1D and 2D Field Effect Transistors in Gas Sensing: A Comprehensive Review

Rapid progress in the synthesis and fundamental understanding of 1D and 2D materials have solicited the incorporation of these nanomaterials into sensor architectures, especially field effect transistors (FETs), for the monitoring of gas and vapor in environmental, food quality, and healthcare applications. Yet, several challenges have remained unaddressed toward the fabrication of 1D and 2D FET gas sensors for real-field applications, which are related to properties, synthesis, and integration of 1D and 2D materials into the transistor architecture. This review paper encompasses the whole assortment of 1D-i.e., metal oxide semiconductors (MOXs), silicon nanowires (SiNWs), carbon nanotubes (CNTs)-and 2D-i.e., graphene, transition metal dichalcogenides (TMD), phosphorene-materials used in FET gas sensors, critically dissecting how the material synthesis, surface functionalization, and transistor fabrication impact on electrical versus sensing properties of these devices. Eventually, pros and cons of 1D and 2D FETs for gas and vapor sensing applications are discussed, pointing out weakness and highlighting future directions.

Resistive switching effects in fluorinated graphene films with graphene quantum dots enhanced by polyvinyl alcohol

Two-layer films of partially fluorinated graphene (PFG) with graphene quantum dots and polyvinyl alcohol (PVA) were prepared by means of 2D printing technology. A stable resistive switching effect with the ON/OFF current ratio amounting from one to 4-5 orders of magnitude is found. The decrease in the PVA thickness leads to a change of the unipolar threshold switchings to the bipolar resistive switchings. The crossbar Ag/PFG/PVA/Ag structures retain their performance up to 6.5% deformation. The switching phenomenon is observed for a period about a year. The traps with characteristic activation energies ∼0.05 eV are suggested to be responsible for resistive switching. The time of charge-carrier emission from the localized states was found to be ∼5 μs. A quality model to describe the resistive switching effect in two-layer films implying the conduction over quantum dots proceeding with the participation of active traps at the PFG/PVA interface is proposed. The structures with the design demonstrated threshold resistive switching have their high potential for development of selector devices integrated to sensor or memristors circuits, for information storage and data processing, for flexible and wearable electronics. The structures with lower PVA thickness and the bipolar threshold switching are perspective for non-volatile memory cells for printed and flexible electronics.

Direct observation of grain boundaries in graphene through vapor hydrofluoric acid (VHF) exposure

The shape and density of grain boundary defects in graphene strongly influence its electrical, mechanical, and chemical properties. However, it is difficult and elaborate to gain information about the large-area distribution of grain boundary defects in graphene. An approach is presented that allows fast visualization of the large-area distribution of grain boundary-based line defects in chemical vapor deposition graphene after transferring graphene from the original copper substrate to a silicon dioxide surface. The approach is based on exposing graphene to vapor hydrofluoric acid (VHF), causing partial etching of the silicon dioxide underneath the graphene as VHF diffuses through graphene defects. The defects can then be identified using optical microscopy, scanning electron microscopy, or Raman spectroscopy. The methodology enables simple evaluation of the grain sizes in polycrystalline graphene and can therefore be a valuable procedure for optimizing graphene synthesis processes.

Towards stoichiometric analogues of graphene: graphane, fluorographene, graphol, graphene acid and others

Stoichiometric derivatives of graphene, having well-defined chemical structure and well-defined chemical bonds, are of a great interest to the 2D materials research.

Two-layer and composite films based on oxidized and fluorinated graphene

This study is devoted to the production and investigation of dielectric films, based on oxidized and fluorinated graphene suspensions.

Fluorinated graphene suspension for inkjet printed technologies

The possibility to control the size of the flakes of graphene suspension in the course of their fluorination in an aqueous hydrofluoric acid solution was demonstrated. The effect of the suspension composition, the fluorination time, temperature and thermal stress on the fragmentation process was investigated. The corrugation of suspension flakes, which occurs at fluorination due to a difference in the constants of graphene and fluorographene lattices, leads to the appearance of nonuniform mechanical stresses. The fact that the flake size after fragmentation is determined by the size of corrugation allows the assumption that the driving force of fragmentation is this mechanical stress. This assumption is confirmed by the break of the corrugated layers from flakes under thermal stress. Moreover, fluorination treatment at elevated temperatures (∼70 °C) significantly accelerates the fragmentation process. Suspensions of fluorinated graphene with nanometer size flakes are of interest for the development of 2D ink-jet printing technologies and production of thermally and chemically stable dielectric films for nanoelectronics. The printed fluorinated graphene films on silicon and flexible substrates have been demonstrated and the charges in metal-insulator-semiconductor structures have been estimated as the ultra low values of (0.5-2) × 10(10) cm(-2).

Fluorinated graphene dielectric films obtained from functionalized graphene suspension: preparation and properties

The fluorinated graphene suspension films were found to have excellent characteristics and be cheap, practically feasible and easy to produce.