Microsoft word - programbook_session_ss+em-tua

Tuesday Afternoon, November 1, 2011
Surface Science Division
molecule with a 3.5 dipole moment. Ordered TiOPc monolayer films of the honeycomb phase thus represent a regular 2-d dipolar lattice, which was Room: 110 - Session SS+EM-TuA
investigated as an electrostatic template for the growth of the highly polarizable C70. Films of C70 grown layer-by-layer revealed the directed Organic Electronic Interfaces
formation of a Kagome lattice. Atomically detailed structural models were obtained for the 0-6 nm C Moderator: J.R. Engstrom, Cornell University
70 thickness (up to 5 ML) range over which the ordering influence of the TiOPc dipolar substrate persists. Unusually low-density C70 molecular packing arrangements result from the ellipsoidal 2:00pm SS+EM-TuA1 The Effect of Structure on Interfacial Energy,
shape, curved surfaces and high polarizability of C70. While Kagome F. Stellacci, EPFL, Switzerland INVITED
lattices have been frequently observed in colloidal and magnetic systems, In this talk I will highlight recent result on solid-liquid interfaces where the this appears to be the first electrostatically-induced Kagome lattice solid has a nanostructure with a characteristic length scale that is only a few liquid molecule wide. The talk will start with the presentation of a new This work has been supported by the National Science Foundation under scanning probe technique able to measure interfacial energy (work of Surface Analytical Chemistry grant CHE0750203 and under the University adhesion to be precise) with atomic/molecular resolution. It will then show how surfaces with alternating stripe-like domains a few nanometer thick have a structural component to their work of adhesion that can account for as much as 20% of the total energy. Finally novel self assembly approaches 4:20pm SS+EM-TuA8 Solvation - Assisted Growth of ZnPc and 4NO2-
to achieve such surfaces will be discussed. ZnPc Monolayer Films on Au(111), L. Tskipuri, Q. Shao, J.E. Reutt-
Robey, University of Maryland, College Park
The UHV spray-jet molecular beam deposition technique marries the
2:40pm SS+EM-TuA3 Interfacial Electronic Structure of Dipolar
chemical versatility and efficiency of solution-film processing with the Organic Semiconductors, O.L.A. Monti, M.P. Steele, N. Ilyas, L.L. Kelly,
atomic-level control and analytical tools of UHV surface science. Here we D.A. Racke, University of Arizona show how the solvent used in aerosol deposition can be used to fine tune We present an investigation of the evolution of the electronic structure at film morphology. Thin films of ZnPc and 4NO2-ZnPc are grown on a the interface of the dipolar organic semiconductor vanadyl Au(111) support with a newly developed spray-jet molecular beam naphthalocyanine with both highly oriented pyrolytic graphite and Au deposition source and characterized in situ via UHV-STM. Phthalocyanes (111). Using angle-resolved two-photon photoemission and other are delivered to the Au(111) surface in a series of N2-entrained μ-sized photoelectron spectroscopies we observe both excitonic as well as strictly solvent droplets of variable surface residence time. The formation of interfacial states in both ground and excited state manifolds, with large submonolayer films with corresponding density variations demonstrates the differences between the two surfaces. Simple electrostatic considerations impact of the ~nm-thick solvation layers on growth kinetics. Phthalocyanine provide a chemisorption model that is capable of quantitatively describing film registration to the herringbone reconstruction of the Au(111) substrate, long- and short-range interface-mediated intermolecular coupling, indicative of thermodyanically-favored structure, is observed only for significantly altering the molecular electronic structure. Additional insights aromatic solvents with long residence times. Vacancy cavities in monolayer are available from full-scale first-principles calculations at these interfaces. films from solvent memory are eliminated with mild annealing, yielding As a consequence, we show that electrostatic multipoles can significantly film structures that rival PVD grown films. Results are interpreted through influence molecular and interfacial electronic structure, with direct and observable impact on interfacial charge-transfer dynamics. Interfacial electrostatic fields may therefore be used to manipulate in a concrete fashion processes of critical importance to solar energy conversion such as 4:40pm SS+EM-TuA9 Direct Observation of NO2 Adsorption onto
photoinduced interfacial electron transfer. CuPc Monolayers with STM, J.H. Park, J. Royer, S. Lee, T. Kent, W.
Trogler, A.C. Kummel, University of California San Diego
Copper phthalocyanine (CuPc) thin film devices have been widely studied
3:00pm SS+EM-TuA4 Characterization of Quinonoid Zwitterion
for use as chemical vapor sensors; however, the molecular scale sensing Molecular Films on Metal Surfaces, L. Routaboul, P. Braunstein, Lab. de
mechanism remains undetermined. This study presents molecular scale Chimie de Coordination (UMR 7177 CNRS), France, B. Doudin, Inst. de Phys. et Chimie des Mat. de Strasbourg, France 2 adsorption onto CuPc monolayers using ultra-high vacuum (UHV) scanning tunneling microscopy (STM). CuPc monolayers Nebraska Ctr. for Mat. & Nanosci., Y.B. Losvyj, O. Kizilkaya, The J. were deposited on Au (111) surfaces by organic molecular beam epitaxy in Bennett Johnston Sr. Ctr. for Adv. Microstructures & Devices, L.G. Rosa, ultra-high vacuum (UHV) and subsequently exposed to different NO , P.A. Dowben, Nebraska Ctr. for Mat. & concentrations at atmospheric pressure. After annealing at 50 ˚C to improve STM imaging, for low NO2 doses (1 ppm for 5min) the STM images reveal There is considerable interest in the functionalization of metal surfaces by NO2 molecules arranged as islands primarily along the domain boundaries. molecules with large dipoles. For this purpose, p-benzoquinonemonimine- The NO2 molecules almost completely desorb from the CuPc monolayer type zwitterions represent ideal candidates. These zwitterions can be after annealing at 100 ˚C for 1 hr. Conversely, at high NO2 doses (10 ppm anchored on gold surfaces where they form homogeneous thin films with for 5 min), the NO2 exhibit irreversible reactions with the CuPc surface. the dipole preferentially oriented along the surface normal.[1] Some After annealing at 50 ˚C, the domain boundaries act as nucleation centers zwitterions will selectively adsorb on patterned gold substrates from for semi-ordered NO2 adsorbates. As the annealing temperature is increased solution while selective deposition of the zwitterions onto specific to 150 ˚C, the islands of NO2 molecules diffuse from the domain boundaries ferroelectric domains has been demonstrated. This represents an attractive to the CuPc terraces to form ordered structures on the terraces. After approach to pattern molecular deposition on optically transparent planar annealing at 250 ˚C for 1 hr, the CuPc monolayer becomes disordered and substrates through electrostatic dipolar interactions or orientation dipole has numerous vacancies. The data is consistent with that NO2 inducing controlled surface chemistry. Taking advantage of the high solubility of two CuPc decomposition. The behavior of NO2 dosed CuPc monolayers zwitterions in both organic solvents and water, we studied the influence of suggests that NO2 undergoes molecular chemisorption with the CuPc metal the solvent on the functionnalization of surface.[2] The goal is to control center at low exposures. However, at high exposures, NO2 not only both packing and selective deposition on a variety of substrates through undergoes molecular chemisorption with the metal center, but also induces decomposition of the CuPc. This direct observation for NO2 dosed CuPc Acknowledgement. This research was supported by the CNRS and the
monolayers with STM can give an insight into reversible versus dosimetric Ministère de la Recherche et des Nouvelles Technologies, the ANR (07- sensing in CuPc organic thin film chemical sensors (chemFETs). While BLAN-0274-04), the National Science Foundation (grants CHE-0909580 nearly all weakly bonding analytes give reversible mobility sensor and DMR-0851703), and the Nebraska Center for Materials and responses on CuPc chemFETs, some strong oxidants are observed to give Nanoscience at the University of Nebraska-Lincoln. reversible mobility responses at short exposures and dosimetric irreversible threshold voltage responses for longer exposures. This is consistent with the larger doses saturating the reversible chemisorption sites and inducing a SS+EM-TuA7 Directed Organization of C70 Kagome Lattice
oxidative decomposition of the CuPc which induces a dosimetric response by TiOPc-Monolayer Template, J.E. Reutt-Robey, Y. Wei, University of
Maryland
via formation of uncompensated positive charge in the CuPc film. Therefore, the data is consistent with two chemisorption mechanisms of a Abrupt molecular semiconductor interfaces between titanyl phthalocyanine strong oxidant on a single molecule given two different classes of sensor (TiOPc) and C70 were prepared by physical vapor deposition and characterizad by UHV-STM. Molecular TiOPc is a highly anisotropic Tuesday Afternoon, November 1, 2011 5:00pm SS+EM-TuA10 Tunneling Spectroscopy of Benzoic Acid
Monolayers: The Role of the Metal-Molecule Interface, J. Kreil, P.
LeClair, G.J. Szulczewski, The University of Alabama
A series of self-assembled monolayers were prepared from para-substituted
benzoic acids (X-C6H5CO2H where X = H, F, Cl, Br, I, and CN) onto
oxidized Al films and characterized by x-ray photoelectron spectroscopy and contact angle measurements. The acids adsorb to the oxide as a carboxylate group with the plane of the aromatic ring largely perpendicular to the surface, which places the para-substitutent away from the surface. Tunnel junctions were made by vapor deposition of Ag and Pb films as the top electrodes onto the monolayers. Four point probe electrical measurements were made from 4 to 300K. At 4 K the superconducting gap of Pb was observed and unequivocally demonstrates tunneling through a barrier without metallic shorts. When Ag was the top electrode, differential conductance [G(V) = dI /dV] measurements at 4 K showed a quadratic dependence on the applied bias voltage and no zero-bias anomalies. These low temperature measurements suggest the monolayers form pin-hole free tunnel barriers. Two trends emerge when comparing G(V) versus bias voltage for junctions with Ag and Pb top electrodes. When Pb was the top electrode the minimum in G(V) versus bias voltage is offset from zero bias for each monolayer, which scales in a systematic manner with the polarity of the para C-X bond. However, when Ag was the top electrode there was no offset the tunneling conductance. The origin of the different tunneling behavior observed for Pb and Ag top electrodes will be discussed in detail. 5:20pm SS+EM-TuA11 Interfacial Engineering of Organic Light
Emitting Diodes with Sputter Treated Molybdenum Oxides as Hole
Injection Layers, C.I. Wu, P. Wang, I. Wu, National Taiwan University,
Republic of China
In this paper, the mechanisms leading to the enhancement of organic light
emitting diodes (OLEDs) with molybdenum oxide MoO3 incorporated in as
hole injecting layers (HILs) will be discussed. The first one is the lowering of hole injection barrier between anodes and organic layers when a thin film of MoO3 is inserted. The high work function of MoO3 serves as a carrier ladder which decreases misalignment between the Fermi level of electrodes and highest occupied molecular orbital (HOMO) level of hole transport layers, such as N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidene (NPB). The second model is the formation of gap states above the valence band edge of MoO3 to the Fermi level of electrodes when NPB molecules are deposited on MoO3 layers. These gap states enhance the conductivity of MoO3 and provide transition paths of carrier to assist the injection of hole from indium tin oxide (ITO) anodes to NPB layers. The third mechanism is the p-type doping effect of MoO3 doped in NPB layers. This p-type doping increases hole concentration in NPB layers and reduces the energy difference between the Fermi level of electrodes and the HOMO of NPB. We will also demonstrate an effective method to improve the current injection efficiency of OLEDs by modifying the oxidation states of as-deposited MoO3 as HILs with in-situ argon ion (Ar+) sputtering. The injection current of devices incorporating this method is enhanced by one order of magnitude, as compared to that of devices without sputter treatment. The luminance of the devices is also improved. Beside device characterization, X-ray photoemission spectroscopy (XPS) and ultra-violet photoelectron spectroscopy (UPS) were carried out to obtain the chemical and electronic information of MoO3 thin films treated with Ar+ sputter and to unveil the origins of improvement in device performance. It is found that, with slight sputter treatments, MoO3 layers represent lower oxidation states and show metallic characteristics in energy band structure, which remarkably elevates the carrier injection efficiency from ITO to NPB. 5:40pm SS+EM-TuA12 Probing Surface Photovoltage Development by
Dynamical XPS Measurements, S. Suzer, Bilkent University, Turkey
Various semiconducting, photoactive and insulating materials have been
investigated using XPS where the data is collected in a dynamic mode. This
is achieved by recording the spectrum while applying an electrical signal in
the form of ± 5 or 10 V d.c. bias, and/or square-wave pulses, without and
under photoillumination using different lasers. This method enables us to
probe and sort out the effects and contributions of the three fundamental
processes operating; Charging, Photovoltage-Development, and
Photoconductivity in a chemically specific fashion. Accordingly, the
chemical shift differences between the n- and p-doped semiconductors are
amplified due to the effect of the photovaltage operating in the opposite
directions. Time and/or frequency dependence of various processes adds a
new dimension to XPS for sorting out the effects of external stimuli
(electrons, ions, photons, etc.) as well as the chemical nature of the material
under investigation. Experimental results and various applications will be
presented and discussed.
Tuesday Afternoon, November 1, 2011 Authors Index
Bold page numbers indicate the presenter
— B — 
Suzer, S.: SS+EM-TuA12, 2
Szulczewski, G.J.: SS+EM-TuA10, 2
— M — 
— D —
— T —
Monti, O.L.A.: SS+EM-TuA3, 1
— P — 
— I —
— W —
— R — 
— K — 
Reutt-Robey, J.E.: SS+EM-TuA7, 1; SS+EM-
— X — 
Kreil, J.: SS+EM-TuA10, 2
Kummel, A.C.: SS+EM-TuA9, 1
— S — 
— Z — 
— L — 

Source: http://www2.avs.org/symposium2011/ProgramBooks/ProgramBook_Session_SS+EM-TuA.pdf