RESUMO
Conjugated polymers are promising candidates for molecular wires in nanoelectronics, with flexibility in mechanics, stability in chemistry and variety in electrical conductivity. Polyene, as a segment of polyacetylene, is a typical conjugated polymer with straightforward structure and wide-range adjustable conductance. To obtain atomic scale understanding of charge transfer in polyene, we have measured the conductance of a single polyene-based molecular chain via lifting it up with scanning tunneling microscopy tip. Different from semiconducting characters in pristine polyene (polyacetylene), high conductance and low decay constant are obtained, along with an electronic state around Fermi level and characteristic vibrational mode. These observed phenomena result from pinned molecular orbital owing to molecule-electrode coupling at the interface, and weakened bond length alternation due to electron-phonon coupling inside single molecular chain. Our findings emphasize the interfacial characteristics in molecular junctions and promising properties of polyene, with single molecular conductance as a vital tool for bringing insights into the design and construction of nanodevices.
RESUMO
Two-dimensional (2D) ferroelectric metals (FEMs) possess intriguing characteristics, such as unconventional superconductivity and the nonlinear anomalous Hall effect. However, their occurrence is exceedingly rare due to mutual repulsion between ferroelectricity and metallicity. In addition, further incorporating other features like ferromagnetism into FEMs to enhance their functionalities poses a significantly greater challenge. Here, via first-principles calculations, we demonstrate a case of an FEM that features a coexistence of room-temperature ferromagnetism, ferroelectricity, and metallicity in a thermodynamically stable 2D Os2Se3. It presents a vertical electric polarization of 3.00 pC/m that exceeds those of most FEMs and a moderate polarization switching barrier of 0.22 eV per formula unit. Moreover, 2D Os2Se3 exhibits robust ferromagnetism (Curie temperature TC ≈ 527 K) and a sizable magnetic anisotropy energy (-30.87 meV per formula unit). Furthermore, highly magnetization-dependent electrical conductivity is revealed, indicative of strong magnetoelectric coupling. Berry curvature calculation suggests that the FEM might exhibit nontrivial band topology.
RESUMO
Free radicals, generally formed through the cleavage of covalent electron-pair bonds, play an important role in diverse fields ranging from synthetic chemistry to spintronics and nonlinear optics. However, the characterization and regulation of the radical state at a single-molecule level face formidable challenges. Here we present the detection and sophisticated tuning of the open-shell character of individual diradicals with a donor-acceptor structure via a sensitive single-molecule electrical approach. The radical is sandwiched between nanogapped graphene electrodes via covalent amide bonds to construct stable graphene-molecule-graphene single-molecule junctions. We measure the electrical conductance as a function of temperature and track the evolution of the closed-shell and open-shell electronic structures in real time, the open-shell triplet state being stabilized with increasing temperature. Furthermore, we tune the spin states by external stimuli, such as electrical and magnetic fields, and extract thermodynamic and kinetic parameters of the transition between closed-shell and open-shell states. Our findings provide insights into the evolution of single-molecule radicals under external stimuli, which may proof instrumental for the development of functional quantum spin-based molecular devices.
RESUMO
Understanding the spinterface between magnetic electrodes and molecules, and realizing the controllable spin filtering effect, are crucial for the development of high-performance molecular devices, but both still face big challenges. Here, based on first-principles calculations of an Fe-Mn(DBTAA)-Fe single molecule spintronic device, we unveil that spin filtering efficiency is highly dependent on interface configurations, which can modulate and even reverse the spin polarization of tunnelling electrons. For Fe-Mn(DBTAA)-Fe, a varied spin filtering from -93% to +75% is observed. The underlying mechanism could be attributed to the distinct magnetic and electronic couplings between the Fe electrode and the Mn(DBTAA) molecule in different interface configurations. This work not only highlights the importance of a magnetic electrode-molecule interface, but also implies that through suitable interface design, the performance, e.g., of the spin filtering channel of single molecule spintronic devices, can be flexibly tuned.
RESUMO
Two-dimensional (2D) intrinsic half-metallic materials with room-temperature ferromagnetism, sizable magnetic anisotropy energy (MAE), and wide half-metallic gap are excellent candidates for pure spin generation, injection, and transport in nanospintronic applications. However, until now, such 2D half metallicity has been rarely observed in experiment. In this work, by using first-principles calculations, we design a series of such materials, namely, Mn2X3 (X = S, Se, Te) nanosheets, which could be obtained by controlling the thickness of synthesized α-MnX(111) nanofilm to a quintuple X-Mn-X-Mn-X layer. All these nanosheets are dynamically and thermally stable. Electronic and magnetic studies reveal they are intrinsic half metals with high Curie temperatures between 718 and 820 K, sizable MAEs with -1.843 meV/Mn for Mn2Te3 nanosheet, and wide half-metallic gaps from 1.55 to 1.94 eV. Above all, the outstanding features of Mn2X3 nanosheets make them promising in fabricating nanospintronic devices working at room temperature.
