Fundamental studies of 2D materials
The atomically thin 2D materials own unique electronic and structural properties which are ideally suited for next-generation miniature devices. I am interested in studying the fundamental properties and applications of novel 2D materials. I have built extremely productive and ongoing collaborations with key experimental (UK, Italy, Ukraine, France, Pakistan) and theoretical (UK, Turkey) groups worldwide.
Synthesis of novel class of 2D layers
I have successfully developed a physical vapor transport method to grow beta-In2Se3 on different substrates (SiO2, mica, and graphite) and different In-Se compounds on GaSe crystal (N. Balakrishnan et al., 2016, 2018). Currently, I am focusing to develop different band alignments and potential profiles by growing III-VI layers on different layered semiconductors. Combining materials with different band gap energies enables the fabrication of different optoelectronic devices.
Growth of In2Se3 layers on GaSe substrate
Optoelectronics
The integration of 2D layered semiconductors with graphene to form heterostructure devices offers new routes to the fabrication of optoelectronic devices such as light emitting diodes (LEDs), fast and ultrasensitive photodetectors, etc. I fabricate van der Waals heterostructure devices to study their optical, electronic, and optoelectronic properties (N. Balakrishnan et al., 2014, 2017).
Ferroelectrics
The miniaturization of ferroelectric devices offers prospects for non-volatile memories, low-power electrical switches, and emerging technologies beyond existing Si-based integrated circuits. An emerging class of ferroelectrics is based on van der Waals 2D materials with potential for nano-ferroelectrics. I am interested to study the ferroelectric properties of novel 2D materials, such as In2Se3 and CuInP2S6 (S. Xie et al., 2021, A. Day et al., 2022).
Thermoelectric
Van der Waals 2D materials offer a versatile platform to tailor heat transfer due to their high surface-to-volume ratio and mechanical flexibility. Recently, we studied the nanoscale thermal properties of 2D InSe layers by scanning thermal microscopy (D. Buckley et al., 2021). I am interested to fabricate and characterize thermoelectric devices.
p-GaSe/n-InSe heterojunction
Gr/In2Se3/Gr vertical tunneling transistor
Schematic of Scanning thermal microscope
Twistronics
The stacking method of 2D materials has another degree of freedom; the individual layers can be aligned with different angles with respect to each other, which creates a Moiré pattern. The twist angle can act as a knob to tune the electronic properties of the stack. Recently, we studied the electronic transport properties of twisted monolayer–bilayer graphene heterostructure. We observed the formation of van Hove singularities that are highly tunable by changing either the twist angle or external electric field and can cause strong correlation effects under optimum conditions (S. Xu et al., 2021). I am interested to explore the other 2D materials based twisted heterostructures.
ρxx(n,D) measured at T = 1.6 K and B = 0 T of samples with twist angles θ ≈ 1.22°, 1.26°, 1.41°,1.47° and 1.6°. The correlated states under D > 0 remain almost at the same D range for all samples, while the correlated states under D < 0 move to larger D when the twist angle increases,
Other ongoing projects
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Strain engineering of 2D materials
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Energy storage devices (supercapacitors, batteries, hydrogen storage)