Supercapacitor is a newly-developed device for electrochemical energy storage with high power density, long life span, as well as rapid capture and storage of energy. Carbon-based materials, from carbon nanospheres, nanotubes and nanofibers to graphene, are the most commonly used electrode materials for supercapacitors. Our group has engaged in the research of carbon nanomaterials over the past decade. Herein we summarize some typical carbon nanomaterials and their synthetic routes based on our published works, which is expected to provide the theoretical and experimental basis for further applications on carbon-based energy storage devices.

Lignocellulosic biofuels have been identified as a possible solution to contribute to the world’s demands in energy and environmental sustainability. However, the fundamental understanding of the physical and chemical traits hindering key reactions during biomass to biofuel conversion processes has been limited by the lack of suitable tools and by the large natural variability in such systems. Reaction wood constitutes a good model system to study variations of cellulose content, given the increase in cellulose content in the cell walls of the region under tension in the plant during growth. In this work, we use confocal Raman mapping and Pulsed Force Mode Atomic Force Microscopy (PFM) to explore the effect of variation in cellulose content on the structure and composition of the plant cell wall at the nanoscale. Using statistical analysis on Raman datasets, the characteristic peaks for cellulose and lignin are examined to reveal changes in peak positions across the different scanned regions of the cross section. PFM is used to study local mechanical properties of the different layers of the cell wall. Our approach facilitates the correlation of structure-composition traits of the plant cell wall for a more fundamental understanding of processes involved in biofuel research.

GdN/SmN based superlattices have been grown by molecular beam epitaxy. In-situ reflection high energy electron diffraction was used to evaluate the evolution of the epitaxial growth and the structural properties were assessed by ex-situ X-ray diffraction. Hall Effect and resistivity measurements as a function of the temperature establish that the superlattices are heavily n-type doped semiconductors and the electrical conduction resides in both REN layers, SmN and GdN.

In this note we discuss two aspects of screw dislocations dynamics: their behavior near the boundary and a way to confine them inside the material. In the former case, we obtain analytical results on the estimates of collision times (one dislocation with the boundary and two dislocations with opposite Burgers vectors with each other); numerical evidence is also provided. In the latter, we obtain analytical results stating that, under imposing a certain type of boundary conditions, it is energetically favorable for dislocations to remain confined inside the domain.

The interaction of laser radiation with low density aerogels is of crucial importance in areas such as the creation of coherent radiation sources in the X-ray range, simulation of astrophysical as well as nuclear fusion phenomena in laboratory and fundamental studies of the properties of soft condensed matter under dynamic pressure in the Mbar range. In the present paper, the experimental results on the X-ray emission of laser induced plasma in TEOS based, MTMS based aerogels and solid quartz targets, are reported. The aerogels were produced by the sol-gel processing of tetraethoxysilane (TEOS) and methyltrimethoxysilane (MTMS) followed by supercritical drying. Silica alcogels were produced using 0.001 M oxalic acid (C2H4O4), 0.5 M ammonium hydroxide (NH4OH) catalysts. Different densities of aerogels varying from 0.02 to 0.06 g/cm3 have been obtained using different molar ratios of TEOS, MTMS, ethanol and catalysts. The laser, with intensity up to 2 x 1014 W/m2, interaction with TEOS and MTMS based aerogels have been conducted using 30J/500 ps Nd : glass laser system. The resulting soft (0.8 – 1.56 Kev) and hard (>4 Kev) X-ray emissions have been measured using semiconductor photodiodes. It has been observed that the soft X-ray yield increases by a factor of two for the silica aerogel targets compared to the X-ray emission from the solid quartz target, whereas the hard X-ray yield reduces. The enhanced soft X-ray yield in silica aerogel targets is attributed to the large volume heating.

Thermal management is a growing challenge for electronics packaging because of increased heat fluxes and device miniaturization. Thermal interface materials (TIMs) are used in electronic devices to transfer heat between two adjacent surfaces. TIMs need to exhibit high thermal conductivity and must be soft to minimize thermal contact resistance. Polymers, despite their relative softness, suffer from low thermal conductivity (∼0.2 W/m-K). To overcome this challenge, we infiltrate nanoporous anodic aluminum oxide (AAO) templates with molten polymer to fabricate large area arrays of vertically aligned polymer nanofibers. Nanoscale confinement effects and flow induced chain elongation improve polymer chain alignment (measured using polarized Raman spectroscopy) and thermal conductivity (measured using the photoacoustic method) along the fiber’s long axis. Conjugated poly(3-hexylthiophene-2,5-diyl) (P3HT) and non- conjugated polyethylene (PE) of various molecular weights are explored to establish a relationship between polymer structure, nanofiber diameter, and the resulting thermal conductivity. In general, thermal conductivity improves with decreasing fiber diameter and increasing polymer molecular weight. Thermal conductivity of approximately 7 W/m-K was achieved for both the ∼200 nm diameter HDPE fibers and the 100 nm diameter P3HT fibers. These results pave the way for optimization of the processing conditions to produce high thermal conductivity fiber arrays using different polymers, which could potentially be used in thermal interface applications.

Ternary Fe-Co-Si B20 phase structure was formed by implanting Fe and Co ions consecutively into Si(100) substrate at 50 keV energy, each with a fluence of 1.0 × 1017 atoms/cm2 and post-thermal vacuum annealing at 500 oC for 60 minutes. An in-situ magnetic field was used to enhance the formation of the ternary phase in the Si substrate during the implantation process. The magnetic field of 0.05 T was applied perpendicular to the incoming ion beam direction and parallel to the substrate surface to form elongated clusters in the transverse direction of the sample. Prior to the implantation of ions, the implant ions depth profiles were simulated using a dynamic ion-solid interaction code (TRIDYN). The TRIDYN simulation predicted a saturation in the peak concentration of the Fe and Co ions at a fluence of 1.0 × 1017 atoms/cm2. XPS measurement at the peak concentration depth (40 nm) showed the presence of Fe (23 %) and Co (32 %) in the Si matrix. XRD characterization confirmed the presence of stable Fe-Co-Si B20 phase structure in the annealed samples implanted with the in-situ magnetic field.

The purpose of this research is to study the viability of photocatalytic water splitting using ASTM A792 Zn-Al-Fe commercial metallic sheets as substrates for electrodeposited and corroded electrodes. The nanostructures were synthesized in two different procedures: via electrodeposition of migrating species from one electrode to another and from the remaining materials after corrosion of electrodes during electrodeposition, both procedures were done immersing the metallic electrodes in FeCl3 salts dissolved in water as cell electrolyte. The released or remaining Zinc-Aluminum-Iron can be used for the construction of nanostructures or as co-catalyst on the coating over the substrate. Actual EDS-SEM data reveals incorporation of Zinc on dendrite-like structures with traces of Al-Fe due to material release and further electrodeposition on working electrode, meanwhile, dendrite-like structures with an increased amount of Iron were obtained from the corrosion in the auxiliary electrode. Finally, samples were tested with lineal voltammetry to measure the photocurrent activity as indicator of photocatalytic viability for water splitting, obtaining an improvement of 31 mA/cm2 over natural photovoltaic current generation of substrates with higher Zinc concentrations under UV-Visible radiation.

While conducting siderite (FeCO3) solubility experiments in NaCl-Na2CO3 brines, evidence for a second phase was detected. Experiments, in which synthesized siderite was reacted with high ionic strength (0.18 – 7.5 m) solutions at room temperature and high pH (>10), were conducted in a glovebox. As the aging time of siderite-bearing experiments increased, the pH of the solution decreased, signaling formation of a hydroxyl-bearing phase. Decreasing pH values are interpreted to indicate that a hydroxyl-bearing phase, such as chukanovite, is the reaction controlling solid in the solid assemblage. Chukanovite was tentatively identified by XRD analysis. We set out, therefore, to determine the thermodynamic stability of chukanovite under the experimental conditions. Aqueous thermodynamic model parameters were determined with experimentally analyzed Fe(II) solubility data, and subsequently yielded a proposed formation free energy of chukanovite (-1149.8 kJ/mol).

This study investigates the use of ‘simple’ glasses, comprising six components, to represent the structure of complex LAW glasses proposed for Immobilized Low Activity Wastes from the Hanford site in the USA. The 18 elements present in ILAW glasses LAW A44, ORP LB2, and LAW A23 were represented by Al2O3, B2O3, CaO, Na2O, SiO2, and ZrO2 according to their coordination chemistry and their roles as network formers and modifiers. The dissolution behavior of each ‘simple’ glass was compared to its corresponding candidate “complex” LAW glass through PCT-B tests. Significant differences were observed; the durability of complex glasses was concluded to be LAW A44 > ORP LB2 ≥ LAW A23 whereas in their simplified versions the order was LAW A44 > LAW A23 > ORP LB2. These results are discussed in relation to compositional differences and highlight the importance of minor glass components in controlling glass durability. The implications of these results for the use of simplified glass compositions are discussed.

Chromium doped II-VI semiconductors (such as ZnSe and ZnS) feature broad mid-IR emission in the 2-3 μm spectral range due to intershell transitions of the Cr2+ ions. These materials show much promise for development of a tunable, electrically-pumped, mid-IR laser source. For integration into a mid-IR active multilayered structure, the ternary alloy ZnSxSe1-x is an attractive waveguiding material due to its lattice-matching ability and lower index of refraction with respect to the Cr2+:ZnSe active material. Epitaxial growth of each layer is desired to achieve the electronic and optical properties necessary for successful integration into a lasing device, so a study was conducted on the effects of sulfur content and growth temperature on the crystal quality of the resulting thin films. Several films of ZnSxSe1-x were deposited by pulsed laser deposition (PLD) using a 248 nm KrF excimer laser source at varying growth temperatures and with various compositional parameters onto (100) GaAs substrates. The samples were analyzed via x-ray diffraction (XRD) and energy dispersive x-rays (EDX) to investigate the crystal quality and elemental content of the films for device integration. Film-substrate epitaxy was achieved and upper bounds to the defect density were calculated for several regimes of compositional parameter and growth temperature. From all samples produced, the lowest defect density of 2.2 x 1010 cm-2 was observed for the x=0.06 film grown at 450°C, while the lowest lattice mismatch between the substrate and epilayer of 0.059% was observed for the x=0.02 film grown at 450°C.

Stainless steel substrates enable a combination of low cost, flexibility, durability, high processing temperatures, and sub-100 um thickness making it well suited for sheet based and roll-to-roll processing. NFC (13.56 MHz) based circuits using high performance polysilicon TFTs on steel sheets have been manufactured using a hybrid printed process in a production environment. The process scheme utilizes a hybrid, additive materials approach encompassing low cost manufacturing steps such as slot die coating and screen printing of silicon and dopant inks to enable a high throughput, low cost, manufacturing flow. This paper describes the approach for migrating from a sheet-based hybrid process flow to a R2R-based process. A comparison of substrate choices and considerations for R2R process integration is presented. A sensitive electrical method for evaluating the feasibility of R2R-based process integration schemes and materials selection is presented. MIM capacitor leakage, TFT device characteristics, NFC circuit performance, and defect density considerations are shown as a function of steel substrate bending, down to a diameter of 0.75 inches. Electrical characteristics and optical inspections show no measurable change to insulator characteristics, demonstrating a high degree of flexibility and overall device and process capability for R2R processing.