Bowtie Nano Color Sorter Fashioned for Optical Nanoantenna, May Mean Increased Bandwidth

Caption: This scanning electron image of a nano color sorter with the vertical bowtie antenna shifted 5 nanometers (nm) to the left of center. In (a) the bowtie has been exited at 820 nm and in (b) at 780 nm. The two modes are spectrally and spatially distinct while maintaining nanoscale mode volumes.

 Credit: James Schuck, Berkeley Lab Molecular Foundry

Looking sharp and looking for light - Berkeley Lab researchers have engineered a new class of bowtie-shaped devices that capture, filter and steer light at the nanoscale. These "nano-colorsorter" devices act as antennae to focus and sort light in tiny spaces, a useful technique for harvesting broadband light for color-sensitive filters and detectors.

Currently, optical fibers employ light to transport data with very high bandwidth, but the technique hits a roadblock as light is squeezed into smaller and smaller photonic circuits. This roadblock is the diffraction limit - a fundamental restriction in concentrating photons into regions smaller than half their wavelength. In contrast, electronic devices are readily fashioned at nanometer scales; however, electronic data transfer operates at frequencies far below those for fiber optics, with much lower bandwidth, reducing the amount of data carried.

A recent technology, coined "plasmonics, " crowds electromagnetic waves into metal structures with dimensions much smaller than the wavelength of light for transmitting data at optical frequencies, marrying the best aspects of optical and electronic communications. A particularly promising class of structures for enhancing this crowding effect is nanoscale optical antennas made of gold, which leverage plasmonic behavior to efficiently capture and confine light in miniscule dimensions.

"Like the antenna on your TV or radio, optical nanoantennas efficiently catch and concentrate energy, but the wavelengths are much smaller," says Jim Schuck, a staff scientist withn the Molecular Foundry, a U.S. Department of Energy (DOE) national user facility at Berkeley Lab that provides support to nanoscience researchers around the world.

"We've made the first engineered and nanofabricated stucture for nanoscale light distribution that can ship and manipulate ultra-confined optical information with a knob you can easily tune—the energy or color of light," says Schuck, who works in the Foundry's Imaging and Manipulation of Nanostructures Facility.

Molecular Foundry post-doctoral researcher Zhaoyu Zhang, working with Schuck and Nanofabrication Facility Director Stefano Cabrini, fabricated nanoantennas from four equilateral triangles of gold lithographically patterned to create a 'cross' geometry.

Breaking the symmetry of this cross-shaped device affects its primary resonance mode - a property best illustrated by the shattering of a champagne flute when it encounters a musical tone of the right pitch. In these cross nanoantennas, the resonant modes correspond to different frequencies, or colors, of light.

"We can now control the plasmonic properties of these devices by introducing asymmetry, and we find red and blue light is literally sent left and right," says Zhang. "By pushing the limits of manipulating light in a smaller volume, we can move information to one place or another quickly and efficiently, which is important for fast, color-sensitive photodetection."

Indeed, shifting the vertically aligned bowtie in the cross nanoantenna just five nanometers left of center generates two resonance modes, producing a two-color filter. The team further demonstrated this effect by breaking other symmetries of the bowties, leading to a three-color filter. This symmetry breaking gives scientists the ability to "auto-tune" a device to a desired set of colors or energies, crucial for filters and other detectors. Using the nanofabrication capabilities available at the Foundry, the scientists plan to explore adjusting the size, shape, and position of the bowties to optimize device properties. For example, thousands of bowties could be packed in an area less than one millimeter across, enabling large, but ultrafast, detector arrays.

"Our findings lend insight into the link between simple symmetry breaking and the coherent coupling properties of localized plasmons, providing a pathway for engineering intricate devices that can control light in extremely confined spaces," Schuck adds.

A scientific paper reporting this research entitled "Manipulating nanoscale light fields with the asymmetric bowtie nano-colorsorter," by Zhaoyu Zhang, Alexander Weber-Bargioni, Shiwei Wu, Scott Dhuey, Stefano Cabrini and James Schuck, appears in Nano Letters and is available in Nano Letters online.

Work at the Molecular Foundry was supported by the Director, Office of Science, Office of Basic Energy Sciences, Division of Materials Science and Engineering, of the DOE under Contract No. DE-AC02-05CH11231.

The Molecular Foundry is one of the five DOE Nanoscale Science Research Centers (NSRCs), premier national user facilities for interdisciplinary research at the nanoscale. Together the NSRCs comprise a suite of complementary facilities that provide researchers with state-of-the-art capabilities to fabricate, process, characterize and model nanoscale materials, and constitute the largest infrastructure investment of the National Nanotechnology Initiative. The NSRCs are located at DOE's Argonne, Brookhaven, Lawrence Berkeley, Oak Ridge and Sandia and Los Alamos National Laboratories.

EU Commission Commits $4.5 Billion for Nanoelectronics Research from 2009-2013

On 29 October 2009, the European Commission adopted the Communication "Nanosciences and Nanotechnologies: an Action Plan for Europe 2005-2009.”  The report outlines the key developments during 2007-2009 in each policy area of the Action Plan, identifies current challenges, and draws conclusions relevant to the future European nanotechnology policy. Where appropriate, for the sake of completeness and continuity, developments in preceding years are included. Detailed supporting information can be found in the accompanying Staff Working Document.

The plan commits $4.5 billion from 2009 to 2013 for nanoelectronics research and development under ENIAC. ENIAC was established in 2004 as the Technology Platform for Nanoelectronics. Its main goal was to define common research and innovation priorities to ensure a truly competitive nanoelectronics industry in Europe. To attain such an objective, ENIAC invested intensive efforts to bring together the key players in nanoelectronics research by gathering within the Platform the main European industrial groups and research organizations, setting up the ENIAC Scientific Community Council to ensure representation of Universities, and encouraging the participation inENIAC of Small and Medium enterprises through national platforms.

Nanoelectronics refer to the application of nanotechnology to semiconductor components and highly miniaturized electronic sub-systems, and their integration in larger products and systems. Semiconductors have enabled the digital revolution that has brought huge productivity gains to our economy and improvements in our quality of life. Constant innovation in the area, together with a strong industrial competition, have given rise to affordable, ever more powerful and energy-efficient computers and other digital devices, for the everyday use of all businesses and virtually all types of consumer. The pace of this digital revolution is still accelerating, enabling new applications in nearly every segment of the world economy, such as medical devices, photovoltaic energy generation, traffic management, and so on.

Current devices are manufactured using 65 nm or 45 nm processes (this dimension being the average half-pitch of a memory cell). In this sense, nanoelectronics is merely the consequence of the evolutionary path of microelectronics into the nanoscale domain. Current transistors still do not fall under the category of nanomaterials, which are produced by manipulating matter at the atomic scale. On the other hand, the properties of future devices may well be defined by interatomic interactions and quantum mechanical properties.