In Situ Synthesis And Photoelectric Performance Of Low-Dimensional Antimony Chalcogenides And Heterostructures

With the advancement of science and technology and the improvement of people's living standards,miniaturization,low power consumption and portab le products have become the goal of people's constant pursuit.Low-dimensional nanomaterials provide the basic foundamentals for manufacturing products with such characteristics.Therefore,controllable preparation,investigations on properties and applications of low-dimensional nanomaterials with high-performance are the basic way to achieve this goal.Sb₂Se₃,a V-VI binary compound,is a p-type semiconductor material with a band gap of 1.1¹.3 eV.It belongs to van der Waals crystal and exhibits high absorption coefficient(>10⁵ cm^-1)in visible light region.On the basis of the above properties,one-dimensional Sb₂Se₃ nanowires possess excellent photoelectric properties.In 2004,graphene,a two-dimensional nanomaterial,was first mechanically exfoliated and exhibited excellent electrical,optical,thermal and flexible properties.However,graphene does not have a band gap,which limits its applications in the field of optoelectronics.This shortcoming promotes the continuous exfoliation or direct growth of other new two-dimensional materials.Typically,transition metal chalcogenides?TMDs?,such as layered molybdenum disulfide?MoS ₂?and tungsten disulfide?WS₂?,have been prepared.Because the band gap of WS₂ is between 1.3 and2.1 eV?varying with the number of layers?,WS₂ is a semiconductor material with the moderate band gap.More importantly,monolayer WS₂ is a semiconductor with a direct bandgap.Therefore,WS₂ has good photoelectric properties based on its above properties.Antimony oxide?Sb₂O₃?is a wide band gap n-type semiconductor material with a bandgap of 3.3 eV and possesses a structure similar to organic molecular crystals.Until now,two-dimensional Sb₂O₃ has rarely been reported.In addition,antimony telluride?Sb₂Te₃?is a topological insulator with a narrow band gap.Because of its small band gap?⁰.3 eV?,it has a wide absorption range of light and has potential application in optoelectronic devices.However,it is difficult to construct multifunctional devices with single nanomaterials,and it is also an important research direction to improve the performance of single materials.Based on the excellent photoelectric and p-type conductive properties of one-dimensional Sb₂Se₃ nanowires,n-type elcctrical output behavior of two-dimensional WS₂,wide band gap of Sb₂O₃ and narrow band gap of Sb₂Te₃,the mixed-dimensional or different band-aligned heterostructures can be constructed,and then the multifunctionality of materials or enhanced photoelectric performance of materials can be realized.In this dissertation,high-quality single-crystalline Sb₂Se₃nanowires were synthesized by an improved vapor phase deposition method without catalyst.Mixed-dimensional Sb₂Se₃/WS₂ pn heterostructures were grown by two-step direct vapor epitaxy.High-quality Sb₂O₃/WS₂ homotype heterostructures were synthesized by two-step vapor epitaxy.Sb₂Te₃/WS₂ heterostructures were successfully synthesized.Finally,the electrical and photoelectric properties of Sb₂Se₃ nanowires and several heterostructures were studied.The main research results are as follows:?1?Single-crystalline Sb₂Se₃ nanowires with high quality were successfully grown on insulating SiO₂/Si substrate by a modified vapor phase epitaxy method.Raman and transmission electron microscopy?TEM?measurements confirm that the synthesized Sb₂Se₃ nanowires have high crystallization quality.The electrical characterization results show that Sb₂Se₃ nanowires are a p-type semiconductor and have obvious gate-tunable output characteristic with current on/off ratio of¹0².The photoelectric test data show that Sb₂Se₃ nanowires have excellent optical detection performance.The photoresponsivity is up to 270 A/W and the response time is less than 8 ms.?2?Mixed-dimensional one-dimensional/two-dimensional Sb₂Se₃/WS₂ pn hetero-structures were synthesized by two-step vapor phase epitaxy.Raman and TEM confirm the formation of heterostructures and the good crystallinity of each component.The electrical and optoelectronic test results show that the heterojunction has an obvious current rectification behavior,significant photovoltaic effect and excellent self-driven optical detection capability.The maximums of open-circuit voltage and short-circuit current are 0.19 V and 45.5 pA,respectively.The photoresponsivity is 1.51 A/W;the response time is less than 8 ms;and the photoswitching on/off current ratio is 334.Finally,we confirm that the combination between Sb₂Se₃ nanowires and WS₂nanosheets is a van der Waals binding mode by using a facile mechanical exfoliation method.?3?The growth of Sb₂O₃/WS₂ homotype heterostructures was successfully achieved by two-step vapor phase epitaxy.Statistical results show that Sb₂O₃nanosheets have six angular orientations on WS₂,which are 0^o,15^o,45^o,60^o,75^o and105^o,respectively,and do not nucleate on the surface of SiO₂/Si substrate.Sb₂O₃nanosheets with different thicknesses can be obtained at varying substrate?WS ₂?temperatures.Photoelectric measurements show that the Sb₂O₃/WS₂ heterojunction has distinct rectification output behavior and good optoelectrical performance.The photoresponsivity is 16.4 A/W,and the heterojunction has the type-I band alignment.?4?Sb₂Te₃/WS₂ heterostructures were successfully synthesized by two-step vapor phase epitaxy.Atomic force microscopy?AFM?results show that the thinnest Sb₂Te₃nanosheet has a thickness of 5.8 nm.Raman and TEM confirm the formation of the heterojunction and the high crystallinity of each component.Photoluminescence measurements show that the fluorescence of WS₂ quenches after Sb₂Te₃/WS₂heterojunction is formed.In addition,the measurement results of fabricated devices show that the Sb₂Te₃/WS₂ heterostructure reveals enhanced photoelectric properties than the individual WS₂.