Estimation of adsorption energy for water molecules on a multi-walled carbon nanotube thin film by measuring electric resistance

Abstract

Gas sensors based on carbon nanotube (CNT) films have attracted attention owing to their low power consumption. For further development of these sensors, we need to understand the surface interaction of the films with gas molecules. In our previous research, we investigated the influence of water molecules on the electrical conductance of multi-walled CNT films and explained this phenomenon using a two-layer adsorption model. This work motivated us to measure the adsorption energy of CNT-H2O. In this study, we focused on the first-layer adsorption and investigated the sheet resistance to water vapor pressure at various temperatures using the transmission line method (TLM). The results were fitted to Langmuir adsorption model and the adsorption equilibrium constant was determined. The temperature dependence of the sheet resistance followed a model of fluctuation induced tunneling (FIT), in which the energy barrier at the CNT junction is regarded as the main factor influencing the electrical conductance of the CNT film. The sheet resistance and equilibrium constant decreased as temperature increased. This result was consistent with the adsorption phenomenon. Finally, the adsorption energy was determined to be 0.22–0.31 eV, which is larger than the previously calculated value. It was also reported that the adsorption energy of the gas molecules in the interstitial site between two carbon nanotubes was larger than that on the CNT surface. These results indicate that the CNT junction plays a key role in the detection of gas molecules.

Development of an ALD-Pt@SWCNT/Graphene 3D Nanohybrid Architecture for Hydrogen Sensing

“…The blue dashed line is a fitting of the H 2 concentration dependence of the responsivity using the Langmuir adsorption model used to explain the microscopic mechanism underlying the gas sensing on SWCNTs. 39,40 Over the H 2 concentration range from 1 to 30%, the experimental data agree well with the theory as expected. The slight deviation of the experimental data point at 20% H 2 concentration from the theoretical curve suggests that this point may be an outlier because of the data scattering.…”

Investigation on the role of interfacial water on the tribology between graphite and metals

“…As reported in the literature, water weakly got adsorbed on Au and HOPG, while the adsorption of water on Pt was signicantly stronger. 10,11,13 We thus conclude that in our friction measurements, the weakly adsorbed water between Au and HOPG was swept away, while the strongly adsorbed water between Pt and HOPG acted as a glue between the solid bodies.…”

“…11 In the case of graphene, the thickness of the adsorbed water layer was computed to be $300 pm, 12 while the adsorption energy was measured on the carbon nanotubes to be $À0.25 eV. 13 It is noteworthy that the ratio of the snap-in forces for the Pt tip and the Au tip, During force spectroscopy measurements in air or ultra-high vacuum, the snap-in of the AFM tip onto a surface is a fast process. In Fig.…”

Response of Palladium and Carbon Nanotube Composite Films to Hydrogen Gas and Behavior of Conductive Carriers

“…Second, we focused on the effect of temperature on the sensitivity of the sensor. As reported in our previous research [ 34 ], the adsorption equilibrium constant is affected by the temperature, which in turn mildly influences the response of the resulting sensor. Figure 6 and Figure 7 display the data measured in winter (temperature less than 10 °C) and summer (temperature more than 25 °C), respectively, using sample 213-1, which showed higher sensitivity in Figure 4 and Figure 5 ; the solid line illustrates how the sensor sensitivity changes, and the dashed line illustrates the main chamber pressure change.…”