Effects of growth interruption on the optical and the structural properties of InGaN/GaN quantum wells grown by metalorganic chemical vapor deposition Effect of buffer layers and stacking faults on the reduction of threading dislocation density in GaN overlayers grown by metalorganic chemical vapor deposition Threading dislocation ͑TD͒ evolution during patterned GaN nanocolumn ͑NC͒ growth and coalescence overgrowth with metal-organic chemical vapor deposition is studied based on the comparisons of NC and coalescence overgrowth samples of different NC cross-section diameters and spacing sizes. From the measurement results of depth-dependent x-ray diffraction and cross-section transmission electron microscopy, it is found that the TD density in an NC depends on the patterned hole size for NC growth. Also, the TD formation at the beginning of coalescence overgrowth is related to the NC spacing size. Although the TD density at the bottom of the overgrown layer is weakly dependent on NC and spacing sizes, at its top surface, the TD density strongly relies on NC size. Among the overgrowth samples of different NC diameters and spacing sizes with a fixed NC diameter/spacing ratio, the one with the smallest size and spacing leads to the lowest TD density, the largest lateral domain size, and the highest photoluminescence efficiency. Also, the optical and crystal qualities at the surfaces of all the overgrowth samples are superior to those of a GaN template.

Given the high demand for miniaturized optoelectronic circuits, plasmonic devices with the capability of generating coherent radiation at deep subwavelength scales have attracted great interest for diverse applications such as nanoantennas, single photon sources, and nanosensors. However, the design of such lasing devices remains a challenging issue because of the long structure requirements for producing strong radiation feedback. Here, a plasmonic laser made by using a nanoscale hyperbolic metamaterial cube, called hyperbolic metacavity, on a multiple quantum-well (MQW), deep-ultraviolet emitter is presented. The specifically designed metacavity merges plasmon resonant modes within the cube and provides a unique resonant radiation feedback to the MQW. This unique plasmon field allows the dipoles of the MQW with various orientations into radiative emission, achieving enhancement of spontaneous emission rate by a factor of 33 and of quantum efficiency by a factor of 2.5, which is beneficial for coherent laser action. The hyperbolic metacavity laser shows a clear clamping of spontaneous emission above the threshold, which demonstrates a near complete radiation coupling of the MQW with the metacavity. This approach shown here can greatly simplify the requirements of plasmonic nanolaser with a long plasmonic structure, and the metacavity effect can be extended to many other material systems.

Production of multicolor or multiple wavelength lasers over the full visible-color spectrum from a single chip device has widespread applications, such as superbright solid-state lighting, color laser displays, light-based version of Wi-Fi (Li-Fi), and bioimaging, etc. However, designing such lasing devices remains a challenging issue owing to the material requirements for producing multicolor emissions and sophisticated design for producing laser action. Here we demonstrate a simple design and highly efficient single segment white random laser based on solution-processed NaYF4:Yb/Er/Tm@NaYF4:Eu core–shell nanoparticles assisted by Au/MoO3 multilayer hyperbolic meta-materials. The multicolor lasing emitted from core–shell nanoparticles covering the red, green, and blue, simultaneously, can be greatly enhanced by the high photonic density of states with a suitable design of hyperbolic meta-materials, which enables decreasing the energy consumption of photon propagation. As a result, the energy upconversion emission is enhanced by ∼50 times with a drastic reduction of the lasing threshold. The multiple scatterings arising from the inherent nature of the disordered nanoparticle matrix provide a convenient way for the formation of closed feedback loops, which is beneficial for the coherent laser action. The experimental results were supported by the electromagnetic simulations derived from the finite-difference time-domain (FDTD) method. The approach shown here can greatly simplify the design of laser structures with color-tunable emissions, which can be extended to many other material systems. Together with the characteristics of angle free laser action, our device provides a promising solution toward the realization of many laser-based practical applications.

Random laser with intrinsically uncomplicated fabrication processes, high spectral radiance, angle-free emission, and conformal onto freeform surfaces is in principle ideal for a variety of applications, ranging from lighting to identification systems. In this work, a white random laser (White-RL) with high-purity and high-stability is designed, fabricated, and demonstrated via the cost-effective materials (e.g., organic laser dyes) and simple methods (e.g., all-solution process and self-assembled structures). Notably, the wavelength, linewidth, and intensity of White-RL are nearly isotropic, nevertheless hard to be achieved in any conventional laser systems. Dynamically fine-tuning colour over a broad visible range is also feasible by on-chip integration of three free-standing monochromatic laser films with selective pumping scheme and appropriate colour balance. With these schematics, White-RL shows great potential and high application values in high-brightness illumination, full-field imaging, full-colour displays, visible-colour communications, and medical biosensing.

The experimental demonstrations of light-emitting diode (LED) fabrication with surface plasmon (SP) coupling with the radiating dipoles in its quantum wells are first reviewed. The SP coupling with a radiating dipole can create an alternative emission channel through SP radiation for enhancing the effective internal quantum efficiency when the intrinsic non-radiative recombination rate is high, reducing the external quantum efficiency droop effect at high current injection levels, and producing partially polarized LED output by inducing polarization-sensitive SP for coupling. Then, we report the theoretical and numerical study results of SP-dipole coupling based on a simple coupling model between a radiating dipole and the SP induced on a nearby Ag nanoparticle (NP). To include the dipole strength variation effect caused by the field distribution built in the coupling system (the feedback effect), the radiating dipole is represented by a saturable two-level system. The spectral and dipole-NP distance dependencies of dipole strength variation and total radiated power enhancement of the coupling system are demonstrated and interpreted. The results show that the dipole-SP coupling can enhance the total radiated power. The enhancement is particularly effective when the feedback effect is included and hence the dipole strength is increased.

Background High tibial osteotomy (HTO) has been used for over 60 years in clinical practice and mainly comprises two major techniques: closed wedge high tibial osteotomy (CWHTO) and open wedge high tibial osteotomy (OWHTO). However, these have been gradually replaced by total knee arthroplasty (TKA), due to inconsistent clinical results and many complications. With the concept of knee-protection and ladder treatment of osteoarthritis, as an effective minimally invasive treatment for knee osteoarthritis, HTO has once again received attention. Methods A systematic literature search was conducted in PubMed, Embase, ClinicalKey, CNKI, and the China Wanfang database. The search terms relating to osteoarthritis and high tibial osteotomy were used. Studies were considered eligible if the participants were adults with knee osteoarthritis (KOA) who had undergone HTO. A total of two reviewers participated in the selection of the studies. Reviewer 1 was assigned to screen titles and abstracts, and reviewer 2 to screen full-text data. Data extraction was completed by reviewer 2, and 30% were checked by the research team. Potential conflicts were resolved through discussion. The methodological quality was assessed using a risk of bias, based on the Cochrane handbook and Newcastle-Ottawa assessment scale. The outcome indicators are (1) posterior slope of tibial plateau, (2) the height of the patella, (3) fracture in the osteotomy plane, (4) survival rate, (5) special surgery knee score (HSS), and (6) the recurrence of varus deformity of the included studies were evaluated according to the guidelines of the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) working group (Atkins et al., BMJ 328:1490, 2004). Results Among the 18 articles included, 10 were prospective cohort studies, five were randomized controlled trial (RCT) studies, one was prospective comparative study (PCS), one was retrospective comparative study (RCS), and one was retrospective cohort. The earliest publication year was 1999, and the most recent was 2018. A total of 6555 eligible cases were included, comprised of 3351 OWHTO patients and 3204 CWHTO patients. Five RCT were assessed using risk of bias, based on the Cochrane handbook. Eleven cohort studies and two case-control studies were assessed using the Newcastle-Ottawa assessment scale. These six outcome indicators for a total of twenty-four evidence individuals were evaluated separately, among which the GRADE classification of 1, 2, and 6 was medium quality, and 3, 4, and 5 were low quality. Based on our systematic review, regardless of whether the chosen procedure was OWHTO or CWHTO, both HSS scores increased significantly as compared with the preoperative scores. Compared with CWHTO, the height of the patella and tibial posterior slope angle increased following OWHTO. Additionally, OWHTO has a better long-term survival rate and lower fracture rate, supporting OWHTO as the first treatment choice. Conclusions For young patients with knee osteoarthritis (KOA), high tibial osteotomy (HTO) can be considered as a treatment option to replace total knee arthroplasty (TKA) to reduce the economic burden and promote the reasonable allocation of medical resources. This study shows that compared with CWHTO, OWHTO has certain advantages in long-term survival rate and lower fracture rate, but the level of evidence is lower. In the future, we will need larger sample sizes and longer follow-up randomized controlled trials to improve our research.

High-quality coalescence overgrowth of patterned-grown GaN nanocolumns on c-plane sapphire substrate with metal organic chemical vapor deposition is demonstrated. Although domain structures of a tens of micron scale in the overgrown layer can be identified with cathodoluminescence measurement, from atomic force microscopy ͑AFM͒ measurement, the surface roughness of the overgrown layer in an area of 5 ϫ 5 m 2 is as small as 0.411 nm, which is only one-half that of the high-quality GaN thin-film template directly grown on sapphire substrate ͑the control sample͒. Based on the AFM and depth-dependent x-ray diffraction measurements near the surface of the overgrown layer, the dislocation density is reduced to the order of 10 7 cm −2 , which is one order of magnitude lower than that of the control sample and two to three orders of magnitude lower than those of ordinary GaN templates for fabricating light-emitting diodes. Also, the lateral domain size, reaching a level of ϳ2.7 m, becomes three times larger than the control sample. Meanwhile, the ratio of photoluminescence intensity at room temperature over that at low temperature of the overgrown sample is at least six times higher than that of the control sample. Although the strain in nanocolumns is almost completely released, a stress of ϳ0.66 GPa is rebuilt when the coalescence overgrowth is implemented.

Hyperbolic metamaterials have emerged as novel materials with exciting functionalities, especially for optoelectronic devices. Here, we provide the first attempt to integrate hyperbolic metamaterials with light emitting nanostructures, which enables to strongly enhance random laser action with reduced lasing threshold. Interestingly, the differential quantum efficiency can be enhanced by more than four times. The underlying mechanism can be interpreted well based on the fact that the high-k modes excited by hyperbolic metamaterials can greatly increase the possibility of forming close loops decreasing the energy consumption for the propagation of scattered photons in the matrix. In addition, out-coupled propagation of the high-k modes reaches to the far-field without being trapped inside the metamaterials due to the coupling with the random distribution of light emitting nanoparticles also plays an important role. Electromagnetic simulations derived from the finite-difference time-domain (FDTD) method are executed to support our interpretation. Realizing strong enhancement of laser action assisted by hyperbolic metamaterials provides an attractive, very simple and efficient scheme for the development of high performance optoelectronic devices, including phototransistors, and many other solid state lighting systems. Besides, because of increasing light absorption assisted by hyperbolic metamaterials structure, our approach shown is also useful for the application of highly efficient solar cells.