Photoinduced Deformation Research Articles

Towards Oxide Electronics: a Roadmap

Giant photovoltaic effect due to bulk photovoltaic effect observed in multiferroic BiFeO3 thin films has triggered a renewed interest on photoferroelectric materials for photovoltaic applications. Tremendous advance has been done to improve power conversion efficiency (up to up to 8.1%) in photoferroelectrics via absorption increase using narrow bandgap ferroelectrics. Other strategies, as it is the more efficient use of ferroelectric internal electric field, are ongoing. Moreover, as a by-product, several progress have been also achieved on photostriction that is the photo-induced deformation phenomenon. Here, we review ongoing and promising routes to improve ferroelectrics photoresponse.

Fast photoinduced deformation of hydrogen-bonded supramolecular polymers containing α-cyanostilbene derivative

This is the first example of photoinduced deformation displayed by α-cyanostilbene-based supramolecular polymers.

Photoinduced multi-directional deformation of azobenzene molecular crystals

Photoinduced multi-directional deformation of azobenzene molecular crystals enabled by photoisomerization and photothermal effects.

Photoinduced deformation and isomerization of azobenzene liquid-crystalline polymer films at cryogenic temperature

We prepared 2 types of crosslinked liquid-crystalline polymers (CLCPs) (polyacrylates) with the same side-chain length but a different position of an azobenzene moiety in the side chain. We evaluated photoinduced deformation behavior of the CLCP films and photoisomerization behavior of azobenzene in the films at cryogenic temperature. Azobenzene moieties in both CLCP films showed no trans-cis isomerization and neither film exhibited bending behavior upon irradiation with UV light in liquid nitrogen [77 K]. On the other hand, when the film included azobenzene with a long spacer and a short tail, cis-trans isomerization of azobenzene and photoinduced deformation were observed in liquid nitrogen.

Area-selective Photodeformation Behavior of N-benzylideneaniline Liquid Crystalline Polymeric Films Prepared with Sublimed Crosslinker

Photomobile materials exhibit deformed macroscopic shape in response to actinic lighting. We report the photoinduced macroscopic deformation behavior of a crosslinked liquid crystalline N-benzylideneaniline (NBA) film. The film is observed to bend toward the highly crosslinked surface upon exposure to UV light and revert to the initial shape when the light is turned off. In this study, we fabricated the crosslinker via vapor deposition to enlarge the nonuniformity of NBA moieties along a direction normal to the plane of the film. Furthermore, we demonstrated the area-selective bending behavior caused by the local formation of NBA-crosslinking points. The film bent toward the highly crosslinked surface, similar to a previous top-coating film. The change in shape was large enough to be observed with the naked eye.

Non-uniform Excitation States in Photoinduced Deformation of Amorphous Carbon Nitride Films

Amorphous carbon nitride (a-CNx) films prepared via reactive radio frequency magnetron sputtering deform under on–off visible light illumination. We investigate the relationship between photoinduced deformation and surface electrical states via scanning electron microscopy with Ar+ laser irradiation (SEM-L). Two samples with different levels of photoinduced deformation are prepared. For the film with small photoinduced deformation, uniform secondary electron emission is observed on the film surface, regardless of whether the laser is on or off. On the a-CNx film, which has fifty times larger photoinduced deformation than the previous film, light and dark patches, similar to a speckle pattern, appear on the film surface in SEM-L images. This anomalous phenomenon indicates non-uniformity of the electrical states excited by laser light irradiation. A size of the patches is well correlated with an inhomogeneous distribution of sp3C and sp2C, Isp3C/Isp2C, obtained using soft X-ray emission spectroscopy (SXES). Simultaneously, temporal decrease in the sp3C component under illumination is obtained via SXES.

Experimental investigation on photo-deformation effect of PLZT ceramic with bias electric field

The lanthanum-doped lead zirconate titannate (PLZT) ceramic has been widely used in light-controlled wireless actuators activated by ultraviolet light for their characteristic of converting light energy directly into the mechanical energy. The photovoltaic effect of PLZT is the result of multi-phys ics fields coupling, and the primary purpose of this article is to provide a comprehensive experimental analysis on the influence of photo-induced deformation of PLZT ceramics under the action of bias electric field. To this end, the amount and the speed of arriving at the electrodes of photo-generated carriers are analyzed. Furthermore, whether the bias electric field promotes the photovoltaic effect is investigated by a series of experiments. The experimental results indicate that the deformation of PLZT ceramic with combined action of ultraviolet light and bias electric field is larger than that with only irradiation action. However, the increment is only contributed by bias electric field based on the converse piezoelectric effect, and the bias electric field has no effect on the photo-generated carriers. Therefore, adding a bias electric field cannot promote the photo-induced deformation of PLZT.

A multiple coupling approach to produce high-performance SERS substrates

Creating hotspots with significantly enhanced electromagnetic (EF) field, efficiently placing target molecules in hotspot region, and achieving uniform and reproducible Raman signals are three critical issues for developing high-performance SERS substrates. In this work, large area gold nanoparticle cluster pillar array with a gold mirror at bottom was facilely fabricated by combined use of nanosphere lithography and self-assembly approach. It is both theoretically and experimentally found that through multiple coupling interactions, the electromagnetic fields at interparticle gaps within the gold clusters were significantly enhanced in our three-dimentional (3D) pillar array substrates, which can result in one order of magnitude stronger as compared with random gold clusters on a two-dimentional planar case. Due to the periodic stucture, our substrates also possess the capbility of producing highly uniform and reproducible SERS signals. Attractively, in our case, a photoresponsive polymer was used for the formation of pillar array structure. Its unique photoinduced deformation makes it possible to reversibly open and close the gaps of the closely packed Au NP array, thus enabling efficient placement or entrapment of probe molecules into hotspot sites between adjacent nanoparticles.

Deposition of amorphous carbon nitride films on flexible substrates by reactive sputtering for applications in light-driven active devices

Amorphous carbon nitride (a-CNx) thin films deposited by reactive sputtering have great potential for driving source applications of light-driven active devices. We demonstrate, for the first time, the photoinduced deformation of a-CNx deposited on flexible substrates, namely, poly(ethylene naphthalate) (PEN) films and transparent cellulose nanopaper. a-CNx films without delamination were obtained on both substrates. By decreasing the thickness of PEN films, the photoinduced deformation became extremely large. A light-driven pump was fabricated using a-CNx-coated PEN films, and then the pumping motion was observed up to 10 Hz. When a He–Ne laser traced the surface of a-CNx films deposited on the nanopaper, the sample moved to the opposite side of the laser spot. The motion involved repeated expansions and contractions similar to the motion of caterpillars occurring owing to the temporary photoinduced deformation of a-CNx films.

Relaxation Dynamics and Strain Persistency of Azobenzene‐Functionalized Polymers and Actuators

AbstractThe accumulation of photoinduced deformation in azobenzene functionalized polymers has received a significant amount of attention in recent years. Critically, the induced photomechanical deformation in these systems experiences varying degrees of relaxation. Control over the persistence of photomechanical strains is vital to the broader utility of these materials in shape programmable systems including soft robotics and engineered origami. Furthermore, investigations of relaxation in light responsive polymer systems triggered by UV light are more prominent than those triggered by blue‐green light. In this study, the impact of chain mobility and initially induced photostrain on the relaxation dynamics of azobenzene‐functionalized polyimides after irradiation with blue light is examined. A modeling effort coupling chromophore population dynamics to material strain is carried out to further explore the relationship between material structure, relaxation dynamics, and macroscopic deformation. The implications for controlling strain persistence are highlighted by simulating one example of a photoprimed bistable actuator.

Photomechanical Motion of Liquid-Crystalline Fibers Bending Away from a Light Source

A series of photomechanical fibers was fabricated with a thermal drawing method by using liquid-crystalline random copolymers containing azobenzene and biphenyl groups in side chain. After being post-cross-linked under mild conditions, these fibers showed photoinduced bending motion away from the light source even though homogeneous alignment of mesogens was observed along the drawing direction. This abnormal photoinduced deformation of the obtained fibers is far different from previously reported light-directed motions about liquid-crystalline fiber and film materials. The interesting photomechanical deformation can be ascribed to the surface volume expansion caused by photoisomerization of azobenzene moieties. Then the photoinduced bending behaviors of these fibers containing different azobenzene concentrations and cross-linking densities were systematically investigated, suggesting that the location of photoresponsive azobenzene played an important role in deciding their photomechanical behaviors. This...

Enhanced Deformation of Azobenzene-Modified Liquid Crystal Polymers under Dual Wavelength Exposure: A Photophysical Model.

Azobenzene-embedded liquid crystal polymers can undergo mechanical deformation in response to ultraviolet (UV) light. The natural rodlike trans state azobenzene absorbs UV light and isomerizes to a bentlike cis state, which disturbs the order of the polymer network, leading to an anisotropic deformation. The current consensus is that the magnitude of the photoinduced deformation is related to the statistical building up of molecules in the cis state. However, a recent experimental study [Liu and Broer, Nat. Commun. 6 8334 (2015).NCAOBW2041-172310.1038/ncomms9334] shows that a drastic (fourfold) increase of the photoinduced deformation can be generated by exposing the samples simultaneously to 365nm (UV) and 455nm (visible) light. To elucidate the physical mechanism that drives this increase, we develop a two-light attenuation model and an optomechanical constitutive relation that not only accounts for the statistical accumulation of cis azobenzenes, but also for the dynamic trans-cis-trans oscillatory isomerization process. Our experimentally calibrated model predicts that the optimal single-wavelength exposure is 395nm light, a pronounced shift towards the visible spectrum. In addition, we identify a range of optimal combinations of two-wavelength lights that generate a favorable response for a given amount of injected energy. Our model provides mechanistic insight into the different (multi)wavelength exposures used in experiments and, at the same time, opens new avenues towards enhanced, multiwavelength optomechanical behavior.

Deformation of a bismuth ferrite nanocrystal imaged by coherent X-ray diffraction

Perovskite materials that contain transition metal-oxides often exhibit multifunctional properties with considerable utility in a device setting. BiFeO3 is a multiferroic perovskite material that exhibits room temperature anti-ferromagnetic and ferroelectric ordering. Optical excitation of BiFeO3 crystals results in an elastic structural deformation of the lattice with a fast response on the pico-second time scale. Here we report on dynamic optical excitation coupled with Bragg coherent X-ray diffraction measurements to investigate the structural properties of BiFeO3 nanoscale crystals. A continuous distortion of the diffraction speckle pattern was observed with increasing illumination. This was attributed to strain resulting from photo-induced lattice deformation.

Ultrafast Independent N-H and N-C Bond Deformation Investigated with Resonant Inelastic X-Ray Scattering.

The femtosecond excited‐state dynamics following resonant photoexcitation enable the selective deformation of N−H and N−C chemical bonds in 2‐thiopyridone in aqueous solution with optical or X‐ray pulses. In combination with multiconfigurational quantum‐chemical calculations, the orbital‐specific electronic structure and its ultrafast dynamics accessed with resonant inelastic X‐ray scattering at the N 1s level using synchrotron radiation and the soft X‐ray free‐electron laser LCLS provide direct evidence for this controlled photoinduced molecular deformation and its ultrashort timescale.

Microspheres of polyurethanes functionalized with push-pull type azo chromophores and their photoinduced deformation behavior

A series of azo polyurethanes bearing push-pull type azo chromophores was synthesized by post-polymerization azo-coupling reactions between a polyurethane precursor and diazonium salts of different aniline derivatives, respectively. Colloidal spheres with narrow size distributions were obtained by aggregation of these azo polyurethanes in DMF-H2O mixed solvents, which were induced by slowly increasing the water content. The self-assembling processes and formed structures were investigated by laser light scattering and transmission electron microscopy. When irradiated with linearly polarized light from Ar+ laser (488 nm) and diode solid state laser (532 nm), the azo polyurethane microspheres showed significant deformations elongated in the light polarization direction. The electron-withdrawing groups on the azo chromophores show a significant effect on the photoinduced deformation degree. These microspheres composed of the azo polyurethanes bearing carboxylic acid and trifluoromethyl groups as the electron-withdrawing substituents shows the largest deformation degrees when irradiated with 488 and 532 nm light, respectively.

Photoresponsive liquid crystalline polymer single-chain nanoparticles

Single-chain nanoparticles prepared from a side-chain liquid crystalline polymer bearing azobenzene moieties can be multifunctional.

Photocontrol of fluid slugs in liquid crystal polymer microactuators.

The manipulation of small amounts of liquids has applications ranging from biomedical devices to liquid transfer. Direct light-driven manipulation of liquids, especially when triggered by light-induced capillary forces, is of particular interest because light can provide contactless spatial and temporal control. However, existing light-driven technologies suffer from an inherent limitation in that liquid motion is strongly resisted by the effect of contact-line pinning. Here we report a strategy to manipulate fluid slugs by photo-induced asymmetric deformation of tubular microactuators, which induces capillary forces for liquid propulsion. Microactuators with various shapes (straight, 'Y'-shaped, serpentine and helical) are fabricated from a mechanically robust linear liquid crystal polymer. These microactuators are able to exert photocontrol of a wide diversity of liquids over a long distance with controllable velocity and direction, and hence to mix multiphase liquids, to combine liquids and even to make liquids run uphill. We anticipate that this photodeformable microactuator will find use in micro-reactors, in laboratory-on-a-chip settings and in micro-optomechanical systems.

Coherent x-ray diffraction imaging of photo-induced structural changes in BiFeO3 nanocrystals

Multiferroic materials that exhibit coupling between ferroelectric and magnetic properties are of considerable utility for technological applications and are also interesting from a fundamental standpoint. When reduced to the nanoscale, multiferroic materials often display additional functionality that is dominated by interfacial and confinement effects. Bismuth ferrite (BiFeO3) is one such material with room temperature anti-ferromagnetic and ferroelectric ordering. Optical excitation of BiFeO3 crystals results in an elastic structural deformation of the lattice with a fast response on the pico-second time scale. Here we report on dynamic measurements to investigate the structural properties of BiFeO3 nanoscale crystals using laser excitation and three-dimensional Bragg coherent x-ray diffraction imaging. Tensile strain beyond 8 was observed predominantly at the surface of the nanoscale crystal as evidenced in the reconstructed phase information and was correlated to photo-induced lattice deformation.

Silver photo-diffusion and photo-induced macroscopic surface deformation of Ge33S67/Ag/Si substrate

Ge-chalcogenide films show various photo-induced changes, and silver photo-diffusion is one of them which attracts lots of interest. In this paper, we report how silver and Ge-chalcogenide layers in Ge33S67/Ag/Si substrate stacks change under light exposure in the depth by measuring time-resolved neutron reflectivity. It was found from the measurement that Ag ions diffuse all over the matrix Ge33S67 layer once Ag dissolves into the layer. We also found that the surface was macroscopically deformed by the extended light exposure. Its structural origin was investigated by a scanning electron microscopy.

Photodegradation Behavior of Ethylene/Vinyl Acetate Copolymer (EVA) Film for Solar Cell Encapsulant

In this study, we investigated the photodegradation behavior of an ethylene/vinyl acetate (EVA) film for solar cell encapsulant. The EVA film was exposed to the weathering apparatus, equipped with a xenon-arc lamp for simulated sunlight exposure conditions. Since photodegradation mainly induces changes and variations on the materials surface, a variety of technical approaches were employed to characterize the modifications of the EVA film surface, and then the deterioration behavior of optical properties was discussed in term of the morphological changes. And also, photo- degradation caused the composition modification of the EVA film surface by the incorporation of oxygen to the polymer chains, which could make the wettability of the film hydrophilic. Finally, the photo-induced deformation behavior of the EVA film influenced by the light intensity depending on the type of lamp was discussed in order to show the importance of the light source.