The Influence of Aminoalcohols on ZnO Films’ Structure

Abstract

Preparing structures with the sol-gel method often requires control of the basal plane of crystallites, crystallite structures, or the appearance of the voids. One of the critical factors in the formation of a layer are additives, such as aminoalcohols, which increase the control of the sol formation reaction. Since aminoalcohols differ in boiling points and alkalinity, their selection may play a significant role in the dynamics of structure formation. The main aim of this work is to examine the properties of ZnO layers grown using different aminoalcohols at different concentration rates. The layers were grown on various substrates, which would provide additional information on the behavior of the layers on a specific substrate, and the mixture was annealed at a relatively low temperature (400 °C). The research was conducted using monoethanolamine (MEA) and diethanolamine (DEA). The aminoalcohols were added to the solutions in equal concentrations. The microscopic image of the structure and the size of the crystallites were determined using micrographs. X-ray diffractometry and Raman spectroscopy were used for structural studies, phase analysis and to establish the purity of the obtained films. UV-vis absorption and photoluminescence were used to evaluate structural defects. This paper shows the influence of the stabilizer on the morphology of samples and the influence of the morphology and structure on the optical properties. The above comparison may allow the preparation of ZnO samples for specific applications.

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

“…A closer look allows ascertaining that those films consist on inhomogeneous, dense, agglomerated particles that accumulate preferentially in the ridges. The thickness of the layers differs depending on the region due to these large fractal structures formed by crystallites that group into larger grains, as reported for MEA [ 44 ]. The overall thickness of the layers ranges between 1 (continuous bottom layer) and 5 μm (including protrusions).…”

“…In general, the SGM requires a Zn(II) salt, an organic compound as stabilizer, and a solvent [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. Among the most common substances that are used as stabilizer are aminoalcohols, especially those having the proper orientation of the N- and O-heteroatoms as to bind to the Zn 2+ ions forming chelates, or acting as bridging ligands in the precursors and, therefore, preventing the precipitation of Zn(OH) 2 [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 43 , 44 , 45 , 46 ]. The world-wide long-term sol-gel ZnO precursor forms from zinc acetate dihydrate (ZAD) and ethanolamine ( Figure 1 , a ) in 2-methoxyethanol (ME) [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 38 , 39 , 40 ].…”

“…The final ZnO obtained by using diethanolamine {HN(CH 2 CH 2 OH) 2 , DEA} as stabilizer retained more N than the one obtained by using aminoalcohol a {H 2 NCH 2 CH 2 OH, MEA} under identical conditions, even after calcination at high temperatures. Moreover, peaks due to other intermediate and undesirable species, such as Zn(OH) 2 , were revealed by X-ray diffraction studies in the first case [ 44 ], thus indicating that the AA has a crucial role in the sol-gel ZnO formation process and also on the properties of the final material.…”

Effect of Thermal Treatment on the Structure and Morphology of Vanadium Doped ZnO Nanostructures Obtained by Microwave Assisted Sol–Gel Method

“…Figure 2 shows the FTIR spectra of the V doped ZnO gels obtained by the microwave assisted sol–gel method (MW) and the classic sol–gel method (SG). The bands in the 3600–2000 cm −1 region corresponded to the vibration mode of the organic groups such as the CH 3 , CH 2 as well as OH group from alcohols [ 37 , 38 , 39 , 40 , 41 ]; these overlapped into a wide band identified in the FTIR spectra of gels. Two bands at 1419 cm −1 and 1570 cm −1 were assigned to symmetric and asymmetric stretching of the C=O bond in the acetate group.…”

“…The bands at 1045 cm −1 and 1070 cm −1 were characteristic to the symmetric and asymmetric stretching modes of the C–O bond in the acetate group. Below 677 cm −1 , bands could be seen due to the Zn–O vibration [ 37 , 38 , 39 , 40 , 41 ]. In the spectra of the samples, the Zn–OH band was observed at 677 cm −1 , and the bands at 502 and 445 cm −1 were attributed to Zn–O vibration.…”