IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Semiconductors Monday Sessions
       Session SC-MoA

Paper SC-MoA3
"Functionalizing" the GaN(0001) Surface: The Chemisorption of Organic Amines

Monday, October 29, 2001, 2:40 pm, Room 124

Session: GaN Surfaces, Interfaces, and Devices
Presenter: V.M. Bermudez, Naval Research Laboratory
Correspondent: Click to Email
The emergence of "molecular electronics" has led to interest in the synthesis of hybrid organic/semiconductor structures. Surfaces "functionalized" by attachment of unsaturated hydrocarbons provide the possibility of subsequently building complex electro- or photoactive molecular films using, e.g., photochemical or cycloaddition reactions. Previous work@footnote 1@ with NH@sub 3@ shows that amines are highly reactive with the Ga-polar GaN(0001) surface. Here we use mainly XPS, UPS and ELS to study chemisorption of amines involving @pi@-bonded hydrocarbons, focusing on a primary amine (aniline, C@sub 6@H@sub 5@-NH@sub 2@) and a secondary amine (3-pyrroline, C@sub 4@H@sub 6@NH) having N in a 5-member ring with one C=C bond. Dosing near 300 K with either amine causes rapid elimination of the GaN 3.4 eV surface-state loss in ELS and growth of a C=C @pi@-@pi@@super *@ loss at 6.5 eV (aniline) or 7.2 eV (3-pyrroline). The background-corrected xray-excited C KLL and N KLL band areas indicate a saturation coverage of about 0.40 molecules per surface Ga site for either species. In contrast, benzene (C@sub 6@H@sub 6@) does not adsorb under these conditions. HeII UPS shows rich orbital structure, differing from that of either free molecule, which has been analyzed with the aid of ab-initio DFT calculations. The results suggest adsorption via the amine N-atom with the hydrocarbon ring remaining intact. UPS has also been used to measure changes in band bending and in electron affinity (@delta@@chi@) with adsorption. This permits construction of energy-level diagrams showing the alignment of the molecular HOMO and LUMO with the GaN band edges. For aniline (3-pyrroline), the surface dipole layer leads to @delta@@chi@ of about -0.55 (-0.92) eV, vs. the clean-surface @chi@ of 3.3 eV. This large reduction in @chi@ may be useful in electron emission devices. @FootnoteText@ @footnote 1@ V.M. Bermudez, Chem. Phys. Lett. 317 (2000) 290.