Fredrik Eriksson

14.5% near-normal incidence reflectance of Cr/Sc x-ray multilayer mirrors for the water window

Cr/Sc multilayer mirrors, synthesized by ion-assisted magnetron sputter deposition, are proved to have a high near-normal reflectivity of R = 14.5% at a grazing angle of 87.5 degrees measured at the wavelength lambda = 3.11 nm, which is an improvement of more than 31% compared with previously published results. Elastic recoil detection analyses show that the mirrors contained as much as 15 at. % of N and traces of C and O. Soft x-ray reflectivity simulations reveal interface widths of sigma = 0.34 nm and an exceptionally small layer thickness drift of approximately 1.6 x 10(-5) nm/multilayer period throughout the stack. Simulations show that a reflectivity of R = 25.6% is attainable if impurities and layer thickness drift can be eliminated. The abrupt interfaces are achieved with ion assistance with a low ion energy of 24 eV and high ion-to-metal flux ratios of 7.1 and 23.1 during Cr and Sc sputter deposition, respectively. In addition, a near-normal incidence reflectivity of 5.5% for the C VI emission line (lambda = 3.374 nm) from a laser plasma source was verified.

Recent advances in ion-assisted growth of Cr/Sc multilayer X-ray mirrors for the water window

Cr/Sc multilayer X-ray mirrors intended for normal incidence reflection in the water window wavelength range, ?=[2.4-4.4nm], have been grown by ion-assisted sputter deposition and characterized usi ...

Enhanced soft x-ray reflectivity of Cr/Sc multilayers by ion-assisted sputter deposition

Cr/Sc multilayers have been grown on Si substrates using dc magnetron sputtering. The multilayers are intended as condenser mirrors in a soft x-ray microscope operating at the wavelength 3.374 nm. ...

Atomic scale interface engineering by modulated ion-assisted deposition applied to soft x-ray multilayer optics

Cr/Sc and Ni/V multilayers, intended as normal incidence soft x-ray mirrors and Brewster angle polarizers, have been synthesized by employing a novel modulated low-energy and high-flux ion assistance as a means of engineering the interfaces between the subnanometer layers on an atomic scale during magnetron sputter deposition. To reduce both roughness and intermixing, the ion energy was modulated within each layer. The flat and abrupt interfaces yielded soft x-ray mirrors with near-normal incidence reflectances of R = 20.7% at the Sc 2p absorption edge and R = 2.7% at the V 2p absorption edge. Multilayers optimized for the Brewster angle showed a reflectance of R = 26.7% and an extinction ratio of R(s)/R(p)=5450 for Cr/Sc and R = 10% and R(s)/R(p)=4190 for Ni/V. Transmission electron microscopy investigations showed an amorphous Cr/Sc structure with an accumulating high spatial frequency roughness. For Ni/V the initial growth mode is amorphous and then turns crystalline after approximately 1/3 of the total thickness, with an accumulating low spatial frequency roughness as a consequence. Elastic recoil detection analyses showed that N was the major impurity in both Cr/Sc and Ni/V with concentrations of 15 at. % and 9 at. %, respectively, but also O (3 at. % and 1.3 at. %) and C (0.5 at. % and 1.9 at. %) were present. Simulations of the possible normal incidence reflective properties in the soft x-ray range of 100-600 eV are given, predicting that reflectivities of more than 31% for Cr/Sc and 5.8% for Ni/V can be achieved if better control of the impurities and the deposition process is employed. The simulations also show that Cr/Sc is a good candidate for mirrors for the photon energies between the absorption edges of B (E = 188 eV) and Sc (E = 398.8 eV).

Measurements of the optical constants of scandium in the 50-1300eV range.

Scandium containing multilayers have been produced with very high reflectivity in the soft x-ray spectrum. Accurate optical constants are required in order to model the multilayer reflectivity. Since there are relatively few measurements of the optical constants of Scandium in the soft x-ray region we have performed measurements over the energy range of 50-1,300 eV. Thin films of Scandium were deposited by ion-assisted magnetron sputtering at Linkoping University and DC Magnetron sputtering at CXRO. Transmission measurements were performed at the Advanced Light Source beamline 6.3.2. The absorption coefficient was deduced from the measurements and the dispersive part of the index of refraction was obtained using the Kramers-Kronig relation. The measured optical constants are used to model the near-normal incidence reflectivity of Cr/Sc multilayers near the Sc L2,3 edge.

Compact soft x-ray reflectometer based on a line-emitting laser-plasma source

We describe a compact soft x-ray reflectometer for in-house characterization of water-window multilayer optics. The instrument is based on a line-emitting, liquid-jet, laser-plasma source in combination with angular scanning of the studied multilayer optics. With a proper choice of target liquid and thin-film filters, one or a few lines of well-defined wavelength dominate the spectrum and multilayer periods are measured with an accuracy of 0.003 nm using a multi-line calibration procedure. Absolute reflectivity may also be estimated with the instrument. The typical measurement time is currently 10 min. Although the principles of the reflectometer may be used in the entire soft x-ray and extreme ultraviolet range, the current instrument is primarily directed towards normal-incidence multilayer optics for water-window x-ray microscopy, and is thus demonstrated on W/B4C multilayers for this wavelength range.

Reflectivity and structural evolution of Cr/Sc and nitrogen containing Cr/Sc multilayers during thermal annealing

It is shown that the thermal stability in vacuum of Cr/Sc multilayer thin films used as reflective optical components in soft x-ray instrumentation has substantial dependence on incorporation of N. ...

Reactive sputtering of δ-ZrH2 thin films by high power impulse magnetron sputtering and direct current magnetron sputtering

Reactive sputtering by high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS) of a Zr target in Ar/H-2 plasmas was employed to deposit Zr-H films on Si(100) ...

Experimental and theoretical investigation of Cr1-xScxN solid solutions for thermoelectrics

We investigate the trends in mixing thermodynamics of Cr1-xScxN solid solutions in the cubic B1 structure and their electronic density of state by first-principle calculations, and thin-film synthe ...

Effects of O and N impurities on the nanostructural evolution during growth of Cr/Sc multilayers

Transition metal multilayers are prime candidates for high reflectivity soft x-ray multilayer mirrors. In particular, Cr/Sc multilayers in the amorphous state have proven to give the highest reflec ...