bluuebunny/crossref_metadata_2025 huggingface dataset:
Clathrate Hydrates for Production of Potable Water
Authors: Bradshaw Robert W. , Simmons Blake A. , Majzoub Eric H , Clift W. Miles , Dedrick Daniel E.
Published: April 2011

Clathrate hydrates are crystalline inclusion compounds of water and a guest molecule (e.g., methane) that form at temperatures below ambient but above the freezing point of water. There are three known crystalline structures of hydrates (structure I, II, and H) in which cavities within the hydrogen bonded water molecule lattice trap the hydrate-forming species. The clathrate structure excludes dissolved solutes, such as sodium chloride, from the aqueous phase and thereby offers a possible means to produce potable water from seawater or brackish water. The concept of using clathrate hydrates for desalination is not new. However, before clathrate hydrate desalination becomes a viable technology, fundamental issues of controlled hydrate formation, hydrate size and morphology, agglomeration, amount of entrapped salt, and the efficient recovery of hydrates must be understood. This paper will report structural characterization of hydrates formed with several guest molecules over a wide range of conditions in an attempt to further the physicochemical insight needed to address these issues.

Clathrate hydrate formation experiments were performed using a variety of host molecules, including R141b, a commercial refrigerant, C2FCl2H3. Hydrates of R141b were formed at temperatures from 2°C to 6°C and atmospheric pressure from deionized water and 2% - 7% NaCl solutions. Samples of the hydrates were characterized by cold-stage x-ray diffraction and Raman spectroscopy and determined to be structure II. Additional experiments were conducted with a gaseous hydrate former, ethylene, which readily formed hydrates with deionized or saline water at 2°C and several atmospheres of pressure. Experiments with several other hydrate forming molecules were conducted and the results obtained from their structural characterization will be reported. We will also present proof-of-concept experiments demonstrating a novel technique of desalination using these hydrate formers.

Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin company, for the United States Department of Energy under contract DE-AC04-94AL85000.
Freely Accessible Internet Resources for Nanoscience and Nanotechnology Education and Research at Portland State University's Research Servers
Authors: Moeck Peter , Seipel Bjoern , Upreti Girish , Harvey Morgan , Garrick William
Published: April 2011

Because a great deal of nanoscience and nanotechnology relies on crystalline nanometer sized or nanometer structured materials, crystallographers have to provide their specific contributions to the National Nanotechnology Initiative. Here we review two open access internet-based crystallographic databases, the Crystallography Open Database (COD) and the Nano-Crystallography Database (NCD), that store information in the Crystallographic Information File (CIF) format. Having more than ten thousand crystallographic data sets available on the internet in a standardized format allows for many kinds of internet-based crystallographic calculations and visualizations. Examples for this that are dealt with in this paper are interactive crystal structure visualizations in three dimensions (3D) and calculations of theoretical lattice-fringe fingerprint plots for the identification of unknown nanocrystals from their atomic-resolution transmission electron microscopy images.
Planting Seeds: Including Nanotechnology Education into Engineering Curricula
Authors: Jaszczak John A. , Seely Bruce E.
Published: April 2011

As part of a Nanotechnology Undergraduate Education program funded by NSF, a team of faculty at Michigan Technological University has developed a suite of educational and research experiences intended to introduce undergraduate students to the exciting prospects and challenges of nanoscale science and engineering. Although open to all students, the program was designed in particular for engineering students whose curricula have relatively little flexibility. Engineering students at Michigan Tech follow a common first-year curriculum, and as is true at most engineering colleges, their courses of study are highly structured. In order to bring introductory nanotechnology content to both engineering and non-engineering majors, activities were developed to fit into or to modestly supplement existing curricular frameworks. The program seeks to introduce students to three foundational aspects of work at the nanoscale: the underlying scientific principles, possible scientific and engineering applications, and the societal implications of implementation of nanotechnology. A web site (http://nano.mtu.edu/) was developed as a central focal point for nano-related research activities at Michigan Tech. This paper presents additional background and discusses the challenges related to the project, a brief overview of the educational activities, a more in-depth description of those activities deemed to be the most successful, and a description of some lessons learned.
Nanotechnology, Biology, Ethics and Society: Overcoming the Multidisciplinary Teaching Challenges
Authors: Vanasupa Linda , Ritter Matthew , Schader Barbara , Chen Katherine , Savage Richard , Schwartz Peter , Slivovsky Lynne
Published: April 2011

One of the inherent challenges of teaching any emerging technology like nanotechnology, is the fact that its core competencies flux in the new disciplines' early stages. Nanotechnology presents an additional challenge in that its underpinnings cross multiple traditional disciplinary boundaries. We have designed a course that aims to address some of these challenges through a handful of structural features: team-based learning; a “reverse of the learning pyramid” approach; team-teaching; embedded information literacy techniques; and application-centered content. Our course is organized around four applications that are in their developmental stages: gold nanoshells for cancer treatment; molecular manufacturing; tissue engineering of a vital organ; and a microfluidic glucose sensor. These applications provide natural contexts for learning biology at the cellular level, the molecular level, the organ level and the biological systems level, respectively. They also provide natural contexts to introduce ideas of scientific uncertainty in emerging fields. In this paper, we will present the design features of our sophomore-level course Nanotechnology, biology, ethics and society and some preliminary results.
Development of Computer Game Based Instruction: The Periodic Table Game
Authors: O'Neal Brenda , McKenzie Leigh , Warren Garry W. , Nancy Earnest , Bryant Timothy , Bakker Martin G.
Published: April 2011

A collaboration between The Materials Research Science and Engineering Center (MRSEC) and the Integrated Science (IS) program run by the Center for Communication and Educational Technology (CCET) at The University of Alabama has been developing a computer game based approach to teaching Periodic Table concepts and facts to middle school students. The game is broken into seven different sections. There are three information centers, which are each paired with a game, and there is a “Dream Room” which provides an incentive for students to master the subject matter of the game. The three information centers focus on learning the elements, their positions in the periodic table, and trends in physical and chemical properties. The games then test the students' knowledge of the concepts and facts in the information centers. The game is currently in a late beta version and can be accessed over the web at http://www.mint.ua.edu/periodictable.

Preliminary results from a large evaluation exercise shows that classes that use the computer games improved significantly more on tests of subject matter than a control group.
Charge Trapping Memory Cell of TANOS (Oxide-SiN-Al2O3-TaN) Structure Erased by Fowler-Nordheim Tunneling of Holes
Authors: Lee Chang-Hyun , Kang Changseok , Shin Yoocheol , Sim Jaesung , Sel Jongsun , Choe Byeong-In , Choi Jungdal , Kim Kinam
Published: April 2011

We present the TANOS (Si-Oxide-SiN-Al2O3-TaN) cell with 40 Å-thick tunnel oxide erased by Fowler-Nordheim (FN) tunneling of hole. Thanks to introducing high-k dielectrics, alumina (Al2O3) as a blocking oxide, the erase threshold voltage can be maintained to less than - 3.0 V, meaning hole-trapping in SiN. We extracted the nitride trap densities of electron and hole for the TANOS cell. It is demonstrated that the TANOS structure is very available to investigate the trap density with shallower energy. The energy level of hole trap (1.28 eV) is found to be deeper than that of electron (0.8 eV). As the cycling stress is performed, persistent hole-trapping is observed unlike endurance characteristics of conventional floating-gate cell. The hole trapping during the cycling stress can be attributed to two possibilities. The injected holes are trapped in neutral trap of tunnel oxide and residue of holes which is not somewhat compensated by injected electrons may be accumulated in SiN. It is demonstrated the erase operation of the TANOS cell is governed by Fowler-Nordheim tunneling of hole due to the field concentration across the tunnel oxide.
Microphotonics Applications of Silicon Microspheres
Authors: Serpengüzel Ali
Published: April 2011

Silicon microspheres with high quality factors morphology dependent resonances are used for resonant detection and filtering in the near-infrared. The near-infrared light is coupled to the silicon microsphere with optical fiber half couplers. The observed morphology dependent resonances have quality factors of 100000. The experimentally measured quality factors are limited by the sensitivity of the experimental setup. These optical resonances provide the necessary narrow linewidths that are needed for high resolution optical filtering, Raman lasers, modulators, complementary metal oxide semiconductor (CMOS) compatible detectors in the near-infrared. The silicon microsphere shows promise as a building block for silicon microphotonics, a complementary technology to the already well established CMOS based microelectronics technology for the realization of future microelectrophotonic integration.
Theoretical Investigation of Strain-balanced GaP1−xNx/GaAs1−yNy superlattices lattice-matched to Si(001) for 1.5-1.8 eV photonic applications
Authors: Bhusal Lekhnath , Zhu Wenkai , Freundlich Alex
Published: April 2011

Dilute nitrides alloys of GaP1−x−yAsyNx alloys have attracted much attention since they exhibit a direct bandgap and their lattice constant matches the one of silicon for y=4.7x-0.1. Thus these alloys offer interesting perspectives for the monolithic integration of III-V optoelectronics with the silicon technology. For practically achievable nitrogen composition (x ≤ 0.04), the band gap of GaP1−x−yAsyNx alloys lattice matched to Si is limited to about 1.75 eV. One may attempt to expand the operation wavelength of these dilute nitrides by fabricating a short period strain-balanced GaP1−xNx/GaAs1−yNy superlattices on silicon where ultra-thin layers of GaAs1−yNy (compressively strained) and GaP1−xNx (tensilely strained) are alternated and where the thickness of each layer is maintained to below the onset of the lattice relaxation.

In this work we present a theoretical study of the electronic band structure of these strain-balanced (and lattice matched to Si) superlattices in the vicinity of the center of the Brillouin zone (Γ-point). A six-band Kane Hamiltonian modified to account for the strain effect and the band anti-crossing model are used to describe the electronic states of the highly strained zinc blende GaP1−xNx and GaAs1−yNy ternaries. The evolution of the conduction band minima and valence subbands maxima of GaP1−xNx and GaAs1−yNy indicates the occurrence of a type I band alignment for the superlattices involving the mj = ±3/2, ±1/2 valence subbands in the range of compositions of interest.

A transfer matrix method has been used to determine the electron and hole minibands of the superlattice structure, predicting the evolution of the band edge transition energies for different nitrogen compositions and alloying/thickness combinations. The results of calculations show the potential to obtain room-temperature photon absorption/emission energies as low as 1.57 eV for a typical nitrogen composition of 5%. The proposed strain balanced structure, thus offers the potential for bandgap engineering ranging from the near IR to visible with host of major applications in silicon-based optoelectronics and multi-bandgap photovoltaics.
Active Photonic Crystals Based multiplexer
Authors: Dardano Principia , Mocella Vito , Sirleto Luigi , Moretti Luigi , Rendina Ivo
Published: April 2011

In the last years, in order to achieve active tuning of photonic crystals devices, the possibility to use liquid crystal inside photonic crystals has been explored.

On this line of argument, in this paper, we numerically investigate a tunable T-shaped waveguide diplexer, based on a two-dimensional square lattice photonic crystal composed of silicon rods in a liquid crystals. We prove that complete splitting of the entire input wavelengths range in two sub-ranges symmetrical with respect to the middle (switching) wavelength, and propagating in right and left arms respectively, can be achieved. Moreover, changing the refractive index of liquid crystals by electro-optical effect, a tuning of switching wavelength of about 60 nm can be obtained.
Nanostructured Ultrathin NbN Film as a Terahertz Hot-Electron Bolometer Mixer
Authors: Gol'tsman Grigory , Maslennikov Sergey , Finkel Matvey , Antipov Sergey , Kaurova Natalia , Grishina Elisaveta , Polyakov Stanislav , Vachtomin Yury , Svechnikov Sergey , Smirnov Konstantin , Voronov Boris
Published: April 2011

Planar spiral antenna coupled and directly lens coupled NbN HEB mixer structures are studied. An additional MgO buffer layer between the superconducting film and Si substrate is introduced. The buffer layer enables us to increase the gain bandwidth of a HEB mixer due to better acoustic transparency. The gain bandwidth is widened as NbN film thickness decreases and amounts to 5.2 GHz. The noise temperature of antenna coupled mixer is 1300 and 3100 K at 2.5 and 3.8 THz respectively. The structure and composition of NbN films is investigated by X-ray diffraction spectroscopy methods. Noise performance degradation at LO frequencies more than 3 THz is due to the use of a planar antenna and signal loss in contacts between the antenna and the sensitive NbN bridge. The mixer is reconfigured for operation at higher frequencies in a manner that receiver's noise temperature is only 2300 K (3 times of quantum limit) at LO frequency of 30 THz.
Terahertz Resonances in the Dielectric Response Due to Second Order Phonons in a GaSe Crystal
Authors: Yu Baolong L. , Altan Hakan , Zeng Fanang , Kartazayev Vladimir , Alfano Robert , Mandal Krishna C.
Published: April 2011

The dielectric function and momentum relaxation time of carriers for a single-crystal GaSe were investigated using terahertz time-domain spectroscopy over the frequency range from 0.4 to 2.4 THz. The key parameters determined from THz data using the Drude model are: the plasma frequency ωp = 6.1 ± 0.5 THz, the average momentum relaxation time <τ> = 51 +± 6 fs for electrons. The THz absorption spectrum showed resonance structures attributed to the difference frequency combinations associated with acoustical and optical phonons. This paper has already been published, see B. L. Yu, F. Zeng, V. Kartazayev, and R. R. Alfano, “Terahertz studies of the dielectric response of and second order phonons in a GaSe crystal,” Appl. Phys. Lett. 86, 182104 (2005).
SiNx barrier layers deposited at 250°C on a clear polymer substrate
Authors: Cherenack Kunigunde , Kattamis Alex , Long Ke , Cheng I-Chun , Wagner Sigurd , Sturm James C.
Published: April 2011

Interest is widespread in flexible thin-film transistor backplanes made on clear polymer foil, which could be universally employed for a variety of applications. All ultralow process temperatures, plastic compatible thin film transistor (TFT) technologies battle short or long term device instabilities. The quality and stability of amorphous silicon thin-film transistors (a-Si:H TFTs) improves with increasing process temperature. TFT stacks deposited at less than 250°C by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) exhibit higher threshold voltage shifts after gate bias stressing than stacks deposited at ∼300°C in the active matrix liquid-crystal display (AMLCD) industry [1]. Therefore, optically clear plastic (CP) substrates are desired that tolerate high process temperatures. The first step in a-Si:H TFT fabrication on a polymer is the deposition of a planarizing barrier and adhesion layer. For this purpose we have been using silicon nitride (SiNx) grown by PECVD.

This paper discusses the substrate preparation and SiNx deposition for the process temperature of 250°C. We study the mechanical strain in the SiNx film on the CP substrate, as a function of RF power. Earlier work has shown that SiNx films deposited at low RF power are under tensile strain, and become increasingly compressed as the deposition power is raised [2]. Additionally, at very high deposition power the substrate is bombarded at the beginning of film growth to achieve good film adhesion. The goal is to identify the correct processing conditions at which the total mismatch strain between the film and the substrate is minimized, to keep the film/substrate composite flat and avoid mechanical fracture as well as peeling due to poor adhesion. Optimal deposition conditions were identified to obtain crack-free SiNx barrier layers. The barrier layers were tested by fabricating a-Si:H TFTs on them at 250°C.
Transparent, Conductive and Flexible Carbon Nanotube Films and Their Application in Organic Light Emitting Diodes
Authors: Ryu Koungmin , Zhang Daihua , Liu Xiaolei , Polikarpov Evgueni , Tompson Mark , Zhou Chongwu
Published: April 2011

We have successfully used a transfer printing technique to directly transfer vacuum-filtered nanotube film to glass and plastic substrates. Our typical SWNT-film has a transparency of ∼80% and a sheet resistance around 400 Ohm/square. Further improvement to the nanotube film includes SOCl2 doping and PEDOT passivation, which significantly improve the sheet conductance and surface quality of the nanotube films. We have applied the optimized SWNT films as hole injection electrodes to demonstrate OLEDs on both rigid glass and flexible substrates.
Optical studies of Poly[p-(2,5-didodecylphenylene)ethynylene] in Thin Films
Authors: Rozanski Lynn , Bout David A. Vanden , Bunz Uwe H.F.
Published: April 2011

Unlike many other conjugated polymers popular for use in LEDs, poly[p-(2,5-didodecylphenylene)ethynylene] (DPPE), shows less interchain interaction between polymer chains after annealing to an ordered film. Evidence of this decreased interchain interaction can be seen in the emission spectra of pristine and annealed films. Thin films of pristine DPPE show a broad featureless green emission, characteristic of an excimer-like state, whereas annealed films blue-shift and become structured, resembling dilute solution emission. DPPE packs into ordered domains after annealing, shown by birefringence, polarization anisotropy NSOM, and x-ray crystallography data. The lack of chromophore interaction in the ordered domains can be explained through a brick-wall-type packing motif, where the polymer backbone is insulated by the side chains of offset neighboring polymers. Electroluminescence spectra of pristine and annealed LEDs are nearly identical, both having green emission, unlike their different photoluminescence spectra. This is evidence that light emission in LEDs comes only from excimer sites within the film, which would indicate a decreased performance for the annealed devices compared to pristine devices. Preliminary data of pristine and annealed LEDs supports this theory, with most pristine devices having a slightly higher electroluminescence intensity compared to annealed devices.
Morphology of Polythiophene Films Produced via Surface Polymerization by Ion-Assisted Deposition: A Combined Experimental and Computational Study
Authors: Tepavcevic Sanja , Hsu Wen-Dung , Sinnott Susan B , Hanley Luke
Published: April 2011

Control of film morphology is widely recognized as one of the limiting factors in the development of conjugated polymers for photonic and electronic applications. Surface polymerization by ion-assisted deposition (SPIAD) is shown to drive film morphology. A wide variety of structures form in the SPIAD polythiophene films, including islands, lamellar structures, nanoscale crystallites, and fractal-like growth patterns. Density functional theory-molecular dynamic simulations are utilized to illustrate the manner in the incident ions affect polymerization, bond dissociation, and other chemical events in SPIAD. These ion-assisted events mediate thermal processes such as neutral deposition, sublimation, diffusion, and dewetting. However, these thermal processes are on longer timescales that cannot be directly studied by the computational techniques reported here.
Failure Mode Investigation for Blue Polymer EL Device
Authors: Kim Mu-Gyeom , Kim Sang Yeol , Lee Tae Woo , Park Sang Hun , Park Ju Cheol , Park Jong Jin , Pu Lyong Sun
Published: April 2011

We report the failure mode observed in polymer EL blue device. Such modes were analyzed by non-destructive and destructive ways. As a non-destructive way, investigation of mobility changes of hole and electron, measuring transient EL corresponding to life curve, had been done. We also observed compositional and morphological variation using TEM-EDX, STM, FT-IR, TOF-SIMS and reverse engineering method as a destructive way. Electron mobility has a higher dependency on life curve, which fact could be reflected on the formation of insoluble layer inside emitting layer on anode side. And such insoluble layer showed relatively ordered surface morphology, and might be a cross-linked layer through C-O-C bond cleavage process while EL operation. But, contrary to sulfur migration mechanism into insoluble layer insisted by CDT, we did confirm no obvious difference of sulfur composition between insoluble and emitting layers. Rather, there's some degree of Ba diffusion into emitting layer from decomposition of BaF2, but, which dose not have a major effect on device degradation.
Magnetoresistance and Magnetic Field Effect on Electroluminescence in Polyfluorene OLEDs
Authors: Veeraraghavan Govindarajan , Nguyen Tho Duc , Sheng Yugang , Mermer Omer , Wohlgenannt Markus
Published: April 2011

We report on the experimental observation of large magnet field effect (MFE) on current and electroluminescence (EL) in polyfluorene organic light emitting diodes (OLEDs). We provide a comprehensive overview of the observed MFE. To the best of our knowledge, the mechanism causing these MFE is currently not known. Moreover, we show that these experiments do not allow determination whether the MFE acts on the carrier density or carrier mobility making any attempt of explaining it ambiguous. As a remedy, we performed magnetoresistance measurements in hole-only OLEDs and show that the MFE acts on the carrier mobility rather than carrier density.
Pentacene Thin-film Transistors Fabricated with a Simple Solution Process
Authors: Natsume Yutaka , Minakata Takashi
Published: April 2011

We have succeeded in developing a simple solution process of pentacene thin films without particular precursor materials. High crystallinity and large plate-like grains of the solution-processed thin films were observed with several analyses. The solution-processed pentacene thin-film transistors (TFTs) were also fabricated and exhibited good transfer characteristics with maximum carrier mobility above 1 cm2/Vs. The solution-processed TFTs also indicated a steep subthreshold swing and high stability of the threshold voltage against the storage in the atmosphere. The trap states and the bulk carrier density in the films were evaluated from the transfer characteristics by using the analytical model. We considered that these good properties could be attributed to the high crystallinity and the large grains of the solution-processed thin films.
Optical Characterization of CdSe Colloidal Quantum Dot/ MEH-PPV Polymer Nanocomposites Spin-cast on GaAs Substrates
Authors: Stiff-Roberts Adrienne D. , Gupta Abhishek , Zhao Zhiya
Published: April 2011

The motivation and distinct approach for this work is the use of intraband transitions within colloidal quantum dots for the detection of mid- (3-5 μm) and/or long-wave (8-14 μm) infrared light. The CdSe colloidal quantum dot/MEH-PPV conducting polymer nanocomposite material is well-suited for this application due to the ∼1.5 eV difference between the corresponding electron affinities. Therefore, CdSe colloidal quantum dots embedded in MEH-PPV should provide electron quantum confinement such that intraband transitions can occur in the conduction band. Further, it is desirable to deposit these nanocomposites on semiconductor substrates to enable charge transfer of photogenerated electron-hole pairs from the substrate to the nanocomposite. In this way, optoelectronic devices analogous to those achieved using Stranski-Krastanow quantum dots grown by epitaxy can be realized. To date, there have been relatively few investigations of colloidal quantum dot nanocomposites deposited on GaAs substrates. However, it is crucial to develop a better understanding of the optical properties of these hybrid material systems if such heterostructures are to be used for optoelectronic devices, such as infrared photodetectors. By depositing the nanocomposites on GaAs substrates featuring different doping characteristics and measuring the corresponding Fourier transform infrared absorbance, the feasibility of these intraband transitions is demonstrated at room temperature.
Incorporation of Colloidal PbSe Quantum Dots into 2-D Photonic Crystal Structures
Authors: Lee Yun-Ju , Subramania Ganapathi , Hernandez-Sanchez Bernadette A. , Niehaus Michael K. , Boyle Timothy J. , Cesarano Joseph , Clem Paul G.
Published: April 2011

We demonstrate the functionalization of 2-D photonic crystal structures operating at ∼ 1.5 μm with colloidal PbSe quantum dots and examine the modified photoluminescence from the functionalized photonic crystal. Using spin coating and airbrushing, monodisperse PbSe quantum dots were deposited from hexanes on lithographically patterned GaAs photonic crystal substrates. The effectiveness of patterning the PbSe quantum dots via standard liftoff process was examined. The near-IR photoluminescence spectra of quantum dot-functionalized photonic crystals were studied. We found that the photoluminescence peak became attenuated by approximately a factor of five and exhibited a narrow peak width (50 nm vs. 120 nm) compared to PbSe deposited on unpatterned GaAs, suggesting that there is some coupling between the quantum dots and the photonic crystal. Future work to improve the coupling and detection efficiency is proposed.
Synthesis and Optical Characterization of Er-Doped GaN Low-Dimensional Structures
Authors: Carvajal Joan , Aguilo Magdalena , Diaz Francesc , Rojo J. Carlos
Published: April 2011

Er-doped GaN rod-shaped low-dimensional structures have been synthesized on the surface of a silicon (001) substrate by the direct reaction of Ga, NH3 and Er using a catalyst-assisted chemical vapor deposition technique. The low-dimensional nanostructures were characterized spectrocopically analyzing the hypersensitive4G11/2and2H11/2bands of Er3+located at 375 and 425 nm, respectively. Green and near-infrared (IR) emission produced by these Er-doped GaN low-dimensional structures has been observed under excitation at 488 and 543 nm in a confocal microscope.
Interplay Between Strain and Effective Electron Mass on the Absorption Strength of Dilute Nitride Semiconductor Quantum Wires
Authors: Feltrin Andrea , Alemu Andenet , Freundlich Alexandre
Published: April 2011

We have investigated the absorption spectrum and strength of InyGa1−yAs1−xNx quantum wires. We show that compounds with varying fractions of indium and nitrogen, but similar band gaps have different absorption patterns. This behavior is related to the interplay between different effects as strain, which mainly affects the band offsets, and the increased electron mass in dilute nitride III-V semiconductors. We also study how the influence of these parameters changes with the optical band gaps associated to common optical telecommunication wavelengths. Our model calculations are performed in the parabolic band approximation and include excitonic effects.
Which states contribute to the tunneling current for large barrier thicknesses?
Authors: Heiliger Christian , Zahn Peter , Mertig Ingrid
Published: April 2011

The transport properties of planar Fe/MgO/Fe tunnel junctions are investigated theoretically by means of ab initio calculations. In particular, the k||-resolved conductance in dependence on the barrier thickness, the interface structure, and the magnetic configuration is studied. The results show that the number of states in the k||-space contributing significantly to the overall current is decreasing with increasing barrier thickness as expected. In contrast to simple parabolic band models the contribution of states in the vicinity of k||=0, however, is only involved for a few considered configurations of the system Fe/MgO/Fe.
Development of Block Co-Polymers as Self-Assembling Templates for Magnetic Media and Spin-Valves
Authors: Warke Vishal Vitthal , Redden Chris , Bakker Martin , Nikles David , Hong Kunlun , Mays Jimmy , Britt Phil
Published: April 2011

Poly(styrene)-Poly(methylmethacrylate) block co-polymers (PS-b-PMMA) of appropriate block length and PS to PMMA ratio self-assemble into a 2-D hexagonal phase in which the PS majority phase is continuous and surrounds cylinders of the minority, PMMA phase. By UV irradiation and washing with acetic acid it is possible to remove the minority phase to leave empty channels. It is also possible to rearrange the PMMA phase with acetic acid to leave somewhat smaller pores. For most substrates the interactions between the polymer and the substrate surface are such that one block is preferentially adsorbed to the substrate resulting in alignment of the PMMA domains parallel to the substrate surface. It is possible to orient the polymer perpendicular to the surface by first adding a thin film of a random PS-PMMA co-polymer before applying the PS-b-PMMA block co-polymer. However thin films of the random PS-PMMA do not give good surface coatings, and thicker films are generally too thick for the pores in the PS-b-PMMA block co-polymer to be propagated to the substrate surface. For a few substrates, thin PS-b-PMMA films naturally adopt a perpendicular orientation after annealing, washing with acetic acid produces arrays of pores of diameter as small as 3 nm. For a number of other substrates the interaction between the polymer blocks and the surface is such that upon annealing the polymer rearranges to form micron sized domains which are not polymer coated, surrounded a areas which have a thicker polymer coating. We have observed this behavior with both carbon coated substrates and with ITO glass substrates. In both cases the areas of polymer are perpendicularly oriented, and upon washing with acetic acid give rise to pores that extend completely through the polymer film. In some cases films on ITO glass are continuous even after annealing. After washing with acetic acid it was possible to electrodeposit nickel into the pores to give nickel nano-pillars of 18 nm diameter.
Synthesis and Control of Nano-Scale CN Particles and its Distributions
Authors: Feng Peter x. , Shi Y. C.
Published: April 2011

Micro-scale to nano-scale carbon nitride (CN) particles were prepared by using plasma sputtering deposition technique. The preferred orientation of nanoscale CN particle distributions was obtained. Particles have been examined by using both Scanning Electron Microscopy (SEM) and Raman scattering (RS) spectroscopy. Setting bias voltage up to 5 kV, plasma-sputtering deposition gave rise to several ring (diameters: 2.4, 3.2, and 4.4 mm) patterns of particle distributions where many small groups of nanoscale particles were observed. Each group of these particles appeared in a sunflower type of distribution, in which the biggest (85 nm) particle at the center was surrounded by many small sizes (30 nm) of CN particles. Disk type of the particles with a diameter of 10 μm was also observed at different experimental conditions. Typical G, D bands and C=N band in the Raman spectra of the samples were identified. The intensity of the D bands obviously varied at the different deposition conditions.
In-Situ Polymerization of Poly (Methyl Methacrylate)/MgAl Layer Double Hydroxides Nanocomposites with High Dispersion and Enhanced Physics Properties
Authors: Tsai Tsung-Yen , Lu Shau-Wen , Li Fu-Shou
Published: April 2011

Poly(methyl methacrylate)/MgAl layer double hydroxides (PMMA/MgAl LDH) nanocomposites were prepared by in situ free radical polymerization with the organic modified MgAl-K2 LDH in the methyl methacrylate monomer and initiator of benzoyl peroxide. The morphology of MgAl-K2 LDH and PMMA/MgAl-K2 LDH nanocomposites were investigated by transmission electron microscopy (TEM) and powder X-ray diffraction, indicated that the MgAl-K2 LDH were dispersed in PMMA matrix to form PMMA/MgAl-K2 LDH nanocomposites with heterogeneous morphology comprising both exfoliated and intercalated PMMA/MgAl-K2 LDH nanocomposites . The thermal and mechanical characterization were carried out by thermogravimetric analysis (TGA) ¡Bdifferential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The properties of PMMA/MgAl-K2 LDH nanocomposites exhibit the better thermal and mechanical properties.
Preparation of High Surface Area Ni-SDC Cermets Using a Surfactant-Assisted Co-Precipitation Method
Authors: Park Sang Joon , Eom Tae Wook , Oh Jae Eun , Yang Hae Kwang , Kim Kyung Hwan
Published: April 2011

A surfactant-assisted co-precipitation method was employed for obtaining high surface area Ni-SDC with improved structural properties for SOFC applications. In the work, a cationic surfactant, cetyltrimethylammonium bromide(CTAB) was employed with NiCl2, SmCl3 and CeCl3 as precursors and NH4OH as mineralizer. The elimination of surfactants upon calcination gives rise to the formation of high surface area NiO-SDC. When calcined at 600°C, the powders with surface area of 249 m2/g, were obtained and the pore size was 14.45 nm. The powders consist of two phases, the cubic NiO and SDC confirmed with X-ray diffraction identification.
Criticality of Electron and Hole Escape Sequence in Nano-Structured Photovoltaic Devices
Authors: Freundlich Alex , Coaquira J.A.H. , Freundlich Alex
Published: April 2011

It has been empirically established that for quantum confined p-i-n solar cells a high electric field across the i-region is necessary for an optimal extraction of carriers from the well. This restriction imposes an upper limit for the total thickness of the i-region beyond which severe performance degradations are reported. For a given material system, the best efficiency trade-off is often achieved in the vicinity of this critical i-region thickness where the Voc degradation remains minimal and a higher photocurrent is afforded by the larger number of wells. But, even for devices that satisfy this condition, occasionally a severe Voc degradation occurs. Here, we show that this degradation is directly correlated to the carrier escape sequence from the wells and that a careful engineering of hole and electron confining potentials can be used to alleviate this shortcoming.
Triple and Quadruple Junctions Thermophotovoltaic Devices Lattice Matched to InP
Authors: Bhusal Lekhnath , Freundlich A
Published: April 2011

Power conversion in thermophotovoltaic (TPV) or any other photovoltaic device can be increased by implementing monolithically series connected multi-bandgap structure in the device. The main concern for multi-bandgap material is the availability of different band gaps for the optimal operation of the device. Based on the recent work, GaAsN/InAsN superlattice lattice matched to InP has shown the potential of achieving band gaps in the range of 0.65-0.35eV at 300K, which is technologically important range for the TPV structure due to the availability of the photon energies in this range from the heat source. In this work, we will present the calculation details and results to find the maximum power generated by the multi-bandgap monolithically series connected devices. Optimized band gaps for p-i-n junction subcells were estimated by finding the optimal current to provide the maximum power through the series-connected double, triple and quadruple junction cells for 1350K blackbody radiation as an incident flux.
Nature of High Critical Current Density in Epitaxial Films of HTS YBCO Cuprate and Coated Conductors
Authors: Pan Vladimir M. , Cherpak Yuriy V. , Pashitskii Ernst A. , Semenov Aleksey V.
Published: April 2011

Currently a problem of crystal defects nanoengineering for pinning enhancement is extensively studied. A number of efforts were done to realize nanodot-like and particulate-dispersive pins to enhance pinning and critical current density in high-Tc cuprate films and coating. Sometimes some effect of Jc enhancement was achieved. However it is important to comprehend mechanisms of such an enhancement. It is known the ensemble of random point-like pins with size ro of order of coherence length, xab(T), can provide Jc(77 K) not to exceed 5§¹104 A/cm2. Estimations give the maximum pinning force of about for linear extended defects (if ). Here eo is the characteristic vortex energy. A model of vortex pinning and supercurrent limitation is developed and discussed on the base of measurements and analysis of magnetic feld and angle dependencies of Jc(H,¦È) in epitaxial c-oriented YBa2Cu3O7-δ (YBCO) films measured by the four-probe transport current technique, low-frequency ac magnetic susceptibility and SQUID magnetometry. Films nanostructure is studied by SEM, TEM, HREM and X-ray diffractometry. Rows of growth-induced out-of-plane edge dislocations (EDs), forming low angle subboundaries (LABs), are shown to play a key role in achievement of the highest critical current density Jc ¡Ý 2 106 A/cm2 at 77 K. The model takes into account the transparency of LABs for supercurrent as well as the pinning of vortex lattice on a network of LABs. Films defect structure parameters, such as a domain size distribution and a mean misorientation angle, are extracted from Jc(H||c)-curves as well as from X-ray diffraction data. Evolution of angle dependencies Jc(¦È) with H is shown to be consistent with the model, supposing dominant pinning on EDs. Strongly pinned vortices parallel to the c-axis exist in strongly tilted magnetic felds up to threshold feld Hp. Below Hp the magnetic induction within a film obeys a simple relation B = Hcos¦È. This feature is shown to explain the absence of the maximum in Jc(¦È)-plot, expecting at H||c in low applied feld. A peak-effect in Jc(H||ab)-dependencies and an angular hysteresis of Jc(¦È) observed in intermediate feld range, are discussed in terms of film thickness, surface quality and orientation of the applied feld. The effects observed are found to be consistent with the developed model. To our mind any nano-, micro- and macro-interfaces, emerging within films or coatings at the deposition process (e.g., nanodot-like and particulate dispersive inclusions) being coherently connected with a YBCO-matrix serve as a source of formation of a multitude of additional dislocations and as a result can promote the essential Jc-enhancement.
Strain Dependent Transport and Mechanical Characteristics of High-current and High-Strength Type Ag/Bi2223 Composite Superconductors
Authors: Adam Malik Idries , Osamura Kozo
Published: April 2011

Tensile strain dependence of electromechanical characteristics of high-current, (Hic) and high-strength, (Hs) type Ag/Bi2223 composite tapes measured at room temperature, RT and 77K is investigated. Mechanical strength of composites revealed strain-hardening signature in Bi2223 filaments due to plastic strain above the elastic limit. Critical current, Ic maintained constant value up to the elastic limit then decreased slowly before finally dropped to about 10% at 0.19% and 0.39% strain, signaling a three-stage limitation. Microstructure observations and electromechanical response of the composites suggest that a limited longitudinal, transverse, interfacial, granular and transgranular microcracks formed during gradual imposition of strain hardening in Bi2223 filaments may be responsible for the slow reduction of Ic in the medium mechanical stage.
Dispersion of Single Walled Carbon Nanotubes by Self Assembly of Polymers
Authors: Dhullipudi Ramasudhakar Babu , Lvov Yuri M , Dobbins Tabbetha A
Published: April 2011

Dispersion and stability of single walled nanotubes (SWNT) is one of the inhibiting factors affecting their tailorability for various electronic, chemical and mechanical applications . The realization of these applications depends on dispersing the SWNTs in aqueous media by inducing high forces of repulsion among the nanotubes. Steric repulsions are induced to the nanotubes by attaching polyelectrolytes, like poly styrene sulfonate (PSS) and poly allyl amine hydrochloride (PAH). In this work, Self Assembly technique is employed to attach polyelectrolytes, and thereby enhance the dispersion of SWNTs in aqueous media. The steric forces produced by the attached polyelectrolytes overcome the high van der waals force of attraction between the nanotubes and aid in the nanotubes dispersion. Characterization of the dispersions with UV-Vis Spectrophotometric method in kinetic mode revealed that nanotubes treated at pH 3 are seen to be more stable than the ones treated at pH 7. The effect of pH of the polyelectrolyte solutions in the assembly and its consequence on dispersion stability is also studied with zeta potential measurements. The morphology of the films produced by drying the nanotubes in vacuum on a silicon substrate is characterized by field emission scanning electron microscopy (FESEM).
Carbon Nanotube Micro-Opto-Mechanical Grippers
Authors: Lu Shaoxin , Liu Ye , Shao Ning , Panchapakesan Balaji
Published: April 2011

We report the integration of single wall carbon nanotube ensembles into micro-mechanical systems to realize a new carbon nanotube micro-optomechanical system (CNT-MOMS). CNT-MOM grippers were fabricated with CMOS compatible techniques involving nanotube film formation, wafer bonding, photo-lithography, plasma etching and dry release. MOM-grippers displacement of ∼24μm was obtained from a gripper of 430μm in length under infra-red laser stimulus and continuous operation of more than 100,000 cycles was acquired. The optical power consumption of the gripper operation was estimated to be as small as ∼240μW. This study is a good example of how nano-materials could be integrated into CMOS compatible techniques for applications in high performance MEMS and nanoscale actuation technologies.
Effect of Solvent Concentration to the Preparation of Polystyrene Nanoparticles Using Polyelectrolyte Block Copolymer
Authors: Edwin Garcia Doronila , Choi Youngjin , Moon Hyeongmin , Jung Bumsuk
Published: April 2011

Particles of sizes within the nano region have attracted many applications in different fields of science. In this study, the self assembly property in a selective solvent of block copolymers has been used for the preparation of polystyrene nanospheres. Sulfonated Styrene-Butadiene-Styrene (SSBS) tri block copolymer was used as a polymeric surfactant for synthesis of uniformly sized polystyrene nanoparticles using emulsion polymerization. The effects of initiator, monomer and block copolymer concentration to the molecular weight distribution and size distribution were investigated. Uniformly sized nanoparticles with a polydispersity index of 1.004 and diameter of 112.9nm was verified by Dynamic Light Scattering (DLS) and Scanning Electron Microscopy (SEM), respectively. Using a mixed continuous phase solution of water and methanol, it was found out that the particle size decreased relative to the increase of methanol added to the reaction solution. Associating behavior of the polyelectrolyte block copolymer in the binary solvent environment regarding size of micelle formed was reflected on the properties of the nanospheres. Nanoparticles prepared with greater methanol concentration were observed to be less than 100 nm. Size distribution was also observed to be narrower in proportion to MeOH concentration.
Polymer Nanofibers Containing Isolated and Aligned Single Wall Carbon Nanotubes
Authors: Young Robert , Eichhorn Stephen , Kannan Prabhakaran
Published: April 2011

Electrospinning has been used to prepare poly(vinyl alcohol) (PVA) nanofibers, with diameters ranging from 1 micron down to 20 nm, that contain dispersions of isolated, well-aligned, single wall carbon nanotubes (SWNTs). The nanofibers were characterized by Raman spectroscopy and single radial breathing modes (RBMs) were found for the SWNTs in the nanofibers indicating debundling of the original SWNT ropes. Moreover a split G' band for some nanotubes and the results of polarized Raman spectroscopy were consistent with the presence of isolated SWNTs, highly aligned along the nanofiber axes.
Conducting polymer fibers of polyaniline doped with camphorsulfonic acid
Authors: Khan Saima Naz , Khan Aurangzeb , Kordesch Martin E.
Published: April 2011

Electrically conducting fibers of polyaniline doped with Camphorsulfonic acid PAn.HCSA in the Polyethylene Oxide (PEO) matrix were prepared using the non-mechanical electrospinning technique. The morphology of the fibers was studied using the scanning electron microscope (SEM) and Transmission electron microscope (TEM), showing a uniform thickness along the fiber length. The fibers had a diameter ranging from 800nm to 2μm. The electrical conductivity of the non-woven fibrous mat and the cast film was measured using the four-point probe method, for different concentrations of Pan.HCSA in the blend. Some possible factors affecting the electrical conductivity of the fibers/films were discussed.
Fabrication of Polymeric Capsules Enclosing Eletrophoretic Particle Dispersion
Authors: Qiao Ru , Zhang Xiao Li , Qiu Ri , Li Yan , Kang Young Soo
Published: April 2011

Poly(urea-formaldehyde) capsules enclosing electrophoretic particle dispersion were formed by carrying out an in-situ polymerization reaction in an oil-in-water emulsion. The internal dispersion was composed of pigment particles Yellow-14 modified by charge control agent to have superior electrophoresis velocity and the mixture of tetrachloroethylene and sec-butylbenzene, using Span 80 as the stabilizer and emulsifier. FE-SEM, TEM, and optical microscope (OM) were performed to investigate on the capsule size and surface morphology. Contact angle measurements showed that UF prepolymer deposited at the o/w interface to form hollow capsules only when the interfacial tension is large enough.
A Comparative Study of the Structure/Property Relationships of Langmuir-Blodgett and Spin-Cast Films of an Amphiphilic, Regioregular Polythiophene Polymer
Authors: Mattu Jusroop , Johansson Thomas , Holdcroft Steven , Leach Gary W.
Published: April 2011

The effects of structural conformation and order on materials properties and reactivity in thin films of an amphiphilic, regioregular polythiophene π-conjugated polymer (πCP) derivative are presented. Thin films deposited by the Langmuir Blodgett technique provide highly ordered anisotropic films compared to those deposited by spin cast methods. Large differences in both the thermal reactivity and physical properties of the films are observed.