Materials Science and Engineering B 151 (2008) 47–52 Contents lists available at ScienceDirect Materials Science and Engineering B journal homepage: www.elsevier.com/locate/mseb Investigation of melt-textured superconductors on the nanoscale M.R. Koblischka a,∗ , A. Koblischka-Veneva b a Institute of Experimental Physics, Saarland University, P.O. Box 151150, D-66041 Saarbr¨ ucken, Germany b Institute of Functional Materials, Saarland University, P.O. Box 151150, D-66041 Saarbr¨ ucken, Germany article info Article history: Received 31 October 2007 Accepted 5 February 2008 Keywords: Melt-textured superconductors Nanostructure SPM EBSD abstract For the further development of the bulk, melt-processed high-T c superconductors it is an essential issue to control the material properties on the nanoscale, as the length scale where flux pinning takes place is of the order of 10 nm. As a consequence, we need to investigate the properties of the samples accordingly on the nanoscale. Therefore, we have performed atomic force microscopy (AFM) and scanning tunnelling microscopy (STM) scans of sample surfaces at ambient conditions which have resolved a rich variety of microstructures in the bulk samples. With the recent developments, also the (electron backscatter diffraction) EBSD technique reaches the nanometre range enabling to study the crystallographic details, especially the effect of embedded nanoparticles on the superconducting matrix. In order to obtain a direct proof of the pinning effect, the output of low-temperature STM revealing the electronic nature of the samples is studied as well. Further developments of the STM technique, e.g., employing ferromagnetic tips, may further bring informations on the flux pinning properties. © 2008 Elsevier B.V. All rights reserved. 1. Introduction The development of bulk high-T c materials is hampered by the need to control the material properties on a nanometre scale due to the size of the coherence length. The small coherence length  of the high-T c superconductors makes the vortex core a true nano-sized object; typical values at T = 0 K are ranging between 2.2 (Bi-2212) and 6 nm (YBCO). As a consequence, not only the flux pinning takes place on the nanoscale, but also the materials optimization must be carried out on a similar or slightly larger length size. Due to this, the further optimization of the flux pinning forces and, hence, the critical current densities requires detailed measurements on an according length scale. To make the situation worse, the ceramic nature of the high-T c superconductors leads to spatial variations of the superconducting properties, which cannot be avoided in the processing [1–3]. However, we may find adapted processing strate- gies which enable these inhomogeneities to be used for beneficiary effects like enhanced flux pinning. The most prominent pinning centre in melt-textured high-T c superconductors is the insulating Y 2 BaCuO 5 (2 1 1) particle, being created during the growth of YBCO and providing flux pinning of the l-pinning type. Furthermore, nanoscale particles may be added to the precursor powders prior to the heat treatment; many attempts using nanoparticles of Al 2 O 3 [4], MgO [5],Y 2 Ba 4 CuMO y with M=U, Nb, Ag, Zr, etc. [6] and even carbon nanotubes [7] are described in the literature. ∗ Corresponding author. Tel.: +49 681 302 4555; fax: +49 681 302 3790. E-mail address: m.koblischka@mx.uni-saarland.de (M.R. Koblischka). In order to review the various measurements performed on the nanoscale of melt-textured bulks, we present here several experi- mental achievements in this field. 2. Experimental procedure As experimental tools, we employ various scanning probe (SPM) techniques as well as the electron backscatter diffraction (EBSD) technique working within a scanning electron microscope environ- ment. The melt-textured (LRE)BCO [(LRE) = light rare earths) samples were produced using the standard procedure [8]. The sample sur- faces were subsequently dry polished using either 3 M polishing papers as described in [9], using ethanol for cleaning purposes. Otherwise, the surfaces were polished using diamond paste and a final step using colloidal silica (OP-S) with a grain size of 40 nm. This procedure yields high quality surfaces, enabling atomic force microscopy (AFM), scanning tunnelling microscopy (STM) and also EBSD measurements to be performed. Magneto-optic investiga- tions on such samples confirmed that the superconductivity is fully retained after the polishing [10]. AFM and STM topographic scans in ambient conditions were performed using Nanoscope III and IV controllers [11,12]. To enable a comparison, AFM scans were performed in contact mode and tap- ping mode using micro-machined, doped Si cantilevers (Nanoworld Services GmbH, Erlangen, Germany). A Q-control unit was used to improve the signal-to-noise ratio in tapping mode. STM was per- formed employing cut Pt/Ir-tips. The use of both AFM and STM allows one to exclude artefacts due to the tips [13]. 0921-5107/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2008.02.011