Improving the creation of SiV centers in diamond via sub-μs pulsed annealing treatment.

Silicon-vacancy (SiV) centers in diamond are emerging as promising quantum emitters in applications such as quantum communication and quantum information processing. Here, we demonstrate a sub-μs pulsed annealing treatment that dramatically increases the photoluminescence of SiV centers in diamond. Using a silane-functionalized adamantane precursor and a laser-heated diamond anvil cell, the temperature and energy conditions required to form SiV centers in diamond were mapped out via an optical thermometry system with an accuracy of ±50 K and a 1 μs temporal resolution.

Ultrafast x-ray detection of low-spin iron in molten silicate under deep planetary interior conditions.

The spin state of Fe can alter the key physical properties of silicate melts, affecting the early differentiation and the dynamic stability of the melts in the deep rocky planets. The low-spin state of Fe can increase the affinity of Fe for the melt over the solid phases and the electrical conductivity of melt at high pressures. However, the spin state of Fe has never been measured in dense silicate melts due to experimental challenges.

Quasi-One-Dimensional Metallicity in Compressed CsSnI.

Low-dimensional metal halides exhibit strong structural and electronic anisotropies, making them candidates for accessing unusual electronic properties. Here, we demonstrate pressure-induced quasi-one-dimensional (quasi-1D) metallicity in δ-CsSnI. With the application of pressure up to 40 GPa, the initially insulating δ-CsSnI transforms to a metallic state.

Cesium-mediated electron redistribution and electron-electron interaction in high-pressure metallic CsPbI.

Electron-phonon coupling was believed to govern the carrier transport in halide perovskites and related phases. Here we demonstrate that electron-electron interaction enhanced by Cs-involved electron redistribution plays a direct and prominent role in the low-temperature electrical transport of compressed CsPbI and renders Fermi liquid (FL)-like behavior. By compressing δ-CsPbI to 80 GPa, an insulator-semimetal-metal transition occurs, concomitant with the completion of a slow structural transition from the one-dimensional Pnma (δ) phase to a three-dimensional Pmn2 (ε) phase.

Tuning Defects in a Halide Double Perovskite with Pressure.

Dopant defects in semiconductors can trap charge carriers or ionize to produce charge carriers─playing a critical role in electronic transport. Halide perovskites are a technologically important semiconductor family with a large pressure response. Yet, to our knowledge, the effect of high pressures on defects in halide perovskites has not been experimentally investigated.

Making the most of metastability.

Researchers seek to preserve materials that are formed at high pressure.

Preservation of high-pressure volatiles in nanostructured diamond capsules.

High pressure induces dramatic changes and novel phenomena in condensed volatiles that are usually not preserved after recovery from pressure vessels. Here we report a process that pressurizes volatiles into nanopores of type 1 glassy carbon precursors, converts glassy carbon into nanocrystalline diamond by heating and synthesizes free-standing nanostructured diamond capsules (NDCs) capable of permanently preserving volatiles at high pressures, even after release back to ambient conditions for various vacuum-based diagnostic probes including electron microscopy. As a demonstration, we perform a comprehensive study of a high-pressure argon sample preserved in NDCs.

Femtosecond Visualization of hcp-Iron Strength and Plasticity under Shock Compression.

Iron is a key constituent of planets and an important technological material. Here, we combine in situ ultrafast x-ray diffraction with laser-induced shock compression experiments on Fe up to 187(10) GPa and 4070(285) K at 10^{8}  s^{-1} in strain rate to study the plasticity of hexagonal-close-packed (hcp)-Fe under extreme loading states. {101[over ¯]2} deformation twinning controls the polycrystalline Fe microstructures and occurs within 1 ns, highlighting the fundamental role of twinning in hcp polycrystals deformation at high strain rates.

Probing the Electronic Band Gap of Solid Hydrogen by Inelastic X-Ray Scattering up to 90 GPa.

Metallization of hydrogen as a key problem in modern physics is the pressure-induced evolution of the hydrogen electronic band from a wide-gap insulator to a closed gap metal. However, due to its remarkably high energy, the electronic band gap of insulating hydrogen has never before been directly observed under pressure. Using high-brilliance, high-energy synchrotron radiation, we developed an inelastic x-ray probe to yield the hydrogen electronic band information in situ under high pressures in a diamond-anvil cell.

Preserving a robust CsPbI perovskite phase via pressure-directed octahedral tilt.

Functional CsPbI perovskite phases are not stable at ambient conditions and spontaneously convert to a non-perovskite δ phase, limiting their applications as solar cell materials. We demonstrate the preservation of a black CsPbI perovskite structure to room temperature by subjecting the δ phase to pressures of 0.1 - 0.

Revealing Local Disorder in a Silver-Bismuth Halide Perovskite upon Compression.

The halide double perovskite CsAgBiBr has emerged as a promising nontoxic alternative to the lead halide perovskites APbX (A = organic cation or Cs; X = I or Br). Here, we perform high-pressure synchrotron X-ray total scattering on CsAgBiBr and discover local disorder that is hidden from conventional Bragg analysis. While our powder diffraction data show that the average structure remains cubic up to 2.

Synthesis of Atomically Thin Hexagonal Diamond with Compression.

Atomically thin diamond, also called diamane, is a two-dimensional carbon allotrope and has attracted considerable scientific interest because of its potential physical properties. However, the successful synthesis of a pristine diamane has up until now not been achieved. We demonstrate the realization of a pristine diamane through diamondization of mechanically exfoliated few-layer graphene via compression.

Nitrogen in black phosphorus structure.

Group V elements in crystal structure isostructural to black phosphorus with unique puckered two-dimensional layers exhibit exciting physical and chemical phenomena. However, as the first element of group V, nitrogen has never been found in the black phosphorus structure. Here, we report the synthesis of the black phosphorus-structured nitrogen at 146 GPa and 2200 K.

Origin of Plasticity in Nanostructured Silicon.

The mechanism of plasticity in nanostructured Si has been intensively studied over the past decade but still remains elusive. Here, we used in situ high-pressure radial x-ray diffraction to simultaneously monitor the deformation and structural evolution of a large number of randomly oriented Si nanoparticles (SiNPs). In contrast to the high-pressure β-Sn phase dominated plasticity observed in large SiNPs (∼100  nm), small SiNPs (∼9  nm) display a high-pressure simple hexagonal phase dominated plasticity.

In situ X-ray diffraction of silicate liquids and glasses under dynamic and static compression to megabar pressures.

Properties of liquid silicates under high-pressure and high-temperature conditions are critical for modeling the dynamics and solidification mechanisms of the magma ocean in the early Earth, as well as for constraining entrainment of melts in the mantle and in the present-day core-mantle boundary. Here we present in situ structural measurements by X-ray diffraction of selected amorphous silicates compressed statically in diamond anvil cells (up to 157 GPa at room temperature) or dynamically by laser-generated shock compression (up to 130 GPa and 6,000 K along the MgSiO glass Hugoniot). The X-ray diffraction patterns of silicate glasses and liquids reveal similar characteristics over a wide pressure and temperature range.

Mineralogy of the deep lower mantle in the presence of HO.

Understanding the mineralogy of the Earth's interior is a prerequisite for unravelling the evolution and dynamics of our planet. Here, we conducted high pressure-temperature experiments mimicking the conditions of the deep lower mantle (DLM, 1800-2890 km in depth) and observed surprising mineralogical transformations in the presence of water. Ferropericlase, (Mg, Fe)O, which is the most abundant oxide mineral in Earth, reacts with HO to form a previously unknown (Mg, Fe)OH ( ≤ 1) phase.

Evidence for oxygenation of Fe-Mg oxides at mid-mantle conditions and the rise of deep oxygen.

As the reaction product of subducted water and the iron core, FeO with more oxygen than hematite (FeO) has been recently recognized as an important component in the D" layer just above the Earth's core-mantle boundary. Here, we report a new oxygen-excess phase (Mg, Fe)O (0 < < 1, denoted as 'OE-phase'). It forms at pressures greater than 40 gigapascal when (Mg, Fe)-bearing hydrous materials are heated over 1500 kelvin.

Facile diamond synthesis from lower diamondoids.

Carbon-based nanomaterials have exceptional properties that make them attractive for a variety of technological applications. Here, we report on the use of diamondoids (diamond-like, saturated hydrocarbons) as promising precursors for laser-induced high-pressure, high-temperature diamond synthesis. The lowest pressure and temperature () conditions that yielded diamond were 12 GPa (at ~2000 K) and 900 K (at ~20 GPa), respectively.

High Compression-Induced Conductivity in a Layered Cu-Br Perovskite.

We show that the onset pressure for appreciable conductivity in layered copper-halide perovskites can decrease by ca. 50 GPa upon replacement of Cl with Br. Layered Cu-Cl perovskites require pressures >50 GPa to show a conductivity of 10  S cm , whereas here a Cu-Br congener, (EA) CuBr (EA=ethylammonium), exhibits conductivity as high as 2×10  S cm at only 2.

Ultrahigh-pressure isostructural electronic transitions in hydrogen.

High-pressure transitions are thought to modify hydrogen molecules to a molecular metallic solid and finally to an atomic metal, which is predicted to have exotic physical properties and the topology of a two-component (electron and proton) superconducting superfluid condensate. Therefore, understanding such transitions remains an important objective in condensed matter physics. However, measurements of the crystal structure of solid hydrogen, which provides crucial information about the metallization of hydrogen under compression, are lacking for most high-pressure phases, owing to the considerable technical challenges involved in X-ray and neutron diffraction measurements under extreme conditions.

Pressure-Induced Emission (PIE) and Phase Transition of a Two-dimensional Halide Double Perovskite (BA) AgBiBr (BA=CH (CH ) NH ).

Two-dimensional (2D) halide perovskites have attracted significant attention due to their compositional flexibility and electronic diversity. Understanding the structure-property relationships in 2D double perovskites is essential for their development for optoelectronic applications. In this work, we observed the emergence of pressure-induced emission (PIE) at 2.

Tuning Optical and Electronic Properties in Low-Toxicity Organic-Inorganic Hybrid (CHNH)BiI under High Pressure.

Low-toxicity, air-stable methylammonium bismuth iodide (CHNH)BiI has been proposed as a candidate to replace lead-based perovskites as highly efficient light absorbers for photovoltaic devices. Here, we investigated the effect of pressure on the optoelectronic properties and crystal structure of (CHNH)BiI up to 65 GPa at room temperature. We achieved impressive photoluminescence enhancement and band gap narrowing over a moderate pressure range.

Altered chemistry of oxygen and iron under deep Earth conditions.

A drastically altered chemistry was recently discovered in the Fe-O-H system under deep Earth conditions, involving the formation of iron superoxide (FeOHx with x = 0 to 1), but the puzzling crystal chemistry of this system at high pressures is largely unknown. Here we present evidence that despite the high O/Fe ratio in FeOHx, iron remains in the ferrous, spin-paired and non-magnetic state at 60-133 GPa, while the presence of hydrogen has minimal effects on the valence of iron. The reduced iron is accompanied by oxidized oxygen due to oxygen-oxygen interactions.

Structure-Controlled Oxygen Concentration in FeO and FeO.

Solid-solid reaction, particularly in the Fe-O binary system, has been extensively studied in the past decades because of its various applications in chemistry and materials and earth sciences. The recently synthesized pyrite-FeO at high pressure suggested a novel oxygen-rich stoichiometry that extends the achievable O-Fe ratio in iron oxides by 33%. Although FeO was synthesized from FeO and O, the underlying solid reaction mechanism remains unclear.