Structure and morphology of surface of silicon crystals to be applied for channeling at relativistic energies Alberto Vomiero a, * , Silvio Restello a , Carlo Scian a , Enrico Boscolo Marchi a , Gianantonio Della Mea a,b , Vincenzo Guidi c , Emiliano Milan c , Stefano Baricordi c , Giuliano Martinelli c , Alberto Carnera d , Andrea Sambo d a INFN – Laboratori Nazionali di Legnaro, Viale Universita` 2, I-35020 Legnaro (PD), Italy b Dipartimento di Ingegneria dei Materiali e Tecnologie Industriali, Via Mesiano 77, I-38050 Trento, Italy c Dipartimento di Fisica – INFN e INFM, Universita` di Ferrara, Via Saragat 1, I-44100 Ferrara, Italy d Dipartimento di Fisica e INFM, Universita` di Padova, Via Marzolo 8, I-35131 Padova, Italy Available online 22 May 2006 Abstract Bent crystals can be successfully applied for extraction/collimation of relativistic particles. A crucial feature to obtain high extraction efficiencies is the treatment of the surfaces being encountered by the beam, since mechanical operations induce considerable lattice imper- fections. In order to remove the superficial damaged layer a planar etching can be applied on the surface exposed to the beam. This work presents a systematic study of the morphology and the crystalline perfection of the surface of the samples that have been used in accelerators with high efficiency. Crystals with different surface treatments have been investigated. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were applied on the characterisation of surface morphology. Low energy backscattering channeling of 2-MeV a particles or protons was used as a probe for the crystalline structure. The presence of a superficial damaged layer in the samples just after mechanical treatment was unveiled, while, in contrast, chemical etching leaves a surface with high crystalline perfection that can be related to the record efficiency. Ó 2006 Elsevier B.V. All rights reserved. PACS: 61.85.+p; 81.65.Ps Keywords: Channeling; Surface treatments 1. Introduction Bent crystals can be successfully applied for extraction/ collimation of relativistic particles [1–3]. High-energy beams can be channeled into bent crystalline lattices that act as highly efficient beam deflectors. Bent crystals can be produced in several ways, and many configurations have been tested in order to optimize crystal design [4–6]. Recent results on extraction efficiency [5,7] pointed out the great importance of the treatment of the surfaces being encountered by the beam, since mechanical operations induce considerable lattice imperfections, and the first por- tion of the crystal lattice has a disorder degree that can exceed the critical angle for channeling. In order to remove the superficial damaged layer and obtain a crystal with high structural perfection, a planar etching can be applied on the surface exposed to the beam. It has been demonstrated that significant improvement in the features of the samples for channeling can be achieved once a specific etching treat- ment is imparted to the crystal surface [5]. Chemically etched crystals allowed record performances in terms of channeling efficiencies. This work presents a systematic study of the morphol- ogy and the crystalline perfection of surface of the samples 0168-583X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2006.03.160 * Corresponding author. Tel.: +39 0498068406; fax: +39 049641925. E-mail address: vomiero@lnl.infn.it (A. Vomiero). www.elsevier.com/locate/nimb Nuclear Instruments and Methods in Physics Research B 249 (2006) 903–906 NIM B Beam Interactions with Materials & Atoms