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arXiv2019

Intermixed Cation-Anion Aqueous Battery Based on an Extremely Fast and Long-Cycling Di-Block Bipyridinium-Naphthalene Diimide Oligomer

Aqueous batteries, particularly those integrating organic active materials functioning in a neutral pH environment, stand out as highly promising contenders in the stationary electrochemical storage domain, owing to their unparalleled safety, sustainability and low-cost materials. Herein, a novel di-block oligomer (DNVBr), serving as the negative electrode of an all-organic aqueous battery, is shown to offer exceptional output capabilities. The battery's performance is further enhanced by a unique intermixed p/n-type storage mechanism, which is able to simultaneously exchange light and naturally abundant Na+, Mg2+ and Cl-. Reaching up to 105 mAh/g, this system shows remarkable capacity retention for several thousand cycles (6500 cycles, ~40 days) in various neutral electrolytes, including raw ocean water (~3000 cycles, ~75 days). The surprisingly fast kinetics of this di-block oligomer allow to attain an unmatched specific capacity of near to 60mAh/g electrode while entirely devoid of conducting additives, and more than 80mAh/g electrode with 10% carbon additive, as well as displaying an areal capacity as high as 3.4mAh/cm2 at C rate. Full cell validation was demonstrated over 1600 cycles by virtue of a commercial TEMPO molecule, which permitted an energy density of close to 40Wh/kgmaterials at C rate in a self-pH-buffered and inexpensive aqueous electrolyte.

physics.app-ph↗

arXiv2021

Nafion-induced reduction of manganese and its impact on the electrocatalytic properties of a highly active MnFeNi oxide for bifunctional oxygen conversion

Electrocatalysts for bifunctional oxygen reduction (ORR) and oxygen evolution reaction (OER) are commonly studied under hydrodynamic conditions, rendering the use of binders necessary to ensure the mechanical stability of the electrode films. The presence of a binder, however, may influence the properties of the materials under examination to an unknown extent. Herein, we investigate the impact of Nafion on a highly active ORR/OER catalyst consisting of MnFeNi oxide nanoparticles supported on multi-walled carbon nanotubes. Electrochemical studies revealed that, in addition to enhancing the mechanical stability and particle connectivity, Nafion poses a major impact on the ORR selectivity, which correlates with a decrease in the valence state of Mn according to X-ray absorption spectroscopy. These findings call for awareness regarding the use of electrode additives, since in some cases the extent of their impact on the properties of electrode films cannot be regarded as negligible.

physics.chem-ph↗

arXiv2018

Accurate color imaging of pathology slides using holography and absorbance spectrum estimation of histochemical stains

Holographic microscopy presents challenges for color reproduction due to the usage of narrow-band illumination sources, which especially impacts the imaging of stained pathology slides for clinical diagnoses. Here, an accurate color holographic microscopy framework using absorbance spectrum estimation is presented. This method uses multispectral holographic images acquired and reconstructed at a small number (e.g., three to six) of wavelengths, estimates the absorbance spectrum of the sample, and projects it onto a color tristimulus. Using this method, the wavelength selection is optimized to holographically image 25 pathology slide samples with different tissue and stain combinations to significantly reduce color errors in the final reconstructed images. The results can be used as a practical guide for various imaging applications and, in particular, to correct color distortions in holographic imaging of pathology samples spanning different dyes and tissue types.

physics.med-ph↗

arXiv2019

Multifunctional photonic integrated circuit for diverse microwave signal generation, transmission and processing

Microwave photonics (MWP) studies the interaction between microwave and optical waves for the generation, transmission and processing of microwave signals (i.e., three key domains), taking advantages of broad bandwidth and low loss offered by modern photonics. Integrated MWP using photonic integrated circuits (PICs) can reach a compact, reliable and green implementation. Most PICs, however, are recently developed to perform one or more functions restricted inside a single domain. In this paper, as highly desired, a multifunctional PIC is proposed to cover the three key domains. The PIC is fabricated on InP platform by monolithically integrating four laser diodes and two modulators. Using the multifunctional PIC, seven fundamental functions across microwave signal generation, transmission and processing are demonstrated experimentally. Outdoor field trials for electromagnetic environment surveillance along an in-service high-speed railway are also performed. The success to such a PIC marks a key step forward for practical and massive MWP implementations.

physics.app-ph↗

arXiv2019

Integrated polarizers based on graphene oxide in waveguides and ring resonators

Integrated waveguide polarizers and polarization-selective micro-ring resonators (MRRs) incorporated with graphene oxide (GO) films are experimentally demonstrated. CMOS-compatible doped silica waveguides and MRRs with both uniformly coated and patterned GO films are fabricated based on a large-area, transfer-free, layer-by-layer GO coating method that yields precise control of the film thickness. Photolithography and lift-off processes are used to achieve photolithographic patterning of GO films with precise control of the placement and coating length. Detailed measurements are performed to characterize the performance of the devices versus GO film thickness and coating length as a function of polarization, wavelength and power. A high polarization dependent loss of ~53.8 dB is achieved for the waveguide coated with 2-mm-long patterned GO films. It is found that intrinsic film material loss anisotropy dominates the performance for less than 20 layers whereas polarization dependent mode overlap dominates for thicker layers. For the MRRs, the GO coating length is reduced to 50 microns, yielding a ~ 8.3-dB polarization extinction ratio between TE and TM resonances. These results offer interesting physical insights and trends of the layered GO films and demonstrate the effectiveness of introducing GO films into photonic integrated devices to realize high-performance polarization selective components.

physics.optics↗

arXiv2019

Mechanical properties of PMMA sepiolite nanocellular materials with a bimodal cellular structure

Bimodal cellular poly(methyl methacrylate) with micron and nano sized (300 to 500 nm) cells with up to 5 weight percent of sepiolite nanoparticles and porosity from 50 weight percent to 75 weight percent are produced by solid state foaming. Uniaxial compression tests are performed to measure the effect of sepiolite concentration on the elastic modulus and the yield strength of the solid and cellular nanocomposites. Single edge notch bend tests are conducted to relate the fracture toughness of the solid and cellular nanocomposites to sepiolite concentration. The relative modulus is independent of sepiolite content to within material scatter when considering the complete porosity range. In contrast, a mild enhancement of the relative modulus is observed by the addition of sepiolite particles for the foamed nanocomposites with a porosity close to 50 percent. The relative compressive strength of the cellular nanocomposites mildly decreases as a function of sepiolite concentration. A strong enhancement of the relative fracture toughness by the addition of sepiolites is observed. The enhancement of the relative fracture toughness and the relative modulus (at 50 percent porosity) can be attributed to an improved dispersion of the particles due to foaming and the migration of micron sized aggregates from the solid phase to the microcellular pores during foaming.

physics.app-ph↗

arXiv2019

Poly(ionic liquid)-derived N-doped carbons with hierarchical porosity for lithium and sodium ion batteries

The performance of lithium and sodium ion batteries relies notably on the accessibility to carbon electrodes of controllable porous structure and chemical composition. This work reports a facile synthesis of well-defined porous N-doped carbons (NPCs) using a poly(ionic liquid) (PIL) as precursor, and graphene oxide (GO)-stabilized poly(methyl methacrylate) (PMMA) nanoparticles as sacrificial template. The GO-stabilized PMMA nanoparticles were first prepared and then decorated by a thin PIL coating before carbonization. The resulting NPCs reached a satisfactory specific surface area of up to 561 m2/g and a hierarchically meso- and macroporous structure while keeping a nitrogen content of 2.6 wt %. Such NPCs delivered a high reversible charge/discharge capacity of 1013 mA h/g over 200 cycles at 0.4 A/g for lithium ion batteries (LIBs), and showed a good capacity of 204 mA h/g over 100 cycles at 0.1 A/g for sodium ion batteries (SIBs).

physics.app-ph↗

arXiv2026

Spin-Polarized Magnetic Metal Electrodes for Magnetic Tunnel Junctions

Magnetic tunnel junctions are foundational components of spintronic memory, sensing, and computing, and their performance depends critically on the magnetic metallic electrodes. This Perspective examines electrode materials through the lens of magnetic order and the distinct microscopic mechanisms that generate spin-selective tunneling. Conventional ferromagnets, including CoFeB and half-metallic Heusler alloys, support exchange-split electronic states and symmetry-filtered tunneling, whereas compensated collinear and noncollinear antiferromagnets exploit sublattice selectivity, spin-orbit anisotropy, vector spin textures, and magnetic multipoles. Altermagnets provide a collinear, zero-net-moment route based on symmetry-allowed momentum-dependent spin splitting. Across these material classes, we compare the origins of tunneling polarization, the roles of barrier evanescent states and interface termination, and strategies for electrically writing and reading the relevant magnetic order. This comparison reveals a broader design principle: effective electrode polarization is not a scalar bulk quantity, but a momentum-, orbital-, symmetry-, and interface-resolved transport property. Beyond the pursuit of ever larger tunneling magnetoresistance, future progress will depend on converting the unconventional spin polarization of emerging magnetic metals into electrically addressable, thermally robust, and reproducible tunneling functionality at realistic interfaces.

cond-mat.mes-hall↗

arXiv2017

Dosimetric evidence confirms computational model for magnetic field induced dose distortions of therapeutic proton beams

Given the sensitivity of proton therapy to anatomical variations, this cancer treatment modality is expected to benefit greatly from integration with magnetic resonance (MR) imaging. One of the obstacles hindering such an integration are strong magnetic field induced dose distortions. These have been predicted in simulation studies, but no experimental validation has been performed so far. Here we show the first measurement of planar distributions of dose deposited by therapeutic proton pencil beams traversing a one-Tesla transversal magnetic field while depositing energy in a tissue-like phantom using film dosimetry. The lateral beam deflection ranges from one millimeter to one centimeter for 80 to 180 MeV beams. Simulated and measured deflection agree within one millimeter for all studied energies. These results proof that the magnetic field induced proton beam deflection is both measurable and accurately predictable. This demonstrates the feasibility of accurate dose measurement and hence validates dose predictions for the framework of MR-integrated proton therapy.

physics.med-ph↗

arXiv2019

Advanced Surface Chemistry Analysis of Carbon Nanotube Fibers by X-ray Photoelectron Spectroscopy

Carbon nanotube fibers are materials with an exceptional combination of properties, including higher toughness than carbon fibers, electrical conductivity above metals, large specific surface area (250 $\frac{m^2}{g}$) and high electrochemical stability. As such, they are a key component in various multifunctional structures combining augmented mechanical properties with efficient interfacial energy storage/transfer processes. This work presents a thorough XPS study of CNT fibers subjected to different purification and chemical treatments, including spatially-resolved micro XPS synchrotron measurements. The dominant feature is an inherently high degree of $sp^2$ conjugation, leading to a strong plasmonic band and a semi-metallic valence band lineshape. This high degree of CNT perfection in terms of longitudinal graphitization helps to explain reported bulk properties including the high electrical and thermal conductivity, and accessible quantum capacitance. There is also presence of organic impurities, mostly heavy carbonaceous molecules formed as by-products during fiber synthesis and which are adsorbed on the CNTs. Sulfur, a promoter used in the CNT growth reaction, is found both in these surface impurities and associated with the Fe catalyst. The observation of strongly-adsorbed surface impurities is consistent with the high ductility of CNT fibers, attributed to interfacial lubricity.

physics.app-ph↗

arXiv2018

Strain effect in highly-doped n-type 3C-SiC-on-glass substrate for mechanical sensors and mobility enhancement

This work reports the strain effect on the electrical properties of highly doped n-type single crystalline cubic silicon carbide (3C-SiC) transferred onto a 6-inch glass substrate employing an anodic bonding technique. The experimental data shows high gauge factors of -8.6 in longitudinal direction and 10.5 in transverse direction along the [100] orientation. The piezoresistive effect in the highly doped 3C-SiC film also exhibits an excellent linearity and consistent reproducibility after several bending cycles. The experimental result was in good agreement with the theoretical analysis based on the phenomenon of electron transfer between many valleys in the conduction band of n-type 3C-SiC. Our finding for the large gauge factor in n-type 3C- SiC coupled with the elimination of the current leak to the insulated substrate could pave the way for the development of single crystal SiC-on-glass based MEMS applications.

physics.app-ph↗

arXiv2019

Two modes of HVPE growth of GaN and related macrodefects

GaN films with thickness up to 3 mm were grown by halide vapour phase epitaxy method. Two growth modes were observed: the high temperature (HT) mode and the low temperature (LT) mode. Films grown in HT mode had smooth surface, however the growth stress was high and caused cracking. Films grown in LT mode had rough surface with high density of V-defects (pits), however such films were crack-free. The influence of growth parameters on the pit shape and evolution was investigated. Origins of pits formation and process of pit overgrowth are discussed. Crack-free films with smooth surface and reduced density of pits were grown using combination of the LT and HT growth modes.

cond-mat.mtrl-sci↗

arXiv2018

Volumetric 3D-printed antennas, manufactured via selective polymer metallization

Additive manufacturing paves new ways to an efficient exploration of the third space dimension, providing advantages over conventional planar architectures. In particular, volumetric electromagnetic antennas can demonstrate superior characteristics, outperforming their planar counterparts. Here a new approach to the fabrication of electromagnetic devices is developed and applied to antennas, implemented on curved surfaces. Highly directive and broadband antennas were 3D-printed on hemispherical supports. The antenna skeleton and the support were simultaneously printed with different polymer materials - PLA mixed with graphene flakes and pure PLA, respectfully. Weakly DC-conductive graphene PLA-based skeleton was post-processed and high-quality conductive copper layer was selectively electrochemically deposited on it. The antenna devices were found to demonstrate radiation performance, similar to that achievable with conventional fabrication approaches. However, additive manufacturing of RF antennas provides superior capabilities of constructing tailor-made devices with properties, pre-defined by non-standardized end users.

physics.app-ph↗

arXiv2021

Tailoring Drug Mobility by Photothermal Heating of Graphene Plasmons

We propose a theoretical approach to quantitatively determine the photothermally driven enhancement of molecular mobility of graphene-indomethacin mixtures under infrared laser irradiation. Graphene plasmons absorb incident electromagnetic energy and dissipate them into heat. The absorbed energy depends on optical properties of graphene plasmons, which are sensitive to structural parameters, and concentration of plasmonic nanostructures. By using theoretical model, we calculate temperature gradients of the bulk drug with different concentrations of graphene plasmons. From these, we determine the temperature dependence of structural molecular relaxation and diffusion of indomethacin and find how the heating process significantly enhances the drug mobility.

cond-mat.mes-hall↗

arXiv2018

Substrate patterning using regular macroporous block copolymer monoliths as sacrificial templates and as capillary microstamps

Polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) monoliths containing regular arrays of macropores (diameter ~1.1 microns, depth ~700 nm) at their surfaces are used to pattern substrates by patterning modes going beyond the functionality of classical solid elastomer stamps. In a first exemplary application, the macroporous PS-b-P2VP monoliths are employed as sacrificial templates for the deposition NaCl nanocrystals and topographically patterned iridium films. One NaCl nanocrystal per macropore is formed by evaporation of NaCl solutions filling the macropores followed by iridium coating. Thermal PS-b-P2VP decomposition yields topographically patterned iridium films consisting of ordered arrays of hexagonal cells, each of which contains one NaCl nanocrystal. For the second exemplary application, spongy-continuous mesopore systems are generated in the macroporous PS-b-P2VP monoliths by selective-swelling induced pore generation. Infiltrating the spongy-continuous mesopore systems with ink allows capillary microstamping of continuous ink films with holes at the positions of the macropores onto glass slides compatible with advanced light microscopy. Capillary microstamping can be performed multiple times under ambient conditions without re-inking and without quality deterioration of the stamped patterns. The macroporous PS-b-P2VP monoliths are prepared by double replication of primary macroporous silicon molds via secondary polydimethylsiloxane molds.

physics.app-ph↗

arXiv2018

Application of compact TiO$_2$ layer fabricated by pulsed laser deposition in organometal trihalide perovskite solar cells

Organometal trihalide perovskite solar cells have been rapidly developed and attracted much attention in recent years due to their high photoelectric conversion efficiency and low cost. Pulsed laser deposition (PLD) is a widely adopted technology which is used in the preparation of thin films, especially oxide thin films. With this technology, the thickness and composition of films can be conveniently and accurately controlled. In the structure of perovskite solar cells, TiO$_2$ layer working as the n-type semiconductor is used to block holes and transport electrons into electrode, which is crucial for the performance of whole devices. We introduced the PLD technique into preparation of TiO$_2$ layer. In comparison with common spin coating method, TiO$_2$ layer prepared by this technique is ultrathin and more compact. Compact TiO$_2$ (c-TiO$_2$) layers with optimized thickness of 32 nm have been prepared by the PLD method and the highest efficiency of 13.95 % for the MAPbI$_3$-based solar cell devices has been achieved.

physics.app-ph↗

arXiv2017

Methylamine Vapor Exposure for Improved Morphology and Stability of Cesium-Methylammonium Lead Halide Perovskite Thin-Films

Mixed-cation Cesium-Methylammonium lead halide perovskite (CsxMA1-xPbI3-xBrx) thin-films have been used to demonstrate stable and efficient perovskite devices. However, a systematic study of the Cs incorporation on the properties of the perovskite films has not been reported. In this report, Impact of Cesium incorporation on the minority carrier recombination lifetime of Cesium-Methylammonium lead halide perovskite thin-films is studied. The lifetime for the as-deposited perovskite films decreases with increasing concentration of cesium. However, mixed cation perovskite film is more stable, showing higher lifetime (15-20 micro seconds) after 9 hours of ambient exposure than just after deposition (6-13 micro seconds). Methylamine Vapor Exposure (MVE) technique was used to improve the morphology of the as-deposited film. MVE treated films are more oriented along (110) direction and were even more stable in ambient, with Cs0.10MA0.90PbI2.90Br0.10 films showing lifetime of almost 50 micro seconds after 9 hours of ambient exposure, twice the lifetime of a comparable MAPbI3 film. These results throw light on why mixed-cation cesium-methylamine lead halide perovskite films are better for highly efficient and stable perovskite solar cells.

physics.app-ph↗

arXiv2018

Formation of periodic surface structures on dielectrics after irradiation with laser beams of spatially variant polarisation: a comparative study

A comparative study is performed to explore the periodic structure formation upon intense femtosecond pulsed irradiation of dielectrics with radially and azimuthally polarised beams. Laser conditions have been selected appropriately to produce excited carriers with densities below the optical breakdown threshold in order to highlight the role of phase transitions in surface modification mechanisms. The frequency of the laser induced structures is calculated based on a theoretical model that comprises estimation of electron density excitation, heat transfer, relaxation processes, and hydrodynamics-related mass transport. The influence of the laser wavelength in the periodicity of the structures is also unveiled. The decreased energy absorption for azimuthally polarised beams yields periodic structures with smaller frequencies which are more pronounced as the number of laser pulses applied to the irradiation spot increases. Similar results are obtained for laser pulses of larger photon energy and higher fluences. All induced periodic structures are oriented parallel to the laser beam polarisation.

physics.app-ph↗