超分子屏蔽效应对富勒烯自由基C59N·稳定性的影响及其诱导的(C59N)2中键接碳笼C-C键的转移重构

富勒烯自由基通常是在空气中短暂存在或不稳定的短寿命物种,超分子屏蔽是近年来被发展用于稳定富勒烯自由基稳定的一种有效策略.本文将共价桥联碳质π电子共轭双嵌N分子碗作为客体C₅₉N·富勒烯自由基的理想宿主体,通过密度泛函理论计算研究了二者之间的主客体相互作用、热力学、自旋电子密度等性质.结果发现C₅₉N·富勒烯自由基嵌螯在该钳形双分子碗的凹穴内而被屏蔽,从而有效避免单电子结构的暴露和C₅₉N·自由基之间的化学二聚,即显著增强其动力学稳定性和寿命,这种策略对富勒烯自由基在自旋电子学、超分子电子器件或光电转换器件等领域的应用具有潜在指导价值.此外,本研究还发现通过超分子屏蔽策略,理论上可以实现对(C₅₉N)₂二聚体分子中键连两个碳笼的C-C进行重构,这也为富勒烯相关体系中C-C键构建的提供了一种新的思路与途径.     

C60/C70晶体形貌的研究

采用电弧法制备了C₆₀/C₇₀,并用光学显微镜、扫描电子显微镜和透射电子显微镜对其结晶形貌进行了研究。研究结果表明,C₆₀/C₇₀晶体依平面状长大方式生长,最终长成规则的四边形,五边形和六边形晶体。 关键词：     

类石墨烯氮化碳结构(C3N)热传导机理研究

类石墨烯氮化碳结构(C₃N)作为一种全新的碳基二维半导体材料,由于其优异的机械和电子性能引起了研究者们的广泛关注,不同结构C₃N的热输运和声子输运机制还待进一步研究.本文构造了4种不同结构的C₃N,采用非平衡分子动力学与晶格动力学方法对不同结构的C₃N的热传导机理进行了研究.研究结果表明:1)在4种结构中M3热导率最高,M1次之,M4热导率最低;2)不同结构的C₃N的热导率具有明显的尺寸效应和温度效应.当样本长度较短时,声子主要以弹道输运的方式进行传输;当样本长度增大,扩散输运占主导地位;随着温度的升高,Umklapp散射在热输运中占据主导地位,使得热导率与温度具有1/T的依赖性.3)与M3相比,M1和M4结构中都存在更大的声子带隙,色散曲线进一步软化,低频和高频声子同时出现了局域化的特征,对热导率产生了显著的抑制作用.本文为更好地设计热管理材料提供了思路.     

Al0.6Ga0.4N/GaN/Al0.3Ga0.7N/Al0.6Ga0.4N量子阱中的Rashba自旋劈裂

正如人们所知, 可以通过电场或者设计非对称的半导体异质结构来调控体系的结构反演不对称性(SIA)和Rashba自旋劈裂. 本文研究了Al_0.6Ga_0.4N/GaN/Al_0.3Ga_0.7N/Al_0.6Ga_0.4N量子阱中第一子带的Rashba 系数和Rashba自旋劈裂随Al_0.3Ga_0.7N插入层(右阱)的厚度w_s以及外加电场的变化关系, 其中GaN层(左阱)的厚度为40-w_s Å. 发现随着w_s的增加, 第一子带的Rashba系数和Rashba自旋劈裂首先增加, 然后在w_s>20 Å 时它们迅速减小, 但是w_s>30 Å时Rashba自旋劈裂减小得更快, 因为此时k_f也迅速减小. 阱层对Rashba系数的贡献最大, 界面的贡献次之且随w_s变化不是太明显, 垒层的贡献相对比较小. 然后, 我们假w_s=20 Å, 发现外加电场可以很大程度上调制该体系的Rashba系数和Rashba自旋劈裂, 当外加电场的方向同极化电场方向相同(相反)时, 它们随着外加电场的增加而增加(减小). 当外加电场从-1.5×10⁸ V·m^-1到1.5×10⁸ V· m^-1变化时, Rashba系数随着外加电场的改变而近似线性变化, Rashba自旋劈裂先增加得很快, 然后近似线性增加, 最后缓慢增加. 研究结果表明可以通过改变GaN层和Al_0.3Ga_0.7N层的相对厚度以及外加电场来调节Al_0.6Ga_0.4N/GaN/Al_0.3Ga_0.7N/Al_0.6Ga_0.4N量子阱中的Rashba 系数和Rashba自旋劈裂, 这对于设计自旋电子学器件有些启示.     

C60晶体中分子取向性的研究

本文用集团模型计算C₆₀晶体的结合能,考察晶体原胞中四个不等价分子之间的相对取向变化时晶体结合能的相应变化。认为低温下C₆₀晶体的有序化结构在能量上是不简并的,存在一个使能量最低的分子相对取向。 关键词：     

C20富勒烯的Ar+离子辐照合成

Ar⁺离子辐照聚乙烯靶表面在室温情况下合成的C₂₀,已采用高分辨率透射电子显微镜/电子衍射装置、飞行时间质谱、红外和拉曼谱仪进行了研究.结果认为,辐照诱发的微晶体由笼式C₂₀组成. 关键词：     

添加Fe(C5H5)2合成氢掺杂金刚石大单晶及其表征

在Ni₇₀Mn₂₅Co₅-C体系中添加含氢化合物Fe(C₅H₅)₂作为新型氢源, 利用温度梯度法, 在压力为5.5-6.0 GPa、温度为1280-1400 ℃的条件下, 成功合成出氢掺杂的宝石级金刚石大单晶. 通过傅里叶显微红外光谱发现, 随着Fe(C₅H₅)₂添加量的增加, 合成晶体中与氢相关的对应于sp³杂化C-H键的对称伸缩振动和反对称伸缩振动的红外特征峰2850和2920 cm^-1逐渐增强, 而晶体中氮含量却逐渐减少. 通过合成晶体的拉曼光谱分析发现, 金刚石的拉曼峰伴随Fe(C₅H₅)₂的添加向高频偏移, 这表明氢的进入在金刚石内部产生了压应力. 观察扫描电子显微镜图像发现, 在低含量Fe(C₅H₅)₂添加时晶体表面平滑, 而高含量添加时晶体表面缺陷增多, 且呈现出气孔状. 使用新的添加剂Fe(C₅H₅)₂作为氢源, 合成出含氢宝石级金刚石单晶, 丰富了金刚石单晶中对氢的研究内容, 也可为理解天然金刚石的形成机理提供帮助.     

H2 分子在Li3N(110)表面吸附的第一性原理研究

采用第一性原理方法研究了H₂分子在Li₃N(110)晶面的表面吸附. 通过研究H₂/Li₃N(110)体系的吸附位置、吸附能和电子结构发现: H₂分子吸附在N桥位要比吸附在其他位置稳定,此时在Li₃N(110)面形成两个-NH基,其吸附能为1.909 eV,属于强化学吸附;H₂与Li₃N(110)面的相互作用主要是H 1s轨道与N 关键词： 第一性原理 3N(110)')" href="#">Li₃N(110) 2')" href="#">H₂ 吸附和解离     

50—5000 eV电子被C4H8O,C5H10O2, C6H5CH3和C4H8O2散射的总截面

使用电子被C, H和O原子散射总截面的实验数据, 利用修正后的可加性规则计算了能量为50—5000eV的电子被4个复杂大分子C₄H₈O, C₅H₁₀O₂, C₆H₅CH₃和C₄H₈O₂散射的总截面, 并将计算结果与实验结果及其他理论计算结果进行了比较. 结果表明, 即 关键词： 电子散射 可加性规则 总截面 几何屏蔽效应     

纳米Cu3N薄膜的制备与性能

采用柱状靶多弧直流磁控溅射法，100℃基底温度下在玻璃衬底上制备了纳米氮化铜(Cu3₃N)薄膜.用x射线衍射研究了不同氮气分压对Cu3₃N薄膜晶体结构 及晶粒尺寸的影响.结果显 示薄膜由Cu3₃N和Cu的纳米微晶复合而成，其中Cu3₃N纳米微晶具有 立方反ReO3₃结构.通 过原子力显微镜对薄膜表征显示，膜表面比较光滑，具有较低的粗糙度.x射线光电子能谱对 薄膜表面的成分分析表明，Cu3 _{关键词： 氮化铜薄膜 多弧直流磁控溅射 3}结构')" href="#">立方反ReO3₃结构     

Geometrical effects of (N@C60)2, N@C60 and C59N endohedral fullerenes within single-walled carbon nanotube as peapods on electronic structure and magnetic properties

Design of spin labels inside for possible molecular spintronics, which contains of 1D spin chain filling single-walled carbon nanotube (SWCNT) with magnetic endohedral fullerenes of (¹⁴N@C₆₀)₂, ¹⁴N@C₆₀ and C₅₉N has been proposed. Electronic structure and magnetic properties of (¹⁴N@C₆₀)₂-SWCNT, ¹⁴N@C₆₀-SWCNT, ¹⁴N@C₆₀ and C₅₉N were characterized. Geometrical effect of (¹⁴N@C₆₀)₂, ¹⁴N@C₆₀ and C₅₉N within SWCNT on chemical shift of ¹³C, principal g-tensor, A-tensor in hfc of nitrogen atom and excited state transition was investigated by ab-initio density functional theory. The magnetic properties would be originated in the spin density distribution with π-electron interaction between encapsulated fullerenes and inner surface on SWCNT and extent of charge transfer.     

Calculated spectroscopic properties for C12H and HC11N, molecules of astrochemical interest

A comparative theoretical study of the (potential) interstellar molecules C₁₂H⁻ and HC₁₁N has been carried out, making use of the coupled cluster variant CCSD(T) in conjunction with large basis sets comprising up to 715 contracted Gaussian-type orbitals. The ground-state rotational constants of C₁₂H⁻ and C₁₂D⁻ are predicted to be 174.11 and 170.32 MHz, respectively. The corresponding quartic centrifugal distortion constant of C₁₂H⁻ is estimated to be 0.26 Hz, to be compared with an experimental value of 0.24 Hz for HC₁₁N. Most of the total infrared intensity of C₁₂H⁻ isotopomers concentrates in one or two bands around 2000 cm⁻¹. The total IR intensity exceeds 13 000 km mol⁻¹ and is thus about 20 times larger than for HC₁₁ N isotopomers. The bending vibrations of C₁₂H⁻, HC₁₁N and their deuterated species are analysed by means of mass plots.     

Specific features of the stone-wales transformation in the C20 and C36 fullerenes

The initial stage of the defect formation in the C₂₀ and C₃₆ fullerenes has been investigated by the ab initio method and in terms of tight-binding models. A comparison with the Stone-Wales transformation in the C₆₀ fullerene has revealed the presence of two independent stages in this process, the first of which is an “incomplete” Stone-Wales transformation. At this stage, the C₂₀ and C₃₆ fullerenes transform into metastable defect configurations with two adjacent “windows” on their surface, whereas a similar configuration of the C₆₀ fullerene is unstable and corresponds to a saddle stationary point of the potential energy of the cluster. A new mechanism of plastic deformation due to the Stone-Wales transformation has been predicted for the (C₃₆) _n fullerites.     

控制成核生长大尺寸C60，C70单晶

通过改进双温区双温度梯度方法，成功地控制成核密度，分别生长出线度可达6mm和5mm的大尺寸C₆₀，C₇₀单晶，并对其表面形貌和晶体结构进行了研究. 关键词：     

The oxidation of fullerene [C70] with various oxidants by ultrasonication

The reaction of C₇₀ by ultrasonication with various oxidants such as 3-chloroperoxy benzoic acid (Fluka 99%), 4-methyl morpholine N-oxide (Aldrich 97%), chromium (VI) oxide (Aldrich 99.9%), and oxone^® monopersulfate compound, at room temperature causes the oxidation of fullerene [C₇₀(O)_n] (n=1–2 or n=1). The FAB-MS, UV–visible, FT-IR spectra, and HPLC analysis confirmed that products of fullerene oxidation are [C₇₀(O)_n] (n=1–2 or n=1).     

Ab initio study of the electronic structure and elastic properties of Al5C3N

We investigate the electronic structure, chemical bonding and elastic properties of the hexagonal aluminum carbonitride, Al₅C₃N, by ab initio calculations. Al₅C₃N is a semiconductor with a narrow indirect gap of 0.81 eV. The valence bands below the Fermi level (E_F) originate from the hybridized Al p-C p and Al p-N p states. The calculated bulk and Young's moduli are 201 GPa and 292 GPa, which are slightly lower than those of Ti₃SiC₂. The values of the bulk-to-shear-modulus and bulk-modulus-to-c44 are 1.73 and 1.97, respectively, which are higher than those of Ti₂AlC and Ti2AlN, indicating that Al₅C₃N is a ductile ceramic.     

Crystal structure and ferromagnetism of (n-C3H7)4N[CoFe(dto)3] (dto=C2O2S2)

Recently, we have discovered a new type of first order phase transition around 120 K for (n-C₃H₇)₄N[Fe^IIFe^III(dto)₃] (dto=C₂O₂S₂), where the charge transfer transition between Fe^II and Fe^III occurs reversibly. In order to elucidate the origin of this peculiar first order phase transition. Detailed information about the crystal structure is indispensable. We have synthesized the single crystal of (n-C₃H₇)₄N[Co^IIFe^III(dto)₃] whose crystal structure is isomorphous to that of (n-C₃H₇)₄N[Fe^IIFe^III(dto)₃], and determined its detailed crystal structure. Crystal data: space group P6₃, a=b=10.044(2) Å, c=15.960(6) Å, α=β=90°, γ=120°, Z=2 (C₁₈H₂₈NS₆O₆FeCo). In this complex, we found a ferromagnetic transition at T_c=3.5 K. Moreover, on the basis of the crystal data of (n-C₃H₇)₄N[Co^IIFe^III(dto)₃], we determined the crystal structure of (n-C₃H₇)₄N[Fe^IIFe^III(dto)₃] by simulation of powder X-ray diffraction results.     

C60单晶的汽相生长

报道使用Ｃ₆₀粉末，利用双炉装置，通过闭管汽相法生长Ｃ₆₀单晶的实验及结果。Ｃ₆₀单晶的质量很好，较大单晶的尺寸为０．５ｍｍ×０．６１ｍｍ×１．０ｍｍ。Ｘ射线衍射和电子衍射图的分析得到室温下Ｃ₆₀单晶为ｆｃｃ结构，确定了晶格常数，还进行了Ｒａｍａｎ光谱实验，实验结果表明，热、冷区温度及两者的温度差是影响大尺寸Ｃ₆₀单晶汽相生长的主要因素，对此进行了详细的讨论。 关键词：     

First principles study of small cobalt clusters encapsulated in C60 and C82 spherical nanocages

Structural, electronic and magnetic properties of the small Co_n clusters (n = 2-7) endohedrally doped in C₆₀ (Ih) and C₈₂ (C2v) fullerenes were investigated using ab initio calculations based on the density functional theory. It is found that the encapsulated Co_n clusters inside C₆₀ and C₈₂ cages are energetically favorable except for Co₇@C₆₀. The encapsulation does not change significantly the structure of the enclosed clusters, but the magnetic moment of the clusters reduces due to a stronger Co-C hybridization for the larger clusters.