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PubMed2006

Cycloadditions on diamond (100) 2 x 1: observation of lowered electron affinity due to hydrocarbon adsorption.

The adsorption of allyl alcohol, acrylic acid, and allyl chloride, as well as unsaturated organic molecules such as acetylene and 1,3 butadiene, on reconstructed diamond (100) 2 x 1 have been investigated using high-resolution electron energy loss (HREELS) spectroscopy and synchrotron radiation spectroscopy. The cycloadditions of these organic molecules produce chemically adsorbed adlayers with varying degree of coverages on the clean diamond. The organic adsorbed surface has a lowered electron affinity and shows a secondary electron yield that varies between 12 and 40% of the yield obtained from a fully hydrogenated diamond surface. The diamond surface can be functionalized with hydroxyl, carboxylic, and chlorine functionalities by the adsorption of these allyl organics. The [2 + 2] adduct of acetylene on the diamond (100) 2 x 1 surface can be observed. 1,3-butadiene attains a higher coverage as well as forms a thermally more stable adlayer on the diamond surface compared to the other organic molecules, due to its ability to undergo [4 + 2] cycloaddition.

Acetylene↗
PubMed2004

Interfacial electrical properties of DNA-modified diamond thin films: intrinsic response and hybridization-induced field effects.

We have investigated the frequency-dependent interfacial electrical properties of nanocrystalline diamond films that were covalently linked to DNA oligonucleotides and how these properties are changed upon exposure to complementary and noncomplementary DNA oligonucleotides. Frequency-dependent electrical measurements at the open-circuit potential show significant changes in impedance at frequencies of >10(4) Hz when DNA-modified diamond films are exposed to complementary DNA, with only minimal changes when exposed to noncomplementary DNA molecules. Measurements as a function of potential show that at 10(5) Hz, the impedance is dominated by the space-charge region of the diamond film. DNA molecules hybridizing at the interface induce a field effect in the diamond space-charge layer, altering the impedance of the diamond film. By identifying a range of impedances where the impedance is dominated by the diamond space-charge layer, we show that it possible to directly observe DNA hybridization, in real time and without additional labels, via simple measurement of the interfacial impedance.

Crystallization↗
PubMed2004

Protein-modified nanocrystalline diamond thin films for biosensor applications.

Diamond exhibits several special properties, for example good biocompatibility and a large electrochemical potential window, that make it particularly suitable for biofunctionalization and biosensing. Here we show that proteins can be attached covalently to nanocrystalline diamond thin films. Moreover, we show that, although the biomolecules are immobilized at the surface, they are still fully functional and active. Hydrogen-terminated nanocrystalline diamond films were modified by using a photochemical process to generate a surface layer of amino groups, to which proteins were covalently attached. We used green fluorescent protein to reveal the successful coupling directly. After functionalization of nanocrystalline diamond electrodes with the enzyme catalase, a direct electron transfer between the enzyme's redox centre and the diamond electrode was detected. Moreover, the modified electrode was found to be sensitive to hydrogen peroxide. Because of its dual role as a substrate for biofunctionalization and as an electrode, nanocrystalline diamond is a very promising candidate for future biosensor applications.

Biosensing Techniques↗
PubMed2003

Electrochemical oxidation of underivatized-nucleic acids at highly boron-doped diamond electrodes.

Boron-doped diamond (BDD) electrodes have been examined for the electrochemical oxidation of underivatized-nucleic acids in terms of single stranded and double stranded DNA. Cyclic voltammetry and square wave voltammetry have been used to study the oxidation reactions and to detect DNA without derivatization or hydrolysis steps. At the diamond electrode, at least two well-defined voltammetric peaks were observed for both single stranded and double stranded DNA. Diamond electrode is the first material to show a well-defined voltammetric peaks for adenine group oxidation directly in the helix structure of nucleic acid due to its wide potential window. For single stranded DNA, a third peak, related to the pyrimidine group oxidation was also observed. As-deposited diamond film with predominantly hydrogen-terminated surface exhibited superior performance over oxygen-terminated diamond in terms of sensitivity. However, by optimizing the ionic strength, sensitivity of O-terminated films could be improved. Linear calibration results have shown linearity of current with concentration in the range 0.1-8 microg mL(-1) for both guanine and adenine residues at as-deposited BDD. Detection limits (S/N = 3) of 3.7 and 10 ng mL(-1) for adenine and guanine residue in single stranded DNA, respectively, and 5.2 and 10 ng mL(-1) for adenine and guanine residue in double stranded DNA, respectively, were observed. This work shows the promising use of diamond as an electrochemical detector for direct detection of nucleic acids. The results also show the possibility of using the oxidation peak current of adenine group that is more sensitive for the direct detection of nucleicacids.

Animals↗
PubMed2006

Neutron detection and dosimetry using polycrystalline CVD diamond detectors with high collection efficiency.

Polycrystalline chemical vapour deposited (CVD) diamond film is an interesting material for neutron detection and dosimetry. However, the use of CVD diamond detectors is still limited by the low-level signal pulse produced because of the high energy required to produce an electron-hole pair in diamond (13.2 eV) and by the reduced charge collection efficiency owing to several types of traps for electrons and holes in CVD films. A new type of CVD diamond detector with high gain (HG) contacts was produced as part of the collaboration between the ENEA Fusion Division and the Faculty of Engineering of Rome 'Tor Vergata' University. In this paper the performance of the HG CVD diamond detector is presented and possible applications of CVD diamond detectors to neutron dosimetry are also discussed.

Crystallization↗
PubMed1999

Comparison of sectioning rates among carbide and diamond burs using three casting alloys.

PURPOSE: This study compared the sectioning rates of commercially available high noble, noble, and base metal casting alloys using two new cross-cut tungsten carbides specifically manufactured for alloy sectioning and two medium grit diamond burs. MATERIALS AND METHODS: Rectangular bars cast from a base metal alloy (Ni-Cr-Mo-Be), a noble alloy (Pd-Cu-Au), and a high noble alloy (Au-Ag-Cu-Pd) were sectioned under controlled conditions. Two types of cross-cut tungsten carbide and two types of medium grit diamond burs were tested using a high-speed handpiece under a coolant flow rate of 20 mL/min and an applied load at the bur tip of 0.9 N (91.5 g). Three 4-mm cuts were made through the alloy specimens using six burs of each type. The time required for Cuts 1, 2, and 3 was recorded, and sectioning rates in millimeters per minute were calculated as a relative measure of cutting efficiency. For each alloy, the total time required for the three cuts was analyzed using one-way analysis of variance (one-way ANOVA) and Scheffé tests (alpha = 0.05) to determine differences in sectioning rate among bur types. RESULTS: In general, mean sectioning rate for Cut 1 through Cut 3 decreased with longer use of the bur. Regarding total sectioning times, the carbide burs sectioned the base metal alloy significantly faster (P < .001) than the diamond burs. However, diamond burs sectioned the high noble alloy significantly faster (P < .001) than the carbide burs. Diamond burs also sectioned the noble alloy more quickly than the carbide burs, but the difference was not statistically significant. CONCLUSIONS: The cross-cut tungsten carbide burs should be used to section the base metal alloy but the medium grit diamond burs should be used to section the high noble alloy.

Analysis of Variance↗
PubMedDate not supplied

Bucky-wires and the instability of diamond (111) surfaces in one-dimension.

Recent advances in the fabrication and characterization of semiconductor and metallic nanowires are meeting the high expectations of nanotechnolgists. Although diamond has remarkable electronic and chemical properties, development of diamond nanowires has been slow, while the development of carbon nanotube-based technologies continues at a furious pace. Recently, the theoretical and experimental observation of the transformation of nanodiamonds into carbon-onions (and vice versa) has led to a new intermediate phase of carbon, denoted "bucky diamond", with a diamond core encased in an carbon onion-like shell. These findings lead to the question of whether a similar transformation occurs in diamond nanowires. We used ab initio techniques to determine the relaxed structure of diamond nanowires with octahedral surface facets, with results exhibiting delamination of octahedral surfaces, and indicating the formation of "bucky-wires". The effects of surface hydrogenation upon this transition also is examined.

Anisotropy↗
PubMed1995

A newly-developed electrodeposited diamond scaler with high abrasive resistance.

A diamond scaler on which blade diamond particles were coated by electrodeposition was developed to improve the abrasive resistance of scaler blades. The electrodeposited coating was tested with diamond particles of four different sizes, designated D-4000 with 2 to 4 microns diameter of the particles; D-800 with 12 to 25 microns; D-600 with 20 to 30 microns; and D-400 with 30 to 40 microns. The abrasive resistance of the scalers was examined quantitatively using a recently-developed automatic scaling apparatus that simulated the scaling process of hand instrumentation, as well as SEM observation of the blades. A series of abrasion tests suggested that all the diamond scalers except D-4000 showed better abrasive resistance than the control (D-0), and that D-600 showed the highest abrasive resistance and cutting quality. The SEM observation also suggested that D-600 and D-400 might have higher abrasive resistance. Furthermore, the profilometric evaluation of the surface roughness of the scaled natural dentin after hand instrumentation indicated that the average surface roughness increased in the order of D-4000, D-800, D-600, and D-400, although no marked differences were observed among D-4000, D-800, D-600 and D-0, but not D-400. These results suggested that the electrodeposited diamond scaler with 20 to 30 microns diamond particles (D-600) might have marked abrasive resistance as well as cutting quality without remarkable damage to the tooth surface after conventional scaling procedure.

Adult↗
PubMed1993

Effect of adding diamond particles on the fracture toughness of apatite ceramics.

Composite ceramics dispersed through diamond particles with hydroxyapatite as a matrix were prepared by firing at 1250 degrees C under reduced pressure or normal atmosphere. The fracture toughness and physical properties of sintered composite ceramics were examined to determine methods of strengthening hydroxyapatite ceramics. The diamond crystal in composite ceramics was transformed to graphite by firing and the fracture toughness of hydroxyapatite ceramics increased with diamond addition. At 10 wt% diamond, the maximum value for fracture toughness was obtained, and the further addition of diamond particles over 10 wt% caused fracture toughness to decrease. Such increases in fracture toughness were considered the result of microcracking which occurred during the transformation from diamond to graphite.

Dental Porcelain↗
PubMed2000

Postadjustment polishing of CAD-CAM ceramic with luminescence diamond gel.

PURPOSES: (1) to investigate by SEM and profilometry the effectiveness of Luminescence diamond polishing gel on machinable ceramic after adjustment grinding with different grit diamond finishing burs, and (2) to define a simple, time-saving ceramic finishing and polishing technique for clinically satisfactory results. MATERIALS AND METHODS: Discs, 3 mm thick, were cut from Vita Mark II CAD-CAM ceramic and ground to a uniform surface finish on 600 grit wet SiC paper. Five specimens in each of the seven groups below were finished unidirectionally by a sweeping mode with the following Two Striper MFS diamond burs: 1. MF1 (45 microm); 2. MF2 (25 microm); 3. MF3 (10 microm); 4. MF1 + MF2; 5. MF1 + MF3; 6. MF2 + MF3; 7. MF1 + MF2 + MF3. Then, Luminescence diamond polishing gel was dispensed on a mandrel-mounted felt applicator and applied at 10,000 rpm for 60 s, and after dipping in water for another 60-s sequence. Surface roughness was determined for each step with a stylus-fitted surface analyzer. On each specimen five parallel tracings (evaluation length 4.0 mm and cut-off length 0.8 mm) were made 1 mm apart. Ra and Rz values were recorded as roughness parameters. Data was subjected to one-way ANOVA and Tukey's multiple comparison test at a significance level of alpha = 0.05. One additional sample for each grinding and polishing step in each of the seven groups was produced for SEM analysis. RESULTS: Diamond polishing after MF1 finishing reduced Ra and Rz significantly from 1.75 to 0.79, and from 10.0 to 4.09 microm, respectively, whereas the Ra and Rz reduction after MF3 finishing and diamond polishing were from 0.64 to 0.49 and from 4.31 to 1.81 microm. The polished surface roughness of specimens prefinished with MF2 or MF3 burs alone or as the final step after preceding grinding with coarser grits was not significantly different. The average Ra and Rz values were 0.42 microm and 1.73 microm. SEM photographs confirmed the uniformity of the surface finish in these groups. The second polishing sequence did not significantly improve the smoothness obtained with the first cycle.

Analysis of Variance↗
PubMed1989

[Experiments on abrasion and wear of dental diamond instruments].

In spite of identical ISO standards for shape, grain size, and largest head diameter of diamond abrasive instruments there are major differences in the machining performance among the various makes. These differences are largely due to variations in shape and diamond partical size. Diamond burs from different manufacturers of the same visual shape and particle size do not show any significant differences in performance. However, not only the abrasive performance but to a greater extent the design of the preparation margin determine the selection of a bur. It would be desirable that manufacturers be more specific about the particle size used and the shape of the bur, since the ISO standard does not include sufficiently accurate data about diamond particle size and shape design. The life of a diamond instrument is limited by the wear of its tip. Here the diamond layer wears off faster than on the rest of the instrument. This calls for early replacement of the instrument in clinical use even if the shaft still might be functionable.

Carbon↗
PubMed1995

[The preparation of ceramic restorations with superfine diamond instruments].

Four groups of computer machined (Cerec 64 microns) Vita Mk II porcelain samples with six blocks (12 x 7 x 1.5 mm) each were finished, using super-fine diamond burs (15, 8, 4 microns) and Proxoshape files (15, 8, 4 microns) and additionally polished with standard round and experimental angular cut discs. Surface roughness was measured after each treatment. For control, porcelain surfaces were high-gloss polished with a laboratory polishing machine (LPM). The roughness values R15/8/4 achieved with 15/8/4 microns diamond burs, were significantly different between the diamond grain sizes used: R15 = 1.49 +/- 0.44 > R8 = 0.86 +/- 0.25 (p < 0.05); R8 = 0.86 +/- 0.25 > R4 = 0.56 +/- 0.10 (p < or = 0.055); R4 = 0.56 +/- 0.10 > RLPM = 0.05 +/- 0.01 (p < 0.001). The diamond coated Proxoshape files caused the following roughness values RP15 = 0.53 U +/- 0.17 > RP8 = 0.24 +/- 0.06 (p < 0.01) and the Proxoshape file with 4 microns diamond coating did not achieve lower roughness values. The 8 microns diamond coating of burs and Proxoshape files caused a very fine "pre-polish" surface quality on porcelain. Angular discs had the same polishing ability as standard round discs but were more effectively used in fissures.

Computer-Aided Design↗
PubMed1997

Autosomal dominantly inherited Diamond-Blackfan anemia resulting in nonimmune hydrops.

BACKGROUND: Autosomal dominant inheritance of Diamond-Blackfan syndrome has been considered an uncommon occurrence. The onset of anemia is characteristically within the first year of life, with 10% of cases presenting at birth. Hydrops fetalis has been reported rarely. CASES: Two women with Diamond-Blackfan anemia had uncomplicated pregnancies without important exacerbation of their anemia. Each delivered an edematous infant affected with Diamond-Blackfan anemia, both of whom required immediate transfusions. One infant is currently 7 years old with transfusion-dependent Diamond-Blackfan anemia. The second infant died 2 days after birth; autopsy showed severe erythroid hypoplasia with absence of extramedullary hematopoiesis and placental villous edema. CONCLUSION: Diamond-Blackfan anemia may result in severe fetal anemia requiring transfusion. Among women with this disorder, a greater percentage than previously suspected are at risk for having an infant with substantial anemia in both the fetal and perinatal periods. Because the penetrance of the disorder is variable, pregnant women with a history of Diamond-Blackfan anemia should be considered at risk.

Adult↗
PubMed2000

Standard electrochemical behavior of high-quality, boron-doped polycrystalline diamond thin-film electrodes

Standard electrochemical data for high-quality, boron-doped diamond thin-film electrodes are presented. Films from two different sources were compared (NRL and USU) and both were highly conductive, hydrogen-terminated, and polycrystalline. The films are acid washed and hydrogen plasma treated prior to use to remove nondiamond carbon impurity phases and to hydrogen terminate the surface. The boron-doping level of the NRL film was estimated to be in the mid 1019 B/cm3 range, and the boron-doping level of the USU films was approximately 5 x 10(20) B/cm(-3) based on boron nuclear reaction analysis. The electrochemical response was evaluated using Fe-(CN)6(3-/4-), Ru(NH3)6(3+/2+), IrCl6(2-/3-), methyl viologen, dopamine, ascorbic acid, Fe(3+/2+), and chlorpromazine. Comparisons are made between the apparent heterogeneous electron-transfer rate constants, k0(app), observed at these high-quality diamond films and the rate constants reported in the literature for freshly activated glassy carbon. Ru(NH3)6(3+/2+), IrCl6(2-/3-), methyl viologen, and chlorpromazine all involve electron transfer that is insensitive to the diamond surface microstructure and chemistry with k0(app) in the 10(-2)-10(-1) cm/s range. The rate constants are mainly influenced by the electronic properites of the films. Fe(CN)6(3-/4-) undergoes electron transfer that is extremely sensitive to the surface chemistry with k0(app) in the range of 10(-2)-10(-1) cm/s at the hydrogen-terminated surface. An oxygen surface termination severely inhibits the rate of electron transfer. Fe(3+/2+) undergoes slow electron transfer at the hydrogen-terminated surface with k0(app) near 10(-5) cm/s. The rate of electron transfer at sp2 carbon electrodes is known to be mediated by surface carbonyl functionalities; however, this inner-sphere, catalytic pathway is absent on diamond due to the hydrogen termination. Dopamine, like other catechol and catecholamines, undergoes sluggish electron transfer with k0(app) between 10(-4) and 10(-5) cm/s. Converting the surface to an oxygen termination has little effect on k0(app). The slow kinetics may be related to weak adsorption of these analytes on the diamond surface. Ascorbic acid oxidation is very sensitive to the surface termination with the most negative Ep(ox) observed at the hydrogen-terminated surface. An oxygen surface termination shifts Ep(ox) positive by some 250 mV or more. An interfacial energy diagram is proposed to explain the electron transfer whereby the midgap density of states results primarily from the boron doping level and the lattice hydrogen. The films were additionally characterized by scanning electron microscopy and micro-Raman imaging spectroscopy. The cyclic voltammetric and kinetic data presented can serve as a benchmark for research groups evaluating the electrochemical properties of semimetallic (i.e., conductive), hydrogen-terminated, polycrystalline diamond.

Journal Article↗
PubMed2003

Application of diamond microelectrodes for end-column electrochemical detection in capillary electrophoresis.

Highly boron-doped diamond microelectrodes were employed in an end-column electrochemical detector for capillary electrophoresis (CE). The diamond microline electrodes were fabricated from conducting diamond thin films (exposed surface area, 300 x 50 microm), and their analytical performance as CE detectors was evaluated in a laboratory-made CE installation. The CE-ED system exhibited high separation efficiency for the detection of several catecholamines, including dopamine (DA), norepinephrine (NE), and epinephrine (E), with excellent analytical performance, for example, 155,000 theoretical plates for DA. The diamond-based electrochemical detection system also displayed low detection limits (approximately 20 nM for E at S/N = 3) and a highly reproducible current response with 10 repetitive injections of mixed analytes containing DA, NE, and E (each 50 microM), with relative standard deviations (RSD) of approximately 5%. The performance of the diamond detector in CE was also evaluated in the detection of chlorinated phenols (CP). When compared to the carbon fiber microelectrode, the diamond electrode exhibited lower detection limits in an end-column CE detection resulting from very low noise levels and highly reproducible analyses without electrode polishing due to analyte fouling, which makes it possible to perform easier and more stable CE analysis.

Journal Article↗
PubMed2003

Diamond formation by reduction of carbon dioxide at low temperatures.

This Communication reports a low-temperature diamond synthesis technique, in which diamonds (10-250 mum) can form at a temperature as low as 440 degrees C by reduction of dense CO2 with metallic Na. The X-ray diffraction pattern of a powder sample shows three reflection peaks, indexed with 111, 220, and 311, corresponding unambiguously to cubic diamond. The Raman spectrum of the product exhibits an intense first-order peak at 1332 cm-1, which is the characteristic signature of the cubic diamond, indicating the formation of well-crystallized diamond. Carbon dioxide is a nontoxic low-energy molecule, abundant on earth. This novel reduction method could allow studies of large-size diamond growth using CO2 as the carbon source.

Journal Article↗
PubMed2005

Interfacial study of cubic boron nitride films deposited on diamond.

We have studied the nucleation and growth of cubic boron nitride (cBN) films deposited on silicon and diamond-coated silicon substrates using fluorine-assisted chemical vapor deposition (CVD). These comparative studies substantiate that the incubation amorphous/turbostratic BN layers, essential for the cBN nucleation on silicon, are not vital precursors for cBN nucleation on diamond, and they are inherently eliminated. At vastly reduced critical bias voltage, down to -10 V, cBN growth is still maintained on diamond surfaces, and cBN and underlying diamond crystallites exhibit an epitaxial relationship. However, the epitaxial growth is associated with stress in the cBN-diamond interfacial region. In addition, some twinning of crystallites and small-angle grain boundaries are observed between the cBN and diamond crystallites because of the slight lattice mismatch of 1.36%. The small-angle grain boundaries could be eliminated by imposing a little higher bias voltage during the initial growth stage. The heteroepitaxial growth of cBN films on different substrate materials are discussed in the view of lattice matching, surface-energy compatibility, and stability of the substrate against ion irradiation.

Journal Article↗
PubMed2006

Electrical bias dependent photochemical functionalization of diamond surfaces.

Diamond is an excellent substrate for many sensing and electronic applications because of its outstanding stability in biological and aqueous environments. When the diamond surface is H-terminated, it can be covalently modified with organic alkenes using wet photochemical methods that are surface-mediated and initiated by the ejection of electrons from the diamond. To develop a better understanding of the photochemical reaction mechanism, we examine the effect of applying an electrical bias to the diamond samples during the photochemical reaction. Applying a 1 V potential between two diamond electrodes significantly increases the rate of functionalization of the negative electrode. Cyclic voltammetry and electrochemical impedance measurements show that the 1 V potential induces strong downward band-bending within the diamond film of the negative electrode. At higher voltages a Faradaic current is observed, with no further acceleration of the functionalization rate. We attribute the bias-dependent changes in rate to a field effect, in which the applied potential induces a strong downward band-bending on the negative electrode and facilitates the ejection of electrons into the adjacent fluid of reactant organic alkenes. We also demonstrate the ability to directly photopattern the surface with reactant molecules on length scales of <25 microm, the smallest we have measured, using simple photomasking techniques.

Journal Article↗