Techniques

Helium ion microscopy

At the Mads Clausen institute a Helium ion microscope (Zeiss Orion Nanofab) is available. With an imaging resolution down to 0.5 nm, the ORION NanoFab can generate high resolution images of sample, providing new insights because the images offer a significant greater depth of field when compared to images acquired with FE-SEMs.

The ORION NanoFab He ion microscope capabilities cover a broad range of applications in physics, material science, biology, and medicine, and can provide sub-10 nanometer nanofabrication and sub-nanometer imaging solutions for industry, and academic research centres.

Due to its very high surface contrast, substantially reduced sample damage, and efficient charging compensation ORION is an especially beneficial tool for studies of the low-dimensional structures, life science, and biotechnology.

ORION tools have been already successfully used for fabrication of superior photonic and plasmonic nanostructures and nano-pours in graphene for DNA sequencing.

Imaging technology

The heart of the ORION helium ion microscope is the gas-field-ion source (GFIS) that is an adaptation of the old concept of the gas field microscope. The beam generated by GIFS is conditioned and aligned by electrostatic lenses and scanned over the sample surface where it generates the imaging signals, such as of secondary electrons, back-scattered ions, and others. These signals are further collected by the corresponding detectors and processed by the image acquisition system.

The superior spatial resolution and other advantages of the ORION helium ion microscope originate from a number of factors specific to the ion beams, such as:

  • Extremely high brightness of the ion-source
  • Very small interaction volume and chromatic energy spread
  • Broglie wave-length and beam convergence are much smaller than in SEM.

 

Sample charging of electrically insulating samples in ORION can be efficiently compensated by the build-in electron flood gun because the sample charging in an ion microscope is positive and relatively small due to small probe currents. This significantly simplifies sample preparation procedures, especially for biological and medical samples and improves resolution of the surface features.

Beyond imaging: Nanofabrication capabilities

Nanofabrication tools of ORION include:

He and Ne beams generated by GFIS and used for fabrication of very fine structures by ion sputtering (ion milling)

Gallium ion source for sputtering away relatively large volumes of matter

Nano-patterning Visualization Engine (NPVE), which is a complex of soft- and hardware that provides nanopatterning and imaging of the nanopatterns in a single process.

Combining Ga and He ion beams in one instrument gives ORION unique tomography capabilities realized as a sequence of layer-stripping and imaging steps performed with Ga and He ion beams respectively.

Time-Encoded (TiCo) stimulated Raman microscopy

At the Medical Laser Center Lübeck GmbH (MLL) the non-linear microscopy method “Time encoded stimulated Raman scattering microscopy” TiCo-SRS-Microscopy is further developed in close cooperation with the Institute of Biomedical Optics (BMO). The method is based on the measurement of Raman spectra for each pixel of the image, which represents a chemical breakdown of the molecules present for each image pixel. The Raman contrast generated does not require any sample processing and is highly specific.

TiCo-SRS-Microscopy allows the detection of single biomolecules within a cell without affecting the function or behavior of the cell by introducing foreign molecules. This allows potential new insights and applications in the field of tumor diagnostics and cancer research. In particular, the spectral range of the so-called “fingerprint region” enables the targeted differentiation of characteristic biomolecules and represents a chemical fingerprint that differs from healthy cells by pathological changes. However, the signals to be measured are very small and given as intensity changes in the range of one to one million, which requires careful technical implementation and measurement times of a few minutes. In return, Raman signals can be measured at the shot noise limit and thus also weakly Raman-active molecules or samples with a low concentration of molecules to be sampled can be resolved.

Outside biomedical optics, stimulated Raman microscopy can be used for material analysis. Potential applications can be seen in the field of food control and contactless sorting of different materials in recycling. The advantage compared to spontaneous Raman spectroscopy lies in the higher signal intensity, the targeted scanning of special Raman bands by TiCo-SRS microscopy and the fluorescence-free Raman signal. Limitations of the radiation intensity of the light sources used, such as in biomedical applications, play only a minor role and allow the integration of potential applications in industrial plants. As a partner of the Vision Center, Medizinische Laserzentrum Lübeck GmbH can look back on 25 years of experience in the field of technology transfer from the university environment and various industrial cooperations.

Optical Coherence Tomography (OCT)

For more than 20 years, the Institute for Biomedical Optics (BMO) is one of the leading facilities that developed Optical Coherence Tomography (OCT) into a versatile imaging technique. With new light sources and reconstruction techniques, OCT uses low-power infrared light to image tissue structures in volumes of up to cubic millimeters with micrometer resolution without the use of dyes. Cellular and subcellular structures become visible without tissue preparation. The high imaging speed enables short measurement times and interactive work, making OCT predestined to make tumor resection in the operating room more precise and gentle. OCT can also be used for contactless monitoring of food.