LeRoy Apker

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Reference excerpt

LeRoy W. Apker (June 11, 1915 – July 5, 1970) was an American experimental physicist. Along with his colleagues E. A. Taft and Jean Dickey, he studied the photoelectric emission of electrons from semiconductors and discovered the phenomenon of exciton-induced photoemission in potassium iodide. In 1955, he received the Oliver E. Buckley Condensed Matter Prize of the American Physical Society for his work.

Biography Born in Rochester, New York on June 11, 1915, Apker attended the University of Rochester, receiving a Bachelor of Arts degree in 1937. He then commenced graduate studies there under Lee Alvin DuBridge, along with fellow graduate students Ernest Courant, Esther M. Conwell, Robert H. Dicke, and others. He received his Ph.D. in physics in 1941. Also in 1941, he began working for the General Electric Research Laboratory in Schenectady, New York. On July 5, 1970, he was found by his wife, suffering from a gunshot wound to the head on the driveway of his home. He was taken to a hospital in Schenectady, where he later died.

Research

Photoelectric effect in semiconductors While at General Electric, he began to research the photoelectric effect, which causes matter to emit electrons when exposed to some types of electromagnetic radiation. In 1916 Robert Andrews Millikan, while verifying the photoelectric equations of Albert Einstein, had proposed the idea that photoelectrons emitted from semiconductors should behave in a different way than those emitted from other types of matter, and a very similar theory was advanced by Edward Condon in 1938. In 1948 Apker, working with E. A. Taft and J. E. Dickey, he completed experiments that confirmed Condon's theory. The main discovery made was that photoelectrons from some semiconductors moved much slower than photoelectrons from metals with the same work function, an unexpected result which was used to increase understanding of the electronic structure of semiconductors.

Flash filament method Apker was also active in the field of vacuum science. In 1948 he developed the flash filament method for measuring very low pressures, which was the first widely used method for measuring pressures less than 10 − 8 {\displaystyle 10^{-}8} Torr. In this method, a gas is allowed to adsorb onto a clean tungsten filament for a set amount of time, and the filament is then rapidly heated. The gas adsorbed onto the filament is released, and the resulting pressure burst can be measured. Though very time-consuming, the flash filament method was later used for thermal desorption spectroscopy.

Potassium iodide Apker followed up his work on the photoelectric effect with an investigation of the photoelectric properties of the alkali halides, particularly potassium iodide. In potassium iodide, an ionic crystal, some iodide ions can be removed and their vacant places will be filled by electrons. Called "F-Centers," these defects absorb visible and ultraviolet light, coloring the crystals at photon energies where they are usually transparent. Additionally, the absorption of visible radiation can free trapped electrons inside the crystal and produce photoconductivity. Apker found that in addition to visible radiation, near-ultraviolet radiation also produces photoconductivity. Deeper into the ultraviolet spectrum, however, potassium iodide has a strong absorption line due to the formation of chargeless particles called excitons. These excitons transfer energy to the electrons in the F-Centers with remarkably high efficiency, and these excited electrons are excited from the crystals in exciton-induced photoemission. Apker observed the same sort of behavior in other crystals such as barium oxide.

Legacy In 1978, Apker's wife and colleague Jean Dickey Apker established the LeRoy Apker Award of the American Physical Society in memory of Apker. The award is presented to two college undergraduates each year.

Bibliography Apker, L.; Taft, E.; Dickey, J. (1948). "Photoelectric Emission and Contact Potentials of Semiconductors". Physical Review. 74 (10): 1462. Bibcode:1948PhRv...74.1462A. doi:10.1103/PhysRev.74.1462. Apker, L. (1948). "Surface Phenomena Useful in Vacuum Technique". Industrial and Engineering Chemistry. 40 (5): 846–847. doi:10.1021/ie50461a016. Apker, L.; Taft, E. (1950). "Photoelectric Emission from F-Centers in KI". Physical Review. 79 (6): 964. Bibcode:1950PhRv...79..964A. doi:10.1103/PhysRev.79.964. Apker, L.; Taft, E. (1951). "Exciton-Enhanced Photoelectric Emission from F-Centers in RbI near 85K". Physical Review. 81 (5): 698–701. Bibcode:1951PhRv...81..698A. doi:10.1103/PhysRev.81.698. Apker, L.; Taft, E.; Dickey, J. (1953). "Electron Scattering and the Photoemission from Cesium Antimonide". Journal of the Optical Society of America. 43 (2): 78–80. doi:10.1364/JOSA.43.000078.

References

Worked examples

Example 1 — a first encounter with LeRoy Apker

Start with the simplest possible case. Write down what LeRoy Apker claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to LeRoy Apker before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about LeRoy Apker ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of LeRoy Apker

In research: LeRoy Apker appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses LeRoy Apker in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: LeRoy Apker is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1915 births, 1970 deaths, 1970 suicides, so understanding it makes those chapters shorter.
In everyday life: Look for LeRoy Apker outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study LeRoy Apker in 20 minutes

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Frequently asked questions

What is LeRoy Apker in simple terms?

LeRoy W. Apker (June 11, 1915 – July 5, 1970) was an American experimental physicist.

Why does LeRoy Apker matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study LeRoy Apker?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

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It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on LeRoy Apker.