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    Group 3 TEM Presentation

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    Himel Kundu
    Transmission Electron Microscopy (TEM) is a powerful imaging technique that uses electron beams instead of light to observe ultra-thin samples at the nanoscale. TEM was developed in the 1930s and provides higher resolution than scanning electron microscopy (SEM). TEM works by transmitting electrons through a thin sample, with heavier or thicker areas absorbing more electrons and appearing darker in the image. High resolution TEM can image individual atoms with resolutions as small as 0.07 nm. STEM is a related technique that forms images by scanning a focused electron probe across the sample.

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    Group 3 TEM Presentation

    Uploaded by

    Himel Kundu
    28 views26 pages
    Transmission Electron Microscopy (TEM) is a powerful imaging technique that uses electron beams instead of light to observe ultra-thin samples at the nanoscale. TEM was developed in the 1930s and provides higher resolution than scanning electron microscopy (SEM). TEM works by transmitting electrons through a thin sample, with heavier or thicker areas absorbing more electrons and appearing darker in the image. High resolution TEM can image individual atoms with resolutions as small as 0.07 nm. STEM is a related technique that forms images by scanning a focused electron probe across the sample.

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    Transmission Electron Microscopy (TEM) is a powerful imaging technique that uses electron beams instead of light to observe ultra-thin samples at the nanoscale. TEM was developed in the 1930s and provides higher resolution than scanning electron microscopy (SEM). TEM works by transmitting electrons through a thin sample, with heavier or thicker areas absorbing more electrons and appearing darker in the image. High resolution TEM can image individual atoms with resolutions as small as 0.07 nm. STEM is a related technique that forms images by scanning a focused electron probe across the sample.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    28 views26 pages

    Group 3 TEM Presentation

    Uploaded by

    Himel Kundu
    Transmission Electron Microscopy (TEM) is a powerful imaging technique that uses electron beams instead of light to observe ultra-thin samples at the nanoscale. TEM was developed in the 1930s and provides higher resolution than scanning electron microscopy (SEM). TEM works by transmitting electrons through a thin sample, with heavier or thicker areas absorbing more electrons and appearing darker in the image. High resolution TEM can image individual atoms with resolutions as small as 0.07 nm. STEM is a related technique that forms images by scanning a focused electron probe across the sample.

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    Transmission Electron Microscopy (TEM)

    Course No.: EEE 463


    Course Title: Introduction to
    Nanotechnology and Nanoelectronics

    Presented by: Group 3


    Student ID:
    1906014, 1906044, 1906055, 1906059,
    1906081,1906086, 1906108,
    1906120, 1906181, 1906186
    Introduction

    TEM is a powerful imaging technique

    that uses transmission electrons

    instead of light to observe ultra-thin

    samples at Nano scale resolutions.


    Historical Development

    • Developed in the 1930s by


    Ernst Ruska and Max Knoll

    • First successful TEM in 1931


    Comparison between
    SEM & TEM
    SEM
    • 3D surface imaging

    • Lower resolution

    TEM
    • 2D Cross-sectional imaging

    • Higher resolution

    • Detailed internal structures


    High Resolution TEM (HRTEM)
    • Developed in the 2005 by
    Carl Zeiss

    • A specialized form of TEM


    that provides even higher
    resolution (0.07 nm)

    • Enables detailed imaging of


    crystal lattices and
    individual atoms
    Basic Working Principle

    • Field Emission Gun produces a single electron beam.

    • Anode accelerates electron beam towards the sample through vacuum tube.

    • Heavy atoms within sample absorb more electron, transmit less electron

    • Light atoms within sample absorb less electron, transmit more electron.

    • Electromagnetic lenses amplify variation of electron transmission.

    • Bright or dark image on fluorescent screen as per transmitted or diffracted beam.

    • CCD camera captures as a digital image.


    Schematic of TEM:
    1. Electron Gun
    2. Anode
    3. Condenser Aperture
    4. Condenser Lens
    5. Objective Lens
    6. Sample Holder
    7. Objective aperture
    8. Intermediate Lens
    9. Projector Lens
    10. Viewing Screen
    11. CCD Camera
    Different components of TEM:
    • Filament: A field emission gun (FEG) is placed inside a casing (a Wehnelt cylinder)
    which emits the electron beam. This is a very high voltage setup of around 100-
    400 keV. The wavelength of the beam is in the picometer range and therefore the
    energy of the beam is very high. A Tungsten tip is used for emission of electron.
    Different components of TEM:
    • Anode: It has the form of a disk with an axial hole and is
    used to accelerate the electron beam.
    • Apertures: Fixed aperture and variable condenser apertures
    are available. They’re used to control the beams so that
    they’re collimated. They can also be used to observe
    transmitted beam (bright field) or diffracted beam (dark
    field) or both simultaneously.
    • Sample: The sample in TEM needs to be ultra thin for better
    transmission. It requires months of training for sample
    preparation. The cross section of the sample is observed
    through the TEM. Sample preparation is a manual process
    that requires grinding, polishing and other complicated
    processes. Fig: Part of sample preparation
    procedure of TEM
    Schematic of TEM:
    Different components of TEM:

    • Intermediate and Projector lenses: The intermediate


    and projector lenses magnify the image or diffraction
    pattern onto the viewing screen.These are electro
    magnetic lenses. Wire coils surround the beam and
    produce a field that generates a deflecting force on
    the electrons. Each lens is constructed of a coil of
    copper wire through which a current runs. There is a
    hole in the center through which the beam travels.
    Magnetic lenses allow the user to change
    magnification and focus of the beam.
    Different components of TEM:
    Detectors:
    Different detectors may be used to capture various
    signals, such as transmitted electrons (bright-field
    imaging), diffracted electrons (electron diffraction),
    and secondary electrons (scanning TEM or
    STEM).We record images digitally using cameras
    that can be mounted either above or below the
    viewing screen. Diffraction work is often carried out
    on cameras above the viewing screen, and high
    resolution imaging tends to be carried out using the
    under-mount camera
    Different components of TEM:
    CCD Camera: A charge-coupled device (CCD) is a
    light-sensitive integrated circuit that captures
    images by converting photons to electrons. A CCD
    sensor breaks the image elements into pixels. Each
    pixel is converted into an electrical charge whose
    intensity is related to the intensity of light captured
    by that pixel.
    The resolution of a good TEM is around 0.2 nm. HRTEM- Developed by Zeiss,
    resolution of 0.07 nm with a 300 KeV field emission gun.
    The CCD was invented in 1969 at Bell Labs (now part of Nokia) by George Smith and
    Willard Boyle.In the 1970s Michael F. Tompsett, also with Bell Labs, refined the CCD's
    design to better accommodate imaging.
    TEM Image Collection(Bright Field)
    Transmitted beam imaging focuses
    on the electrons that pass through
    the specimen, forming an image
    based on electron density
    variations.

    Fig: TEM image of a tissue paper sample in bright field mode


    TEM Image Collection(Dark Field)
    Diffracted beam imaging involves forming an
    image based on the diffraction pattern
    produced by electrons interacting with the
    crystal lattice of the specimen.

    Fig: TEM image of a tissue paper sample in dark field mode


    TEM Image Collection

    Transmitted beam imaging provides


    high-resolution internal structure
    details, while diffracted beam imaging
    provides information about the crystal
    structure of the specimen.
    Structure of STEM
    • A combination of SEM and
    TEM
    • A transmission image is
    obtained using a scanning
    method
    • A TEM can be modified into
    an STEM by the addition of a
    system that scans a focused
    beam across the specimen
    to form the image.
    Main Components of STEM
    Objective Lens : The beam coming off the gun is demagnified by the objective
    lens.

    Specimen: Specimen must be ultra thin. The beam falling on the sample
    produces a diffraction pattern.

    Intermediate Aperture : Electron beam trajectories are varied by the aperture.

    Detectors: A Bright Field Detector along with an Annular Dark Field Detector is
    present in every STEM.
    STEM DETECTORS:
    The electrons contributing to STEM images can be finely controlled by
    varying the camera length and inserting various detectors. STEM detectors
    function the same way objective apertures do in TEM.
    Bright-field (BF):

    The BF detector sits on-axis and


    collects electrons contributing to
    the central disk in the CBED
    pattern. A typical acceptance
    angle for the BF detector is half
    of α. BF-STEM images are
    analogous to phase-contrast
    images in TEM and can provide
    high-resolution information with
    enhanced contrast of light
    elements.
    Annular dark
    field (ADF):
    ADF images are acquired
    using a ring-shaped
    detector that surrounds the
    BF detector so that a large
    portion of the Bragg-
    diffracted electrons are
    collected. These images
    are complementary to the
    BF-STEM images in terms
    of contrast.
    STEM Dark Field Imaging
    Displaced Aperture

    ❑ The dark field images may also be formed by the


    displacement of the aperture.
    ❑ It allows only a specific diffracted beam to pass
    through(marked 1, 2,3,… etc.)
    ❑ Deflection coils placed after the sample are used
    to direct the chosen part of the diffraction pattern
    to the entrance aperture of the spectrometer
    Application of STEM
    Annular Dark Field Imaging

    A typical STEM imaging example will record a 2D grid of probe positions, forming a
    2D image from each of the single-pixel detectors.
    Application of STEM
    Diffraction
    Application of STEM
    Tomography
    Thank You

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