Although both the SEM and TEM (Transmission Electron Microscope) utilise a focused beam of high- energy electrons to produce images, the method of image formation, and the final images are very different. Whereas the TEM produces an image by passing the electron beam through the specimen, the SEM provides an image of the specimen surface. Consequently specimen preparation is vey different but specimens for both SEM and TEM must be dry, able to withstand the high vacuum, and remain stable in the electron beam.
Electron microscope can be used for imaging, and with the addition of an X-ray detector, acquisiton of quantitative elemental analysis data is possible. With the rapid evolution of computer based digital image processing, a wide range of image analysis and enhancement techniques is available to the microscopist.
The CRT beam is not static. It sweeps back and forth across the face of the tube (exactly as in a TV set, which is what a display CRT actually is) and its sweep is synchronized with that of the electron beam in the column. When the column beam knocks off large numbers of secondary electrons from some point on the specimen, the CRT beam produces a bright spot on the viewing screen. Conversely, small numbers of electrons produce low CRT beam output, and a dark point on the viewing screen. Thus the SEM image is really an analog of what is going on inside the column; it's constructed, point-by-point and line-by-line, based on the information supplied to the CRT by the detector circuitry.
When a beam of electrons impinges on the sample, it knocks other electrons loose from the object itself. These secondary electrons scatter in directions determine by the angle of incidence of the beam and the surface topography of the sample.
The column : contains the specimen and the means of observing it.
The display output : produces the image in the form of a television type picture on a cathode ray tube (CRT)
The control console : contains circuitry to maintain stable lens currents, evacuate the specimen chamber, produce a beam of electrons, and so on.
Scanning electron microscopes produce images of specimen surfaces, so thickness is unimportant. The sample size is only limited by the size of the microscope specimen chamber. The sample need to be free from any water or volatile component and it must also be electrically conductive. However, new developments in SEM design are the LOW VACUUM and ENVIRONMENTAL SEM which maintain the specimen chamber at low vacuum, enabling hydrated, uncoated samples to be imaged.
Scanning electron microscopes produce images of specimen surfaces, so thickness is unimportant. The sample size is only limited by the size of the microscope specimen chamber. The sample need to be free from any water or volatile component and it must also be electrically conductive. However, new developments in SEM design are the LOW VACUUM and ENVIRONMENTAL SEM which maintain the specimen chamber at low vacuum, enabling hydrated, uncoated samples to be imaged.
Electron Microscopy has many varied applications in life sciences, earth sciences and in electrical and mechanical engineering, using both transmission and scanning electron microscope.
Gold Coater
The Sample Holder
Column Chamber
The Facility
Contact person:
Science officer:
Zurina binti Marzuki
Tel : 03-7967 4076
e-mail : zurinam@um.edu.my
SEM analysis session with Mr Shahril
The SEM image display
Parts of an SEM
Specimen Preparation
SCANNING ELECTRON MICROSCOPE – ENERGEY DISPERSIVE X-RAY
