Vervuurt René H J, Karasulu Bora, Verheijen Marcel A, Kessels Wilhelmus Erwin M M, Bol Ageeth A
Department of Applied Physics, Eindhoven University of Technology , P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands; Philips Innovation Labs, High Tech Campus 11, 5656 AE Eindhoven, The Netherlands.
Chem Mater. 2017 Mar 14;29(5):2090-2100. doi: 10.1021/acs.chemmater.6b04368. Epub 2017 Feb 23.
A novel method to form ultrathin, uniform AlO layers on graphene using reversible hydrogen plasma functionalization followed by atomic layer deposition (ALD) is presented. ALD on pristine graphene is known to be a challenge due to the absence of dangling bonds, leading to nonuniform film coverage. We show that hydrogen plasma functionalization of graphene leads to uniform ALD of closed AlO films down to 8 nm in thickness. Hall measurements and Raman spectroscopy reveal that the hydrogen plasma functionalization is reversible upon AlO ALD and subsequent annealing at 400 °C and in this way does not deteriorate the graphene's charge carrier mobility. This is in contrast with oxygen plasma functionalization, which can lead to a uniform 5 nm thick closed film, but which is not reversible and leads to a reduction of the charge carrier mobility. Density functional theory (DFT) calculations attribute the uniform growth on both H and O plasma functionalized graphene to the enhanced adsorption of trimethylaluminum (TMA) on these surfaces. A DFT analysis of the possible reaction pathways for TMA precursor adsorption on hydrogenated graphene predicts a binding mechanism that cleans off the hydrogen functionalities from the surface, which explains the observed reversibility of the hydrogen plasma functionalization upon AlO ALD.
本文提出了一种新颖的方法，即在石墨烯上先通过可逆氢等离子体功能化，然后进行原子层沉积（ALD）来形成超薄且均匀的AlO层。由于原始石墨烯不存在悬键，已知在其上进行ALD具有挑战性，这会导致膜覆盖不均匀。我们表明，石墨烯的氢等离子体功能化可实现厚度低至8 nm的封闭AlO膜的均匀ALD。霍尔测量和拉曼光谱表明，在进行AlO ALD以及随后在400°C退火后，氢等离子体功能化是可逆的，并且以这种方式不会降低石墨烯的电荷载流子迁移率。这与氧等离子体功能化形成对比，氧等离子体功能化可形成均匀的5 nm厚封闭膜，但不可逆且会导致电荷载流子迁移率降低。密度泛函理论（DFT）计算将在氢和氧等离子体功能化的石墨烯上的均匀生长归因于三甲基铝（TMA）在这些表面上的吸附增强。对TMA前驱体在氢化石墨烯上吸附的可能反应途径进行的DFT分析预测了一种从表面清除氢官能团的结合机制，这解释了在AlO ALD后观察到的氢等离子体功能化的可逆性。
