Effect of Boron Doping on the Wear Behavior of the Growth and Nucleation Surfaces of Micro- and Nanocrystalline Diamond Films

Optimizing Ni-Cr patterned boron-doped diamond band electrodes: Doping effects on electrochemical efficiency and posaconazole sensing performance

There is growing interest in developing diamond electrodes with defined geometries such as, for example, micrometer-sized electrode arrays to acquire signals for electroanalysis. For electroanalytical sensing applications, it is essential to achieve precise conductive patterns on the insulating surface. This work provides a novel approach to boron-doped diamond patterning using nichrome masking for selective seeding on an oxidized silicon substrate. The optimized process involves nichrome deposition, sonication, chemical etching, seeding, and tailored chemical vapor deposition of boron-doped diamond with an intrinsic layer to suppress boron diffusion. Through a systematic investigation, it was determined that isolated boron-doped diamond band electrodes can be efficiently produced on non-conductive silica. Additionally, the influence of boron doping on electrochemical performance was studied, with higher doping enhancing the electrochemical response of band electrodes. To demonstrate sensing capabilities, boron-doped diamond bands were used to detect posaconazole, an antifungal drug, exploiting its electroactive behaviour. A linear correlation between posaconazole concentration and oxidation peak current was observed over 1.43 × 10-8 - 5.71 × 10-6 M with a 1.4 × 10-8 M detection limit. The developed boron-doped diamond microbands could significantly impact the field of electroanalysis, facilitating detection of diverse biologically relevant molecules. Overall, this diamond patterning approach overcomes major challenges towards all-diamond electrochemical sensor chips.

Application of Nano-Crystalline Diamond in Tribology

Nano-crystalline diamond has been extensively researched and applied in the fields of tribology, optics, quantum information and biomedicine. In virtue of its hardness, the highest in natural materials, diamond outperforms the other materials in terms of wear resistance. Compared to traditional single-crystalline and poly-crystalline diamonds, nano-crystalline diamond consists of disordered grains and thus possesses good toughness and self-sharpening. These merits render nano-crystalline diamonds to have great potential in tribology. Moreover, the re-nucleation of nano-crystalline diamond during preparation is beneficial to decreasing surface roughness due to its ultrafine grain size. Nano-crystalline diamond coatings can have a friction coefficient as low as single-crystal diamonds. This article briefly introduces the approaches to preparing nano-crystalline diamond materials and summarizes their applications in the field of tribology. Firstly, nano-crystalline diamond powders can be used as additives in both oil- and water-based lubricants to significantly enhance their anti-wear property. Nano-crystalline diamond coatings can also act as self-lubricating films when they are deposited on different substrates, exhibiting excellent performance in friction reduction and wear resistance. In addition, the research works related to the tribological applications of nano-crystalline diamond composites have also been reviewed in this paper.

Thickness Effects on Boron Doping and Electrochemical Properties of Boron-Doped Diamond Film

As a significant parameter in tuning the structure and performance of the boron-doped diamond (BDD), the thickness was focused on the mediation of the boron doping level and electrochemical properties. BDD films with different thicknesses were deposited on silicon wafers by the hot filament chemical vapor deposition (HFCVD) method. The surface morphology and composition of the BDD films were characterized by SEM and Raman, respectively. It was found that an increase in the BDD film thickness resulted in larger grain size, a reduced grain boundary, and a higher boron doping level. The electrochemical performance of the electrode equipped with the BDD film was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in potassium ferricyanide. The results revealed that the thicker films exhibited a smaller peak potential difference, a lower charge transfer resistance, and a higher electron transfer rate. It was believed that the BDD film thickness-driven improvements of boron doping and electrochemical properties were mainly due to the columnar growth mode of CVD polycrystalline diamond film, which led to larger grain size and a lower grain boundary density with increasing film thickness.

Templated Synthesis of Diamond Nanopillar Arrays Using Porous Anodic Aluminium Oxide (AAO) Membranes

Diamond nanostructures are mostly produced from bulk diamond (single- or polycrystalline) by using time-consuming and/or costly subtractive manufacturing methods. In this study, we report the bottom-up synthesis of ordered diamond nanopillar arrays by using porous anodic aluminium oxide (AAO). Commercial ultrathin AAO membranes were adopted as the growth template in a straightforward, three-step fabrication process involving chemical vapor deposition (CVD) and the transfer and removal of the alumina foils. Two types of AAO membranes with distinct nominal pore size were employed and transferred onto the nucleation side of CVD diamond sheets. Subsequently, diamond nanopillars were grown directly on these sheets. After removal of the AAO template by chemical etching, ordered arrays of submicron and nanoscale diamond pillars with ~325 nm and ~85 nm diameters were successfully released.

DFT calculations of energetic stability and geometry of O-terminated B- and N-doped diamond (1 1 1)-1 × 1 surfaces

The non- and O-terminated diamond (1 1 1)-1  ×  1 surfaces, with the substitutional B (or N) dopants in different atomic layers, have been modelled in the present study. The influences of the O adsorbates, dopant and dopant position on the adsorption energy, have been studied by performing the density functional theory (DFT) calculations. Various parameters were additionally calculated in order to analyze the obtained results: bond lengths, total electron densities, bond populations, atomic charges, Fukui functions (FFs) and density-of-states. Dangling bonds on non-terminated surfaces, O adsorbates, as well as dopants within various atomic layers were all found to induce local effects. In fact, the degree of influences of the dopant on the adsorption energy of the O adsorbates, as well as on parameters like the near-surface bond lengths, total electron density, bond populations and atomic charges, were all found to be dependent on the dopant position. More generally, the deeper the dopant position, the less influence it had on the surface structures and properties. The influences by the dopant in the 1st or 2nd C atomic layer were observed to be significant, but those in the 3rd to 5th C layers were almost negligible. It was also found that the B dopant would decrease the adsorption energy of the adjacent O adsorbates, while the N dopant in the 2nd layer would increase it. Furthermore, the combination of the O adsorbates, together with the dopants within the 1st or 2nd C layer, could induce significant elongation of the bonds between neighboring atoms within the 1st and 2nd layers (i.e. C-C, C-B or C-N bonds). Moreover, all the terminating O atoms could react strongly with either the electrophilic or the nucleophilic species.

Inkjet-Printed High-Q Nanocrystalline Diamond Resonators

Diamond is a highly desirable material for state-of-the-art micro-electromechanical (MEMS) devices, radio-frequency filters and mass sensors, due to its extreme properties and robustness. However, the fabrication/integration of diamond structures into Si-based components remain costly and complex. In this work, a lithography-free, low-cost method is introduced to fabricate diamond-based micro-resonators: a modified home/office desktop inkjet printer is used to locally deposit nanodiamond ink as ∅50-60 µm spots, which are grown into ≈1 µm thick nanocrystalline diamond film disks by chemical vapor deposition, and suspended by reactive ion etching. The frequency response of the fabricated structures is analyzed by laser interferometry, showing resonance frequencies in the range of ≈9-30 MHz, with Q-factors exceeding 10⁴ , and (f₀ × Q) figure of merit up to ≈2.5 × 10¹¹ Hz in vacuum. Analysis in controlled atmospheres shows a clear dependence of the Q-factors on gas pressure up until 1 atm, with Q ∝ 1/P. When applied as mass sensors, the inkjet-printed diamond resonators yield mass responsivities up to 981 Hz fg^-1 after Au deposition, and ultrahigh mass resolution up to 278 ± 48 zg, thus outperforming many similar devices produced by traditional top-down, lithography-based techniques. In summary, this work demonstrates the fabrication of functional high-performance diamond-based micro-sensors by direct inkjet printing.

Laser-Induced Periodic Surface Structures (LIPSS) on Heavily Boron-Doped Diamond for Electrode Applications

Diamond is known as a promising electrode material in the fields of cell stimulation, energy storage (e.g., supercapacitors), (bio)sensing, catalysis, etc. However, engineering its surface and electrochemical properties often requires costly and complex procedures with addition of foreign material (e.g., carbon nanotube or polymer) scaffolds or cleanroom processing. In this work, we demonstrate a novel approach using laser-induced periodic surface structuring (LIPSS) as a scalable, versatile, and cost-effective technique to nanostructure the surface and tune the electrochemical properties of boron-doped diamond (BDD). We study the effect of LIPSS on heavily doped BDD and investigate its application as electrodes for cell stimulation and energy storage. We show that quasi-periodic ripple structures formed on diamond electrodes laser-textured with a laser accumulated fluence of 0.325 kJ/cm² (800 nm wavelength) displayed a much higher double-layer capacitance of 660 μF/cm² than the as-grown BDD (20 μF/cm²) and that an increased charge-storage capacity of 1.6 mC/cm² (>6-fold increase after laser texturing) and a low impedance of 2.74 Ω cm² turn out to be appreciable properties for cell stimulation. Additional morphological and structural characterization revealed that ripple formation on heavily boron-doped diamond (2.8 atom % [B]) occurs at much lower accumulated fluences than the 2 kJ/cm² typically reported for lower doping levels and that the process involves stronger graphitization of the BDD surface. Finally, we show that the exposed interface between sp² and sp³ carbon layers (i.e. the laser-ablated diamond surface) revealed faster kinetics than the untreated BDD in both ferrocyanide and RuHex mediators, which can be used for electrochemical (bio)sensing. Overall, our work demonstrates that LIPSS is a powerful single-step tool for the fabrication of surface-engineered diamond electrodes with tunable material, electrochemical, and charge-storage properties.

Mesoscopic physical removal of material using sliding nano-diamond contacts

Wear mechanisms including fracture and plastic deformation at the nanoscale are central to understand sliding contacts. Recently, the combination of tip-induced material erosion with the sensing capability of secondary imaging modes of AFM, has enabled a slice-and-view tomographic technique named AFM tomography or Scalpel SPM. However, the elusive laws governing nanoscale wear and the large quantity of atoms involved in the tip-sample contact, require a dedicated mesoscale description to understand and model the tip-induced material removal. Here, we study nanosized sliding contacts made of diamond in the regime whereby thousands of nm³ are removed. We explore the fundamentals of high-pressure tip-induced material removal for various materials. Changes in the load force are systematically combined with AFM and SEM to increase the understanding and the process controllability. The nonlinear variation of the removal rate with the load force is interpreted as a combination of two contact regimes each dominating in a particular force range. By using the gradual transition between the two regimes, (1) the experimental rate of material eroded on each tip passage is modeled, (2) a controllable removal rate below 5 nm/scan for all the materials is demonstrated, thus opening to future development of 3D tomographic AFM.