Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session A24: Focus Session: Transport in Nanostructures I: STM and Atomic Control |
Hide Abstracts |
Sponsoring Units: DMP Chair: Nathan Guisinger, National Institute of Standards and Technology Room: Morial Convention Center 216 |
Monday, March 10, 2008 8:00AM - 8:12AM |
A24.00001: Single electron tunneling measurements of Titanium Silicide islands on Si(100) J.L. Tedesco, J.E. Rowe, R.J. Nemanich Titanium silicide (TiSi$_{2})$ islands have been formed by the ultrahigh vacuum (UHV) deposition of thin films of titanium ($<$ 1 nm) on clean Si(100) surfaces followed by annealing to $\sim $800$^{o}$C. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) have been performed on these islands to demonstrate single electron tunneling (SET). Evidence of Coulomb staircase peaks corresponding to SET has been identified in current-voltage (I-V) curves recorded from islands at room temperature. Predictions of the orthodox model were found to agree with our data, except for slight discrepancies of the shape of the I-V curves at current steps. Many islands that were expected to exhibit SET did not do so. Potential reasons for the absence of SET include Schottky barrier lowering due to Fermi level pinning, and interfacial faceting which was identified as the most likely reason for the absence of observable SET. The positive SET results establish that a Schottky barrier can be used as an effective tunnel junction in a future double barrier tunnel junction (DBTJ) device. Possible approaches to improve the reliability based on control and engineering of surface and interface electronic bands will be discussed. [Preview Abstract] |
Monday, March 10, 2008 8:12AM - 8:24AM |
A24.00002: Tunneling Spectroscopy of Ultrathin Insulating Films: CuN on Cu(100). Charles D. Ruggiero, Taeyoung Choi, Jay A. Gupta Insulating films comprising only a few atomic layers offer insight into the evolution of electronic structure at the nanoscale and are useful for controlling electronic coupling of adsorbates. We have studied the electronic structure of one monolayer thick CuN islands grown on Cu(100) with a low temperature (5K), ultrahigh vacuum scanning tunneling microscope. We find that CuN acts as an insulator, with a band gap that exceeds 4~eV. Measurements of the tunneling barrier height and image potential states indicate that the CuN work function is $\sim $0.9~eV larger than bare Cu. This suggests a significant surface dipole, consistent with charge transfer predicted by theory. We find no significant dependence of these results on CuN coverage, from small islands ($\sim $ 10~nm$^{2})$ to complete films. This suggests that collective electronic structure is already established in the smallest islands. We use the CuN films to decouple metal nanoclusters from the Cu surface electron density. Tunneling spectra of few-atom Nb clusters on CuN reveal an atomic resonance that is not observed for clusters on Cu. http://www.physics.ohio-state.edu/$\sim $jgupta [Preview Abstract] |
Monday, March 10, 2008 8:24AM - 8:36AM |
A24.00003: STM studies of transport through single azobenzene molecules Taeyoung Choi, Jay A. Gupta A microscopic understanding of electrical contact to molecules is needed to improve the performance and reproducibility of devices based on organic materials. We use a low-temperature scanning tunneling microscope to study current flow through single molecules where the contacts and local environment are characterized with atomic resolution. Azobenzene was adsorbed on a Cu(100) surface partially covered with one-monolayer thick islands of CuN, an insulator with a bandgap exceeding 4~eV. Peaks in tunneling spectra attributed to molecular orbitals are observed for molecules on CuN, but not on Cu. This is consistent with the decrease in hybridization expected for adsorbates on insulating films. Current flow through azobenzene molecules which bridge Cu and CuN regions is highly asymmetric with bias voltage, suggestive of rectifying behavior. Atomically precise contacts can be made to the molecules by using the STM tip to manipulate nearby metal atoms. Spectroscopic imaging is used to monitor changes in molecular orbitals due to charge transfer between molecule and contacts. [Preview Abstract] |
Monday, March 10, 2008 8:36AM - 9:12AM |
A24.00004: An atomic switch of electron propagation on Ge (001) by tunneling carrier injection Invited Speaker: Reversible switching of electronic conduction through atom manipulation is one of the important subjects of nanoscience. However, different conducting pathways were not clearly observed with atomic resolution. We have demonstrated the correlation between the change of surface atomic position by tunneling carrier injection and that of the reflection of one-dimensional (1D) surface-state electrons on the Ge (001) surface with a low density of heterogeneous Sn-Ge dimers. [1] On the clean Ge(001) surface, two adjacent atoms form a buckled dimer, and the buckling orientation of the Ge dimer can be locally and reversibly controlled by carrier injection to the surface from the STM tip. [2] The unoccupied surface $\pi^{*}$-electron behaves like a 1D free electron along the Ge dimer row. When Sn atoms are deposited on the clean Ge(001) surface at room temperature, buckled dimers originating from the Sn atoms are formed at the Ge dimer position in the surface. [3] An atomic switch is realized for the $\pi^{*}$ electrons in the Ge dimer- row direction by injection carriers to reversibly flip the buckling orientation of a single Sn-Ge dimer in the dimer row. When the Sn atom of the heterogeneous dimer is at the lower position, the 1D electrons are reflected and a standing wave of this state is observed. Whereas, when it is at the upper position, the 1D electrons pass through the heterogeneous dimer, and no standing wave is observed. In this state, the lower atom of the dimer is Ge, and the $\pi^{*}$ state at the dimer is little different from that of the Ge-Ge dimers. \newline \newline [1] K. Tomatsu, K. Nakatsuji, T. Iimori, Y. Takagi, H. Kusuhara, A. Ishii, F. Komori; Science \textbf{315}, 1696, 2007. \newline [2] Y. Takagi, Y. Yoshimoto, K. Nakatsuji, F. Komori; Surf. Sci. \textbf{559}, 1, 2004. \newline [3] K. Tomatsu, K. Nakatsuji, T. Iimori, F. Komori; Surf. Sci. \textbf{601}, 1736, 2007. [Preview Abstract] |
Monday, March 10, 2008 9:12AM - 9:24AM |
A24.00005: Quantum Channels and Conductance Oscillations in TiOx Nano-switches Feng Miao, J. Joshua Yang, Duncan R. Stewart, R. Stanley Williams, Chun Ning Lau We investigate conductance switching in Pt/TiOx/Pt devices by pressure-modulated conductance microscopy. For devices with conductance G$>>$G$_{Q}$ and G$<<$ G$_{Q}$, where G$_{Q}$ is the conductance quantum, localized pressure-induced conductance peaks are observed, indicating formation of nanoscale conductance pathways on the electrodes. We postulate that these nano-conducting channels are related to the drift of oxygen vacancies under electrical field. For devices with G$\sim $ 1- 2 G$_{Q}$, in addition of conductance peaks, we also observed conductance dips and oscillations in response to localized pressure. These results suggest formation of quantum conductance channels in our devices, and can be modeled by considering interfering electron waves between two partially transmitting electrodes. Our findings suggest the possible use of these devices as atomic-scale switches. [Preview Abstract] |
Monday, March 10, 2008 9:24AM - 9:36AM |
A24.00006: Electronic switching in nanoscale titanium oxide devices Duncan Stewart, J. Joshua Yang, Julien Borghetti, Douglas Ohlberg, Matthew Pickett, Feng Miao, R. Stanley Williams Titanium metal is widely used as a top metal contact for nanoscale molecular electronic devices, where it has been assumed to form a few-atom-thick Ti carbide overlayer. Using a vacuum delamination technique we expose and analyze chemically pristine buried titanium/organic monolayer interfaces from devices that have displayed `molecular electronic switching'. We establish that under many conditions the titanium instead forms a \textit{few-nanometer-thick Ti oxide} overlayer. Both TiO2 and reduced TiOx species exist -- this mixed stoichiometry Ti oxide is responsible for the electronic switching. In the separate field of `conventional' nano-electronics, oxide based electrical-resistance switches are pursued for next generation nonvolatile random access memories (R-RAMs). However, the metal/oxide/metal switching mechanism is poorly understood. We demonstrate in Pt/TiOx/Pt nanocrosspoint devices that the switching is channeling (on) and recovering (off) the Schottky barrier at the Pt/TiO2 interface due to the creation and drift of positively charged oxygen vacancies under electric field. Engineered oxygen vacancy profiles predictively control the switching polarity and conductance to support a general physics model of switching in these devices. [Preview Abstract] |
Monday, March 10, 2008 9:36AM - 9:48AM |
A24.00007: Electron transport simulations through organic adlayers on metal surfaces Manuel Cobian, Nicolas Lorente, Pablo Ordejon Molecular entities at the interface with an inorganic surface are the basis for new hybrid functional materials for microelectronics. In most cases, strong bonding of molecules to metal surfaces perturbs the discrete molecular energy levels leading to a broadening of the molecular density of states. Deposition of $C_{60}$ on a Au(111) surface previously exposed to tetraphenyladamantane give rises to a nanostructured organic layer where the electronic coupling between the $C_{60}$ and the Au(111) surface is significantly reduced compared to $C_{60}$ on a clean Au(111) surface. Calculations based on Density Functional Theory reveal that intermolecular interactions lock $C_{60}$ into a particular orientation in agreement with Scanning Tunneling Microscopy experiments. This system exhibits the presence of negative differential resistance which can be understood by simulations of the transport properties at the ab-initio level using TRANSIESTA. [Preview Abstract] |
Monday, March 10, 2008 9:48AM - 10:00AM |
A24.00008: Scanning tunneling spectroscopy (STS) of DNA and G4-DNA molecules Danny Porath, Errez Shapir, Hezy Cohen, Alexander Kotlyar, Rosa Di Felice Attempts to resolve the energy level structure of single DNA molecules by STS span over the last two decades, thanks to this technique ability to probe the local density of states of objects deposited on a surface. Success was hindered by extreme technical difficulties in stable deposition and reproducibility. By using STS at 78 \r{ }K, for the first time we disclose the energy spectrum of poly(G)-poly(C) DNA molecules deposited on gold. The tunneling current-voltage characteristics and their derivative curves exhibit a clear gap and a peak structure around the gap. By means of ab initio Density Functional Theory calculations the character of the observed peaks is assigned to orbitals originating from the different molecular components. Limited fluctuations in the I-V curves are observed and statistically characterized. [Preview Abstract] |
Monday, March 10, 2008 10:00AM - 10:12AM |
A24.00009: Microscopic Characterization of Organic/Metal Interfaces: a Combined DFT and Many-Body Perturbation Theory Study Yan Li, Deyu Lu, Giulia Galli Aromatic molecules and molecular assemblies have received widespread attention as possible components of molecular electronic devices. An essential prerequisite to understand their stability and transport properties is the microscopic characterization of the interface formed with metallic leads. We present a comprehensive, first-principles study of the interface of Au(111) and a representative aromatic isocyanide molecular SAM (phenylenediisocyanide). We provide predictions about the binding geometries, coverage and stability properties, which are in good agreement with experimental measurements. We also discuss the electronic properties of the organic/metal interface by including self-energy corrections through many-body perturbation theory (GWA), and surface polarization effects. Our results indicate that electronic structure calculations beyond DFT are required to make an accurate assessment of energy level alignments between SAMs and the metallic leads. [Preview Abstract] |
Monday, March 10, 2008 10:12AM - 10:24AM |
A24.00010: Scanning tunneling spectroscopy of mass selected Ag clusters on C$_{60}$ functionalized surfaces Heinz H\"{o}vel, Stefanie Duffe, Lukas Patryarcha, Chunrong Yin, Bernd von Issendorff, Michael Moseler Scanning tunneling spectroscopy (STS), which can be used to study the electronic properties of individual clusters on surfaces [1] is combined with the deposition of mass selected Ag clusters (from Ag$^+_{55}$ to Ag$^+_{561\pm 5}$). A functionalization of the substrate with C$_{60}$ layers proved to be very useful to ensure the soft landing of the clusters and to bind them to fixed positions on the surface [2]. The knowledge of the exact cluster size shows that one has to interpret the STM derived cluster height carefully, considering details of the STM imaging process. For the soft landed clusters we measured identical spectral features for individual clusters with the same selected size using STS at 5\,K. \par \noindent [1] H. H\"{o}vel, I. Barke, Prog. Surf. Sci. 81 (2006) 53. \par \noindent [2] S. Duffe et al., Eur. Phys. J. D (2007), published online. [Preview Abstract] |
Monday, March 10, 2008 10:24AM - 10:36AM |
A24.00011: Rectification in Porphyrin/Fullerene Dyads on Au(111)* Dominic Britti, Ray Phaneuf, Francesca Matino, Valentina Arima, Manuel Piacenza, Fabio Della Sala, Giuseppe Maruccio, Roberta Del Sole, Giuseppe Mele, Giuseppe Vasapollo, Roberto Cingolani, Ross Rinaldi We present an ultrahigh vacuum scanning tunneling microscopy (UHV-STM) and scanning tunneling spectroscopy study of \textit{ex-situ} self assembled supramolecular dyads, consisting of fulleropyrrolidines (PyC$_{2}$C$_{60})$ axially ligated to zinc(II) tetraphenylporphyrin (ZnTPP), self organized by axial ligation to a 4-aminothiophenol (4-ATP), self assembled monolayer on gold (111). By highly diluting the PyC$_{2}$C$_{60}$ solution, and subsequently annealing in vacuum, isolated dyads are obtained; these show both bias polarity-dependent apparent height in STM images, and highly rectifying behaviour in tunneling spectroscopy. First principles density functional theory calculations clarify the conformational and the electronic properties of the 4-ATP/ZnTPP/PyC$_{2}$C$_{60}$ system. The rectifying behavior is explained using a model based on the Aviram-Ratner mechanism. * Work supported by the CNR-INFM, by a NSF US-Italy Cooperative Research Program {\#}OISE-0242579, by the SpiDME European project and by MIUR FIRB 2003 `SYNERGY' grant. Lab for Physical Sciences and in part by a NSF-MRSEC, DMR{\#} 0520471. [Preview Abstract] |
Monday, March 10, 2008 10:36AM - 10:48AM |
A24.00012: Electron transport study of surface-supported nanostructures with a quadraprobe scanning tunneling microscope Tae-Hwan Kim, John Wendelken, An-Ping Li We report the study of the electron transport and structural properties of nanostructured materials with a low temperature quadraprobe scanning tunneling microscope (STM) system. Self-assembled nanostructures including epitaxially grown nanowires and atomic chains have been fabricated by doping with small amounts of metal atoms (Au, Gd, Y, Ag) on a Si surface. The local electronic states and transport properties have been characterized in situ. This research took the advantage of our recent development of the quadraprobe STM system. As a ``nano'' version of a four-probe station, the quadraprobe STM system provides an integrated research platform with a low temperature four-probe STM, a molecular-beam epitaxy growth chamber, a high resolution scanning electron microscope, and a scanning Auger microscope. The four STM probes can be driven independently with sub-nanometer precision, enabling conventional STM imaging and four-point electrical transport study of surface electronic systems and nanostructured materials at temperatures down to 10 K. *Email: apli@ornl.gov [Preview Abstract] |
Monday, March 10, 2008 10:48AM - 11:00AM |
A24.00013: Metallic Transport and Anderson Localization on In Atomic Layers on Silicon Shiro Yamazaki, Yoshikazu Hosomura, Iwao Matsuda, Rei Hobara, Shuji Hasegawa Metallic temperature dependence of electrical resistance have not been observed except extremely limited number of examples[1] below 100K in atomic-scale low-dimensional metal systems due to Anderson localization. Si(111)-$\sqrt 7 \times \sqrt 3 $-In surface reconstruction consist of 1.2 ML In atoms. According to ARPES study, the surface is 2D metal with the large Fermi wave number (k$_{F}$=14nm$^{-1})$ and the large electron density (4.6$\times $10$^{14}$eV$^{-1}$cm$^{-2})$, leading to a low resistance [2]. By using variable-temperature micro-four-point probe method [3], low resistance and metallic transport was found down to 10 K. It is quantitatively explained by the ARPES result by using Boltzmann equation $R_{2D} =\frac{4\pi ^2\lambda m^\ast }{e^2\hbar k_F^2 }k_B T$. By introducing defect, it shows semiconducting temperature dependence of variable range hopping due to Anderson localization. [1]K. Lee, \textit{et al}. , Nature \textbf{441}, 65 (2006). [2]E. Rotenberg, \textit{et al}. , Phys. Rev. Lett. \textbf{91}, 246404 (2003). [3]T. Tanikawa,\textit{ et al}. , e-J. Surf. Sci. Nanotech. \textbf{1}, 50 (2003) [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700