Imaging the surface dynamics of glasses and photoexcited molecules

在化学系化学测量和成像(CMI)计划和材料研究部陶瓷(CER)计划的支持下，伊利诺伊大学香槟分校的Martin Gruebele教授和他的团队将开发两种扫描隧道显微镜(STM)的新实现。第一个目标是检查表面上的量子点、碳纳米管和捕光树枝状大分子，这些表面专门设计用于研究在激光耦合到STM的影响下的单分子/纳米结构的吸收。研究人员将用金/铂、石墨化碳化硅以及石墨烯包裹的蓝宝石开发超平(1 Nm RMS)、透明(15%透射率)和导电(100千欧姆点接触电阻)表面。在这些表面上，他们将研究量子点对碳纳米管的单分子吸收和能量转移，以及在捕光合成有机树枝状大分子和衍生核酸中的吸收和能量转移。第二个目标是研究玻璃表面的动力学，将我们的曲目从简单的金属合金扩展到陶瓷，如二硼化钨，以及半金属(类金属)，如Sb或Se-Sb合金。在这些研究中，制作了表面玻璃动力学的延时电影，以与玻璃动力学模型进行比较。一个主要的检测目标是将当前的时间分辨率从几分钟提高到毫秒。更大的动态范围为动态玻璃理论提供了更严格的测试。纳米材料在微型化、降低功率需求、速度(例如在计算中)和便携性(例如在传感应用中)方面有很大的前景。人们已经对这些新材料进行了大量的工程研究，但在许多情况下，人们还没有很好地了解它们功能的物理基础。这一建议解决了对两个领域的基本物理理解。第一个要回答的问题是，一旦能量沉积在纳米材料中，来自自然光(例如人类工程光合作用)或人造光(例如激光激发)的能量如何在该材料中移动。如果研究人员要将传统微器件的尺寸和能耗缩小到更小的尺寸和能耗，那么在纳米尺度上将能量从一个地方转移到另一个地方，而不造成重大损失和对纳米材料的损害是至关重要的。拟议中的实验可以以近原子的分辨率成像能量在纳米结构中的位置，以及能量如何在该结构的各个相互关联的部分之间传播，甚至可以看到它如何从一个结构跳到另一个结构。第二个要回答的问题是眼镜是如何移动的。玻璃或过冷液体不像水晶一样有序，但它们看起来像水晶一样坚硬，在人类的时间尺度上，从几个小时到几年。尽管如此，它们的流动速度非常慢，它们如何流动的机制也鲜为人知。研究人员将制作具有原子分辨率的玻璃表面的延时电影，直接显示移动的内容、距离和频率。直接可视化是回答玻璃杯如何流动之谜的最直接的方式。原子水平和流动过程的不规则性实际上使玻璃可能比晶体更坚固，晶体在规则的晶体边界断裂。在微观层面上定制玻璃可能会让化学家和陶瓷工程师改善他们的材料性能，以制造出性能优异的隔热瓷砖或触敏玻璃等新材料。来自各个层次的学生都将参与这项拟议的研究。Gruebele教授还计划通过国际合作向越南学生教授化学入门课程。

With support from the Chemical Measurement and Imaging (CMI) Program in the Division of Chemistry, and the Ceramics (CER) Program in the Division of Materials Research, Professor Martin Gruebele at the University of Illinois at Urbana-Champaign and his group will develop two novel implementations of scanning tunneling microscopy (STM). The first aim is to examine quantum dots, carbon nanotubes, and light-harvesting dendrimers on surfaces specifically designed to study single molecule/nanostructure absorption under the influence of a laser coupled to the STM. The researchers will develop ultraflat (1 nm rms), transparent (15% transmission) and conductive (100 kiloOhm point contact resistance) surfaces out of gold/platinum, graphenized silicon carbide, as well as graphene-coated sapphire. On these surfaces, they will study single molecule absorption and energy transfer of quantum dots to carbon nanotubes, and within light-harvesting synthetic organic dendrimers and derivatized nucleic acids. The second aim is to study the dynamics on glass surfaces, expanding our repertoire from simple metal alloys to ceramics such as hafnium diboride, and semimetals (metalloids) such as antimony or selenium-antimony alloys. In these studies, time-lapse movies of glassy dynamics at the surface are produced for comparison with models of glass dynamics. A major instrumentation goal is to improve the current time resolution from minutes to milliseconds. The greater dynamic range affords more rigorous testing of dynamical glass theories.Nanomaterials have great promise in miniaturization, reduced power requirements, speed (e.g. in computing) and portability (e.g. in sensing applications). Much engineering work is done on these novel materials already, but in many cases the physical underpinnings of their function is not well understood. This proposal tackles the fundamental physical understanding of two areas. The first question to be answered is how energy from natural light (e.g. for human-engineered photosynthesis) or artifical light (e.g. laser excitation), once the energy has been deposited in a nanomaterial, moves around within that material. Moving energy from one place to another on a nanoscale without major losses and without damage to the nanomaterial is critical if the researchers are to scale conventional microdevices to smaller size and energy consumption. The proposed experiments can image with near-atomic resolution where the energy is located within a nanostructure, and how it spreads among various interconnected parts of that structure, or even how it hops from one structure to another. The second question to be answered is how glasses move. Glasses, or supercooled liquids, are not ordered like crystals, but they seem rigid like crystals on the 'human time scale' of hours to years. Nonetheless, they flow very slowly, and the mechanism of how they flow is poorly understood. The researchers will make time-lapse movies of glass surfaces with atomic resolution that show directly what's moving, how far, and how often. Direct visualization is the most direct way to answer the mystery of how glasses flow. The irregularity at the atomic level and flow processes actually make glasses potentially more robust than crystals, which fracture at regular crystal boundaries. Tailoring glasses at the microscopic level may allow chemists and ceramic engineers to improve their material properties to make new materials such as superior heat insulation tiles or touch-responsive glasses. Students from all levels will be involved in the proposed research. Professor Gruebele also plans to teach introductory chemistry to Vietnamese students through international collaborations.