Experimental comparison of extreme-ultraviolet multilayers for solar physics

We compare the reflectance and stability of multilayers comprising either Si/Mo, Si/Mo2C, Si/B4C, Si/C, or Si/SiC bilayers, designed for use as extreme-ultraviolet (EUV) reflective coatings. The films were deposited by using magnetron sputtering and characterized by both x-ray and EUV reflectometry. We find that the new Si/SiC multilayer offers the greatest spectral selectivity at the longer wavelengths, as well as the greatest thermal stability. We also describe the optimization of multilayers designed for the Solar-B EIS instrument. Finally, we compare experimental reflectance data with calculations and conclude that currently available optical constants cannot be used to adequately model the performance of many of these multilayers.     

Mo/B4C/Si multilayer-coated photodiode with polarization sensitivity at an extreme-ultraviolet wavelength of 13.5 nm

A silicon photodiode coated with an interface-engineered Mo/Si multilayer was developed as a polarization sensitive detector. The Mo/B4C/Si multilayer was designed to reflect 13.5-nm extreme-ultraviolet (EUV) radiation at an incident angle of 45 degrees, at which the maximum polarization sensitivity occurs. The sensitivity of this specially coated photodiode and its polarization responses were determined by measurement of the reflectance and transmittance of the multilayer coating with synchrotron radiation. The Mo/B4C/Si multilayer was found to reflect 69.9% of the s-polarized radiation and only 2.4% of the p-polarized radiation, thus transmitting approximately 0.2% s-polarized radiation and 8.4% p-polarized radiation at a 13.5-nm wavelength and a 45 degrees angle of incidence. A polarization ratio, (Tp - Ts)/(Tp + Ts), of 95% was achieved with sufficiently high sensitivity from this photodiode. This result demonstrates the high polarization sensitivity and the usefulness of multilayer-coated photodiodes as novel EUV polarimeters.     

Improved analyzer multilayers for aluminium and boron detection with x-ray fluorescence

We have developed improved analyzer multilayers for the detection of aluminium (Al) and boron (B) on silicon (Si) wafers with wavelength-dispersive x-ray fluorescence spectrometers. For the detection of Al on Si wafers we show that WSi(2)/Si and Ta/Si multilayers provide detection limits that are 42% and 60% better, respectively, than with currently used W/Si multilayers. For the detection of B on Si wafers we show that La/B(4)C multilayers improve the detection limit by ~28% compared with a conventionally used Mo/B(4)C multilayer.     

Survey of Ti-, B-, and Y-based soft x-ray-extreme ultraviolet multilayer mirrors for the 2- to 12-nm wavelength region

We have performed an experimental investigation of Ti-, B(4)C-, B-, and Y-based multilayer mirrors for the soft x-ray?extreme ultraviolet (XUV) wavelength region between 2.0 and 12.0 nm. Eleven different material pairs were studied: Ti/Ni, Ti/Co, Ti/Cu, Ti/W, B(4)C/Pd, B/Mo, Y/Pd, Y/Ag, Y/Mo, Y/Nb, and Y/C. The multilayers were sputter deposited and were characterized with a number of techniques, including low-angle x-ray diffraction and normal incidence XUV reflectometry. Among the Ti-based multilayers the best results were obtained with Ti/W, with peak reflectances up to 5.2% at 2.79 nm at 61° from normal incidence. The B(4)C/Pd and B/Mo multilayer mirrors had near-normal incidence (5°) peak reflectances of 11.5% at 8.46 nm and 9.4% at 6.67 nm, respectively, whereas a Y/Mo multilayer mirror had a maximum peak reflectance of 25.6% at 11.30 nm at the same angle. The factors limiting the peak reflectance of these different multilayer mirrors are discussed.     

Reflectance measurements on clean surfaces for the determination of optical constants of silicon in the extreme ultraviolet-soft-x-ray region

The refractive index n = 1 - delta + ibeta of Si in the energy range 50-180 eV is investigated with angle-dependent reflectance measurements. The optical constants delta and beta are both determined by fitting to the Fresnel equations. The results of this method are compared with the values in the atomic tables derived from experimental data for beta and implementation of the Kramers-Kronig relations for delta. The samples were prepared by UV irradiation and HF:ethanol dipping to H passivate the surface. It is found that the values of delta in the atomic tables are 8-15% too high in the region 50-90 eV. This is attributed to missing oscillator strength in the tabulated absorption coefficient for Si. The measured values of beta for crystalline Si exhibit structure below the L (2,3) edge (99.8 eV), as was previously observed in transmission measurements of Si(111). It is also found that the method of least-squares fitting reflectance data to obtain optical constants is most effective for energies well below the edge, where delta > beta, while for a range of energies around and above the edge, where delta < beta, the optical constants are determined with large uncertainties. This behavior is not unique to the Si L(2,3) edge.     

W/SiC x-ray multilayers optimized for use above 100 keV

We have developed a new depth-graded multilayer system comprising W and SiC layers, suitable for use as hard x-ray reflective coatings operating in the energy range 100-200 keV. Grazing-incidence x-ray reflectance at E = 8 keV was used to characterize the interface widths, as well as the temporal and thermal stability in both periodic and depth-graded W/SiC structures, whereas synchrotron radiation was used to measure the hard x-ray reflectance of a depth-graded multilayer designed specifically for use in the range E approximately 150-170 keV. We have modeled the hard x-ray reflectance using newly derived optical constants, which we determined from reflectance versus incidence angle measurements also made using synchrotron radiation, in the range E = 120-180 keV. We describe our experimental investigation in detail compare the new W/SiC multilayers with both W/Si and W/B4C films that have been studied previously, and discuss the significance of these results with regard to the eventual development of a hard x-ray nuclear line telescope.     

Carbon buffer layers for smoothing superpolished glass surfaces as substrates for molybdenum /silicon multilayer soft-x-ray mirrors

Zerodur and BK7 glass substrates (developed by Fa. Glaswerke Schott, D-55014 Mainz, Germany) from Carl Zeiss Oberkochen polished to a standard surface roughness of varsigma = 0.8 nm rms were coated with a C layer by electron-beam evaporation in the UHV. The roughness of the C-layer surfaces is reduced to 0.6 nm rms. A normal-incidence reflectance of 50% at a wavelength of 13 nm was measured for a Mo/Si multilayer soft-x-ray mirror with 30 double layers (N = 30) deposited onto the BK7/C substrate, whereas a similar Mo/Si multilayer (N = 30) evaporated directly onto the bare BK7 surface turned out to show a reflectance of only 42%.     

Thermal stability of sputtered Mo/X and W/X (X = BN:O, B(4)C:O, Si, and C) multilayer soft-x-ray mirrors

We prepared eight samples of Mo/X and W/X (X = BN:O, B(4)C:O, Si, and C) multilayers by magnetron sputtering. Analyses of x-ray photoelectron spectroscopy for the boron nitride and the B(4)C layers showed the concentration of O to be nonnegligible. We have evaluated the thermal stability by measuring soft-x-ray specular reflectances before and after thermal annealing occurs at temperatures as high as 700 °C. The results suggest that the thermal stability depends largely on the inclusion of low-density materials and not on the type of metal. Of the four low-density materials studied, BN:O is thermally the most stable, and the Mo/BN:O multilayer, the most stable among the eight samples, shows stability as high as 700 °C.     

Absolute Photoabsorption Measurements of Molybdenum in the Range 60-930 eV for Optical Constant Determination

Transmission measurements for the optical constants delta, beta of thecomplex refractive index n = 1 - delta + ibeta of molybdenum are performed in the energy range 60-930eV. Free-standing C/Mo/C foils of five different thicknesses are used, and the results are normalized for the presence of the carbon layers in the samples. These absorption results are combined with previous experimental data in the lower energy range and values fromthe atomic tables to obtain the imaginary (absorptive) part of the refractive index for molybdenum in the range 1-30,000 eV. The real(dispersive) part of n was calculated from Kramers-Kronig analysis with the above absorption data. An evaluation with the partial sum rules demonstrates that this new compilation provides an improved set of values for n covering a wider energy range compared with the current tabulated values. The new results are applied so as to calculate thenormal-incidence reflectivities of Mo/Si and Mo/Be multilayer mirrors.     

Investigation of Mo/Si and W/Si interfaces by phase modulated spectroscopic ellipsometry and cross-sectional transmission electron microscopy

Mo and W thin films and Mo/Si/Mo and W/Si/W tri-layers have been deposited by r.f. magnetron sputtering on c-Si substrates as a precursor to the fabrication of Mo/Si and W/Si multilayer X-ray mirrors. The Phase Modulated Spectroscopic Ellipsometry (SE) technique has been used for characterizing the single layer films to derive information regarding the thickness and volume fraction of voids present in the surface layers. The Mo/Si/Mo and W/Si/W tri-layer structures have been characterized by the Cross-sectional Transmission Electron Microscopy (XTEM) technique. The inter-diffusion at the interfaces of the tri-layer structures observed by the XTEM technique has been correlated to the thickness of the surface layers of the metal films obtained from the SE measurement.     

Mo/Si and Mo/Be multilayer thin films on Zerodur substrates for extreme-ultraviolet lithography

Multilayer-coated Zerodur optics are expected to play a pivotal role in an extreme-ultraviolet (EUV) lithography tool. Zerodur is a multiphase, multicomponent material that is a much more complicated substrate than commonly used single-crystal Si or fused-silica substrates. We investigate the effect of Zerodur substrates on the performance of high-EUV reflectance Mo/Si and Mo/Be multilayer thin films. For Mo/Si the EUV reflectance had a nearly linear dependence on substrate roughness for roughness values of 0.06-0.36 nm rms, and the FWHM of the reflectance curves (spectral bandwidth) was essentially constant over this range. For Mo/Be the EUV reflectance was observed to decrease more steeply than Mo/Si for roughness values greater than approximately 0.2-0.3 nm. Little difference was observed in the EUV reflectivity of multilayer thin films deposited on different substrates as long as the substrate roughness values were similar.     

ZnS stacking order influence on the formation of Zn-poor and Zn-rich Cu2ZnSnS4 phase

This paper reports the synthesis and characterization of Cu₂ZnSnS₄ (CZTS) absorber films, prepared by a two-step electrodeposition of a ZnS (zinc sulfide) binary and a CZT (copper, zinc and tin) ternary precursors on Mo/Ti/Si substrates. The as-electrodeposited ZnS/CZT and CZT/ZnS stacks were thermally treated in a tubular furnace in sulfur environment at 550 °C. The role of the ZnS buffer layer is to provide a zinc and sulfur reservoir, needed to complete the formation of kesterite phase. X-ray diffraction and Raman analyses revealed the formation of the CZTS phase. The surface morphology and chemical composition of the films were studied using a scanning electron microscope. The bandgap values inferred from diffuse reflectance data, are discussed with respect to the stoichiometry which is considerably affected by the order of the stacks. Room-temperature photoluminescence of the CZT/ZnS sample showed a board PL band of 1.51 eV. It was found that the film with a ZnS layer on top is preferred for the formation of a Zn-rich single CZTS phase.

     

Antireflective hydrophobic si subwavelength structures using thermally dewetted Ni/SiO2 nanomask patterns

We report the disordered silicon (Si) subwavelength structures (SWSs), which are fabricated with the use of inductively coupled plasma (ICP) etching in SiCl4 gas using nickel/silicon dioxide (Ni/SiO2) nanopattens as the etch mask, on Si substrates by varying the etching parameters for broadband antireflective and self-cleaning surfaces. For the fabricated Si SWSs, the antireflection characteristics are experimentally investigated and a theoretical analysis is made based on the rigorous coupled-wave analysis method. The desirable dot-like Ni nanoparticles on SiO2/Si substrates are formed by the thermal dewetting process of Ni films at 900 degrees C. The truncated cone shaped Si SWS with a high average height of 790 +/- 23 nm, which is fabricated by ICP etching with 5 sccm SiCl4 at 50 W RF power with additional 200 W ICP power under 10 mTorr process pressure, exhibits a low average reflectance of approximately 5% over a wide wavelength range of 450-1050 nm. The water contact angle of 110 degrees is obtained, indicating a hydrophobic surface. The calculated reflectance results are also reasonably consistent with the experimental data.     

高速钢中(M,Si)_6C 碳化物的研究

本文采用 W3Mo2Cr4V 和 Fe-16Mo-0.9C 两种合金,研究了 Si 对 M_6C 碳化物的组成和稳定性的影响,着重讨论了(M,Si)_6C 碳化物的组成和稳定性与含 Si 高速钢的相变和回火硬度的关系。分析表明,(M,Si)_6C 的稳定程度对含 Si 高速钢的回火硬度具有决定性的影响。提出了高速钢中能否使用 Si 作为合金元素的△W 判据。     

W/C, W/Ti, Ni/Ti, and Ni/V Multilayers for the Soft-X-ray Range: Experimental Investigation with Synchrotron Radiation

An experimental investigation of W/C, W/Ti, Ni/Ti, and Ni/V multilayers is presented that uses synchrotron radiation in the soft-x-ray energy region between 100 and 1500 eV with special emphasison the water window. The multilayers were designed as normal incidence reflectors and for polarimetry purposes around the Brewster angle. Both reflection and transmission multilayers were prepared for use as linear polarizers and phase retarders, respectively, to produce or analyze circularly polarized light. Their period was optimized to achieve maximum reflectance at the 1s absorption edge of C (284 eV) and the 2p edges of Ti (454 eV) and V (512 eV), respectively. At these edges the multilayers show an enhancement of reflectance and energy resolution that is in accordance with theoretical calculations.     

Fe基非晶纳米晶喷涂粉末的制备及性能

利用氩气雾化方法制备出了Fe48Cr15Ni15Si5.8B2.7Mo6W4Al2Co非晶合金粉末,利用扫描电镜、透射电镜、X射线衍射仪、粒度分析仪和差示扫描量热仪对粉末的微观结构、相组成、粒径分布以及热稳定性进行了分析。研究表明,所制备的粉末结构为非晶纳米晶结构,纳米晶的尺寸约为20～40nm;粉末颗粒形貌呈球形或椭球形,流动性很好。差热试验表明,粉末具有很强的非晶形成能力并且热稳定性非常好;筛分出来的小于47!m目的粉末粒度正态分布比较窄。     

(Mo,W)5Si3–(Mo,W)Si2 Eutectics: Properties and Application in Composite Materials

Experimental data are presented on (Mo,W)₅Si₃ and (Mo,W)Si₂ solid solutions and are analyzed using the known phase diagrams of the binary systems Mo–Si and W–Si. It is shown that, with increasing tungsten content, the melting temperature of the (Mo,W)₅Si₃–(Mo,W)Si₂ eutectic rises. Surprisingly, the alloys with W : Mo atomic ratios close to unity are found to contain, along with the silicide solid solutions, molybdenum disilicide almost free of tungsten. The mean room-temperature hardness of the eutectic alloys varies nonmonotonically with tungsten content and shows maxima at 33 and 75 at. % W. The surface texture is found to have a significant effect on the rate of high-temperature gas corrosion. The possibility of compositional control (variations in the W : Mo and (Mo,W)₅Si₃ : (Mo,W)Si₂ ratios) over the thermal expansion of the alloys is analyzed. Data are presented on the temperature-dependent resistivity of SiC-matrix composites.     

Effects of sintering aids on the densification of Mo–Si–B alloys

The effects of seven sintering aids (0.5?at.% Ni, Co, Fe, Cr, Zr, Nb, and Pd) on the densification of Mo–Si–B alloys of six different compositions (Mo, Mo–0.2Si, Mo–0.2Si–0.02B, Mo–2.5Si–2.5B, Mo–7Si–5B, and Mo–8.9Si–7.7B?at.%) are systematically investigated. It was found that Ni, Co, and Fe are effective in enhancing densification of Mo–Si–B alloys, and Ni is the most effective sintering aid. This study supports a previously proposed hypothesis that activated sintering results from enhanced mass transport in the sintering-aid-induced quasi-liquid intergranular films (a type of grain boundary complexion). The relative effectiveness of these sintering aids can be rationalized by analyzing several key thermodynamic parameters that control the stability of premelting-like grain boundary complexions. Future studies are needed to develop interfacial thermodynamic models and methods for computing “grain boundary complexion (phase) diagrams” for multicomponent systems, which can be a useful component for the “Materials Genome” project that will enable better predictions of the activated sintering and other materials phenomena.     

Ab initio modeling study of boron diffusion in silicon

We present investigations of boron diffusion in crystalline silicon using ab initio calculations (W. Windl et al., Phys. Rev. Lett. 83 (1999) 4345). Based on these results, a new mechanism for B diffusion mediated by Si self-interstitials was proposed. Rather than kick-out of B into a mobile channel-interstitial, one- or two-step diffusion mechanisms have been found for the different charge states. The predicted activation energy of 3.5–3.8 eV, migration barrier of 0.4–0.7 eV, and diffusion-length exponent of −0.6 to −0.2 eV are in excellent agreement with experiment. We also present results of ab initio calculations for the structure and energetics of boron-interstitial clusters in Si. We show how these first-principles results can be used to create a physical B diffusion model within a continuum simulator which has strongly enhanced predictive power in comparison to traditional diffusion models.     

PVD thermal barrier coating systems for Mo–Si–B alloys

Abstract

Oxidation protective layers with chemical compositions of Mo–70Al, Mo–46Si–24B, Mo–37Si–15B and Mo–47Si–24Al (at.-%) were deposited on Mo–9Si–8B specimens by magnetron sputtering. After pre-oxidation of the coated samples, ceramic topcoats of yttria partially stabilized zirconia (YSZ) and gadolinium zirconate (GZO) were applied using electron-beam physical vapour deposition. Both as-deposited YSZ and GZO topcoats exhibited good adhesion to the pre-oxidised bond coats. The different thermal barrier coating (TBC) systems were exposed to air at 1000 °C for periods between 20 and 100 h. The YSZ topcoat was tightly-adherent to the borosilicate scale grown on the Mo–46Si–24B bond coat after 20 h of exposure. Similar results were obtained for GZO topcoats deposited on Mo–46Si–24B and Mo–37Si–15B bond coats. The TBC system consisting of GZO topcoat and Mo–47Si–24Al bond coat, which formed a mixed scale of silica and mullite-like oxides, survived 100 h at 1000 °C. However, after this exposure time, the bond coats were approaching their lifetime due to the low layer thickness (5–10 μm). Oxidation of the Mo–Si–B substrate at unprotected areas around the suspension hole of the samples caused severe deterioration of the Mo–70Al bond coat and substantial degradation of the outer region of the GZO topcoat due to chemical reactions with MoO₃.