Single Particle Spectroscopy and Microscopy of Doped Colloidal Semiconductor Nanocrystals

半导体纳米晶体是很小的晶体颗粒，只包含数百到数千个原子。在这些小尺寸上，新的光学和电子特性出现了，这些特性可以通过改变粒子的大小和形状来调节。这些特性也可以通过将晶格中的几个原子与另一种元素或掺杂剂的原子交换来控制。精确控制这些掺杂原子在纳米晶体中的数量和位置是一项挑战。在化学学部大分子、超分子和纳米化学项目的支持下，罗切斯特大学的Todd Krauss教授和他的学生正在使用复杂的显微镜方法将单个纳米晶体中掺杂剂的数量和位置与其发光和电子特性联系起来。他们的发现可能对设计用于从太阳能转换到量子信息系统等新兴技术的纳米晶体具有重要意义。该项目还在开发和应用先进的实验物理化学方法方面培养下一代科学家。该团队正在向公众介绍该项目研究，并通过在罗切斯特博物馆、科学中心和其他公共场所的推广工作，培养人们对科学发现的热情。该项目正在发展对纳米晶体掺杂和掺杂机制的详细了解，以合成具有改进化学和光物理性质的纳米晶体和纳米晶体组件。银离子（Ag+）掺杂的硒化镉（CdSe）纳米晶体和纳米薄片的研究揭示了掺杂过程中发生的特定化学机制。最先进的静电力显微镜测量与同时测量单个纳米晶体的光致发光相结合，揭示了杂质原子如何改变固有纳米颗粒的电子和光学性质。该项目还在研究碲化锡（SnTe）纳米晶体的光学特性。这种新兴的直接带隙材料可以作为红外技术中现有材料的环保替代品。然而，SnTe激发态的基本性质（如电子、激子或等离子体）仍然未知。稳态和时间分辨光谱与高分辨率电子显微镜结合使用，将光物理观测与材料成分相关联，以形成SnTe激发态的详细图像。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Semiconductor nanocrystals are small, crystalline particles that contain only hundreds to thousands of atoms. At these small sizes, new optical and electronic properties emerge, which can be adjusted by changing the particle's size and shape. These properties can also be manipulated by swapping just a few atoms in the crystal lattice with atoms of another element, or dopant. The precise control over the number and placement of these dopant atoms within a nanocrystal is challenging. With support from the Macromolecular, Supramolecular and Nanochemistry program in the Chemistry Division, Professor Todd Krauss and his students at the University of Rochester are using sophisticated microscopy methods to correlate the number and position of dopants in a single nanocrystal with their luminescent and electronic properties. Their discoveries could have important implications for designing nanocrystals used in emerging technologies that range from solar energy conversion to quantum information systems. The project is also training the next generation of scientists in the development and application of advanced experimental physical chemistry methods. The team is introducing the project research to the public and fostering an enthusiasm for scientific discovery through outreach efforts at the Rochester Museum and Science Center and other public venues. The project is developing the detailed understanding of nanocrystal doping and doping mechanisms needed to synthesize nanocrystals and nanocrystal assemblies with improved chemical and photophysical properties. Studies of silver cation (Ag+)-doped cadmium selenide (CdSe) nanocrystals and nanoplatelets are uncovering the specific chemical mechanisms occurring during the doping process. State-of-the-art electrostatic force microscopy measurements in combination with simultaneous measurements of photoluminescence from a single nanocrystal reveal how impurity atoms change the electronic and optical properties of the intrinsic nanoparticle. The project is also investigating the optical properties of tin telluride (SnTe) nanocrystals. This emerging direct-bandgap material could be used as an environmentally friendly alternative to current materials in infrared-based technologies. However, the basic properties of the SnTe excited state (e.g. electronic, excitonic, or plasmonic) remain unknown. Steady-state and time-resolved spectroscopies are used in conjunction with high-resolution electron microscopies to correlate photophysical observations with material composition to develop a detailed picture of the SnTe excited state.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.