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Large-scale hierarchical macroscopic moire gratings resembling the surface structure of Peruvian lily flower petals are fabricated on azobenzene molecular glass thin films using a Lloyd’s mirror interferometer. It is shown that nanostructured linear and crossed moire gratings can be made with pitch values reaching a few millimeters. Also, using atomic force microscopy, scanning electron microscopy, optical microscopy, and surface profilometry techniques, it is shown that the obtained moire gratings have two-fold or three-fold hierarchical structures fabricated using a simple all optical technique.

We deposited homogeneous, thin, yellow-colored films of chitosan (Chi)-N,N-dimethyl-4-(2-pyridylazo)aniline (PADA) dye from an acid Chi–PADA solution by spin-coating on glass substrates. We characterized Chi, PADA, and Chi–PADA films by ATR–FTIR spectroscopy, which revealed a slight shift of 3170 and 3268 cm−1 bands, indicating H-bonding between the chitosan hydroxyl (OH) group and the amine (N) of the PADA pyridine ring. Based on these analyses, it was possible to determine the efficiency of the hydrogen bonds to form a Surface Relief Grating (SRG) on azo-polymer thin film. Moreover, we performed UV–VIS spectroscopy analysis of this film, which showed a broad band extending from 400 to 700 nm, with the maximum occurring at 428 nm. Therefore, we selected, within the absorption band, the 532 nm green laser wavelength to irradiate the azo-polymer films at room temperature. For the first time, natural polymer derivative and dye sample Chi–PADA thin films showed unique photoresponsive behavior under irradiation with two interfering laser beams. This permitted us to generate surface inscription patterning known as an SRG, which we confirmed by atomic force microscopy (AFM) and for which we determined a grating depth up to 50 nm. The present study opens the new possibility of using natural polymer-dye thin films.

The unique plasmonic energy exchange occurring within metallic crossed surface relief gratings (CSRGs) has recently motivated their use as biosensors. However, CSRG-based biosensing has been limited to spectroscopic techniques, failing to harness their potential for integration with ubiquitous portable electronics. Here, we introduce biosensing via surface plasmon resonance imaging (SPRi) enabled by CSRGs. The SPRi platform is fully integrated including optics and electronics, has bulk sensitivity of 613 Pixel Intensity Unit (PIU)/Refractive Index Unit (RIU), a resolution of 10-6 RIU and a signal-to-noise ratio of ∼33 dB. Finite-Difference Time-Domain (FDTD) simulations confirm that CSRG-enabled SPRi is supported by an electric field intensity enhancement of ∼30 times, due to plasmon resonance at the metal-dielectric interface. In the context of real-world biosensing applications, we demonstrate the rapid (

The rate of photomechanical formation of surface relief gratings (SRG) in thin films of azobenzene materials depends on their glass transition temperature (Tg), with an optimal Tg around 50–60 °C yielding the fastest SRG growth. Herein, the SRG growth of five analogous Disperse Red 1 molecular glasses with Tg values ranging from 9 to 71 °C was studied with two different laser wavelengths (488 and 532 nm). It was found that the optimal Tg for SRG growth increases with laser irradiance, from approximately 50 °C at 100 mW cm−2 to over 70 °C at 300 mW cm−2. Furthermore, the azobenzene glass with a sub-ambient Tg of 9 °C can inscribe self-erasable gratings that collapse spontaneously when irradiation is stopped in a repeatable fashion, thereby paving the way for light-controlled optical devices.

Nanoscale-patterned azobenzene thin films were incorporated in organic solar cells to scatter incident light, thus increasing the optical path length of photons inside the active area. This ultimately led to significant power conversion efficiency (PCE) enhancements in the active layer. Specifically, the azobenzene thin films were patterned with two-dimensional crossed surface relief gratings inscribed via laser interference lithography. The patterned films were then bleached and thermally stabilized by exposure to strong ultraviolet light before being incorporated in P3HT:PC61BM and PTB7:PC61BM solar cells. The fabricated solar cells exhibited a PCE enhancement of 133%, from 1.37 to 3.19%, for P3HT:PC61BM solar cells, and a PCE enhancement of 302%, from 0.53 to 2.13%, for PTB7:PC61BM solar cells.

Custom acrylic multifaced pyramids were machined in-house and used to fabricate, in a single step, photonic crystals and quasicrystals on azobenzene molecular glass thin films with a surface area within the range of cm2. The obtained microcavity patterns have up to 8 -fold rotational symmetry depending on the number of pyramid faces used for laser inscription. The height of the resulting microcavities increases with the number of pyramid faces used and can even grow beyond the initial azobenzene film thickness. Furthermore, anisotropic and Moiré photonic structures were also fabricated upon changing the laser polarization and the number of exposures respectively.

As part of continuing efforts to deepen the understanding of photo-induced mass transport in azo-containing polymers, we compared the diffraction efficiency (DE) during surface-relief grating (SRG) inscription, photo-induced molecular orientation (), and thermal stability in two sets of supramolecular azopolymer complexes, namely, hydrogen-bonded (H-bonded) and ionically bonded (i-bonded) complexes, both as a function of the polymer degree of polymerization (DP). To that end, poly(4-vinylpyridine) (P4VP) polymers with DPs of 41, 480, and 1900 were H-bonded at an equimolar ratio with 4-hydroxy-4′-dimethylaminoazobenzene (azoOH), and the fully quaternized derivatives of the three P4VPs (P4VPMe) were i-bonded via ion exchange to sodium 4-[(4-dimethylamino)-phenylazo]benzene sulfonate (azoSO3), also known as methyl orange, where the OH functionality of azoOH is replaced by a sulfonate group. The i-bonded complexes show much better DE performances and levels than those of H-bonded complexes, which we relate to the liquid crystal structure of the former complexes. Fitting the curves by a biexponential equation leads to two parameters associated with a fast trans–cis or angular hole burning (AHB) process and a slow angular redistribution (AR) process of the azo, respectively. It is found that AHB is predominant in the H-bonded complexes, whereas the AR contribution is much greater in the i-bonded complexes, assuring their superior SRG efficiency that is enabled by the anisotropic free volume created mainly by the AR process. In each set of complexes, the SRG efficiency is much better for the lowest DP complex, while the AR contribution is constant (and low) for the H-bonded complexes and increases roughly linearly with the decrease in DP for the i-bonded complexes. The latter difference might be related to the presence of entanglements in the complexes with DPs 480 and 1900, which slow down the macroscopic movement during SRG inscription but not the molecular-scale movement in photo-orientation.

This article introduces a bioinspired, cicada wing-like surface-enhanced Raman scattering (SERS) substrate based on template-stripped crossed surface relief grating (TS-CSRG). The substrate is polarization-independent, has tunable nanofeatures and can be fabricated in a cleanroom-free environment via holographic exposure followed by template-stripping using a UV-curable resin. The bioinspired nanostructures in the substrate are strategically designed to minimize the reflection of light for wavelengths shorter than their periodicity, promoting enhanced plasmonic regions for the Raman excitation wavelength at 632.8 nm over a large area. The grating pitch that enables an effective SERS signal is studied using Rhodamine 6G, with enhancement factors of the order of 1 × 104. Water contact angle measurements reveal that the TS-CSRGs are equally hydrophobic to cicada wings, providing them with potential self-cleaning and bactericidal properties. Finite-difference time-domain simulations are used to validate the nanofabrication parameters and to further confirm the polarization-independent electromagnetic field enhancement of the nanostructures. As a real-world application, label-free detection of melamine up to 1 ppm, the maximum concentration of the contaminant in food permitted by the World Health Organization, is demonstrated. The new bioinspired functional TS-CSRG SERS substrate holds great potential as a large-area, label-free SERS-active substrate for medical and biochemical sensing applications.

Plasmonic crossed surface relief gratings were fabricated using interference lithography. Their topographies were studied by AFM as a function of laser exposure time and their surface plasmon resonance at a gold-air interface was measured between crossed polarizers in transmission and in reflection modes. Both modes resulted in emitted plasmonic light at specific wavelengths related to the grating pitch, with the reflectance SPR having a much higher intensity than the transmittance SPR. The use of these gratings as plasmonic sensors was examined and their sensitivities were measured in the reflectance and transmittance modes to be 601 nm/RIU and 589 nm/RIU, respectively.

A thermo-optical process was developed for the erasure of surface relief gratings (SRG) inscribed on various films of mexylaminotriazine molecular glasses functionalized with different azobenzene chromophores, as well as azobenzene polymer films. Irradiation of the samples with a CO2 laser beam causes localized heating of the soda lime substrate, which is then transferred to the azobenzene films, causing complete erasure of the gratings while the temperature of each film was monitored in real time. The erasure temperature has been found to be strongly correlated with the respective glass transition temperature (Tg) of the materials. Therefore, complete and partial all-optical erasure of gratings was successfully demonstrated and occurred in under a minute for azobenzene molecular glass films and under 3 minutes for azo-polymer films. Finally, gratings were shown to erase in specific patterns through the use of a metallic mask.

Nanostructures consisting of crossed surface relief gratings (CSRGs) support surface plasmon resonances (SPRs) that are compatible with biosensing applications [1], [2]. At normal incidence, surface plasmons are excited between a metal and a dielectric at a light wavelength ( $\lambda_{\text{SPR}}$ ) given by $\lambda_{SPR}=n\Lambda[\sqrt{\varepsilon_{m}/(n^{2}+\varepsilon_{m})}]$ , where $n$ is the index of refraction of the dielectric, and $\varepsilon_{m}$ is the real part of the permittivity of the metal and $\Lambda$ is the grating pitch. When placed between crossed linear polarizers, CSRGs allow for plasmonic energy exchange between the two superimposed gratings that eliminate any incident polychromatic light, except for the narrow SPR bandwidth where polarization conversion occurs. The result is an effective transmission of the SPR signal with a high signal-to-noise ratio. The single pitch of CSRGs, however, limit their operation to a specific plasmonic resonance wavelength. Here, we present a plasmonic sensor based on variable-pitch CSRG that allows plasmonic resonances at different wavelength bandwidth depending on the illuminated region. The variable-pitch CSRGs (VP-CSRGs) are fabricated on azobenzene-functionalized films through a simple two-step procedure. Fig. 1a presents an actual AFM image of the surface of a nanofabricated VP-CSRGs. The plasmonic response of the VP-CSRG sensor was evaluated using Finite-Difference Time-Domain (FDTD) simulations to show the e-field intensity distribution on the gold-coated VP-CSRG surface. Electric field enhancement and distribution, due to the plasmonic conversion, was assessed through the change of the RI of the dielectric medium in contact with the metallic crossed gratings, and through the spectral diversity of the light source to excite the surface plasmons. For the simulations, the surface of the CSRGs with pitches of 520, 540 and 560 nm were modeled using the function, $f(x, y)=G(\cos[(2\pi/p)x]+\cos[(2\ \pi/p)y])$ , where $G$ is the amplitude and $p$ the period of the structure (Fig. 1a). The simulations were used to obtain the e-field intensity distribution, normalized with respect to the incident plane wave. Periodic boundary conditions in both $x$ and $y$ directions and a perfectly matched layer (PML) in the $z$ direction were used for the analysis region. A uniform mesh size of 3 nm was used for the envelope of the nanostructure, comprising the azobenzene layer, the gold film and the dielectric medium, in all the directional axes. A plane wave, polarized along the $y$ -axis and orthogonal to the $x-y$ plane, was employed to induce a SPR in the structure. Fig. 1b demonstrates the plasmonic excitation in the $x$ -direction, when using p-polarized light and the absence of plasmonic excitation in the $y$ -direction. However, when s-polarized light is used, the nanostructures are excited in the $y$ -direction. These results present an evidence on the unique plasmonic energy transfer between the crossed gratings that has been hypothesised before [1]. Experimentally, these results can be used to confirm that the transmitted light acquired in a collinear setup using VP-CSRGs between two orthogonal polarizers corresponds, only, to the plasmonic signature of the nanostructure.

Two-dimensional chirped-pitch crossed surface relief gratings (CP-CSRGs) were fabricated on azobenzene-functionalized thin films using a simple two-step procedure. The resulting gratings had a constant pitch in one direction and a varying (chirped) pitch in the orthogonal direction. They were coated with silver and tested for their ability to change the polarization of surface plasmon resonance (SPR) signals, when placed between crossed polarizers. It was observed that several different bandwidths of SPR wavelengths are excitable using a single device, making CP-CSRGs suitable as next generation SPR-based sensors. The SPR wavelengths shifted as much as 10.5 nm/mm along the chirped grating, and a maximum sensitivity of 778.6 nm/RIU was obtained when detecting the refractive index change of various concentrations of aqueous sucrose solutions.

Two-dimensional Resonant Waveguide Crossed Gratings (RWCG) were fabricated on azobenzene molecular glass thin films and their resonance behavior was studied once placed in between orthogonally aligned polarizers. Normally-incident polychromatic light was transmitted and/or reflected from these RWCGs only in narrow positive peaks. In addition, the central wavelength and transmitted intensity of these positive peaks were actively modulated by an external light source. Furthermore, a dynamic volume birefringence behavior related to the photomechanical effect of the azobenzene chromophores was observed. A mechanism to explain the polarization conversion of the resonant light using RWCGs at normal incidence was also proposed.

A simple inline holographic setup is used to fabricate holographic diffractive lenses using off-the-shelf components. The resulting surface relief gratings are inscribed directly in azobenzene-functionalized thin films with pitches that agree well with a theoretical Fresnel zone plate. The annular gratings have an outer radius of approximately 9 mm and an inner radius of less than 4 mm. Interfering laser beams, circularly polarized in the same direction, generally produce poor-quality gratings in azo-films, but the addition of a reference beam lens greatly improved their consistency and produced quality gratings with depths up to 400 nm. Multiple exposures produce multifocal diffractive lenses, while angling the sample resulted in focal lines, instead of focal points.

Nucleation and growth of spontaneous surface relief gratings (SSRGs) on a Disperse Red 1 (DR1) glass-forming derivative were investigated. No interference pattern is applied and surface patterning is induced using single-beam irradiation: the gratings are self-organized. Grating growth is assumed to initiate from an interference pattern formed between the incident light beam and waves scattered at grazing angle by surface defects. However, the mechanism is not yet fully understood and there is not a comprehensive explanation of the structure formation process. Herein, the grating formation procedure is studied by monitoring the surface topology of thin films exposed to one writing beam for various periods of time, under both linear and circular polarizations, using AFM. Even in the absence of surface defects on the initial film, irradiation produces light-induced surface defects due to the reorientation and mass movement of the azo molecules. These defects act as seeds for SSRG around which gratings gradually emerge and propagate throughout the sample. To consolidate this hypothesis, the formation of gratings was studied on samples with controlled surface roughness. Pore-shaped defects do not diffract light on top of the sample, and thus have no impact on SSRG growth, while for hill-shaped defects, growth rate decreases sharply with defect sizes larger than the writing beam wavelength. Two other analogous glass-forming azobenzene derivatives were studied, and in all cases, SSRG formation was correlated with the induction of birefringence in the early stages of the irradiation.

The second-order nonlinear optical coefficients of thin films of mexylaminotriazine-functionalized azobenzene molecular glass derivatives were measured using second harmonic generation. The thin films were poled using a custom corona poling set-up and the second harmonic light from a pulsed 1064-nm laser was detected. Four out of the six tested compounds showed optical nonlinearity and a maximum coefficient of 75 pm/V was obtained. The time dependence of the nonlinear coefficients was studied under ambient light and under dark; the second harmonic generation intensity stayed constant for thiazole-containing derivatives while a significant decay was measured for the other compounds.

Silver-coated Crossed Surface Relief Gratings (CSRGs) are fabricated and used for imaging and detecting localized refractive index variations in inhomogeneous water-based solutions via polarization-contrast Surface Plasmon Resonance (SPR). When placed in between crossed polarizers, incident light was transmitted at intensity levels directly and precisely related to the local refractive index value. This occurred due to the in-plane polarization conversion of the SPR light in between the orthogonal grating vectors. When viewed with a camera, SPR light from a monochromatic source enabled the acquisition of polarization-contrast microscopy images of a water and silicon oil mixture placed over the CSRG’s surface.

Urinary tract infections (UTIs) are one of the major burdens on public healthcare worldwide. One of the primary causes of UTIs is the invasion of the urinary tract by uropathogenic Escherichia coli (UPEC). Improper treatment of bacterial infections like UTIs with broad-spectrum antibiotics has contributed to the rise of antimicrobial resistance, necessitating the development of an inexpensive, rapid and accurate detection of UPEC. Here, we present real-time, selective and label-free detection of UPEC using crossed surface-relief gratings (CSRGs) as nanometallic sensors incorporated into an optical sensing platform. CSRGs enable real-time sensing due to their unique surface plasmon resonance (SPR)-based light energy exchange, resulting in detection of a very-narrow-bandwidth SPR signal after the elimination of residual incident light. The platform&rsquo, s sensing ability is experimentally demonstrated by the detection of bulk refractive index (RI) changes, with a bulk sensitivity of 382.2 nm/RIU and a resolution in the order of 10&minus, 6 RIU. We also demonstrate, for the first time, CSRG-based real-time selective capture and detection of UPEC in phosphate-buffered saline (PBS) solution, in clinically relevant concentrations, as opposed to other UTI-causing Gram-negative bacteria. The platform&rsquo, s detection limit is calculated to be 105 CFU/mL (concentration on par with the clinical threshold for UTI diagnosis), with a dynamic range spanning four orders of magnitude. This work paves the way for the development of inexpensive point-of-care diagnosis devices focusing on effective treatment of UTIs, which are a burden on public healthcare due to the rise in the number of cases and their recurrences in the recent past.

Urinary tract infections (UTIs) are one of the major burdens on public healthcare worldwide. One of the primary causes of UTIs is the invasion of the urinary tract by uropathogenic Escherichia coli (UPEC). Improper treatment of bacterial infections like UTIs with broad-spectrum antibiotics has contributed to the rise of antimicrobial resistance, necessitating the development of an inexpensive, rapid and accurate detection of UPEC. Here, we present real-time, selective and label-free detection of UPEC using crossed surface-relief gratings (CSRGs) as nanometallic sensors incorporated into an optical sensing platform. CSRGs enable real-time sensing due to their unique surface plasmon resonance (SPR)-based light energy exchange, resulting in detection of a very-narrow-bandwidth SPR signal after the elimination of residual incident light. The platform’s sensing ability is experimentally demonstrated by the detection of bulk refractive index (RI) changes, with a bulk sensitivity of 382.2 nm/RIU and a resolution in the order of 10−6 RIU. We also demonstrate, for the first time, CSRG-based real-time selective capture and detection of UPEC in phosphate-buffered saline (PBS) solution, in clinically relevant concentrations, as opposed to other UTI-causing Gram-negative bacteria. The platform’s detection limit is calculated to be 105 CFU/mL (concentration on par with the clinical threshold for UTI diagnosis), with a dynamic range spanning four orders of magnitude. This work paves the way for the development of inexpensive point-of-care diagnosis devices focusing on effective treatment of UTIs, which are a burden on public healthcare due to the rise in the number of cases and their recurrences in the recent past.

Electrically insulating polyolefin composites containing well-dispersed multiwall carbon nanotubes up to 3 wt.-% are subjected to AC electric fields in the range of 71–212 kV m−1. Their resulting filler structure, DC conductivity, and AC dielectric properties are compared with the respective properties of their non-electrified and annealed counterparts. As evidenced by TEM, electrification causes the formation of aligned filler structures in the direction of the electric field within the composite, whereas annealing alone results in the formation of randomly interconnected nanotubes. Dielectric spectroscopy shows that, due to their ordered carbon nanotube structures, the electrified composites exhibit substantially higher conductivity and storage capacity compared to the as-compounded composites and consistently better electrical properties than their annealed counterparts. An equivalent circuit model is fitted to the experimentally obtained impedance data in order to correlate the effects of electric field and processing time to the resulting dielectric characteristics of the treated composites.

Azobenzene-containing materials exhibit various photomechanical properties, including the formation of surface relief gratings (SRG) when irradiated with two interfering laser beams. In a recent study, a novel glass-forming derivative of Disperse Red 1 (DR1) with a mexylaminotriazine group was synthesized in high yield with a simple and efficient procedure, and showed the ability to form high-quality amorphous thin films with a high resistance to crystallization. Irradiation of films of this material yielded SRG with growth rates comparable to other reported azo materials. Herein, a series of closely related molecular glasses containing azobenzene chromophores with various absorption maxima ranging from 410 to 570 nm were synthesized, and their physical and photomechanical properties were studied. All materials studied showed the ability to form stable glassy phases, and irradiation with lasers emitting at various wavelengths allowed to perform a comparative study of SRG growth within a series of analogous chromophores.

We present an original, low-cost nanoplasmonic (bio)sensor based on crossed surface relief gratings (CSRGs) generated from orthogonally superimposed surface relief gratings (SRGs) on gold-coated azo-glass substrate. This surface plasmon resonance (SPR)-based sensing approach is unique, since the light transmitted through a CSRG is zero except in the narrow bandwidth where the SPR conversion occurs, enabling quantitative monitoring of only the plasmonic signal from biomolecular interactions in real time. We validated the individual SRG plasmonic signature of CSRGs by observing their respective SPR excitation peaks, and tested them to detect both bulk and near-surface refractive index (RI) changes. Compared to simple SRGs, CSRGs portray a much-improved sensitivity of 647.8 nm/RIU, a resolution on the order of 10–5 RIU, and a figure of merit (FOM) of 14 for bulk RI-change sensing. We also demonstrate their ability to perform as biosensors, through the detection and monitoring of near-surface biomolecular int...

Large-scale linear diffraction gratings with gradually varying pitch were photo-inscribed onto the surface of azobenzene thin films using a 532 nm laser and a modified Lloyd mirror set-up. By placing a cylindrical lens in front of the direct half of the inscribing beam, gratings with a chirping rate as high as 12.9 nm/mm were produced. Subsequently, when these chirped-pitch gratings were coated with silver, over three-fold bandwidth increase was observed in the surface plasmon transmission peaks at FWHM, when compared to constant-pitch gratings. This was made possible due to the simultaneous excitation of surface plasmon resonance in a band of light wavelengths.

A simple, yet precise, optical angle measurement device was developed by analyzing the light interference pattern from a modified Lloyd’s mirror interferometer combined with a CMOS camera sensor. The resulting spatially heterodyned signal was very sensitive to small angle changes from an incident low-power laser beam, with an accuracy better than 8.9 arcsec over a range of 1.47 degrees. Measurement dead zones, estimated to have an angular span of ± 0.96 arcmin, occurred in the middle of the device’s measurement range at a critical angle where the pitches of the light interference pattern and the CMOS sensor array were equal. Also, a proof-of-concept test successfully demonstrated the use of this device for dual-axis angle measurements using a single CMOS sensor.

Large-scale surface relief diffraction gratings with pitches up to 20 μm were fabricated in thin films of azobenzene molecular glass using a single-step and mask-less photolithography process. A modified Lloyd's mirror interferometer having two degrees of freedom generated an interference pattern that was incident on the azobenzene films. Some of the fabricated gratings had non-periodic profiles resulting from the superposition of multiple sine waves, while others had periodic blazed sawtooth and Dirac comb profiles. Furthermore, careful selection of the experimental parameters resulted in gratings with a beat interference profile having a clearly-visible modulation envelope. A theoretical framework was developed to successfully explain the obtained grating profiles.

Materials containing azobenzene chromophores exhibit photomechanical behaviors, including the formation of surface relief gratings (SRG) caused by irradiation with two interfering laser beams. While azo-functionalized polymers were extensively studied, small molecules offer the advantage of being monodisperse species, which translates into easier synthesis and purification, as well as more uniform behavior. A drawback is that they tend to crystallize and do not always form high-quality thin films. Glass-forming compounds incorporating azobenzene were previously synthesized in several synthetic steps and in low yield. Herein, a Disperse Red 1 (DR1) functionalized with a mexylaminotriazine group is synthesized in 94% yield using a simple and straightforward procedure. It shows both the ability to form extremely stable glassy phases, and the ability to form SRG in the solid state with growth rates and grating heights closely similar to DR1-functionalized polymers.

Real-time surface plasmon signal modulation was achieved by electrically varying the pitch of a nanoscale surface relief diffraction grating inscribed on an azobenzene thin film covered with a layer of silver. The azobenzene film was spin coated on an electrostrictive Lead Lanthanum Zirconate Titanate (PLZT) ceramic substrate and AC electric fields were applied longitudinally on the PLZT ceramic causing a change in the grating pitch as well as the surface plasmon resonance wavelength. This method permits extremely accurate control of the surface plasmon wavelength for tunable optics applications.

Irradiation of azomaterials causes various photophysical and photomechanical effects that can be exploited for the preparation of functional materials such as surface relief gratings (SRGs). Herein, we develop and apply an efficient strategy to optimize the SRG inscription process by decoupling, for the first time, the important effects of the azo content and glass transition temperature (Tg). We prepare blends of a photoactive molecular glass functionalized with the azo Dis‐ perse Red 1 (gDR1) with a series of analogous photopassive molecular glasses. Blends with 10 and 40 mol% of gDR1 are completely miscible, present very similar optical properties, and cover a wide range of Tg from below to well above ambient temperature. SRG inscription experiments show that the diffraction efficiency (DE), residual DE and initial inscription rate reach a maximum when Tg is 25 to 40 °C above ambient temperature for low to high azo content, respectively. Indeed, for a fixed 40 mol% azo content, choosing the optimal Tg enables doubling the SRG inscription rate and increasing DE sixfold. Moreover, a higher azo content enables higher DE for a similar Tg. Spectroscopy measurements indicate that the photo‐ orientation of DR1 and its thermal stability are maximal with Tg around 70 °C, independent of the azo content. We conclude that the SRG potential of azomaterials depends on their capability to photo‐orient but that the matrix rigidity eventually limits the inscription kinetics, leading to an optimal Tg that depends on the azo content. This study exposes clear material design guidelines to optimize the SRG inscription process and the photoactivity of azomaterials.

Real-time surface plasmon modulation was achieved by electrically varying the pitch of a nanoscale surface relief diffraction grating inscribed on an azobenzene thin film covered with a layer of silver. The azobenzene film was spin coated on an electrostrictive Lead Lanthanum Zirconate Titanate (PLZT) ceramic substrate and a combination of DC bias and AC electric fields were applied longitudinally on the PLZT ceramic causing a change in the grating’s pitch as well as the surface plasmon’s resonance wavelength. This method permits extremely accurate control of the surface plasmon wavelength for tunable optics applications.

The influence of the supramolecular interaction type—hydrogen bonding, proton transfer, and pure ionic bonding—on photoresponsive behavior, particularly surface relief grating (SRG) inscription, has been investigated using a homopolymer with an ambient temperature glass transition (Tg). To this end, poly(dimethylaminoethyl methacrylate) (PDMAEMA or PDM) of relatively high molecular weight (42K) was complexed at various azo/DM molar ratios with dimethylaminoazobenzene derivatives functionalized by hydroxyl (azoOH) or carboxylic acid (p-methyl red or azoCOOH) groups, and quaternized PDM (PDMQ) was complexed at equimolar ratio with a sulfonated analogue (methyl orange or azoSO3), and the structural and thermal properties of these complexes were determined. SRG inscription on spin-coated films was found to be possible because complexation increases the Tg above ambient. The efficiency of SRG inscription on spin-coated films, which increases with azo content, is highest for the purely ionic azoSO3/PDMQ complex despite its very high Tg, while the proton transfer azoCOOH/PDM complexes, involving ionic and H-bonding with acid-salt structures, show somewhat more efficient SRG inscription than do the purely hydrogen-bonded azoOH/PDM complexes, and this despite some azoCOOH crystallization at the highest molar ratios. These findings clarify the comparative effectiveness of different supramolecular bond types on SRG inscription and provide a useful guide for the design of supramolecular photoresponsive polymers for SRG applications.

Methodical and intensive surface plasmon (SP) excitation trials were carried out on various dielectric-metal interfaces to optimize plasmonic photocurrent enhancements in organic P3HT-PCBM photovoltaic thin films. The SPs were optically excited via the diffraction grating method using single, crossed, and parallel grating schemes, with trials yielding optimal grating and film thickness parameters. Photocurrent enhancements up to 355% were demonstrated with TM-polarized incident light on single and parallel grating structures, while both TM and TE-polarized incident light enhancements were present on crossed grating structures. When compared with the photocurrent enhancements seen on single gratings, those seen on parallel gratings were comparable in magnitude but were shown over a broader optical band. This broadening of the optical band was due to the simultaneous SP excitations by the two superimposed gratings in the parallel scheme. Copyright © 2012 John Wiley & Sons, Ltd.

Surface plasmon resonance platforms based on laser inscribed azo polymer surface relief diffraction gratings were used to detect the binding of organic and biological molecules. Optical sensors were assembled to operate in transmission mode, resulting in a very simple setup. This new approach is observed to present a high sensitivity when compared to other systems, such as SPR-based biosensors using nanoholes. The corrugated surface provides a relatively large surface area and the improved sensitivity to binding events is related to resonant plasmon enhancement on the surface relief grating. It was found that varying the periodicity from 400 to 410 nm does not improve efficiency, however changing the groove depth from 30 to 65 nm, resulted in a two-fold increase in sensitivity. An interesting result is that sensors with higher energy surface plasmons present higher sensitivity when compared to lower energy ones. This result can drive further studies toward improved surface plasmon-based sensors.

The real-time thermo-optical properties of thin-film relaxor ferroelectric (9/65/35) lead lanthanum zirconate titanate (PLZT) films (∼2 μm) were investigated and compared to identical composition of thick PLZT ceramics (∼1 mm). Since PLZT absorbs strongly in the far-infrared, a CO2 laser beam (λ = 10.6 μm) was used to create a Gaussian temperature distribution at the surface of the material, emulating a lens. Subsequently, a low power visible He–Ne laser, travelling along the same path as the CO2 laser, probed the optical properties of the induced PLZT thermal lens. It was found that identical composition thin-film and thick PLZT ceramics have opposite thermal lensing behaviors. An explanation of this phenomenon is provided from basic physical concepts.

The change in the transverse refractive indices of clamped transparent relaxor ferroelectric PLZT ceramics, having a composition of (9.5/65/35) and (9.0/65/35), were measured as a function of various ac and dc electric fields, as well as frequency and elapsed time, using an interferometric technique. It was found that the refractive index changed only in the same direction of the applied field, and that increasing dc fields decreased this refractive index, while increasing ac fields increased it, especially in composition (9.5/65/35). These results were explained on the basis of movement and creation of domain structures.

Changes in the refractive indices Δn1 and Δn3 of clamped transparent relaxor ferroelectric (9.5/65/35) and (9.0/65/35) PLZT ceramics were measured as a function of temperature ranging from −30 °C to 60 °C, and at various transversely applied DC electric fields E 3 DC . It was found that the refractive index of both PLZT compositions increased linearly with temperature under no DC bias, indicating a constant electronic polarizability of the samples in the tested temperature range. The rate of increase of Δn3 with temperature became higher for both compositions upon the application a DC bias field ( E 3 DC = 774 kV / m ) due to increased electronic polarizability of the samples, while the rate of increase of Δn1 with temperature remained unchanged and was independent of the DC field applied. The quadratic electro-optic coefficients of these two PLZT compositions were also obtained at 0, 20 and 40 °C, and a significant non-linearity was observed: an 85% decrease in the electro-optic coefficient of PLZT (9.5/65/35) was measured at 40 °C compared to 0 °C, while a similar 60% drop was measured for PLZT (9.0/65/35).

The supramolecular assembly of photoactive azobenzenes with passive polymers via halogen or hydrogen bonding is a cost-effective way to design materials for various photomechanical applications that convert light energy directly into macroscopic motion, for instance, in all-optical surface patterning and photochemical imaging of plasmonic structures. To elucidate the molecular-level origins of this motion, we show, by coupling dynamic infrared spectroscopy to a photo-orientation setup, that supramolecular bonds above a certain interaction strength threshold are photostable under vigorous photoisomerization cycling and capable of translating the photo-orientation of azobenzenes into the orientation of nonabsorbing host polymer side chains. A correlation is found between azobenzene photoinduced molecular orientation and macroscopic all-optical surface patterning efficiency. The improved performance of halogen-bonded systems in photopatterning applications can be related to the absence of a plasticizing effect on the polymer matrix, which may enable the material to retain an optimal glass transition temperature, in contrast to hydrogen-bonded and nonbonded references. Thus, our results provide design guidelines in terms of the nature and strength of the supramolecular interaction and of the degree of azo functionalization needed to optimize the motion transfer to passive polymers. acceptedVersion

Novel metallic light-interfering fixtures were designed and fabricated in order to achieve a laser interference pattern of constant-pitch, concentric and sinusoidal light variations. These fixtures consisted of annular rings with the inner diameter shaped conically. Azobenzene-containing solid thin-films were subsequently placed behind the fixture and circular surface-relief diffraction gratings were inscribed due to the azo molecules photochemical isomerization process. Gratings pitches were dependent on the fixture dimensions and ranged from 600 to 1400 nm with depths up to 250 nm.

Circular surface-relief diffraction gratings with a constant pitch were photo-inscribed on thin films of a disperse red 1 functionalized glass-forming compound using a novel holographic technique. Various light-interfering metallic fixtures, which consisted of annular rings with a sloped and polished inner surface, were designed and fabricated. Each of them allowed the inscription of stable and high-quality circular diffraction gratings with pitches ranging from approximately 600–1400 nm and depths up to 250 nm. This was accomplished by exposure to a collimated laser beam with an irradiance of 604 mW/cm2 for 350 s. The resulting gratings had a diameter of 11.4 mm and had the advantage of being produced in a simple single-step procedure with no postprocessing or specialized equipment. The pitch and diameter of these circular gratings were dependent on the fixture geometry, while the depth was related to the exposure time.