尘埃表面化学理论模拟研究进展（英文）

近年来天体化学在解释星际分子的形成过程中起重要作用的尘埃表面化学取得了长足的发展,本文综述了在天体化学模拟中用到的各种数值计算方法,以及尘埃冰幔的化学模型.同时也介绍在实验室天体化学方面获得的结果,及其对尘埃表面化学所起到的促进作用.     

紫外光子在星周天体化学中的作用

介于1到8个太阳质量之间的恒星在演化后期的渐近巨星分支(AGB)阶段，会以气体和尘埃的形式损失大量物质. AGB星提供了星际介质中高达35%的尘埃，其中包含形成太阳系所需要的物质. 此外，AGB星周包层是复杂有机化学所发生的重要场所之一，在其中已探测到的有机分子已超过80多个. 这里展示了AGB星自身或者其近距离的伴星所辐射的紫外光子会显著地改变星周包层的化学特性，尤其是具有团块结构的星周包层. 研究发现，在恒星存在伴星(例如白矮星)的情况下，高通量的紫外光子会破坏富碳AGB星周包层内部的H₂O分子，使其含量低于观测到的水平，并且在星周包层内部产生C⁺等物质，这与以往的星周化学模型的研究结果是不同的.     

γ噪Blazar天体的γ射线和近红外光辐射研究

收集了29个有γ噪的Blazar天体(其中有16个BL Lac天体和13个平谱射电类星体)的近红外流量密度和γ射线流量密度,获得以下主要结果:1)23个天体中的γ射线流量密度和近红外流量密度在低态时存在较强的相关性而在高态时有弱的相关性.2)在29个天体中,有6个天体只有一个观测数据点,将其认为是高态时,γ射线流量密度与近红外光流量密度之间有弱相关性,而认为是低态时有强相关性.3)29个源的γ射线流量密度与X射线流量密度在低态时有相关性,但是γ射线流量与光学流量密度,γ射线流量与射电流量密度均没有相关性.4)在16个BL Lac天体中γ射线流量与近红外光流量不论在高态还是低态都有相关性,而13个平谱射电类星体没有相关性.讨论了γ噪Blazar天体的γ射线辐射机制,认为γ射线的辐射机制主要是同步自康普顿散射.而逆康普顿散射来自绕中心核且温度约为2000K的尘埃,这些尘埃的区域大约有r=3pc,聚束的相对论电子也可能是这种尘埃模型辐射机制的一个重要补充.平谱射电类星体和BL Lac天体的γ辐射机制可能有些不同. 关键词： Blazar天体 星系γ射线观测辐射机制 非热辐射     

对原行星盘中易挥发物质缺失问题的简要综述

年轻恒星周围存在盘状的气体和尘埃分布，称为原行星盘，行星在其中形成. 为了认识恒星和行星的形成和演化以及构成行星的原材料，对这些盘的观测是必须的. 数值模型有助于从观测数据提取出重要的物理参数，包括盘的尘埃和气体的质量. 这些参数可以作为进一步模拟的输入参数，预期热化学模拟能复现各种分子的观测数据. 但是，对于许多原行星盘，模型算出的多种分子的发射强度高于观测值. 真实的盘中这些分子的丰度比理论预期低，这是易挥发物质的缺失问题. 本文指出在这个问题上理论与观测的差异意味着尘埃的演化对气体化学有重要影响，提示在这些盘中行星形成的早期阶段已经开始了.     

天体光谱获取率最高的望远镜——LAMOST

现代天文学所研究的对象,即各种各样的天体,几乎都是“看得见而摸不着”的。于是,1825年法国哲学家孔德在他的《实证哲学讲义》中断言“恒星的化学组成是人类绝不能得到的知识”,以此来说明人类认识的局限性。然而,孔德的预言被30年之后的天体光谱术打破了,方法就是将天体的光通过天文望远镜和光谱仪分解成光谱,再分析研究光谱照片。利用天体光谱不但能够确定天体化学组成,而且还能确定其温度、压力、密度、磁场和运动速度等物理条件。150年来,天文学家为观测各种天体光谱而建造各式各样的望远镜和光谱仪,使人类对天体化学组成和物理本质的…     

原子分子物理—研究宇宙物质的基础科学

艹勾清泉教授所从事、发展和传授的原子、分子结构理论在天体物理、天体化学、固体物理、材料科学以及极端条件物理的发展中起到基础理论的重要作用。他的研究群体活跃在各个相关的基础与应用领域里     

天体原子、离子和分子射电谱线研究进展

简述天体原子、离子和分子射电谱线自首次探测至今,半个世纪以来的研究进展.展示空间特有的非地球稳定的自由基、同位素、同位素分子和离子及其相关的过程.天体微波激射(MASER)因能提供恒星诞生与死亡的珍贵信息成为本文之侧重点.     

星际氧气分子的气相-尘埃模型研究

本文采用气相-尘埃模型Nautilus研究了星际氧气的演化过程，使用了两种典型初始丰度值下的恒温模型和变化物理条件下的加热模型进行模拟计算. 结果表明，在冷致密云的条件下，CO、O₂和H₂O达到峰值的时间依赖于氢核密度的多少，其随氢核密度的增大而减小. 在加热模型中，在温度升高后的10⁵年后，氧气的丰度值与观测结果符合较好. 在温度大于30 K后，氧气的稳态丰度值将不再随氢核密度而变化，且大于此温度可以阻止氧气大量的沉降到尘埃表面. 此外，无论在恒温模型还是在加热模型中，低氢核密度更有利于O₂的生成.     

一个了解宇宙的新窗口——分子天体物理学进展介绍

 50年以前,人们对太阳系以外的化合物几乎一无所知.那时的天体化学主要是通过中性或电离的原子光谱来了解宇宙中元素的成分、比例及分布并根据核物理知识研究元素的演化.著名的天文学家爱丁顿在1937年曾提出星云中相当大部分的物质可能是以分子形式存在.但同时他说:“我在写到分子时是很胆怯的,因为我还没有摆脱‘原子是物理而分子是化学’这种传统.”     

基于Logistic回归模型的Blazar天体的分类

从文献中收集了205个Blazar天体,包括142个BL Lac天体和63个平谱射电类星体(FSRQs).对这些天体的类别与它们的红移、射电5 GHz辐射流量、光学V波段流量、1 keV处X射线流量、X射线光子谱指数进行了相关性和Logistic回归分析.结果表明,对Blazar天体分类产生主要影响的因素是红移、射电5 GHz辐射流量和X射线光子谱指数,综合应用这三个物理量判别Blazar天体的分类的准确率可达到91.2%,得到的分类方程具有良好的预测效果,可以作为Blazar天体分类的一个重要的判据.而光学V波段流量和1 keV处X射线流量不能区分开BL Lac天体和FSRQs,它们与Blazar天体分类没有相关性.本文结果支持将BL Lac天体和FSRQs归为Blazar天体,不同类别的Blazar天体之间能通过一种演化序列相联系. 关键词： Logistic 分类 Blazar天体     

The hydrogen surface chemistry of carbon as a plasma facing material

Recent progress in plasma performance in experiments on controlled thermonuclear fusion will lead to next-generation fusion experiments with the ultimate goal to make a power-generating fusion reactor reality. A major issue in the design of fusion experiments is the selection of the first wall material. Due to its outstanding thermal properties and its low Z carbon is and will be a first choice material, either elemental or in compounds and composites. Given the fact that in magnetically confined hydrogen plasmas of high density and temperature substantial wall fluxes of H species occur, the hydrogen/carbon surface chemistry, in particular chemical erosion and H retention, becomes a concern. Although for more than a decade materials science studies on the H---carbon interaction have been performed, the elementary reaction steps of this interaction have become clear only recently. This report reviews work performed on the H/carbon surface chemistry under the aspects of chemical erosion. It presents in detail model studies directed towards identifying elementary reaction steps. Related fields, e.g. the H/C surface chemistry as relevant for the production of hard a-C:H coatings and low pressure diamond synthesis are covered in the review.     

Metal CVD for microelectronic applications: An examination of surface chemistry and kinetics

We review the surface chemistry and kinetics relevant to the chemical vapor deposition (CVD) of metals used for microelectronic applications. Our efforts focus on the surface chemistry of aluminum, tungsten, and copper CVD, which have received the most recent interest for metallization. We first briefly review a variety of topics concerning the applications and the chemistry and kinetics of metal CVD. We also give a brief overview of the application of surface science techniques to the study of CVD-related surface chemistry.     

The effect of surface contact conditions on grain boundary interdiffusion in a semi-infinite bicrystal

The Kirkendall effect is conditioned by active diffusion as well as by active sources and sinks for vacancies. In the case of grain boundaries under the condition of negligible bulk diffusion, the Kirkendall effect is highly localized and responsible for the formation of an extra material wedge in the grain boundary, which may lead to high stress concentrations. The Kirkendall effect in grain boundaries of a binary system is described by a set of partial differential equations for the mole fraction of one of the diffusing components and for the stress component normal to the grain boundary completed with the respective initial and boundary conditions. The contact conditions of the grain boundary with the surface layer acting as source of one of the diffusing components can be considered as equilibrium ones ensuring the continuity of generalized chemical potentials of both diffusing components. Thus, the boundary conditions are determined by the difference in chemistry (i.e. how the thermodynamic parameters depend on chemical composition) of the grain boundaries and of the surface layer. The simulations based on the present model indicate a drastic influence of the chemistry on the grain boundary interdiffusion and Kirkendall effect.     

Surface chemistry and catalysis of oxide model catalysts from single crystals to nanocrystals

Fundamental understandings of surface chemistry and catalysis of solid catalysts are of great importance for the developments of efficient catalysts and corresponding catalytic processes, but have been remaining as a challenge due to the complex nature of heterogeneous catalysis. Model catalysts approach based on catalytic materials with uniform and well-defined surface structures is an effective strategy. Single crystals-based model catalysts have been successfully used for surface chemistry studies of solid catalysts, but encounter the so-called “materials gap” and “pressure gap” when applied for catalysis studies of solid catalysts. Recently catalytic nanocrystals with uniform and well-defined surface structures have emerged as a novel type of model catalysts whose surface chemistry and catalysis can be studied under the same operational reaction condition as working powder catalysts, and they are recognized as a novel type of model catalysts that can bridge the “materials gap” and “pressure gap” between single crystals-based model catalysts and powder catalysts. Herein we review recent progress of surface chemistry and catalysis of important oxide catalysts including CeO₂, TiO₂ and Cu₂O acquired by model catalysts from single crystals to nanocrystals with an aim at summarizing the commonalities and discussing the differences among model catalysts with complexities at different levels. Firstly, the complex nature of surface chemistry and catalysis of solid catalysts is briefly introduced. In the following sections, the model catalysts approach is described and surface chemistry and catalysis of CeO₂, TiO₂ and Cu₂O single crystal and nanocrystal model catalysts are reviewed. Finally, concluding remarks and future prospects are given on a comprehensive approach of model catalysts from single crystals to nanocrystals for the investigations of surface chemistry and catalysis of powder catalysts approaching the working conditions as closely as possible.     

Surface emitting lasers

In this paper we review the recent progress and basic technology of vertical cavity surface emitting lasers (SEL). First, the concept of surface emitting lasers is introduced, and then device technologies will be presented. We will feature some important issues, such as multi-layer structures and 2-dimensional arrays. Lastly, the future prospects of SELs are discussed.     

The application of quasi-elastic neutron scattering techniques (QENS) in surface diffusion studies

Neutron scattering techniques such as quasi-elastic neutron scattering, QENS, have proven to be well-suited tools for studying structure and dynamics of surface adsorbed molecules. In contrast to many more widely used surface science techniques neutron scattering allows the microscopic characterization of samples under a wide range of thermodynamic conditions, as the samples are not constrained to ultra high vacuum environment. Moreover, neutron scattering allows the separation of coherent and incoherent scattering, giving access to different diffusive mechanisms such as single particle diffusion, mass transport, rotations, or vibrations. In this paper we will review recent progress and the state-of-the-art in neutron scattering experiments on surface adsorbed molecules in the sub-monolayer coverage range with a specific emphasis on studies of carbon and other high surface density substrates. We will also cover recent progress in theoretical modeling, since the usefulness of neutron scattering data on surface dynamics can be strongly enhanced by computational modeling, such as molecular dynamics (MD) simulations and the development of analytical models.     

The interaction of water with solid surfaces: fundamental aspects revisited

Water is perhaps the most important and most pervasive chemical on our planet. The influence of water permeates virtually all areas of biochemical, chemical and physical importance, and is especially evident in phenomena occurring at the interfaces of solid surfaces. Since 1987, when Thiel and Madey (TM) published their review titled ‘The interaction of water with solid surfaces: fundamental aspects’ in Surface Science Reports, there has been considerable progress made in further understanding the fundamental interactions of water with solid surfaces. In the decade and a half, the increased capability of surface scientists to probe at the molecular-level has resulted in more detailed information of the properties of water on progressively more complicated materials and under more stringent conditions. This progress in understanding the properties of water on solid surfaces is evident both in areas for which surface science methodology has traditionally been strong (catalysis and electronic materials) and also in new areas not traditionally studied by surface scientists such as electrochemistry, photoconversion, mineralogy, adhesion, sensors, atmospheric chemistry and tribology. Researchers in all these fields grapple with very basic questions regarding the interactions of water with solid surfaces such as how is water adsorbed, what are the chemical and electrostatic forces that constitute the adsorbed layer, how is water thermally or non-thermally activated and how do coadsorbates influence these properties of water. The attention paid to these and other fundamental questions in the past decade and a half has been immense. In this review, experimental studies published since the TM review are assimilated with those covered by TM to provide a current picture of the fundamental interactions of water with solid surfaces.     

Spectromicroscopic investigation of (NH4)2S treated polycrystalline Cu(In1−xGax)Se2

Device-grade polycrystalline thin-film Cu(In_1−xGa_x)Se₂ was treated with (NH₄)₂S at 60°C to determine the resulting microscopic surface composition/morphology. Scanning electron microscopy was used to evaluate the resultant macroscopic surface morphology. Modification of the surface and grain boundary chemistry of the Cu(In_1−xGa_x)Se₂ polycrystalline films was investigated with scanning photoemission spectromicroscopy. The submicrometer lateral resolution of this technique allows us to directly characterize not only the surface chemistry of the treated films on the submicron scale, but also to probe the grain boundary chemistry. Chemical maps depicting the distribution of chemical species on the surface and at grain boundaries were obtained by monitoring the S 2p, Se 3d, In 4d/Ga 3d and Cu 3d (valence band) photoelectrons while scanning the sample. Background maps were also acquired of each of the peak energies to separate chemical contrast from topographic contrast. Results show that S has been incorporated at the surface, possibly creating a wider bandgap Cu(In_1−xGa_x)(Se_1−yS_y)₂ surface layer, and along the grain boundaries. The purpose of this investigation is to find an environmentally safe replacement for the toxic CdS overlayer commonly used for heterojunction devices without sacrificing overall device performance and reliability.     

Microscopic and Spectroscopic Methods Applied to the Measurements of Nanoparticles in the Environment

Abstract: Currently, thousands of commercially available products contain engineered nanoparticles (ENPs). Because numerous nanoparticles (NPs) are being used in products that will be in contact with water or directly used in water treatment processes, these materials will undoubtedly reside, at least temporarily, in bodies of water. Given the widespread use of NPs and ENPs in consumer goods, a large portion of these materials will soon go into the waste stream, potentially to soil and sediments or added directly to agricultural lands via biosolids. Possible impacts of ENPs on aquatic and terrestrial ecosystems are of great concern. Preliminary data from several research groups have shown that ENPs may have a direct impact on food safety and the food chain. However, our knowledge about detection and characterization of NPs in the environment, especially aquatic environments, is still in its infancy. This review includes the most recent literature about the methods applied to the measurement of NPs and ENPs in the environment. The review covers methods to determine size distribution, shape, structure, surface charge, chemical composition, surface area, agglomeration, surface chemistry, porosity, and solubility.     

Impact of ultrasonic treatment on rice starch and grain functional properties: A review

As a green, nonthermal, and innovative technology, ultrasonication generates acoustic cavitation in an aqueous medium, developing physical forces that affect the starch chemistry and rice grain characteristics. This review describes the current information on the effect of ultrasonication on the morphological, textural, and physicochemical properties of rice starch and grain. In a biphasic system, ultrasonication introduced fissures and cracks, which facilitated higher uptake of water and altered the rice starch characteristics impacting textural properties. In wholegrain rice, ultrasonic treatment stimulated the production of health-related metabolites, facilitated the higher uptake of micronutrient fortificants, and enhanced the palatability by softening the rice texture. This review provides insights into the future direction on the utilization of ultrasonication for the applications towards the improvement of rice functional properties.