Using scanning tunneling microscopy (STM) we observed atomic scale interference patterns on quasi-freestanding WSe2 islands grown on top of graphene. The bias-independent double atomic size periodicity of these patterns and the sharp Brillouin zone edge revealed by 2D STM Fourier analysis indicate formation of optical phonon standing waves due to scattering on intercalating defects supporting these islands. Standing wave patterns of both synchronized and non-synchronized optical phonons, corresponding to resonant and non-resonant phonon scattering regimes, were experimentally observed. We also found the symmetry breaking effect for individual phonon wave packets, one of the unique features distinguishing phonon standing waves. We show that vibrational and electronic anharmonicities are responsible for STM detection of these patterns. A significant contribution to the interference contrast arises from quantum zero-point oscillations.

Silicon nanotubes (SiNTs) represent unique building blocks for future nanoscale biosensor devices merging electronic sensing and nanofluidics. Configured as ion-sensitive field effect transistors (ISFETs), SiNTs have great potential for charge sensing or label-free chemical detection in minute sample volumes flowing through their inner cavity. In the present study, doped SiNTs were synthesized from the gas phase in a bottom-up approach. To study their nanofluidic and electronic transport properties, single SiNTs were functionally integrated as ISFETs and coupled to a microfluidic system. The experimental results for ion diffusion through a SiNT are in full agreement with numerical calculations based on Fick's second law if a diffusion coefficient is assumed approximately one order of magnitude smaller than the bulk value.

Chlorella is a green, photosynthetic single-celled genus of algae. It can be 3D printed as a suspension in sodium alginate and gelled with calcium solutions. We have made “log pile” structures with channels between the gel lines to allow easy transport of nutrients and products. Under white light and immersed in solutions of bicarbonate and phosphate and urea “plant food” the algae multiply with the gel and produce oxygen at a rate comparable to that reported for suspensions of Chlorella. The system is stable for one or two weeks at least. In principle this can be extended to other plant tissues but there are concerns relating to bacterial and fungal infection and toxicity of the gel components. In addition a tougher gel is needed if this was to be converted to a practical bioreactor system.

It has been reported that the addition of liquid rubbers, like poly(dimethylsiloxane) (PDMS), to epoxy resins alter the final morphology, increase the toughness and influence the curing kinetics. Due to immiscibility, there is phase separation of the elastomeric phase during curing giving rise to microdomains embedded in the epoxic matrix. The resultant heterogeneous morphology obtained after the reaction controls to an important extent the properties of the epoxy composite. Here we report a method to obtain well-dispersed rubber nanodomains of silyl-diglycidyl ether terminated polydimethyl siloxane (PDMS-DGE) in diglycidyl ether of bisphenol-A (DGEBA) epoxy by using a prepolymerization step. Light scattering and optical microscopy showed that initial mixing of pre-polymerized rubber produced phase separation with micron-scale droplet formation. However, as the curing reaction proceeded, the rubber domains decreased below optical resolution, light scattering intensity reached a maximum and then decreased. Finally, rubber nanodomains of about 100 nm size were formed at the end of curing reaction, as revealed by transmission electron microscopy (TEM). The pre-polymerization step induced a two-fold increase in gel time, t gel , due to lesser active groups available for reaction. Strikingly, tensile modulus and toughness increased, suggesting rubber-epoxy interaction. The final nanocomposite also exhibited higher thermal stability and char formation.

Studying the transport of ions through single-walled carbon nanotubes (SWCNTs) necessitate the fabrication of a fluidic setup integrating carbon nanotubes. In this article, we report on the development of a simple fabrication protocol of SWCNTs fluidic devices. This protocol allows an excellent control of the system features and of the experimental conditions compared with previously published protocols. Our protocol based on the use of the popular SU-8, the preferred photoresist for the fabrication of high-aspect-ratio patterns, allows one to prepare sealed microfluidic devices incorporating one or several tens of individual carbon nanotubes of length between 20 and 80 µm.

We report the experimental demonstration of a low-cost paradigm for photovoltaicpower generation that utilizes a prismatic Fresnel-like lens to simultaneouslyconcentrate and separate sunlight into laterally spaced spectral bands. Theoptical element is designed using geometric optics and optical dispersion andits performance is simulated with a ray-tracing software. The device, fabricatedby injection molding, suitable for large-scale mass production, isexperimentally characterized. We report an average optical transmittance above85% over the VIS-IR range and spectral separation in excellent agreement withour simulations. Finally, the system is tested with a pair of copper indiumgallium selenide based solar cells. We demonstrate an increase in peakelectrical power output of 160% under outdoor sunlight illumination,corresponding to an increase in power conversion efficiency of 15% relative tosingle-junction full-spectrum one-sun illumination. Given the ease ofmanufacturability and the potential of the proposed solution, we project thatour design can provide a cost-effective alternative to multi-junction solarcells ready for mass production.

Since 1988 the Swedish Nuclear Fuel and Waste Management Co. operates a repository for low- and intermediate-level short-lived radioactive waste, SFR, in Forsmark, Sweden. Due to decommissioning of the nuclear power plants additional storage capacity is needed. In December 2014, an application to extend the repository was therefore submitted. One key component of this application was an assessment of post-closure safety of the extended SFR. For this safety assessment, a methodology based on that developed by SKB for the spent nuclear fuel repository was used and the impact of the degradation of repository components, the evolution of the surface system and changes of future climate on the radiological safety of the repository was assessed over a period of 100,000 years. The central conclusion of the SR-PSU safety assessment is that the extended SFR repository meets requirements on protection of human health and of the environment that have been established by the Swedish radiation safety authority for the final disposal of radioactive waste. Furthermore, the design of the repository was shown suitable for the waste selected and the applied methodology suitable for the safety assessment.

The formation of europium sulfides (Eu3S4 and EuS) via CS2 gas sulfurization of Eu2O3 powder was investigated. Single-phase Eu3S4 was obtained via CS2 gas sulfurization of Eu2O3 at 773 K for periods longer than 0.5 hr and EuS was generated by sulfurization at 1073 K for 8 hr. The higher sulfurization temperature and shorter sulfurization time accelerated the formation of high purity EuS. Synthetic pure Eu3S4 was treated under vacuum, rich-sulfur atmosphere and inert atmosphere, respectively. EuS was obtained when heat treatment was performed at 873 K under vacuum, at 973 K under CS2/Ar atmosphere, and at 1073 K under Ar atmosphere. Heat treatment of Eu3S4 generated a small amount of Eu2O2S due to impurity oxygen. Formation of Eu2O2S could be inhibited by heat treatment under CS2/Ar atmosphere.

Self-assembled TiO2 foam-like films, were grown by the water based Streaming Process for Electrodeless Electrochemical Deposition (SPEED). The morphology of the ∼1 µm thick films consists of a tangled ropy structure with individual strands of ∼200 nm diameter and open pores of 0.1 to 3 micron dimensions. Such films are advantageous for proposed perovskite solar cell comprising CH3NH3PbI3 absorber with additional inorganic films as contact and conduction layers, all deposited by SPEED. Lateral film resistivity is in the range 20 – 200 kΩ-cm, increasing with growth temperature, while sheet resistance is in the range 2 – 20 x 108 Ω/Sq. X-ray diffraction confirms presence of TiO2 crystals of orthorhombic class (Brookite). UV-vis spectroscopy shows high transmission below the expected 3.2 eV TiO2 bandgap. Transmittance increases with growth temperature.

Yttria (Y2O3) films were deposited on stainless steel substrates from ethylenediaminetetraacetic·yttrium·hydrogen (EDTA·Y·H) complexes by flame spraying. The gas mixtures of acetylene-oxygen (C2H2-O2) or hydrogen-oxygen (H2-O2) were used for the combustion flame and the effects of the combustion gas species on Y2O3 films were investigated. Experiments revealed that the particles propelled in the H2-O2 flame had lower temperature and higher velocity compared with the particles in the C2H2-O2 flame. The existence of Y2O3 crystalline phases and complete decomposition of the EDTA·Y·H were confirmed. The porosity of the film was 25% when the H2-O2 flame was used and 32% when the C2H2-O2 flame was used. In addition, the Y2O3 films showed excellent adherability in tape tests. The H2-O2 flame is thus considered suitable for fabricating dense Y2O3 films.

Organic-inorganic hybrid nanocomposites are considered a new generation of high performance materials because they combine both the advantages of inorganic materials (stiffness, high thermal stability, barrier properties, optical, catalytic, electrical and thermal conductivity among others) and organic polymers (flexibility, dielectric, toughness, lightweight, processing). Each part of a nanocomposite has a synergistic function in its performance and has much better combination properties than a single material. We report on the thermo-mechanical properties and morphology of polyacrylic-nanosilica (SiO2) composites prepared in-situ via emulsion polymerization, using a semi-continuous mode. The latex emulsion thus obtained was stable for at least six months. Moreover, this process produced controlled molecular weight in the final latex and low formation of agglomerates. Films drawn from the latex exhibited excellent optical transparency, suggesting good dispersion of the nanosilica, and confirmed by scanning electron microscopy (SEM). There was an increase in glass transition temperature, T g , suggesting a modification of molecular dynamics; hydrophobic behavior, as probed by water contact angle, was also promoted. Moreover, the Young’s modulus of the nanostructured latex films increased up to 57% with only 3 wt% nanosilica, therefore denoting a reinforcing effect of the nanoparticles.

In this work, we report a comparative investigation of InxGa1-xN (SL) and InxGa1-xN/GaN (MQW) structures with an indium content equivalent to x=10%. Both structures are grown on (0001) sapphire substrates using MOCVD and MBE growth techniques. Optical properties are evaluated for samples using PL characteristics. Critical differences between the resulting epitaxy are observed. Microstructures have been assessed in terms of crystalline quality, density of dislocations and surface morphology. We have focused our study towards the fabrication of vertical PIN photodiodes. The technological process has been optimized as a function of the material structure. From the optical and electrical characteristics, this study demonstrates the benefit of InGaN/GaN MQW grown by MOCVD in comparison with MBE for high speed optoelectronic applications.