| AVS 56th International Symposium & Exhibition | |
| Applied Surface Science | Wednesday Sessions |
| Session AS+NS-WeM |
| Session: | Nanoparticle and Nanoscale Surface Chemistry II |
| Presenter: | S.D. Techane, University of Washington |
| Authors: | S.D. Techane, University of Washington L.J. Gamble, University of Washington M.H. Engelhard, Pacific Northwest National Laboratory D.R. Baer, Pacific Northwest National Laboratory D.G. Castner, University of Washington |
| Correspondent: | Click to Email |
In this research gold nanoparticles (AuNP) are used as model nanoparticles and self-assembled monolayers of alkyl thiols as model organic ligands to create functionalized NP with a variety of surface chemistries. The AuNP size and thiol chain length are varied to study their effects on the properties of the AuNP. Our aim is to create a series of well-defined functionalized AuNP for use in complex biological applications and to use the AuNP-SAMs as standard samples to develop XPS (X-ray photoelectron spectroscopy) data analysis methods for coated NP characterization. We have synthesized and characterized four chain lengths of COOH-SAMs (C6, C8, C11, C16 carboxylic thiols) on various sizes of AuNPs (diameter =14nm, 25nm, 40nm) and flat gold surfaces using the surface sensitive techniques of XPS and ToF-SIMS. Many of the trends expects for increasing SAM thickness are observed. In addition data shows that particle size (surface curvature) had an effect on the XPS and ToF-SIMS measurements. Complementary ATR-FTIR (attenuated total reflectance FTIR) measurements were done to characterize the SAM ordering and crystallinity. As SAMs length increased the CH2 stretching vibration frequencies (υCH2) decreased on both AuNPs and flat-Au surfaces. For a given chain length SAMs the υCH2 also decreased as the AuNPs particle size decreased indicating that longer chain SAMs on the smaller AuNPs (i.e. 14nm-C16 COOH-SAMs) have the most crystalline surface structure. As the XPS C/Au atomic ratio depends on the structure of the SAMs as well as the take-off angles (which range from 0 to 90° for particles) there is a need to develop XPS data analysis methods that accurately account for curved NP surfaces. SESSA (Simulated Electron Spectra for Surface Analysis) and QUASES (Quantitative Analysis of Surfaces by Electron Spectroscopy Software) have been used to simulate the experimental XPS results as a function of take-off angle for COOH-SAMs on flat-Au surfaces. Quantities such as SAM density, thickness, surface roughness and instrumental parameters were tuned in SESSA to optimize agreement between simulated and experimental XPS compositions for SAMs on flat Au surfaces. SESSA results were compared with experimental measurements taken from 3 different XPS instruments: Quantum (EMSL/PNNL), Kratos and S-probe (NESAC/BIO). Approaches are being used to apply SESSA and QUASES to analysis of the particle data.