Recently, classical elasticity theory for thin sheets was used to demonstrate the existence of a universal structural behavior describing the confinement of sheets inside cylindrical tubes. However, this kind of formalism was derived to describe macroscopic systems. A natural question is whether this behavior still holds at nanoscale. In this work, we have investigated through molecular dynamics simulations the structural behavior of graphene and boron nitride single layers confined into nanotubes. Our results show that the class of universality observed at macroscale is no longer observed at nanoscale. The origin of this discrepancy is addressed in terms of the relative importance of forces and energies at macro and nano scales.

We describe our approach to a student-centered interdisciplinary research program in material science. Our work in the synthesis and optical characterization of sol-gel materials provides an ideal research setting for undergraduates interested in physics and chemistry. Students fabricate all samples and perform laser spectroscopic measurements. The work is accessible to undergraduates but also of current interest to a wide community of scientists interested in new rare earth based optical materials. Students make meaningful contributions to publishable work, and many go on to do graduate work in physics or chemistry. Two recent students have been recognized with national awards for their research, and many have presented work at international meetings.

Samples of carbon fiber were prepared from polyacrylonitrile (PAN)-based precursors, covering a range of electrical resistivity from 0.9 to 1,000 mΩ cm corresponding to a range of carbonization heat treatment temperatures (HTT) estimated to be between 700 and 2600°C. Experimental gas diffusion media (GDM) were made from these fibers using conventional phenolic resin/carbon fiber construction, prepared at two different carbonization temperatures (950 and 2150°C). GDM thermal and electrical properties displayed similar trends with respect to fiber and paper HTT. Unexpectedly, GDM bending and shear moduli increased with fiber resistivity, possibly due to shortening of the lower resistivity fiber types during GDM production. Results showed that high HTT of either the carbon fiber or the paper was sufficient to enable average (“wet” and “dry”) 5-cm2 fuel cell performance comparable to current state-of-the-art GDM. A proprietary GDM wet-laid production model predicts a potential cost reduction of about 2% at 20 million m2 annual production by reducing the paper HTT.

Electromigration has gained increased prominence in recent years, as semiconductor device scaling has given way to higher current and power densities in computing interconnects and devices. The conventional understanding of electromigration has remained at an uneasy juncture between the mesoscopic semiclassical and atomistic quantum mechanical regimes. Herein, an “atomistic semiclassical” interpretation of electromigration is presented in an attempt to bridge these two perspectives at the nanoscale.

Zwitterionic liquid (ZL) molecules are considered among the surfactant molecular species used in enhanced oil recovery (EOR). The surface activity of asphaltenes (ASP) is crucial for establishing reservoir rock wettability, which impacts enhanced oil recovery (EOR) process. The key to a successful EOR formulation is to carefully select the components that provide ultra-low interfacial tension (IFT) under reservoir conditions. Achieving ultra-low IFT greatly reduces capillary forces that trap oil. The objective of this work is the theoretical study of the influence of a class of germinal zwitterionic liquid on interfacial tension or changes on wettability of the oil-rock system under reservoir conditions. The ZL molecule used in this study was designed by Zamudio et al; while the asphaltene model was originally proposed by Buenrostro-González. Methods of molecular mechanics and dynamics were used in order to calculate interaction energies of all systems. The results indicate that the ZL molecule adheres more strongly to the limestone-rock than the asphaltene molecule does. In addition, our results suggest that the ion-pair formation is the dominant wettability alteration mechanism.

The reaction kinetics of depleted uranium under constant hydrogen pressure (1 bar) have been measured as a function of reaction temperatures between 65 and 385 °C for as-polished and vacuum annealed samples. Enhanced hydrogen reactivity was observed on samples that underwent vacuum annealing prior to hydrogen exposure. The enhanced reactivity was found to be the result of enhanced nucleation rates on annealed samples since the specific rate per reacting unit area remained unaffected. X-ray photoelectron spectroscopy demonstrates that the nucleation kinetics were promoted on annealed samples as a result of the dehydration and partial reduction of the UO2+x outer oxide layer and the formation of an oxycarbide (UOxCy) sub-layer.

Process and electromigration issues of the copper line over a dielectric step etched with a new plasma-based process have been studied. The N2 and CF4 additive gas effects on the line profile, undercut, and “neck” formation at the cusp area were investigated with respect to changes of the plasma phase chemistry and ion bombardment energy. The sidewall passivation layer hindered the excessive attack of the cusp region. The undercut of the photoresist pattern caused the residue formation. The lifetime of the etched copper was related to the line shape and the film topography, which directly affected the local current density and stress. With the proper control the plasma phase chemistry and ion bombardment energy, the Cu film over a topographic surface can be etched into fine lines with a long electromigration lifetime.

Hybrid magnetic/plasmonic nanoparticles possess properties originating from each individual material. Such properties are beneficial for biological applications including bio-imaging, targeted drug delivery, in vivo diagnosis and therapy. Limitations regarding their stability and toxicity, however, challenge their safe use. Here, the one-step flame synthesis of composite SiO2-coated Ag/Fe2O3 nanoparticles is demonstrated. The hermetic SiO2 coating does not influence the morphology, the superparamagnetic properties of the iron oxide particles and the plasmonic optical properties of the silver particles. Therefore, the hybrid SiO2-coated Ag/Fe2O3 nanoparticles exhibit desired properties for their employment in bio-applications.

Zinc Oxide thin films were deposited on sapphire substrates by radio frequency (RF) magnetron sputtering from an ultra-high purity ZnO solid target. The ZnO films were deposited on sapphire substrates heated in oxygen and/or in vacuum prior to deposition. Additional parameters investigated included the substrate temperature varied from 25 °C to 600 °C, the deposition gas pressure varied from 5 mTorr to 40 mTorr and the gas flow rate varied from 5 to 30 standard cubic centimeter per minute (sccm). The resulting films were annealed using a rapid thermal processor in N2 gas at 900 °C for 5 min. Analyses carried out using photoluminescence spectroscopy (PL) and X-ray diffraction (XRD) measurements indicate that films deposited at 300 °C using Ar:O2 (1:1) had the best optical and microstructure qualities. Pre-heating the sapphire substrate in oxygen prior to deposition was found to create a smoother sapphire surface, and this produced a ZnO film with greatly improved qualities. This film had a luminescence peak at 3.362 eV with a full-width-half maximum (FWHM) value of 15.3 meV when measured at 11 K. The XRD 2θ-scans had peaks at 34.4° with the best FWHM value of only 0.10°. Production of high quality ZnO materials is a necessary step towards realizing highly conductive p-type doped ZnO materials which is currently a major goal in research efforts on ZnO.

We have investigated electronic band-gap states in AlGaN/GaN hetero-structures with different growth conditions of GaN buffer layers from a viewpoint of Carbon impurity incorporation into GaN, using photoluminescence (PL), capacitance-voltage (C-V) and steady-state photo-capacitance spectroscopy (SSPC) techniques. The Carbon incorporation was found to be enhanced with decreasing the growth temperature of the GaN buffer layer between 1120 and 1170 °C. Acting in concert, three specific deep levels located at ~2.07, ~2.70, and ~3.23 eV below the conduction band were found to become dense significantly at the low growth temperature. Therefore, these levels are probably attributable to Ga vacancies and/or Carbon acceptors produced by the Carbon impurity incorporation, and are likely in conjunction with each other.

As global energy demand is steadily growing, renewable energy generation by solar cells is becoming increasingly important. The use of mono- and polycrystalline silicon solar cells, which nowadays dominate the market, is limited by wafer size, rigidness of substrates and the requirement of large energy amounts for manufacturing. Organic solar cells (OSC) have the potential to overcome these limitations; especially organic vapor phase deposition (OVPD) technology offers the possibility of reproducible, large-scale production at low temperatures and on flexible substrates.

We report on planar heterojunction OSC utilizing an active layer of pentacene/N, N’- ditridecylperylene-3, 4, 9, 10-tetracarboxylic diimide (PTCDI) fabricated by an Aixtron Gen-1 OVPD tool. The influence of substrate temperature was studied using atomic force microscopy (AFM) on single layers and bilayers. In addition electrical characterization with and without illumination of fully processed solar cells which utilize different cathode layers was carried out.

AFM images indicate that crystallization of pentacene layers can be widely influenced by substrate temperature, a PTCDI-C13H27 layer atop of these covers the crystallites. Open-circuit voltage was found to be 0.47 V and short-circuit current densities beyond 0.8 mA/cm2 were measured under a spectrum close to AM 1.5 with 100 mW/cm2. Fill factors were determined to be as high as 44 %.

Transparent conductive oxide less flexible dye-sensitized solar cells (TCO-less DSC) with flat and cylinder shapes are reported. The cell consists of a plastic cover, a flexible titania/dye sheet back contacted with a metal mesh sheet, a gel electrolyte sheet, and Pt layer on a Ti sheet. How to increase the efficiency were discussed. We concluded that making a titania/dye layer on a metal mesh sheet thinner and using a thinner electrolyte layer were effective for increasing the efficiency. A flat TCO-less DSC with 6.1 % efficiency and a cylindrical TCO-less DSC with 5.1 % efficiency are reported.

A carbon nanotube polymer composite has been used to develop a flexible multi-touch tactile sensor device. Rather than employing the inherent bulk piezoresistive properties of the composite, the contact resistance between polymer and electrode was exploited to achieve finger pressure measurement with fast response. We have synthesized a series of multi-walled nanotube (MWNT) silicone composites to test the feasibility of a force sensor based on the change in surface contact resistance as a function of applied force. A single layer MWNT/polydimethyl-siloxane (PDMS) composite in the range of 1.5-3.0 % w/w nanotubes was employed as a force sensor material in an array of electrodes. It was determined that sensors based on these materials are viable as tactile sensing systems for finger-touch forces in the range of 1-100 N.

In this work the change in the structural properties of cassava (manihot sculenta Crantz) thermoplastic starch (TPS) under controlled environment (humidity and temperature) was studied. Fourier Transform Infrared spectroscopy (FTIR) and X-ray diffraction (XRD) results showed an evident increasing in the amorphous phase of the TPS regarding the native starch. There was a relative decrease of the band at 1047 cm-1 associated to crystalline structure of starch compared to the amorphous peak at 1022 cm-1. The X-ray diffraction patterns confirmed the increment of the amorphous phase in the TPS samples. Likewise the X-ray diffraction patterns shows evidence of residual type C crystallinity and the formation of a new crystalline phase type VH due to the orientation induced in plasticization process. In first stage of conditioning the tensile yield stress drops from 7.5 drops to 0.5 MPa and the break strain increases 1000%. At the same time it seems that the crystallinity of the samples increases as was evidenced by the gradually increasing of the FTIR band at 1047 cm-1. In a second stage, the yield stress increases, the break strain drops and the crystallinity continue growing steadily. These findings suggest that coexist two phenomena simultaneously in the samples. A phenomenon of re-crystallization (retrogradation) that tends to make the material more stiff and a process of plasticization that tends to softening it. It seems that the latter mechanism predominates in the first stage, at short times, and the former in the second stage, at older times.

This paper presents a methodology and results on estimating hydraulic properties of the concrete and mortar considered for the near surface disposal facility in Dessel, Belgium, currently in development by ONDRAF/NIRAS. In a first part, we estimated the van parameters for the water retention curve for concrete and mortar obtained by calibration (i.e. inverse modelling) of the van Genuchten model [1] to experimental water retention data [2]. Data consisted of the degree of saturation measured at different values of relative humidity. In the second part, water retention data and data from a capillary suction experiment on concrete and mortar cores was used jointly to successfully determine the van Genuchten retention parameters and the Mualem hydraulic conductivity parameters (including saturated hydraulic conductivity) by inverse modelling.

We report the degradation of low temperature photoluminescence (PL) from Si/SiGe three-dimensional cluster morphology nanostructures under continuous photoexcitation. The PL intensity initially decreases slowly for about 15 minutes, and then decreases rapidly, until only ∼ 10% of the original PL intensity remains. A complete recovery of the PL requires restoring the sample temperature to ∼ 300K. We propose that a slow accumulation of charge in SiGe clusters enhances the rate of Auger recombination and results in the observed PL degradation.

Developing energy efficient electronics or green electronics is an area that is largely driven by the performance limitations of scaled Si-based CMOS due to the exceptionally high power dissipation and high leakage currents arising in such devices at nanoscale dimensions. It is clear now that Si-based CMOS has been stretched over the past several decades to the point that further miniaturization will make such simple size scaling non-sustainable in the future. New materials and technologies are thus vigorously being explored beyond Si, in order to overcome performance limitations from ultra-miniaturized Si-CMOS. Among these materials, carbon-based nanostructures such as graphene and carbon nanotubes are being considered as viable alternatives to Si-CMOS to enable energy efficient green electronics. Novel architectures for enabling low-power, energy-efficient computation are currently being explored, which include tunneling field-effect-transistors (TFETs), as well as nano-electro-mechanical-systems (NEMS) due to their abrupt ON/OFF transitions, low OFF state currents and high speed operation. In this paper, an overview of carbon nanomaterials is presented and the role they play in enabling energy efficient TFETs and NEMS is also highlighted. Finally, the emergence of a new class of 2D systems beyond graphene is discussed such as MoS2, which may open up new avenues for exploration and enabling applications in electronics.

In this paper, the influence of the doping level at boron doped nanocrystalline diamond (BDND) films in the electrochemical determination of nitrite was reported. The morphology and the structure modifications as function of the boron doping level increase were observed. Two different doping levels were considered. A BDND film with a doping level of 30.000 ppm and one another with a doping level of 10.000 ppm was used. The columnar growth for the 30.000 ppm BDND led to a higher surface roughness and also to a greater grain size when compared to that 10.000 ppm BDND. The Raman spectra shown higher sp2-bonded carbon amount in grain boundary for the 10.000 ppm BDND film due to decrease of the grain size. The morphological and structural modifications of the BDND films were crucial for nitrite oxidation process. The 30.000 ppm BDND electrode presented a better sensitivity to the nitrite oxidation and a lower detection limit (DL) on the “as-grown” condition, while the 10.000 ppm BDND electrode presented a better analytical sensitivity and a lower DL after the surface pre-treatment with hydrogen plasma.