Wavelength Scanning with a Tilting Interference Filter for Glow-Discharge Elemental Imaging

Abstract

Glow discharges have long been used for depth profiling and bulk analysis of solid samples. In addition, over the past decade, several methods of obtaining lateral surface elemental distributions have been introduced, each with its own strengths and weaknesses. Challenges for each of these techniques are acceptable optical throughput and added instrumental complexity. Here, these problems are addressed with a tilting-filter instrument. A pulsed glow discharge is coupled to an optical system comprising an adjustable-angle tilting filter, collimating and imaging lenses, and a gated, intensified charge-coupled device (CCD) camera, which together provide surface elemental mapping of solid samples. The tilting-filter spectrometer is instrumentally simpler, produces less image distortion, and achieves higher optical throughput than a monochromator-based instrument, but has a much more limited tunable spectral range and poorer spectral resolution. As a result, the tilting-filter spectrometer is limited to single-element or two-element determinations, and only when the target spectral lines fall within an appropriate spectral range and can be spectrally discerned. Spectral interferences that result from heterogeneous impurities can be flagged and overcome by observing the spatially resolved signal response across the available tunable spectral range. The instrument has been characterized and evaluated for the spatially resolved analysis of glow-discharge emission from selected but representative samples.

High-throughput single pixel spectral imaging system for glow discharge optical emission spectrometry elemental mapping enabled by compressed sensing

“…On the one hand, wavelength-scan approaches, also known as staring-camera type, allow measuring monochromatic images one wavelength at a time, with the advantage of giving access to both spatial dimensions simultaneously. The wavelength selection device used influences greatly the GDOES EM performance: a monochromator gives access to a wide λ range but λ -scan is slow and it compromises light-throughput vs. spectral resolution; 8,9 a dichroic filter is very cost effective and can have a large numerical aperture (NA) but the λ range and spectral resolution for each filter are very limited, such that tens of filters would be needed for multi-elemental analysis; 14 acousto-optic tunable filters give fast random λ access and can also have a large NA but they have limited λ range and UV capabilities, spectral resolution that varies with λ , and can be costly. 15 On the other hand, line-scan approaches, also known as push-broom type, allow measuring one spatial dimension and the λ dimension simultaneously while the remaining spatial dimension has to be scanned.…”

“…Glow discharge optical emission spectroscopy (GDOES) has been shown to permit EM from within the sputtered area when operated in pulsed power mode and sustained under higher-than-typical pressures. [8][9][10][11][12][13][14][15] Leveraging the inherent GDOES advantages of direct solid sampling, simultaneous multi-elemental analysis, fast sputtering rates, multi-matrix calibration schemes, and depth proling in the nm scale, results in ultra-high throughput elemental mapping capabilities that can be several orders-ofmagnitude faster vs. typical techniques. 2,11,16 One of the aspects that enables GDOES EM is its coupling to an appropriate spectral imaging system for data collection, with several embodiments reported.…”