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A family of silicon nanoparticles
RESEARCH NEWS
Space-saving microchain
Detail of silicon link and pivot on microchain drive. (Courtesy of Sandia National Laboratories.)
Researchers from Sandia National Laboratories are patenting a microchain that could drive multiple microelectromechanical systems (MEMS) devices. Each link of the 50-link Si microchain, constructed using
Sandia’s patented Summit IV and V technology, is separated by a distance of 50 µm. Currently, MEMS devices each require their own motor, but the microchain could rotate many drive shafts – rather like the central steam engine shafts
that were once used to power machines textile mills. MEMS devices could also be driven by motors not situated in the vicinity of the device using these microchains. “All those drives take up a lot of real estate on chips,” says Sandia technician Ed Vernon, explaining why saving space is so important. Each link of Vernon’s microchain can rotate ±52° with respect to its neighboring links without creating any pressure on the support structure – unlike Si belts. The microchain can stretch 500 µm unsupported, with tensioners added for longer spans. The rotational degree of freedom that the chain exhibits allows MEMS designers great flexibility in the positioning of multiple devices. The microchains could be used to power micro-camera shutters, suggests Vernon.
Nanothermometer A carbon nanotube 75 nm in diameter and 10 µm long filled with liquid gallium (Ga) acts a thermometer, claim Japanese researchers [Nature (2002) 415, 599]. The height of the continuous, unidirectional column of Ga inside the nanotube varies linearly with temperatures from 50-500°C. The nanothermometer can be read in situ using a scanning electron microscope, say Yihua Gao and Yoshio Bando from the National Institute for Materials Science in Tsukuba. The nanothermometer could be used in various microenvironments and would extend the range of temperature measurement beyond the 4-80 K capabilities of resistance micron-scale cryogenic thermometers.
A family of silicon nanoparticles A new method for creating silicon (Si) nanoparticles has been developed by researchers at the University of Illinois at Urbana-Champaign. Munir Nayfeh and his colleagues describe the new electrochemical etching process in two recent papers in Applied Physics Letters [(7 Jan 2002), 80 (1), 121123; (4 February 2002), 80 (5), 841-843]. Performing highly catalyzed electrochemical etching of bulk Si in HF and H2 O2 disperses ultrasmall elemental Si nanoparticles. The micronscale colloidal aggregates that form in water are transferred to an acrylic acid colloid, from which they are precipitated.
Once dry, the aggregates are encapsulated with an acrylic polymer. The researchers find that the aggregates produced in this way exhibit laser oscillation under cw excitation by a mercury lamp. Intense, directed Gaussian beams, with band narrowing and speckle patterns can be seen, say the researchers. “At 6 µm in diameter, these clusters of particles are one of the smallest lasers in the world,” says Sahraoui Chaieb. “This microlasing is an important step towards the realization of a laser on a chip, which could ultimately replace wires with optical interconnects.” The researchers used a similar technique, but this time
applying an electric current while gradually immersing the Si wafer into the HF and H2 O2 solution. The resulting network of weakly interconnected nanostructures is then placed in an ultrasonic bath, where the structure crumbles. The hydrogen-capped Sin Hx nanoparticles are then separated into discrete size categories by a process of centrifuging and sonification, or commercial gel permeation chromatography. Each nanoparticle of a particular size fluoresces in a distinct color. The smallest families include 1.0, 1.67, 2.15, 2.9, and 3.7 ±0.1 nm diameter nanoparticles, which fluoresce in blue, green, yellow,
and red. “The availability of specific particle size and emission in the red, green, and blue range makes the particles useful for electronic displays and flash markers,” explains Nayfeh. “The benign nature of silicon also makes the particles useful as ultra-bright fluorescent markers for tagging biologically sensitive materials,” he adds. The nanoparticles are photostable and brighter than the dye markers current used, say the researchers. “By placing particles of different colors in strategic locations,” says Nayfeh, “you could study such phenomena as growth factors in cancer cells or how proteins fold.”
April 2002
7
Space-saving microchain
Detail of silicon link and pivot on microchain drive. (Courtesy of Sandia National Laboratories.)
Researchers from Sandia National Laboratories are patenting a microchain that could drive multiple microelectromechanical systems (MEMS) devices. Each link of the 50-link Si microchain, constructed using
Sandia’s patented Summit IV and V technology, is separated by a distance of 50 µm. Currently, MEMS devices each require their own motor, but the microchain could rotate many drive shafts – rather like the central steam engine shafts
that were once used to power machines textile mills. MEMS devices could also be driven by motors not situated in the vicinity of the device using these microchains. “All those drives take up a lot of real estate on chips,” says Sandia technician Ed Vernon, explaining why saving space is so important. Each link of Vernon’s microchain can rotate ±52° with respect to its neighboring links without creating any pressure on the support structure – unlike Si belts. The microchain can stretch 500 µm unsupported, with tensioners added for longer spans. The rotational degree of freedom that the chain exhibits allows MEMS designers great flexibility in the positioning of multiple devices. The microchains could be used to power micro-camera shutters, suggests Vernon.
Nanothermometer A carbon nanotube 75 nm in diameter and 10 µm long filled with liquid gallium (Ga) acts a thermometer, claim Japanese researchers [Nature (2002) 415, 599]. The height of the continuous, unidirectional column of Ga inside the nanotube varies linearly with temperatures from 50-500°C. The nanothermometer can be read in situ using a scanning electron microscope, say Yihua Gao and Yoshio Bando from the National Institute for Materials Science in Tsukuba. The nanothermometer could be used in various microenvironments and would extend the range of temperature measurement beyond the 4-80 K capabilities of resistance micron-scale cryogenic thermometers.
A family of silicon nanoparticles A new method for creating silicon (Si) nanoparticles has been developed by researchers at the University of Illinois at Urbana-Champaign. Munir Nayfeh and his colleagues describe the new electrochemical etching process in two recent papers in Applied Physics Letters [(7 Jan 2002), 80 (1), 121123; (4 February 2002), 80 (5), 841-843]. Performing highly catalyzed electrochemical etching of bulk Si in HF and H2 O2 disperses ultrasmall elemental Si nanoparticles. The micronscale colloidal aggregates that form in water are transferred to an acrylic acid colloid, from which they are precipitated.
Once dry, the aggregates are encapsulated with an acrylic polymer. The researchers find that the aggregates produced in this way exhibit laser oscillation under cw excitation by a mercury lamp. Intense, directed Gaussian beams, with band narrowing and speckle patterns can be seen, say the researchers. “At 6 µm in diameter, these clusters of particles are one of the smallest lasers in the world,” says Sahraoui Chaieb. “This microlasing is an important step towards the realization of a laser on a chip, which could ultimately replace wires with optical interconnects.” The researchers used a similar technique, but this time
applying an electric current while gradually immersing the Si wafer into the HF and H2 O2 solution. The resulting network of weakly interconnected nanostructures is then placed in an ultrasonic bath, where the structure crumbles. The hydrogen-capped Sin Hx nanoparticles are then separated into discrete size categories by a process of centrifuging and sonification, or commercial gel permeation chromatography. Each nanoparticle of a particular size fluoresces in a distinct color. The smallest families include 1.0, 1.67, 2.15, 2.9, and 3.7 ±0.1 nm diameter nanoparticles, which fluoresce in blue, green, yellow,
and red. “The availability of specific particle size and emission in the red, green, and blue range makes the particles useful for electronic displays and flash markers,” explains Nayfeh. “The benign nature of silicon also makes the particles useful as ultra-bright fluorescent markers for tagging biologically sensitive materials,” he adds. The nanoparticles are photostable and brighter than the dye markers current used, say the researchers. “By placing particles of different colors in strategic locations,” says Nayfeh, “you could study such phenomena as growth factors in cancer cells or how proteins fold.”
April 2002
7