Structural investigation of nanostructures by Extend X-ray Absorption Fine Structure (EXAFS) and Diffraction Anomalous Fine structure (DAFS)

InGaN/GaN半导体纳米结构由于其作为蓝色激光二极管（DVD、HD打印）、UV光发射器（生物恐怖主义检测、水净化）、用于白色光产生（节能照明）和电子器件（在基站、国防和空间卫星中）的应用而具有吸引力。InGaN/GaN量子点与CdSe/ZnSe量子点一起是用于绿色光谱区的激光二极管的有希望的材料。半导体纳米结构（量子威尔斯、线和点）的晶格中原子的化学组成和排序是实质上影响其电学和光学性能的重要参数。因此，重要的是找到一种方法，该方法提供了这种半导体纳米结构的化学组成和局部结构的全面知识。该项目涉及X射线吸收近边结构（XANES）、扩展X射线吸收精细结构（EXAFS）和衍射异常精细结构（DAFS）等方法。由于它们的原子选择性，它可以确定量子点中的原子顺序，从而确定化学成分及其梯度;吸收边的化学位移，即键长和应变。与透射电子显微镜（TEM）相比，所提出的方法是非破坏性的。他们还探测埋在样品表面下的物体，这对于研究过度生长的纳米结构至关重要，并且使用扫描隧道显微镜（STM）无法获得。由于同步辐射（SR）及其优异的特性，如高亮度、宽能谱（同步辐射以宽范围的能量发射，允许产生任何能量的光束），可以获得使用标准方法（TEM、STM、X射线衍射）无法获得的纳米结构信息。

InGaN/GaN semiconductors nanostructure are attractive due to their applications as blue laser diodes (DVD, HD printing), UV-light emitters (detection of bioterrorism, water purification), for white light generation (energy saving illumination) and electronic devices (in base stations, defense and space sattelites). InGaN/GaN quantum dots are together with CdSe/ZnSe dots promising materials for laser diodes in the green spectral region. The chemical compositions and ordering of atoms in crystal lattices of semiconductor nanostructures (quantum wells, wires and dots) are important parameters influencing substantially their electrical and optical performance. Therefore it is important to find a method that provides a comprehensive knowledge of the chemical compositions and of the local structure of such semiconductor nanostructures. The project deals with methods such as X-ray Absorption Near Edge Structure (XANES), Extended X-ray Absorption Fine Structure (EXAFS) and Diffraction Anomalous Fine Structure (DAFS). Due to their atomic selectivity it can determine in quantum dots: the atomic ordering thus the chemical compositions and its gradient; the chemical shift of the absorption edge that is bond length and strain. The proposed methods are non-destructive in contrast to the Transmission Electron Microscopy (TEM). They probe also objects buried below the sample surface what it is essential for investigation of overgrown nanostructures and impossible to gain using Scanning Tunneling Microscopy (STM). Due to the access to the synchrotron radiation (SR) and its excellent properties such as high brightness, wide energy spectrum (synchrotron radiation is emitted with a wide range of energies, allowing a beam of any energy to be produced) it is possible to achieve information about nanostructures that cannot be obtained using standard methods (TEM, STM, X-ray Diffraction).