The optimization of a tungsten trioxide film for application in a surface acoustic wave gas sensor

LeGore, L.J.; Snow, Kathy J.; Galipeau, J.; Vetelino, J.F.

doi:10.1016/s0925-4005(97)80048-2

Cited by 22 publications

(10 citation statements)

References 9 publications

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“…As an illustration of how reducibility affects sensor response for the reaction of NH 3 on WO 3 (see section ), the symbols in Figure shift upward with temperature crossing curves of constant K . We use dimensionality to approximately relate the surface and bulk oxygen vacancy concentrations, [ V Ob ] ≅ N V 3/2 . We note that the Gibbs free energy for vacancy creation precisely determines [ V Ob ] while N V will vary depending on the surface facet.…”

Section: Bulk Conduction Modelmentioning

confidence: 99%

“…Although the time-dependent response of the coupled surface reactions and diffusion of bulk vacancies can be solved with finite element methods, the limiting cases of surface reaction or diffusion-controlled processes reveal qualitative behavior that is useful to identify the transduction mechanism and provide a means to verify numerical solutions of the partial differential equations. We consider a step function in target gas pressure applied at constant temperature, starting from a uniform vacancy depth distribution corresponding to σ air .…”

Section: Bulk Conduction Modelmentioning

confidence: 99%

“…Gold (1.5 nm equivalent film thickness) was deposited onto the planar and GLAD films using electron beam evaporation, which led to Au nanoparticles on the surface. Sensor testing methods were described previously. , Planar films were exposed to 10 ppm of H 2 S at 350 °C and 100–600 ppb of NH 3 at 450 °C, while the GLAD film was exposed to 100–600 ppb of NH 3 at 450 °C.…”

Section: Application To Wo3 Sensorsmentioning

confidence: 99%

“…Williams interpreted the increase in resistance of WO 3 sensors during ozone exposure to reactions between surface oxygen vacancies and O 3 . LeGore developed a model in which surface reactions were coupled to bulk diffusion to explain the oxidation and reduction of WO 3 thin film sensors and their response to H 2 S. A general framework that predicts the characteristics of the bulk conduction transduction mechanism is needed to distinguish it from the band bending mechanism.…”

Section: Introductionmentioning

confidence: 99%

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Distinguishing Bulk Conduction from Band Bending Transduction Mechanisms in Chemiresistive Metal Oxide Gas Sensors

et al. 2018

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Chemiresistive metal oxide gas sensors based on materials including SnO 2 , ZnO, TiO 2 , and WO 3 have been investigated extensively for a wide range of applications. The band bending model, based on the surface chemistry of highly reactive ionosorbed species (O 2 − or O − ) and the semiconducting material properties of SnO 2 , TiO 2 , and ZnO, adequately predicts the dependence of steady state response on target gas pressure and temperature for these materials. However, the assumptions associated with the band bending model are not valid for sensors based on reducible oxides such as WO 3 , MoO 3 , and V 2 O 5 , in which lattice oxygen reacts with adsorbed target gases creating oxygen vacancies which diffuse rapidly into the bulk and modulate the conductivity. Here, we develop a model that includes surface reactions and vacancy diffusion for the bulk conduction mechanism and describe characteristics of the sensor behavior that allow bulk conduction to be distinguished from the band bending transduction mechanism. We illustrate the predictions of the model regarding how the change in conductivity, Δσ, and response time, τ, depend on target gas pressure, temperature, and film thickness using well-characterized WO 3 sensors, including epitaxially oriented polycrystalline thin films and nanorod structured glancing angle deposition (GLAD) films. The physical/ chemical parameters of the model are determined in independent measurements. Expressions for the limiting cases in which τ is determined either by surface reactions or by bulk diffusion provide design criteria to predict the theoretical performance limits of sensors which operate via this transduction mechanism.

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Section: Bulk Conduction Modelmentioning

confidence: 99%

Section: Bulk Conduction Modelmentioning

confidence: 99%

Section: Application To Wo3 Sensorsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Distinguishing Bulk Conduction from Band Bending Transduction Mechanisms in Chemiresistive Metal Oxide Gas Sensors

et al. 2018

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“…Considering the practical application, WO 3 thin lms are more popular than powder types since lm types can be used for electrochromic devices, 10-12 gas sensors 13,14 and photochemical electrodes. 15,16 WO 3 lms can be prepared by various methods such as sputtering, [17][18][19] evaporation, 18 chemical vapor deposition (CVD), 20 pulsed laser deposition (PLD), 21 molecular beam epitaxy (MBE), 22 sol-gel, 23 electrochemical deposition, 16 hydrothermal reaction [10][11][12]15,24 and so on.…”

mentioning

confidence: 99%