过渡金属与F共掺杂ZnO薄膜结构及磁、光特性

Effects of doping F and transition metal on crystal structure and properties of ZnO thin film

采用溶胶-凝胶法在玻璃衬底上制备了过渡金属元素与F共掺杂Zn_(0.98-x) TM_x F_(0.02)O(TM_x=Cu_(0.02),Ni_(0.01),Mn_(0.05),Fe_(0.02),Co_(0.05))薄膜,进而利用X射线衍射仪、扫描电子显微镜、紫外-可见透过谱、光致发光及振动样品磁强计等研究了薄膜的表面形貌、微结构、禁带宽度及光致发光(PL)和室温磁学特性.研究表明:掺杂离子都以替位的方式进入了ZnO晶格,掺杂不会破坏ZnO的纤锌矿结构.其中Zn_(0.93)Co_(0.05)F_(0.02)O薄膜样品的颗粒尺寸最大,薄膜的结晶度最好且c轴择优取向明显;Zn_(0.93)Co_(0.05)F_(0.02)O薄膜样品的颗粒尺寸最小,薄膜结晶度最差且无明显的c轴择优取;Cu,Ni,Fe与F共掺杂样品的颗粒尺寸大小几乎相同.TM掺杂样品均表现出很高的透过率,同时掺杂后的薄膜样品的禁带宽度都有不同程度的红移.PL谱观察到Zn_(0.98-x) TM_x F_(0.02)O薄膜的发射峰主要由较强的紫外发射峰和较弱的蓝光发射峰组成.Zn_(0.93)Co_(0.05)F_(0.02)O薄膜样品的紫外发光峰最弱,蓝光发射最强,饱和磁化强度最大;与之相反的是Zn_(0.96)Cu_(0.02)F_(0.02)O薄膜,其紫外发光峰最强,蓝光发射最弱,饱和磁化强度最小.结合微结构和光学性质对Zn_(0.98-x) TM_x F_(0.02)O薄膜的磁学性质进行了讨论.

Transition metal（TM = Cu, Ni, Mn, Fe and Co）-doped ZnO：F thin films are deposited on glass substrates by a sol-gel method through using ethanol as solvent. All the samples are checked by using X-ray diffraction（XRD）,atomic force microscope（AFM）, X-ray photoelectron spectroscope（XPS）, photoluminescence, UV spectrophotometer,and vibrating sample magnetometer. The XRD reveals that Cu, Ni, Mn, Fe and Co occupy the Zn sites successfully without changing the wurtzite structure of ZnO at moderate doping concentration, and no evidence of any secondary phases is found. The AFM measurements show that the average values of crystallite surface roughness of the samples are in a range from about 2 to 12.7 nm. The surface of Zn O：F thin film becomes less compact and uniform when ZnO：F thin film is doped with TM ions. The TM ions are indeed substituted at the Zn^（2＋） site into the Zn O lattice as shown in the results obtained by XPS and XRD. Further studies show that most of the Zn O films exhibit preferred（002） orientations,while the best c-axis orientation occurs in Zn（0.93）Co（0.05）F（0.02）O film. However, the crystalline quality and preferential orientation of Zn O film become poor in Zn（0.93）Co（0.05）F（0.02）O. The optical bandgaps of all the ZnO：F films decrease after doping TM. All the samples show high transmittance values in the visible region. Strong ultraviolet emission and weak blue emission are observed in the photoluminescence spectra measured at room temperature for all the samples. The Zn（0.93）Co（0.05）F（0.02）O film shows the weakest ultraviolet emission peak and strongest blue emission peak, corresponding to the strongest ferromagnetism; while for the Zn（0.96）Cu（0.02）F（0.02）O film, the strongest ultraviolet emission peak and weakest blue emission peak are observed, accompanied by the weakest ferromagnetism. To determine the optical bandgap（Eg）of TM-doped ZnO：F thin film, we plot the curve of（αhv）-2versus photon energy（hv）. It is found that the Eg decreases from 3.16 eV to 3.01 eV with the TM ions doping. We show the variations of saturation magnetization with the VO concentration for TM-doped ZnO：F thin films with the different transition metal ions. In the case of Cu-doped ZnO：F thin films, the Zn O sample shows that a weaker magnetism. ZnMnFO film exhibits well-defined hysteresis with a coercive field of 7.28 × 10 ^-5emu/g. Further studies reveal that these interesting magnetic properties are correlated with the defect-related model for ferromagnetism. Our results will expand the applications of ZnO：F thin films in visible light emitting diode, photovoltaic devices, photoelectrochromic devices, etc. Meanwhile, extreme cares should be taken to control the codoping of ZnO：F thin films for tuning the magnetization.