role in flexible and tandem solar cell applications compared to other conventional techniques which require higher temperatures.

Micromechanical testing of focused ion beam (FIB) machined cantilevers was used to study oxidised grain boundaries in Ni-alloy 600. The Ni-alloy 600 samples were exposed in simulated PWR primary water at 325°C for 4500h with a hydrogen partial pressure of 30kPa. The FIB was used to machine small cantilever beams at the selected sites in the Ni alloy 600, cut so that the beam contained a selected grain boundary close to the built-in end. The FIB was also used to make a pre-crack, 700 nm deep, on the grain boundary. Cantilevers were loaded at the free end using a nanoindenter. Cantilevers milled in the un-oxidised sample yielded, and did not fracture. The specimens containing oxidised grain boundaries fractured at the boundary after small amounts of plasticity. Load vs. displacement data were used to calculate the fracture toughness of the oxidised grain boundaries. The fracture toughness associated with fracture of grain boundary oxide for these cantilevers was in the range 0.73-1.82MPa (m)1/2, with an average value of 1.3MPa (m)1/2. We believe this to be the first time the fracture toughness of an oxidised grain boundary has been determined.

In the present communication, we report our efforts to integrate chalcogenide-based photoelectrochemical (PEC) materials into a standalone device capable of water-splitting using sunlight as the only source of energy. More specifically, the PEC performances of copper gallium diselenide are presented. First, a brief introduction to the material microstructural characteristics is presented. Then, the PEC properties are discussed, including incident-photonto-current efficiency (>60% in the visible), Faradaic efficiency (uncatalyzed, 86%) and durability (400 hours). Finally, we report the solar-to-hydrogen benchmark efficiency (3.7%) of a device made of a CuGaSe2 photocathode and a-Si solar cells measured in a 2-electrode configuration using a RuO2 counter electrode.

Non-equilibrium Green’s functions (NEGF) simulations are carried out to determine the impact of an unintentional dopant in the middle of the channel of a FinFET. We consider two different geometries scaled according to the ITRS and two different types of dopants, donors and acceptors. We show that there is a degradation of the subthreshold characteristics with the scaling of the smooth device and also a stronger impact of the stray dopants in the middle of the channel, with variations up to 32% in the current in on-state conditions.

In the present study, poly (3, 4-ethylenedioxythiophene) (PEDOT) nanostructures were obtained by oxidative polymerization of monomer ‘3, 4-ethylenedioxythiophene’ in the presence of poly (acrylic acid) (PAA) in FeCl3 as an oxidizing agent. The PEDOT nanostructures were characterized using the Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques respectively. The morphology of PEDOT nanostructures revealed flowerlike-shape agglomerates with an increase in the concentrations of PAA. The SEM, TEM and FTIR studies revealed that the presence of PAA could only induce a change in morphology during polymerization, but could not influence the molecular structure of the PEDOT nanostructures. The synthesized PEDOT nanostructures were used as electrode material for supercapacitor. The electrochemical capacitive properties of the PEDOT nanostructures were investigated with the Cyclic Voltammetry (CV), galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS) techniques in the three-electrode cell system. The capacitance of the PEDOT electrode was measured in 0.1M LiClO4 and 2M H2SO4 electrolytes. The highest specific capacitance value of 215F/g for a PEDOT nanostructured electrode was calculated in 1 M H2SO4 electrolyte.

The many-body correlation effects in the spatially separated electron and hole layers in the coupled quantum wells (CQW) are investigated. A special case of the many-component electron-hole system is considered, ν>>1 being the number of the components. Keeping the main diagrams in the parameter 1/ν allows us to justify the selection of the RPA diagrams. The ground state of the system is found to be the electron-hole liquid with the energy smaller than the dense exciton gas phase. The possible connection is discussed between the results obtained and the experiments in which the inhomogeneous state in the CQW is found.

Nowadays the silicon technology is capable of delivering sub-10 nm devices where ‘every atom counts’. Manipulation of atoms with high precision on such a scale, in principle, can lead to technological innovations, such as transistors with extremely short gate length, quantum computing components and optoelectronic devices. One possible strategy to create this next generation of devices is to precisely place individual discrete dopants (such as phosphorous atoms) in a nanoscale transistor.

In this paper, we report a systematic study of quantum transport simulation of an impact that precisely positioned dopants have on the performance of ultimately scaled gate-all-around silicon nanowire transistors (SNWT) designed for digital circuit applications. Due to strong inhomogeneity of self-consistent electrostatic potential, a full 3-D real-space Non Equilibrium Green’s Function (NEGF) formalism is used. The simulations are carried out for an n-channel NWT with a 2.2 x 2.2 nm2 cross-section and a 6 nm channel length, where locations of precisely arranged dopants in the source drain extensions and in the channel region have been varied. The individual dopants act as localized scatters and, hence, impact of electron transport is directly correlated to the position of the single dopants. As a result, a large variation in the ON-current and modest variation of the subthreshold slope are observed in the I D -V G characteristics when comparing devices with microscopically different discrete dopant configuration. Introducing of channel surface roughness in the Ch Sym 1 wire induces a threshold voltage shift and ON-current variation in the device due to scattering. The variations of the current-voltage characteristics are analyzed with reference to the behaviour of the transmission coefficients. Our calculations provide guidance for a future development of the next generation components with sub-10 nm dimensions for the semiconductor industry.

We study sub-critical fracture driven by thermally activated crack nucleation in the framework of a fiber bundle model. Based on analytic calculations and computer simulations we show that in the presence of stress inhomogeneities, thermally activated cracking results in an anomalous size effect, i.e. the average lifetime of the system decreases as a power law of the system size, where the exponent depends on the external load and on the temperature. We propose a modified form of the Arrhenius law which provides a comprehensive description of the load, temperature, and size dependence of the lifetime of the system. On the micro-level, thermal fluctuations trigger bursts of breaking events which form a stochastic time series as the system evolves towards failure. Numerical and analytical calculations revealed that both the size of bursts and the waiting times between consecutive events have power law distributions, however, the exponents depend on the load and temperature. Analyzing the structural entropy and the location of consecutive bursts we show that in the presence of stress concentration the acceleration of the rupture process close to failure is the consequence of damage localization.

We examine the optical and structural properties of polyaniline–silicon nanoparticle capsules — a novel organic/inorganic material. The Si particles absorb UV/blue efficiently and green moderately, while polyaniline (PANI) in its green emeraldine state absorbs UV and red/IR efficiently, effectively providing absorption over a wide range of the solar spectrum. The capsules are produced by miniemulsion of aniline monomers in the presence of Si nanoparticles. Thin films of the capsules were formed on a variety of substrates. We use high resolution transmission electron microscopy (HTEM) and scanning electron microscopy (SEM) to record the structural properties. We also monitor the optical properties of the Si core and the PANI shell using fluorescence microscopy under UV and visible irradiation. Upon on-off cycles of UV irradiation and visible light, the red core switches reversibly between bright and dark states while PANI switches reversibly between emeraldine green and pernigraniline violet states. The results are analyzed in terms of excitonic excitation, charge separation, and transport between the core and the shell, which is useful for photovoltaic applications.

Papers in the Appendix were published in electronic format as Volume 1534

In this paper, synthesis of Cu2ZnSnSe4 (CZTSe) materials by using simple and cost-effective solid state reaction method from the elemental Cu, ZnO, SnO and elemental Se powders are carried out. The SEM images show spherical, non-uniform size with aggregation of nanopowders. The phase separation and thermal analysis of the milled powders suggested that most of the starting powders reacted because of a mechanical alloying effect during milling process. After the solid state reaction at above 500 °C, the nanopowders crystallized into stannite single phase, which are confirm by XRD spectra. The thermoelectric properties of synthesized powder are under study.

Two new diamines containing three nitriles are synthesized via a 3-step route. They are polymerized with four commercial dianhydrides (i.e. 6FDA, OPDA, BTDA and PMDA) in N,N-dimethylacetamide (DMAc) to afford poly(amic acid)s, which are thermally cured at temperatures up to 300 °C to form tough, creasable films. Most of these polyimides are soluble in common solvents. Their glass transition temperatures range from 216 to 341 °C. The polyimides are stable up to 400 °C. The dielectric constants of these OPDA-based polyimides increase from 2.9 (CP2) to 4.7 as measured by the D-E loops.

MoO3 films with a high work function (5.5 eV), high transparency, and a wide bandgap (3.0 - 3.4 eV) are a potential candidate for the primary back contact of Cu(InGa)Se2 thin film solar cells. This may be advantageous to form ohmic contact in superstrate devices where the back contact will be deposited after the Cu(InGa)Se2 layer and MoSe2 layer doesn’t form during Cu(InGa)Se2 deposition. In addition, the MoO3 may be incorporated in a transparent back contact in tandem or bifacial cells. In this study, MoO3 films for use as a back contact for Cu(In,Ga)Se2 thin film solar cells were prepared by reactive rf sputtering with O2/(O2+Ar) = 35%. The effect of post processing on the structural properties of the deposited films were investigated using x-ray diffraction and scanning electron microscopy. Annealing resulted in crystallization of the films to the α-MoO3 phases at 400°C. Increasing the oxygen partial pressure had no significant effect on optical transmittance of the films, and bandgaps in the range of 2.6-2.9 eV and 3.1-3.4 eV were obtained for the as deposited and annealed films, respectively. Cu(In,Ga)Se2 thin film solar cells prepared using an as-deposited Mo-MoO3 back contact yielded an efficiency of >14% with VOC = 647 (mV), JSC = 28.4 (mA), and FF. = 78.1%. Cells with ITO-MoO3 back contact showed an efficiency of ∼12% with VOC = 642 (mV), JSC = 26.8 (mA), and FF. = 69.2%. The efficiency of cells with an annealed MoO3 back contact was limited to 4%, showing a blocking diode behavior in the forward bias J-V curve. This may be caused by the presence of a barrier between the valence bands of the Cu(In,Ga)Se2 and MoO3, due to the higher bandgap of the annealed MoO3 films. SEM cross section studies showed uniform coverage of the as-deposited MoO3 layer and formation of voids for the annealed MoO3 film. Structural orientation of the Cu(In,Ga)Se2 absorber layer was also altered by the MoO3 film and less-oriented films were observed for either cases.

Rigorous finite element optical simulations have been used to examine the absorption of light in various crystalline silicon based, nanostructured solar cell architectures. The compared structures can all be produced on glass substrates using a periodically structured dielectric coating and a combination of electron-beam evaporation of silicon and subsequent solid phase crystallization. A required post-treatment by selective etching of non-compact silicon regions results in an absorber material loss. We show that by adequately tailoring the optical design around the processed silicon layer, the absorptance loss due to material removal can be completely overcome. The resulting silicon structure, which is an array of holes with non-vertical sidewalls, shows promising light path enhancement and features an even higher absorptance than the initial nanodome structure of the unetched absorber.