The CDEX-1 1 kg Point-Contact Germanium Detector for Low Mass Dark Matter Searches

The CDEX Collaboration has been established for direct detection of light dark matter particles, using ultra-low energy threshold p-type point-contact germanium detectors, in China JinPing underground Laboratory (CJPL). The first 1 kg point-contact germanium detector with a sub-keV energy threshold has been tested in a passive shielding system located in CJPL. The outputs from both the point-contact p+ electrode and the outside n+ electrode make it possible to scan the lower energy range of less than 1 keV and at the same time to detect the higher energy range up to 3 MeV. The outputs from both p+ and n+ electrode may also provide a more powerful method for signal discrimination for dark matter experiment. Some key parameters, including energy resolution, dead time, decay times of internal X-rays, and system stability, have been tested and measured. The results show that the 1 kg point-contact germanium detector, together with its shielding system and electronics, can run smoothly with good performances. This detector system will be deployed for dark matter search experiments.Comment: 6 pages, 8 figure

Green Emission from a Strain-Modulated InGaN Active Layer

Strain-induced quantum dots (QDs) like island formations are demonstrated to effectively suppress pits/dislocation generation in high indium content (26.8%) InGaN active layers. In addition to the strain redistribution in the QD-like islands, strain modulation on the InGaN active layers by using the GaN island capping is employed to form an increased surface potential barrier around the dislocation cores, which inhibits the carrier transport to the surrounding dislocations. Cathodoluminescence shows distinct double-peak emissions at 503 nm and 444 nm, corresponding to the In-rich QD-like emission and the normal quantum well emission, respectively. The QD-like emission becomes dominated in photoluminescence due to the carrier localization effect of In-rich InGaN QDs at relatively low "carrier injection current". Accordingly, green emission may be enhanced by the following origins: (1) reduction in pits/dislocations density, (2) carrier localization and strain reduction in QDs, (3) strain modulation by GaN island capping, (4) enhanced light extraction with faceted GaN islands on the surface.National Natural Science Foundation of China [60876008, 61076091]; Program for New Century Excellent Talents in Fujian Province Universit

Atomic Layer Deposition of 2D Metal Dichalcogenides for Electronics, Catalysis, Energy Storage, and Beyond

2D transition metal dichalcogenides (TMDCs) are among the most exciting materials of today. Their layered crystal structures result in unique and useful electronic, optical, catalytic, and quantum properties. To realize the technological potential of TMDCs, methods depositing uniform films of controlled thickness at low temperatures in a highly controllable, scalable, and repeatable manner are needed. Atomic layer deposition (ALD) is a chemical gas-phase thin film deposition method capable of meeting these challenges. In this review, the applications evaluated for ALD TMDCs are systematically examined, including electronics and optoelectonics, electrocatalysis and photocatalysis, energy storage, lubrication, plasmonics, solar cells, and photonics. This review focuses on understanding the interplay between ALD precursors and deposition conditions, the resulting film characteristics such as thickness, crystallinity, and morphology, and ultimately device performance. Through rational choice of precursors and conditions, ALD is observed to exhibit potential to meet the varying requirements of widely different applications. Beyond the current state of ALD TMDCs, the future prospects, opportunities, and challenges in different applications are discussed. The authors hope that the review aids in bringing together experts in the fields of ALD, TMDCs, and various applications to eventually realize industrial applications of ALD TMDCs.Peer reviewe

Measurement of ultra-high-energy diffuse gamma-ray emission of the Galactic plane from 10 TeV to 1 PeV with LHAASO-KM2A

The diffuse Galactic $\gamma$-ray emission, mainly produced via interactions between cosmic rays and the interstellar medium and/or radiation field, is a very important probe of the distribution, propagation, and interaction of cosmic rays in the Milky Way. In this work we report the measurements of diffuse $\gamma$-rays from the Galactic plane between 10 TeV and 1 PeV energies, with the square kilometer array of the Large High Altitude Air Shower Observatory (LHAASO). Diffuse emissions from the inner ($15^{\circ}<l<125^{\circ}$, $|b|<5^{\circ}$) and outer ($125^{\circ}<l<235^{\circ}$, $|b|<5^{\circ}$) Galactic plane are detected with $29.1\sigma$ and $12.7\sigma$ significance, respectively. The outer Galactic plane diffuse emission is detected for the first time in the very- to ultra-high-energy domain ($E>10$~TeV). The energy spectrum in the inner Galaxy regions can be described by a power-law function with an index of $-2.99\pm0.04$, which is different from the curved spectrum as expected from hadronic interactions between locally measured cosmic rays and the line-of-sight integrated gas content. Furthermore, the measured flux is higher by a factor of $\sim3$ than the prediction. A similar spectrum with an index of $-2.99\pm0.07$ is found in the outer Galaxy region, and the absolute flux for $10\lesssim E\lesssim60$ TeV is again higher than the prediction for hadronic cosmic ray interactions. The latitude distributions of the diffuse emission are consistent with the gas distribution, while the longitude distributions show clear deviation from the gas distribution. The LHAASO measurements imply that either additional emission sources exist or cosmic ray intensities have spatial variations.Comment: 12 pages, 8 figures, 5 tables; accepted for publication in Physical Review Letters; source mask file provided as ancillary fil