The Nucleation Mechanism of Tetrakis(dimethylamido)hafnium on CoO Nanoislands

Abstract

Understanding the nucleation mechanisms and early stages of thin film growth is essential for advancing atomic layer deposition (ALD) processes. Here, we investigate the interaction of tetrakis(dimethylamido)hafnium (TDMAH) with cobalt oxide nanoislands under ultrahigh vacuum (UHV) conditions using infrared reflection absorption spectroscopy (IRAS) and scanning tunneling microscopy (STM). Initial nucleation of TDMAH and species formation were studied by STM at 300 K. Surface reactions were monitored at 300 and 400 K, including experiments on D₂O presaturated surfaces to elucidate the role of −OH groups in precursor adsorption and decomposition. At 300 K, nucleation was driven by hydroxyl-mediated hydrolysis, leading to Hf–O bond formation. In contrast, at 400 K, Lewis acid–base interactions with cobalt and oxygen ions dominated, resulting in precursor decomposition and the formation of surface −OH groups, which subsequently acted as nucleation sites. Experiments on D₂O-presaturated surfaces showed that −OH groups at island edges serve as critical adsorption sites for TDMAH, facilitating hafnium oxide formation while generating surface-adsorbed −NCH_x species that inhibit further precursor adsorption. These results provide molecular-level insights into temperature-dependent nucleation mechanisms, with implications for optimizing ALD processes on cobalt oxide surfaces.