Robust mapping of electrical properties of graphene from terahertz time-domain spectroscopy with timing jitter correction

Whelan, Patrick Rebsdorf; Iwaszczuk, Krzysztof; Wang, Ruizhi; Hofmann, Stephan; Bøggild, Peter; Jepsen, Peter Uhd

doi:10.1364/oe.25.002725

Cited by 34 publications

(33 citation statements)

References 18 publications

(20 reference statements)

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“…The sheet conductivity of graphene on ∼500 μm thick high-resistivity Si is routinely determined from THz-TDS measurements by isolating the signal from one of the transients from internal reflections in the substrate [ Fig. 1(a)] by time-windowing [5,20,21]. The time between internal reflections in the PET substrate is much lower compared to standard Si substrates due to reduced thickness (∼225 μm in this case) and a lower refractive index at THz frequencies (∼1.75).…”

Section: Resultsmentioning

confidence: 99%

“…Figure 1(b) also highlights the necessity of treating the signal as a combination of the directly transmitted and internally reflected transients. The extracted sheet conductivity is seen to have a highly oscillatory appearance if we consider the signal as only consisting of a directly transmitted transient [20,21], which would increase the uncertainty on parameters extracted by fitting to the Drude model [Eq.…”

mentioning

confidence: 99%

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Conductivity mapping of graphene on polymeric films by terahertz time-domain spectroscopy

Whelan¹,

Huang²,

Mackenzie³

et al. 2018

Opt. Express

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Fast inline characterization of the electrical properties of graphene on polymeric substrates is an essential requirement for quality control in industrial graphene production. Here we show that it is possible to measure the sheet conductivity of graphene on polymer films by terahertz time-domain spectroscopy (THz-TDS) when all internally reflected echoes in the substrate are taken into consideration. The conductivity measured by THz-TDS is comparable to values obtained from four point probe measurements. THz-TDS maps of 25x30 cm area graphene films were recorded and the DC conductivity and carrier scattering time were extracted from the measurements. Additionally, the THz-TDS conductivity maps highlight tears and holes in the graphene film, which are not easily visible by optical inspection.

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Conductivity mapping of graphene on polymeric films by terahertz time-domain spectroscopy

Whelan¹,

Huang²,

Mackenzie³

et al. 2018

Opt. Express

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show abstract

“…The spectrally resolved conductivity in turn can be represented by a single real number. It has been shown that phase misalignment would only significantly affect the imaginary part of the conductivity 6 and therefore emphasis is placed only on the real part of the conductivity. As the conductivity spectra are approximately constant over the spectral range, the representative conductivity is taken as the average between 0.6 to 0.9 THz because at higher frequencies, the transmission conductivity spectra (see Supporting Information) become affected by water vapour absorption under ambient conditions.…”

Section: Resultsmentioning

confidence: 99%

“…A single step shift in time here corresponds to a sample being placed approximately 2.5 μm with respect to the reference mirror, and a positive value means that the sample position is shifted in the direction of the incident beam. We note that the phase compensation scheme can be alternatively implemented in the frequency domain by multiplying the phase shift term 6 .…”

Section: Methodsmentioning

confidence: 99%

Contactless graphene conductivity mapping on a wide range of substrates with terahertz time-domain reflection spectroscopy

Lin

Braeuninger‐Weimer

Kamboj

et al. 2017

Sci Rep

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We demonstrate how terahertz time-domain spectroscopy (THz-TDS) operating in reflection geometry can be used for quantitative conductivity mapping of large area chemical vapour deposited graphene films on sapphire, silicon dioxide/silicon and germanium. We validate the technique against measurements performed with previously established conventional transmission based THz-TDS and are able to resolve conductivity changes in response to induced back-gate voltages. Compared to the transmission geometry, measurement in reflection mode requires careful alignment and complex analysis, but circumvents the need of a terahertz transparent substrate, potentially enabling fast, contactless, in-line characterisation of graphene films on non-insulating substrates such as germanium.

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“…1 (e)] was performed at the Department of Photonics Engineering at the Technical University of Denmark, using a Picometrix T-ray 4000 system described in detail elsewhere [27]. For transmission mode measurements the conductivity was extracted from the directly transmitted pulse after applying corrections for timing jitter as described in ref [28]. Scanning was performed with a static detector and scanning the samples in the x and y directions.…”

Section: Terahertz Time-domain Spectroscopymentioning

confidence: 99%

Quality assessment of terahertz time-domain spectroscopy transmission and reflection modes for graphene conductivity mapping

et al. 2018

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We present a comparative study of electrical measurements of graphene using terahertz time-domain spectroscopy in transmission and reflection mode, and compare the measured sheet conductivity values to electrical van der Pauw measurements made independently in three different laboratories. Overall median conductivity variations of up to 15% were observed between laboratories, which are attributed mainly to the well-known temperature and humidity dependence of non-encapsulated graphene devices. We conclude that terahertz time-domain spectroscopy performed in either reflection mode or transmission modes are indeed very accurate methods for mapping electrical conductivity of graphene, and that both methods are interchangeable within measurement uncertainties. The conductivity obtained via terahertz time-domain spectroscopy were consistently in agreement with electrical van der Pauw measurements, while offering the additional advantages associated with contactless mapping, such as high throughput, no lithography requirement, and with the spatial mapping directly revealing the presence of any inhomogeneities or isolating defects. The confirmation of the accuracy of reflection-mode removes the requirement of a specialized THz-transparent substrate to accurately measure the conductivity.

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Robust mapping of electrical properties of graphene from terahertz time-domain spectroscopy with timing jitter correction

Cited by 34 publications

References 18 publications

Conductivity mapping of graphene on polymeric films by terahertz time-domain spectroscopy

Conductivity mapping of graphene on polymeric films by terahertz time-domain spectroscopy

Contactless graphene conductivity mapping on a wide range of substrates with terahertz time-domain reflection spectroscopy

Quality assessment of terahertz time-domain spectroscopy transmission and reflection modes for graphene conductivity mapping

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