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Understanding Molecular Layer Deposition Growth Mechanisms in Polyurea via Picosecond Acoustics Analysis
Chemistry of Materials ( IF 7.2 ) Pub Date : 2020-02-06 , DOI: 10.1021/acs.chemmater.9b04702
Rachel A. Nye 1 , Andrew P. Kelliher 2 , John T. Gaskins 3 , Patrick E. Hopkins 2, 3, 4 , Gregory N. Parsons 1
Affiliation  

Molecular layer deposition (MLD) is an increasingly important thin film synthesis technique in areas such as sensors, microelectronics, protective coatings, and catalysis. However, new analytical approaches are needed to advance fundamental understanding of deposition reaction mechanisms. This work introduces ultrafast laser-based pump–probe picosecond acoustics analysis to characterize thickness-dependent properties of MLD films. Polyurea films are deposited on hydroxylated SiO2 substrates using 1,4-phenylene diisocyanate and a diamine reactant, either ethylenediamine (PDIC/ED polymer) or 1,6-hexanediamine (PDIC/HD), and the expected polymer structure is confirmed by Fourier transform infrared spectroscopy. During the first ∼20 nm of deposition, spectroscopic ellipsometry shows constant refractive index but decreasing growth rate before reaching steady state. X-ray reflectivity also shows approximately constant density during initial growth. However, the measured picosecond acoustics signatures demonstrate a marked increase in sound speed initially, indicating a transition in the physical film structure. The observed trends are ascribed to a transition in the kinetics of active site production and termination with increasing thickness, leading to changes in polymer and oligomer connectivity within the film. These findings provide a basis for better understanding MLD processes and reaction mechanisms that determine deposited film properties.

中文翻译:

通过皮秒声学分析了解聚脲中分子层沉积生长机理

分子层沉积(MLD)是在传感器,微电子学,保护涂层和催化等领域中越来越重要的薄膜合成技术。然而,需要新的分析方法来促进对沉积反应机理的基本理解。这项工作介绍了基于激光的超快泵浦-皮秒皮秒声学分析,以表征MLD膜的厚度依赖性。聚脲薄膜沉积在羟基化的SiO 2上底物使用1,4-亚苯基二异氰酸酯和二胺反应物(乙二胺(PDIC / ED聚合物)或1,6-己二胺(PDIC / HD)),并通过傅立叶变换红外光谱法确认了预期的聚合物结构。在沉积的前20纳米期间,椭圆偏振光谱仪显示出恒定的折射率,但在达到稳态之前降低了生长速率。X射线反射率在初始生长期间也显示出近似恒定的密度。然而,所测量的皮秒声学特征最初显示出声速显着增加,表明物理膜结构发生了转变。观察到的趋势归因于活性部位产生和终止动力学随厚度的增加而转变,从而导致薄膜内聚合物和低聚物的连接性发生变化。
更新日期:2020-02-07
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