Evolution of the localized surface plasmon resonance and electron confinement effect with the film thickness in ultrathin Au films

Li, X. D.; Chen, T. P.; Liu, Y.; Leong, K. C.

doi:10.1007/s11051-015-2880-1

Cited by 8 publications

(8 citation statements)

References 23 publications

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“…For this purpose, the high-quality gold films of various thicknesses (ranging from ~20 to 200 nm) were deposited on silicon substrate by use of conventional e-beam evaporation (EBE) technique. Regarding the films thickness range (which we chose to work with), it is important to note that once the film thickness is less than 20 nm one can get island or highly roughened film surfaces and quantum confinement effects need to be considered [20,21]. At the same time, the films with a thickness of more than 200 nm are guaranteed to behave as a bulk metal.…”

Section: Introductionmentioning

confidence: 99%

Optical constants and structural properties of thin gold films

Yakubovsky¹,

Arsenin²,

Stebunov³

et al. 2017

Opt. Express

309

153

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We report a comprehensive experimental study of optical and electrical properties of thin polycrystalline gold films in a wide range of film thicknesses (from 20 to 200 nm). Our experimental results are supported by theoretical calculations based on the measured morphology of the fabricated gold films. We demonstrate that the dielectric function of the metal is determined by its structural morphology. Although the fabrication process can be absolutely the same for different films, the dielectric function can strongly depend on the film thickness. Our studies show that the imaginary part of the dielectric function of gold, which is responsible for optical losses, rapidly increases as the film thickness decreases for thicknesses below 80 nm. At the same time, we do not observe a noticeable dependence of optical constants on the film thickness for thicker samples. These findings establish design rules for thin-film plasmonic and nanophotonic devices.

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Section: Introductionmentioning

confidence: 99%

Optical constants and structural properties of thin gold films

Yakubovsky¹,

Arsenin²,

Stebunov³

et al. 2017

Opt. Express

309

153

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show abstract

“…The thickness of the metallic films varies from a few tens to hundreds of nanometers depending on the particular plasmonic application. Plasmonic materials are characterized by high real part permittivity

ε^{'}

and a low imaginary part

ε^{″}

responsible for losses, that is,

ε^{″} ≪ |ε^{'}| .

It has been suggested that for the film thickness less than 20 nm one can get island or highly roughened surfaces and quantum confinement effects should be considered while for a thickness of more than 200 nm, the film will behave as a bulk metal [75, 76]. To characterize the optical properties of Au thin films of various thicknesses, the Drude theory can describe the optical response of metals by

ε = ε^{″} + i ε^{″} = ε_{\infty} - \frac{ω_{p}^{2}}{ω^{2} - iγω},

ε = ε_{\infty} - \frac{ω_{p}^{2}}{ω^{2} + γ^{2}} + \frac{{γω}_{p}^{2}}{ω (ω^{2} + γ^{2})},

where

ε_{\infty}

is the infinite‐frequency dielectric constant,

ω_{p}

is the plasma frequency of metal, the imaginary part of the dielectric function

ε^{″} = {italicγω}_{p}^{2} / ω (ω^{2} + γ^{2})

is responsible for the optical absorption in metal,

γ = γ_{italicep} + γ_{italiceg} + γ_{s}

is the damping factor of the Drude model,

γ_{italicep}

is the total electron relaxation rate in bulk Au film due to electron‐phonon scattering,

…”

Section: Resultsmentioning

confidence: 99%

“…Plasmonic materials are characterized by high real part F I G U R E 1 1 SERS spectra of the gold chip biosensor before and after biomarker binding at 637 nm and 4 mW laser power divided into (A) 500 to 2000 cm À1 , (B) 2000 to 2500 cm À1 , (C) 2500 to 3000 cm À1 and (D) 3000 to 3500 cm À1 regions. SERS, surface-enhanced Raman scattering permittivity ε 0 and a low imaginary part ε 00 responsible for losses, that is, ε 00 ( ε 0 j j: It has been suggested that for the film thickness less than 20 nm one can get island or highly roughened surfaces and quantum confinement effects should be considered while for a thickness of more than 200 nm, the film will behave as a bulk metal [75,76]. To characterize the optical properties of Au thin films of various thicknesses, the Drude theory can describe the optical response of metals by…”

mentioning

confidence: 99%

Reflective FT‐NIR and SERS studies of HER‐II breast cancer biomarker using plasmonic‐active nanostructured thin film immobilized oriented antibody

Khosroshahi

Patel

2022

Journal of Biophotonics

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We describe the fabrication of plasmonic‐active nanostructured thin film substrate as a label‐free surface‐enhanced Raman scattering (SERS)‐based biosensor immobilized covalently with monoclonal HER‐II antibody (mAb) to detect overexpressed HER‐II as a biomarker in breast cancer serum (BCS). Oriented conjugation of mAb via hydrazone linkage to provide higher mAb accessibility was characterized by UV‐vis and reflective Fourier transform near‐infrared (FT‐NIR) spectroscopic techniques. The interaction of BCS with mAb was studied by FT‐NIR and nonresonant SERS at 637 nm. The results showed detection of glycoprotein content at different laser powers including a rise in amino acid and glycan content with varying results at higher power. With nonresonant SERS we observed nonlinear behavior of peak intensity. Analysis of variance was implemented to determine the effect of laser power which was found not to be a contributing factor. However, at the nanoscale, factors including the heating effect and aggregation of molecules can contribute to the nonlinearity of peak intensity.

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“…First and second interband transitions are initiated from d-valence band to the empty states of s-and p-bands above the Fermi level, respectively. [50][51][52] With the increase in T a , a marginal blue shi in the interband transitions is observed. Moreover, these absorption peaks become more closely matched to those of Au WA 5 nm sample with the increase in T a .…”

Section: Elemental Characterizationmentioning

confidence: 94%

“…22,49 As the thickness of Au increases from 5 to 10 nm, Drude band becomes comparatively more noticeable than LSPR band. 52 For Au WA 100 nm sample, Drude band completely dominates over LSPR band. It is believed that in thick lms, interlinks are formed between the Au NPs due to an aggregation phenomenon.…”

Section: Elemental Characterizationmentioning

confidence: 98%