An n- to p-type conductivity transition induced by oxygen adsorption on α-Fe2O3

Abstract

The simultaneous measurements of conductance and work function changes induced by gaseous ambient have been performed on α-Fe2O3 thick film polycrystalline samples kept at 280 °C and exposed to different gaseous atmospheres. The switching from n- to p-type conductivity on α-Fe2O3 is shown to have an electronic origin, which is due to the oxygen adsorption and formation of a surface inversion layer and, therefore, to the inversion of the surface conduction type. The modeling of the n–p switching is described in terms of conductance dependence on the band bending induced by gaseous ambient.

Important considerations for effective gas sensors based on metal oxide nanoneedles films

“…The unusual electrical resistance changes of the films to reducing gases indicate a transition from n-to p-type conduction, assigned to the formation of an inversion layer [37], which was also reported for WO 3 nanorod [38] and TeO 2 nanowires [39] based gas sensors upon exposure to EtOH. In fact, this effect is most likely to be presented in NSM, compared to bulk materials, due to the comparable dimensions between the mean free path of the carriers, and the diameter, and/or thickness of the NSM.…”

A Method for Integrating ZnO Coated Nanosprings into a Low Cost Redox-Based Chemical Sensor and Catalytic Tool for Determining Gas Phase Reaction Kinetics

“…The effects of chemisorption on the electrical transport properties of metal oxides is well documented [1][2][3][4][5][6][7][8][9][10][11][19][20][21][22]. In the case of ZnO 1- , where the surface is oxygen deficient, the surface readily oxidized in ambient air to obtain the ideal surface stoichiometry of ZnO.…”

“…, where these act as traps of conduction electrons in the near-surface region of the ZnO layer. It has been reported in the literature [5,7] that below 150 °C the molecular adsorption of oxygen dominates, while above 150 °C dissociative chemisorption of oxygen prevails. On the other hand, at relatively high temperatures (T > 435 °C) the excitation of surface phonons leads to enhancement of oxygen desorption from the ZnO surface.…”

“…On the other hand, these devices are necessary for acquiring a fundamental understanding of corresponding physical and chemical processes triggered by surface-molecule interactions (chemisorption), as well as for interpreting the electrical transport properties of gas sensitive materials. The use of metal oxide nanocrystalline thin films, as well as other more complex nano-morphologies, as the gas sensitive layers in chemiresistors is well documented [1][2][3][4][5][6][7][8][9][10][11]. These studies demonstrated that if the dimensions of the nanostructures are comparable to the characteristic length scales of surface interactions, the sensor will be more responsive to changes in surface stoichiometry.…”

“…In chemiresistors the catalytic oxidation of analyte at the metal oxide surface depletes the surface of oxygen, which leads to a change in the surface depletion layer. If the depletion layer is comparable to the dimensions of the nanostructured metal oxide, small changes in the depth of the surface depletion layer can produce large swings in the resistivity of the chemiresistor [1][2][3][4][5][6][7][8][9][10][11].…”