arXiv subjects

Humberto R. Gutiérrez

Publications and source records attributed to Humberto R. Gutiérrez.

4 recordsLinked to original sources

arXiv2024

Raman Spectra and Excitonic Effects of the novel Ta$_2$Ni$_3$Te$_5$ Monolayer

We have investigated the Raman spectrum and excitonic effects of the novel two-dimensional Ta$_2$Ni$_3$Te$_5$ structure. The monolayer is an indirect band gap semiconductor with an electronic band gap value of 0.09 eV and 0.38 eV, determined using GGA-PBE and HSE06 exchange-correlation functionals, respectively. Since this structure is energetically, dynamically, and mechanically stable, it could be synthesized as a free-standing material. We identify ten Raman and ten infrared active modes for various laser energies, including those commonly used in Raman spectroscopy experiments. It was also observed that the contribution of Ni atoms is minimal in most Raman vibrational modes. In contrast, most infrared vibrational modes do not involve the vibration of the Ta atoms. As far as the optical properties are concerned, this monolayer shows a robust linear anisotropy, an exciton binding energy of 287 meV, and also presents a high reflectivity in the ultraviolet region, which is more intense for linear light polarization along the x-direction.

cond-mat.mtrl-sci↗

arXiv2019

Enhanced Optoelectronic Response in Bilayer Lateral Heterostructures of Transition Metal Dichalcogenides

Two-dimensional lateral heterojunctions are basic components for low-power and flexible optoelectronics. In contrast to monolayers, devices based on few-layer lateral heterostructures could offer superior performance due to their lower susceptibility to environmental conditions. Here, we report the controlled synthesis of multi-junction bilayer lateral heterostructures based on MoS2-WS2 and MoSe2-WSe2, where the hetero-junctions are created via sequential lateral edge-epitaxy that happens simultaneously in both the first and the second layer. With respect to their monolayer counterparts, bilayer lateral heterostructures yield nearly one order of magnitude higher rectification currents. They also display a clear photovoltaic response, with short circuit currents ~103 times larger than those extracted from the monolayers, in addition to room-temperature electroluminescence. The superior performance of bilayer heterostructures significantly expands the functionalities of 2D crystals.

cond-mat.mtrl-sci↗

arXiv2017

Sequential Edge-Epitaxy in 2D Lateral Heterostructures

Two-dimensional (2D) heterojunctions display a remarkable potential for application in high performance, low power electro-optical systems. p-n junctions based on vertically stacked heterostructures have shown very promising performance as tunneling transistors, light emitting devices and photodetectors, and as photovoltaic cells . Although complex vertical heterostructures were fabricated via van der Waals stacking of different 2D materials, atomically sharp multi-junctions in lateral heterostructures is a quite challenging task, but a viable route towards the development of commercial applications. Previously reported approaches to obtain single-junction lateral heterostructures of the type MoX2-WX2 (X= S and/or Se), involve either a single-step or a two-step growth process. However, these methods lack the flexibility to control the lateral width of the TMD domain as well as its composition. Here, we report a simple and yet scalable synthesis approach for the fabrication of lateral multi-junction heterostructures based on the combination of different TMD monolayers [MoX2-WX2 (X2 = S2, Se2 or SSe)]. Atomically sharp lateral junctions are sequentially synthesized from solid precursors by changing only the reactive gas environment in the presence of water vapor. This allows to selectively control the water-induced oxidation, volatilization and hence the relative amount of a specific metal oxide vapor, leading to the selective edge-epitaxial growth of either MoX2 or WX2. Spatially dependent photoluminescence and atomic-resolution images confirm the high crystallinity of the monolayers and the seamless lateral connectivity between the different TMD domains. These findings could be extended to other families of 2D materials, and creates the foundation towards the development of complex and atomically thin in-plane super-lattices, devices and integrated circuits.

cond-mat.mtrl-sci↗

arXiv2012

Extraordinary room-temperature photoluminescence in WS2 monolayers

Individual monolayers of metal dichalcogenides are atomically thin two-dimensional crystals with attractive physical properties different from their bulk layered counterpart. Here we describe the direct synthesis of WS2 monolayers with triangular morphologies and strong room-temperature photoluminescence (PL). Bulk WS2 does not present PL due to its indirect band gap nature. The edges of these monolayers exhibit PL signals with extraordinary intensity, around 25 times stronger than the platelets center. The structure and composition of the platelet edges appear to be critical for the PL enhancement effect. Electron diffraction revealed that platelets present zigzag edges, while first-principles calculations indicate that sulfur-rich zigzag WS2 edges possess metallic edge states, which might tailor the optical response reported here. These novel 2D nanoscale light sources could find diverse applications including the fabrication of flexible/transparent/low-energy optoelectronic devices.

cond-mat.mes-hall↗