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At least 1,045 records · Page 58

A divergent synthetic route to functional copolymer libraries via modular polymers

High-throughput polymer synthesis enables rapid exploration of chemical space but remains limited by batch-to-batch inconsistencies that can obscure structure–property relationship trends. To address this challenge, we developed a synthetic approach to produce multifunctional copolymers using post-polymerization modification of activated ester modular polymers with commercially available amines. Easily derivitized parent polymers—poly(tetrafluorophenyl acrylate) and poly(tetrafluorophenyl styrene sulfonate)—were synthesized by RAFT polymerization to yield single polymer batches containing highly reactive tetrafluorophenyl esters or sulfonate esters on each repeat unit. Tuning post-polymerization modification reaction conditions enabled the addition of sub-stoichiometric amounts of amines (relative to the repeat unit) to yield partially functionalized intermediates that could then be further derivatized. Reaction monitoring by 19 F NMR spectroscopy confirmed good control over these sequential post-polymerization modifications. This synthetic route produced a variety of copolymers with defined comonomer ratios while preserving the underlying polymer structure (degree of polymerization, dispersity, tacticity) for both the acrylate and styrene sulfonate backbones. We further applied this approach in a divergent manner to create a small library of structurally distinct copolymers from a single parent batch in three synthetic steps. This modular, divergent synthesis demonstrates a general route to structurally consistent copolymer libraries that enable systematic studies of structure–property relationships and can accelerate functional materials discovery.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Morphology-driven oxygen evolution performance of NiO x nanostructures and implications for hole transport in perovskite solar cells

Morphology-controlled nanostructures provide an effective strategy to modulate both oxygen evolution reaction (OER) activity and photovoltaic performance in perovskite solar cells (PSCs). However, achieving low OER overpotentials and high power conversion efficiency (PCE) simultaneously through morphology engineering remains challenging. In this work, nickel oxide (NiO x ) nanostructures with spindle-like (NiO x -NS) and plate-like (NiO x -NP) morphologies were synthesized and evaluated as bi-functional OER catalysts and hole transport layers (HTLs) in inverted PSCs. Structural and thermal analyses reveal that NiO x -NS crystallizes into a cubic phase at a lower temperature (300 °C), whereas NiO x -NP requires higher calcination temperatures, reflecting differences in precursor microstructure. Electrochemical measurements indicate that NiO x -NS calcined at 300 °C delivers the lowest OER overpotential (395 mV at 10 mA cm −2 ), outperforming NiO x -NP calcined at 400 °C (565 mV) and 500 °C (474 mV). This enhanced activity is ascribed to favorable surface strain, increased defect density, and advantageous facet exposure. When used as HTLs, NiO x -NS also delivers the highest PCE (13.25%) among all tested devices, exceeding those based on NiO x -NP and commercial NiO x , owing to improved hole extraction and interfacial contact. Overall, this study highlights the importance of morphology control and thermal processing in tailoring NiO x for multifunctional nanomaterials in electrocatalytic and photovoltaic applications.

36 MATERIALS SCIENCE↗

Efficiently recyclable magnetic core-shell photocatalyst for photocatalytic oxidation of chlorophenol in water

Multifunctional Fe{sub 3}O{sub 4}-TiO{sub 2} core-shell submicron particles were fabricated by a simple surface modification process that induces the magnetic submicron particles to be coated with a TiO{sub 2} shell. As characterized by field emission scanning electron microscopy, (FESEM), the as-synthesized Fe{sub 3}O{sub 4}-TiO{sub 2} particles exhibit a narrow size distribution with a typical size of 248 {+-} 19 nm and 8 nm in shell thickness. Magnetic measurement indicates that the as-synthesized Fe{sub 3}O{sub 4}-TiO{sub 2} core-shell particles are superparamagnetic at room temperature. Photocatalytic experiment is demonstrated by utilizing the oxidation reaction of 2,4,6-trichlorophenol (2,4,6-TCP) with the photofunctional magnetic nanoparticles.

36 MATERIALS SCIENCE↗

Bright upconversion luminescence and increased Tc in CaBi{sub 2}Ta{sub 2}O{sub 9}:Er high temperature piezoelectric ceramics

Er{sup 3+} doped CaBi{sub 2}Ta{sub 2}O{sub 9} (CBT) bismuth layered-structure high temperature piezoelectric ceramics were synthesized by the traditional solid state method. The upconversion (UC) emission properties of Er{sup 3+} doped CBT ceramics were investigated as a function of Er{sup 3+} concentration and incident pump power. A bright green upconverted emission was obtained under excitation 980 nm at room temperature. The observed strong green and weak red emission bands corresponded to the transitions from {sup 4}S{sub 3/2} and {sup 4}F{sub 9/2} to {sup 4}I{sub 15/2}, respectively. The dependence of UC emission intensity on pumping power indicated that a three-photon process was involved in UC emissions. Studies of dielectric with temperature have also been carried out. Introduction of Er increased the Curie temperature of CBT, thus, making this ceramic suitable for sensor applications at higher temperatures. Because of its strong up-converted emission and increased Tc, the multifunctional high temperature piezoelectric ceramic may be useful in high temperature sensor, fluorescence thermometry, and optical-electro integration applications.

36 MATERIALS SCIENCE↗

Upconversion luminescence, ferroelectrics and piezoelectrics of Er Doped SrBi{sub 4}Ti{sub 4}O{sub 15}

Er{sup 3+} doped SrBi{sub 4}Ti{sub 4}O{sub 15} (SBT) bismuth layered-structure ferroelectric ceramics were synthesized by the traditional solid-state method, and their upconversion photoluminescent (UC) properties were investigated as a function of Er{sup 3+} concentration and incident pump power. Green (555 nm) and red (670 nm) emission bands were obtained under 980 nm excitation at room temperature, which corresponded to the radiative transitions from {sup 4}S{sub 3/2}, and {sup 4}F{sub 9/2} to {sup 4}I{sub 15/2}, respectively. The emission color of the samples could be changed with moderating the doping concentrations. The dependence of UC intensity on pumping power indicated a two-photon emission process. Studies on dielectric properties indicated that the introduction of Er increased the ferroelectric-paraelectric phase transition temperature (Tc) of SBT, thus making this ceramic suitable for piezoelectric sensor applications at higher temperatures. Piezoelectric measurement showed that the doped SBT had a relative higher piezoelectric constant d{sub 33} compared with the non-doped ceramics. The thermal annealing behaviors of the doped sample revealed a stable piezoelectric property. The doped SBT showed bright UC emission while simultaneously having increased Tc and d{sub 33}. As a multifunctional material, Er doped SBT ferroelectric oxide showed great potential in application of sensor, future optical-electro integration and coupling devices.

36 MATERIALS SCIENCE↗

Interplay between chemical state, electric properties, and ferromagnetism in Fe-doped ZnO films

Valence state of Fe ions plays an important role in the physical properties of Fe doped ZnO films. Here, a series of Zn{sub 1-x}Fe{sub x}O films with different Fe concentrations (x = 0, 2.3, 5.4, 7.1, and 9.3 at. %) were prepared to investigate their structural, piezoelectric, ferroelectric, bipolar resistive switching properties, and electrical-control of ferromagnetism at room temperature. The structure characterizations indicate that the chemical state of Fe ions substituting Zn{sup 2+} site changes from Fe{sup 3+} to Fe{sup 2+} with the increase of Fe dopant concentration. We found enhanced piezoelectric and ferroelectric properties in Zn{sub 0.977}Fe{sub 0.023}O films with more Fe{sup 3+} due to the smaller Fe{sup 3+} ionic size in comparison with Zn{sup 2+} while the increase of Fe{sup 2+} concentration by a larger amount of Fe dopant results in the worse ferroelectric and piezoelectric performance. All Pt/Zn{sub 1-x}Fe{sub x}O/Pt devices show bipolar resistive switching properties. Especially, devices with lower Fe dopant concentration exhibit better endurance properties due to their higher crystalline quality. The variation of oxygen vacancies during resistive switching provides an opportunity to tune ferromagnetism of Fe-doped ZnO films, giving rise to the integration of charge and spin into a simple Pt/Zn{sub 1-x}Fe{sub x}O/Pt devices. The multifunctional properties of Fe-doped ZnO films are promising for communication systems and information storage devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Fabricating functionally graded films with designed gradient profiles using pulsed laser deposition

A novel picosecond-laser pulsed laser deposition method has been developed for fabricating functionally graded films with pre-designed gradient profiles. Theoretically, the developed method is capable of precisely fabricating films with any thicknesses and any gradient profiles by controlling the laser beam powers for the two different targets based on the film composition profiles. As an implementation example, we have successfully constructed functionally graded diamond-like carbon films with six different gradient profiles: linear, quadratic, cubic, square root, cubic root, and sinusoidal. Energy dispersive X-ray spectroscopy is employed for investigating the chemical composition along the thickness of the film, and the deposition profile and thickness errors are found to be less than 3% and 1.04%, respectively. To the best of the authors' knowledge, this is the first method for fabricating films with designed gradient profiles and has huge potential in many areas of coatings and films, including multifunctional optical films. We believe that this method is not only limited to the example considered in this study, but also can be applied to all material combinations as long as they can be deposited using the pulsed laser deposition technique.

36 MATERIALS SCIENCE↗

Phase behaviors of supramolecular graft copolymers with reversible bonding

Phase behaviors of supramolecular graft copolymers with reversible bonding interactions were examined by the random-phase approximation and real-space implemented self-consistent field theory. The studied supramolecular graft copolymers consist of two different types of mutually incompatible yet reactive homopolymers, where one homopolymer (backbone) possesses multifunctional groups that allow second homopolymers (grafts) to be placed on. The calculations carried out show that the bonding strength exerts a pronounced effect on the phase behaviors of supramolecular graft copolymers. The length ratio of backbone to graft and the positions of functional groups along the backbone are also of importance to determine the phase behaviors. Phase diagrams were constructed at high bonding strength to illustrate this architectural dependence. It was found that the excess unbounded homopolymers swell the phase domains and shift the phase boundaries. The results were finally compared with the available experimental observations, and a well agreement is shown. The present work could, in principle, provide a general understanding of the phase behaviors of supramolecular graft copolymers with reversible bonding.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Power consumption monitoring using additional monitoring device

Today, emphasis is placed on reducing power consumption. Computers are large consumers; therefore it is important to know the total consumption of computing systems. Since their optimal functioning requires quite strict environmental conditions, without much variation in temperature and humidity, reducing energy consumption cannot be made without monitoring environmental parameters. Thus, the present work uses a multifunctional electric meter UPT 210 for power consumption monitoring. Two applications were developed: software which carries meter readings provided by electronic and programming facilitates remote device and a device for temperature monitoring and control. Following temperature variations that occur both in the cooling system, as well as the ambient, can reduce energy consumption. For this purpose, some air conditioning units or some computers are stopped in different time slots. These intervals were set so that the economy is high, but the work's Datacenter is not disturbed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Structural, electrical, and magnetic properties of Ba{sub 0.9}Ca{sub 0.1}Ti{sub 0.97}Fe{sub 0.03}O{sub 3} and the effect of oxygen vacancies

Detailed experimental studies have been carried out on a new possible dilute magnetic insulator Ba{sub 0.9}Ca{sub 0.1}Ti{sub 0.97}Fe{sub 0.03}O{sub 3−δ} and its oxygen deficient counterpart. Both the samples stabilize in overall tetragonal BaTiO{sub 3} structure at room temperature as indicated by x-ray diffraction and do exhibit room temperature magnetic order with obvious dependencies on δ. Apart from this, the as-grown sample also retains ferroelectricity at room temperature, which could potentially open up a possibility of achieving multifunctionality at room temperature. However, even though the magnetism is positively influenced by oxygen vacancies, the microscopic phase and ferroelectricity get adversely affected. Finally, using local structural probes, existence of diffused phases has been found, which successfully explains all the observed physical properties.

36 MATERIALS SCIENCE↗

Nd{sup 3+} doped LaF{sub 3} nanoparticles as self-monitored photo-thermal agents

In this work, we demonstrate how LaF{sub 3} nanoparticles activated with large concentrations (up to 25%) of Nd{sup 3+} ions can simultaneously operate as biologically compatible efficient nanoheaters and fluorescent nanothermometers under single beam (808 nm) infrared laser excitation. Nd{sup 3+}:LaF{sub 3} nanoparticles emerge as unique multifunctional agents that could constitute the first step towards the future development of advanced platforms capable of simultaneous deep tissue fluorescence bio-imaging and controlled photo-thermal therapies.

60 APPLIED LIFE SCIENCES↗

Fluorescence of silicon nanoparticles prepared by nanosecond pulsed laser

A pulsed laser fabrication method is used to prepare fluorescent microstructures on silicon substrates in this paper. A 355 nm nanosecond pulsed laser micromachining system was designed, and the performance was verified and optimized. Fluorescence microscopy was used to analyze the photoluminescence of the microstructures which were formed using the pulsed laser processing technique. Photoluminescence spectra of the microstructure reveal a peak emission around 500 nm, from 370 nm laser irradiation. The light intensity also shows an exponential decay with irradiation time, which is similar to attenuation processes seen in porous silicon. The surface morphology and chemical composition of the microstructure in the fabricated region was also analyzed with multifunction scanning electron microscopy. Spherical particles are produced with diameters around 100 nm. The structure is compared with porous silicon. It is likely that these nanoparticles act as luminescence recombination centers on the silicon surface. The small diameter of the particles modifies the band gap of silicon by quantum confinement effects. Electron-hole pairs recombine and the fluorescence emission shifts into the visible range. The chemical elements of the processed region are also changed during the interaction between laser and silicon. Oxidation and carbonization play an important role in the enhancement of fluorescence emission.

36 MATERIALS SCIENCE↗

In situ controlled modification of the helium density in single helium-filled nanobubbles

We demonstrate that the helium density and corresponding pressure can be modified in single nano-scale bubbles embedded in semiconductors by using the electron beam of a scanning transmission electron microscope as a multifunctional probe: the measurement probe for imaging and chemical analysis and the irradiation source to modify concomitantly the pressure in a controllable way by fine tuning of the electron beam parameters. The control of the detrapping rate is achieved by varying the experimental conditions. The underlying physical mechanisms are discussed; our experimental observations suggest that the helium detrapping from bubbles could be interpreted in terms of direct ballistic collisions, leading to the ejection of the helium atoms from the bubble.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

Ferroelectric and ferromagnetic properties of epitaxial BiFeO{sub 3}-BiMnO{sub 3} films on ion-beam-assisted deposited TiN buffered flexible Hastelloy

Growth of multifunctional thin films on flexible substrates is of great technological significance since such a platform is needed for flexible electronics. In this study, we report the growth of biaxially aligned (BiFeO{sub 3}){sub 0.5}:(BiMnO{sub 3}){sub 0.5} [BFO-BMO] films on polycrystalline Hastelloy by using a biaxially aligned TiN as a seed layer deposited by ion-beam-assisted deposited and a La{sub 0.7}Sr{sub 0.3}MnO{sub 3} (LSMO) as a buffer layer deposited by pulsed laser deposition. The LSMO is used not only as a buffer layer but also as the bottom electrode of the BFO-BMO films. X-ray diffraction showed that the BFO-BMO films are biaxially oriented along both in-plane and out-of-plane directions. The BFO-BMO films on flexible metal substrates showed a polarization of 22.9 μC/cm{sup 2}. The magnetization of the BFO-BMO/LSMO is 62 emu/cc at room temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Electro-optic switching in iron oxide nanoparticle embedded paramagnetic chiral liquid crystal via magneto-electric coupling

The variation in optical texture, electro-optic, and dielectric properties of iron oxide nanoparticles (NPs) embedded ferroelectric liquid crystal (FLC) with respect to change in temperature and electrical bias conditions are demonstrated in the current investigations. Improvement in spontaneous polarization and response time in nanocomposites has been attributed to magneto-electric (ME) coupling resulting from the strong interaction among the ferromagnetic nanoparticle's exchange field (due to unpaired e{sup −}) and the field of liquid crystal molecular director. Electron paramagnetic resonance spectrum of FLC material gives a broad resonance signal with superimposed components indicating the presence of a source of spin. This paramagnetic behavior of host FLC material had been a major factor in strengthening the guest host interaction by giving an additional possibility of (a) spin-spin interaction and (b) interactions between magnetic-dipole and electric-dipole moments (ME effects) in the composite materials. Furthermore, the phenomenon of dielectric and static memory effect in these composites are also observed which yet again confirms the coupling of magnetic NP's field with FLC's director orientation. We therefore believe that such advanced soft materials holding the optical and electrical properties of conventional LCs with the magnetic and electronic properties of ferromagnetic nanoparticles are going to play a key role in the development of futuristic multifunctional optical devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Dual anisotropic character in Fe/Pt multilayer grown on (001) MgO substrate

The multilayers of [Fe(5Å)/Pt(25 Å)]{sub ×15} were prepared by dc magnetron sputtering on 50 Å Pt-buffered MgO substrates. The structural characterization of the multilayers was carried out using X-ray diffraction, X-ray reflectivity. The Secondary ion mass spectroscopy measurement reveals the depth profile and compositional modulations of the multilayer films as per our design specifications. Room temperature magnetic measurements were carried out by using SQUID both in-plane and out-of-plane sample geometry. Magnetization measurements show similar M-H loops for both in-plane and out-of-plane directions of external magnetic field with a coercivity of 190 Oe. These measurements indicate that our samples are magnetically soft and have multifunctional character which is important for making magnetic tunnel junctions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Physics of the multi-functionality of lanthanum ferrite ceramics

In the present work, we have illustrated the physics of the multifunctional characteristics of nano-crystalline LaFeO{sub 3} powder prepared using auto-combustion synthesis. The synthesized powders were phase pure and crystallized into centro-symmetric Pnma space group. The temperature dependence of dielectric constant of pure LaFeO{sub 3} exhibits dielectric maxima similar to that observed in ferroelectric ceramics with non-centrosymmetric point group. The dielectric relaxation of LaFeO{sub 3} correlates well with small polaron conduction. The occurrence of polarization hysteresis in LaFeO{sub 3} (with centro-symmetric Pnma space group) is thought to be spin current induced type. The canting of the Fe{sup 3+} spins induce weak ferromagnetism in nano-crystalline LaFeO{sub 3}. Room temperature saturation magnetization of pure LaFeO{sub 3} is reported to be 3.0 emu/g. Due to the presence of both ferromagnetic as well as polarization ordering, LaFeO{sub 3} behaves like a single phase multiferroic ceramics. The magneto-electric coupling in this system has been demonstrated through the magneto-dielectric measurements which yield about 0.8% dielectric tuning (at 10 kHz) with the application of 2 T magnetic field. As a typical application of the synthesized nano-crystalline LaFeO{sub 3} powder, we have studied its butane sensing characteristics. The efficient butane sensing characteristics have been correlated to their catalytic activity towards oxidation of butane. Through X-ray photoelectron spectroscopy analyses, we detect the surface adsorbed oxygen species on LaFeO{sub 3} surface. Surface adsorbed oxygen species play major role in their low temperature butane sensing. Finally, we have hypothesized that the desorbed H{sub 2}O and O{sub 2} (originate from surface adsorbed hydroxyl and oxygen) initiate the catalytic oxidative dehydrogenation of n-butane resulting in weakening of the electrostatics of the gas molecules.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗