Advanced Characterization of Organic Layers: Coupling Raman Spectroscopy and XRF with GD-OES
Application Note Layers GD43
Authors: Suyeon LEE, Hssen FARES¹, Cline EYPERT², Patrick CHAPON
¹Micro-XRF Analysis Expert - hssen.fares@horiba.com, ²Raman Analysis Expert - celine.eypert@horiba.com, suyeon.lee@horiba.com; HORIBA FRANCE SAS, Palaiseau, France.
Abstract
This application note explores an enhanced GD-OES method using an Ar/O₂ gas mixture to achieve uniform erosion of multilayer organic/inorganic coatings, specifically in automotive applications. To study the layer beneath the surface and ensure that the sputtering process does not chemically alter the sample, complementary surface analyses were conducted using Raman spectroscopy (XploRATM PLUS) and micro-XRF (XGT-9000). The results showed no evidence of chemical modification, confirming the integrity of the layers sputtered by GD-OES. This coupling enables reliable, non-destructive chemical characterization of complex layered materials, enhancing analytical confidence for industrial quality control and R&D.
Keywords
- GD-OES
- Raman Spectroscopy
- Micro-XRF
- Organic Coatings
- Depth Profiling
- Ar/O₂ Sputtering
- Multilayer Analysis
- Automotive Materials
- Surface Characterization
Introduction
In the field of surface and coating analysis, glow discharge optical emission spectroscopy (GD-OES) has proven highly effective for depth profiling of metallic and inorganic layers. However, challenges arise when dealing with organic coatings, which are typically carbon-rich and difficult to sputter uniformly using conventional GD-OES methods.
In a previous application note (GD42), a novel approach using a gas mixture of argon (Ar) and oxygen (O₂) was introduced to enhance the sputtering efficiency of organic layers [reference 1]. This method enables uniform erosion of multilayered coatings and allows analysts to access underlying inorganic or intermediate organic layers with precision. Despite this advancement, a critical question remains: Does the GD-OES process alter chemical composition or surface structure of the layers?
Experimental Approach
To address this, the coupling of GD-OES with non-destructive surface characterization techniques, such as Raman spectroscopy and micro-XRF (X-ray fluorescence), was explored to verify the integrity of the exposed surfaces after GD sputtering.
Samples provided by Renault Group, specially designed for automotive applications, were tested. These samples consisted of an unknown inorganic/organic multilayered coating on a metallic substrate. The samples were partially coated, exposing areas of primer that allowed assessment of the analysis depth.
Description of Figure 1: The figure displays three components. The first is a photograph of a test sample showing a circular crater created by the GD-OES process. The second is a 2D graph illustrating the crater's profile, with the x-axis representing horizontal position and the y-axis representing depth, indicating a crater depth of approximately 50 µm. The third component is a GD-OES qualitative depth profile graph, plotting signal intensity against depth, showing peaks for elements like C, H, N, O, Al, Ca, and Na as different layers are eroded.
Description of Figure 2: This figure shows photographs of three analytical instruments. On the left is the HORIBA XploRATM PLUS Raman spectrometer. In the middle is the HORIBA GD-Profiler 2TM, a GD-OES system. On the right is the HORIBA XGT-9000 Micro-XRF system.
Validation via Raman Spectroscopy
The XploRATM PLUS micro-Raman spectrometer (HORIBA) was employed. This instrument offers sub-micron spatial resolution, high sensitivity to molecular vibrations, and non-destructive surface analysis.
Description of Figure 3: This figure presents a comparison of Raman spectra and a microscopic image. The top part shows two Raman spectra, one from an area inside the GD-OES crater (green) and one from an exposed primer layer (blue), plotted as intensity versus Raman shift. A magnified view of key peaks is shown below. The spectra exhibit identical peak positions, suggesting no chemical alteration. The right side displays a microscopic image of the surface within the GD-OES crater.
Micro-Raman spectra were obtained inside the GD-OES crater (green in Figure 3) and compared with the exposed primer layer (blue in Figure 3) as a reference. Identical peak positions with only slight differences in relative intensities were observed. This indicates no carbonization, polymer breakdown, or new bond formation.
This confirms no chemical deformation of the organic layers during GD-OES measurement.
Cross-Verification via Micro-XRF
Further validation was conducted using micro-X-ray fluorescence (XGT-9000, HORIBA) to cross-check the results obtained from XploRATM PLUS micro-Raman. The XGT-9000 enables elemental mapping with minimal sample preparation and complements Raman spectroscopy by providing direct elemental identification.
Description of Figure 4: This figure shows a comparison of micro-XRF spectra for two areas. The green spectrum represents an area inside the crater after GD-OES analysis, while the blue spectrum is from an exposed primer layer used as a reference. Both spectra plot intensity against energy (keV), revealing similar elemental compositions and confirming the integrity of the layers.
Only slight variation in signal intensity was detected in some peaks, likely due to topographic changes or partial thickness reduction.
Consistent elemental composition across both the crater and the exposed primer layer is observed, which also proves no chemical deformation of the layer during GD-OES measurement.
Conclusion
The results demonstrate that GD-OES, when optimized with an Ar and O₂ gas mixture, can uniformly erode organic coatings without altering underlying chemical composition. The successful integration with Raman spectroscopy and micro-XRF enables:
- Reliable characterization of chemical composition of each layer.
- Investigation of any intermediate layer of interest by choosing a precise moment during the measurement.
- Versatile investigation of organic/inorganic multilayer systems.
This combined approach is adaptable for any industrial application, including organic coatings in automotive and photovoltaic cells, where high-resolution layer characterization is critical for product development and quality control.
Acknowledgement
Perle BOYEKA (Physico-chemical analysis Specialist) at Renault Group Materials Excellence Center in Guyancourt (France), for offering test samples and for all discussions.
