钴掺杂二氧化锡纳米粉的光致发光和磁学性质

研究了钴掺杂对二氧化锡纳米粉的光致发光性质和磁学性质的影响,发现钴掺杂对发光带的位置影响很小,但紫外发光带与蓝色发光带的强度之比随掺杂含量的增加而下降.当钴掺杂含量达到0.02时,样品中的铁磁性被完全破坏.讨论了样品中的磁相互作用的机理,认为掺杂离子的不均匀分布、自旋极化子与掺杂离子之间的耦合都可能导致反铁磁性的相互作用,这种反铁磁性的作用破坏了铁磁性. 关键词： 钴掺杂二氧化锡 光致发光 磁学性质     

二维Ti_2CO_2单层吸附H_2S分子的第一性原理研究

采用第一性原理计算方法研究了H_2S分子在二维单层Ti_2CO_2表面上的吸附以及外加应变和电场对其性质的调制,发现该吸附为物理吸附,其吸附强度几乎不受外加拉伸应变的影响,而外加电场使H_2S分子的吸附增强.同时,通过单层Ti_2CO_2表面不同结构(如水分子修饰、官能团掺杂、氧官能团空位)对H_2S分子吸附性质影响的研究表明:(1)表面吸附的水分子促进H_2S分子的吸附,其吸附强度随H_2O分子数增多而增强;(2)官能团OH掺杂浓度低于0.22 ML时,促进H_2S分子的吸附,而较高浓度OH掺杂使H_2S分子吸附减弱;官能团F掺杂对H_2S分子吸附强度几乎没有影响;(3)含氧空位的Ti_2CO_2表面与H_2S分子相互作用较强,吸附能高达-1.06 eV,且电子结构改变明显.     

抛物量子点中弱耦合束缚极化子的相互作用能

研究了抛物量子点中弱耦合束缚极化子的性质,采用改进的线性组合算符和幺正变换方法导出了束缚极化子的振动频率、有效质量和相互作用能。讨论了量子点的有效受限长度、电子LO声子耦合强度和库仑场对抛物量子点中弱耦合极化子的振动频率、有效质量和相互作用能的影响。数值计算结果表明:弱耦合束缚极化子的振动频率和相互作用能随有效受限长度的减少而急剧增大,振动频率随库仑势以及电子LO声子耦合强度的增加而增加,而相互作用能随库仑势以及电子LO声子耦合强度的增加而减小。有效质量仅与电子LO声子耦合强度有关。     

磁场对非对称量子点中弱耦合极化子的相互作用能的影响

采用改进的线性组合算符和幺正变换相结合的方法,研究磁场、量子点的横向和纵向有效受限长度和电子-声子耦合强度对非对称量子点中弱耦合磁极化子的振动频率和相互作用能的影响.导出了振动频率和相互作用能随量子点的横向和纵向有效受限长度、电子-声子耦合强度和磁场的回旋共振频率的变化关系.数值计算结果表明:振动频率和相互作用能随量子点的横向和纵向有效受限长度的减小而迅速增大,随磁场的回旋共振频率的增加而增大,相互作用能随电子-声子耦合强度的减小而呈线性的增大.     

表面非金属掺杂对锐钛矿相TiO2(101) 面吸附NH3特性的影响

采用基于密度泛函理论(DFT-D)体系下的第一性原理平面波超软赝势方法,研究了被不同非金属（B、C、N、F）掺杂的TiO2(101)表面吸附NH3的特性与作用机理。研究发现：被非金属掺杂后的表面对NH3的吸附效果要优于未掺杂表面。不同元素掺杂对比发现：C掺杂后的表面吸附能最大,稳定后吸附距离最小,为最稳定吸附结构。通过Mulliken电荷分布和分态密度的分析,得到了不同吸附条件下NH3在TiO2掺杂表面的催化氧化还原作用机理,并发现各模型吸附能的不同是由于掺杂（X）位原子与NH3分子的相互作用强弱不同所造成。掺杂原子在费米面附近的电子态密度贡献越强,掺杂原子与NH3分子电荷转移的净值越小,吸附距离越小,吸附能越大,吸附更稳定。     

表面非金属掺杂对锐钛矿相TiO2(101) 面吸附NH3特性的影响

采用基于密度泛函理论(DFT-D)体系下的第一性原理平面波超软赝势方法,研究了被不同非金属（B、C、N、F）掺杂的TiO2(101)表面吸附NH3的特性与作用机理。研究发现：被非金属掺杂后的表面对NH3的吸附效果要优于未掺杂表面。不同元素掺杂对比发现：C掺杂后的表面吸附能最大,稳定后吸附距离最小,为最稳定吸附结构。通过Mulliken电荷分布和分态密度的分析,得到了不同吸附条件下NH3在TiO2掺杂表面的催化氧化还原作用机理,并发现各模型吸附能的不同是由于掺杂（X）位原子与NH3分子的相互作用强弱不同所造成。掺杂原子在费米面附近的电子态密度贡献越强,掺杂原子与NH3分子电荷转移的净值越小,吸附距离越小,吸附能越大,吸附更稳定。     

表面非金属掺杂对锐钛矿相TiO_2(101)面吸附NH_3特性的影响

采用基于密度泛函理论(DFT-D)体系下的第一性原理平面波超软赝势方法,研究了被不同非金属(B、C、N、F)掺杂的TiO_2(101)表面吸附NH_3的特性与作用机理.研究发现:被非金属掺杂后的表面对NH_3的吸附效果要优于未掺杂表面.不同元素掺杂对比发现:C掺杂后的表面吸附能最大,稳定后吸附距离最小,为最稳定吸附结构.通过Mulliken电荷分布和分态密度的分析,得到了不同吸附条件下NH_3在TiO_2掺杂表面的催化氧化还原作用机理,并发现各模型吸附能的不同是由于掺杂(X)位原子与NH_3分子的相互作用强弱不同所造成.掺杂原子在费米面附近的电子态密度贡献越强,掺杂原子与NH_3分子电荷转移的净值越小,吸附距离越小,吸附能越大,吸附更稳定.     

Gd掺杂ZnO纳米线磁耦合性质的第一性原理研究

本文利用基于密度泛函理论的第一性原理方法计算了钆(Gd)掺杂氧化锌(ZnO)纳米线的磁耦合特性. 讨论了两个Gd原子替换ZnO纳米线中不同位置Zn原子的各种可能情况. 计算发现, ZnO中掺杂的Gd原子处于相邻的位置时它们之间的相互作用是铁磁性的, 并且体系的铁磁性可以通过注入合适数目的电子来得到加强. 同时发现Gd掺杂ZnO纳米线后s-f耦合作用变得显著, 使得体系的铁磁性变得更加稳定, 这也是Gd掺杂ZnO纳米线呈现铁磁性的原因. 这些结果为实验上发现的Gd掺杂ZnO纳米线呈铁磁性提供了理论依据.     

密度泛函理论研究多巴胺在纯的,Fe和Ca掺杂的石墨烯材料表面的吸附机理

本论文用密度泛函理论方法研究了多巴胺在纯的,Fe和Ca掺杂的石墨烯上的吸附机理.通过它们之间的相互作用能,态密度,布局电荷,差分电荷密度分析发现多巴胺平行躺在纯的石墨烯表面主要是π…π,-CH…π相互作用,而垂直放在纯的石墨烯表面主要是-OH…π相互作用,这些都表现为典型的物理吸附.而Fe和Ca掺杂的石墨烯大大增强了多巴胺的吸附,主要体现为典型的化学吸附,因为掺杂金属原子与多巴胺的邻苯二酚羟基主要形成"bridge bidenate"or"monodenate"共价相互作用.而且我们发现"monodenate"共价作用不一定小于"bridge bidenate"共价作用,主要取决于相互作用原子之间最短距离的大小.研究结果有望为多巴胺-石墨烯基体系在生物组织工程,传感器方面的应用上提供有价值的理论指导.     

N2在页岩干酪根上的吸附特征

采用密度泛函理论的wB97XD方法、RDG函数方法和counterpoise correction理论,研究氮气在干酪根C₂₈H₁₄O和氮掺杂干酪根C₂₇H₁₄ON上的吸附特征。结果表明：N₂在干酪根上的活性吸附位点为苯环上方中心位置,吸附能在8~10 kJ·mol^-1之间,N₂和干酪根之间的相互作用主要是范德华相互作用和空间排斥作用。氮掺杂改变了干酪根的构型和电子云分布,导致含氮杂环不再是稳定的活性吸附位点,增强了排斥作用,使吸附能略有减小。研究结果对理解干酪根吸附小分子的特征有重要意义,能够为页岩气的开采提供理论支持。     

Impurity Effects on Overlayer Structures

The Green function method and the tight-binding approximation are employed to study the indirect interaction between two adatoms. Overlayer structures of hydrogen, oxygen and haloid adsorbed on contaminated nickel substrates are explained. The impurity effects are described by the Koster-Slater model. It is found that the introduction of impurity atoms can even change the overlayer structures.     

Elastic interactions between surface adatoms and between surface clusters

One major term is omitted in most conventional treatments of interactions between surface adatoms or groups of adatoms. This is the elastic interaction, in which adatoms interact through mutual distortion of the substrate. The indirect elastic interaction explains a range of observed surface phenomena in a consistent quantitative way. These phenomena include static and dynamic effects ranging from ordered structures to correlated motions of adatom clusters. It is likely also that substrate distortion is important in clean surface reconstruction. The elastic interaction is typically comparable with or larger than the indirect electronic interactions usually presumed. It follows that detailed calculations which ignore the substrate distortions produced will be of limited value only.     

Surface atom displacement processes

Progress in field ion microscope studies of adatom displacements on metal surfaces is reviewed. It is concluded that of the displacement processes that contribute to surface diffusion only displacements between low-coordination (terrace) sites are well characterised. Procedures and preliminary results of FIM studies of adatom displacement over steps are described. Activation energies measured for passage of Ta, W, Re, Ir and Pt adatoms across (110) W steps are found to equal activation energies for diffusion over (110) W, despite the highly reflecting character of the step for all the adsorbates except Pt. Displacements of adatoms interacting with other adatoms are discussed. Results presented show that interaction of transition metal adatoms forming close-packed dimers on (110) W is rather weak, with a minimum interaction energy [?U(r) < 4kJ/mol] for Re₂ corresponding to a very weak attraction for Re adatoms 0.27 nm apart.     

Composite Anderson-Newns model and density of states due to chemisorption: Quasi-chemical approximation

In this paper a variation in density of states (DOS) of the substrate due to chemisorption of hydrogen on transition metals using composite Anderson-Newns model has been investigated for different coverages in quasi-chemical approximation of Fowler and Guggenhiem, which in the limitz→∞ gives the Bragg-Williams approximation as a special case. Variation in density of states has been studied for one-dimensional periodic substrate with change in adatom interaction energy and coverage. With increase in coverage, the bonding and antibonding (B-AB) peaks are found to shift towards higher energies and at the same time relative height of the peaks also increases. The interesting feature to observe is that both approximations for a particular coverage, give split-off states with different height for both (B-AB) peaks. It particularly indicates change in B-AB states, representing amount of chemisorption, with the change in interaction energy between adatoms. At the same time bond strength is also found to decrease with interaction between adatoms.     

Ab initio investigation of the clustering of carbon adatoms on Fe(001) and Fe(111) surfaces

A theoretical investigation of the interaction between carbon adatoms on the Fe(001) and Fe( 111 ) surfaces is performed using ab initio calculations in terms of density functional theory. Calc ulations of the adsorption energy demonstrate the existence of a strong bonding between single carbon adatoms and the iron surface. An analysis of the calculated energies of the interaction between carbon adatoms reveals for the first time that the repulsion between the carbon adatoms located at the nearest neighbor sites on the Fe(001) surface occurs and that clusters with a looser packing are formed on the surface.     

The effect of Ti on the wetting of CaF<Subscript>2</Subscript> substrate by In–Ti and Ga–Ti alloys. Ab-initio consideration

CaF₂ is a thermodynamically stable, non-reactive compound, displaying a relatively high contact angle with pure liquid metal melts. A remarkable decrease of this contact angle takes place when small amounts of Ti are added to liquid In (a decrease from 125 to 20°) or to liquid Ga (from 118 to 60°). Thermodynamic analysis indicates that this feature cannot be attributed to chemical reactions between the substrate and the melt. It was suggested that the reason for this behavior may be a preferential titanium adsorption from the liquid In–Ti or Ga–Ti solution at the substrate surface. In order to understand the nature of the In–Ti or Ga–Ti bonding in the vicinity of the CaF₂ surface, the adsorption energy of 0.5 monolayer of In and Ga was computed for three different surface conditions: (i) clean CaF₂(111), (ii) CaF₂(111) with In or Ga adatoms, and (iii) CaF₂(111) with Ti adatoms. The differences in adsorption energies for these configurations are related to the electron charge redistribution in the vicinity of the interface, and to the density of states of the electronic subsystems. It was found that the adsorption energy of In or Ga increases due to the lateral interactions with the adatoms. According to the analysis, a strong lateral interaction exists between Ti adatoms and Me, while relatively weak interaction exists between Me and Me adatoms. The difference of the lateral interactions was considered in order to explain the improvement of the wetting of CaF₂ substrate by Ti alloying of In and Ga.     

Surface diffusion of Si,Ge and C adatoms on Si （001） substrate studied the molecular dynamics simulation

Depositions of Si, Ge and C atoms onto a preliminary Si (001) substrate at different temperatures are investigated by using the molecular dynamics method. The mechanism of atomic self-assembling occurring locally on the flat terraces between steps is suggested. Diffusion and arrangement patterns of adatoms at different temperatures are observed. At 900 K, the deposited atoms are more likely to form dimers in the perpendicular [110] direction due to the more favourable movement along the perpendicular [110] direction. C adatoms are more likely to break or reconstruct the dimers on the substrate surface and have larger diffusion distances than Ge and Si adatoms. Exchange between C adatoms and substrate atoms are obvious and the epitaxial thickness is small. Total potential energies of adatoms and substrate atoms involved in the simulation cell are computed. When a newly arrived adatom reaches the stable position, the potential energy of the system will decrease and the curves turns into a ladder-like shape. It is found that C adatoms can lead to more reduction of the system energy and the potential energy of the system will increase as temperature increases.     

小分子在Pd(100)面上的共吸附

本文应用紧束缚模型和单电子理论研究了几种小分子在Pd(100)面上的共吸附特性,结果表明:在Pd(100)面上两个吸附分子(或吸附原子)间的间接相互作用随吸附质与衬底之间的耦合强度的减小呈现振荡性衰减的趋势,并且,当O₂或H₂存在时,NO在Pd(100)面上的解离将受到影响,此外,根据两吸附质之间的间接相互作用,推断出一些吸附层结构,这些结果与实验结果作了比较。 关键词：     

Comparisons between adsorption and diffusion of alkali,alkaline earth metal atoms on silicene and those on silicane:Insight from first-principles calculations

The adsorption and diffusion behaviors of alkali and alkaline-earth metal atoms on silicane and silicene are both investigated by using a first-principles method within the frame of density functional theory.Silicane is staler against the metal adatoms than silicene.Hydrogenation makes the adsorption energies of various metal atoms considered in our calculations on silicane significantly lower than those on silicene.Similar diffusion energy barriers of alkali metal atoms on silicane and silicene could be observed.However,the diffusion energy barriers of alkali-earth metal atoms on silicane are essentially lower than those on silicene due to the small structural distortion and weak interaction between metal atoms and silicane substrate.Combining the adsorption energy with the diffusion energy barriers,it is found that the clustering would occur when depositing metal atoms on perfect hydrogenated silicene with relative high coverage.In order to avoid forming a metal cluster,we need to remove the hydrogen atoms from the silicane substrate to achieve the defective silicane.Our results are helpful for understanding the interaction between metal atoms and silicene-based two-dimensional materials.     

Adsorptions of metal adatoms on graphene-like BC_3 and their rich electronic properties: A first-principles study

Density functional calculations have been performed to investigate the adsorption of twenty two different kinds of metal adatoms on graphene-like BC_3. In contrast to the graphene adsorbed with adatoms, the BC_3 with adatoms shows many interesting properties.(1) The interaction between the metal adatoms and the BC_3 sheet is remarkably strong. The Li, Na, K, and Ca possess the binding energies larger than the cohesive energies of their corresponding bulk metals.(2)The Li, Na, and K adatoms form approximately ideal ionic bonds with BC_3, while the Be, Mg, and Ca adatoms form ionic bonds with BC_3 with slight hybridization of covalent bonds. The Al, Ga, In, Sn, and all transition metal adatoms form covalent bonds with BC_3.(3) For all the structures studied, there exhibit metal, half-metal, semiconducting, and spin-semiconducting behaviors. Especially, the BC_3 with Co adatom shows a quantum anomalous Hall(QAH) phase with a Chern number of -1 based on local density approximation calculations.(4) For Li, Na, K, Ca, Ga, In, Sn, Ti, V, Cr,Ni, Pd, and Pt, there exists a trend that the adatom species with lower ionization potential have lower work function. Our results indicate the potential applications of functionalization of BC_3 with metal adatoms.