Toward Deep Blue Nano Hope Diamonds: Heavily Boron-Doped Diamond Nanoparticles

The production of boron-doped diamond nanoparticles enables the application of this material for a broad range of fields, such as electrochemistry, thermal management, and fundamental superconductivity research. Here we present the production of highly boron-doped diamond nanoparticles using boron-doped CVD diamond films as a starting material. In a multistep milling process followed by purification and surface oxidation we obtained diamond nanoparticles of 10–60 nm with a boron content of approximately 2.3 × 10²¹ cm^–3. Aberration-corrected HRTEM reveals the presence of defects within individual diamond grains, as well as a very thin nondiamond carbon layer at the particle surface. The boron K-edge electron energy-loss near-edge fine structure demonstrates that the B atoms are tetrahedrally embedded into the diamond lattice. The boron-doped diamond nanoparticles have been used to nucleate growth of a boron-doped diamond film by CVD that does not contain an insulating seeding layer

Expanding the Scope of Diamond Surface Chemistry: Stille and Sonogashira Cross-Coupling Reactions

Well-defined covalent surface functionalization of diamond is a crucial, yet nontrivial, matter because of diamond’s intrinsic chemical inertness and stability. Herein, we demonstrate a two-step functionalization approach for H-terminated boron-doped diamond thin films, which can lead to significant advances in the field of diamond hybrid photovoltaics. Primary diamond surface functionalization is performed via electrochemical diazonium grafting of <i>in situ</i> diazotized 4-iodoaniline. The freshly grafted iodophenyl functional moieties are then employed to couple a layer of thiophene molecules to the diamond surface via two well-established Pd-catalyzed cross-coupling reactions, i.e., Stille and Sonogashira. X-ray photoelectron spectroscopy analysis indicates a dense coverage and successful cross-coupling in both cases. However, we find that the Stille reaction is generally accompanied by severe surface contamination, in spite of process optimization and thorough rinsing. Sonogashira cross-coupling on the other hand provides a clean, high quality functionalization over a broad range of reaction conditions. The protocols employing Sonogashira reactions thus appear to be the method of choice toward future fabrication of high-performance dye-functionalized diamond electrodes for photovoltaic applications

Surface morphology of NCD samples without boron doping (A), with boron 133 ppm (B), 1000 ppm (C) and 6700 ppm (D).

<p>Field emission scanning electron microscope (e_Line, Raith). Scale bar is 200 nm.</p

Number of MG 63 cells on day 1, 3 and 7 (A, C, E), their spreading area (D) and their growth dynamics (B) on a standard polystyrene cell culture dish (PS), undoped NCD films (B_0) and NCD films doped with 133, 1000 and 6700 ppm of boron (B_133, B_1000 and B_6700, respectively).

<p>Mean ± S.E.M. from 3 experiments; each included 32 microphotographs (day 1 and 3) and 18 measurements in a hemocytometer (day 7) per experimental group). ANOVA, Student-Newman-Keuls method. Statistical significance: I, II, III, IV, V: <i>p</i>≤0.05 compared to the group labelled with the same Roman number.</p

Neutron depth profiling of boron over doped NCD samples.

<p>Neutron depth profiling of boron over doped NCD samples.</p

The cell population doubling time of MG 63 cells between days 1 and 3 (DT_1–3), days 3 and 7 (DT_3–7) and days 1 and 7 (DT_1–7) after seeding on polystyrene culture dishes (PS) and NCD films doped with 0, 133, 1000 or 6700 ppm of boron.

<p>Mean ± S.E.M. from 3 experiments (in total, 9 measurements for each experimental group and time interval). ANOVA, Student-Newman-Keuls Method. Statistical significance: <b>^{I, II, V}</b>: <i>p</i>≤0.05 compared to polystyrene, undoped NCD and NCD doped with 6700 ppm of B, respectively.</p

Immunofluorescence staining of talin in MG 63 cells on day 3 after seeding on microscopic glass coverslips (A), undoped NCD (B), NCD films doped with boron in concentrations of 133 ppm (C) 1000 ppm (D) and 6700 ppm (E).

<p>The cell nuclei are counterstained with propidium iodide. Olympus IX 51 epifluorescence microscope, DP 70 digital camera, obj. 100×, bar = 10 µm.</p

Dependence of the surface parameters of the NCD samples on the boron doping level.

<p>*Values adjusted to the surface potential of gold.</p><p>For the NDP measurements, the accuracy can achieve 5% (which is the precision of the boron atoms in the etalon). However, the precision of the NDP technique also depends on other parameters, e.g. the stability of the neutron beam intensity, identical geometry of the etalon and the measured sample, etc. Realistically, the NDP data can be routinely measured with accuracy of 10% in our case.</p><p>For roughness, potential, phase and contact angle, the data is presented as Mean ± S.D. (Standard Deviation). In the case of roughness and AFM phase, each <i>rms</i> value was determined from 65 536 data points on each sample type. The mean and S.D. of <i>rms</i> values were calculated from 5 such measurements across the sample. In the case of surface potential, the mean and S.D. values were calculated from 65 536 measurements across each sample. The contact angle was calculated from fitting the curve of the water droplet, and the mean and S.D. values were calculated from 16 measurements for each sample type.</p><p>Statistical Analysis: ANOVA, Student-Newman-Keuls Method. Statistical significance: ^{I, II, III, IV}: <i>p</i>≤0.05 compared to the group labelled with the same Roman number.</p><p>For the room temperature electrical resistivity measurements, the accuracy is better than 1%.</p

Microscopic images of surface potential variations as detected by Kelvin force microscopy (left column), and surface topography as detected by atomic force microscopy (right column) on NCD samples without boron doping (A) and with nominal boron doping of 133 ppm (B), 1000 ppm (C), and 6700 ppm (D).

<p>The AFM oscillation amplitude was 100 nm, the setpoint was 50%. The KFM lift height was 30 nm. The detection frequency was 75 kHz.</p

Concentration of β₁-integrin adhesion receptors, integrin-associated focal adhesion proteins talin and vinculin, markers of osteogenic cell differentiation osteocalcin, alkaline phosphatase, collagen I and osteopontin, and immunoglobuline adhesion molecule ICAM-1, a marker of cell immune activation, in MG 63 cells on day 7 after seeding on polystyrene culture dishes (PS) and NCD films doped with 0, 133, 1000 or 6700 ppm of boron.

<p>Measured by ELISA per mg of protein. The absorbances are given as a percentage of the control values obtained on PS. Mean ± S.E.M. from 3 experiments (each included 12–16 measurements for each experimental group). ANOVA, Student-Newman-Keuls Method. Statistical significance: ^{I, II, III, IV}: <i>p</i>≤0.05 compared to the group labelled with the same Roman number.</p