Three-dimensional Nanostructures Research Articles

High-efficiency of novel hierarchical 3D macroporous g-C3N4 material on solar-driven photocatalytic water-splitting for hydrogen evolution

The use of multi-pore nanostructured g-C3N4 photocatalysts is an efficient approach to separate photogenerated charge carriers and increase visible light photocatalytic performance. Recent progress has yielded nanostructured material through hard templating, which limits potential applications. Integrating the 2D building block into multidimensional porous structures remains a significant challenge in scalable production. Herein, a novel technique based on P407 bubble clusters templating and fixation by freezing is described for the first time to fabricate a 3D opened-up macroporous g-C3N4 nanostructures for photocatalytic H2 evolution. Three-dimensional hierarchical nanostructures provide more contact active sites and synergistically promote the creation of heterogeneous catalytic interfaces. This feature is very useful for understanding the transfer path of photoinduced charges as well as the origins of the high charge separation efficiency in photocatalytic reactions, thus yielding a remarkable visible light-induced H2 evolution rate of 4213.6 μmol h−1 g−1, which is nearly 5.6 times (716 μmol h−1 g−1) higher than that of lamellar bulk g-C3N4. This newly developed approach offers a promising alternative to synthesize broad-spectral response 3D hierarchal g-C3N4 nanostructures and can be extended to assemble other functional nanomaterials as building blocks into macroscopic configurations coupled with electronic modulation strategy simultaneously.

3D Plasmonic Nanostructure-Based Polarized ECL Sensor for Exosome Detection in Tumor Microenvironment.

Exosomes of cancer cells play an important role in the proliferation, adhesion, and migration of tumors. Especially, exosomes in the tumor microenvironment can reflect the proliferation of tumors directly, thus serving as ideal referenced markers of the possibility and grade of malignancy in neoplasms. However, the sensitive and accurate detection of exosomes remains challenging. In this work, a novel three-dimensional (3D) plasmonic nanostructure was constructed for exosomal miRNA detection. It combined the advantages of Au nanostar monolayer and Ag nanowire monolayer to provide multiple hot spots. Moreover, Au nanostar monolayer changed the isotropic electrochemiluminescence (ECL) into polarized emission. The Ag nanowire monolayer worked as waveguides for the light direction. As a result, the polarized resolution and intensity of ECL signal were improved. The polarized ECL emission was significantly increased by 47.1 times. This high-resolution polarized ECL sensor was used for detecting exosomal miRNA-146b-5p in the thyroid tumor microenvironment. This sensor showed the linear range from 1 fM to 1 nM with a detection limit of 0.3 fM. The satisfactory results indicated the developed 3D plasmonic nanostructure-based ECL sensor had great potential in biosensing and clinical diagnosis.

Hollow Spherical Pd/CdS/NiS with Carrier Spatial Separation for Photocatalytic Hydrogen Generation.

Inspired by the unique properties of the three-dimensional hollow nanostructures in the field of photocatalysis, as well as the combination of co-catalyst, porous hollow spherical Pd/CdS/NiS photocatalysts are prepared by stepwise synthesis. The results show that the Schottky junction between Pd and CdS accelerates the transport of photogenerated electrons, while a p-n junction between NiS and CdS traps the photogenerated holes. As co-catalysts, the Pd nanoparticles and the NiS are loaded inside and outside the hollow CdS shell layer, respectively, which combines with the particular characteristic of the hollow structure, resulting in a spatial carrier separation effect. Under the synergy of the dual co-catalyst loading and hollow structure, the Pd/CdS/NiS has favorable stability. Its H2 production under visible light is significantly increased to 3804.6 μmol/g/h, representing 33.4 times more than that of pure CdS. The apparent quantum efficiency is 0.24% at 420 nm. A feasible bridge for the development of efficient photocatalysts is offered by this work.

Rational design of Ni nanoparticles loaded porous N-doped carbon nanostructures for efficient hydrogenation reduction of Cr(VI): Performance, critical role of hydrogen species and mechanism insight

Catalytic hydrogenation via formic acid (FA) activation is an important way for the control of Cr(VI)-contaminated water. In the present study, three-dimensional porous N-doped carbon nanostructures loaded with quasi-spherical Ni nanoparticles (Ni@NC) are rationally prepared by a facile carbonization strategy and developed as a robust catalyst to effectively activate FA for hydrogenation reduction conversion of Cr(VI) to Cr(III). Such carbon nanostructures with large specific surface areas and abundant mesopores not only protect the anchored Ni nanoparticles from poisoning, but also coordinate with Ni nanoparticles to diversify active sites, significantly promoting Cr(VI) reduction efficiency. The optimal Ni@NC catalyst presents the excellent activity for catalytic FA activation and achieves high-efficiency Cr(VI) reduction, delivering the enhanced rate constant of 0.059 min−1 and favorable k-value of 3.15 μmol s−1 g−1, attributing to collaborative cooperation of high-electron-density Ni sites and self-polarized NC. More importantly, the Ni@NC catalyst exhibits robust tolerance of coexisting ions and good reusability for Cr(VI) reduction in acidic environment. Spectroscopic analysis and electrochemical evaluation unveil the critical role of the surface-bonded Ni–Hads* species and hydrogen radicals (·H) in-situ generated in Ni@NC/FA system for hydrogenation reduction of Cr(VI).

Classification of FIB/SEM-tomography images for highly porous multiphase materials using random forest classifiers

FIB/SEM tomography represents an indispensable tool for the characterization of three-dimensional nanostructures in battery research and many other fields. However, contrast and 3D classification/reconstruction problems occur in many cases, which strongly limits the applicability of the technique especially on porous materials, like those used for electrode materials in batteries or fuel cells. Distinguishing the different components like active Li storage particles and carbon/binder materials is difficult and often prevents a reliable quantitative analysis of image data, or may even lead to wrong conclusions about structure-property relationships. In this contribution, we present a novel approach for data classification in three-dimensional image data obtained by FIB/SEM tomography and its applications to NMC battery electrode materials. We use two different image signals, namely the signal of the angled SE2 chamber detector and the Inlens detector signal, combine both signals and train a random forest, i.e. a particular machine learning algorithm. We demonstrate that this approach can overcome current limitations of existing techniques suitable for multi-phase measurements and that it allows for quantitative data reconstruction even where current state-of the art techniques fail, or demand for large training sets. This approach may yield as guideline for future research using FIB/SEM tomography.

Three-Dimensional Nucleic Acid Nanostructures Based on Self-Assembled Polymer-Oligonucleotide Conjugates of Comblike and Coil-Comb Chain Architectures.

Spherical nucleic acids have emerged as a class of nanostructures, exhibiting a wide variety of properties, distinctly different from those of linear nucleic acids, and a plethora of applications in therapeutics and diagnostics. Herein, we report on preparation of 3D nucleic acid nanostructures, prepared by self-assembly of polymer-oligonucleotide conjugates. The latter are obtained by grafting multiple alkyne-functionalized oligonucleotide strands onto azide-modified homo-, block, and random (co)polymers of chloromethylstyrene via initiator-free click coupling chemistry to form conjugates of comblike and coil-comb chain architectures. The resulting conjugates are amphiphilic and form stable nanosized supramolecular structures in aqueous solution. The nanoconstructs are thoroughly investigated and a number of physical characteristics, in particular, molar mass, size, aggregation number, zeta potential, material density, number of oligonucleotide strands per particle, grafting density, and their relation to hallmark properties of spherical nucleic acids - biocompatibility, resistance against DNase I, cellular uptake without the need for transfection agents - are determined.

Review of the key milestones in the development of critical dimension small angle x-ray scattering at National Institute of Standards and Technology

An x-ray scattering based metrology was conceived over 20 years ago as part of a collaboration between National Institute of Standards and Technology (NIST) and International Business Machines Corporation (IBM) to evaluate the performance of lithographic patterning materials for the semiconductor industry. This methodology treated a periodic array of lithographic structures as a diffraction grating and focused on extracting the physical dimensions of the structures in the grating by analyzing the diffraction patterns. In the early stages of the work the focus was on developing the transmission small-angle x-ray scattering (tSAXS) as a metrology tool to measure the critical dimensions (CD) of the lithographic features vital to the integrated circuit chip fabrication. Later, the focus shifted to include grazing incident small-angle x-ray scattering and x-ray reflectivity as parts of the CD metrology tool due to their unique capabilities. Frequently the term critical dimension small-angle x-ray scattering (CDSAXS) has been used as a synonym for the metrology of using tSAXS for CD measurements without mentioning transmission. Various milestones in the CDSAXS development are reviewed in this article together with some prospects regarding the future growth of x-ray-based metrology for complex three-dimensional nanostructures important to semiconductor industries.

Dendrimer-Mediated Delivery of DNA and RNA Vaccines.

DNA and RNA vaccines (nucleic acid-based vaccines) are a promising platform for vaccine development. The first mRNA vaccines (Moderna and Pfizer/BioNTech) were approved in 2020, and a DNA vaccine (Zydus Cadila, India), in 2021. They display unique benefits in the current COVID-19 pandemic. Nucleic acid-based vaccines have a number of advantages, such as safety, efficacy, and low cost. They are potentially faster to develop, cheaper to produce, and easier to store and transport. A crucial step in the technology of DNA or RNA vaccines is choosing an efficient delivery method. Nucleic acid delivery using liposomes is the most popular approach today, but this method has certain disadvantages. Therefore, studies are actively underway to develop various alternative delivery methods, among which synthetic cationic polymers such as dendrimers are very attractive. Dendrimers are three-dimensional nanostructures with a high degree of molecular homogeneity, adjustable size, multivalence, high surface functionality, and high aqueous solubility. The biosafety of some dendrimers has been evaluated in several clinical trials presented in this review. Due to these important and attractive properties, dendrimers are already being used to deliver a number of drugs and are being explored as promising carriers for nucleic acid-based vaccines. This review summarizes the literature data on the development of dendrimer-based delivery systems for DNA and mRNA vaccines.

Establishing highly efficient absorptive and catalytic network for depolarized high-stability lithium-sulfur batteries

Practical operation of lithium-sulfur (Li-S) batteries with high sulfur loading and efficient/stable sulfur conversion requires the suppression of the lithium polysulfides (LiPSs) shuttling and the facilitation of ion and electron transfer on the electrode material surface. Herein, a multifunctional current collector, composed of Ag@polypyrrole (PPy) coated electrospun carbon nanofibers (CNF) framework, was rationally designed to construct a highly efficient catalytic/absorptive/conductive network to improve the performance of Li-S batteries under practical operation condition. At the molecular scale, the Ag@PPy molecular not only effectively inhibits LiPSs shuttle effect, but also achieves the fast sulfur catalysis and depolarization during charge transfer due to the high conductivity of Ag nanoparticles. At the electrode scale, the three-dimensional (3D) robust fibrous nanostructure provides abundant physical space to realize high sulfur loading, maintains electrode integrity during large volume change of active sulfur and under mechanical abuse condition, as well as enables the high-flux Li+ diffusion and electrolyte flow. Consequently, Li-S batteries with the CNF/Ag@PPy current collector delivered excellent cycling stability (capacity fading of 0.048% per cycle over 500cycles at 1.0C) and high energy density (234.2 Wh kgcell-1 under high sulfur loading of 9.77 mg cm−2). Flexible Li-S batteries are also fabricated indicating the feasibility of the CNF/Ag@PPy current collector in flexible devices.

A Reflectivity Enhanced 3D Optical Storage Nanostructure Application Based on Direct Laser Writing Lithography

To enable high-density optical storage, better storage media structures, diversified recording methods, and improved accuracy of readout schemes should be considered. In this study, we propose a novel three-dimensional (3D) sloppy nanostructure as the optical storage device, and this nanostructure can be fabricated using the 3D laser direct writing technology. It is a 900 nm high, 1 × 2 µm wide Si slope on a 200 nm SiO2 layer with 200 nm Si3N4 deposited on top to enhance reflectivity. In this study, we propose a reflected spectrum-based method as the readout recording strategy to stabilize information readout more stable. The corresponding reflected spectrum varied when the side wall angle of the slope and the azimuth angle of the nanostructure were tuned. In addition, an artificial neural network was applied to readout the stored information from the reflected spectrum. To simulate the realistic fabrication error and measurement error, a 20% noise level was added to the study. Our findings showed that the readout accuracy was 99.86% for all 120 data sequences when the slope and azimuth angle were varied. We investigated the possibility of a higher storage density to fully demonstrate the storage superiority of this designed structure. Our findings also showed that the readout accuracy can reach its highest level at 97.25% when the storage step of the encoded structure becomes 7.5 times smaller. The study provides the possibility to further explore different nanostructures to achieve high-density optical storage.

Ultrathin V6O13 nanosheets assembled into 3D micro/nano structured flower-like microspheres for high-performance cathode materials of Li-ion batteries

Benefiting from its unique high theoretical capacity and energy density, V6O13 is considered an outstanding cathode candidate. Nevertheless, the lithium ions will form LixV6O13 when embedded in V6O13, resulting in volume expansion and crystal structure instability. For that reason, the construction of three-dimensional nanostructures is an awfully serviceable method to resolve the above problems. Herein, we adopt a green and convenient hydrothermal method to synthesize three-dimensional microsphere structure composed of nanoflakes, and flower-like V6O13 microspheres are synthesized by adjusting the concentration of nitric acid (HNO3). Meanwhile, the formation mechanism of flower-like V6O13 microspheres is investigated by controlling the hydrothermal reaction time and the concentration of HNO3. As a lithium-ion cathode material, flower-like V6O13 microspheres show an initial discharge specific capacity of up to 368.1 mAh/g at a current density of 0.1 A/g. There was still a discharge specific capacity of up to 313.1 mAh/g after 50 charge/discharge cycles, with a capacity retention rate of 85.1%. The flower-like V6O13 microsphere electrode also combines an excellent rate performance with a satisfactory cycling stability, which achieves a cycle retention rate of 80.2% even after 200 charge/discharge cycles, and an initial discharge specific capacity of 216.9 mA/g even at a high current density of 1 A/g. The results show that, benefitting from its large specific surface area and robust three-dimensional structure, the flower-like V6O13 microsphere electrode material exhibits excellent cycling performance, and the lithium-ion batteries which use it as the cathode material perform equally well in terms of high capacity and high rate.

Influence of Geometry on Quasi-Ballistic Behavior in Silicon Nanowire Geometric Diodes

Diodes are a basic component of electrical circuits to control the flow of charge, and geometric diodes (GDs) are a special class that can operate using ballistic or quasi-ballistic transport in conjunction with geometric asymmetry to direct charge carriers preferentially in one direction, enabling an electron ratcheting effect. Nanomaterials present a unique platform for the development of GDs, and silicon nanowire (NW)-based GDs─cylindrically symmetric but translationally asymmetric three-dimensional nanostructures─have recently been demonstrated functioning at room temperature. These devices can theoretically achieve a near zero-bias turn-on voltage and rectify up to THz frequencies. Here, we synthesize silicon NW GDs and fabricate single-NW devices from which significant changes in diode performance are observed from relatively minor changes in geometry. To elucidate the interplay between geometry and ballistic behavior, we develop a Monte Carlo simulation that describes the quasi-ballistic behavior of electrons within a three-dimensional NW GD. We examine the effects of doping level, temperature, and geometry on charge carrier transport, revealing the relationships between charge carrier mean free path (MFP), specular reflection at surfaces, and geometry on GD performance. As expected, geometry strongly influences performance by directing or blocking charge carrier passage through the nanostructure. Interestingly, we find that the blocking effect is at least as important as the directing effect. Moreover, within certain geometric limits, the diode behavior is less sensitive to the MFP than might be initially expected because of the short relevant length scales and importance of the blocking effect. The results provide guidelines for the future design of NW GDs and enable the prediction and interpretation of trends in experimental results. An improved understanding of quasi-ballistic transport is crucial to guiding future experiments toward realizing THz rectification for applications in high-speed data transfer and long-wavelength energy harvesting.

Defect engineering of nanostructured ZnSnO3 for conductometric room temperature CO2 sensors

Slow response/recovery kinetics and high limit of detection (LOD) are crucial challenges for practical room-temperature carbon dioxide (CO2) gas sensor platforms. Herein, visible light-excited ZnSnO3 three-dimensional nanostructures are utilized for highly sensitive and selective detection of CO2. The sensing performance reveals that fine-controlled oxygen vacancy (OV) and highly-active electron transition of defect-rich nanomaterials are obtained via modulating the hydrogen treatment duration, conducive to the prominently enhanced ppm-level CO2 response with low LOD (3.05 ppm), ultrafast response time (16.814 s) and improved stability (14.658 ± 2.339 @ 400 ppm for 14 days) among all the reported ternary metal oxide semiconductor (TMOS) -based gas sensors. The photophysical enhancement mechanism of analyte is discussed in detail by combining experimental and theoretical investigation through the effect of photoexcitation on both adsorbed CO2 molecules and sensing materials, the role of pre-adsorbed oxygen for regulating targeted gas interaction, the changes of electronic transition in the bandgap, the impact of in-plane OV and bridging OV on CO2 sensing, and the function of OV for modifying the coordination sites and geometry of metal cations at the surface. From a broader perspective, the fabricated sensor provides a remarkably facile and effective technique for rapid and repeatable CO2 monitoring.

Generating nano-incised graphene kirigami membrane via selective tearing

By virtue of its single-layer thickness, nanoscale incisions and flexible structure, graphene kirigami (GK) owns a great prospect to be an ultra-permeable membrane for separation engineering. However, the difficulty in creating nanoscale incisions has prevented GK from being considered as a membrane candidate in the past. This situation has been improved recently by some emerging kirigami-inspired synthetic strategies and techniques for constructing complex three-dimensional nanostructures. Here, we reveal the potential fabrication of nano-incised GK membranes via an innovative selective tearing method using molecular dynamics simulation. The results exhibit that through the selective tearing method, the periodic wrinkles could be generated on the defective graphene, contributing to the stress concentration around the defects and causing the CC bonds to break, finally forming nano-incisions. The initial defective graphene, including its size, defects density, parallelogram angle and aspect ratio, as well as the shear angle, are crucial to the incision distribution on the formed GK-like membrane after selecting tearing treatment. The desalination simulation demonstrates that the selective tearing formed graphene kirigami (STGK) membrane has ultra-high water permeability, achieving 1197 L/m2/h/bar with 100 % salt rejection, 5.2–6.3 times higher than the previously reported nanoporous graphene and more than two orders of magnitude higher than current reverse osmosis membranes. We expect this work will inspire the next-generation membranes for separation and purification technology.

Irregular DNA Triangular Prism/Triplex Assembly for Duplicate MiRNA Analysis with Nicking Endonuclease-Mediated Amplification.

Highly sensitive and selective detection of microRNA (miRNA) is becoming more and more important in the discovery, diagnosis, and prognosis of various diseases. Herein, we develop a three-dimensional DNA nanostructure based electrochemical platform for duplicate detection of miRNA amplified by nicking endonuclease. Target miRNA first helps construction of three-way junction structures on the surfaces of gold nanoparticles. After nicking endonuclease-powered cleavage reactions, single-stranded DNAs labeled with electrochemical species are released. These strands can be facilely immobilized at four edges of the irregular triangular prism DNA (iTPDNA) nanostructure via triplex assembly. By evaluating the electrochemical response, target miRNA levels can be determined. In addition, the triplexes can be disassociated by simply changing pH conditions, and the iTPDNA biointerface can be regenerated for duplicate analyses. The developed electrochemical method not only exhibits an excellent prospect in the detection of miRNA but also may inspire the engineering of recyclable biointerfaces for biosensing platforms.

Synthesis of 3D Porous Cu Nanostructures on Ag Thin Film Using Dynamic Hydrogen Bubble Template for Electrochemical Conversion of CO2 to Ethanol.

Cu-based nanomaterials have been widely considered to be promising electrocatalysts for the direct conversion of CO2 to high-value hydrocarbons. However, poor selectivity and slow kinetics have hindered the use of Cu-based catalysts for large-scale industrial applications. In this work, we report on a tunable Cu-based synthesis strategy using a dynamic hydrogen bubble template (DHBT) coupled with a sputtered Ag thin film for the electrochemical reduction of CO2 to ethanol. Remarkably, the introduction of Ag into the base of the three-dimensional (3D) Cu nanostructure induced changes in the CO2 reduction reaction (CO2RR) pathway, which resulted in the generation of ethanol with high Faradaic Efficiency (FE). This observation was further investigated through Tafel and electrochemical impedance spectroscopic analyses. The rational design of the electrocatalyst was shown to promote the spillover of formed CO intermediates from the Ag sites to the 3D porous Cu nanostructure for further reduction to C2 products. Finally, challenges toward the development of multi-metallic electrocatalysts for the direct catalysis of CO2 to hydrocarbons were elucidated, and future perspectives were highlighted.

Fabrication of core shell Au@Ag supraparticles with 3D hotspots via evaporation self-assembly for sensitive surface enhanced Raman scattering detection

Three-dimensional (3D) plasmonic nanostructures exhibit excellent surface-enhanced Raman scattering (SERS) performance for detecting trace analytes. Nevertheless, fabrication of 3D plasmonic SERS substrates with non-close packed structures via simple evaporation assembly still remains a challenge. Here, we successfully prepared 3D supraparticles in millimeter scale via a simple evaporation assembly of highly concentrated core-shell Au@Ag nanoparticles (NPs) on hydrophobic surface. The formation of supraparticles could account for hydrophobic condensation effect, the huge numbers of spherical NPs, and unique core shell structure of Au@Ag NPs. Such supraparticle was consisting of more than 104 of Au@Ag NPs where nanogaps among NPs created plenty of 3D “hotspots”. The supraparticles with non-close packed structure is benefit for the diffusion of more targets into the hotspots, leading to enhanced interactions that contribute to a higher sensitivity. It was demonstrated that supraparticles could provide great enhancement for SERS behavior, which was eight folds higher than that of Au@Ag NPs assembled 3D multilayered structures. In addition, supraparticles with excellent sensitivity and high reproducibility were successfully applied in the detection of pesticide and antibiotics both in organic and aqueous solvents. This work provides a new way for the fabrication of 3D plasmonic nanostructures with highly sensitive and reproducible SERS performance.

Controllable 3D Flower-Like Ag-CF Electrodes as Flexible Marine Electric Field Sensors with High Stability

Construction of three-dimensional (3D) flower-like nanostructures with controlled morphologies has emerged as an attractive tool by scientists in the marine electric field sensor research field due to their peculiar structural features. Herein, novel 3D flower-like Ag-CF capacitive composite electrodes have been created by an eco-friendly water-bath strategy via AgNO3 as a sliver source and subsequently compounded with carbon fibers (CFs) pretreated by thermal oxidation. A series of electrode samples with various morphologies obtained by modulating different reaction times and temperatures bring about the dominant formation mechanism of these nanostructures and the influence behavior on the CF electrode in detail. Especially, the 3D flower-like Ag-CF electrode shows a large surface area acquired under the conditions of 80 °C and 15 min, which can provide more electroactive sites in electrochemical analysis and exhibit a maximum areal specific capacitance of 619.75 mF·cm-2 at a scanning speed of 10 mV·s-1. This is mainly due to the synergistic behavior of the unique 3D flower-like morphology and the large specific surface area of CFs. Furthermore, a cylinder-shaped Ag-CF sensor is designed, which delivers a superior potential difference of 33.08 μV, a potential difference drift of 18.62 μV/24 h for 30 days, and a self-noise of 0.92 nV/rt (Hz)@1 Hz. In this work, the intriguing synthesis strategy can be a promising facile approach to manufacture the controllable 3D flower-like Ag-CF electrode for electric field sensor applications.

Programmable vapor-phase metal-assisted chemical etching for versatile high-aspect ratio silicon nanomanufacturing

Defying the isotropic nature of traditional chemical etch, metal-assisted chemical etching (MacEtch) has allowed spatially defined anisotropic etching by using patterned metal catalyst films to locally enhance the etch rate of various semiconductors. Significant progress has been made on achieving unprecedented aspect ratio nanostructures using this facile approach, mostly in solution. However, the path to manufacturing scalability remains challenging because of the difficulties in controlling etch morphology (e.g., porosity and aggregation) and etch rate uniformity over a large area. Here, we report the first programmable vapor-phase MacEtch (VP-MacEtch) approach, with independent control of the etchant flow rates, injection and pulse time, and chamber pressure. In addition, another degree of freedom, light irradiation is integrated to allow photo-enhanced VP-MacEtch. Various silicon nanostructures are demonstrated with each of these parameters systematically varied synchronously or asynchronously, positioning MacEtch as a manufacturing technique for versatile arrays of three-dimensional silicon nanostructures. This work represents a critical step or a major milestone in the development of silicon MacEtch technology and also establishes the foundation for VP-MacEtch of compound semiconductors and related heterojunctions, for lasting impact on damage-free 3D electronic, photonic, quantum, and biomedical devices.

Core-Shell Nanorods as Ultraviolet Light-Emitting Diodes.

Existing barriers to efficient deep ultraviolet (UV) light-emitting diodes (LEDs) may be reduced or overcome by moving away from conventional planar growth and toward three-dimensional nanostructuring. Nanorods have the potential for enhanced doping, reduced dislocation densities, improved light extraction efficiency, and quantum wells free from the quantum-confined Stark effect. Here, we demonstrate a hybrid top-down/bottom-up approach to creating highly uniform AlGaN core-shell nanorods on sapphire repeatable on wafer scales. Our GaN-free design avoids self-absorption of the quantum well emission while preserving electrical functionality. The effective junctions formed by doping of both the n-type cores and p-type caps were studied using nanoprobing experiments, where we find low turn-on voltages, strongly rectifying behaviors and significant electron-beam-induced currents. Time-resolved cathodoluminescence measurements find short carrier liftetimes consistent with reduced polarization fields. Our results show nanostructuring to be a promising route to deep-UV-emitting LEDs, achievable using commercially compatible methods.