1

Supporting Information

Stretchable Graphene Thermistor with Tunable

Thermal Index

Chaoyi Yan, Jiangxin Wang, Pooi See Lee*

School of Materials Science and Engineering, 50 Nanyang Avenue, Nanyang Technological

University, Singapore, 639798

*Address correspondence to pslee@ntu.edu.sg.

Figure S1. Resistance comparison of highly conductive AgNW electrodes and resistive

graphene channel. (a) Resistance variations of AgNW and graphene within 0-50% strains.

Graphene resistance was measured at 30 °C and AgNW resistance was measured at room

temperature (~25 °C). (b) Plot showing the ratio between R(Graphene) and R(AgNW). The

resistance of graphene is ~6 orders of magnitude higher than that for AgNW electrodes, thus

the contribution of AgNW electrodes to overall device resistance is negligible.

2

Figure S2. (a,b) Cross-sectional schematic illustrations of the device layouts before and after

being embedded into PDMS substrate. (c,d) SEM images of the AgNW-graphene junction

area before embedding. Graphene layer was on top of AgNW electrodes after filtration so

that the electrodes can be exposed after embedding for electrical connection.

3

Figure S3. The dependence of device resistance on temperature is non-linear, as revealed by

the attempted linear fitting results in (a). A good linear fitting between ln(R) and 1/T was

obtained, as shown in (b).

4

Figure S4. (a) Cross-sectional schematic diagram of the stretched thermistor device on glass

slide. The device was first fixed at one end, then stretched to desire strain and fixed at the

other end using binder clips. (b,c) Image of the thermistor on glass slide substrate at 0% and

50% strains, respectively.

5

Figure S5. I-V curves of the thermistor device at various strains from 0% to 50%. The

vertical axes were set at the same scale for comparison. The temperature range was 30 °C to

100 °C (step 5 °C) at all strains as indicated in (a). Calculated resistance variations with

temperature at different strains are shown in Figure 4a, main text.

6

Figure S6. Thermal index variation upon repeated stretching. (a) Measured thermal index

after 1, 50 and 100 stretching cycles to 50% strain. The thermal properties of graphene

thermistors are stable and can return to initial values after mechanical stretching. (b)

Comparison of thermal index at relaxed state (after repeated stretching) and those at stretched

states.

7

Figure S7. Schematic illustration of the rate limiting step in response behavior measurements.

The graphene detection channel is exposed on top of the PDMS substrate and thus is in direct

contact with the cool air, resulting in a fast response process. However, when the temperature

perturbation was stopped and the thermistor was allowed to recover, the temperature of the

graphene channel experienced a much slower recovering process due to the low thermal

conductivity of PDMS substrate.

PDMS

AgNW AgNWGraphene

Cool Air (~25 °C)

Heating Stage (50 °C)

Direct contact with

graphene channel

Fast heat transferGlass Slide

Slow heat transfer

(rate limiting step)