Three-dimensional organic field-effect transistors with multiple sub-micrometer channels are developed to exhibit high current density and high switching speed. The sub-micrometer channels are arranged perpendicularly to substrates and are defined by the height of a multi-columnar structure fabricated without using electron-beam-lithography technique. For devices with dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene, extremely high current density exceeding 10 A/cm2 and fast switching within 200 ns are realized with an on-off ratio of 105. The unprecedented performance is beyond general requirements to control organic light-emitting diodes, so that even more extensive applications to higher-speed active-matrices and display-driving circuits can be realized with organic semiconductors.

In this paper we investigate the energetic alignment in an organic p-i-n homojunction using ultraviolet photoelectron spectroscopy. The device is made of pentacene and we emploay the small molecules NDN1 for n-doping and NDP2 for p-doping the layers. The full p-i-n structure is deposited stepwise on a silver substrate to learn about the interface dipoles and band bending effects present in the device. From the change in work function between the p- and n-doped layers we gain knowledge of the built-in potential of this junction.

Forming a chemically stable low-resistance back contact for CdTe thin film solar cells is critically important to the cell performance. This paper reports theoretical study of the effects of the back contact material, Sb2Te3, on the performance of the CdTe solar cells. First-principles calculations show that Sb impurities in p-type CdTe are donors and can diffuse with low diffusion barrier. There properties are clearly detrimental to the solar cell performance. The Sb segregation into the grain boundaries may be required to explain the good efficiencies for the CdTe solar cells with Sb2Te3 back contacts.

The forming voltage and set/reset response of sputter-deposited NiO thin films is studied as a function of implant fluence for samples implanted with Ni and O ions. The forming voltage of the films is shown to decrease with increasing ion fluence and to scale with the damage production rate of the different ions. In contrast, the set/reset response of the films was largely unaffected by the ion-implantation. These results are discussed in terms of the filamentary model of conduction and the thermochemical model of resistive switching.

Ge-Sb-Te (GST) thin films were deposited by chemical vapor deposition (CVD) and hot-wire chemical vapor deposition (HW CVD). Several precursor sets (tetraethylgermanium - trimethylantimony - dimethyltellurium (TEGe-TMSb-DMTe), tetraisopropylgermanium - triisopropylantimony - di-tertiarybutyltellurium (TiPGe-TiPSb-DtBTe) and tetraallylgermanium - triisopropylantimony - diisopropyltellurium (TAGe-TiPSb-DiPTe)) were tested for CVD. For the TEGe-TMSb-DMTe precursor set tellurium and germanium could be detected in the films for all deposition temperatures investigated, while Sb was found only in the films deposited at elevated temperature higher than 550 °C. The deposition temperature could be reduced by using two other precursor sets (TiPGe-TiPSb-DtBTe and TAGe-TiPSb-DiPTe). The Ge content, however, could not be sufficiently increased to obtain stoichiometric Ge2Sb2Te5 films. Therefore, the hot wire or catalytic method was applied to improve the decomposition of the precursors. In this case, the desired composition (e.g. Ge2Sb2Te5) was obtained at each investigated temperature by adjusting dosing and deposition parameters. Additionally, film roughness (as low as 2 nm) and deposition rates could be optimized by adjusting deposition temperature and pressure.

We present the progress made in attaining high-efficiency large-area nc-Si:H based multi-junction solar cells using Modified Very High Frequency technology. We focused our effort on improving the spatial uniformity and homogeneity of nc-Si:H film growth and cell performance. We also conducted both indoor and outdoor light soaking studies and achieved 11.2% stabilized efficiency on large-area (≥400 cm2) encapsulated a-Si:H/nc-Si:H/nc-Si:H triple-junction cells.

In this study, the effect of the addition of electrolytes in a given ionic strength to various high-purity silica suspensions was investigated by measurement of the removal rates (RR's) in CMP processes on oxide layers under the same experimental conditions. As so-called slurries the following suspensions were used: i) silica sols produced by the Stöber process, ii) conventional silica sols based on alkali silicate as well as iii) suspensions of fumed silica, with the same SiO2 concentration in each suspension. Ionic strength of the added electrolyte was adjusted to e.g. 0.065 mol/l, with the electrolytes being HCl, NH4Cl, KOH, or binary mixtures of these substances.

These investigations revealed significant differences of the polishing behaviour between the different types of silica dispersions as slurries. While for the Stöber sols investigated, the RR's are highest in the acidic range and almost negligible in the alkaline pH range, fumed silica suspensions show an entirely different behaviour: RR is very low for acidic pH-values, and increases with the alkalinity of the slurry. In contrast to these observations, the RR's of slurries based on conventional silica sols are highest around the neutral point, and show a decrease for both more alkaline and acidic pH-values. In comparison to the other two types of material, these suspensions have a high amount of electrolyte background, originating from their manufacturing process.

A model is developed to explain these results in a comprehensive manner. It involves effects of the electrolyte type and the ionic strengths as well as influences of the particle size.

This study compares p-MOS capacitors fabricated on N+ implanted and on virgin 4H-SiC. The former sample have N at the SiO2/SiC interface, the latter have not. To investigate the presence of deep and shallow hole traps at the SiO2/SiC interface, high frequency and quasi-static capacitance voltage measurements under dark have been compared for bias sweeping from accumulation to depletion and from depletion to accumulation, the latter after white light illumination. The presence of N has an effect on the density of the shallow donor like traps but none effect on the deep ones. The positive charge trapped in the oxide and/or at the oxide interface after equivalent tunneling hole injection have been compared and are equivalent. Time dependent dielectric breakdown tests have been compared too. The oxide grown on N+implanted SiC broken at lower electric field.

Molecular dynamics (MD) simulations with a dedicated force-field and our bond valence (BV) pathway analysis have been employed to reproduce and explain the experimentally observed ultrafast Li+ transport in surface modified LixFePO4-δ as a consequence of heterogeneous doping, i.e. the Li+ redistribution in the vicinity of the interface between LixFePO4 and a pyrophosphate glass surface layer. Over the usual working temperature range of LIBs Li+ ion conductivity in the surface modified LixFePO4 phase is enhanced by 2-3 orders of magnitude, while the enhancement practically vanishes for T > 700K. Simulations for the bulk phase reproduce the experimental conductivities and the activation energy of 0.57eV (for x ≈ 1). A layer-by-layer analysis of structurally relaxed multilayer systems indicates a continuous variation of Li+ mobility with the distance from the interface and the maximum mobility close to the interface, but Li+ diffusion rate remains enhanced (compared to bulk values) even at the center of the simulated cathode material crystallites. Our BV migration pathway analysis in the dynamic local structure models shows that the ion mobility is related to the extension of unoccupied accessible pathway regions. The change in the extent of Li redistribution across the interface with the overall Li content constitutes a fast pseudo-capacitive (dis)charging contribution.

A comparative study of different sorbent materials was performed in order to propose an integrated system to eliminate both, anionic and cationic contaminant ions in drinking water, such as Cr (VI) and BTEX (benzene, toluene, ethylbenzene and xylenes). The adsorption process was studied using several adsorbents: activated carbon, cationic clays (bentonite) and natural zeolite as well as anionic clays (Al-Mg/Nitrate hydrotalcites). The activated carbon and natural zeolites were commercial samples, while hydrotalcite-like compounds were synthesized by an ultrasound-assisted method. It was found that although activated carbon showed a good performance in the cationic sorption, the calcined hydrotalcites presented the highest sorption capacity of chromates compared with activated carbon which had a good performance only up to 100 ppm. For higher concentrations (>100 ppm) activated carbon is saturated rapidly and its sorptive capacity is practically null.

The oxidation behavior of zirconium alloys used as materials for nuclear fuel rod claddings is investigated in the temperature range between 973 and 1673 K in steam and air atmosphere. Parabolic kinetics was found for all materials, atmospheres and temperatures, at least at beginning of the reactions. The temperature dependence of the reaction rate is of Arrhenius type. The parameters of the Arrhenius functions are determined and given for steam oxidation. Due to the formation of a large amount of cracks an acceleration of the reactions can occur. Reasons of the crack formations are phase transformations in the oxide layer known as the breakaway effect and, in case of air atmosphere, local oxygen starvation conditions resulting in reactions with nitrogen. The paper gives a short overview of the relevant mechanisms and processes.

Electronics in “wearable systems” or “smart textiles” are nowadays mainly realized on traditional interconnection substrates, like rigid Printed Circuit Boards (PCB) or mechanically flexible substrates. The electronic modules are detachable to allow cleaning and washing of the textile. In order to achieve a higher degree of integration and user comfort, IMEC-UGent/CMST developed a technology for flexible and stretchable electronic circuits. The electronic system is completely embedded in an elastomer material like PDMS (silicone), resulting in soft and stretchable electronic modules. The technology uses standard packaged components (IC's) and meander shaped copper tracks, so that stretchable systems with complex functionality can be achieved. Testing methods for washability were selected and developed. First tests are showing promising results, leveling the path to washable electronics in textiles. In order to show the possibilities of the technology in the field of textile applications a 7x8 single color stretchable LED-matrix was designed and integrated in textile. This LED-matrix can be applied for example in wearable signage applications.

The goal in this study is to synthesize a Ruddleden-Poper La-Ni phase (La4Ni3O10) using a polymeric route. This material exhibits mixed ionic and electronic conduction (MIEC) properties and can be used as cathode material in the manufacture of Solid Oxide Fuel Cells (SOFC). In addition, an easy and inexpensive synthesis method is presented The polymeric precursors are prepared following the Castillo method using optimized the complexation ratios (HMTA/metallic salts) from 1 to 6. The obtained powders are characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and X-ray diffraction (XRD) in order to determine the processing conditions for formation of the crystalline phase. Experiments performed using complexation ratios of 5 and 6 do not show coagulation. However, the solution prepared using a complexation ratio of 5, is transformed into a gel after few days. Gels produced from solutions prepared with complexation ratios from 2 to 5 were heated at 800, 900 and 1000°C to obtain solid materials. These powders are characterized by TGS, DSC and XRD and it is found that the temperature needed to obtain crystalline La4Ni3O10 was 1000°C.

Scanning capacitance microscopy (SCM) often shows a change in contrast at grain boundaries [1-3]. The origins of this contrast and the efficacy of SCM as a tool to identify band bending at grain boundaries in pc-Si and mc-Si are discussed. Contrast at these grain boundaries could be influenced by different oxide growth rates or by defect states at the oxide interface. In order to determine the influence of such mechanisms on the SCM signal, such effects must be modeled; we show that a simple one-dimensional model agrees well with more detailed models of SCM signal strength and indicates, for example, that very small changes in oxide thickness measurably affect the SCM signal. In our experimental data, the uniformity and quality of the oxide layer are confirmed, and increased contrast consistent with depletion regions is still observed at higher order grain boundaries as identified by electron backscattering diffraction, including 9 and 27a. Scans of the SCM signal as a function of dc probe voltage allow such regions to be more quantitatively investigated.

A Magnetic Coupled Spin-torque Device (MCSTD) is a collective system of three interacting magnetic tunnel junctions (MTJs) that forms a novel magnetic logic gate. The fundamental principle of the MCSTD is the modification of the energy barrier for spin-torque magnetization switching of a central (output) MTJ device arising from changes in the magnetic state of two input MTJ devices. The input MTJs are placed in close proximity of a few tens of nm of the output MTJ such that their magnetic fringing fields are strong enough (> 10 Oersted) to modulate the switching characteristics of the output device. By changing the magnetic states of the two input MTJs four possible net magnetic fields at the center MTJ can be generated. A single MCSTD thereby enables NAND, NOR and XOR operations. In this paper, the fabrication of a prototype MCSTD device is described and preliminary experiment results are reported.

A resistance sensor for use in diesel exhaust is reported. Several soot deposition mechanisms contribute to collection on the sensing electrodes. The sensor is designed to enhance the temperature difference between the electrode surface and the ambient. The resulting thermophoretic force on nanoparticles enhances soot deposition. Exhaust soot concentrations were shown to correlate with resistance decreases and the effect of thermophoresis was studied.

In-field critical current Ic variations, detected using a short sample, angular Ic(77K, H=5.2kOe, Angle) measurement on the ends of a 20 m coated conductor tape fabricated by the MOD / RABiTS process, are shown to be variations in the Ic(H) anisotropy that exist on subcentimeter length scales. A Ic(75 K, H, Angle) study was performed on segments cut from the tape where the power law exponent of the field dependence, α, Ic ∼H−α was calculated for Ic(H, Angle) data. Two extrema behaviors, anisotropic and isotropic, were identified. The isotropic material is shown to outperform the anisotropic material for a wide range of fields and angles at T=26 K.

Protocrystalline silicon, which is a material that has enhanced medium range order (MRO), can be prepared by using high hydrogen dilution in PECVD, or, alternatively, using high atomic H production from pure silane in HWCVD. We show that this material can accommodate percentage-level concentrations of oxygen without deleterious effects. The advantage of protocrystalline SiO:H for application in multijunction solar cells is not only that it has an increased band gap, providing a better match with the solar spectrum, but also that the solar cells incorporating this material have a reduced temperature coefficient. Further, protocrystalline materials have a reduced susceptibility to light-induced defect creation. We present the unique result in the PV field that these oxygenated protocrystalline silicon solar cells have an efficiency temperature coefficient (TCE) that is virtually zero (TCE is between -0.08%/°C and 0.0/°C). It is thus beneficial to make this cell the current limiting cell in multibandgap cells, which will lead to improved annual energy yield.

Humidity can lower the stiffness of beta keratin, which is the main component of spatula pads terminated at the bottom of a gecko's toe. To see if this softening can influence gecko adhesion, numerical simulation of the vertical peeling of a spatula pad adhered on a rough surface is performed, which shows that the reduction in material stiffness indeed leads to substantial increases in the pull-off force ″(Chen, B. and Gao, H. International Journal of Applied Mechanics, 2010). This work provides an alternative explanation of experimental observations on the capillary effect in gecko adhesion.

To apply the superconducting wire to power machines, it is necessary to conduct research on the characteristics of wire phase changes in connection with insulating layers. In this study, according to the presence or absence of insulating layers in the wire, and to the thickness of such layers, the wire's resistance increase trends and the characteristics of its recovery from quenching were examined by current-applied cycle at the temperatures of 90 K, 180 K and 250 K. Towards this end, YBCO thin-film wires that have the same critical temperatures and that have copper and stainless-steel stabilizing layers were prepared. One level and three and five levels of superior-performance polyimide pressure-sensitive adhesive tape was attached to the wires at a very low temperature. The eight prepared test samples were wound around the linear frames, then the wire's voltage and current created owing to the phase change characteristics were measured at each prescribed temperature, using the four-point probe method. Further, near the examination temperatures of 90 K, 180 K and 250 K the wire's resistance and recovery characteristics were examined by cycle.