Hierarchical modeling based on atomistic and continuum simulations were established to describe the fundamental characteristics of plastic deformation in irradiated materials. Typical irradiation defects of a self-interstitial atom (SIA) loop and vacancy loop are considered. At first atomic models, including a SIA loop and a vacancy as well as a straight dislocation loop in single crystals were constructed. Constant strain is applied to each model and the equilibrium configuration under deformation is calculated by a molecular statics simulation. Maximum shear stresses in various radii of irradiated defects are stored in a database for the continuum mechanics analysis. Then local interaction events between glide dislocation and irradiation defects were introduced through crystal plasticity finite element analysis. In this model the effect of radiation hardening was considered by referring to the experiment. We found that softening after the first yield event is caused by annihilation of irradiation defects resulting from unfaulting of the radiation defects.

The creep behavior of a new type of austenitic heat-resistant steel Fe-20Cr-30Ni-2Nb (at.%), strengthened by intermetallic Fe2Nb Laves phase, has been examined. Particular attention has been given to the role of grain boundary Laves phase in the strengthening mechanism during long-term creep. The creep resistance increases with increasing area fraction (ρ) of grain boundary Laves phase according to equation ε/ε = (1−ρ), where ε0 is the creep rate at ρ = 0. In addition, the creep rupture life is also extended with increasing ρ without ductility loss, which can yield up to 77% of elongation even at ρ = 89%. Microstructure analysis revealed local deformation and well-developed subgrains formation near the grain boundary free from precipitates, while dislocation pile-ups were observed near the grain boundary Laves phase. Thus, the grain boundary Laves phase is effective in suppressing the local deformation by preventing dislocation motion, and thereby increases the long-term creep rupture strength. This novel creep strengthening mechanism was proposed as “grain boundary precipitation strengthening mechanism” (GBPS).

We have studied the magnetic properties of 100 nm thick ZnO thin films prepared by magnetron sputtering in different oxygen partial pressures (ratio of oxygen pressure to total pressure in deposition chamber, POxy). Only the films fabricated at POxy below ~ 0.5 show room temperature ferromagnetism. The saturation magnetization at room temperature is initially found to increase as POxy increases and reaches maximum value of ~ 5 emu/gm at POxy ~ 0.3 and then starts to decrease and becomes diamagnetic for POxy > 0.5. From small angle XRD study of structural properties of the films, we find that the lattice stress developed in the film along c-axis also exhibits a similar behavior with the variation of POxy. Thus, both the room temperature ferromagnetism and lattice stress appear to originate from the intrinsic defects present in the sample.

Amorphous indium boron nitride (a-InBN) thin films were successfully fabricated using radio frequency (RF) magnetron sputtering, and were deposited onto fused silica and c-Si(100) substrates. Sputtering was achieved using a target of polycrystalline B and In species with B/In nominal at.% ratio of 25/75 under the flow of nitrogen. The structure and composition of the films have been investigated by X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), respectively. The XRD patterns reveal that the sputtered films are amorphous, and the XPS confirms the presence of boron in the films in addition to an oxide overlayer. The optical absorption of samples grown on silica was obtained using spectrophotometry (SP) technique in the wavelength range (200 - 800) nm. Analysis of the absorption coefficients using the Tauc linear extrapolation gives an optical bandgap of 2.05 eV, indicating a higher bandgap comparing to the measured optical bandgap of a-InN (1.25 eV) due to doping with boron. Films grown on c-Si(100) were characterized by spectroscopic ellipsometry (SE) technique in the wavelength range of (300-1700) nm. The measured ellipsometric spectra are described well by a two-layer model structure, which consists of a transparent layer on top of an absorbing layer. The thicknesses and optical functions of the transparent and absorbing layers were obtained by analyzing the measured ellipsometric spectra, Ψ and Δ within the framework of the Cauchy–Urbach (CU) and Tauc–Lorentz (TL) models, respectively. While the overlayer is completely transparent over the measured range (k (λ) = 0), the absorbing layer underneath it exhibits a clear absorption above its optical bandgap of 2.15 eV, which is in a good agreement with the SP finding. There was an excellent agreement between the bandgap obtained as a fitting parameter from the optical model and that obtained by linear extrapolation using the empirical Tauc and Cody models for amorphous semiconductors.

Most of actual photonic devices being sensitive in the visible (VIS) spectrum are based on crystalline silicon (x-Si). The production of x-Si requires an expensive high temperature process. The color reproduction with x-Si diodes additionally requires an integration of color filters [1] to realize a shift in spectral sensitivity. This work presents an amorphous silicon (a-Si:H) photodiode with an intermediate contact for color separation without color filters. Such detectors can be produced in a low cost and low temperature PECVD process, which allows their direct deposition on a custom specific ASIC [2]. Another advantage of a-Si:H is the up to 10 times higher light absorption compared to that of x-Si in the VIS spectrum [3]. The device consists of a metal (Cr) cathode, an amorphous NIP diode structure and a TCO (Al doped ZnO) anode. The I-layer includes an interior TCO contact buried between two P-layers. The thickness of this TCO layer is about 200 nm; the P-layers have a thickness of about 10 nm. The chromium cathode is sputtered on a glass substrate in a PVD process. The amorphous layers are deposited in a multi-chamber PECVD line; the buried and top TCO contacts are sputtered in the same line continuously under high-vacuum conditions. In a first photolithography step the top anode is patterned while the buried anode is uncovered. Afterwards, the diode must be patterned again, resulting in a final Cr, NIP-a-Si:H, TCO, PIP-a-Si:H and TCO multi-layer stack.

The spectral sensitivity of a common NIP diode can be shifted by external bias voltages. The spectral sensitivity at higher negative voltages overlays those of that at lower voltages and additionally shifts to longer wavelengths. The color reproduction is difficult; it can be improved by reducing the overlap of the spectral sensitivity [4]. The spectral response of the diodes presented in this work also can be shifted by the bias voltage. Furthermore, it can be split by substituting the disclosed anodes. The spectral response, using the cathode and top anode has a maximum at short wavelengths. If the diode between the interior anode and the cathode is used, the spectral sensitivity for longer wavelengths increases. Shorter wavelengths are blocked by the top part of the diode; it works like a filter. The presented device structure offers good prospects to improve color separation compared to currently existing detectors by using an additional intermediate contact.

In the past two decades, there has been growing interests in the design and improvement of thermoelectric (TE) materials and devices largely due to their potential use in technologies such as: 1) the conversion of waste heat to electricity, 2) solid-state refrigeration and heating, 3) biomedical batteries, and 4) power sources for both ground and space-based electronics.1 Recent research has suggested that by using nanotechnology (i.e. nanostructuring / nanoengineering) large advances can be gained in controlling interfaces to hinder thermal transport while allowing electrical movement. Thin film structuring of thermoelectric materials potentially offers several advantages over bulk thermoelectric materials especially for cooling applications. Furthermore, others have advocated that by making thermoelectric materials very small, one can achieve an enhanced ZT (the thermoelectric figure of merit) due to quantum confinement effects.2-5 The structure and physical properties of doped fullerene materials were investigated for use as electrically conducting phonon blocking layers. The synthesis and thermal properties of ZnxC60 thin films are reported. Preliminary results have shown the formation of amorphous fullerides structures with thermal conductivities as low as 0.13 Wm-1K-1. Physical and structural measurements (e.g. Electron Microscopy, Electron Diffraction, and Raman Spectroscopy) will be reported detailing the unique structure-property relationships in these materials.

In this work, the effect of bandgap grading of hydrogenated amorphous silicon germanium (a-Si1-xGex:H) absorber near the p/i and the i/n interfaces was investigated. The a-Si1-xGex:H single-junction solar cells were improved by applying both p/i grading and i/n grading. Our results showed that both the p/i and the i/n grading can increase the open-circuit voltage (VOC) as compared to the cell without grading. The i/n grading can further improve the FF. Presumably the potential gradient created by the i/n grading can facilitate the hole transport thus it can improve the FF. However, the JSC decreased as the i/n grading width increased. The reduction of JSC was due to the loss in the red response, which can be attributed to the replacement of lower bandgap material by the larger ones. Combining the effects of VOC, JSC and FF, a suitable thickness of the p/i and the i/n grading was 20 nm and 45 nm, respectively. Finally, the grading structures accompanied with further optimization of doped layers were integrated to achieve a cell efficiency of 8.59 %.

We report the heterogeneous integration of a multifunctional sensor based onpolymer porous photonic bandgap (P3BG) structure and xerogelbased luminescence sensor technology. The P3BG structure wasfabricated using holographic interferometry. Initially, holographicinterferometry of a photo-activated prepolymer syrup that included avolatile solvent as well as monomer, photoinitiator, and co-initiator wasused to initiate photopolymerization. Subsequent UV curing resulted in welldefined lamellae of the polymer separated by porous polymer regions thatcreated a high quality photonic bandgap structure. The resulting P3BG structure was then integrated with the xerogel basedluminescence element to produce a luminescence sensor with a selectivenarrow band reflector. The prototype xerogel based luminescence sensorelement consisted of an O2 sensing material based on spin coatedtetraethylorthosilane (TEOS) composite xerogel films containing tris(4,7-diphenyl-1,10-phenanthroline) ruthenium (II) ([Ru(dpp)3]2+) luminophore. We demonstratedenhancement of the signal-to-noise ratio (SNR) of this integratedmultifunctional sensor while maintaining the same sensitivity to O2 sensing of the xerogel based element. The resultingadvantages and enhanced SNR of this integrated sensor will provide atemplate for other luminescence based assays to support highly sensitive andcost-effective sensor systems for biomedical applications.

We report an experimental study of photocarrier lifetime, transport, and excitation spectra in silicon-on-insulator doped with sulfur far above thermodynamic saturation. The spectral dependence of photocurrent in coplanar structures is consistent with photocarrier generation throughout the hyperdoped and undoped sub-layers, limited by collection of holes transported along the undoped layer. Holes photoexcited in the hyperdoped layer are able to diffuse to the undoped layer, implying (μτ)h ∼ 5 × 10−9 cm2/V. Although high absorptance of hyperdoped silicon is observed from 1200 to 2000 nm in transmission experiments, the number of collected electrons per absorbed photon is 10−4 of the above-bandgap response of the device, consistent with (μτ)e < 1 × 10−7cm2/V.

Vast numbers of bronze coins have been, and continue to be, excavated from archaeological sites around the Greco-Roman world. While often of little value from a strictly numismatic point of view, these coins provide invaluable data within their respective stratigraphic contexts and are used to date occupational and architectural phases more precisely than by ceramics alone. Unfortunately, the build-up of corrosion and mineralization on these coins during their centuries of burial often obscures their legends. Rather than employing potentially destructive and time-consuming chemical or mechanical cleaning techniques to reveal these features, commercially available Micro-focus X-Ray CT systems are now sufficiently well developed to reveal original surface features and to permit identification by a trained numismatist without any cleaning at all.

We investigated the data transmission performance of indium antimonide (InSb) nanowires (NWs) synthesized on InSb (100) substrate using chemical vapor deposition (CVD) having diameters of 20 nm and below. The results indicate that the data transmission performance of NWs suffer from low mobility values on the order of 10-to-15 cm2V-1s-1 because of the scattering due to their small diameters, crystal defects and oxidation occurs during growth and cooling. The 20 nm NWs can sustain data rates up to 5 mega bits per second (Mbps) without any impedance matching and de-embedding of the parasitic parameters coming from the measurement system with a bit error rate (BER) level of 10-8. The data rate is directly proportional to the diameter of the NWs.

We describe organic aerogels derived from multifunctional isocyanates through reaction with water (polyureas), acid andydrides (polyimides) and carboxylic acids (polyamides). All processes are invariably single-step, one-pot and take place at room or slightly elevated temperatures. The resulting materials are robust, their density may vary over a very wide range and their nanomorphology can be either particulate or fibrous, but in all cases they all consist of similarly sized primary particles.

We performed group-theoretical analysis of the symmetry relationships between lattice structures of R, M1, M2, and T phases of vanadium dioxide in the frameworks of the general Ginzburg-Landau phase transition theory. The analysis leads to a conclusion that the competition between the lower-symmetry phases M1, M2, and T in the metal-insulator transition is pure symmetry driven, since all the three phases correspond to different directions of the same multi-component structural order parameter. Therefore, the lower-symmetry phases can be stabilized in respect to each other by small perturbations such as doping or stress.

Mesoporous organosilicate materials combine tunable binding characteristics, high surface area, and low materials density with an ordered pore network. Surface modifications provide the potential for incorporation of a variety of functional groups. We have taken advantage of these characteristics for the development of a range of materials to be utilized in various applications. In one approach, porphyrins are incorporated into the materials to provide unique catalytic properties. In these materials, the organosilicate scaffold stabilizes the porphyrin catalyst and facilitates interaction of the catalyst and target. Catalysis can be stimulated through exposure to light or application of an electrical current. The selectivity of the materials can be influenced through choice of organic bridging groups in the organosilicate structure and through selection of the porphyrin component. In addition, a type of molecular imprinting can be applied to provide sites on the pore walls that enhance adsorption selectivity for the target. These materials are directed at the development of self-decontaminating surfaces and coatings. Similar materials characteristics have been utilized in the development of solidphase extraction materials for use in the pre-concentration of nitroenergetic targets from ground and surface water samples. These materials are being incorporated into systems for in situ water quality monitoring. Mesoporous organosilicates can also be applied to the encapsulation of proteins and nucleic acids, stabilizing them for wider application of technologies utilizing these reagents. Modifications to the pore surfaces, in this case, are used to incorporate stabilizing agents such as sugars and proteins which should extend shelf-life and reduce storage restrictions.

Silicon carbide (SiC) nanostructures attract interest due to their applications in optoelectronic devices, sensors, and high-power/high temperature electronics. The synthesis of SiC nanowires by chemical vapor deposition using hexamethyldisilane (HMDS) as a source material on SiO2/Si substrate has been investigated. Various catalyst materials, including iron (film and nanoparticles), nickel (film and nanoparticles), and cobalt nanoparticles have been used. The growth runs have been carried out at temperatures between 900 and 1100°C under H2 as carrier gas. 3C-SiC nanowires have successfully been grown at even lower temperatures despite the lower efficiency of source decomposition at low temperatures. The SiC nanowire diameters are in the range of 8 nm to 60 nm, as determined by transmission electron microscopy (TEM). In general, the efficiency of nanowire growth has increased with temperature except the growth on Ni film, which has occasionally resulted in SiC flowers. Higher nanowire density at high temperatures can be attributed to more efficient decomposition of the source at higher temperatures. Further, optical properties of the nanowires have been studied by Fourier transform infrared spectroscopy (FTIR). The fabricated nanowires have also been characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and x-ray diffraction (XRD).

Native American quillwork is well documented in art historical and anthropological literature. Methods for folding quills to create floral and abstract designs are addressed, but studies of the materials used to color the quills are conspicuously absent. This is particularly true for the pre-aniline dyes used by communities east of the Mississippi, as historical recipes tend to be more reflective of Plains and Pacific Northwest quillwork traditions. Research to derive quill dye baths from raw materials has and continues to be pursued, but no large-scale scientific analysis of existing quillwork has previously been undertaken. To address this literature gap, a liquid chromatography-mass spectrometry analysis project has been completed on early quillwork in the collections of the McCord Museum, the National Museum of the American Indian, and the Peabody Museum of Archaeology and Ethnology; reflectance spectroscopy and X-ray fluorescence were also used as complementary techniques and to investigate the use of metal salts as quill stains. An extensive literature review provides a historical understanding of pre-1856 quillwork dyes; this representation will be compared with the usage patterns suggested by the collections’ analysis. A more complete understanding of Native dye technology, addressing assumptions currently made with regards to the use of mordants, mixing of multiple dyestuffs in a single bath, and incorporation of “Old World” dyes, will also be presented.

Powder polymer processing techniques were evaluated as a means to generate homogeneous immiscible polymer blends without the high residence times at elevated temperature and high shear rates required by extrusion. Using emulsion polymerized and cryogenically jet pulverized PMMA and HDPE powder precursors, blends were prepared with morphologies comparable to extruded blends. Advanced EDS imaging methods combined with SiO2 marker spheres enhanced electron imaging and analysis of all blend phases. These processing methods will be useful in producing polymer blends from fragile polymers, such as those used in biomedical applications, that cannot tolerate the temperature or shear rates of conventional melt processing.

Printing of functional materials requires reliable deposition processes. This work describes the development of printing processes for selected functional materials utilizing industrial-type inkjet printheads. A well-controlled printing process with fluids containing the conductive polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is presented, allowing linear printing speeds of up to 0.35 m/s in single-pass, and smallest line width of approximately 40 μm when printing 7 pL drop volumes. In addition reliable processes for producing ZnO-based films, which enable novel applications for electronic and UV-sensitive devices, and for printing of conductive carbon nanotube layers are shown.

The facile bottom-up fabrication of a perfect preferentially-oriented MOF nanofilm, NAFS-1 on a solid surface, which is endowed with highly crystalline order both in the out-of-plane and in-plane orientations to the substrate, as determined by synchrotron X-ray surface crystallography, was achieved by the unique combination of a layer-by-layer growth technique coupled with the Langmuir-Blodgett (LB) method.

The space charge region width of the Schottky barrier that forms on the interface between aluminum and organic semiconductor polymer of bulk-heterojunction organic photodiodes has been investigated according to reverse voltage bias over the device and the capacitance-voltage characteristics. Here, we investigated the space charge region widths according to incident light power. Comparison of the mathematical models and experimental data measured under different light power indicate that effect of light on the space charge region of photodiodes is similar to the effect of base-emitter voltage on the space charge region of base-emitter junction in bipolar junction transistors.