Li Z, Wei S, Wang Y, Zhang X, Lu K, Chen X
National Synchrotron Radiation Laboratory, University of Science & Technology of China, Hefei, P.R. China.
J Synchrotron Radiat. 2001 Mar 1;8(Pt 2):830-2. doi: 10.1107/s0909049501000103.
X-ray absorption fine structure (XAFS) was used to investigate the local structures around Ga atoms in the hexagonal nanocrystalline and crystalline GaN under 78 and 300 K. For the first nearest neighbor coordination shell of Ga-N. the average bond length R (0.194 nm), coordination number N (4.0), thermal disorder sigma (0.0052 nm) and static disorder sigmaS (0.0007 nm) are neatly independent of the measured temperature and crystalline state. This indicates that the Ga-N covalent bond is much stronger, and the 4 nitrogen atoms in first nearest neighbor around Ga atoms keep the tetrahedral structure (Td). For the second nearest neighbor coordination shell of Ga-Ga, their bond lengths are about 0.318 nm. However, the sigmaS (0.0057 nm) of nanocrystalline GaN is 0.0047 nm larger than that of crystalline GaN (0.001 nm), and the sigmaT of nanocrystalline is 0.0053 nm and 0.0085 nm at the temperature of 78 and 300 K, respectively. The result indicates that the difference of local structure around Ga atoms between nanocrystalline and crystalline GaN occurs mainly at the Ga-Ga second nearest-neighbor coordination shell. The reason is explained as the local lattice distortion and unsaturated surface atoms existing in nanocrystalline GaN.
采用X射线吸收精细结构（XAFS）研究了六方纳米晶和晶体GaN中Ga原子在78 K和300 K温度下的局域结构。对于Ga - N的第一近邻配位壳层，平均键长R（0.194 nm）、配位数N（4.0）、热无序度σ（0.0052 nm）和静态无序度σS（0.0007 nm）与测量温度和晶体状态几乎无关。这表明Ga - N共价键更强，且Ga原子周围第一近邻的4个氮原子保持四面体结构（Td）。对于Ga - Ga的第二近邻配位壳层，其键长约为0.318 nm。然而，纳米晶GaN的σS（0.0057 nm）比晶体GaN的（0.001 nm）大0.0047 nm，纳米晶在78 K和300 K温度下的σT分别为0.0053 nm和0.0085 nm。结果表明，纳米晶和晶体GaN中Ga原子周围局域结构的差异主要出现在Ga - Ga第二近邻配位壳层。原因解释为纳米晶GaN中存在局部晶格畸变和不饱和表面原子。
