1-      Nanotube devices

2-      Nanolithography

3-      Photonic crystal 

1-      Nanotube devices

Growth of vertical and conical structures carbon nanotube  that suitable to  fabrication of Novel Self-Defined Field Emission Transistors. We report fabrication of novel field-emission transistors on silicon substrates using vertically grown carbon nano-tubes. Transistors made here are formed on clusters of Carbon Nano-tubes and do not need nano-lithography.

 (Dr. Mohajerzade , Dr. Soleimani, Koohsorkhi, Hosseinzadegan)

SEM images of vertical carbon nanotube at proper condition

SEM images of conical structure of CNTs that suitable to realization the electron source where the temperature has been raised from 500 to 550^oC during the film growth, leading a conic structure

Schematic diagram showing Self-Defined

Field-Emission transistors.

SEM image of Final CNTs with metal coating of  self-defined field emission transistor and electrical properties. As seen, at a voltage of 7.5V the emitted current shows a significant drop, indicating proper control of gate.

2-      Nanolithography

     200-50 nm Electron beam lithography using novel self-defined carbon-nano-tubes is being studied, although reduction of resolution to 50 nm is being pursued.

We report a novel technique for submicron and nanolithography using vertically grown nickel seeded carbon nano-structures (CNS) on silicon substrates. The field emission characteristic of carbon nano-tubes is utilized to create nano-scale features. The structure used here consists of vertical CNT’s encapsulated with titanium-dioxide and chromium (or silver) bi-layers. While CNT is responsible for electron emission, the surrounding metal (separated from inner CNT by a dielectric layer) acts as a self-defined gate to control the level of electron emission as well as an integrated electrostatic lens for beam shaping. The process is completed after chemical mechanical polishing followed by plasma ashing to open up the nano-tips and to form partially hollow nano-pipes. By applying proper voltage between carbon tip(cathode) and a resist-coated substrate (anode) electrons are emitted from negative side and nano-size features are developed on the resist-coated positive side. Using this technique we have drawn lines with a width of 120nm and a length of 5-10µm. Also round dots with sizes smaller than 0.4µm were realized. Straight lines with a thickness less than 100nm have also been achieved, although thinner features are expected by more proper control on the gate electrode and distance between CNT emitter and resist-coated substrates.

Vertical growth of carbon nanotube on silicon substrate

Schematic diagram of structure for nanolithography 

Electrical characteristic of Self-Defined transistors

 Evolution of nano-metric and submicron features by scanning the emitter onto the surface of top substrate

       (Dr. Mohajerzadeh, Koohsorkhi,  Abdi, Hosseinzadegan, Hashemi)

3-      Photonic crystal 

Fabrication of 2D, 3D photonic crystal using the single wall carbon nanotube (SWCNTs),  is underway

(Dr. Mohajerzadeh, Koohsorkhi, Hosseinzadegan, Famini, Hashemi)