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I-1
Nanoindentation of Single Crystal Gold Nanowires
D. Cakiroglu1, D. Coker*1, B. Ozturk2, and B. Flanders2
1School of Mechanical and Aerospace Engineering, 2Department of Physic
Oklahoma State University, Stillwater, OK 74078
Measurement of the mechanical properties of nanowires by indentation is difficult due to the influence of the curvature and substrate. The most widely used method to measure these properties is the Oliver-Pharr method (OP). However, Nix’s group (2006) showed that OP method overestimates the contact area and contact depth in soft materials, thus underestimating the hardness and Young’s modulus which makes use of these geometry parameters. Joslin-Oliver (JO) method can give better approximation for the hardness of soft materials because this method uses the term P/S2 which does not depend on the indentation depth and contact area. JO has been shown to be accurate for the thin film systems having similar moduli such as gold film on a glass substrate. Single crystal gold nanowires of about 200 nm height, 1300 nm width and 200µm length were fabricated between two gold electrodes on a glass substrate using ENFilADIng (Electrochemical Nano-Filament Assembly with Directed Interfacing). The load-displacement behavior is measured using a nanoindenter which are analyzed using the JO and the OP method to obtain the hardness and modulus. The hardness values and modulus values are presented for single crystal gold nanowires using these two methods.
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I-2
Sensitive measurement of deep hole traps in conjugated polymers
Rodrigo E. Palacios, Wei-Shun Chang, John K. Grey, Fu-Ren F. Fan, Allen J. Bard*, and Paul F. Barbara*
Center for Nano and Molecular Science and Technology, University of Texas, Austin, TX
The recently developed single molecule spectroelectrochemistry (SMS-EC) technique was used to investigate deep hole-traps in the conjugated polymer poly(2,5-bis(2’-ethyl-hexyl)-1,4-phenylenevinylene) BEH-PPV at an interface with an indium tin oxide (ITO) electrode. Hole-traps in organic semiconductor materials are known to play an important role in charge injection and transport in organic electronic devices. In this report we demonstrate that the average hole-trap concentration is negligible (< 1011 traps/cm2) in a pristine polymer/electrode interface, corresponding to less than one trap per ~104 oxidizable states. In contrast, under highly oxidizing conditions, “transient” hole-traps were observed. Under re-reducing conditions, the transient hole-traps are converted back to non-trap states over a broad distribution of time scales. Additionally, the rate of converting hole-traps to non-trap states is substantially accelerated by optical excitation. The results give further insight into the chemical nature of hole-traps in organic semiconductor materials.
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I-3
Energy Transfer and Selective Hole Injection in Blend Conjugated Polymers
Wei-Shun Chang, Ya-Lan Chang, Fu-Ren F. Fan, Allen J. Bard*, and Paul F. Barbara*
Center for Nano and Molecular Science and Technology, University of Texas, Austin, TX
Energy transfer and selective hole injection in polymer nanoparticles composing of F8BT (donor) doped with single polymer chain BEH-PPV (acceptor) was studied with the new electrochemical single molecule spectroscopy (EC-SMS) technique. At potential ~ 0.9V only BEH-PPV became oxidized (selectively creating holes on BEH-PPV) allowing us to explore the mechanism of forming deep trap. The relative energy transfer efficiencies (calculated from the intensity ratio of BEH-PPV and blend nanoparticles) were found as change linearly with the amount of the acceptor present, i.e. 0.13±0.11 and 0.66±0.20 for 1% and 6% blend nanoparticle, respectively. Assuming an average nanoparticle diameter of 25nm, we estimated a förster radius of 6nm. At 1% of BEH-PPV in nanoparticles, the acceptor component showed fluorescence intermittency suggesting that single chain doping levels were achieved at this concentration. The ensemble fluorescence intensity of 1% blend nanoparticle was quenched ~15% with applying triangular bias of 0.9V consistent with the fraction of fluorescence for BEH-PPV in 1% blend nanoparticle, while very little fluorescence quenched for pure F8BT aggregates. This result suggests that the potential driven oxidation of BEH-PPV only quenched the fluorescence from BEH-PPV. No further significant intensity quench under a pulse bias of 0.9V with duration of 5s suggests that the holes on BEH-PPV chains are localized and does not diffuse into the F8BT polymers. A symmetric and reversible intensity modulation of 1% blend nanoparticles with applied pulse bias of 0.9V suggests that the holes injection into single BEH-PPV chain does not form a deep trap. This result is consistent with the proposed mechanism that multiple chains are required to form a strong acid to be deprotonated, which is the source of deep trap.
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I-4
3D Nano-photonic Crystal structures for Laser Beam Switching and Steering
Jiaqi Chena), Wei Jiang b), Xiaonan Chen a), Li Wang a), Sasa Zhang a) and Ray T.Chen*
a) Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX 78758
b) Omega Optics, Inc. Austin, TX 78758
Photonic crystal based superprism offers a new way to design new optical components for beam steering and DWDM application. 3D photonic crystals are especially attractive as they could offer more control of the light beam based on the needs. A polygonal prism based holographic fabrication method has been demonstrated for a three-dimensional face-centered-cubic (FCC)-type submicron polymer photonic crystal using SU8 as the photo-sensitive material. Therefore antivibration equipment and complicated optical alignment system are not needed and the requirement for the coherence of the laser source is relaxed compared with the traditional holographic setup. By changing the top-cut prism structure, the polarization of the laser beam, the exposure and development conditions we can achieve different kinds of triclinic or orthorhombic photonic crystals on demand. Special fabrication treatments have been introduced to ensure the survivability of the fabricated large area (cm2) nano-structures. Scanning electron microscopy and diffraction results proved the good uniformity of the fabricated structures. With the proper design of the refraction prism we have achieved a partial bandgap for S+C band (1460-1565nm) in the [111] direction. The transmission and reflection spectra obtained by Fourier transform infrared spectroscopy (FTIR) are in good agreement with simulated band structure. The superprism effects around 1550nm wavelength for the fabricated 3D polymer photonic crystal have been theoretically calculated and such effects can be used for beam steering purpose.
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I-5
Self-Assembled Monolayers Generated from Unsymmetrical Partially Fluorinated Spiroalkanedithiols
Pawilai Chinwangso and T. Randall Lee*
Department of Chemistry, University of Houston
4800 Calhoun Road, Houston, TX 77204-5003
The structural and interfacial properties of self-assembled monolayers (SAMs) generated from the adsorption of the chelating dithiol (CH3(CH2)7C[(CH2)8(CF2)7CF3][CH2SH]2) onto the surface of gold were investigated. These new SAMs were characterized by ellipsometry, contact angle goniometry, polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), and X-ray photoelectron spectroscopy (XPS). These data were compared to those obtained from SAMs generated from n-octadecanethiol (C18SH, CH3(CH2)17SH) and the semifluorinated thiol (F8H10SH, CF3(CF2)7(CH2)10SH). The latter two monothiols possess terminal chains with chemical compositions analogous to those found in the new chelating dithiol.
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I-6
Synthesis, Optical and Fluorescence Studies of Gold nanoparticle Polymer Composites with Carbazole Terminated Dendrons.
Kranthi C. Danda
University of Houston
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I-7
Structural and Mechanical Properties of Graphene Oxide Paper
Dmitriy A. Dikin,† Sasha Stankovich,† Eric J. Zimney,† Geoffrey H. B. Dommett,† SonBinh T. Nguyen,‡ and Rodney S. Ruoff†
†Department of Mechanical Engineering
‡Department of Chemistry
Free standing membranes (graphene oxide paper) were produced by exfoliation of graphite oxide in water to individual ‘graphene oxide’ sheets (as a colloidal suspension) followed by their re-assembly by vacuum filtration. Study of the structure and morphology of the graphene oxide paper revealed that it is composed of highly packed and ordered layers of graphene oxide sheets separated by intercalated and H-bonded water molecules. Measurements of the mechanical response under tensile load revealed elastic deformation for small strain, followed by plastic deformation again for a relatively small region of strain, and then fracture without pullout of individual sheets or multi-layer stacks. Graphene oxide paper possesses high modulus values of about 40 GPa and strength values around 130 MPa, each much higher than modulus or strength values for either bucky-paper or commercial Grafoil. The experimental results support the conclusions of very effective load distribution and good binding between the graphene oxide sheets in which the self-regulated amount of interlayer (intercalated) water plays a central role.
Support from NASA and the NSF is appreciated. Both grants end in August 2007.
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I-8
Particle size influence on the magnetic properties of HoMnO3 multiferroic
E.Galstyan1, K.Martirosyan2, B.Lorenz1, D.Luss2, and C.W.Chu1,3,4
1Texas Center for Superconductivity, University of Houston; 2Chemical Engineering, University of Houston; 3Lawrence Berkeley National Laboratory; 4Hong Kong University of Science and Technology
The hexagonal, nonperovskite HoMnO3 oxide, containing a triangular arrangement of Mn3+, has been prepared with nano- and micro-size particles using the novel self-sustaining one-step process, named Carbon Combustion Synthesis of Oxides. X-ray diffraction and electron probe microanalysis of as-synthesized powders show that essentially complete conversion to single-phase products was accomplished during the synthesis. HoMnO3 single crystals are well known as multiferroic, where the Ho-O displacements give rise to a ferroelectric moment (TC = 875 K), the Mn3+ moments order at Néel temperature TN=72 K, Mn3+-spin reorientation transitions occur at Tsp=34 K, magnetic Ho3+ orders at THo ~ 5.2 K, and the order parameters are naturally coupled through the Ho-Mn exchange and anisotropy interactions. We have investigated the influence of nano/micro size particles on the magnetic behavior in combustion-synthesized HoMnO3 materials in comparison with a polycrystalline samples crushed from a HoMnO3 single crystal. Below 5 K we have observed magnetic hysteresis phenomena. Magnetic coercive field, as well as remnant magnetic moment, increases with diminishing particle size. We assume that the hysteresis behavior in the polycrystalline particles occurs due to a single-domain state, in which the only mechanism for the magnetization reversal is the rotation of the particles magnetic moment. This rotation requires more energy against the anisotropy forces and higher fields are required to reverse the magnetization.
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I-9
Nonlinear elastic behavior of graphene sheets and single-wall carbon nanotubes
Jun Zhou and Rui Huang
Department of Aerospace Engineering and Engineering Mechanics, University of Texas, Austin, Texas 78712
A continuum analysis incorporating interatomic potentials is conducted in order to understand the nonlinear behavior of carbon nanotubes (CNTs) under finite deformation. The classical Cauchy-Born rule provides a bridge linking between atomic interactions and macroscopic stress-strain behavior. However, since the atomic structure of CNTs is not centrosymmetric, it is necessary to modify the Cauchy-Born rule to account for internal relaxation of atoms, which renders locally inhomogeneous deformation at the atomic scale under a macroscopically homogeneous strain. By molecular mechanics simulations, we show that, for a unit cell of planar graphene sheet, the atomic positions shift from those predicted by homogeneous deformation except for the case with equi-biaxial strain. A linear relationship is obtained for the atomic shift under relatively small strains, which becomes nonlinear under larger strains. By incorporating the internal relaxation into the Cauchy-Born rule, we show that the in-plane stress-strain behavior of a graphene sheet becomes nonlinear and anisotropic under finite deformation. In particular, a coupling between normal and shear deformation is predicted along the directions corresponding to chiral CNTs, in agreement with previously reported stretch-induced torsion in single-wall CNTs.
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I-10
An Analysis of SAMs on Gold Derived from CH3CF2(CH2)nSH Provides Insight into the Influence of Fluorine Substitution on Chain Conformation
Andrew C. Jamison, David Barriet and T. Randall Lee*
Department of Chemistry, University of Houston
Self-assembled monolayers (SAMs) prepared from a series of alkanethiols in which the terminal methylene group was selectively fluorinated (CH3CF2(CH2)nSH, where n = 11-16) were analyzed using ab initio calculations employing the 6-31G* basis set at the level of restricted Hartree-Fock (RHF). Additional structural information was gathered using optical ellipsometry, contact angle goniometry, transmission infrared spectroscopy, and polarization modulation infrared reflection absorption spectrometry (PM-IRRAS). The PM-IRRAS spectra show that the presence of the CF2 unit fails to disrupt the formation of well-ordered SAMs in the adsorbates having longer chains; these data also provide evidence that the longer chain SAMs are more crystalline in their packing structure than those having shorter chains. There are, however, indications that the SAMs having odd-numbered chain lengths fail to exhibit the all-trans alignment that is expected for such monolayers. This presentation examines the evidence that the odd-numbered chains of this series are skewed from their anticipated alignment. Moreover, our analysis shows that these deviations from the anti conformation at the end of the chain can occur without disrupting the ordered structure of the SAM.
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I-11
Alternate Ultrathin Films of CdSe Nanoparticles and Conjugated Polymers; Band Gap Design for Solar Cells and Memory Devices.
Jayarathne, L. C.; Park, Y. Baba, A.; Fulghum, T. M.; G. Jiang.; Advincula, R.
Department of Chemistry, University of Houston, Houston, TX-77204.
Electrostatic layer by layer self assembly was incorporated to deposit nanocomposite thin films of a p-type organic semiconductor, Emeraldine base of polyaniline (EB-PANI) and an n-type inorganic semiconductor, thiol coated CdSe nanoparticles (CdSe-T) on ITO coated glass substrates. In-situ Surface Plasmon Resonance Spectroscopy (SPS) was used to obtain the correct concentrations of EB-PANI and CdSe-T solutions, in order to achieve nanoscale control of hybrid thin films. The dielectric constant and thickness of thin films were determined using SPS and Ellipsometry respectively. UV-vis spectroscopy and Cyclic Voltammetry of as deposited films were investigated as a function of number of bilayers and the appropriate band gap and the number of bilayers were proposed to construct solar cells and memory devices.
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I-12
Covalent Immobilization of Patterned Monolayers of Magnetic Nanoparticles on Hydrogen-Terminated Silicon.
Gyu Leem, Shishan Zhang and T. Randall Lee
Departments of Chemistry and Chemical Engineering, University of Houston
4800 Calhoun Road, Houston, TX 77204-5003
In this study, ω-alkenyl-1-carboxylic acids was synthesized as a surfactant, which was used in the direct preparation of magnetic iron oxide (MnFe2O4) nanoparticles with the surfactant subsequently bound to a silicon(100) surface. The magnetite nanoparticles terminated with the α-alkenyl moieties was prepared using a one-pot reaction at high temperature without the need of ligand exchange. This process led to the creation of monodisperse magnetite nanoparticles. Transmission electron microscopy and X-ray diffraction measurement were used to characterize the morphology and structure of the nanoparticles. The nanoparticles were deposited as prepared onto a hydrogen-terminated silicon(100) wafer, and covalently anchored to the surface by UV irradiation at 365 nm. Analysis was conducted by AFM, SEM, SQUID and XPS with UV treatment, confirming that the UV treatment led to covalent immobilization of the nanoparticles on the silicon surface.
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I-13
Fabrication and Mechanical Characterization of Silicon Nanolines
Bin Lia, *, Min K. Kangb, Kuan Lua, Rui Huangb, Paul S. Hoa, Richard A. Allenc, Michael W. Cresswellc
a Microelectronics Research Center, The University of Texas at Austin, 10100 Burnet Road, Bldg 160, Austin, TX 78758
b The University of Texas at Austin, Department of Aerospace Engineering and Engineering Mechanics, College of Engineering,1 University Station C0600, Austin, TX 78712
c Semiconductor Electronics Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-8120
With continuing scaling of device dimension, fabrication of nanoscale structures and characterization of their mechanical properties pose significant challenges for future development of ultra large-scale integrated (ULSI) circuits. In particular, silicon-based nanostructures form essential building blocks for microelectromechnical systems (MEMS) and play an important role in controlling the functionality and reliability of devices. In this study, we demonstrate the feasibility of a method to fabricate nanoscale Si lines using an anisotropic wet etching process. The silicon nanolines have straight and atomically flat sidewalls, almost perfectly rectangular cross sections and highly uniform linewidth at the nanometer scale. Nanolines with a height-width aspect ratio ranging from 1 to 10 have been successfully fabricated. An atomic force microscope (AFM) based nanoindentation system was employed to investigate the scaling effect on mechanical properties of the silicon nanolines. The indentation force-displacement curves were determined for a set of Si lines with line widths ranging from 70 to 500 nm. Interestingly, after the initial elastic response, a large displacement burst was observed for nearly all the lines. After unloading, for silicon lines of 73nm wide no residual deformation was observed, suggesting an elastic deformation mechanism. We attribute the observed displacement burst to buckling of the nanolines as a bifurcation to the initial elastic deformation under indentation. A finite element model is being developed to predict the critical load for buckling and will be used to analyze the observed buckling behavior. Finally the scaling effects on elastic modulus and strength of the silicon nanolines will be discussed.
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I-14
A TiO2-anatase implanted nano-layer on glass curtain to improve indoor air quality
Jiunn-Der Liao*, Chia-Wei Chang, Chi-Yuan Kao
Department of Materials Science and Engineering,
National Cheng Kung University
No. 1, University Road, Tainan 701, Taiwan
A comfortable space is particularly emphasized in modern architecture, while a moderate introduction of natural sunlight and free air is anticipated. This work is to improve indoor air quality by reducing ambient air temperature and cleaning indoor airflow, which aims to make life more comfortable and simultaneously to achieve energy saving more efficient. By upholding the degree of sunlight transmission, the inner glass surface is a TiO2-anatase implanted nano-layer that is photo-catalytic, peeling-resistant and high in contact surface area. The ultra-thin nano-layer is competent to absorb particular wavelengths from the transmitted sunlight and promote the photo-catalytic reactivities such as the decomposition of organic species and odors, the control of bacterial growth. It is therefore functioned to clean a major part of the indoor airflow. In addition, the pathway of the airflow can be installed with air filters that are purposely implanted with silver ions. The silver ion-implanted filters are also applicable to kill bacteria during the night or a cloudy day.
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I-15
A new model developed to evaluate the contact parameters arising during the nano-indentation tests with different loading/unloading rates
Jen-Fin, Lin Chang-Fu, Han
Department of Mechanical Engineering National Cheng Kung University,
No.1, Ta-Hsueh Road, Tainan 701, Taiwan, R.O.C.
A new mechanical model is developed in the present study for hard materials to investigate the behavior arising during the loading/unloading process of an indentation test. Two governing differential equations are derived for the depth of the indenter tip (h*i) and the depth formed at the separation point (h*s) expressed in a power form. The exponent value of h*i in either the loading process or unloading process is considered to be a variable as a function of the indentation depth in the governing differential equation. The exponent value of h*s is proven to be the same value as that of h*i. All spring and damping coefficients shown in these governing differential equations are determined by the real-coded genetic algorithm. With the aids of experimental results of hi shown at large and small indentation depths, the h*i and h*s solutions are obtained. The asymptotic solutions of h*i and h*s at various indentation depths can thus be determined, and the real contact area at any indentation depth can be calculated if h*s is available. Quartz was used as the example of hard materials, and the contact area predicted by the present model is quite close to the solution predicted by the area function of Oliver and Pharr [1]. Under a constant maximum load, the contact projected area is slightly increased by decreasing the loading/unloading rate. The phase lag behavior demonstrated in the indentation test at two different loading/unloading rates was investigated, and it is enhanced by increasing the loading/unloading rate.
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I-16
Quantitative Nano-friction Study of Vertically Aligned Multi-Walled Carbon Nanotube Arrays
J. Lou*, K.-S. Kim#, F. Ding* and B.I. Yakobson*
*Department of Mechanical Engineering and Materials Science, Rice University
6100 Main St., Houston, TX 77005
#Division of Engineering, Brown University
Sliding friction properties of vertically aligned multi-walled carbon nanotube (VAMWNT) arrays have been investigated in current study. The VAMWNT arrays have been obtained on an anodic aluminum oxide (AAO) template by chemical vapor deposition at 650°C. Friction force was measured in air by a modified lateral force microscopy (LFM) tip with 15 µm diameter borosilicate sphere attached to the end of the regular LFM tip. Direct friction force calibration at nano scale was carefully carried out by using a novel diamagnetic levitation calibrator system. A reverse stick-slip behavior was observed and investigated by energy optimization analysis. The effects of protruded lengths (0, 30, 100, 750 nm) of these VAMWNT arrays and different interfaces were studied systematically. It was found the resulting friction forces increases with increasing protruded length. Also, Aluminum coated cantilever-bead assembly results higher friction forces in all samples studied.
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I-17
Nano-ripple structure formation on Silicon surface by gas cluster ion beam fabrication and its applications to III-nitride nanorods fabrication
O. Lozano1, H.W. Seo2, X.M. Wang1, Q.Y. Chen1,3, L.W. Tu3, Y.T. Lin3, Y.L. Cheng3, I.G. Chen4, K.H. Lee4, H.T. Tung4, T.S. Kao4 and Wei-Kan Chu1
1Department of Physics and Texas Center for Superconductivity, University of Houston.
2Department of Physics, University of Arkansas, Little Rock, AR, USA
3Department of Physics and Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung, Taiwan, Republic of China
4Department of Materials Science and Engineering, National Sun at-Sen University, Kaohsiung, Taiwan, Republic of China
Gas cluster ion beam (GCIB) have been used to fabricate nano-ripple structures on Si substrates. In this work, using (Ar)n+ clusters at 30 kV acceleration, where n≈3,000, we have observed nano-ripple formations on the silicon surface after GCIB bombardment. The wavelength, amplitude and the dimensions of the ripples are studied in an effort to characterize the morphology as a function of cluster beam’s angle of incidence, crystallographic orientations of the substrate, and the ion dosages. The underlying physics of ripple formation will be conjectured and the applications of nanostructures fabrication on rippled (111)-Si substrates in producing nanorods of III-nitrides, such as GaN, InGaN, and InAlN, will be presented.
