AVS2004 Session SS-MoP: Poster Session

Monday, November 15, 2004 5:00 PM in Room Exhibit Hall B

Monday Afternoon

Time Period MoP Sessions | Topic SS Sessions | Time Periods | Topics | AVS2004 Schedule

SS-MoP-1 Studies of Hydrogen on Pd{111} at 4 K Utilizing Scanning Tunneling Microscopy and Spectroscopy L.C. Fernández-Torres, E.C.H. Sykes, P. Han, S.U. Nanayakkara, P.S. Weiss (The Pennsylvania State University) The interaction of hydrogen with Pd{111} has been investigated with low temperature scanning tunneling microscopy and spectroscopy. Palladium is unique in its ability to both adsorb and absorb hydrogen. Adsorption of low exposures of hydrogen has allowed for the observation of tip-induced hydrogen atom diffusion at 4 K. The diffusion of atomic hydrogen at 4 K has been ascribed to inelastic tunneling of electrons; inelastic electron tunneling spectroscopy (IETS) corroborates this assignment, and the hydrogen atom diffusion barrier has been determined. Adsorption of high exposures of hydrogen results in formation of two ordered overlayer structures: (1x1)-H and (√3x√3)-2H. Absorption of hydrogen into subsurface sites in Pd, concurrent with H diffusion from the bulk, have been attributed as the predominant reasons for two observed phenomena: tip-induced vacancy ordering, and Pd{111} lattice distortion.
SS-MoP-2 Quartz Crystal Microbalance and Quadruple Mass Spectrometry Studies of Surface Reactions of β-diketonate Precursors and O Radicals T.T. Van, J.P. Chang (University of California, Los Angeles) Pure and Er-doped Y₂O₃ thin films are of interest for next generation of microelectronic and optoelectronic devices. In this work, a radical-enhanced atomic layer deposition (ALD) process was developed for synthesizing these materials. Specifically, quartz crystal microbalance (QCM) and quadruple mass spectrometry (QMS) were used to study the surface reaction kinetics of β-diketonate precursors with O radicals. The β-diketonate complexes chosen for this study are Tris(2,2,6,6-tetramethyl-3,5-heptanedionato) M(III), or M(TMHD)₃, where M = Y or Er. The temperature-controlled QCM was used to measure the real time mass changes, since each reaction steps in ALD cycles causes a specific mass increase or decrease. The evolution of surface species during the deposition was identified and analyzed by QMS. Similar adsorption and desorption kinetics were observed for both Y(TMHD)₃ and Er(TMHD)₃. The surface coverage increased with increasing substrate temperature then saturated. The adsorption isotherms were fitted with the simple Langmuir model and the adsorption rate coefficients were found to decrease with increasing temperature. Conversely, the desorption rate coefficients increased with increasing temperature. The apparent activation energies are ~0.25 eV. The desorption of volatile by-products during the O radical pulse resulted in a rapid mass decrease followed by saturation. The critical O radical dose needed to reach this saturation increased with increasing coverage and approached 2 minutes at high coverage. The O radicals, besides effectively remove the β-diketonate ligands, were found to create reactive site for precursor adsorption. Specifically, the mass increase during a subsequent precursor pulse depended linearly on the preceding O radical pulse time. Finally, well-controlled atomic layer deposition of Er₂O₃ and Y₂O₃ was demonstrated.
SS-MoP-4 Chemical Bonding of Saturated Hydrocarbons to Metal Surfaces H. Öström (Stockholm University, Sweden); L. Triguero (KTH syd, Sweden); M. Nyberg (Stockholm University, Sweden); H. Ogasawara (Stanford Synchrotron Radiation Laboratory); L.G.M. Pettersson, A. Nilsson (Stockholm University, Sweden) We have investigated the electronic and geometric structure of saturated hydrocarbons adsorbed on metal surfaces using x-ray absorption spectroscopy (XAS) and x-ray emission spectroscopy (XES) in combination with density functional theory (DFT) spectrum calculations. XES, which probes the occupied density of states, reveals new adsorption-induced states, which we assign to interaction between the both occupied and unoccupied CH orbitals and the metal d-band. By performing a systematic investigation of how the XA and XE spectra are influenced by different structural parameters, we conclude that the geometry is significantly distorted relative to the gas phase. The bonding to the surface leads to strengthening of CC bonds and weakening of CH bonds. Comparison between different metals shows that the position of the metal d-band is important for the bonding to the surface. These results can be useful for the understanding of the CH bond cleaving mechanism, which is important in catalysis.
SS-MoP-5 UHV Study of Cyclohexane on Zr(0001) N. Stojilovic, J.C. Tokash, R.D. Ramsier (The University of Akron) We investigate the behavior of cyclohexane on Zr(0001) with temperature programmed desorption (TPD), Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED) methods. Following 150 K adsorption cyclohexane dissociates at low exposures with no thermal desorption detected. Relatively broad desorption features (400-750 K) of the parent molecules are observed for higher exposures. The TPD profiles change with exposure, and the yields increase monotonically. AES reveals more carbon after annealing to 850 K than immediately after adsorption. Additionally, AES data indicate different forms of carbon before and after annealing. This work improves our understanding of the behavior of carbon impurities on Zr(0001), and of the influence of temperature-dependent surface-subsurface diffusion.
SS-MoP-6 Study of the Low-Temperature CO+O₂ Reaction Over Pd and Pt Surfaces E. Podgornov (University of California, Riverside); A. Matveev, V. Gorodetskii (Boreskov Institute of Catalysis, Russia); F. Zaera (University of California, Riverside) The kinetics of CO oxidation at low temperature has been studied with effusively-collimated molecular beams (MB) and reactive thermal desorption, combined with an isotope-labeling technique. High-resolution electron energy loss spectroscopy (HREELS), field electron microscopy (FEM), and photoelectron microscopy (PEM) have also been applied to determine the roles of subsurface atomic oxygen and surface reconstruction in self-oscillatory phenomena on Pd(111), Pd(110) and Pt(100) single crystals and on Pd and Pt tip surfaces. It was found that high local concentrations of adsorbed CO during the transition from a Pt(100)-hex reconstructed surface to the unreconstructed 1x1 phase apparently prevents oxygen atoms from occupying hollow sites on the surface, and leads to the formation of a weakly-bound adsorbed atomic oxygen. It was inferred from MB experiments with oxygen isotope that the weakly-bound atomic oxygen is the active form that reacts with CO to form CO₂ at T = 140-160 K. In the experiments involving FEM, sharp tips of Pd and Pt were used to perform in situ investigations of dynamic surface processes. It was concluded that non-linear reaction kinetics is not restricted to macroscopic planes, since planes as small as 200 Å in diameter show the same non-linear kinetics as larger flat surfaces; regular waves appear under oscillatory reaction conditions and propagate through adjacent crystal nanoplanes because of an effective coupling between them. Additional results from isotope-labeling MB experiments led to the conclusion that adsorbed weakly-bound atomic oxygen, and not "hot" oxygen adatoms (excited transient states of adsorbed oxygen which may appear due to excess energy after the dissociation of O₂), is the active form of oxygen that reacts with carbon monoxide at low temperatures.
SS-MoP-7 Adsorption and Reaction of Butyl Groups on Pt(111) I. Lee, F. Zaera (University of California, Riverside) The adsorption and thermal reaction of 1- and 2-butyl moieties on Pt(111) was investigated by using reflection-absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption (TPD). The butyl intermediates were prepared via thermal activation of the C-I bond of 1- and 2-iodobutanes, respectively. Buta-1,2-diyl and buta-2,3-diyl were observed after the first dehydrogenation. The subsequent thermal activation of those butyl groups resulted in a competition between reductive elimination to butane and β-hydride elimination to butene. Coadsorption experiments with hydrogen and deuterium were used to characterize hydrogenation and H-D reactions. It was found that the hydrogenation of 1-butyl to butane is enhanced by predosed hydrogen, while 2-butyl favors the dehydrogenation to butene via β-hydride elimination.
SS-MoP-8 Wetting Behavior of Liquids and Polymer Solutions on the Micro-patterned Fluoroalkylsilane Monolayer Surfaces A. Takahara, M. Morita, J. Fukai, H. Ishizuka (Kyushu University, Japan) Micropatterned fluoroalkylsilane monolayers were fabricated on a Si-wafer substrate by chemical vapor adsorption (CVA) of fluoroalkyltrialkoxysilane and vacuum ultraviolet (VUV)-ray photodecomposition under photomask with line-pattern. Field-emission scanning electron microscopic (FESEM) and atomic force microscopic(AFM) observations revealed that the micropatterned surface of fluoroalkylsilane and bare Si-wafer corresponding to the line-width of photomask was formed. Dynamic and static contact angle measurement revealed the anisotropy of water contact angles parallel and perpendicular to the line direction. Droplets of solution of polystyrene were deposited on the line-pattern by inkjet process from the orifice with a diameter of 50ïm It was revealed that the xylene solution was repelled from the oleophobic fluoroalkylsillane surface and the PS stripe corresponding to the line pattern shape was obtained.
SS-MoP-9 Solvent and Chain Length Dependence of the Conformational Order in Self-Assembled Dialkylammonium Monolayers on Mica G. Haehner, M. Zwahlen (University of St Andrews, United Kingdom); W. Caseri (ETH Zurich, Switzerland) The adsorption of cationic surfactants, for example alkylammonium compounds, can be employed to modify the surface properties of layered silicates, such as micas and clays. This process is of significant importance to many industrial applications, ranging from ore flotation in the mining industry and soil treatment to the pharmaceutical, household, food processing and cosmetics industry. The conformational order in adsorbed monolayer coatings is an important parameter for the reliable use of the layers. Dialkylammonium films on mica substrates prepared via ion exchange in solution can exhibit a high degree of order and orientation, similar to thiol-gold systems. We have studied the quality of such films on mica depending on the solvent and the alkyl chain length. Contact angle measurements, photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure spectroscopy (NEXAFS) were employed to characterize the adsorbed layer. A remarkable difference in the established conformational order was observed for films prepared from different solvents and with different chain lengths.
SS-MoP-10 Single Step Functionalization of Scribed Silicon with Acid Chlorides and Epoxides C.A. Pew, Y.-Y. Lua, W.J.J. Fillmore, M.R. Linford (Brigham Young University) A perpetual problem in surface modification and functionalization is that of finding better and more convenient ways for creating reactive functional groups on surfaces. Two reactive functional groups of great importance in surface modification, and in organic chemistry in general, are the epoxide ring and the acid chloride group. Here we report that epoxide- and acid chloride-terminated monolayers on silicon can be prepared in a single step by chemomechanically scribing silicon that is wet with a bifunctional epoxide (1,2,7,8- diepoxyoctane) or an acid chloride (adipoyl chloride). Surface modification takes place in an open laboratory with compounds that have not been degassed. We also describe the amine-reactivity of these monolayers, using X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, and wetting to prove surface functionalization. Finally, we show that the amine reactivity in these monolayers can be controlled and improved by making mixed monolayers composed of a shorter-chain monofunctional adsorbate and a longer-chain bifunctional adsorbate.
SS-MoP-11 Chemical Functionalisation of High Porosity, Nanostructured Thin Films S. Tsoi, E. Fok, J.G.C. Veinot, J.C. Sit (University of Alberta, Canada) In sensing and catalysis applications, controlled interaction of nanostructured materials with the outside environment is essential. Control over both the structure and the surface properties of these nano-materials allows optimisation for a wide range of applications. Using an advanced technique known as glancing angle deposition (GLAD)¹, we can grow porous thin films with controlled nanostructure and a high surface area easily accessible from the surrounding environment. These structural properties make GLAD films highly suitable for sensing and catalysis; the surface properties can then be controlled through chemical functionalisation. Siloxane-based self-assembly² has been demonstrated as an effective means for functionalisation of a wide variety of simple flat and freestanding structures. Our work is the first application of this technique to the complex, porous, three-dimensional nanostructures grown using GLAD. Goniometer measurements on as-deposited films (hydrophilic, 0° advancing aqueous contact angle) and films treated with various trichlorosilanes (R-SiCl₃) (hydrophobic, ~120° contact angle) support a substantial modification of the hydrophilicity of the GLAD film surfaces. X-ray photoelectron spectroscopy and standard electrochemistry measurements confirm that the siloxane-based self-assembly process effectively penetrates the GLAD film surface, allowing complete functionalisation of the 3D structures and underlying substrate. Of particular importance, varying degrees of hydrophilicity of the GLAD structures can be achieved by further functionalising the tail groups of the assembled molecule. Such flexibility in the self-assembly process allows the surface chemistry of GLAD films to be extensively tailored for specific requirements of a wide range of applications. ¹ K. Robbie and M.J. Brett, J. Vac. Sci. Technol. A 15 (1997). ² J.E. Malinsky, J.G.C. Veinot, et al., Chem. Mat. 14 (2001).
SS-MoP-13 Organic Molecules Self Organization on Metal Surfaces and on Insulator Thin Films L. Ramoino, M. Von Arx, S. Schintke (University of Basel, Switzerland); T.A. Jung (Paul Scherrer Institute and University of Basel, Switzerland); H.-J. Güntherodt (University of Basel, Switzerland) Single molecules on surfaces are promising objects to overcome the limits of current silicon based techniques. Molecular properties like self assembling and preferential adsorption are specially interesting in order to evolve from top-down manufacturing methods to bottom-up techniques. Formation of a wide variety of molecular self organized structures has been achieved on metal and semiconductor surfaces. Much less is known about the adsorption and self organization of organics molecules on insulators. However, decoupling molecules from the conductive substrate and building-up metal-insulator as well as semiconductor-insulator patterns is very interesting in the perspective of molecular electronics. It has been shown as STM and STS are profitable tools to study morphology and electronic structure of ultra-thin insulating structures on booth metallic and semiconductor substrates. In addition, by mean of insulating films it should be possible to tune the molecule sample interaction by varying the thickness of the insulating layer. We are studying the growth of ultra-thin NaCl films on different metal surfaces. STM pictures clearly show the formation of ordered 2D islands between 1 and 3 monolayer thick and with a characteristic square shape. Their size can be reliably controlled in a range between a few and hundreds of nanometers. Self-organization of different organic molecules deposited on the NaCl/metal system, has been studied for various molecule substituents and surface coverages. The possible molecule-surface interactions leading to self-assembled molecular structures on ultra-thin insulators are discussed for the different molecules and coverages in comparison.
SS-MoP-14 Low Energy Electron Diffraction Study of Dodecanethiol Self-Assembled Monolayers Grown on Pt(100) and Pt(111) by Vapor Deposition T.M. Sweeney, P.S. Robbert, C.A. Ventrice, Jr. (University of New Orleans); H. Geisler (Xavier University) One of the most popular substrates for growing self-assembled monolayers (SAMs) is the Au(111) surface. This is primarily due to the fact that it does not oxidize during preparation of the SAMs from solution. However, gold is not compatible with conventional Si-based electronics due to its tendency to diffuse into Si. A more promising candidate for the integration of SAMs with Si-based electronic devices is the use of Pt for the growth of the SAMs. Therefore, we have performed a study of the growth of dodecanethiol SAMs on single-crystal Pt(100) and Pt(111) surfaces by vapor deposition in ultra-high vacuum. The clean Pt(100) surface exhibits a four-domain (5x1) reconstruction. Upon deposition of ~0.1 L of thiol, the (5x1) reconstruction is removed. Doses greater than a few Langmuir result in a weak (1x1) pattern, indicative of the growth of a disordered thiol overlayer on the unreconstructed Pt(100) surface. The clean Pt(111) surface does not exhibit a surface reconstruction. Deposition of ~0.1 L of thiol results in a sharp (2x2) LEED pattern, which indicates that the initial sticking coefficient is near unity and that the thiol molecules most likely have a standing up geometry. As with the Pt(100) surface, doses beyond a few Langmuir result in the formation of a weak (1x1) LEED pattern. In addition, we have initiated a study of the electronic properties of these SAMs using angle-resolved photoelectron spectroscopy. The results of these measurements will also be presented.
SS-MoP-16 Thermal Decomposition of Generation 4-Polyamidoamine Dendrimers Films: Decomposition Catalyzed by Dendrimer-Encapsulated Pt Particles O. Ozturk, T.J. Black, F. Parsons, K. Pizzolato, J.S. Ratliff, C.T. Williams, D.A. Chen (University of South Carolina) The thermal decomposition of hydroxyl terminated generation-4 polyamidoamine dendrimer (G4 OH) films deposited on Au surfaces has been compared with decomposition of the same dendrimer encapsulating a ~40-atom Pt particle (Pt-G4OH). Infrared spectroscopy studies showed that when the films were heated in air to various temperatures up to 275° C, the disappearance of the amide vibrational modes occurred at lower temperature for the Pt-G4OH film. Dendrimer decomposition was also investigated by thermogravimetric analysis (TGA) in both air and argon atmospheres, and decomposition of the dendrimer films on Au surfaces was studied by temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) under ultrahigh vacuum conditions. For both G4OH and Pt-G4OH films, heating to 100° C resulted mainly in the desorption of small molecules such as H₂, H₂O, CO and CO₂. Heating the G4OH films to 200° C induced the desorption of larger dendrimer fragments around 72, 84, 98, 127, 146 and 261 amu. For the Pt-G4OH films, mass fragments above 98 amu were not observed at any temperature, but much larger intensities for H₂ desorption were detected compared to that for the G4OH film. XPS studies of the G4OH films demonstrated that nearly all of oxygen and nitrogen atoms were removed from the surface after heating to 450° C. For the Pt-G4OH dendrimer films, most of the oxygen was also removed after heating to 450° C, but there was little decrease in the intensities of the carbon and nitrogen signals. All of these results are consistent with the fact that the Pt particles inside the G4OH dendrimer catalyze thermal decomposition, allowing dendrimer decomposition to occur at lower temperatures. However, the Pt particles also catalyze bond scission within the dendrimer fragments so that greater concentrations of atomic carbon and nitrogen remain on the surface after heating the dendrimer films in vacuum.
SS-MoP-17 Spontaneous Molecular Row Formation of 9,10-Thiolated Anthracene on Cu(111) K.-Y. Kwon, X. Lin, G. Pawin, K. Wong, B.V. Rao, L. Bartels (University of California, Riverside) Self-assembled monolayers (SAMs) have been the subject of intense research for the recent two decades due to the fact that they can be used to dramatically modify the chemical, physical and electronic properties of surfaces. Thiolate-SAMs offers powerful opportunities for fundamental studies of electron transport, single molecule devices, control of surface wettability, etc. It is known that both alkane- and arene-thiols stand close to upright on the surface at high coverage. Here, we report on the adsorption structure of 9,10-(diacetylthio)anthracene on Cu(111) at low temperatures in ultrahigh vacuum using scanning tunneling microscopy (STM). Before deprotection of the acetyl group, the molecules are mobile even at 80K. Upon heating of the sample in excess of 180K, the acetyl protection group is removed from the thiol and desorbs, as ascertained by thermally programmed desorption experiments. After renewed cooling of the sample to 80K, we find spontaneous assembly of extended molecular rows of dithioantracene molecules. Studies of the attachment and disattachment of diffusing molecules to the end of the rows at various cryogenic temperatures indicate a barrier of 14.8KJ/mol for this process. At increased coverages the antracenes form extended island with a rectangular unit cell.
SS-MoP-18 Effect of Nitrogen Addition on the Liquid Crystal Alignment from Hydrogenated Amorphous Carbon H.J. Ahn, K.C. Kim, J.B. Kim, H.K. Baik, C.J. Park, J.Y. Hwang, H.K. Kang, D.S. Seo (Yonsei University, Korea) In order to control the alignment of nematic liquid crystal (LC), nitrogen addition to the hydrogenated amorphous carbon thin films was investigated. The hydrogenated amorphous carbon layer had been developed the novel inorganic alignment layer for ion beam (IB) irradiation method. The IB method preserved some damage of the alignment layer since it was the non-contact alignment type. However, the low pretilt angle and the weak anchoring force were pointed out the vulnerable points. The alignment layer was deposited by plasma enhanced chemical vapor deposition (PECVD), and the nitrogen addition to the amorphous carbon layer could cause the change of pretilt angle. XPS and the contact angle were measured for analysis of the alignment layer and polarized optical microscope (POM) and pretilt angle measurement instrument were used to estimate the LC cells.
SS-MoP-19 The Coadsorption of Mercury and Molecular Icosahedra on Cu(100) C.C. Ilie, L.G. Rosa, S. Balaz, B. Doudin, P.A. Dowben (University of Nebraska-Lincoln) Mercury and alkali metal mixtures with molecules have a long history in the study of non-metal to metal transitions. Using photoemission and electron energy loss spectroscopy, we have investigated the changes in the electronic structure of molecularly adsorbed orthocarborane films as a function of Hg co-adsorption. Two scenarios for co-adsorption of Hg and the icosahedral molecule closo-1, 2 dicarbadodecaborane (orthocarborane) are considered. The mercury atoms may form a lattice which weakly interacts with orthocarborane lattice, or Hg may form a layer between the Cu substrate and orthocarborane molecular film. Mercury 5d_5/2 shallow core level widths in photoemission suggest interaction with the molecular film, but the binding energies of the molecular orbitals induced photoemission feature suggest that the interaction is weak. D. N. McIlroy, Jiandi Zhang, P. A. Dowben, P. Xu and D. Heskett, "Surface Science", 328, 47-57 (1995)
SS-MoP-21 Reactivity of Metal Carbide Surfaces and Nanoparticles: a Density Functional Study P. Liu, J.A. Rodriguez, J.T. Muckerman (Brookhaven National Laboratory) The destruction of S-containing molecules is a very important issue in the chemical industry and the control of environmental pollution. The reactivity of metal carbide surfaces, M₂C(001) (M=Ti,V,Mo) and MC(001), as well as M₈C₁₂ (metallocarbohedrene, metcar in short) nanoparticles towards sulfur, sulfur dioxide and thiophene was investigated using density functional theory. Our study reveals unexpected ligand and steric effects. Due to the corner or edge sites (ligand effect), the M₈C₁₂ nanoparticle behaves as active as M₂C(001) towards sulfur and sulfur dioxide in spite of the high C/M ratio and C₂ groups. Spontaneous S-O bond cleavage was observed on both M₈C₁₂ and M₂C(001). In contrast, these adsorbates bond weakly with MC(001), and there is an activation barrier for the decomposition of SO₂ on MC(001). Contrary to common assumptions, the C atoms are not simple spectators and play a key role in the energetics for the dissociation of sulfur dioxide. In the case of thiophene adsorption, only M₂C(001) exhibits a high reactivity that leads to a spontaneous S-C bond cleavage. The interaction of thiophene with both MC(001) and M₈C₁₂ is weak. On the nanoparticle, steric repulsion between the C₂ groups and thiophene overcomes the high reactivity of the Mo atoms in corner or edge sites (ligand effect). Our results illustrate the complex interplay of ligand and steric effects in nanoparticles of metal compounds.
SS-MoP-22 Adsorption of Hydrogen on CNT Surfaces and Surface Chemistry on HOPG J. Nakamura, E. Yoo, M. Ishihara, T. Habe, N. Yagai, E. Matsuyama, T. Matsumoto (University of Tsukuba, Japan) Hydrogen storage by carbon nanotubes, graphite and the other carbon materials have been studied from the viewpoints of chemisorption of hydrogen at atmospheric pressure. We find that deposited Pd nanopraticles and formation of defects produced by oxidation increased the chemisorption of H atoms (2 - 4 wt%) on CNT surfaces. IR spectra showed peaks assigned to CH₂ . Desorption of hydrogen was observed around 700 K. In order to study the site of hydrogen on carbon surfaces with scanning tunneling microscopy (STM), we used highly oriented pyrolytic graphite (HOPG) surfaces as a model surface. The hydrogen adsorption is not observed on a clean HOPG surface by STM after dosing H2 or atomic H at 300 K. Temperature programmed desorption (TPD) experiment gives no desorption peak and small desorption peak of H₂ (m/e=2) at ~570 K assignable to H atoms adsorbed at step edges. Defects are produced on HOPG by Ar ion sputtering and annealing at 1173 K. Bright hillocks are observed by STM, and are assigned to pits in graphene sheets due to high local density of states of sp3-like dangling bonds produced by removing adjacent carbon atoms. After dosing atomic H on the defective HOPG at 300 K, the STM topographs show dark lines on the bright hillocks. The average height of the hillock also decreases from 0.71 nm to 0.32 nm. The average height of the hillocks is recovered to 0.69 nm by heating the sample to 873 K where H desorbed fully from the HOPG surface on a TPD spectrum. These results indicate that the atomic H adsorbed on the defect sites at 300 K, and the local density of states was lowered around the pits.
SS-MoP-23 An in situ XPS Study of Fresh Hydrogenated Amorphous Carbon Films Y. Yun, A.J. Gellman (Carnegie Mellon University) In order to develop vapor phase lubrication of hydrogenated amorphous carbon (a-CHx) films for use in hard disk manufacturing insights are needed into the fundamental surface chemistry of vapor deposited lubricants. In vapor phase lubrication, fresh a-CHx will be exposed to lubricants directly. Unfortunately, our current understanding of lubricant surface chemistry on a-CHx is based on studies performed on air-exposed, oxidized a-CHx films. Magnetron sputtering has been used to deposit films in ultra-high vacuum under varying conditions. These films have been characterized by Raman spectroscopy to show that they have characteristics similar to those used commercially. X-ray photoelectron spectroscopy (XPS) was used to study the oxidation of fresh a-CHx during controlled exposure to O2. The film surface saturated at ~20% oxygen after a 20 hour exposure to O2 at 10-4 Torr. One can estimate that under atmospheric conditions where the partial pressure of O2 is roughly 200 Torr, the a-CHx film will be oxidized in a few milliseconds. Thus oxidation of a-CHx is unavoidable between removal of the media from vacuum and dip-coating with lubricant.
SS-MoP-24 Experimental Study of Cluster Size Effects on Damage Formation by Size-selected Gas Cluster Ion Beams N. Toyoda, I. Yamada (University of Hyogo, Japan) A size-selected gas cluster ion beam (GCIB) system has been developed to study the size effects of energetic large cluster ion bombardments on a solid surface for the first time. This system equipped a permanent magnet with a magnetic flux density of 1.2 T. There is a sliding detector and sample holder on a guiding rail perpendicular to the incoming cluster beam axis. By locating a sample at a certain position, particular size of cluster ion can be irradiated continuously with affordable ion current density. With this magnetic filter, the cluster size distribution became 1/20 of those obtained in the conventional GCIB systems. Cluster size effects on damage formations in Si substrates were studied with the size-selected cluster ion beams. When the total acceleration energy of Ar-GCIB was 5keV, both amorphous and oxide thickness on Si substrate increased with decreasing cluster size. In the case of cluster size above 10,000, the irradiation damage in Si was dramatically reduced. This result showed good agreement with that obtained from molecular dynamics simulations. It indicated that very low-damage surface processing can be possible by controlling both the acceleration energy and the cluster size.
SS-MoP-25 Plasma Base Ion Implantation Sterilization Technique and Ion Energy Estimation S. Watanabe (Soken Kogyo Co., Ltd, Japan); T. Tanaka (Hiroshima Institute of Technology, Japan); K. Shibahara, S. Yokoyama (Hiroshima University, Japan); T. Takagi (Hiroshima Institute of Technology, Japan) Plasma base ion implantation (PBII) with negative voltage pulses to the test specimen has been applied to the sterilization process as a technique suitable for three-dimensional work pieces. Pulsed high negative voltage (5μs pulse width, 300 pulses/s, -800 V to -13 kV) was applied to the electrode in this process at a gas pressure of 2.4 Pa of N₂. We found that the PBII process reduced the numbers of active Bacillus pumilus cell using N₂ gas self-ignitted plasma generated by only pulsed voltages. The number of bacteria survivors was reduced by 10^-5 x with 5 min exposure. As the ion energy is the most important processing parameter, a simple method to estimate the nitrogen ion energy calculated using distribution for nitrogen in Si implanted by PBII was developed. The implanted ion energy is discussed from the SIMS in depth profile.
SS-MoP-26 Size-Dependent Resonant Inelastic X-ray Scattering of Ligand-Stabilized Cobalt Nanoparticles in Liquid Suspension H. Liu (Lawrence Berkeley National Laboratory); G. Thornton (University College London, UK); J.-H. Guo (Lawrence Berkeley National Laboratory); Y.D. Yin (University of California, Berkeley); A. Augustsson, C.L. Dong (Lawrence Berkeley National Laboratory); A.P. Alivisatos (University of California, Berkeley); D.F. Ogletree, M. Salmeron (Lawrence Berkeley National Laboratory) The electronic properties of cobalt nanoparticles suspended in liquid have been investigated using synchrotron-based resonant inelastic x-ray scattering (RIXS) spectroscopy. Cobalt nanoparticles of 3, 4, 5, 6, and 9 nm were synthesized using wet-chemical methods. Liquid suspensions of the samples were then sealed into a vacuum-compatible cell closed with an x-ray transparent silicon nitride window, which separated the liquid from the surrounding vacuum during measurements. The experiments were carried out at beamline 7.0.1 of the Advanced Light Source (ALS). Particle oxidation was prevented by performing spectroscopy under the conditions of synthesis. RIXS spectra revealed two main features with energy losses of 1.8 eV and 6 eV. The 1.8 eV feature was assigned to excitations from the ground state to a final state dominated by the 3dⁿ configuration electrons (dd transition), while the 6 eV feature was assigned to charge transfer from the ligand/solvent molecules to metal atoms with a 3dⁿ⁺¹L^-1 final state. RIXS spectra excited at the Co 2p_3/2 XAS peak position showed that the intensity of the 1.8 eV peak (dd excitation) decreased with decreasing particle size. The charge transfer feature also shifted significantly, from ~ 6.9 eV for 9 nm nanoparticles to ~ 6.0 eV for smaller particles. This difference can be attributed to changes in the interaction between the metal core and the ligand/solvent molecules with nanoparticle size.
SS-MoP-27 Design of a High-Speed Digital Feedback Loop for Scanning Tunneling Microscope Applications E. Ulin-Avila, A. Liu, B.V. Rao, L. Bartels (University of California, Riverside) We present the development of a digital feedback loop for Scanning Tunneling Microscope (STM) operation that is capable of updating the tip height and xy position at a frequency of 170kHz. This feedback frequency approximates the maximum update rate of standard 16bit AD/DA converters of 200kHz. Its digital nature allows for precise linearization of the exponential dependence of the tunneling current on the tip-sample separation thereby avoiding oscillatory behavior common with non-linearized feedback loops. In addition, the digital setup allows full control of the z-motion of the tip at any point in time, which permits versatile tip control during lateral manipulation and rapid spectroscopy. The feedback loop incorporates a commercial digital signal processor board (Innovative Integration) utilizing a TI C6200 processor. First application of the new system will be presented.
SS-MoP-28 Potential-induced Surface Stress at the Solid-liquid Interface Measured with a Differential Microcantilever-based Sensor V. Tabard-Cossa, M. Godin (McGill University, Canada); L.Y. Beaulieu (Memorial University, Canada); R.B. Lennox, P. Grutter (McGill University, Canada) We report on a differential microcantilever-based system capable of measuring surface stress changes which occur during electrochemical reactions. Our system is composed of two microcantilever sensors. The first active microcantilever serves as the working electrode (in a conventional three-probe electrochemical cell configuration) and as the mechanical transducer (bending of the microcantilever), yielding simultaneous, real-time, in situ measurements of the current and interfacial stress changes. A second microcantilever serves as a reference sensor to detect any unwanted cantilever deflection resulting from temperature variations, mechanical vibrations and/or uncontrolled chemical reactions. This micromechanical cantilever sensor has a deflection sensitivity of 0.2 nm, which translates to a surface stress sensitivity of 1x10^-4 N/m with a dynamic range up to 50 N/m. This system is used to study the potential-induced surface stress at the solid-liquid interface for the case Au in 0.1 M HClO₄. The dependence of surface stress on surface charge density is examined for different Au surface morphologies. The role played by the morphology of the sensing substrate in microcantilever sensors is studied in order to understand the origin of the surface stress responsible for the sensor's response.
SS-MoP-29 Selective Detection of Cr(VI) Using a Microcantilever Electrode Coated with a Self-Assembled Monolayer F. Tian (Oak Ridge National Laboratory); V. Boiadjiev (University of Tennessee in Knoxville); L. Pinnaduwage, G. Brown, T. Thundat (Oak Ridge National Laboratory) We have demonstrated detection of Cr(VI) ions using functionalized cantilevers under electrochemical control. Au-coated microcantilever working electrodes are modified with self-assembled monolayer of 4-mercapto-pyridinium in sulfuric acid solution. Differential surface stress changes at the modified microcantilever have been measured to determine Cr(VI) by monitoring the potential-induced deflection of the microcantilever and simultaneous current-potential response by cyclic voltammetry. In an electrolyte containing sulfuric acid alone, the increase of potential causes a compressive surface stress resulting in the microcantilever bending away from monolayer coated Au side. Stressogram (first derivative of stress with respect to potential vs electrode potential) shows sweep rate independence, which is consistent with voltammetry. In the presence of 10^-4 M Cr(VI), a compressive stress peak can be observed during cathodic sweep. Surface stress characteristics continue to change during potential cycling at each fix sweep rate although the measured current-potential responses in the voltamogram are still constant. It suggests that there is a strong adsorption of Cr(VI) on pyridinium monolayer coated microcantilever electrode. Because of the adsorption of Cr(VI), the stressogram behavior is only consistent with voltamogram in the very beginning of sweep cycling and at much higher sweep rates. Our results demonstrate that the observed changes of differential surface stress are due not only to potential change, but also to ion adsorption/desorption and electron exchange at the electrode surface. Such potential controlled microcantilever technique offers new insights into the behavior of the solid-liquid interface during electrochemical reactions at modified electrodes.
SS-MoP-30 Formation of Supramolecular Cavitands on Electrode Surfaces C. Safarowsky, A. Rang, C.A. Schalley, K. Wandelt, P. Broekmann (University of Bonn, Germany) Supramolecular host-guest recognition is one the most challenging topics in modern chemistry and physics as well. Combining supramolecular approaches with state of the art surface science techniques allows to gain new insights about the structure and dynamics of supramolecular assemblies which are adsorbed at surfaces. In this contribution we present two approaches to realize supramolecular architectures at electrode surfaces in an electrochemical environment. The most prominent property of these architectures is their molecular host-cavity in which smaller guest molecules can be incorporated. Our method of choice to investigate these electrochemically fabricated arrays of host assemblies is the in-situ scanning tunnelling microscopy. Our first approach is based on the selforganization of small monomers to supramolecular assemblies at the surface. For this purpose we use redox-active dibenzyl-viologen cations which arrange on a chloride modified Cu(100) surface with the formation of square-shaped host assemblies consisting of 4 individual molecules. Characteristically, these assemblies are chiral and, hence, occur in two mirror-domains on the electrode surface. Our second approach is based on the direct adsorption of pre-assembled supramolecular units at the electrode surface from the solution phase. For this purpose we use so called Fujita-squares which are characterized by a fourfold-symmetric arrangement of 4 Pt(II)-cations stabilized by 4 bipyridine ligands and 4 further ethylenediamine molecules. These cationic molecules can also be adsorbed on a chloride modified Cu(100) electrode surface. In both cases we end up with molecular cavities which are oriented towards the solution phase and can, thus, be directly imaged by in-situ STM. The size of these cavities amounts to 1 nm in both cases.
SS-MoP-31 Low Temperature Ultra-High Vacuum Scanning Tunneling/Force Microscopy for Single-Molecule Imaging and Spectroscopy T. Shimizu (University of California, Berkeley); A. mugarza (Lawrence Berkeley National Laboratory, University of California); Y. Qi (University of California, Berkeley); M. Heyde, D.F. Ogletree, M. Salmeron (Lawrence Berkeley National Laboratory, University of California) A low temperature ultra-high vacuum scanning tunneling/force microscope (LT UHV STM/SFM) has been designed and constructed for imaging, spectroscopy, and manipulation at the atomic scale. This microscope is capable of operating in either STM or SFM modes through in-situ tip exchange. In addition, simultaneous STM/SFM is also possible using a conductive SFM tip. Our goal is to investigate inter- and intra-molecular forces between small molecules on metal surfaces, to explore the relation between electronic and mechanical properties, and to perform electronic, vibrational, and force spectroscopy. Preliminary STM images and scanning tunneling spectra of single-molecules will be presented.
SS-MoP-32 Extracting Single Molecule Statistics from Scanning Probe Images B.A. Mantooth, E.C.H. Sykes, P. Han, P.S. Weiss (The Pennsylvania State University) Scanning probe microscopes have enabled the unprecedented real-space visualization of single molecules and atoms on surfaces. Analyses of time-resolved sequences of these images allow the quantification of site-specific interactions and dynamics of adsorbed species. We have used scanning tunneling microscopy to probe and to quantify the weak substrate-mediated interactions in benzene overlayers on Au{111} at 4 K, and to characterize concerted motions of molecular cascades in these benzene overlayers. We use similar techniques to characterize the correlation of CO adsorption site with the charge density waves of the surface state of Ag{111}.
SS-MoP-33 Site-selective Electroless Plating on Amino-terminated Diamond Substrate Patterned by 126 nm Vacuum Ultraviolet Light Lithography A. Hozumi (National Institute of Advanced Industrial Science and Technology, Japan); N. Shirahata (National Institute of Materials Science, Japan); S. Asakura, A. Fuwa (Waseda University, Japan); Y. Yokogawa, T. Kameyama (National Institute of Advanced Industrial Science and Technology, Japan) The use of diamond substrates to manage heat dissipation in microelectronics has recently attracted considerable attention. Diamond metallization technique is of crucial importance in order to fabricate microelectronics devices. However, due to its excellent chemical inertness, it is hard to fabricate metal circuitry on the diamond substrates. Here we report a spatially defined metallization of copper (Cu) through an electroless plating on the amino-terminated diamond surface micropatterned by vacuum ultraviolet (VUV) photolithography. A diamond surface was first photochemically hydrophilized using VUV light of 126 nm. Due to VUV irradiation, the diamond surface became completely hydrophilic with its water-contact angle changing from 102° to 5° or less. According to X-ray photoelectron spectroscopy, polar-functional groups, such as C-O and C=O/O-C-O, were formed on the surface. Amino-terminated organosilane molecules were then chemisorbed onto the photochemically modified surface through a vapor phase. Next, the sample was exposed to 126 nm VUV light through a mesh mask, and subsequently immersed into a PdCl₂ solution kept at pH 5 for 30 min and rinsed with Milli-Q water. Finally, the substrate was immediately immersed into a commercial electroless Cu plating bath for 2 min at room temperature. Cu film with about 40 nm thick was site-selectively deposited onto the amino-terminated surface and remained free of deposits in the VUV-irradiated regions, as evidenced by an optical microscopy. The well-defined Cu microstructures were successfully formed on the diamond surface. Due to thermal treatment at 200 °C for 3 h in vacuum, a resistivity of the Cu film decreased from 17.1 µΩ cm to 13.4 µΩ cm.
SS-MoP-34 Nanotribological Effects of Hair Care Products and Materials on Wet and Dry Human Hair using AFM/IFM C. LaTorre (The Ohio State University); B. Bhushan (The Ohio Sate University) Tribological properties such as friction have been well studied for hair and other biological materials on the macroscale. Lower macroscale coefficient of friction values have been reported in literature for hair treated with various conditioning agents, as opposed to untreated virgin hair. The mechanisms behind lower friction with the application of conditioning products are understood on the macroscale level. However, the interactions between hair and hair care products that occur on the micro/nano scale and the tribological effects of these interactions are not as well understood. Major sources of investigation for treated hair includes localization of various conditioning products, mechanisms behind changes in friction and adhesion on the nanoscale due to conditioner agents, and how the products change the microstructure of the cuticle. The paper presents nanotribological studies investigating adhesion and friction using AFM/LFM. Test samples include Caucasian, Asian, and African hair at virgin and treated conditions in both wet and dry environments. Friction and adhesion measurements were taken using a Si₃N₄ tip and constant force mode in AFM/LFM. Friction force mapping provides insight into the localized change in friction caused by the application of hair care materials. Force-volume plots to study adhesion on the cuticle surface provide information about localization and change as well. A discussion is presented on these properties of hair as a function of ethnicity, wet and dry environments, and conditioning treatments.
SS-MoP-35 A New ³He Spin-Echo Spectrometer for Ultra-High Resolution Inelastic and Quasi-Elastic Helium Atom Scattering A.P. Jardine, P. Fouquet, S. Dworski, G. Alexandrowicz, H. Hedgeland, J. Ellis, A. Allison (University of Cambridge, UK) Quasi-elastic helium atom scattering (QHAS) is a unique tool for studying surface dynamics on atomic length and picosecond time scales¹. Conventional QHAS experiments, using time-of-flight methods, have limited resolution due to the velocity spread in the probing helium beam and can only investigate exceptionally fast processes. The recently established technique of ³He spin-echo²³ is not limited by the velocity spread and can be used to study surface diffusion events over much greater time scales. The method is based on manipulating the precession of the nuclear spin in a polarised beam of ³He atoms. Any energy change at the surface is seen as a change in the final polarisation of the beam. The key difficulty in applying the SE techniques to surface studies is in achieving a fully spin-polarised beam at sufficiently high energy (~8 meV) for a sufficient range of momentum transfers to be probed, to allow full k-space mapping of surface processes. We have have recently completed commissioning of a unique ³He Spin-Echo apparatus, which operates at such beam energies. We show that the instrument increases the range of measurable time scales by three orders of magnitude. The main features of the apparatus are described, and we illustrate its the scope of application with recent experimental data, not only for surface diffusion, but also for the measurement of surface vibrations and helium-surface potentials. The results have unprecedented accuracy. ¹ A. P. Jardine, J. Ellis and W. Allison, J. Phys. Condens. Matter 14, 6173 (2002) ² M. DeKieviet et. al. Phys. Rev. Lett. 75, 1919 (1995) ³ M. DeKieviet et al. Surf. Sci. 377-379, 1112 (1997).
SS-MoP-36 Electrochemical Micromachining with Ultrashort Voltage Pulses: Modeling and Simulation J. Kenney, G.S. Hwang (The University of Texas at Austin) Recent results using electrochemical systems show promise for the areas of three-dimensional etching, high aspect ratio etching, and controlled deposition. These methods employ a â?otoolâ? electrode held in close proximity (~1 micron) to a reactive â?osubstrateâ? electrode in the presence of an electrolyte and utilize ultrashort (~50 ns) voltage pulses to modify the substrate surface selectively. The shape and feature resolution of synthesized structures would be determined by a complex combination of i) charging and discharging of electrochemical double layers at electrode surfaces, ii) electrochemical reactions on the electrodes, and iii) transport of molecules to the electrode surface. Experiments may provide many clues to the fundamental behaviors of electrochemical systems, but their interpretations often remain controversial due largely to difficulties in direct measurement. While current experimental techniques are still limited to providing complementary real space information, the interplay between experiment and theory will contribute to uncovering intricate kinetic phenomena involved in the electrochemical micron-scale patterning. In this talk, we present our multiphysics computational model for electrochemical micromachining with ultrashort voltage pulses. This approach integrates i) a circuit model to describe charging and discharging of electrochemical double layers and electric field variation in electrolytes and ii) the level set method to simulate feature profile evolution during electrochemical etching. Our simulation results of transient current responses and etch profile evolution are qualitatively in excellent agreement with experimental observations. From our simulations, we find that the resolution of etched features is a strong function of the substrate double layer capacity which may be controlled by electrolyte concentration and pulse duration.
SS-MoP-37 Measurement of Gibbs Free Energies of Surfaces in Vacuum, and their Use to Explain the Pressure Dependence of the Thickness of a Lead-Oxide Film L. Bouzidi, A.J. Slavin (Trent University, Canada) A method has been developed, using a high-stability quartz-crystal microbalance (HS-QCM)¹, for determining the difference between Gibbs free energies of different surface oxide phases in ultrahigh vacuum. This is the only technique capable of such measurements, to our knowledge. These measurements have been used to explain the dependence, on oxygen pressure, of the thickness of a lead-oxide film grown on a gold substrate. The HS-QCM has also been used to measure a Pb:O ratio of 1:1, suggesting PbO as the surface oxide. Only the surface Pb monolayer oxidizes at an O₂ pressure of 5 x 10^-6 torr, with 1 x 10^-4 torr required to oxidize a second layer. For large Pb deposits on Au only the top two layers are oxidized up to an oxygen pressure of 10^-2 torr, apparently due to kinetic limitations. These results are quite different from the oxidation of pure Pb. ¹ L. Bouzidi, S.S. Narine, K.G. Stefanov and A. J. Slavin; Rev. Sci. Instrum. 74, 3039-3044 (2003). .
SS-MoP-38 Chemical Binding of N-Containing Aromatic Molecules on Si Surfaces: Mechanistic Understanding of the Selectivity of Reaction Channels F. Tao (Princeton University); G.Q. Xu (National University of Singapore, Singapore) Chemical binding of organic molecules on Si surfaces is an important approach for fabricating molecular architectures to develop Si-based molecular devices and biosensors. Our studies on attachment chemistry of pyrrole, N-methylpyrrole and pyridine demonstrate the diversity of reaction channels of aromatics on Si surfaces. Pyrrole dissociatively chemisorbs onto Si surfaces through breaking the N-H bond, forming a pyrrolyl ring. Due to the absence of the N-H bond, N-methylpyrrole covalently binds to Si surfaces via pericyclic reactions. The difference of chemisorption mechanism between pyrrole and N-methylpyrrole demonstrates a strategy of switching the reaction channel by introducing substituted group. Besides the pericyclic reaction, pyridine can chemically bond to Si surfaces with the formation of SiN dative bond. Compared to pyrrole and N-methylpyrrole, the ability of pyridine to form a dative bond results from higher electron density around the N atom. This is due to localization of the lone-pair electrons on the N-atom for pyridine, contrasted with participation in the aromatic conjugation for pyrrole and N-methylpyrrole.

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