Development of Low Growth-Temperature, Non-toxic High Temperature Superconducting Thin Films

为了制备一种具有较低生长温度和足够性能的新型高温超导薄膜，本课题组采用脉冲激光沉积法制备了（Cu，C）Ba_2CuO_x[（Cu，C）-1201]超导薄膜，并实现了超导性。为了明确（Cu，C）-1201薄膜的生长温度下限和最高超导性能，研究了（Cu，C）-1201薄膜的本征晶体结构和电子结构，以及工艺参数与输运性质之间的关系。C）-1201薄膜在价带费米能级处产生有限的谱权，证明了样品表面的本征特征。随着样品电导率的增加，价带的主峰向费米能级的刚性带移动。这一转变与 ...更多信息 的Tc，这揭示了空穴掺杂诱导的超导电性的该系统。Ba 4d信号结合能在超导电性出现的早期出现大量负移，Cu 2 p信号随Tc的增加而出现大量正移，表明在超导电性出现的早期，Ba离子周围引入了过量氧。然后，它们应优先引入Cu离子周围。在结合能为2 eV附近观察到强的光谱权重，这是具有Cu-O链的铜酸盐超导体的特征。这一特征和芯信号随Tc的变化以及与无限层和其他铜酸盐超导体化合物的比较表明，该体系中的（Cu，C）-O电荷库处于重空穴掺杂状态，类似于YBa_2Cu_3O_<7-δ>中的Cu-O链。在500-600℃的低温下，在（100）SrTiO_3衬底上外延生长薄膜。结果表明，薄膜中CO 3含量随着薄膜生长过程中CO2分压的增加和生长速率的提高而增加。随着CO 3含量的增加，超导性能增强。本研究还揭示了在沉积过程中高能粒子的辐照严重恶化了（Cu，C）-Ba-O薄膜的结构和超导性能。抑制辐射损伤是实现高、均匀超导转变的另一关键。通过这些优化，实现了超导起始温度高于50 K，零电阻温度高于40 K，表明（Cu，C）-1201中的（Cu，C）-O与Ba-O夹层是一种有效的电荷储存体。在沉积过程中进行空穴掺杂并适当抑制辐照损伤是发展该系统超导性能的关键。利用所得的结论，工艺参数的窗口，如生长温度和气氛气体条件，变得宽和足够的重现Tc高于50 K，即使在500 〜 54℃生长的薄膜。这些结果意味着该项目的主要目的已经成功实现。少

In aim of creation of a novel high temperature thin film with a low growth temperature and sufficient performances for electronics applications, we have focused on (Cu, C)Ba_2CuO_x[ (Cu, C)-1201]superconducting films grown by pulsed laser deposition of which superconductivity is realized by our group. For clarifying the lower limit of the growth temperature and the highest superconducting properties of the (Cu, C) -1201 films, i)their intrinsic crystal- and electronic-structure and ii)relationships between process parameters and transport properties have been investigated.i)In-situ measurements of photoemission spectra of the superconducting (Cu, C) -1201 thin films yielded a finite spectral weight at the Fermi level in the valence band, which proofed the intrinsic feature of the sample surface. With an increase of conductivity of the samples, a rigid-band-like shift of the major peaks of the valence band toward the Fermi level was observed. This shift positively correlated with a rise … More of Tc, which reveals hole-doping-induced superconductivity of this system. The large amount of negative shift of binding energy of Ba 4d signal in the early stage of emergence of superconductivity, and positive shift of Cu 2p signals with an increase of Tc beyond 28 K suggest excess oxygen should be introduced around Ba ions in the early stage of the emergence of superconductivity. Then, they should be preferentially introduced around Cu ions. The strong spectral weight around binding energy of 2 eV, is observed, which is characteristic feature of the cuprate-superconductors with Cu-O chains. This feature and changes of core signals with Tc and comparisons of the obtained data with infinite-layer and other cuprate superconductor compounds suggest that the (Cu, C) -O charge reservoir in this system is in the heavily hole-doped state, similar to that of the Cu-O chain in YBa_2Cu_3O_<7-δ>.ii)In order to clarify the dominant parameters for carbon incorporation and the emergence of superconductivity, films were epitaxially grown on (100) SrTiO3 at a low growth temperature of 500-600℃. It has been revealed that the CO3 content in the films increases with increasing both CO2 partial pressure during film growth and growth rate. The rise of CO3 content resulted in an enhancement of superconducting properties. The present study has also revealed that the structural and superconducting properties of the (Cu, C) -Ba-O films are seriously deteriorated by the irradiation of energetic particles during deposition. Suppression of the radiation damage is another key for a high and uniform superconducting transition. By these optimizations, a superconducting onset temperature above 50 K and a zero-resistance temperature above 40 K have been realized.These results mean that the (Cu, C) -O sandwiched with Ba-O layers in (Cu, C) -1201 is an efficient charge reservoir block. Hole-doping during deposition with the proper suppression of irradiation dameges is a key to develop a superconducting properties in this system. By utilizing the obtained conclusions, the window of the process parameters such as growth temperature and atmosphere gas conditions, becomes wide and sufficient for reproduction of Tc above 50 K even in the films grown 500 〜 54℃. These results mean that the main purpose of this project is successfully accomplished. Less