Shivaraman Ramaswamy

Study of magnetization reversal of uniaxial Ni nanodots by magnetic force microscopy and vibrating sample magnetometer

In this work we report on the study of magnetization reversal in zero dimensional nickel nanodots patterned using a novel polymer based soft lithography technique. The nanodots, having their easy axis of magnetization normal to the plane of the sample, were characterized by in situ MFM observations, performed under varying magnetic fields to understand the magnetization reversal process. The average demagnetization curve of the sample was obtained from the MFM images. The results compare well with the demagnetization curve obtained from vibrating sample magnetometer (VSM) measurements. Further, the angular dependence of in-plane magnetization reversal process was investigated by studying the magnetization data obtained from the VSM performed at different angles of field orientation with respect to the sample.

Influence Of Plasma Pretreatment In The Formation Of Diamond-Like Carbon Thin Films

Plasma-enhanced chemical vapor deposition has been used to synthesize diamond-like carbon (DLC) thin films. High purity argon and methane gases were used as precursors for the fabrication of the DLC films. The influence of plasma pretreatment on the growth of the DLC films has been studied by subjecting one of the substrates to plasma pretreatment prior to deposition of the DLC films, while maintaining the other substrate as the control. The structural properties of the DLC films have been characterized using atomic force microscopy and Raman spectroscopy. The film grown on the pretreated substrate shows a more uniform coating as compared to the film grown on non-pretreated silicon substrate. The results are discussed based on diffusivity of carbon on silicon and the effect of the plasma pretreatment.

Low Temperature Growth of Carbon Nanostructures by Radio Frequency‐Plasma Enhanced Chemical Vapor Deposition (Low Temperature Growth of Carbon Nanostructures by RF‐PECVD)

This paper reports the growth of carbon nanostructures on Si (100) substrate in the absence of catalyst using radio‐frequency plasma enhanced chemical vapor deposition (RF‐PECVD). A variety of carbon nanostructures have been grown by low pressure high density plasma process at 400°C using a methane/argon mixture. Various shapes and structures including novel carbon nanoparticles have been found. The surface morphology was studied by Atomic Force Microscope (AFM) and Scanning Electron Microscope (SEM) while the chemical composition was studied using Energy Dispersive Spectroscopy (EDS). The AFM images show that the nanostructures are predominantly either particulate (spherical) in nature or have a sheet‐like morphology. SEM images are in good correspondence to the AFM results and indicate formation of either individual islands or two‐dimensional nanosheet‐like structures. The crux of this work is in the synthesis of the carbon nanostructures at comparatively low fabrication temperature (400°C) as compared to other techniques.

Effect of template engineering on morphology and magnetic properties of Ni nanodots fabricated using polysulfone templated lithography

The fabrication of magnetic nanodots using polysulfone templated lithography has been recently explored as a potential technique for bit patterned media fabrication. This work describes the efforts made to identify the ideal template engineering technique so as to develop a standard media fabrication technique. Nanoporous polysulfone membranes were fabricated using a phase inversion process. Nickel nanodots were then evaporated onto silicon substrates using the polysulfone membrane as a mask. The work maps the changes in the structural and magnetic properties of the nanodots fabricated using one of the three different template engineering techniques identified. The samples were studied using atomic force microscopy and a vibrating sample magnetometer. The results indicated that the fabrication of the mask on the substrate itself gave the best feature size, consistent shape and structure and the least deviation in magnetization due to thermal agitation. The dynamics of the growth process has also been postulated based on the results.

Magnetic properties of carbon nanosheets

Two-dimensional carbon nanosheets have been fabricated using inductively coupled radio frequency plasma-enhanced chemical vapour deposition. The structural properties of the nanosheets have been characterised using atomic force microscopy, scanning electron microscopy and X-ray diffractometer. The magnetisation of the samples was studied using vibrating sample magnetometer. The magnetisation of the nanosheets was found to be diamagnetic for fast synthesis processes (30 and 60 min). On the other hand, the nanosheets exhibited a weak ferromagnetic response for the slow (120 min) synthesis process. Energy dispersive spectrometry and atomic absorption spectroscopy confirmed that the magnetisation exhibited by the carbon nanosheets was an intrinsic property and that it was not due to contamination from the substrate. Raman spectroscopy studies revealed that the ferromagnetic carbon nanosheets have a higher ratio (1.20) of graphite peak (I G) to disordered peak (I D) than normally expected (0.75–0.90). Available data indicated that the magnetisation was due to the presence of structural disorders.

Room temperature magnetoelectric coupling in Zn1−xCoxO/BaTiO3 bilayer system

We report on room temperature magnetoelectric coupling in Zn1−xCoxO/BaTiO3 (x = 0.02, 0.05, and 0.10) bilayer thinfilm multiferroic system (BLS) grown on SrTiO3 (100) substrate. All the BLSs exhibit room temperature ferroelectric response. The BLS with x = 0.02 is paramagnetic, while the BLS with x = 0.05 and 0.10 is weakly ferromagnetic. Increase in Co concentration of the BLS results in reduction of permittivity and electric polarization along with increase of coercive voltage, coercive field, and magnetic moment. The d33 value change from 23 pm/V to 30 pm/V with increase in external magnetic field from 1500 G to 2500 G for BLS with x = 0.05. This shows that Zn1−xCoxO/BaTiO3 is magnetoelectrically coupled at room temperature.

SYNTHESIS OF CARBON NANOSHEETS AND CARBON NANOPARTICLES BY RF-PLASMA ENHANCED CHEMICAL VAPOR DEPOSITION

In this study, thin sheets like carbon nanostructures and carbon nanoparticles have been effectively synthesized with CH4 and Ar as precursors at low temperature (< 400°C) by inductively coupled radio frequency plasma enhanced chemical vapor deposition on silicon and glass substrates. The surface morphology and chemical composition were studied by atomic force microscopy (AFM), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) analysis. AFM studies show that the nanoparticles roughly about 70 to 80 nm in diameter surrounded by nanosheets. Nanosheets are about 100 nm in thickness, which attain approximately 1.75 μm lengths. EDS results revealed that the atomic percentage of carbon in the particle like structure is more than that in the nanosheet like structures.

Effects of quenching on the morphology and crystal structure of ZnO nanostructures

Zinc oxide nanostructures were prepared by a simple wet chemical procedure using zinc acetate and sodium hydroxide as precursors. The process was subjected to quenching treatment and the effect of the treatment on the formation of the nanostructures was studied using atomic force and scanning electron microscopies. The change in crystal structure of the nanostructures due to quenching was studied using an X-ray diffractometry that established that physical and structural properties of the nanostructures were largely influenced by the quenching treatment.