Chemically deposited thin film stack of SnSe-ZnSe-Cu2-xSe was heated in nitrogen with Se vapor at 350-400 oC to produce Cu2ZnSnSe4 (CZTSe) thin films. For this, a thin film of SnSe with 180 nm thickness was deposited at 26 °C from a chemical bath containing tin(II) chloride, triethanolamine, sodium hydroxide, sodium selenosulfate, and a small quantity of polyvinylpyrrolidone. Thin films of ZnSe and Cu2-xSe were subsequently deposited on this SnSe film, also from chemical bath. The CZTSe thin film produced this way shows X-ray diffraction pattern matching that of Cu2ZnSnSe4 (kesterite/stannite) and have a Zn-rich composition. The film has an optical band gap of 0.9-1.0 eV and p-type electrical conductivity, 0.2-0.06 Ω-1 cm-1.

We study hydrogenated amorphous silicon germanium (a-SiGe:H) deposited by HWCVD for the use as low band gap absorber in multijunction junction solar cells. We deposited layers with Tauc optical band gaps of 1.21 to 1.56 eV and studied the hydrogen bonding with FTIR for layers that were deposited at several reaction pressures. For our reaction conditions, we found an optimal reaction pressure of 38 µbar. The material that is obtained under these conditions does not meet all device quality requirements for a-SiGe:H, which is, as we hypothesize, caused by the presence of He that is used to dilute the GeH4 source gas. We present an initial single junction n-i-p solar cell with a Tauc optical band gap of 1.45 eV and a short circuit current density of 18.7 mA/cm2.

Secondary phases are likely to occur in the Cu2ZnSnS4 (CZTS) films since the CZTS is thermodynamically stable in only a narrow region of the phase diagram. The CZTS solar cell performance can be influenced by the existence and precipitated position of secondary phases. Therefore, locally investigate the distribution of secondary phases is important to further improve CZTS solar cell efficiency. In this study, two different kinds of transmission electron microscopy imaging techniques, bright field scanning TEM image (BF-STEM) and High-angle annular dark-field (HAADF) image, are applied to analyze the distribution of secondary phases. Due to the atomic number differences between CZTS and secondary phases, secondary phases are evident in the HAADF images. Therefore, HAADF image is a more powerful and convenient method to analyze the secondary phases than the BF-STEM image.

Ferroelectric barium-strontium-titanate (BST) varactors are becoming extremely important particularly for frequency-agile RF and microwave circuits. Tunable bandstop filters are desired to eliminate unwanted signals for several communication systems. In this paper, a compact tunable bandstop filter (BSF) based on a single hairpin resonator, using ferroelectric BST varactors, is also presented. The frequency response of proposed BSF can be adjusted by increasing or decreasing the length, width, and space for the coupled line hairpin resonator. One pair of variable capacitors has been incorporated to the filter for tuning and miniaturization purposes. The notch frequency of BSF can be tuned from 705 MHz to 1.035 GHz with a tuning voltage of 6 Volts utilizing BST varactors.

Fixed-fixed beams are ubiquitous MEMS structures that are integral components for sensors and actuation mechanisms. However, residual stress inherent in surface micromachining can affect the mechanical behavior of fixed-fixed structures, and even can cause buckling. A self-tensioning support post design that utilizes the compressive residual stress of trapped sacrificial oxide to control the stress state passively and locally in a fixed-fixed beam is proposed and detailed. The thickness and length of the trapped oxide affects the amount of stress in the beam. With this design, compression can be reduced or even converted into tension. An analytical model and a 3D finite element model are presented. The analytical model shows relatively good agreement with a 3D finite element model, indicating that it can be used for design purposes. A series of fixed-fixed beams were fabricated to demonstrate that the tensioning support post causes a reduction in buckling amplitude, even pulling the beam into tension. Phase shifting interferometry deflection measurements were used to confirm the trends observed from the models. Controlling residual stress allows longer fixed-fixed beams to be fabricated without buckling, which can improve the performance range of sensors. This technique can also enable local stress control, which is important for sensors.

We have investigated the electrical properties of a ZnO microwire grown by carbo-thermal evaporation, a ZnO thin film grown by pulsed-laser deposition on an a-plane sapphire, and a hydrothermally grown Zn-face ZnO single crystal (Tokyo Denpa Co. Ltd.). The samples were investigated by means of current-voltage measurements, capacitance-voltage measurements, and deep-level transient spectroscopy.

The defects T2 [1,2] and E3 [1,3,4] were identified in all three sample types. Additionally, in the single crystal and thin film samples E64 [5] and E4 [1] were detected. These findings support the common opinion that T2 is an intrinsic defect since it is found in all the samples investigated and thus its occurrence is not related to any growth technique.

The effect of carbon nanotubes (CNTs) on the thermal and chemical stability of polypropylene (PP) when subjected to oxidation in a fuming nitric was evaluated. The effect of CNTs on the crystalline morphology and melting and crystallization temperature of PP was studied. The results shown a thermal stability increased markedly; the decomposition temperature, increased from 293°C for pure PP to 320°C for PP with CNTs. The crystallization temperature increased perceptibly in presence of CNTs. The oxidative degradation with nitric acid produced a reduction in molecular weight; however, this negative effect was less pronounced in the PP compositions with carbon nanoparticles. The morphological changes evaluated with X-ray diffraction showed that the alpha type crystallinity remains, irrespective of the nucleating agent, and the intensity ratios between reflections peaks was taken as an indication of an increasing nucleating efficiency.

Here we present a single mask sacrificial molding process that allows ultrathin 2-dimensional membranes to be fabricated using biocompatible polymeric materials. For initial investigations, polycaprolactone (PCL) was chosen as a model material. The process is capable of creating 250-500 nm thin, through-hole PCL membranes with various geometries, pore-sizes and spatial features approaching 2.5 micrometers using contact photolithography. The technique uses a mold created from two layers of lift-off resist (LOR). The upper layer is patterned, while the lower layer acts as a sacrificial release layer for the polymer membrane. For mold fabrication, photoresist on top of the layers of lift-off resist is patterned using conventional photolithography. During development the mask pattern is transferred onto the first LOR layer and the photoresist is removed using acetone, leaving behind a thin mold. The mold is filled with a solution of the desired polymer. Subsequently, both the patterned and lower LOR layers are dissolved by immersion in an alkaline solution. The membrane can be mounted onto support structures pre-release to facilitate handling.

We have made a density functional study of the structural and electronic properties of B or N (individual) doped and BN co-doped graphene. The effect of doping has been studied by incorporating the doping concentration amount varying from 2% (one atom of the dopant in 50 host atoms) to 12 % atomic concentration in case of individual doping and from 4% (2 atoms of the dopant in 50 host atoms) to 24 % in case of co-doping, at the same time, altering different doping sites for the same concentration of substitutional doping. We made use of VASP (Vienna Ab-Initio Simulation Package) software based on density functional theory to perform all calculations. While the resulting geometries do not show much of distortion on doping, the electronic properties show a transition from semimetal to semiconductor with increasing number of dopants. The study shows that the BN doping introduces the band gap at the Fermi level unlike individual B and N doping which causes the shifting of Fermi level above or below the Dirac point. It is observed that not only concentration but position of B and N atoms in the hetero-structure also affects the value of band gap introduced.

A molecular dynamics (MD) simulation was performed to study the interaction volume of electron beam in carbon nanomaterials. The interaction between incident electron and carbon atom in the target materials during electron irradiation is introduced by the relativistic binary collision theory. The motion of each atom in the material under electron irradiation is calculated with the MD simulation. The primary energy dependence of the interaction volume in the carbon nanotube and the multi-layered graphene are studied. The secondary damages caused by the knock-on atoms are also discussed.

We developed a new highly porous polyimide (PI) -silica composite with high flexibility, mechanical strength, and heat resistance. The composite was prepared by a new process consisting of (1) phase separation of a mixture of PI precursor (polyamic acid), solvent, and silicon alkoxide, induced by high-pressure CO2 (40 °C, 20 MPa), (2) silicate formation by sol-gel reaction, and (3) supercritical CO2 extraction of the solvent. The composite had a bimodal porous structure with micropores of 10-30 μm and nanopores of ∼50 nm. In the PI matrix, silica nanoparticles (< 100 nm in diameter) were highly dispersed. Porosity of the composite was 78%, which is higher than that of conventional porous PI prepared by physical foaming technique. Relative dielectric constant of the material was lower than 1.4 at 1 MHz. The porous PI-silica composite sheet was flexible enough to be folded without cracking. Notably, the Young’s modulus (0.80 GPa) and the onset decomposition temperature (600 °C) of the PI-silica composite were higher than those of conventional porous PI with similar porosity, respectively. The porous PI-silica composite is promising as a flexible thermal insulator for high-temperature use and as a thermal resistant low-k material.

In the Great Temple at Tenochtitlan, the archaeologists found more than 150 offerings with thousands of pieces, most of them made on foreign raw materials to the Basin of Mexico. Among these votive contexts, the Chamber III of stage IVa (AD 1440-1469), buried during the government of Moctezuma I, is one of the most richness offerings of the temple. Inside this context, the quantity of greenstone beads is huge, and among them, there is a group of translucent appearance that resembles the green calcite objects from the Huastec region. The purpose of this research is to confirm or discard this probable cultural origin and technological manufacture of these beads. To do that, we perform different analysis with neither non-destructive nor invasive techniques like X-Ray Fluorescence (XRF), Fourier Transform Infrared Spectroscopy (FTIR), Raman, Optic Microscopy (OM), and Scanning Electron Microscopy (SEM). By this way we could confirm the similarities among Huastec pieces and these beads, both at mineralogical and technological levels. Based on that, and supported with some written sources from the Colonial period, we propose that these pieces could be war prizes and looted objects by pillage during the Aztec campaigns against Huastec sites; furthermore some of these goods were deposited as victory´s gifts to the gods at the Great Temple of Tenochtitlan.

Arsenic is one of the most toxic elements that can be found. Arsenic is mainly emitted by the copper, lead and zinc production, in agriculture as pesticides and herbicides. Two forms of arsenic are common in natural waters: arsenite (AsO3 3−) and arseniate (AsO4 3−), referred to as As(III) and As(V). The nano-Mg/Al-hydrotalcites present ionic exchange and adsorbent capacities. In this work, the physic-chemical characterization of nano-Mg/Al-hydrotalcites and his arsenic removal capacityis described. The solids were synthesized by the sol-gel method with Mg/Al=2 and 3 ratio. The solids and their thermal treated products were characterized by XRD, FTIR, DTA, TGA and N2 adsorption. The solids were used as adsorbents As(III) in aqueous solutions. Adsorption isotherm studies of As(III) from aqueous solution are described. The adsorbent capacity was determined using the Langmuir, Freundlich and Dubinin–Radushkevich adsorption isotherm models. The As(III) adsorption isotherm data fit best to the isotherm Freundlich model. The maximum As(III) uptake capacity by nano-Mg/Al-hydrotalcites and the heated solids were determined using the Freundlich equation and were found to 547.46, 660.15, 799.88 and 739.12 mg As(III)/g HT-Mg/Al=2, HT-Mg/Al=3, HT-Mg/Al=2 at 350°C and HT-Mg/Al=3 at 350°C respectively. In the kinetic studies using 40 mg/L concentration of As(III) solutions was obtained an excellent removal capacity in contact times less at one minute.

The effects resulting from the introduction of a controlled perturbation in a single pattern membrane on its absorption are first studied and then analyzed on the basis of band folding considerations. The interest of this approach for photovoltaic applications is finally demonstrated by overcoming the integrated absorption of an optimized single pattern membrane through the introduction of a proper pseudo disordered perturbation.

A computational algorithm has been developed to simulate the transport properties of oriented and un-oriented thin film nanocomposites of isotactic Polypropylene (iPP) and carbon nanotubes (CNT) with increasing CNT concentration. Our goal is to be able to design materials with optimal properties using these simulations. We use a cellular automata approach in a Matlab 3-D array environment. The percolation threshold is reproduced in the simulations, matching experimental data. Upon percolation, the thermal transport in the films increases sharply, due to the large difference in the thermal conductivities of the CNTs and the polymer. To verify the simulation, the thin-film samples were sheared in the melt at 200C at 1 Hz in a Linkan microscope shearing hot stage. The thermal conductivity measurements were performed on the same cell arrangement with the transport perpendicular to the thin-film plane using a DC method. The thermal conductivity is higher for the un-sheared as compared to the sheared samples. Our cellular automata simulations provide information about the microstructuremacroscopic property relation in the thin film nanocomposites and can be extended to simulations of other important materials.

Elastmeric materials are of great importance in both academic and industrial field due to the soft and highly stretchable properties. Thus, many theories and models are proposed to correlate the physical properties and structural parameters. However, in general, it is difficult to validate these models experimentally. Thus, to this day, we do not know the requirement conditions for each model or even the validity of each model. The validation of these models has been inhibited by the inherent heterogeneity of polymer networks.

Recently, we, for the first time, succeeded in fabricating polymer network with extremely suppressed heterogeneity with a novel molecular design of prepolymers. The homogeneous polymer network, called Tetra-PEG gel, is prepared by AB-type crosslink-coupling of mutually reactive tetra-arm prepolymers. In this study, we examined the models of elastic modulus and fracture energy using Tetra-PEG gel as a model system. We controlled the structural parameters with tuning the molecular weight and concentration of prepolymers, and reaction conversion of the reaction. This series of controlled network structures, for the first time, enabled us to quantitatively examine these models. We performed the stretching and tearing measurements for these polymer gels. As for the elastic modulus, we observed the shift of the models from the phantom to affine network models around the overlapping concentration of prepolymers. As for the fracture energy, we confirmed the validity of the Lake-Thomas model, which is the most popular model predicting fracture energies of elastomers.

Thin films of AgSbS2 (150 nm) are prepared (75 min at 40 °C) via chemical deposition using a solution mixture containing SbCl3, Na2S2O3 and AgNO3. As-deposited films are amorphous. When they are heated in nitrogen at 180-320 °C, crystalline cubic-AgSbS2 films are formed. They show an optical band gap 1.89 eV and photoconductivity 1.8x10-5 Ω-1cm-1. Silver antimony sulfide-selenide film, AgSb(SxSe1-x)2, is produced from the initial amorphous film when it is heated in presence of Se-vapor. XRD analysis confirms the formation of solid solution AgSbS1.25Se0.75 or AgSbSe2 depending on the extent of Se-vapor available during heating. SnO2:F/CdS/AgSbS2/C solar cell shows V oc 610 mV, J sc 0.88 mA/cm2 ,FF 0.53 and η 0.28%. In SnO2:F/CdS/Sb2S3/AgSb(SxSe1-x)2/C solar cell, V oc is 582 mV, J sc 0.99 mA/cm2, FF 0.51 and η 0.29%.

We investigated the migration behavior of rodlike double-stranded DNA (dsDNA) in polymer gels and polymer solutions. Tetra-PEG gel, which has a homogeneous network structure, was utilized as a model system, allowing us to systematically tune the polymer volume fraction and molecular weight of network strand. Although we examined the applicability of the existing models, all the models failed to predict the migration behavior. Thus, we proposed a new model based on the Ogston model, which well explained the experimental data of polymer solutions and gels. The polymer volume fraction determined the maximum mobility, while the network strand governed the size sieving effect. From these results, we conclude that the polymer network with lower polymer volume fraction and smaller network strand is better in terms of size separation. The homogeneous polymer network is vital for understanding of particles’ dynamics in polymer network and a promising material for high-performance size separation.