Transcript Poster Template - Intelligent Systems Center

FEMTOSECOND LASER FABRICATION OF MICRO/NANO-STRUCTURES FOR
CHEMICAL SENSING AND DETECTION
Student: Yukun Han
Faculty Advisors:
MAE Department
Introduction and Background
Dr. Hai-Lung Tsai
Dr. Hai Xiao
MAE Department
ECE Department
Results-SERS Substrate on Silicon
Femtosecond Laser System
Femtosecond Laser Micromachining Advantages:
Major Parameters of Ti: Sapphire Femtosecond Laser System
 Pulse Width: 120 fs
 Minimal heat-affected-zone
 Minimum Spot Size: < 1 µm
 Wavelength: 300 nm–3000 nm
 High precision
 Pulse Energy: 1 mJ
 Capable of processing any
Laser
ablation
of silicon
 Spatial Mode: TEM00
Objective
lens
 5-axis CNC Operations
 Repetition Rate: 1 kHz
material
One-Step Fabrication of Silicon SERS Substrate
 Average Power: 1 W
Silicon
SERS
substrate
AgNO3
film
2AgNO3 → 2Ag + 2NO2↑ + O2↑
Periodic
structures on
silicon
Silver particles
are reduced
from ions
Immersing in
AgNO3 for 10
minutes
 Coherent Legend
Cleaning in
acetone
Silicon SERS
substrate
 Improved 3D resolution
 Surface modification
Results- SERS Substrate on Fused Silica
Scanning Electron Microscopy Images of Silicon SERS Substrate
Surface Enhanced Roman Scattering (SERS) Background
AgNO3 coating
Miniaturization Trend:
 Raman scattering is an inelastic scattering of photons for materials
analysis
 MEMS
(Microelectromechanical systems)
 Biotechnology
 Medical industry
 Environmental technology
 Information technology
 Microelectronics industry
 Microoptics technology
Fiber SERS Probe Fabrication
500 µm
500µm
40000
 (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.
30000
20000
b
EF was estimated to be 5.4×105
0
400
600
800
1000
1200
1400
1600
1800
Raman shift (cm-1)
Silver Chemical
Planting (Tollen’s
reaction)
SERS Signals
Detection
Conclusion
Monitor
Scanning Electron Microscopy Images of A Fiber Probe
Lamp
l/2
Wave Plate Polarizer
ND
Filter Shutter
Coherent
OPerA
Objective lens
(NA 0.3 -0.9)
 The high controllability and high efficient femtosecond laser
fabrication make the miniaturized sensors attractive for many
applications in chemical and biological sensing.
Sample (glass, polymer,
tissue……)
SERS Spectra of R6G (10-6M solution)
Computer
Five-axis Stage
Driver
Raman spectra of Rhodamine 6G (R6G) with a 1.7
mW He-Ne laser excitation power and 1 sec
integration time.
250000
Illuminator
Half-wave Plate
d (10)
Turning
mirror
90º Flipper
Periscope
Polarizer
Turning mirror
Damper
ND filters
Camera
Intensity (counts)
200000
Optical Parametric
Amplifier
 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.
Dichroic mirror
Shutter
 (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.
50000
10000
CCD
Coherent
Legend
a
60000
Intensity (counts)
 SERS is a surface sensitive technique : The largest enhancements
occur for metal (e.g., silver, gold, copper) surfaces which are rough on
the nanoscale.
Experimental Setup
Frequency
conversion
(300nm –
3000nm)
Silicon
substrate
70000
Femtosecond Laser
Micromachining
Wavelength:
800 nm
Pulse Width:
120 fs
Repetition Rate: 1 kHz
Platinum protection
coating
 (a) freshly cleaved fiber in a 10-3 M solution,
150000
100000
50000
c
a
b
0
700
900
1100
1300
1500
1700
Future Work
 (b) fs laser ablated, silver-coated (10 min) fiber
SERS probe (1 m long) in a 10-6 M solution,
 Working on investigating the laser-silicon interaction mechanisms that
lead to the SERS enhancement.
 (c) fs laser ablated, silver-coated (10 min) planar
fused silica SERS substrate in a 10-6 M solution
with front excitation (shifted), and
 Designing sensors for further chemical and bio applications.
 (d) silver-coated (10 min) unroughened fiber (1 m
long) in a 10-3 M solution (multiplied by 10).
Raman shift (cm-1)
50-50 Beam
Splitter
Humidity
meter
SERS enhancement factor
(EF) calculation:
I SERS N nR
EF 
I nR N SERS
 2.5  10 6
Acknowledgment
The research work was supported by Intelligent Systems Center,
Missouri S&T.