Gas sensing properties and electrical resistance of Langmuir-Blodgett iron oxide nanoparticle arrays

Nanoparticle (NP) sensors are prepared by Langmuir-Blodgett deposition of colloid Fe
₂
O
₃
or CoFe
₂
O
₄
NPs onto alumina substrates. The thickness of the deposit is 1, 2, 4 or 7 NP monolayers (ML). NP arrays are analysed by GIXRD, SEM, SAXS, DLS and XANES. The average NP diameters are 6.4 nm and 7.6 nm for Fe
₂
O
₃
and CoFe
₂
O
₄
, respectively. The response current of the sensor is measured at ≈ 400 °C in the mixtures of dry air with the monitored CO and NO
₂
gases. The best relative response is 38 for 500 ppb of NO
₂
. The resistance of NP arrays was studied between 250 and 500 °C. With 2 ML Fe
₂
O
₃
deposit the sheet resistance decreases with increasing temperature from 10
¹¹
to 10
⁹
Ω. Activation energy of the semiconductor type conductivity is 0.75 eV. High gas monitoring sensitivity of NP sensors is due to the big effective surface of Fe
₂
O
₃
and CoFe
₂
O
₄
NP arrays.