May 20, 2006

What to do now? Helping the environment

Folding bicycles by Dahon, Montague and others folding recumbant bikes can be brought onto public transit. They typically cost about $300 to $900. There are several folding bike buyers guides

For a more comfortable ride, get an electic folding bicycle. The bionx can be used to convert regular bikes to electric bikes

If you currently do not use public transit because of delays with transfers and less freedom of movement at your destination then get a folding bike or electric folding bike. The ones with 20 inch wheels or smaller can also be packed on trips to other countries.

May 18, 2006

More Desalination: Carbon nanotube membranes may reduce energy for desalination by 75%

A prior review of the state of desalination

A nanotube membrane on a silicon chip the size of a quarter may offer a cheaper way to remove salt from water.

Researchers at the Lawrence Livermore National Laboratory have created a membrane made of carbon nanotubes and silicon that may offer, among many possible applications, a less expensive desalinization. The team was able to measure flows of liquids and gases by making a membrane on a silicon chip with carbon nanotube pores making up the holes of the membrane. The membrane is created by filling the gaps between aligned carbon nanotubes with a ceramic matrix material. The pores are so small that only six water molecules could fit across their diameter.

“The gas and water flows that we measured are 100 to 10,000 times faster than what classical models predict,” said Olgica Bakajin, the Livermore scientist who led the research. “This is like having a garden hose that can deliver as much water in the same amount of time as fire hose that is 10 times larger.”

Salt removal from water, commonly performed through reverse-osmosis, uses less permeable membranes, requires large amounts of pressure and is quite expensive. However, these more permeable nanotube membranes could reduce the energy costs of desalination by up to 75 percent compared to conventional membranes used in reverse osmosis.

other tech: Urban Grand Challenge for 2007

The DARPA Urban Challenge will feature autonomous ground vehicles executing simulated military supply missions safely and effectively in a mock urban area. Safe operation in traffic is essential to U.S. military plans to use autonomous ground vehicles to conduct important missions.
DARPA will award prizes for the top three autonomous ground vehicles that compete in
a final event where they must safely complete a 60-mile urban area course in fewer than six hours. First prize is $2 million, second prize is $500,000 and third prize is $250,000. To succeed, vehicles must autonomously obey traffic laws while merging into moving traffic, navigating traffic circles, negotiating busy intersections and avoiding obstacles.

The draft rules are here

more precise control on the way to full MNT: Researchers achieve long-sought goal of using lasers to break specific molecular bonds

Stripping hydrogen from silicon surfaces with light instead of heat promises to improve the quality of computer chips and solar cells A team of researchers has achieved a long-sought scientific goal: using laser light to break specific molecular bonds. The process uses laser light, instead of heat, to strip hydrogen atoms from silicon surfaces. This is a key step in the manufacture of computer chips and solar cells, so the achievement could reduce the cost and improve the quality of a wide variety of semiconductor devices.

The technique was developed by Philip I. Cohen at the University of Minnesota, working with Vanderbilt researchers Leonard C. Feldman, Norman Tolk and Zhiheng Liu along with Zhenyu Zhang from Oak Ridge National Laboratory. It is described in the May 19 issue of the journal Science.

Microelectronic devices are built from multiple layers of silicon. In order to keep silicon surfaces from oxidizing, semiconductor manufacturers routinely expose them to hydrogen atoms that attach to all the available silicon bonds. However, this process known as "passivation" means that the hydrogen atoms must be removed before new layers of silicon can be added. "Desorbing" the hydrogen thermally requires high temperatures and adds substantially to difficulty of process control because these temperatures create thermal defects in the chips and so reduce chip yields.

"One application that we intend to examine is the use of this technique to manufacture field effect transistors (FETs) that operate at speeds about 40 percent faster than ordinary transistors," says Cohen. According to the professor of electrical and computer engineering, it should be possible to reduce the processing temperature of manufacturing FETs by 100 degrees Celsius which should dramatically improve yields.

This degree of selectivity could provide a way to control the growth of nanoscale structures with an unprecedented degree of precision and it is this potential that most excites Cohen, who notes, "By selectively removing the hydrogen atoms from the ends of nanowires, we should be able to control and direct their growth, which currently is a random process."

Human wall crawling product

A product for human wall crawling, gekkomat, is in working prototype form by a small German company. More pictures and video

May 16, 2006

16 atoms of Gold have a hollow center

AU16, AU17, AU18 are the metallic equivalent of carbon 60 in that they are a metallic cage thank could hold other atoms. Scientists have uncovered a class of gold atom clusters that are the first known metallic hollow equivalents of the famous hollow carbon fullerenes known as buckyballs. The fullerene is made up of a sphere of 60 carbon (C) atoms; gold (Au) requires many fewer--16, 17 and 18 atoms, in triangular configurations more gem-like than soccer ball. At more than 6 angstroms across, or roughly a ten-millionth the size of this comma, they are nonetheless roomy enough to cage a smaller atom. Lai-Sheng Wang, the paper's lead corresponding author, is an affiliate senior chief scientist at the Department of Energy's Pacific Northwest National Laboratory and professor of physics at Washington State University. The experiments were buttressed and the clusters' geometry deciphered from theoretical calculations led by Professor Xiao Cheng Zeng of the University of Nebraska and co-corresponding author. "Au-16 is beautiful and can be viewed as the smallest golden cage," Wang said. He pictures it as having "removed the four corner atoms from our Au20 pyramid and then letting the remaining atoms relax a little," and thus opening up space in its center.

It and its larger neighbors are stable at room temperature and are known as "free-standing" cages--unattached to a surface or any other body, in a vacuum. "When deposited on a surface, the cluster may interact with the surface and the structure may change."

Wang and his co-workers suspect "that many different kinds of atoms can be trapped inside" these hollow clusters, a process called "doping." "These doped cages may very well survive on surfaces," suggesting a method for influencing physical and chemical properties at smaller-than-nano scales, "depending on the dopants."

Wang's group has not yet attempted to imprison a foreign atom in the hollow Au cages, but they plan to try.

May 14, 2006

Organizing dumbbells for nanotech devices

Chemist Fraser Stoddart, now at the University of California Los Angeles, and his co-workers have designed and made numerous molecules based on hanging ring-shaped molecules on other chain-like molecules and loops. By incorporating functional chemical groups along the length of the chain or around these loops, they have shown that it is possible to make the molecular beads switch between these various functional groups using heat, light, or electricity. The ultimate aim of creating such molecular-scale devices is to use them as switching units or logic gates in a future computer based on molecules instead of silicon chips.

Before that will be possible, however, the nanoscientists must find a way to organize arrays of these molecules on a surface so that input and output connections can be made between the molecules and the outside world.

Stoddart and colleague Alberto Credi of the University of Bologna, Italy, and co-workers at the University of Birmingham, UK, the University Paul Sabatier, Toulouse, France, and the University of Valencia in Spain recognize that in order to exploit their molecular machines they will need to find a way to organize them at interfaces, deposit them on functional surfaces, or immobilize them into membranes or porous materials. This will allow the molecular machines to work together and to be "addressed" on the nanometer scale. The researchers believe that modifying the surface of an electrode to incorporate an organized layer of molecular machines could be the key to success.

The team reports in the current issue of Advanced Materials how they have recently succeeded in applying an incredibly thin layer, just a few molecules thick, of a particular molecular machine to a glass surface. The molecular machine in question is a switchable rotaxane--a ring-shaped molecule held on a short chain by two blocking groups, making it resemble a dumbbell with a collar around the handle.

A special technique was used to make thin layers of this dumbbell-shaped component in solution on a glass slide coated with ITO (indium tin oxide). By using two solutions--one containing the dumbbells and the other a soapy surfactant compound--the researchers were able to force the molecules to organize themselves because of electrostatic repulsion and attraction between the surfactant, the molecules, and the surface, until ultimately they became attached with the same orientation to the ITO layer on the glass slide.

The researchers then tested their thin layers of dumbbell molecules to see whether they would work as planned. They found that the thin film exhibited a reversible switching behavior when exposed cyclically to an acid and then a base. This, they explain, demonstrates that the thin film is capable of transducing a chemical input signal--the acid-base--into an electrical output signal. This bodes well for interfacing other molecular machines in a similar way.

Ultimately, control using a light source or electricity will be required before such layers will be useful in the development of molecular computers, but this first small step to organizing molecular machines could lead to the required breakthrough.