Pulsed laser deposition synthesis of superconducting (Cu, C)Ba 2 CuO x thin films K. Kikunaga a, * , T. Yamamoto b , Y. Tanaka c , N. Kikuchi c , K. Tokiwa d , T. Watanabe d , N. Terada b,c a National Institute of Advanced Industrial Science and Technology, Tosu 841-0052, Japan b Kagoshima University, Kagoshima 890-0065, Japan c National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8562, Japan d Tokyo University of Science, Noda 278-8510, Japan article info Article history: Received 4 June 2009 Received in revised form 13 April 2010 Accepted 6 July 2010 Available online 10 August 2010 Keywords: High temperature superconductor Thin film PLD (Cu, C)-system 1201 phase Low temperature growth abstract (Cu, C)–Ba–O thin films have been deposited at low growth temperature of 450–570 °C by pulsed laser deposition method. A control of CO 2 gas pressure and the growth temperature, usage of BaCu y O x pellet target resulted in an expansion of twice c-axis length of BaCuO 2 structure (2c phase) and a significant rise of conductivity. Measurements of in-situ XPS suggest that the 2c phase should be (Cu, C)Ba 2 CuO x [(Cu, C)- 1201]. The maximum temperature of onset of the superconducting transition and zero resistance state obtained so far were 60 and 47 K, respectively. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction A crystal structure in high temperature superconducting cup- rates (HTS) is constructed by an alternate stacking of charge reser- voir layer (CRL) and infinite layer (IL), the number of CuO 2 planes (n) in IL is depend on critical temperature T c . The superconductors included in a CuO 2 plane (n = 1) show lower T c than that included in some CuO 2 planes (n > 1) [1]. Then, the number of CuO 2 planes of almost HTS with T c > 60 K is over two. Multi-layered HTSs, such as MBa 2 Ca n1 Cu n O y (M = Hg, Tl, (Cu, C), (Cu, Tl), (Cu, V)) [M-12(n1)n] include two or more crystallographically inequivalent CuO 2 planes in a unit cell. They have the potentials of less-anisotropic proper- ties and high critical temperature T c above 100 K, and unique prop- erties [1–3]. In the highest T c multi-layered Hg-system, Hg-1201 (n = 1) has also higher T c among HTSs included in a CuO 2 plane [4,5]. Therefore, M-1201 superconductors with T c > 60 K have high potentials. (Cu, C)Ba 2 Ca n1 Cu n O x [(Cu, C)-12(n1)n] are one of promising HTS, because of the non-toxic elements and their potential for high critical temperature T c above 100 K and low anisotropy, a possibil- ity of multi-component superconductivity in multi-layered HTS with a proper interband coupling [1–3,6–23]. For pursuing these potentials of the Cu- and (Cu, C)-systems, (Cu, C)Ba 2 Ca 0 CuO x [(Cu, C)-1201] (n = 1), which is a fundamental and simplest structure of (Cu, C)-system, should be fabricated. Then it is important to con- trol a little CO 2 pressure, because these materials sensitive to the carbonate. In this study, we have studied deposition of (Cu, C)- 1201 thin films by pulsed laser deposition (PLD). Characterization of their transport properties has been investigated. Crystal struc- ture of specimen grown in little CO 2 mixed atmosphere was Ba- CuO 2 infinite layered structure. The c-axis length with increases of CO 2 mixed atmosphere was expanded to twice as long as that of BaCuO 2 , that was (Cu, C)-1201 structures. The (Cu, C)-1201 films deposited at 500 °C using BaCu 0.75 O x target showed superconduc- ting transport, T c = 60–47 K [14–17]. 2. Experiment Specimen films were grown on (1 0 0) plane of SrTiO 3 at temper- atures in the range of 450–530 °C by pulsed laser deposition using KrF excimer laser. The used targets were highly dense pellet of BaCu y O x (y = 1.0, 0.75, 0.5). The growth conditions were in the following range: reactive pressure = O 2 (3–10 mTorr) + CO 2 (0.01– 0.25 mTorr) + Ar (0–80 mTorr); laser power of shot and repetition frequency were in the range of 100–200 mJ/pulse and 0.5–2.0 Hz, respectively. In order to maintain residual gas level of growth chamber constant, we utilized a load–lock system. After the depo- sition, the films were cooled at room temperature in an oxygen atmosphere, and protection layers were deposited on the specimen before air exposure. Crystal structure of the films was characterized 0921-4534/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2010.07.002 * Corresponding author at: National Institute of Advanced Industrial Science and Technology, Tosu 841-0052, Japan. E-mail address: k-kikunaga@aist.go.jp (K. Kikunaga). Physica C 470 (2010) 1916–1919 Contents lists available at ScienceDirect Physica C journal homepage: www.elsevier.com/locate/physc