Formation of Inorganic Thin Films by Laser Ablative Cluster Emission

研究表明，激光辐照无机物表面，如含铜氧化物超导体，可导致离子、原子和团簇的发射。这个过程取决于激光的影响。通过利用该激光烧蚀工艺，在氧气氛中在基板上形成无机薄膜。在1989年，我们已经证明了从Bi_2Sr_2CaCu_2O_8和Bi_2Sr_2CuO_6表面发射的团簇，并且这些相是通过团簇形成过程形成的。我们已经开发了这个过程来将目标分解成更小的碎片，即离子和原子。这些离子和原子积聚在衬底上。在烧蚀Bi_2Sr_2CuO_6的情况下，观察到Bi，Sr和Cu的原子物种。Bi_2Sr_2CuO_6薄膜的形成是在各种氧化气体中进行的。结果表明，NO_2>N_2O>O_2对氧化过程的影响顺序为NO_2>N_2O>O_2。在NO_2气氛中，即使在10 μ mol/L的低压<-4>下也能有效地使薄膜晶化。在N_2O气氛中，Bi_2Sr_2CuO_6相的晶化温度比在O_2气氛中低50 ~ 100 ℃。这是由激光照射形成的O自由基的强氧化能力解释的。在N_2O和O_2的混合气体中，氧被充分地引入到薄膜中。在O_2气氛中，杂质CuO偏聚在表面，形成粗糙表面.在薄膜形成期间照射激光对于低温薄膜形成是有效的。即使是10 mJ/cm ^2量级的低强度光也足够有效。因此，激光烧蚀法是制备无机薄膜的有效方法，选择合适的气氛（如NO_2和N_2O）在较低的温度下成膜是很重要的。

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.