FIB-SEM Instrument with Integrated Raman Spectroscopy for Correlative Microscopy

Abstract

Confocal Raman Microscope (CRM) is integrated with Scanning Electron Microscope (SEM) and its standard analyzers such as Energy Dispersive X-ray spectroscope (EDX), that can be further equipped with Focused Ion Beam (FIB). This yields valuable chemical information about molecular composition and chemical bonds in the sample on top of the high resolution SEM image, elemental composition map by EDX, nano-prototyping capability by FIB, etc. In presented system, confocal setup of the Raman Microscope provides lateral resolution of 360 nm (with the 532 nm excitation laser). This is a high standard in the world of light microscopy, however, electron microscopy offers resolution more than 2 orders of magnitude better. Combining the CRM spectral image and high resolution SEM image acquired in-situ is therefore of great benefit. State-of-the-art Raman analyzers inside SEM use parabolic mirror for focusing the primary laser beam on the sample and collecting the Raman-scattered light. The lateral resolution of these systems typically does not exceed 2-5 μm. We achieve the resolution comparable with stand-alone instruments by integrating a full confocal light microscope with SEM. The integrated system is capable of Raman imaging which is an important property. When just a single spectrum is acquired, one can never be sure, whether the position calibration is off. Besides lateral scanning, vertical movement is also supported, which allows non-destructive 3D tomography of laser transparent samples. Combination of CRM chemical analysis and SEM high resolution imaging makes this tool ideal for use in chemistry, medicine, biology, geology, forensic science and many other fields. The integration is feasible with two types of electron columns: conventional (LYRA) and immersion (GAIA). The immersion column [1] is recommended for non-conductive or fragile samples, because it offers better resolution at low acceleration voltages (1 nm at 15 kV and 1.4 nm at 1 kV). Its three-lens design is equipped with a Schottky field-emission gun and it offers multiple display modes (for ultrahigh resolution, large field of view or increased depth of focus) as well as a field-free mode for investigating magnetic samples.