Identical Binding Energies Research Articles

P-type ZnO:N thin films deposited at room temperature on different substrates for p-channel Thin Film Transistor fabrication

A series of ZnO:N thin films were deposited by means of reactive pulsed laser deposition at room temperature on SiO2 glass slides, quartz, Al2O3, polyimide, silicon, and thermally oxidized SiO2. The p-type conductivity was confirmed by Hall effect-Van der Pauw measurements, with electrical parameters varying depending on the substrate deposition as follow: hole concentration between 2.4×1018 - 3.8×1017 cm-3, resistivity between 0.5 - 4 Ωcm, and mobility between 2 - 8 cm2V-1s-1. In situ X-ray photoelectron spectroscopy revealed identical binding energy values of the ZnO:N thin films across all substrates; the relative atomic concentrations varied between 49-53.8 at.%, 44-49 at.% and 2-2.4 at.% for zinc, oxygen and nitrogen respectively, due to over-quantification related to zinc particle splashing. Scanning electron microscopy confirmed a surface roughness of the films below 2 nm. Several wide and defect-related emissions were found by Cathodoluminescence; but the film deposited on quartz exhibited a unique, intense, and narrow blue band, the deconvolution of which revealed peaks at wavelengths of 430 nm and 461 nm. A growth rate of 14 nm/hour, and an etching rate of 2 nm/sec were found; these parameters were confirmed with the fabrication of smooth-walled ZnO:N thin films microstructures using photolithography. Finally, Thin Film Transistors (TFT) were fabricated. The devices exhibited low, but clear field effect current amplification, with a Ion/Ioff = 10. The feasibility of using room-temperature deposited p-type ZnO:N thin films for p-channel TFT fabrication was demonstrated.

Theory of Sequence Effects in Amyloid Aggregation.

We present a simple model for the effect of amino acid sequences on amyloid fibril formation. Using the HP model we find the binding lifetimes of four simple sequences by solving the first passage time for the intermolecular H-bond reaction coordinate. We find that sequences with identical binding energies have widely varying binding times depending on where the aggregation prone amino acids are located in the sequence. In general, longer binding times occur when the aggregation prone amino acids are clustered in a single "hot spot". Similarly, binding times are shortened by clustering weakly bound residues. Both of these effects are explained by an increase in the multiplicity of unbinding trajectories that comes from adding weak binding residues. Our model predicts a transition from ordered to disordered fibrils as the concentration of monomers increases. We apply our model to Aβ, IAPP, and apomyoglobin using binding energy estimates derived from bioinformatics. We find that these sequences are highly selective of the in-register state. This selectivity arises from the having strongly bound segments of varying length and separation.

Aromatic molecules on low-index coinage metal surfaces: Many-body dispersion effects.

Understanding the binding mechanism for aromatic molecules on transition-metal surfaces in atomic scale is a major challenge in designing functional interfaces for to (opto)electronic devices. Here, we employ the state-of-the-art many-body dispersion (MBD) approach, coupled with density functional theory methods, to study the interactions of benzene with low-index coinage metal surfaces. The many-body effects contribute mostly to the (111) surface, and leastly to the (110) surface. This corresponds to the same sequence of planar atomic density of face-centered-cubic lattices, i.e., (111) > (100) > (110). The binding energy for benzene/Au(110) is even stronger than that for benzene/Ag(110), due to a larger broadening of molecular orbitals in the former case. On the other hand, our calculations show almost identical binding energies for benzene on Ag(111) and Au(111), which contradicts the classic d-band center theory that could well predict the trend in chemisorption energies for various small molecules on a number of metal surfaces. Our results provide important insight into the benchmark adsorption systems with opener surfaces, which could help in designing more complex functional interfaces.

Trends for isolated amino acids and dipeptides: Conformation, divalent ion binding, and remarkable similarity of binding to calcium and lead.

We derive structural and binding energy trends for twenty amino acids, their dipeptides, and their interactions with the divalent cations Ca2+, Ba2+, Sr2+, Cd2+, Pb2+, and Hg2+. The underlying data set consists of more than 45,000 first-principles predicted conformers with relative energies up to ~4 eV (~400 kJ/mol). We show that only very few distinct backbone structures of isolated amino acids and their dipeptides emerge as lowest-energy conformers. The isolated amino acids predominantly adopt structures that involve an acidic proton shared between the carboxy and amino function. Dipeptides adopt one of two intramolecular-hydrogen bonded conformations C5 or . Upon complexation with a divalent cation, the accessible conformational space shrinks and intramolecular hydrogen bonding is prevented due to strong electrostatic interaction of backbone and side chain functional groups with cations. Clear correlations emerge from the binding energies of the six divalent ions with amino acids and dipeptides. Cd2+ and Hg2+ show the largest binding energies–a potential correlation with their known high acute toxicities. Ca2+ and Pb2+ reveal almost identical binding energies across the entire series of amino acids and dipeptides. This observation validates past indications that ion-mimicry of calcium and lead should play an important role in a toxicological context.

Identical Binding Energies and Work Functions for Distinct Adsorption Structures: Olympicenes on the Cu(111) Surface.

Reliability is one of the major concerns and challenges in designing organic/inorganic interfaces for (opto)electronic applications. Even small structural differences for molecules on substrates can result in a significant variation in the interface functionality, due to the strong correlation between geometry, stability, and electronic structure. Here, we employed state-of-the-art first-principles calculations with van der Waals interactions, in combination with atomic force microscopy experiments, to explore the interaction mechanism for three structurally related olympicene molecules adsorbed on the Cu(111) surface. The substitution of a single atom in the olympicene molecule switches the nature of adsorption from predominantly physisorptive character [olympicene on Cu(111)], to an intermediate state [olympicene-derived ketone on Cu(111)], then to chemisorptive character [olympicene radical on Cu(111)]. Despite the remarkable difference in adsorption structures (by up to 0.9 Å in adsorption height) and different nature of bonding, the olympicene, its ketone, and its radical derivatives have essentially identical binding energies and work functions upon interaction with the metal substrate. Our findings suggest that the stability and work functions of molecular adsorbates could be rendered insensitive to their adsorption structures, which could be a useful property for (opto)electronic applications.

High-order harmonic generation in laser-irradiated homonuclear diatomics: The velocity gauge version of the molecular strong-field approximation

The generation of high harmonics in laser-irradiated light homonuclear diatomics (H2+, N2 and O2) compared to that in atomic counterparts (of nearly identical binding energy) is studied within the velocity gauge version of conventional strong-field approximation. The applied strong-field approach (we alternatively developed earlier to incorporate rescattering effects beyond the conventional saddle-point approximation) is currently extended to molecular case by means of supplement the standard linear combination of atomic orbitals} and molecular orbitals method. The associated model proved to adequately reproduce a general shape and detailed structure of molecular harmonic spectra, which demonstrate a number of remarkable distinctive differences from respective atomic spectra calculated under the same laser pulses. The revealed differences are found to be strongly dependent on internuclear separation and also very sensitive to the orbital and bonding symmetry of contributing molecular valence shell. In particular, the model correctly predicts the behavior of high-frequency plateau (both for its extent and even details of structure) in molecular harmonic spectra at small (nearly equilibrium) and large internuclear separations. In addition, for some group of harmonics, the harmonic emission rates were ascertained to dominate by contribution from inner molecular shells of higher binding energy and different orbital symmetry compared to the outermost molecular orbital normally predominantly contributing.

Studies on surface composition and chemical states of calcium manganites

This paper describes investigations on atomic composition and chemical states of sintered calcium manganites discs in surface and near surface regions. The atomic composition was determined by 3.05 MeV 16O(α, α) 16O resonance elastic scattering while the chemical states by, X-ray photoelectron spectroscopy (XPS). The specimens examined included undoped and donor (Y 3+, Bi 3+) doped CaMnO 3, and Ca-excess and Mn-excess manganites namely Ca 2MnO 4 and CaMn 2O 4 respectively. Calcium manganite powder used in the preparation of discs was synthesized by a wet chemical method. X-ray diffraction (XRD) results indicated that all the discs are monophasic except CaMn 2O 4, which contained ∼98% requisite manganite. The atomic compositions of undoped specimens are close to the stoichiometric value while Y 3+ and Bi 3+ doped specimens are deficient in Mn and O respectively. The O deficiency may be responsible for comparatively higher electrical conductivity of Bi 3+ doped specimen. Some of the specimens were also examined subsequent to their annealing in low P O 2 atmosphere. This treatment produced significant compositional and structural modifications in the near surface regions. Mn(2p) electrons have identical binding energies in the sintered discs; therefore the valence states of Mn could not be discerned. However lesser binding energies of these electrons in annealed CaMnO 3 indicated the existence of Mn(II)/Mn(III) in the specimen.

Ab initio-based intermolecular carbon–carbon pair potentials for polycyclic aromatic hydrocarbon clusters

We derived the carbon-carbon pair potentials for polycyclic aromatic hydrocarbon (PAH) clusters, which exhibited a strikingly similar geometry to that of the two-layer graphite. The binding energy of PAH clusters ranging in size from the benzene dimer to the pyrene dimer obtained by ab initio calculations at the MP2 level was used to extract the pair potentials in the form of the Lennard-Jones and Exponential-6 functions. Identical binding energy and equilibrium interlayer distance were reproduced by these functions to those calculated by the ab initio method. The pair potentials for PAHs yield the same equilibrium C-C distance as the known pair potentials for graphite and fullerenes, but nearly twice the well depth because of the polarization of the C-H bond.

Theory of molecular tunneling ionization

We have extended the tunneling ionization model of Ammosov-Delone-Krainov (ADK) for atoms to diatomic molecules by considering the symmetry property and the asymptotic behavior of the molecular electronic wave function. The structure parameters of several molecules needed for calculating the ionization rates using this molecular ADK model have been obtained. The theory is applied to calculate the ratios of ionization signals for diatomic molecules with their companion atoms that have nearly identical binding energies. The origin of ionization suppression for some molecules has been identified. The predicted ratios for pairs with suppression $({\mathrm{D}}_{2}:\mathrm{Ar},$ ${\mathrm{O}}_{2}:\mathrm{Xe})$ and pairs without suppression $({\mathrm{N}}_{2}:\mathrm{Ar},$ CO:Kr) are in good agreement with the measurements. However, the theory predicts suppression for ${\mathrm{F}}_{2}:\mathrm{Ar},$ which is in disagreement with the experiment. The ionization signals of NO, ${\mathrm{S}}_{2},$ and of SO have also been derived from the experimental data, and the results are also shown to be in agreement with the prediction of the present molecular ADK theory.

Stereospecific DNA Binding of Luminescent Atropisomeric Viologens

Binding to B-DNA of one enantiomer of dq3pyp, -a member of a novel family of intercalating luminescent viologens derived from N, N′-dialkyl-6-(2-pyridyl)phenanthridine, in which dialkyl is (CH 2) − 2( dq2pyp), -(CH 2) − 3 (dq3pyp), or (-CH 3) 2 ( Me2pyp)-, is strongly favored compared to its estable atropisomer. Evidence of the stereospecific interaction has been gained by resolution of a rac- dq3pyp mixture upon dialysis in the presence of DNA, monitored by circular dichroism. Molecular modeling suggests that the S enantiomer of both dq3pyp and dq2pyp is the one preferred for the binding. No similar resolution has been achieved with rac- dq2pyp due to the lower barrier to interconversion of its atropisomers, as shown by 1H-NMR. The identical binding energy of the two modeled diastereoisomeric Me2pyp-DNA complexes discard enantiospecific interaction of this drug. Affinity chromatography on DNA-cellulose allows isolation of the pure enantiomers of dq3pyp.

An ab initio molecular orbital study of the structures and energetics of the neutral and cationic CuO2 and CuNO molecules in the gas phase

The interactions of neutral and ionic copper atoms with molecular oxygen and nitric oxide have been examined by using relativistic effective core potentials (ECP) and different ab initio MO methods up to the coupled cluster CCSD(T) approach. For neutral CuO2 the ECP calculations reproduce the results of all-electron calculations which prefer the ‘‘side-on’’ structure by 0.9 kcal/mol versus an ‘‘end-on’’ coordination. The binding energy for the ‘‘side-on’’ complex (2A2) has been calculated to be 9.7 kcal/mol. For the cationic end-on CuO+2 (3Σ+) an identical binding energy (9.7 kcal/mol) results from CCSD(T) calculations; the side-on complex (3B1) is 4 kcal/mol less stable. The singlet state (1A′) of the cation is 27 kcal/mol higher in energy and bound with 13.6 kcal/mol with respect to singlet oxygen (1Δ+g) and Cu+ (1S), while the side-on (1A1) state is 3.8 kcal/mol less stable than the 1A′ state. For the interaction of neutral Cu with NO the end-on CuNO coordination (1A′) with a bonding energy of 10.4 kcal/mol is preferred while the related triplet (3A″) is 5.5 kcal/mol less stable. In the cationic system [Cu,N,O]+, both isomers, i.e., CuNO+ and CuON+ represent stable species, with CuNO+ (2A′) being the more stable one. The bond dissociation energies of these two isomers are calculated to 19.3 and 11.4 kcal/mol, respectively.

Nonrelativistic versus ultra-relativistic description of Regge trajectories

Comparing the energy spectrum of the nonrelativistic description of hadrons as bound states of quarks to the one obtained in an ultra-relativistic treatment, we show that both approaches yield almost identical binding energies if the confining interaction is able to reproduce the observed asymptotic linearity of the Regge trajectories.

A new method to detect energy-band bending using x-ray photoemission spectroscopy

A new method to detect energy-band bending using x-ray photoemission spectroscopy has been proposed which measures the changes in the binding energy with the change in the detection angle of photoelectrons. This method was applied to crystalline silicon of various doping conditions with a thin surface oxide and after removing it by ion sputtering. The change in the binding energy with the change in the detection angle was observed only in heavily doped p-type silicon before sputtering, but not in other silicon specimens studied in this work. All specimens showed an identical binding energy independent of the detection angle after removing surface oxides by sputtering. These results are explained semiquantitatively using a simple band-bending model.