The Center for Functional Nanoscale Materials (CFNM), an NSF Center for Research Excellence in Science and Technology, at Clark Atlanta University has partnered with ACS (American Chemical Society) Project SEED. The ACS project SEED program is recognized nationally as providing hands-on research opportunities to disadvantaged high school students who historically lack exposures to scientific careers. The University is a minority serving institution (MSI) and has an excellent relationship with Atlanta area school systems, which serve the African American community. Students entering their junior and senior years in high school were selected based on their academic performance, an essay and letters of recommendation for participation the Center’s eight week summer nanoscholar Program. Professors served as advisors and/or mentors and graduate students and doctoral fellows served as mentors. The Program included a variety of enrichment activities. All summer nanoscholars had personal research projects that were integral to the research programs of their advisors, and they presented their work in the form of a symposium at the end of the Program. We have completed three summers as an ACS Project SEED site. So far we have had one SEED scholar submit a major manuscript, two were invited to present at ACS National Meetings and one was awarded an eight year Gates-Millennium fellowship. Evaluation of the project strongly suggests that our approach is effective for opening doors for the economically disadvantaged students and tapping the best and the brightest for careers in the sciences and engineering. In the words of one of our young scholars “I realized that research is a continuous learning process. You can never know everything. Even a professor has credentials but they’re still continuing to learn.”

We report crystallization of amorphous silicon (a-Si) thin films and improvement of thin film transistors (TFTs) characteristics using 2.45 GHz microwave heating assisted with carbon powders. Undoped 50-nm-thick a-Si films were formed on quartz substrates and heated by microwave irradiation for 2, 3, and 4 min. Raman scattering spectra revealed that the crystalline volume ratio increased to 0.42 for the 4-min heated sample. The dark and photo electrical conductivities measured by Air mass 1.5 at 100 mW/cm2 were 2.6x10-6 and 5.2x10-6 S/cm in the case of 4-min microwave heating followed by 1.3x106-Pa-H2O vapor heat treatment at 260°C for 3 h. N channel polycrystalline silicon TFTs characteristics were improved by the combination of microwave heating with high-pressure H2O vapor heat treatment. The threshold voltage decreased from 5.3 to 4.2 V and the effective carrier mobility increased from 18 to 25 cm2/Vs.

Water-splitting by using electric power produced by solar cells is promising system to produce hydrogen without fossil fuels. Oxygen evolving catalyst is, however, major problem to prevent using this system widely because precious materials are used in the catalyst. Considering from the photosynthesis II of plants, the compound of Ca-Mn-O is one of the candidates for the oxygen evolving catalyst. In this study, the synthesis condition and the oxygen evolving electrocatalytic activity of CaMn2O4•xH2O are investigated. The overpotential at 0.1 mA/cm2 was 0.28 V when using the electrode of carbon paste and CaMn2O4•H2O with the weight ratio of 3:1.

The aim of this work is to process by equal channel angular pressing (ECAP) a low carbon – triple-alloyed steel containing 0.2% C, 0.5% Cr, 0.6% Ni, 0.2% Mo and 0.8 Mo. The process is performed at room temperature for up to four passes using route Bc with an equivalent strain of ∼0.6 after a single pass. Structure evolution before and after deformation is studied using scanning electron microscopy (SEM) and x-ray diffraction (XRD) and mechanical properties are assessed by microhardness and tensile testing. A significant improvement of the mechanical properties is found with increasing number of ECAP passes. Micro-hardness increases from 216 HV for the initial sample to 302 HV after four passes and tensile strength increases to 1200 MPa compared with 430 MPa prior to ECAP. X-ray diffraction and SEM analysis show changes in the original ferritic-perlitic structure through ferrite grain refinement and the deformation of perlite. This nickel-chromium-molybdenum alloy is used in manufacturing as gear material, and when it is hardened and formed through carburizing or boronizing it can be used to make hard-wearing machine parts. However, the ECAP process has not been used to harden this steel and to change its structure to obtain better mechanical performance.

In this paper we present an innovative on-chip platform suitable for the simultaneous manipulation and detection of the transit of a single magnetic bead. This system is based on the controlled displacement of constrained magnetic domain walls (DWs) that are used to move and sense particles in suspension over the chip. To this scope, the high stray field from the transverse DWs created at the corners of ferromagnetic zig-zag structures is used for particles manipulation, while electrical contacts flanking a single corner are employed to simultaneously monitor the DW passage through that corner, via anisotropic magneto resistance (AMR) measurements. A single DW carrying a magnetic particle is nucleated and manipulated within the zig-zag shaped magnetic conduit, trough the action of external magnetic fields. At the same time, the variation of the voltage drop across a corner flanked by a pair of electrical leads is measured, allowing to detect the transit of the DW thanks to the change of the relative orientation of current and spins at the corner related to the peculiar micromagnetic configuration of the DW (AMR). Work is in progress in order to selectively distinguish the transit of a naked DW from that of a DW bound to a magnetic particle. This work paves the way to the development of a closed-loop microlfuidic platform for on-chip bead manipulation, where single bead can be finely moved and their motion continuously checked, via AMR electrical detection and without need of optical monitoring, in a fully integrated closed-loop system.

The use of organic nonlinear optical (ONLO) materials in electro-optic (EO) modulators requires that the active molecular components (chromophores) be acentrically oriented. The fundamental molecular constituents are in a condensed, glassy phase. Molecular orientation in such systems is typically achieved by applying a DC poling field to the glassy material. We are developing efficient coarse-grained classical Monte Carlo (MC) methods to simulate the order of such systems. The most challenging aspects of these simulations are convergence to an experimentally relevant equilibrium ensemble and verification of simulation accuracy. We use a variety of molecular descriptions and a variety of MC methods to achieve proper order in the shortest number of computational cycles possible. Herein, we illustrate a few examples of the types of calculations and compare with experimental results with representative amorphous organic materials, including electro-optic chromophores.

In this paper, we review our recent work on triplet harvesting (TH) and its application in white organic light-emitting diodes (OLEDs). This includes the configuration of highly efficient single unit two-color and tandem four-color white OLEDs reaching efficacies of more than 30 lm/W at 1000 cd/m², as well as the development of new blue fluorescent emitters. The new compounds are chemically designed to exhibit a high triplet energy to allow TH by a green phosphorescent emitter. In a first step towards white TH OLEDs, we fabricated blue-green TH OLEDs to prove the validity of our concept.

Increasing interest in the photocatalytic activity of TiO2 has led to considerations of using TiO2 nanoparticles in energy generation. In order to better understand the electron-hole relaxation of nano scale TiO2 structures, it is important to start with an understanding of TiO2 synthesis building blocks. The solvated titanium (IV) ion is a precursor found in synthesis methods of colloidal TiO2 nanostructures. This simplest test compound may reflect some common basic electronic features for larger structures composed of Ti(IV) coordinated with oxygen. For this computational study, a model of Ti(OH)4 with tetrahedral coordination was created. To simulate the electronic properties of a solution of Ti(IV), the model was surrounded with 27 H2O molecules. The model was explored by means of standard density functional theory (DFT) molecular dynamics (MD) followed by nonadiabatic electron dynamics computed with Reduced Density Matrix approach combined with “on-the-fly coupling”. Results were generated with Vienna ab initio Simulation Package (VASP) using the Perdew-Burke-Ernzerhof (PBE) functional, plane wave basis set, and projector augmented wave (PAW) potentials. The absorption spectra, MD, and electron-hole relaxation rates are presented for the Ti(OH)4 model at various ambient temperatures. The electron-hole relaxation rates show a non-linear dependence on temperature and were found to be near the same order of magnitude as electron-hole relaxation rates in bulk TiO2 calculations. A video of the geometry optimization can be found online.[1]

The paper reports on the growth of group III-Sb’s on silicon, substrate preparation, optimization of AlGaSb metamorphic buffer, formation of defects (threading dislocations, microtwins and anti-phase boundaries) and their effect on the surface morphology and electrical properties of these high hole mobility materials for future III-V CMOS technology. Defect density was found to be 2-3x higher than in similar structures grown on GaAs, resulting in 2x higher roughness. Defects also result in background p-type doping well above 1017 cm-3 causing inversion of polarity from n-type to p-type in thin n-type doped GaSb. MOS Capacitors fabricated on these buffers demonstrate similar characteristics to higher quality GaSb-on-GaAs. The highest hole mobility obtained in a strained InGaSb QW MOS channel grown on silicon is ∼630 cm2/V-s which is ∼30% lower than similar channels grown on GaAs substrates.

The effect of friction stir welding (FSW) on the resultant microstructures in the welded nugget (WN), thermo-mechanically affected zone (TMAZ), heat affected zone (HAZ) and base metal (BM) of a TRIP-780 steel was investigated in this work. Color tint etching was used in the welded regions to disclose the exhibited microstructural constituents. In addition, significant fine grain size material was found in the WN regions. It was found that is considered to have experienced severe plastic deformation due to interaction with the welding tool pin lead to a drop in mechanical properties. Lap shear tensile testing indicated that the steel shear tension strength in the welded condition dropped compared with the BM. Microhardness profiles of the welded regions indicated that the hardness in both the WN and TMAZ were relatively elevated suggesting the development of martensite in these regions. In particular, the WN was found to shear fracture with uniformly distributed elongation shear dimples.

We have fabricated light emitting diodes (LEDs) in which two active regions separated with a Mg-doped GaN intermediate layer were placed in a single pn junction toward periodic gain structures (PGS) for blue vertical-cavity surface emitting lasers (VCSELs). By current density dependence on a emission intensity ratio from two different active regions, we obtained a very stable emission intensity ratio over 1 kA/cm2. This result is also confirmed with the simulation result. Furthermore, we found that the difference of emission wavelength affect the carrier injection and the emission intensity ratio. On the basis of this result, the optimized well-balanced Mg concentration in the intermediate layer for the two identical active regions were estimated approximately 5 x 1018 cm-3.

We report on the effects of the frequency dispersion in light sensitive materials used in photoimpedance wireless sensors. An example of such a sensor is a gated semiconductor connecting two or more fixed capacitances. The impedance of the device under illumination is changed by the change in the photoresistance of the semiconductor layer and the change in the gate-semiconductor capacitance. We report on the design and simulation of the frequency dispersion of the impedance of this device in silicon and discuss the physics and device performance. We also evaluate the dynamic range and sensitivity of the wireless photoimpedance sensors and show their advantages for wireless sensing applications compared to more conventional light sensors.

The agricultural industry worldwide is facing several challenges including environmental pollution problems (soils and water) caused by the unsuitable control on the use of agrochemicals. Recently, nanotechnology has become an option to improve the existing crop management techniques. Polymer nanoparticles can be used for storage and controlledrelease of agrochemicals, such as pesticides and fertilizers. In this regard, chitosan nanoparticles have been considered for agricultural applications due to the capability of size control at the nanoscale and porosity control capability, in addition to biodegradable and biocompatible characteristics. On this basis, this work focuses on the development of a sizecontrolled synthesis method for chitosan nanoparticles for further use as a platform for the controlled-release system of agrochemicals. The chitosan nanoparticles were synthesized by polymerization using methacrylic acid in water. Several chitosan precursor concentrations (0.2- 0.8 wt.%) were evaluated in order to manipulate the size of produced nanoparticles. The hydrodynamic diameter of those nanoparticles was determined by using a Malvern Zetasizer and the suspension stability trough zeta potential measurements. The morphology and geometrical size were investigated by Transmission Electron Microscopy (TEM). Chitosan nanoparticles size was around 17 nm when a precursor 0.2 wt.% chitosan solution was used. X-ray diffraction and Fourier Transform Infrared Spectroscopy techniques confirmed the chitosan nanoparticles formation and its interaction with functional groups of methacrylic acid.

During an archaeological rescue on Tula’s southwestern urban settlement, two zoomorphic pendants made of the nacreous bivalve Pinctada mazatlanica were found. Such elements belong to a residential compound dedicated to the production of prestige goods for the elite at the Toltec capital.

The importance of these objects analysis lies on the fact that both are on-site taxidermy renderings of two canines. This essay main purpose is to identify the biological zoomorphic renderings and its character, since it’s possible that the samples were not living animals but a depiction of their hides. This research will also analyze the manufacturing technology of these pendants using experimental archaeology, Optical Microscopy and Scanning Electron Microscopy, which indicate a local production controlled by the ruling class.

In this work results are presented regarding carbon composites produced by high energy mechanical milling and consolidated by spark plasma sintering. The involved energy input in such a processing method has been used to develop composite materials and to synthesize effective in-situ reinforcement. In the as milled and sintered composites various dispersions of graphene, graphitic carbon, and diamonds in an amorphous matrix are found. The graphene, graphitic carbon and diamond phases are synthesized primarily during milling. The TEAM-05 microscope has been used for characterization that is complemented with Raman results. The spark plasma sintering method enhances the presence of graphene, graphitic carbon and diamonds.

Defect structures in Rubidium Titanyl Phosphate (RTP) crystals (non-doped and doped) grown by the Top Seeded Solution Growth (TSSG) method were characterized using Synchrotron White Beam X-ray Topography. Main defects observed in non-doped crystals are growth sector boundaries while both growth sector boundaries and growth striations are observed in the Nb single doped and (Nb,Yb)-codoped crystals with relatively few linear defects such as dislocations. Results show that the overall crystalline quality is lowered as more doping elements are incorporated. Details of defect distributions are correlated with the growth process to facilitate high quality growth of doped RTP.

We present an improved AC (Alternating Current) method for the determination of the Thomson coefficient, which can be used for obtaining the absolute Seebeck coefficient. While previous work has focused on DC (Direct Current) methods, we analyze the influence of an AC current in order to derive the Thomson coefficient of a thin wire from measurable quantities. Our expression requires five parameters including AC current, resistance, temperature gradient, and the temperature changes due to the Thomson and Joule effects. Thus, a prior determination of thermal conductivity and sample geometry is not required, unlike DC methods. In order to validate our analysis, the Thomson coefficient of a thin Pt wire has been measured at several frequencies. The results agree with those obtained from a conventional DC method.

Although the cadmium chloride treatment is an essential process for high efficiency thin film cadmium telluride photovoltaic devices, the precise mechanisms involved that improve the cadmium telluride layer are not well understood. In this investigation we apply advanced micro-structural characterization techniques to study the effect of varying the time of the cadmium chloride annealing treatment on the micro-structure of cadmium telluride solar cells deposited by close spaced sublimation (CSS) and relate this to cell performance. A range of techniques has been used to observe the morphological changes to the micro-structure as well as the chemical and crystallographic changes as a function of treatment parameters. Electrical tests that link the device performance with the micro-structural properties of the cells have also been undertaken. Techniques used include Transmission Electron Microscopy (TEM) for sub-grain analysis and XPS for composition-depth profiling. The study provides a new insight in to the mechanisms involved in the initiation and the subsequent complete re-crystallization of the cadmium telluride layer.

Current photovoltaic technologies harvest only a fraction of incoming solar energy since they are unable to utilize photons with energies below the cell band gap. Placed behind a solar cell, the upconverter converts transmitted low-energy photons to photons with energies higher than the cell band gap. The higher energy photons are absorbed by the solar cell and contribute to the photocurrent. We developed optical models of several state-of-the-art commercial and research thin-film solar cells incorporating the upconversion layer. We present both analytical models based on published EQE data as well as detailed finite difference time domain (FDTD) models that incorporate absorption in all cell layers. We model the improvement in absorption and overall cell performance of amorphous Si, CIGS, GaAs, CdTe, and Cu2O cells with upconverting layers. We incorporate and discuss the effect of interface texture and different cell layers on the absorption of upconverted photons and make suggestions for improving the overall cell design to get the maximum benefit from upconversion. We estimate that the cell efficiency enhancement can range from 0.5% to up to 5% absolute depending on the cell type and upconversion efficiency. This work connects to the fundamental efficiency limit analysis of narrow-bandwidth solar upconversion by our collaborators [1], but presents concrete optical models of current solar cells and discusses the promise of upconversion for particular applications.