Microscopy and Imaging Center, Texas A&M, College Station, TX 77843, USA.
Nanotechnology. 2013 Mar 22;24(11):115701. doi: 10.1088/0957-4484/24/11/115701. Epub 2013 Feb 28.
The influence of the high surface-to-volume ratio of ZnO nanomaterials, whose sizes are large enough to exclude the quantum effect, on electronic properties was investigated by spatially resolved valence electron energy loss spectroscopy. ZnO nanowires, nanoplates, and nanotubes with different sizes were fabricated and characterized. Both the reduced volume and the increased surface area of the large ZnO nanomaterials were found to be able to modify electronic properties significantly. Hence, a nanoplate and a nanotube with very small volumes show unique energy loss functions and dielectric functions different from those of bulk ZnO at all the probe points. On the other hand, a nanowire with a relatively large diameter (70 nm) has electronic properties similar to those of bulk ZnO at the center. However, they are dissimilar at the edge of the nanowire due to the component of surface parallel to the electron path and the reduced interaction volume. Moreover, some interband transitions shift positions and bulk plasmons change oscillator strength depending upon the size of the volume and the geometry of the surface. These empirical results demonstrate that semiconducting nanomaterials larger than the exciton Bohr radius can still behave differently from bulk materials due to the high ratio between surface area and volume.
采用空间分辨价电子能量损失谱研究了大尺寸 ZnO 纳米材料高的比表面积对电子性质的影响，这些大尺寸的 ZnO 纳米材料的尺寸大到足以排除量子效应。制备并表征了不同尺寸的 ZnO 纳米线、纳米板和纳米管。发现大 ZnO 纳米材料的体积减小和表面积增加都能显著改变电子性质。因此，与体 ZnO 相比，具有非常小体积的纳米板和纳米管在所有探测点都表现出独特的能量损失函数和介电函数。另一方面，直径相对较大的（70nm）纳米线在中心具有与体 ZnO 相似的电子性质。然而，由于与电子路径平行的表面分量和减小的相互作用体积，在纳米线的边缘它们是不同的。此外，一些带间跃迁的位置和体等离子体激元的振子强度取决于体积的大小和表面的几何形状而发生变化。这些经验结果表明，由于表面积与体积之间的高比例，大于激子玻尔半径的半导体纳米材料仍可能表现出与体材料不同的性质。
