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Plasmonic propagations distances for interferometric surface plasmon resonance biosensing.

Lepage D, Carrier D, Jiménez A, Beauvais J, Dubowski JJ - Nanoscale Res Lett (2011)

Bottom Line: The result is an increased traceability of the SPR shifts for biosensing applications.The surface roughness and dielectric values for various deposition rates of very thin Au films are measured.We also investigate an interferometric SPR setup where, due to the power flux transfer between plasmon modes, the specific choice of grating coupler can either decrease or increase the plasmon propagation length.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Electrical and Computer Engineering, Université de Sherbrooke, Sherbrooke, QC J1K 2R1, Canada. Jan.J.Dubowski@USherbrooke.ca.

ABSTRACT
A surface plasmon resonance (SPR) scheme is proposed in which the local phase modulations of the coupled plasmons can interfere and yield phase-sensitive intensity modulations in the measured signal. The result is an increased traceability of the SPR shifts for biosensing applications. The main system limitation is the propagation distance of the coupled plasmon modes. This aspect is therefore studied for thin film microstructures operating in the visible and near-infrared spectral regions. The surface roughness of the substrate layer is examined for different dielectrics and deposition methods. The Au layer, on which the plasmonic modes are propagating and the biosensing occurs, is also examined. The surface roughness and dielectric values for various deposition rates of very thin Au films are measured. We also investigate an interferometric SPR setup where, due to the power flux transfer between plasmon modes, the specific choice of grating coupler can either decrease or increase the plasmon propagation length.

No MeSH data available.


SEM images of surface roughness for of Au surfaces; as presented in [13]for (a) 0.2 Å/s deposition rate. The roughness is high and but relatively homogeneous over the surface. Au grains are clustering over the surface and present a lower density. The inset is a 10 μm2 AFM profile. (b) At 0.7 Å/s deposition rate, the localized surface roughness is smaller, more compact and a lower clusterization with the typical grain size of Au at 6 nm.
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Figure 5: SEM images of surface roughness for of Au surfaces; as presented in [13]for (a) 0.2 Å/s deposition rate. The roughness is high and but relatively homogeneous over the surface. Au grains are clustering over the surface and present a lower density. The inset is a 10 μm2 AFM profile. (b) At 0.7 Å/s deposition rate, the localized surface roughness is smaller, more compact and a lower clusterization with the typical grain size of Au at 6 nm.

Mentions: The successive layers for Figure 1 structure consist in a continuous thin film of Au atop of which a grating region is constructed for the SPs coupling. Again, the surface roughness of Au is studied, this time only for the e-beam evaporation technique (using a BOC Edwards evaporator model Auto 306) for various deposition rates. The target thickness for the Au layers is 20 nm. Figure 4 presents the surface roughness for the various deposition rates [13]. In depth SEM analyses have shown that for small deposition rates (≤1 Å/s), Au nanodroplets tend to cool down and form 100-200 nm wide clusters, thus yielding a relatively high surface roughness. On the other hand, for large deposition rates (>3 Å/s), the Au grains remain small (approximately 6 nm) and are very compact on the surface. However, very large Au pieces, up to about 1 μm2, are found in this case on the surface. Examples of these two behaviours are presented in Figure 5. As shown in Figure 4, a middle value for the deposition rate, at around 1 Å/s, presents tradeoffs of the two regimes and seems to be the ideal case for deposition of low-roughness Au films. Au-plated quartz substrates commercially available have been measured to have a roughness around 40 Å, making them less suited for long range SPs experiments or to achieve narrow SPR peaks. To conclude on surface roughness, we can estimate that our worst case would consists of sputtered SiO2 with a 0.2 Å/s deposition rate, yielding a 55 Å surface roughness while the best case scenario, made of a PECVD SiO2 layer with a Au layer evaporated at 1.5 Å/s, would yield a surface roughness of 15 Å. From these numbers, we can estimate that at a given energy, the contribution of surface roughness to SPs loss in scattering is reduced by a factor of 13 × [9]. Well-known smoothing methods, such as thermal annealing, are generally incompatible with thin film technology. Indeed, heating thin Au films (<50 nm) increases the formation of larger clusters, grains or flakes [14-16], which can be useful for some applications [16], but not for planar SPR where propagating SPs would scatter. Therefore, ab initio precautions have to be taken to generate very thin and flat metallic layers.


Plasmonic propagations distances for interferometric surface plasmon resonance biosensing.

Lepage D, Carrier D, Jiménez A, Beauvais J, Dubowski JJ - Nanoscale Res Lett (2011)

SEM images of surface roughness for of Au surfaces; as presented in [13]for (a) 0.2 Å/s deposition rate. The roughness is high and but relatively homogeneous over the surface. Au grains are clustering over the surface and present a lower density. The inset is a 10 μm2 AFM profile. (b) At 0.7 Å/s deposition rate, the localized surface roughness is smaller, more compact and a lower clusterization with the typical grain size of Au at 6 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211481&req=5

Figure 5: SEM images of surface roughness for of Au surfaces; as presented in [13]for (a) 0.2 Å/s deposition rate. The roughness is high and but relatively homogeneous over the surface. Au grains are clustering over the surface and present a lower density. The inset is a 10 μm2 AFM profile. (b) At 0.7 Å/s deposition rate, the localized surface roughness is smaller, more compact and a lower clusterization with the typical grain size of Au at 6 nm.
Mentions: The successive layers for Figure 1 structure consist in a continuous thin film of Au atop of which a grating region is constructed for the SPs coupling. Again, the surface roughness of Au is studied, this time only for the e-beam evaporation technique (using a BOC Edwards evaporator model Auto 306) for various deposition rates. The target thickness for the Au layers is 20 nm. Figure 4 presents the surface roughness for the various deposition rates [13]. In depth SEM analyses have shown that for small deposition rates (≤1 Å/s), Au nanodroplets tend to cool down and form 100-200 nm wide clusters, thus yielding a relatively high surface roughness. On the other hand, for large deposition rates (>3 Å/s), the Au grains remain small (approximately 6 nm) and are very compact on the surface. However, very large Au pieces, up to about 1 μm2, are found in this case on the surface. Examples of these two behaviours are presented in Figure 5. As shown in Figure 4, a middle value for the deposition rate, at around 1 Å/s, presents tradeoffs of the two regimes and seems to be the ideal case for deposition of low-roughness Au films. Au-plated quartz substrates commercially available have been measured to have a roughness around 40 Å, making them less suited for long range SPs experiments or to achieve narrow SPR peaks. To conclude on surface roughness, we can estimate that our worst case would consists of sputtered SiO2 with a 0.2 Å/s deposition rate, yielding a 55 Å surface roughness while the best case scenario, made of a PECVD SiO2 layer with a Au layer evaporated at 1.5 Å/s, would yield a surface roughness of 15 Å. From these numbers, we can estimate that at a given energy, the contribution of surface roughness to SPs loss in scattering is reduced by a factor of 13 × [9]. Well-known smoothing methods, such as thermal annealing, are generally incompatible with thin film technology. Indeed, heating thin Au films (<50 nm) increases the formation of larger clusters, grains or flakes [14-16], which can be useful for some applications [16], but not for planar SPR where propagating SPs would scatter. Therefore, ab initio precautions have to be taken to generate very thin and flat metallic layers.

Bottom Line: The result is an increased traceability of the SPR shifts for biosensing applications.The surface roughness and dielectric values for various deposition rates of very thin Au films are measured.We also investigate an interferometric SPR setup where, due to the power flux transfer between plasmon modes, the specific choice of grating coupler can either decrease or increase the plasmon propagation length.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Electrical and Computer Engineering, Université de Sherbrooke, Sherbrooke, QC J1K 2R1, Canada. Jan.J.Dubowski@USherbrooke.ca.

ABSTRACT
A surface plasmon resonance (SPR) scheme is proposed in which the local phase modulations of the coupled plasmons can interfere and yield phase-sensitive intensity modulations in the measured signal. The result is an increased traceability of the SPR shifts for biosensing applications. The main system limitation is the propagation distance of the coupled plasmon modes. This aspect is therefore studied for thin film microstructures operating in the visible and near-infrared spectral regions. The surface roughness of the substrate layer is examined for different dielectrics and deposition methods. The Au layer, on which the plasmonic modes are propagating and the biosensing occurs, is also examined. The surface roughness and dielectric values for various deposition rates of very thin Au films are measured. We also investigate an interferometric SPR setup where, due to the power flux transfer between plasmon modes, the specific choice of grating coupler can either decrease or increase the plasmon propagation length.

No MeSH data available.