Use of optoelectronic tweezers in manufacturing – accurate solder bead positioning

In this work, we analyze the use of optoelectronic tweezers (OETs) to manipulate 45 μm diameter Sn62Pb36Ag2 solder beads with light-induced dielectrophoresis force and we demonstrate high positioning accuracy. It was found that the positional deviation of the solder beads increases with the increase of the trap size. To clarify the underlying mechanism, simulations based on the integration of the Maxwell stress tensor were used to study the force profiles of OET traps with different sizes. It was found that the solder beads felt a 0.1 nN static friction or stiction force due to electrical forces pulling them towards the surface and that this force is not dependent on the size of the trap. The stiction limits the positioning accuracy; however, we show that by choosing a trap that is just larger than the solder bead sub-micron positional accuracy can be achieved

Study on the radon adsorption capability of low-background activated carbon

Radon is a significant background source in rare event detection experiments. Activated Carbon (AC) adsorption is widely used for effective radon removal. The selection of AC considers its adsorption capacity and radioactive background. In this study, using self-developed devices, we screened and identified a new kind of low-background AC from Qingdao Inaf Technology Company that has very high Radon adsorption capacity. By adjusting the average pore size to 2.3 nm, this AC demonstrates a radon adsorption capacity of 2.6 or 4.7 times higher than Saratech or Carboact activated carbon under the same conditions.Comment: 21pages, 7 figure

Dark Count of 20-inch PMTs Generated by Natural Radioactivity

The primary objective of the JUNO experiment is to determine the ordering of neutrino masses using a 20-kton liquid-scintillator detector. The 20-inch photomultiplier tube (PMT) plays a crucial role in achieving excellent energy resolution of at least 3% at 1 MeV. Understanding the characteristics and features of the PMT is vital for comprehending the detector's performance, particularly regarding the occurrence of large pulses in PMT dark counts. This research paper aims to further investigate the origin of these large pulses in the 20-inch PMT dark count rate through measurements and simulations. The findings confirm that the main sources of the large pulses are natural radioactivity and muons striking the PMT glass. By analyzing the PMT dark count rate spectrum, it becomes possible to roughly estimate the radioactivity levels in the surrounding environment.Comment: 10 pages, 8 figures, and 5 table

Identifying Reactive Sites and Surface Traps in Chalcopyrite Photocathodes

Gathering information on the atomic nature of reactive sites and trap states is key to fine tuning catalysis and suppressing deleterious surface voltage losses in photoelectrochemical technologies. Here, spectroelectrochemical and computational methods were combined to investigate a model photocathode from the promising chalcopyrite family: CuIn0.3Ga0.7S2. We found that voltage losses are linked to traps induced by surface Ga and In vacancies, whereas operando Raman spectroscopy revealed that catalysis occurred at Ga, In, and S sites. This study allows establishing a bridge between the chalcopyrite's performance and its surface's chemistry, where avoiding formation of Ga and In vacancies is crucial for achieving high activity.This work was supported by the Swiss National Science Foundation (SNSF) under the Ambizione Energy grant (PZENP2_166871) and by the Gaznat-EPFL Research Program. M.B. and U.A. were supported by the Swiss National Science Foundation Professorship Grants PP00P2_157615 and PP00P2_187185. Calculations were performed on UBELIX, the HPC cluster at the University of Bern. M.X. is grateful for the support from the China Scholarship Council (No. CSC201806160172) and the Strategic Japanese–Swiss Science and Technology program (514259). Open access funding provided by Ecole Polytechnique Federale de Lausanne

LEO Satellite Constellations for 5G and Beyond: How Will They Reshape Vertical Domains?

The rapid development of communication technologies in the past decades has provided immense vertical opportunities for individuals and enterprises. However, conventional terrestrial cellular networks have unfortunately neglected the huge geographical digital divide, since high bandwidth wireless coverage is concentrated to urban areas. To meet the goal of ``connecting the unconnected'', integrating low Earth orbit (LEO) satellites with the terrestrial cellular networks has been widely considered as a promising solution. In this article, we first introduce the development roadmap of LEO satellite constellations (SatCons), including early attempts in LEO satellites with the emerging LEO constellations. Further, we discuss the unique opportunities of employing LEO SatCons for the delivery of integrating 5G networks. Specifically, we present their key performance indicators, which offer important guidelines for the design of associated enabling techniques, and then discuss the potential impact of integrating LEO SatCons with typical 5G use cases, where we engrave our vision of various vertical domains reshaped by LEO SatCons. Technical challenges are finally provided to specify future research directions.Comment: 4 figures, 1 table, accepted by Communications Magazin