Synthesis Of PbI₂ Nano Wires And The Study On Its Optoeletronic Properties

Nanomaterials research made the material no longer limited to macroscopic materials science.Studies indicate that when the material size is reduced to nanoscale it will show some special properties such as quantum tunneling.Accordding to their dimensions,the nanomaterials were divided into three categories:zero-dimensional,one-dimensional and two-dimensional material.This article deals with one-dimentional nanomaterials which have two nano-sized dimensions,including nanowires,nanotubes and nanoribbons.Because of their larger surface area and higher surfactant,one-dimensional nanomaterials show good performance in the gas-sensing and the photosensitivity.So,they are expected to be good candidates for nanoscale sensors in various fields.With the development of technologies,the scales of the microelectronic devices are shorten continuously.Maskless ultraviolet lithography is a very important technology in the fabrication process of semiconductor device.Unlike the traditional ultraviolet lithography,maskless ultraviolet lithography uses the computer to design the mask image which not only reduces costs,but also can change lithography electrode pattern flexibly.As a result,it has been widely used in the preparation of microelectronic devices.With the development of detector technologies the sensitivity of the detectors becomes much more important.PbI₂ shows a hexagonal symmetry and a large mass density.Due to its special properties in optoelectronics,PbI₂ nanowires have attracted much attention for applications in research and industry.In this work,PbI₂ nanowires were synthesized based on the PVD mechanism and characterized by XRD,SEM,EDS,respectively.Then FIB technique was employed to fabricate the photodetector,and its optical-electrical properties were also investigated.The main results are summarized as followed:1.PbI₂ nanowires were synthesized by optimizing the experimental conditions.It was prepared 'based on PVD mechanism by using the thermal evaporation of PbI₂ powder in a quartz tube furnace.First,from room temperature to 250 ?,the heating rate was controlled as 10 ?/min.Then the heating rate was 20 ?/min from 250 ?to target temperature 350 ?.Finally,the annealing time at 350 ? lasted for 1 h.The XRD pattern of the PbI₂ nanowires shows only?001?diffraction peaks,indicating a uniformly oriented crystal structures.The compositional analysis of the as-grown isolated nanowires were demonstrated by EDS spectra indicating that the atomic ration of Pb to I was 1:2.2.The photo-electric device was fabricated by optimizing the UV maskless lithographic technology.The optimal dealing conditions for S1805 resist were:500 rad/min spin coating for 6 s;3500 r/min spin coating for 40 s;spin-coating turn-off time is less than 5 s.The thickness of the resist which is sensitive to 434 nm ultraviolet light was 400 nm.At a developing time of 40s,the best exposure time for lO× lens was 5 s.FIB technique was employed to fabricate the nano-device after the bottom electrodes?7-nm Ti/75-nm Au?were deposited by magnetic sputtering.3.PbI₂ nanowires show strong photoelectric effect.The photo-switching current ratio of the single PbI₂ nanowire photo-detector is 48 under the illumination with a wavelength of 450 nm and an incident optical power of 360 mW/cm2 at a bias of 3 V.The responsivity of the detector at 3 V is about 75 mA/W.