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The heat treatment-dependent Raman spectra and complex electrical impedance for the CaO TiO 2 xSiO 2 (CTSO; x = 0.5, 1 and 2) glasses were measured. We investigate the influence of different compositions in CTSO systems on the dielectric and electrical properties with respect to the oxygen-vacancy-related frequencies of 600 Hz ≤ ω ≤ 100 MHz and from room temperature to 600 °C. The observed Raman spectra of as-quenched CTSO glasses are almost identical with these 6 cycles heat-treated samples in the whole range of bands. Impedance measurement shows that the oxygen vacancies remain during the heat treatment for these glasses. We discuss the origin of oxygen vacancy and its role for the electrical conductivity. The dc electrical activation energies E dc for all CTSO glasses are found to be the same as ∼0.83 eV, indicating that dc electrical conduction in bulk does not dependent on changes in glass structure. The dielectric relaxation time for CTSO (x = 0.5) glass is short compared to that of CTSO (x = 1 and 2) glasses. [ABSTRACT FROM AUTHOR]

Hydrostaticity of poly(methyl methacrylate) (PMMA) loaded in a diamond anvil cell (DAC) was investigated up to ∼10 GPa under two conditions, i.e., with and without pressure-transmitting medium. When PMMA was loaded in the DAC without methanol-ethanol mixture, one of the most widely-used pressure-transmitting media, hydrostatic pressure condition was not fulfilled having a pressure gradient. However, the Brillouin frequency shift of the longitudinal acoustic mode of PMMA exhibited nearly the same pressure dependence regardless of the loading condition whether it was loaded with or without the methanol-ethanol mixture. This suggests that the equation of state (pressure-density relationship) of PMMA, which is calculated by using the Brillouin frequency shift, can be obtained reliably without any pressure medium at pressures less than the solidification pressure of the liquid. [ABSTRACT FROM AUTHOR]

We have investigated the structural phase transition and phase stability of newly discovered monoclinic crystal structure of KNbO 3 nanomaterials. Through x-ray diffraction, Raman scattering, and neutron diffraction measurements, we have found that the KNbO 3 grown at low temperature undergoes a successive structural transition from monoclinic, tetragonal, to cubic, while the KNbO 3 grown at high temperature does from monoclinic, orthorhombic, tetragonal, to cubic with the increase of temperature. After heat treatment, the monoclinic structure of KNbO 3 is transformed to an orthorhombic structure at room temperature. Accompanying the structural transformation, the Raman peaks corresponding to surface and lattice hydroxyl groups are strongly suppressed. These results imply that the hydroxyl defects should play a crucial role for the monoclinic structure of KNbO 3 at room temperature. [ABSTRACT FROM AUTHOR]

Wet chemical synthesis of covalent III-V colloidal quantum dots (CQDs) has been challenging because of uncontrolled surfaces and a poor understanding of surface-ligand interactions. We report a simple acid-free approach to synthesize highly crystalline indium phosphide CQDs in the unique tetrahedral shape by using tris(dimethylamino) phosphine and indium trichloride as the phosphorus and indium precursors, dissolved in oleylamine. Our chemical analyses indicate that both the oleylamine and chloride ligands participate in the stabilization of tetrahedral-shaped InP CQDs covered with cation-rich (111) facets. Based on density functional theory calculations, we propose that fractional dangling electrons of the In-rich (111) surface could be completely passivated by three halide and one primary amine ligands per the (2×2) surface unit, satisfying the 8-electron rule. This halide-amine co-passivation strategy will benefit the synthesis of stable III-V CQDs with controlled surfaces. [ABSTRACT FROM AUTHOR]

The dielectric, ferroelectric and impedance properties of (1 − x − y)NBT–yKBT–xBT single crystals were investigated systematically. Our results demonstrate that the addition of KBT leads to enhanced piezoelectric response, thermal stability (e.g., depolarization temperature, T d ). The composition and temperature induced phase transformation mechanisms were characterized by using in-situ Raman spectra. The structure nature of improved electrical performance in (1 − x − y)NBT–yKBT–xBT ternary single crystals were discussed in detail. [ABSTRACT FROM AUTHOR]

In this work, the time and temperature dependence of the piezoelectric and ferroelectric properties of the 0.7Pb(MgNb)O-0.3PbTiO (0.7PMN-0.3PT) single crystals were investigated in order to search for an effective method to improve their properties further. The piezoelectric properties of the [001]-, [110]- and [111]-oriented 0.7PMN-0.3PT single crystals exhibit excellent time stability during the 2-month room-temperature aging process. The re-poling process leads to the improvement of piezoelectric constant d for the [001]-, [110]- and [111]-oriented 0.7PMN-0.3PT single crystals, while the values of electromechanical coupling coefficient k change little. During the thermal aging, the values of the measured d, calculated converse piezoelectric constant $$d_{33}^{*}$$ , maximum strain S% and longitudinal electrostrictive coefficient Q of the [001]-, [110]- and [111]-oriented crystal plates increase gradually before the ferroelectric phase transition temperatures ( T, T, T and T) and then decline continuously. The increase in these values before the T is a result of the phase instability. In general, the [001]- and [110]-oriented 0.7PMN-0.3PT single crystals exhibit large piezoelectricity, excellent time stability and relatively high thermal stability between 20 and 80 °C, which is favorable to the piezoelectric applications. [ABSTRACT FROM AUTHOR]

Abstract: The vitrification process of racemic RS- and enantiomorphic S-ibuprofen was studied by using Brillouin light scattering and modulated differential scanning calorimetry (DSC). The sound velocity and the attenuation coefficient of both compounds were determined for the first time in the glassy, supercooled liquid and liquid states. The sound velocity and the hypersonic damping were similar between the two ibuprofen pharmaceuticals over the whole investigated temperature range including glassy, supercooled liquid and liquid states. The thermal expansion coefficient of the RS-ibuprofen was smaller than that of the S-ibuprofen, which suggests that the intermolecular force of the former is slightly stronger than the latter. The thermal relaxation times derived from the modulated DSC were consistent with the dielectric relaxation times in both RS- and S-ibuprofens. The fragility index of S-ibuprofen just above the glass transition was determined to be 73, which was smaller compared to the value of RS-ibuprofen, 89. This difference in the fragility indicates that the decrease in the fragility of S-ibuprofen compared to the racemic one may improve its stability of the amorphous state below the glass transition temperature against crystallization. [Copyright &y& Elsevier]

Abstract: The longitudinal acoustic (LA) mode of Pb[(Zn1/3Nb2/3)0.93Ti0.07]O3 (PZN-0.07PT) single crystals grown by Bridgman method was investigated over a wide temperature range by using a micro-Brillouin scattering technique. The ferroelectric phase transition of PZN-0.07PT at ∼166 °C was accompanied by a minimum of the Brillouin frequency shift and a sharp maximum of hypersonic damping. These acoustic properties exhibited a thermal hysteresis between cooling and heating processes indicating the first-order nature of the phase transition. The substantial softening of the frequency shift and the increasing damping are typical in ferroelectric relaxors where nano-sized polar clusters appear in the paraelectric phase and interact with acoustic waves via electrostrictive coupling. However, in the present case, acoustic damping consists of a small, sharp peak at the transition temperature (T c) superposed on the broad increasing damping. The broad damping, which becomes substantially large already in the prototype cubic phase, is due to the fluctuation interactions, while the additional sudden peak at T c may be attributed to the growth and merging of polar nanoregions approaching percolation limit that drives the system into a long-range ferroelectric phase at T c. [Copyright &y& Elsevier]

It is observed that epitaxial graphene forms on the surface of a 6H-SiC substrate by irradiating electron beam directly on the sample surface in high vacuum at relatively low temperature (∼670 °C). The symmetric shape and full width at half maximum of 2D peak in the Raman spectra indicate that the formed epitaxial graphene is turbostratic. The gradual change of the Raman spectra with electron beam irradiation time increasing suggests that randomly distributed small grains of epitaxial graphene form first and grow laterally to cover the entire irradiated area. The sheet resistance of epitaxial graphene film is measured to be ∼6.7 kΩ/sq. [ABSTRACT FROM AUTHOR]

[Display omitted] • Optical parameters of carboxymethyl starch identified with THz-TDS. • The boson peak (BP) is extracted using a novel inflection point method. • BP frequency of polymer glasses was slightly lower than that of monomer. • Hydrogen bonding vibrations of polymer glasses affect BP frequency. • α (ν) exponential behaviour above BP frequency suggested the presence of fractons. We investigated the vibrational density of states of sodium carboxymethyl starch (CM-starch) by terahertz (THz) time-domain spectroscopy. The CM-starch showed a broad peak at ∼3 THz. The structure of the peak was similar to those corresponding to glucose-based polymer glasses possessing hydrogen bonds. The boson peak (BP) appeared at 1.16 THz at the lowest temperature and disappeared because of the existence of excess wing at higher temperatures. However, based on our novel BP frequency determination method using the inflection point of the extinction coefficient, the BP frequency showed almost no dependence on temperature. Further, the chain length dependence of the BP frequency of the glucose-based glasses showed that the BP frequency of the polymer glass was slightly lower than that of the monomer glass. The power law behaviour of the absorption coefficient suggested the existence of fractons, and the fractal dimension was estimated to be 2.33. [ABSTRACT FROM AUTHOR]

Herein, Ag-ZnO core-shell nanoparticles (NPs) with enhanced photocatalytic activity were prepared by coating Ag metal cores with ZnO semiconductor shells through atomic layer deposition (ALD). Instrumental analysis revealed that the ultra-thin and conformal nature of the shell allowed the core-shell NPs to simultaneously exploit the photocatalytic properties of ZnO and the plasmonic properties of Ag. In a rhodamine B photodegradation test performed under artificial sunlight, Ag-ZnO core-shell NPs exhibited better photocatalytic performance than other prepared photocatalysts, namely ZnO NPs and ALD-ZnO coated ZnO NPs. The performance enhancement was ascribed to the effect of noble metal-semiconductor heterojunctions, which increased the efficiency of electron-hole separation, i.e., the Ag core effectively captured excited electrons at the ZnO surface, which resulted in the elevated production of hydroxyl radicals from holes remaining at ZnO. A three-dimensional finite-difference time-domain simulation of the Ag-ZnO NPs with variable shell thickness showed that ZnO shells on Ag metal cores increase the intensity of light around NPs, allowing the plasmonic cores to fully utilize incident light. Unlabelled Image • The ALD technology is applied to fabricate Ag-ZnO nanoparticles for photocatalyst. • Stable ZnO shell layers with wurtzite structure are deposited on Ag core particles. • Ag-ZnO shows ~2.5 to 4 times enhanced photodegradation compared with pure ZnO. • SPR effect of Ag increases photocatalytic performance of Ag-ZnO photocatalyst. • Ultra-thin ZnO shells on Ag cores increase photocatalytic performance in UV-region. [ABSTRACT FROM AUTHOR]

The article discusses the crystal structure of N-(4-hydroxyphenyl) acetamide as seen by neutrons at 10K, whose chemical formulae is C8H9NO2. Topics discussed include its physical properties, chemical formula, chemical structure, and its atomic coordinates and displacement parameters.

An atomistic understanding of dry-etching processes with reactive molecules is crucial for achieving geometric integrity in highly scaled semiconductor devices. Molecular dynamics (MD) simulations are instrumental, but the lack of reliable force fields hinders the widespread use of MD in etching simulations. In this work, we develop an accurate neural network potential (NNP) for simulating the etching process of amorphous Si 3 N 4 with HF molecules. The surface reactions in diverse local environments are considered by incorporating several types of training sets: baseline structures, reaction-specific data, and general-purpose training sets. Furthermore, the NNP is refined through iterative comparisons with the density functional theory results. Using the trained NNP, we carry out etching simulations, which allow for detailed observation and analysis of key processes such as preferential sputtering, surface modification, etching yield, threshold energy, and the distribution of etching products. Additionally, we develop a simple continuum model, built from the MD simulation results, which effectively reproduces the surface composition obtained with MD simulations. By establishing a computational framework for atomistic etching simulation and scale bridging, this work will pave the way for more accurate and efficient design of etching processes in the semiconductor industry, enhancing device performance and manufacturing precision.

Hybrid organic-inorganic lead halide perovskites (LHPs) have emerged as a highly significant class of materials due to their tunable and adaptable properties, which make them suitable for a wide range of applications. One of the strategies for tuning and optimizing LHP-based devices is the substitution of cations and/or anions in LHPs. The impact of Cs substitution at the A site on the structural, vibrational, and elastic properties of MA x Cs 1-x PbCl 3 -mixed single crystals was investigated using X-ray diffraction (XRD) and Raman and Brillouin light scattering techniques. The XRD results confirmed the successful synthesis of impurity-free single crystals, which exhibited a phase coexistence of dominant cubic and minor orthorhombic symmetries. Raman spectroscopy was used to analyze the vibrational modes associated with the PbCl 6 octahedra and the A-site cation movements, thereby revealing the influence of cesium incorporation on the lattice dynamics. Brillouin spectroscopy was employed to investigate the changes in elastic properties resulting from the Cs substitution. The incorporation of Cs cations induced lattice distortions within the inorganic framework, disrupting the hydrogen bonding between the MA cations and PbCl 6 octahedra, which in turn affected the elastic constants and the sound velocities. The substitution of the MA cations with smaller Cs cations resulted in a stiffer lattice structure, with the two elastic constants increasing up to a Cs content of 30%. The current findings facilitate a fundamental understanding of mixed lead chloride perovskite materials, providing valuable insights into their structural and vibrational properties.

In this paper, the behavior of quasielastic light scattering (QELS) in a PbMg 1/3 Nb 2/3 O 3 (PMN) crystal under broadband Brillouin light scattering in a temperature range from 750 K to 80 K was studied. It was shown that QELS consists of two components: narrow (0.9 GHz to 11 GHz) and wide (80 GHz to 600 GHz). The dependencies of the intensity, I , of these components on the frequency, ν , are well described by the power law I ~ eν α , with different α, and are determined by the distribution of the relaxation times. The analysis of the Brillouin spectra showed that the behavior of the relaxation time of both the components of QELS with temperature change is well described by the Arrhenius law. Additionally, in the vicinity of the intermediate temperature T * ≈ 380 K, a critical relaxation time behavior for the narrow component of QELS was detected. In the vicinity of the same temperature, a maximum in the integral intensity of both the components of QELS was observed, which is adjacent to another maximum in the region of the Vogel-Fulcher temperature T VF ≈ 250 K corresponding to the transformation of the crystal to a nonergodic state.

Raman spectroscopy was applied to MAPbCl 3 single crystals in a wide frequency range from 10 to 3500 cm -1 over a broad temperature range from -196 °C to 200 °C including both two structural phase transitions and a thermal degradation range. Low-frequency lattice modes of MAPbCl 3 were revealed for the first time, which showed discontinuous anomalies along with the change in the number of Raman modes at the transition points of -114 °C and -110 °C. Several Raman modes related to the C-N stretching and MA rocking modes in addition to the lattice modes displayed temperature dependences similar to those of MAPbBr 3 in both Raman shifts and half widths, indicating that the MA cation arrangement and H-halide bond interactions behave similarly in both systems during the phase transition. The substantial increase in the half widths of nearly all Raman modes especially suggests that the dynamic disorder caused by the free rotational motions of MA cations induces significant anharmonicity in the lattice and thus, reduces the phonon lifetimes. High-temperature Raman and Brillouin scattering measurements showed that the spectral features changed drastically at ~200 °C where the thermal decomposition of MAPbCl 3 into PbCl 2 began. This result exhibits that combined Raman and Brillouin spectroscopic techniques can be a useful tool in monitoring temperature-induced or temporal changes in lead-based halide perovskite materials.

Interaction between dipoles often emerges intriguing physical phenomena, such as exchange bias in the magnetic heterostructures and magnetoelectric effect in multiferroics, which lead to advances in multifunctional heterostructures. However, the defect-dipole tends to be considered the undesired to deteriorate the electronic functionality. Here, deterministic switching between the ferroelectric and the pinched states by exploiting a new substrate of cubic perovskite, BaZrO 3 is reported, which boosts the square-tensile-strain to BaTiO 3 and promotes four-variants in-plane spontaneous polarization with oxygen vacancy creation. First-principles calculations propose a complex of an oxygen vacancy and two Ti 3+ ions coins a charge-neutral defect-dipole. Cooperative control of the defect-dipole and the spontaneous polarization reveals ternary in-plane polar states characterized by biased/pinched hysteresis loops. Furthermore, it is experimentally demonstrated that three electrically controlled polar-ordering states lead to switchable and nonvolatile dielectric states for application of nondestructive electro-dielectric memory. This discovery opens a new route to develop functional materials via manipulating defect-dipoles and offers a novel platform to advance heteroepitaxy beyond the prevalent perovskite substrates., (© 2022 Wiley-VCH GmbH.)

A remote-type white light-emitting diode (LED) consisting of a red quantum-dot (QD) film and a yellow phosphor plate was studied by both experiment and optical simulation. The sequence of the two color-conversion films had a substantial effect on the color-rendering properties of the vertically-stacked white LED, and the optimized configuration exhibited a high color rendering index of more than 90 thanks to the enhanced red component via the QD film. For the design of high-power white LED devices of a remote type, it was necessary to locate the color-conversion films below the diffuser plate to remove the substantial color dispersion depending on the viewing angle. The present study shows that high power and high color-rendering white LED devices can be realized in terms of two vertically-stacked color-conversion materials, which would provide long-term stability due to the remote design.

Inelastic light scattering spectra of organic-inorganic halide perovskite MAPbCl 3 single crystals were investigated by using Brillouin spectroscopy. Sound velocities and acoustic absorption coefficients of longitudinal and transverse acoustic modes propagating along the cubic [100] direction were determined in a wide temperature range. The sound velocities exhibited softening upon cooling in the cubic phase, which was accompanied by the increasing acoustic damping. The obtained relaxation time showed a critical slowing-down behavior, revealing the order-disorder nature of the phase transition, which is consistent with the growth of strong central peaks upon cooling toward the phase transition point. The temperature dependences of the two elastic constants C 11 and C 44 were obtained in the cubic phase for the first time. The comparison of C 11 and C 44 with those of other halide perovskites showed that C 11 of MAPbCl 3 is larger and C 44 is slightly smaller compared to the values of MAPbBr 3 and MAPbI 3 . It suggests that MAPbCl 3 has a more compact structure (smaller lattice constant) along with stronger binding forces, causing larger C 11 and bulk modulus in this compound, and that the shear rigidity is exceedingly small similar to other halide perovskites. The reported elastic constants in this study may serve as a testbed for theoretical and calculational approaches for MAPbCl 3 .

We have investigated the transition kinetics of Sr 0.25 Ba 0.75 Nb 2 O 6 (SBN) and Li 2 B 4 O 7 (LBO) crystals from 0.25SrO-0.75BaO-Nb 2 O 5 -Li 2 O-2B 2 O 3 (SBNLBO) glass under isothermal and non-isothermal processes. With increasing temperature, there are two consecutive steps of crystallization of SBN and LBO from the glass. The Johnson-Mehl-Avrami function indicates that the crystallization mechanism of SBN belongs to an increasing nucleation rate with diffusion-controlled growth. The crystallite size of SBN ranges from 40 to 140 nm but it is confined to within 30-45 nm for LBO during the whole crystallization process. The relationship between the nano size and strain of SBN based on the Williamson-Hall method, and the change of activation energies of SBN and LBO crystallization analyzed by using the isoconversional model are discussed. A comparison of phonon modes between as-quenched glass and fully transformed crystals clearly shows that the low dimensional vibration modes in the structurally disordered glass change to highly dimensional network units with the formation of crystals., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The outcoupling efficiencies (OCEs) of organic light-emitting diodes (OLEDs) were studied for a fractal-like two-dimensional structure consisting of three layers of semicircular microlens on a glass substrate using a finite-difference time-domain (FDTD) method. The OCE with only one semicircular microlens layer was 29.5%, 1.75 times larger than that of the basic OLED. Additional layers with smaller diameters on the first layer did not improve the OCE. The OCE remained constant or slightly decreased with the increase of the number of layers. Two possible origins of this result were suggested; first, the possibility that the escaped light enters the nearby microlens becomes higher with the introduction of an additional protruded layer; second, the Mie scattering effect becomes important with the decrease of the diameter of the semicircular microlens from 20 μ m to 0.8 μ m. An additional FDTD simulation was performed for the OLED with only one microlens array as a function of the diameter. The OCE decreased approximately monotonously with the decrease of the diameter from 20 μ m to 0.2 μ m. In particular, the OCE became lower than that of the basic OLED when the diameter decreased from 0.5 μ m to 0.2 μ m. This is consistent with the observation that smaller fractal-like structures on the large microlens array did not further enhance the OCE.

The nature of precursor phenomena in the paraelectric phase of ferroelectrics is one of the main questions to be resolved from a fundamental point of view. Barium titanate (BaTiO₃) is one of the most representative perovskite-structured ferroelectrics intensively studied until now. The pretransitional behavior of BaTiO₃ single crystal grown using a solid-state crystal growth (SSCG) method was investigated for the first time and compared to previous results. There is no melting process in the SSCG method, thus the crystal grown using a SSCG method have inherent higher levels of impurity and defect concentrations, which is a good candidate for investigating the effect of crystal quality on the precursor phenomena. The acoustic, dielectric, and piezoelectric properties, as well as birefringence, of the SSCG-grown BaTiO₃ were examined over a wide temperature range. Especially, the acoustic phonon behavior was investigated in terms of Brillouin spectroscopy, which is a complementary technique to Raman spectroscopy. The obtained precursor anomalies of the SSCG-grown BaTiO₃ in the cubic phase were similar to those of other single crystals, in particular, of high-quality single crystal grown by top-seeded solution growth method. These results clearly indicate that the observed precursor phenomena are common and intrinsic effect irrespective of the crystal quality., Competing Interests: The authors declare no conflict of interest.

Hole mobility characteristics were investigated with surface roughness and silicon-on-insulator (SOI) thickness variations to investigate the influence of surface roughness to mobility. The root mean square roughness varied between 0.16, 0.85 and 10.6 nm in 220, 100 and 40 nm thick SOI samples. Hole mobility was measured and analyzed as a function of effective field and temperature with the variations of surface roughness. The hole mobility, determined by transconductance, greatly decreased with the increase of effective field due to the increased surface roughness scattering in 40 nm thick SOI samples. On the other hand, phonon scattering was a dominant mechanism with the increase of temperature, irrespective of surface roughness and SOI thickness. The induced surface roughness of the devices increases the phonon scattering, thereby reducing the electron and hole mobility. The hole mobility decreases with the roughening of the samples, with the increase of temperature due to increased phonon scattering. Therefore, for enhanced mobility, surface scattering and phonon scattering should be controlled even in atomic scale roughened samples.

Micro-/nano-electromechanical (M/NEM) switches have received significant attention as promising switching devices for a wide range of applications such as computing, radio frequency communication, and power gating devices. However, M/NEM switches still suffer from unacceptably low reliability because of irreversible degradation at the contacting interfaces, hindering adoption in practical applications and further development. Here, we evaluate and verify graphene as a contact material for reliability-enhanced M/NEM switching devices. Atomic force microscopy experiments and quantum mechanics calculations reveal that energy-efficient mechanical contact-separation characteristics are achieved when a few layers of graphene are used as a contact material on a nickel surface, reducing the energy dissipation by 96.6% relative to that of a bare nickel surface. Importantly, graphene displays almost elastic contact-separation, indicating that little atomic-scale wear, including plastic deformation, fracture, and atomic attrition, is generated. We also develop a feasible fabrication method to demonstrate a MEM switch, which has high-quality graphene as the contact material, and verify that the devices with graphene show mechanically stable and elastic-like contact properties, consistent with our nanoscale contact experiment. The graphene coating extends the switch lifetime >10 3 times under hot switching conditions.

The tribological properties of two-dimensional (2D) atomic layers are quite different from three-dimensional continuum materials because of the unique mechanical responses of 2D layers. It is known that friction on graphene shows a remarkable decreasing behavior as the number of layers increases, which is caused by the puckering effect. On other graphene derivatives, such as graphene oxide (GO) or reduced graphene oxide (rGO), the thickness dependence of friction is important because of the possibilities for technical applications. In this report, we demonstrate unexpected layer-dependent friction behavior on GO and rGO layers. Friction force microscopy measurements show that nanoscale friction on GO does not depend on the number of layers; however, after reduction, friction on rGO shows an inverse thickness dependence compared with pristine graphene. We show that the friction on rGO is higher than that on SiO 2 at low load, and that an interesting crossover behavior at higher load occurs because of the lower friction coefficient and higher adhesion of the rGO. We provide a relevant interpretation that explains the effect of thickness and chemical reduction on nanoscale friction.

The amorphous state of pharmaceuticals has attracted much attention due to its high bioavailability and other advantages. The stability of the amorphous state in relation with the local molecular mobility is important from both fundamental and practical points of view. The acoustic properties of amorphous progesterone, one of the representative steroid hormones, were investigated by using a Brillouin inelastic light scattering technique. The Brillouin spectrum of the longitudinal acoustic mode exhibited distinct changes at the glass transition and the cold-crystallization temperatures. The acoustic dispersions of the longitudinal sound velocity and the acoustic absorption coefficient were attributed to the fast and possibly the secondary relaxation processes in the glassy and supercooled liquid states, while the structural relaxation process was considered as the dominant origin for the significant acoustic damping observed even in the liquid phase. The persisting acoustic dispersion in the liquid state was attributed to the single-molecule nature of the progesterone which does not exhibit hydrogen bonds in the condensed states., Competing Interests: The authors declare no conflict of interest.

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5d pyrochlore oxides with all-in-all-out magnetic order are prime candidates for realizing strongly correlated, topological phases of matter. Despite significant effort, a full understanding of all-in-all-out magnetism remains elusive as the associated magnetic excitations have proven difficult to access with conventional techniques. Here we report a Raman spectroscopy study of spin dynamics in the all-in-all-out magnetic state of the 5d pyrochlore Cd 2 Os 2 O 7 . Through a comparison between the two-magnon scattering and spin-wave theory, we confirm the large single ion anisotropy in this material and show that the Dzyaloshinskii-Moriya and exchange interactions play a significant role in the spin-wave dispersions. The Raman data also reveal complex spin-charge-lattice coupling and indicate that the metal-insulator transition in Cd 2 Os 2 O 7 is Lifshitz-type. Our work establishes Raman scattering as a simple and powerful method for exploring the spin dynamics in 5d pyrochlore magnets.Pyrochlore 5d transition metal oxides are expected to have interesting forms of magnetic order but are hard to study with conventional probes. Here the authors show that Raman scattering can be used to measure magnetic excitations in Cd 2 Os 2 O 7 and that it exhibits complex spin-charge-lattice coupling.

Common experience shows that friction converts mechanical energy into heat. The first part of this process is vibrational excitation of atoms at the interface between rubbing bodies. The second part is the removal of the vibration energy by transferring it from the interface to the substrate. However, it is difficult to disentangle the excitation and energy transfer processes. We solved this by using a system consisting of a SiO 2 -terminated tip sliding over graphene deposited on mica with intercalated water between them. The intercalated water was found to increase friction by a factor of ∼3 relative to dry mica. Density functional theory calculations show that water broadens the spectral range of graphene vibrations-particularly the low-frequency flexural modes-thus providing new excitation channels and also by increasing the overlap with the atomic vibrations of the mica substrate, which facilitates coupling and energy transfer.

Here, we report the size- and shape-controlled synthesis of metal oxide nanoparticles through the introduction of rare-earth metals. The addition of gadolinium oleate in the synthesis of iron oxide nanoparticles induced sphere-to-cube shape changes of nanoparticles and generated iron oxide nanocubes coated with gadolinium. Based on experimental investigations and density functional theory (DFT) calculations, we attribute the shape change to the facet-selective binding of undecomposed gadolinium oleates. While many previous studies on the shape-controlled syntheses of nanoparticles rely on the stabilization of specific crystal facets by anionic surfactants or their decomposition products, this study shows that the interaction between growing transition metal oxide nanoparticles and rare-earth metal complexes can be used as a robust new mechanism for shape-controlled syntheses. Indeed, we demonstrated that this approach was applicable to other transition metal oxide nanoparticles (i.e., manganese oxide and manganese ferrite) and rare earth metals (i.e., gadolinium, europium, and cerium). This study also demonstrates that the nature of metal-ligand bonding can play an important role in the shape control of nanoparticles.

We formulated atomic models of cation-rich surfaces passivated with anionic ligands for IV-VI, II-VI, and III-V colloidal quantum dots, employing electron counting models and quantum mechanical calculations. We found that the fractional dangling bonds of cation-rich (100) and (111) surfaces could be greatly stabilized by dimerization-anion passivation and amine-anion co-passivation.

In spite of extremely high piezoelectric and pyroelectric coefficients, there are few reports on flexible ferroelectric perovskite film based nanogenerators (NGs). Here, we report the successful growth of a flexible Pb(Zr0.52Ti0.48)O3 (PZT) film and its application to hybrid piezoelectric-pyroelectric NG. A highly flexible Ni-Cr metal foil substrate with a conductive LaNiO3 bottom electrode enables the growth of flexible PZT film having high piezoelectric (140 pC/N) and pyroelectric (50 nC/cm(2)K) coefficients at room temperature. The flexible PZT-based NG effectively scavenges mechanical vibration and thermal fluctuation from sources ranging from the human body to the surroundings such as wind. Furthermore, it stably generates electric current even at elevated temperatures of 100 °C, relative humidity of 70%, and pH of 13 by virtue of its high Curie temperature and strong resistance for water and base. As proof of power generation under harsh environments, we demonstrate the generation of extremely high current at the exhaust pipe of a car, where hot CO and CO2 gases are rapidly expelled to air. This work expands the application of flexible PZT film-based NG for the scavenging mechanical vibration and thermal fluctuation energies even at extreme conditions.

The crystallinity of epitaxial graphene (EG) grown on a Hexagonal-SiC substrate is found to be enhanced greatly by capping the substrate with a molybdenum plate (Mo-plate) during vacuum annealing. The crystallinity enhancement of EG layer grown with Mo-plate capping is confirmed by the significant change of measured Raman spectra, compared to the spectra for no capping. Mo-plate capping is considered to induce heat accumulation on SiC surface by thermal radiation mirroring and raise Si partial pressure near surface by confining the sublimated Si atoms between SiC substrate and Mo-plate, which would be the essential contributors of crystallinity enhancement.

PbHfO(3) is investigated theoretically and experimentally with respect to possible precursor effects starting in the paraelectric phase far above the cubic to tetragonal phase transition temperature. The theoretical modeling within the polarizability model predicts a giant softness of the system with spatially large polar and antiferrodistortive domain formation which compete with each other. These predictions are substantiated by the experiments, where the softness and the precursor effects are confirmed by birefringence, dielectric permittivity measurements and elastic properties by Brillouin scattering. The intermediate phase is found to have the polar nature confirmed by P-E hysteresis loop measurements, which is another manifestation of the competition between interrelated instabilities, namely a polar one and an antiferroelectric one.

The fast degradation of lead selenide (PbSe) nanocrystal quantum dots (NQDs) in ambient conditions impedes widespread deployment of the highly excitonic, thus versatile, colloidal NQDs. Here we report a simple in situ post-synthetic halide salt treatment that results in size-independent air stability of PbSe NQDs without significantly altering their optoelectronic characteristics. From TEM, NMR, and XPS results and DFT calculations, we propose that the unprecedented size-independent air stability of the PbSe NQDs can be attributed to the successful passivation of under-coordinated PbSe(100) facets with atomically thin PbX2 (X = Cl, Br, I) adlayers. Conductive films made of halide-treated ultrastable PbSe NQDs exhibit markedly improved air stability and behave as an n-type channel in a field-effect transistor. Our simple in situ wet-chemical passivation scheme will enable broader utilization of PbSe NQDs in ambient conditions in many optoelectronic applications.

To better understand the phase transition mechanism of PbZrO3 (PZO), the lattice dynamics of this antiferroelectric compound are investigated within the polarizability model, with emphasis on the cubic to orthorhombic phase transition. Similarly to ferroelectric phase transitions in ABO3 perovskites, polar dynamical clusters develop and grow in size upon approaching T(C) from the high temperature side and never form a homogeneous state. Simultaneously, elastic anomalies set in and compete with polar cluster dynamics. These unusual dynamics are responsible for precursor effects that drive the PZO lattice towards an incipient ferroelectric state. Comparison of the model calculations with the temperature dependences of elastic coefficients measured on PZO single crystals reveals a striking similarity.

Ambient stability of colloidal nanocrystal quantum dots (QDs) is imperative for low-cost, high-efficiency QD photovoltaics. We synthesized air-stable, ultrasmall PbS QDs with diameter (D) down to 1.5 nm, and found an abrupt transition at D ≈ 4 nm in the air stability as the QD size was varied from 1.5 to 7.5 nm. X-ray photoemission spectroscopy measurements and density functional theory calculations reveal that the stability transition is closely associated with the shape transition of oleate-capped QDs from octahedron to cuboctahedron, driven by steric hindrance and thus size-dependent surface energy of oleate-passivated Pb-rich QD facets. This microscopic understanding of the surface chemistry on ultrasmall QDs, up to a few nanometers, should be very useful for precisely and accurately controlling physicochemical properties of colloidal QDs such as doping polarity, carrier mobility, air stability, and hot-carrier dynamics for solar cell applications.

Catalytic natures of organometallic catalysts are modulated by coordinating organic ligands with proper steric and electronic properties to metal centers. Carbon-based nanomaterials such as graphene nanoplatelets are used with and without N-doping and multiwalled carbon nanotube as a ligand for ethylene polymerizations. Zirconocenes or titanocenes are immobilized on such nanomaterials. Polyethylenes (PEs) produced by such hybrids show a great increase in molecular weight relative to those produced by free catalysts. Specially, ultra-high-molecular-weight PEs are produced from the polymerizations at low temperature using the hybrid with N-doped graphene nanoplatelets. This result shows that such nanomaterials act a crucial role to tune the catalytic natures of metallocenes., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Atomically thin graphene is an ideal model system for studying nanoscale friction due to its intrinsic two-dimensional (2D) anisotropy. Furthermore, modulating its tribological properties could be an important milestone for graphene-based micro- and nanomechanical devices. Here, we report unexpectedly enhanced nanoscale friction on chemically modified graphene and a relevant theoretical analysis associated with flexural phonons. Ultrahigh vacuum friction force microscopy measurements show that nanoscale friction on the graphene surface increases by a factor of 6 after fluorination of the surface, while the adhesion force is slightly reduced. Density functional theory calculations show that the out-of-plane bending stiffness of graphene increases up to 4-fold after fluorination. Thus, the less compliant F-graphene exhibits more friction. This indicates that the mechanics of tip-to-graphene nanoscale friction would be characteristically different from that of conventional solid-on-solid contact and would be dominated by the out-of-plane bending stiffness of the chemically modified graphene. We propose that damping via flexural phonons could be a main source for frictional energy dissipation in 2D systems such as graphene.