Scanning Electron Microscopy Magnified Light Imaging

Microscopy is any method of producing visible images of details or structures too small to be seen by the human eye, by utilizing a microscope or some other type of magnification tool or instrument. SEM magnified light imaging involves passing light reflected from or through the object to be viewed through a series of lenses, which can imaged on a photographic plate, seen directly by the human eye, or captured digitally (in a computer or other storage device). Since resolution is dependent on the wavelength of light, electron microscopy was developed over 70 years ago that uses electron beams instead of a traditional light source. Electron microscope resolution is far higher because of the much lower wavelength. Typically, microscopy image analysis involves the refraction, reflection, or deflection of radiation incident upon the studied object. In several types of microscopy, the studied object is imaged by scanning the subject line by line, utilizing a very fine physical probe (also known as a scanning probe microscope). Examples of scanning probe microscopes include the photonic force microscope, the scanning tunneling microscope and the atomic force microscope.

Scanning Electron Microscopy

Scanning Electron Microscopy (SEM) technology is an invaluable tool for resolving failure analysis problems or characterizing products. Micro-crack location, contamination identification, and electrostatic discharge damage are just a few of the uses of SEM when performing failure analysis. Other applications include the evaluation of materials (mechanical damage, elemental analysis, etc.) and quality control evaluations including weld cross-sections, plating/coating thickness, and dimension verification. In addition, the Scanning Electron Microscope rasters a beam of focused electrons across a small region of a specimen (sample). This focused electron beam produces numerous useful transitions dependent upon the specimen (sample) material and the electron beam energy. Additionally, secondary electrons are a form of low energy electrons which are the primary transition utilized in SEM analysis. Secondary electrons are also useful for the topographic imaging of a specimen’s (sample’s) surface. All imaging is performed on digital medium.

Transmitted Light

Transmitted light microscopy is the term generally used for any kind of microscopy where light is transmitted from a place on the opposite side of the sample (specimen) from the objective. Usually, light passes through a condenser that is focused on the sample (specimen) to achieve very high illumination. After light passes through the sample (specimen), the image of the sample (specimen) goes through the objective lens and then to the opticals where the enlarged image can be viewed.

Bright Field

Using a conventional bright field microscope, the light delivered from an incandescent source is directed toward a lens beneath the stage called the condenser, through the sample (specimen), then through an objective lens, and finally to the human eye through a second magnifying lens, the eyepiece or ocular. Most microscopes include a built-in illuminator. The condenser focuses light on the sample (specimen) through an aperture in the stage. Once it has passed through the sample (specimen), light is displayed to the human eye with an apparent image that is much larger than the area that was illuminated. The image magnification is simply the magnification of the objective lens (which is usually stamped on the body of the lens) multiplied by the ocular magnification.

Dark Field Transmission and Reflected

In order to view a sample (specimen) in a dark field, an opaque disc is placed below the condenser lens allowing only light that has been scattered by objects on the slide to reach the eye. Instead of coming up through the sample (specimen), light is reflected by particles located on the slide. Everything is viewable/visible regardless of color, in this case usually bright white against a dark background. Pigmented objects are frequently viewed in “false colors” – in other words, the reflected light is of a different color than the color of the object. Higher resolution can be acquired by using dark field as opposed to bright field viewing.

Phase Contrast

Light from most subjects is passed through to the center of the lens in addition to the periphery. However, if light from an object to the edges of the objective lens is restricted by half a wavelength and the light to the center is not restricted whatsoever, then the light rays are out of phase by half a wavelength. The out of phase light rays cancel each other when the objective lens brings the image into focus. In addition, a reduction in brightness of the subject can be observed. The degree of reduction in brightness is dependent on the refractive index of the subject.

Dispersion Staining

Materials can be identified and detected by an optical microscope procedure known as dispersion staining (this requires a special aperture). This routine can be handled by most phase contrast equipped microscopes.

Video Microscopy

Digital/video microscopes use digital technology to magnify the images of objects being viewed. These microscopes have built-in cameras as well as a series of high-powered lenses that deliver good image quality and resolution. There are some digital/video microscopes that require users to view subjects through a standard eyepiece, while others provide a computer interface that displays images on a computer monitor. Processing software that performs image analysis allows adjustments to resolution and linear dimensions. The ratio of the image size to the actual object, also known as total magnification, is usually determined by linear measurement.

Other Microscopy Services provided by Polyhedron Laboratories include:

  • SEM-Energy Dispersive Spectrometry
  • Light Element Detector
  • FT-IR Microscopy
  • Reflected Light
  • Normarski Differential Interference Contrast
  • Polarized
  • Micro Photography
  • 35 mm with low light level automatic exposure
  • 4' x 5" Polaroid
  • Microtomy and Ultramicrotomy
  • Vacuum Shadow Casting
  • Polaroid Film - 35 mm Film & Development
  • Scanning Electron Microscopy
  • FT-IR Microscopy
  • Transmitted Light
  • Bright Field
  • Dark Field Transmission and Reflected
  • Phase Contrast
  • Dispersion Staining
  • Video Microscopy

Contact Polyhedron Laboratories about Electron Microscopy Services.