Diamond Facets Research Articles

Controlled lateral positioning of NV centres in diamond by CVD overgrowth

A challenge to this day in the development of diamond devices for quantum applications is the laterally defined and closely spaced positioning of nitrogen-vacancy centres with exceptional coherence properties. Here, we demonstrate a maskless, implantation-free method for the controlled in-plane positioning of NV centres using a combination of focused ion beam (FIB) milling, plasma etching and nitrogen-doped diamond growth. The Ga+ ion beam milling resulted in 1 μm × 1 μm cavities with depths of up to 450 nm, each cavity exhibiting the four [111]-oriented diamond facets after pure hydrogen plasma treatment and a depth of 700 nm. Low-methane, nitrogen-doped chemical vapour deposition (CVD) overgrowth resulted in in situ formation of oriented NV ensembles, exclusively perpendicular to the {111}-planes.

Spectroscopic characterization of rare natural pink diamonds with yellow color zones

A set of 28 uncommon pink diamonds with yellow color zones are identified among thousands of natural pink diamonds examined. The pink color in these diamonds is caused by the 550 nm absorption band associated with plastic deformation, and is concentrated along straight lamellae (also known as deformation lines). These pink diamonds are type Ia with nitrogen concentrations ranging from 118 to 313 ppma, predominantly as A-centers, i.e., type IaA ≫ B (proportion of B-center < 10 %) to IaA > B (proportion of B-center = 11–26 %).Yellow color zones are observed on or beneath the surface of these faceted pink diamonds. Yellow fluorescence and occasionally yellow phosphorescence excited by long-wave (365 nm) or deep UV (<225 nm), corresponding to the yellow color zones, are commonly observed in yellow diamonds colored by the 480 nm absorption band. PL mapping conducted on the diamond surface and along the depth of the pink diamonds in this study reveals that the yellow color zones have features associated with the 480 nm absorption band. Some of these features are associated with nickel-related defects, and are only detected within the yellow color zones. This suggests that the yellow color zones formed in a different growth episode or from a different diamond-forming fluid than the remaining volume of the diamond with pink body color. Post-growth plastic deformation created defects giving rise to the 550 nm absorption band, producing a pink body color to diamond that was presumably colorless, and producing brown color in zones that may have had pre-existing yellow color. Three diamonds in this study contain eclogitic mineral inclusions, indicating that they formed in association with mantle eclogite, prior to plastic deformation.

Selective deposition of silver particles on {111} or {100} diamond facets

In the present work, the surface of synthetic diamond microcrystals was modified by treating them in vials of a planetary mill without milling balls with a silver powder added.

Автоматизированная идентификация природных ограненных алмазов (бриллиантов) по спектру люминесценции

The problem of recognition of natural and synthetic diamonds (diamonds) is relevant today. A technique for computer processing of the luminescence spectra of diamonds using the Origin mathematical package is proposed. The processing technique is presented on specific examples. The spectra were measured using a RAOS-3 spectrometer-fluorimeter. A laser with a wavelength of 532 nm was used to excite diamond luminescence. A method is proposed for identifying diamonds of unknown origin by the number of bands of elementary components in the luminescence spectrum when decomposed into Gaussian curves. Luminescence spectra in faceted diamonds (brilliants) are widely used to study their physical properties. Synthetic faceted diamonds are significantly inferior to natural ones in terms of luminescence intensity. The light signal of photoluminescence in the former, in some cases, is comparable with the noise level of the measuring device. As a result, the instantaneous value of the useful signal can take both positive and negative values over the entire wavelength range of the spectrum. Therefore, the detection of a useful signal against the background of interference is of great importance. Along with this, to identify a diamond, it is necessary to solve the problem of decomposing the spectrum into elementary components in the form of Gaussian curves. Since it has been established that the spectra of natural diamonds consist of two peaks, while synthetic diamonds contain from three to eight peaks, which indicates a loose structure of the diamond crystal lattice. The efficiency of solving a number of these problems can be significantly improved by using software applications with special functionality. To demonstrate the features and advantages of the automated technique, the Origin mathematical package was taken, which, in particular, makes it possible to improve the quality of the results of processing a low luminescence spectrum and to find the number of peaks for Gaussian curves with sufficient accuracy.

Optimal direction and propagation of mid-IR light inside rough and polished diamonds for highly-sensitive transmission measurements of nitrogen content

Optical transmission/absorption measurements in diamond provide a way for determining content of basic nitrogen defects, with their concentrations varying in different crystals by many orders of magnitude. In a traditional scheme of transmission measurement in many diamond crystals only a small fraction of incident light is transmitted and detected due to light refraction and multiple reflections. This significantly reduces signal-to-noise ratio, narrows the dynamic range of measured signal magnitudes and the corresponding range of measurable defects concentrations. In this work optimal input/output points and optical propagation paths of mid-IR light inside most characteristic forms of rough and faceted diamonds were searched and analyzed. Practical acquisition recommendations and measurement configurations are proposed, enabling to expand signal dynamic range by acquiring multiple mid-IR light reflection/transmission replica, using an integrating sphere and immersion material.

Selective Deposition of Mo2C-Containing Coatings on {100} Facets of Synthetic Diamond Crystals.

An efficient way to improve the properties of metal–diamond composites (mechanical strength, wear resistance, thermal conductivity) is the preliminary modification of the diamond surface to improve its wettability by the metal matrix. In the present work, Mo2C-containing coatings were deposited on the diamond crystals under different conditions: hot pressing (atmosphere of argon), spark plasma sintering (forevacuum), and annealing in air. The influence of the sintering parameters on the morphology and phase composition of the coatings deposited on diamond was studied. Mo2C-containing coatings were selectively deposited on the facets of synthetic diamond microcrystals by annealing of the latter with a molybdenum powder. Experiments were carried out to deposit coatings under different conditions: during hot pressing (argon atmosphere), spark plasma sintering (forevacuum), and annealing in air. The process parameters were the temperature, holding time, and concentration of molybdenum in the initial mixture. Experiments with a pre-oxidized molybdenum powder were also conducted. The coated diamond crystals were investigated by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The deposition was enabled by the gas phase transport of molybdenum dioxide, MoO2, contained in the starting powder. The following sequence of the coating formation stages was proposed. First, MoO2 sublimes and is adsorbed mainly on the {100} facets of diamond. Then, it is reduced to metallic molybdenum by carbon of the diamond, which further reacts with carbon to form the Mo2C carbide phase. These processes occurred during treatment of the mixtures in the hot press and the spark plasma sintering facility. When the mixture was annealed in air, no selective deposition was observed. During annealing, MoO3 particles adhered to the diamond surface.

Morphological features and phase composition of W-containing coatings formed on diamond via its interaction with WO3

In the present work, W-containing coatings were deposited on the surface of diamond microcrystals. The coatings formed as diamond reacted with a WO3 powder in the die of a hot press at elevated temperatures. The morphology and phase composition of the coatings were studied as functions of the treatment temperature and treatment time. The coated diamond crystals were investigated by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. After treatment of the mixture at 850 °C for 15 min, WO2 and W18O49 were found on the diamond surface. After treatment at 950 °C (15 min), tungsten was the dominant phase of the coating. Treatment at 1150 °C (15 min) led to the formation of the WC and W2C phases; no metallic tungsten was present in the coating obtained at this temperature. The reaction sequence describing the coating formation process was proposed. During the coating formation, the deposition selectivity with regard to the diamond facet was observed. The {100} facets of diamond were preferentially coated. The coating developed through the formation and coalescence of islands, which were of square shape on the {100} facets and of triangular shape on the {111} facets of diamond.

Preparation of nanoporous gold particles on diamond facets via galvanic replacement and dealloying

In the present work, methods of depositing gold particles of different morphologies on the facets of synthetic diamond microcrystals have been proposed. When diamond crystals with silver particles selectively deposited on the {100} facets are treated by chloroauric acid HAuCl4 solution, partial galvanic replacement of silver by gold leads to the formation of hollow porous hemispheres of an AgAu alloy. Upon annealing of the diamond crystals with particles, in which silver was partially replaced by gold, an AgAu solid solution forms on the {100} facets. Selective dissolution of silver from the AgAu solid solution results in the formation of nanoporous gold via a dealloying process. Gold particles can also be formed by sputtering gold on the surface of the diamond crystals with silver particles adhered to the {100} facets, annealing the modified crystals and dealloying. In that case, gold particles are found on all facets of diamond. However, the morphological features of the particles depend on the crystallographic orientation of the facet. Nanoporous gold particles are found only on the {100} facets of diamond.

The Size and Shape of Diamond Crystals of Different Origin

The size and shape of diamond crystals of different origin are analyzed. Diamonds with a size of less than about 0.5 mm are classified as microcrystals. Diamonds found in meteorites typically show non-faceted anhedral crystals of various sizes. Only the Canyon Diablo iron meteorite has cubic microcrystals of unclear crystallogenesis. Nano, micro- and macro-sized crystals of diamond in meteorites are usually aggregate in nature. The release of diamond polyhedra in meteorites is limited by the too small size of its crystals in chondrites and by its solid-phase transformation from very fine-grained diamond and graphite in ureilites and octahedrites. The size and shape of diamond crystals found in meteorite impact craters are determined by the nature of the source carbon material. The process of solid-phase transformation of graphite or other carbon-bearing materials (e.g., coal, plant remains) to diamond in meteorite craters does not allow euhedral crystal to be formed. At the same time, in the case of diamonds formed from impacts, on the (0001) faces of impact apographitic diamonds, polyhedra of nano-microdiamonds crystallize from the gas phase. These crystals are often form autoepitaxially, because they crystallize in an oriented manner on the lonsdaleite -diamond matrix. Diamonds found in metamorphic rocks, ophiolites and modern volcanites show faceted microcrystals. A wide range of sizes, from 0.1 mm to 10 cm, is characteristic of faceted diamond crystals from kimberlites, lamproites and lamprophyres. Diamond crystals from different mantle rocks acquire a multifaceted shape after reaching certain embryo sizes — the most likely appearance of diamond polyhedra larger than 40-50 nm. Octahedra forms are dominant for natural diamond crystals of different sizes and origin.

A comparative analysis of the frequency spectra of the human eye and a cut diamond in visible light

The paper investigates the frequency characteristics of the spectra of a human eye and a faceted diamond (brilliant). The relevance of the research deals with a large number of modern studies on the use of diamond as a lens of the eye. The results obtained were compared with the averaged data (described in the literature) on the visibility curve of day, evening and night vision of the human eye. The research method is based on the representation of the optical environment of the human eye and diamond in the form of a dynamic link with an input and output. The Gaussian function is used to approximate the spectral curves. The study of the inertial properties of such a link in the time domain is performed by feeding signals to its input in the form of a δ-function or a unit function. The steady-state forced oscillations at the output of the investigated dynamic link are found when a harmonic action is applied to the input. Frequency characteristics discover a relationship between the spectra of the input and output signals, representing the direct Fourier transform of the function of time. It was found that the spectra of the visibility of the human eye and the luminescent radiation of diamond have the properties of ultra-wideband signals. It is shown that the amplification of light takes place in the time domain when the width of the spectrum at its half-maximum does not exceed a certain critical value. This phenomenon also manifests itself in the frequency domain. It was revealed that the dynamic links of diamond and human eyes for day and night vision exhibit amplifying properties. Their comparison in terms of the light amplification factor showed their insignificant difference. The results obtained can find application in the creation of matrix photodetectors and as a standard in identifying a faceted diamond (brilliant) of unknown origin and producing a lens from a diamond.

Ultrafast femtosecond laser micro-marking of single-crystal natural diamond by two-lens focusing system

The inscription of unique logo and security marking on diamonds and gemstones is in high demand by worldwide manufacturers and businesses for anti-counterfeiting purposes and traceability. Short pulsed lasers enable marking of transparent materials, challenge remains to produce digital security micro-features on thin facets of the natural diamond in a non-intrusive manner. We propose the design and demonstration of a novel two-lens focusing system to inscribe diamond at microscale and high throughput by an ultrafast laser scanning process. A threshold laser fluence of ∼2.5 J/cm2 and a scan speed of 2 mm/s realized writing of high-contrast data matrix code and serial number without inducing defects and cracking in the diamond. Characterization revealed smooth ablation depth profile with distinct laser-induced periodic surface structures (LIPSS) in the laser inscribed regions determined through scanning electron microscopy (SEM) and 3D optical microscopy. Raman spectroscopy revealed diamond cubic structure dominating with mixing of graphitic structure in the laser markings at various scanning speeds. Comparing with the 0.05 NA f-theta lens, the two-lens focusing system offered 7x improvement in the marking resolution (3 μm in line-width) in addition to its simplicity and add-on flexibility to industrial laser marking systems.

Selective deposition of platinum hemispheres on the {100} facets of synthetic diamond

In this work, a two-step preparation method of diamond-metal heterostructures, in which platinum particles are attached to the {100} facets of diamond microcrystals, was elaborated. At the first step, silver particles are deposited on the {100} facets of the synthetic diamond crystals by the powder annealing method. At the second step, the microcrystals having silver particles deposited on their surface are treated by aqueous solution of hexachloroplatinic acid H2PtCl6. The treatment results in the formation of hollow platinum hemispheres on the {100} facets of the diamond crystals. Detailed morphological studies of the synthesized heterostructures have been conducted to reveal a nanocrystalline structure of the hollow platinum hemispheres. Diamond-noble metal heterostructures of these morphology and composition have been synthesized and investigated for the first time.

Influence of substrate material on spectral properties and thermal quenching of photoluminescence of silicon vacancy colour centres in diamond thin films

Abstract Nanocrystalline diamond films with bright photoluminescence of silicon-vacancy colour centres have been grown using a microwave plasma enhanced CVD technique. The influence of substrate material (quartz, Al2O3, Mo and Si) on a reproducible fabrication of diamond thin films with Si-V optical centres is presented. Film quality and morphology are characterized by Raman spectroscopy and SEM technique. SEM shows well faceted diamond grains with sizes from 170 to 300 nm. The diamond peak is confirmed in Raman spectra for all samples. In the case of the quartz substrate, a redshift of the diamond peak is observed (≈3.5 cm−1) due to tension in the diamond film. The steady-state photoluminescence intensity was measured in the temperature range from 11 K to 300 K. All spectra consist of a broad emission band with a maximum near 600 nm and of a sharp zero phonon line in the vicinity of 738 nm corresponding to Si-V centres that is accompanied with a phonon sideband peaking at 757 nm. Activation energies for the thermal quenching of Si-V centre photoluminescence were determined and the effect of the substrate on photoluminescence properties is discussed too.

Multiwalled carbon nanotube forests grown on the surface of synthetic diamond crystals

Abstract Forests of multiwalled carbon nanotubes (MWCNTs) were grown on the facets of synthetic diamond crystals by treating them in a rotary chemical vapor deposition reactor. Nickelocene was used as a source of both nickel catalyst and carbon for the formation of MWCNTs. The diamond crystals were not subjected to any surface treatment prior to the MWCNT growth. The MWCNTs were anchored in nickel particles adhered to the diamond facets and were partially filled with nickel. These morphological features of the diamond-MWCNT structures together with nanotube branching suggest the formation of MWCNTs by the combined growth mechanism.

Selective growth of silver particles on the facets of synthetic diamond

We have shown for the first time that simple annealing of silver–synthetic diamond mixtures in air or oxygen at 600–700 °C leads to selective growth of silver particles on the {100} facets of diamond, while no growth is observed on the {111} facets. Annealing at a temperature higher than 750 °C results in significant morphological changes in the heterostructure: silver particles grow not only on the cube but also on the octahedral facets.

International migrations and care provisions for elderly people left behind. The cases of the Republic of Moldova and Romania

International migrations are posing numerous challenges to care systems in both sending and receiving countries. Based on a multi-method research conducted between 2011 and 2013, this article looks at how the care provisions for elderly people are rearranged in two Eastern European countries affected by the care drain phenomenon (the Republic of Moldova and Romania). The author charts and compares how transnational families, but also the other facets of the care diamond, such as the public sector, the market and the not-for-profit sector, provide care to elderly people left to cope at home alone because their close relatives have migrated. The main findings of the article are that transnational families are the principal welfare provider for elderly people left behind, while there is a serious delay in the adoption of specific policies for the elderly.

Interfacial microstructure of copper/diamond composites fabricated via a powder metallurgical route

The interfaces in Pulse Plasma Sintered composites of Cu0.8Cr and diamond have been characterised. The interfaces between the diamond and the Cu0.8Cr matrix generally exhibited a strong degree of bonding, but variations related to the orientation of the diamond facets were revealed. Image analysis established that the surfaces of the diamond particles were partially coated with chromium carbide, which averaged 43% for the {111} facets and 31% for the {100} facets. In addition thin and irregular layers of graphite were also observed. The composite with a 50% volume fraction of diamond possessed a thermal diffusivity of 218mm2/s which infers a thermal conductivity of 589W/(m·K), which is 76% of the maximum theoretical conductivity predicted by the Maxwell model.

Selective secondary nucleation controlled (001)-texture in boron doped diamond films by increasing the concentrations of tetramethylsilane and trimethylborane

Diamond shows anisotropic physical and chemical properties, depending on its crystallographic orientations. Owing to the lack of large-scale single crystalline diamond substrates, however, the growth of textured diamond film becomes a popular way in tailoring its optical, electrical, mechanical, and thermal properties for specific applications. In the present study, we show that the (001)-texture of boron doped diamond (BDD) thin film can be controlled by a selective secondary nucleation process. To achieve this, a low concentration of tetramethylsilane (TMS) was introduced to induce a high secondary nucleation rate on the non-{001} diamond facets, hindering their lateral growth. In contrast, the continuous growth and expansion of the {001} facets are kept, which leads to the formation of (001)-textured diamond film. In addition, the orientation of the film can be continuously improved by increasing the concentration of either TMS or trimethylborane (TMB) in the gas phase within a relatively large parameter window. This study not only presents a new mechanism in controlling the textured of diamond, but also sheds some light on the fundamental research regarding the diamond growth.

Peculiarities of boron distribution in as-grown boron-doped diamond

Boron doped diamond (BDD) single crystals have been grown under conditions of high isostatic pressure by the temperature gradient method. Numerous equilateral triangles were found on the fluorescence images of {111}-diamond facets. Structural peculiarities of BDD were investigated by JEM-2010 transmission electron microscope with GIF Quantum attachment for electron energy loss spectroscopy (EELS). High resolution image of diamond lattice revealed some distorted {111}-layers. EELS testifies the presence of boron in distorted regions of diamond lattice. The crystallographic features of BDD and their connection with the superconductivity are discussed.

Change of diamond film structure and morphology with N2 addition in MW PECVD apparatus with linear antenna delivery system

Deposition of nano‐crystalline diamond (NCD) over large areas is of high interest for industrial applications. For instance NCD is an excellent substrate for cell growth but it is also interesting for photonic applications associated with nitrogen‐vacancy (NV) centres. There have been many studies on the effect of nitrogen addition on the growth of diamond using conventional resonance cavity microwave plasmas (both H and Ar based) but none using MW PECVD apparatus with linear antenna delivery system (MW‐LA‐PECVD). In this work, we show that an ultra nano‐crystalline diamond (UNCD) type of morphology can be prepared upon N2 addition to H2CO2CH4 plasmas at low pressures (0.3 mbar) and low temperature (520 °C); however, these films despite their UNCD character show sp3 dominated Raman spectra and highly isolating behavior. The crystalline structure and morphology of the films were characterized by scanning electron microscopy, atomic force microscopy, Raman spectroscopy, grazing angle X‐ray diffraction, and transmission electron microscopy. Diamond films' composition was evaluated from thermal neutron depth profiling. Films were also characterized by photoluminescence spectroscopy to study the incorporation of luminescent NV centre. Addition of nitrogen increases deposition rate and dramatically changes surface morphology and crystalline structure from well faceted diamond crystals to UNCD like morphology.