Weak Screening Research Articles

Robust excitonic light emission in 2D tin halide perovskites by weak excited state polaronic effect

2D perovskites hold immense promise in optoelectronics due to their strongly bound electron-hole pairs (i.e., excitons). While exciton polaron from interplay between exciton and lattice has been established in 2D lead-based perovskites, the exciton nature and behavior in the emerging 2D tin-based perovskites remains unclear. By combining spin-resolved ultrafast spectroscopy and sophisticated theoretical calculations, we reveal 2D tin-based perovskites as genuine excitonic semiconductors with weak polaronic screening effect and persistent Coulomb interaction, thanks to weak exciton-phonon coupling. We determine an excited state exciton binding energy of ~0.18 eV in n = 2 tin iodide perovskites, nearly twice of that in lead counterpart, despite of same large value of ~0.2 eV from steady state measurement. This finding emphasizes the pivotal role of excited state polaronic effect in these materials. The robust excitons in 2D tin-based perovskites exhibit excitation power-insensitive, high-efficiency and color-purity emission, rendering them superior for light-emitting applications.

Lateral Electronic Junction of a Single Ultrathin Silicon Induced by Interfacial Dipole of Self-Assembled Monolayer.

Interface engineering is pivotal for enhancing the performance and stability of devices with layered structures, including solar cells, electronic devices, and electrochemical systems. Incorporating the interfacial dipole between the bulk layers effectively modulates the energy level difference at the interface and does not significantly influence adjacent layers overall. However, interfaces can drastically affect adjoining layers in ultrathin devices, which are essential for next-generation electronics with high integrity, excellent performance, and low power consumption. In particular, the interfacial effect is pronounced in ultrathin semiconductors, which have a weak electric field screening effect. Herein, the substantial interfacial impact on the ultrathin silicon is shown, the p- to n-type inversion of the semiconductor solely through the deposition of a self-assembled monolayer (SAM) without external bias. The effects of SAMs with different interfacial dipoles are investigated by using Hall measurement and surface analytic techniques, such as UPS, XPS, and KPFM. Furthermore, the lateral electronic junction of the ultrathin silicon is engineered by the regioselective deposition of SAMs with opposite dipoles, and the device exhibits rectification behavior. When the interfacial dipole of SAM is manipulated, the rectification ratio changes sensitively, and thus the fabricated diode shows potential to be developed as a sensing platform.

The Signaling Paradox: Revisiting the Impacts of Overeducation in the Chinese Labor Market

With the widespread popularization of higher education, the increased supply of knowledge laborers has heightened the risk of overeducation, posing a significant threat to employment quality. Utilizing data from the CGSS2015 survey, this study controls for selection bias by matching employed and self-employed individuals using Propensity Score Matching (PSM) to distinguish and estimate the signaling and productivity effects of overeducation in China. The findings indicate that the signaling effects of overeducation are not significant, challenging the Weak Screening Hypothesis (WSH) and suggesting that overeducation in China is not genuine overeducation. It is also acknowledged that overeducation has dual productivity effects, including the loss of personal productivity and the promotion of job productivity. This implies that overeducation has contributed to the increase of social productivity at the cost of personal sacrifice.

Dual role of dissolved black carbon in sensitized ofloxacin photooxidation: Mechanism and influential factors

Dissolved black carbon (DBC) is the more photoactive component of dissolved organic matter (DOM) pool, which plays a dual role in the photoconversion of aquatic contaminants, acting as both a photosensitizer and an inhibitor. However, little is known about the more systematic mechanism by which DBC exhibits a dual effect, which is closely related to the structure composition of DBC. In this study, the differences in characteristics of DBC obtained from 300 °C and 500 °C were compared via UV–vis absorption spectrum, Fluorescence excitation emission matrix spectra (3D-EEM), Fourier transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS), and evaluated the promoting and inhibiting effects of DBC on ofloxacin (OFL) photodegradation. It was found that higher pyrolysis temperature reduced the UV absorbance, molecular weight, aromaticity, and phenolics of DBC while increasing the content of quinone/aromatic ketone and humic substances. Photochemical data showed that 3DBC*, 1O2 and ·OH were all participated in the DBC-mediated OFL photodegradation. Wherein, DBC300 (DBCT, where T = pyrolysis temperature) had strong light screening and dynamic quenching effect, but the formation ability of 3DBC*, 1O2 and ·OH was poor, which significantly retarded the photodegradation of OFL. While DBC500 exhibited a slight promotion effect due to its higher formation ability of reactive species and weak light screening effect. Moreover, DBC500 had higher steady-state concentration and (kOFL,3DBC⁎) than DBC300, which might be due to the higher contents of quinone/aromatic ketone and the lower contents of phenol in DBC500, thus enhancing the reactivity of 3DBC* and OFL. Our research systematically revealed the trade-off mechanism of DBC on the photodegradation of fluoroquinolones, and provided an important theoretical guidance for the photodegradation of fluoroquinolones under the evolution of DBC composition.

Promoting exciton dissociation by metal ion modification in polymeric carbon nitride for photocatalysis

Carbon nitride, a typical low-dimensional conjugated polymer photocatalyst, features a high exciton binding energy due to the weak dielectric screening and the strong Coulombic attraction of photogenerated electrons and holes. The reduction of the exciton binding energy of carbon nitride to promote the conversion from excitons into free carriers is the first priority for the improvement of charge-transfer-dependent photocatalytic reaction activity. In this paper, by introducing a variety of polar metal cations to carbon nitride, it is demonstrated that the charge distribution of the heptazine ring can be improved by ion polarization, which effectively promotes the dissociation of excitons into electrons and holes. The sodium ion shows the best modification effect, which enhances the rate of both photocatalytic hydrogen and hydrogen peroxide production by about 50 %. Characterization shows that the introduction of strongly polar metal cations contributes to the reduction of the exciton dissociation energy of carbon nitride. This study provides a new perspective and a convenient method for the exciton modulation engineering of low-dimensional photocatalysts.

The Effect of Women's E-literacy on Appearance Anxiety in the Information Age

In the information age, the development of social media has brought convenience to people's lives, but it has also had some negative impacts on people's mental health. Especially for women, society's emphasis on appearance and the popularity of electronic media have made women's appearance anxiety increasingly serious. This paper aims to explore the alleviating effect of women's electronic literacy on their appearance anxiety in the information age and provide strategies for improving electronic literacy by strengthening electronic literacy education. This paper argues that the lack of electronic literacy, such as online disinformation and women's weak information screening ability, leads to women's appearance anxiety. Based on this, this paper suggests that the cultivation of women's information ability should be strengthened, and the e-literacy of the whole society should be improved by improving the education system. At the same time, all components of society, such as online platforms, should enhance their sense of social responsibility on the Internet and build a fresh and upward network environment.

Water molecules mute the dependence of the double-layer potential profile on ionic strength.

We present the results of molecular dynamics simulations of a nanoscale electrochemical cell. The simulations include an aqueous electrolyte solution with varying ionic strength (i.e., concentrations ranging from 0-4 M) between a pair of metallic electrodes held at constant potential difference. We analyze these simulations by computing the electrostatic potential profile of the electric double-layer region and find it to be nearly independent of ionic concentration, in stark contrast to the predictions of standard continuum-based theories. We attribute this lack of concentration dependence to the molecular influences of water molecules at the electrode-solution interface. These influences include the molecular manifestation of water's dielectric response, which tends to drown out the comparatively weak screening requirement of the ions. To support our analysis, we decompose water's interfacial response into three primary contributions: molecular layering, intrinsic (zero-field) orientational polarization, and the dipolar dielectric response.

Tuning of excitons in phosphorene atomic chains

An universal scaling between the exciton binding energy and quasiparticle (QP) band gap was first discovered in two-dimensional (2D) semiconductors such as graphene derivatives, various transition materials dichalcogenides, and black phosphorus (Choi et al 2015 Phys. Rev. Lett. 115 066403; Jiang et al 2017 Phys. Rev. Lett. 118 266401), and later extended to quasi one-dimensional (1D) systems such as carbon nanotubes and graphene nanoribbons. In this work we study the excitonic states in phosphorene atomic chains by using the exact diagonalization method and show that the linear scaling between the exciton binding energy (Ex ) and QP shift () can be easily tuned by the dielectric environment. In the presence of weak screening, Ex is seen to increase with and exhibits a similar scaling as those 2D materials. As the screening becomes stronger, however, the dependence is found to be reversed, i.e. Ex now decreases when increases. More interestingly, we also reveal that Ex may even become nearly constant, independent on the system dimension and when the screening reaches a certain strength. These abnormal scaling relations are attributed to the complex nature of excitons in the strongly correlated 1D system.

Strain-modulated band structure and high harmonic generations in two-dimensional MoS2

Two-dimensional (2D) condensed matter is a material that is restricted in one direction while being periodic in the other. Since the restricted size of 2D materials is comparable to the wavelength of electrons, a quantum confinement effect may occur. Moreover, the absence of periodicity provides weak screening in 2D materials, which brings novel physical properties such as the quantum well, which is widely applied in quantum information, and the fine absorption structures in graphene. Among the 2D materials, the monolayer transition metal chalcogenides represented by MoS2 have attracted wide attention due to the direct band gap in the visible light region (1.8 eV) and valley polarizations, which are prospective for solar cells as well as photoelectric devices. High-harmonic generation (HHG) is a strong non-linear process during which a high-energy laser impulse is applied to materials and high-harmonic radiations are yielded. As a typical ultrafast dynamic, HHG has important applications in laser generation, such as EUV lithographic metrology and high-resolution coherent imaging. According to the Bloch oscillation model, HHG is highly dependent on band structure. Here, we report the strain-dependent HHG dynamics in MoS2. Further investigation reveals that the strain-dependence of HHG is caused by band modulation under different strains, which is dominant during HHG. Our research sheds light on ways to achieve effective modulations in ultrafast dynamics, implying an all-optical measurement band structure in strained materials.

Screening induced crossover between phonon- and plasmon-mediated pairing in layered superconductors

Two-dimensional (2D) metals can host gapless plasmonic excitations that strongly couple to electrons and thus may significantly affect superconductivity. To investigate the dynamical interplay of the electron–electron and electron–phonon interactions in the theory of 2D superconductivity, we apply a full momentum- and frequency-dependent one-loop theory treating electron–phonon, electron–plasmon, and phonon–plasmon coupling with the same accuracy. We tune the strength of the Coulomb interaction by varying the external screening to the layered superconductor and find three distinct regions. At weak screening, superconductivity is mediated by plasmons. In the opposite limit conventional electron–phonon interactions dominate. In between, we find a suppressed superconducting state. Our results show that even in conventional electron–phonon coupled layered materials, superconductivity can be significantly enhanced by the electron–plasmon coupling in a manner that can be controlled by the external screening.

Novel educational training of para medical professionals in cervical cancer screening

BackgroundCervical cancer is a public health problem in India due to weak national screening policy compounded by lack of resources including scarcity of trained personnel to carry out community-based screening program. Para medical professionals (PMPs) are closely related to women in local communities. Hence, training PMPs by incorporating novel technology and reduced time duration to achieve adequate competence in screening is an area underutilized and needs to be explored. Materials and methodsA pilot cross sectional analytical study was conducted at a tertiary referral cancer center using a shorter version of educational intervention of 2 weeks duration (EI2W) involving PMPs. Pre- and post-training assessment of knowledge, attitude, and practice (KAP) was done using questionnaires consisting of 5 domains viz. awareness of cervical cancer, awareness of cervical pre-cancer, practical screening methodology (practice oriented), data management and aspects of human papilloma virus (HPV). Wilcoxon signed-rank test was used for comparison and the degree of change was measured using analysis of covariance (ANCOVA). A p value of <0.05 was considered significant. Results118 PMPs were included. There was a significant improvement in scores of all domains (except cervical pre-cancer domain), following introduction of EI2W. Knowledge scores, post EI2W was better in Auxiliary Nurse Midwives (ANMs) than other participants. Awareness regarding cervical cancer was higher with more years of experience. The KAP analysis showed excellent interrater reliability in the practice 0.726 (0.649–0.792) followed by knowledge domain 0.711 (0.626–0.783). ConclusionEI2W was effective in significantly improving the competence of PMPs, thus reducing human resource constraints in cervical cancer prevention and elimination.

Equilibrium configurations and electronic structure of fullerene ultrathin films on SrTiO3(0 0 1) surface

Ultrathin fullerene (C60) films on various metal and semiconductor substrates have been intensively studied but not yet on a perovskite oxide substrate. Using scanning tunneling microscopy and spectroscopy, we investigated the molecular arrangement and electronic structure of C60 ultrathin films grown on a SrTiO3(001) surface. Subject to strong coupling and weak screening from the substrate, the monolayer C60 exhibit short-range ordered molecular arrangement with disordered molecular orientation and a substantially large highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap (∼4.1 eV). In contrast, C60 in the 2nd and 3rd layers are self-assembled into hexagon lattices with a quasi-(2 × 2) superstructure resulted from the arrangement of molecular orientations showing a chiral pinwheel structure. The HOMO-LUMO gap of the multi-layer C60 further expands to ∼ 4.6 eV, very close to that of gas-phase C60, indicating a negligible inter-layer screening effect.

Giant excitonic effects in vacancy-ordered double perovskites

Using first-principles GW plus Bethe-Salpeter equation calculations, we identify anomalously strong excitonic effects in several vacancy-ordered double perovskites Cs2MX6 (M = Ti, Zr; X = I, Br). Giant exciton binding energies about 1 eV are found in these moderate-gap, inorganic bulk semiconductors, pushing the limit of our understanding of electron-hole (e-h) interaction and exciton formation in solids. Not only are the exciton binding energies extremely large compared with any other moderate-gap bulk semiconductors, but they are also larger than typical 2D semiconductors with comparable quasiparticle gaps. Our calculated lowest bright exciton energy agrees well with the experimental optical band gap. The low-energy excitons closely resemble the Frenkel excitons in molecular crystals, as they are highly localized in a single [MX6]2- octahedron and extended in the reciprocal space. The weak dielectric screening effects and the nearly flat frontier electronic bands, which are derived from the weakly bonded [MX6]2- units, together explain the significant excitonic effects. Spin-orbit coupling effects play a crucial role in red-shifting the lowest bright exciton by mixing up spin-singlet and spin-triplet excitons, while exciton-phonon coupling effects have minor impacts on the strong exciton binding energies.

Neighborhoods of last resort: How landlord strategies concentrate violent crime

AbstractStudies of crime hot spots have argued that landlords’ management styles, specifically their tenant screening and property monitoring techniques, affect crime. These studies, however, have rarely considered the political–economic contexts in which these actions take place: specifically, how landlords’ behaviors are shaped by, and themselves reproduce, larger rental market structures. Drawing on data pertaining to eviction rates, criminal incidents, housing code violations, and landlord behavior in Milwaukee, Wisconsin, this study documents how extractive rental management strategies, such as weak tenant screening, frequent eviction filings, and property disinvestment, concentrate crime at particular properties. In turn, high rates of crime in a neighborhood incentivize these extractive landlord strategies. By showing how landlords’ economic strategies are central to urban crime geographies, this study contributes to our understanding of third‐party policing by revealing the limits of market‐based solutions to place management dilemmas.

The Effect of C60 and Pentacene Adsorbates on the Electrical Properties of CVD Graphene on SiO2

Graphene is an excellent 2D material for vertical organic transistors electrodes due to its weak electrostatic screening and field-tunable work function, in addition to its high conductivity, flexibility and optical transparency. Nevertheless, the interaction between graphene and other carbon-based materials, including small organic molecules, can affect the graphene electrical properties and therefore, the device performances. This work investigates the effects of thermally evaporated C60 (n-type) and Pentacene (p-type) thin films on the in-plane charge transport properties of large area CVD graphene under vacuum. This study was performed on a population of 300 graphene field effect transistors. The output characteristic of the transistors revealed that a C60 thin film adsorbate increased the graphene hole density by (1.65 ± 0.36) × 1012 cm-2, whereas a Pentacene thin film increased the graphene electron density by (0.55 ± 0.54) × 1012 cm-2. Hence, C60 induced a graphene Fermi energy downshift of about 100 meV, while Pentacene induced a Fermi energy upshift of about 120 meV. In both cases, the increase in charge carriers was accompanied by a reduced charge mobility, which resulted in a larger graphene sheet resistance of about 3 kΩ at the Dirac point. Interestingly, the contact resistance, which varied in the range 200 Ω-1 kΩ, was not significantly affected by the deposition of the organic molecules.

Ankle strategies for step-aside movement during quiet standing.

The mediolateral ankle strategy plays a crucial role in providing ankle stability in ground obstacle-avoidance behavior. This is achieved by changing basic walking patterns according to the characteristics of the obstacle. In daily life, it is more common to use step-aside movement (i.e., dodging step) for collision avoidance rather than side-stepping (i.e., widening standing base) when encountering an approaching pedestrian or bicycle. While studies have been conducted on the mediolateral ankle strategy contribution in obstacle avoidance using side-stepping, knowledge of step-aside movement is still inadequate. Therefore, we conducted an electromyography (EMG) analysis on the tibialis anterior (TA), peroneus longus (PL), and soleus (SOL) muscles, as well as measured center of pressure (CoP) displacement, and vertical ground reaction force (vGRF) of the standing leg, in order to understand the role of ankle muscles in step-aside movement during quiet standing. Fifteen healthy young men repeated twelve step-aside movements in both left and right directions. A Bayesian one-sample t-test was used to determine the sufficient step and participant counts. Multiple linear regression analysis was used to investigate the correlation between the muscle activity and CoP displacement or vGRF. The regression coefficients (β) of the left push phase and the right loading phase were tested against zero using a Bayesian one-sample t-test to identify the correlation between independent and dependent variables. We used the one-dimensional statistical parametric mapping (SPM1d) method to analyze the differences between and within the groups of EMG data based on the continuous time series. The results showed that the PL displayed a substantial contribution to the mediolateral ankle strategy during the push phase of step-aside movement, and also contributed to maintaining ankle stability during the loading phase. This suggested that screening for PL weakness and providing appropriate interventions and/or training approaches is especially critical for populations with walking stability problems.

First-principles ultrafast exciton dynamics and time-domain spectroscopies: Dark-exciton mediated valley depolarization in monolayer WSe2

Calculations combining first-principles electron-phonon ($e$-ph) interactions with the Boltzmann equation enable studies of ultrafast carrier and phonon dynamics. However, in materials with weak Coulomb screening, electrons and holes form bound excitons so their scattering processes become correlated, posing additional challenges for modeling nonequilibrium physics. Here we show calculations of ultrafast exciton dynamics and related time-domain spectroscopies using ab initio exciton-phonon (ex-ph) interactions together with an excitonic Boltzmann equation. Starting from the nonequilibrium exciton populations, we develop simulations of time-domain absorption and photoemission spectra that take into account electron-hole correlations. We use this method to study monolayer ${\mathrm{WSe}}_{2}$, where our calculations predict subpicosecond timescales for exciton relaxation and valley depolarization and reveal the key role of intermediate dark excitons. The approach introduced in this paper enables a quantitative description of nonequilibrium dynamics and ultrafast spectroscopies in materials with strongly bound excitons.

Polaronic Trions Induced by Strong Interfacial Coupling in Monolayer WSe2

AbstractThe weak dielectric screening in 2D semiconducting transition metal dichalcogenides give rise to strongly bound quasiparticles, which provides a platform to investigate the diverse excitonic phenomena and correlated physics. However, how to effectively control these quasiparticles is still a challenge for their applications in optoelectronic and valleytronic devices. Herein, by means of fabricating monolayer WSe2 and transition metal oxide (TMO) heterostructures, polaronic trion, that is a trion dressed with soft rotational optical (RO) phonons, is realized due to the strong interfacial coupling. This Fröhlich bound state of trion dramatically increases the trion binding energy (BE) from room temperature to 65 meV at 80 K in WSe2/LaAlO3 (LAO). However, the increase of the trion BE for WSe2/SrTiO3 (STO) occurs below the phase transition temperature. This work expands the possibilities of the TMDs/TMOs heterostructures and promotes the development of 2D van der Waals materials for quasiparticle‐based devices.

Diagnostic accuracy of the five times stand-to-sit test for the screening of global muscle weakness in community-dwelling older women

BackgroundAlthough the 5 times stand-to-sit test (5TSST) is indicated for screening for muscle weakness in older adults, its validity is based only on the correlation with quadriceps muscle strength or with the muscle strength of a few muscle groups of the lower limbs. Thus, the objective of the present study was to verify whether in independent older women, the 5TSST can really estimate global muscle strength, considering the sum of muscle strength of the trunk, hip, knee and ankle, which are important for functional activities. Methods119 independent older women participated in this cross-sectional study, undergoing the 5TSST and an isometric muscle strength assessment of the trunk, hip, knee and ankle, using an isokinetic dynamometer. The accuracy of the 5TSST for the discrimination of older women with reduced global muscle strength was evaluated by the ROC curve. ResultsThe ROC curve showed that the 5TSST may discriminate older women with reduced global muscle strength with moderate accuracy (AUC = 0.783; 95 % CI = 0.681–0.886; p < 0.001). The 5TSST score with the best accuracy (sensitivity: 80.0 % and specificity: 61.8 %) to evaluate global muscle strength was 11.64 s. Conclusion5TSST can be used to identify reduced global muscle strength in independent older women, standing out as an accessible tool for the screening of muscle weakness.

Screening in a two-band model for superconducting infinite-layer nickelate

Starting from an effective two-dimensional two-band model for infinite layered nickelates, consisting of bands obtained from $d$ and $s$--like orbitals, we investigate to which extend it can be mapped onto a single-band Hubbard model. We identify screening of the more itinerant $s$-like band as an important driver. In absence of screening one strongly-correlated band gives an antiferromagnetic ground state. For weak screening, the strong correlations push electrons out of the $s$-band so that the undoped nickelate remains a Mott insulator with half filled $d$ orbitals. This regime markedly differs from the observations in high-$T_c$ cuprates and pairing with $s$-wave symmetry would rather be expected in the superconducting state. In contrast, for strong screening, the $s$ and $d_{x^2-y^2}$ bands are both partly filled and couple only weakly, so that one approximately finds a self-doped $d$ band as well as tendencies towards $d$-wave pairing. Particularly in the regime of strong screening mapping to a one-band model gives interesting spectral weight transfers when a second $s$ band is also partly filled. We thus find that both one-band physics and a Kondo-lattice--like regime emerge from the same two-orbital model, depending on the strength of electronic correlations and the size of the $s$-band pocket.