In‐Plane Field‐Driven Excitonic Electro‐Optic Modulation in Monolayer SemiconductorVella, Daniele; Barbosa, Marcelo B.; Trevisanutto, Paolo E.; Verzhbitskiy, Ivan; Zhou, Justin Yong; Watanabe, Kenji; Taniguchi, Takashi; Kajikawa, Kotaro; Eda, Goki
doi: 10.1002/adom.202102132pmid: N/A
2D semiconductors are attractive candidates for on‐chip electro‐optic modulators due to their ease of integration and rich exciton‐mediated phenomena. While electrostatic doping and out‐of‐plane field effect have been extensively studied, in‐plane field‐induced phenomena remain largely unexplored. Here electro‐optic response of monolayer WSe2 subject to modulating in‐plane electric fields probed by electroabsorption and electroreflectance spectroscopy is reported. The devices are found to exhibit spatially varying response near exciton resonance, which cannot be explained by predicted effects such as Pockels and excitonic Stark effect. It is shown that the modulation signal is dominated by exciton linewidth broadening and narrowing associated with local accumulation and depletion of free holes. The field and frequency dependence of the devices is distinct from those of charge modulation devices. The observed behavior is ascribed to elastic scattering of excitons with field‐driven intrinsic free carriers.
High Temperature Mid‐IR Polarizer via Natural In‐Plane Hyperbolic Van der Waals CrystalsSahoo, Nihar Ranjan; Dixit, Saurabh; Singh, Anuj Kumar; Nam, Sang Hoon; Fang, Nicholas X.; Kumar, Anshuman
doi: 10.1002/adom.202101919pmid: N/A
Integration of conventional mid to long‐wavelength infrared (IR) polarizers with chip‐scale platforms is restricted by their bulky size and complex fabrication. Van der Waals materials based polarizer can address these challenges due to its nonlithographic fabrication, ease of integration with chip‐scale platforms, and room temperature operation. In the present work, mid‐IR optical response of the sub‐wavelength thin films of α‐phase molybdenum trioxide (α‐MoO3 ) is investigated for application toward high temperature mid‐IR transmission and reflection type thin film polarizer. To the authors’ knowledge, this is the first report of above room temperature mid‐IR optical response of α‐MoO3 to determine the thermal stability of the proposed device. It is found that the α‐MoO3 based polarizer retains high extinction ratio with peak value exceeding 10 dB, up to a temperature of 140 °C. The experimental findings are explained by natural in‐plane hyperbolic anisotropy of α‐MoO3 in the mid‐IR, high temperature X‐ray diffraction and Raman spectroscopic measurements. This work opens up new avenues for naturally in‐plane hyperbolic van der Waals thin‐films to realize sub‐wavelength IR optical components without lithographic constraints.
Optical Induction and Erasure of Ferroelectric Domains in Tetragonal PMN‐38PT CrystalsChen, Xin; Liu, Dawei; Liu, Shan; Mazur, Leszek M.; Liu, Xin; Wei, Xiaoyong; Xu, Zhuo; Wang, Junli; Sheng, Yan; Wei, Zhiyi; Krolikowski, Wieslaw
doi: 10.1002/adom.202102115pmid: N/A
PT‐relaxor ferroelectrics exhibit excellent piezoelectric and quadratic nonlinear optical properties, making them prominent candidates for realization of phononic and nonlinear photonic crystals which rely on spatially patterned ferroelectric domains. However, formation of domain patterns, especially in three dimensions, has been challenging. This paper presents the first experimental demonstration of localized ferroelectric domains and their 2D and 3D patterns inside 0.62Pb(Mg1/3Nb2/3)O3‐0.38PbTiO3 (PMN‐38PT) single‐domain crystals engineered with focused near‐infrared femtosecond laser pulses. Two types of domains are optically induced. Primary domains are formed in the focal volume of the beam, and secondary domains appearing at higher laser power, in the shape of hollow cylindrical structures, are formed around the beam. A physical mechanism of optical domain inversion involving thermoelectric and space charge fields is proposed. This study contributes to a deeper understanding of domain formation and structuring in PMN‐PT relaxor‐based ferroelectrics, paving the way to integrate electromechanical, acoustic, and nonlinear optical effects in a single crystal.
General Background of SERS Sensing and Perspectives on Polymer‐Supported Plasmon‐Active Multiscale and Hierarchical Sensor ParticlesVisaveliya, Nikunjkumar R.; Mazetyte‐Stasinskiene, Raminta; Köhler, Johann Michael
doi: 10.1002/adom.202102001pmid: N/A
Surface‐enhanced Raman scattering (SERS) is one of the most powerful analytical techniques for the identification of molecules. The substrate, on which SERS is dependent, contains regions of nanoscale gaps (hotspots) that hold the ability to concentrate incident electromagnetic fields and effectively amplify vibrational scattering signals of adsorbed analytes. While surface plasmon resonance from metal nanostructures is a central focus for the SERS effect, the support of polymers can be significantly advantageous to provide larger exposure of structured metal surfaces for efficient interactions with analytes. Characteristics of the polymer particles such as softness, flexibility, swellability, porosity, optical transparency, metal‐loading ability, and high surface area can allow diffusion of analytes and penetrating light deeply that can enormously amplify sensing outcomes. As polymer‐supported plasmon‐active sensor particles can emerge as versatile SERS substrates, the microfluidic platform is promising for the generation of sensor particles as well as for performing sequential SERS analysis of multiple analytes. Therefore, in this perspective article, the development of multifunctional polymer–metal composite particles, and their applications as potential sensors for SERS sensing through microfluidics are presented. A detailed background from the beginning of the SERS field and perspectives for the multifunctional sensor particles for efficient SERS sensing are provided.
Tailoring Transition Dipole Moment in Colloidal Nanocrystal Thin Film on Nanocomposite MaterialsLee, Kwang Jin; Kim, Gahyeon; Lim, Joonhyung; Nah, Sanghee; Jeong, Kwang Seob; Cho, Minhaeng
doi: 10.1002/adom.202102050pmid: N/A
Controlling the transition dipole moment is extremely important for various photophysical characteristics in semiconductors. Especially, suppression of Auger recombination in quantum dots (QDs) is essential for the development of novel applications, including bioimaging, lasing, and optoelectronic devices. To date, most of the studies on the Auger process are conducted on the basis of manipulating the material property such as wavefunction of electron and hole, energy band, and confinement potential. However, a new way of tuning the Auger process using nanocomposite materials is not reported. In this work, the biexciton Auger recombination (BAR) process in CdSe/CdS(1 ML) nanocrystal thin‐film is successfully controlled by introducing nanocomposite materials. Performing pump intensity‐dependent transient absorption experiments, a significant reduction (up to 30%) of BAR rate is observed in the presence of nanocomposite structures. This notable suppression effect is attributed to the modulation of the net transition dipole moment. These findings will provide further insight into the rational design of QDs combining with a nanostructure that efficiently suppresses Auger recombination rates.
Photon Recycling Effect and Lossless Fluorescence Propagation in β‐Sheet Peptide FibersApter, Boris; Lapsker, Igor; Inberg, Alexandra; Rosenman, Gil
doi: 10.1002/adom.202102342pmid: N/A
Light‐delivering optical fibers are widely used for biomedical imaging, theranostics and surgery, and optogenetics. In this work, a new generation of bioinspired optical fibers is proposed. Developed amyloidogenic peptide fibrillary structures with tailored β‐sheet conformation exhibit unique optical properties of full overlapping of broadband visible fluorescence (FL) and optical absorption spectra. This study reports on unexpected lossless propagation of the FL light along 100 µm length β‐sheet microfibers. It is shown that the found FL long‐distance lossless radiative energy transport occurs due to highly effective FL photon recycling phenomenon supported by FL zero Stokes shift and high quantum yield. This new non‐Beer–Lambert FL lossless propagation mechanism is observed in very thin ≈1 µm diameter fibers, providing a single/few‐mode waveguiding regime. The developed model and computer simulations, based on the finite difference time domain method, are consistent with the experimental results. Fabricated peptide FL fiber probes permit delivering intensity‐modulated FL signal with selected wavelength over the whole visible spectrum in wide modulation frequencies range.
Nematic Liquid Crystal Disclination Lines Driven by A Photoaligned Defect GridNys, Inge; Berteloot, Brecht; Beeckman, Jeroen; Neyts, Kristiaan
doi: 10.1002/adom.202101626pmid: N/A
Photoalignment for nematic liquid crystals makes it possible to design complex alignment patterns with point defects, that can act as anchoring points for disclination lines. This feature may be used to realize novel electro‐optical devices with bistability or enhanced scattering and is promising for material applications such as stimuli‐responsive actuators, active matter, and assembly of colloidal particles. However, the applicability is hampered by the limited understanding of the interaction between the defects in the photoalignment pattern and the disclination lines in the nematic liquid crystal. In this work disclination lines are studied that connect surface defects of strength 1/2 arranged in a periodic grid. The elastic tension is estimated in the disclination line and it is shown how the director configuration close to a +1/2 surface defect is influenced by the fact that the three elastic constants are different. A tilt is induced close to the surface that can be amplified and visualized by applying a voltage.