{"id":15,"date":"2024-04-04T04:31:15","date_gmt":"2024-04-04T01:31:15","guid":{"rendered":"https:\/\/sisu.ut.ee\/heritage-analysis\/41-sem-eds\/"},"modified":"2024-07-16T19:38:12","modified_gmt":"2024-07-16T16:38:12","slug":"41-sem-eds","status":"publish","type":"page","link":"https:\/\/sisu.ut.ee\/heritage-analysis\/41-sem-eds\/","title":{"rendered":"4.1. SEM-EDS"},"content":{"rendered":"<div style=\"height:30px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p>In this lecture, the introduction to\u00a0<strong>scanning\u00a0electron microscopy (SEM)<\/strong>\u00a0with\u00a0<strong>energy\u00a0dispersive spectroscopy (EDS)<\/strong>\u00a0will be given, and practical tips for the analysis as well as examples will be given. SEM-EDS (together with <a href=\"https:\/\/sisu.ut.ee\/heritage-analysis\/book\/42-xrf\" target=\"_blank\" rel=\"noopener\">XRF<\/a>) are among the most important elemental methods used for the analysis of cultural heritage objects. During this lecture, the capability and modern approaches (for example, imaging and mapping) of the analysis of various materials (for example, pigments, fillers, construction materials, minerals, clays etc.) will be discussed, and the advantages and disadvantages of the method will be pointed out.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span style=\"color: #b22222;\">1. General aspects of SEM-EDS<\/span><\/h2>\n\n\n\n<p><strong>Scanning electron microscope<\/strong> (usually abbreviated <strong>SEM<\/strong>) is a high-resolution imaging technique that is routinely used in the investigation of materials\u2019 surfaces. SEM can be coupled with an <strong>energy-dispersive X-ray detector<\/strong>, which enables highly local spatially resolved micro- and nano-scale elemental analysis of the surfaces. Due to its excellent spatial resolution, it allows detailed surface analysis at high imaging magnifications and is thus a very suitable method for the analysis of paint cross-sections.<\/p>\n\n\n\n<p><\/p><div class=\"ratio ratio-16x9 mb-3\"><div class=\"video-placeholder-wrapper video-placeholder-wrapper--16x9\">\n\t\t\t    <div class=\"video-placeholder d-flex justify-content-center align-items-center\">\n\t\t\t        <div class=\"overlay text-white p-2 w-100 text-center d-block justify-content-center align-items-center\">\n\t\t\t            <div>To view third-party content, please accept cookies.<\/div>\n\t\t\t            <button class=\"btn btn-secondary btn-sm mt-1 consent-change\">Change consent<\/button>\n\t\t\t        <\/div>\n\t\t\t    <\/div>\n\t\t\t<\/div>\n<\/div>\n\n\n\n<h2 class=\"wp-block-heading\"><span style=\"color: #b22222;\"><em>Scanning electron microscope (SEM)<\/em><\/span> <\/h2>\n\n\n\n<p><strong>SEM\u00a0<\/strong>operates by generating a beam of electrons in a vacuum. The beam is focused by electromagnetic lenses within a column and directed downwards onto the sample surface, focusing it on a very small surface area. The interaction of the electron beam with the sample causes\u00a0several simultaneous processes. The most important of them from the practical analysis point of view\u00a0are three:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong style=\"font-size: revert; text-align: var(--bs-body-text-align);\">ionisation of the sample<\/strong><span style=\"font-size: revert; font-weight: var(--bs-body-font-weight); text-align: var(--bs-body-text-align);\"> \u2013 ejection of\u00a0electrons from the atoms within the sample (whereby they are converted into excited ions), producing the so-called <\/span><strong style=\"font-size: revert; text-align: var(--bs-body-text-align);\"><em>secondary electrons<\/em><\/strong><span style=\"font-size: revert; font-weight: var(--bs-body-font-weight); text-align: var(--bs-body-text-align);\">,<\/span> <\/li>\n\n\n\n<li> <strong style=\"font-size: revert; text-align: var(--bs-body-text-align);\">reflection (back-scattering) of the beam electrons<\/strong><span style=\"font-size: revert; font-weight: var(--bs-body-font-weight); text-align: var(--bs-body-text-align);\"> from the sample surface, producing the so-called <\/span><em style=\"font-size: revert; font-weight: var(--bs-body-font-weight); text-align: var(--bs-body-text-align);\"><strong>backscattered electrons<\/strong> <\/em><span style=\"font-size: revert; font-weight: var(--bs-body-font-weight); text-align: var(--bs-body-text-align);\">and<\/span> <\/li>\n\n\n\n<li><p><strong>relaxation of the excited ions<\/strong> formed in process 1 accompanied by<em> <strong>emission of X-rays<\/strong>.<\/em><\/p><\/li>\n<\/ol>\n\n\n\n<p>Both secondary and backscattered\u00a0of electrons can be detected, amplified, and their abundance distribution across the surface can be used for image formation. The secondary electrons\u00a0give an image where the contrast is achieved on the basis of surface topography. The backscattered electrons give an image that is determined by differences in the elemental composition differences between parts of the sample surface. The electron beam can be very narrowly focused, and thereby high\u00a0surface resolution\u00a0(down to a few or few tens of nm) and high\u00a0magnification\u00a0(up to 100 000)\u00a0is possible.\u00a0<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span style=\"color: #b22222;\"><em>Energy dispersive X-ray spectrometer (EDS)\u00a0<\/em><\/span><\/h2>\n\n\n\n<div class=\"wp-block-group is-vertical is-layout-flex wp-container-core-group-is-layout-8cf370e7 wp-block-group-is-layout-flex\">\n<p><strong>EDS\u00a0<\/strong>detects and identifies the X-rays (as in the XRF method) that are\u00a0<span data-mce-mark=\"1\">emitted\u00a0in the course of the above mentioned process 3\u00a0by the\u00a0excited ions formed upon electron bombardment on the surface of the sample.<\/span> When the incident electron beam interacts with the inner shell electrons of an atom,\u00a0<span data-mce-mark=\"1\">then an electron is ejected (this process generates the above-mentioned secondary electrons)<\/span>. Ejection of the electron produces a\u00a0<span data-mce-mark=\"1\">vacancy in the inner electron shell of the atom.<\/span> That <span data-mce-mark=\"1\">vacancy\u00a0<\/span>is <span data-mce-mark=\"1\">thereafter\u00a0<\/span>filled by an electron from an outer shell. The transition results in the emission of X-rays. Each element emits X-ray photons with energies characteristic to that element. Energy dispersive X-ray analysis\u00a0<span data-mce-mark=\"1\">measures the energy of each emitted<\/span> X-ray <span data-mce-mark=\"1\">photon and uses this information to\u00a0<\/span>identify the elements in the sample <span data-mce-mark=\"1\">(via energies of the photons) and measure the abundance of the specific elements on the sample (via the abundance of the respective photons)<\/span>.<\/p>\n\n\n\n<p>When interpreting the EDS spectra, many elements have lines that overlap with one another (i.e. the energies of their characteristic photons are similar). Sometimes a peak from one element can obscure the peak from another. Some of the notorious overlaps encountered in paint analysis are titanium\/barium (Ti\/Ba), sulphur\/lead\/mercury (S\/Pb\/Hg), chromium\/manganese (Cr\/Mn), iron\/manganese (Fe\/Mn) and nikcel\/zinc (Ni\/Zn).<\/p>\n\n\n\n<p><\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span style=\"color: #b22222;\"><span data-mce-mark=\"1\">2. Analysis with SEM-EDS method<\/span><\/span><\/h2>\n\n\n\n<p><\/p>\n<\/div>\n\n\n\n<p><span data-mce-mark=\"1\">In the following video, geologist Marian K\u00fclaviir, MSc,\u00a0introduces SEM-EDS instrument, sample preparation and how to perform analysis with this instrument.<\/span><\/p>\n\n\n\n<p><span data-mce-mark=\"1\"><div class=\"ratio ratio-16x9 mb-3\"><div class=\"video-placeholder-wrapper video-placeholder-wrapper--16x9\">\n\t\t\t    <div class=\"video-placeholder d-flex justify-content-center align-items-center\">\n\t\t\t        <div class=\"overlay text-white p-2 w-100 text-center d-block justify-content-center align-items-center\">\n\t\t\t            <div>To view third-party content, please accept cookies.<\/div>\n\t\t\t            <button class=\"btn btn-secondary btn-sm mt-1 consent-change\">Change consent<\/button>\n\t\t\t        <\/div>\n\t\t\t    <\/div>\n\t\t\t<\/div>\n<\/div><\/span><\/p>\n\n\n\n<p>The slides used in the video\u00a0can be downloaded from\u00a0here:<\/p>\n\n\n\n<div class=\"wp-block-group attached-files-group is-layout-constrained wp-block-group-is-layout-constrained\">\n<div class=\"wp-block-file\"><a id=\"wp-block-file--media-24a0405f-1843-4f27-8d75-5a35fcdc3bf3\" href=\"https:\/\/sisu.ut.ee\/wp-content\/uploads\/sites\/285\/general_aspects_of_sem-eds.pdf\" target=\"_blank\" rel=\"noreferrer noopener\">General_aspects_of_SEM-EDS.pdf<\/a><\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>In this lecture, the introduction to\u00a0scanning\u00a0electron microscopy (SEM)\u00a0with\u00a0energy\u00a0dispersive spectroscopy (EDS)\u00a0will be given, and practical tips for the analysis as well as examples will be given. SEM-EDS (together with XRF) are among the most important elemental methods used for the analysis &#8230;<\/p>\n","protected":false},"author":151,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":""},"class_list":["post-15","page","type-page","status-publish","hentry"],"acf":[],"_links":{"self":[{"href":"https:\/\/sisu.ut.ee\/heritage-analysis\/wp-json\/wp\/v2\/pages\/15","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/sisu.ut.ee\/heritage-analysis\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/sisu.ut.ee\/heritage-analysis\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/sisu.ut.ee\/heritage-analysis\/wp-json\/wp\/v2\/users\/151"}],"replies":[{"embeddable":true,"href":"https:\/\/sisu.ut.ee\/heritage-analysis\/wp-json\/wp\/v2\/comments?post=15"}],"version-history":[{"count":3,"href":"https:\/\/sisu.ut.ee\/heritage-analysis\/wp-json\/wp\/v2\/pages\/15\/revisions"}],"predecessor-version":[{"id":834,"href":"https:\/\/sisu.ut.ee\/heritage-analysis\/wp-json\/wp\/v2\/pages\/15\/revisions\/834"}],"wp:attachment":[{"href":"https:\/\/sisu.ut.ee\/heritage-analysis\/wp-json\/wp\/v2\/media?parent=15"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}