Dichroic Ratio Research Articles

Van der Waals GeSe with Strain- and Gate-Tunable Linear Dichroism for Wearable Electronics.

The direct detection of light polarization poses a crucial challenge in the field of optoelectronics and photonics. Herein, the tunable linear dichroism (LD) in GeSe-based polarized photodetectors is presented through electronic and structural asymmetry modulation, and demonstrate their application prospects in wearable electronics. An improvement in the dichroic ratio up to 34% is achieved under a gate voltage of 20V, and the improvement reaches 44% by applying a tensile strain along the zigzag direction. Theoretical calculations reveal that the gate regulation of barrier height between GeSe and Au electrodes is responsible for the electrical-tunable LD, while the anisotropic optical absorption in response to strains leads to the strain-tunable LD. Moreover, flexible GeSe transistors are developed for wearable applications including motion sensors and glucose monitors. This study offers viable approaches for modulating the optical anisotropy of low-dimensional materials and emphasizes the versatility of van der Waals materials for practical applications in wearable electronic devices.

CVD‐Synthesized CsAg2I3 Single Crystals toward Polarization UV Photodetection and Anti‐Counterfeiting Identification

AbstractLow‐dimensional ternary silver halide (CsAg2I3), an emerging inorganic lead‐free perovskite, has garnered significant scientific attention due to its strong quantum confinement effects, wide bandgaps, non‐toxicity, and others. However, the photophysical properties and optoelectronic performance of CsAg2I3 materials and devices are significantly compromised by crystal quality and defects arising from liquid‐phase preparation. Herein, 1D CsAg2I3 single crystals newly grown by the chemical vapor deposition method are reported. These crystals display exceptional quality and stability over a 3‐month period despite exposure to air and moisture. The high in‐plane anisotropic structure, phonon vibrations, and refractive index of CsAg2I3 crystals are also experimentally elucidated. Polarization‐sensitive ultraviolet photodetector based on the CsAg2I3 monocrystal features a responsivity of 139 mA W−1, a specific detectivity of 1.05 × 1011 cm Hz1/2 W−1, an ultra‐fast photoresponse speed of 48.2/69.1 µs, and a dichroic ratio of 2.66 upon 360 nm irradiation at −5.0 V bias. The photodetector excels amongst its competitors, moving toward the potential application of rapid optical anti‐counterfeiting identification. This work, which leverages grown high‐crystalline and highly stable CsAg2I3 monocrystals, holds promises for advancing this functional material into a robust next‐generation optoelectronic devices capable of probing sensitive optical sensing and specific azimuth recognition.

Crystal Evolution of Amorphous Poly(lactic acid) During Simultaneous Multi‐step Tensile Deformation and Annealing

ABSTRACTThe cold‐crystallization and crystal evolution of amorphous poly(lactic acid) (PLA) are analyzed during multistep tensile deformation and annealing at 70°C using in situ synchrotron wide‐angle X‐ray scattering (WAXS) measurements. The 2D‐WAXS diffraction pattern reveals that the PLA crystalline structure forms perpendicular to the draw direction. The annealing process lets to a rearrangement of the crystalline structure, while the stretching causes crystal contraction. Both WAXS and FTIR analyses confirm that the crystals developed through stretching and annealing are in the α′‐form. The crystallinity of PLA increases with higher deformation strains and longer annealing times. The orientation degree of both crystalline and amorphous phases of PLA, as indicated by the Hermans orientation factor and dichroic ratio of 956 cm−1 band (evaluated by WAXS and polarized FTIR analysis, respectively) also increase. The enhanced cold‐crystallization ability of PLA is attributed to the synergistic effect of tensile deformation and annealing, rather than either technique alone. The unusual crystallization phenomenon observed during multistep tensile deformation coupled with annealing provides valuable insights into the crystallization and crystal evolution of PLA.

Low-symmetry layered semiconductor In2Te5 for promising polarization-sensitive photodetector

Low-symmetry two-dimensional (2D) materials have attracted significant attention for polarization-sensitive photodetection due to the optoelectronic anisotropy. Here, we demonstrated the strong in-plane anisotropy of In2Te5 through electron density distribution calculations based on density functional theory and developed a polarization-sensitive photodetector. The photodetector shows a responsivity of 171.16 mA/W and a response time of 0.42 s under visible light illumination. Additionally, it presents a polarization-sensitive photoresponse with a dichroic ratio of 1.34. Our work reveals the anisotropic optoelectronic properties of In2Te5, potentially stimulating research interest in Group III-VI 2D materials (Pentatelluride M2Te5, M = Al, Ga, In, etc.).

Angle-resolved polarization Raman spectroscopy of β-Ga2O3 and their application in sensitive solar-blind photodetection

Polarization-sensitive photodetection has promising prospects for civilian and military applications based on anisotropic semiconductors. However, it is greatly limited due to the lack of valid materials as well as the terrible linear dichroism ratio. In this Letter, a metal–oxide–semiconductor β-Ga2O3 with strong anisotropic property is proposed for highly efficient polarizing detection, which can potentially overcome these limitations. Angle-resolved polarization Raman spectroscopy was performed to confirm excellent anisotropic phonon vibration. Unique narrow solar-blind polarization-sensitive photo-absorption (240–270 nm) can be observed, which can be attributed to the natural anisotropy, referring in particular to the polarization-resolved absorption in the surround of the bandgap of β-Ga2O3. Benefiting from the structural anisotropy, the polarization-sensitive photodetector exhibits an excellent linear dichroic ratio of ∼1.8. Moreover, obvious color change is observed under different polarized angles, providing great potential in polarization imaging. With these advantages, we anticipated that this research will pave avenues for the fabrication of polarization-sensitive solar-blind UV photodetectors.

Low-Symmetry Van der Waals Dielectric GaInS3 Triggered 2D MoS2 Giant Anisotropy via Symmetry Engineering.

Low-symmetry structures in van der Waals materials have facilitated the advancement of anisotropic electronic and optoelectronic devices. However, the intrinsic low symmetry structure exhibits a small adjustable anisotropy ratio (1-10), which hinders its further assembly and processing into high-performance devices. Here, a novel 2D anisotropic dielectric, GaInS3 (GIS), which induces isotropic MoS2 to exhibit significant anisotropic optical and electrical responses is demonstrated. With the excellent gate modulation ability of 2D GIS (dielectric constant k ∼12), MoS2 field effect transistor (FET) shows an adjustable conductance ratio from isotropic to anisotropic under dual-gate modulation, up to 106. Theoretical calculations indicate that anisotropy originates from lattice mismatch-induced charge density deformation at the interface. Moreover, the MoS2/GIS photodetector demonstrates high responsivity (≈4750 A W-1) and a large dichroic ratio (≈167). The anisotropic van der Waals dielectric GIS paves the way for the development of 2D transition metal dichalcogenides (TMDCs) in the fields of anisotropic photonics, electronics, and optoelectronics.

β-Ga2O3 Nanoribbon with Ultra-High Solar-Blind Ultraviolet Polarization Ratio.

Solar-blind ultraviolet (UV) detection plays a critical role in imaging and communication due to its low-noise background, high signal-to-noise ratio, and strong anti-interference capabilities. Detecting the polarization state of UV light can enhance image information and expand the communication dimension. Although polarization detection is explored in visible and infrared light, and applied in fields such as astrophysics and submarine seismic wave detection, solar-blind UV polarization detection remains largely unreported. This is primarily due to the challenge of creating UV polarizers with high transmittance, high extinction ratio, and strong resistance to UV radiation. In this study, it is discovered that the space symmetry breaking of the β-Ga2O3's b-c plane results in a significant optical absorption dichroic ratio. Leveraging β-Ga2O3's high solar-blind UV response, a lensless solar-blind UV polarization-sensitive photodetector, circumventing the challenges associated with solar-blind UV polarizers is designed. This photodetector exhibits an exceptionally high intrinsic polarization ratio under 254nm linearly polarized light, approximately two orders of magnitude higher than other reported nanomaterial-based polarization-sensitive photodetectors. Additionally, it demonstrates significant advantages in solar-blind UV imaging and light communication. This work introduces a novel strategy for solar-blind ultraviolet polarization detection and offers a promising approach for solar-blind light communication.

All-in-One 2D Molecular Crystal Optoelectronic Synapse for Polarization-Sensitive Neuromorphic Visual System.

Neuromorphic visual systems (NVSs) hold the potential to not only preserve but also enhance human visual capabilities. One such augmentation lies in harnessing polarization information from light reflected or scattered off surfaces like bees, which can disclose unique characteristics imperceptible to the human eyes. While creating polarization-sensitive optoelectronic synapses presents an intriguing avenue for equipping NVS with this capability, integrating functions like polarization sensitivity, photodetection, and synaptic operations into a singular device has proven challenging. This integration typically necessitates distinct functional components for each performance metric, leading to intricate fabrication processes and constraining overall performance. Herein, a pioneering linear polarized light sensitive synaptic organic phototransistor (OPT) based on 2D molecular crystals (2DMCs) with highly integrated, all-in-one functionality, is demonstrated. By leveraging the superior crystallinity and molecular thinness of 2DMC, the synaptic OPT exhibits comprehensive superior performance, including a linear dichroic ratio up to 3.85, a high responsivity of 1.47 × 104 A W-1, and the adept emulation of biological synapse functions. A sophisticated application in noncontact fingerprint detection achieves a 99.8% recognition accuracy, further highlights its potential. The all-in-one 2DMC optoelectronic synapse for polarization-sensitive NVS marks a new era for intelligent perception systems.

Rolling up 2D WSe2 Nanosheets to 1D Anisotropic Nanoscrolls for Polarization-Sensitive Photodetectors.

The intrinsic low-symmetry crystal structures or external geometries of low-dimensional materials are crucial for polarization-sensitive photodetection. However, these inherently anisotropic materials are limited in variety, and their anisotropy is confined to specific crystal directions. Transforming 2D semiconductors, such as WSe2, from isotropic 2D nanosheets into anisotropic 1D nanoscrolls expands their application in polarization photodetection. Despite this considerable potential, research on polarization photodetection based on nanoscrolls remains scarce. Here, the uniform crystalline orientation of WSe2 nanoscrolls is achieved conveniently and efficiently by applying ethanol droplets to vapor deposition-grown bilayer WSe2 nanosheets. Angle-resolved polarized Raman spectroscopy of WSe2 nanoscrolls demonstrates vibrational anisotropy. Photodetectors based on these nanoscrolls show competitive overall performance with a broadband detection range from 405 to 808nm, a competitive on/off ratio of ≈900, a high detectivity of 3.4×108 Jones, and a fast response speed of ≈30ms. Additionally, WSe2 nanoscroll-based photodetectors exhibit strong polarization-sensitive detection with a maximum dichroic ratio of 1.5. More interestingly, due to high photosensitivity, the WSe2 nanoscroll detectors can easily record sequential puppy images. This work reveals the potential of WSe2 nanoscrolls as excellent polarization-sensitive photodetectors and provides new insights into the development of high-performance optoelectronic devices.

Organic-Inorganic Rubrene/WS2 Heterostructure for Broadband Detection and Polarization Imaging.

Organic single crystals exhibit improved carrier mobility, longer exciton diffusion length, anisotropic charge transport, and unique linear dichroism, while its high exciton binding energy seriously limits the free-carrier generation and photoelectric conversion efficiency. Layered van der Waals heterostructures, which integrate organic crystals with high mobility two-dimensional (2D) inorganic semiconductors, are promising for promoting exciton dissociation and boosting sensitivity by utilizing the interfacial potential and photogating effect. In this work, organic single-crystal rubrene is integrated with a few-layer WS2 to design the high-performance photodetector. The device exhibits an excellent responsivity of 1000 A W-1, and a fast speed of 180 μs, which is far superior to the individual WS2 device. Equally importantly, this device provides excellent polarization detection performance by virtue of the anisotropic properties of rubrene, and the dichroic ratios are 1.56, 1.5, and 1.7 for 375, 405, and 658 nm irradiation, respectively. Finally, several high-resolution single-pixel broadband polarization imaging was demonstrated. Our work shows that organic-inorganic heterostructure is an essential candidate for improving optoelectronics performance and has potential for polarization imaging.

Band Alignment Engineering in 2D Ferroelectric Van der Waals Heterostructures for All‐In‐One Optoelectronic Architecture

Abstract2D van der Waals (vdW) heterostructures consisting of vertically stacking atomically thin semiconductors with different band structures provide a flexible platform to design integrated electronic and optoelectronic devices with multi‐functionalities. However, the realization of device multifunctionality requires the heterostructures with tunable band alignments. Here an efficient strategy is proposed by constructing 2D vdW ferroelectric semiconductor heterostructures composed of atomically thin ferroelectrics and semiconductors to achieve this goal. These calculated results indicate that the local built‐in electric field derived from the ferroelectric polarization can effectively modulate the band alignment of the heterostructures, leading to 36 potential band‐alignment transition pathways. Using SnS/In2Se3 vdW heterostructure as a prototype example, a reversible switching from high‐resistance to low‐resistance state is demonstrated by the band‐alignment transition from type‐II to type‐III driven by ferroelecric polarization switching, consequently leading to giant tunneling electroresistance (TER) ratio as high as 1012%. Moreover, the heterostructure with the momentum‐space matching band structure and in‐plane anisotropy exhibits broadband photoresponse from near‐infrared to ultraviolet regions and excellent polarization sensitivity with the dichroic ratio up to 10.3. The ferroelectric polarization‐dependent conductance state and photoresponse in the heterostructures make them large potential for the realization of all‐in‐one optoelectronic architecture in artificial vision system.

Highly-Polarized Solar-Blind Ultraviolet Organic Photodetectors.

Developing high-performance polarization-sensitive ultraviolet photodetectors is crucial for their application in military remote sensing, detection, bio-inspired navigation, and machine vision. However, the significant absorption in the visible light range severely limits the application of polarization-sensitive ultraviolet photodetectors, such as high-quality anti-interference imaging. Here, based on a wide-bandgap organic semiconductor single crystal (trans-1,2-bis(5-phenyldithieno[2,3-b:3',2'-d]thiophen-2-yl)ethene, BPTTE), high-performance polarization-sensitive solar-blind ultraviolet photodetectors with a dichroic ratio close to 4.26 are demonstrated. The strong anisotropy of 2D grown BPTTE single crystals in molecular vibration and optical absorption is characterized by various techniques. Under voltage modulation, stable and efficient detection of polarized light is demonstrated, attributed to the intrinsic anisotropy of transition dipole moment in the bc crystal plane, rather than other factors. Finally, high-contrast polarimetric imaging and anti-interference imaging are successfully demonstrated based on BPTTE single crystal photodetectors, highlighting the potential of organic semiconductors for polarization-sensitive solar-blind ultraviolet photodetectors.

P‐192: Advancements in Photoaligned Azo‐Dye Thin‐Film Polarizer with Exceptional Dichroic Ratio

This study presents the development of ultra‐thin azo‐dye polarizers, notable for their minimal thickness (100‐200 nm) and superior optical performance, with polarization efficiency exceeding 99.9%, extinction ratios above 4000, transmittance over 45.3%, and dichoric ratio over 100. Utilizing cost‐effective solution‐processing methods, we fabricate these high‐performance polarizers and determine optimal experimental conditions for peak efficacy. Our research includes comprehensive Scanning Electron Microscopy analyses to understand the microstructural properties of these azo‐dye thin film polarizers, contributing significantly to the field of advanced display technologies.

Molding Process Retaining Gold Nanoparticle Assembly Structures during Transfer to a Polycarbonate Surface.

The immobilization of gold nanoparticle (AuNP) linear surface assemblies on polycarbonate (PC) melt surface via molding is investigated. The order of the particle assemblies is preserved during the molding process. The assemblies on PC exhibit plasmonic coupling features and dichroic properties. The structure of the assemblies is quantified based on Scanning Electron Microscopy (SEM) and image analysis data using an orientational order parameter. The transfer process from mold to melt shows high structural fidelity. The order parameter of around 0.98 reflects the orientation of the lines and remains unaffected, independent of the injection direction of the melt relative to the particle lines. This is discussed in the frame of fountain flow during injection molding. The particles were permanently fixed and withstood the injection molding process, detachment of the substrate, and extraction in boiling ethanol. The plasmonic particles coupled strongly within the dense nanoparticle lines to produce anisotropic optical properties, as quantified by dichroic ratios of 0.28 and 0.52 using ultraviolet-visible-near-infrared (UV-Vis-NIR) spectroscopy. AuNP line assemblies on a polymer surface may be a basis for plasmonic devices like surface-enhanced Raman scattering (SERS) sensors or a precursor for nanowires. Their embedding via injection molding constitutes an important link between particle-self-assembly approaches for optically functional surfaces and polymer processing techniques.

Photodetectors Based on ZrS3/MoS2 Heterostructures.

High-performance photodetectors with the detection capability of linearly polarized light have broad applications in both military and civilian fields. Quasi-one-dimensional ZrS3 as an emerging anisotropic two-dimensional material has come under the spotlight owing to its intriguing properties. However, the performance of the ZrS3 photodetector is seriously restricted by its low responsivity. Herein, a novel high-performance photodetector based on the van der Waals ZrS3/MoS2 heterostructure is proposed. Attributed to the charge trapping-assisted photogating effect, interlayer carrier transitions, and fast spatial separation of the photogenerated electron-hole pairs, the device displays superior photoresponse characteristics ranging from the ultraviolet to the visible spectrum in terms of high responsivity up to 212 A/W, an extraordinary external quantum efficiency of 8.5 × 104%, and a prompt rise/decay time of 0.19/0.38 ms. In addition, owing to the profound birefringence and dichroism effects in ZrS3 together with strong light-matter interactions in the heterostructure, profound linear-polarization sensitivity is demonstrated with a dichroic ratio of about 2.8. Overall, this photodetector not only is integrated with the excellent properties of ZrS3 and monolayer MoS2 but also further enhances the advantages through interlayer couplings, which demonstrate the strong potential of the ZrS3-based devices for high-performance, ultrafast, and polarization-sensitive photodetection.

Molecularly Thin 2D Organic Single Crystals: A New Platform for High-Performance Polarization-Sensitive Phototransistors.

The inherent linear dichroism (LD), high absorption, and solution processability of organic semiconductors hold immense potential to revolutionize polarized light detection. However, the disordered molecular packing inherent to polycrystalline thin films obscures their intrinsic diattenuation, resulting in diminished polarization sensitivity. In this study, we develop filter-free organic polarization-sensitive phototransistors (PSPs) with both a high linear dichroic ratio (LDR) and exceptional photosensitivity utilizing molecularly thin dithieno[3,2-b:2',3'-d]thiophene derivatives (DTT-8) two-dimensional molecular crystals (2DMCs) as the active layer. The orderly molecular packing in 2DMCs amplifies the inherent LD, and their molecular-scale thickness enables complete channel depletion, significantly reducing the dark current. As a result, PSPs with an impressive LDR of 3.15 and a photosensitivity reaching 3.02 × 106 are obtained. These findings present a practical demonstration of using the polarization angle as an encryption key in optical communication, showcasing the potential of 2DMCs as a viable and promising category of semiconductors for filter-free, polarization-sensitive photodetectors.

Multifunctional Photodetector with Tunable Response Bandwidth and Polarization Sensitivity

AbstractMultifunctional organic photodetectors (MFOPDs) have garnered significant attention due to their remarkable potential for integrating diverse device functionalities. In contrast to previous MFOPDs that have primarily emphasized the integration of various response bands, a pioneering multifunctional photodetector is introduced based on the P3HT:PC61BM system capable of selectively responding to both wavelength and polarization. Under positive bias, the device operates in a wide‐band, polarization‐insensitive mode, achieving an external quantum efficiency (EQE) of up to 7.01 × 104%. The EQE dichroic ratio (DR) of the device remains <1.01 (at 650 nm). Conversely, under negative bias, the device transitions into a narrow‐band, polarization‐sensitive mode, achieving an EQE of up to 4.82 × 104% with a narrow full width at half maximum (FWHM) of only 25 nm at 650 nm. The EQE DR exceeds 10 in this mode, marking it as one of the highest values within the field of polarization‐sensitive organic photodetectors. This versatile operation is made possible through the strategic use of double‐sided barriers, an oriented light harvesting layer, and a charge injection narrowing (CIN) approach. This work represents a significant advancement toward the realization of multifunctional photodetectors capable of selecting response bands and polarization sensitivity.

Exceptional Alignment in a Donor–Acceptor Conjugated Polymer via a Previously Unobserved Liquid Crystal Mesophase

AbstractOrienting polymer semiconductors is desirable to optimize device characteristics, provide insight into microstructure, and magnify subtle phase behavior. Here, a combination of uniaxial strain and subsequent heating of the donor–acceptor (DA) polymer PBnDT‐FTAZ is discovered to lead to exceptional optical dichroic ratios of up to 38 (and close to 50 near the polymer's absorption edge). This alignment is achieved due to the existence of a previously undetected thermotropic liquid crystal (LC) mesophase. The LC transition, not discernable through calorimetry, is uncovered through a combination of in situ UV–vis spectroscopy, X‐ray scattering, and dynamic mechanical analysis (DMA). Comparing PBnDT‐FTAZ to the non‐fluorinated PBnDT‐HTAZ and the homo polymer PBnDT, all of which show similar thermal transitions, reveals that exceptional alignment is only found in PBnDT‐FTAZ. This is attributed to the PBnDT‐FTAZ film having two distinct liquid crystal populations, and the polymer templating to a highly aligned, high‐clearing temperature population when heated. The DMA thermal relaxation behavior observed here is also seen in other DA conjugated polymers suggesting that such thermotropic LC mesophases may be common in these materials. These findings demonstrate a polymer semiconductor with remarkable alignment and uncover phase behavior with broad implications for process‐structure‐property relationships in polymer semiconductors.

Polarization‐Sensitive Photodetector Based on Quasi‐1D (TaSe4)2I Nanowire Response to 10.6 µm

AbstractPolarization‐sensitive infrared (IR) photodetection plays an important role in fiber optic communication, environmental monitoring, and remote sensing imaging. Semiconductors with quasi‐1D crystal structures exhibit unique optical and electrical properties due to their 1D carrier transport channels and large surface area‐to‐volume ratio, offering the possibility of high‐performance photodetectors with high photogain (G), polarization sensitivity photodetection. Herein, an ultra‐broadband photodetection (405 nm–10.6 µm) based on a quasi‐1D (TaSe4)2I single‐crystal nanowire is reported. The (TaSe4)2I photodetector exhibits excellent polarization‐sensitive photodetection, with a high dichroic ratio of Imax/Imin = 2.32 under 637 nm illumination. Notably, the (TaSe4)2I nanowire photodetector exhibits a competitive performance in uncooled mid‐wave infrared (MWIR) detection with a high photoresponsivity (R) of 110.5 AW−1 and specific detectivity (D*) of 4.8 × 1010 cmHz1/2W−1. Moreover, in the long‐wave infrared (LWIR) spectral range, an R of 67.6 mAW−1 is demonstrated at room temperature (RT). The (TaSe4)2I nanowire photodetector enables significant advancements for polarization‐sensitive and uncooled MWIR and LWIR photodetection.

Optical Anisotropy of Polyethylene Terephthalate Films Characterized by Spectral Means.

Polyethylene terephthalate (PET) films are the subject of intensive research because of great interest in using them in applications, especially in medicine. From an optical point of view, PET films with a low degree of stretching can be considered uniaxial materials, for which the determination of the linear birefringence and its dispersion is very important. Two methods were applied here for the estimation of these parameters: the ellipsometric method and the channeled spectra method. The ellipsometric method uses monochromatic radiation; therefore, the linear birefringence of the PET films is determined for a given value of the radiation wavelength. The channeled spectra method allows for the estimation of the linear birefringence and its dispersion for a large range of wavelengths in the visible spectrum. A decrease in both parameters with the increase in the wavelength was recorded. To evidence the microstructure of PET films and the conformational changes induced by elongation and to evaluate the degree of orientation, a polarized infrared spectral study in attenuated total reflection (ATR-FTIR) mode was performed. The dichroic ratio (between the absorbance measured with linearly polarized radiation parallel and orthogonal relative to the stretching direction, respectively) and the ATR absorbance ratio for the machine direction (MD) and transversal direction (TD) configurations both for the stretched and unstretched PET samples were measured.