[Paper Review] Electronic transport in a two-dimensional superlattice engineered via self-assembled nanostructures

Yingjie Zhang, Young-Seok Kim+2 more|arXiv (Cornell University)|Mar 16, 2017

Graphene research and applications73 references3 citations

TL;DR

This study demonstrates electronic transport in a two-dimensional superlattice formed by transferring graphene onto a self-assembled monolayer of nanospheres, inducing quasi-periodic lattice strain. Conductance dips at commensurate carrier fillings per unit cell confirm miniband formation, with enhanced effects under greater strain, validated by tight-binding simulations of hopping integral modulation.

ABSTRACT

Nanoscience offers a unique opportunity to design modern materials from the bottom up, via low-cost, solution processed assembly of nanoscale building blocks. These systems promise electronic band structure engineering using not only the nanoscale structural modulation, but also the mesoscale spatial patterning, although experimental realization of the latter has been challenging. Here we design and fabricate a new type of artificial solid by stacking graphene on a self-assembled, nearly periodic array of nanospheres, and experimentally observe superlattice miniband effects. We find conductance dips at commensurate fillings of charge carriers per superlattice unit cell, which are key features of minibands that are induced by the quasi-periodic deformation of the graphene lattice. These dips become stronger when the lattice strain is larger. Using a tight-binding model, we simulate the effect of lattice deformation as a parameter affecting the inter-atomic hopping integral, and confirm the superlattice transport behavior. This 2D material-nanoparticle heterostructure enables facile band structure engineering via self-assembly, promising for large area electronics and optoelectronics applications.

Motivation & Objective

• To engineer artificial electronic band structures in 2D materials using bottom-up self-assembly of nanoscale building blocks.
• To explore mesoscale spatial patterning in nanomaterials for tunable electronic properties beyond nanoscale periodicity.
• To experimentally observe superlattice miniband effects in a graphene-nanoparticle heterostructure with controlled lattice deformation.
• To correlate lattice strain with electronic transport features such as conductance dips at commensurate fillings.
• To validate the observed transport behavior using a tight-binding model with strain-modified hopping integrals.

Proposed method

• Fabrication of a graphene-sphere heterostructure via transfer of CVD-grown graphene onto a self-assembled monolayer of polystyrene nanospheres.
• Use of low-cost, solution-processed self-assembly to create a nearly periodic, quasi-periodic deformation in the graphene lattice.
• Measurement of electrical transport in the heterostructure to detect signatures of miniband formation via conductance spectroscopy.
• Modeling of the strained lattice using a tight-binding Hamiltonian with position-dependent hopping integrals to simulate electronic band structure.
• Systematic variation of strain magnitude to correlate lattice deformation with transport features.
• Analysis of conductance dips at integer fillings of charge carriers per superlattice unit cell as evidence of miniband formation.

Experimental results

Research questions

• RQ1 Can self-assembled nanoparticle arrays induce measurable superlattice miniband effects in suspended graphene?
• RQ2 How does lattice strain from quasi-periodic deformation influence electronic transport in 2D materials?
• RQ3 To what extent do conductance dips at commensurate carrier fillings signal the presence of minibands in a strained 2D superlattice?
• RQ4 Can a tight-binding model with strain-modified hopping integrals quantitatively reproduce the observed transport features?
• RQ5 What is the role of mesoscale spatial patterning in enabling band structure engineering in 2D heterostructures?

Key findings

• Conductance dips were experimentally observed at commensurate fillings of charge carriers per superlattice unit cell, indicating the formation of minibands due to quasi-periodic lattice deformation.
• The strength of the conductance dips increased with increasing lattice strain, demonstrating a direct correlation between strain magnitude and miniband visibility.
• The observed transport behavior was successfully reproduced using a tight-binding model where lattice deformation modulates inter-atomic hopping integrals.
• The 2D material-nanoparticle heterostructure enables scalable, solution-processed band structure engineering without complex lithography.
• The results confirm that mesoscale spatial patterning via self-assembly can be used to engineer electronic properties in 2D materials.
• This approach provides a promising route for large-area, low-cost electronics and optoelectronics based on artificial 2D superlattices.