Device makers are looking at ways to obtain graphene patterns of a predefined shape and size at desired locations on dielectric substrates along with tunable electronic properties. One approach being investigated by researchers in India is to derive the graphene like patterns from the pre-patterned carbon feed stocks on insulating substrates via thermal annealing in presence of a metal catalyst layer.

In the study, carbon feed stock patterns are created by a technique called electron beam induced carbonaceous deposition (EBICD) where the electron beam is used to "stitch" carbonaceous patterns onto a given substrate from the abundant residual hydrocarbons in the vacuum chamber of a scanning electron microscope. EBICD is a direct write method of fabricating carbonaceous patterns. The technique does not require any hydrocarbon source to be connected and consumed in the process; the source is "vacuum" itself. Degassing and residuals in vacuum can be an ample supply of hydrocarbons.

p-type behaviour

The team, based at the Jawaharlal Nehru Centre for Advanced Scientific Research, has transformed these robust carbonaceous patterns into nanocrystalline graphene (nc-graphene) directly on the insulating substrates after vacuum annealing with the aid of a minimal Ni catalyst layer. The scientists obtained transfer free nc-graphene patterns exhibiting p-type behaviour with a typical hole mobility of ∼90 cm2/Vs. Interestingly, these nc-graphene patterns are found to be a potential material for the detection of IR radiation.

Adjusting the e-dosage conditions of the EBICD allows operators to control the thickness of graphene/nc-graphene patterns. The lateral dimensions (from mm to nm range) of the graphene-like patterns can be obtained via pre-patterning of the carbon feed stocks using focused and flooded electron beams respectively. Different geometrical shapes, including nanoribbons and nanomeshes, can also be fabricated via this technique.

The process allows developers to obtain graphene patterns with fewer processing steps compared with graphene derived from other solid carbon sources in the literature. By depositing Ni at specific locations, it is possible to have domains of nc-graphene and amorphous carbon, which may be useful for fabricating resistive switching devices and strain sensors.

Full details can be found in the journal Nanotechnology.