La或N掺杂SiC纳米线的制备、场发射性能及第一性原理计算

Preparation, Field Emission Characteristics and First-Principles Calculations of La-Doped or N-Doped Si C Nanowires

采用化学气相沉积法和气相掺杂法,分别制备了La或N掺杂的Si C纳米线.利用场发射扫描电子显微镜(FE-SEM)、透射电子显微镜(TEM)、选区电子衍射(SAED)、高分辨透射电子显微镜(HRTEM)、X射线能量色散谱(EDS)分析和X射线衍射(XRD)等测试手段对两种产物的微观形貌、元素组成和物相结构进行了系统表征.以合成产物作为阴极,对其场发射性能进行测试,结果表明:Si C纳米线的开启电场值和阈值电场值由未掺杂的2.3、6.6 V*μm-1分别降低为1.2、5.2 V*μm-1(La掺杂)和0.9、0.4 V*μm-1(N掺杂).采用Material Studio软件中的Castep模块建立(3×3×2)晶格结构模型,对未掺杂、La或N掺杂Si C的能带结构和态密度进行计算,结果显示:La或N掺杂后,在费米能级附近产生了新的La 5d或N 2p掺杂能级,导致禁带宽度(带隙)变窄,使得价带电子更容易跨越禁带进入导带,从而改善Si C纳米线的场发射性能.

La- and N-doped SiC nanowires were prepared using a vapor-phase doping method and chemical vapor deposition method, respectively. The morphologies, element analysis, and crystal structures of the products were characterized by field emission scanning electron microscope （FE-SEM）, transmission electron microscope （TEM）, selected area electron diffraction （SAED）, high-resolution transmission electron microscope （HRTEM）, X-ray energy dispersive spectrum （EDS）, and X-ray diffraction （XRD）. The field emission properties of the nanowires doped with different elements were tested by field emission measurements, and the results show that the turn on field （Eto） and threshold field （Ethr） of La-doped SiC nanowires are 1.2 and 5.2 V·μm^-1, and those of N-doped SiC nanowires are 0.9 and 4.0 V·μm^-1, respectively, these values are clearly lower than those of 2.3 and 6.6V·μm^-1 for undoped SiC nanowires. In addition, the density of states （DOS） and band structures of undoped, N-doped, and La-doped, SiC nanowires were also calculated using Castep of material studio on the basis of the first-principles. The results of the theoretical calculations suggest that the narrower gap may be attributed to the impurity energy level （La 5d or N 2p） generated near the Fermi level. Because of the narrower gap, electrons transfer from the valence band maximum （VBM） to conduction band minimum （CBM） need less energy, and this enhances the field emission property.