Sample preparation methods for femtosecond electron diffraction experiments

Eichberger, M.; Krumova, Marina; Berger, H.; Demšar, Jure

doi:10.1016/j.ultramic.2012.07.005

Cited by 12 publications

(11 citation statements)

References 24 publications

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“…Single crystals of 4H b -TaSe 2 were grown by chemical vapour transport. From the bulk crystal 90 nm thin sheets > 150 µm in diameter were cut along the TaSe 2 planes using an ultramicrotome and mounted on TEM meshes [28]. Time-resolved electron diffraction experiments were performed in transmission geometry in a collinear excitation scheme applying 200 fs near-infrared pump pulses (λ = 775 nm) for photoexcitation, and delayed ultrashort electron pulses as probe.…”

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confidence: 99%

Ultrafast Dynamics of Charge Density Waves in4Hb−TaSe2Probed by Femtosecond Electron Diffraction

et al. 2012

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The dynamics of the photoinduced commensurate to incommensurate charge density wave (CDW) phase transition in 4H b -TaSe2 are investigated by femtosecond electron diffraction. In the perturbative regime the CDW reforms on a 150 ps timescale, which is two orders of magnitude slower than in other transition-metal dichalcogenides. We attribute this to a weak coupling between the CDW carrying T layers and thus demonstrate the importance of three-dimensionality for the existence of CDWs. With increasing optical excitation the phase transition is achieved showing a second order character in contrast to the first order behavior in thermal equilibrium.Reduced dimensionality seems to be a decisive property governing phenomena like high temperature superconductivity and charge density wave (CDW) formation. The latter is typical for quasi one-or two-dimensional metals where, in the ground state, the crystal displays a static periodic modulation of the conduction electron density accompanied by a periodic lattice displacement (PLD), both characterized by the wave vector q CDW [1]. The standard theory that describes the appearance of this macroscopic quantum state was formulated by Peierls [2]. By considering a one dimensional metal he has shown that the divergent static electronic susceptibility at a wave vector q = 2k F gives rise to an instability of the electronic system against perturbations at this wave vector. This so called Fermi surface nesting lowers the frequencies of q = 2k F phonons, which will eventually evolve into a static lattice displacement. From that band gaps at ± k F result, which reduce the total electronic energy. If the elastic energy cost to modulate atomic positions is lower than the electronic energy gain, the CDW state is the preferred ground state. Recently, this classical picture has been challenged [3][4][5], since (a) the nesting condition derived from the topology of the Fermi surface (2k F ) and the observed CDW modulation vectors (q CDW ) are not generally equal, and (b) the diverging susceptibility at q = 2k F is exceedingly fragile with respect to temperature, scattering or imperfect nesting [3]. Contrasting the standard Fermi surface nesting scenario the transition from the metallic into a CDW state was argued to occur due to strong qdependent electron-phonon coupling [3], particularly in transition-metal dichalcogenides [4].Only the concerted interplay of electronic and lattice degrees of freedom make the CDW formation possible. The two modulations can be individually examined by scanning tunneling microscopy [6], angular resolved photoemission spectroscopy [5] and electron, x-ray or neutron diffraction techniques [7]. In thermal equilibrium, the gap in the electronic spectrum and the atomic displacement amplitude (A) present different projections of the same order parameter [1]. Adding femtosecond temporal resolution to the experiment enables investigation of their dynamical behavior. Since the electronic system can be perturbed on timescales much faster than the characteristic lattic...

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confidence: 99%

Ultrafast Dynamics of Charge Density Waves in4Hb−TaSe2Probed by Femtosecond Electron Diffraction

et al. 2012

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“…Ultramicrotomy 11 and exfoliation have proven effective for layered materials, but non-layered materials present significant difficulties. By comparison, pulsed laser deposition (PLD), sputtering and other thin-film deposition techniques can readily produce very high quality polycrystalline samples for a wide variety of material systems 12 on electron-transparent substrates with controlled thickness 13 .…”

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confidence: 99%

A general method for baseline-removal in ultrafast electron powder diffraction data using the dual-tree complex wavelet transform

Cotret

Siwick

2016

Structural Dynamics

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The general problem of background subtraction in ultrafast electron powder diffraction (UEPD) is presented with a focus on the diffraction patterns obtained from materials of moderately complex structure which contain many overlapping peaks and effectively no scattering vector regions that can be considered exclusively background. We compare the performance of background subtraction algorithms based on discrete and dual-tree complex (DTCWT) wavelet transforms when applied to simulated UEPD data on the M1–R phase transition in VO2 with a time-varying background. We find that the DTCWT approach is capable of extracting intensities that are accurate to better than 2% across the whole range of scattering vector simulated, effectively independent of delay time. A Python package is available.

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“…Recently, the preparation of free-standing films of 1T -TaS 2 using an ultramicrotome was reported [26]. The resulting films had lateral dimensions of ∼ 200 µm and thickness of 30 nm.…”

Section: Preparation Of Free-standing Thin Filmsmentioning

confidence: 99%

“…In Ref. [26], it is suggested that this is caused by a reaction of the tantalum with the diamond blade. In our studies, we did not use a virgin knife, and thus we are unable to classify the origin of the knife damage.…”

Section: Optical Microscopymentioning

confidence: 99%

Structural and magnetic characterization of large area, free-standing thin films of magnetic ion intercalated dichalcogenides Mn_0.25TaS₂and Fe_0.25TaS₂

Danz

Liu

Zhu

et al. 2016

J. Phys.: Condens. Matter

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Free-standing thin films of magnetic ion intercalated transition metal dichalcogenides are produced using ultramicrotoming techniques. Films of thicknesses ranging from 30 nm to 250 nm were achieved and characterized using transmission electron diffraction and X-ray magnetic circular dichroism. Diffraction measurements visualize the long range crystallographic ordering of the intercalated ions, while the dichroism measurements directly assess the orbital contributions to the total magnetic moment. We thus verify the unquenched orbital moment in Fe 0.25 TaS 2 and measure the fully quenched orbital contribution in Mn 0.25 TaS 2 . Such films can be used in a wide variety of ultrafast X-ray and electron techniques that benefit from transmission geometries, and allow measurements of ultrafast structural, electronic, and magnetization dynamics in space and time.

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Sample preparation methods for femtosecond electron diffraction experiments

Cited by 12 publications

References 24 publications

Ultrafast Dynamics of Charge Density Waves in4Hb−TaSe2Probed by Femtosecond Electron Diffraction

Ultrafast Dynamics of Charge Density Waves in4Hb−TaSe2Probed by Femtosecond Electron Diffraction

A general method for baseline-removal in ultrafast electron powder diffraction data using the dual-tree complex wavelet transform

Structural and magnetic characterization of large area, free-standing thin films of magnetic ion intercalated dichalcogenides Mn_0.25TaS₂and Fe_0.25TaS₂

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Sample preparation methods for femtosecond electron diffraction experiments

Cited by 12 publications

References 24 publications

Ultrafast Dynamics of Charge Density Waves in4Hb−TaSe2Probed by Femtosecond Electron Diffraction

Ultrafast Dynamics of Charge Density Waves in4Hb−TaSe2Probed by Femtosecond Electron Diffraction

A general method for baseline-removal in ultrafast electron powder diffraction data using the dual-tree complex wavelet transform

Structural and magnetic characterization of large area, free-standing thin films of magnetic ion intercalated dichalcogenides Mn0.25TaS2and Fe0.25TaS2

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Structural and magnetic characterization of large area, free-standing thin films of magnetic ion intercalated dichalcogenides Mn_0.25TaS₂and Fe_0.25TaS₂