Search

METALLIC DEFORMATION FINGERPRINTS Capturing and predicting the strength of metallic materials subjected to cycling loading, or fatigue strength, just became a lot quicker. A discovery by researchers from the University [...]

A major concern with medical and dental biomaterials is colonization of these materials with microbial biofilms. One material processed using chemical vapor deposition and other conventional top-down nanomanufacturing technologies that has recently been considered for use in preventing growth of microorganisms is the nanocrystalline diamond. Nanocrystalline diamond coatings have been evaluated for use as coatings on medical implants (e.g., hip prostheses) and surgical tools due to their low coefficient of friction, high corrosion resistance, high hardness, and high wear resistance. In this study, the microstructural properties and microorganism interaction behavior of nanocrystalline diamond coatings were examined. A device for examining microbial biofilms known as a CDC biofilm reactor was used to examine the interaction between a fluorescent microorganism, Pseudomonas fluorescens, and nanocrystalline diamond coatings in a continuous perfusion environment. Biofilm formation was evident on the nanocrystalline diamond surface after 24 h. No correlation between grain size or morphology and cell density was observed; large variations in P. fluorescens growth on the coatings were observed, even for the samples with similar grain sizes and morphologies. The results of this study suggest that nanocrystalline diamond coatings do not prevent Pseudomonas fluorescens biofilm development in a continuous perfusion environment. Additional treatment of the nanocrystalline diamond coatings with antimicrobial and/or antifouling agents would be necessary to prevent formation of microbial biofilms. The development of novel continuous flow technologies for evaluating the growth of microbial biofilms on biomaterials will provide a better understanding of biomaterial-microorganism interaction and will enable the creation of enhanced antimicrobial biomaterials. [DOI: 10.1115/1.4001583] Keywords: nanocrystalline diamond, biofilm, chemical vapor deposition, thin films

(100) AlN films are combined with diamonds as a new composite surface acoustic wave (SAW) substrate, where the SAW properties of (100) AlN films on diamonds are analyzed with 4 composite structures. The results have provided a vital basis for further application oh high-velocity SAW devices.

Chemical-vapor-deposited single-crystal diamonds for use in high voltage and high-temperature applications are described. These models provide an explanation for its different conduction, which is due to incomplete ionization of boron dopant, but the limited voltage handling capacity of the CVD is due to residual defects in the intrinsic voltage blocking layer in the structure.

The use of synthetic diamond for intracavity thermal management in compact solid-state lasers is examined. Findings reveal that the synthetic diamond samples possess significantly lower birefringence as compared to natural single-crystal diamond.

Crystal growth mechanisms are crucial to understanding the complexity of crystal morphologies in nature and advanced technological materials, such as the faceting and dendrites found in snowflakes and the microstructure and associated strength properties of structural and icy planetary materials. In this article, we present observations of pressure-induced ice VI crystal growth, which have been predicted theoretically, but had never been observed experimentally to our knowledge. Under modulated pressure conditions in a dynamic-diamond anvil cell, rough single ice VI crystal initially grows into well defined octahedral crystal facets. However, as the compression rate increases, the crystal surface dramatically changes from rough to facet, and from convex to concave because of a surface instability, and thereby the growth rate suddenly increases by an order of magnitude. Depending on the compression rate, this discontinuous jump in crystal growth rate or 'shock crystal growth' eventually produces 2D carpet-type fractal morphology, and moreover dendrites form under sinusoidal compression, whose crystal morphologies are remarkably similar to those predicted in theoretical simulations under a temperature gradient field. The observed strong dependence of the growth mechanism on compression rate, therefore, suggests a different approach to developing a comprehensive understanding of crystal growth dynamics. dynamic-diamond anvil cell

Geologists have 'known' for many years that continental crust is buoyant and cannot be subducted very deep. Microdiamonds 10-80 [micro]m in size discovered in the 1980s within metamorphic rocks related to continental collisions clearly refute this statement, suggesting that material of continental crust has been subducted to a minimum depth of >150 km and incorporated into mountain chains during tectonic exhumation. Over the past decade, the rapidly moving technological advancement has made it possible to examine these diamonds in detail, and to learn that they contain nanometric multiphase inclusions of crystalline and fluid phases and are characterized by a 'crustal' signature of carbon stable isotopes. Scanning and transmission electron microscopy, focused ion beam techniques, synchrotron infrared spectroscopy, and nano-secondary ion mass spectrometry studies of these diamonds provide evidence that they were crystallized from a supercritical carbon-oxygen-hydrogen fluid. These microdiamonds preserve evidence of the pathway by which carbon and water can be subducted to mantle depths and returned back to the earth's surface. crust | microdiamonds | fluid

Fluid-bearing microinclusions in diamonds ( Carbonates appear in all assemblages, together with either halides or silicates, indicative of the importance of carbonatitic high-density fluid during diamond growth and fluid evolution. The presence of halide-carbonate or silicate-carbonate assemblages is in agreement with the bulk composition of the microinclusions as detected by EPMA. The high K content of some microinclusions detected by EPMA cannot be accounted for by the solid phases analyzed by TEM. This discrepancy suggests that K is concentrated in the residual fluid that is lost during TEM sample preparation. In addition to microinclusions, large cavities containing amorphous phases were found in the inner parts of one Siberian and one Canadian diamond. An Al-rich phase is the most abundant, and it is accompanied by Ca-rich and Si-rich phases. These phases may be explained by amorphization of crystalline phases. A breakdown of a single melt into three immiscible components is less likely. Keywords: Crystal structure, high-density fluid, high-silica mica, carbonate, halide, secondary minerals, multi-phase assemblage

At high pressure and temperature, the phase diagram of elemental carbon is poorly known. We present predictions of diamond and BC8 melting lines and their phase boundary in the solid phase, as obtained from first-principles calculations. Maxima are found in both melting lines, with a triple point located at [approximately equal to] 850 GPa and [approximately equal to] 7,400 K. Our results show that hot, compressed diamond is a semiconductor that undergoes metalization upon melting. In contrast, in the stability range of BC8, an insulator to metal transition is likely to occur in the solid phase. Close to the diamond/liquid and BC8/liquid boundaries, molten carbon is a low-coordinated metal retaining some covalent character in its bonding up to extreme pressures. Our results provide constraints on the carbon equation of state, which is of critical importance for devising models of Neptune, Uranus, and white dwarf stars, as well as of extrasolar carbon-rich planets. phase transitions | melting | high pressure | molecular dynamics | metalization

Diamond inclusions are of particular research interest in mantle petrology and diamond exploration as they provide direct information about the chemical composition of upper and lower mantle and about the petrogenetic sources of diamonds in a given deposit. The objective of the present work is to develop semi-quantitative analytical tools for non-destructive in situ identification and characterization of mineral inclusions in diamonds using synchrotron micro-X-ray Fluorescence ([micro]SXRF) spectroscopy and micro-X-ray Absorption Near Edge Structure ([micro]XANES) spectroscopy at a focused spot size of 4 to 5 micrometers. The data were collected at the Pacific Northwest Consortium (PNC-CAT) 20-ID microprobe beamline at the Advanced Photon Source, located at the Argonne National Laboratory, and yielded the first high-resolution maps of Ti, Cr, Fe, Ni, Cu, and Zn for natural diamond grains, along with quantitative [micro]SXRF analysis of select chemical elements in exposed kimberlite indicator mineral grains. The distribution of diamond inclusions inside the natural diamond host, both visible and invisible using optical transmitted-light microscopy, can be mapped using synchrotron [micro]XRF analysis. Overall, the relative abundances of chemical elements determined by [micro]SXRF elemental analyses are broadly similar to their expected ratios in the mineral and therefore can be used to identify inclusions in diamonds in situ. Synchrotron [micro]XRF quantitative analysis provides accurate e stimates of Cr contents of exposed polished minerals when calibrated using the concentration of Fe as a standard. Corresponding Cr K-edge [micro]XANES analyses on selected inclusions yield unique information regarding the formal oxidation state and local coordination of Cr.

To evaluate the dissolution processes of diamond crystals in kimberlitic and lamproitic magmas, a series of diamond dissolution experiments were carried out in the graphite stability field at 1300--1420 [degrees]C and 1 GPa under the WI, MW, and HM buffers. Dissolution agents used include an aphanitic kimberlite from Wesselton Mine, South Africa, and a lamproite from Mount North, West Kimberley, Australia. With increasing run duration, diamond morphology changed from a sharp octahedron through combinations of octahedron and tetrahexahedroidal forms to spherical tetrahexahedroid having rounded faces. Negatively oriented trigons were formed on the octahedral {111} face. As the degree of diamond dissolution increased, the trigons changed from smaller shallow types to larger deep types. The dissolution rate in the kimberlitic solvent at 1300 [degrees]C was 0.12 mm/h under the HM buffer, 0.0034 mm/h under the MW buffer, and 0.0017 mm/h under the WI buffer, whereas that at 1420 [degrees]C was 0.014 mm/h under the WI buffer. In the lamproitic solvent, the dissolution rate was 0.0024 mm/h at 1420 [degrees]C under the WI buffer. The data indicate that diamond dissolves in silicate melts as carbonate ions through an oxidizing reaction. The degree of dissolution strongly depends on temperature, oxidation state, and the compositional dependence of C[O.sub.2] solubility in the melts.

A study analysis the high resolution x-ray diffraction peaks of diamond nanosize powders of nominal sizes ranging from 5 to 250 nm. Details of the apparent lattice method that is applied to characterize the structure of a shell-core model of nanosize particles are discussed.

The friction force was found to increase linearly with the normal load, indicating that Amontons' law also holds true in the microscale world. The goal of this study was to model the atomic-scale friction of a hydrogenated diamond (111) surface, C13H22, with a suitable ab initio method.

Cylindrical diamond columns of 15 nm height and 10 nm diameter are prepared on a diamond (100) substrate by exploiting the self-organization of metal-loaded diblock copolymers. The study shows that after burning off the blockcopolymer in an oxygen-plasma the resulting Au nanoparticles act as a mask during further etching the diamond substrate in this plasma and Au-capped diamond columns are formed with an approximate size of the former gold particles.

Field emission characteristics of undoped polycrystalline diamond films with different structural properties are investigated. The study from an investigation of the spatial distribution of emission sites concludes that the transport path of field-emitted electrons and the resulting field emission mechanism depend solely on the nondiamond carbon content in diamond films.

Electronic band structure calculations are used to examine the origin of a band gap present in most 18-electron half-Heusler compounds and its absence in the Zintl compound NaTl. The results have shown that the presence or absence of a band gap in this diamond like compounds is controlled by the extent of the [sigma] antibonding between the valence s orbitals, and the bonding characteristics of the late-main-group elements have depended on the extent of their ns/np hybridization.

The article explains the structure and properties of the different synchrotron instrumentation x-ray optics, which are made of nanocrystalline diamond. This optics is shown to be very transparent, strong and is also subjected to low thermal expansion.

Several Hall effect measurements are conducted to explain the characterization and the electrical properties of the B-doped homoepitaxially grown diamond. The extracted carrier type, concentration and mobility of these compounds are shown to be highly dependent on the measurement contact configuration.

The ultrahigh vacuum atomic force microscope (AFM) technique is employed for the characterization of the nterfacial friction for a single-asperity diamond contact on a diamondlike carbon (DLC) substrate over a nominal substrate temperature range. The dependence of the friction on the temperature of the system is also analyzed.

The van der Pauw technique is used for determining the resistivity of materials and finite element analysis is used for studying the effect of contact placement error induced by pressure on the resistivity measurement accuracy in a diamond anvil cell by van der Pauw method. The results have shown that the contact placement has a major impact on determination accuracy.

The structure and physical properties of novel nanocarbon hybrids of single-walled carbon nanotubes (SWCNT) and ultradispersed diamond (UDD) forming truly tetragonal-trigonal nanocomposite ensemble with and without gamma irradiation are described. The results have shown that irradiation has generated microscopic defects in a hierarchical manner much below amorphization threshold and that nanocomposites has tended to be radiation resilient, which is analyzed by the intensity, bandwidth and position variation in prominent Raman spectroscopy signatures.

The stress developed in phosphorus-doped layers grown on (110)-textured polycrystalline diamond templates is examined. The shifts of the diamond Raman diffusion and the exciton recombination energies are followed by Raman and cathodoluminescence spectroscopies.

Systematic studies for diamond thin films deposited on WC-Co substrates are conducted to determine the relation between substrate surface irregularities and also study the effect of particular size on diamond nucleation. The deposited films of WC-Co substrate with higher surface fractal dimension are preseeded by fine diamond suspension in advance exhibited high diamond-rich composition and adhesion strength.

Systematic studies about the modification on microstructure of diamond films due to the incorporation of [H.sub.2] species into the Ar/C[H.sub.4] plasma are reported. The integration of 0.1% hydrogen in the Ar/C[H.sub.4] plasma which is sufficient to induce the formation of platelike grains suggested that the platelike grains are formed via the competition between the attachment and the etching of hydrocarbons onto the existing diamond surfaces.

The interfaces between diamond and metals with different carbide formation enthalpies (Cu, Ti, and Al) are studied to understand the basic material properties required in selecting a metallic interlayer for enhanced adhesion of diamond coatings on the substrates. The results indicated that a strong carbide-forming ability and a large surface energy of the interlayer could promote nucleation and enhance the adhesion and interface strength of the coating/substrate system.

The impedance spectroscopy and Hall effect measurements are utilized to study the electrical properties of both intrinsic and lightly boron-doped nanocrystalline diamond (NCD) fabricated by a nanodiamond seeding technique. Both grain boundaries and grains themselves for intrinsic material contributed to the frequency dependant impedance values and the films could become highly resistive by removing the boundary conduction.

The structural, electrical, optical and dielectrical properties of Pb([Zr.sub.0.52],[Ti.sub.0.48])[O.sub.3] (PZT) thin films integrated on single crystal diamond (100) substrates are described. The PZT film grown on SrTi[O.sub.3]/[Al.sub.2][O.sub.3]/diamond has displayed better in-plane polarization than that of the PZT film on [Al.sub.2][O.sub.3]/diamond and photoresponse behavior revealed that carriers trapping effect is trivial in the PZT film.

A detailed study was conducted to characterize the detonation nanodiamonds (DNDs) whose surface is chemically modified by copper with the aid of ion exchange in water DND suspension. The concentration of magnetically observable copper ions [Cu.sup.2+] (spin S=1/2) localized on the nanodiamonds surface is found to increase with increasing concentration of copper acetate in starting solutions.

The characterization of field emission properties from hydrogen-terminated intrinsic diamond covered by adsorbate films as a function of surface adsorbate coverage and bulk doping with n- and p-type is described. Comparison of obtained data with p- and n-type diamonds showed a continuous rise of emission current as a function of electric field while the calculations based on the Fowler-Nordheim equation revealed a 2D-quantized energy level in the surface conductive layer.

High pressure high temperature and chemical vapor deposition synthetic diamonds with varying nitrogen concentration is examined and an accurate method is described for estimating the concentration of the nitrogen-vacancy (N-V) centers created by ion implantation. The ion irradiation route has produced up to 6 ppm of optically active (N-V) centers, while nitrogen implantation has produced up to 3 ppm of optically active (N-V) with 8% conversion efficiency.

The interdigital transducer (IDT)/AlN/conducting layer/diamond structures are examined to design surface acoustic wave (SAW) devices in the super high frequency band. The results obtained from the finite element method have shown that a thin conducting layer has increased the coupling coefficient and has broadened the bandwidth of SAW devices.

Impedance spectroscopy is used to study the conductivity exhibited by diamond doped with boron in an intrinsic-[delta]-layer-intrinsic multilayer system with differing [delta]-layer thicknesses. The introduction of the capping layer is found to create a third conduction path associated with unwanted boron in the capping layer-[delta]-layer interface.

The hydrogen bonding, phase composition, the surface microstructure, and composition of diamond films consisting of 30-50 nm crystallites, deposited onto silicon substrates were explored to examine the impact of high temperature annealing up to 1200 degree [Celsius on the film. The results suggested that formation of SiC phase preferentially consumes [sp.sup.2]/sp hybridized carbon matrix, produced by thermal desorption of hydrogen atoms at diamond grain boundary and at the diamond film-silicon substrate interface.

The comparison between the point doses evaluated with the synthetic single crystal diamond detector (SCDD), with a PTW semiflex air ionization chamber and calculated with the treatment planning system (TPS) is described. The results have shown the potentiality of chemical vapor deposited SCDD for dosimetry of intensity-modulated radiation therapy (IMRT) fields and have opened up the field for diamond dosimeters toward novel applications such as very small beam monitoring.

A broadly applicable energy model based on quantitative wear experiments is described for the evolution of scanning probe tip radii. Undoped diamond atomic force microscopy tips are nearly ten times more wear resistant than silicon nitride probes and a linear relationship is identified between wear volume and total dissipation energy for a constant applied force.

Atomic force microscopy (AFM) is used for studying the conductance of hydrogenated single-crystal diamond (100) surfaces over submicron length scales. Conducting AFM measurements have shown the variations in the current and resistance that are related to the topography have explained the surface inhomogeneity of the electronic structure in the contact resistance due to the surface roughness.

The characteristics of the edge emission of homoepitaxial diamond sample grown by chemical vapor deposition (CVD) are analyzed and photoluminescence is excited by using a tunable optical parameteric oscillator laser. Free exciton emission and its phonon replicas are observed at all temperatures and excitonic lifetime has shown a nonmonotonic dependence on the sample temperature.

Several studies are conducted to analyze the thermionic emission energy distributions (TEEDs) that take place from the various nanocrystalline diamond (NCD) films. The NCD films are shown to exhibit emission peaks, which make them feasible for numerous direct thermal-electrical energy conversion applications.

Micron-crystalline diamond (MCD) films with a unique microstructure are prepared by using a modified nucleation and growth process, in which a thin layer of ultrananocrystalline diamond (UNCD) is used as nucleation layer for growing diamond films in [H.sub.2]-plasma. Transmission electron microscopy has shown that the unique microstructure is formed by agglomeration and coalescence of the nanosized UNCD grains.

The diamond growth rates for gas-phase microwave plasma chemical vapor deposition and in-liquid microwave plasma chemical vapor deposition are compared for effective fabrication of high-speed deposition of diamond. The growth rate of in-liquid microwave plasma chemical vapor deposition process is found to be greater and more effective compared to the conventional gas-phase microwave plasma chemical vapor deposition process under the same pressure conditions.

Pink crystals composed of antiferromagnetic chains are transformed into blue crystals composed of a ferromagnetic diamondoid framework with structural and magnetic changes.

The enhanced electron field emission (EFE) property observed in ultrananocrystalline diamond (UNCD) and microcrystalline diamond (MCD) films upon irradiation with 100 MeV [Ag.sup.9+]-ions in a fluence of 5*[10.sup.11] ions/square cm is reported. The melting and recrystallization process occurring along the trajectory of the heavy ions induced the formation of interconnected nanocluster networks which facilitated the electron conduction and enhanced the EFE properties for the materials.