Spontaneous Nucleation Of Diamond Research Articles

Analysis of the mechanism of the effect of N–H–O impurities on diamond growth under HPHT

In this work, diamond crystals were synthesized with N–H–O impurities by the temperature gradient method (TGM) under high pressure and high temperature (HPHT) conditions using FeNi alloy as the metal solvent (MS). The results indicated that the spontaneous nucleation rate and proportion, growth characteristics, surface growth texture, and the impurity concentration of diamond crystals changed drastically upon changing the impurity content in the system. Mutual diffusion between the MS and carbon source (CS) was also blocked, which seriously inhibited the growth rate of diamond crystals. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses corroborated that the zero-valent iron (Fe0) and nickel (Ni0) contents declined after N–H–O impurities were introduced. The newly formed graphite can be found in the MS, but the ferric carbide disappears. XPS also confirmed shifts in the binding energy of FeNi MS peaks, more iron oxide and nickel oxide were identified in MS, hindering the mass transfer process. CO and NO were absorbed on the surface of MS, which hindered the surface processes of diamond growth. The formation of intermediates (Fe3C) was impeded during diamond growth and blocked the spontaneous nucleation of diamond. All of these phenomena contributed to a poor growth rate and changed the surface growth process of diamond crystals.

Crystallization of Diamond from Melts of Europium Salts

Diamond crystallization in melts of europium salts (Eu2(C2O4)3·10H2O, Eu2(CO3)3·3H2O, EuCl3, EuF3, EuF2) at 7.8 GPa and in a temperature range of 1800–2000 °C was studied for the first time. Diamond growth on seed crystals was realized at a temperature of 2000 °C. Spontaneous diamond nucleation at these parameters was observed only in an Eu oxalate melt. The maximum growth rate in the europium oxalate melt was 22.5 μm/h on the {100} faces and 12.5 μm/h on the {111} faces. The diamond formation intensity in the tested systems was found to decrease in the following sequence: Eu2(C2O4)3·10H2O > Eu2(CO3)3·3H2O > EuF3 > EuF2 = EuCl3. Diamond crystallization occurred in the region of stable octahedral growth in melts of Eu3+ salts and in the region of cubo-octahedral growth in an EuF2 melt. The microrelief of faces was characterized by specific features, depending on the system composition and diamond growth rate. In parallel with diamond growth, the formation of metastable graphite in the form of independent crystals and inclusions in diamond was observed. From the spectroscopic characterization, it was found that diamonds synthesized from Eu oxalate contain relatively high concentrations of nitrogen (about 1000−1200 ppm) and show weak PL features due to inclusions of Eu-containing species.

An effect of reduced S-rich fluids on diamond formation under mantle-slab interaction

Experimental study, dedicated to understanding the effect of S-rich reduced fluids on the diamond-forming processes under subduction settings, was performed using a multi-anvil high-pressure split-sphere apparatus in Fe3C-(Mg,Ca)CO3-S and Fe0-(Mg,Ca)CO3-S systems at the pressure of 6.3 GPa, temperatures in the range of 900–1600 °C and run time of 18–60 h. At the temperatures of 900 and 1000 °C in the carbide-carbonate-sulfur system, extraction of carbon from cohenite through the interaction with S-rich reduced fluid, as well as C0-producing redox reactions of carbonate with carbide were realized. As a result, graphite formation in assemblage with magnesiowüstite, cohenite and pyrrhotite (±aragonite) was established. At higher temperatures (≥1100 °C) formation of assemblage of Fe3+-magnesiowüstite and graphite was accompanied by generation of fO2-contrasting melts - metal-sulfide with dissolved carbon (Fe-S-C) and sulfide-oxide (Fe-S-O). In the temperature range of 1400–1600 °C spontaneous diamond nucleation was found to occur via redox interactions of carbide or iron with carbonate. It was established, that interactions of Fe-S-C and Fe-S-O melts as well as of Fe-S-C melt and magnesiowüstite, were С0-forming processes, accompanied by disproportionation of Fe. These resulted in the crystallization of Fe3+-magnesiowüstite+graphite assemblage and growth of diamond. We show that a participation of sulfur in subduction-related elemental carbon-forming processes results in sharp decrease of partial melting temperatures (~300 °C), reducting the reactivity of the Fe-S-C melt relatively to FeC melt with respect to graphite and diamond crystallization and decrease of diamond growth rate.

Nucleation of diamond micro-patterns with photoluminescent SiV centers controlled by amorphous silicon thin films

Selective deposition of diamond allows bottom-up growth of diamond nanostructures and nanoscale devices. However, it remains challenging to reduce the size of the patterns and to suppress parasitic spontaneous nucleation. We show here that thin layers of hydrogenated amorphous silicon (down to 40 nm) efficiently suppress spontaneous nucleation of diamond. The suppression of diamond nucleation does not depend on the substrate materials below hydrogenated amorphous silicon (Si, SiO2, Pt, Ni). We attribute the suppressed diamond nucleation to surface disorder on atomic scale. By using a structured layer of hydrogenated amorphous silicon, highly selective growth of diamond micro-patterns with optically active SiV centers by low-temperature microwave plasma chemical vapor deposition is achieved.

The characteristics of diamonds crystallized using Fe-C-H at high pressure and temperature

Diamond crystallization in an Fe–C system with C10H10Fe additive(collectively called the Fe-C-H system) has been studied at 5.0–6.0GPa and temperatures ranging from 1400 to 1700°C. Both spontaneous diamond nucleation and growth were studied. The results showed that the stable form of diamond growth is octahedral in Fe-C-H systems, which is similar to pure Fe-C systems. However, the diamond morphologies changed from high quality octahedral to aggregated octahedral as the amount of C10H10Fe increased, accompanied by a deterioration of the surfaces. The FTIR results indicated that hydrogen-doped diamonds with less than 1ppm nitrogen are easily synthesized in this system. The crystallization of diamonds in the Fe-C-H system was not only affected by the pressure and temperature conditions, but also by the amount of C10H10Fe additive. This was attributed to changes in the pure Fe catalyst caused by the elemental hydrogen produced by the decomposition of C10H10Fe.

Diamond crystallization with a carbonyl nickel catalyst under high pressure and temperature

For decades, the origin of aggregated nitrogen in diamond has been studied and has led to an important stage in solving the problems of natural diamond genesis. However, clarifying how B-centers (groups of four nitrogen atoms around a vacancy) form in diamond is still one of the most challenging issues in material science. In this work, we apply carbonyl nickel powders as a catalyst to grow diamond over a wide range of pressures, 5.0–6.2 GPa, and temperatures, 1300 to 1800 °C, and we report the first synthesis of high-quality diamonds containing nitrogen impurities with IaB characteristics. Both spontaneous nucleation of diamond and growth of diamond on seeds have been achieved by film growth and temperature gradient growth methods. By Fourier-transform infrared spectrometry, we reveal a novel formation mechanism for aggregated nitrogen impurities in B-centers, that is, B-centers can be readily aggregated by four C-centers (single-substitutional nitrogen atoms) during a diamond growth process under high pressure and temperature. High reaction temperatures can effectively contribute to the formation of nitrogen-vacancy defects in diamond and play a key role in the formation of B-centers during diamond growth. Our current findings will be helpful for further understanding and constructing a clear model of aggregated nitrogen, and thus provide us with deeper insights into the genesis of natural diamond.

Reduced sediment melting at 7.5–12 GPa: phase relations, geochemical signals and diamond nucleation

Melting of carbonated sediment in the presence of graphite or diamond was experimentally investigated at 7.5–12 GPa and 800–1600 °C in a multianvil apparatus. Two starting materials similar to GLOSS of Plank and Langmuir (Chem Geol 145:325–394, 1998) were prepared from oxides, carbonates, hydroxides and graphite. One mixture (Na-gloss) was identical in major element composition to GLOSS, and the other was poorer in Na and richer in K (K-gloss). Both starting mixtures contained ~6 wt% CO2 and 7 wt% H2O and were doped at a ~100 ppm level with a number of trace elements, including REE, LILE and HFSE. The near-solidus mineral assemblage contained a silica polymorph (coesite or stishovite), garnet, kyanite, clinopyroxene, carbonates (aragonite and magnesite–siderite solid solution), zircon, rutile, bearthite and hydrous phases (phengite and lawsonite at 10 GPa). Hydrous phases disappear at ~900 °C, and carbonates persist up to 1000–1100 °C. At temperatures >1200 °C, the mineral assemblage consists of coesite or stishovite, kyanite and garnet. Clinopyroxene stability depends strongly on the Na content in the starting mixture; it remains in the Na-gloss composition up to 1600 °C at 12 GPa, but was not observed in K-gloss experiments above 1200 °C. The composition of melt or fluid changes gradually with increasing temperature from hydrous carbonate-rich ( 1). Aragonite and Fe–Mg carbonate have very different REE partition coefficients (DMst-Sd/L ~ 0.01 and DArg/L ~ 1). Nb, Ta, Zr and Hf are strongly incompatible in both carbonates. The bearthite/melt partition coefficients are very high for LREE (>10) and decrease to ~1 for HREE. All HFSE are strongly incompatible in bearthite. In contrast, Ta, Nb, Zr and Hf are moderately to strongly compatible in ZrSiO4 and TiO2 phases. Based on the obtained partition coefficients, the composition of a mobile phase derived by sediment melting in deep subduction zones was calculated. This phase is strongly enriched in incompatible elements and displays a pronounced negative Ta–Nb anomaly but no Zr–Hf anomaly. Although all experiments were conducted in the diamond stability field, only graphite was observed in low-temperature experiments. Spontaneous diamond nucleation and the complete transformation of graphite to diamond were observed at temperatures above 1200–1300 °C. We speculate that the observed character of graphite–diamond transformation is controlled by relationships between the kinetics of metastable graphite dissolution and diamond nucleation in a hydrous silicocarbonate melt that is oversaturated in C.

Selective area deposition of diamond films on AlGaN/GaN heterostructures

Diamond‐on‐GaN heterostructure is a promising hybrid material system with a variety of applications such as heat spreaders, high‐temperature, and high‐power devices. From a practical point of view, polycrystalline diamond is shown to be an attractive solution to the limited use of the expensive monocrystalline diamond substrates. Here we present selective area diamond deposition on AlGaN/GaN layers focusing on the elimination of surface and metal contact damage (Ni, NiO, Ir, and IrO2) and suppressing the spontaneous nucleation of diamond. Metal contacts are important for further applications such as diamond‐coated GaN based electronic devices. The growth of diamond films was performed by microwave chemical vapor deposition in different gas mixtures with the addition of CO2 or N2 to CH4/H2. Adding CO2 resulted in polycrystalline (PCD), while adding N2 led to the formation of nanocrystalline diamond film (NCD). The diamond deposition was carried out using selective area nucleation in a three‐layer sandwich structure (polymer/seeding layer/polymer), which avoided damage to the electrode and GaN surfaces from ultrasonic seeding by diamond particles. No protective layer was used on the GaN surface before diamond deposition, i.e., diamond films were grown directly on the AlGaN/GaN heterostructures. In the case of NCD deposition, no surface damaging of GaN was observed. For both NCD and PCD films, increasing methane from 1% to 2% in H2 minimized the surface damage of GaN films.

Diamond formation by carbon saturation in C–O–H fluids during cold subduction of oceanic lithosphere

Microdiamonds in garnet of graphite-free ultrahigh pressure metamorphic (UHPM) rocks from Lago di Cignana (western Alps, Italy) represent the first occurrence of diamond in a low-temperature subduction complex of oceanic origin (T=∼600°C; P⩾3.2GPa). The presence of diamonds in fluid inclusions provides evidence for carbon transport and precipitation in an oxidized H2O-rich C–O–H crustal fluid buffered by mineral equilibria at sub-arc mantle depths. The structural state of carbon in fluid-precipitated diamonds was analyzed with 514nm excitation source confocal Raman microspectroscopy. The first order peak of sp3-bonded carbon in crystalline diamonds lies at 1331 (±2)cm−1, similar to diamonds in other UHPM terranes. The analysis of the spectra shows additional Raman features due to sp2 carbon phases indicating the presence of both hydrogenated carbon (assigned to trans-polyacetylene segments) in grain boundaries, and graphite-like amorphous carbon in the bulk, i.e. showing a structural disorder much greater than that found in graphite of other UHPM rocks. In one rock sample, disordered microdiamonds are recognized inside fluid inclusions by the presence of a weaker and broader Raman band, downshifted from 1332 to 1328cm−1. The association of sp3- with sp2-bonded carbon indicates variable kinetics during diamond precipitation. We suggest that precipitation of disordered sp2 carbon acted as a precursor for diamond formation outside the thermodynamic stability field of crystalline graphite. Diamond formation started when the H2O-rich fluid reached the excess concentration of C required for the spontaneous nucleation of diamond. The interplay of rock buffered fO2 and the prograde P–T path at high pressures controlled carbon saturation. Thermodynamic modeling confirms that the C–O–H fluids from which diamond precipitated must have been water rich (0.992<XH2O<0.997), assuming that fO2 is fixed by the EMOD equilibrium.

Diamond formation in the system MgO–SiO2–H2O–C at 7.5 GPa and 1,600°C

Diamond crystallization has been studied in the SiO2–H2O–С, Mg2SiO4–H2O–С and H2O–С subsystems at 7.5 GPa and 1,600°C. We found that dissolution of initial graphite is followed by spontaneous nucleation of diamond and growth of diamond on seed crystals. In 15-h runs, the degree of graphite to diamond transformation [α = MDm/(MDm + MGr)100, where MDm is mass of obtained diamond and MGr mass of residual graphite] reached 100% in H2O-rich fluids but was only 35–50% in water-saturated silicate melts. In 40-h runs, an abrupt decrease of α has been established at the weight ratio H2O/(H2O + SiO2) ≤ 0.16 or H2O/(H2O + Mg2SiO4) ≤ 0.15. Our results indicate that α is a function of the concentration of water, which controls both the kinetics of diamond nucleation and the intensity of carbon mass transfer in the systems. The most favorable conditions for diamond crystallization in the mantle silicate environment at reliable PT-parameters occur in the fluid phase with low concentration of silicates solute. In H2O-poor silicate melts diamond formation is questionable.

Sulfide melts–graphite interaction at HPHT conditions: Implications for diamond genesis

The interaction of graphite with (Fe,Ni) 9S 8 and FeS sulfide melts has been studied at P = 6.3–7.5 GPa and T = 1450–2200 °C in experiments with a duration from 2 to 65 h. It has been found that both pentlandite and pyrrhotite melts interacting with graphite show similar behavior. At < 7.5 GPa and 1450–1800 °C and at 7.5 GPa and < 1600 °C carbon crystallizes predominantly as metastable graphite and to the minor extent as diamond on the seed crystals. Only at a pressure of 7.5 GPa and a temperature of 1600 °C and higher, sulfide melts provide spontaneous diamond nucleation at the melt–graphite interface and directly within carbon-saturated sulfide melt. In this case no metastable graphite was found in the products. Diamond crystals synthesized in the (Fe,Ni) 9S 8–C system were found to contain nitrogen impurity with concentrations of an order of 1000 ppm and exhibited IR absorption peaks due to hydrogen. The luminescence measurements revealed specific optical centers related to nickel impurity in the crystals. It is concluded that sulfide melts are less efficient diamond forming media as compared to carbonate, carbonate–silicate–fluid and fluid systems. The results of the study suggest that diamond nucleation from carbon-supersaturated sulfide melt as supposed in the sulfide model of diamond genesis seems improbable at the UHP conditions of the formation of most natural diamonds.

HPHT synthesis of diamond with high nitrogen content from an Fe 3N–C system

The capability of iron nitride, Fe 3N for converting graphite to diamond was explored at P=7 GPa and T=1550–1850 °C in experiments with a duration of 20 h. It was established that depending on the synthesis temperature the iron nitride melt provides conditions for crystallisation of diamond and/or graphite, with the minimal temperature for spontaneous diamond nucleation being approximately 1700 °C. Based on the results obtained it was argued that the iron nitride acts as the solvent-catalyst for diamond formation. The crystallised diamonds were found to contain nitrogen in concentration up to approximately 3300 ppm, which depending on the synthesis temperature was present in either the A form or both A and C forms. Absorption peaks caused by hydrogen-related defects were observed in IR spectra of all diamonds examined. For the 3107 cm −1 line a tendency to increase in intensity with increasing the nitrogen content was found. The well-known blue band-A, N3, H3 and 2.156 eV systems as well as a band with zero-phonon energy at 1.787 eV were observed in cathodoluminescence.

An experimental demonstration of diamond formation in the dolomite-carbon and dolomite-fluid-carbon systems

The results of a study of diamond crystallisation in dry and fluid-rich dolomite-carbon systems are presented. For the dry system an induction period preceding spontaneous diamond nucleation was found of about 4 h at 7 GPa, 1700 °C. No diamonds were observed after 42 h of reaction at 5.7 GPa, 1420 °C. Adding H 2 O and H 2 O-CO 2 fluids to the dolomite-carbon system resulted in spontaneous diamond nucleation at 1420 °C, and growth of diamond on seed crystals at 1300–1420 °C. In the presence of H 2 O or H 2 O-CO 2 fluids, dolomite decomposes to dolomite solid solution + brucite + aragonite. Results of the experiments indicate that dolomitic melts in the mantle, enriched in H 2 O and CO 2 , promote the formation of natural diamond.

Spontaneous nucleation of diamond in the system MgCO3–CaCO3–C at 7.7 GPa

Abstract High-pressure and high-temperature experiments were carried out to determine the minimum temperature required for spontaneous nucleation of diamond in the system comprising a carbonate mixture (60 mol% MgCO 3 and 40 mol% CaCO 3 ) and graphite at 7.7 GPa, for 1 h and longer reaction times up to 12.5 h, and also in the systems MgCO 3 –graphite and CaCO 3 –graphite for comparison. The above carbonate mixture melted at a temperature between 1600°C and 1700°C. The minimum temperature for spontaneous nucleation of diamond was 1900°C for a reaction time of 1 h; it was lowered to 1700°C for 11 h, but no diamond was formed at 1600°C for 12.5 h. These results indicate that the molten state of the solvent-catalyst and enough reaction time are necessary for diamond nucleation in the systems examined at 7.7 GPa.