Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Due to its large absorption coefficient and high carrier mobility, SnS exhibits strong promise in the area of optoelectronic devices. Nevertheless, the fabrication of large-area, high-quality films for SnS photodetectors (PDs) with superior photoresponse remains a formidable task, seriously limiting its further practical application. In the present study, a superior-performance broadband PD founded on the epitaxial SnS film. Large-area uniform SnS films were grown epitaxially on (100)-oriented KBr using magnetron sputtering technique, further exfoliated and transferred in a wafer size to fabricated two- terminal photodetector devices. Benefitting from high crystallization and unique photoconductive-bolometric coupling effect, the fabricated PDs exhibit a wide range of spectral response from the visible to near-infrared (NIR) wavelength (405 - 1550 nm), which is far beyond the limitation of the energy band gap. Particularly noteworthy is the SnS device we fabricated, which demonstrates an impressive responsivity of 95.5 A/W and a detectivity of 7.8×1011 Jones, outperforming other devices by 1-2 orders of magnitude. In addition, SnS PD shows excellent environmental durability. This work provides a robust approach to develop high-performance broadband SnS PDs, while simultaneously offering deep insight into the light-matter interactions.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Constructing twisted mixed dimensional graphene-based van der Waals heterostructure (vdWH) is an effective strategy to manipulate the electronic structures and improve the quantum capacitance (<jats:italic>C</jats:italic> <jats:sub>q</jats:sub>) of graphene. In this work, mixed dimensional vdWH of graphene/C<jats:sub>2</jats:sub>H has been proposed owing to similar Dirac semimetal character of one-dimensional C<jats:sub>2</jats:sub>H with that of graphene. Meanwhile, the influence of twisting angle (<jats:italic>θ</jats:italic>) and interlayer interaction strength on the electronic structures and the <jats:italic>C</jats:italic> <jats:sub>q</jats:sub> of the MD vdWH are systemically explored based on tight binding model. With the fitted hopping integral parameters, it is found that the linear dispersion of the graphene is basically preserved but the bandwidth is decreased with modulating twisting angle and interlayer interaction, and the <jats:italic>C</jats:italic> <jats:sub>q</jats:sub> of mixed dimensional vdWH is improved 5~19 times compared with graphene at zero bias. Moreover, the compressed strain could enhance the <jats:italic>C</jats:italic> <jats:sub>q</jats:sub> of mixed dimensional vdWH to 74.57 μF/cm<jats:sup>2</jats:sup> at zero bias and broaden the low working voltage window of mixed-dimensional vdWH with considerable <jats:italic>C</jats:italic> <jats:sub>q</jats:sub>. Our results provide suitable tight-binding model parameters and theoretical guidance for exploring the twisted MD vdWH of graphene/C<jats:sub>2</jats:sub>H and offer an effective strategy to modulate the electronic structures and the <jats:italic>C</jats:italic> <jats:sub>q</jats:sub> of graphene through constructing the MD vdWH.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>NiPS<jats:sub>3</jats:sub> is a Van der Waals antiferromagnet which has been shown to exhibit spin-phonon and spin-charge coupling in the antiferromagnetically ordered state below TN = 155 K. It is also a rare Ni-based negative charge-transfer-type (NCT) insulator with Ni valence in a linear superposition state ψ= αd8+ βd9L_+ γ d10L_2, where L_ is the ligand hole. Here, we study high-quality single-crystals of Ni1-xZnxPS3 (0 &lt; x &lt; 0.2) using temperature-dependent specific heat and Raman spectroscopy probes. We show that in pristine NiPS3, the phonon mode at 176 cm-1 (P2), associated with the vibrations of Ni, exhibits a distinct Fano asymmetry. The Fano resonance is found to be particularly pronounced in the paramagnetic phase above TN, which was further confirmed by temperature dependent Raman data on the Zn-doped crystals. In the Zn-doped crystals, while the magnetism weakens following the mean-field prediction for site-dilution in a honeycomb lattice, the Fano coupling 1/q strengthens, increasing monotonically with increasing Zn-doping. The X-ray photoemission spectra suggest an increase in the weight of the d9 and d10 components in the Zn-doped crystals. These observations indicate the presence of strong electron-phonon coupling in Ni1-xZnxPS3, in addition to the spin-phonon, and spin-charge coupling previously reported.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report hyperspectral imaging in the UV-C spectral domain in epitaxial monolayers of hexagonal boron nitride (hBN). Under quasi-resonant laser excitation, the UV-C emission of monolayer hBN consists in resonant Raman scattering and photoluminescence, which appear to be spatially uncorrelated. Systematic measurements as a function of the excitation energy bring evidence of a photoluminescence singlet at ~6.045 eV. The spatial variations of the photoluminescence energy are found to be around ~10 meV, revealing that the inhomogeneous broadening is lower than the average photoluminescence linewidth of ~25 meV, a value close to the radiative limit in monolayer hBN. Our methodology provides an accurate framework for assessing the opto-electronic properties of hBN in the prospect of scalable hBN-based devices fabricated by epitaxy.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Over the years, two-dimensional (2D) materials have attracted increasing technological interest due to their unique physical, electronic, and photonic properties, making them excellent candidates for applications in electronics, nanoelectronics, optoelectronics, sensors, and modern telecommunications. Unfortunately, their development often requires special conditions and strict protocols, making it challenging to integrate them directly into devices. Some of the requirements include high temperatures, precursors, and special catalytic substrates with specific lattice parameters. Consequently, methods have been developed to transfer these materials from the growth substrates onto target substrates. These transfer techniques aim to minimize intermediate steps and minimize defects introduced into the 2D material during the process. This review focuses on the transfer techniques directly from the development substrates of 2D materials, which play a crucial role in their utilization.&amp;#xD;</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The high susceptibility of ultrathin two-dimensional (2D) material resonators to force and temperature makes them ideal systems for sensing applications and exploring thermomechanical coupling. Although the dynamics of these systems at high stress has been thoroughly investigated, their behaviour near the buckling transition has received less attention. Here, we demonstrate that the force sensitivity and frequency tunability of 2D material resonators are significantly enhanced near the buckling bifurcation. This bifurcation is triggered by compressive stress that we induce via thermal expansion of the devices, while measuring their dynamics via an optomechanical technique. We understand the frequency tuning of the devices through a mechanical buckling model, which allows to extract the pre-strain, central deflection and boundary compressive stress of the membrane. Surprisingly, we obtain a remarkable enhancement of up to 14× the vibration amplitude attributed to a very low stiffness of the membrane at the buckling transition, as well as a high frequency tunability by temperature of more than 4.02 % /K. The presented results provide insights into the effects of buckling on the dynamics of free-standing 2D materials and thereby open up opportunities for the realization of 2D resonant sensors with buckling-enhanced sensitivity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In the light of new experimental evidence we study the insulating ground state of the $3d^2$-transition metal trihalides VX$_3$ (X=Cl, I). Based on Density Functional Theory with the Hubbard correction (DFT$+U$) we systematically show how these systems host multiple metastable states characterized by different orbital ordering and electronic behaviour. Our calculations reveal the importance of imposing a precondition in the on site $d$ density matrix and of considering a symmetry broken unit cell to correctly take into account the correlation effects in a mean field framework. Furthermore we ultimately found a ground state with the $a_{1g}$ orbital occupied in a distorted VX$_6$ octahedra driven by an optical phonon mode.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>For a time-reversal symmetric system, the quantum spin Hall phase is assumed to be the same as the Z<jats:sub>2</jats:sub> topological insulator phase in the existing literature. The spin Chern number C<jats:sub>s</jats:sub> is supposed to yield the same topological classification as the Z<jats:sub>2</jats:sub> invariant. Here, by investigating the topological electronic structures of monolayer α-phase group V elements, we uncover the presence of a topological phase in α-Sb, which can be characterized by a spin Chern number C<jats:sub>s</jats:sub>=2, even though it is Z<jats:sub>2</jats:sub> trivial. Although both being classified as trivial insulators by the existing topological classification schemes, we demonstrate the existence of a phase transition between α-As and Sb, which is induced by band inversions at two generic k points. In the absence of spin-orbit coupling (SOC), α-As is a trivial insulator, while α-Sb is a Dirac semimetal with four Dirac points (DPs) located away from the high-symmetry lines. Inclusion of the SOC gaps out the Dirac points and induces a nontrivial Berry curvature, endowing α-Sb with a high spin Chern number of C<jats:sub>s</jats:sub>=2. We further show that monolayer α-Sb exhibits either a gapless band structure or a gapless spin spectrum on its edges as expected from topological considerations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>MoS<jats:sub>2</jats:sub> and WS<jats:sub>2</jats:sub> mono- and multilayers were grown on SiO<jats:sub>2</jats:sub> /Si substrates. Growth by atomic layer deposition at fast growth rates is compared to sub-atomic layer deposition, which is a slow growth rate process with only partial precursor surface coverage per cycle. A Raman spectroscopic analysis of the intensity and frequency difference of the modes reveals different stages of growth from partial to full surface layer coverage followed by layer-by-layer formation. The initial layer thickness and structural quality strongly depends on the growth rate and monolayers only form using sub-atomic layer deposition. Optical activity is demonstrated by photoluminescence characterisation which shows typical excitonic emission from MoS<jats:sub>2</jats:sub> and WS<jats:sub>2</jats:sub> monolayers. A chemical analysis confirming the stoichiometry of MoS<jats:sub>2</jats:sub> is performed by X-ray photoelectron spectroscopy. The surface morphology of layers grown with different growth rates is studied by atomic force microscopy. Plan-view transmission electron microscopy analysis of MoS<jats:sub>2</jats:sub> directly grown on freestanding graphene reveals the local crystalline quality of the layers, in agreement with Raman and photoluminescence results.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a time-resolved optical study of recently developed narrow-line MoSe<jats:sub>2</jats:sub> monolayers grown on hexagonal boron nitride with means of Molecular Beam Epitaxy. We find that the photoluminescence decay times are significantly shorter than in the case of the exfoliated samples, even below one picosecond. Such a short timescale requires measurements with better resolution than achievable with a streak camera. Therefore, we employ an Excitation Correlation Spectroscopy (ECS) pump-probe technique. This approach allows us to identify two distinct non-radiative recombination channels attributed to lattice imperfections. The first channel is active at helium temperatures. It reduces the lifetime of the neutral exciton to below one picosecond. The second channel becomes active at elevated temperatures, further shortening the lifetimes of both neutral and charged exciton. The high effectiveness of both radiative and non-radiative recombination makes epitaxial MoSe<jats:sub>2</jats:sub> a promising material for ultrafast optoelectronics.</jats:p>