XUV laser mass spectrometry for nano-scale 3D elemental profiling of functional thin films

Abstract

Direct nano-scale microanalysis is important for photovoltaic functional thin films to characterize their homogeneity and purity. This demands combining spatial resolution in the micro/nano-scale and sensitivity in the trace-level range, which is at the moment beyond state-of-the-art. As dictated by counting statistics, the reduction of the spot size degrades the detection limit. The utilization of a tabletop XUV laser at λ = 46.9 nm has shown to dramatically improve the ablation efficiency with respect to that of visible lasers, such that ablation spot of 1 μm limits. Li-doped Cu 2 ZnSn(S,Se) 4 (so-called kesterite) thin films were irradiated across 3D ablation arrays for hyperspectral mapping by means of time-of-flight mass spectrometry. The nominal 3D data node lattices were the initialisation perceptron, filled with measured values, and for a detailed supervised learning postprocessing, the node-to-node links were analysed by means of a 2D-kernel covariance algorithm. The latter permitted to obtain robust 3D elemental distribution functions well below the measurement spacing, giving insights into the inhomogeneity and impurities.Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Soft X-ray laser ablation for nano-scale chemical mapping microanalysis

“…2 summarizes the detection limit (DL) as a function of lateral (spot) and depth (ablation yield) resolution for different nominal sensitivities in counts/second (cps). One could plot the nominal specication of a number of microanalytical techniques, as done previously, 26 and observe the complementarity of the methods. The theoretical limit given by counting statistics is shown as a tradeoff between the spatial resolution and detection limit, 27 as discussed below in detail.…”

Nano-imaging mass spectrometry by means of high-energy laser desorption ionization (HELDI)

“…The strong absorption cross-section permits improving the depth resolution to the nano-scale. 28 As a combined effect, laser microanalysis using XUV pulses offers sub-micron-scale lateral and nano-scale depth resolution sampling, while effectively enabling the direct desorption and ionization of any element of the periodic table (elemental nano-tomography).…”

“…[21][22][23] Pulses at l ∼ 46.9 nm can shrink the diffraction limit and allow accessing nano-scale lateral resolution. [24][25][26][27][28][29] As a further advantage, the high-energy photon at ∼26 eV is just above the ionization energy of He, i.e. of any element in the periodic table.…”