bluuebunny/crossref_metadata_2025 huggingface dataset:
Control of Materials and Interfaces in μc-Si:H-based Solar Cells Grown at High Rate
Authors: Sobajima Yasushi , Sada Chitose , Matsuda Akihisa , Okamoto Hiroaki
Published: September 2011

Growth process of microcrystalline silicon (μc-Si:H) using plasma-enhanced chemicalvapor- deposition method under high-rate-growth condition has been studied for the control of optoelectronic properties in the resulting materials. We have found two important things for the spatial-defect distribution in the resulting μc-Si:H through a precise dangling-bond-density measurement, e. g., (1) dangling-bond defects are uniformly distributed in the bulk region of μc- Si:H films independent of their crystallite size and (2) large number of dangling bonds are located at the surface of μc-Si:H especially when the film is deposited at high growth rate. Starting procedure of film growth has been investigated as an important process to control the dangling-bond-defect density in the bulk region of resulting μc-Si:H through the change in the electron temperature by the presence of particulates produced at the starting period of the plasma. Deposition of Si-compress thin layer on μc-Si:H grown at high rate followed by thermal annealing has been proposed as an effective method to reduce the defect density at the surface of resulting μc-Si:H. Utilizing the starting-procedure-controlling method and the compress-layerdeposition method together with several interface-controlling methods, we have demonstrated the fabrication of high conversion-efficiency (9.27%) substrate-type (n-i-p) μc-Si:H solar cells whose intrinsic μc-Si:H layer is deposited at high growth rate of 2.3 nm/sec.
A Study of the Post-hydrogenation Passivation Mechanism of Crystallized Poly-Si Films
Authors: Luo Chong , Li Juan , Li He , Meng Zhiguo , Wu Chunya , Huang Qian , Shengzhi Xu , Kwok Hoi Sing , Xiong Shaozhen
Published: September 2011

The roles of hydrogen plasma radicals on passivation of several kinds of crystallized poly-Si thin films were investigated using optical emission spectroscopy (OES) combined with Hall mobility, Raman spectra, and absorption coefficient spectra. It was found that different kinds of hydrogen plasma radicals are responsible for passivation of dissimilar poly-Si crystallized by different method. Radicals Hα with lower energy are mainly responsible for passivating the poly-Si crystallized by solid phase crystallization (SPC) whose crystallization precursor was made by plasma enhanced chemical vapor deposition (PECVD). Higher energy radicals H* are more effective in passivating defects left over by Ni in poly-Si crystallized by Metal Induced Crystallization (MIC). The highest energy radicals Hβ and Hγ are needed to passivate the defects in poly-Si crystallized by SPC but whose precursor was made by low pressure CVD (LPCVD).
Use of a-SiC:H multilayer transducers for detection of fluorescence signals from reactive cyan and yellow fluorophores
Authors: Louro P. , Vieira M. , Vieira M. A. , Costa J. , Fernandes M. , Karmali A.
Published: September 2011

The transducer consists of a p-i’(a-SiC:H)-n/p-i(a-Si:H)-n heterostructures produced by PECVD and optimized for the detection of the fluorescence resonance energy transfer between fluorophores with excitation in the violet(400 nm) and emissions in the cyan (470 nm) and yellow (588 nm) range of the spectrum. The thickness and the absorption coefficient of the i’- and i- layers were tailored for cyan and yellow optical confinement, respectively in the front and back photodiodes acting both as optical filters. The devices were characterized through transmittance and spectral response measurements and under different electrical.

To simulate the FRET pairs and the excitation light a chromatic time dependent combination of violet, cyan and yellow wavelengths was applied to the device. The generated photocurrent was measured under negative and positive bias to readout the combined spectra. The independent test signals were chosen in order to sample all the possible chromatic. Different wavelength backgrounds were also superimposed.

Results show that under negative bias the phorocurrent signal presents eight separate levels each one assigned to the different polychromatic mixtures. If a blue background is superimposed the yellow channel is enhanced and the cyan suppressed while under red irradiation the opposite behavior occurs. So under appropriated steady state optical bias the sensor will detect separately the cyan and yellow fluorescence pairs. An electrical model, supported by a numerical simulation, gives insight into the transduction mechanism.
Copper Indium Diselenide thin films using a hybrid method of chemical bath deposition and thermal evaporation
Authors: Ornelas A R. Ernesto , Shaji Sadasivan , Arato Omar , Avellaneda David , Castillo Alan , Das Roy Tushar Kanti , Krishnan Bindu
Published: September 2011

Copper indium diselenide (CIS) based solar cells are one among the promising thin film solar cells. Most of the processes reported for the preparation of CIS directly or indirectly involve Se vapor or H2Se gases which are extremely toxic to health and environment. In this work, we report the preparation of CIS thin films by stacked layers of Glass/In/Se/Cu2Se and Glass/In/Se/Cu2Se/Se. For this, first indium (In) thin film was thermally evaporated on glass substrate on which selenium (Se) and copper selenide (Cu2Se) thin films were deposited sequentially by chemical bath deposition. Selenium thin films were grown from an aqueous solution containing Na2SeSO3 and CH3COOH at room temperature, triple deposition for 7, 7 and 10 min from consecutive baths. Copper selenide thin films were deposited at 35 °C for 1 hour from an aqueous bath containing CuSO4, Na2SeSO3 and NH4OH. Analysis of the X-ray diffraction patterns of the thin films formed at 400 °C from the precursor layer containing extra selenium layer showed the presence of chalcopyrite CuInSe2, without any secondary phase. Morphology of all the samples was analyzed using Scanning Electron Microscopy. Optical band gap was evaluated from the UV-Visible absorption spectra of these films and the values were 1.1 eV and 1 eV respectively for CIS thin films formed at 400 °C from the selenium deficient and selenium rich precursor layers. Electrical characterizations were done using photocurrent measurements. Thus preparation of a CuInSe2 absorber material by a non-toxic selenization process may open up a low cost technique for the fabrication of CIS based solar cells.
Surface Properties, Crystal Morphology, and Reactivity of La2Zr2O7-based Cathode Infiltrate in Solid Oxide Fuel Cells: A Theoretical Study
Authors: Mantz Yves A.
Published: September 2011

Selected properties of the lanthanum zirconate (La2Zr2O7, LZ) low-index faces, representing the first theoretical attempt to characterize the surfaces of a pyrochlore oxide, as well as oxygen (O2) interacting with LZ are predicted at the level of density-functional theory. All possible surface terminations formed by cleaving a perfect crystal are considered, as well as selected defective surfaces. After deriving the expression for the free energy of an LZ surface, surface free energies are computed. The most stable surfaces are identified, and it is suggested how to refine the ratios of surface free energies for comparison to experimental results obtained by the analysis of x-ray diffraction (XRD) patterns. The interaction of O2 with selected faces is examined. A strong dependence of the binding energy on surface oxygen content is predicted.
Electrical Through-Hole and Planar Interconnect Generation in Roll-to-Roll LED Lighting Manufacturing using Industrial Inkjet Printheads
Authors: Reinhold Ingo , Thielen Moritz , Voit Wolfgang , Zapka Werner , Götzen Reiner , Bohlmann Helge
Published: September 2011

Despite the availability of many high-volume and low-cost manufacturing processes for LED-based lighting applications, relying mainly on fixed patterns such as LED-backlights and RGB-pixelated displays, novel applications, such as “mood lighting” or interior wall displays call for more complicated and shaped LED arrangements. The presented work is based of a novel roll-to-roll (R2R) process to adaptively and cost-efficiently generate LED arrangements on RMPD® substrates.

Inkjet printing of planar and though-hole electrical interconnections is of high importance to the process, as it provides a fully digital way of interconnecting devices electrically, accounting for the actual position of the component and spatially provide different ink film thicknesses.

Xaar’s industrial inkjet printheads are used to dispense defined volumes of 50 pL of a silver nanoparticle ink in order to provide high reliability and good positioning accuracy while main-taining low satellite drop densities. Specific printing strategies are investigated at a print speed of 0.1 m/s to allow for a reliable electrical connection in case of up to 50 μm deep via connections to the buried component.

Due to the low glass-transition nature of the underlying substrates, low sintering tempera-tures are required to preserve the mechanical properties of the substrate. Low temperature oven sintering yielding sufficient conductivity to drive a current of 40 mA will be discussed.
Magnetic and dielectric properties study of cobalt ferrite nanoparticles synthesized by co-precipitation method
Authors: Krishna Surendra M. , Kannan D. , Ramachandra Rao M. S.
Published: September 2011

Cobalt ferrite nanoparticles were prepared by co-precipitation method and were heat treated at 100 oC, 200 oC, 400 oC and 600 oC for 2 h to increase the particle size. Phase purity of samples was confirmed by X-ray diffraction. Scherrer formula calculations showed crystallite size varied from 12 to 24 nm when heated from 100 oC to 600 oC. Transmission electron microscopy reveals a uniform and narrow particle size distribution about 12 nm for as-prepared cobalt ferrite particles. Room temperature saturation magnetization was found to vary from 40.8 to 67.0 emu/g as the particle size increased from12 nm to 24 nm. Increase in saturation magnetization with increase in particle size was attributed to the presence of magnetic inert layer on the surface of nanoparticles. Inert layer thickness calculated at 10 K and 300 K was 6 Å and 11 Å respectively. The dielectric properties ε’, tanδ, Z and θ have been studied as a function of frequency and particles size. For the 12 nm grain size, the dielectric constant is one order higher than that of bulk cobalt ferrite. Increase in the grain size showed an increase in the dielectric constant. The increase in the conductivity with grain size is mainly due to the grain size effects. The present study shows that the dielectric properties can be tailor-made to suit the requirement of a particular application by controlling the grain size.
High Rate Deposition of High Quality ZnO:Al by Filtered Cathodic Arc
Authors: Mendelsberg Rueben J. , Lim Sunnie H.N. , Milliron Delia J. , Anders André
Published: September 2011

High quality ZnO:Al (AZO) thin films were prepared on glass substrates by direct current filtered cathodic arc deposition. Substrate temperature was varied from room temperature to 425°C, and samples were grown with and without the assistance of low power oxygen plasma (75W). For each growth condition, at least 3 samples were grown to give a statistical look at the effect of the growth environment on the film properties and to explore the reproducibility of the technique. Growth rate was in the 100-400 nm/min range but was apparently random and could not be easily traced to the growth conditions explored. For optimized growth conditions, 300-600 nm AZO films had resistivities of 3-6 x 10-4 Ωcm, carrier concentrations in the range of 2-4 x 1020 cm3, Hall mobility as high as 55 cm2/Vs, and optical transmittance greater than 90%. These films are also highly oriented with the c-axis perpendicular to the substrate and a surface roughness of 2-4 nm.
Effective Medium Analysis of Plasmonic Silver Nanoparticle Films
Authors: Santbergen Rudi , Sap Jeroen , Temple Tristan , Solntsev Serge , Smets Arno HM , van Swaaij René , Zeman Miro
Published: September 2011

Films of silver nanoparticles have optical properties that are useful for applications such as plasmonic light trapping in solar cells. We illustrate experimentally and by means of simulations how the particle shape affects the optical properties. In addition we show that these nanoparticle films can be represented by an effective medium layer with an almost identical reflectance and transmittance. The Bergman effective medium theory that we used provides a link between the nanoparticle shape and the optical properties. This insight can be used for the optical analysis of nanoparticle films and for further optimization of plasmonic solar cells.
EXPLORING THE LIMITS OF PHOSPHOR-BASED SPECTRAL MANAGEMENT FOR PHOTOVOLTAIC APPLICATIONS
Authors: Magsi Komal , Lee Rose , Shank Jason , Kang Yeona , Fortmann C.M.
Published: September 2011

A detailed analysis of photovoltaic front surface phosphor-based spectral modification and light scattering by hetero-structure was conducted. Phosphor based spectral downconversion is a well known laser technology. The analysis assumes that both sunlight energy and photovoltaic performance are at peak sunlight photon flux within the spectral range. Further, the analysis presented here indicates that parasitic losses and light scattering within the spectral range are large enough to offset any expected gains. For example, analysis of up-conversion phosphor-based approaches indicates that these are likely to suffer unexpectedly large losses in the peak spectral region due to parasitic absorption when attempting to down convert UV light.
Thermal Annealing Effect on P3HT:PCBM Free Polarons Lifetime and Charge Transport
Authors: Li Kejia , Shen Yang , Li Lijun , Khlyabich Petr , Reifler Ellen S. , Thompson Barry C. , Campbell Joe C.
Published: September 2011

A transient response technique has been employed to investigate the lifetime of free polarons in bulk heterojunction blends of regioregular poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methylester (PCBM) at different annealing temperatures. Device efficiency and charge mobility were also measured. The longest lifetime, ∼ 1.5 microseceonds, was achieved for an annealing temperature of 140˚C; this represents a 2.5 x increase in lifetime relative to unannealed samples. The 140˚C annealing temperature also yields the highest efficiency. These measurements provide an estimate of the mobility-lifetime product, a figure of merit for charge transport in organic bulk heterojunctions.
Growth of AZO on flexible substrate using ALD system as a transparent conducting oxide for solar cells
Authors: Dhakal Tara , Nandur Abhishek , Christian Rachel , Vanhart Daniel , Vasekar Parag , Westgate Charles R.
Published: September 2011

Aluminum doped zinc oxide (AZO) thin film is gaining momentum as a transparent conducting oxide because its optical and electrical properties are optimal for a photovoltaic device. We report growth of AZO thin film using an Atomic Layer Deposition (ALD) system, which is known to deposit layers on a substrate with atomic layer precision. The precursors used for aluminum and zinc were Trimethylaluminum (TMA) and Dimethylzinc (DMZ) respectively. Alternating cycles of TMA and DMZ were introduced to the heated deposition chamber such that a desired aluminum doping was obtained on the AZO films grown. The films were grown on flexible substrates like PET and also on single crystalline Si(100) and float-glass substrates. An optimal aluminum doping (3 at.%) on the AZO film of thickness 575 nm gave a sheet resistance (Rs) of 97 Ω/□ with corresponding resistivity of 5.6 x 10-3 Ω.cm. The value of the carrier concentration and hall mobility were 1.86 x 1020 cm-3 and 6.5 cm2V-1s-1 respectively. Optical measurement showed 90% transmission in most of the visible spectrum. X-ray diffraction spectra of the film showed all characteristic ZnO hexagonal lattice peaks.
Influence of dopant nature on the TCO properties of ZnO:M (M=Al, Ga, Sn, Si, Ge) thin films
Authors: Clatot J. , Campet G. , Jean M. , Nistor M. , Rougier A.
Published: September 2011

Aiming at clarifying the opto-electronic properties of ZnO based n-type Transparent Conducting Oxides, TCOs, properties of ZnO thin films are studied as a function of cationic doping. In addition to commonly reported, Al and Ga trivalent dopant, similar performances are reported for Si doping. In the visible region, ZnO:Si (3 %) thin film exhibit a transmittance higher than 80 % for a resistivity as low as 8x10-4 Ω.cm when grown at 100 °C under 1.0 Pa oxygen pressure. The influence of tetravalent cations as dopant is also investigated through Sn and Ge additions. It shows that not only the oxidation state plays a role but also the cation nature. Indeed, ZnO:Sn thin films are insulating whereas the ZnO:Ge thin films are conductive with resistivity values higher than the ones of ZnO:Si thin films.
Simulation of Symmetrically Doped Silicon Nanowire Solar Cells
Authors: Voigt Felix , Stelzner Thomas , Christiansen Silke H.
Published: September 2011

Silicon nanowire solar cells were simulated using the Silvaco TCAD software kit. For optimization of speed the simulations were performed in cylinder coordinates with cylindrical symmetry. Symmetric doping was assumed with a dopant density of 1018 cm-3 in the p-type core and inside the n-type shell. In the implementation a cathode contact was wrapped around the semiconductor nanorod and an anode was assumed at the bottom of the rod. Optimization of cell efficiency was performed with regard to the rod radius and the rod length. In both optimization processes clear maxima in efficiency were visible, resulting in an optimal radius of 66 nm with the pn junction at 43.5 nm and an optimal rod length of about 48 μm. The maximum of efficiency with respect to the rod radius is due to a decrease of short-circuit current density (Jsc) and an increase of open-circuit voltage (Uoc) with radius, while the maximum with respect to the rod length is explained by the combination of an increase of Jsc and a decrease of Uoc. Fill factors stay rather constant at values between 0.6 and 0.8. Further, the influence of a back surface field (BSF) layer was surveyed in simulations. Positioning the BSF next to the cathode contact considerably improved cell efficiency. In addition, simulations with a cathode contact on top of the nanowire structure were undertaken. No severe deterioration of cell performance with increasing radius was observed so far in this configuration. Hence, nanorods with much larger radii can be used for solar cells using this contact scheme. In comparison to simulations with wrapped cathode contacts, Jsc and Uoc and therefore efficiency is considerably improved.
Diameter Dependent Current-Voltage Characteristics of InSb Nanowires
Authors: Penchev Miroslav , Zhong Jiebin , Lin Jian , Ozkan Cengiz S. , Ozkan Mihrimah
Published: September 2011

Single crystalline Indium Antimonide (InSb) nanowires were synthesized by chemical vapor deposition (CVD) technique, using gold (Au) nanoparticles as catalyst, via a vapor liquid solid mechanism. Structural properties of the as-grown InSb nanowires were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Nanowire field effect transistors (NWFETs) were fabricated in back-gate configuration, on Si/SO2 substrates, using SiO2 as gate insulator. The diameter of InSb nanowires used in the fabricated devices varied from 15-80 nm. Current-voltage measurements were conducted to determine the dependence of NWFETs parameters on the InSb nanowire diameter. Carrier mobility was shown to decrease with decrease of nanowire diameter. Temperature dependen current-voltage measurements were conducted to determine the effect of operating temperature on the InSb NWFET device performance.
Functionalization and Environmental Stabilization of ZnO Nanobridge Sensors Fabricated using Carbonized Photoresist
Authors: Mason Ashley D. , Huang Chien-Chih , Koesdjojo Myra T. , Stephon Nate D. , Remcho Vincent T. , Conley John F.
Published: September 2011

ZnO nanobridge sensors were selectively grown and electrically connected using lithographically patterned carbonized photoresist (C-PR). As ZnO is known to dissolve in deionized (DI) water, parylene-A was investigated as a moisture barrier and potential functionalization platform. A chemical vapor deposition (CVD) process for parylene-A was developed and it was demonstrated that parylene-A coated ZnO NWs do not show any signs of dissolution after 24 hours in an aqueous solution. The impact of the parylene-A coating on the electrical performance and sensitivity of ZnO nanobridge devices was investigated. A comparison of UV, O2, and H2O sensitivity between uncoated and coated devices revealed that a thin coating of parylene-A attenuated all of these responses, suggesting the ability to modulate environmental sensitivity using this non-covalently bound polymer passivation layer.
Electrochemical performance of anodized TiO2Nanotubes for rechargeable Lithium Batteries
Authors: Prasada Rao R. , Kangle L. , Adams S. , Reddy M.V. , Chowdari B.V.R.
Published: September 2011

The electrochemical storage performance of anatase TiO2nanotubes (NT) is compared to the performance of TiO2nanotubes covered by sulfur. Charge/discharge curves and cycling performance of TiO2NT with and without sulfur deposition with respect to lithium anodes are demonstrated in electrochemical test cells. At 0.5C cycle rate the TiO2NT exhibited a first cycle specific charge/discharge capacity of 180/155 mAh/g, whereas the TiO2NT deposited with sulfur showed a remarkably higher performance at 0.5C cycle rate with first cycle charge/ discharge specific capacities of 258/260 mAh/g and a coulombic efficiency of 98%.
5MeV Si Ion Modification on Thermoelectric SiO2/SiO2+Cu Multilayer Films
Authors: Smith C. , Budak S. , Jordan T. , Chacha J. , Chhay B. , Heidary K. , Johnson R. B. , Muntele C. , ILA D.
Published: September 2011

We prepared samples by electron beam physical vapor deposition EB-PVD followed by ion bombardment. The samples were than characterized by photoluminescence (PL), x-ray photoelectron spectroscopy (XPS). PL was used to characterize the available energy states. XPS was used to determine the binding energies. The ML’s are comprised of 100 alternating layers of SiO2/SiO2+Cu.
A Comparative Study of the Thin-Film CdTe Solar Cells with ZnSe/TCO and the CdS/TCO Buffer Layers
Authors: Potlog Tamara , Spalatu Nicolae , Mere Arvo , Hiie Jaan , Mikli Valdek
Published: September 2011

The growth of ZnSe and CdTe thin films by close spaced sublimation is examined. The investigations show that ZnSe films deposited on glass substrates are polycrystalline and exhibit wurtzite-zinc-blende polytypism. The CdTe films grown on glass/SnO2/ZnSe are polycrystalline and have an f.c.c. zinc-blende structure as in the case of a glass/SnO2/CdS buffer layer. The electric and photovoltaic parameters of ZnSe/CdTe solar cells depend on the ZnSe film thickness. Furthermore, it is shown for the first time that the best photovoltaic parameters are achieved using a Zn buffer layer at the interface between ZnSe and CdTe.
Top-Gate Graphene-on-UNCD Transistors with Enhanced Performance
Authors: Yu Jie , Liu Guanxiong , Sumant Anirudha V. , Balandin Alexander A.
Published: September 2011

We fabricated a number of top-gate graphene field-effect transistors on the ultrananocrystalline diamond (UNCD) – Si composite substrates. Raman spectroscopy, scanning electron microscopy and atomic force microscopy were used to verify the quality of UNCD and graphene device channels. The thermal measurements were carried out with the “hot disk” and “laser flash” methods. It was found that graphene on UNCD devices have increased breakdown current density by ∼50% compared to the reference devices fabricated on Si/SiO2. The relatively smooth surface of UNCD, as compared to other synthetic diamond films, allowed us to fabricate top gate graphene devices with the drift mobility of up to ∼ 2587 cm2V-1s-1.
Numerical Study of Scaling Issues in Graphene Nanoribbon Transistors
Authors: Chen Man-Tieh , Wu Yuh-Renn
Published: September 2011

This paper addresses scaling issues in graphene nanoribbon transistors (GNRFETs) by using a two-dimensional (2-D) Poisson and drift-diffusion solver with finite element method (FEM). GNRFETs with the back gate control and the channel width down to less than 5nm have been reported to have Ion=Ioff ratio up to 106. Our simulations show an agreement with the published experimental work and show a potential to reach unit current gain cut-off frequency, fT , up to more than 1THz with a satisfying Ion=Ioff ratio at the same time. This makes GNRFETs attractive for high speed logic.
Rapid large-scale Characterization of CVD Graphene Layers on Glass using Fluorescence Quenching Microscopy
Authors: Kyle Jennifer Reiber , Guvenc Ali , Wang Wei , Lin Jian , Ghazinejad Maziar , Ozkan Cengiz , Ozkan Mihrimah
Published: September 2011

The exceptional electrical, optical, and mechanical properties of graphene make it a promising material for many industrial applications such as solar cells, semiconductor devices, and thermal heat sinks. However, the greatest obstacle in the use of graphene in industry is high-throughput scaling of its production and characterization. Chemical-vapor deposition growth of graphene has allowed for industrial-scale graphene production. In this work we introduce complimentary high-throughput metrology technique for characterization of chemical-vapor deposition-grown graphene. This metrology technique provides quick identification of thickness and uniformity of entire large-area chemical-vapor deposition-grown graphene sheets on a glass substrate and allows for easy identification of folds and cracks in the graphene samples. This metrology technique utilizes fluorescence quenching microscopy, which is based on resonant energy transfer between a dye molecule and graphene, to increase allow graphene visualization on the glass substrate and increase the contrast between graphene layers.
1/f Noise in Graphene Field-Effect Transistors: Dependence on the Device Channel Area
Authors: Liu Guanxiong , Rumyantsev Sergey , Stillman William , Shur Michael , Balandin Alexander A.
Published: September 2011

We carried out a systematic experimental study of the low-frequency noise characteristics in a large number of single and bilayer graphene transistors. The prime purpose was to determine the dominant noise sources in these devices and the effect of aging on the current-voltage and noise characteristics. The analysis of the noise spectral density dependence on the surface area of the graphene channel indicates that the dominant contributions to the 1/f electronic noise come from the graphene channel region itself. Aging of graphene transistors due to exposure to ambient for over a month resulted in substantially increased noise, which was attributed to the decreasing mobility of graphene and increasing contact resistance. The noise spectral density in both single and bilayer graphene transistors shows a non-monotonic dependence on the gate bias. This observation confirms that the 1/f noise characteristics of graphene transistors are qualitatively different from those of conventional silicon metal-oxide-semiconductor field-effect transistors.
Amine-rich Polyelectrolyte Adhesion Layers as an Alternative to APTES for Surface Immobilization of Biomolecules and Nanostructures
Authors: Stoianov Stefan V. , Ridley Jason I. , Robinson Hans D.
Published: September 2011

We propose the use of amine-rich polyelectrolyte multilayers as a versatile, high quality, tunable adhesive surfaces for biomedical and nanotechnological applications. The films are simple to fabricate under mild conditions and provide at least as good adhesion as standard aminopropyltriethoxysilane terminated glass substrates. In addition, the multilayer surface can be reliably passivated by acetylation with acetic anhydride which reduces the adhesion to the point that non-specific binding of proteins and nanoparticles becomes all but negligible. We demonstrate that this property, in combination with the robustness of the film, makes it possible to pattern the adhesiveness of the film at the nanoscale level.
Large-Area Industrial-Scale Identification and Quality Control of Graphene
Authors: Nolen Craig M. , Denina Giovanni , Teweldebrhan Desalegne , Bhanu Bir , Balandin Alexander A.
Published: September 2011

A large-area graphene layer identification technique was developed for research and industrial applications. It is based on the analysis of optical microscopy images using computational image processing algorithms. The initial calibration is performed with the micro-Raman spectroscopy. The method can be applied to the wafer-scale graphene samples. The technique has the potential to be the gateway in the development of fully automated statistical process control methods for the next generation thin-film materials used by the semiconductor industry. The proposed technique can be applied to graphene on arbitrary substrates and used for other atomically thin materials.
All-Carbon Composite for Photovoltaics
Authors: Tan Alvin T.L. , Tung Vincent C. , Kim Jaemyung , Huang Jen-Hsien , Tevis Ian , Chu Chih-Wei , Stupp Samuel I. , Huang Jiaxing
Published: September 2011

Graphitic nanomaterials such as graphene, carbon nanotubes (CNT), and C60 fullerenes are promising materials for energy applications because of their extraordinary electrical and optical properties. However, graphitic materials are not readily dispersible in water. Strategies to fabricate all-carbon nanocomposites typically involve covalent linking or surface functionalization, which breaks the conjugated electronic networks or contaminates functional carbon surfaces. Here, we demonstrate a facile surfactant-free strategy to create such all-carbon composites. Fullerenes, unfunctionalized single walled carbon nanotubes, and graphene oxide sheets can be conveniently co-assembled in water, resulting in a stable colloidal dispersion amenable to thin film processing. The thin film composite can be made conductive by mild thermal heating. Photovoltaic devices fabricated using the all-carbon composite as the active layer demonstrated an on-off ratio of nearly 106, an open circuit voltage of 0.59V, and a power conversion efficiency of 0.21%. This photoconductive and photovoltaic response is unprecedented among all-carbon based materials. Therefore, this surfactant-free, aqueous based approach to making all-carbon composites is promising for applications in optoelectronic devices.
Optimizing in vivo Assessment of Nano/bio Interactions to Guide Safer Material Design
Authors: Tanguay Robert. L. , Truong Lisa
Published: September 2011

The rapid rate of discovery and development in the nanotechnology field will undoubtedly increase both human and environmental exposures to engineered nanomaterials. Whether these exposures pose a significant risk remains uncertain. Despite recent collective progress there remain gaps in our understanding of the nanomaterials physiochemical properties that drive or dictate biological responses. The development and implementation of rapid relevant and efficient testing strategies to assess these emerging materials prior to large-scale exposures could help advance this exciting field. I present a powerful approach that utilizes a dynamic in vivo zebrafish embryonic assay to rapidly define the biological responses to nanomaterial exposures. Early developmental life stages are often uniquely sensitive to environmental insults, due in part to the enormous changes in cellular differentiation, proliferation and migration required to form the required cell types, tissues and organs. Molecular signaling underlies all of these processes. Most toxic responses result from disruption of proper molecular signaling, thus, early developmental life stages are perhaps the ideal life stage to determine if nanomaterials perturb normal biological pathways. Through automation and rapid throughput approaches, a systematic and iterative strategy has been deployed to help elucidate the nanomaterials properties that drive biological responses.
The suppression of leakage current in the solid phase crystallized silicon (SPC-Si) TFT employing off-state bias annealing under light illumination.
Authors: Park Sang-Geun , Kuk Seung-Hee , Woo Jong-Seok , Han Min-Koo
Published: September 2011

We fabricated PMOS SPC-Si TFTs which show better current uniformity than ELA poly-Si TFTs and superior stability compare to a-Si:H TFT on a glass substrate employing alternating magnetic field crystallization. However the leakage current of SPC-Si TFT was rather high for circuit element of AMOLED display due to many grain boundaries which could be electron hole generation centers. We applied off-state bias annealing of VGS=5V, VDS=-20V in order to suppress the leakage current of SPC-Si TFT. When the off-state bias annealing was applied on the SPC-Si TFT, the electron carriers were trapped in the gate insulator by high gate-drain voltage (25V). The trapped electron carriers could reduce the gate-drain field, so that the leakage current of SPC-Si TFT was reduced after off-state bias annealing. . We also applied same off state bias annealing at SPC-Si TFT with 20,000 lx light illumination in order to verify the reduction of leakage current of SPC-Si TFT under light illumination. The leakage current of SPC-Si TFT was reduced successfully even under light illumination during off-state bias annealing. The off-state bias annealed SPC-Si TFT could be used as pixel element of high quality AMOLED display.
Utilization of Industrial Inkjet Technologies for the Deposition of Conductive Polymers, Functional Oxides and CNTs
Authors: Voit Wolfgang , Reinhold Ingo , Zapka Werner , Belova Lyubov , Rao K.V.
Published: September 2011

Printing of functional materials requires reliable deposition processes. This work describes the development of printing processes for selected functional materials utilizing industrial-type inkjet printheads. A well-controlled printing process with fluids containing the conductive polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is presented, allowing linear printing speeds of up to 0.35 m/s in single-pass, and smallest line width of approximately 40 μm when printing 7 pL drop volumes. In addition reliable processes for producing ZnO-based films, which enable novel applications for electronic and UV-sensitive devices, and for printing of conductive carbon nanotube layers are shown.
Characteristic band gap structures of high dielectric contrast photonic crystals
Authors: Chao Sheng D. , Peng Hsin Y.
Published: September 2011

Conventional photonic crystals exhibit low-lying full band gaps for the dielectric contrast smaller than 15. As the dielectric contrast increases, the band gap patterns change characteristics and exhibit interesting properties. In particular, the dispersion curves near the band gap region become concentrated to the middle band frequencies and exhibit an overall red shift in frequency. For a dielectric column photonic crystal made of a hexagonal lattice of circular cylinders, the maximum full band gap was found at the dielectric contrast as high as 27.5, which is attainable by using ceramics materials. The gap opens at high-lying bands, has simultaneous TM and TE band edges, and exhibit flattened dispersion curves near the band edges.
Universal Biomolecule Binding Interlayers Created by Energetic Ion Bombardment
Authors: Bilek Marcela M.M. , McKenzie David R. , Bax Daniel V. , Kondyurin Alexey , Yin Yongbai , Nosworthy Neil. J. , Hirsh Stacey , Fisher Keith , Weiss Anthony S.
Published: September 2011

The ability to strongly attach biomolecules such as enzymes and antibodies to surfaces underpins a host of technologies that are rapidly growing in utility and importance. Such technologies include biosensors for medical and environmental applications and protein or antibody diagnostic arrays for early disease detection. Emerging new applications include continuous flow reactors for enzymatic chemical, textile or biofuels processing and implantable biomaterials that interact with their host via an interfacial layer of active biomolecules. In many of these applications it is desirable to maintain physical properties of an underlying material whilst engineering a surface suitable for attachment of proteins or peptide constructs. Nanoscale polymeric interlayers are attractive for this purpose.

We have developed interlayers[1] that form the basis of a new biomolecule binding technology with significant advantages over other currently available methods. The interlayers, created by the ion implantation of polymer like surfaces, achieve covalent immobilization on immersion of the surface in protein solution. The interlayers can be created on any underlying material and ion stitched into its surface. The covalent immobilization of biomolecules from solution is achieved through the action of highly reactive free radicals in the interlayer.

In this paper, we present characterisation of the structure and properties of the interlayers and describe a detailed kinetic model for the covalent attachment of protein molecules directly from solution.
A Novel Technology for Green(er) Manufacturing of CNTs via Recycling of Waste Plastics
Authors: Zhuo Chuanwei , Hall Brendan , Levendis Yiannis , Richter Henning
Published: September 2011

Costly and often highly-flammable chemicals, such as hydrogen and carbon-containing gases, are largely used for carbon supply in current carbon nanotube (CNT) synthesis technologies. To mitigate related economic and safety concerns, we have developed a versatile CNT synthesis sequence, where low-cost and safe-to-handle-and-store waste solid polymers (plastics) are used for in situ generation of hydrogen and carbon-containing gases. Introduction of different waste plastics, such as polyethylene, polypropylene and polystyrene, into a multi-stage pyrolysis/ combustion/synthesis reactor allows for efficient CNT formation. This process is largely exothermic and scalable. It uses low-cost stainless steel screens to serve both as substrates as well as catalysts for CNT synthesis. This technique enables a solution for both waste plastic utilization and sustainable CNT production.
Siliceous Materials for Immobilization of Photoheterotrophic Bacteria
Authors: Stodolny Mikolaj , Thiel Michal , Wlodarczak Marcin , Laniecki Marek
Published: September 2011

Preparation of transparent silica as potential carrier for photocatalysts and photosynthetic bacteria is presented. SiO2 was obtained by sol-gel techniques using tetraethyl orthosilicate as precursor. Glycol and glycerol were used as solvents. The increase of porosity of the studied materials was reached by application of soluble and commercial potato starch as a filler. Calcinations at 825 K for 6 hours removed all organic compounds. The rate of gelation was enhanced applying hydrochloric acid. Different materials were obtained in a series of syntheses with different concentrations of individual components. Transparency of the obtained materials varied between 50 and 97% (in range of λ 350 - 800 nm). Surface area varied between 300 and 400 m2/g and pore diameter was 5 – 18 nm. Samples were studied with SEM, nitrogen sorption at 77 K and UV-Vis spectroscopy. The obtained transparent materials with occluded TiO2 or CaTiO3 were tested in photocatalytic splitting of water.
Carbon Nanotubes Induced Changes in the Phase Diagram and Crystal Structure of 5CB Liquid Crystal
Authors: Georgiev Georgi Y. , McIntyre Michael B. , Gombos Erin A. , Cebe Peggy
Published: September 2011

Multiwall Carbon Nanotubes (MWCNTs) form a nematic liquid crystalline (LC) phase in their lyotropic form, enabling their mixing and coupling of their director to that of nematic LCs. An important aspect of this LC/MWCNT interaction, for applications other than display technology, is looking at the ways the MWCNTs affect the physical properties of the LCs. We study the effect of MWCNTs on the nematic to crystal (N-C) phase transition of 4-cyano-4-npentylbiphenyl (5CB). Our Differential Scanning Calorimetry (DSC) results show a dramatic increase in N-C phase transition temperature of 14°C for only 0.1% and of 20°C for 1% MWCNT, due to the crystal nucleation activity of the nanotubes. Using Polarized Microscopy we observe a change in the crystalline order of 5CB from spherulitic at 0% MWCNTs to a multidomain in presence of MWCNTs. The new crystals resemble those formed by a smectic LC 4- Decyloxybenzoic acid. This is in line with predictions from simulations, that the MWCNTs form smectic order in nematic 5CB at their interface. MWCNTs induced modifications of the crystal phase of 5CB promise to create controlled novel crystal forms for the purposes of optical transmission and other applications.
Study on the Mechanical Properties and Creep Behaviour of Carbon Fiber Nano-Composites
Authors: LI Yi-Luen , Chen Wei-Jen , Chiang Chin-Lung , Yip Ming-Chuen
Published: September 2011

The surface modification of carbon nanotubes（CNTs）has been recently observed to influence the distribution of CNTs in epoxy resin and the mechanical properties and electrical conductivities of these CNTs. Accordingly, the treatment of CNTs with organic acids to oxidize them generates functional groups on the surface of CNTs. This investigation studies the consequent enhancement of the mechanical properties and electrical conductivities of CNTs. The influence of adding various proportions of CNTs to the epoxy resin on the mechanical properties and electrical conductivities of the composites thus formed is investigated, and the strength of the material is tested at different temperatures. Moreover, the creep behavior of carbon fiber （CF）/epoxy resin thermosetting composites was tested and analyzed at different temperatures and stresses. The creep exhibits only two stages- primary creep and steady-state creep. The effects of creep stress, creep time, and humidity on the creep of composites that contain various proportion of CNTs were investigated at various temperatures.

Creep strain is believed to increase with applied stress, creep time, humidity, and temperature. It also increases as hardness decrease. The test results also indicate that mechanical strength and electrical conductivity increase with the amount of CNTs added to the composites. Different coefficients of expansion of the matrix, fiber and CNTs, are such that overexpansion of the matrix at high temperature results in cracking in it. An SEM image of the fracture surface reveals debonding and the pulling out of longitudinal fibers because of poor interfacial bonding between fiber and matrix, which reduce overall strength.
Influence of Preparation Method and Molecular parameters on the Rheology of Model PEO/ Laponite Nanocomposites
Authors: Jose Jesmy , Omar Abakar Adam , Brotons Guillaume , Tassin Jean-François
Published: September 2011

Model polymer nanocomposites based on geometrically well defined and protected Laponite particles dispersed in Poly(ethylene oxide) were investigated in order to improve the understanding of the filler dispersion effects on rheology by varying two experimental factors, namely preparation method and PEO matrix molecular weight. Preparation methods are divided into a solution dispersion and a melt dispersion by twin screw extrusion. The linear viscoelastic properties of the samples prepared by solution method revealed an elastic solid like behaviour at Laponite weight fractions as low as 0.1%, dramatically lower than the percolation threshold so far reported for such kind of systems. The sample preparation by melt dispersion, although leading to dispersed particles, does not achieve the same levels of modulus as compared to solution prepared mixtures. We propose a qualitative interpretation of this phenomenon, based on the mixture between a liquid and a dispersed phase of rather solid character. Further experiments using small angle X-ray scattering techniques (SAXS) show that the modulus level is not necessarily related to the height of the correlation peak characteristic of the Laponite stacks. However, for samples prepared with varying PEO matrix molecular weight the fraction of Laponite stacks decreases with increasing PEO molecular weight. The rheology master curve analyses show that confinements of polymer chains arising from high concentrations of particles and high molecular weight matrix chains do not impact the level of the low frequency modulus. However, a slower polymer dynamics, as observed for higher molecular weights, leads to an increase of the modulus at low particle loadings.
Characterization of Textured PZT Thin Films Prepared by Sol-gel Method onto Stainless Steel Substrates
Authors: Zhao Xuelian , Yu Xufang , Yu Shengwen , Cheng Jinrong
Published: September 2011

PbZr0.53Ti0.47O3 (PZT) ferroelectric thin films were deposited on LaNiO3 (LNO) buffered stainless steel (SS) substrates by sol-gel method. The effect of LNO buffer layer on the orientation and electric properties of PZT thin films for different thicknesses were studied. X-ray diffraction (XRD) results indicated that PZT thin films on SS substrates exhibit the (100) preferred orientation with the LNO buffer layers. Scanning electron microscope (SEM) images show that PZT thin films were well crystallized with grain size of about 100 nm. PZT thin films deposited on SS maintain the excellent ferroelectric properties with remnant polarization of about 20 μC/cm2.
Synthesis of Resorcinol Formaldehyde Aerogel Using Photo-Acid Generators for Inertial Confinement Fusion Experiments
Authors: Saito K.M. , Paguio R.R. , Hund J.F. , Jimenez R. M.
Published: September 2011

Traditionally, the synthesis of resorcinol formaldehyde (R/F) aerogels consists of a 2-step (base/acid catalysis) polycondensation reaction. Since the acid catalyst in the reaction controls the gelation time, the replacement of the acid catalyst with a non-ionic photo-acid generator decreased the gelation time from hours, down to a few minutes at room temperature using a UV light source. The reaction rate was not only fast, but the liquid precursor was stable for several hours prior to UV exposure. After drying, the resulting aerogel porosity was characterized by scanning electron microscopy (SEM) and confirmed the internal structure of the aerogel was similar to the original R/F pore structures. This paper will discuss the modifications made to the traditional R/F formulation, as well as the benefits of a fast gelation time for aerogel casting applications such as thin films, cylinders, and solid and hollow microspheres.
Nonadiabatic Chemical-to-Electrical Energy Conversion in Catalytic Schottky Junction Nanostructures
Authors: Karpov Eduard G. , Mohan Jyotsna
Published: September 2011

Nonadiabatic energy dissipation by electron subsystem of nanostructured solids unveil interesting opportunities for the solid-state energy conversion and sensor applications. We found that planar Pd/n-SiC, Pt/n-GaP and Pd/n-GaP Schottky structures with nanometer thickness metallization demonstrates a nonadiabatic channel for the conversion into electricity the energy of a catalytic hydrogen-to-water oxidation process on the metal layer surface. The observed abovethermal current greatly complements the usual thermionic emission current, and its magnitude is linearly proportional to the rate of formation and desorption of product water molecules from the nanostructure surface. The possibilities and advantages of utilizing the nonadiabatic functionality in a novel class of chemical-to-electrical energy conversion devices are discussed. The technology has a potential for a very high volumetric energy density due to the intrinsically planar device architecture.