Haut PDF In situ Lorentz microscopy and electron holography in magnetic nanostructures

In situ Lorentz microscopy and electron holography in magnetic nanostructures

In situ Lorentz microscopy and electron holography in magnetic nanostructures

3.1. Motivation 65 component of the magnetic field is just B 0  sin( a ), where B 0 is the magnetic field intensity of the OL at the sample plane in the optical axis, and a is the tilt angle, see Figure 3.1(b). Due to its simplicity, this procedure to perform in situ magnetic field TEM experiments has been widely used to study locally the evolution of magnetic configurations as a function of the in-plane magnetic field in various types of magnetic nanostructures such as nanoparticles, nanowires, heterostructures or magnetic tunnel junctions (MTJ) [1–6,14,15]. The versatility of this procedure can be improved using a double-tilt TEM stage where, combining two orthogonal tilt angles, the orientation of the in-plane component of the field in any desired direction can be achieved. This however requires performing a series of calculations to determine the modulus and direction of the in-plane magnetic field. Mathematical procedures to make a precise control of double-tilt rotations in a double-tilt stage have been reported in different TEM techniques such as electron diffraction, diffraction-contrast and phase-contrast imaging, electron tomography, among others [31–40] but, to our knowledge, never yet to control the direction of the magnetic fields generated by the OL. The main drawback of this method is that we cannot apply solely an in-plane field, as the out-of-plane component of the magnetic field on the sample is always present. Few works have analyzed the effect of this unavoidable out-of-plane component of the applied field [3,4] which, as we will show later, under certain circumstances can drastically influence the quantitative magnetic measurements and the magnetization switching process.
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In situ Lorentz microscopy and electron holography in magnetic nanostructures

In situ Lorentz microscopy and electron holography in magnetic nanostructures

component of the magnetic field is just B 0  sin( a ), where B 0 is the magnetic field intensity of the OL at the sample plane in the optical axis, and a is the tilt angle, see Figure 3.1(b). Due to its simplicity, this procedure to perform in situ magnetic field TEM experiments has been widely used to study locally the evolution of magnetic configurations as a function of the in-plane magnetic field in various types of magnetic nanostructures such as nanoparticles, nanowires, heterostructures or magnetic tunnel junctions (MTJ) [1–6,14,15]. The versatility of this procedure can be improved using a double-tilt TEM stage where, combining two orthogonal tilt angles, the orientation of the in-plane component of the field in any desired direction can be achieved. This however requires performing a series of calculations to determine the modulus and direction of the in-plane magnetic field. Mathematical procedures to make a precise control of double-tilt rotations in a double-tilt stage have been reported in different TEM techniques such as electron diffraction, diffraction-contrast and phase-contrast imaging, electron tomography, among others [31–40] but, to our knowledge, never yet to control the direction of the magnetic fields generated by the OL. The main drawback of this method is that we cannot apply solely an in-plane field, as the out-of-plane component of the magnetic field on the sample is always present. Few works have analyzed the effect of this unavoidable out-of-plane component of the applied field [3,4] which, as we will show later, under certain circumstances can drastically influence the quantitative magnetic measurements and the magnetization switching process.
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Electron Microscopy Investigation of Magnetization Process in Thin Foils and Nanostructures

Electron Microscopy Investigation of Magnetization Process in Thin Foils and Nanostructures

DISCUSSION FePd analysis: Among the numerous materials considered for the magnetic layers of future hard drives, FePd is one of the best candidates for fundamental magnetic structure analysis. When growth conditions are optimized on MgO (001), the chemically ordered phase, with chemical axis parallel to the growth direction, exhibits strong PMA. The magnetic configuration of the layer is then made of domains with either up or down orientation. The domain walls separating up and down magnetic domains can be described in terms of Néel-capped Bloch walls, wide enough to be resolved by LTEM. This is shown by the micro-magnetic simulation of Figure 1. The bi-layer sample, at the same time, exhibits a significant perpendicular magnetic component (in the L1 0
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In situ break-junction sample holder for transmission electron microscopy

In situ break-junction sample holder for transmission electron microscopy

1 Introduction In situ experiments in transmission electron microscopes (TEM) offer enormous advantages by enabling direct observations and analyses of physical and chemical behav- iors of materials at superior spatial-resolution. Such tech- niques allow probing materials properties to gain funda- mental understanding as well as to study in-service behav- ior to develop materials technology. Over the past several decades, in situ sample holder capabilities have been devel- oped primarily for heating [ 1 ], cryogenic [ 2 ], straining [ 3 ] and magnetizing [ 4 ] (Lorentz microscopy) studies. An- other notable development in this domain is environmental TEM which allows studying chemical reac- tions in situ by controlling the gas pressure in the sample chamber [ 5 ]. More recently, with the advent of nanoscale positioning capabilities offered by piezoelectric ceramics, new capabilities such as nanoindentation [ 6 ] as well as in situ STM/AFM holders have been added to the in situ capabilities of electron microscopes [ 7 , 8 ].
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Dark-field electron holography for the mapping of strain in nanostructures: correcting artefacts and aberrations

Dark-field electron holography for the mapping of strain in nanostructures: correcting artefacts and aberrations

[9] Hÿtch M J and Plamann T 2001 Ultramicroscopy 87 199 [10] Hüe F, Hÿtch M J, Houdellier F, Claverie A and Bender H 2009 Appl. Phys. Lett. 95 073103 Acknowledgments The authors thank the European Union for support under the IP3 project ESTEEM (Enabling Science and Technology through European Electron Microscopy, IP3: 0260019), the French Government (MINEFI) through the NANO2012 initiative (project IMASTRAIN), and the French National Agency for Research (ANR) through its program in Nanosciences and Nanotechnologies (HD STRAIN Project No. ANR-08-NANO-0 32). Laurent Clément and Pierre Morin (STMicro, Crolles) are gratefully acknowledged for supplying the stress liner sample. We are indebted to Peter Hartel, Haiko Müller, Stephan Uhlemann and Max Haider (CEOS) for the design and installation of the aberration-corrected Lorentz mode.
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Energy-filtered electron microscopy for imaging core–shell nanostructures

Energy-filtered electron microscopy for imaging core–shell nanostructures

1. Introduction Core–shell nanostructures have recently attracted much attention, from both experimental and theoretical point of views, since it is possible to enhance or to design new physical and chemical properties that cannot be obtained in the single components nanoparticles. It is also possible, by modifying the thickness of the shell to tailor these properties in a certain range. Core– shell nanoparticles have been used for catalysis applications, optical and magnetic properties. For the catalysis applications, the association of two different metals offers higher catalytic activity, better selectivity of catalytic reactions and stability (Sao-Joao et al., 2005; Skarman et al., 2002; Toshima, 2000; Toshima et al., 1992). In the case of magnetic properties, core–shell nanostructures have been developed to obtain nanoparticles with individual improved magnetic properties by reducing the direct interaction between the nanoparticles (Favre et al., 2004; Zeng et al., 2004). In the optical domain, semiconductor core–shell nanostructures have been synthesized to enhance photoluminescence by the passivation of the core material with a shell having a higher band gap energy (Chen et al., 2003; Reiss et al., 2002), to improve stability against photochemical oxidation and to perform band structure engineering (Correa-Duarte et al., 1998; Kim et al., 2003). Metal/oxide and metallic core–shell nanostructures have also been developed in order to modify the surface plasmon resonance energy to a given value by varying the relative composition of the core and the shell as well as their relative size (Basu & Chakravorty, 2006; Gaudry et al., 2003; Zhu et al., 2004). Finally, some recent papers report the use of core–shell nanocomposite materials formed with metal, oxide and/or semiconductor in order to combine magnetic and optical properties in a single nanostructure (Kim et al., 2005; Lu et al., 2002).
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Correlated and in-situ electrical transmission electron microscopy studies and related membrane fabrication

Correlated and in-situ electrical transmission electron microscopy studies and related membrane fabrication

tify the same nano-objects in subsequent mea- surements. Thereby, optical emission features can be attributed to specific structural defects, or the emission and absorption properties of a semi- conductor heterostructure can be correlated to its precise structural properties, which increases the accuracy of theoretical modelling. In-situ Joule heating can be applied to observe solid state re- actions such as the propagation of metal into a semiconductor NW. Finally, in-situ biasing dur- ing off-axis electron holography allows discrimi- nating electronic effects from other influences on the phase, in order to extract information about doping levels and depletion regions. Therefore, these experiments can give access to the charge, electric field and electrostatic potential distribu- tion. The advantage of our approach and the use of custom-fabricated membrane-chips is the com- patibility with lithographic methods to establish electrical contacts with the NWs. Commercial membrane-chips are not optimised for lithogra- phy as typically no suitable markers for EBL are defined on the chip (both to localize the object or calibrate the EBL writing field), and these are sold per chip complicating the batch contacting of sev- eral NWs in the same EBL step. Thus, the main advantages of home made membrane-chips are:
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Micromagnetic study of flux-closure states in Fe dots using quantitative Lorentz Microscopy

Micromagnetic study of flux-closure states in Fe dots using quantitative Lorentz Microscopy

A/m. Two microscopes were used for Lorentz Microscopy : a JEOL 3010 with a thermionic electron gun and a FEI Titan fitted in with a Schottky gun. Both of them are working at 300kV and are fitted with a Gatan Imaging Filter for zero loss filtering [28] and thickness mapping [29]. The Titan is also equipped with a dedicated Lorentz lens for high resolution magnetic field-free imaging while the JEOL is fitted with a conventional objective mini- lens initially dedicated to low magnification imaging. In-situ experiments were performed using the field produced by the objective lens of the microscope (previously calibrated using dedicated sample holders mounted with a Hall probe). The sample was then tilted to produce an in-plane magnetic field. Magnetic field values provided in that manuscript refer to the in-plane component of the field with respect to the tilt angle. Sample was prepared using a mechanical polishing and ion milling. Phase retrieval using the Transport of Intensity equation [30] was thus coupled to substrate contribution removal as proposed in [31].
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In Situ Characterization Methods in Transmission Electron Microscopy

In Situ Characterization Methods in Transmission Electron Microscopy

Mechanical : Along with electron irradiation, mechanical stress was perhaps the first in situ field of TEM. The first approach is to use a holder applying the strength uniformly at the macroscopic scale (Kubin and Louchet, 1979) (see Figure 1.c). In such a case the sample has to be previously designed to enable a thin area for TEM observation as well as an overall design to afford such a mechanical constraint. These in situ observations are generally carried out using diffraction, conventional, or even high resolution imaging (Oh et al., 2009). Following the general evolution of TEM sample holder design, new forms of strain application appeared in the last decade. Among others are the use of moving probe (Stach et al., 2001) for local indentation or MEMS devices to carefully apply controlled forces on reduced dimension objects such as material covered tips (Ishida et al., 2010), nanowires (Pant et al., 2011) or nanotubes (Muoth et al., 2009). Such an integration is thus becoming one of the major concerns for in situ strain experimentalists as it is the only known method to associate in situ strain application with the emerging methods of TEM as electron holography or tomography (Midgley and Dunin-Borkowski, 2009). The moving probe will be detailed in the next part of this chapter (see also Figure 1.a).
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Lorentz microscopy mapping for domain walls structure study in L10 FePd thin films

Lorentz microscopy mapping for domain walls structure study in L10 FePd thin films

then covered with a 1.5 nm Pt capping layer to prevent oxidation. The structural and magnetic properties of this type of alloy can be found elsewhere [6]. Sample for electron microscopy was prepared using a classical method by mechanical polishing and Ar ion milling. The preparation was in a plan-view geometry and the angle used for ion milling was 6 degrees. The microscope used for the study was an FEI TITAN equipped with a dedicated Lorentz lens operating at 300 kV and fitted with a Tridiem GATAN Imaging Filter. All images were zero-loss filtered and data processing has been completed by scripts we have developped in Digital Micrograph from Gatan. The TIE operation was carefully done using the fourier approach[13], enhanced by image symetrization[14]. Micromagnetic simulations were performed with GL FFT (copyright CNRS, Institut N´eel Grenoble [22]). The micromagnetic configuration was used to simulate Fresnel contrast and compared to experimental images.
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In-Situ Surface Analysis of SOFC Cathode Degradation Using High Temperature Environmental Scanning Electron Microscopy

In-Situ Surface Analysis of SOFC Cathode Degradation Using High Temperature Environmental Scanning Electron Microscopy

As can be seen in Fig. 3 the evolution of the surface occurs in three distinct stages: (1) the exsolution of precipitates on a number of grain boundary triple points, (2) the thermal etching of the grain boundaries and defects induced during polishing and (3) the growth of rod shaped strontium and oxygen containing precipitates on both the grain boundaries as well as the centre of the grain. It is clear that the Sr containing precipitates appear to grow with crystallographic direction as, within each grain, they tend to orientate themselves in a similar direction. Unusually, some grain surfaces populate with precipitates more quickly than others, but they will eventually populate given time. During the isotherm at 1000 o C the precipitates do not continue to grow or coarsen over
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Measurement and correction of aberrations in light and electron microscopy

Measurement and correction of aberrations in light and electron microscopy

µm (Figure 3-2a). A high numerical aperture is critical for the visibility of these fibers: while they are still visible at an NA of 0.3, they cannot be discerned using ff-OCT at an NA of 0.1 (Claude Boccara and LLTech the Inc., private communication). To confirm that these fibers corresponded to myelin, we performed several control experiments, which were coordinated by post-doc Juliette Ben Arous at ENS Paris. Using brain slices from genetically modified mice expressing enhanced green fluorescent protein (EGFP) under the cyclic nucleotide phosphodiesterase (CNP) promoter (Yuan, et al., 2002), we compared confocal fluorescence images to deep-OCM images. CNP-EGFP is expressed specifically in oligodendrocytes. In CNP-EGFP fluorescence images of the corpus callosum with a pixel size of 1.12 µm and a field of view of 594x672 µm, oligodendrocyte cell bodies and bundles of myelin fibers are visible (Figure 3-2b, left). The structures visible in deep- OCM of the same region of the sample correspond directly to the myelin fiber bundles visible in the fluorescence images (Figure 3-2b, right). Note that the cell bodies are not visible, so deep-OCM is not specific to oligodendrocytes, but to the strong local refractive index gradients of the myelin sheath, which scatter the incident light much more strongly than the surrounding tissue.
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Phase transformation of molybdenum trioxide to molybdenum dioxide: an in-situ transmission electron microscopy investigation

Phase transformation of molybdenum trioxide to molybdenum dioxide: an in-situ transmission electron microscopy investigation

thermore, the distortion of MoO 6 splits t 2g and e g into four peaks. Because of the energy resolution of the EELS spec- trum (~1.5 eV), we can only resolve peak 1 and its shoul- der. Compared to that in ambient temperature, the full width at half maximum (FWHM) of peak 1 increases at 450°C. When temperature reaches 916°C, the FWHM becomes larger. This is because that the intensity of the shoulder of peak 1 (highlighted by the arrow in EELS spectrum at 450°C) increases with temperature while the sharp part of peak 1 keeps decreases. In the end, a flat peak forms. In MoO 3 , the six t 2g and the four e g orbitals
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An in-situ electron microscopy study of dual ion-beam irradiated xenotime-type ErPO$_4$

An in-situ electron microscopy study of dual ion-beam irradiated xenotime-type ErPO$_4$

Xenotime minerals have been exposed to radiation events due to the α-decay of 238 U and 232 Th over geological timescales. During an α-decay event, recoil atom (70 – 100 keV) and α- particles (4.5 – 5.8 MeV) are produced. The energies of the recoil atoms and α-particles are deposited in the mineral through ballistic and ionization process, respectively. Ballistic effects are primarily responsible for initiating the metamictization (i.e., crystalline to amorphous transformation) events commonly observed in natural minerals. Thus, assessing the impact of radiation on the mineral structure is necessary to adjudge whether synthetic analogues of xenotime mineral could be useful as a host-matrix for the immobilization of minor actinides (e.g., Np, Am, Cm). Yet, to the best of our knowledge, very limited data is available on the radiation response of natural xenotime samples. Anderson et al. have studied the effects of radiation on natural xenotime
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Early stages of UO2+x Sintering by in situ High-Temperature Environmental Scanning Electron Microscopy

Early stages of UO2+x Sintering by in situ High-Temperature Environmental Scanning Electron Microscopy

On this basis, it is important to remember that several diffusion mechanisms always operate simultaneously during the sintering of ceramic or metallic materials. In the case of uranium oxides, it is then likely that volume and grain boundary diffusion present comparable contributions to the global kinetics. The modification of experimental parameters, such as the temperature, the atmosphere, or the grain size, could then generate inversion in the prevailing diffusion path. As such, the use of sub-micrometric particles in our study could be considered as one important explanation to the differences observed with other works employing bulk materials composed of micrometric grains. In these conditions, it is crucial to consider all the diffusive processes possible when modeling the first step of sintering. This is particularly the case for UO 2+x , for which the models frequently consider surface and grain boundary diffusion but neglect volume diffusion [49].
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Determination of precipitate strength in aluminium alloy 6056-T6 from transmission electron microscopy in situ straining data

Determination of precipitate strength in aluminium alloy 6056-T6 from transmission electron microscopy in situ straining data

Note that the distribution of precipitates is quite homogeneous and that particles lie preferentially along the (100) directions of the aluminium matrix. The high-resoluti[r]

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Carbon formation mechanism of C₂H₂ in Ni-based catalysts revealed by in situ electron microscopy and molecular dynamics simulations

Carbon formation mechanism of C₂H₂ in Ni-based catalysts revealed by in situ electron microscopy and molecular dynamics simulations

On close observation of the region where the carbon layers generate, as indicated by the black arrows in Figure 4 , we find that the carbon layers come from a modulated region. Since modulation is usually related to an intermediate phase between phase changes, 38 we believe that the formation of the graphitic layers results from the decomposition of modulated carbide. Besides, there is no melting phenomenon happening during this process. This possibly explains the slower graphitic layer growth rate as compared with that in NiO. Fourier transformation image processing on the chosen area within the modulated carbide region (marked by a square) shows the existence of the dislocation within the structure (marked by arrows in the inset in Figure 4 ). This is due to the strain induced by the decomposition of carbide. The results revealed by Figure 4 suggest that there are possible di fferent mechanisms governing graphitic layer formation in NiO and MgO-modi fied NiO, respectively. Heracleous et al. found that it is extremely di fficult to reduce Ni−Mg−O mixed metal oxides. 39 They attribute it to the solid solution formed between NiO and MgO. 39 The actual mechanism will be discussed in the following section.
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Carbon formation mechanism of C₂H₂ in Ni-based catalysts revealed by in situ electron microscopy and molecular dynamics simulations

Carbon formation mechanism of C₂H₂ in Ni-based catalysts revealed by in situ electron microscopy and molecular dynamics simulations

Chunwen Sun 1,2,6* , Rui Su 3,5 , Jian Chen 4* , Liang Lu, 1 Pengfei Guan 3* 1 CAS Center for Excellence in Nanoscience, Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100083, P. R. China 2 School of Nanoscience and Technology, University of Chinese Academy of Sciences, Beijing

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Multi magnetic states in Co/Cu multilayered cylindrical nanowires studied by combination of off-axis electron holography imaging and micromagnetic simulations

Multi magnetic states in Co/Cu multilayered cylindrical nanowires studied by combination of off-axis electron holography imaging and micromagnetic simulations

1 CEMES CNRS-UPR 8011, Université de Toulouse, 31055 Toulouse, France 2 Laboratoire des Solides Irradiés, Ecole Polytechnique, CNRS, CEA, Université Paris Saclay, F 91128 Palaiseau, France Abstract: We report on a wide variety of magnetic states in Co/Cu multilayered nanocyli nders grown by electrodeposition with different thicknesses of both elements. The remnant magnetic states in individual Co layers have quantitatively been determined at the nanoscale by micromagnetic reconstruction of the magnetic phase shift image obtained by electron holography. We demonstrate that the magnetization in the Co layers can present either uniform or vortex states. Also, different magnetic configurations can be observed within the same nanocylinder. In the case of vortices, the direction of the core can rotate almost at 90° from the nanocylinder axis for layers with aspect ratio close to 1. We show that the occurrence of each magnetic configuration depends on the aspect ratio of the layers, the direction of magnetocrystalline anisotropy and in some cases on the interlayer dipolar coupling. Such a wide variety of magnetic states are observed due to lower values of the Co magnetic constants (magnetization, exchange, anisotropy) with respect to bulk, typical of electrodeposition process in a single bath, and to the local geometrical variation of the layers. We also calculated the phase diagram of the remnant magnetic states in a single layer for various amplitudes and orientations of the magnetocrystalline anisotropy and different directions of the saturation field. In particular cases, these phase diagrams in addition to statistics of occurrence of each kind of magnetic configurations in the multilayer and the application of a saturation field in different directions allows recovering information on the preferential orientation of the crystalline anisotropy.
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Measurement of local magnetic properties of devices with transmission electron microscopy

Measurement of local magnetic properties of devices with transmission electron microscopy

First and foremost, I would like to thank my supervisors Virginie Serin and Bénédicte Warot-Fonrose. Before starting my PhD work, I dreamed to have a supervisor who is very nice and patient to me, and lead me to take a good first step toward my future scientific research career. The dream then came true. How lucky I am to be a student of Virginie and Bénédicte. They taught me hand by hand how to make better experiments, led me to think, patiently answered my questions, showed me how to organize the literature more efficiently, guided me to write a good paper, provided me chances to visit other labs, encouraged me to present myself in more academic activities, and even like families, helped me to solve tricky problems in my daily life. What I have learned from them is far more than how to be a good researcher, but also how to be a good person. I really appreciate the help from Sebastien Joulie. He is the one who taught me how to use transmission electron microscope step by step from the beginning, and always solved the technical problems of the microscope. In the first year, around the microscope, I was like a child who knew little about the new world but was very curious. I could not remember how many times I have asked him “Sebastien, why it is like this?” “Sebastien, how to do that?” With his help, I started my happy journey of microscopy.
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