Giant Carrier Mobility in a Room-Temperature Ferromagnetic VSi2N4 Monolayer.

Using density functional theory (DFT), we investigate that two possible phases of VSi2N4 (VSN) may be realized, one called the "H phase" corresponding to what is known from calculation and herein the other new "T phase" being stabilized by a biaxial tensile strain of 3%. Significantly, the H phase is predicted to display a giant carrier mobility of 1 × 106 cm2 V-1 s-1, which exceeds that for most 2D magnetic materials, with a Curie temperature (TC) exceeding room temperature and a band gap of 2.01 eV at the K point. Following the H-T phase transition, the direct band gap shifts to the Γ point and increases to 2.59 eV. The Monte Carlo (MC) simulations also indicate that TC of the T phase VSN can be effectively modulated by strain, reaching room temperature under a biaxial strain of -4%. These results show that VSN should be a promising functional material for future nanoelectronics.

CEEM: a Chemically Explainable Deep Learning Platform for Identifying Compounds with Low Effective Mass.

The semiconductor industry occupies a crucial position in the fields of integrated circuits, energy, and communication systems. Effective mass (mE ), which is closely related to electron transition, thermal excitation, and carrier mobility, is a key performance indicator of semiconductor. However, the highly neglected mE is onerous to measure experimentally, which seriously hinders the evaluation of semiconductor properties and the understanding of the carrier migration mechanisms. Here, a chemically explainable effective mass predictive platform (CEEM) is constructed by deep learning, to identify n-type and p-type semiconductors with low mE . Based on the graph network, a versatile explainable network is innovatively designed that enables CEEM to efficiently predict the mE of any structure, with the area under the curve of 0.904 for n-type semiconductors and 0.896 for p-type semiconductors, and derive the most relevant chemical factors. Using CEEM, the currently largest mE database is built that contains 126 335 entries and screens out 466 semiconductors with low mE for transparent conductive materials, photovoltaic materials, and water-splitting materials. Moreover, a user-friendly and interactive CEEM web is provided that supports query, prediction, and explanation of mE . CEEM's high efficiency, accuracy, flexibility, and explainability open up new avenues for the discovery and design of high-performance semiconductors.

Using the Diamagnetic Coefficients to Estimate the Reduced Effective Mass in 2D Layered Perovskites: New Insight from High Magnetic Field Spectroscopy.

In this work, the current state of research concerning the determination of the effective mass in 2D layered perovskites is presented. The available experimental reports in which the reduced effective mass µ has been directly measured using magneto-absorption spectroscopy of interband Landau levels are reviewed. By comparing these results with DFT computational studies and various other methods, it is concluded that depending on the approach used, the µ found spans a broad range of values from as low as 0.05 up to 0.3 me. To facilitate quick and reliable estimation of µ, a model is proposed based solely on the available experimental data that bypass the complexity of interband Landau level spectroscopy. The model takes advantage of the µ value measured for (PEA)2PbI4 and approximates the reduced effective mass of the given 2D layered perovskites based on only two experimental parameters-the diamagnetic coefficient and the effective dielectric constant. The proposed model is tested on a broad range of 2D layered perovskites and captures well the main experimental and theoretical trends.

Torsional strain engineering of transition metal dichalcogenide nanotubes: anab initiostudy.

We study the effect of torsional deformations on the electronic properties of single-walled transition metal dichalcogenide (TMD) nanotubes. In particular, considering forty-five select armchair and zigzag TMD nanotubes, we perform symmetry-adapted Kohn-Sham density functional theory calculations to determine the variation in bandgap and effective mass of charge carriers with twist. We find that metallic nanotubes remain so even after deformation, whereas semiconducting nanotubes experience a decrease in bandgap with twist-originally direct bandgaps become indirect-resulting in semiconductor to metal transitions. In addition, the effective mass of holes and electrons continuously decrease and increase with twist, respectively, resulting in n-type to p-type semiconductor transitions. We find that this behavior is likely due to rehybridization of orbitals in the metal and chalcogen atoms, rather than charge transfer between them. Overall, torsional deformations represent a powerful avenue to engineer the electronic properties of semiconducting TMD nanotubes, with applications to devices like sensors and semiconductor switches.

Multimodal Functional Analysis Platform: 3. Spherical Treadmill System for Small Animals.

In the application of advanced neuroscience techniques including optogenetics to small awake animals, it is often necessary to restrict the animal's movements. A spherical treadmill is a beneficial option that enables virtual locomotion of body- or head-restrained small animals. Besides, it has a wide application range, including virtual reality experiments. This chapter describes the fundamentals of a spherical treadmill for researchers who want to start experiments with it. First, we describe the physical aspect of a spherical treadmill based on the simple mechanical analysis. Next, we explain the basics of data logging and preprocessing for behavioral analysis. We also provide simple computer programs that work for the purpose.

Large Band Edge Tunability in Colloidal Nanoplatelets.

We study the impact of organic surface ligands on the electronic structure and electronic band edge energies of quasi-two-dimensional (2D) colloidal cadmium selenide nanoplatelets (NPLs) using density functional theory. We show how control of the ligand and ligand-NPL interface dipoles results in large band edge energy shifts, over a range of 5 eV for common organic ligands with a minor effect on the NPL band gaps. Using a model self-energy to account for the dielectric contrast and an effective mass model of the excitons, we show that the band edge tunability of NPLs together with the strong dependence of the optical band gap on NPL thickness can lead to favorable photochemical and optoelectronic properties.

Thermopower Modulation Clarification of the Operating Mechanism in Wide Bandgap BaSnO3 -SrSnO3 Solid-Solution Based Thin Film Transistors.

The transparent oxide semiconductor (TOS) with large bandgap (Eg ≈ 4 eV) based thin-film transistors (TFTs) showing both high carrier mobility and UV-visible transparency has attracted increasing attention as a promising component for next generation optoelectronics. Among TOSs, BaSnO3 -SrSnO3 solid-solutions (Eg = 3.5-4.2 eV) are good candidates because the single crystal shows very high mobility. However, the TFT performance has not been optimized due to the lack of fundamental knowledge especially the effective thickness (teff ) and the carrier effective mass (m*). Here, it is demonstrated that the electric field thermopower (S) modulation method addresses this problem by combining with the standard volume carrier concentration (n3D ) dependence of S measurements. By comparing the electric field accumulated sheet carrier concentration (n2D ) and n3D at same S, it is clarified that the teff (n2D /n3D ) of the conducting channel becomes thicker with increasing Sr concentration, whereas the m* becomes lighter. The former would be due to the increase of Eg and latter would be due to the enhancement of overlap population of neighboring Sn 5s orbitals. The present analyses technique is useful to experimentally clarify the teff and m*, and essentially important to realize advanced TOS-based TFTs showing both high optical transparency and high mobility.

First-Principles Calculations of Angular and Strain Dependence on Effective Masses of Two-Dimensional Phosphorene Analogues (Monolayer α-Phase Group-IV Monochalcogenides MX).

Group IV monochalcogenides M X (M = Ge, Sn; X = S, Se)-semiconductor isostructure to black phosphorene-have recently emerged as promising two-dimensional materials for ultrathin-film photovoltaic applications owing to the fascinating electronic and optical properties. Herein, using first-principles calculations, we systematically investigate the orbital contribution electronic properties, angular and strain dependence on the carrier effective masses of monolayer M X . Based on analysis on the orbital-projected band structure, the VBMs are found to be dominantly contributed from the p z orbital of X atom, while the CBM is mainly dominated by p x or p y orbital of M atom. 2D SnS has the largest anisotropy ratio due to the lacking of s orbital contribution which increases the anisotropy. Moreover, the electron/hole effective masses along the x direction have the steeper tendency of increase under the uniaxial tensile strain compared to those along y direction.

Mixed Two-Dimensional Organic-Inorganic Halide Perovskites for Highly Efficient and Stable Photovoltaic Application.

Solar cells made of hybrid organic-inorganic perovskite (HOIP) materials have attracted ever-increasing attention due to their high efficiency and easy fabrication. However, issues regarding their poor stability remain a challenge for practical applications. Engineering the composition and structure of HOIP can effectively enhance the thermal stability and improve the power conversion efficiency (PCE). In this work, mixed two-dimensional (2D) HOIPs are systematically investigated for solar-power harvesting using first-principles calculations. We find that their electronic properties depend strongly on the mixed atoms (Cs, Rb, Ge and Pb) and the formation energy is related to the HOIP's composition, where the atoms are more easily mixed in SnI-2D-HOIPs due to low formation energy at the same composition ratio. We further show that optimal solar energy harvesting can be achieved on the solar cells composed of mixed SnI-2D-HOIPs because of reduced bandgaps, enhanced mobility and improved stability. Importantly, we find that the mixed atoms (Cs, Rb, Ge and Pb) with the appropriate composition ratios can effectively enhance the solar-to-power efficiency and show greatly improved resistance to moisture. The findings demonstrate that mixed 2D-HOIPs can replace the bulk HOIPs or pure 2D-HOIPs for applications into solar cells with high efficiency and stability.

Addressing the Fundamental Electronic Properties of Wurtzite GaAs Nanowires by High-Field Magneto-Photoluminescence Spectroscopy.

At ambient conditions, GaAs forms in the zincblende (ZB) phase with the notable exception of nanowires (NWs) where the wurtzite (WZ) lattice is also found. The WZ formation is both a complication to be dealt with and a potential feature to be exploited, for example, in NW homostructures wherein ZB and WZ phases alternate controllably and thus band gap engineering is achieved. Despite intense studies, some of the fundamental electronic properties of WZ GaAs NWs are not fully assessed yet. In this work, by using photoluminescence (PL) under high magnetic fields (B = 0-28 T), we measure the diamagnetic shift, ΔEd, and the Zeeman splitting of the band gap free exciton in WZ GaAs formed in core-shell InGaAs-GaAs NWs. The quantitative analysis of ΔEd at different temperatures (T = 4.2 and 77 K) and for different directions of B⃗ allows the determination of the exciton reduced mass, µexc, in planes perpendicular (µexc = 0.052 m0, where m0 is the electron mass in vacuum) and parallel (µexc = 0.057 m0) to the c axis of the WZ lattice. The value and anisotropy of the exciton reduced mass are compatible with the electron lowest-energy state having Γ7C instead of Γ8C symmetry. This finding answers a long discussed issue about the correct ordering of the conduction band states in WZ GaAs. As for the Zeeman splitting, it varies considerably with the field direction, resulting in an exciton gyromagnetic factor equal to 5.4 and ∼0 for B⃗//c and B⃗⊥c, respectively. This latter result provides fundamental insight into the band structure of wurtzite GaAs.

Value and Anisotropy of the Electron and Hole Mass in Pure Wurtzite InP Nanowires.

The effective mass of electrons and holes in semiconductors is pivotal in determining the dynamics of carriers and their confinement energy in nanostructured materials. Surprisingly, this quantity is still unknown in wurtzite (WZ) nanowires (NWs) made of III-V compounds (e.g., GaAs, InAs, GaP, InP), where the WZ phase has no bulk counterpart. Here, we investigate the magneto-optical properties of InP WZ NWs grown by selective-area epitaxy that provides perfectly ordered NWs featuring high-crystalline quality. The combined analysis of the energy of free exciton states and impurity levels under magnetic field (B up to 29 T) allows us to disentangle the dynamics of oppositely charged carriers from the Coulomb interaction and thus to determine the values of the electron and hole effective mass. By application of B⃗ along different crystallographic directions, we also assess the dependence of the transport properties with respect to the NW growth axis (namely, the WZ c axis). The effective mass of electrons along c is me∥ = (0.078 ± 0.002) m0 (m0 is the electron mass in vacuum) and perpendicular to c is me⊥ = (0.093 ± 0.001) m0, resulting in a 20% mass anisotropy. Holes exhibit a much larger (∼320%) and opposite mass anisotropy with their effective mass along and perpendicular to c equal to mh∥ = (0.81 ± 0.18) m0 and mh⊥ = (0.250 ± 0.016) m0, respectively. While no full consensus is found with current theoretical results on WZ InP, our findings show trends remarkably similar to the experimental data available in WZ bulk materials, such as InN, GaN, and ZnO.

Quantized Conductance and Large g-Factor Anisotropy in InSb Quantum Point Contacts.

Because of a strong spin-orbit interaction and a large Landé g-factor, InSb plays an important role in research on Majorana fermions. To further explore novel properties of Majorana fermions, hybrid devices based on quantum wells are conceived as an alternative approach to nanowires. In this work, we report a pronounced conductance quantization of quantum point contact devices in InSb/InAlSb quantum wells. Using a rotating magnetic field, we observe a large in-plane (|g1| = 26) and out-of-plane (|g1| = 52) g-factor anisotropy. Additionally, we investigate crossings of subbands with opposite spins and extract the electron effective mass from magnetic depopulation of one-dimensional subbands.

Two-Dimensional Phosphorus Carbide: Competition between sp(2) and sp(3) Bonding.

We propose previously unknown allotropes of phosphorus carbide (PC) in the stable shape of an atomically thin layer. Different stable geometries, which result from the competition between sp(2) bonding found in graphitic C and sp(3) bonding found in black P, may be mapped onto 2D tiling patterns that simplify categorizing of the structures. Depending on the category, we identify 2D-PC structures that can be metallic, semimetallic with an anisotropic Dirac cone, or direct-gap semiconductors with their gap tunable by in-layer strain.

Quantitative Imaging of Cell Membrane-associated Effective Mass Density Using Photonic Crystal Enhanced Microscopy (PCEM).

Adhesion is a critical cellular process that contributes to migration, apoptosis, differentiation, and division. It is followed by the redistribution of cellular materials at the cell membrane or at the cell-surface interface for cells interacting with surfaces, such as basement membranes. Dynamic and quantitative tracking of changes in cell adhesion mass redistribution is challenging because cells are rapidly moving, inhomogeneous, and nonequilibrium objects, whose physical and mechanical properties are difficult to measure or predict. Here, we report a novel biosensor based microscopy approach termed Photonic Crystal Enhanced Microscopy (PCEM) that enables the movement of cellular materials at the plasma membrane of individual live cells to be dynamically monitored and quantitatively imaged. PCEM utilizes a photonic crystal biosensor surface, which can be coated with arbitrary extracellular matrix materials to facilitate cellular interactions, within a modified brightfield microscope with a low intensity non-coherent light source. Benefiting from the high sensitivity, narrow resonance peak, and tight spatial confinement of the evanescent field atop the photonic crystal biosensor, PCEM enables label-free live cell imaging with high sensitivity and high lateral and axial spatial-resolution, thereby allowing dynamic adhesion phenotyping of single cells without the use of fluorescent tags or stains. We apply PCEM to investigate adhesion and the early stage migration of different types of stem cells and cancer cells. By applying image processing algorithms to analyze the complex spatiotemporal information generated by PCEM, we offer insight into how the plasma membrane of anchorage dependent cells is dynamically organized during cell adhesion. The imaging and analysis results presented here provide a new tool for biologists to gain a deeper understanding of the fundamental mechanisms involved with cell adhesion and concurrent or subsequent migration events.

Electronic conduction in La-based perovskite-type oxides.

A systematic study of La-based perovskite-type oxides from the viewpoint of their electronic conduction properties was performed. LaCo0.5Ni0.5O3±Î´ was found to be a promising candidate as a replacement for standard metals used in oxide electrodes and wiring that are operated at temperatures up to 1173 K in air because of its high electrical conductivity and stability at high temperatures. LaCo0.5Ni0.5O3±Î´ exhibits a high conductivity of 1.9 × 103 S cm-1 at room temperature (R.T.) because of a high carrier concentration n of 2.2 × 1022 cm-3 and a small effective mass m∗ of 0.10 me. Notably, LaCo0.5Ni0.5O3±Î´ exhibits this high electrical conductivity from R.T. to 1173 K, and little change in the oxygen content occurs under these conditions. LaCo0.5Ni0.5O3±Î´ is the most suitable for the fabrication of oxide electrodes and wiring, though La1-x Sr x CoO3±Î´ and La1-x Sr x MnO3±Î´ also exhibit high electronic conductivity at R.T., with maximum electrical conductivities of 4.4 × 103 S cm-1 for La0.5Sr0.5CoO3±Î´ and 1.5 × 103 S cm-1 for La0.6Sr0.4MnO3±Î´ because oxygen release occurs in La1-x Sr x CoO3±Î´ as elevating temperature and the electrical conductivity of La0.6Sr0.4MnO3±Î´ slightly decreases at temperatures above 400 K.

Comparison of boundary conditions to describe drying of turmeric (Curcuma longa) rhizomes using diffusion models.

Turmeric is harvested with high moisture content and should be dried before the storage. It is observed that drying is quickest when the rhizomes are peeled and cut in small cylindrical pieces. In order to describe the process, normally a diffusive model is used, considering boundary condition of the first kind for the diffusion equation. This article uses analytical solutions considering boundaries conditions of the first (model 1) and third (model 2) kinds coupled to an optimizer to describe the drying process. It is shown that, for model 1, the fit of the analytical solution to the experimental data is biased, despite the good statistical indicators (chi-square χ(2) equal to 1.7095 × 10(-3) and coefficient of correlation R(2) of 0.9988). For model 2, the errors of the experimental points about the simulated curve can be considered randomly distributed, and the statistical indicators are much better than those obtained for model 1: χ(2) = 3.5596 × 10(-4) and R(2) = 0.9996.

The Minima of Viscosities.

The Trachenko-Brazhkin equation of the minimal possible viscosity is analysed, emphasising its validity by the account of multibody interactions between flowing species through some effective masses replacing their true (bare) masses. Pressure affects the effective masses, decreasing them and shifting the minimal viscosity and the temperature at which it is attained to higher values. The analysis shows that effective masses in the Trachenko-Brazhkin equation are typically lighter compared bare masses; e.g., for tin (Sn) the effective mass is m = 0.21mSn, whereas for supercritical argon (Ar), it changes from m = 0.165mAr to m = 0.129mAr at the pressures of 20 and 100 MPa, respectively.

Enhanced Thermoelectric Performance in Vacancy-Filling Heuslers due to Kondo-Like Effect.

To improve thermoelectric efficiency, various tactics have been employed with considerable success to decouple intertwined material attributes. However, the integration of magnetism, derived from the unique spin characteristic that other methods cannot replicate, has been comparatively underexplored and presents an ongoing intellectual challenge. A previous research has shown that vacancy-filling Heuslers offer a highly adaptable framework for modulating thermoelectric properties. Here, it is demonstrated how intrinsic magnetic-electrical-thermal coupling can enhance the thermoelectric performance of vacancy-filling Heusler alloys. The materials, Nb0.75Ti0.25FeCrxSb with 0 ≤ x ≤ 0.1, feature a fraction of magnetic Cr ions that randomly occupy the vacancy sites of the Nb0.75Ti0.25FeSb half-Heusler matrix. These alloys achieve a remarkable thermoelectric figure of merit (zT) of 1.21 at 973 K, owing to increased Seebeck coefficient and decreased thermal conductivity. The mechanism is primarily due to the introduction of magnetism, which increases the density-of-states effective mass (reaching levels up to 15 times that of a free electron's mass) and simultaneously reduces the electronic thermal conductivity. Mass and strain-field fluctuations further reduce the lattice thermal conductivity. Even higher zT values can potentially be achieved by carefully balancing electron mobility and effective mass. This work underscores the substantial prospects for exploiting magnetic-electrical-thermal synergies in cutting-edge thermoelectric materials.

Quantum mechanics of particles constrained to spiral curves with application to polyene chains.

CONTEXT: Due to advances in synthesizing lower-dimensional materials, there is the challenge of finding the wave equation that effectively describes quantum particles moving on 1D and 2D domains. Jensen and Koppe and Da Costa independently introduced a confining potential formalism showing that the effective constrained dynamics is subjected to a scalar geometry-induced potential; for the confinement to a curve, the potential depends on the curve's curvature function. METHOD: To characterize the π electrons in polyenes, we follow two approaches. First, we utilize a weakened Coulomb potential associated with a spiral curve. The solution to the Schrödinger equation with Dirichlet boundary conditions yields Bessel functions, and the spectrum is obtained analytically. We employ the particle-in-a-box model in the second approach, incorporating effective mass corrections. The π - π ∗ transitions of polyenes were calculated in good experimental agreement with both approaches, although with different wave functions.

Visualizing the Low-Energy Electronic Structure of Prototypical Hybrid Halide Perovskite through Clear Band Measurements.

Organic-inorganic hybrid perovskites (OIHPs) are a promising class of materials that rival conventional semiconductors in various optoelectronic applications. However, unraveling the precise nature of their low-energy electronic structures continues to pose a significant challenge, primarily due to the absence of clear band measurements. Here, we investigate the low-energy electronic structure of CH3NH3PbI3 (MAPI3) using angle-resolved photoelectron spectroscopy combined with ab initio density functional theory. We successfully visualize the electronic structure of MAPI3 near the bulk valence band maximum by using a laboratory photon source (He Iα, 21.2 eV) at low temperature and explore its fundamental properties. The observed valence band exhibits a highly isotropic and parabolic band characterized by small effective masses of 0.20-0.21 me, without notable spectral signatures associated with a large polaron or the Rashba effect, subjects that are intensely debated in the literature. Concurrently, our spin-resolved measurements directly disprove the giant Rashba scenario previously suggested in a similar perovskite compound by establishing an upper limit for the Rashba parameter (αR) of 0.28 eV Å. Our results unveil the unusually complex nature of the low-energy electronic structure of OIHPs, thereby advancing our fundamental understanding of this important class of materials.