P-type Mg doped CuCrO2 thin films have been deposited on fused silica substrates by Radio-Frequency (RF) magnetron sputtering. The as-deposited CuCrO2:Mg thin films have been annealed at different temperatures (from 450 to 650 °C) under primary vacuum to obtain the delafossite phase. The annealed samples exhibit 3R delafossite structure. Electrical conductivity σ and Seebeck coefficient S of all annealed films have been measured from 40 to 220 °C. The optimized properties have been obtained for CuCrO2:Mg thin film annealed at 550 °C. At a measurement temperature of 40 °C, this sample exhibited the highest electrical conductivity of 0.60 S·cm−1 with a Seebeck coefficient of +329 µV·K−1. The calculated power factor (PF = σS²) was 6 µW·m−1·K−2 at 40 °C and due to the constant Seebeck coefficient and the increasing electrical conductivity with measurement temperature, it reached 38 µW·m−1·K−2 at 220 °C. Moreover, according to measurement of the Seebeck coefficient and electrical conductivity in temperature, we confirmed that CuCrO2:Mg exhibits hopping conduction and degenerates semiconductor behavior. Carrier concentration, Fermi level, and hole effective mass have been discussed.

Influence of thickness and microstructure on thermoelectric properties of Mgdoped CuCrO2 delafossite thin films deposited by RF-magnetron sputtering. (2018) Applied Surface Science, 455. 244-250.

Thermoelectric performance of a material is determined using a figure of merit (FOM) determined as ZT (ZT = σS2T/κ where σ is the electrical conductivity, S is the Seebeck coefficient, κ is the thermal conductivity, and T is the temperature). In the case of a thin film, it is normal in the first approach to consider calculating the FOM by using the thermal conductivity of the film. However, both the thermal influence of the substrate and the emissivity of the film must also be taken into account. In the present work, the heat transfer model is used in order to study the influence of the thermal conductivity, the thickness, and the emissivity of the film on the thermal gradient of the stack (substrate + thin film). The limits of these three parameters are determined in order to have the temperature variation due to the presence of the film compared to the substrate alone that remains less than 1%. Under these limits, the thermal conductivity of the substrate can be taken into account instead of the thermal conductivity of the thin film, and a modified FOM (Z’T) can be calculated. The present study leads to the determination of the validity of modified ZT. In the case of CuCrO2:Mg thin films, the model shows that the use of Z’T is valid. The calculated value of Z’T with the measured Seebeck coefficient and the electrical conductivity as a function of the temperature for 100 nm thick films and the temperature dependent thermal conductivity taken from the literature reached 0.02 at 210 °C. A thermoelectric module made with this material showed 10.6 nW when 220 °C is applied at the hot side.

and transport properties of Mg doped CuFeO2 thin films: A promising material for high accuracy miniaturized temperature sensors based on the Seebeck effect. (2020) Journal of Alloys and Compounds, 827. 154199.

Ga doped ZnO thin films have been deposited by Radio-Frequency (RF) magnetron sputtering on fused silica substrates. The structural analysis of the n-type sensitive material showed a preferential orientation in the [00l] direction. The microstructure of the thin film indicated an increasing grain size with the increase of the thicknesses. The micro sensor platforms have been fabricated with ZnO:Ga thin film deposited using a reliable stencil mask onto interdigitated electrodes containing micro-hotplates. The as fabricated micro sensor allowed to sense sub-ppm concentration (500 ppb) of nitrogen dioxide under cycled temperature mode. This system revealed promising sensing performance with a response R/R0 up to 18 at low temperature step (50 °C).

The authors wish to make the following correction to this paper [1]. In Equation (8), logarithm (ln) term is missing[...]

In this work Ga doped ZnO thin films have been deposited by RF magnetron sputtering onto a silicon micro-hotplate and their structural, microstructural and gas sensing properties have been studied. ZnO:Ga thin film with a thickness of 50 nm has been deposited onto a silicon based micro-hotplates without any photolithography process thanks to a low cost and reliable stencil mask process. Sub-ppm sensing (500 ppb) of NO2 gas at low temperature (50 °C) has been obtained with promising responses R/R0 up to 18.

CoxFe3-xO4 oxide powders were synthesised by an oxalate decomposition process. Microstructural analysis like Xray fluorescence spectroscopy confirmed the composition of the prepared powders. These powders were then deposited onto alumina substrates in order to study their response under ethanol gas pulses. The gas sensing experiment was carried by a defined test protocol and several characteristics were tracked. Results showed a direct link between the proportion of cobalt and gas sensing performances.