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Crystallographic dislocation has been well-known to be one of the major causes responsible for the unfavorable carrier dynamics in conventional semiconductor devices. Halide perovskite has exhibited promising applications in optoelectronic devices. However, how dislocation impacts its carrier dynamics in the ‘defects-tolerant’ halide perovskite is largely unknown. Here, via a remote epitaxy approach using polar substrates coated with graphene, we synthesize epitaxial halide perovskite with controlled dislocation density. First-principle calculations and molecular-dynamics simulations reveal weak film-substrate interaction and low density dislocation mechanism in remote epitaxy, respectively. High-resolution transmission electron microscopy, high-resolution atomic force microscopy and Cs-corrected scanning transmission electron microscopy unveil the lattice/atomic and dislocation structure of the remote epitaxial film. The controlling of dislocation density enables the unveiling of the dislocation-carrier dynamic relation in halide perovskite. The study provides an avenue to develop free-standing halide perovskite film with low dislocation density and improved carried dynamics., Crystallographic dislocation has proven harmful to the carrier dynamics in conventional semiconductors but it is unexplored in metal halide perovskites. Here Jiang et al. grow remote epitaxial perovskite films on graphene with density-controlled dislocations and confirm their negative impact.

We fabricated ambipolar field-effect transistors (FETs) from multi-layered triclinic ReSe2, mechanically exfoliated onto a SiO2 layer grown on p-doped Si. In contrast to previous reports on thin layers (~2 to 3 layers), we extract field-effect carrier mobilities in excess of 10^2 cm^2/Vs at room temperature in crystals with nearly ~10 atomic layers. These thicker FETs also show nearly zero threshold gate voltage for conduction and high ON to OFF current ratios when compared to the FETs built from thinner layers. We also demonstrate that it is possible to utilize this ambipolarity to fabricate logical elements or digital synthesizers. For instance, we demonstrate that one can produce simple, gate-voltage tunable phase modulators with the ability to shift the phase of the input signal by either 90^o or nearly 180^o. Given that it is possible to engineer these same elements with improved architectures, for example on h-BN in order to decrease the threshold gate voltage and increase the carrier mobilities, it is possible to improve their characteristics in order to engineer ultra-thin layered logic elements based on ReSe2., Scientific Reports 2018

First principles methods are used to explicitly calculate the nonlinear susceptibility (χ(2)(2ω, ω, ω)) representing the second harmonic generation (SHG) of two dimensional semiconducting materials, namely transition metal dichalcogenides (TMDs) and Boron Nitride (BN). It is found that alloying TMDs improves their second harmonic response, with MoTeS alloys exhibiting the highest of all hexagonal alloys at low photon energies. Moreover, careful examination of the relationship between the concentration of Se in MoxSeySz alloys shows that the SHG intensity can be tuned by modifying the stoichiometry. In addition, materials with curvature can have large second harmonic susceptibility. Of all the calculated monolayer structures, the hypothetical TMD Haeckelites NbSSe and Nb0.5Ta0.5S2 exhibit the highest χ(2), while one of the porous 3D structures constructed from 2D hBN exhibits a larger χ(2) than known large band gap 3-D materials.

Crystallographic dislocation has been well-known to be one of the major causes responsible for the unfavorable carrier dynamics in conventional semiconductor devices. Halide perovskite has exhibited promising applications in optoelectronic devices. However, how dislocation impacts its carrier dynamics in the 'defects-tolerant' halide perovskite is largely unknown. Here, via a remote epitaxy approach using polar substrates coated with graphene, we synthesize epitaxial halide perovskite with controlled dislocation density. First-principle calculations and molecular-dynamics simulations reveal weak film-substrate interaction and low density dislocation mechanism in remote epitaxy, respectively. High-resolution transmission electron microscopy, high-resolution atomic force microscopy and Cs-corrected scanning transmission electron microscopy unveil the lattice/atomic and dislocation structure of the remote epitaxial film. The controlling of dislocation density enables the unveiling of the dislocation-carrier dynamic relation in halide perovskite. The study provides an avenue to develop free-standing halide perovskite film with low dislocation density and improved carried dynamics.

Shortly after the discovery of fullerenes, many researchers pointed out that carbon nanotubes could be considered as elongated fullerenes. However, the detailed formation mechanism for both structures has been a topic of debate for several years, and consequently it has been difficult to draw a clear connection between the two systems. While the synthesis conditions appear to be different for both fullerenes and nanotubes, here, we demonstrate that it is highly likely that, at an initial growth stage, single-walled carbon nanotubes begin to grow from a hemisphere-like fullerene cap. More importantly, by analysing the minimum-energy path, it is shown that the insertion of C 2 fragments drives the transformation of this fullerene cap into an elongated structure that leads to the formation of very short carbon nanotubes. This article is part of the themed issue ‘Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene’.

We propose a new family of layered sp(2)-like carbon crystals, incorporating five-, six-, and seven-membered rings in 2D Bravais lattices. These periodic sheets can be rolled so as to generate nanotubes of different diameter and chirality. We demonstrate that these sheets and tubes are metastable and more favorable than C-60, and it is also shown that their mechanical properties are similar to those of graphene. Density of states calculations of all structures revealed an intrinsic metallic behavior, independent of orientation, tube diameter, and chirality.

We report the controlled formation and characterization of heterojunctions between carbon nanotubes and different metal nanocrystals (Fe, Co, Ni, and FeCo). The heterojunctions are formed from metal-filled multiwall carbon nanotubes (MWNTs) via intense electron beam irradiation at temperatures in the range of 450–700 °C and observed in situ in a transmission electron microscope. Under irradiation, the segregation of metal and carbon atoms occurs, leading to the formation of heterojunctions between metal and graphite. Metallic conductivity of the metal–nanotube junctions was found by using in situ transport measurements in an electron microscope. Density functional calculations show that these structures are mechanically strong, the bonding at the interface is covalent, and the electronic states at and around the Fermi level are delocalized across the entire system. These properties are essential for the application of such heterojunctions as contacts in electronic devices and vital for the fabrication of robust nanotube–metal composite materials.

In this work, strong third order nonlinear optical properties exhibited by WS2 layers are presented. Optical Kerr effect was identified as the dominant physical mechanism responsible for these third order optical nonlinearities. An extraordinary nonlinear refractive index together with an important contribution of a saturated absorptive response was observed to depend on the atomic layer stacking. Comparative experiments performed in mono- and few-layer samples of WS2 revealed that this material is potentially capable of modulating nonlinear optical processes by selective near resonant induced birefringence. In conclusion, we envision applications for developing all-optical bidimensional nonlinear optical devices.

Vapor sensors are easily fabricated onto alumina substrates using foils of silver-decorated nitrogen-doped multiwalled carbon nanotubes (CNX-MWNTs-Ag) as active sensing material. The vapor sensors are tested using carbon disulfide, acetone, ethanol, and chloroform vapors. The CNX-MWNTs are produced by chemical vapor deposition process and then decorated with 14 nm Ag nanoparticles (Ag-NPs). The samples are characterized using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. Our results demonstrate that Ag-decorated CNX-MWNTs exhibit a better response and sensitivity when compared with pristine CNX-MWNTs based sensors, making them promising candidates for air-pollutants environmental monitoring. The temperature effect on the sensor performance is also studied; we found that the detection mechanism could be tuned from physisorption, at room temperature, to chemisorption at higher working temperature. Finally, first-principles density functional calculations are carried out to understand the interactions between the systems involved in the sensors, finding good agreement between experimental results and the theoretical approach.

In an effort to enhance our knowledge on how to control the movement of metallic nanodroplets, here we have used classical molecular dynamics simulations to investigate whether Cu nanostructures deposited on nanopillared substrates can be made to jump at desired angles. We find that such control is possible, especially for Cu nanostructures that are symmetric; for asymmetric nanostructures, however, control is more uncertain. The work presented here borrows ideas from two seemingly different fields, metallic droplets and water droplets in the dynamic Leidenfrost regime. Despite the differences in the respective systems, we find common ground in their behavior on nanostructured surfaces. Due to this, we suggest that the ongoing research in Leidenfrost droplets is a fertile area for scientists working on metallic nanodroplets.

Large-area Si-doped graphene (SiG) is controllably synthesized for the first time. A much-enhanced molecular-sensing performance is achieved when SiG is used as a probing surface. This will open up opportunities for developing high-performance sensors that are able to detect trace amounts of organic and fluorescent molecules. Furthermore, many fascinating properties predicted by theoretical calculations can be tested based on the as-synthesized SiG.

Ternary two-dimensional dichalcogenide alloys exhibit compositionally modulated electronic structure, and hence, control of dopant concentration within each individual layer of these compounds provides a powerful tool to efficiently modify their physical and chemical properties. The main challenge arises when quantifying and locating the dopant atoms within each layer in order to better understand and fine-tune the desired properties. Here we report the synthesis of molybdenum disulfide substitutionally doped with a broad range of selenium concentrations, resulting in over 10% optical band gap modulations in atomic layers. Chemical analysis using Z-contrast imaging provides direct maps of the dopant atom distribution in individual MoS2 layers and hence a measure of the local optical band gaps. Furthermore, in a bilayer structure, the dopant distribution is imaged layer-by-layer. This. work demonstrates that each layer in the bilayer system contains similar local Se concentrations, randomly distributed, providing new insights into the growth mechanism and alloying behavior in two-dimensional dichalcogenide atomic layers. The results show that growth of uniform, ternary, two-dimensional dichalcogenide alloy films with tunable electronic properties is feasible.

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.

The Raman scattering of single- and few-layered WS2 is studied as a function of the number of S-W-S layers and the excitation wavelength in the visible range (488, 514 and 647 nm). For the three excitation wavelengths used in this study, the frequency of the A1g(Γ) phonon mode monotonically decreases with the number of layers. For single-layer WS2, the 514.5 nm laser excitation generates a second-order Raman resonance involving the longitudinal acoustic mode (LA(M)). This resonance results from a coupling between the electronic band structure and lattice vibrations. First-principles calculations were used to determine the electronic and phonon band structures of single-layer and bulk WS2. The reduced intensity of the 2LA mode was then computed, as a function of the laser wavelength, from the fourth-order Fermi golden rule. Our observations establish an unambiguous and nondestructive Raman fingerprint for identifying single- and few-layered WS2 films.

Although bulk hexagonal phases of layered semiconducting transition metal dichalcogenides (STMD) such as MoS2, WS2, WSe2 and MoSe2 exhibit indirect band gaps, a mono-layer of STMD possesses a direct band gap which could be used in the construction of novel optoelectronic devices, catalysts, sensors and valleytronic components. Unfortunately, the direct band gap only occurs for mono-layered STMD. We have found, using first principles calculations, that by alternating individual layers of different STMD (MoS2, WS2, WSe2 and MoSe2) with particular stackings, it is possible to generate direct band gap bi-layers ranging from 0.79 eV to 1.157 eV. Interestingly, in this direct band gap, electrons and holes are physically separated and localized in different layers. We foresee that the alternation of different STMD would result in the fabrication of materials with unprecedented optical and physico-chemical properties that would need further experimental and theoretical investigations.

Graphene is a two-dimensional network in which sp(2)-hybridized carbon atoms are arranged in two different triangular sub-lattices (A and B). By incorporating nitrogen atoms into graphene, its physico-chemical properties could be significantly altered depending on the doping configuration within the sub-lattices. Here, we describe the synthesis of large-area, highly-crystalline monolayer N-doped graphene (NG) sheets via atmospheric-pressure chemical vapor deposition, yielding a unique N-doping site composed of two quasi-adjacent substitutional nitrogen atoms within the same graphene sub-lattice (N(2)(AA)). Scanning tunneling microscopy and spectroscopy (STM and STS) of NG revealed the presence of localized states in the conduction band induced by N(2)(AA)-doping, which was confirmed by ab initio calculations. Furthermore, we demonstrated for the first time that NG could be used to efficiently probe organic molecules via a highly improved graphene enhanced Raman scattering.

We first describe the synthesis of novel and highly porous boron nitride (BN) nanospheres (100-400 nm o.d.) that exhibit a rough surface consisting of open BN nanocones and corrugated BN ribbons-The material was produced by reacting B2O3 with nanoporous carbon spheres under nitrogen at ca. 1750 °C. The BN nanospheres were characterized using scanning electron microscopy, high-resolution electron microscopy, and electron energy loss spectroscopy. The porous BN spheres show relatively large surface areas of ca. 290 m2/g and exhibit surprisingly stable field emission properties at low turn-on voltages (e.g., 1-1.3 Vlμm). We attribute these outstanding electron emission properties to the presence of finite BN ribbons located at the surface of the nanospheres (exhibiting zigzag edges), which behave like metals as confirmed by first-principles calculations. In addition, our ab initio theoretical results indicate that the work function associated to these zigzag BN ribbons is 1.3 eV lower when compared with BN-bulk material. Refereed/Peer-reviewed

High yields of dense, ‘clean’ and uniform arrays of well-aligned carbon nanotubes, with bamboo-like structure encapsulating gaseous nitrogen, were obtained by thermolyzing uniform aerosols of ferrocene/benzylamine solutions at 850 °C. Electron energy loss spectroscopy (EELS) studies reveal that up to 90% of these tubes contain molecular nitrogen in their cores. The materials were characterized by scanning electron microscopy, X-ray powder diffraction, high-resolution transmission electron microscopy, and EELS elemental mappings using an Omega Filter microscope. We envisage the material useful for storing large concentrations of relatively heavy gases such as nitrogen in confined volumes.

The temperature dependent thermoelectric power (TEP) of boron and nitrogen doped multi-walled carbon nanotube mats has been measured showing that such dopants can be used to modify the majority conduction from p-type to n-type. The TEP of boron doped nanotubes is positive, indicating hole-like carriers. In contrast, the nitrogen doped material exhibits negative TEP over the same temperature range, suggesting electron-like conduction. Therefore, the TEP distinct nonlinearites are primarily due to the formation of donor and acceptor states in the B- and N- doped materials. The sharply varying density of states used in our model can be directly correlated to the scanning tunneling spectroscopy studies of these materials., Comment: 4 pages, 3 figures, revtex 4, submitted to PRL

Gold nanoparticles were selectively attached to chemically functionalized surface sites on nitrogen-doped carbon (CNx) nanotubes. A cationic polyelectrolyte was adsorbed on the surface of the nanotubes by electrostatic interaction between carboxyl groups on the chemically oxidized nanotube surface and polyelectrolyte chains. Negatively charged 10 nm gold nanoparticles from a gold colloid suspension were subsequently anchored to the surface of the nanotubes through the electrostatic interaction between the polyelectrolyte and the nanoparticles. This approach provides an efficient method to attach other nanostructures to carbon nanotubes and can be used as an illustrative detection of the functional groups on carbon nanotube surfaces.

Field emission properties of B-doped carbon nanotubes are investigated from both theoretical and experimental standpoints. Using tight-binding and ab initio calculations, it is observed that B-saturating tip edges of carbon nanotubes induce the presence of large peaks within the local density of states (LDOS) located in an energy region close to the Fermi level (Ef). These localized states suggest a field emission enhancement for the B-doped tubes. In addition, ab initio theoretical results indicate that the work function for B-doped tubes is 1.7 eV lower when compared to pure carbon-terminated nanotubes. Experimentally, it is found that B-doped tubes, which are produced by arc discharge techniques and contain B mainly at the tips, exhibit stable electron field emission at lower turn-on voltages (1.4 V/mum) when compared to pure single- and multiwalled carbon nanotubes (2.8 and 3.0 V/mum, respectively) measured under the same conditions. We strongly believe our results will bring new insights in the fabrication of stable field emission sources.

Crossing single-walled carbon nanotubes can be joined by electron beam welding to form molecular junctions. Stable junctions of various geometries are created in situ in a transmission electron microscope. Electron beam exposure at high temperatures induces structural defects which promote the joining of tubes via cross-linking of dangling bonds. The observations are supported by molecular dynamics simulations which show that the creation of vacancies and interstitials induces the formation of junctions involving seven- or eight-membered carbon rings at the surface between the tubes.

Self-assembly pyrolytic routes to large arrays (

B x C y N z nanoscale materials, hybrids of h-BN and graphite, have been recently synthesised using various techniques. Here, we present the latest advances in the synthesis and characterisation of B–C–N nanotubes and nanofibres. In particular, we focus on layered BC 2 N, BN, BC and CN x systems, reviewing their production methods as well as their structural and electronic properties. These materials may find important applications in the fabrication of nanotransistors, robust nanocomposites, conducting polymers, storage components and field emission sources.

Molybdenum disulfide ((MoS2)n) nanotubes are generated when polycrystalline MoS2 powder, covered by Mo foil, is heated to ca. 1300 °C in the presence of H2S. Electron diffraction reveals the presence of zigzag arrangements within the tube walls.

Paramagnetism in boron-containing carbon nanotubes was detected by SQUID measurements, and a g -value of 2.0020, corresponding to the free carrier spin, was observed over a wide temperature range (108–455 K). This value implies intrinsic metallic behaviour and contrasts with thermally activated semiconduction which multi-walled carbon nanotubes usually exhibit.

The morphological and structural features of WS2 nanotubes, generated from WOx (x ≅ 2.7) needles, by an in-situ heating process, have been studied by electron microscopy and X-ray diffraction (XRD), in conjunction with computer simulation. The results show that these inorganic fullerene nanotubes exhibit interesting differences when compared with carbon nanotubes (CNTs). In some cases the tube tips or segments are open. Occasionally the tube walls may be uneven. The sulfur distribution within the tubes is uniform, except for the edge layers which appear to contain less sulfur. Defects are often observed, particularly in the outer shells, which may be due to defective encapsulated WOx phases. Octagonal and square-like defects appear to be associated with the closure of tube caps. Electron diffraction (ED) reveals that nearly half of the non-helical WS2 nanotubes are of the armchair-type. A mechanism has been proposed to account for the extended inorganic nanotube growth.

When nanotubes form in a carbon arc, the presence of boron results in long boron-doped carbon nanotubes which are generated as dominant zigzags. Metallic behaviour is observed, in contrast to carbon nanotubes, which are semi-conducting.

Powders of the nanoparticles were obtained from the colloidal solutions by removing the water with a rotary evaporator (bath temperature 50 C). Transmission electron micrographs of the samples were taken using a Philips CM 300 UT electron microscope, working at 300 kV acceleration voltage. A Philips Xpert system was used to measure the X-ray diffraction pattern of powder samples. UV-vis absorption spectra of the colloidal solutions were recorded with a Lambda 40 spectrometer (Perkin‐Elmer). Photoluminescence spectra were recorded with a Spex Fluoromax 2 spectrometer having a spectral resolution of 0.5 nm.

Carbon-encapsulated Sn−Pb nanowires are generated by electrolysis of graphite in molten LiCl containing these metals. SA-EDX analyses indicate a distinctive profile for the metal cores in which Sn predominates at one end and Pb at the other of the individual nanowires; X-ray diffraction measurements reveal that separate crystals of each metal can be distinguished, thus zone refining has occurred. The cores exhibit dynamic behavior under electron irradiation. A growth mechanism is proposed for the nanowires.

We investigate the growth of B-doped carbon nanotubes combining experimental and theoretical techniques. Electron microscopy observations and electron diffraction patterns reveal that B doping considerably increases the length of carbon tubes and leads to a remarkable preferred zigzag chirality. These findings are corroborated by first-principles static add dynamical simulations which indicate that, in the zigzag geometry, B atoms act as a surfactant during growth, preventing tube closure. This mechanism does not extend to armchair tubes, suggesting a helicity selection during growth.

and Ni deposited on a silica plate at 950 °C. High-resolution transmission electron microscopy (HRTEM) studies reveal that these tapered structures are almost completely filled with Ni and are closed at both ends. The diameters of the needles (2–5 μm in length) range between 10–20 nm at one end and 30–200 nm at the other. A surprisingly high degree of graphitization is observed in the walls of the nanotubes. These unique structures may prove useful as electrodes with various applications such as precision probes in biological systems or scanning tunnelling microscope tips.

Novel flower-like nanostructures consisting of silicon oxide nanofibers, radially attached to a single catalytic particle, were generated by solid-solid and gas-solid reactions under a temperature gradient. In this process, a mixture of SiC and Co powders, deposited on silica substrates and heated under an Ar/CO atmosphere at ca. 1500C, produced material with unusual three-dimensional (3D) networks of nanofibers of uniform diameter (ca. 20-120nm) and length (ca. 10-250mu;m). Scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray powder diffraction and energy dispersive X-ray (EDX) analyses reveal that the nanofibres are amorphous and consist only of silicon oxide, generated from the reaction of CO with SiC. Nanostructure formation is catalyzed by Co particles, which act as nucleation sites and templates for 3D growth. Experiments using Si3N4 and Si in conjunction with other catalysts (e.g. Fe, Ni and CoO) yield similar results and confirm that the resulting SiOx fibres display virtually unique and remarkable radial growth starting from single metal particles. These structures exhibit morphologies comparable to radiolarian and diatom skeletons and may provide insight into the formation of microbiological systems.

Pyrolysis of 2-amino-4,6-dichloro-s-triazine over laser-etched thin films of cobalt deposited on an inverted silica substrate generates aligned bundles and films of carbon nanotubes of uniform dimensions. Scanning electron microscopy, high resolution transmission electron microscopy, energy dispersive X-ray analyses, electron energy loss spectroscopy and electron diffraction studies reveal that the aligned tubes, which usually grow perpendicular to the substrate surface, are mainly straight (length ⩽100 μm; 30–50 nm OD), contain traces of nitrogen (

The electronic structure and spin magnetism for few-layer-graphene nanoribbons synthesized by chemical vapor deposition have been investigated using near-edge x-ray absorption fine structure (NEXAFS) and electron-spin resonance (ESR). For the pristine sample, a prepeak was observed below the pi* peak close to the Fermi level in NEXAFS, indicating the presence of additional electronic states close to the Fermi level. The intensity of this prepeak decreased with increasing annealing temperature and disappeared after annealing above 1500 degrees C. The ESR spectra, which proved the presence of localized spins, tracked the annealing-temperature-dependent behavior of the prepeak with fidelity. The NEXAFS and ESR results jointly confirm the existence of a magnetic edge state that originates from open nanographene edges. The disappearance of the edge state after annealing at higher temperatures is explained by the decrease in the population of open edges owing to loop formation of adjacent graphene edges.

"La nanociencia y nanotecnología se dedica a la creación de nuevos materiales con propiedades interesantes como dureza, conductividad, propiedades magnéticas. Ahora también, se está estudiando el uso de estos nanomateriales como bloques de construcción para crear nuevos materiales. En este trabajo se estudiaron arreglos ordenados y desordenados: 1) ópalo inverso de carbono y 2) bosques de nanotubos de carbono. Respecto al ópalo inverso de carbono, utilizamos un ópalo con nanopartículas de SiO2 (300 nm) ordenadas de manera FCC como molde para la fabricación de ópalo inverso de carbono. Este ópalo inverso de carbono fue sintetizado mediante la infiltración de una solución conteniendo sacarosa como fuente de carbono; además, en esta misma solución se agrego pirazina como fuente de nitrógeno para así obtener ópalo inverso de carbono dopado con nitrógeno. Por otro lado, utilizamos nanopartículas de SiO2 (10 y 100 nm) desordenadas como molde para sintetizar ópalo inverso de carbono dopado con nitrógeno. Estas muestras se caracterizaron mediante SEM, TEM, espectroscopía Raman, análisis termogravimétrico, adsorción de nitrógeno, difracción de rayos-X y espectroscopía de reflexión óptica. En los resultados obtenidos observamos ligeros cambios en la estructura de las muestras dependiendo de la concentración del dopaje, también observamos el corrimiento del pico de reflexión óptica dependiente a la concentración nitrógeno en la muestra; el corrimiento hacia el azul del pico de reflexión óptica dependiente a la concentración nitrógeno en la muestra. Posteriormente, realizamos el estudio de las propiedades físicas de ópalo inverso dopado con diferente contenido de nitrógeno y tamaño de poro. En general, variando la concentración de nitrógeno y el tamaño de poro se puede variar controladamente sus propiedades físicas como la resistencia, emisión de campo, magnetoresistencia y magnetización. La resistencia se variar desde 0.30 hasta 0.02  cm y dependiendo de su nivel de dopaje el mecanismo de transporte electrónico puede variar. En magnetoresistencia (MR) hay una transición de MR positivo a MR negativo, al variar de bajas hacia altas temperaturas. Así también, la magnetización de las muestras exhiben una transición de paramagnético a diamagnético al incrementar la temperatura; la temperatura de transición es más alta para poros más pequeños." "Nanoscience and nanotechnology are dedicated to the creation of new materials with interesting properties like hardness, conductivity, magnetic properties, among others. Now, there is also interest in the use of these materials as building blocks to create new materials. In this work ordered and disordered arrays were studied: 1) carbon inverse opal and 2) carbon nanotube forests. Regarding the carbon inverse opal, we used an opal with SiO2 nanoparticles (300 nm) ordered in a FCC manner as a template for the fabrication of carbon inverse opal. This carbon inverse opal was synthesized by the infiltration of a solution containing sucrose as a carbon source; also, in this same solution we added pyrazine as a nitrogen source to obtain nitrogen doped carbon inverse opal. On another hand, we used disordered SiO2 nanoparticles as a template to synthesize nitrogen doped carbon inverse opal. These samples were characterized by SEM, TEM, Raman spectroscopy, thermogravimetric analysis, nitrogen adsorption, X-ray diffraction and optical reflection spectroscopy. In the obtained results we observed slight changes in the structure depending on the doping concentration, also we observed the shift of the optical reflection peak depending upon the nitrogen concentration in the sample; observed a blue shift of the optical reflection peak dependent on the nitrogen concentration in the sample. Furthermore, we realized the study of the physical properties of the carbon inverse opal with different contents of nitrogen and pore size. In general, varying the nitrogen concentration and pore size it is possible to vary in a controlled manner the physical properties such as resistance, field emission, magnetoresistance and magnetization. The resistance was varied between 0.30 down to 0.02  cm and depending upon the degree of doping the transport mechanism of electrons may vary. In magnetoresistance (MR) there is a transition from positive MR to negative MR, when varying from low to high temperatures. Also, the magnetization of the samples exhibits a transition from paramagnetic to diamagnetic when increasing the temperature; the transition temperature is higher for smaller pore size. Finally, the carbon inverse opal doped with nitrogen was used as an acetone, ethanol and chloroform sensor, showing that doping with nitrogen effectively increases the sensing response signal."

Tesis (Maestría en Nanociencias y Nanotecnología) "Los nanotubos de carbono de pared múltiple (MWCNTs) exhiben excelentes propiedades mecánicas y electrónicas. Debido a su estructura y tamaño, los MWCNTs podrían ser utilizados como sustratos para la deposición de nanopartículas metálicas u óxidos metálicos que permitan el desarrollo de novedosos materiales compuestos. Estos materiales podrían ser utilizados como catalizadores, adsorbedores de gases, intercambiadores de iones, sensores químicos, bio-marcadores, etc. En este trabajo se presentan los resultados obtenidos al utilizar los MWCNTs como sustratos para el crecimiento de nanopartículas de óxido de zinc (ZnO), óxido de manganeso (III) (-Mn2O3) y plata (Ag). Nanopartículas de ZnO han sido eficiente y homogéneamente ancladas en dos tipos de nanotubos de carbono. Hemos utilizado como sustrato a nanotubos de carbono dopados con nitrógeno (CNx-MWNTs) y nanotubos de carbono funcionalizados con grupos carbonilo e hidroxilo (COx-MWNTs). El tamaño de partícula más pequeño fue obtenido utilizando los COx-MWNTs con un diámetro medio de partícula de 4.1 nm. Posteriormente, se desarrolló una novedosa metodología que nos permitió recubrir eficientemente a los MWCNTs con -Mn2O3 (tamaño de partícula desde 6 a 10 nm), sin emplear reactivos costosos y/o peligrosos. Finalmente, se diseñó un proceso sencillo para el anclaje de partículas de plata en diferentes tipos de nanotubos de carbono. Este método permite depositar nanopartículas de Ag (con un tamaño de partícula de 3 a 7 nm) sin el uso de agentes reductores externos, en este caso los MWCNTs podrían actuar como agentes reductores." "Multi-walled carbon nanotubes (MWCNTs) exhibit outstanding mechanical and electronic properties. Due to their structure, the MWCNTs could also play an important role as substrates for the deposition of metal and metal oxide nanoparticles that allow the development of novel composite materials. These materials could be used as catalysts, gas sensors, ion-exchange materials, gas adsorbers, biomarkers, drugs delivery systems, etc. The results obtained from the use of the MWCNTs as substrates for metal and metal oxide (e.g. ZnO, -Mn2O3 and Ag) nanoparticles are presented in this work. ZnO nanoparticles have been efficiently and homogeneously anchored on the surfaces of two types of carbon nanotubes. We use nitrogen-doped (CNx-MWNTs) and functionalized carbon nanotubes with oxygen groups (COx-MWNTs) as substrate. The smallest particles were deposited on the COx-MWNTs with a mean size of 4.1 nm. Furthermore, we developed a novel methodology that allows us to coat efficiently carbon nanotubes with -Mn2O3 nanoparticles (particle size from 6 to 10 nm) without employing expensive and hazardous chemicals. Finally, we developed a simple process able to anchor efficiently small Ag nanoparticles on different carbon nanotubes. This method is able to attach Ag particles (ranging from 3 to 7 nm in size) without any external reducing agent. In this case, the CNTs could act as reducing agents for the silver ions."