From the Labs: Nanotechnology

Bio-Inspired Nano Synthesis
Sponge studies lead to a method for making novel materials

SOURCE: “Kinetically Controlled Vapor-Diffusion Synthesis of Novel Nano-structured Metal Hydroxide and Phosphate Films Using No Organic Reagents” Birgit Schwenzer et al. Journal of Materials Chemistry 16: 401-407

RESULTS: Using mechanisms inspired by marine sponges, researchers at the University of California, Santa Barbara, have developed a technique for making a variety of thin-film materials, including semiconductors, structured at the nanoscale. Unlike other methods, the technique can produce semiconducting thin films without the use of harsh chemicals, and it works at room temperature, whereas some techniques require temperatures of 400 to 1,500 ºC. So far, the researchers have used the process to synthesize 30 types of materials, some of which have novel electronic and optical properties.

WHY IT MATTERS: The process is more environmentally sound and potentially less expensive than other techniques for manufacturing thin-film materials, which are used in a variety of electronic devices. Furthermore, it could open the way for new types of materials or allow existing materials to take on new properties. For example, the large surface area of the nanostructured films could lead to higher-power batteries and more efficient solar panels.

METHODS: The process is similar to one seen in marine sponges, which assemble their intricate glass skeletons with the help of an enzyme that doubles as a physical template. The researchers expose a solution of molecular precursors to ammonia vapor, which, as it slowly diffuses into the solution, catalyzes the assembly of the precursors into the desired material. The surface of the solution acts in some ways like the sponge’s enzyme template, helping to determine the material’s structure. At the surface, the vapor concentration is greatest, and the material forms a smooth, thin film. As the concentration of ammonia decreases, the material grows down, extending from the film like stalactites.

NEXT STEPS: The researchers are beginning to build and test rudimentary photovoltaic and electrical storage devices made from the new materials. To produce materials that perform as well as possible, they will also need to fine-tune the assembly method and apply it to additional compounds.

Carbon Nanotube Computers
IBM researchers have found a way to arrange nanotube transistors into complex circuits

SOURCE: “Field-Effect Transistors Assembled from Functionalized Carbon Nanotubes”
Christian Klinke et al. Nano Letters 6(5): 906-910

RESULTS: Researchers at IBM have selectively arranged carbon nanotubes on a surface to make transistors, an important step toward arranging them into complex circuits. To control the placement of the nanotubes, they attached them to molecules that bind to patterns of metal-oxide lines on a surface. They then demonstrated high-performance transistors assembled through this technique.

WHY IT MATTERS: Researchers estimate that transistors based on carbon nanotubes could run many times faster than anticipated future generations of silicon-based devices but would use less power. The IBM work overcomes one of the serious obstacles to nanotube-based computers: the difficulty of deliberately arranging the molecules so that they can form complex circuits.

METHODS: To make working transistors, the researchers first laid down aluminum wires using a lithographic technique. These wires served as the gates that turned the transistors on and off. They then oxidized the aluminum, creating a thin layer of aluminum oxide that acted as an insulator. The oxidized aluminum also served as a template for the carbon nanotubes. After arranging the nanotubes by allowing them to bind to the aluminum oxide, the researchers deposited palladium leads perpendicular to the aluminum wires. These leads crossed over the nanotubes, becoming the sources and drains of high-performance transistors.

NEXT STEPS: The speed of the transistors is currently limited by the large size of the leads and their poor contact with the nanotubes. One possible solution is to replace the palladium wires with metallic nanotubes. Because current fabrication techniques produce a mix of nanotubes with different sizes and electronic properties, not all of which will work well in integrated circuits, another challenge is to find reliable and inexpensive ways to isolate a preferred type of carbon nanotube.

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