Bond-breaking Processes Research Articles

Analysis of the Features of Hot-Carrier Degradation in FinFETs

For the first time, hot-carrier degradation (HCD) is simulated in non-planar field-effect transistors with a fin-shaped channel (FinFETs). For this purpose, a physical model considering single-carrier and multiple-carrier silicon–hydrogen bond breaking processes and their superpositions is used. To calculate the bond-dissociation rate, carrier energy distribution functions are used, which are determined by solving the Boltzmann transport equation. A HCD analysis shows that degradation is localized in the channel region adjacent to the transistor drain in the top channel-wall region. Good agreement between the experimental and calculated degradation characteristics is achieved with the same model parameters which were used for HCD reproduction in planar short-channel transistors and high-power semiconductor devices.

Seniority based energy renormalization group (Ω-ERG) approach in quantum chemistry: Initial formulation and application to potential energy surfaces

This investigation combines the concept of the seniority number Ω (defined as the total number of singly occupied orbitals in a determinant) with the energy renormalization group (ERG) approach to obtain the lowest-energy electronic states on molecular potential energy surfaces. The proposed Ω-ERG method uses Slater determinants that are ordered according to seniority number Ω in ascending order. In the Ω-ERG procedure, the active system consists of M (N-electron) states and K additional complement (N-electron) states (complement-system). Among the M states in the active system the lowest-energy m states represent target states of interest (target-states), thus m ≤ M. The environment consists of Full Configuration Interaction (FCI) determinants that represent a reservoir from which the complement-states K are being selected. The goal of the Ω-ERG procedure is to obtain lowest-energy target states m of FCI quality in an iterative way at a reduced computational cost. In general, the convergence rate of Ω-ERG energies towards FCI values depends on m and M, thus, the notation Ω-ERG(m, M) is used. It is found that the Ω-ERG(m, M) method can be very effective for calculating lowest-energy m (ground and excited) target states when a sufficiently large number of sweeps is used. We find that the fastest convergence is observed when M > m. The performance of the Ω-ERG(m, M) procedure in describing strongly correlated molecular systems has been illustrated by examining bond-breaking processes in N2, H8, H2O and C2. The present, proof-of-principle study yields encouraging results for calculating multiple electronic states on potential energy surfaces with near Full CI quality.

A Photoionization Reflectron Time-of-flight Mass Spectrometric Study on the Formation of Acetic Acid (CH3COOH) in Interstellar Analog Ices

Abstract This work investigates the synthesis of complex organic molecules with special focus on acetic acid (CH3COOH) via experiments involving the processing of astrophysical model ices of carbon dioxide–methane (CO2–CH4) by low doses of ionizing radiation, exposing the initial bond-breaking processes and successive reactions initiated by energetic electrons generated in the track of galactic cosmic-ray particles penetrating ice-coated interstellar grains, deep inside molecular clouds in their early stages of evolution. The key results were obtained through single photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS) and exploiting isotopically labeled samples (C18O2–CH4; CO2–CD4). Not only acetic acid (CH3COOH), along with fragments of acetic acid dimers (CH3COOH)2, but also the hitherto elusive interstellar methyl hydroperoxide (CH3OOH) and the hydrocarbons ethane (C2H6) and butane (C4H10), along with species belonging to C2H4O, C2H6O, and C3H6O2 isomers, are swiftly formed via suprathermal reactions at doses of only 0.88 ± 0.12 eV per molecule of carbon dioxide and 0.32 ± 0.04 eV per molecule of methane, which is equivalent to doses deposited in just (2.0 ± 0.5) × 106 yr in a typical molecular cloud. The results suggest further that the search for acetic acid dimers (CH3COOH)2 toward star-forming regions has a significant potential to be successful. Finally, methyl hydroperoxide (CH3OOH) and dimethyl peroxide (CH3OOCH3), as identified previously in our laboratory, are predicted to be present in the interstellar medium, thus providing a homologous series of peroxides—HOOH, CH3OOH, and CH3OOCH3—to shed light on the interstellar oxygen chemistry.

Multireference Methods for Calculating the Dissociation Enthalpy of Tetrahedral P4 to Two P2.

The potential energy surface for the thermal decomposition of P4 → 2P2 was computed along the C2 v reaction trajectory. Single-reference methods were not suitable for describing this complex bond-breaking process, so two multiconfigurational methods, namely, multistate complete active space second-order perturbation theory (MS-CASPT2) and multiconfiguration pair-density functional theory (MC-PDFT), were used with the aim of determining the accuracy and efficiency of these methods for this process. Several active spaces and basis sets were explored. It was found that the multiconfiguration pair-density functional theory method was up to 900 times faster than multistate complete active space second-order perturbation theory while providing similar accuracy.

Long-lived transient anion of c-C4F8O.

We report partial cross sections for electron attachment to c-C4F8O, a gas with promising technological applications in free-electron-rich environments. The dissociative electron attachment leads to a number of anionic fragments resulting from complex bond-breaking and bond-forming processes. However, the anion with the highest abundance is the non-dissociated (transient) parent anion which is formed around 0.9 eV electron energy. Its lifetime reaches tens of microseconds. We discuss the origin of this long lifetime, the anion's strong interactions with other molecules, and the consequences for electron-scavenging properties of c-C4F8O in denser environments, in particular for its use in mixtures with CO2 and N2.

Анализ особенностей деградации, вызываемой горячими носителями, в транзисторах с каналом в форме плавника

AbstractFor the first time, hot-carrier degradation (HCD) is simulated in non-planar field-effect transistors with a fin-shaped channel (FinFETs). For this purpose, a physical model considering single-carrier and multiple-carrier silicon–hydrogen bond breaking processes and their superpositions is used. To calculate the bond-dissociation rate, carrier energy distribution functions are used, which are determined by solving the Boltzmann transport equation. A HCD analysis shows that degradation is localized in the channel region adjacent to the transistor drain in the top channel-wall region. Good agreement between the experimental and calculated degradation characteristics is achieved with the same model parameters which were used for HCD reproduction in planar short-channel transistors and high-power semiconductor devices.

ETS-NOCV decomposition of the reaction force for double-proton transfer in formamide-derived systems

The analysis of the electronic-structure changes along IRC paths for double-proton-transfer reactions in the formamide dimer (R1), formamide–thioformamide system (R2), and the thioformamide dimer (R3) was performed based on the extended-transition-state natural orbitals for chemical valence (ETS-NOCV) partitioning of the reaction force, considering the intra-fragments strain and the inter-fragments interaction terms, and further—the electrostatic, Pauli-repulsion and orbital interaction components, with the latter being decomposed into the NOCV components. Two methods of the system partitioning into the fragments were considered (‘reactant perspective’/bond-formation, ‘product perspective’ / bond-breaking). In agreement with previous studies, the results indicate that the major changes in the electronic structure occur in the transition state region; the bond-breaking processes are, however, initiated already in the reactant region, prior to entering the TS region. The electrostatic contributions were identified as the main factor responsible for the increase in the activation barrier in the order R1 < R2 < R3.

State‐to‐state photodissociation dynamics of the water molecule

Photodissociation provides an ideal proving ground for an in‐depth understanding of the microscopic mechanism and dynamics of bond breaking processes at a state‐to‐state level. After a brief outline of the requisite theory, we review the latest developments on the state‐to‐state photodissociation dynamics of the water molecule via the lowest two excited states, focusing on the absorption spectrum and product state distributions. A detailed discussion is given on the competition between different adiabatic and nonadiabatic pathways of the dissociation. Quantum mechanical studies of this prototypical system on accurate coupled potential energy surfaces not only offer an interpretation of the existing experimental results but also provide a clear and comprehensive dynamical picture of water photodissociation. WIREs Comput Mol Sci 2018, 8:e1350. doi: 10.1002/wcms.1350This article is categorized under: Theoretical and Physical Chemistry &gt; Reaction Dynamics and Kinetics

Strong laser field control of fragment spatial distributions from a photodissociation reaction

The notion that strong laser light can intervene and modify the dynamical processes of matter has been demonstrated and exploited both in gas and condensed phases. The central objective of laser control schemes has been the modification of branching ratios in chemical processes, under the philosophy that conveniently tailored light can steer the dynamics of a chemical mechanism towards desired targets. Less explored is the role that strong laser control can play on chemical stereodynamics, i.e. the angular distribution of the products of a chemical reaction in space. This work demonstrates for the case of methyl iodide that when a molecular bond breaking process takes place in the presence of an intense infrared laser field, its stereodynamics is profoundly affected, and that the intensity of this laser field can be used as an external knob to control it.

Benchmark of Dynamic Electron Correlation Models for Seniority-Zero Wave Functions and Their Application to Thermochemistry.

Wave functions restricted to electron-pair states are promising models to describe static/nondynamic electron correlation effects encountered, for instance, in bond-dissociation processes and transition-metal and actinide chemistry. To reach spectroscopic accuracy, however, the missing dynamic electron correlation effects that cannot be described by electron-pair states need to be included a posteriori. In this Article, we extend the previously presented perturbation theory models with an Antisymmetric Product of 1-reference orbital Geminal (AP1roG) reference function that allows us to describe both static/nondynamic and dynamic electron correlation effects. Specifically, our perturbation theory models combine a diagonal and off-diagonal zero-order Hamiltonian, a single-reference and multireference dual state, and different excitation operators used to construct the projection manifold. We benchmark all proposed models as well as an a posteriori Linearized Coupled Cluster correction on top of AP1roG against CR-CC(2,3) reference data for reaction energies of several closed-shell molecules that are extrapolated to the basis set limit. Moreover, we test the performance of our new methods for multiple bond breaking processes in the homonuclear N2, C2, and F2 dimers as well as the heteronuclear BN, CO, and CN+ dimers against MRCI-SD, MRCI-SD+Q, and CR-CC(2,3) reference data. Our numerical results indicate that the best performance is obtained from a Linearized Coupled Cluster correction as well as second-order perturbation theory corrections employing a diagonal and off-diagonal zero-order Hamiltonian and a single-determinant dual state. These dynamic corrections on top of AP1roG provide substantial improvements for binding energies and spectroscopic properties obtained with the AP1roG approach, while allowing us to approach chemical accuracy for reaction energies involving closed-shell species.

Automated Construction of Molecular Active Spaces from Atomic Valence Orbitals.

We introduce the atomic valence active space (AVAS), a simple and well-defined automated technique for constructing active orbital spaces for use in multiconfiguration and multireference (MR) electronic structure calculations. Concretely, the technique constructs active molecular orbitals capable of describing all relevant electronic configurations emerging from a targeted set of atomic valence orbitals (e.g., the metal d orbitals in a coordination complex). This is achieved via a linear transformation of the occupied and unoccupied orbital spaces from an easily obtainable single-reference wave function (such as from a Hartree-Fock or Kohn-Sham calculations) based on projectors to targeted atomic valence orbitals. We discuss the premises, theory, and implementation of the idea, and several of its variations are tested. To investigate the performance and accuracy, we calculate the excitation energies for various transition-metal complexes in typical application scenarios. Additionally, we follow the homolytic bond breaking process of a Fenton reaction along its reaction coordinate. While the described AVAS technique is not a universal solution to the active space problem, its premises are fulfilled in many application scenarios of transition-metal chemistry and bond dissociation processes. In these cases the technique makes MR calculations easier to execute, easier to reproduce by any user, and simplifies the determination of the appropriate size of the active space required for accurate results.

ETS-NOCV Decomposition of the Reaction Force: The HCN/CNH Isomerization Reaction Assisted by Water.

The partitioning of the reaction force based on the extended-transition-state natural orbital for chemical valence (ETS-NOCV) scheme has been proposed. This approach, together with the analysis of reaction electronic flux (REF), has been applied in a description of the changes in the electronic structure along the IRC pathway for the HCN/CNH isomerization reaction assisted by water. Two complementary ways of partitioning the system into molecular fragments have been considered ("reactant perspective" and "product perspective"). The results show that the ETS-NOCV picture is fully consistent with REF and bond-order changes. In addition, proposed ETS-NOCV decomposition of the reaction force allows for the quantitative assessment of the influence of the observed bond-breaking and bond-formation processes, providing detailed information about the reaction-driving and reaction-retarding force components within the assumed partitioning scheme. © 2017 Wiley Periodicals, Inc.

Thermal stability, structural and electrical characteristics of the modulated HfO2/Al2O3 films fabricated by atomic layer deposition

Atomic layer deposition is adopted to fabricate HfO2/Al2O3 multilayer thin films to study the sub-layer-thickness-dependent thermal stability. The nano-laminated structure with too thin sub-layer might degrade into a nano-composite configuration. Upon thermal annealing, the HfO2 sub-layers in the laminated configuration crystallize into the monoclinic phase without expanding into the neighboring Al2O3 sub-layers, while the crystallization occurs across the Al2O3 sub-layers in the nano-composite configuration. The thermal stability is enhanced with decreasing thickness of the HfO2 sub-layer and is essentially structure dependent, which can be regulated by the stacking numbers and the stacking sequence per supercycle. Doped Al could induce the phase transition from the monoclinic to the tetragonal phase. In thermodynamics, a thicker HfO2 sub-layer is more likely to initiate the crystallization owing to more bulk Gibbs free energy contributed to the total energy. However, the lost energy in the bond-breaking process impedes the crystallization, resulting in the enhanced thermal stability. The dielectric constant is significantly enhanced owing to the phase transformation from the monoclinic to the tetragonal phase. The leakage current density of the post-annealed nano-composite structure films is 3 × 10−6 A/cm2 at bias of −2 V, which is much lower than in other structures.

The crucial role of water clusters (H2O)n (n = 0–5) on the catalytic oxidation of AsH3: An accurate theoretical investigation

The removal of AsH3 is typically accomplished by catalytic oxidation process. In the process, the existence of water molecules plays a crucial role on the removal efficiency, but prior studies have not thoroughly investigated the role of water in reaction mechanism, due to lack of experimental and computational techniques. In this study, the role of explicit water molecules on the AsH3 catalytic oxidation AsH3+O2+nH2O (n=0–5) was investigated using Density Functional Theory (DFT) method at B3LYP/6-311+G (d,p) level. The addition of (H2O)n (n=1–5) shows promoting catalytic effect on the oxidation process by reducing the reaction barrier energy of 3.27–10.70kcal/mol compared to the reaction without water molecule (16.44kcal/mol). One explicit H2O addition shows best catalytic effect on the oxidation process. The decreasing order of reaction energy barrier is 0H2O>(H2O)5>(H2O)4>(H2O)2>(H2O)3>H2O. Natural bond orbital (NBO) analysis was also conducted to confirm the bond-breaking and bond-making processes. Furthermore, reaction rate constants (kTS) of six catalytic oxidation reactions from 293K to 433K have been calculated to determine the catalytic role of water clusters. The values of kTS increase progressively with increasing temperature in the six reaction paths (n=0–5). Three water addition is most kinetically favourable among the six reactions.

Understanding the Dual Active Sites of the FeO/Pt(111) Interface and Reaction Kinetics: Density Functional Theory Study on Methanol Oxidation to Formaldehyde

Identifying the active sites and reaction kinetics for a catalytic reaction can provide significant insight into the catalytic systems. By use of DFT calculations, the catalytic activity of FeO/Pt(111) interfacial sites, which is an important class of catalyst with excellent activity, for methanol partial oxidation is carefully examined and compared. The O–H cleavage barrier of methanol is significantly diminished to below 0.1 eV with the aid of interfacial oxygen, which is much lower than that on the Pt(111) surface (>0.8 eV). The CH3O* intermediate can further undergo a C–H bond breaking process to produce formaldehyde via a low barrier (∼0.2 eV) at the interfacial Pt sites. Assisted by an interfacial Pt–O ensemble, the O–H and C–H bond cleavages are greatly facilitated, suggesting that the FeO/Pt biphasic system could effectively combine the advantages of two individual phases. To investigate the rate-determining steps, a multisite microkinetic model is applied at the FeO/Pt interface. The results show...

Failure of Weibull distribution to represent switching statistics in OxRAM

Considering the reasonable similarity in the physical mechanisms governing oxide breakdown and filamentary resistive switching, the use of the Weibull distribution has been widespread in the RRAM community for describing the stochastics of Forming, SET, RESET and read disturb data sets. Upon close examination, it is apparent that the Weibull fitting tends to be poor at the high percentiles for most of these data sets in RRAM (both vacancy based (OxRAM) and metal filament (CBRAM) based switching). The fundamental origin of these deviations is investigated in this work for OxRAM stacks through an analytical model making use of the percolation theory as the backbone framework and considering the physical process of thermochemical bond breaking that governs forming and SET events in resistance switching and the cycle-to-cycle variability inherent in the filament size and shape due to these atomistic events. Our model is compared with the standard Weibull distribution for fitting several data sets reported in the literature. The recently proposed defect clustering model is shown to be a better representative of the statistical physics governing the forming and SET switching process.

Structural Tuning of Anion-Templated Motifs with External Stimuli through Crystal-to-Crystal Transformation.

Protonation of trans-1,2-bis(4-pyridyl)ethylene (4,4'-bpe) with dilute sulfuric acid (33 %) afforded a protonated adduct [{4,4'-bpe⋅2 H+ }2 {HSO4 }-2 {SO4 }-2 {H2 O}2 ] (1). The neighboring olefinic bond in 1 is in a suitable range (3.931-4.064 Å) to undergo a photochemical [2+2] cycloaddition reaction. Upon irradiation with UV light (365 nm), 1 undergoes a molecular sliding involving the 4,4'-bpe⋅2 H+ units, affording 2, stabilized through OSO4 ⋅⋅⋅π interactions. Heating 1 to 50° C leads to a 3D hydrogen-bonded organic framework (HOF) (3). This process occurs through thermal dissociation of the bisulfate anion. Diffusion of iodine through the crystal lattice of 1 and 3 enables the reduction of sulfate to bisulfate, affording a 1D hydrogen-bonded chain (4). Solid-state 13 C CPMAS NMR, IR, DSC, and powder XRD studies further support stimuli-responsive structural tuning through crystal-to-crystal transformation. All these conversions occur with significant translational and rotational movements along with a series of bond-breaking and bond-forming processes.

Reductive Decomposition Mechanism of Prop-1-ene-1,3-sultone in the Formation of a Solid–Electrolyte Interphase on the Anode of a Lithium-Ion Battery

A novel electrolyte additive, prop-1-ene-1,3-sultone (PES), has recently attracted great attention due to its formation of effective solid–electrolyte interphase (SEI) films and remarkable cell performance in lithium-ion batteries. Herein, the reductive decomposition of PES is investigated through density functional calculations combined with a self-consistent reaction field method, in which the bulk solvent effect is accounted for by the geometry optimization and transition-state search. We examine three ring-opening pathways, namely, O–C, S–C, and S–O bond-breaking processes. Our calculations reveal that the Li+ ion plays a pivotal role in the reductive decomposition of PES. While the most kinetically favored process—the S–O bond breaking—is effectively blocked via the formation of an intermediate structure, namely, the Li+-participated seven-membered ring, the other decomposition processes via O–C and S–C bond breaking lead to stable decomposition products. The constituents of SEI observed in previous ...

Unexpected mechanochemical complexity in the mechanistic scenarios of disulfide bond reduction in alkaline solution.

The reduction of disulfides has a broad importance in chemistry, biochemistry and materials science, particularly those methods that use mechanochemical activation. Here we show, using isotensional simulations, that strikingly different mechanisms govern disulfide cleavage depending on the external force. Desolvation and resolvation processes are found to be crucial, as they have a direct impact on activation free energies. The preferred pathway at moderate forces, a bimolecular SN2 attack of OH- at sulfur, competes with unimolecular C-S bond rupture at about 2 nN, and the latter even becomes barrierless at greater applied forces. Moreover, our study unveils a surprisingly rich reactivity scenario that also includes the transformation of concerted SN2 reactions into pure bond-breaking processes at specific forces. Given that these forces are easily reached in experiments, these insights will fundamentally change our understanding of mechanochemical activation in general, which is now expected to be considerably more intricate than previously thought.

Iron Oxide Plasmonic Nanostructures for Energy Harvesting

Recently Iron oxide (Fe2O3) nano structure has drawn renewed interest in electrocatalysis process for carbon-carbon (C-C) bond breaking in ethanol. We design and fabricate Fe2O3 plasmonic nanostructures for C-C bond-breaking processes in high density fuels. After patterning Fe2O3 film, we use inductively coupled plasma (ICP) etching equipped with an Argon (Ar) plasma to create the film with nanometer scale dimensions. We used both photoresist mask and hard mask like silicon dioxide film for selecting etching. Fe2O3 film etching process is optimized by using different parameters like ICP power, base electrode power, pressure, temperature, and Ar gas flow etc. We used elliposmetric method as well as UV/Vis reflectance spectroscopy to determine the resonance wavelength of the plasmonic nanostructures suitable for electrocatalysis experiment. Iron oxide (Fe2O3) has recently received much attention among the various semiconductor photo-electrode materials due to its favorable optical band gap (~2.2 eV), excellent chemical stability in high pH media, natural abundance, and low cost [1,2]. However, Fe2O3 exhibits a relatively poor absorptivity of photons near its band-edge due to an indirect band gap, poor electronic conductivity (PEC), and picosecond recombination of excited states, thus leading to a photo-generated hole diffusion length of ~2-4 nm [3]. These non-ideal optoelectronic properties hinder the transport of photo-generated carries and increase the recombination rate, which results in a lowering of the PEC efficiency compared to theoretically predicted values. Controlling the nanostructure of Fe2O3 may provide an effective technology for overcoming the aforementioned problems of Fe2O3 due to the geometry and mechanism-dependent semiconductor structure [4]. The shape of the Fe2O3structures with cone, cylinder, sphere, etc. features alters the electric field dependent absorption and transport processes. We use electron beam evaporation system to deposit thin Fe2o3 film (100-500 nm) on silicon substrate with thin layer of gold (Au) film. We then use an inductively coupled plasma (ICP) etching process to define Fe2O3 nano-structured pillars with various diameters (50nm -5 µm) and heights. We use either e-beam lithography or optical lithography process to define the plasmonic nanostructures. ICP etching process with Ar plasma is used with varying power, pressure and substrate temperature etc. to optimize the Fe2O3 etching process. Scanning electron (SEM) and atomic force (AFM) microscopy tools are used to determine the surface morphology of the nanostructures, whereas ellipsometer and UV-Vis spectrometer elucidate the optical properties. Galvanometeric current-voltage measurement is performed to determine the optimum nano plasmonic structure for carbon-carbon (C-C) bond breaking process in high energy density chemicals. In figure 1, we have shown the etch rate of Fe2O3 film with different substrate temperatures and Ar pressure in the reaction chamber. We find that in order to achieve a smooth surface and reasonable etch rate, the substrate temperature should be between 15-18 ᵒC and the ICP power between 800-1000 W. Detailed deposition, annealing, etching and characterization results of Fe2O3 nano plasmonic structures will be presented in a full paper.