Chemical control over the electrical, electronic, and electrochemical properties of Si surfaces

Abstract

We have developed mixed monolayer chem. that allows for incorporation of a versatile component and a 'filler' component to impart simultaneous stability and function at Si surfaces. Optoelectronic device efficiency depends on control over chem. and electronic properties. We were able to functionalize silicon surfaces with mixed thiophene/methyl monolayers. The mixed monolayer method allowed for functionalization with thiophene groups while maintaining a low surface recombination velocity, S, of 27±9 cm s^(-1), while the single component thiophene-functionalized Si(111) surface displayed S=670±190 cm s^(-1). Pd-catalyzed Heck coupling was achieved at mixed thienylBr/CH_3-Si(111) surfaces. Coverage of θ = 0.11±0.03 was achieved for Heck-coupled fluorostyrene. The Heck coupling reaction was versatile, vinylferrocene and protoporphyrin-IX were also successfully coupled to the surface, and low surface recombination velocity was maintained after the coupling chem. Thienybromide functionalization induced an interfacial dipole, which was studied via spectroscopic and electronic experimentation and was investigated by ab initio methods. The band-edge positions were favorably shifted 400 mV from those at the CH_3-Si(111) surfaces. The mixed monolayer technique can be similarly applied to attach protected aldehydes. Once deprotected, mixed propanal/methyl-Si(111) assisted at. layer deposition of Al_2O_3 and MnO_x. Increased deposition and decreased surface electronic defects were obsd. at propanal functionalized surfaces as compared to H-Si(111) surfaces. This has direct benefits for both surface protection and field effect transistors. The mixed monolayer method was shown to increase synthetic versatility, decrease electronic trap state d., and improve control of interfacial energetics.