The Study On The Shearing And Photoelectric And Magnetic Properties Of Van Der Waals/Non-Van Der Waals Two-dimensional Materials

Electronic devices are limited by the quantum size effect,and the development of Moore’s Law has encountered a bottleneck.Due to unique properties and ultra-thin size of two-dimensional materials,they are expected to last Moore’s Law.Among the the two-dimensional（2D）material family,there is a kind of materials with spin properties,known as 2D magnetic materials.Spin of spin electrons is a new regulatory variable,exhibiting phenomena such as spin-valley locking effect,giant magnetoresistance effect,and so on However,low magnetic phase transition temperature limits the room temperature applications.In order to solve this problem,it is necessary to optimize 2D magnetism and discover 2D magnetic materials with room temperature of magnetic phase transition.At the same time,it is urgent to possess the interaction between nonmagnetic photoelectric materials and magnetic two-dimensional materials,especially the impact of spin on the photoelectric properties of heterojunctions.Based on the above,the following research work is carried out,with the content being divided into the following three parts:（1）Comparative Study on Optimized Thinning and Physical Properties of Layered Materials:In this work,Fe₃Ge Te₂（FGT）and black phosphorus（BP）nanosheets are exfoliated by dry and wet exfoliation,respectively.The dry exfoliated FGT don’t exhibit magnetism at room temperature.Wet exfoliation of FGT regulated the ferromagnetic properties by introducing resident charges.Controlling the time of exfoliation to 1.5 hours could achieve Curie temperature of 385 K.Meanwhile,a vertical exchange bias phenomenon is found at 4 K.Wet exfoliation injects charge through organic cation intercalation.Resident charges can affect FGT spin polarization.Uneven cation occupation or distribution can lead to differences in interlayer polarization,which may be the cause of vertical magnetization shift.Compared to the dry exfoliation,wet exfoliated BP nanosheet have a surface with wrinkles and defects left during the charge injection,resulting in uneven surfaces and reduced photoelectric performance,with nearly 20-fold increase in resistance and 10-fold decrease in response speed.Selection of exfoliation strategy fits the requirements of optoelectronic/magnetic heterostructure construction.（2）Study on the photoelectric properties of Fe₃Ge Te₂ and Black Phosphorus Van der Waals heterojunction:In this work,a two-layer heterojunction was constructed.The upper layer is dry exfoliated BP,and the lower layer is wet exfoliated FGT.The photoelectric properties are controlled by magnetic proximity effect.Through magnetic measurements,the magnetic properties of the heterojunction were enhanced by 60%.Microscopic magnetic characterization revealed that interlayer spin coupling lead to local spin ordering in BP nanosheet.The magnetism fades after illumination,and recovers when the laser light source is turned off.According to Kelvin probe force microscope testing,electrons spontaneously transfer from BP to FGT,indicating the transferred electrons are spin polarized in FGT,enhancing the magnetic proximity effect.The reversible transfer of charge between layers is realized by illumination to regulate the magnetic proximity effect.The spin ordering inside the BP nanosheet improves the photoelectric detection performance,increasing the rising and falling response time to 2 ms and 8 ms respectively.The responsivity increase nearly three times.This heterojunction exhibits wide band photoelectric detection performance from 405 to 980 nm wavelengths.BP in heterojunctions is less prone to oxidation and has better stability than original BP.（3）Study on antiferromagnetic phase transitions and semiconductor properties of non layered iron borates:In this work,thinning of bulk Fe B is achieved by electrochemical exfoliation and intercalation of non van der Waals material Fe B.Fe B nanosheets have thickness of 5±0.3 nm and length of 9.6±0.4μm.Using magnetic measurements to characterize the bulk and nanosheets of Fe B,it is found that the magnetic properties are ferromagnetic and antiferromagnetic respectively,indicating that the magnetic phase transition occurred during the thinning process.Through testing with Kelvin probe force microscope,ultraviolet light irradiation can increase the Fermi level of Fe B nanosheets.Conducting electrical performance tests on it,compared to bulk Fe B,the resistance of two-dimensional Fe B was increased by 4×10⁹ times,indicating transition towards semiconductor or even insulator.According to the regulation of the Fermi level by illumination and the increase in resistance,two-dimensional Fe B has semiconductor characteristics.The sample has obvious photothermal current under illumination,and it is further verified with a photothermal imager that two-dimensional Fe B has good photothermal performance.This indicates that high-quality bulk thinning method achieves magnetic and semiconductor transitions.