bluuebunny/crossref_metadata_2025_split huggingface dataset:
Size-Related Plasticity Effects in AFM Silicon Cantilever Tips
Authors: Kopycinska-Mueller Malgorzata , Geiss Roy H. , Hurley Donna C. 
Published: April 2011

ABSTRACTWe are developing dynamic atomic force microscopy (AFM) techniques to determine nanoscale elastic properties. Atomic force acoustic microscopy (AFAM) makes use of the resonant frequencies of an AFM cantilever while its tip contacts the sample surface at a given static load. Our methods involve nanosized silicon probes with tip radius R ranging from approximately 10 nm to 150 nm. The resulting radius of contact between the tip and the sample is less than 20 nm. However, the contact stress can be greater than a few tens of GPa, exceeding the theoretical yield strength of silicon by a factor of two to four. Our AFAM experiments indicate that, contrary to expectation, tips can sometimes withstand such stresses without fracture. We subjected ten tips to the same sequence of AFAM experiments. Each tip was brought into contact with a fused quartz sample at different static loads. The load was systematically increased from about 0.4 μN to 6 μN. Changes in tip geometry were observed in images acquired in a scanning electron microscope (SEM) between the individual AFAM experiments. All of the tips with R < 10 nm broke during the first AFAM experiments at static loads less than 1.6 μN. Tips with R > 40 nm plastically deformed under such loads. However, a group of tips with R from 25 nm to 30 nm neither broke nor deformed during the tests. In order to reach higher contact stresses, two additional tips with similar values of R were used in identical experiments on nickel and sapphire samples. Although the estimated stresses exceeded 40 GPa, we did not observe any tip fracture events. Our qualitative observations agree with more systematic studies performed by other groups on various nanostructures. The results emphasize the necessity of understanding the mechanics of nanometer-scaled bodies and the impact of size effects on measurements of mechanical properties on such scales.
Size-Dependent Elastic Moduli of FCC Crystal Nanofilms
Authors: Chang Shih-Hsiang , Chang I-Ling 
Published: April 2011

ABSTRACTA semi-continuum model is constructed to study the size effects on the mechanical properties of face-cubic-center crystal structure nanofilms. Unlike the classical continuum theory, the current model directly takes the discrete nature in the thickness direction into consideration. In-plane and out-plane Poisson's ratios as well as in-plane Young's modulus are investigated with this model. It is found that the values of the Young's modulus and Poisson's ratio depend on the film thickness and approach the respective bulk values asymptotically.
Stress Driven Rearrangement Instability of Crystalline Films with Electromechanical Interaction
Authors: Chung Peter , Clayton John , Cole Melanie M , Grinfeld Michael , Grinfeld Pavel , Nothwang William 
Published: April 2011

AbstractIt was demonstrated, on general thermodynamic grounds, that, in non-hydrostatically stressed elastic systems, phase and grain interfaces undergo morphological destabilization due to different mechanisms of “mass rearrangement”. Destabilization of free surfaces due to the combined action of mass rearrangement in the presence of electrostatic field has been well known since the end of the 19th century. Currently, morphological instabilities of thin solid films with electro-mechanical interactions have found various applications in physics and engineering. In this paper, we investigate the combined effects of the stress driven rearrangement instabilities and the destabilization due to the electro-mechanical interactions. The paper presents relevant results of theoretical studies for ferroelectric thin films. Theoretical analysis involves highly nonlinear equations allowing analytical methods only for the initial stage of unstable growth. At present, we are unable to explore analytically the most important, deeply nonlinear regimes of growth. To avoid this difficulty, we developed numerical tools facilitating the process of solving and interpreting the results by means of visualization of developing morphologies.
Properties of the surface-modified layer of plasma-oxidized poly(dimethylsiloxane)
Authors: Mills Kristen L. , Zhu Xiaoyue , Lee Donghee , Takayama Shuichi , Thouless M. D. 
Published: April 2011

ABSTRACTExposure of poly(dimethylsiloxane) (PDMS) to oxygen plasma creates a thin, stiff surface-modified layer that reaches a submicron depth. Due to a significant modulus mismatch between the stiff surface-modified layer and the compliant bulk PDMS the surface-modified layer forms intricate patterns of surface buckles when under compressive stress and nano-cracks when under tensile stress. It is desirable to be able to design patterns of nano-cracks, or at least to have an understanding of them. Among the properties necessary to do this are the thickness and elastic modulus of the surface-modified layer. Due to the very small length scale of the surface-modified layer, it is a significant challenge to measure these properties. In this proceedings paper, a two-step method is described for determining the thickness and elastic modulus of the surface-modified layer using the atomic force microscope (AFM). First, nanoindentation is performed from which the bending stiffness of the surface-modified layer is calculated. Second, the surface-modified layer thickness is determined by using phase imaging on the cross-section of oxidized PDMS to map the region of the relatively stiffer surface-modified layer.
Synthesis of Silicon Carbonitride for the Machining of Resonant Nanomechanical Biosensors
Authors: Fishcer Lee M. , Wilding Neal , Gel Murat , Evoy Stephane 
Published: April 2011

ABSTRACTWe report a study on the plasma-enhanced chemical vapor deposition of silicon carbonitride, as well as the resonant behavior of nanomachined SiCN structures. Films with thicknesses of 1 um, and 200 nm were deposited at varying gas ratios using ammonia (NH3), nitrogen (N2), and diethylsilane (DES) as precursors. X-ray photoelectron spectroscopy revealed high nitrogen and low carbon content in films deposited at high NH3:DES gas flow ratios. Selected samples annealed at varying temperatures experienced shifts in stress towards tensile of Δσ = 235 MPa, 432 MPa, 724 MPa, and 1140 MPa, at annealing temperatures of T = 400 °C, 500 °C, 600 °C, and 700 °C respectively. Infrared spectroscopy reported a loss of incorporated hydrogen as a mechanism of stress modulation. Resonant assaying of cantilevers fabricated from 200 nm-thick SiCN yielded root-modulus-over-density values of √(E/ρ) = 6.95 × 103 m/s and √(E/ρ) = 8.35 × 103 m/s, comparable to those of silicon.
Nanocomposites for Neural Interfaces
Authors: Kmecko Tanja , Hughes Gareth , Cauller Larry , Lee Jeong-Bong , Romero-Ortega Mario 
Published: April 2011

ABSTRACTWe have fabricated micro-probes consisting of gold microelectrode sites (500 μm long and 12 μm wide) modified with conductive polymers and carbon nanotubes to achieve intimate contact with the nervous system. The fabrication process includes photolithography, electroplating and micromachining techniques. In order to obtain a high quality neural contact, we have investigated the preparation and characterization of neural interface materials. Electrochemical polymerization using potentiostatic and galvanostatic methods was used to optimize the surface of the metal electrode sites. Scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were used to study the surface morphology, electrochemical properties, and stability of electrodeposited polymers. Cytotoxicity tests using fibroblasts and Schwann cells were performed to evaluate the biocompatibility of the micro-probes and neural interface materials. Dorsal root ganglion (DRG) in vitro preparation was used to evaluate neuronal cell cell adhesion to the electrode. Polypyrrole (PPy) and poly(3,4-ethylendioxythiophene) (EDOT) with various thicknesses and dopants were deposited onto microelectrode sites from aqueous solution. Our results demonstrate that we can control the morphology, size and electrical properties of PPy and PEDOT by changing the polymerization conditions and adding dopant structures, such as chloride and carbon nanotubes (CNT). It was observed that the addition of carbon nanotubes favors the formation of nodules and increases the surface roughness. Also, electrochemical impedance spectroscopy revealed that conductive polymer composites lower the impedance of gold microelectrodes by three orders of magnitude. We found that PPy and PEDOT carbon nanotubes composite coated electrodes maintain intimate contact with axons. Using these conductive polymer composites, high quality nerve spike signals can be detected and electrical stimulation of axons can be achieved.
Monitoring of Traumatically Injured Organotypic Hippocampal Cultures with Stretchable Microelectrode Arrays
Authors: Yu Zhe , Tsay Candice , Lacour Stéphanie P. , Wagner Sigurd , Morrison Barclay 
Published: April 2011

ABSTRACTTraumatic brain injury (TBI) can be caused by motor vehicle accidents, falls and firearms. Approximately 2% of the US population lives with disabilities cause by TBI. To discover mechanisms of functional deficits underlying TBI, as well as to develop strategies to restore lost function with neural interfaces, we developed a stretchable microelectrode array (SMEA), which can be used for continuous recording of neuronal function, pre-, during, and post-stretch injury. The SMEAs were fabricated on elastomeric substrates, consisting of stretchable 100μm wide, 25nm thick gold electrodes patterned on a polydimethylsiloxane (PDMS) substrate, and encapsulated with a 10-20μm thick, photo-patternable silicone (WL-5150, Dow Corning) insulation layer. Finally, the SMEA was packaged between two printed circuit boards and mounted in a commercial Multi Channel Systems amplifier. Combining with our TBI model, which can generate precise and reproducible injury of hippocampal cultures, SMEAs were able to monitor the extracellular field potentials of neuronal populations within the cultures grown on SMEAs and injured by bi-axialy stretching the stretchable membranes. Previous biocompatibility tests showed no overt necrosis or cell death caused by the SMEAs after 2 weeks in culture [2]. The electrical performance of the SMEAs was tested in electrophysiological saline solution before, during and after biaxial stretching. The initial electrode impedance at 1kHz was ∼2kΩ. The SMEA was stretched to 8.5% biaxial strain. The microelectrode impedance increased with the strain to reach 800kΩ at 8.5% strain. Upon relaxation, the impedance recovered to 10kΩ. The working noise level of the sMEA remained below 20 ΩVpp during the whole process. New methodologies for improving the design of microelectrode arrays structure, the choice of materials and the new technology of fabrication were tested on gold microelectrode arrays supported on glass. By using the prototype arrays, population spikes were able to be recorded from organotypic hippocampal slice cultures of brain tissue. Our results demonstrate that the prototype arrays have good electrical performance compatible with existing multielectrode array systems. Moreover, the results indicate the ability of the prototype arrays to record neuronal activity from hippocampal slices. This novel technology of SMEAs will enable new studies to understand injury mechanisms leading to post-traumatic neuronal dysfunction.
Precision Teng-Man Electro-Optic Measurements Using Highly Near-Infrared Transparent Electrodes
Authors: Wang Lian , Yang Yu , Liu Zhifu , Marks Tobin J. , Ho Seng-Tiong 
Published: April 2011

AbstractA series of highly near-infrared (NIR) transparent In2O3 thin films has been grown by ion-assisted deposition (IAD) at room temperature, and their optical and electrical properties characterized. The NIR transparency and the plasma edge can be engineered through control of the film deposition conditions. The as-deposited In2O3 thin films were employed as transparent electrodes for direct electro-optic (EO) characterization measurements via the Teng-Man technique. Using LiNbO3 as the standard, the relationship between the degree of electrode NIR transparency and Teng-Man EO measurement accuracy was evaluated. It is found that In2O3 electrodes can be tailored to be highly NIR transparent, thus providing more accurate Teng-Man EO coefficient quantification than ITO (tin-doped indium oxide). In addition, the EO coefficients of stilbazolium-based self-assembled superlattice (SAS) thin films were directly determined for the first time by the Teng-Man technique using an optimized In2O3 electrode. EO coefficients r33 of 42.2, 13.1, and 6.4 pm/V are obtained at 633, 1064, and 1310 nm, respectively.
Structural and Microwave Characterization of Magnetron Sputtered Ba0.5Sr0.5TiO3 Films on c-plane Sapphire Substrates
Authors: Fardin Ernest Anthony , Holland A. S. , Ghorbani K. , Usher B. F. 
Published: April 2011

ABSTRACTMany studies of Barium Strontium Titanate (BST) thin films for RF / microwave applications have employed MgO, LaAlO3 or Pt/Si as the substrate material for BST deposition. However, there have been relatively few reports of BST films grown on sapphire, despite the excellent microwave properties of this material. In this investigation, BST thin films were deposited by RF magnetron sputtering on (001) single crystal c-plane sapphire substrates. Interdigitated capacitors (IDCs) patterned on the film surface were used to measure the dielectric tunability and loss tangent at microwave frequencies. Thick Au conductors were electroplated to minimize conductor losses. Post deposition annealing in air was found to significantly improve the tunability of the sputtered films.
Enhanced contrast ratio of an electrochromic window (ECW) based on a V2O5-TiO2 composite thin film as a counter electrode
Authors: Kim Sooyeun , Xu Chunye , Taya Minoru 
Published: April 2011

ABSTRACTAn Electrochromic window (ECW) is a strong candidate for an optical shutter. An ECW is composed of the conductive polymer as a working electrode and V2O5 as a counter electrode. The ECW technology switches between colored and bleached stages. In this paper the modification of a V2O5 thin film as a counter electrode is studied to increase contrast ratio of ECWs by adding TiO2 into V2O5. The dependence of the intercalation properties and transmissivity of V2O5-TiO2 composite films on various chemical compositions, a preparation and characterization of the films for use as a transparent ion storage layer in organic ECWs are focused on in this paper. A V2O5-TiO2 composite film was synthesized with sol-gel electrophoresis deposition method. Indium Tin Oxide (ITO) coated glass was used as an electrically conductive and transparent substrate. A V2O5-TiO2 composite film with V/Ti ratio of 70/30 in the reduced state showed 6 to 13% improvement of transmissivity between 380 nm and 800 nm wavelengths as compared to a V2O5 thin film in the same state. Li+ intercalation rate was also observed to be higher. The composite film exhibited twice of capacitance than that of the V2O5 film. An ECW with the composite film exhibited 6% higher contrast ratio than that with the V2O5 film. The contrast ratio of the ECW, measured as Δ%T, was equal to 56%, and ranged from 2% to 58% between the colored and bleached state measured at 580 nm wavelength. The color change response speed was also faster, i.e., only two seconds between fully colored and bleached stages.Key words: electrochromic window (ECW), V2O5-TiO2 composite film, contrast ratio, transmissivity, Li+ intercalation rate
High Flux Polyamide Composite Hollow Fiber Membranes for Reverse Osmosis Applications
Authors: Norris Ian D. , Morrison Malcolm C. , Mattes Benjamin R. 
Published: April 2011

ABSTRACTHigh flux composite hollow fiber membranes for brackish water desalination based on the interfacial polymerization of a cross-linked polyamide salt rejecting layer onto a semi-permeable hollow fiber support have been developed. These hollow fiber membranes exploit the advantages of using a thin-film composite reverse osmosis membrane (higher flux and salt rejection) with the higher surface area/volume ratio of hollow fiber membrane elements. The composite hollow fiber membranes were prepared by coating a polysulfone hollow fiber with a polyamide salt rejecting layer based on the interfacial polymerization reaction between m-phenylenediamine and trimesoyl chloride/isophthaloyl dichloride. The RO figures-of-merit of these composite polyamide hollow fiber membranes were evaluated for the desalination of a synthetic brackish water feed (2,000 ppm NaCl) at 225 psi over a 60 hour period. After an initial break-in period in which the flux declined 30% due to membrane compaction, the stabilized RO figures-of-merit for these hollow fiber membranes were a water flux of 280 L/m2·day and a salt rejection of 99.1%. Based on the water flux and packing density of the membrane, it is estimated that the stable production of potable water of a hollow fiber membrane element containing these composite membranes will be between 20 and 30% greater than that of a similarly sized spiral wound brackish water membrane element.
Does Exceptional Viscous Drag Impede Flow Through a Nano-Sieve's Pores?
Authors: Feibelman Peter J. , Houston J. E. 
Published: April 2011

ABSTRACTTo address the concern that a material functionalized to reject dissolved ions may give rise to a highly viscous aqueous interphase within nanometers of its surface, we conducted and interpreted Interfacial Force Microscope measurements of the dissipative forces that resist motion of a tip parallel to a sample, in water. The results are consistent with earlier measurements where the tip approached the sample. They confirm that near hydrophilically functionalized surfaces, interphase viscosities more than a million times that of bulk water can be expected.
Including Nanoscale Investigations in Undergraduate Physics Laboratories at all Levels of the Curriculum
Authors: Vandervoort Kurt , Hyder Asif , Barker Stephanie , Torrico Raul 
Published: April 2011

ABSTRACTA series of laboratory modules were developed to introduce atomic force microscope (AFM) applications into undergraduate physics courses. The goal is to elucidate fundamental physics concepts at the nanoscale that will complement existing investigations at the macroscale, and to expose students to advanced instrumentation at an early level. The experiments allow students to experience the full range of scanning probe modes available, which include contact, intermittent contact, lateral force, and magnetic force microscopy as well as force distance spectroscopy. The course levels span the range from freshman introductory to advanced senior level and allow students to experience AFM applications at successive levels of complexity.
Real Time Nanostructure Imaging for Teaching Nanoscience and Nanotechnology
Authors: Chizmeshya A. V. G. , Drucker J. , Sharma R. , Carpenter R. W. 
Published: April 2011

ABSTRACTOur experiences in research on nanoscience and technology using various microscopies to observe materials synthesis reactions and to measure local (∼ 0.1-100 nm scale) structure and composition variations in solids provide some very useful examples to introduce students to important concepts of the field. The fundamental concept to illustrate is the nanometer length scale, of course, but other concepts such as mass and energy flows at the nanometer level and their effects on materials properties are at least as important, but more difficult to bring to students in a challenging but understandable way. We are using dynamicin situor animated microscopy experiments in several material systems to teach these concepts. These experimental research results provide a useful basis for student computer modeling experiments, to give them direct participation in nanoscale materials research at an appropriate level. We are also exploring student group participation in live (interactive) electron microscopy experience via remote access into a suitably equipped computer visualization classroom.
Size dependence in one-dimensional nano-materials and one-dimensional heterojunctions
Authors: Zhu Jing , Luo Jun , Chen Changqiang , Shi Yu , Liu Xiaohua , Zhang Jiong , Peng Kuiqing , Huang Zhipeng 
Published: April 2011

ABSTRACTOne-dimensional (1D) nano-materials have attracted a plenty of attention due to their novel structures and properties. Our group has carried out researches on synthesis, structure and property of 1D nano-materials, which are introduced in this paper. First, size effects on the crystal structure of Ag nanowires and on Young's modulus in [0001] oriented ZnO nanowires, respectively, have been revealed and modeled. The former is concerning the systemic energy of an individual Ag nanowire. The latter is caused by the surface stiffening effect arising from surface relaxation induced bond length contractions in the ZnO nanowires. Second, structures of 1D helical nano-materials including SWCNT (single-walled carbon nanotube), B-DNA and MWCNT (mutli-walled carbon nanotube) have been studied. It is shown that there is strong orientation dependence of diffraction intensities from SWCNT and B-DNA, which can even result in certain layer lines missing in their diffraction patterns. Also, it is demonstrated that high-resolution transmission electron microscope (TEM) images of sidewall regions of MWCNTs are not structural ones and from the interference of the {0002} and the {1011} diffraction waves. Third, arrays of four types of 1D heterojunctions have been synthesized. Among these 1D heterojunctions, the interfacial structures of the Ni/MWCNT/a-CNT(amorphous carbon nanotube) heterojunctions show that multiple outer walls in the MWCNTs can simultaneously participate in electrical transport. The electrical properties of the Ni/MWCNT/a-CNT and the Ag/a-CNT heterojunctions have been measured. As a result, it is found that the contacts between the Ag nanowires and the a-CNTs are ohmic ones with universal significance, and that each Ni/MWCNT/ a-CNT contains two diodes connected in series face-to-face. Moreover, most of the diodes have the most nearly ideal characteristics of Schottky contacts, indicated by quantitative analysis with the thermionic emission theory. Last, our group has developed a novel technique for rapidly producing large-area highly-oriented Si nanowire arrays on Si wafers by scratching the Si surface with metal nanoparticles near room temperature in HF solution. By this method, Si nanowires with desirable axial crystallographic directions, desirable doping characteristics and remarkable antireflection property can be readily obtained. The Si nanowire arrays have the potential applicability as an antireflective layer for photovoltaic devices and optical detectors. Furthermore, a combination of this method and the nanosphere lithography has been developed to fabricate large-scale Si and Si1−xGex quantum dot arrays with controllable height, diameter and center-to-center distance.