Spectroscopy of Two Dimensional Molecular Carbon

哈佛大学的Eric Heller获得了NSF化学部化学理论、模型和计算方法项目的奖项支持，以更好地了解碳材料，特别是石墨烯的惊人潜力。 石墨烯是一种由碳原子组成的蜂窝状结构，只有一个原子厚。 它既有固体的特性，又有分子的特性。 涉及石墨烯作为基本成分的有用设备和应用的列表已经很长，例如晶体管，光电探测器，太阳能电池和电极。 两层可以堆叠起来得到超导体，即没有电阻的材料。 石墨烯片对所有原子和分子都是不渗透的。 Heller小组对石墨烯碳晶格及其周围的导电电子在与光相互作用之前，期间和之后的行为进行了新的理论理解，包括持续时间仅为飞秒的明亮脉冲。 用光探测石墨烯是揭示其秘密的最有力的实验工具，但实验必须得到适当的解释。 Heller小组试图使用其开发的新理论和计算方法来揭示石墨烯的基本量子特性。 海勒小组正在修改对石墨烯中光吸收后快速电子弛豫的理解，这一新的理解与开发基于石墨烯和相关碳基材料的实用设备有关。Heller小组正在对石墨烯和相关碳材料中的快速电子过程进行强烈修订的理解，基于适当地纳入某些重要但以前被忽视的间接（声子产生或破坏）电子光诱导跃迁。 关键是恢复凝聚态光谱学的全部物理学，包括电子跃迁矩的声子坐标依赖性。 跃迁矩以前普遍被认为是恒定的，与声子坐标无关，但海勒和他的同事已经表明，忽略这种坐标依赖性牺牲了正确的物理理解。 在首次将完整的Kramers-Heisenberg-Dirac拉曼理论引入石墨烯光谱学之后，由于更全面和更正确的理解，许多机会打开了。 Heller小组正在探索这些新的含义，包括那些与实验相关的，并建议实验来测试他们的理论预测。他们还在探索玻恩-奥本海默近似在这些关键间接跃迁中的作用。 该小组正在探索间接跃迁的新理解的广泛意义，这是包括硅太阳能电池在内的许多设备的关键，在整个凝聚态物质光谱学中。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

Eric Heller of Harvard University is supported by an award from the Chemical Theory, Models and Computational Methods program in the NSF Division of Chemistry, to better understand the amazing potential of carbon materials, especially graphene. Graphene is an extended honeycomb sheet of carbon atoms only a single atom thick. It has both solid state and molecular characteristics. The list of useful devices and applications involving graphene as an essential component is already very long, for example transistors, photodetectors, solar cells, and electrodes. Two layers can be stacked to give a superconductor, i.e. a material with no electrical resistance. Graphene sheets are impervious to all atoms and molecules. The Heller group develops new theoretical understanding of what the graphene carbon lattice and the conductive electrons surrounding it are doing before, during, and after interaction with light, including bright pulses only femtoseconds in duration. Probing graphene with light is the most powerful experimental tool for revealing its secrets, but the experiments must be properly interpreted. The Heller group seeks to reveal the fundamental quantum properties of graphene using new theoretical and computational methods that it has developed. The Heller group is revising the understanding of fast electron relaxation following light absorption in graphene This new understanding is relevant for developing practical devices based on graphene and related carbon-based materials. The Heller group is developing a strongly revised understanding of fast electron processes in graphene and related carbon materials, based on properly incorporating certain important but previously neglected indirect (phonon producing or destroying) electronic light induced transitions. The key has been to restore the full physics of condensed matter spectroscopy, including the phonon coordinate dependence of the electronic transition moments. The transition moments had previously universally been taken to be constant, independent of phonon coordinate, but Heller and coworkers has shown that neglecting this coordinate dependence sacrifices the correct physical understanding. After importing the full Kramers-Heisenberg-Dirac Raman theory to graphene spectroscopy for the first time, many opportunities open up because of a fuller and more correct understanding. The Heller group is exploring these new implications including those which have experimental relevance and suggesting experiments to test their theoretical predictions. They are also probing the role of the Born-Oppenheimer approximation in these key indirect transitions. The group is exploring wide implications of this new understanding of indirect transitions, which are key to many devices including silicon solar cells, throughout condensed matter spectroscopy.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.