2014 Nobel Prizes for Advances in LEDs and Microscopy

By Michael Lucibella

Physicists received this year’s Nobel Prizes for both physics and chemistry — the physics prize for the invention of efficient blue LEDs, and the chemistry prize for surpassing the resolution limit long believed to constrain optical microscopes. The physics prize went to Isamu Akasaki of Meijo University and Nagoya University, Hiroshi Amano of Nagoya University, and Shuji Nakamura of the University of California, Santa Barbara. In announcing the award, the Nobel Committee emphasized that the work done by the physics prize winners launched a revolution in energy-efficient lighting. The chemistry award went to Eric Betzig of the Howard Hughes Medical Institute, Stefan W. Hell of the Max Planck Institute for Biophysical Chemistry, and William E. Moerner of Stanford University for their contributions to the development of “super-resolved fluorescence microscopy.”

The Physics of Blue
“Thanks to the blue LED, we can now get white light sources [that] have very high efficiency and very long lifetimes,” said Staffan Normark, the permanent secretary of the Royal Swedish Academy of Sciences. “This LED technology is now replacing older technologies.”

Red and green LEDs have been around in more or less their present form since the 1960s, but blue LEDs proved much more difficult to fabricate. The difficulties lay in creating high quality gallium nitride crystals and then combining them with other elements to increase their efficiency. It took nearly thirty years of work in basic materials physics, crystal growth and device fabrication to create a marketable blue LED.

Akasaki started experimenting with growing pure gallium nitride crystals in 1974, first at the Matsushita Research Institute in Tokyo, then at Nagoya University. Amano joined Akasaki in the 1980s and helped develop ways to dope the gallium nitride crystals. Akasaki and Amano are members of the American Physical Society.

In 1992, while at the Nichia Corporation in Tokushima, Japan, Nakamura and his collaborators, who were also working on the problem, helped explain how electron irradiation eliminated some of the inefficiencies Akasaki’s team had been encountering.

Both research teams were then able to create the gallium nitride alloys needed to produce the junctions between the semiconductor layers that are the building blocks for blue LEDs. Nakamura and his team saw the first efficient blue glow in 1994, and over the following two years, both teams created the first blue lasers. In 1999, Nakamura left Nichia to join the faculty at the University of California, Santa Barbara.

“I am very honored to receive the Nobel Prize from the Royal Swedish Academy of Sciences for my invention of the blue LED,” Nakamura said in a press release put out by Soraa, the LED company he founded in 2008. “It is very satisfying to see that my dream of LED lighting has become a reality. I hope that energy-efficient LED light bulbs will help reduce energy use and lower the cost of lighting worldwide.”

Members of the Committee for Physics emphasized how the practical uses of the device were the deciding factors behind their choice for this year’s prize. “This is really an invention prize, it’s less a discovery prize,” said Anne L’Huillier, a physicist at the academy and member of the committee. “In this kind of prize we really emphasize the usefulness of the invention.”

The researchers’ work has already made it into many common electronic devices. Blue LEDs can be found in most touch-screen devices. White LEDs usually use a blue LED to excite a phosphor to emit white light, and can be found in the camera flashes of most modern smart phones.

“We emphasized very strongly the fact that it can be used for white lighting, but we’ve seen over the years how the invention of the blue light emitting diode was used in the blue laser diodes, used for optical storage, how coming generations of communications will rely on the use of light rather than radio waves, in li-fi rather than wi-fi, in how you can use this blue or UV light to sterilize water,” said Olle Inganäs, a physicist at the academy and member of the committee. “There are so many uses of this, and these uses are what I think would make Alfred Nobel very happy.

He added that increasing energy efficiency around the world is one of the most promising applications. “What you see is of course an enormous increase in power efficiency,” Inganäs said. “Something like a fourth of our electricity consumption in most industrialized economies goes towards illumination, so these effects, having much more light for much less electricity…[are] really going to have a big impact on our modern civilization.”

The three scientists’ work built on research begun in the late 1960s at RCA’s research labs in Princeton, New Jersey. There, a team led by Herbert Paul Maruska constructed the first dim but functional blue LED in 1972, using a slightly different technique than used to fabricate today’s blue LEDs. However, due to budget cuts, many of RCA’s labs were shut down before work on blue LEDs could be finished.

Seeing Small
“This year’s [chemistry] prize is about how the optical microscope became a nano-scope,” Normark said on the following day.

The award is for two similar but distinct techniques that overcome Abbe’s limit. First described in 1873, Abbe’s limit says a microscope can’t resolve objects smaller than approximately half the wavelength of the light used, or about 200 nanometers for visible light.  The best microscopes now using the Nobel-Prize-winning methods have a resolution below 10 nm.

Hell developed stimulated emission depletion microscopy in 2000, which uses two concentric lasers to scan a cell’s image. The finely focused central laser excites fluorescent molecules in the sample, while the broader outer laser quenches out all other fluorescence. The detector scans back and forth, registering the fluorescent glow to create an image with resolution better than 200 nanometers.

“Light microscopy is very important to the life sciences because the use of focused light is the only way that allows you to see living things; however, the resolution of light microscopy was fundamentally limited,” Hell said. “What we have found is that you can overcome this limit. You can see details at much much higher spatial resolution, and that of course discloses how the cell works at the nanometer scale, so that’s at the molecular scale.”

Though Betzig and Moerner never collaborated directly, their work was instrumental in laying the groundwork for stimulated emission depletion microscopy.

After Moerner was first able to detect a single fluorescent molecule in 1989, Betzig came up with the concept of using overlaid images of individual glowing molecules to create a complete image. The process he outlined in a 1995 paper described shining different wavelengths of light on a cell to get different molecules to fluoresce, and then to record where light spots appeared. This way, when all the images were combined, the discrete spots would resolve themselves into a coherent outline.

However, to make a coherent image, many different colors from unique molecules would be needed, far more than was practical. It wasn’t until 2005, when Betzig found a specific protein identified by Moerner that the technique could be put into use. Moerner’s protein would glow briefly, and then, most importantly, it turned itself off. A cell stained with this protein could be hit multiple times with a laser pulse and each time a different set of proteins would fluoresce, giving Betzig the constellation of glowing spots needed to create a coherent image.

Electron microscopes have long been able to image objects smaller than 200 nanometers, but that technique severely damages the sample. It can’t image living things, and electrons can penetrate only a shallow depth into cells. “It is fluorescence that makes the miracle possible,” said Mans Ehrenberg of Uppsala University.

“We can observe E. coli…in all the glory of super resolution without having to kill them, slice them.… and subject them to intense radiation and high vacuum,” said Sven Lidin, chair of the Nobel Committee for Chemistry. “They can be studied in real time while they live long and prosper.”

Moerner is an APS Fellow and has previously been awarded the Earle K. Plyler Prize for Molecular Spectroscopy and Dynamics and the Irving Langmuir Prize in Chemical Physics for his work. Hell is a member of APS and won the Kavli Prize this year for his work.