Research

Our laboratory integrates scanning probe microscopy and fabrication of custom materials and nanodevices. We aim to advance knowledge of physical phenomena that emerge as a result of low dimensionality, presence of surfaces and interfaces, and proximity between different states of matter.


Projects at Argonne National Laboratory, Center for Nanoscale Materials 

 

  • Strongly correlated layered materials in the atomically thin limit

    • Understand the changes in the electronic properties of 1T-TaS2 from bulk to single layers.

 


Projects from Ph.D. thesis at Rutgers in Prof. Eva Andrei lab

 

  • Spatially resolved electronic properties of graphene in the quantum Hall regime

             In the presence of a magneti c
field, normal to the plane, the
 energy spectrum of graphene 
breaks up into a sequence of
 discrete Landau levels (LLs).

Observation of Landau levels - Using Scanning tunneling microscopy and spectroscopy (STM/STS) we observed the LLs on different substrates: graphene on graphite, graphene on SiO2, graphene on boron nitride. 

Phys. Rev. B 83, 041405(R)  (2011)

Nature Communications 4, 1744 (2013)

Phys. Rev. Lett. 102, 176804 (2009)

Solid State Communications, 149, 27–28, (2009)

Physica B, 404, p. 2673 (2009)

Tuning the carrier concentration - Using a sample geometry where graphene flakes are placed on the surface on a Si/SiO2 wafer we measured the  dependence of the LL spectrum on charge-carrier density.

Phys. Rev. B 83, 041405(R)  (2011)

Rev. Sci. Instruments. 82, 073701 (2011) 

Effects of a single charged impurity on the LLs - Performing spatially resolved STM/STS we demonstrate, for the first time, the true discrete quantum mechanical electronic spectrum within the Landau level band near an impurity in graphene in the quantum Hall regime. 

Phys. Rev. Lett. 112, 036804 (2014)

arXiv:1504.0740 (2015)

 

  • Graphene with a twist

If two layers of graphene stack on top of each other in the
 equilibrium Bernal stacking, we obtain a massive Dirac
 fermion system - bilayer graphene. If, however, we rotate the 
top layer with respect to the bottom one we obtain a new material system - twisted
 bilayer graphene. 

Our experiments were the first 
demonstration that these systems have angle-tunable
 electronic properties distinctly different than the single layer
 graphene or the bilayer graphene.  Scanning tunneling microscopy (STM) reveals the emerging Moiré patterns associated with the twist and. Scanning tunneling spectroscopy (STS) showed in the density of states the presence of two Van Hove singularities, as consequence of saddle points in the band structure. The hybridized cones of the corresponding two twisted layers create those points. Moreover, when measured in the presence of a magnetic field, from the spacing and field dependence of the LL, the Fermi velocity is found to depend strongly on the angle.

Nature Physics 6, 109 - 113 (2010) 

          Phys. Rev. Lett. 106, 126802 (2011)