Large Electron Affinity Research Articles

Investigation of the impact of insulator material on the performance of dissimilar electrode metal-insulator-metal diodes

The performance of thin film metal-insulator-metal (MIM) diodes is investigated for a variety of large and small electron affinity insulators using ultrasmooth amorphous metal as the bottom electrode. Nb2O5, Ta2O5, ZrO2, HfO2, Al2O3, and SiO2 amorphous insulators are deposited via atomic layer deposition (ALD). Reflection electron energy loss spectroscopy (REELS) is utilized to measure the band-gap energy (EG) and energy position of intrinsic sub-gap defect states for each insulator. EG of as-deposited ALD insulators are found to be Nb2O5 = 3.8 eV, Ta2O5 = 4.4 eV, ZrO2 = 5.4 eV, HfO2 = 5.6 eV, Al2O3 = 6.4 eV, and SiO2 = 8.8 eV with uncertainty of ±0.2 eV. Current vs. voltage asymmetry, non-linearity, turn-on voltage, and dominant conduction mechanisms are compared. Al2O3 and SiO2 are found to operate based on Fowler-Nordheim tunneling. Al2O3 shows the highest asymmetry. ZrO2, Nb2O5, and Ta2O5 based diodes are found to be dominated by Frenkel-Poole emission at large biases and exhibit lower asymmetry. The electrically estimated trap energy levels for defects that dominate Frenkel-Poole conduction are found to be consistent with the energy levels of surface oxygen vacancy defects observed in REELS measurements. For HfO2, conduction is found to be a mix of trap assisted tunneling and Frenkel-Poole emission. Insulator selection criteria in regards to MIM diodes applications are discussed.

Spectral and Kinetic Properties of Radical Cations Derived from Oxoisoaporphines: Relevance to Electron-Transfer Processes Involving Phytoalexins.

The thermally induced intermolecular electron transfer reaction in acetonitrile between the tetracyanoethylene (TCNE), a π-electron acceptor with a large electron affinity, and six oxoisoaporphines (2,3-dihydro-7H-dibenzo[de,h]quinolin-7-one, 5-methoxy-2,3-dihydro-7H-dibenzo[de,h]quinolin-7-one, 1-azabenzo[de]anthracen-7-one, 5-methoxy-1-azabenzo[de]anthracen-7-one, 7H-benzo[e]perimidin-7-one, and 2-methyl-7h-benzo[e]perimidin-7-one) is reported. Spectral and kinetic characteristics are presented for radical cations derived from these six oxoisoaporphines either generated by a thermal reaction or generated radiolytically in argon-saturated 1,2-dichloroethane, oxygen-saturated acetone, and acetonitrile. The radical cations of oxoisoaporphines are insensitive to oxygen and are mostly characterized by absorption maxima of their most intense bands located at λmax = 400-410 nm, except of the radical cations derived from 2,3-dihydrooxoisoaporphines. For the latter compounds, the absorption maxima of the most intense absorption bands are located at λmax = 290-295 nm. Their locations are independent of the presence of functional groups and the solvents used. They are formed in bimolecular processes with pseudo-first-order rate constants ranging from 2.1 × 105 to 1.5 × 106 s-1 (in solutions containing 10-4 M of the substrate), depending on the derivative and the solvent used. They are stable either when formed via the electron-transfer reaction with TCNE or when generated in isolation in pulse radiolysis of Ar-saturated 1,2-dichloroethane. In acetone and acetonitrile they decay predominantly by first-order kinetics with the first-order rate constants ranging from 2.3 × 104 to 5.1 × 104 s-1. Formation of dimeric radical cations for all of the oxoisoaporphines studied was observed in acetonitrile solutions, and for azaoxoisoaporphines also in acetone solutions. The experimental spectra show a reasonably good agreement with the ZINDO/S semiempirical quantum mechanical calculations of radical cation absorptions.

Near-threshold electron elastic scattering cross sections for Ta, W, Re, Mo, Tc and Rh atoms: Determination of electron affinities and Ramsauer-Townsend minima

Near-threshold electron scattering by the Ta, W, Re, Mo, Tc and Rh atoms is explored through the elastic cross sections calculated using the recent complex angular momentum method [1]. Electron affinities (EAs) are extracted and the Ramsauer-Townsend (R-T) minima are identified for each atom. Implications for the new large EAs are discussed.

Tetrapositive Plutonium, Neptunium, Uranium, and Thorium Coordination Complexes: Chemistry Revealed by Electron Transfer and Collision Induced Dissociation

The Pu(4+), Np(4+), and U(4+) ions, which have large electron affinities of ∼34.6, ∼33.6, and ∼32.6 eV, respectively, were stabilized from solution to the gas phase upon coordination by three neutral tetramethyl-3-oxa-glutaramide ligands (TMOGA). Both collision induced dissociation (CID) and electron transfer dissociation (ETD) of Pu(TMOGA)3(4+) reveal the propensity for reduction of Pu(IV) to Pu(III), by loss of TMOGA(+) in CID and by simple electron transfer in ETD. The reduction of Pu(IV) is in distinct contrast to retention of Th(IV) in both CID and ETD of Th(TMOGA)3(4+), where only the C-Oether bond cleavage product was observed. U(TMOGA)3(4+) behaves similarly to Th(TMOGA)3(4+) upon CID and ETD, while the fragmentation patterns of Np(TMOGA)3(4+) lie between those of Pu(TMOGA)3(4+) and U(TMOGA)3(4+). It is notable that the gas-phase fragmentation behaviors of these exceptional tetrapositive complexes parallel fundamental differences in condensed phase chemistry within the actinide series, specifically the tendency for reduction from the IV to III oxidation states.

Theoretical investigation on the crystal structures and electron transport properties of several nitrogen-rich pentacene derivatives

Exploring and synthesizing new simple n-channel organic semiconductor materials with large electron mobility and high air stability have remained a major challenge and hot issue in the field of organic electronics. In the current work, the electron transport properties of four novel nitrogen-rich pentacene derivatives (PBD1, PBD2, PBD3, and PBD4) with two cyano groups as potential n-channel OFET materials have been investigated at the molecular and crystal levels by means of density functional theory (DFT) calculations coupled with the prediction of crystal structures and the incoherent charge-hopping model. Calculations reveal that the studied compounds, which possess low-lying frontier molecular energy levels, large ionization potentials and electron affinities, are very stable exposed to air. Based on predicted crystal structures, the average electron mobility at room temperature (T = 300 K) for PBD1, PBD2, PBD3, and PBD4 is predicted to be as high as 0.950, 0.558, 0.518, and 1.052 cm²·V⁻¹·s⁻¹, which indicate that these four compounds are more than likely to be promising candidates as n-type OFET materials under favorable device conditions. However, this claim needs experimental verification. In addition, the angular-dependent simulation for electron mobility shows that the electron transport is remarkably anisotropic in these molecular crystals and the maximum μ(e) appears along the crystal axis direction since molecules along this direction exhibit the close face-to-face stacking arrangement with short interplanar distances (~3.6-4.0 Å), which induces large electronic couplings.

Facile synthesis and characterization of well-defined soluble poly(benzimidazobenzophenanthroline)-like derivatives

A simple and efficient route to the synthesis of soluble BBL-like compounds is developed. All of the compounds have good solubility in common organic solvents and large electron affinity (3.8–4.0 eV), comparable to those of BBL and PCBM. Perylene-based BBL derivatives more readily aggregate and show broad absorption.

Insights into Desorption Ionization on Silicon (DIOS)

Desorption ionization on silicon (DIOS), a variant of surface-assisted laser desorption ionization (SALDI) which uses porous silicon (pSi) as a substrate, is a well-established and effective soft-ionization technique in mass spectrometry. In this work DIOS experiments found that the caffeine analyte could be detected by mass spectrometry as both a radical cation and a protonated species with relative intensities that depend critically on the position of the incident laser focus relative to substrate surface. In both cases analyte desorption appears to be driven by a thermal mechanism. Radical cation formation is attributed to electron transfer reactions between the desorbed neutral analyte and pSi due to the large electron affinity of the substrate. Preliminary experiments where different incident laser wavelengths were used suggest that the ionization mechanism leading to the detection of protonated peptide Dalargin involves in part electrons and holes formed when photoexciting pSi above its electronic band gap.

Unusual bonding and electron affinity of nickel group transition metal oxide clusters

We perform density functional calculations on the ground state geometries of MOn clusters (M = Ni, Pd, Pt; n = 1–5) in neutral as well as anionic forms. Our calculations reveal that Ni can bind up to three O atoms while Pd and Pt bind with four O atomically indicating the fact that the maximum oxidation state of Ni can take the value of +6 and can go as high as +8 in case of Pd or Pt. The electron affinities of MOn suggest that these species behave as superhalogens for n ≥ 2. The large electron affinities of MOn species along with stability of their anions further point towards the synthesis of new class of compounds having unusual oxidising capabilities.

Theoretical investigations on the superhalogen properties and interaction of PdO n (n = 1-5) species

Density functional calculations on the ground state geometries and stabilities of PdOn species (n = 1–5) are performed in neutral as well as anionic forms. Calculations reveal that Pd can bind stably with four O atoms indicating the maximum oxidation state of Pd as high as +8. The electron affinities of PdOn suggest that these species behave as superhalogens for n ≥ 2. The large electron affinities of PdOn species along with stability of their anions point toward the synthesis of new class of compounds having unusual oxidizing capabilities. This possibility is explored by considering the interaction of PdO2 superhalogen with Ca atom which forms a stable CaPdO2 complex. In this complex, PdO2 unit closely mimics the behavior of O atom when compared with CaO molecule. © 2013 Wiley Periodicals, Inc.

Convergence Acceleration of Parallel Monte Carlo Second-Order Many-Body Perturbation Calculations Using Redundant Walkers.

A Monte Carlo (MC) integration of the second-order many-body perturbation (MP2) corrections to energies and self-energies eliminates the usual computational bottleneck of the MP2 algorithm (i.e., the basis transformation of two-electron integrals), thereby achieving near-linear size dependence of its operation cost, a negligible core and disk memory cost, and a naturally parallel computational kernel. In this method, the correlation correction expressions are recast into high-dimensional integrals, which are approximated as the sums of integrands evaluated at coordinates of four electron random walkers guided by a Metropolis algorithm for importance sampling. The gravest drawback of this method, however, is the inevitable statistical uncertainties in its results, which decay slowly as the inverse square-root of the number of MC steps. We propose an algorithm that can increase the number of MC sampling points in each MC step by many orders of magnitude by having 2m electron walkers (m > 2) and then using m(m - 1)/2 permutations of their coordinates in evaluating the integrands. Hence, this algorithm brings an O(m(2))-fold increase in the number of MC sampling points at a mere O(m) additional cost of propagating redundant walkers, which is a net O(m)-fold enhancement in sampling efficiency. We have demonstrated a large performance increase in the Monte Carlo MP2 calculations for the correlation energies of benzene and benzene dimer as well as for the correlation corrections to the energy, ionization potential, and electron affinity of C60. The calculation for C60 has been performed with a parallel implementation of this method running on up to 400 processors of a supercomputer, yielding an accurate prediction of its large electron affinity, which makes its derivative useful as an electron acceptor in bulk heterojunction organic solar cells.

空气稳定的氮杂蒄电子传输材料分子设计及三氮杂蒄衍生物迁移率计算

The successive replacement of CH moieties by nitrogen atoms in coronene was studied computationally using the density functional theory (DFT). And the effects of different N-substituted patterns on geometries, electronic properties, and charge transport parameters were discussed in detail. The results show that the frontier molecular orbital energies decrease linearly with the increase of the number of nitrogen atoms, which is not only ideal for electron injection but also contribute to improved air stability of these semiconductors. Relatively, the ortho nitrogen-substitution is the most efficient strategy stabilizing the HOMO and LUMO levels compared with the peri -and sym -substitutions. Particularly, dodecazacoronene ( 12ac ) with a unique bowl-shape structure may be a potential building block as air-stable n-channel materials due to its large electron affinity (3.45 eV). In addition, the predicted room-temperature electron mobility for 2,6,10-tri(4-methoxyphenyl)-3,4,7,8,11,12-hexamethoxy-1,5,9-triazacoronene ( 3b ) single crystal reaches to 0.242 cm2/V s, which indicates that 3b is a promising n-channel OFET material.

All‐Metal Clusters that Mimic the Chemistry of Halogens

Owing to their s(2)p(5) electronic configuration, halogen atoms are highly electronegative and constitute the anionic components of salts. Whereas clusters that contain no halogen atoms, such as AlH(4), mimic the chemistry of halogens and readily form salts (e.g., Na(+)(AlH(4))(-)), clusters that are solely composed of metal atoms and yet behave in the same manner as a halogen are rare. Because coinage-metal atoms (Cu, Ag, and Au) only have one valence electron in their outermost electronic shell, as in H, we examined the possibility that, on interacting with Al, in particular as AlX(4) (X=Cu, Ag, Au), these metal atoms may exhibit halogen-like properties. By using density functional theory, we show that AlAu(4) not only mimics the chemistry of halogens, but also, with a vertical detachment energy (VDE) of 3.98 eV in its anionic form, is a superhalogen. Similarly, analogous to XHX superhalogens (X=F, Cl, Br), XAuX species with VDEs of 4.65, 4.50, and 4.34 eV in their anionic form, respectively, also form superhalogens. In addition, Au can also form hyperhalogens, a recently discovered species that show electron affinities (EAs) that are even higher than those of their corresponding superhalogen building blocks. For example, the VDEs of M(AlAu(4))(2)(-) (M=Na and K) and anionic (FAuF)Au(FAuF) range from 4.06 to 5.70 eV. Au-based superhalogen anions, such as AlAu(4)(-) and AuF(2)(-), have the additional advantage that they exhibit wider optical absorption ranges than their H-based analogues, AlH(4)(-) and HF(2)(-). Because of the catalytic properties and the biocompatibility of Au, Au-based superhalogens may be multifunctional. However, similar studies that were carried out for Cu and Ag atoms have shown that, unlike AlAu(4), AlX(4) (X=Cu, Ag) clusters are not superhalogens, a property that can be attributed to the large EA of the Au atom.

DFT/TDDFT study on the electronic structures and optoelectronic properties of a series of iridium(III) complexes based on quinoline derivatives in OLEDs

The electronic structures and photophysical properties of several heteroleptic iridium(III) complexes Ir(C∧N)2(acac) with acetylacetonate (acac) ligand, including 1 [C∧N = 2‐phenylisoquinoline], 2 [C∧N = 2‐biphenyl‐4‐yl‐quinoline], 3 [C∧N = 2‐(fluoren‐2‐yl)‐quinoline], 4 [C∧N = 2‐dibenzofuran‐3‐yl‐quinoline], 5 [C∧N = 2‐dibenzothiophen‐3‐yl‐quinoline], and 6 [C∧N = 2‐phenanthren‐2‐yl‐quinoline], have been investigated by density functional theory (DFT) and time‐dependent DFT. They show a wide color tuning of photoluminescence from orange–red (λ = 601 nm) to saturated red (λ = 685 nm). The calculated absorption and emission properties of complexes 1 and 2 are in good agreement with the available experimental data. Complex 6 has the smallest ionization potentials (IP) value, which is consistent with its highest occupied molecular orbital energy level, and thus its hole injection is easiest. Corresponding to its lowest unoccupied molecular orbital energy level, the assumed complex 5 has the large electron affinities value and enhanced electron injection ability compared to the others. These calculated results show that the assumed complex 3 may possess better charge transfer abilities than others and is the potential candidate for an efficient electrophosphorescent polymer‐based red‐emitting material. Copyright © 2013 John Wiley & Sons, Ltd.

Theoretical Studies on the Electronic Structures and Spectral Properties of Three Iridium(III) Complexes With Different NˆN Ligands

We report a quantum chemical study of the electronic structures and spectral properties of three iridium(III) biscarbene complexes with different heteroleptic N^N ligands. The theoretical calculation reveals that the lowest-lying singlet absorptions at 434 nm for 1 and 487 nm for 3 are attributed to the mixed transition characters of metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT). However, for 2, the lowest-lying singlet absorption at 509 nm is attributed to the MLCT. For 1–3, the phosphorescence at 739, 913, and 737 nm are mainly attributed to 3MLCT and 3LLCT characters. For 1 and 3, the emission energies are nearly the same, which is larger than that of 2. Ionization potentials (IP) and electron affinities (EA) calculations show that the assumed complex 3 has large EA value and enhanced electron injection ability as compared to complexes 1 and 2. Moreover, the reasons for different transition characters and phosphorescence quantum yield for the three complexes have been discussed in this paper. This theoretical contribution allows the factors determining the efficiency of radiative and nonradiative decay pathways in the three complexes.

Transition Metal Oxide-Diamond Interfaces for Electron Emission Applications

Diamond surfaces with suitable adsorbed chemical species can exhibit both negative and positive electron affinities, arising from the complex electrostatic interplay between adsorbates and surface carbon atoms of diamond lattice. We presents the results of density functional calculations into the energetics and the electron affinity of diamond (100) surfaces terminated with the oxides of selected transition metals. We find that for a correct stoichiometry, oxides of transition metals, such as Ti and Zn, exhibit a large negative electron affinity of around 3 eV. The desorption of transition metal oxides is found to be highly endothermic. We therefore propose that transition metal oxides are promising for the surface coating of diamond-based electron emitters, as these exhibit higher thermal stability in comparison to the commonly used CsO terminations, while retaining the advantage of inducing a large negative electron affinity.

Theoretical study on aluminum carbide endohedral fullerene-Al4C@C80

The possibility of a new endohedral fullerene with a trapped aluminum carbide cluster, Al(4)C@C(80)-I( h ), was theoretical investigated. The geometries and electronic properties of it were investigated using density functional theory methods. The Al(4)C unit formally transfers six electrons to the C(80) cage which induces stabilization of Al(4)C@C(80). A favorable binding energy, relatively large HOMO-LUMO gap, electron affinities and ionization potentials suggested the Al(4)C@C(80) is rather stable. The analysis of vertical ionization potential and vertical electron affinity indicate Al(4)C@C(80) is a good electron acceptor.

The effect of chlorine atoms on the charging kinetics of carbon nanoparticles forming in shock-heated plasma

This work continues the study on the charging kinetics of soot during the formation of carbon nanoparticles in hydrogen-free systems upon the pyrolysis of carbon-containing materials behind shock waves. The experimental results and results of computer simulation of electrical charging of the carbon nanoparticles formed during the pyrolysis of CCl4 behind the shock waves are given. It is shown that the natural impurity of sodium atoms amounting to 1012–1013 cm−3 are the main source of free electrons. It is established that the time required for relaxation of the charge distribution in the gas-nanoparticle system at 15–30 bar decreases from 400 to 100 μs in a 0.5% CCl4 + Ar mixture with increasing the equilibrium temperature from 2000 to 3600 K and from 350 to 50 μs in a 5% CCl4 + Ar mixture with increasing the equilibrium temperature from 1500 to 2500 K. The equilibrium concentration of free electrons in the presence of the nanoparticles in the system decreases by one to two orders of magnitude compared to that in the system without nanoparticles. The presence of chlorine atoms in the mixture leads to a considerable decrease in the concentration of electrons in the gas-nanoparticle system and to a decrease in the concentration of charged nanoparticles. The electron kinetics in the mixtures under consideration is characterized by a high (as compared with sodium) concentration of chlorine atoms having a larger electron affinity.

Theoretical study of the spectroscopically relevant parameters for the detection of HNPq and HPNq (q = 0, +1, −1) in the gas phase

High level ab initio electronic structure calculations at different levels of theory have been performed on HNP and HPN neutrals, anions, and cations. This includes standard coupled cluster CCSD(T) level with augmented correlation-consistent basis sets, internally contacted multi-reference configuration interaction, and the newly developed CCSD(T)-F12 methods in connection with the explicitly correlated basis sets. Core-valence correction and scalar relativistic effects were examined. We present optimized equilibrium geometries, harmonic vibrational frequencies, rotational constants, adiabatic ionization energies, electron affinities, vertical detachment energies, and relative energies. In addition, the three-dimensional potential energy surfaces of HNP(-1,0,+1) and of HPN(-1,0,+1) were generated at the (R)CCSD(T)-F12b∕cc-pVTZ-F12 level. The anharmonic terms and fundamentals were derived using second order perturbation theory. For HNP, our best estimate for the adiabatic ionization energy is 7.31 eV, for the adiabatic electron affinity is 0.47 eV. The higher energy isomer, HPN, is 23.23 kcal∕mol above HNP. HPN possesses a rather large adiabatic electron affinity of 1.62 eV. The intramolecular isomerization pathways were computed. Our calculations show that HNP(-) to HPN(-) reaction is subject to electron detachment.

Zn in the +III Oxidation State

The possibility that the group 12 elements Zn, Cd, and Hg can exist in an oxidation state of +III or higher has fascinated chemists for decades. It took nearly 20 years before experiments could confirm the theoretical prediction that Hg indeed can exist in the +IV oxidation state. While this unusual property of Hg is attributed to relativistic effects, Zn, which is much less massive than Hg, has not been expected to have an oxidation state higher than +II. Using density functional theory, we have shown that an oxidation state of +III for Zn can be realized by choosing specific ligands with large electron affinities. We demonstrate this by a systematic study of the interaction of Zn with the ligands F, BO(2), and AuF(6), whose electron affinities are progressively higher (3.4, 4.5, and 8.4 eV, respectively). The discovery of higher oxidation states of elements can help in the formulation of new reactions and hence in the development of new chemistry.

Structures and hydrogen adsorption of [formula omitted] ([formula omitted]) clusters

According to the charge polarization mechanism, high charges carried on metal ions are favorable to improve hydrogen storage capacity. This can be achieved by linking light metal atoms such as Mg with light molecules having large electron affinity such as NCN. Using first-principles calculations based on density functional theory including dispersion corrections, we investigate the geometries, electronic structures, and hydrogen adsorption properties of (MgCN2)n (n=1–4) clusters. The results show that these small clusters exhibit moderate affinity to hydrogen with the average adsorption energy in the range of 0.10–0.20 eV. The gravimetric storage densities for (MgCN2)2 and (MgCN2)3 are 5.9 wt%, suggesting that these clusters can be used as building blocks for assembling hydrogen storage materials or introduced to porous structures for enhancing H2 adsorption capacity.