Yanko Alexandrov Kranov

Nanoparticle formation in microchannel glass by plasma enhanced chemical vapor deposition

Iron nanoparticles were synthesized in situ within the channels of a microchannel glass by differentially pumping across the plate in conjunction with plasma enhanced chemical vapor deposition. The microchannel glass was mounted on a custom designed differentially pumped sample holder, which produced 10 Torr of differential pressure across the 5 μm channels. The iron precursor was ferrocene [(C5H5)2–Fe]. The composition and structure of the nanoparticles was determined by electron diffraction to be Fe3O4, where oxidation of the nanoparticles occurred upon exposure to air. Transmission electron microscopy revealed the formation of nanoparticles ranging in size from 150 to 960 nm, which are formed from smaller nanoparticles on the order of 5–10 nm. The large nanoparticles (150–960 nm) grow independently of one another and are largely freestanding within the channels, i.e., they are not highly attached to the channel walls or agglomerated. The magnetic signature of the large nanoparticles is consistent with ...

The magnetic domain configuration in Co/Ni/Co nanoscale antidot arrays

We performed superconducting quantum interference devices and magnetic force microscopy (MFM) measurements on magnetic multilayer Co(60 A)/Ni(90 A)/Co(60 A) nanoscale antidot samples. The antidot samples were fabricated on nanochannel glass substrates with different antidot diameters and the antidots ordered as a two dimensional hexagonal lattice structure. The results indicate that a self-organized domain structure is formed due to the pinning effect of the antidots. The strong uniaxial anisotropy of Co suppresses the shape anisotropy of the antidots and results in an uncommon domain structure. The field dependent MFM data reveal a reversal of magnetization.

Barium Hexaferrite Thick Films Made by Liquid Phase Epitaxy Reflow Method

In this paper, we report on the growth of BaFe12O19 (BaM) thick films on sapphire Al2 O3 (0001) substrate. Our goal is to fabricate barium ferrite thick films which can be self-biased for circulator applications. We have modified the liquid phase epitaxy (LPE) method by conducting the experiment in vacuum. A small piece of the melt weighing approximately 0.035 g was placed on 1times1 cm Al2O3 substrate and remelted at 1200degC for 1 h. The thickness of our thick films grown by this reflow method range from 300 to 550 mum. The coercivities of the thick films in the perpendicular direction were about 100 Oe

The domain formation in Fe/Ni/Fe nanoscale magnetic antidot arrays

In this paper we report the superconducting quantum interference device (SQUID) and magnetic force microscope (MFM) measurements of magnetic multilayer nanoscale antidot samples. The systems used consist of Fe(60 A)/Ni(90 A)/Fe(60 A) (FeNiFe) multilayer antidots with hexagonal lattice fabricated on nanochannel glass (NCG) substrates with antidot diameters of 260, 362, 530, and 800 nm. The results indicate that the domain structure is commensurate with the holes due to the pinning effect of the antidots. This pinning effect is inversely proportional to the diameter of the antidots. The field dependent MFM data show that the hexagonal antidot lattice induces a weak anisotropy with the magnetic easy axis along the nearest neighbor direction. The unit cell in the antidot arrays could be used for data storage.

The Effects of Crystallinity and Catalyst Dynamics on Boron Carbide Nanospring Formation

The formation of helical nanowires—nanosprings—of boron carbide have been observed and a growth mechanism, based on the work of adhesion of the metal catalyst and the tip of the nanowire, developed. The model demonstrates that the asymmetry necessary for helical growth is introduced when the following conditions are met: (1) The radius of the droplet is larger than the radius of the nanowire, and (2) The center of mass of the metal droplet is displaced laterally from the central axis of the nanowire. Furthermore, this model indicates that only amorphous nanowires will exhibit this unique form of growth and that in monocrystalline nanowires it is the crystal structure that inhibits helical growth. High-resolution transmission electron microscopy and electron diffraction has been used to compare the structure of both amorphous and crystalline nanowires.

The effects of crystallinity and catalyst dynamics on boron carbide nanospring formation (Invited Paper)

The formation of helical nanowires -- nanosprings -- of boron carbide have been observed and a growth mechanism, based on the work of adhesion of the metal catalyst and the tip of the nanowire, developed. The model demonstrates that the asymmetry necessary for helical growth is introduced when the following conditions are met: (1) The radius of the droplet is larger than the radius of the nanowire, and (2) The center of mass of the metal droplet is displaced laterally from the central axis of the nanowire. Furthermore, this model indicates that only amorphous nanowires will exhibit this unique form of growth and that in monocrystalline nanowires it is the crystal structure that inhibits helical growth. High-resolution transmission electron microscopy and electron diffraction has been used to compare the structure of both amorphous and crystalline nanowires.