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 provides an overview of characterization techniques for nanoparticles. It discusses how characterization refers to studying the features, composition, structure and properties of materials. Nanoparticles are defined as particles between 1 to 100 nanometers in at least one dimension. Their small size results in unique physical, chemical and biological properties compared to bulk materials. A variety of characterization techniques are described including optical microscopy techniques like dynamic light scattering, electron microscopy techniques like scanning electron microscopy, and other methods like photon spectroscopy. The techniques allow analyzing properties of nanoparticles like size, shape, structure and chemical composition.
The document discusses various characterization techniques used to analyze nanomaterials. It begins by providing historical context on the origins of nanotechnology and then describes several microscopy and spectroscopy methods. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, small angle X-ray scattering, and scanning probe microscopy are some of the key techniques explained in the document.
Carbon nanotubes are hollow cylinders composed of rolled graphene sheets, with diameters on the nanoscale. They were first observed in 1952 in the Soviet Union in hollow graphite fibers 50nm wide. In 1979 evidence of carbon nanotubes was presented at a conference in the US, and in 1991 nanotubes were discovered in arc discharge soot in Japan. Carbon nanotubes are the strongest and stiffest materials known, with tensile strength and elastic modulus greater than diamond. They have very high electrical conductivity due to their symmetrical graphene structure.
The document discusses scanning probe microscopy (SPM) techniques. It defines local density of states (LDOS) and artifacts. It then discusses the motivation for surface research in electrical engineering due to modern devices' dominance of surface properties. It provides overviews of SPM, atomic force microscopy (AFM), and SPM software. Modes of AFM including contact, friction, tapping, and phase are summarized.
The document discusses atomic force microscopy (AFM) and its use to characterize crystalline cellulose distributions on natural and pretreated plant cell wall surfaces. AFM uses a sharp tip to scan surfaces with nanoscale resolution. The document finds that dilute acid pretreatment increases the percentage of plant cell wall surfaces covered by crystalline cellulose from 17-20% naturally to 23-38% after pretreatment. Optimized pretreatment with 0.5% sulfuric acid at 135°C resulted in 23% coverage on poplar, 28% on switchgrass, and 38% on corn stover. AFM provides detailed surface information that can improve understanding of pretreatment effects and lead to biomass processing enhancements.
Synthesis and Characterization of nanoparticleMohammad Azam
This document summarizes the history and applications of nanoparticles. It discusses early examples of nanomaterials like the Lycurgus Cup from the 4th century. It classifies nanostructured materials and describes how properties change at the nanoscale. Applications discussed include electronics, medicine, energy, and environmental remediation. Common synthesis methods are outlined as well as characterization techniques like UV-Vis spectroscopy, FTIR, XRD, SEM, TEM, and AFM. Scanning probe microscopes like SEM, STM, and AFM are also briefly described.
The document summarizes atomic force microscopy (AFM). AFM was invented in 1985 and works by scanning a probe tip across a sample surface while monitoring interatomic forces. AFM can be used to create high-resolution topographic images of samples without extensive preparation. It has advantages over other techniques as it can image samples in liquid, at varying temperatures, and allow repeated studies without damage. AFM is commonly used to image biological samples like DNA, proteins, and cells.
The document provides an overview of characterization techniques for nanoparticles. It discusses how characterization refers to studying the features, composition, structure and properties of materials. Nanoparticles are defined as particles between 1 to 100 nanometers in at least one dimension. Their small size results in unique physical, chemical and biological properties compared to bulk materials. A variety of characterization techniques are described including optical microscopy techniques like dynamic light scattering, electron microscopy techniques like scanning electron microscopy, and other methods like photon spectroscopy. The techniques allow analyzing properties of nanoparticles like size, shape, structure and chemical composition.
The document discusses various characterization techniques used to analyze nanomaterials. It begins by providing historical context on the origins of nanotechnology and then describes several microscopy and spectroscopy methods. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, small angle X-ray scattering, and scanning probe microscopy are some of the key techniques explained in the document.
Carbon nanotubes are hollow cylinders composed of rolled graphene sheets, with diameters on the nanoscale. They were first observed in 1952 in the Soviet Union in hollow graphite fibers 50nm wide. In 1979 evidence of carbon nanotubes was presented at a conference in the US, and in 1991 nanotubes were discovered in arc discharge soot in Japan. Carbon nanotubes are the strongest and stiffest materials known, with tensile strength and elastic modulus greater than diamond. They have very high electrical conductivity due to their symmetrical graphene structure.
The document discusses scanning probe microscopy (SPM) techniques. It defines local density of states (LDOS) and artifacts. It then discusses the motivation for surface research in electrical engineering due to modern devices' dominance of surface properties. It provides overviews of SPM, atomic force microscopy (AFM), and SPM software. Modes of AFM including contact, friction, tapping, and phase are summarized.
The document discusses atomic force microscopy (AFM) and its use to characterize crystalline cellulose distributions on natural and pretreated plant cell wall surfaces. AFM uses a sharp tip to scan surfaces with nanoscale resolution. The document finds that dilute acid pretreatment increases the percentage of plant cell wall surfaces covered by crystalline cellulose from 17-20% naturally to 23-38% after pretreatment. Optimized pretreatment with 0.5% sulfuric acid at 135°C resulted in 23% coverage on poplar, 28% on switchgrass, and 38% on corn stover. AFM provides detailed surface information that can improve understanding of pretreatment effects and lead to biomass processing enhancements.
Synthesis and Characterization of nanoparticleMohammad Azam
This document summarizes the history and applications of nanoparticles. It discusses early examples of nanomaterials like the Lycurgus Cup from the 4th century. It classifies nanostructured materials and describes how properties change at the nanoscale. Applications discussed include electronics, medicine, energy, and environmental remediation. Common synthesis methods are outlined as well as characterization techniques like UV-Vis spectroscopy, FTIR, XRD, SEM, TEM, and AFM. Scanning probe microscopes like SEM, STM, and AFM are also briefly described.
The document summarizes atomic force microscopy (AFM). AFM was invented in 1985 and works by scanning a probe tip across a sample surface while monitoring interatomic forces. AFM can be used to create high-resolution topographic images of samples without extensive preparation. It has advantages over other techniques as it can image samples in liquid, at varying temperatures, and allow repeated studies without damage. AFM is commonly used to image biological samples like DNA, proteins, and cells.
This document provides an introduction to nanotechnology and methods for synthesizing nanomaterials. It discusses that nanotechnology involves working at the nanoscale of 1 to 100 nanometers. Richard Feynman is considered the father of nanotechnology for his 1959 talk describing manipulating atoms and molecules. Common synthesis methods described include mechanical methods like ball milling and melt mixing, as well as physical vapor deposition techniques using evaporation, laser ablation, and ionized cluster beam deposition. The document outlines the advantages of nanotechnology in tuning material properties at small scales.
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.
Scanning tunneling microscopy (STM) is a technique used to image surfaces at the atomic level. It was developed in 1981 by Gerd Binnig and Heinrich Rohrer at IBM, based on the concept of quantum tunneling. The STM works by using a scanning tip, typically made of tungsten, which is brought very close to the sample surface. A bias is applied between the tip and sample, allowing electrons to tunnel through the vacuum gap. The tunneling current depends on factors like the voltage and position of the tip relative to the sample, enabling atomic resolution images to be produced. Piezoelectric materials are crucial for providing precise movement of the tip in the angstrom scale needed. STM opened
This document discusses metal matrix nanocomposites. It defines nanocomposites as consisting of two phases, with one being nanosized particles embedded in a matrix material. Metal matrix nanocomposites (MMNCs) specifically use a metal as the matrix and a ceramic as the reinforcement. Carbon nanotube metal matrix nanocomposites are also discussed. The document outlines various synthesis routes for fabricating MMNCs, including solid-state and liquid-state processing methods, and discusses some advantages and limitations of different processing techniques. Properties of MMNCs include increased hardness, strength, and superplasticity as well as lowered melting point and improved electrical and magnetic properties.
The atomic force microscope (AFM) was invented in 1985 by Gerd Binnig and Cristoph Gerber. It uses a sharp tip mounted on a flexible cantilever to scan the topography of a sample at an extremely high resolution down to the atomic level. The AFM works by measuring the interaction forces between the tip and sample surface. It consists of a probe with a sharp tip, a scanner that controls the tip's movement in the x, y, and z directions, and an optical lever system using a laser and photodetector to measure the cantilever's deflection. The AFM can image a variety of samples at the nanoscale and provide 3D topographic information.
Self assembled monolayers (SAMs) are organized layers of amphiphilic molecules that spontaneously form on substrates. SAMs consist of molecules with a "head group" that chemically binds to the substrate, and a "tail" with a functional group. Well-ordered SAMs form when alkanethiol molecules with chain lengths of 12 or more carbons chemisorb to gold surfaces from solution over time. Characterization techniques like infrared spectroscopy, ellipsometry, and contact angle measurements indicate high quality SAMs have densely packed, crystalline structures with few defects in the alkyl chains.
The document discusses different types of microscopy techniques. It describes three main branches of microscopy - optical, electron, and scanning probe microscopy. Optical and electron microscopy use light and electron beams respectively to image samples, while scanning probe microscopy uses a physical probe that interacts with the sample surface. The document then focuses on atomic force microscopy (AFM), providing details on its working principle, modes, image generation process, and applications in measuring surface roughness and thickness. Other scanning probe techniques are also briefly mentioned.
The document provides an overview of scanning electron microscopes (SEMs). It discusses the history and development of SEMs. Key components of SEMs are described, including the electron gun, electromagnetic lenses, vacuum chamber, detectors, and sample stage. SEMs produce high-resolution images of sample surfaces by scanning them with a focused beam of electrons. Signals produced by electron-sample interactions reveal information about morphology, composition, and structure. Applications of SEMs discussed include nanomaterial characterization, archaeology, biology, and industrial quality control. Limitations include sample size constraints and specialized training required.
SEM is a type of electron microscope designed for directly studying the surfaces of solid objects, that utilizes a beam of focused electron of relatively low energy as an electron probe that is scanned in a regular manner over the specimen.
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.
NSOM/SNOM is a scanning probe microscopy technique that can achieve higher resolution than far-field optical microscopy, around 50 nm. It works by exploiting evanescent waves from a sample that are detected using a probe placed within the near-field zone. PINEM is a related technique that uses ultrafast electron pulses synchronized with optical pulses to map photon-electron interactions and image plasmonic fields with high spatiotemporal resolution. Both techniques allow studying nanoscale optical and material properties with applications in nanotechnology, biophysics, and materials science.
The scanning electron microscope (SEM) uses a focused beam of electrons to generate high-resolution images of surfaces. SEMs can provide information about topography, morphology, and composition through detection of signals from electron interactions with the sample surface. There are two main types: transmission electron microscopes study inner structures while scanning electron microscopes are used to visualize surfaces. SEMs work by scanning a focused electron beam across the sample; electrons interact with atoms and produce signals containing surface and composition data. Proper sample preparation including cleaning, fixation, dehydration and coating with a conductive material is required for clear SEM imaging.
Nanoparticles are solid colloidal particles ranging in size from 10 to 1000 nm.
Nanoparticles are made of a macromolecular material which can be of synthetic or natural origin.
Scanning electron microscopy (SEM) is used to characterize nanoparticles by examining their morphology, crystalline structure, and composition. SEM works by scanning a beam of electrons across a sample, detecting signals from interactions between the electrons and the sample's atoms. This allows examination of a sample's topography, texture, size and shape of particles, elemental composition, and crystalline arrangement at high resolution down to 1-5 nm.
This document discusses the scanning tunneling microscope (STM). It begins by introducing STM and its ability to image surfaces with atomic resolution. It then explains the principle of STM, which uses a voltage applied between a metal tip and sample surface to create a tunneling current that is exponentially dependent on tip-sample separation. The document outlines the tip positioning system, describes the constant current and variable current imaging modes, and notes STM's advantages of high resolution and ability to study various environments and its disadvantage of requiring precise tip positioning and stable/clean surfaces.
This document discusses pulsed laser deposition (PLD), a physical vapor deposition technique used to deposit thin films. In PLD, a high-power pulsed laser beam is focused onto a target material, vaporizing it and creating a plasma plume that expands toward a substrate where the ablated material is deposited as a thin film. Factors like laser parameters, substrate temperature, background pressure influence the nucleation and growth of the deposited film. PLD offers benefits like exact transfer of complex materials and variable growth rates compared to other thin film deposition methods.
Electron microscopy provides high resolution imaging of nanoscale structures using electron beams. There are two main types: transmission electron microscopy (TEM) and scanning electron microscopy (SEM). TEM uses transmitted electrons to image ultra thin samples, allowing visualization of structures less than an angstrom in size. SEM scans a focused electron beam across a sample to generate topographical and compositional information from electron interactions within microns of the surface. Both techniques require specialized sample preparation and equipment to produce high quality images for research applications across biology, materials science, and other fields.
superparamagnetism and its biological applicationsudhay roopavath
- Superparamagnetism occurs in small ferromagnetic or ferrimagnetic nanoparticles and implies single-domain particle sizes of a few nanometers. The magnetic moments of individual atoms combine to form a giant magnetic moment for the nanoparticle as a whole.
- Below the blocking temperature, nanoparticles behave superparamagnetically, with spontaneous fluctuations of the magnetization direction between θ=00 and θ=1800. Above the blocking temperature, nanoparticles behave paramagnetically.
- Superparamagnetism allows applications in areas like drug delivery, hyperthermia cancer treatment, magnetic resonance imaging, and gene therapy by exploiting the magnetic properties at the nanoscale.
Scanning probe microscopy (SPM) uses a probe that interacts with the sample surface without lenses to resolve images. The first SPM was invented in 1981 by Binning and Roher, winning them the Nobel Prize. For SPM techniques like STM and AFM to provide atomic-level surface structure information, the tip-sample position must be controlled within 0.1 Angstroms and the tip must be very sharp. STM uses tunneling current between a biased tip and conducting sample, while AFM measures cantilever deflection from tip-surface interactions to map topography. SPM provides higher resolution than diffraction-limited techniques and can image insulators and conductors.
The document discusses the working principle of scanning electron microscopy (SEM). It describes how SEM uses a focused beam of electrons to scan the surface of a sample to produce images. SEM provides higher resolution than light microscopes due to the much shorter wavelength of electrons. The document outlines the various components of an SEM, including the electron gun, electromagnetic lenses, detectors for secondary electrons and backscattered electrons, and how these are used to control magnification and resolution. It also discusses some imaging parameters and artifacts that can influence SEM results.
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 introduction to nanotechnology and methods for synthesizing nanomaterials. It discusses that nanotechnology involves working at the nanoscale of 1 to 100 nanometers. Richard Feynman is considered the father of nanotechnology for his 1959 talk describing manipulating atoms and molecules. Common synthesis methods described include mechanical methods like ball milling and melt mixing, as well as physical vapor deposition techniques using evaporation, laser ablation, and ionized cluster beam deposition. The document outlines the advantages of nanotechnology in tuning material properties at small scales.
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.
Scanning tunneling microscopy (STM) is a technique used to image surfaces at the atomic level. It was developed in 1981 by Gerd Binnig and Heinrich Rohrer at IBM, based on the concept of quantum tunneling. The STM works by using a scanning tip, typically made of tungsten, which is brought very close to the sample surface. A bias is applied between the tip and sample, allowing electrons to tunnel through the vacuum gap. The tunneling current depends on factors like the voltage and position of the tip relative to the sample, enabling atomic resolution images to be produced. Piezoelectric materials are crucial for providing precise movement of the tip in the angstrom scale needed. STM opened
This document discusses metal matrix nanocomposites. It defines nanocomposites as consisting of two phases, with one being nanosized particles embedded in a matrix material. Metal matrix nanocomposites (MMNCs) specifically use a metal as the matrix and a ceramic as the reinforcement. Carbon nanotube metal matrix nanocomposites are also discussed. The document outlines various synthesis routes for fabricating MMNCs, including solid-state and liquid-state processing methods, and discusses some advantages and limitations of different processing techniques. Properties of MMNCs include increased hardness, strength, and superplasticity as well as lowered melting point and improved electrical and magnetic properties.
The atomic force microscope (AFM) was invented in 1985 by Gerd Binnig and Cristoph Gerber. It uses a sharp tip mounted on a flexible cantilever to scan the topography of a sample at an extremely high resolution down to the atomic level. The AFM works by measuring the interaction forces between the tip and sample surface. It consists of a probe with a sharp tip, a scanner that controls the tip's movement in the x, y, and z directions, and an optical lever system using a laser and photodetector to measure the cantilever's deflection. The AFM can image a variety of samples at the nanoscale and provide 3D topographic information.
Self assembled monolayers (SAMs) are organized layers of amphiphilic molecules that spontaneously form on substrates. SAMs consist of molecules with a "head group" that chemically binds to the substrate, and a "tail" with a functional group. Well-ordered SAMs form when alkanethiol molecules with chain lengths of 12 or more carbons chemisorb to gold surfaces from solution over time. Characterization techniques like infrared spectroscopy, ellipsometry, and contact angle measurements indicate high quality SAMs have densely packed, crystalline structures with few defects in the alkyl chains.
The document discusses different types of microscopy techniques. It describes three main branches of microscopy - optical, electron, and scanning probe microscopy. Optical and electron microscopy use light and electron beams respectively to image samples, while scanning probe microscopy uses a physical probe that interacts with the sample surface. The document then focuses on atomic force microscopy (AFM), providing details on its working principle, modes, image generation process, and applications in measuring surface roughness and thickness. Other scanning probe techniques are also briefly mentioned.
The document provides an overview of scanning electron microscopes (SEMs). It discusses the history and development of SEMs. Key components of SEMs are described, including the electron gun, electromagnetic lenses, vacuum chamber, detectors, and sample stage. SEMs produce high-resolution images of sample surfaces by scanning them with a focused beam of electrons. Signals produced by electron-sample interactions reveal information about morphology, composition, and structure. Applications of SEMs discussed include nanomaterial characterization, archaeology, biology, and industrial quality control. Limitations include sample size constraints and specialized training required.
SEM is a type of electron microscope designed for directly studying the surfaces of solid objects, that utilizes a beam of focused electron of relatively low energy as an electron probe that is scanned in a regular manner over the specimen.
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.
NSOM/SNOM is a scanning probe microscopy technique that can achieve higher resolution than far-field optical microscopy, around 50 nm. It works by exploiting evanescent waves from a sample that are detected using a probe placed within the near-field zone. PINEM is a related technique that uses ultrafast electron pulses synchronized with optical pulses to map photon-electron interactions and image plasmonic fields with high spatiotemporal resolution. Both techniques allow studying nanoscale optical and material properties with applications in nanotechnology, biophysics, and materials science.
The scanning electron microscope (SEM) uses a focused beam of electrons to generate high-resolution images of surfaces. SEMs can provide information about topography, morphology, and composition through detection of signals from electron interactions with the sample surface. There are two main types: transmission electron microscopes study inner structures while scanning electron microscopes are used to visualize surfaces. SEMs work by scanning a focused electron beam across the sample; electrons interact with atoms and produce signals containing surface and composition data. Proper sample preparation including cleaning, fixation, dehydration and coating with a conductive material is required for clear SEM imaging.
Nanoparticles are solid colloidal particles ranging in size from 10 to 1000 nm.
Nanoparticles are made of a macromolecular material which can be of synthetic or natural origin.
Scanning electron microscopy (SEM) is used to characterize nanoparticles by examining their morphology, crystalline structure, and composition. SEM works by scanning a beam of electrons across a sample, detecting signals from interactions between the electrons and the sample's atoms. This allows examination of a sample's topography, texture, size and shape of particles, elemental composition, and crystalline arrangement at high resolution down to 1-5 nm.
This document discusses the scanning tunneling microscope (STM). It begins by introducing STM and its ability to image surfaces with atomic resolution. It then explains the principle of STM, which uses a voltage applied between a metal tip and sample surface to create a tunneling current that is exponentially dependent on tip-sample separation. The document outlines the tip positioning system, describes the constant current and variable current imaging modes, and notes STM's advantages of high resolution and ability to study various environments and its disadvantage of requiring precise tip positioning and stable/clean surfaces.
This document discusses pulsed laser deposition (PLD), a physical vapor deposition technique used to deposit thin films. In PLD, a high-power pulsed laser beam is focused onto a target material, vaporizing it and creating a plasma plume that expands toward a substrate where the ablated material is deposited as a thin film. Factors like laser parameters, substrate temperature, background pressure influence the nucleation and growth of the deposited film. PLD offers benefits like exact transfer of complex materials and variable growth rates compared to other thin film deposition methods.
Electron microscopy provides high resolution imaging of nanoscale structures using electron beams. There are two main types: transmission electron microscopy (TEM) and scanning electron microscopy (SEM). TEM uses transmitted electrons to image ultra thin samples, allowing visualization of structures less than an angstrom in size. SEM scans a focused electron beam across a sample to generate topographical and compositional information from electron interactions within microns of the surface. Both techniques require specialized sample preparation and equipment to produce high quality images for research applications across biology, materials science, and other fields.
superparamagnetism and its biological applicationsudhay roopavath
- Superparamagnetism occurs in small ferromagnetic or ferrimagnetic nanoparticles and implies single-domain particle sizes of a few nanometers. The magnetic moments of individual atoms combine to form a giant magnetic moment for the nanoparticle as a whole.
- Below the blocking temperature, nanoparticles behave superparamagnetically, with spontaneous fluctuations of the magnetization direction between θ=00 and θ=1800. Above the blocking temperature, nanoparticles behave paramagnetically.
- Superparamagnetism allows applications in areas like drug delivery, hyperthermia cancer treatment, magnetic resonance imaging, and gene therapy by exploiting the magnetic properties at the nanoscale.
Scanning probe microscopy (SPM) uses a probe that interacts with the sample surface without lenses to resolve images. The first SPM was invented in 1981 by Binning and Roher, winning them the Nobel Prize. For SPM techniques like STM and AFM to provide atomic-level surface structure information, the tip-sample position must be controlled within 0.1 Angstroms and the tip must be very sharp. STM uses tunneling current between a biased tip and conducting sample, while AFM measures cantilever deflection from tip-surface interactions to map topography. SPM provides higher resolution than diffraction-limited techniques and can image insulators and conductors.
The document discusses the working principle of scanning electron microscopy (SEM). It describes how SEM uses a focused beam of electrons to scan the surface of a sample to produce images. SEM provides higher resolution than light microscopes due to the much shorter wavelength of electrons. The document outlines the various components of an SEM, including the electron gun, electromagnetic lenses, detectors for secondary electrons and backscattered electrons, and how these are used to control magnification and resolution. It also discusses some imaging parameters and artifacts that can influence SEM results.
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 discusses different types of electron microscopy techniques. It begins by explaining the need for high resolution in electron microscopy due to the small scale of samples. Different electron microscopy techniques are then described, including transmission electron microscopy (TEM), scanning electron microscopy (SEM), and scanning tunneling microscopy (STM). The document focuses on SEM, explaining how it works by scanning a sample with a beam of electrons to produce signals containing information about the sample's surface topography and composition. Sample preparation methods and interactions between the electron beam and sample are also outlined.
Electron microscopes use electrons instead of light to form magnified images of samples. They can achieve much higher resolutions than light microscopes due to electrons having much shorter wavelengths than visible light. The basic components of an electron microscope include an electron gun that produces the electron beam, electromagnetic lenses that focus the beam, detectors that detect signals from sample interactions, and vacuum systems to allow unimpeded beam travel. Scanning electron microscopes in particular scan samples with a focused electron beam to produce topographical images at magnifications up to 200,000x and resolutions down to 1-4 nm.
Transmission Electron Microscope (TEM), RESOLVING POWER, Scanning Electron Microscope, PRINCIPLE AND WORKING OF SEM, SEM SAMPLE PREPARATION, Limitations of Scanning Electron Microscopy (SEM), ADVANTAGES & DISADVANTAGES OF SEM, APPLICATIONS OF SEM, PRINCIPLE, AND WORKING OF TEM, SAMPLE PREPARATION FOR TEM, ADVANTAGES & DISADVANTAGES OF TEM, APPLICATIONS OF TEM, Differences between SEM and TEM.
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 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 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.
This document provides an overview of the scanning electron microscope (SEM). It describes that the SEM uses a focused beam of electrons to scan the surface of a sample to produce images of its surface topography and composition. The key components of an SEM include an electron gun, magnetic lenses, scanning coils, electron detectors, and a cathode ray tube display. SEMs offer higher magnification, greater depth of field, better resolution, and compositional analysis compared to optical microscopes. Example applications of SEMs include examining the structures of large specimens and samples across various fields like biology, materials science, and engineering.
Materials characterization techniques are used to analyze the internal structure and properties of a material. Common techniques include microscopic analysis using optical microscopes, scanning electron microscopes, and transmission electron microscopes to visualize internal structure at different magnifications. Other techniques include chemical analysis using techniques like x-ray spectroscopy and diffraction to determine composition, and thermal analysis to examine properties under temperature changes. Characterization provides information on properties like structure, defects, composition, and thermal behavior.
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.
This document provides an overview of electron microscopy techniques, specifically scanning electron microscopy (SEM). It begins with a comparison of light microscopes and electron microscopes, noting that electrons have a much shorter wavelength than visible light, allowing for higher resolution images. It then discusses the basic principles and components of SEM, including how the electron beam scans the sample surface and interacts with atoms to produce signals used to form images. Applications mentioned include materials science, nanotechnology, biology, and more. Overall, the document serves as an introduction to SEM, covering its historical development, instrumentation, imaging modes, and various uses.
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.
scanning electron microscope for analysisM Ali Mohsin
SEM stands for scanning electron microscope. The SEM is a microscope that uses electrons instead of light to form an image. Since their development in the early 1950's, scanning electron microscopes have developed new areas of study in the medical and physical science communities.
Scanning Electron Microscopy (SEM 2013).pptxAryaSehrawat1
The document provides an overview of scanning electron microscopy (SEM). It discusses the history and development of SEM, describing how early SEMs from the 1940s had lower resolution (~50 nm) and only provided morphological information, while modern SEMs can achieve ~10 nm resolution and also provide analytical capabilities. The document explains how SEM works, including how the electron beam interacts with and penetrates the sample, generating various signals like secondary electrons, backscattered electrons, and X-rays from within the interaction volume. It describes the components of an SEM, such as the electron gun, magnetic lenses for beam focusing, detectors for signals, and how changing microscope parameters can affect resolution and depth of field.
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 discusses the design of an HVAC system for a multiplex building. It begins with an introduction to air conditioning and controlling indoor air properties. It then discusses components of summer, winter, and year-round air conditioning systems. The document provides calculations to determine the cooling load of a sample classroom and design considerations for ductwork. It emphasizes the importance of HVAC system maintenance for health, efficiency, longevity, and reducing emergency repairs.
The document is a project report for designing an air conditioning system for the Government Medical College in Bokaro, Jharkhand. It includes calculations of the total heat load of the buildings which is determined to be 600 tons. The report proposes a central air conditioning system using four 200-ton water-cooled screw chilling machines. It also includes designs for chilled water pumps, cooling towers, air handling units, ducting, and other necessary equipment to distribute conditioned air throughout the buildings. The system is designed to maintain comfortable indoor conditions during summer, monsoon, and winter seasons.
This document presents the design of an air conditioning system for a multiplex. It includes sections on introduction, types of air conditioning, design criteria, cooling load calculation, and the importance of designing HVAC systems. The introduction discusses increasing temperatures and energy needs for air conditioning. The types of air conditioning systems section describes summer, winter, and year-round systems. The design criteria section outlines considerations for cooling/heating load and indoor/outdoor conditions. The cooling load calculation section explains estimating required capacities based on design conditions, building specifications, and load components from the building envelope and internal sources.
The document discusses the principles and techniques of x-ray crystallography, including how x-rays are produced and used to determine crystal structures by measuring diffraction patterns and applying Bragg's law. It also describes how real diffraction patterns may differ from ideal ones due to factors like strain, crystallite size, and instrumentation.
Supercapacitors store electrical energy through ion movement rather than chemical reactions. They have higher power density than batteries, allowing them to charge and discharge energy more quickly. Supercapacitors have rough electrode surfaces and a liquid electrolyte, unlike conventional capacitors with smooth surfaces and a solid dielectric. While supercapacitors have lower energy density than batteries, they can undergo hundreds of thousands more charge/discharge cycles and maintain performance over a wider temperature range. Supercapacitors are well-suited for applications requiring bursts of power like regenerative braking and acceleration assistance in vehicles.
The document provides an overview of scanning electron microscopes (SEM). It discusses the history and development of SEMs, including key inventors. The main components of an SEM are described, including the electron gun, electromagnetic optics, detectors, and vacuum system. The document explains how SEMs form images using an electron beam that scans the sample surface and interacts with the sample to emit signals like secondary electrons, backscattered electrons, and X-rays. Factors that influence SEM resolution are covered such as accelerating voltage, probe size, and working distance. The document provides examples of the types of samples and features that can be observed using SEMs.
Physical vapor deposition (PVD) involves vaporizing a material source and condensing it as a thin film on a substrate. Thermal evaporation and sputtering are two common PVD methods. Thermal evaporation heats a source material to vaporize it, while sputtering uses a plasma to bombard a target material and eject atoms to deposit on the substrate. PVD requires vacuum conditions to allow vapor transport without collisions between vapor particles and gases. Common applications of PVD thin films include electronics, optics, tool coatings, and decorative coatings.
This industrial training report summarizes different types of air conditioning systems used by ETA General Private Limited, a joint venture company between ETA-ASCON STAR and Fujitsu General. It describes window air conditioning systems, split air conditioning systems, central air conditioning plants, and packaged air conditioners. It then provides more detailed explanations of the working and components of split air conditioners and Variable Refrigerant Flow (VRF) systems, highlighting advantages such as varying compressor speed for individualized comfort control and simultaneous heating/cooling.
mahfooz_toughness of finegrained copperMahfooz Alam
This document summarizes research on the toughness of ultrafine-grained copper processed using equal channel angular pressing (ECAP) for 2 and 16 passes. Copper samples were characterized using tensile testing, Charpy impact testing, and microscopy. Both UFG copper samples had comparable impact toughness to the initial coarse-grained copper, despite having different grain structures. High strain rates were found to enhance strain hardening in the UFG copper. Along crack paths, recrystallized grains formed in the ECAP-2 copper while larger grains grew in the ECAP-16 copper, even though temperature rises were similar for both.
Supercapacitor materials were presented. Supercapacitors store electrical energy at the interface between an electrode and electrolyte through ion adsorption, unlike batteries which store chemical energy. They have higher power density than batteries and higher energy density than conventional capacitors. Common electrode materials include activated carbon, graphene, metal oxides like ruthenium oxide and nickel oxide, and conducting polymers. Supercapacitors can be used in applications requiring bursts of energy like regenerative braking and have a longer lifespan than batteries. Future work aims to improve capacitance and energy density through nanocomposite electrodes.
mahfooz_pulsed electrodeposition technologyMahfooz Alam
The document discusses pulsed electrodeposition technology. It describes pulsed electrodeposition as a unique non-line-of-sight electrolytic deposition technique that uses modulated currents to obtain wear and corrosion resistant nanocrystalline coatings. Key factors that affect pulsed electrodeposition include pulse amplitude, width, and the use of heated baths. The technique has applications in corrosion resistance coatings for automobiles and wear resistance coatings for industrial tools and machinery. Recent research has focused on developing nanocomposite coatings for hard chrome replacement.
Piezoelectricity is the ability of certain materials to generate an electric charge in response to applied mechanical stress. Pierre Curie discovered this effect in 1880 in quartz crystals. When pressure is applied to piezoelectric materials, the ions in the crystal unit cells are displaced, causing an electric polarization. Conversely, an electric field will cause the crystals to mechanically deform. Common piezoelectric materials include quartz and barium titanate. Piezoelectricity is used in applications such as smart sensors, medical imaging, energy harvesting, and more. Lead-based piezoelectrics are widely used but lead-free materials are being developed due to environmental concerns.
This document discusses materials for hydrogen storage and some of the challenges. It notes that hydrogen is not an energy source itself but an energy carrier, and currently it is stored as either high-pressure gas or cryogenic liquid. Solid materials could provide an alternative storage method. Sorbent materials like carbon nanotubes and metal-organic frameworks can store hydrogen at low temperatures but have low storage capacities at room temperature. Complex hydrides can store more but are heavy, expensive, and only work at high temperatures. Nanostructured materials show potential through properties unlike bulk materials, but have yet to emerge as practical solutions and require more research into catalysts, intermediate phases, and kinetics.
Mahfooz Alam presented on the application of lasers. The presentation described lasers as coherent, focused beams of light. It then outlined several laser facilities available at the Centre for Laser Processing of Materials, including a 6 kW fiber coupled diode laser system, 3.5 kW CO2 slab laser, pulsed Nd:YAG laser system, ultrafast laser micro machining system, DCO35 slab CO2 laser/laser mig hybrid welding system, and an automated cold metal transform welding machine. The presentation concluded with acknowledgments.
mahfooz_inhibition of stress corrosion cracking in stainless steelsMahfooz Alam
The document discusses stress corrosion cracking (SCC) in stainless steels and methods for its inhibition. SCC occurs due to the combined effect of corrosion and stress and can lead to sudden failure of ductile metals. Austenitic stainless steels are most susceptible to SCC in chloride environments. Methods for inhibiting SCC in stainless steels include lowering stress through heat treatment, controlling corrosive environments, alloying to increase resistance, using protective coatings, and introducing compressive residual stresses through techniques like shot peening, laser peening, and buffing. Cathodic protection is also discussed as an effective method by making the metal a cathode.
mahfooz_hall-petch-effect-in-bulk-nanostructured-materialMahfooz Alam
This document summarizes research on the Hall-Petch effect in nanostructured bulk materials. It discusses how nanostructured materials are synthesized using solid-state and liquid processing techniques. It then reviews studies that have examined the relationship between grain size and strength based on the Hall-Petch model in various materials like BCC, FCC, and HCP metals. Several models for grain-size strengthening are described, including dislocation pile-up and excess dislocation generation at grain boundaries. The document also notes that the Hall-Petch relationship can break down at very small grain sizes in nanocrystalline materials.
Dr. Venkata Girish Kotnur of the University of Hyderabad presented a course on graphene. Graphene is a one atom thick sheet of carbon atoms arranged in a honeycomb lattice that was first isolated in 2004. It has exceptional properties such as being 200 times stronger than steel and more electrically conductive than silicon. Potential applications of graphene include flexible displays, DNA sequencing, water filtration, and energy storage. Challenges remain in reducing the cost of graphene and developing large-scale growth and production methods.
Mahfooz Alam presented on the science of galvanic corrosion. The presentation covered the history of galvanic corrosion discoveries in the 17th century Royal Navy. It defined galvanic corrosion as corrosion damage induced when two dissimilar metals are coupled in an electrolyte. The mechanism involves the more noble metal acting as the cathode and the less noble metal corroding as the anode due to potential differences between the metals. Factors like material properties, surface area ratios, and electrolyte composition affect the corrosion rate. Measures to reduce galvanic corrosion include choosing metals close in the galvanic series, insulating dissimilar metals, and using cathodic protection with a sacrificial anode. Applications of galvan
Slip and twinning are two important deformation mechanisms in crystals. Slip involves the sliding of atomic planes over one another along crystallographic planes called slip planes, and occurs when the critical resolved shear stress is exceeded. It is controlled by dislocations. Twinning involves mirror-image reflections on either side of a twinning plane, where successive atomic planes are displaced by increasing amounts. Twinning accommodates deformation by changing the crystal orientation and is important when slip systems are limited. The key differences between slip and twinning are that slip is a line defect controlled by dislocations while twinning is a grain boundary surface defect.
This document summarizes several modern materials: artificial spider silk created from a hydrogel that evaporates leaving strong stretchy threads, Shrilk which is a biodegradable plastic made from shrimp shells that releases fertilizer when composted, Starlite whose heat resistant properties are unique but its composition remains a secret, and D3O which is a polyurethane material that flows freely but locks together on impact to absorb and disperse energy as heat before returning to its fluid state. These materials show promise for applications in textiles, plastics, insulation, and protective equipment.
Comparative analysis between traditional aquaponics and reconstructed aquapon...bijceesjournal
The aquaponic system of planting is a method that does not require soil usage. It is a method that only needs water, fish, lava rocks (a substitute for soil), and plants. Aquaponic systems are sustainable and environmentally friendly. Its use not only helps to plant in small spaces but also helps reduce artificial chemical use and minimizes excess water use, as aquaponics consumes 90% less water than soil-based gardening. The study applied a descriptive and experimental design to assess and compare conventional and reconstructed aquaponic methods for reproducing tomatoes. The researchers created an observation checklist to determine the significant factors of the study. The study aims to determine the significant difference between traditional aquaponics and reconstructed aquaponics systems propagating tomatoes in terms of height, weight, girth, and number of fruits. The reconstructed aquaponics system’s higher growth yield results in a much more nourished crop than the traditional aquaponics system. It is superior in its number of fruits, height, weight, and girth measurement. Moreover, the reconstructed aquaponics system is proven to eliminate all the hindrances present in the traditional aquaponics system, which are overcrowding of fish, algae growth, pest problems, contaminated water, and dead fish.
Advanced control scheme of doubly fed induction generator for wind turbine us...IJECEIAES
This paper describes a speed control device for generating electrical energy on an electricity network based on the doubly fed induction generator (DFIG) used for wind power conversion systems. At first, a double-fed induction generator model was constructed. A control law is formulated to govern the flow of energy between the stator of a DFIG and the energy network using three types of controllers: proportional integral (PI), sliding mode controller (SMC) and second order sliding mode controller (SOSMC). Their different results in terms of power reference tracking, reaction to unexpected speed fluctuations, sensitivity to perturbations, and resilience against machine parameter alterations are compared. MATLAB/Simulink was used to conduct the simulations for the preceding study. Multiple simulations have shown very satisfying results, and the investigations demonstrate the efficacy and power-enhancing capabilities of the suggested control system.
Redefining brain tumor segmentation: a cutting-edge convolutional neural netw...IJECEIAES
Medical image analysis has witnessed significant advancements with deep learning techniques. In the domain of brain tumor segmentation, the ability to
precisely delineate tumor boundaries from magnetic resonance imaging (MRI)
scans holds profound implications for diagnosis. This study presents an ensemble convolutional neural network (CNN) with transfer learning, integrating
the state-of-the-art Deeplabv3+ architecture with the ResNet18 backbone. The
model is rigorously trained and evaluated, exhibiting remarkable performance
metrics, including an impressive global accuracy of 99.286%, a high-class accuracy of 82.191%, a mean intersection over union (IoU) of 79.900%, a weighted
IoU of 98.620%, and a Boundary F1 (BF) score of 83.303%. Notably, a detailed comparative analysis with existing methods showcases the superiority of
our proposed model. These findings underscore the model’s competence in precise brain tumor localization, underscoring its potential to revolutionize medical
image analysis and enhance healthcare outcomes. This research paves the way
for future exploration and optimization of advanced CNN models in medical
imaging, emphasizing addressing false positives and resource efficiency.
Rainfall intensity duration frequency curve statistical analysis and modeling...bijceesjournal
Using data from 41 years in Patna’ India’ the study’s goal is to analyze the trends of how often it rains on a weekly, seasonal, and annual basis (1981−2020). First, utilizing the intensity-duration-frequency (IDF) curve and the relationship by statistically analyzing rainfall’ the historical rainfall data set for Patna’ India’ during a 41 year period (1981−2020), was evaluated for its quality. Changes in the hydrologic cycle as a result of increased greenhouse gas emissions are expected to induce variations in the intensity, length, and frequency of precipitation events. One strategy to lessen vulnerability is to quantify probable changes and adapt to them. Techniques such as log-normal, normal, and Gumbel are used (EV-I). Distributions were created with durations of 1, 2, 3, 6, and 24 h and return times of 2, 5, 10, 25, and 100 years. There were also mathematical correlations discovered between rainfall and recurrence interval.
Findings: Based on findings, the Gumbel approach produced the highest intensity values, whereas the other approaches produced values that were close to each other. The data indicates that 461.9 mm of rain fell during the monsoon season’s 301st week. However, it was found that the 29th week had the greatest average rainfall, 92.6 mm. With 952.6 mm on average, the monsoon season saw the highest rainfall. Calculations revealed that the yearly rainfall averaged 1171.1 mm. Using Weibull’s method, the study was subsequently expanded to examine rainfall distribution at different recurrence intervals of 2, 5, 10, and 25 years. Rainfall and recurrence interval mathematical correlations were also developed. Further regression analysis revealed that short wave irrigation, wind direction, wind speed, pressure, relative humidity, and temperature all had a substantial influence on rainfall.
Originality and value: The results of the rainfall IDF curves can provide useful information to policymakers in making appropriate decisions in managing and minimizing floods in the study area.
artificial intelligence and data science contents.pptxGauravCar
What is artificial intelligence? Artificial intelligence is the ability of a computer or computer-controlled robot to perform tasks that are commonly associated with the intellectual processes characteristic of humans, such as the ability to reason.
› ...
Artificial intelligence (AI) | Definitio
1. WORKING
PRINCIPLE OF
SEM
Mahfooz Alam
17ETMM10
COURSE : SEMINAR II{MT456}
M. Tech.
Materials Engineering
School of Engineering Sciences & Technology
University Of Hyderabad
Course instructors :
Dr.-Ing. V.V.S.S SRIKANTH
Dr. JAI PRAKASH GAUTAM
2. Microscopy
• Microscopy is the technical field of using microscopes to view objects and
related areas, that cannot be seen with the naked eye .
2
3. TYPES
3
The various types of light
microscopy include
1. bright-field,
2. dark-field,
3. fluorescence, and
4. phase contrast
microscopy
1)SEM
2)TEM
3)STEM
1. X-Ray Microscopy
2. Focused Ion Beam
(FIB)
etc
1. Scanning Tunneling
Microscopy (STM)
2. Atomic Force Microscopy
(AFM)
3. Magnetic Force Microscopy
(MFM)
4. MAGNIFICATION
• Magnification in physical terms is defined as "a measure of the ability of a
lens or other optical instruments to magnify, expressed as the ratio of the
size of the image to that of the object". This means, that an object of any size
is magnified to form an enlarged image.
• In SEM defined as the ratio of the size of the rastered area on the sample to
the size of the rastered area of the output.
4
5. RESOLUTION
• Itis the smallest distance at which two neighbouring points can be
distinguished, and is dependent on wavelength.
• The wavelength of accelerated electrons (6 pm) is several orders of
magnitude shorter than that of light (600 nm).
5
6. 6
Scanning Electron
Microscope (SEM)
is a type of electron microscope that
produces images of a sample by
scanning the surface with a focused
beam of electrons.
The electrons interact with atoms in
the sample, producing various signals
that contain information about the
sample's surface topography and
composition.
7. PRINCIPLE
7
When the accelerated primary electrons strikes the sample , it produces secondary electrons. These
secondary electrons are collected by a positive charged electron detector which in turn gives a 3-dimensional
image of the sample.
OR
The electron detector (Scintillator) is used to collect the secondary electrons and can be
converted into electrical signal. These signals can be fed into CRO through video amplifier
as shown.
8. 8
Stream of electrons are produced by the
electron gun and these primary electrons
are accelerated by the grid and anode.
These accelerated primary electrons are
made to be incident on the sample
through condensing lenses and scanning
coil.
These high speed primary electrons on
falling over the sample produces low
energy secondary electrons. The collection
of secondary electrons are very difficult
and hence a high voltage is applied to the
collector.
These collected electrons produce
scintillations on to the photo multiplier
tube are converted into electrical signals.
These signals are amplified by the video
amplifier and is fed to the CRO.
By similar procedure the electron beam
scans from left to right and the whole
picture of the sample is obtained in the
CRO screen.
9. • The function of the electron gun is to provide a large and stable current in a
small beam.
• There are two classes of emission source: thermionic emitter and field
emitter.
• Thermionic Emitters use electrical current to heat up a filament; the two most
common materials used for filaments are Tungsten (W) and Lanthanum
Hexaboride (LaB6).
• Thermionic sources have relative low brightness , & evaporation of cathode
material and thermal drift during operation occurs.
• Field Emission is one way of generating electrons that avoids these problems.
A Field Emission Gun (FEG); also called a cold cathode field emitter
does not heat the filament.
9
IMPORTANCE OF ELECTRON GUN
10. • The emission is reached by placing the filament in a huge electrical potential gradient.
• The FEG is usually a wire of Tungsten (W) fashioned into a sharp point. The significance of
the small tip radius (~ 100 nm) is that an electric field can be concentrated to an extreme
level, becoming so big that the work function of the material is lowered and electrons can
leave the cathode.
• FESEM uses Field Emission Gun producing a cleaner image, less electrostatic distortions
and spatial resolution < 2nm (that means better than SEM with Thermionic gun).
10
13. COMPONENTS OF SEM
• 1. Condenser lens :
• The current in the condenser determines the diameter of the beam. a low current results
in a small diameter, a higher current in a larger beam.
• A narrow beam has the advantage that the resolution is better, but the disadvantage that
the signal to noise ratio is worse.
• The situation is reversed when the beam has a large diameter.
• 2. Scan coils :
• The scan coils deflect the electron beam over the object according to a zig-zag pattern.
The formation of the image on the monitor occurs in synchrony with this scan movement.
• The scan velocity determines the refreshing rate on the screen and the amount of noise in
the image (rapid scan = rapid refreshing = low signal = much noise).
• The smaller the scanned region on the object, the larger the magnification becomes at a
constant window size. 13
14. • 3. The objective lens:
• The objective lens is the lowest lens in the column.
• The objective focuses the electron beam on the object. At a short working distance the
objective lens needs to apply a greater force to deflect the electron beam.
• The shortest working distance produces the smallest beam diameter, the best resolution,
but also the poorest depth of field. (The depth of field indicates which range in vertical
direction in the object can still be visualized sharply).
• 4. The stigmator coils:
• The stigmator coils are utilized to correct irregularities in the x and y deflection of the
beam and thus to obtain a perfectly round-shaped beam.
• When the beam is not circular, but ellipsoidal, the image looks blurred and stretched.
14
15. 15
A light microscope uses light as its illumination source where as an electron microscope uses
electrons.
Vacuum is needed for the electrons to travel from the electron source to the sample surface
unimpeded.
Without vacuum the beam of electrons would be scattered (mean free path is low) by air particles.
So, a high level of vacuum is needed for an electron microscope i.e ( mean free path of the electron
should be larger than the electron column).
18. Secondary Electrons
(SE)
• Produced by inelastic interactions of
high energy electrons with valence
electrons of atoms in the specimen
which cause the ejection of the
electrons from the atoms.
• After undergoing additional
scattering events while traveling
through the specimen, some of these
ejected electrons emerge from the
surface of the specimen.
• Arbitrarily, such emergent electrons
with energies less than 50 eV are
called secondary electrons; 90% of
secondary electrons have energies
less than 10 eV; most, from 2 to 5 eV. 18
Backscattered Electrons (BSE)
• Backscattered electrons (BSE) are beam electrons whose
trajectories have intercepted a surface usually, but not necessarily,
the entrance surface and which thus escape the specimen.
• Backscattered electrons remove a significant amount of the total
energy of the primary beam.
• Backscattering is quantified by the backscatter coefficient η which is
defined as
• where ηB is the number of beam electrons incident on the specimen
and ηBSE is the number of backscattered electrons (BSE).
• The backscatter coefficient can also be expressed in terms of
currents, where iB refers to the beam current injected into the
specimen and iBSE to the backscattered electron current passing out
of the specimen.
19. • DETECTOR USED FOR SECONDARY ELECTRONS
19
Information that can be obtained : Topography and Morphology details
21. • 4 parameters controls different imaging modes in SEM
• Electron probe size dia. (dp) - Dia. Of electron beam
focused at the specimen
• Electron probe current (ip) – Current impinging upon the
specimen and generating various signals
• Electron probe convergence angle (αp) – Half cone angle
of electrons converging onto the specimen
• Electron beam accelerating voltage (Vo) kV
21
22. Mode I -Resolution Mode
• This mode is governed by the Electron probe size dia.(dp)
• Resolution refers to the size of finest detail that can be observed.
• To image the finest details dp must be comparable with or smaller than the
feature itself.
• Resolution mode is only meaningful at high image magnifications (>10,000 X),
Beam should contain sufficient current to exceed visibility threshold.
22
Mode II –High Current Mode
• This mode is governed by the Electron probe current(ip).
• For the best image visibility and quality –Large ip.
• Unless a sufficient amount of current (required to overcome random noise) is
there details, cannot be seen even if the spot size is small enough.
24. 24
Mode III –Depth-of-Focus Mode
• This mode is governed by the probe convergence angle(αp).
• For the best image quality –αp as small as possible.
• With low beam convergence angle, beam dia. changes only a little over a long
vertical distance, so surface features at different heights will all appear to be
in focus at the same time.
25. Acceleration voltage
• In theory, an increase in accelerating voltage will result in a higher signal (and
lower noise) in the final image (micrograph).
• But the situation is not so simple.
• There are some disadvantages:
• Reduction in structural details of the specimen surface in SE mode.
• Increased electron build up in insulating samples, causing charging effects.
• Increased heating and the possibility of specimen damage.
• With a higher accelerating voltage the electron beam penetration is greater
and the interaction volume is larger. Therefore, the spatial resolution of
micrographs created from those signals will be reduced.
• So there will be a brighter image because the number of backscattered 25
26. 26
• The solution therefore,
for obtaining fine surface
structure is to exclude
these backscattered
electrons by using lower
kVs such as 3-10kV.
• Hence lower energy
provides better detail of
surface structure.
27. EDGE EFFECTS
• Edge effects are due to the enhanced emission of electrons from edges and
peaks within the specimen.
• They are caused by the effects of topography on the generation of secondary
electrons and are what gives form and outline to the images produced by the
Secondary Electron detector.
• Electrons preferentially flow to and are emitted from edges and peaks. Poor
signal intensity occurs in those regions shielded from the detector, such as
depressions.
• Topographic contrast is also enhanced by Back Scattered electrons emitted
from regions of the sample facing towards the detector. Lowering the beam kV
can reduce edge effect.
27
28. Charging
• Charging is produced by build-up of electrons in the sample and their
uncontrolled discharge, and can produce unwanted effects, particularly in
secondary electron images.
• When the number of incident electrons is greater than the number of
electrons escaping from the specimen, then a negative charge builds up at the
point where the beam hits the sample. This phenomenon is called charging.
• and it causes a range of unusual effects such as abnormal contrast and image
deformation and shift. Sometimes a sudden discharge of electrons from a
charged area may cause a bright flash on the screen. These make it impossible
to capture a uniform image of the specimen and may even be violent enough
to cause small specimens to be dislodged from the mounting stub.
• The level of charge will relate to,
• (1) the energy of the electrons and
• (2) the number of electrons. 28
29. • In a SEM, magnification results
from the ratio of the dimensions of
the raster on the specimen and the
raster on the display device.
• Assuming that the display screen
has a fixed size, higher
magnification results from
reducing the size of the raster on
the specimen, and vice versa.
• Magnification is therefore
controlled by the current supplied
to the x, y scanning coils,, and not
by objective lens power.
29
30. • The spatial resolution of the SEM depends on the size of the electron spot,
which in turn depends on both the wavelength of the electrons and the
electron-optical system which produces the scanning beam.
• The resolution is also limited by the size of the interaction volume, or the
extent to which the material interacts with the electron beam.
• The spot size and the interaction volume are both large compared to the
distances between atoms, so the resolution of the SEM is not high enough
to image individual atoms.
30
TILTING
31. CONCLUSION
31
SEM Advantages
• Advantages of a Scanning Electron Microscope include its wide range of applications, the
detailed three-dimensional and topographical imaging and the versatile information
obtained from different detectors.
• SEMs are also easy to operate with the proper training and advances in computer
technology and associated software make operation user-friendly.
• The instrument works fast, often completing SEI, BSE and EDS analyses in less than five
minutes.
• Although all samples must be prepared before placed in the vacuum chamber, most SEM
samples require minimal preparation actions.
32. 32
SEM Disadvantages
• The disadvantages of a Scanning Electron Microscope start with the size and cost.
• SEMs are expensive, large and must be housed in an area free of any possible electric, magnetic or vibration
interference.
• Maintenance involves keeping a steady voltage, currents to electromagnetic coils and circulation of cool water.
• Special training is required to operate an SEM as well as prepare samples.
• In addition, SEMs are limited to solid, inorganic samples small enough to fit inside the vacuum chamber that can
handle moderate vacuum pressure.
• Finally, SEMs carry a small risk of radiation exposure associated with the electrons that scatter from beneath the
sample surface.
• The sample chamber is designed to prevent any electrical and magnetic interference, which should eliminate the
33. ACKNOWLEDGEMENTS
• I would like to thank DR.-ING. V.V.S.S SRIKANTH & DR. JAI PRAKASH
GAUTAM for their valuable insight and suggestions on my technical
presentation skills.
• Thanks to the Dean of “school of engineering sciences and technology”, Dr
Ghansyam Krishna, to make this course as a part of Academic curriculum.
• I am truly grateful to the AICTE, GATE FELLOWSHIP PROGRAMME. For
providing the funding.
• I would like to thank other faculty members of SEST, who helped in getting
better understanding of topics which were dealt with in this course.
{SEMINAR-II} 33