Nanotechnology - Online Article

In the next 50 years, machines will get increasingly smaller -- so small that thousands of these tiny machines would fit into the period at the end of this sentence. Within a few decades, we will use these nanomachines to manufacture consumer goods at the molecular level, piecing together one atom or molecule at a time to make baseballs, telephones and cars. This is the goal of nanotechnology.

Some of the current innovations

IBM Researchers Build World's First Single - Molecule Computer Circuit

IBM researchers today announced they have created and demonstrated the world's first logic-performing computer circuit within a single molecule, which may someday lead to a new class of smaller and faster computers that consume less power than today's machines. The IBM team made a " voltage inverter " -- one of the three fundamental logic circuits that are the basis for all of today's computers -- from a carbon nanotube, a tube-shaped molecule of carbon atoms that is 100,000 times thinner than a human hair.

Building a Computer Circuit "Inverter" Out of Carbon Nanotubes

The IBM scientists used nanotubes to make a "voltage inverter" circuit, also known as a "NOT" gate . They encoded the entire inverter logic function along the length of a single carbon nanotube, forming the world's first intra-molecular -- or single-molecule -- logic circuit. In the binary digital world of zeros and ones, a voltage inverter changes a '1' into a '0', and a ' 0' into a '1' inside computer chips. The processors at the heart of today' s computers are basically vast and intricate combinations of the NOT gate, with two other basic functions, "AND" and "OR" gates, which perform other computations.

Voltage inverters typically comprise two types of transistors with different electronic properties "n-type" (in which electrons carry the electrical current) and "p-type" (in which electron-deficient regions called "holes" carry the electrical current). All previous carbon nanotube transistors have been p-type only. These transistors, while fine for scientific studies, are not sufficient to build logic-performing computer circuits. Scientists at IBM and elsewhere have been able to alter the properties of nanotube transistors by adding atoms of another element, such as potassium, to the carbon nanotube. However, researchers have recently discovered a new, simpler way to convert p-type nanotube transistors into n-type transistors. They found that they could simply heat p-type transistors in a vacuum, which turns them into n-type transistors and that they could reverse this process by exposing the transistors to air.

The team also discovered that in addition to converting an entire nanotube from p-type to n-type, they could also selectively convert part of a single nanotube to n-type, leaving the remaining part of the single nanotube p-type. The researchers used this process to build the world's first single-molecule logic circuit.

More importantly, the output signal from IBM's new nanotube circuit is stronger than the input. This phenomenon, called "gain," is essential for assembling gates and other circuit elements into useful microprocessors. Circuits with a gain less than one are ultimately useless -- the electrical signal becomes so faint that it cannot be detected. Since IBM's nanotube circuit has a gain of 1.6, researchers are hopeful that even more complex circuits could be made along single nanotubes.

Researchers produce strong, transparent carbon nanotube sheets

Carbon nanotubes are like minute bits of string, and untold trillions of these invisible strings must be assembled to make useful macroscopic articles that can exploit the phenomenal mechanical and electronic properties of the individual nanotubes. University of Texas at Dallas (UTD) nanotechnologists and an Australian colleague have produced transparent carbon nanotube sheets that are stronger than the same-weight steel sheets and have demonstrated applicability for organic light-emitting displays, low-noise electronic sensors, artificial muscles, conducting appliques and broad-band polarized light sources that can be switched in one ten-thousandths of a second.

Strength normalized to weight is important for many applications, especially in space and aerospace, and this property of the nanotube sheets already exceeds that of the strongest steel sheets and the Mylar and Kapton sheets used for ultralight air vehicles and proposed for solar sails for space applications, according to the researchers. The nanotube sheets can be made so thin that a square kilometer of solar sail would weigh only 30 kilograms. While sheets normally have much lower strength than fibers or yarns, the strength of the nanotube sheets in the nanotube alignment direction already approaches the highest reported values for polymer-free nanotube yarn.

The nanotube sheets combine high transparency with high electronic conductivity, are highly flexible and provide giant gravimetric surface areas, which has enabled researchers to demonstrate their use as electrodes for bright organic light emitting diodes for displays and as solar cells for light harvesting. Electrodes that can be reversibly deformed over 100 percent without losing electrical conductivity are needed for high stroke artificial muscles, and the Science article describes a simple method that makes this possible for the nanotube sheets.

The use of the nanotube sheets as planar incandescent sources of highly polarized infrared and visible radiation is also reported. Since the nanotube sheets strongly absorb microwave radiation, which causes localized heating, the scientists were able to utilize a kitchen microwave oven to weld together plexiglas plates to make a window. Neither the electrical conductivity of the nanotube sheets nor their transparency was affected by the welding process -- which suggests a novel way to imbed these sheets as transparent heating elements and antennas for car windows. The nanotube sheets generate surprisingly low electronic noise and have an exceptionally low dependence of electronic conductivity on temperature. That suggests their possible application as high-quality sensors - which is a very active area of nanotube research.

Numerous other applications possibilities exist and are being explored, including structural composites that are strong and tough; supercapacitors, batteries, fuel cells and thermal-energy-harvesting cells exploiting giant-surface-area nanotube sheet electrodes; light sources, displays, and X-ray sources that use the nanotube sheets as high-intensity sources of field-emitted electrons; and heat pipes for electronic equipment that exploit the high thermal conductivity of nanotubes. Multifunctional applications like nanotube sheets that simultaneously store energy and provide structural reinforcement for a side panel of an electrically powered vehicle also are promising.

Hands-on nanotechnology: Towards a nanorobotic assembly line

Until the twentieth century, a single craftsman or team of craftsmen would normally create each part of an industrial product individually and assemble them together into a single item, making changes in the parts so that they would fit together and work together. Then Henry Ford came along and in 1907-08 developed the assembly line for his Model T automobile. This innovation revolutionized not only industry but also our society because it allowed mass production of industrial goods at much lower cost than before. At its core, an assembly line is a manufacturing process in which interchangeable parts are added to a product in a sequential manner to create a finished product.

A group of researchers from Denmark and Germany have now developed the rudimentary beginnings of the nanotechnology equivalent of an assembly line. They have shown 'pick-and-place' assembly of a working device using a silicon gripper - a robotic 'hand' some 10000 times smaller than a human hand. This nanogripper, controlled by a nanorobotic arm, is capable of picking up a carbon nanofiber (CN) and fix it onto the tip of an atomic force microscope cantilever. They have managed to break off a sturdy carbon nanofiber, mount it at the pyramidal tip of an atomic force cantilever and used it for scanning in a deep groove.

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How does the gripper work?

Parts of the silicon gripper are heated up with an electrical current, and the thermal expansion is converted into a powerful gripping action of the jaws. The distance of the jaws can then be reduced from about 3 micron to zero.

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So far carbon nanotubes and nanofibers with diameters down to 100 nm have been manipulated, but in two years smaller tools will manipulate 10-20 nm wide wires and tubes. There are many problems to solve to reach this goal, however. On the nanoscale, 3D manipulation is painstakingly difficult: the robotic arms must work with extreme precision, and real-time imaging of nanostructures is just about possible. Creating the tiny 'hands' for the robot is a great challenge: the fingers must be thin and flexible, and yet have sufficient strength to break off nanotubes from their initial position. Finally, the powerful surface forces on the nanoscale make all objects sticky.

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