Deposition of high-resolution Carbon/Carbon multilayers on large areas for X-ray optical applications

To synthesize X-ray optical multilayers showing both high resolution and high reflectivity spacer and absorber materials with low absorption coefficients for the desired spectral range are required. Simulations of C/C multilayers with different period thicknesses, d, and single layer densities, show that a reflectance R ([Cu]K alpha)>80% and a resolving power of about lambda/Delta lambda about 600 can be achieved for C/C layer stacks with d=3 nm and N=1000 periods. An advanced large area PLD technique was used to deposit C/C single- and multilayers onto Si-substrates up to 6" in diameter. By variation of the laser parameters, we achieved densities of the carbon single layers in the range of C=2.0...2.7 g/cm3 (measured by XRR) and surface roughnesses sigma C=0.13...0.19 nm (measured by AFM). Due to the interface intermixing and penetration depth of highly energetic ions, especially during the deposition of the absorber layers, the density contrast of multilayers with period thicknesses lower than 5 nm is noticeably reduced. C/C multilayers with period thicknesses d=1.1...7.0 nm, more than 500 periods and density contrasts of about 0.2 g/cm3 were deposited.