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Density of States (DOS)

  • Density of States and Its Local Fluctuations Determined in Disordered Graphene


→ 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.

 

→We 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.

 

images/stories/QC5.jpg

 


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 .....

images/stories/QC6.jpg

 

 

 

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Copyright © 2013  Dr. Ning WANG. Department of Physics, The Hong Kong University of Science and Technology. All rights reserved.