Highly polarized photoluminescence and photodetection from single indium phosphide nanowires

Alternate InP synthesis with aminophosphines: solution-liquid-solid nanowire growth

Indium phosphide nanowires are important components in high-speed electronics and optoelectronics, including photodetectors and photovoltaics. However, most syntheses either use high-temperature and costly vapor-phase methodology or highly toxic and pyrophoric tris(trimethylsilyl)phosphine. To expand on the success of the aminophosphine-based InP colloidal quantum dot synthesis, we developed a synthesis for thin (∼11 nm) zinc blende InP nanowires at 180 °C using indium tris(trifluoroacetate) and tris(diethylamino)phosphine. A flat nanoribbon morphology was identified by transmission electron and atomic force microscopy analysis, with the stoichiometric (110) lattice plane exposed. Nanowire growth proceeded through a solution-liquid-solid mechanism from in situ-formed indium metal nanoparticles. Molecular byproducts of tris(oleylamino)phosphine oxide and N-oleyltrifluoroacetamide observed by 31P and 19F NMR spectroscopy inform a proposed mechanism of indium reduction by the aminophosphine. Morphological control over the nanowire product was achieved by varying the phosphorus injection to control the aspect ratio, the In : P ratio to toggle between nanowires and multipods, and the pre-hot injection evacuation step to favor a quantum dot product. Replacing the indium precursor with indium tris(trifluoromethanesulfonate) was found to make bulk zinc blende InP nanowires with an average diameter of >250 nm and tens of microns in length.

Direct on-Chip Optical Communication between Nano Optoelectronic Devices

On-chip optical communication between individual nano optoelectronic components is important to reduce the footprint and improve energy efficiency of photonic neuromorphic solutions. Although nanoscale photon emitters and receivers have been reported separately, communication between them remains largely unexplored. We demonstrate direct on-chip directional broadcasting of light between individual InP nanowire photodiodes on silicon. The performance of multiple wire-to-wire communication circuits is mapped, demonstrating robust performance with up to 5 bit resolution as needed in biological networks and a minimum component driving power for continuous operation of 0.5 μW which is below that of conventional hardware. The results agree well with theoretical modeling that allows us to understand network performance limits and identify where significant improvements could be achieved. We estimate that an energy per operation of ∼1 fJ and signal fan-out from one emitter to hundreds of other nodes is possible. We find that the nanowire circuit performance parameters can satisfy the quantitative requirements to run the tasks of neural nodes in a bioderived neural network for autonomous navigation.

Development and challenges of polarization-sensitive photodetectors based on 2D materials

Polarization-sensitive photodetectors based on two-dimensional (2D) materials have garnered significant research attention owing to their distinctive architectures and exceptional photophysical properties. Specifically, anisotropic 2D materials, including semiconductors such as black phosphorus (BP), tellurium (Te), transition metal dichalcogenides (TMDs), and tantalum nickel pentaselenide (Ta2NiSe5), as well as semimetals like 1T'-MoTe2 and PdSe2, and their diverse van der Waals (vdW) heterojunctions, exhibit broad detection spectral ranges and possess inherent functional advantages. To date, numerous polarization-sensitive photodetectors based on 2D materials have been documented. This review initially provides a concise overview of the detection mechanisms and performance metrics of 2D polarization-sensitive photodetectors, which are pivotal for assessing their photodetection capabilities. It then examines the latest advancements in polarization-sensitive photodetectors based on individual 2D materials, 2D vdW heterojunctions, nanoantenna/electrode engineering, and structural strain integrated with 2D structures, encompassing a range of devices from the ultraviolet to infrared bands. However, several challenges persist in developing more comprehensive and functional 2D polarization-sensitive photodetectors. Further research in this area is essential. Ultimately, this review offers insights into the current limitations and challenges in the field and presents general recommendations to propel advancements and guide the progress of 2D polarization-sensitive photodetectors.

Liquid Crystalline Nanorods by Synchronized Polymerization, Self-Assembly and Oriented Attachment for Utilization in Magnetically Responsive Displays

The creation of anisotropic nanoparticles (NPs) by polymerization and/or self-assembly (SA) has significantly promoted the applications of polymer nanomaterials in many fields. However, polymer nanorods are not easily accessible via conventional polymerization or SA. Here we report a one-step route to synthesize single-domain smectic liquid crystalline (LC) nanorods utilizing oriented attachment (OA) that was usually found in the synthesis of inorganic NPs, synchronized with polymerization and SA. The synchronization was achieved by developing a novel stabilizer derived from a thermo-responsive polyelectrolyte system. Mechanistic studies reveal that controlling the thermo-responsive behavior and the distribution of stabilizers on NPs enabled OA. The LC nanorods can further form hierarchical colloidal LCs, which show much larger light transmittance than that of non-LC nanorods. Moreover, we demonstrate that this LC system can be manipulated by an external magnetic field, thus providing a candidate material for magnetic-responsive display.

Transforming achiral semiconductors into chiral domains with exceptional circular dichroism

Highly concentrated solutions of asymmetric semiconductor magic-sized clusters (MSCs) of cadmium sulfide, cadmium selenide, and cadmium telluride were directed through a controlled drying meniscus front, resulting in the formation of chiral MSC assemblies. This process aligned their transition dipole moments and produced chiroptic films with exceptionally strong circular dichroism. G-factors reached magnitudes as high as 1.30 for drop-cast films and 1.06 for patterned films, approaching theoretical limits. By controlling the evaporation geometry, various domain shapes and sizes were achieved, with homochiral domains exceeding 6 square millimeters that transition smoothly between left- and right-handed chirality. Our results uncovered fundamental relationships between meniscus deposition processes, the alignment of supramolecular filaments and their MSC constituents, and their connection to emergent chiral properties.

Magnetoplasmonic Triblock Nanorods for Collective Linear Dichroism

Polarized light detection is crucial for advancements in optical imaging, positioning, and obstacle avoidance systems. While optical nanomaterials sensitive to polarization are well-established, the ability to align these materials remains a significant challenge. Here, we introduce Au-Fe3O4-Au triblock nanorods as a novel solution. Synthesized via a space-confined seeded growth method, these magnetoplasmonic nanocomposites uniquely combine the strong polarization capabilities of Au nanorods with the magnetic alignment properties of Fe3O4 nanorods. This architecture results in exceptional collective linear dichroism, achieving a polarization ratio of approximately 14 at the device level. Our nanorods exhibit high detection sensitivity and laser damage resistance, positioning them as a promising platform for developing advanced optical devices.

Spatiotemporally modulated full-polarized light emission for multiplexed optical encryption

Spatiotemporal control of full freedoms of polarized light emission is crucial in multiplexed optical computing, encryption and communication. Although recent advancements have been made in active emission or passive conversion of polarized light through solution-processed nanomaterials or metasurfaces, these design paths usually encounter limitations, such as small polarization degrees, low light utilization efficiency, limited polarization states, and lack of spatiotemporal control. Here, we addressed these challenges by integrating the spatiotemporal modulation of the LED device, the precise control and efficient polarization emission through nanomaterial assembly, and the programmable patterning/positioning using 3D printing. We achieved an extremely high degree of polarization for both linearly and circularly polarized emission from ultrathin inorganic nanowires and quantum nanorods thanks to the shear-force-induced alignment effect during the protruding of printing filaments. Real-time polarization modulation covering the entire Poincaré sphere can be conveniently obtained through the programming of the on-off state of each LED pixel. Further, the output polarization states can be encoded by an ordered chiral plasmonic film. Our device provides an excellent platform for multiplexing spatiotemporal polarization information, enabling visible light communication with an exceptionally elevated level of physical layer security and multifunctional encrypted displays that can encode both 2D and 3D information.

Molecular templating of layered halide perovskite nanowires

Layered metal-halide perovskites, or two-dimensional perovskites, can be synthesized in solution, and their optical and electronic properties can be tuned by changing their composition. We report a molecular templating method that restricted crystal growth along all crystallographic directions except for [110] and promoted one-dimensional growth. Our approach is widely applicable to synthesize a range of high-quality layered perovskite nanowires with large aspect ratios and tunable organic-inorganic chemical compositions. These nanowires form exceptionally well-defined and flexible cavities that exhibited a wide range of unusual optical properties beyond those of conventional perovskite nanowires. We observed anisotropic emission polarization, low-loss waveguiding (below 3 decibels per millimeter), and efficient low-threshold light amplification (below 20 microjoules per square centimeter).

Highly Sensitive Broadband Polarized Photodetector Based on the As0.6P0.4/WSe2 Heterostructure toward Imaging and Optical Communication Application

Polarization-sensitive photodetectors based on two-dimensional anisotropic materials still encounter the issues of narrow spectral coverage and low polarization sensitivity. To address these obstacles, anisotropic As0.6P0.4 with a narrow band gap has been integrated with WSe2 to construct a type-II heterostructure, realizing a high-performance polarization-sensitive photodetector with broad spectral range from 405 to 2200 nm. By operating in photovoltaic mode at zero bias, the device shows a very low dark current of ∼0.02 picoampere, high responsivity of 492 m A/W, and high photoswitching ratio of 6 × 104, yielding a high specific detectivity of 1.4 × 1012 Jones. The strong in-plane anisotropy of As0.6P0.4 endows the device with a capability of polarization-sensitive detection with a high polarization ratio of 6.85 under a bias voltage. As an image sensor and signal receiver, the device shows great potential in imaging and optical communication applications. This work develops an anisotropic vdW heterojunction to realize polarization-sensitive photodetectors with wide spectral coverage, fast response, and high sensitivity, providing a new candidate for potential applications of polarization-resolved electronics and photonics.

Low-Dimensional-Materials-Based Photodetectors for Next-Generation Polarized Detection and Imaging

The vector characteristics of light and the vectorial transformations during its transmission lay a foundation for polarized photodetection of objects, which broadens the applications of related detectors in complex environments. With the breakthrough of low-dimensional materials (LDMs) in optics and electronics over the past few years, the combination of these novel LDMs and traditional working modes is expected to bring new development opportunities in this field. Here, the state-of-the-art progress of LDMs, as polarization-sensitive components in polarized photodetection and even the imaging, is the main focus, with emphasis on the relationship between traditional working principle of polarized photodetectors (PPs) and photoresponse mechanisms of LDMs. Particularly, from the view of constitutive equations, the existing works are reorganized, reclassified, and reviewed. Perspectives on the opportunities and challenges are also discussed. It is hoped that this work can provide a more general overview in the use of LDMs in this field, sorting out the way of related devices for "more than Moore" or even the "beyond Moore" research.

Polarization-Resolved Position-Sensitive Self-Powered Binary Photodetection in Multilayer Janus CrSBr

Recent progress in polarization-resolved photodetection based on low-symmetry 2D materials has formed the basis of cutting-edge optoelectronic devices, including quantum optical communication, 3D image processing, and sensing applications. Here, we report an optical polarization-resolving photodetector (PD) fabricated from multilayer semiconducting CrSBr single crystals with high structural anisotropy. We have demonstrated self-powered photodetection due to the formation of Schottky junctions at the Au-CrSBr interfaces, which also caused the photocurrent to display a position-sensitive and binary nature. The self-biased CrSBr PD showed a photoresponsivity of ∼0.26 mA/W with a detectivity of 3.4 × 108 Jones at 514 nm excitation of fluency (0.42 mW/cm2) under ambient conditions. The optical polarization-induced photoresponse exhibits a large dichroic ratio of 3.4, while the polarization is set along the a- and the b-axes of single-crystalline CrSBr. The PD also showed excellent stability, retaining >95% of the initial photoresponsivity in ambient conditions for more than five months without encapsulation. Thus, we demonstrate CrSBr as a fascinating material for ultralow-powered optical polarization-resolving optoelectronic devices for cutting-edge technology.

Mid-Infrared Bipolar and Unipolar Linear Polarization Detections in Nb2 GeTe4 /MoS2 Heterostructures

Detecting and distinguishing light polarization states, one of the most basic elements of optical fields, have significant importance in both scientific studies and industry applications. Artificially fabricated structures, e.g., metasurfaces with anisotropic absorptions, have shown the capabilities of detecting polarization light and controlling. However, their operations mainly rely on resonant absorptions based on structural designs that are usually narrow bands. Here, a mid-infrared (MIR) broadband polarization photodetector with high PRs and wavelength-dependent polarities using a 2D anisotropic/isotropic Nb2 GeTe4 /MoS2 van der Waals (vdWs) heterostructure is demonstrated. It is shown that the photodetector exhibits high PRs of 48 and 34 at 4.6  and 11.0 µm wavelengths, respectively, and even a negative PR of -3.38 for 3.7 µm under the zero bias condition at room temperature. Such interesting results can be attributed to the superimposed effects of a photovoltaic (PV) mechanism in the Nb2 GeTe4 /MoS2 hetero-junction region and a bolometric mechanism in the MoS2 layer. Furthermore, the photodetector demonstrates its effectiveness in bipolar and unipolar polarization encoding communications and polarization imaging enabled by its unique and high PRs.

One-step rolling fabrication of VO2 tubular bolometers with polarization-sensitive and omnidirectional detection

Uncooled infrared detection based on vanadium dioxide (VO2) radiometer is highly demanded in temperature monitoring and security protection. The key to its breakthrough is to fabricate bolometer arrays with great absorbance and excellent thermal insulation using a straightforward procedure. Here, we show a tubular bolometer by one-step rolling VO2 nanomembranes with enhanced infrared detection. The tubular geometry enhances the thermal insulation, light absorption, and temperature sensitivity of freestanding VO2 nanomembranes. This tubular VO2 bolometer exhibits a detectivity of ~2 × 108 cm Hz1/2 W-1 in the ultrabroad infrared spectrum, a response time of ~2.0 ms, and a calculated noise-equivalent temperature difference of 64.5 mK. Furthermore, our device presents a workable structural paradigm for polarization-sensitive and omnidirectional light coupling bolometers. The demonstrated overall characteristics suggest that tubular bolometers have the potential to narrow performance and cost gap between photon detectors and thermal detectors with low cost and broad applications.

Responsive Regulation of Energy Transfer in Lanthanide-Doped Nanomaterials Dispersed in Chiral Nematic Structure

The responsive control of energy transfer (ET) plays a key role in the broad applications of lanthanide-doped nanomaterials. Photonic crystals (PCs) are excellent materials for ET regulation. Among the numerous materials that can be used to fabricate PCs, chiral nematic liquid crystals are highly attractive due to their good photoelectric responsiveness and biocompatibility. Here, the mechanisms of ET and the photonic effect of chiral nematic structures on ET are introduced; the regulation methods of chiral nematic structures and the resulting changes in ET of lanthanide-doped nanomaterials are highlighted; and the challenges and promising opportunities for ET in chiral nematic structures are discussed.

Giant Polarization Sensitivity via the Anomalous Photovoltaic Effect in a Two-Dimensional Perovskite Ferroelectric

Polarization sensitivity, which shows great potential in photoelectric detection, is expected to be significantly improved by the ferroelectric anomalous photovoltaic (APV) effect. However, it is challenging to explore new APV-active ferroelectrics due to severe polarization fatigue induced by the leakage current of photoexcited carriers. For the first time, we report a strong APV effect in a 2D hybrid perovskite ferroelectric assembled by alloying mixed organic cations, (HA)₂(EA)₂Pb₃Br₁₀ (1, where HA⁺ is n-hexylammonium and EA⁺ is ethylammonium), which has a large spontaneous polarization ∼3.8 μC/cm² and high a Curie temperature ∼378 K. Its ferroelectricity allows a strong APV effect with an above-bandgap photovoltage up to 7.4 V, which exceeds its bandgap (∼2.7 eV). Most strikingly, based on the dependence on polarized-light angle, this strong APV effect renders the highest level of polarization sensitivity with a giant current ratio of ∼25, far beyond other 2D single-phase materials. This study sheds light on the exploration of APV-active ferroelectrics and inspires their future high-performance optoelectronic device applications.

Short-wave infrared cavity resonances in a single GeSn nanowire

Nanowires are promising platforms for realizing ultra-compact light sources for photonic integrated circuits. In contrast to impressive progress on light confinement and stimulated emission in III-V and II-VI semiconductor nanowires, there has been no experimental demonstration showing the potential to achieve strong cavity effects in a bottom-up grown single group-IV nanowire, which is a prerequisite for realizing silicon-compatible infrared nanolasers. Herein, we address this limitation and present an experimental observation of cavity-enhanced strong photoluminescence from a single Ge/GeSn core/shell nanowire. A sufficiently large Sn content ( ~ 10 at%) in the GeSn shell leads to a direct bandgap gain medium, allowing a strong reduction in material loss upon optical pumping. Efficient optical confinement in a single nanowire enables many round trips of emitted photons between two facets of a nanowire, achieving a narrow width of 3.3 nm. Our demonstration opens new possibilities for ultrasmall on-chip light sources towards realizing photonic-integrated circuits in the underexplored range of short-wave infrared (SWIR).

Resolving the Emission Transition Dipole Moments of Single Doubly Excited Seeded Nanorods via Heralded Defocused Imaging

Semiconductor nanocrystal emission polarization is a crucial probe of nanocrystal physics and an essential factor for nanocrystal-based technologies. While the transition dipole moment for the lowest excited state to ground state transition is well characterized, the dipole moment of higher multiexcitonic transitions is inaccessible via most spectroscopy techniques. Here, we realize direct characterization of the doubly excited-state relaxation transition dipole by heralded defocused imaging. Defocused imaging maps the dipole emission pattern onto a fast single-photon avalanche diode detector array, allowing the postselection of photon pairs emitted from the biexciton-exciton emission cascade and resolving the differences in transition dipole moments. Type-I¹/₂ seeded nanorods exhibit higher anisotropy of the biexciton-to-exciton transition compared to the exciton-to-ground state transition. In contrast, type-II seeded nanorods display a reduction of biexciton emission anisotropy. These findings are rationalized in terms of an interplay between the transient dynamics of the refractive index and the excitonic fine structure.

Optical anisotropy of CsPbBr3 perovskite nanoplatelets

The two-dimensional CsPbBr3 nanoplatelets have a quantum well electronic structure with a band gap tunable with sample thicknesses in discreet steps based upon the number of monolayers. The polarized optical properties of CsPbBr3 nanoplatelets are studied using fluorescence anisotropy and polarized transient absorption spectroscopies. Polarized spectroscopy shows that they have absorption and emission transitions which are strongly plane-polarized. In particular, photoluminescence excitation and transient absorption measurements reveal a band-edge polarization approaching 0.1, the limit of isotropic two-dimensional ensembles. The degree of anisotropy is found to depend on the thickness of the nanoplatelets: multiple measurements show a progressive decrease in optical anisotropy from 2 to 5 monolayer thick nanoplatelets. In turn, larger cuboidal CsPbBr3 nanocrystals, are found to have consistently positive anisotropy which may be attributed to symmetry breaking from ideal perovskite cubes. Optical measurements of anisotropy are described with respect to the theoretical framework developed to describe exciton fine structure in these materials. The observed planar absorption and emission are close to predicted values at thinner nanoplatelet sizes and follow the predicted trend in anisotropy with thickness, but with larger anisotropy than theoretical predictions. Dominant planar emission, albeit confined to the thinnest nanoplatelets, is a valuable attribute for enhanced efficiency of light-emitting devices.

Controllable Fabrication of Zn2+ Self-Doped TiO2 Tubular Nanocomposite for Highly Efficient Water Treatment

Tailoring high-efficiency photocatalytic composites for various implementations is a major research topic. 1D TNTs-based nanomaterials show promise as a photocatalyst for the remediation of organic pigments in an aqueous solution. Despite this, TiO2 (TNTs) is only photoactive in the UV range due to its inherent restriction on absorption of light in the UV range. Herein, we provide a facile recipe to tailor the optical characteristics and photocatalytic activity of TNTs by incorporating Zn (II) ionic species via an ion-exchange approach in an aqueous solution. The inclusion of Zn (II) ions into the TNTs framework expands its absorption of light toward the visible light range, therefore TiO2 nanotubes shows the visible-light photo-performance. Activity performance on photocatalytic decontamination of RhB at ambient temperature demonstrates that Zn-TNTs offer considerable boosted catalytic performance compared with untreated tubular TiO2 during the illumination of visible light. RhB (10 mg L−1) degradation of around 95% was achieved at 120 min. Radical scavenger experiment demonstrated that when electron (e−) or holes (h+) scavengers are introduced to the photodegradation process, the assessment of decontamination efficacy decreased by 45% and 76%, respectively. This demonstrates a more efficient engagement of the photoexcited electrons over photogenerated holes in the photodegradation mechanism. Furthermore, there seems to be no significant decrease in the activity of the Zn-TNTs after five consecutive runs. As a result, the fabricated Zn-TNTs composite has a high economic potential in the energy and environmental domains.

Analytical and Numerical Investigation of Nanowire Transistor X-ray Detector

Recently, nanowire detectors have been attracting increasing interest thanks to their advantages of high resolution and gain. The potential of using nanowire detectors is investigated in this work by developing a physically based model for Indium Phosphide (InP) phototransistor as well as by performing TCAD simulations. The model is based on solving the basic semiconductor equations for bipolar transistors and considering the effects of charge distribution on the bulk and on the surface. The developed model also takes into consideration the impact of surface traps, which are induced by photogenerated carriers situated at the surface of the nanowire. Further, photogating phenomena and photodoping are also included. Moreover, displacement damage (DD) is also investigated; an issue arises when the detector is exposed to repeated doses. The presented analytical model can predict the current produced from the incident X-ray beam at various energies. The calculation of the gain of the presented nanowire carefully considers the different governing effects at several values of energies as well as biasing voltage and doping. The proposed model is built in MATLAB, and the validity check of the model results is achieved using SILVACO TCAD device simulation. Comparisons between the proposed model results and SILVACO TCAD device simulation are provided and show good agreement.

Anisotropic Heavy-Metal-Free Semiconductor Nanocrystals: Synthesis, Properties, and Applications

Heavy-metal (Cd, Hg, and Pb)-containing semiconductor nanocrystals (NCs) have been explored widely due to their unique optical and electrical properties. However, the toxicity risks of heavy metals can be a drawback of heavy-metal-containing NCs in some applications. Anisotropic heavy-metal-free semiconductor NCs are desirable replacements and can be realized following the establishment of anisotropic growth mechanisms. These anisotropic heavy-metal-free semiconductor NCs can possess lower toxicity risks, while still exhibiting unique optical and electrical properties originating from both the morphological and compositional anisotropy. As a result, they are promising light-emitting materials in use various applications. In this review, we provide an overview on the syntheses, properties, and applications of anisotropic heavy-metal-free semiconductor NCs. In the first section, we discuss hazards of heavy metals and introduce the typical heavy-metal-containing and heavy-metal-free NCs. In the next section, we discuss anisotropic growth mechanisms, including solution-liquid-solid (SLS), oriented attachment, ripening, templated-assisted growth, and others. We discuss mechanisms leading both to morphological anisotropy and to compositional anisotropy. Examples of morphological anisotropy include growth of nanorods (NRs)/nanowires (NWs), nanotubes, nanoplatelets (NPLs)/nanosheets, nanocubes, and branched structures. Examples of compositional anisotropy, including heterostructures and core/shell structures, are summarized. Third, we provide insights into the properties of anisotropic heavy-metal-free NCs including optical polarization, fast electron transfer, localized surface plasmon resonances (LSPR), and so on, which originate from the NCs' anisotropic morphologies and compositions. Finally, we summarize some applications of anisotropic heavy-metal-free NCs including catalysis, solar cells, photodetectors, lighting-emitting diodes (LEDs), and biological applications. Despite the huge progress on the syntheses and applications of anisotropic heavy-metal-free NCs, some issues still exist in the novel anisotropic heavy-metal-free NCs and the corresponding energy conversion applications. Therefore, we also discuss the challenges of this field and provide possible solutions to tackle these challenges in the future.

Ultrafast One-Step Deposition Route to Fabricate Single-Crystal CsPbX3 (X = Cl, Cl/Br, Br, and Br/I) Photodetectors

Inorganic perovskites have received much attention due to their stability and high performance in luminescence, photoelectric conversion, and photodetection. However, perovskite optoelectronic devices prepared by the solution technique are still suffering from time-consuming and complex operations. In this paper, a single-crystal perovskite-based photodetector (PD) is prepared by very fast one-step deposition of synthesizing microplatelets (MPs) on the electrode directly. The saturated precursor is carefully optimized by adding appropriate antisolvent chlorobenzene (CB) to fabricate the MPs with their PL wavelength ranging from 418 to 600 nm. Furthermore, the PDs with a low dark current on order of nanoangstroms, high responsivity and detectivity of up to 10.7 A W^-1 and 10¹² Jones, respectively, and an ultrafast response rate featured by 278/287 μs (rise/decay time) are achieved. These all-inorganic perovskite PDs with a simple fabricating process and tunable detection wavelength meet the evolution tendency of PDs toward low cost and high performance, which is a high-profile strategy to realize high-performance perovskite PDs.

Non-〈111〉-oriented semiconductor nanowires: growth, properties, and applications

In recent years, non-〈111〉-oriented semiconductor nanowires have attracted increasing interest in terms of fundamental research and promising applications due to their outstanding crystal quality and distinctive physical properties. Here, a comprehensive overview of recent advances in the study of non-〈111〉-oriented semiconductor nanowires is presented. We start by introducing various growth techniques for obtaining nanowires with certain orientations, for which the growth energetics and kinetics are discussed. Attention is then given to the physical properties of non-〈111〉 nanowires, as predicted by theoretical calculations or demonstrated experimentally. After that, we review the advantages and challenges of non-〈111〉 nanowires as building blocks for electronic and optoelectronic devices. Finally, we discuss the possible challenges and opportunities in the research field of non-〈111〉 semiconductor nanowires.

High Performance Polarization-Resolved Photodetectors Based on Intrinsically Stretchable Organic Semiconductors

Polarization-sensitive photodetectors based on anisotropic semiconductors sense both the intensity and polarization state information without extra optical components. Here, a self-powered organic photodetector (OPD) composed of intrinsically stretchable polymer donor PNTB6-Cl and non-fullerene acceptor Y6 is reported. The PNTB6-Cl:Y6 photoactive film accommodates a remarkable 100% strain without fracture, exhibiting a high optical anisotropy of 1.8 after strain alignment. The resulting OPD not only shows an impressive faint-light detection capability (high spectral responsivity of 0.45 A W-1 and high specific detectivity of 1012 Jones), but also has a high anisotropic responsivity ratio of 1.42 under the illumination of parallel and traversed polarized light. To the best of the authors' knowledge, both the detector performance and polarization features are among the best-performing OPDs and polarization-sensitive photodetectors. As a proof-of-concept, polarization-sensitive OPDs are also utilized to set up a polarimetric imaging system and full-Stokes polarimeter. This work explores the potential of highly stretchable organic semiconductors for state-of-art polarization imaging and spectroscopy applications.

Advanced functional nanofibers: strategies to improve performance and expand functions

Nanofibers have a wide range of applications in many fields such as energy generation and storage, environmental sensing and treatment, biomedical and health, thanks to their large specific surface area, excellent flexibility, and superior mechanical properties. With the expansion of application fields and the upgrade of application requirements, there is an inevitable trend of improving the performance and functions of nanofibers. Over the past few decades, numerous studies have demonstrated how nanofibers can be adapted to more complex needs through modifications of their structures, materials, and assembly. Thus, it is necessary to systematically review the field of nanofibers in which new ideas and technologies are emerging. Here we summarize the recent advanced strategies to improve the performances and expand the functions of nanofibers. We first introduce the common methods of preparing nanofibers, then summarize the advances in the field of nanofibers, especially up-to-date strategies for further enhancing their functionalities. We classify these strategies into three categories: design of nanofiber structures, tuning of nanofiber materials, and improvement of nanofibers assemblies. Finally, the optimization methods, materials, application areas, and fabrication methods are summarized, and existing challenges and future research directions are discussed. We hope this review can provide useful guidance for subsequent related work.

Graphical abstract

Effects of Thermal Annealing on Optical and Microscopic Ferromagnetic Properties in InZnP:Ag Nano-Rods

InZnP:Ag nano-rods fabricated by the ion milling method were thermally annealed in the 250~350 °C temperature range and investigated the optimum thermal annealing conditions to further understand the mutual correlation between the optical properties and the microscopic magnetic properties. The formation of InZnP:Ag nano-rods was determined from transmission electron microscopy (TEM), total reflectivity and Raman scattering analyses. The downward shifts of peak position for LO and TO modes in the Raman spectrum are indicative of the production of Ag ion-induced strain during the annealing process of the InZnP:Ag nano-rod samples. The appearance of two emission peaks of both (A0 X) and (e, Ag) in the PL spectrum indicated that acceptor states by Ag diffusion are visible due to the effective incorporation of Ag-creating acceptor states. The binding energy between the acceptor and the exciton measured as a function of temperature was found to be 21.2 meV for the sample annealed at 300 °C. The noticeable MFM image contrast and the clear change in the MFM phase with the scanning distance indicate the formation of the ferromagnetic spin coupling interaction on the surface of InZnP:Ag nano-rods by Ag diffusion. This study suggests that the InZnP:Ag nano-rods should be a potential candidate for the application of spintronic devices.

Transition metal dichalcogenide magnetic atomic chains

Reducing the dimensions of a material to the atomic scale endows them with novel properties that are significantly different from their bulk counterparts. A family of stoichiometric transition metal dichalcogenide (TMD) MX₂ (M = Ti to Mn, and X = S to Te) atomic chains is proposed. The results reveal that the MX₂ atomic chains, the smallest possible nanostructure of a TMD, are lattice-dynamically stable, as confirmed from their phonon spectra and ab initio molecular dynamics simulations. In contrast to their bulk and two-dimensional (2D) counterparts, the TiX₂ atomic chains are nonmagnetic semiconductors, while the VX₂, CrX₂, and MnX₂ chains are unipolar magnetic, bipolar magnetic, and antiferromagnetic semiconductors, respectively. In addition, the VX₂, CrX₂, and MnX₂ chains can be converted via carrier doping from magnetic semiconductors to half metals with reversible spin-polarization orientation at the Fermi level. Of these chains, the MnX₂ chains exhibit either ferromagnetic or antiferromagnetic half metallicity depending on the injected carrier type and concentration. The diverse and tunable electronic and magnetic properties in the MX₂ chains originate, based on crystal field theory, from the occupation of the metal d orbitals and the exchange interaction between the tetrahedrally coordinated metal atoms in the atomic chain. The calculated interaction between the carbon nanotubes and the MX₂ chains implies that armchair (7,7) or armchair (8,8) carbon nanotubes are appropriate sheaths for growing MX₂ atomic single-chains in a confined channel. This study reveals the diverse magnetic properties of MX₂ atomic single-chains and provides a promising building block for nanoscale electronic and spintronic devices.

Anisotropic charge trapping in phototransistors unlocks ultrasensitive polarimetry for bionic navigation

Being able to probe the polarization states of light is crucial for applications from medical diagnostics and intelligent recognition to information encryption and bio-inspired navigation. Current state-of-the-art polarimeters based on anisotropic semiconductors enable direct linear dichroism photodetection without the need for bulky and complex external optics. However, their polarization sensitivity is restricted by the inherent optical anisotropy, leading to low dichroic ratios of typically smaller than ten. Here, we unveil an effective and general strategy to achieve more than 2,000-fold enhanced polarization sensitivity by exploiting an anisotropic charge trapping effect in organic phototransistors. The polarization-dependent trapping of photogenerated charge carriers provides an anisotropic photo-induced gate bias for current amplification, which has resulted in a record-high dichroic ratio of >10⁴, reaching over the extinction ratios of commercial polarizers. These findings further enable the demonstration of an on-chip polarizer-free bionic celestial compass for skylight-based polarization navigation. Our results offer a fundamental design principle and an effective route for the development of next-generation highly polarization-sensitive optoelectronics.

Integrated photodetectors for compact Fourier-transform waveguide spectrometers

Extreme miniaturization of infrared spectrometers is critical for their integration into next-generation consumer electronics, wearables and ultrasmall satellites. In the infrared, there is a necessary compromise between high spectral bandwidth and high spectral resolution when miniaturizing dispersive elements, narrow band-pass filters and reconstructive spectrometers. Fourier-transform spectrometers are known for their large bandwidth and high spectral resolution in the infrared; however, they have not been fully miniaturized. Waveguide-based Fourier-transform spectrometers offer a low device footprint, but rely on an external imaging sensor such as bulky and expensive InGaAs cameras. Here we demonstrate a proof-of-concept miniaturized Fourier-transform waveguide spectrometer that incorporates a subwavelength and complementary-metal-oxide-semiconductor-compatible colloidal quantum dot photodetector as a light sensor. The resulting spectrometer exhibits a large spectral bandwidth and moderate spectral resolution of 50 cm^-1 at a total active spectrometer volume below 100 μm × 100 μm × 100 μm. This ultracompact spectrometer design allows the integration of optical/analytical measurement instruments into consumer electronics and space devices.

Controllable Inverse Photoconductance in Semiconducting Nanowire Films

As a typical p-type semiconductor, tellurium (Te) has been widely studied for the construction of photodetectors. However, only the positive photoconductance of Te-based photodetectors based on the photoconductive effect has been observed in the reported literature. Herein, an unusual but interesting phenomenon, in that tellurium nanowires (NWs) behave with negative photoresponse to positive photoresponse under enlarged optical intensities from the UV to VIS-IR region is reported. According to the experiments and simulations, adsorbed oxygen on the surface of Te NWs plays a significant role in the abnormal photoresponse. The inverse photoconductance can be attributed to the competition between the photoconductive effect and the oxygen desorption effect. Moreover, the influence of the size and layers of Te NWs is also discussed. This inverse photoconductance phenomenon is further explored by introducing the Te-Au heterojunction system. Hot-electron injection at the Te-Au heterojunction interface induces a more obvious tendency to behave with a negative photoresponse. These findings will be beneficial for potential applications of Te-NW-based photodetectors.

Zwitterionic Polymers toward the Development of Orientation-Sensitive Bioprobes

Dynamics with an orientational degree of freedom are fundamental in biological events. Probes with polarized luminescence enable a determination of the orientation. Lanthanide-doped nanocrystals can provide more precise analysis than quantum dots due to the nonphotoblinking/bleaching nature and the multiple line-shaped emission. However, the intrinsic polarization property of the original nanocrystals often deteriorates in complex physiological environments because the colloidal stability easily breaks and the probes aggregate in the media with abundant salts and macromolecules. Engineering the surface chemistry of the probes is thus essential to be compatible with biosystems, which has remained a challenging task that should be exclusively addressed for each specific probe. Here, we demonstrate a facile and efficient surface functionalization of lanthanide-doped nanorods by zwitterionic block copolymers. Due to the steric interaction and the intrinsic zwitterionic nature of the polymers, high colloidal stability of the zwitterionic nanorod suspension is achieved over wide ranges of pH and concentration of salts, even giving rise to the lyotropic liquid crystalline behavior of the nanorods in physiological media. The shear-aligned ability is shown to be unaltered by the coated polymers, and thus, the strongly polarized emission of Eu³⁺ is preserved. Besides, biological experiments reveal good biocompatibility of the zwitterionic nanorods with negligible nonspecific binding. This study is a stepping stone for the use of the nanorods as orientation probes in biofluids and validates the strategy of coupling zwitterions to lanthanide-doped nanocrystals for various bioapplications.

Polarization-Resolved p-Se/n-WS2 Heterojunctions toward Application in Microcomputer System as Multivalued Signal Trigger

Polarization-sensitive photodetectors based on van der Waals heterojunctions (vdWH) have excellent polarization-resolved optoelectronic properties that can enable the applications in polarized light identification and imaging. With the development of optical microcomputer control systems (OMCS), it is crucial and energy efficient to adopt the self-powered and polarization-resolved signal-generators to optimize the circuit design of OMCS. In this work, the selenium (Se) flakes with in-plane anisotropy and p-type character are grown and incorporated with n-type tungsten disulfide (WS₂ ) to construct the type-II vdWH for polarization-sensitive and self-powered photodetectors. Under 405 nm monochrome laser with 1.33 mW cm^-2 power density, the photovoltaic device exhibits superior photodetection performance with the photoelectric conversion efficiency (PCE) of 3.6%, the responsivity (R) of 196 mA W^-1 and the external quantum efficiency (EQE) of about 60%. The strong in-plane anisotropy of Se crystal structure gives rise to the capability of polarized light detection with anisotropic photocurrent ratio of ≈2.2 under the 405 nm laser (13.71 mW cm^-2 ). Benefiting from the well polarization-sensitive and photovoltaic properties, the p-Se/n-WS₂ vdWH is successfully applied in the OMCS as multivalued signal trigger. This work develops the new anisotropic vdWH and demonstrates its feasibility for applications in logic circuits and control systems.

On-wire bandgap engineering via a magnetic-pulled CVD approach and optoelectronic applications of one-dimensional nanostructures

Since the emergence of one-dimensional nanostructures, in particular the bandgap-graded semiconductor nanowires/ribbons or heterostructures, lots of attentions have been devoted to unraveling their intriguing properties and finding applications for future developments in optical communications and integrated optoelectronic devices. In particular, the ability to modulate the bandgap along a single nanostructure greatly enhances their functionalities in optoelectronics, and hence these studies are essential to pave the way for future high-integrated devices and circuits. Herein, we focus on a brief review on recent advances about the synthesis through a magnetic-pulled chemical vapor deposition approach, crystal structure and the unique optical and electronic properties of on-nanostructures semiconductors, including axial nanowire heterostructures, asymmetrical/symmetric bandgap gradient nanowires, lateral heterostructure nanoribbons, lateral bandgap graded ribbons. Moreover, recent developments in applications using low-dimensional bandgap modulated structures, especially in bandgap-graded nanowires and heterostructures, are summarized, including multicolor lasers, waveguides, white-light sources, photodetectors, and spectrometers, where the main strategies and unique features are addressed. Finally, future outlook and perspectives for the current challenges and the future opportunities of one-dimensional nanostructures with bandgap engineering are discussed to provide a roadmap future development in the field.

Anisotropic and hyperbranched InP nanocrystals via chemical transformation of in situ produced In2O3

We synthesized indium phosphide (InP) nanoparticles of different shapes and sizes, utilizing triphenyl phosphite (TPOP) as the phosphorus source. We show that this reaction proceeds via the formation of in situ formed In₂O₃ nanoparticles followed by subsequent transformation with triphenyl TPOP acting as the phosphorus source. Our findings open up new synthetic possibilities utilizing a cost-effective, non-pyrophoric and non-toxic phosphorus precursor. The large surface area of hyperbranched InP NCs might be ideally suited for surface-driven processes such as catalysis and energy storage.

Tunable Circularly Polarized Luminescence from Inorganic Chiral Photonic Crystals Doped with Quantum Dots

Chiral semiconductor nanostructures have received enormous attention due to their emerging circularly polarized luminescence (CPL) properties. However, compared with well-studied photoluminescence (PL), the reported CPL is much weaker and more challenging to be modulated. Herein, we describe a new approach for acquiring the intense and tunable CPL from inorganic chiral photonic crystals (CPCs) doped with semiconductor quantum dots (QDs). Unprecedentedly, the sign, position and intensity of CPL peaks can be precisely controlled by manipulating either the photonic band gap of CPCs or luminescence wavelength of QDs and a giant absolute dissymmetry factor |g_lum | up to 0.25 is obtained. More importantly, the origin of the CPL modulation is clearly elucidated by both experiment and theory. This work lays the foundation for the construction of next-generation high-performance CPL-based devices.

Elastic Properties of Single-Walled Phosphide Nanotubes: Numerical Simulation Study

After a large-scale investigation into carbon nanotubes, significant research efforts have been devoted to discovering and synthesizing other nanotubes formed by chemical elements other than carbon. Among them, non-carbon nanotubes based on compounds of the elements of the 13th group of the periodic table and phosphorus. These inorganic nanotubes have proved to be more suitable candidates than carbon nanotubes for the construction of novel electronic and optical-electronic nano-devices. For this reason, until recently, mainly the structural and electrical properties of phosphide nanotubes were investigated, and studies to understand their mechanical behavior are infrequent. In the present work, the elastic properties of single-walled boron phosphide, aluminum phosphide, gallium phosphide and indium phosphide nanotubes were numerically evaluated using a nanoscale continuum modelling (also called molecular structural mechanics) approach. The force field constants required to assess the input parameters for numerical simulations were calculated for boron phosphide, aluminum phosphide, gallium phosphide and indium phosphide nanostructures using two different methods. The influence of input parameters on the elastic properties evaluated by numerical simulation was studied. A robust methodology to calculate the surface elastic moduli of phosphide nanotubes is proposed.

Engineering the Dipole Orientation and Symmetry Breaking with Mixed-Dimensional Heterostructures

Engineering of the dipole and the symmetry of materials plays an important role in fundamental research and technical applications. Here, a novel morphological manipulation strategy to engineer the dipole orientation and symmetry of 2D layered materials by integrating them with 1D nanowires (NWs) is reported. This 2D InSe -1D AlGaAs NW heterostructure example shows that the in-plane dipole moments in InSe can be engineered in the mixed-dimensional heterostructure to significantly enhance linear and nonlinear optical responses (e.g., photoluminescence, Raman, and second harmonic generation) with an enhancement factor of up to ≈12. Further, the 1D NW can break the threefold rotational symmetry of 2D InSe, leading to a strong optical anisotropy of up to ≈65%. These results of engineering dipole orientation and symmetry breaking with the mixed-dimensional heterostructures open a new path for photonic and optoelectronic applications.

Unconventional excitonic states with phonon sidebands in layered silicon diphosphide

Complex correlated states emerging from many-body interactions between quasiparticles (electrons, excitons and phonons) are at the core of condensed matter physics and material science. In low-dimensional materials, quantum confinement affects the electronic, and subsequently, optical properties for these correlated states. Here, by combining photoluminescence, optical reflection measurements and ab initio theoretical calculations, we demonstrate an unconventional excitonic state and its bound phonon sideband in layered silicon diphosphide (SiP2), where the bound electron-hole pair is composed of electrons confined within one-dimensional phosphorus-phosphorus chains and holes extended in two-dimensional SiP2 layers. The excitonic state and emergent phonon sideband show linear dichroism and large energy redshifts with increasing temperature. Our ab initio many-body calculations confirm that the observed phonon sideband results from the correlated interaction between excitons and optical phonons. With these results, we propose layered SiP2 as a platform for the study of excitonic physics and many-particle effects.

Ultra-sensitive polarization-resolved black phosphorus homojunction photodetector defined by ferroelectric domains

With the further miniaturization and integration of multi-dimensional optical information detection devices, polarization-sensitive photodetectors based on anisotropic low-dimension materials have attractive potential applications. However, the performance of these devices is restricted by intrinsic property of materials leading to a small polarization ratio of the detectors. Here, we construct a black phosphorus (BP) homojunction photodetector defined by ferroelectric domains with ultra-sensitive polarization photoresponse. With the modulation of ferroelectric field, the BP exhibits anisotropic dispersion changes, leading an increased photothermalelectric (PTE) current in the armchair (AC) direction. Moreover, the PN junction can promote the PTE current and accelerate carrier separation. As a result, the BP photodetector demonstrates an ultrahigh polarization ratio (PR) of 288 at 1450 nm incident light, a large photoresponsivity of 1.06 A/W, and a high detectivity of 1.27 × 10¹¹ cmHz^1/2W⁻¹ at room temperature. This work reveals the great potential of BP in future polarized light detection.

Integrated polarization-sensitive photodetectors are important for sensing applications and optical communication. Here, the authors report the realization of 2D black phosphorus homojunction photodetectors defined by ferroelectric substrates, showing polarization ratios up to 288 and high responsivity in the near-infrared.

Phosphide in gallium bismuth: structural, electronic, elastic, and optical properties of GaPxBi1-x alloys

The structural, electronic, elastic, and optical properties of ternary alloys GaP_xBi_1-x as a function of phosphorus concentration were studied using ab initio calculations. We have used the full-potential linearized augmented plane wave method-based density functional theory. The potentials have been described by the generalized gradient and modified Becke-Johnson approximations. Results on lattice parameters, energy band gap, bulk modulus, elastic, and optical properties are reported. They are in good agreement with available theoretical and experimental data. Moreover, the dependence of structural and electronic properties on the composition has been analyzed. A deviation from linearity is observed for the lattice constant and the bulk modulus. In addition, the elastic constants and moduli were calculated and used to examine the mechanical stability. Both parts of dielectric-function and other optical parameters have been analyzed.

Electrically tunable quantum confinement of neutral excitons

Confining particles to distances below their de Broglie wavelength discretizes their motional state. This fundamental effect is observed in many physical systems, ranging from electrons confined in atoms or quantum dots^1,2 to ultracold atoms trapped in optical tweezers^3,4. In solid-state photonics, a long-standing goal has been to achieve fully tunable quantum confinement of optically active electron-hole pairs, known as excitons. To confine excitons, existing approaches mainly rely on material modulation⁵, which suffers from poor control over the energy and position of trapping potentials. This has severely impeded the engineering of large-scale quantum photonic systems. Here we demonstrate electrically controlled quantum confinement of neutral excitons in 2D semiconductors. By combining gate-defined in-plane electric fields with inherent interactions between excitons and free charges in a lateral p-i-n junction, we achieve exciton confinement below 10 nm. Quantization of excitonic motion manifests in the measured optical response as a ladder of discrete voltage-dependent states below the continuum. Furthermore, we observe that our confining potentials lead to a strong modification of the relative wave function of excitons. Our technique provides an experimental route towards creating scalable arrays of identical single-photon sources and has wide-ranging implications for realizing strongly correlated photonic phases^6,7 and on-chip optical quantum information processors^8,9.

Near-Infrared Polarimetric Image Sensors Based on Ordered Sulfur-Passivation GaSb Nanowire Arrays

The near-infrared polarimetric image sensor has a wide range of applications in the military and civilian fields, thus developing into a research hotspot in recent years. Because of their distinguishing 1D structure features, the ordered GaSb nanowire (NW) arrays possess potential applications for near-infrared polarization photodetection. In this work, single-crystalline GaSb NWs are synthesized through a sulfur-catalyzed chemical vapor deposition process. A sulfur-passivation thin layer is formed on the NW surface, which prevents the GaSb NW core from being oxidized. The photodetector based on sulfur-passivation GaSb (S-GaSb) NWs has a lower dark current and higher responsivity than that built with pure GaSb NWs. The photodetector exhibits a large responsivity of 9.39 × 10² A/W and an ultrahigh detectivity of 1.10 × 10¹¹ Jones for 1.55 μm incident light. Furthermore, the dichroic ratio of the device is measured to reach 2.65 for polarized 1.55 μm light. Through a COMSOL simulation, it is elucidated that the origin of the polarized photoresponse is the attenuation of a light electric field inside the NW when the angle of incident polarization light rotates. Moreover, a flexible polarimetric image sensor with 5 × 5 pixels is successfully constructed on the ordered S-GaSb NW arrays, and it exhibits a good imaging ability for incident near-infrared polarization light. These good photoresponse properties and polarized imaging abilities can empower ordered S-GaSb NW arrays with technological potentials in next-generation large-scale near-infrared polarimetric imaging sensors.

A high-performance polarization-sensitive and stable self-powered UV photodetector based on a dendritic crystal lead-free metal-halide CsCu2I3/GaN heterostructure

Polarization-sensitive photodetectors are the core of optics applications and have been successfully demonstrated in photodetectors based on the newly-emerging metal-halide perovskites. However, achieving high polarization sensitivity is still extremely challenging. In addition, most of the previously reported photodetectors were concentrated on 1D lead-halide perovskites and 2D asymmetric intrinsic structure materials, but suffered from being external bias driven, lead-toxicity, poor stability and complex processes, severely limiting their practical applications. Here, we demonstrate a high-performance polarization-sensitive and stable polarization-sensitive UV photodetector based on a dendritic crystal lead-free metal-halide CsCu₂I₃/GaN heterostructure. By combining the anisotropic morphology and asymmetric intrinsic structure of CsCu₂I₃ dendrites with the isotropic material GaN film, a high specific surface area and built-in electric field are achieved, exhibiting an ultra-high polarization selectivity up to 28.7 and 102.8 under self-driving mode and -3 V bias, respectively. To our knowledge, such a high polarization selectivity has exceeded those of all of the reported perovskite-based devices, and is comparable to, or even superior to, those of the conventional 2D heterostructure materials. Interestingly, the unsealed device shows outstanding stability, and can be stored for over 2 months, and effectively maintained the performance even after repeated heating (373K)-cooling (300K) for different periods of time in ambient air, indicating a remarkable temperature tolerance and desired compatibility for applications under harsh conditions. Such excellent performance and simple method strongly show that the CsCu₂I₃/GaN heterojunction photodetector has great potential in practical applications with high polarization-sensitivity. This work provides a new insight into designing novel high-performance polarization-sensitive optoelectronic devices.

Lasing action in a strongly coupled silicon nanowire pair

High-index dielectric nanostructures are of particular interest for nanoscale lasing due to their low absorption losses. However, the relatively weak near-field restricts the isolated dielectric cavities as low-threshold integrated on-chip laser sources. Here, we demonstrate lasing action in a silicon nanowire pair with 32 nm gap coated with dye-doped shell on the silicon-on-insulator platform. It is found that the quality factor Q is dominated by the coupling of the silicon nanowire pair, which depends on the gap size, the nanowire width, and the dye thickness. A lasing peak at the wavelength of 529 nm with FWHM of 0.6 nm is experimentally realized by the Si nanowire pair width, and the corresponding pumping power threshold is ∼34 µW/cm². The proposed strategy, based on the well-established Si planar process, lays the groundwork for practical integrated nanolasers that have potential applications in photonic circuits.

Hydration Intermediate Phase Regulated In-Plane and Out-Plane Epitaxy Growth of Oriented Nano-Array Structures on Perovskite Single Crystals

Fabrication of organic-metal-halide perovskite micro-nano array structures draws attention to the potential application in polarized light, high-resolution X-ray imaging, light-emitting diodes, and lasers. However, it is still challenging to achieve the growth of controllable long-range ordered nanostructure arrays by chemical solution-based techniques. Herein, controllable epitaxial growth of long-range ordered micro-nano arrays on MAPbI₃ single crystal (SC) surface is reported. A hydrated intermediate phase is found that can effectively regulate in-plane and out-plane orientated growth, respectively. This is attributed to the regulation of growth thermodynamics by hydration 0D perovskite intermediate phase enabling free recombination of PbI₄^2- octahedral cages. Further, it is found that the degree of hydration is the key to the realization of in-plane and out-plane growth. Meanwhile, polarization emission and amplified spontaneous emission property are observed in highly oriented nanorod arrays with potential applications in anti-counterfeiting polarized emission.

Electromechanical conversion efficiency of GaN NWs: critical influence of the NW stiffness, the Schottky nano-contact and the surface charge effects

The piezoelectric nanowires (NWs) are considered as promising nanomaterials to develop high-efficient piezoelectric generators. Establishing the relationship between their characteristics and their piezoelectric conversion properties is now essential to further improve the devices. However, due to their nanoscale dimensions, the NWs are characterized by new properties that are challenging to investigate. Here, we use an advanced nano-characterization tool derived from AFM to quantify the piezo-conversion properties of NWs axially compressed with a well-controlled applied force. This unique technique allows to establish the direct relation between the output signal generation and the NW stiffness and to quantify the electromechanical coupling coefficient of GaN NWs, which can reach up to 43.4%. We highlight that this coefficient is affected by the formation of the Schottky nano-contact harvesting the piezo-generated energy, and is extremely sensitive to the surface charge effects, strongly pronounced in sub-100 nm wide GaN NWs. These results constitute a new building block in the improvement of NW-based nanogenerator devices.