Nanopatterning and Devices
We use photo-lithography and e-beam lithography based methods to pattern materials on the nano and micro scale. This top-down approach is used to cut graphene and other 2D crystals into precise nanostructures essential for their application in electronics. We also use polymer-based resist lithography to define metal electrode patterns to make electrical contacts to nanometerials in order to probe their properties.
The active materials in the devices are typically nanowires, nanotubes and 2D crystals. The nanoelectronic devices are made on doped Si substrates with oxide layer, quartz, and specialized TEM grids for in-situ microscopy measurements.
Devices on doped Si substrates with thin oxide layer
The figure to the left shows an SEM image of a CVD grown carbon nanotube (CNT) with two metal contacts deposited by electron beam lithography methods. The contacts are Cr:Au, deposited by evaporation and are less than 100nm thick. The CNT runs vertically in the image.
The heavily doped Si substrate has a 300nm SiO2 insulating layer that isolates the CNT from the conductive Si, which is used as a global back gate for field effect transistor measurements of the CNT.
Characterization of single CNT devices show semiconducting behaviour for FETs. (Shown to the right)
When large continuous sheets of 2D crystals are transferred onto similar Si substrates we can use photo and electron beam lithography methods to cut it into shapes of any kind. Hall bars, nanoribbons, constrictions and connectors are all patterned into graphene and other 2D materials.
Electrical contacts are made to the patterned graphene by a second step of lithographic processing, leaving final device systems on the target substrate. The optical image below shows a Hall bar in graphene with Cr:Au electrodes and next to it a SEM image of Cr:Au contacts deposited onto semiconducting WS2 monolayer 2D crystals.
Devices on SiN TEM compatible grids
Custom built probe station for electronic measurements
Some examples of contacts made to Tin nanowires by electron beam lithography:
