Collaborative Research: OP: Transition Metal Alloys: Emergent Properties for Near-Infrared Hot-Carrier Optoelectronics

现代电子学是基于半导体中电子和空穴的电荷传输。具有多余能量的载流子（称为“热”载流子）的行为特别令人感兴趣。热载体材料具有广泛的应用范围，包括制氢、纳米治疗的局部加热和光电探测器。热载流子光电探测器具有可调性和超快的响应特性，具有广阔的应用前景。不幸的是，热载子材料的低效率使它们在设备中使用不现实。pi最近发现，贵金属和过渡金属合金有潜力有效地产生长寿命的热载流子，这是该领域的一个突破。该项目将研究过渡金属合金及其在光电器件中产生和有效传输高于平衡的“热”电子和空穴的能力。所提出的工作有望为近红外热载子光电探测器的效率提供变革性的进步。该项目的教育和推广将通过研究活动教授学生，并使不同年龄和背景的人了解合金、金属光学和光电子学的概念。研究团队将包括研究生和本科生在团队的实验室进行这项研究，并与当地的初中和高中合作，让6年级到12年级的学生参与动手科学工作。来自巴吞鲁日当地高中的高中生将参加一年一度的夏季实验室实习项目，费城地区的中学生将通过建造、测试和比赛鞋盒大小的太阳能汽车来参加太阳能比赛。该项目由材料研究部的电子与光子材料（EPM）和金属与金属纳米结构（MMN）项目共同资助。金属热载流子的产生是近红外光电器件中光子转化为电荷的一种很有前途的途径。热载流子光电器件提供带隙以下的电荷产生，超快的响应时间，以及光谱和偏振控制。这些特征有望导致光电子学的变革性进步。然而，目前的热载流子器件由于载流子产生和收集速率差而表现出低效率。光激发金属可以通过带间、带内和等离子体辅助朗道阻尼产生热载流子。虽然贵金属已被广泛探索通过带间跃迁产生热载流子，但近红外光子没有足够的能量来克服它们的带间能量阈值。带内和等离子体驱动的热载流子产生可以发生在这些较低的激发能，但只有在额外的动量提供。研究小组假设过渡金属合金中的能带杂化将产生新特性和近红外热载子生成的新途径。该团队最近报告说，当光激发1550 nm时，具有近红外可达带间跃迁的Au50Pd50合金显示出比纯Au多20倍的0.8 eV热孔，比纯Pd长3倍的寿命。团队将在这一令人兴奋的结果的基础上，通过追求以下具体目标：1)。使用第一性原理模拟来确定在近红外热载流子生成方面表现优异的候选过渡金属合金，2)。通过热共蒸发沉积合金薄膜，并使用基于共振同步加速器的光电发射来验证预测的电子性质，3)。利用瞬态吸收光谱和4)确定合金化对载流子寿命的影响。利用合金吸收剂制造带隙下光导体，并对其电响应进行表征。该研究团队在合金理论、光发射、金属薄膜生长、器件制造和超快光谱方面的专业知识非常适合实现这些目标。过渡金属合金为合成新的热载体材料提供了一个令人兴奋的调色板，该团队很好地研究了它们的结构-功能关系。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。

Modern electronics are based on charge transport by electrons and holes in semiconductors. The behavior of carriers with excess energy, called “hot” carriers, is of particular interest. Hot-carrier materials have a broad range of applications including hydrogen production, local heating for nanotherapeutics, and photodetectors. Hot-carrier photodetectors show great promise due to their tunability and ultrafast response. Unfortunately, the low efficiencies of hot carrier materials have made them impractical for use in devices. The PIs have recently discovered that alloys of noble metals and transition metals have the potential to efficiently generate long-lived hot carriers, a breakthrough in the field. This project will investigate transition metal alloys and their ability to generate and efficiently transport above-equilibrium “hot” electrons and holes in an optoelectronic devices. The proposed work is expected to provide transformational advances in the efficiency of near-infrared hot-carrier photodetectors. Education and outreach for this project will teach students through research activities and will expose people of diverse ages and backgrounds to the concepts of alloying, metal-optics, and optoelectronics. The research team will involve graduate and undergraduate students to perform this research in the team's laboratories and partner with local middle and high schools to involve 6th through 12th-grade students in hands-on scientific work. High school students from local Baton Rouge high schools will participate in annual summer in-lab residency programs and middle-school students in the Philadelphia area will participate in a solar race by building, testing, and racing shoebox-sized solar powered cars. This project is jointly funded by the Electronic and Photonic Materials (EPM) and Metals and Metallic Nanostructures (MMN) programs of the Division of Materials Research.Hot-carrier generation in metals is a promising route to convert photons into electrical charges for near-infrared (NIR) optoelectronic devices. Hot-carrier optoelectronic devices offer below-bandgap charge generation, ultrafast response times, and spectral and polarization control. These features are expected to result in transformative advances in optoelectronics. However, current hot-carrier devices exhibit low efficiencies due to poor carrier generation and collection rates. Photoexcited metals can generate hot carriers via interband, intraband, and plasmon-assisted Landau damping. While noble metals have been extensively explored for generating hot carriers via interband transitions, NIR photons do not have enough energy to overcome their interband energy threshold. Intraband- and plasmon-driven hot-carrier generation can occur at these lower excitation energies, but only if additional momentum is provided. The research team hypothesizes that band hybridization in transition metal alloys will result in emergent properties and new pathways for NIR hot-carrier generation. The team recently reported that, when photoexcited at 1550 nm, an Au50Pd50 alloy having NIR accessible interband transitions exhibited 20-fold more 0.8 eV hot holes than pure Au and 3-times longer lifetime than pure Pd. The team will build on this exciting result by pursuing the following specific aims: 1). Use first-principles simulations to determine candidate transition metal alloys that excel at hot-carrier generation in the NIR, 2). Deposit alloy films via thermal co-evaporation and use resonant synchrotron-based photoemission to verify the predicted electronic properties, 3). Determine the effect alloying has on carrier lifetime using transient absorption spectroscopy and 4). Fabricate below-bandgap photoconductors using alloy absorbers and characterize their electrical response. The research team is well suited to pursue these aims with expertise in alloy theory, photoemission, metal film growth, device fabrication, and ultrafast spectroscopy. Transition metal alloys offer an exciting palette for synthesizing new hot-carrier materials, and the team is well-positioned to investigate their structure-function relationship.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.