The adsorption of metalorganic and metal halide precursors on the SiO2 surface plays an essential role in thin-film deposition processes such as atomic layer deposition (ALD). In the case of aluminum oxide (Al2O3) films, the growth characteristics are influenced by the precursor structure, which controls both chemical reactivity and the geometrical constraints during deposition. In this work, a systematic study using a series of Al(CH3) x Cl3–x (x = 0, 1, 2, and 3) and Al(C y H2y+1)3 (y = 1, 2, and 3) precursors is carried out using a combination of experimental spectroscopic techniques together with density functional theory calculations and Monte Carlo simulations to analyze differences across precursor molecules. Results show that reactivity and steric hindrance mutually influence the ALD surface reaction. The increase in the number of chlorine ligands in the precursor shifts the deposition temperature higher, an effect attributed to more favorable binding of the intermediate species due to higher Lewis acidity, while differences between precursors in film growth per cycle are shown to originate from variations in adsorption activation barriers and size-dependent saturation coverage. Comparison between the theoretical and experimental results indicates that the Al(C y H2y+1)3 precursors are favored to undergo two ligand exchange reactions upon adsorption at the surface, whereas only a single Cl-ligand exchange reaction is energetically favorable upon adsorption by the AlCl3 precursor. By pursuing the first-principles design of ALD precursors combined with experimental analysis of thin-film growth, this work enables a robust understanding of the effect of precursor chemistry on ALD processes.
We proposed the concept of atomic layer modulation (ALM) based on precursor chemical reactivities and steric hindrance effects to fabricate multicomponent nanofilms. Because ALM employs consecutive precursor exposures followed by exposure to a counter reactant, the composition of ALM films is determined by the molecular size and chemical reactivities of the precursors. For the demonstration, dicarbonyl-bis(5-methyl-2,4-hexanediketonato)Ru(II) (Carish) and trimethylaluminum (TMA) were used as Ru and Al precursors, respectively, and H2O was used as the counter reactant. Prior to the experiments, the chemical reactivity and sterically hindered physisorption of the Ru and Al precursors were theoretically calculated using density functional theory (DFT) and Monte Carlo (MC) simulations, respectively. The transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) results were highly consistent with the theoretical results, and the growth characteristics were well explained by the MC- and DFT-based reaction models. We believe that ALM could be extended to other material systems, thereby providing a different method of fabricating multicomponent nanofilms for various applications including semiconductors and nanodevices.
The continuously increasing demand for miniaturized devices in the semiconductor industry has increased the need for ultrathin films. Atomic layer deposition (ALD) is the most favorable technique for this purpose and has attracted significant interest. Prior to experimentation, understanding the reaction mechanism of the precursor with the substrate surface is crucial. However, research on the growth mechanism of ALD is limited as compared with research on its process development. Currently, ALD reaction mechanisms are typically studied using computational methods, such as molecular dynamics. However, they are complex and focus predominantly on chemical reactions between molecules and surfaces. In this study, the ALD reaction mechanisms are investigated using Monte Carlo (MC) simulations based on a simple steric hindrance model. The physical surface reactions of the precursors are modeled using MC simulations. Therefore, the steric hindrance effect of precursor adsorption on surfaces is easily predicted using a home desktop computer without requiring significant computing resources. The proposed MC simulation models yield highly consistent results with experimental data and theoretical results obtained from density functional theory calculations. We believe that this simulation method can be a useful tool with a laptop-scale computer for researchers and students working on understanding surface reactions.
We successfully fabricated a conductive E-textile and color-coated E-textile by depositing multilayer Al 2 O 3 /TiO 2 on a conductive E-textile through atomic layer deposition (ALD). Pt was deposited on an E-textile as a conductive layer via lowtemperature ALD. The color of the coated conductive E-textile could be tuned to violet, green, or pink by simply varying the thickness of the Al 2 O 3 and TiO 2 layers. Both experimental and simulation results revealed that seven different colors can be obtained with single-layer TiO 2 and multilayer Al 2 O 3 /TiO 2 , depending on the film thickness and their refractive indices. This method is highly effective for enhancing the fastness of structural color on conductive E-textiles. Furthermore, the mechanical properties and chemical stability of the color-coated E-textiles were investigated. The color-coated E-textiles could withstand acidic and basic solutions, with almost negligible changes in their morphology; this in turn indicates their excellent chemical stability. These switchable stable color-based conductive E-textiles can be used as a platform to directly integrate future wearable electronics in textiles.
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