pubs.acs.org/crystal Published on Web 09/16/2010 r 2010 American Chemical Society DOI: 10.1021/cg1004006 2010, Vol. 10 4363–4369 X-ray Bragg-Surface Diffraction: A Tool to Study In-Plane Strain Anisotropy Due to Ion-Beam-Induced Epitaxial Crystallization in Fe þ -Implanted Si(001) Rossano Lang, †,‡ Alan S. de Menezes, § Adenilson O. dos Santos, §,# Shay Reboh, †,‡ Eliermes A. Meneses, § Livio Amaral, † and Lisandro P. Cardoso* ,§ † Programa de P os-Graduac - ~ ao em Ci^ encias dos Materiais (PGCIMAT ), Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, Rio Grande do Sul, Brazil, ‡ Instituto de Fı´sica, Universidade Federal do Rio Grande do Sul (UFRGS), 191501-970 Porto Alegre, Rio Grande do Sul, Brazil, § Instituto de Fı´sica Gleb Wataghin, Universidade Estadual de Campinas - UNICAMP, 13083-970 Campinas, S~ ao Paulo, Brazil, and # Centro de Ci^ encias Sociais, Sa  ude e Tecnologia (CCSST ), Universidade Federal do Maranh ~ ao, 65900-410 Imperatriz, Maranh ~ ao, Brazil Received March 25, 2010; Revised Manuscript Received August 9, 2010 ABSTRACT: In-plane strain anisotropy was clearly observed by the X-ray Bragg-surface diffraction technique in the silicon lattice surrounded by nanoparticles that were synthesized by an ion-beam-induced epitaxial recrystallization process of Fe-implanted amorphous Si layer. High resolution transmission electron microscopy images have shown the occurrence of metallic spherical and plate-like γ-FeSi 2 nanoparticles in the implanted/recrystallized region. These were found in different orientations within the sample, being responsible for the strain anisotropy detected. The striking anisotropy effect, due to mainly the plate-like nanoparticles in the recrystallized region, appears when comparing two (-6.04° and 83.96°) (002) rocking curves at Bragg-surface diffraction exact condition. Furthermore, the mappings of the (111) Bragg-surface diffraction reflections show an evident anisotropy between φ = -6.04° and 83.96° mappings and also a marked broadening of the implanted sample profile as compared to that of the Si (matrix). Reciprocal space maps obtained for both perpendicular directions clearly exhibit this anisotropic effect in the q x direction, thus confirming the Bragg-surface diffraction results. I. Introduction Metal nanocrystal memory devices employing discrete charge traps as storage elements have attracted considerable research attention as promising candidates to replace conven- tional dynamic random access memory (DRAM) or flash memories. 1 The advantages of metal nanocrystals (NCs) over their semiconductor counterparts (e.g., Si, Ge, or SiGe NCs) 2-5 include smaller energy perturbation caused by carrier confine- ment, higher density of states, better size scalability, and design freedom of the work-function engineering to optimize device characteristics. 6 In this context, transition-metal silicide are of significant interest, in particular FeSi 2 , as a potential material for this application due to its high density of d states at the Fermi level. 7 The iron disilicide binary compound presents two distinct metallic crystalline phases: a cubic fluorite γ-FeSi 2 phase of high symmetry, with a lattice parameter similar to that of Si (a ≈ 5.431 A ˚ ), 8,9 and a tetragonal R-FeSi 2 phase, with a = b = 2.690 A ˚ and c = 5.134 A ˚ . 10,11 The valence band density of states of the R-FeSi 2 phase is slightly different from that of the γ-FeSi 2 . 12 It has been recognized that not only lattice defects but also lattice stress/strain (thermal expansion coefficient) near NCs interfaces are factors that crucially influence the device per- formance. Furthermore, the shape and dimensions of the materials also affect the lattice strain distribution. 13 On the other hand, improving nonvolatile memories technology has led to element sizes of the subnano order, which has required the establishment of high spatial resolution analytical techniques to evaluate lattice strain distributions quantita- tively at the nanometric scale. Lattice strain is usually mea- sured by conventional X-ray diffraction and micro-Raman scattering spectroscopy techniques. 14,15 However, their spatial resolution is insufficient to meet this recent demand. A very useful, high resolution, and versatile technique has been developed and successfully applied as a three-dimensional (3D) probe to study single crystals in general, and with very interesting contributions to the semiconductor epitaxial systems - the X-ray multiple diffraction (XRMD) technique. 16 It is a powerful tool based on the simultaneous diffraction of an incident X-ray beam by different crystallographic planes of a single crystal. As these planes are parallel (primary) and inclined (secondary) with respect to the crystal surface, XRMD provides 3D information on the analyzed crystalline lattice, given that different beam orientations at different depths within the crystal are simultaneously observed. It has already been applied to study dislocations at the interface plane of a GaAs layer on top of a Si substrate, 17 as well as lattice coherence in InGaP/GaAs(001) with the detection of very small changes (<0.1 A ˚ ) in the interface distance. 18 Also, since the lattice symmetry plays a fundamental role in XRMD, the technique has enough sensitivity for detecting subtle distortions in the lattice through any symmetry change. Significant contributions to the piezoelectric phenomenon have been shown by this technique when using it as a novel method to determine the piezoelectric coefficients of crystals based on symmetry change due to electric field applica- tion. 19,20 This method has been shown to be very versatile since just by using three single crystals adequately cut into the desired crystallographic directions one is able to determine all eight Rochelle salt piezoelectric coefficients. 21 *To whom correspondence should be addressed. E-mail: cardoso@ifi. unicamp.br.