Crystallinity of a-axis oriented YBa2Cu3O7−δ thin film epitaxially grown on NdGaO3 (110) by 95 MHz magnetron sputtering

Abstract

An a-axis oriented 400 Å YBa2Cu3O7−δ film has been epitaxially deposited on a NdGaO3 (110) substrate by rf magnetron sputtering using a single YBa2Cu5Ox target. An excitation frequency of 94.92 MHz, seven times as high as the conventionally used 13.56 MHz, results in a lower self-bias voltage which reduces degradation of films caused by resputtering due to negatively charged oxygen. Sharp streaks corresponding to the c-axis lattice parameter of YBa2Cu3O7−δ have been observed by reflection high-energy electron diffraction, showing that the c-axis is parallel to the surface of the NdGaO3 substrate and the film surface is smooth on an atomic scale. The crystallinity has been characterized by Rutherford backscattering channeling analysis. A minimum yield, χmin of 3.2%, has confirmed excellent crystallinity of the a-axis oriented film.

Liquid phase epitaxy (LPE) growth of high-temperature superconducting films

“…According to the above results it was implied that at the initial period of LPE growth of the c-dominated film, a-axis YBCO grains nucleated prior to c-axis grains, which is similar to the a-axis oriented preference in VPE growth of thin films. 23,24 But subsequently, c-phase growth occupied most volume and promptly exceeded, which led to a complete covering of a-phase growth after only several seconds, with the absence of protruding a-axis grains.…”

“…Moreover, the [100] axis of MgO substrate is parallel to the 7. 24 The optical micrograph of as-grown 45°-oriented YBCO-LPE film, in which the 45°-oriented growth hillocks are distinct.…”

Growth mechanism of YBa2Cu3O7–δthin films and precipitates on planar and vicinal SrTiO3substrates

“…25 The YBCO (200) peak intensity increased with temperature up to 750°C and decreased as the temperature increased further to 850°C. 26,35,38 For the Y0S films grown at 700 and 750°C, the YBCO (200) and (005) peaks were narrow and intensified, indicating that both a-axis-and c-axis-oriented YBCO structures were equally distributed. The a-axis oriented YBCO films have been fabricated at ∼750°C to obtain highquality films, and the quality of a-axis-oriented films degraded due to increase of the c-axis orientation with the increase of the growth temperature.…”

“…20,21 The chemical compositions of precipitates have been reported as Y-rich or Cu-rich phases, 6,7,10,22 while a similar composition as the YBCO film matrix has been frequently observed for island-shaped precipitates. 25,26 Since the shape and growth of precipitates was strongly related to the growth of the film matrix, especially from the very early growth stage, there might be a relationship between the film and precipitate growth mechanism. 24 The a-axis YBCO films grown at low temperatures (<700°C) resulted in smooth film surfaces without precipitates.…”

Structural strain ina-axis oriented thin films studied by electron backscatter diffraction

“…Epitaxial thin films of YBa 2 Cu 3 O 7−δ (YBCO) with a welldefined a-axis orientation are of great interest for the study of anisotropy of YBCO and the applications to electronic devices [1][2][3]. The simplest way to make a-axis oriented YBCO films is to lower the deposition temperature by about 100 • C from that used to grow c-axis films [4,5]. The transition temperature (T c ) of the films made in such a way is significantly lower than that of c-axis films.…”