Petr Wandrol

In Situ WetSTEM Observation of Gold Nanorod Self-Assembly Dynamics in a Drying Colloidal Droplet

Direct in situ visualization of nanoparticles in a liquid is an important challenge of modern electron microscopy. The increasing significance of bottom-up methods in nanotechnology requires a direct method to observe nanoparticle interactions in a liquid as the counterpart to the ex situ electron microscopy and indirect scattering and spectroscopy methods. Especially, the self-assembly of anisometric nanoparticles represents a difficult task, and the requirement to trace the route and orientation of an individual nanoparticle is of highest importance. In our approach we utilize scanning transmission electron microscopy under environmental conditions to visualize the mobility and self-assembly of cetyltrimethylammonium bromide (CTAB)-capped gold nanorods (AuNRs) in an aqueous colloidal solution. We directly observed the drying-mediated AuNR self-assembly in situ during rapid evaporation of a colloidal droplet at 4°C and pressure of about 900 Pa. Several types of final AuNR packing were documented including side-by-side oriented chains, tip-to-tip loosely arranged nanorods, and domains of vertically aligned AuNR arrays. The effect of local heating by electron beam is used to qualitatively asses the visco-elastic properties of the formed AuNR/CTAB/water membrane. Local heating induces the dehydration and contraction of a formed membrane indicated either by its rupture and/or by movement of the embedded AuNRs.

New approaches to in-situ heating in FIB/SEM systems

Over last decades significant effort has been made on in-situ heating experiments inside SEM and FIB/SEM chambers. Traditional way is to use low vacuum environment in the entire chamber. Although this valuable approach brings various undeniable advantages, new state of the art experiments coincide with new requirements, such as rapid changes in temperature, high-vacuum operation to maximize experiment cleanliness, ultra-high resolution SEM imaging and on top of it adaptable geometry in order to investigate sample’s crystallography and composition changes using EBSD and EDS detectors. In this contribution we introduce an integration of two new modules fulfilling these requirements by allowing in-situ heating in FIB/SEM systems under high vacuum conditions. Moreover, heating in high vacuum combined with injection of selected gases was also proven capable of providing sample surface oxidation [1] or reduction (Figure 1), [2].

A New, Versatile, High Performance SEM

The quality of an image is determined by both resolution and contrast: the size of the features we can see and the type of information that the image gives about them. Recent advances in scanning electron microscopy have improved both, for example using magnetic immersion or electrostatic lenses for improved resolution, or by using in-lens, angle-sensitive detection for tunable contrast. Here, we introduce a new FEI SEM that presents a further improvement both in resolution and in contrast using a new compound electrostatic-magnetic final lens.

New Method for Multiple Immunodetection on Resin Ultrathin Section in the Field Emission Scanning Electron Microscope

Localization of a specific protein within the cell ultrastructure in high resolution is based on a specific bond between the molecule of interest (antigen) and an antibody conjugated to an electron dense nanoparticle clearly visible in consecutive observation in the electron microscope. Colloidal gold nanoparticles are usually used as the label. Diameter of the nanoparticle must be small enough to ensure good labeling efficiency together with good visualization of particles in cell structures, typically 6 – 12 nm. Localization of multiple molecules within the same sample area can be done by using gold particles of different sizes. However, detection of more than two molecules is difficult because of a narrow diameter range. Polydispersity of the diameter of colloidal particles can also cause problem when multiple particle sizes are applied. Several approaches of immunodetection of more than three proteins by the electron microscope were used, such as using nanoparticles of different shapes [1] or composition [2].

Polymer imaging in SEM—charge, damage and coating free

Typical information provided by the SEM is sample morphology and composition. Acquiring an image is an easy task if samples are conductive but it becomes difficult in case of soft matter insulators, such as polymers. Two main challenges are sample charging and radiation damage. Traditional approach is to coat the polymer by thin conductive layer. However, coating has severe disadvantages, such as masking tiny surface details or impossibility of using the sample for further analysis. This article summarizes the best practices for imaging and analysis of polymers in the SEM without coating to deliver information about their morphology and composition.

Selective Detection of Backscattered Electrons in the Compound Lens Equipped UHR SEM

Detection of signal electrons belongs amongst the key parameters of the Scanning Electron Microscope (SEM). The traditional approach is the ETD detector for secondary electrons (SE) and a below-the-lens detector for backscattered electrons (BSE). State-of-the-art SEMs can be equipped with up to three inlens detectors capable of collecting both the SE and BSE signal. Moreover, the possibility to sort electrons according to their energies and/or emission angles is becoming common. Such a selective detection is usually done by influencing the SE or BSE trajectories by electric or magnetic fields. This paper introduces compound-lens-controlled energy selective detection of BSE on a new FEI SEM.

Optimized Electron Column and Detection Scheme for Advanced Imaging and Analysis of Metals

In recent years, there has been a large growth in the development of detectors for FIB/SEM systems as the number of applications and techniques is growing. In-lens detectors have traditionally been optimized for imaging low take-off-angle back-scattered electrons with higher energies (low loss). This signal typically generates images which are high in materials contrast [1]. Conversely, below-lens detectors have the ability to capture much higher take-off-angle backscattered electrons due to their geometry [2]. Recent advances in detector segmentation with concentric rings have further allowed the separation of take-off angle signal without the need to change the working distance between the final lens and the sample. This higher take off angle delivers a strong channeling contrast in the specimen, while the highest take off angle reveals topographic information.

Strategies for Collection of Secondary Electrons in the SEM

The standard way of secondary electron (SE) detection in the scanning electron microscope (SEM) is to use the Everhart-Thornley (ET) detector. Only weak electrostatic field attracts low energy SEs. Let us call this system the standard detector. Although the ET detector has been around for more than fifty years, it remains the most frequently used type of detector in SEMs. Modern SEMs have improved their image resolution by so called immersion systems, allowing a strong magnetic field of the objective lens to penetrate into the specimen region. In that case, two ET detectors are usually used: one is located above the objective lens, and the other below it (upper and lower detector). The resulting contrast of the SE images depends on SE energy and on the angular sensitivity of detectors, which is a result of specific distributions of electrostatic and magnetic fields in the specimen region.