bluuebunny/crossref_metadata_2025 huggingface dataset:
Tuning the Elasticity of Biopolymer Gels for Optimal Wound Healing
Authors: Georges Penelope , McCormick Margaret , Flanagan Lisa , Ju Yo-El , Sawyer Evelyn , Janmey Paul
Published: April 2011

Soft polymer networks with large mesh size, not flat rigid surfaces, are the normal environment for most animal cells. Cell structure and function depend on the stiffness of the surfaces on which cells adhere as well as on the type of adhesion complex by which the cell binds its extracellular ligand. Many cell types, including fibroblasts and endothelial cells, switch from a round to spread morphology as stiffness is increased between 1000 and 10,000 Pa. Coincident with the change in morphology are a host of differences in protein phosphorylation levels, expression of integrins, and changes in cytoskeletal protein expression and assembly. In contrast, other cells types such as neutrophils and platelets do not require rigid substrates in order to spread, and neurons extend processes better on soft (50 Pa) materials than on stiffer gels. We compare the stiffness sensing of four cell types: platelets, neurons and astrocytes, a glial cell type derived from embryonic rat brain, and melanoma cells. Astrocytes switch from a round to spread morphology as substrate stiffness increases, but do so over a stiffness range 10 times softer than that over which fibroblasts alter morphology. Stiffness-dependent morphologic changes observed from studies of cells grown on surfaces of protein-laminated polyacrylamide gels that have linear elasticity are also seen when cells are on matrices of natural biopolymers such as fibrin. Biopolymer gels like fibrin can be formed with appropriate stiffness to optimize for neuronal cell survival and patterning, and may have utility for repair of damaged neural tissues. The complex non-linear rheology of fibrin and other gels formed by semi-flexible biopolymers that exhibit strain-stiffening provide additional mechanisms by which cells can respond to and actively remodel the mechanical features of their environment.
Solvent behavior in hydrophobic silica nanotubes
Authors: English Douglas , Luckett Charles , Jayaraman Karthik , Lee Sang Bok , Son Sang Jun , Okamoto Kenji
Published: April 2011

Template-synthesized silica nanotubes offer a unique and interesting opportunity for studying fluids in confined spaces. Their versatility stems from our ability to independently vary the inside diameter and surface chemistry. In this work we investigated capillarity for binary mixtures of water and methanol in hydrophobic nanotubes with internal diameters of both 30 and 170 nm. An improved sol-gel template synthesis process was used to prepare silica nanotubes with smooth and uniform walls within the pores of alumina template membranes. The pore diameter and thickness of the template membrane determined the outer diameter and length of the nanotube, respectively. The number of deposition cycles controlled the wall thickness. An octadecylsilane coating was selectively applied to the nanotube interior while leaving the nanotube exterior unmodified. The interiors of hydrophobic nanotubes prepared in this way were then labeled with trace amounts of adsorbed dyes. The diffusion of the dye molecules inside individual immersed nanotubes was investigated using fluorescence recovery after photobleaching (FRAP) experiments. Dye diffusion was used to determine the wettability of the nanotube interior as a function of solvent composition. Several important observations are reported here. First, a clear transition is observed in which all nanotubes change from non-wetting to wetting when the methanol mole fraction approaches 0.5. This transition appears at the same solvent composition for both nanotube sizes. Interestingly, the Young-Laplace equation fails to accurately predict the wetting transition. The difference between the observed and predicted wetting transition may be due to reliance on macroscopic values of contact angles or surface tensions in our predictions or may be related to the presence of liquid phase instability, dry-layers or non-spherical menisci within the hydrophobic pore.
Synchrotron X-Ray Scattering Studies of the Surface Structure and Dynamics of Liquids and Liquid Films
Authors: Kim Hyunjung , Jiang Zhang , Lee Heeju , Lee Young Joo , Jiao Xuesong , Li Chunhua , Lurio Laurence , Hu Xuesong , Lal Jyotsana , Rafailovich Miriam , Sinha Sunil K
Published: April 2011

The dynamics of surface fluctuations in thin supported polystyrene films have been investigated using x-ray photon correlation spectroscopy (XPCS) in reflection geometry. The results from the films thicker than four times of the radius of gyration (Rg) of polystyrene show the behavior of the capillary waves expected in viscous liquid. However, thinner films show a deviation indicating the need to account for viscoelasticity. Theoretical considerations with viscoelastic liquid model has been performed by introducing frequency dependent viscosity and compared with Fredrickson’s brush model (Macromolecules, 25, 2882 (1992)). The theory has been extended to the surface and interfacial modes in a bilayer film system. The results will be discussed in terms of surface tension, viscosity, and shear modulus.
Creating Nanostructures with Controllable Sidewall Profiles for Mechanical Sensor Applications
Authors: Zhao Yi , Zhang Xin
Published: April 2011

This paper presents a novel approach to create silicon nanostructures with controlled sidewall profiles. The nanostructures are fabricated by alternating the reactive ion etching process and the exposure process to the atmosphere with moisture. The air exposure is believed attributed to the sidewall passivation by facilitating the fast formation of a thin SiO2/SiOxFy layer. Using this approach, three types of representative nanostructures are demonstrated, namely: nanopillars with vertical sidewall, nanopillars with narrowed necks, and suspending nanocantilevers. Without requiring expensive facilities and extensive expertise, this work is expected to provide an alternative for developing nanostructures with a variety of geometric profiles for mechanical sensing applications.
Vanadium Oxide Nanostructures: Growth, Characterization and Applications
Authors: Mathur Sanjay , Ruegamer Thomas
Published: April 2011

Vanadium oxide nanostructures (V2O5 and VO2) were obtained by chemical vapor deposition of the alkoxide precursor [VO(OPri)3]. The nanomaterials were studied with respect to their morphological features (HR-SEM) and phase structure (XRD) followed by characterization as resisitive-type gas sensors. Given the high surface area, vanadium oxide (VOx) nanostructures show significant sensor response via resistance change upon reaction induced by carbon monoxide and desorption of adsorbed oxygen at 400 °C. Tin-doped VOx showed enhanced sensitivity of the films which suggests a higher number of active sensing sites or alternations in the intrinsic electrical properties of VOx by addition of SnO2 as dopant.
Microstructure and ferroelectric properties of ultrathin PbTiO3 films by MOCVD
Authors: Fujisawa Hironori , Horii Toru , Takashima Yoshiyuki , Shimizu Masaru , Kotaka Yasutoshi , Honda Koichiro
Published: April 2011

We report on microstructure and ferroelectric properties of ultrathin PbTiO3 films epitaxially grown on SrTiO3(100), La-doped SrTiO3(100) and SrRuO3/SrTiO3(100) by MOCVD. High angle annular dark field scanning transmission electron microscopy, atomic force microscopy, x-ray diffraction and x-ray reflectivity measurements demonstrated that 1-20 monolayer (ML)-thick epitaxial PbTiO3 films had high-crystallinity, atomically flat surface and sharp interface at an atomic scale. The epitaxial relationship and thickness were also confirmed by these methods. Kelvin force probe microscopy and contact resonance piezoresponse force microscopy revealed that a 7ML (2.7nm)-thick PbTiO3 film grown on SrRuO3/SrTiO3 had the ferroelectric polarization.
Influence of Crystal Phase and Orientation on Electro-Optic Effect of PLZT Epitaxial Films
Authors: Sato Keisuke , Ishii Masatoshi , Kondo Masao , Kurihara Kazuaki
Published: April 2011

Lanthanum-modified lead zirconate titanate and lead zirconate titanate epitaxial films with (100) and (111) orientations are grown respectively on (100) and (111) niobium, lending conductivity to strontium titanate through chemical solution deposition. This study investigates changes in the ordinary and extraordinary refractive index no and ne induced by the electric field in these films using the prism-coupling method. Anisotropic electrooptic effects arise from Pockels effect and switching among polar clusters. Isotropic electrooptic effect is realized on PLZT 8/65/35 and PZT 70/30 of (100) epitaxial films.
The effects of PBB on the dielectric properties of BST film
Authors: Kim Jin Cheol , Oh Jun Rok
Published: April 2011

The mixture of PbO-Bi2O3-B2O3 (PBB) were formed on the Ba0.5Sr0.5TiO3 (BST) film and the effects of PBB phase on the dielectric properties of the BST film were investigated. The amorphous PBB layer was deposited on the BST film using rf magnetron sputtering and diffused into the film by heat treatment. The PBB phase in BST film was identified by energy dispersive spectrometer (EDS). Dielectric properties of BST film were significantly improved after the diffusion of PBB. The leakage current density of BST film decreased from 3.24×10-5 A/cm2 to 9.45×10-8 A/cm2 at 1.5 V and the dielectric constant increased from 238 to 533. These results show that the diffusion of insulating metal oxide into the ferroelectric thin film can improve the dielectric properties of the film.
Phase Transition Temperature of Ferroelectric Thin Film Evaluated by Four-State Potts Model
Authors: Chung Wing Yee Winnie , Lo Veng Cheong
Published: April 2011

An epitaxial ferroelectric thin film can be modeled by a two-dimensional array of dipoles. The orientation of each dipole is assigned to one of the four possible states which are mutually perpendicular to each other. Consequently, the whole film can be divided into domains with both 90° and 180° domain walls. The dominant switching mechanism for individual dipole is implemented by a 90° rotation. Two different conditions have been considered. For the first one (model A), every dipole inside the film is allowed to rotate, provided that it is thermally activated. For the second (model B), only the dipole rotation is restricted to those at the domain walls. The phase transition temperatures under these two models have been evaluated. Furthermore, the effects of sample size and boundary condition are discussed.
Silicon Carbide Growth: C/Si Ratio Evaluation and Modeling
Authors: Pons Michel , Nishizawa Shin-Ichi , Wellmann Peter , Blanquet Elisabeth , Chaussende Didier , Dedulle Jean Marc
Published: April 2011

Modeling and simulation of the SiC growth processes, Physical Vapor Transport (PVT), Chemical Vapor Deposition (CVD) and hybrid techniques, are sufficiently mature to be used as a training tool for engineers as well as a growth machine design tool, e.g. when building new process equipment or up-scaling old ones. It is possible (i) to simulate accurately temperature and deposition distributions, as well as doping (ii) to quantify the limiting phenomena, (iii) to understand the important role of different precursors in CVD and hydrogen additions in PVT. The first conclusion of this paper is the importance of the "effective" C/Si ratio during CVD epitaxy in hot-wall reactors and its capability to explain the doping concentrations. The second conclusion is the influence of the C/Si ratio in alternative bulk growth technique involving gas additions. Preliminary results show that fine tuning of H2 or precursor additions allow a better control of concentrations of residual and intentional doping.
Characterization of SiC Materials and Devices by SIMS
Authors: Li Yupu , Gao Yumin
Published: April 2011

Based on the various implanted standards, we have used SIMS (Secondary Ion Mass Spectrometry) to characterize SiC materials and devices. We develop the SIMS analysis on 2'' and 3'' full SiC wafers using our customized sample load chamber at a Cameca 4f magnetic sector SIMS tool. This feature is particularly useful for the on-line control of the wafer processing. With our special mounting skills, we provide SIMS analyses on small patterned area (say 50 microns × 50 microns or larger) of the tiny or large SiC dies. The detailed comparison between the implanted profiles for the major dopants (such as B, Al, and N) measured by SIMS and the simulated profiles by SRIM code [1] will be discussed. The detection limits for selected elements will also be discussed. In addition, it is well know that nitrogen has a very high ionization potential and zero electronic affinity. Therefore, nitrogen is normally profiled with a Cs+ primary beam and monitored negative molecular ions of (matrix+N)- [such as (Al+N)- in Al [2], (Si+N)- in Si, and (C+N)- in SiC]. However, such negative molecular detection mode cannot be applied to the multi-layers with different matrix elements (such as Al/SiC and Cu/SiC samples). Fortunately, like to detect nitrogen in Cu [3], we have found that using a Cs+ primary ion beam and monitoring (Cs2N)+ molecular ions by Cameca magnetic sector SIMS tools, nitrogen in the multi-layer samples including SiC layer can be detected by the (Cs2N)+ detection model [3,4] with a very low profiling energy (such as 2.5keV).
Development of PECVD SiC for MEMS Using 3MS as the Precursor
Authors: Du Jiangang , Singh Neha , Summers James B. , Zorman Christian A.
Published: April 2011

This paper reports our effort to develop amorphous hydrogenated silicon carbide (a-SiC:H ) films specifically designed for MEMS applications using a semiconductor-grade organosilane known as trimethylsilane (3MS) as the precursor. In our work, the a-SiC:H films were deposited in a commercial PECVD system at a fixed temperature of 350˚C using 3MS diluted in helium (He). Films with thicknesses from ~ 100 nm to ~ 2μm, a typical range for MEMS applications, were deposited. Deposition parameters such RF power, deposition pressure, and 3MS-to-He ratio were explored to obtain films with low residual compressive stresses. Low temperature, post-deposition annealing at 450˚C was used to convert the as-deposited compressive residual stresses to moderate tensile stresses, which are desired for micromachined bridges, membranes and other anchored structures. Compositional analysis indicated that films with a Si-to-C ratio of 1 could be deposited under certain conditions. Mechanical properties such as Young's modulus and fracture strength were derived from the load-deflection behavior of micromachined freestanding membranes. Nanoindentation was used to verify the Young's modulus and determine the hardness. As expected, the films exhibit insulating properties with a relative dielectric constant at 3.90 for as-deposited films and 2.69 after annealing at 1100˚C, as determined from C-V measurements. Chemical inertness was tested in aqueous, corrosive solutions such as KOH and HNA. Prototype structures were fabricated using both surface micromachining and bulk micromachining techniques to demonstrate the potential of the a-SiC:H films for MEMS applications.
A Study of V3+/4+ Levels in Semi-insulating 6H-SiC using Optical Admittance and Electron Paramagnetic Resonance Spectroscopies
Authors: Lee Wonwoo , Zvanut Mary E
Published: April 2011

The purpose of this study is to identify the vanadium acceptor levels in semi-insulating (SI) 6H-SiC using optical admittance spectroscopy (OAS) and electron paramagnetic resonance (EPR) spectroscopy. OAS conductance peaks near at 0.67 ± 0.02 eV and 0.70 ± 0.02 eV are identified as V3+/4+ levels at the quasi-cubic sites. An OAS peak at 0.87 eV is assigned to the same transition at the hexagonal site. EPR measurements before illumination revealed the characteristic spectrum of V3+. The presence of the V3+ signal supports the identification of the OAS peaks as transitions from the V3+/4+ level to the conduction band. Photo-induced EPR measurements reveal a change in the intensity of V3+ and V4+ at 0.8 ± 0.1 eV, where the amplitude of the V3+ charge state decreases and that of V4+ increases by approximately equal amounts. Although the individual sites are not resolved in the photo-induced EPR data, the 0.8 eV feature strongly supports the assignment of the three OAS peaks as acceptor levels.
Ion Implanted p+/n 4H-SiC Junctions: effect of the Heating Rate during Post Implantation Annealing
Authors: Nipoti Roberta , Carnera Alberto , Bergamini Fabio , Canino Mariaconcetta , Poggi Antonella , Solmi Sandro , Passini Mara
Published: April 2011

Structural, morphological and electrical characteristics of Al-implanted p+/n 4H-SiC diodes are compared for the same implantation process and post implantation annealing with identical stationary and cooling cycles but different heating velocity. Al+ ions were implanted at 400°C, with energies in the range 250-350 keV and total fluence of 1.2×1015 cm−2. Post implantation annealing processes were done at 1600°C for 30 min with a constant heating velocity in the range 7 – 40°C/sec and an abrupt cooling cycle. Gas in the annealing ambient was high purity Ar. The Al depth profile of annealed and as implanted samples were equal except for concentrations below 10E17 cm−3 where the former profiles showed a diffusion tail. With the increase of the heating velocity of the post implantation annealing process, sheet resistance of the Al implanted layer and diode leakage currents decrease while the surface roughness increases.
Effects of Different Defect Types on the Performance of Devices Fabricated on a 4H-SiC Homoepitaxial Layer
Authors: Chen Hui , Raghothamachar Balaji , Vetter William , Dudley Michael , Wang Y. , Skromme B. J.
Published: April 2011

An 8° off-axis 4H-SiC wafer with circular Schottky contacts fabricated on a CVD grown 4H-SiC homoepitaxial layer was studied to investigate the influence of various defects, including small (closed-core) screw dislocations (Burgers vector of 1c or 2c), hollow-core (micropipes; Burgers vector larger than 2c), threading edge dislocations (from conversion of basal plane dislocations from the substrate into the epilayer), grain boundaries and triangular defects, on the device performance in the form of breakdown voltages. The defects were examined using synchrotron white beam x-ray topography (SWBXT) based techniques and molten KOH etching. The devices commonly contained basal plane dislocations, small screw dislocations and threading edge dislocations, the latter two of which could give rise to low breakdown voltages for the devices. In addition, less commonly observed defects such as micropipes, grain boundaries and triangular defects are much more destructive to device performance than closed-core screw dislocations and threading edge dislocations.
Photopolymerization and Metalization for Fabricating Functional Devices and Metamaterials
Authors: Kawata Satoshi , Tanaka Takuo , Takeyasu Nobuyuki , Nakanishi Sana
Published: April 2011

We present three-dimensional micro/nano-fabrication techniques to create new photonic and functional devices. We have demonstrated two-photon-induced photopolymerization for fabricating 3D micro/nano-structures [1, 2]. In this method, arbitrary three-dimensional polymer structures are fabricated by scanning tightly focused infrared femto-second laser in three dimensions. Recently, we extended this technique to fabricate functional micro devices including photonic band-gap crystals [3] and movable micro-springs. The shrinkage of polymer during polymerization is utilized to reduce the structure size beyond the diffraction limit of light [4]. A micro-lens array with 2500 lenses is used to produce a mass of structures in parallel. By using this micro-lens array system, we fabricated 800 micro-springs and micro-cubic structures by single laser scanning [5]. In this presentation, metalization of fabricated polymer structures will also be described. We coat metal on the surface of polymer by electroless metal plating, but not on the glass substrate [6]. Hydrophobic coating was pre-made on the glass substrates and polymer surface is modified with Sn2+-ions. With this method micro-coil array is metalized [7]. Micro-coil array exhibits negative refraction due to the excitation of magnetic field through coils. We would like to show our design of the structure [8]. In the end, we talk about our newly invented diffraction-free imaging with nano metal rod array [9].
Fabrication of Polymeric Composite Nanostructures Containing Ferritin Nanoparticles and Carbon Nanotubes
Authors: Shin Min Kyoon , Park Sang Jun , Yoon Seong Gil , Lee Chang Kee , Shin Kwang Min , Shin Su Ryon , Gu Bon Kang , Kim Min Sup , Kim Yu Jin , Kim Seon Jeong
Published: April 2011

Composite nanofibers including ferritin nanoparticles or multiwalled carbon nanotubes (MWCNTs) were fabricated to enhance the physical properties of the nanofibers, such as the elastic modulus and electrical conductivity. The ferritin was homogeneously incorporated in the polymeric nanofibers, but excess carbon nanotubes (CNTs) added to the polymer solution resulted in the fabrication of composite nanofibers with rough surfaces. PVA/ferritin/CNT composite nanofibers were fabricated that had smooth surfaces, and had a good dispersion of ferritin and CNTs. These composite nanofibers are applicable to artificial muscles requiring enhanced physical properties.
Effects of the Ultra Low Diluted Ceria-Based Slurry on the Planarization Characteristics of Multi-Layer Exposed Surfaces
Authors: Hwang Kyung Ho , Choi Jae Gon , Lee Myung Shin , Choi Yong Soo , Choi Geun Min , Song Yong Wook
Published: April 2011

Planarization characteristics of ultra low diluted Ceria (CeO2) based slurry, especially a multi-layered Chemical Mechanical Polishing (CMP) process, have been studied. The multi-layer represents the polished film consists of more than two different materials, so that, more than two different materials are exposed to the polished surface. In this work, ultra low diluted ceria based slurry was introduced to minimize micro-dishing effect of the process such as a storage node contact and a bit line contact in 80nm feature sized DRAM device, which has multi-layer film surfaces. As a result, we can minimize micro dishing of silicon dioxide and polycrystalline silicon at memory cell area, and silicon dioxide dishing at peripheral area.
Rapid Synthesis of Dielectric Films by Microwave Assisted CVD
Authors: Ndiege Nicholas , Subramanian Vaidyanathan , Shannon Mark , Masel Rich
Published: April 2011

Film deposition methods have been the focus of renewed interest in the past decade due to calls for cheaper and more environment friendly deposition techniques as well as better quality of films. This paper describes a novel deposition technique: Microwave assisted chemical vapor deposition (MACVD). This technique utilizes inexpensive equipment and works at temperatures close to room temperature and ambient pressures. Deposition rates are very high (>1 micron a minute) and the resulting films are of high quality i.e. high density, stability. Conventional deposition techniques such as epitaxy, e-beam evaporation and LPCVD can achieve high quality films but the financial and environmental costs are high. This study considers the MACVD of a high k dielectric film (Ta2O5) on silicon for dielectric and insulation applications. Films generated are dense and stable with thicknesses varying from 60 nm to 62 microns. Depth profile studies of 575nm thick MACVD derived films show results similar to that of high quality films generated via MOCVD. Characterization of the resulting films was done using XRD, SEM, XPS, AES and profilometry techniques.
Stack of BioCells Converting ATP to Electrical Power and Possible Applications
Authors: Sundaresan Vishnu Baba , Sarles Stephen Andrew , Leo Donald J.
Published: April 2011

Plant and animals convert absorbed nutrients into the most readily available form of biochemical energy in cells - Adenosine triphosphate (ATP). Ion transporter proteins in the cell membranes hydrolyze ATP and use the energy from the reaction for ion transport across cell membranes. The BioCell is an energy conversion device inspired by ion transport through cell membranes that uses a proton-sucrose cotransporter (SUT4) to convert the chemical energy in ATP into electrical energy. Experiments on a single cell demonstrated that the BioCell behaves like a constant current power source with 10 - 22 kΩ internal resistance. The single cell developed a peak power of 0.7 μW per cm2 of bilayer lipid membrane (BLM) area reconstituted with 1 mg of SUT4 and 1 μl of ATP-ase at 10 kΩ load in the external circuit. The actual peak power output from the cell was 160 nW for a BLM area of 0.079 cm2 carrying 0.2 mg of SUT4 and 15 μl of ATP-ase. The 160 nW of electrical power that could be sourced from the cell with a 10 kΩ load (41 mV and 4 μA) is not sufficient to run a low power electronic device and needs to be scaled up to few microwatts. This article discusses our experimental results from stacking a BioCell in series and parallel to develop higher stack voltage and current. We observe that the cell voltage adds linearly by connecting the BioCells in series and a 10-cell stack developed a peak power of 750 nW (500 mV @ 2.5 μA observed at 265 kΩ. The peak power from the stack by connecting the cells in parallel was 1.4 μW (125 mV and 11.2 μA) at 1kΩ. The experimental results demonstrate that the power from a single cell can be scaled by connecting them in series and in parallel without appreciable losses. A survey of electronic devices indicated that a minimum of 20 μW will be required to run a demonstration application from a stack and also gives us the direction to scale the power output from a single cell.
Interactions Between Chemical Functionality and Nanoscale Surface Topography Impact Fibronectin Conformation and Neuronal Differentiation on Model Sol-gel Silica Substrates
Authors: Jedlicka Sabrina , Leavesley Silas J. , Little Kenneth M , Robinson J. Paul , Nivens David E. , Rickus Jenna L.
Published: April 2011

Functional relationships between the biomaterial interface and extracellular matrix (ECM) proteins are intimately involved in cellular adhesion and function. Structural changes of ECM proteins upon adsorption to a surface alter the protein's biological activity by varying the availability of molecular binding sites. Recent work using native and organically modified sol-gel silica as a neuronal biointerface revealed that changes in surface nanotopography of bulk versus thin film materials result in dramatic differences in fibronectin structure, cell survival, and neuronal differentiation. In order to further investigate interactions between chemical functionality and surface topography, we evaluated the global conformation of human fibronectin adsorbed to seven different organically modified silica gels and thin films. Chemical functional groups were introduced into the materials either by altering the starting precursor or by doping with poly-l-lysine or polyethylenimine. Surface topography measurements by atomic force microscopy show that films have surface features less than 25 nm while bulk materials of the same precursor chemistry have features ranging from 50 – 100 nm in size. Fluorescence resonance energy transfer spectroscopy (FRET) revealed a strong interaction between surface topography and chemical functionality. Fibronectin remain globular on all bulk materials regardless of chemical modification. The same changes in precursors or dopant chemistry, however, induced changes in the conformation of fibronectin on the thin films. The differentiation of PC12 cells on the surface indicated a strong impact of the surface features and suggest a possible optimal fibronectin folding state.
Cell Viability and Adhesion on as Grown Vertically Aligned Carbon Nanotubes√
Authors: Lobo Anderson O. , Antunes Erica F. , Palma Mariana B. S. , Pacheco-Soares Cristina , Trava-Airoldi Vladimir J. , Corat Evaldo J.
Published: April 2011

This work studies cell viability and cell adhesion on as grown dense films of vertically aligned carbon nanotubes (MWCNT). The MWCNTs were produced by a microwave plasma chemical vapor deposition (2,45GHz) on silicon (Si) and titanium (Ti) surfaces, using a nickel and iron catalyst, respectively. The citotoxicity tests (MTT assay and cellular adhesion) were evaluated by various incubations times with Fibroblast L929 mouse cells. The results show very high cell viability and many layers of cells adhered on the surface formed by the nanotubes tips at films grown on Si surfaces. The MWCNT grown on Ti surfaces presented lower cell viability and a reduced number of cells on the surface formed by the nanotubes tips. The different behavior is most probably related to excess iron contamination present in the case of titanium substrate, while nickel catalyst is probably enclosed by the nanotubes.
Decreased Macrophage Density on Carbon Nanofiber Patterns
Authors: Kim Jong Youl , Khang Dongwoo , Lee Jong Eun , Webster Thomas J.
Published: April 2011

In this study, we describe the selective adhesion 4 hour and proliferation 24 hour and 4 days of inflammatory cells (specifically, macrophages) on aligned carbon nanofiber/nanotube patterns on a polymer matrix. The results showed for the first time that macrophage adhesion and proliferation on aligned Carbon nanofibers (CNFs) was significantly less than on the polymer matrix. The present in vitro study thus provided evidence of the ability of CNFs to down-regulate macrophage adhesion and proliferation important to decrease harmful body reaction, which is imperative for the future consideration of CNFs for numerous implant applications.
Functionalized Waveguides for Biological Assays
Authors: Anderson Aaron S. , Dattelbaum Andrew M. , Montaño Gabriel A. , Schmidt Jurgen G. , Martinez Jennifer S. , Grace W. Kevin , Grace Karen M. , Swanson Basil I.
Published: April 2011

We report here a procedure for the functioalization of SiO2-coated, SiONx waveguides for biological assays. Surface functionalization occurs by self-assembly of an amine-terminated silane monolayer on the waveguide, followed by partial chemical modification with functionalized polyethylene glycol (PEG) groups. Functionalized surfaces were characterized by atomic force microscopy and contact angle measurements. When combined with a BSA blocking step, these functional PEG surfaces significantly reduced non-specific binding and allowed for specific binding to occur. An antibody sandwich assay for detection of Bacillus anthracis protective antigen was used to validate these surfaces for sensing applications.
Inkjet Printing of Biomedical Adhesives
Authors: Doraiswamy Anand , Sumerel Jan , Wilker Jonathan , Narayan Roger J
Published: April 2011

Synthetic adhesives have largely displaced natural adhesives in the automotive, aerospace, biomedical, electronic, and marine equipment industries over the past century. We have demonstrated the thin film deposition of biological adhesives using piezoelectric inkjet technology. A MEMS based piezoelectric actuator was controlled to jet uniform fluid flow of the adhesive solution through the ink jet nozzles. Microscopic deposition of adhesives enables improved bonding for a range of advanced electronic and biomedical applications. By printing such small and spatially aligned drops, bond lines between materials are reduced, ultimately resulting in increased bond strength and structural integrity. Piezoelectric ink jet deposition of biological adhesives may greatly improve wound repair in next generation eye repair, fracture fixation, organ fixation, and wound closure.
In vitro Evaluation of Macrophage Adhesion and Proliferation on Alumina
Authors: Liu-Snyder Peishan , Webster Thomas J.
Published: April 2011

Extensive interactions of inflammatory cells (such as macrophages) with biomaterials at the host-implant interface are often blamed for failure of implanted biomedical devices [1]. While previous studies have shown increased in vitro and in vivo bone cell (osteoblast) responses on nanophase ceramics [2], few (if any) studies have been conducted to elucidate inflammatory cell responses on such novel materials. In this study, we reported that macrophage adhesion and proliferation on nanophase (97.7 nm grain size) alumina (Al2O3) was significantly less than conventional (187.4 nm grain size) alumina, respectively, after 4, 12, 24 h. The present study provides evidence of the ability of nanophase alumina to down-regulate macrophage adhesion and proliferation, which is imperative for the future consideration of nanophase materials for orthopedic and dental applications.
Increased Osteoblast Adhesion on Nanograined Hydroxyapatite and Tricalcium Phosphate Calcium Titanate Composites
Authors: Liu Huinan , Ergun Celaletdin , Halloran John W. , Webster Thomas J.
Published: April 2011

Depending on the coating method utilized and subsequent heat treatments (such as through the use of plasma-spray deposition), inter-diffusion of atomic species across titanium (Ti) and hydroxyapatite (HA) coatings may result. These events may lead to structural and compositional changes that consequently cause unexpected HA phase transformations which may clearly influence the performance of an orthopedic implant. Thus, the objective of the present in vitro study was to compare the cytocompatibility properties of chemistries that may form at the Ti:HA interface, specifically HA, tricalcium phosphate (TCP), Ti doped HA, and those containing calcium titanate (CaTiO3). In doing so, results of this in vitro study showed that osteoblast adhesion increased with greater CaTiO3 substitutions in either HA or TCP. Specifically, osteoblast adhesion on HA and TCP composites with CaTiO3 was almost 4.5 times higher than over pure HA. Material characterization studies revealed that enhanced osteoblast adhesion on these compacts may be due to increasing shrinkage in the unit lattice parameters and consequent decrease in grain size. Although all CaTiO3 composites exhibited excellent osteoblast adhesion results, Ca9HPO4(PO4)5OH phase formation into TCP/CaTiO3 increased osteoblast adhesion the most; due to these reasons, these materials should be further studied for orthopedic applications.
Fabrication of Carbon Nanotube Langmuir-Blodgett Film by Polyion Complex Method
Authors: Matsui Jun , Iko Manabu , Inokuma Nobuhiro , Orikasa Hironori , Kyotani Takashi , Miyashita Tokuji
Published: April 2011

Carbon nanotube Langmuir-Blodgett film was fabricated using polyion complex method. Multi-walled carbon nanotube (MWCNT) synthesized by template method form a stable polyion complex monolayer at the air/water interface. The monolayer can be transferred onto a solid substrate. The AFM image of the monolayer shows a one-dimensional network structure of MWCNT..
Improvement of Emission Current by Using CNT Based X-ray Tube
Authors: Choi Haeyoung , Kim Jong Uk
Published: April 2011

Studies on the electronic structure of carbon nanotube (CNT) are of much importance because of its efficient utilization in electronic vacuum devices [1]. These CNTs have many applications such as field emission display (FED), LCD backlight units, microwave amplifiers, lighting lamps, x-ray sources and so on. One of these applications is the electron emitter for x-ray source. In order to obtain x-ray images of relatively hard instruments or components such as PCB board or machine tools, high quantity of x-ray current is generally required. In this study, we report that the current density of x-ray source can be greatly enhanced by using the CNT emitter as a cathode. In general, the emission current of CNT emitter is very sensitive to gap distance between CNT emitter and grid metal mesh. In addition, the emission current is appeared to be different with respect to the kinds of metal meshes and their sizes employed in the measurement. Extensive results of these were reported in our recent works [2]. For example, as the distance between CNT emitter and grid metal mesh was getting shorter, the current density of the triode was getting larger. Detailed parameters and corresponding results were presented and some preliminary x-ray images were obtained and discussed in this study.
Geometry Dependent Resistivity in Single-walled Carbon Nanotube Films Patterned Down to Submicron Dimensions
Authors: Behnam Ashkan , Noriega Leila , Choi Yongho , Wu Zhuangchun , Rinzler Andrew G , Ural Ant
Published: April 2011

We demonstrate patterning of SWNT films down to 200 nm lateral dimensions using e-beam lithography and reactive ion etching with good selectivity and directionality and then we fabricate standard four-point-probe structures to characterize the resistivity of these films as a function of device geometry. The resistivity is found to be independent of device length for a given width and thickness, while increasing over three orders of magnitude compared to bulk films, as the width and the thickness of the films shrink. In particular, the resistivity of SWNT films starts to increase with decreasing device width below 20 μm, exhibiting an inverse power law dependence on device width at sub-micron dimensions. We explain this behavior by a purely geometrical argument. Although the “top-down” patterning of nanotube films allows for their use in sub-micron device structures and perhaps their integration into standard silicon fabrication technology, the resistivity scaling is an important effect that needs to be taken into account when fabricating small devices in which nanotube film transport characteristics play a vital role.
Spin-Orbital Coupling Effects on Magnetoresistance in Organic Light-Emitting Diodes
Authors: Hu Bin , Wu Yue
Published: April 2011

The magnetoresistance of conjugated polymer poly [2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) based organic light-emitting diodes (OLED) was investigated at both forward and reverse bias at liquid nitrogen temperature. We find that the reverse bias yields a largely increased magnetoresistance when the electron-hole capture zone is away from the metal electrode as compared to the forward bias with the electron-hole capture zone close to the metal electrode. The electroluminescence suggests that the deposited metal atoms enhance the spin-orbital coupling at the polymer/metal interface and consequently lead to electron-hole capture zone-dependent magnetic field effects in organic semiconductor devices.
Highly Reproducible Electric Bistability in an Organic Single Layer Device with Ag Top Electrode
Authors: Terai Masaya , Fujita Katsuhiko , Tsutsui Tetsuo
Published: April 2011

High reproducible electrical bistability was observed and we deliberated its working mechanism through measurements of dynamic dielectric response in single organic layer sandwiched structure using top Ag electrode. The electrical transition between high-impedance state (OFF state) and low-impedance state (ON state) happened by the change of applied voltage patterns. Distinction between the OFF state and the ON state was not induced by change of static charge accumulation but reflected the difference of the response of mobile electric careers in the organic film. We proposed plausible working mechanism of transition from the pristine state to the bistable state. Namely, the electrical bistable state of our device is generated by penetration of Ag nanoparticles and creation of charge pathways across the organic film.
Molecular Multilayer Organic Solar Cells with Large Excitonic Diffusion Length
Authors: Yoo Seunghyup , Potscavage William J , Domercq Benoit , Han Sung-Ho , Levi Dean , Kippelen Bernard
Published: April 2011

We report on the photovoltaic properties of organic solar cells based on pentacene and C60 thin films. A peak external quantum efficiency (EQE) of 69 % at a wavelength of λ = 668 nm is achieved upon optimization of the exciton blocking layer (EBL) thickness. Complex optical functions of pentacene films are measured as a function of wavelength by spectroscopic ellipsometry and used to analyze the EQE spectra. Detailed analysis of the EQE spectra indicate that the pentacene layers exhibit large excitonic diffusion lengths of ∼70 nm and that the performance improvement in EQE can be attributed to the influence of the thickness of the EBL layer on the carrier collection efficiency.
Robust Circular Polarized Emission from Nanoscopic Single-Molecule Sources: Application to Solid State Devices
Authors: Hassey Ruthanne , Swain Ellen J , Hammer Nathan I , Richards Emily L , Venkataraman Dhandapani , Barnes Michael D
Published: April 2011

Controlling the polarization state of fluorescence emission in solid state devices is an important goal in optical display technologies. High-purity (right or left) circular polarized emission is particularly desirable because an arbitrary linearly polarized state can be generated with much higher efficiency (lower loss) as compared with a non-polarized fluorescence input. Here we discuss observation of resonant chiroptical effects (fluorescence detected circular dichroism (FDCD), and circular polarized luminescence (CPL)) from single (bridged-triarylamine) helicene molecules in a solid-film format. In the FDCD experiment using 457-nm excitation – an excitation wavelength where the bulk circular dichroism is negligible – single-molecule fluorescence from enantiomerically pure helicene samples show surprising distribution of dissymmetry (g) parameters centered near zero but with a significant contribution from molecules showing an almost perfectly pure response to either right or left circularly polarized light. Experiments combining a well-defined circularly polarized excitation (either right or left) with decomposition of the fluorescence into left- and right-circular polarization component show only a weak correlation between the dissymmetry (sign and magnitude) of the CPL with the polarization state of the input. Current efforts are directed at wavelength resolved CPL, FDCD at wavelengths that are more closely match to bulk circular dichroism features, and orientational dependence of FDCD and CPL. These results provide new insight into chiroptical properties of chiral fluorophores at the single molecule level and suggests new optical device possibilities with chiral fluorophores.
Exciton and Defect Photoluminescence Signatures in Single Crystal Rubrene
Authors: Mitrofanov Oleg , Lang David V , Kloc Christian , Siegrist Theo , So Woo-Young , Sergent Michael A , Ramirez Arthur P
Published: April 2011

Radiative recombination processes provide valuable information about exciton dynamics and allow detection of defects in rubrene crystals. We demonstrate that the photoluminescence spectra of crystalline rubrene reflect exciton dissociation through oxygen-related defects in addition to the direct exciton recombination. The defect-assisted exciton dissociation results in a well-defined photoluminescence band. These defects play an important role in charge transport. Dark- and photo-conductivity is higher in rubrene crystals with a large density of the defects. The observations strongly suggest that the oxygen-related defect forms a bandgap state and acts as an acceptor center in crystalline rubrene.
Requirements and Constraints on Optimizing UV Processing of Low-k Dielectrics
Authors: Berry III Ivan L , Waldfried Carlo , Durr Kevin
Published: April 2011

UV curing of low-k dielectrics presents a unique challenge in that the cure process is expected to do the impossible – increase hardness, modulus, cohesive strength, adhesion and reliability, decrease water absorbtion and dielectric constant, remove porogens (for porogen containing films), improve dielectric breakdown and chemical stability, all while minimizing shrinkage and contributions to film stress. Achieving this, in general, requires optimization of all of the cure parameters, such as UV spectral intensity, temperature, time, pressure, background gas, and process sequence, as well as the formulation of the low-k material itself. The spectral dependence of many of these important parameters will be discussed. A good figure of merit for modulus and k-value is the ratio of modulus/k-value. If one plots the spectral response of this ratio, one finds it peaks at a specific wavelength range. In principle it is possible to measure the UV spectral response of all of the critical parameters (not just modulus and k-value) and by overlaying these responses together determine what the proper UV exposure wavelength ranges should be. An example of this will be shown for an idealized porogen containing low-k material, for modulus, k-value, porogen removal and porogen crosslinking. A real low-k dielectric system has many more wavelength parameters to consider and the problem of bulb spectral intensity optimization becomes complex. It is also found that the relative intensity of the important wavelength bands also plays a significant role, requiring a great deal of spectral optimization experiments.

UV cure performance is also dependent on cure temperature, time, background gases and ironically, the deposition or post-deposition bake temperature. Most cure parameters such as modulus, hardness, leakage, adhesion, etc, have a strong and generally exponential dependence on cure temperature. As a result, most UV cures are performed at the highest temperature allowable as defined by thermal budget constraints and copper voiding thresholds. Background ambient can also play a critical role in the UV cure, especially for porous low-k materials and those containing porogens. Changes in composition of the background gases can alter interface. The ultimate in performance is obtained when the low-k material formulation itself is included as a key parameter in the cure optimization. By optimizing the material, UV spectrum, and cure parameters together, significant improvements can be made.

In conclusion, UV curing cannot be implemented without serious consideration to the wavelength dependence on many critical process factors. The interdependence of all components that makeup the optical system such as the wavelengths employed, light source technology, chamber design and ironically, the dielectric film itself must be considered. Only with these factors in mind, can the full benefit of UV curing be realized.
The Role of Pore Characterization in the Challenge to Integrate Porous low-k Dielectrics
Authors: Gidley David W. , Vallery Richard S. , Liu Ming
Published: April 2011

Extended abstract to Symposium B
Extendibility of the PECVD Porogen Approach for ULK Materials
Authors: Gourhant Olivier , Jousseaume Vincent , Favennec Laurent , Zenasni Aziz , Maury Patrick , Mage Lucile , Gonon Patrice , Vincent Gilbert
Published: April 2011

The increase of integrated circuits performances requires ultra-low dielectric constant (ULK) materials to minimize the drawbacks of miniaturization. Amorphous SiOCH are promising candidates for ULK materials as porosity can be introduced via a two steps elaboration. In a first step, organo-silicon species and organic species are co-deposited by PECVD. Then, a thermal annealing, alone or assisted by UV radiation, removes the organic labile phase and creates pore inclusions into the final material. In this work, the extendibility of this porogen approach is investigated in order to lower the dielectric constant. An increase of the porogen loading in hybrid film is studied by tuning the precursors ratio injected in the plasma gas feed. The increase of organic species amount is operated in order to create more pores sites. However, the post-treatment does not lead automatically to higher porosity. Actually, an increase of the porosity is observed only until a porogen loading limit and decreases above this limit. The shrinkage of the film during the post-treatment can explain this limitation. For high ratios of porogen, the film shrinkage increases drastically and leads to a decrease of the porosity finally created. At last, the link between porosity and dielectric constant is enlightened and a minimum in term of K value is reached with both post-treatments: dielectric constant of 2.1 and 2.3 are obtained using respectively thermal treatment and UV curing.