Yenny Hernandez

• PhD
• Professor (Assistant) at Los Andes University (Colombia)

Bismuth Telluride (Bi2Te3) is a widely studied topological insulator, recognized for its unique surface states, low electronic bandgap, and low thermal conductivity. In this study, we characterize exfoliated Bi2Te3 dispersions produced via solvothermal intercalation, where ferromagnetism was measured at room temperature. Density functional theory (...

Transition metal dichalcogenides (TMDs) are a family of layered two-dimensional materials which find great interest in fields such as medicine, energy conversion, water treatment, and electronics. Nevertheless, the interesting properties that arise as the number of layers is reduced, do not necessarily persist when the nanosheets are printed on sub...

Bismuth Telluride (Bi$_2$Te$_3$) is a widely studied topological insulator, recognized for its unique surface states, low electronic bandgap, and low thermal conductivity. In this study, we characterize exfoliated Bi$_2$Te$_3$ dispersions produced via solvothermal intercalation, where ferromagnetism was measured at room temperature. DFT simulations...

Photoconductivity is an important feature of semiconductors that finds major attention in the fields of solar cells, hydrogen and oxygen evolution reactions, and photodetectors. This feature involves a change of density of charge carriers induced by light, which is dependent on the generation of light-induced carriers and the recombination of excit...

Liquid phase exfoliation of layered materials has proven successful for a range of applications [1]. However, the range of organic solvents needed, and the broad distribution of thicknesses [2] can be aided by applying intercalation steps such as electrochemical or solvothermal expansion which leads to thinner crystals in the dispersion [2, 3]. In...

The discharge of synthetic dyes from different industrial sources has become a global issue of concern. Enormous amounts are released into wastewater each year, causing concerns due to the high toxic consequences. Photocatalytic semiconductors appear as a green and sustainable form of remediation. Among them, graphitic carbon nitride (g-C3N4) has b...

We report on the synthesis and characterization of V2O5 nanoparticles grown using a sol–gel method at different calcination temperatures. We observed a surprising reduction in the optical band gap from 2.20 to 1.18 eV with increasing calcination temperature from 400 to 500 °C. Raman and X-Ray diffraction measurements indicated slight changes in the...

Exfoliation in liquid phase of Transition Metal Dichalcogenides promotes the industrialization of low dimensional structures in photonic and material science applications, due to its high nonlinear optical and piezoelectric responses on monolayers and few odd layers. Here, we report piezoelectricity and prospects of non-linear optics through Switch...

The use of simple, fast, and economic experimental tools to characterize low‐dimensional materials is an important step in the process of democratizing their use. Raman spectroscopy has arisen as a way of indirectly determining the thickness of nanolayers of transition metal dichalcogenides (TMDs), avoiding the use of more expensive tools such as a...

Exfoliation in liquid phase of Transition Metal Dichalcogenides promotes the industrialization of low dimensional structures in photonic and material science applications, due to high nonlinear optical and piezoelectric responses on monolayers and few odd layers of these materials. Here, we report piezoelectricity and prospects of non-linear optics...

The use of simple, fast and economic experimental tools to characterize low-dimensional materials is an important step in the process of democratizing the use of such materials in laboratories around the world. Raman spectroscopy has arisen as a way of indirectly determining the thickness of nanolayers of transition metal dichalcogenides (TMDs), av...

Dispersions of 2D materials were produced by liquid phase exfoliation. Spectral differences are attributed to an increased presence of functional groups, the optical extinction coefficient and band-gap. This methodology allows integration in actuator and piezoelectric devices.

Dye-sensitized solar cells (DSSCs) have been highlighted as the promising alternative to generate clean energy based on low pay-back time materials. These devices have been designed to mimic solar energy conversion processes from photosynthetic organisms (the most efficient energy transduction phenomenon observed in nature) with the aid of low-cost...

Dye-sensitized solar cells (DSSCs) have been highlighted as the promising alternative to generate clean energy based on low pay-back time materials. These devices have been designed to mimic solar energy conversion processes from photosynthetic organisms (the most efficient energy transduction phenomenon observed in nature) with the aid of low-cost...

The quantum nature of low dimensional materials such as graphene and C 60 is yet to be exploited in thermoelectric (TE) applications. A source of reproducible high-quality graphene is its growth by chemical vapour deposition (CVD) and subsequent transfer onto arbitrary substrates. In this work, heterostructures based on graphene and C 60 clusters w...

Nanostructured materials have emerged as an alternative to enhance the figure of merit (ZT) of thermoelectric (TE) devices. Graphene exhibits a high electrical conductivity (in-plane) that is necessary for a high ZT; however, this effect is countered by its impressive thermal conductivity. In this work TE layered devices composed of electrochemical...

Nanostructured materials have emerged as an alternative to enhance the figure of merit (ZT) of thermoelectric (TE) devices. Graphene exhibits a high electrical conductivity (in-plane) that is necessary for a high ZT; however, this effect is countered by its impressive thermal conductivity. In this work TE layered devices composed of electrochemical...

We report on the electronic properties of turbostratic graphitic microdisks, rotationally stacked systems of graphene layers, where interlayer twisting leads to electronic decoupling resulting in charge-transport properties that retain the two dimensionality of graphene, despite the presence of a large number of layers. A key fingerprint of this re...

High surface area graphene sheets were obtained by electrochemical exfoliation of graphite in an acid media under constant potential conditions. Filtration and centrifugation processes played an important role in order to obtain stable dispersions in water. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging reveal...

High surface area graphene sheets were obtained by electrochemical exfoliation of graphite in an acid media under constant potential conditions. Filtration and centrifugation processes played an important role in order to obtain stable dispersions in water. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging reveal...

Extended all-sp2-carbon macromolecules have the potential to replace silicon in integrated nanometer-scale devices. Up to now, studies on the electronic properties of such structures, for example, graphene nanoribbons, have been focused mostly on the infinitely long limit, which is inadequate when approaching future devices with sub-10 nm control....

The properties of graphene nanoribbons (GNRs) make them good candidates for next-generation electronic materials. Whereas 'top-down' methods, such as the lithographical patterning of graphene and the unzipping of carbon nanotubes, give mixtures of different GNRs, structurally well-defined GNRs can be made using a 'bottom-up' organic synthesis appro...

Solution processable thin layer graphene is an intriguing nanomaterial with tremendous potential for electronic applications. In this work, we demonstrate that electrochemical exfoliation of graphite furnishes graphene sheets in high quality. The electrochemically exfoliated graphene (EG) contains a high yield (> 80 %) of 1 to 3 layer graphene flak...

Carbon nanomaterials continue to amaze scientists due to their exceptional physical properties. Recently there have been theoretical predictions and first reports on graphene multilayers, where, due to the rotation of the stacked layers, outstanding electronic properties are retained while the susceptibility to degradation and mechanical stress is...

Graphene, an individual two-dimensional, atomically thick sheet of graphite composed of a hexagonal network of sp(2) carbon atoms, has been intensively investigated since its first isolation in 2004, which was based on repeated peeling of highly oriented pyrolyzed graphite (HOPG). The extraordinary electronic, thermal, and mechanical properties of...

Since the isolation and identification of graphene it has become clear that in order to exploit its outstanding physical properties, high-quality samples must be produced in a reproducible and scalable way. In this chapter, we discuss a number of paths undertaken by several groups around the world to produce high-yield graphene in liquid phase by b...

Oxidative cyclodehydrogenation of laterally extended polyphenylene precursor allowed bottom-up synthesis of structurally defined graphene nanoribbons (GNRs) with unprecedented width. The efficiency of the cyclodehydrogenation was validated by means of MALDI-TOF MS, FT-IR, Raman, and UV-vis absorption spectroscopies as well as investigation of a rep...

The high cost of platinum-based electrocatalysts for the oxygen reduction reaction (ORR) has hindered the practical application of fuel cells. Thanks to its unique chemical and structural properties, nitrogen-doped graphene (NG) is among the most promising metal-free catalysts for replacing platinum. In this work, we have developed a cost-effective...

Graphen, eine einzelne, zweidimensionale Graphitschicht aus einem hexagonalen Netzwerk von sp2‐hybridisierten Kohlenstoffatomen, ist wegen seiner außergewöhnlichen elektronischen, thermischen und mechanischen Eigenschaften ein vielversprechender Kandidat für praktische Anwendungen in Elektronik, Sensorik, Katalyse sowie Energiespeicherung und ‐umwa...

We have studied the exfoliation and dispersion of hexabenzocoronene (HBC) in 28 different solvents. We see a wide range of dispersed concentrations and aggregation states, all of which can be related to the solvent properties. To a first approximation, the dispersed concentration is maximized for solvents with Hildebrand solubility parameter close...

A well-designed nanostructure of transition metal oxides has been regarded as a key to solve their problems of large volume changes during lithium insertion-desertion processes which are associated with pulverization of the electrodes and rapid capacity decay. Here we report an effective approach for the fabrication of porous iron oxide ribbons by...

Generation of glass models

Graphene nanoribbons (GNRs) are strips of graphene cut along a specific direction that feature peculiar electronic and optical properties owing to lateral confinement effects. We show here by means of (time-dependent) density functional theory calculations that GNRs with properly designed edge structures fulfill the requirements in terms of electro...

Large-area graphene grown by chemical vapour deposition (CVD) is promising for applications; however, the interaction between graphene and the substrate is still not well understood. In this report, we use a combination of two non-destructive characterization techniques, i. e., electron backscatter diffraction (EBSD) and Raman mapping to locally pr...

Organic electronics have led to a rapidly growing market for flexible transparent electrodes. Novel two-dimensional graphene is considered a realistic candidate to replace ITO electrode due to its unique properties, such as favorable work function, low resistance, high optical transmittance, good chemical and thermal stability, high mechanical stre...

An extrinsic corrugation-assisted mechanical exfoliation process is introduced to fabricate ultralarge, patterned mono layer graphene on silicon substrates. This exfoliation method, without any contamination, offers not only an ideal alternative for the scalable deposition of monolayer graphene on silicon substrates, but also provides a promising b...

The unoxidized, defect-free graphene dispersions exhibit broadband optical limiting at 532nm and 1064nm. Nonlinear scattering, originated from the thermally induced solvent bubbles and microplasmas, is responsible for this nonlinear behaviour.

Graphite is exfoliated in water to give dispersions of mono- and few-layer graphene stabilized by surfactant. These dispersions can be used to form thin, disordered films of randomly stacked, oxide-free, few-layer graphenes. These films are transparent with a direct current conductivity of up to 1.5 x 10(4) S m(-1). The conductivity is stable under...

Employing high-yield production of graphene by liquid-phase exfoliation, a series of dispersions with large populations of graphene single and few layers was prepared. Nonlinear optical properties of these graphene dispersions were studied using the open aperture Z-scan technique at 532 nm and 1064 nm. The graphene dispersions exhibit broadband non...

We have measured the dispersibility of graphene in 40 solvents, with 28 of them previously unreported. We have shown that good solvents for graphene are characterized by a Hildebrand solubility parameter of delta(T) approximately 23 MPa(1/2) and Hansen solubility parameters of delta(D) approximately 18 MPa(1/2), delta(P) approximately 9.3 MPa(1/2),...

The large populations of graphene monolayers and few layers by dispersing graphite in organic solvent was produced thereby providing a route to examine fundamental quantum phenomena as quantum hall effect in condensed-matter materials. The study employed the Z-scan method to characterize the NLO properties of materials including nonlinear absorptio...

The electron field-emission (FE) characteristics of functionalized single-walled carbon-nanotube (CNT)-polymer composites produced by solution processing are reported. It is shown that excellent electron emission can be obtained by using as little as 0.7% volume fraction of nanotubes in the composite. Furthermore by tailoring the nanotube concentra...

Buckypaper-metal composites are prepared by substrate-enhanced electroless deposition of copper onto strips of buckypaper (see picture). Electrical conductivity and mechanical properties of these buckypaper-copper composites at different copper content are investigated. The conductivity is shown to increases by up to 350 %, and the Young's modulus...

We have demonstrated a method to disperse and exfoliate graphite to give graphene suspended in water-surfactant solutions. Optical characterization of these suspensions allowed the partial optimization of the dispersion process. Transmission electron microscopy showed the dispersed phase to consist of small graphitic flakes. More than 40% of these...

Fully exploiting the properties of graphene will require a method for the mass production of this remarkable material. Two main routes are possible: large-scale growth or large-scale exfoliation. Here, we demonstrate graphene dispersions with concentrations up to approximately 0.01 mg ml(-1), produced by dispersion and exfoliation of graphite in or...

Composites based on polyvinylalcohol have been fabricated from solution with either carbon nanotubes or carbon nanodisks as fillers. Addition of both filler types resulted in conductivity scaling with volume fraction according to sigma = sigma(0)(p - p(c))(t). The nanotube-based composites displayed percolation thresholds of 0.4 vol.% compared to 2...

A novel method is used to produce high mass fraction polymer-nanotube composite films that display extremely high conductivity. Nanotube-containing composites are limited to nanotube-contents below 10%, we have fabricated composites with nanotube mass fractions between 22% and 82%. These films have extremely high conductivities, varying between ~10...

Homogenous composite films were fabricated from a polymer doped with Mo6S4.5I4.5 nanowires. Alternating current and direct current electrical testing revealed percolative behavior characterized by an extremely low percolation threshold, pc = 1.3 × 10−5 and a maximum conductivity of 4 × 10−3 S/m. The low value of the percolation threshold can be exp...