We report how to control the self-assembly of magnetic nanoparticles and a prototypical amphiphilic block-copolymer composed of poly(acrylic acid) and polystyrene (PAA-b-PS). Three distinct structures were obtained by controlling the solvent-nanoparticle and polymer-nanoparticle interactions: (1) polymersomes densely packed with nanoparticles (magneto-polymersomes), (2) core-shell type polymer assemblies where nanoparticles are radially arranged at the interface between the polymer core and the shell (magneto-core shell), and (3) polymer micelles where nanoparticles are homogeneously incorporated (magneto-micelles). Importantly, we show that the incorporation of nanoparticles drastically affects the self-assembly structure of block-copolymers by modifying the relative volume ratio between the hydrophobic block and the hydrophilic block. As a consequence, the self-assembly of micelle-forming block-copolymers typically produces magneto-polymersomes instead of magneto-micelles. On the other hand, vesicle-forming polymers tend to form magneto-micelles due to the solubilization of nanoparticles in polymer assemblies. The nanoparticle-polymer interaction also controls the nanoparticle arrangement in the polymer matrix. In N,N-dimethylformamide (DMF) where PS is not well-solvated, nanoparticles segregate from PS and form unique radial assemblies. In tetrahydrofuran (THF), which is a good solvent for both nanoparticles and PS, nanoparticles are homogeneously distributed in the polymer matrix. Furthermore, we demonstrated that the morphology of nanoparticle-encapsulating polymer assemblies significantly affects their magnetic relaxation properties, emphasizing the importance of the self-assembly structure and nanoparticle arrangement as well as the size of the assemblies.

The APSe6 (A = K, K(1–x)Cs x , Cs) family of one-dimensional (1D) materials was studied to examine the effects of the cation size on the nonlinear optical (NLO) response. The family has high-performing NLO properties with the noncentrosymmetric parent material, KPSe6, having infinite 1D chains of 1/∞[PSe6 –]. This structure has been successfully substituted with cesium up to K0.6Cs0.4PSe6 while retaining the polar character. All compounds crystallize in the space group Pca21 and have band gaps of 2.1 eV. In situ powder X-ray diffraction experiments using synchrotron radiation were used to determine the specifics of the amorphous to crystalline behavior and the crystallization and melting kinetics of the APSe6 system. These measurements revealed a new phase, β-CsPSe6, which is metastable and crystallizes in the noncentrosymmetric tetragonal space group P 4̅21 c with a = 12.526(2) Å, c = 12.781(3) Å, V = 2005.3(6) Å3, and Z = 8. The structure is composed of 2 sets of mutually perpendicular 1/∞[PSe6 –] chains charge-balanced by Cs cations, and the band gap of β-CsPSe6 is 1.9 eV. Second harmonic generation (SHG) measurements demonstrate that substitution of Cs into KPSe6 maintains the strong NLO signal with a very high SHG coefficient (χ(2)) of ∼150 pm/V for K(1‑x)Cs x PSe6 and 30 pm/V for β-CsPSe6. Laser-induced damage threshold analysis reveals APSe6 exhibits two-photon absorption (2PA) at 1064 nm with input laser intensity greater than 1 GW/cm2 and optical damage from 2PA at ∼2 GW/cm2. The materials also exhibit strong third harmonic generation (THG) with THG coefficients (χ(3) × 105) for KPSe6, K0.6Cs0.4PSe6, α-CsPSe6, and β-CsPSe6 to be 2.6, 3.1, 1.8, and 1.1 pm2/V2, respectively.

The common approach to the synthesis of a new material involves reactions held at high temperatures under certain conditions such as heating in a robust vessel in the dark for a period until it is judged to have concluded. Analysis of the vessel contents afterward provides knowledge of the final products only. Intermediates that may form during the reaction process remain unknown. This lack of awareness of transient intermediates represents lost opportunities for discovering materials or understanding how the final products form. Here we present new results using an emerging in situ monitoring approach that shows high potential in discovering new compounds. In situ synchrotron X-ray diffraction studies were conducted in the Cs/Sn/P/Se system. Powder mixtures of CsSe, Sn, and PSe were heated to 650 °C and then cooled to room temperature while acquiring consecutive in situ synchrotron diffraction patterns from the beginning to the end of the reaction process. The diffraction data was translated into the relationship of phases present versus temperature. Seven known crystalline phases were observed to form on warming in the experiment: Sn, CsSe, CsSe, CsSe, CsSnSe, CsPSe, and CsPSe. Six unknown phases were also detected; using the in situ synchrotron data as a guide three of them were isolated and characterized ex situ. These are CsSn(PSe), α-CsSnPSe, and Cs(SnSe)[Sn(PSe)]. Cs(SnSe)[Sn(PSe)] is a two-dimensional compound that behaves as an n-type doped semiconductor below 50 K and acts more like a semimetal at higher temperatures. Because all crystalline phases are revealed during the reaction, we call this approach "panoramic synthesis".

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Cs2Hg3S4 was synthesized by slowly cooling a melted stoichiometric mixture of Hg and Cs2S4. Cs2Hg3S4 crystallizes in the Ibam spacegroup with a = 6.278(1) Å, b = 11.601(2) Å, and c = 14.431(3)­Å; d calc = 6.29 g/cm3. Its crystal structure consists of straight chains of [Hg3S4] n 2n– that engage in side-by-side weak bonding interactions forming layers and are charge balanced by Cs+ cations. The thermal stability of this compound was investigated with differential thermal analysis and temperature dependent in situ synchrotron powder diffraction. The thermal expansion coefficients of the a, b, and c axes were assessed at 1.56 × 10–5, 2.79 × 10–5, and 3.04 × 10–5 K–1, respectively. Large single-crystals up to ∼5 cm in length and ∼1 cm in diameter were grown using a vertical Bridgman method. Electrical conductivity and photoconductivity measurements on naturally cleaved crystals of Cs2Hg3S4 gave resistivity ρ of ≥108 Ω·cm and carrier mobility-lifetime (μτ) products of 4.2 × 10–4 and 5.82 × 10–5 cm2 V–1 for electrons and holes, respectively. Cs2Hg3S4 is a semiconductor with a bandgap E g ∼ 2.8 eV and exhibits photoluminescence (PL) at low temperature. Electronic band structure calculations within the density functional theory (DFT) framework employing the nonlocal hybrid functional within Heyd–Scuseria–Ernzerhof (HSE) formalism indicate a direct bandgap of 2.81 eV at Γ. The theoretical calculations show that the conduction band minimum has a highly dispersive and relatively isotropic mercury-based s-orbital-like character while the valence band maximum features a much less dispersive and more anisotropic sulfur orbital-based band.