Ultramicroscopy最新文献

{"title":"Beyond the random phase approximation (RPA): First principles calculation of the valence EELS spectrum for KBr including local field, quasiparticle, excitonic and spin orbit coupling effects.","authors":"V J Keast","doi":"10.1016/j.ultramic.2024.114070","DOIUrl":"https://doi.org/10.1016/j.ultramic.2024.114070","url":null,"abstract":"<p><p>The low energy region (< 50 eV) of the electron energy loss spectrum (EELS) can contain a great deal of spectral detail associated with excitations of the valence electrons. Calculation of the spectra from first principles can assist with interpretation and the most widely used method is the random phase approximation (RPA), usually neglecting local field effects (LFE). For KBr this approach is insufficient due to the importance of quasiparticle and excitonic effects. Calculations including these multi-electron effects are shown to give much improved agreement with the experimental spectra, and the inclusion of spin-orbit coupling (SOC) reproduces the excitonic doublet just above band-edge onset. A review of the complex theory behind these methods is given along with practical guidance on performing these calculations.</p>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142606608","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A high-performance reconstruction method for partially coherent ptychography","authors":"Wenhui Xu ,&nbsp;Shoucong Ning ,&nbsp;Pengju Sheng ,&nbsp;Huixiang Lin ,&nbsp;Angus I Kirkland ,&nbsp;Yong Peng ,&nbsp;Fucai Zhang","doi":"10.1016/j.ultramic.2024.114068","DOIUrl":"10.1016/j.ultramic.2024.114068","url":null,"abstract":"<div><div>Ptychography is now integrated as a tool in mainstream microscopy allowing quantitative and high-resolution imaging capabilities over a wide field of view. However, its ultimate performance is inevitably limited by the available coherent flux when implemented using electrons or laboratory X-ray sources. We present a universal reconstruction algorithm with high tolerance to low coherence for both far-field and near-field ptychography. The approach is practical for partial temporal and spatial coherence and requires no <em>prior</em> knowledge of the source properties. Our initial visible-light and electron data show that the method can dramatically improve the reconstruction quality and accelerate the convergence rate of the reconstruction. The approach also integrates well into existing ptychographic engines. It can also improve mixed-state and numerical monochromatisation methods, requiring a smaller number of coherent modes or lower dimensionality of Krylov subspace while providing more stable and faster convergence. We propose that this approach could have significant impact on ptychography of weakly scattering samples.</div></div>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142554993","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A simple circularity-based approach for nanoparticle size histograms beyond the spherical approximation.","authors":"Florent Tournus","doi":"10.1016/j.ultramic.2024.114067","DOIUrl":"https://doi.org/10.1016/j.ultramic.2024.114067","url":null,"abstract":"<p><p>Conventional Transmission Electron Microscopy (TEM) is widely used for routine characterization of the size and shape of an assembly of (nano)particles. While the most basic approach only uses the projected area of each particle to infer its size (the \"circular equivalent diameter\" corresponding to the so-called \"spherical approximation\"), other shape descriptors can be determined and used for more elaborate analyses. In this article we present a generic model of particles, considered to be made of a few individual grains, and show how the equivalent size (i.e. a particle volume information) can be reliably deduced using only two basic parameters: the projected area and the perimeter of a particle. We compare this simple model to the spherical and ellipsoidal approximations and discuss its benefits. Then, partial coalescence of grains in a particle is also considered and we show how a simple analytical approximation, based on the circularity parameter of each particle, can improve the experimental determination of a particle size histogram. The analysis of experimental observations on nanoparticles assemblies obtained by mass-selected cluster deposition is presented, to illustrate the efficiency of the proposed approach for the determination of particle size just from conventional TEM images. We show how the presence of multimers offers an excellent opportunity to validate our improved and simple procedure. In addition, since the circularity plays a central role in this approach, attention is attracted on the perimeter determination in a pixelated image.</p>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142606606","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Corrigendum to \"Structure-preserving Gaussian denoising of FIB-SEM volumes\" [Ultramicroscopy Volume 246, 113674].","authors":"V González-Ruiz, M R Fernández-Fernández, J J Fernández","doi":"10.1016/j.ultramic.2024.114065","DOIUrl":"https://doi.org/10.1016/j.ultramic.2024.114065","url":null,"abstract":"","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142569693","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On the instrument-dependent appearance of ion dissociation events in atom probe tomography mass spectra","authors":"Benjamin W. Caplins ,&nbsp;Ann N. Chiaramonti ,&nbsp;Jacob M. Garcia ,&nbsp;Luis Miaja-Avila ,&nbsp;Kayla H. Yano ,&nbsp;Daniel K. Schreiber ,&nbsp;Joseph H. Bunton","doi":"10.1016/j.ultramic.2024.114061","DOIUrl":"10.1016/j.ultramic.2024.114061","url":null,"abstract":"<div><div>The successful application of atom probe tomography (APT) relies on the accurate interpretation of the mass spectrum (<em>i.e.</em> <span><math><mrow><mi>m</mi><mo>/</mo><mi>z</mi></mrow></math></span> histogram) from a sample. Some materials yield mass spectra that are amenable to a straightforward peak assignment/ranging, however, there are many materials that produce mass spectra with features that defy simple interpretation. One such example is Ga<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>O<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span> which yields mass spectra containing several broad and difficult to interpret features. Herein, we study the GaO<span><math><msup><mrow></mrow><mrow><mn>2</mn><mo>+</mo></mrow></msup></math></span> <span><math><mo>→</mo></math></span> O<span><math><mrow><msup><mrow></mrow><mrow><mn>1</mn><mo>+</mo></mrow></msup><mo>+</mo></mrow></math></span> Ga<span><math><msup><mrow></mrow><mrow><mn>1</mn><mo>+</mo></mrow></msup></math></span> dissociation and we explain how this dissociation process gives rise to broad and previously unassigned features in the mass spectrum. Trajectory simulations are performed for the dissociation reaction utilizing realistic electrostatic models and compared to experiments using commercially available straight flight and reflectron based local electrode (LE) APT instruments. It is shown that the appearance of these features is strongly dependent on the specific design of the time-of-flight (ToF) mass analyzer. We explore how various experimental parameters can affect the appearance of the dissociation process in the one-dimensional (1D) mass spectrum and in the two-dimensional (2D) correlation histogram. While the focus of this work is on a particular dissociation process related to Ga<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>O<span><math><msub><mrow></mrow><mrow><mn>3</mn></mrow></msub></math></span>, the understanding gained in the course of these simulations and experiments should be applicable to the interpretation of dissociation processes in other materials.</div></div>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142578087","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A refined plan-view specimen preparation technique for high-quality electron microscopy studies of epitaxially grown atomically thin 2D layers","authors":"A.S. Prikhodko ,&nbsp;E. Zallo ,&nbsp;R. Calarco ,&nbsp;N.I. Borgardt","doi":"10.1016/j.ultramic.2024.114063","DOIUrl":"10.1016/j.ultramic.2024.114063","url":null,"abstract":"<div><div>The structural studies of two-dimensional (2D) van der Waals heterostructures and understanding of their relationship with the orientation of crystalline substrates using transmission electron microscopy (TEM) presents a challenge in developing an easy-to-use plan-view specimen preparation technique. In this report, we introduce a simple approach for high-quality plan-view specimen preparation utilizing a dual beam system comprising focused ion beam and scanning electron microscopy.</div><div>To protect the atomically thin 2D heterostructure during the preparation process, we employ an epoxy layer. This layer serves as a protective barrier and enables the creation of a TEM specimen comprising a thin substrate fragment with an overgrown 2D structure covered by a thin, electron-transparent epoxy layer. The coexistence of both 2D layers and substrate is essential for investigating the relative crystallographic orientations between the grown 2D structures and the substrates. The thickness of the specimen is monitored using low-voltage scanning electron microscopy.</div><div>We apply this technique to prepare plan-view specimens of 2D germanium-antimony-telluride (GST) on Si and hexagonal boron nitride (h-BN)/epitaxial graphene (EG) heterostructures grown on 6H-SiC substrates. The grain-like atomic structure observed in the 2.2 nm thick GST layer on Si substrate provides evidence of the mosaicity of GST during the early stages of epitaxial growth. H-BN/EG on 6H-SiC structural studies indicate a rotation of h-BN/EG around the 6H-SiC[0001] axis by an angle of 30°. The observed BN particles with sizes in the nanometer range on top of the sample have the wurtzite lattice type and random orientation.</div><div>The developed specimen preparation technique offers a powerful tool for TEM studies of atomically thin layers on crystals. Its simplicity and ability to provide valuable insights into the in-plane relationships between 2D structures and crystalline substrates make it a promising complement to grazing incident X-ray diffraction.</div></div>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142528062","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Development of ultrafast four-dimensional precession electron diffraction","authors":"Toshiya Shiratori ,&nbsp;Jumpei Koga ,&nbsp;Takahiro Shimojima ,&nbsp;Kyoko Ishizaka ,&nbsp;Asuka Nakamura","doi":"10.1016/j.ultramic.2024.114064","DOIUrl":"10.1016/j.ultramic.2024.114064","url":null,"abstract":"<div><div>Ultrafast electron diffraction/microscopy technique enables us to investigate the nonequilibrium dynamics of crystal structures in the femtosecond-nanosecond time domain. However, the electron diffraction intensities are in general extremely sensitive to the excitation errors (i.e., deviation from the Bragg condition) and the dynamical effects, which had prevented us from quantitatively discussing the crystal structure dynamics particularly in thick samples. Here, we develop a four-dimensional precession electron diffraction (4D-PED) system by which time (<em>t</em>) and electron-incident-angle <span><math><mrow><mo>(</mo><mi>ϕ</mi><mo>)</mo></mrow></math></span> dependences of electron diffraction patterns <span><math><mrow><mo>(</mo><mrow><msub><mi>q</mi><mi>x</mi></msub><mo>,</mo><mspace></mspace><msub><mi>q</mi><mi>y</mi></msub></mrow><mo>)</mo></mrow></math></span> are recorded. Nonequilibrium crystal structure refinement on VTe₂ demonstrates that the ultrafast change in the crystal structure can be quantitatively determined from 4D-PED. We further perform the analysis of the <span><math><mi>ϕ</mi></math></span> dependence, from which we can qualitatively estimate the change in the reciprocal lattice vector parallel to the optical axis. These results show the capability of the 4D-PED method for the quantitative investigation of ultrafast crystal structural dynamics.</div></div>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142523240","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Parameter dependence of depth and lateral resolution of transmission Kikuchi diffraction","authors":"Glenn C. Sneddon ,&nbsp;Patrick W. Trimby ,&nbsp;Levi Tegg ,&nbsp;Julie M. Cairney","doi":"10.1016/j.ultramic.2024.114062","DOIUrl":"10.1016/j.ultramic.2024.114062","url":null,"abstract":"<div><div>The spatial resolution of transmission Kikuchi diffraction (TKD) depends on experimental parameters such as atomic number, accelerating voltage, sample backtilt and thickness. In this work, the dependence of spatial resolution on these parameters is explored by using bilayered coarse-grained/nanocrystalline samples to determine the depth resolution. Digital image correlation of the Kikuchi patterns across grain boundaries is used to measure the lateral resolution. The depth resolutions of TKD in aluminium, copper and platinum at 30 kV for an untilted sample were 80, 32 and 14 nm respectively. These worsened with increasing sample backtilt and slightly improved with decreasing accelerating voltage. The best physical lateral resolution obtained was 6 nm, at 30 keV in a 41 nm thick aluminium sample with no backtilt. The lateral resolution worsened with increasing sample thickness and backtilt, contrasting with some previous reports. Accelerating voltage and atomic number did not have a significant impact on the measured lateral resolution within the scatter in the data.</div></div>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142508922","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The reference window for reduced perturbation of the reference wave in electrical biasing off-axis electron holography","authors":"Tolga Wagner ,&nbsp;Robin Kraft ,&nbsp;Franz Nowak ,&nbsp;Dirk Berger ,&nbsp;Christian M. Günther ,&nbsp;Hüseyin Çelik ,&nbsp;Christoph T. Koch ,&nbsp;Michael Lehmann","doi":"10.1016/j.ultramic.2024.114060","DOIUrl":"10.1016/j.ultramic.2024.114060","url":null,"abstract":"<div><div>The perturbation of the reference wave due to electric stray fields represents a major challenge in quantitative electron holographic investigations. By introducing a focused-ion-beam-milled rectangular hole, the reference window, in an area of nearly constant electrostatic potential of the sample, this perturbation can be significantly reduced. The edge of the window forms a closed conducting loop, acting similarly to a Faraday cage, shielding the influence of the stray field on the reference wave to some extent. In this work, the shielding effect of the reference window is systematically investigated by comparing electron holograms of an electrically biased coplanar capacitor, as a well-known reference sample, with finite element simulations. It is shown that the introduction of the reference window into electrical biasing samples both suppresses unknown lateral phase distortions substantially and in addition improves the agreement of the experimentally observed phase slope with that expected by simulation significantly, particularly for small object-reference wave distances. Consequently, a slight adjustment of the sample geometry results in an improved reproducibility of electron holographic electrical biasing experiments, which is a significant step towards quantitative evaluation.</div></div>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-10-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142446267","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Principle of TEM alignment using convolutional neural networks: Case study on condenser aperture alignment","authors":"Loïc Grossetête ,&nbsp;Cécile Marcelot ,&nbsp;Christophe Gatel ,&nbsp;Sylvain Pauchet ,&nbsp;Martin Hytch","doi":"10.1016/j.ultramic.2024.114047","DOIUrl":"10.1016/j.ultramic.2024.114047","url":null,"abstract":"<div><div>The possibility of automatically aligning the transmission electron microscope (TEM) is explored using an approach based on artificial intelligence (AI). After presenting the general concept, we test the method on the first step of the alignment process which involves centering the condenser aperture. We propose using a convolutional neural network (CNN) that learns to predict the x and y-shifts needed to realign the aperture in one step. The learning data sets were acquired automatically on the microscope by using a simplified digital twin. Different models were tested and analysed to choose the optimal design. We have developed a human-level estimator and intend to use it safely on all apertures. A similar process could be used for most steps of the alignment process with minimal changes, allowing microscopists to reduce the time and training required to perform this task. The method is also compatible with continuous correction of alignment drift during lengthy experiments or to ensure uniformity of illumination conditions during data acquisition.</div></div>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2024-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142437665","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}