The work is another step toward "laboratory on a chip" applications in which vibrating strings can be used to detect and identify biological molecules. The devices also can be used as very precisely tuned oscillators in radio-frequency circuits, replacing relatively bulky quartz crystals.
When you strike a bell or pluck a guitar string, it will vibrate within a small range of frequencies, centering on what is called the resonant frequency. Quality factor, or Q, refers to how narrow that range will be. It is defined as the ratio of the resonant frequency to the range of frequencies over which resonance occurs. A radio receiver with high-Q circuitry, for example, will be more selective in separating one station from another.
Cornell researchers have already used vibrating strings and cantilevers to detect masses as small as a single bacterium or virus. Resonant frequency depends on the mass of a vibrating object (a thick guitar string has a lower pitch than a thin one). If a nanoscale vibrator is coated with antibodies that cause a virus or some other molecule to adhere to it, the change in mass causes a measurable change in frequency. In a high Q nanostring, the researchers say, a small change in mass will produce a much more noticeable shift.
The new nanostrings, made by graduate student Scott Verbridge and colleagues in the laboratories of Harold Craighead, Cornell professor of applied and engineering physics, and Jeevak Parpia, professor of physics, are made of silicon nitride under stress. By controlling the temperature, pressure and other factors as the film is deposited, the experimenters can cause the silicon nitride to be, in effect, stretched.
The longest string the researchers made was 200 nanometers (nm) wide, 105 nm thick and 60 microns long and had a resonant frequency of 4.5 megaHertz with a quality factor of 207,000. (A nanometer is one-billionth of a meter, about as long as three atoms in a row; a micron, or micrometer, is one-millionth of a meter.) Comparing the results with those reported by other workers in the field, Verbridge said others have reached similar Q factors in samples cooled to within a few degrees of absolute zero, but he believes this is the highest Q achieved at room temperature.
To demonstrate the possible applications in electronics, Verbridge's colleague, graduate student Robert Reichenbach, has built what he calls "the world's most expensive radio," using about $200,000 worth of lab equipment to mix the vibration of a nanoscale resonator with the off-the-air signal from local radio station WICB and read the output with a laser. The quartz crystals ordinarily used in radios are about one-half-inch square and require relatively large batteries to operate, Reichenbach said. The replacement is about the size of a human hair and requires little power. Radio transmitters using such devices could be made small enough to implant in the body to report on medical conditions, and cell phones could shrink to wristwatch size or smaller, he said.
In addition to having a high quality factor, the stressed silicon nitride strings are very robust mechanically, the researchers said, making them practical for consumer devices.
The research is described in a paper, "High Quality Factor Resonance at Room Temperature With Nanostrings Under High Tensile-Stress," in the June 15 issue of the Journal of Applied Physics.
Fabrication by electrospinning
Cornell is famous for its interdisciplinary collaborations, but workers in the Craighead Research Group may hold a record for the most unlikely combination, using tools from the Department of Textiles and Apparel to advance nanotechnology.
At the Cornell NanoScale Facility, the smallest devices are usually made by a process called electron beam lithography: A sharply focused beam of electrons cuts a pattern into a chemical film covering a wafer of silicon or a similar substance. The wafer is then etched with acid that cuts away the silicon in the places the resist has been removed,
As an alternative way of making simple straight lines, researchers turned to electrospinning, in which a liquid polymer is forced through a row of openings just a few nanometers in diameter, creating very fine fibers. Textiles and apparel researchers have been using electrospinning to create a sort of fabric by letting the fibers collect and mat up. The nanotech researchers allow them to flow smoothly onto a moving silicon wafer, creating a series of parallel lines that act as a chemical resist and guide an etchant to carve out nanostrings.
The process is faster and much cheaper than electron-beam lithography, and it allows researchers to test a wide variety of materials and configurations in a short time and on a low budget.
"Given the substrate, I can make you a nanobeam resonator in under an hour," said graduate student Scott Verbridge.
Bill Steele | EurekAlert!
NASA spacecraft investigate clues in radiation belts
28.03.2017 | NASA/Goddard Space Flight Center
Researchers create artificial materials atom-by-atom
28.03.2017 | Aalto University
The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.
To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
28.03.2017 | Life Sciences
28.03.2017 | Information Technology
28.03.2017 | Physics and Astronomy