Bioplasmonic Alloyed Nanoislands Using Dewetting of Bilayer Thin Films

Plasmon-enhanced optoacoustic transducer with Ecoflex thin film for broadband ultrasound generation using overdriven pulsed laser diode

Significance

Ultrasonic transducers facilitate noninvasive biomedical imaging and therapeutic applications. Optoacoustic generation using nanoplasmonic structures provides a technical solution for highly efficient broadband ultrasonic transducer. However, bulky and high-cost nanosecond lasers as conventional excitation sources hinder a compact configuration of transducer.

Aim

Here, we report a plasmon-enhanced optoacoustic transducer (PEAT) for broadband ultrasound generation, featuring an overdriven pulsed laser diode (LD) and an Ecoflex thin film. The PEAT module consists of an LD, a collimating lens, a focusing lens, and an Ecoflex-coated 3D nanoplasmonic substrate (NPS).

Approach

The LD is overdriven above its nominal current and precisely modulated to achieve nanosecond pulsed beam with high optical peak power. The focused laser beam is injected on the NPS with high-density electromagnetic hotspots, which allows for the efficient plasmonic photothermal effect. The thermal expansion of Ecoflex finally generates broadband ultrasound.

Results

The overdriven pulsed LD achieves a maximum optical peak power of 40 W, exceeding the average optical power of 3 W. The 22    μ m thick Ecoflex-coated NPS exhibits an eightfold optoacoustic enhancement with a fractional - 6    dB bandwidth higher than 160% and a peak frequency of 2.5 MHz. In addition, the optoacoustic amplitude is precisely controlled by the optical peak power or the laser pulse width. The PEAT-integrated microfluidic chip clearly demonstrates acoustic atomization by generating aerosol droplets at the air-liquid interface.

Conclusions

Plasmon-enhanced optoacoustic generation using PEAT can provide an approach for compact and on-demand biomedical applications, such as ultrasound imaging and lab-on-a-chip technologies.

Impact of thermal annealing and laser treatment on the morphology and optical responses of mono- and bi-metallic plasmonic honeycomb lattice

Plasmonic nanoparticle arrays with a specific lattice arrangement can support surface lattice resonances (SLRs). SLR exhibits a sharp spectral peak and finds many applications including optical sensing and plasmonic lasers. To optimize SLR for application, a robust method that allows the mass production of plasmonic nanoparticle arrays with refined particle morphology and well-defined lattice arrangement is required. In this work, we combine nanosphere lithography (NSL) with thermal annealing or nanosecond-pulsed laser treatment to refine plasmonic nanoparticles in a honeycomb lattice. We comparatively study the effects of the two treatment methods on the particle morphology and lattice arrangement of mono (Ag and Pd) and bi-metallic (Ag-Pd) nanoparticle lattices. In general, thermal annealing preserves the lattice arrangement but fairly changes the particle roundness, while laser treatment produces particles with varying morphologies and spatial distribution. We also theoretically and experimentally investigate the optical responses of Ag nanoparticle lattices produced by different treatment methods. The observed difference in spectra can be attributed to the varying particle morphology, which shifts the localized surface plasmon resonance differently, resulting in a significant change in SLR. These findings provide valuable insights for optimizing plasmonic nanoparticle arrays for various applications.

Phage-targeting bimetallic nanoplasmonic biochip functionalized with bacterial outer membranes as a biorecognition element

The use of phages-a natural predator of bacteria-has emerged as a therapeutic strategy for treating multidrug-resistant bacterial infections; thus, the isolation and detection of phages from the environment is crucial for advancing phage therapy. Herein, for the first time, we propose a nanoplasmonic-based biodetection platform for phages that utilizes bacterial outer membranes (OMs) as a biorecognition element. Conventional biosensors based on phage-bacteria interactions encounter multiple challenges due to the bacteriolytic phages and potentially toxic bacteria, resulting in instability and risk in the measurement. Therefore, instead of whole living bacteria, we employ a safe biochemical OMs fraction presenting phage-specific receptors, allowing the robust and reliable phage detection. In addition, the biochip is constructed on bimetallic nanoplasmonic islands through solid-state dewetting for synergy between Au and Ag, whereby sensitive detection of phage-OMs interactions is achieved by monitoring the absorption peak shift. For high detection performance, the nanoplasmonic chip is optimized by systematically investigating the morphological features, e.g., size and packing density of the nanoislands. Using our optimized device, phages are detected with high sensitivity (≥∼104 plaques), specificity (little cross-reactivity), and affinity (stronger binding to the host OMs than anti-bacterial antibodies), further exhibiting the cell-killing activities.

Facile and Low-Cost Fabrication of SiO2-Covered Au Nanoislands for Combined Plasmonic Enhanced Fluorescence Microscopy and SERS

An easy and low-cost way to fabricate monometallic Au nanoislands for plasmonic enhanced spectroscopy is presented. The method is based on direct thermal evaporation of Au on glass substrates to form nanoislands, with thicknesses between 2 and 15 nm, which are subsequently covered by a thin layer of silicon dioxide. We have used HR-SEM and AFM to characterize the nanoislands, and their optical transmission reveals strong plasmon resonances in the visible. The plasmonic performance of the fabricated substrates has been tested in fluorescence and Raman scattering measurements of two probe materials. Enhancement factors up to 1.8 and 9×104 are reported for confocal fluorescence and Raman microscopies, respectively, which are comparable to others obtained by more elaborated fabrication procedures.

Endorsing a Hidden Plasmonic Mode for Enhancement of LSPR Sensing Performance in Evolved Metal-insulator Geometry Using an Unsupervised Machine Learning Algorithm

Large-area nanoplasmonic structures with pillared metal-insulator geometry, also called nanomushrooms (NM), consist of an active spherical-shaped plasmonic material such as gold as its cap and silicon dioxide as its stem. NM is a geometry which evolves from its precursor, nanoislands (NI) consisting of aforementioned spherical structures on flat silicon dioxide substrates, via selective physical or chemical etching of the silicon dioxide. The NM geometry is well-known to provide enhanced localized surface plasmon resonance (LSPR) sensitivity in biosensing applications as compared to NI. However, precise optical phenomenon behind this enhancement is unknown and often associated with the existence of electric fields in the large fraction of the spatial region between the pillars of NM, usually accessible by the biomolecules. Here, we uncover the association of LSPR enhancement in such geometries with a hidden plasmonic mode by conducting magneto-optics measurements and by deconvoluting the absorbance spectra obtained during the local refractive index change of the NM and NI geometries. By the virtue of principal component analysis, an unsupervised machine learning technique, we observe an explicit relationship between the deconvoluted modes of LSPR, the differential absorption of left and right circular polarized light, and the refractive index sensitivity of the LSPR sensor. Our findings may lead to the development of new approaches to extract unknown properties of plasmonic materials or establish new fundamental relationships between less understood photonic properties of nanomaterials.

Photothermal Structural Dynamics of Au Nanofurnace for In Situ Enhancement in Desorption and Ionization

Fundamental properties of nanostructured substrates govern the performance of laser desorption/ionization mass spectrometry (LDI-MS); however, limited studies have elucidated the desorption/ionization mechanism based on the physicochemical properties of substrates. Herein, the enhancement in desorption/ionization is investigated using a hybrid matrix of Au nanoisland-functionalized ZnO nanotubes (AuNI-ZNTs). The underlying origin is explored in terms of the photo-electronic and -thermal properties of the matrix. This is the first study to report the effect of laser-induced surface restructuring/melting phenomenon on the LDI-MS performance. AuNI plays a central role as a photothermal nanofurnace, which facilitates the internal energy transfer from the AuNI to the adsorbed analytes by reconstruction in the structurally dynamic AuNI and therefore favors the desorption process. Moreover, piezoelectricity is driven in situ in the AuNI-ZNT hybrid, which modulates the overall band structure and thereby promotes the ionization process. Ultimately, high LDI-MS performance is demonstrated by analyzing small metabolites of fatty acids and monosaccharides, which are challenged to be detected in conventional LDI-MS. This study emphasizing the understanding of matrix properties can provide insights into the design and development of a novel nanomaterial as an efficient LDI matrix. Furthermore, the developed hybrid matrix can overcome the major hurdles existing in conventional LDI-MS.

Extraordinary sensitivity enhancement of Ag-Au alloy nanohole arrays for label-free detection of Escherichia Coli

Alloy nanostructures unveil extraordinary plasmonic phenomena that supersede the mono-metallic counterparts. Here we report silver-gold (Ag-Au) alloy nanohole arrays (α-NHA) for ultra-sensitive plasmonic label-free detection of Escherichia Coli (E. coli). Large-area α-NHA were fabricated by using nanoimprint lithography and concurrent thermal evaporation of Ag and Au. The completely miscible Ag-Au alloy exhibits an entirely different dielectric function in the near infra-red wavelength range compared to mono-metallic Ag or Au. The α-NHA demonstrate substantially enhanced refractive index sensitivity of 387 nm/RIU, surpassing those of Ag or Au mono-metallic nanohole arrays by approximately 40%. Moreover, the α-NHA provide highly durable material stability to corrosion and oxidation during over one-month observation. The ultra-sensitive α-NHA allow the label-free detection of E. coli in various concentration levels ranging from 10³ to 10⁸ cfu/ml with a calculated limit of detection of 59 cfu/ml. This novel alloy plasmonic material provides a new outlook for widely applicable biosensing and bio-medical applications.

Paper-Based Multiplex Surface-Enhanced Raman Scattering Detection Using Polymerase Chain Reaction Probe Codification

We construct a multiplex surface-enhanced Raman scattering (SERS) platform based on a plasmonic paper substrate and a double-labeled probe for the detection of multiple fluorescent dyes at high sensitivity in a single-wavelength light source system. Plasmonic paper, made of silver nanodots on three-dimensional cellulose fibers, enables highly sensitive SERS biosensing based on localized surface plasmon resonance (LSPR). The proposed method enables the identification and quantification of a range of fluorescent dyes ranging from picomolar to millimolar concentrations. The use of 5' fluorescent dyes and 3' biotin-modified probes as SERS-coded probes renders possible the separation of fluorescent dyes with streptavidin-coated magnetic beads (SMBs) and the sensitive detection of multiple dyes after the reverse transcription polymerase chain reaction (RT-PCR). This experimental study reveals the multiplex detection capability of PCR-based SERS under existing PCR conditions without modifying primer and probe sequences. The combination of magnetic bead-based separation and paper SERS platform is efficient, economical, and can be used for the simultaneous detection of two or more pathogens.

Gold Nano-Island Platforms for Localized Surface Plasmon Resonance Sensing: A Short Review

Nano-islands are entities (droplets or other shapes) that are formed by spontaneous dewetting (agglomeration, in the early literature) of thin and very thin metallic (especially gold) films on a substrate, done by post-deposition heating or by using other sources of energy. In addition to thermally generated nano-islands, more recently, nanoparticle films have also been dewetted, in order to form nano-islands. The localized surface plasmon resonance (LSPR) band of gold nano-islands was found to be sensitive to changes in the surrounding environment, making it a suitable platform for sensing and biosensing applications. In this review, we revisit the development of the concept of nano-island(s), the thermodynamics of dewetting of thin metal films, and the effect of the substrate on the morphology and optical properties of nano-islands. A special emphasis is made on nanoparticle films and their applications to biosensing, with ample examples from the authors’ work.

Self-assembled plasmonics for angle-independent structural color displays with actively addressed black states

Functional nanomaterials will enable the next generation of displays, detectors, and photovoltaic devices by interacting with light at subwavelength length scales. However, performance and practical integration with current electronic systems remain a scientific and engineering challenge. Here, we report the wafer-scale self-assembly/growth of nanoparticles which reproduce the cyan, magenta, and yellow color space. We explore the physics of the optical resonances and the advantageous properties they manifest for color filter technology, such as angle insensitivity and high saturation. The versatile formation process then enables integration with commercial devices to realize a hybrid, nanoparticle–liquid crystal reflective display.

Nanostructured plasmonic materials can lead to the extremely compact pixels and color filters needed for next-generation displays by interacting with light at fundamentally small length scales. However, previous demonstrations suffer from severe angle sensitivity, lack of saturated color, and absence of black/gray states and/or are impractical to integrate with actively addressed electronics. Here, we report a vivid self-assembled nanostructured system which overcomes these challenges via the multidimensional hybridization of plasmonic resonances. By exploiting the thin-film growth mechanisms of aluminum during ultrahigh vacuum physical vapor deposition, dense arrays of particles are created in near-field proximity to a mirror. The sub-10-nm gaps between adjacent particles and mirror lead to strong multidimensional coupling of localized plasmonic modes, resulting in a singular resonance with negligible angular dispersion and ∼98% absorption of incident light at a desired wavelength. The process is compatible with arbitrarily structured substrates and can produce wafer-scale, diffusive, angle-independent, and flexible plasmonic materials. We then demonstrate the unique capabilities of the strongly coupled plasmonic system via integration with an actively addressed reflective liquid crystal display with control over black states. The hybrid display is readily programmed to display images and video.

Improved Photoresponse of UV Photodetectors by the Incorporation of Plasmonic Nanoparticles on GaN Through the Resonant Coupling of Localized Surface Plasmon Resonance

Very small metallic nanostructures, i.e., plasmonic nanoparticles (NPs), can demonstrate the localized surface plasmon resonance (LSPR) effect, a characteristic of the strong light absorption, scattering and localized electromagnetic field via the collective oscillation of surface electrons upon on the excitation by the incident photons. The LSPR of plasmonic NPs can significantly improve the photoresponse of the photodetectors. In this work, significantly enhanced photoresponse of UV photodetectors is demonstrated by the incorporation of various plasmonic NPs in the detector architecture. Various size and elemental composition of monometallic Ag and Au NPs, as well as bimetallic alloy AgAu NPs, are fabricated on GaN (0001) by the solid-state dewetting approach. The photoresponse of various NPs are tailored based on the geometric and elemental evolution of NPs, resulting in the highly enhanced photoresponsivity of 112 A W-1, detectivity of 2.4 × 1012 Jones and external quantum efficiency of 3.6 × 104% with the high Ag percentage of AgAu alloy NPs at a low bias of 0.1 V. The AgAu alloy NP detector also demonstrates a fast photoresponse with the relatively short rise and fall time of less than 160 and 630 ms, respectively. The improved photoresponse with the AgAu alloy NPs is correlated with the simultaneous effect of strong plasmon absorption and scattering, increased injection of hot electrons into the GaN conduction band and reduced barrier height at the alloy NPs/GaN interface.

Strongly confined localized surface plasmon resonance (LSPR) bands of Pt, AgPt, AgAuPt nanoparticles

Multi-metallic alloy nanoparticles (NPs) can enable the advanced applications in the energy, biology, electronics, optics and catalysis due to their multi-functionality, wide tunable range and electronic heterogeneity. In this work, various mono-, bi- and tri-metallic nanostructures composed of Ag, Au and Pt are demonstrated on transparent c-plane sapphire (0001) substrates and the corresponding morphological and optical characteristics are thoroughly investigated. The resulting Pt and AuPt NPs in this study demonstrate much enhanced LSPR responses as compared to the pure Pt NPs from the previous studies, which was contributed by the synergistic effect of Au and Pt and improved surface morphology. These results are sharply distinct in terms of surface morphology and elemental variability from those obtained by the dewetting of monometallic Ag, Au and Pt films under the similar growth conditions, which is due to the distinct dewetting kinetics of the bi-layer and tri-layer films. These NPs exhibit strongly enhanced localized surface plasmon resonance (LSPR) bands in the UV-VIS wavelengths such as dipolar, quadrupolar, multipolar and higher order resonance modes depending upon the size and elemental composition of NPs. The LSPR bands are much stronger with the high Ag content and gradually attenuated with the Ag sublimation. Furthermore, the VIS region LSPR bands are readily blue shifted along with the reduction of NP size. The Ag/Pt bi-layers and Ag/Au/Pt tri-layers are systematically dewetted and transformed into various AgPt and AgAuPt nanostructures such as networked, elongated and semispherical configurations by means of enhanced surface diffusion, intermixing and energy minimization along with the temperature control. The sublimation of Ag atoms plays a significant role in the structural and elemental composition of NPs such that more isolated and semispherical Pt and AuPt NPs are evolved from the AgPt and AgAuPt NPs respectively.

Enhanced Localized Surface Plasmon Resonance of Fully Alloyed AgAuPdPt, AgAuPt, AuPt, AgPt, and Pt Nanocrystals: Systematical Investigation on the Morphological and LSPR Properties of Mono Bi-, Tri-, and Quad-Metallic Nanoparticles

Multi-metallic alloy nanoparticles (NPs) can offer tunable or modifiable localized surface plasmon resonance (LSPR) properties depending upon their configurational and elemental alterations, which can be utilized in various applications, that is, in photon energy harvesting, optical sensing, biomedical imaging, photocatalysis, and spectroscopy. In this work, a systematic investigation on the morphological and LSPR properties of multi-metallic alloy NPs incorporating Ag, Au, Pd, and Pt is presented on c-plane sapphire (0001). The resulting NPs exhibit much enhanced and tunable LSPR bands in the UV-VIS wavelength as compared to the previously reported mono-metallic NPs based on the considerable improvement in size and shape of nanostructures along with the electronic heterogeneity. Solid-state dewetting of sputtered bilayers (Ag/Pt), tri-layers (Ag/Au/Pt), and quad-layers (Ag/Au/Pd/Pt) is employed to demonstrate a wide variety of configurations, sizes, densities, and elemental compositions of Pt, AgPt, AuPt, AgAuPt, AgAuPt, and AgAuPdPt NPs by the systematic control of annealing temperature and deposition schemes. The distinct morphology and elemental composition of surface nanostructures are obtained by means of surface diffusion, intermixing, and surface/interface energy minimization along with the applied thermal energy. In addition, the sublimation of Ag atoms from the alloy nanostructure matrix significantly influences the structural, elemental, and thus optical properties of NPs by reducing the average size and Ag percentage in the alloy NPs. Based on the specific size, shape, and elemental composition of NPs, the excitation of LSPR is correlated to the dipolar, quadrupolar, multi-polar, and higher order (HO) modes along with the finite difference time domain simulation of local electric-field. The LSPR intensity is generally stronger with a higher percentage of Ag atoms in the alloy NPs and gradually diminished by the sublimation loss. However, even the mono-metallic and alloy NPs without Ag exhibited significantly improved and dynamic nature of plasmonic bands in the UV and VIS wavelength.

Systematic investigation on quad-metallic AgAuPdPt and tri-metallic AuPdPt NPs through the solid-state dewetting of quad-layer Ag/Au/Pd/Pt thin films on c-plane sapphire

Multi-metallic alloy nanoparticles (MNPs) can offer valuable opportunities to meet the various demands of applications. MNPs consist of various noble metallic elements can combine diverse electronic, optical and catalytic properties in a single NP configuration, thus taking the advantage of each element. In this paper, the fabrication of tri- and quad- metallic alloy NPs with noble elements (Ag, Au, Pd and Pt) and the corresponding localized surface plasmon resonance (LPSR) properties are systematically demonstrated. Tri- and quad-metallic alloy NPs come in various size and configurations by the solid-state dewetting of Ag/Au/Pd/Pt quad-layers on sapphire (0001). Tri-metallic AuPdPt NPs are demonstrated by the systematic control of growth temperature along with the significant Ag atom sublimation. Strongly enhanced and tunable LPSR is exerted in the UV-VIS regions depending upon the size, configuration, spacing and elemental composition of the MNPs. The size dependent LSPR response of MNPs is discussed based on the absorption and scattering along with the excitation of dipolar, quadrupolar, high order and multipolar resonance modes. The MNPs exhibit much stronger and dynamic LSPR bands as compared with the monometallic Pt and Pd NPs with the comparable size and configurations.

Improved LSPR Properties of Ag–Pt and Pt Nanoparticles: A Systematic Study on Various Configurations and Compositions of NPs via the Solid-State Dewetting of Ag–Pt Bilayers

The localized surface plasmon resonance (LSPR) of noble metal nanoparticles (NPs) has become an important research topic in various fields and can be systematically tuned to obtain the desired device performance through the appropriate structural and elemental modifications. In this research, the improved LSPR properties of Pt NPs and diverse configurations and compositions of Ag–Pt bimetallic alloy NPs were demonstrated on sapphire (0001) via the solid-state dewetting (SSD) of Ag–Pt bilayers. A strong and dynamic LSPR response in the ultraviolet (UV) and visible (VIS) regions was demonstrated depending on the elemental composition and surface morphology of the NPs, which is discussed along with finite difference time domain (FDTD) simulations. In comparison, the Ag–Pt NPs exhibited stronger LSPR excitation, whereas the Pt NPs showed a relatively weaker and broader response. Meanwhile, the Pt NPs fabricated in this study still demonstrated a much-enhanced LSPR response compared to previous studies on the solid-state dewetting of pure Pt films due to improvements in configuration, uniformity, and interparticle gaps. Various surface morphologies of NPs, such as connected nanoclusters, elongated NPs, and isolated spherical NPs, were obtained on the basis of alloying, diffusion, Rayleigh instability, and a surface minimization mechanism, which were different from those of pure Ag and Pt NPs in similar growth conditions. Particularly, one-step annealing of an Ag–Pt bilayer yielded Ag–Pt alloy NPs below 600 °C, which subsequently transformed into pure Pt NPs above 650 °C, in which the high diffusivity and high vapor pressure of Ag atoms significantly facilitated the overall growth process of the NPs.

Ag/Au Alloyed Nanoislands for Wafer-Level Plasmonic Color Filter Arrays

Alloyed metals in nanoscale exhibit some intriguing features that are absent in mono-metallic nanostructures. Here we report silver and gold alloyed nanoislands with high tunability of localized surface plasmon resonance (LSPR) wavelength in the visible range for wafer-level plasmonic color filter arrays. The nanofabrication includes two simple steps of concurrent thermal evaporation of Ag and Au grains and solid-state dewetting of the as-deposited nanocomposite thin film. The alloy ratio during the evaporation precisely tunes the LSPR wavelengths within 415-609 nm spectrum range. The elemental composition map reveals that alloyed nanoislands are completely miscible while preserving uniform size, regardless of the alloy ratio. Besides, the multiple lift-off processes and thermal dewetting of Ag/Au nanocomposite thin films successfully demonstrate the wafer-level nanofabrication of plasmonic color filter mosaic. Each plasmonic color pixel comprises different alloy ratio and efficiently transmits colors ranging from cyan, yellow, and magenta. The transmission spectra transposed onto a CIE 1931 color map show comparable color diversity to the plasmonic color filters fabricated by conventional e-beam lithographic techniques. This novel method provides a new direction for large-scale and visible plasmonic color filter arrays in advanced display or imaging applications.

Nanoislands as plasmonic materials

Subwavelength metal nanoislands thermally dewetted from a thin film emerge as a powerful and cost-effective photonic material, due to the formation of substantially strong nano-gap-based plasmonic hot spots and their simple large-area nanofabrication. Unlike conventional nanostructures, nanoislands dewetted from thin metal films can be formed on a large scale at the wafer level and show substrate-dependent plasmonic phenomena across a broad spectral range from ultraviolet to infrared. Substrate-selective dewetting methods for metal nanoislands enable diverse nanophotonic and optoelectronic technologies, underlining mechanical, structural, and material properties of a substrate. Emerging bioplasmonic technology using metal nanoislands also serves as a high-throughput and surface-sensitive analytical technique with wide-ranging application in rapid, real-time, and point-of-care medical diagnostics. This review introduces an assortment of dewetting fabrication methods for metal nanoislands on distinct substrates from glass to cellulose fibers and provides novel findings for metal nanoislands on a substrate by three-dimensional numerical modeling. Furthermore, the plasmonic properties of metal nanoislands and recent examples for their photonic applications, in particular, biological sensing, are technically summarized and discussed.

Laser-Induced Dewetting of Metal Thin Films for Template-Free Plasmonic Color Printing

Plasmonic color laser printing has several advantages over pigment-based technology, including the absence of ink and toner and the production of nonfading colors. However, the current printing method requires a template that should be prepared via nanofabrication processes, making it impractical for large-area color images. In this study, we show that laser-induced dewetting of metal thin films by a nanosecond pulsed laser can be effectively utilized for plasmonic color printing. Ag, Au, and their complex films deposited on a glass substrate were dewetted into different surface structures such as droplets, rods, and ripples, depending on the incident laser energy. The resulting morphological evolutions could be explained by Rayleigh and capillary instabilities. For a bimetallic film comprising Ag nanowires coated on a Au layer, a few different plasmonic colors were generated from a single sample simply by changing the laser fluence. This provides a possible method for implementing plasmonic color laser printing without using a prepatterned template.

Investigation on the morphological and optical evolution of bimetallic Pd-Ag nanoparticles on sapphire (0001) by the systematic control of composition, annealing temperature and time

Multi-metallic alloy nanoparticles (NPs) can offer additional opportunities for modifying the electronic, optical and catalytic properties by the control of composition, configuration and size of individual nanostructures that are consisted of more than single element. In this paper, the fabrication of bimetallic Pd-Ag NPs is systematically demonstrated via the solid state dewetting of bilayer thin films on c-plane sapphire by governing the temperature, time as well as composition. The composition of Pd-Ag bilayer remarkably affects the morphology of alloy nanostructures, in which the higher Ag composition, i.e. Pd_0.25Ag_0.75, leads to the enhanced dewetting of bilayers whereas the higher Pd composition (Pd_0.75Ag_0.25) hinders the dewetting. Depending on the annealing temperature, Pd-Ag alloy nanostructures evolve with a series of configurations, i.e. nucleation of voids, porous network, elongated nanoclusters and round alloy NPs. In addition, with the annealing time set, the gradual configuration transformation from the elongated to round alloy NPs as well as size reduction is demonstrated due to the enhanced diffusion and sublimation of Ag atoms. The evolution of various morphology of Pd-Ag nanostructures is described based on the surface diffusion and inter-diffusion of Pd and Ag adatoms along with the Ag sublimation, Rayleigh instability and energy minimization mechanism. The reflectance spectra of bimetallic Pd-Ag nanostructures exhibit various quadrupolar and dipolar resonance peaks, peak shifts and absorption dips owing to the surface plasmon resonance of nanostructures depending on the surface morphology. The intensity of reflectance spectra is gradually decreased along with the surface coverage and NP size evolution. The absorption dips are red-shifted towards the longer wavelength for the larger alloy NPs and vice-versa.