Laser Photoionization Spectroscopy of Single Atoms and Molecules

A new, highly sensitive method of laser spectroscopy of atoms and molecules based on multiple photon ionization is described. The history, characteristics and some key applications of this method are presented.     

ESR and X-ray Investigations of Deuterium Atoms and Molecules in Impurity-Helium Solids

Impurity-helium solids created by injecting deuterium atoms and molecules into superfluid ⁴He have been studied via electron spin resonance (ESR) and x-ray diffraction methods. We measured the g-factor, the hyperfine constant and the spin-lattice relaxation time of D atoms in D-D₂-He solids. These measurements show that D atoms are mainly stabilized in D₂ clusters. Using an x-ray method we found the size of D₂ clusters to be ～90Å in diameter and the densities of D₂ molecules in the samples to be of order 2.5?10²¹ cm^?3 . The highest average concentration of D atoms achieved in D-D₂-He solids was ～1.5?10¹⁸ cm^?3 . The local concentrations of D atoms within D₂ clusters is found to be large (～2?10¹⁹ cm^?3).     

Catalysis of a Single Transition Metal Site for Water Oxidation: From Mononuclear Molecules to Single Atoms

Low-cost, nonprecious transition metal (TM) catalysts toward efficient water oxidation are of critical importance to future sustainable energy technologies. The advances in structure engineering of water oxidation catalysts (WOCs) with single TM centers as active sites, for example, single metallic molecular complexes (SMMCs), supported SMMCs, and single-atom catalysts (SACs) in recent reports are examined. The efforts made on these configurations in terms of design principle, advanced characterization, performances and theoretical studies, are critically reviewed. A clear roadmap with the correlations between the single-TM-site-based structures (coordination and geometric structure, TM species, support), and the catalytic performances in water oxidation is provided. The insights bridging SMMCs with SACs are also given. Finally, the challenges and opportunities in the single-TM-site catalysis are proposed.     

The Possibility of Using Repulsive Interaction Potentials for the Calculation of High-Temperature Integrals of Collisions between Atoms and Molecules

The possibility is demonstrated of using exponential repulsive interaction potentials for the calculation of high-temperature integrals of collisions between atoms and molecules. An analytical formula is suggested, and the values of employed parameters are determined. The difference between the calculation results for complex interaction potentials with due regard for repulsion, potential well, and long-range attraction and the calculation results for the repulsive exponential interaction potential in the entire range of impact parameters is investigated. The dependence of the calculation accuracy on the choice of the region of approximation of the model potential by the exponential one is noted.     

Controlling Electronic States and Transport Properties at the Level of Single Molecules

Since molecular electronics has been rapidly growing as a promising alternative to conventional electronics towards the ultimate miniaturization of electronic devices through the bottom‐up strategy, it has become a long‐term desire to understand and control the transport properties at the level of single molecules. In this Research News article it is shown that one may modify the electronic states of single molecules and thus control their transport properties through designing and fabrication of functional molecules or manipulating molecules with scanning tunneling microscopy. The rectifying effect of single molecules can be realized by designing a donor–barrier–acceptor architecture of Pyridine–σ–C₆₀ molecules to achieve the Aviram–Ratner rectifier and by modifying electronic states through azafullerene C₅₉N molecules. The effect of the negative differential resistances can be realized by appropriately matching the molecular orbital symmetries between a cobalt phthalocyanine (CoPc) molecule and a Ni electrode. The electronic states and transport properties of single molecules, such as CoPc and melamine molecules, can be altered through manipulation or modifying molecular structures, leading to functionalized molecular devices.     

An Atomistic Tomographic Study of Oxygen and Hydrogen Atoms and their Molecules in CVD Grown Graphene

The properties and growth processes of graphene are greatly influenced by the elemental distributions of impurity atoms and their functional groups within or on the hexagonal carbon lattice. Oxygen and hydrogen atoms and their functional molecules (OH, CO, and CO₂) positions' and chemical identities are tomographically mapped in three dimensions in a graphene monolayer film grown on a copper substrate, at the atomic part‐per‐million (atomic ppm) detection level, employing laser assisted atom‐probe tomography. The atomistic plan and cross‐sectional views of graphene indicate that oxygen, hydrogen, and their co‐functionalities, OH, CO, and CO₂, which are locally clustered under or within the graphene lattice. The experimental 3D atomistic portrait of the chemistry is combined with computational density‐functional theory (DFT) calculations to enhance the understanding of the surface state of graphene, the positions of the chemical functional groups, their interactions with the underlying Cu substrate, and their influences on the growth of graphene.     

The Transport Properties of Sodium Atoms and the Heat Capacity of Sodium Dimers at High Temperatures

Including the contribution of excited state atoms can improve calculations of dilute gaseous transport properties at high temperatures. For sodium, experimental and/or theoretical information is available about the potential energy curves associated with each of ten low-lying states of the sodium dimer. These include the ${{\rm X}^{1}\Sigma_{\rm g}{}^{+}}$ and ${^{3}\Sigma_{\rm u}{}{}^{+}}$ states that dissociate to two ground state ²S sodium atoms and the four ${^{3}\Sigma_{\rm g,u}{}^{+},\,^{1}\Sigma _{\rm g,u}{}^{+},\,^{1}\Pi _{\rm g,u},\,^{3}\Pi _{\rm g,u}}$ gerade/ungerade pairs of states that dissociate to a ground state ²S atom and an excited state ²P atom. Nine of these are bound states and have been fitted with the Hulburt–Hirschfelder potential, a very good general purpose atom–atom potential. The ³Π_g state is not bound and has been fitted with the exponential repulsive potential. We have used these potentials to calculate viscosity collision integrals as a function of temperature, and employed degeneracy-weighted averaging to determine the viscosity and translational contribution to the thermal conductivity of the sodium atoms. These same potentials have been used to calculate the heat capacity, ${C_{p}^{\rm o}}$ , of the sodium dimer using an approach that depends on the second virial coefficient and its first two temperature derivatives. Again, the inclusion of molecular states that dissociate to an excited state atom allows ${C_{p}^{\rm o}}$ to be determined with improved accuracy at higher temperatures. Thus, thermophysical property calculations for sodium have been extended to 25,000 K. These results are compared with previous results, including heat capacities given in the NIST-JANAF Thermochemical Tables.     

Local Environment and Migration in Nickel Metal of 57Co Impurity Atoms Formed by a Nuclear Reaction

The local environment of ^{5 7}Co impurity atoms formed in nickel metal by the ^{5 8}Ni(,p) reaction was studied by emission Müossbauer spectroscopy. The positions of ^{5 7}Co atoms after irradiation and short isochronous (1800 s) heat treatments of the cyclotron targets at 500-1100 K were evaluated. The processes of impurity transfer during treatment of irradiated targets were analyzed. The rate of impurity transfer is determined by the damage of the irradiated metal lattice and stabilization forms of impurity atoms (i.e., their location in the substitution sites or at the crystallite grain boundary).     

光传送网中光监控通道信号Q值在线监测技术

提出了一种带有光监控通道（OSC）子系统的光传送网（OTN）分层结构模型,分析了OSC中的信号特点,指出OSC信号质量决定了运行、管理和维护（OAM）信号的可靠性。依据Q值与误码率（BER）的一一对应关系,提出了一种可在线监测OSC信号Q值的方案,并基于数字信号处理芯片（DSP）技术设计了监测模块,实现了OSC信号在线Q值监测。     

Anisotropic Quantum Transport through a Single Spin Channel in the Magnetic Semiconductor EuTiO3

Magnetic semiconductors are a vital component in the understanding of quantum transport phenomena. To explore such delicate, yet fundamentally important, effects, it is crucial to maintain a high carrier mobility in the presence of magnetic moments. In practice, however, magnetization often diminishes the carrier mobility. Here, it is shown that EuTiO₃ is a rare example of a magnetic semiconductor that can be desirably grown using the molecular beam epitaxy to possess a high carrier mobility exceeding 3000 cm² V⁻¹ s⁻¹ at 2 K, while intrinsically hosting a large magnetization value, 7 μ_B per formula unit. This is demonstrated by measuring the Shubnikov–de Haas (SdH) oscillations in the ferromagnetic state of EuTiO₃ films with various carrier densities. Using first-principles calculations, it is shown that the observed SdH oscillations originate genuinely from Ti 3d-t_2g states which are fully spin-polarized due to their energetical proximity to the in-gap Eu 4f bands. Such an exchange coupling is further shown to have a profound effect on the effective mass and fermiology of the Ti 3d-t_2g electrons, manifested by a directional anisotropy in the SdH oscillations. These findings suggest that EuTiO₃ film is an ideal magnetic semiconductor, offering a fertile field to explore quantum phenomena suitable for spintronic applications.     

Creating Local Reinforcement of a Channel in a Composite Casting Using Electromagnetic Separation

This article presents a new method to obtain local reinforcement in near-surface layers of channels in castings made of a particle-reinforced metal matrix composite in the alternating electromagnetic field generated by an inductor placed inside the channel. In centrifugal casting, the centrifugal force on the particles leads to the formation of composite structures, while in the proposed method, the electromagnetic force field on the particles results in the designed structure of the composite casting. The article reports the experimental verification of this method using an aluminium sleeve reinforced locally with Si C particles at the inner wall.