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     

Dual-facing-target-sputtered amorphous CoMoN/CN compound soft-X-ray multilayers: structures and thermal stability

Amorphous CoMoN/CN compound soft-X-ray multilayers were fabricated by dual-facing-target sputtering. Their structural thermal stability has been investigated by monitoring the structural evolutions of CN and CoMoN sublayers at annealing temperatures up to 800 °C using complementary measurement techniques, and measuring the coefficient of interfacial diffusion at annealing temperatures below 300 °C. The period expansion at annealing temperatures below 600 °C, which is usually observed in annealed metal/carbon soft-X-ray multilayers, is only 5%. The enhanced sp² to sp³ bond ratio caused by the incorporation annealing effect of nitrogen [1] is thought to be responsible for the improved thermal stability of CN sublayers. Mo addition greatly suppresses the structural thermal evolution of CoMoN sublayers. XPS and TEM analyses indicate that the strong chemical bonding between N and Co atoms and Mo nitride aggregation in the grain boundary of cobalt are the main mechanisms for the high thermal stability of CoMoN sublayers. The layered structure of the CoMoN/CN multilayers still exists at the annealing temperature of 800 °C, while Co/C and CoN/CN multilayers have already been destroyed at this temperature. Compared with Co/C and CoN/CN multilayers, the smaller negative interdiffusivity measured by X-ray diffraction reveals the stable interfaces of CoMoN/CN multilayers. These results illustrate that refractory metal incorporation and strong chemical bond establishment are quite effective in obtaining thermally highly stable compound soft-X-ray optical multilayers . PACS 68.65+g; 68.55.Ln; 68.35.Fx; 68.60.Dv     

Structural stability of heat-treated Co/C soft X-ray multilayers fabricated by dual-facing-target sputtering

Thermal stability of Co/C multilayers prepared by a dual-facing-target sputtering system was studied. A picture of the thermally induced changes in the microstructure was obtained using complementary measurement techniques including low-angle and high-angle X-ray diffraction, transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. It was found that the period expansion, reflectivity change and compound formation, that were observed after annealing are caused by structural changes both in the sublayers and at the interfaces. Below 400°C, the period expansion is mainly caused by the graphitization of the amorphous carbon layers, and a significant increase in the reflectivity at grazing incidence was observed. By 500°C, the crystallization and agglomeration of Co layers induce an enormous period expansion and a serious decrease in reflectivity. A small amount of carbide is found to form at this temperature. Our results imply that new multilayer structures, e.g., compound multilayers will have to be developed for use at high temperatures or under high X-ray incident flux.     

Bias voltage and annealing-temperature dependences of magnetoresistance ratio in Ir–Mn exchange-biased double tunnel junctions

Dual-spin-valve-type double tunnel junctions (DTJs) of sputtered Ir–Mn/Co–Fe/AlO_x/Co₉₀Fe₁₀/AlO_x/Co–Fe/Ir–Mn were fabricated using photolithography and ion-beam milling. The DTJs were annealed at various temperatures (150–400°C) to introduce interdiffusion. The magnetoresistance (MR) ratio and DC bias voltage value at which the MR ratio decreases in half value (V_1/2) were measured before and after annealing. A maximum MR ratio and V_1/2 obtained after annealing at ∼320°C was 42.4% and 952 mV, respectively, at room temperature. There is a correlation between the loss of the MR ratio and that of V_1/2 above 320°C. The loss of the MR ratio and that of V_1/2 are well explained by considering two phenomena, i.e., interdiffusion of O and Mn at the AlO_x/Co–Fe/Ir–Mn interfaces. The mechanism for the loss of MR ratio is not only related to the loss of interface polarization, but is also related to the barrier properties, taking into account the spin-independent two-steps tunneling via defect states in the barrier. These results are consistent with the X-ray photoelectron spectroscopy and cross-sectional transmission electron spectroscopy measurements, which indicate the existence of an Al–Mn–O barrier above 320°C.     

The thermal stability of Al(1%wtSi)/Zr EUV mirrors

Six Al(1%wtSi)/Zr multilayers are deposited on Si substrates by using the direct-current magnetron sputtering system, and annealed from 100?°C to 500?°C temperature in a vacuum furnace for 1?h. To evaluate the thermal stability of Al(1%wtSi)/Zr multilayers, the multilayers were characterized by grazing incidence X-ray reflectance, X-ray diffraction, X-ray emission spectroscopy, and near-normal incident extreme ultraviolet (EUV) reflection. The symmetric and asymmetric interlayer models are used to present the interfacial structure before and after 300?°C. The Al(1%wtSi)/Zr multilayer annealed up to 200?°C maintains the initial symmetric multilayer structure, and keeps almost the similar EUV reflectivity as the nonannealed sample. From 300?°C, interdiffusion is much greater at the Zr/Al interface compared with the Al/Zr interface. And the interfacial phases of Al-Zr alloy transform from amorphous to polycrystalline, which induces the deterioration of multilayer structure and the decrease of EUV reflectivity. However, up to 500?°C, the polycrystalline Al-Zr compound does not destroy the multilayer completely.     

Defect formation of Au thin films on SiO2/Si upon annealing

We have studied structural changes of Au film surfaces grown on Si with native oxide layers. Using X-ray photoelectron spectroscopy (XPS), we found that annealing above 200°C can cause formation of defects (or cracks), which is most likely driven by interdiffusion of Au and Si accompanying strong Au–Si interactions at the interface regime. Scanning tunneling microscopy (STM) study is also in line with defect formation upon annealing. Interaction of O₂ with rough Au surfaces is discussed in connection with catalytic activities of Au surfaces.     

Introduction of Zr in nanometric periodic Mg/Co multilayers

We study the introduction of a third material, namely Zr, within a nanometric periodic Mg/Co structure designed to work as optical component in the extreme UV (EUV) spectral range. Mg/Co, Mg/Zr/Co, Mg/Co/Zr and Mg/Zr/Co/Zr multilayers are designed, and then characterized in terms of structural quality and optical performances through X-ray and EUV reflectometry measurements, respectively. For the Mg/Co/Zr structure, the reflectance value is equal to 50% at 25.1?nm and 45° of grazing incidence and reaches 51.3% upon annealing at 200°C. Measured EUV reflectivity values of tri-layered systems are discussed in terms of material order within a period and compared to the predictions of the theoretical model of Larruquert. Possible applications are pointed out.     

高温退火处理下SiNx薄膜组成及键合结构变化

采用等离子增强化学气相沉积法, 以氨气和硅烷为反应气体, p型单晶硅为衬底, 低温下(200 ℃)制备了非化学计量比氮化硅(SiN_x)薄膜. 在N₂氛围中, 于500–1100 ℃范围内对薄膜进行热退火处理. 室温下分别使用Fourier变换红外吸收(FTIR)光谱技术和X射线光电子能谱(XPS)技术测量未退火以及退火处理后SiN_x薄膜的Si–N, Si–H, N–H键键合结构和Si 2p, N 1s电子结合能以及薄膜内N和Si原子含量比值R的变化. 详细讨论了不同温度退火处理下SiN_x薄膜的FTIR和XPS光谱演化同薄膜内Si, N, H原子间键合方式变化之间的关系. 通过分析FTIR和XPS光谱发现退火温度低于800 ℃时, SiN_x薄膜内Si–H和N–H键断裂后主要形成Si–N键; 当退火温度高于800 ℃时薄膜内Si–H和N–H键断裂利于N元素逸出和Si纳米粒子的形成; 当退火温度达到1100 ℃时N₂与SiN_x薄膜产生化学反应导致薄膜内N和Si原子含量比值R增加. 这些结果有助于控制高温下SiN_x薄膜可能产生的化学反应和优化SiN_x薄膜内的Si纳米粒子制备参数. 关键词： x薄膜')" href="#">SiN_x薄膜 Fourier变换红外吸收光谱 X射线光电子能谱 键合结构     

Electronic state of nitrogen incorporated into CNx nanotubes

CN_x nanotubes have been prepared by acetonitrile decomposition over Ni, Co and Ni/Co catalysts. X-ray photoelectron spectroscopy study on the samples revealed a change of nitrogen concentration and shape of N 1s line with variation of the catalyst used. Quantum-chemical calculations on tube fragments showed the energy of N 1s level depends on the atomic structure of carbon tube and kind of incorporated nitrogen. The largest binding energies were found to be characteristic of three-coordinated nitrogen atoms doping the zigzag and chiral carbon nanotubes.     

Studies of Li intercalation of hydrogenated graphene on SiC(0001)

The effects of Li deposition on hydrogenated bilayer graphene on SiC(0001) samples, i.e. on quasi-freestanding bilayer graphene samples, are studied using low energy electron microscopy, micro-low-energy electron diffraction and photoelectron spectroscopy. After deposition, some Li atoms form islands on the surface creating defects that are observed to disappear after annealing. Some other Li atoms are found to penetrate through the bilayer graphene sample and into the interface where H already resides. This is revealed by the existence of shifted components, related to H–SiC and Li–SiC bonding, in recorded core level spectra. The Dirac point is found to exhibit a rigid shift to about 1.25 eV below the Fermi level, indicating strong electron doping of the graphene by the deposited Li. After annealing the sample at 300–400 °C formation of LiH at the interface is suggested from the observed change of the dipole layer at the interface. Annealing at 600 °C or higher removes both Li and H from the sample and a monolayer graphene sample is re-established. The Li thus promotes the removal of H from the interface at a considerably lower temperature than after pure H intercalation.     

Phase transformations in Mn/Fe(001) films: Structural and magnetic investigations

The solid-phase synthesis in epitaxial Mn/Fe(001) bilayer film systems with 24 at % of Mn has been shown to start at a temperature of 220°C with the formation of a γ-austenite lattice and the Mn and Fe films react completely under annealing to 600°C. In the sample cooling process after annealing below 220°C, the γ austenite undergoes a martensitic transformation to an oriented ∈(100) martensite. When the annealing temperature is increased above 600°C, Mn atoms migrate from the γ-lattice, which becomes unstable, and the film is partially again transformed to the epitaxial Fe(001) layer. The solid-phase synthesis in Mn/Fe(001) bilayer nanofilms and multilayers is assumingly determined by the inverse ε → γ martensitic transformation in the Mn-Fe system. The existence of a new low-temperature (～220°C) structure transition in the Mn-Fe system with a high iron content is assumed.     

Thermal cycles, interface chemistry and optical performance of Mg/SiC multilayers

The interplay between optical performance and the thermally activated interface chemistry of periodic Mg/SiC multilayers designed for application at 30.4 nm are investigated by optical (hard X-ray, soft X-ray and ultraviolet ranges, i.e. from 0.154 to 30.4 nm) reflectivity and X-ray emission spectroscopy. The multilayers are prepared by magnetron sputtering and then annealed up to a temperature of 500 °C. Two clear changes take place in the multilayer upon annealing. At first, between 200 and 300 °C a strong decrease of the reflectivity is observed, due to the development of interfacial roughness following the crystallization of the Mg layers. No interfacial compound is detected. Then, between 350 and 400 °C there is formation of the Mg₂Si magnesium silicide at the interfaces following the reaction between the Mg and SiC layers. This also leads to the almost total loss of reflectivity of the multilayer. Thus, this kind of multilayer is thermally stable only for application requiring no heating above 200 °C.     

热处理Co/C软X射线多层膜的掠入射反射率增强

研究了低温退火Co/C软X射线多层膜中掠入射反射率的增强现象．通过测量一级调制峰强度随退火温度和时间的变化，测得了低至-10^-25m²s^－1的有效扩散系数．由于所研究的Co/C多层膜的调制波长远大于Co-C系统的扩散临界波长，有效扩散系数近似等于真实宏观扩散系数．负的宏观扩散系数表明，在Co-C系统中有相分离的趋势．这一结果可解释为由Miedema宏观原子模型计算得到的正的Co-C系统的混合焓．高退火温度下反射率的降低是界面锐化与界面粗糙化 关键词：     

Atomic Diffusion in Cu/Si （111） and Cu/SiO2/Si （111） Systems by Neutral Cluster Beam Deposition

The Cu films are deposited on two kinds of p-type Si （111） substrates by ionized duster beam （ICB） technique. The interface reaction and atomic diffusion of Cu/Si （111） and Cu/SiO2/Si （111） systems are studied at different annealing temperatures by x-ray diffraction （XRD） and Rutherford backscattering spectrometry （RBS）. Some significant results are obtained： For the Cu/Si （111） samples prepared by neutral dusters, the interdiffusion of Cu and Si atoms occurs when annealed at 230℃. The diffusion coefficients of the samples annealed at 230℃ and 500℃ are 8.5 ×10^-15 cm^2.s^-1 and 3.0 ×10^-14 cm^2.s^-1, respectively. The formation of the copper-silicide phase is observed by XRD, and its intensity becomes stronger with the increase of annealing temperature. For the Cu/SiO2//Si （111） samples prepared by neutral dusters, the interdiffusion of Cu and Si atoms occurs and copper silicides are formed when annealed at 450℃. The diffusion coefficients of Cu in Si are calculated to be 6.0 ×10^-16 cm^2.s^-1 at 450℃, due to the fact that the existence of the SiO2 layer suppresses the interdiffusion of Cu and Si.     

Thermal behaviour of Co/Si/W/Si multilayers under rapid thermal annealing

The e-beam deposited multilayers (MLS) were studied under rapid thermal annealing (RTA) between 250°C and 1000°C during 30 s. MLS with five Co/Si/W/Si periods, each 13.9 nm (MLS1) and 18 nm (MLS2) were deposited onto oxidized Si substrates. Samples were analyzed by X-ray diffraction, hard and soft X-ray reflectivity measurements and grazing incidence X-ray diffuse scattering. The MLS period, interface roughness and its lateral and vertical correlations were obtained by simulation of the hard X-ray reflectivity and diffuse scattering spectra. The MLS1 with thinner Co layers is more temperature resistant. However, its soft X-ray reflectivity is smaller. The results show that this is because of shorter lateral and vertical correlation lengths of the interface roughness which may considerably influence the X-ray reflectivity of multilayers.     

Formation of a quasi-free-standing graphene with a band gap at the dirac point by Pb atoms intercalation under graphene on Re(0001)

The control of the graphene electronic structure is one of the most important problems in modern condensed matter physics. The graphene monolayer synthesized on the Re(0001) surface and then subjected to the intercalation of Pb atoms is studied by angle-resolved photoelectron spectroscopy and low-energy electron diffraction. The intercalation of Pb atoms under graphene takes place when the substrate is annealed above 500°C. As a result of the intercalation of Pb atoms, graphene becomes quasi-free-standing and a local band gap appears at the Dirac point. The band gap changes with the substrate temperature during the formation of the graphene/Pb/Re(0001) system. The band gap is 0.3 eV at an annealing temperature of 620°C and it increases up to 0.4 eV upon annealing at 830°C. Based on our data, we conclude that the band gap is mainly caused by the hybridization of the graphene π state with the rhenium 5d states located near the Dirac point of the graphene π state.     

InSb(111)表面硫处理的研究

本文用俄歇电子能谱、X射线光电子能谱和紫外光电子能谱对用硫化铵溶液处理的InSb表面进行研究。结果表明,硫处理以后在样品表面生成。一层厚度约8?的硫化物钝化层,它对防止表面的氧化和碳沾污有明显的钝化作用。钝化层中,破原子既与锑原子成键,引起Sb3d芯能级发生1.9eV的化学位移;又与铟原子成键,引起In4d芯能级发生0.6—0.7eV的化学位移。350℃的真空退火使锑的硫化物发生分解。500℃退火没能使铟的硫化物完全分解,仍有一部分硫原子以铟的硫化物形式留在样品表面。 关键词：     

Interaction of iron atoms with the silicon surface coated with a native oxide layer

The solid-phase epitaxy of iron silicide on the Si(111) surface coated with a native oxide layer is studied by high-resolution photoelectron spectroscopy using synchrotron radiation and by atomic force microscopy. The iron deposition dose changes up to 1 nm, and the annealing temperature changes up to 500°C. At room temperature, the native oxide layer is shown to be impermeable to Fe atoms and an iron film grows on the sample surface. An increase in the annealing temperature to ～100°C results in a change in the film morphology, increasing its heterogeneity. As the annealing temperature increases to ～250°C, Fe and Si atoms diffuse through the oxide layer and undergo a solid-phase reaction. As a result, stable iron monosilicide ?-FeSi forms.     

Chemical states of GeTe thin-film during structural phase-change by annealing in ultra-high vacuum

The chemical states of GeTe thin film are investigated using high-resolution X-ray photoelectron spectroscopy (HRXPS) with synchrotron radiation, during amorphous to crystalline structural phase transition. As the temperature increases from 250 to 400 °C, we observe the rock-salt crystalline structure and phase with X-ray diffraction (XRD) and transmission electron microscopy (TEM). Spin-orbit splitting of the Ge 3d core-level spectrum clearly appears after annealing at 400 °C for 5 min. However, the binding energy of the Ge 3d_5/2 core-level peak of 29.8 eV does not change in the amorphous to crystalline structural phase transition. In the case of the Te 4d core-level, change in binding energy and peak shapes is also negligible. We assume that the Te atom is fixed at a site between the amorphous and crystalline phases. Although the structural environment of the Ge atoms changes during the structural phase transition, the chemical environment does not.     

Influence of vacuum annealing on structures and mechanical properties of Al–Ti–N films deposited by multi-arc ion plating

The Al–Ti–N films deposited by multi-arc ion plating have been annealed in vacuum within the range of 700–1100 °C. X-ray diffraction results showed that the structure of the films underwent the formation of coherent c-TiN and c-AlN for the annealing temperatures were up to 900 °C. A new phase AlTi_x (x = 0.50, 0.56, 3) was observed after annealing. The X-ray photoelectron spectroscopy results showed the intensity of Ti–Al bonds decreased as annealing temperatures increased, indicating the decomposition of (Al, Ti)N into c-TiN and c-AlN were at the expense of Ti–Al bonds. Differential scanning calorimetry experiments were used to investigate the dynamic behavior of the films during annealing process and the results showed that the N₂ formed as a consequence of the phase transformation process. The release of the N₂ resulted in the peeling of the films from the substrates. The film exhibited a maximum hardness of 39 GPa after 900 °C annealing due to the formation of coherent c-TiN and c-AlN phases. In addition, we also investigated the influence of vacuum annealing on adhesive strength.