Abstract
We report on the use of time-resolved optical ellipsometry to monitor the deposition of single atomic layers with subatomic sensitivity. Ruddlesden–Popper thin films of SrO(SrTiO3)n=4 were grown by means of metalorganic aerosol deposition in the atomic layer epitaxy mode on SrTiO3(1 0 0), LSAT(1 0 0) and DyScO3(1 1 0) substrates. The measured time dependences of ellipsometric angles, Δ(t) and Ψ(t), were described by using a simple optical model, considering the sequence of atomic layers SrO and TiO2 with corresponding bulk refractive indices. As a result, valuable online information on the atomic layer epitaxy process was obtained. Ex situ characterization techniques, i.e. transmission electron microscopy, x-ray diffraction and x-ray reflectometry verify the crystal structure and confirm the predictions of optical ellipsometry.
Highlights
Nanoscience and modern material physics are based on the growth and study of thin films with thicknesses spreading down to one atomic layer
We report on the use of time-resolved optical ellipsometry to monitor the deposition of single atomic layers with subatomic sensitivity
We demonstrated the great potential of in situ ellipsometry for monitoring and studying thin film growth down to the scale of single atomic layers
Summary
Nanoscience and modern material physics are based on the growth and study of thin films with thicknesses spreading down to one atomic layer (monolayer, ML). To avoid light scattering an UHV setup is required, which has to be coupled to a synchrotron source to provide a well-collimated, monochromatic incident beam with very high intensity Optical probe techniques such as reflectance-difference spectroscopy (RDS), p-polarized reflectance spectroscopy and spectral ellipsometry (SE) [7, 8] are advantageous because of their noninvasive and nondestructive character, as well as due to their compatibility to non-vacuum chemical deposition methods. In situ ellipsometry was compared to RHEED, where a good agreement between these two monitoring techniques for an interrupted growth cycle and full u.c. of an STO thin film on an STO substrate was established In later publications, they developed a relatively complex mean-field theory to describe the optical response [12, 13]. The information obtained from in situ ellipsometry was verified by ex situ characterization of the crystal structure by means of transmission electron microscopy (TEM), x-ray diffraction (XRD) and reflection (XRR)
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