Spectrum tuning in phosphor converted white light emitting diodes (pc-WLED) is done by mixing powders of phosphor compounds (with different emission wavelengths) in different weight ratios. In this paper, a new methodology for designing unique full spectrum phosphor mixtures (with fixed weight ratios of different emission phosphor) has been presented that could provide a wide range of pc-WLED spectrum. This is done by optimizing the excitation and emission spectra of the phosphor compounds used in the mixture. A unique phosphor mixture comprising of Eu2+ and Ce3+-Na1+ activated compounds of SrGa2S4, CaGa2S4, SrS, CaS and CaF2 was used to produce full spectrum warm, neutral and cool white LEDs with color temperatures between 2500 K and 7500 K and with color rendering index exceeding 95.

Recently, molybdenum oxide (MoO2) has been found to be a chemically stable and relatively inexpensive material for the application as the anode in a lithium ion battery [1-5]. We believe the use of MoO2 in battery applications has been hindered due to a long, complicated, and multistep synthesis process. We present a simple one-pot hydrothermal technique to synthesize MoO2 nanoparticles directly onto a copper (Cu) substrate.

We believe this is a first report of the synthesis of MoO2 directly onto a Cu substrate, and could lead to the ability to both fabricate other materials in a similar manner as well as depositing MoO2 onto other substrates. This technique can reduce anode production time by eliminating the coating process, and also decrease the total amount of chemicals used when compared to a typical powder synthesis and coating processes. The MoO2 coated Cu electrode was characterized using Raman Spectroscopy, Grazing Incident X-ray Diffraction (GIXRD) and scanning electron microscopy (SEM) techniques to confirm the composition, crystallinity and structure of the synthesized MoO2 nanomaterial.

Transition metal dichalcogenides (TMDs) are emerging among the potential alternatives to graphene. The monolayer of TMDs can easily be exfoliated mechanically and their electronic properties can also be tuned by controlling the number of layers. TMDs possess an advantage over graphene by controlling band gap magnitude appropriate for the electronic and optoelectronic applications. Here we show, mechanically exfoliated TMDs such as NbSe2 and MoTe2 exhibit metallic and fluctuating conductance behavior respectively. Metallic conduction in NbSe2 was investigated under atmospheric conditions and compered with vacuum conditions. Furthermore, NbSe2 resistance was measured at low temperature up to 5.6 K. The above electronic investigations clearly demonstrate ohmic and fluctuating conduction in NbSe2 and MoTe2 respectively which could be applicable for electronic and optoelectronic devices.

The cross-plane thermal conductivities of InGaZnO (IGZO) thin films in different morphologies were measured on three occasions within 19 months, using the 3ω method at room temperature 300 K. Amorphous (a-), semi-crystalline (semi-c-) and crystalline (c-) IGZO films were grown by pulsed laser deposition (PLD), followed by X-ray diffraction (XRD) for evaluation of film quality and crystallinity. Semi-c-IGZO shows the highest thermal conductivity, even higher than the most ordered crystal-like phase. After being stored in dry low-oxygen environment for months, a drastic decrease of semi-c-IGZO thermal conductivity was observed, while the thermal conductivity slightly reduced in c-IGZO and remained unchanged in a-IGZO. This change in thermal conductivity with storage time can be attributed to film structural relaxation and vacancy diffusion to grain boundaries.

The hydrogen solubility and the vacancy concentration in Ni single crystals at thermal equilibrium with a H2 gas have been determined from a combination of first principles calculations and statistical mechanics up to the melting point. We show that the H solubility increases and the vacancy formation is promoted at high PH2. The apparent solution enthalpy and entropy are extracted from the fit of the solubility with the Sieverts’s law. We show that our results are in good agreement with previous experimental data at PH2=1 bar. The vacancy concentration increases with PH2 whatever the temperature but the effect of H is more significant at low temperature. However, the vacancy concentration and the H solubility in single crystals remain small and a comparison with the experimental data on polycrystals indicates that the grain boundaries may play the most important source of superabundant vacancies and preferential sites for H incorporation.

AIZO (Al and In codoped ZnO) thin films were deposited on soda lime glasssubstrates by the ultrasonic spray pyrolysis (USP) technique. The sprayingsolution was prepared from zinc acetate dihydrate, aluminum acetyl acetonate andindium acetate. Depositions were carried out at three different temperatures,425, 450 and 475 °C. Structural, morphological, optical and electricalproperties were examined with respected to the deposition temperatures. All AIZOfilms grown with (002) preferential orientation confirmed from X-ray diffractionanalysis. Hexagonal nanostructures were observed from Scanning electronmicroscopy (SEM) analysis. Minimum electrical resistivity of 2.52x10-3 Ω-cm was achieved for AIZO films.

The magnesium compound Mg2Si and its solid solutions are expected as n-type thermoelectric (TE) material because they are non-toxic, have a large Clarke number, and are light weight. In this study, we improved TE performance by doping Ge into Sb-doped Mg2Si to cause phonon scattering and increase carrier concentration. A bulk of Sb-doped Si-Ge alloy as the raw material was fabricated using an arc-melting method. A high-purity Mg2Si was synthesized from metal Mg and Sb-doped Si-Ge alloy using spark plasma sintering equipment. For the samples with the same Sb concentration, the electrical conductivity was equivalent. On the other hand, the Seebeck coefficient was dependent on Ge concentration. Due to phonon scattering, thermal conductivity decreased by a small amount of Ge doping and κph dominated for thermal conduction. The minimum thermal conductivity of Mg2Si0.90Ge0.10 was 2.25 W/mK (κph: 2.06 W/mK, κel: 0.19 W/mK). The dimensionless figure of merit (ZT) for the Mg2Si0.945Ge0.05Sb0.005 sample was higher than that of the others due to reducing thermal conductivity and increasing carrier concentration. The maximum ZT was 0.47 at 713 K.

Epitaxial Ge films are useful as a substrate for high-efficiency solar cell applications. It is possible to grow epitaxial Ge films on low cost, cube textured Ni(001) sheets using CaF2(001) as a buffer layer. Transmission electron microscopy (TEM) analysis indicates that the CaF2(001) lattice has a 45o in-plane rotation relative to the Ni(001) lattice. The in-plane epitaxy relationships are CaF2[110]//Ni[100] and CaF2[ $\bar 1$ 10]//Ni[010]. Energy dispersive spectroscopy (EDS) shows a sharp interface between Ge/CaF2 as well as between CaF2/Ni. Electron backscatter diffraction (EBSD) shows that the Ge(001) film has a large grain size (∼50 μm) with small angle grain boundaries (< 8o). The epitaxial Ge thin film has the potential to be used as a substrate to grow high quality III-V and II-VI semiconductors for optoelectronic applications.

Two segments of horizontally grown crystalline ZnO nanorods (NRs) connected with an amorphous layer have been successfully and reproducibly synthesized using one-step hydrothermal technique by controlling the growth rate. The confocal photoluminescence (PL) imaging and spectroscopy of twin ZnO NRs at different temperatures shows intense red emission with comparably week UV emission. The strong red emission from the twin NRs is a consequence of structural imperfections. Both UV and red bands showed signatures of strong temperature dependent exciton-phonon scattering. Using the intensity ratio of the UV and red emissions, we show that the individual ZnO NRs can be used as highly sensitive cryogenic temperature sensors below ∼175 K.

A ferroelectric nanogenerator without any electric poling treatment has been realized by incorporation of ytterbium (Yb) salt incorporated porous PVDF composite film. The composite film compose of electroactive β- and γ-phases, demonstrates higher dielectric and ferroelectric polarization responses than pure PVDF film. The 3 V of open circuit voltage with 0.47 µW/cm2 power density was generated by the nanogenerator upon single finger touch. It can also operate capacitor and light emitting diode without any subsidiary batteries.

The biomedical applications of ZnO are drastically limited by its intrinsic solubility, which shortens the stability and lifetime of devices. We show that the functionality of ZnO in human mesenchymal stem cell (hMSC) studies is limited due to poor cell adhesion. The sol-gel route has been employed to obtain zinc titanate thin films for their integration as surface protective layer on ZnO. These films were obtained from zinc acetate (ZnAc) and titanium isopropoxide (TIPT). So derived xerogels were dried and their thermal evolution studied by TGM-DTA to identify critical annealing temperatures. The evolution of the microstructure and composition of spun cast films was determined by XRD and FTIR. Organic and ionic byproducts were eliminated at T>300°C, which kickstarts a transformation of the amorphous materials into polycrystalline. Thin films consisted of the ZnTiO3 perovskite from annealing temperatures of 500°C. Cell adhesion on the synthesized samples (both amorphous and crystalline) was assayed by culturing hMSCs. Immunofluorescence images of actin cytoskeleton were obtained and proliferation studied using Ki67. Cell density, single cell area and proliferation rates on ZnTiO3 films were closer to control TiO2 surfaces than to ZnO films. Such behavior validates the short term biocompatibility of ZnTiO3 films and its potential use as surface layer for ZnO biomedical devices.

PtCu nanoparticles were synthesized with different pH and support conditionsusing radiochemical process. The nanoparticle structures were characterized bytransmission electron microscopy, inductively coupled plasma atomic emissionspectrometry, X-ray absorption spectroscopy, and X-ray diffraction techniques.The nanoparticle structure was relevant to the pH of the precursor solutions.The lattice parameter of PtCu alloy increased in high pH samples, whichindicates the critical effect of metal ion adsorption in precursor solution onnanoparticle structure.

Nano-inkjet printing using an Electrohydrodynamic's (EHD) pulsed cone-jet approach has the potential to bring affordable additive manufacturing to the micro and nanoscale. Ink technology is a major limitation of current EHD techniques. Specifically, most EHD printing processes print either nanoparticles or polymers. The materials are structurally weak and often have poor electrical or mechanical properties. For example, printing nanoparticles effectively creates a cluster of nanoparticles that must be sintered to create a continuous material. To address these issues, we have been adapting reactive inks to work with an EHD pulsed cone-jet. Specifically, we demonstrate that silver micron-scale structures can be printed using an EHD pulsed cone-jet regime. These inks produce solid structures without sintering steps and with good electrical properties.1,2 This work shows that reactive ink chemistries can be combined with EHD printing to produce fine-resolution features consisting of solid metal without an annealing step.

It is well-known that dual phase (DP) steels composed of ferrite and martensite have good ductility and plasticity as well as high strength. Due to their excellent mechanical properties, DP steels are widely used in the industrial field. The mechanical properties of DP steels strongly depend on several factors such as fraction, distribution and grain size of each phase. In this study, the grain size effect on mechanical properties of DP steels was investigated. In order to obtain DP structures with different grain sizes, intercritical heat treatment in ferrite + austenite two-phase region was carried out for ferrite-pearlite structures having coarse and fine ferrite grain sizes. These ferrite-pearlite structures with coarse and fine grains were fabricated by two types of heat treatments; austenitizing heat treatment and repetitive heat treatment. Ferrite grain sizes of the specimens heat-treated by austenitizing and repetitive heat treatment were 47.5 µm (coarse grain) and 4.5 µm (fine grain), respectively. The ferrite grain sizes in the final DP structures fabricated from the coarse-grained and fine-grained ferrite-pearlite structures were 58.3 µm and 4.1µm, respectively. The mechanical behavior of the DP structures with different grain sizes was evaluated by an uniaxial tensile test at room temperature. The local strain distribution in the specimens during tensile test was obtained by a digital image correlation (DIC) technique. Results of the tensile test showed that the fine-grained DP structure had higher strength and larger elongation than the coarse-grained DP structure. It was found by the DIC analysis that the fine-grained DP structure showed homogeneous deformation compared with the coarse-grained DP structure.

Liposome reinforced by adding cholesterol was synthesized using the dipalmitoyl-phosphatidylcholine (DPPC). Phase stability of the phospholipid bilayers was examined by FT-IR spectroscopy. The reinforced liposomes filled with ultrapure water or physiological saline were observed by the conventional TEM equipped with a mass spectrometer. It was confirmed that the liposomes filled with water or saline solution were stable in the vacuum at room temperature. However, during electron irradiation, water molecules escaped gradually, and a single crystal of rock salt precipitated in the liposome.

Topological (GeTe)/(Sb2Te3) superlattices (SL) are ofpractical interest for memory applications because of different mechanism ofelectric conductance switching in the crystalline phase. In the work, electricalswitching behavior of individual SL grains was examined employing a multimodescanning probe microscope (MSPM) in a lithography mode at room temperature.Using programmed bias voltage with different amplitude and pulse duration, weobserved the position-dependent variations of the switching voltage and thecurrent injection delay for [(GeTe)2(Sb2Te3)]4 SLs on Si(100). The results sheda light on the role of electric field and hot-electron injection on the SLconductance switching.