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Chemical Vapor Deposited (CVD) diamond growth on (111)-diamond surfaces has received increased attention lately because of the use of N-V related centers in quantum computing as well as application of these defect centers in sensing nano-Tesla strength magnetic fields. We have carried out a detailed study of homoepitaxial diamond deposition on (111)-single crystal diamond (SCD) surfaces using a 1.2 kW microwave plasma CVD (MPCVD) system employing methane/hydrogen/nitrogen/oxygen gas phase chemistry. We have utilized Type Ib (111)-oriented single crystal diamonds as seed crystals in our study. The homoepitaxially grown diamond films were analyzed by Raman spectroscopy, Photoluminescence Spectroscopy (PL), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The nitrogen concentration in the plasma was carefully varied between 0 and 1500 ppm while a ppm level of silicon impurity is present in the plasma from the quartz bell jar. The concentration of N-V defect centers with PL zero phonon lines (ZPL) at 575nm and 637nm and the Si-defect center with a ZPL at 737nm were experimentally detected from a variation in CVD growth conditions and were quantitatively studied. Altering nitrogen and oxygen concentration in the plasma was observed to directly affect N-V and Si-defect incorporation into the (111)-oriented diamond lattice and these findings are presented.

The boron-doped single crystal diamond films were grown homoepitaxially on synthetic (100) oriented Type Ib diamond substrates using a Microwave Plasma Chemical Vapor Deposition (MPCVD) technique. Raman spectrum showed a few additional bands at the lower wavenumber regions along with the zone center optical phonon mode for diamond. The change in the peak profile of the zone center optical phonon mode and its downshift were observed with the increasing boron content in the film. A modification in surface morphology of the film with increasing boron content had been observed by atomic force microscopy. Four point probe electrical measurement indicated that different conduction mechanisms are operating in various temperature regions for these semiconducting films.

High pressure low temperature electrical resistance measurements were carried out on a series of 122 iron-based superconductors using a designer diamond anvil cell. These studies were complemented by image plate x-ray diffraction measurements under high pressures and low temperatures at beamline 16-BM-D, HPCAT, Advanced Photon Source. A common feature of the 1-2-2 iron-based materials is the observation of anomalous compressibility effects under pressure and a Tetragonal (T) to Collapsed Tetragonal (CT) phase transition under high pressures. Specific studies on antiferromagnetic spin-density-wave Ba0.5Sr0.5Fe2As2 and Ba(Fe0.9Ru0.1)2As2 samples are presented to 10 K and 41 GPa. The collapsed tetragonal phase was observed at a pressure of 14 GPa in Ba0.5Sr0.5Fe2As2 at ambient temperature. The highest superconducting transition temperature in Ba0.5Sr0.5Fe2As2 was observed to be at 32 K at a pressure of 4.7 GPa. The superconductivity was observed to be suppressed on transformation to the CT phase in 122 materials.

High-pressure studies have been performed on heavy rare earth metals Terbium (Tb) to 155 GPa and Holmium (Ho) to 134 GPa in a diamond anvil cell at room temperature. The following crystal structure sequence was observed in both metals hcp ⟶ Sm-type ⟶ dhcp ⟶ distorted fcc (hR-24) ⟶ monoclinic (C2/m) with increasing pressure. The last transformation to a low symmetry monoclinic phase is accompanied by a volume collapse of 5 % for Tb at 51 GPa and a volume collapse of 3 % for Ho at 103 GPa. This volume collapse under high pressure is reminiscent of f-shell delocalization in light rare earth metal Cerium (Ce), Praseodymium (Pr), and heavy actinide metals Americium (Am) and Curium (Cm). The orthorhombic Pnma phase that has been reported in Am and Cm after f-shell delocalization is not observed in heavy rare earth metals under high pressures.

Electrospun composite scaffolds were prepared by mixing gelatin with nanoparticles of hydroxyapatite (nanoHA) in 2,2,2-trifluoroethanol (TFE) solution. The fibrous composite scaffolds with nanoHA content from 0 to 40 wt% were compared in terms of structure and morphology via x-ray diffraction (XRD) and scanning electron microscopy (SEM). Results show that dispersion of nanoHA in the scaffolds is uniform for 0%, 10%, 20%, and 30% nanoHA content, but significant nanoHA agglomeration can be observed for scaffolds with 40% nanoHA. In order to study the effect of nanoHA content on mechanical properties at the nanoscale level, the fibrous scaffolds were pressed into dense pellets and tested by nanoindentation to determine Young's modulus. Young's modulus was found to increase linearly with nanoHA content, reaching unexpectedly high values of 10.2 ± 0.8 GPa. Results are compared with other polymer/HA composites including those made with polycaprolactone or collagen.

The orientation distribution of crystalline grains in calcium phosphate coatings produced by pulsed laser deposition was investigated using an X-ray pole-figure diffractometer. Increased laser energy density of a KrF excimer laser in the 4–7 J/cm2 range leads to the formation of hydroxyapatite grains with the c-axis preferentially aligned perpendicularly to the substrates. This preferred orientation is most pronounced when the plume direction of incidence is normal to the substrate. This crystallographic texture of hydroxyapatite grains in the coatings is associated with the highly directional and energetic nature of the ablation plume. Anisotropic stresses, transport of hydroxyl groups, and dehydroxylation effects during deposition all seem to play important roles in texture development. Studies of cell adsorption using human Mesenchymal stem cells reveal that hydroxyapatite coatings with strong texture and random orientation show different cell adsorption behavior, which is consistent with the notion that protein attach differently on different faces of hydroxyapatite crystals. Cells seeded on textured coatings exhibit better spreading and adhesion compared to those placed on randomly oriented coatings.

New high-pressure x-ray diffraction data on uranium metal (99.9 %) in a diamond anvil cell is presented to 100 GPa (Volume compression V/Vo = 0.700) at room temperature using a variety of pressure markers like ruby, copper, and platinum. The diffraction patterns are carefully indexed allowing for reversal of peak positions based on anisotropic compression. We report anisotropic compression of the orthorhombic unit cell with the axial ratio b/a increasing initially to 40 GPa followed by a rapid decrease at higher pressure. On the other hand, axial ratio c/a shows a rapid increase with increasing pressure followed by saturation at megabar pressures. The most recent full potential electronic structure calculations reproduce the increasing tend of axial ratio c/a to 100 GPa but do not explain the variation in the b/a ratio. Our detailed analysis of all available experimental data also indicates that the observed anisotropic effects are intrinsic to Uranium and are independent of the pressure medium used in the high-pressure experiments.

A chemical vapor deposition hydrogen/methane/nitrogen feedgas mixture with unconventionally high methane (15% CH4 by volume) normally used to grow ultra-hard and smooth nanostructured diamond films on Ti-6Al-4V alloy substrates was modified to include diborane (10% B2H6 in hydrogen) for boron-doping. The flow rate for B2H6 was varied to investigate its effect on plasma chemistry, film structure, and mechanical properties. It was found that boron in the plasma can easily be incorporated into diamond films and change the lattice parameter and affect film structure as measured by Raman spectroscopy. Grazing angle x-ray diffraction shows a strong dependence of diamond lattice parameter with diborane flow rate and B2H6:CH4 flow rate ratio. Thermal stability of these films was evaluated by heating in an oxygen environment above 700 °C. Nanoindentation measurements show that the films have high hardness close to that of nanostructured diamond. High film hardness and toughness, combined with good thermal stability and low surface roughness indicate great potential as wear resistant coatings able to withstand high temperature oxidizing environments.

A functionally graded nanocrystalline metalloceramic coating on cobalt-chrome alloy was investigated using thin film x-ray diffraction (XRD), cross-sectional transmission electron microscopy (TEM), nanoindentation, and scratch adhesion testing. The gradual transition in bonding from metallic (Cr/CrTi) near the interface to predominantly covalent (CrTiN) near the surface provides a combination of high toughness and high surface hardness. XRD analysis of the (CrTiN) coating suggests a cubic sodium chloride type phase structure with lattice parameter a = 4.2169±0.0035 Å. The surface layer structure is described as a tertiary Ti-N-Cr disordered solid solution that is predominantly cubic TiN, but with some Cr atoms substituted for Ti. TEM shows a transition from equiaxed 20-40 nm-sized grains at the surface to larger, elongated columnar grains below the surface. Nanoindentation measurements of the coating result in a hardness of 27 GPa and Young's modulus of 320 GPa. In addition, the high plasticity of 55% observed for this coating represents an increase in toughness over other ceramic coatings having similar hardness. The unique, functionally graded, smooth nanocrystalline metalloceramic coating structure provides an opportunity to reduce wear and increase longevity of total hip joint replacements.

We deposited multilayer Nanocrystalline Diamond (NCD) thin films on Ti-6Al-4V substrates that were machined to imitate the shapes of the condyle and fossa of the temporomandibular joint (TMJ). We performed low stress wear assessment experiments on condyle/fossa pairs mounted in a custom-built mandibular movement simulator (MMS) for 5 x 105 loaded cycles at 1.2 Hz, which is equivalent to 4.4 years of clinical use. Analysis of wear surfaces on the control and the NCD-coated pairs indicated that no film delamination occurred on the NCD-coated condyle/fossa couple and that wear damage was extensive on the uncoated condyle/fossa pair. The high stress wear tests performed using the Ortho-POD machine at loads of 80 and 165 N showed that loss of film on the condyle specimens occurred after 3300 and 341 cycles, respectively. A subsequent evaluation of the influence of condyle curvature on wear by articulating a multilayer condyle/disk pair at a load of 50 N and 250 000 cycles at 1.2 Hz, showed that film delamination on the condyle occurred after 12500 cycles and no loss of film was observed on the disk after 250 000 cycles of articulation. Our results show that the observed lower film lifetimes on the condyles at high stresses are not related to intrinsic stresses in the film but probably due to lower film adhesion on the curved surfaces of the condyle.

Chemical Vapor Deposition (CVD) using hydrogen, methane, and nitrogen feed gases has proven to be useful in depositing well-adhered diamond films on metal substrates. These films have already found a market in the cutting tool industry as coatings on cobalt-cemented tungsten carbide (WC-Co) inserts. The purpose of this investigation is to examine how the thermal and chemical pre-treatments typically used for carbide inserts (to remove the cobalt binder near the surface) affect the structure and interfacial adhesion of the diamond coating. Removal of the cobalt binder phase in various pre-treatment methods has been shown to minimize its catalytic effect of graphite formation during diamond deposition by CVD. The diamond-coated inserts in our study were characterized using x-ray diffraction, Raman spectroscopy, atomic force microscopy, and Rockwell indentation testing. We use an unconventionally high methane concentration in the feedgas in order to saturate the growth surface with carbon, thereby limiting cobalt migration from the bulk to the surface and reducing the dissolution and diffusion of carbon atoms coming from the plasma. Nitrogen is used in the feedgas in order to provide a tough, single-layer nanocrystalline diamond film structure. In addition, a multi-layer (nano-/micro-/nano-crystalline) CVD diamond film was grown by controlling the flow of nitrogen in order to show its characteristics in comparison with the single layer nanocrystalline diamond film. The multilayer film on the thermally-treated insert shows enhanced interfacial adhesion and fracture toughness when compared to other pretreatments and diamond coatings. This was demonstrated by indentation tests using 1470 N load.

We have obtained nanostructured hydroxyapatite thin films on titanium alloy substrates by pulsed laser deposition. Deposition was carried out using a KrF excimer laser (248 nm) with the energy density of 4 – 7 J/cm2 at substrate temperatures in the 550°C - 650°C range. The crystallinity of the coatings was probed by X-ray diffraction. Phase transitions from hydroxyapatite to other calcium phosphate compounds were observed with varying the substrate temperature during the growth process. Scanning electron microscopy revealed thin films made up of partially sintered nanoscale grains. The average size of nanoscale grains increased significantly with film thickness, suggesting a growth mechanism involving the coalescence of nanoscale grains. As the laser energy density increases, the hydroxyapatite crystallites in the coatings are oriented preferentially along the c-axis perpendicular to the substrate. Mechanical properties of the highly c-axis oriented coatings such as hardness and Young's modulus were studied by using nanoindentation technique.

In this work, the open-air thermal stability of nanocrystalline diamond films grown on mirror-polished titanium alloy substrates by the Microwave Plasma Chemical Vapor Deposition (MPCVD) technique was studied. The results of this investigation show that nanocrystalline diamond films are highly stable in air up to 600°C with no significant change in mechanical properties. Samples annealed between 600°C and 650°C, however, exhibit values of hardness lower by as much as 40% compared to as-grown samples. Above 650°C serious delamination effects were observed in the coatings.

The sample size employed in high pressure diamond anvil cells is limited to a diameter of typically 25 to 150 microns. While this size is often sufficient for diagnostics using synchrotron x-ray diffraction and Raman scattering, ex-situ measurements of mechanical properties using conventional microhardness indentation techniques is not feasible. For some materials, the high pressure phase(s) can be quenched to ambient pressure allowing further characterization by other techniques. We make use of the very small probe volume allowed by nanoindentation to investigate the pressure-quenched structures of both C70 fullerene and zirconium. For the case of C70, we show that the amorphous phase established above 35 GPa can be quenched to ambient, and that it shows a largely elastic indentation loading behavior with a hardness of 30 GPa. We establish that this hard carbon phase contains a mixture of sp2- and sp3-bonded carbon and that it can be produced from C70 fullerene by application of pressure at room temperature. With regard to zirconium metal, we confirm the irreversible transformation from the ambient hexagonal-close-packed phase to the simple hexagonal Ω-phase (AlB2 structure) and document an 80% increase in hardness that may be attributed to the presence of covalent bonding based on sd2-hybridized orbitals forming graphite-like nets in the (0001) plane of the AlB2 structure.

The cobalt chrome alloy Co-28Cr-6Mo is widely used in human joint replacement applications. These joints are highly sensitive to wear and are usually replaced after approximately ten years of use. In order to extend these implants' service lifetimes, a thin film of diamond may be applied to the implant wear surfaces by microwave plasma chemical vapor deposition (MPCVD) following MPCVD nitridation. Diamond films often delaminate from cobalt chrome due to a high thermal expansion mismatch. Additionally, under most conditions diamond films degrade into graphite by dissolution of nuclei into solvents like Co and Cr. By nitriding the cobalt chrome through MPCVD prior to diamond deposition, a usable diamond film may be achieved. It may be possible to merge both the nitriding and deposition steps into a single process, since both nitridation and deposition will be performed by MPCVD. In addition, controlled amounts of nitrogen in hydrogen/methane plasma under CVD conditions result in a nanostructured diamond coating. We have investigated the formation of both micro- and nanocrystalline diamond formation on cobalt chrome.

Homoepitaxial diamond films were grown on polished single crystal {100} oriented natural type Ila diamond circular substrates using high density microwave plasma chemical vapor deposition (MPCVD). Twelve homoepitaxial diamond films were grown under a variety of substrate temperatures (1000 C-2000 C), methane concentration (1% - 3% in hydrogen gas) and processing pressure(60 - 150 torr). Electron paramagnetic resonance (EPR) studies demonstrate that nitrogen is largely incorporated as singly substitutional impurity (P1-center) and nitrogen's concentration is in the range of 10 -100 parts per million. Nitrogen's concentration also shows a systematic decrease with increasing substrate temperatures. The temperature variation of nitrogen at high temperatures is discussed within a model where single substitutional nitrogen aggregates to form nitrogen defects which are not EPR active.

Microwave plasma chemical vapor deposition (CVD) was used to grow nanocrystalline diamond films by adding nitrogen to a high density plasma defined by a high operating pressure (125 Torr) and high methane feedgas concentration (15% in a balance of hydrogen). Films grown at these conditions but without nitrogen exhibited well-faceted, high phase purity crystalline diamond while those grown with added nitrogen showed a nanocrystalline structure and were an order of magnitude smoother. The nitrogen-induced nanocrystalline films are believed to be comprised predominantly of diamond nanocrystallites in a matrix of tetrahedral amorphous carbon. The films were characterized by Raman spectroscopy, grazing-angle x-ray diffraction, surface profilometry, nano-indentation, electron microscopy, and pin-on-disc tribometry. In contrast to standard CVD conditions, the high density plasma results in adhered films on Ti-6AI-4V substrates even at substrate temperatures of 850°C. We present plasma optical emission spectroscopy results which are correlated with changes in the Raman spectra and the film microstructure. The hardness of the films (∼90 GPa), their low rms surface roughness (27 nm), and their good adhesion to the substrate makes these films potentially useful for tribological applications.

Gem quality diamond crystals are employed as anvils in high-pressure diamond cell research. Homoepitaxial growth experiments by microwave plasma-assisted chemical vapor deposition (MPCVD) have produced 1.76 mm (diameter) by 0.65 mm (thickness) sized diamonds. We report fundamental studies on diamond growth rate and quality as a function of reactor pressure and methane concentration, in a hydrogen plasma. By varying the growth conditions, large, single crystal diamond can be produced, which is ideal for manufacturing high pressure anvils.Traditional high pressure, high temperature (HPHT) techniques for production of synthetic diamond anvils are extremely expensive and chemical vapor deposition (CVD) provides an economically viable alternative. We report diamond growth rates up to 0.32 mg/hr, which are comparable to HPHT growth rates, and crystal quality approaching that of gem diamond. When perfected, diamond anvils produced from chemical vapor deposition methods could replace those manufactured by high pressure, high temperature synthesis.

Low temperature diamond deposition on metal substrates is motivated by the need to reduce thermal stress so that the film adhesion is satisfactory. Although the use of oxygen-con- taining gas mixtures have been shown to extend the temperature range for which diamond can grow as well as to improve film quality, most studies have focused on the use of silicon as sub- strates and have neglected technologically important metallic systems. To this end, microwave plasma chemical vapor deposition (MPCVD) was used to grow diamond films on Ti-6A1-4V alloy at low temperature (615 to 780 C) using CH4/O2/H2 and CO/H2 gas mixtures. In-situ pyrometric interferometry (ISPI) shows that as the oxygen concentration increases, the onset time for dia- mond nucleation and subsequent film surface roughness increases while the average growth rate decreases. Micro-Raman spectroscopy shows improved film quality and suggests a trend toward increasing in-plane compressive stress with increasing oxygen concentration. Glancing-angle x- ray diffraction (XRD) was complimentary to the Raman data and indicates the presence of a TiC interfacial layer thickness which decreases with increasing oxygen concentration. We found that the CO/H2 mixture resulted in poorly adhered “white soot” films with low diamond content whereas the CH4/O2/H2 mixture yielded well adhered high quality diamond films.

A high-pressure phase of gadolinium is completely described for the first time. This phase, HR24, is found to exist at 46 GPa. The structure is examined for evidence of delocalization of the f shell, and the evolution of the HR24 phase with increasing pressure is discussed.

A thick (130 im) homoepitaxial diamond film was grown on a polished, single crystal {100} oriented natural type Ila diamond circular plate using high density microwave plasma chemical vapor deposition (MPCVD). The as-grown film shows facets around its perimeter, approaching the form of a cubo-octahedral crystal. The plate dimensions increased from 1.50 mm diameter and 0.25 mm thickness to 1.64 mm diameter and 0.38 mm thickness, corresponding to a growth rate of nearly 11 μm per hour. The substrate temperature during growth was approximately 900 C. The film was characterized by optical microscopy, Raman spectroscopy, photoluminescence spectroscopy (PL), and electron paramagnetic resonance (EPR) before and after deposition. The surface morphology of the as-grown film shows large growth steps and a few scattered penetration twins. The diamond film is transparent except for localized regions containing the twin defects. Raman spectroscopy shows a strong diamond peak at 1332 cm−1 superimposed on a background fluorescence. A broad Raman band at 1550 cm−1 is present on the surface defects and is indicative of an amorphous network of sp2-bonded carbon. The luminescence of the film reveals the presence of a nitrogen-vacancy pair. The homoepitaxially-grown diamond layer also exhibits the P1 substitutional nitrogen impurity with a concentration of 8 parts per million (ppm) as determined by EPR. No nitrogen impurities were detected in the original substrate before deposition. EPR is also used to confirm the single crystal nature of the grown diamond.

Diamond-like carbon (DLC) films have a unique combination of physical and chemical properties such as high hardness, optical transparency, low coefficient of friction and chemical inertness. A pulsed laser (248 nm) has been used to ablate a pyrolytic graphite target to deposit DLC films on Si (100) and 7059 Corning glass substrates. The deposition was carried out in high vacuum (≤ 10−6 Torr) at different temperatures ranging from room temperature to 400°C. The films were characterized by x-ray diffraction, scanning electron microscope, and Raman spectroscopie techniques. The mechanical properties (hardness and Young's modulus) of these films were characterized by nanoindentation. We have found that the films deposited at room temperature and 100°C show the characteristic features of DLC films and have the better hardness and modulus properties compared to the films fabricated at higher temperatures, which transform into amorphous carbon. Correlations of pulsed laser deposition process parameters with the properties of deposited DLC films will be discussed in this paper.

We have carried out diamond deposition by microwave plasma-assisted chemical vapor deposition (MPCVD) on planar and nonplanar diamond substrates at temperatures between 850° and 2000° C. The nonplanar and planar substrates were the polished (100) surfaces of type la natural diamond anvils and isotopically pure (99.95% 12C) type IIa synthetic crystals, respectively. The extremely low level of lattice and optical defects in the isopure substrates relative to natural crystals makes them ideal for optical characterization and defect studies, as well as high performance optical and electronic applications [1]. The goals of this effort were to observe and compare the film morphology and defect incorporation as functions of the substrate’s (1) geometry, (2) type (defect density), and (3) temperature. The phase purity and defect structure of the films were analyzed by micro-Raman and low temperature photoluminescence (PL) spectroscopy. Optical and atomic force microscopy (AFM) were used to examine the surface morphology of the films. High temperature growth on the nonplanar anvil tip was anisotropic and extremely rapid (50-400 µm/ hr), with significant incorporation of optically active defects. A possible model for the observed rapid growth is discussed. The films grown at lower temperatures on planar isopure substrates showed a dense array of oriented, stepped, square growth hillocks with penetration twins at their tops, while those grown at higher temperatures exhibited reasonably smooth, oriented macrosteps. The higher temperature planar films showed a larger variety of incorporated optical centers than the lower temperature films.