|INSTNM||Arkansas State University-Beebe|
|ADDR||1000 Iowa Street|
|F1SYSNAM||Arkansas State University System|
brownlindsay on 2018-03-31:
When you see something with your eyes, you see the light that is reflected from it (or emitted from it, in the case of something like a light bulb). But the resolution is somewhat limited by the wavelength of the light we can see with our human eyes; it is difficult to resolve features that are finer than the light’s wavelength. With an electron microscope we can resolve finer features, because an electron has an effective wavelength that is quite small. But since our eyes don’t detect electrons well, we use a machine to turn the electron signal into light that we can see. Instead of reflecting light off a sample, we aim a finely focused beam of electrons at it. We then use a detector to determine the electrons that go through the sample (in the case of a Transmission Electron Microscope, or TEM) or the electrons that come off the sample (in the case of a Scanning Electron Microscope, or SEM). With a SEM or a Scanning TEM (STEM) the beam is scanned back and forth, up and down to rapidly cover the entire sample. If we then send the sensor output to a display screen that is being scanned at the same rate, we “see” what is happening on the very tiny area that the beam is scanning. When the sensor is receiving a strong signal, the display scan shows a bright spot; when the sensor is bath bombs order online a weak signal, the display shows a dim spot. Keep in mind that since we want very high magnification, the area that is being scanned is very, very tiny. Much smaller than the screen we will view it on. This effectively magnifies the image. Since the display is always the same size, if we focus the SEM or STEM beam onto a smaller area, the effective magnification goes up. The smaller the area we can scan the beam across, the greater the magnification.