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FEMTOSECOND LASER FABRICATION OF MICRO/NANO-STRUCTURES FOR CHEMICAL SENSING AND DETECTION Student : Yukun Han MAE Department Faculty Advisors : Dr. Hai-Lung Tsai MAE Department Dr. Hai Xiao ECE Department Introduction and Background ND Filter l/2 Wave Plate Polarizer Shutter Dichroic mirror CCD Driver Computer Wavelength: 800 nm Pulse Width: 120 fs Repetition Rate: 1 kHz Coherent Legend Coherent OPerA Frequency conversion (300nm – 3000nm) Objective lens (NA 0.3 -0.9) Sample (glass, polymer, tissue……) Five-axis Stage Lamp Monitor Experimental Setup Major Parameters of Ti: Sapphire Femtosecond Laser System Pulse Width: 120 fs Wavelength: 300 nm–3000 nm Pulse Energy: 1 mJ Repetition Rate: 1 kHz Average Power: 1 W Minimum Spot Size: < 1 µm Spatial Mode: TEM 00 5-axis CNC Operations Coherent Legend Femtosecond Laser System Scanning Electron Microscopy Images of A Fiber Probe Periscope Optical Parametric Amplifier Illuminato r Shutter Humidity meter Camera Turning mirror Half-wave Plate Polarizer Damper ND filters Turning mirror 90º Flipper 50-50 Beam Splitter One-Step Fabrication of Silicon SERS Substrate Results-SERS Substrate on Silicon SERS Spectra of R6G (10 -6 M solution) Conclusion A fiber probe for SERS detection has been demonstrated by femtosecond laser machining with post chemical silver planting. The enhancement factor of the SERS substrate is up to 10 6 . we also present a way to ablate the silicon SERS substrate and reduce the silver ions simultaneously by femtosecond laser pulses. The process confirms the silicon SERS substrate can be completed with one step fabrication with EF of 5.4×10 5 . The high controllability and high efficient femtosecond laser fabrication make the miniaturized sensors attractive for many applications in chemical and biological sensing. Future Work Working on investigating the laser-silicon interaction mechanisms that lead to the SERS enhancement. Designing sensors for further chemical and bio applications. Acknowledgment The research work was supported by Intelligent Systems Center, Missouri S&T. Minimal heat- affected-zone High precision Capable of processing any material Improved 3D resolution Surface modification Femtosecond Laser Micromachining Advantages: Miniaturizatio n Trend: MEMS (Microelectromechanical systems) Biotechnology Medical industry Environmental technology Information technology Microelectronics industry Microoptics technology Results- SERS Substrate on Fused Silica 500 µm 0 50000 100000 150000 200000 250000 700 900 1100 1300 1500 1700 Intensity (counts) Ram an shift(cm -1 ) a b c d (10) Raman spectra of Rhodamine 6G (R6G) with a 1.7 mW He-Ne laser excitation power and 1 sec integration time. (a) freshly cleaved fiber in a 10 -3 M solution, (b) fs laser ablated, silver-coated (10 min) fiber SERS probe (1 m long) in a 10 -6 M solution, (c) fs laser ablated, silver- coated (10 min) planar fused silica SERS substrate in a 10 -6 M solution with front excitation (shifted), and (d) silver-coated (10 min) unroughened fiber (1 m long) in a 10 - 3 M solution (multiplied by 10). Femtosecond Laser Micromachining Silver Chemical Planting (Tollen’s reaction) SERS Signals Detection Raman scattering is an inelastic scattering of photons for materials analysis SERS is a surface sensitive technique : The largest enhancements occur for metal (e.g., silver, gold, copper) surfaces which are rough on the nanoscale. Fiber SERS Probe Fabrication Surface Enhanced Roman Scattering (SERS) Background 6 2.5 10 SERS nR nR SERS I N EF I N SERS enhancement factor (EF) calculation: Immersing in AgNO 3 for 10 minutes AgNO 3 film Objectiv e lens Cleaning in acetone Silicon SERS substra te 2AgNO 3 → 2Ag + 2NO 2 ↑ + O 2 Laser ablatio n of silicon Periodic structures on silicon Silver particles are reduced from ions Silicon SERS substrate Platinum protection coating AgNO3 coating Silicon substrate Scanning Electron Microscopy Images of Silicon SERS Substrate a Raman shift (cm -1 ) Intensity (counts) (a) Raman spectrum of R6G 10 -6 M solution on laser ablated SERS silicon substrate with an excitation laser power of 1.7 mW and integrated time of 2 sec. (b) Raman spectrum of R6G 10 -3 M solution on the unablated silicon substrate with pre AgNO 3 soaking with an excitation power of 17 mW and integrated time of 2 sec. EF was estimated to be 5.4×10 5 500µm

FEMTOSECOND LASER FABRICATION OF MICRO/NANO-STRUCTURES FOR CHEMICAL SENSING AND DETECTION Student: Yukun Han MAE Department Faculty Advisors: Dr. Hai-Lung

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Poster TemplateStudent: Yukun Han MAE Department
Faculty Advisors: Dr. Hai-Lung Tsai MAE Department
Dr. Hai Xiao ECE Department
Introduction and Background
Pulse Width: 120 fs
Pulse Energy: 1 mJ
Repetition Rate: 1 kHz
Average Power: 1 W
Spatial Mode: TEM00
5-axis CNC Operations
One-Step Fabrication of Silicon SERS Substrate
Results-SERS Substrate on Silicon
Conclusion
A fiber probe for SERS detection has been demonstrated by femtosecond laser machining with post chemical silver planting. The enhancement factor of the SERS substrate is up to 106.
we also present a way to ablate the silicon SERS substrate and reduce the silver ions simultaneously by femtosecond laser pulses. The process confirms the silicon SERS substrate can be completed with one step fabrication with EF of 5.4×105.
The high controllability and high efficient femtosecond laser fabrication make the miniaturized sensors attractive for many applications in chemical and biological sensing.
Future Work
Working on investigating the laser-silicon interaction mechanisms that lead to the SERS enhancement.
Designing sensors for further chemical and bio applications.
Acknowledgment
The research work was supported by Intelligent Systems Center, Missouri S&T.
Minimal heat-affected-zone
High precision
Improved 3D resolution
Results- SERS Substrate on Fused Silica
Raman spectra of Rhodamine 6G (R6G) with a 1.7 mW He-Ne laser excitation power and 1 sec integration time.
(a) freshly cleaved fiber in a 10-3 M solution,
(b) fs laser ablated, silver-coated (10 min) fiber SERS probe (1 m long) in a 10-6 M solution,
(c) fs laser ablated, silver-coated (10 min) planar fused silica SERS substrate in a 10-6 M solution with front excitation (shifted), and
(d) silver-coated (10 min) unroughened fiber (1 m long) in a 10-3 M solution (multiplied by 10).
Femtosecond Laser Micromachining
SERS Signals Detection
Raman scattering is an inelastic scattering of photons for materials analysis
SERS is a surface sensitive technique : The largest enhancements occur for metal (e.g., silver, gold, copper) surfaces which are rough on the nanoscale.
Fiber SERS Probe Fabrication
SERS enhancement factor (EF) calculation:
Scanning Electron Microscopy Images of Silicon SERS Substrate
(a) Raman spectrum of R6G 10-6M solution on laser ablated SERS silicon substrate with an excitation laser power of 1.7 mW and integrated time of 2 sec.
(b) Raman spectrum of R6G 10-3M solution on the unablated silicon substrate with pre AgNO3 soaking with an excitation power of 17 mW and integrated time of 2 sec.
EF was estimated to be 5.4×105
500µm
ND
Filter
l/2
AgNO3 film
Objective lens
Silicon SERS substrate