Change In Ionization Potential Research Articles

Exploring the room temperature chemiresistive LPG and humidity sensing properties of MWCNT/TiO2 nanocomposite with DFT interpretations

A nano-sized multi-walled carbon nanotube/titanium dioxide (MWCNT/TiO2) composite gas sensing material was synthesized using the chemical vapor deposition method and extensively characterized through advanced techniques. Scanning electron microscopy (SEM) revealed a microporous surface featuring a cross-linked nanotube structure in the thin film. The bandgap, determined from absorption spectra, was calculated to be 3.89 eV. Electrical resistance variations in response to liquefied petroleum gas (LPG) concentrations (0.5–2 vol%) were systematically recorded over time, with the maximum %sensor response of 423.2 at 2 vol%, indicating high sensitivity. The sensor response towards humidity was found as 1.05 MΩ/%RH at room temperature. The limit of detection (LOD) for LPG by using MWCNT/TiO2 at room temperature was found to be 0.063 vol%. Ab initio density functional theory (DFT) calculations provided insights into the adsorption mechanisms of LPG and H2O on the CNT/TiO2 surface, assessing changes in ionization potential, HOMO-LUMO gap, and electronegativity upon interaction with hydroxyl and CnH2n+2 groups. This comprehensive approach highlights the development of a robust, cost-effective, and technologically advanced sensor for LPG and humidity detection.

Change in ionization potential of magnesium tin oxide films before and after photochromism

Magnesium-tin oxide (MTO) became a cell storage material after strong UV irradiation, and the appearance of the photochromic phenomenon was the sign of initiation of such a function. This phenomenon is not an independent behavior occurring in magnesium-tin oxide films, but we found that the phenomenon occurred in the interface between the MTO layer and indium tin oxide layer prepared under the MTO layer. To clarify this phenomenon, analysis of the MTO layer is the key issue and investigation under the environmental condition is required. The photochromic color change does not reproduce by excess heating treatment. In this paper, we focused on the change in the ionization potential of the MTO film before/after the reversible color change and irreversible erase, and to achieve this experiment, we constructed a novel photoelectron yield spectrometer and measured the ionization potential of a magnesium tin oxide film.

The mixture toxicity of heavy metals on Photobacterium phosphoreum and its modeling by ion characteristics-based QSAR.

Organisms are frequently exposed to mixtures of heavy metals because of their persistence in the environment. The mixture toxicity of heavy metals should therefore be evaluated to perform a rational environmental risk assessment for organisms. In this study, we determined the inhibition toxicity of five heavy metals (Cu2+, Co2+, Zn2+, Fe3+ and Cr3+) and their binary mixtures to Photobacterium phosphoreum (P. phosphoreum). We obtained the following results: (1) the order of individual toxicity was Zn2+>Cu2+>Co2+>Cr3+>Fe3+, and (2) different combined effects (additive, synergistic and antagonistic) were observed in the binary mixtures of heavy metals, with toxicity unit (TU) values ranging from 0.15 to 3.50. To predict the mixture toxicity of heavy metals, we derived the ion characteristic parameters of heavy metal mixtures and explored the ion-characteristic-based quantitative structure–activity relationship (QSAR) model (R2 = 0.750, Q2 = 0.649). The developed QSAR model indicated that the mixture toxicity of heavy metals is related to the change in ionization potential ((ΔIP)mix), the first hydrolysis constant (log(KOH)mix) and the formation constant value ().

Relation between DNA ionization potentials, single base substitutions and pathogenic variants

BackgroundIt is nowadays clear that single base substitutions that occur in the human genome, of which some lead to pathogenic conditions, are non-random and influenced by their flanking nucleobase sequences. However, despite recent progress, the understanding of these "non-local" effects is still far from being achieved.ResultsTo advance this problem, we analyzed the relationship between the base mutability in specific gene regions and the electron hole transport along the DNA base stacks, as it is one of the mechanisms that have been suggested to contribute to these effects. More precisely, we studied the connection between the normalized frequency of single base substitutions and the vertical ionization potential of the base and its flanking sequence, estimated using MP2/6-31G* ab initio quantum chemistry calculations. We found a statistically significant overall anticorrelation between these two quantities: the lower the vIP value, the more probable the substitution. Moreover, the slope of the regression lines varies. It is larger for introns than for exons and untranslated regions, and for synonymous than for missense substitutions. Interestingly, the correlation appears to be more pronounced when considering the flanking sequence of the substituted base in the 3’ rather than in the 5’ direction, which corresponds to the preferred direction of charge migration. A weaker but still statistically significant correlation is found between the ionization potentials and the pathogenicity of the base substitutions. Moreover, pathogenicity is also preferentially associated with larger changes in ionization potentials upon base substitution.ConclusionsWith this analysis we gained new insights into the complex biophysical mechanisms that are at the basis of mutagenesis and pathogenicity, and supported the role of electron-hole transport in these matters.

Mapping and controlling ultrafast dynamics of highly excited H2 molecules by VUV-IR pump-probe schemes

We used ultrashort femtosecond vacuum ultraviolet (VUV) and infrared (IR) pulses in a pump-probe scheme to map the dynamics and nonequilibrium dissociation channels of excited neutral ${\text{H}}_{2}$ molecules. A nuclear wave packet is created in the $B\phantom{\rule{0.16em}{0ex}}^{1}\mathrm{\ensuremath{\Sigma}}_{u}^{+}$ state of the neutral ${\text{H}}_{2}$ molecule by absorption of the ninth harmonic of the driving infrared laser field. Due to the large stretching amplitude of the molecule excited in the $B\phantom{\rule{0.16em}{0ex}}^{1}\mathrm{\ensuremath{\Sigma}}_{u}^{+}$ electronic state, the effective ${\text{H}}_{2}{}^{+}$ ionization potential changes significantly as the nuclear wave packet vibrates in the bound, highly electronically and vibrationally excited $B$ potential-energy curve. We probed such dynamics by ionizing the excited neutral molecule using time-delayed VUV-or-IR radiation. We identified the nonequilibrium dissociation channels by utilizing three-dimensional momentum imaging of the ion fragments. We found that different dissociation channels can be controlled, to some extent, by changing the IR laser intensity and by choosing the wavelength of the probe laser light. Furthermore, we concluded that even in a benchmark molecular system such as ${\text{H}}_{2}$*, the interpretation of the nonequilibrium multiphoton and multicolor ionization processes is still a challenging task, requiring intricate theoretical analysis.

Ensemble-Average Representation of Pt Clusters in Conditions of Catalysis Accessed through GPU Accelerated Deep Neural Network Fitting Global Optimization.

We first report a global optimization approach based on GPU accelerated Deep Neural Network (DNN) fitting, for modeling metal clusters at realistic temperatures. The seven-layer multidimensional and locally connected DNN is combined with limited-step Density Functional Theory (DFT) geometry optimization to reduce the time cost of full DFT local optimization, which is considered to be the most time-consuming step in global optimization. An algorithm based on bond length distribution analysis is used to efficiently sample the configuration space and generate random initial structures. A structure similarity measurement method based on depth-first search is used to identify duplicates. The performance of the new approach is examined by the application to the global minimum searching for Pt9 and Pt13. The ensemble-average representations of the two clusters are constructed based on all geometrically different isomers, on which the structure transition is predicted at low and high temperatures, for Pt9 and Pt13 clusters, respectively. Finally, the ensemble-averaged vertical ionization potential changes when temperature increases, and the property in conditions of catalysis can be different from that evaluated at the global minimum structure.

Optical parameters and work function of Zn–In–Sn–O films

The work function behavior of Zn–In–Sn–O (ZITO) films with various Zn and Sn contents were studied. The work function increased with addition of Zn content. With further increase of Zn contents, the work function gradually decreased. The work function behavior can be investigated by (1) Fermi level position relative the carrier concentration, (2) ionization potential by the surface dipole change. The Fermi level position related the carrier concentration was calculated by Drude parameters, and ionization potential measured by UPS. As results, we confirmed that the work function of ZITO may be linked to changes in ionization potential, not carrier concentration.

Electronic Structure of Organic/organic Interface Depending on Heteroepitaxial Growth Using Templating Layer

The electronic structure at organic-organic interface gives essential information on device performance such as charge transport and mobility. Especially, the molecular orientation of organic material can affect the electronic structure at interface and ultimately the device performance in organic photovoltaics. The molecular orientation is examined by the change in ionization potential (IP) for metal phthalocyanines (MPc, M=Zn, Cu)/fullerene (C60) interfaces on ITO by adding the CuI templating layer through ultraviolet photoelectron spectroscopy measurement. On CuPc/C60 bilayer, the addition of CuI templating layer represents the noticeable change in IP, while it hardly affects the electronic structure of ZnPc/C60 bilayer. The CuPc molecules on CuI represent relatively lying down orientation with intermolecular π-π overlap being aligned in vertical direction. Consequently, in organic photovoltaics consisting of CuPc and C60 as donor and acceptor, respectively, the carrier transport along the direction is enhanced by the insertion of CuI templaing layer. In addition, optical absorption in CuPc molecules is increased due to aligned transition matrix elements. Overall the lying down orientation of CuPc on CuI will improve photovoltaic efficiency.

A QICAR model for metal ion toxicity established via PLS method

The partial least squares(PLS) method was employed to establish a quantitative ion characteristics-activity relationship(QICAR) model for metal ion toxicity(EC50 of 15 metal ions). The ion characteristics included AN(the atomic number), ΔIP(the change in ionization potential, eV), Xm(the electronegativity, eV), AW(the atomic weight), Xm2r(the covalent index), ΔE0(the absolute difference between electrochemical potential of the ion and that of its first stable reduced state, eV), |lgKOH|(the absolute value of the lg of the first hydrolysis constant), AR(the atomic radius, nm), AR/AW(the ratio between atomic radius and atomic weight) and σp(the softness index) selected based on relative correlation analysis. The simulated and tested(with the other four metals) efficiency coefficients of the model are 0.88 and 0.96, respectively. The information revealed from the QICAR model indicates that the value of the metal ion toxicity was positively correlated with variables AN, ΔIP, Xm, AW and Xm2r; negatively correlated with variables ΔE0, |lgKOH|, AR/AW, AR and σp, and ion characteristics ΔE0, Xm, σp and Xm2r were found to contribute more to the toxicity of metal ions via the accurate analysis method provided by PLS. The model could be used to predict the toxicity of the target metals and preliminary to assess combined pollution and environmental risk for heavy metals in the environments.

Changes in ionization potentials of MgO and CaO films upon heating in air and vacuum investigated by metastable de-excitation spectroscopy

Changes in the ionization potential of MgO and CaO film surfaces upon heating in air and vacuum, which are necessary processes in the manufacture of plasma display panels, were investigated by metastable de-excitation spectroscopy. Heating at 500°C for 1min in vacuum is effective for cleaning an MgO film surface previously heated in air, resulting in the recovery of the ionization potential of the cleaned MgO surface from the increased value upon heating in air. A similar treatment is not effective for the CaO surface. This difference in behavior can be attributed to the stronger bonding states of H2O and CO2 on CaO than those on MgO. This is consistent with the fact that CaO has not yet been practically used as a protective layer in plasma display panels. Furthermore, the firing voltages of the plasma predicted for the MgO and CaO protective layers from the ionization potentials determined by metastable de-excitation spectroscopy were found to qualitatively agree with measured firing voltages obtained for a test panel. The present results confirmed that metastable de-excitation spectroscopy is effective for evaluating protective layers used in plasma display panels.

Density functional studies of the structural variety of the Cu2S2 core of the CuA site

AbstractThe biological CuA site functions as the proximate electron‐transfer intermediate from an electron source in cytochrome c oxidase and nitrous oxide reductase. It provides a characteristic electronic structure for rapid electron transfer. In the CuA site, two copper ions bridged with two bridging cysteinyl thiolate groups form an almost planar Cu2S2 core. Each copper ion is coordinated equatorially with a histidine residue and axially with either a methionine residue or a carbonyl group of the polypeptide backbone. Three‐dimensional X‐ray crystallographic structures show that the structural variety of the Cu2S2 core of the CuA site with a short CuCu distance of 2.34–2.59 Å and a SS distance of 3.76–4.24 Å. In the present study, we address the origin of the structural variety of the Cu2S2 core of the CuA site, using the density functional theory. Our computation demonstrated that we found the structural dependence of the energy gap between the σ and πu oxidized states, the ionization potentials, and total energies, though the structural variety is insensitive to the shape and symmetry of the σ and πu redox active molecular orbitals and the πu ground state of the Cu2S2 core of the CuA site. In addition, the σ oxidized state is more robust to the structural changes in ionization potentials and total energies than the πu oxidized state. This robustness indicates the small reorganization energy in the redox reaction between σ oxidized and reduced states of the CuA site. The optimized Cu2S2 cores have almost same structures in all the states, indicating that surrounding proteins are responsible for the structural variety of the Cu2S2 core of the CuA site. © 2012 Wiley Periodicals, Inc.

Covalent Anchoring of Re6Sei8 Cluster Cores Monolayers on Modified n- and p-Type Si(111) Surfaces: Effect of Coverage on Electronic Properties

The electronic properties of redox-active transition metal clusters (Re6Se8) covalently immobilized on modified Si(111) surfaces through linear alkyl spacers have been studied as a function of the cluster coverage (1 × 1013-6 × 1013 cm-2). The latter is controlled by using Si(111)/H surfaces modified by dense mixed alkyl/acid-terminated monolayers with variable fraction of the acid grafting sites from 5 to 100% in solution. Quantitative X-ray photoemission analysis, spectroscopic ellipsometry, and scanning tunnelling microscopy indicate a covalent attachment of a submonolayer to densely packed monolayer of Re6Se8 clusters, while the vibrational Raman signature confirms the cluster integrity within the monolayer. Electrical band gaps as deduced from scanning tunnelling spectroscopy have been obtained for low Re6Se8 cluster coverage. Using ultraviolet photoemission spectroscopy, electronic properties such as ionization potential changes and energy level alignments at organic/inorganic interfaces are studied. We show that the lowest unoccupied molecular orbital of the Re6Se8 cluster is close to the bottom of the Si conduction band. At high cluster coverage, this affects the current-voltage characteristics measured using a weakly interacting top mercury contact onto the organic monolayer/silicon junctions. Indeed, on n-type silicon, the high level current at low bias and the shape of the conductance G(V) curve indicate a Schottky barrier height lowering. On the other hand, the current-voltage characteristics are the same for both acid-terminated and low coverage Re6Se8 cluster junctions at low bias; the high Schottky barrier height limits the current at low bias. When the forward bias increases, the current is tunnelling limited. As expected from the band alignment deduced from photoemission data, the opposite behavior is obtained on p-type silicon.

Photocurrent switching method based on photoisomerization of diarylethene layer for nondestructive readout of photochromic optical memory

We report on photocurrent switching based on photoisomerization for the nondestructive readout of photochromic optical memory. The photoisomerization of a diarylethene (DAE) memory layer switched the photocurrent generated in a light-absorbing phthalocyanine layer upon irradiation of a laser light. This switching is based on the ionization potential change of the DAE molecules. Switching characteristics of the photocurrent were investigated for the laser light with a wavelength of 410 nm, 630 nm, or 780 nm. Excellent on-off ratios of the photocurrent were achieved by irradiation at 630 nm and 780 nm. When the pulsed laser light with a wavelength of 780 nm was repeatedly irradiated to the colored and uncolored memory devices, no change of the photocurrent signal levels was observed, even after 8 x 10(5) cycles, indicating a successful demonstration of the nondestructive readout.

Optical and Electronic Properties of Doubly Ortho-linked cis-4,4'-Bis(diarylamino)stilbene/Fluorene Hybrids

Doubly ortho-linked cis-4,4′-bis(diarylamino)stilbene/fluorene hybrids have potential application in organic light emitting diodes. These organic molecules can function as efficient hole transport materials, with sky-blue emission and high efficiency and stability. To reveal the relationship between the properties and structures of these functional materials, we apply quantum-chemical techniques to investigate their optical properties and electronic structures. It is found that 8- and 8′-substituents give an antibonding contribution to the highest occupied molecular orbitals (HOMO), thus increasing the HOMO energy, implying an enhancement of hole-creating ability. Changes in ionization potentials confirm this presumption. The absorption and emission spectra exhibit red shifts to some extent with the various 8- and 8′-substituents, which are in good agreement with the experimental values. The Stoke shifts range moderately from 40 to 86 nm, due to the rigid spiral structure that hinders geometrical relaxation.

A systematic understanding of orbital energy shift in polar solvent

The orbital energy of molecule is significantly shifted upon going from gas phase to solution phase. Based on Koopmans' theorem, the shift should be related to the change of ionization potential. However, the computed shift looks usually random and clear understanding has not been attained yet. Furthermore it is obtained only after solving complicated equations. In this study, we report a systematic framework for understanding the orbital energy shift by solvation effect and simple approximate formulae are presented.

Effect of shell structure on transversal heating and cooling of channeled ions

It is shown that an abrupt change in ionization potential at the transition from one shell to the next one can result in a repeated transition from the heating of channeled ion beam to the cooling and vice versa with an increase in ion velocity.

Effect of ionization potential change in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) on the performance of polymer light emitting diodes due to its reaction with indium tin oxide

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) is usually used to facilitate hole injection in polymer light emitting diodes. The authors used ultraviolet photoelectron spectroscopy to investigate ionization potential (IP) changes of PEDOT:PSS spin coated on indium tin oxide (ITO), and found that increasing delay time to baking after spin coating decreases its IP and increases hole injection barrier to emitting polymer. The IP change is attributed to dedoping of PEDOT in PEDOT:PSS due to reaction of ITO with protons in PSS and those in doped PEDOT in the presence of water. To get good performance of bipolar device, PEDOT:PSS film should be baked right after spin coating.

Dehydrogenated Cations of Coronene, C 24 H[FORMULA][F][SUP]+[/SUP][INF]x[/INF][/F][/FORMULA]: The Source of Many Diffuse Interstellar Bands

Electronic transition energies have been predicted for cations of dehydrogenated coronene, C24H, based on laboratory data for hydrogenated molecules. This has resulted in the tentative simulation of many of the diffuse interstellar bands, including the majority of the strongest bands. It is shown that many of the diffuse bands can be identified with π ← π-2,-3, π ← π-4,-5, and π ← π-6,-7 transitions of C24H, where x {12, 10, 8, 6, 4, 2, 0}. A π ← π transition in the fully dehydrogenated cation, C, occurs at 442.8 nm. Diffuse interstellar band spectra reveal a well-defined spectral sequence between 653.2 and 628.4 nm correlating with the small change in ionization potential that accompanies the sequential removal of H atoms from coronene. As previously suggested by mass spectra, only cations with an even number of H atoms are observed. All bands associated with these ions show vibronic structure, with vibrational frequencies that correspond to those observed in aromatic infrared emission sources. This establishes that the molecules responsible for the diffuse interstellar bands are also likely the source of the aromatic emission bands.

Theory of Alkyl-Terminated Silicon Quantum Dots

We have carried out a series of ab initio calculations to investigate changes in the optical properties of Si quantum dots as a function of surface passivation. In particular, we have compared hydrogen-passivated dots with those having alkyl groups at the surface. We find that, while on clusters with reconstructed surfaces complete alkyl passivation is possible, steric repulsion prevents full passivation of Si dots with unreconstructed surfaces. In addition, our calculations show that steric repulsion may have a dominant effect in determining the surface structure and eventually the stability of alkyl-passivated clusters, with results dependent on the length of the carbon chain. Alkyl passivation weakly affects optical gaps of silicon quantum dots, while it substantially decreases ionization potentials and electron affinities and affects their excited state properties. On the basis of our results, we propose that alkyl-terminated quantum dots may be size selected, taking advantage of the change in ionization potential as a function of the cluster size.

An approach to quantum chemical consideration of "hydride" transfer reaction

An approach to the quantum chemical study of "hydride ion" transfer has been proposed, according to which the sequences of changes in ionization potentials, enthalpies and free energies of the affinities to the hydride ion, to the hydrogen atom and to the proton of substrates molecules and their derivatives (cations, radicals, anions), are compared with the experimentally substantiated series of "hydride" mobility. It has been established that the experimental series of "hydride" mobility for six chalcogenopyrans based on "semicyclic" 1,5-diketones is in conformity with the computed ionization potentials of themolecules, and with the affinity of the corresponding radicals to the hydrogen atom involved in the transfer. The direct splitting-out of the hydride ion and the primary deprotonation of the substrates followed by the withdrawal of two electrons was elucidated to be unlikely. Feasible are the mechanisms of "hydride" mobility, the first step of which consists of electron or hydrogen atom transfer from the chalcogenopyrans molecules.