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

现代电子学基于半导体中的电子和空穴的电荷传输。具有过剩能量的载流子（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，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由于其可调谐性和超快响应而显示出巨大的前景。不幸的是，热载流子材料的低效率使得它们在器件中的使用不切实际。PI最近发现，贵金属和过渡金属的合金有可能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。预计这项工作将为近红外热载流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，并将使不同年龄和背景的人接触合金，金属光学和光电子学的概念。研究团队将让研究生和本科生在团队的实验室进行这项研究，并与当地初中和高中合作，让6至12年级的学生参与实际科学工作。来自当地巴吞鲁日高中的高中生将参加一年一度的夏季实验室居住计划，费城地区的中学生将参加太阳能比赛，建造、测试和比赛鞋盒大小的太阳能汽车。该项目由材料研究部的电子和光子材料（Electronic and Photonic Materials，EMPs）和金属和金属纳米结构（Metals and Metallic Nanostructures，MMN）项目共同资助。金属中的热载流子生成是一种有前途的将光子转化为近红外（NIR）光电器件电荷的途径。热载流子光电器件提供带隙以下电荷产生、超快响应时间以及光谱和偏振控制。这些功能预计将导致光电子学的变革性进步。然而，由于差的载流子生成和收集速率，当前的热载流子器件表现出低效率。光激发金属可以通过带间、带内和等离子体辅助的朗道阻尼产生热载流子。虽然贵金属已经被广泛探索用于通过带间跃迁产生热载流子，但NIR光子没有足够的能量来克服它们的带间能量阈值。带内和等离子体激元驱动的热载流子产生可以发生在这些较低的激发能量，但只有当提供额外的动量。研究小组假设，过渡金属合金中的能带杂化将导致NIR热载流子产生的新特性和新途径。该团队最近报告说，当在1550 nm光激发时，具有NIR可访问带间跃迁的Au50 Pd 50合金显示出比纯Au多20倍的0.8 eV热空穴，比纯Pd长3倍的寿命。该团队将在这一令人兴奋的结果的基础上，追求以下具体目标：1）。使用第一原理模拟来确定在NIR中擅长热载流子生成的候选过渡金属合金，2）。通过热共蒸发沉积存款合金膜，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）。使用瞬态吸收光谱法确定合金化对载流子寿命的影响; 4）.利用合金吸收体制作带隙以下的光电导体并表征其电响应。该研究团队非常适合在合金理论，光电发射，金属薄膜生长，器件制造和超快光谱学方面的专业知识来实现这些目标。过渡金属合金为合成新的热载体材料提供了令人兴奋的调色板，该团队有能力研究其结构-功能关系。该奖项反映了NSF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.