This work investigates an alternative way to modify the pore size of a 100 mg/cc resorcinol formaldehyde (R/F) aerogel without any significant change to the aerogel target density. This was successfully accomplished by an addition of hydrophilic polymer additive [Poly Vinyl Alcohol (PVA) or Poly Acrylic Acid (PAA)] to the R/F precursor solution which acts as an impurity in the reaction. The polymer can modify the cross linking or aggregation of the primary particles which can change the structure formation of the aerogel, thus changing the pore size. This paper will discuss this process modification and the fabrication of hollow, large pore R/F aerogel spheres that are used for direct drive inertial confinement fusion (ICF) cryogenic ice layering experiments at the University of Rochester Laboratory for Laser Energetics (LLE). The aerogels were characterized using scanning electron microscopy (SEM), nitrogen gas adsorption, and ultra small angle x-ray scattering (USAXS).

This paper reports structural, morphological, optical and humidity sensing characteristics of pulsed laser deposited ZnO film. The XRD pattern reveals amorphous structure of the film. Scanning electron micrograph indicates formation of ZnO rods in micron size. Transmission increases gradually in the UV-VIS region. For studying the humidity sensing characteristics of the film, base of a right angled isosceles glass prism has been coated. Chopped light from a polarized He-Ne laser incident on the entry face of the prism gets reflected from the base – film – humid air interfaces and then emergent light is collected by the detector placed in front of the exit face of the prism. The least change in relative humidity which could be measured using the present configuration is 1.06RH%. Further the film is annealed at 400°C for four hours and its humidity sensing behavior is investigated in the similar manner which now shows a reversed trend. The sensitivity to humidity has decreased and the least change which could be detected now is 1.16RH%.

This paper presents a multiple magnetoelastic (ME) biosensor system for in-situ detection of S. typhimurium and B. anthracis spores in a flowing bacterial/spore suspension (5 x 101 - 5 x 108 cfu/ml). The ME biosensor was formed by immobilizing filamentous phage (specific to each detection target) on the ME platforms. An alternating magnetic field was used to resonate the ME biosensor to determine its resonance frequency. When cells/spores are bound to a ME biosensor surface, the additional mass of the cells/spores causes a decrease in the resonance frequency of the biosensor. The detection system was composed of a control sensor, an E2 phage-based biosensor (specific to S. typhimurium) and a JRB7 phage-based biosensor (specific to B. anthracis spores). The frequency response curves of the ME biosensors as a function of exposure time were then measured and the detection limit of the ME biosensor was observed to be 5 x 103 cfu/ml. The results show that phage-based ME biosensors can detect multiple pathogens simultaneously and offer good performance, including good sensitivity and rapid detection.

Bulk samples of six Ln2TiO5 compounds with Ln = La, Pr, Nd, Eu, Gd and Tb were prepared and characterised. Most of the samples have a phase purity of ∼95% (based on BEI and EDS) with the predominant secondary phase primarily being Ln2Ti2O7. Using XRD, TEM selected area diffraction and high resolution imaging techniques, we have confirmed the results of previous studies which showed that at room temperature Pr2TiO5, Nd2TiO5, Eu2TiO5 and Tb2TiO5 have orthorhombic structures with Pnma symmetry. The structure of Tb2TiO5 was further monitored as a function of temperature. The relevance of Ln2TiO5 compounds to advanced nuclear fuel cycles is discussed.

By using a high density microwave plasma source, an ultrafast deposition rate over 1000 nm/s has been achieved for polycrystalline silicon (poly-Si) film deposition. We find that crystalline structure of the deposited film evolves along the film growth direction, i.e. large grains in surface region while small grains in the bottom region of the film. Systematic study of the deposition process has been performed as a function of the deposition duration. Based on the observed results, a possible mechanism, the annealing-assisted plasma-enhanced chemical vapor deposition, is proposed to describe the film growth process.

Intrinsic point defects determine to a large extent the semiconductor crystal quality both mechanically and electrically not only during crystal growth or when tuning polished wafer properties by thermal treatments, but also and not the least during device processing. Point defects play e.g. a crucial role in dopant diffusion and activation, in gettering processes and in extended lattice defect formation.

Available experimental data and results of numerical calculation of the formation energy and diffusivity of the intrinsic point defects in Si and Ge are compared and discussed. Intrinsic point defect clustering is illustrated by defect formation during Czochralski crystal growth.

The fundamental characterization and understanding of 5f electron behavior in actinide complexes is imperative to provide an enhanced basis for the rational and accelerated development of improved processes relevant to nuclear energy. Soft x-ray absorption spectroscopy utilizing the scanning transmission x-ray microscope (STXM) at the Advanced Light Source-Molecular Environmental Science (ALS-MES) Beamline 11.0.2 has been used to probe the electronic characteristics of a nitrogen donor ligand 2,6-Bis(2-benzimidazyl)pyridine (BBP) and its resulting U(IV) complex. The nitrogen K- and carbon K-edges have been collected from both ligand and uranium complex, as well as the uranium 4d-edge from the complex. Upon complexation, the light element absorption spectra change markedly and the uranium spectra from the complex is compared to the reference spectrum obtained from U(IV)Cl4. The evolution of the spectral features are described and interpreted within a simple conceptual framework. Based on spectral evidence alone, the uranium is bound through the pyridine-like nitrogens and the oxidation state of the uranium is consistent with a U(IV) species.

Thin films based on nano-composites have attracted considerable attention for their possible applications in devices and sensors. These nano-composite thin films are formed by embedding metal or semiconductor nano-particles in a host material and they exhibit interesting electrical transport properties. Using pulsed laser deposition technique, we have prepared nano-composite thin films of gold-strontium titanate on quartz substrate. Gold and strontium titanate were used as targets for pulsed laser deposition. Thin films having different compositions were grown. The effect of different composition on their electrical and optical properties has been studied in details. The structural characterizations of the films were done by x-ray diffraction, transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. Transmission electron microscopy as well as atomic force microscopy shows the presence of gold nano-particles in these films. X-ray diffraction and energy dispersive x-ray spectroscopy shows the existence of strontium titanate and gold. Current-voltage characteristics and temperature dependent resistivity measurements were made to characterize electrical properties of these films. Electrical properties can be manipulated from metal to insulator through semiconductor by varying the composition. In addition, it is observed that the absorption of visible light increases with increase in gold percentage. This indicates that these nano-composites could also use as active materials for many electronic as well as optical sensors.

The insertion of an AlN interlayer for tensile strain relief in GaN thin films grown on Si (111) on-axis and vicinal substrates by nitrogen rf plasma source molecular beam epitaxy has been investigated. The 15 nm AlN interlayer was inserted between the bottom 0.5 micron GaN layer and the top 1.0 micron GaN layer. The interlayer was very effective to reduce the tensile stress in the overall 1.5 micron GaN/Si film to the level required for complete avoidance of microcracks, which were present in high densities in GaN/Si heterostructures grown without an AlN interlayer. The strain of the AlN interlayer, as well as the strain in all the layers of the entire GaN/Si heterostructure was analyzed by x-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. Reciprocal space map in XRD indicated that the 15 nm AlN interlayer was coherently strained with the GaN films. However TEM observations revealed that the AlN interlayer was partially relaxed in local regions. The AlN interlayer was also observed to interfere with the GaN growth process. In particular, above morphological features such as V-defects, GaN was overgrown with a large density of threading dislocations and inversion domain boundaries.

The University of Puerto Rico-Mayaguez and University of Wisconsin-Madison Partnership for Research and Education in Materials (UPRM-UW PREM) aims to create richer educational and research opportunities for Hispanic students in Materials Science and Engineering (MSE) and increase their representation in the Materials Science community. The educational and outreach (E&O) components for the UPRM-UW PREM include interventions for high school students and teachers, and undergraduate and graduate students at UPRM. The present report focuses on activities conducted with high school and university students during the third year of the program (2006-07). Results of surveys with student participants indicate that their participation contributes positively to their learning and development in laboratory, research and professional skills, as well as increases student interest in pursuing graduate studies in MSE.

Oxides have always been an integral part of semiconductor manufacturing both in front and back-end processing. With the necessary increase in performance, the demand on these oxides has been increasing leading to their (future) replacement by more complex materials, such as high-k's in gate oxide and metal gates. With the increasing material complexity, a thorough characterization of all aspects of these materials is necessary, covering, for instance, surfaces and interfaces, nucleation, growth, atomic structure, …

This article focuses on the characterization of front-end oxides and their interfaces. It shows that detailed information can be achieved by sophisticated experimental techniques such as synchrotron radiation, high energy ERD or AtomProbe but that adequate sample preparation and/or analysis by a combination of more routinely available techniques may achieve similar results. This is shown through the study of three different systems/problems in the gate stack analysis. We will first focus on the determination of substrate surface preparation conditions before deposition and their influence on growth mode and the growth characteristics by different growth techniques (ALD, MOCVD, …). Second, we present the possibilities of compositional depth profiling of thin layers both with nuclear techniques and Angle-Resolved XPS. Finally, we will show that using conventional XPS and a combination of front and back-side analysis, the interface between high-k oxide and metal gates can be investigated. More examples of gate stack characterization can be found elsewhere

Synchrotron white beam x-ray reticulography was used to quantitatively map the residual stress/strain in SiC wafers. The basic principle of our study is that there exists a relationship between the stress state in a crystal and the local lattice plane orientation and that this relationship can be exploited in order to determine the full strain tensor as a function of position inside the crystal. The theoretical background of the stress mapping using synchrotron white beam x-ray reticulography is introduced and it is based on the change of plane normal of the lattice plane due to the distortion associated with the residual strain. The stress mapping of a crystal region from a commercial 4H silicon carbide wafer has been studied using this technique and the results are discussed. This technique can in principle be used in any single crystal material.

Lead zirconate titanate (PZT) nanofibers are obtained by electrospinning a sol-gel based solution and polyvinyl pyrrolidone (PVP) polymer, and subsequent sintering of the electrospun precursor fibers. The PVP content of the precursor solution is critical in the formation of the fully fibrous mats. Scanning electron microscope (SEM) is used to examine the morphology of the precursor fibers and annealed PZT nanofibers. The diameters of the precursor PZT/PVP green fibers have increased with the aging of the precursor solution along with an increase in the viscosity. The viscosity of 500 mPa results in successful fibrous mats, yielding green PZT/PVP fibers with a diameter of 400 nm. The fiber mats are then sintered at 700°C. X-ray diffraction (XRD) pattern of the annealed PZT fibers exhibits no preferred orientation and a pure tetragonal perovskite phase. Preparation of piezocomposites by infusion of epoxy into the nanofiber mat facilitates successful handling of the fragile mats and enables measurements of dielectric properties.

A carbon nanofiber-based sensor film is designed and calibrated for force measurement. The sensor is designed for use in structural health monitoring of composite materials. The sensing scheme is based on creating a network of carbon nanofibers on the surface of the composite material. In the experimental scheme a patch of nanofiber reinforced epoxy resin film is developed and adhesively bonded to the laminate. The extension of the sensor film due to the applied force leads to a change in the connectivity of carbon nanofibers in the film, resulting in the change in the resistance of the network. Results show that such sensing schemes have high sensitivity and repeatability. Use of nanofibers can provide a low cost and more efficient alternative to other sensor films that rely on carbon nanotubes.

We report the synthesis of ZnO aggregates in the presence of lithium salt and the enhancement on the energy conversion efficiency of dye sensitized solar cells when the photoelectrode films consist of as-synthesized ZnO aggregates. The conversion efficiency for ZnO film consisting of aggregates synthesized with lithium involvement is significantly improved up to 5.8%, which is 32% higher than that of 4.4% obtained for pure ZnO film. Such an enhancement can be attributed to the effect of lithium-induced changes on the morphology and crystallinity of aggregates, the optical absorption of films, and the surface chemistry of ZnO, which provides the film with decreased electron trapping and increased refractive index, and enhances the electronic coupling between the dye molecules and ZnO.

We have demonstrated that a number of known good dies (KGDs) can be precisely aligned in batch and stacked on LSI wafers by our chip-to-wafer three-dimensional (3D) integration technology using an innovative self-assembly technique. Compared with conventional robotic pick-and-place chip assembly, the fluidic self-assembly can provide high-throughput chip alignment and bonding, and the resulting self-assembled chips have high alignment accuracy of approximately 0.3 micron on average. Immediately after chip release, the chips are aligned onto the predetermined hydrophilic bonding areas in a short time within 0.1 sec by the surface tension of aqueous liquid used in our self-assembly. By using the self-assembly, a number of KGDs with different chip sizes, different materials and different devices can be stacked in high yield to give highly integrated 3D chips we call the 3D Super Chip.

Poly (cyclohexanedimethanol cyclohexanedicarboxlic acid) (PCC), a fairly newly synthesized polyester, has been studied. Having a good experience of increasing both thermal stability and service temperature when applied to typical polymers, poly (tetramethylene glycol) (PTMG) was selected as a softening agent that was randomly copolymerized into the PCC chains. Another widely-used polyester, poly (ethylene terephthalate) (PET) was also produced in order to investigate the effect of PTMG, which was compared with the properties of the newly developed random PCC-PTMG copolymers (PCCP). In this study, the crystalline structures, the thermal and the mechanical properties of both PCC and PET containing different ratios of the random segment of PTMG were investigated by differential scanning calorimetery (DSC) and tensile tester.

It was found that the crystallization rate of pure PCC was significantly slow, whereas for PCCP, PTMG effectively accelerated the crystallization rate with increasing PTMG, and the sample with 25 wt% of PTMG had the fastest crystallization rate in all PCCP samples. Here, the PTMG acted as an accelerator, simultaneously depressing the movement of PCC molecular chains. The elastic recovery test indicated that the ability of PTMG as a softening agent was highly demonstrated at 20 wt% of PTMG. The results of PCCP were compared with those of PET-PTMG copolymers (PETP) and it was found that there were optimum values of PTMG for the crystallization rate on both samples. Additionally, the results of the elastic recovery test indicated that the softening effects observed in PCCP were more pronounced than those observed in PETP.

We used a surface-plasmon antenna to obtain small photodetectors for LSI on-chip optical interconnection by using near-field light generated by the antenna. Such near-field devices are not constrained by the diffraction limit and they offer an approach to integrated nanoscale photonic devices. A small semiconductor structure is located near the antenna to absorb the near-field light. This structure can be made as small as the Schottky depletion layer, so the separation between electrodes can be reduced to almost the size of the near-field region. We have demonstrated a “Si nano-photodiode” or plasmon photodiode that uses the near-field localized in a subwavelength region, which is usually relatively large in size because of the long absorption length for Si (˜10 μm at a wavelength of ˜800 nm). The Si nano-photodiode has a fast impulse response with a full-width at half-maximum of ˜20 ps even when the bias voltage is small (˜1 V or less). We demonstrated an on-chip optical interconnect chip to operate circuitry in an LSI chip by using waveguide-coupled Si nano-photodiodes.

Complementary indicators have been used in developing a safety case in order to avoid uncertainties in the biosphere modeling used to estimate conventional dose or risk. For example, radionuclide fluxes can be used to evaluate the effectiveness of barrier performance. However, it is difficult to define relevant yardsticks for comparison, because the fluxes of naturally occurring radionuclides due to geological processes vary considerably depending on time and location. This paper discusses the relevance of alternative yardsticks for assessing modeled radionuclide fluxes by selecting yardsticks calculated from fluxes of natural radionuclides at the groundwater discharge point from the geosphere to an aquifer; these are then compared with fluxes of repository-derived radionuclides at the same point. Such yardsticks avoid surface geological processes that may also contribute to natural fluxes, allowing comparison at a suitable, common evaluation point that avoids dependence on site-specific conditions. The effectiveness and robustness of barrier performance is demonstrated using the developed yardsticks and the sensitivity of the analysis to groundwater flux is illustrated.

The growth of high-quality crystalline ZnO thin films on ZnO bulk substrates and of amorphous In-Ga-O and Ga-Al-O thin films has been demonstrated by using the solution-based cost-effective and environmental friendly ultrasonic spray assisted mist-CVD method. The homoepitaxial ZnO thin films with atomically flat surfaces were successfully grown on Zn-polar ZnO substrates via a step-flow growth mode, in spite of different miscut angles of the substrate, at the furnace temperature of 1000°C. The compositions and optical absorption edges of the amorphous In-Ga-O and Ga-Al-O thin films were controlled by means of the concentration ratios of [In]/([In]+[Ga]) and [Al]/([Al]+[Ga]) in the starting solutions.