Wednesday, September 29, 2004

"NANOTECH: Low-temp polymer nanotubes foretell plastic circuits"
Chemists at Central Michigan University have grown carbon nanotubes at a record-low 175 degrees C using a polymer type known as dendrimers as the substrate. "This is the first time anyone has grown carbon nanotubes directly from a dendrimer catalyst at temperatures low enough that the dendrimer is not destroyed," said CMU professor Bradley Fahlman, lead researcher on the project. Whereas conventional polymers grow in long, tangled chains, dendrimers branch out from a core in a symmetrical, tree-like arrangement. In the growth process, the ends of one generation of branches sprout new polymer chains, creating a next-generation shell. The process grows nanotubes from the ends of the dendrimer's branches. Functionalizing the tubes with metal, semiconducting or photoelectric molecules will create materials with varied properties, the researchers said.

Friday, September 24, 2004

"METAMATERIAL: Composites enable 'perfect' lens"
Composite metamaterials that exhibit a negative index of refraction are being harnessed to enable a variety of hitherto impossible applications, promising to reduce size and cost while simultaneously increasing accuracy and range. "Electrical engineers will be interested to know that our metamaterial technology is now being adapted to make microwave devices and antennas with unprecedented levels of performance and functionality," said University of Toronto professor George Eleftheriades, himself an EE. "Our latest results are very promising for both basestation and handheld hardware. . . . Now is the time for electrical engineers to really start creating a whole new range of useful devices for the cell phone industry." Metamaterials enable lenses without an optical axis, despite their planarity, to focus waves by means of refraction. Metamaterials substitute macroscopic objects for atoms in a giant, crystalline-like lattice. The Toronto team's lattice was constructed of perpendicular wires that defined a grid whose spacing was set to a subwavelength of the wavelength affected.

Thursday, September 23, 2004

"METAMATERIAL: Lens focuses sound, not light"
Metamaterials reverse the ordinary laws of nature, such as Snell's "right-hand" law for electromagnetism, which states that magnetism curls in the same direction in which the fingers of your right hand curl around a wire when you point with your thumb in the direction of current flow. By 2003, researchers had verified that not only were these engineered materials possible, but they also could enable "perfect" lenses that were nevertheless flat. Now metamaterials are being demonstrated not just for electromagnetic waves, but for anything that can be described by wave functions, thereby reversing the laws of nature for acoustic engineering, ultrasound, microwaves, light and magnetism. "What we have is a larger version, structurally, of a photonic crystal, adjusted for the wavelength of ultrasound," said John Page, a professor at the University of Manitoba in Winnipeg. "Our metamaterials use artificial atoms arranged in a lattice that filters acoustic wavelengths the way that photonic crystals filter optical wavelengths." Metamaterials substitute macroscopic objects for atoms in a giant crystalline lattice-here made from tungsten carbide beads surrounded by water and packed flat into planes, with a spacing between beads set to a subwavelength of the wavelength you want to affect.

Friday, September 17, 2004

"CHIPS:IBM taps spintronics to reset molecular memories"
IBM Corp.'s progress in characterizing the magnetic spin of individual atoms and in flipping them from "up" to "down" could lead to molecular-cascade memories, a new type of memory chip that would pack a bit of data in every atom. IBM Fellow Don Eigler's group at Almaden Research Center (San Jose, Calif.) recently demonstrated IBM's new nanoscale characterization method, dubbed "spin-flip spectroscopy." To study how to switch the spin of individual atoms, IBM constructed a new type of measuring device. It combines a scanning tunneling microscope with a superconducting coil providing a high-strength magnetic field. The whole machine is supercooled to near-absolute zero. "We invented spin-flip spectroscopy so that we can study how to use magnetic spin for information storage, because at IBM our ultimate goal is the ultimate memory density possible � storing bits on individual atoms," said Andreas Heinrich, a researcher in Eigler's lab. "For instance, we demonstrated our molecular-cascade memories two years ago, but at that time we didn't have a way to reset them � they just fell over like dominoes, then we had to pick them back up one by one. Now we think we can use magnetism to reset a future version of molecular cascades." Eigler and Heinrich performed the work with IBM researcher Christopher Lutz and Jay Gupta, an assistant professor at Ohio State University. With the machine, IBM was able to characterize the precise amount of energy required to flip the spin of an atom from up to down � which is usually encoded to mean "1" and "0." The result was 0.0005 electron-volts, some 10,000 times less than the energy of a single molecular bond.
"NANOTECH: Tuned radio frequency oscillator built from nanotubes"
Researchers at Cornell University have created the world's smallest mechanical oscillator that is capable of being tuned electrically. The nanoelectromechanical system (NEMS), which might be a forerunner of sensors that can detect individual atoms, stretches a 1-nanometer-diameter nanotube across a 1,500-nm-wide trench. The system creates a guitar-stringlike device that could also be used as a mechanical RF oscillator or as a clock reference in future nanoscale chips. "Very simply, what we have here is a smaller version of a MEMS [microelectromechanical systems] RF oscillator, but using carbon nanotubes and being electrically tunable," said Paul McEuen, a Cornell physics professor. "All of its applications are years away from being practical, but it is an interesting new direction for researchers plumbing the nanoscale." To construct the nanoscale oscillator, which the researchers tuned as high as 200 MHz in the lab, the team first grew an oxide on a standard single-crystal silicon wafer. Next they grew nanotubes with 1- to 4-nm diameters and laid them on the oxide's surface, then etched a micronwide trench under the nanotubes' middle so that they were suspended. "We use an atomic-force microscope to locate the nanotube. Then we use lithography to define a trench with photoresist. Then we just etch out about a 1-micron-wide section underneath the nanotube. The middle of the nanotube was suspended over the trench with nothing more than van der Waals forces holding it there," said McEuen. Since the width of the trench � about 1.2 to 1.5 microns � is more than 1,000x wider than the width of the nanotube, the arrangement is similar to a stretched guitar string.

Wednesday, September 15, 2004

"QUANTUM: Yale team builds chips for quantum computing"
Demonstrating a new paradigm for quantum computing, Yale University researchers have built what they call QED integrated circuits to manipulate quantum bits. While the almost mystical allure of quantum computing has been verified time and again using qubits in a physics lab, building real circuitry on silicon chips has had only sporadic success, until now. The QED-for quantum electrodynamics-circuits operate on quantum bits by using a superconducting "Cooper box" to store oscillating microwave photons that can be read and written without disturbing their quantum states. Quantum computers promise to outpace digital computers by using qubits, which can represent a superposition of simultaneous values, thereby achieving parallel processing without parallel hardware. "I think that EEs understand how qubits involve a superposition of quantum states, but they may not know that you can build integrated circuits that way," said Steven Girvin, a professor of physics at Yale. By superpositioning quantum states that simultaneously perform parallel operations, quantum computers can break encryption codes and work other technological miracles that a digital computer would find impossible. Many quantum state mechanisms, some of them potential building blocks for future quantum computers, have been demonstrated in physics labs. But Yale's demonstration of how to build chips using what it calls "qutons"-a qubit on a photon-enable quantum computers using QED circuits to be put onto chips today

Friday, September 10, 2004

"QUANTUM: computer chip circuitry demonstrated"
Yale University researchers have demonstrated how to build a quantum computer operating on quantum bits, or qubits, which hold a superposition of quantum states. The computer uses a superconducting "Cooper box" to store oscillating microwave photons which can be read and written without disturbing their quantum states. Qubits based on the superposition of quantum states can be used to make integrated circuits. "Heisenberg's Uncertainty principle says you can't measure the velocity and position of a particle, and likewise in QED [quantum electrodynamic] circuits you can't measure the voltage and the current at the same time," explained Yale University professor Steven Girvin. Quantum computers derive their power from enabling a superposition of quantum states to simultaneously perform many parallel operations. Those operations allow quantum computers to perform tasks like breaking encryption codes that are impossible for digital computers. Many quantum-state mechanisms have been demonstrated in physics labs, some of which could serve as building blocks for future quantum computers. Likewise, Yale's "qutons," or "qubit on a photon," invention may enable quantum computers to be placed on chips even sooner. The advantages of Yale's method include the relatively small size of its qubit repositories � about a square micron � and the ability to read a qubit's state without disturbing it � the bane of quantum computers to date.
"CHIPS: Self-assembly technique enables 10-nm litho"
A novel processing technique that combines known molecules to realize a new class of synthesized material has enabled 10-nanometer precision lithography. The invention enables the lithographic-like self-assembly of molecules into one-, two- or three-dimensional nanoscale structures by combining a block copolymer with a dendrimer. The latter is a "cascade molecule" in which the atoms are arrayed along a backbone of carbon. "In our experiment we demonstrated 10-nm feature sizes, but we envision our invention working with traditional lithography to encode information into a material that enables it to self-assemble into domains with angstrom-scale precision," said Ulrich Wiesner, professor of materials science and engineering at Cornell University. He performed the work at the university with the help of physics professor Sol Gruner, director of the Cornell High Energy Synchrotron Source; postdoctoral researcher Byoung-Ki Cho; and doctoral candidate Anurag Jain. The researchers said their invention could lead to ultraprecise nanoscale features that improve the efficiency of batteries, solar cells and fuel cells.

Thursday, September 09, 2004

"NANOTECH: Researchers demonstrate nanoscale self-assembly"
A new processing technique developed by Cornell University researchers promises to usher in lithographic-like self-assembly into single and multidimensional nanoscale structures. The technique enabled 10-nm precision lithography. One-, two- and three-dimensional nanoscale structures self-assembled by combining a block copolymer with a "cascade molecule" called a dendrimer in which atoms are arrayed along a carbon backbone, the researchers said. "We demonstrated 10-nanometer feature sizes, but we envision our invention working with traditional lithography to encode information into a material that enables it to self-assemble into domains with angstrom-scale precision," said Ulrich Wiesner, professor of materials science and engineering at Cornell University. Besides subnanoscale precision lithography, the researchers said their invention could lead to ultraprecise nanoscale features that improve the efficiency of batteries, solar cells and fuel cells.

Wednesday, September 08, 2004

"NANOTECH: thermal dip pens read, write, repair nanostructures"
Creating ultratiny, nanoscale systems is often easier than verifying the accuracy of the resulting structures. Indeed, in some instances the structures can actually be lost. Nanoscale techniques produce minute features, but imaging tools are sometimes too crude to spot breaks in them. To the rescue come atomic-force microscopy and now its interactive "can-do" sibling, thermal dip pen nanolithography. Traditional atomic-force microscopy (AFM) techniques drag a probe with a 100-nanometer tip over nanoscale structures to record a small deflection, thereby producing an image of the surface by mapping its valleys and peaks. By first dipping the AFM tip in liquid metal, a semiconductor or an oxide, dip pen nanolithography (DPN) can directly write 100-nanometer lines-but can't interactively switch between read/write.

Friday, September 03, 2004

"NANOTECH: Nanodots to launch large memories"
Arrays of 7-nanometer magnetic nickel nanodots, assembled by researchers at the National Science Foundation's Center for Advanced Materials and Smart Structures (CAMSS), aim at a 500x increase in memory density, to 10 trillion bits per square inch. At such densities, coin-sized chips holding 5 terabits each could pack the entire Library of Congress into "a pocket full of change," said Jagdish Narayan, professor of materials science and engineering at North Carolina State University and CAMSS director at the university. Narayan performed the work with research associate Ashutosh Tiwari. The technique, which uses pulsed-laser ablation to make nanodots that are said to be 10 times smaller than previously possible, can also be used to make more-efficient LEDs, single-electron transistors, spin transistors, hybrid devices, superhard coatings and novel biomaterials.