Loss Of Atoms Research Articles

Atomic scale insight into the mechanisms of chloride induced steel corrosion in concrete

Chloride (Cl) induced steel corrosion is a major cause of durability issues of reinforced concrete (RC) structures and causes a large economic loss every year. Understanding the mechanisms of Cl induced steel corrosion in concrete is of great importance to develop anti-corrosion methods and further lowers down the repair and strengthening frequency and cost. Hence, the nature of steel depassivation and corrosion induced by Cl at atomic scale was revealed through the density functional theory (DFT) calculations to better understand the Cl induced corrosion mechanism. The results indicated that Cl species weakened the bonding of oxygen (O) with outer iron (Fe) atoms while enhanced the hybridization of O with inner Fe atoms, thus induced the breakdown of passive films. Besides, Cl facilitated the charge loss of outer Fe atoms and improved the interactions of water molecular (H2O) with these Fe atoms. When co-adsorption with O atom, hydroxyl (OH) generated by dissociative adsorption of H2O enhanced the charge loss of outer Fe atoms. Then OH strongly bonded with the neighboring Fe atoms to form the initial corrosion products, iron hydroxides (Fe-OH). The above DFT calculations are consistent with the experimental results about the steel depassivation and corrosion processes in concrete and hopefully these results can guide the anti-corrosion design of RC structures.

Unraveling the Effect of Intrinsic Carbon Defects on Potassium Storage Performance

AbstractDefects engineering is an attractive strategy to improve the potassium storage performance of carbon anodes. The current studies mainly focus on the introduction of external defects via heteroatom doping, however, the exploration on the effect of intrinsic defects caused by the loss of atoms or distortion in the crystal lattice on potassium storage is still lacking to date. Hence, a series of carbon materials with different intrinsic defect levels are developed via a soft‐template assisted method. It is found that intrinsic defects content in carbon is synergistically determined by the application of template and pyrolysis temperature, and a higher defects content is more likely to expose enormous edge active sites. This greatly promotes K‐adsorption storage during surface‐induced capacitive process, and therefore a strong positive correlation between capacity/capacity retention and intrinsic defects content is confirmed. As a result, the electrode with maximum defects content realizes a good capacity and a rate capability with long cycle lifespan (225.9 mAh g−1 at 2 A g−1 over 2000 cycles). This study offers an insight into the role of intrinsic defects of carbon materials in potassium storage performance.

Atomic Imaging and Thermally Induced Dynamic Structural Evolution of Two-Dimensional Cr2S3.

In this study, facile salt-assisted chemical vapor deposition (CVD) was used to synthesize ultrathin non-van der Waals chromium sulfide (Cr2S3) with a thickness of ∼1.9 nm. The structural transformation of as-grown Cr2S3 was studied using advanced in situ heating techniques combined with transmission electron microscopy (TEM). Two-dimensional (2D) and quasi-one-dimensional (1D) samples were fabricated to investigate the connection between specific planes and the dynamic behavior of the structural variation. The rearrangement of atoms during the phase transition was driven by the loss of sulfur atoms at elevated temperatures, resulting in increased free energy. A decrease in the ratio of the (001) plane led to an overall increase in surface energy, thus lowering the critical phase transition temperature. Our study provides detailed insight into the mechanism of structural transformation and the critical factors governing transition temperature, thus paving the way for future studies on intriguing Cr-S compounds.

Disentangling Electronic Spectra of Linear and Cyclic Hydrogenated Carbon Cluster Cations, C2n+1H+ (n = 3-10).

Electronic spectra are measured for protonated carbon clusters (C2n+1H+) containing between 7 and 21 carbon atoms. Linear and cyclic C2n+1H+ isomers are separated and selected using a drift tube ion mobility stage before being mass selected and introduced into a cryogenically cooled ion trap. Spectra are measured using a two-color resonance-enhanced photodissociation strategy, monitoring C2n+1+ photofragments (H atom loss channel) as a function of excitation wavelength. The linear C7H+, C9H+, C11H+, C13H+, C15H+, and C17H+ clusters, which are predicted to have polyynic structures, possess sharp 11Σ+ ← X̃1Σ+ transitions with well-resolved vibronic progressions in C-C stretch vibrational modes. The vibronic features are reproduced by spectral simulations based on vibrational frequencies and geometries calculated with time-dependent density functional theory (ωB97X-D/cc-pVDZ level). The cyclic C15H+, C17H+, C19H+, and C21H+ clusters exhibit weak, broad transitions at a shorter wavelength compared to their linear counterparts. Wavelengths for the origin transitions of both linear and cyclic isomers shift linearly with the number of constituent carbon atoms, indicating that in both cases, the clusters possess a common structural motif.

Flash pyrolysis mechanism of trimethylchlorosilane

The thermal decomposition mechanism of trimethylchlorosilane at temperatures up to 1400 K was investigated using flash pyrolysis microreactor coupled with vacuum ultraviolet (118.2 nm) photoionization time-of-flight mass spectrometry. The main initiation reaction of the parent molecule was identified to be HCl molecular elimination producing Me2Si=CH2, and its onset temperature was estimated to be around 1210 K. The methyl loss channel was also observed at an onset temperature of ∼1280 K. Other possible initiation pathways such as chlorine atom loss and methane molecular elimination were considered to be insignificant. Quantum chemistry calculations at the UCCSD(T)/cc-pVTZ//UM05–2X/aug-cc-pVDZ level of theory were performed to study the energetics of the possible initiation pathways. The theoretical calculations revealed that the HCl elimination channel via a van der Waals intermediate was the most energetically favored pathway among all the initiation channels, in agreement with the experimental observations. Transition state theory (TST) and variational transition state theory (VTST) calculations were employed to calculate unimolecular dissociation rate constants of the initiation reactions at elevated temperatures. The results supported the experimental observations and reaction energetics calculations that the HCl molecular elimination reaction was the most prominent initiation reaction and the CH3 loss channel was a significant initiation reaction channel. Secondary reactions of the initial products were identified, and the possible mechanisms were proposed.

Realization of space-dependent interactions by an optically controlled magnetic p -wave Feshbach resonance in degenerate Fermi gases

We report experimental realization of the space-dependent interaction by optical controlled narrow $p$-wave magnetic Feshbach resonance in a $^{40}\mathrm{K}$ Fermi gas. A space varied optical field at the tune-out wavelength is applied to illuminate the atomic sample, which drives the bound-to-bound molecular transition to shift the energy of a closed-channel molecule state. Due to the position varied atomic interaction induced by the different laser intensity distribution across the entire Fermi atom cloud, the space-dependent atomic loss rate is observed. This scheme provides a control technique to study the Fermi gas with the space-dependent atomic $p$-wave interaction, and has great potential in quantum simulation.

Mathematical and Kinetic Study of Horiuti-Polanyi Reaction Mechanism for the Methylcyclohexane Dehydrogenation Over Various Pt/Al2O3 Catalysts

The Horiuti-Polanyi (HP) mechanism has been studied for the methylcyclohexane dehydrogenation reaction over a Pt/AlO catalyst. Three HP mechanistic schemes such as competitive, non-competitive, and combined-competitive-non-competitive were used in the kinetic modeling of the experimental data. The loss of first hydrogen atom was regarded as the rate-determining step and the mathematical expressions were developed and fitted against the data. A FORTRAN routine was employed where 4th order Runge-Kutta method was used to solve the related differential equation and Marquardt algorithm was used for the parametric estimation. A kinetically and statistically best-fit HP kinetic equation was obtained with 87.96 kJ/mol of activation energy. The best-fit kinetic model was tested with five additional Pt-containing AlO catalysts and yet again found in good agreement with the experimental data.

Molecular dynamics simulations probing the effects of interfacial interactions on the tribological properties of nitrile butadiene rubber/nano-SiO2 under water lubrication

Nitrile butadiene rubber (NBR) is a water-lubricated bearing material with excellent vibrational absorption and impact resistance properties. However, its rapid wear under abnormal conditions is still a serious problem that needs to be solved. In this study, silica 69 (TESPT) was grafted onto the hydroxyl groups on the SiO2 surface to increase its interfacial interactions with NBR, and a molecular dynamics simulation method was employed to investigate how these interactions influence the tribological properties of NBR. The results showed that the introduction of SiO2 or SiO2(TESPT) significantly improved the mechanical properties and wear properties of NBR, but these fillers had little effect on the friction behavior of NBR. Compared with SiO2, SiO2(TESPT) exhibited stronger interfacial bonding with NBR, which further enhanced the van der Waals forces between NBR molecular chains. During the friction process, stronger interfacial interactions more effectively reduce the flexibility of the NBR molecular chains and the concentration of NBR atoms around the copper bar, thus reducing the binding energy between the copper bar and the polymer. These phenomena and the strong van der Waals interactions between NBR molecular chains can hinder the detachment of NBR chains (i.e., reduce the wear-induced atomic loss) and further improve the wear performance of NBR-based materials.

New Insights into Human Biotransformation of BDE-209: Unique Occurrence of Metabolites of Ortho-Substituted Hydroxylated Higher Brominated Diphenyl Ethers in the Serum of e-Waste Dismantlers

Extremely high levels of decabromodiphenyl ether (BDE-209) are frequently found in the serum of occupationally exposed groups, such as e-waste dismantlers and firefighters. However, the metabolism of BDE-209 in the human body is not adequately studied. In this study, 24 serum samples were collected from workers at a typical e-waste recycling workshop in Taizhou, Eastern China, and the occurrence and fate of these higher brominated diphenyl ethers (PBDEs) were investigated. The median concentration of the total PBDEs in the serum was 199 ng/g lipid weight (lw), ranging from 125 to 622 ng/g lw. Higher brominated octa- to deca-BDEs accounted for more than 80% of the total PBDEs. Three ortho-hydroxylated metabolites of PBDEs─6-OH-BDE196, 6-OH-BDE199, and 6'-OH-BDE206─were widely detected with a total concentration (median) of 92.7 ng/g lw. The concentrations of the three OH-PBDEs were significantly higher than their octa- and nona-PBDE homologues, even exceeding those of the total PBDEs in several samples, indicating that the formation of OH-PBDEs was a major metabolic pathway of the higher brominated PBDEs in occupationally exposed workers. An almost linear correlation between 6-OH-BDE196 and 6-OH-BDE199 (R = 0.971, P < 0.001) indicates that they might undergo a similar biotransformation pathway in the human body or may be derived from the same precursor. In addition, the occurrence of a series of penta- to hepta- ortho-substituted OH-PBDEs was preliminarily identified according to their unique "predioxin" mass spectral profiles by GC-ECNI-MS. Taken together, the tentative metabolic pathway for BDE-209 in e-waste dismantlers was proposed. The oxidative metabolism of BDE-209 was mainly observed at the ortho positions to form 6'-OH-BDE-206, which later underwent a consecutive loss of bromine atoms at the meta or para positions to generate other ortho-OH-PBDEs. Further studies are urgently needed to identify the chemical structures of these ortho-OH-PBDE metabolites, and perhaps more importantly to clarify the potentially toxic effects, along with their underlying molecular mechanisms.

The synthesis of MDA from helional and characterisation by isotope ratio mass spectrometry

Presented here is an investigation into the stable isotopic ratios of 3,4-methylenedioxyamphetamine (MDA) prepared from the alternative precursor helional. Two methods for the synthesis of MDA were investigated, both utilising hydroxylamine as the nitrogen source. Recent publications found both helional and hydroxylamine with isotopic compositions significantly different to traditional precursors and nitrogen sources. While minimal fractionation was observed in carbon isotopic compositions, apparent fractionation occurred to hydrogen, nitrogen and oxygen isotopic compositions during the synthesis of MDA. Fractionation observed in δ15N were explained by the reaction conditions during the addition of hydroxylamine. The fractionation observed in δ18O was consistent with the replacement and loss of an oxygen atom during the synthesis of the amide intermediate and MDA. A brief investigation into isotopic fractionation during MDA hydrogen chloride (HCl) salt precipitation was also conducted, and additional fractionation may be expected in both δ2H and δ15N during the process, consistent with the proposed mechanism. These results suggest that tactical intelligence can be gained from the batch-to-batch variations to isotopic composition of MDA during the synthesis from helional.

Efficient Two-Dimensional Defect-Free Dual-Species Atom Arrays Rearrangement Algorithm with Near-Fewest Atom Moves

Dual-species single-atom array in optical tweezers has several advantages over the single-species atom array as a platform for quantum computing and quantum simulation. Thus, creating the defect-free dual-species single-atom array with atom numbers over hundreds is essential. As recent experiments demonstrated, one of the main difficulties lies in designing an efficient algorithm to rearrange the stochastically loaded dual-species atoms arrays into arbitrary demanded configurations. We propose a heuristic connectivity optimization algorithm to provide the near-fewest number of atom moves. Our algorithm introduces the concept of using articulation points in an undirected graph to optimize connectivity as a critical consideration for arranging the atom moving paths. Tested in array size of hundreds atoms and various configurations, our algorithm shows a high success rate (>97%), low extra atom moves ratio, good scalability, and flexibility. Furthermore, we propose a complementary step to solve the problem of atom loss during the rearrangement.

Ammonia Borane, NH3 BH3 : A Threshold Photoelectron-Photoion Coincidence Study of a Potential Hydrogen-Storage Material.

We have investigated the photoionization of ammonia borane (AB) and determined adiabatic ionization energy to be 9.26±0.03 eV for the X+ 2E←X 1A1 transition. Although the threshold photoelectron spectrum appears at first glance to be similar to the one of the isosteric ethane, the electronic situation differs markedly, due to different orbital energies. In addition, an appearance energy AE0K(NH3BH3, NH3BH2 +)= 10.00±0.03 eV has been determined, corresponding to the loss of a hydrogen atom at the BH3‐site. From the data, a 0 K bond dissociation energy for the B−H bond in the cation of 71.5±3 kJ mol−1 was derived, whereas the one in the neutral compound has been estimated to be 419±10 kJ mol−1.

Active W Sites Promoted by Defect Engineering Enhanced C2H6S3 Sensing Performance of WO3 Nanosheets.

Defect engineering has received extensive attention as an effective method to tune the gas sensing properties of semiconductor materials. Here, defective WO3 (D-WO3) nanosheets were obtained by a simple hydrogenation process with a detection limit as low as 5 ppb for dimethyl trisulfide (DMTS) and a response of 2.3 times that of the initial WO3 nanosheets to 100 ppb DMTS. Importantly, X-ray photoelectron spectroscopy and Raman spectroscopy confirmed the partial loss of oxygen atoms in D-WO3 nanosheets, and density functional theory calculations found that the W sites near the oxygen defect showed higher adsorption energy for DMTS and transferred more electrons during the gas interaction, indicating that the active W site caused by oxygen atom loss can effectively enhance the reactivity of two-dimensional WO3 nanosheets. Different from the traditional oxygen defect model, this work reveals the positive effect of active metal sites on gas sensing for the first time, which is expected to provide an effective reference for the sensing application of defect engineering in metal oxides.

Parametric Excitation of Ultracold Sodium Atoms in an Optical Dipole Trap

Parametric modulation is an effective tool to measure the trap frequency and investigate the atom dynamics in an optical dipole trap or lattices. Herein, we report on experimental research of parametric resonances in an optical dipole trap. By modulating the trapping potential, we have measured the atomic loss dependence on the frequency of the parametric modulations. The resonance loss spectra and the evolution of atom populations at the resonant frequency have been demonstrated and compared under three modulation waveforms (sine, triangle and square waves). A phenomenological theoretical simulation has been performed and shown good accordance with the observed resonance loss spectra and the evolution of atom populations. The theoretical analysis can be easily extended to a complex waveform modulation and reproduce enough of the experiments.

Disulfide Dichloride: A High Efficiency Vulcanizing Agent for Sulfurized Polyacrylonitrile

Sulfurized polyacrylonitrile (SPAN) cathodes have shown great prospects in commercial applications due to the high discharge capacity, good cycle stability, and low self-discharge rate. However, high sulfurization temperature results in loss of nitrogen atoms, which leads to imperfect SPAN structure and is not conducive to fast electron transfer. A high efficiency vulcanizing agent of S2Cl2 was used to reduce the reaction temperature in this work. We found that S2Cl2 promotes PAN cyclization, reduces the cyclization reaction temperature, and avoids the loss of nitrogen atoms and the agglomeration of SPAN primary particles in high-temperature reactions. The SPAN cathode material prepared using S2Cl2 has a more regular structure six-membered ring main chain structure and a smaller primary particle size, which is beneficial to the rapid conduction of electrons and lithium ions in the electrode material. The electrochemical test results confirmed that the SPAN cathode material prepared by S2Cl2 has higher active material utilization, better cycle stability, and better rate performance.

Plasma-enhanced atomic layer deposition of molybdenum oxides using molybdenum hexacarbonyl as the precursor

Molybdenum oxide (MoOx) thin films are fabricated by plasma-enhanced atomic layer deposition (PEALD) using molybdenum hexacarbonyl Mo(CO)6 as the precursor and oxygen as the reactant. The effect of plasma power for oxygen has been investigated on the evolution of film structure. Molybdenum oxide shows the orthorhombic α-MoO3 phase at low powers and gradually changes to the metastable monoclinic β-MoO3 phase as the power continually increases, which is confirmed by Raman spectroscopy. α-MoO3 is two-dimensional (2-D) phase with Pbnm space group, while β-MoO3 film belongs to three-dimensional phase with P21/c. From the observation of scanning electron microscopy (SEM), a rod-like structure has been detected, whereas a bulk-like grain corresponds to a high ratio of β-MoO3 to α-MoO3 phase at higher power of 150 W. Due to better coverage of 2-D layer preventing surface from oxidation, the interfacial layer of α-MoO3 checked from transmission electron microscopy (TEM) shows thinner at low powers when contacting with silicon substrate, which is consistent with the performance of leakage current. The changes in binding energies of Mo 3d and O 1s orbits at different milling depths are compared by different powers. Though the significant amount of Mo4+ oxidation state is shown from x-ray photoelectron spectroscopy (XPS), only α-MoO3 and β-MoO3 crystallites with +6 state of Mo are observed from x-ray diffraction (XRD) patterns. Above phenomenon is due to the structural change caused by the loss of oxygen atoms. Thus, according to the charge transformation and compensation, the defect reaction model can well explain that oxygen vacancies inside films are more prevalent in orthorhombic phase at low plasma power for oxygen of our reduced MoO3-x.

Gain/loss effects on spin-orbit coupled ultracold atoms in two-dimensional optical lattices

Due to the fundamental position of spin-orbit coupled ultracold atoms in the simulation of topological insulators, the gain/loss effects on these systems should be evaluated when considering the measurement or the coupling to the environment. Here, incorporating the mature gain/loss techniques into the experimentally realized spin-orbit coupled ultracold atoms in two-dimensional optical lattices, we investigate the corresponding non-Hermitian tight-binding model and evaluate the gain/loss effects on various properties of the system, revealing the interplay of the non-Hermiticity and the spin-orbit coupling. Under periodic boundary conditions, we analytically obtain the topological phase diagram, which undergoes a non-Hermitian gapless interval instead of a point that the Hermitian counterpart encounters for a topological phase transition. We also unveil that the band inversion is just a necessary but not sufficient condition for a topological phase in two-level spin-orbit coupled non-Hermitian systems. Because the nodal loops of the upper or lower two dressed bands of the Hermitian counterpart can be split into exceptional loops in this non-Hermitian model, a gauge-independent Wilson-loop method is developed for numerically calculating the Chern number of multiple degenerate complex bands. Under open boundary conditions, we find that the conventional bulk-boundary correspondence does not break down with only on-site gain/loss due to the lack of non-Hermitian skin effect, but the dissipation of chiral edge states depends on the boundary selection, which may be used in the control of edge-state dynamics. Given the technical accessibility of state-dependent atom loss, this model could be realized in current cold-atom experiments.

Tunable single photon nonreciprocal scattering based on giant atom-waveguide chiral couplings.

We theoretically investigate the single photon scattering properties in a waveguide chirally coupling to a giant atom. The single photon transmission spectrum depends on the direction of the single photon incident when the energy loss of the giant atom can not be neglected. The difference between the transmission probabilities corresponding to opposite transport direction ΔT is calculated. It shows that both of the position and width of the ΔT are dependent on the size of the giant atom. Furthermore, the position of the maximum ΔT and the frequency width of ΔT can be modulated by a classical laser beam. Our results will be beneficial to control single photons in quantum devices design involving giant atoms.

Long-lifetime supersolid in a two-component dipolar Bose-Einstein condensate

Recent studies on supersolidity in a single-component Bose-Einstein condensate (BEC) have relied on the Lee-Huang-Yang (LHY) correction for stabilization of self-bound droplets, which, however, involves a high density inside the droplets, limiting the lifetime of the supersolid. Here we propose a two-component mixture of dipolar and nondipolar BECs, such as an $^{166}\mathrm{Er}\text{\ensuremath{-}}^{87}\mathrm{Rb}$ mixture, to create and stabilize a supersolid without the LHY correction, which can suppress the atomic loss and may allow observation of the long-time dynamics of the supersolid. In such a system, supersolidity can be controlled by the difference in the trap centers between the two components.

Sustainable production of lignin-derived porous carbons for high-voltage electrochemical capacitors

• CuCl 2 activation mechanism is elucidated. • Lignin-derived porous carbon with high specific surface area. • Lignin-derived porous carbon with high yields up to 49.4%. • High-voltage electrochemical capacitors are fabricated. The high energy storage cost is a crucial factor limiting the wide application of electrochemical capacitors. Herein, we proposed a comprehensive strategy to reduce the cost of electrochemical capacitors with aqueous electrolytes, i.e. , reducing the cost of electrode materials and increasing the energy density of electrochemical capacitors. Low-cost lignin-derived porous carbon electrode materials with high specific surface area and hierarchical porous structure were prepared by CuCl 2 activation. The CuCl 2 activation agent was recycled and thus can be reused. What is more, we proposed that the mechanism of CuCl 2 activation is a solid-phase reaction in which the chloride ions in copper chloride deprive the hydrogen atoms in lignin, resulting in the loss of hydrogen atoms and the formation of pores. High energy density C//C symmetric electrochemical capacitors, Zn//C and Pb//C asymmetric electrochemical capacitors based on lignin-derived porous carbon were fabricated using sulfate electrolytes which endow high working voltage window. This work provides a comprehensive strategy for designing electrochemical capacitors with high energy densities and low cost of energy storage, which is expected to promote the industrial application of electrochemical capacitors with aqueous electrolytes.