Abdul Rumaiz

Studies of the growth parameters for silver nanoparticle synthesis by inert gas condensation

Silver nanoparticles were synthesized by an inert gas condensation method using flowing helium in the process chamber. Nucleation, growth mechanism, and the kinetics of nanoparticle formation in vapor phase are studied. Effect of process parameters, such as evaporation temperature and inert gas pressure, on the particle crystallinity, morphology, and size distribution are examined. Particles were synthesized at evaporation temperatures of 1123, 1273, and 1423 K and at helium pressures of 0.5, 1, 5, 50, and 100 Torr. Synthesized silver nanoparticles were characterized by x-ray diffraction (XRD) and transmission electron microscopy (TEM). The particle size ranged from 9 to 32 nm, depending on the growth conditions. At lower evaporation temperature and inert gas pressure, smaller particles with spherical shape showing less agglomeration are formed. Based on the experimental results and theoretical model of surface free energy and undercooling as a function of evaporation temperature and inert gas pressure, particle formation is analyzed. A simple operating map for nanoparticle synthesis is presented. The theoretical model is well supported by the experimental data.

Real-time evolution of tunneling magnetoresistance during annealing in CoFeB∕MgO∕CoFeB magnetic tunnel junctions

We report the study of the real-time evolution of tunneling magnetoresistance (TMR) in CoFeB∕MgO∕CoFeB junctions during annealing at 380°C. The TMR quickly developed at the early stage of the annealing, with 200% magnetoresistance observed in less than 10min, followed by a slow approach to saturation. This evolution of TMR was correlated with the structural changes, including crystallization of amorphous CoFeB electrodes and improvement of barrier quality during the annealing.

Competing Effects of Cu Ionic Charge and Oxygen Vacancies on the Ferromagnetism of (Zn, Co)O Nanoparticles

We report the effects on the ferromagnetism due to co-doping of ZnO with Co and Cu in the presence of variable numbers of oxygen vacancies. The co-doped nanoparticles Zn0.95−Co0.05CuyO (0.00≤y<0.009) were prepared via the chemical route with oxygen vacancies introduced via annealing in a reducing atmosphere for variable amounts of time. In addition to the magnetization, the particles were characterized by x-ray diffraction (XRD), x-ray photoemission spectroscopy (XPS) and x-ray absorption near edge spectroscopy (XANES). The Co ions were determined to be in the +2 state in a tetrahedral symmetry, with no evidence for metallic Co or Cu. However, the ionic state of Cu is found to change from +2 to +1 state with increasing Cu concentration, which appears to strongly decrease the concentration of oxygen vacancies. It is found that the ferromagnetic moment initially increases with the addition of Cu but decreases above a typical concentration that coincides with the appearance of the Cu+1 state and the decrease of O vacancy concentration. It is concluded that the effect of Cu in the very low range of concentrations, where it appears to go in as Cu+2, is to stabilize ferromagnetism indirectly via generation of O vacancies. The effects of O vacancy concentration on the ferromagnetism are interpreted in the light of the F-center exchange (FCE) model.

Inert gas condensation of evaporated Ni and laser ablated CoO

Magnetic core/shell nanoparticles have been prepared using a method that is modified version of inert gas condensation (IGC) technique. Using resistive evaporation and laser ablation techniques combined in an IGC system, we have shown that it is possible to synthesize core/shell nanostructures made of different materials. Resistively evaporated Ni and laser ablated CoO have formed the core/shell particles. It has been found that these particles have improved magnetic properties due to their layered structures that form as a result of oxidation of Ni core before it gets coated by CoO. Investigation of magnetic properties of the particles has revealed that the particles are single domain and have superparamagnetic behavior at room temperature as a result of their small sizes. However, low temperature measurements showed that due to the exchange interactions of the different magnetically ordered layers, there is a shift of hysteresis loops for field cooled magnetization measurements. The exchange bias at 5K ...

Band alignment in Ge/GeOx/HfO2/TiO2 heterojunctions as measured by hard x-ray photoelectron spectroscopy

We investigate the interlayer (IL) thickness dependence of band offsets in a germanium based bilayer metal-oxide-semiconductor sandwich with an amorphous plasma enhanced atomic layer deposited (PE-ALD) HfO2 IL and PE-ALD grown TiO2 high k gate dielectric using hard x-ray photoelectron spectroscopy. The native Ge oxide shifts to higher oxidation state as the thickness of the IL layer was increased. The Hf 4f core line shows a broadening with increasing thickness, indicating the formation of Hf-Ge germanate. We observed a deviation from the bulk offset for films with ultra thin layers of HfO2.

Synthesis and characterization of TiO2–Ge nanocomposites

Thin films of TiO2–Ge nanocomposites were deposited by rf magnetron sputtering from a composite target prepared by pressing a mixture of TiO2 and Ge powders with a ratio 2:1. Thin films were deposited at various rf powers and temperatures and characterized by using x-ray diffraction, x-ray photoelectron spectroscopy, and transmission electron microscopy (TEM). The analyses showed that the film composition changes with the target rf power and substrate temperature with rf power being a bigger contributor to the change. TEM analyses of films revealed that segregated Ge nanograins were formed and were dispersed within the TiO2 matrix. The average grain size of Ge nanograins was between 9 and 15nm.

Stoichiometry dependence of potential screening at La ( 1 - δ ) Al ( 1 + δ ) O 3 / SrTiO 3 interfaces

Hard x-ray photoelectron spectroscopy (HAXPES) and variable kinetic energy x-ray photoelectron spectroscopy (VKE-XPS) analyses have been performed on 10 unit cell La

Stoichiometry Dependence of Potential Screening at La

_{(1-{\delta})}

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Al

Al

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