We perform density functional theory calculations to determine equilibrium lattice parameters of wurtzite Zn1-x Mgx O alloys for Mg concentrations x ranging from 0 to 31.25 %. We use the local density approximation (LDA) as well as the generalized gradient approximation (GGA) for the exchange correlation functional. For the lattice constants a and c we find a deviation from Vegard's law and a constant unit cell volume independent of the Mg concentration.

Pure and Zn1-xCoxO nanoparticles have been synthesized by a simple sol-gel method at low temperature where neither a chelating agent nor subsequent annealing was required. The effect of Cobalt atomic fraction, ‘x’ ≤ 0.0625, on the structural and magnetic properties of the doped ZnO powders was evaluated. X-ray diffraction and Fourier-transform infrared spectroscopy analyses evidenced the exclusive formation of the ZnO-wurtzite structure; no isolated Co-phases were detected. The linear dependence of cell parameters a and c with ‘x’, suggested the actual replacement of Zn by Co ions in the oxide lattice. Micro Raman spectroscopy measurements showed a band centered at 534cm-1, which can be assigned to a local vibrational mode related to Co species, in addition to the normal modes associated with wurtzite. The intensity and broadening of this band at 534 cm-1 were enhanced by increasing ‘x’. In turn, the other bands corresponding to A1 (E2, E1) and E2 High modes were red shifted at higher Co contents. Room-temperature magnetization measurements revealed the paramagnetic behavior of the Co-doped ZnO nanoparticles.

We report on structural, electronic, and optical properties of boron-doped, hydrogenated nanocrystalline silicon (nc-Si:H) thin films deposited by plasma-enhanced chemical vapor deposition (PECVD) at a substrate temperature of 150°C. Film properties were studied as a function of trimethylboron-to-silane ratio and film thickness. The film thickness was varied in the range from 14 to 100 nm. The conductivity of 60 nm thick films reached a peak value of 0.07 S/cm at a doping ratio of 1%. As a result of amorphization of the film structure, which was indicated by Raman spectra measurements, any further increase in doping reduced conductivity. We also observed an abrupt increase in conductivity with increasing film thickness ascribed to a percolation cluster composed of silicon nanocrystallites. The absorption loss of 25% at a wavelength of 400 nm was measured for the films with optimized conductivity deposited on glass and glass/ZnO:Al substrates. A low-leakage, blue-enhanced p-i-n photodiode with an nc-Si p-layer was also fabricated and characterized.

In this study, we fabricated and examined a series of multiphase type composites constructed of Nb-doped SrTiO3 / TiO2 fine particles. The composition of the composites and the sintering temperatures were selected in a two-phase region where a perovskite SrTiO3 and a rutile TiO2 phases coexist. The composites obtained here were found to commonly have a mosaic type texture constructed of TiO2 and SrTiO3 fine particles with a typical size of about 500 nm. In some samples we also found additive phases such as Sr6Ti7Nb9O42. The thermal conductivity values measured for the most samples with different contents are ranged between 2 and 5 Wm-1K-1. The values are apparently lower than the value for single crystal SrTiO3 samples presented in literature. A sample with rather low relative density of about 80% showed a quite low thermal conductivity, about 1 Wm-1K-1. Taking account the other TE data, e.g. Seebeck coefficient and electrical conductivity, we calculated dimensionless figure of merit, ZT, to be at maximum 0.24 at 600°C.

Self-aligned TiSi2 coated Si nanocrystal nonvolatile memory is fabricated. This kind of MOSFET memory device is not only thermally stable, but also shows better performance in charge storage capacity, writing, erasing speed and retention characteristics. This indicates that CMOS compatible silicidation process to fabricate TiSi2 coated Si nanocrystal memory is promising in memory device applications.

In this work, we optimized different thin film silicon layers in a single junction p-i-n solar cell at deposition temperature of 150 °C. Using the optimized doped and undoped layers, 0.5 cm2 test cells fabricated both on glass and polyethylene naphthalate (PEN) substrates. The cells show identical open circuit voltages and fill factors, whereas the short circuit current and consequently the efficiency of the cell fabricated on glass is higher than the efficiency of 3.99% of the cell fabricated on PEN substrate.

The size dependence of the photoluminescence spectra from silver nanoparticles embedded in a silica host medium was observed. The quantum yield of the photoluminescence increased when the size of the nanoparticles was decreased. The quantum yield for 8 nm silver nanoparticle was estimated to be on the order of 10-2 which is 108 times higher than the one observed for bulk silver. The two photoluminescence bands observed from silver nanoparticles were rationalized as the radiative electron interband transitions and radiative decay of the surface plasmons in silver nanoparticles. The strong local electric field induced by the surface plasmon resonance in silver nanoparticles enhances the exciting and emitted photons and increases the quantum yield of the photoluminescence.

In the current work we report results of tribological testing of stable colloidal dispersions of detonation nanodiamond (DND) and polytetrafluoroethylene (PTFE) in mineral oil based greases as well as in polyalphaolefin (PAO) oil. Testing has been performed on these formula-tions using ring-on-ring, shaft/bushing and four ball test techniques. The test results demon-strated significant improvements for tribological characteristics (friction coefficient, extreme pressure failure load anddiameter of wear spot) for certain formulations. A strong synergistic effect when using a combination of DND/PTFE additives was observed by a sharp decrease of friction coefficient. It was also demonstrated that using DND with smaller aggregate size (10nm versus 150nm) resulted in better lubricating performance of PAO-based composition.

Capacitive field-effect electrolyte-diamond-insulator-semiconductor (EDIS) structures with O-terminated nanocrystalline diamond (NCD) as sensitive gate material have been realized and investigated for the detection of pH, penicillin concentration, and layer-by-layer adsorption of polyelectrolytes. The surface oxidizing procedure of NCD thin films as well as the seeding and NCD growth process on a Si-SiO2 substrate have been improved to provide high pH-sensitive, non-porous thin films without damage of the underlying SiO2 layer and with a high coverage of O-terminated sites. The NCD surface topography, roughness, and coverage of the surface groups have been characterized by SEM, AFM and XPS methods. The EDIS sensors with O-terminated NCD film treated in oxidizing boiling mixture for 45 min show a pH sensitivity of about 50 mV/pH. The pH-sensitive properties of the NCD have been used to develop an EDIS-based penicillin biosensor with high sensitivity (65-70 mV/decade in the concentration range of 0.25-2.5 mM penicillin G) and low detection limit (5 μM). The results of label-free electrical detection of layer-by-layer adsorption of charged polyelectrolytes are presented, too.

This paper focuses on manufacturing process of regular Metallic Hollow Sphere Structures (MHSS) through brazing technique. As a large stress level is generally confined into the necks formed by brazed spheres, the influence of the filler material on mechanical behavior of cellular metal has been studied. The microstructures of joints resulting from nickel hollow spheres brazing with different commercial fillers “MBF 30” and “MBF 1006” were compared by Scanning Electron Microscopy (SEM) and microhardness testing. These studies revealed a wide boron diffusion into nickel shells through grain boundaries for “MBF 30” brazing, with the formation of borides in a fine brittle eutectic structure. Conversely it was observed that the eutectic structure concentrates at the necks for “MBF 1006” and can be completely eliminated by diffusion-brazing, despite of the shells thinness. The uniaxial compressive tests of HSP specimens have shown two different strain mechanisms depending on brazing process.

Composite phase change materials (PCM) were prepared by mixing exfoliated graphite nanoplatelets (xGnP) into paraffin wax. The two types of graphite nanoplatelets that were investigated were xGnP-1 having thickness of 10 nm and a diameter of 1 um and xGnP-15 having the same thickness with a platelet diameter of 15 um. Direct casting and two roll milling were used to prepare samples. Scanning electron microscopy images show that the nanofillers disperse very well in paraffin matrix without noticeable agglomeration. Paraffin/xGnP-15 PCM consistently exhibited higher thermal conductivity than xGnP-1 PCM. The improvement in thermal conductivity was as high as 5 fold for xGnP-15 composites and 2 fold for xGnP-1 composites at 4 vol%. The aspect ratio, particle orientation, and interface density between the conductive particles and the polymer matrix were found to be the critical parameters in determining the conductivities of the resulting nanocomposites. The thermal physical properties of the nanocomposites were investigated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). It was found that the latent heat of nanocomposites was not negatively affected in the presence of xGnP particles and the thermal stability improved.

Over the past few decades, there has been considerable research and advancement in surface acoustic wave (SAW) technology. At present, SAW devices have been highly successful as frequency band pass filters for the mobile telecommunications and electronics industries. In addition to their inherent frequency selectivity, SAW devices are also highly sensitive to surface perturbations. This sensitivity, along with a relative ease of manufacture, makes SAW devices ideally suited for many sensing applications including mass, pressure, temperature, and biosensors. In the area of biosensing, surface plasmon resonance (SPR) and quartz crystal microbalances (QCM) are still in the forefront of research and development, but advancement in SAW sensors could prove to have significant advantages over these technologies. This study investigates the advantages of using aluminum nitride (AlN) as a material for SAW sensors. AlN retains its piezoelectric properties at relatively high temperatures when compared to more common piezoelectric materials such as lead zirconium titanate (PZT), lithium tantalate (LiTaO3) and zinc oxide (ZnO). AlN is also a very robust material making it suitable for biosensing applications where the sensing target is selectively absorbed by an active layer on the device which may attack the piezoelectric layer. AlN thin films of different thicknesses have been deposited on Si substrates by DC reactive sputtering. Rayleigh-wave SAW devices have been fabricated by the deposition of platinum contacts and interdigital transducers (IDTs) onto AlN thin films using standard photolithographic processes. Experiments have been conducted to measure Rayleigh velocities, resonant frequencies, and insertion loss. Experimental results are compared to theoretical calculations.

An intermediate-band material based on thiospinel semiconductor MgIn2S4 is presented. This material is proposed as high efficiency photovoltaic material for intermediate-band solar cells. We analyze V substitution for In in the parent compound MgIn2S4 and the formation of the V d-states intermediate band. For the proper characterization of the width and position of this band inside the band gap, the standard one-shot GW method within the plasmon-pole approximation is applied. The electronic properties thus obtained are discussed and compared to those studied with Density Functional Theory (DFT), and the advantages and the limitations of the two methods are discussed. In addition, DFT electronic-charge density analysis is shown.

With materials innovation driving recent logic and memory scaling in the semiconductor industry, High-Productivity Combinatorial™ (HPC) technology can be a powerful tool for finding optimum materials solutions in a cost-effective and efficient manner. This paper will review unique HPC wet processing, physical vapor deposition (PVD), and atomic layer deposition (ALD) capabilities that were developed, enabling site-isolated testing of multiple conditions on a single 300mm wafer. These capabilities were utilized for exploration of new chalcogenide alloys for phase change memory, and for metal gate and high-K dielectric development for high-performance logic. Using an HPC PVD chamber, a workflow was developed in which up to 40 different precisely controlled GeSbTe alloy compositions can be deposited in discrete site-isolated areas on a single 300mm wafer and tested for electrical & material properties, using a custom in-situ high-throughput sheet-resistance measurement setup, to get very accurate measurements of the amorphous – crystalline transition temperature. We will review how resistivity as a function of temperature, crystallization temperature, final and intermediate (if any) crystalline phases were mapped for a section of the GeSbTe phase diagram, using only a few wafers. Another area where HPC can be very valuable is for finding optimum materials for high-k dielectrics and metal gates for high-performance logic transistors. Assessing the effective work-function (EWF) for a given high-k dielectric metal-gate stack for PFET and NFET transistors is a critical step for selecting the right materials before further integration. One way to obtain EWF is by using a terraced oxide wafer with different SiO2 thickness bands underneath the high-k dielectric. We report a HPC workflow using our wet, ALD & PVD capabilities, to quickly assess EWF for multiple different high-k dielectrics and metal gate stacks. This workflow starts with a HPC wet etch of thermal silicon oxide, creating different oxide thicknesses 1–10nm in select areas of the same substrate. This is followed by atomic layer deposition of a high-k dielectric film such as HfO2. Next, a metal e.g., TaN is deposited through a physical mask or patterned post-deposition to complete the formation of MOS capacitors. The final step is C-V measurements and C-V modeling to extract Vfb, high-k dielectric constant, EOT, and EWF from Vfb vs EOT plot. This workflow was used to extract EWF for a TaN metal gate with an ALD HfO2 high-k dielectric using a metal-organic precursor. We will discuss how EWF for this system was affected by annealing post-dielectric deposition & post-metallization, different annealing temperatures & ambients, Hf pre-cursors and interfacial cap layers e.g., La2O3 & Al2O3. Finally, we will also discuss more advanced versions of this workflow where the ALD high-k dielectric and PVD metal gate is also varied on the same wafer using HPC versions of ALD & PVD chambers.

The enhancement of optical transmittance at the air/glass interface of amorphous silicon thin film solar cells was shown by application of a nanoporous polymethyl methacrylate (PMMA) antireflection (AR) coating. The PMMA coating was prepared by spin coating of PMMA solution in chloroform in the presence of a small amount of nonane. Because of the difference of the vapor pressure of chloroform and nonane, phase separated structure formed after complete evaporation of both of them during spin coating process. The Corning 1737 glass with the AR coating has high transmittance near 95% from 450-1100nm wavelengths. The amorphous silicon solar cells with the nanoporous PMMA AR coating realize an improvement in quantum efficiency (QE) up to 4% in 450-650nm spectral regions.

We have demonstrated electrostatic switching in vertically oriented nanotubes or nanofibers, where a nanoprobe was used as the actuating electrode inside an SEM. When the nanoprobe was manipulated to be in close proximity to a single tube, switching voltages between 10 V – 40 V were observed, depending on the geometrical parameters. The turn-on transitions appeared to be much sharper than the turn-off transitions which were limited by the tube-to-probe contact resistances. In many cases, stiction forces at these dimensions were dominant, since the tube appeared stuck to the probe even after the voltage returned to 0 V, suggesting that such structures are promising for nonvolatile memory applications. The stiction effects, to some extent, can be adjusted by engineering the switch geometry appropriately. Nanoscale mechanical measurements were also conducted on the tubes using a custom-built nanoindentor inside an SEM, from which preliminary material parameters, such as the elastic modulus, were extracted. The mechanical measurements also revealed that the tubes appear to be well adhered to the substrate. The material parameters gathered from the mechanical measurements were then used in developing an electrostatic model of the switch using a commercially available finite-element simulator. The calculated pull-in voltages appeared to be in agreement to the experimentally obtained switching voltages to first order.

We present a theoretical model for carrier conductivity and Seebeck coefficient of thermoelectric materials composed of nanogranular regions. The model is used to successfully describe experimental data for chalcogenide PbTe nanocomposites. We also present similar calculations for skutterudite CoSb3 nanocomposites. The carrier scattering mechanism is considered explicitly and it is determined that it is a key factor in the thermoelectric transport process. The grain interfaces are described as potential barriers. We investigate theoretically the role of the barrier heights, widths, and distances between the barriers to obtain an optimum regime for the composites thermoelectric characetristics.

For spintronic device applications, large and in particular tunable tunnel magnetoresistance (TMR) ratios are inevitable. Fully crystalline and epitaxially grown Fe/MgO/Fe magnetic tunnel junctions (MTJs) are well suited for this purpose and, thus, are being intensively studied [1]. However, due to imperfect interfaces it is difficult to obtain sufficiently large TMR ratios that fulfill industrial demands (e.g. [2]).

A new means to increase TMR ratios is the insertion of ultra-thin metallic buffer layers at one or at both of the Fe/MgO interfaces. With regard to their magnetic and electronic properties as well as their small lattice mismatch to Fe(001), Co and Cr spacer are being preferably investigated.

We report on a systematic first-principles study of the effect of Co and Cr buffers (with thicknesses up to 6 ML) in Fe/MgO/Fe magnetic tunnel junctions (MTJs) on the spin-dependent conductance. The results of the transport calculations reveal options to specifically tune the TMR ratio. Symmetric junctions, i.e. with Co buffers at both interfaces, exhibit for some thicknesses much larger TMR ratios in comparison to those obtained for Fe-only electrodes. Further, antiferromagnetic Cr films at a single interface introduce TMR oscillations with a period of 2 ML, a feature which provides another degree of freedom in device applications. The comparison of our results with experimental findings shows agreement and highlights the importance of interfaces for the TMR effect.

We have demonstrated that 30BaO–15TiO2–30GeO2–25SiO2 (BTGS25) glass is a candidate for fiber-type nonlinear optical devices using crystallization of glass matrix. We determined the glass composition is suitable for crystallized fiber using partial substitution of Ge in 30BaO–15TiO2–55GeO2 (BTG55) by Si. The BTGS25 satisfied both thermal stability for fiber drawing and electronic polarizability for nonlinear optical property. After crystallization, the BTGS25 bulk crystallized glass showed surface crystallization behavior with the polar c-orientation of fresnoite phase, which was favorable for large second-order optical susceptibility. Following the results of the bulk glass, we prepared the BTGS25 glass fiber without precipitation of fresnoite crystallites. The BTGS25 crystallized fiber also showed c-oriented surface crystallization of fresnoite and second harmonic generation, which shows that the crystallized fiber is a promising material for fiber-type optical active devices.

Hydrogen peroxide is considered as one of the main oxidants formed due to the radiolysis of water. In a spent nuclear fuel repository, it is necessary to establish the interaction of hydrogen peroxide with the elements constituting the repository. The objective of this work is to study the consumption of hydrogen peroxide via reaction with the elements of the canister.

In this sense, two different series of experiments were conducted, with iron steel an magnetite, respectively. Each series consisted on three different experiments that contained a coupon of the solid and different hydrogen peroxide concentrations (10−4 mol·dm−3, 10−5 mol·dm−3 and 10−6 mol·dm−3). Hydrogen concentration in solution was measured at different intervals of time by means of chemiluminescence. At the end of the experiments, the coupons were studied by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) in order to determine the possible secondary solid phases formed on the coupons.

In both series of experiments, a decrease of the hydrogen peroxide concentration in solution with time was observed. The determined consumption rates increased with hydrogen peroxide concentration and were higher in steel than in magnetite. The reaction orders relative to hydrogen peroxide concentration were very close to the unity on both solids.

The study of the carbon steel coupons by SEM at the end of the experiments showed that they were more attacked at higher hydrogen peroxide concentrations. On the other hand, the XRD measurements in the steel coupons showed that lepidocrocite (γ-FeO(OH)), and magnetite (Fe3O4) were formed on the coupon as iron secondary solid phases.