There are significant advantages for using a compact capillary discharge soft x-ray laser (SXRL) with wavelength of 46.9 nm for mass spectrometry applications. The 26.4 eV energy photons provide efficient single-photon ionization while preserving the structure of molecules and clusters. The tens of nanometers absorption depth of the radiation coupled with the focusing of the laser beam to diameter of ∼100 nm result in the ablation of atto-liter scale craters which in turn enable high resolution mass spectral imaging of solid samples. In this paper we describe results on the analysis of composition depth-profiling of multilayer oxide stack and material studies in photoresists, ionic crystals, and magnesium corrosion products using SXRL ablation mass spectrometry, a method first demonstrated by our group. These materials are used in a variety of soft x-ray applications such as detectors, multilayer optics, and many more.
Mass spectrometry plays a vital role in the direct examination of the chemical composition of solids. We have introduced the use of soft x-ray laser ablation for mass spectrometry imaging. Here we demonstrate the method potential for composition depth profiling of multilayer stacks consisting of tens of nanometers thick metal and dielectric films.
Neutral AlmCn clusters are investigated both experimentally and theoretically for the first time. Single photon ionization through 193 nm, and 46.9 nm lasers is used to detected neutral cluster distributions. AlmCn clusters are generated through laser ablation of a mixture of Al and C powders pressed into a disk. An oscillation of the VIEs of AlmCn clusters is observed in the experiments. The ionization energies of AlmCn clusters change as a function of the numbers of Al and C atoms in the clusters. Theoretical density functional theory and ab initio calculations are carried out to explore the structures, ionization energies, and molecular orbitals of the AlmCn clusters. C=C bonds are favored for the lowest energy structures for AlmCn clusters. Based on calculations of HOMOs (highest occupied molecular orbitals) of AlmCn clusters we find that the ionization energies of these clusters do not simply depend on open or closed shell valence electron configurations, but also depend on the electronic structure details of the clusters. The calculational results provide good
and consistent explanations of the experimental observations, and are consistent with them.
The reactivity of prospective capping layer extreme ultraviolet (EUV) mirror materials with hydrocarbons, alcohols, and
water is studied in the gas phase using mass spectroscopy of metal-oxide clusters. We report the results of chemistry
studies for Si, Ti, Hf, Zr, and Ru metal oxide nanoclusters in which the reaction products were ionized with little or no
fragmentation by 26.5 eV photons from a desk-top size 46.9 nm Ne-like Ar laser. Hf and Zr oxides are found to be much
less reactive than Si or Ti oxides in the presence EUV light. Ru oxides show different chemistry and are inactive with
water/alcohols, and active with saturated/unsaturated hydrocarbons. The results are relevant to the design of EUV mirror
capping layers that are resistant to carbon contamination.
Metal oxide clusters are employed in studies to help understand an important, specific, type of surface chemical
problem: the contamination of soft x-ray mirrors by carbon deposits. Herein we report nanocluster chemistry studies that
are relevant to the use of silicon oxide and titanium oxide capping layers. Systems involving SimOn, and TimOn metal
oxide nanoclusters are generated in a pulsed supersonic expansion/ablation source and passed through a reactor
containing any reactant desired. The reaction products of these gas phase clusters are ionized using single photon
ionization from a desk-top sized 46.9 nm Ne-like Ar laser providing the advantage of little or no fragmentation of
desired nanoclusters. The ionized products are analyzed by a time of flight mass spectrometer and experimental results
supply useful information related to condensed phase soft x-ray optical surfaces. The results illustrate the great potential
of the use of very compact soft x-ray lasers in photochemistry and photophysics studies.
We report the demonstration of a high repetition rate desktop-size capillary discharge laser emitting at (= 46.9 nm (26.5 eV) used for experiments in photochemistry. Laser pulses with energy ~ 13 uJ were generated at 12 Hz repetition rate by single pass amplification in a 21 cm long Ne-like Ar capillary discharge plasma column. The capillary lifetime is 2-3 104 shots. This new type of portable laser is of interest for numerous applications requiring a compact intense source of short wavelength laser light. One such application that we are currently pursuing is the study of small molecules using time of flight mass spectroscopy. Molecules include ammonia, NO, oxygen, hydrogen bonded nanoclusters, and metal oxide nanoclusters. Through single photon ionization the reactivity and catalytic behavior of these molecules is studied.
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