Research On Prepration And Properties Of Cd-doped ZnO Nanostructures

Nanostructured ZnO has attracted much interest due to its fascinating properties. Synthesis of ZnO nanomaterials with controlled morphology,size,chemical composition and crystal structure is a key step toward nanotechnological applications. In order to realize such optoelectronic devices,two crucial challenges are p-type doping and modulation of the band-gap.The research indicated that the band-gap can be modulated by doping with Cd.In this paper,ternary Zn_1-xCd_xO single-crystal bramble-like nanostructures were synthesized through a thermal evaporation approach.The effects of the various factors on the performance were discussed,and the growth mechanism was analyzed.The morphological,structural,and optical properties of the synthesized sample were investigated by using field-emission scanning electron microscopy(FESEM,Hitachi S-4700),X-ray diffraction(XRD,Rigaku D/max-RB),energy-dispersive X-ray spectroscopy(EDX),high-resolution transmission electron microscopy(HRTEM, Philips,CM200-FEG),and photoluminescence(PL,Renishaw-1000).The photolinumence(PL) spectrum was obtained with a 325 nm He-Cd laser and measured at room temperature.According to the analysis aboved,main innovative results were listed as follows:(1) Ternary Zn_1-xCd_xO single-crystal bramble-like nanostructures were synthesized by thermal evaporat meathod.The as-grown Zn_1-xCd_xO nanobrambles have fairly uniform trunk,and their diameters are approximately 100 nm,lengths are several micrometer.The diameters and lengths of the two-sided nano-thorn are about 10 and 50～80 nm,respectively.Almost all of the thorns are perpendicular to the trunk and their surfaces are rough.(2) The Cd content of Zn_1-xCd_xO bramble-like nanostructures evaluated to be about 6.7 at.%,which is larger than the thermodynamic solid solubility limits in ZnO bulk materials,indicating that the nanostructures can strongly increase solid solubility of Cd in the ZnO.(3) PL spectrum of the Zn_1-xCd_xO single-crystal bramble-like nanostructures measured at room temperature show that,comparing with that of pure ZNO(3.37 eV), the-near-band edge emission(NBE) has a red-shift of 0.24 eV owing to the modulation of band-gap caused by Cd substitution.Meanwhile,the strong blue-green band around 2.54 eV was found in the PL spectrum.The reason possibly is the bramble-like morphology has much larger surface-to-volume ratio than other structures.(4) It was found that Au nanoparticles as catalyst plays an important role in the formation of Zn_1-xCd_xO bramble-like nanostructures.We suggest that the growth of Zn_1-xCd_xO nanobrambles follow a typical vapor-liquid-solid(VLS) process.The super-saturation oxygen concentration is deemed as the critical experimental parameter for the formation of the bramble-like Zn_1-xCd_xO nanostructures.