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The melting properties and kinetics of glass formation in 2D perovskites can be finely tuned using isomeric organic cations bearing distinct substitutional functional group positions, resulting in enhancement of glass-crystalline switching speed. 

Mobile devices with dynamic refresh rate (DRR) switching displays have recently become increasingly common. For power optimization, these devices switch to lower refresh rates when idling, and switch to higher refresh rates when the content displayed requires smoother transitions. However, the security and privacy vulnerabilities of DRR switching have not been investigated properly. In this paper, we propose a novel attack vector called RefreshChannels that exploits DRR switching capabilities for mobile device attacks. Specifically, we first create a covert channel between two colluding apps that are able to stealthily share users' private information by modulating the data with the refresh rates, bypassing the OS sandboxing and isolation measures. Second, we further extend its applicability by creating a covert channel between a malicious app and either a phishing webpage or a malicious advertisement on a benign webpage. Our extensive evaluations on five popular mobile devices from four different vendors demonstrate the effectiveness and widespread impacts of these attacks. Finally, we investigate several countermeasures, such as restricting access to refresh rates, and find they are inadequate for thwarting RefreshChannels due to DDR's unique characteristics 

Hybrid lead-halide perovskites have been studied extensively for their promising optoelectronic properties and prospective applications including photovoltaics, solid-state lighting, and radiation detection. Research into these materials has also been aided by the simple and low temperature synthetic conditions involved in solution-state deposition/crystallization or melt processing techniques. However, concern over lead toxicity has plagued the field since its early days. One of the most promising routes to mitigating toxicity in hybrid perovskite materials is substituting isoelectronic Bi(III) for Pb(II). Various methods have been developed to allow pnictide-based systems to capture properties of the Pb(II) analogs, but the ability to melt process extended hybrid pnictide-halide materials has not been investigated. In this work, we prepare a series of 1D antimony and bismuth-iodide hybrid materials employing tetramethylpiperazinium (TMPZ)-related cations. We observe, for the first time, the ability to melt hybrid pnictide-halide materials for both Sb(III) and Bi(III) systems. Additionally, we find that Sb(III) analogs melt at lower temperatures, and attribute this observation to structural changes induced by the increased stereochemical activity of the Sb(III) lone pair coupled with reduction in effective dimensionality due to steric interactions with the organic cations. Finally, we demonstrate the ability to melt process phase pure thin films of (S-MeTMPZ)SbI5. 

While crystalline 2D metal halide perovskites (MHPs) represent a well-celebrated semiconductor class, with ensuing applications in the fields of photovoltaics, emitters, and sensors, the recent discovery of glass formation in an MHP opens many new opportunities associated with reversible glass-crystalline switching, with each state offering distinct optoelectronic properties. However, the previously reported [S-(−)-1-(1-naphthyl)ethylammonium]2PbBr4 perovskite is a strong glass former with sluggish glass-crystal transformation timescales, pointing to a need for glassy MHPs with a broader range of compositions and crystallization kinetics. Herein we report glass formation in low melting temperature 1-MeHa2PbI4 (1-MeHa = 1-methyl-hexylammonium) using ultrafast calorimetry, thereby extending the range of MHP glass formation across a broader range of organic (fused ring to branched aliphatic) and halide (bromide to iodide) compositions. The importance of a slight loss of organic and hydrogen iodide components from the MHP in stabilizing the glassy state is elucidated. Furthermore, the underlying kinetics of glass-crystal transformation, including activation energies, crystal growth rate, Angell plot, and fragility index is studied using a combination of kinetic, thermodynamic, and rheological modeling techniques. An inferred fast crystal growth rate of 0.21 m/s for 1-MeHa2PbI4 shows promise toward suitability in extended application spaces, for example in metamaterials, nonvolatile memory, and optical and neuromorphic computing devices. 

1-Methylhexylammonium tin iodide yields the lowest reported melting temperature ( T m = 142 °C) to date among lead-free hybrid perovskite semiconductors. Molecular branching near the organic ammonium group coupled with tuning of metal/halogen character suppresses T m and facilitates effective melt-based deposition of films with 568 nm absorption onset. 

Structure-aware machine learning captures strain impact on molecule-surface interactions for rapid catalyst evaluation.