Electron theory of thin-film gas sensors

Adsorption–desorption noise in gas sensors: Modelling using Langmuir and Wolkenstein models for adsorption

“…According to this assumption, non-interacting adsorbates are assumed, and therefore, the model is valid only for sub-monolayer coverages. However, some works on n-type semiconductor [7], revealed that the degree of coverage of charged adions, in the case of (depletive) oxygen chemisorption is limited to a small fraction of a monolayer (the Weisz limitation), and therefore, this is consistent with our assumption.…”

“…This model was developed using Langmuir's isotherm which assumes a constant binding energy between adsorbate and adsorbent. However, in the case of chemisorption on semiconductors where charge transfer is involved, the binding energy (adsorption heat) varies with the degree of coverage of chemisorbed species due to the strong electronic interaction between adsorbate and adsorbent [7]. Therefore, while in the previous paper [4] we have used Langmuir-based approach, in the present paper, we propose to model the adsorption-desorption noise using the theory of Wolkenstein's which takes into account the electronic interactions and their effect on the adsorptivity of the semiconductor substrate [5].…”

Interplay between O2 and SnO2: Oxygen Ionosorption and Spectroscopic Evidence for Adsorbed Oxygen

“…[3] As a consequence, ambitious efforts have been made to calculate the surface coverage by different types of ionosorbed oxygen [31,[58][59][60] ( Figure 5) and to correlate the overall conductance of the sensors with the chemical state of charged oxygen species at the surface. [6,61] Two assumptions are made 1) that thermally stimulated dissociation of molecular oxygen and formation of atomic oxygen ions occurs and 2) that there is spectroscopic and theoretical evidence for the species.…”

Characterization of carrier states in CuWO4 thin-films at elevated temperatures using conductometric analysis

“…[39]. Formation of an increasing number of oxygen states with both [O 2 ] and temperature features a kinetics limitation, which is related to a limited surface for formation of oxygen adsorbates (saturation effect), and electronic repulsion effects (interaction between conduction electrons and negative oxygen species), and a thermodynamic limitation related to both the destabilization of oxygen adsorbates with increasing temperature (which is evidenced by the reduction of effective coverage with temperature), and an increase in oxygen vacancies at high temperature [12,[57][58][59][60][61].…”