Multi-component oxide nanosystems by Chemical Vapor Deposition and related routes: challenges and perspectives

Multi-component oxide-based nanosystems are of primary technological importance for various applications of current interest, spanning from optoelectronics to catalysis, from chemical sensing to energy conversion and storage. Such a broad range of functional utilizations results from the joint features of nano-organized systems and the synergistic combination of constituent properties, which, in turn, can be tailored by means of flexible and scalable preparative strategies. An amenable synthetic option potentially meeting these standards is Chemical Vapor Deposition (CVD), either as such or in combination with other fabrication routes. To this regard, the present highlight provides an overview on the CVD-based growth and applicative potential of oxide-based nanocomposite systems. Special attention is devoted to three different categories, i.e. metal/oxide, oxide/oxide and carbon/oxide nanomaterials. For each of them, selected results on synthesis/applications of composite architectures with tailored morphology are presented, trying to address actual challenges and future trends in the field

Investigation of niobium nitride and oxy-nitride films grown by MOCVD

Niobium nitride (NbN) and niobium oxy-nitride (NbOxNy) thin films were grown by metalorganic chemical vapor deposition (MOCVD) on Si(100) and Si(111) substrates using [Nb(NtBu)(NMe2){C(NiPr)2(NMe2)}2] [NB; tBu=(CH3)3C; Me=CH3; iPr=(CH3)2CH] as a simultaneous Nb and N precursor. While NbN films were synthesized under a pure N2 atmosphere, NbOxNy films were synthesized under N2\u2013O2 flow (N2:O2=1\u20135) in the temperature range 400\u2013600 \ub0C, as well as by NbN deposition followed by ex-situ thermal treatments under flowing O2 at 400\u2013600 \ub0C. The samples were subjected to a multi-technique characterization in order to elucidate the interplay between their structure, morphology and composition and the adopted processing parameters. Particular attentionwas devoted to the presence of Nb\u2013N and Nb\u2013O\u2013N phases and their distribution in the films, as well as to surface oxidation phenomena. For the first time, niobium oxy-nitride coatings were obtained by CVD starting from the above precursor compound, with growth rates up to 270 \uc5/min on Si(111) at 600 \ub0C. The films were characterized by a columnar-like/globular morphology when supported on Si(100)/Si(111) and revealed a higher crystallinity on the latter substrate. Surface and in-depth compositional analyses evidenced a limited carbon contamination and the Co-existence of niobiumnitride, NbON and Nb2O5. In particular, the presence of the latter in the outermost sample layers was explained by oxidation phenomena occurring upon contact with the outer atmosphere

Plasma Processing of Nanomaterials: Emerging Technologies for Sensing and Energy Applications

Plasma processing represents an attractive and versatile option for the fabrication of lowdimensional nanomaterials, whose chemical and physical properties can be conveniently tailored for the development of advanced technologies. In particular, Plasma Enhanced-Chemical Vapor Deposition (PE-CVD) is an appealing route to multi-functional oxide nanoarchitectures under relatively mild conditions, owing to the unique features and activation mechanisms of non-equilibrium plasmas. In this context, the potential of plasma-assisted fabrication in advanced nanosystem development is discussed. After a brief introduction on the basic categories of plasma approaches, the perspectives of application to CVD processes are commented, reporting on the growth and characterization of Co3O4 nanomaterials as a case study. Besides examining the interrelations between the material properties and the synthesis conditions, special focus is given to their emerging applications as catalysts for photo-assisted hydrogen production and solid state gas sensors

1D ZnO nano-assemblies by Plasma-CVD as chemical sensors for flammable toxic and gases

In this work, 1D ZnO nano-assemblies were prepared on Al(2)O(3) substrates by plasma enhanced-chemical vapor deposition (PE-CVD), and characterized in their morphology and chemical composition by field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDXS) and X-ray photoelectron spectroscopy (XPS). For the first time, the sensing performances of PE-CVD ZnO nanosystems were tested in the detection of toxic/combustible gases (CO, H(2) and CH(4)), revealing very good responses already at moderate working temperatures. In particular, carbon monoxide and hydrogen detection was possible already at 100 degrees C. whereas methane sensing required a minimum temperature of 200 degrees C. The performances of the present ZnO nanosystems, that make them attractive candidates for technological applications, are presented and discussed in terms of their unique and controllable morphological organization. (C) 2010 Elsevier B.V. All rights reserved

Epitaxial-like growth of Co 3O 4/ZnO quasi-1D nanocomposites

The development of quasi-1D Co3O4/ZnO nanocomposites by a two-step plasma enhanced-chemical vapor deposition (PE-CVD) process is presented. Arrays of < 001 > oriented ZnO nanorods were first grown on Si(100) and subsequently used as templates for the PE-CVD of Co3O4, whose amount was tailored as a function of deposition time. The obtained composites were thoroughly characterized by means of a multitechnique approach, involving field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDXS), micro-Raman and Fourier-transform infrared (FT-IR) spectroscopies, X-ray photoelectron and X-ray excited Auger electron spectroscopies (XPS, XE-AES), glancing incidence X-ray diffraction (GIXRD), and reflection high energy electron diffraction (RHEED). The use of moderate deposition temperatures (<= 300 degrees C), together with the unique activation provided by nonequilibrium plasmas, prevented state reactions between the two oxides and promoted Co3O4 growth on the tips of vertically aligned ZnO nanostructures. In particular, the resulting quasi-1D Co3O4/ZnO composites were characterized by an interface epitaxial-like relationship, an important issue for the development of semiconductor-based functional nanosystems. Photoinduced hydrophilic (PH) and photocatalytic (PC) performances of the present nanocomposites were preliminarily investigated, showing attractive results toward the possible fabrication of advanced smart materials

Co3O4/ZnO Nanocomposites: From Plasma Synthesis to Gas Sensing Applications

Herein, we describe the design, fabrication and gas sensing tests of p-Co3O4/n-ZnO nanocomposites. Specifically, arrays of oriented ZnO nanoparticles were grown on alumina substrates by plasma enhanced-chemical vapor deposition (PECVD) and used as templates for the Subsequent PECVD of Co3O4 nanograins. Structural, morphological and compositional analyses evidenced the successful formation of pure and high-area nanocomposites with a tailored overdispersion of Co3O4 particles on ZnO and an intimate contact between the two oxides. Preliminary functional tests for the detection of flammable/toxic analytes (CH3COCH3, CH3CH2OH, NO2) indicated promising sensing responses and the possibility of discriminating between reducing and oxidizing species as a function of the operating temperature

Supported F-doped alfa-Fe2O3 nanomaterials: synthesis, characterization and photo-assisted H2 production

Supported fluorine doped alfa-Fe2O3 nanomaterials were synthesized by Plasma Enhanced-Chemical Vapor Deposition (PE-CVD) at temperatures between 300 and 500\ub0C, using a fluorinated iron(II) diketonate-diamine compound as a single-source precursor for both Fe and F. The system structure, morphology and composition were thoroughly investigated by various characterization techniques, highlighting the possibility of controlling the fluorine doping level by varying the sole growth temperature. Photocatalytic H2 production from water/ethanol solutions under simulated solar irradiation evidenced promising gas evolution rates, candidating the present PE-CVD approach as a valuable strategy to fabricate highly active supported materials