Aluminum Oxide Thin Films from Aqueous Solutions: Insights from Solid-State NMR and Dielectric Response

Abstract

Here, we employ a combination of 27 Al solidstate nuclear magnetic resonance (SSNMR) and conventional spectroscopic and microscopic techniques to investigate the structural evolution of aqueous aluminum precursors to a uniform and smooth aluminum oxide film. The route involves no organic ligands and relies on dehydration, dehydroxylation, and nitrate loss for condensation and formation of the threedimensional aluminum oxide structure. Local chemical environments are tracked as films evolve over the temperature range 200−1100 °C. 27 Al SSNMR reveals that Al centers are predominantly four-and five-coordinate in amorphous films annealed between 200 and 800 °C and four-and six-coordinate in crystalline phases that form above 800 °C. The Al coordination of the aqueous-deposited aluminum oxide films are compared to data from SSNMR studies on vapor-phasedeposited aluminum oxide thin films. Additionally, dielectric constants of aluminum oxide-based capacitors are measured and correlated with the SSNMR results. Aluminum oxide is an important material for protective coatings, catalysis, and microelectronic applications. For the latter application, amorphous materials are preferred, but a lack of long-range order complicates structural characterization and determination of structure−property relationships. Solution deposition approaches are attractive alternatives to traditional vapor-phase deposition methods because precursors are commonly stable in air, and they enable printing and direct lithographic patterning on common semiconductor wafers as well as large-area and flexible substratesuseful for scale-up to applications in windows and photovoltaic devices.

On the Nature of Extra-Framework Aluminum Species and Improved Catalytic Properties in Steamed Zeolites

“…Accordingly, in steamed H-MFI, the 27 Al NMR signals of tetra- and octahedral Al 3+ sites broaden in comparison to those in fresh H-MFI, consistent with alumina cluster formation and new signals developing which partially overlap with existing Al resonances. This is fully consistent with previous Al ssNMR findings for thin alumina films [ 16 ]. It is often seen in steamed zeolites that the broadening of a tetrahedral Al signal, the formation of new octa-sites, and the appearance of abundant penta-Al sites occur.…”

Gas-phase aluminium acetylacetonate decomposition: revision of the current mechanism by VUV synchrotron radiation

“…Due to its wear and corrosion resistance, high band gap and beneficial refractive index, aluminium oxide (Al2O3) is a popular coating, widely used in a variety of applications in, for instance, protective coatings, microelectronics, and optical devices. In particular, Al2O3 can act as a passivating layer, as an alternative gate dielectric oxide, 1,2 anti-corrosion and permeation barrier coating, [3][4][5][6] as well as surface enhancement coating in the cutting tool industry. 7,8 Thanks to high growth rates and comprehensive surface coverage, Al2O3 layers are frequently synthesized by metal-organic chemical vapour deposition (MOCVD), a widely used technique for the preparation of functional coatings.…”

Probing the transformation paths from aluminum (oxy)hydroxides (boehmite, bayerite, and gibbsite) to metastable alumina: A view from high-resolution 27Al MAS NMR

“…Diverse experimental techniques such as differential thermal analysis (DTA), infrared (IR) spectroscopy, X-ray diffraction (XRD), and solid-state nuclear magnetic resonance (NMR) have observed phase transformation from aluminum (oxy)hydroxides into metastable aluminas (e.g., Bastow et al, 1994;Tsukada et al, 1999;Alphonse and Courty, 2005;Karouia et al, 2016;Chen et al, 2018;Chandran et al, 2019). In particular, 27 Al NMR has revealed the Al coordination environments in diverse disordered crystalline (i.e., metastable)/amorphous Al 2 O 3 and Al-(oxy)hydroxides (e.g., Lippmaa et al, 1986;Boissiere et al, 2006;Shen et al, 2007;Lee et al, 2009b;Lee et al, 2010;Sabarinathan et al, 2010;Kim and Lee, 2013b;Cui et al, 2018;Lee and Ryu, 2018;He et al, 2019 and references therein). The Al coordination environments and the NMR parameters, including quadrupolar coupling constant (C q ), isotropic chemical shifts ( iso ), and asymmetry parameter () for aluminum (oxy)hydroxides and metastable aluminas from these earlier studies are summarized in Table 2.…”