Olaf Hollricher

High-Resolution Optical and Confocal Microscopy

In this chapter, the theory of optical image formation in an optical microscope is described, and the difference between conventional and confocal microscopy is explained. The selection of the appropriate pinhole diameter is discussed in detail, as the pinhole diameter is crucial in obtaining the highest depth resolution as well as optimizing collection efficiency, because the Raman signal is typically very weak.

FIB-SEM Instrument with Integrated Raman Spectroscopy for Correlative Microscopy

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.

Integrating focused ion beam–scanning electron microscope with confocal Raman microscope into a single instrument

The authors have developed a new method to integrate a scanning electron microscope (SEM) with a confocal Raman microscope (CRM) that uses full optical microscopy inside the vacuum chamber of the SEM, and thus bring the capabilities of a stand-alone CRM instrument into the combined tool. A focused ion beam is also integrated into the system, thereby equipping a single instrument with electron, ion, and photon beams. Chemical imaging with the CRM is done by objective lens scanning. The confocal arrangement of the instrument is also capable of nondestructive three-dimensional Raman tomography on transparent samples.

Confocal Raman AFM, a powerful tool for the nondestructive characterization of heterogeneous materials

The combination of an atomic force microscope (AFM) and a Confocal Raman Microscope (CRM) has been used to study an emulsion consisting of alkyd and acrylic latexes. Alkyds and acrylics are used as binders in paints and coatings. These materials produce a shiny, hard finish that is highly water-resistant. The high spatial resolution of the AFM enables the morphological characterization of the dried emulsion on the nanometer scale. Furthermore, when operating the AFM in Digital Pulsed Force Mode (DPFM), topographic information and local mechanical properties can be simultaneously recorded, allowing a comparison of the mechanical properties of the emulsion components. Raman spectroscopy provides additional information on the chemical composition of materials. In combination with a confocal microscope, the spatial distribution of the various phases can be determined with a resolution down to 200 nm. Therefore, the topographically different structures observed in AFM images can be associated to the chemical composition by using the Confocal Raman Microscope (CRM).

RISE: Correlative Confocal Raman and Scanning Electron Microscopy

RISE , the combination of Raman Imaging and Scanning Electron microscopy is a promising technique that adds chemical information to the high resolution imaging capability of electron microscopy. By automatically transferring the sample from the electron beam to a separate Raman position inside the vacuum chamber, Raman molecular imaging can be performed without compromising SEM performance. Chemical information can be acquired with a resolution down to 300 nm and results obtained with both techniques can be overlaid with high precision.

Multimodal Low-Dimensional Materials Characterization with Correlative Microscopy: Raman-PL-FLIM-AFM-SNOM-SEM

The characterization of low-dimensional materials such as graphene or transition metal dichalogenides (TMDCs) often requires more than one technique to obtain a thorough understanding of their attributes for specific applications. Graphene and TMDCs both have layered structures and properties that vary significantly with thickness as compared to single layer conformations, making them very interesting for electronics design [1]. Their photonic and optoelectronic qualities have been shown to enable ultrafast carrier dynamics and ultra-sensitivity in UV-VIS, IR and THz frequency ranges [2]. Electronic device performance optimization can benefit greatly from knowledge of their crystalline structure and exciton dynamics. The aim of the following analysis is to show how several spectroscopy (Raman/Photoluminescence) and microscopy techniques (AFM/SEM) can, in correlation, provide a more richly detailed depiction of low-dimensional materials than the constituent measurements could offer in isolation.

New Developments in RISE Microscopy: Correlative Raman and SEM Imaging

Instruments that incorporate the strengths of several measurement techniques facilitate a more comprehensive sample characterization. The combination of a fully automated confocal Raman Imaging microscope and a stand-alone Scanning Electron microscope (SEM), known as a RISE microscope, has demonstrated an ability to provide insight and detail beyond that available with the constituent methods individually.