The oxygen evolution reaction (OER) is the bottleneck that limits the energy efficiency of water-splitting. The process involves four electrons' transfer and the generation of triplet state O
from ...singlet state species (OH
or H
O). Recently, explicit spin selection was described as a possible way to promote OER in alkaline conditions, but the specific spin-polarized kinetics remains unclear. Here, we report that by using ferromagnetic ordered catalysts as the spin polarizer for spin selection under a constant magnetic field, the OER can be enhanced. However, it does not applicable to non-ferromagnetic catalysts. We found that the spin polarization occurs at the first electron transfer step in OER, where coherent spin exchange happens between the ferromagnetic catalyst and the adsorbed oxygen species with fast kinetics, under the principle of spin angular momentum conservation. In the next three electron transfer steps, as the adsorbed O species adopt fixed spin direction, the OER electrons need to follow the Hund rule and Pauling exclusion principle, thus to carry out spin polarization spontaneously and finally lead to the generation of triplet state O
. Here, we showcase spin-polarized kinetics of oxygen evolution reaction, which gives references in the understanding and design of spin-dependent catalysts.
2D transition metal chalcogenides have attracted tremendous attention due to their novel properties and potential applications. Although 2D transition metal dichalcogenides are easily fabricated due ...to their layer‐stacked bulk phase, 2D transition metal monochalcogenides are difficult to obtain. Recently, a single atomic layer transition metal monochalcogenide (CuSe) with an intrinsic pattern of nanoscale triangular holes is fabricated on Cu(111). The first‐principles calculations show that free‐standing monolayer CuSe with holes is not stable, while hole‐free CuSe is endowed with the Dirac nodal line fermion (DNLF), protected by mirror reflection symmetry. This very rare DNLF state is evidenced by topologically nontrivial edge states situated inside the spin–orbit coupling gaps. Motivated by the promising properties of hole‐free honeycomb CuSe, monolayer CuSe is fabricated on Cu(111) surfaces by molecular beam epitaxy and confirmed success with high resolution scanning tunneling microscopy. The good agreement of angle resolved photoemission spectra with the calculated band structures of CuSe/Cu(111) demonstrates that the sample is monolayer CuSe with a honeycomb lattice. These results suggest that the honeycomb monolayer transition metal monochalcogenide can be a new platform to study 2D DNLFs.
2D transition metal chalcogenides are attracting tremendous attention due to their novel properties and potential applications. Monolayer honeycomb CuSe on Cu(111) is successfully fabricated. First‐principles calculations show that free‐standing monolayer CuSe is endowed with the Dirac nodal line fermion, protected by mirror reflection symmetry. It is further evidenced by topologically nontrivial edge states situated inside the spin–orbit coupling gaps.
Abstract
The discovery of ferromagnetic two-dimensional van der Waals materials has opened up opportunities to explore intriguing physics and to develop innovative spintronic devices. However, ...controllable synthesis of these 2D ferromagnets and enhancing their stability under ambient conditions remain challenging. Here, we report chemical vapor deposition growth of air-stable 2D metallic 1T-CrTe
2
ultrathin crystals with controlled thickness. Their long-range ferromagnetic ordering is confirmed by a robust anomalous Hall effect, which has seldom been observed in other layered 2D materials grown by chemical vapor deposition. With reducing the thickness of 1T-CrTe
2
from tens of nanometers to several nanometers, the easy axis changes from in-plane to out-of-plane. Monotonic increase of Curie temperature with the thickness decreasing from ~130.0 to ~7.6 nm is observed. Theoretical calculations indicate that the weakening of the Coulomb screening in the two-dimensional limit plays a crucial role in the change of magnetic properties.
Abstract
Producing hydrogen by water electrolysis suffers from the kinetic barriers in the oxygen evolution reaction (OER) that limits the overall efficiency. With spin-dependent kinetics in OER, to ...manipulate the spin ordering of ferromagnetic OER catalysts (e.g., by magnetization) can reduce the kinetic barrier. However, most active OER catalysts are not ferromagnetic, which makes the spin manipulation challenging. In this work, we report a strategy with spin pinning effect to make the spins in paramagnetic oxyhydroxides more aligned for higher intrinsic OER activity. The spin pinning effect is established in oxide
FM
/oxyhydroxide interface which is realized by a controlled surface reconstruction of ferromagnetic oxides. Under spin pinning, simple magnetization further increases the spin alignment and thus the OER activity, which validates the spin effect in rate-limiting OER step. The spin polarization in OER highly relies on oxyl radicals (O∙) created by 1
st
dehydrogenation to reduce the barrier for subsequent O-O coupling.
Abstract
Iron-chalcogenide superconductors have emerged as a promising Majorana platform for topological quantum computation. By combining topological band and superconductivity in a single material, ...they provide significant advantage to realize isolated Majorana zero modes. However, iron-chalcogenide superconductors, especially Fe(Te,Se), suffer from strong inhomogeneity which may hamper their practical application. In addition, some iron-pnictide superconductors have been demonstrated to have topological surface states, yet no Majorana zero mode has been observed inside their vortices, raising a question of universality about this new Majorana platform. In this work, through angle-resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy measurement, we identify Dirac surface states and Majorana zero modes, respectively, for the first time in an iron-pnictide superconductor, CaKFe
4
As
4
. More strikingly, the multiple vortex bound states with integer-quantization sequences can be accurately reproduced by our model calculation, firmly establishing Majorana nature of the zero mode.
We report the first bottom‐up synthesis of NBN‐doped zigzag‐edged GNRs (NBN‐ZGNR1 and NBN‐ZGNR2) through surface‐assisted polymerization and cyclodehydrogenation based on two U‐shaped molecular ...precursors with an NBN unit preinstalled at the zigzag edge. The resultant zigzag‐edge topologies of GNRs are elucidated by high‐resolution scanning tunneling microscopy (STM) in combination with noncontact atomic force microscopy (nc‐AFM). Scanning tunneling spectroscopy (STS) measurements and density functional theory (DFT) calculations reveal that the electronic structures of NBN‐ZGNR1 and NBN‐ZGNR2 are significantly different from those of their corresponding pristine fully‐carbon‐based ZGNRs. Additionally, DFT calculations predict that the electronic structures of NBN‐ZGNRs can be further tailored to be gapless and metallic through one‐electron oxidation of each NBN unit into the corresponding radical cations. This work reported herein provides a feasible strategy for the synthesis of GNRs with stable zigzag edges yet tunable electronic properties.
Close to the edge: Two novel NBN‐doped zigzag‐edged graphene nanoribbons (ZGNRs) are derived through surface‐assisted synthesis. Experiments and calculations reveal the importance of the NBN units in modulating the electronic structures of the ZGNRs. Moreover, theoretical calculations predict that the electronic structures of NBN‐ZGNRs can be further tailored through one‐electron oxidation of each NBN unit into the corresponding radical cations.
Combining solution‐based and surface‐assisted synthesis, we demonstrate the first synthesis of NBN‐doped bis‐tetracene (NBN‐BT) and peri‐tetracene (NBN‐PT). The chemical structures are clearly ...elucidated by high‐resolution scanning tunneling microscopy (STM) in combination with noncontact atomic force microscopy (nc‐AFM). Scanning tunneling spectroscopy (STS) characterizations reveal that NBN‐BT and NBN‐PT possess higher energy gaps than bis‐tetracene and peri‐tetracene. Interestingly, NBN‐BT can undergo stepwise one‐electron oxidation and convert into its corresponding radical cation and then to its dication. The energy gap of the NBN‐BT dication is similar to that of bis‐tetracene, indicating their isoelectronic relationship. Moreover, a similar energy gap between the NBN‐PT dication and peri‐tetracene can be predicted by DFT calculations. This work provides a novel synthesis along with characterizations of multi‐NBN‐doped zigzag‐edged peri‐acenes with tunable electronic properties.
Two novel double NBN‐doped zigzag‐edged nanographenes, bis‐tetracene (NBN‐BT) and peri‐tetracene (NBN‐PT), are achieved through a combined in‐solution and on‐surface synthesis. The chemical structures are clearly characterized by STM and AFM. Moreover, NBN‐BT and NBN‐PT can be further tailored to dications, which demonstrate similar electronic properties to their all‐carbon‐based isoelectronic structures bis‐tetracene and peri‐tetracene.
Monolayer SixCy constitutes an important family of 2D materials that is predicted to feature a honeycomb structure and appreciable bandgaps. However, due to its binary chemical nature and the lack of ...bulk polymorphs with a layered structure, the fabrication of such materials has so far been challenging. Here, the synthesis of atomic monolayer Si9C15 on Ru (0001) and Rh(111) substrates is reported. A combination of scanning tunneling microscopy (STM), X‐ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and density functional theory (DFT) calculations is used to infer that the 2D lattice of Si9C15 is a buckled honeycomb structure. Monolayer Si9C15 shows semiconducting behavior with a bandgap of ≈1.9 eV. Remarkably, the Si9C15 lattice remains intact after exposure to ambient conditions, indicating good air stability. The present work expands the 2D‐materials library and provides a promising platform for future studies in nanoelectronics and nanophotonics.
2D Si9C15 monolayer is fabricated on Ru (0001) and Rh(111) substrates via the reaction between Si and graphene under high temperatures. The as‐grown Si9C15 layer is micrometer‐scale, high quality, and single crystalline with a bandgap of ≈1.9 eV. Combined measurements and density functional calculations confirm the buckled honeycomb structure. The novel 2D material also shows good air stability.
PDF
