Raman spectroscopy signatures for monomeric, dimeric and trimeric zinc dimethoxide with tetrahydrofuran adduct and early hydrolysis-condensation products on Au(111) surface: theoretical and experimental approach

Evidence of Graphene-like ZnO Nanostructures via Zinc Dimethoxide Hydrolysis–Condensation Under Ambient Conditions on a Au(111) Surface Using SERS: Simulation and Experiment

“…DFT , calculations were performed utilizing Gaussian 09 by selecting the B3LYP − exchange–correlation potential at the 6-31++g­(d,p) level of theory including frequency calculations to confirm the local minima of our cluster’s geometries and to compute the corresponding Raman activities. This level of theory has also shown reasonable results for similar clusters in the literature , and balances the computational cost for our purposes. In order to compare the theoretical and experimental Raman spectra, a scale factor of 0.964 was applied, as suggested by the Computational Chemistry Comparison and Benchmark DataBase for the current level of theory.…”

“…The height profile for Au/g-ZnO indicates the presence of ultrathin layers with thickness below ∼3 nm that can be probably associated with zinc–oxo species as a result of the hydrolysis–condensation of zinc dimethoxide, as already observed . X-ray reflectometry (XRR) and grazing incidence X-ray scattering (GI-SAXS) analyses were performed to complement these results by accessing a larger sampling area.…”

“…The presence of hydroxyl termination in our graphene-like ZnO nanosized systems is inspired by the fact that our preparation is given at ambient conditions with 50% RH and that we have already evidenced the presence of small hydroxyl-terminated zinc–oxo planar clusters derived from zinc dimethoxide early hydrolysis–condensation products. , Our nanosized systems were proposed following a rational design from a small cluster consisting of fused (ZnO) 3 planar rings growing in a triangular fashion under the typical hydrolysis–condensation scenario. The growth stages were simplified by considering the successive addition of three Zn­(OH) 2 entities at the “vertices” of the triangle-shaped clusters, yielding g-(ZnO) n [Zn­(OH) 2 ] 6 with n = 3, 6, 9 and 12, with their corresponding after-optimization structures depicted in Figure a.…”

“…The height profile for Au/g-ZnO indicates the presence of ultrathin layers with thickness below ∼3 nm that can be probably associated with zinc−oxo species as a result of the hydrolysis−condensation of zinc dimethoxide, as already observed. 36 X-ray reflectometry (XRR) and grazing incidence X-ray scattering (GI-SAXS) analyses were performed to complement these results by accessing a larger sampling area. XRR analysis indicates that the critical angle (θ c ) shifts from θ c ∼ 1.02°toward ∼1.55°, as shown in Figure 1b, in agreement with the formation of nanostructures with an associated higher electronic density compared to that ascribed to the Au surface valley's empty spaces, analogously to that schematized in the right panel of Figure 1a.…”

“…A large variety of zinc oxide (ZnO) nanostructures, mainly in the Wurtzite polymorph, has been reported to exhibit excellent electrical, optical, and electrochemical properties in a wide range of applications. − However, recent experimental and theoretical studies have been focused on the study of atomic-scale layered ZnO nanostructures with graphene-like structures, usually abbreviated as g-ZnO. − The most common synthetic route toward g-ZnO is based on a chemical vapor deposition (CVD) process under ultrahigh vacuum conditions not only over Cu(111), Pd(111), Ag(111), − Pt(111), and Au(111) − but also over defectuous and nondefectuous graphene. − Moreover, the preparation of layered zinc oxide using zinc nitrate as a precursor in hydrothermal conditions, as well as the preparation of layered zinc hydroxide materials by the hydrolysis of diethyl zinc and zinc carboxylate at room temperature has also been explored recently. , The study of organozinc compounds such as dialkyl zinc or alkyl zinc alkoxides and their corresponding transformation toward zinc oxo–hydroxide clusters and nanostructures have been extensively studied. − More recently, Terlecki et al has shown that various reactions involving hydrolysis of organozinc precursors can provide completely different ZnO- or even Zn­(OH) 2 -based nanostructures . However, although zinc dialkoxides exhibit easier handling in air moisture conditions compared to dialkyl zinc or alkyl zinc alkoxides, only a few reports on the hydrolysis and condensation of zinc dialkoxides are reported in the literature. , We have recently reported, both theoretically and experimentally, that the formation of small hydroxyl-terminated (ZnO) n planar clusters with n < 6 is possible via the hydrolysis–condensation of zinc dimethoxide. , However, regardless of the preparation methodology, characterizing these g-ZnO structures has so far been a hard task. It is well-known that the g-ZnO structures are reported to be stable only in their monolayered and bilayered structures while higher-order layered structures (more than 3 layers) are thermodynamically stable on Wurtzite structures based on high-resolution transmission electron or scanning tunneling microscopies. − …”