bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation into the thermoelectric properties of GaSb/InAs superlattice structures
Authors: Barletta Philip T. , Bulman Gary E. , Dezsi Geza , Colpitts Thomas S. , Venkatasubramanian Rama
Published: September 2011

We report on our investigation into the use of III-V superlattice structures for thermoelectric (TE) applications. Preliminary review of III-V materials trends indicate that the GaSb/InAs superlattice system should offer one of the best potentials for high thermoelectric performance in the 500K-800K range. MOCVD growth of GaSb/InAs superlattice structures was carried out, and relevant structural, thermal, and electrical characterization has been performed. TEM and XRD results demonstrate a well-ordered superlattice structure. Thermal conductivity measurements reveal a reduction in the room-temperature thermal conductivity of GaSb/InAs superlattices (4.4-10.0 W/m-K), relative to either binary GaSb (32 W/m-K) or InAs (27 W/m-K). Additionally, we have worked to optimize the thermoelectric power factor (α2σ), studying both Se- and Te-doping of the superlattice structures, in an effort to demonstrate optimal thermoelectric performance. Our results demonstrate a maximum ZT of 0.36 at 400K for optimally doped n-type GaSb/InAs superlattice structures.
Design and Demonstration of Concentration Cells for Small Scale Energy Harvesting based on Reverse Electrodialysis
Authors: Sadeghian Ramin Banan , Pantchenko Oxana , Tate Daniel Scott , Shabani Javad , Zarandi Mehrdad M. , Shakouri Ali
Published: September 2011

Experimental results are presented to demonstrate feasibility of small scale power generation using static reverse electrodialysis (RED) of CuSO4 solutions. In contrast to conventional macro scale reverse electrodialysis, the concentrated and diluate compartments were not refreshed, resulting in limited power delivery times. This is important in energy harvesting applications from limited supply of ionic concentrations. Maximum output power density of 0.17 μW·cm−2 was recorded using microfiltration membranes. The evolution of the open circuit output voltage with time is accurately modeled at various concentration ratios.
Correlated photoluminescence spectroscopy investigation of grain boundaries and diffusion processes in nanocrystalline and amorphous silicon (nc-Si:H) mixtures
Authors: Fields Jeremy D. , Kiriluk K. G. , Bobela D. C. , Gedvilas L. , Taylor P. C.
Published: September 2011

Photoluminescence (PL) spectra obtained with correlated set of experiments investigating grain boundary characteristics and diffusion processes in nanocrystalline silicon alloys (nc-Si:H), provide insight regarding formation and passivation of electronic defects in these regions. Based upon current results and previous works we believe thermally driven processes induce a PL band centered at 0.7 eV upon thermal annealing, and most likely involve diffusion of hydrogen and oxygen near interfaces. A nc-Si:H sample set with varied crystal volume fraction, Xc, was subject to thermal annealing treatments at different temperatures – each exceeding the deposition temperature. Fourier-transform photoluminescence (FTPL) and Fourier-transform infrared absorption spectroscopy (FTIR), were employed to correlate the relative 0.7 eV defect band emergence with compositional changes indicative of Si–Hx and Si–O species, for each sample, at each temperature, respectively. Hydrogen effusion data provide additional perspective.

We find the Xc to strongly affect susceptibility of nc-Si:H to oxygen related effects. The higher the Xc, the more readily oxygen penetrates the nc-Si:H network. We attribute this relationship to elevated diffusivity of oxygen in highly crystalline nc-Si:H materials, owing to their abundance of gain boundaries and interfaces, which serve as pathways for impurity migration. These findings corroborate the expectation that oxygen impurities and diffusion processes contribute to development of microstructural features giving rise to radiative recombination through deep defects in nc-Si:H.
ENHANCING PHOTOCURRENT IN UNANNEALED NiSx/CdS PHOTOELECTROCHEMICAL SYSTEM FOR WATER SPLITTING AND HYDROGEN PRODUCTION
Authors: Zhang Ning , Guo Liejin
Published: September 2011

In this work, NiSx was deposited on FTO by chemical bath and worked as the inner layer in order to enhance the photocurrent of CdS film. It is found the unannealed CdS/NiSx had a higher photocurrent than unannealed CdS, but after annealing, the photocurrent of CdS/NiSx showed dramatical decrease. The mechanism was discussed in detail by UPS and current-potential curves.
Ultra Low-k Materials Based on Self-Assembled Organic Polymers
Authors: Pantouvaki M. , Zhao L. , Huffman C. , Vanstreels K. , Ciofi I. , Vereecke G. , Conard T. , Ono Y. , Nakajima M. , Nakatani K. , Beyer G. P. , Baklanov M. R.
Published: September 2011

The material properties of two ultra low-k organic polymers are characterized for copper interconnect integration. The k-values are 2.2-2.3 for both. Compared to OSG materials of similar k-values, these polymers have lower porosity and smaller pore size, achieved using selfassembled chemistry. Both materials demonstrate excellent resistance to plasma damage: no water uptake was detected after exposure to selected etching plasmas. This characteristic, combined with the small pore size and low porosity, results in the successful integration of the organic low-ks in 80 nm spacing with no significant increase in the integrated k-values.

It is found that higher open porosity in polymer A is accompanied by higher leakage current, which is not however linked to lower dielectric breakdown lifetimes.
Amorphous Ta-N as a Diffusion Barrier for Cu Metallization
Authors: Dalili Neda , Liu Qi , Ivey Douglas G.
Published: September 2011

Amorphous Ta-N thin films (14 and 62 nm thick) are deposited on Si substrates by reactive magnetron sputtering followed by Cu film deposition. The interlayer reaction and failure mechanism of the annealed metallization stacks are investigated by resistance measurements, xray diffraction (XRD) and detailed electron microscopy analysis accompanied with electron energy-loss spectroscopy (EELS). Amorphous Ta-N crystallizes at 600°C by a polymorphous transformation to Ta2N. The crystallized Ta2N barrier prevents Cu-Si interaction and intermixing up to 700-800°C, depending on the barrier thickness. Copper appears to be the main diffusing species and reacts with Si at the Ta-N/Si interface to form η˝-Cu3Si. Local Cu-Si reaction enhances the formation of TaSi2 precipitates. Silicon also diffuses, though at a much slower rate, to the surface and reacts with Cu. Local oxidation of Cu3Si occurs upon exposure to air, accompanied by SiO2 formation.
Growth of Ultra-High Density 3C-SiC Nanowires via Single Source CVD
Authors: Teker Kasif , Oxenham Joseph A.
Published: September 2011

Silicon carbide (SiC) nanostructures attract interest due to their applications in optoelectronic devices, sensors, and high-power/high temperature electronics. The synthesis of SiC nanowires by chemical vapor deposition using hexamethyldisilane (HMDS) as a source material on SiO2/Si substrate has been investigated. Various catalyst materials, including iron (film and nanoparticles), nickel (film and nanoparticles), and cobalt nanoparticles have been used. The growth runs have been carried out at temperatures between 900 and 1100°C under H2 as carrier gas. 3C-SiC nanowires have successfully been grown at even lower temperatures despite the lower efficiency of source decomposition at low temperatures. The SiC nanowire diameters are in the range of 8 nm to 60 nm, as determined by transmission electron microscopy (TEM). In general, the efficiency of nanowire growth has increased with temperature except the growth on Ni film, which has occasionally resulted in SiC flowers. Higher nanowire density at high temperatures can be attributed to more efficient decomposition of the source at higher temperatures. Further, optical properties of the nanowires have been studied by Fourier transform infrared spectroscopy (FTIR). The fabricated nanowires have also been characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and x-ray diffraction (XRD).
How to Grow a Startup Company – Nano or Otherwise
Authors: Cesario Frank J.
Published: September 2011

New ventures in the nanomaterials industry are subject to the same laws of physics as all other entities – they compete for capital, customers, and work through similar variables. Ultimately, success is determined by the degree to which customers prefer the new venture product(s) to alternatives, thus, thinking from the perspective of the customer is critical to success. Often we focus on what the idea is, how it improves on alternatives in the marketplace, and don’t spend adequate time considering the world from the customer’s view. In reviewing choices that must be made and examples of successes and failures, the case for a thorough business plan is presented.
Modeling of approximated electron transport across ion beam patterned quantum dot nanostructures
Authors: Lassiter J. , Chacha J. , Muntele C. , Budak S. , Elsamadicy A. , ILA D.
Published: September 2011

High energy ion beams are used to modify co-deposited nanolayer films of alternated materials (e.g. insulator and metal, two different semiconductors, even more complex arrangements) to form nanodots through localized nucleation. The particular application being considered here is for high efficiency thermoelectric conversion systems. The performance of a thermoelectric converter is generally given by the figure of merit, ZT, which is a function of the Seebeck coefficient, electrical conductivity, and thermal conductivity. A high performance device would have a maximized electrical conductivity and a minimized thermal conductivity (maximum electron transport, minimal phonon transport). The current models of electron and phonon transportation through 1D, 2D, 3D quantum regimented structures assume an infinitely repetitive perfect structural “cell”, with complicated algorithms requiring intensive computing power. The main focus for this modeling effort is to reduce the three-dimensional problem to a single dimensional approximation without sacrificing the quality of the result. The nanostructure being investigated has Si and Ge quantum dots arranged with perfect periodicity in all three Cartesian directions, with the heat and electricity flow monitored in the z-direction (cross-plane as initially layered). Non-Equilibrium Green’s Functions Formalism (NEGF) is the mode for calculating the theoretical electrical properties assuming a one-dimensional quantum well arrangement in the z-direction (with finite boundaries in the x and y directions) with tight binding (nearest neighbor approximation). The results are to be compared with experimental measurements on such structures.
High Performance Nanostructured Coatings and Nanopowders by NanoSpraySM Combustion Processing
Authors: Jiang Yong Dong , Venugopal Ganesh , White Marvis , Choi Kwang , Hunt Andrew T.
Published: September 2011

nGimat has commercialized a number of nanotechnology applications with all being based on its core competence of fabricating low cost high quality nanomaterials. The company offers a wide range of compositions as coatings and also in both nanopowder and dispersion forms. A few of these nanomaterials and applications will be covered as examples including superhydrophobic coatings, various nanopowders (including Li-battery based), high temperature thin wire coatings, and tunable RF components.

The combustion chemical vapor deposition (CCVD) technique, which is the thin film NanoSpraySM combustion process, can be easily scaled up to large substrates and integrated into an existing production line, thus enabling a license business model. The combustion chemical vapor condensation (CCVC) technique or NanoSpraySM CCVC (nCCVC), which is the nanopowder NanoSpraySM combustion process, is also readily scalable. The manufacture of these nanopowder based products is internationally competitive even when made in the USA.
Emerging Potential and Challenges of Convergence, Heterogeneity, and Hierarchical Integration of Nanotechnologies in Commercial Applications
Authors: Vaseashta Ashok
Published: September 2011

Paradigmatically, the convergence of science has exceptionally high potential for transforming the manner in which state-of-the-art information is gathered, analyzed, and leveraged to enable future advances and applications. Highlighting the potential and challenges of hierarchically integrating nanotechnologies is essential for realizing commercial applications. The heterogeneity of structures and compositions of nanomaterials present limitless possibilities; yet these envisioned benefits may be accompanied by certain technological limitations of integrating nanomaterials in commercial products. A balanced overview is presented of the realistic capabilities and potential, as well as the limitations, challenges of system engineering nanomaterials in platform integration. Examples of integrating nanomaterials in useable platforms are also presented. Most notably, the review suggests that nanomaterial based systems and devices that do not require a nano to micro/macro interface integration have reached commercialization whereas those needing a nano-to-micro/macro interface require further investigations. These selected studies provide an insight in obstacles and challenges presented by hierarchical integration of nanomaterials in commercial systems/devices and are crucial for commercialization as the research transitions from laboratory to marketplace, having the potential to transform into a multi-billion dollar niche market.
A Finite Element Model of Self-Resonating Bimorph Microcantilever for Fast Temperature Cycling in A Pyroelectric Energy Harvester.
Authors: Mostafa Salwa , Lavrik Nicolay , Bannuru Thirumalesh , Rajic Slo , Islam Syed K. , Datskos Panos G. , Hunter Scott R.
Published: September 2011

A self resonating bimorph cantilever structure for fast temperature cycling in a pyroelectric energy harvester has been modeled using finite element method. Effect of constituting material properties and system parameters on the frequency and magnitude of temperature cycling and the efficiency of energy recycling using the proposed structure has been investigated. Results show that thermal contact conductance and heat source temperature play a key role in dominating the cycling frequency and efficiency of energy recycling. Studying the performance trend with various parameters such as thermal contact conductance, heat source temperature, device aspect ratio and constituent material of varying thermal conductivity and expansion coefficient, an optimal solution for most efficient energy scavenging process has been sought.
Ozone Treatment on Nanoporous Ultralow Dielectric Materials to Optimize their Mechanical and Dielectrical Properties
Authors: Kang Il-Yong , Shin Bo-Ra , Rhee Hee-Woo
Published: September 2011

The continual miniaturization of microprocessors has resulted in increased RC delay and cross talk noise. To solve these problems ultralow nanoporous dielectric materials are required but have not developed yet. To develop ultralow dielectric materials with required mechanical and dielectrical properties for next generation semiconductors, it is essential to control the pore size in nm range and its morphology by preventing porogen aggregation. Thus we have used ozone treatment during thermal curing process of the nanoporous dielectrics in order to increase the reactivity between the matrix and reactive porogens and to possibly induced changes in Si bond structures.

Ozone treatment was quite effective in enhancing the reactivity of the low-k matrix and the reactive porogen, which converted effectively the alkoxy or alkyl groups into Si-OH groups, which mostly converted to the formation of Si-O-Si network structures. Therefore, ozone treatment greatly increased modulus up to 11.25 GPa at the same porogen loading (60 vol%). The modulus increased by more than 23% compared with non-treated samples (9.1 GPa). The porosity of the ozone-treated sample reduced to 19.3 vol% at the same porogen loading. Solid state Si-NMR showed that less porosity was related to the breakage of methyl groups in the matrix by ozone irradiation, which also resulted in a little sacrificed dielectric constant.

In general, the mechanical properties of nanoporous dielectrics deteriorate sharply above certain high porosity ca. 15 ~20 vol% due to non-uniform distribution of nanopores, their aggregation and resultant open pores. Therefore, this result may suggest the possibility of increasing mechanical properties of nanoporous dielectrics. However, we need to experimentally control processing variables such as irradiation time, intensity, temperature and so forth in order to optimize both mechanical and dielectrical properties.
Optical Interconnect Technologies based on Silicon Photonics
Authors: Bogaerts Wim , Absil Philippe , Van Thourhout Dries , Van Campenhout Joris , Selvaraja Shankar Kumar , Dumon Pieter , Yu Hui , Masood Adil , Roelkens Gunther , Baets Roel
Published: September 2011

We discuss the principles of Optical interconnects, and discuss the potential of silicon photonics to provide all the necessary building blocks to construct dense, high-bandwidth, lowpower optical links. We discuss waveguides, wavelength division multiplexing, modulators and photodetectors. We also take a look at the options for implementing light sources, a function which silicon cannot natively provide, with a focus on implementations in the IMEC silicon photonics platform.
Two-stage Laser Thermal Processing of Nanoparticle Inks on Flexible Substrates for High Performance Electronics
Authors: Willemann Michael H. , Thompson Michael O.
Published: September 2011

Zinc oxide is a promising semiconductor film for active devices on flexible substrates, and synthesis routes using nanoparticle inks enable greater variety of applications. We introduce and characterize a two-step transient laser annealing process to create fully densified zinc oxide films from nanoparticle ink precursors. A low temperature sub-millisecond calcining step to remove solvent and organic stabilizing ligands was followed by a high-temperature pulsed laser sintering step to form densified 50-100 nm thin films with resistivities of 10-1 to 10-3 Ω-cm. Film microstructures can be varied between crystalline and amorphous without significant film damage by adjusting the fluence of the high-temperature sintering step. These processes would be compatible with a variety of nanoparticle species, deposition methods, and patterning methods, including roll-to-roll processing paradigms.
Defects in Low-k Insulators (κ=2.5 – 2.0): ESR Analysis and Charge Injection
Authors: Afanas’ev V. V. , Keunen K. , Nguyen A. P. D. , Jivanescu M. , Stesmans A. , Tokei Zs. , Baklanov M. R. , Beyer G. P.
Published: September 2011

Electron spin resonance study of low-κ insulating layers reveals that from a defect perspective these materials resemble oxygen-rich silicon dioxide matrices. The films fabricated using chemical vapor deposition in combination with porogen technology also contain a considerable amount of residual carbon in the form of clusters. Furthermore, ion sputtering damage generates additional defects provisionally identified as dangling bonds in the silicon oxycarbide clusters. The density of these defects is found to increase with increasing porosity of the low-κ insulator. Nevertheless, a lower defect density may be attained if using a porogen-free self-assembly technology.
Characterization of Dye-Sensitized Solar Cell with Different Nanoparticle sizes
Authors: Htun Aung , Munukutla Lakshmi V. , Radhakrishnan Sailaja , Jen Chih Y. , Kannan Arunachalanadar M. , Kinhal Karthik
Published: September 2011

The Dye-sensitized Solar Cell (DSSC) has been regarded as the next-generation solar cell because of its simple and low cost fabrication process. The experiments for optimizing the cell efficiency were carried out in this work include varying the TiO2 layer thickness on the working electrode and determining the most favorable nanoparticle size in the TiO2 paste. The TiO2 electrode or working electrode was fabricated using screen printing technique with the Coatema tool with thicknesses ranging from ~20 to 66 μm. It was observed that both open circuit voltage and short circuit current were found to have measurable dependence on the TiO2 layer thickness. The open circuit voltage changed from 0.77 to 0.82 V and correspondingly the short circuit current also varied from ~19 to 23 mA/cm2 depending on the TiO2 layer thickness. Additionally, the cell with 40 μm TiO2 thickness showed 9.06% photo conversion efficiency compared to 6.4% and 8.5% efficiency obtained for the cells with 20 μm and 66 μm TiO2 thicknesses respectively. The second part of the experiment was conducted using three different nanoparticle sizes of 13 nm, 20 nm and 37nm in the TiO2 layer to identify optimum nanoparticle size by maintaining the TiO2 film thickness at 40 μm. The cell with 20 nm size nanoparticle, in combination with 40 μm TiO2 thickness showed 11.2% efficiency that is in par or slightly better than the efficiency value reported for the DSSC in the literature as of now. The work described in this paper showed best possible values for the TiO2 layer thickness and nanoparticle size in the TiO2 for obtaining improved cell efficiency of 11.2%.
Gold Nanolayers Embedded in Zinc Oxide for Large Area Flexible Photovoltaics
Authors: Alford T. L. , Sivaramakrishnan K.
Published: September 2011

Transparent conducting ZnO/Au/ZnO thin film structures were grown by the magnetron sputtering technique on flexible polymer substrates. These films displayed a seven orders of magnitude drop in resistivity (200 to 5.2×10-5 Ω-cm) upon increase of the Au layer thickness from 0 nm to 12 nm. The sheet resistance also showed a substantial decrease to a value of 6.5 _/sq. These films displayed a photopically average transmittance between 75% and 85% depending upon the gold thickness, and a peak transmittance of up to 93%. The best Haacke figure of merit was 15.1×10-3 Ω−1. As the Au layer thickness was increased, the conduction changed from conduction through the substrate when the nanometal islands are small and far apart to activated tunneling between discontinuous islands, and finally to direct tunneling between larger islands and metallic conduction through a near-continuous layer. Optical transmission behavior of the films was described in terms of the Au’s absorption due to interband electronic transitions in the shorter visible wavelengths, and free carrier absorption losses at the longer red wavelengths. This was combined with the limitation of the mean free path in discontinuous films and the size-dependent dielectric constant of the Au particles that enhances absorption in the longer visible wavelengths.
Chalcogenide Glass Thin Films for Nanodipole Junctionless Photovoltaics
Authors: Junaghadwala Sakina , Georgiev Daniel G. , Karpov Victor G. , Todorov Rossen , Jiang Nanke
Published: September 2011

We examine the potential of Bi-Ge-Se chalcogenide glass films as materials for a new type of photovoltaic devices, referred to as junctionless nanodipole PV. Glasses of a chemical composition providing a significant optical absorption were synthesized in quartz ampoules from high-purity Bi, Ge, and Se elements by a conventional melt quenching technique. This material was then used to deposit thin films with different thicknesses on various substrates by thermal evaporation under high-vacuum conditions. The original bulk glasses and the films were characterized by electron microscopy with EDS, XRD, Raman spectroscopy, differential scanning calorimetry, and spectrophotometry. Open-circuit voltage (Voc) readings under incandescent illumination were obtained from the as-deposited and annealed films. Results from this characterization work are presented and discussed. Although the efficiency of nanodipole PV material structures, based on this material remains of no practical interest, our initial results indicate a possible path for the implementation of the nanodipole PV concept.
Dependence on the parameters of the equivalent electrical circuit model with the thickness of viologen-based electrochromic mixture on glass substrate devices
Authors: Barrios David , Vergaz Ricardo , Torres Juan Carlos , Sánchez-Pena José-Manuel , Viñuales Ana , Salsamendi M.
Published: September 2011

Several viologen electrochromic devices with different thicknesses on glass substrates were constructed, using a mixture of 4,4’-bipyridine and 1-bromoethane. The thickness of each device was fixed using a thermoplastic spacer. The devices were electrochemically tested with optical and impedance analysis. The range of the transmittance change is highly dependent on thickness. The electrical behavior of the material and the physical and chemical characteristics are derived from the proposed electrical equivalent circuit model. A simple Randles circuit including a Warburg diffusion impedance element, a charge transfer resistance and a double layer capacitive element is proposed for the fittings process. Variations on thickness of internal layer of devices lead to use a short or an open circuit Warburg element. A threshold potential, from which the device is colored, indicates the charge diffusion effects.
Effect of Substrate Temperature on the Electrochromic Properties of Cobalt Hydroxide Thin Films Prepared by Reactive Sputtering
Authors: Lee KyoungMoo , Abe Yoshio , Kawamura Midori , Itoh Hidenobu
Published: September 2011

Cobalt hydroxide thin films with a thickness of 100 nm were deposited onto glass, Si and indium tin oxide (ITO)-coated glass substrates by reactively sputtering a Co target in H2O gas. The substrate temperature was varied from -20 to +200°C. The EC performance of the films was investigated in 0.1 M KOH aqueous solution. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy of the samples indicated that Co3O4 films were formed at substrate temperatures above 100°C, and amorphous CoOOH films were deposited in the range from 10 to -20°C. A large change in transmittance of approximately 26% and high EC coloration efficiency of 47 cm2/C were obtained at a wavelength of 600 nm for the CoOOH thin film deposited at -20°C. The good EC performance of the CoOOH films is attributed to the low film density and amorphous structure.
Au-assisted Growth of Indium Antimonide Nanowires by Chemical Vapor Deposition: Temperature and Growth Duration Effects
Authors: Zhong Jiebin , Lin Jian , Penchev Miroslav , Ozkan Mihrimah , Ozkan Cengiz S.
Published: September 2011

In this paper, we investigate the morphology variation of Au-assisted epitaxial InSb nanowires (NWs) dependence on growth temperature and growth duration by chemical vapor deposition (CVD). The NW length and tapering factor correlated to the NW morphology are determined as a function of growth temperature (300°C-480°C). Higher density and longer NWs were observed on the substrate as proportional to the growth duration. The growth direction of the NWs is <110> by Transmission Electron Microscopy (TEM) studies. The aim of this study is to gain better understanding of the III-V NWs growth mechanism and achieve control over the growth of InSb NWs.
Eosin Y-sensitized ZnO/TiO2 for efficient visible light photocatalytic hydrogen evolution
Authors: Liu Haipei , Jing Dengwei , Guo Liejin
Published: September 2011

In this work a series of Eosin Y-ZnO(x%)/TiO2 were prepared. ZnO well dispersed on the surface of TiO2, which improves the adsorption of Eosin Y and the excited electron to transfer to the conduction band of TiO2. Therefore the visible light activity of 0.2%Pt-Eosin Y-ZnO(x%)/TiO2 is much higher than that of the 0.2%Pt-Eosin Y-TiO2 and 0.2%Pt-Eosin Y-ZnO. The 0.2%Pt-Eosin Y- ZnO(1.5%)/TiO2 has the highest visible light activity among the catalysts coupled with various ZnO amount, whose activity is increased by a factor of 3.5 compared to that of 0.2%Pt-Eosin Y-TiO2. It is proposed that, 0.2%Pt-Eosin Y-ZnO(1.5%)/TiO2 has the optimal trapping sites of carriers and thickness of the space-charge layer on the TiO2 particle surface, so these factors result a more efficient charge separation, an increased lifetime of the charge carriers, and the enhanced of hydrogen production .
Experimental Demonstration of Thermal Management of High-Power GaN Transistors with Graphene Lateral Heat Spreaders
Authors: Yan Zhong , Liu Guanxiong , Khan Javed , Yu Jie , Subrina Samia , Balandin Alexander
Published: September 2011

Graphene is a promising candidate material for thermal management of high-power electronics owing to its high intrinsic thermal conductivity. Here we report preliminary results of the proof-of-concept demonstration of graphene lateral heat spreaders. Graphene flakes were transferred on top of GaN devices through the mechanical exfoliation method. The temperature rise in the GaN device channels was monitored in-situ using micro-Raman spectroscopy. The local temperature was measured from the shift in the Raman peak positions. By comparing Raman spectra of GaN devices with and without graphene heat spreader, we demonstrated that graphene lateral heat spreaders effectively reduced the local temperature by ~ 20oC for a given dissipated power density. Numerical simulation of heat dissipation in the considered device structures gave results consistent with the experimental data.
DNA Gating effect from single layer graphene
Authors: Lin Jian , Teweldebrhan Desalegne , Ashraf Khalid , Liu Guanxiong , Jing Xiaoye , Yan Zhong , Ozkan Mihrimah , Lake Roger K. , Balandin Alexander A. , Ozkan Cengiz S.
Published: September 2011

In this letter, single stranded Deoxyribonucleic Acids (ssDNA) are found to act as negative potential gating agents that increase the hole density in single layer graphene (SLG). Current-voltage measurement of the hybrid ssDNA/graphene system indicates a shift in the Dirac point and “intrinsic” conductance after ssDNA is patterned. The effect of ssDNA is to increase the hole density in the graphene layer, which is calculated to be on the order of 1.8×1012 cm-2. This increased density is consistent with the Raman frequency shifts in the G-peak and 2D band positions and the corresponding changes in the G-peak full-width half maximum. This patterning of DNA on graphene layers could provide new avenues to modulate their electrical properties and for novel electronic devices.
The Dynamics of Formation of Graphane-like Fluorinated Graphene Membranes (Fluorographene): A Reactive Molecular Dynamics Study
Authors: Santos Ricardo P. B. , Autreto Pedro A. S. , Legoas Sergio B. , Galvao Douglas S.
Published: September 2011

Using fully reactive molecular dynamics methodologies we investigated the structural and dynamical aspects of the fluorination mechanism leading to fluorographene formation from graphene membranes. Fluorination tends to produce significant defective areas on the membranes with variation on the typical carbon-carbon distances, sometimes with the presence of large holes due to carbon losses. The results obtained in our simulations are in good agreement with the broad distribution of values for the lattice parameter experimentally observed. We have also investigated mixed atmospheres composed by H and F atoms. When H is present in small quantities an expressive reduction on the rate of incorporation of fluorine was observed. On the other hand when fluorine atoms are present in small quantities in a hydrogen atmosphere, they induce an increasing on the hydrogen incorporation and the formation of locally self-organized structure of adsorbed H and F atoms.
Stable superconducting niobium ultrathin films
Authors: Delacour Cécile , Ortega Luc , Pannetier Bernard , Bouchiat Vincent
Published: September 2011

We report on a combined structural and electronic analysis of niobium ultrathin films (from 2.5 to 10 nm) epitaxially grown in ultra-high vacuum on atomically flat sapphire wafers. We demonstrate a structural transition in the early stages of Nb growth, which coincides with the onset of a superconducting-metallic transition (SMT). The SMT takes place on a very narrow thickness range (1 ML). The thinnest superconducting sample (3 nm/ 9ML) has an offset critical temperature above 4.2K and allows to be processed by standard nanofabrication techniques to generate air and time stable superconducting nanostructures.
Langmuir-Blodgett Assembly of Soft Carbon Sheets
Authors: Cote Laura J. , Kim Jaemyung , Huang Jiaxing
Published: September 2011

Graphene oxide sheets have recently gained immense interest as a building block for graphene based materials and devices. Rapid developments have been made in the chemistry and applications of GO. However, assembly, too, plays a critical role in the final properties of bulk graphene based materials as it determines the microstructures of the 2D sheets. There is thus a pressing need for controllable assembly strategies. Based on the recent identification of the pH dependent surfactant-like behavior of GO sheets, we are now able to control the tiling morphologies of such sheets to produce thin films with either wrinkled or overlapped types of microstructures. This allows for the deconvolution of the effects of these two basic morphological features in the electrical and optical properties of the resulting thin films, providing a well-defined example of the processing-microstructure-properties relationship for this unique soft material building block.
Cost Effective Fabrication of Wafer Scale Nanoholes for Solar Cells Application
Authors: Zhao Y Q , Leung K K , Surya C , Feng C K , Chen Y F , Chen D M , Shen H , Zhang B J
Published: September 2011

We report fabrication of random nanometer-scale radial p-n junction solar cells (SCs). Nanoholes were fabricated on the Si wafer by combining silver film annealing and metal catalyzed electrochemical etching (MECC) of the material. The dimension of the holes can be adjusted by varying the annealing conditions and the thickness of the Ag film. Systematic investigations on the effects of the nanohole size and the doping conditions on the cell efficiency were performed.
Aerosol technology and Si nano-composite electrode assembly for Li-ion batteries
Authors: Munao David , Valvo Mario , van Erven Jan , Garcia-Tamayo Esteban , Kelder Erik
Published: September 2011

In this work novel approaches to fabricate silicon-based electrodes are shown. Starting from silicon nano-particles it is possible to create nano-structured porous thin films. Both the synthesis of the Si nano-particles and the electrode assembly are performed via aerosol routes. This guarantees a very good control on the particle size and the particle size distribution, on the purity of the product and on the morphology and texture of the deposited layers. Particles are produced via Laser assisted Chemical Vapor Pyrolysis whereas electrode thin layers are deposited via Electro Spray method. The range of particle sizes can be tailored according to the selected application. Here, particles of a mean size of about 10 nm have been synthesized. Since Si is well known to forms highly lithiated intermetallic compounds [1], it is regarded as one of the most promising material for energy storage [2], especially looking at high energy density applications, such as hybrid/electric vehicle traction. In this work its promising performance are presented. The role of the additives in the composite formulation is also taken into account for a more clear understanding of the capacity fading mechanism of such electrodes.
Nano-engineering with a focused helium ion beam
Authors: Maas Diederik J. , van der Drift Emile W. , Veldhoven Emile van , Meessen Jeroen , Rudneva Maria , Alkemade Paul F. A.
Published: September 2011

Although Helium Ion Microscopy (HIM) was introduced only a few years ago, many new application fields are budding. The connecting factor between these novel applications is the unique interaction of the primary helium ion beam with the sample material at and just below its surface. In particular, the HIM secondary electron (SE) signal stems from an area that is very well localized around the point of incidence of the primary beam. This makes the HIM well-suited for both high-resolution imaging as well as high resolution nanofabrication. Another advantage in nanofabrication is the low ion backscattering fraction, leading to a weak proximity effect. The lack of a quantitative materials analysis mode (like EDX in Scanning Electron Microscopy, SEM) and a relatively low beam current as compared to the SEM and the Gallium Focused Ion Beam are the present drawbacks of the HIM.
Silicon Nanocavity Based Light Sources
Authors: Gong Yiyang , Ishikawa Satoshi , Cheng Szu-Lin , Nishi Yoshio , Yerci Selcuk , Li Rui , Negro Luca Dal , Vuckovic Jelena
Published: September 2011

We develop Si-based nano-photonic devices for the control of light at the nano-scales. We design high quality (Q) factor photonic crystal nanobeam cavities for a variety of Si compatible materials with low index, such as silicon rich oxide and silicon nitride, all with Q > 9,000 and small mode volumes. We apply these cavity designs to active materials such as Sinanocrystal doped silicon oxide and Er doped silicon nitride. By placing emitters in these cavities, we demonstrate that the cavity enhances emission processes. We show that the free carrier absorption process is greatly enhanced in the nanobeam cavities at both room and cryogenic temperatures. In addition, we demonstrate that nanobeam cavities made of Er-doped amorphous silicon nitride have enhanced absorption and gain characteristics compared to earlier designs that included silicon in the cavity. Because of the reduced losses, we observe linewidth narrowing and material transparency at both room temperature and cryogenic temperatures.
Formation of ultra-shallow Ohmic contacts on n-Ge by Sb delta-doping
Authors: Sawano K. , Hoshi Y. , Kasahara K. , Yamane K. , Hamaya K. , Miyao M. , Shiraki Y.
Published: September 2011

We demonstrate low-resistivity Ohmic contacts for n-Ge with ultra-shallow junction. Using the impurity δ-doping techniques with Ge homoepitaxy on Ge(111) below 400 ºC, we can achieve a very abrupt doping profile within a nanometer-scale width. By introducing the δ-doping to atomically controlled metal/Ge contacts, the current-voltage characteristics clearly show Ohmic conductions owing to the effective tunneling through the Schottky barrier. This approach is promising for a formation technology of ultra-shallow source/drain contacts for scaled Ge devices.
Structural Properties of Iron Nitride on Cu(100): an Ab-initio Molecular Dynamics study
Authors: Heryadi Dodi , Schwingenschlögl Udo
Published: September 2011

Due to their potential applications in magnetic storage devices, iron nitrides have been a subject of numerous experimental and theoretical investigations. Thin films of iron nitride have been successfully grown on different substrates. To study the structural properties of a single monolayer film of FeN we have performed an ab-initio molecular dynamics simulation of its formation on a Cu(100) substrate. The iron nitride layer formed in our simulation shows a p4gm(2x2) reconstructed surface, in agreement with experimental results. In addition to its structural properties, we are also able to determine the magnetization of this thin film. Our results show that one monolayer of iron nitride on Cu(100) is ferromagnetic with a magnetic moment of 1.67μB.
Morphology and Magneto-optical Properties of Amorphous AlN Films Doped with Nickel
Authors: Jadwisienczak W. M. , Tanaka H. , Chen G. , Kordesch M. , Khan A.
Published: September 2011

Structural and magneto-optical properties of Ni-doped amorphous AlN layers (a-AlN) deposited by radio frequency (rf) sputtering on Silicon (001) substrates were investigated. The as-grown material exhibits weak ferromagnetic behavior as evidenced by the magneto-optic Kerr effect (MOKE) measurement with Kerr rotation less than 100 μrad at room temperature regardless of the Ni fraction. The samples with a Ni concentration below 10 at.% show a weak but monotonically increasing MOKE signal with post-growth annealing temperature. A hundred-fold increase in the Kerr rotation value was observed for samples with Ni content exceeding 20 at.% after thermal annealing at 450°C in nitrogen; and the Kerr rotation value abruptly decreases above that temperature. The morphology of as-grown and annealed a-AlN:Ni films were characterized by small angle x-ray scattering and transmission electron microscopy. It was found that the as-deposited film contains nano-particles of different sizes with average diameters less than 30 nm. The size distribution of nano-particles in the thermally annealed a-AlN:Ni was studied as a function of annealing time and temperature. The results correlate well with those obtained from the MOKE measurements.
In-situ Observations of Restructuring Carbon Nanotubes via Low-voltage Aberration-corrected Transmission Electron Microscopy
Authors: Börrnert Felix , Bachmatiuk Alicja , Gorantla Sandeep , Warner Jamie H. , Büchner Bernd , Rümmeli Mark H.
Published: September 2011

The molecular structure and dynamics of carbon nanostructures is much discussed throughout the literature, mostly from the theoretical side because of a lack of suitable experimental techniques to adequately engage the problem. A technique that has recently become available is low-voltage aberration-corrected transmission electron microscopy. It is a valuable tool with which to directly observe the atomic structure and dynamics of the specimen in situ. Time series aberration-corrected low-voltage transmission electron microscopy is used to study the dynamics of single-wall carbon nanotubes in situ. We confirm experimentally previous theoretical predictions for the agglomeration of adatoms forming protrusions and subsequent removal. A model is proposed how lattice reconstruction sites spread. In addition, the complete healing of a multi-vacancy consisting of ca. 20 missing atoms in a nanotube wall is followed.
Glancing Angle Deposited Platinum Nanorod Arrays for Oxygen Reduction Reaction
Authors: Khudhayer Wisam J. , Kariuki Nancy , Myers Deborah , Shaikh Ali , Karabacak Tansel
Published: September 2011

In this work, we investigated the electrocatalytic oxygen reduction reaction (ORR) activity of vertically aligned, single-layer, carbon-free, and single crystal Pt nanorod arrays utilizing cyclic voltammetry (CV) and rotating-disk electrode (RDE) techniques. A glancing angle deposition (GLAD) technique was used to fabricate 200 nm long Pt nanorods, which corresponds to Pt loading of 0.16 mg/cm2, on glassy carbon (GC) electrode at a glancing angle of 85° as measured from the substrate normal. An electrode comprised of conventional carbon-supported Pt nanoparticles (Pt/C) was also prepared for comparison with the electrocatalytic ORR activity and stability of Pt nanorods. CV results showed that the Pt nanorod electrocatalyst exhibits a more positive oxide reduction peak potential compared to Pt/C, indicating that GLAD Pt nanorods are less oxophilic. In addition, a series of CV cycles in acidic electrolyte revealed that Pt nanorods are significantly more stable against electrochemically-active surface area loss than Pt/C. Moreover, room temperature RDE results demonstrated that GLAD Pt nanorods exhibit higher area-specific ORR activity than Pt/C. The enhanced electrocatalytic ORR activity of Pt nanorods is attributed to their larger crystallite size, single-crystal property, and the dominance of (110) crystal planes on the large surface area nanorods sidewalls, which has been found to be the most active plane for ORR. However, the Pt nanorods showed lower mass specific activity than the Pt/C electrocatalyst due to the large diameter of the Pt nanorods.
Resonance behavior of metallic glass resonators and their application as sensor platform
Authors: Zhang K.W. , Fu L.L. , Li S.Q. , Cheng Z.-Y.
Published: September 2011

Utilizing magnetostrictive effect, the metallic glass is used to form mechanical resonators with different configurations. The resonance behaviors of these resonators are studied under different conditions, including different dc magnetic bias fields and different ac magnetic driving field. It is found that the resonators made of metallic glass exhibit a higher quality merit factor. Based on the results, it is also found that the acoustic wave velocity of the metallic glass decreases with increasing frequency. The application of these resonators as sensor platform is investigated. It is found that both odd and even vibration modes can be detected. Therefore, it provides a unique device that is capable to detect the target species on the sensor surface without “blind point(s)”, which is a challenge for all sensors based on other types of resonators. For the biosensors based on these resonators, a high sensitivity was observed. The advantages of these sensors over the current devices are demonstrated by the detection of Salmonella typhimurium (S. typhimurium) in water.
Elimination of Degenerate Epitaxy in the Growth of High Quality B12As2 Single Crystalline Epitaxial Films
Authors: Zhang Yu , Chen Hui , Dudley Michael , Zhang Yi , Edgar J. H. , Gong Yinyan , Bakalova Silvia , Kuball Martin , Zhang Lihua , Su Dong , Zhu Yimei
Published: September 2011

Elimination of degenerate epitaxy in the growth of icosahedral boron arsenide (B12As2, abbreviated as IBA) was achieved on m-plane 15R-SiC substrates and 4H-SiC substrates intentionally misoriented by 7 degrees from (0001) towards [1-100]. Synchrotron white beam x-ray topography (SWBXT) revealed that only single orientation IBA was present in the epitaxial layers demonstrating the absence of twin variants which dominantly constitute the effects of degenerate epitaxy. Additionally, low asterism in the IBA diffraction spots compared to those grown on other SiC substrates indicates a superior film quality. Cross-sectional high resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM) both confirmed the absence of twins in the IBA films and their high quality. The ease of nucleation on the ordered step structures present on these unique substrates overrides symmetry considerations that drive degenerate epitaxy and dominates the nucleation process of the IBA.
Facile Synthesis of Pure Boron Nanotubes and Nanofibers
Authors: Liu Jinwen , Iqbal Zafar
Published: September 2011

A facile and scalable chemical vapor deposition (CVD) process in flowing argon using a solid instead of a reactive gaseous boron precursor has been carried out to synthesize crystalline boron nanostructures comprising of relatively straight boron nanotubes (BNTs) and nanofibers (BNFs). The synthesis involves the use of solid magnesium boride as the boron and magnesium catalyst precursor, nickel boride as co-catalyst, and MCM-41 zeolite as the growth template. The BNTs and BNFs produced have a narrow distribution of diameters between about 10 nm to 20 nm and lengths from about 500 nm to above 1 μm. Scanning and transmission electron microscope (SEM and TEM) imaging together with electron energy loss spectroscopy (EELS) and energy dispersive spectroscopy (EDS) have been conducted to characterize the structure, morphology and growth mechanism of these novel nanostructures. High resolution TEM imaging has been used to identify BNTs and BNFs in the nanostructures synthesized.
Growth and Field Emission Properties of Boron Nitride Island Films by Low-energy Ion-assisted Deposition
Authors: Teii K. , Yang J. H. C. , Yamao R. , Matsumoto S.
Published: September 2011

We report the growth and field emission properties of boron nitride (BN) island films by chemical vapor deposition in inductively coupled plasma. Fine-grained island films with large surface roughness can be grown for initial sp2-bonded BN and subsequent cubic BN (cBN) phases by using low-energy (~20 eV) ion bombardment. Ultraviolet photoelectron spectroscopy indicates that the electron affinity is as low as 0.3 eV for both sp2-bonded BN and cBN phases. The evolution of cBN islands reduces the turn-on field down to around 9 V/μm and increases the current density up to 10-4 A/cm2. The surface potential barrier height is estimated to be about 3.4 eV for emission from the Fermi level.