Plasmonic sensing of heat transport and phase change near solid-liquid interfaces
David G. Cahill and Jonglo ParkDepartment of Materials Science and Engineering
University of Illinois at Urbana-Champaign
supported by ONR
Collaboration with Patrick Hopkins and Pam Norris, U. Virginia
Motivation (big picture): Improve experimental methods for probing heat transfer and phase transformations at solid/liquid and vapor/liquid interfaces
• Prior study of thermal conductance of hydrophobic and hydrophilic interfaces with water
Ge et al., Phys. Rev. Lett. (2006)
Motivation (big picture): Improve experimental methods for probing heat transfer and phase transformations at solid/liquid and vapor/liquid interfaces
• Prior study of fast water desorption from a hydrophilic surfaces by time-resolved ellipsometry
Min et al., J. Phys. Chem. C (2012)
Outline
• Thermal conductance of interfaces
• Nanodisk sensors (prepared for us by Insplorion) and characterization of their sensitivity and depth resolution.
• Application to interface thermal conductance and thermal diffusivity of fluids by separating the response from the Au temperature and the index change in the adjacent fluid. (unpublished)
• Initial application to fast condensation and evaporation of a refrigerant (R124) from interfaces with controlled chemistry. (work in progress)
Thermal transport coefficients
• Thermal conductance (per unit area) G is a property of an interface
• Thermal conductivity is a property of the continuum
Interface conductance spans a factor of 60 range at room temperature
nanotube/alkane
W/Al2O3
Au/water
PMMA/Al2O3
Lyeo and Cahill, PRB (2006)
Insplorion nanodisk plasmonic sensors
• Fabricated by “hole-mask colloidal lithography”
• Au adhesion to SiO2 substrate is good even though they avoided the use of a conventional Cr or Ti adhesion layer (Cr or Ti would damp the plasmon)
Au disk diameter 120 ± 10 nm, height 20 ± 2 nm
SEM AFM
Sensitivity d(Tr)/dn (change in transmission coefficient with respect to optical index) approaches unity
• Coat with PMMA and take difference spectra of the absorption.
• Noise floor of pump-probe measurements should be
1/2
1/2
13 1/2
0.3 ppm Hz3 mK Hz
10 m Hzliquid
liquid
nT
h
Tr=transmission
Sensitivity to dn is localized to within 13 nm of the Au surface
• Atomic-layer deposition of alumina
• Assuming constant deposition rate per cycle
Long-pass optical filter
Short-pass optical filter
Kang et al., RSI (2008)
Time-domain thermoreflectance and transient absorption
Signal is a combination of the temperature change of the Au and the temperature (or pressure or density) change of the surroundings
• Isolate the two terms using a linear combination of the response at two wavelengths.
• “breathing mode” acoustic oscillation is minimized at the same wavelength that minimizes the sensitivity to fluid temperature.
( ) ( )
Au fluidAu fluid
d Tr d TrTr T TdT dT
Vary the contributions from TAu and Tfluid by varying wavelength of the probe light
0 1000 2000 3000 4000100
101
102
103
780 nm 790 nm 800 nm 810 nm 820 nm
Vin (
V)
time (ps)
Signal from the lateral “breathing mode” acoustic oscillation is minimized at the same wavelength that minimizes the sensitivity to fluid temperature
0 100 200 300 400 500-120
-80
-40
0
40
80
Vin(d
ata)
-Vin(th
erm
al)
time (ps)
780 nm 790 nm 800 nm 810 nm 820 nm
Data after subtracting thermal response
Modeling of heat transfer builds on our standard methods of analyzing TDTR data.
• Model the 120 nm diameter, 20 nm thick heat source as a 120 nm diameter uniform intensity laser beam heating a blanket 20 nm Au film that has zero in-plane thermal conductivity.
• dn/dT of the fluid dominates over dn/dT of the glass substrate so model the signal as a weighted average of the temperature of the fluid within 13 nm of the Au
Control the surface chemistry using self-assembled monolayers (thiol bond to Au surface)
• Plasmon resonance is a built-in diagnostic for what is happening near the interface.
1.32 1.34 1.36790
800
810
820
Pea
k w
avel
engt
h (n
m)
Refractive index (n)
hydrophilic
bare
hydrophobic
Water Ethanol1.0 1.2 1.4 1.6
720
740
760
780
800
820
840
Pea
k w
avel
engt
h (n
m)
Refractive index (n)
hydrophilic
bare
hydrophobic
Hydrophilic HS(CH2)3SO3 and hydrophobic HS(CH2)9CH3
Data acquisition and analysis for interfaces with fluid mixtures
• First step: select wavelength that minimizes contribution from fluid temperature
• Compare to thermal model with interface conductance as a free parameter using literature values for fluid thermophysical properties
100 101 102 103101
102
data (785 nm) 80 MW m-2 K-1
160 MW m-2 K-1
240 MW m-2 K-1
Vin (
V)
time (ps)100 101 102 103101
102
data (790 nm) 40 MW m-2 K-1
80 MW m-2 K-1
160 MW m-2 K-1
Vin (
V)
time (ps)
0% Ethanol (Water)
100% Ethanol
Data acquisition and analysis for interfaces with fluid mixtures• Next step: shift wavelength to provide greater sensitivity to
fluid temperature near the interface.• Subtract breathing mode acoustic signal by fitting to a
damped oscillator• Compare to thermal model with interface conductance as a
free parameter
100 101 102 103101
102
data (810 nm) data (810 nm) 80 MW m-2 K-1 (A = 0.65, B = 0.063) 120 MW m-2 K-1 (A = 0.65, B = 0.063) 180 MW m-2 K-1 (A = 0.65, B = 0.063) 240 MW m-2 K-1 (A = 0.65, B = 0.063)
Vin (
V)
time(ps)100 101 102 103101
102
data (810 nm) data (810 nm) 40 MW m-2 K-1 (A = 2, B = 0.25) 80 MW m-2 K-1 (A = 2, B = 0.25) 160 MW m-2 K-1 (A = 2, B = 0.25)
Vin (
V)
time(ps)
100 % Ethanol
0% Ethanol (Water)
Vary liquid composition between pure ethanol and pure water for hydrophobic SAM, hydrophilic SAM, and “bare” Au.
• Data for pure water and pure ethanol are in agreement with prior work for planar interfaces and supported nanoparticles.
• Data for pure ethanol are relatively insensitive to the interface chemistry.
• Competitive adsorption of water at the hydrophilic interface (?)
0.0 0.2 0.4 0.6 0.8 1.00
50
100
150
200
G (M
W m
-2 K
-1)
Ethanol / Water
hydrophilic
Bare
Hydrophobic
Kapitza lengthLK = /G ≈ 3 nm
Initial experiments on a refrigerant as a function of pressure
plasmonic substrate
R124 gas chromatograph analysis1-chloro-1,2,2,2-tetrafluoroethane (99.79%)1,1,1,2,2 – pentafluoropropane (0.21 %)
• Vapor pressure is ≈40 psi at lab temperature
200 300 400 500
10-1
100
101
102
Pre
ssur
e (p
si)
Teperature (K)
Data from NIST webbook (http://webbook.nist.gov/chemistry/)
wikipedia.org
Initial experiments are “frequency domain” (not “time-domain”) to access longer time scales
• Fixed negative delay time (probe pulse arrives 20 ps before pump pulse)
• Vary frequency of pump over a wide range (10 Hz to 10 MHz)• Correct for the phase and amplitude of the system response
using pump beam directly incident on the fast photodiode.• In vacuum, the signal is due to the Au temperature
100 101 102 103 104 105 106 107 108
-50
0
50
in-phase out-of-phase (negative)
V in, V
out (V
)
Frequency (Hz)100 101 102 103 104 105 106 10710-2
10-1
100
101
102
in-phase out-of-phase (negative)
V in, V
out (V
)
Frequency (Hz)
vacuum vacuum
Only at the highest frequencies (>1 MHz) is the temperature not laterally homogeneous on the length scale of the separation between Au nanodisks (200 nm)
100 101 102 103 104 105 106 107
10-2
10-1
100
101
102
Single nanodisk (r = 60 nm) r = 10 m
T
(K)
Frequency (Hz)100 101 102 103 104 105 106 107
-80
-60
-40
-20
0
Single nanodisk (r = 60 nm) r = 10 m
Pha
seFrequency (Hz)
Calculated thermal response, 3 mW pump
Now add R124 at 17 psi (approximately ½ of the vapor pressure)
• Difference between vacuum and 17 psi only appears at f<10 kHz.• Work in progress. Results are not what we were expecting. (Much
smaller and much slower).• Au surface is coated by hydrophobic SAM. Maybe not completely
stable in contact with refrigerant vapor• Will need to consider Maragoni effects (fluid flow) in addition to
evaporation/condensation
100 101 102 103 104 105 106 107
-20
0
20
40
in-phase out-of-phase
V in, V
out (V
)
Frequency (Hz)100 101 102 103 104 105 106 107
0.01
0.1
1
10
100
in-phase out-of-phase (negative) out-of-phase (positive)
Vin, V
out (V
)
Frequency (Hz)
Comparison of vacuum and 17 psi of R124
100 101 102 103 104 105 106 107
-20
0
20
40
in-phase out-of-phase
Vin, V
out (V
)
Frequency (Hz)100 101 102 103 104 105 106 107 108
-50
0
50
in-phase out-of-phase (negative)
V in, V
out (V
)
Frequency (Hz)
vacuum 17 psi
Summary
• Plasmonic nanodisks are powerful platform for probing small changes in index of refraction due to temperature excursions in liquids or evaporation/condensation of thin layers (or changes in density/pressure) near an interface.
• Signal due to the index of refraction of the fluid provides greater sensitivity to interface conductance (needed when the thermal effusivity of the fluid is small).
• Kaptiza length for ethanol in contact with hydrophilic and hydrophobic SAMs is ≈3 nm.
• Experiments on refrigerant (R124) as a function of pressure, temperature, and surface chemistry are in progress.