碱土金属锡酸盐杂化分子束外延中前驱体的选择
Precursor Selection in Hybrid Molecular Beam Epitaxy of Alkaline-Earth Stannates
摘要：
氧化物分子束外延（MBE）的挑战之一是合成含有高电负性金属（难以氧化的金属）的氧化物。使用反应性有机金属前体可以潜在地解决这个问题。为了研究分子束外延中自由基的形成，我们探索了三种精心选择的金属有机锡前体的SnO 2和BaSnO 3生长：四甲基锡（TMT），四乙基锡（TET），和六甲基二锡（HMDT）。所有这三种前体产生单晶，原子级光滑，和外延的SnO 2（101）薄膜上的r-Al 2 O3在氧等离子体的存在下。生长动力学的研究揭示了反应限制和通量限制的制度，除了TET，这也表现出下降的沉积速率随着温度的升高超过800 ℃。相反，这些前体的性能是显着不同的BaSnO 3生长。TMT和TET是无效的，在提供足够的锡，而HMDT产生相纯，化学计量的BaSnO 3薄膜。值得注意的是，即使不使用氧等离子体（即，仅用分子氧）。使用HMDT形成锡自由基的能力并因此辅助Sn至Sn 4+氧化反应来讨论这些结果。结构和电子输运性质的薄膜生长使用HMDT与无氧等离子体进行了比较。该研究为分子束外延中反应自由基合成难氧化金属氧化物前驱体的选择提供了指导。
英文摘要：
One of the challenges of oxide molecular beam epitaxy (MBE) is the synthesis of oxides containing metals with high electronegativity (metals that are hard to oxidize). The use of reactive organometallic precursors can potentially address this issue. To investigate the formation of radicals in MBE, we explored three carefully chosen metal-organic precursors of tin for SnO2 and BaSnO3 growth: tetramethyltin (TMT), tetraethyltin (TET), and hexamethylditin (HMDT). All three precursors produced single-crystalline, atomically smooth, and epitaxial SnO2 (101) films on r-Al2O3 in the presence of an oxygen plasma. The study of growth kinetics revealed reaction-limited and flux-limited regimes except for TET, which also exhibited a decrease in deposition rate with increasing temperature above 800 C. Contrary to these similarities, the performance of these precursors was dramatically different for BaSnO3 growth. TMT and TET were ineffective in supplying adequate tin whereas HMDT yielded phase-pure, stoichiometric BaSnO3 films. Significantly, HMDT resulted in phase-pure and stoichiometric BaSnO3 films even without the use of an oxygen plasma (i.e., with molecular oxygen alone). These results are discussed using the ability of HMDT to form tin radicals and therefore, assisting with Sn to Sn4+ oxidation reaction. Structural and electronic transport properties of films grown using HMDT with and without oxygen plasma are compared. This study provides guideline for the choice of precursors that will enable synthesis of metal oxides containing hard-to-oxidize metals using reactive radicals in MBE.
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