The unique capabilities and characteristics provided by afterglow or remote plasma chemical oxide growth processing of silicon carbide are reviewed. Such processing provides for thermal growth of oxide films at temperatures far below those employed by conventional atmospheric processing methods. Overshadowing this growth capability is the ability to create chemistries, sequential procedures, and specific process environments to address material and defect issues in a manner not possible under conventional atmospheric conditions. The details and outcomes of multi-step afterglow oxidation processing of SiC will be discussed. An example sequence might include; 1) surface conditioning, 2) film growth at 850C and 1 Torr total pressure, and 3) reduced pressure unexcited media post-growth treatments. Surface conditioning impacts the thickness uniformity of the final oxide film and the oxidation rate. The film growth interval produces a nominal 500Å of oxide film in 90 minutes at 850C, a temperature that would not produce any significant oxide film at atmospheric pressure. And the post-growth processing improves the performance of the dielectric film. Using in-line corona-Kelvin metrology the electrical characteristics stemming from these processes have been determined. Electrical effective oxide thickness results were used to assess thickness uniformity and to estimate process rate constants for comparison to other process methods. Fowler-Nordheim, F-N, characteristics determined with the same metrology demonstrate that afterglow, AG, oxides require higher field levels to produce the same F-N current as thermal oxides and that AG films are less susceptible to stress fluence. Process extensions from these and other results are discussed and related to chemical, physical, and electrical film outcomes and potential pathways to improve control over dielectric SiC structures.

Both a low resistance state and a high resistance state which were written by the voltage application in a local region of NiO/Pt films by using conducting atomic force microscopy (C-AFM) were observed by using scanning electron microscope (SEM) and electron probe micro analysis (EPMA). The writing regions are distinguishable as dark areas in a secondary electron image and thus can be specified without using complicated sample fabrication process to narrow down the writing regions such as the photolithography technique. In addition, the writing regions were analyzed by using energy dispersive X-ray spectroscopy (EDS) mapping. No difference between the inside and outside of the writing regions is observed for all the mapped elements including C and Rh. Here, C and Rh are the most probable candidates for contamination which affect the secondary electron image. Therefore, our results suggested that the observed change in the contrast of the second electron image is related to the intrinsic change in the electronic state of the NiO film and a secondary electron yield is correlated to the physical properties of the film.

We will describe the development and application of n-type microcrystalline silicon oxide (μc-SiOx:H) alloys as window layers in thin film silicon solar cells with microcrystalline silicon (μc-Si:H) absorber layers. Cells are prepared in n–i–p deposition sequence with illumination through the n-side. The layers were deposited by radio-frequency plasma enhanced chemical vapour deposition (RF-PECVD) at 185°C substrate temperature, using a mixture of phosphine (PH3), silane (SiH4), carbon dioxide (CO2) and hydrogen (H2) gases, at CO2 flows varied between 0.5 and 2 sccm and different thickness. Films were characterised by dark conductivity measurements, Photothermal Deflection Spectroscopy (PDS) and Raman spectroscopy to evaluate optical band gap E04, refractive index n and crystallinity ICRS, respectively. The results were compared with the data of alternative optimised window layers, such as n-type μc-Si:H and silicon carbide (μc-SiC:H) films. Also solar cells with conventional illumination through the p-side window were investigated for comparison. Solar cells were prepared with μc-SiOx:H n-layers of varied compositions and characterised by current-voltage (J-V) measurements under AM 1.5 illumination (and also under modified AM 1.5 illumination with red (OG590) and blue (OG7) filters) and reflectance measurements. The effects of the μc-SiOx n-layer composition and thickness on the performance of n-i-p cells were investigated and correlated with the optical, electrical and structural properties of the μc-SiOx:H n-layers. The results indicate that n-type μc-SiOx:H provides a sufficient combination of conductivity (up to 0.1 S/cm) and crystallinity (ICRS up to 30%) to function well as a doped layer for the internal electric field and the carrier transport and as a nucleation layer for the growth of the μc-Si:H i-layer. As a window layer, it also results in an enhanced spectral response, particularly in the long wavelength part of the spectrum of the solar cells, in comparison with the cells containing alternative window layers. An improved short circuit current density (Jsc) can be attributed to the wide optical gap E04 (around 2.3 eV) in the μc-SiOx:H window layers and reduced reflection in the long wavelength region of the spectrum. A minimum total reflectance of only 6% at 570nm wavelength was achieved with such μc-SiOx:H window layers. Using optimised n-type μc-SiOx:H as a window layer, an efficiency of 8.0% for 1cm2 cell area was achieved with 1 μm thick μc-Si:H absorber layer and Ag back reflector.

This work presents an analytical model of crystalline phase formation in nanoglasses of phase change memory. We describe a data loss mechanism when the cell resistance changes significantly at elevated temperatures over long periods of time with no electrical bias applied. Unlike the standard approach, which relates crystalline shunt formation to aggregates of crystalline particles forming the percolation cluster, we look at the rare events of almost rectilinear path formation in very thin structures. They can occur at crystalline volume fractions considerably lower than the critical volume fraction required for percolation. We find the characteristic parameters which can describe statistics of these rare events.

In this paper a comparative study of the hydration process in a very early age, first 20 hours, between a conventional cement paste and its equivalent with a replacement of fly ash of about 7.9%, is done. The study was undertaken through semiadibatic calorimetry, electrical impedance spectroscopy and X-ray diffraction. It shows that using electrical impedance spectroscopy we can determine the state of crystallization of the material with and without additions, thereby determining the time at which the different processes are started in the hydration

Polymer micro- and nanotubes are of growing interest for design of microfluidic devices, chromatography, biotechnology, medicine chemical sensors, etc. One approach for the design of tubes is based on use of self-rolling thin films. Here we overview our recent progress in the fabrication of polymeric self-rolling tube.

We report our progress toward high-performance hydrogenated amorphous silicon (a-Si:H) solar cells fabricated in NREL's newly installed multi-chamber film Si deposition system. The a-Si:H layers are made by standard radio frequency plasma-enhanced chemical vapor deposition. This system produces a-Si:H p-i-n single-junction devices on Asahi U-type transparent conducting oxide glass with >10% initial efficiency. The importance of the p-layer to the cell is identified: it plays a critical role in further improving cell performance. Our optimization process involves changing p-layer parameters such as dopant levels, bandgap, and thickness in cells as well as applying a double p-layer. With the optimized p-layer, we are able to increase the fill factor of our cells to as high as 72% while maintaining high open-circuit voltage.

A high-molecular-weight perfluoropolyether (PFPE-YR) and a perfluoropolyether containing ammonium phosphate (PFPE-F10) have been evaluated as fluorinated coating for high-surface-area titanium oxides. Coated nano-TiO2 shows hydrophobic properties and excellent buoyancy on water. In addition to photoactivity toward the degradation of toluene in gas phase, specific trial analyses have been completed to estimate the modified titanium oxide features. Brunauer–Emmett–Teller (BET) analysis for the surface area determination, ultraviolet-visible spectroscopy (UV-Vis) for the material electronic band gap, high-resolution transmission electron microscopy (HRTEM), x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS) for the morphology, structure, and surface composition, respectively, and water contact angle and infrared (IR) analysis have been performed to estimate the wettability and stability of coated titanium.

Sodium aluminum hydroxy carbonate and potassium aluminum hydroxy carbonate, commonly named sodium dawsonite and potassium dawsonite respectively, with formula MAl(OH)2CO3 (M=Na,K), were prepared by slow evaporation of a solution obtained by dissolution of basic aluminum sulfate in 1M sodium carbonate or 1M potassium carbonate, respectively. The basic aluminum sulfate was prepared by precipitation in homogeneous solution of an aluminum bisulfite solution. The basic aluminum sulfate was dissolved in 1M sodium carbonate or 1M potassium carbonate at 80 °C. Then, the solution was heated at 60 °C in order to the crystallization of sodium or potassium dawsonite takes place. The crystallized solid was separated from the liquid by vacuum filtration and oven dried at 90 °C before to be analyzed. The synthesized powders were characterized by differential thermal analysis (DTA), thermogravimetry (TG), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). By this method crystalline sodium dawsonite and potassium dawsonite were obtained. The morphology of the particles was acicular in shape with high aspect ratio (≈267).

Dysprosium oxide (Dy2O3) films are grown epitaxially on high mobility Ge(100) substrates by molecular beam epitaxy system. Reflection high energy electron diffraction patterns and X-ray diffraction spectra show that single crystalline cubic Dy2O3 films are formed on Ge(100) substrates. The epitaxial-relationship is identified as Dy2O3 (110)║Ge(100) and Dy2O3 [001]║Ge[011]. Atomic force microscopy results show that the surface of the Dy2O3 film is uniform, flat and smooth with root mean square surface roughness of about 4.6Å. X-ray photoelectron spectroscopy including depth profiles confirms the composition of the films being close to Dy2O3. TEM measurements reveal a sharp, crystalline interface between the oxide and Ge.

In this paper, results of designing, fabricating and characterizing photovoltaic devices made from tailored silicon nanoparticles are shown as proof-of-principle to adopt this material into the photovoltaic sector. The silicon nanoparticles are used as active material for direct separation of the light induced charge carriers. Homo pn-junctions were constructed by silicon wafers and silicon nanocrystals, the latter doped with the opposite carrier type than the wafers. Nanocrystals were sintered on top of the wafer by a spark plasma sintering process, maintaining the nanocrystalline character. This way, the nanoparticle layers are a combined absorbing and charge separating medium. Electrical characterization measurements of the devices show a reproducible short-circuit current of up to 20 μA under illumination. A maximum short-circuit current density of 6.25 μA/cm2 was realized.

Biocompatible, water-soluble, green luminescent silicon quantum dots (SiQDs) were developed as transfection tool for small interfering RNA (siRNA). The research goal was to down-regulate via the RNA interference (RNAi) mechanism the P-glycoprotein expression of the multidrug resistant gene 1 (MDR1) in a human colon carcinoma cell line (Caco-2). The internalization of 2-vinylpyridine terminated SiQDs (2-vipySiQDs) by Caco-2 cells as observed in confocal laser scanning microscopy imaging studies occurs via endocytosis. Experiments employing agarose gel electrophoresis revealed that 2-vipySiQD-siRNA complexes are formed through electrostatic interactions. The release of siRNA in the cytosol with subsequently RNAi induced down-regulation of the P-glycoprotein translation was verified by detecting a reduced ABCB1 mRNA level in transfected Caco-2 cells employing real-time PCR. Additional evidence for successful ABCB1 gene silencing was obtained by measuring a significant decrease of the P-glycoprotein transporter efficiency for the fluorescent substrate Rhodamine 123 (Rh123).

Effective thermoelectric materials have a low thermal conductivity and a high electrical conductivity. The performance of the thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT = S2σT/K, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature and K is the thermal conductivity. ZT can be increased by increasing S, increasing σ or decreasing K. MeV ion bombardment caused defects and disorder in the film and the grain boundaries of these nano-scale clusters increase phonon scattering and increase the chance of an inelastic interaction and phonon annihilation. We have prepared 100 alternating layers of Si/Si+Ge nanolayered superlattice films using the ion beam assisted deposition (IBAD). The 5 MeV Si ions bombardments have been performed using the AAMU Pelletron ion beam accelerator to make quantum clusters in the nanolayered superlattice films to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and cross plane electrical conductivity. We have characterized the thermoelectric thin films before and after Si ion bombardments as we measured the cross-plane Seebeck coefficient, the cross-plane electrical conductivity, and the cross-plane thermal conductivity for different fluences

Photo-induced structural changes and defect creation are common phenomena in a large variety of polymeric and non-crystalline semiconductors. The photo-induced degradation of a-Si:H and its alloys, discovered by Staebler and Wronski in 1977, belongs to a special category with quite unique features, which so far has resisted an explanation. Part of the problem is that the near 4-fold coordinated network does not naturally form an amorphous material. It is over-constrained and forms a stress relief void structure. While reviewing the experimental evidence it will be argued that some of our commonly held views regarding the underlying mechanisms of the Staebler-Wronski effect (SWE) may have to be abandoned. First, the internal void surfaces seem to be the principal locations of the photo-structural changes. Second, non-radiative bimolecular recombinations of photo carriers do not seem to be the driving force of defect creation at helium temperatures. Alternative pathways for the photo-induced processes will be suggested.

Osteogenesis imperfecta (abbreviated as OI) is a genetic disorder in collagen characterized by mechanically weakened tendon, fragile bones, skeletal deformities and in severe cases prenatal death. Even though many studies have attempted to associate specific mutation types with phenotypic severity, the molecular and mesoscale mechanisms by which a single point mutation influences the mechanical behavior of tissues at multiple length-scales remain unknown. Here we review results of a hierarchy of full atomistic and mesoscale simulations that demonstrated that OI mutations severely compromise the mechanical properties of collagenous tissues at multiple scales, from single molecules to collagen fibrils. Notably, mutations that lead to the most severe OI phenotype correlate with the strongest effects, leading to weakened intermolecular adhesion, increased intermolecular spacing, reduced stiffness, as well as a reduced failure strength of collagen fibrils (Gautieri et al., Biophys. J., 2009). Our study explains how single point mutations can control the breakdown of tissue at much larger length-scales, a question of great relevance for a broad class of genetic diseases. Furthermore, by extending the MARTINI coarse-grained force field, we provide a new modeling tool to study collagen molecules and fibrils at much larger scales than accessible to existing full atomistic models, while incorporating key chemical and mechanical features and thereby presents a powerful approach to computational materiomics (Gautieri et al., Journal of Chemical Theory and Computation, 2010). We describe the coarse-graining approach and present preliminary findings based on this model in applying it to large-scale models of molecular assemblies into fibrils.

The impact of interfacial oxygen content on the band offsets of GaAs:HfO2 interfaces was investigated using the density functional theory (DFT) method. Reference potential method was used to determine the band offsets. Moreover, GW correction was utilized to find more accurate value of the valence band edge of HfO2 and hence obtain more accurate band offsets. With gradually decreasing the interfacial O content from 100% to 30% (by changing O chemical potential corresponding to varying the growth condition), the valence band offset increases from 1.06 to 3.34 eV. It is found that this increase of the valence band offsets is inversely proportional to the charge loss of interfacial Ga atoms. Specifically, less charge loss of interfacial Ga induces less charge transfer from GaAs to HfO2 side. Consequently, the less charge loss of interfacial Ga essentially leads to an increase of the valence band offsets.

Yittria stabilized zirconia (YSZ) has long been of interest as a promising material for nuclear energy applications. It is the cubic form of zirconium oxide stabilized at room temperature by the addition of yttria. Previous studies of radiation damage in YSZ focused primarily on microstructural changes in the bulk or in the near surface layer whereas irradiation induced changes on the surface received little attention. Here we use atomic force microscopy, AFM, to study the fluence-dependent generation of surface modifications to YSZ due to 150 keV Ar+ ion implantation at fluences from 3×1015 to 1×1017 ions/cm2. The microstructural changes in the near surface region were previously investigated by Rutherford backscattering spectrometry in channeling geometry (RBS/C). Further, we investigated implantation in (100), (110), and (111) oriented single crystals of YSZ to explore differences in crystal orientation sensitivity to damage to ion irradiation. At the highest fluence, a dense packing of large round surface hillocks was observed. The ion induced surface modifications revealed by AFM differ slightly from the bulk lattice damage measured by RBS, although both indicate that under these implantation conditions, the (110) oriented crystal shows the most radiation damage resistance. The mean size of the hillocks scaled with concentration of implanted Ar atoms.

Purified Si film is prepared directly from metallurgical-grade Si (MG-Si) by chemical transport using subatmospheric-pressure H2 plasma. The purification mechanism is based on the selective etching of Si by atomic H. Since most metals are not etched by H, this process is efficient to reduce metal impurities in Si films. It is demonstrated that the concentrations of most metal impurities (Fe, Mn, Ti, Co, Cr, Ni, etc.) in the prepared Si film are in the acceptable range for applying it to solar-grade Si (SOG-Si) material, or below the determination limit of the present measurements. On the other hand B and P atoms, which make volatile hydrogen compounds such as B2H6 and PH3, are difficult to eliminate by the present principle. From the infrared absorption measurements of the etching product produced by the reaction between H2 plasma and MG-Si, it is found that the main etching product is SiH4. Therefore, a remote-type chemical transport process is possible to produce SiH4 gas directly from MG-Si. Combining other purifying principle (such as a pyrolysis filter), this process may have an advantage to eliminate B2H6 and PH3 from the produced SiH4 gas.

Modifications to the p-type semiconductor TIPS-Pentacene can result in elimination of the solid-solid thermal transition at 124 °C. This new material has shown mobility higher than 1 cm2/Vs. Elimination of the solid-solid thermal transition leaves the melting point as the lowest temperature transition at 199 °C.

Semiconducting hexathiapentacene (HTP) single–crystal nanowires were synthesized using a simple solution-phase route. Quartz Crystal Microbalance and complex resistance measurements were employed to investigate the sensing properties of an HTP nanowire to analytes including acid, amine, and hydrocarbon vapors. Cole-Cole plots (0.01Hz-4 MHz) of measured impedance spectra, modeled using equivalent circuits, were used to resolve the effects of adsorption and charge migration.