Simulation of Spatially Resolved Electron Energy Loss Near-Edge Structure for Scanning Transmission Electron Microscopy

Prange, Micah P.; Oxley, Mark P.; Varela, M.; Pennycook, Stephen J.; Pantelides, Sokrates T.

doi:10.1103/physrevlett.109.246101

Cited by 20 publications

(16 citation statements)

References 36 publications

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“…For the Nion UltraSTEM 100 used in these results . The resulting probe intensity is easily calculated as an incoherent sum of probe intensities for different defocus values (11) where is a weighting factor depending on the geometry of the energy/defocus spread.…”

Section: A Probe Wavefuctionmentioning

confidence: 99%

“…In addition, inelastic scattering of the focused beam yields spatially-resolved electron-energy-loss spectra (EELS). The advent of aberrationcorrected (S)TEMs has led to significantly enhanced spatial resolution [4][5][6][7] and ushered the era of "core-loss" EELS (electron excitations from core levels, analogs of XAS) with atomic resolution, especially at lower accelerating voltages [8][9][10][11]. These spectra enable the construction of "chemical maps" that are constructed by plotting the integrated EELS of a characteristic edge of individual atomic species (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…It was recently demonstrated that such maps can be simulated by using a combination of density functional theory (DFT) to describe core-electron excitations and dynamical scattering theory to describe the evolution of the STEM's focused electron beam in the sample, including interference effects and the collection of the scattered electrons in the detector. [6,11,17] These simulations enable detailed analysis of the origins of excitations that give rise to individual spectral features and their variations as a function of the local environment.In addition to the core-loss EELS, so-called "low-loss" EELS arise from low-energy excitations, typically valence-electron excitations (valence-electron-energy-loss spectra or VEELS). These are the analogs of optical and infrared absorption spectra.…”

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confidence: 99%

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Low-loss electron energy loss spectroscopy: An atomic-resolution complement to optical spectroscopies and application to graphene

et al. 2015

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Photon-based spectroscopies have played a central role in exploring the electronic properties of crystalline solids and thin films. Though they remain a powerful tool for probing the electronic properties of nanostructures, they are limited by lack of spatial resolution. On the other hand, electron-based spectroscopies, e.g., electron-energy-loss spectroscopy (EELS) are now capable of sub-Angstrom spatial resolution. Core-loss EELS, a spatially-resolved analog of X-ray absorption, has been used extensively in the study of inhomogeneous complex systems. In this paper, we demonstrate that low-loss EELS in an aberration-corrected scanning transmission electron microscope, which probes low-energy excitations, combined with a theoretical framework for simulating and analyzing the spectra, is a powerful tool to probe low-energy electron excitations with atomic-scale resolution. The theoretical component of the method combines densityfunctional-theory (DFT) based calculations of the excitations with dynamical scattering theory for the electron beam. We apply the method to monolayer graphene in order to demonstrate that atomic-scale contrast is inherent in low-loss EELS even in a perfectly periodic structure. The method is a complement to optical spectroscopy as it probes transitions entailing momentum transfer. The theoretical analysis identifies the spatial and orbital origins of excitations, holding the promise of ultimately becoming a powerful probe of the structure and electronic properties of individual point and extended defects in both crystals and inhomogeneous complex nanostructures. The method can be extended to probe magnetic and vibrational properties with atomic resolution. I. INTRODUCTIONOptical spectroscopies along with energy-band theory were the cornerstones upon which modern solid-state physics was founded. Ultraviolet and X-ray photoemission spectroscopies (UPS and XPS) were subsequently instrumental in the field of surface science. X-ray emission and absorption spectra (XAE and XAS) and their many variants, e.g., resonant x-ray scattering, have also played significant roles in probing the electronic properties of solids. Infrared absorption has been a powerful probe of phonons and lowenergy electronic excitations. The spatial resolution of these spectroscopies, however, is quite limited by the respective photon wavelengths and other factors.[1,2] Nevertheless, they continue to make major contributions in the study of nanostructures.Electron-based spectroscopies have the advantage of ultrasmall de Broglie wave lengths, which enable high spatial resolution. Scanning transmission electron microscopes (STEMs) employ a highly focused electron beam, which produces direct images of crystalline films with atomic resolution. The primary imaging mode of the STEM is Z-contrast imaging, which relies on high-angle Rutherford scattering by atomic nuclei [3]. The intensity of scattered electrons is proportional to approximately the square of the atomic number Z. In addition, inelastic scattering of the foc...

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Section: A Probe Wavefuctionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Low-loss electron energy loss spectroscopy: An atomic-resolution complement to optical spectroscopies and application to graphene

et al. 2015

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“…Recently, several examples have been found where low loss images show atomic resolution (Zhou et al 2012; Zhou et al 2012; Zhou et al 2012). Quantum mechanical simulations show that such contrast arises from specific high momentum transfer transitions; hence, there is no violation of the uncertainty principle (Prange et al 2012; Oxley et al 2014; Kapetanakis et al 2015; Kapetanakis et al 2016).…”

Section: Imaging and Spectroscopic Modesmentioning

confidence: 99%

Material structure, properties, and dynamics through scanning transmission electron microscopy

Pennycook

et al. 2018

J Anal Sci Technol

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Scanning transmission electron microscopy (STEM) has advanced rapidly in the last decade thanks to the ability to correct the major aberrations of the probe-forming lens. Now, atomic-sized beams are routine, even at accelerating voltages as low as 40 kV, allowing knock-on damage to be minimized in beam sensitive materials. The aberration-corrected probes can contain sufficient current for high-quality, simultaneous, imaging and analysis in multiple modes. Atomic positions can be mapped with picometer precision, revealing ferroelectric domain structures, composition can be mapped by energy-dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS), and charge transfer can be tracked unit cell by unit cell using the EELS fine structure. Furthermore, dynamics of point defects can be investigated through rapid acquisition of multiple image scans. Today STEM has become an indispensable tool for analytical science at the atomic level, providing a whole new level of insights into the complex interplays that control material properties.

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“…6 and 7. These figures show atomic-resolution energy-filtered images [55] of the nonmagnetic signal (N ) and absolute (M z ) and relative (M z /N ) magnitudes of the magnetic signal, respectively. Figure 6 shows BF image for a detector aperture with diameter 1.8q max (collection semiangle β = 42.7 mrad) and Fig.…”

Section: B Detector Shape Considerationsmentioning

confidence: 99%

Scattering of electron vortex beams on a magnetic crystal: Towards atomic-resolution magnetic measurements

et al. 2014

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Use of electron vortex beams (EVB), that is, convergent electron beams carrying an orbital angular momentum (OAM), is a novel development in the field of transmission electron microscopy. They should allow measurement of element-specific magnetic properties of thin crystals using electron magnetic circular dichroism (EMCD)-a phenomenon similar to the x-ray magnetic circular dichroism. Recently, it has been shown computationally that EVBs can detect magnetic signal in a scanning mode only at atomic resolution. In this follow-up work, we explore in detail the elastic and inelastic scattering properties of EVBs on crystals, as a function of beam diameter, initial OAM, acceleration voltage, and beam displacement from an atomic column. We suggest that for a 10-nm layer of bcc iron oriented along (001) zone axis, an optimal configuration for a detection of EMCD is an EVB with OAM of 1 and a full width at half maximum diffraction-limited beam diameter of 1.6Å, acceleration voltage 200 kV, and an annular detector with inner and outer radii of 7 and 44 mrad, respectively.

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Simulation of Spatially Resolved Electron Energy Loss Near-Edge Structure for Scanning Transmission Electron Microscopy

Cited by 20 publications

References 36 publications

Low-loss electron energy loss spectroscopy: An atomic-resolution complement to optical spectroscopies and application to graphene

Low-loss electron energy loss spectroscopy: An atomic-resolution complement to optical spectroscopies and application to graphene

Material structure, properties, and dynamics through scanning transmission electron microscopy

Scattering of electron vortex beams on a magnetic crystal: Towards atomic-resolution magnetic measurements

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