# Study of thin layer materials presenting interfaces using white light interference measurements

Renzo Meyer, François Stock, Christophe Cordier, Jesse Schiffler, P.

Montgomery, Manuel Flury, Frédéric Antoni

► To cite this version:

Renzo Meyer, François Stock, Christophe Cordier, Jesse Schiffler, P. Montgomery, et al., Study of thin layer materials presenting interfaces using white light interference measurements. Optics and Laser Technology, 2025, 184, pp.112444. 10.1016/j.optlastec.2025.112444. hal-04929871

HAL Id: hal-04929871

https://hal.science/hal-04929871v1

Submitted on 5 Feb 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_2.png" /></figure>

Full length article

# Study of thin layer materials presenting interfaces using white light interference measurements

R. Meyer*, F. Stock, C. Cordier, J. Schiffler, P. Montgomery, M. Flury, F. Antoni

ICube, Université de Strasbourg, CNRS, INSA F-67000 Strasbourg, France

## ARTICLE INFO

### Keywords:

- Diamond-like carbon (DLC)
- Thin graphitic layer (TGL)
- White light interferometry (WLIM)
- Coherence scanning interferometry (CSI)
- Phase shifting interferometry (PSI)
- Optical metrology

## ABSTRACT

Thin layers of materials are widely used for diverse applications, ranging from protective coatings to doping layers. There is currently a strong development of different processes that allow the synthesis of thin layers, that can be organic or non-organic. There exists great interest in measuring their topography since their roughness and texturing are critical characteristics for many applications. Low coherence interferometry can provide both topographic measurements and the spectral response of the probed material in the same position. Not only are the measurements fast but the technique is one of the few that allows measurement of both of these characteristics at the same time. Being non-destructive, this technique could become a standard for materials used in the optoelectronics field.

## 1. Introduction

Different measurement systems are often required to characterize both the topography and the spectral response such as atomic force microscopy (AFM) and scanning electron microscopy (SEM) or mechanical or optical profilometry for topographical data and energy dispersive spectroscopy or X-ray photoelectron spectrometry for probing the composition of the sample, in combination with UV-VIS spectrometry or spectral goniometry [1-3]. However, if the topography of the sample needs to be measured at the micrometre scale, white light interference microscopy (WLIM) is often preferred [3]. This is because, compared with the previous techniques mentioned, WLIM has the advantage of being non-destructive, cost-effective, label free, easy to use, fast and allowing full-field imaging. The fringe envelope of low coherence interferometry provides deep micrometric roughness measurement and phase shifting is used to give nanometric sensitivity along the optical axis [4-7]. The technique is also known as White Light Scanning Interferometry (WLSI) and Coherence Scanning Interferometry (CSI). In recent years, many improvements have been made to the technique in terms of the equipment used, the acquisition techniques, the signal processing [8-11] and tomography [12-14]. Notably, WLIM now provides multi-modal measurements, being capable of providing both spectral as well as topographic data in a single measurement that takes less than three minutes to make [15,16]. Indeed, it allows a 3D topography and a spectral response over a given area by obtaining a 1D

spectrum [17-19]. Being contactless, this measurement system is non-destructive for most samples, making it a system of choice for coupling it to other means of measurements such as structural ones for example.

Other processes can be applied to the same interferometric signal to obtain new information. For example, by processing the data with a Fast Fourier Transform (FFT), it is possible to extract information about the reflectance of the surface [15]. If the sample is transparent, this technique can even be used at depth, subject to certain recording conditions [20]. Compared with conventional methods of measuring spectral information, determining the reflectance by interferometry has the advantage of providing spectral information locally, over an area defined by the Airy disc (generally a few µm²). The reflectance of different materials measured by CSI is demonstrated in the references [21,22]. The thickness and dispersion law of a thin film can also be deduced by measuring the overall reflectance of the film using this method and then applying an interpolation [23]. In previous work, different optical setups and acquisition processes were employed [22,23] to improve the quality of the interferometric signal since it was shown that the accuracy of the reflectance measurement is directly related to the quality of the interferometric signal.

Here we will look at the viability of this means of measurement to characterize thin layers and more specifically, thin graphitic layers (TGL).

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: renzo.meyer@etu.unistra.fr (R. Meyer).</footnote>
<figure><img src="image_3.png" /><figcaption>Fig. 1. Sketch of the measurement setup.</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>Fig. 2. Intensity spectrum of the two light sources used in the measurement setup. The intensity values are normalized and evaluated from the beginning of the visible spectrum to near infrared. In this study the OO HL-2000-HP light source was mainly used.</figcaption></figure>

## 2. Materials and methods

### 2.1. WLIM setup and theory of the measurement system

Fig. 1 shows the optical measurement setup used in this study. It is a compact white light interferometer based on a Mirau microscope objective. A Köhler illumination system is used with a white light beam coming from a LED source (Thorlabs TL MBB1L3, Reference LDD1B) or HL2000 Halogen source (Fig. 2), that is directly inserted into the beam splitter which transfers half the light into the Mirau Objective (Nikon x10, NA = 0.3). This is mounted on a piezo stepper (PI PIFOC P-721. C20), controlled in closed loop by a controller (PI E-709) with a 100 µm dynamic range, which allows movement with a 10 nm precision of the objective, in order to modify the optical path difference. This objective is infinite distance corrected and designed to work with a 200 mm focal tube lens (typically a TTL200 system from Thorlabs). The image from the sample is recorded by an 8-bits high-speed colour Basler camera (ACA640-750uc, about 800 frames per second for 640*860 pixels, USB 3.0 connection, colour images are converted into grayscale). The use of a high-speed camera allows to perform measurements faster than with a conventional one. Moreover, as the camera's frame rate is higher than the piezo stepper speed, the measurement system can acquire multiple images of the surface for each position of the piezo allowing to average multiples images. The sample is placed on a goniometer to adapt its inclination, which is itself placed on two micrometric tables to provide precise displacement in X and Y in order to image the region of interest. The whole interferometric system is supported by a micrometric translation stage with a large range of travel to allow movement along the vertical optical axis. This allows coarse focusing of the sample, and then a fine focusing made with the piezo device. The interferometer is included directly in the Mirau objective, consisting of a semi-reflecting window and an in-line reference mirror. The semi-reflecting window transfers half of the light onto the sample and reflects back the other half to the reference mirror. The sample in the focus and the mirror are separated by the same optical distance compared to the semi-reflecting window. After reflection, the beams recombine at the semi-reflecting window, so forming the interference pattern on the camera. Thus, the Mirau objective ensures the optimum superposition of the focal and coherence planes. The optical setup is placed on an anti-vibration table (Thorlabs Nexus Breadboard 60 mm thick), maintained by sorbothane isolators, acting as vibration absorbing feet. The acquisition (control of the camera and the piezo device) into grayscale and the processing of the measurement can be performed using several types of software developed in IGORPro, Labview 2017 or Matlab 2022. The theoretical lateral resolution, according to the Rayleigh criterion, is about 1 µm and the experimental value Δx is determined to be about 1.2 µm using a contrast

<figure><img src="image_5.png" /><figcaption>Fig. 3. Structure of the samples used for studying the reliability of WLIM. (A) Sample S1. (B) Sample S2. (C) Sample S3. The glass substrate is shown in blue, the DLC in grey and the annealed areas of S2 and S3 are boxed in red dashes. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>**Fig. 4.** (A) Direct observation of the sample S1. The two boxes correspond to where the reflectance was evaluated (Fig. 3A and 3C). (B) 2D view of the topography extracted from the WLIM measurement of the interface between glass and DLC on the sample S1. (C) Horizontal profile extracted from the topography of S1.</figcaption></figure>
<figure><img src="image_7.png" /><figcaption>**Fig. 5.** (A) Reflectance value for glass substrate averaged over the area corresponding to the green box on Fig. 2A. (B) Reflectance value for the DLC averaged over the area corresponding to the blue box on Fig. 2A. On both figures the black curve represents the reflectance measurement and the red curves the standard deviation of the measurement. The green dashed curve represents the reflectance of standard glass (BK7). The x-coordinate of the figures corresponds to the wavelength at which the transmittance is evaluated. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

grating (silicon on glass gratings, with different spatial frequencies). Care has to be made in making this measurement since the fringe pattern is always present on the image of the sample. A magnification of 10x is achieved using precise mounting and respecting the correct distance between the tube lens and the objective. The algorithm for measuring topography is inspired by phase shift interferometry techniques [18] with five step solution. For the reflectance measurement, the method is fully described in references [19–23] with the entire acquisition and signal processing protocol. In our case, we use a 15 µm displacement with a piezo system step of 80 nm.

## 2.2. Presentation of the samples studied

The samples used in the following study are transparent electrodes synthesized on glass substrates. The detailed process used to synthesize them is presented in [24,25,26]. Here we will summarize this process and detail the experimental particularities of the synthesizing process to make the samples. The measurements were conducted on three different samples. The process we used is made of a combination of two different forms of carbon: diamond-like carbon (DLC) and thin graphitic layers

(TGL). We synthesize DLC on the glass substrate using pulsed laser deposition (PLD), using an Excimer Lambda physics pulsed laser having a wavelength of 248 nm using a KrF gas mix. The whole synthesis is performed in a PLD chamber under high vacuum, typically of about $10^{-8}$ mBar, to remove any hydrogen or oxygen atoms that could be integrated into the DLC layer. The dimensions of the DLC coating on the glass substrate are 1 cm by 1 cm with a thickness of about 20 nm. After synthesizing the DLC layer, the surface is irradiated with the same laser used during the PLD process. This annealing step changes the $sp^3$ hybridization of the carbon to a $sp^2$ hybridization. By doing so, the stacking of graphene layers is obtained, known as stacked thin graphitic layers, which are highly conductive, over the DLC layer which is transparent and behaves as an electrical insulator. The typical thickness of the TGL can vary between 1 to 5 nm according to the experimental parameters.

The three samples studied were synthesized with small variations in the experimental setup. The first sample, called S1, was not laser annealed and consists of pristine DLC deposited onto a glass substrate. For the other two, S2 and S3, the DLC deposited on the glass substrate was annealed in its centre following the process described previously. However, in the case of S3, the annealed area was previously masked
<figure><img src="image_8.png" /><figcaption>**Fig. 6.** UV/Vis/NIR measurements of pristine DLC, TGL and Glass [25]. The figure presents the transmittance spectrum of each material. Thus, transmittance values are displayed for each wavelength ranging over all the visible spectrum.</figcaption></figure>

using a thin metal sheet. Thus, the DLC beneath the mask did not see the laser beam and was only exposed of the heat of the metal sheet being irradiated. The annealed area has a size of 3.7 mm by 3.7 mm which correspond to the laser beam size. Each annealed area faced 1000 laser shots of 25 ns at an energy density of 0.2 J/cm². Fig. 3A, 3B and 3C present the geometry of the samples S1, S2 and S3 and where the DLC was masked during the laser annealing in the case of S1.

### 3. Results/discussion

The first sample studied is S1 which presents a simple interface between glass and a thin layer material being DLC. The sample was chosen in this study because of the simplicity of its composition, so that it could be used as a reference for probing the relevance of the absolute values of the topographical and spectral measurements provided by WLIM.

Fig. 4A presents the direct observation of the probed area of S1, Fig. 4B corresponds to the 2D view of the topography extracted from the WLIM measurement at the interface between glass (left) and DLC (right) and Fig. 4C corresponds to a profile extracted along the red line in Fig. 4B. The two boxes on Fig. 4A show the areas where the reflectance of both materials was evaluated. These measurements will be discussed later and are presented on Fig. 5A and 5B. The morphology extracted from the WLIM topography of the interface between glass and DLC presented on Fig. 4B corresponds to what can be seen on the direct observation of the probed area presented on Fig. 4A. As can be observed, the step between the glass and the DLC is roughly 28 nm, which fits with the thickness expected of the synthesized DLC layer. Moreover, evaluating the roughness of the DLC layer using the topography measured by WLIM, an RMS roughness Sq of 0.8 nm is obtained and a mean roughness Sa equal to 0.6 nm, which correspond to the roughness of the DLC when measured by atomic force microscopy (AFM). The roughness of the DLC layer was studied using AFM in the non-contact mode. Thus, the WLIM can be considered as reliable to probe the topography of thin layer material presenting an interface.

As mentioned previously, two reflectance measurements were made over the visible spectrum on two different areas of 30x30 µm² which are boxed in green and blue (Fig. 4A), for the glass and DLC areas respectively. The results are presented on Fig. 5A, 5B.

Fig. 6 presents transmittance measurements on glass, DLC and TGL and can be considered as reference measurements [25] for discussing the reflectance measurements shown on Fig. 5A and 5B. These measurements were performed by using an UV/Vis/NIR spectrometer. A clear increase of reflectance between glass and DLC areas can be seen by comparing Fig. 5A and 5B. The reflectance of the glass area is around 5 % and the one of DLC around 20 % at 550 nm. These values are in agreement with the transmittance measurements presented on Fig. 6 as the glass has a higher transmittance than the DLC, respectively 90 % and 55 % at 550 nm.

The next sample studied with WLIM is S2, the results of which present a clear interface between DLC and TGL areas. While S1 was composed of an interface between one bulk material and a thin layer material, S2 presents an interface between two thin layer materials. Fig. 7A presents a direct observation of the probed area and Fig. 7B corresponds to a 2D view of the topography extracted from the WLIM measurement of this area. Fig. 7C, 8A and 8B correspond to the reflectance measured respectively around the interface, on the DLC area and on the TGL area. Just as for S1, by comparing the Fig. 7A and 7B it can be seen that the same morphology of the interface is obtained in the direct observation and in the topography extracted from the WLIM. This interface has an interesting topography as the height rise from 60 nm to around 130 nm and drops back to roughly 60 nm. Thus, it can be stated from this topography that the interface between DLC and TGL consists into a swollen area. As this swelling should not be induced by the graphitization of the DLC the nature of the material obtained at the interface will be discussed later. Just as for S1, two reflectance measurements were made over the visible spectrum on two different areas of 30x30 µm² and boxed in green and blue, for the DLC and TGL areas respectively. For the interface between DLC and TGL, the measurements were not averaged but presented in the form of a reflectance mapping itself. As can be seen, an average reflectance of about 10 % is obtained over the DLC area and around 5 % for the TGL area which are in perfect accordance with the transmittance measured on these materials Fig. 6.

Looking at the interface on the reflectance map, a variation from 10 % to almost 0 % is observed. This drop in the reflectance value seems to be stronger at the interface than on the TGL surface where it increases to 5 %. Raman measurements were performed to see if this variation of reflectance correlate with a change in the nature of the graphitized area.

As can be seen on Fig. 9 the interface does not present a TGL spectrum but a graphite one. Indeed, the D and G peak have a larger full width at half maximum on the interface than in the TGL area. This is a proof that the material probed at the interface is not as crystalline as TGL. Moreover, the absence of a clear 2D peak around the 2700 cm⁻¹ zone of the spectrum leads to state that the interface is made of bulk graphite [27,28]. This explains the drop in terms of reflectance at the interface as graphite has a higher absorbance than thin graphitic layers. Thus, the reflectance variation along the interface is descriptive of a real change of the material.

The last sample to be studied is S3 which went under a specific annealing as it was masked with a metal sheet while annealed. The DLC surface was not treated uniformly and exhibits surface texturing, making it an interesting sample to study using WLIM. Fig. 10A and 10B correspond respectively to the reflectance mapping and the 2D view of the topography extracted from the WLIM measurement. Fig. 10C and 10D are direct observations of the same area of S3 performed respectively using optical microscopy and scanning electron microscopy (SEM). Looking at the reflectance mapping at 550 nm in Fig. 10A of the DLC area it can be seen that the reflectance of the DLC layer is mostly equal to 10 % and drops to almost 0 % in numerous zones. By comparing Fig. 10A and 10B, it can be seen that the variations in reflectance follow the specific texturing of the DLC surface. Indeed on Fig. 10A, the black filamentary-like structure seems to follow the same texturing than the
<figure><img src="image_9.png" /><figcaption>Fig. 7. (A) Direct observation of the sample S2. The three boxes correspond to where the reflectance was evaluated. (B) Topographic measurement of the sample S2 extracted from the WLIM raw data. (C) Reflectance mapping taken over the area corresponding to the red box. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>
<figure><img src="image_10.png" /><figcaption>**Fig. 8.** (A) Reflectance value for DLC averaged over the area corresponding to the green box. (B) Reflectance value for the TGL averaged over the area corresponding to the blue box. On both figures the black curve represents the reflectance measurement and the red curves the standard deviation of the measurement. The green dashed curve represents the reflectance of standard glass (BK7). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>
<figure><img src="image_11.png" /><figcaption>**Fig. 9.** Raman measurement on S2. The measurements were performed on the DLC area (blue), the interface between DLC and TGL (red) and on the TGL area (black). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

filaments seen on Fig. 10B, 10C and 10D. This texturing has a height of about 130 nm just as for the texturing observed at the interface between DLC and TGL on sample S2 as presented on Fig. 7B. Thus, it can be supposed that this texturing may be a form of bulk graphite forming on the top of the DLC layer. Raman measurements were therefore performed on the filamentary structures to see if the drop in reflectance was correlated with the same change in the structure of the DLC (Fig. 11).

Probing the surface having a reflectance of 10 %, D and G peaks that are convoluted can be observed, corresponding to a Raman spectrum of amorphous DLC. However, when the measurement is performed on the textured part while the D and G peaks can be clearly observed, there is no appearance of a 2D peak in the 2700⁻¹ cm⁻¹ zone of the spectrum. This leads to the conclusion that the texturing observed is indeed bulk graphite beginning to form over the DLC surface in filamentary structures [27,28]. It can thus be stated that the variation in the reflectance seen in the spectral response corresponds to the filamentary structures appearing on top of the DLC layer. This explains why the reflectance drops to almost 0 % following the texturing of the DLC surface as bulk graphite has a very high absorbance in the visible spectrum. As can be seen on this sample, both topographic and spectral acquisitions are

obtained that are coherent with the knowledge of the material obtained by the study of S2. Moreover, looking at Fig. 10B, 10C and 10D it can be estimated that the thickness of the filaments is about 1 µm. The agreement between WLIM, SEM and the optical observation using Raman microscopy assure that these filaments are not measurement artefact. By comparing WLIM performed on S2 and S3 it can be stated that the graphitic structures observed both at the interface between DLC and TGL on S2 and all over the probed area on S3 were induced by heat propagation and not the laser irradiation itself.

## 4. Conclusion

Looking at characterization of samples S1, S2 and S3 using WLIM, both topographic and spectroscopic measurements were in good agreement with expected values. Moreover, the reflectance mapping alone gives interesting information about the local variations of nature of the material probed over a large surface. Indeed, crossing Raman and reflectance measurements can explain the reasons leading to a local change in the reflectance of the material as seen in the case of S2 and S3. Therefore, the next series of measurements can be interpreted only using reflectance mapping as the correlation between the variation of reflectance and structure is known. Thus, the reflectance mapping given by WLIM can, in this specific context, be considered as a way to easily access the nature of the material studied. Without such a measurement system it would be quite difficult to state the nature of the material at the interface between the DLC and TGL areas. Indeed, to do so, it would be necessary to perform structural, optical and topographical measurements over the very same areas. Here, just with one measurement, it is possible to access both optical and morphological measurements and by referring to the knowledge obtained from the study of sample S2, it is straightforward to determine the change of nature of an uniform material. Even though the spatial resolution of the device is not as high as for the other measurement systems, the fact that WLIM can conduct both topographic and spectroscopic measurements with a micrometric lateral resolution in less than three minutes makes it a system of choice for quick and non-destructive characterization. WLIM and specifically the reflectance mapping, allows zones with unusual texturing to be quickly distinguished that would not have been seen as simply otherwise. Indeed, the fact that in the end the observation is an optical observation assures users that they are not biased by the principle used to probe the surface of the material.

### CRediT authorship contribution statement

**R. Meyer:** Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Resources, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. **F. Stock:** Writing – review & editing, Validation, Supervision, Project administration. **C. Cordier:** Writing – review & editing, Validation, Supervision, Resources, Project administration. **J. Schiffler:** Writing – review & editing, Validation, Supervision, Resources, Project administration. **P. Montgomery:** Writing – review & editing, Validation, Supervision, Project administration. **M. Flury:** Writing – review & editing, Validation, Supervision, Resources, Project administration. **F. Antoni:** Writing – review & editing, Validation, Supervision, Project administration.

### Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
<figure><img src="image_12.png" /><figcaption>Fig. 10. (A) Reflectance mapping of the sample S3 over an area that has been masked during the surface annealing using the Excimer laser. The scale of reflectance is at right. (B) Topographic measurement extracted from the WLIM raw data. The scale is at right. (C) Simple optical observation of the sample S3 using the microscope of the Raman measurement setup. (D) SEM acquisition of the sample S3.</figcaption></figure>

<figure><img src="image_13.png" /><figcaption>Fig. 11. Raman measurement on the filamentary structures observe of the surface of the sample S1.</figcaption></figure>

## Acknowledgements

We specially thank Mr ROQUES Stéphane, Mr DIETRICH Florent and Mr ZIMMERMANN Nicolas from ICube C3Fab platform for technical and material support provided to during this study. We also thank Mr DUCATEL Thomas for his advice on the paper.

## Data availability

Data will be made available on request.

## References

[1] R.K. Upadhyay, A.K. Lakshmi, Bearing failure issues and corrective measures through surface engineering, in [Handbook of Materials Failure Analysis], Butterworth-Heinemann, 209-233 (2018).

[2] L. Gao, R.T. Smith, Optical hyperspectral imaging in microscopy and spectroscopy - a review of data acquisition, J Biophoton 8 (2015) 441-456, https://doi.org/10.1002/jbio.201400051.

[3] R. Leach, Optical measurement of surface topography, Springer, Berlin, 2011.

[4] P. De Groot, Principles of interference microscopy for the measurement of surface topography, Adv. Opt. Photon. 7 (2015) 1, https://doi.org/10.1364/AOP.7.000001.

[5] P. De Groot, J. Biegen, Interference microscope objectives for wide-field areal surface topography measurements, Opt. Eng. 55 (7) (2016) 1-6.
[6] P. De Groot, Interference Microscopy for Surface Structure Analysis. Handbook of Optical Metrology, 2nd ed., CRC Press, 2015.

[7] A. Dubois, L. Vabre, A. Boccara, P. Montgomery, B. Cunin, Y. Reibel, C. Draman, Real-time high-resolution topographic imagery using interference microscopy, Eur. Phys. J. - A Appl. Phys. 20 (2002) 169.

[8] C. Giusca, R. Leach, Calibration of the scales of areal surface topography measuring instruments: part 3. resolution, Meas. Sci. Technol. 24 (10) (2013) 105010.

[9] P.C. Montgomery, F. Anstotz, J. Montagna, D. Montaner, L. Pramatarova, E. Pecheva, Towards real time 3D quantitative characterisation of in situ layer growth using white light interference microscopy, J. Phys.: Conf. Ser. 253(1), 012017, IOP Publishing (2010).

[10] J.M. Coupland, J. Lobera, Measurement of step surfaces using white light interferometry, Strain 46 (1) (2010) 69-78.

[11] P. Harris, I. Smith, R. Leach, C. Giusca, X. Jiang, P. Scott, Software measurement standards for areal surface texture parameters: part 1—algorithms, Meas. Sci. Technol. 23 (10) (2012) 105008.

[12] A. Dubois, L. Vabre, A.-C. Boccara, E. Beaurepaire, High-resolution full-field optical coherence tomography with a Linnik microscope, Appl. Opt. 41 (4) (2002) 805-812.

[13] A. Dubois, K. Grieve, G. Moneron, R. Lecaque, L. Vabre, C. Boccara, Ultrahigh-resolution full-field optical coherence tomography, Appl. Opt. 43 (14) (2004) 2874-2883.

[14] P. Lehmann, S. Tereschenko, W. Xie, Fundamental aspects of resolution and precision in vertical scanning white-light interferometry, Surf. Topogr. Metrol. Prop. 4 (2016) 024004, https://doi.org/10.1088/2051-672X/4/2/024004.

[15] A. Dubois, J. Moreau, C. Boccara, Spectroscopic ultrahigh-resolution full-field optical coherence microscopy, Opt. Express 16 (2008) 17082-17091, https://doi.org/10.1364/OE.16.017082.

[16] R. Claveau, P.C. Montgomery, M. Flury, Spatially resolved spectroscopic characterization of reflective and transparent materials at a micro meter scale using coherence scanning interferometry, Phys. Status Solidi C 14 (2017) 1700157, https://doi.org/10.1002/pssc.201700157.

[17] J.-Y. Kim, S. Kim, M.-G. Kim, H.J. Pahk, Generating a true color image with data from scanning white-light interferometry by using a fourier transform, Curr. Opt. Photon. 3 (2019) 408-414, https://doi.org/10.3807/COPP.2019.3.5.408.

[18] P. Hariharan, B.F. Oreb, T. Eiju, Digital phase-shifting interferometry: a simple error-compensating phase calculation algorithm, Appl. Opt. 26 (1987) 2504, https://doi.org/10.1364/AO.26.002504.

[19] R. Claveau, P. Montgomery, M. Flury, D. Montaner, Depth-resolved local reflectance spectra measurements in full-field optical coherence tomography, Opt. Express 25 (2017) 20216, https://doi.org/10.1364/OE.25.020216.

[20] R. Claveau, P. Montgomery, M. Flury, Coherence scanning interferometry allows accurate characterization of micrometric spherical particles contained in complex media, Ultramicroscopy 208 (2020) 112859, https://doi.org/10.1016/j.ultramic.2019.112859.

[21] S. Marbach, R. Claveau, F. Wang, J. Schiffler, P. Montgomery, M. Flury, Wide-field parallel mapping of local spectral and topographic information with white light interference microscopy, Opt. Lett. 46 (2021) 809-812, https://doi.org/10.1364/OL.413036.

[22] S. Marbach, R. Claveau, F. Ogor, C. Cordier, J. Schiffler, P. Montgomery, M. Flury, Simultaneous local spectral, colorimetric and topographic characterization of laser induced colored stainless steel with low coherence interference microscopy, Opt. Lasers Eng. 162 (2023) 107402, https://doi.org/10.1016/j.optlaseng.2022.107402.

[23] R. Claveau, P. Montgomery, M. Flury, G. Ferblantier, Local inspection of refractive index and thickness of thick transparent layers using spectral reflectance measurements in low coherence scanning interferometry, Opt. Mater. 86 (2018) 100-105, https://doi.org/10.1016/j.optmat.2018.09.046.

[24] F. Stock et al., High performance diamond-like carbon layers obtained by pulsed laser deposition for conductive electrode applications, Appl. Phys. A, vol. 123, no 9, p. 590, sept. 2017, doi: 10.1007/s00339-017-1207-8.

[25] F. Stock, F. Antoni, D. Aubel, S. Hajjar-Garreau, et D. Muller, Pure carbon conductive transparent electrodes synthetized by a full laser deposition and annealing process, Appl. Surf. Sci. 505 (2020) 144505, doi: 10.1016/j.apsusc.2019.144505.

[26] R. Meyer, F. Stock, F. Antoni, et al., Investigation of laser-induced changes in structural and optoelectrical properties of pulsed laser-deposited Diamond-Like Carbon layers, J. Mater. Sci. Mater. Electron. 34 (2023) 1368, https://doi.org/10.1007/s10854-023-10802-2.

[27] A.C. Ferrari, J. Robertson, Interpretation of Raman spectra of disordered and amorphous carbon, Phys. Rev. B, vol. 61, no 20, p. 14095-14107, mai 2000, doi: 10.1103/PhysRevB.61.14095.

[28] A. C. Ferrari, Raman spectroscopy of graphene and graphite: disorder, electron-phonon coupling, doping and nonadiabatic effects, Solid State Communications 143(1-2) (2007) 47-57, doi: 10.1016/j.ssc.2007.03.052.