J. E. Wittig

Physical and optical properties of Cu nanoclusters fabricated by ion implantation in fused silica

Cu clusters of nanometer dimensions were created by implantation of Cu ions into pure fused silica substrates at energies of 160 keV. The sizes and size distributions of the Cu clusters were measured by transmission electron microscopy, and were found to be determined by the ion‐beam current during implantation. Optical‐absorption spectra of these materials show the size‐dependent surface plasmon resonance characteristic of noble‐metal clusters. There are also significant size‐dependent effects in both the nonlinear index of refraction and two‐photon absorption coefficients. The distinctive variations in linear and nonlinear optical properties with Cu nanocluster sizes and size distributions affords potentially interesting possibilities for using these materials in nonlinear optical devices.

Soft anisotropic high magnetization Cu/FeCo films

A remarkable reduction in the coercivity Hc of sputtered Fe65Co35 films from 9.6 to 0.7 kA/m was observed using a Cu underlayer as thin as 2.5 nm. The FeCo without Cu exhibited a wide distribution of anisotropy fields up to >80 kA/m while the FeCo with Cu showed a well-defined in-plane uniaxial anisotropy field of 2.3 kA/m up to FeCo thicknesses of at least 1 μm. The saturation magnetostriction was (4.7±0.4)×10−5, independent of Cu thickness while the in-plane tensile stress gradually decreased from 2 to 0.2 GPa as the Cu thickness increased to 10 nm. The Cu changed the preferred orientation of the FeCo from (100) to (110) but more significantly reduced the average grain size from ∼50 to ∼9 nm. This alone is sufficient to explain quantitatively the reduction in Hc using Hoffmann’s ripple theory.

Fabrication of Cu-coated Ag nanocrystals in silica by sequential ion implantation

Abstract Metal nanocrystal glass composites were fabricated by single and sequential element implantations of Ag + and Cu + ions into high purity silica. Implantation doses (×10 16 ions/cm 2 ) were 3Ag, 9Cu and 3Ag/9Cu. Composites were analyzed using Rutherford backscattering techniques (RBS), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and optical spectroscopy. An optical density spectrum based on the size distribution observed in the sequentially implanted sample for Cu shell and Ag core nanocrystals has been calculated using the dipole and quadrupole terms in a Mie series summation and is compared with the observed absorption spectrum. Results from TEM and EDS as well as the optical simulations demonstrate that Cu shell and Ag core nanocrystals are formed by the sequential implantation of Ag and Cu.

Optical properties of multicomponent nanometer dimension metal colloids formed in silica by sequential ion implantation of In and Ag and In and Cu

A series of nanometer dimension colloids in silica have been fabricated by sequential implantation of Ag and In, and a series by sequential implantation of In and Cu. Energies of implantation were chosen using TRIM 89 to overlay the depth distributions of the sequentially implanted ions. The implanted layers were characterized using Rutherford backscattering spectroscopy, transmission electron microscopy, and optical spectroscopy. Nanometer dimension metal multicomponent colloids were formed. The depth distribution, particle size, and optical response of the composites were found to depend strongly on the ion species implanted and the relative ratio of the ion species. The optical responses are correlated with composition of the multicomponent nanoclusters.

ORGANOMETALLIC COMPOUNDS AS SINGLE-SOURCE PRECURSORS TO NANOCOMPOSITE MATERIALS : AN OVERVIEW

Abstract Molecularly doped silica xerogels are prepared by adding either main-group or transition metal organometallic compounds containing bifunctional ligands to conventional sol–gel formulations. These bifunctional ligands contain distal (alkoxy or hydroxy)silyl groups, so that the dopant molecules become covalently incorporated into the silica xerogel matrix as it is being formed. Subsequent thermal treatment under reducing or oxidizing-then-reducing conditions leads to the decomposition of molecular precursor and to the formation of a nanoparticulate material with precise stoichiometry highly dispersed throughout the xerogel matrix.

Chromium segregation in CoCrTa/Cr and CoCrPt/Cr thin films for longitudinal recording media

Analytical electron microscopy is employed to correlate Cr segregation in Co/sub 34/Cr/sub 12/Ta/sub 4//Cr and Co/sub 76/Cr/sub 12/Pt/sub 12//Cr films with specific microstructural features such as grain boundary misorientation. Energy-filtered (EFTEM) chemical maps show that Cr segregation occurs independently of the Cr underlayer, and is highly alloy dependent. The CoCrTa film contained extensive grain boundary Cr enrichment whereas EFTEM images from the CoCrPt media show homogeneous Cr distribution. No statistically significant Ta or Pt segregation was observed. EFTEM elemental maps and energy dispersive spectroscopy (EDS) indicate that grain boundary Cr segregation depends on the type of boundary. Quantitative analysis of the Cr levels using nanoprobe EDS shows that the random angle grain boundaries contain more Cr (23/spl plusmn/4 at%) than 90/spl deg/ boundaries (17/spl plusmn/4 at%). EDS and EFTEM composition profiles show Cr enriched grain boundaries surrounded by regions of Cr depletion.

Exchange coupling in FeTaN/IrMn/FeTaN and NiFe/IrMn/NiFe trilayer films

The dependence of the exchange bias field Heb in FeTaN/IrMn and NiFe/IrMn systems on the microstructure has been investigated. Bilayer and trilayer films of 50 nm thick FeTaN and NiFe and 10 nm thick IrMn were prepared by dc magnetron sputtering. The glass/FeTaN/IrMn/FeTaN trilayer showed that the top FeTaN did not influence Heb in the bottom FeTaN, closest to the substrate, during deposition and annealing. High-resolution transmission electron microscopy results showed limited evidence of epitaxial growth with both columnar single IrMn grains and multiple IrMn grains. In contrast, in the glass/NiFe/IrMn/NiFe trilayer, the top NiFe significantly influenced Heb in the bottom NiFe during deposition and annealing. X-ray diffraction data for both systems showed no detectable changes in either the crystallinity or (111) texture of the IrMn layer during annealing. In the NiFe system, the trend in Heb in the as-deposited and annealed states may be explained by assuming single columnar grains in the IrMn which co...

Chromium Distribution in CoCrTa/Cr Longitudinal Recording Media

The current study of CoCr 12 Ta 4 /Cr longitudinal recording media combines high resolution electron microscopy (HRTEM) with nanoprobe energy dispersive spectroscopy (EDS) and energy-filtered imaging (EFTEM) to correlate the Cr distribution with specific microstructural features. EFTEM images show Cr enrichment at grain boundaries, both random angle boundaries and 90° bicrystal boundaries. Cr segregation within grains is also observed in the elemental maps. This intragrain segregation often occurs at a series of defects that may define separately nucleated grains having 00 misorientation. Nanoprobe EDS measurements indicate that these defects contain localized concentrations of 25 to 30 % Cr. The random angle grain boundary Cr concentration occurs with a wide range, 19 to 36 at% (mean 22%) whereas the more crystallographically related 900 boundaries contain less Cr with less variation, 15 to 21 at% (mean 17% Cr). Composition profiles across grain boundaries using both nanoprobe EDS and EFTEM images show the full-width-half-maximum of the segregation to be approximately 4 nm, with Cr depleted regions next to the grain boundary having less than 7 at% Cr. The Ta concentration revealed no statistical evidence of segregation.

AG:CD and CD:AG implantations into high purity silica

Abstract Silica composites containing nanometer dimension colloids were fabricated by implantation of Ag ions followed by Cd ions, and by implantation of Cd ions followed by Ag ions. These samples were characterized using transmission electron microscopy and optical spectroscopy. Doses used for the sequential implantations were 6×1016 ions/cm2 of Ag and Cd in a 1 to 1 ratio. Single element colloids were also fabricated by implantation of Ag or Cd using the same nominal dose and implantation energy as the sequential implantations. Sequential implantation of Ag and Cd leads to the formation of multi-component metal nanoclusters and elemental nanoclusters. Different microstructures were obtained depending on the order of implantation. Optical responses are consistent with results expected from effective medium theory.

Characterization of the microstructure of diamond pyramidal microtip emitters

Abstract The topology, morphology and microstructure of micro-patterned diamond pyramidal tips have been characterized by transmission electron microscopy, atomic force microscopy scanning tunneling microscopy, and Raman spectroscopy. The results show that the diamond microtips are polycrystalline in structure. AFM and STM results provide detail information as to the surface and tip shape of the diamond emitters. The results suggest a nucleation and growth process whereby the manner in which CVD diamond nucleates on the planar top surface of the tip substrate is distinct and different from the way the diamond grows in the cavity “mold”. Likewise, the TEM results contrast the diamond microstructure in the field area with that of the tip where distinct differences are observed.