AVS 62nd International Symposium & Exhibition
    Surface Science Thursday Sessions
       Session SS+AS+EM+EN-ThM

Paper SS+AS+EM+EN-ThM2
Ethylenediamine Grafting on Oxide-free H-, F-, and Cl- terminated Si(111) Surfaces

Thursday, October 22, 2015, 8:20 am, Room 113

Session: Semiconductor Surfaces and Interfaces - I
Presenter: Tatiana P. Chopra, University of Texas at Dallas
Authors: T.P. Chopra, University of Texas at Dallas
R.C. Longo, University of Texas at Dallas
K.J. Cho, University of Texas at Dallas
M.D. Halls, Schrodinger, Inc.
P. Thissen, Karlsruhe Institute of Technology, Germany
Y.J. Chabal, University of Texas at Dallas
Correspondent: Click to Email
Amine termination of surfaces constitutes a core platform for fields as diverse as microelectronics and bioengineering, and for nanotechnology in general. Diamines are particularly attractive for surface amination because, unlike ammonia or simple amine molecules, they have a metal chelating capability useful in fabricating heterostructures. They can act as a linker molecule between inorganic electronic materials and biomolecules or photoactive quantum dots for applications in microlectronic, photonics and biosensing. Most work in the field utilizes self-assembled monolayers (SAMs) on oxidized substrates to present an amine termination of the surface. However, grafting on oxides through silanes or phosphonates is not robust. Moreover, several applications require as short a distance between the substrate and the amine group, which is hindered by the thickness of the oxide. Therefore, diamine grafting directly on oxide-free substrates is important, yet remains unexplored.

In this work, the attachment of liquid and vapor-phase ethylenediamine on three types of oxide-free (H-, F- and Cl-terminated) Si(111) surfaces is examined by infrared absorption spectroscopy and X-ray photoelectron spectroscopy in conjunction with first-principles calculations. We find that chemisorption is only possible on F- and Cl-terminated Si surfaces, with H-terminated Si surfaces yielding only physisorbed diamine molecules. On Cl-terminated Si surfaces, diamines adsorb in a mixture of monodentate and bridging configurations (chemical reaction of both amine endgroups), while on partially F-terminated Si surfaces the adsorption occurs primarily at one end of the molecule. The reaction of ethylenediamine with Cl-terminated Si surfaces is also characterized by complete removal of Cl and partial Si-H (~25% ML) formation on the surface. This unexpected result suggests that a proton-chlorine exchange may take place, with the endothermic barrier possibly reduced via a silicon lattice assisted process after an initial attachment of ethylenediamine to the surface.