Molecules adsorbed on metal surfaces: buckyball-induced metal reconstruction, TCNQ self-assembled with Mn, and a flexible complex molecule

Michel A. Van Hove
Department of Physics and Materials Science,
City University of Hong Kong,
Hong Kong, China

Vendredi , 11 juin 2010, 16 h 30, amphi Astier, UPMC, site Jussieu


We have studied the adsorption and supramolecular assembly of several large molecules on metal surfaces, including C60, TCNQ, and BTP-TPE on either Cu(111), Cu(100) or Pt(111). Starting from experimental data (structure and microscopy), we calculated total energies while optimizing the adsorption configuration, and simulated images obtained by scanning tunneling microscopy (STM). The aim is to enhance our understanding of the bonding of such molecules to metal surfaces.

C60 molecules (buckyballs) were studied on both Cu(111) [1] and Pt(111) [2]. It was found that buckyballs can reconstruct both metal surfaces by expelling metal atoms, displaying a remarkably strong C60-metal interaction. Simulation of STM in the spectroscopic mode ("STS") enables detecting the metal reconstruction and also predicts the possibility to use this system to generate negative differential resistance (NDR) for molecular electronic devices [3].

TCNQ molecules (7,7,8,8-tetracyanoquinodimethane) were mixed with Mn atoms to form a compound two-dimensional monolayer by supramolecular assembly on a Cu(100) surface [4]. The interactions in the Mn(TCNQ)2 network and in the full system are analyzed from a molecular orbital perspective and in the light of scanning tunneling microscopy (STM) imaging and simulations. Structural, electronic and magnetic properties are studied in detail using density functional theory (DFT) calculations.

BTP-TPE molecules (1,2-bis[4'-(4'-2,2':6',2"-terpyridyl)-biphenyl-4-yl]-1,2-diphenylethene) were deposited on Cu(111) and found to exhibit the properties of single-molecule type-I double heterojunctions [5]. Their intra-molecular electronic structure while adsorbed has been revealed by means of STM, STS and DFT calculations.

Attachment of a single Cu atom to either side group lowers the energy level of the molecular orbitals localized at that group without noticeably affecting other parts of the molecule: this presents the possibility of regulating the energy-level alignment of intra-molecular double heterojunctions.

Acknowledgment: This work was supported in part by the Hong Kong Research Grant Council and the CityU Centre for Applied Computing and Interactive Media.

References:
1. Woei Wu Pai, H.T. Jeng, C.-M. Cheng, C.-H. Lin, X.D. Xiao, A.D. Zhao, X.Q. Zhang, Xu Geng, X.Q. Shi, M.A. Van Hove, C.-S. Hsue, and K.-D. Tsuei, "Optimal doping of a C60  monolayer on Cu(111) via interface reconstruction", Phys. Rev. Lett. 104, 036103 (2010)

2. X.Q. Shi, M. Altman, and M.A. Van Hove, in preparation

3. X.Q. Shi, W.W. Pai, X.D. Xiao, J.I. Cerdá, R.Q. Zhang, C. Minot, and M.A. Van Hove, "Significant Negative Differential Resistance Predicted in Scanning Tunneling Spectroscopy for a C60 Monolayer on a Metal Surface", Phys. Rev. B 80, 075403 (2009).

4. Tsu-Chun Tseng, Chensheng Lin, X.Q. Shi, Steven L. Tait, Xiong Liu, Ulrich Starke, Nian Lin, R.Q. Zhang, J. Cerdá, C. Minot, M.A. Van Hove, J.I. Cerdá and Klaus Kern, "Two-dimensional metal-organic coordination networks of Mn-7,7,8,8-tetracyanoquinodimethane (TCNQ) assembled on Cu (100): structural, electronic and magnetic properties", Phys. Rev. B 80, 155458 (2009)

5. Weihua Wang, Xingqiang Shi, Chensheng Lin, R.Q. Zhang, C. Minot, M.A. Van Hove, Yuning Hong, Ben Zhong Tang and Nian Lin, "Imaging and Shifting Intra-molecular Energy Levels of a Type-I Double Heterojunction in Single Molecules", submitted for publication.