Webinar Title: ZEISS on Campus: Electron Microscopy and Spectrometer
Speaker/ Author (Date): Dr. Chiawat Prawettongsopon, Dr Mun Kit Leong (April 7,
2022 9:00 PHT)
Summary:
Imagine the possibilities of a microscope that allows you to see so much in such
detail. Electron microscopy (EM) lets you observe a world exponentially smaller than the
one you can see with your eyes. In fact, electron microscopes use their own kind of
light—electrons—to “see” these micro-sized materials. An electron microscope can let
you take a virtual look inside a cell and watch its tiny parts at work, or you can see
individual proteins or atoms within an alloy.
In the webinar, Dr. Benjamin Te of Zeiss Philippines introduced us to our first
speaker, Dr. Chiawat Prawettongsopon. Dr Prawettonsopon is the Senior Regional
Application and Sales Specialist of Zeiss Thailand. His field of expertise focuses mainly
on electron microscopies, and he also has an extensive background and experience in
research and development.
In this webinar we have gone over the types of tissue and cells present in the
human body and also discussed the procedure for TEM and SEM. Like the ordinary
microscope, these devices use a system of light lenses to magnify specimens, but
unlike their optical counterparts, they use an electron beam rather than a beam of light
to transmit information about a specimen to the viewer. The resulting images give a
detailed view of the internal structures (such as complex protein structures forming
organelles like nuclei, mitochondria and ribosomes).
The scanning electron microscope (SEM) works much like a standard optical
microscope, but because it uses electrons to detect and record images, it has different
capabilities and limitations. SEM is ideal for imaging a wide range of materials, including
industrial metals, geological samples, and biological specimens such as cells, spores,
and insects. Its ability to provide high-magnification views has made SEM the preferred
microscope for surface studies. While TEM can reveal more detailed structural
information about a sample, this technique involves preparing a thin slice of the sample
(a process called sectioning), which is not possible with some kinds of samples or with
some kinds of experiments. Moreover, the preparation of samples for observation under
TEM requires time and money.
Transmission electron microscopes can analyze samples that are too thin to be
examined with a conventional scanning electron microscope. TEMs can view materials
at the atomic level, revealing details that cannot be found with any other imaging device.
Transmission electron microscopes (TEMs) allow the observation of fine and even
ultrafine details. TEM is capable of identifying detailed information about the structure at
the atomic level, providing much more complete structural detail than an electron
microscope. However, transmission electron microscopy is restricted to conducting
samples that are thin enough to let electrons pass through them. This thinning process
is technically challenging and requires special tools.
Electron microscopy is traditionally used for high-resolution imaging of cellular
and subcellular structures. TEMs have been the preferred choice due to their ultrahigh
resolution but have not been compatible with nonconductive specimens because of
electron charging and damage. However, non-conductive biological samples can be
challenging to image using SEM and may require charging effects and damage to the
sample.
ZEISS Sense BSD combines TEM-like imaging with a new degree of efficiency
and image quality, allowing structural properties to be typically observed in biological
samples and reducing charging effects in non-conductive specimens. ZEISS Sense
BSD is a beam-sensitive detector system for use with a wide range of microscopes,
including biological and environmental systems. Its high resolution and high contrast are
particularly suitable for applications requiring low acceleration voltages and low electron
doses. Its gentle excitation conditions reduce charging effects that are a source of
image quality deterioration.
The next speaker is Dr. Mun Kit Leong of Oxford Malaysia.He worked as a
semiconductor process engineer for a few years before joining a scientific and research
solution provider, where he specialized in application engineering for over nine years.
He has extensive experience working with many different kinds of characterization tools,
including scanning electron microscopy, transmission electron microscopy, and atomic
force microscopy. He is the territory sales manager of Oxford Instruments in Malaysia
and specializes in applications such as energy dispersive spectroscopy, wavelength
dispersive spectroscopy, electron backscattered diffraction, and nanomechanical
properties.
EDS (Energy Dispersive X-ray Spectroscopy) is a technique used to detect the
x-rays generated when a charged particle beam interacts with matter, typically mounted
on the stage of an electron microscope in a state of high vacuum.This method is often
used for basic materials characterization and for point quantification. In this context,
point quantification refers to the analysis of a material at a specific location. EDS
elemental analysis in SEM is non-destructive when the area analyzed has a thin surface
layer that is representative of the bulk material and is sufficiently electrically conducting.
The disadvantage of EDS analysis is not being aware of the geometry or morphology of
the composition elements, which may result in higher or lower apparent concentrations
than their actual values.
Modern-day EDS detectors are silicon drift detectors (SDD), an advancement
over the more primitive mineral-insulated germanium detectors (MIX). X-rays, which
originate from a microscope's electron gun or from a synchrotron source, are converted
into changes in voltage, which are then measured and analyzed in a pulse processor
and sent to a software program such as AZtec to present the signal in a spectrum. A
spectrum can be generated by collecting data in every position the beam of light
interacts with the specimen by using a detector to measure both the intensity of the light
and where it is being reflected and absorbed. Maps can be produced using STEM
modes.
The spectrum is relatively easy to interpret. The x-ray energy (the x axis) can be
interpreted along with peaks indicating which elements were present in a sample. AZtec
can identify the elements which caused each peak and deconvoluted spectra and maps
to correct for various known artifacts. Maps created by combining the relative intensities
of different color-coded spectra across an area. The colors reflect the elements present
in the different substances sampled. For example, darker blue could represent greater
abundance of Sodium and lesser abundance of Calcium. Layered maps composed of
several element maps are used to create color electron micrographs that reveal
ultrastructural details within certain areas of the specimen while also showing the
specimen's composition.
Oxford Instruments manufactures a range of detectors for transmission electron
microscopy and scanning electron microscopy.Energy dispersive spectrometry (EDS)
can be used to analyze samples of tissue stained using different protocols, which allows
access to new information about the samples. Differential staining is an important step
in producing images of cells and tissues for electron microscopy. Energy-dispersive
x-ray spectrometry (EDS) provides qualitative and quantitative data about the
distribution of elements associated with the staining of a specimen, and it can give
relative concentrations of elements. The detection of trace elements using
energy-dispersive spectroscopy (EDS) is a growing area of interest in medical and
biological research. Specimen preparation can affect the distribution of native elements,
so efficient and effective sample preparation methods are crucial. EDS can be used to
analyze samples stained using specific tissue staining protocols, providing new
information about the samples.
References
Carl Zeiss Microscopy GmbH. (n.d.). TEM-like imaging with your SEM.
Energy Dispersive X-ray Spectrometry (EDS) for Biology. (n.d.). Dartmouth. Retrieved
April 18, 2022, from
https://www.dartmouth.edu/emlab/docs/eds_for_biology_oxford_instruments.pdf
Energy Dispersive X-ray Spectrometry (EDS) for Biology. (n.d.). Dartmouth. Retrieved
April 18, 2022, from
https://www.dartmouth.edu/emlab/docs/eds_for_biology_oxford_instruments.pdf
Ilitchev, A. (2019, January 11). TEM vs SEM - Electron Microscopes - Accelerating
Microscopy. Thermo Fisher.
https://www.thermofisher.com/blog/microscopy/tem-vs-sem-whats-the-difference/
Appendices