Nickel nanoparticles supported on carbon cloth (NiNP/CC) were prepared via Pulsed Laser Deposition (PLD) with three different deposition time (20 s, 40 s and 60 s). The materials were tested as electrocatalysts for urea electro-oxidation reaction (UER) in alkaline media. From Scanning Electron Microscopy (SEM), it was observed that the agglomeration of the nickel nanoparticles increased as the deposition time by PLD increased. Regarding UER, the maximum current density from cyclic voltammetry (CV) experiments, normalized by electroactive surface area (ESA), on NiNP/CC 20s catalysts was about 35.5% and 67.9% higher than that one obtained using NiNP/CC 40s and NiNP/CC 60s catalysts. The results from chronoamperometry (CA) measurements showed the same trend. Electrochemical Impedance Spectroscopy (EIS) measurements proved that the charge transfer resistance significantly decreased for UER process as the electrocatalytic activity of nickel nanoparticles increased. Thus, NiNP/CC 20s stands out as the best catalyst for UER in this study, probably due its small size of the particle's agglomeration and its better dispersion on the carbon cloth (CC), the support material.

The appearance of an sp-hybridization signal has previously been reported in Surface-Enhanced Raman spectra of carbon nanofoams prepared by pulsed laser deposition (PLD). The details of the mechanism for the formation of the sp-hybridized carbon atoms need still further clarification. For a better understanding we have studied two samples produced by PLD in the same experimental run by placing one substrate in front of the plasma plume and a second one beside the graphite target. In this configuration the gas pressure is the same at both sites but the collision energies between the formed nanoparticles are very different. Our present results from Surface Enhanced Raman Spectroscopy and High-Resolution Transmission Electron Microscopy lead us to propose that the sp signal comes mostly from short carbon atom chains formed between carbon nanoparticles due to relatively low-energy collisions at deposition.

We investigated the chemical, physical, and tribological properties of nanolubricants consisting of epoxidized sunflower oil with Cu nanoparticles as additive. These latter are produced by magnetron sputtering at distinct current levels in the deposition, to improve the development of nanolubricants by enhancing the nanoparticles dispersion. The nanolubricants are here characterized by Fourier transform infrared spectroscopy, zeta potential, ultraviolet–visible absorbance spectroscopy, small-angle X-ray scattering, and scanning electron microscopy. After all, the tribological properties of the bionanolubricants are investigated using a high-frequency reciprocating rig equipment, scanning electron microscopy, and energy dispersive spectroscopy. Our results disclose the nanolubricants produced using the magnetron sputtering technique have excellent nanoparticle dispersion, as well as good tribological performance.

Manganese oxide nanofoam has been prepared by pulsed laser deposition, from a metallic Mn target in a 5 Torr pressure O2 buffer atmosphere. The as-prepared samples were heat-treated at different temperatures (300 °C–500 °C) in air. Both as-deposited and heat-treated samples have a high porosity foam-like morphology, as shown by Field Emission Scanning Electron Microscopy. High Resolution Transmission Electron Microscopy revealed that the nanofoam is composed by linked nanoparticles with slight crystallization and growth of the nanoparticles due to heat-treatment, which was confirmed by X-ray diffraction, Raman Spectroscopy and X-ray Photoelectron Spectroscopy. These techniques also showed a variable oxide composition upon heat treatment. The supercapacitive properties of manganese oxide nanofoam treated at 300 °C exhibited a specific capacitance higher than 1000 F/g, in the 0 to +1.0 V potential range. After heat treatment at 400 °C and 500 °C, the specific capacitance decreased compared to that of the 300 °C treated sample. An increase of about 130% in the initial capacitance was obtained after 500 cycles for this sample. However, it decreases to one third of the maximum value after 5000 cycles. The results shows that the obtained manganese oxide nanofoam has very high specific capacitance but need to improve the cycle stability.

Nickel nanoparticles supported by commercial carbon paper (CP) are prepared by pulsed laser deposition with deposition time of 3, 6, and 12 min as a catalyst for urea electro-oxidation. The surface conditions and the morphologies of the prepared electrodes have been characterized by Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. Urea electro-oxidation reaction in KOH solution on the Ni/CP electrodes is investigated by cyclic voltammetry and chronoamperometry. The results show that the electrode with less Ni nanoparticle agglomeration shows higher peak current density, which was achieved in the 3 min deposition samples when normalized by electroactive surface areas. However, the highest current normalized by the area of the carbon paper was achieved in the 6 min deposition sample due to the larger quantity of Ni nanoparticles. All the samples show good stability. Our results suggest that the low density, low cost, and environmental friendly CP can be used as support for Ni nanoparticle as a catalyst for urea electro-oxidation. It thus has great potential for many applications involving urea oxidation, such as wastewater treatments.

Two superconducting intermetallic compounds in the Ni-Bi system, namely NiBi and NiBi3, can be formed as result of interdiffusion, if Ni/Bi are produced as bilayers at room temperature by pulsed laser deposition (PLD). These two equilibrium phases are responsible for the observed superconductivity in this kind of bilayer material. Due to different behavior in external magnetic fields, there appear two-step superconducting transitions in the electrical transport measurements. In this work we studied the superconducting and magnetic properties of the Ni-Bi bilayers with the formation of the two intermetallic compounds, NiBi and NiBi3, which have similar T-c similar to 4.0 K but very different upper critical magnetic fields at zero temperature [B-c2(0)]. The magnetic hysteresis loops of the pure NiBi3 phase show the behavior of a weak type II superconductor without strong pinning effect. Upon formation of the NiBi phase caused by highly energetic atoms during pulsed laser deposition, strong pinning effects appeared in the hysteresis loops below T-c. The isotherm V(I) curves show that the residual Ni layer does not induce spontaneous vortices in the NiBi or NiBi3 phases.

We prepared three distinct MnO2 nanostructures, and 976 F g−1 and 830 F cm−3 at 5 mV s−1 were obtained with a perpendicular columnar structure.

In this work, thin films of hydrogenated amorphous carbon (a-C:H) were deposited on silicon substrates from heptane and methane precursors by the radio frequency plasma-enhanced chemical vapor deposition (PECVD) technique, varying the self-bias voltage from -100 V to -900 V. As a liquid, heptane is safer, easier to handle, to store and stock, and presented advantages over methane as a precursor in the deposition of a-C:H films by PECVD as it allows deposition rates more than 4 times higher than of methane. Diamond-like carbon films deposited from heptane were also harder (22.5 GPa) and presented smaller intrinsic stress (3.5 GPa) than those obtained from methane (18.8 GPa and 4.1 GPa, respectively). In addition, these films have a smaller hydrogen content and a reduced sp(2) character. The observed behavior is consistent with the subplantation model, caused by the ion bombardment energy during deposition. The differences observed in the deposition from both precursors are related to the different number of carbon atoms of the parent molecules and lead to a change of structure and hardness that could be closely related to the structural changes observed by Raman spectroscopy. Films deposited from heptane may be promising for applications due to a higher hardness to elastic modulus ratio H/E of approximately 0.13 when compared to films deposited from methane.

Bi/Ni bilayers with varying Bi and Ni layer thicknesses have been prepared by (a) pulsed-laser deposition (PLD) at 300 K and (b) thermal evaporation at 4.2 K. A two-step superconducting transition appears on the electrical transport measurements in the samples prepared by PLD. High-resolution transmission and scanning transmission electron microscopy, supported by energy-dispersive x-ray spectroscopy (EDXS) analysis, reveal that two superconducting intermetallic alloys, namelyNiBi and NiBi3, are formed by interdiffusion, if the bilayers are prepared at 300 K. The T-c of the two phases behaves very differently in an external magnetic field and the upper critical magnetic fields at zero temperature [B-c2(0)] were estimated as 1.1 and 7.4 T, respectively. The lower value corresponds to the B-c2(0) of NiBi3 phase and the higher one is supposed to be of NiBi. These alloys are responsible for the superconductivity and the two-step transition appearing in the Bi/Ni bilayer system. Surprisingly, the Bi-rich phase (NiBi3) is formed near the Ni layer, while the Ni-rich phase (NiBi) is formed far from the Ni layer. The EDXS analysis at nanometer scale clearly shows an unusual increase of Ni concentration near the interface of Bi/substrate. The limited thickness of Bi layer in the interdiffusion process results in an unexpected distribution of Ni concentration. Samples prepared at 4.2 K after annealing at 300 K do not show any superconductivity, which indicates that a nonepitaxial Bi/Ni interface does not induce superconductivity in the case interdiffusion does not occur. These results offer a deeper understanding of the superconductivity in the Bi/Ni bilayer system.

In spite of crystalline bismuth (rhombohedra structure) and nickel (Face Centered Cubic structure) are not superconducting, Bi/Ni bi-layers show a superconducting transition at ~ 4 K and this has been attracted grate attention [1]. There are different interpretations of the superconductivity in Bi/Ni: Ni induced FCC Bi [2]; magnetic fluctuation at the interface of Ni/Bi induced superconductivity [3]; formation of NiBi3 at the interface [4], Bi induced superconductivity in Ni layer and formation of a very thin amorphous Bi layer formed at the interface of Ni and Bi [5], etc. In this work we study the superconductivity and microstructure of the Bi/Ni bilayer by means of transport and high resolution transmission electron microscopy (HRTEM), in order to find out what induced the superconductivity in Bi/Ni bilayer system. The thickness of the first deposited Bi layer is fixed as 38 nm and the followed deposited Ni layer changes from 2 nm to ~ 40 nm. The transport measurements exhibits superconductivity as expected (as shown in Fig. 1) and the critical superconducting transition temperature (Tc) is ~ 4 K, which is in agreement with the results in the literatures. The cross-section samples for TEM study have been prepared by FIB and when the deposited Ni layer is less than 8 nm, pure Ni layer cannot be seen in the sample (Fig. 2). It indicates that the Ni atoms diffused into the Bi layer during deposition.

In this work, we investigated the effects of postdeposition heat treatment on structural and magnetic properties of CoFe2O4 nanoparticles produced by pulsed laser deposition. Structural analysis by X-ray diffraction, transmission electron microscopy (TEM) and Mössbauer spectroscopy indicate the formation of a single phase cobalt ferrite nanoparticles with the size ranging from 4.3 to 33.3 nm depending on the annealing temperature. The magnetic properties of the samples were investigated in a wide temperature range (50–400 K). Noticeable effects of the cubic magnetocrystalline anisotropy on the magnetization process of nanoparticles were observed for samples annealed at 450 °C and 600 °C, while for samples as-deposited and annealed at 300 °C the magnetization properties were dominated by a uniaxial effective anisotropy. ΔM technique was used to investigate the magnetic interaction among the nanoparticles. Only demagnetizing interactions were observed for the sample annealed up to 300 °C, while for the samples treated at 450 °C and 600 °C, both magnetizing and demagnetizing interactions were observed. The results are discussed considering the evolution of the nanoparticles' nanostructure with anneals and its effects on the magnetic properties.

Bulk bismuth is a very unique semimetal with a rhombohedral structure and it has special properties such as large Fermi wavelengths, strong diamagnetism, and very high magnetoresistance. It is well known that the bulk Bi does not have a superconducting transition down to 50 mK at ambient pressure [1]. However, the Bi nanoparticles (NPs) embedded in insulator matrix [2], Bi nanowires [3] and Bi/Ni thin films [4] show a superconducting transition. For both the Bi nanoparticles and Bi/Ni layers, the interface plays a very important role in the superconducting transition and it needs a more detailed microstructural study at the atomic scale.

Journal Article HRTEM and HRSTEM Study of Nanostructured Materials Prepared by Pulsed Laser Deposition Get access Y T Xing, Y T Xing Instituto de Fisica, Universidade Federal Fluminense, Niteroi, Brasil Search for other works by this author on: Oxford Academic Google Scholar LY Liu, LY Liu DEMa, Pontificia Universidade Catolica do Rio de Janeiro, Rio de Janeiro, Brasil Search for other works by this author on: Oxford Academic Google Scholar D F Franceschini, D F Franceschini Instituto de Fisica, Universidade Federal Fluminense, Niteroi, Brasil Search for other works by this author on: Oxford Academic Google Scholar W C Nunes, W C Nunes Instituto de Fisica, Universidade Federal Fluminense, Niteroi, Brasil Search for other works by this author on: Oxford Academic Google Scholar DJ Smith, DJ Smith Department of Physics, Arizona State University, Tempe, USA Search for other works by this author on: Oxford Academic Google Scholar I G Solorzano I G Solorzano DEMa, Pontificia Universidade Catolica do Rio de Janeiro, Rio de Janeiro, Brasil Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 22, Issue S3, 1 July 2016, Pages 2012–2013, https://doi.org/10.1017/S1431927616010904 Published: 25 July 2016

Synthesis of nanoparticles free from toxic chemicals and solvents is highly seen for large-scale production processes, particularly for use in biomedical/biotechnological applications. So far, although several methods for synthesis of metal nanoparticles using citrus extracts have been described, none of them clarify which compounds are responsible for both reduction and stabilization of NPs. Here we report the role of citrus flavonoids, hesperidin, hesperetin, rutin, naringenin, quercetin and diosmin, in the synthesis of gold nanoparticles (AuNP) at room temperature. Only in the presence of the citrus flavonoids, diosmin (Dm), and hesperetin (Ht), the reduction of HAuCl4 in concentrations as high as 7 mM under alkaline conditions yielded concentrated and self-stabilized suspensions of uniform spherical nanoparticles with a narrow size distribution. We went further and focused on Ht, the most abundant flavonoid aglycone from citrus fruits known for its medicinal properties. HtAuNPs were characterized using high-resolution transmission electron microscopy, dynamic light scattering, X-ray photoelectron spectrometry and UV-Vis spectrophotometry. The NPs remained stable for months without significant changes in their shape and optical properties. Theoretical calculations using density functional theory were used to identify the functional groups involved in the electron transfer from the Ht molecules to gold, which seems to be the consequence of an initial complexation, leading to the reduction of Au3+ ions into Au-0. Besides, this procedure provides a one-pot method, showing potential for large-scale.

Several analytical techniques, such as N2 physisorption, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), temperature programmed reduction (TPR) and chemisorption were employed to characterize the structure of Co/γAl2O3 catalysts used for the production of carbon nanotubes by methane vapor deposition. The catalysts were studied after the calcination step and presented three main cobalt species, CoAl2O4, CoO and Co3O4. The CoAl2O4 species were well dispersed and were reduced only at high temperatures, rendering them inactive for the carbon nanotube production. In the case of the 1%Co/Al2O3 catalyst, the main cobalt species found was CoAl2O4. However, increasing the cobalt content in the catalysts led to a higher formation of Co3O4 as compared to CoO and CoAl2O4 species. The 2 and 3%Co/Al2O3 catalysts showed particle agglomeration during the pretreatment step that decreased selectivity towards nanotube production. The 4%Co/Al2O3 catalyst did not show particle agglomeration and presented a higher selectivity to carbon nanotube production, 71%, mainly multi-walled carbon nanotubes (MWNT).

A facile electrochemical method was applied to synthesize graphene oxide nanoplatelets and polyaniline nanofiber composite thin film electrodes for supercapacitors.

The influence of the support on carbon nanotube production by methane chemical vapor deposition (CVD) on cobalt catalysts was investigated. N-2 physisorption, X-ray diffractometry (XRD), temperature programmed reduction (TPR) and H-2 and CO chemisorption techniques were used to characterize the structure of cobalt catalysts supported on different metal oxides (Al2O3, SiO2, Nb2O5 and TiO2). Raman spectroscopy, temperature programmed oxidation (TPO) and scanning electron microscopy (SEM) were used for the characterization and quantification of produced carbon species. On carbon nanotube growth, the catalyst produced three main carbon species: amorphous carbon, single walled carbon nanotubes (SWNT) and multi walled carbon nanotubes (MWNT). The characterization techniques showed that the catalyst selectivity to each kind of nanotube depended on the cobalt particle size distribution, which was influenced by the textural properties of the support. Co/TiO2 showed the highest selectivity towards single wall nanotube formation. This high selectivity results from the narrow size distribution of cobalt particles on TiO2.

Combustion synthesis, a widely spread technique employed to produce low-cost high-yield oxide powders, was used to prepare fluoride powders for the first time. Surface morphology and structure of erbium (Er3+) doped strontium fluoride (SrF2) powders were investigated by scanning electronic microscopy, energy dispersive X-ray and X-ray powder diffraction. Samples were prepared with and without aluminum (Al) and we observed that the presence of Al helps the powder to crystallize in a pure SrF2 single cubic phase. Luminescence spectral analysis was also performed and we observed that among the samples investigated the Er3+:SrF2 powder prepared with Al using glycine is the most efficient luminescence up-converter. The luminescence results concords with Raman data of the samples.

Nanostrucured Europium oxide and hydroxide films were obtained by pulsed Nd:Yag (532 nm) laser ablation of an Europium metallic target, in the presence of a 1 mbar Helium buffer atmosphere. Both the produced film and the ambient plasma were characterized. The plasma was monitored by an electrostatic probe, for plume expansion in vacuum or in the presence of the buffer atmosphere. The time evolution of the ion saturation current was obtained for several probe to substrate distances. The results show the splitting of the plume into two velocity groups, being the lower velocity profile associated with metal cluster formation within the plume. The films were obtained in the presence of helium atmosphere, for several target to substrate distances. They were analyzed by Rutherford backscattering spectrometry (RBS), X-Ray Diffraction (XRD) and Atomic Force Microscopy, for samples as-deposited and treated at 600 degrees C in air. The results show that the as-deposited samples are amorphous and have chemical composition compatible with Europium hydroxide. The thermally treated samples show X-Ray diffraction peaks of Eu_2O_3, with chemical composition showing excess oxygen. Film nanostructuring was shown to be strongly correlated to cluster formation, as shown by velocity splitting in probe current versus time plots.