Traceable thickness determination of organic nanolayers by X‐ray reflectometry1. (29th January 2014)

• Record Type: Journal Article
• Authors: Wernecke, Jan; Shard, Alexander G.; Krumrey, Michael; Abel, Marie‐Laure; Rossi, Antonella; Watts, John F.
• Is Part Of: Surface and interface analysis. Volume 46:Number 10/11(2014)
• Page Start: 911
• Page End: 914
• Publication Date: 2014-01-29
• Subjects: Surfaces (Physics) -- Periodicals; Surface chemistry -- Periodicals; Thin films -- Periodicals; 541.33
• DOI: 10.1002/sia.5371
• Languages: English
• ISSNs: 0142-2421

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <p>While several methods are available for layer thickness determination in the nanometer range, very few of them are suited for absolute measurements that can be traced to the SI units. Layer thickness determination from the oscillations that are observed in X‐ray reflectometry for metallic layers or oxides is well established, but the low density of most organic materials results in low contrast and thus weak oscillations. However, by using synchrotron radiation instead of X‐ray tubes, any photon energy can be selected, also in the range below 2 keV, to enhance the contrast significantly. The organic layers systems investigated here are Irganox 1010 and Fmoc‐pentafluoro‐L‐phenylalanine layers with nominal thicknesses between 20 and 100 nm, deposited on silicon wafers with a nominal 20 nm SiO<sub>2</sub> layer. The measurements were performed at a photon energy of 1841 eV close to the Si K‐absorption edge. Pronounced oscillations with different periodicities were observed for all investigated systems. After determination of the critical angle, the measured reflectance is divided by the Fresnel reflectance. A Fourier transform of the remaining signal results in the power spectral density. The peaks in the spectra correspond to the thicknesses of individual layers or groups of layers. These organic bilayer systems can be clearly distinguished from monolayers and, with some knowledge on the sample structure, the individual layer thicknesses are obtained with low uncertainties. This enables the development of reference materials with certified thickness of organic layers. Copyright © 2014 John Wiley & Sons, Ltd.</p> </abstract>