钯金属吸附对半导体性碳纳米管电输运的影响

利用物理蒸发技术,在半导体性的碳纳米管上沉积钯金属,利用导电原子力显微镜检测钯吸附对碳纳米管电输运的影响.结果表明:沉积的钯在碳纳米管上形成纳米颗粒,随着钯颗粒密度的增加,半导体性碳纳米管逐渐向金属性转变.利用第一性原理计算了吸附有钯原子的半导体性单壁碳纳米管的能带结构.研究发现,钯的覆盖率越高,其禁带宽度越窄,直至为零,定性说明了实验结果的合理性. 关键词： 单壁碳纳米管 钯纳米颗粒 导电原子力显微镜 第一性原理计算     

单壁碳纳米管吸附氧分子的电子输运性质理论研究

用基于第一性原理的密度泛函理论和非平衡态格林函数方法对(4,4)单壁碳纳米管及其吸附氧气分子情况下的平衡态和非平衡态电导性质进行了研究. 发现在小于2 V的偏压下,系统对电压的增加呈现两种不同增长速率的电流响应,其中电压小于1.1 V时电流增加速率较大;而当电压大于该值后,电流对电压增加速率变缓. 吸附的氧分子提供双重的作用,一方面氧分子提供的能级有利于电子隧穿中心散射区;另一方面氧分子的电子态会破坏碳管的平移对称性,从而降低电子对系统的透射能力. 关键词： 单壁碳纳米管 氧分子吸附 电子输运 非平衡态格林函数     

超小碳纳米管的高效率光致可见发光

镶嵌在分子筛骨架中的4A直径的单壁碳纳米管可发出高效的、位于可见光区的光致发光．发光谱呈较宽的线形，其效率约为1％—5％．无论是对激发光的响应，还是发光强度都有很强的偏振依赖特性．结合其吸收光谱、拉曼光谱以及电子能带结构的理论计算，作者讨论了4A碳纳米管的发光机制，并给出了合理的解释．     

硼原子掺杂对碳纳米管吸附Ne原子影响的第一性原理计算

采用基于第一性原理的密度泛函理论(DFT)和局域密度近似(LDA)方法,优化计算得到碳纳米管(CNT),硼原子取代碳原子及其吸附氖原子前后系统的几何结构,能量,电子能带和态密度.结果显示,碳纳米管的能带结构与石墨的层状几何结构相似,能量的变化只在kz=0和kz=0.5平面之间沿着c轴方向出现.B原子取代C原子使价带和导带分别分裂为两个和三个能带.对Ne原子的吸附使价带能量沿着c轴方向升高并导致Fermi面附近的态密度下降.Ne原子的吸附在谷位H最稳定,顶位A其次.C-C间σ键的弯曲使Ne原子吸附在桥位b1比桥位b2处更为稳定.Ne原子在管外的吸附均为放热过程,而管内则为吸热过程.结构分析表明Ne原子对C原子有排斥作用,对B原子却具有吸引作用.B原子取代C原子的位置略凸出于CNT的管壁之外,使Ne原子的吸附能增加.     

硼磷掺杂小直径单壁碳纳米管的第一性原理研究

利用基于密度泛函理论的第一性原理计算方法,研究了小直径锯齿形单壁碳纳米管（3,0）的硼（B）、磷（P）单个原子掺杂和B/P共掺杂效应. 计算了B、P单原子掺杂的形成能、能带结构和电子态密度,分析得出B、P掺杂（3,0）单壁碳纳米管是可行的,并且碳纳米管的导电性没有发生明显改变. 本文还计算了在不同掺杂位点,（3,0）金属性碳纳米管的形成能和能带结构,发现B/P共掺杂也是可行的,B和P趋于形成B/P对,并且B/P的掺入使（3,0）金属性碳纳米管的能带打开,由金属性变成半导体性.     

硼磷掺杂小直径单壁碳纳米管的第一性原理研究简

利用基于密度泛函理论的第一性原理计算方法,研究了小直径锯齿形单壁碳纳米管(3,0)的硼(B)、磷(P)单个原子掺杂和B/P共掺杂效应.计算了B、P单原子掺杂的形成能、能带结构和电子态密度,分析得出B、P掺杂(3,0)单壁碳纳米管是可行的,并且碳纳米管的导电性没有发生明显改变.本文还计算了在不同掺杂位点,(3,0)金属性碳纳米管的形成能和能带结构,发现B/P共掺杂也是可行的,B和P趋于形成B/P对,并且B/P的掺入使(3,0)金属性碳纳米管的能带打开,由金属性变成半导体性.     

硼原子掺杂对碳纳米管吸附Ne原子影响的第一性原理计算

采用基于第一性原理的密度泛函理论（DFT）和局域密度近似（LDA）方法，优化计算得到碳纳米管（CNT），硼原子取代碳原子及其吸附氖原子前后系统的几何结构，能量，电子能带和态密度。结果显示，碳纳米管的能带结构与石墨的层状几何结构相似，能量的变化只在kz=0和kz=0.5平面之间沿着c轴方向出现。B原子取代C原子使价带和导带分别分裂为两个和三个能带。对Ne原子的吸附使价带能量沿着c轴方向升高并导致Fermi面附近的态密度下降。Ne原子的吸附在谷位H最稳定，顶位A其次。C-C间σ键的弯曲使Ne原子吸附在桥位b1比桥位b2处更为稳定。Ne原子在管外的吸附均为放热过程，而管内则为吸热过程。结构分析表明Ne原子对C原子有排斥作用，对B原子却具有吸引作用。B原子取代C原子的位置略凸出于CNT的管壁之外，使Ne原子的吸附能增加。     

多壁碳纳米管储氢的物理吸附特性

采用巨正则蒙特卡罗方法 ,模拟常温、1 0MPa下氢在扶手椅型多壁壁碳纳米管中的物理吸附过程 .氢分子之间、氢分子与碳原子之间的相互作用采用Lennard Jones势能模型 .研究了双壁碳纳米管外 (内 )径固定而内 (外 )径改变时的物理吸附储氢情况 ,发现氢分子主要储存在双壁碳纳米管的管壁附近 ,当双壁碳纳米管的内外管壁间距由 0 .34nm增大到 0 .6 1或 0 .88nm时可有效增加物理吸附储氢量 ,并给出了相应的理论解释 .在此基础上 ,计算了管壁间距为 0 .34、0 .6 1和 0 .88nm时的三壁碳纳米管的物理吸附储氢量 ,并与相同条件下单壁和双壁碳纳米管的物理吸附储氢量作了比较 ,发现多壁碳纳米管的物理吸附储氢量随碳管层数的增加而减小 .     

基于第一性原理的二维材料黑磷砷气体传感器的机理研究

通过密度泛函理论计算,研究了气体小分子吸附在单层黑磷砷表面的电学和磁学特性.选择4个初始吸附点位来探索CO,CO_2,NH_3,SO_2,NO和NO_2气体分子最优的吸附位置,计算了吸附能、吸附距离和电荷转移等电子结构参数,确定了吸附类型和敏感气体.结果表明,单层黑磷砷以强的物理吸附对NO_2和SO_2气体敏感,而通过化学吸附对NO气体敏感并且N原子和P原子间还形成新的化学键.从能带结构角度,CO,CO_2和NH_3这三种气体吸附对黑磷砷的能带结构影响很小,SO_2气体吸附增大带隙宽度.磁性气体NO和NO_2的吸附则在费米能级附近引入杂质能带,这主要来源于N原子和O原子的p轨道,并且减小了带隙宽度.NO和NO_2气体还分别诱导了 0.83μ_B和0.78μ_B的磁矩,使得整个体系带有磁性.理论研究表明,单层黑磷砷是检测NO,NO_2和SO_2气体的良好气敏材料.     

氧在理想的和重构的Si（100）面吸附研究

本文分别用ＡＳＥＤ－ＭＯ和ＤＶ－Ｘａ方法对氧在理想的Ｓｉ（１００）面以及用ＤＶ－Ｘａ方法对氧在重构的Ｓｉ（１００）面吸附进行了研究，对不同吸附位的计算结果表明，当氧在硅表面暴露量较少时，其吸附为氧原子和氧分子共存。     

Adsorption on the graphene surface of carbon nanotubes and their energy spectrum

The conditions of formation of local states in the energy spectra of semi-infinite carbon nanotubes with regularly arranged atoms adsorbed on the outer surface are studied in the π-electron approximation. The influence of the adsorption type (physical and chemical), the donor-acceptor properties of adsorbed atoms, their concentration on the graphene surface, and the nanotube diameter on the characteristics of the local states that arise is considered. It is shown that both physical and chemical adsorptions cause a decrease in the band gap separating the upper filled energy band and the lower vacant band. This effect can significantly change the electrical and optical properties of the nanotubes under consideration in comparison with the initial “pure” tubulene.     

通过不同烷基链取代调控喹吖啶酮分子在Ag(110)表面上的自组织结构

采用低能电子衍射、扫描隧道显微镜、第一性原理密度泛函理论计算以及分子力学计算，分别对不同烷基链取代的喹吖啶酮（QA）分子在Ag（110）基底上的吸附和生长进行了研究．QA和Ag基底的相互作用主要来自分子中0原子和Ag基底的共价键，它决定了分子的取向和最优吸附位置；而烷基链决定了分子吸附层的取向，QA分子间的排列可以通过烷基链的长度来调节．由此借助调节烷基链的长度，能够可控地制备具有不同物理性质的单层分子薄膜．     

锐钛矿型氧化物XO2（X=Ti,Sn,Zr,Ir）表面氧化性对NH3气体光学气敏传感特性的影响

摘要 金属氧化物气敏传感材料一直是当今的热门研究课题,锐钛矿相金属氧化物XO2（X=Ti,Sn,Zr,Ir）是具有传感特性的常见材料。光学气敏效应是指气体分子吸附在气敏传感材料上,与表面氧空位发生氧化还原反应,由于光学性质发生改变而检测出气体的成分和浓度,因此,氧化还原反应的强弱是反应传感性能的核心原因。本文采用密度泛函理论(DFT)体系下广义梯度近似(GGA)第一性原理平面波超软赝势方法,分析和计算了含氧空位的锐钛矿相XO2（X=Ti,Sn,Zr,Ir）表面特性。通过以NH3为目标分子,研究分子表面吸附引起的氧化还原反应的机理,分析不相同的氧化物表面的几何结构、吸附能、态密度、差分电荷密度、电荷布居、电荷转移、光学性质等。研究发现：目标分子稳定吸附在氧化物表面后改变材料光学性质。SnO2表面对分子的吸附能最大,IrO2表面与分子的吸附距离最小。NH3分子与表面间存在电荷转移,其转移电子数目大小为:IrO2＞TiO2＞ZrO2＞SnO2,氧化物表面氧化性的大小为:IrO2氧空位＞TiO2氧空位＞ZrO2氧空位＞SnO2氧空位;比较吸收谱和反射谱发生变化最为明显的是TiO2表面。结论,在可见光范围内,波长在400~530nm时,SnO2表面光学气敏传感效应更好。而在530~760nm范围TiO2表面光学气敏传感效应更好。     

Effects of adsorbed carbon and oxygen on the chemisorption of H2 and Co on Mo(100)

The deposit of carbon and oxygen adatoms on Mo(100) was characterized by AES and LEED. Carbon was introduced by the thermal cracking of ethylene; several ordered structures were observed as a function of coverage with carbon atoms residing on four-fold sites. The Mo(100)—O system exhibited two different sequences of LEED patterns depending on the adsorption temperature of oxygen. The effects of adsorbed carbon and oxygen on the chemisorption properties of Mo(100) was investigated by FDS. The presence of either carbon or oxygen severely hindered the ability of Mo(100) to dissociatively adsorb hydrogen or carbon monoxide. The amount of CO dissociated was directly related to the available four-fold sites on the carbide surfaces. The molecular adsorption of CO was not significantly affected by the adlayers. It was found that one monolayer of adsorbed oxygen reduced the binding energy of molecular CO considerably more than the same amount of adsorbed carbon. A continuous shift in the binding energy of CO with the C/O ratio on the surface was observed.     

Role of lateral alkyl chains in modulation of molecular structures on metal surfaces

We use low energy electron diffraction, scanning tunneling microscopy, first-principles density-functional theory, and molecular mechanics calculations to analyze the adsorption and growth of quinacridone derivatives (QA) with alkyl chains of 4 and 16 carbon atoms on a Ag(110) substrate. Surprisingly, we find that the alkyl chains determine the orientation of the molecular overlayers. While the interaction of QA and the Ag substrate is primarily due to chemical bonding of oxygen to the silver substrate, determining the molecular orientation and preferred adsorption site, the intermolecular arrangement can be adjusted via the length of alkyl chains. We are thus able to fabricate uniform QA films with very well controlled physical properties.     

First principles study of oxygen adsorption on nickel-doped graphite

Density functional theory is used in a spin-polarized plane wave pseudopotential implementation to investigate molecular oxygen adsorption and dissociation on graphite and nickel-doped graphite surfaces. Molecular oxygen physisorbs on graphite surface retaining its magnetic property. The calculated adsorption energy is consistent with the experimental value of ?0.1?eV. It is found that substituting a carbon atom of the graphite surface by a single doping nickel atom (2.8% content) makes the surface active for oxygen chemisorption. It is found that the molecular oxygen never adsorbs on doping nickel atom while it adsorbs and dissociates spontaneously into atomic oxygens on the carbon atoms which are bound to the nickel. The adsorption energy of ?1.4?eV and zero activation energy barrier indicate that O₂ dissociative adsorption is both thermodynamically and kinetically favoured over the surface. The large electric field near the doping nickel atom along with the excess electrons on the neighbouring carbon atoms, which are bound to the nickel induce molecular oxygen to adsorb and dissociate favourably.     

The chiral effect of adsorption of univalent atoms and diatomic molecules on the surface of carbon nanotubes

Quantum-chemical semiempirical calculations were performed of the adsorption of fluorine and hydrogen atoms and molecules on the surface of single-layered carbon nanotubes with various diameters. Semiempirical quantum-chemical MNDO calculations were based on the model of a molecular cluster with boundary pseudoatoms. The energy characteristics of adsorption were determined. Changes in physical properties caused by the adsorption of atoms and diatomic molecules were analyzed.     

Electronic properties of oxidized carbon nanotubes

The effect of oxygenation on the electronic properties of semiconducting carbon nanotubes is studied from first principles. The O2 is found to bind to a single-walled nanotube with an adsorption energy of about 0.25 eV and to dope semiconducting nanotubes with hole carriers. Weak hybridization between carbon and oxygen is predicted for the valence-band edge states. The calculated density of states shows that weak coupling leads to conducting states near the band gap. The oxygen-induced gap closing for large-diameter semiconducting tubes is discussed as well. The influence of oxygen on the magnetic property is also addressed through a spin-polarized calculation and compared to experiment.     

Surface studies of novel hydrophobic active carbons

The efficient adsorption of toxic organic species from humid airstreams by active carbons is impeded by the competitive adsorption of water vapour which, at low values of p/p^s, occurs at specific (polar) adsorption sites located at the edges of the carbon layer-planes and at in-plane defects. At higher pressures, adsorption in micropores and mesopores also occurs. The concentration of polar adsorption sites therefore determines the hydrophilicity of the carbon structure and their accelerated formation, by exposure to air and water vapour, is also responsible for the ‘ageing’ of active carbons. Overall, the adsorption of water reduces the volume of porosity available for the adsorption of target species and the hydrophilic nature of active carbons is recognized as a major barrier to their effective use in many applications.We present here results for the adsorption of nitrogen, organic and water vapours by a hydrophobic respirator granular active carbon produced by the thermal treatment of a base carbon, to desorb polar oxygen groups, followed by use of a plasma enhanced chemical vapour deposition (PECVD) treatment to apply a hydrophobic, fluorine containing, surface nanolayer. We show that at equivalent %RH values the treated carbon adsorbs significantly less water compared to an untreated (control) carbon and that the treatment does not reduce the levels of open porosity or impede the adsorption of a range of organic vapours at ambient temperatures. Preliminary evidence for the presence, after treatment, of constrictions at pore entrances which act as molecular gates is also presented. The treated carbon (after ageing for 6 weeks at 80%RH) is shown to have greater adsorptivity than an untreated base carbon toward hexane present in a humid (80%RH) airstream. This results in a 39% increase in break-through time. These hydrophobic properties persist one year after manufacture. The mechanism leading to the modified water adsorption properties is the partial desorption of polar oxygen sites followed by deposition at the external carbon surfaces of hydrophobic plasma polymer species. This reduces the polar surface free energy of the carbon and hence the amount of water adsorption occurring by the primary mechanism. This in turn retards the diffusion of water molecules into the micropores and leads to lower adsorption volumes at higher pressures.     

Crystal field surface orbital-bond energy bond order (CFSO-BEBO) calculations of adsorption: II. Carbon monoxide,oxygen and carbon dioxide on platinum (111) and oxygen on nickel (111)

The Crystal Field Surface Orbital-Bond Energy Bond Order (CFSO-BEBO) model of chemisorption is applied to the interaction of carbon monoxide, oxygen and carbon dioxide with a (111) platinum surface; and the interaction of oxygen with a (111) nickel surface. No activation energy for molecular adsorption of carbon monoxide on platinum is predicted; however a large activation energy for dissociative chemisorption is calculated. The molecular state has a binding energy of approximately 28 kcal/mole, and vibrational stretching frequencies of 1935 and 1975 cm^?1 are calculated by combining the CFSO-BEBO model with Badger's Rule. The adsorption of oxygen on (111) platinum and (111) nickel are predicted to be different in the following respects: (1) There is an activation energy of 2.1–4.5 kcal/mole on platinum, whereas adsorption on nickel is unactivated; and (2) The dissociative heat of chemisorption on platinum is 58–68 kcal/mole, whereas on nickel it is substantially larger, 112–116 kcal/mole. The adsorption of carbon dioxide on (111) platinum is predicted to be not only highly activated but also endothermic. All of the calculated results are essentially in quantitative agreement with available experimental data.