Influence of localized surface plasmon resonance and free electrons on the optical properties of ultrathin Au films: a study of the aggregation effect

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

doi:10.1364/oe.22.005124

Cited by 42 publications

(47 citation statements)

References 21 publications

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“…4, dark cyan and cyan triangles, respectively) with 7 nm effective thicknesses. An increasing LSPR strength is observed, progressing gradually from the sputtered to the EBE and finally to ERAN deposited Ag after MWA, which indicates increasing isolation of Ag nanoparticles and elimination of aggregation for ERAN [49]. From the previous discussion it is evident that MWA for 5 s is not enough to produce well-isolated Ag nanoparticles.…”

Section: B Optical Properties Of Plasmonic Templatesmentioning

confidence: 89%

Self-assembled plasmonic templates produced by microwave annealing: applications to surface-enhanced Raman scattering

et al. 2015

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Perhaps the simplest method for creating metal nanoparticles on a substrate is by driving their selfassembly with the thermal annealing of a thin metal film. By properly tuning the annealing parameters one hopes to discover a recipe that allows the pre-determined design of the nanoparticle (NP) arrangement. However, thermal treatment is known for detrimental effects and is not really the manufacturer's route of choice when it comes to largescale applications. An alternative method is the use of microwave annealing, a method that has never been applied for metal processing, due to the high reflectance of microwave radiation at the surface of a metal. However, in this work we challenge the widely used nanostructuring methods by proving microwave's annealing ability to produce plasmonic templates, out of extremely thin metal films, by simply using a domestic microwave oven apparatus. We show that this process is generic and independent of the deposition method used for the metal and we further quantify the suitability of these plasmonic templates for use in surface-enhanced Raman scattering applications.

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Section: B Optical Properties Of Plasmonic Templatesmentioning

confidence: 89%

Self-assembled plasmonic templates produced by microwave annealing: applications to surface-enhanced Raman scattering

et al. 2015

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“…As the probe in the NIR region corresponds to intraband transition one would expect photobleach signal (∆R/R with a positive sign) due to the thermalized distribution of carrieres near E f . However, as the observed ∆R/R signal in this region is negative, a photoinduced absorption is possible due to the transition from 6s band to 6p band [58,59]. The probe in this region is excited state absorption by the thermalized carriers above E f and detects the electron with energy E = E 6p − E pr , where E 6p ∼ 4.32 eV [58] is the position of the 6p band and E pr is the probe photon energy.…”

Section: Experimental and Simulation Detailsmentioning

confidence: 99%

Plasmon-induced efficient hot carrier generation in graphene on gold ultrathin film with periodic array of holes: Ultrafast pump-probe spectroscopy

Prakash

Srivastava

Gupta

2019

The Journal of Chemical Physics

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Using ultrafast pump-probe reflectivity with 3.1 eV pump and coherent white light probe (1.1 to 2.6 eV), we show that graphene on gold nanostructures exhibits a strong coupling to the plasmonic resonances of the ordered lattice hole array, thus injecting a high density of hot carriers in graphene through plasmons. The system being studied is single-layer graphene on ultrathin film of gold with periodic arrangements of holes showing anomalous transmission. A comparison is made with gold film with and without hole array. By selectively probing transient carrier dynamics in the spectral regions corresponding to plasmonic resonances, we show efficient plasmon induced hot carrier generation in graphene. We also show that due to high electromagnetic field intensities at the edge of the sub-micron holes, fast decay time (10-100 fs) and short decay length (1 nm) of plasmons, a highly confined density of hot carriers (very close to edge of the holes) is generated by Landau damping of plasmons within the holey gold film. A contribution to transient decay dynamics due to diffusion of initial non-uniform distribution of hot carriers away from the hole edges is observed.Our results are important for future applications of novel hot carrier device concepts where hot carriers with tunable energy can be generated in different graphene regions connected seamlessly. 1 I. INTRODUCTION Surface plasmon polaritons (SPPs) due to their inherent property of nanoscale confinement and localization, smaller than the interacting light wavelength, show strong lightmatter interaction. This leads plasmonics to a wide variety of applications from efficient harvesting of solar energy to nanoscale optical devices [1-3]. Efficient generation and transfer of hot electron-hole pairs has been at the heart of efficient conversion of solar energy in photovoltaic and photocatalytic devices [4]. Plasmons in nanostructures decay through Landau damping (with damping time of few tens of fs [5-8]) to generate energetic electrons, with energies larger than those of the thermal excitation (known as the hot electrons) at ambient temperatures, [9-14]. Hot carriers can be accessed through plasmon induced hot-electron charge transfer into adjacent interface material [7, 10, 15, 16]. If a high conductance pathway is available, the plasmon generated hot electrons can rapidly conduct over long distances, which might also discourage the electrons once transferred from returning to the plasmonic material. In graphene, electrons move with high velocities (v F =10 6 m/s) and behave like massless Fermions, making it the most desirable material for the high-speed electronics and optoelectronics applications. A substantial challenge to the performance of most of the graphene-based optoelectronic devices [17-19] comes from the weak absorption of light (only 2.3% at normal incidence) in graphene. Thus, efficient hot electron injection in graphene through plasmons gains valuable importance. Graphene in a hybrid plasmonic structure are promising elements for high-speed electrica...

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“…6.5(c) and 6.5(d), the corresponding real parts of the anisotropic complex permittivities of the 5.5 nm gold film in air are 22.8 and 15 for the TM and TE polarizations, respectively, which are included within the above reported values. Moreover, the estimated complex refractive indices of the gold evaporated films with "nominal"thicknesses of 4 nm and 5 nm were found to be about 5-i1.5 and 4.5−i2.5 at 1570 nm in air,146 i.e. a similar real part as the one obtained here, but a much larger imaginary part.…”

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confidence: 78%

“…In the EMA models, the gold aggregates are represented by point dipoles embedded in the homogenous background, and the resulting effective permittivity of the mixture is dependent on the complex permittivities of the two constituents (gold and surrounding material), and on the volume fraction of gold. For experimental studies of thin gold films, spectroscopic ellipsometry is one of the most common measurement tools as it is highly sensitive to the optical properties of thin films 140,[145][146][147]. However, most of the previous work in this area was focused on measuring the thickness-dependent complex permittivity calculated from the ellipsometric angles to investigate the effect of various thin film growth mechanisms, including the impact of the shape and distribution of the NPs making up the ultrathin films.…”

mentioning

confidence: 99%

“…Comparatively few studies exist on the impact of the surrounding medium permittivity of these films,148,149 and in such cases the gold NPs films are always embedded in solid dielectric material, making it impossible to study the same film under different surroundings. Moreover, the anisotropic optical properties of the ultrathin metal films caused by the nonspherical shape of their NP constituents limit the measurement accuracy of the conventional measurement methods, such as spectral reflectometry,49,140 ellipsometry,145,146 and interferometric picometrology124 This is one of the reasons for which previous works often neglected the optical anisotropy in measurements of gold films with thicknesses spanning the insulator-to-metal transition. The purpose of the present paper is to investigate the impact of the surrounding medium on the anisotropic optical properties of highly disordered, morphologically complex gold NP aggregates with an average thickness of 5.5 nm.…”

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confidence: 99%

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In-situ Optical Characterization of Noble Metal Thin Film Deposition and Development of a High-Performance Plasmonic Sensor

Mandia¹

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With ever-growing industry demand for more uniform and conductive metal or metal oxide thin film coatings, an improvement to the techniques that produce these materials must be done in parallel. Two techniques that have shown great utility in this regard are referred to as chemical vapour deposition (CVD) and atomic layer deposition (ALD). While both techniques offer highly modular reactor designs and robust precursorsubstrate chemistries (e.g., the benchmark Al 2 O 3 process), many processes result in nonuniformity issues, ultimately leading to poor device performance. One such challenging process has been the fabrication of high-purity and uniform noble metal thin films such as gold. Equally as challenging is the ability to characterize metal CVD and ALD processes when the metallic film is just beginning to nucleate. This "nucleation delay", or induction process,is especially common in metal ALD processes and techniques such as ellipsometry lack sensitivity in the low-cycle regime of ALD (or pulsed CVD) processes. The present work addressed in this thesis introduces, for the first time, the use of tilted fiber Bragg grating (TFBG) sensors for accurate, real-time, and in-situ characterization of CVD and ALD processes for noble metals, but with a particular focus on gold due to its desirable optical and plasmonic properties. Through the use of orthogonally-polarized transverse electric (TE) and transverse magnetic (TM) resonance modes imposed by a boundary condition at the cladding-metal interface of the optical fiber, polarizationdependent resonances excited by the TFBG are easily decoupled. It was found that for ultrathin thicknesses of gold films from CVD (~6-65 nm), the anisotropic property of these films made it non-trivial to characterize their effective optical properties such as the real component of the permittivity. Nevertheless, the TFBG introduces a new sensing platform to the ALD and CVD community for extremely sensitive in-situ process monitoring. We later also demonstrate thin film growth at low (<10 cycle) numbers for the well-known Al 2 O 3 thermal ALD process, as well as the plasma-enhanced gold ALD process. Finally, the use of ALD-grown gold coatings has been employed for the development of a plasmonic TFBG sensor with ultimate refractometric sensitivity (~550 nm/RIU).

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Influence of localized surface plasmon resonance and free electrons on the optical properties of ultrathin Au films: a study of the aggregation effect

Cited by 42 publications

References 21 publications

Self-assembled plasmonic templates produced by microwave annealing: applications to surface-enhanced Raman scattering

Self-assembled plasmonic templates produced by microwave annealing: applications to surface-enhanced Raman scattering

Plasmon-induced efficient hot carrier generation in graphene on gold ultrathin film with periodic array of holes: Ultrafast pump-probe spectroscopy

In-situ Optical Characterization of Noble Metal Thin Film Deposition and Development of a High-Performance Plasmonic Sensor

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