Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Engineers create vibrant colors in vertical silicon nanowires

04.04.2011
Surprising phenomenon may lead to greater sensitivity in image sensor devices

Engineers may soon be singing, "I'm going to wash that gray right out of my nanowires," thanks to a colorful discovery by a team of researchers from Harvard University and Zena Technologies. In contrast to the somber gray hue of silicon wafers, Kenneth B. Crozier and colleagues demonstrated that individual, vertical silicon nanowires can shine in all colors of the spectrum.

The vibrant display, dependent on the diameter of the individual wires, is even visible to the naked eye. In addition to adding a splash of color to the lab, the finding has potential for use in nanoscale image sensor devices, offering increased efficiency and the ability to detect color without the use of filters.

"It is surprising," says Crozier, John L. Loeb Associate Professor of the Natural Sciences at the Harvard School of Engineering and Applied Science (SEAS). "A lot of people are making nanowires, and you really don't think of the color so much. In this vertical configuration you can get very strong color effects, and you can tune them over a range of wavelengths of the visible region. The strong effects can be seen right down to the level of the individual wire."

The finding, published in the March 17, 2011, online edition of Nano Letters, may be the first experimental report that silicon nanowires can take on a variety of colors depending on their diameter and under bright-field illumination. Previous work has shown that nanowires can take on different colors but only by looking at scattered, rather than directly reflected, light.

To create the multicolored array of vertical silicon nanowires, the engineers at Harvard and Zena Technologies used a combination of electron beam lithography and inductively coupled plasma reactive ion etching.

A smooth wafer of silicon was plasma etched until all that remained were the vertically protruding nanowires, resembling bristles on a toothbrush. While the nanowires were created in arrays of thousands for convenience, the colors they exhibited were due to the properties of the individual wires, not by the way light was scattered or diffracted in the group.

"Each nanowire acts as a waveguide, like a nano-sized optical fiber—but an optically absorbing one," explains Crozier. "At short wavelengths there is not much optical coupling to the nanowire. At long wavelengths, the coupling is better, but the properties of the waveguide are such that there is not much absorption. In between, there is a range of wavelengths where the light is coupled to the nanowire and absorbed. This range is determined by the nanowire diameter. We made nanowires with diameters of 90, 100, and 130 nm that appeared red, blue and green, respectively."

To demonstrate the remarkable phenomenon and the relative ease of controlling and positioning the colorful nanowires, the researchers created a nanoscale-sized tribute to Harvard, designing a pattern resembling the engineering school's Veritas seal and spelling out the acronym SEAS in a rainbow of colors.

While the Harvard image closely matched the school's seal, the desired color eluded the engineers.

"We actually wanted to make the seal red rather than blue, but it turned out that the diameter was a little bit wrong," says Crozier.

As even small changes in the radius of a wire can alter the color, the seal turned out to be blue, more suitable for the famous seal of a certain other Ivy League institution.

Fortunately, the technology has other promising applications. The researchers' eventual aim is to use the wires in image sensors. Traditional photodetectors in image sensor devices can gauge the intensity of light but not determine its color without the use of an additional filter, which throws away much of the light, limiting the device's sensitivity.

The researchers hope to address this by fabricating vertical nanowires containing photodetectors above standard photodetectors formed on a silicon wafer. The nanowire and standard photodetectors could each detect a different part of the spectrum of the incident light. By comparing the signals from each, the color could be determined without losing so much of the light.

"With image sensors, every little bit of efficiency counts. Moreover, we even imagine using the colored wires to encode data in a read-only type of information storage," adds Crozier.

The researchers have filed a provisional patent for their work.

Crozier's co-authors included Kwanyong Seo, Paul Steinvurzel, Ethan Schonbrun, Yaping Dan, and Tal Ellenbogen, all from SEAS, and Munib Wober, from Zena Technologies. The study was supported by funding from Zena Technologies and the United States Department of Energy, Office of Science and Basic Energy Sciences. In addition, the research team acknowledges the Center for Nanoscale Systems at Harvard for fabrication work.

Michael Patrick Rutter | EurekAlert!
Further information:
http://www.harvard.edu

More articles from Power and Electrical Engineering:

nachricht Producing electricity during flight
20.09.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau

nachricht Solar-to-fuel system recycles CO2 to make ethanol and ethylene
19.09.2017 | DOE/Lawrence Berkeley National Laboratory

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

Im Focus: Quantum Sensors Decipher Magnetic Ordering in a New Semiconducting Material

For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.

Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...

Im Focus: Fast, convenient & standardized: New lab innovation for automated tissue engineering & drug

MBM ScienceBridge GmbH successfully negotiated a license agreement between University Medical Center Göttingen (UMG) and the biotech company Tissue Systems Holding GmbH about commercial use of a multi-well tissue plate for automated and reliable tissue engineering & drug testing.

MBM ScienceBridge GmbH successfully negotiated a license agreement between University Medical Center Göttingen (UMG) and the biotech company Tissue Systems...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Comet or asteroid? Hubble discovers that a unique object is a binary

21.09.2017 | Physics and Astronomy

Cnidarians remotely control bacteria

21.09.2017 | Life Sciences

Monitoring the heart's mitochondria to predict cardiac arrest?

21.09.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>