arXiv subjects

D. Mendoza

Publications and source records attributed to D. Mendoza.

8 recordsLinked to original sources

arXiv2016

Sulfur and few-layer graphene interaction under thermal treatments

In this work we study sulfur confined between two multilayer graphene films under thermal treatments by means of electrical and Raman spectroscopy characterization. We found some similarities between the electrical behavior and differential scanning calorimetry of sulfur immersed into nanoporous anodic alumina template during sulfur phase transitions, this suggests that sulfur has a different thermal behavior when it is in confining conditions compared to the free state. In addition, multilayer graphene was exposed to sulfur vapors at 500 °C to induce chemical reaction. This method effectively produced covalent bonding between sulfur and multilayer graphene and a p-type doping of about 2x10^13 cm^-2 in charge concentration. Finally, based on first principle calculations we speculate on the existence of a new bidimensional structure of sulfur.

cond-mat.mtrl-sci↗

arXiv2013

Modulation of the Optical Transmittance in Multilayer Graphene by an Electrical Signal

The modulation of the optical transmittance in multilayer graphene by means of an electrical signal in the simple configuration of coplanar electrodes is reported. Besides the fundamental frequency of modulation, higher harmonics also appear in the transmitted signal. Modulation is also observed in the optical reflectance. The modulation of the optical properties in multilayer graphene by electrical signals may be useful for the transmission of information by optical means.

cond-mat.mes-hall↗

arXiv2012

Assisted-hydrothermal Synthesis and Characterization of Flower-like ZnO Nanostructures

Flower-like nanostructures formed by ZnO nanorods were synthesized and deposited on seeded silicon and glass substrates by a hexamethylenetetramine (HMTA) - assisted hydrothermal method at low temperature (90 oC) with methenamine ((CH3)6N4), as surfactant and catalyst. The substrates were seeded with ZnO nanoparticles. The structure and morphology of the nanostructures were studied by means of x-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and scanning electron microscopy (SEM) techniques. Influence of the seed nanoparticle on the formation of the flower-like ZnO nanostructures is demonstrated. The influence of the organic oxygenated chains on the crystalline habit during the growth process is also observed.

cond-mat.mtrl-sci↗

arXiv2012

Electrical conductivity of collapsed multilayer graphene tubes

Synthesis of multilayer graphene on copper wires by a chemical vapor deposition method is reported. After copper etching, the multilayer tube collapses forming stripes of graphitic films, their electrical conductance as a function of temperature indicate a semiconductor-like behavior. Using the multilayer graphene stripes, a cross junction is built and owing to its electrical behavior we propose that a tunneling process exists in the device.

cond-mat.mes-hall↗

arXiv2011

Multilayer Graphene Synthesized by CVD Using Liquid Hexane as the Carbon Precursor

We produce multilayer graphene by the Chemical Vapor Deposition (CVD) method at atmospheric pressure and 1000 °C, using flexible copper substrates as catalyst and liquid hexane as the source of carbon. We designed an optical device to measure the transmittance of the carbon films; with this information we calculate that the approximate number of layers is 11.

cond-mat.mes-hall↗

arXiv2011

Band structure of a two dimensional metallic photonic crystal and the experimental observation of negative refraction in the microwave region

In this paper we describe an application of the finite difference method to obtain the transverse magnetic photonic band gap diagram of a photonic crystal. The strategy of this method is to formulate the Maxwell equations in finite differences in order to write a computational code. We present experiments that confirm the validity of the calculations of the photonic band diagram as well as the refraction indix of such structure. All calculations were made for two dimensional metallic photonic crystal.

physics.optics↗

arXiv2010

MAGNETIC ANOMALY IN SUPERCONDUCTING FeSe

Synthesis, electrical and magnetic characterization of superconducting FeSe0.85 compound is reported. An anomaly in the magnetization against temperature around 90K is observed. Magnetic characterization of a commercial compound with nominal FeSe stoichiometry is also presented. The overall magnetic behaviors as well as the magnetic anomaly in both compounds are discussed in terms of magnetic impurities and secondary phases. Keyword: A. Superconductors

cond-mat.supr-con↗

arXiv1998

Surface shape resonances in lamellar metallic gratings

The specular reflectivity of lamellar gratings of gold with grooves 0.5 microns wide separated by a distance of 3.5 microns was measured on the 2000 cm$^{-1}$ - 7000 cm$^{-1}$ spectral range for p-polarized light. For the first time, experimental evidence of the excitation of electromagnetic surface shape resonances for optical frequencies is given. In these resonances the electric field is highly localized inside the grooves and is almost zero in all other regions. For grooves of depth equal to 0.6 microns, we have analyzed one of these modes whose wavelength (3.3 microns) is much greater than the lateral dimension of the grooves.

cond-mat.mtrl-sci↗