Catálogo de publicaciones - revistas

<jats:p>Two-dimensional surface-enhanced Raman scattering (SERS) substrates have drawn intense attention due to their excellent spectral reproducibility, high uniformity and perfect anti-interference ability. However, the inferior detection sensitivity and low enhancement have limited the practical application of two-dimensional SERS substrates. To address this issue, we propose that the interaction between the MoTe<jats:sub>2</jats:sub> substrate and the analyte rhodamine 6G molecules could be remarkably enhanced by the introduced p-doping effect and lattice distortion of MoTe<jats:sub>2</jats:sub> via hydrogen plasma treatment. After the treatment, the SERS is greatly improved, the enhancement factor of probe molecules reaches 1.83 × 10<jats:sup>6</jats:sup> as well as the limit of detection concentration reaches 10<jats:sup>−13</jats:sup> M. This method is anticipated to afford new enhancement probability for other 2D materials, even non-metal oxide semiconductor SERS substrates.</jats:p>

<jats:p>Searching for new carbon allotropes with superior properties has been a longstanding interest in material sciences and condensed matter physics. Here we identify a novel superhard carbon phase with an 18-atom trigonal unit cell in a full-<jats:italic>sp</jats:italic> <jats:sup>3</jats:sup> bonding network, termed tri-C<jats:sub>18</jats:sub> carbon, by first-principles calculations. Its structural stability has been verified by total energy, phonon spectra, elastic constants, and molecular dynamics simulations. Furthermore, tri-C<jats:sub>18</jats:sub> carbon has a high bulk modulus of 400 GPa and Vickers hardness of 79.0 GPa, comparable to those of diamond. Meanwhile, the simulated x-ray diffraction pattern of tri-C<jats:sub>18</jats:sub> carbon matches well with the previously unexplained diffraction peaks found in chimney soot, indicating the possible presence of tri-C<jats:sub>18</jats:sub> carbon. Remarkably, electronic band structure calculations reveal that tri-C<jats:sub>18</jats:sub> carbon has a wide indirect bandgap of 6.32 eV, larger than that of cubic diamond, indicating its great potential in electronic or optoelectronic devices working in the deep ultraviolet region.</jats:p>

<jats:p>Strategies to prolong operational life are highly pursued to strengthen the advantage of cost-effectiveness on sodium-ion batteries (SIBs). We demonstrate the crucial influence of particles – internal mechanical strains on durability of cathode, which does not attract enough attentions from the community. Among the investigated samples, 2% Ti-modified-Na<jats:sub>0.67</jats:sub>Ni<jats:sub>0.1</jats:sub>Co<jats:sub>0.1</jats:sub>Mn<jats:sub>0.8</jats:sub>O<jats:sub>2</jats:sub> suppresses the <jats:italic>c</jats:italic>-axis lattice variation by 38%, attains the reversible capacity 86% higher after 200 cycles, and still keeps intact morphology. This approach indicates that the mechanical properties could tailor cyclic stability of cathode, which is particular important to further improve competitiveness for SIBs.</jats:p>

<jats:p>As a new electrochemical power system, safety (especially thermal safety) of Na-ion batteries (NIBs) is the key towards large-scale industrialization and market application. Thus, research on the thermal stability of NIBs is helpful to evaluate the safety properties and to provide effective strategies to prevent the occurrence of battery safety failure. Thermal stability of the high-power 26650 cylindrical NIBs using Cu-based layered oxide cathode and hard carbon anode is studied. The high power NIBs can achieve fast charge and discharge at 5–10 C rate and maintain 80% capacity after 4729 cycles at 2 C/2C rate, where the unit C denotes a measure of the rate at which a battery is charge-discharged relative to its maximum capacity. The results of accelerating rate calorimeter and differential scanning calorimetry (ARC-DSC) test results show that NIBs have a higher initial decomposition temperature (≥110 °C) and a lower maximum thermal runaway temperature (≤350 °C) than those of Li-ion batteries (LIBs), exhibiting a favorable thermal stability. It should be noted that the heat generation of cathode accounts for a large proportion of the total heat generation while the thermal stability of the anode determines the initial thermal runaway temperature, which is similar to LIBs. Finally, the whole temperature characteristics of the NIBs in the range of –60 °C–1000 °C are summarized, which provide guidance for the safety design and applications of NIBs.</jats:p>

<jats:p>Based on first-principles calculations and symmetry arguments, we reveal that the non-centrosymmetric ternary tetradymite BiSbTe<jats:sub>3</jats:sub> possesses exotic dual topological features of Weyl semimetallic phases with <jats:italic>Z</jats:italic> <jats:sub>2</jats:sub> index (1:000). The results show that the helical Dirac-type surface states protected by the time-reversal symmetry are present in the vicinity of the Brillouin zone center, which is consistent with the experimental report. Furthermore, we show that four pairs of Weyl points reside exactly at the Fermi level, which are guaranteed to be located on high-symmetry planes due to mirror symmetries. The helical surface states and the projected Weyl nodes are well separated in the momentum space, facilitating their observations in experiments. This work not only uncovers a unique quantum phenomenon with dual topological features in the tetradymite family but also paves a fascinating avenue for exploring the coexistence of multi-topological states with wide applications.</jats:p>

<jats:p>GdTe<jats:sub>3</jats:sub> is a layered antiferromagnetic (AFM) metal with charge density wave (CDW). We grew monolayer (ML) GdTe<jats:sub>3</jats:sub> on graphene/6H-SiC(0001) substrates by molecular beam epitaxy. The electronic and magnetic structures are studied by scanning tunneling microscopy/spectroscopy, quasi-particle interference (QPI) and first-principles calculations. Strong evidence of CDW persisting at the two-dimensional (2D) limit is found. Band dispersions and partially gapped energy bands near the Fermi surface are revealed by the QPI patterns. By density functional theory +<jats:italic>U</jats:italic> calculations, AFM order with stripe pattern is found to be the magnetic ground state for ML GdTe<jats:sub>3</jats:sub>. These results provide fundamental understanding and pave the way for further investigation of GdTe<jats:sub>3</jats:sub> at the 2D limit.</jats:p>

<jats:p>The relationship between structural and electronic phase transitions in V<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> thin films is of critical importance for understanding of the mechanism behind metal–insulator transition (MIT) and related technological applications. Despite being extensively studied, there are currently no clear consensus and picture of the relation between structural and electronic phase transitions so far. Using V<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> thin films grown on <jats:italic>r</jats:italic>-plane Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> substrates, which exhibit abrupt MIT and structural phase transition, we show that the electronic phase transition occurs concurrently with the structural phase transition as revealed by the electrical transport and Raman spectra measurements. Our result provides experimental evidence for clarifying this issue, which could form the basis of theoretical studies as well as technological applications in V<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>.</jats:p>

<jats:p>A <jats:italic> <jats:bold>k</jats:bold> </jats:italic> · <jats:italic> <jats:bold>p</jats:bold> </jats:italic> effective Hamiltonian is important for theoretical analysis in condensed matter physics. Based on the kdotp-symmetry package, we develop an upgraded package named as <jats:italic>kdotp-generator</jats:italic>. This generator takes in arbitrary magnetic symmetries with their representations and returns symmetry-allowed <jats:italic> <jats:bold>k</jats:bold> </jats:italic> · <jats:italic> <jats:bold>p</jats:bold> </jats:italic> Hamiltonians. Using this package, we calculate <jats:italic> <jats:bold>k</jats:bold> </jats:italic> · <jats:italic> <jats:bold>p</jats:bold> </jats:italic> Hamiltonians for irreducible co-representations in 1651 magnetic space groups up to the third order, and their linear coupling to external fields including the electromagnetic field and the strain tensor. We hope that the package will facilitate related research in the future.</jats:p>

<jats:p>In the band theory, first-principles calculations, the tight-binding method and the effective <jats:italic> <jats:bold>k</jats:bold> </jats:italic> · <jats:italic> <jats:bold>p</jats:bold> </jats:italic> model are usually employed to investigate electronic structures of condensed matters. The effective <jats:italic> <jats:bold>k</jats:bold> </jats:italic> · <jats:italic> <jats:bold>p</jats:bold> </jats:italic> model has a compact form with a clear physical picture, and first-principles calculations can give more accurate results. Nowadays, it has been widely recognized to combine the <jats:italic> <jats:bold>k</jats:bold> </jats:italic> · <jats:italic> <jats:bold>p</jats:bold> </jats:italic> model and first-principles calculations to explore topological materials. However, the traditional method to derive the <jats:italic> <jats:bold>k</jats:bold> </jats:italic> · <jats:italic> <jats:bold>p</jats:bold> </jats:italic> Hamiltonian is complicated and time-consuming by hand. We independently developed a programmable algorithm to construct effective <jats:italic> <jats:bold>k</jats:bold> </jats:italic> · <jats:italic> <jats:bold>p</jats:bold> </jats:italic> Hamiltonians for condensed matters. Symmetries and orbitals are used as the input information to produce the one-/two-/three-dimensional <jats:italic> <jats:bold>k</jats:bold> </jats:italic> · <jats:italic> <jats:bold>p</jats:bold> </jats:italic> Hamiltonian in our method, and the open-source code can be directly downloaded online. At last, we also demonstrated the application to MnBi<jats:sub>2</jats:sub>Te<jats:sub>4</jats:sub>-family magnetic topological materials.</jats:p>

<jats:p>Magnetic topological materials have attracted much attention due to the correlation between topology and magnetism. Recent studies suggest that EuCd<jats:sub>2</jats:sub>As<jats:sub>2</jats:sub> is an antiferromagnetic topological material. Here by carrying out thorough magnetic, electrical and thermodynamic property measurements, we discover a long-time relaxation of the magnetic susceptibility in EuCd<jats:sub>2</jats:sub>As<jats:sub>2</jats:sub>. The (001) in-plane magnetic susceptibility at 5 K is found to continuously increase up to ∼10% over the time of ∼14 hours. The magnetic relaxation is anisotropic and strongly depends on the temperature and the applied magnetic field. These results will stimulate further theoretical and experimental studies to understand the origin of the relaxation process and its effect on the electronic structure and physical properties of the magnetic topological materials.</jats:p>