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Li3YX6(X = Cl, Br) materials are Li-ion conductors that can be used as solid electrolytes in all solid-state batteries. Solid electrolytes ideally have high ionic conductivity and (electro)chemical compatibility with the electrodes. It was proven that introducing Br to Li3YCl6increases ionic conductivity but, according to thermodynamic calculations, should also reduce oxidative stability. In this paper, the trade-off between ionic conductivity and electrochemical stability in Li3YBrxCl6–xhalogen-substituted compounds is investigated. The compositions of Li3YBr1.5Cl4.5and Li3YBr4.5Cl1.5are reported for the first time, along with a consistent analysis of the whole Li3YBrxCl6–x(x= 0–6) tie-line. The results show that, while Br-rich materials are more conductive (5.36 × 10–3S/cm at 30 °C for x= 4.5), the oxidative stability is lower (∼3 V compared to ∼3.5 V). Small Br content (x= 1.5) does not affect oxidative stability but substantially increases ionic conductivity compared to pristine Li3YCl6(2.1 compared to 0.049 × 10–3S/cm at 30 °C). This work highlights that optimization of substitutions in the anion framework provide prolific and rational avenues for tailoring the properties of solid electrolytes.

This paper discusses the process of determining the energy density and electronic properties of sodium-ion batteries with nickel doping and the manganese–oxygen combination (Na2Mn3–zNizO7) using the density-functional theory calculation in Quantum Espresso software. These materials were chosen due to their abundance in nature as an alternative to overcome the limitations of lithium materials. Moreover, Na2Mn3–zNizO7has a similar structure to lithium-based batteries that have been widely used. The Na transfer process and activation energy were simulated, and the voltage and the electronic properties of the material were analyzed using first-principles calculation. This research shows that the material (Na2Mn3–zNizO7) has the potential to be implemented as a cathode material in secondary batteries.

One of the potential strategies to solve renewable energy shortage is to design low-cost efficient photocatalysts for water splitting to aid hydrogen and oxygen evolution reactions (HER and OER). Two-dimensional (2D) materials like MXenes and transition metal dichalcogenides (TMDs) have caught special attention owing to their unique optical, electrical, and mechanical properties, but come with issues like photocorrosion and poor charge separation. Bilayer vdW heterojunctions of suitable constitutive monolayers are coming up as a potential solution to these hazards, accredited to their tunable band gap and efficient charge separation. In this paper, we have investigated the possibility of Ti2CO2–WX2(X = S, Se, Te) vdW heterostructures to perform as Z-scheme photocatalysts by employing first-principle density functional calculations, and thereby, the Ti2CO–WSe2heterostructure has emerged as the most promising material for Z-scheme photocatalysis. Further, excited-state dynamics simulation reveals that the timescales of electron transfer and hole transfer are greater (1.13 and 1.22 ps, respectively) than the maximum time limit of the photogenerated electron–hole recombination (1.0 ps) owing to the weaker non-adiabatic coupling and electron–phonon coupling. This affirms the fact that photogenerated electrons and holes with greater redox ability are preserved to drive the photocatalytic pathway. In addition to that, the free energy calculations associated with the HER and OER processes entail that the processes occur spontaneously on the surface of the heterostructure without any co-catalyst. This establishes the Ti2CO–WSe2heterostructure as a potential mediator-free direct Z-scheme photocatalyst for overall water splitting.

The results in this paper show that holes are rapidly and reversibly transferred from red-emitting InP/ZnSe/ZnS quantum dots (QDs) to adsorbed hexadecanethiol (HDT) forming an equilibrium between the thiols and the QD valence band. Photoexcitation results in populations of holes in the valence band and in slightly higher-energy shell-localized traps. Trap to valence band hole tunneling results in a photoluminescence risetime having time constants varying from 300 ps to 2 ns. The presence of adsorbed HDT eliminates the slower risetime component, indicating that hole transfer from the shell-localized traps that are closest to the particle surface efficiently competes with tunneling to the QD core. This shows that the interfacial charge transfer equilibrium is established in less than 2 ns. The population of the shell-localized traps corresponds to a reservoir of hole states that eventually tunnel to the core-localized valence band, resulting in delayed emission. The amount of delayed emission increases rapidly with ZnSe shell thickness and is slightly blue-shifted from the prompt photoluminescence. We propose an energetic model in which the HDT/valence band equilibrium is affected by the extent of valence band quantum confinement and an electric field produced by core–shell interfacial dipoles. This model explains the core size, shell thickness, and photoluminescence (PL) wavelength dependence of this equilibrium.

When semiconducting nanowires are grown by vapor–liquid–solid mechanism using gold as catalyst, the first stages, i.e., gold deposition and subsequent annealing, are of prime importance as they determine nanowire size and repartition. In this paper, we aim at identifying key factors which drive the first stages when growing nanowires, viz., surface preparation of the silicon wafer, gold deposition, and subsequent annealing. As silicon wafer surface preparation may or may not include the etching of the silica protecting overlayer, we have investigated the surface composition (a) after in situgold deposition on Si(001) substrates that are either clean or “epiready” (i.e., SiO2-covered) and (b) during the subsequent in situannealing from room temperature up to 600 °C, using soft X-ray photoelectron spectroscopy at the TEMPO beamline (SOLEIL synchrotron radiation facility). When Au is deposited directly on clean Si(001), our results reveal the formation of a AuSi alloy at surface, even when Au deposition is performed at room temperature. Postdeposition annealing prompts a complex dewetting/demixing of this initial AuSi alloy. When gold is deposited at room temperature on SiO2-covered Si(001) substrate, it slightly sinks into silica. During postdeposition annealing, a complex dynamic process takes place: As the temperature increases, gold gradually sinks into the silica and catalyzes its decomposition, which starts at 365 °C thus lower than usual (840 °C). This etching process is concomitant with Au dewetting on silica, which acts as a barrier against alloying. This gold dewetting implies local changes in surface potential and therefore local shifts of the Au–Si region toward higher binding energies. The result is a superposition of spectra, which can be used to monitor Au dewetting and therefore substrate coverage by Au. When Au finally reaches the substrate after completing the catalytic desorption of silica, it undergoes mixing with Si as on a clean Si substrate. All these results give new insights in the VLS mechanism, which is widely used for growing nanowires.

Understanding the dynamic processes involved in the interaction of hydrogen with oxides is of fundamental importance in catalysis. This paper probes the reduction of Cu2O-“29” surfaces by hydrogen at room temperature combining in situambient pressure scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. Reduction of the atomic layer thin Cu2O film is observed to be preferentially initiated at step edges and terrace defects, where perfect Cu2O(111) terraces are found to be stable toward hydrogenation under the same conditions. After a long induction period, regions of partially reduced Cu2O-“29” and metallic Cu coexist before the surface is fully reduced to Cu(111). The reduction rate strongly depends on the nature of nearby Cu step edges. We propose a mechanism for the reduction of Cu2O-“29” by hydrogen where free copper atoms from ascending metallic step edges facilitate the formation of active ensembles for H2dissociation and transfer H to the edges of Cu2O regions.

The gas diffusion layer (GDL) is one of the core components of the proton exchange membrane fuel cell. The complex internal structure of the GDL makes it challenging to accurately predict the mechanical response during clamping compression. In this study, the mechanical properties of the carbon paper-based GDL were investigated using a combination of experimental and numerical simulation. The explicit finite element method (FEM) was used to perform quasi-static compression simulations on the reconstructed GDL. The simulation accounted for the fiber dynamic contact, predicting the true deformation of the GDL. Validation between simulation and experiments was conducted, identifying the initiation point of fiber fracture failure during the compression. The effective range of the elastic constitutive model was determined. The changes in tortuosity, effective diffusivity, absolute permeability, and conductivity in different directions were examined. Reliable experimental results were obtained when the sample quantity was five. Initially, the stress–strain curve exhibited distinct nonlinear characteristics. The equivalent elastic modulus of the GDL continuously increased, stabilizing after a certain compression ratio. With a compression ratio of 27%, the elastic model could accurately reflect the mechanical properties of GDL. Beyond this range, the fiber began to fracture, at which point the stress was 0.064 MPa. Bending and frictional sliding were the main deformation modes of the carbon fibers. The gas diffusion capacity increased first and then decreased; for in-plane direction and through-plane direction, the maximum value appeared at 10 and 5% compression ratio, respectively. The permeability was reduced monotonously. The mass transfer capacity in the in-plane direction of the carbon paper was superior to that in the through-plane direction. The effective conductivity increases in through-plane and in-plane directions were 1354.8 and 57.9%, respectively, at a compression ratio of 35%. Combined with the macroscopic and microscopic levels, it provides a reference for an in-depth understanding of the compressive mechanical properties of fiber porous media and improving the performance of fuel cells.

In recent years, two-dimensional van der Waals (2D-vdW) magnets have been widely employed in spintronic devices since they can be reduced to the monolayer while maintaining structural integrity. In this paper, an interfacial effect of the heterostructure including the Co60Fe20B20(CFB) layer and Fe3GeTe2(FGT) flake is explored. At the Curie temperature (Tc) of FGT, a reduction in the magnetization of the CFB/FGT bilayer is found compared to that of CFB itself unlike at 300 K. It is possible that non-parallel magnetic moments are formed at the interface due to the strong perpendicular magnetic anisotropy (PMA) of magnetic FGT below Tc. Using a ferromagnetic resonance technique, we find that both PMA and the magnetic damping of CFB are enhanced by the FGT interface. Particularly, the PMA constant K⊥is increased by 20.2% at 300 K, much larger than that at 150 K, which indicates that the enhancement of PMA is induced by orbital hybridization at the interface instead of the magnetic proximity effect. The exchange interaction at the interface for moments between CFB and FGT may play a minor role in the enhancement of PMA of CFB induced by FGT. Also, such a less PMA enhancement at 150 K may be blocked by the magnetic interface of FGT below Tc. This research highlights that the magnetism of CFB can be modulated by the interface of FGT even at room temperature, which provides a new approach for the application of 2D-vdW magnets in spintronics.

Despite credible reports of several high-pressure electrides of alkali earth metal elements, high-pressure electrides composed of two elements of the alkali earth metal group remain a mystery. In this paper, taking the typical intermetallic compound BaMg2as a representative, we systematically investigate the high-pressure electronic behavior of alkali earth metal intermetallic compounds by using first-principles calculations in conjunction of particle swarm optimization. BaMg2undergoes phase transitions from the ambient P63/mmcphase to the high-pressure P4/nmmphase at 19.6 GPa and then to the high-pressure I4/mmmphase at 260 GPa, accomplishing an electron state transformation from nonelectride to electride. Although some electrons are trapped in the interstitial lattice of BaMg2, the high-pressure P4/nmmand I4/mmmphases exhibit different anionic electron-dominated metallicity. Although Mg and Ba have similar valence electron configurations, the electride state of BaMg2is completely dominated by Mg atoms because its electride state orbital has more favorable energy than the atomic orbital of Mg under high pressure. Different from that of Mg, the d orbitals of Ba have energy advantages over its electride state. This work not only enriches the knowledge of the family of electrides but also provides new insight into the electride formation mechanism.

Room-temperature (RT) ferromagnetic semiconductors can be used to construct new information devices, which will significantly promote the performance of applications. However, the experimental realization of such semiconductors is rarely reported and is restricted by the understanding of the intrinsic mechanism. In this sense, theoretical predictions which can provide candidates of RT ferromagnetic semiconductors for experiments are highly desired. Here, in this paper, we reported that the CrMoSe2Br2monolayer is a potential RT ferromagnetic semiconductor, which is constructed by introducing Mo atoms to substitute half of Cr atoms in the CrAB monolayers. The dynamic and thermal stabilities of the alloyed monolayers are confirmed by phonon calculations and ab initio MD simulations. Electronic structures show that the CrMoSe2Br2monolayer is semiconducting with a moderate direct energy gap. Monte Carlo simulations based on the the Heisenberg model present that introducing Mo atoms significantly increases the FM couplings, and the estimated Curie temperature is about 480 K in CrMoSe2Br2. Thus, the excellent electronic and magnetic properties endow the CrMoSe2Br2monolayer with great potential in future information devices.

Kröger–Vink diagrams (KVD) are used to visualize the concentrations of defects across different thermodynamic conditions, such as temperature and chemical potential. For doped semiconductors, KVDs provide insights into the doping effect on changing the electronic charge carriers’ concentrations. Though KVDs with fixed doping levels are widely used, calculating the fraction of each charge state of the dopant is rarely discussed and is not straightforward in comparison to calculating the same fractions when the chemical potential is specified. Therefore, this paper presents an implementation of a self-consistent algorithm that finds the correct value of the dopant’s chemical potential corresponding to a specific doping concentration. Thus, the distribution of the dopant’s charge states is consequently calculated based on this chemical potential. This algorithm facilitates exploring the maximum electronic carrier-to-dopant ratio, which is a recently introduced metric to judge the dopant’s ability to inject excess electronic carriers in a semiconductor. The hematite phase of iron oxide (α-Fe2O3) was taken as a model system, and five different dopants at different temperatures (700–1300 K) and concentrations (0.25–1%) were analyzed. The analysis shows that higher temperatures and lower dopant’s concentrations maximize this ratio for both donors and acceptors. The origins of these observations were explained based on the equilibria of both native and dopant defects depicted by the KVDs. The implications of these results on doped hematite sample preparation conditions are discussed. The herein presented algorithm and analyses have broad applicability to compound semiconductors in the dilute limit of doping.

Hydrogen bonds impact many material properties due to the bond directionality and collective strength. For them to exist, the atoms connected to hydrogen should possess high electronegativity, the distance between the interacting atoms should be less than their van der Waals radii, and there should be a charge transfer between them. In hybrid perovskites, the impact of hydrogen bonds is ascribed to several phenomena. Among them are the effect of passivation at the surface, structural stability of the mixed cation compounds, structural instability of FAPbI3, and ferroelectric behavior. In this paper, we applied a deterministic method to prove the existence of hydrogen bonds using Raman spectroscopy. This approach was successfully applied to water and is based on the emergence of a Raman mode as a result of the intermolecular charge transfer, which is not measured for the isolated molecule. With the help of DFT calculations, we attributed the Raman modes detected at room temperature (RT) for MAI and FAI and compared them with the Raman spectra of MAPbX3and FAPbX3. This comparison has shown that there are no hydrogen bonds in hybrid lead halide perovskites at RT.

In this paper, synchrotron radiation photoemission techniques are used to unravel the pending nature of the two Ba 4d components, also observed on Ba 3d lines, and commonly named Ba(α) and Ba(β). Investigations were carried out on the (001) surface of epitaxial very thin (≤20 nm) films combined with DFT calculations. Photoelectron diffraction experiments reveal different behaviors for Ba(α) and Ba(β) components. While six well-defined diffraction features corresponding to the BaTiO3bulk structure are observed for the Ba(α) component, no feature really appears in the diffraction pattern of Ba(β). This observations reveal the absence of forward scattering processes, hence this component comes mostly from surface BaO plane. Supporting these results, DFT calculations demonstrate a shift to lower binding energy (BE) only for the Ba 4d peak from the topmost BaO layer with respect to the photoelectron peak stemming from bulk layers. Hence, only one peak (the Ba(α) one) should be observed for a sample with a complete TiO2termination. This hypothesis is supported by photoemission measurements carried out at low photon energy in grazing angle emission, in order to enhance the signal from topmost layers with respect to the bulk. For each sample, the Ba(β)/Ba(α) intensity ratio is well reproduced by a model where the Ba(β) signal is only coming from the topmost surface BaO plane.

This paper has demonstrated the role of manganese (Mn) doping in cadmium sulfide (CdS) quantum dots (QDs) and their surface passivation for the fabrication of highly sensitive broadband photodetectors. These photodetectors have been fabricated in a p–n heterojunction geometry using the Mn-doped CdS (CdS:Mn) QDs with TiO2nanoparticles. The thin film of CdS:Mn QDs has been passivated with lead iodide (PbI2) for faster charge transport and broadening of the spectral response of the device. Our detailed X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy indicate a partial PbS formation, which also causes spectral broadening. In addition, this passivation process enables us to enhance the photosensitivity of the device with a spectrally flat response of quantum efficiency throughout the visible range spectrum (350–700 nm). This work also demonstrated that the photosensitivity of the device gradually increases with Mn doping with a faster photoresponse. The highest detectivity of the device was obtained with 4% Mn-doped dots with a value of ∼3.9 × 1012Jones under −0.5 V external bias with a photoresponse time of 0.2 s, indicating its very high detectivity with a fast response.

Current multiscale plasmonic systems pose a modeling challenge. Classical macroscopic theories fail to capture quantum effects in such systems, whereas quantum electrodynamics is impractical given the total size of the experimentally relevant systems, as the number of interactions is too large to be addressed one by one. To tackle the challenge, in this paper we propose to use the Madelung form of the hydrodynamic Drude model, in which the quantum effect electron spill-out is incorporated by describing the metal–dielectric interface using a super-Gaussian function. The results for a two-dimensional nanoplasmonic wedge are correlated to those from nonlocal full-wave numerical calculations based on a linearized hydrodynamic Drude model commonly employed in the literature, showing good qualitative agreement. Additionally, a conformal transformation perspective is provided to explain qualitatively the findings. The methodology described here may be applied to understand, both numerically and theoretically, the modular inclusions of additional quantum effects, such as electron spill-out and nonlocality, that cannot be incorporated seamlessly by using other approaches.

Gas sensors based on hybrid materials of reduced graphene oxide/metal oxide semiconductors are an effective way to improve sensor performance. In this paper, rGO (reduced graphene oxide) was uniformly and compactly anchored on the surface of presynthesized ZnO rods using a facile hydrothermal synthesis. The ZnO rods and reduced graphene oxide combined to form an np-type heterojunction structure for use in a nitrogen dioxide (NO2) sensor. Compared with pure ZnO rods and rGO, the ZnO rod/rGO composites display abnormal sensing behavior in the form of reversible transitions from p- to n-type sensing induced by changes in the NO2gas concentration (C) and temperature (T). Based on familiar phase diagrams, a binary (T–C) transition diagram was created in terms of the gas-sensing response, which can be directly used to design and control p–n transitions. In addition, we also found that as the doping ratios (c) change, the semiconductor type of the composite also changes. Finally, the mechanisms underlying the NO2-sensing transitions are described based on the dual conduction path model: electron transfer in the internal region and chemical reactions at the surface. This reversible p–n transition of ZnO/rGO materials upon NO2sensing is interesting and holds great potential for the efficient detection of NO2.

Nanoribbons are crucial nanostructures due to their superior mechanical and electrical properties. This paper is devoted to hybrid studies of the elastic mechanical anisotropy of phosphorene nanoribbons whose edges connect the terminals of devices such as bridges. Fundamental mechanical properties, including Young’s modulus, Poisson’s ratio, and density, were estimated from first-principles calculations for 1-layer, 3-layer, and 6-layer nanoribbons with widths of 10 Å. The data achieved from the ab initio simulations supplied the finite-element model (FEM) of the nanoribbons. The directional coefficients of strain pressure curves were estimated as Young’s effective modulus since the structure is one-dimensional (1D). The modulus values were equal to 85.8, 111.8, and 134 GPa for 6, 3 and 1 layers, respectively. Moreover, the variation in Poisson’s coefficient for the armchair direction was significantly smaller than for the zigzag direction. Monotonic changes in this twist were observed for structures with 3 and 6 layers within the plane along the zigzag axis. The phosphorene nanoribbons subjected to periodic excitation behaved similarly to those subjected to static loading, while their whippiness was inversely proportional to the length. Next, the deflection under static force, resonance frequencies, and response to a variable driving force were calculated.

The electrical 3 dB bandwidth is regularly used as a measure for the response speed of a photodetector and is estimated via various approaches in literature, ranging from direct measurements to gauged values via approximations. Great care must be taken when comparing these 3 dB bandwidths, since approximations are only strictly valid for ideal circuits. This paper demonstrates that for typical photodetectors based on new emerging nanostructured materials, namely, quantum dots and transition metal dichalcogenides, the bandwidth can deviate up to 103depending on the chosen approach for the bandwidth specification.

The ultraviolet emission of ZnO has great advantages for realizing applications in optoelectronics. Recent efforts to enhance their photoluminescence (PL) intensity have a profound importance to device efficiency. Enhanced PL spectra are always accompanied by large asymmetric broadening, and the recombination mechanism remains unclear. In this paper, the emission of ZnO thin films is enhanced by Ar and H2plasma treatments, showing an increase of 30-fold in the intensity and 4-fold in the full width at half-maximum (FWHM). The systematic time-resolved photoluminescence measurements illustrate an extraordinary recombination mechanism, as a wide range of photon energies possess identical dynamic features and temperature-dependent characteristics. The asymmetric broadening is attributed to strong electron–phonon coupling introduced by the variation of carrier distribution. As a theoretical confirmation, the multimode Brownian oscillator (MBO) model is used to quantitatively describe the line shape of spectra with a perfect agreement and evaluates the coupling strength between the primary oscillator and LO phonon. The recombination mechanism of enhanced and broadened PL spectrum is applicable to other materials with strong phonon interaction, which will be beneficial to improving the performance of optoelectronic devices.

Magnetic topological insulators (MTIs) have received considerable attention owing to the demonstration of various quantum phenomena, such as the quantum anomalous Hall effect and topological magnetoelectric effect. The intrinsic superlattice-like layered MTIs MnBi2Te4/(Bi2Te3)nhave been extensively investigated mainly through transport measurements; however, a direct investigation of their superlattice-sensitive magnetic behaviors is relatively rare. In this paper, we report a microscopic real-space investigation of the magnetic phase behaviors in MnBi4Te7using cryogenic magnetic force microscopy. The intrinsic robust A-type antiferromagnetic (AFM), surface spin-flip (SSF) + AFM, ferromagnetic (FM) + SSF + AFM, and forced FM phases are sequentially visualized via the increased external magnetic field, consistent with the magnetic behavior in the M–H curve. The temperature-dependent magnetic phase evolution behaviors are further investigated to obtain a complete H–Tphase diagram of MnBi4Te7. Tentative local phase manipulation via the stray field of the magnetic tip is demonstrated by transforming the AFM into the FM phase in the surface layers of MnBi4Te7. Our study provides key real-space ingredients for understanding the complicated magnetic, electronic, and topological properties of such intrinsic MTIs and suggests new directions for manipulating spin textures and locally controlling their exotic properties.

Metal halide perovskite (MHP) devices often show different types of hysteresis in separate voltage domains. At low voltage, the impedance response is capacitive, and the cell gives regular hysteresis. At high voltage, the hysteresis is inverted, corresponding to an inductive response that causes a negative capacitance feature. We calculate the hysteresis current due to a chemical inductor model, and we show that the current is inversely proportional to the voltage scan rate. We formulate a general dynamical model for the solar cell response in the style of neuronal models for the action potential, based on a few differential equations. The model allows us to track the transition from capacitive to inductive properties, both by impedance spectroscopy and current–voltage measurements at different voltage sweep rates. We obtain a correlation of the time constants for the capacitor and the inductor. We interpret the origin of the low-frequency features in terms of ion-controlled surface recombination. This explains the strong correlation of the low-frequency capacitance and inductor, as both originate from the same mechanism. The methodology derived in this paper provides great control over the dynamic properties of metal halide perovskite solar cells, even in cases in which there are qualitative changes of the solar cell current–voltage response over a broad voltage range.

The heterostructure CdS/CdTe is one of the most important interfaces in solar energy cells, however, its exact structure is not well-known due to the large lattice mismatch, thus hindering the studies of interfacial properties. In this paper, we present a scheme to explore the interface structures by combining the differential evolution (DE) algorithm and the neural network potential. A high-accuracy neural network potential is trained to describe the interatomic interactions, and then the interfacial structures are searched using our DE program that started from a CdS/CdTe interface model that consists of about 1740 atoms. We identify a series of interfacial structures with defects and assess their stabilities by considering the interfacial energies. We find that the CdS-like interface I is generally energetically more favorable and prefers to be defect-free under the Cd-poor condition. Therefore, the Cd-poor condition might be beneficial for improving the solar cell efficiencies by suppressing possible defect recombination at the interface. Our work provides a general scheme to study structures of complex interfaces with a large number of atoms.

The mass transfer limitation of gas products in heterogeneous photocatalytic reactors is a key step in governing the reaction efficiency, and the bubble behavior on the catalyst surface directly affects the mass transfer process. In this study, a method for the directional regulation of bubble behavior by the periodic chopping was proposed. The specific chopping modes drove the bubble to bounce on the photoelectrode surface, and the growth curve of the bouncing bubble was stepped. The bubble bouncing characteristics were directionally regulated by adjusting the chopping mode, and the bubble growth time and detachment diameter were significantly reduced. A force analysis model of the bubble bouncing process was established, and a multiphysics simulation of the bubble bouncing behavior was performed. The competition of forces is the physical mechanism that drives the bubble to bounce, and the thermal Marangoni force is the driving force that causes the bubble to return. The heat and mass transfer processes were dominated by convection, and the bubble bouncing behavior could significantly enhance convective transport near the photoelectrode surface. This paper provides an experimental and theoretical basis for promoting the bubble detachment and the heat and mass transfer rate on the gas evolving electrode surface during photoelectrocatalytic conversion.

Plagioclase crystals are earth-abundant and low-cost aluminosilicate materials with a high diffusivity of Cu at high temperatures over 1050 °C. The exploration of copper (Cu2+)-doped plagioclase crystals is hindered by the thermodynamic instability of Cu2+at high temperatures over 1050 °C. In this paper, we developed the high-temperature copper–lithium diffusion method for the preparation of blue–green plagioclase crystals doped with Cu2+ions. By combining quantitative element distribution characterization and spectroscopic measurement, we illustrate the thermodynamic mechanism of stabilizing Cu2+at high temperatures up to 1150 °C by adding Li2O in the diffusant and the diffusion process of Cu2+from the diffusant to the plagioclase crystals. Moreover, the high-temperature copper diffusion in the form of Cu+and lithium diffusion in the form of Li+are separated to further verify the diffusion process of Cu2+. The as-fabricated fascinating blue–green plagioclase crystals doped with chromogenic Cu2+ions have high application prospects in the fields of jewelry decoration materials and mineral pigments.

In this paper, the heterostructures between the BiOM (M = Cl, Br, I) (001) and the β-Bi2O3(001) crystal facet, denoted as BiOM/β-Bi2O3, are reasonably constructed. The hybrid density functional approach investigates their electronic structures, optical absorption, band alignments, and photocatalytic activities. It is found that I-doped BiOM (M = Cl, Br) can make the type I heterostructures BiOM (M = Cl, Br)/β-Bi2O3change to the direct Z-scheme with increasing I doping concentration. Under a higher I doping concentration, the BiOCl1–xIx/β-Bi2O3has a stronger reduction potential than the BiOBr1–xIx/β-Bi2O3. Significantly, the BiOI/β-Bi2O3is the direct Z-scheme heterojunction. Combining the direct Z-scheme heterostructure characters of BiOM1–xIx(M = Cl, Br)/β-Bi2O3and BiOI/β-Bi2O3with appropriate band alignments, their electrons and holes can be excited and separated highly effectively. The BiOM1–xIx(M = Cl, Br) or BiOI part has a higher reduction ability, gathers electrons, and works as the reduction catalyst. In contrast, the β-Bi2O3part has a higher oxidation ability, gathers holes, and works as the oxidation catalyst. Remarkably, the O vacancy in bismuth oxyhalides can further improve the direct Z-scheme alignment structure, accelerate the separation and migration of the photogenerated electron–hole pairs, and also enormously intensify the visible light absorption. The synergistic effect of the direct Z-scheme band alignment character and O vacancy makes the BiOCl28/32I4/32(VO)/β-Bi2O3and BiOI (VO)/β-Bi2O3present superior photocatalytic activities. The calculated results can provide insights into the designs and preparations of the visible light response BiOM (M = Cl, Br, I)-based semiconductor photocatalysts.

The rich structural polymorphism of TiO2provides an opportunity to construct a heterophase junction, which reportedly improves the photocatalyst performance. In the past, using the partial phase transition to fabricate brookite/rutile biphase materials has attracted much attention. Although many of the experiments have studied the phase transition of brookite to rutile, to date, the atomistic mechanisms and its atomic heterophase junction structure remain unclear. In this paper, the stochastic surface walking method and neural network method (SSW-NN) are utilized to map out the local potential energy surface (PES) of brookite and resolve the lowest energy barrier transition path. We show that brookite first transforms into the TiO2-II structure, and then the TiO2-II transforms into rutile with the overall orientation relation (100)B//(100)II, [010]B//[010]II, and (001)II//(101)R, [100]II//[010]R. Anatase is a byproduct rather than an intermediate phase during the brookite-to-rutile phase transition. The well-matched interfaces between brookite and TiO2-II, TiO2-II, and rutile possess spatially separated CBM and VBM, while the disordered junction between brookite and rutile shows frustrated electron/hole transport. The proposed mechanisms not only clarify the role of anatase in the brookite-to-rutile transition but also help to understand the nature of higher photocatalyst performance of the biphase.

The development of lithium batteries, including lithium-ion batteries and lithium-air batteries, is the key technological breakthrough in the field of renewable energy storage. However, to date, it is still challenging to design a lithium battery with both high specific power and stability. Specifically, the solvation structure and thermodynamic stability of various electrolytes, mostly Li salts and aprotic solvents, have not been systematically studied from an atomic viewpoint. In this paper, we studied the solution chemistry of three most common inorganic Li salts (LiClO4, LiBF4, and LiPF6) and O2in two aprotic (dimethyl sulfoxide (DMSO) and acetonitrile (CH3CN)) solvents. The Born–Oppenheimer molecular dynamics simulations and enhanced free energy samplings are employed to obtain their solvation structures, diffusion coefficients, and stability performances at room temperature. As a result, the tetrahedral Li(DMSO)4+and Li(CH3CN)4+are obtained as the stable solvation shells of Li+in DMSO and CH3CN solvents, respectively. Among the three inorganic Li salts, the stability performances are found in the order of LiClO4> LiBF4> LiPF6in both DMSO and CH3CN solvents. Compared with CH3CN, DMSO provides a more stable environment for the long-term usage of Li salts for that increases the energetic barriers of the degradation reactions of solvated Li+components. However, DMSO shows a weaker ability (than CH3CN) to transport the main redox species (solvated Li+and O2) in the electrolyte, which limits the discharging and charging rate in the batteries.

This paper presents an attempt on deconvoluting diffusion-control current (id) and surface-control current (is) from total current in a galvanostatic charge–discharge (GCD) test. Using this strategy, the pseudocapacitive behavior of nanosized Ce-CoO dispersed on graphene support was studied in detail. The results show that idis greatly affected by operating potential and occupies some proportion of the total pseudocapacitive current. The main functions of Ce in the composite material include promoting the proportion of isor inhibiting idand finally stimulating a specific capacitance (Cs) value increased from 192 to 726 F g–1. The Bode curve in the low-frequency region also proves that Ce can promote the performance of pseudocapacitance.

Surface reconstruction processes and effects of reconstructed species during the formate oxidation reaction (FOR) remain unclear, limiting the ability to guide the design of efficient stable electrocatalysts through the reconstruction–performance relationship. In this paper, globally stable structures of the adlayer–alloy interface on AgPdF alloy from fluorination-enabled surface reconstruction are predicted via the particle swarm optimization algorithms coupled with density functional theory (DFT) calculations. Various 2D surface metal fluoride (Ag,Pd)Fxadlayers and their FOR catalytic behavior are revealed on the reconstructed AgPdF alloy. Typically, the (Ag3Pd1)F4–AgPd(111) interface is a globally stable structure among all heterointerfaces, and an adlayer of (Ag3Pd1)Fxwith x= 1, 2 or x= 3, 4 on the AgPd(111) interface has a fluorine on-surface superstructure or a surface fluoride structure with one surface Pd atom coordinated by four F atoms. Unexpectedly, a metastable (Ag3Pd1)F1–AgPd(111) interface demonstrates all downhill pathways in free energy diagram and an activation energy of 0.04 eV in the rate-determining step from HCOO*bi–to HCOO*mo–, indicating a thermodynamically spontaneous reaction on the heterointerface due to its moderate d-band center and a suitable H, OH, and HCOO–adsorption. This study explores the challenge of designing nanoalloys that undergo reconstruction during catalysis and fill the gap in the reconstruction–performance relationship.

The fast emerging field of multivalent (MV) battery systems offers promising methods for addressing safety, energy density, cost, and manufacturing issues concerning currently available Li-ion battery technology, particularly in the application of large-scale energy storage devices. Although some obstacles still remain, remarkable progress has been made toward developing electrode materials for the MV systems. This paper focuses on showcasing the significant breakthroughs achieved in nonaqueous Ca-ion and Al-ion battery technologies, specifically, in terms of the advancements concerning their positive electrodes in the past three years. The crucial role of computation and machine learning techniques for the customization of existing materials and the discovery of new materials for MV battery applications are highlighted. Finally, recommendations for further MV battery related research and development are provided.

Efficient charge transfer is closely related to improvement of the performance of quantum dot (QD)-based solar cells. In this paper, the effects of surface ligands with different alkyl chain lengths ((1-dodecanethiol (DDT) and 1-octanethiol (OT)) on the electron transfer process in InP/ZnS QDs were studied by ultrafast spectroscopy. With adsorption of the electron acceptor anthraquinone (AQ), both hot electron transfer and band-edge electron transfer between the QDs and acceptor were observed. The analysis shows that there is a more efficient (hot) electron transfer process in shorter-chain ligand OT-capped QDs compared with DDT-capped QDs, which is probably because of the improved passivation and lower density of trap states for OT-capped QDs in which electron trapping may compete with electron transfer and reduce the efficiency of electron transfer. This work enhances the understanding of how the chain length of ligands affects the electron transfer process from the perspective of ultrafast photophysical properties, and it may provide valuable insight into how to improve the performance of optoelectronic devices through surface-ligand engineering.

Edge reconstruction is a major challenge for the application of black phosphorus nanosheets as anodes of lithium-ion batteries. Recently, it was reported that a lateral heterostructure of black phosphorus flakes linked with graphite flakes as an anode material is capable of operating under high rate and high capacity. This raises some interesting problems concerning the geometry, P–C bonding property, and transport property of the heterostructure. In this paper, we first demonstrated energetically the stability of the phosphorene–graphene lateral heterostructure (BP–G) employing first-principles calculations. Furthermore, it is further revealed that the phosphorus and carbon atoms of the BP–G are strongly bonded by sp2-hybridized mode, and the electronic conductivity of the combined system is significantly improved compared with that of isolated phosphorene. Besides, it is found that BP–G allows strong Li adsorption, offering a theoretical specific capacity higher than or similar to graphite and phosphorene. Li migration from the interface to phosphorene side is confirmed to be fast along the zigzag direction, owing to a low barrier of ∼0.12 eV, which is much lower than that of edge reconstructed phosphorene. These results give an underlying explanation to the performance of the BP–G as an anode of lithium-ion batteries.

Effects of adsorbed water on methanol photochemistry on TiO2surfaces is an interesting and important issue. In this paper, we have studied coadsorption and photochemistry of water and methanol on TiO2nanocrystals with different predominantly exposed facets using in situ diffuse-reflectance infrared spectroscopy and an isotope labeling technique. Preadsorbed water on TiO2exerts versatile influences on methanol photochemistry. Water competes with methanol for surface sites on TiO2; meanwhile, surface OH groups are capable of assisting methanol decomposition to methoxy species. Surface OH groups can trap photoexcited electrons, which open up photocatalytic reactions of adsorbed methanol species in the absence of O2; moreover, the acquiring surface •OH radicals can directly participate in photocatalytic conversions of adsorbed methanol species. In the presence of O2, water influences photocatalytic oxidation of adsorbed methanol species on TiO2NCs mainly by affecting methanol and O2adsorption. All these effects vary sensitively with exposed facets and surface structures of TiO2nanocrystals. These results unveil the complex nature of influences of adsorbed water on methanol photochemistry on TiO2surfaces.

In this paper, we introduce different polyhedral Au nanoparticles (AuNPs) as the core of Au@SiO2@Au and analyze the effect of internal nanogap morphology on local field enhancement. Compared with spherical Au core, polyhedral Au core has sharper edges and vertices, and it can make the plasmon resonance peaks of Au core and shell closer to each other by changing the internal polyhedron-shell nanogap morphology, so the polyhedral-Au@SiO2@Au nanoparticle can realize a broadband and tunable strong local electric field enhancement, especially for tetrahedral-Au@SiO2@Au and octahedral-Au@SiO2@Au nanoparticles. We numerically demonstrate that the polyhedral-Au@SiO2@Au nanoparticle can even produce a 100–200 nm broadband window and a 2–3 orders of magnitude stronger local electric field enhancement compared with the spherical-Au@SiO2@Au nanoparticle, which produces only a 50–60 nm narrow band. This polyhedral-Au@SiO2@Au core–shell nanoparticle is a promising plasmonic nanostructure for signal enhancement during excitation and radiation processes for enhanced fluorescence or Raman imaging, especially for multiwavelength Raman analysis of multiple reporter molecules whose signals need to be enhanced simultaneously.

Nanopore single-molecule technology, especially DNA/RNA sequencing based on nanopores, requires a high spatial resolution. In this paper, we theoretically studied the spatial resolution of the cross-disjoint mortise-confined solid-state nanopore (CDM-nanopore) structure that is formed by two perpendicular and disjoint nanochannels and a middle nanopore. When the thickness of the middle layer (nanopore) is 0 nm (i.e., the zero-depth interfacial nanopore), 0.6 nm, and 1 nm, the geometric resolution (δz) is 0.24, 0.32, and 0.39 nm, respectively. The ultrahigh spatial resolution of the CDM nanopore with an ultrathin middle layer is comparable with that of the conventional ultrashort nanopore (e.g., two-dimensional material nanopore). We also demonstrate that for cylindrical segments with a diameter difference of 0.2 nm, the current difference (δI) will reach the maximum when the middle layer is about half of the length of one segment. In addition to the high resolution of CDM nanopores with an ultrathin middle layer, its outstanding mechanical stability and low noise characteristics provide the possibility of extending the application of the CDM nanopore to DNA/RNA sequencing.

Designing the ferromagnetic/nonmagnetic (FM/NM) heterostructure with desirable low magnetic damping is important for spintronic devices to reduce the critical current density of magnetization switching. For ultrathin FM/NM films, magnetic damping from the two-magnon scattering (TMS) effect is a critical component, and suppressing TMS damping becomes one of the crucial ways to achieve low damping. In this paper, we have demonstrated the depressed linewidth in Ta (1 nm)/NiFe (3 nm)/NM (4 nm)/Ta (1.5 nm) heterostructure with Cu instead of Pt as the NM layer, where the maximal linewidth of ferromagnetic resonance (FMR) decreases from 440 to 190 Oe. And the decrease of TMS damping from 55 to 0 Oe is one of the main reasons for the lower FMR linewidth. The nonzero surface magnetic anisotropy implies that the suppression of interfacial defect scattering causes reduced TMS damping. Meanwhile, a noticeable enhancement of TMS damping from the lack of seed layer may be due to the lattice structure change. Thereby, our findings provide a way toward the design of low-damping spintronic devices.

A pair of tetraphenylethylene (TPE)-based E/Zisomers (E-TPE2PDand Z-TPE2PD) using two dicyanovinyl groups as the electron-accepting moieties have been synthesized and separated successfully. Reversible E/Zisomerization for each isomer is achieved, in which the isomerization speed from Eto Zis higher than that from Zto E. This pair of pure E/Zisomers exhibits obvious AIEE properties. Z-TPE2PDshows highly morphology-dependent solid-state photoluminescent properties, whose solid-state emission is red-shifted from 564 to 588 nm with an enhancement of crystalline degree together with a decrease in the emission intensity. In contrast, E-TPE2PDleads to a slightly blue-shifted emission of 5 nm dependent on its crystalline degree. To the best of our knowledge, the discrepancy in emissive color between TPE-based Eand Zisomers is much larger than most of the reported ones. The absence and presence of π–π interactions between adjacent PDCV units observed in their crystal packing structures are suggested to be responsible for the distinct solid fluorescence of Eand Zisomers. More interestingly, Z-TPE2PDexhibits blue-shifted mechanoresponsive luminescence (MRL) turn-on behavior when subjected to grinding, while E-TPE2PDshows a remarkable two-color photoluminescence (PL) nature. This paper offers a synthetic strategy by introducing strong polar dicyanovinyl groups into the TPE core to increase the molecular polarity difference of Eand Zisomers and facilitate their separation, which makes the exploration of distinguishing morphology-dependent solid-state PL properties possible. This is the first report on an isomeric pair of E/Z tetraphenylethene-cored luminogens displaying different MRL turn-on and dichromic behavior.

This paper studied the competing oxidization mechanism of char on a zigzag carbon functionality based on the first principles by density functional theory. Studies were carried out on different oxygen chemisorption scenarios, with and without site vacancies on the edge of the char molecule, which represent an essential char oxidation at high and low temperatures, respectively. It is shown that a process of rearrangement or migration of the atom O might happen along the active carbonaceous edge before final desorptions, except for certain direct mechanisms of CO desorption by one step. CO2can also be generated from the oxygen complex at the edge but only in an indirect way with intermediate steps. The competing characteristics were characterized and compared to produce CO and/or CO2based on the typical reaction pathways obtained. Typically, CO proved always easier to desorb when compared to CO2by thermal desorption from C(O). The model was essentially verified with theoretical and experimental results from the literature. Thus, the oxidation of carbon of char to yield CO and CO2is expected to be better recovered from the view in the microscale.

Transition metal dichalcogenides (TMDs) are essential due to their fascinating electronic and optical properties, strong exciton binding energy, and layer-dependent bandgap. They can be tuned to function as a single-photon emitter, but the quantum yield of photoluminescence of single-layer WSe2is low. There is some evidence that a bright emissive state can be produced by introducing local defects through functionalization. In this paper we use spin-polarized periodic density functional theory (DFT) to study the effect of functionalization for the specific case of cyclic carbenes. We find that the simplest of these molecules, cyclopentadiene carbene (Cyc), binds to the surface by a covalent bond leading to a substantial change in the bandgap (1.24 eV compared to 1.64 eV for the pristine surface). Moreover, there are semiflat bands below the Fermi level that originate from σ bonding and the interaction between the lone-pair p orbitals on the carbon of Cyc that bonds with Se on the TMD. Cyc is found to form a Type IIa heterojunction before and after contact with the surface, where the “a” refers to ordering of the energy levels where the TMD levels have the larger splitting and “b” to the reverse. The effect of various electron-withdrawing and electron-donating groups on Cyc is investigated, and it is found that the direct bandgap and heterointerfaces can be chemically tuned with covalently bound functional groups. With an electron-withdrawing group (EWG) such as −CHO, −COCl, and −CN attached to Cyc, a Type III//Type IIa interface is formed, whereas all other EWGs used in this study form a Type IIa junction, before and after contact to the surface. The electron-donating groups (EDG) form Type Ib//Type Ia junctions, and in particular, we find that the system WSe2+ Cyc-Me band structure consists of semiflat bands at valence band maxima localized on Cyc-Me and the conduction band minimum is coupled between the surface and functional group with a direct bandgap of 0.88 eV. Hence, we predict that the Cyc-Me-functionalized monolayer WSe2will produce a red-shifted bright emissive state. We also find that carbenes with the Cyc all-carbon ring have (1) a triplet ground state and (2) form covalent bonds to WSe2, while heterocyclic carbenes (1) have a singlet ground state and (2) do not form covalent bonds to WSe2.

Exploring 2D electrode materials with high quantum capacitance (CQ) is particularly important to improve the energy density of electrical double-layer capacitors. Generally, the structure and composition of materials determine their capacitance characteristics. In this paper, the effects of co-doping of N and transition metal (TM = Sc–Zn) atoms on the structure, stability, electronic, and capacitive properties of silicene were studied by first-principles calculation. Our results show that the co-doped TMNx–Si systems, especially TMN3–Si, are more stable than the silicene system doped with N or TM atoms. TMNx–Si systems have more advantages than single-doped silicene and co-doped graphene in improving CQand surface charge density (Q). Among all TMNx–Si systems studied, ScN2–Si has the best CQand Qperformance, with maximum values 224.88 μF/cm2and 74.41 μC/cm2, respectively. Furthermore, it is observed that the CQand Qvalues of ScN2–Si increase monotonically with the increase of doping concentration, but the bias position corresponding to the maximum CQdoes not change and remains at −0.6 V, which is obviously better than the co-doped graphene system. In the studied systems, except Sc and Ti, the CQand Qvalues of TMN3–Si are obviously higher than those of TMN2–Si and TMN1–Si.

Size-dependent change of the electronic band structure is one of the key features of nanoparticles in the quantum confinement region. CuFeS2nanoparticles have a strong absorption feature in the visible region that has, controversially, been described as neither an excitonic transition nor a free carrier plasmon oscillation. Instead, the absorption feature in CuFeS2nanoparticles has been attributed to quasi-static optical resonances from inter-band transitions between the valence band (VB), intermediate band (IB), and conduction band (CB). As such, we hypothesized that the feature should be subject to quantum confinement effects through modification of the electronic bands. In this paper, we show experimentally that the optical resonance absorption peak red-shifts and the optical band gap blue-shifts as the particle size decreases. Through density functional theory (DFT) and the tight binding (TB) modeling, we elucidate the size dependence of the band structure, especially focusing on the change in the IB. Using a Lorentzian oscillator optical model to simulate the absorption spectrum with inputs from the DFT-calculated band structure and band shifts from the TB model, we find that the size-dependent shifts of the optical resonance peak position in CuFeS2are due to a tri-band quantum confinement effect that results in both the VB to IB and IB to CB gap expansion that accompanies a decrease in particle size. We also find that the transitions between the IB and CB play only a minor role in the optical spectrum. Moreover, the linear optical Lorentzian model predicts that the optical resonance peak is tunable across the visible range by partially filling the IB, lowering the CB, or expanding the IB.

In this paper we report the classification of all 394 magnetic rod groups into seven spin splitting prototypes, in analogy to a similar classification previously reported for the 1651 magnetic space groups and 528 magnetic layer groups. According to this classification, electrically induced (Pekar–Rashba) spin splitting is possible in the antiferromagnetic (AFM) structures described by magnetic rod groups of type I (no antiunitary operations) and type III, both in the presence and in the absence of the space inversion operation. A novel symmetry-based procedure is proposed for determining spin projection distribution in nanorods. DFT calculations are performed for cobalt oxide based nanorods with magnetic symmetry P63mc(type I) and P63′mc′ (type III), corresponding to two different AFM spin distributions over cobalt atoms. In agreement with group-theoretical analysis, a colossal spin splitting (on the order of electronvolts) is obtained for the nanorod described by the magnetic symmetry group of type I.

Ti doping can improve the photoelectrochemical water splitting performance of hematite. However, the effect of doping on regulating small polaron hopping in the bulk and charge transfer properties on the solid–liquid interface is not fully understood. In this paper, we investigate the effects of titanium doping on hematite by decoupling a hematite homojunction structure into bulk and surface layers. We found that 3% Ti doping remarkably reduces the small polaron hopping (SPH) barrier, which leads to the high bulk charge transport, and 5% Ti doping significantly passivates the recombination of the surface states (r-SS) of hematite and promotes the conversion of the surface holes to long-lived reaction intermediates (i-SS) on the solid–liquid interface, which leads to the high surface charge transfer. Based on the above results, we report first an unconventional Ti-doped hematite homojunction design that is established with 3% Ti-doped hematite as the underlayer and 5% Ti-doped hematite as the surface layer. The homojunction exhibits a significantly enhanced photocurrent density (1.27 mA cm–2) compared to that of the typical type-II hematite structure at 1.5 VRHE. This work has well demonstrated a new homojunction design strategy for enhancing the photoelectrochemical water splitting.

Niobium oxides have a prominent role in many technological applications, including electrochemical energy storage where they are employed as anodes for lithium- and sodium-ion batteries, hybrid supercapacitors, electrocatalysts in vanadium redox flow batteries, and electrochemical support in fuel cells. Owing to the great complexity of the available coordination environment, they can host other transition metals without phase changes. In this paper, multiple techniques are employed, for the first time, to study the influence of iron cations on the structural and functional properties of monoclinic and orthorhombic FeNb11O29. The element-selectivity of X-ray absorption spectroscopy and Mössbauer spectroscopy demonstrated the disorder of Fe3+cations over the six octahedral sites of FeNb11O29. Ab-initioDensity Functional Theory calculations were used in tandem with spectroscopic techniques to confirm the cationic disorder of the material and link its implications to the conductivity investigated with electrochemical impedance spectroscopy. The paramagnetism given by Fe3+was confirmed with muon spin relaxation spectroscopy. The differences between FeNb11O29and other analogous niobium-based compounds were rationalized and discussed, in view of their electrochemical applications.

Molecular dynamics (MD) simulations have long had an important role in the study of equilibrium and nonequilibrium phase transitions. However, the effects of finite system sizes and periodic boundary conditions on such simulation are still not fully understood. In the present paper, we investigate this issue using simulations of the homogeneous melting of superheated crystals, specifically the effect of system size on the delay time before melting (which we call “melting time”). Because melting is a random and relatively rare event, we perform a systematic and extensive MD simulation study of a simple molecular system, solid-phase argon in a perfect fcc crystal superheated above the melting point. Using extensive replicate simulations, we first confirm that the distribution of melting times is accurately characterized by a gamma distribution. Next, we use the model of melting being triggered by random dislocations to derive an equation for the mean melting time as a function of system size and show that this model well-matches our MD data over a range of periodic boxes containing from 256 to 296,352 argon atoms. This equation shows that the system-size effect is inversely proportional to the number of atoms (or equivalently, proportional to L–3with Lbeing the side length of the periodic box) and could be used as a correction factor for melting times calculated in finite systems. We also study the effects of temperature on melting and find that the mean melting time exponentially decreases to a nonzero asymptotic value with increasing temperature. We observe that the melting time distributions shift toward more Gaussian-like forms of the gamma distribution (i.e., with larger values of the shape parameter) at elevated temperatures. Finally, we also present the results of the melting of water ice Ihto show that our findings apply to molecules and melting processes more complex than simple Lennard-Jones systems.

This paper explores the stability and physical properties of double-walled carbon nanotubes and the bilayer graphene obtained from their unfolding. It can be found that the stability is almost unchanged within a certain range of diameter of the double-walled carbon nanotubes. As the diameter of the carbon nanotubes increases to around 27.798 Å, the rising average atomic energy indicates a decrease in their stability. The smallest diameter group in the zigzag-shaped DWCNT has the lowest energy and the highest stability, while the largest diameter group of armchair-shaped nanotubes has the highest energy and the worst stability. Single-walled carbon nanotubes have a tendency to metallize when combined into double-walled carbon nanotubes. The metallization trend of carbon nanotubes is influenced by the tube diameter and chiral index: as the tube diameter increases, its curvature becomes smaller and the potential difference increases, and the metallization trend becomes more pronounced. As the curvature decreases to zero, the semiconducting double-walled carbon nanotubes turn into metallic bilayer graphene as the surface gradually flattens out. However, by unfolding the (18,0)@(27,0) zigzag-shaped carbon nanotubes, which originally have metallic properties, the resulting graphene has semimetallic properties. Usually, π-bonds play a role in the interlayer coupling of bilayer graphene structures and double-walled carbon nanotube structures. Therefore, as the curvature decreases, the π-bonding of the carbon nanotubes increases the binding energy of the two layers. This further explains the nanotube unfolding leading to metallization. With the exception of the group (18,0)@(27,0), the electrons are mainly concentrated in the outer tube and the inner layer is almost completely depleted. During the unfolding process, electrons migrate toward the inner tube, arriving at the inner layer as the curvature approaches zero. So this bilayer graphene obtained by (18,0)@(27,0) double-walled carbon nanotube unfolding does not have metallicity.

Optical spectroscopy techniques represent a powerful tool to study the vibrational modes of nano-objects and address both their intrinsic properties (related to nanoparticle morphology, crystallinity, and local environment) and their interaction with light, which plays a key role in nanophotonics and optomechanics applications. In this paper, we report low-frequency inelastic light scattering measurements on single gold nanocrystals, combined with detailed characterizations of their morphology and environment using transmission electron microscopy and tomography and numerical simulations of their optical and vibrational responses. Our studies confirm the conclusions of previous ensemble measurements regarding the large impact of the nanoparticle crystallinity on inelastic scattering spectra. Moreover, their single-particle character allows us to address subtle shape and environment effects. We show that slight nanoparticle shape anisotropies induce further splitting of Raman-active modes. We also demonstrate that local environment anisotropies lead to richer inelastic light scattering spectra and allow the detection of vibrational modes predicted to be Raman-inactive by usual Raman selection rules, which are based on the (here invalid) assumption of a symmetric internal electric field.

In photothermal heterodyne imaging (PHI) experiments a time-modulated pump beam heats the sample, creating a thermal lens that is detected by a nonresonant probe. This technique is very sensitive and has been used to study a variety of systems. The extent of heat diffusion in the system depends on the time scale for the experiment, which is determined by the pump beam modulation frequency. In this paper the way the spatial resolution in PHI microscopy changes with modulation frequency was studied through experiments and heat transfer simulations on gold nanoparticles. The experiments were performed with both focused and widefield pump beams. For a focused pump beam, changing modulation frequency had no effect on the spatial resolution. A small frequency effect was observed for a widefield pump, but the magnitude was much less than that expected from the thermal diffusion lengths in the system. The simulations also showed a small frequency dependence for the spatial extent of heating, consistent with the measurements. This arises because the system rapidly reaches a steady-state condition in these experiments, where the rate of optically heating the particle matches the rate of heat dissipation. In this limit the temperature profile around the particle simply decays inversely with distance and is independent of the thermal diffusion length.

While the effects of the morphology and composition of plasmonic substrates in Surface-Enhanced Raman Spectroscopy (SERS) are widely studied, surface chemistry and, more specifically, the role of preadsorbed species on colloidal substrates (i.e., stabilizers and synthesis byproducts) are typically less explored. In this paper, a surfactant-free synthesis of sparingly capped bimetallic colloidal AuAg nanostars was selected as a basis to (1) examine the effect of varying stabilizers and (2) systematically assess the impact of the resulting surface environment on SERS intensity. The latter entailed the characterization of the colloidal formulations in terms of optical reproducibility, suitability for analytical applications, long-term colloidal stability, and SERS performance. Emphasis was given to the elucidation of the stabilizer–metal interactions, which were studied by electrophoretic light scattering and infrared spectroscopy. It was found that the capping process is the result of chemisorption to an essentially neutral alloy and that the capping environment has effects on the SERS response that can overtop those caused by nanoparticle morphology. The model stabilizer, citrate, was found to weakly chemisorb (−4.36 ± 0.08 and −4.58 ± 0.05 kJ/mol at 10 and 20 °C, respectively) to the bimetallic surface in a positively cooperative fashion (nHill> 1) via the unidentate mode.

Lead halide perovskites have drawn considerable attention on account of their potential applications in solar cell and optoelectronic devices. To realize such technological possibilities, the optical characterizations of these materials must be assessed. This paper presents a comprehensive study of the temperature-dependent optical properties of CH3NH3PbBr3single crystals between 4.5 and 400 K within an energy range of 0.73 to 6.42 eV determined through spectroscopic ellipsometry. The profile of the room-temperature refractive index was typical of a semiconductor and decreased markedly with an increase in temperature with thermo-optic coefficients of approximately −4.18 × 10–4and −3.29 × 10–4K–1at 600 and 1200 nm, respectively. The cooling–heating cycles of the extinction coefficient reflected the thermal hysteresis of the first-order orthorhombic–tetragonal structural phase transition. Moreover, the Urbach energy, fundamental band gap, exciton peak position, exciton binding energy, and interband transition energies were considerably affected during the structural phase transitions of orthorhombic–tetragonal I at 130 K, tetragonal I–tetragonal II at 150 K, and tetragonal II–cubic at 240 K. These results provide crucial information for the design and fabrication of lead halide perovskite-based devices at various temperatures.