3.1.1

High throughput micro-tomography

The micro-tomography setup is located on the I13-2 Diamond-Manchester Imaging Branchline, consisting of a high-precision rotation stage and a visible light detector using an X-ray to visible light converting scintillation screen coupled to a visible light microscope. Most experiments are carried out in pink-beam mode, with a minimal ID gap of 5mm, a set of filters (typically 1.3mm glassy carbon, 3mm aluminium and for higher photon energies either 100 μm steel or palladium and silver filters) and either the silicon, platinum or rhodium strip of the horizontally deflecting mirror. The distance between sample and detector can be increased to up to about 2 meters for in-line phase contrast imaging, suitable for investigating unstained soft biological tissues¹⁶. Typical scanning times are in the range of minutes.

Most recently a sample changing system has been added to the setup (see figure 3, left). The system consists of a robotic arm, a plate for intermediate storage of the samples and a (cryo-compatible) sample gripper. The current version of the gripper can handle samples with up to 5mm diameter. Samples are identified by the barcode, engraved on the base of the sample holder. The scheme is very similar to the sample handling systems used at the Diamond protein crystallography (MX) beamlines. The robot system is interlocked to the safety system. The alignment procedure and the tomographic reconstruction is automated, using tailor-made software for alignment and the Diamond SAVU data pipeline for reconstruction¹⁷.

Figure 3:

left: Sample changing robotic arm; right: example of surface rendered Mycetophagidae (hairy fungus beetle: sample courtesy A. Goswami, National History Museum London).

Up to 300 samples can be scanned per day. It allows exploring for example parameter space in materials with variable composition and preparation. Figure 3 right shows an application for life sciences in the area of bio-diversity (collaboration A. Goswami, NHM, London). Insects represent over a million known species and the development and evolution of this diversity is a central question. Phenotype encompasses morphology, development, physiology, and behavior and is the interface between an organism and their environment, including other individuals. Information on phenotype is critical for understanding how species evolve and respond to change, which is important in today’s rapidly evolving environment. The current data acquisition and analyses capabilities will be improved further in terms of samples to be scanned and the automation of data analyses and requires a significant investment in data infrastructure.

3.1.2

Operando imaging

Operando imaging is typically performed with a large variety of sample environments, including heating, cooling, chemical reactors, rigs studying for example strain displacements below 100nm load³ (see also references in¹⁸). Many experiments are carried out with the in-line phase contrast geometry, but apply also to other techniques. For increased sensitivity the (single-) grating interferometry setup is used^19-24, which is compatible not only with the energy bandwidth provided by the multilayer monochromator but also in pink beam mode^{10, 11}. Grating interferometry provides in addition phase and small angle scattering information. The phase signal is much more sensitive compared to the absorption and eases segmentation of data. Small angle scattering scales with electron density fluctuations and might help identifying the early stages of phase separation/transition occurring in materials⁶. As an example for operando imaging, the different processes for phase transition in anti-solvent transition is shown in figure 4. The picture on the left side shows the experimental setup including the reactor. At the tip of an inner and an outer tube, an anti-solvent is mixed with a solution, inducing a large variety of crystallization processes, see figure 4 (right). The technique will be improved and upgraded for a faster, more sensitive and detailed study and a better understanding of these processes, see also comments for the Diamond II upgrade including figure 6.

Figure 4:

Operando imaging with dedicated sample environment/chemical reactor; left: experimental setup for crystallization studies induced by anti-solvent; right: different crystallization processes occurring in the mixing zone.

3.1.3

Fast Nano-tomography

For nano-imaging with 100nm resolution and below several methods are available on the imaging and coherence branch. While the timescales for the full-field microscope (TXM) are comparable to the other direct imaging methods, imaging in reciprocal space is significantly slower (see table 1).

The transmission X-ray microscope (TXM), located on the imaging branch, is using diffractive optics. The condenser optic is a so-called beam shaper²⁵, creating an illumination of 50-100 μm side length with the option of illumination of Zernike phase contrast (see references ^{9, 26} and also ^{27, 28}). The Fresnel-zone plate objective lenses provide a resolution of about 50-100 nm spatial resolution. For fast imaging using the multilayer monochromator the energy bandwidth is ΔE/E=10^-3. Tomographic scans are typically recorded within minutes and has the potential to be reduced to the sub-minute to second regime by further optimising the setup and for specific cases, using machine learning algorithms⁹.

Figure 5:

left and center: Deterioration of a 40 μm-thick X65 steel pin in a CO₂ saturated brine solution, heated at 80 °C. The formation of an oxide scale and a localized corrosion site can be observed. Siderite crystals are formed, shown in yellow; right: TXM with dedicated sample environment, here an in-situ flow cell, to study corrosion as a function of temperature, solution chemistry, and exposure time. All images courtesy Brian Connolly, Manchester University.

For the methods operating in reciprocal space (ptychography, Bragg-CDI), 3D data can be currently recorded within a couple of hours. For ptychography data acquisition with pink beam^29-31 and a data rate of up to 10kHz³¹ have been demonstrated. Today a typical data acquisition rate is 800 Hz in fly-scan mode, scanning 200 μm²s^-1. For this reason temporal evolving structures can be studied in 2D, time series for tomographic studies can be achieved for any ‘frozen’ systems, where it is possible to interrupt and halt processes. Figure 6 shows a typical example for this kind of studies, investigating the crack propagation within a battery electrode³². The mechanical degradation of a LiNi_0.8Co_0.1Mn_0.1O₂ (NMC) cathode by Li+ cycling was performed by cycling the sample in-situ, halting the process and scanning the sample over 12 hours.

Figure 6:

Formation of cracks within battery cathode material (NMC) along cycling process, recorded with ptychographic tomography³².