多壁碳纳米管对p型Ba0.3FeCo3Sb12化合物热电性能的影响

用两步固相反应法合成了P型Ba填充方钴矿化合物Ba0.3FeCo3Sb12，并采用放电等离子烧结法(SPS)制备了Ba0.3FeCo3Sb12／多壁碳纳米管复合材料．研究了Ba0.3FeCo3Sb12／多壁碳纳米管复合材料的结构及多壁碳纳米管对其热电性能的影响规律：SEM分析表明多壁碳纳米管比较均匀地分布在Ba0.3FeCo3Sb12基体中；随着碳纳米管添加量的增加，Ba0.3FeCo3Sb12／多壁碳纳米管复合材料的电导率下降、塞贝克系数略微下降、晶格热导率大幅度降低，当碳纳米管含量为5％时其晶格热导率最小；当碳纳米管的含量为3％时，本研究得到的Ba0.3FeCo3Sb12／碳纳米管复合材料的最大ZT值达0．78．     

负碳离子（2s^22p^3）和（2s^12p^4）的光离解

电子关联效应在负离子中的作用相当重要，本文讨论了负碳离子（２ｓ＾２２ｐ＾２）和（２ｓ＾１２ｐ＾４）的能级结构、光谱跃迁、寿命和光离解通道等。碳负离子（１ｓ＾２２ｓ＾１ｐ＾４）的双重态比四重态稳定，（２ｓ＾２２ｐ＾４）和（２ｓ＾１２ｐ＾４）之间各辐射谱线波长位于超紫外区域的上限附近，其光谱强度很大的波长有６条，为研制Ｘ射线激光提供了有利的工作物质。     

Synthesis of carbon nitride films by low-power inductively coupled plasma-activated transport reactions from a solid carbon source

Thin films of carbon nitride were prepared by low-power inductively coupled plasma chemical vapor deposition from a solid carbon source by utilizing transport reactions. The maximum deposition rate achieved was 10 nm/min and depended mainly on the substrate position in the reactor. The nitrogen fraction in the films was not so sensitive to the process parameters and was at about 0.5 for all experiments as measured by Auger electron spectroscopy (AES) and elastic recoil detection (ERD) analysis. The chemical bonding structure studied by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) showed the presence of triple, double and single bonds between carbon and nitrogen atoms. Received: 12 May 1999 / Accepted: 12 May 1999 / Published online: 24 June 1999     

Smallest carbon nanotube is 3 a in diameter

Previous energetic considerations have led to the belief that carbon nanotubes (CNTs) of 4 A in diameter are the smallest stable CNTs. Using high-resolution transmission electron microscopy, we find that a stable 3 A CNT can be grown inside a multiwalled carbon nanotube. Density functional calculations indicate that the 3 A CNT is the armchair CNT(2,2) with a radial breathing mode at 787 cm(-1). Each end can be capped by half of a C12 cage (hexagonal prism) containing tetragons.     

Tailorable acceptor C(60-n)B(n) and donor C(60-m)N(m) pairs for molecular electronics

Our first-principles calculations demonstrate that C(60-n)B(n) and C(60-m)N(m) can be engineered as the acceptors and donors, respectively, needed for molecular electronics by properly controlling the dopant number n and m in C60. We show that acceptor C48B12 and donor C48N12 are promising components for molecular rectifiers, carbon nanotube-based n-p-n (p-n-p) transistors, and p-n junctions.     

Effects of high pressure and temperature on carbon isotope compositions of some acyclic alkanes and preservation of organic matter

The effects of high pressure and temperature on carbon isotopic compositions of acyclic alkanes and the stability of the acyclic alkanes were experimentally investigated. The pyrolysis of lignite with water in a closed system was conducted at 400–700°C and 1–3 GPa. The carbon isotope data, variations of peak carbon and evident odd–even predominance of acyclic alkanes indicated that: (1) the high pressure retarded the maturation of organic matter and destruction of hydrocarbons, (2) n-C₁₂₊ hydrocarbons from biogenic sources could be preserved in the cool slab subducted into the upper mantle, and (3) some organic compounds might preserve the carbon isotope signals inherited from biogenic sources. The results favor tracing the origins of organic matter in mantle rocks and extraterrestrial organic matter in meteorites and the process of deep carbon cycle.     

C掺杂MgB2超导线材的失超特性研究

研究了不同芯数(单芯、6芯和12芯)的C掺杂MgB2超导线材的失超特性.在制冷机环境(20K)下测量了C掺杂MgB2超导线材样品在自场下的最小触发能及失超传播速度.实验结果表明,失超传播速度随着工作电流的增大而线性增加.失超传播速度的大小跟测量位置有关,离触发区越近的传播速度越大.单芯样品的最小触发能最小,6芯和12芯线的最小触发能相差不大.最小触发能随工作电流的增加成指数形式衰减.     

Synthesis and electrochemical properties of Li4Ti5O12/C composite by the PVB rheological phase method

Spinel Li₄Ti₅O₁₂/C powders were synthesized successfully by a simple rheological phase method using polyvinylbutyral (PVB) as both template and carbon source. The structure and morphology characteristics of the composite were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy and transmission electron microscopy. The XRD results showed that the composite had a good crystallinity. Its average particle size was about 2.1 μm with a narrow size distribution as a result of homogeneous mixing of the precursors. The in situ carbon coating produced by decomposition of PVB played an important role in improving electrical conductivity, thereby enhancing the rate capacity of Li₄Ti₅O₁₂ as anode material in Li-ion batteries. The Li₄Ti₅O₁₂/C composite, synthesized at 800 °C for 15 h under argon, containing 0.98 wt% of carbon, exhibited better electrochemical properties in comparison with the pristine Li₄Ti₅O₁₂, which could be attributed to the enhanced electrical conductive network of the carbon coating on the particle surface.     

Synthesis and magnetic properties of size-controlled FeNi alloy nanoparticles attached on multiwalled carbon nanotubes

FeNi alloy nanoparticles with controllable sizes were attached on the multiwalled carbon nanotubes by adjusting the atomic ratio of metal to carbon in the mixed solution of nitrate with Fe:Ni=1:1 (atomic ratio) via wet chemistry. Transmission electron microscopy (TEM) and high-resolution TEM indicated that quasi-spherical FeNi alloy nanoparticles with sizes in the range 12-25 nm are obtained. FeNi alloy composed of major face center cubic (fcc) and minor body center cubic (bcc) structures, which is proved by the X-ray powder diffraction (XRD). Magnetization measured by vibrating sample magnetometer demonstrated that both the coercive force and saturation magnetizations decrease as the size of the FeNi alloy nanoparticles decreased. The chemical method is promising for fabricating FeNi alloy nanoparticles attached on carbon nanotubes for magnetic storage and ultra high-density magnetic recording applications.     

Aerosol source (biomass,traffic and coal emission) apportionment in Lithuania using stable carbon and radiocarbon analysis*

In the present study, a combination of the stable carbon isotope ratio (¹³C/¹²C) with radiocarbon data (¹⁴C) allowed us to perform the aerosol source apportionment. Filter samples of PM₁ were collected during the warm and cold periods in rural and urban sites in Lithuania. The ¹⁴C/¹²C ratio of total carbon (TC) was measured using the single stage accelerator mass spectrometer quantifying of fossil and non-fossil derived aerosol emissions. The δ¹³C value was measured using an elemental analyser interfaced with an isotope ratio mass spectrometer. We have found that the highest fraction of contemporary carbon (f_c?=?0.82) was measured during a warm period in a rural location. A higher fraction of fossil fuel-derived carbon was observed for air masses transported from highly industrialized Western European regions during both seasons. Isotope mass balance calculations revealed that the traffic emissions composed 15 and 25?% in rural and urban sites, respectively, and did not change during either season. Input from coal-derived aerosol particles was estimated to be 15?% at an urban site during the cold period. The combination of the stable carbon isotope ratio with the radiocarbon data allowed us to distinguish coal, liquid fossil fuel combustion, and non-fossil derived aerosol particle emissions.     

Low-energy electron diffraction study of the reconstruction and orientational stability of Si(331)

Using low-energy electron diffraction, we have studied the reconstruction of Si(331). We find a previously unreported (12 × 1) reconstruction is characteristic of the clean surface; we present evident that a previously observed (13 × 1) reconstruction is not the equilibrium structure. The (12 × 1) reconstruction disorders via a strongly first-order phase transition at approximately 810°C. Heating carbon contaminated surfaces to about 950°C causes faceting to (111) and {17151} orientations.     

剪切形变对硼氮掺杂碳纳米管超晶格电子结构和光学性能的影响

碳纳米管作为最先进的纳米材料之一, 在电子和光学器件领域有潜在的应用前景, 因此引起了广泛关注. 掺杂、变形及形成超晶格为调制纳米管电子、光学性质提供了有效途径. 为了理解相关机理, 利用第一性原理方法研究了不同剪切形变下扶手椅型硼氮交替环状掺杂碳纳米管超晶格的空间结构、电子结构和光学性质. 研究发现, 剪切形变会改变碳纳米管的几何结构, 当剪切形变大于12%后, 其几何结构有较大畸变. 结合能计算表明, 剪切形变改变了掺杂碳纳米管超晶格的稳定性, 剪切形变越大, 稳定性越低. 电荷布居分析表明, 硼氮掺杂碳纳米管超晶格中离子键和共价键共存. 能带和态密度分析发现硼氮交替环状掺杂使碳纳米管超晶格从金属转变为半导体. 随着剪切形变加剧, 纳米管超晶格能隙逐渐减小, 当剪切形变大于12%后, 碳纳米管又从半导体变为金属. 在光学性能中, 剪切形变的硼氮掺杂碳纳米管超晶格的光吸收系数及反射率峰值较未受剪切形变的均减小, 且均出现了红移.     

TR-LII for sizing of carbon particles forming at room temperature

Time-resolved laser-induced incandescence (TR-LII) was applied for the determination of particle sizes during carbon-particle formation from supersaturated atomic carbon vapor that was generated by laser photolysis of carbon suboxide (C₃O₂) at room temperature. Thus, the solid carbon particles were formed under hydrogen-free conditions. The TR-LII technique was used for in situ size measurement of growing carbon particles and samples of final particles were analyzed by transmission electron microscopy (TEM). It was found that the particles grow to a final size of 4–12 nm within 0.02–1 ms. The properties of the obtained particles depend on the initial conditions in the reaction volume, i.e. concentration of carbon suboxide, pressure and type of gas diluter, photolysis wavelength, and laser pulse energy. The comparison of TR-LII and TEM particle sizing results yields information about the effective thermal energy accommodation coefficients for He, Ar, CO, and C₃O₂ molecules on carbon particles. PACS 61.46.Df; 07.60.-j; 78.70.-g     

炸药爆轰制备纳米石墨粉储放氢性能实验研究

介绍了一种新的制备纳米石墨粉的方法——炸药爆轰法.通过对爆轰合成的黑色粉末进行x射线衍射分析，确认其为六方结构的纳米石墨，平均晶粒度为1.86—2.61nm.用BET气体吸附仪测试纳米石墨粉的比表面积约为500—650m2/g，由比表面积计算得到的纳米石墨粒度为4.41—6.85nm.在室温（≈290K）和12MPa压力条件下对纳米石墨粉进行储放氢气性能测试，结果表明纳米石墨粉样品的储放氢量为0.33wt%—0.37wt％.在相同实验条件下，纳米石墨粉原始样品的储放氢能力较原始纳米炭纤维（0.15wt%—0.35wt％）和多壁碳纳米管（0.15wt%—0.20wt％）的储放氢能力略强,但低于超级活性炭（0.92wt%—0.98wt％）.纳米碳材料的比表面积在其储放氢实验中起关键作用. 关键词： 爆轰 纳米石墨粉 比表面积 储放氢量     

Optical Readout Time Projection Chamber (O-TPC) for a study of oxygen formation in stellar helium burning

We are developing an Optical Readout Time Projection Chamber (O-TPC) detector for the study of the ¹²C(α, γ) ¹⁶O reaction that determines the ratio of carbon to oxygen in helium burning. This ratio is crucial for understanding the final fate of a progenitor star and the nucleosynthesis of elements prior to a Type II supernova; an oxygen rich star is predicted to collapse to a black hole, and a carbon rich star to a neutron star. Type Ia supernovae (SNeIa) are used as standard candles for measuring cosmological distances with the use of an empirical light curve-luminosity stretching factor. It is essential to understand helium burning that yields the carbon/oxygen white dwarf and thus the initial stage of SNeIa. The O-TPC is intended for use with high intensity photon beams extracted from the HIγS/TUNL facility at Duke University to study the ¹⁶O(γ, α) ¹²C reaction, and thus the direct reaction at energies as low as 0.7 MeV. We are conducting a systematical study of the best oxygen containing gas with light emitting admixture(s) for use in such an O-TPC. Preliminary results with CO₂+TEA mixture were obtained.     

Behavior of disordered boron carbide under stress

Gibbs free-energy calculations based on density functional theory have been used to determine the possible source of failure of boron carbide just above the Hugoniot elastic limit (HEL). A range of B4C polytypes is found to be stable at room pressure. The energetic barrier for shock amorphization of boron carbide is by far the lowest for the B12(CCC) polytype, requiring only 6 GPa approximately = P(HEL) for collapse under hydrostatic conditions. The results clearly demonstrate that the collapse of the B12(CCC) phase leads to segregation of B12 and amorphous carbon in the form of 2-3 nm bands along the (113) lattice direction, in excellent agreement with recent transmission electron microscopy results.     

Formation of CNx thin films by reactive pulsed laser deposition assisted by electron cyclotron resonance microwave discharge

Amorphous carbon nitride thin films were synthesized by pulsed laser deposition combined with electron cyclotron resonance (ECR) microwave discharge in nitrogen gas. The ECR discharge supplies active nitrogen species in the deposition environment and to the growing film surface, enhancing the film growth in complex processes accompanied by chemical reaction. The synthesized films were characterized by Rutherford backscattering spectroscopy (RBS), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy. The films were determined to consist purely of carbon and nitrogen with a nitrogen concentration of 42%, and have a thickness of 550 nm over which carbon and nitrogen are well distributed. Structural characterizations based on XPS, FTIR and Raman analysis showed that these films appear to contain several bonding configurations between carbon and nitrogen with a small amount of C≡N bonds compared with other bonding states. Received: 31 August 2000 / Accepted: 12 December 2000 / Published online: 23 May 2001     

Effect of thermobaric conditions in a uniform bed on the displacement of low-viscosity oil by supercritical carbon dioxide

An experimental setup was constructed that makes it possible to study oil displacement over wide pressure (up to 20 MPa) and temperature (up to 373 K) ranges under conditions reproducing the thermobaric, geological, and physicochemical conditions in real oil beds, as well as the parameters of displacing agents. Experiments on the displacement of kerosene from a model oil bed with supercritical carbon dioxide at temperatures of 313–353 K and pressures within 7–12 MPa were performed. The results are indicative of a high efficiency of recovery of low-viscosity oils with supercritical carbon dioxide.     

Stable carbon isotopic composition of tree rings from a pine tree from Augustów Wilderness, Poland, as a temperature and local environment conditions indicator

Tree rings can be used as archives of climatic and environmental data with annual resolution. Tree rings widths, maximum late wood density and other parameters as stable composition in tree rings can be used for the reconstruction of past climatic and environmental changes. Stable carbon isotope ratios in tree rings may provide valuable information on past climatic conditions. 13C/12C ratios of plant organic matter can reflect corresponding 13C/12C ratio of atmospheric CO2 during formation of the rings. Investigations of isotopic carbon composition in tree rings from in the ecologically clean the Augustów Wilderness region in the north-eastern part of Poland (22 degrees 58'E, 53 degrees 51'N) (nowadays a sanctuary) were undertaken. Series of delta13C in alpha-cellulose and in wholewood were acquired. Those measurements constituted a part of more complex investigations of carbon isotope composition in tree rings including the measurements of radiocarbon concentration and tree ring widths. This article presents preliminary results. It is argued that contrary to the tree ring widths and delta13C in wholewood that do not reveal significant correlation with temperature, the variation of delta13C in the latewood alpha-cellulose is correlated with combined July and August temperatures.     

Irradiation-induced magnetism in carbon nanostructures

Nitrogen (15N) and carbon (12C) ion implantations with implant energy of 100 keV for different doses were performed on nanosized diamond (ND) particles. Magnetic measurements on the doped ND show ferromagnetic hysteresis behavior at room temperature. The saturation magnetization (M(s)) in the case of 15N implanted samples was found to be higher compared to the 12C implanted samples for dose sizes greater than 10(14) cm(-2). The role of structural modification or defects along with the carbon-nitrogen (C-N) bonding states for the observed enhanced ferromagnetic ordering in 15N doped samples is explained on the basis of x-ray photoelectron spectroscopy measurements.