## 4 Results
### Microheater Characterization  
To enhance the sensor's sensitivity and selectivity and to achieve ultra-fast response and recovery times, a microheater and a temperature sensor were integrated into the SAW sensor. The temperature sensor is specifically used to monitor the performance of the microheater. For calibration, a known external temperature is applied, and the resistance of the temperature sensor is measured. Then, voltage is applied to the microheater, and the corresponding resistance change in the temperature sensor is monitored to assess the temperature variation induced by the microheater. During testing, the sensor was integrated into the microprobe system (NEXTRON Co., Busan, Republic of Korea), and external temperatures were applied using the MPS temperature controller (NEXTRON Co.). Resistance changes were measured with respect to the externally applied temperature to establish a calibration dataset for future experiments involving voltage application. The measurement system consisted of a chamber equipped with a microprobe system (NEXTRON Co.), a controller (NEXTRON Co.), and a power supply to regulate the sensor surface temperature by applying voltage to the microheater. A source meter (Keithley-2400, Seoul, Republic of Korea) was used to precisely measure the resistance of the sensor. The voltage was supplied through a 4-probe connection, and the change in resistance was monitored using the source meter. Temperature control was managed via the NEXTRON automated program. Data from the temperature sensor were analyzed in real time and saved for calibration purposes. The resistance-temperature correlation data, which are critical for calibrating voltage-driven thermal responses, are presented already in detail in the manuscript. Figure 8 illustrates the temperature change on the SAW sensor surface when voltage is applied to the integrated microheater. As shown in Figure 8a, the resistance of the temperature sensor increases with externally applied temperature, confirming its sensitivity to temperature variations. Figure 8b presents the calibrated temperature sensor response, demonstrating a linear trend with a high coefficient of determination (R\({}^{2}\) = 0.998), ensuring accurate temperature measurement. Figure 8c depicts the temperature variation of the microheater at different applied voltages, confirming that the temperature reaches 90 \({}^{\circ}\)C with a 12.5 V input to the microheater (calibrated through the resistance change in the temperature sensor), which is slightly different than the simulation result because of differences between the simulated and real-world conditions, such as heat loss, material properties,  
Figure 7: Raman peaks of (**a**) the deposited MoS\({}_{2}\) film and (**b**) the transferred graphene. and experimental setup variations. This figure further confirms the microheater's response time and long-term stability as a function of applied voltage, showing that the temperature remains steady and approaches a stable condition (rather than saturation). Figure 8d presents the temperature measurements on the sensor surface and calibrated resistance change measurements of the temperature sensor. The power consumed by the microheater at 12.5 V is 2.5 W. Additionally, the temperature change detected by the temperature sensor quickly reaches stability. Once this is achieved, the temperature remains stable for an extended period, demonstrating rapid recovery time and excellent repeatability, as confirmed by the integrated temperature sensor. Figure 8e shows the temperature distribution across the entire SAW sensor surface, captured by an infrared camera (FLIR C5, Seoul, Republic of Korea), in response to the applied voltage to the microheater. The emissivity value used to measure the temperature was set to 0.8, as MoS\({}_{2}\)/graphene composites typically have emissivity values around 0.8 [30; 31; 32; 33]. A theoretical model explaining the thermodynamics of multi-material properties is discussed in other studies [30; 31; 32; 33].