Direct Interfacial Charge Separation in Plasmonic Heterostructures Revealed by Single-Particle Spectroscopy

非技术描述该项目正在开发方法，以了解比头发宽度小1000倍的金属纳米颗粒如何在接触金属氧化物半导体时捕获光并将其转化为可用能量。虽然金属纳米颗粒有效地吸收光，但大部分吸收的能量被转化为热。另一方面，金属氧化物半导体存储光能的时间比金属长得多，这使得它们在光检测等应用中很有用。然而，金属氧化物半导体不会像在特定波长上那样强烈或经常地吸收，而金属纳米颗粒可以设计成与任何颜色的光强烈相互作用。该项目通过将金属纳米颗粒的高吸收率与金属氧化物半导体中吸收的光能的更长寿命相结合，克服了这些限制。首席研究人员使用的技术使他能够研究金属纳米颗粒吸收的光能是如何转移到邻近的金属氧化物半导体层的。这些实验是一次针对一个纳米颗粒进行的，以解决材料合成产生的异质性。此外，PI继续长期参与莱斯大学的公民科学家计划和教师研究经验，使他能够教育K-12学生纳米技术，激励他们追求科学事业，并为教师提供经验，反过来帮助学生在这些追求。技术说明这个项目的目标是了解和最大限度地利用等离子激元激发后的直接电荷转移，使金属纳米粒子和邻近的金属氧化物半导体之间的等离子激元衰变为电荷分离态。首席研究员将通过解决下列目标来实现这一目标：1)设计和制备等离子体金属-半导体异质结构，并通过改变均匀的等离子激元线宽，建立与界面诱导的等离子体激元衰变的关联；2)利用单粒子超快光谱定量确定电荷注入等离子体纳米结构周围的半导体，并与等离子体激元衰减获得的效率相关联；3)应用斯托克斯和反斯托克斯发射光谱，独立跟踪单光子和多光子激发条件下通过发射猝灭的界面电荷转移。这些研究将阐明等离子体异质结中界面电荷转移的机制，以及决定效率的基本材料参数，重点是由等离子体共振和相对能带排列(包括肖特基势垒高度)决定的过剩能量。由于等离子体纳米粒子的大小和局部环境的异质性，如果没有单粒子技术，就不可能获得如此详细的机制信息。拟议的研究可能会对开发基于等离子体金属-半导体异质结的高效光伏器件产生革命性的影响，利用宽波长灵敏度、大吸收截面和长热载流子寿命。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical DescriptionThis project is developing methods to understand how metal nanoparticles, 1000 times smaller than the width of a hair, capture and convert light into usable energy when contacting metal oxide semiconductors. Although metal nanoparticles efficiently absorb light, most of the absorbed energy is converted into heat. On the other hand, metal oxide semiconductors can store light energy for much longer times than metals making them useful for applications such as photodetection. However, metal oxide semiconductors do not absorb as strongly or often only at specific wavelengths, while metal nanoparticle can be designed to strongly interact with light of any color. This project overcomes these limitations by combining the high absorption of metal nanoparticles with the longer lifetimes of the absorbed light energy in metal oxide semiconductors. The principal investigator uses techniques that allow him to study how the light energy absorbed by a metal nanoparticle is transferred to an adjacent metal oxide semiconductor layer. These experiments are carried out for one nanoparticle at a time to resolve heterogeneities that arise from materials synthesis. In addition, the PI is continuing his longstanding participation in Rice University’s Civic Scientist Program and Research Experience for Teachers, allowing him to educate K-12 students about nanotechnology and inspire them to pursue scientific careers as well as to provide teachers with experience to in turn help students in those pursuits.Technical DescriptionThe goal of this project is to understand and maximize plasmon decay into charge separated states between a metal nanoparticle and an adjacent metal oxide semiconductor via direct charge transfer following plasmon excitation. The principal investigator will accomplish this goal by addressing the following objectives: 1) Design and fabricate plasmonic metal–semiconductor heterostructures and establish a correlation with interface induced plasmon decay via changes to the homogeneous plasmon linewidth; 2) Quantitatively determine charge injection into semiconductors surrounding plasmonic nanostructures using single particle ultrafast spectroscopy and correlate with efficiencies obtained from plasmon damping; 3) Apply Stokes and anti-Stokes emission spectroscopy to independently follow interfacial charge transfer through emission quenching under both one- and multi-photon excitation conditions. These proposed studies will elucidate the mechanism of interfacial charge transfer in plasmonic heterostructures and the underlying material parameters that determine efficiencies with a focus on excess energy as determined by the plasmon resonance and the relative band alignment including Schottky barrier height. Such detailed mechanistic information would be impossible to obtain without single-particle techniques due to the heterogeneity of plasmonic nanoparticle sizes and local environments. The proposed studies will potentially have a transformative impact on developing efficient photovoltaic devices based on plasmonic metal-semiconductor heterostructures taking advantage of a wide wavelength sensitivity, large absorption cross section, and long hot carrier lifetime.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.