Properties of Nanoporous Silica Thin Films Determined by High-Resolution X-Ray Reflectivity and Small-Angle Neutron Scattering

Published

February 1, 2000

Author(s)

Wen-Li Wu, William E. Wallace, Eric K. Lin, G W. Lynn, Charles J. Glinka, E T. Ryan, H M. Ho

Abstract

A new methodology based on a novel combination of a high-resolution specular x-ray reflectivity and small-angle neutron scattering has been developed to evaluate the structural properties of low-dielectric-constant porous silica thin films about one micrometer thick supported on silicon wafer substrates. To complement these results film composition was determined by high-energy ion scattering techniques. For the example thin film presented here, the overall film density was found to be (0.55 0.01) g/cm³ with a pore wall density of (1.16 0.05) g/cm³ and a porosity of (53 1)%. The characteristic average dimension for the pores was found to be (65 1) . It was determined that (22.1 0.5)% of the pures had connective paths to the free surface. The mass fraction of water absorption was (3.0 0.5)% and the coefficient of thermal expansion was (60 20)X10^-6/ C from room temperature to 175 C. Lastly, model fitting of the specular x-ray reflectivity data indicated the presence of a thin surface layer with an increased electron density compared to the bulk of the film as well as an interfacial layer with a reduced electron density.

Citation

Journal of Applied Physics

Volume

87

Issue

No. 3

Pub Type

Journals

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Keywords

coefficient of thermal expansion, density, moisture uptake, pore size, porosity, silica, small angle neutron scattering

Citation

Wu, W. , Wallace, W. , Lin, E. , Lynn, G. , Glinka, C. , Ryan, E. and Ho, H. (2000), Properties of Nanoporous Silica Thin Films Determined by High-Resolution X-Ray Reflectivity and Small-Angle Neutron Scattering, Journal of Applied Physics, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=851582 (Accessed October 9, 2025)