Ernie Caine

Magnetic material in the human hippocampus

Magnetic analyses of hippocampal material from deceased normal and epileptic subjects, and from the surgically removed epileptogenic zone of a living patient have been carried out. All had magnetic characteristics similar to those reported for other parts of the brain [6]. These characteristics along with low temperature analysis indicate that the magnetic material is present in a wide range of grain sizes. The low temperature analysis also revealed the presence of magnetite through manifestation of its low temperature transition. The wide range of grain sizes is similar to magnetite produced extracellularly by the GS-15 strain of bacteria and unlike that found in magnetotactic bacteria MV-1, which has a restricted grain size range. Optical microscopy of slices revealed rare 5-10 micron clusters of finer opaque particles, which were demonstrated with Magnetic Force Microscopy to be magnetic. One of these was shown with EDAX to contain AI, Ca, Fe, and K, with approximate weight percentages of 55, 19, 19, and 5, respectively.

Metal layer Bragg–Fresnel lenses for diffraction focusing of hard x-rays

A thin-film Bragg–Fresnel lens (BFL) was developed for diffractive focusing of hard x-rays into submicron to nanometer spots for scanning x-ray spectromicroscopy. The lens is made of metal-layer Fresnel zones deposited on an x-ray reflective substrate. The use of a high-density lens structure reduces the thickness of the lens and simplifies the fabrication process. Linear and elliptical lenses made of a 200-nm-thick Au film were fabricated using e-beam lithography and a metal deposition process. The focusing capabilities of the Au layer BFLs were demonstrated at the Advanced Photon Source.

Bragg-fresnel optics for hard x-ray microscopy : development of fabrication process and x-ray characterization at the Advanced Photon Source.

Results are presented on development of processes for fabricating linear and circular Bragg–Fresnel lenses (BFLs) on Si and III–V compound material substrates, and on x-ray characterization of linear BFLs at the Advanced Photon Source (APS). Processes were developed for fabricating long (zone length >5 mm) linear BFLs on Si with enhanced capability for focusing high-energy x rays. By stitching together 20 sequentially exposed 400-μm-long linear BFLs, we were able to fabricate 8-mm-long linear BFLs with 0.5-μm finest zone width. BFLs were also fabricated on III–V compound semiconductor substrates GaAs and InP, with improved process control due to the substantially reduced zone thickness required (∼50% less than Si). Reduction of the zone aspect ratio (thickness/width) lessens the demand on the process technology, and may lead to higher lens resolution and pattern transfer accuracy. A process was explored to fabricate BFLs on a GaAs/AlGaAs heterostructure incorporating a built-in “etch stop” layer to ensure...

Fabrication and characterization of III-V compound semiconductor Bragg-Fresnel lenses for hard x-ray microfocusing

Abstract Hard x-ray phase Bragg-Fresnel lenses (BFLs) have been made in III–V semiconductors of (111) GaAs and InP, and in Si for comparison purposes. Diffractive linear and circular patterns were defined with conventional electron beam lithography. Pattern transfer was accomplished with reactive ion etching (RIE) using gases of BCl3/Cl2/SiCl4, CH4/H2/Ar, and BCl 3 Cl 2 , respectively. In addition, selective etching of heteroepitaxial GaAs devices for better process depth control was demonstrated by incorporating an epitaxial AlGaAs etch stop layer between the GaAs top layer and substrate and then etching with Cl 2 O 2 . Preliminary tests on focusing have been made at the Stanford Synchrotron Radiation Laboratory (SSRL) showing the ability to focus a 50 micron x-ray beam to ∼5 microns for Si structures. This is an essential requirement for x-ray microprobe technology development which has wide applications in x-ray imaging, deep field x-ray lithography, and in probing nanometer scale complex fluids such as boundary lubrication layers.

Characterizing the hard x-ray diffraction properties of a GaAs linear Bragg–Fresnel lens

We investigated the diffractive focusing properties of (111) GaAs linear Bragg–Fresnel lenses (BFLs) developed for hard x-ray microscopy and microdiffraction of complex materials in confined geometries. We demonstrated that the use of GaAs yields significant processing advantages due to the reduced zone depth. Focal plane diffraction patterns of linear BFLs measured at the advanced photon source using 8–40 keV x rays were compared to a simple model based on Kirchhoff–Fresnel diffraction theory. Good agreement was obtained between experimental data and model calculations using only zones within an effective aperture defined by the transverse coherence of the source.

Structural studies of DNA: Cationic lipid complexes confined in lithographically patterned microchannel arrays

We have used lithographically patterned microchannel arrays with channel widths ranging from 1 to 20 μm, fabricated using electron beam lithography and reactive ion etching, in structural studies of DNA–cationic lipid complexes in confinement. Various techniques have been developed for loading these DNA–membrane complexes into the microchannels or to form the complexes in situ by sequentially depositing DNA and lipid solutions into the microchannels. Optical microscopy studies indicate that such complex formation is strongly influenced by the periodic channel structure even at channel widths much larger than the persistent length of the DNA molecules. Preliminary x-ray diffraction experiments conducted at Stanford Synchrotron Radiation Laboratory (SSRL) yielded only a weak signal from the lipid bilayers in the complexes. The use of a microfocused x-ray beam produced by the newly developed Bragg–Fresnel optics at a third-generation synchrotron facility may dramatically increase the signal-to-noise ratio and allow observation of orientational as well as positional ordering of DNA molecules induced by the microchannels. Structural control of the DNA–membrane complexes has a broad range of potential applications in gene probe technology and as mesoscopic biomolecular composites.

Imaging Complex Fluids Under Confinement and Flow: Development of Bragg-Fresnel Optics for X-ray Microdiffraction

We present results of simultaneous efforts to develop: 1.) Bragg-Fresnel Optics(BFO) to be used in X-ray microdiffraction methods, in particular as applied to structural studies of complex fluids and biomaterials under confinement and flow conditions; and 2.) Methodologies for confining complex fluids and biomaterials for in-situ structural studies. Using microelectronics process technology, we have fabricated linear and circular Bragg-Fresnel Lenses (BFL) in Si and III-V compound semiconductor substrates such as InP, GaAs and GaAs heterostructures with outermost zone width to 0.25 μm. X-ray characterization of linear BFLs were performed on a wiggler beamline at Stanford Synchrotron Radiation Laboratory (SSRL) at x-ray energies of 8 keV and 16 keV. A ∼5 μm focal spot size was obtained with a 50 μm incident beam, which was determined by the partial coherence of the source. On the confinement techniques, we have developed the X-ray Surface Force Apparatus (XSFA) which allows in-situ x-ray diffraction measurements to be made on fluid thin films confined between two atomically smooth surfaces. A new approach is being pursued to study the effects of confinement and flow on complex fluids and biological materials using microchannels fabricated on glass substrates.