Journal of Nano Research Vol. 28

Abstract: Silicene is becoming one of the most important two-dimensional materials. In this work, EEL Spectra were calculated for α-silicene (flat), and β-silicene (low-buckled, and theoretically the most stable). Band structures were determined using the semi-empirical Tight-Binding Method considering second nearest neighbors, sp³ model, Harrison's rule, and Slater-Koster parameterization. The dielectric function was calculated within the Random Phase Approximation and a space discretization scheme. We found that, compared to bulk Si, additional resonances appear which are red-shifted. Buckling gives rise to a richer structure at low energy.

Abstract: In this work, the effect of Pd addition on nanostructured TiO₂ powders is studied. The materials were obtained by the sol-gel method and characterized by XRD, Rietveld refinement, TEM, Raman and UV-vis spectroscopies. The crystal structure and the nature of the different TiO₂ phases were modified by varying the palladium/TiO₂ ratio: 0.01, 0.03, and 0.05. The XRD results revealed the presence of different combinations of TiO₂ (B), anatase, rutile and PdO phases as well as their coexistence in the different samples. The Rietveld analysis showed that the composition of the phases is rather affected by the amount of Pd added to the TiO₂ structure. The Raman spectroscopy confirmed the characteristic bands of the TiO₂ phases in the samples and their variation depending on the Pd/TiO₂ ratio. The TEM results indicated that the as-prepared samples displayed crystal sizes of nanometric order (˂ 80nm). The observed reduction of the band gap was also correlated with the combination of phases due to the palladium addition. All the Pd/TiO₂ samples showed a significant improvement in the elimination of 4-chlorophenol during the application of water treatment technology.

Abstract: The effect of magnesium doping in C₆₀ films grown on mica was studied. An improvement on the conductivity of the films was observed when the concentration of magnesium was increased. Structural changes were also observed from the diffraction patterns of x-ray at high magnesium concentrations. A new peak in the photoconductivity spectra was observed. This new peak was also attributed to structural changes, which would lead to some changes in the carrier transport properties. The pentagonal pinch A_g(2) mode of the Raman spectra weakened and shifted to lower frequencies when the magnesium concentration increased, which indicates that the C₆₀ molecule cage changed.

Abstract: Polymeric nanoparticles like chitosan nanoparticles may be used to deliver drugs to particular organs, such as heart. However, due to the lack of information about acute effects of chitosan nanoparticles in cardiac calcium handling, we evaluated the same in intact rat left ventricular myocytes. Chitosan nanoparticles were synthesized by ionic gelation method for three different concentrations of chitosan and tripolyphosphate (TPP) such as 1:1, 2:1 and 3:1, respectively. The size of the particles was below 100 nm for the 2:1 and 3:1 chitosan:TPP ratio and 300 nm for 1:1 ratio. The particles synthesized in 3:1 ratio were incubated for 0, 15, 30 and 60 minutes with Fluo-3 loaded cardiomyocytes, their effects were evaluated in local Ca²⁺ release events using confocal microscopy and compared with control cells. Chitosan nanoparticles increased the amplitude and size of Ca²⁺ spark by 14.1% and 24.1% at 30 minutes of incubation; while the increment was 24.7% and 28.4% at 60 minutes respectively. Accordingly, rising time of Ca²⁺ sparks was decreased by 47% at 30 minutes. These changes were reflected in increased local Ca²⁺ flux by 58.3% and spark-mediated Ca²⁺ leak by 145.9% and 146.5% at 30, and 60 minutes, respectively. Hence, these results indicate that chitosan nanoparticles modify the properties of local Ca²⁺ release events mainly at short incubation times and must be taken into account while using these nanoparticles in drug delivery.

Abstract: Nitrogen-doped multi-walled carbon nanotubes (CNxMWNTs) with multiple morphological defects were produced using a modified chemical vapor deposition (CVD) method. In a typical CNxMWNTs synthesis by CVD, an acetone trap is used to catch organic by-products from pyrolysis. In the present work, an aqueous solution of NaCl (26.82 wt%) was used in the trap, instead of acetone. Carbon nanotubes with sharp tips and lumps were found in the products. Scanning electron microscopy (SEM) and high resolution transmission electron microscopy showed the formation of nanoparticles of different shapes inside the nanotubes. The electronic and magnetic properties were studied using a physical properties measurement Evercool system (PPMS). With this simple change in the CVD-trap, it is possible to control the morphology of carbon nanotubes and metallic nanoparticles. Differences in gas flow are proposed as a possible mechanism to produce these changes in both nanoparticles and CNxMWNTs.

Abstract: This work presents the study of the electrical conductivity in MWNT as a function of three different chemical functionalization conditions. Unmodified and chemically modified MWNT were characterized by microRaman spectroscopy, XPS and SEM whereas the electrical conductivity was determined by dust compression technique. MWNT were modified using three different oxidation conditions: (1) a mix of concentrated acids, H₂SO₄/HNO₃ (3:1, v/v) sonicated for 2 h; (2) same mixture as (1) but using mechanical stirring for 6 h and (3) a reflux of an aqueous solution of HNO₃ (20%, v/v) and mechanical stirring for 6 h. The characterization evidenced different functionalization degrees, based on the formation and detection of functional groups such as ether, carbonyl and carboxyl in different percentages. The unmodified CNT presented a conductivity of 510 S/m which decreased as the functionalization degree increased. For reactions (1) and (2) such conductivity was reduced by 8.8 and 15.5%, respectively, whereas for condition (3) it only decreased 0.98%.

Abstract: Nickel hydroxide nanoporous electrochromic thin films were obtained by chemical bath deposition method using nickel nitrate in two different formulations. In one case, ammonium hydroxide controlled the precipitation of the β-Ni (OH)₂ phase through the formation of coordination compounds. In the second case, the decomposition of urea yielded the α-Ni (OH)₂ phase. After thermal annealing in air in between 250 and 300 °C, the electrochromic behavior of the films was examined by cyclic voltammetry and single wavelength transmittance. The optical contrast and structural transformations between colored and bleached states of the samples were studied by ex-situ optical transmittance, X-ray diffraction, as well as Raman and infrared reflectance spectroscopies. The α-Ni (OH)₂ films showed higher optical contrast and reversibility, properties associated with their porous morphology which is revealed by scanning electron microscopy studies.

Abstract: A comparative study between micropowders and nanopowders of Y₃Fe₅O₁₂ (YIG) by means of ferromagnetic resonance (FMR) is reported. Significant changes in lineshape of the FMR spectra between both samples are observed, in particular, the absorption mode in nanopowders have an internal structure which can be associated with magnetostatic modes. Additionally, a method to measure the non-resonant microwave absorption, as function of an applied magnetic field around zero field, known as the low-field microwave absorption (LFMA) is also employed. LFMA technique is used to give a further knowledge on the YIG samples, showing their main characteristics highlighted. These techniques are powerful tools for the research of magnetic materials at microwave frequencies.

Abstract: Experimental evidence of photon Bloch Oscillations (PBOs) and Zener tunneling (ZT) in dual-periodical (DP) superlattices made of porous silicon (PSi), is presented. An introduction of linear gradient in physical layer thicknesses in DP structure, composed by stacking two different periodic substructures N times, where (N-1) resonances appear, i.e, WSLs resonances and Zener tunneling of the nearest resonances of two consecutive minibands can be observed depending on the values of applied gradient. Theoretical time-resolved reflection and scattering state maps show photonic Bloch oscillations (BOs) and Zener tunneling for a range of incidence angles. Measured reflection reveals the presence of Wannier-Stark ladders (WSLs) and ZT in the near infrared region.

Abstract: SnS nanocrystals of sub-10 nm in size were synthesized by a room temperature, non-aqueous chemical route in the presence of different amounts of triethanolamine (TEA) used as a complexing agent. The crystallinity, size, morphology, chemical composition and optical properties of the as-prepared SnS nanoparticles were investigated by powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Energy-dispersive X-ray spectroscopy (EDS), micro Raman and optical absorption spectroscopy. The XRD analysis and HRTEM investigation of SnS nanoparticles confirmed the presence of crystalline orthorhombic SnS phase. Upon increasing the amount of TEA, the crystallite size of the samples decreased gradually showing evidence of quantum confinement. EDS analysis showed that SnS nanoparticles (NPs) grown in absence of TEA were highly stoichiometric whereas in TEA capped samples, the atomic concentration of S is slightly higher than that of Sn. As-synthesized SnS nanocrystals displayed strong absorption in the visible and near-infrared spectral regions followed by a blue shift of their absorption edge on increasing the TEA concentration. These nanoparticles were used to prepare SnS paste which was deposited on conducting glass substrates to obtain thin films for photovoltaic applications. The crystallinity, morphology, chemical composition and optical properties of annealed SnS films were investigated.