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Papers by abdul rumaiz

IEEE Transactions on Nuclear Science, 2019

Physical Review Materials, 2018

Current Applied Physics, 2015

ABSTRACT Pulsed laser deposition technique has been used to manipulate the structural order of Fe... more ABSTRACT Pulsed laser deposition technique has been used to manipulate the structural order of Fe67Co33 films grown at various substrate temperatures. Films deposited at room temperature exhibited two phases including the stable crystalline phase embedded in the amorphous phase. The crystalline phase separated into two distinct bcc phases as evident from the splitting of (110) reflections, as compared to the bulk counterpart which crystalize into the single phase bcc structure. Both crystalline phases and the amorphous phase were metastable. Films prepared at higher substrate temperatures (∼500oC), crystallized into the single stable equilibrium bcc structure. Orientation dependent magnetic properties are also presented for the films prepared at both room temperature and higher substrate temperatures. As expected, the easy axes lie parallel to the plane of the substrate due to shape anisotropy. Out of plane magnetization for the films which exhibited short range ordering is found to saturate at smaller field compared to films where single phase bcc structure is stabilized.

ABSTRACT We report the hard x-ray photo-electron spectroscopy (HAXPES) and near edge x-ray absorp... more ABSTRACT We report the hard x-ray photo-electron spectroscopy (HAXPES) and near edge x-ray absorption fine structure (NEXAFS) of CoFeB|MgO|CoFeB tunnel junctions as a function of annealing time. Upon annealing, the oxidation state of B changes from predominantly elemental (0 valence) boron in the as deposited sample to higher oxidation in annealed samples as evident from HAXPES spectra. The NEXAFS spectroscopy results showed that upon heating, B species migrate towards the MgO and interact with it. A comparison of the tunnel junction NEXAFS signature with some standards suggests that the B forms a 3-fold coordinated boron compound in the MgO environment and 4-fold coordinated boron resembling Kotoite mineral in the CoFe/MgO interface.

IEEE Transactions on Nuclear Science, 2014

MRS Proceedings, 2002

ABSTRACTNanostructured WCx thin films were reactively sputtered in argon-methane plasma. A DC pla... more ABSTRACTNanostructured WCx thin films were reactively sputtered in argon-methane plasma. A DC planar magnetron with a pure tungsten target was used. Films were deposited on glass, quartz, silicon and sapphire substrates at temperatures up to 700 °C. The carbon content in the film was varied by changing the partial pressure of methane. The carbon content in the films was analyzed by using X-ray Photon Spectroscopy (XPS) and Rutherford Backscattering Spectroscopy (RBS).The effect of temperature on the grain size was studied using Transmission Electron Microscopy (TEM). The target poisoning behavior was studied by measuring the target current. The critical methane concentration at which the metal – poison mode transition occurs was measured to be around 42% of CH4 in Ar. This transition is characterized by a sharp fall in the target current. The hysteresis in the target current can also be attributed to target poisoning. In this paper we describe the effects of film growth parameters o...

Solid State Communications, 2007

Materials Science and Engineering: B, 2008

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 2008

Thin films of TiO2–Ge nanocomposites were deposited by rf magnetron sputtering from a composite t... more 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.

Journal of Physics D: Applied Physics, 2010

Nickel ferrite thin films were synthesized by pulsed laser deposition. It was determined that the... more Nickel ferrite thin films were synthesized by pulsed laser deposition. It was determined that the monotonic increase in saturation magnetization and the non-monotonic increase in electrical conductivity depend on the oxygen partial pressure during the growth of the thin films. A substantial reduction in magnetization was found which ranged between 0.4% and 40% of the bulk value as the oxygen partial pressure increased from 0.2 × 10−6 Torr to 500 mTorr during the deposition of the films. There was a three orders of magnitude increase in conductivity for the sample prepared under the most oxygen deficient environment (partial pressure of oxygen 0.2 × 10−6 Torr). These variations in saturation magnetization and conductivity are described within the framework of cation/oxygen vacancies in an inverse spinel nickel ferrite structure. The changes in the electronic structure due to the presence of the vacancies were investigated using x-ray photoelectron spectroscopy, which confirmed the fo...

Journal of Applied Physics, 2007

Magnetic core/shell nanoparticles have been prepared using a method that is modified version of i... more 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. T...

Applied Physics Letters, 2011

We report the hard x-ray photo-electron spectroscopy (HAXPES) and near edge x-ray absorption fine... more We report the hard x-ray photo-electron spectroscopy (HAXPES) and near edge x-ray absorption fine structure (NEXAFS) of CoFeB|MgO|CoFeB interfaces as a function of annealing time. Upon annealing, the oxidation state of B changes from predominantly elemental (0 valence) boron in the as deposited sample to higher oxidation in annealed samples as evident from HAXPES spectra. The NEXAFS spectroscopy results showed that upon heating, B species migrate towards the MgO and interact with it. A comparison of the tunnel junction NEXAFS signature with some standards suggests that the B forms a 3-fold coordinated boron compound in the MgO environment and 4-fold coordinated boron resembling Kotoite mineral in the CoFe/MgO interface.

Applied Physics Letters, 2008

We report the study of the real-time evolution of tunneling magnetoresistance (TMR) in CoFeB∕MgO∕... more 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.

Applied Physics Letters, 2012

We investigate the interlayer (IL) thickness dependence of band offsets in a germanium based bila... more 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.

Applied Physics Letters, 2010

Extended x-ray-absorption fine structure (EXAFS) was used to study the evolution of the local str... more Extended x-ray-absorption fine structure (EXAFS) was used to study the evolution of the local structure of Fe and Co as a function of annealing time in CoFeB/MgO/CoFeB magnetic tunnel junctions. EXAFS indicates B depletion and crystallization of the CoFeB layers within a few seconds of the post growth high temperature anneal. The decrease in first-shell Debye–Waller factor and hence the increase in structural order during annealing explains the increase in tunnel magnetoresistance observed as a result of post deposition annealing.

Applied Physics Letters, 2010

Hard x-ray photoelectron spectroscopy has been used to study the band alignment between atomic la... more Hard x-ray photoelectron spectroscopy has been used to study the band alignment between atomic layer deposited HfO2 on clean Ge (100) and nitrogen treated Ge (100) surfaces. The position of the valence-band maximum was determined by convolving theoretically calculated density of states from first-principles calculations and comparing with experimental valence-band data. Using Kraut’s method, the valence-band offsets were found to be 3.2±0.1 and 3.3±0.1 eV for the samples grown on clean and N passivated Ge, respectively. The oxide charge measured from capacitance-voltage measurements shows a significant increase between the two samples; however, the small change in the band offset between the two systems strongly indicates negligible contribution of the interface to the conduction/valence-band barrier and the band alignment of the heterojunctions.

Journal of Instrumentation, 2018

IEEE Transactions on Nuclear Science, 2019

Physical Review Materials, 2018

Current Applied Physics, 2015

ABSTRACT Pulsed laser deposition technique has been used to manipulate the structural order of Fe... more ABSTRACT Pulsed laser deposition technique has been used to manipulate the structural order of Fe67Co33 films grown at various substrate temperatures. Films deposited at room temperature exhibited two phases including the stable crystalline phase embedded in the amorphous phase. The crystalline phase separated into two distinct bcc phases as evident from the splitting of (110) reflections, as compared to the bulk counterpart which crystalize into the single phase bcc structure. Both crystalline phases and the amorphous phase were metastable. Films prepared at higher substrate temperatures (∼500oC), crystallized into the single stable equilibrium bcc structure. Orientation dependent magnetic properties are also presented for the films prepared at both room temperature and higher substrate temperatures. As expected, the easy axes lie parallel to the plane of the substrate due to shape anisotropy. Out of plane magnetization for the films which exhibited short range ordering is found to saturate at smaller field compared to films where single phase bcc structure is stabilized.

ABSTRACT We report the hard x-ray photo-electron spectroscopy (HAXPES) and near edge x-ray absorp... more ABSTRACT We report the hard x-ray photo-electron spectroscopy (HAXPES) and near edge x-ray absorption fine structure (NEXAFS) of CoFeB|MgO|CoFeB tunnel junctions as a function of annealing time. Upon annealing, the oxidation state of B changes from predominantly elemental (0 valence) boron in the as deposited sample to higher oxidation in annealed samples as evident from HAXPES spectra. The NEXAFS spectroscopy results showed that upon heating, B species migrate towards the MgO and interact with it. A comparison of the tunnel junction NEXAFS signature with some standards suggests that the B forms a 3-fold coordinated boron compound in the MgO environment and 4-fold coordinated boron resembling Kotoite mineral in the CoFe/MgO interface.

IEEE Transactions on Nuclear Science, 2014

MRS Proceedings, 2002

ABSTRACTNanostructured WCx thin films were reactively sputtered in argon-methane plasma. A DC pla... more ABSTRACTNanostructured WCx thin films were reactively sputtered in argon-methane plasma. A DC planar magnetron with a pure tungsten target was used. Films were deposited on glass, quartz, silicon and sapphire substrates at temperatures up to 700 °C. The carbon content in the film was varied by changing the partial pressure of methane. The carbon content in the films was analyzed by using X-ray Photon Spectroscopy (XPS) and Rutherford Backscattering Spectroscopy (RBS).The effect of temperature on the grain size was studied using Transmission Electron Microscopy (TEM). The target poisoning behavior was studied by measuring the target current. The critical methane concentration at which the metal – poison mode transition occurs was measured to be around 42% of CH4 in Ar. This transition is characterized by a sharp fall in the target current. The hysteresis in the target current can also be attributed to target poisoning. In this paper we describe the effects of film growth parameters o...

Solid State Communications, 2007

Materials Science and Engineering: B, 2008

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 2008

Thin films of TiO2–Ge nanocomposites were deposited by rf magnetron sputtering from a composite t... more 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.

Journal of Physics D: Applied Physics, 2010

Nickel ferrite thin films were synthesized by pulsed laser deposition. It was determined that the... more Nickel ferrite thin films were synthesized by pulsed laser deposition. It was determined that the monotonic increase in saturation magnetization and the non-monotonic increase in electrical conductivity depend on the oxygen partial pressure during the growth of the thin films. A substantial reduction in magnetization was found which ranged between 0.4% and 40% of the bulk value as the oxygen partial pressure increased from 0.2 × 10−6 Torr to 500 mTorr during the deposition of the films. There was a three orders of magnitude increase in conductivity for the sample prepared under the most oxygen deficient environment (partial pressure of oxygen 0.2 × 10−6 Torr). These variations in saturation magnetization and conductivity are described within the framework of cation/oxygen vacancies in an inverse spinel nickel ferrite structure. The changes in the electronic structure due to the presence of the vacancies were investigated using x-ray photoelectron spectroscopy, which confirmed the fo...

Journal of Applied Physics, 2007

Magnetic core/shell nanoparticles have been prepared using a method that is modified version of i... more 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. T...

Applied Physics Letters, 2011

We report the hard x-ray photo-electron spectroscopy (HAXPES) and near edge x-ray absorption fine... more We report the hard x-ray photo-electron spectroscopy (HAXPES) and near edge x-ray absorption fine structure (NEXAFS) of CoFeB|MgO|CoFeB interfaces as a function of annealing time. Upon annealing, the oxidation state of B changes from predominantly elemental (0 valence) boron in the as deposited sample to higher oxidation in annealed samples as evident from HAXPES spectra. The NEXAFS spectroscopy results showed that upon heating, B species migrate towards the MgO and interact with it. A comparison of the tunnel junction NEXAFS signature with some standards suggests that the B forms a 3-fold coordinated boron compound in the MgO environment and 4-fold coordinated boron resembling Kotoite mineral in the CoFe/MgO interface.

Applied Physics Letters, 2008

We report the study of the real-time evolution of tunneling magnetoresistance (TMR) in CoFeB∕MgO∕... more 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.

Applied Physics Letters, 2012

We investigate the interlayer (IL) thickness dependence of band offsets in a germanium based bila... more 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.

Applied Physics Letters, 2010

Extended x-ray-absorption fine structure (EXAFS) was used to study the evolution of the local str... more Extended x-ray-absorption fine structure (EXAFS) was used to study the evolution of the local structure of Fe and Co as a function of annealing time in CoFeB/MgO/CoFeB magnetic tunnel junctions. EXAFS indicates B depletion and crystallization of the CoFeB layers within a few seconds of the post growth high temperature anneal. The decrease in first-shell Debye–Waller factor and hence the increase in structural order during annealing explains the increase in tunnel magnetoresistance observed as a result of post deposition annealing.

Applied Physics Letters, 2010

Hard x-ray photoelectron spectroscopy has been used to study the band alignment between atomic la... more Hard x-ray photoelectron spectroscopy has been used to study the band alignment between atomic layer deposited HfO2 on clean Ge (100) and nitrogen treated Ge (100) surfaces. The position of the valence-band maximum was determined by convolving theoretically calculated density of states from first-principles calculations and comparing with experimental valence-band data. Using Kraut’s method, the valence-band offsets were found to be 3.2±0.1 and 3.3±0.1 eV for the samples grown on clean and N passivated Ge, respectively. The oxide charge measured from capacitance-voltage measurements shows a significant increase between the two samples; however, the small change in the band offset between the two systems strongly indicates negligible contribution of the interface to the conduction/valence-band barrier and the band alignment of the heterojunctions.

Journal of Instrumentation, 2018