The structure of rare earth thin films: holmium and gadolinium on yttrium

• Published in: Journal of physics. Condensed matter 2003-11, Vol.15 (43), p.7155-7174
• Main Authors: Bentall, M J, Cowley, R A, Ward, R C C, Wells, M R, Stunault, A
• Format: Article
• Language: English
• Subjects: Applied sciences; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Metals. Metallurgy; Physics; Structure and morphology; thickness; Structure of solids and liquids; crystallography; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology; X-ray diffraction and scattering; X-ray scattering (including small-angle scattering)
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/0953-8984/15/43/002

Single-crystal holmium and gadolinium layers have been grown on yttrium substrates using the molecular beam epitaxy technique and their structures investigated using high resolution x-ray scattering. The experiments were performed using a Philips MRD diffractometer in Oxford, and with the XMaS facility at the ESRF. Holmium layers with a thickness below T'c = 115 A give scattering that is characteristic of a pseudomorphic film structure with the same in-plane lattice parameter as the yttrium substrate to within 0.05%. For layers thicker than T'c, there is a sharp reduction in misfit strain due to the creation of edge dislocations. The transverse lineshape of the holmium peaks exhibits a two-component lineshape for thicknesses above T'c but below about 500 A. Above 500 A the lineshape of the transverse scans becomes Gaussian and is characteristic of a mosaic crystal. The gadolinium layers show no sharp change of strain for layers as thick as 2920 A and the transverse peak shape remained similar for all films. This is characteristic of pseudomorphic film growth and a failure to nucleate dislocations.