This work presents a method for reducing acoustic resonances in ferroelectric barium strontium titanate (BST)-based bulk ceramic varactors, which are capable of operation in high-power matching circuits. Two versions of parallel-plate varactors are manufactured here: one with pure BST and one with 10 vol-% magnesium borate, Mg3B2O6 (MBO). Each varactor includes a 0.85-mm-thick ferroelectric layer. Acoustic resonances that are present in the pure BST varactor are strongly suppressed in the BST-MBO varactor and, hence, the Q-factor is increased over a wide frequency range by the addition of small amounts of a low-dielectric-constant (LDK) MBO. Although the tunability is reduced due to the presence of non-tunable MBO, the increased Q-factor extends the varactor’s availability for low-loss and high-power applications.

Low loss, ferroelectric, fully-printed varactors for high-power matching applications are presented. Piezoelectric-induced acoustic resonances reduce the power handling capabilities of these varactors by lowering the Q-factor at the operational frequency of 13.56 MHz. Here, a quality factor of maximum 142 is achieved with an interference-based acoustic suppression approach utilizing double metal-insulator-metal structures. The varactors show a tunability of maximum 34% at 300 W of input power. At a power level of 1 kW, the acoustic suppression technique greatly reduces the dissipated power by 62% from 37 W of a previous design to 14.2 W. At this power level, the varactors remain tunable with maximum 18.2% and 200 V of biasing voltage.

This work addresses the piezoelectric induced reduction of quality factor in fully-printed metal-insulator-metal (MIM) barium strontium titanate (BST) thick film varactors designed for high power operation. An acoustically optimized varactor design is presented and compared to a non-optimized high-power varactor. The design is utilized to present a narrowband acoustic suppression technique based on defined weights. The acoustically optimized varactor consists of 162 varactor cells in a capacitive matrix. The cells in the matrix are interconnect-able allowing for a variable unbiased capacitance and power rating. Due to this setup, surface acoustic waves are interrupted, and the reduced size of the cells allows for a reduced BST layer thickness, shifting the acoustic resonance away from the operational frequency. Therefore, an inverted behavior in comparison to the high-power varactor is observed with an increasing quality factor with biasing voltage. Compared to the high-power varactor, the acoustically optimized varactor design shows a 40% increased quality factor in biased state. By applying the narrowband acoustic suppression technique, an increase in quality factor of 145% is achieved compared to the unsuppressed design. In comparison to the high-power varactor, the acoustical suppressed design shows an increase in quality factor of 480% at the first acoustic resonance frequency.

This work presents three fully-printed, acoustically optimized metal-insulator-metal (MIM) thick film varactor modules, capable of operating in matching circuits rated with up to 700W. The varactors are based on a barium strontium titanate (BST) dielectric layer with a thickness of \pmb25 μ m to \pmb36 μm, which is utilized to adjust the acoustical behavior of the varactor. At room temperature, the varactors show a tunability of 17 % to 28 % with 220 V of biasing voltage and a quality factor of 37 to 62 in unbiased state. In biased state, the quality factor is either increased or decreased, depending on the acoustical adjustment of the varactor. With 700 W of input power, one varactor shows a maximum tunability of 7 % withstanding 118 V and 13.6 A of RMS RF voltage and current, respectively, dissipating 67 W of RF power.

This work presents a fully-printed metal-insulator-metal (MIM) thick film varactor capable of operation in matching circuits rated with up to 1 kW. The varactor utilizes a 20 μm thick layer of barium strontium titanate (BST) as tunable ferroelectric material. The design is based on a serial stack of capacitive MIM structures. The obtained overall capacitance is 1.9 nF with a maximum tunability of 37 % for a biasing voltage of 200 V and a quality factor of 58 at room temperature and 13.56 MHz. At 70 °C the tunability of the varactor is decreased to 22 %, while the quality factor increases to its maximum of 93. With 1 kW of input power, the varactor shows a tunability of 19 % for 150 V of DC biasing voltage, withstanding 121V and 17 A of RMS RF voltage and current, respectively. The varactor with integrated resistive matching dissipates 37 W of power, equal to 3.7 %.

A fully screen printed metal-insulator-metal (MIM) thick-film varactor is presented, designed for high-power application. The varactor is based on a 9.9 μm thick film layer of the tunable, ferroelectric material barium strontium titanate (BST) resulting in a capacitance at room temperature of 4.2 nF and a quality factor of 26 at 13.56 MHz. A tunability of 37.2% is measured with a biasing voltage of 100 V decreasing the capacitance to 2.88 nF and increasing the quality factor to 32.3. The power handling capabilities of the varactor are evaluated in a 50 Ω setup in back to back configuration at 13.56 MHz. The varactor is placed in the shunt branch of an L-match circuit. At maximum RF input power of 515 W the varactor withstands an RF RMS voltage of 66 V and an RMS current of 11A with 37 W of dissipated power. At 400 W of RF input power the varactor shows a tunability of 18 % with a DC biasing voltage of 128 V.

Accumulation of aggregates rich in an abnormally folded form of the prion protein characterize the neurodegeneration caused by transmissible spongiform encephalopathies (TSEs). The molecular triggers of plaque formation and neurodegeneration remain unknown, but analyses of TSE-infected brain homogenates and preparations enriched for abnormal prion protein suggest that reduced levels of copper and increased levels of manganese are associated with disease. The objectives of this study were to: (1) assess copper and manganese levels in healthy and TSE-infected Syrian hamster brain homogenates; (2) determine if the distribution of these metals can be mapped in TSE-infected brain tissue using X-ray photoelectron emission microscopy (X-PEEM) with synchrotron radiation; and (3) use X-PEEM to assess the relative amounts of copper and manganese in prion plaques in situ. In agreement with studies of other TSEs and species, we found reduced brain levels of copper and increased levels of manganese associated with disease in our hamster model. We also found that the in situ levels of these metals in brainstem were sufficient to image by X-PEEM. Using immunolabeled prion plaques in directly adjacent tissue sections to identify regions to image by X-PEEM, we found a statistically significant relationship of copper-manganese dysregulation in prion plaques: copper was depleted whereas manganese was enriched. These data provide evidence for prion plaques altering local transition metal distribution in the TSE-infected central nervous system.

Two alternative processes complicate understanding of the biochemical origins and geochemical alteration of organic matter over geologic time: selective preservation of original biopolymers and in situ generation of new geopolymers. One of the best constrained potential sources of bio- and geochemical information about extinct fossil plants is frequently overlooked. Permineralized anatomically preserved plant fossils allow analysis of individual cell and tissue types that have an original biochemical composition already known from living plants. The original composition of more enigmatic fossils can be constrained by geochemical comparisons to tissues of better understood fossils from the same locality. This strategy is possible using synchrotron-based techniques for submicron-scale imaging with X-rays over a range of frequencies in order to provide information concerning the relative abundance of different organic bonds with X-ray Absorption Near Edge Spectroscopy. In this study, X-ray PhotoElectron Emission spectroMicroscopy (X-PEEM) was used to analyze the tissues of Lepidodendron, one of the lycopsid trees that were canopy dominants of many Pennsylvanian coal swamp forests. Its periderm or bark—the single greatest biomass contributor to many Late Paleozoic coals—is found to have a greater aliphatic content and an overall greater density of organic matter than lignified wood. Because X-PEEM allows simultaneous analysis of organic matter and matrix calcite in fully mineralized fossils, this technique also has great potential for analysis of fossil preservation, including documentation of significant traces of organic matter entrained in the calcite crystal fabric that fills the cell lumens.

This study reports reaction pathways to form TiAlx metallic complexes during the high energy ball milling of 4 mol% TiCl3 with NaAlH4 powders determined using local structure analysis of Tix+ and Alx+ species. Using x-ray photoemission electron microscopy (XPEEM) and x-ray diffraction (XRD), the oxidation state of Alx+ and Tix+ and the crystalline compounds existing in equilibrium with NaAlH4 were tracked for samples milled for times of 0 (i.e. mixing), 5, and 25 min. XPEEM analysis of the Al K edge after 5 min of milling reveals that Al remains in the 3+ oxidation state (i.e. in NaAlH4) around Ti0-rich regions of the sample. After 25 min of high energy milling, Ti0 has reacted with Al3+ (in nearby NaAlH4) to form TiAlx complexes. This study reports the pathway for TiAlx complex formation during milling of 4 mol% TiCl3catalyzed NaAlH4 to be as follows: (1) Ti3+ reduces to Ti0 (with Al3+ near Ti0 regions) and (2) Ti0 reacts with Al3+ in NaAlH4 to form TiAlx complexes.

Many biominerals contain micro- or nanocrystalline mineral components, organized accurately into architectures that confer the material with improved mechanical performance at the macroscopic scale. We present here an effect which enables us to observe the relative orientation of individual crystals at the submicron scale. We call it polarization-dependent imaging contrast (PIC), as it is an imaging development of the well-known x-ray linear dichroism. Most importantly, PIC is obtained in situ, in biominerals. We present here PIC in the prismatic and nacreous layers of Haliotis rufescens (red abalone), confirm it in geologic calcite and aragonite, and corroborate the experimental data with theoretical simulated spectra. PIC reveals different and unexpected aspects of nacre architecture that have inspired theoretical models for nacre formation.

It is widely known that macromolecules, such as proteins, can control the nucleation and growth of inorganic solids in biomineralizing organisms. However, what is not known are the complementary molecular interactions, organization, and rearrangements that occur when proteins interact with inorganic solids during the formation of biominerals. The organic-mineral interface (OMI) is expected to be the site for these phenomena, and is therefore extraordinarily interesting to investigate. In this report, we employ X-ray absorption near edge (XANES) spectromicroscopy to investigate the electronic structure of both calcium carbonate mineral crystals and polypeptides, and detect changing bonds at the OMI during crystal growth in the presence of polypeptides. We acquired XANES spectra from calcium carbonate crystals grown in the presence of three mollusk nacre-associated polypeptides (AP7N, AP24N, n16N) and in the presence of a sea urchin spicule matrix protein, LSM34. All these model biominerals gave similar results, including the disruption of CO bonds in calcite and enhancement of the peaks associated with C-H bonds and C-O bonds in peptides, indicating ordering of the amino acid side chains in the mineral-associated polypeptides and carboxylate binding. This is the first evidence of the mutual effect of calcite on peptide chain and peptide chain on calcite during biomineralization. We also show that these changes do not occur when Asp and Glu are replaced in the n16N sequence with Asn and Gln, respectively, demonstrating that carboxyl groups in Asp and Glu do participate in polypeptide-mineral molecular associations.

Many biominerals, including mollusk and echinoderm shells, avian eggshells, modern and fossil bacterial sediments, planktonic coccolithophores, and foraminifera, contain carbonates in the form of biogenic aragonite or calcite. Here we analyze biogenic and geologic aragonite using different kinds of surface- and bulk-sensitive X-ray absorption near-edge structure (XANES) spectroscopy at the carbon K-edge, as well as high-resolution scanning transmission X-ray microscopy (STXM). Besides the well-known main pi* and sigma* carbonate peaks, we observed and fully characterized four minor peaks, at energies between the main pi* and sigma* peaks. As expected, the main peaks are similar in geologic and biogenic aragonite, while the minor peaks differ in relative intensity. In this and previous work, the minor peaks appear to be the ones most affected in biomineralization processes, hence the interest in characterizing them. Peak assignment was achieved by correlation of polarization-dependent behavior of the minor peaks with that of the main pi* and sigma* peaks. The present characterization provides the background for future studies of aragonitic biominerals.

Since 1997 we systematically perform Direct ARPES (=DARPES) on in-situ grown, non-cleaved, ultra-thin (<25nm) cuprate films. Specifically, we probe low energy electronic structure and properties of high-T-c films under different degree of epitaxial (compressive vs tensile) strain. In overdoped in-plane compressed La2-xSrxCuO4 (LSCO) thin films we double T-c from 20K to 40K, yet the Fermi surface (FS) remains essentially 2-dimensional (213). In contrast, tensile strained films show 3-dimensional (313) dispersion, while T-c is drastically reduced. It seems that the in-plane compressive strain tends to push the apical oxygen far away from the CuO2 plane, enhances the 2D character of the dispersion and increases T-C, while the tensile strain seems to act exactly in the opposite direction and the resulting dispersion is 3D. We have the FS topology for both cases. As the actual lattice of cuprates is 'Napoleon-cake'-like i.e. rigid CuO2 planes alternate with softer 'reservoir' (that strains distort differently) our results tend to rule out 2D rigid lattice mean field models. Finally, we briefly discuss recent successful determination of the FS topology from the observed wavevector quantization by DARPES in cuprate films thinner than 18 units cells (<24nm). Such an approach is of broader interest as it can be extended to other similar confined (ultra-thin) functional oxide systems.

Sea urchin larval spicules transform amorphous calcium carbonate (ACC) into calcite single crystals. The mechanism of transformation is enigmatic: the transforming spicule displays both amorphous and crystalline properties, with no defined crystallization front. Here, we use X-ray photoelectron emission spectromicroscopy with probing size of 40-200 nm. We resolve 3 distinct mineral phases: An initial short-lived, presumably hydrated ACC phase, followed by an intermediate transient form of ACC, and finally the biogenic crystalline calcite phase. The amorphous and crystalline phases are juxtaposed, often appearing in adjacent sites at a scale of tens of nanometers. We propose that the amorphous-crystal transformation propagates in a tortuous path through preexisting 40- to 100-nm amorphous units, via a secondary nucleation mechanism.

Since 1997 we systematically perform direct angle resolved photoemission spectroscopy (ARPES) on in-situ grown thin (<30 nm) cuprate films. Specifically, we probe low-energy electronic structure and properties of high-T c superconductors (HTSC) under different degrees of epitaxial (compressive vs. tensile) strain. In overdoped and underdoped in-plane compressed (the strain is induced by the choice of substrate) ≈15 nm thin La2 − x Sr x CuO4 (LSCO) films we almost double T c to 40 K, from 20 K and 24 K, respectively. Yet the Fermi surface (FS) remains essentially two-dimensional. In contrast, ARPES data under tensile strain exhibit the dispersion that is three-dimensional, yet T c drastically decreases. It seems that the in-plane compressive strain tends to push the apical oxygen far away from the CuO2 plane, enhances the two-dimensional character of the dispersion and increases T c, while the tensile strain acts in the opposite direction and the resulting dispersion is three-dimensional. We have established the shape of the FS for both cases, and all our data are consistent with other ongoing studies, like EXAFS. As the actual lattice of cuprates is like a ‘Napoleon-cake’, i.e. rigid CuO2 planes alternating with softer ‘reservoir’, that distort differently under strain, our data rule out all oversimplified two-dimensional (rigid lattice) mean field models. The work is still in progress on optimized La-doped Bi-2201 films with enhanced T c.

The combination of spectroscopy and microscopy enables unprecedented insights into the molecular and crystal structures of organic and inorganic materials, and their interfaces. This is relevant to the field of biomaterials in general and biominerals in particular. In this framework, we extensively analyzed various proteins, minerals and biominerals. Here we present two novel observations: x‐ray absorption near‐edge structure (XANES) spectroscopy at the carbon K‐edge is sensitive to protein misfolding and aggregation into amyloid fibrils, and to the polar and azimuthal rotation of the CaCO3 polymorph aragonite.

The morphology, composition, and bonding character (carbon hybridization state) of continuous, ultra-thin (thickness similar to 60 nm) nanocrystalline diamond (NCD) membranes are reported. NCD films were deposited on a silicon substrate that was pretreated using an optimized, two-step seeding process. The surface after each of the two steps, the as-grown NCD topside and the NCD underside (revealed by etching away the silicon substrate) is examined by X-ray PhotoElectron Emission spectroMicroscopy (X-PEEM) combined with X-ray absorption near edge structure (XANES) spectroscopy, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The first step in the seeding process, a short exposure to a hydrocarbon plasma, induces the formation of SiC at the diamond/Si interface along with a thin, uniform layer of hydrogenated, amorphous carbon on top. This amorphous carbon layer allows for a uniform, dense layer of nanodiamond seed particles to be spread over the substrate in the second step. This facilitates the growth of a homogeneous, continuous, smooth, and highly sp(3) -bonded NCD film. We show for the first time that the underside of this film possesses atomic-scale smoothness (RMS roughness: 0.3 nm) and > 98% diamond content, demonstrating the effectiveness of the two-step seeding method for diamond film nucleation. (C) 2007 Elsevier B.V. All rights reserved.