Al/ZnO/Al薄膜的结构与磁性分析

采用直流磁控溅射的方法制备了Al/ZnO/Al纳米薄膜,并对薄膜分别在真空及空气中进行退火处理.利用X射线衍射仪(XRD)和物理性能测量仪(PPMS)分别对薄膜样品的结构和磁性进行了表征.XRD分析表明,不同的退火氛围对薄膜的微结构有着很大的影响.采用了一种新的修正方法对磁测量结果进行修正,计算了基底拟合误差的最大值,并对修正后样品的磁性进行了分析.结果显示,室温铁磁性可能与Al和ZnO基体之间发生的电荷转移以及在不同退火氛围下Al在ZnO晶格中的地位变化有关. 关键词： Al/ZnO/Al薄膜 铁磁性 磁性表征     

Al掺杂ZnO薄膜的厚度对其结构及磁学性能的影响

采用直流磁控共溅的方法在玻璃基底上制备了不同厚度的Al掺杂ZnO薄膜,并在真空和空气中分别退火.利用X射线衍射仪(XRD)和物理性能测量仪(PPMS)对系列薄膜的结构和磁性进行了表征.XRD结果显示:随着膜厚的增加,晶粒尺寸逐渐增大,薄膜的内应力逐渐减小.在空气退火的薄膜样品中观察到了室温的铁磁性,薄膜的饱和磁化强度M_s 随着膜厚的增加而增大,而矫顽力H_c却随着膜厚的增加而减小. 关键词： Al掺杂ZnO薄膜 薄膜厚度 应力 铁磁性     

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     

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     

Co掺杂的ZnO室温铁磁半导体材料制备与磁性和光学特性研究

采用溶胶-凝胶法制备出具有室温铁磁性的Co掺杂的ZnO稀磁半导体材料. 通过对样品的结构、磁性和发光特性的研究发现,样品具有室温铁磁性,并发现其铁磁性源于磁性离子对ZnO中Zn离子的取代. 对不同温度制备的样品的磁性以及其发光特性的变化研究发现,样品的铁磁性与样品中锌间隙位（Zn_i）缺陷的密度有关. 关键词： ZnO 稀磁半导体 铁磁性     

H掺杂对ZnCoO稀磁半导体薄膜结构及磁性能的影响

利用磁控溅射法,采用亚分子分层掺杂技术交替溅射Co靶和ZnO靶,在Si衬底上制备了不同氢氩流量比的H:ZCO薄膜样品,研究了氢氩流量比对薄膜结构特性和磁学性能的影响。所制备的薄膜样品具有c轴择优取向。由于H对表面和界面处悬挂键的钝化作用,随H₂流量比的增加,薄膜的择优取向变差。磁性测量结果显示,薄膜样品的铁磁性随着氢氩流量比的增大而增强。XPS结果表明,随着H含量的增大,金属态Co团簇的相对含量逐渐增加,而氧化态Co离子的相对含量逐渐减小。H:ZCO样品中的铁磁性可能来源于Co金属团簇,H的掺入促使ZnO中的Co离子还原成Co金属团簇,从而增强了薄膜样品的室温铁磁性。     

(Cu,Al)掺杂ZnO薄膜表面处缺陷的拉曼光谱研究

采用电感耦合等离子体增强物理气相沉积法制备了(Cu,Al)掺杂ZnO薄膜,超导量子干涉磁强计测试结果表明,薄膜具有室温的铁磁性。采用激光共聚焦拉曼(Raman)光谱研究了(Cu,Al)掺杂ZnO薄膜的表面特性,以两种处理方式对薄膜进行了Raman光谱测试:共聚焦模式从薄膜表面开始至不同深度处进行测试;对薄膜样品进行预处理加工,采用面扫描模式在薄膜平面对(Cu,Al)掺杂ZnO薄膜的斜面进行测试。分析了Raman光谱A₁(LO)峰的中心位置和强度变化,结果表明,界面处晶格应力和缺陷明显增强。这些晶格畸变和点缺陷的存在会对体系的铁磁性有促进作用。     

脉冲激光沉积法（PLD）生长Co掺杂ZnO薄膜及其磁学性能

采用脉冲激光沉积(PLD)法在单晶Si(100)及石英衬底上生长Co掺杂ZnO薄膜,并且比较了不同生长条件下薄膜的性能。实验观察到了700℃、0.02Pa氧压气氛下生长的Co掺杂ZnO薄膜显示室温磁滞回线。采用XRD、SEM等手段对Co掺杂ZnO薄膜的晶体结构及微观形貌进行了分析,得到的ZnO薄膜具有高度的c轴择优取向,结构比较致密,表面平整度较高,并且没有发现Co的相关分相,初步表明Co有效地掺入了ZnO的晶格当中。霍尔测试表明Co掺杂ZnO薄膜样品保持了半导体的电学性能,电阻率为0.04Ω·cm左右,载流子浓度约为1018/cm3,迁移率都在18.7cm2/V·s以上。实验结果表明材料保持了ZnO半导体的性能,并具有室温铁磁性。     

Sn掺杂ZnO薄膜的室温气敏性能及其气敏机理

采用化学气相沉积方法在预制好电极的玻璃基底上制备出Sn掺杂ZnO薄膜和纯ZnO薄膜. 两种样品典型的形貌为四足状ZnO晶须, 其直径约为150-400 nm, 呈疏松状结构. 气敏测试结果显示Sn掺杂ZnO薄膜具有优良的室温气敏性, 并对乙醇具有良好的气敏选择性, 而纯ZnO薄膜在室温条件下对乙醇和丙酮均没有气敏响应. X射线衍射结果表明两种样品均为六方纤锌矿结构. Sn掺杂ZnO样品中没有出现Sn及其氧化物的衍射峰, 其衍射结果与纯ZnO样品对比, 衍射峰向小角度偏移. 光致发光结果表明, Sn掺杂ZnO薄膜与纯ZnO薄膜均出现紫外发光峰和缺陷发光峰, 但是Sn的掺杂使得ZnO的缺陷发光峰明显增强. 将Sn掺杂ZnO样品在空气中退火后, 其室温气敏性消失, 说明Sn掺杂ZnO样品的室温气敏性可能与其缺陷含量高有关. 采用自由电子散射模型解释了Sn掺杂ZnO薄膜的室温气敏机理.     

Co掺杂的ZnO稀磁半导体块体的退火热处理研究

采用固相反应法制备了Zn_0.95Co_0.05O块体样品,并对其进行了不同方式的退火处理.实验表明在锌气氛中500℃退火的样品表现出铁磁性,而在真空中退火的样品却没有磁性,进一步,在锌气氛中1100℃退火的样品虽然表现出铁磁性,但其铁磁性来源于样品在锌气氛中1100℃退火过程中产生了1%左右的Co金属团簇杂质相.另外,在低温时所有样品都表现出较大的正磁电阻,认为正磁电阻效应是由于s-d电子交换相互作用引起的自旋劈裂造成的,而高场时出现的负磁电阻效应则可能归因于磁场 关键词： Co掺杂ZnO X射线衍射 铁磁性 磁电阻     

Two magnetic regimes in doped ZnO corresponding to a dilute magnetic semiconductor and a dilute magnetic insulator

Films of ZnO doped with magnetic ions Mn and Co and, in some cases, with Al have been fabricated with a very wide range of carrier densities. Ferromagnetic behavior is observed in both insulating and metallic films, but not when the carrier density is intermediate. Insulating films exhibit variable range hopping at low temperatures and are ferromagnetic at room temperature due to the interaction of the localized spins with static localized states. The magnetism is quenched when carriers in the localized states become mobile. In the metallic (degenerate semiconductor) range, robust ferromagnetism reappears together with very strong magneto-optic signals and room temperature anomalous Hall data. This demonstrates the polarization of the conduction bands and indicates that, when ZnO is doped into the metallic regime, it behaves as a genuine magnetic semiconductor.     

磁控溅射法制备钴掺杂氧化锌薄膜室温磁学性质

钴掺杂氧化锌是室温稀磁半导体的重要候选材料,其磁学特性和钴掺杂浓度、显微结构及光学性质密切相关。磁控溅射具有成本低、易于大面积沉积高质量薄膜等特点,是广受关注的稀磁半导体薄膜制备方法。利用磁控溅射方法制备了不同浓度的钴掺杂氧化锌薄膜,并对其显微结构、光学性质和磁学特性进行了系统分析。结果表明:当掺杂原子分数在8%以内时,钴掺杂氧化锌薄膜保持单一的铅锌矿晶体结构,钴元素完全溶解在氧化锌晶格之中;薄膜在可见光区域有很高的透射率,但在567, 615和659 nm处有明显吸收峰,这些吸收峰源于Co2+处于O2-形成的四面体晶体场中的特征d-d跃迁。磁学特性测试结果表明钴掺杂氧化锌薄膜具有室温铁磁性,且钴的掺杂浓度对薄膜的磁学特性有重要影响。结合薄膜结构、光学和电学性质分析,实验中观察到的室温铁磁性应源于钴掺杂氧化锌薄膜的本征属性,其铁磁耦合机理可由束缚磁极化子模型进行解释。     

ZnO-Fe3O4 composite prepared by sol-gel method with H2 deoxidation

Fe doped ZnO powder samples (Fe/Zn=0.05 and 0.1) were prepared by sol-gel method with H₂ deoxidation at 450 ^°C for several hours or just heated in air at the same temperature. It was showed by vibrating sample magnetometer (VSM) that samples heat treated in H₂ could show strong ferromagnetism at room temperature while samples treated in air only show very weak magnetism. XRD using Co kα X-ray revealed that the samples heated in H₂ were not pure phase but like a granular system and the magnetism mainly results from Fe₃O₄ in samples while samples heated in air showed pure ZnO phase. Our work indicated that H₂ deoxidation treatment may be an effective technique to fabricate such magnetic semiconductor-like materials with Curie temperature higher than room temperature.     

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.     

The dopant concentration and annealing temperature dependence of ferromagnetism in Co-doped ZnO thin films

A series of Zn_1−xCo_xO thin films with the atomic fraction, x, in the range of 0.03–0.10 were deposited on glass substrates at room temperature by magnetron co-sputtering technique and subsequently coupled with the post-annealing treatment for half hour at different temperatures (350 °C and 500 °C) under vacuum. A systematic study was done on the structural, optical and magnetic properties of Zn_1−xCo_xO thin films as a function of Co concentration and annealing temperature. X-ray diffraction and UV–vis spectroscopy results indicated that there are not any secondary phases and Co²⁺ substituted for Zn²⁺ of ZnO host. Magnetic hysteresis loops were observed at room temperature, indicating that both the as-deposited samples and the annealed ones exhibit the room temperature ferromagnetism. It was also found that the magnetic saturation moment per Co atom decreases with increasing Co concentration, while the post-annealing treatment can enhance the magnetic moment of the films effectively.     

Temperature dependent carrier induced ferromagnetism in Zn(Fe)O and Zn(FeAl)O thin films

Epitaxial films of ZnO doped with magnetic ion Fe and, in some cases, with 1% Al show clear evidence of room temperature ferromagnetic ordering but containing huge amount of paramagnetic moment in it. The total ferromagnetic and paramagnetic contributions have been extracted from the low temperature SQUID measurements. A clear correlation between the magnetization per transition metal ion and the ratio of the number of carriers and number of donors have been found in these films and established the theory of carrier induced ferromagnetism. The experimental data has been best explained through the modification of electronic structure of oxide semiconductors with impurity states.     

N掺杂SiO2纳米薄膜的制备及其磁性

利用射频磁控反应溅射技术,制备了氮掺杂的SiO₂纳米薄膜.发现N掺杂SiO₂体系纳米薄膜具有铁磁性.较小的氮化硅颗粒均匀分布在氧化硅基质中有利于磁有序的形成.基底温度为400℃时,样品薄膜具有最大的饱和磁化强度和矫顽力,分别为35 emu/cm³和75 Oe.薄膜的磁性可能产生于氮化硅和氧化硅的界面.理论计算表明,N掺杂SiO₂体系具有净自旋.同时,由氮化硅和氧化硅界面之间的电荷转移导致的轨道磁矩也会对样品的磁性有贡献 关键词： 2薄膜')" href="#">N掺杂SiO₂薄膜 射频磁控反应溅射 界面磁性 基底温度     

Room-temperature anomalous Hall effect and magnetroresistance in (Ga, Co)-codoped ZnO diluted magnetic semiconductor films

This paper reports that the(Ga,Co)-codoped ZnO thin films have been grown by inductively coupled plasma enhanced physical vapour deposition.Room-temperature ferromagnetism is observed for the as-grown thin films.The x-ray absorption fine structure characterization reveals that Co 2+ and Ga 3+ ions substitute for Zn 2+ ions in the ZnO lattice and exclude the possibility of extrinsic ferromagnetism origin.The ferromagnetic(Ga,Co)-codoped ZnO thin films exhibit carrier concentration dependent anomalous Hall effect and positive magnetoresistance at room temperature.The mechanism of anomalous Hall effect and magneto-transport in ferromagnetic ZnO-based diluted magnetic semiconductors is discussed.