Self-assembled monolayers of alkyl-thiols on InAs: A Kelvin probe force microscopy study

Authors:

• Anna Teresa Szwajca,
• J. Wei,
• M.I. Schukfeh,
• M. Tornow

Abstract

We report on the preparation and characterization of self-assembled monolayers from aliphatic thiols with different chain length and termination on InAs (100) planar surfaces. This included as first step the development and investigation of a thorough chemical InAs surface preparation step using a dedicated bromine/NH₄OH-based etching process. Ellipsometry, contact angle measurements and atomic force microscopy (AFM) indicated the formation of smooth, surface conforming monolayers. The molecular tilt angles were obtained as 30 ± 10° with respect to the surface normal. Kelvin probe force microscopy (KPFM) measurements in hand with Parameterized Model number 5 (PM5) calculations of the involved molecular dipoles allowed for an estimation of themolecular packing densities on the surface.Weobtained values of up to n = 1014 cm^-2 for the SAMs under study. These are close to what is predicted from a simple geometrical model that would calculate a maximum density of about n = 2.7 × 10¹⁴ cm^-2. We take this as additional conformation of the substrate smoothness and quality of our InAs-SAM hybrid layer systems.