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Artificial magnetic domains by interlayer coupling in an in plane perpendicular to plane magnetic bilayer system
Full text linkArtificial magnetic domains are induced into a soft magnetic in plane Co60Fe20B19Si1 CoFeBSi alloy by interlayer coupling to a perpendicular to plane FePt underlayer. We present images documenting the thickness dependence of the size of magnetic domains inside the CoFeBSi ferromagnetic layer. The magnetic domain walls in FePt induce a continuous progression of domain walls into the CoFeBSi at the vicinity of the interface to FePt. With femtosecond laser pulses, the recurrent domain pattern in CoFeBSi has been investigated after reversing the magnetization and we observe a reorganization into the thickness dependent multidomain state inside the CoFeBSi with strong domain wall pinning at the interfac
Robust Laser Induced Graphene Boron Doped Diamond Nanowall Hybrid Nanostructures with Enhanced Field Electron Emission Performance for Microplasma Illumination Devices
Full text linkThis investigation introduces a scalable fabrication method for laser induced graphene LIG boron doped diamond nanowall BDNW hybrid nanostructures, designed for field electron emission FEE cathode materials in microplasma illumination amp; 956;PI devices. The two step process involves fabricating BDNWs via microwave plasma enhanced chemical vapor deposition, followed by drop casting BDNW dispersion onto polyimide foils to create LIG BDNW hybrid nanostructures. Topographic studies reveal that BDNWs on LIG boosts surface area and prevent graphene restacking. High resolution transmission electron microscopy confirms precise BDNW decoration, creating sharp edges and high porosity. The effects of boron and nitrogen dopants, highlighted by Raman spectroscopy, are corroborated by near edge X ray absorption fire structure and X ray photoelectron spectroscopies. The hybrid nanostructures exhibit high electrical conductivity and superior FEE properties, with a low turn on field of 2.9 amp; 8201;V amp; 8201; amp; 956;m amp; 8722;1, a large FEE current density of 3.0 amp; 8201;mA amp; 8201;cm amp; 8722;2 at an applied field of 7.9 amp; 8201;V amp; 8201; amp; 956;m amp; 8722;1, and a field enhancement factor of 5,480. The hybrid nanostructures demonstrate an exceptionally low breakdown voltage of 320 amp; 8201;V and a plasma current density of 9.48 amp; 8201;mA amp; 8201;cm amp; 8722;1 at an applied voltage of 550 amp; 8201;V. Ab initio calculations of the electronic structure further support the experimental findings of these diamond graphene hybrids, underscoring their potential in advanced electronic application
Influence of Co and Mn Doping on the Surface Reconstruction of Faceted NiO 111 Nanosheets after the Oxygen Evolution Reaction
Full text linkUnderstanding dynamic surface reconstruction processes on transition metal oxides for the oxygen evolution reaction OER in alkaline electrolytes is crucial to the development of more active catalysts in water electrolysis technologies. Effective strategies in material development for activity enhancement include doping with additional transition metals and surface structuring through controlled exposure of defined surface facets. Here, a microwave assisted synthesis route was used, that resulted in phase pure Co and Mn doped NiO with various doping levels while maintaining the rock salt crystal structure of the pure, faceted NiO 111 nanosheets. X ray diffraction and transmission electron microscopy showed an unaltered structure and morphology up to doping levels of 10 mol . The impact of doping levels between 2 and 10 on the electrochemistry and OER overpotential was studied using the rotating disc electrode technique. A modest overpotential reduction of 34 mV was achieved for 5 Co doping, being the most active material in the comparison, and an increase in overpotential of 56 mV for 10 Mn doping, being the least active material, compared to the undoped NiO 111 material. Associated changes in the physical surface area and charges associated with surface redox reactions were aligned with detailed X ray absorption spectroscopy and X ray photoelectron spectroscopy analysis before and after electrochemical measurements, which showed different extents of surface reconstruction depending on the dopant and doping level. Thus, transformation of the less active rock salt structure to more active NiOOH functionalities was hampered by a low extent of surface reconstruction, explaining the modest activity enhancement after potentiodynamic cycling for 350 scans. The results demonstrate the effective synthesis of facet controlled doped NiO based model catalysts to scrutinize the impact of individual dopants on the electrochemical behavior and, thus the OER electrode activit
Tripodal Triptycenes as a Versatile Building Block for Highly Ordered Molecular Films and Self Assembled Monolayers
No full textThe design of properties and functions of molecular assemblies requires not only a proper choice of building blocks but also control over their packing arrangements. A highly versatile unit in this context is a particular type of triptycene with substituents at the 1,8,13 positions, called tripodal triptycene, which offers predictable molecular packing and multiple functionalization sites, both at the opposite 4,5,16 or 10 bridgehead positions. These triptycene building blocks are capable of two dimensional 2D nested hexagonal packing, leading to the formation of 2D sheets, which undergo one dimensional 1D stacking into well defined 2D 1D structures. This ability makes it possible to form large area molecular films having long range structural integrity even on polymer substrates, which can be used to enhance the performance of organic devices. Importantly, the 2D assembly ability of tripodal triptycenes is robust and not impaired when chemically modified with functional molecular units and even with polymer chains. In addition, introducing suitable functionalities that act as anchoring groups results in reliable tripodal monomolecular assembly on application relevant inorganic substrates, which is generally considered quite a challenging task. Self assembled monolayers SAMs have been formed on Au 111 , Ag 111 , and indium tin oxide. On gold, these SAMs feature the nested hexagonal packing typical of 2D triptycene sheets, whereas, on silver, a distinct polymorphism with several different packing motifs occurs. Along with basic, nonsubstituted tripodal SAMs, specifically functionalized monolayers have been designed. A substitution pattern in which three nitrile tail groups build the outermost surface of a tripodal triptycene based SAM has allowed for the study of femtosecond charge transfer dynamics across the triptycene framework, with a particular emphasis on the so called matrix effects involving intramolecular pathways. The functionalization of the bridgehead position with a ferrocene tail group has enabled single molecule observation of redox reactions and the creation of assemblies of unique molecular rectifiers, exhibiting highly effective rectification at a very low bias voltage. Complementary to the synthesis of these complex functional triptycenes, a strategy of on surface click reactions has been designed. Indeed, a tripodal triptycene having an ethynyl tail group at the 10 position, capable of click reactions with azide functionalities, works well, allowing successive molecular layer deposition. The performance of tripodal triptycene based SAMs has also been tested in the context of electron beam lithography EBL and nanofabrication, leading to the finding that these SAMs can serve as negative resists for EBL due to the efficient cross linking, giving rise to triptycene stemming carbon nanomembranes CNM . These membranes feature the lowest lateral material densities used to date for CNM preparation, which makes them unique in this regar
An enhanced three stage model for sodium storage in hard carbons
No full textA comprehensive understanding of the sodium storage mechanism in hard carbons is essential for developing more efficient anode materials and improving the electrochemical performance of sodium ion batteries. The mechanism has been the subject of ongoing debate, particularly regarding the role of intercalation, which we found to be insignificant in our study. By combining electrochemical analyses with operando characterization techniques, we propose a refined model of sodium storage in hard carbons. Our findings reveal a three stage process first, a fast capacitive mechanism dominates in the slope region; second, a transition phase occurs at the early plateau, where faradaic processes become significant at the carbon micropore inner surface; and finally, micro and slit pore filling becomes dominant at the late plateau, driven by a multilayer like deposition of quasimetallic sodium in the micropores. We believe this refined mechanism promotes a better understanding of the sodium storage mechanism in hard carbons and provides the basis for the rational design of carbon anode materials with superior performance for sodium ion batterie
Reductive Treatment of Ga Pt Supported Catalytically Active Liquid Metal Solutions SCALMS for Propane Dehydrogenation
Full text linkA comprehensive investigation of the impact of hydrogen H2 pretreatments on Ga Pt supported catalytic active liquid metal solution SCALMS for propane dehydrogenation PDH is reported. Our approach bridges from model system investigations to real world catalytic systems, which are tested in continuously operating PDH reactors. The microscopic and spectroscopic findings on model Ga Pt systems suggest changes in the electronic structure and surface chemistry during SCALMS sample oxidation and H2 pretreatment, indicating potential modifications of the active sites involved in PDH. H2 pretreatments of technical Ga Pt SCALMS prepared by ultrasonication US led to significantly improved activity, i.e., the conversion of propane increased from 10 for the untreated catalyst to 26 for the H2 pretreated 5 h at 823 K catalyst. We attribute this enhanced activity to the removal of a gallium oxide GaOx shell, as confirmed by synchrotron based in situ X ray photoelectron spectroscopy XPS as well as in situ transmission electron microscopy TEM investigations of Ga Pt model alloys. These findings are supported by density functional theory DFT and machine learned force field ML FF calculations. Increasing the temperature of the H2 treatment to 923 K reduced the deactivation rate of the catalyst to as low as 0.01 h 1, which is 3 times more stable than what was observed for the untreated catalyst. This deactivation is ascribed to bulk restructuring of the alloy, leading to the formation of less active Pt species as confirmed by spectroscopic and microscopic analysis. Our work not only elucidates the fundamental properties, i.e., typology, electronic structure, and reactivity, of isolated Pt atoms in Ga Pt SCALMS but also proposes underlying mechanisms for the activation and deactivation of PDH catalyst
Controlled Formation of Skyrmion Bags
Full text linkTopologically non trivial magnetic solitons are complex spin textures with a distinct single particle nature. Although magnetic skyrmions, especially those with unity topological charge, have attracted substantial interest due to their potential applications, more complex topological textures remain largely theoretical. In this work, the stabilization of isolated higher order skyrmion bags beyond the prototypical amp; 960; skyrmion in ferromagnetic thin films is experimentally demonstrate, which has posed considerable challenges to date. Specifically, controlled generation of skyrmionium 2 amp; 960; skyrmion , target skyrmion 3 amp; 960; skyrmion , and skyrmion bags with variable topological charge are achieved through the introduction of artificially engineered anisotropy defects via local ion irradiation. They act as preferential sites for the field or laser induced nucleation of skyrmion bags. Remarkably, ultrafast laser pulses achieve a substantially higher conversion rate transforming skyrmions into higher order skyrmion bags compared to their formation driven by magnetic fields. High resolution x ray imaging enables direct observation of the resulting skyrmion bags. Complementary micromagnetic simulations reveal the pivotal role of defect geometry particularly diameter in stabilizing closed loop domain textures. The findings not only broaden the experimental horizon for skyrmion research, but also suggest strategies for exploiting complex topological spin textures within a unified material platform for practical application
Photodegradation of 2D Ruddlesden Popper Perovskites Consequences and Design Principles for Photoelectrochemical Applications
No full textHalide perovskites HaP , with their exceptional optoelectronic properties and high power conversion efficiencies in photovoltaic devices, hold promise for photoelectrochemical PEC applications in green fuel and chemical production. However, their stability in aqueous environments remains a challenge. This study investigates the stability and degradation mechanisms of the 2D Ruddlesden Popper phase phenylethyl ammonium lead iodide PEA 2PbI4 thin films in aqueous electrolytes under dark and illuminated conditions. While PEA 2PbI4 thin films appear to be thermodynamically stable in an aqueous electrolyte with phenylethyl ammonium iodide PEAI , illumination causes significant photodegradation generating a deprotonated and dehalogenated 2D intercalation product phenylethylamine lead iodide, 2PEA 0 PbI2. The degradation of the 2D semiconductor leads to substantial reduction in the photovoltage, adversely impacting the material performance in photoelectrochemical PEC devices. To intercept photo excited charge carriers in the 2D semiconductor, the I3 amp; 8722; I amp; 8722; redox is added, which reduced photodegradation. The findings underscore that while catalytic reactions at halide perovskite electrodes in aqueous electrolytes are feasible, reversible and irreversible photodegradation remains a critical limitation that must be addressed in the design of PEC devices employing metal halide semiconductor layers for direct electrochemical energy conversio
Ammonia tolerant alkaline oxygen reduction reaction on bimetallic cobalt spinels
Full text linkAmmonia, supported by its well established transportation and distribution infrastructure, is considered as a promising carbon free hydrogen carrier and emerging as an energy source via low temperature anion exchange membrane direct ammonia fuel cells AEM DAFC . However, ammonia crossover from the anode can poison cathode catalysts, reducing oxygen reduction reaction ORR efficiency and cell voltage. Herein, to substitute the state of the art catalyst, Pt C, and to develop stable, ammonia tolerant ORR catalysts, monometallic oxides of Co, Fe, Ni, Mn, and bimetallic M CoOx M Fe, Ni, Mn were synthesized on gas diffusion electrode GDE with microporous layer and tested for ORR activity. Among these, MnCoOx 1 Mn Co 1 2 demonstrated high NH3 tolerance and ORR activity comparable to benchmark fuel cell catalyst, Pt C under GDE conditions. In situ Raman spectroscopy performed under GDE conditions revealed that the structure of MnCoOx 1 remains stable, with no detectable changes, even at current densities as high as amp; 8722;25 mA cm amp; 8722;2. During the accelerated stress test conducted at 80 C with 3.0 M NH3 in 3.0 M KOH and compressed air at 1.0 bar back pressure feed, MnCoOx 1 showed an overpotential increase of less than 50 mV at amp; 8722;500 mA cm amp; 8722;2 in a 1.0 cm2 membrane electrode assembly type GDE half cell. Post mortem X ray analysis revealed a slight change in the relative atomic composition of MnCoOx 1 after the AST. This comprehensive study reveals that MnCoOx 1 is a stable NH3 tolerant ORR catalyst, making it a promising cathode candidate for low temperature AEM DAFC application
Observation of a non reciprocal skyrmion Hall effect of hybrid chiral skyrmion tubes in synthetic antiferromagnetic multilayers
Full text linkA hybrid chiral skyrmion tube is a well known example of a 3D topological spin texture, exhibiting an intriguing chirality transition along the thickness direction. This transition progresses from left handed to right handed N el type chirality, passing through a Bloch type intermediate state. Such an exotic spin configuration potentially exhibits distinctly different dynamics from that of the common skyrmion tube that exhibits a homogeneous chirality; yet these dynamics have not been ascertained so far. Here, we reveal the distinct features of current induced dynamics that result from the hybrid chiral skyrmion tube structure in synthetic antiferromagnetic SyAFM multilayers. Strikingly, the SyAFM hybrid chiral skyrmion tubes exhibit a non reciprocal skyrmion Hall effect in the flow regime. The non reciprocity can even be tuned by the degree of magnetic compensation in the SyAFM systems. Our theoretical modeling qualitatively corroborates that the non reciprocity stems from the dynamic oscillation of skyrmion helicity during its current induced motion. The findings highlight the critical role of the internal degrees of freedom of these complex skyrmion tubes for their current induced dynamic