Operando Spatial and Temporal Tracking of Axial Stresses and Interfaces in Solid-state Batteries.

Solid-state batteries have the potential to replace the current generation of liquid electrolyte batteries. However, the major limitation resulting from their solid-state architecture is the gradual loss of ionic conductivity due to the loss of physical contact between the individual battery components during charging/discharging. This is mainly due to mechanical stresses caused by volume changes in the cathode and anode during lithiation and delithiation. To date, limited research has been devoted to understanding the spatio-temporal distribution of stresses during battery operation. Here, operando scanning high-energy X-ray diffraction to quantify cross-sectional axial stresses with a spatial resolution of 10 µm is used. It is shown how a non-monotonous stress distribution evolves over time during the cycling of the solid-state battery. In addition, degradation of the solid-state electrolyte in the vicinity of the lithium anode is observed and tracked periodic changes in the unit cell volume in the cathode. The presented methodology of tracking the chemo-mechanically induced stresses and interface morphology in real time in correlation with other battery parameters is believed, can provide a valuable platform for the future optimization of solid-state batteries.

Langmuir-Scheaffer Technique as a Method for Controlled Alignment of 1D Materials.

A widely applicable method for aligning 1D materials, and in particular carbon nanotubes (CNTs), independent of their preparation would be very useful as the growth methods for these materials are substance-specific. Langmuir-Schaefer (LS) deposition could be such an approach for alignment, as it aligns a large number of 1D materials independently of the desired substrate. However, the mechanism and required conditions for alignment of 1D nanomaterials in a Langmuir trough are still unclear. Here we show, relying on numerical simulations of the Langmuir film compression, that the LS method is a powerful tool to achieve maximal alignment of 1D material in a controllable manner. In particular, 1D materials terminated with a suitable surfactant can align only if the velocity induced by the attraction between individual 1D entities is low enough relative to the flow speed. To validate this model, we achieved an efficient LS alignment of single-walled carbon nanotubes covered with a suitable surfactant relying on the numerical simulations. In situ polarized Raman microspectroscopy during the compression of Langmuir film revealed good quantitative agreement between the numerical simulations and the experiment. This suggests the applicability of the LS technique as a versatile method for the controlled alignment of 1D materials.

Reorientation of π-conjugated molecules on few-layer MoS2 films.

Small π-conjugated organic molecules have attracted substantial attention in the past decade as they are considered as candidates for future organic-based (opto-)electronic applications. The molecular arrangement in the organic layer is one of the crucial parameters that determine the efficiency of a given device. The desired orientation of the molecules is achieved by a proper choice of the underlying substrate and growth conditions. Typically, one underlying material supports only one inherent molecular orientation at its interface. Here, we report on two different orientations of diindenoperylene (DIP) molecules on the same underlayer, i.e. on a few-layer MoS2 substrate. We show that DIP molecules adopt a lying-down orientation when deposited on few-layer MoS2 with horizontally oriented layers. In contrast, for vertically aligned MoS2 layers, DIP molecules are arranged in a standing-up manner. Employing in situ and real-time grazing-incidence wide-angle X-ray scattering (GIWAXS), we monitored the stress evolution within the thin DIP layer from the early stages of the growth, revealing different substrate-induced phases for the two molecular orientations. Our study opens up new possibilities for the next-generation of flexible electronics, which might benefit from the combination of MoS2 layers with unique optical and electronic properties and an extensive reservoir of small organic molecules.

Tailoring the interparticle distance in Langmuir nanoparticle films.

The ability to control the interparticle distance in self-assembled arrays of nanoparticles plays an important role in a large number of applications, which require tunable electronic and photonic properties. Importantly, practical applications in real devices rely on arrays satisfying more stringent requirements of lateral homogeneity controlled over a large scale. Herein, the interparticle distance in ordered nanoparticle assemblies was controlled by varying the nanoparticle effective size via the molecular chemical nature and chain length of the ligand. Iron oxide nanoparticles (IONPs) were functionalized by three types of ligands, namely (i) a mixture of oleic acid/oleylamine (OA/OAm), (ii) poly(n-butyl acrylate) (PBA) and (iii) polystyrene (PS), while two different molar masses of PBA and PS were used. The polymeric ligands with narrow dispersity and bearing phosphonic chain-end groups were prepared by atom transfer radical polymerization. Functionalization of the IONPs with polymeric ligands was achieved using a ligand exchange method. Both the hydrodynamic diameter and size distribution of the nanoparticles in colloidal solution were determined by dynamic light scattering (DLS). The mean interparticle distances in Langmuir-Schaefer monolayers prepared on solid substrates were assessed by means of the pair correlation function calculated from the atomic force microscopy (AFM) images. Furthermore, the lateral ordering, homogeneity, and interparticle distances averaged over a mesoscopic scale of the ordered monolayers were studied by the grazing-incidence small-angle X-ray scattering (GISAXS) technique. We demonstrate that the (nanoparticle) centre-to-centre distance in the ordered assemblies constituted by the IONPs with the core diameter of about 6 nm can be varied from 7.6 to about 12 nm with the resulting interparticle gap change by a factor of about 4.

Evolution of Defects, Morphology, and Strain during FAMAPbI3 Perovskite Vacuum Deposition: Insights from In Situ Photoluminescence and X-ray Scattering.

At present, the power conversion efficiency of single-junction perovskite-based solar cells reaches over 26%. The further efficiency increase of perovskite-based optoelectronic devices is limited mainly by defects, causing the nonradiative recombination of charge carriers. To improve efficiency and ensure reproducible fabrication of high-quality layers, it is crucial to understand the perovskite nucleation and growth mechanism along with associated process control to reduce the defect density. In this study, we investigate the growth kinetics of a promising narrow bandgap perovskite, formamidinium methylammonium lead iodide (FAMAPbI3), for high-performance single-junction solar cells. The temporal evolution of structural and optoelectronic properties during FAMAPbI3 vacuum codeposition was inspected in real time by grazing-incidence wide-angle X-ray scattering and photoluminescence. Such a combination of analytical techniques unravels the evolution of intrinsic defect density and layer morphology correlated with lattice strain from the early stages of the perovskite deposition.

SERS Performance of Ti3C2Tx MXene-Based Substrates Correlates with Surface Morphology.

The surface-enhanced Raman scattering (SERS) properties of low-dimensional semiconducting MXene nanoflakes have been investigated over the last decade. Despite this fact, the relationship between the surface characteristics and SERSing performance of a MXene layer has yet to be comprehensively investigated and elucidated. This work shows the importance of surface morphology on the overall SERS effect by studying few-layer Ti3C2Tx MXene-based SERS substrates fabricated by vacuum-assisted filtration (VAF) and spray coating on filter paper. The VAF deposition results in a dense MXene layer suitable for SERS with high spot-to-spot and substrate-to-substrate reproducibility, with a significant limit of detection (LoD) of 20 nM for Rhodamine B analyte. The spray-coated MXenes film revealed lower uniformity, with a LoD of 50 nM for drop-casted analytes. Moreover, we concluded that the distribution of the analyte deposited onto the MXene layer is affected by the presence of MXene aggregates created during the deposition of the MXene layer. Accumulation of the analyte molecules in the vicinity of MXene aggregates was observed for drop-casted deposition of the analyte, which affects the resulting SERS enhancement. Ti3C2Tx MXene layers deposited on filter paper by VAF offer great potential as a cost-effective, easy-to-manufacture, yet robust, platform for sensing applications.

Lithium-Induced Reorientation of Few-Layer MoS2 Films.

Molybdenum disulfide (MoS2) few-layer films have gained considerable attention for their possible applications in electronics and optics and also as a promising material for energy conversion and storage. Intercalating alkali metals, such as lithium, offers the opportunity to engineer the electronic properties of MoS2. However, the influence of lithium on the growth of MoS2 layers has not been fully explored. Here, we have studied how lithium affects the structural and optical properties of the MoS2 few-layer films prepared using a new method based on one-zone sulfurization with Li2S as a source of lithium. This method enables incorporation of Li into octahedral and tetrahedral sites of the already prepared MoS2 films or during MoS2 formation. Our results discover an important effect of lithium promoting the epitaxial growth and horizontal alignment of the films. Moreover, we have observed a vertical-to-horizontal reorientation in vertically aligned MoS2 films upon lithiation. The measurements show long-term stability and preserved chemical composition of the horizontally aligned Li-doped MoS2.

Evolution of Structure and Optoelectronic Properties During Halide Perovskite Vapor Deposition.

The efficiency of perovskite-based solar cells has increased dramatically over the past decade to as high as 25%, making them very attractive for commercial use. Vapor deposition is a promising technique that potentially enables fabrication of perovskite solar cells on large areas. However, to implement a large-scale deposition method, understanding and controlling the specific growth mechanisms are essential for the reproducible fabrication of high-quality layers. Here, we study the structural and optoelectronic kinetics of MAPbI3, employing in-situ photoluminescence (PL) spectroscopy and grazing-incidence small/wide-angle X-ray scattering (GI-SAXS/WAXS) simultaneously during perovskite vapor deposition. Such a unique combination of techniques reveals MAPbI3 formation from the early stages and uncovers the morphology, crystallographic structure, and defect density evolution. Furthermore, we show that the nonmonotonous character of PL intensity contrasts with the increasing volume of the perovskite phase during the growth, although bringing valuable information about the presence of defect states.

Structure and Thermal Stability of ε/κ-Ga2O3 Films Deposited by Liquid-Injection MOCVD.

We report on crystal structure and thermal stability of epitaxial ε/κ-Ga2O3 thin films grown by liquid-injection metal−organic chemical vapor deposition (LI-MOCVD). Si-doped Ga2O3 films with a thickness of 120 nm and root mean square surface roughness of ~1 nm were grown using gallium-tetramethylheptanedionate (Ga(thd)3) and tetraethyl orthosilicate (TEOS) as Ga and Si precursor, respectively, on c-plane sapphire substrates at 600 °C. In particular, the possibility to discriminate between ε and κ-phase Ga2O3 using X-ray diffraction (XRD) φ-scan analysis or electron diffraction analysis using conventional TEM was investigated. It is shown that the hexagonal ε-phase can be unambiguously identified by XRD or TEM only in the case that the orthorhombic κ-phase is completely suppressed. Additionally, thermal stability of prepared ε/κ-Ga2O3 films was studied by in situ and ex situ XRD analysis and atomic force microscopy. The films were found to preserve their crystal structure at temperatures as high as 1100 °C for 5 min or annealing at 900 °C for 10 min in vacuum ambient (<1 mBar). Prolonged annealing at these temperatures led to partial transformation to ß-phase Ga2O3 and possible amorphization of the films.

Combined in Situ Photoluminescence and X-ray Scattering Reveals Defect Formation in Lead-Halide Perovskite Films.

Lead-halide perovskites have established a firm foothold in photovoltaics and optoelectronics due to their steadily increasing power conversion efficiencies approaching conventional inorganic single-crystal semiconductors. However, further performance improvement requires reducing defect-assisted, nonradiative recombination of charge carriers in the perovskite layers. A deeper understanding of perovskite formation and associated process control is a prerequisite for effective defect reduction. In this study, we analyze the crystallization kinetics of the lead-halide perovskite MAPbI3-xClx during thermal annealing, employing in situ photoluminescence (PL) spectroscopy complemented by lab-based grazing-incidence wide-angle X-ray scattering (GIWAXS). In situ GIWAXS measurements are used to quantify the transition from a crystalline precursor to the perovskite structure. We show that the nonmonotonous character of PL intensity development reflects the perovskite phase volume, as well as the occurrence of the defects states at the perovskite layer surface and grain boundaries. The combined characterization approach enables easy determination of defect kinetics during perovskite formation in real-time.

Effect of Dexamethasone on Thermoresponsive Behavior of Poly(2-Oxazoline) Diblock Copolymers.

Thermoresponsive polymers play an important role in designing drug delivery systems for biomedical applications. In this contribution, the effect of encapsulated hydrophobic drug dexamethasone on thermoresponsive behavior of diblock copolymers was studied. A small series of diblock copoly(2-oxazoline)s was prepared by combining thermoresponsive 2-n-propyl-2-oxazoline (nPrOx) and hydrophilic 2-methyl-2-oxazoline (MeOx) in two ratios and two polymer chain lengths. The addition of dexamethasone affected the thermoresponsive behavior of one of the copolymers, nPrOx20-MeOx180, in the aqueous medium by shifting the cloud point temperature to lower values. In addition, the formation of microparticles containing dexamethasone was observed during the heating of the samples. The morphology and number of microparticles were affected by the structure and concentration of copolymer, the drug concentration, and the temperature. The crystalline nature of formed microparticles was confirmed by polarized light microscopy, confocal Raman microscopy, and wide-angle X-ray scattering. The results demonstrate the importance of studying drug/polymer interactions for the future development of thermoresponsive drug carriers.

3D Networks of Ge Quantum Wires in Amorphous Alumina Matrix.

Recently demonstrated 3D networks of Ge quantum wires in an alumina matrix, produced by a simple magnetron sputtering deposition enables the realization of nanodevices with tailored conductivity and opto-electrical properties. Their growth and ordering mechanisms as well as possibilities in the design of their structure have not been explored yet. Here, we investigate a broad range of deposition conditions leading to the formation of such quantum wire networks. The resulting structures show an extraordinary tenability of the networks' geometrical properties. These properties are easily controllable by deposition temperature and Ge concentration. The network's geometry is shown to retain the same basic structure, adjusting its parameters according to Ge concentration in the material. In addition, the networks' growth and ordering mechanisms are explained. Furthermore, optical measurements demonstrate that the presented networks show strong confinement effects controllable by their geometrical parameters. Interestingly, energy shift is the largest for the longest quantum wires, and quantum wire length is the main parameter for control of confinement. Presented results demonstrate a method to produce unique materials with designable properties by a simple self-assembled growth method and reveal a self-assembling growth mechanism of novel 3D ordered Ge nanostructures with highly designable optical properties.

Kinetics of Polymer-Fullerene Phase Separation during Solvent Annealing Studied by Table-Top X-ray Scattering.

Solvent annealing is an efficient way of phase separation in polymer-fullerene blends to optimize bulk heterojunction morphology of active layer in polymer solar cells. To track the process in real time across all relevant stages of solvent evaporation, laboratory-based in situ small- and wide-angle X-ray scattering measurements were applied simultaneously to a model P3HT:PCBM blend dissolved in dichlorobenzene. The PCBM molecule agglomeration starts at ∼7 wt % concentration of solid content of the blend in solvent. Although PCBM agglomeration is slowed-down at ∼10 wt % of solid content, the rate constant of phase separation is not changed, suggesting agglomeration and reordering of P3HT molecular chains. Having the longest duration, this stage most affects BHJ morphology. Phase separation is accelerated rapidly at concentration of ∼25 wt %, having the same rate constant as the growth of P3HT crystals. P3HT crystallization is driving force for phase separation at final stages before a complete solvent evaporation, having no visible temporal overlap with PCBM agglomeration. For the first time, such a study was done in laboratory demonstrating potential of the latest generation table-top high-brilliance X-ray source as a viable alternative before more sophisticated X-ray scattering experiments at synchrotron facilities are performed.