Morphological and structural investigation of (Zn,Al) layered double hydroxides (LDH) nanoplatelets synthesized on aluminum-coated substrates|Studio morfologico di nanostrutture di layered double hydroxides (LDH) depositate su film sottili di alluminio

We have synthesized nanoplatelets of crystalline (Zn,AI) Layered Double Hydroxide (LDH) by a single-step and room temperature hydrothermal process on aluminum thin layers sputtered on different substrates. The structure, morphology, dimensions and compositions of nanoplatelets have been investigated by Scanning Electron Microscopy (SEM), X-Rays diffraction '(XRD), Energy Dispersion Spectroscopy (EDS) and Photoluminescence (PL). Different behaviours of the thickness of nanoplatelets have been obtained by varying the most important growth parameters (thickness of Al coatings, growth temperature and duration). The thickness of the observed nanoplatelets results to be clearly dependent on the aluminun content available in the coating. On the contrary, the stoichiometry and the Zn/AI ratio does not change appreciably. Furthermore, for the thinnest aluminum layer, the LDH nanostructures result to be not well-shaped, and the excess zinc, on the one hand does not cause changes in the composition, on the other hand has as a consequence the formation of insulated ZnO nanorods. These samples show the defect-related visible luminescence, approximately centered at 600nm, and due to the nanorods presence, while no significant luminescence was expected from LDH nanosheets. Results obtained show that a controlled and spatially localized synthesis of Zn/AI LDH nanoplatelets can be obtained even on substrates having large surface area provided that the sputtered aluminum coating results to be thicker than 10nm, thus making possible the integration of these nanostructures on substrates of different nature.Sono state realizzate delle nanolamelle di cristalli di Layered Double Hydroxide (LDH) con processo di sintesi a singolo step, mediante crescita idrotermale su substrati ricoperti da un rivestimento di alluminio realizzato mediante sputtering. In questo lavoro sono stati studiati la morfologia, le dimensioni e la composizione delle nanostrutture realizzate, in funzione dello spessore del layer di alluminio, tramite misure con miscroscopio elettronico a scansione (SEM), di diffrazione di raggi X (XRD), spettroscopia da dispersione di energia (EDS) e fotoluminescenza (PL). Mentre la dimensione laterale delle nanostrutture osservate dipende dallo spessore di alluminio disponibile, la stechiometria non cambia apprezzabilmente. Anche per i più bassi valori dello spessore di alluminio, l’eccesso di zinco non altera la composizione chimica degli LDH, ma piuttosto produce dei “nanorods” di ossido di zinco, che mostrano la caratteristica banda larga di fotoluminescenza nel visibile legata ai difetti. I risultati mostrano che si può ottenere una crescita controllata di (Zn,Al) LDH anche su substrati di grandi superfici ricoperti con alluminio mediante sputtering, con rivestimenti aventi spessori sottili fino a 10 nm, rendendo pertanto possibile l’integrazione degli LDH su substrati generici.We have synthesized nanoplatelets of crystalline (Zn,Al) Layered Double Hydroxide (LDH) by a single-step and room temperature hydrothermal process on aluminum thin layers sputtered on different substrates. The structure, morphology, dimensions and compositions of nanoplatelets have been investigated by Scanning Electron Microscopy (SEM), X-Rays diffraction (XRD), Energy Dispersion Spectroscopy (EDS) and Photoluminescence (PL). Different behaviours of the thickness of nanoplatelets have been obtained by varying the most important growth parameters (thickness of Al coatings, growth temperature and duration). The thickness of the observed nanoplatelets result to be clearly dependent on the aluminun content available in the coating. On the contrary, the stoichiometry and the Zn/Al ratio does not change appreciably. Furthermore, for the thinnest aluminum layer, the LDH nanostructures result to be not well-shaped, and the excess zinc, on the one hand does not cause changes in the composition, on the other hand has as a consequence the formation of insulated ZnO nanorods. These samples show the defect-related visible luminescence, approximately centered at 600nm, and due to the nanorods presence, while no significant luminescence was expected from LDH nanosheets. Results obtained show that a controlled and spatially localized synthesis of Zn/Al LDH nanoplatelets can be obtained even on substrates having large surface area provided that the sputtered aluminum coating results to be thicker than 10nm, thus making possible the integration of these nanostructures on substrates of different nature