M.E. Kiziroglou

Metal catalyst-free low-temperature carbon nanotube growth on SiGe islands

A metal-catalyst-free growth method of carbon nanotubes (CNTs) has been developed using chemical vapor deposition of CNTs on carbon-implanted SiGe islands on Si substrates. From scanning electron microscopy and Raman measurements, the fabricated CNTs are identified as single-walled CNTs with a diameter ranging from 1.2 to 1.6 nm. Essential parts of the substrate preparation after CVD SiGe growth and carbon implant are a chemical oxidization by hydrogen peroxide solution and a heat treatment at 1000u2009°C prior to CNT growth. We believe that these processes enhance surface decomposition and assist the formation of carbon clusters, which play a role in seeding CNT growth. The growth technique is a practical method of growing metal-free CNTs for a variety of applications, while at the same time opening up the prospect of merging CNT devices into silicon very-large-scale-integration technology.

Electrodeposition of Ni-Si Schottky barriers

Electrodeposition is being used to fabricate magnetic microstructures directly on patterned n-type Si wafers of various substrate resistivities. The Ni-Si Schottky barrier is characterized and found to be of high quality for relatively low Si resistivities (1-2 /spl Omega//spl middot/cm), with extremely low reverse leakage. It is shown that a direct correlation exists among the electrodeposition potential, the roughness, and the coercivity of the films. A conductive seed layer or a back contact is not compulsory for electrodeposition on Si with resistivities up to 15 /spl Omega//spl middot/cm. This shows that electrodeposition of magnetic materials on Si might be a viable fabrication technique for magnetoresistance and spintronics applications.

Orientation and symmetry control of inverse sphere magnetic nanoarrays by guided self-assembly

Inverse sphere shaped Ni arrays were fabricated by electrodeposition on Si through the guided self-assembly of polystyrene latex spheres in Si/SiO2 patterns. It is shown that the size commensurability of the etched tracks is critical for the long range ordering of the spheres. Moreover, noncommensurate guiding results in the reproducible periodic triangular distortion of the close packed self-assembly. Magnetoresistance measurements on the Ni arrays were performed showing room temperature anisotropic magnetoresistance of 0.85%. These results are promising for self-assembled patterned storage media and magnetoresistance devices.

Catalyst free low temperature direct growth of carbon nanotubes

A metal catalyst free direct growth process has been developed for the CVD of carbon nanotubes (CNTs) on carbon implanted SiGe islands or Ge dots on Si substrates. From TEM and Raman measurements, the fabricated CNTs are identified as single-walled CNTs (SWNTs) with diameter ranging from 1.2 to 2.1 nm. Essential parts of the substrate preparation after SiGe or Ge dot growth and carbon ion implantation are a chemical oxidation and preheating at 1000/spl deg/C prior to CNT growth. We believe that the lower melting point of Ge and oxidation enhanced surface decomposition assist the formation of carbon clusters.

Shape-induced anisotropy in antidot arrays from self-assembled templates

Using self-assembly of polystyrene spheres, well-ordered templates have been prepared on glass and silicon substrates. Strong guiding of self-assembly is obtained on photolithographically structured silicon substrates. Magnetic antidot arrays with three-dimensional architecture have been prepared by electrodeposition in the pores of these templates. The shape anisotropy demonstrates a crucial impact on magnetization reversal processes.

Transport mechanisms at Ni-Si Schottky barriers for spin injection

Spin injection from a magnetic metal into a semiconductor requires spin conservation during the transport of electrons. It is particularly interesting because it allows the integration of magnetic devices with microelectronics. The conductivity mismatch problem has been shown to prevent ohmic contacts from being used for spin injection. Instead, Schottky barriers and ferromagnet/insulator/semiconductor contacts have been proposed. It has been shown that electrodeposition is a promising technique for Ni-Si Schottky barriers. In this digest, the transport mechanisms in electrodeposited Ni-Si Schottky barriers are studied. Moderately doped Si shows a high quality Schottky barrier with ultra low reverse leakage and domination of thermionic emission. Tunneling takes over for highly doped Si, giving leakage-free thermionic field emission in reverse bias.

Shape induced anisotropy in hybrid anti-dot arrays from guided self-assembly templates

Ordered templates are used for electro-deposition of different magnetic materials. This technique offers new opportunities, which are not easily realized by standard lithographic methods, and which allows creation of magnetic nanostructures with 3D architectures on broad range of length scale. To address limitations of self-assembly, hybrid techniques using well established Si technology to guide and confine self-assembly templates is employed. Magnetic measurements are performed using superconducting quantum interference device (SQUID), a vibrating sample magnetometer and a magneto-optical Kerr effect rig. Electrical properties are studied using a four-point probe configuration. Magnetic structures have been imaged using magnetic force microscopy (MFM). Obtained results are analysed using micromagnetic simulations and simple analytical models of domain wall pinning and magnetization curling behavior.