Control of Catalytic Reactions at the Surface of a Metal Oxide Nanowire by Manipulating Electron Density Inside It

Abstract

We show that the rates and extent of oxidation and reduction reactions taking place at the surface of a SnO 2 nanowire, configured as a field-effect transistor, can be modified by changing the electron density in the wire with a gate voltage.Oxygen vacancies on many oxide surfaces (e.g., TiO 2 , SnO 2 , etc.) are electrically and chemically active. When vacancies are created, the electrons left behind are localized in states whose energies lie close to the conduction band and function as n-type donors. 1 As a result, the vacancy creation increases the conductivity of the oxide, often significantly. Furthermore, atoms or molecules interacting with the oxide surface tend to bind at the oxygen vacancy sites. [1][2][3] If the adsorbed molecules are charge acceptors (such as oxygen), then they use the electrons localized at the vacancy sites to make the chemical bond to the surface. As a result, the adsorption of an electron acceptor lowers the conductivity of the n-type oxide. Molecules that react with surface oxygen and remove it create shallow donor states and increase the conductivity. Many solid-state gas sensors make use of this property. [4][5][6][7] Quasi-1D metal oxide nanowires are, in principle, able to improve the performance of chemical sensors significantly and can contribute to a fundamental understanding of these phenomena because they are highly sensitive and tunable electrical transducers of the chemical processes occurring on their surfaces. [8][9][10][11][12] Experimental observations, supported by calculations, suggest that the availability of electrons at the vacancy site affects the chemical activity of the oxide surface. 1,13,14 The influence of an electrostatic field (and the concomitant change in the near-surface electron density) on adsorption and catalysis occurring on macroscopic semiconductor surfaces was predicted and experimentally verified long ago. [15][16][17][18][19] This subject was revisited in connection with the development of FET-based gas sensors. [20][21][22][23] The latter property was inferred from the field dependence of the work function

Binding of propene on small gold clusters and on Au(111): Simple rules for binding sites and relative binding energies

“…These results suggest that it is possible to manipulate the reactivity of small gold clusters, or other catalytic systems such as oxide surfaces, by injecting or removing electron density from them. One step in this direction has been made in Moskovits group, 69 by using a gate to change the electron density in a SnO 2 nanowire and manipulate its ability to adsorb oxygen or to oxidize CO. ͑2͒ The most stable isomer of ͓Au n (C 3 H 6 )͔ q (qϭϪ1, 0, ϩ1) is the one in which propene adsorbs on a site where LUMO1 has the most prominent lobe. Higher energy isomers are formed by binding to the protruding lobes of LUMO2, etc.…”

Facile integration of ordered nanowires in functional devices

“…In the particular case of metal oxide nanowire-devices, this configuration has successfully led to a high number of applications and proof-of-concept prototypes, proving their interest in high temperature and power electronics, in which highly miniaturized field-effect transistors of wideband gap semiconductor are sought after [16][17][18].…”

Electrical Properties and Magnetoresistance of Nanogranular SnO2Films

“…SnO 2 films and nanostructures are known as prospective materials for gas sensors [1], solar cells [2], photoconductors [3], lithium batteries [4] and transparent conductive coatings [5] due to their excellent electrical properties such as good electrical conductivity, high transparency in the visible region and high reflectivity for infrared radiation. The properties of SnO 2 are mainly determined by doping, interfaces and defects.…”