Augmented reality (AR) and virtual reality (VR) technologies enable interactive and immersive user experiences through head-worn devices that contain microdisplays. These microdisplays must have superior pixel density, brightness, contrast and response times, owing to the proximity of the AR glasses or VR headset to the eyes. Advanced microdisplay technologies in light engines such as liquid crystal on silicon (LCoS), organic light-emitting diodes on silicon (OLEDoS) and light-emitting diodes on silicon (LEDoS) have emerged to meet the demands of AR and VR, and are typically integrated with optical components such as free-space, freeform or waveguide combiners. In this Perspective, we explore the key requirements for AR and VR microdisplays, consider the advantages of each light-engine technology and discuss how their performance can be accurately characterized. We also examine how LCoS, OLEDoS and LEDoS technologies are integrated with complementary metal–oxide–semiconductor (CMOS) backplanes, and paired with optical combiners in AR displays, to merge virtual images with real-world scenes. Microdisplays for the glasses and headsets used in augmented reality and virtual reality must provide high pixel density, brightness and contrast, and fast response times. This Perspective explores three advanced technologies — liquid crystal on silicon, organic light-emitting diodes on silicon, and light-emitting diodes on silicon — that can meet the challenge.

Highly efficient, ultrahigh-density inorganic micro-LED displays are gaining a strong position in the market for use in augmented reality glasses. When applied to electronic contact lenses with an eye-adaptive form factor, the micro-LED displays evolve into next generation augmented reality viewers. Here, we report 1-nm-thick epitaxial AlN passivation for 1.5-μm-diameter InGaN red micro-LEDs with high external quantum efficiency of 6.5% at the peak wavelength of 649 nm. The flexible form factor of the red micro-LEDs is achieved through the development of a near-complete device transfer. By overcoming the existing bottlenecks of red spectral efficiency and form factor of inorganic micro-LEDs, we believe this will pave the way for another revolution in the augmented reality and metaverse industries.

Bandgaps and defect-state energies are key electrical characteristics of semiconductor materials and devices, thereby necessitating nanoscale analysis with a heightened detection threshold. An example of such a device is an InGaN-based light-emitting diode (LED), which is used to create fine pixels in augmented-reality micro-LED glasses. This process requires an in-depth understanding of the spatial variations of the bandgap and its defect states in the implanted area, especially for small-sized pixelation requiring electroluminescence. In this study, we developed a new algorithm to achieve two-dimensional mappings of bandgaps and defect-state energies in pixelated InGaN micro-LEDs, using automated electron energy-loss spectroscopy integrated with scanning transmission electron microscopy. The algorithm replaces conventional background subtraction-based methods with a linear fitting approach, enabling enhanced accuracy and efficiency. This novel method offers several advantages, including the independent calculation of the defect energy (Ed) and bandgap energy (Eg), reduced thickness effects, and improved signal-to-noise ratio by eliminating the need for zero-loss spectrum calibration. These advancements allow us to reveal the relationship between the bandgap, defect states, microstructure, and electroluminescence of the semiconductor under ion-implantation conditions. The streamlined analysis achieves a spatial resolution of approximately 5 nm and an exceptional detection limit. Additionally, ab initio calculations indicate gallium vacancies as the predominant defects.

InGaN-based blue light-emitting diodes (LEDs), with their high efficiency and brightness, are entering the display industry. However, a significant gap remains between the expectation of highly efficient light sources and their experimental realization into tiny pixels for ultrahigh-density displays for augmented reality (AR). Her, we report using tailored ion implantation (TIIP) to fabricate highly-efficient, electrically-driven pixelated InGaN microLEDs (μLEDs) at the mid-submicron scale (line/space of 0.5/0.5 μm. Moreover, we demonstrate high-density TFT and QD C/F integration technologies.

InGaN-based blue light-emitting diodes (LEDs), with their high efficiency and brightness, are entering the display industry. However, a significant gap remains between the expectation of highly efficient light sources and their experimental realization into tiny pixels for ultrahigh-density displays for augmented reality. Herein, we report using tailored ion implantation (TIIP) to fabricate highly efficient, electrically-driven pixelated InGaN micro-LEDs (μLEDs) at the mid-submicrometre scale (line/space of 0.5/0.5 μm), corresponding to 8,500 pixels per inch (ppi) (RGB). Creating a laterally confined non-radiative region around each pixel with a controlled amount of mobile vacancies, TIIP pixelation produces relatively invariant luminance, and high pixel distinctiveness, at submicrometre-sized pixels. Moreover, with the incomparable integration capability of TIIP pixelation due to its planar geometry, we demonstrate 2,000 ppi μLED displays with monolithically integrated thin-film transistor pixel circuits, and 5,000 ppi compatible core technologies. We expect that the demonstrated method will pave the way toward high-performance μLED displays for seamless augmented-reality glasses. Submicrometre-sized InGaN-based light-emitting diodes are fabricated by tailored ion implantation. The devices are free from electrical leakage and show a luminance of 7,440 nit at 4.9 A cm−2 even at the line/space scale of 0.5/0.5 μm (= 8,500 ppi).

A discrete core-shell-like micro-light-emitting diode (micro-LED) array was grown on a 100 nm-thick sapphire nano-membrane array without harmful plasma etching for chip singulation. Due to proper design for the sapphire nano-membrane array, an array of multi-faceted micro-LEDs with size of 4 μm × 16 μm was grown. Threading dislocation density in the micro-LED formed on sapphire nano-membrane was reduced by 59.6% due to the sapphire nano-membranes, which serve as compliant substrates, compared to GaN formed on a planar substrate. Enhancements in internal quantum efficiency by 44% and 3.3 times higher photoluminescence intensity were also observed from it. Cathodoluminescence emission at 435 nm was measured from c-plane multiple quantum wells (MQWs), whereas negligible emissions were detected from semi-polar sidewall facets. A core-shell-like MQWs were formed on all facets, hopefully lowering concentration of non-radiative surface recombination centers and reducing leakage current paths. This study provides an attractive platform for micro-LEDs by using sapphire nano-membrane.

InGaN-based blue light-emitting diodes (LEDs), with their high efficiency and brightness, are entering the display industry. However, a significant gap remains between the expectation of highly efficient light sources and their experimental realization into tiny pixels for ultrahigh-density displays for augmented reality (AR).Herein, we report using tailored ion implantation (TIIP) to fabricate highly-efficient, electrically-driven pixelated InGaN microLEDs (µLEDs) at the mid-submicron scale (line/space of 0.5/0.5 µm), corresponding to 8500ppi (RGB). Creating a laterally confined nonradiative region around each pixel with controlled amount of mobile vacancies, TIIP pixelation materializes relatively invariant luminance, and high pixel distinctiveness, at submicron-sized pixels. Moreover, with incomparable integration capability of TIIP pixelation owing to its planar geometry, we demonstrate 2000 ppi µLED displays with monolithically integrated thin-film transistor pixel circuits, and 5000 ppi compatible core technologies. We expect that the demonstrated method will pave the way toward high-performance µLED displays for seamless AR glasses in the near future.

As potential high-performance anodes for Li-ion batteries (LIBs), hierarchical heteronanostructures consisting of TiNb2O7 nanofibers and ultrathin MoS2 nanosheets (TNO@MS HRs) were synthesized by simple electrospinning/hydrothermal processes. With their growth mechanism revealed, the TNO@MS HRs exhibited an entangled structure both for their ionic and electronic conducting pathways, which enabled the synergetic combination of one- and two-dimensional structures to be realized. In the potential range of 0.001-3 V vs Li/Li+, the TNO@MS HR-based LIBs exhibited high capacities of 872 and 740 mAh g-1 after 42 and 200 cycles at a current density of 1 A g-1, respectively, and excellent rate performance of 611 mAh g-1 at 4 A g-1. We believe that the fabrication route of TNO@MS HRs will find visibility for the use of anode electrodes for high capacity LIBs at low cost.

Adv. Mater. 2015, 27, 4551 In the published communication, the peaks in the XRD patterns in Figure 3d were mislabeled. The figure is hereby corrected. The labels for AgCl and KCl should be reversed, as shown below. The authors apologize for any inconvenience caused.

In this letter, we propose sub-terahertz (sub-THz) slow-wave circuits for coherent radiation sources through beam wave interaction mechanism. The circuits are prepared using microfabrication in advanced silicon (Si) technologies. Our approach is to split the circuit into multi levels allowing a low aspect ratio configuration and alleviating the loading effect of deep-reactive-ion etching on silicon wafers. This makes it easier to achieve flat-etched bottom and smooth sidewall profiles in nanoscale accuracy for high frequency operation. The dispersion relation retrieved from the measurement, therefore, corresponds well to the theoretical estimation. In particular, the sub-THz radiation is successfully measured in pulsed operation through the vacuum-sealed integration of the slow-wave circuit with a 15-kV, 90-mA thermionic electron gun. This observation offers a promising opportunity for the development of terahertz radiation sources based on silicon micro- and nanofabrication technologies.

The as-electrospun polymeric lithium titanate nanofibers are crystallized into Li4Ti5O12 nanofibers (denoted as LTO NFs) via post-annealing. The LTO NFs are coated with a carbon layer using a glucose polymer via hydrothermal synthesis. The GO layer electrostatically attracts to the positively charged LTO NFs, resulting in the uniform wrapping of individual LTO NFs without aggregation. The introduction of uniformly coated carbon and GO double layers led to an enhanced rate capability (110 mAh g (1) at 20C) and over two orders of magnitude higher diffusion coefficient (D-Li = similar to 1.04 x 10 (11) cm(2) s (1)) of the tailored LTO NFs with carbon and GO network compared with those of the pristine LTO NFs. Extended testing for over 100 cycles demonstrates the cyclic stability and Coulombic efficiency of over 99% of this system. These results indicate that the interconnection and networks of LTO NFs through carbon coating and the individual GO wrapping, which facilitates the lithium ion and electron transportation, may show excellent electrochemical performance. (C) 2016 Elsevier Ltd. All rights reserved.

We examine exciton recombination, energy-, and charge transfer in multilayer CdS/ZnS quantum dots (QDs) on silver plasmonic resonators using photoluminescence (PL) and excitation spectroscopy along with kinetic modeling and simulations. The exciton dynamics including all the processes are strongly affected by the separation distance between QDs and silver resonators, excitation wavelength, and QD film thickness. For a direct contact or very small distance, interfacial charge transfer and tunneling dominate over intrinsic radiative recombination and exciton energy transfer to surface plasmons (SPs), resulting in PL suppression. With increasing distance, however, tunneling diminishes dramatically, while long-range exciton-SP coupling takes place much faster (>6.5 ns) than intrinsic recombination (~200 ns) causing considerable PL enhancement. The exciton-SP coupling strength shows a strong dependence on excitation wavelengths, suggesting the state-specific dynamics of excitons and the down-conversion of surface plasmons involved. The overlayers as well as the bottom monolayer of QD multilayers exhibit significant PL enhancement mainly through long-range exciton-SP coupling. The overall emission behaviors from single- and multilayer QD films on silver resonators are described quantitatively by a photophysical kinetic model and simulations. The present experimental and simulation results provide important and useful design rules for QD-based light harvesting applications using the exciton-surface plasmon coupling.

SnO2 hollow nanofibers (SnO2 hNFs) are prepared through electrospinning and annealing processes. The polypyrrole layers coated onto the surface of the SnO2 hNFs are annealed in a nitrogen atmosphere. The nitrogen-doped carbon-coated SnO2 hNFs (SnO2/NC hNFs) are composed of SnO2 hNFs with a wall thickness of 60-80 nm and a nitrogen-doped carbon layer similar to 10 nm thick. The nitrogen content in the carbon layer is approximately 7.95%. Owing to the nitrogen-doped carbon shell layers, the specific reversible capacity of SnO2/NC hNFs at a current density of 0.2 A g(-1) after 100 cycles is 1648 mAh g(-1) which is 427% higher than that of (386 mAh g(-1)) SnO2 hNFs. This strategy may open new avenues for the design of other composite architectures as electrode materials in order to achieve high-performance lithium ion batteries. (C) 2016 Elsevier Ltd. All rights reserved.

There have been significant recent developments in the growth of single‐crystal gallium nitride (GaN) on unconventional templates for large‐area blue or green light‐emitting diodes (LEDs) which, together with layer transfer onto foreign substrates, can enable flexible and stretchable lighting applications. Here, the heteroepitaxial growth of GaN on amorphous and single‐crystal substrates employing various interlayers and nucleation layers is reviewed, as well as the use of weak interfaces for layer‐transfer onto foreign substrates. Recent progress in low‐temperature GaN‐based red–green–blue (RGB) LEDs on glass substrates, which has exhibited a calculated efficiency of 11% compared with that from commertial LEDs, is discussed. Layer‐transfer techniques with various interlayers are also discussed. These heteroepitaxial GaN growth and layer‐transfer technologies are expected to lead to new lighting and display devices with high efficiency and full‐color tunability, which are suitable for large‐area, stretchable display and lighting applications.

We report the electrochemical performance of carbon-coated TiO2 nanobarbed fibers (TiO2@C NBFs) as anode material for lithium-ion batteries. The TiO2@C NBFs are composed of TiO2 nanorods grown on TiO2 nanofibers as a core, coated with a carbon shell. These nanostructures form a conductive network showing high capacity and C-rate performance due to fast lithium-ion diffusion and effective electron transfer. The TiO2@C NBFs show a specific reversible capacity of approximately 170mAh g−1 after 200cycles at a 0.5A g−1 current density, and exhibit a discharge rate capability of 4A g−1 while retaining a capacity of about 70mAh g−1. The uniformly coated amorphous carbon layer plays an important role to improve the electrical conductivity during the lithiation–delithiation process.

3D mesostructured AgCl-KCl photonic crystals emerge from colloidal templating of eutectic solidification. Solvent removal of the KCl phase results in a mesostructured AgCl inverse opal. The 3D-template-induced confinement leads to the emergence of a complex microstructure. The 3D mesostructured eutectic photonic crystals have a large stop band ranging from the near-infrared to the visible tuned by the processing.

New optically active three-dimensionally (3D) mesostructured AgCl–KCl eutectic photonic crystals and a 3D mesoporous AgCl inverse opal structure emerge from the combination of the characteristic periodic structure of a 3D template, and the native self-organizing structure of a AgCl–KCl eutectic. This is described by K. Thornton, P. V. Braun, and co-workers on page 4551.

Stability and high energy densities are essential qualities for emerging battery electrodes. Because of its high specific capacity, silicon has been considered a promising anode candidate. However, the several-fold volume changes during lithiation and delithiation leads to fractures and continuous formation of an unstable solid-electrolyte interphase (SEI) layer, resulting in rapid capacity decay. Here, we present a carbon-silicon-carbon (C@Si@C) nanotube sandwich structure that addresses the mechanical and chemical stability issues commonly associated with Si anodes. The C@Si@C nanotube array exhibits a capacity of ∼2200 mAh g(-1) (∼750 mAh cm(-3)), which significantly exceeds that of a commercial graphite anode, and a nearly constant Coulombic efficiency of ∼98% over 60 cycles. In addition, the C@Si@C nanotube array gives much better capacity and structure stability compared to the Si nanotubes without carbon coatings, the ZnO@C@Si@C nanorods, a Si thin film on Ni foam, and C@Si and Si@C nanotubes. In situ SEM during cycling shows that the tubes expand both inward and outward upon lithiation, as well as elongate, and then revert back to their initial size and shape after delithiation, suggesting stability during volume changes. The mechanical modeling indicates the overall plastic strain in a nanotube is much less than in a nanorod, which may significantly reduce low-cycle fatigue. The sandwich-structured nanotube design is quite general, and may serve as a guide for many emerging anode and cathode systems.

In our earlier paper dealing with dispersion retrieval from ultra-deep, reactive-ion-etched, slow-wave circuits on silicon substrates, it was proposed that splitting high-aspect-ratio circuits into multilevels enabled precise characterization in sub-terahertz frequency regime. This achievement prompted us to investigate beam-wave interaction through a vacuum-sealed integration with a 15-kV, 85-mA, thermionic, electron gun. Our experimental study demonstrates sub-terahertz, backward-wave amplification driven by an external oscillator. The measured output shows a frequency downshift, as well as power amplification, from beam loading even with low beam perveance. This offers a promising opportunity for the development of terahertz radiation sources, based on silicon technologies.

A tunneling rectifier prepared from vertically stacked two-dimensional (2D) materials composed of chemically doped graphene electrodes and hexagonal boron nitride (h-BN) tunneling barrier was demonstrated. The asymmetric chemical doping to graphene with linear dispersion property induces rectifying behavior effectively, by facilitating Fowler-Nordheim tunneling at high forward biases. It results in excellent diode performances of a hetero-structured graphene/h-BN/graphene tunneling diode, with an asymmetric factor exceeding 1000, a nonlinearity of ∼40, and a peak sensitivity of ∼12 V−1, which are superior to contending metal-insulator-metal diodes, showing great potential for future flexible and transparent electronic devices.