[[University of California,Los Angeles]] ([[M. S.|MS]])
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Thomas Eugene Everhart | |
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![]() Everhart in 1987 | |
5thPresident of the California Institute of Technology | |
In office 1987–1997 | |
Preceded by | Marvin Goldberger |
Succeeded by | David Baltimore |
4thChancellor of the University of Illinois at Urbana-Champaign | |
In office 1984–1987 | |
Preceded by | John E. Cribbet |
Succeeded by | Morton W. Weir |
Personal details | |
Born | Kansas City,Missouri,U.S. | February 15,1932
Education | Harvard University (BA) University of California,Los Angeles (MS) Clare College,Cambridge (PhD) |
Awards | IEEE Centennial Medal (1984) Clark Kerr Award (1992) ASEE Centennial Medallion (1993) IEEE Founders Medal (2002) Okawa Prize (2002) |
Scientific career | |
Fields | Electrical Engineering,Applied Physics |
Institutions | University of California,Berkeley,Cornell University,University of Illinois at Urbana-Champaign,California Institute of Technology,University of Cambridge |
Thesis | Contrast formation in the scanning electron microscope (1958) |
Doctoral advisor | Charles Oatley |
Thomas Eugene Everhart FREng (born February 15,1932,Kansas City,Missouri) [1] is an American educator and physicist. His area of expertise is the physics of electron beams. Together with Richard F. M. Thornley he designed the Everhart–Thornley detector. These detectors are still in use in scanning electron microscopes,even though the first such detector was made available as early as 1956.
Everhart was elected a member of the National Academy of Engineering in 1978 for contributions to the electron optics of the scanning electron microscope and to its use in electronics and biology. He was appointed an International Fellow of the Royal Academy of Engineering in 1990. [2] He served as chancellor of the University of Illinois at Urbana-Champaign from 1984 to 1987 and as the president of the California Institute of Technology from 1987 to 1997.
Everhart's parents were William E. Everhart and Elizabeth A. West. Everhart received his A.B. in physics from Harvard University in 1953,and his M.S. in applied physics from the University of California,Los Angeles,in 1955. He held a Marshall Scholarship at Clare College,Cambridge,where he completed a PhD in Physics under Professor Charles Oatley in 1958. [1]
Everhart began working on electron detection and the design of scanning electron microscopes (SEMs) as a student with Charles Oatley at Cambridge in 1955. [3] An initial prototype,the SEM1,had been developed by Dennis McMullen,who published his dissertation Investigations relating to the design of electron microscopes in 1952. [3] [4] It was further modified by Ken C. A. Smith,who developed a way to efficiently detect low-energy secondary electrons. [5] Oatley and his students used SEM to develop a variety of new techniques for studying surface topography. [3] [6]
Everhart developed techniques to detect low-energy secondaries. His Ph.D. thesis,in 1958,was Contrast formation in the scanning electron microscope. [6] Analyzing the electrons detected by the SEM,he reported that about 67% of the signal measured could be attributed to low energy secondaries from the specimen. [7] About 3% was due to higher-energy reflected electrons. [5] He also presented equations to model the noise introduced. [3] [7]
Use of the term "voltage contrast" to describe the relationship between the voltage applied to a specimen and the resulting image contrast,is attributed to Everhart. [8] [9] As of 1959,Everhart produced the first voltage-contrast images of p-n junctions of biased silicon diodes. [10] Voltage contrast,the ability to detect variations in surface electrical potentials on a specimen,is now one of several imaging modes used for the characterization,diagnosis and failure analysis of semiconductors. As many as half of the SEMs sold are believed to be used in semiconductor applications. [11]
Everhart studied contrast mechanisms in detail and developed a new theory of reflection of electrons from solids. [12] He also made some of the first quantitative studies of the effects of beam penetration on image formation in the SEM.
In 1960 Everhart and Richard F. M. Thornley published a description for the improved design of a secondary electron detector,since known as the Everhart–Thornley detector. Everhart and Thornley increased the efficiency of existing detectors by adding a light pipe to carry the photon signal from the scintillator inside the evacuated specimen chamber of the scanning electron microscopes to the photomultiplier outside the chamber. [13] This strengthened the signal collected and improved the signal-to-noise ratio. In 1963,Pease and Nixon incorporated the Everhart-Thornley detector into their prototype for the first commercial SEM,later developed as the Cambridge Scientific Instruments Mark I Stereoscan. This type of secondary electron and back-scattered electron detector is still used in modern scanning electron microscopes (SEMs). [14]
By using various types of detectors with SEM,it becomes possible to map the topography,crystallography and composition of specimens being examined. [4] In the 1960s,Wells,Everhart,and Matta built an advanced SEM for semiconductor studies and microfabrication at Westinghouse Laboratories in Pittsburgh. They were able to combine signals so to more effectively examine multiple layers in active devices,an early example of EBIC imaging. [15] [16]
From 1958-1978 Everhart was a professor and latterly department chairman of engineering and computer science,at the University of California at Berkeley. [1] There he supported the construction of the first scanning electron microscope in a U.S. university. [17]
In January 1979,he became Joseph Silbert Dean of the college of engineering at Cornell University,Ithaca,New York. [18]
Everhart served as chancellor of the University of Illinois at Urbana-Champaign from 1984 to 1987. As chancellor,Everhart was involved in proposals for and development of the Beckman Institute for Advanced Science and Technology,an interdisciplinary research institute substantially funded by an appeal to Arnold Orville Beckman. [19] : 9–14 In a formal invitation to proposed members of the Administrative Committee for the Beckman Institute,Everhart wrote that creation of the Beckman Institute was "an exceptional opportunity,perhaps the most dramatic and exciting one that we will see in our working lifetimes." [19] : 97
Everhart was president of the California Institute of Technology from 1987 to 1997. [20] As Caltech's president,Everhart authorized the Laser Interferometer Gravitational-Wave Observatory (LIGO) project,a large-scale experiment that seeks to detect gravitational waves and use them for fundamental research in physics and astronomy. [21]
While at Caltech,Everhart was involved in substantial expansion of the university,heading a $350-million fund-raising drive. In 1989,he helped dedicate the Beckman Institute at Caltech,a research center for biology,chemistry,and related sciences. [22] It was the second of five research centers supported by Arnold Orville Beckman and his wife Mabel. Everhart also was involved in the development of the W. M. Keck Observatory in Hawaii,supported by the W. M. Keck Foundation; [23] the Gordon and Betty Moore Laboratory of Engineering,supported by Gordon Moore of Intel; [24] and the Fairchild Engineering Library,supported by the Sherman Fairchild Foundation. [20] [25]
Everhart promoted efforts to hire more female faculty and increase the enrollment of women. In his final year at Caltech the number of women in the freshmen class was double that of the year he joined Caltech. [20]
Since 1998,Everhart has served as a trustee of the California Institute of Technology. [26] He sits on the boards of directors of Raytheon and the Kavli Foundation,among others. [18]
In 1999,Everhart was elected to a six-year terms as Overseer of Harvard University. In 2001 he became a member of the Overseers executive committee. He was one of three overseers who participated in the university's presidential search committee in 2000-01. In 2004,he was elected president of Harvard's Board of Overseers for 2004-05. [27]
Everhart has been elected to a number of scientific societies,including the following: [1]
Everhart has received a number of awards,including the following: [1]
An electron microscope is a microscope that uses a beam of electrons as a source of illumination. They use electron optics that are analogous to the glass lenses of an optical light microscope to control the electron beam,for instance focusing them to produce magnified images or electron diffraction patterns. As the wavelength of an electron can be up to 100,000 times smaller than that of visible light,electron microscopes have a much higher resolution of about 0.1 nm,which compares to about 200 nm for light microscopes. Electron microscope may refer to:
Microscopy is the technical field of using microscopes to view objects and areas of objects that cannot be seen with the naked eye. There are three well-known branches of microscopy:optical,electron,and scanning probe microscopy,along with the emerging field of X-ray microscopy.
A microscope is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisible to the eye unless aided by a microscope.
A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample,producing various signals that contain information about the surface topography and composition of the sample. The electron beam is scanned in a raster scan pattern,and the position of the beam is combined with the intensity of the detected signal to produce an image. In the most common SEM mode,secondary electrons emitted by atoms excited by the electron beam are detected using a secondary electron detector. The number of secondary electrons that can be detected,and thus the signal intensity,depends,among other things,on specimen topography. Some SEMs can achieve resolutions better than 1 nanometer.
Cathodoluminescence is an optical and electromagnetic phenomenon in which electrons impacting on a luminescent material such as a phosphor,cause the emission of photons which may have wavelengths in the visible spectrum. A familiar example is the generation of light by an electron beam scanning the phosphor-coated inner surface of the screen of a television that uses a cathode ray tube. Cathodoluminescence is the inverse of the photoelectric effect,in which electron emission is induced by irradiation with photons.
Transmission electron microscopy (TEM) is a microscopy technique in which a beam of electrons is transmitted through a specimen to form an image. The specimen is most often an ultrathin section less than 100 nm thick or a suspension on a grid. An image is formed from the interaction of the electrons with the sample as the beam is transmitted through the specimen. The image is then magnified and focused onto an imaging device,such as a fluorescent screen,a layer of photographic film,or a detector such as a scintillator attached to a charge-coupled device or a direct electron detector.
Energy-dispersive X-ray spectroscopy,sometimes called energy dispersive X-ray analysis or energy dispersive X-ray microanalysis (EDXMA),is an analytical technique used for the elemental analysis or chemical characterization of a sample. It relies on an interaction of some source of X-ray excitation and a sample. Its characterization capabilities are due in large part to the fundamental principle that each element has a unique atomic structure allowing a unique set of peaks on its electromagnetic emission spectrum. The peak positions are predicted by the Moseley's law with accuracy much better than experimental resolution of a typical EDX instrument.
An electron microprobe (EMP),also known as an electron probe microanalyzer (EPMA) or electron micro probe analyzer (EMPA),is an analytical tool used to non-destructively determine the chemical composition of small volumes of solid materials. It works similarly to a scanning electron microscope:the sample is bombarded with an electron beam,emitting x-rays at wavelengths characteristic to the elements being analyzed. This enables the abundances of elements present within small sample volumes to be determined,when a conventional accelerating voltage of 15-20 kV is used. The concentrations of elements from lithium to plutonium may be measured at levels as low as 100 parts per million (ppm),material dependent,although with care,levels below 10 ppm are possible. The ability to quantify lithium by EPMA became a reality in 2008.
Alec Nigel Broers,Baron Broers,is a British electrical engineer.
A scanning transmission electron microscope (STEM) is a type of transmission electron microscope (TEM). Pronunciation is [stɛm] or [ɛsti:i:ɛm]. As with a conventional transmission electron microscope (CTEM),images are formed by electrons passing through a sufficiently thin specimen. However,unlike CTEM,in STEM the electron beam is focused to a fine spot which is then scanned over the sample in a raster illumination system constructed so that the sample is illuminated at each point with the beam parallel to the optical axis. The rastering of the beam across the sample makes STEM suitable for analytical techniques such as Z-contrast annular dark-field imaging,and spectroscopic mapping by energy dispersive X-ray (EDX) spectroscopy,or electron energy loss spectroscopy (EELS). These signals can be obtained simultaneously,allowing direct correlation of images and spectroscopic data.
Focused ion beam,also known as FIB,is a technique used particularly in the semiconductor industry,materials science and increasingly in the biological field for site-specific analysis,deposition,and ablation of materials. A FIB setup is a scientific instrument that resembles a scanning electron microscope (SEM). However,while the SEM uses a focused beam of electrons to image the sample in the chamber,a FIB setup uses a focused beam of ions instead. FIB can also be incorporated in a system with both electron and ion beam columns,allowing the same feature to be investigated using either of the beams. FIB should not be confused with using a beam of focused ions for direct write lithography. These are generally quite different systems where the material is modified by other mechanisms.
The Everhart–Thornley detector is a secondary electron and back-scattered electron detector used in scanning electron microscopes (SEMs). It is named after its designers,Thomas E. Everhart and Richard F. M. Thornley,who in 1960 published their design to increase the efficiency of existing secondary electron detectors by adding a light pipe to carry the photon signal from the scintillator inside the evacuated specimen chamber of the SEM to the photomultiplier outside the chamber. Prior to this Everhart had improved a design for a secondary electron detection by Vladimir Zworykin and Jan A. Rajchman by changing the electron multiplier to a photomultiplier. The Everhart–Thornley Detector with its lightguide and highly efficient photomultiplier is the most frequently used detector in SEMs.
Secondary electrons are electrons generated as ionization products. They are called 'secondary' because they are generated by other radiation. This radiation can be in the form of ions,electrons,or photons with sufficiently high energy,i.e. exceeding the ionization potential. Photoelectrons can be considered an example of secondary electrons where the primary radiation are photons;in some discussions photoelectrons with higher energy (>50 eV) are still considered "primary" while the electrons freed by the photoelectrons are "secondary".
A scanning helium ion microscope is an imaging technology based on a scanning helium ion beam. Similar to other focused ion beam techniques,it allows to combine milling and cutting of samples with their observation at sub-nanometer resolution.
Sir Charles William Oatley OBE,FRS FREng was Professor of Electrical Engineering,University of Cambridge,1960–1971,and developer of one of the first commercial scanning electron microscopes. He was also a founder member of the Royal Academy of Engineering.
Electron-beam-induced current (EBIC) is a semiconductor analysis technique performed in a scanning electron microscope (SEM) or scanning transmission electron microscope (STEM). It is most commonly used to identify buried junctions or defects in semiconductors,or to examine minority carrier properties. EBIC is similar to cathodoluminescence in that it depends on the creation of electron–hole pairs in the semiconductor sample by the microscope's electron beam. This technique is used in semiconductor failure analysis and solid-state physics.
The environmental scanning electron microscope (ESEM) is a scanning electron microscope (SEM) that allows for the option of collecting electron micrographs of specimens that are wet,uncoated,or both by allowing for a gaseous environment in the specimen chamber. Although there were earlier successes at viewing wet specimens in internal chambers in modified SEMs,the ESEM with its specialized electron detectors and its differential pumping systems,to allow for the transfer of the electron beam from the high vacuum in the gun area to the high pressure attainable in its specimen chamber,make it a complete and unique instrument designed for the purpose of imaging specimens in their natural state. The instrument was designed originally by Gerasimos Danilatos while working at the University of New South Wales.
The gaseous detection device (GDD) is a method and apparatus for the detection of signals in the gaseous environment of an environmental scanning electron microscope (ESEM) and all scanned beam type of instruments that allow a minimum gas pressure for the detector to operate.
Electron channelling contrast imaging (ECCI) is a scanning electron microscope (SEM) diffraction technique used in the study of defects in materials. These can be dislocations or stacking faults that are close to the surface of the sample,low angle grain boundaries or atomic steps. Unlike the use of transmission electron microscopy (TEM) for the investigation of dislocations,the ECCI approach has been called a rapid and non-destructive characterisation technique
Ultrafast scanning electron microscopy (UFSEM) combines two microscopic modalities,Pump-probe microscopy and Scanning electron microscope,to gather temporal and spatial resolution phenomena. The technique uses ultrashort laser pulses for pump excitation of the material and the sample response will be detected by an Everhart-Thornley detector. Acquiring data depends mainly on formation of images by raster scan mode after pumping with short laser pulse at different delay times. The characterization of the output image will be done through the temporal resolution aspect. Thus,the idea is to exploit the shorter DeBroglie wavelength in respect to the photons which has great impact to increase the resolution about 1 nm. That technique is an up-to-date approach to study the dynamic of charge on material surfaces.