电化学沉积法制备Co_(0.36)Cu_(0.64)合金纳米线及其磁性

利用电化学沉积的方法制备了具有fcc结构的Co0.36Cu0.64合金纳米线阵列,并对样品在400-700℃进行了退火处理.X-射线衍射及磁测量结果显示,随着退火温度的升高CoCu合金出现相分离,伴随着相分离矫顽力显著增大.综合分析得到矫顽力的增加是由于纳米线中Co和cu的相分离使得一些Co的单畴颗粒分散在Cu之间造成的.     

Magnetoresistance and microstructure evolution upon rapid thermal annealing of giant magnetoresistive Co/Cu/Co/CoNbZr multilayers

The magnetoresistance (MR) variation of Co/Cu/Co/CoNbZr spin valves as a result of rapid thermal annealing has been investigated. MR ratio of 3.8% was obtained in the as-deposited sample and a considerable increase to 6.86% was observed in the 450°C×60 s treated sample. Microstructure studies show that the enhancement of MR ratio is a consequence of the nano-crystallization of amorphous CoNbZr soft layer. The nano-crystallized CoNbZr possess fine and dense microstructure and excellent electrical and soft magnetic properties which leads to the MR enhancement. With increasing annealing temperature or annealing time, interface roughness caused by rapid grain growth decrease the MR ratio rapidly. XRD studies imply that the interfusion of Cu atom into the Co layer is another possible degradation mechanism of Co/Cu/Co/CoNbZr spin valves at annealing temperature beyond 550°C.     

掠射角溅射沉积纳米结构氧化钨薄膜

采用掠射角反应磁控溅射法在室温下沉积了纳米结构氧化钨(WO₃)薄膜, 并对薄膜进行热处理。利用场发射扫描电镜(FE-SEM)和X射线衍射仪(XRD)对氧化钨薄膜的形貌和结构进行了表征。当掠射角度为80°时, 采用直流电源沉积的氧化钨薄膜具有纳米斜柱状结构, 而采用脉冲直流电源沉积的薄膜呈现纳米孔结构。纳米薄膜经450℃热处理3 h后, 纳米斜柱彼此连接, 失去规整结构, 而纳米孔结构的孔尺寸变大。XRD分析表明室温沉积的氧化钨薄膜具有无定形结构, 经450℃热处理1 h后, 转变为单斜晶相。具有纳米斜柱状或纳米孔结构氧化钨薄膜的光学调制幅度在波长600 nm时达到60%, 且电致变色性能可逆。     

Effect of Co Ion Implantation on GMR of [NiFeCo(10 nm)/Ag(10 nm)]×20 Multilayer Film

The composition, phase structure and microstructure of the discontinuous multilayer film [NiFeCo(10 nm)/ Ag(10 nm)]×20 were investigated after Co ion implantation and annealing at 280, 320, 360 and 400℃, respectively. GMR (giant magnetoresistance) ratio of the film with/without Co ion implantation was measured. The results showed that Co ion implantation decreased the granule size of the annealed multilayer film, and increased Hc value and GMR ratio of the multilayer film. After annealing at 360℃, the multilayer film [NiFeCo(10 nm)/Ag(10 nm)]×20 with/without Co ion implantation both exhibited the highest GMR ratio of 12.4%/11% under 79.6 kA/m of applied saturation magnetic field.     

Effect of Co Ion Implantation on GMR of [NiFeCo(10 nm)/Ag(10 nm)] ×20Multilayer Film

The composition, phase structure and microstructure of the discontinuous multilayer film [NiFeCo(10 nm)/Ag(10 nm)]×20 were investigated after Co ion implantation and annealing at 280, 320, 360 and 400℃, respectively.GMR (giant magnetoresistance) ratio of the film with/without Co ion implantation was measured. The results showed that Co ion implantation decreased the granule size of the annealed multilayer film, and increased Hc value and GM R ratio of the multilayer film. After annealing at 360℃, the multilayer film [NiFeCo(10 nm)/Ag(10 nm)] ×20with/without Co ion implantation both exhibited the highest GMR ratio of 12.4%/11% under 79.6 kA/m of applied saturation magnetic field.     

Effect of Cu on the Spinodal Decomposition of AlZn Alloy with Symmetrical Composition

1. IntroductionThe spinodal decomposition, as a method ofmaking ultra-fine microstructure, has recently beenadverted[1~3]. The Al-Zn binary system is the basis ofsome practically important systems among Al-based lightalloys, and a typical example with spinodal decomposi-tion. However, being different from others such as Cr-W with broad temperature range, the miscibility gapof the Al-Zn system remains stable at higher tempera-tures (277~350°C)[4]. The discontinuous precipitation ofthe β Z…     

Characterization of electrodeposited magnetic multilayers

Electrodeposition will prove to be a promising candidate for the preparation of magnetic nanostructures. Multilayered Co/Pt nanostructures grown on a Cu(111) single-crystal substrate by electrodeposition under potential control exhibit a remanent perpendicular magnetization and a large coercivity, which depend on the deposition overpotential and hence the multilayer growth mechanism. Giant magnetoresistance and oscillatory antiferromagnetic interlayer coupling have been observed in a face-centered cubic (fcc) (111) textured Co/Cu multilayered nanostructure. Moreover, a large saturation magnetoresistance of more than 20% has been achieved at room temperature for a heterogeneous Co-Cu alloy, which consists of ultrafine fcc Co-rich clusters in a nonmagnetic Cu matrix     

N掺杂Cu2O薄膜的低温沉积及快速热退火研究

采用氧化亚铜(Cu_2O)陶瓷靶,利用射频磁控溅射沉积法在氮气和氩气的混合气氛下制备了N掺杂Cu_2O(Cu_2O∶N)薄膜,并在N_2气氛下对薄膜进行了快速热退火处理,研究了N_2流量和退火温度对Cu_2O∶N薄膜的生长行为、物相结构、表面形貌及光电性能的影响。结果显示,在衬底温度300℃、N_2流量12sccm条件下生长的薄膜为纯相Cu_2O薄膜;在N_2气氛下对预沉积薄膜进行快速热退火处理不影响薄膜的物相结构,薄膜的结晶质量随退火温度(450℃)的升高而显著改善;快速热退火处理能改善薄膜的结晶质量和缺陷,降低光生载流子的散射,增强载流子的传输,预沉积Cu_2O∶N薄膜经400℃退火处理后展示出较好的电性能,薄膜的霍尔迁移率(μ)为27.8cm~2·V~(-1)·s~(-1)、电阻率(ρ)为2.47×10~3Ω·cm。研究表明低温溅射沉积和快速热退火处理能有效改善Cu_2O∶N薄膜的光电性能。     

Nanoalloying and phase transformations during thermal treatment of physical mixtures of Pd and Cu nanoparticles

Nanoscale alloying and phase transformations in physical mixtures of Pd and Cu ultrafine nanoparticles are investigated in real time with in situ synchrotron-based x-ray diffraction complemented by ex situ high-resolution transmission electron microscopy. The combination of metal–support interaction and reactive/non-reactive environment was found to determine the thermal evolution and ultimate structure of this binary system. At 300 °C, the nanoparticles supported on silica and carbon black intermix to form a chemically ordered CsCl-type (B2) alloy phase. The B2 phase transforms into a disordered fcc alloy at higher temperature (> 450 °C). The alloy nanoparticles supported on silica and carbon black are homogeneous in volume, but evidence was found of Pd surface enrichment. In sharp contrast, when supported on alumina, the two metals segregated at 300 °C to produce almost pure fcc Cu and Pd phases. Upon further annealing of the mixture on alumina above 600 °C, the two metals interdiffused, forming two distinct disordered alloys of compositions 30% and 90% Pd. The annealing atmosphere also plays a major role in the structural evolution of these bimetallic nanoparticles. The nanoparticles annealed in forming gas are larger than the nanoparticles annealing in helium due to reduction of the surface oxides that promotes coalescence and sintering.     

Equilibrium Phase Constituents and Discontinuous Precipitation Behavior of Al-Zn-Cu Alloy with Symmetrical Composition

Through microstructure observation and X-ray diffraction analysis, the equilibrium phase constituents of Al-Zn alloy that contains 2 at. pct Cu at room temperature have been determined as AI-based solid solution (α), Zn-based solid solution and AlCu3Zn phase (T′-phase), which are different from α phase, Zn phase and CuZn4 phase originally believed. It is determined that the products of discontinuous precipitation transformation below 277℃ are not the equilibrium phase constituents, but the metastable phases made up of α phase, Zn phase and CuZn4 phase. The phase constituents after discontinuous precipitation of AlZn-2Cu alloy would transform to the ones in equilibrium status: Al-based solid solution (α) in fcc structure, Zn-based solid solution in hcp structure and Al4Cu3Zn phase (T′-phase) ultimately through plastic deformation at room temperature and re-heating treatment below 277℃.     

磁控溅射法制备CIGS薄膜太阳能电池的工艺及性能研究

采用磁控溅射方法直接溅射铜铟镓硒(CIGS)靶材,制备得到了用于太阳能电池吸收层的CIGS薄膜,然后在Se气氛中对该CIGS薄膜进行退火处理。采用扫描电镜、X射线衍射、Raman、XRF、Hall等方法观察和分析了退火的主要工艺参数对薄膜表面形貌、组织结构、成分以及电学性能的影响,并制备了CIGS太阳能电池。结果表明,采用磁控溅射CIGS靶材+Se气氛中退火处理的方法,可以制备得到成分均匀、电学性能优良、单一黄铜矿相的CIGS薄膜;退火温度和退火时间是影响退火后薄膜质量的主要因素。退火温度低于350℃时,退火效果不明显。退火温度在400℃,退火时间达120 min时,薄膜完成再结晶过程,并制得单一黄铜矿相的CIGS薄膜;退火过程存在Cu-Se二次相的析出和消融,同时具有为薄膜补Se的作用。本文采用该方法制备出的CIGS太阳能电池的最高转换效率为7.69%。     

TMR at 4.2 K for Amorphous Magnetic-Tunnel-Junctions with Co60Fe20B20 as Free and Pinned Layers

Single barrier magnetic-tunnel-junctions (MTJs) with the layer structure of Ta(5)/Cu(30)/Ta(5)/Ni79Fe21(5)/Ir22Mn78(12)/Co60Fe20B20(4)/Al(0.8)-oxide/Co60Fe20B20(4)/Cu(30)/Ta(5) [thickness unit: nm] using the amorphous Co60Fe20B20 alloy as free and pinned layers were micro-fabricated. The experimental investigations showed that the tunnel magnetoresistance (TMR) ratio and the resistance decrease with increasing dc bias voltage from 0 to 500~mV or with increasing temperature from 4.2 K to RT. A high TMR ratio of 86.2% at 4.2 K, which corresponds to the high spin polarization of Co60Fe20B20 55%, was observed in the MTJs after annealing at 270℃ for 1 h. High TMR ratio of 53.1%, low junction resistance-area product RS of 3.56 kΩμm2, small coercivity Hc of ≤4 Oe, and relatively large bias-voltage-at-half-maximum TMR with the value V1/2 of greater than 570 mV at RT have been achieved in such Co-Fe-B MTJs.     

86% TMR at 4.2 K for Amorphous Magnetic-Tunnel-Junctions with Co60Fe20B20 as Free and Pinned Layers

Single barrier magnetic-tunnel-junctions (MTJs) with the layer structure of Ta(5)/Cu(30)/Ta(5)/Ni79Fe21(5)/Ir22 Mn78(12)/Co60Fe20B20(4)/Al(0.8)-oxide/Co60Fe20B20(4)/Cu(30)/Ta(5) [thickness unit: nm] using the amorphous Co60Fe20B20 alloy as free and pinned layers were micro-fabricated. The experimental investigations showed that the tunnel magnetoresistance (TMR) ratio and the resistance decrease with increasing dc bias voltage from 0 to 500 mV or with increasing temperature from 4.2 K to RT. A high TMR ratio of 86.2% at 4.2 K, which corresponds to the high spin polarization of Co60Fe20B20, 55%, was observed in the MTJs after annealing at 270℃for 1 h. High TMR ratio of 53.1%, low junction resistance-area product RS of 3.56 kΩμm2, small coercivity HC of ≤4 Oe, and relatively large bias-voltage-at-half-maximum TMR with the value V1/2 of greater than 570 mV at RT have been achieved in such Co-Fe-B MTJs.     

Growth and characterisation of electrodeposited Co/Cu superlattices

Ferromagnetic/non-ferromagnetic Co/Cu superlattices were grown on polycrystalline Titanium (Ti) from a single electrolyte by electrodeposition. Microstructure and magnetoresistance (MR) of the superlattices were investigated as a function of the electrolyte pH as well as the layer thicknesses. Structural characterisation by X-ray diffraction (XRD) showed that the superlattices have face-centred cubic (fcc) structure with a strong (111) texture at the studied pH levels, but the texture degree is affected by the electrolyte pH. The scanning electron microscope (SEM) studies revealed that the superlattices grown at low pH (2.0) have smoother surfaces compared to those grown at high pH (3.0). The superlattices exhibited either anisotropic magnetoresistance (AMR) or giant magnetoresistance (GMR) depending on the Cu layer thickness. The shape of MR curves changes depending on the combination of Co and Cu layer thicknesses. The superlattices with Co layers less than 3 nm and Cu layers less than 2 nm have broad and non-saturating curves, indicating the predominance of a superparamagnetic contribution, possibly due to the discontinuous nature of the ferromagnetic (Co) layer. For superlattices with the same bilayer and total thicknesses, the GMR magnitude decreased as the electrolyte pH increased. Besides possible structural differences such as the texture degree and the surface roughness, this may arises from the variation in the Cu content of the ferromagnetic layers caused by the electrolyte pH.     

Sol-gel法制备多铁性Bi_(0.85)Eu_(0.15)FeO_3薄膜及其性能

采用Sol-gel法在Pt/Ti/SiO2/Si衬底上制备了Bi0.85Eu0.15FeO3薄膜。研究了退火温度对其晶相形成的影响,发现在较低温度退火(450℃)时,Bi0.85Eu0.15FeO3晶相开始形成,但存在杂相,而且结晶度较差;在490～600℃可以获得结晶较好的单相Bi0.85Eu0.15FeO3薄膜。同时对经550℃退火的薄膜的介电、铁电和铁磁性能进行了研究,结果表明,Bi0.85Eu0.15FeO3薄膜具有较好的介电及铁磁性能。当测试频率为1MHz时,薄膜的介电常数和介电损耗分别为80、0.024,饱和磁化强度约为26.2emu/cm3。     

退火温度对SmCo永磁薄膜微结构及磁性能的影响

采用直流磁控溅射法制备SmCo薄膜,研究了退火温度对薄膜微结构及磁性能的影响。XRD分析结果表明,当退火温度为600℃时,SmCo5相析出,而Sm2Co17相在700℃析出。SEM照片可看出,退火温度高于900℃时,六方柱状的SmCo5相和菱方状的Sm2Co17相全部析出。随着退火温度的升高,晶粒尺寸增大,当温度达940℃时,晶粒尺寸减小,而在980℃时,晶粒尺寸又将增大。VSM测试表明,与制备态的薄膜相比,退火后的薄膜在垂直于膜面方向的矫顽力、剩余磁化强度及最大磁能积都增大。960℃时得到矫顽力和剩余磁化强度的最大值,800℃时得到最大磁能积的最大值。     

Evolution of surface roughness parameters and microstructure in two-phase nanocrystalline Co–Cu films electrodeposited onto ITO coated glass substrates at different deposition potentials

In the present research, we have studied the effect of deposition potential on the film composition, structural, and morphological properties of the electrodeposited Co–Cu thin films grown onto indium tin oxide coated glass substrates. For this purpose, the properties of the films were analyzed by means of X-ray diffraction, energy dispersive X-ray spectroscopy (EDX), and atomic force microscopy (AFM) characterization techniques. Structural characterizations showed that all of the Co–Cu films consist of hexagonal close-packed (hcp) Co and face-centered cubic (fcc) Cu phases. The hcp Co (002)/fcc Cu (111) peak intensity ratio was found to increase as the deposition potential decreased towards more negative values. An increase in the Co content in the Co–Cu films was observed as the applied deposition potential was made more negative according to EDX analysis. The decrease of the applied deposition potential towards more negative values also induced a decrease in the average crystallite sizes of both Co and Cu particles. AFM study indicated that a granular structure of the electrodeposited Co–Cu films regardless of deposition potential. As the applied deposition potential was made more negative, the surface roughness and particle size decreased considerably. Besides, two additional roughness parameters, surface kurtosis and the surface skewness were also obtained and discussed by means of the obtained results under the study.     

Mechanically Driven Alloying and Structural Evolution of Nanocrystalline Fe_(60)Cu_(40) Powder

Highly supersaturated nanocrystalline fcc Fe60Cu40 alloy has been prepared by mechanical alloying of elemental powders. The phase transformation is monitored by X-ray diffraction (XRD),Mossbauer spectroscopy and extended X-ray absorption fine structure (EXAFS). The powder obtained after milling is of single fcc structure with grain size of nanometer order. The Mossbauer spectra of the milled powder can be fitted by two subspectra whose hyperfine magnetic fields are 16 MA/m and 20 MA/m while that of pure Fe disappeared. EXAFS results show that the radial structure function (RSF) of Fe K-edge changed drastically and finally became similar to that of reference Cu K-edge, while that of Cu K-edge nearly keeps unchanged in the process of milling. These imply that bcc Fe really transforms to fcc structure and alloying between Fe and Cu occurs truly on an atomic scale. EXAFS results indicate that iron atoms tend to segregate at the boundaries and Cu atoms are rich in the fcc lattice. Annealing experiments show that the Fe atoms at the interfaces are easy to cluster to α-Fe at a lower temperature, whereas the iron atoms in the lattice will form γ-Fe first at temperature above 350℃, and then transform to bcc Fe     

Microstructural dependence of giant-magnetoresistance in electrodeposited Cu-Co alloys

The relationship between the microstructure and the magnetic properties of heterogeneous Cu-Co [Cu92.5-Co7.5] (at.%) thin films prepared by electrodeposition was studied. Electron spectroscopic imaging (ESI) studies clearly revealed the evolution of the cobalt microstructure as a function of thermal treatments. The as-deposited film is composed of more than one phase; metastable Cu-Co, copper and cobalt. During annealing the metastable phase decomposes into two fcc phases; Cu and Co. Grain growth occurs with increasing annealing duration, such that the cobalt grains are more homogeneously distributed in the copper matrix. A maximum GMR effect was found after annealing at 450°C for 1.5 h, which corresponds to an average cobalt grain size of 5.5 nm according to magnetization characterization. A significant fraction of the cobalt in the Cu-Co film did not contribute to the GMR effect, due to interactions between the different magnetic grains and large ferromagnetic (FM) grains. The percolation threshold of cobalt in metastable Cu-Co alloys formed by electrodeposition is lower (less than 7.5 at.%) than that prepared by physical deposition methods (35 at.%).     

Effects of supercooling and cooling rate on the microstructure of Cu–Co–Fe alloys

The effects of supercooling and cooling rate on the microstructure of ternary Cu–Fe–Co alloys were investigated. Electromagnetic levitation was used to supercool the liquids down by 180 K. Alloys with 11 at.% Cu and less than 19 at.% Fe contained fcc (Fe, Co) and fcc Cu phases; those with 19 to 23 at.% Fe contained bcc (Fe, Co), fcc (Fe, Co) and fcc Cu; those with more than 23 at.% Fe contained bcc (Fe, Co) and fcc Cu. The primary dendrites contained 10 to 20 at.% Cu, with Fe and Co contents depending on the alloy composition. Supercooling the melt below a certain temperature resulted in metastable separation of the melt into two liquids, one (Co + Fe)-rich, the other Cu-rich. The metastable phase separation temperatures and the two liquid compositions were determined experimentaly, and compared with calculated ones. Isothermal cross-sections at various temperatures were constructed for stable and metastable cases based on thermodynamic and experimental data of the Cu–Co, Cu–Fe, and Co–Fe systems. A peritectic reaction for the ternary alloys was found at approximately 1100°C.