Zn1-xCoxO稀磁半导体薄膜的结构及其磁性研究

利用X射线吸收精细结构、X射线衍射和磁性测量等技术研究脉冲激光气相沉积法制备的Zn_1-xCo_xO (x＝0.01,0.02)稀磁半导体薄膜的结构和磁性.磁性测量结果表明Zn₁-xCo_xO样品都具有室温铁磁性.X射线衍射结果显示其薄膜样品具有结晶良好的纤锌矿结构.荧光X射线吸收精细结构测试结果表明,脉冲激光气相沉积法制备的样品中的Co离子全部进入ZnO晶格中替代了部分Zn的格点位置,生成单一相的Zn_1-xCo_xO 稀磁半导体.通过对X射线吸收近边结构谱的分析,确定Zn_1-xCo_xO薄膜中存在O空位,表明Co离子与O空位的相互作用是诱导Zn_1-xCo_xO产生室温铁磁性的主要原因. 关键词： 1-xCo_xO稀磁半导体')" href="#">Zn_1-xCo_xO稀磁半导体 X射线吸收精细结构谱 脉冲激光气相沉积法     

稀磁半导体Zn1-xFexO纳米颗粒的光谱研究

利用水热法制备了Zn1-xFexO(x=0,0.01,0.05,0.10和0.20)纳米稀磁半导体材料。由X射线衍射图谱的结果表明,制备的Zn1-xFexO样品为纤锌矿结构,没有金属铁等第二相出现;高分辨透射电子显微镜的结果表明,形貌为分散性良好的纳米颗粒,晶格清晰;拉曼光谱结果表明(E2High)峰位向高频移动,半高宽宽化,峰强减弱;光致发光光谱结果表明,随着Fe离子的掺入,紫外峰向低能移动,光致发光光谱发生了猝灭现象;UV-Vis光谱可看出,光学带隙减小,发生了红移现象。这些结果表明Fe3+成功替代Zn2+进入到ZnO晶格。     

溶胶凝胶法制备Zn1-xFexO稀磁半导体

使用溶胶-凝胶法,制备了Fe掺杂的ZnO粉末衡磁半导体材料。通过X射线衍射对样品的晶格结构进行了分析,发现衍射峰的峰位随着Fe掺杂量出现偏移。当掺杂浓度低于6.66%时,Fe较好地替代了Zn的晶格位置,当掺杂浓度达到6.66%时出现杂相峰。使用超导量子干涉仪对所制备的磁性材料进行表征,得到了材料磁化率随温度变化关系曲线,并观察到明显的低温磁滞现象。对其磁性来源进行了分析。     

Co掺杂ZnO薄膜的局域结构和电荷转移特性研究

采用磁束缚电感耦合等离子体溅射沉积法在不同的氧气分压下制备了Zn_0.95Co_0.05O和Zn_0.94Co_0.05Al_0.01O薄膜.利用X射线吸收精细结构技术对薄膜O-K,Co-K和Co-L边进行了局域结构研究,结果表明：Co²⁺取代了四配位晶体场中的Zn²⁺而未改变ZnO的六方纤锌矿结构,高真空条件下制备的薄膜 关键词： Co掺杂ZnO 稀磁半导体 X射线吸收精细结构 共振非弹性X射线散射     

Mn掺杂ZnO稀磁半导体材料的制备和磁性研究

采用共沉淀方法制备了名义组分为Zn_1-xMn_xO(x=0.001,0.005,0.007,0.01)的Mn掺杂的ZnO基稀磁半导体材料,并研究了在大气气氛下经过不同温度退火后样品的结构和磁性的变化.结果表明：样品在600℃的大气条件下退火后, 仍为单一的六方纤锌矿结构的ZnO颗粒材料;当样品经过800℃退火后,Mn掺杂量为0.007,0.01的样品中除了ZnO纤锌矿结构外还观察到ZnMnO₃第二相的存在.磁性测量表明,大气条件下600℃退火后的样品,呈现出室温铁磁性;而800℃退火后的样品,其室温铁磁性显著减弱,并表现为明显的顺磁性.结合对样品的光致发光谱的分析,认为合成样品的室温铁磁性是由于Mn离子对ZnO中的Zn离子的替代形成的. 关键词： ZnO 掺杂 稀磁半导体 铁磁性     

Zn1-xCoxO稀磁半导体薄膜的结构及其磁性研究

利用X射线吸收精细结构、X射线衍射和磁性测量等技术研究脉冲激光气相沉积法制备的Zn1-zCoxO(x=0.01,0.02)稀磁半导体薄膜的结构和磁性.磁性测量结果表明Zn1-xCoxO样品都具有室温铁磁性.X射线衍射结果显示其薄膜样品具有结晶良好的纤锌矿结构.荧光X射线吸收精细结构测试结果表明,脉冲激光气相沉积法制备的样品中的Co离子全部进入ZnO晶格中替代了部分Zn的格点位置,生成单一相的Zn1-xCoxO稀磁半导体.通过对X射线吸收近边结构谱的分析,确定Zn1-xCoxO薄膜中存在O空位,表明Co离子与O空位的相互作用是诱导Zn1-xCoxO产生室温铁磁性的主要原因.     

稀磁半导体的制备与性质

报道了稀磁半导体的制备、性质与实验研究进展，介绍了稀磁半导体的应用及发展前景．     

N型稀磁半导体Ge_(0.96–x) Bi_xFe_(0.04)Te薄膜的磁电性质研究

GeTe基稀磁半导体材料因具有可独立调控载流子浓度和磁性离子浓度的特性而受到广泛关注.本文利用脉冲激光沉积技术制备了该体系的单晶外延薄膜,并通过高价态Bi元素部分取代Ge元素的方法实现了材料中载流子类型从空穴向电子的转变,即制备出N型GeTe基稀磁半导体.测量结果表明,无论是室温还是低温下的Hall电阻曲线皆呈现负斜率,说明体系中载流子是电子;并且当Bi掺杂量达到32%时,电子浓度为10~(21)/cm~3.变温输运性质的测量证明体系的输运行为呈现半导体特征.通过测量低温10 K下的绝热磁化曲线,在高Bi掺杂体系中观测到了明显的铁磁行为,而低于32%Bi掺杂量的体系中未观察到.这一结果说明,高掺杂Bi的替代导致载流子浓度的增加,促进了载流子传递Ruderman-Kittel-Kasuya-Yoshida相互作用,使得分散的Fe-Fe之间产生磁耦合作用,进而形成铁磁有序态.     

脉冲磁场对水热法制备Mn掺杂ZnO稀磁半导体的影响

本文以Zn(CH₃COO)₂·2H₂O, Mn(CH₃COO)₂·4H₂O和氨水缓冲溶液为原料, 在4 T脉冲磁场下利用水热法制备了Mn掺杂ZnO稀磁半导体晶体, 通过X射线衍射、 扫描电子显微镜、透射电子显微镜、拉曼光谱、荧光分光光度计及振动样品磁强计等对样品的微观结构及磁性能等进行了表征, 结果表明: Mn掺杂ZnO稀磁半导体晶体仍保持ZnO六方纤锌矿结构, 4 T脉冲磁场下合成的Mn掺杂ZnO稀磁半导体晶体具有明显的室温铁磁性, 其饱和磁化强度(M_s)为0.028 emu/g, 比无脉冲磁场下制备的样品提高一倍以上, 且4 T 脉冲磁场将样品的居里温度提高了15 K.     

脉冲磁场下水热法制备Cr掺杂ZnO稀磁 半导体晶体

本文以ZnCl₂, CrCl₃. 6H₂O和氨水缓冲溶液为原料, 在4T脉冲磁场下水热法制备了Cr掺杂ZnO稀磁半导体晶体, 通过X射线衍射分析、扫描电子显微镜观察及采用振动样品磁强计进行磁性分析等, 探讨了脉冲磁场对其微观结构及磁性能的影响. 结果表明: Cr掺杂ZnO稀磁半导体晶体仍保持ZnO的六方纤锌矿结构, 脉冲磁场具有促进晶粒生长及取向排列的作用, 4T脉冲磁场条件下合成的Cr掺杂ZnO稀磁半导体具有良好的室温铁磁性, 其饱和磁化强度(M_s)为0.068 emu/g, 而无脉冲磁场情况下制备的样品室温下呈顺磁性, 并且, 脉冲磁场下制备将稀磁半导体的居里温度提高了16 K.     

Influence of reducing anneal on the ferromagnetism in single crystalline Co-doped ZnO thin films

This paper reports that the high-quality Co-doped ZnO single crystalline films have been grown on $a$-plane sapphire substrates by using molecular-beam epitaxy. The as-grown films show high resistivity and non-ferromagnetism at room temperature, while they become good conductive and ferromagnetic after annealing in the reducing atmosphere either in the presence or absence of Zn vapour. The x-ray absorption studies indicate that all Co ions in these samples actually substituted into the ZnO lattice without formatting any detectable secondary phase. Compared with weak ferromagnetism (0.16~$\mu _{\rm B}$/Co$^{2 + })$ in the Zn6110M, 7550P, 7280E, 7870Dhttp://cpb.iphy.ac.cn/CN/10.1088/1674-1056/19/5/056101https://cpb.iphy.ac.cn/CN/article/downloadArticleFile.do?attachType=PDF&id=111756Co-doped ZnO, diluted magnetic semiconductors, x-ray absorption fine structure, single crystalline thin filmsProject partially supported by National Science Foundation of China (Grant No.~10804017), National Science Foundation of Jiangsu Province of China (Grant No.~BK2007118), Research Fund for the Doctoral Program of Higher Education of China (Grant No.~20070286037), Cyanine-Project Foundation of Jiangsu Province of China (Grant No.~1107020060), Foundation for Climax Talents Plan in Six-Big Fields of Jiangsu Province of China (Grant No.~1107020070) and New Century Excellent Talents in University (NCET-05-0452).This paper reports that the high-quality Co-doped ZnO single crystalline films have been grown on $a$-plane sapphire substrates by using molecular-beam epitaxy. The as-grown films show high resistivity and non-ferromagnetism at room temperature, while they become good conductive and ferromagnetic after annealing in the reducing atmosphere either in the presence or absence of Zn vapour. The x-ray absorption studies indicate that all Co ions in these samples actually substituted into the ZnO lattice without formatting any detectable secondary phase. Compared with weak ferromagnetism (0.16~$\mu _{\rm B}$/Co$^{2 + })$ in the Zn$_{0.95}$Co$_{0.05}$O single crystalline film with reducing annealing in the absence of Zn vapour, the films annealed in the reducing atmosphere with Zn vapour are found to have much stronger ferromagnetism (0.65~$\mu _{\rm B}$/Co$^{2 + })$ at room temperature. This experimental studies clearly indicate that Zn interstitials are more effective than oxygen vacancies to activate the high-temperature ferromagnetism in Co-doped ZnO films, and the corresponding ferromagnetic mechanism is discussed.Co-doped;ZnO;diluted;magnetic;semiconductors;x-ray;absorption;fine;structure;single;crystalline;thin;filmsThis paper reports that the high-quality Co-doped ZnO single crystalline films have been grown on a-plane sapphire substrates by using molecular-beam epitaxy.The as-grown films show high resistivity and non-ferromagnetism at room temperature,while they become more conductive and ferromagnetic after annealing in the reducing atmosphere either in the presence or absence of Zn vapour.The x-ray absorption studies indicate that all Co ions in these samples actually substituted into the ZnO lattice without formatting any detectable secondary phase.Compared with weak ferromagnetism(0.16 μB/Co2+) in the Zn0.95Co0.05O single crystalline film with reducing annealing in the absence of Zn vapour,the films annealed in the reducing atmosphere with Zn vapour are found to have much stronger ferromagnetism(0.65 μB/Co2+) at room temperature.This experimental studies clearly indicate that Zn interstitials are more effective than oxygen vacancies to activate the high-temperature ferromagnetism in Co-doped ZnO films,and the corresponding ferromagnetic mechanism is discussed.     

Structural and electrical properties of single crystalline and bi-crystalline ZnO thin films grown by molecular beam epitaxy

C-oriented ZnO epitaxial thin films are grown separately on the a-plane and c-plane sapphire substrates by using a molecular-beam epitaxy technique. In contrast to single crystalline ZnO films grown on a-plane sapphire, the films grown on c-plane sapphire are found to be bi-crystalline; some domains have a 30o rotation to reduce the large mismatch between the film and the substrate. The presence of these rotation domains in the bi-crystalline ZnO thin film causes much more carrier scatterings at the boundaries, leading to much lower mobility and smaller mean free path of the mobile carriers than those of the single crystalline one. In addition, the complex impedance spectra are also studied to identify relaxation mechanisms due to the domains and/or domain boundaries in both the single crystalline and bi-crystalline ZnO thin films.     

Difference in magnetic properties between Co-doped ZnO powder and thin film

This paper reports that the Zn掺钴;氧化锌粉末;氧化锌薄膜;磁性差异;晶体取向ZnO, Co-doped, crystalline orientation, magnetismProject supported by the Shanghai Nanotechnology Promotion Center (Grant No~0452nm071).2006-09-152006-11-29This paper reports that the Zn0.95Co0.05O polycrystalline powder and thin film were prepared by sol-gel technique under the similar preparation conditions. The former does not show typical ferromagnetic behaviour, while the latter exhibits obvious ferromagnetic properties at 5 K and room temperature. The UV-vis spectra and x-ray absorption spectra show that Co2＋ ions are homogeneously incorporated into ZnO lattice without forming secondary phases.The distinct difference between film and powder sample is the c-axis （002） preferential orientation indicated by the x-ray diffraction pattern and field emission scanning electron microscopy measurement, which may be the reason why Zn0.95Co0.05O film shows ferromagnetic behaviour.     

Co掺杂ZnO薄膜的结构和磁学性能

研究了用单束脉冲激光沉积法制备的Co掺杂ZnO薄膜的结构和磁学性能。XRD表征结果表明制备的薄膜是具有沿c轴择优取向的纤锌矿点阵结构。然而,进一步的高分辨电子显微镜结果显示整个样品上的晶体取向并不完全相同。很难说明形成了单晶。结果分析表明Co占据了部分Zn的格点,并对电子结构产生了影响。室温下观察到了磁滞回线,显示掺杂Co可以实现ZnO的磁性翻转,但磁性比较小。该薄膜与我们以前用双束脉冲激光沉积法制备的Co掺杂ZnO薄膜具有相似的性能,提示我们其内部的机制可能相似。     

Comparative studies on Zn0.95Co0.05O thin films on C- and R-sapphire substrates

Zn0.95Co0.05 O precipitate-free single crystal thin films were synthesized by a dual beam pulsed laser deposition method.The films form a wurtzite structure whose hexagonal axis is perpendicular or parallel to the plane of the surface depending on the C-plane (0001) or R-plane (11 ˉ 20) sapphire substrate.Based on the results of high-resolution transmission electron microscopy and x-ray diffraction,C-plane films show larger lattice mismatch.The films exhibit magnetic and semiconductor properties at room temperature.The coercivity of the film is about 8000 A/m at room temperature.They are soft magnetic materials with small remanent squareness S for both crystal orientations.There is no evidence to show that the anisotropy is fixed to the hexagonal axis (C-axis) for the wurtzite structure.     

Effects of temperature and atmosphere on the magnetic properties of Co-doped ZnO rods

Co-doped ZnO (Zn_0.95Co_0.05O) rods are fabricated by co-precipitation method at different temperatures and atmospheres. X-ray diffraction, Energy dispersive X-ray spectroscopy and Raman results indicate that the samples were crystalline with wurtzite structure and no metallic Co or other secondary phases were found. Raman results indicate that the Co-doped ZnO powders annealed at different temperatures have different oxygen vacancy concentrations. The oxygen vacancies play an important role in the magnetic origin for diluted magnetic semiconductors. At low oxygen vacancy concentration, room temperature ferromagnetism is presented in Co-doped ZnO rods, and the ferromagnetism increases with the increment of oxygen vacancy concentration. But at very high oxygen vacancy concentration, large paramagnetic or antiferromagnetic effects are observed in Co-doped ZnO rods due to the ferromagnetic-antiferromagnetic competition. In addition, the sample annealed in Ar gas has better magnetic properties than that annealed in air, which indicates that O₂ plays an important role. Therefore, the ferromagnetism is affected by the amounts of structural defects, which depend sensitively on atmosphere and annealing temperature.     

氧空位对钴掺杂氧化锌半导体磁性能的影响

从实验和理论上阐述了氧空位对Co掺杂ZnO半导体磁性能的影响.采用磁控溅射法在不同的氧分压下制备了Zn_095Co_005O薄膜,研究了氧分压对薄膜磁性能的影响.实验结果表明,高真空条件下制备的Zn_095Co_005O薄膜具有室温铁磁性,提高氧分压后制备的薄膜铁磁性逐渐消失.第一性原理计算表明,在Co掺杂ZnO体系中引入氧空位有利于降低铁磁态的能量,铁磁态的稳定性与氧空位和Co之间的距离密切相关. 关键词： Co掺杂ZnO 稀磁半导体 第一性原理计算 氧空位缺陷     

Study on field-emission characteristics of electrodeposited Co-doped ZnO thin films

Co-doped ZnO films were fabricated using electrodeposition method on the ITO substrates. The structure of the Co-doped ZnO films was analyzed by X-ray diffraction and scanning electron microscope. The field-emission characteristics of the prepared Co-doped ZnO films were examined using diode structure in a vacuum chamber. The examined results indicate that the Co-doping cause the turn-on field increasing by increasing the concentration of the Co-dopant, probably due to the band gap changing, which could attributed to the sp-d exchange interactions between the band electrons and the localized d electrons of the Co²⁺ ions substituting Zn ions in the films.     

A first-principles study of the magnetic properties in boron-doped ZnO

First-principles calculations based on density functional theory are performed to study the origin of ferromagnetism in boron-doped ZnO. It is found that boron atoms tend to reside at Zn sites. The induced Zn vacancy is a key factor for ferromagnetism in Zn1-xBxO (0相似文献