Among the different possibilities to control the size, the shape and the spatial organization of nano-objects, one consists in the use of the ordered mesoporosity of silica matrices as nanoreactors for their synthesis. This strategy has been used to elaborate Prussian Blue Analogues (PBA) exhibiting photomagnetic properties. Since the synthesis of these nanocomposites begins with the obtention of mesoporous silica monoliths containing Co2+ ions, we focus in this paper on the effect of the quantity of Co2+ ions and the amount of surfactant on the nanostructuration of these monoliths.

In this paper, silver nanoparticles with a mean diameter of 40 nm are studied for future applications in microelectronic devices. The enhanced diffusivity of nanoparticles is exploited to fabricate electrical interconnects at low temperature. Sintering condition has been tuned to tailor the grain size so that electrical resistivity can be lowered down to 3.4 μOhm∙cm. In this study, a {111}-textured gold thin film has been used to increase diffusion routes. The combined effects of the substrate crystalline orientation and the sintering condition have been demonstrated to have a significant impact on microstructures. In particular, a {111} fiber texture is developed above 300°C in printed silver only if the underlying film exhibits a preferential orientation. This condition appeared as essential for the efficiency of the gold wire-bonding process step. Thus, inkjet-printed interconnects show a prospective potential compared to conventional subtractive technique and offers new opportunities for low cost metallization in electronics packaging.

The mixed-conducting perovskite oxide Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF), given its outstanding oxygen ionic and electronic transport properties, is considered a promising material composition for oxygen transport membranes (OTM) operated at high temperatures.

Its long-term stability under operating conditions is, however, still an important issue. Although the incompatibility of BSCF with CO2-containing atmospheres can be avoided by appropriate means (oxyfuel processes in the absence of carbon dioxide), the thermal as well as the chemical stability of BSCF itself are still under thorough investigation.

This work is focused on the stability of BSCF in the targeted temperature range for OTM applications (700…900 °C) and in atmospheres with low oxygen contents. Previous studies in literature suggest limited chemical stability below oxygen partial pressures pO2 of around 10-6 bar.

By using a coulometric titration method based on a zirconia “oxygen pump” setup, precise control of the oxygen partial pressure pO2 between 1 bar and 10-18 bar was facilitated. Combining electrical measurements on dense ceramic bulk samples performed as a function of pO2 with an XRD phase composition study of single phase BSCF powders subjected to various pO2 treatments, an assessment of the chemical stability of BSCF is facilitated as a function of oxygen partial pressure. It could thus be shown that the pO2 stability limit is considerably lower than previously assumed in literature.

Nanocomposites are of increasing interest due to their unique structural, electronic, and thermal properties. Simultaneously, multiscale molecular modeling is becoming more robust. Therefore computational models are able to be examined with increased accuracy, complexity, and dimension. Graphene based molecules are lauded for their conductive properties as well as their architecture-like geometry which may allow bottom up nanoscale fabrication of nanoscopic structures. Furthermore, these macrocycled molecules allow high interactivity with other molecules including highly tensiled polymers that yield other novel supramolecular structures when interacted. These supramolecular structures are being investigated in lieu of a variety of potential applications. Nanocomposites of cured epoxy resin reinforced by single-walled carbon nanotubes exhibit a plethora of interesting behavior at the molecular level. A fundamental issue is how the self-organized dynamic structure of functional molecular systems affects the interactions of the nano-reinforced composites. A combination of force-field based molecular dynamics and local density-functional calculations shows that the stacking between the aromatic macrocycle and the surface of the SWNTs manifests itself via increased interfacial binding. First-principles calculations on the electronic structures further reveal that there exists distinct level hybridization behavior for metallic and semiconducting nanotubes. In addition there is a monatomic increase in binding energy with an increase in the nanotube diameter. The simulation studies suggest that graphene nanoplatelets are potentially the best fillers of epoxy matrices. The implications of these results for understanding dispersion mechanism and future nanocomposite developments are discussed.

The crystallographic properties of bulk icosahedral boron arsenide (B12As2) crystals grown by precipitation from molten nickel solutions were characterized. Large crystals (5-8 mm) were produced by dissolving the boron in nickel at 1150°C for 48-72 hours, reacting with arsenic vapor, and slowly cooling to room temperature. The crystals varied in color from black and opaque to clear and transparent. Raman spectroscopy, x-ray topography (XRT), and defect selective etching revealed that the B12As2 single crystals were high quality with low dislocation densities. Furthermore, XRT results suggest that the major face of the plate-like crystals was (111) type, while (100), (010) and (001) type facets were also observed optically. The predominant defect in these crystals was edge character growth dislocations with a <001> Burgers vector, and <-110> line direction. In short, XRT characterization shows that solution growth is a viable method for producing good quality B12As2 crystals.

Air-mediated molecular ordering in self-organized polymer semiconductors of regioregular poly(3-hexylthiophene) (P3HT) and poly[(9,9′-dioctylfluorenyl-2,7-diyl)-(2,2′-bithiophene-5,5′-diyl)] (F8T2) was investigated using organic field-effect transistors (OFETs) fabricated by transfer-printing using poly(dimethylsiloxane) stamps with various surface energies. OFET measurements revealed that the charge transport in the polymer semiconductors via the air interface layer was better than that via the substrate interface layer. The results indicated that the formation of a highly ordered microstructure at the polymer/air interface through air-mediated self-organization occurs in many polymer semiconductors. This air-mediated self-organization was weaker than substrate-mediated self-organization, whose influence appeared in OFETs with thin semiconductor films.

Frisch collar detectors were fabricated from TlBr crystals with the dimensions of 2 mm × 2 mm × 4.4 mm. Spectroscopic performance of the TlBr Frisch collar detectors was evaluated at room temperature. An energy resolution of 2.9% FWHM at 662 keV was obtained from the detector without the depth correction. The detector exhibited stable spectral performance for 12 hours. Direct measurements of electron mobility-lifetime products were performed with the detectors. The TlBr crystals exhibited the electron mobility-lifetime products of ∼10−3 cm2/V at room temperature.

Polycrystalline thin-film CdS/CdTe PV cells nearly always require “activation” with vapors containing chlorine and oxygen near 400 oC in order to realize the highest cell performance, even when growth occurs near 600 oC. In this study we have used film growth near 270 oC by magnetron sputtering in an oxygen-free ambient and have studied the effects of post-deposition heat treatments for 20 minutes at 400, 425 and 450 oC without CdCl2 in a dry air ambient. The heat treatments enhanced grain growth and produced re-crystallization of the CdTe film at all three temperatures, but 450 oC was required to reach the best electrical performance. Grain size increased from a couple of hundred nanometers to more than a micron as the preferred (111) growth orientation decreased. Efficiencies up to 11.6% were achieved with no CdCl2 compared to ~13% with activation at 387 oC in the presence of CdCl2 vapors. X-ray diffraction and quantum efficiency measurements show interdiffusion of CdS and CdTe at 450 oC comparable with a standard CdCl2 treatment at 387 oC. The results are discussed in terms of CdSTe alloy gradients and minority-carrier diffusion lengths.

We demonstrated the enhancement of electroluminescence (EL) from green CdSe/ZnS QDs in hybrid QD/organic light-emitting diodes (QD-LEDs) by employing blue phosphorescent dyes Bis(4,6-difluorophenylpyridinato-N,C2)picolinatoiridium (FIrpic) as efficient exciton harvesters and energy transfer donors. Precise control of the concentration of the FIrpic donors doped in a 4,4’-N, N’-dicarbazole-biphenyl (CBP) host and their distance from the QD layer led to complete triplet exciton energy transfer and EL enhancement by a factor of 2.5. The Förster distance between FIrpic molecules and green CdSe/ZnS QDs was determined to be ∼ 8 nm, which is in a good agreement with the value calculated using the Förster model. Our study shows that integrating colloidal QDs with phosphorescent organic dyes provides an effective means for improving the quantum efficiency of QD-based hybrid LEDs.

In this study, the morphological changes of chemically treated (orpreserved) with aqueous solutions of 1) a sodium chloride (NaCl) and 2) acompound containing sodium silicate, so called “wasserglass”, and untreatedI-type collagen fibers of Mongolian goatskin are investigated by atomicforce microscopy in ambient condition and at room temperature. Theexperimental results show that the difference between D period for bothchemically treated and untreated collagen fibers are a relatively stable formorphological behavior. However, we find that the width of collagen fiberstreated with the NaCl solution is more increasing with approximately 112 nmthan those of samples (untreated and treated with wasserglass solution) forthe range 93.4-94.8 nm. We also observe that a typically structure of thecollagen fibers generally, a dense packing of the untreated and treated bywasserglass collagen fibers in bundles in a nearly parallel arrangement,with little changes in orientation can be seen. The collagen fibers treatedby NaCl are a more destructive than untreated and treated by wasserglass forcollagen fibers.

The effect of the nanofiller chemistry on the mechanical behaviour of thermoset polymer matrix nanocomposites is investigated. The interaction between a crosslinked polymer resin and the reinforcing nanofibers driven by their chemistry is revealed by molecular dynamics simulations. Specifically, crosslinked network systems of neat epoxy and epoxy-P(St-co-GMA) are modeled to discuss the effect of various molecular interactions as a function of temperature on a molecular basis. At 433K°, incorporation of single molecule of bonded P(St-co-GMA) and nonbonded P(St-co-GMA) lead to increase in Young’s modulus by 10% and 6%, respectively, compared to neat epoxy system.

Nanocrystalline Zn1-xCoxO powders exhibiting a preferential crystal growth along the (002) plane have been synthesized in the atomic fraction, ‘x’, range of 0.0-0.0625 by a wet chemical method. The effect of the dopant concentration on the corresponding structural, optical and magnetic properties was also evaluated. XRD analyses evidenced the development of single-phase wurtzite with no traces of any impurity for all the dopant levels. The higher intensity of the (002) peak, when compared to the XRD peaks in bulk ZnO, indicates the preferential crystal growth along the c-axis in hexagonal wurtzite cell. The linear dependence of cell parameters a and c with ‘x’ suggests the actual replacement of Zn by Co ions in the host oxide lattice. Micro Raman spectroscopy measurements showed a band centered at 535cm-1, which can be assigned to a local vibrational mode related to Co species in addition to the normal modes associated with wurtzite. The relative broadening of this band at 535cm-1 was enhanced by increasing ‘x’. The other characteristic bands of ZnO corresponding to A1 (E2, E1) and E2 High modes were red shifted for all Co contents. UV-vis measurements showed that the energy band gap of as-synthesized nanopowders decreased with increasing Co2+ content up to x = 0.03 and increased for higher contents. Room-temperature magnetization measurements revealed the paramagnetic behavior of the Co-doped ZnO nanopowders.

We describe two techniques to create sharp tips. The first involves thebuckling of thin metal films deposited on soft, stretchable substrates. Thesecond involves the formation of narrow necked capillary bridges.

Hybrid field-effect-transistors (FETs) with germanium nanowire (NW) arrays and organic gate dielectric are presented. The nanowire deposition steps are fully compatible with printed electronics route. NW FETs demonstrate good performance with On/Off ratios of ~103 and hole mobilities of ~13 cm2/Vs in both nitrogen and air atmosphere. These results suggest that the hybrid nanowire FETs could be used in large area inexpensive electronics.

CdS host nanocrystals with 4.2-5.5 nm in diameter have been synthesized from air stable precursors via a synthetic chemical route and doped with rare earth (RE) terbium (Tb3+) and ytterbium (Yb3+) ions. RE3+-doped CdS cores were shelled by ZnS layers of different thicknesses. The resulting core/shell nanocrystals show a complete broadband absorption below 400-460 nm to the deep UV region depending on the size of the cores. RE3+-doped CdS nanocrystals showed a red shift in the emission as observed under irradiation of 302 nm UV light and was confirmed by room temperature photoluminescence (PL) measurements. The nanocrystals were further characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive x-ray (EDX) analysis. The results show that these RE3+-doped nanocrystals can be used as solar spectral matching downconversion material to enhance photovoltaic efficiency of existing solar cells.

We report site-selective studies of the Zeeman splittings that are observed for magnetic fields up to 6.6T for different Eu incorporation sites in GaN. Utilizing resonant excitation with visible light, we are able to distinguish the site and find for one center (Eu1) a splitting into five components as expected for C3v symmetry. The corresponding g-values are 1.66 and 1.90. The two lines of another center Eu2 each split into two levels corresponding to g-values of 1.9 and 2.84. Most surprisingly a third center, for which only one line is clearly identified, a g-value of 6.16 is found which is larger than can be explained for a 7F2 purely ionic Eu state.

Intermetallic γ-TiAl based alloys with additional amounts of the ternary bcc β phase attracted increasing attention in recent years due to their improved workability at elevated temperatures. At lower temperatures the ductile high-temperature β phase can transform to several ordered phases. However, actually available phase diagrams of these multiphase alloys are quite uncertain and the precipitation kinetics of some metastable phases is far from understood.

In the present study various transformations of the third phase are observed in situ by means of high-energy x-ray diffraction using synchrotron radiation. A Ti-45Al-10Nb (at.%) specimen is subject to a temperature ramp of repeated heating cycles (700 °C - 1100 °C) with subsequent quenching at different rates. Depending on the quenching rate reversible transformations of the B2-ordered βo phase to different ω related phases are observed in Ti-45Al-10Nb. At low quenching rates the hexagonal B82-ordered ωo phase is formed while at high quenching rates the metastable intermediate trigonal ω’’ phase can be preserved. The results indicate that the complete transformation from βo to hexagonal B82-ordered ωo consists of two steps which are both diffusion controlled.

We are developing highly transparent ceramic oxide scintillators for high energy (MeV) radiography screens. Lutetium oxide doped with europium (Lu2O3:Eu) is the material of choice due to its high light yield and stopping power. As an alternative to hot-pressing, we are utilizing vacuum sintering followed by hot isostatic pressing (HIP). Nano-scale starting powder was uniaxially pressed into compacts and then sintered under high vacuum, followed by HIP’ing. Vacuum sintering temperature proved to be a critical parameter in order to obtain highly transparent Lu2O3:Eu. Under-sintering resulted in open porosity disabling the driving force for densification during HIP’ing, while over-sintering lead to trapped pores in the Lu2O3:Eu grain interiors. Optimal vacuum sintering conditions allowed the pores to remain mobile during the subsequent HIP’ing step which provided enough pressure to close the pores completely resulting in fully-dense highly transparent ceramics. Currently, we have produced 3 mm thick by 4.5 cm diameter ceramics with excellent transparency, and anticipate scaling to larger sizes while maintaining comparable optical properties.

Magnesium and titanium doped indium oxide (IMTO) thin films were grown using pulsed laser deposition technique. Magnesium was added to enhance the bandgap, whereas titanium was added to improve carrier concentrations and mobility of indium oxide films. The effect of growth temperature on structural, optical, and electrical properties were studied. It was observed that the optical transparency of the films strongly depends on growth temperature and increases with increase in growth temperature. The films grown at 600 °C showed optical transparency > 85%. We observed widening in bandgap of indium oxide by doping with magnesium and titanium. The bandgap of IMTO films increases with increase in growth temperature. The maximum bandgap of 3.9 eV was observed for film grown at 600 °C. It was observed that growth temperature strongly affects the electrical properties such as resistivity, carrier concentration, and mobility. The electrical resistivity and mobility of the films increases with increase in growth temperature. On the other hand, carrier concentration decreases with increase in growth temperature. Temperature dependence electrical resistivity measurements showed that films grown at low temperatures are semiconducting in nature, while films grown at high temperature showed transition from semiconducting to metallic behavior. These wide bandgap, highly transparent, and high mobility films could be used for photovoltaic applications.