A. Majid

ZnO nanoparticles as drug delivery agent for photodynamic therapy

Multidrug resistance (MDR) limits the success of many tumoricidal drugs. Non-significant accumulation of the drug into the target site is one major problem in photodynamic therapy. Nanoparticles are extensively used as efficient drug carriers in various local infectious and premalignant biological tissues. Due to their unique physical and chemical properties, PEGylated zinc oxide nanoparticles (ZnO NPs) exhibit high drug loading capacities, sustained drug release profiles and long-term anticancer efficacy. (Polyethylene glycol) PEG-zinc oxide nanoparticles were synthesized using the aquis chemical technique. Morphology/structural analysis of the said nanoparticles was confirmed by applying many techniques, e.g. scanning electron microscopy (SEM) and XRD. Average grain size of the nanoparticles, which was ≈100 nm, was calculated by applying the Scherrer formula. The PEGylated ZnO NPs were loaded with protoporphyrin IX (PpIX) to enhance the capability of drug carrying potency. Current work focused on the comparison of the cell killing effect (apoptosis/necrosis) by functionalizing different nanostructures via PEGylated ZnO NPs and bare ZnO NPs using the free-standing drug delivery procedure. ZnO NPs were used as anticancer drug vehicles because of their biocompatibility and bio-safety profile. The apoptotic effect of PEGylated tumoricidal drugs has been studied in human muscle carcinoma (RD cell line) in the dark as well as under laser exposure. It was concluded that PpIX localization was a significant time greater using encapsulation as compared to a conventional drug delivery system. This new technique may find excellent opportunities in the field of nanomedicine, especially in a multidrug delivery system.

Corrigendum: ZnO nanoparticles as drug delivery agent for photodynamic therapy (2014 Laser Phys. Lett. 11 025601)

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4d transition-metal impurity rhodium in GaAs grown by metal-organic chemical vapor deposition

Deep levels associated with 4d transition-metal impurity rhodium have been investigated in GaAs epitaxial layers grown by metal-organic chemical vapor deposition, using deep level transient spectroscopy (DLTS) technique. A comprehensive study of deep levels in the entire bandgap of GaAs has been carried out using both n- and p-type GaAs crystals over a wide temperature scan range, 12–470 K. In the n-type, Rh-doped material, two prominent broadbands of deep levels are found to be associated with Rh impurity; one in the upper-half and the other in the lower-half bandgap. In addition, one relatively small peak at the high temperature end of the majority-carrier emission spectra, corresponds to a deep level at Ec−0.92u2002eV, is also detected in the n-type Rh-doped samples. The minority carrier (hole) emission band in n-type material is found to consist of a doublet of hole emitting deep levels, labeled RhA and RhB, in the lower-half bandgap. This doublet is clearly observed to correspond to two Rh-related deep l...

Rhodium-related deep levels in n-type MOCVD GaAs

Abstract Preliminary results on the study of deep levels associated with 4d-transition metal, rhodium, in crystalline GaAs grown by metal-organic chemical vapour deposition (MOCVD) technique are reported for the first time. Deep level transient spectroscopy on n-type GaAs doped in situ with Rh during MOCVD growth reveals a broad majority carrier emission peak. The peak corresponds to a band of deep levels extending over the energy range 0.57–0.65xa0eV below the conduction band edge with lower-energy states having lower electron capture cross-sections. The deep levels show a pronounced dependence of electron emission rate on the junction electric field. Minority carrier (hole) emission spectra at zero bias show a pronounced Rh-related deep-level peak with a low-temperature shoulder. The dominant level in the lower half-gap is found to have a position E v +0.44xa0eV, with a field-dependent emission rate signature.

Temperature effect on device characteristics of InGaAs/GaAs quantum dot solar cell

This paper investigated the temperature effect on the electrical properties of an In0.5Ga0.5As/GaAs QD solar cell, leading to a better understanding of the basic cell characteristics influenced by QD incorporation which is of great importance for future design of high efficiency QD solar cells.

MOCVD Grown Quantum Dot-in-a-Well Solar Cells

This paper reports the experimental work on the characterization of quantum dot-in-well (DWELL) solar cell grown by metal-organic chemical vapor deposition (MOCVD) without employing any post-growing optimization like antireflection coating and metal grid. The structure of the 10-layer DWELL solar cells is studied by cross-sectional transmission electron microscopy (TEM). Room temperature photoluminescence (PL) spectra show strong quantization at 1178.5 nm with a linewidth of 79.9 nm. External quantum efficiency spectra show enhancement in the spectral response of the photocurrent with respect to the reference quantum dot cell (without DWELL structure). In spite of the reduction in conversion efficiency due to poor collection of current in external circuit compared to reference quantum dot cell it show the improvement in open circuit voltage.

Electric-Field-Enhanced Thermal Emission from Osmium-Related Deep Level in n-GaAs

Deep-level defects related with 5d transition metal, osmium (Os) have been studied in ntype GaAs. Os has been incorporated in epitaxial n-GaAs layers in situ, during growth by lowpressure metal-organic chemical vapour phase epitaxy (MOVPE) technique. Mesa p+nn+ junction diodes are fabricated for investigations by deep level transient spectroscopy (DLTS). Two deeplevel peaks, observed in majority carrier (electron) emission spectra, Os1 and Os2, show a significant shift in peak positions to lower temperatures with the applied junction reverse bias, demonstrating enhancement of the thermal emission rate by the junction electric field. Doublecorrelation DLTS (DDLTS) measurements have been employed for accurate quantitative investigations of the observed field dependence. However, in view of the relatively small concentration of the deep level Os1, this technique is found to yield reliable data only for the deep level corresponding to the dominant peak, Os2. Detailed data have been obtained on the field effect for Os2, extending over junction electric field values 3 x 106 V/m - 1.2 x 107 V/m. The measured emission rate signatures show a reduction of the thermal activation energy from 0.48 eV to 0.21 eV for Os2 over this electric field range. Analysis of the data in terms of the recent theoretical work on field dependence indicates that Os2 is associated with a substitutional Os donor.

Deep levels in Ruthenium doped p‐type MOCVD GaAs

Ruthenium is introduced into GaAs during epitaxial growth by MOCVD. Preliminary results of DLTS investigation of the defect states associated with this 4d transition‐metal impurity are reported for the first time. At least three deep levels are identified with Ru in the lower half‐bandgap of GaAs at energy positions Ev + 0.38 eV, Ev + 0.52 eV and Ev + 0.65 eV, the last with a relatively higher concentration than the first two. At least one Ru‐related deep level is observed in the upper half‐bandgap at Ec − 0.66 eV with a significantly high concentration. Emission rate signatures and associated characteristics of all these defect levels are reported. The Ev + 0.65 eV level is found to exhibit an electric field dependent thermal emission characteristic.

Deep levels in osmium doped p‐type GaAs grown by metal organic chemical vapor deposition

Results of a preliminary study on deep level transient spectroscopy (DLTS) investigations of osmium (Os) impurity in p‐type GaAs, introduced in situ during MOCVD crystal growth, are reported for the first time. Os is clearly shown to introduce two prominent deep levels in the lower half‐bandgap of GaAs at energy positions Ev + 0.42 eV (OsA) and Ev + 0.72 eV (OsB). A minority‐carrier emitting defect feature observed in the upper half‐bandgap is shown to consist of a band of Os‐related deep levels with a concentration significantly higher than that of the majority carrier emitting deep levels. Detailed data on the emission rate signatures and related parameters of the Os‐related deep levels are reported.

Deep levels associated with alpha irradiation of n-type MOCVD InP

Abstract Deep level transient spectroscopy has been used to observe the effect of alpha particle irradiation on n-type InP grown by metal organic chemical vapour deposition (MOCVD). Eight majority carrier emitting levels Eα1, Eα2, …, Eα8 are found to be produced as a result of this irradiation. At least two of the observed levels (Eα2 and Eα4) are found to show interesting metastable behaviour. One important result of this work is complete absence of the well-known metastable M-level (observed in electron irradiated LEC InP) in our alpha-irradiated MOCVD material.