Oct 25, 2012
Selective growth patterns prepare graphene for device applications
Graphene, a 2D crystalline nanoallotrope with an sp2 honeycomb carbon lattice, has made a strong impact on the research community due to its intriguing electronic, optical and opto-electronic properties. A variety of methods have been used for producing graphene from bulk graphite by mechanical, chemical and liquid phase exfoliation. Growth of graphene has also been realised by thermal decomposition of SiC and chemical vapour deposition (CVD) over catalytic metal substrates using hydrocarbon sources. Recently, solid carbon sources such as polymers, food materials, insects and even waste materials have been transformed into graphene via thermal treatment in the presence of metal catalyst layers.
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.
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.
About the author
G U Kulkarni received his PhD in Solid State Chemistry (1992) from the Indian Institute of Science in Bangalore. He is a professor in the Materials Unit at the Jawaharlal Nehru Centre for Advanced Scientific Research. His main research interests are direct write nanolithography, self assembly, optical and electronic properties of nanomaterials, molecular wires and crystals. He has published over 190 research articles and coauthored a book on nanocrystals.