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September 29, 2003
Volume 81, Number 39
CENEAR 81 39 p. 37
ISSN 0009-2347


Pioneering studies of molecule-thick films led to inventions and new areas of research


Long before surface-analysis equipment was sold commercially--indeed, before most chemists had ever heard of surface science--investigators at General Electric's Research Laboratory in Schenectady, N.Y., were studying the properties of films just one molecule thick. These surface studies, conducted in the early 1900s, mushroomed into a new scientific discipline and led to laboratory techniques that are still used today.

Irving Langmuir's investigations of electron emission from metals and chemical reactions at low pressures led him to study the process of gas adsorption on solids. The GE scientist probed the chemical nature of forces acting between gases and solid surfaces, the effects of pressure and temperature on adsorption, and other surface phenomena. Many of the observations and conclusions Langmuir drew from his pioneering surface studies were published 85 years ago in the Journal of the American Chemical Society [40, 1361 (1918)]. Langmuir's paper, "The Adsorption of Gases on Plane Surfaces of Glass, Mica, and Platinum" has come to be one of the all-time most highly cited JACS papers.

CAUGHT ON FILM Blodgett poses at the General Electric Research Laboratory in 1928.

"A measure of Langmuir's genius is his design of the 1918 experiments leading to the Langmuir isotherm," comments John T. Yates Jr., a professor of chemistry and physics at the University of Pittsburgh. "Langmuir isotherm" refers to a plot (or the mathematical relationship describing a plot) of the volume of gas adsorbed on a solid as a function of pressure at constant temperature.

Langmuir reasoned that surface roughness and the existence of more than one type of elementary binding site would affect the outcome of adsorption measurements. So he took precautions to minimize these variations, using smooth, and in some cases, crystalline materials in his experiments. For example, in the section of the 1918 JACS paper describing adsorption measurements on mica (naturally available as large single-crystal sheets), Langmuir noted that he used "high-grade muscovite ... rejecting all pieces which showed any fissures." The GE researcher was far ahead of his time, Yates asserts. "Langmuir recognized the need for site homogeneity five decades before surface science adsorption experiments on single-crystal wafers became fashionable."

SCRATCHING THE SURFACE Langmuir is seen here holding a vacuum tube used to amplify electrical current in a photo taken 75 years ago.
Langmuir's interest in adsorption processes played a role in his development of gas-filled incandescent lamps and other inventions, such as high-vacuum radio tubes and other types of electron tubes used for current amplification. He was awarded the 1932 Nobel Prize in Chemistry "for his discoveries and investigations in surface chemistry."

THIN FILMS OF OILS on the surface of water were another area of interest to Langmuir and his longtime GE colleague, Katharine B. Blodgett. Langmuir proposed that these types of films, similar to gases on solids, tend to be a single molecule thick, ordered, and oriented in specific ways. He published a number of research papers discussing properties of such films and related topics. But it was a paper published by Blodgett in which she described a method for transferring the films from the surface of water to the surface of a solid that helped glue together the names of the two scientists [J. Am. Chem. Soc., 57, 1007 (1935)]. Like Langmuir's 1918 paper, Blodgett's 1935 paper became one of the all-time most highly cited JACS papers.

"It certainly is a landmark paper," remarks Peidong Yang, an assistant professor of chemistry at the University of California, Berkeley. "Blodgett's technique built a foundation for several decades' worth of research on ordered organic thin films." The method for preparing so-called Langmuir-Blodgett films, in which the molecules of the film are ordered through compression and transferred to a solid via a simple dipping procedure, is still widely used today. Amazingly, the technique has remained essentially unchanged since it was reported nearly 70 years ago.

But new applications continue to come to light. Blodgett used the method to build up multilayer antireflective coatings on glass and a color gauge to measure thin-film thickness. The technique has also been used to study fluorescence in dye molecules and to prepare ordered films of nanoclusters and, very recently, nanowires.

Langmuir died in 1957 at the age of 76. Blodgett, who was 17 years younger than Langmuir, died in 1979.

C&EN is celebrating the 125th volume of the Journal of the American Chemical Society by highlighting selected papers from the list of its 125 most highly cited publications. Langmuir's paper ranks 42nd on the list; Blodgett's ranks 70th.

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