Defect study of SnO2 nanostructures by cathodoluminescence analysis: Application to nanowires

Abstract

Abstract:Defects in SnO 2 nanowires have been studied by cathodoluminescence, and the obtained spectra have been compared with those measured on SnO 2 nanocrystals of different sizes in order to reveal information about point defects not determined by other characterization techniques. Dependence of the luminescence bands on the thermal treatment temperatures and pre-treatment conditions have been determined pointing out their possible relation, due to the used treatment conditions, with the oxygen vacancy concentration. To explain these cathodoluminescence spectra and their behavior, a model based on first-principles calculations of the surface oxygen vacancies in the different crystallographic directions is proposed for corroborating the existence of surface state bands localized at energy values compatible with the found cathodoluminescence bands and with the gas sensing mechanisms. CL bands centered at 1.90 eV and 2.20 eV are attributed to the surface oxygen vacancies 100º coordinated with tin atoms whereas CL bands centered at 2.37 eV and 2.75 eV are related to the surface oxygen vacancies 130º coordinated. This combined process of cathodoluminescence and ab initio calculations is shown to be a powerful tool for nanowire defect analysis. Key words:SnO 2 , CATHODOLUMINESCENCE, NANOSTRUCTURE, NANOWIRE, OXYGEN VACANCY, AB INITIO Manuscript 2 1.-Introduction:Tin dioxide (SnO 2 ) plays a key role in solid state gas sensors [1]. So a lot of experimental work has been done in order to characterize SnO 2 not only from the technological point of view as a sensor of different gases [2] but also from the materials science standpoint [3] so as to achieve improved performances by means of a better knowledge of the synthesized materials. The vacancy defects investigation deserves special attention as they have been clearly related to conductive and sensing properties of metal oxides [2]. This article will deal with the analysis of point defects using cathodoluminescence (CL) spectra of nanostructured SnO 2 , as this technique reveals complementary information about radiative transitions related to these point defects that is not determined by other characterization techniques This experimental procedure is not new. Since the mid-1970s, however, few works have been published presenting the CL spectra of SnO 2 with different morphologies [4,5,6,7]. In all known cases, several bands between 1.9 and 2.6eV have been reported but there still remains some uncertainty on their origin [6]. However, there are no systematic and detailed works considering nanowires and their comparison with nanoparticles of different sizes.On the other hand, first-principles methodologies based on the density functional theory (DFT) now provide precise calculations of the energetic properties of bulk materials and their surfaces in moderate computing times [8]. Consequently, it is attractive to link theoretical findings with unclearly interpreted experimental results in order to attain better materials knowledge with a straightforward technological ...

VLS and VS effect on ferromagnetic behaviour of SnO2nanobelts

“…The split spin states are formed on the surface of VLS based nanobelts caused by oxygen vacancies. Theoretical studies reveal that yellow CL emission is due to oxygen vacancies [48]. We conclude that the ferromagnetism in VLS based nanobelts is due to oxygen vacancies.…”

Facile fabrication of morphology-tunable SnO nanostructures by catalyst-free growth

“…The PL spectrum of the NRs grown at 900 1C (black color) is characterized by a weak blue emission band and a broad orange emission band centered at around 440 nm and 620 nm, respectively. According to literature reports, the origin of the blue band is related to structural defects and surface oxygen vacancies [13][14][15][16]. The broad peak at 620 nm is related to the crystalline defects leading to the interaction of oxygen vacancies with tin interstitials, forming a substantial amount of trapped states in the bandgap [17][18][19].…”

Promotion of acceptor formation in SnO2 nanowires by e-beam bombardment and impacts to sensor application

“…Irradiation with an electron beam can generate holes by two mechanisms30. One possibility is that positively charged holes are generated via the following reaction: 1/2O 2(gas)  = O int i −  +  ih 3031.…”