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Volume 5, Number 3, September 2017

Nowadays nanomaterials play important roles in the development of technologies such as LEDs, solar cells, etc. Inasmuch as, improving fabrication methods by minimizing cost and time remains the most important challenge for the incorporation of nanomaterials in technologies. In this special issue of the journal Advances in Nano Research, An International Journal, we include some selected research articles where apart from controlled synthesis, optical, electrical and magnetic behaviors of nanomaterials have been explored. In these articles, apart from fabrication and characterization of nanomaterial, their possible technological applications have been highlighted. The works highlight the progress in the area of nanomaterials in Mexico and some of other Latin American counties. The articles were received through invitation to the major research groups in Mexico and some other Latin American countries. They were peer reviewed by at least two reviewers, experts in their respective areas. We hope this special volume would be useful to the readers working on nanomaterials and their technological applications. Finally, we would like to thank Dr. Umapada Pal, Associate Editor of the Advances in Nano Research (ANR), for inviting us to work as guest editors for this special issue.

Key Words

(1) Dr. Ana L. Gonzalez:
Institute of Physics, Autonomous University of Puebla, Puebla, Pue. 72570, Mexico;
(2) Dr. Julio Villanueva-Cab:
Institute of Physics, Autonomous University of Puebla, Puebla, Pue. 72570, Mexico.

ZnO, ZnO: Cu, Ga, and ZnO: Cu, Ga, Ag thin films were obtained by oxidization of ZnS and ZnS: Cu, Ga films deposited onto glass substrates by electron-beam evaporation from ZnS and ZnS: Cu, Ga targets and from ZnS: Cu, Ga film additionally doped with Ag by the closed space sublimation technique at atmospheric pressure. The film thickness was about 1 μm. The oxidation was carried out at 600-650°C in air or in an atmosphere containing water vapor. Structural characteristics were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM). Photoluminescence (PL) spectra of the films were measured at 30-300 K using the excitation wavelengths of 337, 405 and 457.9 nm. As-deposited ZnS and ZnS: Cu, Ga films had cubic structure. The oxidation of the doped films in air or in water vapors led to complete ZnO phase transition. XRD and AFM studies showed that the grain sizes of oxidized films at wet annealing were larger than of the films after dry annealing. As-deposited doped and undoped ZnS thin films did not emit PL. Shape and intensity of the PL emission depended on doping and oxidation conditions. Emission intensity of the films annealed in water vapors was higher than of the films annealed in the air. PL of ZnO: Cu, Ga films excited by 337 nm wavelength exhibits UV (380 nm) and green emission (500 nm). PL spectra at 300 and 30 K excited by 457.9 and 405 nm wavelengths consisted of two bands – the green band at 500 nm and the red band at 650 nm. Location and intensities ratio depended on the preparation conditions.

Key Words
zinc oxide; zinc sulphide; oxidation; photoluminescence; x-ray diffraction

(1) Roberto Benjamín Cortés Herrera:
Instituto Politécnico Nacional - ENCB, Prolongación de Carpio y Plan de Ayala s/n, Col. Santo Tomás, 11340, Ciudad de México, México;
(2) Tetyana Kryshtab:
Instituto Politécnico Nacional - ESFM, Av. IPN, U.P.A.L.M., Edif. 9, 07738, Ciudad de México, México;
(3) José Alberto Andraca Adame:
Instituto Politécnico Nacional - CNMN, Av. Luis Enrique Erro S/N, U.P.A.L.M., 07738, Ciudad de México, México;
(4) Andriy Kryvko:
Instituto Politécnico Nacional - ESIME Zacatenco, U.P.A.L.M., Av. IPN, U.P.A.L.M., Edif. Z-4, C.P. 07738, Cuidad de México, México.

In this study we present the reaction mechanism of Cu2ZnSnSe4 (CZTSe) nanoparticles synthesized by microwave-assisted chemical synthesis. We performed reactions every 10 minutes in order to identify different phases during quaternary CZTSe formation. The powder samples were analyzed by x-ray diffraction (XRD), Raman spectroscopy, energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results showed that in the first minutes copper phases are predominant, then copper and tin secondary phases react to form ternary phase. The quaternary phase is formed at 50 minutes while ternary and secondary phases are consumed. At 60 minutes pure quaternary CZTSe phase is present. After 60 minutes the quaternary phase decomposes in the previous ternary and secondary phases, which indicates that 60 minutes is ideal reaction time. The EDS analysis of pure quaternary nanocrystals (CZTSe) showed stoichiometric relations similar to the reported research in the literature, which falls in the range of Cu/(Zn+Sn): 0.8-1.0, Zn/Sn: 1.0-1.20. In conclusion, the evolution pathway of CZTSe synthesized by this novel method is similar to other synthesis methods reported before. Nanoparticles synthesized in this study present desirable properties in order to use them in solar cell and photoelectrochemical cell applications.

Key Words
CZTSe; solar cell; nanoparticles; microwave-assisted chemical synthesis

(1) Odín Reyes, Mónica F. Sánchez, P.J. Sebastian:
Instituto de Energias Renovables-UNAM, Temixco, Morelos, 62580, México;
(2) Mou Pal:
Instituto de Fisica, BUAP, Puebla, 72570, Mexico;
(3) Jordi Llorca:
Institute of Energy Technologies and Barcelona Research Center, in Multiscale Science and Engineering, Universitat Politècnica de Catalunya, EEBE, Eduard Maristany 10-14, 08019 Barcelona, Spain.

The development of hybrid systems comprising nanoparticles and polymers is an opening pathway for engineering nanocomposites exhibiting outstanding mechanical, optical, electrical, and magnetic properties. Among inorganic counterpart, iron oxide nanoparticles (IONP) exhibit high magnetization, controllable surface chemistry, spintronic properties, and biological compatibility. These characteristics enable them as a platform for biomedical applications and building blocks for bottom-up approaches, such as the layer-by-layer (LbL). In this regard, the present study is addressed to investigate IONP synthesised through co-precipitation route (average diameter around 7 nm), with either positive or negative surface charges, LbL assembled with sodium sulfonated polystyrene (PSS) or polyaniline (PANI). The surface and internal morphologies, and electrochemical properties of these nanocomposites were probed with atomic force microscopy, UV-vis and Raman spectroscopy, scanning electron microscopy, cross-sectional transmission electron microscopy, and electrochemical measurements. The nanocomposites display a globular morphology with IONP densely packed while surface dressed by polyelectrolytes. The investigation of the effect of thermal annealing (300 up to 600

Key Words
nanocomposite; iron oxide nanoparticles; nanostructured electrodes; oxidation; layer-by-layer; polyaniline; sulfonated polystyrene; supercapacitors

(1) Camila J. Letti, Paulo C. Morais, Maria A.G. Soler:
Instituto de Fisica, Universidade de Brasilia, Brasilia-DF 70910-900, Brazil;
(2) Karla A.G. Costa, Marcos A. Gross, Leonardo G. Paterno:
Instituto de Quimica, Universidade de Brasilia, Brasilia-DF 70910-900, Brazil;
(3) Marcelo A. Pereira-da-Silva:
Instituto de Fisica de São Carlos USP, São Carlos-SP 13560-970, Brazil;
(4) Marcelo A. Pereira-da-Silva:
Centro Universitario Central Paulista – UNICEP, São Carlos-SP 13563-470, Brazil;
(5) Paulo C. Morais:
Schol of Chemistry and Chemical Engineering, Anhui University, Hefei 230601, China.

Graphene oxide (GO) was prepared by modified Hummer's method to produce reduced graphene oxide (RGO) following standard thermal and chemical reduction processes. Prepared RGO colloids were utilized to fabricate RGO films over glass and FTO coated glass substrates through drop-coating. A systematic study was performed to evaluate the effect of reduction degree on the optical and electrical properties of the RGO film. We demonstrate that both the reduction process (thermal and chemical) produce RGO films of similar optical and electrical behaviors. However, the RGO films fabricated using chemically reduced GO colloid render better performance in dye sensitized solar cells (DSSCs), when they are used as counter electrodes (CEs). It has been demonstrated that RGO films of optimum thicknesses fabricated using RGO colloids prepared using lower concentration of hydrazine reducer have better catalytic performance in DSSCs due to a better catalytic interaction with redox couple. The better catalytic performance of the RGO films fabricated at optimal hydrazine concentration is associated to their higher available surface area and lower grain boundaries.

Key Words
graphene oxide; reduced graphene oxide; DSSC; graphe film

(1) Manuel Rodriguez-Prez, Julio Villanueva-Cab, Umapada Pal:
Instituto de Física, Benemérita Universidad Autónoma de Puebla, Apdo. Postal J-48, Puebla, Pue. 72570, México;
(2) Manuel Rodriguez-Prez:
Facultad de Ingenieriá, Universidad Autónoma de Campeche, Campus V, s/n por Av. Ing. Humberto Lnz Cárdenas y Fracc. Ecológico Ambiental Siglo XXIII, Colonia Ex Hacienda Kála. C.P.24085. San Francisco de Campeche, México.

Multiwalled carbon-nanotubes (MWCNT) and micro-structured carbon, such as biochar or activated carbon (AC), have been seen to significantly increase the growth indices of certain plant species such as maize (Zea mays L.). Seed imbibition is the stage where environmental factors that affect water transport across the seed coat barrier, make a large impact. This work explores the effect on water imbibition by maize seeds when the aqueous environment surrounding the seed is diluted by small concentrations (10 and 20 mg/l) of pristine MWCNT (p-MWCNT), carboxylate functionalized MWCNT (COO-MWCNT) and AC. The degree of sensitivity of the process to (i) large structural changes is seen by utilizing the nano (the MWCNT) and the micro (the AC) allotropic forms of carbon; (ii) to small changes in the purity and morphology of the p-MWCNT by utilizing 95% pure and 99% pure p-MWCNTs of slightly differing morphologies; and (iii) to MWCNT functionalization by using highly pure (97%) COO-MWCNT. Water imbibition was monitored over a 15 hour period by Near Infrared Thermography (NIRT) and also by seed weighing. Seed surface topography was seen by SEM imaging. Analysis of the NIRT images suggests rapid seed surface topological changes with the quantity of water imbibed. While further work is necessary to arrive at a conclusive answer, this work shows that the imbibition phase of the maize seed is sensitive to the presence of MWCNT even to small differences in the purity of the p-MWCNT and to small differences in the physicochemical properties of the medium caused by the hydrophilic COO-MWCNT.

Key Words
MWCNT; maize; activated carbon; imbibitions; infrared thermography

(1) N. Dasgupta-Schubert:
Facultad de Ciencias Fisico-Matematicas, Instituto de Fisica y Matemáticas; Universidad Michoacana de San Nicolás de Hidalgo (U.M.S.N.H), Cd. Universitaria, Morelia, Mich. 58060, México;
(2) D.K. Tiwari:
CONACYT-El Colegio de Michoacán, La Piedad, Mich. 59370, México;
(3) E. Reyes Francis:
Facultad de Ingeniería Química, Instituto de Física y Matemáticas; Universidad Michoacana de San Nicolás de Hidalgo (U.M.S.N.H), Cd. Universitaria, Morelia, Mich. 58060, México;
(4) P. Martinez Torres, L.M. Villaseñor Cendejas:
Instituto de Física y Matemáticas; Universidad Michoacana de San Nicolás de Hidalgo (U.M.S.N.H), Cd. Universitaria, Morelia, Mich. 58060, Méexico;
(5) C. Villaseñor Mora:
Department de Ingeniería Quimica, Electronica y Biomédica, Universidad de Guanajuato (Campus León), León, Gto. 37150, México.

We report a simple eco-friendly process for the synthesis of gold nanoparticles (AuNPs) using aqueous extract from Coffea Arabica fruit. The formation of AuNPs was confirmed using absorption spectroscopy and scanning electron microscopy images. FT-IR analysis demonstrates the major functional groups present in Coffee Arabica fruit extract before and after synthesizing AuNPs. The Face Center Cubic (FCC) polycrystalline nature of these particles was identified by X-Ray diffraction (XRD) analysis. Taking into account the contribution of the biomass surrounding the AuNPs, dynamic light scattering (DLS) results revealed an average particle size of ~59 nm.

Key Words
green synthesis; AuNPs; FCC; Coffea Arabica; FE-SEM; DLS

(1) Naveen Kumar Reddy Bogireddy, V. Agarwal:
CIICAp, UAEM, Av. Universidad 1001 Col. Chamilpa, Cuernavaca, Morelos, 62210 Mexico;
(2) L. Martinez Gomez:
Universidad Nacional Autonoma de Mexico, Instituto de Ciencias Fisicas, Avenida Universidad s/n, Cuernavaca, MOR, 62210 Mexico;
(3) I. Osorio-Roman:
Facultad de Quimica, Pontificia Universidad Catolica de Chile, Santiago, Chile.

Spectroscopic investigation of Si quantum dots (Si-QDs) embedded in silicon nitride was performed over a broad stoichiometry range to optimize light emission. Plasma-enhanced chemical vapor deposition was used to grow the SiNx films on Si (001) substrates. The film composition was controlled via the flow ratio of silane (SiH4) and ammonia (NH3) in the range of R = 0.45-1.0 allowed to vary the Si excess in the range of 21-62 at.%. The films were submitted to annealing at 1100°C for 30 min in nitrogen to form the Si-QDs. The properties of as-deposited and annealed films were investigated using spectroscopic ellipsometry, Fourier transform infrared spectroscopy, Raman scattering and photoluminescence (PL) methods. Si-QDs were detected in SiNx films demonstrating the increase of sizes with Si excess. The residual amorphous Si clusters were found to be present in the films grown with Si excess higher than 50 at.%. Multi-component PL spectra at 300K in the range of 1.5-3.5 eV were detected and non-monotonous varying total PL peak versus Si excess was revealed. To identify the different PL components, the temperature dependence of PL spectra was investigated in the range of 20-300 K. The analysis allowed concluding that the "blue-orange" emission is due to the radiative defects in a SiNx matrix, whereas the "red" and "infrared" PL bands are caused by the exciton recombination in crystalline Si-QDs and amorphous Si clusters. The nature of radiative and no radiative defects in SiNx films is discussed. The ways to control the dominant PL emission mechanisms are proposed.

Key Words
silicon nanocrystals; silicon nitride; photoluminescence; spectroscopic ellipsometry; FTIR

(1) Tetyana V. Torchynska:
Instituto Politécnico Nacional, ESFM, Av. IPN, México DF, 07320, México;
(2) Leonardo G. Vega-Macotela:
Instituto Politécnico Nacional, ESIME, Av. IPN, México DF, 07320, México;
(3) Larysa Khomenkova:
V. Lashkaryov Institute of Semiconductor Physics at NASU, Av. Nauky 45, Kyiv, 03028, Ukraine;
(4) Abdelilah Slaoui:
ICube, 23 rue du Loess, BP 20 CR, 67037 Strasbourg Cedex 2, France.

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