Metal-dielectric Interface Research Articles

Effect of the interface on femtosecond laser damage of a metal-dielectric low dispersion mirror

Metal-dielectric low dispersion mirrors (MLDM) have a promising application prospect in petawatt (PW) laser systems. We studied the damage characteristics of MLDM and found that the damage source of MLDM (Ag + Al2O3+SiO2) is located at the metal-dielectric interface. We present the effect of the interface on the femtosecond laser damage of MLDM. Finite element analysis shows that thermal stress is distributed at the interface, causing stress damage which is consistent with the damage morphology. After enhancing the interface adhesion and reducing the residual stress, the damage source transfers from the interface to a surface SiO2 layer, and the damage threshold can be increased from 0.60 J/cm2 to 0.73 J/cm2. This work contributes to the search for new techniques to improve the damage threshold of MLDM used in PW laser systems.

Kinetic theory of electroconductivity of metal nanoparticles in the condition of surface plasmon resonance

In recent years, there has been increasing interest in the study of the optical properties of metallic nanostructures. This interest is primarily related to the practical application of such nanostructures in quantum optical computers, micro- and nanosensors. These applications are based on the fundamental optical effect of excitation of surface plasmons. Surface plasmons are electromagnetic excitations of electron plasma of metals at the metal-dielectric interface, which are accompanied by fluctuations in the surface charge density. The consequence of this phenomenon is surface plasmon resonance (SPR) – an increase in the energy absorption cross-section of a metal nanoparticle as the light frequency (laser irradiation) approaches to the frequency of the nanoparticle SPR. The SPR frequency for metallic nanoparticles in a dielectric matrix is found. Using the kinetic subdivision, the components of the optical power tensor for ellipsoidal metal nanoparticles were developed.

Simulation design of silver nanoparticle coated photonic crystal fiber sensor based on surface plasmon resonance

Surface Plasmon Resonance (SPR) is the charge density excitation oscillation (surface Plasmon’s, (SP)) caused by the polarized light along with the metal-dielectric interface by agreeing to phase-matching condition between polarized light and SPR. SPR method has unusual advantages like label-free, real-time and high resolutions with less than 10-7 RIU which is not consenting with other sensing methods. Photonic Crystal Fiber (PCF) presents unique features like design elasticity, geometric flexible and extraordinary guiding mechanism which head for better performance contrast conventional optical fibre, Additionally, the presence of air holes gives the possibility to insert multi able materials, that can recognize the interaction of travelling light and materials operatively. Adding the advantages of PCF to the properties of SPR, lead to design very strong and unique devices in different applications. In this paper, the PCF sensor based on SPR technique had been presented. The inner holes of PCF were coated with silver and then filled with air and ethanol. This was achieved theoretically by Finite Element Method (FEM). When the phase-matching condition was achieved at a fixed wavelength, the energy of the core-guided mode is shifted to the plasmon area and a resonant loss peak is observed at this wavelength. The simulated results show that a blue shifting is obtained when the outer air holes of PCF is filling with ethanol while the inner ring is filled with silver nano-particles. The maximum resolution and sensitivity are 5.66*10-4 RIU, 132.3 nm/RIU respectively in the sensing range of air refractive index to ethanol refractive index are obtained. The submitted design could be very useful in many fields like refractive index and temperature sensing applications.

Gaussian Beam Shaping and Multivariate Analysis in Plasmonic Sensing.

This work demonstrates a novel strategy to improve the sensing performance of a prism-coupled surface plasmon resonance system by Gaussian beam shaping and multivariate data analysis. The propagation of the beam along the optical system has been studied using the Gaussian beam approximation to design the incident beam such that the beam waist is aligned precisely and that stability is assured at the metal-dielectric interface. This renders a collimated incident beam, hence least angular dispersion, yielding a stronger and sharper plasmonic resonance. Moreover, we use the multivariate analysis method partial least squares that combines multiple features of the surface plasmon resonance curve and allows for a more precise analysis of the plasmonic response. Compared to univariate analysis, partial least squares improves typical sensing performance parameters remarkably. The combination of both aspects, beam shaping and multivariate analysis, overcomes current limitations of plasmonic detection systems. Thereby, we improve analytical sensitivity by a factor of 16, decrease the prediction error of the concentration of an unknown analyte by a factor of 11, and enhance resolution to the order of 5 × 10-7 RIU in angular interrogation.

Sensitivity enhancement with anti-reflection coating of silicon nitride (Si3N4) layer in silver-based Surface Plasmon Resonance (SPR) sensor for sensing of DNA hybridization

This work presents a highly sensitive silver (Ag) based Surface Plasmon Resonance (SPR) sensor with graphene-coated over Silicon nitride (Si3N4) for sensing of Deoxyribonucleic acid (DNA) hybridization. The design consists of five layers namely Ag, Si3N4, graphene, and sensing medium along with BK7 glass prism that couple light at the metal–dielectric interface. The performance of the present structure has been evaluated using the angular interrogation method. The present investigation reveals the difference in complementary DNA strands and mismatched DNA strands as well as single-nucleotide polymorphisms (SNP) event by examining the variation of resonance angle in the reflectivity spectrum. The performance of the present structure is compared with the contemporary structures and found better than existing sensors. Therefore, the proposed structure is suitable in the biochemical field for the detection of biomolecules interactions.

Optical Magnetism in Surface Plasmon Resonance–Based Sensors for Enhanced Performance

Surface plasmon resonance (SPR)–based structures are finding important applications in sensing biological as well as inorganic samples. In SPR techniques, an angle-resolved reflection (R) profile of the incident light from a metal-dielectric interface is measured and the resonance characteristics are extracted for the identification of the target sample. However, the performance, and hence the applicability of these structures, suffers when the weight and concentration of the target samples are small. Here, we show that SPR-based sensors can create strong magnetism at optical frequency, which can be used for the detection of target samples instead of using the conventional R profiles, as the magnetic resonance varies depending on the refractive index of the target sample. Using scattering parameters retrieval method, we computationally find out the effective permeability (μeff) of a SPR sensor with a structure based on Kretschmann configuration, and use it to calculate the performance of the sensor. A comparison with the conventional technique that uses R profile to detect a target sample shows a significant increase in the sensor performance when μeff is used instead.

Optimizing the Sensing Efficiency of Plasmonic Based Gas Sensor

This paper investigates the behavior of the surface plasmon polaritons (SPPs) on dielectric-metal interface using Ag thin film on glass substrate. The Kretschman configuration, which is sensitive to the change in the local environment adjacent to Ag thin film, has been modeled using COMSOL Multiphysics, RF module. The graphical presentation for the change in excitation spectra of SPPs on the interface has been analyzed by adjusting the incident angle greater than critical angle of glass while keeping the thickness of Ag thin film constant. The cross-sectional view reveals that the maximum amplitude of electric field occurs at 43° incidence. In order to study the behavior of resonance dip at varying refractive index (from 1.00 to 1.01), the reflection spectra for transverse magnetic (TM) mode of incident light has been extracted using far-field analysis. To further explore the sensitivity and resolution of the device, nm/RIU is collected by using the change in the wavelength (nm) of SPPs for minimum reflection. The remarkably maximum sensitivity of the device has been calculated as 23,000 nm/RI and Q value calculated for Ag-based sensing is 13.

Plasmon-assisted interaction of Si with light, for cancer hyperthermia and electromagnetic energy harvest

Metal-assisted chemical etching (MACE) is applied for fabrication of silicon nanowires (SiNWs). We have shown the effect of amorphous sheath of SiNWs by treating the nanowires with SF6 and the resulting reduction of absorption bandwidth, i.e. making SiNWs semi-transparent in near-infrared (IR). For the first time, by treating the fabricated SiNWs with copper containing HF∕H2O2∕H2O solution, we have generated crystalline nanowires with broader light absorption spectrum, up to λ = 1 μm. Both the absorption and photo-luminescence (PL) of the SiNWs are observed from visible to IR wavelengths. It is found that the SiNWs have PL at visible and near Infrared wavelengths, which may infer presence of mechanisms such as forbidden gap transitions other can involvement of plasmonic resonances. Non-radiative recombination of excitons is one of the reasons behind absorption of SiNWs. Also, on the dielectric metal interface, the absorption mechanism can be due to plasmonic dissipation or plasmon-assisted generation of excitons in the indirect band-gap material. Comparison between nanowires with and without metallic nanoparticles has revealed the effect of nanoparticles on absorption enhancement. The broader near IR absorption, paves the way for applications like hyperthermia of cancer while the optical transition in near IR also facilitates harvesting electromagnetic energy at a broad spectrum from visible to IR.

Terahertz Spoof Surface Plasmonic Logic Gates.

SummaryLogic gates are important components in integrated photonic circuitry. Here, a series of logic gates to achieve fundamental logic operations based on linear interference in spoof surface plasmon polariton waveguides are demonstrated at terahertz frequencies. A metasurface-based plasmonic source is adopted to couple free-space terahertz radiation into surface waves, followed by a funnel-shaped metasurface to efficiently couple the surface waves to the waveguides built on a domino structure. A single Mach-Zehnder waveguide interferometer can work as logic gates for four logic functions: AND, NOT, OR, and XOR. By cascading two such interferometers, NAND and NOR operations can also be achieved. Experimental investigations are supported by numerical simulations, and good agreement is obtained. The logic gates have compact sizes and high intensity contrasts for the output “1” and “0” states. More complicated functions can be envisioned and will be of great value for future terahertz integrated computing.

Plasmon-Assisted Direction- and Polarization-Sensitive Organic Thin-Film Detector.

Utilizing Bragg surface plasmon polaritons (SPPs) on metal nanostructures for the use in optical devices has been intensively investigated in recent years. Here, we demonstrate the integration of nanostructured metal electrodes into an ITO-free thin film bulk heterojunction organic solar cell, by direct fabrication on a nanoimprinted substrate. The nanostructured device shows interesting optical and electrical behavior, depending on angle and polarization of incidence and the side of excitation. Remarkably, for incidence through the top electrode, a dependency on linear polarization and angle of incidence can be observed. We show that these peculiar characteristics can be attributed to the excitation of dispersive and non-dispersive Bragg SPPs on the metal–dielectric interface on the top electrode and compare it with incidence through the bottom electrode. Furthermore, the optical and electrical response can be controlled by the organic photoactive material, the nanostructures, the materials used for the electrodes and the epoxy encapsulation. Our device can be used as a detector, which generates a direct electrical readout and therefore enables the measuring of the angle of incidence of up to 60° or the linear polarization state of light, in a spectral region, which is determined by the active material. Our results could furthermore lead to novel organic Bragg SPP-based sensor for a number of applications.

Experimental demonstration of controllable flat focusing mirror excited by surface plasmon polaritons

In this study, we investigate an optical modulation of the focusing mirror based on photonic jet effect working in the reflection mode The photonic jet effects excited by surface plasmon polariton (SPP) in the near-field on the front-side of different core–shell micro-cuboids positioned on a substrate are presented. The core–shell micro-cuboid consists of a metallic shell (silver or gold) and a dielectric core (polydimethylsiloxane). The specific localized intensity distributions of the generated photonic jet at different core–shell micro-cuboids are simulated by using finite-difference time-domain technique. The experimental observations of focusing modulation are performed by a scanning optical microscope with oblique illumination. Due to the nature of SPP, the highly focused electric field near the metal–dielectric interface of the gold-coating micro-cuboids is enhanced by about 4 times. The generation of the focusing mirror based on SPP photonic jet can be flexibly controlled by varying the metallic shell. The controllable focusing mirror is a great possibility for integrated plasmonic circuits, surface optical tweezers, and biosensing.

A novel approach to mitigate stress induced defects at metal-dielectric interface in Redistribution layers for 3D IC stacking

Abstract The reliability of a redistribution layers in 3D IC is dependent on how well the different shape and size of metal connection with varying density are connected at the different metallization levels. The widely different coefficient of thermal expansion of metal (Cu ~16.5 × 10−6 m/mK) and dielectric (SiO2 ~ 3 × 10−6 m/mK) often leads to defects, such as cracking at the metal-dielectric interface. In this work, we present a manufacturing level friendly process modification to the conventional approach to present an almost crack free metal-dielectric interface for subsequent processing in the RDL fabrication. After the copper electroplating and chemical mechanical planarization (CMP), we use a cap layer to protect the top layer and anneal the metal. Finally, we repeat the CMP to remove the cap layer before sending the wafers for subsequent processing.

Efficient formation and tunability of optical scattering directivity of surface waves by a linear array of nanoantennas on a metallic film

Photonic spin Hall effect (PSHE) related to spin–orbit interaction of light leads to spin-momentum locking of longitudinal-spin photons of a pump beam into transverse-spin photons of an inherently circularly polarized surface wave like surface plasmon polaritons (SPPs). An excited nanoparticle (NP) above a metal–dielectric interface optically couples pump beam photons into the SPP photons, though an array of NPs may provide a desired and remarkable scattering directivity pattern (SDP). Here we show how a linear array of alike nanoantennas illuminated by an optical beam with different wave polarizations and incidence directions forms the unique SDPs, and we show how the PSHE affects the propagation direction of the scattered SPPs and their SDPs. The scattering patterns for the excited surface wave with remarkable tunability and functionality are studied in two principle cases, namely, broadside and endfire, in which the PSHE may efficiently emerge. The theoretical results developed based on Green’s tensor approach accompanied by the mode-matching technique and quasistatic modeling are in good agreement with the computational results. In this way, the crucial parameters’ effects on the SDPs, such as the elements’ spacing and number in the array, are thoroughly investigated. The reported results pave the way to adaptively engineer the scattering formation of the SPP-type waves for surface optics and photonics applications.

Novel Au nano-grating for detection of water in various electrolytes

This paper reports an advanced and novel sensing idea by utilizing the concept of surface plasmon resonance. A numerically designed model of plasmonic-based sensor has been proposed that is capable of detecting the mixture of water in alcohol and in a variety of other electrolytes including milk, hemoglobin, octane, etc. The sensor uses gold as a recognition element with equidistant slits for the transmission of incoming light which give rise to plasmon polaritons on metal–dielectric–interface. The zeroth-order transmission spectra have been extracted for this investigation and optimization. A transverse magnetic wave illuminates the noble metal normally through a glass substrate generating surface plasmon polaritons (SPPs) on a particular wavelength which changes with respect to the refractive index of adjacent medium. The sensor model has been numerically solved after optimization of slit size by keeping other parameters fixed utilizing the fundamental plasmonic mode for efficient excitation of SPPs. In this sensing chip, a uniform spatial period of about 660 nm, a constant slit size of 320 nm, a gold thickness of 50 nm for sensing element and 500 nm for glass substrate are used. An appreciable increment in the value of refractive index sensitivity of 668.66 nm per RIU has been found which is noteworthy. Such sensors are likely been welcomed in biological investigation, along with chemical and environmental detection techniques.

Quantum teleportation mediated by surface plasmon polariton

Surface plasmon polaritons (SPPs) are collective excitations of free electrons propagating along a metal-dielectric interface. Although some basic quantum properties of SPPs, such as the preservation of entanglement, the wave-particle duality of a single plasmon, the quantum interference of two plasmons, and the verification of entanglement generation, have been shown, more advanced quantum information protocols have yet to be demonstrated with SPPs. Here, we experimentally realize quantum state teleportation between single photons and SPPs. To achieve this, we use polarization-entangled photon pairs, coherent photon–plasmon–photon conversion on a metallic subwavelength hole array, complete Bell-state measurements and an active feed-forward technique. The results of both quantum state and quantum process tomography confirm the quantum nature of the SPP mediated teleportation. An average state fidelity of 0.889pm 0.004 and a process fidelity of 0.820pm 0.005, which are well above the classical limit, are achieved. Our work shows that SPPs may be useful for realizing complex quantum protocols in a photonic-plasmonic hybrid quantum network.

On the Issue of Crack Formation in a Thin Dielectric Layer on Silicon under Thermal Shock

The work is devoted to the problem of crack formation in thin sublayers of silicon oxide during pulsed heating of interconnects on single-crystal silicon wafers. It was shown that the passage of current pulses with an amplitude of up to 8 × 1010 A/m2 and a duration of up to 500 μs leads to thermal destruction of the interconnects and contributes to the formation of microcracks in SiO2 films along the metallization path. The magnitude of the mechanical stresses arising in the structure during thermal shock is estimated. It is shown that in contrast to SiO2 films, the level of mechanical stresses in silicon is insufficient for cracking near the source of thermal shock. It was also found that the nature of cracking in a dielectric film depends on the quality of the deposition of the dielectric film and the metal film, as well as the state of the dielectric-metal interface.

Theoretical and experimental studies on broadband photoacoustic response of surface plasmon sensing

The surface plasmon (SP) sensing technique demonstrates high sensitivity and a broad bandwidth of measuring photoacoustic (PA) pressure transients. In this work, we further present a systematic investigation on PA response characteristics of the recently developed SP-based ultrasonic detector, where the ensemble of surface plasmon polaritons (SPPs) at the metal-dielectric interface is approximated as an equivalent acoustic detector. Relying on the intrinsically ultrafast temporal response (∼140 fs) and highly localized evanescent field (optical penetration depth of ∼185 nm) of the SPPs, the SP sensing can respond ultrasounds with the gigahertz frequency band theoretically, which, however, is far higher than the bandwidth in practical PA detection. We reveal that, due to acoustic interference, the finite lateral probing dimension in the SP sensor imposes an ultimate constraint on the accessible ultrasonic cutoff frequency, representing good agreement with the experimental results by acquiring PA impulses from an optically absorbing graphene film using our SP sensor. The theoretical framework enables analyzing the SP response characteristics of ultrasonic/PA pressure transients, which, therefore, offers guidelines for configuring the SP sensor with adequate sensitivity and bandwidths to access various biomedical PA applications, including volumetric imaging and spectroscopic analysis.

Realizing Anderson localization of surface plasmon polaritons and enhancing their interactions with excitons in 2D disordered nanostructures

Surface plasmon polaritons (SPPs) propagating on a metal–dielectric interface suffer from inevitable energy losses originating from metals, especially in a visible regime, which degrades the quality of SPP-based devices. However, if the size of the devices is sufficiently miniaturized, we can thereby limit the propagation length of the signals and effectively circumvent the problems of large propagation losses. Anderson localization is a possible approach to squeeze SPPs. In this Letter, we experimentally demonstrate the Anderson localization of SPPs at optical frequencies in two-dimensional (2D) nanostructures. By increasing the positional disorder of the silver nanohole arrays on a glass substrate, strong 2D localization of SPPs appears with an exponentially decreased electric field, reduced propagation length, and the rapid disappearance of the autocorrelation coefficient. Moreover, we manage to realize the localized SPP-exciton interactions in the 2D disordered silver nanoarrays combined with fluorescent dye molecules. Due to the disorder in the nanoarray, the collected photoluminescence from fluorescent dye molecules is enhanced by over three orders of magnitude compared to that on the silver film without nanostructures. Our study extends Anderson localization of SPPs at the visible regime to 2D disordered systems and provides a unique way to enhance light–matter interaction in SPP-based nanodevices.

Absence of unidirectionally propagating surface plasmon-polaritons at nonreciprocal metal-dielectric interfaces

In the presence of an external magnetic field, the surface plasmon polariton that exists at the metal-dielectric interface is believed to support a unidirectional frequency range near the surface plasmon frequency, where the surface plasmon polariton propagates along one but not the opposite direction. Recent works have pointed to some of the paradoxical consequences of such a unidirectional range, including in particular the violation of the time-bandwidth product constraint that should otherwise apply in general in static systems. Here we show that such a unidirectional frequency range is nonphysical using both a general thermodynamic argument and a detailed calculation based on a nonlocal hydrodynamic Drude model for the metal permittivity. Our calculation reveals that the surface plasmon-polariton at metal-dielectric interfaces remains bidirectional for all frequencies.

Generation of non-classical states of photons from a metal-dielectric interface: a novel architecture for quantum information processing.

We show the possibility to generate photons in a certain class of non-classical states from a metal-dielectric interface using dipole emitters on the interface. The photons emitted into the surface plasmon mode from the initially excited emitters radiate out in free space in a cone-shaped geometry. When detected at two detectors, these photons exhibit coalescence, a clear signature of non-classicality. Such a system can also be employed as a building block for a distributed quantum network. We further show that it is indeed feasible to implement our model using available technology.