Published: March 14, 2011 r2011 American Chemical Society 3774 dx.doi.org/10.1021/la104963v | Langmuir 2011, 27, 3774–3782 ARTICLE pubs.acs.org/Langmuir Characterization of Peptide Adsorption on InAs Using X-ray Photoelectron Spectroscopy Scott Jewett, † Dmitry Zemlyanov, ‡,§ and Albena Ivanisevic †,||, * † Weldon School of Biomedical Engineering, ‡ Birck Nanotechnology Center, § Department of Chemical Engineering, and ) Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States b S Supporting Information ’ INTRODUCTION Group IIIV semiconductors have received considerable attention for use in applications such as nanosized electronic devices, biochemical and chemical sensors, and high-speed field effect transistors (FETs). Indium arsenide (InAs) is a IIIV semiconductor that is particularly attractive in high-speed electronics 1,2 and chemical sensing 3 because of its unique electronic properties. Due to its small bandgap, surface states can have a dramatic effect on the electronic properties of InAs. As such, surface adsorbates that alter the charge character of surface states in turn lead to high sensitivity of InAs to biological or chemical species. Device effectiveness, therefore, is highly dependent on the purity and stability of the semiconductor surface. Thus, minimiza- tion of outside contaminants is a key factor in the design of all InAs- based devices. This poses a problem, because in ambient or aqueous conditions, oxide growth and unwanted molecular contamination can cause instability and wreak havoc on overall device function. One common way of stabilizing semiconductor surfaces is by surface passivation through the adsorption of self-assembled mono- layers (SAMs), which act as a protective barrier against contami- nants and oxide growth, while still allowing for device function. Simple alkanethiols have emerged as particularly attractive to passivate InAs surfaces and have received the bulk of attention in the literature. 36 Alkanethiols have a relatively high affinity for InAs, and they have been shown to preserve or even improve the electronic properties of InAs. 7,8 However, several applications of IIIV semiconductors re- quire modification with more complex biomolecules. There have been several reports of using DNA in conjunction with IIIV semiconductors for sensing applications, 911 but there is also much interest in using biomolecules as templates to assemble or grow nanostructures. Viruses, 1214 DNA, 1517 and peptides 1824 offer consistent, well-defined structures that allow for the assembly of nanostructures in relatively mild conditions. Most applications use self-assembly to form hierarchal nanostructures, but with the advent of low-temperature nanocrystal growth techniques, such as the solutionliquidsolid 25,26 (SLS) method, it is also possible to use biomolecules as templates for the growth of single nanocrystal structures. Peptides are particularly promising bio- templates for nanocrystal growth. For example, one group demonstrated the growth of ZnO nanocrystals catalyzed by a collagen-mimetic peptide, which was engineered to withstand high pH levels. 18 Despite the wealth of applications, the exact mechanism of peptide/IIIV semiconductor binding remains unknown. The binding of peptides to IIIV semiconductors has been of particular interest for the past decade and began with using phage libraries to select peptides with high affinities for GaAs. 24 Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) studies indicate that peptide binding to semiconductors is most likely mediated by both the charge 24 and order 27,28 of the peptide amino acid structure. Additionally, AFM studies show Received: December 14, 2010 Revised: February 25, 2011 ABSTRACT: The well-defined structure and high stability of peptides make them attractive biotemplates for low-temperature synthesis of semiconductor nanocrystals. Adsorbed peptide monolayers could also potentially passivate semiconductors by preventing regrowth of the oxide layer. In this work, the adsorption and passivation capabilities of different collagen- binding peptides on InAs surfaces were analyzed by X-ray photoelectron spectroscopy (XPS). Before peptide functionalization, Br 2 - and HCl-based etches were used to remove the native oxide layer on the InAs surfaces. The presence of the N 1s peak for peptide-functionalized samples confirms the adsorption of peptides onto the etched InAs surfaces. Calculated coverages were similar for all peptide sequences and ranged from ∼20 to 40% of a monolayer using the deconvoluted C 1s spectra and from ∼2 to 5% for the N 1s spectra. The passivation ability of the peptides was analyzed by comparing the ratios of the oxide components to the nonoxide components in the XPS spectra. The thickness of the oxide layer was also approximated by accounting for the attenuation of the substrate photoelectrons through the oxide layer. We find that the oxide layer regrowth still occurs after peptide functionalization. However, the oxide layer thicknesses for peptide-functionalized samples do not reach as received levels, indicating that the peptides do have some passivation ability on InAs.