Probing the charge transfer and electron-hole asymmetry in graphene-graphene quantum dot heterostructure

Possible charge ordering and anomalous transport in graphene/graphene quantum dot heterostructure

Observations of superconductivity and charge density waves (CDW) in graphene have been elusive thus far due to weak electron-phonon coupling (EPC) interactions. Here, we report a unique observation of anomalous transport and multiple charge ordering phases at high temperatures (T1∼213K,T2∼325K) in a 0D-2D van der Waals (vdW) heterostructure comprising of single layer graphene (SLG) and functionalized (amine) graphene quantum dots (GQD). The presence of functionalized GQD contributed to charge transfer with shifting of the Dirac point ∼ 0.05 eV above the Fermi level (ab initio   simulations) and carrier densityn∼-0.3×1012 cm-2confirming p-doping in SLG and two-fold increase in EPC interaction was achieved. Moreover, we elucidate the interplay between electron-electron and electron-phonon interactions to substantiate high temperature EPC driven charge ordering in the heterostructure through analyses of magnetotransport and weak anti-localization (WAL) framework. Our results provide impetus to investigate strongly correlated phenomena such as CDW and superconducting phase transitions in novel graphene based heterostructures.

The Electronic Origin of the Zeta Potential is Supported by the Redox Mechanism on an Aqueous Dispersion of Exfoliated Graphite

Herein we have proposed that a redox mechanism can produce surface charges and negative zeta potential on an aqueous graphite dispersion. Graphite was kept in contact with a concentrated ammonia aqueous solution, washed, and exfoliated in water, resulting in a dispersion with lyophobic nature. Ammonia treatment did not provide functional groups or nitrogen doping to graphite. Moreover, this material was washed twice before sonication to remove most hydroxide. Therefore, neither functional groups, nitrogen atoms, nor hydroxide excess is responsible for the zeta potential. Kelvin probe force microscopy has shown that the ammonia-treated and exfoliated graphite has higher Fermi level than the water-treated material, indicating that the contact between ammonia and graphite promotes redox reactions that provide electrons to graphite. These electrons raise the Fermi level of graphite and generate the negative zeta potential, consequently, they account for the colloidal stability.