Metal quantum dots make Coulomb blockade transistor
A team led by Christian Klinke chemically synthesised colloidal cobalt-platinum particles with diameters of approximately 2nm to 4nm diameter and laid them down on silicon-dioxide insulator material using the Langmuir-Blodgett method. The assembly of nanoparticles is gated and has a back-gate and result in well-defined and controllable transistor characteristics that operate at room temperature.
Due to their small size the metallic particles display semiconductor properties that can be controlled by voltage.
The team reported transistors with on/off ratios above 90 percent, reliable and sinusoidal Coulomb oscillations in an article in Science Advances. The approach allows for tuning of the device properties such as Coulomb energy gap and threshold voltage, as well as the period, position, and strength of the oscillations.
This is because the metal particles are so small that they quantum confinement effects and they lose their metallic character but exhibit an energy gap caused by the Coulomb repulsion of the electrons among one another.
A controlling voltage is used to shift the energy gap and the current can thus be switched on and off.
Next: Three characteristics
Three characteristics of the Hamburg approach makes such metallic transistors of interest for commercial exploitation. This is because metal nanoparticles synthesized by colloidal chemistry are controllable, scalable and can be stored in solvents; Langmuir-Blodgett deposition produces monolayered films; and is suitable for subsequent definition with standard lithographic methods.
“Of course, there is still a lot of research to be done, but our work shows that there are alternatives to traditional transistor concepts that can be used in the future in various fields of application,” said Christian Klinke, in a statement. “The devices developed in our group can not only be used as transistors, but they are also very interesting as chemical sensors because the interstices between the nanoparticles, which act as so-called tunnel barriers, react highly sensitive to chemical deposits.”
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