Organic monolayers on silicon surfaces: Synthesis, characterization and studies toward their effect on charge injection at the silicon/organic solid interface

I have studied the photo-reaction of hydrogen-terminated silicon (H-Si(111)) with unsaturated molecules. The reaction of H-Si(111) with dioxygen is strongly wavelength dependant. UV-light illumination of H-Si(111) in the presence of neat deoxygenated 1-octene, 1-octadecene, 1-octyne, styrene or phenyl acetylene affords a film of molecular thickness with densely-packed organic adsorbates. I propose of these reactions to occur through a radical-chain mechanism initiated by the wavelength-dependent photodesorption of surface hydrogen by UV light. A method for quantifying surface coverage using x-ray photoelectron spectroscopy and ellipsometry is outlined.; Chapter 3 looks closer at the reaction of styrene with H-Si(111). Electrons from a scanning tunneling microscope are used to break individual Si-H bonds in ultra-high vacuum on a H-Si(111) prepared by aqueous ammonium fluoride etch. I observe that the dangling bonds created in ultra-high vacuum act as initiation sites for the chain reaction of styrene with the surface giving multiple styrene adsorbates for each initial dangling bond. From these observations mechanism presented in Chapter 2 is possible.; I then extend the methods presented in Chapter 2 to prepare multi-component organic monolayers on silicon containing fully conjugated organic molecules. Films containing both 4-(p-trifluoromethyl styryl) phenyl acetylene and either 1-octene, 1-octyne, styrene or phenyl acetylene are formed. I find a dramatic increase in the concentration of surface adsorbed 4-( p-trifluoromethyl styryl) phenyl acetylene relative to its precursor solution concentration. I also find that the relative incorporation of 4-( p-trifluoromethyl styryl) phenyl acetylene into a monolayer depends strongly on the diluent coadsorbate used.; The monolayers prepared in this thesis are studied for their effect on charge injection at the silicon/organic solid interface. Organic light emitting diodes were constructed using hydrogen-terminated and organic-monolayer modified silicon substrates, poly [2-methoxy-5-(2′-ethyl-hexoxy)1,4-phenylene vinylene] (MEH-PPV) as the electroluminescent organic solid and semi-transparent metallic top electrodes. I find both n- and p-type silicon devices emit light when silicon is used as an anode. Further work is needed to gain sufficient control of device reproducibility before quantitative conclusions can be drawn from my data concerning the effects of surface termination.