Bakhtyar Ali

Effect of Zn interstitials on the magnetic and transport properties of bulk Co-doped ZnO

We have demonstrated that the bound magnetic polaron model is responsible for ferromagnetism in Co?ZnO semiconductors, where the carriers are provided by the interstitial zinc (Zni). Our experiment is unique since by changing the temperature, we are able to cross the carrier concentration threshold above which a long-range ferromagnetic order is established. Consequently, the ferromagnetic order is observed at room temperature but is weakened at temperatures below 100?K. To support our conclusion we have performed a systematic investigation on the structural, magnetic and transport properties which all give consistent results in the context of our proposed two-region model, i.e. (a) a Zni layer where carriers are sufficient to couple Co ions ferromagnetically and (b) a region with little carriers that remain in a paramagnetic state.

Development of heparin-coated magnetic nanoparticles for targeted drug delivery applications

We have designed a potential drug delivery system by combining low-molecular-weight heparin to iron oxide magnetic nanoparticles with an average size of 20 nm. The particles were synthesized by the NaBH4 reduction of FeCl2 and then coated with poly-L-lysine. Heparin was noncovalently conjugated on these nanoparticles via the interactions between the negatively charged sulfate and carboxylate groups of heparin and the positively charged amine group of poly-L-lysine. The nanoparticles were examined by using transmission electron microscopy, x-ray diffraction, Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, and zeta potential measurements. The data provide direct evidence that the heparin was immobilized at the surface of poly-L-lysine-coated iron oxide nanoparticles. Magnetic measurements revealed the particles are ferromagnetic with a saturation magnetization of 31 emu/g.

Role of dopant, defect, and host oxide in the observed room temperature ferromagnetism : Co-ZnO versus Co-CeO2

A comparative study on the room temperature ferromagnetism of Co doped ZnO and CeO2 bulk samples is presented. Co–ZnO system has been observed to switch between ferromagnetic and paramagnetic by controlling the donor defects, interstitial zinc: Zni. On the other hand, Co–CeO2 is always ferromagnetic. However, ferromagnetism increases/decreases with increase/decrease in donor defects, oxygen vacancies: VO. Systemic structural, magnetic, and transport analyses reveal that the nature of donor defects and host oxide plays a vital role in establishing ferromagnetism. This study provides an insight into the underlying mechanisms that are responsible for the ferromagnetism in Co–ZnO and Co–CeO2. Moreover, the proposed mechanisms are supported by the electronic structure of magnetic impurity ions and defects.

Evaporation: Processes, Bulk Microstructures, and Mechanical Properties

Publisher Summary This chapter reviews the evaporation technologies, theory and mechanisms, processes, deposition of various types of materials, the evolution of the microstructure and its relationship to the properties of the deposits, preparation of high-purity metals, current and future applications, and cost analysis. Physical vapor deposition (PVD) technology consists of the techniques of evaporation, ion plating and sputtering. It is used to deposit films and coatings or self-supported shapes such as sheet, foil, and tubing. The thickness of the deposits can vary from angstroms to millimeters. The wide variety of applications of these techniques ranges from decorative to utilitarian over significant segments of the engineering, chemical, nuclear, microelectronics and related industries. Their use has been increasing at a very rapid rate since modern technology demands multiple, and often conflicting, sets of properties from engineering materials, e.g., combinations of two or more of the following: high-temperature strength, impact strength, specific optical, electrical or magnetic properties, wear resistance, ability to be fabricated into complex shapes, biocompatibility, cost, etc. A single or monolithic material cannot meet such demands in high-technology applications. The solution is, therefore, a composite material, i.e. a core material and a coating each having the requisite properties to fulfill the specifications. PVD technology is very versatile, enabling one to deposit virtually every type of inorganic material – metals, alloys, compounds and mixtures thereof, as well as some organic materials. The thickness limits for thin and thick films are somewhat arbitrary.

Analysis of voltage and temperature dependent photocurrent collection in p3ht/pcbm solar cells

Current-voltage (J-V) analysis of poly (3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) blend organic solar cells (OSC) at various temperatures has been recorded and analyzed. The photovoltaic parameters extracted from a lumped circuit analysis completely describe the illuminated J-V data from far reverse bias to beyond the open circuit voltage (Voc). A simple model for carrier collection, previously applied to inorganic thin film solar cells, has been used to describe the voltage dependence of the photocurrent, JL(V), with only one adjustable parameter, Lc/D, the ratio of the carrier collection length to the active-layer thickness. Measured J-V curves of a variety of OSCs with varying thickness and blend ratios are closely fit with this model. Effect of resistive and collection losses has been quantified and removed, allowing the intrinsic junction behavior to be uncovered. The temperature dependence of Voc is linear with negative temperature coefficient, dVoc/dT,∼ −1 mV/K. The v...

EFFECTIVE MAGNETIC ANISOTROPY AND COERCIVITY IN Fe NANOPARTICLES PREPARED BY INERT GAS CONDENSATION

We present magnetic measurements on iron (Fe) nanoparticles in the size range 10–30 nm produced by the Inert Gas Condensation process (IGC). Structural characterization studies show the presence of a core/shell structure, where the core is bcc Fe while the surface layer is Fe-oxide. Analysis of the magnetic measurements shows that the nanoparticles display very large uniaxial anisotropy, Keff≈3 - 4 × 106 erg/cc. The observed room temperature coercivities lie in the range ≈600 – 973Oe, much larger than those expected from the Stoner–Wohlfarth model using the bulk iron anisotropy. It can be inferred from the coercivity variation with the particle size that there is a general trend of the coercivity increasing with size, culminating finally in a decrease for high sizes (30 nm) possibly due to the onset of non-coherent magnetization reversal processes.