氨化反应自组装GaN纳米线

通过氨化射频溅射工艺生长的纳米Ga2O3薄膜，在石英衬底上反应自组装生成了高质量的GaN纳米线。用x射线衍射(XRD)、透射电镜(TEM)和高分辨电镜(HRTEM)对样品的组分、形貌和结构进行了分析。生成的GaN纳米线平直光滑，其直径为20～120nm，长可达50μm；纳米线为高质量的单晶六方纤锌矿GaN，沿[110]方向生长。用此工艺制备GaN纳米线，简单新颖，不需要模板或催化剂的辅助作用。     

立方相纳米氮化钒粉体制备方法

中国科学院上海硅酸盐研究所近日向社会推出立方相纳米氮化钒粉体制备方法。据介绍 ,这种制备立方相纳米氮化钒粉体的方法 ,主要特征是以沉淀法制备的一水合五氧二钒 (V2 O5·H2 O)粉体为原料、在氨气气氛中将一水合五氧二钒粉体于管式反应炉中高温氮化制得立方相纳米氮化钒粉体。通过改变氮化温度、氮化时间等工艺条件、可获得小于 5 0nm的不同晶粒尺寸的纳米氮化钒粉体。氮化反应温度控制在 5 0 0～80 0℃ ,氮化保温时间 3～ 5h ,氮化升温速率为 5～ 10℃ /min。在优化条件下 ,可得到立方相纳米氮化钒粉体。立方相纳米氮化钒粉体制备方…     

衬底氮化对HVPE法生长GaN的影响

研究了衬底氮化过程对于氢化物气相外延(HVPE)方法生长的GaN膜性质的影响。X射线衍射和原子力显微镜以及光荧光测量的结果表明，不同的氮化时间导致Al2O3表面的成核层发生变化，进一步影响了外延层中的位错密度和应力分布。     

花状TeO_2微/纳米结构的制备及Raman光谱研究

以Bi_2Te_3粉末为原料,采用热蒸发的方法成功制备出花状TeO_2微/纳米结构。利用扫描电子显微镜(SEM)对合成产物的形貌进行表征,结果显示样品的微/纳米结构是由大量微/纳米片堆叠成的花状团簇。通过EDS发现,样品由Te和O两种元素组成。利用激光共聚焦拉曼光谱仪对合成产物的Raman光谱进行表征,结果显示合成产物的光谱与TeO_2晶体一致,并且随着热蒸发温度的升高,拉曼谱峰的峰值越高,特征峰越锐利,在硅片上制备出的产物的结晶度越好。     

乙二醇溶液燃烧法一步合成纳米CoO

以硝酸钴为氧化剂,乙二醇为燃料,采用溶液燃烧法在200～400℃合成了纳米CoO晶体。采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、低温N2吸附等手段对产物的晶相结构、形貌和比表面积进行了表征,系统地研究了不同燃料比和燃烧温度对合成产物的影响。结果发现:乙二醇燃料缺50%时制备得到纳米Co3O4,化学计量比量燃料时得到CoO,而燃料过量50%时则得到CoO和金属Co的混晶。通过选取化学计量比量的乙二醇,燃烧温度300～400℃的反应条件,可以控制合成出多孔网状结构的纯相纳米CoO晶体,晶粒大小约为17 nm,BET比表面积7.7 m2·g-1。     

制备SiO_2包覆的Fe_3O_4磁性纳米复合粒子

首先用化学共沉淀法制备出柠檬酸三铵改性的Fe3O4磁性纳米粒子,然后用反相微乳液法制备了SiO2包覆的Fe3O4磁性纳米复合粒子。用X射线衍射仪(XRD),透射电子显微镜(TEM),傅立叶-红外光谱仪(FTIR)和振动样品磁强计(VSM)表征SiO2包覆的Fe3O4磁性纳米复合粒子。结果表明,SiO2成功包覆在Fe3O4表面,且饱和磁化强度下降,但矫顽力趋近于零,仍显示超顺磁性。     

碳热还原氮化制备氮化硅粉体反应条件研究

对二氧化硅碳热还原氮化合成氮化硅的反应体系进行了热力学和动力学分析,主要研究了反应温度和氮气流量对Si3N4、Si2N2O和SiC生成的影响。热力学研究表明,Si3N4的生成需要足够高的温度(高于1800K)和充足的氮气气氛;Si2N2O的生成条件是较低的温度(低于1700K)和不充足的氮气气氛;SiC的生成条件是更高的温度(高于2000K)和不充足的氮气气氛。试验研究验证了热力学的分析,并确定了碳热还原氮化合成氮化硅的主要工艺条件(氮气流量为3L/min、煅烧温度为1500℃)。在以上工艺条件下,可制备出纯的Si3N4粉体。     

溶胶凝胶/高温氢还原法制备纳米Mo-ZrO2(Y2O3)复合粉末

纳米Mo-ZrO2(Y2O3)复合粉末是一种很有发展前景的粉末冶金材料.采用溶胶凝胶法制备前驱体复合粉末,并对得到的前驱体复合粉末采用高温氢还原工艺制备Mo-ZrO2(Y2O3)复合粉末.通过X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和能谱分析(EDS)等分析检测技术对前驱体复合粉末的物相...     

双缓冲层法在硅上外延生长GaN研究

利用金属有机物化学金相沉积MOCVD在Si(111)衬底上，以高温AlN和低温GaN为缓冲层生长的GaN薄膜，得到GaN(0002)和(10-12)的双晶X射线衍射(DCXRD)半高宽(FWHM)分别为721和840s。采用高分辨率DCXRD，扫描电子显微镜(SEM)分析。结果表明，以1040℃生长的AlN缓冲层能防止Ga与Si反应形成无定形的Si-Ga结构，是后续生长的“模板”。低温的GaN缓冲层可有效减低外延层的缺陷。DCXRD测得的FWHM为0．21，GaN峰强达7K。     

纳米/微米Al2O3-ZrO2内衬复相陶瓷的自蔓延高温合成

采用SHS重力分离技术制备出内衬Al2O3-ZrO2复相陶瓷.复相陶瓷基体主要由纤维状(Al2O3+ZrO2)共晶体组成,其中共晶体的ZrO2纤维直径达到纳米/微米尺度.经Vickers压痕法测试其断裂韧度为15.96MPa·m1/2,SEM观察和陶瓷材料断裂韧度测试得出裂纹的扩展主要受共晶体中Al2O3-ZrO2纳米/微米相增韧机制控制,迫使裂纹沿共晶体边界或层片共晶体Al2O3-ZrO2相界偏转,从而维持了该复相陶瓷较高的断裂韧度.     

A novel approach for synthesis of hierarchical mesoporous Nd_2O_3 nanomaterials

A novel route to the fabrication of hierarchical mesoporous Nd_2O_3 nanostructures including nanospheres and nanoporous network was described. Their structure and morphology evolution of the as-synthesized materials were determined by various techniques such as scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, Fourier transforminfrared spectra, nitrogen adsorption/desorption isotherm, and a formation mechanism was proposed. The results revealed that the Nd_2O_3 nanospheres had the diameter of 300 nm, which were composed of small primary nanoparticles(NPs) with the size of 10 nm. The nanoporous structure also formed the NPs of ca. 10 nm which were connected with each other to form a three-dimensional(3D) texture. This simple and mild approach to fabricate hierarchical mesoporous Nd_2O_3 nanostructures could be easily scaled up and potentially extended to synthesize other oxide hierarchical structures.     

Dysprosium cerate nanostructures:facile synthesis,characterization,optical and photocatalytic properties

A facile approach was developed to prepare Dy_2Ce_2O_7 nanostructures. Dy_2Ce_2O_7 nanostructures were prepared by applying cerium(IV) ammonium nitrate and dysprosium nitrate as Ce and Dy precursors. It was found that the kind of connecting agent, space-filling template and chelating agent were significant factors for the control in shape and size. Transmission electron microscopy(TEM), X-ray diffraction(XRD), diffuse reflectance UV-vis spectroscopy(DR-UV-vis), field emission scanning electron microscopy(FESEM), photoluminescence spectroscopy(PL) and energy dispersive X-ray microanalysis(EDX) techniques were applied to characterize the Dy_2Ce_2O_7 nanostructures and investigate their optical characteristics. To examine the photocatalytic activity of as-produced Dy_2Ce_2O_7 nanostructures, the photocatalytic degradation of erythrosine dye as water pollutant was carried out. The results of the photocatalytic investigations suggest as-obtained nano-sized Dy_2Ce_2O_7 product as a new, proper and efficient candidate for photocatalytic usages under UV illumination.     

Enhanced photocatalytic activity of Gd~(3+) doped TiO_2 and Gd_2O_3 modified TiO_2 prepared via ball milling method

Gd~(3+)/TiO_2 and Gd_2O_3/TiO_2 nanoparticles were prepared by ball milling method.The effects of Gd~(3+)ion and Gd_2O_3 on the structure and optical property of TiO_2 were studied by XRD and UV-vis DRS.Specific surface area was determined by Brunauer-Emmett-Teller(BET)method.The morphology and elemental composition were characterized by SEM-EDS.XPS was used to determine the surface compositions and chemical character of elements.The sample sizes and microstructures were observed by TEM.The photocatalytic activities of TiO_2 nanoparticles modified with rare earth metal gadolinium(Gd~(3+)ion or Gd_2O_3)were evaluated by degradation of methylene blue(MB)under UV light.Experimental results indicate that 2,5 mol%Gd~(3+)/TiO_2 shows the best photocatalytic activity compared with Gd_2O_3/TiO_2 and pure TiO_2.The existence of gadolinium can exhibit the aggregation and induce lattice distortion of TiO_2 obtained from XRD,SEM and TEM results.The band gap energy of 2.5 mol%Gd~(3+)/TiO_2 decreases to3.07 eV and it leads to visible light absorption response which can be seen from UV-vis absorption spectra.The surface area of 2.5 mol%Gd~(3+)/TiO_2 equals to 85.8 m~2/g and average crystal size is 21.1 nm.EDS and XPS analyses reveal that gadolinium can be introduced either into TiO_2 lattice or adsorbed on the surface of TiO_2.The content of surface OH groups in 2.5 mol%Gd~(3+)/TiO_2 is 50,88%(1.55 times higher than that of pure TiO_2)and the content of lattice oxygen decreases to 11.26%.The MB(25 mg/L)degradation reaction rate constants of 2,5 mol%Gd~(3+)/TiO_2,0.5 mol%Gd_2O_3/TiO_2 and pure TiO_2 were0.0713,0.0588 and 0.0263 min~(-1),respectively.The degradation rates of rhodamine B(30 mg/L)in 60 min are 97,9%,90.1%and 84.6%for 2,5 mol%Gd~(3+)/TiO_2,0.5 mol%Gd_2O_3/TiO_2 and pure TiO_2,respectively.     

AlxGa1-xN/GaN异质结构中二维电子气的磁致子带间散射效应

通过在低温和强磁场下的磁输运测量研究了非故意掺杂Al0．22Ga0.78N／GaN异质结二维电子气(2DEG)的磁电阻振荡现象。观察到了磁致子带间散射(MIS)效应。在极低温下观察到了表征两个子带被2DEG占据的双周期舒勃尼科夫一德哈斯(SdH)振荡。实验观察到MIS效应引起的磁电阻振荡的幅度随温度上升略有减小，振荡的频率为两个子带SdH振荡频率之差。随着温度的升高，MIS振荡成为主要的振荡。由于SdH振荡和MIS振荡对温度的依赖关系不同，实验观察到SdH和MIS振荡之间的调制在温度10和17K之间最为强烈，其它温度下的调制很弱。     

Persistent luminescence from Y_3Al_2Ga_3O_(12) doped with Ce~(3+) and Cr~(3+) after X-ray and blue light irradiation

The persistent luminescence(PersL) dependence on the dopants and derived mechanism of trapping and de-trapping processes were investigated in Y_3Al_2Ga_3O_(12)(YAGG) based nanophosphor,doped with Ce~(3+) and/or Cr~(3+).It is found that the presence of Cr~(3+) ions produce electron and hole traps and capture suitable charge after X-ray irradiation.The effect of irradiation on the carriers trapping and their pathways after excitation was studied by means of thermo luminescence technique.On the other hand,for blue light irradiation the mechanism seems to be different.In the latter case,the Ce~(3+) ions,having the position of energy levels in the conduction band,become sensitizers for the electrons and main emission centres for the PersL(de-trapping process goes through Ce~(3+)).     

Oriented attachment(OA) mediated characteristic growth of Gd_2O_3 nanorods from nanoparticle seeds

Herein, we demonstrated the oriented attachment(OA) driven formation and characterization of Gd_2O_3 nanorods. The nanorods were synthesized via a surfactant free, inexpensive hydrothermal route and considering ~30 nm nanoparticles as the seed. While maintaining a cubic phase throughout the process, complete transformation of Gd_2O_3 nanoparticles to nanorods was found to occur at an elevated temperature(~180 oC) of the hydrothermal reaction. The elongated Gd_2O_3 nanostructures, as revealed from transmission electron microscopic imaging, possessed an average diameter of ~33 nm and an approximate length of 172 nm. From the kinetics of OA process, the activation energy of formation was estimated to be ~25 k J/mole. The existence of defect mediated radiative emission was ascertained from the asymmetric broadening of luminescence spectra. The defect emission arising from the Gd_2O_3 nanorods was nearly 1.4 times stronger than that of nanoparticles. The morphological evolution and growth kinetics were discussed along with the luminescence and electron paramagnetic resonance features.     

Eco-friendly green synthesis of novel magnetic Fe_3O_4/SiO_2/ZnO-Pr_6O_(11) nanocomposites for photocatalytic degradation of organic pollutant

This study reports the successful so nochemical synthesis of novel Fe_3O_4/SiO_2/ZnO-Pr_6O_(11)(Fe/Si/Zn-Pr_6O_(11)) nanocomposites using fructose as a green capping agent.The influence of various parameters containing capping agent,power and time of ultrasound irradiation was investigated to reach optimum morphology and size conditions.The products obtained were characterized by transmission electron microscopy(TEM),UV/Vis diffuse reflectance spectroscopy(DRS),Fourier transform infrared spectra(FT-IR),vibration sample magnetometer(VSM),scanning electron microscopy(SEM),energy dispersive X-ray microanalysis(EDS) and X-ray diffraction(XRD).The Fe_3O_4/SiO_2/ZnO-Pr_6O_(11) nanocomposites display remarkably enhanced photocatalytic activity towards rhodamine b degradation(89.6%)and Congo red(84.7%) under UV irradiation compared with the other products.The results illustrate that the photocatalytic efficiency of magnetic nanocomposites is very much higher than pure Pr_6O_(11)nanostructures.Magnetic photocatalyst still has good stability after five successive runs.So,these recyclable nanocomposites can play a role in the treatment of both industrial and domestic contaminated water.     

Effect of red emitting fluorescent pigment on fluorescent color of SrAl_2O_4:Eu~(2+),Dy~(3+) phosphors

Green-blue fluorescence emitting SrAl_2O_4:Eu~(2+),Dy~(3+) phosphors(SAOED) were coated by SiO_2 and a coumarin type red-emitting fluorescent pigment(FP).The effects of the FP on the morphology,crystal structure,photoluminescence properties and fluorescent color of the SAOED phosphors were systematically investigated by scanning electron microscopy(SEM),FT-IR,X-ray diffraction(XRD),photoluminescence spectra and CIE-1931 chromaticity coordinates characterization.Even though the surface of the SAOED phosphors became rough after being coated with SiO_2 and FP,crystal lattice of SrAl_2O_4 did not have any obvious lattice distortions.The photoluminescence spectra indicated that the SAOED phosphors could be used as the excitation light source to excite the FP to emit red fluorescence.The emission spectrum of the FP-coated SAOED consisted of a broad band with two emission peaks at 520 and 610 nm,and its fluorescence emission color was a mixed color of the SAOED phosphors and FP.The fluorescence color of the SAOED/SiO_2/FP composites tended to transfer to red area with the increase of the FP content varying from 0.1%to 0.9%.     

Microstructure and high-temperature properties of Fe-Ti-Cr-Mo-B-C-Y_2O_3 laser cladding coating

Fe-based composite coatings were fabricated on 5 CrNiMo die steel by laser beam melting a precursor mixture of ferrotitanium,ferrochromium,ferromolybdenum,B4 C and Y_2 O_3 powders.Micro structure and properties of the coatings were studied by X-ray diffraction(XRD),scanning electron microscopy(SEM),energy-dispersive spectrometer(EDS),resistance furnace and high-temperature tribometer.The results show that(Ti,Mo)C particles with flower-like and(Ti,Mo)B_2 with block-like shapes are in situ formed during laser cladding.Volume faction of multiple ceramic particles increases with the increasing of Y_2 O_3.The cumulative oxidation mass of the coating with 2 wt% Y_2 O_3 is decreased by one-third than that of the coating without Y_2 O_3.The oxidation layer of the coating with Y_2 O_3 is getting smooth.Meanwhile,high temperature wear volume loss of the coating with 2 wt% Y_2 O_3 is about 40% that of the coating without Y_2 O_3.The coating with 2 wt% Y_2 O_3 shows a smoother wear scar and few flat grooves are observed after high temperature wear test.     

La~(3+) doped LiCo_(0.25)Zn_(0.25)Fe_2O_4 spinel ferrite nanocrystals:Insights on structural,optical and magnetic properties

This paper addresses the manipulation of structural,morphology,optical and magnetic properties of LiCo_(0.25)Zn_(0.25)Fe_2 O_4 ferrite via incorporation of different proportions of La~(3+) at the expense of iron ions using a sol-gel method.The samples were characterized using the X-ray diffraction technique(XRD),Fourier transform infrared(FT-IR) spectroscopy,the energy dispersive X-ray spectra(EDX),inductively coupled plasma optical emission spectroscopy(ICP-OES),high resolution scanning electron microscopy(SEM),Brunauer-Emmett-Teller(BET) surface area analysis,ultraviolet-diffuse reflectance spectroscopy(UV-DRS),and vibrating sample magnetometer(VSM) technique.The Rietveld refinements of the samples indicate that at higher concentrations of La3+,nanostructures with dual phase,i.e.cubic spinel and orthorhombic LaFeO_3 perovskite with space group(Pbnm) appear.Optical studies show that the energy band gap(E_g) of the bare LiCo_(0.25)Zn_(0.25)Fe_2 O_4 ferrite sample(2.18 eV) reaches up to 2.47 eV at x=0.06 and above this concentration,it drops sharply to 2.00 eV.Although the saturation magnetization and the coercivity of LiCo_(0.25)Zn_(0.25)La_xFe_(2-x)O_4 are lower than that of LiCo_(0.25)Zn_(0.25)Fe_2 O_4 NPs.Overall,the superparamagnetic nature and low values of saturation magnetization and coercivity of LiCo_(0.25)Zn_(0.25)La_xFe_(2-x)O_4 NPs are suitable to be applied in transformers core.