Relative Humidity Dependent Resistance Switching of Bi₂S₃Nanowires

Abstract

Electrical properties of Bi 2 S 3 nanowires grown using a single source precursor in anodic aluminum oxide templates are sensitive to the relative humidity in an inert gas environment. Dynamic sensing dependency is obtained and shows presence of spontaneous resistance switching effect between low and high relative humidity states. Employing the thermionic field emission theory, heights of Schottky barriers are estimated from the current-voltage characteristics and in relation to the humidity response. The change of Schottky barrier height is explained by local changes in physically adsorbed water molecules on the surface of the nanowire.

Humidity-dependent electrical performance of CuO nanowire networks studied by electrochemical impedance spectroscopy

“…0.5 GΩ) are lower than impedances of 2–8 GΩ measured in the RH region of 20–50% ( Figure 3a ). Possibly, at these RH levels, the concentration of free charge carriers in the CuO nanowires reduces, as hole trapping [ 32 ] occurs due to adsorption of gaseous H 2 O molecules on the CuO surface, dissociation in H + and OH − , and formation of surface dipoles (Cu + –OH − ). Water reactions with the adsorbed oxygen and Cu sites on the surface also neutralize holes: [ 30 ].…”

“…The decrease of the impedance down to a few megaohms starting at RH levels of 50–60% ( Figure 3a ) could mean an increasing dominance of ionic conductivity on the CuO surface. As the first (chemisorbed) OH − layer on the nanowire surface becomes continuous ( Figure 3d ), a further increase in humidity causes physisorption of the second layer, that is, H 2 O molecules forming hydrogen bonds with the hydroxy groups [ 23 , 29 , 32 ]. This enables the formation of H + and H 3 O + ions, for example, when a proton is transferred from a hydroxy group to a water molecule [ 33 ].…”

“…At all RH, the resistance of a metallic electrode ( R 1 ) is much smaller than the load resistance R 2 from the CuO nanowire interconnects ( Figure 4a ). An increase of Y 0 , which is a frequency-independent component of C or Q , with RH above 50–60% ( Figure 4b ) can mean that the polarization of water molecules on the surface of the nanowires becomes stronger when the thickness of the physisorbed water layer grows [ 27 , 32 ]. At RH above 60% ( Figure 4b ) the Warburg element appears and it grows with increasing the humidity, which suggests increased contribution of the diffusion processes to the total impedance with increased thickness of the water layer adsorbed at the nanowire interconnects ( Figure 3e ) and condensation of liquid water in pores.…”