Density of States and
Its Local Fluctuations Determined in Disordered
→ For disordered graphene,
theoretical predictions suggest that as the disorder strength increases, the average density of states (ADOS) increases accordingly, in comparison with
pristine graphene. The changes of the ADOS near the charge neutrality point
(NP) still remain ambiguous and under debate.
One of the theoretical
predictions on disordered graphene suggested that the ADOS followed a power
law. Thus, the ADOS is expected
to increase when disorder becomes stronger in graphene.
demonstrate that fluctuations of the local density of states (LDOS) in strongly
disordered graphene play an
important role in determining the quantum capacitance of the top-gate graphene
devices. Depending on the
strength of the disorder induced by metal-cluster decoration, the measured
quantum capacitance of disordered
graphene can dramatically decrease in comparison with pristine graphene. This
is opposite to the common
belief that quantum capacitance should increase with disorder.
Figure 1 | (a) The
geometry of a top-gate Ag-decorated graphene device. The small white islands
represent the Ag clusters. (b) The equivalent circuit of the three-terminal
capacitance measurement. The p-Si substrate is grounded to avoid its parasitic
capacitance. (c) The quantum capacitance of one pristine graphene device
with Cox~1:14mF=cm2. The inset shows the optical image of the device. The
dashed line indicates the outline of the graphene flake and the scale bar is 5
mm. (d) The measured quantum capacitance of three Ag-decorated graphene devices
sputtered for 1 s, 5 s, and 10 s, respectively.
→To explain this
counterintuitive behavior, we present a two-parameter model which incorporates
both the non-universal power law behavior for the ADOS and a lognormal
distribution of LDOS. We find excellent quantitative agreements between the model
and measured quantum capacitance for three disordered samples in a wide range
of Fermi energies. Thus, by measuring the quantum capacitance, we can
simultaneously determine the ADOS and its fluctuations. It is the LDOS
fluctuations that cause the dramatic reduction of the quantum capacitance.
See details in the following paper by Click here .....