of rgey ov c AS, M olid S echno film puls pressure of 0.3 mbar and temperatures higher than 700 �C. X-ray diffraction reveals that films on (1 1 0)NdGaO3 substrates are single crystals of high quality without twinning and with extremely narrow (less then 0.05�) rocking curves. An expansion of the c-axis lattice constant is observed as Sr replaces Ca in CCO films. Transport measurements Epitaxial CaCuO2 films were grown by laser ablation on substrates of (1 1 0)NdGaO3 (NGO), (0 0 1)SrTiO3 and NdGaO3 substrates. Only (0 0 n)CaCuO2 reflec- tions, corresponding to c-axis oriented tetragonal films, are seen in those as well in YBa2Cu3Ox/CaCuO2/ epitaxial film but one order of magnitude larger than for the one of the (1 1 0)NdGaO3 substrate (0.006�), see Fig. perature dependence (down to 77 K) of the film resis- tivity is shown in Fig. 3. As the FWHMwas reduced, the resistivity changed from 104 to 10�1 X cm. The temper- ature dependence follows a hopping type conductivity for all measured samples: 1=4 (2004 * Corresponding author. (STO), (0 0 1)LaAlO3 (LAO), and buffer layer CeO2 fabricated on r-plane sapphire. The films were deposited by pulsed laser ablation from a single stoichiometric target at a pressure of 0.3 mbar and temperatures higher than 730 �C [2]. Films with thickness 100–200 nm were grown. Crystallographic and transport properties of the films were investigated. X-ray diffraction data, h–2h scans (Fig. 1), show the crystallographic quality of the film deposited on LaAlO3 2. Note that FWHM¼ 0.2� for a typical YBa2Cu3Ox epitaxial film. The lattice constants were determined to a ¼ b ¼ 0:3855 nm, c ¼ 0:318 nm. The c-axis lattice parameter increased to c ¼ 0:323 nm when 15% of Sr replaced Ca in CaCuO2. We observed no (0 0 n) CaCuO2 peaks for the film grown on CeO2/Al2O3 indicating a chemical interaction between CaCuO2 and CeO2. Good correlation of the in plane current transport with crystallographic quality was observed. The tem- show that CCO films have a hopping conductivity for all films deposited on all the substrates with a resistivity within the range 10�1–104 X cm. � 2004 Elsevier B.V. All rights reserved. Keywords: Epitaxial thin films; Laser ablation; Rocking curve; Resistivity The growth of the critical temperature of a cuprate superconductor with the number of CuO2� , layers makes materials with an infinite number of cuprate layers, like CaCuO2, interesting [1]. NdGaO3 heterostructures. Reflection amplitudes are close to those of the substrates except for CaCuO2/La- AlO3. The FWHM of the rocking curve around the (0 0 1)CaCuO2 peak is extremely small (0.05�) for the The growth and conductivity Gennady A. Ovsyannikov a,c,*, Se Zdravko G. Ivan a Institute of Radio Engineering and Electronics R b Physics RAS, Russian Institute of S c Chalmers University of T Abstract Growth, structure and conductivity of epitaxial thin substrates were investigated. The films were deposited by Physica C 408–410 E-mail address:
[email protected] (G.A. Ovsyannikov). 0921-4534/$ - see front matter � 2004 Elsevier B.V. All rights reserv doi:10.1016/j.physc.2004.03.050 CaCuO2 epitaxial thin films A. Denisuk a, Igor K. Bdikin b, , Tord Claeson c okhovaya 11 Building 7, Moscow 125009, Russia tate, Chernogolovka, Moscow, Russia logy, Gothenburg, Sweden s of CaCuO2 (CCO) on SrTiO3, LaAlO3 and NdGaO3 ed laser ablation from a single stoichiometric target at a www.elsevier.com/locate/physc ) 616–617 lnðrÞ ¼ lnðr0Þ þ ðT0=T Þ ð1Þ ed. 0.24 0.26 0.28 0.30 0.32 0.34 100 101 102 103 104 105 106 r, Ω cm 110N13C N3CCO S4CCO L1CCO T-1/4 , K-1/4 Fig. 3. Temperature dependences of the resistance of CaCuO2, films deposited on three types of substrates. The lines connected experimental data corresponds to dependence (1). -0.5 0.0 0.5 CCO NGO YBCO DQ (o) Fig. 2. Rocking curves for YBa2Cu3Ox/CaCuO2/NdGaO3 heterosructures namely (0 0 5)YBa2Cu3Ox, (0 0 1)CaCuO2 and (2 2 0)NdGaO3 reflections (peak amplitudes are normalized). 20 40 60 80 100 120 00 13 Y 00 12 Y 00 11 Y 00 10 Y 00 8 Y 00 9 Y0 07 Y 00 4 Y 00 5 Y 00 2 Y 20 0 C 10 0 C 44 0 N 33 0 N 22 0 N + 00 6 Y 11 0 N + 00 3 Y 40 0 S 10 0 C 20 0 S 10 0 S 20 0 C 30 0 C 20 0 C 10 0 C 40 0 L 30 0 L20 0 L 10 0 L Y/CCO/NGO CCO/STO CCO/LAO In te ns ity (a rb. u n its ) 2Q (o) Fig. 1. h–2h X-ray scans for CaCuO2 films deposited on La- AlO3, SrTiO3 and NdGaO3 substrates. G.A. Ovsyannikov et al. / Physica C 408–410 (2004) 616–617 617 [1] T. Siegrist, S.M. Zahurak, D.W. Murphy, R.S. Roth, Nature 334 (1988) 231. [2] D.P. Norton, B.C. Chakomokos, J.D. Budai, D.H. Lown- des, Appl. Phys. Lett. 62 (1993) 1679. RFBR, INTAS 01-0249 are acknowledged. References This is not surprising since hopping should be observed for q > 3� 10�3 X cm when kFl < 1 (l is the mean free path, kF is the Fermi wave vector) [3]. Acknowledgements [3] N.F. Mott, E.A. Davis, Electronic Processes in Non Crystalline Materials, second ed., Clarendon, Oxford, 1979. The growth and conductivity of CaCuO2 epitaxial thin films Acknowledgements References