Please cite this article in press as: R. Sobota, et al., Surface properties of Co-doped BaFe 2 As 2 thin films deposited on MgO with Fe buffer layer and CaF 2 substrates, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.03.094 ARTICLE IN PRESS G Model APSUSC-27495; No. of Pages 6 Applied Surface Science xxx (2014) xxx–xxx Contents lists available at ScienceDirect Applied Surface Science jou rn al h om ep age: www.elsevier.com/locate/apsusc Surface properties of Co-doped BaFe 2 As 2 thin films deposited on MgO with Fe buffer layer and CaF 2 substrates R. Sobota a , T. Plecenik a,∗ , M. Gregor a , M. Truchly a , L. Satrapinskyy a , M. Vidis a , K. Secianska a , F. Kurth b , B. Holzapfel b , K. Iida b , P. Kus a , A. Plecenik a a Department of Experimental Physics, FMPI, Comenius University, 842 48 Bratislava, Slovakia b Institute for Metallic Materials, IFW Dresden, PO Box 270116, D-01171 Dresden, Germany a r t i c l e i n f o Article history: Received 30 January 2014 Received in revised form 13 March 2014 Accepted 14 March 2014 Available online xxx Keywords: Iron based superconductors Ba-122 Surface properties Substrate a b s t r a c t Surface properties of Co-doped BaFe 2 As 2 (Ba-122) thin films prepared by pulsed laser deposition on MgO with Fe buffer layer and CaF 2 substrates were inspected by atomic force microscopy, scanning spreading resistance microscopy, scanning tunneling microscopy, X-ray photoelectron spectroscopy, auger elec- tron spectroscopy/microscopy and point contact spectroscopy (PCS). Selected PCS spectra were fitted by extended 1D BTK model. The measurements were done on as-received as well as ion beam etched surfaces. Our results show that the substrate is considerably influencing the surface properties of the films, particularly the topography and surface conductivity distribution, what can affect results obtained by surface-sensitive techniques like PCS. © 2014 Elsevier B.V. All rights reserved. Since the discovery of the iron-based superconductors (FBS), a great effort has been made to understand their intrinsic prop- erties, such as width of the energy gap, the pairing symmetry etc. and explore possible novel superconducting electronic devices [1–5]. Many groups have prepared FBS thin films of so called “122” family, which is mainly Co-doped BaFe 2 As 2 (Ba-122) due to its readily fabrication. Thin films of this material class have been epi- taxially grown by pulsed laser deposition (PLD) on various bare substrates [6–8]. In Refs. [9–11], it was shown that (La,Sr)(Al,Ta)O 3 , MgO and fluoride substrates lead to sharp biaxial texture and hence good in-field transport properties. Additionally it was also pro- posed to employ buffer layers such as SrTiO 3 , BaTiO 3 and Fe, which also yields epitaxial growth of Co-doped Ba-122 with good crys- talline quality [12–14]. However, the Fe buffer layer appeared to have some disadvantages such as shunting of the current in the normal state [15]. Influence of the Fe buffer layer on Josephson junctions has also been already studied in Ref. [16]. Up to now, the best superconducting parameters (e.g. critical temperature, upper critical field and critical current) were obtained on films prepared on CaF 2 substrates [11]. However, for many applications and mea- surement techniques the condition of the surface or interface is at least as important as the bulk intrinsic properties of the film. It ∗ Corresponding author. Tel.: +421 260295517; fax: +421 2 654 12 305. E-mail address: tomas.plecenik@fmph.uniba.sk (T. Plecenik). has been shown that the surface of Ba-122 is unstable on ambi- ent air and degrades by oxidation of Ba and Fe [17]. This fact leads to undefined surfaces or interfaces in samples which have been exposed to air and might result in difficulties in device fabrication as well as varying experimental results obtained by surface sensi- tive analytical techniques. For example, point contact spectroscopy (PCS) results [5,18,19] as well as differential conductivity measure- ments on other types of junctions [20] vary from each other and are being interpreted in both one gap and two gap models with vary- ing value of energy gaps. Applications of the FBS in cryoelectronic devices, especially SQUIDs and Josephson junctions also turned to be problematic, quite likely for the same reason (although short coherence length is also problematic). Understanding the surface properties of these materials is thus crucial for both basic research and possible applications. In this work, we have focused on surface properties of Co-doped Ba-122 prepared on (i) MgO substrate with Fe buffer layer and (ii) CaF 2 substrate. In both cases, as-received as well as ion beam etched (IBE) surfaces were studied by atomic force microscopy (AFM), scanning spreading resistance microscopy (SSRM), scanning tunneling microscopy (STM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Auger electron spec- troscopy/microscopy (AES/AEM) and point-contact spectroscopy (PCS). Our results show that the substrate considerably influences the surface properties of the films, particularly the topography and surface conductivity distribution, what can also affect the PCS spec- tra obtained on such surfaces. http://dx.doi.org/10.1016/j.apsusc.2014.03.094 0169-4332/© 2014 Elsevier B.V. All rights reserved.