| AVS 56th International Symposium & Exhibition | |
| Surface Science | Friday Sessions |
| Session SS2-FrM |
| Session: | Semiconductor Surfaces and Interfaces II: Si |
| Presenter: | X. Wang, University of Wisconsin-Madison |
| Authors: | X. Wang, University of Wisconsin-Madison J. Streifer, University of Wisconsin-Madison P. Colavita, University of Wisconsin-Madison R.J. Hamers, University of Wisconsin-Madison |
| Correspondent: | Click to Email |
The grafting of organic molecules on semiconductor surfaces initiated by UV light has become an efficient means to tailor the chemical and physical properties of surfaces of materials, enabling their integration with various applications of the devices. In situ photoelectron yield experiments were performed in the spectral range from 3 to 6 eV on alkene liquid/nanocrystalline diamond (NCD) interfaces. N-Alkenes carrying different terminal functional groups: trifluoroacetamide-protected 1-aminodec-1-ene (TFAAD) and 10-N-Boc-aminodec-1-ene (tBoc) were used to investigate the dependence of photoelectron yield on the energy of the molecular acceptor level. Amorphous carbon was used in addition to NCD to study the influence of the substrate electronic structure on the photoelectron yield threshold. The photochemical attachment of TFAAD on H-terminated NCD surfaces at various incident photon energies was characterized by X-ray photoelectron spectroscopy (XPS) to investigate the correlation between the excitation energy and the reaction efficiency. These measurements reveal that the photochemical reaction on carbon surfaces is initiated via the photoejection of electrons from the solid valence band into the acceptor levels of the alkenes. SEM images of patterned molecular layers on two H-terminated single crystal diamonds (SCD, type Ib and IIb) with different hole mobilities reveal much sharper transition between functionalized and non-functionalized regions on the sample with much lower hole mobility (type Ib SCD). However, the surface coverage of grafted alkenes as characterized by XPS is quite similar on these two surfaces. These data imply that while the photoemission of electrons controls the reaction efficiency, the holes left in the substrates can diffuse and control the grafting sites.
Recent data exploring the mechanism on silicon will also be presented. Our comparison of silicon and diamond suggests that there are some common factors underlying the ability to graft alkenes onto various semiconductors, but also some important differences. These results suggest that photochemical grafting may be broadly applicable to a wide range of materials, and that a fundamental understanding of the mechanism facilitates the design and synthesis of well defined functional interfaces.