Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>High electrical conductivity is desired in MXene films for applications such as electromagnetic interference shielding, antennas, and electrodes for electrochemical energy storage and conversion applications. Due to the acid etching-based synthesis method, it is challenging to deconvolute the relative importance that factors such as chemical composition and flake size contribute to resistivity. To understand the intrinsic and extrinsic contributions to the macroscopic electronic transport properties, a systematic study controlling compositional and structural parameters was conducted with solid solutions in the Ti<jats:italic> <jats:sub>y</jats:sub> </jats:italic>Nb<jats:sub>2-<jats:italic>y</jats:italic> </jats:sub>CT<jats:italic> <jats:sub>x</jats:sub> </jats:italic> system. In particular, we investigated the different roles played by metal (M) site composition, flake size, and d-spacing on macroscopic transport. Hard x-ray photoemission spectroscopy and spectroscopic ellipsometry revealed changes to electronic structure induced by the M-site alloying. Consistent with the spectroscopic results, the low- and room-temperature conductivities and effective carrier mobility are correlated with the Ti content, while the impact of flake size and <jats:italic>d</jats:italic>-spacing is most prominent in low temperature transport. The results provide guidance for designing and engineering MXenes with a wide range of conductivities.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Prostate cancer (PCa) is a common type of cancer in men worldwide. Metabolic reprogramming is an important factor in its pathogenesis. Two-dimensional (2D) nanomaterials have tremendous potential for cancer treatment owing to their unique physicochemical properties. However, very few studies have focused on the metabolic reprogramming mechanisms of PCa using 2D nanomaterials. In this study, for the first time, 2D graphdiyne (GDY) was used as a template to immobilize copper (Cu) ions to form a novel nanocomposite (GDY-Cu). GDY provides a large π-conjugated architecture that spatiotemporally restricts Cu ions spatiotemporally to realize the functional moiety of Cu ions as tumor therapeutics. The GDY-Cu nanocomposite with a 2D morphological structure was characterized using a transmission electron microscopy and atomic force microscopy. The distribution of Cu loaded on the GDY was confirmed by high-resolution transmission electron microscopy with energy-dispersive x-ray spectroscopy analysis. In vitro and in vivo, GDY-Cu exhibits a good antitumor effect and is associated with specific metabolic reprogramming characteristics of PCa. In this study, the effect of GDY-Cu on the metabolic reprogramming of PCa cells was analyzed using untargeted metabolomics. Differences in metabolites in DU145 cells treated with GDY-Cu were analyzed by clustering and target analysis using bioinformatics methods. GDY-Cu inhibited the growth of PCa cells by decreasing the expression levels of acetyl-CoA carboxylase and cytoplasmic acetyl-CoA synthase, which inhibits the synthesis of related fatty acids and lipid metabolism. These results indicated that GDY-Cu inhibits the growth of PCa cells mainly via lipid metabolic pathways. At present, combinatory therapeutic modalities based on GDY and Cu are in their infancy. Further exploration is required to promote the development of 2D nanocomposite combinatory therapeutic modalities based on metabolic reprogramming.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Transition metal carbides and nitrides, generally known as MXenes have emerged as an alternative to improve photocatalytic performance in renewable energy and environmental remediation applications because of their high surface area, tunable chemistry, and easily adjustable elemental compositions. MXenes have many interlayer groups, surface group operations, and a flexible layer spacing that makes them ideal catalysts. Over 30 different members of the MXenes family have been explored and successfully utilized as catalysts. Particularly, MXenes have achieved success as a photocatalyst for carbon dioxide reduction, nitrogen fixation, hydrogen evolution, and photochemical degradation. The structure of MXenes and the presence of hydrophilic functional groups on the surface results in excellent photocatalytic hydrogen evolution. In addition, MXenes’ surface defects provide abundant CO2 adsorption sites. Moreover, their highly efficient catalytic oxidation activity is a result of their excellent two-dimensional nanomaterial structure and high-speed electron transport channels. This article, comprehensively discusses the structure, synthesis techniques, photocatalytic applications (i.e., H2 evolution, N2 fixation, CO2 reduction, and degradation of pollutants), and recyclability of MXenes. This review also critically evaluates the MXene-based heterostructure and composites photocatalyst synthesis process and their performance for organic pollutant degradation. Finally, a prospect for further research is presented in environmental and energy sciences.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Linear nonsaturating magnetoresistance (LMR) represents a class of anomalous resistivity response to external magnetic field that has been observed in a variety of materials including but not limited to topological semi-metals, high-Tc superconductors and materials with charge/spin density wave (CDW/SDW) orders. Here we report the observation of LMR in layered kagome superconductor and CDW material CsV3Sb5 thin flakes, as well as the dimensional crossover and temperature (T) crossover of such LMR. Specifically, in ultrathin CsV3Sb5 crystals, the magnetoresistance (MR) exhibits a crossover from LMR at low T to quadratic B dependence above the CDW transition temperature; the MR also exhibits a crossover from LMR to sublinear MR for sample thickness at around ~20 nm at low T. We discuss several possible origins of the LMR and attribute the effect to two-dimensional (2D) CDW fluctuations. Our results may provide a new perspective for understanding the interactions between competing orders in kagome superconductors.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Integrating 2D materials into high-quality optical microcavities opens the door to fascinating many-particle phenomena including the formation of exciton-polaritons. These are hybrid quasi-particles inheriting properties of both the constituent photons and excitons. In this work, we investigate the so-far overlooked impact of dark excitons on the momentum-resolved absorption spectra of hBN-encapsulated WSe$_2$ and MoSe$_2$ monolayers in the strong-coupling regime. In particular, thanks to the efficient phonon-mediated scattering of polaritons into energetically lower dark exciton states, the absorption of the lower polariton branch in WSe$_2$ is much higher than in MoSe$_2$. It shows unique step-like increases in the momentum-resolved profile indicating opening of specific scattering channels. We study how different externally accessible quantities, such as temperature or mirror reflectance, change the optical response of polaritons. Our study contributes to an improved microscopic understanding of exciton-polaritons and their interaction with phonons, potentially suggesting experiments that could determine the energy of dark exciton states via momentum-resolved polariton absorption.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Superconductivity occurs in electrochemically doped molybdenum dichalcogenides samples thicker than four layers. While the critical temperature (T<jats:sub>c</jats:sub>) strongly depends on the field effect geometry (single or double gate) and on the sample (MoS<jats:sub>2</jats:sub> or MoSe<jats:sub>2</jats:sub>), T<jats:sub>c</jats:sub> always saturates at high doping. The pairing mechanism and the complicate dependence of T<jats:sub>c</jats:sub> on doping, samples and field-effect geometry are currently not understood. Previous theoretical works assumed homogeneous doping of a single layer and attributed the T<jats:sub>c</jats:sub> saturation to a charge density wave instability, however the calculated values of the electron-phonon coupling in the harmonic approximation were one order of magnitude larger than the experimental estimates based on transport data. Here, by performing fully relativistic first principles calculations accounting for the sample thickness, the field-effect geometry and anharmonicity, we rule out the occurrence of charge density waves in the experimental doping range and demonstrate a suppression of one order of magnitude in the electron-phonon coupling, now in excellent agreement with transport data. By solving the anisotropic Migdal-Eliashberg equations, we explain the behaviour of T<jats:sub>c</jats:sub> in different systems and geometries. As our first principles calculations show an ever increasing T<jats:sub>c</jats:sub> as a function of doping, we suggest that extrinsic mechanisms may be responsible for the experimentally observed saturating trend.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Designing 2D materials that exhibit half-metallic properties is crucially important in spintronic devices that are used in low-power high-density logic circuits. The large pores in the C2N morphology can stably accommodate various configurations of transition-metal atoms that can lead to ferromagnetic and anti-ferromagnetic coupling interactions amongst them, thus paving the way for achieving half-metallic characteristics. In the present study, we use manganese “Mn” as a promising catalyst and the spin-polarized density-functional theory (DFT) to search for suitable configurations of metal atoms that yield half-metallicity. Test samples comprised of single-atom catalyst (SAC) and double-atom catalyst (DAC) of Mn embedded in a C2N sample of size 2x2 primitive cells (PCs) as well as their combinations in neighboring large pores (i.e., SAC-SAC, SAC-DAC, and DAC-DAC). Tests were extended to screen many other TM catalysts and the results showed the existence of half metallicity in just five cases: (i) C2N:Mn (DAC, SAC-SAC, and SAC-DAC); (ii) C2N:Fe (DAC); and (iii) C2N:Ni (SAC-DAC). Our results further showed the origins of half-metallicity to be attributed to ferromagnetic coupling (FMC) interactions between the catalysts with the 6 mirror images, formed by the periodic-boundary conditions. The FMC interaction is found to have a strength of about 20 meV and a critical length scale up to about ~ 21-29 Å, dependent on both the type of magnetic impurity and the synergetic effects. The potential relevance of half-metallicity to spintronic device application is discussed. Our theoretical results have been benchmarked to the available data in the literature and they were found to be in good agreement.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This work was inspired by new experimental findings where we discovered a two-dimensional (2D) material comprised of titanium-oxide-based one-dimensional (1D) sub-nanometer filaments. Preliminary results suggest that the 2D material contains considerable amounts of carbon, C, in addition to titanium, Ti, and oxygen, O. The aim of this study is to investigate the low-energy, stable atomic forms of 2D titanium carbo-oxides as a function of C content. Via a combination of first-principles calculations and an effective structure sampling scheme, the stable configurations of C-substitutions are comprehensively searched by templating different 2D TiO2 polymorphs and considering a two O to one C replacement scheme. Among the searched stable configurations, a structure where the (101) planes of anatase bound the top and bottom surfaces with a chemical formula of TiC<jats:sub>1/4</jats:sub>O<jats:sub>3/2</jats:sub> was of particularly low energy. Furthermore, the variations in the electronic band structure and chemical bonding environments caused by the high-content C substitution are investigated via additional calculations using a hybrid exchange-correlation functional.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The manipulation of spin transport is always a central task in spintronics and two very well-known findings along this line thus far are the observations of half-metallicity and pure spin current, both very important in practical applications. In this paper, we propose another control over spin, termed as a spin splitter, with an aim to split the two spin channels from the spatially overlapped paths into two isolated branches. Based on a density functional study, we implement this idea in ferromagnetic zigzag graphene nanoribbons (ZGNRs) and find that <jats:italic>h</jats:italic>-BN nanoribbon embedded in the ZGNR acts as a perfect spin splitter. It originates from the different interfacial dipoles developed at the N-C and B-C interfaces and the subsequent different built-in transverse electric fields, which drives the two narrow side ZGNRs into half-metallicity with different spin polarity. The findings will be of great significance in spintronics.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent advances in the field of vertically stacked 2D materials have revealed a rich exciton landscape. In particular, it has been demonstrated that out-of-plane electrical fields can be used to tune the spectral position of spatially separated interlayer excitons. Other studies have shown that there is a strong hybridization of exciton states, resulting from the mixing of electronic states in both layers. However, the connection between the twist-angle dependent hybridization and field-induced energy shifts has remained in the dark. Here, we investigate on a microscopic footing the interplay of electrical and twist-angle tuning of moiré excitons in MoSe<jats:sub>2</jats:sub>. We reveal distinct energy regions in PL spectra that are clearly dominated by either intralayer or interlayer excitons, or even dark excitons. Consequently, we predict twist-angle-dependent critical electrical fields at which the material is being transformed from a direct into an indirect semiconductor. Our work provides new microscopic insights into experimentally accessible knobs to significantly tune the moiré exciton physics in atomically thin nanomaterials.</jats:p>