We present a practical technique for fabricating silicon nanowire bridges on pre-patterned Si electrodes arrays. Silicon nanowires, catalyzed by gold nanoparticles, were grown on silicon electrodes from HF treated Au colloid as well as on electrodes treated with poly-L-lysine. Negligible growth was observed on untreated substrates due to poor adhesion of gold nanoparticles to the hydrogen terminated Si surface. In contrast, the treatments significantly increased occurrence of silicon nanowire bridges, which can be attributed to improved deposition of gold nanoparticles on the surface. Deposition time and concentrations of colloids also affected the occurrence of SiNW bridges. These results indicate that our techniqute for fabricating nanowire bridge arrays will be useful for large-area nanowire applications.

Formation of domain structures in two-step phase separation in Fe-based Fe-Ni-Al alloys are investigated by applying a time-dependent Ginzburg-Landau (TDGL) model. The present authors recently developed a TDGL formulation for ordering processes of B2 and D03 in binary alloys, taking into account the symmetrical relationships between these ordered phases. In this formulation, multiple types of variants of the structures are represented by three order parameters which can be measured independently through crystal structure factors. Mean-field free energies are defined in a form of Landau type expansion with the order parameters and a composition parameter. Interfacial energies due to local variations of degrees of order and composition are given in a gradient square approximation. Kinetic equations for time-evolution of the order parameters and the composition one are derived from the Ginzburg-Landau type potential consisting of the mean-field free energies and the interfacial energy terms. On the other hand, coauthors have investigated domain structures in two-step phase separation of Fe-based Fe-Ni-Al alloys. The evolution of three-dimensional domain structures and composition profiles has been analyzed by electron tomography imaging and energy-dispersive X-ray spectroscopy. In this work the authors performed three-dimensional numerical simulations assuming the thermal processing. The results of the simulations well reproduced the characteristics of the micro-structures obtained from the observations.

Cadmium sulfide nanoparticles were synthesized by a microwave-assisted route in aqueous dispersion. The cadmium sulfide nanoparticles showed an average diameter around 5 nm and a cubic phase corresponding to hawleyite. The aqueous dispersions of the nanoparticles were characterized by UV-Vis spectroscopy, luminescence analysis, transmission electron microscopy and X-ray diffraction. The addition of sodium hydroxide solutions at different concentrations causes a red-shift in the wavelength of the first excitonic absorption peak of the cadmium sulfide nanoparticles, indicating a reduction of the band gap energy. Besides, the intensity of the luminescence of the nanoparticle dispersions was increased. However, there is a threshold concentration of the hydroxide ion above which the precipitation of the cadmium sulfide nanoparticles occurs.

NaF precursor layers used for providing Na to Cu(In,Ga)Se2 (CIGS) grown on Na-free substrates have been studied. The NaF layers were deposited on top of the Mo back contact prior to the CIGS co-evaporation process. The co-evaporation process was interrupted after the preheating steps, and after part of the CIGS layer was grown. Completed samples were also studied. After the preheating, the NaF layers were analyzed with X-ray Photoelectron Spectroscopy and after growing part and all of the CIGS film, the Mo/NaF/CIGS stack was characterized using transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS). The NaF layers were found to be stable in thickness and composition during the pre-heating in selenium containing atmosphere before the CIGS process. The TEM analyses on the partly grown samples show a layer at the CIGS/Mo interface, which we interpret as a partly consumed NaF layer. This is corroborated by the SIMS analysis. In finalized samples the results are less clear, but TEM images show an increased porosity at the position of the NaF layer.

High integrity SiO2/Al2O3 gate stack has been demonstrated for GaN metal-oxide-semiconductor (MOS) transistors. The SiO2 film formed on GaN by the microwave-excited plasma enhanced chemical vapor deposition (MW-PECVD) exhibits good properties compared that by the LP (Low Pressure)-CVD. Then, by incorporating the advantages of both of SiO2 with a high insulating and Al2O3 with good interface characteristics, the SiO2/Al2O3 gate stack structure has been employed in GaN MOS devices. The structure shows a low interface state density between gate insulator and GaN, a high breakdown field, and a large charge-to-breakdown by applying 3-nm Al2O3. The SiO2/Al2O3 gate stack has also been applied to AlGaN/GaN hybrid MOS heterojunction field-effect transistor (HFET) and the HFET shows excellent properties with the threshold voltage of 4.2 V and the maximum field-effect mobility of 192 cm2/Vs.

Few techniques are available to systematically synthesize and characterize metal particles below 1nm in size. We build nanoparticles in an atomically defined manner through the use of a high-fidelity molecular container we call an atomic metron, which is used to select and count the metallic ions that will make up the resultant nanoparticle. After a defined number of ions are selected, the metron may be spatially isolated and the metallic ions reduced to an isolated nanoparticle. Each step in the process is characterized via analytical methods. AFM is used to demonstrate the formation of sub-nanometer particles. The counting of atoms, isolation, and formation of nanoparticles, shows high potential for easy synthesis of sub-nanometer particles with fine control over the number of atoms in each particle.

Investigation of optical absorption in ∼25μm thick, monocrystalline silicon (Si) substrates obtained from a novel exfoliation technique is done by fabricating solar cells with single heterojunction architecture (without using intrinsic amorphous silicon layer) with diffused back junction and local back contact. The ease of process flow and the rugged and flexible nature of the substrates due to thick metal backing enables use of various light-trapping and optical absorption enhancement schemes traditionally practiced in the industry for thicker (>120μm) substrates. Optical measurement of solar cells using antireflective coating, texturing on both surfaces, and back surface dielectric/metal stack as mirror to reflect the long wavelength light from the back surface show a very low front surface reflectance of 4.6% in the broadband spectrum (300nm-1200nm). The illuminated current voltage (IV) and external quantum efficiency (EQE) measurement of such solar cell shows a high integrated current density of 34.4mA/cm2, which implies significant internal photon reflection. Our best cell with intrinsic amorphous silicon (i-a-Si) layer with only rear surface textured shows an efficiency of 14.9%. EQE data shows improved blue response and current density due to better front surface passivation. Simulations suggest that with optimized light trapping and surface passivation, such thin c-Si cells can reach efficiencies >20%.

Transparent electronic devices that retain their electrical properties upon stretching and twisting are envisioned to be used in transparent wearable electronics and stretchable displays. An integral part of stretchable transparent electronic devices is the stretchable transparent conductor. In this work, we demonstrate biaxially stretchable transparent conductors that use metallic single-walled carbon nanotube films. Two dimensionally buckled metallic single-walled carbon nanotube films are realized. The “wavy” film “flattens out” when stretched and its electrical resistance hardly changes up to 3% applied strain. A similar film without any buckled structures suffers a severe degradation in electrical conductivity. Besides exhibiting stretchability, these transparent conductors display good sheet resistance (down to 3 kΩ/□) and transmittance (∼ 80% at a wavelength of 550 nm).

Nanoporous gold (np-Au) with its high surface area to volume ratio, tunable pore morphology, ease of surface modification with well-studied thiol chemistry, as well as integration with conventional microfabrication techniques is a promising candidate for controlled drug delivery studies. While it has been demonstrated that np-Au can retain and release drugs, release mechanisms and governing parameters are unclear. This paper reports on the effect of film thickness and morphology on the molecular release from np-Au films.

Two types of as-cast microstructures have been observed in a series of near-equiatomic FeNiMnAl alloys: 1) an ultrafine microstructure in Fe30Ni20Mn20Al30 [1] and Fe25Ni25Mn20Al30, which consists of (Fe, Mn)-rich B2-ordered (ordered b.c.c.) and (Ni, Al)-rich L21-ordered (Heusler) phases aligned along <100>; and 2) a fine two-phase microstructure in Fe30Ni20Mn30Al20 and Fe25Ni25Mn30Al20, which consists of alternating (Fe, Mn)-rich f.c.c. and (Ni, Al)-rich B2-ordered platelets with an orientation relationship close to f.c.c (002) // B2 (002); f.c.c. [011] // B2 [001] [2]. The phases in Fe25Ni25Mn20Al30 coarsened upon annealing with no significant change in the chemical partitioning. The hardness behavior was studied as a function of the annealing time at 823 K. AnL21-to-B2 transition, which occurred at 573-623K, was observed using in-situ heating in a TEM. After annealing at 973 K for 100 h, needle-shaped clusters of (Fe, Mn)-rich precipitates were observed along the grain boundaries and in the matrix. The temperature dependence of the yield strength of as-cast Fe25Ni25Mn20Al30 was also studied.

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

The solid oxide membrane (SOM) electrolysis process has been successfully tested on a laboratory scale to produce silicon directly from silica in a cost-effective and eco-friendly way. A one-end-closed yttria-stabilized zirconia (YSZ) tube was employed to separate a molten salt containing dissolved silica from a liquid metal anode placed inside the YSZ tube. When an applied electric potential between a liquid tin cathode in the molten salt and the anode exceeds the dissociation potential of silica, oxygen ions are transported out of the molten salt through the YSZ membrane and oxidized at the anode while the silicon cations in the flux are reduced to silicon on the surface of the liquid tin cathode. A potentiodynamic scan (PDS) was performed to determine the dissociation potential of silica in the molten salt system. Electrolysis was performed at 1.05 V for 8 hours. The presence of high-purity silicon crystals on the surface of liquid tin cathode was confirmed by scanning electron microscopy (SEM) and electron dispersive X-ray spectroscopy (EDS).

Gelatin can be covalently crosslinked in aqueous solution by application of diisocyanates like L-lysine diisocyanate ethyl ester in order to form hydrogels. Reaction of isocyanate groups with water is however a limiting factor in hydrogel network formation and can strongly influence the outcome of the crosslinking process. Here, diisocyanates with different water solubility and reactivity were applied for the formation of gelatin-based hydrogel networks and the mechanical properties of the hydrogels were investigated to gain a better understanding of starting material/ hydrogel property relations. L-Lysin diisocyanate ethyl ester (LDI), 2,4-toluene diisocyanate (TDI), 1,4-butane diisocyanate (BDI), and isophorone diisocyanate (IPDI) were selected, having different solubility in water ranging from 10-4 to 10-2 mol·L-1. BDI and LDI were estimated to have average reactive isocyanates groups, whereas TDI is highly reactive and IPDI has low reactivity. Formed hydrogels showed different morphologies and were partially very inhomogeneous. Gelation time (1 to 50 minutes), water uptake (300 to 900 wt.-%), and mechanical properties determined by tensile tests (E-moduli 35 to 370 kPa) and rheology (Shear moduli 4.5 to 19.5 kPa) showed that high water solubility as well as high reactivity leads to the formation of poorly crosslinked or inhomogeneous materials. Nevertheless, diisocyanates with lower solubility in water and low reactivity are able to form stable, homogeneous hydrogel networks with gelatin in water.

The influence of material properties on bacterial attachment to surfaces needs to be understood when applying polymer-based biomaterials. Positively charged materials can kill adhered bacteria when the charge density is sufficiently high [1] but such materials initially increase the adherence of some bacteria such as Escherichia coli [2]. On the other hand, negatively charged materials have been shown to inhibit initial bacterial adhesion [3], but this effect has only been demonstrated in relatively few biomaterial classes and needs to be evaluated using additional systems. Gradients in surface charge can impact bacterial adhesion and this was tested in our experimental setup.

Moreover, the evaluation of bacterial adhesion to biomaterials is required to assess their potential for biological applications. Here, we studied the bacterial adhesion of E. coli and Bacillus subtilis on the surfaces of acrylonitrile-based copolymer samples with different amounts of 2-methyl-2-propene-1-sulfonic acid sodium salt (NaMAS) comonomer. The content related to NaMAS based repeating units nNaMAS varied in the range from 0.9 to 1.5 mol%.

We found a reduced colonized area of E. coli for NaMAS containing copolymers in comparison to pure PAN materials, whereby the bacterial colonization was similar for copolymers with different nNaMAS amounts. A different adhesion behavior was obtained for the second tested organism B. subtilis, where the implementation of negative charges into PAN did not change the overall adhesion pattern. Furthermore, it was observed that B. subtilis adhesion was significantly increased on copolymer samples that exhibited a more irregular surface roughness.

The 20th century saw rapid and dramatic improvements in permanent magnet materials. It has been 31 years since the discovery of neodymium-iron-boron and numerous companies and laboratories are seeking to produce a new and superior material. Topics discussed herein are material options, economics of selected materials and market drivers in material selection. Market issues include manufacturability by shape, size, and material yield; raw material supply including cost and dependability of the supply chain; raw material and magnet product price stability; development of applications based on commercial needs, government legislation and consumer demand. “Need is the mother of invention” and no discussion would be complete without covering why a new material would be beneficial from an applications point of view especially in energy production and consumption. Therefore, an introduction will be provided for select, major applications using permanent magnets and the growth forecasts for these.

Graphene, a monolayer of sp2-bonded carbon atoms, has been attracting worldwide interests because of its unique two-dimensional structure, various fascinating properties and a wide range of intriguing potential applications. The graphene research is very active in China and has been developing rapidly in the past few years, which covers nearly all the areas related to graphene including theories, synthesis, physical and chemical properties, and applications. Over 100 research institutions have been involved in graphene research with fast-growing project supports. In this paper, the status of graphene research in China is first discussed based on the number of publications and patents as well as the institutions involved. Then the projects and fundings from both government and companies for graphene research are briefly introduced. Finally, the highlights of graphene research in China are reviewed, which include chemical vapor deposition growth and transfer, mass production, and assembly of graphene, and its applications in energy storage, sensing, composites and solar cells.

Quasi-continuum (QC) methods are computational techniques, which reduce the complexity of atomistic simulations in a static setting while keeping information on small-scale structures and effects. The main idea is to couple atomistic and continuum models and thus to obtain quite detailed but still not too expensive numerical simulations.

We aim at a mathematically rigorous verification of QC methods by means of discrete to continuum limits. In this article we present our first results for the so-called quasi-nonlocal QC method in the context of fracture mechanics. To this end we start from a one-dimensional chain of atoms with nearest and next-to-nearest neighbour interactions of Lennard-Jones type. This is considered as a fully atomistic model of which the Γ-limits (of zeroth and first order) for an infinite number of atoms are known [7].

The QC models we construct are equal to this fully atomistic model in the atomistic region; in the continuum regime we approximate the next-to-nearest neighbour interactions by some nearest neighbour potential which is related to the so-called Cauchy-Born rule. Further we choose certain representative atoms in order to coarsen the mesh in the continuum region. It turns out that the selection of the representative atoms is crucial and influences the Γ-limits.

We regard a QC model as good if the Γ-limits of zeroth and first order or at least their minimal values and minimizers are the same as those of the fully atomistic model. Our analysis shows that, while in an elastic regime only the size of the atomistic region matters, in the case of fracture a proper choice of the representative atoms is an essential ingredient.

We present the fabrication of a high-temperature stable thermoelectric generator based on nanocrystalline silicon. Highly doped silicon nanoparticles were sintered by a current activated sintering technique to get nanocrystalline bulk silicon. The metalization of silicon was realized by (electro-)chemical plating and the specific electrical contact resistance ρc of the semiconductor-metal interface was measured by a transfer length method. Values as low as $\rho _C< 1 \cdot 10^{ - 6} \,\Omega cm^2 $ were measured. The metalized nanocrystalline silicon legs were sintered to metalized ceramic substrates using a silver-based sinter paste. The device figure of merit of the thermoelectric generator was determined by a Harman measurement with a maximum ZT of approximately 0.13 at 600 °C.

The United States dependence on fossil fuels has become mandatory over the past few decades. The fuel shortage during the 1970s and after Hurricane Katrina has catalyzed a need for creating alternative energy sources, improving the efficacy of these alternative energy sources, and enhancing energy sustainability. The U.S. Department of Energy has set goals to replace 30% of the liquid petroleum transportation fuel with biofuels and to replace 25% of industrial organic chemicals with biomass-derived chemicals by 2025. In the southeast United States, subterranean termites are prevalent and microbes in their gut degrade wood based materials such as cellulose which produce simple sugars that can be used to produce bioethanol. Upon seasonal change, subterranean termites undergo less enzymatic activity and wood-eating capability limiting the amount of sugars that may be produced. This limited activity sparks an interest to investigate this poorly understood phenomenon of how temperature may affect the enzymatic activity in subterranean termites’ guts. In this study, we report the development thermoresponsive biomaterial nanofiber mats containing cellulose to model cellulase activity. Using electrospinning techniques, poly(N-vinylcaprolactam) celluose fiber mats have been prepared via alkaline hydrolysis and labeled with fluorescent tags. Subterranean termites (reticulitermes species) were feed fiber mats for 10 consecutive days to assess enzyme mapping and kinetics. Fluorescent microscopy images confirmed spatial and temporal localization of cellulase enzyme throughout the termite gut upon time and temperature change. These novel high affinity enzyme detection membranes show promise towards future biofuel production.