Surendra Gupta

Crystallization and grain growth behavior of CoFeB and MgO layers in multilayer magnetic tunnel junctions

The relationship between crystallization, grain growth behavior, and the diffusion of B out of CoFeB has been investigated in annealed film stacks of sputtered CoFeB∣MgO using a combination of two dimensional x-ray diffraction, transmission electron microscopy, and parallel electron energy loss spectroscopy (PEELS). The analysis shows grain growth in MgO layers. It shows crystallization at approximately 350°C, and subsequent grain growth in CoFeB layers with annealing. The orientations of the grains of MgO and CoFe are definitively shown to be (002) in the out-of-plane direction. The MgO lattice is seen to have an in-plane tensile stress, while CoFe lattice is shown to have an in-plane compressive stress. CoFe grains are observed to be smaller than MgO grains, rather than being of equal size as previously understood. The physical process of B diffusion into MgO has also been investigated using PEELS and is determined that the diffusion of B through MgO is mediated through vacancies and defect states by th...

Vacuum UV photo-oxidation of polystyrene

Abstract Polystyrene (PS) was treated with vacuum UV (VUV) (λ = 104.8 and 106.7 nm) photo-oxidation and X-ray photoelectron spectroscopy detected a controlled increase in the atomic percentage of oxygen up to a saturation level of ca. 20 at% O. Initially, C–O and carbonyl groups are observed due to the formation of alcohols, ethers, esters, and ketones. Water contact angle measurements showed ca. 25% increase in hydrophilicity of the surface with oxidation. Atomic Force Microscopy observed little changes in surface roughness with treatment time. The super water absorbent polymer poly(acrylic acid) was thinly grafted to the modified PS surface.

Microelectronic engineering education for emerging technologies

The Department of Microelectronic Engineering at Rochester Institute of Technology received NSF Department Level Reform (DLR) planning and implementation grants in 2003–04 and 2005–10, respectively. The primary mission of these efforts was to evaluate and develop educational initiatives towards nanotechnology aligned with recommendations from the institution of National Nanotechnology Initiatives published by the US Government in 2000. The Department proposed to take this opportunity further and guide its curriculum toward new frontiers in nanotechnology and micro-electro-mechanical systems (MEMs). Advances in semiconductor technology have resulted in micro/nanofabrication techniques being employed in MEMs, chemical & bio sensors, and in energy harvesting devices and systems. The technology has evolved through aggressive process control and scalability characterized by Moores Law. The result has been emergence of a multifunctional “More than Moore” regime that is increasingly multidisciplinary in nature. Under this effort, new courses and curricula in Microelectronics and Nanofabrication providing access to state-of-the art semiconductor fabrication facilities to students from different science and engineering programs have been formulated.

Investigation of Phase Transitions in Stacked GeTe/SnTe and Ge2Se3/SnTe Chalcogenide Films

Phase transitions in stacked GeTe/SnTe and Ge2Se3/SnTe thin layers for potential phase-change memory applications have been investigated by X-ray diffraction using an area detector system and by scanning electron microscopy. The as-deposited underlying GeTe or Ge2Se3 layer is amorphous, whereas the top SnTe layer is crystalline. In GeTe/SnTe stack, the crystallization of GeTe phase occurs near 170°C, and upon further heating, GeTe phase disappears, followed by the formation of rocksalt-structured GexSn1-xTe solid solution. In Ge2Se3/SnTe stack, the phase transition starts with the separation of SnSe phase due to the migration of Sn ions into the Ge2Se3 layer. The migration of Sn ions and the formation of SnSe are believed to facilitate the crystallization of Ge2Se3 solid solution at ~360°C, which is much lower than the crystallization temperature of Ge2Se3, therefore consuming less power during the phase transition.

Vacuum UV photo-oxidation of poly(ethylene terephthalate)

Abstract Poly(ethylene terephthalate) (PET) was treated with vacuum UV (VUV) (λ = 104.8 and 106.7 nm) photo-oxidation using a microwave (MW) plasma of Ar as the radiation source and the results were compared to treatment with O atoms produced from a remote MW plasma of a gaseous mixture of Ar-O2 in the absence of radiation. X-ray photo-electron spectroscopy (XPS) detected a lower saturation level for the atomic % of O with VUV photo-oxidation (32 at%) than with O atom treatment (34 at% O). The C 1s curve fitting results for both treatment methods show a decrease in aromatic sp2 carbons and an increase in the amount of carbon-oxygen bonding due to the formation of the carbonyl (C=O) and carbonate-like (O-(C=O)-O) moieties for VUV photo-oxidation; and C-O-C, C=O, and O-C=O moieties for O atom treatment, respectively. Advancing water contact angle measurements showed more of an increase in hydrophilicity with the O atom treated samples than VUV photo-oxidation. Atomic Force Microscopy images displayed smoother surfaces after VUV photo-oxidation while O atom treatment resulted in insignificant changes in surface roughness. Rinsing the treated surfaces with ethanol solvent partially decreased the at% O indicating the formation of a weak boundary during treatment.

Reaction of ozone with polybenzimidazole (PBI)

ABSTRACT Ozone reacted with the polybenzimidazole (PBI) film surface and X-ray photoelectron spectroscopy (XPS) detected a rapid increase in O atom concentration up to a saturation level of 27 ± 1 atomic %. Atomic force microscopy measurements showed little change in surface roughness. The water contact angle of the treated film decreased by ca. 60% compared to untreated PBI film indicating an increase in hydrophilicity and hydrogen bonding due the formation of the polar oxygenated functional groups. With treatment, the curve fitting of the XPS chemical states showed a decrease in the C–C sp2, C–C sp3, and C=N functional groups, and an increase in C–N, C=O, O–C=O, O–(C=O)–O, and N–C=O moieties which were explained using mechanisms associated with the dissociation of the primary ozonide formed from the addition of ozone to the C=C and C=N bonds and reaction with the amine groups in PBI. Washing the treated surface with water partially washed away the O concentration which indicated the formation of a weak boundary layer due to the breakage of bonds in the decomposition of the primary ozonide.

Atomic Force Microscopy of Annealed Plain Carbon Steels

Microstructure of annealed plain carbon steels is examined using optical microscopy. When the inter-lamellar spacing in pearlite is small, optical microscope at 1000X is unable to resolve the ferrite and cementite lamellae. In hyper-eutectoid steels, cementite in pearlite appears as darker phase whereas the pro-eutectoid cementite appears as a lighter phase. Atomic force microscopy (AFM) of etched steels is able to resolve ferrite and cementite lamellae in pearlite at similar magnifications. Both cementite in pearlite as well as pro-eutectoid cementite appear as raised areas (hills) in AFM images. Interlamellar spacing in pearlite increases with increasing hardenability of steel.Copyright

Microstructural Characterization of Sm-Co Magnets

Samarium cobalt permanent magnets have been widely used for their excellent intrinsic magnetic properties such as very high Curie temperature, high anisotropy fields and most importantly excellent temperature coefficients of induction and coercivity. These materials have continuing industrial interest especially for applications operating at elevated temperatures and in the presence of high demagnetizing fields, such as particle accelerators, high frequency traveling wave tubes (TWTs), servo-motors and automotive and aerospace applications. An area of opportunity for improving performance of SmCo magnets is increasing magnet toughness — resistance to fracture.Like all other sintered rare earth magnetic materials, SmCo magnets are based on intermetallic compounds which are intrinsically brittle and can crack in the course of fabrication, machine work, and installation in the application. Increased toughness would also reduce handling sensitivity of magnetized magnets. For many years, studies on SmCo magnets have been focused on their magnetic properties, but the mechanical characteristics, strengthening and toughening mechanisms have been rarely reported. Understanding the phase and structural transformations induced in the SmCo magnets during the manufacturing process offers insight into potential modifications — chemical or processing-related. In this study, microstructural characterizations of 1:5 and 2:17 Sm-Co magnets were carried out using optical and scanning electron microscopes. In scanning electron microscopy (SEM), backscattered electron imaging and energy dispersive X-ray (EDX) microanalysis were used to investigate different phases and oxides. Finally, crystal structure of the magnets was studied using an X-ray diffractometer (XRD). The study correlates the microstructure characterization with the thermal processing history of different grades of SmCo magnets.Copyright