Spontaneous Grafting of OH-Terminated Molecules on Si−H Surfaces via Si–O–C Covalent Bonding

Essam M Dief,Nadim Darwish,Simone Ciampi,Anton P Le Brun

doi:10.3390/surfaces4010010

Essam M Dief, Nadim Darwish + Show 2 more

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https://doi.org/10.3390/surfaces4010010

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Abstract

The surface functionalization of oxide-free hydrogen-terminated silicon (Si−H) enables predictably tuning its electronic properties, by incorporating tailored functionality for applications such as photovoltaics, biosensing and molecular electronics devices. Most of the available chemical functionalization approaches require an external radical initiator, such as UV light, heat or chemical reagents. Here, we report forming organic monolayers on Si–H surfaces using molecules comprising terminal alcohol (–OH) groups. Self-assembled monolayer (SAM) formation is spontaneous, requires no external stimuli–and yields Si–O–C covalently bound monolayers. The SAMs were characterized by X-ray photoelectron spectroscopy (XPS) to determine the chemical bonding, by X-ray reflectometry (XRR) to determine the monolayers thicknesses on the surface and by atomic force microscopy (AFM) to probe surface topography and surface roughness. The redox activity and the electrochemical properties of the SAMs were studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The availability and the ease of incorporating OH groups in organic molecules, makes this spontaneous grafting as a reliable method to attach molecules to Si surfaces in applications ranging from sensing to molecular electronics where incorporating radical initiator setups is not accessible.

Highlights

Silicon (Si) is the most commonly used semiconductor in the current electronic devices’technologies, due to its low cost, abundance and intriguing semiconducting properties [1,2,3,4,5].the semiconducting electronic properties of Si are desired, the surface of Si is covered, at ambient conditions, by an electrically insulating thin layer of oxide that masks its electronic properties [6,7,8,9]
Crystalline Si requires etching the oxide layer by fluoride ions (e.g., HF and NH4 F) in order to expose the Si–H surface and its semiconducting properties but etched Si–H surfaces have short lifespan stability towards re-oxidation and require surface functionalization to protect them against oxidation
We have demonstrated the formation of Self-assembled monolayer (SAM) on Si by incubating freshly

Summary

Introduction

Silicon (Si) is the most commonly used semiconductor in the current electronic devices’technologies, due to its low cost, abundance and intriguing semiconducting properties [1,2,3,4,5].the semiconducting electronic properties of Si are desired, the surface of Si is covered, at ambient conditions, by an electrically insulating thin layer of oxide that masks its electronic properties [6,7,8,9]. Hydroxyl-terminated molecules such as alkyl silanols have been utilized to form self-assembled monolayers (SAMs) on SiOx surfaces. Modification of the Si surfaces with molecules while avoiding the interference of the insulating surface oxides is desired for better performing devices and wider range of application. In this context, crystalline Si requires etching the oxide layer by fluoride ions (e.g., HF and NH4 F) in order to expose the Si–H surface and its semiconducting properties but etched Si–H surfaces have short lifespan stability towards re-oxidation and require surface functionalization to protect them against oxidation

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