Supporting Information for
“Enhancement of graphene thermoelectric performance through defect engineering”
Yuki Anno, Yuki Imakita, Kuniharu Takei, Seiji Akita, and Takayuki Arie*
Department of Physics and Electronics, Osaka Prefecture University
1-1 Gakuen-cho, Nakaku, Sakai, Osaka 599-8531, Japan
1. Thermal conductivity measurement of the suspended graphene with defects
Figure S1. (a) Raman 2D peak shift as a function of the substrate temperature. Inset shows the Raman raw data with a Lorentzian fitting at 293 K and 393 K. (b) Actual Raman 2D peak at the two different laser power.The peak shift represents the temperature difference induced by the laser.
We measured the thermal conductivity of suspended graphene with defects using Raman spectroscopyaccording to the reference [24].The sample used for the thermal measurement was single domain, monolayer graphene synthesized by CVD.Raman spectra was obtained by using a 532 nm wavelength laser with a 100× objective lens (NA=0.9).Initially, the position of Raman 2D peak as a function of the temperature was measuredwith increasing the substrate temperature (Fig. S1(a)). The measured temperature coefficient of Raman 2D peaks was calculated to be -0.118 cm-1/K. We then measured the Raman 2D peak when the suspended graphene was optically heated by the laser.Since the relativelyhigh laser power induce the temperature rise at the center of the graphene membrane as shown in Fig. S1(b), we can estimate the thermal conductivity of graphene using the equation given by [24]
(1)
where R is the radius of the hole, r0 is the radius of the laser, t is the thickness of graphene, Q is the power absorbed by the suspended graphene, is the temperature difference between the center of the graphene (Tg) and room temperature (T0).
2. Thermal conductivity measurement of the graphene with defects supported on SiO2
Figure S2.(a) Raman 2D peak shift with respect to the laser power absorbed by supported graphene. Two different objective lenses, 100× and 50× are used for estimating the thermal conductivity. Inset shows the Raman 2D peak shift with two laser powers. (b) Thermal conductivity of supported graphene with respect to D/G. Inset represents the relative thermal conductivity estimated from suspended and supported graphene samples.
The thermal conductivity of graphene supported on SiO2/Si substrates was measured using Raman spectroscopy according to the reference [24, 31]. The Raman 2D peak shift was also used for the measurement. The laser with the wavelength of 532 nm was focused on the graphene for optical heating and Raman measurement using the 100× and 50×objective lenses with NA=0.9 and 0.5, respectively. The temperature rise at the graphene by the laser irradiation was estimated using the equation written as [31]
(2)
where P is the laser power absorbed by the supported graphene and χis the temperature coefficient of the Raman 2D peak. Fig. S2(a) shows the 2D peak shift with 100× and 50× objectives as a function of the absorbed laser power, which is described as in Eq. 2. For estimating the thermal conductivity of the supported graphene, the thermal resistance , and total interfacial thermal conductance per unit area g are defined. From the linear relation between the temperature and absorbed laser power, , Rm was estimated to be 7.34 × 105 K/W for 100× and 4.38 × 105 K/W for 50× objectives. Fig. S2(b) summarizes the thermal conductivity of graphene with defects supported on the SiO2/Si substrate. The thermal conductivity for the supported pristine graphene is 543 W/mK, which is in the range of the reported room temperature thermal conductivity values of exfoliated graphene supported on SiO2[32]. Clearly, with increasing D/G the thermal conductivity decreases. The thermal conductivity of graphene with defectsrelative to that of the pristine graphene (Fig. S2(b) inset) indicates the same trend for the reduction in the thermal conductivity. Therefore, ZT values are expected to be enhanced not only for suspended but for supported graphene samples as the defect density increases.
3. Enhancement of ZT values for supported graphene samples
Figure S3.Normalized ZT values, ZT/ZT0, for supported graphene samples with respect to D/G at room temperature.
Using the thermal conductivity obtained from the graphene samples supported on SiO2, we calculated the ZT values with respect to D/G. Similar to the results from suspended graphene samples, at the low defect density,normalized ZT is almost constant, while at the high defect density, ZT increases 2.2 times with increasing D/G.
1