Shrinkage Effects of the Conduction Zone in the Electrical Properties of Metal Oxide Nanocrystals: The Basis for Room Temperature Conductometric Gas Sensor

The influence of charge localized at the surface of minute metal oxide nanocrystals was studied in and nanostructures, which were obtained replicating mesoporous silica templates. Here, it is shown that the very high resistive states observed at room temperature and dark conditions were originated by the total shrinkage of the conductive zone in the inner part of these nanocrystals. On the contrary, at room temperature and under UV illumination, both photogenerated electron-hole pairs and empty surface states generated by photons diminished the negative charge accumulated at the surface, enlarging the conductive zone and, as a consequence, leading to a reduction of the electrical resistance. Under these conditions, empty surface states produced by UV light reacted with oxidizing gaseous molecules. The charge exchange associated to these reactions also affected the size of the inner conductive zone, and leaded to a new steady-state resistance. These chemical, physical and geometrical effects can be used for gas detection, and constitutes the basis for developing novel room temperature conductometric gas sensors responsive to oxidizing species.

[1]  Marco Stefancich,et al.  Model for Schottky barrier and surface states in nanostructured n-type semiconductors , 2002 .

[2]  Francesca Peiró,et al.  Assessment of the thermal stability of anodic alumina membranes at high temperatures , 2008 .

[3]  Jordi Arbiol,et al.  Optimization of tin dioxide nanosticks faceting for the improvement of palladium nanocluster epitaxy , 2002 .

[4]  Geoffrey A. Ozin,et al.  Engineered Sensitivity of Structured Tin Dioxide Chemical Sensors: Opaline Architectures with Controlled Necking , 2003 .

[5]  Anna Vilà,et al.  Analysis of the catalytic activity and electrical characteristics of different modified SnO2 layers for gas sensors , 2002 .

[6]  Nicholas M. Harrison,et al.  An ab initio study of oxygen adsorption on tin dioxide , 2008 .

[7]  Jordi Arbiol,et al.  Gadolinium doped Ceria nanocrystals synthesized from mesoporous silica , 2008 .

[8]  Gunnar A. Niklasson,et al.  Electrochromics for smart windows: thin films of tungsten oxide and nickel oxide, and devices based on these , 2007 .

[9]  Joan Daniel Prades,et al.  Ab initio study of NOx compounds adsorption on SnO2 surface , 2007 .

[10]  Norio Miura,et al.  Correlation between Gas Sensitivity and Crystallite Size in Porous SnO2-Based Sensors , 1990 .

[11]  Fredrickson,et al.  Triblock copolymer syntheses of mesoporous silica with periodic 50 to 300 angstrom pores , 1998, Science.

[12]  Sanjay Mathur,et al.  Electrical properties of individual tin oxide nanowires contacted to platinum electrodes , 2007 .

[13]  T. Andreu,et al.  The effects of electron–hole separation on the photoconductivity of individual metal oxide nanowires , 2008, Nanotechnology.

[14]  Giorgio Sberveglieri,et al.  Defect study of SnO2 nanostructures by cathodoluminescence analysis: Application to nanowires , 2007 .

[15]  Bozhi Tian,et al.  Nanostructured metal oxides synthesized by hard template method for gas sensing applications , 2005 .

[16]  Jordi Arbiol,et al.  Synthesis of Tin Oxide Nanostructures with Controlled Particle Size Using Mesoporous Frameworks , 2004 .

[17]  Sanjay Mathur,et al.  Equivalence between thermal and room temperature UV light-modulated responses of gas sensors based on individual SnO2 nanowires , 2009 .

[18]  Sanjay Mathur,et al.  Toward a Systematic Understanding of Photodetectors Based on Individual Metal Oxide Nanowires , 2008 .

[19]  Bozhi Tian,et al.  Synthesis and Characterization of Chromium‐Doped Mesoporous Tungsten Oxide for Gas Sensing Applications , 2007 .

[20]  Francesca Peiró,et al.  A Novel Mesoporous CaO‐Loaded In2O3 Material for CO2 Sensing , 2007 .

[21]  Sanjay Mathur,et al.  Insight into the Role of Oxygen Diffusion in the Sensing Mechanisms of SnO2 Nanowires , 2008 .

[22]  Joan Daniel Prades,et al.  First-Principles Study of NO x and SO2 Adsorption onto SnO2 ( 110 ) , 2007 .

[23]  Jordi Arbiol,et al.  High response and stability in CO and humidity measures using a single SnO2 nanowire , 2007 .

[24]  David E. Williams,et al.  Classification of reactive sites on the surface of polycrystalline tin dioxide , 1998 .

[25]  Masahiro Nishikawa,et al.  Hall measurement studies and an electrical conduction model of tin oxide ultrafine particle films , 1982 .

[26]  Giorgio Sberveglieri,et al.  Stable and highly sensitive gas sensors based on semiconducting oxide nanobelts , 2002 .

[27]  G. Sberveglieri,et al.  Photosensitivity activation of SnO2 thin film gas sensors at room temperature , 1996 .

[28]  Udo Weimar,et al.  Influence on the gas sensor performances of the metal chemical states introduced by impregnation of calcinated SnO2 sol–gel nanocrystals , 2000 .

[29]  F. Kleitz,et al.  Cubic Ia3d large mesoporous silica: synthesis and replication to platinum nanowires, carbon nanorods and carbon nanotubes. , 2003, Chemical communications.

[30]  Bradley F. Chmelka,et al.  Nonionic Triblock and Star Diblock Copolymer and Oligomeric Surfactant Syntheses of Highly Ordered, Hydrothermally Stable, Mesoporous Silica Structures , 1998 .

[31]  N. Bârsan,et al.  Metal oxide-based gas sensor research: How to? , 2007 .