Electron Microscopy: The Basics
... the small (<1 mm) hole in the Whenelt Cap and then move down the column to be later used in imaging. A field emission gun consists of a sharply pointed tungsten tip held at several kilovolts negative potential relative to a nearby electrode, so that there is a very high potential gradient at the sur ...
... the small (<1 mm) hole in the Whenelt Cap and then move down the column to be later used in imaging. A field emission gun consists of a sharply pointed tungsten tip held at several kilovolts negative potential relative to a nearby electrode, so that there is a very high potential gradient at the sur ...
1 PHYS:1200 LECTURE 28 — ELECTRICITY AND MAGNETISM (6
... of the work of Oersted on the production of magnetic fields by currents. He surmised that if currents produced magnetic fields that magnetic fields might produce currents. Faraday set up a circuit to study whether a magnetic field could regulate the flow of a current in an adj ...
... of the work of Oersted on the production of magnetic fields by currents. He surmised that if currents produced magnetic fields that magnetic fields might produce currents. Faraday set up a circuit to study whether a magnetic field could regulate the flow of a current in an adj ...
UW- Madison Geology 777
... One common SEM resolution is defined as “point to point” resolution and is the smallest separation of adjacent particles that can be detected in an image. The manufacturers “cheat” by using optimal images, sputtered gold balls on carbon (image to right), where there is good secondary electron genera ...
... One common SEM resolution is defined as “point to point” resolution and is the smallest separation of adjacent particles that can be detected in an image. The manufacturers “cheat” by using optimal images, sputtered gold balls on carbon (image to right), where there is good secondary electron genera ...
Photomultiplier
Photomultiplier tubes (photomultipliers or PMTs for short), members of the class of vacuum tubes, and more specifically vacuum phototubes, are extremely sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum. These detectors multiply the current produced by incident light by as much as 100 million times (i.e., 160 dB), in multiple dynode stages, enabling (for example) individual photons to be detected when the incident flux of light is very low. Unlike most vacuum tubes, they are not obsolete.The combination of high gain, low noise, high frequency response or, equivalently, ultra-fast response, and large area of collection has maintained photomultipliers an essential place in nuclear and particle physics, astronomy, medical diagnostics including blood tests, medical imaging, motion picture film scanning (telecine), radar jamming, and high-end image scanners known as drum scanners. Elements of photomultiplier technology, when integrated differently, are the basis of night vision devices.Semiconductor devices, particularly avalanche photodiodes, are alternatives to photomultipliers; however, photomultipliers are uniquely well-suited for applications requiring low-noise, high-sensitivity detection of light that is imperfectly collimated.