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The design of atomically dispersed single atom catalysts (SACs) must consider high metal-atom loading amount, effective confinement, and strong interactions with matrix, which can maximize their catalytic performance. Here reported is a promising method to synthesize SACs on highly conductive multiwall carbon nanotube (MWCNT) supports using pulsed laser confinement (PLC) process in liquid. Atomic cobalt (Co) and phosphorus (P) with a high loading density are homogeneously incorporated on the outer wall of the MWCNT (Co-P SAC MWCNT). Density functional theory (DFT) calculations in combination with systematic control experiments found that the incorporated Co and P adatoms act as an adsorption energy optimizer and a charge transfer promoter, respectively. Hence, favorable kinetics and thermodynamics in Co-P SAC MWCNT can be simultaneously achieved for water oxidation resulting in a superior catalytic performance than the benchmark RuO2 catalyst. Crucially, total processing time for assembling Co-P SAC MWCNT via PLC process is less than 60 min, shedding light on the promising practical applications of our SAC design strategy.

Metal–fluoride possesses a high potential as new high-performance water oxidation catalysts due to a highly polarized electronic configuration. However, low conductivity, related to high iconicity ...

It has recently been demonstrated that the OER activity of transition metal sulfides (TMSs) could be enhanced by the introduction of a thin amorphous layer on a pristine surface. We report here a novel strategy to enhance the OER by developing cobalt nickel sulfide (CoxNi1−xS2, CNS) with a high density of crystalline and amorphous phase boundaries. Electrochemical activation (ECA) can partially amorphize hollow CNS nanoparticles derived from surface-selective sulfidation. The ECA-treated CNS (ECA-CNS) electrocatalyst, which is comprised of CNS nanodots separated by thin amorphous layers, shows high densities of crystalline and amorphous phase boundaries. This catalyst shows superior OER catalytic performance with a current density of 10 mA cm−2 at a small overpotential of 290 mV, a low Tafel slope of 46 mV dec−1, a high mass activity of 217 A g−1, a high turnover frequency of 0.21 s−1 at an overpotential of 340 mV, and excellent stability in alkaline media.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The electrocatalytic performance of transition metal sulfide (TMS)–graphene composites has been simply regarded as the results of high conductivity and the large surface/volume ratio. However, unavoidable factors such as degree of oxidation of TMSs have been hardly considered for the origin of this catalytic activity of TMS–graphene composites. To accomplish the reliable application of TMS-based electrocatalytic materials, a clear understanding of the thermodynamic stability of TMS and effects of oxidation on catalytic activity is necessary. In addition, the mechanism of charge transfer at the TMS–graphene interface must be studied in depth to properly design composite materials. Herein, we report a comprehensive study of the physical chemistry at the junction of a Co1–xNixS2–graphene composite, which is a prototype designed to unravel the mechanisms of charge transfer between TMS and graphene. Specifically, the thermodynamic stability and the effects of oxidation of TMSs during the oxygen evolution react...

Sr substituted BaTiO 3 (BST) nanopowders were prepared using oxalate co-precipitation methods. During synthesis, oxygen was applied to the oxalate solution in order to control the oxidation states of Ti. Control of pH in the solution results in different crystalline phases of the powders after calcination; pure perovskite BST was obtained in the powder prepared at pH 3 solution, while perovskite BaTiO 3 (BTO) and impurities were observed in powders prepared at pH 1 solution. Phase transformation from amorphous to crystalline BST during heat treatment was discussed by different analysis technique. Also, morphology and elemental distribution of the pure BST was investigated.

Given the abundance of water on the surface of the Earth, water splitting using seawater may be an effective solution to the future energy crisis. However, oxygen evolution reaction (OER) electrocatalysts require several specific characteristics to be used in seawater electrolysis, such as high catalytic activity, selectivity, and resistivity against chlorine corrosion. This paper reports that sulfur incorporation into nickel–iron layered double hydroxide (NiFe-LDH-S) can fulfill the abovementioned requirements for seawater oxidation. Sulfidation was performed on NiFe-LDH nanosheets homogeneously grown on a porous carbon scaffold via a facile chemical vapor deposition (CVD) process. The best NiFe-LDH-S sample demonstrated excellent catalytic activity with a high corrosion resistance for seawater oxidation.

Titanium dioxide (TiO2) with exposed (001) facets (TiO2(001)) has attractive photocatalytic properties. However, the high recombination rate of the photo-excited charge carriers on this surface often limits its application. Here, we report that a few-layered 1T-MoS2 coating on TiO2(001) nanosheets (abbreviated as MST) can be a promising candidate that overcomes some of the challenges of TiO2(001). Computational and experimental results demonstrate that MST as a photocatalyst exhibits a significantly low-charge recombination rate as well as excellent long-term durability. The synthesized MST 2D nanocomposites show a 31.9% increase in photocatalytic activity for hydrogen (H2) production relative to the counterpart TiO2(001). MST offers a new route for further improvement of the photocatalytic activity of TiO2 with exposed high energy facets.

Graphene oxide quantum dots (GOQDs) are usually prepared using expensive carbon precursors such as carbon nanotubes (CNT) or graphene under the strong acidic condition, which requires an additional purifying process. Here, we first develop a facile pulsed laser ablation in liquid (PLAL) technique for preparing GOQDs using earth-abundant and low-cost coal as a precursor. Only ethanol and coal are used to produce GOQDs with excellent optical properties. The prepared GOQDs exhibit excellent optoelectronic properties which can be successfully utilized in bioimaging applications.

Transition–metal-doped carbon-based electrocatalysts have attracted attention as alternatives to noble metal electrocatalysts (e.g. IrO2 and RuO2) for oxygen evolution reaction (OER) because they are inexpensive and highly efficient. However, their poor catalytic activity and time-consuming synthesis remain a challenge. Herein, we report a facile and green technique using pulsed laser ablation for preparing Ni-doped multi-walled carbon nanotubes (Ni-MWCNTs) as OER catalysts. Ni-MWCNTs exhibit high surface area, oxygen-rich functional groups (e.g., hydroxyl and carboxyl), and successful doping of Ni in the carbon framework. The as-prepared Ni-MWCNTs exhibited excellent OER catalytic performance, with an overpotential of 320 mV at the current density of 10 mA cm−2 in an alkaline medium, which is lower than that of the commercial RuO2 catalyst. Furthermore, Ni-MWCNTs displayed the initial electrocatalytic activity after 10-h stability tests, demonstrating good electrochemical durability. We believe that this work provides a simple protocol for fabricating heteroatom-doped carbon nanotubes as high-performance OER electrocatalysts.

Diabetes is a chronic disease, which can give serious damages to the human organs that affect life expectancy. Such a life-threatening diabetes is diagnosed by systematic monitoring of blood glucose levels; thus, accurate detection of glucose within a specified target range becomes more important for glucose sensor to provide detailed information relating with diabetes, which can result in reliable decision for diabetes treatment. Thanks to many efforts developing the reliable glucose sensors, electrochemical performance of the sensor including sensitivity and selectivity in response to glucose is gradually improved. Herein, we developed spinel type NiCo2O4 (NCO) nanostructure with excellent sensitivity, selectivity and chemical robustness for glucose detection. NCO was prepared by conversion of NiCo-layered double hydroxide (NCH) at comparatively low temperature, which is synthesized by simple and facile chemical bath method and following post-heat treatment of the NCH. Electrochemical sensitivity, selectivity and detection time of the NCO in response to glucose was investigated, compared to those of the NCH. Also, long-term stability of the NCO on repetitive glucose detection was evaluated. Based on the systematic analysis on materials properties and electrochemical performance of the NCO, possible mechanism of the glucose oxidation, which significantly improves electrochemical performance of the NCO, is discussed.

BDTI (backside deep trench isolation) structures parallel to a depth direction of a Si wafer may generate a stress concentration under the warpage caused by a mechanical loading on the wafer during handling or moving. Our work aims to provide a better understanding for minimizing a stress concentration effectively at the BDTI. To address shape factors of the BDTIs with a void, we change ? (open width), dBDTI (distance between Si-surface and BDTI bottom), ? (angle between Si-surface and sidewall of BDTI), and t1st HfOx (thickness of 1st HfOx film on silicon surface). Among the geometrical factors changed in this work, our simulation predicts that the opening length and the thickness of 1st HfOx films are key factors to control a maximum stress concentration at a 1st HfOx film below an oxide bottom. Comparing only a final geometry of various BDTIs, it is consequently very effective to decrease the interface curvature between an HfOx and oxide films in order to get low stress structures.

Crystal structures and hopping motions of cobalt manganese spinel oxides across a wide composition range (CoxMn3−xO4 (CMO), 0.9 ≤ x ≤ 2.7) are investigated in order to clarify the corresponding mechanisms of electrical behaviors as negative temperature coefficient thermistors. Based on the diffraction measurements, a tetragonal to cubic spinel transition are observed mostly with increasing Co content. Hopping distance for a series of CMO are calculated by the variable range hopping mechanism, which is changed as a function of composition, resulting to the observed unique electrical properties. According to the electrical and structural analysis, the electrical properties of CMO compounds with different Co contents majorly determined by tetragonal to cubic phase transition, cation distribution, and hopping distance. In addition, the formation of secondary phase (i.e., CoO) and another CMO phase may also significantly affect the electrical properties.

Transition metal layered double hydroxides (LDHs) have received much attention as high-performance oxygen evolution reaction (OER) catalysts due to their large number of active sites with favorable adsorption/desorption energies for intermittent reactants. However, the relatively sluggish charge transfer kinetics of transition metal LDHs due to their intrinsically low conductivity often hinders their use in practical applications as high-performance water oxidation catalysts. Here, we disclose a novel strategy of metalloid incorporation into transition metal LDHs, allowing us to simultaneously optimize surface electronic configuration and charge transfer between adsorbed reactants and catalyst surface. Importantly, incorporated metalloid can enhance the density of states (DOS) near the Fermi level and alter the nature of the chemical bonds in the catalytically active atoms, resulting in fast reaction kinetics. Thus, metalloid incorporation into transition metal LDHs can substantially improve the overall reaction kinetics and thermodynamics for water oxidation due to a large number of active sites and high conductivity, boosting OER performance of transition metal LDHs. The metalloid-incorporated transition metal LDHs far outperform their counterpart transition metal LDHs and even the noble metal catalyst RuO2.

The crystallization of lead zirconate titanate (PZT) thin films was evaluated on two different platinum-coated Si substrates. One substrate consisted of a Pt coating on a Ti adhesion layer, whereas the other consisted of a Pt coating on a TiO2 adhesion layer. The Pt deposited on TiO2 exhibited a higher degree of preferred orientation than the Pt deposited on Ti (as measured by the Full Width at Half Maximum of the 111 peak about the sample normal). PZT thin films with a nominal Zr/Ti ratio of 52/48 were deposited on the substrates using the inverted mixing order (IMO) route. Phase and texture evolution of the thin films were monitored during crystallization using in situ X-ray diffraction at a synchrotron source. The intensity of the Pt3Pb phase indicated that deposition on a highly oriented Pt/TiO2 substrate resulted in less diffusion of Pb into the substrate relative to films deposited on Pt/Ti. There was also no evidence of the pyrochlore phase influencing texture evolution. The results suggest that PZT nucleates directly on Pt, which explains the observation of a more highly oriented 111 texture of PZT on the Pt/TiO2 substrate than on the Pt/Ti substrate.

High-performance oxygen evolution reaction (OER) electrocatalysts are needed to produce hydrogen for energy generation through a carbon-free route. In this work, the solution combustion synthesis (SCS) method was employed to synthesize mixed phases of Co- and Mn-based oxides, and the relationships between the crystalline structure and the catalytic properties in the mixed phases were established. The mixed phases of Co- and Mn-based oxides shows promising OER properties, such as acceptable overpotential (450 mV for 10 mA∙cm&minus, 2) and Tafel slope (35.8 mV∙dec&minus, 1), highlighting the use of the mixed phases of Co- and Mn-based oxides as a new efficient catalysts for water splitting. Electronic structure of the mixed phases of Co- and Mn based oxides is studied in detail to give insight for the origin of high catalytic activities. In addition, excellent long-term stability for OER in alkaline media is achieved for the mixed phase of Co- and Mn based oxides.

The crystallization behavior of solution-derived lead zirconate titanate (PZT) thin films in different atmospheric environments was studied using in situ X-ray diffraction. The stability of the transient intermetallic Pt3Pb phase and perovskite PZT is dependent on oxygen partial pressure during crystallization. Based on the relationship between oxygen partial pressure and the resultant phase stability of intermediate phases, a new route to produce PZT thin films was developed. The new route involves switching atmospheres during crystallization and is shown to mitigate the formation of the transient intermetallic Pt3Pb phase and to promote the perovskite PZT phase. The route evidences a new and significant variable controlling film synthesis and film microstructure.

International audience; Hopping motions in cobalt manganese spinel oxides with high cobalt concentration (CoxMn3−xO4, 2.3 ≤ x ≤ 2.7) are investigated in order to clarify the origin of unusual electrical behaviors as negative temperature coefficient (NTC) thermistors. Based on the resistance versus temperature (R−T) characteristics, hopping conduction mechanisms in MCO compounds (x = 2.3 and 2.5) are attributed to variable range hopping (VRH) motion with a parabolic distribution of the density of states (DOS) near the Fermi level. However, when Co content increases up to 2.7, transition in the hopping motion occurs from VRH to the nearest neighboring hopping (NNH) motion, which can be responsible for a huge increase of the resistance accompanied by decrease of the factor of thermal sensitivity (B value) in MCO compounds (x = 2.7). Also, hopping distance and activation energies for MCO (x = 2.3 and 2.5) compounds following VRH conduction are calculated as a function of temperature, indicating that higher B value observed in MCO (x = 2.5) compound is due to the larger hopping distance compared to that of MCO (x = 2.3) compound.

The development of electrochemical devices for renewable energy depends to a large extent on fundamental improvements in catalysts for oxygen evolution reactions (OERs). OER activity of transition metal sulfides (TMSs) can be improved by compositing with highly conductive supports possessing a high surface-to-volume ratio, such as reduced graphene oxide (rGO). Herein we report on the relationship between synthetic conditions and the OER catalytic properties of TMSs and rGO (TMS–rGO) hybrids. Starting materials, reaction temperature and reaction time were controlled to synergistically boost the OER catalytic activity of TMS–rGO hybrids. Our results showed that (i) compared with sulfides, hydroxides are favourable as starting materials to produce the desired TMS–rGO hybrid nanostructure and (ii) high reaction temperatures and longer reaction times can increase physico-chemical interaction between TMSs and rGO supports, resulting in highly efficient OER catalytic activity.

Pulsed laser ablation in a liquid phase was successfully employed to synthesize a barium molybdate (BaMoO4) nanocolloidal suspension. The nanocolloidal suspension was composed of well-dispersed and horizontally assembled BaMoO4 aggregates. The BaMoO4 aggregates showed predominantly elliptically shaped nanorods with sizes between 100 and 200 nm. The preferential elliptical growth was rationalized from the viewpoint of the intrinsic structure of BaMoO4. The optical properties of the prepared BaMoO4 colloidal nanoparticles were investigated using Raman spectroscopy, UV–vis spectroscopy and photoluminescence (PL) spectrophotometry. The optical band gap was estimated by Tauc and Menth’s law. The PL emission feature was decomposed into several individual Gaussian components, which could be interpreted by a Jahn–Teller splitting effect on the [MoO4]2- tetrahedron of the BaMoO4 colloidal nanoparticles.

Epitaxial Ba2FeMoO6 thin films were grown via pulsed laser deposition under low oxygen pressure and their structural, chemical, and magnetic properties were examined, focusing on the effects of oxygen pressure. The chemical disorder, off-stoichiometry in B site cations (Fe and Mo) increased with increasing oxygen pressure and thus magnetic properties were degraded. Interestingly, in contrast, negative magneto-resistance, which is the characteristics of this double perovskite material, was enhanced with increasing oxygen pressure. It is believed that phase segregation of highly disordered thin films is responsible for the increased magneto-resistance of thin films grown at high oxygen pressure. The anomalous Hall effect, which behaves hole-like, was also observed due to spin-polarized itinerant electrons under low magnetic field below 1 T and the ordinary electron-like Hall effect was dominant at higher magnetic fields.

The authors report a novel synthetic route for Ho3+/Yb3+ codoped calcium molybdate (CaMoO4) nanoparticles by pulsed laser ablation in ethanol. Well-dispersed Ho3+/Yb3+ codoped CaMoO4 nanocolloid was prepared without any surfactant. Crystallographic information, microstructure, and the upconversion (UC) luminescent properties of the nanocolloid were investigated. Under the excitation at 980 nm, Ho3+/Yb3+ codoped CaMoO4 nanocolloid exhibited strong yellow emission visible to the naked eyes, which is the combination of green emission near 542 nm and strong red emission around 656 nm. Based on the pump power dependence, UC mechanism of Ho3+/Yb3+ codoped CaMoO4 nanocolloid was discussed in detail.

Understanding interfaces between dissimilar materials is crucial to the development of modern technologies, for example, semiconductor–dielectric and thermoelectric–semiconductor interfaces in emerging electronic devices. However, the structural characterization of buried interfaces is challenging because many measurement techniques are surface sensitive by design. When interested in interface evolution during synthesis, the experimental challenges multiply and often necessitate in situ techniques. For solution-derived lead zirconate titanate (PZT) ferroelectric thin films, the evolution of buried interfaces during synthesis (including dielectric–metal and metal–metal) is thought to dramatically influence the resultant dielectric and ferroelectric properties. In the present work, multiple experimental and computational methods are combined to characterize interface evolution during synthesis of ferroelectric PZT films on platinized Si wafers—including in situ X-ray diffraction during thermal treatment, aberration-corrected scanning transmission electron microscopy of samples quenched from various synthesis states, and calculations using density functional theory. Substantial interactions at buried interfaces in the PZT/Pt/Ti/SiO x /Si heterostructure are observed and discussed relative to their role(s) in the synthesis process. The results prove that perovskite PZT nucleates directly from the platinum (111)-oriented bottom electrode and reveal the roles of Pb and O diffusion and intermetallic Pt3Pb and Pt3Ti phases.

An in situ measurement technique is developed and presented, which utilizes x-rays from a synchrotron source with a two-dimensional detector to measure thin film microstructural and crystallographic evolution during heating. A demonstration experiment is also shown wherein the measured diffraction patterns are used to describe phase and texture evolution during heating and crystallization of solution-derived thin films. The diffraction images are measured sequentially while heating the thin film with an infrared lamp. Data reduction methodologies and representations are also outlined to extract phase and texture information from the diffraction images as a function of time and temperature. These techniques and data reduction methods are demonstrated during crystallization of solution-derived lead zirconate titanate ferroelectric thin films heated at a rate of 30 °C/min and using an acquisition time of 8 s. During heating and crystallization, a PtxPb type phase was not observed. A pyrochlore phase was obse...

The polycrystalline Ho3+/Tm3+/Yb3+ co-doped CaMoO4 phosphors were successfully synthesized by complex citrate-gel method. Under the laser excitation of 980 nm, Ho3+/Tm3+/Yb3+ co-doped CaMoO4 shows the bright white upconversion (UC) emission visible to the naked eye, which is composed of a blue emission at 475 nm from Tm3+, and green and red emissions at 543 nm and 651 nm from Ho3+. The coordinates of Ho3+/Tm3+/Yb3+ co-doped CaMoO4 in the commission international de'eclairage (CIE) chromaticity diagram can be controlled from a cool to a warm white color depending on the Tm3+ and Ho3+ concentrations. In Ho3+/Tm3+/Yb3+ co-doped CaMoO4, the UC luminescent properties on Tm3+ and Ho3+ concentrations and mechanism based on laser pump power were discussed in detail.

Ce 3+ -doped nanocrystalline terbium aluminum garnet (Tb 3 Al 5 O 12 :Ce 3+ , TAG:Ce 3+ ) phosphors were successfully synthesized in low temperature by nitrate-citrate gel combustion method using microwave irradiation as a heating source. The pure TAG phase was obtained after calcining at 800°C for 6 h. The prepared nanocrystalline phosphors showed a broad peak at 551 nm, and the maximum doping concentration of Ce 3+ for the highest emission intensity was 0.8 mol % at 551 nm. The temperature dependence on photoluminescence properties of the prepared TAG:Ce 3+ phosphors was investigated from 25 to 275°C, and the activation energies (ΔE) for thermal quenching was determined by Arrhenius fitting. The experimental results clearly indicate that prepared nanocryatalline TAG: Ce 3+ has great potentials for a down-conversion yellow phosphor in white light emitting diodes.