反应源温度对ZnO纳米线阵列定向性及发光性能的影响

Effects of reactant temperature on the alignment and photoluminescence properties of ZnO nanowire arrays

以Au薄膜为催化剂、ZnO与碳混合粉末为反应源,采用碳热还原法在单晶Si衬底上制备了ZnO纳米线阵列。通过扫描电子显微镜(SEM)、X射线衍射仪(XRD)、荧光分光光度计对样品的表征,研究了反应源温度对ZnO纳米线阵列的定向性和光致发光性能的影响。样品在源温度920℃条件下沿(002)方向择优生长,定向性最好,温度过低不利于ZnO纳米线阵列密集生长,而温度过高导致Zn原子二次蒸发,因而也不利于纳米线阵列的定向和择优生长;样品在源温度880℃有最强的近紫外带边发射,表明温度过高和过低都不利于ZnO晶体结构的优化;由于ZnO纳米线在缺氧氛围下生长,氧空位是缺陷存在的主要形式,因此所有样品都有较强的绿光发射。温度升高导致纳米线生长速度提高而增加了氧空位缺陷数量,从而使样品绿峰强度增强并在源温度920℃时达最大值,但温度的进一步升高可导致ZnO纳米线表面Zn元素的蒸发而降低氧空位缺陷的数量,从而抑制绿峰强度。

Using gold film as catalyst and mixture of ZnO and carbon powder as source of reactive precursors, respectively, ZnO nanowire arrays were synthesized on the monocrystalline silicon substrates by carbon-thermal method. Influence of source temperature on the surface morphology, crystal and optical properties were investigated by scanning electron microscopy （SEM）, X-ray diffraction （XRD） and photoluminescence （PL）. ZnO nanowire arrays obtain good alignment with （002） preferential orientation at 920℃, because lower temperature is not favorable for dense growth of ZnO nanowires and higer temperature will result in secondary evaporation of Zn atoms which is also not advantageous for good alignment and preferential growth of ZnO nanowire arrays. It is revealed that ZnO nanowires obtained the most perfect crystal structrure at source temperature of 880℃ by showing the strongest uhraviolet（UV） emission. As ZnO nanowires were synthesized in oxygen-deficient environment, oxygen vacancies which are responsible for green emission are the predominant defects. Rising temperature will result in the accelerated growth rate of ZnO nanowire and more oxygen vacancies in the thicker ZnO nanowire arrays, hence, green emission was increased by rising temperature and would get the maximum intensity at 920℃, but was suppressed by further higher temperature which will result in the number decreasing of oxygen vacancies by evaporation of Zn atoms from the nanowire Surface.