Environmental scanning electron microscopy (ESEM) enables electron imaging of gas-mediated, direct-write nanolithography processes, liquids, and hydrated biomaterials. However, ESEM is limited by poor image quality at gas pressures in excess of ∼600Pa. Here the authors achieve high quality secondary electron imaging at 2kPa of H2O by optimizing boundary conditions that govern beam scatter and the energy distribution of low energy electrons in the gas, dielectric breakdown of the gas, and detector collection efficiency. The presented high pressure imaging method will enable imaging of hydrated materials at close to room temperature, and gas-mediated surface modification processes occurring at high pressures.

The nano-scale dispersion of ordered/disordered phases in semi-crystalline polymers can strongly influence their performance e.g. in terms of mechanical properties and/or electronic properties. However, to reveal the latter in scanning electron microscopy (SEM) often requires invasive sample preparation (etching of amorphous phase), because SEM usually exploits topographical contrast or yield differences between different materials. However, for pure carbon materials the secondary spectra were shown to differ substantially with increased order/disorder. The aims here is to gain an understanding of the shape of secondary electron spectrum (SES) of a widely used semi-crystalline polymer regioregular poly(3-hexylthiophene-2,5-diyl), commonly known as P3HT, and its links to the underlying secondary electron emission mechanisms so SES can be exploited for the mapping the nanomorphology. The comparison of simulated and experimental SES shows an excellent agreement, revealing a peak (at about 0.8eV) followed by a broad shoulder (between 2eV and 4.5eV) with respective relative intensities reflecting order/disorder.

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High resolution low-kV STEM imaging is getting more and more attention in the materials research and semiconductor industry, as well as in life sciences research [1]. This has been driven by the need to work with thinner TEM lamella, and with samples containing low-Z and beam sensitive materials. Decreasing electron energies is often favorable from a radiation damage point of view, moreover it improves scattering contrast. In this contribution we focus on STEM imaging extended by diffraction analysis, by integration of pixelated detectors into the FIB/SEM platform.There are two main types of STEM instrumentationdedicated S/TEM systems (which can typically perform in both STEM and TEM modes) and general purpose FIB/SEM systems with a STEM option. The dedicated S/TEM instruments offer higher ultimate imaging performance, usually can go to higher accelerating voltages, might use correctors and advanced analytical techniques such as EELS. In contrast, FIB/SEM platforms offer high system versatility, combining sample preparation with imaging and analysis. However, the STEM options have historically been limited to ~6Å or more, limiting their usefulness on the most challenging samples. Significant improvements in this field was achieved by introducing the Helios G4 platform which brings 3Å STEM resolution, as well in-situ site specific ultrathin lamellas with damage below 1 nm and maximum cut fidelity [2].Resolution of a 30 kV field emission SEM is mainly limited by spherical aberration of the objective lens. The easiest way how to reduce the spherical aberration is to shorten the focal length of the objective lens. In SEMs with conventional lenses the minimum focal length is usually more than 10 mm, in instruments with immersion magnetic (single pole) lenses more than 4 mm. On the other hand, in TEMs where the objective lens utilizes two pole pieces with small gap in between (an in-lens configuration), the focal length can be several times shorter and consequently the coefficients of axial aberrations smaller. The presented accomplishment of STEM performance improvement in a SEM is to equip the system with a second (lower) pole piece in such a way that the system is in-situ configurable and can be operated both in a traditional single-pole SEM (or FIB/SEM) mode and in a high resolution in-lens STEM mode. In order to have the system user-configurable the lower pole piece with integrated multi-segment solid state detector is mounted on a retractable mechanism, which also assures precise mechanical alignment to avoid unwanted aberrations. Improvements in resolution at 30 kV was demonstrated by lattice planes visualizations on several materials such as carbon nanotubes (0.34 nm), silicon (0.31 nm) or tungsten disulfide (0.27 nm) as shown in Figure 1c.To augment the STEM imaging it is desirable to view the diffraction pattern from the sample (as would typically be the case in a conventional S/TEM), which can provide information about sample crystallography, as well as lamella orientation. To investigate this, a pixelated d...

Summary Commercially available graphene samples are examined by Raman spectroscopy and very low energy scanning transmission electron microscopy. Limited lateral resolution of Raman spectroscopy may produce a Raman spectrum corresponding to a single graphene layer even for flakes that can be identified by very low energy electron microscopy as an aggregate of smaller flakes of various thicknesses. In addition to diagnostics of graphene samples at larger dimensions, their electron transmittance can also be measured at very low energies.