Detection of trace phosphorus in water by plasma amplification laser-induced breakdown spectroscopy.

For monitoring the extent of eutrophication in water, phosphorus (P) was detected by laser-induced breakdown spectroscopy (LIBS). A plasma amplification method was proposed and the filtered aerosol was guided to interact with the collinear laser in conjunction with a nebulizer, cyclonic spray chamber, and quartz tube. With this method, the length of the plasma was amplified from 5.27∼8.73 to 17.58 mm. Moreover, the limit of detection (LoD) values of P in water improved from 6.13∼17.75 to 3.60 ppm. Furthermore, the average relative error (REAV) values reduced from 10.23∼23.84 to 6.17%. The root mean square error of cross-validation (RMSECV) values decreased from 16.68∼64.29 to 3.24 ppm. This demonstrated that plasma amplification LIBS could improve the quantitative analysis performance of LIBS detection of trace phosphorus in water.

Strain Tunable Thermoelectric Material: Janus ZrSSe Monolayer.

Thermoelectric (TE) performance of the Janus ZrSSe monolayer under biaxial strain is systematically explored by the first-principles approach and Boltzmann transport theory. Our results show that the Janus ZrSSe monolayer has excellent chemical, dynamical, thermal, and mechanical stabilities, which provide a reliable platform for strain tuning. The electronic structure and TE transport parameters of the Janus ZrSSe monolayer can be obviously tuned by biaxial strain. Under 2% tensile strain, the optimal power factor PF of the n-type-doped Janus ZrSSe monolayer reaches 46.36 m W m-1 K-2 at 300 K. This value is higher than that of the most classical TE materials. Under 6% tensile strain, the maximum ZT values for the p-type- and n-type-doped Janus ZrSSe monolayers are 4.41 and 4.88, respectively, which are about 3.83 and 1.49 times the results of no strain, respectively. Such high TE performance can be attributed to high band degeneracy and short phonon relaxation time under strain, causing simultaneous increase of the Seebeck coefficient and suppression of the phonon thermal transport. Present work demonstrates that the Janus ZrSSe monolayer is a promising candidate as a strain-tunable TE material and stimulates further experimental synthesis.

Boosting thermoelectric performance of HfSe2 monolayer by selectivity chemical adsorption.

In this work, a strategy to boosting thermoelectric (TE) performance of 2D materials is explored. We find that, appropriate chemical adsorption of atoms can effectively increase the TE performance of HfSe2 monolayer. Our results show that the adsorption of Ni atom on HfSe2 monolayer (Ni-HfSe2) can improve the optimal power factor PF and ZT at 300 K, increased by more than ∼67% and ∼340%, respectively. The PF and ZT of Ni-HfSe2 at 300 K can reach 85.06 mW m-1 K-2 and 3.09, respectively. The detailed study reveal that the adsorption of Ni atom can induce additional conductional channels of electrons, enhance the coupling of acoustic-optical phonons and the phonon anharmonicity, resulting in an obvious increment of electrical conductivity (increased by more than ∼89%) in n-type doped system and an ultralow phonon thermal conductivity (1.17 W/mK at 300 K). The high electrical conductivity and ultralow phonon thermal conductivity results in the significant increments of PF and ZT. Our study also shows that, Ni-HfSe2 is a thermal, dynamic and mechanical stable structure, which can be employed in TE application. Our research indicates that selectivity chemical adsorption is a promising way to increase TE performance of 2D materials.

First-principle study of neutron irradiation induced performance degradation of amorphous porous silica.

Neutron irradiation induced degradation of porous silica film is studied by Molecular Dynamics and Density-Functional theory-based methods. The degradation of microscopic structure, thermal property, and optical property of porous silica film are systematically investigated. Low-energy recoil is used to simulate the neutron irradiation effect. The pair and bond angle distributions, and coordination number distributions reveal that, under neutron irradiation, the microscopic structure of porous silica film is obviously modified, and the coordination defects are induced. We find that the higher recoil energy, the more coordination defects are formed in the film. The increased defects lead to a decrease in thermal conductivity. In addition, neutron irradiation induces additional optical absorption peaks in UV region and increasement in refractive index, resulting in a noticeable reduction in light transmittance. The detailed calculation of density of states reveals that these optical absorption peaks originate from the irradiation induced defect states in band gap. Our work shows that low-energy neutron irradiation can induce obvious defect density and degrade thermal and optical properties of porous silica film, which are responsible for subsequent laser-induced damage.

PM-PCF birefringence distribution measurement over a wide wavelength range based on SSFS and LSSI.

A linear self-reference spectral interferometry has been proposed to measure the distribution of polarization-maintaining photonic crystal fiber (PM-PCF) birefringence over a wide wavelength range combined with the soliton self-frequency shift and birefringence effect. The birefringence of PM-PCF is measured experimentally over the range of 800-970 nm, which is larger than 5×10-4 and shows a segmented change trend. The air micropore structure has a significant effect on the characteristics of PM-PCF, which makes it have a highly nonlinear coefficient, and at the same time, changes the dispersion and birefringence distributions of the PM-PCF. The distribution of PM-PCF birefringence, measured by experiment, provides a new dimension for the design of PM-PCF, which is helpful for a detailed fiber model and an iterative optimization of fiber structure.

Bi(trifluoromethyl) Benzoic Acid-Assisted Shallow Defect Passivation for Perovskite Solar Cells with an Efficiency Exceeding 21.

Chemical additive engineering is reported to be a simple yet effective approach to passivate shallow defects at the surface and grain boundaries, restrict nonradiative recombination losses, and further enhance the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). Herein, we successfully introduce a small organic molecule 3,5-bis(trifluoromethyl)benzoic acid (6FBzA) into an antisolvent as a shallow defect passivator for perovskite films. The Pb2+ defects at the surface are greatly healed due to the coordination interaction of carbonyl and fluorine groups of 6FBzA with Pb2+. Consequently, the trap-assisted nonradiative recombination is effectively suppressed, as well as the interfacial charge extraction and transfer is significantly enhanced. As a result, the 6FBzA-treated PSC obtains a champion PCE of 21.09% with negligible hysteresis, which is obviously superior to the reference device (18.45%). Furthermore, on account of the high hydrophobicity of 6FBzA, the unencapsulated 6FBzA-treated device exhibits a good long-term stability, maintaining 82% of its initial PCE at a relative humidity of 30-40% in ambient air after 1800 h of aging.

Strong UV laser absorption source near 355 nm in fused silica and its origination.

As a high-performance optical material, fused silica is widely applied in high-power laser and photoelectric systems. However, laser induced damage (LID) of fused silica severely limits the output power and performance of these systems. Due to the values in strong field physics and improving the load capacity and performance of high power systems at UV laser, LID at 355 nm of fused silica has attracted much attention. It has been found that, even be treated by advanced processing technologies, the actual damage threshold of fused silica at 355 nm is far below the intrinsic threshold. It means that there is an absorption source near 355 nm in fused silica. However, to date, the absorption source is still unknown. In this paper, a absorption source near 355 nm is found by first-principles calculations. We find that the absorption source near 355 nm is neutral oxygen-vacancy defect (NOV, ≡Si-Si≡) and this defect originates from the oxygen deficiency of fused silica. Our results indicate that NOV defect can be taken as a damage precursor for 355 nm UV laser, and this precursor can be obviously reduced by increasing the ratio of oxygen to silicon. Present work is valuable for exploring damage mechanisms and methods to improve the damage threshold of fused silica at UV laser.

The structural characteristics and influential factors of psychological stress of urban residents in Jiangxi province during the COVID-19 pandemic: cross sectional study.

AIMS: To explore the structural characteristics and influential factors of psychological stress of urban residents in Jiangxi province during the COVID-19 pandemic through a survey of psychological stress, personality traits, family function and life satisfaction. METHODS: By the convenient sampling, 1422 urban residents from Jiangxi province were assessed with Eysenck Personality Questionnaire Short Scale (EPQ-RSC), Psychological Questionnaires for Emergent Events of Public Health (PQEEPH), Family APGAR Scale (APGAR) and Satisfaction With Life Scale (SWLS). The relation among personality traits, psychological stress, family function and life satisfaction during the COVID-19 pandemic was analyzed by using the canonical correlation analysis and the serial mediation model. RESULTS: (1) Among the estimated correlation coefficients, the first two pairs were significant (P < 0.001 in each). (2) In the first pair of canonical variables, the loadings of neuroticism and neurasthenia were the higher (0.94, 0.70). (3) Neuroticism and life satisfaction mediated the relationship between family function and neurasthenia (ß neuroticism = -0.174; 95%CI:-0.224, -0.134; ß life satisfaction = -0.034, 95%CI:-0.012, -0.062), respectively. In addition, serial mediation analyses indicated that the association of family function and neurasthenia is mediated by neuroticism and life satisfaction in a sequential manner (ß = -0.010; 95%CI:-0.020, -0.004). CONCLUSIONS: During the COVID-19 pandemic, neuroticism was closely related to psychological stress of urban residents, especially neurasthenia. In addition, the serial mediating effect of neuroticism and life satisfaction played an important role in the process of family function influencing neurasthenia. These findings contributed to a more comprehensive understanding of the influential factors for psychological stress of urban residents during the COVID-19 pandemic.

Surface Defect Passivation and Energy Level Alignment Engineering with a Fluorine-Substituted Hole Transport Material for Efficient Perovskite Solar Cells.

The surface and boundary defects present in the perovskite film are reported to be nonradiative recombination and degradation centers, restricting further improvement of the power conversion efficiency (PCE) and long-term stability of perovskite solar cells. To address this problem, herein, we introduce a fluorine-substituted small molecular material 2FBTA-1 as a bifunctional buffer layer to efficiently passivate the surface defects of perovskite and tune the energy level alignment between the perovskite/2,2',7,7'-tetrakis(N,N-di-(p-methoxyphenyl)amino)-9,9'-spirobifluorene (Spiro-OMeTAD) interface. X-ray photoelectron spectroscopy shows that with the insertion of 2FBTA-1 between perovskite and Spiro-OMeTAD, the metallic Pb0 defects and uncoordinated Pb2+ defects are well restricted. Consequently, the average PCE is distinctly improved from 18.4 ± 0.51 to 20.3 ± 0.40%. Moreover, the long-term stability of unencapsulated devices with 2FBTA-1 treatment under ambient conditions (relative humidity 40-60%) is effectively enhanced, retaining 87% of the initial efficiency after storage for 500 h.