Chang K. Hong

Cation distribution, structural, morphological and magnetic properties of Co1−xZnxFe2O4 (x = 0–1) nanoparticles

Co1−xZnxFe2O4 (x = 0.0, 0.2, 0.5, 0.6, 0.8, 1.0) nanoparticles (NPs) are prepared by a wet chemical co-precipitation method. The presence of zinc ions causes appreciable changes in the structural and magnetic properties of the Zn-substituted CoFe2O4. The structural, morphological and magnetic properties of the samples are determined and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). The particle size measured from TEM and XRD patterns confirms the nanosized dimension of the NPs in the size range of 9.0–15 nm. The saturation magnetization and the experimental magnetic moment are observed to initially increase (up to x = 0.2), which is explained by Neels collinear two-sublattice model, and then continuously decrease with further increase in Zn content x. This decrease obeys the three-sublattice model suggested by Yafet–Kittel (Y–K). The Y–K angle is zero for the CoFe2O4 NPs, it increases gradually with increasing Zn concentrations and can be extrapolated to 79.71 for ZnFe2O4 NPs.

Development of nanocoral-like Cd(SSe) thin films using an arrested precipitation technique and their application

Nanocrystalline cadmium sulfoselenide thin films have been synthesized using a self-organized arrested precipitation technique with different deposition times using triethanolamine as a complexing agent. Optical, structural, morphological and photoelectrochemical solar cell properties were investigated as a function of deposition time. A UV-Vis-NIR absorption study suggested a direct allowed transition type and the band gap energy decreased from 2.01 to 1.86 eV with the increase in deposition time. X-ray diffraction studies revealed that the thin films are nanocrystalline by nature with a pure hexagonal crystal structure and a calculated crystallite size of 51–68 nm. Field emission scanning electron microscopy demonstrated that the surface morphology was altered from nanoflakes to assorted nanoflakes–nanospheres and finally to a nanocoral-like morphology. X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy showed that the composition of the Cd(SSe) thin films was of good stoichiometry. Electrical conductivity and thermoelectric power measurements confirmed that the deposited films were n-type semiconductors. From J–V measurements, a highest photo-conversion efficiency of 0.57% was achieved. The significant boost in the PEC performance might be due to the improved crystallinity along with lower values of the grain boundary resistance, dislocation density and the microstrain of the Cd(SSe) thin films.

Single step hydrothermal synthesis of hierarchical TiO2 microflowers with radially assembled nanorods for enhanced photovoltaic performance

Herein, 3D hierarchical TiO2 microflowers with a well faceted profile and high crystallinity were successfully obtained via a surfactant directed single step facile hydrothermal technique. TiO2 thin films were subjected to different characterization techniques such as UV-Vis-NIR spectrometry, X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) for their optical, structural, morphological and compositional analysis. The morphological characterization indicated that the microflowers are made from numerous nanorods growing homocentrically. The length, diameter and degree of aggregation of the nanorods increase rapidly and become aggregated with increase in concentration of CTAB. The effect of CTAB concentration on the microstructure and photoelectric properties of solar cells i.e. open circuit voltage (Voc), short circuit current density (Jsc) and photoelectric conversion efficiency (η%) were investigated under UV illumination. The synthesized 3D hierarchical microflowers can act as a scattering overlayer and 1D nanorod underlayer. 1D nanorods can accelerate the movement of electrons in one direction, while microflowers can scatter light and can enhance the cell performance by light harvesting. An effective improvement in the photoconversion efficiency was observed and lies in the range 0.23% to 3.72%.

Langmuir–Blodgett self organized nanocrystalline tungsten oxide thin films for electrochromic performance

We explore a novel method to synthesize pebble-like nanocrystalline WO3 thin films for the first time by thermal decomposition of a multilayer Langmuir–Blodgett film of an octadecylamine–tungsten complex. The resulting film was thoroughly characterized by various characterization techniques. The electrochromic performance was evaluated in Li+ as a charge-balancing ion. The WO3 thin film displays a state-of-the-art performance with respect to optical modulation of 25.94% at λ630 nm with a very rapid coloration and bleaching time of 3.57 s and 3.14 s, respectively and a high coloration efficiency of 71.26 cm2 C−1. The excellent electrochromic performance can be attributed to the high size uniformity of WO3 nanoparticles, whose crystalline nature offer more active sites for Li+ diffusion and control the diffusion path length. Thus, the Langmuir–Blodgett WO3 film contributes to high energy conversion devices.

A facile and low cost strategy to synthesize Cd1−xZnxSe thin films for photoelectrochemical performance: effect of zinc content

In the present work, we report a facile chemical route for the deposition of Cd1−xZnxSe thin films using a simple, self-organized arrested precipitation technique (APT). The effect of Zn content on optical, structural, morphological, compositional and photoelectrochemical properties in Cd1−xZnxSe thin films was investigated. The optical properties and band gap profile of Cd1−xZnxSe thin films were varied with respect to Zn content. The estimated direct optical band gap was found to be in the range of 1.77 to 1.98 eV. X-ray diffraction (XRD) studies revealed that the films were nanocrystalline in nature with a pure cubic crystal structure and the calculated crystallite size lies in the range 36.5 to 66.3 nm. Scanning electron microscopy (SEM) demonstrates that the surface morphology can be improved with incorporation of Zn into the CdSe lattice. Compositional analysis of all samples was carried out using energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS), which confirms the stoichiometric deposition of Cd1−xZnxSe thin films. J–V characteristics of all samples were studied in sulphide/polysulphide redox electrolyte. A high efficiency of 0.68% was observed due to lower crystallite size and higher surface area. These results show that by varying Zn content in Cd1−xZnxSe thin films, the photoelectrochemical performance can be enhanced.

Effect of copper content on optostructural, morphological and photoelectrochemical properties of MoBi2−xCuxSe4 thin films

In the present investigation we have reported a facile chemical route for the deposition of MoBi2−xCuxSe4 (xxa0=xa00.0, 0.2, 0.4, 0.6, 0.8 and 1.0) thin films at room temperature by using a simple and self-organised arrested precipitation technique. The deposited samples were characterised for their structural, morphological, optical and photoelectrochemical properties. X-ray diffraction patterns revealed that, undoped MoBi2Se5 shows a rhombohedral crystal structure, while mixed rhombohedral and orthorhombic crystal structures were observed with shifting of diffraction peaks after copper doping. The scanning electron microscopy and transmission electron microscopy images revealed that the surface morphology was improved with copper content. Compositional analysis of all samples was carried out by using energy dispersive X-ray spectroscopy. The direct band gap energy of all the samples estimated from absorbance spectra varies from 1.26 to 1.60xa0eV. The photoelectrochemical properties of all samples were studied in I−/I3− redox electrolyte which demonstrated that the electrical conductivity was transformed from n-type to p-type after copper doping and photoelectrochemical response of p-type MoBi2−xCuxSe4 thin film electrode was improved with increasing copper content. The mechanism of change in the type of electrical conductivity and augmentation in photoelectrochemical response after copper doping are discussed.

Colloidal stability of polyethylene glycol functionalized Co0.5Zn0.5Fe2O4 nanoparticles: effect of pH, sample and salt concentration for hyperthermia application

The long-term colloidal stability of magnetic nanoparticles (MNPs) is an important goal when such MNPs are used for biomedical applications. Co0.5Zn0.5Fe2O4 (CZF) MNPs were functionalized with polyethylene glycol (PEG) and the effect of surface functionalization on the colloidal stability was investigated by dispersing them in double distilled water , phosphate buffer saline (PBS) and Dulbeccos modified Eagles medium with bovine serum albumin (DMEM-BSA) for possible application in magnetic hyperthermia. The colloidal stability was studied by measuring the particle charge and hydrodynamic diameter as a function of pH and ionic strength using the dynamic light scattering (DLS) method and zeta potential measurement. DLS and zeta potential results indicated that PEG-CZF MNPs dispersed in DDW exhibited poor stability, whereas those dispersed in PBS and DMEM-BSA exhibited excellent stability. An induction heating experiment revealed that the hyperthermia temperature (42–43 °C) could be achieved by the PEG-coated sample at a magnetic field of 168–335 Oe and a fixed frequency of 265 kHz. Interestingly, a high specific absorption rate (SAR) of 193 W g−1 was observed in the case of PEG coated MNPs in PBS medium, this is a very important parameter in hyperthermia applications and such a high SAR comes from the high contrition from the Brownian rotational relaxation because of the better dispersion of MNPs in PBS medium. PEG coated MNPs at concentrations below 1.8 mg mL−1 exhibited good viability above 86% in mice fibroblast L929 cells. The results suggest that co-precipitation synthesized CZF MNPs coated with PEG can be used as potential heating agents for magnetic particle hyperthermia.

The influence of coating on the structural, magnetic and colloidal properties of LSMO manganite and the heating mechanism for magnetic fluid hyperthermia application

Combustion synthesized superparamagnetic La0.7Sr0.3MnO3 nanoparticles have been studied for magnetic fluid hyperthermia applications. The effect of the coating concentration of acrypol on the colloidal, magnetic and heating properties of L0.7Sr0.3MnO3 have been studied. Uncoated and acrypol coated samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy and vibrating sample magnetometer studies. The power absorbed by acrypol coated nanoparticles suspended in phosphate buffer solution from a 265 kHz radio frequency field was measured as a function of coating concentration and field amplitude H. For H = 40.4 kA m−1 the maximum specific absorption rate was 80.82 W g−1 for 4% coating concentration. All results evidenced that among all the coated samples, 2, 4, 6 and 8% coating concentrations, the sample with 4% coating concentration shows the highest induced heating temperature, the highest specific absorption rate and the highest biocompatibility.

Effect of substrate on the nanostructured Bi2Se3 thin films for solar cell applications

In this article, we are reporting the effect of different substrates on the growth of nanostructured bismuth selenide (Bi2Se3) thin films for photoelectrochemical (PEC) application. Three different substrates are used such as glass, indium doped tin oxide (ITO) and fluorine doped tin oxide (FTO) for the deposition of Bi2Se3 thin film using arrested precipitation technique at room temperature (300xa0K). The optical, structural, morphological, compositional and PEC properties of Bi2Se3 thin films were studied by using various characterization techniques such as UV–Vis–NIR, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and PEC as a function of different substrates. Finally, the PEC performance of deposited thin films shows highest conversion efficiency 0.14xa0% for Bi2Se3 thin films deposited on FTO coated substrate surface.

An approach towards TiO2 chrysanthemum flowers with tunable properties: influence of reaction time in hydrothermal process

Rutile TiO2 chrysanthemum flowers were successfully synthesized by simple single step hydrothermal method. A possible formation mechanism based on hydrothermal synthesis was proposed on the basis of time dependent evolution of TiO2 chrysanthemum flowers. A series of TiO2 thin films with different morphologies and photoelectrochemical performance were prepared by varying the reaction time. Reaction time plays an important role in controlling the shape and size of nanorods as building blocks i.e. from orderly arranged TiO2 nanorods to well and completely grown TiO2 chrysanthemum flowers. The synthesized TiO2 chrysanthemum flowers were found to be nanocrystalline and there is formation of single pure phase TiO2 as confirmed by X-ray diffraction. The hierarchical TiO2 chrysanthemum structure endowed the high specific surface area and excellent light scattering property. Thus, this hierarchical architecture based photoanodes produce higher photoconversion efficiency i.e. 1.95xa0%. The enhanced photoelectrochemical performance can be attributed to improved charge separation by superior charge transportation through crystalline 3D TiO2 chrysanthemum flowers.