Magma/lava temperature is one of the most basic and critical parameters in volcanology. Yet at many active volcanoes, including during eruptions, this parameter remains poorly constrained due to vent accessibility, with estimates from different geothermometers commonly varying by several tens to more than a hundred degrees. One such volcano is Villarrica, one of the most active and hazardous volcanoes in South America and whose crater hosts a persistent lava lake. Here, we use experimentally determined phase equilibria to constrain the temperature of the Villarrica lava lake. The experiments were all performed at ambient pressure (i.e. 0.1 MPa), ranged in temperature from 1000°C to 1250°C and in oxygen fugacity from QFM + 1 to QFM–1 (where QFM stands for the quartz-fayalite-magnetite redox buffer). Within the investigated range, fO2 was found to have little to no effect on the phase equilibria and hence the lava lake fO2 could not be constrained. The temperature range explored, however, did bracket the entire liquidus to solidus assemblage evolution. On the basis of these experiments, two empirical geothermometers calibrated strictly between 1050°C and 1200°C (i.e. not to be used outside this range) were developed for the Villarrica lava lake based on its matrix glass composition and modal proportion. The 2015 state of the natural system was experimentally reproduced at temperatures around 1141°C. In detail, the lava lake melt composition in the period 1963 to 2015 indicates a cooling trend from 1186 ± 19°C in 1963 to 1153 ± 8°C in 1999–2000 and 1149 ± 28°C in 2015. A generic glass geothermometer was also developed for any Basaltic Andesite composition from the compilation of 175 phase equilibria experiments giving the relation: $Melt\ Temperature\ \left({}^{\circ}C\right)=12.43\times {\mathrm{Al}}_2{\mathrm{O}}_3+10.73\times \mathrm{MgO}+8.51\times \mathrm{CaO}+5.91\times \left({Na}_2\mathrm{O}+{K}_2\mathrm{O}\right)+814.08$ with all oxides in wt.% normalized. The geothermometers we have developed can be used to follow future temperature evolutions of the Villarrica lava lake or to estimate the lava temperature at any basaltic andesite eruption. Their application is simple, requiring only petrographic observations (to quantify the melt proportion) or analysis of the melt composition.

Superfluid $^4$He is a promising target material for direct detection of light ($<$ 1 GeV) dark matter. Possible signal channels available for readout in this medium include prompt photons, triplet excimers, and roton and phonon quasiparticles. The relative yield of these signals has implications for the sensitivity and discrimination power of a superfluid $^4$He dark matter detector. Using a 16~cm$^3$ volume of 1.75~K superfluid $^4$He read out by six immersed photomultiplier tubes, we measured the scintillation from electronic recoils ranging between 36.3 and 185 keV$_\mathrm{ee}$, yielding a mean signal size of $1.25^{+0.03}_{-0.03}$~phe/keV$_\mathrm{ee}$, and nuclear recoils from 53.2 to 1090 keV$_\mathrm{nr}$. We compare the results of our relative scintillation yield measurements to an existing semiempirical model based on helium-helium and electron-helium interaction cross sections. We also study the behavior of delayed scintillation components as a function of recoil type and energy, a further avenue for signal discrimination in superfluid $^4$He.

Metallic transition-metal dichalcogenides (TMDs) are rich material systems in which the interplay between strong electron-electron and electron-phonon interactions often results in a variety of collective electronic states, such as charge density waves (CDWs) and superconductivity. While most metallic group V TMDs exhibit coexisting superconducting and CDW phases, 2H-NbS2 stands out with no charge ordering. Further, due to strong interlayer interaction, the preparation of ultrathin samples of 2H-NbS2 has been challenging, limiting the exploration of presumably rich quantum phenomena in reduced dimensionality. Here, we demonstrate experimentally and theoretically that light substitutional doping of NbS2 with heavy atoms is an effective approach to modify both interlayer interaction and collective electronic states in NbS2. Very low concentrations of Re dopants (<1%) make NbS2 exfoliable (down to monolayer) while maintaining its 2H crystal structure and superconducting behavior. In addition, first-principles calculations suggest that Re dopants can stabilize some native CDW patterns that are not stable in pristine NbS2.

The development of room-temperature sensing devices for detecting small concentrations of molecular species is imperative for a wide range of low-power sensor applications. We demonstrate a room-temperature, highly sensitive, selective, stable, and reversible chemical sensor based on a monolayer of the transition-metal dichalcogenide Re0.5Nb0.5S2. The sensing device exhibits a thickness-dependent carrier type, and upon exposure to NO2 molecules, its electrical resistance considerably increases or decreases depending on the layer number. The sensor is selective to NO2 with only minimal response to other gases such as NH3, CH2O, and CO2. In the presence of humidity, not only are the sensing properties not deteriorated but also the monolayer sensor shows complete reversibility with fast recovery at room temperature. We present a theoretical analysis of the sensing platform and identify the atomically sensitive transduction mechanism.

Alloying of semiconductors enables fabrication of materials with continuously tunable properties such as lattice constant, bandgap, and carrier mobility, which is the key in development of next generation devices with new design and function (1-4).However, it has long been an open question whether the atoms in the lattice of a multispecies alloy are distributed randomly or they are ordered in some way ( 5).The answer is fundamentally important as the fundamental properties of the alloy could be significantly affected by the ordering (3,(6)(7)(8)(9).Ordering in semiconductor alloys has been experimentally studied, but most of the reports have been limited to reciprocal space (10,11).Atomically-thin two-dimensional (2D) materials (12-15) offer an ultimate playground to explore atomic-scale structural features in the lattice through direct imaging of their atomic registry in real space.

Frustrated interactions can lead to short-range ordering arising from incompatible interactions of fundamental physical quantities with the underlying lattice. The simplest example is the triangular lattice of spins with antiferromagnetic interactions, where the nearest-neighbor spin-spin interactions cannot simultaneously be energy minimized. Here we show that engineering frustrated interactions is a possible route for controlling structural and electronic phenomena in semiconductor alloys. Using aberration-corrected scanning transmission electron microscopy in conjunction with density functional theory calculations, we demonstrate atomic ordering in a two-dimensional semiconductor alloy as a result of the competition between geometrical constraints and nearest-neighbor interactions. Statistical analyses uncover the presence of short-range ordering in the lattice. In addition, we show how the induced ordering can be used as another degree of freedom to considerably modify the band gap of monolayer semiconductor alloys.

The self-assembly of nanoscale materials at the liquid liquid interface allows for fabrication of threedimensionally structured liquids with nearly arbitrary geometries and tailored electronic, optical, and magnetic properties. Two-dimensional (2D) materials are highly anisotropic, with thicknesses on the order of a nanometer and lateral dimensions upward of hundreds of nanometers to micrometers. Controlling the assembly of these materials has direct implications for their properties and performance. We here describe the interfacial assembly and jamming of Ti3C2Tx MXene nanosheets at the oil water interface. Planar, as well as complex, programmed three-dimensional all-liquid objects are realized. Our approach presents potential for the creation of all-liquid 3D-printed devices for possible applications in all-liquid electrochemical and energy storage devices and electrically active, all-liquid fluidics that exploits the versatile structure, functionality, and reconfigurability of liquids.