Mechanical and electronic properties of ultrathin nanodiamonds under uniaxial compressions

Mechanical and electronic properties of ultrathin hydrogenated nanodiamonds (with diameters from 0.71 nm to 1.4 nm) under uniaxial compression have been investigated by means of density functional theory calculations. The computed Young's moduli of nanodiamonds are lower than the bulk value and increase with size, which can be fitted to an empirical function of diameter. Similar to the bulk diamond, the HOMO–LUMO gaps of nanodiamond reduces under uniaxial strain, implying tunable electronic properties via mechanical deformations.     

Surface planarization of zirconia ceramic achieved by polyacrylamide grafted nanodiamond composite abrasives through chemical mechanical polishing

Zirconia ceramics are the promising materials for cell phone backplanes in the 5G era, and smoother surfaces and higher removal efficiency are sought after for their precision machining. Although nanodiamond abrasives have high polishing rates, it is easy to bring mechanical scratches and pits on the ceramic surface because of their high hardness, resulting in degradation of the surface quality of the finished workpiece. Therefore, polyacrylamide grafted nanodiamond particles were prepared by solution polymerization method for polishing ceramic wafers. As confirmed by Fourier transform infrared spectroscopy (FTIR), the polyacrylamide has been grafted on the nanodiamond surface. According to the scanning electron microscopy (SEM) and particle size distribution, the composite abrasives have better dispersion than pure nanodiamond abrasives. The results of chemical mechanical polishing (CMP) experiments showed that the composite abrasives could reduce the average surface roughness (Sa, arithmetic mean height) of zirconia ceramic from 28.31 nm to 2.68 nm (scanning area is 500 μm × 500 μm), and the polishing rate remained high compared to pure nanodiamond abrasives, showing superior CMP performance. X-ray photoelectron spectroscopy (XPS) demonstrated that solid-phase chemical reactions occurred during the polishing process to form ZrSiO₄. Meanwhile, contact-wear model combined with contact angle testing indicates that the introduction of polyacrylamide increases the contact area of the nanodiamond on the zirconia wafer surface, thereby significantly enhanced the mechanical effect.     

Micro-Raman,SEM, XPS,and electron field emission characterizations of nitrogen-induced shallow defects on nanodiamond films fabricated with different growth parameters

Nitrogen-induced shallow defects on nanodiamond films have been systematically characterized as a function of growth parameters using micro-Raman, SEM, XPS, and field emission measurements. Distinct peaks indicating diamond and graphite phases were observed in the micro-Raman spectroscopy. The increased in peak intensity and peak shifts due to growth parameters including pressure, power, and nitrogen flow-rate were observed and explained. The electronic behavior is further supplemented with SEM and XPS studies. Finally, electron field emission measurement is used to verify the deduced findings. The result of this study indicates that depending on the growth conditions nitrogen can act as a shallow donor in nanodiamond due to the formation of shallow defects with effective work functions ranging between 0.023 eV and 0.045 eV, as deduced from field emission characteristics. The correlation of film morphologies, spectroscopic analysis and field emission measurements to the growth conditions provide a better understanding of the nitrogen-induced shallow defects on the electronic properties of nanodiamond films.     

The RF plasma surface chemical modification of nanodiamond films grown on glass and silicon at low temperature

Glass slides (standard 1 × 3 in. size) coated with nanocrystalline diamond were successfully tested for DNA immobilization. The nanodiamond films were grown on glass substrates at temperature below 400 °C, while keeping the excellent material properties of diamond, such as low background luminescence and high optical transparency. The nanodiamond surface to which proteins were attached was functionalized by ultra-thin amino-polymer film in the radio-frequency (RF) plasma discharge of vaporized organosilane coupling agent N-(6-aminohexyl) aminopropyl trimethoxysilane (AHAPS). Several different IR spectroscopy methods (transmission and reflection–absorption spectroscopy (IRRAS), attenuated total reflectance (ATR) and grazing angle reflectance (GAR)) are discussed with respect of their ability of detecting the functional groups on bio-functionalized diamond surface. The IR absorbance spectra of just a few nm thick RF plasma polymer films deposited on nanodiamond surface are presented.     

Genotoxic and mutagenic activity of diamond nanoparticles in human peripheral lymphocytes in vitro

Carbon nanomaterials have the numerous applications in biomedical sciences and nanotechnology-based industries. Nanodiamonds due to their unique physico-chemical properties compared to other carbon nanomaterials are suggested to be better drug carriers or implant coating. Nevertheless, little is known about their short- and long-term toxicological effects on humans, other biological systems and surrounding environment. In the present study, we evaluated genotoxic and mutagenic potential of nanodiamond (particle size <10 nm) in human lymphocytes in vitro. Starting from concentration of 50 μg/ml, diamond nanopowder was cytotoxic, inhibited cell proliferation and induced apoptotic cell death. Nanodiamond-associated oxidative stress was revealed, the effect was dose-dependent and statistically significant. Nanodiamond-mediated DNA oxidative damage (8-oxoG level) and changes in chromatin stability was observed even at as low as 1 μg/ml concentration, which was especially seen for DNA single strand breaks estimated with alkaline comet assay. In contrast, no induction of DNA double strand breaks (neutral comet assay) was documented after nanodiamond treatment. Nanodiamond at concentration of 10 μg/ml was able to stimulate micronuclei production. Centromeric signals found in nanodiamond-induced micronuclei may be due to aneugenic activity of diamond nanopowder. Taken together, we showed that nanodiamond-mediated oxidative stress may contribute to DNA damage limiting nanodiamond biocompatibility.     

Controlled synthesis,efficient purification,and electrochemical characterization of arc-discharge carbon nano-onions

Arc-produced carbon nano-onions (A-CNOs), with a hollow core surrounded by multilayered sp² carbon shells, possess unique structural and electronic properties. While nanodiamond derived CNOs (5–7 nm) are attracting significant attentions, for A-CNOs (20–50 nm) controlling the growth and separating them from carbon impurities are the major challenges that impede further study and application of these materials. We have addressed these issues; first by designing an in-house automated underwater arc discharge apparatus to control the arc plasma that produces homogeneous A-CNOs (diameter 25–35 nm) with minimal carbon impurities. Secondly, for further purification we have developed a very efficient method by utilizing the strong preferential adsorption of polyoxometalates. A-CNO growth and purification were investigated using thermogravimetric analysis (TGA), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy and X-ray diffraction (XRD). Furthermore, the electrochemical properties and electrocatalytic activities of purified A-CNOs were investigated with various redox species including neurotransmitter molecules. Compared to glassy carbon (GC) electrode, A-CNO showed excellent electrochemical performances including larger faradaic currents and facilitated electron-transfer kinetics. Controlled synthesis, efficient purification and the excellent electrocatalytic activities of A-CNOs reported herein will enable the utilization of these materials for various applications including biosensing, fuel-cell catalysts and energy-storage devices.     

Ultra-fine polishing of glass-ceramics by disaggregated and fractionated detonation nanodiamond

Ultra-fine polishing of glass-ceramics is extraordinarily difficult because of structure inconsistency, chemical inhomogeneity and high rigidity. Detonation nanodiamond particles(NDs) were disaggregated and fractionated by serial centrifuge separation to obtain four stable suspension with average sizes of 54.9 nm,103.8 nm,145.6 nm and 245.4 nm respectively. Those suspensions were then employed to polish glass-ceramics. The evolution of NDs has been carefully characterized by FTIR, Raman and XRD analysis and the finish surfaces of glass-ceramics were investigated with AFM. Results showed that disaggregation treatment modified only nanodiamond surface other than its structure. The amount of nitro-groups on NDs surface increased and the absolute value of ξ-potential was enhanced by least 6 times at the pH 4–5, which was propitious to disperse NDs in mild acidic solution and polish glass-ceramics. Coarse particles performed both higher removal rate and average roughness (Sa) than the finer one. By using the suspension with average size of 54.9 nm, a super smooth surface with Sa 0.208 nm (5 µm×5 µm) was achieved.     

Detonation of nanosized explosive: New mechanistic model for nanodiamond formation

While nanodiamonds are synthesized by detonation of microstructured explosives since 50 years ago, we developed a novel approach to synthesize these particles by using nanostructured explosives. This new synthesis method leads to novel results not only in the control of the size, but also in the understanding of the nanodiamond synthesis and the detonation mechanisms. The use of explosive particles with size down to 40 nm results in the formation of detonation nanodiamonds with a mean size of 2.8 nm. In the light of these experiments, a model based on the size of the material involved during the detonation process has been developed to explain the size of the obtained nanodiamond. According to hypotheses based on the number of the nanodiamond nucleation sites, the experimental results are in favor of a decrease in the size of the nanodiamonds formed when the size of the explosive particles used during detonation is decreased.     

Elemental analysis of nanodiamonds by inductively-coupled plasma atomic emission spectroscopy

A 68-element survey study was carried out on micro-impurities from 20 commercial nanodiamond samples from eight international manufacturers. The measurements were made using inductively coupled plasma atomic emission spectroscopy with detection limits for most elements below 1 ppm. Various methods of sample preparation were compared: direct introduction of suspensions, ashing with microwave-assisted acid digestion, and microwave-assisted acid extraction, and their advantages and disadvantages evaluated. The work demonstrates the feasibility of nanodiamond analysis by direct slurry nebulization, which provides a multi-element, rapid, simple, and relatively low-cost route for nanodiamond purity estimation. Most of the samples contain relatively high amounts of Fe, Na, Ca, Si, Cu, Al, S, and Ti (>100 ppm), while Pb, Zn, K, Mn, B, Cr, Mg, Mo, Sn, W, Ba, Sb, Co, and Sr are at low but significant amounts. In addition, in several samples, we found some uncommon elements like Ag, Ce, Y, Hf, Zr, and Hg. This study provides new possibilities for certifying nanodiamond purity, understanding their properties and behavior, and advancing their production technology.     

Combustion synthesis of AlN doped with carbon and oxygen

Carbon-and-oxygen-doped AlN specimens were prepared by combustion synthesis using Al, graphite, and AlN. Graphite addition changed the product color from white to blue. By XRD, the lattice constant increased slightly with increasing carbon content. Blue AlN powder was synthesized with a molar ratio of the diluent AlN of 0.2-0.5 with a fixed graphite content of 0.05. At an AlN molar ratio exceeding 0.6, carbon was not successfully incorporated due to the lower reaction temperature. Calcination at 800°C in air removed residual graphite without changing the crystal structure or product color. Oxygen, nitrogen, and carbon analyses revealed that blue AlN powders contained 0.45-0.54 mass% carbon and 1.4-1.6 mass% oxygen, while the undoped AlN contained 0.021 mass% carbon and 0.94 mass% oxygen. The origin of the white-to-blue color change was investigated via reflection measurements. Blue AlN exhibits an absorption peak at 634 nm (1.96 eV). From first-principles electronic structure calculations, the C-doped AlN and carbon-and-oxygen-doped AlN with a 1:1 ratio could be classified as p-type, whereas the O-doped AlN and 1:3 carbon-and-oxygen-doped AlN were n-type. One reason for the absorption peak at 634 nm may be a transition from the conduction band to an upper unoccupied state. These results suggest the possible control of optical and electronic properties of AlN via carbon-and-oxygen doping.     

Molecular dynamics simulations of nanocarbons at high pressure and temperature

A molecular dynamics study of carbon nanoparticles (980 and 10,034 atoms) under high temperature (1000–7000 K) and high pressure (2–45 GPa) has been made using the reactive LCBOPII potential. The most stable structure of the small cluster is onion-like (encapsulated fullerenic) on the whole pressure range, whereas a transition from onion-like to nanodiamond is observed for the big cluster as pressure increases from 2 to 45 GPa. The melting mechanism depends on the structure, initiated in the core in the case of an onion cluster and at the surface for the nanodiamond. A schematic phase diagram is proposed, that takes into account the finite size effects.     

C8-structured carbon quantum dots: Synthesis,blue and green double luminescence,and origins of surface defects

Nanoscale carbon generally exists as nanodiamond or graphite quantum dot (QD). In this study, we report the first synthesis of the third allotrope carbon QDs with an average size of 2 nm through carbonization of sucrose and study their photoluminescence properties. These QDs have a body-centered cubic structure and each lattice point is composed of eight atoms which form a sub-cube (so called C₈ crystal structure). High-resolution transmission electron microscopy and X-ray diffraction confirm the C₈ structure of the synthesized nanocrystallites. The C₈ QDs exhibit double-band luminescence with two peaks centered at around 432 and 520 nm. The study based on the photoluminescence, UV–Vis absorption, Fourier-transform infrared, and X-ray photoelectron spectroscopies reveals that the green emission originates from the CO related surface defect whereas the blue emission originates from another surface defect.     

The effect of electron irradiation on the structure and properties of α-Fe2O3 nanoparticles as cathode material

The work is devoted to the study of the effect of electron irradiation on the ordering of the crystal structure and properties of Fe oxide nanoparticles obtained by chemical synthesis and subsequent thermal annealing. X-ray diffractometry, scanning electron microscopy, energy dispersive analysis and ⁵⁷Fe Mössbauer spectroscopy were used as research methods. It was found that increasing the irradiation dose from 50 to 150 kGy leads to enlargement of particles from initial size 40 nm to 45–50 nm, while subsequent irradiation leads to the formation of ellipsoidal or rhombic particles, the average size of which is no more than 50–60 nm. Using the method of Mössbauer spectroscopy, it was found that with an increase in the irradiation dose, the relative intensity of the subspectrum of ⁵⁷Fe nuclei in locally heterogeneous areas decreases from 9.7 ± 0.8% to 0.6 ± 0.6%, which indicates a significant decrease in the density of oxygen vacancies and the ordering of the crystal and magnetic structure nanoparticles. A decrease in the density of oxygen vacancies and a decrease in deformation distortions in the structure indicate the promise of using electronic irradiation to modify the properties of nanoparticles. In the course of life tests of the applicability of the studied nanoparticles as cathode materials for lithium-ion batteries, it was found that increasing the irradiation dose leads to an increase in the specific capacitance from 202 to 215–218 mA g⁻¹, as well as a decrease in capacitance loss in case of a change in the charge/discharge rate, which indicates an increase in the stability of nanoparticles to degradation arising in the process of life tests.     

Grain size engineered high-performance nanograined BaTiO3-based ceramics: Experimental and numerical prediction

The ultra-thin multilayer ceramic capacitors (MLCCs) with layer thickness less than 1 μm or even 0.5 μm are in urgent demand due to the rapid development of modern electronic industries. Notably, the dielectric and ferroelectric properties of nanograined BaTiO₃-based ceramics, which are widely used as dielectric materials in MLCCs, are highly related to grain size. In this work, nanograined BaTiO₃-based ceramics with various grain sizes (50-100 nm) were prepared via the chemical coating method. The grain size effect on the dielectric and energy storage properties were systematically investigated. TEM and EDS images demonstrate that the typical core-shell structure is obtained inside ceramic grains even if the grain size is reduced to 50 nm. The fine-grain ceramic displays a lower maximal polarization but a higher breakdown strength, which ascribes to its weaker ferroelectric contribution and higher grain boundary ratio, respectively. As a result, it is confirmed that there exists an optimal grain size around 70 nm where maximum discharge energy density is achieved under the synergy effect of breakdown strength and polarization, which is also verified by a finite element analysis based on a modified hyperbolic tangent model. All these features provide important guidance towards the design of ultra-thin layer MLCCs by optimizing the dielectric properties and energy storage performance while pursuing miniaturization.     

First-principles density-functional investigation on the electronic properties and field emission of a hydrogenated nanodiamond

First-principles calculations using quantum-mechanical density functional theory (DFT) are carried out to investigate the geometrical structure and electronic properties for hydrogen terminated nanometer-sized diamonds. The results reveal that the size dependent feature in the electronic structures for nanodiamonds is different from that of Si clusters. The field emission properties for nanodiamonds are also explored, and it is found that under applied electric field Mulliken charges redistribute and accumulate on the emission side. Furthermore, the emission currents from the occupied orbitals for nanodiamond are calculated and it is revealed that the largest emission current comes from the third highest occupied molecular orbital.     

Effects of multiwall carbon nanotubes on dielectric and mechanical properties of CaCu3Ti4O12 composite

This work reports the synthesis of calcium copper titanate (CaCu₃Ti₄O₁₂)/multiwall carbon nanotubes (MWCNT) composites using ultrasonic technique followed by sintering in a high vacuum furnace. The effect of MWCNT content (0.05, 0.1, 0.15, and 0.2 wt%) on the structural, dielectric, and mechanical properties of CaCu₃Ti₄O₁₂ (abbreviated as CCTO) were investigated by TEM, XRD, FTIR, FESEM-EDAX, dielectric measurement, as well as tensile strength and flexural strength tests. XRD patterns revealed that the MWCNT loading did not affect the phase structure; however, the average crystallite size (D) was reduced from 60.88 nm to 40.79 nm. The samples had porous structures and the porosity reduced from 45.57% to 40.73% with MWCNT loading. The dielectric and mechanical properties of CCTO were enhanced with an increase in MWCNT loading. An important observation was that the CCTO mixed with 0.2 wt% MWCNT exhibited the highest dielectric permittivity (ε_r = 27,768) and the lowest dielectric loss (tan δ = 0.52) at 1 kHz. With the addition of 0.2 wt% MWCNT, the values of load, tensile, and flexural strength increased to 10.38 kN, 101.88 MPa, and 275.07 MPa, respectively, due to improvement in densification. These outcomes have values for the fabrication of CCTO and the optimization of its performance for electronic devices such as capacitors and antennas.     

Surface peculiarities of detonation nanodiamonds in dependence of fabrication and purification methods

A variety of post-treatments, such as thermal annealing and liquid phase oxidation, were used to determine the surface properties of six blasting synthesized nanodiamond powders, produced by various purification conditions. Methods of FTIR-spectroscopy, oxidative titration and pH-measurement were applied for comparing the surface functional groups. All spectra exhibited the characteristic IR-bands of detonation diamond in the regions 3400–2700 cm^− 1 and 1000–400 cm^− 1. The differences were revealed by the dissimilarity of the bands in the region 2000–1000 cm^− 1. The nanodiamond powder annealing up to 600 °C in air most fully revealed the specificity of the attached groups on diamond surface. The chemical oxidation with H₂O₂ modified nanodiamond surface groups and prevented them from further oxidative attack during thermal treatment.     

Nonlinear optical properties of detonation nanodiamond in the near infrared: Effects of concentration and size distribution

The present work investigates the nonlinear optical (NLO) properties of detonation nanodiamond (DND), focusing on their optical power limiting efficiency in optronics. Among the relatively numerous types of tested nanomaterials, the nanocarbonaceous ones are particularly promising. Here, we show that stable colloidal DND hydrosols are very efficient at blocking high energy beams (1064 nm), with very good linear transmittances over the whole visible and near infrared (Vis-NIR) range at low fluencies. Through the use of ultracentrifugation we could demonstrate that the power limiting efficiency of DND hydrosols is directly linked to the polydispersity.     

Magnetic and EPR studies of edge-localized spin paramagnetism in multi-shell nanographites derived from nanodiamonds

Prolonged (up to 2 h) heat treatment at 1600 °C of nanodiamond particles (5 nm) leads to their conversion to the mixture of quasi-spherical carbon onions and multi-shell polyhedral nanographites. Structural and magnetic properties of two (A and B) series of nanographite samples obtained at various annealing intervals were studied. XRD data show that both multi-shell nanographite samples have practically the same crystalline structures. HRTEM evidences that the most of particles obtained by short time (7 min) annealing have a spherical like shape whereas the long time (~ 2 h) annealing leads to the majority of particles having a polyhedral shape with a hollow inside. Electronic and magnetic properties of these nanocarbons were investigated by magnetic susceptibility and EPR. Annealing results in entire transformation of the EPR signal of nanodiamond to new EPR signals of various line shapes and widths. These signals are extremely sensitive to ambient oxygen. Concentrations for all EPR active spins vary from ~ 1 × 10¹⁹ spins/g (7 min) to ~ 2 × 10¹⁹ spins/g (2 h). Temperature dependences of EPR spectra' parameters were obtained for vacuum-processed samples within the range 4?600 K. Intensity vs. T plots may be well-fitted by the combination of Curie–Weiss and temperature-independent Pauli susceptibility contributions. The latter one increases on heat treatment. Significant extension of electron spin-lattice relaxation time on decreasing temperature was found.     

Effect of nanodiamond surface functionalization using oleylamine on the scratch behavior of polyacrylic/nanodiamond nanocomposite

Addition of hard particles such as nanodiamonds to polymers to improve their physical and mechanical properties is very common. However, nanodiamonds are usually hydrophilic so their tendency to form agglomerates in a polymeric matrix is quite strong. In this study, the effect of nanodiamond surface modification on its uniform dispersion in a polymeric matrix such as polyacrylic-base polymer clear coat was investigated. For this purpose, detonation nanodiamond (DND) with an average particle diameter of 4–6 nm was used. To improve dispersion of as-received DND (AR-DND) in the polymeric matrix, the surfaces of the particles were modified by heat treatment (oxidation) in air and followed by functionalization using oleylamine (OLA) as surfactant. So, nanocomposites with different contents of AR-DND, HT-DND and OLA treated HT- DND (OLA-HT-DND) particles were produced. Their characterizations were investigated by employing many analytical methods such as: Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and thermo-gravimetry analysis (TGA). Scratch resistance test and study of coating surfaces, using scanning tunneling microscopy (STM), were carried out on the polymeric nanocomposites. The results showed that the surface-functionalized nanodiamonds are highly dispersive and stable in the polymeric matrix. In addition, scratch resistance was increased with the addition of nanoparticles.