Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session U12: Focus Session: Electrochemical and Related Growth |
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Sponsoring Units: DMP DCMP Chair: Shirley Chiang, University of California, Davis Room: Baltimore Convention Center 304 |
Thursday, March 16, 2006 8:00AM - 8:36AM |
U12.00001: Physical Origin of Long-Range-Order in Lateral Development of Crystallites: A New Lateral Growth Mode Invited Speaker: The basic picture of hetroepitaxial growth can be summarized as formation of islands on a foreign substrate first, followed by horizontal expansion of the islands on the substrate. Previously little attention has been paid to how the interfacial tensions affect the horizontal expansion of a crystalline island over the substrate, which has recently been found to affect the physical property of thin film significantly. For example, tilting of crystallographic orientation has frequently been observed in epitaxial layers, and our understanding of such effect is very limited. Recently Wang and his colleagues studied lateral growth of NH$_{4}$Cl crystallite on a foreign substrate mediated by successive nucleation. With state-of-the-art structural and morphological characterization methods, they observed that the crystallographic orientation is consecutively rotated, leading to periodic structures on the surface of crystallite aggregate. They demonstrated that this unusual effect is related to the asymmetric surface/interface tensions in the early stage of nucleation, and should be enlightening for a class of thin film growth where nucleation plays a dominate role. Mu Wang, D.-W. Li, D.-J. Shu, P. Bennema, et.al., Phys. Rev. Lett., \textbf{94}, 125505 (2005) D. W. Li, Mu Wang, P. Liu, et.al., J. Phys. Chem. \textbf{B107}, 96-101, 2003, X. Y. Liu, Mu Wang, D. W. Li, et al., J. Cryst. Growth \textbf{208}, 687-695 (2000) Mu Wang, X.Y. Liu, C. Strom, et al., Phys. Rev. Lett. \textbf{80}, 3089 (1998) [Preview Abstract] |
Thursday, March 16, 2006 8:36AM - 8:48AM |
U12.00002: Steering induced growth anisotropy as a probe for long range interaction Frits Rabbering, Teun Warnaar, Herbert Wormeester, Bene Poelsema Grazing incidence homo-epitaxy of 0.5 ML on Cu(001) leads to anisotropic structures as determined with high-resolution LEED. This is the result of attractive forces between the surface and the incoming particle. The trajectory of an incoming particle changes so dramatically that a large deposition flux enhancement on protruding structures results [1]. Trajectory calculations based on an attractive Lennard-Jones potential were combined with a kMC simulation that treats the surface diffusions processes in order to investigate the evolution of the observed anisotropy. Modifications of this potential at short range distances only slightly influence the anisotropy, while modifications at long range has a significant influence on the anisotropy as observed during sub-monolayer growth. This enables to probe the long range interaction. The experimental feasibility of the detailed probing will be discussed. [1] S. van Dijken, L.C. Jorritsma and B. Poelsema, Phys. Rev. Lett. 82 4038 (1999) [Preview Abstract] |
Thursday, March 16, 2006 8:48AM - 9:00AM |
U12.00003: Analysis of Chemical Reactions between Radical Growth Precursors Adsorbed on Plasma-Deposited Silicon Thin-Film Surfaces Tamas Bakos, Mayur Valipa, Dimitrios Maroudas The dominant precursor in the plasma deposition of hydrogenated amorphous silicon (a-Si:H) thin films is the SiH$_{3}$ radical. In this presentation, we report results of first-principles density functional theory calculations on the crystalline Si(001)-(2$\times $1):H surface and molecular-dynamics simulations on a-Si:H surfaces for the interactions between SiH$_{3}$ radicals adsorbed on Si thin-film surfaces. The analysis reveals that two SiH$_{3}$ radicals may either form disilane (Si$_{2}$H$_{6})$ that desorbs from the surface or undergo a disproportionation reaction producing an SiH$_{2}$ radical that is incorporated in the film and a silane molecule that is released in the gas phase. The corresponding activation barriers depend on the local atomic coordination of the surface Si atoms; Si$_{2}$H$_{6}$ formation is barrierless if both radicals are bonded to overcoordinated surface Si atoms and exhibits barriers in excess of 1 eV for two chemisorbed SiH$_{3}$ radicals. [Preview Abstract] |
Thursday, March 16, 2006 9:00AM - 9:12AM |
U12.00004: Controlling the periodicity of the Si(112)nx1-Ga surface via tuning of the chemical potential E.J. Moon, P.C. Snijders, S. Rogge, H.H. Weitering We show that the chemical potential, an important parameter in the initial stages of (hetero-) epitaxial semiconductor growth, can be tuned for the Ga atoms on the Si(112)nx1-Ga surface. As a result the periodicity of the surface can be controlled in the range of n=5 to n=6. STM shows that meandering vacancy lines determine the local size of the unit cell. Large scale statistics of the unit cell size extracted from STM images show that the average periodicity n is not an integer, but lies somewhere in between 5 and 6. These findings are confirmed by a careful analysis of new LEED data, which show a range of periodicities in between 5x1 and 6x1 depending on the surface preparation conditions. The extracted periodicities are consistent with periodicities extracted from Fourier Transform STM images. Thus, changes of the chemical potential of the Ga atoms on the surface can be easily monitored in situe by extracting the average surface periodicity from LEED images. [Preview Abstract] |
Thursday, March 16, 2006 9:12AM - 9:24AM |
U12.00005: Nanolithographic Write, Read and Erase via Reversible Nanotemplated Nanostructure Electrodeposition on Alkanethiol Modified Au(111) in an Aqueous Solution Kyoungja Seo, Eric Borguet A Write, Read and Erase nanolithographic method, combining \textit{in-situ} electrodeposition of metal nanostructures with atomic force microscopy (AFM) nanoshaving of a 1-hexadecanethiol (HDT) self-assembled monolayer (SAM) on Au(111) in an aqueous solution, is reported. The AFM tip defines the local positioning of nanotemplates via the irreversible removal HDT molecules. Nanotemplates with lateral dimensions as narrow as 25 nm are created. The electroactive nanotemplates determine the size, shape and position of the metal nanostructures. The potential applied to the substrate controls the amount of metal deposited and the kinetics of deposition. Metal nanostructures can be reversibly and repeatedly electrodeposited and stripped out of the nanotemplates by applying appropriate potentials. [Preview Abstract] |
Thursday, March 16, 2006 9:24AM - 9:36AM |
U12.00006: Growth of Electrodeposited Ag Nanowires in Anionic Surfactant Nanotemplates on Au(111) Eric Borguet, Kyoungja Seo, Tao Ye Ordered molecular systems should provide templates of molecular dimensions as demonstrated by the growth of silver nanostructures in the potential induced nanotemplates of SDS (sodium dodecyl sulfate). Electrochemical STM (Scanning Tunneling Microscopy) results suggest that SDS molecules form hemicylinders on the Au(111) surface in 0.1M HClO$_{4}$ solution. The hydrophilic sulfate groups self-assemble to face to the aqueous interface while the hydrophobic backbone adopts a tail to tail configuration. The SDS hemicylinders structures are stable over the potential range of -0.1 V$_{SCE}$ to 0.4 V$_{SCE}$. Silver electrodeposition takes place near the hydrophilic sulfate head, and leads to the formation of nanowires that grow in the same direction as the SDS hemicylinders. Ag nanowires are typically less than 2 nm wide. [Preview Abstract] |
Thursday, March 16, 2006 9:36AM - 9:48AM |
U12.00007: A New Phase of the Au(111) Surface in Electrolyte Revealed by STM and Asymmetric Potential Pulse Perturbation. Yufan He, Eric Borguet Asymmetric potential pulse perturbations were combined with STM to separately the (22$\times \sqrt 3 ) \quad \leftrightarrow $ (1$\times $1) phase transition from the dynamics of the dynamics of nanoscale island growth and dissolution at Au(111)/0.1M HClO$_{4}$ interfaces. In the course of these experiments a new surface phase, characterized by a gas of highly mobile Au adatoms on the surface, the absence of islands and a paucity of reconstruction stripes, was observed. This phase coexists with a low density of reconstructed stripes in ``holes''. This new phase is an intermediate state and can only be observed over a potential range range from 0.3 V$_{SCE}$ to 0.45V$_{SCE}$, after a potential pulse lifting the reconstruction. In addition, and contrary to previous reports, the(1$\times $1) $\diamondsuit $ (22$\times \sqrt 3 )$ reconstruction process can be fast. [Preview Abstract] |
Thursday, March 16, 2006 9:48AM - 10:00AM |
U12.00008: Observation of surface layering in a nonmetallic liquid Haiding Mo, Guennadi Evmenenko, Sumit Kewalramani, Kyungil Kim, Pulak Dutta, Steven Ehrlich Non-monotonic density profiles (layers) have previously been observed at the free surfaces of many metallic liquids, but not in isotropic dielectric liquids. Whether the presence of an electron gas is necessary for surface layering has been the subject of debate. Until recently, MD simulations have suggested that layering at free liquid interface may be a generic phenomenon and is not limited to the metallic liquids$^{1}$. The theories predict that if normal liquids can be cooled down to temperatures low enough, layering structure should be observed experimentally. However, this is difficult for most molecular liquids because these liquids freeze well above the temperature necessary for observing the layering structure. By studying the surface structure of liquid TEHOS (tetrakis(2-ethylhexoxy)silane), which combines relatively low freezing point and high boiling point compared to that of most molecular liquids, we have observed the evidence of layering at the free interface of liquid TEHOS using x-ray reflectivity. When cooled to T/T$_{c} \quad \approx $0.25 (well above the bulk freezing point, Tc is the critical temperature of TEHOS), the surface roughness drops sharply and density oscillations appear near the surface. Lateral ordering of the surface layers is liquid-like, just as at liquid metal surfaces. 1. E. Chac\'{o}n and P. Tarazona, Phys. Rev. Lett.\textbf{ 91} 166103-1 (2003) [Preview Abstract] |
Thursday, March 16, 2006 10:00AM - 10:12AM |
U12.00009: Chemical Electrode Modification for Charge Injection in Organic Thin Film Transistors Elba Gomar-Nadal, Daniel Hines, Andrew Tunnell, Winston Yan, Ellen Williams The nature of the interface between an organic material and an inorganic electrode (metal or semiconductor) is critical to the performance of organic electronic and optoelectronic devises. To improve the electrical contact between gold electrodes and pentacene thin film transistors prepared by nanotransfer printing [1], the effect of coating the gold electrodes with self-assembled monolayers (SAMs) of organic molecules with electro-withdrawing groups is being explored. The first experiments have been done with commercially-available molecules and oligo(phenylene ethylene) derivatives have been synthesized for further investigation. The transport and noise characteristics of pentacene TFTs fabricated using the different coating groups will be presented. [1] D.R. Hines et al, Appl. Phys. Lett. 86, 163101 (2005). [Preview Abstract] |
Thursday, March 16, 2006 10:12AM - 10:24AM |
U12.00010: Effects of Stress and Void-Void Interactions on Current-Driven Void Surface Evolution in Metallic Thin Films Jaeseol Cho, M. Rauf Gungor, Dimitrios Maroudas We report results of electromigration- and stress-induced migration and morphological evolution of voids in metallic thin films based on self-consistent numerical simulations. The analysis reveals the complex nature of void-void interactions and their implications for the evolution of metallic thin-film electrical resistance, providing interpretation for experimental measurements in interconnect lines. Interestingly, for two voids migrating in the same direction under certain conditions, we find that a smaller void does not always approach and coalesce with a larger one, while a larger void may approach and coalesce with a smaller one. In addition, we find that under certain electromechanical conditions, biaxially applied mechanical stress can cause substantial retardation of void motion, as measured by the constant speed of electromigration-induced translation of morphologically stable voids. This effect suggests the possibility for complete inhibition of current-driven void motion under stress. [Preview Abstract] |
Thursday, March 16, 2006 10:24AM - 10:36AM |
U12.00011: Characterization and Control of Microstructure in Combinatorially Prepared Aluminum-Silicon Thin Film Nanocomposites Daad Haddad, Charles Olk, Michael Lukitsch In this presentation, we describe the application of thin film combinatorial methods to systematically control the microstructure of Al$_{x}$Si$_{(1-x)}$ alloys through variations in composition and growth temperature. Libraries of compositionally graded films have been sputter deposited onto silicon substrates. The microstructure was investigated using x-ray diffraction while atomic force microscopy techniques were employed to obtain surface morphology and phase distribution. We will also report the results of the mechanical properties we have investigated on these films. [Preview Abstract] |
Thursday, March 16, 2006 10:36AM - 10:48AM |
U12.00012: Mechanical Properties of Electrophoretically-Deposited CdSe Nanocrystal Films Shengguo Jia, Sarbajit Banerjee, Dongyun Lee, Wei Wang, Joze Bevk, Jeffrey Kysar, Irving Herman Approaches to measuring and then minimizing the strain in electrophoretically deposited CdSe nanocrystal films are investigated. The films are seen to fracture above a critical thickness which vaies with nanocrystal size. Cracking and delamination have been studied by SEM and AFM and are attributed to the high strain energy in the film. Raman microprobe scattering and EDX mapping show the strain distribution in the nanocrystal films. The Young's modulus measured by nanoindentation is in good agreement with the parameters obtained from Raman scattering. The deposition conditions have been varied to minimize this strain, which is thought to be due to the evaporation of residual hexane solvent after electrophoretic deposition. In situ observations confirm this assumption about the origin of film strain. Thermogravimetric analysis and differential scanning calorimetry measurements provide the chemical composition of CdSe nanocrystals. The CdSe nanocrystal films become mechanically stronger and more resistant to chemical dissolution after being treated by different cross-linker molecules. This work was supported primarily by the MRSEC Program of the National Science Foundation under Award No. DMR-0213574 and by the NYSTAR. [Preview Abstract] |
Thursday, March 16, 2006 10:48AM - 11:00AM |
U12.00013: Characterization of electromigration in semiconductor device interconnects using microscopic techniques Narahara Dingari, David Heskett Electromigration is an important failure mechanism which affects the functionality and lifetime of integrated circuits. The addition of relatively small amounts of copper has been previously shown to improve device interconnect lifetimes. Through the use of Scanning Electron Microscope (SEM) with Energy Dispersive Spectroscopic (EDS) capabilities we have measured the copper concentration as a function of position along an interconnect after several accelerated stress time periods. We observe a migration of copper atoms from the cathode to the anode side of the interconnect as a function of stressing time. In some cases, a pileup of copper near the middle of the interconnect indicates a blocking of copper diffusion and creates a site for interconnect failure. Metal pileup (hillocks) and depletion (voids) are observed by Atomic Force Microscopy (AFM). We also observe a correlation between relative reflectance using optical microscopy and roughness (observed by AFM) of an interconnect line. [Preview Abstract] |
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