Mn和N共掺ZnO稀磁半导体薄膜的研究

使用对Zn₂N₃:Mn薄膜热氧化的方法成功制备了高含N量的Mn和N共掺ZnO的稀磁半导体薄膜.在没有N离子共掺的情况下，ZnO:Mn薄膜的铁磁性非常微弱；如果进行N离子的共掺杂，就会发现ZnO:Mn薄膜在室温下表现出非常明显的铁磁性，饱和离子磁矩为0.23 μ_B—0.61 μ_B.这说明N的共掺激发了ZnO:Mn薄膜中的室温铁磁性，也就是受主的共掺引起的空穴有利于ZnO中二价Mn离子的铁磁性耦合，这和最近的相关理论研究符合很好. 关键词： 磁性半导体 受主掺杂 空穴媒介的铁磁性     

铁酸钴纳米微粒的共沉淀法制备和磁性质(英)

The cobalt ferrite nanoparticles were prepared by coprecipitation in the presence of poly (N-vinylpyrrolidone) (PVP) and characterized by XRD, TEM, EDX and magnetometry. XRD results suggest the formation of pure cobalt ferrite. The mean particle sizes of CoFe₂O₄ samples annealed at 400 ℃ and 600 ℃ were ca. 6 and 25 nm, respectively as obtained by transmission electron microscopy (TEM). The magnetic measurements indicated that nano-particles obtained at 400 ℃ were superparamagnetic while that prepared at 600 ℃ were ferrimagnetic.     

Structural and Electrical Properties of Single Crystalline Ga-Doped ZnO Thin Films Grown by Molecular Beam Epitaxy

High-quality Ga-doped ZnO （ZnO：Ga） single crystalline films with various Ga concentrations are grown on a- plane sapphire substrates using molecular-beam epitaxy. The site configuration of doped Ga atoms is studied by means of x-ray absorption spectroscopy. It is found that nearly all Ga can substitute into ZnO lattice as electrically active donors, a generating high density of free carriers with about one electron per Ga dopant when the Ga concentration is no more than 2%. However, further increasing the Ga doping concentration leads to a decrease of the conductivity due to partial segregation of Ga atoms to the minor phase of the spinel ZnGa2O4 or other intermediate phase. It seems that the maximum solubility of Ga in the ZnO single crystalline film is about 2at.% and the lowest resistivity can reach 1.92 ×10-4Ω·cm at room temperature, close to the best value reported. In contrast to ZnO：Ga thin film with 1% or 2% Ga doping, the film with 4% Ga doping exhibits a metal semiconductor transition at 80 K. The scattering mechanism of conducting electrons in single crystalline ZnO：Ga thin film is discussed.     

SiO_2基底中MnFe_2O_4纳米晶的制备与表征

在N,N-二甲基甲酰胺(DMF)存在下,以溶胶-凝胶技术成功地制备了无定形二氧化硅基底中均匀分布的MnFe_2O_4纳米晶.由粉末X射线衍射和电子衍射确证了MnFe_2O_4纯相的生成. 由粉末X射线衍射和红外吸收光谱研究了MnFe_2O_4纳米晶形成过程.尖晶石结构的MnFe_2O_4在800℃时开始形成,900℃时基本完成.磁性质测量表明在烧结到900℃的样品中,MnFe_2O_4纳米晶室温具有超顺磁性,78K时为软磁性.1000℃ 和1100℃下得到的样品室温和78K时都具有软磁性.     

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 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.     

共沉淀法制备Co掺杂ZnO的室温铁磁性的研究

利用共沉淀法并在5vol.%H₂/Ar气流中于300 ℃退火3 h，制备了Zn_1-xCo_xO稀磁半导体. 扫描电子微探针分析表明，对Co的名义组分分别为0.05，0.10，0.15的样品，其实际组分分别为x＝0.054， 0.100和0.159. X射线衍射表明, 主相为纤锌矿结构, x=0.100和 0.159的样品中含有CoO杂相. X射线光电子谱显示出Co有３种状态: 替代进入Z 关键词： 稀磁半导体 ZnO 共沉淀法 磁性来源     

单晶和孪晶的Zn0.96Co0.04O稀磁半导体薄膜的制备与研究

采用分子束外延技术分别在不同晶面的蓝宝石（sapphire Al₂O₃）基片上制备了沿c轴生长的Zn_0.96Co_0.04O稀磁半导体薄膜.发现在Al₂O₃（1120）晶面（a面）上薄膜是二维层状外延生长的高质量单晶薄膜，而在Al₂O₃（0001）晶面（c面）上薄膜却具有有趣的孪晶结构，部分区域相互之间有一个30°的面内转动来减少和基片之间的失配度.在孪晶薄膜中存在的这些相互旋转形成的区域界面上会引起载流子强烈的散射作用，导致载流子迁移率的下降和平均自由程的缩短.利用X射线吸收精细结构技术证明了无论单晶还是孪晶的Zn_0.96Co_0.04O薄膜中所有的Co都以+2价替代进入了ZnO的晶格，而没有形成任何杂相.而对其磁性研究发现，孪晶的薄膜样品比高质量的单晶薄膜样品具有大得多的饱和磁矩.这充分说明孪晶薄膜中的铁磁性来源与缺陷有关.我们还对铁磁性耦合机制进行了探讨. 关键词： Co掺杂ZnO 稀磁半导体 X射线吸收精细结构 单晶和孪晶薄膜     

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 30 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.     

Room-Temperature Ferromagnetic ZnMnO Thin Films Synthesized by Plasma Enhanced Chemical Vapour Deposition Method

Room-temperature ferromagnetic Mn-doped ZnO films are grown on Si （001） substrates by plasma enhanced chemical vapour deposition （PECVD）. X-ray diffraction measurements reveal that the Znl-xMn.O films have the single-phase wurtzite structure. X-ray photoelectron spectroscopy indicates the existence of Mn^2＋ ions in Mndoped ZnO films. Furthermore, the decreasing additional Raman peak with increasing Mn-doping is considered to relate to the substitution of Mn ions for the Zn ions in ZnO lattice. Superconducting quantum interference device （SQUID） measurements demonstrate that Mn-doped ZnO films have ferromagnetic behaviour at room temperature.