Dear colleagues,
My name is Konstantin Gochua and I am currently conducting my postdoctoral research on the fabrication of graphene- and boron-nitride based transistor structures and study of their optical properties in THz and far-IR range and I kindly request you to answer my following question:
We're performing an experiment on extraction of graphene sheet conductivity by THz time domain spectroscopy. A sheet of graphene is transferred on a moderately doped p-Si substrate. The substrate thickness is ~725 mkm, it is slightly oxidized atop (~100 nm SiO2). The THz time domain spectrometer measures the transmission coefficient through the stack, and the relative phase between two beams (one passes through the stack and another one travels in vacuum). The information is obtained in ~1-3 THz range of frequencies at once, as the source emits quite narrow (broadband) pulses from photoconductive antenna. Attached you can find examples of measured transmission and phase of bare Si/SiO2 substrate without graphene, and the same substrate with graphene (we just measured in a different position).
My question is how to extract the frequency dependence of graphene conductivity \sigma(\omega) (units Ohm^-1).
It is expected that silicon substrate has the DC conductivity of 10 Ohm-1m-1, its permittivity is approx 11. This data can be refined by fitting the transmission/phase spectra.
Please also take into account that the phase is determined accurately within to a constant, we also don't know exactly the path of beam in vacuum, so a linear function of frequency can also be freely subtracted.
Best regards and thank you in advance,
Konstantin.
If you mean measuring by extracting and as I understood your question, I think you need to deposit two ohmic contact on graphene surface with very small separation distance (few microns) then you can use your spectrometer or suitable impedance analyzer or vector network analyzer.
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