Felipe Cervantes Sodi | Universidad Iberoamericana - Mexico (original) (raw)

Papers by Felipe Cervantes Sodi

Research paper thumbnail of Chiraltube, rolling 2D materials into chiral nanotubes

Nanoscale advances, Dec 31, 2023

Research paper thumbnail of WS$_2$ Monolayer Integration in a FAPbI$_3$-based Heterostructure

arXiv (Cornell University), Apr 4, 2024

Incorporating a monolayer of WS2 via interface engineering enhances the overall physical properti... more Incorporating a monolayer of WS2 via interface engineering enhances the overall physical properties of a FAPbI3 perovskite based heterostructure. FAPbI3/WS2/TiO2/ITO and FAPbI3/TiO2/ITO heterostructures were analyzed by UV-Vis spectroscopy, X-ray diffraction, scanning electron microscopy and atomic force microscopy. The configuration with WS2 interlayer presents higher absorption in the visible region with a bandgap of ~1.44 eV. WS2 also enhances the deposition process of FAPbI3, resulting in the formation of pure photoactive α-phase without the non-photoactive-phase nor residual plumbates. The incorporation of the monolayer improves the crystalline structure of the FAPbI3, promoting a preferential growth in the [100] direction. The smooth surface of WS2 favors a homogeneous morphology and an increase of the grain size to ~4.5 μm, the largest reported for similar structures. Furthermore, the work function obtained lets us propose an enhance an adequate energy band alignment between FAPbI3 and the n-type layers for the electron flux to the cathode. These findings strongly suggest that the interfacial coupling of FAPbI3/WS2 could be a promising candidate in photovoltaic applications.

Research paper thumbnail of Chiraltube, rolling 2D materials into chiral nanotubes

Nanoscale Advances, 2024

Carbon nanotubes (NTs) are graphene sheets rolled into a 1D material, with a specific chirality t... more Carbon nanotubes (NTs) are graphene sheets rolled into a 1D material, with a specific chirality that defines its structure and properties. Graphene has triggered the development of thousands of 2D materials, which in principle could also be rolled into 1D NTs. However, most of these NTs have not been proposed due to difficulties in the generation of atomic coordinates for chiral NTs from 2D materials with a non-hexagonal lattice or multi-layered materials. In this paper we present Chiraltube, an open-source Python code that allows the quick generation of a complete NT with any chirality from the unit cell of its original 2D material. We explain the inner workings of the code as well as the theoretical background on which it is built, generalizing concepts from the construction of chiral and achiral carbon NTs to work on any other 2D material. We show various examples of the resulting chiral NT structures built from phosphorene, MoS 2 and Ti 3 C 2 , and present some analysis on the interatomic distortion in the outermost layers of these NTs, as well as the results of ab initio electronic structure calculations on a set of phosphorene NTs generated by the program, showing the immediate practicality and usefulness of the program. We also explore some limitations and details of the tool as well as further work to be done.

Research paper thumbnail of Observation on WSe 2 /WS 2 hetero-bilayer spectroscopic and transport features

Bulletin of the American Physical Society, Mar 2, 2020

Research paper thumbnail of Topotactical Route to Multiwalled Cerium Oxide Nanotubes from MWCNTs

Particle & Particle Systems Characterization

Research paper thumbnail of Viscous State Effect on the Activity of Fe

atalytic chemical vapor deposi-tion (CVD) is an effective site/size-selective synthesis technique... more atalytic chemical vapor deposi-tion (CVD) is an effective site/size-selective synthesis technique.17 The properties of the catalytic particle play a key role in the nucleation and growth processes, as well as in the final nanostructure morphology.711 At the nanoscale, two aspects are inter-related: the possibility of bulk and surface diffu-sion of the feedstock in and on the nanoparticles1214 and the thermody-namic state of the catalyst interacting with the growing nanostructure.1216 Feedstock diffusion has been thoroughly investigated in previous works,1214 but

Research paper thumbnail of Carbon Nanotubes Functionalized by Nanoparticles of Platinum

Materials Science Forum, 2014

Carbon nanotubes (CNT) based gas sensors have attracted interest due to their excellent propertie... more Carbon nanotubes (CNT) based gas sensors have attracted interest due to their excellent properties. Several studies have reported changes in the CNT’s electrical properties when functionalized with platinum (Pt) nanoparticles. In this investigation, the vapor phase impregnation decomposition (VPID) method was employed to incorporate Pt nanoparticles on CNT. Both, Pt nanoparticles and CNT were characterized by high resolution transmission electron microscopy (HR-TEM). The sensitivity of sensors based on CNT doped with Pt, was evaluated with ozone molecules. TEM images showed low and heterogeneous distribution on the surface of carbon nanotubes. The gas evaluation of CNT-Pt sensor presents good and quick response to ozone molecules at different concentrations and temperatures. The best response was found to be at 120 °C.

Research paper thumbnail of Ozone Sensing Based on Palladium Decorated Carbon Nanotubes

Sensors, 2014

Multiwall carbon nanotubes (MWCNTs) were easily and efficiently decorated with Pd nanoparticles t... more Multiwall carbon nanotubes (MWCNTs) were easily and efficiently decorated with Pd nanoparticles through a vapor-phase impregnation-decomposition method starting from palladium acetylacetonates. The sensor device consisted on a film of sensitive material (MWCNTs-Pd) deposited by drop coating on platinum interdigitated electrodes on a SiO 2 substrate. The sensor exhibited a resistance change to ozone (O 3) with a response time of 60 s at different temperatures and the capability of detecting concentrations up to 20 ppb. The sensor shows the best response when exposed to O 3 at 120 °C. The device shows a very reproducible sensor performance, with high repeatability, full recovery and efficient response.

Research paper thumbnail of Evaluating the biological risk of functionalized multiwalled carbon nanotubes and functionalized oxygen-doped multiwalled carbon nanotubes as possible toxic, carcinogenic, and embryotoxic agents

International journal of nanomedicine, 2017

Carbon nanotubes (CNTs) have been a focus of attention due to their possible applications in medi... more Carbon nanotubes (CNTs) have been a focus of attention due to their possible applications in medicine, by serving as scaffolds for cell growth and proliferation and improving mesenchymal cell transplantation and engraftment. The emphasis on the benefits of CNTs has been offset by the ample debate on the safety of nanotechnologies. In this study, we determine whether functionalized multiwalled CNTs (fMWCNTs) and functionalized oxygen-doped multiwalled CNTs (fCOxs) have toxic effects on rat mesenchymal stem cells (MSCs) in vitro by analyzing morphology and cell proliferation and, using in vivo models, whether they are able to transform MSCs in cancer cells or induce embryotoxicity. Our results demonstrate that there are statistically significant differences in cell proliferation and the cell cycle of MSCs in culture. We identified dramatic changes in cells that were treated with fMWCNTs. Our evaluation of the transformation to cancer cells and cytotoxicity process showed little effect...

Research paper thumbnail of Effect of cellulose nanoparticles from garlic waste on the structural, mechanical, thermal, and dye removal properties of chitosan/alginate aerogels

Journal of Polymer Research, 2022

Research paper thumbnail of Structured light using carbon nanostructures driven by Kerr nonlinearities and a magnetic field

Physical Chemistry Chemical Physics, 2021

A substantial influence of a magnetic field on the third-order nonlinear optical properties exhib... more A substantial influence of a magnetic field on the third-order nonlinear optical properties exhibited by aggregated networks of aligned carbon nanotubes (CNT) is reported by systematic measurements. A two-wave mixing...

Research paper thumbnail of Effect of ball milling on cellulose nanoparticles structure obtained from garlic and agave waste

Carbohydrate Polymers, 2021

The aim of this study was to obtain cellulose and cellulose nanoparticles (CNP) from garlic and a... more The aim of this study was to obtain cellulose and cellulose nanoparticles (CNP) from garlic and agave wastes, as well as elucidating its structure at different scales using microscopy and spectroscopy techniques. Cellulose is isolated by using a sequential extractive process and monitored by CLSM and SEM, while CNP are produced in a high-energy planetary mill. FTIR and XRD confirmed the presence of cellulose type I and CI and Dhkl was used to evaluate the size of CNP. The corresponding crystalline structure, d-spacing and angles obtained from crystalline regions of CNP were estimated by TEM and computational simulation. It is shown that the triclinic phase is predominant in G, and a monoclinic conformation in CNP for A. The novelty of this contribution is to demonstrate that the crystalline structure of CNP, extracted from different agro-food wastes, depends on its initial microstructural arrangement (laminar or fibrillar).

Research paper thumbnail of A Spray Pyrolysis Method to Grow Carbon Nanotubes on Carbon Fibres, Steel and Ceramic Bricks

Journal of Nanoscience and Nanotechnology, 2015

We demonstrate a spray pyrolysis method to grow carbon nanotubes (CNTs) with high degree of cryst... more We demonstrate a spray pyrolysis method to grow carbon nanotubes (CNTs) with high degree of crystallinity, aspect ratio and degree of alignment on a variety of different substrates, such as conventional steel, carbon fibres (CF) and ceramics. The process consists in the chemical vapour deposition of both a thin SiO 2 layer and CNTs that subsequently grow on this thin layer. After CNT growth, increases in specific surface by factors of 1000 and 30 for the steel and CF samples, respectively, are observed. CNTs growth on ceramic surfaces results in a surface resistance of 37.5 Ohm/sq. When using conventional steel as a rector tube, we observed CNTs growth rates of 0.6 g/min. Details of nanotube morphology and the growth mechanism are discussed. Since the method discussed here is highly versatile, it opens up a wide variety of applications in which specific substrates could be used in combination with CNTs.

Research paper thumbnail of Selective synthesis of double helices of carbon nanotube bundles grown on treated metallic substrates

physica status solidi (b), 2012

Research paper thumbnail of Influence of silver decoration on the nonlinear optical absorption exhibited by multiwall carbon nanotubes

Journal of Nanoparticle Research, 2014

A study about the optical and electrical response exhibited by multi-wall carbon nanotubes (MWCNT... more A study about the optical and electrical response exhibited by multi-wall carbon nanotubes (MWCNTs) decorated by silver nanoparticles (Ag NPs) is presented. The size of the NPs varies in the range from 35 to 65 nm, with an average size of 47 nm. The samples were prepared by a chemical vapor deposition method. The third-order nonlinear optical response of the samples was evaluated by using single pulses of 1 ns at 532 nm wavelength. A vectorial two-wave mixing configuration was employed in order to measure the absorptive and refractive nonlinearities. An optical Kerr effect and a two-photon absorption process were identified as the main physical phenomena responsible for the thirdorder optical nonlinearities in the MWCNTs; however, a saturated optical absorption was developed by the sample when the tubes were decorated by Ag. Moreover, an important modification in the electrical capacitance exhibited by the studied sample after the inclusion of Ag NPs was observed. It is estimated that metallic NPs are capable to modulate nonlinear optical processes in decorated CNTs by selective near-resonant energy transfers.

Research paper thumbnail of Synthesis of highly dispersed platinum particles on carbon nanotubes by an in situ vapor-phase method

Journal of Alloys and Compounds, 2014

Highly dispersed Pt nanoparticles were prepared on functionalized multi-walled carbon nanotubes (... more Highly dispersed Pt nanoparticles were prepared on functionalized multi-walled carbon nanotubes (f-MWCNTs) using a simple in situ vapor-phase method. The method consisted in two-step procedure in which an initial mixture of Pt precursor (Pt-acac) and f-MWCNTs was heated in a quartz tube reactor, first at 180°C and then at 400°C. Fourier transform infrared spectroscopy (FTIR-ATR), thermal gravimetric analysis (TGA) and X-ray diffraction (XRD) were used to follow the chemical and structural transformations of mixture components during heating steps. The functionalization of MWCNTs with HNO 3 / H 2 SO 4 solution resulted in formation of surface carbonyl groups. The FTIR-ATR and XRD results indicated that individual Pt-acac withstood heating at 180°C, whereas it was dissociated when heated in contact with f-MWCNTs at the same temperature. Thus, the functional carbonyl groups were found to be responsible for assisted decomposition of Pt-acac at 180°C. Since carbonyl groups served as reaction sites for decomposition of Pt-acac, the resulting particles were highly and homogeneously dispersed on the surface of MWCNTs even the relatively high metallic loading of 27 wt%. TEM observations revealed that crystalline Pt particles exhibit narrow size distribution with a mean size of 2.3 nm.

Research paper thumbnail of Carbon nanotube bundles self-assembled in double helix microstructures

Carbon, 2012

Double helix microstructures consisting of two parallel strands, each composed of hundreds of mul... more Double helix microstructures consisting of two parallel strands, each composed of hundreds of multiwalled carbon nanotubes (MWCNTs) are synthesised by chemical vapour deposition (CVD) of ferrocene/toluene vapours on thermochemically treated metal substrates, such as steel, Cu, Al and W. The thermochemical treatment produces a thin and brittle layer of SiO x. During the CVD process, carbon nanotubes (CNT) grow adhered to this layer, and as growth progresses, small SiO x microparticles detach from the substrate, directing the helical development of the growing MWCNTs double strands. This growth model for the helical microstructures is compared in the manuscript with models previously reported for coiled carbon fibres grown in the gas phase. A unique aspect of these double helices when they are composed of carbon nanotubes is that they grow on top of a forest of aligned CNTs.

Research paper thumbnail of Photoconductive logic gate based on platinum decorated carbon nanotubes

Applied Optics, 2013

Electrical and nonlinear optical experiments were performed on multiwall carbon nanotubes (CNTs) ... more Electrical and nonlinear optical experiments were performed on multiwall carbon nanotubes (CNTs) prepared by a chemical vapor deposition method. We report that the incorporation of platinum particles on the CNTs surface originates an enhancement in the photoconductive properties with noticeable capabilities to modulate optical and electrical signals. The photoconductive logic gate function OR was experimentally demonstrated using a simple photoconductive platform based on our samples. A two-photon absorption effect was identified as the main mechanism of third-order optical nonlinearity under a nonresonant nanosecond excitation. Multiphotonic interactions were described in order to explain the observed behavior.

Research paper thumbnail of Investigation of Growth Kinetics of Fe2B Layers on AISI 1518 Steel by the Integral Method

High Temperature Materials and Processes, 2019

The AISI 1518 steel was pack-borided in the temperature range 1123–1273 K for a treatment ranging... more The AISI 1518 steel was pack-borided in the temperature range 1123–1273 K for a treatment ranging from 2 to 8 h. A compact single boride layer (Fe2B) was formed at the surface of the AISI 1518 steel using the mixture of powders composed of 20 % B4C, 10 % KBF4 and 70 % SiC. The following experimental techniques such as scanning electron microscopy coupled with EDS analysis and X-ray diffraction analysis were employed to characterize the pack-borided AISI 1518 steel. An alternative model, based on the integral mass balance equation, was used to estimate the boron diffusion coefficients in the Fe2B layers in the temperature range 1123–1273 K. Finally, the value of activation energy for boron diffusion in the AISI 1518 steel was estimated and compared with the literature data. Furthermore, the present model was validated by comparing the experimental value of Fe2B layer thickness, obtained at 1253 K for 2 h of treatment, with the predicted value.

Research paper thumbnail of Effect of Functionalized Carbon Nanotubes and their Citric Acid Polymerization on Mesenchymal Stem Cells In Vitro

Journal of Nanomaterials

The effects of acid-functionalized and polycitric acid- (PCA-) polymerized carbon nanotubes (CNTs... more The effects of acid-functionalized and polycitric acid- (PCA-) polymerized carbon nanotubes (CNTs) in contact with the extracellular membrane of mesenchymal stem cells (MSC), a genetically unmodified cell line with differentiation capability, was evaluated with different cellular parameters. The modified CNTs show differences in the analyzed biological behaviors, that is, intracellular incorporation, cell proliferation, apoptosis, and cytotoxicity as compared with those unpolymerized nanotubes. Due to the reduced cellular uptake of polymerized CNTs, PCA-polymerized CNTs are less cytotoxic and are associated with less apoptotic cell death than the acid-functionalized ones. The effects of nitrogen-doped CNTs (CNx) is also reported, showing that functionalized undoped CNTs present strong stimulation of cell proliferation, whereas functionalized and polymerized CNxs stimulate an apoptotic behavior. The study of MSCs in contact with CNTs and PCA is challenging due to the complexity of it...

Research paper thumbnail of Chiraltube, rolling 2D materials into chiral nanotubes

Nanoscale advances, Dec 31, 2023

Research paper thumbnail of WS$_2$ Monolayer Integration in a FAPbI$_3$-based Heterostructure

arXiv (Cornell University), Apr 4, 2024

Incorporating a monolayer of WS2 via interface engineering enhances the overall physical properti... more Incorporating a monolayer of WS2 via interface engineering enhances the overall physical properties of a FAPbI3 perovskite based heterostructure. FAPbI3/WS2/TiO2/ITO and FAPbI3/TiO2/ITO heterostructures were analyzed by UV-Vis spectroscopy, X-ray diffraction, scanning electron microscopy and atomic force microscopy. The configuration with WS2 interlayer presents higher absorption in the visible region with a bandgap of ~1.44 eV. WS2 also enhances the deposition process of FAPbI3, resulting in the formation of pure photoactive α-phase without the non-photoactive-phase nor residual plumbates. The incorporation of the monolayer improves the crystalline structure of the FAPbI3, promoting a preferential growth in the [100] direction. The smooth surface of WS2 favors a homogeneous morphology and an increase of the grain size to ~4.5 μm, the largest reported for similar structures. Furthermore, the work function obtained lets us propose an enhance an adequate energy band alignment between FAPbI3 and the n-type layers for the electron flux to the cathode. These findings strongly suggest that the interfacial coupling of FAPbI3/WS2 could be a promising candidate in photovoltaic applications.

Research paper thumbnail of Chiraltube, rolling 2D materials into chiral nanotubes

Nanoscale Advances, 2024

Carbon nanotubes (NTs) are graphene sheets rolled into a 1D material, with a specific chirality t... more Carbon nanotubes (NTs) are graphene sheets rolled into a 1D material, with a specific chirality that defines its structure and properties. Graphene has triggered the development of thousands of 2D materials, which in principle could also be rolled into 1D NTs. However, most of these NTs have not been proposed due to difficulties in the generation of atomic coordinates for chiral NTs from 2D materials with a non-hexagonal lattice or multi-layered materials. In this paper we present Chiraltube, an open-source Python code that allows the quick generation of a complete NT with any chirality from the unit cell of its original 2D material. We explain the inner workings of the code as well as the theoretical background on which it is built, generalizing concepts from the construction of chiral and achiral carbon NTs to work on any other 2D material. We show various examples of the resulting chiral NT structures built from phosphorene, MoS 2 and Ti 3 C 2 , and present some analysis on the interatomic distortion in the outermost layers of these NTs, as well as the results of ab initio electronic structure calculations on a set of phosphorene NTs generated by the program, showing the immediate practicality and usefulness of the program. We also explore some limitations and details of the tool as well as further work to be done.

Research paper thumbnail of Observation on WSe 2 /WS 2 hetero-bilayer spectroscopic and transport features

Bulletin of the American Physical Society, Mar 2, 2020

Research paper thumbnail of Topotactical Route to Multiwalled Cerium Oxide Nanotubes from MWCNTs

Particle & Particle Systems Characterization

Research paper thumbnail of Viscous State Effect on the Activity of Fe

atalytic chemical vapor deposi-tion (CVD) is an effective site/size-selective synthesis technique... more atalytic chemical vapor deposi-tion (CVD) is an effective site/size-selective synthesis technique.17 The properties of the catalytic particle play a key role in the nucleation and growth processes, as well as in the final nanostructure morphology.711 At the nanoscale, two aspects are inter-related: the possibility of bulk and surface diffu-sion of the feedstock in and on the nanoparticles1214 and the thermody-namic state of the catalyst interacting with the growing nanostructure.1216 Feedstock diffusion has been thoroughly investigated in previous works,1214 but

Research paper thumbnail of Carbon Nanotubes Functionalized by Nanoparticles of Platinum

Materials Science Forum, 2014

Carbon nanotubes (CNT) based gas sensors have attracted interest due to their excellent propertie... more Carbon nanotubes (CNT) based gas sensors have attracted interest due to their excellent properties. Several studies have reported changes in the CNT’s electrical properties when functionalized with platinum (Pt) nanoparticles. In this investigation, the vapor phase impregnation decomposition (VPID) method was employed to incorporate Pt nanoparticles on CNT. Both, Pt nanoparticles and CNT were characterized by high resolution transmission electron microscopy (HR-TEM). The sensitivity of sensors based on CNT doped with Pt, was evaluated with ozone molecules. TEM images showed low and heterogeneous distribution on the surface of carbon nanotubes. The gas evaluation of CNT-Pt sensor presents good and quick response to ozone molecules at different concentrations and temperatures. The best response was found to be at 120 °C.

Research paper thumbnail of Ozone Sensing Based on Palladium Decorated Carbon Nanotubes

Sensors, 2014

Multiwall carbon nanotubes (MWCNTs) were easily and efficiently decorated with Pd nanoparticles t... more Multiwall carbon nanotubes (MWCNTs) were easily and efficiently decorated with Pd nanoparticles through a vapor-phase impregnation-decomposition method starting from palladium acetylacetonates. The sensor device consisted on a film of sensitive material (MWCNTs-Pd) deposited by drop coating on platinum interdigitated electrodes on a SiO 2 substrate. The sensor exhibited a resistance change to ozone (O 3) with a response time of 60 s at different temperatures and the capability of detecting concentrations up to 20 ppb. The sensor shows the best response when exposed to O 3 at 120 °C. The device shows a very reproducible sensor performance, with high repeatability, full recovery and efficient response.

Research paper thumbnail of Evaluating the biological risk of functionalized multiwalled carbon nanotubes and functionalized oxygen-doped multiwalled carbon nanotubes as possible toxic, carcinogenic, and embryotoxic agents

International journal of nanomedicine, 2017

Carbon nanotubes (CNTs) have been a focus of attention due to their possible applications in medi... more Carbon nanotubes (CNTs) have been a focus of attention due to their possible applications in medicine, by serving as scaffolds for cell growth and proliferation and improving mesenchymal cell transplantation and engraftment. The emphasis on the benefits of CNTs has been offset by the ample debate on the safety of nanotechnologies. In this study, we determine whether functionalized multiwalled CNTs (fMWCNTs) and functionalized oxygen-doped multiwalled CNTs (fCOxs) have toxic effects on rat mesenchymal stem cells (MSCs) in vitro by analyzing morphology and cell proliferation and, using in vivo models, whether they are able to transform MSCs in cancer cells or induce embryotoxicity. Our results demonstrate that there are statistically significant differences in cell proliferation and the cell cycle of MSCs in culture. We identified dramatic changes in cells that were treated with fMWCNTs. Our evaluation of the transformation to cancer cells and cytotoxicity process showed little effect...

Research paper thumbnail of Effect of cellulose nanoparticles from garlic waste on the structural, mechanical, thermal, and dye removal properties of chitosan/alginate aerogels

Journal of Polymer Research, 2022

Research paper thumbnail of Structured light using carbon nanostructures driven by Kerr nonlinearities and a magnetic field

Physical Chemistry Chemical Physics, 2021

A substantial influence of a magnetic field on the third-order nonlinear optical properties exhib... more A substantial influence of a magnetic field on the third-order nonlinear optical properties exhibited by aggregated networks of aligned carbon nanotubes (CNT) is reported by systematic measurements. A two-wave mixing...

Research paper thumbnail of Effect of ball milling on cellulose nanoparticles structure obtained from garlic and agave waste

Carbohydrate Polymers, 2021

The aim of this study was to obtain cellulose and cellulose nanoparticles (CNP) from garlic and a... more The aim of this study was to obtain cellulose and cellulose nanoparticles (CNP) from garlic and agave wastes, as well as elucidating its structure at different scales using microscopy and spectroscopy techniques. Cellulose is isolated by using a sequential extractive process and monitored by CLSM and SEM, while CNP are produced in a high-energy planetary mill. FTIR and XRD confirmed the presence of cellulose type I and CI and Dhkl was used to evaluate the size of CNP. The corresponding crystalline structure, d-spacing and angles obtained from crystalline regions of CNP were estimated by TEM and computational simulation. It is shown that the triclinic phase is predominant in G, and a monoclinic conformation in CNP for A. The novelty of this contribution is to demonstrate that the crystalline structure of CNP, extracted from different agro-food wastes, depends on its initial microstructural arrangement (laminar or fibrillar).

Research paper thumbnail of A Spray Pyrolysis Method to Grow Carbon Nanotubes on Carbon Fibres, Steel and Ceramic Bricks

Journal of Nanoscience and Nanotechnology, 2015

We demonstrate a spray pyrolysis method to grow carbon nanotubes (CNTs) with high degree of cryst... more We demonstrate a spray pyrolysis method to grow carbon nanotubes (CNTs) with high degree of crystallinity, aspect ratio and degree of alignment on a variety of different substrates, such as conventional steel, carbon fibres (CF) and ceramics. The process consists in the chemical vapour deposition of both a thin SiO 2 layer and CNTs that subsequently grow on this thin layer. After CNT growth, increases in specific surface by factors of 1000 and 30 for the steel and CF samples, respectively, are observed. CNTs growth on ceramic surfaces results in a surface resistance of 37.5 Ohm/sq. When using conventional steel as a rector tube, we observed CNTs growth rates of 0.6 g/min. Details of nanotube morphology and the growth mechanism are discussed. Since the method discussed here is highly versatile, it opens up a wide variety of applications in which specific substrates could be used in combination with CNTs.

Research paper thumbnail of Selective synthesis of double helices of carbon nanotube bundles grown on treated metallic substrates

physica status solidi (b), 2012

Research paper thumbnail of Influence of silver decoration on the nonlinear optical absorption exhibited by multiwall carbon nanotubes

Journal of Nanoparticle Research, 2014

A study about the optical and electrical response exhibited by multi-wall carbon nanotubes (MWCNT... more A study about the optical and electrical response exhibited by multi-wall carbon nanotubes (MWCNTs) decorated by silver nanoparticles (Ag NPs) is presented. The size of the NPs varies in the range from 35 to 65 nm, with an average size of 47 nm. The samples were prepared by a chemical vapor deposition method. The third-order nonlinear optical response of the samples was evaluated by using single pulses of 1 ns at 532 nm wavelength. A vectorial two-wave mixing configuration was employed in order to measure the absorptive and refractive nonlinearities. An optical Kerr effect and a two-photon absorption process were identified as the main physical phenomena responsible for the thirdorder optical nonlinearities in the MWCNTs; however, a saturated optical absorption was developed by the sample when the tubes were decorated by Ag. Moreover, an important modification in the electrical capacitance exhibited by the studied sample after the inclusion of Ag NPs was observed. It is estimated that metallic NPs are capable to modulate nonlinear optical processes in decorated CNTs by selective near-resonant energy transfers.

Research paper thumbnail of Synthesis of highly dispersed platinum particles on carbon nanotubes by an in situ vapor-phase method

Journal of Alloys and Compounds, 2014

Highly dispersed Pt nanoparticles were prepared on functionalized multi-walled carbon nanotubes (... more Highly dispersed Pt nanoparticles were prepared on functionalized multi-walled carbon nanotubes (f-MWCNTs) using a simple in situ vapor-phase method. The method consisted in two-step procedure in which an initial mixture of Pt precursor (Pt-acac) and f-MWCNTs was heated in a quartz tube reactor, first at 180°C and then at 400°C. Fourier transform infrared spectroscopy (FTIR-ATR), thermal gravimetric analysis (TGA) and X-ray diffraction (XRD) were used to follow the chemical and structural transformations of mixture components during heating steps. The functionalization of MWCNTs with HNO 3 / H 2 SO 4 solution resulted in formation of surface carbonyl groups. The FTIR-ATR and XRD results indicated that individual Pt-acac withstood heating at 180°C, whereas it was dissociated when heated in contact with f-MWCNTs at the same temperature. Thus, the functional carbonyl groups were found to be responsible for assisted decomposition of Pt-acac at 180°C. Since carbonyl groups served as reaction sites for decomposition of Pt-acac, the resulting particles were highly and homogeneously dispersed on the surface of MWCNTs even the relatively high metallic loading of 27 wt%. TEM observations revealed that crystalline Pt particles exhibit narrow size distribution with a mean size of 2.3 nm.

Research paper thumbnail of Carbon nanotube bundles self-assembled in double helix microstructures

Carbon, 2012

Double helix microstructures consisting of two parallel strands, each composed of hundreds of mul... more Double helix microstructures consisting of two parallel strands, each composed of hundreds of multiwalled carbon nanotubes (MWCNTs) are synthesised by chemical vapour deposition (CVD) of ferrocene/toluene vapours on thermochemically treated metal substrates, such as steel, Cu, Al and W. The thermochemical treatment produces a thin and brittle layer of SiO x. During the CVD process, carbon nanotubes (CNT) grow adhered to this layer, and as growth progresses, small SiO x microparticles detach from the substrate, directing the helical development of the growing MWCNTs double strands. This growth model for the helical microstructures is compared in the manuscript with models previously reported for coiled carbon fibres grown in the gas phase. A unique aspect of these double helices when they are composed of carbon nanotubes is that they grow on top of a forest of aligned CNTs.

Research paper thumbnail of Photoconductive logic gate based on platinum decorated carbon nanotubes

Applied Optics, 2013

Electrical and nonlinear optical experiments were performed on multiwall carbon nanotubes (CNTs) ... more Electrical and nonlinear optical experiments were performed on multiwall carbon nanotubes (CNTs) prepared by a chemical vapor deposition method. We report that the incorporation of platinum particles on the CNTs surface originates an enhancement in the photoconductive properties with noticeable capabilities to modulate optical and electrical signals. The photoconductive logic gate function OR was experimentally demonstrated using a simple photoconductive platform based on our samples. A two-photon absorption effect was identified as the main mechanism of third-order optical nonlinearity under a nonresonant nanosecond excitation. Multiphotonic interactions were described in order to explain the observed behavior.

Research paper thumbnail of Investigation of Growth Kinetics of Fe2B Layers on AISI 1518 Steel by the Integral Method

High Temperature Materials and Processes, 2019

The AISI 1518 steel was pack-borided in the temperature range 1123–1273 K for a treatment ranging... more The AISI 1518 steel was pack-borided in the temperature range 1123–1273 K for a treatment ranging from 2 to 8 h. A compact single boride layer (Fe2B) was formed at the surface of the AISI 1518 steel using the mixture of powders composed of 20 % B4C, 10 % KBF4 and 70 % SiC. The following experimental techniques such as scanning electron microscopy coupled with EDS analysis and X-ray diffraction analysis were employed to characterize the pack-borided AISI 1518 steel. An alternative model, based on the integral mass balance equation, was used to estimate the boron diffusion coefficients in the Fe2B layers in the temperature range 1123–1273 K. Finally, the value of activation energy for boron diffusion in the AISI 1518 steel was estimated and compared with the literature data. Furthermore, the present model was validated by comparing the experimental value of Fe2B layer thickness, obtained at 1253 K for 2 h of treatment, with the predicted value.

Research paper thumbnail of Effect of Functionalized Carbon Nanotubes and their Citric Acid Polymerization on Mesenchymal Stem Cells In Vitro

Journal of Nanomaterials

The effects of acid-functionalized and polycitric acid- (PCA-) polymerized carbon nanotubes (CNTs... more The effects of acid-functionalized and polycitric acid- (PCA-) polymerized carbon nanotubes (CNTs) in contact with the extracellular membrane of mesenchymal stem cells (MSC), a genetically unmodified cell line with differentiation capability, was evaluated with different cellular parameters. The modified CNTs show differences in the analyzed biological behaviors, that is, intracellular incorporation, cell proliferation, apoptosis, and cytotoxicity as compared with those unpolymerized nanotubes. Due to the reduced cellular uptake of polymerized CNTs, PCA-polymerized CNTs are less cytotoxic and are associated with less apoptotic cell death than the acid-functionalized ones. The effects of nitrogen-doped CNTs (CNx) is also reported, showing that functionalized undoped CNTs present strong stimulation of cell proliferation, whereas functionalized and polymerized CNxs stimulate an apoptotic behavior. The study of MSCs in contact with CNTs and PCA is challenging due to the complexity of it...