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At least 199 records · Page 11Linked to original sources
PubMed2005

Self-assembly of patchy particles into diamond structures through molecular mimicry.

Fabrication of diamond structures by self-assembly is a fundamental challenge in making three-dimensional photonic crystals. We simulate a system of model hard particles with attractive patches and show that they can self-assemble into a diamond structure from an initially disordered state. We quantify the extent to which the formation of the diamond structure can be facilitated by "seeding" the system with small diamond crystallites or by introducing a rotation interaction to mimic a carbon-carbon antibonding interaction. Our results suggest patchy particles may serve as colloidal "atoms" and "molecules" for the bottom-up self-assembly of three-dimensional crystals.

Journal Article↗
PubMed1999

Diamond-like carbon coatings for orthopaedic applications: an evaluation of tribological performance.

A detailed investigation of the tribological behaviour of vacuum arc diamond-like carbon coated Ti-6Al-4V against a medical grade ultra-high molecular weight polyethylene is conducted in this work in order to investigate the potential use of diamond-like carbon coatings for orthopaedic appplications. Lubricated and non-lubricated wear experiments are performed using a standard pin-on-disc wear tester. The coefficient of friction is monitored continuously during testing and wear rate calculations are performed using surface profilometry measurements of worn disc surfaces. Sliding wear tests show the existence of two distinct friction and wear regimes distinguished by physically different mechanisms. In the first stages of wear, adhesion and abrasion are the dominant mechanisms of wear while fatigue processes are activated later in the tests. The effects of diamond-like carbon coating structure, surface roughness and lubrication on tribological behaviour are presented. Optimal process-structure-property design for vacuum arc plasma deposition is utilized in order to obtain strong adhesion to the titanium alloy substrate. Diamond-like carbon coatings significantly improve the friction and wear performance of the orthopaedic bearing pair and show exceptional promise for biomedical applications.

Journal Article↗
PubMed2001

Atomic-scale imaging of insulating diamond through resonant electron injection.

The electronic properties of insulators such as diamond are of interest not only for their passive dielectric capabilities for use in electronic devices, but also for their strong electron confinement on atomic scales. However, the inherent lack of electrical conductivity in insulators usually prevents the investigation of their surfaces by atomic-scale characterization techniques such as scanning tunnelling microscopy (STM). And although atomic force microscopy could in principle be used, imaging diamond surfaces has not yet been possible. Here, we demonstrate that STM can be used in an unconventional resonant electron injection mode to image insulating diamond surfaces and to probe their electronic properties at the atomic scale. Our results reveal striking electronic features in high-purity diamond single crystals, such as the existence of one-dimensional fully delocalized electronic states and a very long diffusion length for conduction-band electrons. We expect that our method can be applied to investigate the electronic properties of other insulating materials and so help in the design of atomic-scale electronic devices.

Journal Article↗
PubMed2003

Epitaxy of cubic boron nitride on (001)-oriented diamond.

Cubic boron nitride (c-BN), although offering a number of highly attractive properties comparable to diamond, like hardness, chemical inertness and a large electronic bandgap, up to now has not found the attention it deserves. This mostly has to do with preparational problems, with easy chemical routes not available and, instead, the necessity to apply ion-bombardment-assisted methods. Hence, most of the c-BN samples prepared as thin films have been nanocrystalline, making the prospect of using this material for high-temperature electronic applications an illusion. Although heteroepitaxial nucleation of c-BN on diamond substrates has been demonstrated using the high-pressure-high-temperature technique, none of the low-pressure methods ever succeeded in the epitaxial growth of c-BN on any substrate. Here, we demonstrate that heteroepitaxial c-BN films can be prepared at 900 degrees C on highly (001)-oriented diamond films, formed by chemical vapour deposition, using ion-beam-assisted deposition as a low-pressure technique. The orientation relationship was found to be c-BN(001)[100]||diamond(001)[100]. High-resolution transmission electron microscopy additionally proved that epitaxy can be achieved without an intermediate hexagonal BN layer that is commonly observed on various substrates.

Journal Article↗
PubMed2001

Diamond stents for palliation of malignant bile duct obstruction: a prospective multicenter evaluation.

BACKGROUND AND STUDY AIMS: Various types of self-expandable metal stents have been introduced for biliary drainage in patients with malignant jaundice, showing prolonged patency compared with plastic endoprostheses. However, there has only been prolonged experience with a meaningful number of patients using the Wallstent. We evaluated the Diamond stent, a self-expanding uncoated biliary metal stent, in a prospective uncontrolled multicenter setting. PATIENTS AND METHODS: The eligibility criterion was obstructive jaundice due to inoperable malignant disease. Between August 1995 and January 2000, 126 patients, who received a total of 134 Diamond stents in four European centers, were followed prospectively. RESULTS: Technical and clinical success rates were 96 % and 98 %, respectively. No major procedure-related complications occurred. The 30-day mortality rate was 13 %. Stent occlusion occurred in 28 patients (22 %). Overall median stent patency was 477 days; overall median survival was 173 days. Stent occlusion, confirmed by endoscopic retrograde cholangiopancreatography, was successfully treated with plastic stents in all patients. Cost analysis revealed estimated costs of 3440 euros per patient for palliative treatment with the Diamond stent. CONCLUSIONS: The Diamond stent compares favorably with other biliary metal stents for patients requiring biliary drainage of malignant jaundice.

Adult↗
PubMed2001

Laboratory evaluation of the phoenix CRx diamond valve.

OBJECTIVE: To assess the long-term hydrodynamic properties of a new cerebrospinal fluid flow-regulating hydrocephalus shunt called the CRx Diamond valve (Phoenix Biomedical Corp., Valley Forge, PA). METHODS: Three samples of a Diamond valve were tested in the United Kingdom Shunt Evaluation Laboratory during a 40-day period. Tests were performed for long-term pressure-flow performance, overdrainage, susceptibility to ambient temperature changes, external pressure, reflux, presence of small particles in the reagent, mechanical durability, and magnetic resonance imaging compatibility. RESULTS: Tests demonstrated that the Diamond valve stabilized flow within the range of 0.36 to 0.62 ml/min when pressure varied from 14 to 23 mm Hg. Hydrodynamic resistance demonstrated pressure-dependent variability from 20 to 78 mm Hg/(ml/min). The time drift of hydrodynamic parameters was significant (P < 0.001). The valve was insensitive to changes in temperature, external pressure, rapid fluctuations of differential pressure, small particles in fluid, and reflux. CONCLUSION: The Diamond valve demonstrated the intended variable resistance, which increased as the pressure increased. This property may help it limit overdrainage related to body posture as well as nocturnal vasogenic waves. Flow through the valve stabilizes within a wide range, which may contribute to the prevention of excessive pressure buildup after implantation. However, shunt placement should be avoided in patients who present with normal baseline intracranial pressure but an increased incidence of high vasogenic intracranial pressure waves.

Cerebrospinal Fluid Shunts↗
PubMed2005

Platelet function disorder in Gardner-Diamond syndrome: a case report and review of the literature.

The Gardner-Diamond syndrome is a disorder characterized by recurrent spontaneous painful bruising in patients with underlying psychosis and neurosis. Despite the presence of other symptoms suggestive of an underlying disorder of primary hemostasis in a large percentage of reported patients, results of testing for von Willebrand disease or platelet function disorders are lacking. The authors describe a case of Gardner-Diamond syndrome in an adolescent girl who had abnormal platelet responses during platelet aggregation studies. A review of the literature revealed only three additional patients with Gardner-Diamond syndrome who have had platelet aggregation studies reported. To date, all patients with Gardner-Diamond syndrome reported to have undergone platelet aggregation studies have had abnormal results.

Adenosine Diphosphate↗
PubMed2000

Laser-induced graphitization on a diamond (111) surface.

We report an atomistic simulation study of laser-induced graphitization on the diamond (111) surface. Our simulation results show that the diamond to graphite transition occurs along different pathways depending on the length of the laser pulse being used. Under nanosecond or longer laser pulses, graphitization propagates vertically into bulk layers, leading to the formation of diamond-graphite interfaces after the laser treatment. By contrast, with femtosecond (0.2-0.5 ps) laser pulses, graphitization of the surface occurs layer by layer, resulting in a clean diamond surface after the ablation. This atomistic picture provides an explanation of recent experimental observations.

Journal Article↗
PubMed2002

Novel pathway to the growth of diamond on cubic beta-SiC(001).

By carrying out first-principles calculations on diamond-forming processes, we predict a method for the heteroepitaxial growth of diamond on cubic beta-SiC(001). In the method, we used two processes: (i) the preformation of an sp(3)-like surface configuration of beta-SiC(001) by the adsorption of group-V surfactants; (ii) the successive growth of diamond by the segregation of the surfactants onto a surface and the desorption of surface hydrogen. Analyzing the segregation energies, we found that the atomic size effect plays a crucial role in the surfactant-mediated growth of diamond on beta-SiC(001).

Journal Article↗
PubMed2006

CVD diamond-based semi-transparent beam-position monitors for synchrotron beamlines: preliminary studies and device developments at CEA/Saclay.

Polycrystalline diamond synthesized using the chemical vapour deposition (CVD) technique can be used to fabricate new types of photodetectors for the characterization of X-ray light in synchrotron beamlines. Since diamond exhibits a low absorption to low-energy photons, such devices allow beam-position monitoring with very little beam attenuation at photon energies as low as 2 keV up to 15-20 keV. Here it is shown how diamond-based devices can simply be processed as ionization chambers for advanced semi-transparent position monitoring with high position resolution (<2 microm). Other configurations using the same principle can also enable in-line field profiling. It is also shown what can be expected from these devices in terms of performances, signal-to-noise ratios and reliability, together with their inherent limitations caused by the presence of defects in polycrystalline materials. In particular, diamond devices with extremely low carrier lifetimes, owing to quenched transport properties, could also be of particular interest for the characterization of the temporal structure of synchrotron light. Interest in these devices lies in the permanent insertion into beamlines and withstanding high levels of radiation for continuous beam monitoring.

Journal Article↗
PubMed1998

A uniformly cleaved epitaxically grown diamond crystal for synchrotron radiation.

A homoepitaxic single-crystal diamond (111) film grown by microwave-assisted chemical vapour deposition (CVD) and fractured along the [110] directions to form small triangles was investigated by X-ray double-crystal topography. The X-ray topographic image showed that all parts of the cleaved CVD diamond film sections uniformly reflected X-rays at the peak position of the rocking curve, which was measured in the Bragg case. Furthermore, no bending effect was observed and the CVD diamond film appeared to be more perfect than and showed higher integrated intensity than the natural diamond substrate.

Journal Article↗
PubMed2005

Growth of A1N piezoelectric film on diamond for high-frequency surface acoustic wave devices.

Diamond films are very desirable for application to SAW devices because of their high acoustic wave velocity, which allows the extending of the frequency limit of operation at a given interdigital transducer line-width resolution. Use of high-quality AIN as the piezoelectric layer in conjunction with diamond is also desirable because of its high SAW velocity--the highest among all piezoelectric materials--together with its excellent electrical, mechanical, and chemical properties. The problems arising in the growth of A1N films on diamond have prevented, until now, the use of this combination of materials. In this paper we present recent results on the growth of highly oriented, low-stressed A1N films on diamond. SAW propagation on A1N/diamond has been theoretically investigated together with electromechanical coupling for both the Rayleigh and the Sezawa modes. The theoretical calculations show that high SAW velocities are achievable with good coupling efficiencies. Under proper conditions very large piezoelectric couplings are predicted--k2 = 2.2 and 4% for the Rayleigh and the Sezawa wave, respectively--comparable to those observed in strongly piezoelectric single crystals such as LiNbO3, but with SAW velocities approximately two-fold higher. Experiments performed on A1N/diamond/Si SAW test devices have shown good agreement between experimental results and theoretical predictions and demonstrate the feasibility of SAW devices based on this technology.

Journal Article↗
PubMed2005

Effect of crystalline quality of diamond film to the propagation loss of surface acoustic wave devices.

Diamond films with various crystal qualities were grown by chemical vapor deposition on silicon wafers. Their crystallinity was characterized by Raman scattering and electron backscattering diffraction. By fabricating a device structure for surface acoustic wave (SAW) using these diamond films, the propagation loss was measured at 1.8 GHz and compared with the crystallinity. It was found that the propagation loss was lowered in relatively degraded films having small crystallites, a narrow distribution in the diamond crystallite size, and preferential grain orientation. This experiment clarifies diamond film characteristics required for high-frequency applications in SAW filters.

Journal Article↗
PubMed1979

Diamond-Blackfan syndrome: evidence for T-cell mediated suppression of erythroid development and a serum blocking factor associated with remission.

Diamond-Blackfan syndrome may be a disorder of cellular immunity. Lymphocytes from some patients are capable of suppressing erythropoiesis in cultures of normal bone marrow. We studied two adults with this disorder, both in complete unmaintained remission, using a technique for cloning peripheral blood erythroid precursors (BFU-E) in culture. The BFU-E may be early, erythropoietin sensitive, erythroid committed stem cell. Under culture conditions, which employ fetal calf serum, neither patients cells formed normal numbers of erythroid colonies. Controls yielded 15.3 +/- 5.2 BFU-E/2.5 X 10(5) mononuclear cells. Culture of patients cells using autologous serum, promoted more normal growth of BFU-E (21.4 +/- 6.9 and 7.3 +/- 2.3 BFU-E/2.5 X 10(5) cells). Patient mononuclear cells, cocultured normal cells, generally suppressed BFU-E generation. Cocultures of normals were not inhibitory. Removal of T-lymphocytes from patient mononuclear cells permitted normal growth of BFU-E in coculture with controls. T-cells depleted Diamond-Blackfan mononuclear cells showed BFU-E formation in fetal calf and autologous serum. Diamond-Blackfan T-cells inhibited BFU-E formation by normal mononuclear cells. The cellular defect in Diamond-Blackfan syndrome persists during complete remission and may be mediated by lymphocytes. The development of a serum factor which blocks the suppressive effects on erythroid precursors of a subpopulation of autologous T-cells may be responsible for the development of remission in our patients.

Adolescent↗
PubMed1987

Facial dermabrasion: advantages of the diamond fraise technique.

The first effective method of performing facial dermabrasion employed the use of a wire brush. The introduction of diamond fraises has, in the author's opinion, provided greater safety and more versatility than the wire brush. The diamond fraise is a more exacting instrument and with the recent introduction of the extra-coarse grit diamond fraise, the instrument is as abrasive as the standard wire brush. The diamond fraise is more easily controlled by the less experienced surgeon and because of its availability in many different shapes, widths, and grits, it provides greater versatility to the surgeon than the wire brush.

Dermabrasion↗
PubMed2001

Ultraviolet emission from a diamond pn junction.

We report the realization of an ultraviolet light-emitting diode with the use of a diamond pn junction. The pn junction was formed from a boron-doped p-type diamond layer and phosphorus-doped n-type diamond layer grown epitaxially on the 111 surface of single crystalline diamond. The pn junction exhibited good diode characteristics, and at forward bias of about 20 volts strong ultraviolet light emission at 235 nanometers was observed and was attributed to free exciton recombination.

Journal Article↗
PubMed2002

High carrier mobility in single-crystal plasma-deposited diamond.

Room-temperature drift mobilities of 4500 square centimeters per volt second for electrons and 3800 square centimeters per volt second for holes have been measured in high-purity single-crystal diamond grown using a chemical vapor deposition process. The low-field drift mobility values were determined by using the time-of-flight technique on thick, intrinsic, freestanding diamond plates and were verified by current-voltage measurements on p-i junction diodes. The improvement of the electronic properties of single-crystal diamond and the reproducibility of those properties are encouraging for research on, and development of, high-performance diamond electronics.

Journal Article↗
PubMed1998

A reduction-pyrolysis-catalysis synthesis of diamond

Diamond powder was synthesized through a metallic reduction-pyrolysis-catalysis route with the reaction of carbon tetrachloride and sodium at 700 degreesC, in which the sodium was used as reductant and flux. This temperature is much lower than that of traditional methods. The x-ray powder diffraction patterns showed three strong peaks of diamond. The Raman spectrum showed a sharp peak at 1332 inverse centimeters, which is characteristic of diamond. Although the yield was only 2 percent, this method is a simple means of forming diamond.

Journal Article↗