Diversity in plasma arrival sequence correlated to oxygen deficiencies of oxide thin films grown by PLD

Abstract

Oxide thin films grown in vacuum by pulsed laser deposition (PLD) are usually oxygen deficient, due to the well-known reasons such as preferential plasma scatterings or resputtering. The present work demonstrates another possibility that results in oxygen deficiencies associated to the much earlier arrival of O⁺ as compared to other cation ions. The earlier arrived O⁺ cannot be independently deposited as solid without other cation constituents. In particular, this effect is pronounced when performing PLD using a 248 nm laser, with a large proportion of O⁺ generated via a 3-photon ionization process during the initial laser solid interactions.

摘要

利用脉冲激光沉积法在真空条件下生长的氧化物薄膜通常存在氧元素缺失现象. 在以往研究中, 上述氧元素缺失的原因被归结于等离子体中较轻的氧离子更易被散射或薄膜中的氧元素更易被高能量等离子体再溅射等. 本文提出了真空下脉冲激光沉积氧化物薄膜中造成氧元素缺失的另一个可能原因: 由于等离子体中O⁺离子到达衬底的时间早于金属离子, 较早到达的氧元 素不能单独在衬底上以固体形式沉积, 从而造成薄膜氧元素的缺失. 当使用波长为248 nm的脉冲激光时, O⁺离子通过三光子过程大量产生, 证实了上述原因.