Study On The Microwave Synthesis Technique And Electromagnetic Performances Of ZnO Whiskers

ZnO single-crystal is a kind of multi-functional crystal material, which has many special properties in semi-conductivity, light emitting, piezoelectricity, optoelectronics, flashing etc. At room temperature, the forbidden band width and stimulus bonding energy of ZnO single-crystal is 3.37eV, 60meV respectively. Some short-wavelength optoelectronic devices can be developed by applying emitting performances of ZnO single-crystal. Comparing with SiC, GaN and other materials that have wide band gap, ZnO has more advantages in rich resources, low price, high chemical and thermal stability, better resistance to destroy of irradiation, suitable to be made as long-life devices. Therefore, the synthesis and application of low-dimensional morphological form has become an important researching field in optoelectronic materials.In this thesis, technical process, characteristics, morphological form as well as other factors have been researched in synthesizing ZnO crystal whiskers, with 2.45GHz resonance chamber of microwave (MW) heating equipment. The ideal technology of synthesizing ZnO whiskers is sought. The experiments show that the methods of MW solid-phase synthesis can be applied in controlling microscopic structure so as to obtain various morphological form crystal whiskers. The techniques of synthesizing line, bar, tube of ZnO crystal whiskers have finally gotten through a large numbers of experiments. Above ideal techniques are that line and bar of ZnO crystal whiskers can be gotten in lower temperature zone and higher temperature zone of MW chamber, respectively, at highest temperature 1300°C for 50 minutes with pure ZnO nano-scale powder. And also bar of crystal whiskers (complying with morphological form structure in crystallization) can be gotten at highest temperature 1300℃ for 50 minutes with mixture of ZnO nano-scale powder and micrometer scale, in which nano-scale powder of ZnO is 40wt%. If nano-scale powder of ZnO is 30wt%, the tube ZnO crystal whiskers can be obtained at the same conditions.According to advantages of MW heating as well as characteristics in polarized growth of ZnO crystal whiskers, the growth mechanism of different morphological forms is discussed in this thesis. The Researching results show that the growth mechanism of MW solid-phase synthesizing ZnO crystal whiskers is a kind of solid-gas growth. In MW field, ZnO powder increases temperature rapidly, after absorbing MW energy. Then evaporating in high temperature zone, electrolyzing into Zn vapor and O₂ by, Zn vapor and O₂ bind and react into solid-phase ZnO to deposit on interface of gas-solid so as to form core and to grow. Different morphological forms of ZnO crystal whiskers can be grow through controlling technical conditions.The microscopic structure and morphological form of ZnO crystal whiskers are studied and described with XRD, SEM in this thesis. The results show line, bar, tube of ZnO whiskers have better crystallization degree, especially, line and bar of ZnO crystal whiskers are uniform in diameter and regular in morphological forms.The MW electromagnetic performances of nano-scale ZnO powder, micrometer scale ZnO powder, bar of ZnO crystal whiskers are analyzed, respectively, with wave guide method as well as Model Agilent N5230A vector-net analyzer. The results show that bar of ZnO crystal whiskers have strong absorption at about 11GHz.