Customized Y-shaped carbon nanotubes can compute
Researchers at UCSD and Clemson University have discovered that specially synthesized carbon nanotube structures exhibit electronic properties that are improved over conventional transistors used in computers. UCSD Mechanical and Aerospace Engineering professors Prabhakar Bandaru and Sungho Jin, graduate student Chiara Daraio, and Clemson physicist Apparao M. Rao reported that Y-shaped nanotubes behave as electronic switches similar to conventional MOS (metal oxide semiconductor) transistors, the workhorses of modern microprocessors, digital memory, and application-specific integrated circuits.
The stunning increase in the speed and power efficiency of electronics over the past two decades was primarily due to the steady shrinkage in size of conventional transistors. Chip makers have reduced the minimum feature size of transistors to about 100 nanometers, and that dimension is expected to shrink by the end of this decade. However, industry experts predict that fundamental technological and financial limits will prevent the makers of conventional MOS transistors to reduce their size much further. The Y-shaped nanotubes are only a few tens of nanometers thick and can be made as thin as a few nanometers.
UCSD professors Sungho Jin (left) and Prabhakar Bandaru, and graduate student Chiara Daraio measured dramatic electronic switching behavior of Y-shaped nanotubes that were specially synthesized by Clemson University professor Apparao M. Rao. The new transistors were initially grown as straight nanotube elements. Titanium-modified iron catalyst particles added to the synthesis mixture were then attached to the straight nanotubes, nucleating additional growth, which continued like branches growing from a tree trunk. Consequently, the nascent nanotubes assumed a Y-shape with the catalyst particle gradually becoming absorbed at the junction of the stem and two branches.
When electrical contacts are attached to the nanotube structures, electrons travel into one arm of the Y, hop onto the catalyst particle, and then hop to the other arm and flow outward. Experiments conducted in Bandaru's lab at UCSD's Jacobs School of Engineering showed that the movement of electrons through the Y-junction can be finely controlled, or gated, by applying a voltage to the stem. Bandaru hypothesized that positive charge applied to the stem enhances the flow of electrons through the two arms, producing a strong "on" signal. Then, when the polarity of the charge is reversed, the movement of electrons through the arms essentially stops, creating an "off" signal. Such binary logic is the basis of nearly all transistors.
"Among electrical device engineers, this phenomenon is called gating," said Bandaru. He said the phenomenon effectively makes Y-shaped nanotubes the smallest ready-made transistor yet, with rapid switching speeds and possible three-way gating capability. In earlier attempts to make carbon nanotube-based transistors, separate gates were added rather than built in.
The researchers plan to experiment with various other catalyst particles in order to tailor the three-way gating properties of the Y-junctions. "If we can easily fabricate, manipulate, and assemble these nano-devices on a large scale they could become the basis of a new kind of transistor and nanotechnology," said Bandaru.
Original publication: P.R. Bandaru, C. Daraio, S. Jin, A.M. Rao; "Novel electrical switching behaviour and logic in carbon nanotube Y-junctions"; Nature Materials 2005.
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Topic world Synthesis
Chemical synthesis is at the heart of modern chemistry and enables the targeted production of molecules with specific properties. By combining starting materials in defined reaction conditions, chemists can create a wide range of compounds, from simple molecules to complex active ingredients.
Topic world Synthesis
Chemical synthesis is at the heart of modern chemistry and enables the targeted production of molecules with specific properties. By combining starting materials in defined reaction conditions, chemists can create a wide range of compounds, from simple molecules to complex active ingredients.
