Supramolecular Coordination of Pb2+ Defects in Hybrid Lead Halide Perovskite Films Using Truxene Derivatives as Lewis Base Interlayers

Truxene derivatives, due to their molecular structure and properties, are good candidates for the passivation of defects when deposited onto hybrid lead halide perovskite thin films. Moreover, their semiconductor characteristics can be tailored through the modification of their chemical structure, which allows-upon light irradiation- the interfacial charge transfer between the perovskite film and the truxene molecules. In this work, we analysed the use of the molecules as surface passivation agents and their use in complete functional solar cells. We observed that these molecules reduce the non-radiative carrier recombination dynamics in the perovskite thin film through the supramolecular complex formation between the Truxene molecule and the Pb²⁺ defects at the perovskite surface. Interestingly, this supramolecular complexation neither affect the carrier recombination kinetics nor the carriers collection but induced noticeable hysteresis on the photocurrent vs voltage curves of the solar cells under 1 sun illumination.     

Kinetic study of the "surface explosion" phenomenon in the NO+CO reaction on Pt(100) through dynamic Monte Carlo simulation

The extremely narrow production peak of N2 and CO2 which occurs in the reaction of NO+CO on Pt(100), a phenomenon known as "surface explosion," is studied using a dynamic Monte Carlo method on a square lattice at low pressure under isothermal conditions. This analysis incorporates recent experimental evidence obtained for the same reaction on a Rh(111) surface, which has shown that N2 production occurs either from the classical N+N recombination step or by the formation and successive decay of a (N-NO)* intermediary species. Moreover, the NO dissociation rate is inhibited by coadsorbed NO and CO molecules and is enhanced both by the presence of empty sites and adsorbed N atoms as nearest neighbors. These effects are taken into account in this study, along with the experimental adsorption, desorption, and diffusion rates of the reactants. The "explosive" phenomenon is analyzed through the evolution over time of an adsorbed NO+CO monolayer at a fixed temperature of 400 K. Furthermore, as the diffusion processes of the adsorbates are included, cellular structures are observed. Our simulations show quantitative agreement in the position of maxima with those obtained through experiments using isothermal desorption mass spectroscopy.     

Interaction of the t-butylcalix[4]arene Anion with Ammonium Cations in Acetonitrile: Host–Guest Complexes or exo Counterions? A Molecular Dynamics Investigation

We report a theoretical study of the NR4+salts (R = H; Me; Et) of the t-butylcalix[4]arenemonooxyanion L- inacetonitrile solution, to compare the endocomplexes NR4+ inside the cone of thehost) with the exo ones. For a given cation, wefind that the complexes display structures of similartype in the gas phase and in acetonitrile solution.Intrinsically, the endo forms are more stablethan exo ones, but they are less well solvated.As a result, exo complexes are predicted to bemore stable than the endo ones in acetonitrile.In the gas phase and in solution, the exocomplexes of NMe4+ and NEt4+display interesting examples of fluctional intimateion pairs, where the cation oscillates between theoxygen lower rim region of L- and exo stacking with the phenolic rings ofL-. Based on free energy perturbation calculations,we compare endo NH4+/NMe4+complexes and find that the hypotheticalNH4+ complex is more stable in acetonitrile solution.     

Cooperativity in ordinary ice and breaking of hydrogen bonds

The total interaction energy between two H-bonded water molecules in a condensed phase is composed of a binding energy between them and an energy due to a cooperative effect. An approximate simple expression is suggested for the dependence of the interaction energy between two H-bonded water molecules on the number of neighboring water molecules with which they are H-bonded. Using this expression, the probabilities of breaking a H bond with various numbers of H-bonded neighbors are estimated. These probabilities are used in computer simulations of the breaking of specified fractions of H bonds in an ordinary (hexagonal) ice. A large "piece" of hexagonal ice (up to 8 millions molecules) is built up, and various percentages of H bonds are considered broken. It is shown that 62-63% of H bonds must be broken in order to disintegrate the "piece" of ice into disconnected clusters. This value is only a little larger than the percolation threshold (61%) predicted both by the percolation theory for tetrahedral ice and by simulations in which all H bonds were considered equally probable to be broken. When the percentage of broken bonds is smaller than 62-63%, there is a network of H-bonded molecules which contains the overwhelming majority of water molecules. This result contradicts some models of water which consider that water consists of a mixture of water clusters of various sizes. The distribution of water molecules with unequal probabilities for breaking is compared with the simulation involving equal probabilities for breaking. It was found that in the former case, there is an enhanced number of water monomers without H bonds, that the numbers of 2- and 3-bonded molecules are smaller, and the number of 4-bonded molecules is larger than in the latter case.     

Capture and recombination of charge carriers in a strong electric field in quasi-one-dimensional crystals with scattering centers

The asymmetric random walk method is used to find the time dependence of the density of free charge carriers in a chain containing traps and neutral barriers, assuming a strong electric field. Fluctuations in the density of defects are taken into account exactly. The kinetics of the density decay has two stages: fast exponential decay at small times and slow decay (-[ln(t) + const]t^-, where a l is a combination of the parameters of the system) at long times. It is also shown that in the presence of barrier defects the asymptotic forms of the decrease in the number of charge carriers due to capture by traps and due to germinal recombination are the same.Institute of Theoretical Physics, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 2, pp. 129–133, March–April, 1991. Original article submitted May 21, 1990.     

UV-induced protonation of molecules adsorbed on ice surfaces at low temperature

UV irradiation of ice films adsorbed with methylamine molecules induces protonation of the adsorbate molecules at low temperature (50-130 K). The observation indicates that long-lived protonic defects are created in the ice film by UV light, and they transfer protons to the adsorbate molecules via tunneling mechanism at low temperature. The methylammonium ion formed by proton transfer remains to be stable at the ice surface. It is suggested that this solid-phase protonation might play a significant role in the production of molecular ions in interstellar clouds.     

Interaction of atomic and molecular deuterium with a nonporous amorphous water ice surface between 8 and 30 K

Molecular and atomic interactions of hydrogen on dust grains covered with ice at low temperatures are key mechanisms for star formation and chemistry in dark interstellar clouds. We have experimentally studied the interaction of atomic and molecular deuterium on nonporous amorphous water ice surfaces between 8 and 30 K, in conditions compatible with an extrapolation to an astrophysical context. The adsorption energy of D(2) presents a wide distribution, as already observed on porous water ice surfaces. At low coverage, the sticking coefficient of D(2) increases linearly with the number of deuterium molecules already adsorbed on the surface. Recombination of atomic D occurs via a prompt reaction that releases molecules into the gas phase. Part of the newly formed molecules are in vibrationally excited states (v=1-7). The atomic recombination efficiency increases with the presence of D(2) molecules already adsorbed on the water ice, probably because these increase the sticking coefficient of the atoms, as in the case of incident D(2). We have measured the atomic recombination efficiency in the presence of already absorbed D(2), as it is expected to occur in the interstellar medium. The recombination efficiency decreases rapidly with increasing temperature and is zero at 13 K. This allows us to estimate an upper limit to the value of the atom adsorption energy E(a) approximately 29 meV, in agreement with previous calculations.     

Some problems of recombination kinetics. II

The general phenomenological theory of diffusion-controlled defect recombination, in which the identity of similar and dissimilar defects are consistently taken into account and which was presented in part I of this series, is applied here to the reactions A + B → C (Frenkel defect recombination). A + B → B (energy transfer), A + A → B (exciton annihilation). It is shown that during the reaction A + B → C at long reaction times spatial correlations of similar defects (dynamic aggregates) are produced thus leading to a deviation from the quasi-steady reaction constant well known in formal chemical kinetics. (This confirms once more our general idea about the back-coupling of similar and dissimilar reagent spatial correlations.) The validity range of Kirkwood's standard superposition approximation used to decouple three-point densities is also discussed.     

Ice nanocrystals in glycerol-water mixtures

We discuss the minimum size of ice nanoparticles in water-rich glycerol-water mixtures, as studied by broadband dielectric spectroscopy (BDS) in the frequency range from 1 Hz to 250 MHz and differential scanning calorimetry (DSC) at the temperature interval from 138 to 313 K. It is known that the extra water which is free from the glycerol hydrogen bond network forms the water cooperative domain. This cooperative domain leads to a freezing of water. With the formation of the frozen water state, another distinct water structure forms on the interface between the ice nanocrystal and mesoscopic glycerol-water domain. The mole fractions of different stages of water (i.e., water molecules in the mesoscopic domain, ice nanocrystals, and the interface between the two) were determined, and the minimum number of water molecules that can gain the bulk ice properties was estimated as approximately 300 water molecules.     

The mechanism of metal corrosion acceleration in ice caused by structural transformations and crystallization of water

Mathematical models are suggested for metal corrosion acceleration in ice undergoing thermally stimulated structural transformations and in ice at the front of water crystallization. Corrosion acceleration is explained by barrier overcoming at the expense of the recombination energy of nonequilibrium orientation defects released as a result of structural and phase transitions.     

How many amorphous ices are there?

Many acronyms are used in the literature for describing different kinds of amorphous ice, mainly because many different preparation routes and many different sample histories need to be distinguished. We here introduce these amorphous ices and discuss the question of how many of these forms are of relevance in the context of polyamorphism. We employ the criterion of reversible transitions between amorphous "states" in finite intervals of pressure and temperature to discriminate between independent metastable amorphous "states" and between "substates" of the same amorphous "state". We argue that the experimental evidence suggests we should consider there to be three polyamorphic "states" of ice, namely low-(LDA), high-(HDA) and very high-density amorphous ice (VHDA). In addition to the realization of reversible transitions between them, they differ in terms of their properties, e.g., compressibility, or number of "interstitial" water molecules. Thus they cannot be regarded as structurally relaxed variants of each other and so we suggest considering them as three distinct megabasins in an energy landscape visualization.     

Formation and stability of cubic ice in water droplets

There is growing evidence that a metastable phase of ice, cubic ice, plays an important role in the Earth's troposphere and stratosphere. Cubic ice may also be important in diverse fields such as cryobiology and planetary sciences. Using X-ray diffraction, we studied the formation of cubic ice in pure water droplets suspended in an oil matrix as a function of droplet size. The results show that droplets of volume median diameter 5.6 microm froze dominantly to cubic ice with stacking faults. These results support previous suggestions that cubic ice is the crystalline phase that nucleates when pure water droplets freeze homogeneously at approximately 235 K. It is also shown that as the size of the water droplets increased from 5.6 to 17.0 microm, the formation of the stable phase of ice, hexagonal ice, was favoured. This size dependence can be rationalised with heat transfer calculations. We also investigated the stability of cubic ice that forms in water droplets suspended in an oil matrix. We observe cubic ice up to 243 K, much higher in temperature than observed in many previous studies. This result adds to the existing literature that shows bulk ice I(c) can persist up to approximately 240 K. The transformation of cubic ice to hexagonal ice also showed a complex time and temperature dependence, proceeding rapidly at first and then slowing down and coming to a halt. These combined results help explain why cubic ice forms in some experiments described in the literature and not others.     

Comparison of the Dynamics of Water Molecules in Crystals of Proton-Ordered Ice IX and Its Proton-Disordered Analog III

A computer simulation of proton-ordered ice IX and its proton-disordered analog III (768 molecules, 90 K) was carried out by the molecular dynamics method using Poltev–Malenkov's potential. For ice IX, the differences in the dynamic characteristics of molecules with O(1) and O(2) are much wider than those in the case of ice III. The libration spectrum of ice IX has a number of distinct acute peaks, and the spectrum of ice III is strongly smoothed. These peculiarities are explained by the proton ordering of ice IX and disordering of ice III. The latter is responsible for the great differences in the short- and especially long-range environment of water molecules in ice crystals and hence for the presence of many molecules with different dynamic characteristics. Thus averaging over a large number of different vibrational spectra of molecules leads to a smoothed total spectrum in the case of the proton-disordered crystal modification of ice.     

An approximate theory of the ozone isotopic effects: rate constant ratios and pressure dependence

The isotopic effects in ozone recombination reactions at low pressures are studied using an approximate theory which yields simple analytic expressions for the individual rate constant ratios, observed under "unscrambled" conditions. It is shown that the rate constant ratio between the two competing channels XYZ-->X+YZ and XYZ-->XY+Z is mainly determined by the difference of the zero-point energies of diatomic molecules YZ and XY and by the efficiency of the deactivation of the newly formed excited ozone molecules, whereas the mass-independent fractionation depends on a "nonstatistical" symmetry factor eta and the collisional deactivation efficiency. Formulas for the pressure effects on the enrichment and on the rate constant ratios are obtained, and the calculated results are compared with experiments and more exact calculations. In all cases, ratios of isotope rates and the pressure dependence of enrichments, the agreement is good. While the initial focus was on isotope effects in the formation of O(3), predictions are made for isotope effects on ratios of rate constants in other reactions such as O+CO-->CO(2), O+NO-->NO(2), and O+SO-->SO(2).     

New simulation model of multicomponent crystal growth and inhibition

We review a novel computational model for the study of crystal structures both on their own and in conjunction with inhibitor molecules. The model advances existing Monte Carlo (MC) simulation techniques by extending them from modeling 3D crystal surface patches to modeling entire 3D crystals, and by including the use of "complex" multicomponent molecules within the simulations. These advances makes it possible to incorporate the 3D shape and non-uniform surface properties of inhibitors into simulations, and to study what effect these inhibitor properties have on the growth of whole crystals containing up to tens of millions of molecules. The application of this extended MC model to the study of antifreeze proteins (AFPs) and their effects on ice formation is reported, including the success of the technique in achieving AFP-induced ice-growth inhibition with concurrent changes to ice morphology that mimic experimental results. Simulations of ice-growth inhibition suggest that the degree of inhibition afforded by an AFP is a function of its ice-binding position relative to the underlying anisotropic growth pattern of ice. This extended MC technique is applicable to other crystal and crystal-inhibitor systems, including more complex crystal systems such as clathrates.     

Interaction of low-energy ions and atoms of light elements with a fluorinated carbon molecular lattice

The mechanism of interaction of low-energy atoms and ions of light elements (H, H+, He, Li, the kinetic energy of the particles 2-40 eV) with C6H6, C6F12, C60, and C60F48 molecules was studied by ab initio MD simulations and quantum-chemical calculations. It was shown that starting from 6 A from the carbon skeleton for the "C6H6 + proton" and "C60 + proton" systems, the electronic charge transfer from the aromatic molecule to H+ occurs with a probability close to 1. The process transforms the H+ to a hydrogen atom and the neutral C6H6 and C60 molecules to cation radicals. The mechanism of interaction of low-energy protons with C6F12 and C60F48 molecules has a substantially different character and can be considered qualitatively as the interaction between a neutral molecule and a point charge. The Coulomb perturbation of the system arising from the interaction of the uncompensated proton charge with the Mulliken charges of fluorine atoms results in an inversion of the energies of the electronic states localized on the proton and on the C6F12 and C60F48 molecules and makes the electronic charge transfer energetically unfavorable. On the different levels of theory, the barriers of the proton penetration for the C6F12 and C60F48 molecules are from two to four times lower than those for the corresponding parent systems (C6H6 and C60). The penetration barriers of the He atom and Li+ ion depend mainly on the effective radii of the bombarding particles. The theoretical penetration and escaped barriers for the "Li+ + C60" process qualitatively explain the experimental conditions of synthesis of the Li@C60 complex.     

On the Debye-Waller factor of hexagonal ice: a computer simulation study

We investigate by molecular dynamics (MD) simulations the temperature dependence of the Debye-Waller (DW) factor of hexagonal ice with 25 different proton-disordered configurations. Each initial configuration is composed of 288 water molecules with no net dipole moment. The intermolecular interaction of water is described by TIP4P potential. Each production run of the simulation is 15 ns or longer. We observe a change in slope of the DW factor around 200 K, which cannot be explained within the framework of either classical or quantum harmonic approximation. Configurations generated by MD simulations are subjected to the steepest descent energy minimization. Analysis of the local energy minimum structures reveals that water molecules above 200 K jump to other lattice sites via some local energy minimum structures which contain some water molecules sitting on the locations other than the lattice sites. As time evolves, these defect molecules move back and forth to the lattice sites yielding defect-free structures. Those motions are responsible for the unusual increase in the DW factor at high temperatures. In making a transition from an energy-minimum structure to another one, a small number of water molecules are involved in a highly cooperative fashion. The larger DW factor at higher temperature arises from jump-like motions of water molecules among these locally stable configurations which may or may not be a family of the proton-disordered ice forms satisfying the "ice rule".     

On understanding stacking fault formation in ice

Despite dedicated efforts aimed at revealing possible molecular structures of the ice defects associated with stacking faults in ice (I), these molecular arrangements have remained a puzzle. Here we demonstrate how the reorganization of water molecules on different faces of ice (I) can facilitate formation of stacking faults within a crystal. We show that a pair of point defects can manifest a particular combination of coupled five- and eight-membered rings (5-8 rings). These structural motifs can facilitate a shift in layers within an ice (I) crystal, thereby inducing stacking faults. Furthermore, the presence of molecular solutes such as methane at the ice interface appears to trigger the formation of coupled 5-8 rings. The observation of such coupled 5-8 ring defects provides insights into the possible molecular mechanisms of stacking fault formation in ice (I) and has implications for ice crystal growth phenomenology and the consequent physical and chemical properties of ice.     

Local angular momentum-local impact parameter analysis: derivation and properties of the fundamental identity, with applications to the F+H2, H+D2, and Cl+HCl chemical reactions

The technique of local angular momentum-local impact parameter (LAM-LIP) analysis has recently been shown to provide valuable dynamical information on the angular scattering of chemical reactions under semiclassical conditions. The LAM-LIP technique exploits a nearside-farside (NF) decomposition of the scattering amplitude, which is assumed to be a Legendre partial wave series. In this paper, we derive the "fundamental NF LAM identity," which relates the full LAM to the NF LAMs (there is a similar identity for the LIP case). Two derivations are presented. The first uses complex variable techniques, while the second exploits an analogy between the motion of the scattering amplitude in the Argand plane with changing angle and the classical mechanical motion of a particle in a plane with changing time. Alternative forms of the fundamental LAM-LIP identity are described, one of which gives rise to a CLAM-CLIP plot, where CLAM denotes (Cross section) x LAM and CLIP denotes (Cross section) x LIP. Applications of the NF LAM theory, together with CLAM plots, are reported for state-to-state transitions of the benchmark reactions F+H2-->FH+H, H+D2-->HD+D, and Cl+HCl-->ClH+Cl, using as input both numerical and parametrized scattering matrix elements. We use the fundamental LAM identity to explain the important empirical observation that a NF cross section analysis and a NF LAM analysis provide consistent (and complementary) information on the dynamics of chemical reactions.