title: Cysteamine-based functionalization of InAs surfaces: revealing the critical role of oxide interactions in biasing attachment.
abstract: Attaching functional molecules such as thiols and proteins to semiconductor surfaces is increasingly exploited in functional devices such as sensors. Despite extensive research to understand this interface and demonstrate a robust protocol for attachment, the bonding chemistry of thiolates to III-V surfaces has been under great debate in the literature. This study provides a comprehensive chemical model for the attachment of thiols to InAs, an increasingly device-relevant III-V semiconductor, using cysteamine as a model molecule. We examine the attachment of cysteamine to InAs via the thiol group using X-ray photoelectron spectroscopy and spectroscopic ellipsometry and confirm that thiolate bonding to the substrate occurs preferentially to As sites over In sites as a limit. These experiments explore the interplay of the native oxide chemical properties, the cysteamine concentration, and the evolving InAs surface chemistry with functionalization. The thiol-InAs interaction can be framed as a general acid-base reaction, where the nucleophilic and/or electrophilic attack of the surface (i.e., binding to In sites and/or As sites) depends on the acidity of the thiol. The roles of the initial oxide composition, the solvent of the functionalizing solution, and the cysteamine as a limiting reagent in fully displacing the oxide and creating In-S and As-S bonds are highlighted.
authors: Electrical and Computer Engineering Department, Duke University, Durham, North Carolina 27708, USA. maria.losurdo@ba.imip.cnr.it
authors: Maria
authors: M
authors: Losurdo
authors: Pae C
authors: PC
authors: Wu
authors: Tong-Ho
authors: TH
authors: Kim
authors: Giovanni
authors: G
authors: Bruno
authors: April S
authors: AS
authors: Brown