H. C. Jeon

Electronic and optical properties of CdZnO quantum well structures with electric field and polarization effects

Electronic, optical, and electrical properties of CdZnO/MgZnO quantum well (QW) structures, considering internal field and polarization effect, are investigated by using many-body theory. The CdZnO/MgZnO QW structure with higher Cd composition, which has deeper and stronger confinement, is found to have smaller optical gain because the strain-induced piezoelectric polarization and spontaneous polarization in the well increase with the inclusion of Cd. The internal field and polarization is reduced effectively by using the ferroelectric dipole moment of the Li addition in the well region of the Li-doped CdZnO/ZnMgO QW structure. These results demonstrate that a high-performance optical devices operation can be realized in CdZnO/MgZnO QW structures by eliminating the droop phenomenon.

Clarification of enhanced ferromagnetism in Be-codoped InMnP fabricated using Mn/InP:Be bilayers grown by molecular beam epitaxy

The p-type InMnP:Be epilayers were prepared by the sequential growth of Mn/InP:Be bilayers using molecular-beam-epitaxy and the subsequent in-situ annealing at 200–300 °C. In triple-axis x-ray diffraction patterns, the samples revealed a shoulder peak indicative of intrinsic InMnP. The ferromagnetic transition in InMnP:Be was observed to occur at the elevated temperature of ∼140 K, and the ferromagnetic spin-domains clearly appeared in magnetic force microscopy images. The improved ferromagnetic properties are attributed to the increased p–d hybridation due to high p-type conductivity of InMnP:Be (p ∼ 1020 cm−3). The results suggest that enhanced ferromagnetism can be effectively obtained from Be-codoped InMnP.

Phototoxicity free quantum dot-based niosome formulation for controlled drug release and its monitoring

A novel niosomes-based system composed of Hypromellose (HPMC) functionalized fluorescent, biocompatible ZnS:Mn quantum dots (QDs), and anti-HIV drug Tenofovir disoproxil fumarate (TDF) was designed. An appropriate ratio of surfactant Sorbitan Monostearate (SPAN-60) and cholesterol was used to obtain an optimal entrapment efficiency. Initially, after observing the successful interaction of HPMC with SPAN-60, the noisome formulation including (QDs + drug) and HPMC-coated QDs was synthesized by a wet chemical route and characterized by X-ray diffraction (XRD), Transmission electron microscope (TEM) and Selected Electron Diffraction (SAED). Secondly, (QDs + drug) loaded niosome formulations were studied by varying the ratio of SPAN-60 and cholesterol. Multiple studies were done to characterize the shape, size, viscosity, colloidal stability, and entrapment efficiency of (QDs + drug) loaded niosomes. Lastly, pH-dependent (QDs + drug) release profiles were studied by a spectroscopic technique considering the pH of the human gastrointestinal region to obtain the formulation stability of (QDs + drug) release from the niosome vesicles. These studies also include pH-dependent photo-stability measurements based on laser-induced multiphoton excitation technique in the Infrared region. The multiphoton time-resolved studies were completed to avoid the UV induced phototoxicity in the drug delivery modules. Current studies on the formulation of niosomes-based (QDs + drug) system laid a foundation to make a complete phototoxicity free system for tracking controlled drug release and its imaging.

Development of Humidity Sensor Using Nanoporous Polycarbonate Membranes

In the present work, the effect of temperature and moisture has been studied on nano-porous polycarbonate membranes of size 15, 50, and 80 nm, respectively to formulate the calibration curves for the future development of humidity sensors. These studies were conducted for virgin as well as humid samples while the temperature range was kept from room temperature to 160°C. Interesting variations in the capacitance with pore size and temperature have been observed. Calibration curves demonstrate that nanoporous polycarbonate samples are one of the important candidates for developing humidity sensors. In addition surface behavior has also been studied for the selective samples to better understand the dielectric behavior for nascent as well as moisturized samples.

Effects of applied electric fields on the optical properties of CdZnO quantum well structures

CdZnO/MgZnO QW structures with higher Cd quantity are found to have smaller optical gain because of the strain-induced piezoelectric polarization and the spontaneous polarization. These strain-induced polarizations can be reduced effectively by applied electric fields in CdZnO/ZnMgO QW structures with high Cd quantity. For optical properties of CdZnO/MgZnO QW structures, the optical gain is increased because the internal field is compensated with the reverse field, confirmed by Stark shifts. These results demonstrate that a high-performance optical-devices operation can be realized in CdZnO/MgZnO QW structures by eliminating the droop phenomenon.