碳纳米管的电子自旋共振研究

在直流碳弧法中,用氦气氛和气氛制备碳纳米管,在７７０℃下将阴极沉积物氧化至原重量的１％,得到纯的碳纳米管,测量不同气氛及压强下制备的碳纳米管的室温电子自旋共振说,讨论了不同惰性气氛及压强对所制备碳管的ＥＳＲ谱线型,ｇ因子,线宽的影响。     

不同惰性气氛及压强下的碳纳米管的拉曼光谱

本文比较了央弧法中在两种不同气氛和不同压强下制备出的碳纳米管的一级和二级拉曼光谱。我们用直流碳弧法分别在He气氛下和Ar气氛下，压强从11kPa到92kPa制备出碳纳米管，对它们的拉曼光谱进行了分析和比较，发现谱线的峰位置和峰宽度取决于所制备的惰性气氛种类和气体压强。在Ar气氛下制备的碳纳米管的拉曼光谱更接近于石墨的拉曼光谱，而He气氛下制备的碳纳米管，其拉曼光谱与石墨比较，差别较大。并且拉曼位移的峰位置和宽度随着压强的变化而改变，在较高压强下产生的碳纳米管的拉曼光谱更类似于石墨的拉曼光谱。     

用微米级LaNi5为催化剂生长的碳管的ESR谱研究

用微米级LaNi₅合金粉末为催化剂, 以乙炔为原料, 采用化学气相沉积(CVD)法合成了多壁碳纳米管. 在100~290 K温度下测量了41 μm≤d≤150 μm粒径催化剂制备的不同直径分布的碳纳米管的电子自旋共振（ESR）谱,研究了测量温度、微米级催化剂粒径及制备过程的氢气氛对生成的碳纳米管的ESR谱线型、g因子、线宽的影响. 发现碳纳米管的g因子随其直径的增大而增大,分别为2.040 0（催化剂粒径41 μm≤d≤50 μm, 碳纳米管的直径分布为10 nm到20 nm）和2.089 8（催化剂粒径100 μm≤d≤150 μm,碳纳米管的直径分布为70 nm到120 nm）. 发现小管径纳米管的ESR谱图有一个峰, 而大管径纳米管的ESR谱图有两个峰A和B, 且随测量温度的升高, 峰B强度增大.     

碳纳米管的热解法制备、电子显微镜观察及拉曼光谱研究

以二茂铁和二甲苯为原料在Ar和H2 气氛中不同温度下热解制备出了不同直径分布的碳纳米管。在 740℃、780℃、82 0℃和 880℃下制备出的碳纳米管的外径分布分别为 1 7-80nm、2 0 - 73nm、40 - 70nm、1 7- 2 7nm。拉曼光谱和透射电子显微镜 (TEM )观察表明 ,在82 0℃下制备的碳纳米管晶形最完整     

电弧法磁性超细微粒分析

利用X射线衍射分析、电子显微镜和X射线能谱分析技术,研究了不同Ar气氛压强下以电弧法制备的铁磁超细微粒Fe3O4和FeC.发现超细微粒的粒径、微结构和化学组分对气氛压强的依赖性,并对此作初步探索. 关键词：     

CO2连续激光蒸发制备单壁碳纳米管及其Raman光谱的研究

讨论了在室温下用波长10.6μm的CO2连续激光制备单壁碳纳米管的工艺条件和生长机理.用大功率CO2连续激光蒸发制备单壁碳纳米管,所用激光功率400—900W,高分辨透射电镜观察表明单壁碳纳米管直径1.1—16nm,随着激光功率的增加稍微增加.本文还分别用波长为514.5nm和632.8nm激发光测量了CO2红外激光制备的单壁碳纳米管的一级和二级Raman光谱,发现在Raman特征峰的位置、强度上都存在差异.还将用CO2红外激光制备的单壁碳纳米管的Raman光谱与用YAG激光制备的单壁碳纳米管的Raman光谱进行了比较. 关键词： 单壁碳纳米管 CO2连续激光 Raman光谱     

单壁碳纳米管低温及常温下储氢行为的模拟计算研究

采用巨正则系综蒙特卡罗方法, 通过含有此方法模块的GULP软件, 系统地研究了扶手椅式单壁碳纳米管在低温和常温下的储氢性能, 给出了5种半径的扶手椅管在液氮温度(77 K)和常温(280 K)下的吸附等温线, 同一管径在不同温度不同压强下氢分子在碳纳米管中的分布构型图等. 对77 K和280 K下不同压强不同管径的碳纳米管储氢能力做了较为全面的对比分析, 最后根据模拟计算的结果, 对碳纳米管储氢能力的强化提出了一些建设性意见.     

LPCVD法制备的高纯半绝缘4H-SiC晶体ESR谱特性

利用电子自旋共振波谱（ESR）仪,分析由低压化学气相沉积（LPCVD）法制备的高纯半绝缘4H-SiC材料本征缺陷.结果发现,在暗场条件下获得的缺陷信息具有碳空位（V_C）及其络合物的特征;谱线具有半高宽较大、峰谷明显不对称的特点.分析认为造成ESR谱线半高宽较大及峰谷不对称现象的主要原因是测试温度较高.同时,吸收谱中峰谷不对称现象及较大半高宽现象的出现还与不对称的晶格结构及缺陷浓度的不均匀分布有关.在110 K测试温度下,能级上的电子分布对ESR谱特性影响很小. 关键词： 低压化学气相沉积 高纯半绝缘4H-SiC 电子自旋共振 本征缺陷     

高质量三维光子晶体的制备及其透射谱研究

设计了简易的压强可控自组装实验装置,制备了由直径为260 nm的聚苯乙烯(PS)胶体球组成的面心立方光子晶体.分析了压强的变化对光子禁带(PBG)深度及光子带隙边缘(PBE)坡度的影响,确定了合适的压强生长环境(P=5999.5 Pa).利用该实验装置,还进行了光子晶体的小批量制备,一次性制得了三块光子晶体,并从不同角度对每一块光子晶体的透射谱及不同光子晶体的透射谱进行了测量.同一光子晶体不同位置透射谱的重合、同一批次制备的不同光子晶体透射谱的一致性及光子禁带两侧的Fabry-Pérot振荡等均说明:该装置制备的光子晶体在大区域、大面积上是高度有序、均一和平整的;利用该实验装置进行光子晶体的小批量制备是可行的.     

原位核磁共振技术研究反应环境对光催化甲醇重整过程的影响

本文利用原位核磁共振技术，系统研究了在真实反应体系中反应环境（气氛、压强、气体量等）对甲醇光催化重整反应产物的影响.发现不同气氛对甲醇光催化重整的反应产物有着不同的抑制作用，而环境压强及气体量对于甲醇光催化重整反应产物产率的影响较小.在此基础上，本文进一步讨论了气体在催化剂表面的吸附方式和环境气氛影响甲醇光催化重整反应产物的机理.     

THE RAMAN SCATTERING OF CARBON NANOTUBES PRODUCED IN DIFFERENT INERT GASES AND THEIR PRESSURES BY ARC DISCHARGE

First- and second-order Raman spectra of carbon nanotubes produced in helium and argon atmospheres at a pressure ranging from 11 to 92 kPa by arc discharge have been measured and compared with each other. The position and bandwidth of the spectral lines depend on the kind of inert gases and their pressure. The Raman spectra of the nanotubes produced in argon gas atmosphere are much more similar to that of polycrystalline graphite than those of the nanotubes produced in helium gas atmosphere. The position and bandwidth of nanotube Raman peaks change with gas pressure in arc discharge because different diameter distribution of nanotubes is produced at different inert gas pressure. The Raman spectra of nanotubes produced at high pressure is much more like that of graphite than those produced in lower pressure     

Emission characteristics of a discharge iodine vapor plasma in the spectral region of the main absorption maximum of DNA molecules

Radiation of glow and capacitive discharges in inert gas-iodine vapor mixtures is studied in the spectral range 150–210 nm, which coincides with the main absorption maximum of the DNA molecules. Iodine atomic spectral lines at 150.7, 161.8, 170.2, 183.0, and 206.2 nm are observed in the spectra. The emission intensity of the iodine spectral lines is optimized by varying the glow discharge current, capacitive discharge frequency, as well as pressure and composition of the gas mixtures. The glow and capacitive discharges are ignited in cylindrical quartz tubes with interelectrode gaps of 10 and 6 cm. Helium and neon are found to be the most effective buffer gases. The optimum partial pressures of the light inert gases and iodine vapor in the glow discharge are within 0.4–0.6 kPa and 100–150 Pa, respectively. In the capacitive discharge in He(Ne)-I₂ mixtures, the optimum partial helium, neon, and iodine vapor pressures are within 0.8–2.0 kPa, 0.5–1.0 kPa, and ≤ 60 Pa, respectively. It is demonstrated that pulsed bactericidal radiation sources with light pulse lengths of 400–500 ns and continuous radiation sources emitting within the spectral range 150–207 nm can be designed on the basis of low-density iodine vapor plasma.     

自悬浮定向流技术中铜纳米微粒的粒度控制研究

 采用自悬浮定向流技术制备了金属铜纳米微粒，根据TEM的行貌像对样品平均粒度进行标定，并结合样品制备的条件对制备工艺进行了研究。结果表明，自悬浮定向流技术可以方便地制备出不同粒度的金属铜纳米微粒，微粒平均粒径随熔球温度的降低而减小，随冷却气体流速的增大而减小；在1 200℃下微粒平均粒径随惰性气体压强的增大而减小，而在1 300℃时惰性气体压强对微粒平均粒径的影响不再具有规律性。     

Electron spin resonance signal of Luttinger liquids and single-wall carbon nanotubes

A comprehensive theory of electron spin resonance (ESR) for a Luttinger liquid state of correlated metals is presented. The ESR measurables such as the signal intensity and the linewidth are calculated in the framework of Luttinger liquid theory with broken spin rotational symmetry as a function of magnetic field and temperature. We obtain a significant temperature dependent homogeneous line broadening which is related to the spin-symmetry breaking and the electron-electron interaction. The result crosses over smoothly to the ESR of itinerant electrons in the noninteracting limit. These findings explain the absence of the long-sought ESR signal of itinerant electrons in single-wall carbon nanotubes when considering realistic experimental conditions.     

Electron spin resonance from annealed titania nanotubes

Titania nanotubes were prepared using a hydrothermal method. Hydrogen titanate nanotubes (H-TNTs) with an anatase phase changed to anatase nanocrystals at about 500 °C, and then a rutile structure at ∼800 °C. A sharp and symmetrical electron spin resonance (ESR) signal (g=2.003), attributed to a single-electron-trapped oxygen-vacancy (SETOV), was obtained at the annealed H-TNTs (T<500 °C). The SETOV signal increased and maximized remarkably at about 400–500 °C. Then, the nanotube structure appeared to be demolished. Yet, when the vacuum-heated H-TNTs were sealed in N₂ or Ar ambient, some additional ESR signals appeared besides the SETOV signal. The broad asymmetric ESR signal (g=1.98) was attributed to a surface oxygen vacancy related to the Ti³⁺ sites in a reduced TiO₂ matrix. The vacuum-heated sodium titanate nanotubes (Na-TNTs) showed only the SETOV signal (T<500 °C). PACS 61.46.Fg; 61.72.Ji; 76.30.-v     

Electron spin resonance investigation of ultra-small double walled carbon nanotubes embedded in zeolite nanochannels

We report on the low temperature electron spin resonance (ESR) properties of ultra-small (0.45?nm) double walled carbon nanotubes (DWCNTs) embedded in zeolite nanochannels. An isotropic ESR signal is observed at g(c)?=?2.002?77 with the spin density (S?=?1/2)?～?10(19)?g(-1), which is suggested to originate from the carbon related point defects in the DWCNTs. Measurements of the ESR line width and signal intensity as a function of temperature indicate that the spins are of a localized nature as opposed to the conduction type electrons observed in large diameter CNTs. The results are consistent with the suggestion that electrons are trapped at interstitial defects. The observed linear frequency dependence of the ESR line width of embedded DWCNTs points to 'strain' as the prime source of broadening. By contrast, the study of free standing DWCNTs shows the presence of a distinctly superlinear frequency dependence of the signal width at low temperatures. The possible origin of the frequency dependence is discussed.     

Hyperfine coupling constants of muonium-substituted cyclohexadienyl radicals in the gas phase: C6H6Mu, C6D6Mu, C6F6Mu

Muon spin rotation (μSR) and avoided level crossing resonance (ALCR) have been used to determine the hyperfine coupling constants (hfcs) of the muonium-substituted cyclohexadienyl radicals C₆H₆Mu, C₆D₆Mu and C₆F₆Mu in the gas phase, at pressures ～1 and 15 atm and temperatures in the range 40–80°C. Equivalent studies of polyatomic free radicals in gases, by electron spin resonance (ESR) spectroscopy, are generally not possible in this pressure range. The present gas phase results support the findings of earlier studies of cyclohexadienyl radicals in the condensed phase, by both μSR and ESR. Minor but not insignificant (～1%) effects on the hfcs are observed, which can be qualitatively understood for such nonpolar media in terms of their differing polarizabilities. This is the first time that comparisons of this nature have been possible between different phases at the same temperatures. These μSR/ALCR gas-phase results provide a valuable benchmark for computational studies on radicals, free from possible effects of solvent or matrix environments.