共查询到10条相似文献,搜索用时 93 毫秒
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Using first principles density functional theory calculations, we investigated the X and X–N–X (X = Al and Ga) doped 3C–SiC
nanowires grown along the [111] crystal direction with diameter of 1.00 and 1.33 nm. We found that the ionization energy of
acceptor state is much larger in nanowires than that in the bulk SiC as a result of quantum confinement effect. Simulation
results show that the reduced dimensionality in p-type SiC nanowires strongly reduces the capability of the materials to generate free carriers. It is also found that X–N–X
(X = Al and Ga) complexes are energetically favored to form in the materials and have lower ionization energy than single
doping. It is confirm that codoping is more suitable method for achieving low-resistivity semiconductors either in nano materials
or bulk material. 相似文献
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《Physics letters. A》2006,357(2):136-140
CdS nanoarrays with the particles' diameter of about 1 nm were assembled in the nanochannels of the host of VSB-5 nanorods. Obvious UV–vis absorption peaks with the onsets of about 350–400 nm were clearly observed. Compared with the band-gap absorption at about 515 nm of the large CdS particles at room temperature, about 115–165 nm of the blue-shifts occurred for the nanoarrays due to the quantum confinement effect. 相似文献
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Abhishek Verma Swati Nagpal Praveen K. Pandey P. K. Bhatnagar P. C. Mathur 《Journal of nanoparticle research》2007,9(6):1125-1131
Quantum Dots of CdS
x
Se1−x
embedded in borosilicate glass matrix have been grown using Double-Step annealing method. Optical characterization of the
quantum dots has been done through the combinative analysis of optical absorption and photoluminescence spectroscopy at room
temperature. Decreasing trend of photoluminescence intensity with aging has been observed and is attributed to trap elimination.
The changes in particle size, size distribution, number of quantum dots, volume fraction, trap related phenomenon and Gibbs
free energy of quantum dots, has been explained on the basis of the diffusion-controlled growth process, which continues with
passage of time. For a typical case, it was found that after 24 months of aging, the average radii increased from 3.05 to
3.12 nm with the increase in number of quantum dots by 190% and the size-dispersion decreased from 10.8% to 9.9%. For this
sample, the initial size range of the quantum dots was 2.85 to 3.18 nm. After that no significant change was found in these
parameters for the next 12 months. This shows that the system attains almost a stable nature after 24 months of aging. It
was also observed that the size-dispersion in quantum dots reduces with the increase in annealing duration, but at the cost
of quantum confinement effect. Therefore, a trade off optimization has to be done between the size-dispersion and the quantum
confinement. 相似文献
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The electronic properties of twinned ZnS nanowires (NWs) with different diameters were investigated based on first-principles calculations. The energy band structures, projected density of states and the spatial distributions of the bottom of conduction band and the top of the valence band were presented. The results show that the twinned nanowires exhibit a semiconducting character and the band gap decreases with increasing nanowire diameter due to quantum confinement effects. The valence band maximum and conduction band minimum originate mainly from the S-p and Zn-s orbitals at the core of the nanowires, respectively, which was confirmed by their spatial charge density distribution. We also found that no heterostructure is formed in the twinned ZnS NWs since the valence band maximum and conduction band minimum states are distributed along the NW axis uniformly. We suggest that the hexagonal (2H) stacking inside the cubic (3C) stacking has no effect on the electronic properties of thin ZnS NWs. 相似文献
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Laurence Latu-Romain Maelig Ollivier Arnaud Mantoux Geoffroy Auvert Odette Chaix-Pluchery Eirini Sarigiannidou Edwige Bano Bernard Pelissier Charbel Roukoss Herv�� Roussel Florian Dhalluin Bassem Salem Nikoletta Jegenyes Gabriel Ferro Didier Chaussende Thierry Baron 《Journal of nanoparticle research》2011,13(10):5425-5433
Si nanowires (NWs), with diameters of about 800 nm and lengths of about 10 ??m, previously synthesized by the VLS method with gold catalyst, were carburized at 1,100 °C under methane for conversion into SiC nanostructures. These experiments have shown that Si NWs have been transformed into SiC nanotubes (NTs) with approximately the same sizes. Nanotubes?? sidewall thickness varies from 20 to 150 nm depending on the NTs?? height. These SiC nanotubes are hexagonal in shape and polycrystalline. A model of growth based on the out-diffusion of Si through the SiC layer was proposed to explain the transformation from Si nanowires to SiC nanotubes. This model was completed with thermodynamic calculations on the Si?CH2?CCH4?CO2 system and with results from complementary experiment using propane precursor. Routes for obtaining crystalline SiC NTs using this reaction are proposed. 相似文献
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We present a theoretical investigation of the electronic and optical properties of hydrogen-coated silicon nanocrystals (Si:H NCs). On one hand, the density-functional theory (DFT) is used to both calculate the total energy and relax the NCs. On a second hand, the tight-binding method, which includes the minimal sp3-basis set within the second-nearest-neighbor interaction scheme, is applied to calculate the electronic structures, oscillator strength (OS) and recombination rate (RR) versus the NC size, coating and atomic relaxation. Three main findings are reported: (i) The quantum confinement in these NCs do follow similar rule to the case of a single-particle in a box, where the confinement energy decays in power-law with the increasing NC's size. (ii) The coating is shown to play the essential role in creation of large band-gap energy lying within the visible-light energy spectrum. (iii) The surface atomic relaxation is found to reduce the band-gap energy by about 150 meV and enhance both OS and RR. Our claims are corroborated by the available experimental data. 相似文献
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采用多元醇法,在不同温度,不同PVP滴加速度和加入量的条件下合成了银纳米线。利用XRD,UV-Vis,SEM和TEM对银纳米线及其侧向生长过程进行了观察和分析。UV-Vis表明银纳米线在纵向生长的同时发生了侧向生长。而且表示银纳米线侧向生长的紫外吸收光谱峰在银纳米线合成后期发生了明显的红移,由384nm红移至约388nm处,表明银纳米线合成后期直径迅速增长,银纳米线发生了快速的侧向生长。SEM研究表明银纳米线直径在反应前期(15~23min)只增加了20nm,而在反应后期(23~30min)银纳米线直径增加了近150nm,SEM观察结果与UV-Vis分析结论一致。同时还发现银纳米线直径不仅与晶种大小有关而且与银线外覆盖的银层厚度有关,银源以吸附在银线侧面的小银颗粒为附着点沿其侧面多点沉积导致了银纳米线的侧向生长;降低反应液温度(165℃降至155℃),降低PVP滴加速度(67mL·h~(-1)减小到49mL·h~(-1))以及减少银纳米线合成后期PVP加入量可抑制银纳米线的侧向生长,显著提高银纳米线长径比,银纳米线直径由200nm减小至100nm左右,长度仍保持在100μm以上。 相似文献
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We study the optical-gain characteristics of a Si-based MQW laser, in which the active region has 20 Si0.15Ge0.621Sn0.229 quantum wells separated by 20 Si0.637Ge0.018Sn0.345 barriers. We reach a maximum optical gain of 2300 cm?1 with an estimated carrier concentration of 5·1018 cm?3, which is equivalent to the transparent current density equal to 0.5 kA/cm2. Furthermore, we discuss the optical confinement factor and modal gain. The modal gain depends sensitively on the number of the quantum wells (QWs), and this fact restricts the optical confinement factor. The modal gain of the model we proposed can reach 1500 cm?1 at the injection current density equal to 3 kA/cm2. We hope that our results show the possibility to obtain a Si-based near-infrared laser. 相似文献