Large Area Profilometry for Topographic Raman Imaging
WITec´s award winning TrueSurface Microscopy allows confocal Raman imaging along heavily inclined or very rough samples with the surface held in constant focus while maintaining the highest confocality. The core element of this revolutionary imaging mode is an integrated sensor for optical profilometry. It is directly installed at the microscope turret which facilitates user-friendly and convenient handling.
The TrueSurface Principle
The key element of this novel imaging mode is a topographic sensor that works using the principle of chromatic aberration. With this non-contact, purely optical profilometer technique it is possible to trace a sample's topography and follow it in a subsequent Raman measurement, thus remaining in focus throughout.
For profilometry a white light point-source is focused onto the sample with a hyperchromatic lens assembly: A lens system with a good point mapping capability, but a strong linear chromatic error. Every color has therefore a different focal distance. The light reflected from the sample is collected with the lens and focused through a pinhole into a spectrometer. As only one color is in focus at the sample surface, only this light can pass through the confocal pinhole. The detected wavelength is therefore related to the surface topography. Scanning the sample in the XY plane reveals a topographic map of the sample. This map can then be followed in a subsequent Raman image so that the Raman laser is always kept in focus with the sample surface (or at any distance below the surface). The results are images revealing chemical and/or optical properties at the surface of the sample, even if the surface is rough or inclined.
The profilometric capabilities of the TrueSurface Imaging mode allows scan ranges of up to 50x100 mm with a spatial resolution on the order of 40-120 nm vertically and 10-25 µm laterally.
The large-area topographic coordinates from the profilometer measurement can be precisely correlated with the large-area confocal Raman imaging data. In combination with AFM, the True Surface profilometer can be used as a pre-inspection tool to determine topographic features of interest for high-resolution AFM investigations on large samples.
TrueSurface Microscopy is beneficial for a large variety of applications, including the characterization of micromechanical, medical, or semiconductor devices, the mapping of functionalized surfaces, or the imaging of biomedical or pharmaceutical material surface properties.
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