Energy Mismatch Research Articles

Comparative studies of magnetic properties in osmates with the double perovskite structure

Using the first-principles density functional approach, we comparatively studied the electronic and magnetic properties of two series of ordered double perovskite, $\mathrm{B}{\mathrm{a}}_{2}B\mathrm{Os}{\mathrm{O}}_{6}\phantom{\rule{4pt}{0ex}}(B=\mathrm{Sc},\text{Y},\phantom{\rule{4pt}{0ex}}\text{and In})$ and ${A}_{2}\mathrm{ScOs}{\mathrm{O}}_{6}\phantom{\rule{4pt}{0ex}}(A=\text{Ba},\text{Sr},\phantom{\rule{4pt}{0ex}}\text{and Ca})$. The electronic structure calculations indicate that the Os ion bears the nominal ${t}_{2g}^{3}$ state with oxidation state $5+$ and is the only magnetically active one in all compounds. In nice agreement with the experimental observations, all of them stabilized in the type I antiferromagnetic alignment, which is mediated by the moderate nearest-neighbor antiferromagnetic interactions through the $\mathrm{Os}\text{\ensuremath{-}}\mathrm{O}\text{\ensuremath{-}}B\text{\ensuremath{-}}\mathrm{O}\text{\ensuremath{-}}\mathrm{Os}90$\ifmmode^\circ\else\textdegree\fi{} route and accompanied by mild next-nearest-neighbor antiferromagnetic coupling via the $\mathrm{Os}\text{\ensuremath{-}}\mathrm{O}\text{\ensuremath{-}}B\text{\ensuremath{-}}\mathrm{O}\text{\ensuremath{-}}\mathrm{Os}180$\ifmmode^\circ\else\textdegree\fi{} route, in spite of the geometric frustration. The mechanism of the antiferromagnetic interaction has been proposed based on the density of states analysis. In addition, the computed magnetic moment on Os ions, $\ensuremath{\sim}2\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{B}$, is remarkably smaller than the ideal spin-only value. In conjunction with the modest spin-orbit coupling effect, strong covalency between the $\mathrm{Os}\text{\ensuremath{-}}5d$ and $\mathrm{O}\text{\ensuremath{-}}2p$ states reduces the magnetic moments. More importantly, our results demonstrated that the magnitude of the magnetic couplings as well as magnetic transition temperature ${T}_{N}$ are directly proportional to the reciprocal of the absolute value of energy mismatch between the $B\text{\ensuremath{-}}nd$ and occupied $\mathrm{Os}\text{\ensuremath{-}}{t}_{2g}$ band; in addition, they are also a function of the Sc-O-Os bond angles, i.e., the buckling of the octahedral connectivity. Moreover, comparison of these two series helps to identify the energy mismatch as the efficient factor to adjust the magnetic interactions.

Robust adaptive beamforming method for active sonar in single snapshot

Forming narrow beams is a useful way for active sonar to anti-reverberation when it works in the shallow water. High-resolution adaptive beamforming with the performance of narrow beamwidths and low sidelobe levels is a better and more efficient method, particularly in the scenario where the installation space for sonar array is limited, such as hull-mounted sonar. Due to the short duration of target echo signal in the complex and varying acoustic channel, conventional adaptive beamforming methods are invalid. Therefore, this paper proposes a robust adaptive beamforming method for active sonar in single snapshot, also called the steered dominant mode rejection (STDMR). Firstly, STDMR steered the sample covariance matrix (STCM) based on wide-band focusing, which the needed number of snapshots is greatly reduced. Secondly, by partial eigendecomposition, the large eigenvalues of the STCM which are greater than the noise energy and their eigenvectors are used for dominant mode rejection (DMR). DMR is a typical eigenspace-based algorithm which has small computational load and fast convergence speed. Finally, modified with the methods of diagonal loading of 3-5dB over the noise energy and signal mismatch protection, improved the robustness of this method. Simulation and experimental data analysis shows that the STDMR method achieves narrow beams and low-level sidelobes in single snapshot. Hence, the STDMR beamformer is an appropriate implementation to use for active sonar detection systems.

Quadrant-separable multi-singularity vortices manipulation by coherent superposed mode with spatial-energy mismatch.

We propose a new method of phase-singularities manipulation in optical vortices carrying orbital angular momentum (OAM), namely, quadrant-separable multi-singularity manipulation (QSMSM). In QSMSM, the positions of partial vortices in a quadrant region can be manipulated, while the singularities in other regions remain unchanged. The basic model of the multi-singularity OAM beam is obtained by the principle of coherent superposition of two Hermite-Gaussian modes with spatial mismatch. The actual multi-singularity beams are generated by external modulation with a spatial light modulator. The distribution of vortices trajectory can be controlled by the energy mismatch degree and the spatial mismatch degree. The vortices in a quadrant region can be independently manipulated by partially controlling the energy mismatch degree. The technology of partially tuning singularities in QSMSM improves the flexibility of vortices control and has great potential in applications of optical tweezers and optical modulators.

Ultrapure NIR-to-NIR single band emission of β-PbF2: Yb3+/Tm3+ in glass ceramics

An ultrapure near infrared (NIR) emission entered at 800 nm upon 976 nm laser excitation (NIR-to-NIR) was observed in β-PbF2: Yb3+/Tm3+ glass ceramics (GCs). The ultrapure NIR-to-NIR single band emission originated from the 3H4 → 3H6 transition of Tm3+ with the ratio of NIR emission, and a blue band up to 9633 was obtained. Through detailed analysis of the crystal structure and the energy transfer between Tm3+ and Yb3+, it is elucidated that the host lattice with low phonon energy cooperative with the energy mismatch results in a dramatic population of the 3H4 state as well as ultrapure NIR-to-NIR single band emission. Moreover, up-conversion (UC) emission properties and the decay lifetimes of β-PbF2: Yb3+/Tm3+ in GCs were explored thoroughly. The results illustrate that efficient cross relaxation (CR) processes between Tm3+ generate the energy redistribution in UC emission spectra, further concentrating energy to NIR emission. These two issues can be treated as crucial factors on ultrapure NIR-to-NIR single band emission in β-PbF2: Yb3+/Tm3+ in GCs. The ultrapure NIR-to-NIR single band emission through 976 nm laser excitation is advantageous for enhancing resolution and has potential application in bio-imaging fields.

Quench dynamics of quantum spin models with flat bands of excitations

We investigate the unitary evolution following a quantum quench in quantum spin models possessing a (nearly) flat band in the linear excitation spectrum. Inspired by the perspective offered by ensembles of individually trapped Rydberg atoms, we focus on the paradigmatic trasverse-field Ising model on two dimensional lattices featuring a flat band as a result of destructive interference effects (Lieb and Kagom\'e lattice); or a nearly flat band due to a strong energy mismatch among sublattices (triangular lattice). Making use of linear spin-wave theory, we show that quantum quenches, equipped with single-spin imaging, can directly reveal the spatially localized nature of the dispersionless excitations, and their slow propagation or lack of propagation altogether. Moreover we show that Fourier analysis applied to the post-quench time evolution of wavevector-dependent quantities allows for the spectroscopic reconstruction of the flat bands. Our results pave the way for future experiments with Rydberg quantum simulators, which can extend our linear spin-wave study to the fully nonlinear regime, characterized by the appearance of dense, strongly interacting gases of dispersionless excitations.

Failure to sense energy depletion may be a novel therapeutic target in chronic kidney disease

The kidneys consume a large amount of energy to regulate volume status and blood pressure and to excrete uremic toxins. The identification of factors that cause energy mismatch in the setting of chronic kidney disease (CKD) and the development of interventions aimed at improving this mismatch are key research imperatives. Although the critical cellular energy sensor 5'-adenosine monophosphate (AMP)-activated protein kinase (AMPK) is known to be inactivated in CKD, the mechanism of AMPK dysregulation is unknown. In a mouse model of CKD, metabolome analysis confirmed a decrease in AMPK activation in the kidneys despite a high AMP: ATP ratio, suggesting that AMPK did not sense energy depletion. Similar AMPK inactivation was found in heart and skeletal muscle in CKD mice. Several uremic factors were shown to inactivate AMPK invitro and in exvivo preparations of kidney tissue. The specific AMPK activator A-769662, which bypasses the AMP sensing mechanism, ameliorated fibrosis and improved energy status in the kidneys of CKD mice, whereas an AMP analog did not. We further demonstrated that a low-protein diet activated AMPK independent of the AMP sensing mechanism, leading to improvement in energy metabolism and kidney fibrosis. These results suggest that a failure to sense AMP is the key mechanism underlying the vicious cycle of energy depletion and CKD progression and direct AMPK activation may be a novel therapeutic approach in CKD.

Adaptive Consensus Algorithm for Distributed Heat-Electricity Energy Management of an Islanded Microgrid

This paper proposes a novel adaptive consensus algorithm (ACA) for distributed heat-electricity energy management (HEEM) of an islanded microgrid. In order to simultaneously satisfy the heat-electricity energy balance constraints, ACA is implemented with a switch between unified consensus and independent consensus according to the dynamic energy mismatches. The feasible operation region of a combined heat and power (CHP) unit is decomposed into eight searching sub-regions, thus its electricity and heat energy outputs can simultaneously match the incremental cost consensus requirement and the heat-electricity energy balance constraints. Case studies are thoroughly carried out to verify the performance of ACA for distributed HEEM of an islanded microgrid.

Membrane-Modulating Drugs can Affect the Size of Amyloid-\u03b225\u201335 Aggregates in Anionic Membranes

The formation of amyloid-β plaques is one of the hallmarks of Alzheimer’s disease. The presence of an amphiphatic cell membrane can accelerate the formation of amyloid-β aggregates, making it a potential druggable target to delay the progression of Alzheimer’s disease. We have prepared unsaturated anionic membranes made of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1,2-dimyristoyl-sn-glycero-3-phospho-L-serine (DMPS) and added the trans-membrane segment Aβ25–35. Peptide plaques spontaneously form in these membranes at high peptide concentrations of 20 mol%, which show the characteristic cross-β motif (concentrations are relative to the number of membrane lipids and indicate the peptide-to-lipid ratio). We used atomic force microscopy, fluorescence microscopy, x-ray microscopy, x-ray diffraction, UV-vis spectroscopy and Molecular Dynamics (MD) simulations to study three membrane-active molecules which have been speculated to have an effect in Alzheimer’s disease: melatonin, acetylsalicyclic acid (ASA) and curcumin at concentrations of 5 mol% (drug-to-peptide ratio). Melatonin did not change the structural parameters of the membranes and did not impact the size or extent of peptide clusters. While ASA led to a membrane thickening and stiffening, curcumin made membranes softer and thinner. As a result, ASA was found to lead to the formation of larger peptide aggregates, whereas curcumin reduced the volume fraction of cross-β sheets by ~70%. We speculate that the interface between membrane and peptide cluster becomes less favorable in thick and stiff membranes, which favors the formation of larger aggregates, while the corresponding energy mismatch is reduced in soft and thin membranes. Our results present evidence that cross-β sheets of Aβ25–35 in anionic unsaturated lipid membranes can be re-dissolved by changing membrane properties to reduce domain mismatch.

Quantum photonic integrated circuits based on tunable dots and tunable cavities

Quantum photonic integrated circuits hold great potential as a novel class of semiconductor technologies that exploit the evolution of a quantum state of light to manipulate information. Quantum dots encapsulated in photonic crystal structures are promising single-photon sources that can be integrated within these circuits. However, the unavoidable energy mismatch between distant cavities and dots, along with the difficulties in coupling to a waveguide network, has hampered the implementation of circuits manipulating single photons simultaneously generated by remote sources. Here we present a waveguide architecture that combines electromechanical actuation and Stark-tuning to reconfigure the state of distinct cavity-emitter nodes on a chip. The Purcell-enhancement from an electrically controlled exciton coupled to a ridge waveguide is reported. Besides, using this platform, we implement an integrated Hanbury-Twiss and Brown experiment with a source and a splitter on the same chip. These results open new avenues to scale the number of indistinguishable single photons produced on-demand by distinct emitters.

Surface polarization and recombination in organic-inorganic hybrid perovskite solar cells based on photo- and electrically induced negative capacitance studies

Abstract Recent studies have shown that organic-inorganic hybrid perovskites (OIHPs) exhibit unprecedented optoelectronic properties for photovoltaic applications. Complete realizations of photo- and electrically induced surface polarization and recombination are critically important for extensively upgrading solar cell performance. We have explored such effects in a planar solar cell comprising ITO(glass)/PEDOT:PSS/CH3NH3PbI3-xClx/PC60BM/PEI/Ag with a maximum power conversion efficiency (PCE) of 15.4%. A remarkable frequency-dependence of surface polarization was observed for the operating device under illumination (i.e. short-circuit current J s c condition) and at steady state (i.e. open-circuit voltage V o c condition). A sign reversal of the capacitance (i.e. negative capacitance) associated with the surface polarization and recombination was detected at some specific steady states. Based on capacitance-voltage (C-V) spectroscopic measurements and theoretical fittings, they can be understood that, (i) a naturally formed surface depletion region due to energy mismatch can be fully suppressed at a very low fluence and moderate forward bias voltage; (ii) a surface capacitance ( C s ) appears at lower ac-modulation frequencies only; (iii) remarkable trap-assist and band to band surface recombination may play the dominant roles for generating the negative capacitive effect in the CH3NH3PbI3-xClx based photovoltaic system.

Influence of interfaces on the phonon density of states of nanoscale metallic multilayers: Phonon confinement and localization

Isotope-selective $^{57}\mathrm{Fe}$ nuclear resonant inelastic x-ray scattering (NRIXS) measurements and atomic-layer resolved density functional theory (DFT) calculations were used to investigate the effect of interfaces on the vibrational (phonon) density of states (VDOS) of (001)-oriented nanoscale Fe/Ag and Fe/Cr multilayers. The multilayers in the experiment contained isotopically enriched $^{57}\mathrm{Fe}$ monolayers as probe layers located either at the Fe/Ag or Fe/Cr interfaces or in the center of the Fe films. This allows probing of the vibrational dynamics of Fe sites either at the buried interfaces or in the center of the Fe films. For Fe/Ag multilayers, distinct differences were observed experimentally between the Fe-partial VDOS at the interface and in the center. At the Fe/Ag interface, the high-energy longitudinal-acoustic (LA) phonon peak of Fe near $\ensuremath{\sim}35$ meV is suppressed and slightly shifted to lower energy, and the low-energy part of the VDOS below $\ensuremath{\sim}20$ meV is drastically enhanced, as compared to the Fe-specific VDOS in the center Fe layers or in bulk Fe. Similar phenomena are found to a less degree in the Fe/Cr multilayers. The measured Fe-partial VDOS was used to determine the Fe site-selective vibrational thermodynamic properties of the multilayers. Our theoretical findings for the layer-dependent VDOS of the multilayers are in qualitative agreement with the experimental results obtained by NRIXS. For Fe/Ag multilayers, which are characterized by a large atomic mass ratio, the experimental and theoretical results demonstrate phonon confinement in the Fe layers and phonon localization at the Fe/Ag interfaces due to the energy mismatch between Ag and Fe LA phonons. These phenomena are reduced or suppressed in the Fe/Cr multilayers with their about equal atomic masses. Moreover, direction-projected Fe VDOS along the (nearly in-plane) incident x-ray beam was computed in order to address the intrinsic vibrational anisotropy of the Fe/Ag multilayer. We have also performed spin-resolved electronic band structure (DFT) calculations, predicting an enhanced magnetic moment $({\ensuremath{\mu}}_{\mathrm{Fe}}=2.8\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}})$ of the interfacial Fe atoms and a high electron spin polarization (79%) at the Fermi energy for the Fe/Ag interface, as compared to the case of Fe center layers. This is a result of charge transfer from Fe to Ag at the interface. On the contrary, Cr tends to donate electrons to Fe, thus reducing the interfacial Fe moment $({\ensuremath{\mu}}_{\mathrm{Fe}}=1.9\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}})$. This implies strong chemical bonding at the Fe/Ag and Fe/Cr interfaces, affecting the interfacial VDOS.

Combining solvents and surfactants for inkjet printing PEDOT:PSS on P3HT/PCBM in organic solar cells

Abstract A commonly used strategy in the fabrication of organic electronics involves the use of orthogonal solvents, i.e. the alternating use of organic solvents and water for the application of consecutive layers to prevent dissolution of previous layers. This strategy therefore requires the deposition of sequential layers with a large mismatch in surface energy. In case of organic photovoltaics (OPV) a particularly challenging deposition is that of the aqueous Poly(3,4-ethylenedioxythiophene) Polystyrene sulfonate (PEDOT:PSS) on the hydrophobic Poly(3-hexylthiophene-2,5-diyl/Phenyl-C61-butyric acid methyl ester (P3HT/PCBM) layer. The mismatch in surface energy causes dewetting and inhomogeneous layer formation. In inkjet printing individually placed droplets should spread sufficiently far to form a homogeneous closed layer before the solvents in the droplet evaporate. A formulation for the aqueous PEDOT:PSS layer has been developed in which the combination of solvents and surfactants is essential for achieving a homogenous layer on the timescales needed for inkjet printing. Homogenous layers of PEDOT:PSS on P3HT/PCBM were achieved for layer thicknesses from 400 nm to 50 nm. The efficiency of the OPV's fabricated with the new formulation were comparable with reference devices, where evaporated molybdenum oxide (MoOx) was used as a topelectrode. This shows that by the addition of solvents and surfactants a hydrophilic solution can be inkjet printed successfully to form homogenous layers on hydrophobic surfaces and achieve good efficiencies in an inverted organic solar cell.

Controlling Band Alignment in Molecular Junctions: Utilizing Two-Dimensional Transition-Metal Dichalcogenides as Electrodes for Thermoelectric Devices

Although chemical space is vast, there are many instances where chemical modifications make only insignificant changes in the current that passes through a molecule. This insensitivity comes, in part, from the energy mismatch between the molecular resonances and the Fermi level of the electrodes used. Here, we present a strategy to overcome this problem by employing two-dimensional transition-metal dichalcogenides as electrodes. The work function of the electrodes can be tuned across the entire molecular energy range (from the highest occupied molecular orbital to the lowest unoccupied molecular orbital) at a low bias with the appropriate choice of electrode material. We illustrate the effectiveness of this strategy by investigating the thermoelectric properties of the junctions with a model molecular system, as optimal thermoelectric performance requires a delicate balance between the electronic and the heat transport properties. By using van der Waals contacts between the binding groups and the electrod...

Origin of Pronounced Nonlinear Band Gap Behavior in Lead–Tin Hybrid Perovskite Alloys

Mixed lead–tin hybrid perovskite alloy CH3NH3(Pb1–x Sn x )I3 attracted significant attention lately because of the reduction of its band gap below both end compounds, which makes it a promising bottom cell material in all-perovskite tandem solar cells. The effect is a consequence of a strongly nonlinear dependence of the alloy band gap on chemical composition. Here, we use electronic structure calculations at different levels of theory (density functional theory (DFT), hybrid DFT, and QSGW, with and without spin–orbit interactions) to investigate the presently elusive origin of this effect. Contrary to current conflicting studies, our results show that neither spin–orbit interactions nor the composition induced changes of the crystal structure and ordering of atoms contributes to the nonlinearity of the band gap. We find that the strong nonlinearity is primarily a consequence of chemical effects, i.e., the mismatch in energy between s and p atomic orbitals of Pb and Sn, which form the band edges of the al...

High sensitivity of the anomalies in the rotational and ro-vibrational bands of carbon monoxide to small changes in the molecular potential and dipole moment

We compare the intensities of purely rotational and ro-vibrational transitions within the ground electronic state of CO calculated with two dipole moment functions (DMFs) of Li et al. (2015) and four potential energy functions (PEFs), a semi-empirical PEF of Meshkov et al. (doi: https://doi.org//10.5281/zenodo.1198744) and three empirical ones due to Coxon and Hajigeorgiou (2004, 2016, 2017). All these PEFs reproduce the experimental line positions with similar normalized standard deviations (NSDs), and the energy mismatch between the vibrational levels with v⩽5 does not exceed 0.0002 cm−1 among all PEFs. Despite these similarities, we find that the rotational anomalies in the 0-0, 1-1, 2-2, 3-3, 4-4, and 5-0 bands shown in Figs. 3 and 4 of Medvedev et al. (2017) change their intensities by a factor of 2 to 250 among the above PEFs at a given DMF. Both the positions and intensities of the anomalies change between two DMFs at a given PEF.

Multifunctional Dithiadiazolyl Radicals: Fluorescence, Electroluminescence, and Photoconducting Behavior in Pyren-1′-yl-dithiadiazolyl

The pyren-1'-yl-functionalized dithiadiazolyl (DTDA) radical, C16H9CNSSN (1), is monomeric in solution and exhibits fluorescence in the deep-blue region of the visible spectrum (440 nm) upon excitation at 241 nm. The salt [1][GaCl4] exhibits similar emission, reflecting the largely spectator nature of the radical in the fluorescence process, although the presence of the radical leads to a modest quenching of emission (ΦF = 98% for 1+ and 50% for 1) through enhancement of non-radiative decay processes. Time-dependent density functional theory studies on 1 coupled with the similar emission profiles of both 1+ and 1 are consistent with the initial excitation being of predominantly pyrene π-π* character. Spectroscopic studies indicate stabilization of the excited state in polar media, with the fluorescence lifetime for 1 (τ = 5 ns) indicative of a short-lived excited state. Comparative studies between the energies of the frontier orbitals of pyren-1'-yl nitronyl nitroxide (2, which is not fluorescent) and 1 reveal that the energy mismatch and poor spatial overlap between the DTDA radical SOMO and the pyrene π manifold in 1 efficiently inhibit the non-radiative electron-electron exchange relaxation pathway previously described for 2. Solid-state films of both 1 and [1][GaCl4] exhibit broad emission bands at 509 and 545 nm, respectively. Incorporation of 1 within a host matrix for OLED fabrication revealed electroluminescence, with CIE coordinates of (0.205, 0.280) corresponding to a sky-blue emission. The brightness of the device reached 1934 cd/m2 at an applied voltage of 16 V. The crystal structure of 1 reveals a distorted π-stacked motif with almost regular distances between the pyrene rings but alternating long-short contacts between DTDA radicals. Solid state measurements on a thin film of 1 reveal emission occurs at shorter wavelengths (375 nm) whereas conductivity measurements on a single crystal of 1 show a photoconducting response at longer wavelength excitation (455 nm).

Mixed intermediate effect on mechanical and rheological performances in Zn[sbnd]Mg silicate glasses

In contrast to the mixed alkali or mixed alkaline earth effect, the mixed intermediate effect has received little attention in glass community. Here, we focus on the mixed intermediate effects, i.e. mixed MgZn effects, by partial substitution of MgO for ZnO in sodium silicate glassy series. Opposite to the previously reported “mixed alkaline earth effects”, here the compositional dependences of microhardness and isokom temperature following the gradual substitution of Mg by Zn show a positive deviation from the linear tendency between the two end-members, which is maybe due to the competition between cationic potential energy mismatch and network polymerization. Through the structural identification by Raman scattering technique, we give a microscopic explanation for the observed mixed MgZn effects. Finally, we identified the mixed MgZn effects on viscosity and configurational entropy, which indicates that the Zn and Mg have a similar dynamic role at glass transition temperature but play a more different role at lower viscosity.

Scandium Terminal Imido Chemistry.

Research into transition metal complexes bearing multiply bonded main-group ligands has developed into a thriving and fruitful field over the past half century. These complexes, featuring terminal M═E/M≡E (M = transition metal; E = main-group element) multiple bonds, exhibit unique structural properties as well as rich reactivity, which render them attractive targets for inorganic/organometallic chemists as well as indispensable tools for organic/catalytic chemists. This fact has been highlighted by their widespread applications in organic synthesis, for example, as olefin metathesis catalysts. In the ongoing renaissance of transition metal-ligand multiple-bonding chemistry, there have been reports of M═E/M≡E interactions for the majority of the metallic elements of the periodic table, even some actinide metals. In stark contrast, the largest subgroup of the periodic table, rare-earth metals (Ln = Sc, Y, and lanthanides), have been excluded from this upsurge. Indeed, the synthesis of terminal Ln═E/Ln≡E multiple-bonding species lagged behind that of the transition metal and actinide congeners for decades. Although these species had been pursued since the discovery of a rare-earth metal bridging imide in 1991, such a terminal (nonpincer/bridging hapticities) Ln═E/Ln≡E bond species was not obtained until 2010. The scarcity is mainly attributed to the energy mismatch between the frontier orbitals of the metal and the ligand atoms. This renders the putative terminal Ln═E/Ln≡E bonds extremely reactive, thus resulting in the formation of aggregates and/or reaction with the ligand/environment, quenching the multiple-bond character. In 2010, the stalemate was broken by the isolation and structural characterization of the first rare-earth metal terminal imide-a scandium terminal imide-by our group. The double-bond character of the Sc═N bond was unequivocally confirmed by single-crystal X-ray diffraction. Theoretical investigations revealed the presence of two p-d π bonds between the scandium ion and the nitrogen atom of the imido ligand and showed that the dianionic [NR]2- imido ligand acts as a 2σ,4π electron donor. Subsequent studies of the scandium terminal imides revealed highly versatile and intriguing reactivity of the Sc═N bond. This included cycloaddition toward various unsaturated bonds, C-H/Si-H/B-H bond activations and catalytic hydrosilylation, dehydrofluorination of fluoro-substituted benzenes/alkanes, CO2 and H2 activations, activation of elemental selenium, coordination with other transition metal halides, etc. Since our initial success in 2010, and with contributions from us and across the community, this young, vibrant research field has rapidly flourished into one of the most active frontiers of rare-earth metal chemistry. The prospect of extending Ln═N chemistry to other rare-earth metals and/or different metal oxidation states, as well as exploiting their stoichiometric and catalytic reactivities, continues to attract research effort. Herein we present an account of our investigations into scandium terminal imido chemistry as a timely summary, in the hope that our studies will be of interest to this readership.

Thermal energy storage (TES) technology for active and passive cooling in buildings: A Review

Thermal energy storage (TES) system is one of the outstanding technologies available contributes for achieving sustainable energy demand. The energy storage system has been proven capable of narrowing down the energy mismatch between energy supply and demand. The thermal energy storage (TES) - buildings integration is expected to minimize the energy demand shortage and also offers for better energy management in building sector. This paper presents a state of art of the active and passive TES technologies integrated in the building sector. The integration method, advantages and disadvantages of both techniques were discussed. The TES for low energy building is inevitably needed. This study prescribes that the integration of TES system for both active and passive cooling techniques are proven to be beneficial towards a better energy management in buildings.

Effects of Buffer Layer Treatments on the Characteristics and Performances of OLEDs

The authors demonstrated the performance of Organic Light Emitting Diodes (OLEDs) with hexylphosphonic acid (PA) or UV-ozone treatment on their molybdenum trioxide (MoO3) anode buffer layers. The OLEDs with a PA treated (5 mM @1 h) MoO3 layer have lower turn-on voltage and low current efficiency roll-off under high operating current. The hole-only device (ITO/MoO3 with PA or UV-ozone treatment/NPB/Al) was fabricated to calculate the active energy via temperature dependent I-V measurement. When the devices were operated at high temperatures, the activation energy of the UV-ozone treated, and untreated hole-only devices became nonlinear. However, the activation energy of the PA treated devices had a more stable performance at high temperatures. The interfacial resistance of the untreated hole-only devices and the PA and UV-ozone treated devices were calculated by Admittance Spectroscopy (AS) to be 204.5, 363, and 450 Ω. These results indicated that the PA treated devices reduced the activation energy, surface energy mismatch, and interface resistance to enhance the efficiency of carrier injection, which in turn lowers the turn on voltage. Moreover, PA treatment produces a long carbon chain and smooths the morphology of MoO3 to prevent roll-off phenomenon of OLEDs under high operating current.