Category: Nanoscale Bulk Technologies

More coverage of the work to create cylinder-shaped nanoscopic nanowire bundles that interweave substances with different compositions and properties (see Nanodot post from 2 February 2002). As a result, well-defined junctions and interfaces with potentially important functionalities were incorporated within individual nanowires. The alternating bands of different semiconductor materials in the super-thin wires serve as the electron and photon manipulators.

• An item on the Technology Research News website: "Tiny wires turn chips inside out", by Eric Smalley, 13 February 2002.
• An article in the online version of Science News: "Circuitry in a nanowire: Novel growth method may transform chips", by Peter Weiss, 9 February 2002

According to a press release (1 February 2002) from the American Chemical Society (ACS), two independent groups have published reports in Nano Letters, an ACS publication, on methods for making lattices that they say will enable nanowires to be constructed with otherwise incompatible materials. Such mixed bundles may be useful in making electronics and other devices on an increasingly smaller scale:

• A report by a U.S. team led by Peidong Yang, assistant professor in the Department of Chemistry at the University of California-Berkeley and a faculty scientist in the Materials Science Division at the Lawrence Berkeley National Laboratory, details how they successfully fabricated ìsuperlatticeî nanowire, so named because the nanowireís cylinder-shaped nanoscopic bundle interweaves substances with different compositions and properties. As a result, well-defined junctions and interfaces with potentially important functionalities were incorporated within individual nanowires.
• A related paper by Swedish researchers working in the Materials Chemistry and Solid State Physics Departments in Lund Universityís Nanometer Consortium used related but different methods than their California peers.

In both cases, manufacture is relatively straightforward and results in stable nanowires that can operate at room temperature, Yang reports. Based on the findings of both research groups, tiny components known as nanowires that meld together a variety of materials could soon be routinely and cheaply built using little more than a special mixture of gases deposited on a foundation material.

Additional information on the Berkeley teamís work can be found in this press release (31 January 2002) issued by Nanosys, Inc. Yang is a cofounder of Nanosys, a company focused on the development of nanotechnology-enabled systems. These systems incorporate novel and patent-protected zero and one-dimensional nanometer-scale materials such as nanowires, nanotubes and nanodots (quantum dots) as their principal active elements. Another cofounder of Nanosys is Charles Lieber, a Harvard chemistry professor and winner of the 2001 Foresight Feynman Prize for Experimental work. Lieber has also been conducting significant research into the production and properties of nanowires and other nano-scale materials.

According to a press release (25 January 2002), researchers at The Scripps Research Institute (TSRI) and The Skaggs Institute for Chemical Biology have found a way to attach a wide range of molecules to the surface of a virus, enhancing the virus with the properties of those molecules. The researchers say their technique may find applications in materials science, medicine, and molecular electronics, including the possibility of building circuits of conducting molecules on the surfaces of the viruses and form a component of a molecular-scale computer, or a new type of "nanowire." The work is reported in the 1 February 2002 issue of Angewandte Chemie.

The researchers found a method of putting a chemically reactive cysteine residue (a type of amino acid) on the surface of each of the 60 identical protein modules that make up the viral shell. The shell has an icosahedral shape, which provides 60 equivalent sites for attaching molecules. The researchers report they have been able to attach fluorescent dyes and clusters of gold molecules to the cysteine residues, which could be easily imaged. They also have successfully attached biotin (Vitamin B), sugars, and organic chemicals. The technique can be used to immobilize large molecules on the viral surface — whole proteins even. In addition, the virus particles can self-organize into network arrays in a crystal, which may make it a useful building block for various applications in nanotechnology. "You can, in principle, determine the type of assembly you get by programming the building blocks," says one researcher.

Update: Additional coverage is available in this article from United Press International

An article on the Technology Research News website ("Nanotube array could form chips", by Ted Smalley Bowen) describes work by a group of researcers from the Samsung Advanced Institute of Technology and the Chonbuk National University in Korea who have made nanotube field-effect transistors in bulk by a relatively crude process that involves growing them in vertical bunches, then using electron beam lithography and ion etching to make the source, gate and drain electrodes that control the flow of electrons. Their carbon nanotube transistors worked at temperatures up to an extremely cold -243 degrees Celsius. The report dryly notes that the transistors will need to work at much warmer temperatures to be used in practical devices, and includes comments from other nanotube researchers to the effect that the researchers' method is still very rough, and they did not demonstrate that individual transistors could be accessed. The nanotubes rough composition limits their use, said Yue Wu, associate professor of physics at the University of North Carolina. "The carbon nanotubes are very defective. The device won't work at room temperature because the tubes are not clean semiconductors," he said. The work was reported in the 26 November 2001 issue of Applied Physics Letters.

A pair of brief press releases tell of recent work with carbon nanotubes by researchers at Rensselaer Polytechnic Institute (RPI):

• Two RPI researchers, G. Ramanath and P. Ajayan in the Department of Materials Science and Engineering, claim in a press release (28 January 2002) they are the first to grow nanotubes into any set of predetermined directions on silicon-based substrates. They say their work paves the way for making nanoscale devices that depend on the connection of tiny wires in many directions.
• In a second, rather short press release (29 January 2002), two other RPI researchers said static electricity poses serious problems with nanoscale elements in a circuit. P. Keblinski, assistant professor of materials science and engineering, and S. Nayak, assistant professor of physics, combined quantum mechanics in theoretical computer simulations with classical electrostatics analysis. According to their analysis, small zap of static electricity destabilizes the nanotubes, making them useless as a semiconductor. They found that the electrostatic charge is concentrated at the tube ends. The charge eventually destroys the entire nanotube. The researchers suggest doping the nanotubes may help, and that addition of elements such as nitrogen could provide new electrical characteristics to the tubes or could be used to increase the bonding between the tubes and other materials.

United Press International reports ("Superhard electrical crystal carbon film", 25 January 2002) that Japanese scientists have made very thin crystalline films of carbon, nearly as hard as diamond but many times more electrically conductive, which they hope will have practical use in nanometer-scale electronics.

According to the report, the researchers created a form of carbon possessing both diamond bonds and weaker, sp² bonds — the type found in graphite and some fullerenes. This hybrid film is an intricate lattice made up of fine nanocrystalline sheets of carbon atoms linked to each other in graphite bonds whose edges rise up from a surface about 45 nanometers. In turn, these sheets are bonded together with diamond-like bonds. According to the researchers, the carbon film is almost as hard as diamond, but its electrical conductivity is 19 orders of magnitude larger than diamond's. This makes the films about as electrically conductive as the chemically modified semiconductors used in microchips. The process for creating the hybrid diamondoid films occurs at room temperature.

from the earl-grey,-hot,-please dept.
According to a press release (3 January 2002), researchers at the Max-Planck-Institute for Quantum Optics in Garching and at the Ludwig-Maximilians University of Munich have been able to manipulate atoms in a Bose-Einstein condensate with an optical lattice, allowing them to create a new phase of matter with an exact number of atoms at each lattice site. The researchers observed the phase transition between two dramatically different states of matter close to temperatures of absolute zero.

In a Bose-Einstein condensate, the atoms loose their individuality and a wave-like state of matter is created that can be compared in many ways to laser light. In the new work, the scientists store a Bose-Einstein condensate in a three-dimensional lattice of microscopic light traps. By increasing the strength of the lattice, the researchers are able to dramatically alter the properties of the dilute gas of atoms and induce a quantum phase transition from the superfluid phase of a Bose-Einstein condensate to a Mott insulator phase.

For a weak optical lattice the atoms form a superfluid phase of a Bose-Einstein condensate. In this phase, each atom is spread out over the entire lattice in a wave-like manner as predicted by quantum mechanics. The gas of atoms may then move freely through the lattice. For a strong optical lattice the researchers observe a transition to an insulating phase, with an exact number of atoms at each lattice site. Now the movement of the atoms through the lattice is blocked due to the repulsive interactions between them. The researchers were also able to show that it is possible to reversibly cross the phase transition between these two states of matter.