Clocking the anisotropic lattice dynamics of multi-walled carbon nanotubes by four-dimensional ultrafast transmission electron microscopy

Abstract

Recent advances in the four-dimensional ultrafast transmission electron microscope (4D-UTEM) with combined spatial and temporal resolutions have made it possible to directly visualize structural dynamics of materials at the atomic level. Herein, we report on our development on a 4D-UTEM which can be operated properly on either the photo-emission or the thermionic mode. We demonstrate its ability to obtain sequences of snapshots with high spatial and temporal resolutions in the study of lattice dynamics of the multi-walled carbon nanotubes (MWCNTs). This investigation provides an atomic level description of remarkable anisotropic lattice dynamics at the picosecond timescales. Moreover, our UTEM measurements clearly reveal that distinguishable lattice relaxations appear in intra-tubular sheets on an ultrafast timescale of a few picoseconds and after then an evident lattice expansion along the radial direction. These anisotropic behaviors in the MWCNTs are considered arising from the variety of chemical bonding, i.e. the weak van der Waals bonding between the tubular planes and the strong covalent sp2-hybridized bonds in the tubular sheets.

High brightness ultrafast transmission electron microscope based on a laser-driven cold-field emission source: principle and applications

“…The diffracted intensities recorded inside these disks exhibit specific excess lines of electrons while the central transmitted disk contained the superimposition of all the associated deficiency lines. The profile of each line, usually called Rocking curve, can be used to quantitatively determine a wide range of information such as crystal thickness, structure factor, Debye Waller factor, while their positions can be used to determine the crystal strain state with a very high precision [14]. By increasing the incident convergence angle, Kossel-Möllensted patterns are obtained.…”

“…Pioneered in the late 1980s by O. Bostanjoglo and coworkers at the Technical University of Berlin, the field of Time-resolved Transmission Electron Microscopy has been boosted by the spectacular improvement in spatio-temporal resolution achieved in 2005 in the group of A. Zewail at the California Institute of Technology [5,6,7,8,9,10,11]. Contrary to Dynamic Transmission Electron Microscopes (DTEM) which use single pulses containing each a very large number of electrons, Ultrafast Transmission Electron Microscopes (UTEM) rely on stroboscopic observations with electron pulses each containing only a few particles [12,13,14,15]. This operation in the single electron regime cancels the coulombic interparticle repulsion that deteriorates the resolution of DTEMs [16].…”

Picosecond view of a martensitic transition and nucleation in the shape memory alloy Mn50Ni40Sn10Zhang1, Cao2, Tian3 et al. 2017Phys. Rev. BSelf Cite110120View full textAdd to dashboardCite

“…Mn 50 Ni 40 Sn 10 is the classical Heusler magnetic shape memory alloy with a magnetic transition at T c = 270 K and a MT transition at T m = 214 K [4] (from the hightemperature cubic AUS phase to the orthorhombic MT phase). This Heusler alloy contains visible MT domains at low temperature, and upon ultrafast photoexcitation, it undergoes a dynamic evolution from the MT phase to the high-temperature AUS phase, which is associated with collective microstructure changes.In this paper, we report our study of the MT phase transition and reverse transition in Mn 50 Ni 40 Sn 10 , as observed using high spatiotemporal resolution 4D-TEM [19]. We demonstrate that the MT phase transition occurs at a picosecond scale, and a coherent coupling between photoexcitation and structural transformation is observed for the acoustic breathing mode [25], which strongly modulated the MT transition and domain nucleation.…”

“…It is well known that the martensitic transformation as a typical diffusionless transformation exhibits a variety of collective phenomena involving the synchronous movements of atoms [8]. Despite the fact that detailed structural characterization of both AUS and MT phases has been achieved using static characterization tools, experimentally direct imaging of the dynamics of MT phase transition remains a significant challenge.Recently, ultrafast electron diffraction [9][10][11], ultrafast x-ray diffraction [12][13][14], and four-dimensional ultrafast transmission electron microscopy (4D-UTEM) [15][16][17][18] have been demonstrated as effective techniques for revealing the remarkable ultrafast structural dynamic features and structural phase transitions in a variety of materials, such as nanotubes [19,20], charge density waves (CDWs) [21,22], and biomaterials [23,24]. 4D-TEM is a novel technique for real-space imaging and reciprocal-space diffraction; it is capable of revealing the essential transient states in phase transitions and * hftian@iphy.ac.cn † ljq@iphy.ac.cn can potentially be a significant technique for characterizing MT materials.…”

Sub-100 nanosecond temporally resolved imaging with the Medipix3 direct electron detector

“…This has enabled the specialised field of ultra-fast electron microscopy (UEM) in which the illumination duration is of the order of the femtosecond laser pulse duration [4,5,6,7,8]. Utilising a pump-probe imaging methodology for the study of repeatable phenomena has led to insights in areas such as nanophotonics [9], atomic structural dynamics [10], magnetic dynamics [11], and even electron dynamics [12]. Stochastic, non-repeatable, processes have also been studied using high intensity, nanosecond duration laser pulses in dynamic TEM (DTEM).…”