Bulletin of the American Physical Society
61st Annual Gaseous Electronics Conference
Volume 53, Number 10
Monday–Friday, October 13–17, 2008; Dallas, Texas
Session GW2: Charged Particle Surface Interactions |
Hide Abstracts |
Chair: Steve Shannon, North Carolina State University Room: Salon A-D |
Wednesday, October 15, 2008 8:00AM - 8:30AM |
GW2.00001: Organising Atoms, Clusters and Proteins on Surfaces Invited Speaker: This talk will discuss new developments in the creation of nanoscale surface features and their applications in biomedicine. Electron-surface interactions and plasma methods play a crucial role in both the production and analysis of these ``atomic architectures.'' At the extreme limit, electron injection from the tip of a scanning tunnelling microscope (STM) enables bond-selective manipulation of individual polyatomic molecules [1]. On a more practical level, the controlled deposition of size-selected clusters [2], generated by magnetron sputtering and gas condensation followed by mass selection, represents a surprisingly efficient route to the fabrication of surface features of size 1-10 nm, the size scale of biological molecules such as proteins. STM and AFM measurements show the clusters can act as binding sites for individual protein molecules. For example, the pinning of size-selected AuN clusters (N = 1--2000) to the (hydrophobic) graphite surface presents bindings site for sulphur atoms and thus for the cysteine residues in protein molecules. Systematic studies of different proteins [3] provide ``ground rules'' for residue-specific protein immobilisation by clusters and have led to the development of a novel biochip for protein screening by a spin-off company. The 3D atomic structure of the clusters is highly relevant to such applications. We show that measurement of the scattered electron beam intensity - specifically, the high angle annular dark field (HAADF) signal - in the scanning transmission electron microscope (STEM) allows us (a) to count the number of atoms in a cluster on the surface and (b) to determine a 3D atom-density map of the cluster when an aberration-corrected STEM is used [4]. \newline 1. P.A. Sloan and R.E. Palmer, Nature 434 367 (2005). \newline 2. S. Pratontep, P. Preece, C. Xirouchaki, R.E. Palmer, C.F. Sanz-Navarro, S.D. Kenny and R. Smith, Phys. Rev. Lett. 90 055503 (2003). \newline 3. R.E. Palmer, S. Pratontep and H.-G. Boyen, Nature Materials 2 443 (2003); R.E. Palmer and C. Leung, Trends in Biotechnology 25 48 (2007). \newline 4. Z.Y. Li, N.P. Young, M. Di Vece, R.E. Palmer, A.L. Bleloch, B.C. Curley, R.L. Johnston, J. Jiang, J. Yuan, Nature 451 46 (2008). [Preview Abstract] |
Wednesday, October 15, 2008 8:30AM - 9:00AM |
GW2.00002: Neutralization dynamics of hydrogen anions near flat and vicinal surfaces$^\dagger$ Invited Speaker: I will scrutinize the role of intermediate electronic surface and image states on the charge-transfer dynamics during collisions of H$^-$ anions with atomically flat Pd, Cu, and Ag surfaces of (100) and (111) symmetries using a wave-packet propagation approach [1]. For these surfaces I will show how differently located band gaps, surface -, and image states lead to easily visualized differences in the evolution of the active electron's probability density: i)Long-lived surface states of the (111) surfaces tend to localize electronic density near the surface and facilitate recapture by the projectile, while H$^-$ is more efficiently neutralized near (100) surfaces whose surface state appears as a broad resonance embedded in the bulk valence band. ii) Image states that are degenerate with the metal conduction band favor, while image states that are degenerate with the band gap hinder recapture. In the second part of my talk I will discuss negative-ion interactions with stepped nano-structured surfaces based on effective potentials for the active electron's interaction with the surface that we derived within a Thomas-Fermi von Weizsaecker model [2]. For 50eV projectiles, we find an enhancement of electron loss near the steps due to the Smoluchowski effect. In consequence, negative-ion survival is more likely for projectiles that approach steps from above than from below [3]. $^\dagger$ In collaboration with Himadri Chakraborty (Northwest Missouri State Univ.) and Boyan Obreshkov (Kansas State Univ.) \newline \newline [1] H. Chakraborty, T. Niederhausen, and U. Thumm., Nucl. Instrum. Meth. B \textbf{241}, 43 (2005) ; Phys. Rev. A {\bf 70}, 052903 (2004). \newline [2] B. Obreshkov and U. Thumm, Phys. Rev. A {\bf 74}, 012901 (2006); \newline [3] B. Obreshkov and U. Thumm, Surf. Sci. {\bf 601}, 622 (2007). [Preview Abstract] |
Wednesday, October 15, 2008 9:00AM - 9:15AM |
GW2.00003: Revibrational Spectra of Molecules Sputtered of Carbon Surfaces Predrag Krstic Irradiation of the carbon surfaces by hydrogen isotopes results in processes of crucial importance for the carbon based divertor tiles of a fusion reactor. Thus the sputtering and implantation, result in erosion, plasma pollution, and tritium retention, as well as carbon deposition all over the reactor first wall. The molecules chemically sputtered upon impact of deuterium of deuterated carbon surface are various hydrocarbons as well as We study the translational and rovibrational energy and angular spectra of sputtered molecules. The energy distributions of ejected molecules confirm the partial thermalization of the impact cascade. Sputtered hydrocarbon molecules have rovibrational energies in the range 1.5-2 eV, with relatively cold translational and rotational motion, close to 0.5 eV. In contrast, translational and rovibrational energies of sputtered deuterium molecules are close to 1 eV, with approximate equipartition between rotational and vibrational modes. [Preview Abstract] |
Wednesday, October 15, 2008 9:15AM - 9:30AM |
GW2.00004: ABSTRACT WITHDRAWN |
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