Periodic cracks and temperature-dependent stress in Mo/Si multilayers on Si substrates

This work examines formation of the peculiar periodic crack patterns observed in the thermally loaded Mo/Si multilayers. Using the substrate curvature measurements, the macroscopic film stress evolution during thermal cycling was investigated. Then high-speed microscopic observation of crack propagation in the annealed Mo/Si multilayers was presented providing experimental evidence of the mechanism underlying formation of the periodic crack patterns. The origin of the peculiar periodic crack patterns was determined. They were observed to form by the slow crack propagation under quasi-static conditions as a result of the interaction between the channelling crack propagation and the advance of the delamination front.     

Si adhesion interlayer effects in hydrogen passivated Si/W soft X-ray multilayer mirrors

The use of hydrogen passivation of the silicon layers in Si/W soft X-ray reflective multilayer mirrors is investigated. Standard passivation, corresponding to Si:H/W structures, led to reduced growth properties of the W layers. The additional use of atomically thin Si adhesion layers, corresponding to Si:H/Si/W, led to improved growth and increased soft X-ray reflectivity. The effects taking place at the interfaces are analysed by bright field planar TEM and in situ X-ray reflectivity, and are described in terms of interface and surface energies, with quantitatively analysis of intermixing, materials density, and geometrical optical effects.     

中心波长为13．9nm的正入射Mo／Si多层膜

用由铜靶激光等离子体光源等组成的反射率计对自行设计的周期厚度为7.14nm的120层Mo/Si多层膜进行极紫外(EUV)波段反射率测量。由于多层膜层数增加所引起的吸收、膜层界面之间的扩散以及镀膜过程中的膜厚控制误差或表面被氧化(污染)等原因,正入射Mo/Si多层膜在13.9nm处的反射率低于理论计算值73.2%,最后用原子力显微镜(AFM)测量其表面粗糙度为σ=0.401nm。     

Thermal stability of Mo/Si multilayer soft-X-ray mirrors fabricated by electron-beam evaporation

Mo/Si multilayers are fabricated by electron-beam evaporation in UHV at different temperatures (30° C, 150° C, 200° C) during deposition. After completion their thermal stability is tested by baking them at temperatures (T _bak) between 200° C and 800° C in steps of 50° C or 100° C. After each baking step the multilayers are characterized by small angle Cu_K-X-ray diffraction. Additionally, the normal incidence soft-X-ray reflectivity for wavelengths between 11 nm and 19 nm is determined after baking at 500° C. Furthermore, the layer structure of the multilayers is investigated by means of Rutherford Backscattering Spectroscopy (RBS) and sputter/Auger Electron Spectroscopy (AES) technique. While the reflectivity turns out to be highest for a deposition temperature of 150° C, the thermal stability of the multilayer increases with deposition temperature. The multilayer deposited at 200° C stands even a 20 min 500° C baking without considerable changes in the reflectivity behaviour.     

Si／SiNx／SiO2多层膜的光致发光

采用射频磁控溅射法,制备了具有强光致可见发光的纳米Si/SiNx/SiO2多层膜,利用傅立叶红外吸收(FTIR)谱,光致发光(PL)谱对其进行了研究。用260nm光激发得到的PL谱中观察到高强度的392nm(3.2eV)和670nm(1.9eV)光致发光峰,分析认为它们分别来自于缺陷态≡Si-到价带顶和从导带底到缺陷态≡Si-的辐射跃迁而产生的光致激发辐射复合发光。PL谱中只有370nm(3.4eV)处发光峰的峰位会受退火温度的影响,结合FTIR谱认为370nm发光与低价氧化物—SiOx(x<2.0)结合体有密不可分的关系。当SiO2层的厚度增大时,发光强度有所增强,800℃退火后出现最强发光,认为具有较大SiO2层厚度的Si/SiNx/SiO2结构多层膜更有利于退火后形成Si—N网络,能够得到更高效的光致发光。用量子限制-发光中心(QCLC)模型解释了可能的发光机制,并建立了发光的能隙态(EGS)模型。     

Sub-ps laser microstructuring of soft X-ray Mo/Si multilayer gratings

The sub-picosecond laser microstructuring of multilayer gratings is presented in this paper. A micromachining system operating with a 0.5 ps KrF laser at 248 nm was used to etch grating structures with a groove width of 1–2 μm in Mo/Si and Si/Mo multilayers. Atomic force microscopy, scanning electron microscopy and X-ray reflectivity were used to characterize the microetched patterns. The ω-scans around the 1st Bragg maximum show symmetric satellites up to 3rd order, with positions corresponding to the grating period. The use of sub-picosecond laser pulses minimizes the thermally affected zone and enhances the quality of the etched features. Short pulse laser processing is advantageous for the fabrication of high spatial resolution microstructures required in X-ray optics. Received: 21 May 2002 / Accepted: 19 August 2002 / Published online: 15 January 2003 RID="*" ID="*"Corresponding author. Email: dpapa@iesl.forth.gr     

Reflecting a single attosecond pulse by using periodic Mo/Si multilayer mirrors with different layers

The reflecting of a single attosecond pulse from a periodic Mo/Si multilayer was investigated. By changing the number of bi-layers, the periodic multilayer showed greatly different spectral and temporal responses of the attosecond pulse reflection, which has been discussed in detail in this paper. The capability of attosecond pulse reflection of the periodic multilayers with different bi-layer numbers has been evaluated using suitable temporal parameters. In addition, the condition for obtaining high-efficiency reflected pulses has been analyzed by comparing the pulse responses of the periodic multilayer with different layers. The transfer-matrix method together with the fast Fourier transform has been used in our simulation.     

Rectifying and photovoltaic properties of ZnCo_2O_4/Si heterostructure grown by pulsed laser deposition

ZnCo2O4/Si heterostructures have been fabricated by a pulsed laser deposition method, and their transport behaviors and photovoltaic properties have been characterized. The ZnCo2O4/Si heterostructures show a good rectifying behavior at five different temperatures ranging from 50 K to 290 K. The measurements of the photovoltaic response reveals that a photovoltage of 33 mV is generated when the heterostructures are illuminated by a 532 nm laser of 250 mW/cm2and mechanically chopped at 2500 Hz. Both the photocurrent and the photovoltage clearly increase with the increase of the laser intensity at room temperature. However, the heterostructures' photovoltage peak decreases with the increase of the temperature. This work may open new perspectives for ZnCo2O4/Si heterostructure-based devices.     

Si/SiO2 multilayers: synthesis by reactive magnetron sputtering and photoluminescence emission

This paper relates a complete study of Si/SiO₂ multilayer (ML) structures. First, we suggest an original way of synthesis based on reactive magnetron sputtering of a pure silica target. The photoluminescence spectra of these MLs consist of two Gaussian bands in the visible-near infrared spectral region. The stronger one (I band) is fixed at about 780 nm and probably due to interface states. The weaker one (Q band) is tuneable with the Si sublayer thickness and originates from a radiative recombination within the nanosized Si layers. For this latter band the peak position is a function of the Si sublayer thickness and shows a discontinuity at 30 Å. This corresponds to an Si phase change. For thicknesses above 30 Å, the sublayers are composed of nanocrystalline silicon whereas below 30 Å the sublayers are made of amorphous silicon. We develop a model based on a quantum well to which we have added an interfacial region between Si and SiO₂. It is characterised by an interfacial potential of 0.3 eV. This model depicts the simultaneous behaviour of Q and I bands for an Si sublayer thickness below 30 Å.     

Single-mode SiON/SiO2/Si optical waveguides prepared by plasma-enhanced chemical vapor deposition

We present the characteristics of low-propagation-loss single-mode SiON / SiO₂ / Si planar optical waveguides using plasma-enhanced chemical vapor deposition (PECVD). Using a thermal annealing process and a thick silicon dioxide buffer layer, we get an improvement on the propagation loss by the amounts of 1.24 dB /cm and 1.1 dB /cm, respectively. Optical waveguides with propagation loss lower than 0.3 dB /cm can be achieved.     

磁控溅射法制备极紫外6.8～11.0nm波段Mo/B_4C横向梯度多层膜（英文）

用直流磁控溅射法结合掩模板控制膜厚的方法在Si衬底上制备了工作于6.8～11.0nm波段的[Mo/B_4C]60横向梯度多层膜。利用X射线掠入射反射测试以及同步辐射反射率测试对梯度多层膜的结构及性能进行了测试。X射线掠入射反射测试结果表明,多层膜周期厚度沿着长轴方向从4.39nm逐渐增加到7.82nm,周期厚度平均梯度为0.054nm/mm。对横向梯度多层膜沿长轴方向每隔5mm进行了一次同步辐射反射率测试,结果显示,横向梯度多层膜在45°入射角下的反射率约为10%,反射峰的半高全宽介于0.13nm到0.31nm之间。     

ICP-AES法测定铝合金中Fe、Si、Mo、Zr、Ti、Y的研究

本文采用ＩＣＰ－ＡＥＳ法测定了铝合金中Ｆｅ、Ｓｉ、Ｍｏ、Ｚｒ、Ｔｉ、Ｙ,并对样品的溶解方法、共存元素间的光谱干扰、内标元素的选择等进行了研究,建立的分析方法简便快速,有较好的精密度和准确度。     

Dimensional evolution of silicon nanowires synthesized by Au–Si island-catalyzed chemical vapor deposition

This study explores the nucleation and morphological evolution of silicon nanowires (Si-NWs) on Si (0 0 1) and (1 1 1) substrates synthesized using nanoscale Au–Si island-catalyzed rapid thermal chemical vapor deposition. The Au–Si islands are formed by Au thin film (1.2–3.0 nm) deposition at room temperature followed by annealing at 700 °C, which are employed as a liquid-droplet catalysis during the growth of the Si-NWs. The Si-NWs are grown by exposing the substrates with Au–Si islands to a mixture of gasses SiH₄ and H₂. The growth temperatures and the pressures are 500–600 °C and 0.1–1.0 Torr, respectively. We found a critical thickness of the Au film for Si-NWs nucleation at a given growth condition. Also, we observed that the dimensional evolution of the NWs significantly depends on the growth pressure and temperature. The resulting NWs are 30–100 nm in diameter and 0.4–12.0 μm in length. For Si (0 0 1) substrates 80% of the NWs are aligned along the 1 1 1 direction which are 30° and 60° with respect to the substrate surface while for Si (1 1 1) most of the NWs are aligned vertically along the 1 1 1 direction. In particular, we observed that there appears to be two types of NWs; one with a straight and another with a tapered shape. The morphological and dimensional evolution of the Si-NWs is significantly related to atomic diffusion kinetics and energetics in the vapor–liquid–solid processes.     

Characterization of heat-treated CN films fabricated by dual-facing-target sputtering for soft X-ray multilayer mirrors

The structural characterization of heat-treated CN films fabricated by dual-facing-target sputtering for soft X-ray multilayer mirrors was performed by means of X-ray diffraction (XRD), Raman spectroscopy (RS) and X-ray photoelectron spectroscopy (XPS). The XRD analyses indicate a graphization process in the CN films during thermal annealing. The Raman analyses imply that the primary bonding in the CN films is sp². In other words, the formation of the sp³ bonding in the CN films can be suppressed effectively by doping with N atoms, and thus the thickness expansion resulting from the changes in the density of CN films during annealing can be decreased considerably. This result is also clarified by the increased conductivity measured. The XPS results give the information of the existence of the strong covalent bonding between N and C atoms, which can slow down the tendency of the structural relaxation during annealing. These results suggest that CN films suitable for soft X-ray multilayers used at high-temperature environments can be obtained by reactive dual-facing-target sputtering. With the low-angle X-ray diffraction measurements, we do observe the enhanced thermal stability of CoN/CN multilayers. Received: 2 October 1998 / Accepted: 21 April 1999 / Published online: 23 September 1999     

Investigation in the interface roughness of DC-sputtered Mo/B4C multilayer mirrors with variable layer pairs for 7-nm soft X-ray polarizers

The surface and interface roughness of Mo/B₄C multilayer mirrors for 7-nm soft X-ray polarizer with variable layer pairs (N = 50, 70, 90 and 110), fabricated by DC sputtering technique is investigated by atomic force microscopy and X-ray scattering and reflecting. The experimental results present that the surface and interface roughness of Mo/B₄C multilayer mirrors increase layer by layer from its substrate as its Mo layer thickness greater than 2 nm, and the roughness grown tendency could be characterized by a quadratic function.     

Anneal temperature dependence of Si/SiO2 superlattices photoluminescence

Photoluminescence spectroscopy, Fourier transform infrared spectroscopy, X-ray reflectometry and high resolution electron microscopy have been used to interpret the photoluminescence properties of annealed (3/19 nm) Si/SiO₂ multilayers grown by reactive magnetron sputtering. The multilayers show an emission in the visible and near-infrared range after heat treatment from 900°C which tends to decrease from 1200°C. Three different origins for the photoluminescence activity have been found. An anneal temperature of 1200°C is necessary to optimise the silicon crystallisation within the silicon sublayers.     

Evolution of self-assembled Ge/Si island grown by ion beam sputtering deposition

The effect of temperature and Ge coverage on the evolution of self-assembled Ge/Si islands grown by ion beam sputtering deposition is studied. Atomic force microscopy and Raman spectroscopy are used to analyze the island morphology and the intermixing between Si and Ge. The experiments are presented in two aspects. First, when the temperature is increased, intermixing is promoted, resulting in the reappearance of low aspect ratio islands. Second, a different evolution pathway is observed, in which short islands initially don’t grow along the constant ratio of 11:1 (diameter:height) and the islands always grow faster in vertical direction. In summary, the interdiffusion, surface diffusion, and amount of Ge determines the evolution of Ge/Si islands.     

Photoluminescence properties of SiNx/Si amorphous multilayer structures grown by plasma-enhanced chemical vapor deposition

Very thin (nanometric) silicon layers were grown in between silicon nitride barriers by SiH₂Cl₂/H₂/NH₃ plasma-enhanced chemical vapor deposition (PECVD). The multilayer structures were deposited onto fused silica and silicon substrates. Deposition conditions were selected to favor Si cluster formation of different sizes in between the barriers of silicon nitride. The samples were thermally treated in an inert atmosphere for 1 h at 500 °C for dehydrogenation. Room-temperature photoluminescence (RT-PL) and optical transmission in different ranges were used to evaluate the optical properties of the structures. UV-VIS absorption spectra present two band edges. These band edges are well fitted by the Tauc model typically used for amorphous materials. RT-PL spectra are characterized by strong broad bands, which have a blue shift as a function of the deposition time of the silicon layer, even for as-grown samples. The broad luminescence could be associated with the confinement effect in the silicon clusters. After annealing of the samples, the PL bands red shift. This is probably due to the thermal decomposition of N-H bonds with further effusion of hydrogen and better nitrogen passivation of the nc-Si/SiN_x interfaces.     

Influence of layer thickness on the structure and the magnetic properties of Co/Pd epitaxial multilayer films

Co/Pd epitaxial multilayer films were prepared on Pd(111)_fcc underlayers hetero-epitaxially grown on MgO(111)_B1 single-crystal substrates at room temperature by ultra-high vacuum RF magnetron sputtering. In-situ reflection high energy electron diffraction shows that the in-plane lattice spacing of Co on Pd layer gradually decreases with increasing the Co layer thickness, whereas that of Pd on Co layer remains unchanged during the Pd layer formation. The CoPd alloy phase formation is observed around the Co/Pd interface. The atomic mixing is enhanced for thinner Co and Pd layers in multilayer structure. With decreasing the Co and the Pd layer thicknesses and increasing the repetition number of Co/Pd multilayer film, stronger perpendicular magnetic anisotropy is observed. The relationships between the film structure and the magnetic properties are discussed.     

Nanolayered multilayer coatings of CrN/CrAlN prepared by reactive DC magnetron sputtering

Single-phase CrN and CrAlN coatings were deposited on silicon and mild steel substrates using a reactive DC magnetron sputtering system. The structural characterization of the coatings was done using X-ray diffraction (XRD). The XRD data showed that both the CrN and CrAlN coatings exhibited B1 NaCl structure with a prominent reflection along (2 0 0) plane. The bonding structure of the coatings was characterized by X-ray photoelectron spectroscopy and the surface morphology of the coatings was studied using atomic force microscopy. Subsequently, nanolayered CrN/CrAlN multilayer coatings with a total thickness of approximately 1 μm were deposited on silicon substrates at different modulation wavelengths (Λ). The XRD data showed that all the multilayer coatings were textured along {2 0 0}. The CrN/CrAlN multilayer coatings exhibited a maximum nanoindentation hardness of 3125 kg/mm² at a modulation wavelength of 72 Å, whereas single layer CrN and CrAlN deposited under similar conditions exhibited hardness values of 2375 and 2800 kg/mm², respectively. Structural changes as a result of heating of the multilayer coatings in air (400-800 °C) were characterized using XRD and micro-Raman spectroscopy. The XRD data showed that the multilayer coatings were stable up to a temperature of 650 °C and peaks pertaining to Cr₂O₃ started appearing at 700 °C. These results were confirmed by micro-Raman spectroscopy. Nanoindentation measurements performed on the heat-treated coatings revealed that the multilayer coatings retained hardness as high as 2250 kg/mm² after annealing up to a temperature of 600 °C.