Metallodielectric Photonic Crystals Research Articles

Bottom-up colloidal synthesis of PMMA@Au core–shell based metallodielectric photonic crystals as substrates for surface-enhanced Raman spectroscopy

The bottom-up colloidal synthesis of photonic band gap (PBG) materials or photonic crystals (PCs) has attracted considerable interest in comparison to top-down approaches due to the relatively simple processing steps involved, the potential for large area sample production and the relatively low-costs associated with this approach for the fabrication of complex 3-dimensional (3D) structures.This research focuses on the colloidal synthesis of poly(methyl methacrylate) (PMMA)@Au core–shell (CS) structures, their bottom-up assembly into 3D metallodielectric PCs (MDPCs) and the demonstration of their potential to be used as surface enhanced Raman substrates (SERS) using the commonly deployed SERS reporter molecule, 4- aminothiolphenol. Here, monodispersed spherical PMMA particles were used both as a host material for Au nanoparticles (NPs) and as a crystal template to produce the MDPC structures. The materials engineering employed which involved combining the synthesis of monodispersed CS particles and the fabrication of their corresponding MDPCs enabled us to control the distribution of Au NPs in the PC structure and thereby investigate their light scattering, reflection and transmission properties including Raman scattering.

Photonic Stopband Tuning in Metallo-Dielectric Photonic Crystals

One of the most appealing aspects of photonic crystal structures is the photonic bandgap created in structures with sufficiently high dielectric contrasts between constituent materials. Periodic structures with a modest dielectric contrast between high and low index regions instead form a photonic stopband; the photonic stopband is linked to the principal diffraction resonance from the (111) crystal plane in the photonic crystal. Understanding how specific photonic crystal structures and their associated stopband positions can selectively interfere with incoming light is vital for implementing these structured dielectrics in a range of optical applications. Among the many methods existing to modify the signature optical response of photonic crystal materials, metallo-dielectric photonic crystals act to incorporate metal particles into the ordered arrangement of these structures. We examined the optical changes to the transmission spectrum resulting from copper, nickel and gold metal infiltration into polystyrene opals and TiO2 inverse opals. We report a consistent and interesting optical phenomena directly associated with the creation of metallo-dielectric photonic crystal structures. More pronounced and numerous diffraction resonances emerge in opal photonic crystals with a metal deposited across the top layer. Common to both opal and inverse opal structures, was a blue-shift in the position of the (111) photonic stopband which increased in magnitude with greater metal content in the structure. We investigate the origin of the photonic stopband blue-shift by variation of the metal content and the placement of metal in the photonic crystal structure. Our results suggest that metal introduced to structured dielectric media acts to tune the position of the photonic stopband by slight alterations to the effective dielectric constant or effective refractive index of the photonic crystal material.

Colloidal Co-Crystallization: A New Route for Production of Three-Dimensional Metallodielectric Photonic Crystals

Colloidal Co-Crystallization: A New Route for Production of Three-Dimensional Metallodielectric Photonic Crystals

Investigation of TE-polarized photonic band gap properties in matallodielectric photonic crystals composed of metal coated dielectric cylinders

Using the Dirichlet-to-Neumann map method and generalization of this method, we have been able to calculate the photonic band structure of two-dimensional (2D) metallodielectric photonic crystals composed of metal-coated circular dielectric rods. The rods are embedded in an air background with a square array. We are interested in considering transverse electric (TE) mode of electromagnetic waves. The resulting band structures show the existence of photonic band gaps as well as some flat band regions. We theoretically study the effect of the dielectric constant and radius of the dielectric core on the photonic band structures. There are some interesting results compared to the case of solid metallic rods (without dielectric core) such as appearing the new photonic band gaps and a flat band region with the characteristic of cavity modes.

Effect of background dielectric on TE-polarized photonic bandgap of metallodielectric photonic crystals using Dirichlet-to-Neumann map method.

Using the Dirichlet-to-Neumann map method, we have calculated the photonic band structure of two-dimensional metallodielectric photonic crystals having the square and triangular lattices of circular metal rods in a dielectric background. We have selected the transverse electric mode of electromagnetic waves, and the resulting band structures showed the existence of photonic bandgap in these structures. We theoretically study the effect of background dielectric on the photonic bandgap.

Role of Stopband and Localized Surface Plasmon Resonance in Raman Scattering from Metallo-Dielectric Photonic Crystals

Self-assembled photonic crystals grown from different colloidal sizes are coated with gold nanoparticles preferentially on their surface. The effect of localized surface plasmon resonance and the photonic stopband on the Raman scattering from these crystals is analyzed from the angle-dependent scattering measurements. The coupling of photonic and plasmonic modes at the surface of the photonic crystal is verified by measuring the increment in Raman scattering from the crystals containing the gold nanoparticles, and this increment is found to follow the spectral trend of localized surface plasmon resonance.

Thermally Tunable Metallodielectric Photonic Crystals from the Self‐Assembly of Brush Block Copolymers and Gold Nanoparticles

A robust strategy for the rapid and scalable fabrication of well-ordered metallodielectric 1D photonic crystals through the self-assembly of brush block copolymers and gold nanoparticles is demonstrated. The optical properties of the photonic crystals containing ultrahigh loadings of the gold nanoparticles are thermally tunable through the creation of a network structure of the nanoparticles.

Plasmonic Resonance-Induced Effects on Stopband and Emission Characteristics of Dye-Doped Opals

Three-dimensional colloidal photonic crystals containing a fluorophore, and fabricated by inward growing self-assembly method, are infiltrated with gold nanoparticles of 5-nm diameter. The effects of localized surface plasmon resonance of gold nanoparticles on the stopband of the photonic crystal are investigated by tuning the reflection band to overlap with the plasmonic band. Interestingly, reflection spectra of gold-infiltrated PhC show a clear suppression in the reflection band around the stopband center at higher angles of incidence due to the efficient coupling between the plasmon and photon modes inside the crystal. The resonant absorption appears only when there is a significant overlap between the stopband and the plasmonic resonance. The role of plasmonic resonance towards the enhancement of emission at the band edges is also discussed from the experimental results on the dielectric and metallo-dielectric photonic crystals.

Energy streamlines in near-field radiative heat transfer between hyperbolic metamaterials.

Metallodielectric photonic crystals having hyperbolic dispersions are called indefinite materials because of their ability to guide modes with extremely large lateral wavevectors. While this is useful for enhancing near-field radiative heat transfer, it could also give rise to large lateral displacements of the energy pathways. The energy streamlines can be used to depict the flow of electromagnetic energy through a structure when wave propagation does not follow ray optics. We obtain the energy streamlines through two semi-infinite uniaxial anisotropic effective medium structures, separated by a small vacuum gap, using the Green functions and fluctuation-dissipation theorem. The lateral shifts are determined from the streamlines within two penetration depths. For hyperbolic modes, the predicted lateral shift can be several thousand times of the vacuum gap width.

Subwavelength imaging through one-dimensional metallodielectric photonic crystals at optical frequencies

We present a study of mode characteristics of multilayer metal-dielectric (M-D) structure and use the Eigen mode expansion (EME) method to simulate the subwavelength imaging effect that can be realized at the designed position. We show that the quality of the image is affected not only by absorption but also the finite width of the layers. By proper design and considering the real losses, a super lens with a resolution of about λ0/6 (λ0 is the wavelength in the air) can be obtained. Our researches of this structure point to that a transparent material can be composed from non-transparent materials by alternatively stacking different materials of thin nanofilms, which also provide an opportunity to expand the exploration of the wave propagation in metals, both in the linear and nonlinear regimes.

Successive, Seed‐Mediated Growth for the Synthesis of Single‐Crystal Gold Nanospheres with Uniform Diameters Controlled in the Range of 5–150 nm

A simple and robust route is described to the synthesis of single‐crystal Au nanospheres with diameters controlled in the range of 5 nm to 150 nm. The success of this synthesis relies on the use of single‐crystal Au spheres with different diameters as the seeds for successive growth and the use of a slow injection rate for the precursor to enable surface diffusion for the atoms added onto the surface of a seed. The diameters could be precisely controlled by varying the size and/or number of the seeds. The products exhibit excellent uniformity in terms of both size and shape and they are expected to find widespread use in a number of applications, including self‐assembly, fabrication of metallodielectric photonic crystals, plasmonics, and biomedical research.

Fabrication of Metallodielectric Photonic Crystals to Exhibit Perfect Millimeter Wave Band Gaps

Metallodielectric photonic crystals with periodic arrangements of dielectric ceramics and conductive metals were fabricated in submillimeter–order sizes to control millimeter waves. Polyester resins with titania particle dispersions were injected into inverse sphere structures with body‐ and face‐centered cubic lattices formed by laser scanning stereolithography. The transmission properties of the millimeter waves passing through the crystals were measured using time domain spectroscopy and simulated using transmission line modeling. Photonic band gaps could be opened for all crystal directions to totally reflect the incident waves by spatial Bragg diffraction. Modified crystals with compressed lattice spacings were processed to modulate the diffraction wavelengths.

Optical minibands in metallodielectric superlattices

Metallodielectric photonic crystals (MDBRs) display intriguing optical analogies to electronic transport phenomena in superlattices. The nearest-neighbor coupling between dielectric cavities leads to the formation of transmission minibands and minigaps. The properties of these optical Bloch modes are described in detail and related to the structural parameters of the MDBRs fabricated using a release-roll-up assembly technique. The angular and polarization dependencies of these miniband mode dispersion well matches transfer matrix simulations. As the cavity thicknesses are scaled down to $<$20 nm, these superlattices are predicted to exhibit metamaterial features based on the strongly anisotropic dielectric constant of the composite.

A facile method for the synthesis of highly monodisperse silica@gold@silica core–shell–shell particles and their use in the fabrication of three-dimensional metallodielectric photonic crystals

We report here (i) a method for the synthesis of highly monodisperse silica@gold@silica core–shell–shell (CSS) particles (<6% deviation in size) with coherent outer silica shells of directly tunable thickness and porosity, (ii) the fabrication of three unit cell thick (12 layers) metallodielectric photonic crystals (MDPCs) from these particles and (iii) their angle-resolved optical reflectance properties demonstrating the influence of dielectric contrast modification and metal plasmonic modes on photonic band gap properties. The synthetic route presented describes the use of two alkylamines, the first, 1,3-diaminopropane (DAP), as a surface manipulating agent, and the second, N,N-dimethyldodecylamine (DMDDA), as a catalyst for the outer silica shell formation, for the reproducible synthesis of monodisperse CSS particles avoiding the formation of the unwanted side-products such as core-free silica particles and aggregated particles with multiple cores. A rational chemical reaction mechanism describing the pathways involved in the formation of coherent silica shells, demonstrating the roles of both the amines, is proposed. The creation of partial wetting/de-wetting sites on gold nanoparticle surfaces by the adsorbed DAP molecules, the surface silanol modification by DAP and the slow hydrolysis–condensation reactions catalyzed by DMDDA are found to be responsible for the selective deposition of silica (heterogeneous nucleation) only onto the existing silica@gold core–shell particles leading to the formation of monodisperse CSS particles. The optical reflectance of the MDPC formed from these CSS particles shows an angle-dependent blue-shift that perfectly obeys the Bragg–Snell law predictions for photonic crystals. The dielectric contrast modification and the possible metal plasmonic mode-coupling in the MDPC also result in a high gap-to-midgap ratio (23%) as compared to the PC made of neat silica particles of comparable size (9%).

Fabrication and characterization of three-dimensional metallodielectric photonic crystals for infrared spectral region

We propose a technique for the realization of three-dimensional metallodielectric photonic crystals based on fabricating polymeric structures using the interference lithography followed by the magnetron deposition of a gold nanolayer. The infrared reflectance spectra of the fabricated photonic crystals are studied. The spectrometry and finite-difference time-domain modeling data show that there is a photonic band gap centered at the wavelength approximately equal to the photonic crystal period.

Metallo-Dielectric Photonic Crystals for Surface-Enhanced Raman Scattering

Metallo-dielectric photonic crystals (MDPCs) are used as ultrasensitive molecular detectors for concentrations down to picomolar level based on surface-enhanced Raman spectroscopy (SERS). Calculations show that the amorphous silicon photonic crystals (a-Si PCs) embedded in multiple metallo-dielectric (MD) units can significantly increase the electromagnetic fields at the air-dielectric interface, leading to remarkable Raman enhancement. Corresponding experiments show the multiple MDPC structures can serve as an ultrasensitive SERS substrate with excellent reproducibility and stability, capable of quantitative analysis down to 10 pM level. The MDPC structure can be generalized to other applications, such as plasmonic devices, ultrasensitive sensors, and nanophotonic systems.

The three-dimensional photonic crystals coated by gold nanoparticles

We report on the fabrication of metallodielectric photonic crystals by means of interference lithography and subsequent coating by gold nanoparticles. The grating is realized in a SU-8 photoresist using a He–Cd laser of wavelength 442 nm. The use of the wavelength found within the photoresist low absorption band enables fabricating structures that are uniform in depth. Parameters of the photoresist exposure and development for obtaining a porous structure corresponding to an orthorhombic lattice are determined. Coating of photonic crystals by gold nanoparticles is realized by reduction of chloroauric acid by a number of reductants in a water solution. This research shows that the combination of interference lithography and chemical coating by metal is attractive for the fabrication of metallodielectric three-dimensionally periodic microstructures.

Template-Assisted Three-Dimensional Nanolithography via Geometrically Irreversible Processing

An innovative and versatile nanofabrication technique based on template assisted three-dimensional (3D) nanolithography is presented that takes advantage of the irreversibility of conformal growth and conformal etching at locations with negative surface curvatures in 3D templates. Using colloidal crystals as templates, nanoring particles are generated with quantity much higher than conventional methods. Relying on the same principle, metallodielectric photonic crystals with discrete metal elements are fabricated that show strong absorption in the near-IR and transmission at longer wavelengths.

Angular variation of absorption and thermal emission from photonic crystals

The absorption and thermal exitance of two-dimensional (2D) metallic and metallodielectric photonic crystals (PCs) is simulated with rigorous scattering matrix methods. These PCs have strong thermal exitance and absorption peaks in the normal direction that shift to larger and smaller wavelengths as the angle varies away from the normal direction. These PCs redistribute the thermal emission at different wavelengths into different emission angles. There is partial suppression of photon emission at long wavelengths and enhancement at the shorter wavelength spectral range where the thermal exitance has a maximum. Surface plasmon models describe well the angular dependent absorption. Thermophotovoltaic devices utilizing PCs need to account for the strong spectral variation of the thermal exitance with angle.

Photonic bands in two-dimensional metallodielectric photonic crystals composed of metal coated cylinders

Photonic bands in two-dimensional metallodielectric (MD) periodic systems composed of metal coated cylinders are investigated theoretically based on frequency dependent plane-wave expansion method. For the case of E-polarization, although the thickness of metal coating is less than half of the cylinder’s radius, most of MD photonic bands are the same as photonic bands composed of pure metal cylinders. This property provides us with a way to substitute metal photonic crystals with MD photonic crystals in many applications. In addition, flatbands are discovered in MD photonic band structures, which can be tuned by changing the thickness of metal coating while other photonic bands do not change their positions. For the case of H-polarization, the lowest frequency band gap (between the first and the second bands) can open up when the thickness of metal coating is thick enough. According to approximate calculation based on Maxwell–Garnett type effective medium theory and comparison with recent studies on three-dimensional MD photonic band structures, we predict that the lowest frequency band gap is not because of Bragg scattering but result from the individual metal coated dielectric cylinders, so that the gap is independent on geometry of photonic crystal lattices. Then, numerical calculation validates that our prediction is right.