Atmospheric Pressure CVD of Antimony Oxides

Abstract

Semiconducting metal oxides are the key components in one of the most widely exploited forms of generic sensor devices and represent a fast growing sector of the market. [1±4] Tin oxide in particular has been widely studied in this respect, and numerous studies have shown that sensor selectivity can be brought about by the introduction of a second, dopant metal. [5±10] We have recently demonstrated the fabrication of Pt-doped tin oxide by a dual-source CVD approach. [11,12] Other metal oxides that have been shown to act as sensors include ZnO, [13] In 2 O 3 , [13] TiO 2 , [2,14,15] Ba(Ti,Sn)O 3 , [2,14] Ba 6 (Fe,Nb) 10 O 30 , [2,14] TiNb 2 O 7 , [2,14] as well as a range of other mixed oxides. [1] Two key issues are central to the development of enhanced metal oxide sensors: the morphology of the sensor film, [16±22] and its response integrity under conditions of changing humidity. [23,24] With regard to morphology, the sensing mechanism begins at the surface of the material and subsequent electron transport through the film is grain boundary-limited in granular films. [23,25] Clearly, the production of a sensor thin film by CVD, with experimental control over parameters such as precursor choice, deposition temperature, flow rates, etc., can have a significant impact on the grain size, surface area, intergranular coupling, and, hence, the ultimate properties of the sensor. Indeed, CVD has been noted as a potential solution to many of the current problems (selectivity, temperature/humidity dependence, power consumption) associated with existing ceramic and thick film sensors. [3] Secondly, sensor drift under conditions of variable humidity is one of the key drawbacks of current tin oxide sensors. In this context, a report concerning non-stoichiometric Cd 2 Sb 2 O 7 , detailing its selectivity (e.g., chiral discrimination of R-and S-limonene) and lack of moisture sensitivity, suggests it could form the basis for a new generation of enhanced oxide sensors. [26] Other reports on antimony-based sensors include the use of FeSbO 4 as a sensor for liquid petroleum gas, [27] though, in general, the potential of antimony oxide-based sensors seems to have been largely ignored. We have thus embarked on a programme of study aimed at evaluating the potential of antimony oxide thin films as base materials for sensor devices. The first stage in this process is the delineation of CVD routes to the various antimony oxide phases, which to date have been largely overlooked. To our knowledge, the only report on the CVD of any antimony oxide is the formation of Sb 2 O 5 by aerosol-assisted (AA) CVD from SbCl 5 and H 2 O. [28,29] Though the physical properties of the films were extensively examined, the composition and morphology were largely ignored. In this initial report, we present our findings on the use of two commercially available antimony(III) alkoxides, (RO) 3 Sb (R = Et, n Bu), as CVD precursors for antimony oxides.Our CVD apparatus has been described elsewhere. [30] Pyrex glass slides were used as substrates for the depo...

Synthesis and structural characterization of tris(phenolate)amine complexes of antimony derived from

“…The Lewis acidity of the antimony center is expected to be diminished by nitrogen lone pair donation and the extent of this interaction is evidently greater for ½j 4 -NðCH 2 Ar Bu t 2 OÞ 3 SbðOSMe 2 Þ on the basis that the Sb-N bond length [2.265(6) Å ] is much shorter than that in [j 4 …”

“…PET (e.g. Dacron Ò , Mylar Ò and Terylene Ò ) [1][2][3], and as precursors for the deposition of thin films of Sb 2 O 3 and Sb 6 O 13 [4]. The coordination chemistry of antimony alkoxide and aryloxide compounds is, however, complex, as illustrated by the structural variations that are observed for [Sb(OMe) 3 ] n [5], [Sb(OPr i ) 3 ] 2 [6], [Sb(OSiMe 3 ) 3 ] 2 [7,8], Sb(OC 6 H 3 -2,6-Me 2 ) 3 [9], and [Sb 2 (OCH 2 CH 2 O) 3 ] n [10].…”

“…Specifically, the Sb-OSMe 2 bond length for ½j 4 [17]. The difference in Sb-OSMe 2 bond lengths is a consequence of the fact that these are dative covalent bonds and the magnitude of the interaction depends critically on the electronic nature of the acceptor, i.e.…”

“…its Lewis acidity [18]. On the basis of these bond lengths, it is evident that the antimony center of ½j 4 -NðCH 2 Ar Bu t 2 OÞ 3 Sb is less Lewis acidic than that of [j 4 …”

Studies on the SbOx species of SbOx/SiO2 catalysts for methane-selective oxidation to formaldehyde

“…It was also found that Sb 2 O 3 was easily spread on TiO 2 by heating at elevated temperatures and that the spread Sb 2 O 3 species could be oxidized to Sb 6 O 13 [20]. The decomposition of ( n BuO) 3 Sb on Pyrex glass solids at 650 8C in the absence of O 2 was found to produce Sb 2 O 3 in sebarmonite form, while the decomposition of (EtO) 3 Sb at 700 8C produces Sb 6 O 13 [21].…”