Multi-scale time-resolved electron diffraction: A case study in moiré materials

Duncan, Cameron; Kaemingk, M.; Li, W.H.; Andorf, Matthew; Bartnik, Adam; Galdi, Alice; Gordon, Mollie; Pennington, Christopher; Bazarov, Ivan; Zeng, Hong; Liu, F.; Luo, Duan; Sood, Aditya; Lindenberg, Aaron M.; Täte, Mark W.; Muller, David A.; Thom-Levy, Julia; Grüner, Sol M.; Maxson, Jared

doi:10.1016/j.ultramic.2023.113771

Cited by 4 publications

(1 citation statement)

References 55 publications

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“…Upon resonant excitation of the MoSe 2 layer, the MSD of both layers rises immediately. At later times, the MSD falls due to heat dissipation into the underlying Si 3 N 4 substrate and surrounding Si substrate, which act as heat sinks ( 48 ). The overall time-dependent MSD can be fitted correspondingly with a fast single-exponential rise and a multiexponential decay (convolved with the instrument response function).…”

Section: Resultsmentioning

confidence: 99%

Hidden phonon highways promote photoinduced interlayer energy transfer in twisted transition metal dichalcogenide heterostructures

Johnson,

Georgaras,

Shen

et al. 2024

Sci. Adv.

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Vertically stacked van der Waals (vdW) heterostructures exhibit unique electronic, optical, and thermal properties that can be manipulated by twist-angle engineering. However, the weak phononic coupling at a bilayer interface imposes a fundamental thermal bottleneck for future two-dimensional devices. Using ultrafast electron diffraction, we directly investigated photoinduced nonequilibrium phonon dynamics in MoS 2 /WS 2 at 4° twist angle and WSe 2 /MoSe 2 heterobilayers with twist angles of 7°, 16°, and 25°. We identified an interlayer heat transfer channel with a characteristic timescale of ~20 picoseconds, about one order of magnitude faster than molecular dynamics simulations assuming initial intralayer thermalization. Atomistic calculations involving phonon-phonon scattering suggest that this process originates from the nonthermal phonon population following the initial interlayer charge transfer and scattering. Our findings present an avenue for thermal management in vdW heterostructures by tailoring nonequilibrium phonon populations.

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Section: Resultsmentioning

confidence: 99%

Hidden phonon highways promote photoinduced interlayer energy transfer in twisted transition metal dichalcogenide heterostructures

Johnson,

Georgaras,

Shen

et al. 2024

Sci. Adv.

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Stability and Electronic Properties of K‐Sb and Na‐Sb Binary Crystals from High‐Throughput Ab Initio Calculations

Schier,

Guo,

Saßnick

et al. 2024

Advcd Theory and Sims

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The study of the fundamental properties of alkali antimonide photocathodes for particle accelerators is currently hindered by the limited purity of the samples. First‐principles studies can effectively complement experiments to gain insight into the stability and the electronic structure of these compounds. In this high‐throughput analysis based on density‐functional theory (DFT), two families of binary crystals with K‐Sb and Na‐Sb compositions expected to form during evaporation of multi‐alkali antimonide photocathodes are investigated. Starting from an initial pool of structures mined from existing computational databases, automatized routines included in the in‐house developed library aim2dat are employed to determine the stability and the electronic properties of the aforementioned systems. By analyzing the formation energy, the structures are ranked in a convex hull retaining the information of their crystalline arrangement. Next, the band structure and the projected density of states of selected stable compounds are analyzed. Adopting the r2SCAN functional for the DFT calculations, reliable estimates of the character and size of the bandgaps are obtained and discussed in relation to the relative alkali content in the crystals. These results provide useful indications to predict and characterize binary phases forming during the growth of multi‐alkali antimonide photocathodes.

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High-repetition-rate ultrafast electron diffraction with direct electron detection

Rodrigues Diaz,

Mero,

Amini

2024

Structural Dynamics

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Ultrafast electron diffraction (UED) instruments typically operate at kHz or lower repetition rates and rely on indirect detection of electrons. However, these experiments encounter limitations because they are required to use electron beams containing a relatively large number of electrons (≫100 electrons/pulse), leading to severe space-charge effects. Consequently, electron pulses with long durations and large transverse diameters are used to interrogate the sample. Here, we introduce a novel UED instrument operating at a high repetition rate and employing direct electron detection. We operate significantly below the severe space-charge regime by using electron beams containing 1–140 electrons per pulse at 30 kHz. We demonstrate the ability to detect time-resolved signals from thin film solid samples with a difference contrast signal, ΔI/I0, and an instrument response function as low as 10−5 and 184-fs (FWHM), respectively, without temporal compression. Overall, our findings underscore the importance of increasing the repetition rate of UED experiments and adopting a direct electron detection scheme, which will be particularly impactful for gas-phase UED. Our newly developed scheme enables more efficient and sensitive investigations of ultrafast dynamics in photoexcited samples using ultrashort electron beams.

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Multi-scale time-resolved electron diffraction: A case study in moiré materials

Cited by 4 publications

References 55 publications

Hidden phonon highways promote photoinduced interlayer energy transfer in twisted transition metal dichalcogenide heterostructures

Hidden phonon highways promote photoinduced interlayer energy transfer in twisted transition metal dichalcogenide heterostructures

Stability and Electronic Properties of K‐Sb and Na‐Sb Binary Crystals from High‐Throughput Ab Initio Calculations

High-repetition-rate ultrafast electron diffraction with direct electron detection

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