BN管状团簇到单壁纳米管的几何结构和电子性质

利用密度泛函理论(DFT),对氮化硼(BN)管状团簇的几何结构、稳定性和电子性质进行了研究.选取合适的BN结构单元作为结构生长基元,采用逐层生长的方式计算得到有限长度、不同截面尺寸的稳定管状团簇.结构中B-N交替排列,结构组成中的四元环和六元环数目均符合一般表达式.计算结果表明,通过适当组装管状团簇以及碳原子掺杂,可以制备出带隙可调的单壁氮化硼纳米管.     

C在不同位置掺杂(n,n)型BN纳米管的密度泛函研究

用密度泛函B3LYP/3-21G(d)方法,并利用周期边界条件,研究了C原子在不同位置掺杂的(n,n)型BN纳米管的结构与性质.揭示了几何结构特征、能量、稳定性和能带结构的变化规律.研究了C原子在B位或N位置分别掺杂的BN纳米管的模型(掺杂浓度x=1/(4n),n=3—9),部分B位掺杂管发生了变形,而所有N位掺杂管则几乎不变形,而且N位比B位的掺杂能更低(管更稳定),B位掺杂管的能隙为1.054—2.411 eV,N掺杂管的能隙为0.252—1.207 eV,所有掺杂管都是半导体,所有掺杂管都具有直接带隙.     

N-F共掺杂锐钛矿二氧化钛(101)面纳米管的第一性原理研究

共掺杂是提高二氧化钛纳米管可见光催化性能的一种有效方式. 采用基于密度泛函理论的第一性原理方法, 研究了N单掺杂、F单掺杂及N-F共掺杂二氧化钛纳米管的原子结构、电子性质和光学性质. 计算结果表明, 相比N单掺杂和F单掺杂, N-F共掺杂二氧化钛纳米管的形成能更低, 掺杂后的体系热力学稳定性更好. 此外, 相比未掺杂时的带隙, N-F共掺杂后体系的带隙变化最多, 减少了0.557 eV, 而这主要源于价带顶附近的杂质能级的贡献. 此外, 通过分析掺杂后的光催化活性发现, N-F共掺杂时纳米管的还原性和氧化性都有所降低, 但并没有丧失活性, 并且光吸收谱表明, 共掺杂体系的红移现象最为明显. 因此, N-F共掺杂可有效提高二氧化钛纳米管可见光的光催化性能.     

Mn/C共掺杂ZnS纳米管磁性质研究

采用第一性原理密度泛函理论系统地研究Mn原子单掺杂和双掺杂ZnS纳米管的结构、电子性质和磁性质.掺杂纳米管的形成能比纯纳米管形成能更低,表明掺杂是个放热过程.掺杂纳米管的能隙远小于纯纳米管能隙.计算结果表明Mn掺杂纳米管趋于反铁磁态.为了获得室温铁磁性,用一个C原子替代一个S原子.发现铁磁态能量比反铁磁态能量低0.454 eV.如此大的能量差表明这类材料中有可能获得室温铁磁性.     

Mn/C共掺杂ZnS纳米管磁性质研究（英文）

采用第一性原理密度泛函理论系统地研究Mn原子单掺杂和双掺杂ZnS纳米管的结构、电子性质和磁性质.掺杂纳米管的形成能比纯纳米管形成能更低,表明掺杂是个放热过程.掺杂纳米管的能隙远小于纯纳米管能隙.计算结果表明Mn掺杂纳米管趋于反铁磁态.为了获得室温铁磁性,用一个C原子替代一个S原子.发现铁磁态能量比反铁磁态能量低0.454 e V.如此大的能量差表明这类材料中有可能获得室温铁磁性.     

硫化锌纳米管稳定性、电子性质和磁性质的比较研究

用第一性原理方法系统地研究硫化锌纳米管的稳定性、电子性质和掺杂磁性质.比较三种纳米管的稳定性.研究表明,六边形截面的双壁管的稳定性最高,相同截面的单壁管稳定性次之,而圆截面的之字形和扶手椅纳米管稳定性最低.电子能带结构计算表明它们都是直接带隙半导体.纳米管表面氢吸附后,六边形截面的单壁管转变为间接带隙半导体.研究了磁性原子掺杂六边形截面管的磁性质.发现掺杂纳米管的形成能比纯纳米管的形成能低,说明掺杂过程是一个放热反应.纳米管的总磁矩等于掺杂的磁性原子的磁矩.这些单掺杂纳米管在可调磁的新材料方面有潜在的应用价值.     

Fe掺杂单壁ZnS纳米管磁性质

采用第一性原理密度泛函理论系统研究Fe原子掺杂单壁ZnS纳米管的结构和磁性质.首先比较掺杂纳米管的稳定性.结果表明,掺杂纳米管的形成能比纯纳米管的形成能低,说明掺杂过程是一个放热反应.单掺杂纳米管的总磁矩等于掺杂的磁性原子的磁矩,主要来自Fe原子3d态的贡献.Fe原子掺杂单壁ZnS纳米管趋向于反铁磁态.为了得到稳定的铁磁态,用一个C原子替代掺杂体系中的一个S原子.计算发现铁磁态的能量比亚铁磁态低0.164 eV的.在铁磁态和反铁磁态之间存在的巨大的能量差,表明此掺杂体系可能获得室温铁磁性.     

“锥形嵌套"结构CNx纳米管的生长机理及拉曼光谱研究

在氮气、氢气以及氯化铵热解产生的氨气环境下,以钴作为催化剂,在780℃—940℃温度范围内使二甲苯与二茂铁受热分解,合成了CNx纳米管.在高分辨率透射电子显微镜下观察,合成的纳米管呈现“锥形嵌套”的形貌特征.从不同结构的分子面形成能的角度探讨了CNx纳米管的催化生长机理.不同温度下所制备样品的拉曼光谱研究表明,ID/IG值可以反映氮的掺杂所带来的纳米管结晶有序程度的降低,并通过G带向高波数移动证实了氮的掺杂.     

Cr掺杂ZnS纳米管结构和磁性质

采用第一性原理密度泛函理论系统研究Cr原子单掺杂和双掺杂单壁ZnS纳米管的结构和磁性质.研究发现掺杂纳米管的形成能比纯纳米管的形成能低,说明掺杂过程是放热的.单掺杂纳米管的总磁矩主要来自Cr原子3d态的贡献.结果表明Cr原子掺杂单壁ZnS纳米管趋向于铁磁态.但铁磁态和反铁磁态的能量差仅为0.036 eV.为获得室温铁磁性,我们用一个C原子替代掺杂体系中的一个S原子.计算发现铁磁态的能量比反铁磁态低0.497eV.表明此掺杂体系可能获得室温铁磁性.     

Cr掺杂ZnS纳米管结构和磁性质（英文）

采用第一性原理密度泛函理论系统研究Cr原子单掺杂和双掺杂单壁Zn S纳米管的结构和磁性质.研究发现掺杂纳米管的形成能比纯纳米管的形成能低,说明掺杂过程是放热的.单掺杂纳米管的总磁矩主要来自Cr原子3d态的贡献.结果表明Cr原子掺杂单壁Zn S纳米管趋向于铁磁态.但铁磁态和反铁磁态的能量差仅为0.036 e V.为获得室温铁磁性,我们用一个C原子替代掺杂体系中的一个S原子.计算发现铁磁态的能量比反铁磁态低0.497e V.表明此掺杂体系可能获得室温铁磁性.     

Optical excitations in hexagonal nanonetwork materials

Optical excitations in hexagonal nanonetwork materials, for example, Boron-Nitride (BN) sheets and nanotubes, are investigated theoretically. Exciton dipoles directed from the B site to the N site are considered along the BN bond. When the exciton hopping integral is restricted to the nearest neighbors, two flat bands of excitons appear. The symmetry of these exciton bands is optically forbidden. Possible relations to experiment are discussed.     

Formation and structure of boron nitride conical nanotubes

Nanotubes exhibiting a novel structure - boron nitride (BN) conical nanotubes whose walls consist of conical layers with their cone axis parallel to the tube axis, as opposed to ordinary nanotubes, composed of concentric cylindrical layers with their normal perpendicular to the tube axis - were synthesized simultaneously with BN nanotubes by using carbon nanotubes (CNTs) as templates. The diameters of the BN conical nanotubes are typically about 15 nm, which is similar to those of the starting CNTs. Apex angles and inner diameters of most BN conical nanotubes are about 40° and 1 nm, respectively. The lengths of the BN conical nanotubes range from 50 nm to up to several micrometers.     

铬银氧共掺n型，p型特性氮化硼纳米管第一性原理研究

基于第一性原理的平面波超软赝势法对(6, 0)单壁氮化硼纳米管、Cr掺杂、Ag掺杂、以及Cr-O共掺纳米管进行电子结构和光学性质的计算。结果表明：Cr掺杂和Cr-O共掺体系相比于本征体系的带隙值均减小,掺杂体系的导带底穿过费米能级从而实现了氮化硼纳米管的n型掺杂。Ag掺杂实现了纳米管的p型掺杂。本征氮化硼纳米管、Ag掺杂、Cr掺杂、以及Cr-O共掺纳米管的静态介电常数分别为1.17、1.61、1.32和1.48,相对于本征体系静介电性能有所提高。     

Single-walled BN nanostructures

We describe in situ synthesis and characterization of single-walled BN nanotubes terminated by fullerenelike structures using electron-cyclotron resonance nitrogen and electron beam boron sources onto polycrystalline tungsten substrates. Detailed comparisons of experimental high-resolution electron microscopy images and simulations based upon molecular models show a dominance of kinks and bends involving fourfold and eightfold ring structures as against fivefold or sevenfold which have been found with carbon. Analysis of the structures as a function of film thickness indicates that they are growing by addition of atoms to the exposed ends of single sheets, not at the substrate-nanostructure interface.     

氮化硼、碳化硅、锗纳米管的熔化与拉伸力学特性

该论文采用Tersoff势的分子动力学方法分析了单壁(5,5)氮化硼、碳化硅、锗纳米管的熔化与轴向拉伸力学特性,讨论了三种纳米管熔化与轴向拉伸力学性能的差异.研究表明:氮化硼管熔化后呈现为网状,碳化硅管为疏松的不规则的团状,锗管呈现为紧密排布的近似球状;相同温度下,碳化硅及氮化硼纳米管的熔点、比热容以及熔化热却均远高于锗管,但系统能量却远低于锗管;三种纳米管中,氮化硼管的抗变形抗能力最大,锗管的抗变形与抗载荷能力最小,而氮化硼、碳化硅管的抗载荷能力相当.     

First-principles studies of BN sheets with absorbed transition metal single atoms or dimers: stabilities, electronic structures, and magnetic properties

BN sheets with absorbed transition metal (TM) single atoms, including Fe, Co, and Ni, and their dimers have been investigated by using a first-principles method within the generalized gradient approximation. All of the TM atoms studied are found to be chemically adsorbed on BN sheets. Upon adsorption, the binding energies of the Fe and Co single atoms are modest and almost independent of the adsorption sites, indicating the high mobility of the adatoms and isolated particles to be easily formed on the surface. However, Ni atoms are found to bind tightly to BN sheets and may adopt a layer-by-layer growth mode. The Fe, Co, and Ni dimers tend to lie (nearly) perpendicular to the BN plane. Due to the wide band gap of the pure BN sheet, the electronic structures of the BN sheets with TM adatoms are determined primarily by the distribution of TM electronic states around the Fermi level. Very interesting spin gapless semiconductors or half-metals can be obtained in the studied systems. The magnetism of the TM atoms is preserved well on the BN sheet, very close to that of the corresponding free atoms and often weakly dependent on the adsorption sites. The present results indicate that BN sheets with adsorbed TM atoms have potential applications in fields such as spintronics and magnetic data storage due to the special spin-polarized electronic structures and magnetic properties they possess.     

毛刺状竹节结构氮化硼纳米管的合成与生长机理

以非晶硼和氧化镍纳米颗粒为原料,在氨气中1100 oC下合成了毛刺状竹节结构的氮化硼纳米管. 利用X射线衍射和透射电镜研究了氮化硼纳米管的结构和形貌. 竹节结构纳米管表面的毛刺是六方氮化硼的纳米薄片. 提出了一种基于固态硼和气态二氧化硼扩散的毛刺形貌生长机理.     

Synthesis and morphology of boron nitride nanotubes and nanohorns

Boron nitride (BN) nanotubes have been synthesized by evaporating a mixture of boron and gallium oxide in the presence of ammonia gas. The synthesized BN nanotubes exhibit a well-crystallized concentric structure with diameters less than 30 nm, and no carbon contamination or defects could be observed, while the BN nanotubes with large diameters usually show a number of defects. Some BN nanohorn structures could also be observed in the product. The carbon-free growth of BN nanotubes was explained based on the vapor–liquid–solid growth mechanism, and the catalytic activity of liquid gallium for BN one-dimensional growth was also demonstrated. Received: 16 April 2002 / Accepted: 25 May 2002 / Published online: 19 July 2002     

First-principles study of single-walled armchair Cx(BN)y nanotubes

The structural and electronic properties of the armchair C_x(BN)_y nanotubes are studied using the density functional theory with a generalized gradient approximation. The results show that the properties of the C_x(BN)_y nanotubes are intermediate between those of carbon nanotubes and BN nanotubes, and also adjustable by their radius, ratio of carbon component, and configurations.     

Phonon structure and dynamics of boron nitride single wall nanotube

We report a detailed study of the phonon properties of hexagonal boron nitride (BN) monolayers as well as nanotubes by using De Launay type of angular force model. The force constants used for calculation of phonon dispersion relations of the nanotube are derived from those for the monolayers of hexagonal by employing force constant method. These force constants have been modified to include the effect of curvature of the tubule. The results are then used to derive the phonon dispersion relations for (10,10) BN nanotubes using ‘zone-folding’ method. Calculated phonon modes are in good agreement with the experimental values obtained so far, for (10,10) armchair BN nanotubes.