Formation of Inorganic Thin Films by Laser Ablative Cluster Emission

研究表明，激光照射含铜氧化物超导体等无机物表面会导致离子、原子和团簇的发射。这一过程依赖于激光的影响。利用这种激光烧蚀工艺，在氧气气氛中在衬底上形成了无机薄膜。在中，我们已经证明了从Bi2Sr2CaCu2O8和Bi2Sr2CuO6表面发射出团簇，这些相是通过这种团簇形成过程形成的。我们开发了这一过程，将目标分解成更小的碎片，即离子和原子。这些离子和原子聚集在衬底上。在Bi2Sr2CuO6烧蚀的情况下，观察到了铋、锶和铜的原子物种。Bi2Sr2CuO6薄膜的形成是在各种氧化气体中进行的。结果表明，NO_2&GT；N_2O&GT；O_2对氧化过程的影响顺序为：NO2&GT；N_2O&GT；O_2。在NO2气氛中，即使在10^~(-4)~(-4)TORR的低气压下也能有效地晶化薄膜。在N2O气氛中，Bi2Sr2CuO6相在比O2气氛中低50~100℃的温度下结晶。这是由于激光照射形成的氧自由基具有很强的氧化能力。在N_2O和O_2混合气体中，薄膜中的氧被充分吸收。仅在O_2气氛中，杂质CuO被分离到表面，形成粗糙的表面。薄膜形成过程中的激光照射对低温薄膜的形成是有效的。即使是10mJ/cm^2量级的低强度光也足够有效。因此，激光烧蚀方法对于无机薄膜的形成是有效的，而且选择NO2和N2O等气氛在较低的温度下形成薄膜也是很重要的。

It has been revealed that the laser irradiation of the surface of inorganic substances, such as copper containing oxide superconductor, leads to the emission of ions, atoms and clusters. This process is dependent on the laser influence. By utilizing this laser ablation process, inorganic thin films are formed on substrates in the oxygen atmosphere. In 1989, we have demonstrated that clusters are emitted from the Bi_2Sr_2CaCu_2O_8 and Bi_2Sr_2CuO_6 surface, and these phases are formed using this cluster formation process. We have developed this process to decompose the targets into smaller pieces, that is ions and atoms. These ions and atoms are accumulated on the substrates. In the case of Bi_2Sr_2CuO_6 ablation, atomic species of Bi, Sr and Cu are observed. The thin film formation of Bi_2Sr_2CuO_6 is carried out in the various oxidation gases. As a result, it has been revealed that NO_2>N_2O>O_2 are effective in this order for the oxidation process. In the NO_2 atmosphere, even the low pressure of 10^<-4> torr is effective to crystallize the thin films. In the N_2O atmosphere, the Bi_2Sr_2CuO_6 phase is crystallized at 50 to 100C lower temperature than in the O_2 gas. This is explained by the strong oxidation power of O radical formed by the laser irradiation. In the mixed N_2O and O_2 gas, the oxygen is incorporated enough in the films. In the O_2 atmosphere alone, the impurity CuO is segregated an the surface to make a rough surface. The irradiation of laser light during the thin film formation is effective for the low temperature thin film formation. Even the low intensity light of the order of 10mJ/cm^2 is effective enough. Thus, the laser ablation method is effective for the formation of inorganic thin films and also it is important to choose the atmosphere, such as NO_2 and N_2O, to form thin films at lower temperature.