Synthesis,Characterization And Nanodevices Investigation Of Low Dimensional Semiconductor Nanomaterials

Low-dimensional nanostructured materials have sparked a worldwide interest due to their unique optical, electronical, magnetical and mechanical properties and their potential applications in nanodevices and functional materials.Synthesis, characterization and physical properties of low dimensional semiconductor nanomaterials as well as nano optic-electric devices and sensors were systematically investigated in this thesis.By using simple solution routes, high quality one dimensional materials such as CdS nanowires, ZnS nanowires, ZnO nanocones, PbSe nanotubes and one dimensional transition metals(Mn, Co, Ni) doped II-VI type diluted magnetic semiconductors were prepared successfully.The optical, magnetical related physical properties of above nanomaterials were also studied. Moreover, ZnO nanocones based UV photodetectors, single PbSe nanotube based near infrared photodetectors, ZnO nanorods chemical gas sensors, as well as CuPc nanowires based organic semiconductors field effect transistor and photoswitches were fabricated, and the related devices properties were measured. The obtained research results were as follows:(一). A series of one dimensional II-VI type semiconductors such as CdS,ZnS nanowiers and ZnO nanocones, low dimensional IV-IV type semiconductor PbSe nanostructures were prepared successfully by simple solution routes:(1). We have developed a facile solvothermal route to synthesize PbSe nanocubes, submicrometer cubes and truncated octahedron by adjusting the reaction parameter. The possible growth mechanism of PbSe cubes was also investigated, we found that the polyacrylamide (PAM) additives played an important role in the morphology of PbSe, which is very valuable to further understand the PbSe crystal growth.(2). A general solvothermal route to prepare sulfide nanowires was provided. High quality single crystalline, straight and smooth wurtzite CdS,ZnS nanowires were fabricated for the fist time by using PEG-400 as a new soft template, ethylenediamine as the reaction medium and thioureas as the sulfur source at 170℃。The optical properties of CdS and ZnS nanowires were investigated by UV-vis and PL spectra. The PL spectra show that an intense emission peak at 340 nm and 315 nm was observed in CdS nanowires and ZnS nanowires sample, respectively.(3). Large scale, uniform novel ZnO nanocones with tips of about 200 nm and length of about 50μm were successfully prepared by a simple hydrothermal route for the first time.The morphology and structures of as obtained products were characterized by XRD,SEM,TEM and HRETM. The effect of reaction time and PEG-400 additive on the morphology of products, and the ZnO nanocones growth mechanism were also discussed.An intense near band edge emission peak centred at 387 nm was observed in PL spectra of ZnO nanocones, which demonstrates it possess excellent UV emission property.(4). PbSe nanotubes with diameter of ~150 nm, length of severalμm were prepared by a facile solution route by using precursor nanowires as the sacrificed template at room temperature.The optical properties of PbSe nanotubes were investigared by UV-vis and PL spectra, the band gap of PbSe nanotube is estimated to be ~1.2 eV.(二). A facile molten assisted method was developed to synthesize mutiforms-structures SnO2 nanobelts including zigzag, branching, and straight structures for the first time.The as obtained products were characterized by XRD,SEM and TEM. The growth mechanism of zigzag SnO2 nanobelts was proposed, which follow to ostwald ripening mechanism.A strong blue emission peak at ~425 nm was observed in PL spectra, which is attribured to the oxygen deficiency.These novel SnO2 nanobelts will be beneficial to further understand the degree SnO2 of nanostructures.(三). High quality one dimensional II-VI type diluted magetic semiconductors were fabricated by magnetic element doping, the optical and magnetic properties of DMSs were studied:(1). Single crystalline Mn doped CdS diluted magetic semiconductors nanowires were synthesized by solvothermal route for the first time, the XRD, HRTEM, EDX and XRF characterizations demonstrated that the Mn ions have been doped into the inside of CdS,the Mn ions related characteristic (4T1-6A1 transition) emission peak at ~595 nm was observed in PL spectra, and room temperature EPR measurement indicated that the Mn doped CdS nanowires show paramagnetic properties.(2). High quality one dimensional Zn1?xNixO and Zn1?xCoxO based diluted magetic semiconductors were perepared by hydrothermal route at 140℃for the first time, the structure analysis indicated that the as prepared samples were single crystalline wurtzite structure, and no other phase was observed. An intense UV emission peak centered at 386 nm was observed both in pure and doped ZnO sample by PL spectra, the magnetic properties were investigated by SQUID,both Zn0.95Ni0.05O and Zn0.95Co0.05O sample show ferromagnetic properties at room temperature, the saturation magnetization and coercive field (HC ) were obtained to be 0.4 emu/g and ~72 Oe for Zn0.95Ni0.05O nanorods, while for Zn0.95Co0.05O nanowires, the saturation magnetization and coercive field (HC ) were 0.1emu/g, ~70 Oe, respectively.We attributed the room temperature magnetism to the exchange interaction between free delocalized carriers(hole or electron from the valence band) and the localized d spins on the Ni or Co ions.Combining the optical properties with room-temperature ferromagnetism, the synthesized ZnO based DMSs may be potentially applied as build components in spintronic devices.(四). A series of functional nanodevices was fabricated by using one dimensional nanomaterials as building blocks:(1). ZnO nanocones based UV photodetectors were fabricated, the devices have good photoresponse to 360 nm UV light; Ultraminiature near infrared light photodetectors were fabricated by ultizing single PbSe nanotubes for the first time, the device has good photoresponse to 780 nm near infrared light and low work voltage, the single nanotube responsivity Rres was 12.5 mAW–1; our results demonstrate that PbSe nanotube based photodectors is very valuable in applications in the fields of imaging and communication as high-speed and low-power photodetector.(2). A simple, fast response, reliable and reproductive ZnO nanorods chemical gas sensor which can work at room temperature was developed for the first time.The sensors present highly sensing ability and fas response time to ethonal and ammonia gas at room temperature.Compared to traditional films based gas sensor(work temperature during 300~600℃), our sensor devices greatly reduced the work temperature,which will be potentially applied in the field of environmental dangerous gas detection and safety monitoring.(3). A simple,cost-effective method to synthesize CuPc organic semiconductor nanowires was developed.Large scale CuPc organic semiconductor nanowires were fabricated by solution self-assembled route for the first time.And the CuPc nanowireswere fabricated into nanodevices: photoswicthes and field effect transistors as a solution processed material model. the devices were capable of switching on/off reversibly and fast by turning the 808 nm infrared light source on/off, the organic field effect transistors presented good field effect properties, and the field effect mobilityμwas ~0.02 cm2 /V s.Our results demonstrate that the self-assembled CuPc organic semiconductor nanowires will have important application in fabrication of cost-effectice,large area electronic component and molecular flexible electronic devices.