Ultramicroscopy最新文献

{"title":"New experimental methodology for determining the second crossover energy in insulators under stationary e-irradiation in a SEM","authors":"H. Hammami,&nbsp;S. Fakhfakh","doi":"10.1016/j.ultramic.2024.114069","DOIUrl":"10.1016/j.ultramic.2024.114069","url":null,"abstract":"<div><div>A new experimental methodology is proposed which uses the electrostatic influence method (EIM) in scanning electron microscope (SEM) in order to estimate the second crossover energy E_C2 for uncharged insulators. This experimental methodology based on simultaneous time measurement of the displacement and leakage currents, is approached to the short pulse irradiation technique but under stationary e-irradiation and allows determining the intrinsic secondary electron emission yield, σ₀ (σ₀ is the value of the total secondary electron yield just at the beginning of the irradiation before significant charge accumulation or before the formation of a surface potential). The obtained value of E_C2 for soda-lime glass is confirmed by two additional experiments based on secondary electron imaging. This value is in good agreement with those previously obtained by other studies based on the surface potential measurement or the pulsed irradiation technique.</div></div>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":"268 ","pages":"Article 114069"},"PeriodicalIF":2.1,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142629440","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":"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":"10.1016/j.ultramic.2024.114070","url":null,"abstract":"<div><div>The low energy region (&lt; 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.</div></div>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":"268 ","pages":"Article 114070"},"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":"OA","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":"267 ","pages":"Article 114068"},"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":"10.1016/j.ultramic.2024.114067","url":null,"abstract":"<div><div>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.</div></div>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":"268 ","pages":"Article 114067"},"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":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Towards atom counting from first moment STEM images: Methodology and possibilities","authors":"Yansong Hao ,&nbsp;Annick De Backer ,&nbsp;Scott David Findlay ,&nbsp;Sandra Van Aert","doi":"10.1016/j.ultramic.2024.114066","DOIUrl":"10.1016/j.ultramic.2024.114066","url":null,"abstract":"<div><div>Through a simulation-based study we develop a statistical model-based quantification method for atomic resolution first moment scanning transmission electron microscopy (STEM) images. This method uses the uniformly weighted least squares estimator to determine the unknown structure parameters of the images and to isolate contributions from individual atomic columns. In this way, a quantification of the projected potential per atomic column is achieved. Since the integrated projected potential of an atomic column scales linearly with the number of atoms it contains, it can serve as a basis for atom counting. The performance of atom counting from first moment STEM imaging is compared to that from traditional HAADF STEM in the presence of noise. Through this comparison, we demonstrate the advantage of first moment STEM images to attain more precise atom counts. Finally, we compare the integrated potential extracted from first-moment images of a wedge-shaped sample to those values from the bulk crystal. The excellent agreement found between these values proves the robustness of using bulk crystal simulations as a reference library. This enables atom counting for samples with different shapes by comparison with these library values.</div></div>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":"268 ","pages":"Article 114066"},"PeriodicalIF":2.1,"publicationDate":"2024-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142629443","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 ,&nbsp;M.R. Fernández-Fernández ,&nbsp;J.J. Fernández","doi":"10.1016/j.ultramic.2024.114065","DOIUrl":"10.1016/j.ultramic.2024.114065","url":null,"abstract":"","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":"267 ","pages":"Article 114065"},"PeriodicalIF":2.1,"publicationDate":"2024-10-26","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":"267 ","pages":"Article 114061"},"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":"267 ","pages":"Article 114063"},"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":"267 ","pages":"Article 114064"},"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":"267 ","pages":"Article 114062"},"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}