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Applications of Raman in Science: Material Characterization and Measurements

Yusuke N1, Yongjie Zhan2, Sina Najmaei2, Jun Lou2

NanoJapan Program

1 Department of System Design Engineering, Keio University 2 Department of Mechanical Engineering and Material Science, Rice University

Raman spectroscopy is a powerful tool for characterizing and measuring . Synthesis of MoS2 films, a novel material with applications in technology, requires accurate and robust characterization. We applied to characterize CVD synthesized MoS2. This technique will provide information about existence and quality of these materials. In addition, we used Raman spectroscopy to measure and calibrate temperature in mechanical testing devices. These devices consist of a circuit designed for Joel heating of the samples and allow for mechanical measurements to be taken at elevated temperatures. Our aim is to correlate the input voltage or current to the temperatures reached in the samples.

Applications of Raman Spectroscopy in Material Science: Material Characterization and Temperature Measurements Replace w/ Logo Yusuke Nakamura1,2, Yongjie Zhan1, Sina Najmaei1, Jun Lou1 1NanoJapan Program, Department of Mechanical Engineering and Material Science, Rice University 2Department of System Design Engineering, Keio University

Introduction Methods (cont.) Results and Discussion (cont.)

Raman Spectroscopy: Mechanical Testing Device Single-layered or Few layered MoS2 A powerful tool to characterize chemical and physical properties of materials. Experimental Procedures Here I Have Applied This Technique to: 1. Pass current through the • Molybdenum Disulfide (MoS2) Raman device for Ohmic Heating Goal: Synthesis of single- and few-layered MoS2 by Chemical Vapor Lab 2. Scan the device via Raman Deposition (CVD) method. View Device Microscope after 90 sec. of ---> Chemical and quality characterization of MoS2 heating and record the spectra • Mechanical Testing Device 6. Use CPD to dry device Note: before CPD, do not expose device in air. 3. Turn off the power supply Goal: Mechanical testing at elevated temperatures and wait for 2 min. (for the --->To correlate the input power to ohmic Testing setupheating and procedures of the device by means Power In the following shows the manufactured devices. The MEMS devices present here are Conducting device to cool down) of Raman shift analysis parallel unfolded beam device and serial unfolded beam device. Supply Wire 4. Acquire similar data for different voltages Fig. 7 A simplified schematic of an experiment 5. Quantify silicon band Fig. 10 SEM images of MoS2 films (shown by red arrows) and gold particles on silicon position for each voltage and

[1] Fig. 2 MechanicalFig 26. Parallel unfolded Testing beam device Device [2] Fig. 1 3D representation of the structure of MoS2 Data Analysis : anti-Stokes intensity (1) : Stokes intensity : the of the Methods : the phonon of the laser : constant (2) T : absolute temperature CVD Method Fig 27. Serial unfolded beam device h :

! ! ! ! ! ! Many! different! ways !have been tried toquartz carry out the jouletube heating experiment for the k : Boltzmann constant MEMS device inside Raman spectroscopy. Here is the successful one. sulfur Fig. 11 MoS2 films synthesized by CVD method on gold substrate (3) C, D: constant depending on materials gas C = 10.53 /cm D = 0.587 Future Work gas inlet outlet MoS2 is on the whole surface. The red arrow shows the suspended MoS2. ! = 525 /cm (Raman line position at 0K) ! ! ---> Easy to remove it from Au The equation (3) is used to find the relationship between Raman shift and ! ! ! ! ! ! ! ! ! the corresponding temperature and input electrical current Mo sample 6000" quartz Mechanical ! 5000" Why is the boat exfoliated 4000" single- discrepancy? oven 750℃ layered N2 Results and Discussion 3000" Fig. 3 A Simplified Schematic of CVD experimental system MoS2! ---> CVD 2000" CVD synthesized

800 (a.u.) Intensity synthesized

) 1000" MoS2 is thicker ℃ Mechanical Testing Device 600 750 750 MoS2! 0" Au as a substrate : ! 900" ! 900& than and 800" 360" 370" 380" 390" 400" 410" 420" 400 500 800& 834.2& 761.2& 700" - No reaction with S 700& Raman!shi%!(/cm)! suspended. 600" 200 600& 538.9& 500" Temperature ( 500& Fig. 12 Raman shift - intensity relationship - Tight bonding with Mo 462.9& 400" 0 400& y = -44.302x + 23430! 385.0& 0 30 120 140 260 300& 300" 200& 200" Time (min.) 100& 100" Fig. 4 CVD process 0& 0" 508& 510& 512& 514& 516& 518& 520& 522& 0" 20" 40" 60" 80" 100" 120" 140" 160" 180" Temperature (K) Temperature Temperature (K) Temperature Raman shift (/cm)! Voltage (V)! References Mo (3nm) Fig. 8 Raman shift-temperature Fig. 9 Voltage-temperature relationship Au (300nm) Temperatures as high as 800K were achieved and temperature vs. voltage B. Radisavljevic et al., nature technology, 2011 Si characteristics of the device was quantified. Yezeng Cheng,Thermal MEMS Device Design, Simulation, Testing and Problem: Wire bonding due to weak Si Au adhesion Analysis, 2011 Fig. 5 Schematic of Synthesis of MoS2 ---> Solution: Deposit Cr on Si

Acknowledgments: This research conducted at Rice University as a participant of NanoJapan 2011 program supported by the National Science Foundation under Grant No. OISE – 0530220. Special thanks to Prof. J. Kono, S. Phillips, Dr. Lou, Y. Zhan, S. Najmaei, and P. Dong.