Influence of the Nature of Aminoalcohol on ZnO Films Formed by Sol-Gel Methods

Abstract

Here we present comparative studies of: (i) the formation of ZnO thin films via the sol-gel method using zinc acetate dihydrate (ZAD), 2-methoxyethanol (ME) as solvent, and the aminoalcohols (AA): ethanolamine, (S)-(+)-2-amino-1-propanol, (S)-(+)-2-amino-3-methyl-1-butanol, 2-aminophenol, and aminobenzyl alcohol, and (ii) elemental analyses, infrared spectroscopy, X-ray diffraction, scanning electron microscopy, absorption and emission spectra of films obtained after deposition by drop coating on glass surface, and thermal treatments at 300, 400, 500 and 600 °C. The results obtained provide conclusive evidences of the influence of the AA used (aliphatic vs. aromatic) on the ink stability (prior to deposition), and on the composition, structures, morphologies, and properties of films after calcination, in particular, those due to the different substituents, H, Me, or iPr, and to the presence or the absence of a –CH2 unit. Aliphatic films, more stable and purer than aromatic ones, contained the ZnO wurtzite form for all annealing temperatures, while the cubic sphalerite (zinc-blende) form was also detected after using aromatic AAs. Films having frayed fibers or quartered layers or uniform yarns evolved to “neuron-like” patterns. UV and photoluminescence studies revealed that these AAs also affect the optical band gap, the structural defects, and photo-optical properties of the films.

Optically Transparent TiO2 and ZnO Photocatalytic Thin Films via Salicylate-Based Sol Formulations

“…The ZnO films (Figure 6d-f) exhibit a comparable morphology, featuring slightly more granular structures. Notably, this morphology differs from traditional sol-gel films obtained from ZAD:MEA:2-ME sols, often defined as "wrinkled," ganglia-like patterns [26], and is more consistent with the one obtained by the EDTA-based MPM method [25]. Nevertheless, the solvent influence cannot be ignored, as evidenced by the work of Vajargah et al [20], where uniform, finely granular morphologies were achieved using ethanolamine-stabilized sols based on 1-propanol.…”

“…Isopropyl alcohol (IPA) is generally used as a solvent in the TTIP case. As for ZnO deposition sols, while examples based on zinc alkoxides have been demonstrated [23], ionic Zn(II) compounds like zinc nitrate [17,24] and, in the predominant case, zinc acetate dihydrate (ZAD, Zn(CH 3 COO) 2 •2H 2 O), are more commonly employed in the literature [13,[25][26][27]. Formulating ZAD-based ZnO deposition sols presents challenges due to ZAD's poor solubility in organic solvents and proneness for self-hydrolysis, even in anhydrous media, due to the hydration water molecules [28].…”

“…Formulating ZAD-based ZnO deposition sols presents challenges due to ZAD's poor solubility in organic solvents and proneness for self-hydrolysis, even in anhydrous media, due to the hydration water molecules [28]. These factors affect both the ease of preparation and long-term stability of ZAD-based formulations, necessitating the use of specialized, harmful solvents like 2-methoxyethanol (2-ME) [24][25][26][27].…”

“…The choice of stabilizing agent in both TiO 2 and ZnO sol formulations significantly impacts the quality and structure of the resulting thin films. Acetylacetone (AcAc) is typically used to stabilize TTIP-based sols [13,21,29], while monoethanolamine (MEA) or other substituted amines are employed in the ZAD case [20,26]. However, some studies have shown the interchangeability of these chelating agents between the two cases [13,30].…”

“…Vajargah et al studied the effects of different substituted amines on ZAD-based ZnO deposition sols and found that the stabilizer significantly affects sol stability, with mono-and di-substituted amines having the strongest effect [20]. Vilà et al compared the influence of MEA and its substituted derivatives to aromatic amino alcohols and observed that aromatic-based stabilizers resulted in films with increased transparency [26].…”