| A variety of surface-sensitive characterization tools together with density functional theory (DFT) modeling have been applied to study the atomic-scale structures of the self-assembly of pi-conjugated molecules on silicon surfaces. Through the studies of covalently bound p-bromostyrene (BrSty)-, p-(4-bromophenyl)styrene (BPS)-, p-(4-bromophenylethynyl)styrene (BPES)-, (4-bromophenyl)acetylene (BPA)-, (p-(4-bromophenyl)phenyl)acetylene (BPPA)-, and (p-(4-bromophenylethynyl)phenyl)acetylene (BPEPA)- based self-assembled monolayers (SAMs) on H-Si(111), and BrSty- and BPA- based SAMs on H-Si(001), a structure characterization strategy for SAMs/Si was developed. In each case DFT calculations predicted several possible atomic-scale models from which the most correct structure was experimentally determined by the characterization package using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray reflectivity (XRR), X-ray fluorescence (XRF), and X-ray standing wave (XSW). The XSW determined atomic density maps, in conjunction with the coarser-length-scale XRR analysis and DFT modeling, provided the atomic-scale structure of a SAM on Si.;The comparisons of the three alkyl SAMs/Si(111) with the three alkenyl SAMs/Si(111) show a higher degree of order for the alkenyl SAMs relative to the alkyl SAMs in the AFM and 111 XSW analyses. In addition, DFT shows that a sp2 alkenyl C=C bond at the surface will azimuthally align over the sp3 Si-Si bond from the substrate, whereas the sp3 alkyl C-C bond at the surface will azimuthally bisect two sp3 Si-Si bonds. With this hypothesis, the (2 x 1) periodic DFT, where the linear packing of molecules on Si(111) is approximated by a periodic attachment to every other surface silicon, was found to best simulate the structures of the SAMs on Si(111).;In addition to the studies of SAMs on Si, the characterization package was successfully applied in the development of the microwave-assisted Sonogashira coupling chemistry. The microwave-assisted Sonogashira coupling reaction provides a strategy to extend the conjugated organic structures on Si surfaces and tailor the electronic property of the hybrid materials. |
