Real-time Synchrotron Research Articles

In-situ observation of high-temperature Pb-free electric interconnections by synchrotron microradiography

Despite a large amount of research on transient liquid phase (TLP) bonding methods for high operating temperature Pb-free solder electric interconnections using Cu6Sn5 intermetallics (IMCs), two fundamental difficulties remain, namely, slow TLP process kinetics and uncontrolled void formation. Here we observe the TLP processes for rapid Cu6Sn5 growth using a recently developed technique via real-time synchrotron X-ray imaging. The technique enables in-situ characterization of the growth kinetics and real-time observation of the IMC evolution at the molten solder/solid substrate interfaces and the formation of voids and cracking during TLP bonding, which will contribute to the development of products suitable for high reliability and high-temperature applications, e.g., electric vehicles.

3D Phase Field Modeling of Multi-Dendrites Evolution in Solidification and Validation by Synchrotron X-ray Tomography.

In this paper, the dynamics of multi-dendrite concurrent growth and coarsening of an Al-15 wt.% Cu alloy was studied using a highly computationally efficient 3D phase field model and real-time synchrotron X-ray micro-tomography. High fidelity multi-dendrite simulations were achieved and the results were compared directly with the time-evolved tomography datasets to quantify the relative importance of multi-dendritic growth and coarsening. Coarsening mechanisms under different solidification conditions were further elucidated. The dominant coarsening mechanisms change from small arm melting and interdendritic groove advancement to coalescence when the solid volume fraction approaches ~0.70. Both tomography experiments and phase field simulations indicated that multi-dendrite coarsening obeys the classical Lifshitz–Slyozov–Wagner theory , but with a higher constant of n = 4.3.

Microstructure Evolution of Ag/TiO2 Thin Film

Ag/TiO2 thin films were prepared using the sol-gel spin coating method. The microstructural growth behaviors of the prepared Ag/TiO2 thin films were elucidated using real-time synchrotron radiation imaging, its structure was determined using grazing incidence X-ray diffraction (GIXRD), its morphology was imaged using the field emission scanning electron microscopy (FESEM), and its surface topography was examined using the atomic force microscope (AFM) in contact mode. The cubical shape was detected and identified as Ag, while the anatase, TiO2 thin film resembled a porous ring-like structure. It was found that each ring that coalesced and formed channels occurred at a low annealing temperature of 280 °C. The energy dispersive X-ray (EDX) result revealed a small amount of Ag presence in the Ag/TiO2 thin films. From the in-situ synchrotron radiation imaging, it was observed that as the annealing time increased, the growth of Ag/TiO2 also increased in terms of area and the number of junctions. The growth rate of Ag/TiO2 at 600 s was 47.26 µm2/s, and after 1200 s it decreased to 11.50 µm2/s and 11.55 µm2/s at 1800 s. Prolonged annealing will further decrease the growth rate to 5.94 µm2/s, 4.12 µm2/s and 4.86 µm2/s at 2400 s, 3000 s and 3600 s, respectively.

Microstructure and growth kinetic study in Sn–Cu transient liquid phase sintering solder paste

The feasibility of the highly reliable and replicable microstructure formation of the transient liquid phase sintering (TLPS) paste during the early soldering and isothermal aging on the Cu substrate had been successfully investigated in this study. By using the Sn–0.7 wt% Cu (SC) solder paste as the base material and the Cu particles in the production of the TLPS Sn–10 wt% Cu (SC10) solder paste, the ensuing Cu6Sn5 phase from the isothermal aging process was found to have reduced the β-Sn area of the bulk SC10 solder microstructure. The growth kinetic for TLPS SC10 resulted in a 26.76 kJ/mol of activation energy level. The real-time synchrotron radiation imaging technique that was employed in studying the growth and formation of the primary intermetallic phases at the solder joints had also discovered the primary intermetallic in TLPS SC10 was not only found to have experienced an early nucleation just after the solder had melted, but its growth was also restricted prior to the solidification of the liquid solder. Therefore, the relevance of the results that were obtained from this research may offer a possible solution for aiding the future development of highly reliable solder joints in high temperature solder applications.

Mechanical response of cortical bone in compression and tension at the mineralized fibrillar level in steroid induced osteoporosis

Nanocomposites like bone are used in vivo in a dynamic mechanical environment, and musculoskeletal fracture during traumatic events lead to pain and immobilisation, especially significant in elderly and patients with metabolic bone diseases. To mitigate against these occurrences, it is essential to understand the dynamic mechanical response of bone over short timescales, but the underlying matrix-level mechanisms are not well understood. Here, we studied the mechanical response of cortical bone at nano- and micro-scale in a mouse model with glucocorticoid induced osteoporosis and their wild type littermates using real-time synchrotron small-angle X-ray diffraction (SAXD) combined with in situ compression testing and micro-tensile testing under controlled strain rates. Under compression, the tissue modulus, yield stress, effective fibril modulus and fibrillar reorientation rate in osteoporotic bone is significantly lower than that in healthy bone. Under tension, when going from low to high strain rates, the effective fibril modulus of healthy bone increase by a factor of 4.8, but this tendency is suppressed in osteoporotic bone. Also, bone microstructure in osteoporotic showed large fraction of cavities with disrupted mineralization. Our results demonstrate how the nano- and microscale deformation mechanisms of bone ultrastructure change in osteoporotic bone under compression and tension. Our results suggest that material level changes of bone matrix contributed to the reduced mechanical competence of bone in metabolic bone diseases such as osteoporosis.

In situ oxidation studies of Cu thin films: Growth kinetics and oxide phase evolution

A comprehensive understanding of the oxidation of Cu thin films in the low-temperature regime is of fundamental interest and particularly relevant for applications in the fields of micro- and nanoelectronics, sensors, catalysis, and solar cells. The current study reports on the oxidation kinetics of PVD grown Cu thin films (20–150 nm thick) and the oxide phase evolution from Cu2O to CuO upon thermal oxidation in the temperature range of 100–450 °C. XRD investigations in the laboratory and at the synchrotron show that the oxide phase formation critically depends on the oxidation conditions such as temperature and oxygen partial pressure. The real-time synchrotron XRD measurements reveal that the formation of the CuO phase only starts after complete oxidation of the Cu films to Cu2O films. In situ resistance measurements were performed to follow the oxide growth rate of Cu2O on Cu films in the temperature range of 100–300 °C in air and in 10 mbar pO2. It is found that the oxidation kinetics of Cu films to Cu2O films follows the linear rate law, which is attributed to surface reaction controlled oxidation. The oxygen dissociation rate at the gas–solid interface is the rate-limiting process. A dramatic decrease in the linear oxidation rate is observed at low oxygen partial pressures. The fundamental differences between the oxidation rate-limiting processes of Cu as compared to other transition metal films are discussed.

On the observation of annealing twins during simulating β-grain refinement in Ti–6Al–4V high deposition rate AM with in-process deformation

Additive Manufacture (AM) of Ti–6Al–4V frequently leads to undesirable, coarse, columnar β-grain structures with a strong <100> fibre texture. In Wire-Arc AM (WAAM), it has been found that the application of a low plastic strain, by methods such as inter-pass rolling, can disrupt β columnar growth and produce a refined, equiaxed grain structure that is more randomly orientated. The origin of this desirable effect has been investigated by thermo-mechanical simulation, direct in-situ EBSD observation, as well as by real-time synchrotron X-ray diffraction (SXRD) during rapid heating. These complementary approaches have shown that, when starting with a WAAM microstructure, the grain refinement process produces a unique micro-texture represented by a four-pole motif symmetrically centred on the parent grain {100} orientations. These new β-grain orientations can be reproduced by a double {112}<111> twinning operation, which produces 12 new, unique, β-orientation variants. High-resolution orientation-mapping techniques and in-situ SXRD heating simulations suggest that the prior β does not twin during deformation, but rather the grain refinement and related texture may be caused by annealing twinning during β re-growth on rapid re-heating of the deformed AM microstructure. Although this is the first time such a unique texture has been observed in a deformed and β annealed Ti–6Al–4V material, it was only found to dominate under the unusual conditions that occur in AM of rapid heating – a fine, lightly deformed α transformation microstructure, with a very coarse starting β-grain structure.

Sintering Behaviors of Au Nanopowders with Different Particle Sizes: A Real-Time Synchrotron X-ray Scattering Study.

We have studied the solid-phase sintering behaviors of Au nanopowders with different particle sizes using real-time synchrotron X-ray scattering and field-emission scanning electron microscopy (FESEM) experiments in air. Au powders with large particle size of 173 nm at room temperature showed a defect-free crystal domain size of 47 nm. Most of these powders showed multiple grains within the particle. Solid-phase sintering typically occurred via surface diffusion of Au atoms near the surface of powders at temperatures above 300 °C, Au nanopowders with small particle size of 50 nm at room temperature showed a crystal domain size of 43 nm. Most of these powders showed a single grain inside the particle. Solid-phase sintering occurred simultaneously with volume diffusion of Au atoms near the grain boundary inside powders at temperatures above 250 °C and surface diffusion near the surface of powders at temperatures above 300 °C. Our study revealed that the solid-phase sintering behaviors of Au nanopowders began at temperatures over 250 °C, which is much lower than the melting temperature of 1064 °C. The thermal analysis results were consistent with the results of real-time synchrotron X-ray scattering and FE-SEM.

Oxidation Behaviors of Co, Cr, and Ni Nanopowders: A Real-Time Synchrotron X-ray Scattering Study.

We have studied the oxidation behaviors of Co, Cr, and Ni nanopowders for applications in biomedicine using a real-time synchrotron X-ray scattering in air. The Co nanopowders have a crystal domain size of 70 nm at room temperature (RT). The surface of the Co nanopowders was oxidized to CoO phase at RT. The interior of the Co nanopowders was rapidly oxidized at above 300 °C and was mostly oxidized above 550 °C. The Cr nanopowders have a crystal domain size of 92 nm at RT. The surface of the Cr nanopowders was oxidized to Cr₂O₃ phase at RT, but the interior of the nanopowders was present as Cr phase without being oxidized up to 650 °C. On the other hand, the Ni nanopowders have a crystal domain size of 93 nm at RT. The surface of the Ni nanopowders began to oxidize to Ni₂O₃ phase at 300 °C, and the interior of the nanopowders was mostly oxidized above 600 °C.

The effect of Bi on the microstructure, electrical, wettability and mechanical properties of Sn-0.7Cu-0.05Ni alloys for high strength soldering

This paper elucidated the effects of the Bi element (0 wt%, 0.5 wt% and 1.5 wt%) on the microstructure, electrical, wettability and mechanical properties of the Sn-0.7Cu-0.05Ni as a high strength solder. Besides using the conventional cross-sectioned microstructure image, the real-time synchrotron radiation imaging and synchrotron micro-X-ray fluorescence (XRF) technique was also used to investigate the microstructure, focusing on the in-situ growth behaviour of the primary (Cu,Ni)6Sn5 intermetallic and elemental distribution that had occurred in the Sn-0.7Cu-0.05Ni-1.5Bi. Other essential properties of solder material, such as wettability, electrical resistance, and shear strength, were also determined. The results showed that the addition of 1.5 wt% Bi refined the primary (Cu,Ni)6Sn5 intermetallics formation in the solder joint, where it grew earlier and faster relative to that in the Sn-0.7Cu-0.05Ni/Cu joint. Additionally, the addition of 1.5 wt% Bi resulted with a 3% reduction of its electrical resistance while increasing the wettability of the solder alloy. 1.5 wt% addition of the Bi element also found to have contributed to a significant increment of shear strength relative to that of the Sn-0.7Cu-0.05Ni. The results confirmed that the developed material is applicable as a potential high strength solder material in the context of advanced interconnecting applications.

Tailoring the isothermal crystallization kinetics of isodimorphic poly (butylene succinate-ran-butylene azelate) random copolymers by changing composition

A detailed isothermal crystallization study of biobased and biodegradable isodimorphic poly (butylene succinate-ran-butylene azelate) random copolyesters (PBS-ran-PBAz) with a wide composition range has been carried out to determine nucleation kinetics, spherulitic growth rates and overall crystallization kinetics. Differential Scanning Calorimetry (DSC) and Polarized Light Optical Microscopy (PLOM) analysis show that for the PBS-rich phase, the incorporation of BAz comonomer leads to a significant increase in nucleation density and a decrease in spherulitic growth. On the contrary, for the PBAz-rich phase, an antinucleating effect of the incorporation of BS comonomer has been observed. Both effects agree with the thermodynamic analysis of the equilibrium melting point depression as a function of composition, which predicts that only a small amount of BAz comonomer is included within the PBS-rich crystals and a larger amount of comonomer is included in PBAz-rich crystals. In addition, the enthalpy of melting of 100% crystalline PBS and PBAz were determined by a different practical approach: extrapolating real time synchrotron Wide Angle X-ray Scattering (WAXS) isothermal crystallization data and isothermal DSC data.

In-Situ Study of Multistep Lithium-Bismuth Alloying Mechanisms

With the high energy density, anode materials storing energy based on alloying mechanisms are promising anode candidate in rechargeable lithium ion batteries. Here, we target bismuth (Bi) nanostructures (theoretical volumetric capacity ~3800mAh/cm−3 with formation of Li3Bi) and explore the (de)alloying mechanisms upon insertion/extractiong of Li+. Real-time synchrotron XRD and in situ TEM of the (de)alloying kinetics of Bi working as a LIB anode are carried out, which reveals the reaction mechanism at both bulk level and at single-nanoparticle level. As analyzed by both two methods, the Li-Bi (de)alloying proceeds via a reversible two-step mechanmism featuring two two-phase reactions, where Li1Bi is identified as the intermediate phase. A preferred alloying pathway along Bi-(012) lattice during the Bi-Li1Bi transitioning stage is revealed and further studied by DFT. We expect such fundamentals discussed here to direct the design of alloying electrode materials with enhanced battery performance.

Numerical simulation of wave-like nucleation events

The Interdependence model [1] predicted that nucleation would occur in waves of events with regions of no nucleation in between each wave. The waves continue to form until nucleation covers the sample. The cause of this phenomenon was attributed to the formation of a nucleation-free zone which incorporates solute suppressed nucleation and inhibited nucleation zones. Recent real-time synchrotron x-ray studies by Prasad et al [2], Liotti et al [3] and Xu et al [4] have confirmed this hypothesis showing nucleation occurs in a step-wise fashion with a number of events occurring followed by little or no nucleation for a short period before another set of events occurs. A microscale solidification model that predicts diffusion-controlled dendritic growth has successfully shown the effect of the developing constitutional supercooling on the selection of nucleation events. In this study, we use this model to predict the solidification behaviour under the conditions experienced during these real-time synchrotron studies.

Al8Mn5 Particle Settling and Interactions with Oxide Films in Liquid AZ91 Magnesium Alloys

Al8Mn5 particles form as primary solidification phases in Mg-Al-based alloys and are important for ensuring adequate corrosion resistance. However, excessive Al8Mn5 formation above the α-Mg liquidus temperature can lead to sludge formation, and the clustering of Al8Mn5 particles on oxide films can generate deleterious casting defects. Here, we use analytical SEM and real-time synchrotron x-ray radiography to study Al8Mn5 particle settling, the formation of a sludge layer, and the mechanism of Al8Mn5 clustering on oxides in AZ91 containing two Fe levels. It is shown that settling Al8Mn5 can become trapped in entrained oxide and that new Al8Mn5 particles also seem to nucleate on oxide films. On cooling, these Al8Mn5 particles continue to grow, creating large Al8Mn5 clusters.

Crystalline Structures and Structural Transitions of Copolyamides Derived from 1,4-Diaminobutane and Different Ratios of Glutaric and Azelaic Acids.

Copolyamides derived from even 1,4-butanediamine and different mixtures of odd dicarboxylic acids with a great difference in the number of methylene groups (i.e., glutaric and azelaic acids with 3 and 7 groups, respectively) have been synthesized, characterized and structurally studied. Calorimetric analyses revealed a complex behavior with multiple melting peaks associated to lamellar reordering and the presence of defective crystals. Equilibrium melting temperatures were evaluated and showed a eutectic behavior with composition. Copolymers were able to crystallize even for samples with comonomer percentages close to 50%. Negative and ringed spherulites from the melt state and small lath-like lamellar crystals from dilute solution crystallizations were attained. Furthermore, calorimetric data pointed out the exclusion of the less abundant monomer from the lattice of the predominant structure. All samples at room temperature showed a similar crystalline structure (form I) defined by two predominant reflections at spacings close to 0.430 and 0.380 nm, which has been related for even-odd nylons with a two-hydrogen bonded structure. Real time synchrotron experiments showed that melt crystallized samples have two polymorphic transitions on heating, which were practically reversible and consequently were also detected during cooling from the melt state. Interestingly, a different behavior was detected among solution crystallized samples and specifically the transition to the intermediate structure (form II) was not detected during heating for samples enriched on the azelate component or more precisely when they were exclusively crystallized in the form I.

In-situ understanding of pore nucleation and growth in polyurethane foams by using real-time synchrotron X-ray tomography

The nucleation and growth of pores in PU foams have been visualized and quantified for the first time in 4D using in-situ tomographic microscopy. Acquiring sequences of 3D images in 156 ms each, we describe homogeneous and heterogeneous nucleation and subsequent bubble growth dynamics for materials with and without nucleating nanoparticles. Exploiting the time resolved tomographic sequences we obtained the bubble nucleation rate, bubble density and size evolution, based on which the diffusion coefficient of gas molecules in polymer can be calculated, evidencing the reduction of diffusivity provoked by the inclusion of nanoparticles. We found that nucleation and growth are in a large extend decoupled in time.

Non-steady 3D dendrite tip growth under diffusive and weakly convective conditions

Three dimensional α-Al dendrite tip growth under varying solute gradients in an Al-Cu-Si alloy melt has been studied using real time synchrotron X-ray imaging and mathematical modelling. X-radiographic image sequences with high temporal and spatial resolution were processed and analysed to retrieve three-dimensional spatial details of the evolving dendrite and the solute concentration field, providing vastly improved estimates for the latter, in particular for the melt regions adjacent to the dendrite tips. Computational results obtained from an extended Horvay-Cahn dendrite tip model, capable of taking into account the effects of sample confinement, showed good agreement with the experimental data, and can be taken to verify the robustness of the 3D data extraction protocol.

Fat crystallization and melting in W/O/W double emulsions: Comparison between bulk and emulsified state

Water-in-oil-in-water (W/O/W) technology enables the development of an emulsion-based delivery system for functional food applications. The functionality of this system depends on the oil barrier of the double emulsion, whereby the fat matrix properties (e.g. solid fat content) play an important role. First, the effect of W/O/W emulsification on fat crystallization and melting behavior was studied and compared to bulk fat. Second, the effect of fat composition was investigated. As such, W/O/W emulsions were produced with a slow and fast crystallizing fat, i.e. soft palm mid fraction (sPMF) and partially hydrogenated sunflower oil, respectively, upon cooling and subsequent isothermal crystallization. Low resolution NMR and DSC techniques were applied, and indications about the polymorphic behavior were verified by real-time synchrotron XRD measurements. Except from increased supercooling, the overall fat crystallization dynamics in the W/O/W emulsions were similar to bulk, irrespective of the used fat. Yet, broadening of the long spacing peaks in the W/O/W emulsions indicated less ordered triacylglycerol longitudinal stacking compared to bulk. This effect was more pronounced in case of α-crystals than β’-crystals. With respect to W/O/W functionality, the melting behavior of the W/O/WsPMF emulsion showed promise as a possible carrier system with a thermo-responsive release mechanism for functional foods.

Enhanced oxidation resistance of NaBH4-treated mackinawite (FeS): Application to Cr(VI) and As(III) removal

Sulfide minerals are important in immobilizing toxic contaminants in reducing environments. Iron sulfide (FeS) is ubiquitous in anoxic conditions and is a good scavenger of various organic and redox sensitive contaminants and heavy metals. Despite its contaminant removal capabilities, FeS has not been used as a practical adsorbent in contaminant removal due to its rapid oxidation under atmospheric conditions. To increase its applicability, we developed a method of modifying FeS by the addition of NaBH4 to form the less oxygen-sensitive NaBH4–FeS. We conducted oxidation tests using laboratory batch testing and real-time synchrotron X-ray absorption spectroscopy (XAS). The Fe K-edge XAS results showed that the oxidation rate of NaBH4–FeS was eight times slower than that of unmodified FeS while maintaining comparable contaminant removal capacities for Cr(VI) and As(III). The results of mechanistic density functional theory (DFT) calculations demonstrated that the oxidation of FeS occurred through electron transfer from sulfur of FeS to an oxidizing agent of oxygen, and that the hydride ion provided by NaBH4 retarded electron transfer from the FeS surface.

In situ and real-time monitoring of structure formation during non-reactive sputter deposition of lanthanum and reactive sputter deposition of lanthanum nitride.

Lanthanum and lanthanum nitride thin films were deposited by magnetron sputtering onto silicon wafers covered by natural oxide. In situ and real-time synchrotron radiation experiments during deposition reveal that lanthanum crystallizes in the face-centred cubic bulk phase. Lanthanum nitride, however, does not form the expected NaCl structure but crystallizes in the theoretically predicted metastable wurtzite and zincblende phases, whereas post-growth nitridation results in zincblende LaN. During deposition of the initial 2-3 nm, amorphous or disordered films with very small crystallites form, while the surface becomes smoother. At larger thicknesses, the La and LaN crystallites are preferentially oriented with the close-packed lattice planes parallel to the substrate surface. For LaN, the onset of texture formation coincides with a sudden increase in roughness. For La, the smoothing process continues even during crystal formation, up to a thickness of about 6 nm. This different growth behaviour is probably related to the lower mobility of the nitride compared with the metal. It is likely that the characteristic void structure of nitride thin films, and the similarity between the crystal structures of wurtzite LaN and La2O3, evoke the different degradation behaviours of La/B and LaN/B multilayer mirrors for off-normal incidence at 6.x nm wavelength.