Magnetisation of isolated single crystalline Fe-nanoparticles measured by a ballistic Hall micro-magnetometer

We present here the first magnetisation measurements on isolated single crystalline Fe-nanoparticles performed with a ballistic Hall micro-magnetometer. The measurements have a sensitivity of and thus provide us the possibility to study the mechanisms of magnetisation reversal in a single nanoparticle. The magnetic properties of the nanoparticles are influenced by their crystal structure and shape, and the presence of an oxide surface layer. They exhibit curling of the magnetic moments, but also a novel hysteresis behaviour. The spin configurations found for the system agree well with numerical calculations based on a Heisenberg Hamiltonian including the exchange and dipole interaction and surface anisotropy. Received: 1st September 1998 and Received in final form 21 June 1999     

Study of Nanocrystalline Diamond Film Deposited Rapidly by 500 W Excimer Laser

High quality nanocrystalline diamond film deposited rapidly by an XeCl excimer laser operated at high laser power (500 W) and repetition rate (300～500 Hz) is presented. A high deposition rate, 250 nm/thousand pulses, was obtained. The effects of laser energy fluence and repetition rate on the deposition of diamond film were investigated.     

电化学沉积CdSe纳晶薄膜的性能及沉积机理

电化学沉积是半导体薄膜制备的一种简便方法,常用于Ⅱ-族化合物半导体薄膜的制备.通过电沉积条件的适当改变可成功地在导电衬底上制备半导体纳晶薄膜^[1].CdSe薄膜作为一种透光性好、导电性好的半导体材料,可进行光学性能和光电性能方面的研究,而半导体纳晶多孔电极的光电化学特性与体材料之间有很大不同.本文采用电化学沉积法制备了CdSe纳晶薄膜并研究了其性能,通过扫描隧道显微镜(STM)形貌分形分析进一步研究其沉积机理.     

微波辐射下纳米水滑石的合成

在微波辐射下用变速滴加共沉淀法合成了粒径为10 nm~40 nm的Mg-A l纳米水滑石(nano-HT),其结构经XRD,TEM,TG和元素分析表征。以nano-HT为载体,制备了Cu/nano-HT和CuN i/nano-HT催化剂,通过苯酚羟基化反应考察了它们的催化活性,实验结果表明,双氧水有效利用率和产物的选择性均比以常规水滑石为载体的催化剂高。     

Abnormal variation of magnetic properties with Ce content in(PrNdCe)_2Fe_(14)B sintered magnets prepared by dual alloy method

Resource-saving(PrNdCe)_2Fe_(14)B sintered magnets with nominal composition(PrNd)_(15-x)Ce_xFe_(77)B_8(x=0–10)were prepared using a dual alloy method by mixing(PrNd)_5Ce_(10)Fe_(77)B_8 with(PrNd)_(15)Fe_(77)B_8 powders. For Ce atomic percent of 1% and 2%, coercivity decreases dramatically. With further increase of Ce atomic percent, the coercivity increases, peaks at 6.38 kOe in(PrNd)_(11)Ce_4Fe_(77)B_8, and then declines gradually. The abnormal dependence of coercivity is likely related to the inhomogeneity of rare earth chemical composition in the intergranular phase, where Pr Nd concentration is strongly dependent on the additive amount of(PrNd)_5Ce_(10)Fe_(77)B_8 powders. In addition, for Ce atomic percent of 8%,7%, and 6% the coercivity is higher than that of magnets prepared by the conventional method, which shows the advantage of the dual alloy method in preparing high abundant rare earth magnets.     

Crystal Growth Kinetics of Nanocrystalline ZnS under Surface Adsorption

The crystal growth mechanism,kinetics,and microstructure development play a fundamental role in tailoring the materials with controllable size and morphology. In this study,by introducing the strong surface adsorption of the concentrated NaOH,two-stage crystal growth kinetics of ZnS nanoparticles was observed. In the first stage,the primary particles grow into a size over a hundred times of the original volume and the growth is controlled by the crystal-lographically specific oriented attachment. The first stage data were fitted by the "multistep OA kinetic model" built based on the molecular collision and reaction. In the second stage,following the dispersal of nanoparticles,an abrupt transition from asymptotic to parabola growth kinetics occurs,which can be fitted by a standard Ostwald ripening volume diffusion model. The presence of surface adsorption causes the two-stage growth kinetics and permits an almost exclusive OA-based growth to dominate in the first stage.     

Low Temperature Solvent Evaporation-induced Crystallization Synthesis of Nanocrystalline TiO2 Photocatalyst

A novel and efficient methodology for obtaining highly active photocatalyst of bi-phase TiO2 with small particle size and high specific surface area was developed by solvent evaporation-in-duced crystallization (SEIC) method at low temperature. The prepared TiO2 powder was characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM) and BET surface areas. The photocatalyfic activity was evaluated by the photocatalyflc oxidation of acetone in air. The results showed that the photocatalytic activity of the TiO2 powder preDared by this method approached that of Degnssa P25. This may be atotributed to the fact that the predated TiO2 powder had larzer specific surface areas (265 m2. g- 1 ) and smaller crystallite size (about 5 nm), but relatively low crystallinity, as compared with Degussa P25.     

纳米晶镁铝水滑石的制备及其热分解机理

研究了无机阻燃剂镁铝水滑石纳米晶的制备及其热分解机理.采用常压下,一步反应的液相法制备镁铝水滑石试样，用XRD和TEM测试试样的相组成和形貌，针状镁铝水滑石纳米晶体的长度约80 nm.依据DSC和DTA-TG测试结果，发现镁铝水滑石纳米晶的热分解由两个阶段组成:第一个吸热峰出现在220 ℃左右，第二个吸热峰出现在380 ℃左右.研究了反应时间对所得镁铝水滑石试样的热分解性能的影响，发现延长反应时间，镁铝水滑石试样的第一次、第二次热分解的起始温度升高,第一次热分解的失重值增大，最后剩余氧化物的量增大，从而增强镁铝水滑石阻燃剂的阻燃性能.根据不同升温速率下获得的DSC测试数据，应用Achar微分法、Šatava-Šesták积分法和Ozawa积分法对镁铝水滑石纳米晶热分解的第二个阶段进行了动力学计算和分析，确定该段的热分解机理函数积分式为(1－α)－1－1.     

染料敏化纳米晶太阳能电池

半导体纳米晶颗粒形成的膜具有非常大的比表面积，其表面上可以吸附大量的染料分子，因而可以有效地吸收太阳光，并将其转化为电能。本文介绍了染料敏化纳米晶太阳能电池的基本原理以及电池的结构。从电池各个组成部分分别介绍了染料敏化纳米晶太阳能电池的发展及其研究现状。     

提高速凝铸带母合金制备的烧结钕铁硼磁体磁性能的研究

通过对速凝带钕铁硼母合金制备烧结钕铁硼永磁体后续工艺的研究，发现对速凝带进行900℃等温热处理，200℃和0．1MPa条件下氢破碎，可以有效地提高磁体的性能，改善退磁曲线的方形度。