Chester A. Faunce

Microstructure of sputter-deposited Co/Si multilayer thin films

This article presents the results of an investigation by transmission electron microscopy, electron diffraction, x-ray diffraction, and x-ray reflectivity of sputter-deposited Co/Si multilayers. Structures with individual layer thicknesses above about 5 nm retain elemental regions and also some interfacial mixing, but below this thickness very significant intermixing occurs with alloy formation through interdiffusion. Changes in composition in these interfacial regions reveal themselves as a change in atomic arrangement from crystalline to amorphous phases. This can be induced either by increasing the Si or reducing the Co layer thickness, resulting in alloy formation over a limited distance with a variable average composition. A simple model is proposed to explain the observed microstructural changes.

Magneto-optical characteristics of magnetic nanowire arrays in anodic aluminum oxide templates

Nanocomposite films consisting of regularly ordered iron nanowires embedded in anodic aluminum oxide templates have been fabricated and their magneto-optical properties studied by determining the four Stokes parameters of the transmitted laser beam (λ=670 nm), originally linearly polarized and at normal incidence to the film surfaces. The results of the nanowire arrays are found to be considerably different from that of bulk iron. While an increase in diameter of the nanowire leads to a substantial increase in the values of the Faraday rotation angles per unit length at a fixed value of the magnetic fields, they are substantially less than that of bulk iron, indicating that the effective media theory may not be directly applicable.

The structure and properties of sputter-deposited Co-Si alloy thin films

The structural and magnetic properties of Co1-xSix alloy thin films in the composition range 0 0.7-0.8, Co atoms are incorporated in the covalent random network structure of Si and paramagnetism is observed. A correlation of the PEELS Co L2/L3 edge loss intensity ratio with the effective Co moment suggests that the magnetic changes could arise from differing local environments as Si is added, rather than a change in the particle size. Compositional mapping shows that some of the films have a composition that is not spatially uniform.

Thin solid film sample preparation by a small-angle cleavage for transmission electron microscopy

Thin solid film samples have been prepared by a small-angle cleavage technique using hand tools. Cleaved wedges from the same material are mounted both as plan-view and cross-sectional samples on the same transmission electron microscopy (TEM) specimen grid allowing convenient examination in both views. The samples of Si3N4, Zr and Co films deposited on Si prepared by this technique are shown to be suitable for analysis in TEM.

The liquidlike ordering of lipid A-diphosphate colloidal crystals: the influence of Ca2+, Mg2+, Na+, and K+ on the ordering of colloidal suspensions of lipid A-diphosphate in aqueous solutions

A comprehensive study was performed on electrostatically stabilized aqueous dispersion of lipid A-diphosphate in the presence of bound Ca2+, Mg2+, K+, and Na+ ions at low ionic strength (0.10-10.0-mM NaCl, 25 degrees C) over a range of volume fraction of 1.0 x 10(-4)< or =phi< or =4.95 x 10(-4). These suspensions were characterized by light scattering (LS), quasielastic light scattering, small-angle x-ray scattering, transmission electron microscopy, scanning electron microscopy, conductivity measurements, and acid-base titrations. LS and electron microscopy yielded similar values for particle sizes, particle size distributions, and polydispersity. The measured static structure factor, S(Q), of lipid A-diphosphate was seen to be heavily dependent on the nature and concentration of the counterions, e.g., Ca2+ at 5.0 nM, Mg2+ at 15.0 microM, and K+ at 100.0 microM (25 degrees C). The magnitude and position of the S(Q) peaks depend not only on the divalent ion concentration (Ca2+ and Mg2+) but also on the order of addition of the counterions to the lipid A-diphosphate suspension in the presence of 0.1-microM NaCl. Significant changes in the rms radii of gyration (R2G) 1/2 of the lipid A-diphosphate particles were observed in the presence of Ca2+ (24.8+/-0.8 nm), Mg2+ (28.5+/-0.7 nm), and K+ (25.2+/-0.6 nm), whereas the Na+ salt (29.1+/-0.8 nm) has a value similar to the one found for the de-ionized lipid A-diphosphate suspensions (29.2+/-0.8 nm). Effective particle charges were determined by fits of the integral equation calculations of the polydisperse static structure factor, S(Q), to the light-scattering data and they were found to be in the range of Z*=700-750 for the lipid A-diphosphate salts under investigation. The light-scattering data indicated that only a small fraction of the ionizable surface sites (phosphate) of the lipid A-diphosphate was partly dissociated (approximately 30%). It was also discovered that a given amount of Ca2+ (1.0-5.0 nM) or K+ (100 microM) influenced the structure much more than Na+ (0.1-10.0-mM NaCl) or Mg2+ (50 microM). By comparing the heights and positions of the structure factor peaks S(Q) for lipid A-diphosphate-Na+ and lipid A-diphosphate-Ca2+, it was concluded that the structure factor does not depend simply on ionic strength but more importantly on the internal structural arrangements of the lipid A-diphosphate assembly in the presence of the bound cations. The liquidlike interactions revealed a considerable degree of ordering in solution accounting for the primary S(Q) peak and also the secondary minimum at large particle separation. The ordering of lipid A-diphosphate-Ca2+ colloidal crystals in suspension showed six to seven discrete diffraction peaks and revealed a face-centered-cubic (fcc) lattice type (a=56.3 nm) at a volume fraction of 3.2 x 10(-4)< or =phi< or =3.9 x 10(-4). The K+ salt also exhibited a fcc lattice (a=55.92 nm) at the same volume fractions, but reveals a different peak intensity distribution, as seen for the lipid A-diphosphate-Ca2+ salt. However, the Mg2+ and the Na+ salts of lipid A-diphosphate showed body-centered-cubic (bcc) lattices with a=45.50 nm and a=41.50 nm, respectively (3.2 x 10(-4)< or =phi< or =3.9 x 10(-4)), displaying the same intensity distribution with the exception of the (220) diffraction peaks, which differ in intensity for both salts of lipid A-diphosphate.

Ion irradiation of Co/Pt multilayer films

This article describes a microstructural and magnetic investigation of the modification of Co/Pt multilayer films by Ar ion irradiation which results in a change of the orientation of the magnetization from perpendicular to the film plane to the in-plane direction. Transmission electron microscopy observation confirms the general structure of the as-deposited samples and correlates with the x-ray reflectivity measurements in showing the eventual mixing of the layers and a large increase in grain size caused by the irradiation. TRIM (transport of ions in matter) calculations show that large numbers of recoils are placed outside the individual layers and in the adjacent layers on irradiation. This signifies considerable roughening of the interfaces and mixing in the multilayer structure. Magnetic measurements and magnetic force microscopy observations confirm the decrease of perpendicular anisotropy and the changes of the magnetization direction from the perpendicular direction to an in-plane direction afte...

Liquid-like ordered colloidal suspensions of lipid A: The influence of lipid A particle concentration

Electrostatically stabilized aqueous dispersions of nm-sized free lipid A particles at low volume fractions (1.0×10−4⩽∅⩽3.5×10−4) in the presence of 1.0–10.0 mM NaCl (25 °C) have been characterized by static and quasielastic light scattering (QELS) techniques, electron microscopy (SEM and TEM), conductivity measurements, and acid–base titrations. QELS and electron microscopy (ρTEM=8.0±0.6%) yield similar values for the particle size and particle size distribution (ρQELS=10.9±0.75 %), whereas conductivity and acid–base titrations estimate surface chemical parameters (dissociation constant, ionizable sites, and Stern capacitance). Effective particle charges were determined by fits of the integral equation calculations of the polydisperse static structure factor, S(Q), to the light scattering data. Using the particle properties as determined from these experiments, the polydisperse structure factor, S(Q), was calculated as a function of volume fraction, ∅, which was found to be consistent with a S(Q) de...

Ion beam modified Co/Si multilayers

This article briefly reports microstructural, electrical transport, and magnetic measurements on Co/Si multilayers which are structurally modified by argon ion irradiation during growth. The periodicity and ferromagnetism of the multilayers is retained at ion energies approaching 400 eV. At and above this energy structural modification results in resputtering and thinning of the film, extensive mixing and a destruction of the periodic layered structure with the formation of nonequilibrium microstructures. The measurements show that the modified film is metallic in character, with the presence of low resistance paths and possible spin glass behavior in an amorphous matrix that surrounds a second microstructural component of mainly superparamagnetic nanoclusters.

Observations of liquidlike order of charged rodlike lipid A diphosphate assemblies at pH 8.5

A new structural form of charged lipid A diphosphate, with a molecular weight of 5.9x10(6) Da and a rodlike shape (L=800 nm), was found in aqueous solutions at pH 8.5. The experimental techniques used in the investigation were light scattering, small-angle x-ray scattering (SAXS), and electron microscopy. Measurements of the static-structure factor S(Q) as a function of the ionic strength are presented over the concentration regimes C>C(*) and C<C(*), with C(*)=1 particle/length(3). The position of the first maximum of the structure factor S(Q) was found to scale with C(13) below and with C(12) above, the critical concentration C(*) (2.5 microg mL). SAXS results in the semidilute concentration range C> or =C(*) show that strong interparticle correlations exist even at concentrations as high as 15C(*), in contrast with results for hard-rod systems. The magnitude of the correlations depends on both the lipid A diphosphate concentration at pH 8.5 and the Debye screening length k(-1). For a constant lipid A diphosphate concentration at pH 8.5, as the amount of salt was increased a decrease in structure was observed. There was also a shift in the peak of the first maximum position Q(max) to larger scattering wave vectors. The observed phase behavior (C=15C(*)) exhibited an isotropic I-Sm transition and an I-N-Sm transition, which were recorded on electron microscope images.

Interdiffusion in direct ion beam deposited isotopic Fe/Si trilayers

Interdiffusion and intermixing have been examined in Fe/Si trilayers prepared with ions of different energies, using the direct ion beam deposition technique. Isotope-pure layers were deposited and spin-polarized neutron reflectivity used to determine the role of Fe diffusion in iron silicide formation. It was found that a nonmagnetic iron silicide was formed that contained Fe from both the top and bottom layers in the trilayer, suggesting complete diffusion across the spacer region. Electron microscopy observations revealed the presence of an iron silicide phase and crystalline interface layers in films prepared with low energy ions (30 eV), while mixed and amorphous-like regions were found at higher ion energies (100 eV).