Performance of Co/Ti multilayers in a water window soft x-ray regime

• Published in: Applied optics (2004) 2017-09, Vol.56 (27), p.7525
• Main Authors: Sarkar, Piyali, Biswas, Arup, De, Rajnarayan, Divakar Rao, K, Ghosh, Subir, Modi, M H, John, Siju, Barshilia, H C, Bhattacharyya, Dibyendu, Sahoo, Naba Kishor
• Format: Article
• Language: English
• ISSN: 1559-128X; 2155-3165
• DOI: 10.1364/AO.56.007525

The DC magnetron sputter grown Co/Ti multilayers, with ultra-low bi-layer thicknesses and with Co layers deposited under mixed ambience of argon and dry air, have been investigated for use in the water window soft x-ray regime of 23-44 Å. Initially, deposition parameters have been optimized for obtaining smooth and continuous low thickness Co and Ti single-layer films, and, then, multilayers with five bi-layers of various bi-layer thicknesses were deposited. The samples have been primarily characterized by the grazing incidence x-ray reflectivity (GIXR) measurements with a hard x-ray laboratory source. Subsequently, a set of multilayers with an increasing number of bi-layers has been deposited with a constant bi-layer thickness of 42 Å. GIXR results show that hard x-ray reflectivity at the first Bragg peak is maximum for the 20 bi-layer sample, beyond which the reflectivity decreases. Finally, the samples with the most promising hard x-ray GIXR have been used for soft x-ray reflectivity measurement with synchrotron radiation, and ∼2.5% peak reflectivity has been obtained in the multilayer sample at a 30.7 Å wavelength for a 21.5° grazing angle of incidence. The fitting results for both hard and soft x-ray reflectivities have been thoroughly investigated to find out the cause of the saturation of reflectivity with the increase in the number of bi-layers.