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Point defects in two-dimensional materials are of key interest for quantum information science. However, the parameter space of possible defects is immense, making the identification of high-performance quantum defects very challenging. Here, we perform high-throughput (HT) first-principles computational screening to search for promising quantum defects within WS2, which present localized levels in the band gap that can lead to bright optical transitions in the visible or telecom regime. Our computed database spans more than 700 charged defects formed through substitution on the tungsten or sulfur site. We found that sulfur substitutions enable the most promising quantum defects. We computationally identify the neutral cobalt substitution to sulfur (Co S0 ) and fabricate it with scanning tunneling microscopy (STM). The Co S0 electronic structure measured by STM agrees with first principles and showcases an attractive quantum defect. Our work shows how HT computational screening and nanoscale synthesis routes can be combined to design promising quantum defects.

Abstract: Point defects in two-dimensional materials are of key interest for quantum information science. However, the space of possible defects is immense, making the identification of high-performance quantum defects extremely challenging. Here, we perform high-throughput (HT) first-principles computational screening to search for promising quantum defects within WS2, which present localized levels in the band gap that can lead to bright optical transitions in the visible or telecom regime. Our computed database spans more than 700 charged defects formed through substitution on the tungsten or sulfur site. We found that sulfur substitutions enable the most promising quantum defects. We computationally identify the neutral cobalt substitution to sulfur (Co$_{\rm S}^{0}$) as very promising and fabricate it with scanning tunneling microscopy (STM). The Co$_{\rm S}^{0}$ electronic structure measured by STM agrees with first principles and showcases an attractive new quantum defect. Our work shows how HT computational screening and novel defect synthesis routes can be combined to design new quantum defects.

Tip-enhanced photoluminescence (TRPL) is a powerful technique for spatially and spectrally probing local optical properties of 2-dimensional (2D) materials that are modulated by the local heterogeneities, revealing inaccessible dark states due to bright state overlap in conventional far-field microscopy at room temperature. While scattering-type near-field probes have shown the potential to selectively enhance and reveal dark exciton emission, their technical complexity and sensitivity can pose challenges under certain experimental conditions. Here, we present a highly reproducible and easy-to-fabricate near-field probe based on nanoimprint lithography and fiber-optic excitation and collection. The novel near-field measurement configuration provides an ∼3 orders of magnitude out-of-plane Purcell enhancement, diffraction-limited excitation spot, and subdiffraction hyperspectral imaging resolution (below 50 nm) of dark exciton emission. The effectiveness of this high spatial XD mapping technique was then demonstrated through reproducible hyperspectral mapping of oxidized sites and bubble areas.

The ability to correlate optical hyperspectral mapping and high resolution topographic imaging is critically important to gain deep insight into the structure-function relationship of nanomaterial systems. Scanning near-field optical microscopy can achieve this goal, but at the cost of significant effort in probe fabrication and experimental expertise. To overcome these two limitations, we have developed a low-cost and high-throughput nanoimprinting technique to integrate a sharp pyramid structure on the end facet of a single-mode fiber that can be scanned with a simple tuning-fork technique. The nanoimprinted pyramid has two main features: (1) a large taper angle (∼70°), which determines the far-field confinement at the tip, resulting in a spatial resolution of 275 nm, an effective numerical aperture of 1.06, and (2) a sharp apex with a radius of curvature of ∼20 nm, which enables high resolution topographic imaging. Optical performance is demonstrated through evanescent field distribution mapping of a plasmonic nanogroove sample, followed by hyperspectral photoluminescence mapping of nanocrystals using a fiber-in-fiber-out light coupling mode. Through comparative photoluminescence mapping on 2D monolayers, we also show a threefold improvement in spatial resolution over chemically etched fibers. These results show that the bare nanoimprinted near-field probes provide simple access to spectromicroscopy correlated with high resolution topographic mapping and have the potential to advance reproducible fiber-tip-based scanning near-field microscopy.

[This corrects the article DOI: 10.1039/D0NA00434K.].

ZnO is a highly promising, multifunctional nanomaterial having various versatile applications in the fields of sensors, optoelectronics, photovoltaics, photocatalysts and water purification. However, the real challenge lies in producing large scale, well-aligned, highly reproducible ZnO nanowires (NWs) using low cost techniques. This large-scale production of ZnO NWs has stunted the development and practical usage of these NWs in fast rising fields such as photocatalysis or in photovoltaic applications. The present article shows an effective, simple approach for the uniform, aligned growth of ZnO NWs on entire silicon wafers (sizes 3 or 4 inches), using a low-temperature Chemical Bath Deposition (CBD) technique. In addition to this, a systematic study of the substrate size dependent growth of NWs has been conducted to better understand the effect of the limitation in the deposition rate of Zn2+ ions on the growth of NWs. The growth rate of ZnO NWs is seen to have a strong relationship with the substrate size. Also, the loading efficiency of the Zn2+ ions is higher in ZnO NWs grown on a 3-inch silicon wafer in comparison to those grown on a small piece. An in-depth time dependent growth study conducted on entire 3-inch wafers to track the morphological evolution (length, diameter and number of the NWs) reveals that the growth rate of the length of the NWs reaches a saturation state in a short time span of 20 min. Assessment of the overall homogeneity of the NWs grown on the 3-inch wafer and simultaneous growth on two entire 4-inch silicon wafers has also been demonstrated in this article. This demonstration of large-scale, well-aligned controllable, aligned growth of ZnO NWs on entire silicon wafers is a first step towards NW based devices especially for applications such as photovoltaic, water purification, photocatalysis or biomedical applications.

Zinc oxide (ZnO) is a stable, direct bandgap semiconductor emitting in the UV with a multitude of technical applications. It is well known that ZnO emission can be shifted into the green for visible light applications through the introduction of defects. However, generating consistent and efficient green emission through this process is challenging, particularly given that the chemical or atomic origin of the green emission in ZnO is still under debate. In this work we present a new method, for which we coin term desulfurization, for creating green emitting ZnO with significantly enhanced quantum efficiency. Solution grown ZnO nanowires are partially converted to ZnS, then desulfurized back to ZnO, resulting in a highly controlled concentration of oxygen defects as determined by X-ray photoelectron spectroscopy and electron paramagnetic resonance. Using this controlled placement of oxygen vacancies we observe a greater than 40-fold enhancement of integrated emission intensity and explore the nature of this enhancement through low temperature photoluminescence experiments.

Point defects in two-dimensional materials are of key interest for quantum information science. However, the parameter space of possible defects is immense, making the identification of high-performance quantum defects very challenging. Here, we perform high-throughput (HT) first-principles computational screening to search for promising quantum defects within WS2, which present localized levels in the band gap that can lead to bright optical transitions in the visible or telecom regime. Our computed database spans more than 700 charged defects formed through substitution on the tungsten or sulfur site. We found that sulfur substitutions enable the most promising quantum defects. We computationally identify the neutral cobalt substitution to sulfur ( Co S 0 ) and fabricate it with scanning tunneling microscopy (STM). The Co S 0 electronic structure measured by STM agrees with first principles and showcases an attractive quantum defect. Our work shows how HT computational screening and nanoscale synthesis routes can be combined to design promising quantum defects. Point defects in 2D semiconductors have potential for quantum computing applications, but their controlled design and synthesis remains challenging. Here, the authors identify and fabricate a promising quantum defect in 2D WS2 via high-throughput computational screening and scanning tunnelling microscopy. [ABSTRACT FROM AUTHOR]

We report an in-depth analysis of ZnO micropods emission. A strong correlation between defect and interband emissions is observed. ZnO micropods were grown using low-temperature chemical bath deposition (CBD). ZnO micropods exhibited perfectly-crystalline hexagonally-shaped facets with various numbers of branches. Raman studies showed that ZnO micropods contained trapped zinc hydroxide (OH) and imidogen (NH) defects that originate from the precursor solution used in the CBD technique. These defects were evacuated by thermal annealing, leading to the recrystallization in the volume of the micropods and the formation of structural defects at their surface, as attested by scanning electron microscopy and X-ray diffraction. More importantly, the thermal annealing was accompanied by a breakdown of the NH defects, which resulted in a nitrogen doping of the ZnO micropods. The structural changes as well as the nitrogen doping resulted in a drastic change in the photoluminescence (PL) spectrum of the ZnO micropods that exhibited a stronger free exciton UV emission as well as a stronger visible (white) emission. An in-depth low-temperature PL study of both UV and visible emission reveals a strong interplay between the structural-defect bound excitonic UV emission (Y-band) and the deep donor (visible) emission, which suggests a rather complex emission mechanism involving an efficient nonradiative energy transfer between the Y-band states and defect states leading to the enhanced visible emission of ZnO micropods after high temperature annealing. [ABSTRACT FROM AUTHOR]

Aimed at the problems that it is difficult to judge the setting position of the conventional hanger seal and the defect of the sealing structure, the mechanical calculation of the seal performance of the conventional casing hanger seal structure was carried out. The influence factors on the seal width and contact pressure of the contact surface of the conventional seal structure were studied, the working mechanical mechanism and the seal structure were simulated, and the problems existing in the existing sealing structure were found out.Based on the design concept of elliptical metal seal structure, combined with the existing metal seal structure, a large diameter mandrel casing hanger with conical multi curved surface elliptical all metal seal structure was developed.The indoor high-pressure gas seal test shows that the designed metal seal structure is reliable, which lays a foundation for the field application of all metal mandrel hanger. [ABSTRACT FROM AUTHOR]

Probing strongly coupled quasiparticle excitations at their intrinsic length scales offers unique insights into their properties and facilitates the design of devices with novel functionalities. In this work, we investigate the formation and emission characteristics of plexcitons, arising from the interaction between surface plasmons in narrow gold nanotrenches and excitons in monolayer WSe 2 . We study this strong plasmon-exciton coupling in both the far-field and the near-field. Specifically, we observe a Rabi splitting in the far-field reflection spectra of about 80 meV under ambient conditions, consistent with our theoretical modeling. Using a custom-designed near-field probe, we find that plexciton emission originates predominantly from the lower-frequency branch, which we can directly probe and map its local field distribution. We precisely determine the plexciton's spatial extension, similar to the trench width, with nanometric precision by collecting spectra at controlled probe locations. Our work opens exciting prospects for nanoscale mapping and engineering of plexcitons in complex nanostructures with potential applications in nanophotonic devices, optoelectronics, and quantum electrodynamics in nanoscale cavities., (© 2024. The Author(s).)

Point defects in two-dimensional materials are of key interest for quantum information science. However, the parameter space of possible defects is immense, making the identification of high-performance quantum defects very challenging. Here, we perform high-throughput (HT) first-principles computational screening to search for promising quantum defects within WS 2 , which present localized levels in the band gap that can lead to bright optical transitions in the visible or telecom regime. Our computed database spans more than 700 charged defects formed through substitution on the tungsten or sulfur site. We found that sulfur substitutions enable the most promising quantum defects. We computationally identify the neutral cobalt substitution to sulfur (Co S 0 ) and fabricate it with scanning tunneling microscopy (STM). The Co S 0 electronic structure measured by STM agrees with first principles and showcases an attractive quantum defect. Our work shows how HT computational screening and nanoscale synthesis routes can be combined to design promising quantum defects., (© 2024. The Author(s).)