| Zinc oxide (ZnO), which is a wide band gap (3.37eV) semiconductor material with a large exciton (60meV), has multiple properties such as excellent chemical and thermal stability, photoelectric properties, and under the high field strength, the band bent.Recently, ZnO has become one of the most promising cathode materias for field emission. Since cathode materias is the decisive factor of the field emission, so the field emission properties of ZnO nanomaterials research has great realistic significance and application value.Firstly, ZnO nanorod arrays were grown on Si substrate by a simple two-step process with sol-gel and hydrothermal methods. To investigate the effect of seed layers on the growth of ZnO nanorods, different numbers of the seed layers have been spin-coated on the substrate. The morphology of ZnO nanorods including diameter, density, length and orientation, crystallization and band structure have been studied by SEM, XRD, PL spectra. And the correlation between the nanorod arrays grown on different seed layers and field emission (FE) properties have also been analyzed. The ZnO nanorod array grown on 4 seed layers possesses the best field emission properties, including a lowest turn-on electric field of 13.3 V/μm and largest field emission current. Besides, it also provides the biggest the effective emission area with considering the shielding effect. It can be attributed to higher the field enhancement factor, the vertical orientation, larger density, and better conductivity of the nanorod array.Secondly, Ag/ZnO heterostructure with different Ag content are successfully prepared by hydrothermal growth and has been characterized with SEM, TEM, XRD, PL spectra.It is found that the content of Ag nanoparticle increases with Ag+ concentration. According to the PL spectrum analysis, the addition of Ag nanoparticles make the number of visible light emission peaks increases while the number of the UV emission peaks decrease, and that will increase Ag-intrinsic defects of ZnO. Besides, the more the Ag nanoparticles content, the better the performance of field emission. According to the F-N theory, the I-E curve are analyzed by the e index fitting. The I-E test curve is composed of different e index curve, each e index curve represents one kind of electron emission process. Results show that field emission process of Ag-ZnO nanomaterias including the emission of Ag and valence band.In light irradiation condition, the electron on some defect level will absorb the photon energy and transmit, as a result the field emission current is enhanced. Therefore, the effect of the visible blue light and ultraviolet light irradiation of ZnO nanorods and Ag-ZnO nanorods on the field emission properties is discussed. It is found that different intensity of visible blue light and ultraviolet light will significantly enhanced field emission current. And the stronger the light intensity, the more obvious is the enhancement effect. The e index fitting is also used to analysis the I-E curve, it is found that field emission process contains conduction band electron emission, defect energy level electron emission and valence band electron emission respectively. In addition, different wavelengths of light irradiation, the emission mechanism is different for the unique crystal structure of ZnO. Because the UV-light photon energy is larger than blue, is similar with ZnO energy gap, which will be more conducive to enhance the field emission properties. |
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