The document discusses transmission electron microscopy (TEM). It begins by explaining that TEM uses a beam of electrons to produce high resolution images of specimens. TEM provides higher resolution than optical microscopes because electrons have shorter wavelengths than visible light. The document then describes the basic components and functioning of TEM, including how electromagnetic lenses are used to focus the electron beam onto thin specimen samples and form magnified images. Specimen preparation methods for TEM like chemical fixation and staining are also covered.
Transmission electron microscopy uses electrons instead of light to image samples. Ernst Ruska developed the first electron microscope in 1931. A TEM uses an electron gun to produce an electron beam that passes through a thin sample. Electron lenses magnify the beam up to 250,000x to form an image on a screen. Key components include the electron gun, lens system, vacuum pumps, specimen stage and aperture. TEMs are expensive but can provide very high resolution imaging down to the atomic scale, finding wide application in fields like materials science and biology.
X-ray photoelectron spectroscopy (XPS) or Electron spectroscopy for chemical analysis (ESCA) is used to investigate the chemistry at the surface of the samples. The basic mechanism behind an XPS instrument is that the photons of a specific energy are used to excite the electronic states of atoms at and just below the surface of the sample.
There are several areas suited to measurement by XPS:
1. Elemental composition
2. Empirical formula determination
3. Chemical state
4. Electronic state
5. Binding energy
6. Layer thickness in the upper portion of surfaces
XPS has many advantages, such as it is is good for identifying all but two elements, identifying the chemical state on surfaces, and is good with quantitative analysis. XPS is capable of detecting the difference in the chemical state between samples. XPS is also able to differentiate between oxidations states of molecules.
XPS has also some limitations, for instance, samples for XPS must be compatible with the ultra high vacuum environment. XPS is limited to measurements of elements having atomic numbers of 3 or greater, making it unable to detect hydrogen or helium. XPS spectra also take a long time to obtain. The use of a monochromator can also reduce the time per experiment.
The document provides information about scanning electron microscopes (SEMs), including:
- A brief history of the development of SEMs from the 1930s to modern commercial versions.
- An overview of the basic components and working principles of SEMs, such as using an electron beam to scan samples and detect signals to form images.
- Descriptions and diagrams of key parts like the electron gun, electromagnetic lenses, detectors, and vacuum system.
- Explanations of imaging modes and how SEMs can be used for chemical analysis of samples.
- Advantages and limitations of SEM technology.
The document provides an overview of scanning electron microscopy (SEM). It describes how SEM can be used to study topography, morphology, chemistry, crystallography, and orientation of grains in samples. SEM also allows for in-situ experiments by using accessories like hot stages. Images are formed by detecting signals from electron beam and sample interactions, including secondary electrons, backscattered electrons, and x-rays. The document discusses the various components of SEM and factors that influence resolution.
Transmission electron microscopy uses electrons instead of light to image samples. Ernst Ruska developed the first electron microscope in 1931. A TEM uses an electron gun to produce an electron beam that passes through a thin sample. Electron lenses magnify the beam up to 250,000x to form an image on a screen. Key components include the electron gun, lens system, vacuum pumps, specimen stage and aperture. TEMs are expensive but can provide very high resolution imaging down to the atomic scale, finding wide application in fields like materials science and biology.
X-ray photoelectron spectroscopy (XPS) or Electron spectroscopy for chemical analysis (ESCA) is used to investigate the chemistry at the surface of the samples. The basic mechanism behind an XPS instrument is that the photons of a specific energy are used to excite the electronic states of atoms at and just below the surface of the sample.
There are several areas suited to measurement by XPS:
1. Elemental composition
2. Empirical formula determination
3. Chemical state
4. Electronic state
5. Binding energy
6. Layer thickness in the upper portion of surfaces
XPS has many advantages, such as it is is good for identifying all but two elements, identifying the chemical state on surfaces, and is good with quantitative analysis. XPS is capable of detecting the difference in the chemical state between samples. XPS is also able to differentiate between oxidations states of molecules.
XPS has also some limitations, for instance, samples for XPS must be compatible with the ultra high vacuum environment. XPS is limited to measurements of elements having atomic numbers of 3 or greater, making it unable to detect hydrogen or helium. XPS spectra also take a long time to obtain. The use of a monochromator can also reduce the time per experiment.
The document provides information about scanning electron microscopes (SEMs), including:
- A brief history of the development of SEMs from the 1930s to modern commercial versions.
- An overview of the basic components and working principles of SEMs, such as using an electron beam to scan samples and detect signals to form images.
- Descriptions and diagrams of key parts like the electron gun, electromagnetic lenses, detectors, and vacuum system.
- Explanations of imaging modes and how SEMs can be used for chemical analysis of samples.
- Advantages and limitations of SEM technology.
The document provides an overview of scanning electron microscopy (SEM). It describes how SEM can be used to study topography, morphology, chemistry, crystallography, and orientation of grains in samples. SEM also allows for in-situ experiments by using accessories like hot stages. Images are formed by detecting signals from electron beam and sample interactions, including secondary electrons, backscattered electrons, and x-rays. The document discusses the various components of SEM and factors that influence resolution.
Transmission electron microscopy (TEM) uses a beam of electrons to image the internal structure of ultra-thin specimens. TEMs can achieve significantly higher resolutions than light microscopes due to the much shorter wavelength of electrons. Samples must be carefully prepared to be only a few hundred nanometers thick to be electron transparent. The electron beam is transmitted through the sample, interacting with it, and an image is formed from the transmitted electrons and magnified onto a viewing screen. TEM is widely used across various scientific fields including materials science, biology, and medicine.
Electron microscopes use beams of electrons rather than light to image objects at a very fine scale. The scanning electron microscope (SEM) was developed in the 1930s-1960s to overcome limitations of light microscopes. An SEM scans samples with a high-energy electron beam, producing signals containing information about surface topography, composition, and other properties. Key advantages of SEMs over light microscopes are their greater magnification, depth of field, and resolution. Proper sample preparation including cleaning, fixation, dehydration and coating is required to image non-conductive biological samples in the SEM's vacuum environment.
This document provides an overview of transmission electron microscopy (TEM). It discusses the history and development of TEM, the theoretical background explaining why electron microscopes were needed, an explanation of TEM instrumentation including the electron gun, condenser lens, objective lens and screen. It also covers TEM sample preparation techniques and the types of information that can be obtained from TEM such as thickness, orientation, composition and bonding states. Finally, it notes some limitations of TEM including small sample size, challenges of interpreting 2D images of 3D samples, potential radiation hazards, and the need for very thin electron transparent samples.
Xps (x ray photoelectron spectroscopy)Zaahir Salam
The document provides an overview of X-ray photoelectron spectroscopy (XPS) technology. XPS works by irradiating a sample surface with x-rays and measuring the kinetic energy and number of electrons that escape from the top 1-10 nm of the material. This allows one to determine the sample's elemental composition and chemical/electronic states. Key aspects discussed include the use of ultra-high vacuum conditions to prevent surface contamination and allow for accurate analysis. Characteristic XPS spectra are produced that contain peaks corresponding to different elemental binding energies.
- The atomic force microscope (AFM) is a type of scanning probe microscope used to image surfaces at the nanoscale. It measures forces between a sharp probe and the sample surface.
- In contact mode, the AFM tip is in contact with the sample surface and repulsive forces are measured. In tapping mode, the tip lightly taps the surface to reduce lateral forces and damage.
- The AFM has many applications in biology like imaging living cells, studying protein unfolding, measuring molecular interactions like DNA binding, and more. It can be used to map molecular recognition with single molecule resolution.
The document discusses the transmission electron microscope (TEM). It begins by explaining that a TEM uses a beam of electrons rather than light to produce highly magnified images of thin specimens. It then provides details on the history and development of the TEM. The body of the document describes the main components of a TEM, including the electron gun, image producing system, and image recording system. It explains how each component works and its role in producing a magnified image. Applications of the TEM in fields like biology and nanotechnology are also mentioned.
The document provides an overview of the transmission electron microscope (TEM). It discusses key components of the TEM including the electron gun, condenser lenses, objective lens, and vacuum system. The document explains that TEM uses electromagnetic lenses to focus a beam of electrons onto a thin specimen, and forms an image from the interaction of electrons transmitted through the specimen. TEM allows higher magnification and resolution than light microscopes, and can be used to investigate the morphology, structure, and composition of materials down to the atomic scale.
Electron microscopes use a beam of electrons to examine objects on a very fine scale. There are two main types: transmission electron microscopes, which allow study of inner structures, and scanning electron microscopes, which are used to visualize surface features. Scanning electron microscopes work by scanning a focused beam of electrons across a sample to detect signals emitted from interactions between the electrons and the sample. These signals provide information about the sample's topography, morphology, composition, and other characteristics at high magnifications.
X-ray photoelectron spectroscopy (XPS) is a surface-sensitive technique that uses X-rays to eject core electrons from the surface of a sample. It can be used to identify the elements present in the sample and provide information about the chemical and electronic states of the elements. In XPS, X-rays eject core electrons, which are then analyzed based on their kinetic energy. This kinetic energy is related to the electron binding energy and can be used to identify the element and chemical environment. XPS requires ultra-high vacuum to avoid surface contamination and provide high-resolution spectra with sharp elemental peaks and broader Auger peaks.
This document provides an overview of scanning electron microscopy (SEM). It discusses the basic principles and instrumentation of SEM, including how electron beams are used to generate images by interacting with sample surfaces. The document explains that SEM provides higher resolution than light microscopes and can be used to examine surface topography, morphology, composition, and crystallographic structure at nanometer to micrometer scales. It describes the major components of an SEM, including the electron gun, electromagnetic lenses, vacuum system, detectors for secondary electrons and backscattered electrons, and how these are used to scan samples and form images.
This document provides an overview of scanning electron microscopy (SEM). It discusses how SEM works by using a beam of electrons to examine objects at a very fine scale, with greater resolving power than light microscopes. The first SEM debuted in 1938. SEM can provide information about a sample's topography, morphology, composition, and crystal structure. Diagrams show the major components of an SEM, including the electron gun and various detectors. Imaging modes like secondary electron and backscattered electron are described. Applications and limitations of SEM are also summarized.
This document provides an overview of scanning electron microscopy (SEM). It discusses the history and development of SEM from the 1930s to present. The key components of an SEM are described, including the electron gun, lenses, scan coils, vacuum system and detectors. SEM provides higher magnification and resolution than light microscopes. Specimen preparation such as fixation, dehydration and coating are outlined. Applications include examining the structure of cells, crystals, and biological and inorganic materials. Advantages are high magnification and digital image capture, while limitations include expense and inability to view non-conductive samples.
The document discusses the scanning electron microscope (SEM). The SEM uses a focused beam of electrons to scan the surface of a sample and produce images with high magnification and resolution. It has several advantages over optical microscopes, including higher magnification, greater depth of field, and the ability to provide 3D images and determine sample composition. The SEM has many applications in science and industry such as structural analysis, measurements, and failure inspection. It provides valuable but has some limitations like requiring solid samples and being costly.
The document discusses scanning electron microscopy (SEM). It describes SEM as using a beam of electrons to examine objects on a fine scale, yielding information about topography, morphology, composition, and crystal structure. It outlines the main parts of an SEM, including the electron gun, electromagnetic lenses, vacuum chamber, and detectors for secondary electrons, backscattered electrons, and X-rays. The document explains that SEM works by scanning a focused electron beam across the sample surface and detecting signals from emitted electrons and X-rays to form images at magnifications up to 200,000x and resolutions of 1-2 nm.
The document summarizes the key components and operating principles of a scanning electron microscope (SEM). It describes the electron gun that generates the electron beam, the condenser lenses that focus the beam, the scan coils that scan the beam across the sample, and various detectors that detect signals from the sample. It outlines applications in fields like biology, materials science, and forensics. Advantages include detailed imaging and versatile information from detectors, while disadvantages include high costs and specialized training required.
Molecular beam epitaxy (MBE) is a method for growing thin films one layer at a time under ultra-high vacuum conditions. It involves heating solid sources of material in effusion cells to create molecular beams that are deposited on a heated substrate. The absence of carrier gases and ultra-high vacuum environment result in films of the highest purity. MBE is widely used to manufacture semiconductor devices and is considered a fundamental tool for nanotechnology development due to its precise control over layer thickness down to a single atomic layer.
The document discusses the transmission electron microscope (TEM). It begins by providing a brief history and overview, explaining that TEM uses electrons rather than light to image specimens. It then describes the key components and working principles of TEM, including how it produces higher resolution images than light microscopes due to electrons' lower wavelength. Finally, it outlines some common applications of TEM in fields like materials science, biology, and manufacturing, and notes advantages like powerful magnification but also disadvantages like high costs and specialized training needs.
Transmission electron microscopy (TEM) uses a beam of electrons to examine objects at a very fine scale. TEM can image at a higher resolution than light microscopes due to the shorter wavelength of electron beams. In TEM, a beam of electrons is transmitted through an ultrathin specimen, interacting with the sample as it passes through. This interaction is used to form an image that is magnified and focused onto a screen, with resolutions down to fractions of a nanometer. TEM is widely used in materials science, biology, and medicine for examining nanostructures.
This document discusses transmission electron microscopy (TEM). TEM uses beams of electrons instead of light to image objects at a much higher resolution. TEM can image objects as small as a single column of atoms. It works by transmitting a beam of electrons through a thin sample. The electrons interact with the sample and are used to form a magnified image. TEM allows observation of nano-scale structures and can provide information about material composition and crystal structure.
Transmission electron microscopy (TEM) uses a beam of electrons to image the internal structure of ultra-thin specimens. TEMs can achieve significantly higher resolutions than light microscopes due to the much shorter wavelength of electrons. Samples must be carefully prepared to be only a few hundred nanometers thick to be electron transparent. The electron beam is transmitted through the sample, interacting with it, and an image is formed from the transmitted electrons and magnified onto a viewing screen. TEM is widely used across various scientific fields including materials science, biology, and medicine.
Electron microscopes use beams of electrons rather than light to image objects at a very fine scale. The scanning electron microscope (SEM) was developed in the 1930s-1960s to overcome limitations of light microscopes. An SEM scans samples with a high-energy electron beam, producing signals containing information about surface topography, composition, and other properties. Key advantages of SEMs over light microscopes are their greater magnification, depth of field, and resolution. Proper sample preparation including cleaning, fixation, dehydration and coating is required to image non-conductive biological samples in the SEM's vacuum environment.
This document provides an overview of transmission electron microscopy (TEM). It discusses the history and development of TEM, the theoretical background explaining why electron microscopes were needed, an explanation of TEM instrumentation including the electron gun, condenser lens, objective lens and screen. It also covers TEM sample preparation techniques and the types of information that can be obtained from TEM such as thickness, orientation, composition and bonding states. Finally, it notes some limitations of TEM including small sample size, challenges of interpreting 2D images of 3D samples, potential radiation hazards, and the need for very thin electron transparent samples.
Xps (x ray photoelectron spectroscopy)Zaahir Salam
The document provides an overview of X-ray photoelectron spectroscopy (XPS) technology. XPS works by irradiating a sample surface with x-rays and measuring the kinetic energy and number of electrons that escape from the top 1-10 nm of the material. This allows one to determine the sample's elemental composition and chemical/electronic states. Key aspects discussed include the use of ultra-high vacuum conditions to prevent surface contamination and allow for accurate analysis. Characteristic XPS spectra are produced that contain peaks corresponding to different elemental binding energies.
- The atomic force microscope (AFM) is a type of scanning probe microscope used to image surfaces at the nanoscale. It measures forces between a sharp probe and the sample surface.
- In contact mode, the AFM tip is in contact with the sample surface and repulsive forces are measured. In tapping mode, the tip lightly taps the surface to reduce lateral forces and damage.
- The AFM has many applications in biology like imaging living cells, studying protein unfolding, measuring molecular interactions like DNA binding, and more. It can be used to map molecular recognition with single molecule resolution.
The document discusses the transmission electron microscope (TEM). It begins by explaining that a TEM uses a beam of electrons rather than light to produce highly magnified images of thin specimens. It then provides details on the history and development of the TEM. The body of the document describes the main components of a TEM, including the electron gun, image producing system, and image recording system. It explains how each component works and its role in producing a magnified image. Applications of the TEM in fields like biology and nanotechnology are also mentioned.
The document provides an overview of the transmission electron microscope (TEM). It discusses key components of the TEM including the electron gun, condenser lenses, objective lens, and vacuum system. The document explains that TEM uses electromagnetic lenses to focus a beam of electrons onto a thin specimen, and forms an image from the interaction of electrons transmitted through the specimen. TEM allows higher magnification and resolution than light microscopes, and can be used to investigate the morphology, structure, and composition of materials down to the atomic scale.
Electron microscopes use a beam of electrons to examine objects on a very fine scale. There are two main types: transmission electron microscopes, which allow study of inner structures, and scanning electron microscopes, which are used to visualize surface features. Scanning electron microscopes work by scanning a focused beam of electrons across a sample to detect signals emitted from interactions between the electrons and the sample. These signals provide information about the sample's topography, morphology, composition, and other characteristics at high magnifications.
X-ray photoelectron spectroscopy (XPS) is a surface-sensitive technique that uses X-rays to eject core electrons from the surface of a sample. It can be used to identify the elements present in the sample and provide information about the chemical and electronic states of the elements. In XPS, X-rays eject core electrons, which are then analyzed based on their kinetic energy. This kinetic energy is related to the electron binding energy and can be used to identify the element and chemical environment. XPS requires ultra-high vacuum to avoid surface contamination and provide high-resolution spectra with sharp elemental peaks and broader Auger peaks.
This document provides an overview of scanning electron microscopy (SEM). It discusses the basic principles and instrumentation of SEM, including how electron beams are used to generate images by interacting with sample surfaces. The document explains that SEM provides higher resolution than light microscopes and can be used to examine surface topography, morphology, composition, and crystallographic structure at nanometer to micrometer scales. It describes the major components of an SEM, including the electron gun, electromagnetic lenses, vacuum system, detectors for secondary electrons and backscattered electrons, and how these are used to scan samples and form images.
This document provides an overview of scanning electron microscopy (SEM). It discusses how SEM works by using a beam of electrons to examine objects at a very fine scale, with greater resolving power than light microscopes. The first SEM debuted in 1938. SEM can provide information about a sample's topography, morphology, composition, and crystal structure. Diagrams show the major components of an SEM, including the electron gun and various detectors. Imaging modes like secondary electron and backscattered electron are described. Applications and limitations of SEM are also summarized.
This document provides an overview of scanning electron microscopy (SEM). It discusses the history and development of SEM from the 1930s to present. The key components of an SEM are described, including the electron gun, lenses, scan coils, vacuum system and detectors. SEM provides higher magnification and resolution than light microscopes. Specimen preparation such as fixation, dehydration and coating are outlined. Applications include examining the structure of cells, crystals, and biological and inorganic materials. Advantages are high magnification and digital image capture, while limitations include expense and inability to view non-conductive samples.
The document discusses the scanning electron microscope (SEM). The SEM uses a focused beam of electrons to scan the surface of a sample and produce images with high magnification and resolution. It has several advantages over optical microscopes, including higher magnification, greater depth of field, and the ability to provide 3D images and determine sample composition. The SEM has many applications in science and industry such as structural analysis, measurements, and failure inspection. It provides valuable but has some limitations like requiring solid samples and being costly.
The document discusses scanning electron microscopy (SEM). It describes SEM as using a beam of electrons to examine objects on a fine scale, yielding information about topography, morphology, composition, and crystal structure. It outlines the main parts of an SEM, including the electron gun, electromagnetic lenses, vacuum chamber, and detectors for secondary electrons, backscattered electrons, and X-rays. The document explains that SEM works by scanning a focused electron beam across the sample surface and detecting signals from emitted electrons and X-rays to form images at magnifications up to 200,000x and resolutions of 1-2 nm.
The document summarizes the key components and operating principles of a scanning electron microscope (SEM). It describes the electron gun that generates the electron beam, the condenser lenses that focus the beam, the scan coils that scan the beam across the sample, and various detectors that detect signals from the sample. It outlines applications in fields like biology, materials science, and forensics. Advantages include detailed imaging and versatile information from detectors, while disadvantages include high costs and specialized training required.
Molecular beam epitaxy (MBE) is a method for growing thin films one layer at a time under ultra-high vacuum conditions. It involves heating solid sources of material in effusion cells to create molecular beams that are deposited on a heated substrate. The absence of carrier gases and ultra-high vacuum environment result in films of the highest purity. MBE is widely used to manufacture semiconductor devices and is considered a fundamental tool for nanotechnology development due to its precise control over layer thickness down to a single atomic layer.
The document discusses the transmission electron microscope (TEM). It begins by providing a brief history and overview, explaining that TEM uses electrons rather than light to image specimens. It then describes the key components and working principles of TEM, including how it produces higher resolution images than light microscopes due to electrons' lower wavelength. Finally, it outlines some common applications of TEM in fields like materials science, biology, and manufacturing, and notes advantages like powerful magnification but also disadvantages like high costs and specialized training needs.
Transmission electron microscopy (TEM) uses a beam of electrons to examine objects at a very fine scale. TEM can image at a higher resolution than light microscopes due to the shorter wavelength of electron beams. In TEM, a beam of electrons is transmitted through an ultrathin specimen, interacting with the sample as it passes through. This interaction is used to form an image that is magnified and focused onto a screen, with resolutions down to fractions of a nanometer. TEM is widely used in materials science, biology, and medicine for examining nanostructures.
This document discusses transmission electron microscopy (TEM). TEM uses beams of electrons instead of light to image objects at a much higher resolution. TEM can image objects as small as a single column of atoms. It works by transmitting a beam of electrons through a thin sample. The electrons interact with the sample and are used to form a magnified image. TEM allows observation of nano-scale structures and can provide information about material composition and crystal structure.
The document discusses electron microscopes and optical microscopes. It describes the basic components and working principles of transmission electron microscopes (TEM) and scanning electron microscopes (SEM). TEM uses electron beams to form images with very high resolution, while SEM scans the sample surface with a focused electron beam to produce 3D images. Optical microscopes like compound microscopes use lenses and light to magnify samples, but have lower resolution than electron microscopes. Examples of applications for each type of microscope are also provided.
The document describes and compares scanning electron microscopes (SEM) and transmission electron microscopes (TEM). SEMs produce images by scanning a sample's surface with an electron beam, while TEMs transmit an electron beam through a thin sample to form a magnified image. Both use electromagnetic lenses and electron beam interactions with samples, but SEMs detect signals from secondary electrons at the surface, while TEMs detect transmitted electrons. Key applications include nanotechnology, materials science, biology, and medicine.
The document provides information about electron microscopes. It discusses how electron microscopes work by using a beam of electrons instead of light to illuminate samples. This allows for higher magnifications and resolutions compared to light microscopes. It describes the key components of transmission electron microscopes and scanning electron microscopes, including the electron gun, electromagnetic lenses, sample stage, detectors, and vacuum system. It also explains how electron microscopes can be used to study thin sections and surface topography of samples at nanometer or micrometer scales.
The document discusses electron microscopes and their components and operation. Electron microscopes use a beam of electrons instead of light to examine objects at a very fine scale. There are two main types - scanning electron microscopes (SEM) and transmission electron microscopes (TEM). SEMs produce higher resolution images than optical microscopes and work by scanning a focused beam of electrons across a sample. TEMs require electron-transparent samples and work by transmitting electrons through a sample to form an image. Both types of electron microscopes have advanced scientific understanding by allowing observation of microscopic structures.
This document provides an overview of various characterization techniques used for nanomaterials and nanostructures. It begins by explaining that characterization of nanostructures requires high sensitivity, accuracy, and atomic-level resolution. It then classifies characterization techniques as either chemical or structural characterization. The document goes on to describe several common tools used, including XRD, SEM, TEM, optical spectroscopy, SPM techniques like AFM and STM, and their basic working principles and applications in nanomaterial characterization.
Scanning and transmission electroscopy.pptxNirmal P J
This document provides information about the transmission electron microscope (TEM). It begins by explaining that a TEM uses electron beams to produce highly magnified images of incredibly thin samples, up to 10-50 million times magnification and less than 150nm thick. It describes the basic components and functioning of a TEM, including the electron gun, magnetic lenses, sample stage, imaging system, and detector. Key points are that TEMs allow viewing structures at the molecular level and have a resolution limit of 0.2 micrometers. The document also discusses applications in fields like virology and nanotechnology, and advantages like high magnification and quality images.
The document provides information on electron microscopy. It discusses the basic components and operating principles of transmission electron microscopes and scanning electron microscopes. Key points include: TEMs use electromagnetic lenses to focus electrons into an image, while SEMs scan specimen surfaces with a focused electron beam to produce topographical images. Both require specimens to be prepared through fixation, dehydration, embedding and sectioning to withstand the vacuum conditions. Contrast in electron micrographs is obtained through interactions between electrons and the specimen.
The document discusses different types of microscopes used to view very small objects. It compares light microscopes and electron microscopes. Electron microscopes use beams of electrons instead of light to form higher magnification and resolution images. There are two main types - scanning electron microscopes, which view surface features, and transmission electron microscopes, which can view inside thin specimens at up to 500,000x magnification. Electron microscopes require specimens to be prepared differently and have more complex components than light microscopes to generate and control the electron beam.
Presentationon optical and electron microscopy by deepak kumar Drx Kumar
This document provides information on optical and electron microscopy. It discusses the basic principles and components of simple microscopes, compound microscopes, transmission electron microscopy, and scanning electron microscopy. Compound microscopes use lenses to magnify real images, allowing higher magnification than simple microscopes. Transmission electron microscopy uses electron beams and electromagnetic lenses to image very thin samples at resolutions up to 2.5 nm. Scanning electron microscopy scans sample surfaces with an electron beam to produce 3D images at magnifications up to 10,000x. Both electron microscopy techniques provide higher resolution than optical microscopy but have specific sample preparation and imaging requirements.
Beam of electrons is transmitted through an ultra thin specimen,
An image is formed from the interaction of the electrons transmitted through the specimen,
The image is magnified and focused onto an imaging device, such as a fluorescent screen, on a layer of photographic film, or to be detected by a sensor such as a CCD camera
The document discusses confocal and electron microscopy. It describes the components and working principles of the confocal microscope, including point illumination. Applications of confocal microscopy include biomedical sciences, cell biology, and pharmaceutical quality control. Electron microscopy uses electron beams instead of light. Transmission electron microscopes view thin specimens through which electrons can pass, while scanning electron microscopes scan surfaces with a focused electron beam. Both provide high magnification and resolution views of cells, molecules, and materials.
The transmission electron microscope is a very powerful tool for material science. A high energy beam of electrons is shone through a very thin sample, and the interactions between the electrons and the atoms can be used to observe features such as the crystal structure and features in the structure like dislocations and grain boundaries. Chemical analysis can also be performed. TEM can be used to study the growth of layers, their composition and defects in semiconductors. High resolution can be used to analyze the quality, shape, size and density of quantum wells, wires and dots.
This document provides an introduction to electron microscopy. It begins with fundamental concepts and then discusses the construction of transmission and scanning electron microscopes. It explains key differences between electron microscopes and optical microscopes, such as electrons having no visible wavelength. The document compares the similarities and differences between EM and LM, such as both having illumination, specimen, and imaging systems, but EM using magnetic lenses. It discusses electron-specimen interactions that EM can detect such as backscattered electrons, secondary electrons, Auger electrons, X-rays, and diffraction patterns. Finally, it covers high resolution EM and examples of discoveries it enabled.
The document discusses the history and operating principles of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It explains that SEM uses a scanned beam of electrons to generate signals from the surface of a sample to form an image, while TEM shoots electrons through a thin sample. TEM can view interior structures and has higher magnification, while SEM provides 3D surface images. Both techniques greatly exceed the resolution of light microscopes and revolutionized microscopy by enabling visualization of structures at the nanoscale.
This document provides an overview of the working principle of a scanning electron microscope (SEM). It discusses key components of an SEM like the electron gun, condenser lenses, scan coils, objective lens, and detectors. It explains how SEM produces high-resolution images by scanning a focused beam of electrons across a sample. Secondary electrons and backscattered electrons are generated from sample-electron interactions and detected to form images. Factors affecting resolution, magnification and other imaging modes are also summarized. Advantages of SEM like high resolution and versatility are mentioned along with disadvantages like high cost, vacuum requirements and sample preparation needs.
The document discusses microscopy and different types of microscopes. It begins by defining microscopy as the technology that makes small objects visible to the human eye using microscopes. It then describes different types of microscopes, focusing on light microscopes and electron microscopes. Electron microscopes use a beam of electrons rather than light, allowing them to achieve much higher magnifications and resolving power than light microscopes. The document discusses the basic components and working principles of transmission electron microscopes and scanning electron microscopes. It also covers sample preparation techniques, applications, limitations, and recent research using electron microscopy.
Similar to 2018 HM-Transmission electron microscope (20)
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18 HM-- RADIATION SOURCES -NATURAL AND MAN MADEHarsh Mohan
The document discusses natural and man-made sources of radiation. It covers three main types of natural radiation exposure: 1) Cosmic radiation from sources outside the earth like the sun and solar system formation. Cosmic rays interact with the atmosphere to produce secondary particles. 2) External radiation from natural radioactive elements in the earth's crust like uranium, thorium, and potassium. 3) Internal exposure from radioactive elements in the body like carbon-14 and potassium-40. The document provides details on cosmic radiation levels at different altitudes and its interaction with the atmosphere. Natural sources are the main contributor to background radiation levels.
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3. Microscopy
• main branches: optical, electron and scanning
probe microscopy.
• Optical and electron microscopy involves the
diffraction, reflection, or refraction of radiation
incident upon the subject of study, and the
subsequent collection of this scattered
radiation in order to build up an image.
• Scanning probe microscopy involves the
interaction of a scanning probe with the
surface or object of interest.
4. • Optical or light microscopy involves passing
visible light transmitted through or reflected from
the sample through a single or multiple lenses to
allow a magnified view of the sample.
• The resulting image can be detected directly by
the eye, imaged on a photographic plate or
captured digitally.
• The single lens with its attachments, or the system
of lenses and imaging equipment, along with the
appropriate lighting equipment, sample stage and
support, makes up the basic light microscope.
Optical microscopy - definition
8. Optical microscopy - limitations
OM can only image dark or strongly
refracting objects effectively
.
Out of focus light from points outside the
focal plane reduces image clarity.
Compound optical microscopes are limited
in their ability to resolve fine details by the
properties of light and the refractive
materials used to manufacture lenses. A
lens magnifies by bending light..
9. Optical microscopes are restricted in their ability to
resolve features by a phenomenon called diffraction
which, based on the numerical aperture AN of the
optical system and the wavelengths of light used (λ),
sets a definite limit (d) to the optical resolution.
Assuming that optical aberrations are negligible, the
resolution (d) is given by:
In case of λ = 550 nm (green light), with air as medium,
the highest practical AN is 0.95, with oil, up to 1.5.
Due to diffraction, even the best optical microscope is
limited to a resolution of around 0.2 micrometres
10. What is a Microscope?
• A tool that magnifies and improves resolution
of the components of a structure
• Has three components:
• sources of illumination,
• a magnifying system,
• detectors.
13. Remember that there are 1000 micrometers (µm) in 1 mm and
1000 nanometers (nm) in 1 µm.
The human eye can separate 0.2 mm at a normal viewing
distance of 25 cm
The light microscope can separate 0.2 µm (0.002mm)
depending on wavelength of light used
Electrons have a smaller wavelength than light therefore
provide the highest resolving power – about 2 nm
(0.000002mm)
14. Electron Microscope vs. Optical Microscope
• Electron vs. Photon
Electron: charged, has rest mass, not visible
Photon: neutral, has no rest mass, visible at the
wavelength ~ 400 nm-760 nm.
Because of these differences, the microscope construction will also be different
(first one built in 1931 by Ruska and Knoll) (Leeuwenhoek in 17th
century)
What is the common property?
15. 16
The Compound Microscope
• Magnification
–Multiply magnifying power of the
objective lens X magnifying power of the
eyepiece lens
• Mechanical system
–Supports the microscope
• Optical system
–Illuminates object
–Passes light through a series of lenses
16. 17
• Optical instrument
– Lens or combination of lenses
– Magnify, resolve fine details
• Earliest methods for examining physical
evidence
• Magnified image = virtual image
• Image viewed directly = real image.
18. Sources of Illumination
• Light microscopes use a beam of light for
illumination and include fluorescence and
confocal microscopes
• Electron microscopes use electrons as a source
of illumination and include transmission and
scanning electron microscopes.
25. A short history
• TEM constructed in 1931
• Von Ardenne first STEM in 1938 by rastering
the electron beam in a TEM
• Zworykin et al. 1942, first SEM for bulk
samples
• 1965 first commercial SEM by Cambridge
Scientific Instruments
Resolution at that time ~ 50 nm <-> Today < 1 nm
Morphology only at that time <-> Today analytical instrument
29. Types of Electron Microscope
• Transmission Electron Microscope (TEM) uses a
wide beam of electrons passing through a thin
sliced specimen to form an image. This
microscope is analogous to a standard upright or
inverted light microscope
• Scanning Electron Microscope (SEM) uses
focused beam of electrons scanning over the
surface of thick or thin specimens. Images are
produced one spot at a time in a grid-like raster
pattern.
38. Electron Microscopy - definition and types
• developed in the 1930s that use electron beams instead of light.
• because of the much lower wavelength of the electron beam
than of light, resolution is far higher.
TYPES
• Transmission electron microscopy (TEM) is principally
quite similar to the compound light microscope, by sending an
electron beam through a very thin slice of the specimen. The
resolution limit (in 2005) is around 0.05 nanometer.
• Scanning electron microscopy (SEM) visualizes details on
the surfaces of cells and particles and gives a very nice 3D
view. The magnification is in the lower range than that of the
transmission electron microscope.
39. Transmission Electron Microscopy (TEM)
• beam of electrons is transmitted through a specimen, then an
image is formed, magnified and directed to appear either on a
fluorescent screen or layer of photographic film or to be
detected by a sensor (e.g. charge-coupled device, CCD camera.
• involves a high voltage electron beam emitted by a cathode,
usually a tungsten filament and focused by electrostatic and
electromagnetic lenses.
• electron beam that has been transmitted through a specimen
that is in part transparent to electrons carries information
about the inner structure of the specimen in the electron beam
that reaches the imaging system of the microscope.
• spatial variation in this information (the "image") is then
magnified by a series of electromagnetic lenses until it is
recorded by hitting a fluorescent screen, photographic plate, or
CCD camera. The image detected by the CCD may be
displayed in real time on a monitor or computer.
40. The resolution is proportional to the
wave length!
Electron equivalent wavelength and accelerating voltage
The dualism wave/particle is quantified by the
De Broglie equation:
λ = h/p = h/mv
λ : wavelength; h: Planck constant; p:
momentum
41. At the acceleration voltages used in TEM, relativistic effects
have to be taken into account (e.g. E>100 keV)
λ = h / [2m0eV (1 + eV/2m0/c2
)]1/2
The energy of accelerate electrons is equal to their kinetic
energy:
E = eV = m0v2
/2
V: acceleration voltage
e / m0 / v: charge / rest mass / velocity of the electron
These equations can be combined to calculate the wave
length of an electron with a certain energy:
p = m0v = (2m0eV)1/2
λ = h / (2m0eV)1/2
(≈ 1.22 / V1/2
nm)
48. Light and Electron Microscopes
• Lenses are
used to
control a
beam of
illumination,
magnify, and
direct an
image to a
detector
49. Principal features of an optical microscope, a transmission electron microscope
and a scanning electron microscope, drawn to emphasize the similarities of
overall design.
Comparison of OM,TEM and SEM
OM TEM SEM
Magnetic
lenses
detector
CRT
Cathode Ray
Tube
Light source
Source of
electrons
Condenser
Specimen
Objective
Eyepiece
Projector Specimen
50. TEM
Transmission Electron
Microscope
Illumination source is
beam of electrons from
tungsten wire
Electromagnetic lenses
perform same function
as glass lenses in LM
Higher resolution and
higher magnification of
thin specimens
51. FEI Tecnai 20
For TEM, since the electrons
need to penetrate the specimen, it
must be very thin (< 100 nm)
52. Comparison of TEM and LM
a. Similarities (Arrangement and function of components are similar)
1) Illumination system: produces required radiation and directs it onto the
specimen. Consists of a source, which emits the radiation, and a
condenser lens, which focuses the illuminating beam (allowing variations
of intensity to be made) on the specimen.
2) Specimen stage: situated between the illumination and imaging
systems.
3) Imaging system: Lenses which together produce the final magnified
image of the specimen. Consists of i) an objective lens which focuses the
beam after it passes through the specimen and forms an intermediate
image of the specimen and ii) the projector lens(es) which magnifies a
portion of the intermediate image to form the final image.
4) Image recording system: Converts the radiation into a permanent
image (typically on a photographic emulsion) that can be viewed.
53. Comparison of TEM and LM
b. Differences
1) Optical lenses are generally made of glass with fixed focal lengths whereas magnetic lenses are
constructed with ferromagnetic materials and windings of copper wire producing a focal length which
can be changed by varying the current through the coil.
2) Magnification in the LM is generally changed by switching between different power objective lenses
mounted on a rotating turret above the specimen. It can also be changed if oculars (eyepieces) of
different power are used. In the TEM the magnification (focal length) of the objective remains fixed
while the focal length of the projector lens is changed to vary magnification.
3) The LM has a small depth of field, thus different focal levels can be seen in the specimen. The large
(relative) depth of field in the TEM means that the entire (thin) specimen is in focus simultaneously.
4) Mechanisms of image formation vary (phase and amplitude contrast).
5) TEMs are generally constructed with the radiation source at the top of the instrument: the source is
generally situated at the bottom of LMs.
6) TEM is operated at high vacuum (since the mean free path of electrons in air is very small) so most
specimens (biological) must be dehydrated (i.e. dead !!).
7) TEM specimens (biological) are rapidly damaged by the electron beam.
8) TEMs can achieve higher magnification and better resolution than LMs.
9) Price tag!!! (100x more than LM)
60. •All rays from a point in the object are gathered by the lens and
converge to a point in the image.
•All parallel rays are focused in the focal plane.
•The back focal plane of the objective lens contains groupings of
rays that have left the object at the same angle.
•The back focal plane contains the diffraction pattern of the sample.
•Diffraction pattern and image are both formed in the imaging
process
•The intermediate lens is then focused on either the image plane
(for the image), or the back focal plane (for the diffraction pattern).
61.
62.
63.
64.
65.
66.
67. •Advantages and disadvantages of Dark Field Imaging :-
•Advantages
•Provides high contrast for examining molecules with
very low contrast such as DNA.
•For crystalline objects, specific diffraction spots can be
selected in the back focal plane of the objective lens in
order to form a dark field image only from the electrons
scattered by a chosen set of crystal planes.
•Disadvantages
•More difficult to focus and correct for astigmatism since
phase contrast is not present.
•Image brightness is low, since the objective aperture
transmits only a small fraction of the scattered beam,,
•Longer exposure times needed to get good
photographic images.
•Consequently, specimens are subjected to greater
levels of radiation damage.
Dark Field – Advantages and Disadvantages
68. Imaging Modes
•Two principle modes of TEM operation, A – Projecting the diffraction pattern,
B – Projecting the image.
• The intermediate lens selects either the Back Focal Plane or the image plane of
the objective lens.
69. Bright field/dark field depends on the aperture position. Modern way for
diffraction tilts the beam instead of moving the aperture
TEM imaging modes
73. Electron Beam and Specimen Interactions
Electron/Specimen InteractionsSources of Image Information
(1-50KeV)
Electron Beam Induced Current (EBIC)
74.
75. Polymer crystalline
structure and
morphology
Polymer crystalline
structure and
morphology
ApplicationApplication
Distribution and size of
micropores
Distribution and size of
micropores
Polymer compositionPolymer composition Distribution of dispersed
phase
Distribution of dispersed
phase
lattice distortionlattice distortion
82. Scanning electron microscopy is used for inspecting topographies of specimens at
very high magnifications using a piece of equipment called the scanning electron
microscope. SEM magnifications can go to more than 300,000 X but most
semiconductor manufacturing applications require magnifications of less than 3,000
X only. SEM inspection is often used in the analysis of die/package cracks and
fracture surfaces, bond failures, and physical defects on the die or package surface.
During SEM inspection, a beam of electrons is focused on a spot volume of the
specimen, resulting in the transfer of energy to the spot. These bombarding
electrons, also referred to as primary electrons, dislodge electrons from the
specimen itself. The dislodged electrons, also known as secondary electrons, are
attracted and collected by a positively biased grid or detector, and then translated
into a signal.
To produce the SEM image, the electron beam is swept across the area being
inspected, producing many such signals. These signals are then amplified, analyzed,
and translated into images of the topography being inspected. Finally, the image is
shown on a CRT.
Scanning Electron Microscopy (SEM)
83. Scanning Electron Microscopy (SEM)
• The energy of the primary electrons determines the quantity of
secondary electrons collected during inspection. The emission of
secondary electrons from the specimen increases as the energy of
the primary electron beam increases, until a certain limit is reached.
Beyond this limit, the collected secondary electrons diminish as the
energy of the primary beam is increased, because the primary beam
is already activating electrons deep below the surface of the
specimen. Electrons coming from such depths usually recombine
before reaching the surface for emission.
•
• Aside from secondary electrons, the primary electron beam results
in the emission of backscattered (or reflected) electrons from the
specimen. Backscattered electrons possess more energy than
secondary electrons, and have a definite direction. As such, they
can not be collected by a secondary electron detector, unless the
detector is directly in their path of travel. All emissions above 50 eV
are considered to be backscattered electrons.
84. • Backscattered electron imaging is useful in distinguishing one
material from another, since the yield of the collected backscattered
electrons increases monotonically with the specimen's atomic
number. Backscatter imaging can distinguish elements with atomic
number differences of at least 3, i.e., materials with atomic number
differences of at least 3 would appear with good contrast on the
image. For example, inspecting the remaining Au on an Al bond pad
after its Au ball bond has lifted off would be easier using backscatter
imaging, since the Au islets would stand out from the Al background.
•
• A SEM may be equipped with an EDX analysis system to enable it
to perform compositional analysis on specimens. EDX analysis is
useful in identifying materials and contaminants, as well as
estimating their relative concentrations on the surface of the
specimen.
Scanning Electron Microscopy (SEM)
85. • type of electron microscope capable of producing high-
resolution images of a sample surface.
• due to the manner in which the image is created, SEM
images have a characteristic 3D appearance and are
useful for judging the surface structure of the sample.
Resolution
• depends on the size of the electron spot, which in turn
depends on the magnetic electron-optical system which
produces the scanning beam.
• is not high enough to image individual atoms, as is
possible in the TEM … so that, it is 1-20 nm
Scanning Electron Microscopy (SEM)
86. Advantages of Using SEM over OM
Magnification Depth of Field Resolution
OM 4x – 1000x 15.5mm – 0.19mm ~ 0.2mm
SEM 10x – 3000000x 4mm – 0.4mm 1-10nm
The SEM has a large depth of field, which allows a large amount of the
sample to be in focus at one time and produces an image that is a good
representation of the three-dimensional sample. The SEM also produces
images of high resolution, which means that closely features can be
examined at a high magnification.
The combination of higher magnification, larger depth of field, greater
resolution and compositional and crystallographic information makes the
SEM one of the most heavily used instruments in research areas and
industries, especially in semiconductor industry.
87. Scanning Electron Microscope
– a Totally Different Imaging Concept
• Instead of using the full-field image, a point-to-
point measurement strategy is used.
• High energy electron beam is used to excite the
specimen and the signals are collected and analyzed
so that an image can be constructed.
• The signals carry topological, chemical and
crystallographic information, respectively, of the
samples surface.
90. Image Formation in SEM
beam
e-
Beam is scanned over specimen in a raster pattern in synchronization with
beam in CRT.
Intensity at A on CRT is proportional to signal detected from A on specimen
and signal is modulated by amplifier.
A
A
Detector
Amplifier
10cm
10cm
M= C/x
91. 92
The Scanning Electron Microscope
• (SEM) bombards a specimen with a beam of
electrons instead of light
• Produces a highly magnified image from 100x to
100,0000
• Depth of focus 300X better than optical systems at
similar magnification
• Bombardment of the specimen’s surface with
electrons
– Produces x-ray emissions
– Characterize elements present in the material under
investigation
92.
93. • An electron gun produces a beam of electrons that
scans the surface of a whole specimen.
• Secondary electrons emitted from the specimen
produce the image.
Scanning Electron Microscopy (SEM)
Figure 3.9b
94. Beam passes down the
microscope column
Electron beam now tends to
diverge
But is converged by
electromagnetic lenses
Cross section of
electromagnetic
lenses
Electron beam
produced here
Sample
Diagram of Scanning Electron Microscope or SEM
in cross section - the electrons are in green
97. What is SEM
Scanning electron microscope (SEM) is a microscope that uses electrons
rather than light to form an image. There are many advantages to using the
SEM instead of a OM.
The SEM is designed
for direct studying of
the surfaces of solid
objects
Cost: $0.8-2.4M
Column
Sample
Chamber
TV Screens
104. Cathode Ray Tube (CRT) accelerates electrons towards the
phosphor coated screen where they produce flashes of light
upon hitting the phosphor. Deflection coilsDeflection coils create a scan
pattern forming an image in a point by point manner
107. How an Electron Beam is Produced?
• Electron guns are used to produce a
fine, controlled beam of electrons
which are then focused at the
specimen surface.
• The electron guns may either be
thermionic gun or field-emission gun
109. Thermionic Emission Gun
• A tungsten filament
heated by DC to
approximately 2700K or
LaB6 rod heated to around
2000K
• A vacuum of 10-3
Pa (10-4
Pa for LaB6) is needed to
prevent oxidation of the
filament
• Electrons “boil off” from
the tip of the filament
• Electrons are accelerated
by an acceleration voltage
of 1-50kV
-
+
110. Source of Electrons
T: ~1500o
C
Thermionic Gun
W and LaB6 Cold- and thermal FEG
Electron Gun Properties
Source Brightness Stability(%) Size Energy spread Vacuum
W 3X105
~1 50µm 3.0(eV) 10-5
(τ )
LaB6 3x106
~2 5µm 1.5 10-6
C-FEG 109
~5 5nm 0.3 10-10
T-FEG 109
<1 20nm 0.7 10-9
(5-50µm)
E: >10MV/cm
(5nm)
Filament
W
Brightness – beam current density per unit solid angle
112. Thermionic Sources
Increasing the filament current will increase the beam current but
only to the point of saturation at which point an increase in the
filament current will only shorten the life of the emitter
115. Magnetic Lenses
• Condenser lens – focusing
determines the beam current
which impinges on the sample.
• Objective lens – final probe
forming
determines the final spot size of
the electron beam, i.e., the
resolution of a SEM.
116. Electromagnetic Lenses
An electromagnetic lens is essentially soft iron core wrapped in
wire
As we increase the current in the wire we increase the strength
of the magnetic field
Recall the right hand rule electron will move in a helical path
spiralling towards the centre of the magnetic field
118. Why Need a Vacuum?
When a SEM is used, the electron-optical column and
sample chamber must always be at a vacuum.
1. If the column is in a gas filled environment, electrons will be
scattered by gas molecules which would lead to reduction of the
beam intensity and stability.
2. Other gas molecules, which could come from the sample or the
microscope itself, could form compounds and condense on the
sample. This would lower the contrast and obscure detail in the
image.
119. The Condenser Lens
• For a thermionic gun, the diameter of
the first cross-over point ~20-50µm
• If we want to focus the beam to a size
< 10 nm on the specimen surface, the
magnification should be ~1/5000, which
is not easily attained with one lens (say,
the objective lens) only.
• Therefore, condenser lenses are added
to demagnify the cross-over points.
121. The objective lens aperture
Aperture in SEM: either to limit the amount of electrons or enhance contrast
122. How Is Electron Beam Focused?
A magnetic lens is a solenoid designed to produce
a specific magnetic flux distribution.
p
q
Magnetic lens
(solenoid)
Lens formula: 1/f = 1/p + 1/q
M = q/pDemagnification:
(Beam diameter)
F = -e(v x B)
f ∝ Bo
2
f can be adjusted by changing Bo, i.e., changing the current through
coil.
124. C1 controls the spot size
C2 changes the convergence of the beam
Condenser-lens system
The condenser aperture must be centered
125. The Objective Lens
• The objective lens
controls the final
focus of the electron
beam by changing the
magnetic field strength
• The cross-over image is
finally demagnified to
an ~10nm beam spot
which carries a beam
current of
approximately 10-9
-10-
10-12
A.
126. The Objective Lens - Focusing
• By changing the
current in the
objective lens, the
magnetic field
strength changes
and therefore the
focal length of
the objective lens
is changed.
Out of focus in focus out of focus
lens current lens current lens current
too strong optimized too weak
Objective
lens
130. Topographical Contrast
Topographic contrast arises because SE generation depend on the
angle of incidence between the beam and sample.
Bright
Dark
+200V
e-
lens polepiece
SE
sample
Everhart-Thornley
SE Detector
Scintillator
light pipe
Quartz
window
+10kV
Faraday
cage
Photomultiplier
tube
PMT
131. Electron beam – Specimen Interaction. Note the two types
of electrons produced.
132. Electrons from the focused beam interact with the sample
to produce a spray of electrons up from the sample. These
come in two types – either secondary electrons or
backscattered electrons.
As the beam travels across (scans across) the sample the
spray of electrons is then collected little by little and forms
the image of our sample on a computer screen.
We can look more closely at these two types of electrons
because we use them for different purposes.
133. +
-
Inelastic scattering
+
-
Elastic scattering
Energy of electron from beam is
lost to atom
An incoming electron rebounds
back out (as a backscattered
electron)
A new electron is knocked
out (as a secondary
electron)
134. • Secondary Electrons:
Source
Caused by an incident electron passing "near" an atom in the specimen, near
enough to impart some of its energy to a lower energy electron (usually in the K-
shell). This causes a slight energy loss and path change in the incident electron and
the ionization of the electron in the specimen atom. This ionized electron then
leaves the atom with a very small kinetic energy (5eV) and is then termed a
"secondary electron". Each incident electron can produce several secondary
electrons.
Utilization
Production of secondary electrons is very topography related. Due to their low
energy, 5eV, only secondaries that are very near the surface (< 10 nm) can exit the
sample and be examined. Any changes in topography in the sample that are larger
than this sampling depth will change the yield of secondaries due to collection
efficiencies. Collection of these electrons is aided by using a "collector" in
conjunction with the secondary electron detector. The collector is a grid or mesh
with a +100V potential applied to it which is placed in front of the detector,
attracting the negatively charged secondary electrons to it which then pass
through the grid-holes and into the detector to be counted.
135. A conventional secondary electron detector is positioned off to the
side of the specimen. A faraday cage (kept at a positive bias) draws
in the low energy secondary electrons. The electrons are then
accelerated towards a scintillator which is kept at a very high bias
in order to accelerate them into the phosphor.
136. The position of the secondary electron detector also affects
signal collection and shadow. An in-lens detector within the
column is more efficient at collecting secondary electrons that
are generated close to the final lens (i.e. short working distance).
138. • Backscattered Electrons:
Formation
Caused by an incident electron colliding with an atom in the
specimen which is nearly normal to the incident's path. The
incident electron is then scattered "backward" 180 degrees.
Utilization
The production of backscattered electrons varies directly with
the specimen's atomic number. This differing production
rates causes higher atomic number elements to appear
brighter than lower atomic number elements. This interaction
is utilized to differentiate parts of the specimen that have
different average atomic number.
139. The most common design is a four quadrant solid state detector that is positioned
directly above the specimen
Backscatter Detector
140. Example of an image using a scanning electron microscope and
secondary electrons
Here the contrast of these grains is all quite similar.
We get a three-dimensional image of the surfaces.
141. Grain containing
titanium so it is
whiter
Grain containing
of silica so it is
darker
Example of an image using a scanning electron microscope and
backscattered electrons
Here the differing contrast of the
grains tells us about composition
142. So how does this work – telling composition from
backscattered electrons?
The higher the atomic number of the atoms the more
backscattered electrons are ‘bounced back’ out
This makes the image brighter for the larger atoms
Titanium – Atomic
Number 22
Silica – Atomic Number
14
143. +
-
Inelastic scattering
If the yellow electron falls
back again to the inner
ring, that is to a lower
energy state or valence,
then a burst of X-ray
energy is given off that
equals this loss.
This is a characteristic
packet of energy and can
tell us what element we
are dealing with
Understanding compositional analysis using X-rays and the
scanning electron microscope
144. Backscattered Electrons (BSE)
BSE are produced by elastic interactions of beam electrons with nuclei of
atoms in the specimen and they have high energy and large escape depth.
BSE yield: η=nBS/nB ~ function of atomic number, Z
BSE images show characteristics of atomic number contrast, i.e., high
average Z appear brighter than those of low average Z. η increases with tilt.
Primary
BSE image from flat surface of an Al
(Z=13) and Cu (Z=29) alloy
146. Interaction Volume: I
The incident electrons do not go along a
straight line in the specimen, but a zig-zag
path instead.
Monte Carlo simulations of 100 electron trajectories
e-
147. Interaction Volume: II
The penetration or,
more precisely, the
interaction volume
depends on the
acceleration voltage
(energy of electron)
and the atomic
number of the
specimen.
148. Escape Volume of Various SignalsEscape Volume of Various Signals
• The incident electrons interact with specimen
atoms along their path in the specimen and
generate various signals.
• Owing to the difference in energy of these
signals, their ‘penetration depths’ are
different
• Therefore different signal observable on the
specimen surface comes from different parts
of the interaction volume
• The volume responsible for the respective
signal is called the escape volume of that
signal.
149. If the diameter of primary
electron beam is ~5nm
- Dimensions of escape
zone of
Escape Volumes of Various Signals
•Secondary electron:
diameter~10nm; depth~10nm
•Backscattered electron:
diameter~1µm; depth~1µm
•X-ray: from the whole
interaction volume, i.e., ~5µm
in diameter and depth
150. Electron Interaction Volume
5µm
a b
a.Schematic illustration of electron beam interaction in Ni
b.Electron interaction volume in polymethylmethacrylate
(plastic-a low Z matrix) is indirectly revealed by etching
Pear shape
151. Magnification
The magnification is simply the ratio of the length of the scan C on the
Cathode Ray Tube (CRT) to the length of the scan x on the specimen. For a
CRT screen that is 10 cm square:
M= C/x = 10cm/x
Increasing M is achieved by decreasing x.
M x M x
100 1 mm 10000 10 µm
1000 100 µm 100000 1 µm
Low M
Large x
40µm
High M
small x
7µm
2500x 15000x
1.2µm
e-
x
152. Resolution Limitations
Ultimate resolution obtainable in an SEM image can be
limited by:
1. Electron Optical limitations
Diffraction: dd=1.22λ/α
for a 20-keV beam, λ =0.0087nm and α=5x10-3
dd=2.1nm
Chromatic and spherical aberrations: dmin=1.29λ3/4
Cs
1/4
A SEM fitted with an FEG has an achievable resolution of ~1.0nm at 30 kV
due to smaller Cs (~20mm) and λ.
2. Specimen Contrast Limitations
Contrast dmin
1.0 2.3nm
0.5 4.6nm
0.1 23nm
0.01 230nm
3. Sampling Volume Limitations (Escape volume)
153. How Fine Can We See with SEM?
• If we can scan an area with width 10 nm
(10,000,000×) we may actually see
atoms!! But, can we?
• Image on the CRT consists of spots called
pixels (e.g. your PC screen displays
1024×768 pixels of ~0.25mm pitch)
which are the basic units in the image.
• You cannot have details finer than
one pixel!
154. Resolution of Images: I
• Assume that there the screen can display 1000
pixels/(raster line), then you can imagine that
there are 1000 pixels on each raster line on the
specimen.
• The resolution is the pixel diameter on
specimen surface.
P=D/Mag = 100um/Mag
P-pixel diameter on specimen surface
D-pixel diameter on CRT, Mag-magnification
Mag P(µm) Mag P(nm)
10x 10 10kx 10
1kx 0.1 100kx 1
155. • The optimum condition for imaging is when
the escape volume of the signal concerned
equals to the pixel size.
Resolution of Images: II
156. • Signal will be weak if escape volume,
which depends on beam size, is smaller
than pixel size, but the resolution is still
achieved. (Image is ‘noisy’)
Resolution of Images: III
157. Resolution of Images: IV
• Signal from different pixel will overlap
if escape volume is larger than the
pixel size. The image will appeared
out of focus (Resolution decreased)
158. Resolution of Images: V
Pixel diameter on Specimen
Magnification µm nm
10 10 10000
100 1 1000
1000 0.1 100
10000 0.01 10
100000 0.001 1
In extremely good SEM, resolution can be a few nm. The
limit is set by the electron probe size, which in turn depends
on the quality of the objective lens and electron gun.
159. Depth of Field
D = (µm)
AM
4x105
W
To increase D
Decrease aperture size, A
Decrease magnification, M
Increase working distance, W (mm)
Depth of Field
160. Image Contrast
Image contrast, C
is defined by
SA-SB ∆S
C= ________
=____
SA SA
SA, SB Represent signals
generated from two
points, e.g., A and B, in
the scanned area.
In order to detect objects of small size and low contrast in an SEM it is
necessary to use a high beam current and a slow scan speed (i.e., improve
signal to noise ratio).
SE-topographic and BSE-atomic number contrast
SE Images
162. The Scanning Electron Microscope is analogous to the
stereo binocular light microscope because it looks at
surfaces rather than through the specimen.
163. Main Applications
• Topography
The surface features of an object and its texture
(hardness, reflectivity… etc.)
• Morphology
The shape and size of the particles making up the
object (strength, defects in IC and chips...etc.)
• Composition
The elements and compounds that the object is
composed of and the relative amounts of them
(melting point, reactivity, hardness...etc.)
• Crystallographic Information
How the grains are arranged in the object
(conductivity, electrical properties, strength...etc.)
164. SE Images - Topographic Contrast
The debris shown here is an oxide fiber
got stuck at a semiconductor device
detected by SEM
1µm
Defect in a semiconductor device Molybdenum
trioxide crystals
165. BSE Image – Atomic Number Contrast
BSE atomic number contrast image showing a niobium-rich
intermetallic phase (bright contrast) dispersed in an alumina matrix
(dark contrast).
Z (Nb) = 41, Z (Al) = 13 and Z(O) = 8
Alumina-Al2O3
2µm
Specimen interaction is what makes Electron Microscopy possible. Elastic and inelastic scattering are the elementary atomic interaction processes, though the final signal used for image formation is, with only a few exceptions, not the result of single scattering processes but of the complete electron diffusion caused by the gradual loss of the electron energy and by lateral spreading caused by multiple elastic large-angle scattering.
All signals come from different depth of sample. Right:mainly imaging and left: chemical
Cathodoluminescence (CL)-The emission of ultraviolet, visible or infrared light stimulated by electron bombardment. A great many substances, especially semiconductors and minerals show CL. CL contains much analytical information and can reveal material differences that cannot be detected by other methods, e.g., dopants distribution (information is only qualitative). However, CL is frequently used in combination with EBIC and the recombination of charge carries at lattice defects also allows lattice defects to be imaged.
EBIC-Inelastic scattering in semiconductors results in the generation of electron-hole pairs, and a few thousands of electron-hole pairs are created per incident electron. In the depletion layer of a p-n junction, the strong electric field separates the charge carries and minority carries can hence reach the junction by diffusion. This results in a charge-collection current or electron-beam-induced-current, which can be amplified and used in a quantitative manner to measure the width of the junction and its depth below the surface, the diffusion length and the surface recombination rate of minority carries.
The largest fraction of the primary electron energy that is lost during the cascade of inelastic scattering processes is converted into phonons or heat.
The electron beam scans across a rectangular area on the specimen surface. The electron beam in the cathode ray tube (CRT) scans across the screen for viewing the image and the scanning is synchronized with that of the electron beam in the microscope. The intensity of a certain point on the screen is modulated by the intensity of the signal from the detectors (e.g. BSE or SE detectors)
http://www.mse.iastate.edu/microscopy/
Ideally the field emission tip is used in a vacuum of 10nPa or better. Even in that condition, however, a few gas molecules will still land on the tip from time to time and these will cause fluctuations in the emission current. Eventually the whole tip will be covered and the output will become very unstable. The cathode must then be cleaned by rapidly heating it to a high T (2000C) for a few seconds (Cold FEG). Alternatively the tip can be kept warm (800-1000C, thermal FEG), in which case the majority of impinging molecules are immediately reevaporated. In this case acceptably stable emission is maintained even in a vacuum of 100 nPa or so.
The lenses used in the SEM are normally weak and the lens formula can be used.
The objective lens is machined to very high precision and the magnetic field pattern is very carefully designed.
However, the precision attainable by machining cannot match that required for controlling a beam with Ø10 nm.
The stigmator, which consist of two pairs of pole-pieces arranged in the X and Y directions, is added to correct the minor imperfections in the objective lens.
http://emalwww.engin.umich.edu/newemal/courses/SEM_lectureCW/SEM_se2.html
Topographic contrast occurs because the efficiency of generating both SEs and BSEs depends on the angle of incidence between the scanning beam and the specimen. Thus local variations in the angle of the surface to the beam (roughness) affects the numbers of electrons leaving from point to point. The resulting “topographic contrast is a function of the physical shape of the specimen. In areas where the surface is tilted relative to the incident beam, the electrons travel greater distances in the region close to the surface of the specimen. This means more SE are generated within the escape depth in tilted areas than in areas which are normal to the beam.
In addition, SE can escape from both sides of ridges and edges.
These effects cause tilted surfaces to appear brighter than flat surfaces, and edges and ridges to be markedly highlighted, in images formed with secondary electrons
Topographic contrast is weak in BSE mode which usually use sample with flat surface.
Secondary electron attracted to collector grid (or Faraday Cage) by a positive bias ~200-300V. Collected electron further accelerated to scintillation disc inside the cage by 10-12 kV. Photon of visible light generated when electrons strike the scintillator. Photons reach the photomultiplier, in which the light signal is amplified, through the light guide pipe. The final electrical signal from the anode is used for modulating the intensity of electron beam on the display CRT screen.
As the name implies, elastic scattering results in little or no change in energy of the scattered electron, although there is a change in momentum. Since momentum, p=mv, and m doesn&apos;t change, the direction of the velocity vector must change. The angle of scattering can range from 0-180 degrees. Elastic scattering occurs between the negative electron and the positive nucleus. Sometimes the angle is such that the electron comes back out of the sample. These are backscattered electrons.
This escape volume limits the resolution in images produced with BSE and x-ray (element mapping) to a value that is of the order of size of the escape volume, regardless of how small the actual diameter of the incident electron beam may be.
Interaction volume will determine resolution of EDS in SEM and will be discussed more
Later. Keep in mind interaction volume inversely proportional to atomic number, Z.
Electrons can penetrate into sample and the higher the energy, the deeper range the electrons can penetrate. Beam-sample interaction volume is proportional to the electron energy. On the other hand, the x-ray generation range depends on critical ionization energy of elements, Ec. Ec-K line &gt;&gt; Ec-L line. Electrons lose their energy due to multiple inelastic scattering while they are penetrating the sample. That is why the x-ray generation range of K line is smaller than that of L line, since the former needs higher energy to be excited, whereas the energy of electrons become smaller and smaller as they penetrate deeper and deeper into the sample.
Need small electron beam probe to achieve high magnification.
Changing magnification does not involve changing any lens current, only changing the current in the scan coils, and so:
focus does not change as magnification is changed
the image does not rotate with magnification change (as in TEM)
http://micro.magnet.fsu.edu/primer/java/electronmicroscopy/magnify1/index.html
–fruit fly
Ultimate resolution depends on the electron-optical specification and achievable resolution is subject to operational factors (e.g., correction of astigmatism which arises from the illumination system.
http://emalwww.engin.umich.edu/newemal/courses/SEM_lectureCW/SEM_Magnification.html effect of pixel size on image resolution.
The unaided human cannot reliably resolve features smaller than about 0.1 mm (100 µm), and so the diameter of the beam in the CRT need not be made smaller than this. Thus, the diameter of an image point on the CRT is D = 100 µm. The conjugate point on the specimen from which the image signal is produced, which is called the &apos;pixel&apos; P, will have a smaller diameter, depending on the magnification, of:
P=D/Mag = 100um/Mag
At low magnifications, the resolution of the image is determined by the pixel size. At high magnifications the beam diameter limits resolution.
Small beam size is needed for high resolution. Decrease the beam size by:
1.Increasing the current on condenser lens 2.Decreasing the working distance
Decreasing the beam size also decreases the beam current and therefore the signal to noise ratio gets worse. http://emalwww.engin.umich.edu/newemal/courses/SEM_lectureCW/SEM_SpotSize2.html
http://emalwww.engin.umich.edu/newemal/courses/SEM_lectureCW/SEM_SignalNoise.html - single/noise ratio effect
Take EDS as an example. Beam size~5nm, but escape volume~5m, so spatial resolution at best is ~ 5m.
Pixel diameter 0.001m, screen can display 1000 pixels/raster lines,
scan length=1000x0.001 m=1 m. Magnification=10cm/1m=100,000
Here, we talking about SE image resolution.
http://emalwww.engin.umich.edu/newemal/courses/SEM_lectureCW/SEM_DepthofFocus.html - One of the great advantages of SEM images is the unusually great depth of field they exhibit. This makes it possible to examine surfaces much rougher, and at much higher magnifications, than is possible with light microscopes. The reason for this great depth of field arises from the geometry of the beam optics. The final lens of the SEM focuses the electron beam to a &apos;crossover&apos; at the plane of best focus. The beam diameter increases as the beam converges and diverges above and below this plane. At some distance D/2 above and below the focus plane the diameter of the beam becomes twice the pixel diameter for the mag being used, whereupon the signals from adjacent pixels overlap enough to cause the image to appear blurred.
Over the distance D between these limits, however, the image will appear to be in acceptably sharp focus, and so this distance is called &apos;the depth of field&apos; or &apos;the depth of focus&apos;.
For two small objects to be detected against a background of random noise, studies show that their signal difference must be at least five times the noise level.