Faculty of Sciences - University of Kufa



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      Electron Microscope Lab




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Introduction:





One of the primary objectives of Electron microscope Lab to provide best research and analytical services facilities, keeping in view the technological needs of the country, for all its undergraduate, postgraduate and research activities. It located on the ground floor in the Department of surgery, Faculty of medicine, University of Kufa. The charges finalized by the EM Users Committee, are displayed on the SEM website of the institute and are non-negotiable under any circumstances.

The EMLab is equipped with following equipment's:
- Transmission Electron MicroscopeTecnai G2 Spirit BioTwin (www.feicompany.com)
- Scanning Electron Microscope /Inspect S50 (www.feicompany.com)
- Bruker-AXS Energy Dispersive X-ray System
- Ultra - microtome (Leica EM UC6)
- Polaron Gold / Silver Sputter Coating unit




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Principle of SEM/EDX





The scanning electron microscope uses a focused electron beam which is scanned on the surface of the sample to produce high quality images of the surface topography. SEM essentially offers a very high magnification with very high resolution capabilities and a large depth of focus. This characteristic makes it an indispensable tool for analysis of a wide class of conducting, semi-conducting and insulating materials. A strong beam of electrons called primary electron beam is produced by thermionic emission using either tungsten or a Lanthanum Hexaboride (LaB6) filament. The primary beam of electrons thus emitted by thermionic emission interacts with the top atomic layers of surface of the sample. This gives out a variety of signals that can be collected and processed to derive a good quality of information about the morphology of the sample, atomic contrast in the sample and the elemental composition of the top surface of the material. The different possible interactions of the sample with a high energy electron beam are:

Primary electrons generate very low energy electrons called secondary electrons from the top atomic layers of the sample that are used to analyze its topographic nature.
Primary electrons that are backscattered during interaction with sample surface produce images with a high degree of atomic number contrast.
Primary beam of electrons can ionize atoms of the sample that stabilize by shell-to-shell transitions of electrons, which causes either emission of X-rays or Auger electron. The X-rays so emitted are characteristic of the elements that make the top surface layers of the sample.

The Scanning Electron Microscope (SEM) has many applications across a multitude of different sectors. It can produce extremely high magnification images (up to 2000000x) at high resolution up to 3nm combined with the ability to generate localized chemical information (EDX). This means the SEM/EDX instrument is a powerful and flexible tool for solving a wide range of product and processing problems for a diverse range of metals and materials.EM Lab Services has extensive experience in using SEM/EDX analysis in many medical devices pharmaceutical , chemicals ,industrial sectors, electronics and semiconductors, , petrochemicals, plastics and polymers, aerospace, automotive, , engineering, , materials and metallurgy.



The main features and benefits of the SEM are:-





o EDX analysis of known or unknown materials
o Image magnification and resolution
o Magnification range X 15 - X 2000,000
o Resolution 3 nm
o Accelerating voltage 1 - 30 keV
o Secondary and backscatter electron imaging
o Stereo imaging and stereo height measurement
o Qualitative and quantitative analysis for all elements from carbon upwards
o Quantitative analysis of bulk materials and features
o Qualitative analysis of features
o Detection limits typically 0.1 - 100 Wt% for most elements
o Multi-element X-ray mapping and line scans
o Multi-layer, multi-element thin film analysis - Thickness and composition
o Particle / Phase analysis - Detection, analysis, morphology and size
o Image Analysis
o Automatic particle counting and characterization



Applications of SEM





o Powder morphology, particle size and analysis
o Identification of metals and materials
o Particle contamination identification and elimination
o Classification of materials
o Contamination or stain investigation
o Structural analysis
o Paint and coating failure and delamination investigation
o Paint, Adhesive, Sealant and Gasket Filler Fingerprinting
o Identification and elimination of corrosion and oxidisation problems
o Reverse engineering of products and processes
o Product and process failure and defect analysis
o Examination of surface morphology (including stereo imaging)
o Analysis and identification of surface and airborne contamination
o Cleaning problems and chemical etching
o Welding and joining technology quality evaluation and failure investigation



Types of materials for Investigation by SEM/EDX:-





o Powders and Dust
o Biological and medical samples
o Metals, Glass and Ceramics
o Semiconductors
o Plastics and polymers
o Composite Materials
o Fibres (Textile, fabric , man-made, natural, carbon fibres, glass fibres, kevlar)



Energy-Dispersive X-Ray Spectroscopy (EDS)





Interaction of an electron beam with a sample target produces a variety of emissions, including x-rays. An energy-dispersive (EDS) detector is used to separate the characteristic x-rays of different elements into an energy spectrum, and EDS system software is used to analyze the energy spectrum in order to determine the abundance of specific elements. EDS can be used to find the chemical composition of materials down to a spot size of a few microns, and to create element composition maps over a much broader raster area. Together, these capabilities provide fundamental compositional information for a wide variety of materials.

EDS systems are typically integrated into an SEM instrument. EDS systems include a sensitive x-ray detector, and software to collect and analyze energy spectra. The most common detectors are made of Si(Li) crystals that operate at low voltages to improve sensitivity, but recent advances in detector technology make availabale so-called "silicon drift detectors" that operate at higher count rates without liquid nitrogen cooling.An EDS detector contains a crystal that absorbs the energy of incoming x-rays by ionization, yielding free electrons in the crystal that become conductive and produce an electrical charge bias. The x-ray absorption thus converts the energy of individual x-rays into electrical voltages of proportional size; the electrical pulses correspond to the characteristic x-rays of the element.



Strengths





When used in "spot" mode, a user can acquire a full elemental spectrum in only a few seconds. Supporting software makes it possible to readily identify peaks, which makes EDS a great survey tool to quickly identify unknown phases prior to quantitative analysis.
EDS can be used in semi-quantitative mode to determine chemical composition by peak-height ratio relative to a standard.



Limitations





There are energy peak overlaps among different elements, particularly those corresponding to x-rays generated by emission from different energy-level shells (K, L and M) in different elements. For example, there are close overlaps of Mn-K? and Cr-K?, or Ti-K? and various L lines in Ba. Particularly at higher energies, individual peaks may correspond to several different elements; in this case, the user can apply deconvolution methods to try peak separation, or simply consider which elements make "most sense" given the known context of the sample.
Because the wavelength-dispersive (WDS) method is more precise and capable of detecting lower elemental abundances, EDS is less commonly used for actual chemical analysis although improvements in detector resolution make EDS a reliable and precise alternative.
EDS cannot detect the lightest elements, typically below the atomic number of Na for detectors equipped with a Be window. Polymer-based thin windows allow for detection of light elements, depending on the instrument and operating conditions.



Results





A typical EDS spectrum is portrayed as a plot of x-ray counts vs. energy (in keV). Energy peaks correspond to the various elements in the sample. Generally they are narrow and readily resolved, but many elements yield multiple peaks. For example, iron commonly shows strong K? and K? peaks. Elements in low abundance will generate x-ray peaks that may not be resolvable from the background radiation.



staff & Contact





Dr.Nawfal Hussein Aldujaili
Haider Lateef Farhan

  Email: [email protected]
   Tel.: 07812450415



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Faculty of Science

Faculty of Science © IT Division 2016

University of
K U F A

Faculty of Science
     Phone: 00964(0)726009011
       Email: [email protected]