Vandalon V, Mackus A J M, Kessels W M M
Department of Applied Physics, Eindhoven University of Technology, 5600MB Eindhoven, The Netherlands.
J Phys Chem C Nanomater Interfaces. 2022 Feb 10;126(5):2463-2474. doi: 10.1021/acs.jpcc.1c06947. Epub 2022 Jan 31.
A detailed understanding of the growth of noble metals by atomic layer deposition (ALD) is key for various applications of these materials in catalysis and nanoelectronics. The Pt ALD process using MeCpPtMe and O gas as reactants serves as a model system for the ALD processes of noble metals in general. The surface chemistry of this process was studied by vibrational broadband sum-frequency generation (BB-SFG) spectroscopy, and the results are placed in the context of a literature overview of the reaction mechanism. The BB-SFG experiments provided direct evidence for the presence of CH groups on the Pt surface after precursor chemisorption at 250 °C. Strong evidence was found for the presence of a C=C containing complex (., the form of Cp species) and for partial dehydrogenation of the surface species during the precursor half-cycle. The reaction kinetics of the precursor half-cycle were followed at 250 °C, showing that the C=C coverage saturated before the saturation of CH. This complex behavior points to the competition of multiple surface reactions, also reflected in the temperature dependence of the reaction mechanism. The CH saturation coverage decreased significantly with temperature, while the C=C coverage remained constant after precursor chemisorption on the Pt surface for temperatures from 80 to 300 °C. These SFG results have resulted in a better understanding of the Pt ALD process and also highlight the surface chemistry during thin-film growth as a promising field of study for the BB-SFG community.
详细了解通过原子层沉积（ALD）法生长贵金属对于这些材料在催化和纳米电子学中的各种应用至关重要。以甲基环戊二烯铂（MeCpPtMe）和氧气作为反应物的铂原子层沉积工艺通常可作为贵金属原子层沉积工艺的模型系统。利用振动宽带和频产生（BB-SFG）光谱对该工艺的表面化学进行了研究，并将结果置于反应机理的文献综述背景中。BB-SFG实验为250℃下前驱体化学吸附后铂表面存在CH基团提供了直接证据。发现有力证据表明存在含C=C的络合物（即Cp物种的形式）以及在前驱体半周期内表面物种的部分脱氢。在250℃下跟踪前驱体半周期的反应动力学，结果表明C=C覆盖率在CH覆盖率饱和之前就已饱和。这种复杂行为表明存在多种表面反应的竞争，这也反映在反应机理的温度依赖性上。CH的饱和覆盖率随温度显著降低，而在80至300℃的温度范围内，前驱体在铂表面化学吸附后，C=C覆盖率保持恒定。这些SFG结果有助于更好地理解铂原子层沉积工艺，也突出了薄膜生长过程中的表面化学作为BB-SFG领域一个有前景的研究方向。
