bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanisms of Stacking Fault Growth in SiC PiN Diodes
Authors: Stahlbush R. E. , Twigg M. E. , Sumakeris J. J. , Irvine K. G. , Losee P. A.
Published: April 2011

The early development of stacking faults in SiC PiN diodes fabricated on 8° off c-axis 4H wafers has been studied. The 150μm drift region and p-n junction were epitaxially grown. The initial evolution of the stacking faults was examined by low injection electroluminescence using current-time product steps as low as 0.05 coul/cm2. The properties of the dislocations present before electrical stressing were determined based on previously observed differences of Si-core and C-core partial dislocations and the patterns of stacking fault expansion. The initial stacking fault expansion often forms a chain of equilateral triangles and at higher currents and/or longer times these triangles coalesce. All of the faulting examined in this paper originated between 10 and 40 μm below the SiC surface. The expansion rate of the bounding partial dislocations is very sensitive to the partials' line directions, their core types and the density of kinks. From these patterns it is concluded that the stacking faults originate from edge-like basal plane dislocations that have Burgers vectors either parallel or anti-parallel to the off-cut direction. Evidence for dislocation conversions between basal-plane and threading throughout the epitaxial drift region is also presented.
Challenges and Rewards of Low-Abrasive Copper CMP: Evaluation and Integration for Single-Damascene Cu/Low-k Interconnects for the 90nm Node
Authors: Borst Christopher L. , Smith Stanley M. , Eissa Mona
Published: April 2011

Low-abrasive content slurries for copper (Cu) chemical-mechanical planarization (CMP) have been developed to achieve removal rate and removal uniformity comparable to conventional slurries. They can improve post-CMP defectivity, improve topography and allow operation at lower polish pressures that are more compatible with the low-dielectric constant (low-k) materials required for current and future high-performance interconnects. Integration of these slurries into a yielding product with 9-level Cu/low-k metallization requires fundamental learning and process characterization. This paper discusses the some of the challenges encountered during development, integration, and qualification of a low-abrasive Cu CMP process for Texas Instruments (TI) Incorporated's 90 nm technology node with copper/organosilicate interconnect. As abrasive content is reduced, the slurry chemistry must play a larger role in CMP removal. A more aggressive reactive chemical formulation requires an effective inhibitive component to keep Cu static etch rate low. As a result, wafer-scale process and consumable interactions, die-scale planarization efficiency, and feature-scale removal rates each become more sensitive to process changes. Pressure and temperature have larger effects on removal rate/profile than conventional slurries, and complete clearing of Cu puddled over underlying topography becomes more difficult. Successful integration of these slurries, however, can achieve excellent results in dishing and erosion topography, Cu thickness uniformity, and Cu loss in small features such as vias and landing pads. Low-abrasive content solutions are also more stable and easy to handle in slurry distribution vessels and lines, have lower scratch and residue defectivity, and have greatly extended margin for overpolish. As lowabrasive content Cu slurry options continue to evolve to become manufacturable solutions, their benefits far outweigh the costs and challenges encountered in their successful integration.
Adaptive Piezo-Controlled Carrier for CMP Processing
Authors: Weber Christian-Toralf , Weiser Jürgen , Zeidler Dieter , Bartha Johann W.
Published: April 2011

The IGAM engineering company for applied mechanics Ltd. developed an active piezocontrolled carrier for CMP. It uses several, by means of piezo-stacks individually controllable rings. The carrier is optimized regarding its stiffness and reliability by means of threedimensional finite element calculations. The high stiffness and positioning accuracy of the system allows the exact control of different surface profiles and thus the purposeful attitude of the pressure and removal profile independently of the polishing pressure. Tests show a very homogeneous pressure and removal distribution in the circumference of the wafer. The concept is transferable on further wafer diameters, whereby the width of the individual zones can be widely adapted to the requirements of the desired removal profile. Results of finite element analysis for a 12” prototype are available. The variable concept allows to upgrade existing CMP machines. The aims of current developments are the integration of in-situ-pressure determination to control the process, wireless transfer of energy and data to the carrier and the control of the local removal profile.
Measurement of Electroplated Copper Overburden for Advanced Process Development and Control
Authors: Tower Joshua , Maznev Alexei , Gostein Michael , Otsubo Koichi
Published: April 2011

We used a non-contact metrology system based on laser-induced surface acoustic waves to evaluate the thickness uniformity of electroplated copper. Several wafers were prepared using different plating conditions that affect the copper overburden thickness and uniformity. Measurements of overburden were made on a variety of pattern features including trench arrays of several pattern densities, solid bond pads, and the surrounding field area. In general, the overburden was found to be thicker above the arrays of narrow linewidth, as compared to the surrounding field. However, the magnitude of this “mounding” effect is dependent on the plating process, pattern density, and position on the wafer. For example, as the accelerator in the plating solution increases, the mounding on a 50% density line array varies from zero to 5000 Angstroms. Under all plating conditions used, the mounding was found to be progressively higher as the pattern density of the array increases (in the range of 20% to 50% copper). The solid pads were found to have conformal filling, in all cases. It was also found that the overburden in the field area is reduced as the adjacent mounding increases, presumably because the reactant in the plating bath becomes depleted in the vicinity of the high overburden regions above the arrays.
Effect of Abrasive in Cu-CMP Slurry on Global Planarization
Authors: Nomura Yutaka , Ono Hiroshi , Terazaki Hiroki , Kamigata Yasuo , Yoshida Masato
Published: April 2011

We investigated the mechanical effect of an abrasive in an abrasive-free-like (AFL) slurry using CMP evaluation and ζ potential evaluation. The amount of abrasive strongly influenced CMP performance. We found out the optimum amount of abrasive for optimal CMP performance. The ζ potential of the abrasive was positive, and those of the Cu and barrier metal were negative. We discussed a planarization model of the AFL slurry in detail based on the ζ potential results obtained.
The Application of Chemical Mechanical Polishing for Nickel Used in MEMS Devices
Authors: Vijayakumar Arun , Du Tianbao , Sundaram Kalpathy B. , Desai Vimal
Published: April 2011

Chemical mechanical planarization (CMP) has found extensive application in the fabrication of micro-electro-mechanical systems (MEMS). Nickel and Nickel based alloys are known to possess favorable properties that make them promising candidates to realize movable structures for MEMS applications. The development of CMP slurry chemistry for Ni that provides good CMP performance is the key in enabling CMP technology for Nickel based MEMS device fabrication. Unfortunately, very little work has been reported in terms of the electrochemical interaction of Ni with various CMP slurry constituents such as oxidizers, complexants and inhibitors. In this study, CMP of nickel was performed using H2O2 as oxidizer and alumina particles as abrasives. Electrochemical techniques were used to investigate the dissolution/passivation behavior of high-purity Ni under static and dynamic conditions in slurries at pH 4 with the addition of oxidizer, complexing agent and nickel salt. The affected surface layers of the statically etched Ni-disc were investigated using X-ray photoelectron spectroscopy (XPS). The Ni removal rate increased with the addition of oxidizer and further increased with the addition of complexing agent and nickel salt. The electrochemical results indicate that the surface chemistry and electrochemical characteristic of Ni play an important role in controlling the polishing behavior.
Planarization Issues in Wafer-Level Three-Dimensional (3D) Integration
Authors: Lu J.-Q. , Rajagopalan G. , Gupta M. , Cale T.S. , Gutmann R.J.
Published: April 2011

Monolithic wafer-level three-dimensional (3D) ICs based upon bonding of processed wafers and die-to-wafer 3D ICs based upon bonding die to a host wafer require additional planarization considerations compared to conventional planar ICs and wafer-scale packaging. Various planarization issues are described, focusing on the more stringent technology requirements of monolithic wafer-level 3D ICs. The specific 3D IC technology approach considered here consists of wafer bonding with dielectric adhesives, a three-step thinning process of grinding, polishing and etching, and an inter-wafer interconnect process using copper damascene patterning. The use of a bonding adhesive to relax pre-bonding wafer planarization requirements is a key to process compatibility with standard IC processes. Minimizing edge chipping during wafer thinning requires understanding of the relationships between wafer bonding, thinning and pre-bonding IC processes. The advantage of silicon-on-insulator technology in alleviating planarization issues with wafer thinning for 3D ICs is described.
Material Removal Mechanisms of Oxide and Nitride CMP with Ceria and Silica-Based Slurries - Analysis of Slurry Particles Pre- and Post-Dielectric CMP
Authors: Chandrasekaran Naga
Published: April 2011

The effect of CMP process parameters (pressure and pad hardness) on the ceria and silica abrasive particle-size distribution (PSD), morphology, and surface composition when polishing oxide and nitride surfaces was investigated in detail. The PSD was observed to shift post-CMP, with ceria and silica exhibiting a decrease and increase, respectively, in the number of particles towards the tail end of the distribution. The shift in ceria PSD was observed to increase as pad hardness increased. An increase in polish pressure and work surface hardness resulted in an equivalent shift in the PSD when polished on a soft pad. The inclusion of an additive reduced the oxide removal rate, and the abrasive particles exhibited the presence of a thin organic coating on the surface. The difference in material removal mechanisms and selectivity when polishing oxide and nitride with ceria and silica-based slurries was also investigated in detail.
Compact All Pass Transmission Filter using Photonic Crystal Slabs
Authors: Suh Wonjoo , Fan Shanhui
Published: April 2011

We show that both the coupled photonic crystal slab and the single photonic crystal slab structure can function as an optical all-pass transmission filter for normally incident light. The filter function is synthesized by designing the spectral properties of guided resonance in the slab. We expect this compact device to be useful for optical communication systems.
Optical Study of SiO2/nanocrystalline-Si Multilayers Using Ellipsometry
Authors: Lee Kang-Joo , Kang Tae-Dong , Lee Hosun , Hong Seung Hui , Choi Suk-Ho , Kim Kyung Joong , Moon Dae Won
Published: April 2011

Using variable-angle spectroscopic ellipsometry, we measure the pseudo-dielectric functions of as-deposited and annealed SiO2/SiOxmultilayers (MLs). The SiO2(2nm)/SiOx(2nm) MLs have been prepared under various deposition temperature by ion beam sputtering. The annealing at temperatures ≥ 1100°C leads to the formation of Si nanocrystals (nc-Si) in the SiOxlayer of MLs. Transmission electron microscopy images clearly demonstrate the existence of nc-Si. We assume a Tauc-Lorentzian lineshape for the dielectric function of nc-Si, and use an effective medium approximation for SiO2/nc-Si MLs as a mixture of nc-Si and SiO2. We successfully estimate the dielectric function of nc-Si and its volume fraction. We find that the volume fraction of nc-Si decreases after annealing, with increasing x in as-deposited SiOxlayer. This result is compared to expected nc-Si volume fraction, which was estimated from stoichiometry of SiOx.
Solvothermal Synthesis and Characterization of Zn(NH3)CO3 Single Crystal
Authors: Wen Fushan , Chen Jiesheng , Kim Jin Hyeok , Kim Taeun , Li Wenlian
Published: April 2011

A new 3-dimensional zinc carbonate Zn(NH3)CO3 has been synthesized from a glycol system with urea and zinc acetate as raw materials. The crystal structure and photoluminescent properties have been investigated using X-ray diffraction, smart CCD and FL. The compound had an orthorhombic system with space group of Pna21 with M = 142.41, a = 9.1449(18) Å, b = 7.5963(15) Å, c = 5.4982(11) Å, V = 381.95(13) Å3, Z = 4, R = 0.0285 and RW = 0.0745. The NH3 and CO32- were connected through the Zn-N bond and Zn-O bond in the symmetric unit. Photoluminescent property was observed in the compound at room temperature and the exited and emission peaks were located at about 350 nm and 426 nm, respectively.
Growth and patterning of strontium-titanate-oxide thin films for optical devices applications
Authors: Gaidi M. , Stafford L. , Chaker M. , Margot J. , Kulishov M.
Published: April 2011

Strontium-titanate-oxide (STO) thin films have been deposited on silicon substrates by means of a reactive pulsed-laser-deposition technique. The influence of the oxygen deposition pressure on the microstructural properties of the films has been investigated by means of various characterization techniques. It was found that the crystalline quality of the film significantly deteriorates as the oxygen pressure increases. This is accompanied by an increase of the film microporosity. The microstructure of the film is found to directly impact the optical quality of the films. In particular, due to the higher density and crystallinity of the films deposited at lower oxygen pressure, films characterized by lower optical losses can be achieved in such conditions. These films have been used in the context of the development of optical waveguides. For this purpose, patterning of the STO films was investigated using sputter-etching with a high-density argon plasma operated in the very low pressure regime. Highly anisotropic features have been produced with high etch rate and good selectivity over resist. Preliminary results indicate the STO films can be successfully incorporated in functional waveguides.
Active Photonic Crystal Devices in Self-Assembled Electro-Optic Polymeric Materials
Authors: Li J. , Neyman P. J. , Vercellino M. , Heflin J. R. , Duncan R. , Evoy S.
Published: April 2011

Photonic crystals (PC) offer novel approaches for integrated photonics by allowing the manipulation of light based on the photonic bandgap effect rather than internal-reflection mechanisms employed in traditional devices. Electro-optic polymers represent interesting possibilities for the development of devices leveraging control over the phase of a confined propagating wave. We here report on the development of such active photonic crystal technology in ionically self-assembled monolayers. The simulation of active photonic devices such as Mach-Zehnder interferometers and wavelength multiplexers is first presented. We then report on the synthesis and optical characterization of electro-optic films grown through the ISAM technique. We conclude by presenting the preliminary development of a nanofabrication platform that would enable the realization of active photonic devices in such materials.
The Investigation of Erbium Complexes and Erbium Doped Materials
Authors: Lee Seunghoon , Kim Ung , Kim Juntae , Koo Sang Man
Published: April 2011

Erbium ion (Er3+) doped materials are of great interest for their optical amplification, lasing and frequency up-conversion properties. When preparing such materials, a major problem that often arises is the formation of Er-rich oxide clusters inducing optical quenching. The materials prepared at low Er3+-ion concentrations to overcome the problem have severely reduced the optical yield. Such clustering might be avoided by preparing suitable precursors. If Er is encapsulated with proper materials, clustering can be avoided and higher doping levels can be achieved. In this study, erbium phenoxide complex was obtained by metathesis reaction of erbium chloride (ErCl3) with potassium phenoxide (KOPh). And heterometallic complexes were also synthesized by encapsulation of the Er with Al or Ti derivatives. The complexes were characterized by elemental analysis, infrared and nuclear magnetic resonance spectroscopic analysis. Their crystal structures were determined by X-ray single crystal diffraction analysis. In addition, the Er-doped organic-inorganic matrices using the erbium complexes were investigated about their optical properties.
Growth of SiOx Nanowires on Self-Assembled Hexagonal Au Particle Networks
Authors: Chiang Tian Fu , Cheng Shao Liang , Chen Lih Juann
Published: April 2011

Self-assembled hexagonal networks with discrete Au particles on Al2O3 (00.1) and Si (111) have been synthesized. SiOx nanowires were grown on individual Au particles using a vapor transport deposition process. The growth of SiOx nanowires was found to cover completely the surface of Au particles on Al2O3 (00.1). On the other hand, the SiOx nanowires were grown selectively on Au particles on Si (111). Interaction of Au and Si substrate is invoked to explain the difference.
Ni Nanoparticles Elaborated with an Ar Ion Polishing Technique
Authors: Torres-Castro Alejandro
Published: April 2011

Ni nanoparticles where obtained from a Ni sample milled with Ar ions by using a Gatan precision ion polishing system, normally used for Transmission Electron Microscopy (TEM) sample preparation. Deposition of Ni nanoparticles was performed over two different surfaces: on a double sided carbon tape and, on a Cu grid covered with collodion film. A continuos film of Ni was characterized, over the carbon tape by SEM and EDAX techniques. The last surface was analysed by TEM. In both cases, a thin film composed of Ni nanoparticles, was founded and result obtained by TEM, show a nanoparticle diameter of about 4 nm.
Improvement of Electrical Properties of Tin Oxide Nanoparticle by Controlling its Surface Structure
Authors: Hong Sung-Jei , Han Jeong-In
Published: April 2011

In this study, a novel SnO2 nanoparticle was successfully synthesized by controlling its surface structure. The surface structure on the nanoparticle is consistent of Pd and PdO clusters of which size is smaller than 1nm. For uniform dispersion of the clusters, in-situ synthetic method was applied using Sn acetate and Pd acetate. The method enhances uniformity by mixing two elements as an aqueous solution. Also, those materials lower the processing temperature since the removal of organic components is possible below 300°C. HRTEM observation reveals that the size of the synthesized particle is ranged from 2 to 7 nm and the Pd cluster is uniformly distributed in the lattice of SnO2 particle. In fact, XRD analysis certifies the uniform solid solution of the Pd cluster in SnO2 since the localized Pd peak was not found. Specific surface area of the synthesized particle measured with BET surface analyzer exceeded 100 m2/g. Also, the SnO2-5wt%Pd nanoparticle exhibits the excellent change in resistance of 0.62 after aging at 400°C for 5 hours. Also, the electrical properties show very stable phenomena in spite of long- term aging for 400 hours at 400°C. So, the ultrafine SnO2-Pd nanoparticle could be synthesized by using the in-situ synthetic method.
Synthesis and Characterization of Self-Organized Nanostructure Arrays Generated by Laser Irradiation
Authors: Guan Yingfeng , Pedraza A.J.
Published: April 2011

One and two-dimensional arrays of nanoripples and nanoprotrusions can be generated by pulsed laser irradiation. Nanoprotrusions were produced on the surface of silicon when a Lloyd's mirror configuration was used, and could develop to a height of 80 nm. Atomic force and high resolution scanning electron microscopy studies revealed that these structures are preceded by the formation of extended ripples that can reach a height of up to 12 nm. It is shown that one or two identifiable arrays of mutually orthogonal ripples may form. Out of the four differently- spaced ripple arrays that were found, three indicated a very close connection with the production of laser-induced periodic surface structures (LIPSS). Interference of the incoming or refracted laser beam and the laser light scattered by surface undulations has been recognized as the cause of LIPSS formation. The present experiments show that the Lloyd's mirror configuration strongly enhances the formation of ripples and that nanoprotrusions form, sometimes at the intersection of two mutually orthogonal sets of ripples. Each of the beams, the directly incident and the mirror-reflected beam, independently produce an interference pattern with their corresponding scattered beams. However, these two independently generated patterns coincide because their periodicity is only a function of the angle of incidence. Thus, the two interference patterns reinforce each other's effects on the substrate. Single beam, direct irradiation of the substrate failed to induce nanoprotrusions, although 1-D ripple arrays developed.
Line Pattern in Plasma Polymer Films with Embedded Gold and Silver Nanoparticles by Irradiation with Ultrashort Laser Pulses
Authors: Kiesow Andreas , Strohkark Sven , Löschner Katrin , Heilmann Andreas , Podlipensky Alexander , Abdolvand Amin , Seifert Gerhard , Graener Heinrich , Optik Fachgruppe , Physik Fachbereich
Published: April 2011

A method to generate line pattern structures in thin organic films with embedded gold and silver nanoparticles is introduced. The films are irradiated with ultrashort, linearly polarized laser pulses. As we find out from electron microscopy (TEM, SEM), periodically arranged line-like structures are formed after the irradiation. We have used so far three different laser wavelengths (266 nm, 400 nm, 800 nm). The resulting structure periods in the range of 170 nm to 600 nm indicate a linear correlation of the period length of the line structures and the wavelength of the incident laser light. The direction of the particle lines corresponds to the linear polarization of the laser pulses. The anisotropic structure modification is mirrored in corresponding anisotropic optical film properties.
Optical Properties of One-Dimensional Metal Nanostructures
Authors: Hao Encai , Zou Shengli , Schatz George C.
Published: April 2011

We present a theoretical study of the optical properties of one-dimensional (1-D) metal nanostructures including nanorods and nanotubes. Although the optical properties of gold nanotubes are similar to that of gold nanorods, both the longitudinal and transverse plasmon resonances of gold nanotubes show much larger red-shifting and narrower. The E-field calculations indicate that the 1-D gold nanostructures, particularly gold nanotubes have great potential for applications to SERS.
Self-Catalytic Branch Growth of SnO2Nanowire Junctions
Authors: Chen Y. X. , Campbell L. J. , Zhou W. L.
Published: April 2011

Multiple branched SnO2 nanowire junctions have been synthesized by thermal evaporation of SnO powder. Their nanostructures were studied by transmission electron microscopy and field emission scanning electron microcopy. It was observed that Sn nanoparticles generated from decomposition of the SnO powder acted as self-catalysts to control the SnO2 nanojunction growth. Orthorhombic SnO2 was found as a dominate phase in nanojunction growth instead of rutile structure. The branches and stems of nanojunctions were found to be an epitaxial growth by electron diffraction analysis and high resolution electron microscopy observation. The growth directions of the branched SnO2 nanojunctions were along the orthorhombic [110] and [1 1 0]. The growth of SnO2 nanojunction is controlled by a self-catalytic vapor-liquid-solid growth using Sn nanoparticle catalysts.
ZnO Nanostructures Prepared by Different Methods
Authors: Leung Y. H. , Djurišić A. B. , Choy W. C. H. , Chan W. K. , Cheah K. W.
Published: April 2011

ZnO is of great interest for photonic applications due to its wide band gap (3.37 eV) and large exciton binding energy (60 meV). Variety of preparation methods and obtained morphologies (such as nanorods, tetrapod nanorods, nanowires, nanoribbons, hierarchical structures, nanobridges, and nanonails) were reported for this material. In this work, the morphology and optical properties of ZnO nanostructures prepared by three different methods were studied. ZnO nanostructures were prepared by oxidation of Zn (no catalyst) at 950°C, heating of a mixture of ZnO:graphite (1:1) at 1100°C, and chemical method (from solution of zinc nitrate hydrate and hexamethylenetetramine at 90°C). The properties of obtained products were examined using scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, X-ray diffraction, room temperature photoluminescence and electron paramagnetic resonance spectroscopy. Chemical synthesis method produced different morphology compared to heating of Zn and ZnO:graphite. In the former case, straight rods are obtained, while in the latter case ZnO tetrapod structures are formed. The ZnO tetrapods, both from Zn and ZnO:graphite, exhibit similar photoluminescence spectra with UV peak and characteristic broad green emission but they have different EPR spectra. The EPR signal g≈1.96 is clearly visible in ZnO tetrapods synthesized from ZnO:graphite, while it is at noise level in ZnO tetrapods synthesized from Zn. Therefore, it can be concluded that the type of intrinsic defects in ZnO nanostructures is strongly dependent on the fabrication conditions, and that the green photoluminescence is not necessarily related to ≈1.96 EPR peak which is commonly assigned to shallow donors.
Magnetic and Electric Manipulation of a Single Cell in Fluid
Authors: Lee Hakho , Hunt Tom P. , Westervelt Robert M.
Published: April 2011

Magnetic and electric manipulation of a single cell in a microfluidic channel was demonstrated using a microelectromagnet matrix and a micropost matrix. The microelectromagnet matrix is two perpendicular arrays of straight wires that are separated and topped by insulating layers. The micropost matrix is an array of post-shaped electrodes embedded in an insulting layer. By controlling the current in each wire of the microelectromagnet matrix or the voltage on each electrode of the micropost matrix, versatile magnetic or electric fields were created on micrometer length scales, controlling the motion of individual cells in fluid. Single or multiple yeast cells attached to magnetic beads were trapped and moved by the microelectromagnet matrix; a single yeast cell was directly trapped and moved by the micropost matrix.
Actin Nanotracks for Hybrid Nanodevices Based on Linear Protein Molecular Motors
Authors: Watson G. S. , Cahill C. , Blach J. , Myhra S. , Alexeeva Y. , Ivanova E.P. , Nicolau D. V.
Published: April 2011

Hybrid nano-devices based on linear protein molecular motors working on micro/nano-engineered surfaces that operate in a “cargo architecture”, i.e. motor functionalized nano-objects running on nano-tracks, offer more opportunities than the inverse “sliding architecture” because it fully uses the information regarding directionality which is encoded in tracks, i.e. actin filaments or microtubules. However, this architecture requires the development of techniques for nanolithography with actin filaments (or microtubules) based on molecular self-assembly on engineered surfaces. The present contribution reports on the progress we have made regarding the building of actin nanostructures that would preserve the inherent information over extended micro-sized areas.
Decoration of Carbon Nanotubes with Gold Nanoparticles for Catalytic Applications
Authors: Lü Wei , Ma Xicheng , Lun Ning , Wen Shulin
Published: April 2011

Gold nanoparticles supported on carbon nanotubes (CNTs) were prepared by using electroless plating technique. High-resolution transmission electron microscopy (HRTEM) has shown that spherical gold nanoparticles were homogeneously dispersed on the surfaces of the carbon nanotubes with a distribution of particle sizes sharply at around 3-4 nm in diameter. The results presented in this work will probably provide new catalysts with better performances.
Experimental study of filling carbon nanotubes with nucleic acids
Authors: Cui Daxiang , Ozkan Cengiz S. , Kong Yong , Gao Huajian
Published: April 2011

Encapsulation of DNA molecules inside carbon nanotubes (CNT) in water were performed under the conditions of 400K and 3Bar. Double stranded DNAs of 2kb and 400bp in length, and single stranded oligonucleotides of 60bp in length were selected as target molecules. Au and Pt nanoparticles and fluorescent dye Cy3 were used as tags. Agarose gel electrophoresis was used to remove DNA molecules attached on the outside walls of CNTs. Laser confocal microscopy, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM), energy dispersive x-ray spectroscopy (EDX) were employed to confirm the encapsulation process. The results demonstrated that DNA molecules attached to the outside of CNTs can be removed by electrophoresis. Confocal microscopy and HR-TEM observations as well as EDX analysis confirmed that the Cy3-labelled DNA molecules, Au-labelled oligonucleotides and Pt-labelled DNA fragments can indeed be encapsulated inside CNTs. These experimental results support our earlier molecular dynamics simulations on encapsulating oligonucleotides inside CNTs. The DNA-CNT hybrids could be further explored for potential applications in bio-nanotechnology.
Control of Doping and Electronic Transport in Nanowires
Authors: Zhong Jianxin , Stocks G. Malcolm
Published: April 2011

We propose a novel concept, namely, delta-doping of nanowires, to control the carrier mobility in nanowires. Different from the traditional doping, our approach features doping of a nanowire only on its surface. Our calculations based on Anderson models for nanowires with surface disorder showed remarkably different results from the traditional doping where impurities are distributed inside the nanowire. We found that there exist transition energy levels similar to the mobility edges in three-dimensional disordered systems. If the Fermi energy is below the transition energy level, the delta-doped nanowire is simply an insulator. But once the Fermi energy exceeds this energy level, the carrier mobility increases significantly. The transition levels are almost independent of the degree of disorder in the regime of strong disorder.
Liquid Phase Deposition of Poly(ethylene terephthalate) Films
Authors: Bryce Robert M. , Nguyen Hue T. , Tykwinski Rik R. , DeCorby Ray G. , Freeman Mark R. , Tsui Ying Y.
Published: April 2011

Poly(ethylene terephthalate), or PET, has been widely used in experiments due to its excellent properties and availability in sheets as thin as 1.5 µm. Its resistance to chemical attack makes PET a good choice as an inert substrate, but makes liquid phase deposition of thin films from solution challenging. Further, attempts to deposit films from the vapor phase have shown limited success. High quality PET films are desirable, as PET is transparent, hydrophobic, amenable to micropatterning, and is well characterized. As such, PET films are suited for use in microdevices. We report on liquid phase deposition of PET films, and on characterization of the films using optical methods.
Fabrication and Characterization of Platinum-Iridium Electrodes with Micro-Structured Surfaces For Neural Stimulation Applications
Authors: Thanawala Sachin S. , Georgiev Daniel G. , Khan Afzal , Baird Ronald J. , Auner Gregory
Published: April 2011

Controlled structuring of electrode surfaces on a microscopic scale is expected to decrease the impedance and improve the current injection capabilities of neural stimulation electrodes. We have identified conditions for the fabrication of micro-bumps on platinum-iridium alloy surfaces by means of KrF excimer laser (λ=248nm) irradiation under ambient conditions. A regular array of closely spaced micro-bumps with diameters of about 5µm and heights of about 3µm was generated on the polished face of a platinum-20%iridium wire with a diameter of 75µm. A projection system with a demagnification factor of 9 was used to image a mask with a pattern of circular-holes on the polished face of the wire. Several thousand pulses at a repetition rate of 10Hz and a fluence of 3.0 J/cm2 were applied to produce the micro-bumps. The modified electrode surfaces were studied by optical microscopy and scanning electron microscopy, and the results show the formation of micro-bumps of reproducible shape. Simple two-electrode AC impedance measurements in physiological saline in the frequency range of interest to neural stimulation applications show a considerable decrease in the impedance of micro-structured electrodes with respect to the impedance of a polished electrode.
Electroactive Polymer Deformable Micromirrors (EAPDM) for Biomedical Optics
Authors: Huang Cheng , Bai Bo , Chu Baojun , Ding Jim , Zhang Q.M.
Published: April 2011

Electroactive polymers (EAPs) are capable of converting energy in the form of electric charge and voltage to mechanical force and movement and vice versa. Several electroactive polymer actuator materials whose responses are controlled by external electric fields, e.g. poly(vinylidene fluoride-trifluoroethylene) based fluoroterpolymers, have generated considerable interest for use in applications such as artificial muscles, sensors, parasitic energy capture, integrated bio-microelectromechanical systems (BioMEMS) and microfluidic devices due to their high electric-field induced strain, high elastic modulus, high electromechanical coupling and high frequency operation, etc. Scaling the EAP down into microsystems is one of the promising trends of EAP actuators and sensors especially for biomedical engineering. The combination of micro-optics and integrated BioMEMS, referred to as bio-micro-opto-electromechanical systems (BioMOEMS), makes a new opportunity for innovation in the EAP field. We present an approach to the fabrication of low-cost, large-stroke deformable micromirrors based on high performance electroactive polymer film microactuator arrays. Integrated Optic-BioMEMS based on electroactive polymer deformable micromirror (EAPDM) technology provide potential applications in biomedical optics such as ophthalmology (retinal imaging and vision care) and cancer detection and treatment.
Rapid Prototyping of Glass Microfluidic Devices using Femtosecond Laser Pulses
Authors: Park Myung-Il , Choi Jun Rye , Park Mira , Choi Dae Sik , Jeoung Sae Chae , Park Chong-Ook
Published: April 2011

Laser micromachining technology with 150 femtosecond pulses is developed to fabricate glass microfluidic devices. A short theoretical analysis of femtosecond laser ablation is reported to characterize the femtosecond laser micromachining. The ablated crater diameter is measured as a function of the number of laser pulses as well as laser fluence. Two different ablation regimes are observed and the transition between the regimes is dependent on both the laser fluence and the number of laser shots. Based on the ablation phenomena described, microfluidic devices are fabricated with commercially available soda lime glasses (76 mm × 26 mm × 1 mm, Knittel Glaser, Germany). In addition to a microchannel for microfluidics, the capillary as well as optical fiber for detecting is integrated on the same substrate. The substrate is successively packaged with a lid slide glass by a thermal direct bonding. The presented developments are suitable for fast turn-around design cycle and inexpensive procedure, which provide rapid prototyping of MEMS devices.
Polariton-enhanced near field lithography and imaging with infrared light
Authors: Shvets Gennady , Urzhumov Yaroslav A.
Published: April 2011

A novel approach to making a material with negative index of refraction in the infrared frequency band is described. Materials with negative dielectric permittivity ε are utilized in this approach. Those could be either plasmonic (metals) or polaritonic (semiconductors) in nature. A sub-wavelength plasmonic crystal (SPC), with the period much smaller than the wavelength of light, consisting of nearly-touching metallic cylinders is shown to support waves with negative group velocity. The usage of such waves for sub-wavelength resolution imaging is demonstrated in a numerical double-slit experiment. Another application of the negative-epsilon materials is laser-driven near field nanolithography. Any plasmonic or polaritonic material with nega- tive ε = –εd sandwiched between dielectric layers with εd > 0 can be used to significantly decrease the feature size. It is shown that a thin slab of SiC is capable of focusing the mid- IR radiation of a CO2 laser to several hundred nanometers, thus paving the way for a new nano-lithographic technique: Phonon Enhanced Near Field Lithography in Infrared (PENFIL). Although an essentially near-field effect, this resolution enhancement can be quantified using far-field measurements. Numerical simulations supporting such experiments are presented.
Morphologically Well-defined Gold Nanoparticles Embedded in Thermo-Responsive Hydrogel Matrices
Authors: Wang Chun , Flynn Nolan T. , Langer Robert
Published: April 2011

Nanocomposite materials consisting of colloidal gold (Au) nanoparticles embedded in thermo-responsive poly(N-isopropylacrylamide) (PNIPAm) hydrogels are synthesized. Thiol groups that bind to both Au3+ ions and colloidal Au are incorporated into the side-chains of the PNIPAm hydrogels through copolymerization. This report describes formation of morphologically well-defined Au nanoparticles with varying long-term stability inside the hydrogel matrices containing adjustable concentrations of thiols. Compared with the non-Au containing PNIPAm hydrogels, the Au-PNIPAm nanocomposite hydrogels have shown higher degrees of equilibrium swelling and different temperature-triggered phase transitions. It is hypothesized that these remarkable changes in hydrogel bulk properties are related to the different morphologies and sizes, and possibly the amount of surface charges, of the Au nanoparticles.
Patterning and Reactive Ion Etching of Diamond Films using Light Coupling Masks
Authors: Leech Patrick W. , Reeves Geoff K. , Holland Anthony S.
Published: April 2011

We describe the novel application of light coupling masks (LCM) in the lithographic patterning of fine structures in diamond films. A PDMS mask was used in the exposure of complex patterns of gratings in AZP 1205 resist on a substrate of Al/ diamond. The profiles of these grating patterns were then modified on a localized scale by a process of reflow of the resist. We report on the transfer of the patterns formed in resist by the LCMs into the diamond film using a sputtered Al layer as a mask. The two-stage process comprised etching of the pattern into the Al followed by transfer into the diamond film using CF4/ O2 and CHF3/ O2 gases. The presence of O2 in the CF4/ O2 and CHF3/ O2 gas mixtures produced Al oxides on the surface of the mask. The etch selectivity of the mask was greater in CF4/ O2 than in CHF3/ O2 gases and was only weakly dependent on the concentration of O2 (0-12 sccm).
Atomic Force Microscopy Applications to Neuroscience
Authors: McNally Helen A.
Published: April 2011

In this research, Atomic Force Microscopy (AFM) is used to investigate living neurons. Three-dimensional images of developing and dying neurons have been obtained, providing neuroscientists their first views of these dynamic structures. The unparalleled resolution provided by AFM reveals dorsal root ganglion (DRG) cells to be more complex and variable than anticipated. AFM is also used to physically contact or manipulate the cell, and thus perturb its development, and/or to measure important physiologically parameters such as surface pressure. Neural cell damage is induced by the AFM tip, which is subsequently used to image the cell's morphological response. A 3-D view of the neural cell collapse, due to this insult, suggests alternative ideas concerning acute neuronal (cellular) sealing and repair. Repair of the injured neuron using electric fields and biomolecules is also investigated, supporting clinical trials for paralysis research. AFM force measurements are used to monitor cellular activity and membrane interactions during various stages of the neural cell life cycle. The full versatility of AFM will be applied to further the understanding of neurogenesis and neurotrauma.
A Molecular Dynamics Study of Short Nanoparticle Chains under Mechanical Strain: Linear and Kinked Configurations
Authors: Dalis Adamos , Friedlander Sheldon K.
Published: April 2011

Previous studies in our laboratory have shown that individual nanoparticle chain aggregates (NCA) exhibit remarkable mechanical behavior when under strain inside the transmission electron microscope. NCA made of various materials (e.g. carbon, metal oxides, metals, etc.) were strained by as much as 100% when tension was applied to them. After breaking, the NCA rapidly contracted to form more compact structures. In this study, molecular dynamics (MD) computer simulations are employed to investigate, at the atomic scale, the behavior of short nanoparticle chains under strain and to obtain quantitative information of the forces involved in chain straining and fracturing. The interaction potential used is that of copper obtained with the embedded atom method (EAM). Although the methodology is generally applicable, copper was selected as a test material because reliable interatomic potentials are available. Seven single- crystal nanoparticles, each 2.452 nm in diameter, are placed in contact in two chain configurations, linear and kinked. The structures are initially relaxed adiabatically with MD steps for 225 ps, at a starting temperature of 300 K. The bonding energy between any two nanoparticles in contact ranges from about 20 eV to 30 eV at 0 K. The two relaxed chain configurations are strained along their longest dimension, to the breaking point, at strain rates spanning from 0.3 m/s to 10 m/s. We identify mechanisms of stress accommodation that lead to plastic deformation and eventually fracture for both chain configurations, linear and kinked, and we construct the corresponding stress-strain curves. The two chain configurations exhibit different mechanical behavior. Applications of our experimental and simulation studies on NCA are to the behavior of nanocomposite materials, including carbon black reinforced rubber, sampling of aggregates by high speed impactors and the formation of flexible coatings of nanoparticles.
Nanoscale Structure and High Velocity Sliding at Cu/Ag Interfaces
Authors: Hammerberg James E. , Germann Timothy C. , Holian Brad Lee , Ravelo Ramon
Published: April 2011

We present the results of large-scale NonEquilibrium Molecular Dynamics (NEMD) simulations for Cu/Ag interfaces sliding in the velocity regime 0≤v≤1Km/sec. System sizes of 2.8 × 106 atoms are considered using Embedded Atom Method (EAM) potentials. Single crystals with 010 interfaces sliding along the <100> direction are considered. We discuss the observed velocity weakening in the tangential force at high velocities, and its connection with the observed dislocation structure and nanostructure that are nucleated during dry sliding.
Improved Fracture Toughness in Advanced Nanocrystalline Ceramic Composites
Authors: Kuntz Joshua D. , Zhan Guo-Dong , Mukherjee Amiya K.
Published: April 2011

Nanocrystalline materials have demonstrated very interesting changes in physical, chemical and mechanical properties at severely diminished length scales. This article focuses on the topic of nanocrystalline ceramic composites specifically designed for applications requiring improved fracture toughness. The difficulty in producing fully consolidated ceramic composites that retain a nanocrystalline structure is the main hurdle for thorough investigations in this area. This obstacle has been overcome in the current investigation through the use of a fast, comparably lower temperature, sintering technique e.g., Spark Plasma Sintering. Alumina based nanocomposites incorporating carbon nanotubes and additionally incorporating nanocrystalline niobium have yielded fracture toughness values that have exceeded that for pure nanocrystalline alumina by more that 300%. This introduces the question of whether this improvement is merely additive or evidence of a synergistic toughening mechanism involving ductile phase and fiber toughening.
Analysis of Residual Stress and Damage Durability with Thermal Fatigue Behavior in Thermal Barrier Coatings
Authors: Park Dong-Ho , Jang Hyung-Jun , Jung Yeon-Gil , Chang Jung-Chel , Paik Ungyu
Published: April 2011

Static thermal fatigue tests for thermal barrier coatings (TBCs) were conducted to observe effects of temperature and holding time on its mechanical properties, hardness and modulus, and damage durability. For which three TBCs samples with different thickness in bonding layer (0.08, 0.14, and 0.28 mm) were prepared using an air plasma spraying (APS) method. Temperature of 950 and 1100°C and holding time of 10 and 100 hr were selected for the thermal fatigue tests. The TBCs with thin bonding layer (0.08 mm) maintain sound condition for all the thermal fatigue tests, even showing an evidence of cracking at the interface between coating and bonding layers. However, the TBCs with intermediate (0.14 mm) and thick (0.28 mm) bonding layers show delamination at interface and fracture of coating layer after the thermal fatigue tests at 1100°C for 100 hr. Thermal growth oxide (TGO) layer is created at the interface between coating and bonding layers in all the TBCs after the thermal fatigue tests, and the TGO layer thickness is mainly affected by temperature. Modulus and hardness of coating layer are increased with an increase of temperature in the thermal fatigue tests, due to the re-sintering of coating layer during the thermal fatigue tests. Effects of bonding layer thickness and thermal fatigue condition on mechanical properties, residual stresses, damage durability of the TBCs are discussed extensively.
Analysis of a one-billion atom simulation of work-hardening in ductile materials
Authors: Buehler Markus J. , Hartmaier Alexander , Duchaineau Mark , Abraham Farid F. , Gao Huajian
Published: April 2011

We analyze a large-scale molecular dynamics simulation of work hardening in a ductile model material comprising of 500 million atoms interacting with a Lennard-Jones pair potential within a classical molecular dynamics scheme. With tensile loading, we observe emission of thousands of dislocations from two sharp cracks. The dislocations interact in a complex way, revealing three fundamental mechanisms of work-hardening. These are (1) dislocation cutting processes, jog formation and generation of point defects; (2) activation of secondary slip systems by cross-slip; and (3) formation of sessile Lomer-Cottrell locks. The dislocations self-organize into a complex sessile defect topology. Our analysis illustrates mechanisms formerly only known from textbooks and observed indirectly in experiment. It is the first time that such a rich set of fundamental phenomena has been seen in a single computer simulation.