质子辐照下Mo/Si多层膜反射镜的微观结构状态

利用透射电子显微镜对质子辐照前后空间太阳望远镜Mo/Si多层膜的微观结构进行了表征, 并对其辐照前后反射率的变化进行了测量.研究表明, Mo/Si多层膜经质子辐照后形成了一些缺陷结构,局部区域Mo/Si的周期性遭到破坏, Mo层与Si层的宽度发生了变化,多层膜层与层之间的界面也比辐照前更为粗糙,部分层状结构由于质子辐照发生了明显的扭曲和折断等现象;此外,质子辐照导致了Mo/Si多层膜反射率的下降,这些微观缺陷的形成是光学性能降低的直接诱因. 关键词： 空间太阳望远镜 Mo/Si多层膜 微观结构 反射率     

研究扩散屏障层对Mo/Si多层膜软X射线反射率影响的模拟

在特定波长下,用四层结构模型模拟了Mo/Si多层膜的软X射线反射率.研究了扩散屏障层dMo-on-Si和dSi-on-Mo对Mo/Si多层膜软X射线反射率的影响.研究发现,扩散屏障层并不总是损害Mo/Si多层膜的光学性能,通过合理设计dMo-on-Si和dSi-on-Mo厚度,增加dMo-on-Si与dSi-on-Mo的比值,也能提高多层膜的软X射线反射率.     

低温退火的X射线W/Si多层膜应力和结构性能

W/Si多层膜反射镜在硬X射线天文望远镜中有重要应用. 为减小其应力对反射镜面形和望远镜分辨率的影响, 同时保证较高的反射率, 采用150, 175和200 ℃ 的低温退火工艺对采用磁控溅射镀制的W/Si周期多层膜进行后处理. 利用掠入射X射线反射测试和样品表面面形测试对退火前后W/Si多层膜的应力和结构进行表征. 结果表明, 在150 ℃ 退火3 h 后, 多层膜1级峰反射率和膜层结构几乎没有发生变化, 应力减少约27%; 在175 ℃ 退火3 h后, 多层膜膜层结构开始发生变化, 应力减少约50%; 在200 ℃退火3 h 后, 多层膜应力减小超过60%, 但1级布拉格峰反射率相对下降17%, 且膜层结构发生了较大变化. W, Si界面层的增大和相互扩散加剧是应力和反射率下降的主要原因.     

磁控溅射法合成纳米β-FeSi2/a-Si多层结构

β-FeSi₂作为一种环境友好的半导体材料，颗粒化及非晶化正在成为提高其应用性能和改善薄膜质量、膜基界面失配度的有效途径.利用射频磁控溅射法在单晶Si基体上沉积Fe/Si多层膜，合成纳米β-FeSi₂/Si多层结构.通过透射电子显微镜、高分辨电子显微术等分析手段，研究了多层结构和制备工艺之间的相互关系.研究结果表明，采用磁控溅射Fe/Si多层膜的方法，不需要退火就可以直接沉积得到β-FeSi₂相小颗粒.β-FeSi₂相 关键词： 2')" href="#">β-FeSi₂ 磁控溅射 透射电子显微镜 半导体薄膜     

入射光单色性与界面粗糙度对多层膜反射性能的不同影响

多层膜界面粗糙度、入射光单色性对软X射线多层膜实际反射率均有影响。利用数学卷积积分,理论上推导出一个在入射光不同单色性下精确计算多层膜反射率的公式。利用给出的理论计算公式,简要分析了入射光不同单色性、不同界面粗糙度对Mo/Si多层膜反射率的影响。理论分析发现这两种因素对Mo/Si多层膜反射率影响完全不同:入射光低的单色性不但极大降低Mo/Si多层膜峰值反射率,而且使反射曲线的半峰全宽增加;而界面粗糙度是降低Mo/Si多层膜反射曲线上各点对应值,基本不改变Mo/Si反射曲线的半峰全宽,不改变反射曲线的形状。说明这两个因素在软X射线的长波段对多层膜反射性能的影响不同。     

硅衬底生长的InGaN/GaN多层量子阱中δ型硅掺杂n-GaN层对载流子复合过程的调节作用

为了解决在单晶硅衬底上生长的InGaN/GaN多层量子阱发光二极管器件发光效率显著降低的问题,使用周期性δ型Si掺杂的GaN取代Si均匀掺杂的GaN作为n型层释放多层界面间的张应力。采用稳态荧光谱及时间分辨荧光谱测量,提取并分析了使用该方案前后的多层量子阱中辐射/非辐射复合速率随温度（10~300 K）的变化规律。实验结果表明引入δ-Si掺杂的n-GaN层后,非辐射复合平均激活能由（18±3）meV升高到（38±10）meV,对应非辐射复合速率随温度升高而上升的趋势变缓,室温下非辐射复合速率下降,体系中与阱宽涨落有关的浅能级复合中心浓度减小,PL峰位由531 nm左右红移至579 nm左右,样品PL效率随温度的衰减受到抑制。使用周期性δ型Si掺杂的GaN取代Si均匀掺杂的GaN作为生长在Si衬底上的InGaN/GaN多层量子阱LED器件n型层,由于应力释放,降低了多层量子阱与n-GaN界面、InGaN/GaN界面的缺陷密度,使得器件性能得到了改善。     

极紫外多层膜残余应力初步研究

 针对极紫外多层膜在激光等离子体诊断、极紫外光刻等方面的应用,进行了Mo/Si多层膜残余应力的实验研究,讨论了多层膜残余应力的成因。实验结果表明：Mo单层膜表现为张应力, Si单层膜表现为压应力;通过传统方法制备的13.0 nm处高反射率的40对Mo/Si多层膜会产生-500 MPa左右的压应力,其压应力主要是由膜层之间的贯穿扩散引起的;通过改变膜层比率可以在一定程度上补偿因贯穿扩散产生的压应力,但是以牺牲多层膜反射率为代价。     

小波变换表征多层膜氧化层、界面层和膜厚漂移

用小波变换的方法分析了纳米多层膜的X射线掠入射反射率测试曲线.从小波变换的自相关函数峰位和峰强度信息中得到了常规曲线拟合方法难以表征的含有氧化层、界面层或厚度漂移的多层膜结构,利用其作为多层膜的初始结构再进行常规的曲线拟合,可实现多层膜结构精确表征的目的.研究成功地鉴别出钒单层膜的表面存在约3 nm厚的氧化层,分析得到Mo/Si多层膜的界面纯粗糙度约0.42 nm,表明在Ni/C多层膜中接近表面和基底的膜层存在大于5%的厚度漂移.     

磁控溅射Fe/Mo多层膜的巨磁电阻及层间耦合

研究了DC/RF磁控溅射Fe/Mo多层膜的磁电阻特性.在反铁磁性耦合的样品中,观察到了磁电阻比率约为12%的巨磁电阻效应.当Mo层厚度改变时,还观察到了周期约为1.0—1.2nm的层间耦合振荡.另外,F/Mo多层膜的磁电阻比率不仅随Mo层厚度改变出现振荡,而且与Fe层厚度的改变也有着很强的依赖关系. 关键词：     

磁控溅射法合成纳米β-FeSi2/a-Si多层结构

β-FeSi2作为一种环境友好的半导体材料,颗粒化及非晶化正在成为提高其应用性能和改善薄膜质量、膜基界面失配度的有效途径.利用射频磁控溅射法在单晶Si基体上沉积Fe/Si多层膜,合成纳米β-FeSi2/Si多层结构.通过透射电子显微镜、高分辨电子显微术等分析手段,研究了多层结构和制备工艺之间的相互关系.研究结果表明,采用磁控溅射Fe/Si多层膜的方法,不需要退火就可以直接沉积得到β-FeSi2相小颗粒.β-FeSi2相颗粒尺寸在20 nm以下,小的颗粒尺寸导致发光蓝移,带隙宽度变大,Edg值约为0.94 eV.经过850 ℃的真空退火处理后,β-FeSi2相没有发生改变,颗粒尺寸变大、蓝移效果消失,β-FeSi2相小颗粒的尺寸仍小于100 nm,结构的稳定性较好.     

Mössbauer study of magnetic Fe/FeSi multilayers

Many useful properties of magnetic multilayers depend on the coupling between the ferromagnetic layers. The coupling often oscillates with the thickness of non-magnetic spacer layers: it is ferro- or antiferromagnetic or even non-collinear near a critical thickness. We investigated the magnetron-sputtered Fe/FeSi multilayers with spacer thickness around 1.7 nm by means of Conversion Electron Mössbauer Spectroscopy with oblique incidence of the γ beam in order to gain information on the orientation of the local magnetic moments in the multilayer plane. The results show that the local moments make an angle of 45°–50° with the direction of the remanent magnetization. This is consistent with strong biquadratic coupling which in turn is expected at this spacer thickness from our magnetic measurements. An analysis of the distribution ofB _hf corresponding to different numbers of n.n. Si atoms in the bcc Fe structure points to weak diffusion of Si through the Fe/FeSi interface characterized by a diffusion length of about twice the substrate roughness.     

Magnetic and electric properties of (Fe,Co)/(Si,Ge) multilayers

We review selected results concerning the interlayer exchange coupling in Fe/Si _x Fe_1−x , Fe/Ge and Co/Si layered structures. Among the ferromagnet/semiconductor systems, Fe/Si structures are the most popular owing to their strong antiferromagnetic interlayer coupling. We show that such interaction depends not only on semiconducting sublayer thickness, but also on deposition techniques and on the chemical composition of the sublayer as well. In similar heterostructures e.g. Fe/Ge, antiferromagnetic coupling was observed only in ion-beam deposited trilayers at low temperatures. In contrast, in Fe/Ge multilayers deposited by sputtering, no such coupling was found. However, when the Ge is partially substituted by Si, antiferromagnetic interlayer coupling appears. For Co/Si multilayers, we observed a very weak exchange coupling and its oscillatory behavior. The growth of Co on Si occurs in an island growth mode. The evolution of magnetic loop shapes can be successfully explained by the interplay between interlayer coupling and anisotropy terms.     

Magnetic and transport properties of sputtered Fe/Si multilayers

The structural, magnetic and transport properties of sputtered Fe/Si multilayers were studied. The analyses of the data of the X-ray diffraction, resistance and magnetic measurements show that heavy atomic interdiffusion between Fe and Si occurs, resulting in multilayers of different complicated structures according to different sublayer thicknesses. The nominal Fe layers in the multilayers generally consist of Fe layers doped with Si, ferromagnetic Fe-Si silicide layers and nonmagnetic Fe-Si silicide interface layers, while the nominal Si spacers turn out to be Fe-Si compound layers with additional amorphous Si sublayers only under the condition either for the series or for the series multilayers. A strong antiferromagnetic (AFM) coupling and negative magnetoresistance (MR) effect, about 1%, were observed only in multilayers with iron silicide spacers and disappeared when -Si layers appear in the spacers. The dependences of MR on and on bilayer numbers N resemble the dependence of AFM coupling. The increase of MR ratio with increasing N is mainly attributed to the improvement of AFM coupling for multilayers with N. The dependence of MR ratio is similar to that in metal/metal system with predominant bulk spin dependent scattering and is fitted by a phenomenological formula for GMR. At 77 K both the MR effect and saturation field increase. All these facts suggest that the mechanisms of the AFM coupling and MR effect in sputtered Fe/Si multilayers are similar to those in metal/metal system. Received: 11 February 1998 / Revised: 9 March 1998 / Accepted: 9 March 1998     

Competing exchange interactions in magnetic multilayers

We have studied alloying of the nonmagnetic spacer layer with a magnetic material as a method of tuning the interlayer coupling in magnetic multilayers. We have specifically studied the Fe/V(100) system by alloying the spacer V with various amounts of Fe. For some Fe concentrations in the spacer, it is possible to create a competition between antiferromagnetic Ruderman-Kittel-Kasuya-Yoshida exchange and direct ferromagnetic exchange coupling. The exchange coupling and transport properties for a large span of systems with different spacer concentrations and thicknesses were calculated and measured experimentally and good agreement between observations and theory was observed. A reduction in magnetoresistance of about 50% was observed close to the switchover from antiferromagnetic to ferromagnetic coupling.     

[Fe/Cr]多层膜及掺入Si中介层后的层间耦合和磁电阻效应

用真空蒸镀方法制备了［Ｆｅ／Ｃｒ］，［Ｆｅ／Ｃｒ／Ｓｉ］和［Ｆｅ／Ｓｉ］多层膜．研究了Ｃｒ层、Ｓｉ层和Ｃｒ＋Ｓｉ层厚度变化对层间耦合和磁电阻的影响．Ｆｅ层厚为２ｎｍ，Ｃｒ层厚度变化存在耦合振荡和巨磁电阻及其振荡．磁电阻值为１４.６％（４.２Ｋ）．在Ｃｒ层中加入一半Ｓｉ层或全部由Ｓｉ层替代，振荡消失，磁电阻减小到千分之几．根据掺Ｓｉ层后多层膜的电阻率变化，认为Ｓｉ加入使非磁层中自由电子数减少，随之极化效应也变弱，导致振荡消失，磁电阻大为降低 关键词：     

The fragile magnetic structures of Fe/CeH2−δ multilayers

Fe/CeH_2−δ multilayers exhibit at room temperature evidence of interlayer exchange coupling. Subsequent Fe layers are either parallel or antiparallel to each other, depending on the Fe and CeH_2−δ layer thickness. However, when both layers have thickness larger than 15 Å, the antiferromagnetic structure becomes fragmented into domains laterally limited to a few microns, and the magnetic structures become very fragile. Small magnetic fields of a few Oersteds acting on the samples during growth induce helimagnetic configurations which coexist with antiferromagnetic coupling. The magnetic structures can be permanently destroyed by applying magnetic fields larger than 150 Oe.     

Effect of roughness, frustration, and antiferromagnetic order on magnetic coupling of Fe/Cr multilayers

The interplay between interfacial disorder and the antiferromagnetic order in Cr leads to complex behavior in Fe/Cr multilayers. Measurements of interlayer coupling are discussed for samples with different amounts of disorder ranging from optimally fabricated trilayers of Fe/Cr/Fe on Fe(0 0 1) whiskers, to trilayers with increasing degrees of interfacial roughness, and finally to superlattices of Fe/Cr. The coupling of ferromagnets through noble-metal spacer layers can be described by a model that consists of bilinear coupling averaged over thickness fluctuations and extrinsic biquadratic coupling induced by the thickness fluctuations. This, the conventional model, also describes much of the behavior observed for Fe/Cr multilayers. However, in this case, the antiferromagnetism in Cr leads to results not explained by the conventional model. For nearly ideal interfaces, the Fe–Cr coupling can induce order in Cr, modifying the temperature dependence of the interlayer coupling. In addition, interfacial disorder can frustrate the antiferromagnetic order in the Cr, leading to a variety of ordered states which have been observed by neutron scattering. Each of these ordered states, in turn modifies the interlayer coupling in unexpected ways. The different ways in which the systems minimize the frustration can explain the experimental results.     

Exchange couplings in magnetic films

Recent advances in the study of exchange couplings in magnetic films are introduced.To provide a comprehensive understanding of exchange coupling,we have designed different bilayers,trilayers and multilayers,such as anisotropic hard/soft-magnetic multilayer films,ferromagnetic/antiferromagnetic/ferromagnetic trilayers,[Pt/Co]/NiFe/NiO heterostructures,Co/NiO and Co/NiO/Fe trilayers on an anodic aluminum oxide(AAO) template.The exchange-coupling interaction between soft-and hard-magnetic phases,interlayer and interfacial exchange couplings and magnetic and magnetotransport properties in these magnetic films have been investigated in detail by adjusting the magnetic anisotropy of ferromagnetic layers and by changing the thickness of the spacer layer,ferromagnetic layer,and antiferromagnetic layer.Some particular physical phenomena have been observed and explained.     

An estimation of the magnetic disorder at Fe/Cr interfaces in coupled and non-coupled Fe/Cr multilayers

The antiferromagnetic coupling at the Fe/Cr interfaces, inferred from the orientation of the Cr magnetic moments, is used to estimate the magnetic disorder resulting from the interfacial roughness in Fe/Cr multilayers. A crossover from in-plane to out-of-plane orientation of Cr moments depends on the energy cost in either case: (i) to break the interfacial Fe–Cr antiferromagnetic coupling or (ii) having sites with frustrated Cr–Cr antiferromagnetic coupling in the Cr interlayers. A quantitative model of the magnetic frustration due to interfacial disorder in Fe/Cr multilayer systems is described. The step edge density, or terrace size, required to break the interfacial Fe–Cr coupling and destroy the Fe–Fe interlayer exchange coupling is estimated.     

Hydrogen-controlled interlayer exchange coupling in Fe/LaHx multilayers

Magneto-optic Kerr magnetometry and neutron reflectometry reveal that Fe layers exhibit magnetic exchange coupling through LaH_x spacer layers. Ferromagnetic and antiferromagnetic coupling is observed on multilayers of these materials depending on the thickness of the hydride layers, but without oscillatory behavior. Starting from metallic La dihydride spacer layers the effect of dissolving increasingly more hydrogen was examined. Sign and value of the coupling depend crucially on the hydrogen content x. The coupling can be inverted from antiferromagnetic to ferromagnetic and vice versa. These alterations are due to modifications of the electronic structure of the hydride. When the hydrogen absorption saturates the hydride layers become insulating and the exchange coupling is likely to disappear. In this final state the multilayers are always characterized by a very soft ferromagnetic rectangular hysteresis curve. Upon removal of the hydrogen to the initial concentration the original magnetic structure is restored.