A kiloelectron-volt ultrafast electron micro-diffraction apparatus using low emittance semiconductor photocathodes

Li, W. H.; Duncan, Cameron; Andorf, Matthew; Bartnik, Adam; Bianco, Elisabeth; Cultrera, L.; Galdi, Alice; Gordon, Mollie; Kaemingk, M.; Pennington, Christopher; Kourkoutis, Lena F.; Bazarov, Ivan; Maxson, Jared

doi:10.1063/4.0000138

Cited by 16 publications

(21 citation statements)

References 79 publications

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“…A growing body of literature in UED/M is focused on improvement to critical transverse metrics, namely the probe transverse size and divergence, summarized via the normalized emittance [21][22][23][24]. The emittance of the electron beam can increase in transport due to nonlinear fields coming from space charge and electron optics [25,26].…”

Section: Introductionmentioning

confidence: 99%

Four-dimensional emittance measurements of ultrafast electron diffraction optics corrected up to sextupole order

Gordon

Andorf

et al. 2022

Phys. Rev. Accel. Beams

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Ultrafast electron diffraction (UED) is a technique in which short-pulse electron beams can probe the femtosecond-scale evolution of atomic structure in matter driven far from equilibrium. As an accelerator physics challenge, UED imposes stringent constraints on the brightness of the probe electron beam. The low normalized emittance employed in UED, often at the 10 nm scale and below, is particularly sensitive to both applied field aberrations and space charge effects. The role of aberrations is increasingly important in small probe systems that often feature multiple orders of magnitude variations in beam size during transport. In this work, we report the correction of normal quadrupole, skew quadrupole, and sextupole aberrations via dedicated corrector elements in an ultrafast electron micro-diffraction beamline. To do this, we generate precise 4-dimensional phase space maps of rf-compressed electron beams, and find excellent agreement with aberrationfree space charge simulations. Finally, we discuss the role a probe-forming aperture can play in improving the brightness of bunches with appreciable space charge effects.

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Section: Introductionmentioning

confidence: 99%

Four-dimensional emittance measurements of ultrafast electron diffraction optics corrected up to sextupole order

Gordon

Andorf

et al. 2022

Phys. Rev. Accel. Beams

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“…Alkali antimonides have been, and continue to be of great interest as potential high-quality electron emitters for various applications, including electron accelerators and ultrafast electron diffraction and microscopy. [1][2][3][4][5][6] Despite their promise, these materials are not very wellunderstood, in part because growth of single-crystal alkali antimonides remains very challenging: the resulting materials are often polycrystalline or disordered, 2,5 thereby limiting the understanding of the equilibrium crystal structures and thus of the ultimate promise of these materials as electron emitters. Moreover, even once successfully grown, single-crystal versions of these materials are extremely sensitive to vacuum conditions and can survive only in ultra-high-vacuum in their thin film forms, making experimental studies of their structural and optoelectronic properties extremely challenging.…”

Section: Introductionmentioning

confidence: 99%

Ab initio study of the crystal and electronic structure of mono- and bi-alkali antimonides: Stability, Goldschmidt-like tolerance factors, and optical properties

Nangoi¹,

Gaowei²,

Galdi³

et al. 2022

Preprint

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Mono-and bi-alkali antimonides, X2YSb (X and Y from Group I), are promising for nextgeneration electron emitters due to their capability of producing high-quality electron beams. However, these materials are not yet well understood, in part due to the technical challenges in growing pure, ordered alkali antimonides. For example, in the current literature there is a lack of complete understanding of the mechanically stable crystal structures of these materials. As a first step towards understanding this issue, this paper presents an ab initio study of stability of single-crystal monoand bi-alkali antimonides in the D03 structure, the structure generally assumed in the literature for these materials. Finding that many of these materials actually are unstable in the D03 structure, we formulate a new set of Goldschmidt-like tolerance factors that accurately predict D03 stability using a procedure analogous to machine-learning perceptron-based analysis. Next, we consider possible stable structures for materials that we predict to be unstable in the D03 structure. Taking as examples the mono-and bi-alkali antimonides Cs3Sb and Cs2KSb, which also are technologically interesting for photoemission and photoabsorption applications, respectively, we note that the most unstable phonon displacements are consistent with the cubic structure, and we therefore perform extensive ab initio searches to identify potential ground-state structures in a cubic lattice. Our X-ray diffraction experiments confirm that indeed these two materials are not stable in the D03 structure and show scattering that is consistent with our new, proposed stable structures. Finally, we explore ab initio the implications of the breaking of the D03 symmetry on the electronic structure, showing significant impact on the location of the optical absorption edge.

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“…Here we deploy a leading example of integrating detector technology -the Electron Microscope Pixel Array Detector (EMPAD) -to study the multiscale out-of-equilibrium dynamics of a WSe 2 /MoSe 2 moiré bilayer [27][28][29][30]. For the first time in UED, we resolve the 10 nm periodicity of the moiré superlattice.…”

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confidence: 99%

“…Our beamline setup is summarized in the Supplemental Material and described in detail elsewhere [28]. To take best advantage of the detector frame rate, we independently gate pump and probe pulse trains obtained from a seed laser pulsing at 125 kHz.…”

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confidence: 99%

“…S1. (a)Schematic of the UED beamline, see reference[28] for details: a 1030 nm Yb-fiber laser drives an optical parametric amplifier that sends 650 nm light pulses to the photocathode.Photoemitted bunches are accelerated to 140 keV, compressed by an rf cavity, collimated by a probe-defining aperture, and are collected by the detector after scattering on the sample; the same 1030 nm pulses are split and frequency doubled to synchronously pump the sample. (b) Modification of the detector section of the beamline to accommodate a magnetic quadruple electron lens triplet.…”

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confidence: 99%

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Multi-scale time-resolved electron diffraction enabled by high repetition rate, high dynamic range direct electron detection

Duncan¹,

Kaemingk²,

Li³

et al. 2022

Preprint

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Ultrafast-optical-pump -structural-probe measurements, including ultrafast electron and xray scattering, provide direct experimental access to the fundamental timescales of atomic motion, and are thus foundational techniques for studying matter out of equilibrium. High-performance detectors are needed in scattering experiments to obtain maximum scientific value from every probe particle. We present the first ultrafast electron diffraction experiments to deploy a hybrid pixel array direct electron detector, and we show that its single-particle sensitivity, high dynamic range and 1 kHz frame rate enable new probe modalities in electron-based structural dynamics.Specifically, we perform measurements on a WSe 2 /MoSe 2 2D heterobilayer that resolve the weak features of diffuse scattering and moiré superlattice structure without saturating the zero order peak. Enabled by the detector's high frame rate, we show that a lock-in technique provides diffraction difference images with signal-to-noise at the shot noise limit. Finally, we demonstrate that a fast detector frame rate coupled with a high repetition rate probe can provide continuous time resolution from femtoseconds to seconds, enabling us to perform a scanning ultrafast electron diffraction experiment that maps thermal transport in WSe 2 /MoSe 2 and resolves distinct diffusion mechanisms in space and time.

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A kiloelectron-volt ultrafast electron micro-diffraction apparatus using low emittance semiconductor photocathodes

Cited by 16 publications

References 79 publications

Four-dimensional emittance measurements of ultrafast electron diffraction optics corrected up to sextupole order

Four-dimensional emittance measurements of ultrafast electron diffraction optics corrected up to sextupole order

Ab initio study of the crystal and electronic structure of mono- and bi-alkali antimonides: Stability, Goldschmidt-like tolerance factors, and optical properties

Multi-scale time-resolved electron diffraction enabled by high repetition rate, high dynamic range direct electron detection

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