纳米金刚石的结构、光学性能和热稳定性研究

纳米金刚石兼具纳米材料和金刚石的双重特性,呈现出与微米金刚石、块体金刚石截然不同的特点。本文以不同尺寸金刚石样品为研究对象,采用扫描电镜、X射线衍射、光谱学、热重分析技术对其结构、光学性能和热稳定性进行研究。结果显示样品尺寸分别为300 μm、30 μm和100 nm,大尺寸样品结晶质量较好,富含孤氮杂质,为Ⅰb型金刚石。纳米金刚石样品结晶较差,含有少量石墨残留,并含有H₂O、N—H和C—H键,说明其表面存在诸多有机活性基团。大尺寸金刚石样品存在中性和带负电荷的氮空位缺陷,产生较强荧光,而纳米金刚石由于存在诸多的有机基团和表面缺陷,形成非辐射中心,导致荧光猝灭。大尺寸样品在300~525 nm具有较强吸收,而纳米金刚石样品在紫外-可见-近红外整个区域均呈现出较强吸收,透过率显著较低。随着颗粒尺寸的减小,金刚石的起始氧化温度逐渐下降,氧化速率降低,因此大颗粒尺寸金刚石样品具有更好的热稳定性。

Structure,Optical Properties and Thermal Stability of Nanodiamond

Nanodiamond combines the properties of both nanomaterials and diamond materials, resulting in different characteristics from that of micron and bulk diamond. In this work, the structure, optical properties and thermal stability of diamond samples with different sizes were studied by scanning electron microscopy, X-ray diffraction, spectroscopy techniques and thermogravimetric analysis. The results show that the sizes of three samples are 300 μm, 30 μm and 100 nm, respectively. Diamond samples with larger size present better crystal quality, and are confirmed to be Ⅰb type diamond because single nitrogen impurities are observed. In contrast, the crystallinity of nanodiamond samples is poor, and residual graphite is detected in nanodiamond samples from both XRD and Raman results. In addition, H₂O, N—H and C—H bonds are observed in nanodiamond, suggesting there may be many organic reactive groups on surface. Two emission peaks are observed in both samples of 300 μm and 30 μm, originated from two types of nitrogen vacancy defects with neutral and negative charge respectively. In contrast, no emission is observed for nanodiamond because of fluorescence quenching from nonradiative center originated from organic groups and surface defects in the nanodiamond. Diamond samples with large size have the intensive absorption in the range from 300 nm to 525 nm, while the nanodiamond sample show strong absorption in the entire UV-visible-NIR region resulting in much lower transmittance. With the decrease of particle size, both the initial oxidizing temperature and oxidizing rate gradually decline. As a result, larger size samples have better thermal stability.