Micromachined Chip Scale Thermal Sensor. for Thermal Imaging

Transcription

1 Micromachined Chip Scale Thermal Sensor for Thermal Imaging Gajendra S. Shekhawat, #*1 Srinivasan Ramachandran, *2 Hossein Jiryaei Sharahi, 3 Souravi Sarkar, 1 Karl Hujsak, 1 Yuan Li, 1 Karl Hagglund, 1 Seonghwan Kim, 3 Gary Aden, 2 Ami Chand, 2# and Vinayak P. Dravid, 1# 1 Department of Material Science and Engineering and NUANCE Center, Northwestern University, Evanston, IL APPNANO, 415 Clyde Ave., Mountain View, California Department of Mechanical and Manufacturing Engineering, University of Calgary, AB, Canada.

2 Figure S1. Schematic showing the AFM optical lever laser position for temperature mapping mode (TMM) and conductivity mapping mode (CMM).

3 The probe design allows easy switching between temperature and conductivity mapping modes by adjusting the position of AFM optical lever laser. In the CMM, the laser is positioned in such a way that it spills into the hollow pyramid and heats up the thermocouple (typically 20 C above the ambient) while having enough SUM signal for monitoring the feedback deflection signal for AFM imaging. This obviates the need for expensive precision current source that is required in thermistor based systems. In TMM, the laser is pulled back to minimize heating the thermocouple. Offsetting the background temperature signal and thermal calibration of the probe ensures accurate determination of sample temperature. Figure S2. Finite element simulation of temperature contrast on silica-coated gold nanoparticle. (a) Heat flow from tip to the homogenous silica sample without gold nanoparticle. In this case the nanoparticle element has the same material properties of silica. (b) Heat flow from tip to the silica-coated gold nanoparticle. Because of high thermal conductivity of gold, the tip temperature is decreased to C.

4 To show that the thermocouple can be heated to high temperatures without cantilever bending, an external laser (10 mw) was focused on the tip and its power was modulated by pulse width from 0.1 to 85.1% duty cycle at 30 khz. The power was changed every 5 seconds and the tip temperature was every 150 msec. The amplifier gain was Figure S3. Thermal probe temperature over a period of time. Thermal Probe Temperature vs Time Temperature (C) Time (s) 1000x and the bandwidth about 3 khz. The Thermal data showed (Figure S3) linear behavior throughout the temperature range and was symmetrical going up and down from room temperature (23 C) up to 760 C. This ability to measure extended temperatures has potential applications in thermo mechanical analysis and determination of phase transition temperature etc.

5 Materials and Methods Figure S4. Schematic of thermal system interface with AFM. Topography Data Pathway Probe Calibration: For accurate measurement of surface temperature, the sensitivity of the Thermal Probe AFM Scanner AFM Computer thermal probe (µv/ C) is required which is determined by calibrating it Electronic Amplifier against a range of known temperatures. A probe was brought Thermal Data Pathway into contact with the micro heater that is integrated with a standard K-type thermocouple. The heater is programmed to reach a set point temperature through a PID controller with feedback from the integrated Voltage response of the thermocouple probe. The thermocouple sensor behaves linearly with an R 2 coefficient of 0.99 over the investigated temperature range. reference thermocouple. The thermal probe is allowed to stabilize before recording its

6 temperature. This process is repeated for several temperatures (25 to 200 C) to determine its thermal sensitivity. The sensitivity of these probes found to be between 9-13 µv/ C. Figure S5. Thermal conducting mapping across the silicon surface and b) thermal profile across the image demonstrate negligible temperature variation thus eliminating any change due to other variables in the experiment.

7 To rule out thermal contrast arising from other factors like variations in laser intensity/environmental changes, we used a clean silicon wafer as a control to check for any variations in temperature across the surface Fig.S5 shows a uniform surface temperature with variation around 0.02 C. The thermal profile clearly indicates negligible effect from other variables in the thermal contrast.