Small Binding Energy Research Articles

Lorentz-boosted description of a heavy quarkonium

In this paper we study the relation between the light-front (infinite momentum) and rest-frame descriptions of quarkonia. While the former is more convenient for high-energy production, the latter is usually used for the evaluation of charmonium properties. In particular, we discuss the dynamics of a relativistically moving system with nonrelativistic internal motion and give relations between rest frame and light-front potentials used for the description of quarkonium states. We consider two approximations, first the small coupling regime, and next the nonperturbative small binding energy approximation. In both cases we get consistent results. Our results could be relevant for the description of final state interactions in a wide class of processes, including quarkonium production on nuclei and plasma. Moreover, they can be extended to the description of final state interactions in the production of weakly bound systems, such as for example the deuteron.

Exciton and Free Charge Dynamics of Methylammonium Lead Iodide Perovskites Are Different in the Tetragonal and Orthorhombic Phases

The small exciton binding energy of perovskite suggests that the long-lived photoluminescence and slow recovery of the ground state bleaching of the tetragonal phase at room temperature results primarily from the decay of free charges rather than the decay of the initially created excitons. Here we demonstrate the ground state bleaching recovery of the orthorhombic phase of methylammonium lead iodide (CH3NH3PbI3) is much faster than that of the tetragonal phase using temperature dependent transient absorption spectroscopy. The distribution in orientation of the methylammonium group which is disordered in the tetragonal phase and ordered in the orthorhombic phase results in smaller dielectric constant and larger exciton binding energy in the latter phase. We observe the recovery of the ground state bleaching in the orthorhombic phase to be comprised of decays of both excitons and free charges. Our findings suggest CH3NH3PbI3 behaves like a nonexcitonic semiconductor in the tetragonal phase and an excitonic...

Photoelectron spectroscopy on the charge reorganization energy and small polaron binding energy of molecular film

Understanding of electron-phonon coupling as well as intermolecular interaction is required to discuss the mobility of charge carrier in functional molecular solids. This article summarizes recent progress in direct measurements of valence hole-vibration coupling in ultrathin films of organic semiconductors by using ultraviolet photoelectron spectroscopy (UPS). The experimental study of hole-vibration coupling of the highest occupied molecular orbital (HOMO) state in ordered monolayer film by UPS is essential to comprehend hole-hopping transport and small-polaron related transport in organic semiconductors. Only careful measurements can attain the high-resolution spectra and provide key parameters in hole-transport dynamics, namely the charge reorganization energy and small polaron binding energy. Analyses methods of the UPS HOMO fine feature and resulting charge reorganization energy and small polaron binding energy are described for pentacene and perfluoropentacene films. Difference between thin-film and gas-phase results is discussed by using newly measured high-quality gas-phase spectra of pentacene. Methodology for achieving high-resolution UPS measurements for molecular films is also described.

Unusual energy separation of subbands in Si(111) p-channels induced by In adsorption

We investigated the dispersion structure of the hole subbands in vicinal Si(111)4 × 1-In surfaces directly by angle-resolved photoelectron spectroscopy. In this study, three inversion layers with different impurity concentrations and numbers of times of flash annealing (FA) were investigated. We observed wider energy separations of subbands levels for the sample with a less number of FA and a higher impurity concentration. However, the observed energy levels and separations had smaller binding energy than those calculated by triangle potential approximation. We found that the discrepancies were due to the out-diffusion of Arsenic atoms from the sub-surface region of silicon via high temperature FA. The possible potential profile of the space charge layer after considering the out-diffusion of Arsenic dopant atoms at the sub-surface region was proposed.

Proficient electron injection lithium complexes designed by molecular energy calculation for high performance OLEDs

We report new electron injection lithium complexes, lithium 2-(2-pyridyl)-3-pyridinolate (LIPPy) and lithium 4-phenyl-2-(2-pyridyl)phenolate (LIPPP) for low driving voltage and better stability of organic light emitting diodes (OLEDs). These materials were designed with the help of molecular simulation of anion formation energy and lithium binding energy calculations. Small anion formation energy and low binding energy of lithium complexes show good correlation with expected experimental driving voltage of the OLEDs. Fabricated OLEDs with these new lithium complexes exhibit lower driving voltage, higher power efficiency and longer lifetime as compare to the widely used and commercially available lithium 8-quinolate (Liq) and lithium 2-(2-pyridyl)phenolate (LIPP).

Origin of the high open circuit voltage in planar heterojunction perovskite solar cells: Role of the reduced bimolecular recombination

The high open circuit voltage is an attractive feature for the currently popular organic-inorganic hybrid perovskite solar cells. In this paper, by employing the macroscopic device model simulation, we investigate its origin for the planar heterojunction perovskite solar cells. Based on the calculated current density-voltage characteristics, it is revealed that compared to the excitonic solar cells, the fast thermal-activated exciton dissociation in the bulk due to the small exciton binding energy may improve the short circuit current and the fill factor, but its beneficial role on the open circuit voltage is marginal. The most significant contribution for the open circuit voltage comes from the reduced bimolecular recombination. In the perovskites, with the recombination prefactor many orders of magnitude smaller than that based on the Langevin's theory, the internal charge density level is significantly enhanced and the density gradient is removed, leading to the high quasi-Fermi level splitting and thus the small open circuit voltage loss. For the nonradiative recombination pathway due to the deep trap states, it may induce significant loss of open circuit voltage as the trap density is high, while for the moderately low density its effect on the open circuit voltage is small and negligible.

Investigation ofN23in a three-body model

The neutron-drip-line nucleus $^{23}$N is investigated in a three-body model consisting of a $^{21}$N core and two valence neutrons. By solving the Faddeev equations with the realistic neutron-neutron potentials and the neutron-core potentials, we calculate the ground state properties of $^{23}$N and also find that there is a new excited state with two-neutron separation energy at about 0.18 MeV. The properties, such as the two-neutron separation energies, are obtained with a good agreement with experiments. By calculating the root-mean-square matter radii, the average distances between the valence neutrons, and the average distances between the core and the center-of-mass of the neutron pair, we show that the excited state of $^{23}$N has a clear halo structure. The correlation density distributions of the three-body system are also calculated to analyze its geometric configuration. At last, we find that the excited state of $^{23}$N has a very small binding energy, a large radius and distribution, and a triangular shape similar with the ground state. These roperties of the excited state indicate that it can be an Efimov state.

Vibrational predissociation of aniline(pyrrole)(water)2+ and aniline(pyrrole)(water)3+: Structures and dissociation dynamics

Vibrational predissociation spectra of aniline(pyrrole)(water)2+ and aniline(pyrrole)(water)3+ clusters were taken at 2700–4000cm−1 to verify their most stable structures. One NH of aniline was bonded to the π electron of pyrrole while the other NH was bonded to water. Pyrrole molecule was arranged in such a way that NH of pyrrole formed another hydrogen bond with a water molecule nearby. Water molecule was more easily ejected than pyrrole for both AnPyW2+ and AnPyW3+ although pyrrole had smaller binding energy than water.

Adsorption of CO and NO molecules on SiC nanotubes and nanocages: DFT study

Abstract Silicon carbide (SiC) nanostructures have attracted extensive researches regarding their unique properties. Surface modification of the SiC nanotubes and nanocages can be useful for developing their potential applications to the gas sensors. In this paper we have studied the adsorption properties of the CO and NO molecules at different situations on a zigzag SiCNT(10,0) and armchair SiCNT(6,6) nanotubes and Si12C12 nanocage using density functional theory (DFT) calculations. The spin polarized DFT with PBE functional is employed in all calculations for the total energy calculation and optimization of the considered structures. Our results reveal that both zigzag and armchair nanotubes can adsorb CO molecule due to chemisorption and physisorption processes as its binding energy in its most stable configuration is about 0.95 and 0.89 eV, respectively. The binding energy of the NO molecule to the considered SiC nanotubes and nanocages is somewhat higher than CO binding energy in its most stable configuration. The most stable configuration for NO adsorption on SiC nanotubes is inside the nanotubes with a small different binding energy value for considered zigzag and armchair SiC nanotubes. The electronic structure of the SiC nanocage interacting with CO and NO is also discussed in this paper as our results show that the geometry structure of the nanocages is very important to the adsorption properties of the CO and NO molecules. Moreover, the present results may be useful for the design of the SiC based nanodevices for gas adsorption, storage and sensors.

Medium-heavy nuclei from nucleon-nucleon interactions in lattice QCD

On the basis of the Brueckner-Hartree-Fock method with the nucleon-nucleon forces obtained from lattice QCD simulations, the properties of the medium-heavy doubly-magic nuclei such as 16^O and 40^Ca are investigated. We found that those nuclei are bound for the pseudo-scalar meson mass M_PS ~ 470 MeV. The mass number dependence of the binding energies, single-particle spectra and density distributions are qualitatively consistent with those expected from empirical data at the physical point, although these hypothetical nuclei at heavy quark mass have smaller binding energies than the real nuclei.

The electronic structures of group-V-group-IV hetero-bilayer structures: a first-principles study.

Recent findings of group-V nanosheets provide new building units for van der Waals hetero-nanostructures. Based on first-principles calculation, we investigate the structural and electronic properties of bilayer hetero-sheets composed of group-V (arsenene/antimonene) and group-IV (graphene/silicene) layers. These hetero-sheets exhibit typical van der Waals features with small binding energies and soft interlayer elastic constants. In the hetero-sheets, the Dirac characteristics of the group-IV layer and the semiconducting feature of the group-V one are well preserved, which causes a Schottky contact at the metal-semiconductor interface. The Schottky barriers are always p-type in the Si-based hetero-sheets, whereas in the C-based ones, the interfacial feature is sensitive to the interlayer distance. A tensile strain would induce a p-type-to-n-type Schottky barrier transition for the As-C hetero-sheet, while a compressive strain can cause a Schottky-to-ohmic contact transition in the Sb-C one. Moreover, due to the inhomogeneous charge redistribution, a sizeable band gap is opened at the Dirac point of the Sb-Si hetero-sheet, which could be linearly modulated by perpendicular strains around the equilibrium site. The versatile electronic structures and tunable interfacial properties enable the group-V-group-IV hetero-bilayer structures to have many potential applications in nano-devices and nano-electronics.

Aloof baby Skyrmions

We show that a suitable choice for the potential term in the two-dimensional baby Skyrme model yields solitons that have a short-range repulsion and a long-range attraction. The solitons are therefore aloof, in the sense that static multi-soliton bound states have constituents that preserve their individual identities and are sufficiently far apart that tail interactions yield small binding energies. The static multi-soliton solutions are found to have a cluster structure that is reproduced by a simple binary species particle model. In the standard three-dimensional Skyrme model of nuclei, solitons are too tightly bound and are often too symmetric, due to symmetry enhancement as solitons coalesce to form bound states. The aloof baby Skyrmion results endorse a way to resolve these issues and provides motivation for a detailed study of the related three-dimensional version of the Skyrme model.

Traditional and ion-pair halogen-bonded complexes between chlorine and bromine derivatives and a nitrogen-heterocyclic carbene.

A theoretical study of the halogen-bonded complexes (A-X···C) formed between halogenated derivatives (A-X; A = F, Cl, Br, CN, CCH, CF3, CH3, H; and X = Cl, Br) and a nitrogen heterocyclic carbene, 1,3-dimethylimidazole-2-ylidene (MeIC) has been performed using MP2/aug'-cc-pVDZ level of theory. Two types of A-X:MeIC complexes, called here type-I and -II, were found and characterized. The first group is described by long C-X distances and small binding energies (8-54 kJ·mol(-1)). In general, these complexes show the traditional behavior of systems containing halogen-bonding interactions. The second type is characterized by short C-X distances and large binding energies (148-200 kJ·mol(-1)), and on the basis of the topological analysis of the electron density, they correspond to ion-pair halogen-bonded complexes. These complexes can be seen as the interaction between two charged fragments: A(-) and (+)[X-CIMe] with a high electrostatic contribution in the binding energy. The charge transfer between lone pair A(LP) to the σ* orbital of C-X bond is also identified as a significant stabilizing interaction in type-II complexes.

Time-dependent density-matrix functional theory for trion excitations: Application to monolayerMoS2and other transition-metal dichalcogenides

To examine optically excited bound states, excitons and trions, in monolayer ${\mathrm{MoS}}_{2}$, ${\mathrm{MoSe}}_{2}$, and ${\mathrm{WSe}}_{2}$, we have formulated and applied a generalized time-dependent density-matrix functional theory approach. Three different types of exchange-correlation (XC) kernels were used and their validity was evaluated through comparison with available experimental data. For excitons, we find that the local kernels, from the local density approximation and its gradient-corrected form, lead to much smaller binding energy than that extracted from experimental data, while those based on long-range (LR) interactions fare much better. The same is the case for the trion binding energy once screening effects are taken into account. Our results suggest that for both excitons and trions, the LR form of the XC kernel is necessary to describe bound states. These results confirm information from experimental data on single-layer dichalcogenides that their exciton and trion binding energies are of the order of hundreds (excitons) and tens (trions) of milli-electron volts, a result that may suggest technological application of these materials at room temperature. The proposed methodology can be straightforwardly extended to bound states with a larger number of electrons and holes than considered here.

Unique bonding nature of carbon-substituted Be2 dimer inside the carbon (sp(2)) network.

Controlled doping of active carbon materials (viz., graphenes, carbon nanotubes etc.) may lead to the enhancement of their desired properties. The least studied case of C/Be substitution offers an attractive possibility in this respect. The interactions of Be2 with Be or C atoms are dominated by the large repulsive Pauli exchange contributions, which in turn offsets the attractive interactions leading to relatively small binding energies. The Be2 dimer, e.g., after being doped inside a planar carbon network, undergoes orbital adjustments due to charge transfer and unusual intermolecular interactions and is oriented perpendicular to the plane of the carbon network with the Be-Be bond center located inside the plane. The present theoretical investigation on the nature of bonding in C/Be2 exchange complexes, using state of the art quantum chemical techniques, reveals a sp(2) carbon-like bonding scheme in Be2 arising due to the molecular hybridization of σ and two π orbitals. The perturbations imposed by doped Be2 dimers exhibit a local character of the structural and electronic properties of the complexes, and the separation by two carbon atoms between beryllium active centers is sufficient to consider these centers as independent sites.

Solid argon as a possible substrate for quasi-freestanding silicene

We study the structural and electronic properties of silicene on solid Ar(111) substrate using ab initio calculations. We demonstrate that due to weak interaction, quasi-freestanding silicene is realized in this system. The small binding energy of only meV per Si atom also indicates the possibility to separate silicene from the solid Ar(111) substrate. In addition, a band gap of 11 meV and a significant splitting of the energy levels due to spin-orbit coupling are observed.

Near-BPS Skyrmions: Constant baryon density

Although it provides a relatively good picture of the nucleons, the Skyrme Model is unable to reproduce the small binding energy in nuclei. This suggests that Skyrme-like models that nearly saturate the Bogomol'nyi bound may be more appropriate since their mass is roughly proportional to the baryon number A. For that purpose, we propose a near-BPS Skyrme Model. It consists of terms up to order six in derivatives of the pion fields, including the nonlinear and Skyrme terms which are assumed to be relatively small. For our special choice of mass term, we obtain well-behaved analytical BPS-type solutions with constant baryon density configurations, as opposed to the more complex shell-like configurations found in most extensions of the Skyrme Model. Fitting the four model parameters, we find a remarkable agreement for the binding energy per nucleon B/A with respect to experimental data. These results support the idea that nuclei could be near-BPS Skyrmions.

Dynamical calculation of theΔΔdibaryon candidates

We perform a dynamical calculation of the $\Delta\Delta$ dibaryon candidates with $IJ^{P}=03^{+}$ and $IJ^{P}=30^{+}$ in the framework of two constituent quark models: the quark delocalization color screening model and the chiral quark model. Our results show that the dibaryon resonances with $IJ^{P}=03^{+}$ and $IJ^{P}=30^{+}$ can be formed in both models. The mass and width of $IJ^{P}=03^{+}$ state are smaller than that of $IJ^{P}=30^{+}$ state due to the one-gluon-exchange interaction between quarks. The resonance mass and decay width of $IJ^{P}=03^{+}$ state in both models agree with that of the recent observed resonance in the reaction $pn \rightarrow d\pi^{0}\pi^{0}$. The $IJ^{P}=30^{+}$ $\Delta\Delta$ is another dibaryon candidate with smaller binding energy and larger width. The hidden-color channel coupling is added to the chiral quark model, and we find it can lower the mass of the dibaryons by 10-20 MeV.

Sputtering of metals at ion-electron irradiation

It has been found that, in contrast to the commonly accepted opinion, simultaneous irradiation by 15-keV Ar+ ions and 2.5-keV electrons at temperatures above 0.5T m (T m is the melting temperature) induces much larger sputtering of metallic copper, nickel, and steel than irradiation only by Ar+ ions. The effect increases with the temperature. At T = 0.7T m, the sputtering coefficients in the case of ion-electron irradiation are more than twice as large as the sputtering coefficients in the case of irradiation by Ar+ ions. The experiments on the sublimation of copper show that the sublimation rate in the case of the heating of a sample by an electron beam is higher than that in the case of heating in an electric vacuum oven. The revealed effects are explained by the electron-induced excitation of adatoms (atoms stuck over the surface, which appear owing to ion bombardment). Excited adatoms have a smaller binding energy with the surface and are sputtered more easily.

Adsorption of formaldehyde on graphene and graphyne

The adsorption of formaldehyde on graphene and graphyne was investigated to search high sensitivity sensors for detection of formaldehyde. We have used density functional theory to study the effect of formaldehyde on the electronic properties of graphene and graphyne. It is found that formaldehyde is physisorbed on the graphene and graphyne with small binding energy, large binding distance, and small charge transfer. The calculations also indicate that formaldehyde adsorption modifies the electronic properties of semimetallic graphene, α-graphyne, and β-graphyne and semiconducting γ-graphyne. The graphene and graphyne show semiconducting property in the presence of formaldehyde. The effect of formaldehyde on the electronic properties of graphene and graphyne suggests the potential application of these carbon nanomaterials for formaldehyde detection.