Surface Science of Semiconductor Nanocrystals

半导体纳米晶体是一种新型材料，具有广泛的光学、电学和热力学性质。目前，人们对纳米晶体的内部组成和结构已经了解得很多，但对它们的界面却知之甚少。这项工作的目的是发展控制半导体纳米晶体界面的组成和结构的能力。在理解量子约束的物理学和评估这类材料的技术前景之前，这是必要的。主要使用两种工具：1)光电子能谱及其相关技术；2)红外反射吸收光谱。使用普通的x射线源，将有可能常规识别和潜在地操纵纳米晶体表面物种的化学特性。有了先进的光源同步加速器，将有可能以更高的分辨率和可变光子能量进行光电发射实验。这些实验的目标是测量平均键长，以及内部和表面电子态的密度，包括已占据和未占据的电子态。红外反射吸收光谱学将用于识别存在的化学物质及其键合的性质。如果纳米晶体在化学沉积过程中可以定向，那么取向信息也可以被提取出来。半导体纳米晶体是一种新型材料，具有多种尺寸相关的光学、电学和热力学性质。在科学和技术上限制纳米晶体研究的因素是对纳米晶体表面的认识和控制不足。在光谱学中，与界面相关的阱能级强烈影响吸收和发射线宽和寿命。在电学研究中，所有载流子都必须通过界面。在热力学研究中，50%以上的原子在表面这一事实对相图有很大的影响。目前，人们对纳米晶体的内部组成和结构已经了解得很多，但对它们的界面却知之甚少。这项工作的目标是构建纳米晶体的“表面科学”，就像平面晶体表面一样。

Abstract 9505302 Alivisatos Semiconductor nanocrystals are a new type of material exhibiting a wide range of size dependent optical, electrical, and thermodynamic properties. A great deal is now known about the interior composition and structure of nanocrystals, but relatively little is known about their interfaces. The aim of this work is to develop the ability to control the composition and structure of semiconductor nanocrystal interfaces. This is necessary before the physics of quantum confinement can be understood and before the technological promise of this class of materials can be assessed. Two main tools will be used: 1) photoelectron spectroscopy and related techniques, and 2) infrared reflection-absorption spectroscopy. Using an ordinary X-ray source, it will be possible to routinely identify and potentially to manipulate the chemical identity of the nanocrystal surface species. With the Advanced Light Source synchrotron, it will be possible to perform photoemission experiments at higher resolution and with variable photon energy. These experiments will be targeted at measuring average bond lengths, and the density of interior and surface electronic states, both occupied and unoccupied. Infrared reflection-absorption spectroscopy will be used to identify the chemical species present, and the nature of their bonding. If the nanocrystals can be oriented in the chemical deposition process, then orientational information can also be extracted. %%% Semiconductor nanocrystals are a new type of material exhibiting a wide range of size dependent optical, electrical, and thermodynamic properties. The limiting factor scientifically and technologically in the area of nanocrystals is inadequate understanding and control of the nanocrystal surface. In optical spectroscopy, trap levels associated with the interface strongly influence absorption and emission linewidths and lifetimes. In electrical studies, all carriers must pass through the interface. In thermo dynamic studies, the fact that order 50% of the atoms are at the surface strongly influences the phase diagrams. A great deal is now known about the interior composition and structure of nanocrystals, but relatively little is known about their interfaces. The objective of this work is to construct a "surface science" of nanocrystals, just as there is one for plane crystal surfaces.