Preparation And Photoelectronic Properties Study Of The AuNPs@CdSe NB

With development of nanoscale science and technology and the promotion of modern micro-nano fabrication process technology,noble metal hybrid nanostructured semiconductors have gradually been a research focus.The special properties of hybrid nanostructured semiconductors are realized by artificially control their structures,make them use in a specific field.Hybridization between noble metal nanoparticles and nanostructured materials can generate surface plasmon resonance and localized plasmon resonance phenomena,which is used to improve the performance of optoelectronic devices,and the high-response,highly sensitive,and rapid-response of the photodetectors have been achieved.The main work of this thesis is to synthesize gold nanoparticles?Au NPs?,pure CdSe nanobelts?CdSe NB?and CdSe nanobelts hybridized by gold nanoparticle?AuNPs@CdSe NB?,and then to characterize their morphologies?structure?composition?microstructures and their optical properties.Finally,a photodetector based on single pure CdSe NB/AuNPs@CdSe NB was fabricated and then explore its photoelectronic property.We compared their photoelectronic parameters and performance.Finally,the working mechanism of the hybrid device was discussed.The main contents are as follows:In the first chapter,we elucidate and summarize research progress of semiconductor nanomaterials,especially CdSe nanomaterials,surface plasmons based on noble metal nanostructures,noble metal and semiconductor hybrid nanocomposites.In the second chapter,gold nanoparticles were synthesized by sputtering gold nano-films and annealing process.It is found that the size and spacing of the gold nanoparticles can be effectively controlled by adjusting thickness of the sputtered gold film and the annealing temperature and time,and then their absorption spectra are tuned.In the third chapter,pure CdSe nanobelts were prepared by thermal evaporation method.Based on it,AuNPs@CdSe NBs were obtained by assembling gold nanoparticles with different geometries on CdSe nanobelts mentioned in Chapter 2.The experimental results show that the prepared CdSe NBs have a smooth surface,regular shape,uniform thickness,and good crystallinity.For AuNPs@CdSe NBs,AuNPs closely contact with CdSeNBs,the morphology of AuNPs is regular and can be controlled,and the crystal structure of CdSe NBs is not changed during the assembly process.Pure CdSe NBs have a distinct luminescence peak at around 720nm,which corresponds to a bandgap width of¹.7 eV.Compared with pure CdSe NBs,AuNPs@CdSe NBs have an extra luminescence peak located at 500-600 nm range,corresponding to the surface plasmon resonance of Au NPs.In the UV-Vis absorption spectrum,AuNPs@CdSe NBs have the intrinsic absorption of CdSe NBs,and an additional surface plasmon resonance absorption peak at 500-600 nm,and the plasmon resonance absorption peak is red-shifted with increasing the diameter of AuNPs.In the fourth chapter,single pure CdSeNB and different single AuNPs@CdSe NB hybrid photodetectors were fabricated by using tungsten metal as hard template.We systemically measured their photoelectronic properties.It is revealed that all devices exhibit a broad-band response from ultraviolet to near-infrared?300-720 nm?,and AuNPs@CdSeNB hybridized devices exhibit more excellent performance.For example,the response R_?of the AuNPs-100s@CdSeNB devices is 5.53×10 ⁴ A·W^-1?at 550 nm?,which is 1813%of the pure CdSe nanoribbon device(3.05×10³ A·W^-1at 610 nm).The detection to weak light of hybridized devices is more sensitive,and the photocurrent ratio between the AuNPs-100s@CdSe NB device and the pure CdSe NB device with low-light illuminating(power density 0.199mW·cm^-2)is 2894%,higher than 1546%with high-light illuminating(power density 3.98 mW·cm^-2)at550nm and 1V bias.The turn/on ratio of the AuNPs-100s@CdSe NB device?2.65×10⁴?between the pure CdSe NB?1.66×10⁴?is 160%.The response speed?rise/delay time?of AuNPs-100s@CdSe NB device is 0.2/1.0 ms,which much faster than that of the pure CdSe NB device?0.8/1.4 ms?.It is especially important that the diameter and spacing of the nanoparticles can be controlled by controlling the sputtering time and annealing temperature.Thus,the detection wavelength of the AuNPs@CdSe NB device is tuned.The tunable detection wavelength can be attributed to the surface plasmon resonance,whose theoretical fundament is that the surface plasmon resonant frequency red-shifts with an increase of the diameter in gold nanoparticles.Therefore,the plasmon resonance effect enhances the absorption of hybridized materials,and generates more electron-hole pairs,resulting in the enhanced photoconductivity of the material,and improving their performance.In the fifth chapter,the discrete dipole approximation?DDA?method is used to simulate the optical properties of Au nanoparticles.The simulated extinction spectra of gold nanoparticles are in good agreement with the ultraviolet visible light absorption spectra measured by the experiment and the light response frequency of the devices.The near-field electric field distribution of gold nanoparticles further indicates that the plasma resonance effect can effectively enhance the optical detection performance of CdSe NB devices.Chapter 6 summarizes the main work and results,and then proposes research perspectives.