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Statistical and correlative analysis are increasingly important in the design and study of new materials, from semiconductors to metals. Non-destructive measurement techniques, with high spatial resolution, capable of correlating composition and/or structure with device properties, are few and far between. For the case of polycrystalline and inhomogeneous materials, the added challenge is that nanoscale resolution is in general not compatible with the large sampling areas necessary to have a statistical representation of the specimen under study. For the study of grain cores and grain boundaries in polycrystalline solar absorbers this is of particular importance since their dissimilar behavior and variability throughout the samples makes it difficult to draw conclusions and ultimately optimize the material. In this study, we present a nanoscale in-operando approach based on the multimodal utilization of synchrotron nano x-ray fluorescence and x-ray beam induced current collected for grain core and grain boundary areas and correlated pixel-by-pixel in fully operational Cu ( In ( 1 − x ) Ga x ) Se 2 solar cells. We observe that low gallium cells have grain boundaries that over perform compared to the grain cores and high gallium cells have boundaries that under perform. These results demonstrate how nanoscale correlative X-ray microscopy can guide research pathways towards grain engineering low cost, high efficiency solar cells.

The reasons for the start and end of the induction period of cement hydration remain topic of controversy. One long-standing hypothesis is that a thin metastable hydrate forming on the surface of cement grains significantly reduces the particle dissolution rate; the eventual disappearance of this layer re-establishes higher dissolution rates at the beginning of the acceleration period. However, the importance, or even the existence, of this metastable layer has been questioned because it cannot be directly detected in most experiments. In this work, a combined analysis using nano-tomography and nano-X-ray fluorescence makes the direct imaging of early hydration products possible. These novel X-ray imaging techniques provide quantitative measurements of 3D structure, chemical composition, and mass density of the hydration products during the induction period. This work does not observe a low density product on the surface of the particle, but does provide insights into the formation of etch pits and the subsequent hydration products that fill them.

While there is great interest in characterizing and modifying materials at the nanoscale, progress has been slow because few techniques allow for critical observations at this length scale. This work presents a data fusion technique that combines synchrotron-based X-ray nano computed tomography and nano X-ray fluorescence to non-destructively investigate complex nanoscale materials and provide combined three-dimensional (3-D) renderings of microstructure and chemistry. The technique has been named nano tomography-assisted chemical correlation (nTACCo) and is demonstrated on fly ash particles with nanoscale chemical inhomogeneities. Our findings show that nTACCo is capable of providing the concentration and location of seven different nano-inclusions within a particle. This work also provides direct observations of reactivity and chemical distribution of fly ash. This ability to combine 3-D structure and chemistry at the nanoscale will provide unprecedented tools for nanoscience in material science, biology, chemistry and medical science.

Synchrotron nanoprobe X-ray fluorescence maps show for the first time discrete iron-rich, titanium-rich and manganese/silicon-rich particles present in blast furnace slag grains, and these particles remain intact when the slag is used as a precursor for alkali-activated slag (AAS) binders. These particles appear to be entrained during slag production, and remain stable under the reducing conditions prevailing during alkali-activation. There is no evidence of chemical interaction between these particles and the AAS binder, which mainly comprises calcium silicate hydrates. These results are important for the understanding of iron chemistry in AAS, and the potential reactivity of metallic and other redox-sensitive species within AAS binders.

This paper presents the outcomes of a series of beamline-based studies, the results of which are combined to provide a more detailed multiscale understanding of the structure and chemistry of geopolymer binders. The range of beamline-based characterization techniques which have been applied to the study of geopolymer binders is increasing rapidly; although no single technique can provide a holistic view of binder structure across all the length scales which are of importance in determining strength development and durability, the synergy achievable through the combination of multiple beamline techniques is leading to rapid advances in knowledge in this area. Studies based around beamline infrared and X-ray fluorescence microscopy, in situ and ex situ neutron pair distribution function analysis, and nano- and micro-tomography, are combined to provide an understanding of geopolymer gel chemistry, nano- and microstructure in two and three dimensions, and the influences of seeded nucleation and precursor chemistry in these key areas. The application of advanced characterization methods in recent years has brought the understanding of geopolymer chemistry from a point, not more than a decade ago, when the analysis of the detailed chemistry of the aluminosilicate binder gel was considered intractable due to its disordered (“X-ray amorphous”) nature, to the present day where the influence of key compositional parameters on nanostructure is well understood, and both gel structure and reaction kinetics can be manipulated through methods including seeding, temperature variation, and careful mix design. This paper therefore provides a review outlining the value of nanotechnology – and particularly nanostructural characterization – in the development and optimization of a new class of environmentally beneficial cements and concretes. Key engineering parameters, in particularly strength development and permeability, are determined at a nanostructural level, and so it is essential that gel structures can be analyzed and manipulated at this level; beamline-based characterization techniques are critical in providing the ability to achieve this goal.

Durability of alkali-activated binders is of vital importance in their commercial application, and depends strongly on microstructure and pore network characteristics. X-ray microtomography (μCT) offers, for the first time, direct insight into microstructural and pore structure characteristics in three dimensions. Here, μCT is performed on a set of sodium metasilicate-activated fly ash/slag blends, using a synchrotron beamline instrument. Segmentation of the samples into pore and solid regions is then conducted, and pore tortuosity is calculated by a random walker method. Segmented porosity and diffusion tortuosity are correlated, and vary as a function of slag content (slag addition reduces porosity and increases tortuosity), and sample age (extended curing gives lower porosity and higher tortuosity). This is particularly notable for samples with ≥ 50% slag content, where a space-filling calcium (alumino)silicate hydrate gel provides porosity reductions which are not observed for the sodium aluminosilicate (‘geopolymer’) gels which do not chemically bind water of hydration.

Nanotomographic reconstruction of a sample of low-CO2 “geopolymer” cement provides the first three-dimensional view of the pore structure of the aluminosilicate geopolymer gel, as well as evidence for direct binding of geopolymer gel onto unreacted fly ash precursor particles. This is central to understanding and optimizing the durability of concretes made using this new class of binder, and demonstrates the value of nanotomography in providing a three-dimensional view of nanoporous inorganic materials.

Structural evolution in pastes produced from alkali silicate-activated granulated blast furnace slag (GBFS)/metakaolin (MK) blends is assessed. In the initial period of the reaction, the addition of MK leads to an increase in the total setting time, reduces the heat release, and affects the reaction mechanism by introduction of a large quantity of additional Al. This effect is more significant when an activating solution with a higher silicate modulus is used, and leads to a slight reduction in the final mechanical strength of mortars but a significant increase in setting time, which is valuable in the development of alkali-activated slag binders as these are known to sometimes harden more rapidly than is desirable. High-energy synchrotron X-ray diffractometry reveals that the main reaction products in alkali-activated GBFS/MK blends are segregated and partially crystalline calcium silicate hydrate and aluminosilicate phases, including a small component with a zeolitic (gismondine) structure. No hydrotalcite-type phases are observed in these samples, which are synthesized from a low-Mg slag. A secondary reaction product (Na-substituted C–S–H) is also identified in pastes activated with a modulus of solution of 2.0. Infrared spectroscopy carried out over a period of 180 days shows the development of the gel structure, with aluminum incorporation leading to an increase in the extent of crosslinking, and higher alkalinity giving a more depolymerized gel structure.

Accelerated carbonation is induced in pastes and mortars produced from alkali silicate-activated granulated blast furnace slag (GBFS)–metakaolin (MK) blends, by exposure to CO2-rich gas atmospheres. Uncarbonated specimens show compressive strengths of up to 63 MPa after 28 days of curing when GBFS is used as the sole binder, and this decreases by 40–50% upon complete carbonation. The final strength of carbonated samples is largely independent of the extent of metakaolin incorporation up to 20%. Increasing the metakaolin content of the binder leads to a reduction in mechanical strength, more rapid carbonation, and an increase in capillary sorptivity. A higher susceptibility to carbonation is identified when activation is carried out with a lower solution modulus (SiO2/Na2O ratio) in metakaolin-free samples, but this trend is reversed when metakaolin is added due to the formation of secondary aluminosilicate phases. High-energy synchrotron X-ray diffractometry of uncarbonated paste samples shows that the main reaction products in alkali-activated GBFS/MK blends are C–S–H gels, and aluminosilicates with a zeolitic (gismondine) structure. The main crystalline carbonation products are calcite in all samples and trona only in samples containing no metakaolin, with carbonation taking place in the C–S–H gels of all samples, and involving the free Na+ present in the pore solution of the metakaolin-free samples. Samples containing metakaolin do not appear to have the same availability of Na+ for carbonation, indicating that this is more effectively bound in the presence of a secondary aluminosilicate gel phase. It is clear that claims of exceptional carbonation resistance in alkali-activated binders are not universally true, but by developing a fuller mechanistic understanding of this process, it will certainly be possible to improve performance in this area.

We have investigated the growth of Co nanoparticles on {theta}-Al{sub 2}O{sub 3}/CoAl(1 0 0) by means of Auger electron spectroscopy (AES), high-resolution electron energy loss spectroscopy (EELS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Due to Volmer--Weber growth, Co forms particles with a mean diameter of approximately 2.5 nm and height of 0.8 nm. Even on the entirely covered oxide, there is no Ostwald ripening and Co particles stay structurally isolated. The nanoparticles exhibit a small size distribution and tend to form chains, as predetermined by the streak structure of the oxide template. For sufficient high coverages Co-core-CoO-shell nanoparticles may be evidenced, which is explained as a result of surfactant oxygen. The nanostructured particles may open the door to numerous applications, such as in catalysis and magnetoelectronic applications, where large areas of ordered nanodots are desired.

We have employed Auger electron spectroscopy (AES), high resolution electron energy loss spectroscopy (EELS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) to investigate the growth of an Al2O3 film on CoAl(1 0 0). While exposure to oxygen at room temperature leads to the formation of amorphous alumina, subsequent annealing at higher temperatures results in the growth of well-ordered θ-Al2O3. Well-ordered Al2O3 films are also formed by oxidation at temperatures of 800 K and above. The oxide is characterized by Fuchs–Kliewer modes at around 430, 630, 780 and 920 cm−1. Oxide islands grow in two sets of domains perpendicular to each other. Under ultra-high vacuum conditions, self-limiting thickness of the oxide layer (9–10 A) has been found. The band gap of the θ-Al2O3 film on CoAl(1 0 0) is 4.3–4.5 eV.

The oxidation of a CoAl(1 0 0) surface at 300 K was studied by means of Auger electron spectroscopy, high resolution electron energy loss spectroscopy (EELS), low energy electron diffraction and scanning tunneling microscopy (STM). For an exposure ⩽0.3 L, the oxygen atoms are chemisorbed on the CoAl(1 0 0) surface, while for a larger O2 exposure the oxidation of the surface sets in. For an exposure ⩾300 L the surface is entirely covered with amorphous Al2O3 (a-Al2O3) whereas the Co atoms seem to be unaffected. The EEL spectra of a-Al2O3 exhibit Fuchs–Kliewer modes at around 640 and 890 cm−1. The thickness of the a-Al2O3 film is estimated to be 7.1 ± 0.7 A. The STM images show that the oxide grows as large islands which cover the whole surface. The band gap of the ultra-thin a-Al2O3 film on CoAl(1 0 0) is found to be 3.2 eV and thus it is strongly diminished with respect to the bulk value.