Adsorbed Molecules as Interchangeable Dopants and Scatterers with a Van der Waals Bonding Memory in Graphene Sensors

Abstract

Molecular adsorption-induced doping and scattering play a central role in the detection mechanism of graphene gas sensors. However, while the doping contributions in electric field-enhanced gas sensing is well studied, an understanding of the effects of scattering is still lacking. In this work, the scattering contribution of the graphene−molecule van der Waals (vdW) complex is studied under various electric fields and the associated vdW bonding retention in the complex is investigated. We show that contrary to the generally opined view, doping does not always dominate the graphene−molecule vdW complex interaction and consequently the conductivity response in graphene sensors, rather the vdW complex interaction only shows doping-dominated interaction at zero electric fields while scattering increases with electric field modulation. The experimentally observed electric fielddependent scattering response agrees with electron difference density analysis from density functional theory (DFT) calculations, which shows that scattering is directly dependent on the electric field-induced molecular reorientation as well as the redistribution and delocalization of charge in the graphene−gas molecule vdW complex. Furthermore, "vdW bonding memory", i.e., retention of electric field-induced vdW bonding states after turning off the electric field, is observed and shown to result from the high binding energies of the vdW complexes, which are an order of magnitude higher than the sensing measurement thermal energy. This vdW bonding memory in the graphene−molecule complexes is important for the molecular identification of adsorbed gases based on their tunable charge transfer characteristics.

Adsorption of Hydrogen Sulfide at Low Temperatures Using an Industrial Molecular Sieve: An Experimental and Theoretical Study

“… 42 , 43 On the other hand, a reversible process can be achieved in physisorption since it is dominated by weak van der Waals forces and electrostatic interactions, but the selective adsorption of H 2 S seems to pose an insurmountable challenge. 44 …”

“…Bearing in mind the aforementioned discussion, chemisorption can satisfy the demand for the selective capture of H 2 S; however, the downside is that it causes the formation of irreversible bonds that compromises the regeneration potential and eventually leads to the substitution of the sorbent. , On the other hand, a reversible process can be achieved in physisorption since it is dominated by weak van der Waals forces and electrostatic interactions, but the selective adsorption of H 2 S seems to pose an insurmountable challenge …”

“…42,43 On the other hand, a reversible process can be achieved in physisorption since it is dominated by weak van der Waals forces and electrostatic interactions, but the selective adsorption of H 2 S seems to pose an insurmountable challenge. 44 The objective of this study is to determine the adsorption performance of the industrial molecular sieve (IMS) in H 2 S removal at different temperatures, H 2 S inlet concentrations, gas matrixes, and adsorption/desorption cycles. In addition, effort was spent in investigating the adsorption equilibrium, sorption kinetics, and thermodynamic parameters to further elucidate the mechanisms that govern the adsorption process.…”

Interfacial Ammonia Selectivity, Atmospheric Passivation, and Molecular Identification in Graphene-Nanopored Activated Carbon Molecular-Sieve Gas Sensors

“…Since the measured CNPD values depend on both applied V t and tuning time, the same tuning voltage (∓40 V) and tuning time (1 min) were used for all comparative analyses in this work, except otherwise stated. It is important to note that the V t -induced states have a van der Waals bonding memory and so are not completely lost immediately after turning off V t . Additionally, our results show that they can also be reversibly switched between different V t - induced states (Figures d and S9, Supporting Information).…”

“…Hence, developing gas-specific electronic responses remain a priority in graphene e-nose sensing. In this regard, the van der Waals (vdW) interaction between adsorbed molecules and graphene offers a means to characterize gases on a single graphene channel as previously predicted. ,, These vdW interactions are easily modulated by an external electric field , inducing signature electrically tunable charge transfer specific to the gases, with a vdW bonding memory …”