1
|
Diaz FR, Mero M, Amini K. High-repetition-rate ultrafast electron diffraction with direct electron detection. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2024; 11:054302. [PMID: 39346930 PMCID: PMC11438501 DOI: 10.1063/4.0000256] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/02/2024] [Accepted: 08/06/2024] [Indexed: 10/01/2024]
Abstract
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, Δ I / I 0 , 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.
Collapse
Affiliation(s)
- F. R. Diaz
- Max-Born-Institut, Max-Born-Straße 2A, 12489 Berlin, Germany
| | - M. Mero
- Max-Born-Institut, Max-Born-Straße 2A, 12489 Berlin, Germany
| | - K. Amini
- Max-Born-Institut, Max-Born-Straße 2A, 12489 Berlin, Germany
| |
Collapse
|
2
|
Johnson AC, Georgaras JD, Shen X, Yao H, Saunders AP, Zeng HJ, Kim H, Sood A, Heinz TF, Lindenberg AM, Luo D, da Jornada FH, Liu F. Hidden phonon highways promote photoinduced interlayer energy transfer in twisted transition metal dichalcogenide heterostructures. SCIENCE ADVANCES 2024; 10:eadj8819. [PMID: 38266081 PMCID: PMC10807799 DOI: 10.1126/sciadv.adj8819] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2023] [Accepted: 12/22/2023] [Indexed: 01/26/2024]
Abstract
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 MoS2/WS2 at 4° twist angle and WSe2/MoSe2 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.
Collapse
Affiliation(s)
- Amalya C. Johnson
- Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA
| | - Johnathan D. Georgaras
- Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA
| | - Xiaozhe Shen
- SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
| | - Helen Yao
- Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA
- SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
| | | | - Helen J. Zeng
- Department of Chemistry, Stanford University, Stanford, CA 94305, USA
| | - Hyungjin Kim
- Department of Chemistry, Stanford University, Stanford, CA 94305, USA
| | - Aditya Sood
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
| | - Tony F. Heinz
- SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
- Department of Applied Physics, Stanford University, Stanford, CA 94305, USA
| | - Aaron M. Lindenberg
- Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA
- Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
| | - Duan Luo
- Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA
- SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
| | - Felipe H. da Jornada
- Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA
| | - Fang Liu
- Department of Chemistry, Stanford University, Stanford, CA 94305, USA
| |
Collapse
|