William Gardner Pfann
Encyclopedia
William Gardner Pfann was an inventor and materials scientist with Bell Labs
Bell Labs
Bell Laboratories is the research and development subsidiary of the French-owned Alcatel-Lucent and previously of the American Telephone & Telegraph Company , half-owned through its Western Electric manufacturing subsidiary.Bell Laboratories operates its...

. Pfann is known for his development of zone melting
Zone melting
Zone melting is a group of similar methods of purifying crystals, in which a narrow region of a crystal is molten, and this molten zone is moved along the crystal...

 which is essential to the semiconductor industry
Semiconductor industry
The semiconductor industry is the aggregate collection of companies engaged in the design and fabrication of semiconductor devices. It formed around 1960, once the fabrication of semiconductors became a viable business...

. As stated in an official history of Bell Labs, "Timely invention of zone refining by W.G.Pfann ... was a major contribution that helped bring the impurities in germanium and silicon under control."

Early life

Pfann was born October 27, 1917 in Brooklyn
Brooklyn
Brooklyn is the most populous of New York City's five boroughs, with nearly 2.6 million residents, and the second-largest in area. Since 1896, Brooklyn has had the same boundaries as Kings County, which is now the most populous county in New York State and the second-most densely populated...

, New York City
New York City
New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...

. Showing unusual facility with materials, in 1935, when he was only eighteen years of age, he started with the Chemical Research Department of Bell Labs. He had no college degree at that time, but attending night school at Cooper Union
Cooper Union
The Cooper Union for the Advancement of Science and Art, commonly referred to simply as Cooper Union, is a privately funded college in the East Village neighborhood of Manhattan, New York City, United States, located at Cooper Square and Astor Place...

 led to a bachelor's degree in chemical engineering
Chemical engineering
Chemical engineering is the branch of engineering that deals with physical science , and life sciences with mathematics and economics, to the process of converting raw materials or chemicals into more useful or valuable forms...

 in 1940.

Pfann was involved in William Shockley
William Shockley
William Bradford Shockley Jr. was an American physicist and inventor. Along with John Bardeen and Walter Houser Brattain, Shockley co-invented the transistor, for which all three were awarded the 1956 Nobel Prize in Physics.Shockley's attempts to commercialize a new transistor design in the 1950s...

's efforts with Bell Labs to use semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...

s to make devices to replace vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...

s. The early efforts used germanium
Germanium
Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. The isolated element is a semiconductor, with an appearance most similar to elemental silicon....

. They made high back-voltage germanium rectifiers in 1945.
Pfann devised one of the first point-contact transistor
Point-contact transistor
A point-contact transistor was the first type of solid-state electronic transistor ever constructed. It was made by researchers John Bardeen and Walter Houser Brattain at Bell Laboratories in December 1947. They worked in a group led by physicist William Bradford Shockley...

s: "Specifically, W.G. Pfann had modified the Western Electric 1N26 shielded point-contact (silicon) diode to include two spring-loaded cat whisker point contacts, making a three-electrode configuration with good electrical amplifying properties. This configuration became known at the Type A transistor."
He and Walter Brattain developed the process of "forming" these transistors to make them more uniform. Pfann also invented a method of bonding fine gold wires to germanium that made the device functional.

"The quiet, unassuming man grew steadily in everyone's esteem as he made one valuable contribution after another to the semiconductor research effort.".

Breakthrough

The zone melting process that Pfann is known for revolutionized engineering possibilities: "The purity that can be attained by zone refining was absolutely unprecedented in the history of materials processing. Impurity levels of a few parts per million had previously been considered excellent; Pfann's technique improved on this by factors of over 1,000.".

In 1952 Pfann published the revelatory article "Principles of Zone-Melting" in the Transactions of the American Institute of Mining, Metallurgical, and Petroleum Engineers
American Institute of Mining, Metallurgical, and Petroleum Engineers
The American Institute of Mining, Metallurgical, and Petroleum Engineers is a professional body for mining and metallurgy, with 90,000 members. It was founded in 1871 by 22 mining engineers in Wilkes-Barre, Pennsylvania, United States, being one of the first national engineering societies in the...

. This article applied zone melting in two industrial processes: purification of a solvent material (called zone refining), and production of a uniform distribution of a solute in an ingot (called zone leveling). Three appendices described mathematical model
Mathematical model
A mathematical model is a description of a system using mathematical concepts and language. The process of developing a mathematical model is termed mathematical modeling. Mathematical models are used not only in the natural sciences and engineering disciplines A mathematical model is a...

s of the processes in zone melting.

In 1958 Pfann published the first edition of his text Zone Melting with John Wiley
John Wiley & Sons
John Wiley & Sons, Inc., also referred to as Wiley, is a global publishing company that specializes in academic publishing and markets its products to professionals and consumers, students and instructors in higher education, and researchers and practitioners in scientific, technical, medical, and...

. A second edition appeared in 1966, and in 1978 publisher Robert E. Krieger of Huntington, New York issued the third edition.

In 1962 the journal Science
Science (journal)
Science is the academic journal of the American Association for the Advancement of Science and is one of the world's top scientific journals....

 published a short digest of the zone melting method by Pfann. This article concludes by treating the slightly larger topic of temperature gradient zone melting. Pfann describes how and why a drop of gold on a germanium slab moves toward the hottest spot. He says this method was used to "make complex p-n junction shapes for special transistors". He observes the motion of brine on sea ice and proposes the purification of sea water. Further he notes the relation to the physics of geological formations.

Later years

Pfann was elected to the National Academy of Sciences
United States National Academy of Sciences
The National Academy of Sciences is a corporation in the United States whose members serve pro bono as "advisers to the nation on science, engineering, and medicine." As a national academy, new members of the organization are elected annually by current members, based on their distinguished and...

 (U.S.) in 1975. In 1976 the American Institute of Physics
American Institute of Physics
The American Institute of Physics promotes science, the profession of physics, publishes physics journals, and produces publications for scientific and engineering societies. The AIP is made up of various member societies...

 awarded him the James C. McGroddy Prize for New Materials.

William G. Pfann died October 22, 1982. On his passing some coworkers wrote
His energy, his high standards of honesty in experimentation and his unprejudiced approach to the new, the untried, and even the heretical, helped define the word scientist for a large number of his acquaintances.

Riordan & Hoddeson

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