In-situ Raman spectra of indented fused silica

In-situ Raman spectroscopic measurements were conducted during indentation of fused silica (FS) samples. The experiments were conducted using Raman spectroscopy-enhanced instrumented indentation testing (RS-IT). RS-IT was developed at the National Institute of Standards and Technology (NIST) and employs an in-house built instrumented indentation testing device that is coupled to a custom Raman microscope.[Rev. Sci. Instrum. 83 125106 (2012)]

Spectroscopic data were collected with different microscope objectives installed in the Raman microscope: (a) 80X metallurgical objective (MO) with a numerical aperture (NA) of 0.75, (b) 40X objective with a variable coverslip correction (CO) and an NA of 0.95, and (c) 100X objective with a variable correction for thick glass substrates (TO) and an NA of 0.6. The samples used in the experiments were made of optically polished, Corning 7980 UV Grade FS: The thin FS sample has a thickness of 0.2 mm +/- 0.025 mm and the thick FS sample has a thickness of 1 mm +/- 0.05 mm. In-situ spectroscopic measurements were conducted with two test protocols (z-profile and load-sequence experiments).
In the z-profile experiments, the indenter probe was brought in contact with the sample and continuously loaded to a maximum indentation force of 300 mN. Then the indentation force was held constant to perform a series of in-situ Raman measurements in the center of the indentation. The surface spectrum was collected with the microscope objective focus set at the surface of the specimen. Then seven consecutive Raman spectra were measured where the z-axis position of the microscope objective was shifted 1 ?m lower, moving the focal plane into the bulk of the sample away from the indenter for each spectrum along the indentation axis. The z-profile experiments were conducted for the objective/ sample pairings: (a) MO/thin FS, (b) MO/thick FS, (c) CO/thin FS, (d) TO/thick FS.
In the load-sequence experiments, the indenter probe was brought in contact with the sample and an indentation force of 50 mN was applied. The indentation force was held constant while a Raman spectrum was collected in-situ from the center of the indentation with the microscope objective being focused on the top surface of the specimen. Following collection of the spectrum, the indentation force was increased by 50 mN. A Raman spectrum was then collected at that load after re-adjusting the focus of the objective onto the top surface of the specimen. This routine was continued until a maximum force of 300 mN was reached. Then the indentation force was reduced in 50 mN steps until the sample was completely unloaded. At each unloading step, a Raman spectrum was collected in-situ. The load sequence experiments were conducted for the CO/thin FS and TO/Thick FS objective/sample pairings.
The indenter probe was a three-sided, pyramidal diamond probe with a semi-apical angle of 68.8° and a nominal tip radius of about 150 nm.

The raw experimental data (Raman spectra, indentation curves and while light images) collected in the two test regimens are compiled in datasets A through H of this data publication. In this context, raw spectral data are defined as being direct from the camera with the exception of conversion of the photon energy to Raman shift (1/cm) and application of the instrument non-uniformity correction. Raw indentation data are defined as being direct from the instrument corrected for machine compliance. The aforementioned datasets built the foundation of and serve as companion to the publication: Y.B. Gerbig and C.A. Michaels, J. Non-Cryst. Solids 530 119828 (2020). More details about data collection and processing than already described in this summary can be found in the publication. The data directly underlying the figures presented in this publication are compiled in datasets I through P of this data publication. The accompanying Readme document contains details about organization, content and format of the data sets.

Tags: fused-silica, in-situ, instrumented-indentation, raman-spectroscopy
Organization: National Institute of Standards and Technology