Temperature Effects on Thin film Based SPR- Sensor
S. Benaziez and N. Benaziez Physics Department, Faculty of Matter Sciences
University of Batna 1, Algeria safia.mag1@gmail.com
Z. Dibi*and B. Abdelhadi**
*Electronic Department, Faculty of Science of Engineering
**Department of electrical engineering Technology University of Batna2, Algeria2
*zohirdibi@yahoo.fr
**Abdelhadi3b@yahoo.com
Abstract—In this paper, using the angle interrogation methods, we simulate the effect of temperature fluctuation on thin film based SPR- sensor. The sensor configuration is a three layer Krestchmann configuration consisting of glass prism, thin metallic layer, and bulk sensing layer. The temperature sensor uses RPS geometry of three interfaces where the refractive index of the layer adjacent to the environment is very sensitive to changes in the environmental temperature. The final results indicate that, as the temperature decreases,
min (resonance angle)shift to larger angles and increased inR
min.These results can be used in the development of chemical, biomedical sensors, is suggestedKeywords— surface plasmon resonance (SPR), thermo-optic effect, temperature sensor.
I. INTRODUCTION
Thin films are very common in biochemistry and physics. For example, they are widely used in semiconductor technology, spectroscopy, plasmonics, nanophotonics and optics in general (e.g., antireflection coatings, filters, and semitransparent mirrors)[1].
Surface plasmon resonance is a resonance phenomenon of electromagnetic wave at the interface between a metal layer and a dielectric layer; witch can be resonantly excited by TM- polarized light. The resonance condition depends on many parameters such as incident angle, wavelength, and the dielectric functions of the metal and dielectric [2]. The method called ATR (Attenuated Total Reflection) is the most used to excite surface plasmons. It was put into practice for the first time by A. Otto then by E.Kretshmann which using a prism such as coupler [3,4]. The SPR technology was first employed for gas detection and biosensing by Nylander et al and Liedberg et al [5], and now widely implemented chemical and biological detection [2,6].
In general, the SPR sensors are refractometers thin layer measuring changes in the index of refraction occurring on the surface of a metal film supporting surface plasmons. A change of the dielectric refractive index causes a change in
propagation constant of the surface Plasmon, that changes according to the coupling conditions when the light wave coupled with surface plasmons (e.g., coupling angle, coupling length of wave, current, phase). [7]
The SPR sensor should be exposed to environments with variable temperature, metal and dielectric properties will be changed by thermal expansion effect, the phonon-electron scattering, electron-electron scattering and thermo-optical effect. All of these effects influence the performance of the SPR sensor. In this article the effect of temperature, including the dependence of the thermal expansion coefficient of the metal and also the dependence of them dielectric function, the study theoretically on the Kretschmann configuration, with the approach called angular interrogation is considered for our RPS sensor. The Kretschmann geometry is a three-layer system: A silver film having a thickness d is deposited on the bottom of the prism; the analyte with a refractive indexnais just on the surface of the silver film. , the incident light wavelength is entered into the prism. SPR geometry of three interfaces used in this analysis is shown in Fig. 1. The p- polarized light is incident from the prism side. Using the formulation Fresnel reflection coefficient of this system with three interfaces can be written as [2]:
R = ( )
( ) (1)
= (2)
= (3)
= − pour j= p ,m ,a.
= sin (4)
Fig 1. Illustration of the SPR geometry of three interfaces[8]
II. EFFECT OF TEMPERATURE ON THE SENSOR SPR The SPR has been extensively studied and developed useful technique to probe the changes in thickness and refractive index that enabled the construction of optical sensors measuring the concentration of chemicals, humidity, pressure, temperature, and biomolecular interactions.
The temperature has deteriorating effects on the SPR spectrum which causes the decrease of the sensitivity of SPR sensors. The temperature effects are manifested as changes in the thickness and the layer refractive index in the SPR geometry.
The effect of the refractive indexn1of the metal film on our design must be investigated in detail because it is well known that the thermal changes affect this factor significantly [8]. To perform this analysis, we can use the Drude model:
= ( ) = ( + ) = 1 −
( ) (5)
Where, and are the dielectric permittivity and the real and imaginary parts of the refractive index of the metal, respectively, is the angular frequency of the electromagnetic wave, and wp et = + represent the Plasmon frequency and collision frequency of electrons in metal, respectively. The plasma frequency can be found using the following expression.
*
² 4
m w p Ne
(6) WhereN and
m
* are the density and effective mass of the electrons, respectively. Both of these parameters are temperature dependent, however, the relatively very small temperature dependence ofm
* can be neglected.Therefore,
w
p at a given temperatureT
can be calculated using the following expression0
0 1/ 2
[1 ( )]
p p
w w
T T (7)
Where , p0
w
is the plasma frequency at a reference temperatureT
0 Here, the temperature dependence of N, which is defined as:N(T) = N( )= N( )[1 3
(T T0)]1, is exploited. The contributions of phonon-electron and electron–electron scattering onw
c are described as follows:
T zcp e
dz z w T
w 0 5 / 4
4 1 5
2
(8)
2 2
3 ' ( ) / 2
12
1 k T w
w E B
ce F
(9)
The value 0
w
is a constant.Thus, all the equations above provide a model which shows the temperature dependence of
[9].TABLE 1 The parameter values used [9]
Symbole Meaning value Unit
Fermi surface average of the probability of scattering
0.55
coefficient of expansion
of the metal 19 1 06K 1
Fractional Umklapp
scattering 0.73
D Debye temperature 220 K
EF Fermi energy 5.48 e V
Planck’s constant 1.0546 1 03 4J s
K B Boltzmann constant 1.3806 1 02 3J K 1
Poisson number 0.42
(0.32)
In this article we made a simulation on the effect of temperature on the RPS sensor based on geometry of three interfaces (Fig.1).
In Figure.2, we showed first the effect of the refractive index of the target layer (SF) on the spectrum.
40 50 60 70 80 90 0.0
0.2 0.4 0.6 0.8 1.0
Réflectance
Angle d'incidence (degré)
n2=1,35 n2=1,4 n2=1,5 n2=1,6
Fig2. Effect of the refractive index of the target layer on the SPR spectrum It is evident that any change in the real part of the refractive index of the sensing layer affects the real part of the surface Plasmon wave, and therefore
minand
where
min is the resonance angle,
is the half width at half maximum (FWHM). An increase inn
2 shifts
min to larger angles and reduced the minimum reflectionR
min. Therefore, we can say that SF has a refractive index strongly affected by changes in temperature can be utilized to probe the temperature by the angular interrogation approach.In figure.3a we presented the refractive index of the environment modulation effect on the resonance angle spectrum
minto different values of the thickness of the target layer SF. This figure shows that we can eliminate the effect of volume if we choose a broad thickness.The figure3.b, shows the effect of temperature on PR response of geometry. It appears that the reduction of T is accompanied by the shift to larger angles
minand increasedR
min.1,0 1,1 1,2 1,3 1,4 1,5 1,6
46 48 50 52 54 56 58 60 62 64 66
min(degré)
Indice de réfraction de volume n3 d=100nm
d=250nm d=300nm
(a)
50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 0.4
0.5 0.6 0.7 0.8 0.9 1.0
Réflectance
Angle d'incidence (degré) T=100K T=300K T=400K
fig.3 : a) Effect of the refractive index of the environment onmin at different values of the thickness of the target layer, b) Effect of temperature on the response of the SPR geometry
III. CONCLUSION
In summary, a Simulation of temperature Effects on Thin film Based SPR-Sensor has been investigated.
A detailed analysis of RPS phenomena with geometries to three interfaces is presented with a focus on temperature dependence of effect on the response of the RPS sensors. The RPS curve is shifted and broadened at high temperatures. It is clearly demonstrated that thermal changes affect the RPS spectrum by modulating the thickness and refractive index of the materials used in the different layers of the RPS geometry.
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