- Email: [email protected]
Ceramics display a new application
RESEARCH NEWS
Space control Instead of worrying about material properties, scientists at Bell Labs in Murray Hill, New Jersey, have turned their attention to empty space. In quantum electrodynamics, the Casimir effect dictates that the space between two uncharged metal surfaces a few nanometers apart can contain only a limited number of electromagnetic vibrations. The vibrations that occupy the rest of space outside this region create a force – the Casimir force – that pushes the surfaces together. Federico Capasso and his colleagues, report in Physical Review Letters [(2001) 87, 211801], that they can exploit this effect
to control a mechanical oscillator. With a gold plated 100 µm sphere attached to the end of a probe, the researchers can control the amplitude and frequency of an oscillating metallic paddle simply by varying the distance between the two objects. A more thorough understanding of the Casimir force is essential for the development of micromechanical systems (MEMS) and machines as it can predict whether minute components will stick together – and could even allow empty space to be used as a component of such devices.
Ceramics display a new application
The Casimir force between metal surfaces - here a 100 µm gold-plated sphere and a metal paddle - means that empty space could be used as a component in micromachines. (Courtesy of Bell Labs.)
Self-assembling and -repairing microwires Electrically conducting wires that both assemble and repair themselves sound too good to be true. But such microwires do exist according to Orlin Velev and his co-workers at the University of Delaware (Velev is now at North Carolina State University). The researchers found that metallic (gold) nanoparticles suspended in water spontaneously form wires between two electrodes under an alternating (AC) field – a process know as dielectrophoresis. “Nothing was expected to happen with waterborne metallic nanoparticles in the AC electrical field because the force between these tiny particles is so small,” says Velev, expressing his surprise
10
January 2002
at the result, reported in the November 2 issue of Science [(2001) 294, 1082-1086]. He certainly didn’t expect that metallic wires a micron in diameter would grow at a rate of 50 µm/s to lengths exceeding 5 mm. The microwires show a simple ohmic behavior and resistivities of the order of many metallic alloys. Velev suggests that particle aggregation at the tip of fibers gives rise to the microwire growth in the direction of the field gradient – this is a collective effect and requires a minimum number of nanoparticles before growth can start. The researchers also found that the wires selfrepair themselves if damaged to form a new, and equivalent,
electrical connection. Complex patterns of microwires can be formed by introducing conductive elements between the electrodes – with the patterns still preserved when the current is turned off. Silver, platinum, composite and carbon wires could be constructed in this way, say the researchers, and they even demonstrate a metallic wire with a latex shell – all selfassembled from a single solution. A host of applications can be envisaged for such nanowires and Velev demonstrates one immediate possibility. By introducing a surface functionalizing agent, the researchers were able to use the microwires to detect cyanide.
Japanese company NGK Insulators Ltd. announces what it claims to be the first commercial application of ceramic displays as billboards on the Nagoya subway. The piezoelectric ceramic displays rely on NGK’s proprietary technology, using micro ceramic actuators to activate the pixels. More than 16 million colors, including white, can be achieved by controlling the contact and distance between pixels and the optical waveguide plate. Compared to competing technologies, the pixel pitch of 2.8 mm is significantly smaller than that of LED (light emitting diode) displays commonly used for large screens, ensuring high resolution. Response times – typically less than a millisecond – are faster than LCDs (liquid crystal displays), allowing high-speed moving images to be displayed. Large screens are also possible (ranging from 150 cm diagonal for Ceram Vision to 120 x 29 cm for Ceram Board) and can be built-up by tiling together smaller (9 x 9 cm) panels. Since no gases, liquid crystals or other such materials are used, there are no sealing margins around each panel and continuous images can be displayed across the screen. Despite the large screen size, high luminescence from 200-1000 cd/m2 and wide viewing angles can be achieved, claim NGK.
Space control Instead of worrying about material properties, scientists at Bell Labs in Murray Hill, New Jersey, have turned their attention to empty space. In quantum electrodynamics, the Casimir effect dictates that the space between two uncharged metal surfaces a few nanometers apart can contain only a limited number of electromagnetic vibrations. The vibrations that occupy the rest of space outside this region create a force – the Casimir force – that pushes the surfaces together. Federico Capasso and his colleagues, report in Physical Review Letters [(2001) 87, 211801], that they can exploit this effect
to control a mechanical oscillator. With a gold plated 100 µm sphere attached to the end of a probe, the researchers can control the amplitude and frequency of an oscillating metallic paddle simply by varying the distance between the two objects. A more thorough understanding of the Casimir force is essential for the development of micromechanical systems (MEMS) and machines as it can predict whether minute components will stick together – and could even allow empty space to be used as a component of such devices.
Ceramics display a new application
The Casimir force between metal surfaces - here a 100 µm gold-plated sphere and a metal paddle - means that empty space could be used as a component in micromachines. (Courtesy of Bell Labs.)
Self-assembling and -repairing microwires Electrically conducting wires that both assemble and repair themselves sound too good to be true. But such microwires do exist according to Orlin Velev and his co-workers at the University of Delaware (Velev is now at North Carolina State University). The researchers found that metallic (gold) nanoparticles suspended in water spontaneously form wires between two electrodes under an alternating (AC) field – a process know as dielectrophoresis. “Nothing was expected to happen with waterborne metallic nanoparticles in the AC electrical field because the force between these tiny particles is so small,” says Velev, expressing his surprise
10
January 2002
at the result, reported in the November 2 issue of Science [(2001) 294, 1082-1086]. He certainly didn’t expect that metallic wires a micron in diameter would grow at a rate of 50 µm/s to lengths exceeding 5 mm. The microwires show a simple ohmic behavior and resistivities of the order of many metallic alloys. Velev suggests that particle aggregation at the tip of fibers gives rise to the microwire growth in the direction of the field gradient – this is a collective effect and requires a minimum number of nanoparticles before growth can start. The researchers also found that the wires selfrepair themselves if damaged to form a new, and equivalent,
electrical connection. Complex patterns of microwires can be formed by introducing conductive elements between the electrodes – with the patterns still preserved when the current is turned off. Silver, platinum, composite and carbon wires could be constructed in this way, say the researchers, and they even demonstrate a metallic wire with a latex shell – all selfassembled from a single solution. A host of applications can be envisaged for such nanowires and Velev demonstrates one immediate possibility. By introducing a surface functionalizing agent, the researchers were able to use the microwires to detect cyanide.
Japanese company NGK Insulators Ltd. announces what it claims to be the first commercial application of ceramic displays as billboards on the Nagoya subway. The piezoelectric ceramic displays rely on NGK’s proprietary technology, using micro ceramic actuators to activate the pixels. More than 16 million colors, including white, can be achieved by controlling the contact and distance between pixels and the optical waveguide plate. Compared to competing technologies, the pixel pitch of 2.8 mm is significantly smaller than that of LED (light emitting diode) displays commonly used for large screens, ensuring high resolution. Response times – typically less than a millisecond – are faster than LCDs (liquid crystal displays), allowing high-speed moving images to be displayed. Large screens are also possible (ranging from 150 cm diagonal for Ceram Vision to 120 x 29 cm for Ceram Board) and can be built-up by tiling together smaller (9 x 9 cm) panels. Since no gases, liquid crystals or other such materials are used, there are no sealing margins around each panel and continuous images can be displayed across the screen. Despite the large screen size, high luminescence from 200-1000 cd/m2 and wide viewing angles can be achieved, claim NGK.