激光沉积高温超导薄膜的研究

Laser Deposition of High Tc Superconducting Thin Films

本文利用激光剥离超导靶材的技术,在相当低的基片温度下,原位生长出了零电阻温度90K左右、C-轴取向择优生长的Y-Ba-Cu-O超导薄膜;给出了激光剥离材料的新模型;推导了激光剥离材料的功率密度阈值、剥离层厚度和被剥离而喷射出来的粒子所受到的反冲压的数学表达式.

Superconducting Y-Ba Cu-O thin films on zirconia substrates have been deposited in situ using XeCl laser (wavelength of 308 nm, pulse duration of 28 ns) ablation of a target of superconducting oxide ceramies under the conditions of substrate temperature below 600℃, oxygen ambient about 30 Pa and laser fluence of 5J/cm2. The films exhibit zero resistance around a temperature of 90 K, with a critical current density greater than 105A/cm2 at 77 K. The crystal structure revealed by X-ray diffraction spectra is a C-axis orientation normal to the surface. A new model is presented for explaining two features, that is, the films deposited have almost the same composition as that of the target and the particles from laser ablation of target are ejected in the direction of the target normal. According to this model, the expressions for the threshold of laser flux density It for laser ablation of material, IT=PEx/(br) ,for the depth Z of ablation layer per laser shot, z= In (Iv/It) IB, and for the recoil pressure p of the target on ejecting particles, p=Io v/u(Es +v2/2), have been derived.