In light of the intense recent interest in the methylammonium lead halides, CHNHPbX (X = Cl, Br, and I) as sensitizers for photovoltaic cells, the dynamics of the methylammonium (MA) cation in these perovskite salts has been reinvestigated as a function of temperature via H,N, and Pb NMR spectroscopy. In the cubic phase of all three salts, the MA cation undergoes pseudoisotropic tumbling (picosecond time scale). For example, the correlation time, τ, for the C-N axis of the iodide salt is 0.85 ± 0.30 ps at 330 K. The dynamics of the MA cation are essentially continuous across the cubic ↔ tetragonal phase transition; however, H andN NMR line shapes indicate that subtle ordering of the MA cation occurs in the tetragonal phase. The temperature dependence of the cation ordering is rationalized using a six-site model, with two equivalent sites along the c-axis and four equivalent sites either perpendicular or approximately perpendicular to this axis. As the cubic ↔ tetragonal phase transition temperature is approached, the six sites are nearly equally populated. Below the tetragonal ↔ orthorhombic phase transition, H NMR line shapes indicate that the C-N axis is essentially frozen.

The stability of derivatized mesoporous silicon mirrors in simulated human blood plasma has been assessed. The rate at which they are dissolved in‐vivo is predicted to be tunable by surface chemistry over timescales of weeks to years, and high reflectivity can be maintained until the bottom of the multilayer stack starts to corrode. Such biodegradable optical components could be utilized to direct and define optical path lengths for therapeutic treatments and minimally‐invasive diagnostics.

Silicon-based anodes for Li-ion batteries have been gaining a great deal of attention due to their high theoretical gravimetric energy density. Approaches for overcoming the challenge of pulverization associated with Sibased electrodes are required for efficient, reversible, and stable operation of such high energy batteries. This study focuses on addressing the source of pulverization of amorphous silicon films upon cycling, which is typically attributed to the formation of the c-Li 3.75 Si phase. Cross-sectional samples prepared by focused-ion beam milling revealed fractured sponge-like silicon structures after 150 cycles at a lithiation cutoff voltage of 5 mV Li , at which the c-Li 3.75 Si phase forms. Cycling at a higher lithiation cutoff voltage, 50 mV Li , however, resulted in a film with a higher degree of integrity, along with the absence of the c-Li 3.75 Si phase. These results clearly verify and underscore the deleterious effects of the c-Li 3.75 Si phase. Alternating carbon and silicon layers results in suppression of the formation of the c-Li 3.75 Si phase to a degree dependent upon the relative thicknesses of both the silicon and carbon layers. Best results were observed for multilayers of 8 nm Si/4 nm C, with which no evidence for the c-Li 3.75 Si phase up to 149 cycles was observed. Carbon interlayers were also found to beneficially lower the relative irreversible capacity loss due to solidelectrolyte interphase formation and associated electrical disconnection.

Porous germanium (PG) is prepared by a novel bipolar electrochemical etching (BEE) technique; scanning electron microscopy (SEM) clearly reveals formation of a porous layer up to a few microns thick that is Ge-H x terminated as indicated by FTIR spectroscopy; the hydride terminated PG material is quite resistant to oxidation, even under thermal conditions, but can be induced to undergo hydrogermylation reactions with alkenes and alkynes.

Silicon has a theoretical sodium-storage capacity of 954 mAh/g, which even exceeds that of tin (847 mAh/g). However, this capacity has never been reached in practice. Antimony is one of the best-performing Na-storage materials in terms of both capacity and cycling stability. By combining silicon and antimony, either by cosputtering or depositing multilayers with bilayer thickness down to 2 nm, we can achieve capacities exceeding even the theoretical capacity of Sb (660 mAh/g). Minor addition of silicon, 7 at. % or 7 wt % (25 at. %), increases the measured reversible capacity from 625 mAh/g for pure Sb to 663 and 680 mAh/g, respectively. All Sb-rich (>50 at. %) compositions show improved cycling stability over elemental Sb. Si 0.07 Sb 0.93 reached a maximum capacity of 663 mAh/g after 140 cycles and showed negligible capacity degradation up to 200 cycles. The fully sodiated state in cosputtered films evolves from single-phase amorphous to a mixture of a Sb-rich and Si-rich sodiated phases as cycling progresses, when the Si content is between 75 and 50 at. %. The typical desodiation signature of c-Na 3 Sb is observed only after 100 cycles or more. Careful examination of the voltage profiles of multilayers shows that they initially tend toward intermixing between the Si and Sb layers, contrary to expectations based on the phase diagram. When the Si and Sb layer thickness is decreased to 2 nm, the multilayer and cosputtered film behave almost identically. A general direction for finding promising multicomponent sodium-ion battery (SIB) alloy anodes is proposed.

for their contributions that have led to the modern lithium ion battery (Figure 1). As the Nobel Prize Committee states succinctly, "They created a rechargeable world." 1 The commercial and societal rewards of experimental research typically require decades to reach fruition, and lithium ion batteries were no different, with crucial leads dating back to the 1960s, and even earlier. 2 Materials chemistry journals only emerged 30 years ago with the advent of Chemistry of Materials, the Journal of Materials Chemistry, and Advanced Materials in 1989. Much of the earlier work in battery materials appeared beforehand in electrochemistry, physics, and solid state journals. The key fundamental discovery underpinning the lithium ion battery was the understanding and application of ion intercalation, in this case, 3 lithium ions inserted between the layers in graphite, metal sulfides, and, eventually, oxides that were commercialized. This Nobel Prize was evenly split three ways because, as the Nobel committee correctly observed, the contributions of all three inventors were essential to the success of the commercialization of the lithium ion battery.Goodenough and Whittingham are prolific, having published more than 1000 and 500 publications each, respectively. Yoshino, who performed most of his research in industry, is credited with having assembled the first commercial lithium ion battery in 1983, combining Goodenough's Li x CoO 2 material as the cathode material with a heat-treated petroleum coke-based carbon anode. Whittingham published the first of his 32 publications in Chemistry of Materials beginning in 1990, focusing not on electrode materials, but on sodium tungstates that were of more fundamental interest for their conducting and electrochromic properties. His first publication in Chemistry of Materials that emphasized battery applications appeared in 2007, when he correlated the electronic properties and chemistry of lithium manganese nickel oxide materials with their magnetic properties. His most recent publication with us, published in September of 2019, examined layered oxide cathodes for lithium ion batteries and their structural degradation associated with the loss of oxygen in the material.The first of Goodenough's 42 papers in Chemistry of Materials appeared in 1997 and was a fundamental study of perovskite transition metal oxides. Like Whittingham, he was an expert in solid-state materials more generally, and thus understood them from an in-depth and fundamental perspective that allowed him and his co-workers to make great strides in the battery area. Goodenough's first bonafide battery publication in Chemistry of Materials was published in 2001, where he described the effects of ball-milling of spinel lithium−manganese oxide cathodes. Of note is Goodenough's 2010 review with Youngsik Kim in Chemistry of Materials, entitled "Challenges for Rechargeable Li Batteries", which has over 4700 citations according to Web of Science, and greater than 6000 per Google Scholar. This review has resided, almost with...

In this work plasmonic stamps are harnessed to drive surface chemistry on silicon. The plasmonic stamps were prepared by sputtering gold films on PDMS, followed by thermal annealing to dewet the gold and form gold nanoparticles. By changing the film thickness of the sputtered gold, the approximate size and shape of these gold nanoparticles can be changed, leading to a shift of the optical absorbance maximum of the plasmonic stamp, from 535 nm to 625 nm. Applying the plasmonic stamp to a Si(111)-H surface using 1-dodecene as the ink, illumination with green light results in covalent attachment of 1-dodecyl groups to the surface. Of the dewetted gold films on PDMS used to make the plasmonic stamps, the thinnest three (5.0, 7.0, 9.2 nm) resulted in the most effective plasmonic stamps for hydrosilylation. The thicker stamps had lower efficacy due to the increased fraction of non-spherical particles, which have lower-energy LSPRs that are not excited by green light. Since the electric field generated by the LSPR should be very local, hydrosilylation on the silicon surface should only take place within close proximity of the gold particles on the plasmonic stamps.To complement AFM imaging of the hydrosilylated silicon surfaces, galvanic displacement of gold(III) salts on the silicon was carried out and the samples imaged by SEM-the domains of hydrosilylated alkyl chains would be expected to block the deposition of gold. The bright areas of metallic gold surround dark spots, with the sizes and spacing of these dark spots increasing with the size of the gold particles on the plasmonic stamps. These results underline the central role played by the LSPR in driving the hydrosilylation on silicon surfaces, mediated with plasmonic stamps. File list (2) download file view on ChemRxiv Submission_MaintextMarch21.pdf (8.86 MiB) download file view on ChemRxiv SI_March21_PDF.pdf (7.67 MiB)

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