Showing papers by "Eric M. Gullikson published in 2021"

Near total reflection X-ray photoelectron spectroscopy: Quantifying chemistry at solid/liquid and solid/solid interfaces

Abstract: Author(s): Martins, HP; Conti, G; Cordova, I; Falling, L; Kersell, H; Salmassi, F; Gullikson, E; Vishik, I; Baeumer, C; Naulleau, P; Schneider, CM; Nemsak, S | Abstract: Near total reflection regime has been widely used in x-ray science, specifically in grazing incidence small angle x-ray scattering and in hard x-ray photoelectron spectroscopy (XPS). In this work, we introduce some practical aspects of using near total reflection (NTR) in ambient pressure XPS and apply this technique to study chemical concentration gradients in a substrate/photoresist system. Experimental data are accompanied by x-ray optical and photoemission simulations to quantitatively probe the photoresist and the interface with the depth accuracy of ∼1 nm. Together, our calculations and experiments confirm that NTR XPS is a suitable method to extract information from buried interfaces with highest depth-resolution, which can help address open research questions regarding our understanding of concentration profiles, electrical gradients, and charge transfer phenomena at such interfaces. The presented methodology is especially attractive for solid/liquid interface studies, since it provides all the strengths of a Bragg-reflection standing-wave spectroscopy without the need of an artificial multilayer mirror serving as a standing wave generator, thus dramatically simplifying the sample synthesis.

The Globe Orbiting Soft X-ray (GOSoX) polarimeter concept study

Abstract: We describe an implementation of a broad-band soft X-ray polarimeter, substantially based on previous designs. The Globe-Orbiting Soft X-ray Polarimeter (GOSoX) is a SmallSat. As in a related mission concept the PiSoX Polarimeter, the grating arrangement is designed optimally for the purpose of polarimetry matching the dispersion of a spectrometer to a laterally graded multilayer (LGML). For GOSoX, the optics are lightweight Si mirrors in a one-bounce parabolic configuration. The instrument covers the wavelength range from 31 A to 75 A (165 - 400 eV). Upon satellite rotation, the intensities of the dispersed spectra, after reflection and polarizing by the LGMLs, give the three Stokes parameters needed to determine a source's linear polarization fraction and orientation. The design can be extended to higher energies as LGMLs are developed further. We describe the potential scientific return and the proposed mission concept following the results of a JPL Team X concept study.

Manufacture and performance of blazed soft x-ray transmission gratings for Arcus and Lynx

Abstract: The soft x-ray band covers the characteristic lines of the highly ionized low-atomic-number elements, providing diagnostics of the warm and hot plasmas in star atmospheres, interstellar dust, galaxy halos and clusters, and the cosmic web. High-resolution spectroscopy in this band is best performed with grating spectrometers. Soft x-ray grating spectroscopy with R = λ / Δ λ = > 104 has been demonstrated with critical-angle transmission (CAT) gratings. CAT gratings combine the relaxed alignment and temperature tolerances and the low mass of transmission gratings with high diffraction efficiency blazed in high orders. They are an enabling technology for the proposed Arcus grating explorer and were selected for the Lynx Design Reference Mission grating spectrometer instrument. Both Arcus and Lynx require the manufacture of hundreds to perhaps ~2000 large-area CAT gratings. We are moving toward CAT grating volume manufacturing using 200 mm silicon-on-insulator wafers, 4X optical projection lithography tools, deep reactive-ion etching, and KOH polishing. We have, for the first time, produced high-throughput 200 nm-period CAT gratings ~50% deeper than previously fabricated. X-ray diffraction efficiency is significantly improved in the ~1:25 - 1.75 nm wavelength range, peaking above 40% (sum of blazed orders). A new grating-to-grating alignment technique utilizing cross-support diffraction of visible light is presented, as well as the results of CAT grating emissivity measurements.λ

Highly efficient ultra-low blaze angle multilayer grating.

Abstract: We have developed an advanced process for blaze angle reduction of x-ray gratings for the soft, tender, and EUV spectral ranges. The process is based on planarization of an anisotropically etched Si blazed grating followed by a chemically selective plasma etch. This provides a way to adjust the blaze angle to any lower value with high accuracy. Here we demonstrate the reduction of the blaze angle to an extremely low value of 0.04°±0.004°. For a 100 lines/mm grating with a Mo/Si multilayer coating, the grating exhibits diffraction efficiency of 58% in the 1st diffraction order at a wavelength of 13.3 nm. This technique will be applicable to a wide range of uses of high efficiency gratings for synchrotron sources, as well as for Free Electron Lasers (FEL).

Near total reflection X-ray photoelectron spectroscopy: Quantifying chemistry at solid/liquid and solid/solid interfaces

Abstract: Near total reflection regime has been widely used in X-ray science, specifically in grazing incidence small angle X-ray scattering and in hard X-ray photoelectron spectroscopy. In this work, we introduce some practical aspects of using near total reflection in ambient pressure X-ray photoelectron spectroscopy and apply this technique to study chemical concentration gradients in a substrate/photoresist system. Experimental data are accompanied by X-ray optical and photoemission simulations to quantitatively probe the photoresist and the interface with the depth accuracy of ~1 nm. Together, our calculations and experiments confirm that near total reflection X-ray photoelectron spectroscopy is a suitable method to extract information from buried interfaces with highest depth-resolution, which can help address open research questions regarding our understanding of concentration profiles, electrical gradients, and charge transfer phenomena at such interfaces. The presented methodology is especially attractive for solid/liquid interface studies, since it provides all the strengths of a Bragg-reflection standing-wave spectroscopy without the need of an artificial multilayer mirror serving as a standing wave generator, thus dramatically simplifying the sample synthesis.

Using Temporally Synthesized Laser Pulses to Enhance the Conversion Efficiency of Sn Plasmas for EUV Lithography

Abstract: We have studied the laser pulse shape dependence of the conversion efficiency of λ = 1.03 μm laser pulse energy into 13.5 nm extreme ultraviolet (EUV) emission from a Sn laser-produced plasma. Laser pulses of arbitrary temporal shape ranging from hundreds of picoseconds to several nanoseconds were generated using a programmable pulse synthesizer based on a diode-pumped chirped pulse amplification Yb: YAG laser. Measurements show that the conversion efficiency favors the use of nearly square pulses of duration longer than 2 ns, in agreement with hydrodynamic/atomic physics simulations. A 35% increase in conversion efficiency was obtained when Q-switched pulses were substituted by square pulses of a similar duration. Experiments conducted irradiating a Sn target with a sequence of two time-delayed 250 ps pulses showed a 30 percent increase in the EUV yield respect to a single pulse of the same total energy when the pulse separation was optimum at 2.1 ns. This suggests that re-heating of the plasma with delayed laser pulses could be used to improve the EUV yield. The spectroscopic characterization of EUV emission and in-band EUV images that characterize the source size are also presented.

Low blaze angle gratings for x-ray and EUV applications

Abstract: Low groove density gratings with blaze angles as low as 0.1‡ are required for plane grating monochromators for x-ray synchrotron and Free Electron Laser applications. To achieve so small a blaze angles we developed a process of reduction of the blaze angle of a coarse Si grating fabricated by anisotropic wet etching. The coarse grating with a blaze angle of 4° is planarized by a polymer layer and then plasma etching is applied to remove the polymer and underlying silicon material. The appropriate ratio of etch rates of Si and the polymer material provides reduction of the groove depth and the blaze angle. We developed a set of reduction recipes which provide blaze angle reduction down to 0.04° with high accuracy and which preserves the perfect triangular shape of the grooves. The ultra-low blaze angle grating coated with a Mo/Si multilayer exhibits a record diffraction efficiency of 58% due to the perfect match of the groove depth with the multilayer d-spacing. This opens up wide possibilities for making highly accurate and efficient diffraction gratings for tender x-ray, free electron laser, and EUV lithography applications. The low blaze angle gratings have a perfect triangular groove profile and highly smooth surfaces of the blazed facets which ensures high diffraction efficiency of the x-ray gratings.

Calibration of the MaGIXS experiment II: Flight Instrument Calibration

Abstract: The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) is a sounding rocket experiment that observes the soft X-ray spectrum of the Sun from 6.0 - 24 Angstrom (0.5 - 2.0 keV), successfully launched on 30 July 2021. End-to-end alignment of the flight instrument and calibration experiments are carried out using the X-ray and Cryogenic Facility (XRCF) at NASA Marshall Space Flight Center. In this paper, we present the calibration experiments of MaGIXS, which include wavelength calibration, measurement of line spread function, and determination of effective area. Finally, we use the measured instrument response function to predict the expected count rates for MaGIXS flight observation looking at a typical solar active region