Anisotropic photoresponse of layered rhenium disulfide synaptic transistors

Layered ReS_(2) with direct bandgap and strong in-plane anisotropy shows great potential to develop high-performance angle-resolved photodetectors and optoelectronic devices.However,systematic characterizations of the angle-dependent photoresponse of ReS_(2) are still very limited.Here,we studied the anisotropic photoresponse of layered ReS_(2) phototransistors in depth.Angel-resolved Raman spectrum and field-effect mobility are tested to confirm the inconsistency between its electrical and optical anisotropies,which are along 120°and 90°,respectively.We further measured the angle-resolved photoresponse of a ReS_(2) transistor with 6 diagonally paired electrodes.The maximum photoresponsivity exceeds 0.515 A·W^(-1) along b-axis,which is around 3.8 times larger than that along the direction perpendicular to b axis,which is consistent with the optical anisotropic directions.The incident wavelength-and power-dependent photoresponse measurement along two anisotropic axes further demonstrates that b axis has stronger light-ReS_(2) interaction,which explains the anisotropic photoresponse.We also observed angle-dependent photoresistive switching behavior of the ReS_(2) transistor,which leads to the formation of angle-resolved phototransistor memory.It has simplified structure to create dynamic optoelectronic resistive random access memory controlled spatially through polarized light.This capability has great potential for real-time pattern recognition and photoconfiguration of artificial neural networks(ANN)in a wide spectral range of sensitivity provided by polarized light.

Birefringent response of graphene oxide film structurized via femtosecond laser

In-plane birefringent materials present an effective modulation of the optical properties and more degrees of freedom for the signal detection in low dimension,and thus remain a hot topic in realizing the integrated,miniature,and flexible devices for multiple applications.Here,the artificial in-plane birefringence properties have been successfully achieved on a graphene oxide film by a novel femtosecond laser lithography method,which provides a high-speed,large-area,and regular subwavelength gratings(~380 nm)fabrication and photoreduction.The obtained sample manifests an evident optical birefringence(~0.18)and anisotropic photoresponse(~1.21)in the visible range,both of which can be significantly modulated by either the structural morphology or the degree of oxide reduction.Based on the analysis of effective-medium theory and measurements of angle-resolved polarized Raman spectroscopy,the artificial in-plane birefringence is originated from various optical responses of the periodic subwavelength structures for the incident light with different polarization states.This technique shows great advantages for the fabrication of integrated in-plane polarization-dependent devices,which is expected to solve the problems in this field,such as the deficient selection of materials,complex design of micro/nanostructure,and inflexible processing technology.