Design And Fabrication Of Graphene Nanoribbon Based Gas Sensors

Graphene nanoribbons?GNRs?,thin strips of graphene with high length-to-width ratios and straight edges,are a new class of quasi-one-dimensional?1-D?graphene based materials.GNRs combine the structures and properties of CNTs and graphene sheets.GNRs possess long and reactive edges that could not only enhance the adsorption of certain molecules on their surface,but also make them more accessible to doping and chemical modification.Moreover,quantum confinement and edge effects result in that their electronic properties could be controlled by tailoring the ribbon width or edge functionalization.Therefore,GNRs are very potential gas sensing materials.In this paper,we fabricated GNRs through longitudinal unzipping of multi-walled nanotubes?MWNTs?and investigated their gas sensing properties.Since pristine GNRs are only sensitive to a few gases and their sensitivities are always poor,so we designed and fabricated ammonia?NH3?and hydrogen?H2?gas sensors based on novel GNRs film/SiO₂/Si heterojunction structures.Firstly,we synthesized oxidative graphene nanoribbon?GONRs?,and fabricated GNRs film on interdigital electrodes through transfer printing and low-temperature reduction processes.We found that the GNRs film had obvious response to NH3.To further enhance the NH3 sensing properties of GNRs based sensors,GNRs/SiO₂/p-Si heterojunction were fabricated on silicon substrates with native oxide layers and then modified by polyaniline?PANI?through in-situ polymerization.Finally,we fabricated a NH3 gas sensor based on PANI-GNRs/SiO₂/p-Si structure.Experimental results showed that the sensor exhibited good response air?35?R R?⁹0%?to 1000 ppm NH3 at room temperature,and had much shorter response and recovery time.We think that is because PANI enhanced adsorption of gas molecules on the sensor and the adsorbed gas molecules changed the carrier concentration in PANI and GNRs,which increases the interface potential barrier between GNRs and p-Si,then leading to the large changes in the current across the junction under reverse bias.We experimentally investigated the NH3 sensing properties of GNRs for the first time,and explored new approach to enhance their NH3 sensing properties by fabricating GNRs/SiO₂/Si junction structure.Our study provided new strategy to develop high performance NH3 sensors.Secondly,we fabricated Pd-GNRs films by a one-step chemical modification and reduction process and investigated their H2 sensing properties.Then,we fabricated Pd-GNRs/SiO₂/Si heterojunction structures by transfer printing method and found that they exhibited more outstanding H2 sensing properties.For example,the novel Pd-GNR/SiO₂/p-Si junction structure showed an excellent response?air?35?R R?of ⁹4% to 100 ppm H2 in air and its response to 10000 ppm was nearly 2000%.Based on p-n junction theory,we proposed the sensing mechanisms: the heterojunction current varies dramatically in reverse bias as the hydrogen gas molecular adsorption induces junction potential barrier height change.We fabricated Pd nanoparticles-modified GNRs by chemical modification method and applied them in the research of H2 sensors.Furthermore,we enhanced their H2 sensing properties by fabricating Pd-GNRs/SiO₂/Si heterojunction structure,which also provides new strategy to develop high performance GNRs based gas sensors.