Image simulation of high resolution energy filtered TEM images

Verbeeck, Johan; Schattschneider, P.; Rosenauer, A.

doi:10.1016/j.ultramic.2009.01.003

Cited by 43 publications

(40 citation statements)

References 34 publications

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“…Proper settings were chosen to avoid beam damage and provide the best combination of signal-tonoise ratio, spatial and energy resolution. The results were simulated with the STEMSIM software package mimicking the experimental conditions [30][31][32][33]. Detailed experimental and simulation parameters can be found in the supplementary information [28].…”

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confidence: 99%

“…However, a discrepancy between signals A, B and the references is also apparent. This can be explained in terms of intermixing of the inelastic EELS signal due to delocalization and elastic scattering [31]. This intermixing causes a fraction of Mn 2þ signal to be measured at Mn 3þ columns and vice versa.…”

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“…To check the validity of the local interpretation of the data, inelastic simulations at 16 nm thickness were performed using the STEMSIM software, making use of a double channeling approximation and a dipole model with Bethe ridge cutoff for the inelastic scattering [30,31,40,41]. All details of the simulation can be found in the supplementary information [28].…”

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2D Atomic Mapping of Oxidation States in Transition Metal Oxides by Scanning Transmission Electron Microscopy and Electron Energy-Loss Spectroscopy

et al. 2011

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Using a combination of high-angle annular dark-field scanning transmission electron microscopy and atomically resolved electron energy-loss spectroscopy in an aberration-corrected transmission electron microscope we demonstrate the possibility of 2D atom by atom valence mapping in the mixed valence compound Mn 3 O 4 . The Mn L 2;3 energy-loss near-edge structures from Mn 2þ and Mn 3þ cation sites are similar to those of MnO and Mn 2 O 3 references. Comparison with simulations shows that even though a local interpretation is valid here, intermixing of the inelastic signal plays a significant role. This type of experiment should be applicable to challenging topics in materials science, such as the investigation of charge ordering or single atom column oxidation states in, e.g., dislocations. DOI: 10.1103/PhysRevLett.107.107602 PACS numbers: 79.20.Uv, 68.37.Ma, 75.25.Dk In transition metal oxides, the oxidation state of the transition metal cations is of fundamental importance as the physical properties of many oxides are determined by the occupancy of the cation d bands. Multiferroicity, for example, can be driven by charge ordering of these cations, as in Fe 3 O 4 and Pr 1Àx Ca x MnO 3 [1-3]. However, the exact mechanism of multiferroic behavior is not fully understood to date. A method allowing for direct mapping of cation valence states in these materials at atomic resolution should therefore provide further insight into the origin of multiferroicity.Recently, atomic resolution elemental mapping has become feasible by means of spatially resolved electron energy-loss spectroscopy and energy dispersive x-ray spectroscopy in a scanning transmission electron microscope (STEM-EELS and STEM-EDX) [4][5][6][7][8][9]. At the same time, tremendous effort is being invested into the identification of the oxidation states of cations using electron energy-loss spectroscopy (EELS). The shape of the L 2;3 edge [10], the chemical shift [11,12] and the L 3 =L 2 ratio [13] have all been used as a fingerprint for the transition metal valence. In fact, the correlation between the energy-loss near-edge structure (ELNES) and valence in different transition metal oxides was confirmed by several experiments in literature [10,[14][15][16][17][18][19][20][21]. The higher the energy resolution, the more convincing this link between valence and ELNES features becomes. Combining the atomic resolution capabilities of a STEM with bonding and valence information from EELS is a highly attractive prospect. While bonding information has been obtained at atomic resolution [7,17,22], 2D oxidation state mapping at the atomic level in, e.g., metaloxide materials has remained challenging due to poor EELS signal-to-noise ratio and the need for simultaneous high spatial and energy resolution of the instrument [10,17,23].Mn 3 O 4 is known to be a mixed valence compound, containing both Mn 2þ and Mn 3þ ions at room temperature [24]. It has a spinel structure with lattice parameters a ¼ 5:762 A and c ¼ 9:4696 A and space group I41=amd. Many interesting...

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2D Atomic Mapping of Oxidation States in Transition Metal Oxides by Scanning Transmission Electron Microscopy and Electron Energy-Loss Spectroscopy

et al. 2011

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“…The final image or diffraction pattern is the intensity averaged over the different configurations. The electronic excitations are usually included by using the density matrix approach under the assumption that a single inelastic event takes place on a single atom at a given depth [4].The MULTEM program was developed with the purpose of performing accurate and fast multislice simulations for all different TEM experiments including high resolution TEM, electron diffraction (ED), precession ED, hollow cone imaging, convergent beam electron diffraction (CBED), convergent beam electron imaging, STEM, imaging STEM, energy filter transmission electron microscopy and STEM energy loss spectroscopy. MULTEM includes the phase object approximation (POA) and weak POA which provides qualitative description of the electron specimen interaction as well as the main atomic electron scattering parameterizations.…”

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Recent Advances of the Open Source MULTEM Program to Provide Accurate and Fast Electron Microscopy Simulations

2017

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Nowadays, modern transmission electron microscopy (TEM) is capable of reaching sub-Angstrom resolution in both TEM and scanning TEM (STEM) mode [1,2]. Furthermore, the microscope becomes less restricting and the quality of the experimental images is mainly set by the unavoidable presence of electron counting noise. However, due to the quantum mechanical nature of the electron-specimen interaction, images are no longer related to the specimen structure in a simple manner and therefore all experimental work needs to be complemented by numerical simulations.The most practical method for TEM image simulations is the multislice method, which is known to be an accurate numerical procedure for solving the quantum mechanical electron-specimen interaction. In the multislice formulation, the specimen potential is divided into many slices perpendicular to the electron beam. Each slice is chosen thin enough to be considered as a weak phase object, modifying only the phase of the incident wave. The potential between two consecutive slices is considered to be zero and the propagation of the electron wave between the slices is approximated by the Fresnel propagator. The electron wave at any depth in the crystal can be calculated by using this process.It is known that in order to match TEM experiments with simulations, inelastic scattering cannot be neglected and it has to be included in the simulations. Electron-phonon scattering is often incorporated by using the frozen phonon model [3]. The basic idea of this model is to perform repeated multislice simulations for different atomic coordinate configurations. Each configuration needs to be taken as the outcome of realistic phonon calculations or by using the Einstein model in which the atoms vibrate independently. The final image or diffraction pattern is the intensity averaged over the different configurations. The electronic excitations are usually included by using the density matrix approach under the assumption that a single inelastic event takes place on a single atom at a given depth [4].The MULTEM program was developed with the purpose of performing accurate and fast multislice simulations for all different TEM experiments including high resolution TEM, electron diffraction (ED), precession ED, hollow cone imaging, convergent beam electron diffraction (CBED), convergent beam electron imaging, STEM, imaging STEM, energy filter transmission electron microscopy and STEM energy loss spectroscopy. MULTEM includes the phase object approximation (POA) and weak POA which provides qualitative description of the electron specimen interaction as well as the main atomic electron scattering parameterizations. In order to perform accurate simulations, we include the frozen phonon approach for the electron-phonon interaction, the density matrix approach for electronic excitations, correct inclusion of the spatial and temporal incoherences for plane wave and convergent beam illumination. To be able to perform fast simulations, MULTEM is optimized for computer cluster and GPUs which sp...

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Accurate and fast electron microscopy simulations using the open source MULTEM program

Lobato

Aert

Verbeeck

2016

European Microscopy Congress 2016: Proceedings

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The most practical method for TEM image simulations is the multislice method, which is known to be an accurate numerical procedure for solving the quantum mechanical electron‐specimen interaction. Although most simulation codes treat the scattering process as purely elastic and coherent, inelastic scattering cannot be neglected and it has to be included in realistic simulations. Inelastic phonon scattering is often incorporated by using the frozen phonon model [1, 2] and the electronic excitations by using the density matrix approach [3, 4]. Nowadays, new computer technologies allow us to perform large TEM calculations with inclusion of accurate approximations of the electron‐specimen interaction in an acceptable amount of time. A general overview of the MULTEM program along with a number of examples has been reported in [5]. In this work we present a new version of the open source MULTEM program, which adds key features including a graphical user interface, tapering truncation of the atomic potential, CPU multithreading, single/double precision calculations, STEM simulations using experimental detector sensitivities, ISTEM simulations, EFTEM simulations, STEM‐EELS simulations along with other improvements in the algorithms. A screenshot of the user interface is shown in Fig. 1. This figure shows the main available options of the program. In Fig. 2, a simulated HRTEM image and ED pattern of an isolated gold nanoparticle of 21127 atoms are shown. In these simulations, plane‐wave illumination is assumed with the following electron microscope setting: acceleration voltage (300 keV), spherical aberration (0.002 mm), defocus (19.8 Å), defocus spread (30 Å) and beam divergence angle (0.1 mrad). A numerical real space grid of 4096x4096 pixels has been used. The frozen atom simulation is performed by using the Einstein model with 200 configurations, slice thickness of 0.5Å and the three‐dimensional rms displacements of all the atoms are set to 0.085Å. For the HRTEM simulation, the spatial and temporal incoherences are included by applying the partially coherent microscope transfer function to each exit wave of the frozen atom. A multislice simulation of each frozen atom configuration only took 2.6 s on a Nvidia GeForce GTX TITAN GPU card. The MULTEM's C++ classes, Matlab mex functions and the GUI are available in the GitHub repository https://github.com/Ivanlh20/MULTEM .

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Image simulation of high resolution energy filtered TEM images

Cited by 43 publications

References 34 publications

2D Atomic Mapping of Oxidation States in Transition Metal Oxides by Scanning Transmission Electron Microscopy and Electron Energy-Loss Spectroscopy

2D Atomic Mapping of Oxidation States in Transition Metal Oxides by Scanning Transmission Electron Microscopy and Electron Energy-Loss Spectroscopy

Recent Advances of the Open Source MULTEM Program to Provide Accurate and Fast Electron Microscopy Simulations

Accurate and fast electron microscopy simulations using the open source MULTEM program

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