DETERMINATION OF THE SURFACE SILANOL CONCENTRATION OF AMORPHOUS SILICA SURFACES USING STATIC SECONDARY-ION MASS-SPECTROSCOPY

A novel method has been developed to determine the concentration of si lanol (Si-OH) groups on planar, amorphous silica glass surfaces. This method involves neutral beam static secondary ion mass spectroscopy (S IMS) analysis as a function of sample temperature. The calibration nec essary to achieve absolute quantification of the silanol concentration s with static SIMS was obtained using a combination of Fourier-transfo rm infrared (FTIR) spectroscopy and x-ray photoemission spectroscopy ( XPS), High purity, amorphous silica glass samples with varying silanol and molecular water concentrations were prepared ex situ, and in vacu o by fracturing and dosing silica rods with water in the sample prepar ation chamber of a UHV system. Static SIMS spectra collected as a func tion of sample temperature show a decreasing SiOH+/Si+ peak area ratio with increasing temperature due to desorption of physisorbed, molecul ar water. It is shown that the equilibrium SiOH+ signal intensity obta ined after the heat treatment is proportional to the silanol concentra tion of the silica surface, XPS analysis of derivatized samples was us ed to confirm the results of the static SIMS experiments. In order to achieve absolute quantification of the silanol concentration in OH/nm( 2), FTIR was used to calibrate the SiOH+/Si+ peak area ratios measured from the static SIMS spectra. (C) 1997 American Vacuum Society.