Functional metal oxide nanosystems by a hybrid CVD/Sol-Gel approach

The present contribution is devoted to outlining some recent results from an innovative approach to metal oxide nanosystems. The proposed synthesis pathway is based on three successive steps: i) preparation of a porous xerogel layer (host) via sol\u2013gel (SG); ii) CVD of a guest phase on the above matrix, making it possible to achieve an intimate host/guest intermixing; iii) ex situ thermal treatment under suitable conditions, aimed at tailoring the system properties as a function of the desired application. In particular, the above route has been adopted in two specific cases, LaCoO3 and CeO2\u2013ZrO2 nanostructured thin films, which are acquiring increasing importance in the development of fuel cell technology. The most significant results, obtained by glancing incidence X-ray diffraction (GIXRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), and transmission electron microscopy (TEM), will be critically discussed, emphasizing the achievement of tailored material properties by design

Tailored synthesis of ZnO : Er(III) nanosystems by a hybrid rf-sputtering/sol-gel route

The rational design of rare-earth doped materials represents one of the major goals of current research in the field of optoelectronics. In this study, ZnO:Er(III) nanosystems were synthesized by means of a hybrid rf-sputtering/sol-gel (SG) route, consisting of the erbium (guest) rf-sputtering on porous zinc oxide xerogels (host) obtained by the SG method, followed by ex situ thermal treatments in air (300\u2013600 \ub0C, 1\u20135 h). Particular attention was focused on tailoring the erbium content and distribution in the resulting systems by optimization of the processing conditions. The structural, morphological, and compositional characteristics and their interplay with the synthesis procedure were investigated by glancing incidence x-ray diffraction, x-ray photoelectron spectroscopy, x-ray excited Auger electron spectroscopy, secondary ion mass spectrometry, UV-visible-near IR absorption spectroscopy, and atomic force microscopy. The obtained results highlight the advantages and versatility of the adopted preparation strategy in tailoring the amount and distribution of Er(III) species in high purity ZnO matrices, resulting in nanosystems endowed with compositional and morphological homogeneity at nanoscale level

Nanoscale ZnS and CdS thin films from single-source molecular precursors

In recent years, a great interest has been focused on II-VI semiconductor films for applications in different technological fields, with particular regard to optics and optoelectronics. In the present work the CVD (Chemical Vapor Deposition) technique was employed for the synthesis of ZnS and CdS nanocrystalline coatings. To this aim, O-isopropyl xanthates [M(O-iPrXan)2; M=Zn, Cd] were synthesised and used as single-source precursors. Film depositions were performed in N2 flow on silica substrates in a low pressure cold-wall CVD apparatus at temperatures between 200 and 450°C. Film crystallinity was studied by Glancing Incidence X-Ray Diffraction (GIXRD), while their chemical composition was analyzed by X-ray Photoelectron (XPS) and X-ray Excited Auger Electron (XE-AES) Spectroscopies. Their surface morphology was analyzed by Atomic Force Microscopy (AFM). Finally, the optical properties were investigated by UV-Vis absorption spectroscopy

Hybrid Chemical Vapor Deposition/Sol-Gel Route in the preparation of nanophasic LaCoO3 films

Lanthanum cobaltite (LaCoO3) thin films were synthesized by an innovative route based on the combination of chemical vapor deposition (CVD) and sol-gel (SG) methods. In particular, the approach is based on the sequential deposition of binary oxide systems (Co-O on La-O) and on the ex situ thermal treatment of the final product (T = 400-900 \ub0C, t = 1-8 h), aimed at favoring solid-state reactions for the formation of a ternary La-Co-O nanosystem. To highlight the peculiar effects of these procedures on the characteristics of the final product, both SG and CVD routes were used for the preparation of single-phase La-O and Co-O species. The process resulted in the formation of LaCoO3 nanostructured films with an average crystallite size lower than 20 nm. The required processing conditions were strongly dependent on the specific synthetic pathway: (i) SG of Co-O on CVD La-O; (ii) CVD of Co-O on SG La-O. In this framework, particular attention was focused on the analogies and differences between the two sequences and on a study of the most relevant compositional, structural, and morphological system features

A sol-gel approach to nanophasic copper oxide thin films

Nanostructured copper oxide films were prepared via sol\u2013gel starting from ethanolic solutions of copper (II) acetate wCu(CH3COO)H2Ox.Films were obtained by dip-coating at room temperature in air and were subsequently heat-treated at different temperatures (100\u2013900\ub0C) in oxidizing (air), inert (N2) or reducing (4%H2 in N2) atmospheres. The evolution of the oxide coatings under thermal treatment was studied by glancing incidence X-ray diffraction, X-ray photoelectron spectroscopy and X-ray excited Auger electron spectroscopy. Different crystalline phases were observed as a function of the annealing conditions. Depending on both temperature and atmosphere, the film composition resulted single-o rmulti-phasic. All the layers were nanostructured with an average crystallite size lower than 20nm.The most relevant results concerning sample composition and microstructure as well as their mutual relations with the synthesis conditions are presented and discussed

Study of Ag/SiO2 nanosystems by XPS

Silica-supported silver nanocomposites were synthesized by rf sputtering of Ag from Ar plasmas. Depositions were performed on amorphous silica substrates at temperatures as low as 60 \ub0C. As a general rule, a careful choice of the synthesis conditions allowed the obtainment of Ag/SiO2 nanosystems with well-tailored chemico-physical properties. In fact, a proper combination of the applied rf power and total pressure resulted in a fine tailoring of the nanosystem structure and morphology, enabling the preparation of both cluster/island-like systems or continuous thin films. A detailed characterization of the obtained specimens was attained by the combined use of several analytical techniques. While laser reflection interferometry (LRI) was employed for an in situ real-time investigation of growth dynamics, glancing-incidence x-ray diffraction (GIXRD), and transmission electron microscopy (TEM) provided useful information on the system nanostructure. Furthermore, x-ray photoelectron spectroscopy (XPS), UV-Vis spectroscopy, and atomic force microscopy (AFM) were used to investigate the chemical composition, optical properties, and surface morphology, respectively. This work has been focused on the XPS characterization of two representative Ag/SiO2 specimens. In particular, detailed scans for the Ag 3d, Ag MVV, Si 2s, O 1s, and C 1s regions and related data for a silver thin film on silica and a discontinuous Ag/SiO2 specimen are presented and discussed

Copper-silica nanocomposites tailored by the sol-gel route

Nanocomposite silica glassy layers (host) containing copper-based species (guest) were developed and tailored by the sol-gel route. The systems were obtained by starting from ethanolic solutions of tetraethoxysilane (Si(OC2H5)4, TEOS) and copper(II) acetate (Cu(CH3COO)2\u201a4H2O) in a single-step process and subsequently annealed ex situ under different atmospheres (air, nitrogen, or 4% H2 in N2 mixture). In particular, the attention was focused on the possibility of tailoring the system composition and microstructure through a proper choice of the treatment temperatures (100-900 \ub0C), duration (1-5 h), and environment. The composite evolution under annealing was investigated by glancing incidence X-ray diffraction, optical absorption spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. Pure copper-silica-based nanosystems, with guest composition ranging from CuO to Cu and controllable particle size and distribution, were obtained. The stepwise formation of CuO, Cu2O, and Cu nanoclusters in the silica network as a function of the adopted conditions is critically discussed, highlighting the crucial points involved in the design and development of composites endowed with peculiar chemicophysical properties

Advances in synthetic strategies for metal oxide nanosystems: a non-conventional hybrid CVD/Sol-Gel approach

This paper presents a hybrid molecular approach to the synthesis of metal-oxide nanosystems. The adopted strategy is based on the CVD infiltration of a guest phase in the sponge-like structure of a xerogel host matrix prepared by the Sol-Gel route. Such a combined preparation methodology allows an intimate host-guest intermixing, resulting in chemico-physical properties widely tunable as a function of the synthesis conditions. A further ex-situ annealing can lead to the formation of different kinds of nanosystems with controlled composition, structure and morphology. In order to evidence the peculiar advantages of this method, two selected case studies are presented and discussed, namely CeO2-ZrO2 and LaCoO3 nanostructured thin films. Attention is focused on the system evolution as a function of the processing parameters, highlighting the key issues of the adopted procedure