III-nitride structures on Si are of great technological importance due to the availability of large area, epi ready Si substrates and the ability to heterointegrate with mature silicon micro and nanoelectronics. High voltage, high power density, and high frequency attributes of GaN make the III-N on Si platform the most promising technology for next-generation power devices. However, the large lattice and thermal mismatch between GaN and Si (111) introduces a large density of dislocations and cracks in the epilayer. Cracking occurs along three equivalent {1−100} planes which limits the useable device area. Hence, efforts to obtain crack-free GaN on Si have been put forth with the most commonly reported technique being the insertion of low temperature (LT) AlN interlayers. However, these layers tend to further degrade the quality of the devices due to the poor quality of films grown at a lower temperature using metal organic chemical vapor deposition (MOCVD). Our substrate engineering technique shows a considerable improvement in the quality of 2 μm thick GaN on Si (111), with a simultaneous decrease in dislocations and cracks. Dislocation reduction by an order of magnitude and crack separation of > 1 mm has been achieved. Here we combine our method with step-graded AlGaN layers and LT AlN interlayers to obtain crack-free structures greater than 3.5 μm on 2” Si (111) substrates. A comparison of these film stacks before and after substrate engineering is done using atomic force microscopy (AFM) and optical microscopy. High electron mobility transistor (HEMT) devices developed on a systematic set of samples are tested to understand the effects of our technique in combination with crack reduction techniques. Although there is degradation in the quality upon the insertion of LT AlN interlayers, this degradation is less prominent in the stack grown on the engineered substrates. Also, this methodology enables a crack-free surface with the capability of growing thicker layers.

High energy ion beams are used to modify co-deposited nanolayer films of alternated materials (e.g. insulator and metal, two different semiconductors, even more complex arrangements) to form nanodots through localized nucleation. The particular application being considered here is for high efficiency thermoelectric conversion systems. The performance of a thermoelectric converter is generally given by the figure of merit, ZT, which is a function of the Seebeck coefficient, electrical conductivity, and thermal conductivity. A high performance device would have a maximized electrical conductivity and a minimized thermal conductivity (maximum electron transport, minimal phonon transport). The current models of electron and phonon transportation through 1D, 2D, 3D quantum regimented structures assume an infinitely repetitive perfect structural “cell”, with complicated algorithms requiring intensive computing power. The main focus for this modeling effort is to reduce the three-dimensional problem to a single dimensional approximation without sacrificing the quality of the result. The nanostructure being investigated has Si and Ge quantum dots arranged with perfect periodicity in all three Cartesian directions, with the heat and electricity flow monitored in the z-direction (cross-plane as initially layered). Non-Equilibrium Green’s Functions Formalism (NEGF) is the mode for calculating the theoretical electrical properties assuming a one-dimensional quantum well arrangement in the z-direction (with finite boundaries in the x and y directions) with tight binding (nearest neighbor approximation). The results are to be compared with experimental measurements on such structures.

We have studied nanostructure, electric transport and microwave properties of HTS YBa2Cu3O7-δ films prepared by PLD on LaAlO3 single crystal substrates using targets doped with BaZrO3. Two essentially different types of nanoparticles are revealed by HREM: “nanopancakes” and “nanorods”. Tiny nanopancakes are 1-4 nm in ab-plane and only few atomic layers thick. Nanopancakes are surrounded with deformed area and numerous dislocations. Such nanoparticles seem to be responsible for jc enhancement. Nanopancakes evolve to much wider and longer nanorods at higher substrate temperatures and/or slower deposition. There are no dislocations around nanorods. Elastic strains are avoided due to slight inclination of the c-axis. Dislocations around nanopancakes are suggested to be additional flux pinning centers and retard thermally activated relaxation of the dislocation nanostructure.

In this work, the one dimensional (1D) titanate nanotubes (TNT)/nanowires (TNW), bulk titanate micro-particles (TMP), and three dimensional (3D) titanate microsphere particles (TMS) with high specific surface area were synthesized via different approaches. The chemical composition and structure of these products have been characterized by field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM) study and Raman scattering spectroscopy. The as-prepared TMS shows excellent adsorption performance compared with TMP, TNW and TNT when methylene blue (MB) and PbII ions are used as representative organic and inorganic pollutants.

Titanium possesses an excellent corrosion resistance in biological environments because the titanium dioxide formed on its surface is extremely stable. When aluminium and vanadium are added to titanium in small quantities, the alloy achieves considerably higher tensile properties than of pure titanium and this alloy is used in high stress-bearing situations. But these metals may also influence the chemostatic mechanisms that are involved in the attraction of biocells. V presence can be associated with potential cytotoxic effects and adverse tissue reactions. The alloys with aluminium and iron or with aluminium and niobium occur to be more suitable for implant applications: it possesses similar corrosion resistance and mechanical properties to those of titanium-aluminium-vanadium alloy; moreover, these alloys have no toxicity.

In this paper, pure Ti, Ti-6Al-7Nb and Ti-6Al-4Fe with a nanostructured surface were studied. Data about mechanical behavior are presented. The mechanical behavior was determined using optical metallography, tensile strength and Vickers microhardness.

For the electrochemical measurements a conventional three-electrode cell with a Pt grid as counter electrode and saturated calomel (SCE) as reference electrode was used. AC impedance data were obtained at open circuit potential using a PAR 263A potentiostat connected with a PAR 5210 lock-in amplifier. The ESEM and EDAX observation were carried out with an environmental scanning electronic microscope Fei XL30 ESEM with LaB6-cathode attached with an energy-dispersive electron probe X-ray analyzer (EDAX Sapphire). After 3 days of immersion in simulated body fluid the nucleation of the bone growth was observed on the implant surface.

It resulted that the tested oxide films presented passivation tendency and a very good stability and no form of local corrosion was detected. The mechanical data confirm the presence of an outer porous passive layer and an inner compact and protective passive layer. EIS confirms the mechanical results. The thicknesses of these layers were measured. SEM photographs of the surface and EDX profiles for the samples illustrate the appearance of a microporous layer made up of an alkaline titanate hydrogel. The apatite-forming ability of the metal is attributed to the amorphous sodium titanate that is formed on the metal during the surface treatment.

The results emphasized that the surface treatment increases the passive layer adhesion to the metal surface and improves the biocompatibility of the biomedical devices inducing the bone growth on the implant surface.

In this paper, we present technique to fabricate nanopatterns on Cu thin films via an electrochemical nanomachining (ECN) using an atomic force microscope (AFM). A conductive AFM cantilever tip (Pt/Ir5 coated) was used to form an electric field between tip and Cu substrate with applying a voltage pulse, resulting in the generation of an etched nanopattern. In order to precisely construct the nanopatterns, an ultra-short pulse was applied onto the Cu film through the AFM cantilever tip. The line width of the nanopatterns (the lateral dimension) increased with increased pulse amplitude, on-time, and frequency. The tip velocity effect on the nanopattern line width was also investigated that the line width is decreased with increasing tip velocity. Experimental results were compared with an equivalent electrochemical circuit model representing an ECN technique. The study described here provides important insight for fabricating nanopatterns precisely using electrochemical methods with an AFM cantilever tip.

A polarization-independent, broadband, antireflecting compound aperture array is designed, fabricated and characterized. The structure is composed of an aluminum film with a periodic array of perforations (apertures) configured in a square lattice with a unit cell consisting of two apertures with different diameters, both filled with silicon oxynitride. Light-channeling waveguide cavity modes of different energies are excited within the two different apertures within each unit cell thereby transmitting different parts of the solar spectrum into the substrate. Experimental characterization shows low reflection (<10%) and low diffuse backscatter. Numerous applications of the films include light detecting and emitting structures and devices.

Here we describe a doping approach that enables selective and variable doping on graphene. The doping level reflected in the successive shift of the Raman G mode can be progressively changed by varying the coverage of molecular adsorption on graphene. We make use of lattice defects which serve as anchor groups for the non-covalent functionalization on graphene to enhance molecule adsorption on defective sites at the elevated processing temperatures and also orbital overlap between graphene and adsorbates (melamine). Low density of defects, which can be monitored by seeing the intensity ratio of the D to G mode in the Raman spectra, was generated by exposing graphene to short Ar plasma pulses, followed by dopant adsorption. The controllable creation of defects makes the precise doping on graphene feasible. Systematic characterizations by Raman scattering show that holes are transferred to graphene, with the doping level depending on the surface coverage of melamine. The charge transfer is also identified by the downshift of the charge neutrality point in the transfer characteristics.

We present low-temperature inelastic neutron scattering spectra collected on two metal oxide nanoparticle systems, isostructural TiO2 rutile and SnO2 cassiterite, between 0-550 meV. Data were collected on samples with varying levels of water coverage, and in the case of SnO2, particles of different sizes. This study provides a comprehensive understanding of the structure and dynamics of the water confined on the surface of these particles. The translational movement of water confined on the surface of these nanoparticles is suppressed relative to that in ice-Ih and water molecules on the surface of rutile nanoparticles are more strongly restrained that molecules residing on the surface of cassiterite nanoparticles. The INS spectra also indicate that the hydrogen bond network within the hydration layers on rutile is more perturbed than for water on cassiterite. This result is indicative of stronger water-surface interactions between water on the rutile nanoparticles than for water confined on the surface of cassiterite nanoparticles. These differences are consistent with the recently reported differences in the surface energy of these two nanoparticle systems.

The aim of this study is two-fold: first we reexamine the thermodynamic stability of γ’-Co3(Al,W) phase in the Co-Al-W ternary system. Secondly, we investigate the effect of a fourth alloying element (Ti or Ta) on the thermodynamic stability of the γ’ phase through microstructure observation, DSC measurement and EPMA analysis. Coarsened areas with γ/CoAl/Co3W phases are formed after annealing at 900 ºC for 2000 h in Co-Al-W ternary alloys with different Al/W ratios, which confirms that the three phases are in equilibrium with each other and that the γ’ phase is metastable at this temperature. The addition of a fourth alloying elements does not drastically change the microstructure formed after long term annealing at 900 ºC, indicating that the alloying elements do not improve the stability of the γ’ phase.

The combination of the molecular beam epitaxy growth method with the in-situ reflection high energy electron diffraction measurements currently offers unprecedented control of crystalline growth materials. We present here a stoichiometric study of MnxSc(1-x) [x = 0, 0.03, 0.05, 0.15, 0.25, 0.35, and 0.50] thin films grown on MgO(001) substrates with this growth method. Reflection high energy electron diffraction and atomic force microscopy measurements reveal alloy behavior for all of our samples. In addition, we found that samples Mn0.10Sc0.90 and Mn0.50Sc0.50 display surface self-assembled nanowires with a length/width ratio of ~ 800 – 2000.

Optical materials in the optical circuit board are required to overcome soldering process. In detail, the material should not have absorption and shape changes after several tens of seconds heating at around 250 °C. For such application field, we have developed a novel organic-inorganic hybrid material having a high thermal stability and low absorption at telecom wavelength.

The hybrid material was designed to solvent less resin, which is free radical curable with heating at 150 °C or UV exposure at room temperature, for the sake of device fabrication activity. We demonstrated the waveguides fabrication by photolithography, and obtained high uniformity cured materials. Transparency of the waveguide sample at telecom wavelength was 0.10 dB/cm at 850 nm, 0.12 dB/cm at 1060 nm, 0.29 dB/cm at 1310 nm, and 0.45 dB/cm at 1550 nm. These values are good low attenuation for the Near-IR optical communication in optical interconnects. Without any further treatment such as post bake, the cured materials showed a high thermal stability. The temperature of 5 % weight loss was over 400 °C, and the transparency hardly changed after 1 min heating at 300 °C.

In addition, the cured material showed a high refractive index of n=1.60 at 633 nm and a low curing shrinkage about 4.7 %. From these properties, the developed organic-inorganic material is expected to be beneficial for the optical interconnection such as micro lenses and optical packages.

Metallography, chemical analysis, and microhardness testing of copper-alloy objects from Anau, Turkmenistan (c. 3000-2400 B.C.), were undertaken to determine how technological choices influenced the properties of the finished objects. Additionally, this analytical program assessed the position of the Anau metals in the development of metallurgy in southern Central Asia. Metallographic analysis of three bladed objects, all copper-arsenic alloys with 1% to 5% arsenic, showed that their edges had been cold-worked to a greater or lesser degree to create a blade that maintained a sharp edge, but also had flexibility to withstand impacts. Microhardness testing confirmed that the blade edges had a higher hardness than the interior metal. One of the objects had sulfur-rich inclusions in the metal matrix, suggesting the original charge had at least some sulfide ore. Conversely, a curved rod, made from a copper-lead-tin alloy, was cast to shape and showed no additional working of the metal. Lead, visible as black particles in the microstructure, was likely added to make the molten metal flow more easily. The metallographic and chemical analyses showed that the Anau objects fit into the tradition of Southern Central Asian metallurgy, though the presence of tin in objects of this period is more rare here than in later periods. Anau smiths displayed an ability to manipulate both physical and chemical properties of metal in order to produce functional objects with optimal characteristics.

The doping behavior of bilayers of electropolymerized poly(3,4-ethylenedioxythiophene) doped with hexafluorophosphate and drop-cast poly(benzobisimidazobenzophenanthroline) was studied with cyclic voltammetry, and with in situ ultraviolet-visible and attenuated total reflectance Fourier transform infrared spectroscopy. The spectroelectrochemical characterization of the polymer bilayers provided us with fundamental information of the properties of the materials, information being essential in order to be able to use the conducting polymers in future real-life applications, e.g., as organic semiconducting components.

Dye sensitized solar cells (DSSC) are attractive because they hold promise for devices that are easy to fabricate and inexpensive. In the present work, highly crystalline mesoporous TiO2 has been synthesized by evaporation induced self assembly (EISA) method using triblock copolymer Pluronic P123 as the organic template. The synthesized TiO2 is anatase in nature with a pore size of 10-15 nm. DSSC made from mesoporous TiO2 demonstrated solar conversion efficiency of ∼7%. This comes from the benefits of increased surface roughness, surface area and uniform porosity. In addition, well ordered and crystalline pores provided good sunlight absorption and low recombination path for charge carriers. To further enhance the efficiency of the DSSCs, light scattering centers were introduced in the mesoporous TiO2 film. Nanoparticles light scatterers are introduced to scatter the incoming light and hence to increase the light harvesting capability of the device. A 26 % increase in DSSC efficiency was observed with the implementation of scattering centers.

Polypropylene(PP)/Fe2O3 nanocomposites are fabricated using an in-situ method to uniformly disperse the magnetic nanoparticles (NPs) in polymer matrix. Maleic anhydride functionalized PP (f-PP) with different molecular weight is used as surfactant to stabilize the in-situ produced nanoparticles. The thermal behavior of PP and its nanocomposites with the incorporation of small amount f-PP is studied with thermal gravimetric analysis (TGA). The results show that the onset degradation temperature is increased by ~117 o C with the addition of NPs. Both melt rheology and transmission electron microscopy are used to investigate the NPs dispersion. Strong saturated magnetization (Ms ) is observed after introducing f-PP to the nanocomposites through protecting the as-formed NPs from oxidation.

Infrared radiation (IR) detection and imaging are of great importance to a variety of military and civilian applications. Microcantilever-based IR detectors have recently gained a lot of interest because of their potential to achieve extremely low noise equivalent temperature difference (NETD) while maintaining low cost to make them affordable to more applications. However, the curvature induced by residual strain mismatch within the microcantilever severely decreases the device performance. To meet performance and reliability requirement, it is important to fully understand the deformation of IR detectors. Therefore, the purpose of this study is threefold: (1) to develop an engineering approach to flatten IR detectors, (2) to model and predict the elastic deformation of IR detectors using finite element analysis (FEA), and (3) to study the inelastic deformation during isothermal holding.

In this study electron backscatter diffraction (EBSD) investigation is carried out for CuIn1-xGaXS2 (CIGS2) samples that were prepared by two stage process in which the initial precursor was deposited by DC magnetron sputtering followed by sulfurization in conventional furnace. Due to high surface roughness, low quality EBSD signal was obtained in the samples that were initially polished with ion milling. Polishing with dimpler grinder followed by chemical treatment with bromine/methanol solution improved the quality of EBSD patterns. Efforts are being made to build the database for CIGS2 in the system using high quality EBSD patterns and finally to obtain grain orientation maps.

We report on electrical properties in [(Ge+SiO2)/SiO2]×2 films deposited by magnetron sputtering on a periodically corrugated-rippled substrate and annealed in vacuum and forming gas. The rippled substrate caused a self-ordered growth of Ge quantum dots, while annealing in different environments enabled us to separate charge trapping in quantum dots from the trapping at the dot-matrix and matrix-substrate interfaces. We show that the charge trapping occurs mainly in Ge quantum dots in the films annealed in the forming gas, while Si–SiO2 interface trapping is dominant for the vacuum annealed films.

Aluminum doped ZnOx (ZnOx:Al) films have been deposited on glass in an in-line industrialtype reactor by a metalorganic chemical vapor deposition process at atmospheric pressure. ZnOx:Al films can be grown at very high deposition rates of ~ 14 nm/s for a substrate speed from 150 mm/min to 500 mm/min. ZnOx:Al films are highly conductive (R < 9 Ohm/sq, for a film thickness above 1300 nm) and transparent in the visible range (> 80%). Amorphous silicon p-i-n solar cells have been grown on as deposited ZnOx:Al films, without optimizing the surface texturing of ZnOx:Al films to enhance light scattering. An initial efficiency of approximately 8% has been achieved.