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Congratulations to our new paper “Bio-compatible and highly sensitive two-dimensional plasmonic sensor ” by A.S. Nasiri, S. M. Hamidi

We propose a novel bio-compatible two dimensional plasmonic sensor with array of ring and the hole structure on an optically thick gold film for biochemical sensing. We use finite-difference time-domain simulation for design and calculation of sensitivity in the Near-Infrared Region. The bio-compatible and cheap plasmonic Glycerol sensor with high sensitivity by interferometer style as a motif in the sensor’s structure. The proposed sensor can be applied as highly sensitivity sensor with a good linear response under different glycerol concentrations.

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Congratulations to our new paper ” Electrically driven flexible two dimensional plasmonic structure based on nematic liquid crystal ” by Hossein Mbarak, Seyedeh Mehri Hamidi, Ezeddin Mohajerani and Z Zattar

A novel two dimensional active plasmonic grating based on liquid crystal (LC) infiltration is demonstrated by combining the plasmonic properties of the gold nanostructure and the optical properties of the liquid crystal. In this structure, a thin layer of E7 liquid crystal was typically injected onto a gold nanostructure, deposited on a PDMS substrate, using nanoimprint lithography method. The surface plasmon resonance (SPR) of the fabricated plasmonic structure can be controlled by changing the refractive index of LC, which was achieved with an external electric field. LC molecules confined between the gold nanostructure and an indium–tin-oxide (ITO) glass are randomly aligned, and they can exhibit a reversible refractive index, depending on their orientation under the external voltage and the polarization of the incident light. Results demonstrates that the wavelength of the resonance peak can be red shifted by the electric field-dependent refractive index of liquid crystal. This experimental work provides us an active control of surface plasmon resonance using liquid crystal which can act as an ideal active medium for different applications such as low voltage sensor with the sensitivity of 0.4375nm/V.

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Recognizing special molecules is crucial in many biochemical processes, and thus, highly enhanced sensing methods are in high demand. In this work, we designed a microrod array metasurface with a SiO2-loaded subwavelength lithium niobate waveguide as a unique platform for enhanced experimental fingerprint detection of lactose. The metasurface could lead to strong surface wave modes due to the near-field coupling of the spoof localized surface plasmon, which also could provide a stronger interaction length between light and matter. The selectivity was remarkable in the transmission spectrum at an intrinsic characteristic frequency of 0.529 THz with a thin layer of lactose, while it was faint while transmitting terahertz (THz) waves normally through a lactose layer of the same thickness. Together with the ability to freely design the shape of the metasurface and the electromagnetic properties, we believe that this platform can function as an elegant on-chip-scale enhanced THz sensing platform.

(a) Schematic of THz detection of an analyte using a microrod array metasurface
as an on-chip sensor. A column of y-polarized dipoles located inside the LN
waveguide is used to excite THz waves (blue oscillation signal). The thickness of
the SiO2 layer is h¼2 lm. The inset shows the detailed design parameters: p, a,
l and g are 20, 10, 55, and 15 lm, respectively. (b) Enhanced field confined to the
surface of the composite structure. (c) and (d) Distribution of the field components
Ey and Ez at f¼0.529 THz.

In summary, we show the potential of a platform relying on a microrod array metasurface with a SiO2-loaded LN subwavelength waveguide as a generic design for THz sensing. Remarkable selectivity can be seen from the experimental and simulated transmission spectra with a minute amount of the analyte. The stronger confinement of surface wave modes owing to near-field SLSP coupling and the longer interaction length along the waveguide would effectively increase the molecular absorption, thereby enabling detection of a thin lactose layer. Meanwhile, the results agree well with each other. This is difficult to distinguish with normally incident THz waves transmitting through a lactose of the same thickness without a metasurface. The myriad of geometries for the composite structure provides engineers with enormous flexibility to design sensing platforms that operate over a broad range of frequencies. We believe that this platform is truly simple and efficient while providing a versatile method for enhanced fingerprint detection in the THz regime. This would bring THz sensing benefits to mainstream applications.

For more information: doi: 10.1063/1.5087609

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Congratulations to our new paper “Role of higher order plasmonic modes in one-dimensional nanogratings ” by Foozieh Sohrabi, Seyedeh Mehri Hamidi, Ershad Mohammadi

By theoretically investigating the optical behavior of one-dimensional gold nanogratings using Fourier Modal Method, we have shown that both integer and non-integer multiples of surface plasmon polariton wavelengths should be taken into consideration in special optical contrast ratio for highly sensitive sensing. The emergence of higher modes is the key factor for the formation of observed plasmonic band gap. Through considering the significant role of grating period and thickness respectively in horizontal and vertical surface resonances, it was demonstrated that for gold thicknesses below 100 nm, the dominant phenomenon is horizontal surface resonances while for increased thicknesses both horizontal and vertical surface resonances mediate. The transmission minima are insensitive to the grating thickness, which confirms that their origins are not vertical surface resonances. This study can open an avenue towards designing highly sensitive sensors with focus not only on the plasmonic resonance wavelength but also on its integer and non-integer multiples whose origins should be investigated in both horizontal and vertical surface resonances.

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Plant leaves have a natural superpower—they’re designed with water repelling characteristics. Called a superhydrophobic surface, this trait allows leaves to cleanse themselves from dust particles. Inspired by such natural designs, a team of researchers at Texas A&M University has developed an innovative way to control the hydrophobicity of a surface to benefit to the biomedical field. applications in the biomedical field including biosensing, lab-on-a-chip, blood-repellent, anti-fouling and self-cleaning applications. Superhydrophobic materials are used extensively for self-cleaning characteristic of devices. However, current materials require alteration to the chemistry or topography of the surface to work. This limits the use of superhydrophobic materials. “Designing hydrophobic surfaces and controlling the wetting behavior has long been of great interest, as it plays crucial role in accomplishing self-cleaning ability,” Gaharwar said. “However, there are limited biocompatible approach to control the wetting behavior of the surface as desired in several biomedical and biotechnological applications.” The Texas A&M design adopts a ‘nanoflower-like’ assembly of two-dimensional (2-D) atomic layers to protect the surface from wetting. The team recently released a study published in Chemical Communications. 2-D nanomaterials are an ultrathin class of nanomaterials and have received considerable attention in research. Gaharwar’s lab used 2-D molybdenum disulfide (MoS2), a new class of 2-D nanomaterials that has shown enormous potential in nanoelectronics, optical sensors, renewable energy sources, catalysis and lubrication, but has not been investigated for biomedical applications. This innovative approach demonstrates applications of this unique class of materials to the biomedical industry.

This innovative technique opens many doors for expanded applications in several scientific and technological areas. The superhydrophobic coating can be easily applied over various substrates such as glass, tissue paper, rubber or silica using the solvent evaporation method. These superhydrophobic coatings have wide-spread applications, not only in developing self-cleaning surfaces in nanoelectronics devices, but also for biomedical applications. Specifically, the study demonstrated that blood and cell culture media containing proteins do not adhere to the surface, which is very promising. In addition, the team is currently exploring the potential applications of controlled hydrophobicity in stem cell fate.

For more information:
https://phys.org/news/2019-07-superhydrophobic-nanoflower-biomedical-applications.html

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Congratulations to our new paper “Adjustable plasmonic bandgap in one-dimensional nanograting based on localized and propagating surface plasmons” by Foozieh Sohrabi and Seyedeh Mehri Hamidi.

Compared to the long history of plasmonic gratings, there are only a few studies regarding the bandgap in the propagation of plasmonic surface waves. Considering the previous studies on interpretation of plasmonic bandgap formation, we discuss this phenomenon using the effect of both surface plasmon polariton (SPP) and localized surface plasmon (LSP) for our fabricated one-dimensional metallic-polymeric grating. This structure is composed of metallic grating on the surface of PDMS with different concentration of embedded gold nanoparticles. By sweeping the incident angles, we have seen that the SPP, LSP and their coupling cause two gaps in reflection regime which are originated from SPP supported by thin film gold film and LSP supported by gold nanoparticles. The first gap is attributed to the patterned metallic film because it vanishes by increasing the nanoparticles which may destroy the pattern while the second gap can be formed by embedded nanoparticles because it becomes more considerable by raising the incubation time.  Therefore, the drowning time of patterned samples (e.g. 24h. 48h and 72h) in HAuCl4 plays the key role in adjustability of plasmonic bandgap. Notably, the interaction between SPP and LSP can be the origin of the shift in gap center from 300 to 550. To best of over knowledge, this study is the first study on the plasmonic band gap as a function of both SPP and LSP.

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The interaction between plasmons in metal nanostructures and excitons in layered materials attracts recent interests due to its fascinating properties inherited from the two constituents, e.g., the high tunability on its spectral or spatial properties from the plasmonic component, and the large optical
nonlinearity or light emitting properties from the excitonic counterpart. Here, we demonstrate the light-emitting plexcitons from the coupling between the neutral excitons in monolayer WSe2 and highly-confined nanocavity plasmons in nanocube-over-mirror system. We observe, simultaneously, an anti-crossing dispersion curve of the hybrid system in the dark-field scattering spectrum and a 1700 times enhancement in the photoluminescence. We attribute the large photoluminescence enhancement to the increased local density of states by both the plasmonic and excitonic constituents in the intermediate coupling regime. What’s more, increasing the confinement of the hybrid systems is achieved by shrinking down the size of hot spot within the gap between the nanocube and the metal film. Numerical calculations reproduce the experimental observations and provide the effective number of excitons taking part in the interaction. This highly compact system provides a room temperature testing platform for quantum cavity electromagnetics at the deep subwavelength scale.

Our hybrid NCOM sample consists of a monolayer WSe2 inserted into the gap between a silver nanocube and a gold film (Figure 1a). Interestingly, the emission of this mode is shown to be highly directional along the film normal, making it addressable by free space radiation.30 Under the illumination of a normal incident x-polarized plane wave (as shown in Figure 1b inset), Figures 1c-e show the scattered electric field of x, y, z- component of the M mode normalized to the incident electric field E0.

For more information: DOI: 10.1021/acsnano.8b05880

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They report the first observation of subradiance in plasmonic nanocrystals. Amplitude- and phaseresolved ultrafast transmission experiments directly reveal the coherent coupling between surface plasmon polaritons (SPPs) induced by periodic variations in the dielectric function. This interaction results in the formation of plasmonic band gaps and coupled SPP eigenmodes with different symmetries, as directly shown by near-field imaging. In antisymmetric modes, radiative SPP damping is strongly suppressed, increasing the SPP lifetime from 30 fs to more than 200 fs. The findings are analyzed within a coupled resonance model.


FIG. 1 (color online). (a) Time structure of the electric field Ein(t) of the incident 11 fs pulses and of the pulses Eout(t) transmitted through a nanoslit array with a0=650 nm at an angle θ of 8°. (b) Representative transmission spectrum T(ω)=│Eout(ω)/Ein(ω)│2 and (c) spectral phase φ(ω)=arg[Eout(ω)/Ein(ω)] (open circles) near the SM[ _ 2] resonance. Solid lines: Fit to Eq. (1) with parameters indicated in (b).

For more information: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.94.113901

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WO3 thin films fabricated by glancing angle deposition (GLAD) are proposed as excellent electrochromic coatings with favorable ion diffusion. A = 500-nm film prepared by GLAD had a relatively large transmittance
modulation. The crystallization structure, surface morphology, chemical state, optical and electrochromic properties of WO3 thin films were systematically characterized upon annealing treatment. Compared with annealed WO3 porous nanostructured films, the amorphous as-deposited films exhibited a high coloration efficiency and stable reversibility. Furthermore, the GLAD WO3 films exhibit the tunable angular selectivity under illumination with p-polarized light because of the birefringence, which could extend the application range of nanostructured films in the electrochromic field.

Transmittance of WO3 films under ±45 p-polarized light: (a) colored and bleached state; (b) optical contrasts (%DT). (For interpretation of the references to colour in
this figure legend, the reader is referred to the web version of this article.)

WO3 thin films were fabricated by glancing angle deposition technique (GLAD) and annealed at different temperatures. The WO3 films begin to crystallize at around 300 C. Comparing with the annealed films, the as-grown GLAD WO3 film exhibits relatively optimum electrochromic properties, along with a satisfactory cycling stability and large optical modulation (42.2%, 633 nm), because the loose structure facilitated fast ion diffusion and rapid color alteration. Furthermore, a noteworthy feature of tilted columnar structured films is that under illumination with p polarized light, the transmittance modulation contrast between the +45 and -45 incidence can be up to 11%. The angular selectivity of the colored and bleached states of GLAD WO3 films illuminated with p-polarized light can be tuned by applying different voltages, which provides new application features and development potential.

For more information: https://doi.org/10.1016/j.apsusc.2018.03.248

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Many species of octopus and squid rapidly alter their skin colors and patterns to camouflage themselves from both predators and prey. Scientists in the United Kingdom have developed a new type of pixel—reportedly, the smallest ever—that could make large-scale displays cheap enough to wrap around entire buildings and achieve similar color-changing effects. The researchers already knew that the combination of plasmonic metasurfaces and certain types of electrically conducting polymers can function as optical switches or pixels. By altering the refractive index of the polymer medium surrounding the plasmonic material, scientists can change the peak of the local surface plasmon resonance and the corresponding emitted color. However, the group faced two challenges: speeding up the slow refresh rate of these devices and ensuring that they emit in the visible instead of the infrared range. To solve these problems, Nanophotonics Center director Jeremy Baumberg and his colleagues manufactured large quantities of “electrochromic nanoparticle-on-mirror constructs,” or eNPoMs. These tiny objects are 80-nm-wide gold spheres coated with a shell, between 11 and 20 nm thick, of a conductive polymer called polyaniline. The thickness of that polymer shell crucially determines the gap between the gold core and the planar mirror—a gold sheet supported by flexible plastic—to which they are attached by simply spraying them on. “It is hard to get nano-assembly of tiny gaps to work on roll-to-roll processes, but we found a way to use solution processing to control the gaps simply,” Baumberg says.


Electrochromic nanoparticle-on-mirror constructs (eNPoMs) formed from gold nanoparticles encapsulated in a conductive polymer shell. [Image: NanoPhotonics Cambridge/Hyeon-Ho Jeong, Jialong Peng]

When voltage is applied to the mirror, the eNPoMs give off light, with shorter wavelengths emitted from the particles with thicker shells. The authors claim that their proof-of-concept display operated for more than three months at power densities below 300 μW per square centimeter (using 9 fJ of energy per pixel), which is a factor of 10 times less than the conventional e-paper of today. The display also had more than 109 pixels per inch and optical contrast of better than 50 percent. For a follow-up, the Cambridge team is optimizing the blue end of the generated visible spectrum of the nanopixels and making flexible array demonstrators to show to potential partners.

For more information: doi: 10.1126/sciadv.aaw2205


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