Fabrication Of Monolayer Molybdenum Disulfide Photo-synaptic Devices And Simulation Of Visual Nociceptive Behavior

With the advent of the era of artificial intelligence and Internet of things,massive data analysis and processing require computing systems to have faster computing speed and lower computing energy consumption.The traditional von Neumann computing architecture cannot meet the increasing computing needs of people.Therefore,researchers have developed bionic synaptic devices with higher efficiency and lower energy consumption.Among them,photo-synaptic devices have the advantages of non-contact and low crosstalk,which have received extensive attention and research.2D transition metal sulfides exhibit great potential in photonic synapsis due to their layer-dependent band structure,large exciton binding energy and high carrier mobility.However,current synaptic devices based on 2D transition metal sulfides are mainly used as artificial photoreceptors to acquire and process visual information,while the research on the nociception ability to protect the visual system is neglected.Visual nociception is a very important function of the biological visual system,which has the characteristics of threshold,relaxation,hyperalgesia,allodynia,and wavelength dependent threshold light intensity.When a noxious stimulus is detected or the stimulus intensity exceeds a certain threshold,the visual nociceptor transmits the pain signal to the cerebral cortex for higher level processing to avoid potential harm.Therefore,the development of bionic visual nociceptors is of great significance for the future development of artificial intelligence vision systems and bionic intelligent robots.Based on this,in this paper,molybdenum disulfide（MoS₂）,a typical two-dimensional transition metal sulfide,was selected as the research object,and a monolayer MoS₂ film was prepared by the gold-assisted peeling-off method,and a monolayer MoS₂ based optical synaptic device with a planar structure was constructed by the transfer-bonding electrode process.Through the coupling of different wavelengths of light,the multi-synaptic simulation,logic operation,number recognition and other efficient information processing functions were realized.By using the human-like characteristics of its strong response to short-wave（ultraviolet and blue light）and weak response to long-wave（green and red light）,the wavelength dependent visual nociception behavior was simulated,and the characteristics of threshold,relaxation,hyperalgesia and allodynia were simulated.The specific research content is as follows:（1）The monolayer MoS₂ was prepared by the method of gold assisted stripping,and the optical characteristics such as photoluminescence spectrum,Raman spectrum and absorption spectrum were carried out.By testing the response of the device to different wavelengths of light,the sustained photoconductance phenomenon was detected.Under the same power and pulse time test conditions,the device showed strong short-wave（ultraviolet and blue light）response,and weak long-wave（green and red light）response behavior.Moreover,the mechanism of the persistent photoconductance was explored in detail by fitting the relaxation curve and adding h-BN isolation layer.In addition,the photoresponse current amplitude and relaxation time increase with the source-drain voltage,and the device can be tested at a low voltage of 10 m V.（2）The monolayer MoS₂ photonic synaptic device was simulated,and the optical pulse was used as the input signal to successfully simulate the basic characteristics of synapses such as short-term plasticity and long-term plasticity,and realize the digital recognition function with100%recognition rate.In addition,through the synergistic effect of different wavelength light sources,the spatiotemporal dynamic function of the multi-synaptic system,the logical operation function and the associative learning function of Pavlovian dogs were successfully simulated.Furthermore,the synaptic function simulation showed that it could be used to fabricate visual nociceptors.（3）Based on the simulation of visual nociception function of single-layer monolayer MoS₂ photonic synaptic device,the nociceptor characteristics such as threshold,relaxation,maladaptation,hyperalgesia and allodynia are simulated.In particular,the threshold characteristics of visual nociceptor to different wavelength light were simulated.Under the stimulation of 1 s pulse width,the threshold light intensity of 532 nm pulse was 20 times that of 320 nm pulse light,and the secondary damage effect of long wavelength light after the damage of nociceptor caused by short wavelength light was explored.