Hard X-ray one dimensional nano-focusing at the SSRF using a WSi2/Si multilayer Laue lens

The multilayer Laue lens (MLL) is a novel diffraction optics which can realize nanometer focusing of hard X-rays with high efficiency. In this paper, a 7.9 μm-thick MLL with the outmost layer thickness of 15 nm is designed based on dynamical diffraction theory. The MLL is fabricated by first depositing the depth-graded multilayer using direct current (DC) magnetron sputtering technology. Then, the multilayer sample is sliced, and both cross-sections are thinned and polished to a depth of 35-41 μ. The focusing property of the MLL is measured at the Shanghai Synchrotron Facility (SSRF). One-dimensional (1D) focusing resolutions of 205 nm and 221 nm are obtained at E=14 keV and 18 keV, respectively. It demonstrates that the fabricated MLL can focus hard X-rays into nanometer scale.     

X-ray nanometer focusing at the SSRF based on a multilayer Laue lens

We designed and fabricated a multilayer Laue lens(MLL) as a hard X-ray focusing device.WSi_2/Si multilayers were chosen owing to their excellent optical properties and relatively sharp interface.The multilayer sample was fabricated by using direct current(DC) magnetron sputtering technology and then was sliced and thinned to form an MLL.The thickness of each layer was determined by scanning electron microscopy(SEM) image analysis with marking layers.The focusing property of the MLL was measured at Beamline 15 U,Shanghai Synchrotron Facility(SSRF).One-dimensional(1D) focusing resolutions of 92 nm are obtained at photon energy of 14 keV.     

Small d-spacing WSi2/Si multilayers for X-ray monochromators

A WSi2 /Si multilayer, with 300 bi-layers and a 2.18-nm d-spacing, is designed for X-ray monochroma-tor application. The multilayer is deposited using direct current magnetron sputtering technology. The reflectivity of the 1st-order Bragg peak measured at E = 8.05 keV is 38%, and the angular resolution (Δθ/θ) is less than 1.0%. Fitting results of the reflectivity curve indicate a layer thickness drift of 1.6%, mainly accounting for the broadening of the Bragg peaks. The layer morphology is further characterized by transmission electron microscopy, and a well-ordered multilayer structure with sharp interfaces is observed from the substrate to the surface. The material combination of WSi2 /Si is a promising candidate for the fabrication of a high-resolution multilayer monochromator in the hard X-ray region.     

Thinning and polishing of cross-section of depth-graded WSi2 /Si multilayer for linear zone plate application

A linear zone plate named multilayer laue lens (MLL) is fabricated using a depth-graded multilayer structure. The lens shows considerable potential in focusing an X-ray beam into a nanometer scale with high efficiency. In this letter, a depth-graded multilayer consisting of 324 alternating WSi 2 and Si layers with a total thickness of 7.9 μm is deposited based on the thickness sequence according to the demands of the zone plate law. Subsequently, the multilayer sample is sliced and thinned to an ideal depth along the cross-section direction using raw abrasives and diamond lapping. Finally, the cross-section is polished by a chemical mechanical polishing (CMP) technique to remove the damages and improve the surface smoothness. The final depth of the MLL is approximately 7 μm with an achieved aspect ratio greater than 400. Results of scanning electron microscopy (SEM) and atomic force microscopy (AFM) indicate that interfaces are sharp, and the multilayer structure remains undamaged after the thinning and polishing processes. The surface roughness achieved is 0.33 nm.     

Reactive diffusion in Sc/Si multilayer X-ray mirrors with CrB2 barrier layers

Processes undergoing in Sc/Si multilayer X-ray mirrors (MXMs) with periods of ∼27 nm and barrier layers of CrB₂0.3- and 0.7-nm thick within the temperature range of 420–780 K were studied by methods of small-angle X-ray reflectivity (λ=0.154 nm) and cross-sectional transmission electron microscopy. All layers with the exception of Sc ones are amorphous. Barrier layers are stable at least up to a temperature of 625 K and double the activation energy of diffusional intermixing at moderate temperatures. Introduction of barriers improves the thermal stability of Sc/Si MXMs at least by 80 degrees. Diffusion of Si atoms through barrier layers into Sc layers with formation of silicides was shown to be the main degradation mechanism of MXMs. A comparison of the stability for Sc/Si MXMs with different barriers published in the literature is conducted. The ways of further improvement of barrier properties are discussed.     

Submicron focusing of XUV radiation from a laser plasma source using a multilayer Laue lens

The focusing properties of a one-dimensional multilayer Laue lens (MLL) were investigated using monochromatic soft X-ray radiation from a table-top, laser-produced plasma source. The MLL was fabricated by a focused ion beam (FIB) structuring of pulsed laser deposited ZrO₂/Ti multilayers. This novel method offers the potential to overcome limitations encountered in electron lithographic processes. Utilizing this multilayer Laue lens, a line focus of XUV radiation from a laser-induced plasma in a nitrogen gas puff target could be generated. The evaluated focal length is close to the designed value of 220 μm for the measurement wavelength of 2.88 nm. Divergence angle and beam waist diameter are measured by a moving knife edge and a far-field experiment, determining all relevant second-order moments based beam parameters. The waist diameter has been found to be approximately 370 nm (FWHM).     

Nanostructuring Si surface and Si/SiO2 interface using porous-alumina-on-Si template technology. Electrical characterization of Si/SiO2 interface

In this work, anodic porous alumina thin films with pores in the nanometer range are grown on silicon by electrochemistry and are used as masking material for the nanopatterning of the silicon substrate. The pore diameter and density are controlled by the electrochemical process. Through the pores of the alumina film chemical oxidation of the silicon substrate is performed, leading to the formation of regular arrays of well-separated stoichiometric silicon dioxide nanodots on silicon, with a density following the alumina pores density and a diameter adjustable by adjusting the chemical oxidation time. The alumina film is dissolved chemically after the SiO₂ nanodots growth, revealing the arrays of silicon dioxide dots on silicon. In a next step, the nanodots are also removed, leaving a nanopatterned bare silicon surface with regular arrays of nanopits at the footprint of each nanodot. This silicon surface structuring finds interesting applications in nanoelectronics. One such application is in silicon nanocrystals memories, where the structuring of the oxidized silicon surface leads to the growth of discrete silicon nanocrystals of uniform size. In this work, we examine the electrical quality of the Si/SiO₂ interface of a nanostructured oxidized silicon surface fabricated as above and we find that it is appropriate for electronic applications (an interface trap density below 1–3×10¹⁰ eV⁻¹ cm⁻² is obtained, indicative of the high quality of the thermal silicon oxide).     

Praseodymium silicide formation at the Pr2O3/Si interface

The interface and layer structure of praseodymium (Pr) oxide layers grown on Si(0 0 1) from a high-temperature effusion cell are studied using grazing incidence X-ray diffraction. Due to the interdiffusion of praseodymium and silicon atoms, Pr silicide forms in the layers. We find that Pr silicide is the favorable structure under oxygen deficient growth conditions in the Pr oxide layer. To avoid the silicidation, additional oxygen must be supplied. The formation of Pr silicide is suppressed for layers grown with an oxygen partial pressure of 10⁻⁷ mbar at a substrate temperature of 700 °C.     

Interfaces analysis of the HfO2/SiO2/Si structure

The physical and chemical properties of the HfO₂/SiO₂/Si stack have been analyzed using cross-section HR TEM, XPS, IR-spectroscopy and ellipsometry. HfO₂ films were deposited by the MO CVD method using as precursors the tetrakis 2,2,6,6 tetramethyl-3,5 heptanedionate hafnium—Hf(dpm)₄ and dicyclopentadienil-hafnium-bis-diethylamide—Сp₂Hf(N(C₂H₅)₂)₂.The amorphous interface layer (IL) between HfO₂ and silicon native oxide has been observed by the HRTEM method. The interface layer comprises hafnium silicate with a smooth varying of chemical composition through the IL thickness. The interface layer formation occurs both during HfO₂ synthesis, and at the annealing of the HfO₂/SiO₂/Si stack. It was concluded from the XPS, and the IR-spectroscopy that the hafnium silicate formation occurs via a solid-state reaction at the HfO₂/SiO₂ interface, and its chemical structure depends on the thickness of the SiO₂ underlayer.     

Microstructure and tribological properties of WS2/MoS2 multilayer films

In this paper, a novel method, namely, magnetron sputtering and low temperature ion sulfurizing combined technique was used to fabricate the solid lubrication WS₂/MoS₂ multilayer films. Scanning Electron Microscopy (SEM) was used to observe the surface and worn scar morphologies. X-ray diffraction (XRD) was utilized to analyze the phase structure. The nano-hardness and elastic modulus of WS₂/MoS₂ multilayer films were surveyed by the nano-indentation tester. The friction and wear test were conducted on a ball-on-disk wear tester under dry sliding condition. The results obtained showed that the WS₂/MoS₂ multilayer films exhibited a lower friction coefficient and better wear-resistance when compared with single WS₂ film and original 1045 steel.     

Spin-wave response in the one dimensional anisotropic antiferromagnet CsCoCl3

The magnetic excitation spectrum of CsCoCl₃ has been studied by neutron scattering. Evidence is presented that the long wavelength spectrum consists of a sharp spin-wave-like peak superposed on a broader band of excitations that extends up to the Ising-limit zone-boundary frequency. In contrast, the zone boundary response is sharp, suggesting that the continuum has a greater breadth at the zone centre. Further, it is found that the spectral weight of longitudinal scattering within the spin-wave band is small.     

Influence of ZrO2 in HfO2 on reflectance of HfO2/SiO2 multilayer at 248 nm prepared by electron-beam evaporation

Influence of ZrO₂ in HfO₂ on the reflectance of HfO₂/SiO₂ multilayer at 248 nm was investigated. Two kinds of HfO₂ with different ZrO₂ content were chosen as high refractive index material and the same kind of SiO₂ as low refractive index material to prepare the mirrors by electron-beam evaporation. The impurities in two kinds of HfO₂ starting coating materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum (GDMS) technology and secondary ion mass spectrometry (SIMS) equipment, respectively. It showed that between the two kinds of HfO₂, either the bulk materials or their corresponding films, the difference of ZrO₂ was much larger than that of the other impurities such as Ti and Fe. It is the Zr element that affects the property of thin films. Both in theoretical and in experimental, the mirror prepared with the HfO₂ starting material containing more Zr content has a lower reflectance. Because the extinction coefficient of zirconia is relatively high in UV region, it can be treated as one kind of absorbing defects to influence the optical property of the mirrors.     

Characteristics of nodular defect in HfO2/SiO2 multilayer optical coatings

Laser-induced damage is associated with nodular defects in HfO₂/SiO₂ multilayer films. In order to investigate the damage characteristics of HfO₂/SiO₂ multilayer mirrors and find the information of improving laser-induced damage threshold, nodular defects are characterized by multiple analytical techniques; the damage morphologies induced by nodular-ejections are presented; the depths of nodular-ejection pits are investigated; the laser-induced damage threshold of zero probability and the stabilities of nodular-ejection pits exposed to repetitive illuminations are studied. Results show that domes in the film surface are nodular defects. Reliable depth information of nodular-ejection pits is obtained by counting layers from the damage edge. The depth statistical result implies nodular defects in these samples are usually originated from deep seeds. Some process optimizations suggestions are given based on the depth information. A simple tractable method is proposed to determine the functional damage threshold of these HfO₂/SiO₂ multilayer films basing on the damage experiments.     

Optical description of HfO2/Al/HfO2 multilayer thin film devices

A three-layer system of dielectric/metal/dielectric (D/M/D) has been prepared on Marienfeld commercial glass substrates with Metal = Al, and Dielectric = HfO₂ for energy efficient windows applications. Subsequently, HfO₂/Al/HfO₂ multilayers have been deposited with 10 nm each HfO₂ layer and 5 nm thick Al layer using electron beam evaporation. The microstructural characteristics of D/M/D thin films have been investigated using X-ray diffraction (XRD) and atomic force microscopy (AFM). Present results indicate the formation of HfO₂ weak polycrystals embedded in the disordered lattice. AFM data reveals quite a smooth surface involving a structure of slightly elongated grains with almost Gaussian size distribution with mean grain size in the range from 7 to 23 nm. Regarding optical properties, maximum transmittance of the D/M/D structure is noticed to occur in the UV-region, whereas reflectance rises to ∼60% in the visible to near infrared (NIR)-regions. To optimize the performance of these D/M/D devices, computer calculations have been performed by varying either the thickness of both HfO₂ layers and/or thickness of metallic Al layer. A satisfactory agreement between theoretical and experimental spectra is noticed. Such D/M/D structures can be useful in heat mirror applications involving energy efficient windows etc.     

上海光源真空波荡器Sm2Co17永磁铁的实验研究

对国产Sm2Co17永磁铁(XG30/20)研制工艺进行了改进,对三种成型-烧结设计所得到的永磁铁样品(65 mm27 mm7.2 mm)进行了测试与分析,结果表明,磁性能有所改善,磁矩一致性和稳定性良好,获得了国产真空波荡器Sm2Co17永磁铁的优化成型-烧结设计和磁场分布规律数据,对永磁铁实验研究结果原理进行了解释。     

上海光源真空波荡器Sm2Co17永磁铁的实验研究

对国产Sm2Co17永磁铁(XG30/20)研制工艺进行了改进,对三种成型-烧结设计所得到的永磁铁样品(65 mm27 mm7.2 mm)进行了测试与分析,结果表明,磁性能有所改善,磁矩一致性和稳定性良好,获得了国产真空波荡器Sm2Co17永磁铁的优化成型-烧结设计和磁场分布规律数据,对永磁铁实验研究结果原理进行了解释。     

Effect of SiO2 protective layer on the femtosecond laser-induced damage of HfO2/SiO2 multilayer high-reflective coatings

Two kinds of HfO₂/SiO₂ 800 nm high-reflective (HR) coatings, with and without SiO₂ protective layer were deposited by electron beam evaporation. Laser-induced damage thresholds (LIDT) were measured for all samples with femtosecond laser pulses. The surface morphologies and the depth information of all samples were observed by Leica optical microscopy and WYKO surface profiler, respectively. It is found that SiO₂ protective layer had no positive effect on improving the LIDT of HR coating. A simple model including the conduction band electron production via multiphoton ionization and impact ionization is used to explain this phenomenon. Theoretical calculations show that the damage occurs first in the SiO₂ protective layer for HfO₂/SiO₂ HR coating with SiO₂ protective layer. The relation of LIDT for two kinds of HfO₂/SiO₂ HR coatings in calculation agrees with the experiment result.     

X-ray and UV photoelectron spectra of the oxides NbO2, MoO2 and RuO2

HeI and Mg Kα_1,2 valence band photoelectron spectra of polycrystalline samples of NbO₂, MoO₂ and RuO₂ are reported. A marked increase is observed in the intensity of the metal 4d structure, relative to that due to oxygen 2p electrons, on changing from X-ray to UV excitation. The superior resolution of the 4d signals in the HeI spectra reveals the presence of the Fermi edge in the metallic oxides MoO₂ and RuO₂. In addition, the HeI spectrum of MoO₂ shows a splitting of the metal 4d signal, confirming established ideas concerning the electronic structure of such materials.     

Regular step arrays at the SiO2/Si(111) interface

A set of slightly misoriented Si(11) wafers have been oxidized and annealed in different ways. After removal of the oxide the structure of the Si/SiO₂ interface has been studied by a high-resolution LEED system. The resulting LEED spots showed relatively sharp splitting for out-of-phase condition, indicating a nearly regular step array. The spot profiles are described precisely by a closed form terrace width distribution. The energy dependence of the spot profiles yields the vertical roughness of the samples. It can be shown that the selection of appropriate oxidation parameters decreases the deviations from the periodic structure.     

High temperature reaction and defect chemistry at the Si/SiO2 interface

The generation of structural and electrical defects in Si/SiO₂ structures upon high temperature annealing by the oxide decomposition reaction Si+SiO₂→2SiO ↑ has been studied using scanning electron microscopy (SEM) and ramped current-voltage measurements. The SiO decomposition is nucleated at crystalline defects in the substrate and results in the formation of voids in the oxide. The voids grow laterally with annealing time, independent of the nature of the defect. Prior to the formation of physical voids in the oxide, defects become electrically active, leading to low field dielectric breakdown. The breakdown degradation is prevented when the O₂ pressure in the annealing ambient is sufficient to reverse the decomposition reaction by reoxidizing the SiO product at the interface.