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用分子动力学方法研究了N,O,Si,P,S等5种杂质对扶手椅型(5,5)和锯齿型(9,0)单壁碳纳米管杨氏模量的影响.结果表明:直径为0.678和0.704 nm的扶手椅型(5,5)和锯齿型(9,0)碳纳米管在无掺杂时其杨氏模量分别为948和804 GPa.在掺杂浓度10%以下,碳纳米管的拉伸杨氏模量均随掺杂浓度增加近似呈线性下降规律,下降率以Si掺杂最大,N掺杂最小.对与C同周期的元素掺杂,随原子序数增加碳纳米管的杨氏模量下降率增大;与C不同周期的元素掺杂,碳纳米管的杨氏模量随掺杂浓度增加下降率更大,但
关键词:
碳纳米管
杂质
杨氏模量
分子动力学方法 相似文献
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稀土掺杂锰氧化物庞磁电阻效应 总被引:26,自引:0,他引:26
过去十多年来,具有庞磁电阻效应的稀土掺杂锰氧化物成为了凝聚态物理研究的重要领域。锰氧化物的载流子自旋极化率高,且在居里温度附近表现出很大的磁电阻效应,因此在自旋电子学中有潜在的应用前景。另一方面,锰氧化物是典型的强关联电子体系,它对目前有关强关联体系的认识提出了很大挑战。本文综述了锰氧化物的各种性质及其物理原因。全文首先概述了锰氧化物的庞磁电阻效应及其晶格和电子结构,简单介绍了其他一些庞磁电阻材料;随后综述了锰氧化物的电荷/轨道有序相及其输运性质;在第四部分简单介绍了锰氧化物中庞磁电阻效应的机制;最后讨论了锰氧化物的一些可能的应用,如低场磁电阻效应、磁隧道结、磁p-n结以及全钙钛矿的场效应管和自旋极化电子注入装置等。 相似文献
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过去十多年来,具有庞磁电阻效应的稀土掺杂锰氧化物成为了凝聚态物理研究的重要领域。锰氧化物的载流子自旋极化率高,且在居里温度附近表现出很大的磁电阻效应,因此在自旋电子学中有潜在的应用前景。另一方面,锰氧化物是典型的强关联电子体系,它对目前有关强关联体系的认识提出了很大挑战。本文综述了锰氧化物的各种性质及其物理原因。全文首先概述了锰氧化物的庞磁电阻效应及其晶格和电子结构,简单介绍了其他一些庞磁电阻材料;随后综述了锰氧化物的电荷/轨道有序相及其输运性质;在第四部分简单介绍了锰氧化物中庞磁电阻效应的机制;最后讨论了锰氧化物的一些可能的应用,如低场磁电阻效应、磁隧道结、磁p_n结以及全钙钛矿的场效应管和自旋极化电子注入装置等。 相似文献
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目前,相分离仍是锰基氧化物超大磁电阻材料研究的热点,渗流效应假设已广泛用于解释其电输运特性.作者用变温磁力显微镜首次在La0.33Pr0.34Ca0.33MnO3薄膜中直接观察到了渗流过程,微观上证明了渗流效应假设的正确性.实验发现,降温过程中电阻率的陡降是铁磁金属相的渗流效应引起的,升温过程中电阻率的上升,则是由导电路径上磁畴的磁化强度随温度的升高而降低引起的,而导电路径一直存在.微观的磁回滞和宏观的电阻回滞相吻合.当然要定量解释锰氧化物中的超大磁电阻效应还需要做大量的理论和实验工作. 相似文献
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氧化锌纳米晶体的光谱分析 总被引:7,自引:5,他引:2
采用沉淀法并通过控制前驱体的煅烧温度来制备粒径不同的氧化锌(ZnO)纳米晶体,对粒子的透射电镜照片进行分析,结果表明,制备出的纳米粒子分散性好、形貌一致、粒径分布集中。样品的X射线衍射光谱分析表明,随着前驱体煅烧温度增加,晶体粒径增大、结晶度提高;样品的紫外-可见吸收光谱的峰位随粒径减小而发生蓝移,这一实验结果表明ZnO纳米晶体呈现出较明显的量子限域效应;红外吸收光谱测量结果表明,用沉淀法制备的ZnO纳米晶体的表面会吸附一小部分残余的离子,对红外吸收光谱中的ZnO特征振动峰随粒径减小发生宽化和红移的现象进行了理论分析;光致发光光谱测量结果表明,ZnO纳米晶体在紫外区(360 nm)存在一较弱的发光峰,而在可见区(468 nm)存在一较强的发光峰,与理论计算结果进行比较后,认为锌空位点缺陷是导致ZnO纳米晶体可见区发光的主要原因。 相似文献
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CdTe nanocrystals were grown from commercially available RG850 Schott filter glass by two-step heat-treatment process which almost doubles the particle to matrix volume fraction. A calculation shows that a quantized-state effective mass model in the strong confinement regime might be used to deduce the average radius for the nanocrystals larger than 2 nm in radius from the energetic position of the first exciton peak in optical absorption spectrum. Size-induced shift of ∼360 meV in the first exciton peak position was observed. The steady state photoluminescence spectra exhibit a broad band red shifted relative to the first exciton band, which indicates the existence of shallow trap states. The non-linear optical properties of CdTe nanocrystals were studied by room temperature resonant photoabsorption spectroscopy. The differential absorption spectra had three-lobed structure whose size-dependent evolution was explained by bleaching of the absorption, red shift and broadening in the Gaussian absorption band used to fit the first exciton peak. A maximum red shift of 2.32 meV for the average nanocrystal radius of 4.65 nm was estimated by fitting the photomodulation spectra with a combination of first and second derivative Gaussian absorption bands. We presume that the red shift is induced by the electric field of trapped charges in surface states. Internal electric field strengths of 23 and 65 kV/cm were predicted for the average nanocrystal radii of 3.95 and 4.65 nm, respectively, with the help of second-order perturbation theory in the strong confinement limit. 相似文献
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Chitosan–ZnO nanostructures were prepared by chemical precipitation method using different concentration of zinc chloride and sodium hydroxide solutions. Nanorod-shaped grains with hexagonal structure for samples annealed at 300 °C and porous structure with amorphous morphology for samples annealed at 600 °C were revealed in SEM analysis. X-ray diffraction patterns confirmed the hexagonal phase ZnO with crystallite size found to be in the range of ~24.15–34.83 nm. Blue shift of UV–Vis absorption shows formation of nanocrystals/nanorods of ZnO with marginal increase in band gap. Photoluminescence spectra show that blue–green emission band at 380–580 nm. The chitosan–ZnO nanostructures used on surface of a glassy carbon electrode gives the oxidation peak potential at ~0.6 V. The electrical conductivity of chitosan–ZnO composites were observed at 2.1?×?10?5 to 2.85?×?10?5?S/m. The nanorods with high surface area and nontoxicity nature of chitosan–ZnO nanostructures observed in samples annealed at 300 °C were suitable as a potential material for biosensing. 相似文献
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Indium(III) sulfide quantum dots were deposited in thin film form using both a conventional chemical bath deposition method
and a sonochemical route. The developed routes allow deposition of cubic α-In2S3 nanocrystals in thin film form. The as-deposited films produced by the conventional and sonochemical approaches are highly
nanocrystalline, with average crystal sizes of 2.5 and 2.0 nm correspondingly (as determined from the Scherrer formula), which
increase to 4.1 nm upon annealing treatment, due to coalescence and crystal-growth processes. Refinement of the lattice-constant
value in the case of as-deposited and annealed films was performed using linear regression analysis. Blue-shifted band-gap
energy values of as-deposited films with respect to those corresponding to bulk specimen, accompanied with the red shift of
absorption onset upon annealing, strongly indicate the quantum-dot behavior of the synthesized nanocrystals. The detected
three-dimensional quantum-confinement effects in the synthesized nanocrystals were discussed in terms of the Brus model. On
the basis of optical spectroscopic data, we estimated the Bohr's excitonic radius value in this semiconductor.
Presented at the X-th Symposium on Suface Physics, Prague, Czech Republic, July 11–15, 2005. 相似文献
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Irradiation of zinc selenide at ~ 20°K with electrons capable of displacing zinc atoms results in the production of cathodoluminescence emission bands at 610 and 630 nm. Enhancement of the 630 nm emission band by electron damage requires the presence of copper in the samples. These emissions have been shown to give a peak energy shift to lower energies after excitation, as is characteristic of donor-acceptor pair recombination. It is concluded that the 610 and 630 nm emission bands of zinc selenide are equivalent to the self-activated and copper green emission bands of zinc sulphide. The 530 nm emission band of zinc selenide is not sensitive to electron damage, shows no time shift and is thought to be equivalent to the copper blue emission of zinc sulphide. 相似文献
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G. Murugadoss 《Journal of luminescence》2010,130(11):2207-2214
Zinc sulfide semiconductor nanocrystals doped Mn2+ have been synthesized via a solution-based method utilizing optimum dopant concentration (4%) and employing polyvinyl pyrrolidone (PVP) and sodium hexametapolyphosphate (SHMP) as capping agents. UV-vis absorbance spectra for all of the synthesized nanocrystals show an exitonic peak at around 310 nm. The particle size and morphology were characterized by scanning electron microscopy (SEM), FT-IR, X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence spectrum (PL). Diffraction data confirmed that the crystallite size is around 3-5 nm. Room temperature photoluminescence (PL) spectrum for the bare ZnS sample shows a strong band at ∼445 nm. The uncapped and capped(SHMP, PVP) ZnS:Mn2+ samples show a strong and broad band in the ∼580-585 nm range. 相似文献
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Aimin Shi Jianhui Sun Qinghui Zeng Zaicheng Sun Xianggui Kong 《Journal of luminescence》2011,131(7):1536-1540
Photoluminescence (PL) properties of 3-mercaptopropionic acid (MPA) coated CdTe/CdS core-shell quantum dots (QDs) in aqueous solution in the presence of ZnO colloidal nanocrystals were studied by steady-state and time-resolved PL spectroscopy. The PL quenching of CdTe/CdS core-shell QDs with addition of purified ZnO nanocrystals resulted in a decrease in PL lifetime and a small red shift of the PL band. It was found that CdTe(1.5 nm)/CdS type II core-shell QDs exhibited higher efficiency of PL quenching than the CdTe(3.0 nm)/CdS type I core-shell QDs, indicating an electron transfer process from CdTe/CdS core-shell QDs to ZnO nanocrystals. The experimental results indicated that the efficient electron transfer process from CdTe/CdS core-shell QDs to ZnO nanocrystals could be controlled by changing the CdTe core size on the basis of the quantum confinement effect. 相似文献
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Ultrasound assisted synthesis of yellow rare earth cerium zinc molybdate anticorrosion nanopigment is presented. This new class of pigment is eco-friendly alternatives to lead, cadmium and chromium pigment as these pigments contains carcinogenic species like Cr6+ which is responsible for human disease. The synthesis of nanosized cerium zinc molybdate was carried out using cerium nitrate, sodium zinc molybdate as a precursor materials by conventional and ultrasound assisted chemical precipitation method without addition of emulsification agent. XRD, FTIR and elemental analysis confirm the formation of cerium zinc molybdate nanoparticles. The conductivity results indicate that conventional synthesis takes longer time, while in sonochemical technique (US), reaction completes within short period of time. Improved solute transfer rate, rapid nucleation, and formation of large number of nuclei are attributed to presence of cavitation. Saturation of the Ce3+ ions reaches earlier in case of sonochemical technique which restricts the growth of particles hence smaller size is obtained. The crystallite size of cerium zinc molybdate was found to be 27 nm from XRD analysis. 相似文献
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C.S. PrajapatiP.P. Sahay 《Applied Surface Science》2012,258(7):2823-2828
Nanocrystalline ZnO thin films were chemically deposited on glass substrates using two different precursors namely, zinc sulphate and zinc nitrate. XRD studies confirm that the films are polycrystalline zinc oxide having hexagonal wurtzite structure with crystallite size in the range 25-33 nm. The surface morphology of film prepared using zinc sulphate exhibits agglomeration of small grains throughout the surface with no visible holes or faulty zones, while the film prepared using zinc nitrate shows a porous structure consisting of grains with different sizes separated by empty spaces. The film prepared using zinc sulphate shows higher reflectance due to its larger refractive index which is related to the packing density of grains in the film. Further, the film prepared using zinc sulphate is found to have normal dispersion for the wavelength range 550-750 nm, whereas the film prepared using zinc nitrate has normal dispersion for the wavelength range 450-750 nm. The direct optical band gaps in the two films are estimated to be 3.01 eV and 3.00 eV, respectively. The change in film resistance with temperature has been explained on the basis of two competing processes, viz. thermal excitation of electrons and atmospheric oxygen adsorption, occurring simultaneously. The activation energies of the films in two different regions indicate the presence of two energy levels - one deep and one shallow near the bottom of the conduction band in the bandgap. 相似文献