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Porous aluminum oxide (PAOX) is one of the most studied examples of spontaneous self-organization in electrochemistry. Despite the intense research efforts over more then 50 years, there is still no overarching theory that is able to explain and predict the electrolyte-specific self-assembly potentials. Therefore, in this paper, we present the derivation and application of a consistent theoretical framework that allows us to determine this potentials for all employed electrolytes at which the highest proportion of hexagonally arranged pores can be expected. The model is based on the idea that the pores can be regarded as invariant physical objects during a stationary electrochemical process. This makes it possible to use a multinomial coefficient to determine an extreme point at which entropy production becomes minimal when a hexagonal pore arrangement is present. Therefore, the self-arrangement potentials can be identified as the argument of the extreme point.

The development of inexpensive and efficient Co-based heterogeneous catalysts for hydroformylation reactions remains an enormous challenge. In this paper, N-doped carbon supported CoFe bimetallic catalysts (CoFe/NC) are successfully synthesized through a simple thermal decomposition of a mixture of Co(acac)2and Fe(acac)3, and melamine with activated carbon in N2atmosphere. With the CoFe/NC-800 as the catalyst, hydroformylation of diisobutene proceeded smoothly in THF under 4 MPa syngas at 130 °C to obtain 92% conversion of diisobutene and 79.6% selectivity to isononyl aldehydes. Detailed studies revealed that the N-doped carbon supported FeCo alloy may be the active species in which nitrogen might act as ligand played an important role in improvement of catalytic performance of hydroformylation reactions. The present study provided meaningful insights into tuning the catalytic performance of non-noble metal heterogeneous catalysts for carbonylation reaction.

There is growing demand for convenient and cost-efficient ethanol sensing techniques in daily life and industry. However, the complexity, high cost, and large volume of the equipment hinder the widespread use of conventional ethanol sensing techniques. Here, we introduce a test paperlike visualized label-free ethanol sensing platform by taking advantage of the instability of 2D Ruddlesden–Popper perovskite in ethanol. The photoluminescence of PEA2Csn–1PbnBr3n+12D perovskite changes from deep blue to green distinctly when exposed to ethanol. A cheap demo ethanol test paper is fabricated by this 2D perovskite and paper using a simple method, demonstrating interesting rapid and convenient ethanol sensing performance. Crystal analysis, constituent analysis, spectral analysis, and molecular dynamic (MD) simulation reveal the crystal structure transformation from 2D to 3D induced by the migration of PEA+cations in the original 2D perovskite when exposed to ethanol. In addition, a chemiresistive sensor based on the 2D perovskite and on the 2D–3D phase transformation is developed and demonstrates a high ethanol detection sensitivity with a limit down to 0.7 ppm. The photodetector fabricated by the 2D perovskite also demonstrates tunable sensitivity upon the controllable 2D–3D transformation. This remarkable colorimetric, chemiresistive, and photosensitive perovskite is expected to highlight its future application and be a supplement to the existing ethanol sensing and photodetector techniques.

Porous magnetic nanomaterials are attracting increasing attention due to their potential applications in environmental remediation, catalysis, biomedical fields, and magnetic storage media. This paper presents a leaching-based pore engineering approach for the synthesis of porous γ-Fe2O3. This environmentally benign approach uses a citrate buffer for the leaching process. The citrate ligands play a role by binding to surface/interface ions and leaching them into the solution, affecting micropore widths. Concurrently, the citrate ligands also lixiviate smaller-sized particles in the size distribution, resulting in a 6% increase in the average mesopore size. A two-level hierarchical pore size regime is created. The smaller size regime results in a 33% increase in adsorption capacity, and the bigger size regime leads to a 36% enhancement in the mass transport rate of methylene blue (MB) in γ-Fe2O3nanoparticles leached for 6 days. During ultrasonication for MB adsorption studies, a dynamic pore evolution is observed, leading to a remarkable 183% increase in the MB adsorption capacity for sixth-day leached samples after 60 min. Changes in the pore width influence interparticle magnetic interactions. The blocking temperature decreases from 126 K in the as-prepared sample to 116 K in the sixth-day sample. This study highlights the potential of the citrate leaching process for pore engineering.

This work focused on studying the synthesis of zinc selenide (ZnSe) particles using a methodology based on a two-level factorial design (23). Subsequently, based on the results obtained, the synthesized ZnSe structures were chemically doped with nitrogen and then supported on graphene oxide (GO). The synthesized compounds were evaluated as photocatalysts for the degradation of lignin, a complex molecule derived from paper production processes. The ZnSe was prepared through a chemical route using sodium selenite and zinc nitrate as precursors, and it was processed in an autoclave under specific conditions of time, temperature, and concentration. In the second stage, one of the ZnSe compounds was doped with nitrogen in a microwave reactor using urea or thiourea as nitrogen sources. These compounds were supported on GO to enhance their photocatalytic performance. Afterward, the samples were characterized with field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and ultraviolet–visible (UV–vis) spectroscopy. Also their specific surface area was determined, and degradation studies under UV and visible energy irradiation were carried out. It was determined that nitrogen-doped ZnSe/GO samples showed an improved performance for lignin degradation of 93% under UV irradiation and 40% under visible irradiation.

Two-dimensional transition-metal dichalcogenides (TMDs) have attracted significant attention due to their unique layer-dependent electronic properties. Yet the growth of large-area TMDs with controllable layers has remained challenging. In this paper, we report the robust synthesis of large-area monolayer MoSe2films using confined chemical vapor deposition. The size of monolayer MoSe2films can reach approximately 1 cm. We systematically investigated the influence of growth temperature, gas flow, the Se/Mo ratio, and sodium chloride on the synthesis process. Additionally, we propose a method for growing bilayer AA and AB-stacked MoSe2. Bilayer MoSe2nanoribbon, twisted bilayer MoSe2, and substrate-mediated aligned bilayer MoSe2are also produced. Distinct optical properties observed in the Raman and photoluminescence spectra of bilayer MoSe2indicate different interlayer interactions. Our study enhances the understanding of the synthesis mechanisms behind monolayer and bilayer TMD materials and provides insights into controlling interlayer interaction in few-layer TMDs.

This paper presents the linear and nonlinear optical (NLO) properties of two donor–acceptor organic materials, namely, N,N-dimethyl-4-((E)-(4-((E)-((5-phenylthiophen-2-yl)methylene)amino)phenyl)diazenyl)aniline Aand (E)-4-((E)-(4-nitrophenyl)diazenyl)-N-((5-phenylthiophen-2-yl)methylene)aniline B. The studied compounds differ from each other by the nature of the substituent (donor or acceptor) on the azobenzene moiety, giving rise to D−π–D and D−π–A systems, respectively, for Aand B. The thin-film deposition process was carried out using two different techniques: physical vapor deposition (PVD) and spin-coating. The aim of this work is to elucidate the influence of both the molecular structure of the compounds and thin-film deposition technique on their linear and nonlinear optical responses. Absorbance, photoluminescence, and decay time were used to measure the linear optical properties, while second and third harmonic generation techniques were used as tools for the nonlinear optical responses. The comparison of the results obtained for both Aand Bindicates a much better NLO performance with a value of 8.18 ± 0.09 pm V–1for compound Bwith a D−π–A shape and a value of 1.32 ± 0.07 pm V–1for compound Awith a D−π–D structure. A more detailed analysis of the NLO properties revealed a noteworthy finding: the compounds exhibited considerably elevated third-order nonlinear susceptibility values in comparison to the reference material, with discrepancies spanning 1–2 orders of magnitude. Of particular interest was compound B, which demonstrated the highest χ(3)elecvalue equal (225.91 ± 0.92) × 10–22m2V–2. The research was completed by theoretical quantum chemical calculations, which included the determination of dipole moments and the evaluation of molecular orbital frontier highest occupied molecular orbital and lowest unoccupied molecular orbital energies. These comprehensive studies demonstrate the significant potential of azo-based phenylthiophene derivatives in optoelectronics and quantum optics applications and also show that it is a valuable candidate for the production of organic light-emitting diodes.

While extensive research has been conducted on gas adsorption-induced segregation in transition metal (TM) alloys, the specific case of water vapor, one ubiquitous gas in natural environments, has not been well studied. In this paper, we employ density functional theory (DFT) calculations coupled with thermodynamic analysis under reaction conditions to quantitatively describe the phenomenon of water-vapor-induced segregation in 24 TM impurities doped in the Cu host. Our results reveal that the adsorption of water molecules significantly influences the segregation energies of early and middle TM impurities in different Cu surfaces. We further elucidate the temperatures and pressures that lead to strong water-vapor-induced segregation. The segregated impurities could activate the surface for water dissociation, a critical step in the water–gas shift reaction. This finding provides new knowledge of bimetallic alloy segregation under reaction conditions and helps us understand the working mechanism of Cu alloys in material science and catalysis.

In this paper, the local bonding structure in amorphous zinc tin oxide (a-ZTO) is probed using a combination of XANES and EXAFS techniques at the Zn and Sn K-edges to gain insight into charge carrier generation in the material. a-ZTO is prepared using two growth methods; spray pyrolysis and magnetron sputtering. It is seen that a-ZTO grown by magnetron sputtering shows no changes in the chemical environment as the cation ratio is varied; meanwhile, XANES analysis of spray pyrolysis grown samples shows alterations to spectra likely due to the effects caused by different precursors. Although a slight shift in Sn–O bond length is visible between magnetron sputtered and spray grown samples, no correlation could be discerned between bond length and variation in cation ratio. It is concluded that a-ZTO, while amorphous over longer ranges, is locally composed of ZnO and SnO2“building blocks”. An alteration in the cation ratio changes the hybridization at the conduction band minimum, resulting in the observed variation in the mobility, charge carrier concentration, and bandgap.

Sulfamethoxazole has been extensively detected in aquatic environments worldwide, posing a great risk to human health. Although clay minerals are effective adsorbents for contaminants, investigations of the adsorption of sulfamethoxazole on clay minerals remain limited. In this paper, the adsorption of anionic sulfamethoxazole (SMX–) from bulk to layered double hydroxides (LDH) surface was simulated by molecular dynamics. The electrostatic interaction between LDH and SMX–drove the adsorption. Four adsorption configurations of SMX–were identified: two with NO3–ions inserted between SMX–and the LDH surface, one via water bridging and one directly forming hydrogen bonding with the hydroxyl hydrogen atoms of LDH. The adsorbed SMX–exhibited significantly lower diffusion coefficient than that in the bulk, indicating that LDH has an advantage over common clay adsorbents (e.g., montmorillonite) in removing SMX–from water. The adsorption process was demonstrated to be enthalpy-driven by thermodynamic analysis. The free energy well in the weakly ordered water layer was deeper than that in the strongly ordered water layer, which explained why SMX–preferred to stay in the former. To enter the free energy barrier in the latter, SMX–was required to overcome the barrier by exchanging with adsorbed NO3–ions or breaking the ordered water layer.

Here, we present a one-step synthesis method of nickel–ruthenium materials, based on electrodeposition from an ethylene glycol-choline chloride (ethaline)-based bath containing inorganic additives. The electrochemical codeposition of Ni and Ru was carried out onto carbon fiber paper (CFP) under constant potentials. The morphology and composition of the obtained materials have been examined by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. It has been revealed that depending on deposition conditions, either branch-like or porous, mostly amorphous structures are formed on the CFP support. Selected Ni–Ru materials were subjected to thermal selenization, and their electrocatalytic properties toward the hydrogen evolution reaction were evaluated in both 0.5 M H2SO4and 1.0 M KOH solutions. The experimental results demonstrated a notable enhancement in activity compared to that of Ni–Se materials. Moreover, the NiRuSe materials exhibited good stability over 100 h of continuous electrocatalysis, indicating their large potential as durable electrocatalysts for hydrogen production.

The proton exchange membrane fuel cell (PEMFC) is one of the most important devices for the conversion of hydrogen energy to electricity. However, it is difficult to obtain an interfacial gas–liquid mass transfer balance at varying humidity. In this work, buffer layers were prepared at the interface of the gas diffusion layer (GDL) and catalyst layer. Different inorganic oxides (SiO2, Al2O3, and CeO2) were used to modify the morphology, hydrophobicity, and gas permeability. It is found that particle size and agglomeration degree in the slurry significantly influence the physicochemical characteristic of buffer layers. The membrane electrode assemblies (MEAs) were operated at varying humidity levels to evaluate water management efficiency. Compared with a commercial GDL, these buffer layers effectively improve the interfacial mass transfer balance. Significantly, for the buffer layer containing CeO2, the rough surface and porous structure accelerated oxygen transfer and water removal. The mean maximum power density at varying humidity was 1.562 W cm–2, which was 16.6% higher than that of an MEA containing a commercial GDL. In addition, the phenomenon of the gas–liquid separate flow process was also verified by interfacial two-phase flow simulation. According to electrochemical impedance spectroscopy, the charge transfer resistance and mass transfer resistance of MEAs containing a buffer layer were effectively controlled. In summary, this paper pointed out a novel strategy to improve the interfacial mass transfer efficiency of PEMFCs at complex operating conditions.

With the fast development of the perovskite solar cell, its energy conversion efficiency has improved rapidly. In this paper, a CH3NH3PbI3–xClxorganic–inorganic perovskite solar cell (PSC) was successfully prepared by the one-step solvent engineering method, and the planar heterojunction perovskite solar cell was optimized by interface engineering of the cathode interlayers. It was found that TiCl4treatment could effectively reduce the TiO2surface roughness, decrease the surface defects, improve the perovskite thin film crystallinity, and reduce the charge carrier recombination; hence, the short-circuit current density of PSCs and charge extraction and collection efficiencies were enhanced. Furthermore, PC60BM fullerene treatment could optimize the contact condition and reduce the interfacial potential loss. The device hysteresis effects after PCBM treatment were also reduced. The combination of TiCl4and PC60BM treatments could largely improve the PSC device performance with a power conversion efficiency of 16.4% due to the synergetic effect.

InP based quantum dots (QDs) are coming in a big way as an alternative to toxic Cd, or Pb based QDs. Unlike many literature reports in this work, green-yellow-orange-red emitting highly photoluminescent (PLQY as high as 65%) and photostable InP/ZnSeS core/alloy shell quantum dots (CAS QDs) have been synthesized using a less toxic, air-stable aminophosphine precursor (P(DMA)3). Unlike literature predictions in this paper, we show that green-yellow-orange-red emitting InP based alloyed QDs can be prepared with InCl3only. We report here the hitherto unobserved and quite interesting excitation wavelength dependent PLQY for all of these green-yellow-orange-red emitting InP based CAS QDs. PLQY increases monotonically with increasing excitation wavelength. Significant deviation of the PL excitation spectrum from the absorption spectrum has been observed in the shorter wavelength region. This observation is perhaps because the surface mediated nonradiative pathways predominate over radiative charge carrier recombination when excited at shorter wavelength. PL decay for these QDs generally follows a triexponential decay equation with the shortest lifetime of 3–10 ns, the moderate one with a lifetime of 24–30 ns, and the longest one with a lifetime > 60 ns. Moderate and long lifetimes have been shown to be associated with two mutually interdependent excited-state decay channels, and the competition between these two decay channels dictates the PLQY of these CAS QDs. The moderate lifetime has been shown to be associated with an electron–hole recombination process, and the long lifetime is associated with delayed emission from the band edge due to interaction with the manifold of shallow traps. Quite interestingly, amplitude of the moderate lifetime (dynamical property) has been observed to be correlated with the PLQY (spectral property). PL decay for all of these InP based CAS QDs has been observed to be excitation wavelength independent. However, PL decay gets slower with increasing monitoring wavelength. Thus, the presence of shallow trap states is evidenced. Single particle blinking dynamics of InP based CAS QDs has been investigated for the first time. We could achieve the lowest reported magnitude of the mONexponent for InP based QDs and the value is 1.19, which speaks about the much longer On-times or, in other words, superiority of our InP based CAS QD system in comparison to other reported InP based QDs, for example, InP core only, or InP/ZnS, InP/ZnSe/ZnS, InP/GaP/ZnS core/shell or core/shell/shell QD systems.

One of the major problems facing the successful development of Li–O2batteries is the decomposition of nonaqueous electrolytes, where the decomposition can be chemical or electrochemical during discharge or charge. In this paper, the decomposition pathways of dimethoxy ethane (DME) by the chemical reaction with the major discharge product, Li2O2, are investigated using theoretical methods. The computations were carried out using small Li2O2clusters as models for potential sites on Li2O2surfaces. Both hydrogen and proton abstraction mechanisms were considered. The computations suggest that the most favorable decomposition of ether solvents occurs on certain sites on the lithium peroxide surfaces involving hydrogen abstraction followed by reaction with oxygen, which leads to oxidized species such as aldehydes and carboxylates as well as LiOH on the surface of the lithium peroxide. The most favorable site is a Li–O–Li site that may be present on small nanoparticles or as a defect site on a surface. The decomposition route initiated by the proton abstraction from the secondary position of DME by the singlet cluster (O–O site) requires a much larger enthalpy of activation, and subsequent reactions may require the presence of oxygen or superoxide. Thus, pathways involving proton abstraction are less likely than that involving hydrogen abstraction. This type of electrolyte decomposition (electrolyte with hydrogen atoms) may influence the cell performance including the crystal growth, nanomorphologies of the discharge products, and charge overpotential.

Flashing electron ratchets oscillate a periodic asymmetric potential to rectify nondirectional forces and thereby produce directional transport of electrons with zero source-drain bias. The relationship between the oscillation frequency of the potential and the ratchet (short-circuit) current reflects microscopic mechanisms of charge transport within the device. This paper describes experimental mappings of the “optimal frequency(ies)” of the ratchet fpeak—the oscillation frequencies that produce the largest ratchet current—to the carrier concentration, nh, and to the linear field effect transistor mobility, μh, for a poly(3-hexylthiophene-2,5-diyl) (P3HT) transport layer. Measurements on multiple devices, multiple P3HT films per device, and a range of annealing and photoexcitation conditions yield the empirical relationships fpeak∝ nhand fpeak∝ μh2/3. Finite-element simulations suggest the sublinear relationship between mobility and peak frequency arises due to a combination of damped and inertial motion of the holes. This work also provides evidence that the frequency response of ratchets is sensitive to multiple length scales of asymmetry encoded within the periodic electrical potential. These multiple asymmetries cause changes in the polarity of the ratchet current at points within the frequency response, a long-mysterious characteristic of particle ratchets called “current inversion”, by encouraging transport in opposite directions in different frequency regimes.

Colloidal nanocrystals are an interesting platform for the design of low cost optoelectronic devices especially in the infrared range of wavelengths. Mercury chalcogenides have reached high maturity to address wavelengths above the telecom range (1.5 μm). However, no screening of the surface chemistry influence has been conducted yet. In this paper, we systematically probe the influence of a series of ligands, Cl–, SCN–, 1,2-ethanedithiol, 1,4-benzenedithiol, 1-octanethiol, 1-butanethiol, As2S3, and S2–, on the photoconductive properties of HgTe nanocrystal thin films. A high bandwidth, large dynamic transient photocurrent setup is used to determine the photocarrier dynamics. Two regimes are clearly identified. At the early stage (few nanoseconds) a fast decay of the photocurrent is resulting from recombination and trapping. Then transport enters in a multiple trapping regime where carriers present a continuously decreasing effective value of their mobility. The power law dependence of the conductance can be used to estimate the trap carrier density and determine the value of the Urbach energy (35–50 meV). We demonstrate that a proper choice of ligand is necessary for a trade-off between the material performance (μτ product) and the quality of the surface passivation (to keep a low Urbach energy).

Dissociation of CO2molecules in plasma is a subject of enormous importance for fundamental studies and in view of the recent interest in carbon capture and carbon-neutral fuels. Vibrational excitation of the CO2molecule plays an important role in the process. The complexity of the present state-to-state (STS) models makes it difficult to find the key parameters. In this paper we propose, as an alternative, a numerical method based on the diffusion formalism developed in the past for analytical studies. The nonlinear Fokker–Planck equation is solved by the time-dependent diffusion Monte Carlo method. Transport quantities are calculated from STS rate coefficients. The asymmetric stretching mode of CO2is used as a test case. We show that the method reproduces the STS results or a Treanor distribution depending on the choice of the boundary conditions. A positive drift, whose energy onset is determined by the vibrational to translational temperature ratio, brings molecules from mid-energy range to dissociation. Vibrational–translational energy transfers have negligible effect at the gas temperature considered in this study. The possibility of describing dissociation kinetics as a transport process provides insight toward the goal of achieving efficient CO2conversion.

This paper reports on the successful synthesis of visible light photoactive N–TiO2nanolayers and the investigation of charge carrier dynamics in dependence on N-doping and irradiation wavelengths. Grazing incidence X-ray diffractometry exhibited that N-doping supports the formation of an anatase phase with a higher crystallinity than observed for undoped TiO2. Photoelectrochemical measurements gave evidence that N–TiO2is characterized by a significantly higher incident photon conversion efficiency (IPCE) upon both UV and visible light irradiation. Photoelectrochemical impedance spectroscopy revealed that the higher IPCE of N–TiO2in UV can be explained by a lowered charge transfer resistance, probably due to its higher crystallinity. The higher photoactivity in the visible can be explained by the incorporation of intrabandgap states upon N-doping. This is supported by X-ray photoelectron spectroscopy indicating the incorporation of N atoms in the titania layer, the observed bandgap narrowing by at least 250 meV as measured by ultraviolet–visible absorption spectroscopy, and the decrease of the work function by 50 meV, as derived from scanning Kelvin probe microscopy. Intensity-modulated photocurrent/photovoltage spectroscopy proved that the generally lower quantum yield at visible light is caused not only by the generation of less photoexcited charge carriers, but also by a higher surface hole recombination rate and hence lower hole charge transport efficiency.

This paper concerns thin water films and their hydrogen-bond patterns on ionic surfaces. As far as we are aware, this is the first time H-bond correlations for surface water and hydroxide species are presented in the literature while hydrogen-bond relations in the solid state have been scrutinized for at least five decades. Our data set, which was derived using density functional theory, consists of 116 unique surface OH groups–intact water molecules as well as hydroxides–on MgO(001), CaO(001) and NaCl(001), covering the whole range fromstrong toweak tono H-bonds. The intact surface water molecules are found to always be redshifted with respect to the gas-phase water OH vibrational frequency, whereas the surface hydroxide groups are either redshifted (OsH) or blueshifted (OHf) compared to the gas-phase OH–frequency. The surface H-bond relations are compared with the traditional relations for bulk crystals. We find that the “ν(OH) vs R(H···O)” correlation curve for surface water does not coincide with the solid state curve: it is redshifted by about 200 cm–1or more. The intact water molecules and hydroxide groups on the ionic surfaces essentially follow the same H-bond correlation curve.

The search for nanoporous materials that are highly performing for gas storage and separation is one of the contemporary challenges in material design. The computational tools to aid these experimental efforts are widely available, and adsorption isotherms are routinely computed for huge sets of (hypothetical) frameworks. Clearly the computational results depend on the interactions between the adsorbed species and the adsorbent, which are commonly described using force fields. In this paper, an extensive comparison and in-depth investigation of several force fields from literature is reported for the case of methane adsorption in the Zr-based Metal–Organic Frameworks UiO-66, UiO-67, DUT-52, NU-1000, and MOF-808. Significant quantitative differences in the computed uptake are observed when comparing different force fields, but most qualitative features are common which suggests some predictive power of the simulations when it comes to these properties. More insight into the host–guest interactions is obtained by benchmarking the force fields with an extensive number of ab initio computed single molecule interaction energies. This analysis at the molecular level reveals that especially ab initio derived force fields perform well in reproducing the ab initio interaction energies. Finally, the high sensitivity of uptake predictions on the underlying potential energy surface is explored.

This paper demonstrates both the high-performance microwave absorption properties and the superior thermal stability of graphene/multiwalled carbon nanotubes (MWNTs)/poly(p-phenylenebenzobisoxazole) (PBO) composites synthesized via in situ polymerization of functionalized PBO precursor with graphene oxide/MWNTs nanocomposites, followed by high-temperature calcination. The incorporation of three-dimensional graphene/MWNTs network significantly improved the reflection loss of PBO composites (−50.17 dB at 12.58 GHz) by over 20 times than that of pure PBO (−2.33 dB at 12.58 GHz) with a sample thickness of only 2.6 mm. The effect of graphene/MWNTs content on the microwave absorption performance was also investigated. The graphene/MWNTs/PBO composite shows great promise as a microwave absorber in high-temperature environments.

This paper reports a simple and scalable colloidal templating technology for fabricating wafer-scale periodic plasmonic nanodimple arrays with tunable nanostructures. A double-layer, non-close-packed colloidal crystal–polymer nanocomposite created by a spin-coating technique is used as structural template in a simple oxygen plasma etching process to fabricate periodic arrays of nanodimples. The resulting plasmonic arrays can sense a small dielectric refractive index change of ∼0.008, and they exhibit high SPR sensitivity of up to ∼520 nm per refractive index unit. The experimental plasmonic performance of the nanodimple arrays matches with the numerical simulations using a finite-difference time-domain model.

This paper reports the possible reaction paths of small silicon clusters Sin(n= 1−4) with the oxygen molecule based on density functional theoretical calculations. It is shown that their potential energy surfaces are very complex, involving spin conserving and inversion. There are no net barriers on any of the proposed reaction paths for the oxidation of Si, Si2, and Si3clusters, but their reverse reactions are endothermic with high energy barriers. The Si4cluster cannot react with the ground-state, spin-triplet oxygen molecule because of the potential barrier of its spin inversion. The most favorable and accessible reaction path for Si/Si2/Si3+ O2may be the one with a high exothermic value since there are no net barriers on the potential energy surfaces. The reactions of silicon clusters with the oxygen molecule are easier than the oxidations of their corresponding suboxides. Our findings are expected to provide valuable information to help understand the growth mechanism of silicon nanowires.

This paper describes a facile and effective method to construct graphene nanosheet film (GNF) by controllable adsorption of reduced graphene oxide (rGO) onto the self-assembled monolayer (SAM) of n-octadecyl mercaptan (C18H37SH) at Au electrodes. Nyquist plots show a gradual decrease of the charge transfer resistance (Rct) of the [Fe(CN)6]3−/4−redox couple at the GNF/SAM electrode with prolonging the self-assembly time, suggesting the controllable adsorption of rGO onto the SAM. Cyclic voltammetry (CV) studies reveal that the GNF/SAM electrodes have tunable dimensions ranging from a nanoelectrode ensemble to a conventional electrode, depending on the self-assembly time of rGO. The excellent electrocatalytic activity of the GNF/SAM electrode toward ascorbic acid, dopamine, and uric acid further indicates that our approach is successful for the fabrication of stable GNF with excellent electrochemical properties, which is very attractive for electrochemical studies and electroanalytical applications. At the same time, as a new kind of nanosheet film electrode, the GNF electrode could be exploited in a new field for micro- and nanoelectrodes in electrochemical investigations and practical applications, e.g., electroanalysis in vivo and in vitro.

In this paper, we integrate machine learning (ML) with two-dimensional material screening to develop novel halogenated silicene-based materials with considerable potential for photocatalytic and photovoltaic applications. We proposed a data-driven framework that incorporates first-principles electronic structure calculations and 286 self-contained databases trained by supervised learning to accurately predict the structural stability and electronic properties of halogenated silicene-based compounds. A total of 110 potential candidates for photocatalytic water splitting were identified, and five materials with high predicted stability exhibited ideal band edges and demonstrated high carrier mobility rates. Among the 321 heterojunctions composed of halogenated silicene compounds with potential type-II band alignments, we randomly screened a Si8HFCl5I/Si8FClBrI5heterojunction and validated that it can achieve a high photoelectric conversion efficiency of 21.04%.

In this paper, we introduce a method called waveguide coupling surface plasmon-coupled directional emission Raman (WCSPCR), which utilizes a bimetallic waveguide-coupled surface plasmon resonance structure (WCSPR) to enhance the directional emission Raman spectrum by utilizing excited surface plasmons in the evanescent field. We further enhance Raman scattering by utilizing localized and propagating surface plasmons. The further enhanced Raman scattering was directionally emitted due to the resonance effect of the propagating surface plasmons in the WCSPR structure. We obtained angle-dependent directional emission Raman scattering spectra using an in-house angle-dependent SPR-SERS microspectrometer. Compared to a traditional SPR structure, the WCSPR structure showed a superior electromagnetic field and a narrower emission angle. This led to an eight-fold increase in the directional emission Raman signal and a narrower full width at half-maximum of the directional emission angle under the WCSPR configuration. This could further improve the directional emission of Raman signals and enhance the collection efficiency of Raman signals. To further enhance the directional emission Raman signal, we incorporated silver nanoparticles (AgNps) into the WCSPR configuration, creating a WCSPR/4-Mpy/AgNps sandwich structure. Under this configuration, localized and propagating surface plasmons are effectively coupled, resulting in a significant enhancement of the directional emission Raman signal for 4-mercaptopyridine. The combination of local and propagating surface plasmons further amplified the AgNp-assisted SERS signal in the WCSPR/4-Mpy/AgNps sandwich structure, the amplified SERS signal was directionally emitted due to the interaction with the propagating surface plasmons, yielding a signal strength 30 times that of the traditional SPR structure. These findings are consistent with electric field simulations. The WCSPCR method shows promise in enhancing SERS signals, simplifying SERS instruments, and may have applications in biochemical testing.

The active center of the TiCl4/MgCl2Ziegler-Natta catalyst (TMC) has an important impact on alkadiene polymerization. In this paper, density functional theory was used to study the adsorption behavior of monomeric TiCl4and dimeric Ti2Cl8on different surfaces of MgCl2(110) and (104). Additionally, the influence of the distribution of active center TiCl4on the kinetics of isoprene polymerization catalyzed by TMC was also investigated, aiming to gain a better understanding of the potential active site structures in the TMC for the polymerization of dienes. Three different active models were employed to analyze the catalysts: TMC-1 with isolated mononuclear TiCl4, TMC-2 with clustered mononuclear TiCl4, and TMC-3 with larger-size cluster mononuclear TiCl4. Moreover, TMC-2 was further divided into TMC-2aand TMC-2bfor discussion. In the TMC-2amodel, the central Ti site was selected as the active center for the coordinating and insertion process with cis-isoprene, while in the TMC-2bmodel, the left Ti site was selected as the coordination and insertion process with cis-isoprene. The calculation results showed that monomeric TiCl4adsorption on the (110) surface is the most stable adsorption configuration. For cis-isoprene, TMC-1 showed the highest stereoselectivity, while TMC-3 showed the lowest stereoselectivity. In the coordination stage, the TMC-1 model, with isolated mononuclear TiCl4, had a preference for the si configuration, while the TMC-2a, TMC-2b, and TMC-3 models, with clustered mononuclear TiCl4, had a preference for the re configuration. In the insertion process of cis-isoprene, the re configuration in TMC-1 had a relatively lower reaction barrier, while the si configuration in TMC-2band TMC-3 had relatively lower reaction barriers.

Graphdiyne (GDY), a new carbon allotrope, is composed of two types of hybridized (sp and sp2) carbon atoms to form a 2D planar network structure. After being synthesized in 2010, pristine GDY has attracted the attention of researchers, because of its large π-conjugated structure and excellent electronic properties. In recent years, there have been many reviews on GDY, but most reviews only briefly describe its synthesis and applications. Due to experimental limitations, it is difficult to gain insight into the electronic structure of GDY concerning its properties and applications. At the same time, there is also a lack of a thorough understanding of the application mechanism of GDY and GDY-based materials. By utilizing theoretical computation, not only the above problems can be solved but also experimental results can be predicted. Thus, in this paper, we review some of the physical properties of GDY-based materials from the perspective of theoretical calculations. Then, their theoretical prediction in the fields of energy storage and conversion is introduced, which points out the research direction and provides a theoretical basis for the experiments. It is hoped that this Review will play a positive part in developing GDY and its related calculations.

The efficacy of vibrational excitation for reaction promotion can be well-described by the Fridman–Macheret (F–M) α-model, which was initially developed for processes in the gas phase. However, it is widely used for analysis of the efficacy of vibrational excitation of heterogeneous processes, such as NH3synthesis, reduction of CO2, and activation of CH4. For plasma-assisted heterogeneous processes, the contribution of species with high vibrational excitation into reaction is emphasized. The aim of this paper is to check the applicability of the F–M model for the case of activation of the N2molecule on the Ru(113) and Ru(0001) surfaces using molecular dynamics with machine learning potential (MLP). The results show that the F–M model appears to be a reasonable approximation for estimate of vibrational efficacy of highly excited states (v≥ 7) which are important under nonequilibrium plasma conditions.

A novel strategy to control the generation of singlet oxygen by a photosensitizer using cucurbit[n]urils inclusion complexes is shown herein, and the strategy has great potential for therapeutic applications. We show the basic requirements of the photosensitizer complexes in order to develop an on–offswitch for singlet oxygen that is reversible using competitive binding. The supramolecular strategy proposed in this paper avoids complex synthetic schemes in order to activate or deactivate the photosensitizer as previous work has shown and supports the use of biocompatible materials. Mechanistic insights into the control over the generation of singlet oxygen are provided, which strongly emphasize the key role of the cucurbit[n]uril macrocycles in the stabilization or deactivation of the triplet excited state.

In this paper, mechanoresponsive fluorescent molecules with high “off–on” contrast ratios that undergo molecular packing transformation from amorphous phase to crystalline by scratching are first reported. Three 2-aminobenzophenone derivatives 1, 2, and 3, which possess crystallization-induced fluorescence characteristics, exhibited bright cyan, blue, and green fluorescence colors with “off–on” contrast ratios as high as 175-fold by scratching. The scratching induced transformation from amorphous phase to crystalline of 1, 2, and 3were directly observed by XRD and SEM studies. In addition, the fluorescence of the scratched sample can readily convert back into the initial nonfluorescent state by fuming in ethanol or heating. Letters with three fluorescence emission colors of 1, 2, and 3in ethanol solution smeared on a glass surface can be easily written by scratching and erased by fumigation, demonstrating the potential value as reversible mechanoresponsive fluorescent materials.

Capacitors that provide high power density have attracted scientific and commercial interest, while often suffering from low energy density. Preparing a core–shell structured ceramic is regarded as a kind of effective method to improve the energy density, which is largely determined by the shell in the interfacial region. However, the current state-of-the-art of interfacial layer modification is predominantly based on utilizing flexible polymers, which are random polymer coils that collapse on the surface of any modified ceramic nanoparticles. Because of the characteristic properties of rigidity and orientation, the liquid-crystalline polymer poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) is utilized to engineer the interfacial layer thickness on BaTiO3nanowire surfaces via surface-initiated reversible addition–fragmentation chain transfer polymerization (RAFT) method, in this paper. As a result, a high discharged energy density of 7.5 J/cm3and an energy efficiency of 55.1% at 300 MV/m are achieved, respectively. The findings proved that rigid liquid-crystalline polymer is a promising modifier to prepare high performance capacitors and to explore the interfacial effect in dielectric nanocomposites.

In this paper, to study the two-dimensional (2D) conjugated side chain effect on the polymer donor for the non-fullerene polymer solar cells (NFPSCs), the thiophenothiophene (TT) side-chained benzodithiophene (BDT) and bithiophene copolymer (PBDTDT-TT) has been prepared by the Stille coupling reaction and compared with the copolymer (PBDTDT-O) with an alkoxy side group and the same polymer backbone. The 2D conjugated polymer PBDTDT-TT exhibits better thermal stability and wider and red-shifted ultraviolet–visible absorption spectra. These two copolymers were used as the donor materials blended with a new non-fullerene receptor ITM, successfully fabricating the positive devices with an ITO/PEDOT:PSS/polymer:ITM/PFN-Br/Al structure. Compared with the PBDTDT-O:ITM blend film, the PBDTDT-TT:ITM blend film shows a lower LUMO energy level, a narrower optical band gap, and a higher electron and hole mobility in the devices. The best power conversion efficiency (PCE) is 8.43% for the PBDTDT-TT polymer, while the PCE for the PBDTDT-O polymer is <1%. Extending the conjugated plane through the 2D conjugated side chain can help the PBDTDT-TT-based PSC devices show higher exciton dissociation efficiencies of 85.36% [compared with that of PBDTDT-O-based device (13.12%)] and thereby enhance the photovoltaic performance of the NFPSCs.

Solid solution nanocrystals of gallium nitride–zinc oxide have been realized as potential photocatalysts for visible light driven overall water splitting. The band gap of these materials has been found to narrow further into the visible region as a function of increasing zinc oxide concentration, and thus, it is desirable to synthesize zinc oxide-rich gallium nitride–zinc oxide solid solutions. In this paper, we discuss the effects of using nitridation temperature to control zinc oxide content on the electronic and chemical properties of gallium nitride–zinc oxide solid solution nanostructures. The effect of nitridation temperature was studied using X-ray absorption fine structure (XAFS), including both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), and X-ray excited optical luminescence (XEOL). It was determined that using nitridation temperature as a method of controlling zinc oxide concentration results in solid solutions with poor crystallinity, phase separation, and mixed surface oxide formation. These findings suggest that many complications arise from using nitridation temperature to control zinc oxide concentration in gallium nitride–zinc oxide solid solutions, and thus, it is possible that the resultant materials would exhibit poor photocatalytic activity.

In this paper we critically examine the literature and provide new data on fundamental optical properties of II–VI quantum dots (QDs). Specifically, we examine the integrated extinction coefficients and radiative lifetimes of different sizes of CdSe and CdTe QDs and different shell thicknesses in CdTe/CdSe core/shell QDs. We have synthesized particles having very high quantum yields and find that the measured radiative lifetimes are considerably longer and have a very different size dependence than what has been previously reported. In a simple two-level system the integrated extinction coefficients (or oscillator strengths) are related to the radiative lifetimes through the Einstein relations. The situation is more complicated in the case of II–VI QDs because of the thermal accessibility of dark states resulting from the valence band fine structure. There are significant but not equal populations in both bright and dark sublevels of the 1Se-1S3/2exciton and in the dark 1Se-1P3/2exciton. These Boltzmann populations depend on the QD size and shape. We find that in all three cases, quantitative or semiquantitative agreement between the measured radiative lifetimes and values calculated from the integrated extinction coefficients is obtained only if Boltzmann populations in all of the thermally accessible bright and dark states are considered. We also find that the shell thickness dependence of the radiative lifetimes of the CdTe/CdSe core/shell particles can be quantitatively understood in terms of overlap of calculated electron and hole wave functions. The results and analyses presented here clarify several discrepancies in the literature.

A comment on our recent paper makes several points, and highlights places where additional clarification on our part is warranted. The broader emphasis, beyond any particular statements about the nature of light and the absorption process, is that excited state delocalization at short timescales exerts an important influence on the charge separation dynamics in organic solar cells. It is important to point out that no arguments in the commentary attempted to contradict this conclusion. On the contrary, the novelty of this idea was questioned.

Understanding and improving Li transport through crystalline Li2CO3, a stable component of the solid electrolyte interphase (SEI) films in Li-ion batteries, is critical to battery rate performance, capacity drop, and power loss. Identification of the dominant diffusion carriers and their diffusion pathways in SEI films coated on anode and cathode surfaces is a necessary step toward the development of methods to increase Li conductivity. In this paper, we identify the dominant Li diffusion carriers in Li2CO3over a voltage range (0–4.4 V) that includes typical anode and cathode materials by computing and comparing thermodynamics of all seven Li-associated point defects with density functional theory (DFT). The main diffusion carriers in Li2CO3below 0.98 V are excess Li-ion interstitials; however, above 3.98 V, Li-ion vacancies become the dominant diffusion carrier type, and they have the same concentration in the voltage range of 0.98–3.98 V. Diffusion mechanisms of the main diffusion carriers were computed via the climbing image nudged elastic band method (CI-NEB). On the basis of the computed diffusion carrier concentration and diffusion barriers, the Li ionic conductivity was computed as a function of voltage, and it varies by ∼5 orders of magnitude. Insights gained from our calculations allow us to suggest different dopants to enhance Li conductivity in SEI films and propose a new mechanism for electron leakage through an SEI film into the electrolyte. Li2CO3is the one of the main stable components in the solid electrolyte interphase (SEI) in lithium-ion batteries and can be found in SEI films grown on both cathode and anode surfaces. On the basis of the concentrations and diffusion barriers computed for each of the identified point defects from first-principles calculations, the Li conductivity in Li2CO3is mapped as a function of battery voltage. It is found that the diffusion carriers in the Li2CO3on a negative electrode (graphite) are Li+interstitials but changed to Li+vacancies in the Li2CO3coated on cathode materials. While Li+vacancies diffuse via a typical direct hopping mechanism, the excess Li+interstitials diffuse via repetitive knock-off with the Li+ions on lattice sites. The Li+interstitial conductivity in Li2CO3on graphite is ∼5 orders of magnitude faster than that of a Li+vacancy in Li2CO3on the cathode. This suggests that Li transport through an SEI film on a cathode material can be dramatically different from Li transport through an SEI film on an anode material, despite the fact that SEI component chemistries appear to be similar in both cases. Thus, different doping strategies for the SEI on the anode and cathode could be taken to increase diffusion carrier concentrations in order to increase Li conductivity in an SEI film.

Face-centered cubic (fcc) (111)-orientated two-dimensional (2D) and three-dimensional (3D) crack-free silica colloidal crystals (CCs) were fabricated on patterned silicon substrates via a vertical deposition method. The influence of the surface properties of the substrate and the concentration of colloidal microspheres on the self-assembly were studied. The results showed that monolayer of silica microspheres self-assembled on a hydrophobic substrate surface while on a hydrophilic surface multilayer of silica microspheres formed under otherwise the same experimental conditions. The number of CC layers grown on the patterned substrate was proportional to the volume fraction of the colloidal microspheres. The optical properties of the samples were less influenced by the patterned surface with increasing the volume fraction of the colloidal suspension when the patterned substrates were fully covered by the CCs. The results presented in this paper reveal that the vertical deposition method can allow the formation of crack-free and well-ordered 3D CCs in large domains on patterned surfaces.

A common strategy to calculate electronic coupling matrix elements for charge or energy transfer is to take the adiabatic states generated by electronic structure computations and rotate them to form localized diabatic states. In this paper, we show that, for intermolecular transfer of singlet electronic excitation, usually we cannot fully localize the electronic excitations in this way. Instead, we calculate putative initial and final states with small excitation tails caused by weak interactions with high energy excited states in the electronic manifold. These tails do not lead to substantial changes in the total diabatic coupling between states, but they do lead to a different partitioning of the total coupling between Coulomb (Förster), exchange (Dexter), and one-electron components. The tails may be reduced by using a multistate diabatic model or eliminated entirely by truncation (denoted as “chopping”). Without more information, we are unable to conclude with certainty whether the observed diabatic tails are a physical reality or a computational artifact. This research suggests that decomposition of the diabatic coupling between chromophores into Coulomb, exchange, and one-electron components may depend strongly on the number of states considered, and such results should be treated with caution.

Hydrogen fuel cells, as vital clean energy representatives, hold vast prospects in the energy domain. However, their actual processes involve numerous intricate physical and chemical reactions. To comprehend and optimize their functionality, various characterization techniques are employed to provide crucial insights into the electrochemical properties, structural composition, and reaction kinetics of fuel cells. This paper reviews the latest research advancements in in situ/operandocharacterization of hydrogen fuel cells, such as in situ/operandospectroscopic, electrochemical, and microscopy techniques. Initially, we briefly introduce the basic structure and principle of fuel cells, and the advantages and disadvantages of traditional characterization methods are outlined. Subsequently, the in situRaman and infrared spectroscopy studies on the catalytic reaction mechanisms at the fuel cell interface are introduced. Then, using different in situ/operandocharacterizations, the water management, thermal management, membrane electrode degradation, and reaction process of fuel cells were monitored, obtaining information on morphology and species distribution. Finally, various characterization methods were summarized, and the future development of in situ/operandocharacterization techniques for fuel cells was discussed.

Self-organization is usually observed in two- or three-dimensional nonequilibrium processes, where an ordered pattern spontaneously emerges in an initial disordered system. Since spontaneous ordering is not prohibited in one dimension, it is interesting to investigate the ordering behavior in the quasi-one-dimensional nanofluids such as a single-file chain of water molecules. In this paper, we show that spatiotemporal ordering of the single-file water, in the form of collective oscillating unidirectional flows, spontaneously emerges inside a narrow nanotube between two independently heated water reservoirs by molecular dynamics simulations. The spatiotemporal ordering of the single-file water induces a low-frequency coupling and a unidirectional duration time up to nanoseconds and also low-configuration entropy in the flow pattern that separates itself from the chaotic motion of water molecules. Mass density fluctuation plays a critical role in the ordered flow pattern formation, and its crossover from an exponential to a power-law decay decides the disappearance of the ordered flow pattern. We further find that spatiotemporal ordering induces high heat-transfer enhancement that is comparable to thermal conductivity of gaseous water. Our result reveals a peculiar self-organization phenomenon and entirely different dynamics in the single-file water that departs from macroscopic flows in the continuum limit.

Raman scattering is widely used to study underdampedvibrational normal modes of molecules, their intramolecular potentials and molecular structures via the change of polarizability associated with structural deformation. Inspired by the classical Raman effect, this paper presents the relationship of the symmetry of overdampedcollective fluctuation modes (analogous to underdamped normal modes) of optical matter (OM) arrays to their coordinate-dependent changes in induced-polarization and light scattering. OM systems consist of (nano)particles that form 2-dimensional ordered (often trigonal lattice) structures due to electromagnetic interactions in coherent fields. The interactions among the particles are mediated by incident and scattered coherent light. While the influence of incident light on the dynamics of the OM system has been explored and the relationships of electrodynamic interference and induced-polarization to the scattered light have been studied, there is less appreciation of the relationship of the scattered light and the nanoparticle dynamics of OM structures. We demonstrate a homomorphism between the monotonic fluctuation mode-dependence of the scattering properties of OM systems and the monotonic coordinate-dependent polarizability of Raman active modes. We show that the induced-polarization and total scattering cross-section changes monotonically along modes with high symmetry but nonmonotonically along lower symmetry modes. Furthermore, the broken symmetry due to the chirality of the incident circularly polarized light vs the rotationally symmetric trigonal lattice structure(s) can be described by changes in the irreducible representations such that some “Raman inactive” modes become active. Our analysis opens new opportunities to explore dynamics of N-body systems.

In this paper, we present a comprehensive theoretical study, based on density-functional theory calculations, and which focuses on the structural and electronic properties of silver vanadium oxide (AgVO3) in the monoclinic [Cm(β-AgVO3), C2/c(α-AgVO3), and Cc], orthorhombic (Amm2), and cubic (Pm3̅m) phases from 0–30 GPa. The structural and electronic properties, the stability of different phases, and the pressure-induced solid–solid phase transitions of AgVO3have been previously studied. The effects of pressure on the band structures, energy–gap values, density of states, and vibrational frequencies are also studied. Numerical and analytical calculations are conducted to obtain the lattice parameters, the bulk modulus Kand their pressure derivative K′, and the energy-volume equations of state. The influence of different parametrizations of the exchange-correlation functional (B3LYP, HSE06, and PBE) on the investigated properties is analyzed, and the results are compared to available experimental data. For the first time, a complex and unexpected structural and chemical behavior as a function of pressure is reported. The β-phase is the most stable and the first phase transition between the monoclinic β-AgVO3and Ccphase takes place at 5 GPa (B3LYP), 3 GPa (HSE06), and 2 GPa (PBE). There are pressure-induced transitions among the β-, α-monoclinic, and cubic structures, and the corresponding values for the pressure transitions are dependent on the functional used. Two new polymorphs, monoclinic Ccand orthorhombic (Amm2), have been characterized for the first time, and their contrasting structural stabilities as well as their transition mechanisms can be understood from the intrinsic characteristics of the crystal lattices. The Badger’s rule is fulfilled for Cm, Amm2, and Pm3̅mpolymorphs, while it is invalid for the C2/cand Ccphases. Theoretical results show that the studied reactive channels from β-AgVO3toward binary oxides, Ag2O and V2O5, AgO and VO2; the elements Ag, V and O2; silver pyrovanadate, Ag4V2O7and V2O5, as well as Ag2V4O11and Ag2O are not thermodynamic favorable processes at pressures up to 30 GPa. These results contribute to the understanding of the pressure behavior of AgVO3-based compounds. In addition, it would be interesting to determine whether further measurements and calculations would confirm the predicted structural and thermodynamic properties as well as the solid-state transformations of AgVO3polymorphs, which have not yet been experimentally shown.

There is a significant effect of particle size on the solid–solid phase transition of nanocrystals, but the precise relations of integral enthalpy and entropy of phase transition with particle size have not been reported. In this paper, we deduced the fundamental equations of the integral enthalpy and entropy of solid–solid phase transitions for nanocrystals with different particle sizes, respectively. These universal and precise thermodynamic relations, free of any adjustable parameter, can precisely describe the real process of phase transition. Experimentally, we researched the phase transition from tetragonal to cubic of nano-PbTiO3with different diameters (24.8, 35.6, 41.9, 54.2, 63.7, and 70.1 nm). The regularities obtained from these experiments were consistent with the theoretical relations. There were linear relations between the integral enthalpy and entropy of solid–solid phase transition and the reciprocal of size of nanocrystals as the radius exceeds 10 nm. Our thermodynamic relations and the quantitative size-dependent regularities of solid–solid phase transition can provide references for explaining and confirming the solid–solid phase transitions involved in the real processes of preparation and application of nanocrystals.

Recently, Si quantum dots (QDs) with porous and amorphous characteristics have shown tremendous potential applications in photovoltaics and biomedical fields. However, in general, their preparation involves meticulous synthetic procedures. Herein, we present the first report of the synthesis of Si QDs in aqueous solution with amorphous and porous features using γ-ray irradiation, which is a facile, one-pot, and reproducible approach. Fourier transform infrared and X-ray photoelectron spectroscopy indicated the formation of a shell of Si oxides (SiOx, 0 < x< 2) surrounding the Si core. The Brunauer–Emmett–Teller method confirmed the formation of mesoporous structure with a specific surface area of ∼53 m2/g. The average size of the QDs was <2 nm, as determined from high-resolution transmission electron microscopy. Moreover, the size of the QDs could be tuned by varying the dose, as was indicated from the shift in their absorption peaks. The QDs displayed bright blue emission under ultraviolet light. Detailed and systematic investigations involving various sets of experiments such as aging, annealing, acid treatment, and temperature-dependent PL studies of the QDs indicate the origin of the blue photoluminescence (PL) is the radiative processes originating from the defects located in the oxide shell as well as at/or near the Si/SiOxinterface. This has been further substantiated from the size-independent emission spectra at various absorbed doses and short PL lifetime (in nanoseconds). Nonetheless, these QDs showed highly sensitive and robust thermosensing properties, as their PL intensity varied linearly and reproducibly with temperature, ranging from 278 to 338 K. In addition, the QDs were found to be noncytotoxic and therefore can be utilized in cell imaging. Furthermore, the blue PL and the nontoxic aspects of these QDs can be utilized in anticounterfeiting measures, the potential application of which is also demonstrated in this work. The possible mechanism behind the formation of Si QDs and the role of the total dose in the introduction of mesoporous and amorphous features are proposed and explained in this paper.

We show the significant role of the Rydberg-like unoccupied molecular orbital in the photoexcitation process at the rubrene/graphite interface. Two-photon photoemission (2PPE) spectroscopy revealed a prominently strong resonant excitation of an unoccupied molecular orbital (MO) at 3.26 eV above the Fermi level (J. Phys. Chem. C2012, 116, 5821). The excitation was attributed to be mediated by the image potential state (IPS) on graphite. We investigate in this paper the nature of the MO by 2PPE spectroscopy and density functional theory (DFT) calculations. The DFT calculation involving diffuse atomic orbitals predicts a nearly cylindrical unoccupied MO extending over four phenyl rings at the energy of the interest. Polarization dependence of 2PPE spectroscopy shows that the unoccupied MO is nearly symmetric to the plane of the light incidence in accordance with the calculated MO. The two-dimensional free electron wave function of the IPS can interact with the MO that has no node within the molecular framework. The bonding interactions of diffuse atomic orbitals are the origin of the cylindrical MO. It can be seen as a Rydberg-like orbital and is similar to the superatom molecular orbital (SAMO) known for C60.

This paper deals with the understanding of depolarization mechanisms in ferroelectric materials and how to improve energy harvesting by converting thermal or mechanical energy into electrical energy. Depolarization mechanisms caused by temperature were studied using X-ray diffraction (XRD) to describe the evolution of the domain organization. Polarization variations, constituting the key parameter for energy harvesting, were simulated from the XRD data and explained in terms of domain switching, variation of the dipole moment, and rotation of the dipole. The latter concerned structural transitions induced by an excitation and gave rise to significant nonlinearities in the material properties. Energy harvesting should combine two excitations (e.g., temperature and electric field, or stress and electric field) describing intelligent thermodynamical cycles. Various examples have been given to illustrate the possibilities for harvesting energy.

In this paper, a high molecular weight organic compound, poly(N-vinyl-2-pyrrolidone) (PVP), was added to silver nitrate to fabricate silver conductive lines and arrays by inkjet printing on flexible Kapton substrates. With the assistance of PVP, the dimension of conductive lines can be controlled more accurately. In addition, the morphological control and resolution of arrays and lines were further improved by using UV/O3treatment of substrates and changing the substrate temperature. The silver nitrate/PVP inks can be reduced in ethylene glycol vapor to form silver conductive lines at low temperatures. By using a high concentration of silver nitrate/PVP ink, continuous and smooth silver conductive lines with a resistivity of 2.71 × 10−5Ω cm have been produced. Their resistivity is close to the resistivity of bulk silver.

Because of its unique physical properties, domain wall (DW) in ferroelectrics not only plays a key role in the electrical properties of ferroelectric film but also has shown tremendous prospect in the DW-based memory and logic devices. However, the motion mechanism of ferroelectric DW, which is of great significance for the application of ferroelectric films, has not been clearly understood. In this paper, the 180° DW motions in BaTiO3(BTO) and PbTiO3(PTO) were studied by using the nudged elastic band method based on the density functional theory. The evolutions of atomic structure, local polarization, and energy of the system for the DW motion process between the two adjacent equilibrium positions were systematically revealed. The DW migration across the oxygen vacancy was also simulated, and the corresponding potential well for the DW motion was obtained. It was also found that the DW motion barrier could be significantly influenced by the in-plane strain. The “activation field” deduced from the energy barrier of DW motion in the present calculation agrees with experimental values, which may provide a fundamental understanding of DW dynamics.