Distributed Bragg Reflectors (DBRs) are an important component of various optoelectronic devices for ultra violet and visible wavelengths. In the III-Nitride material system, Aluminum Nitride (AlN) and Gallium Nitride (GaN) offer a large contrast in refractive index and are therefore well suited for fabricating DBRs with high reflectivity and wide bandwidths using relatively few periods. However, the large lattice and thermal mismatch leads to cracking in these heterostructures. In this work short period superlattice layers have been used to fabricate high reflectivity (> 94%) nitride based DBRs via Metal Organic Vapor Phase Epitaxy. Short period AlN/GaN superlattices containing three to four monolayers of GaN have been employed as the low refractive index layer in DBRs to minimize cracking. Using this technique, crack-free DBRs reflecting from 440-475 nm with up to 25 periods have been fabricated. The technique has been proven to be versatile and resulted in large area yield DBRs grown on a variety of different sapphire substrates.

During the excavations made at a burial of the post-Classic Mayan period (1220-1521 A.D.) in the pyramid number 2 of the pre-Hispanic site of Lagartero, Chiapas, Mexico, a set of four small metallic artifacts depicting reptile’s heads, were recovered. The objects were in poor conservation conditions and were taken to the Metal Conservation Laboratory of the National School of Conservation (ENCRyM- INAH) for suitable cleaning and conservation treatments.

Analyses allowed identifying important technological features such as gilding remains. The analytical techniques included optical microscopy followed by X-Ray Fluorescence Spectroscopy (XRF), and Scanning Electron Microscope-coupled with Energy Dispersive Spectrometer (MEB-EDS). For the elemental depth profile a combined Particle X-Ray Emission Spectroscopy and Rutherford Backscattering Spectrometry (PIXE–RBS) analysis was carried out.

The results indicate that the objects are made of a copper alloy, and then gilded probably using electrochemical replacement gilding (thickness has less than 1 μm). This technology has been observed in other metallic objects recovered from the Chichen-Itza Cenote in Yucatan, but it was not available in Mesoamerican areas so far. So, it could imply that these artifacts might have been imported from South American areas.

Ni/Mg/Al mixed oxides were obtained from hydrotalcite-like precursors by thermal decomposition at 400º, 600º and 800ºC using co-precipitation method at pH 7. The mixed oxides were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Energy-dispersive X-ray spectroscopy (EDS) techniques. XRD analysis revealed the formation of NixMg1-xO (x = 0 - 1), α-Al2O3 and traces of MgAl2O4 (NiAl2O4) phases. The diffraction peak positions for MgO or NiO oxides were shifted towards 2θ values higher than simulated for pure bulk oxides that can be attributed to the possible presence of lattice vacancies or surface compressive stress. The evaluated grain size by XRD technique was about 8 -10 nm. It was also detected the presence of microstrains that can be associated with the presence of extended defects in the grains. SEM observations showed that the particles of oxides are formed as agglomerates with the particle sizes of 50 nm up to 200 nm. EDS detected the presence of Mg2+, Ni2+, and Al3+ cations and oxygen in all particles independently on their size. The obtained results revealed the presence of mixture of Ni/Mg/Al oxides in each particle obtained. The oxides calcined at temperatures of 400º and 600ºC were unstable and under air storage they revert to the precursor. The incorporation of Ni2+ in Mg-Al mixed oxides leads to stability of the compounds calcined at 800ºC.

Optimization of the interface between the organic semiconductor (OSC) & the source-drain (S/D) electrode is critical in order to improve organic thin film transistor (OTFT) device performance. This process typically involves coating the metal S/D electrodes with an optimal self-assembled thiol layer; a process that requires pristine metal surfaces for successful treatment. Obtaining contamination free surfaces can be challenging in the case of printed metal electrodes. Here we demonstrate an effective strategy to address this issue by introducing a brief low power forming gas plasma treatment prior to the surface coating step. We show a two orders of magnitude decrease in the contact resistance as a result of this treatment.

Oxide materials for electronics show recently significant progress. Among the most interesting are oxide composite heterostructures made of thin films. They are taking advantage of integration, anisotropy and synergetic concepts leading to new types of devices and functionalities. Remarkable is that, in the last few years, new devices and artificial materials showing new phenomena were demonstrated. At the same time, their synthesis, processing or fabrication is very often by complex, sophisticated, and, hence, by expensive methods. For further industrial implementation, deep understanding of the growth principles and concepts is required. On a higher level, understanding of the bi-directional relationship between the general and particular principles becomes important and deserves much attention. The immediate benefit is that knowledge on growth for one material can be transferred to another one. This may lead for search of less expensive but optimum technological approaches and can also lead to generation of new materials and devices. In our work we have analyzed the relationship between the particular and general growth principles for some oxide multicomponent perovskites. Materials used in our examples are Bi-Sr-Ca-Cu-O and YBa2Cu3O7, (Ca, Sr)CuO2, (Ca, Ba)CuO2 and Bi4Ti3O12. Presented thin films or heterostructures are with c-axis and non-c-axis orientations. We discuss and we review based on our results film-substrate lattice relationships, principles to control the growth mechanism, the morphology/roughness, the uniformity, and the stability domain and inter diffusion aspects.

Carbon nanotube-spinel lithium titanate (CNT-Li4Ti5O12) nanoparticles have been synthesized by hydrothermal reaction and higher-temperature calcinations with LiOH·H2O and TiO2 precursors in the presence of carbon nanotubes sources. The CNT-Li4Ti5O12 nanoparticles have been characterized by X-ray diffraction (XRD), high angle annular dark field (HAADF) images, and selected area electron diffraction (SAED). The particles exhibited a spinel cubic crystal phase and homogenous size distribution, with sizes around 50-70 nm. HAADF imaging confirmed that carbon content exists on the surface of the CNT-Li4Ti5O12 nanoparticles with graphitic carbon coating of 3-5 nm thickness under 800oC in the Ar gas. The graphitic carbon phase was further confirmed with Raman spectroscopy analysis on powder samples. Electrochemical characteristics were evaluated with galvanostatic discharge/charge tests, which showed that the initial discharge capacity is 172 mA·h/g at 0.1C. The nanoscale carbon layers uniformly coated the particles, and the interconnected carbon nanotube network is responsible for the improved charge rate capability and conductivity.

In this paper the thermoelectric properties–the Seebeck coefficient, the electrical conductivity and the power factor – of GaN and InGaN thin films grown by Metal Organic Vapor Deposition (MOCVD) are reported. The Seebeck coefficient and power factor of InGaN decreases with increasing indium content, although the electrical conductivity shows an inverse behavior. P-type doped samples demonstrated the highest Seebeck coefficient (637 μV/K in GaN:Mg, 1200 μV/K in InGaN:Mg) but the lowest power factor (0.1x10-4 W/m-K for GaN:Mg, 0.4x10-4 W/m-K for InGaN:Mg). The Seebeck coefficient of the doped GaN thin films decreased linearly with log of the carrier concentration. GaN:Si exhibited a maximum power factor of 9.1x10-4 W/m-K with a carrier concentration of 1.6x1018 cm-3, and In0.1Ga0.9N exhibited a maximum power factor of 109x10-4 W/m-K with a carrier concentration of 1.2x1018 cm-3. The results also indicate that GaN and InGaN-based materials could potentially be useful materials for TE applications at high temperatures.

Type I collagen is one of the most vital proteins in our bodies and serves a number of structural roles. Despite collagen’s importance, little is known about its nanoscale morphology in tissues and how morphology relates to mechanical function. This study directly probes nanoscale structure and mechanics in collagen as a function of hydration utilizing atomic force microscopy investigations of the mouse tail tendon. We demonstrate that collagen morphology and mechanical properties at the nanoscale change with dehydration, indicating that hydration is a factor which must be considered when performing studies at any length scale in collagen-based tissues. Studies are underway to further investigate this phenomenon and to determine how these properties change with disease in tendon and other Type I collagen-based tissues.

We report an experimental investigation on employing Ag nanoparticles to provide electrical and mechanical contacts between transfer-printed semiconductor devices in the shape of micro/nano- wires and pillars. The Ag nanoparticles have diameters ranging between 200-800nm and are assembled on a 200nm Au film deposited on glass substrates. With a customized tool, an ensemble of silicon pillars were brought into contact with the silver (Ag) nanoparticles (AgNPs) by precisely controlling the displacement and applied force (pressure). Current-voltage measurements were done at force resolution of ~0.2N. The test method aims to illuminate the pillar-particle contact mechanism using the nanoparticles as conductive fillers for the next generation of high performance heteroepitaxial device transfer-printing applications.

The temperature effect on the magnetoelectric response of hybrid magnetostrictive/piezoelectric laminated composites in the range from room temperature up to 85 ºC is presented. The samples analyzed consisted of alternating, stacked, layers of a magnetostrictive amorphous metal, and a piezoelectric polymer, bonded to each other with an epoxy. The maximum magnetoelectric effect was observed when the composites were driven at their electromechanical resonance. First, we present results on the fabricability of the laminated composite sensor consisting on Vitrovac 4040® (Fe39Ni39Mo4Si6B12) as the magnetostrictive amorphous component and two different piezoelectric polymers: poly(vinylidene fluoride) (PVDF) and 2,6(β-CN)APB/ODPA (poli 2,6) polyimide, a new type of high temperature piezoelectric polymer. At room temperature induced magnetoelectric voltages of 79.6 and 0.35 V/cm.Oe were measured when using PVDF and poli 2,6 polyimide respectively as the piezoelectric components. When heating, we have observed that the magnetoelectric response of the PVDF-containing device quickly decayed to about 5 V/cm.Oe, while for the poli 2,6- containing one it remained almost constat. We discuss the advantage of using this new piezoelectric polymer due to its good performance at high temperatures, making these magnetoelectric laminate composites suitable for high temperature applications.

Vector magneto-optical generalized ellipsometry on passivated ferromagnetic permalloy slanted columnar thin films is reported. The nanostructured thin film was grown by electron-beam glancing angle deposition and subsequently coated with a thin Al2O3 layer by atomic layer deposition. Magneto-optical generalized ellipsometry data have been acquired while an external magnetic field H with constant amplitude was rotated with respect to the sample (spatial hysteresis loops). The magneto-optical coupling parameters, which are proportional to the sample magnetization M, reveal intriguing anisotropic magnetic behavior of the slanted columnar thin film. Three-dimensional graphs of the magneto-optical coupling parameters with respect to spatial hysteresis loops shown here are representative for the sample magnetization.

In this paper, we discuss the low-frequency range of the Raman spectrum of individual suspended index-identified single-walled (SWCNTs) and double-walled carbon nanotubes (DWCNTs). In SWCNTs, the role of environment on the radial breathing mode (RBM) frequency is discussed. We show that the interaction between the surrounding air and the nanotube does not induce a RBM upshift. In several DWCNTs, we evidence that the low-frequency modes cannot be connected to the RBM of each related layer. We discuss this result in terms of mechanical coupling between the layers which results in collective radial breathing-like modes. The mechanical coupling qualitatively explains the observation of Raman lines of radial breathing-like modes, whenever only one of the layers is in resonance with the incident laser energy.

Aragonite can grow from calcium carbonate solutions as the favored phase, at ambient conditions, in the presence of 1:1 volume % water:ethanol. Its form is single and branched needles, with pseudohexagonal symmetry. Morphological evidence demonstrates that all precipitated aragonite is twinned. The recently popularized hypothesis of nonclassical growth by nanocrystal self assembly cannot describe the aragonite crystal form. Rather, its formation is effectively described as spherulitic growth, i.e. by classical crystal growth theory.

In this research we have focused on the influence of thermal treatment for periods of time on the thermal and mechanical properties of extruded films of a series of high-performance thermotropic liquid crystal polymers (LCPs). The dependence of microstructure, thermal and mechanical properties on the extent of thermal treatment is investigated. Especially synthesized wholly aromatic LCPs based on hydroxybenzoic acid (B), hydroxynaphthoic acid (N), terephthalic acid (TA) and biphenol (BP) are kindly supplied by Hoechst Celanese Research Corp in the form of 50 μm thick extruded films. Thus, the influence of monomer composition is also studied in order to contrast the influence of molecular conformation. Thermal treatments are carried out at temperatures close to the solid-to-nematic transition (Ts→n ) for up to several hours under dry air conditions. The results show a profound influence of thermal annealing on morphology and mechanical modulus when annealing is carried out c.a. 40ºC below Ts→n , where solid-to-nematic transition and Young’s modulus are significantly increased.

MgZnO becomes amorphous or short-range-ordered with the addition of hafnium oxide. The films are rf-sputter deposited onto glass substrates (Eagle 2000, Corning Inc.) from Mg0.05HfxZn0.95-xO targets (x=0, 0.025, 0.05, 0.075, 0.1) in pure Ar ambient at room temperature. The sputtered Mg0.05Zn0.95O exhibits strong (002) preferred orientation with XRD peak located at 2θ=34.16o. The XRD peak intensity is also greatly reduced, indicating the material amorphorization proceeds with the addition of Hf. The grain size, estimated from the full-width-at-half-maximum (FWHM) of the (002) XRD peak, decreases from 24.1 to 3.3 nm as the Hf content x increases from 0 to 0.025 in Mg0.05HfxZn0.95-xO. No sharp XRD peaks are detected in the as-sputtered films when more than 5.0 at.% Hf are added into the materials. The films remain in amorphous or short-range-ordered states after annealing at 600 oC for 30 mins. All Mg0.05HfxZn0.95-xO films (100 nm in thickness) are highly transparent (> 80 %) in the visible region from 400 to 800 nm and have sharp absorption edges in the UV region. The tauc bandgap ΔE (eV), as a function of hafnium composition x, is fitted as ΔE=3.336+6.08x for room temperature as-deposited films, and ΔE=3.302+2.60x for films after 30 min 600 oC annealing. The annealing process decreases the bandgap shift caused by the incorporation of Hf in the materials.

Hexagonal ZnO was grown on hexagonal (001) sapphire substrate, then cubic La(Sr)MnO3(LSMO) was grown on ZnO underlayer by ion beam sputtering at substrate temperatures of 550-750°C to obtain double-layer of LSMO/ZnO. Out-of-plane (001) oriented ZnO was grown with in-plane orientation of [10-10](0001)ZnO//[11-20](0001)sapphire. Mixed phase of LSMO with out-of-plane (001), (110) and (111) orientations was grown on (001) ZnO usually. However each single phase of LSMO could be grown by controlling deposition conditions. The LSMO grains have their in-plane orientations of [110](110)LSMO //[10-10](0001)ZnO and [110](111)LSMO//[11-20](0001)ZnO.

The stress corrosion cracking (SCC) of Alloy 22 in concentrated ground waters was associated to the presence of bicarbonate and chloride ions in the water. SCC occurred when an anodic peak appeared in the polarization curve of Alloy 22. The aim of this work was to investigate further which element in Alloy 22 was responsible for the anodic peak and therefore SCC. Four alloys (22, 800H, 600 and 201) were mainly used for this study. It has been found that Alloy 22, 600 and 800H show anodic peaks; which are affected by chloride and temperature. It is likely that the anodic peak is associated to the presence of either chromium, molybdenum or both.

Solid electrolyte materials have the potential to improve performance and safety characteristics of lithium-ion batteries by replacing conventional solvent-based electrolytes. A candidate solid polymer electrolyte, AMLi/PEGDM, has been synthesized by crosslinking an anionic monomer AMLi, with poly(ethylene glycol) dimethacrylate. The main goal of the synthesis is to produce a single-ion conducting polymer network where lithium cations can move freely and fluorinated anions are immobilized as part of the polymer network. A comprehensive characterization of anion and cation mobility in the resulting material is therefore required. Using pulsed-field gradient nuclear magnetic resonance (PFG-NMR), we are able to measure and quantify the individual diffusion coefficients of mobile species in the material (19 F and 7 Li) and confirm the extent to which the fluorinated anionic component is immobilized. We have characterized dry (σ~3.0 x10-7 S/cm at 30°C) and propylene carbonate (PC) saturated gel (σ~1.0x10-4 S/cm at 30°C) samples. Experimental results include NMR spin-spin and spin-lattice relaxation times in addition to diffusion coefficient measurements over a temperature range up to 100°C. Practically, the diffusion measurements are extremely challenging, as the spin-spin (T2) relaxation times are very short, necessitating the development of specialized pulsed-field gradient apparatus. Diffusion coefficients for the most mobile components of the lithium cations and fluorinated anions at 100°C in dry membranes have been found to be 3.4 x10-8 cm2/s and 2.1 x10-8 cm2/s respectively. These results provide valuable insight into the conduction mechanisms in these materials, and will drive further optimization of solid polymer electrolytes.