Beam Deceleration is a relatively simple method to reduce electron beam energy and improve imaging parameters such as resolution and contrast. The scanning electron microscope (SEM) uses a sharply focused electron beam to probe the specimen surface. The energy of the electrons forming such a probe is determined by the electrical potential of the electron source, referred to as accelerating voltage or high voltage (HV). No matter how many times the electrons are accelerated or decelerated inside the column, they leave the column with an energy corresponding to the high voltage. The high voltage is usually controllable within a range of 200 V to 30 kV for most commercially available SEMs, allowing the operator to select the electron beam energy suitable for the application. Imaging with very low electron beam energy has great importance, which is illustrated by SEM instrumentation development over the last few decades [1–2]. Low voltage microscopy is a topic discussed at most microscopy-related conferences these days, but generally, it is approached with an immersion lens and field emission gun (FEG) SEM system because of the better beam current densities. However, beam deceleration is also a means to bring low kV improvement to SEMs with thermionic electron sources.

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.

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.The compound final lens combines the magnetic final lens inside the pole piece (ML1), the immersion magnetic lens (ML2) and the electrostatic lens (EL1) formed by the potential at the T1 detector (Fig. 1a). Main function of the compound final lens is to focus the primary electron beam to the sample. However, independent control of these three lenses enables us to use ML1 and EL1 to focus the primary beam and the ML2 to affect the trajectories of signal electrons. The ML2 behaves as a chromatic sensitive lens which focuses the high-loss BSE into the aperture of the annular T1 detector. The low-loss BSE are less sensitive to the ML2 magnetic field and reach the T1 detector (Fig. 1b). SE also pass through the aperture in the T1 and are collected further in the column by the T2 and T3 detectors.The main goal of the energy selective BSE detection is the enhancement of the compositional contrast. The BSE signal typically contains both the high-and the low-loss fractions. The BSE coefficient (η) is little dependent on the atomic number (Z) for the high-loss BSE, while it is strongly dependent in the case of the low-loss BSE. Therefore, in order to enhance the compositional contrast, low-loss BSE need to be selectively detected. This is exactly the mechanism behind the contrast enhancement with the compound lens. Besides the BSE filtration, the magnetic field of the ML2 decreases the diameter of the primary beam and thus improves the resolution. This enables us to acquire compositional contrast images in high resolution, such as the Pd nano-particles on the CeO2 matrix in Fig. 2a [2]. Another important improvement is the collection efficiency of the T1 BSE detector. Thanks to its design and position, the T1 detector covers a large BSE emission angle and provides high signal to noise ratio even at low probe currents. Naturally, BSE filtering cuts off a significant part of the T1 signal. However, the T1 detector keeps providing low noise images at probe currents down to 25 pA and less. The possibility to work at low probe currents together with the energy selective BSE detection enables charge-free imaging of non-conductive samples. The high-loss BSE carrying the charge information are filtered out so they don't contribute to the T1 detector image. Collection of low-loss BSE at probe current of 25pA produces charge free images of insul...

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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 surfaceThe module choice essentially depends on the sample size and the type of analysis required. For millimeter-sized samples, a bulk heating stage can be selected, which allows a heating rate of unit degrees per second for heating up to 1000°C. The heating stage is made of materials with negligible outgassing that assures experiment cleanness and can also provide high vacuum environment arround the heated sample with SEM chamber pressure in the order of 10-5 Pa. In-situ observation of microstructure evolution can be achieved by standard SEM detectors collecting SE and BSE signal passing through a user replaceable heat shield, which protects sensitive parts in SEM chamber from overheating. In addition, geometry of a dedicated heat shield permits EBSD mapping as well as EDS analysis of a heated sample placed on this heating stage. However, quality of the EDS and EBSD data is influenced by infrared radiation interference at temperatures above 600°C. This background can be reduced to minimum by employing a microheatingplate device.A novel microheatingplate device based on microelectromechanical systems (MEMS) technology provides a maximum temperature of 1200°C and a very high heating/cooling rate in the order of 10 5 degrees per second [3]. This MEMS chip is able to support nano-scale to sub-millimeter-sized samples (samples with dimensions in tens of µm are typically used). In-situ imaging of samples placed on the MEMS chip during heating can be obtained using all types of detectors [4] including STEM, EBSD and EDS. The localised heating and small thermal mass capacity bear indespensible merits such as high uniformity of the heating area, high stability even during operations above 1000°C, site specification and minor sample displacement and drift stablilization. Chunk samples (typically metallic samples for Materials Science research) can be first fabricated using FIB milling in the bulk, then in-situ lifted out, welded on the MEMS chip and optionally the sample surface can be cleaned with low kV ions. We present in Figure 2 EBSD results of microstructure evolution of a slightly deformed Ti6Al4V chunk sample obtained during in-situ heating at ...

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SummaryThe new scintillation detector of backscattered electrons that is capable of working at primary beam energy as low as 0.5 keV is introduced. Low energy backscattered electrons are accelerated in order to generate a sufficient number of photons. Secondary electrons are deflected back by the energy filter so that the true compositional contrast of the specimen is obtained. The theoretical models of the detector function are described and first demonstration images are presented.