Emergent Properties of Noble-Transition Metal Alloys—Near-Infrared Interband Hot-Carrier Generation for Ultrafast Optoelectronic Devices

Noble-transition metal alloys are a promising class of materials for interband-driven hot hole generation with NIR light.¹ NIR hot-carrier generation in pure, noble metals suffers from insufficient energy to exceed the interband energy threshold (IET) (e.g.,&gt; 2 eV), and in pure transition metals, rapid hot-carrier thermalization. Band hybridization in select noble-transition metal alloys can overcome these issues, yielding emergent properties that facilitate tuning the hot-carrier distribution and lifetime.<br/><br/>We deposit disordered Cu_xPd_1-x alloy thin films under non-equilibrium conditions and investigate their stoichiometry-dependent optical, structural, electronic, and transient near-infrared absorption properties.² We show experimentally through ultraviolet photoelectron spectroscopy and computationally through the projected density of states calculations that strong hybridization between the Cu 3d and Pd 4d bands exists in the alloy films. Unlike the Au 5d band, the Cu 3d band does not exhibit strong spin-orbit coupling. Therefore, we observe the formation of a common band between the full Cu 3d and Pd 4d bands. This strong d-band hybridization in the alloy films drives emergent behavior across various measurement techniques.<br/><br/>Time-resolved terahertz spectroscopy with near-infrared (e.g., 1550 nm) excitation displays composition tunable electron dynamics. We posit that the negative peak in ΔT/T below 2 ps from dilute Pd alloys is due to non-thermalized hot-carrier generation and field-driven electron emission. On the other hand, Pd-rich alloys exhibit an increase in ΔT/T due to thermalization effects upon ultrafast NIR photoexcitation. Cu_xPd_1-x alloys in the dilute Pd regime may be a promising material for future ultrafast NIR optoelectronic devices.<br/><br/>1. Sara KF Stofela, Orhan Kizilkaya, Benjamin T Diroll, Tiago R Leite, Mohammad M Taheri, Daniel E Willis, Jason B Baxter, William A Shelton, Phillip T Sprunger, Kevin M McPeak, “A Noble-Transition Alloy Excels at Hot-Carrier Generation in the Near Infrared,” <i>Advanced Materials</i> 32 (23), 1906478 (2020)<br/><br/>2. Orhan Kizilkaya, Gregory Manoukian, Sergi Lendinez, Luis D. B. Manuel, Tiago R. Leite, Karunya S. Shirali, William A. Shelton, Phillip T. Sprunger, Jason B. Baxter, Kevin M. McPeak “Emergent Properties from CuPd Alloy Films under Near-Infrared Excitation,” <i>J Chem Phys</i> (Under Review)