Enhancing the nucleation of palladium atomic layer deposition on Al2O3 using trimethylaluminum to prevent surface poisoning by reaction products

Abstract

Metal atomic layer deposition (ALD) on oxides can display long nucleation periods and high growth temperatures that may be caused by surface poisoning by reaction products. Exposures of trimethylaluminum (TMA) during Pd ALD using Pd(hfac)2 and formalin on Al2O3 surfaces can shorten the nucleation period and reduce the growth temperatures. Fourier transform infrared spectroscopy studies indicate that TMA removes Al(hfac)∗ species that block surface sites. Pd ALD nucleates more readily and grows at lower temperatures because higher temperatures are not needed to desorb Al(hfac)∗ species. Transmission electron microscopy analysis shows the differences between Pd ALD films deposited with and without TMA.

Recent Developments in the Synthesis of Supported Catalysts

“…It was postulated that when Pd(hfac) 2 is deposited, Al(hfac)* species are formed which are not removed during subsequent formalin exposure, and thus are poisoning the surface. 244 The formalin treatment only removed hfac ligands on the Pd and replaced them with hydrogen adatoms, which formed new nucleation sites for further Pd cycles, resulting in an increased Pd uptake as particles became larger due to an increasing amount of nucleation sites for additional Pd(hfac) 2 . A similar growth behavior was observed on MgO and TiO 2 layers; however, no Pd particles were observed on pure silica, suggesting a limited reactivity of the Si−OH hydroxyl groups with Pd(hfac) 2 .…”

Low‐Temperature ABC‐Type Atomic Layer Deposition: Synthesis of Highly Uniform Ultrafine Supported Metal Nanoparticles

“…It demonstrates that there is essentially no reaction between either [Pd(hfac) 2 ] and TMA at 80 8C (Figure 2 a), or [Pd(hfac) 2 ] and TTIP at 110 8C (Figure 2 b), which is consistent with the literature results. [26] However, a common feature in Figures 2 a and b, is the observation of significant mass gain after the first [Pd(hfac) 2 ] exposure, followed by remarkably decreasing mass gain in subsequent cycles. The significant mass gain after the first [Pd(hfac) 2 ] exposure demonstrates the key role of the BC steps in the ABC-type ALD process.…”

A β-ketoiminato palladium(II) complex for palladium deposition

“…To produce thin films of palladium different deposition methods such as sputtering [2], electro-deposition [16], immersion deposition [17], spin-coating [18,19], CVD (chemical vapor deposition) [20][21][22] and ALD (atomic layer deposition) [23][24][25] can be applied. For the deposition of Pd or PdO, the most commonly used gasphase precursors are η 3 -allyl-and β-diketonato palladium complexes [21,26].…”