Strontium titanate (STO) thin films (45-67 % Sr) were deposited by atomic layer deposition using Sr(tBu3Cp)2/Ti(OMe)4/H2O as precursors. The Sr content of the layers is well controlled by the precursor pulse ratio, as indicated by Rutherford backscattering spectroscopy (RBS). The amount of Sr and Ti deposited depends on the Sr:Ti pulse ratio and indicates the enhancement of the Ti precursor reactivity in the presence of Sr-OH. STO compositions that are closer to stoichiometric SrTiO3 result in denser films with correspondingly higher index of refraction. The increase (decrease) of the Sr content over (below) 50 % leads to an expansion (contraction) of the lattice parameter corresponding to cubic SrTiO3 with a perovskite structure. The dielectric constant (extracted from film thickness series) and leakage current strongly depends both on the Sr content and the crystalline state of the films.

Europium-doped strontium iodide scintillators offer a light yield exceeding 100,000 photons/MeV and excellent light yield proportionality, while at the same time, SrI2 is readily grown in single crystal form. Thus far, our collaboration has demonstrated an energy resolution with strontium iodide of 2.6% at 662 keV and 7.6% at 60 keV, and we have grown single crystals surpassing 30 cm3 in size (with lower resolution). Our analysis indicates that SrI2(Eu) has the potential to offer 2% energy resolution at 662 keV with optimized material, optics, and read-out. In particular, improvements in feedstock purity may result in crystal structural and chemical homogeneity, leading to improved light yield uniformity throughout the crystal volume, and consequently, better energy resolution. Uniform, efficient light collection and detection, is also required to achieve the best energy resolution with a SrI2(Eu) scintillator device.

Creating a single photon to a light field or removing a single photon from a light field reveals interesting quantum phenomena. For theoretical modeling and understanding of these experiments it is essential to be able to model the coupling of the optical field to the measurement apparatus. We investigate a cascaded field–quantum system–reservoir setup to obtain a theoretical model that can, in contrast to previous models, simultaneously model both the weak and the strong coupling regimes of the field–detector system. Furthermore, our theory can be applied to model optical fields coupled to dissipative systems or to active amplifying systems including for example operation of various optical instruments and devices, such as detectors, LEDs and lasers.

Recent experiments on ultrasonic measurements of non-doped and boron-doped silicon indicate that vacancies in crystalline silicon can be detected through the elastic softening at low temperature. This is attributed to enhanced response of electronic quadrupole localized at the vacancies to the elastic strain. In the present work, the electronic quadrupole moment of the vacancy orbital in silicon and their strain susceptibility are evaluated quantitatively by using the density-functional method. We show the orbital of gap state is localized around vacancy but extended over several neighbors. The effect of applied magnetic field on the vacancy orbital and its multipole structures are also investigated. We find that the results obtained from these calculations are consistent with the ultrasonic experiments.

The purpose of the study was to reveal the effects of a new electropolishing process carried out under a constant magnetic field, termed as magnetoelectropolishing (MEP). In this work we investigated Nitinol rotary endodontic instruments by surface and morphology change after MEP. The MEP process greatly affects both surface also mechanical properties like the bending and fatigue resistance.

The investigation covered surface interferometry measurements, X-ray Photoelectron Spectroscopy (XPS) studies, and Scanning Electron Microscopy (SEM) with EDAX studies referred to two groups of endodontic instruments: ready-to-use or as-received (AR) files, and magnetoelectropolished (MEP) instruments, in comparison with the instruments surface after a conventional electropolishing (EP). The treated surfaces of NiTi endodontic files were studied by interferometric method in view of getting multiple surface characteristics, together with digital data concerning the arithmetic mean height Sa and the maximum height of scale limited surface Sz.

The investigation results obtained have indicated a considerable improvement of MEP surface in comparison with both AR and EP surfaces. Such a surface after MEP reveals several positive features, decreased roughness, elimination of metallic state (here Ni and Ti elements) in the surface film, much enriched with titanium oxides and diminished nickel oxides. The study results show that the contents of Ni compounds is higher after EP (18.3%) than after MEP (10.2%), whereas the contents of Ti compounds is higher after MEP (83.4%) than after EP (76.6%). The total Ti/Ni ratio indicates almost double surpass of titanium over nickel in the surface film after MEP in comparison with the total amount of that ratio after EP.

The qualitative investigation of fatigue tests have indicated much better performance of NiTi endodontic file samples after MEP than those related to AR and/or after EP. We have proved that the magnetoelectropolishing process may further modify surface. The following studies are to be directed onto performance and specific mechanical properties of the endodontic files at work.

Near-equiatomic porous nickel-titanium shape memory alloys (NiTi SMAs) are becoming one of the most promising biomaterials in bone implants because of their unique advantages over currently used biomaterials. For example, they have good mechanical properties and lower Young�s modulus relative to dense NiTi, Ti, and Ti-based alloys. Porous NiTi SMAs are relatively easy to machine compared to porous ceramics such as hydroxyapatite and calcium phosphate that tend to exhibit brittle failure. The porous structure with interconnecting open pores can also allow tissue in-growth and favors bone osseointegration. In addition, porous NiTi alloys remain exhibiting good shape memory effect (SME) and superelasticity (SE) similar to dense NiTi alloys. To optimize porous NiTi SMAs in bone implant applications, the current research focuses on the fabrication methods and surface modification techniques in order to obtain adjustable bone-like structures with good mechanical properties, excellent superelasticity, as well as bioactive passivation on the entire exposed surface areas to block nickel ion leaching and enhance the surface biological activity. This invited paper describes progress in the fabrication of the porous materials and our recent work on surface nanorization of porous NiTi scaffolds in bone grafts applications.

Studies of hard biological materials such as marine shells, animal teeth, horns and bones have produced fascinating ideas for mimicking their micro/nanostructure in the lab. The nacre in the abalone shell has a well-defined organic/inorganic structure that has a fracture resistance that is much higher than the individual constituents. By using biocompatible materials we have fabricated zirconium nitride/ polymethylmethacrylate alternating layers that are based on the structure of nacre. A combination of DC-magnetron sputtering and pulsed laser deposition on (100) silicon substrates was used to fabricate multilayers in a single chamber without breaking the vacuum. The ZrN films showed nanocrystalline columnar growth on the silicon substrates or on the PMMA nanolayer. High resolution SEM analysis at the inorganic/organic interface revealed well formed, uniform thickness inorganic films which are separated by the polymeric layer (30-90 nm). The ratio of the ceramic/polymer is the same as in nacre. Nanoindentation hardness values of ˜ 20GPa were measured on both the ZrN single film, similar to published values, and the ZrN/PMMA composite layers and the elastic modulus remained constant, independent of the number of layers.

In this work we report about the design and construction of a simple and cheap calorimeter for phase transitions monitoring using Peltier elements and based in the well known inverse (front) photopyroelectric method for thermophysical characterization of materials. We describe its application for the detection of phase transitions in chocolate samples, as an alternative, for example, to the most widely used and more expensive Differential Scanning Calorimetry technique. The manufacture of chocolate requires an understanding of the chemistry and the physical properties of the product. Thus the involved problems during the confection process are those of the so-called materials science. Among them, those related with tempering are of particular importance. Because the fats in cocoa butter experience the so-called polymorphous crystallization, the primary purpose of tempering is to assure that only the best form is present in the final product. One way to characterize this is by measurement of the temperature dependence of the thermal properties of the chocolate and the monitoring of the temperature at which phase transitions take place. We show that the photopyroelectric method, aided with Peltier cells temperature control, can be a useful choice for this purpose.

Low temperature hydrothermal methods allow for growth of nanowires on novel substrates. We examine the impact of variations in chemical concentration, time, temperature, and seed layer on nanowire (NW) growth and crystallite formation. The majority of growth (NWs and crystallites) was found to occur within the first two hours. Lower Zn(NO3)2 concentrations produced a reduction in the undesired large crystallites, whereas hexamethylene tetramine (HMT) concentration did not largely impact crystallite density or nanowire morphology. Growth temperature appeared to impact NW diameter variation. Nanowires grow only on the ZnO seed layer and crystallites seem to attach preferentially to the bare Kevlar surface.

Conversion efficiency of a solar energy in the electric is substantially determined not only by the total impurity concentration in solar cell element, but also by impurity chemical and physical state. Gettering processes, which are included in the technology of solar cell manufacturing, are usually used for such impurity redistribution. In order to optimize gettering processes we developed a program tool based on the fundamental physical and chemical laws. The description of physical and chemical behaviour of impurities in silicon is based both on known experimental data, and on calculations of necessary parameters by means of present-day thermodynamic and quantum-chemical methods. Developed tool helps to choose a gettering regime (a temperature profile, time, getter layer thickness) for optimization of these processes for the given initial chemical composition of the silicon wafer. Possibility of analysis of recombination activity of various types of defects in silicon on the basis of carrier lifetime criterion allows to obtain an estimation of efficiency of the gettering processes. Using this program tool we demonstrated that solar cell efficiency can be significantly increased by optimal choice of gettering conditions.

Bulk metallic glasses exhibit confined low and high frequency vibrational properties resulting from the significant bon and topological disorder occuring at the atomic scale. The precise nature of the low frequency modes and how they are influenced by local atomic structure remains unclear. Using standard harmonic analysis, the current work investigates various aspects of the problem by diagonalizing the Hessian of atomistic samples derived from molecular dynamics simulations via a model binary Lennard Jones pair potential.

InGaAs can be used to enhance the response of solar cells past the 1.43 eV cutoff of GaAs. Strained-layer superlattice (SLS) structures with high indium and phosphorus compositions (up to 35% and 68% respectively) have been grown successfully. SLS solar cells with indium and high phosphorus compositions (up to 15% and 85% respectively) have been grown successfully. The spectral response of the solar cells has been extended to as low as 1.27 eV. This enhancement is also shown by an increase in the short circuit current, with a small reduction in the short circuit voltage as compared to standard GaAs p-n junction for AM1.5 and one sun.

Dark current curves show the extent of recombination in the superlattice. The reverse saturation current in the recombination region (0.2-0.8 V) was determined using a non-linear least squares fitting routine. An Arrhenius plot was generated by finding the reverse saturation current over a temperature range of 300-370 K. The low recombination devices show non-ideality constants of 1.7 with activation energies of 1.3-1.4 eV. The high recombination devices have non-ideality constants (˜2.3) and lower activation energies of 1.1 eV.

Large-signal radiofrequency performances of surface channel diamond MESFET fabricated on hydrogenated polycrystalline diamond are investigated. The adopted device structure is a typical coplanar two-finger gate layout, characterized in DC by an accumulation-like behavior with threshold voltage Vt ∼ 0-0.5 V and maximum DC drain current of 120 mA/mm. The best radiofrequency performances (in terms of f T and f max) were obtained close to the threshold voltage. Realized devices are analyzed in standard class A operation, at an operating frequency of 2 GHz. The MESFET devices show a linear power gain of 8 dB and approximately 0.2 Wmm RF output power with 22% power added efficiency. An output power density of about 0.8 W/mm can be then extrapolated at 1 GHz, showing the potential of surface channel MESFET technology on polycrystalline diamond for microwave power devices.

Non-polar cubic AlGaN/GaN HFETs were grown by plasma assisted MBE on 3C-SiC substrates. Both normally-on and normally-off HFETs were fabricated using contact lithography. Our devices have a gate length of 2 μm, a gate width of 25 μm, and source-to-drain spacing of 8 μm. For the source and drain contacts the Al0.36Ga0.64N top layer was removed by reactive ion etching (RIE) with SiCl4 and Ti/Al/Ni/Au ohmic contacts were thermally evaporated. The gate metal was Pd/Ni/Au. At room temperature the DC-characteristics clearly demonstrate enhancement and depletion mode operation with threshold voltages of +0.7 V and −8.0 V, respectively. A transconductance of about 5 mS/mm was measured at a drain source voltage of 10 V for our cubic AlGaN/GaN HFETs, which is comparable to that observed in non-polar a-plane devices. From capacity voltage measurements a 2D carrier concentration of about 7×1012 cm-2 is estimated. The influence of source and drain contact resistance, leakage current through the gate contact and parallel conductivity in the underlaying GaN buffer are discussed.

Stromal derived factor-1α (SDF-1α) is an important chemokine in stem cell trafficking and plays a critical role in the homing, osteogenesis as well as angiogenesis of bone marrow stromal (BMS) cells. The objective of this work was to investigate the release characteristics of SDF-1α from the degradable poly(lactide ethylene oxide fumarate) (PLEOF) hydrogels and to determine the effect of sustained release of SDF-1α on migration of BMS cells. Three PLEOF macromers with PLA content of 6, 9, and 24 by weight were synthesized by condensation polymerization. The cumulative amount of biologically-active SDF-1α released from the PLEOF hydrogels after 3 weeks was between 20-25% of the initial loading and was independent of PLA/PEG ratio in the hydrogel. The migration of BMS cells in response to the time-release SDF-1α from PLEOF hydrogels closely followed the release kinetics of SDF-1α from the hydrogels. Results demonstrate that migration of BMS cells was significantly increased by the sustained release of SDF-1α from PLEOF hydrogels.

The role of thermal annealing and of CdCl2 as a main source of electrically active but vaporizable chlorine doping in chemical bath deposited CdS thin films is studied. The films were deposited on glass substrates from aqueous solution of either CdCl2, NH4Cl, NH4OH, and thiourea, or CdSO4, (NH4)2SO4, NH4OH, and thiourea. Films deposited in the presence of CdCl2 and annealed in H2 atmosphere at 310 and 420 °C show a resistivity lower than 10 Ω·cm, one order of magnitude less than for identically annealed films deposited in absence of CdCl2. Annealing at 420 °C in closed ampoules, where a counter pressure of CdCl2 builds up, leads to a lower resistivity on the order of 10−1 Ω·cm, confirming the key role of chlorine on the electronic properties. However, further characterization via photoluminescence raises new questions about chlorine-related defects and their role in the mechanisms that govern film resistivity.

A parallel high-sensitivity hydrogen sorption, and in situ Raman/IR emissivity measurement system has been developed using a stainless-steel sample cell with a sapphire window to act as a bridge between the PCT and optical measurements. The cell can be pressurized up to 4.5 MPa and heated up to 723 K. The system can measure small changes in hydrogen content, down to 0.5 μg, allowing for characterization of small quantities of powers and thin films. Hydrogen desorption in LiNH2 - LiBH4 - MgH2 nanocomposites has been studied by in-situ Raman and PCT measurement, while that of MgH2 powers and thin films has been studied by in-situ PCT and IR emissivity. In powder samples, qualitative trend is observed between changes in the Raman peak intensity/IR emissivity and the amount of hydrogen absorbed or desorbed.

Nanocrystalline diamond films have generated much interested due to their diamond-like properties and low surface roughness. Several techniques have been used to obtain a high re-nucleation rate, such as hydrogen poor or high methane concentration plasmas. In this work, the properties of nano-diamond films grown on silicon substrates using a continuous DC bias voltage during the complete duration of growth are studied. Subsequently, the layers were characterised by several morphological, structural and optical techniques. Besides a thorough investigation of the surface structure, using SEM and AFM, special attention was paid to the bulk structure of the films. The application of FTIR, XRD, multi wavelength Raman spectroscopy, TEM and EELS yielded a detailed insight in important properties such as the amount of crystallinity, the hydrogen content and grain size. Although these films are smooth, they are under a considerable compressive stress. FTIR spectroscopy points to a high hydrogen content in the films, while Raman and EELS indicate a high concentration of sp2 carbon. TEM and EELS show that these films consist of diamond nano-grains mixed with an amorphous sp2 bonded carbon, these results are consistent with the XRD and UV Raman spectroscopy data.

We report ultrafast measurements of thermal transport in plasma polymerized CHF3 films deposited on standard Si substrates with Al sputtered on top. We characterize the thin films by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and spectroscopic ellipsometry and measure polymer thicknesses ranging from 33 nm down to 6 nm. Time-domain thermoreflectance (TDTR) provides quantitative data on the polymer thermal response to periodic heating from a pulsed laser source. A pump beam heats the Al layer, which acts as an opto-thermal transducer to the stack (Al-Polymer-Si) and a delayed probe beam measures the change in Al surface reflectance. We extract the polymer thermal conductivity by comparing TDTR data to a thermal diffusion model and find it to increase with decreasing polymer thicknesses below 30 nm.

The artificial nano-clay powder was newly examined as a gelator of electrolyte of quasi-solid-state dye-sensitized solar cell (DSSC). The size of clay has two main distributions with 1.4 nm and 20 nm in diameter which are confirmed by STEM observation. The gelation point was determined by using Rheometer. The gel state maintained with more than 5wt% nano-clay in the acetonitrile based solvent. The quasi-solid-state DSSC with nano-clay electrolyte (10 wt%) was successfully showed a high photoelectric conversion efficiency of 10.3%, which is equivalent to that using a liquid electrolyte.