Abstract Molecular single-source precursors are a promising way of obtaining multi-element extended solids directly. We show that thermal decomposition of well-defined mono-, bi- and trimetallic polyoxovanadates (POVs) proceeds through a series of intermediate amorphous and crystalline species which we characterise using solid-state NMR spectroscopy, pair-distribution function (PDF) analysis and in-situ X-ray diffraction, before forming crystalline V2O5 and BiVO4 products. This synthetic strategy enables the formation of phases inaccessible using other routes, including a previously unknown polymorph of BiVO4 which we name β-BiVO4 due to its similarity to β-SnWO4. Local structure information also reveals the temperature dependent incorporation of Zn do pants into BiVO4. The study also explores the electrochemical properties of amorphous mixed-valence vanadium oxides as Li-ion battery electrodes. We suggest that careful analysis of the thermal decomposition of molecular species may be a way of obtaining hitherto unknown kinetically stabilised polymorphs and amorphous variants of extended solids.

This study investigates the influence of post-deposition annealing (PDA) ambient and temperature on atomic layer deposition (ALD)-grown SiO2 and HfO2/SiO2 gate dielectrics for 4H-silicon carbide (SiC) MOS devices. PDAs were conducted in either nitrogen (N2) or forming gas (FG) environments over a temperature range of 600-1100 degrees C. Comprehensive electrical characterization including capacitance-voltage (C-V), current-voltage (I-V), interface trap density (DIT), before implementing optimum PDA conditions in lateral MOSFETs. DIT values as low as similar to 0.8 & times; 1011 cm-2 eV-1 and 0.95 & times; 1011 cm-2 eV-1 for ALD grown SiO2 and HfO2/SiO2 stacks. Lateral MOSFETs with the SiO2-only dielectric layer annealed in FG at 1100 degrees C achieved a field-effect mobility of 33.93 +/- 1.87 cm2/V s. In contrast, the same hydrogen-containing FG anneal had a deleterious effect on the HfO2/SiO2 stacks; instead annealing the HfO2/SiO2 layers in pure N2 at 1100 degrees C resulted in an increased mobility of 43.91 +/- 2.07 cm2/V s. Grazing incidence X-ray diffraction (GI-XRD) confirmed that high-temperature annealing induces crystallization in the HfO2 layer, while the SiO2 layer remains amorphous. These findings emphasize the critical influence of PDA conditions and ambient atmospheres on dielectric quality, interface stability, and overall device performance for SiC-based MOSFETs.

Layered nickel-rich lithium transition metal oxides (LiNixMnyCo1−x−yO2; where x ≥ 0.8), with single-crystalline morphology, are promising future high-energy-density Li-ion battery cathodes due to their ability to mitigate particle-cracking-induced degradation. This is due to the absence of grain boundaries in these materials, which prevents the build-up of bulk crystallographic strain during electrochemical cycling. Compared to their polycrystalline counterparts, there is a need to study single-crystalline Ni-rich cathodes using operando X-ray methods in uncompromised machine-manufactured industry-like full cells to understand their bulk degradation mechanisms as a function of different electrochemical cycling protocols. This can help us identify factors to improve their long-term performance. Here, through in-house operando X-ray studies of pilot-line-built LiNi0.8Mn0.1Co0.1O2–Graphite A7 pouch cells, it is shown that their electrochemical capacity fade under harsh conditions (2.5–4.4 V and 40 °C for 100 cycles at C/3 rate) primarily stems from the high-voltage reconstruction of the cathode surface from a layered to a cubic (rock salt) phase that impedes Li+ kinetics and increases cell impedance. Post-mortem electron and X-ray microscopy show that these cathodes can withstand severe anisotropic structural changes and show no cracking when cycled under such conditions. Comparing these results to those from commercial Li-ion cells with surface-modified single-crystalline Ni-rich cathodes, it is identified that cathode surface passivation can mitigate this type of degradation and prolong cycle life. In addition to furthering our understanding of degradation in single-crystalline Ni-rich cathodes, this work also accentuates the need for practically relevant and reproducible fundamental investigations of Li-ion cells and presents a methodology for achieving this.

Layered nickel-rich lithium transition-metal oxides (LiNi_{x}Mn_{y}Co_{1−x−y}O_{2}; where x ≥ 0.8), with single-crystalline morphology, are promising future high-energy-density Li-ion battery cathodes due to their ability to mitigate particle-cracking-induced degradation. This is due to the absence of grain boundaries in these materials, which prevents the build-up of bulk crystallographic strain during electrochemical cycling. Compared to their polycrystalline counterparts, there is a need to study single-crystalline Ni-rich cathodes using operando x-ray methods in uncompromised machine-manufactured industrylike full cells to understand their bulk degradation mechanisms as a function of different electrochemical cycling protocols. This can help us identify factors to improve their long-term performance. Here, through in-house operando x-ray studies of pilot-line-built LiNi_{0.8}Mn_{0.1}Co_{0.1}O_{2}–graphite A7 pouch cells, it is shown that their electrochemical-capacity fade under harsh conditions (2.5–4.4 V and 40 °C for 100 cycles at a C/3 rate) primarily stems from the high-voltage reconstruction of the cathode surface from a layered to a cubic (rock-salt) phase that impedes the Li^{+} kinetics and increases cell impedance. Postmortem electron and x-ray microscopy show that these cathodes can withstand severe anisotropic structural changes and show no cracking when cycled under such conditions. Comparing these results to those from commercial Li-ion cells with surface-modified single-crystalline Ni-rich cathodes, it is identified that cathode surface passivation can mitigate this type of degradation and prolong cycle life. In addition to furthering our understanding of degradation in single-crystalline Ni-rich cathodes, this work also accentuates the need for practically relevant and reproducible fundamental investigations of Li-ion cells and presents a methodology for achieving this.

Improved knowledge of the influence of temperature upon layered perovskites is essential to enable perovskite-based devices to operate over a broad temperature range and to elucidate the impact of structural changes upon the optoelectronic properties. We examined the Ruddlesden-Popper layered perovskite 2-thiophenemethylammonium lead iodide (ThMA(2)PbI(4)) and observed a structural phase transition between a high- and a low-temperature phase at 220 K using temperature-dependent X-ray diffraction, UV-visible absorption, and photoluminescence (PL) spectroscopy. The structural phase transition altered the tilt pattern of the inorganic octahedra layer, modifying the absorption and PL spectra. Further, we found a narrow and intense additional PL peak in the low-temperature phase, which we assigned to radiative emission from a defect-bound exciton state. In both phases we determined the thermal expansion coefficient and found values similar to those of cubic 3D perovskites, i.e., larger than those of typical substrates such as glass. These results demonstrate that the organic spacer plays a critical role in controlling the temperature-dependent structural and optoelectronic properties of layered perovskites and suggests more widely that strain management strategies may be needed to fully utilize layered perovskites in device applications.

Prussian blue nanoparticles are radiolabelled with Tl-201 and characterised to provide the unambiguous confirmation of the inclusion mechanism.

Using lab-based operando X-ray and post-mortem techniques, researchers visualize the origins of electrochemical capacity fade under high-voltage conditions in pilot line single-crystalline LiNi${}_{0.8}$Mn${}_{0.1}$Co${}_{0.1}$O${}_{2}$-graphite cells.

Understanding surface passivation arising from aluminium oxide (Al2O3) films is of significant relevance for silicon-based solar cells and devices that require negligible surface recombination. This study aims to understand the competing bulk and surface lifetime effects which occur during the activation of atomic layer deposited Al2O3. We demonstrate that maximum passivation is achieved on n- and p-type silicon with activation at similar to 450 degrees C, irrespective of annealing ambient. Upon stripping the Al2O3 films and re-passivating the surface using a superacid-based technique, we find the bulk lifetime of float-zone and Czochralski silicon wafers degrade at annealing temperatures > 450 degrees C. By accounting for this bulk lifetime degradation, we demonstrate that the chemical passivation component associated with Al2O3 remains stable at activation temperatures of 450 & horbar;500 degrees C, achieving an SRV of < 1 cm/s on n- and p-type silicon. In conjunction with the thermal stability, we show that films in the range of 3-30 nm maintain an SRV of < 1 cm/s when annealed at 450 degrees C. From atomic-level energy dispersive X-ray analysis, we demonstrate that, post deposition, the interface has a structure of Si/SiO2/Al2O3. After activation at > 300 degrees C, the interface becomes Si/SixAlyO2/Al2O3 due to diffusion of aluminium into the thin silicon oxide layer.

Hafnium oxide (HfOx) films grown by atomic layer deposition (ALD) have recently been demonstrated to provide high‐quality silicon surface passivation. Reports have suggested that changing the composition of the hafnium‐containing precursor can enable films of both charge polarities to be produced. Herein, the passivation quality of hafnium oxide grown with metal amide precursors and a tetrakis(ethylmethylamido)hafnium (TEMAHf) precursor is examined, considering film charge polarity, chemical‐ and field‐based passivation effects, and film crystallinity. Throughout, the properties of TEMAHf‐HfOx are benchmarked against that of hafnium oxide grown with a tetrakis(dimethylamido)hafnium precursor. It is found that precursor choice has no influence on the fixed negative charge polarity (of order −1012 q cm−2) of HfOx films grown via plasma‐enhanced ALD. TEMAHf‐HfOx passivation is influenced by post‐deposition annealing temperature and can passivate with a surface recombination velocity ≤3 cm s−1 on n‐type silicon, compared to surface recombination velocities ≤11 cm s−1 for TDMAHf‐HfOx of a similar thickness.

Electric polarization is well defined only in insulators not metals, and there is no general scheme to induce and control bulk polarity in metals. Here we circumvent this limitation by utilizing a pseudo-electric field generated by inhomogeneous lattice strain, namely a flexoelectric field, as a means of polarizing and controlling a metal. Using heteroepitaxy and atomic-scale imaging, we show that flexoelectric fields polarize the bulk of an otherwise centrosymmetric metal SrRuO 3 , with off-centre displacements of Ru ions. This further impacts the electronic bands and lattice anisotropy of the flexo-polar SrRuO 3 , potentially leading to an enhancement of electron correlation, ferromagnetism and its anisotropy. Beyond conventional electric fields, flexoelectric fields may be used to create and control electronic states through pure atomic displacements.

Hafnium oxide thin films have attracted considerable interest for passivation layers, protective barriers, and anti-reflection coatings. This study presents a systematic investigation into the role of film growth co-reactant on film properties.

Understanding dehydration of Prussian white systems to enable processability of water-based electrodes for sustainable and high capacity sodium-ion batteries.

PURPOSE OF REVIEW:The purpose of this review is to discuss the current evidence for Cognitive Behavioral Therapy for Insomnia (CBT-I) for patients with migraine and comorbid insomnia. In this article, we provide a narrative review of the literature on CBT-I and migraine, highlighting recent advances in research into this topic. Finally, we propose a way for clinicians to integrate CBT-I into clinical practice.RECENT FINDINGS:Multiple studies support CBT-I as a validated modality for the treatment of insomnia in migraine. CBT-I is used to treat insomnia and should be offered as first line therapy. Clinicians should screen for insomnia in all patients with headache, especially in those with migraine, to best manage this condition through the implementation of specific insomnia treatment.

We report on the emission of high-intensity pulsed terahertz radiation from the metal-free halide perovskite single crystal methyl-DABCO ammonium iodide (MDNI) under femtosecond illumination. The power and angular dependence of the THz output implicate optical rectification of the 800 nm pump as the mechanism of THz generation. Further characterization finds that, for certain crystal orientations, the angular dependence of THz emission is modulated by phonon resonances attributable to the motion of the methyl-DABCO moiety. At maximum, the THz emission spectrum of MDNI is free from significant phonon resonances, resulting in THz pulses with a temporal width of <900 fs and a peak-to-peak electric field strength of approximately 0.8 kV cm-1-2 orders of magnitude higher than any other reported halide perovskite emitters. Our results point toward metal-free perovskites as a promising new class of THz emitters that brings to bear many of the advantages enjoyed by other halide perovskite materials. In particular, the broad tunability of optoelectronic properties and ease of fabrication of perovskite materials opens up the possibility of further optimizing the THz emission properties within this material class.

THz emission from the all-organic, halide perovskite N-methyl-1,4-diazabicyclo [2.2.2] octan-1-ium (methyl-DABCO) ammonium iodide (MDNI) has been demonstrated for the first time. The generation mechanism was shown to be optical rectification, and a peak field strength of up to 0.8 kV/cm was achieved, demonstrating the promise of this class of materials as efficient THz emitters.

We investigate the potential of ultra-thin HfO2 films grown by atomic layer deposition for passivating contacts to silicon focusing on variations in film thickness and post-deposition annealing temperature. A peak in passivation quality - as assessed by carrier lifetime measurements - is reported for 2.2 nm thick films annealed at 475 degrees C, for which a surface recombination velocity <1 cm/s is determined. For films <2.2 nm thick, there is a marked decrease in passivation quality. X-ray diffraction highlights a change from crystallised monoclinic to amorphous HfO2 as film thickness decreases from 12 nm to 2.2 nm. Kelvin probe results indicate that as-deposited 2.2-12 nm films have similar effective work functions, although the work function of 1 nm films is considerably lower. Upon post-deposition annealing in vacuum, all films exhibit a reduction in effective work function at temperatures coincident with the onset of passivation in air-annealed samples. An initial investigation into the contact resistivity in a passivating contact structure utilizing HfO2 reveals a strong post-deposition annealing temperature dependence, with the lowest resistance achieved below 375 degrees C, followed by a decrease in performance as temperature increases towards the optimal temperature for passivation (475 degrees C). Limitations of the contact structure used are discussed.

Thin film dielectrics are ubiquitous in the manufacture of electronic devices and are frequently deposited and etched away at various stages of device fabrication. We demonstrate that hafnium oxide (HfO2) thin films grown via atomic layer deposition on silicon and silicon pre-coated with aluminum oxide (Al2O3) have etch resistance properties, which can be tuned simply by changing the post-deposition annealing temperature. The etching rates of films in hydrofluoric acid (HF) solutions were found to be dependent on annealing temperature, with the etch rate decreasing with increasing temperature. A transition region in the etch rate was identified between 300 and 350 °C, corresponding to the crystallization of the HfO2 films, as identified via x-ray diffraction. HfO2 films deposited directly onto silicon annealed above 350 °C were resistant to 10% HF solutions over the course of several hours. In the case of Si/Al2O3/HfO2 stacks, closer inspection reveals the existence of channels, which reduces the etch resistance of HF acid, as evidenced by tetramethylammonium hydroxide etching of the silicon substrate. Crystallized HfO2 can be used to protect other dielectrics in device processing, and we demonstrate its use in single-sided fabrication of patterned structures of Al2O3, which can control the effective charge-carrier lifetime in silicon wafers for use in modulating THz and mm-wave radiation.

Single-crystalline Ni-rich layered oxides (LiNi x Mn y Co1−x−y O2; x ≥ 0.8) are promising high-energy-density cathodes for future Li-ion batteries as they can withstand cathode particle cracking, which is a significant contributor to electrochemical capacity loss. The absence of grain/particle boundaries substantially mitigates the build-up of bulk structural strain in these materials generated from the anisotropic structural evolution (i.e., lattice collapse) during electrochemical cycling. However, compared to their polycrystalline counterparts, rigorous evaluations of their long-term electrochemical performance and their dependence on electrode structure changes, impedance, and particle cracking, are still necessary to take it towards commercialisation. Operando X-ray diffraction (XRD) and absorption spectroscopy (XAS) are ideal probes of these bulk electrode structure properties and provide a direct temporal correlation between the battery electrochemistry and the non-equilibrium structural changes in the electrodes. However, such studies often use electrochemically compromised cells modified for X-ray transmission that are neither representative of a real-world full-cell architecture nor operable long-term under industrially relevant cycling conditions, thereby compromising the results' practicality. This is especially problematic for technologically mature cathodes like single-crystalline Ni-rich layered oxides, which require greater scrutiny of their long-term degradation modes after hundreds of cycles. In this work, using in-house operando X-ray studies and large-area post-mortem electron tomography of a (TRL-5) pilot-line-built A7 pouch full cells with industry-relevant specifications, we demonstrate how single-crystalline LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes can withstand the severe anisotropic structural evolution and show no particle cracking even when cycled under harsh conditions of 2.5–4.4 V at 40 °C for 100 cycles. The bulk structural changes in both electrodes as well as the associated electrochemical performance loss are also evaluated. Furthermore, the validity of the in-house pilot line cell results is benchmarked against a commercially sourced Li-ion cell. In addition to furthering our understanding of single-crystalline Ni-rich cathodes, this work emphasises the need for real-world-relevant reproducible fundamental investigations of academic Li-ion cells and presents a methodology for doing so. Figure 1

We have studied the mechanisms underpinning effective surface passivation of silicon with hafnium oxide (HfO2) thin films grown via atomic layer deposition (ALD). Plasma-enhanced ALD with O2 plasma and a tetrakis(dimethylamido)hafnium precursor was used to deposit 12 nm thick HfO2 films at 200 °C on high-lifetime 5 Ωcm n-type Czochralski silicon wafers. The passivation was activated by postdeposition annealing, with 30 min in air at 475 °C found to be the most effective. High-resolution grazing incidence X-ray diffraction measurements revealed the film crystallized between 325 and 375 °C, and this coincided with the onset of good passivation. Once crystallized, the level of passivation continued to increase with higher annealing temperatures, exhibiting a peak at 475 °C and yielding surface recombination velocities of <5 cm s−1 at 5 × 1014 cm−3 injection. A steady decrease in effective lifetime was then observed for activation temperatures >475 °C. By superacid repassivation, we demonstrated this reduction in lifetime was not because of a decrease in the bulk lifetime, but rather because of changes in the passivating films themselves. Kelvin probe measurements showed the films are negatively charged. Corona charging experiments showed the charge magnitude is of order 1012 qcm−2 and that the reduced passivation above 475 °C was mainly because of a loss of chemical passivation. Our study, therefore, demonstrates the development of highly charged HfO2 films and quantifies their benefits as a standalone passivating film for silicon-based solar cells.

Potassium dihydrogen phosphate (KDP) and its deuterated analog (DKDP) are unique nonlinear optical materials for high power laser systems. They are used widely for frequency conversion and polarization control by virtue of the ability to grow optical-quality crystals at apertures suitable for fusion-class laser systems. Existing methods for freeform figuring of KDP/DKDP optics do not produce surfaces with sufficient laser-induced–damage thresholds (LIDT’s) for operation in the ultraviolet portion of high-peak-power laser systems. In this work, we investigate fluid jet polishing (FJP) using a nonaqueous slurry as a sub-aperture finishing method for producing freeform KDP surfaces. This method was used to selectively polish surface areas to different depths on the same substrate with removals ranging from 0.16 μm to 5.13 μm. The finished surfaces demonstrated a slight increase in roughness as the removal depth increased along with a small number of fracture pits. Laser damage testing with 351 nm, 1 ns pulses demonstrated excellent surface damage thresholds, with the highest values in areas devoid of fracture pits. This work demonstrates, for the first time, a method that enables fabrication of a waveplate that provides tailored polarization randomization that can be scaled to meter-sized optics. Furthermore, this method is based on FJP technology that incorporates a nonaqueous slurry specially designed for use with KDP. This novel nonaqueous FJP process can be also used for figuring other types of materials that exhibit similar challenging inherent properties such as softness, brittleness, water-solubility, and temperature sensitivity.