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Bromination of 2D materials
No full textThe adsorption, reaction and thermal stability of bromine on Rh 111 supported hexagonal boron nitride h BN and graphene were investigated. Synchrotron radiation based high resolution x ray photoelectron spectroscopy XPS and temperature programmed XPS allowed us to follow the adsorption process and the thermal evolution in situ on the molecular scale. On h BN Rh 111 , bromine adsorbs exclusively in the pores of the nanomesh while we observe no such selectivity for graphene Rh 111 . Upon heating, bromine undergoes an on surface reaction on h BN to form polybromides 170 240 K , which subsequently decompose to bromide 240 640 K . The high thermal stability of Br h BN Rh 111 suggests strong covalent bonding. Bromine on graphene Rh 111 , on the other hand, reveals no distinct reactivity except for intercalation of small amounts of bromine underneath the 2D layer at high temperatures. In both cases, adsorption is reversible upon heating. Our experiments are supported by a comprehensive theoretical study. DFT calculations were used to describe the nature of the h BN nanomesh and the graphene moir in detail and to study the adsorption energetics and substrate interaction of bromine. In addition, the adsorption of bromine on h BN Rh 111 was simulated by molecular dynamics using a machine learning force fiel
In situ cell for grazing incidence x ray diffraction on thin films in thermal catalysis
Get PDFA cell for synchrotron based grazing incidence x ray diffraction at ambient pressures and moderate temperatures in a controlled gas atmosphere is presented. The cell is suited for the in situ study of thin film samples under catalytically relevant conditions. To some extent, in addition to diffraction, the cell can be simultaneously applied for x ray reflectometry and fluorescence studies. Different domes enclosing the sample have been studied and selected to ensure minimum contribution to the diffraction patterns. The applicability of the cell is demonstrated using synchrotron radiation by monitoring structural changes of a 3 nm Pd thin film upon interaction with gas phase hydrogen and during acetylene semihydrogenation at 150 amp; 8201; C. The cell allows investigation of very thin films under catalytically relevant condition
Hybrid Orbital Formation and Multicenter Bonding of Hydrogen Atoms and Molecules in Ti3C2 MXenes
Get PDFThe formation and stability of solids and molecules is not possible without chemical bonds, which are divided into covalent, ionic, metallic, and van der Waals bonds. A special type of intermolecular bond is hydrogen bonding, which plays a crucial role for chemical, biological, and physical processes. However, hydrogen shows a far more complex behavior when it is present in solids. In this paper, it is shown that the chemical bonding of hydrogen atoms and molecules extends far beyond the simple picture of conventional, ionic, covalent, and multicenter bonds. The interaction of H with its host material is particularly important for hydrogen storage in metallic materials such as Ti3C2 MXenes. Hydrogen atoms and H 2 molecules form multicenter bonds in Ti3C2. On the surface and between two Ti3C2 sheets this is limited to the formation of H Ti bonds. However, H and H 2 on interstitial sites form multicenter bonds not only with nearest neighbor Ti atoms but also with carbon atoms. Interestingly, the H C bonds are characterized by the formation of s p hybrid orbitals. For H 2 molecules, multicenter bond formation is accompanied by an increase of the bond length to 2.07 and 1.85 angstrom for H 2 on the surface and at the interstitial site, respectively. On the other hand, placing H 2 between two sheets of Ti3C2 leads to dissociation. For all H and H 2 complexes the vibrational eigenmodes are calculated. Their frequencies are in the range of 890 to 1610 cm 1 , which indicates that the bonds are remarkably stron
X ray Absorption Spectroscopic Study of the Transition Metal Only Double Perovskite Oxide Mn2CoReO6
No full textBy means of X ray absorption spectroscopic studies, both experimentally and theoretically, we investigated the magnetic properties of the transition metal only double perovskite oxide Mn2CoReO6, which experiences an antiferromagnetic transition at TN 93 K, whereas it holds a considerable net moment at low temperature. Internal exchange fields against the applied magnetic field for all the transition metal ions were identified, providing a microscopic insight into the intrasite antiferromagnetic couplings. Nevertheless, parallelly oriented canted spins of the Mn, Co, and Re cations were observed. In particularly, the Mn and Co cations hold considerable canting moments, which can be ascribed to the competition between the ferromagnetic intersite and antiferromagnetic intrasite magnetic interactions. Moreover, a spin valve type magnetoresistance was observed below the TN. The concurrence of the magnetoresistance effect and the antiferromagnetic semiconductive nature make Mn2CoReO6 a promising candidate for high speed and energy saving spintronics application
Binary Addressable Optical Multiplexing Waveguides via Electrochromic Switching
Get PDFPhotonic circuits attract much attention as promising candidates to overcome the drawbacks of their electronic counterparts. By utilizing the broad bandwidth and low energy consumption of optical communication, hybrid circuits can provide a comprehensive platform for the era beyond Moore s law. In particular, parallel matrix operations, the heavy lifting behind neural networks, remain challenging for traditional electronics due to high heat dissipation. To enable these parallel computations optically, de multiplexing is crucial to address the different channels. Previously this has been accomplished with complex spectral or time encodings in wave division or time division methods. However, herein, a simple method to address parallel optical channels exclusively with 2 bit signals is presented. By using PEDOT PSS as electrochromic material for intensity modulation, light transmission or absorption is controlled by oxidation and reduction with an electrolyte. Y branch structures are used to design the multiplexing layout and to assign the 2 bit states to the channels. This binary addressable optical multiplexer, therefore, combines optical communication with electronic signals into a hybrid circui
Correction Controlling effective field contributions to laser induced magnetization precession by heterostructure design
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Binary cations minimize energy loss in the wide band gap perovskite toward efficient all perovskite tandem solar cells
No full textContext amp; scale Enhancing the performance of perovskite solar cells relies crucially on the surface post treatment of the perovskite film using large spacer cations. These cations play multifunctional roles, encompassing bulk surface defect passivation, interfacial energy level alignment, and the creation of protective low dimensional phases. Particularly in perovskite based tandem solar cells that extend beyond the detailed balance DB limit, wide band gap perovskite front cells encounter significant open circuit voltage VOC and fill factor FF losses, constraining overall device performance. In this study, we present a novel approach involving a mixed spacer cation system i.e., GABr and F PEAI applied to the perovskite surface. This innovative treatment leads to a substantial increase in both VOC and FF. A comprehensive experimental theoretical synergy elucidates that the primary mechanisms behind the enhanced performance are surface defect passivation and interfacial energetic alignment induced by the mixed cations, with a noteworthy exclusion of contributions from low dimensional phases. These findings deepen our comprehension of the surface passivation mechanism employing large spacer cations on the perovskite surface, offering a pioneering and dependable strategy to mitigate energy losses, thereby advancing the path toward the commercialization of perovskite photovoltaic technologie
An introduction to infinite projected entangled pair state methods for variational ground state simulations using automatic differentiation
Get PDFTensor networks capture large classes of ground states of phases of quantum matter faithfully and efficiently. Their manipulation and contraction has remained a challenge over the years, however. For most of the history, ground state simulations of two dimensional quantum lattice systems using infinite projected entangled pair states have relied on what is called a time evolving block decimation. In recent years, multiple proposals for the variational optimization of the quantum state have been put forward, overcoming accuracy and convergence problems of previously known methods. The incorporation of automatic differentiation in tensor networks algorithms has ultimately enabled a new, flexible way for variational simulation of ground states and excited states. In this work we review the state of the art of the variational iPEPS framework, providing a detailed introduction to automatic differentiation, a description of a general foundation into which various two dimensional lattices can be conveniently incorporated, and demonstrative benchmarking result
Inhibiting Interfacial Nonradiative Recombination in Inverted Perovskite Solar Cells with a Multifunctional Molecule
Get PDFInterface induced nonradiative recombination losses at the perovskite electron transport layer ETL are an impediment to improving the efficiency and stability of inverted p i n perovskite solar cells PSCs . Tridecafluorohexane 1 sulfonic acid potassium TFHSP is employed as a multifunctional dipole molecule to modify the perovskite surface. The solid coordination and hydrogen bonding efficiently passivate the surface defects, thereby reducing nonradiative recombination. The induced positive dipole layer between the perovskite and ETLs improves the energy band alignment, enhancing interface charge extraction. Additionally, the strong interaction between TFHSP and the perovskite stabilizes the perovskite surface, while the hydrophobic fluorinated moieties prevent the ingress of water and oxygen, enhancing the device stability. The resultant devices achieve a power conversion efficiency PCE of 24.6 . The unencapsulated devices retain 91 of their initial efficiency after 1000 h in air with 60 relative humidity, and 95 after 500 h under maximum power point MPP tracking at 35 C. The utilization of multifunctional dipole molecules opens new avenues for high performance and long term stable perovskite device
Learning Fermionic Correlations by Evolving with Random Translationally Invariant Hamiltonians
No full textSchemes of classical shadows have been developed to facilitate the readout of digital quantum devices, but similar tools for analog quantum simulators are scarce and experimentally impractical. In this Letter, we provide a measurement scheme for fermionic quantum devices that estimates second and fourth order correlation functions by means of free fermionic, translationally invariant evolutions or quenches and measurements in the mode occupation number basis. We precisely characterize what correlation functions can be recovered and equip the estimates with rigorous bounds on sample complexities, a particularly important feature in light of the difficulty of getting good statistics in reasonable experimental platforms, with measurements being slow. Finally, we demonstrate how our procedure can be approximately implemented with just nearest neighbor, translationally invariant hopping quenches, a very plausible procedure under current experimental requirements and requiring only random time evolution with respect to a single native Hamiltonian. On a conceptual level, this Letter brings the idea of classical shadows to the realm of large scale analog quantum simulator