AVS1997 Session NS-TuP: Aspects of Nanometer-scale Science and Technology
Tuesday, October 21, 1997 5:30 PM in Room Exhibit Hall 1
Tuesday Afternoon
Time Period TuP Sessions | Topic NS Sessions | Time Periods | Topics | AVS1997 Schedule
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NS-TuP-1 Nanoindentation and Scratch Hardness Properties of Carbon Nitride Thin Films
A.V. Kulkarni (Hysitron, Inc.); J. Judy (University of Minnesota) Carbon Nitride (CNx) thin films of various thickness were deposited on Si(100) dc magnetron sputtering technique. The surface morphology was studied by atomic force microscopy. The film replicated the topography of the substrate with a r.m.s. roughness as low as 0.5 nm. The carbon-nitrogen bonding was studied using infrared absorption. Infrared studies revealed multiple bonding states for nitrogen and carbon in the film. µN load nanoindentation studies revealed that the CNx films have a hardness of 23-30 GPa. Scratch test were performed on these coatings and critical load at which the film debonds the surface was used to determine the adhesion and yield strength of the film. Hardness did not vary significantly as a function of N/C ratio in the film. CNx film exhibited excellent resistance as compated to Si(100). The improved performance of the CNx film is attributed to the high yield strength of the coating. |
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NS-TuP-2 Positioning and Precision Manipulation of Au Nanoparticles
C. Baur, B.C. Gazen, A. Bugacov, T.R. Ramachandran, B.E. Koel, A. Madukar, A. Requicha, P. Will (University of Southern California) Nanostructures and nanoarrays have interesting physical and electrical properties. Tuning of these properties in devices requires precise control and alteration of structure. To aid in development of this enabling technology, we first focused on the precise positioning of spherical Au nanoparticles as model systems. We accomplish this manipulation by using an atomic force microscope (AFM) under the control of specialized software that we have developed, enabling the operator to move a specific particle to any location within the scan range of the microscope. The sample, consisting of 15 or 30 nm colloidal Au particles on a mica substrate, is first imaged in non-contact mode to determine the location of each particle and to establish reference points. Then, a single line scan is made along the path that the particle is to be moved along. The position, length, and direction of this line scan is controlled by a mouse-driven cursor. The software also allows the operator to center the line scan over the particle. In this way, we can achieve the necessary compensation for thermal drift, hysterisis, and creep. In the next step, the feedback loop is disabled over a specific region of the line scan so that the particle is intercepted by the tip and pushed to the new location. Requirements for reliable pushing/manipulation have been investigated, e.g., non-contact vibrational amplitude, set-point of the feedback loop, and minimum pushing distance. We demonstrated the capability of precise positioning by constructing linear arrays and by pushing on one particle to move another. |
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NS-TuP-3 Nanolithography on Surfaces of SiWx and ITO Films by STM
I.A. Ryzhikov, V.I. Kuzkin, S.A. Maklakov, I.A. Obukhov ("Delta" Research Institute, Russia) We investigated the following reactions stimulated by local STM-action: - reactive adsorption and segregation on the surfaces of structures based on SiWx layers, - deposition of the organic nanosize objects on the ITO films. Under condition of CHCl3 vapour injection into chamber the local creation of specific regions with sizes about 50-100 nm was observed on SiWx surface around the points of actions by STM. Conductivity of these regions was a factor of 105 - 106 lower than conductivity of starting SiWx layer. Experiments were provided in different gaseous mediums but effect was observed only in CHCl3 vapour. It was shown that under special conditions the process of local STM-stimulated deposition of the organic nanosize objects on the ITO films don't observe in region direct under the tip of STM. The nanosize object was formed in region around point of action in form of the ring. In the case when points of STM electric pulses action are along the straight line the two parallel nanosize lines were formed. In both cases the picture looks as if the tip of STM casts a shadow in the region under it and deposition process in this region is absent. Both described here phenomena may be used for nanofabrication, for example, for masks creation. |
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NS-TuP-4 Nanofabrication Using Monolayer Polymers
C.E. Evans, M.D. Mowery (University of Michigan); H. Menzel (University of Hannover, Germany) The interfacial design and fabrication of organic assemblies within a single molecular layer requires control over structure in the micro-, nano-, and molecular-scale domains. In this presentation, we demonstrate the advantages of using polymerization within single molecular layers to meet these important fabrication criteria. Conjugated diacetylene groups are incorporated within spontaneously assembled monolayer structures to facilitate covalent linking using photoinduced polymerization. The lack of expansion or contraction upon polymerization yields monolayer assemblies that are very robust. However, the polymerization process is highly dependent on the distance between diacetylene groups in neighboring molecules within the monolayer assembly. We present evidence that the topography of the underlying gold substrate has a direct impact on the polymerization process. Such substrate selective polymerization has interesting implications for the nano-scale control of interfacial structure that is key for applications ranging from lubrication to sensor design. |
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NS-TuP-5 Thin Film Nanostructures Using GLAD (GLancing Angle Deposition)
K. Robbie, J.C. Sit, M.J. Brett (University of Alberta, Canada) A novel deposition technique called GLancing Angle Deposition (GLAD) was developed to produce thin films with microstructure controlled on the 10 nm scale. Fabrication of helical columnar microstructure results in optical activity in GLAD films, giving rise to optical filter applications [1]. With previous deposition methods, control of microstructural features such as density (porosity) and column angle has been hampered by the inability to vary the features individually. We have developed a new technique for deposition of GLAD thin films using a computerized feedback control system that combines GLAD with three dimensional substrate motion, based on rotation about two axes and with feedback from a crystal thickness monitor. The new control system provides much better control over microstructure parameters than before, as microstructure property interdependence has been largely eliminated. Whereas in earlier efforts [2] there was a fixed relationship between column orientation and porosity, with both determined by incident flux angle, that constraint has now been removed and we are able to independently manipulate column orientation and porosity. With the improved control over microstructure features, an extensive range of micrometer scale shapes can be fabricated. These include microstructures composed of spiral columnar helices, "precessing" helices, and an "s" shaped structure similar to a theoretical form of liquid crystals called periodically bent nematic [1,3]. Characteristics such as rise angle, radius, and pitch can now be independently controlled with this new process. In addition, control algorithms using this system have been designed to generate a dense capping layer on top of the porous microstructure. 1. K. Robbie, M. J. Brett, and A. Lakhtakia, Nature 384, 616 (1996). 2. K. Robbie et al., J. Vac. Sci. Technol. A 13(3), 1032 (1995). 3. K. Robbie, M. J. Brett, J. Vac. Sci. Technol. A 15(3), (1997). |
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NS-TuP-6 Relationships of Surface, Step, and Dislocation Energies to the Variation of Pit Morphology at Calcite Surfaces.
Y. Liang, D.R. Baer (Pacific Northwest National Laboratory) Based on the AFM measurements on the variation of etch pit morphology on single crystal calcite (CaCO3) surface under different solution conditions, the relationships among surface energy, step energy, and dislocation energy have been investigated. When the solution was far from saturation, anisotropy in atomic step velocity and etch pit (ten to hundred atomic layers deep) morphology was observed. Results show that the slopes of the side of the etch pits differ by a factor of 2.3 under this solution condition. As the solution approaching to saturation, the ratio of the slopes reversed from initial 2.3 under the far from saturated condition to nearly 0.3 under the saturated condition. Based on the variation of the pit morphology under different solution conditions, the relationships among surface energy, step energy, and dislocation energy are obtained. The effect of entropy on dissolution reaction will also be discussed. This work was supported by DOE, Division of Geosciences, Office of Basic Energy Sciences. |
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NS-TuP-7 In-situ AFM Observation of Initial Stages of Corrosion at 18Cr-8Ni Stainless Steel
F. Katsuki, Y. Matsuda, M. Matsumoto, T. Tomida (Sumitomo Metal Industries Ltd., Japan) The change of surface morphology of stainless steel in aqueous solutions during the initial stage of corrosion has not fully been understood, because of difficulty in high- resolution in-situ observation of corroded surfaces and in controlling the corrosion during observation. The purpose of this paper is to clarify the effect of the initial surface roughness and the presence of chloride ions in aqueous solutions on the morphological change during the initial stage of corrosion. The in-situ AFM, for which the surface area of a counter electrode in the fluid cell is comparable to that of specimens to control the corrosion electrochemically, has been employed to investigate the morphological changes during corrosion. AFM observations have revealed that in NaCl solutions a mechanically polished rough surface (MP) anisotropically dissolves and transforms into the faceted surface with increasing electrode potential, while an electropolished smooth surface (EP) is covered with transpassive films of a rectangular shape. In chloride free Na2SO4solutions, such morphological changes have not been observed on the surface of both MP and EP. The relationship between these morphological changes and the corrosion process will be discussed. |
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NS-TuP-8 Electron Transfer of Nanoparticles Attached onto Organic Monolayers Self-Assembled on Gold and Silicon Surfaces
C.Z. Li, J. D'Agnese, B. Doung, N.J. Tao (Florida International University) We have studied electron transfer between nanoscale Au particles and Au and Si substrates separated by insulating organic monolayers. The negatively charged Au nanoparticles are attached onto positively charged aminofunctional alkanethiols self-assembled on Au and onto aminofunctional silane self-assembled on Si via electrostatic force. The particles are uniformly distributed on both organic monolayers as characterized by a tapping mode atomic force microscope. The electron transfer current between the attached nanoparticles and the substrates has been investigated by cyclic voltammetry in 0.1 M NaClO4. Work supported by the AFSOR (F49620-96-1-0346). |
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NS-TuP-9 Probing Conducting Particles in a Nix(SiO2)1-x Composite by Conducting Atomic Force Microscopy
E.Z. Luo, I.H. Wilson, J.B. Xu, J.X. Ma (The Chinese University of Hong Kong); X. Yan (Hong Kong University of Science and Technology) In this paper, an experimental study on probing conducting particles buried in an insulating layer with conducting atomic force microscopy (C-AFM) will be presented. The experiments were carried out on a metal-insulator nano composite Nix(SiO2)1-x thin film with x around xc, where xc is the percolation threshold. This granular material was chosen because it exhibts Giant Hall Effect at the percolation threshold. The buried conducting particles were "observed" via the electric current image of C-AFM at constant bias. The electric current from buried conducting particles originates from the field assisted tunneling through the insulating layer. Examples of measuring the thickness of the insulating layer will be given. The analysis shows that it is possible to probe buried metal particles as deep as several nano-meters underneath the surface. By correlating the surface topography and the electrical current image obtained in the constant bias mode, the profile and roughness of metal-insulator interface can be measured. General issues on spatial resolution will also be discussed in this paper. |
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NS-TuP-10 Chemical and Mechanical Stability of Carbon Nanotube Electronic Devices
R.L. Jaffe, J. Han (NASA Ames Research Center) Individual carbon nanotubes have been shown to exhibit either metallic or semiconducting properties depending on their helicity. Nanotube heterojunctions can be created by joining different diameter or helicity tubes through the introduction of one or more pairs of pentagon-heptagon defects. It is been proposed that these heterojunctions could serve as switches in nanometer-size electronic devices. In this work we study the chemical and mechanical stability of various nanotube heterojunctions using quantum chemistry calculations and molecular dynamics simulations. Density functional theory calculations are used to determine the energetic preferences for different geometric arrangements of pentagon and heptagon defects. We propose an "isolated defect" rule as an extension of the isolated pentagon rule for fullerenes. We have also studied the thermal and mechanical stability of some nanotube heterojunctions using molecular dynamics simulations. Our objective is to identify stable heterojunction structures for future studies of their electronic properties. |
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NS-TuP-11 Identification of Carbon Nanotube Heterojunctions and Tori
J. Han, R.L. Jaffe (NASA Ames Research Center) Metallic straight single wall carbon nanotubes (SWNTs) have been demonstrated to be quantum wires1. More recently, toroidal SWNTs with torus diameters of 100-500 nm and tube diameters of 1-1.5 nm have been observed2. The tori are of great interest owing to their potential novel device applications as they inherit conductivity of, for example, (10,10) metallic nanotubes3. This offers a prototype for studying unusual electronic, magnetic and even superconductivity properties in a quantum wire ring where the turning of the current can create a magnetic moment. In this work, We investigate the energetics and structures of circular and polygonal SWNTs using ab initio quantum chemistry and empirical Tersoff-Brenner potential4 calculations. The circular tori are formed by bending an (n, n) tube, whereas the polygonal tori are constructed by turning the heterojunction5 of two tubes of (n, n), (n+1, n-1) and (n+2, n-2) with topological pentagon-heptagon defects, in which n=5, 8 and 10. The strain energy of circular tori relative to straight tube decreases by D-2 where D is torus diameter. As D increases, these tori undergo a transition from a buckled to energetically stable state. The stable tori are perfectly circular in both toroidal and tubular geometry with strain <0.03 eV/atom when D>10, 20 and 40 nm for tori constructed from (5,5), (8,8) and (10,10) tubes. Polygonal tori, whose strain is proportional to the number of defects and 1/D, are energetically stable even for D<10 nm. However, their strain is higher than that of perfectly circular tori. In addition, the local maxium strain of polygonal tori is much higher than that of circular tori. It is ~0.03 eV/atom or less for the circular torus (5,5), but 0.13 and 0.21 eV/atom for polygonal tori (6,4)/(5,5) and (7,3)/(5,5). Therefore, we conclude that circular tori with no topological defects are more energetically stable and kinetically accessible than the polygonal tori containing pentagon-heptagon defects for laser-grown SWNTs. Based on this work, we are studying the Aharanov-Bohm effect in circular toroidal SWNTs.
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NS-TuP-12 Chemical Vapor Deposition Based Synthesis Methods for Preparation of Microtubular Battery Electrodes
G. Che, C.R. Martin, E.R. Fisher (Colorado State University) We have developed a new approach to preparing microtubular battery electrodes using the "template synthesis" method.1 This approach entails the use of chemical vapor deposition (CVD) either within the pores of an alumina membrane or onto a current collector that consists of an ensemble of metal microtubules protruding from a metal surface. Using the first method, we have prepared graphitic carbon nanofiber and nanotube ensembles with or without Ni catalyst. The CVD precursors used were ethylene and pyrene. TEM and electron diffraction data show that the graphitic carbon nanofiber synthesized with the Ni catalyst was not highly ordered initially. After heating the membrane containing the carbon nanotubes, however, the electron diffraction data show a pattern characteristic of single crystal graphite. The electrochemical properties of these materials will also be discussed. With the second method, we have prepared a microtubular composite TiS2/Au Li+ battery electrode. The thin walls of the TiS2 tubes insure that the distance the Li+ must diffuse is small, and the high surface area ensures that the current density is low. These microtubular TiS2 electrodes show higher capacities, lower resistance, and lower susceptibility to slow electron transfer kinetics than thin film TiS2 electrodes prepared from the same amount of TiS2.
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