S. Velumani

Development of CdTe thin films on flexible substrates—a review

In the recent years there has been an increased interest in photovoltaic structures on lightweight flexible substrates. Photovoltaic structures on lightweight substrates have several advantages over the heavy glass-based structures in both terrestrial and space applications. CdTe is one of the leading candidates for the solar cells due to its optimum band gap and the variety of film preparation methods. The development of CdTe thin films on flexible substrates is discussed. The film growth and characterization are reviewed.

Structural and optical characterization of ball-milled copper-doped bismuth vanadium oxide (BiVO4)

Copper-doped BiVO4 nanoparticles were synthesized by a mechano-chemical method under optimized conditions to obtain a monoclinic scheelite structure. The crystal structure and its evolution with doping were investigated by X-ray powder diffraction, micro-Raman spectroscopy, field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HRTEM). Spherical shape particles with sizes ranging between 40 and 160 nm, which possess a monoclinic scheelite structure, were obtained. From the structural data analysis, it can be observed that the particle size decreases and distortions occur as the copper content increases in doped BiVO4. Chemical bonding and valence states of the Bi-4f, V-2p, O-1s and Cu-2p ions were investigated by XPS which revealed the location of Cu ions in the host lattice of BiVO4 in agreement with EPR investigations. UV-visible absorption experiments showed a broad band in the visible range with a small shift of the energy band-gap from 2.41 eV for undoped BiVO4 to 2.34 eV for 10 at.% Cu–BiVO4. Additional absorption band shoulders and widening of the optical absorption spectrum in the visible range with a well crystalline monoclinic scheelite structure pave the way for efficient visible light-driven photocatalytic activity. Photocatalytic measurements reprinted in supplementary data.

Camphor-mediated synthesis of carbon nanoparticles, graphitic shell encapsulated carbon nanocubes and carbon dots for bioimaging

A green method for an efficient synthesis of water-soluble carbon nanoparticles (CNPs), graphitic shell encapsulated carbon nanocubes (CNCs), Carbon dots (CDs) using Camphor (Cinnamomum camphora) is demonstrated. Here, we describe a competent molecular fusion and fission route for step-wise synthesis of CDs. Camphor on acidification and carbonization forms CNPs, which on alkaline hydrolysis form CNCs that are encapsulated by thick graphitic layers and on further reduction by sodium borohydride yielded CDs. Though excitation wavelength dependent photoluminescence is observed in all the three carbon nanostructures, CDs possess enhanced photoluminescent properties due to more defective carbonaceous structures. The surface hydroxyl and carboxyl functional groups make them water soluble in nature. They possess excellent photostability, higher quantum yield, increased absorption, decreased cytotoxicity and hence can be utilized as a proficient bio imaging agent.

Microplastics in tourist beaches of Huatulco Bay, Pacific coast of southern Mexico

The presence and impacts of plastic marine debris (PMD) have been documented in the oceans worldwide, and they deserve special attention. This study is the first to report the presence of microplastics in tourist beaches located in Huatulco Bay, southern Mexico. A total of 70 beach sediment samples (for 2 distinct seasons) were collected from Huatulco Bay in April 2013 and December 2014. The samples were subsequently extracted by scanning electron microscopy (SEM) to identify the fibrous microplastics (diameter<5mm). The maximum number of fibrous materials was found in April 2013 and December 2014 in the Rincón Sabroso beach (48/30g sediment) and the Cuatunalco beach (69/30g sediment), respectively. Overall, a high amount of microplastics is present in the Conejos, Tangolunda, Santa Cruz, and San Agustin beaches. The microplastics are mainly derived from tourism-based activities and effluents discharged from the hotels and restaurants located along the beaches.

Plasmonic/Magnetic Multifunctional nanoplatform for Cancer Theranostics

A multifunctional magneto-plasmonic CoFe2O4@Au core-shell nanoparticle was developed by iterative-seeding based method. This nanocargo consists of a cobalt ferrite kernel as a core (Nk) and multiple layers of gold as a functionalizable active stratum, (named as Nk@A after fifth iteration). Nk@A helps in augmenting the physiological stability and enhancing surface plasmon resonance (SPR) property. The targeted delivery of Doxorubicin using Nk@A as a nanopayload is demonstrated in this report. The drug release profile followed first order rate kinetics optimally at pH 5.4, which is considered as an endosomal pH of cells. The cellular MR imaging showed that Nk@A is an efficient T2 contrast agent for both L6 (r2-118.08 mM−1s−1) and Hep2 (r2-217.24 mM−1s−1) cells. Microwave based magnetic hyperthermia studies exhibited an augmentation in the temperature due to the transformation of radiation energy into heat at 2.45 GHz. There was an enhancement in cancer cell cytotoxicity when hyperthermia combined with chemotherapy. Hence, this single nanoplatform can deliver 3-pronged theranostic applications viz., targeted drug-delivery, T2 MR imaging and hyperthermia.

Cobalt ferrite nanowhiskers as T2 MRI contrast agent

A novel, one-step synthesis of one-dimensional cobalt ferrite nanowhiskers (CfW) is reported. SQUID studies confirmed that the monodispersed surfactant-free CfW exhibit superparamagnetic behaviour. This characteristic makes CfW an ideally suited contrast agent for T2-weighted MRI, thus proving to be very effective for biomedical applications.

Characterization of electrodeposited Zn1?xHgxSe thin films

In this work the synthesis of zinc mercury selenide thin films (Zn1−xHgxSe) by electrodeposition is carried out. The films were deposited onto conducting glass (SnO2) substrates from an aqueous solution bath containing ZnSO4, HgCl2 and SeO2 at bath temperatures between 30 °C and 70 °C. The influence of deposition parameters such as electrolyte composition, deposition potential and temperature on the crystallinity and composition of the films is studied. It is found that the amount of mercury content in the solution bath and deposition potential control the composition and structure of the alloy films. The films were characterized by x-ray diffraction (XRD), energy dispersive x-ray analysis (EDAX), optical absorption and scanning electron microscope (SEM) studies. Photoelectrochemical solar cells studies using Zn1−xHgxSe thin films showed improved performance for annealed and etched electrodes and the results are discussed.

Structural studies of BaTiO3:Er3+ and BaTiO3:Yb3+ powders synthesized by hydrothermal method

Erbium and ytterbium doped barium titanate nanopowders were prepared using the hydrothermal method. A barium titanate structure doped with rare earth ions manifested new characteristics and improved the field of application of optical devices such as trichromatic tubes, LCD displays, lamps, and infrared lasers. In this work, BaTiO3:Er3+ and BaTiO3:Yb3+ were prepared using barium chloride [BaCl2], titanium butoxide [C16H36O4Ti], erbium chloride [ErCl3] and ytterbium chloride [YbCl3] as precursors. Anhydrous methanol was employed as a solvent. Metallic potassium was used to promote solubility in the system and increase the pH to 13. This method yielded the formation of a predominantly cubic structure in both Er3+ and Yb3+ doped BaTiO3 powders. Characteristic bondings of BaTiO3 were observed with FT-IR spectroscopy. The predominantly cubic structure was confirmed by X-ray diffraction and micro-Raman analyses. The particle size (∼30 nm) was estimated using the Scherrer equation and X-ray diffraction data. The results were presented and discussed.

Electrochemical Deposition and Characterization of Cd-Fe-Se Thin Films

Cadmium iron selenide (Cd-Fe-Se) thin films were deposited onto tin oxide (SnO2) coated conducting glass substrates from an aqueous electrolytic bath containing CdSO4, FeSO4 and SeO2 by potentiostatic electrodeposition. The deposition potentials of Cadmium (Cd), Iron (Fe), Selenium (Se) and Cadmium-Iron-Selenide (Cd-Fe-Se) were determined from linear cathodic polarization curves. The deposited films were characterized by x-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive analysis by x-rays (EDX) and optical absorption techniques, respectively. X-ray diffraction patterns shows that the deposited films are found to be hexagonal structure with preferential orientation along (100) plane. The effect of FeSO4 concentration on structural, morphological, compositional and optical properties of the films are studied and discussed in detail.

Synthesis of ZnO nanorods using different precursor solutions and their two terminal device characterization

Abstract ZnO nanostructures such as nanoparticles, nanorods, nanotubes and nanoplates were prepared by the novel chemical solution route using different combinations of precursors such as zinc nitrate [Zn(NO3)2·6H2O] and sodium hydroxide [NaOH], zinc nitrate [Zn(NO3)2·6H2O] and hexamethylenetetramine (HMT) (C6H12N4), and zinc acetate [Zn(CH3COO)2·2H2O] and NaOH at low temperature. The effects of temperature and bath concentration for the synthesis of various ZnO nanostructures have been studied. Synthesized powders were characterized by X-ray diffraction, scanning electron microscope and photoluminescence. The crystalline structure, size and shape of the synthesized particles have been analyzed. Energy band gap values and photoluminescence emissions of the nanostructures were found to change according to the kind of the particles. Rod shaped ZnO have been obtained from the combination of zinc nitrate and HMT. The synthesized ZnO nanorods were aligned between lithographically patterned finger type metal contacts and their current–voltage response were measured.