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461.
Fe3O4和Zn2+掺杂型Zn1-xFe2+xO4纳米晶的溶剂热合成和电磁性能 总被引:1,自引:0,他引:1
利用溶剂热法, 在醋酸钠静电保护剂的辅助下, 成功制备出Fe3O4和Zn2+掺杂型Zn0.07Fe2.93O4纳米晶. 利用X射线衍射仪和扫描电子显微镜等对样品的晶体结构、粒径、形貌和化学组成进行了分析. 结果表明, 所得纳米晶的粒径均匀, 形貌为球形, 分散度好; Zn0.07Fe2.93O4纳米晶的平均粒径(70 nm)明显小于Fe3O4(170 nm). 磁性能测量结果表明, 室温下Zn0.07Fe2.93O4的饱和磁化强度(54.2 A·m2·kg-1)小于Fe3O4 (81.6 A·m2·kg-1). 利用矢量网络分析仪对样品的电磁性能和吸波性能进行了研究. 结果表明, Zn2+掺杂型Zn0.07Fe2.93O4纳米晶的吸波性能优于Fe3O4, 前者的最大吸收峰(-19.3 dB)大于后者(-9.8 dB), 且吸收峰低于-10 dB的峰宽达2.5 GHz. 相似文献
462.
Optical properties of nanocrystalline silver halides 总被引:4,自引:0,他引:4
Michal Ilana Freedhoff Alfred P. Marchetti George L. McLendon 《Journal of luminescence》1996,70(1-6):400-413
A review of quantum confinement effects in nanocrystals of silver bromide (AgBr) and silver iodide (AgI) is presented. AgBr is an indirect gap semiconductor while AgI has a direct band-to-band lowest energy transition. An examination of the low-temperature optical properties of quantum confined AgBr grown using a variety of synthetic techniques will be made. The dynamics of some of the involved excitonic processes will be measured and discussed in reference to a possible breakdown in the momentum selection rules as the nanocrystals are made smaller. Other explanations for this behavior such as impurity exclusion and surface effects will also be considered, as will the dynamics associated with the trapping of excitons at intrinsic iodide impurities in AgBr. Absorption measurements on AgI nanocrystals will be discussed and compared with the exciton photophysics in AgBr. Both AgBr and AgI display an increasing blue shift of their luminescence, arising from the recombination of excitons, as the crystallite size decreases. The luminescence intensity arising from this process increases with decreasing size in AgBr but it disappears in small crystals of AgI. This leads to the conclusion that in the latter material nonradiative decay channels are opening up as the size decreases. 相似文献
463.
Nanocrystalline Y2Si2O7:Eu phosphor with an average size about 60 nm is easily prepared using silica aerogel as raw material under ultrasonic irradiation and annealing temperature at 300-600 °C and this nanocrystalline decomposes into Y2O3:Eu and silica by heat treatment at 700-900 °C. The excitation broad band centered at 283 and 254 nm results from Eu3+ substituting for Y3+ in Y2Si2O7 and Y2O3/SiO2, respectively. Compared with Y2O3:Eu/SiO2 crystalline, the PL excitation and emission peaks of Y2Si2O7:Eu nanocrystalline red-shift and lead to the enhance of its luminescence intensity due to the different chemical surroundings of Eu3+ in above nanocrystallines. The decrease of PL intensity may be ascribed to quenching effect resulting from more defects in Y2O3:Eu/SiO2 crystalline. 相似文献
464.
A heterostructure of n-type hydrogenated nanocrystalline silicon (nc-Si:H) film with p-type crystalline silicon, i.e., (n)nc-Si:H/(p)C-Si, was fabricated to investigate carrier characteristics and transport. After electrical experiments, carrier information, such as hole and electron as well as 2-dimension electronic gas in the studied system, was identified respectively. The forward current conduction was analyzed while the reverse current transport was distinguished as different mechanisms within the different range of negative applied voltage. The performed study also leads us to ascribe the main origin of short transient times on the produced structure to a tunneling mechanism. 相似文献
465.
We have obtained intense cathodoluminescence (CL) emission from electron beam modified porous silicon films by excitation with electrons with kinetic energies below 2 keV. Two types of CL emissions were observed, a stable one and a non-stable one. The first type is obtained in well-oxidized samples and is characterized by a spectral peak that is red shifted with respect to the photoluminescence (PL) peak. The physically interesting and technologically promising CL is however the CL that correlates closely with the PL. Tuning of this CL emission was achieved by controlling the average size of the nanostructure thus showing that the origin of this CL emission is associated with the quantum confinement and the surface chemistry effects that are known to exist in the porous silicon system. We also found that the electron bombardment causes microscale morphological modifications of the films, but the nanoscale features appear to be unchanged. The structural changes are manifested by the increase in the density of the nanoparticles which explains the significant enhancement of the PL that follows the electron irradiation. 相似文献
466.
The photo-induced change in wettability of hydrophobized TiO2 films has been investigated for steel coated with acidic TiO2 nanosols containing varying concentrations of dispersed nanocrystalline titania, such as Degussa P25. The photo-induced change in wettability was evaluated by measuring the time-dependent drop of water contact angle (WCA) after samples had been soaked in either n-octyltriethoxysilane (OTS) or decanoic acid (DA). TiO2 films treated in this way exhibit superhydrophobic behaviour, with WCA greater than 160°. After radiation with UV (black light), the superhydrophobic properties are transformed into superhydrophilic properties, with WCA of almost 0°. As P25 content and layer thickness increase, high rates of photo-induced change are found, but a moderate calcination regime is required. On the other hand, hardness and E modulus pass through a maximum at 25 wt% P25, so that a P25 content between 25 and 50 wt% is the optimum for practical uses. With such stable coatings, wettability can be controlled over a wide range, and the switch between hydrophobic and hydrophilic states can be carried out repeatedly when DA is used as the hydrophobizing agent. Use of a low calcination temperature (450 °C) for the intermediate annealing of the single layers in multilayer coatings and a short final sintering step at a relatively high temperature (e.g. 630 °C for 10 min) allow the preparation of relatively thin TiO2 films on steel with a high photoactivity. 相似文献
467.
S. Khazzan N. Mliki L. Bessais C. Djga-Mariadassou 《Journal of magnetism and magnetic materials》2010,322(2):224-229
The structural and magnetic properties of Sm2Fe17-xMox, its out of equilibrium precursor SmFe9-yMoy and their carbides are investigated by means of powder X-ray diffraction, magnetic measurements and high-resolution transmission electron microscopy. The structure of the nanocrystalline Sm1-s(Fe,Mo)5+2s alloys are governed by the s Sm vacancy rate and the x amount of Mo. In this work, the Rietveld analysis shows that for s=0.33 the structure is of Th2Zn17-type and P6/mmm with the stoichiometry 1/9 for s=0.36. Moreover, it points out a lattice expansion along the c-axis after Mo substitution for Fe and reveals a 6c preferential occupation for Mo atoms in structure, and 2e for the out of equilibrium hexagonal precursor. Upon carbon insertion, the lattice expansion favors the Curie temperature increase up to 35% for Sm2Fe16.42Mo0.58C2 and 49% for the metastable SmFe8.7Mo0.3C carbide. The Curie temperature and the coercive field of the 1/9 carbides are higher than those of 2/17 ones. This makes the out of equilibrium hexagonal precursor a competitive candidate for use as permanent magnet. 相似文献
468.
Thermal annealing induced formation of nanocrystalline Zinc silicate (α-Zn2SiO4) at the interface of ZnO-porous silicon (PSi) nanocomposites is reported. The PSi templates were formed by electrochemical anodization of p-type (100) Si and ZnO crystallites were deposited on the PSi surface by a Sol-gel spin coating process. The formation of α-Zn2SiO4 is confirmed by glancing angle X-ray diffraction and Fourier transform infrared spectroscopy studies. The presence of intense yellow-green emission also confirms the formation of α-Zn2SiO4. The mechanism of silicate phase formation at the ZnO-PSi interface and the origin of various photoluminescence (PL) bands are discussed in view of its potential applications in advanced optoelectronic devices. 相似文献
469.
Raghavendra Sagar 《Solid State Communications》2011,151(24):1949-1952
Ceramic solid solution of nanocrystalline barium zirconium titanate in the form of Ba(Zr0.52Ti0.48)O3 substituted by samarium (Sm3+) was prepared using the conventional solid state reaction method. The phase assemblage analyzed by the X-ray diffraction technique was fitted for cubic-crystal-symmetry. The change in the grain size depicted the influence of Sm3+ ions on the microstructure. The electrical behavior was studied in the temperature range from 323 to 773 K. The sintered samples exhibited a negative temperature coefficient of resistance (NTCR) and superior semiconducting behavior above 513 K. Addition of Sm3+ increased the room temperature resistivity of Ba(Zr0.52Ti0.48)O3 solid solution. The results obtained from the thermoelectric power measurement confirm electrons as the majority charge carriers. 相似文献
470.
Nanocrystalline SnO2 thin films were deposited by simple and inexpensive chemical route. The films were characterized for their structural, morphological, wettability and electrochemical properties using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy techniques (SEM), transmission electron microscopy (TEM), contact angle measurement, and cyclic voltammetry techniques. The XRD study revealed the deposited films were nanocrystalline with tetragonal rutile structure of SnO2. The FT-IR studies confirmed the formation of SnO2 with the characteristic vibrational mode of Sn-O. The SEM studies showed formation of loosely connected agglomerates with average size of 5-10 nm as observed from TEM studies. The surface wettability showed the hydrophilic nature of SnO2 thin film (water contact angle 9°). The SnO2 showed a maximum specific capacitance of 66 F g−1 in 0.5 Na2SO4 electrolyte at 10 mV s−1 scan rate. 相似文献