Elastic properties of CdSe/Zns core/shell nanorods and nanowires

由于尺寸的减小，纳米线或纳米棒的物理性质与相应的块状材料有质的不同。我们计划研究几种纳米结构在可见光照射和加热下的热性能。纳米结构的高表面体积比导致平衡温度，该温度主要由周围气体的热导率给出，而不是像文献中通常假设的那样由沿着纳米线的热传导给出。例如，硅纳米线可以用作气体型或气体压力传感器，因为周围气体的热导率取决于其分子量和压力。众所周知，对于大多数材料来说，声子频率的温度依赖关系可以通过拉曼光谱来确定纳米结构的温度。两种极限情况特别有趣：在真空中，沿纳米线的辐射和热传导主导了散热。其次，当纳米结构浸入超流氦中时，纳米结构与液氦界面处的热阻（Kapitza阻力）限制了纳米结构的冷却。在具有核心和外壳材料的纳米结构中——纳米棒的一个特别重要的应用——有一个额外的界面，有助于热阻。我们计划通过si纳米线和CdSe纳米棒的Kapitza电阻来研究界面，在该区域，它成为散热的限制物理效应。尺寸量子化对纳米线降维材料的电子态和振动态有重要影响，需要在分析中加以考虑。我们将用拉曼散射和发光技术研究硅纳米线和CdSe纳米棒的量子化。实验结果与分子动力学的热性质计算结果以及电子态和振动态的从头计算结果进行了比较。

The physical properties of nanowires or nanorods differ qualitatively from the corresponding bulk materials due to the reduced dimension. We plan to investigate the thermal properties of several nanostructures when illuminated and heated with visible light. The high surfaceto- volume ratio of nanostructures leads to an equilibrium temperature which is given mostly by the thermal conductivity of the surrounding gas and not by thermal conduction along the nanowire as often assumed in the literature. Si nanowires, e.g., can be used as gas-type or gaspressure sensors, since the thermal conductivity of a surrounding gas depends on its molecular weight and pressure. From the ¿ for most materials well-known ¿ temperature dependence of the phonon frequency the temperature of a nanostructure can be determined optically via Raman spectroscopy.Two limiting cases are particularly interesting: In vacuum the heat dissipation is dominated by radiation and thermal conduction along a nanowire. And secondly, when immersed in superfluid helium the thermal resistance (Kapitza resistance) at the interface of a nanostructure to liquid helium limits the cooling of the nanostructure. In nanostructures with core and shell materials ¿ a particularly important application of nanorods ¿ there is an additional interface which contributes to the thermal resistance. We plan to study the interface via the Kapitza resistance of Si-nanowires and CdSe nanorods in a region where it becomes the limiting physical effect for heat dissipation.Size quantization has an important influence on the electronic and vibrational states of a material in reduced dimension of nanowires which needs to be taken into account in the analysis. We will study with Raman scattering and luminescence the quantization in Si nanowires and CdSe nanorods. The experimental results are compared to results of molecular dynamics of the thermal properties and ab initio computations of the electronic and vibrational states.