Hydrogenated polymorphous silicon (pm-Si:H) is one of the most promising candidates for a stable top cell material in multi-junction thin film solar cells. Solar cells using pm-Si:H as their absorbing layer show very interesting degradation kinetics when compared to hydrogenated amorphous silicon (a-Si:H), summarized by macroscopic structural changes and irreversible changes in solar cell characteristics, while nevertheless preserving a higher stabilized efficiency. Notably, pm-Si:H solar cells, once degraded, respond to neither annealing nor further light-soaking. Such results suggest a device degradation mechanism including structural changes, active hydrogen motion, and interface delamination mediated by fast hydrogen diffusion and accumulation at the interface. Interestingly, a similar behavior was reported for a-Si:H solar cells under severe light soaking conditions (at 350 °C or under 50 suns) while pm-Si:H solar cells show such behavior under 1 sun at 40 °C.

Organic light-emitting devices (OLEDs) have attracted a lot of attention as a next generation display. In this study, we fabricated the micro-OLEDs by room-temperature curing nanoimprint lithography (RTC-NIL) using diamond molds. The diamond has superior durability and was used as mold material for RTC-NIL. The diamond molds have been fabricated by electron cyclotron resonance (ECR) oxygen ion shower with polysiloxane oxide mask in the electron beam (EB) lithography technology. We fabricated the diamond mold pattern with 10 μm-square dot. The diamond molds have been used to form an insulating layer in micro-OLEDs. The optimum thickness of N,N’-Diphenyl-N,N’-di(m-tolyl)benzidine (TPD) [hole transport layer],Tris(8-quinolinolato)aluminum (Alq3) [electron transport layer] and aluminum (Al) [cathode] were 40 nm, 40 nm and 200 nm, respectively. We succeeded in formation of insulating layer in micro-OLEDs and operation of micro-OLEDs with 10 μm-square-dot by RTC-NIL using diamond molds.

Recombinant human bone morphogenetic protein (rhBMP-2) plays a major role in differentiation of marrow stromal cells (MSCs). Peptides based on the active domains of rhBMP- 2, like the LYLTSIASLETPVSSAKPIK (BMP peptide), have been proposed as an alternative to reduce the side effects associated with high doses of rhBMP-2. The objective of this work was to determine the osteogenic activity of the BMP peptide grafted to poly(lactide fumarate) nanoparticles (PLAF NPs). A cysteine-terminated BMP peptide was grafted to PLAF NPs by linking the cysteine residue to the fumarate groups. Groups included blank NPs, free BMP peptide, free BMP-2 protein, and BMP-grafted NPs. The decrease in cell numbers after 21 days was consistent with an increase in mineral content and decrease in proliferation with osteogenic differentiation of MSCs. Alkaline phosphatase (ALPase) activity peaked at 14 days, consistent with the start of the osteogenic cascade. A slightly higher mineral content was observed in the BMP-grafted NP group after 14 days. m-RNA and immunostaining showed that cells in the BMP-grafted NP group had a higher content of osteocalcin protein after 21 days. Results suggest that the BMP-grafted NPs have a greater affinity to BMP cell surface receptors, leading to a stronger activation of the pathways leading to osteogenesis.

We have investigated microstructures in both the antiferroelectric (AFE) and relaxor states of Pb(In1/2Nb1/2)O3 (PIN) with the perovskite structure by a transmission electron microscopy (TEM). Electron diffraction (ED) experiments revealed that the AFE state is characterized as the modulated structure with the modulation vector of q =1/4 1/4 0. High-resolution TEM images clearly show the coexistence of two types of domains consisting of the modulated and the nonmodulated structures with the 100 ∼ 200 nm size. On the other hand, in the relaxor state there appear two types of diffuse scatterings in the ED patterns. One is diffuse spots at the 1/2 1/2 0-type reciprocal positions and the other is diffuse streaks elongating along the <110> direction around the fundamental spots. The real-space TEM images clearly demonstrate the presence of nanodomains with the average size of ∼ 5 nm. These nanodomains in the relaxor state should be responsible for the characteristic dielectric properties.

Zirconia and Yttrium stabilized zirconia are well-known ceramic materials. Scaling down the dimension of these ceramics can result in a faster sintering process at lower temperatures. Microwave synthesis of nano-structured particles is a very attractive synthesis route because of the short synthesis time and low reaction temperature. This allows a fast screening of the influence of different parameters such as time, temperature and pressure on the final size and crystal phase of the particles. In this study Zr and Zr/Y aqueous precursors are mixed with a variety of complexing agents or surfactants in different ratios. The reason is twofold: (1) we aim for a stable precursor solution which is established by lowering the free ion concentration and (2) we want to see the influence of the complexing agents on the growth of the particles and the formation of crystalline phases. Particle sizes of these particle vary from 40 -200 nm. The crystallinity is confirmed by X-ray diffraction. The stabilization of these particles and possible exchange of the ligands is examined with NMR measurements (1D - proton combined with 2D NOESY) and is compared with TGA-DTA analysis of the isolated particles.

We report the formation and optical properties of site-controlled InAs/GaAs quantum dots (QDs) embedded in GaAs nanowires (NWs) by selective metalorganic chemical vapor deposition for application to single photon sources. InAs/GaAs QD-in-NWs with various InAs thicknesses are realized on patterned GaAs(111)B substrates in the form of InAs/GaAs heterostructures and identified by structural analyses using scanning transmission electron microscopy and photoluminescence characterization. Sharp excitonic emission peaks at 10 K from single QD-in-NWs with the narrowest exciton linewidth of 87 μeV are observed. Light emission from the single QD-in-NW shows photon antibunching which evidences single photon emission from high-quality QD-in-NWs.

Higher burn-up (> 50 GWd/t) spent nuclear fuels (SNF) present problems for long-term management and disposal in mined repositories, principally because of their higher heat output. Here we present results from heat flow modeling of an alternative scheme for disposing of SNF - deep borehole disposal (DBD). We focus on how temperatures on the outer surface of the containers evolve, affect the melting and re-solidification of the high density support matrix (HDSM) and their consequences for the feasibility of this disposal concept. We conclude that not only is DBD a viable option for higher burn-up SNF, but it could be a practical disposal route for a range of combinations of SNF ages and number of fuel pins per container.

Termination of the Yucca Mountain repository program implies that U.S. spent nuclear fuel (SNF) and high-level radioactive waste may be stored for very long periods, i.e., more than 100 years.Many of the storage systems for commercial SNF are large, cylindrical, welded, stainless-steel canisters containing 24-80 SNF assemblies in an inert gas (helium) environment.Each canister is contained in a massive reinforced concrete structure for shielding, safety, and security reasons.Airflow in the annular space between the canister and the concrete structure removes SNF decay heat by natural convection.

Undetected defects in the canister-lid welds and stress corrosion cracking (SCC) in the canister-lid weld area may combine to form pathways for slow escape of the inert fill gas from the canister.SCC may not occur until many decades after SNF is loaded into the canister because SNF decay heat initially would keep the canister surface temperatures above the temperature where liquid water, a prerequisite for SCC, could condense.The period required for inert gas to escape from the canister once pathways have formed and for air subsequently to enter the canister may also be measured in decades, depending on the size and shape of the pathways.

In this paper, the authors explore the limits of weld-flaw detectability; when necessary conditions for SCC could occur in the canister-lid weld area; the period for loss of inert fill gas if through-weld cracks occur; and the possible consequences of fill gas loss.The authors also develop a list of research and study needs to address the possibility of SCC resulting in the loss of fill gas.

Since its introduction in early 1990s, bulk-heterojunction organic photovoltaic solar cell (BHJ-OPV) has promised high-efficiency at ultra-low cost and weight, with potential for non-traditional applications such as building-integrated PV. There is a widespread presumption, however, that the complexity of morphology makes carrier transport in OPV irreducibly complicated, and possibly, beyond predictive modeling. In this paper, we use elementary and intuitive arguments to derive the fundamental thermodynamic as well as morphology-specific practical limits of BHJ-OPV efficiency. We find that constraints of the percolation threshold and trade-off among short-circuit current, open circuit voltage, and fill factor make substantial improvement in OPV efficiency difficult. We posit that future improvement in OPV will rely not on morphology engineering, or reducing the polymer bandgap, but on increasing both the effective μ × τ product and the cross-gap between donor/acceptors. Even if the OPV fails to achieve the highest efficiency anticipated by the thermodynamic limit, its novel form factor, lightweight, and transparency can make it a commercially viable option for many applications.

In this study, Ag doped hydroxyapatite (HA) samples prepared by EDTA chelatedecomposition method were characterized with X-Ray Diffraction Spectroscopy(XRD), Scanning Electron Microscopy (SEM) and antimicrobial sensitivitytest. Hydroxyapatite (Ca10(PO)6(OH)2) and NaCaPO4 (rhenanite) phases were observed while Ag was presentin the form of Ag2O. Results showed that microstructurallycontrolled HA-based composites with NaCaPO4 interphase can beprepared, which significantly enhances sinterability of hydroxyapatite at1100° C without formation of any undesired second phases, such as tricalciumphosphate (TCP) known to decrease the stability of HA. The antibacterialsensitivity was tested with E.Coli gram-negative bacteria. The radius ofcircle enclosing the sample increases with increasing Ag content in thestructure as an indication of the region of non-bacterial activity.

Semiconductor-based thermistors are very attractive sensor materials for uncooled thermal infrared (IR) bolometers. Very large scale heterogeneous integration of MEMS is an emerging technology that allows the integration of epitaxially grown, high-performance IR bolometer thermistor materials with pre-processed CMOS-based integrated circuits for the sensor read-out. Thermistor materials based on alternating silicon (Si) and silicon-germanium (SiGe) epitaxial layers have been demonstrated and their performance is continuously increasing. Compared to a single layer of silicon or SiGe, the temperature coefficient of resistance (TCR) can be strongly enhanced to about 3 %/K, by using thin alternating layers. In this paper we report on the optimization of alternating Si/SiGe layers by advanced physically based simulations, including quantum mechanical corrections. Our simulation framework provides reliable predictions for a wide range of SiGe layer compositions, including concentration gradients. Finally, our SiGe thermistor layers have been evaluated in terms of low-frequency noise performance, in order to optimize the bolometer detectivity.

Sb2O3, Sb-metal, Bi2O3 or Bi-metal, powders were mixed with MgB2 powder. Starting compositions were ((MgB2)(M2O3)x, x = 0.0025, 0.005, 0.015, and (MgB2)(M)y, y = 0.01, M = Sb, Bi. Mixtures were processed by Spark Plasma Sintering (SPS) technique. As obtained composite samples show high density, above 94% of the theoretical density. While the secondary phases indicate on similar reactions, samples show different behavior vs. addition type and amount. This does not directly correlate with the melting temperature of the addition. From the critical current density (Jc ) and irreversibility field (Hirr ) enhancement viewpoints, optimum additions are oxides for x=0.025, 0.005. Both oxides are improving Jc at high fields, but Sb2O3 is effective up to 10 K, while Bi2O3 is up to 30 K. Metal additions are decreasing Jc and Hirr when compared to pristine MgB2sample.

In this paper we report about combining inkjet printing technology and self-assembly as a scalable manufacturing tool for spherical, well-ordered aggregates. The aggregates consist of a high number of ordered colloidal nanospheres arranged as ball-shaped structures. Applying inkjet printing based on the principle of droplet ejection the spherical aggregates can be deposited on various surfaces in dry environment and under ambient conditions. The aggregation of the nanospheres is independent of the surface energy of the substrate leading to the assumption that the main part of the assembly and aggregation process takes place in-flight [1].

By applying inkjet printing with an adapted control signal, small droplets of a water-based ink formulation containing monodisperse polystyrene nanoparticles are ejected out of the inkjet nozzles. The ejected droplets serve as a confined geometry for the nanospheres in the carrier liquid during evaporation. As a result, the particles form stable ball-shaped aggregates with hexagonal order. Due to the in-flight self-assembly of the nanospheres, our approach is suitable for any solid surface in dry environment and allows the deposition of the ball-shaped aggregates in appropriate patterns.

The high temperature decarburization-oxidation behavior of hot rolled, non-oriented electrical steel strips is investigated during air-annealing treatments. Annealing temperature and time are varied from 700 – 1050 °C and 10 to 150 min, respectively. The experimental results show that uniform external oxidation affects strongly the rate at which carbon can be removed from this material. The thickness of the oxide layer formed after 150 minutes of annealing increases linearly with increasing temperature in the range 828 and 920 °C. The effect of temperature on the thickness of the oxide scale at temperatures outside this range is significantly smaller. These results indicate that the rate of oxidation in this material is strongly influenced by the microstructure of the steel during annealing. Decarburization rates are very slow during annealing at T ≤ 750 °C where the oxide layer is thin and porous. In contrast, fast and intense decarburization of the strips is observed as a result of annealing at temperatures between 800 and 850 °C. Finally, decarburization at T ≥ 875 °C becomes slower as the temperature is increased until at T ≥ 950 °C this process is practically inhibited. Measurements of C content as a function of time and temperature show that the observed decarburization kinetics follows Wagner’s model at 800 and 850 °C. However, at higher annealing temperatures decarburization is slower than that predicted by the model. This behavior is related to the increment of the oxide scale thickness and a transition from cracked to crack-free oxide structure which makes C diffusion through the oxide film very difficult.

Via the Dissipative Particle Dynamics (DPD) approach, we study the self-assembly of hybrid structures comprising lipids and end-functionalized nanotubes. Individual lipids are composed of a hydrophilic head group and two hydrophobic tails. Each bare nanotube encompasses an ABA architecture, with a hydrophobic shaft (B) and two hydrophilic ends (A). To allow for regulated transport through the nanotube, we also introduce hydrophilic hairs at one end of the tube. The amphiphilic lipids are composed of a hydrophilic head group (A) and two hydrophobic tails (B). We select the dimensions of the nanotube architecture to minimize its hydrophobic mismatch with the lipid bilayer. We find the amphiphilic lipids and functionalized nanotubes to self-assemble into a stable hybrid vesicle or a bicelle in the presence of a hydrophilic solvent. We demonstrate that the morphology of the self-assembled functionalized nanotube-lipid hybrid structures is controlled by the rigidity of the lipid molecules and concentration of the nanotubes.

This study presents a materials development of composite electrode materials of graphene oxide (GO) and transition metal oxide nanostructures. Reduced graphene oxide (rGO) films were obtained by electrophoretic deposition (EPD) onto a conductive substrate. Co3O4 and MnO2 nanostructures were synthesized to form composites with rGO. Graphene materials, with high electrical conductivity, high specific surface area and excellent mechanical properties are ideal for a host of electrical applications. The properties of metal oxides like Co3O4 and MnO2 has allowed for increased energy density, while rGO increases charge storage and transport in the electrical double layer at the electrode/electrolyte interface. Graphene and metal oxide composites offer increased energy density and capacitance compared with traditional double layer supercapacitors.

In this work, an Atomic Force Microscope in the so-called Piezoresponse mode and Kelvin mode is used to image the grains, ferroelectric domains and surface potential in lithium niobate thin films. A RF magnetron sputter system was used to deposit LiNbO3 thin films on (100)-oriented Si substrates with SiO2 layer. The surface of the sample shows small grains which diameter ranges from 70 nm to 150 nm and roughness is less than 13 nm. Using the electric field from a biased conducting AFM tip, we show that possible to form and subsequently to visualize ferroelectric state. Also, we report surface charge retention on ferroelectric thin films by Kelvin probe microscope in comparison with the piezoresponse signal.

Thermal analysis techniques are routinely applied to characterize the thermal behavior of metal organic precursors used for oxide film preparation. Since the mass of films is very low, researchers do their thermal analyses on powders and consider that the results are representative of films. We will show here that, in general, this assumption is not true. Several examples involving precursors of YBa2Cu3O7-x (Ba and Y trifluoroacetates and Ba propionate) will serve to appreciate that films can behave very differently than powders due to their enhanced heat and mass transport paths. Ultimately, we will demonstrate that, in some cases, relying on powders thermal analysis may lead to erroneous conclusions.

Ultrafast time resolved transmission electron diffraction (TED) in a reflection geometry was used to study the cooling behavior of self-organized, well defined nanoscale germanium hut and dome clusters on Si(001). The clusters were heated in a pump-probe scheme by fs-laser pulses. The resulting transient temperature rise was then determined from the drop in diffraction intensity caused by the Debye-Waller effect. From a cooling time of τ =177 ps we estimated a strongly reduced heat transfer compared with homogeneous films of equivalent thickness.

Two dimensional Er3+-TeO2 thin film photonics crystals (PhCs) are fabricated. These PhCs demonstrate broadband enhancement of PL emission at near Infrared (NIR). The PhC structures are written by dual beam focused ion beam (FIB). Highly uniformed patterns with smooth surfaces are observed. A pattern resolution better than hundred nanometers is achieved. PhCs arrays with photonic lattice constants from 350 nm to 1700 nm are examined in order to optimize the PL extraction efficiency. Strong photoluminescence around 1530 nm is observed by 488-532 nm lasers pumping. A confocal microscopy with spectrometer is used to capture the broadband PL signals from individual PhC array.

The emission enhancement factor and spectral dependent extraction ratio are analyzed to find the interaction between PL lightwave and PhC structures. By optimize the PhC structures, 1500 um-1560 um broadband PL is successfully converted between the PL emission layer and the external cavity. A 60 % enhancement of surface extraction efficiency is achieved when PhC with periodicity a=800 nm is applied. When photonic lattice constants a are smaller than the critical periodicity 600 nm, the PL light becomes confined inside the thin film layer. Simulation is also performed by two dimensional finite difference time domain (FDTD) calculation in order to explain the experimental observed anisotropic PL enhancements.

The broadband PL enhancement enables Er3+-TeO2 PhCs thin film as a potential light source for three dimensional integrated photonic circuits.