Terahertz imaging and spectroscopy of large-area single-layer graphene

Abstract

We demonstrate terahertz (THz) imaging and spectroscopy of a 15 × 15-mm2 single-layer graphene film on Si using broadband THz pulses. The THz images clearly map out the THz carrier dynamics of the graphene-on-Si sample, allowing us to measure sheet conductivity with sub-mm resolution without fabricating electrodes. The THz carrier dynamics are dominated by intraband transitions and the THz-induced electron motion is characterized by a flat spectral response. A theoretical analysis based on the Fresnel coefficients for a metallic thin film shows that the local sheet conductivity varies across the sample from σ(s) = 1.7 × 10(-3) to 2.4 × 10(-3) Ω(-1) (sheet resistance, ρ(s) = 420 - 590 Ω/sq).

High-Contrast Imaging of Graphene via Time-Domain Terahertz Spectroscopy

“…This result agrees very well with our previous work (σ s 02.04×10 −3 Ω −1 ), where we used a Si: Bolometer to measure the transmitted THz power through the sample [14].…”

“…THz spectroscopy of epitaxial graphene on SiC has shown that the carrier scattering time is estimated as~2 fs [13]. It was recently demonstrated that THz imaging and spectroscopy of a large-area, single-layer graphene film clearly mapped out the THz carrier dynamics of the graphene and measured the sheet conductivity with sub-mm resolution without fabricating electrodes [14].…”

Terahertz graphene optics

“…In addition, most of the far-IR work to date has only measured the relative change in transparency/reflectivity/conductivity, and not the absolute value, which is more difficult to ascertain. A complementary time-domain (sub-ps pulse) technique has demonstrated sheet conductivity of single-layer graphene of up to 30 e 2 /4ħ from 0.5-2 THz at room temperature [6], and low temperatures [7]. These time-domain techniques provide lower spectral resolution than the continuous wave (CW) frequencydomain techniques presented here, but in principle yield the same physical information.…”

Terahertz Properties of Graphene

“…In the THz regime, however, a Drude absorption peak is expected due to free carriers [40]. This prediction has been tested on both CVD and epitaxially grown graphene, using both THz TDS and far-IR Fourier transform interferometer (far-IR FTIR) spectroscopy [40][41][42][43].…”

“…In addition to these FTIR measurements, Tomaino et al utilised THz time domain spectroscopy to map the carrier dynamics of a large area CVD sample on a silicon substrate with > 90% monolayer coverage [43]. THz transmission through the sheet as a function of position was measured, and used to deduce the local sheet conductivity, σ s .…”