Nanoscale Structures And Their Electrical, Thermal Behaviors Of MoO₃, SnS Nanosheets

Great attentions have been increasingly paid to two dimensional materials?2D?since the advent of graphene.2D materials exhibit lots of excellent properties,and can be considered as one of the most important materials in the post-Moller times.Such materials could be found in power,promising applications such as novel electronics,optoelectronics and energy harvesting devices,especially in the newly flexible electronics like touch sensors,electromechanical sensors,bio-integrated sensors and wearable electronic technology.In 2D materials,more studies are now focused on characterizing nanostructures and their physical response to the multifields like electric,temperature,stress fields and so on.In the present thesis,Advanced scanning probe microscopy?conductive-atomic force microscopy,piezoresponse force microscopy,3w-scanning thermal microscopy and scanning thermoelectric microscopy?were employed to perform studies of nanostructure imaging and their local thermal,electrical properties.Some conclusions were obtained as follows:1.MoO₃,Sn S nanosheets were successfully prepared with homogenous composition.A new approach for 2D materials' thinning to single atomic thickness was developed based on the in-situ heated AFM conductive tip due to nanoscale thermal stress.2.Nanoscale hydrogen ions were induced by AFM lithography and successfully intercalated into the ?-MoO₃ lattice with Hx MoO₃ formation,which give rise to the reduction in the bandgap,electrical change and ultrahigh piezoresponse behavior.3.?-MoO₃ nanosheets exhibit complex thickness dependent of local electrical properties,especially in response to the AFM tip's loads.Local thermal conductivities were characterized with 3w-STh M,demonstrating first an increase,then a decrease behavior with nanosheet's thickness.4.Nanoscale piezoresponse imaging were successfully performed in Sn S nanosheets,and domain width was found to be 14 nm.Local electromechanical characterization demonstrated closely nanosheet's thickness depondent.The rollover electrical behavior were clearly revealed in the Sn S-MoO₃ heterostructures,while good conductivity in Sn S-modified AFM tip-MoO₃ heterostructures.5.Local thermoelectric parameters?thermal conductivity,Seebeck coefficient?of Sn S nanosheets were in-situ characterized by scanning thermoelectric microscopy,and were found to be thickness dependent.Local electrical I-V measurement under low and high temperatures reveals different response behavior to the temperature dynamics.In summary,nanostructure and their local electrical,thermal and thermoelectric properties were characterized by advanced scanning probe microscopy.The present findings in our work enrich our understanding the fundamental physics of 2D materials,and also promote the application of scanning probe microscopy.