Multilayer Film Research In Dynamic Black Cavity Spectral Diagnosis

In the Z-pinch array driven dynamic hohlraum experiments,the important parameters such as hohlraum radiation power,yield and radiation temperature can be evaluated by the hohlraum spectral diagnostics.A multi-channel spectrometer has been proposed to develop for this purpose.The hohlraum radiation spectrum is in an extreme ultraviolet(EUV)and soft X-ray range of 50 eV-1500 eV,where multilayer is the excellent optical disperse element.Fifteen energy points have been selected for the multi-channel spectrometer and the corresponding multilayers need to be manufactured.The multilayer design,deposition and measurement of the fifteen multilayers have been introduced in this thesis.Three multilayers working around 75 eV,95 eV and 395 eV have been thoroughly studied,in order to improve the optical,structural,stress and stability performance of the multilayers.Chapter 3 and chapter 4 is the research focus.In the study of the multilayer working around 395 eV(3.14 nm),the V/Sc multilayer with short period and large bilayers was deposited.The high reflectivity of the V/Sc multilayer mirror working around the Sc-L absorption edge of the water window range has been firstly demonstrated in experiment.V/Sc multilayer has shown an evidently smaller interface width of 0.27 nm/0.32 um,comparing with the 30-bilayer Cr/Sc multilayer by GIXR deposited under the same condition with an interface width of 0.28 nm/0.47 nm.As the multilayer grows from 30 bilayers to 400 bilayers,it has been observed that the polycrystalline structure was slightly enhanced.Meanwhile,a highest reflectance of 18.4%was measured at λ=3.129 nm under a grazing incidence of 9°.In addition,it has been found that the a reflectivity of 5.3%can be realized near the V-L absorption edge by this 400-bilayer V/Sc multilayer,which is the special advantage of the V/Sc material combination.In the thermal stability study of the V/Sc multilayers,it has been found from the GIXR that the layer structure starts to deteriorate at 200℃,get much worse after annealing at 250℃ and get to be destroyed after annealing at 300℃.The phase transformation of the hexagonal Sc(101)to the hexagonal Sc(002)was observed during the evolution of the XRD patterns with annealing temperatures to 250 ℃,at which temperature an additional diffraction peak corresponding to the cubic V(110)also emerge.The grain sizes were further increased after annealing at 300℃.The TEM result of the sample after annealing at 250℃ have found that the layer structure of the middle part of the multilayer was severely destroyed while it can be only partially seen at the top and the bottom part.The hexagonal Sc(002)and the cubic V(110)were observed from the TEM and the selective area electron diffraction(SAED)measurements for the sample annealed at 250℃,which has further demonstrated the previous XRD patterns.Energy dispersive X-ray spectrum discovered that the periodic oscillation of the relative concentration of V and Sc almost disappeared after annealing,which indicated a severe elemental diffusion mixing.All the results compared with that of Cr/Sc multilayers have shown that the crystallization of V/Sc occurred at a lower annealing temperature.As a result of the thermal dynamically process by the mutual promotion of the diffusion mixing and crystallization,the layer structure degraded with increasing annealing temperatures and finally broke down.In the temporal stability study,the GIXR measurements for the V/Sc multilayer with 400 bilayers after a storage of 6 months period have that,oscillation of the reflectance curve at about 1°～2° was shifted to the lower angle with time The change of the GIXR and the SXR was considered as a result of a gradual oxidation and some other chemical change of the surface B4C layer and probably the first few bilayers of V and Sc.Narrow bandwidth Si/C multilayer mirrors were developed at the energy of 75 eV(16.5 nm)while the structure,stress and EUV performance were characterized.To reduce the large stress of the multilayer and maintain a practical reflectivity,different working pressures,from 0.13 Pa to 0.52 Pa,are optimized during the deposition.The grazing incidence X-ray reflectometry(GIXR)measurement and the fitting results indicate that an interlayer was formed at the interfaces while both the interlayer thickness and interface widths increase with larger working pressure.The surface roughness of the multilayers also increases from 0.13 nm at 0.13 Pa to 0.29 nm at 0.52 Pa,as revealed by the atomic force microscope(AFM)measurements.The multilayer stress decreases from-682 MPa to-384 MPa,as the working pressure increases from 0.13 Pa to 0.52 Pa,respectively.The experimental EUV reflectivity of the samples with 20 bilayers gradually decreased from 26.3%to 18.9%with increased working pressure.The bandwidth of the reflection peak remains similar for the different samples with a full width half maximum(FWHM)value of around 0.87 nm.A maximum EUV reflectivity of 33.2%and a bandwidth of 0.64 nm were achieved by the sample with 50 bilayers fabricated under a working pressure of 0.13 Pa.In the development of the multilayer working at 95 eV(13 nm),given the design requirement of the spectrometer,the multilayer was required to be operated under a grazing incidence of 60 degree given to the facility condition.A highest reflectivity can be achieved by the conventional Mo/Si multilayer,but it will also display a large bandwidth,which cannot satisfy the quasi-monochromatic requirement for the multilayer.It was proposed in this paper that taking Mo and C together as the absorbing materials to combine with Si to form Si/Mo/C multilayer,which can significantly reduce the bandwidth with a slight decrease of the reflectivity.This Si/Mo/C multilayer was fabricated by direct current magnetron sputtering technique.The GIXR measurement has shown the multilayer with a clear and complete structure.The EUV reflectivity measurement at the synchrotron radiation light source has demonstrated this Si/Mo/C multilayer with a reflectivity of 56.2%and a bandwidth of 0.49 nm(3.7 eV).The bandwidth is significantly narrower than that of Mo/Si multilayer,which makes it more suitable to be used as an optical disperse element during the spectral diagnostics of the dynamic hohlraum.