Morphology Of Diamond Crystals Research Articles

Morphology of Diamond Crystals and Mechanism of Their Growth

Morphology of Diamond Crystals and Mechanism of Their Growth

Regulation mechanism of catalyst structure on diamond crystal morphology under HPHT process**Project supported by the National Natural Science Foundation of China (Grant No. 11804305), the Natural Science Foundation of Chongqing, China (Grant No. cstc2019jcyj-msxmX0391), the Science and Technology Research Program of Chongqing Municipal Education Commission, China (Grant No. KJ201901405), and the Open Project of State Key Laboratory of Superhard Materials,

To elucidate the regulation mechanism of catalyst geometry structure to diamond growth, we establish three catalyst modes with different structures. The simulation results show that with the decrease of the protruding height of the catalyst, the low-temperature region gradually moves toward the center of the catalyst, which causes the distribution characteristics of the temperature and convection field in the catalyst to change. The temperature difference in vertical direction of the catalyst decreases gradually and increases in the horizontal direction, while the catalyst convection velocity has the same variation regularity in the corresponding directions. The variation of temperature difference and convection velocity lead the crystal growth rate in different crystal orientations to change, which directly affects the crystal morphology of the synthetic diamond. The simulation results are consistent with the experimental results, which shows the correctness of the theoretical rational analysis. This work is expected to be able to facilitate the understanding of catalyst structure regulation mechanism on diamond morphology and the providing of an important theoretical basis for the controllable growth of special crystal shape diamond under HPHT process.

Microrelief of Rounded Diamond Crystals as an Indicator of the Redox Conditions of Their Resorption in a Kimberlite Melt

We conducted a detailed study of the morphology of diamond crystals partially dissolved in a water-bearing kimberlite melt at pressure of 6.3 GPa, temperature of 1400 °C, and two oxygen fugacities (fO2) corresponding to the Re-ReO2 buffer and near the magnetite–hematite (MH) buffer. The triangular etch pits on the {111} faces, which formed during experimental diamond dissolution, were found to completely correspond to negative trigons on natural diamond crystals in the shape and sidewalls inclination angle. Furthermore, two experimental fO2 values were associated with two relief types of the rounded tetrahexahedroid surfaces typical of natural rounded diamonds. Therefore, the surface microrelief on rounded natural diamond crystals was concluded to be an indicator of the redox conditions of natural diamond resorption.

Effect of sulfur on diamond growth and morphology in metal–carbon systems

Sulfur additives inhibit diamond crystallization in the Fe–Ni–C system at 6 GPa and 1400 °C and affect the diamond crystal morphology and nitrogen impurity content.

Effect of Rare-Earth Element Oxides on Diamond Crystallization in Mg-Based Systems

Diamond crystallization in Mg-R2O3-C systems (R = Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb) was studied at 7.8 GPa and 1800 °C. It was found that rare-earth oxide additives in an amount of 10 wt % did not significantly affect both the degree of graphite-to-diamond conversion and crystal morphology relative to the Mg-C system. The effect of higher amounts of rare-earth oxide additives on diamond crystallization was studied for a Mg-Sm2O3-C system with a Sm2O3 content varied from 0 to 50 wt %. It was established that with an increase in the Sm2O3 content in the growth system, the degree of graphite-to-diamond conversion decreased from 80% at 10% Sm2O3 to 0% at 40% Sm2O3. At high Sm2O3 contents (40 and 50 wt %), instead of diamond, mass crystallization of metastable graphite was established. The observed changes in the degree of the graphite-to-diamond conversion, the changeover of diamond crystallization to the crystallization of metastable graphite, and the changes in diamond crystal morphology with increasing the Sm2O3 content attested the inhibiting effect of rare-earth oxides on diamond crystallization processes in the Mg-Sm-O-C system. The crystallized diamonds were studied by a suite of optical spectroscopy techniques, and the major characteristics of their defect and impurity structures were revealed. For diamond crystals produced with 10 wt % and 20 wt % Sm2O3 additives, a specific photoluminescence signal comprising four groups of lines centered at approximately 580, 620, 670, and 725 nm was detected, which was tentatively assigned to emission characteristic of Sm3+ ions.

Influence of a silicon impurity on growth of diamond crystals in the Mg-C system

This article reports a study of the morphology of diamond crystals grown at 7.0 GPa and 1800 °C in the Mg-C system with the addition of silicon in an amount of 0.5 wt%. Step patterns on {111} and {100} faces were studied in a wide range of magnifications using optical microscopy (DIC), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Morphological studies revealed that a reduction in the growth rate and a change in the morphological significance of the {100} and {111} faces were associated with adsorption of a mobile impurity (silicon) leading to poisoning of kinks and (or) steps. This leads to roughing of the faces and formation of macrosteps as well as 2D and 3D nucleation islands. At a silicon concentration of 1.0 wt% or more, immobile impurity particles are apparently formed on macrostep terraces, and growth inhibition occurs according to the Cabrera-Vermilyea model.

Effects of catalyst height on diamond crystal morphology under high pressure and high temperature**Project supported by the National Natural Science Foundation of China (Grant No. 51172089), the Program for New Century Excellent Talents in University, the Natural Science Foundation of Guizhou Provincial Education Department (Grant No. KY[2013]183), and the Collaborative Fund of Science and Technology Office of Guizhou Province, China

The effect of the catalyst height on the morphology of diamond crystal is investigated by means of temperature gradient growth (TGG) under high pressure and high temperature (HPHT) conditions with using a Ni-based catalyst in this article. The experimental results show that the morphology of diamond changes from an octahedral shape to a cub-octahedral shape as the catalyst height rises. Moreover, the finite element method (FEM) is used to simulate the temperature field of the melted catalyst/solvent. The results show that the temperature at the location of the seed diamond continues to decrease with the increase of catalyst height, which is conducive to changing the morphology of diamond. This work provides a new way to change the diamond crystal morphology.

Morphology of diamond crystals grown in magnesium-based systems at high temperatures and high pressures

A series of experiments on diamond growth in the Mg45Cu55–C, Mg50Ni50–C, Mg50Cu25Ni25–C, Mg50Ag25Ni25–C and Mg25Cu25Ni50–C systems at a pressure of 6.3GPa in the temperature range of 1550–1650°C was conducted. The morphology of diamond crystals and the features of their growth were studied. The {111} and {100} faces, with the cube faces playing the dominant role, were found to be the plane-faced forms of diamond crystal growth. If the magnesium content in the system is 45−50at%, crystal growth occurs in the regime of inhibition of the {100} faces with the formation of antiskeletal crystals. In case of a constant intensity of the face inhibition up to its complete growing out, the quasi-faces of trapezohedron {311} are formed with striations in the [110] direction. The inhibition of face growth and formation of antiskeletal crystals are related to oxygen inflow from the cell parts and are accompanied by crystallization of magnesium oxide on the diamond surface. A reduction in the magnesium content in the system from 50 to 25at% or an increase in the temperature leads to the cessation of {100} face inhibition and promotes growth of plane-faced crystals.

Evolution of diamond resorption in a silicic aqueous fluid at 1–3 GPa: Application to kimberlite emplacement and mantle metasomatism

Natural diamonds grow and partially dissolve during mantle metasomatism and undergo further resorption during the ascent to the Earth's surface in kimberlite magmas. This study uses atomic force microscopy (AFM) for quantitative characterization of diamond resorption morphology in order to provide robust constraints of the composition of kimberlitic and mantle metasomatic fluids. We performed experiments in a piston–cylinder apparatus at pressures (P) of 1–3GPa and temperatures (T) of 1150–1400°C to examine the impact of P, T, and silica content of an aqueous fluid on diamond dissolution. Petrographic observation and microthermometry of synthetic fluid inclusions trapped in olivine at the run conditions provide constraints on the composition and density of the fluid reacting with the diamond. Our results confirm an inverse relationship between P and T on diamond dissolution kinetics. A P increase of 1GPa suppresses diamond oxidation rates by the same value as a T decrease by ~50°C, while the transformation rate of diamond crystal morphology from octahedron to tetrahexahedron increases with both P and T. All dissolved diamonds develop glossy surfaces, ditrigonal {111} faces, sheaf striations, and negative trigons, while circular pits only occur in aqueous fluids with low silica content (≤4.2mol/kg) at 1GPa. We identify five distinct morphological groups of trigons: two types of point-bottomed (p/b) (trumpet- and V-shaped) and three types of flat-bottomed (f/b) (trumpet-shaped, trapezoid-shaped and rounded). AFM measurements of trigons from two successive runs showed three stages of their evolution. Etch pits nucleate at defects as trumpet p/b trigons with the vertical dissolution rate (Vd) faster than the dissolution rates at the surface free of defects; they further develop by growth of the bottoms in (111) plane to create trumpet-shaped f/b trigons accompanied by decrease in Vd; and finally form trapezoid-shaped f/b trigon with constant wall angles. The diameter of f/b trigons developed in the aqueous fluids depends on the diamond weight loss and dissolution kinetics, and does not correlate with their depth. Integration of our AFM data with the theoretical model for trigon formation suggests that the change from point- to flat-bottomed trigons depends on the defect sizes and dissolution conditions. Application of our results to the diamonds from Ekati diamond Mine, Canada, suggests that variations in diamond rounding in different pipes implies variable depth of fluid exsolution; presence of circular pits on diamonds indicates predominantly aqueous fluid during the latest stages of kimberlite emplacement; and comparison to the mantle-derived morphologies on Ekati diamonds implies the importance of CO2-rich fluids and/or carbonate melts during mantle metasomatism. The constrained effect of P on diamond dissolution kinetics indicates that appreciable diamond weight loss can only happen at P<1GPa and therefore the conditions at the latest stages of kimberlite emplacement are very important for assessments of diamond preservation in a kimberlite pipe.

Effect of temperature on the (100) surface features of type Ib and type IIa large single crystal diamonds

In this paper, by choosing FeNiMnCo alloy as a catalyst and the (100) face of a seed crystal as the growth face, high quality type Ib and type IIa large diamond single crystals (diameter about 3-4 mm) can be successfully synthesized using temperature gradient method, at 5.6 GPa pressure and different temperatures between 1250-1340 ℃. To control the diamond crystal morphology, the growth temperature should be adjusted. Then the morphology of the synthesized large diamonds is plate-like at low temperatures, tower-like at medium temperatures, and spire tower-like at high temperatures. For the same crystal morphology, the synthetic temperature of type IIa diamond single crystals is about 30 ℃ higher than that of type Ib. The central and angularity regions of the top (100) surface, for the synthesized samples of type Ib and type IIa large diamond single crystals at different temperatures, are examined by laser Raman microscope respectively. It is found that the black lines of the type Ib and type IIa large diamond single crystals become dimmed and dense on the same top surface from center to the edge. It is indicated that the priority growth mechanism is in the angularity regions, compared with the central regions. Namely the solute of carbon is primarily precipitated in the angularity regions of the (100) surface. With increasing synthesis temperature, the black lines on the top surface (100) of type Ib diamond single crystals become gradually denser, and the characteristics of the lines are transformed from irregular distribution to typical dendritic distribution. The reason of the above results is that the rate of carbon deposition (the growth rate of diamond crystal), which is along the direction of the diamond crystal [100], will gradually rise as the synthesis temperature of the crystal is increased. The characteristics of the lines on the top surfaces (100) of type IIa large diamond single crystals, which are synthesized under different temperatures, are similar to that of type Ib. However, the lines on the top (100) surface of type IIa diamonds are not so obvious and denser than that of type Ib diamonds at different synthesis temperatures. Similar characteristics of lines on the top (100) surface of both types of diamond single crystals can be explained by the axis and radial growth rate variation at different temperatures. These different characteristics of the lines are due to the fact that the growth rate of type IIa diamonds is slower than that of type Ib diamonds, and the nitrogen concentrations in type IIa diamonds are lower than those of type Ib diamonds. Finally, the full width at half maximum (5.554 cm-1) of the tower-like type IIa diamond is narrower than that (5.842 cm-1) of tower-like type Ib diamond from the test of Raman spectra. It is shown that the quality of type IIa diamond single crystals is better than that of type Ib.

In-situ Incorporation of Lithium and Nitrogen into CVD Diamond Thin Films

ABSTRACTExperiments were performed to incorporate Li and N simultaneously into the diamond lattice during hot-filament chemical vapour deposition in an attempt to produce n-type semiconducting diamond with useful electronic characteristics. Microcrystalline diamond films were grown using a mixture of methane/ammonia/hydrogen gases with tantalum as the filament. The Li was added by placing crystals of lithium nitride (Li3N) on the substrate and allowing them to melt and then slowly diffuse into the film. SIMS depth profiles showed that this process produced high levels of Li and N (0.05% - 0.5%) situated in the same region within the diamond film. The crystallinity and morphology of diamond crystals produced were confirmed using laser Raman spectrometry and scanning electron microscopy.

Identification of etch‐pit crystallographic faces induced on diamond surface by H2/O2 etching plasma treatment

AbstractEven for samples exhibiting excellent electronic properties in terms of carrier mobility, sample‐to‐sample variability remains considerable and dislocation density is still very high, the latter characteristic being often related to damages induced either by the substrate polishing step or by substrate bulk dislocations. In order to limit the polishing effect, a pre‐treatment based on H2/O2 plasma etching under relatively high pressure (a few 100 mbar) has been routinely used for several years. Nevertheless, those bulk dislocations present in the substrate that reach its surface lead to square etch‐pit formation which depth can grow to several 100 nm, preventing the growth of smooth and flat thin films (&lt;few µm). In order to overcome this limitation, we have focused our work on the identification of the crystallographic faces constitutive of the etch‐pits. Starting from a geometrical model describing the diamond crystal morphology evolution, and by carefully choosing the initial growth conditions, we show that it is possible to fill the etch‐pits rapidly and thus to recover the H2/O2 plasma pre‐treatment advantages, even for thin film deposition with smooth surface.

Diamond Crystallization from a Sulfur−Carbon System at HPHT Conditions

In this paper, we report on diamond synthesis in the sulfur−carbon (S−C) system at temperatures in the range of 1550−2000 °C and pressures of 6.3−7.5 GPa. It is established that crystallization of carbon phases (diamond and graphite), the degree of the graphite-to-diamond conversion, and diamond crystal morphology are primarily determined by the pressure−temperature (P−T) conditions. It is suggested that the most probable medium of diamond crystallization in the S−C system is the melting of carbon disulfide CS2. Fourier transform infrared (FTIR) microspectroscopy revealed that synthesized diamond crystals contained nitrogen impurity in the form of A and C defects with a total nitrogen concentration up to 1500 ppm. For the crystals with high nitrogen content, hydrogen-related centers are typically observed. Addition of water to the S−C system results in a decrease in the diamond synthesis temperature and a change in diamond crystal morphology from cuboctahedron to octahedron.

Diamond Formation in UHP Dolomite Marbles and Garnet-Pyroxene Rocks of the Kokchetav Massif, Northern Kazakhstan: Natural and Experimental Evidence

Based upon detailed studies of diamondiferous metamorphic rocks, many authors share the opinion that diamonds crystallize in the field of their thermodynamic stability. Nevertheless, some problems remain, and the most important questions are as follows: (1) What is the pressure under which diamond crystallized? (2) Does the composition of diamondiferous rocks correspond to the medium of diamond crystallization? (3) Why are microdiamonds irregularly distributed in dolomite marbles and garnet-pyroxene rocks? (4) What is the role of carbonates in diamond genesis? To answer these questions, we carried out petrographic and mineralogical studies and experimentally modeled the process of microdiamond crystallization in diamondiferous garnet-pyroxene rocks and dolomite marbles. Diamondiferous marbles and garnet-pyroxene rocks occur as layers and lenses in biotite gneisses of the Kumdy-Kol microdiamond deposit, northern Kazakhstan. Mineralogical and petrographical data demonstrate that pyroxene of diamondiferous rocks differs in composition from pyroxene of nondiamondiferous rocks. The pyroxene in diamondiferous garnet-pyroxene rocks and dolomite marbles is characterized by the presence of potassium and by occurrences of lamellae of K-feldspar and phengite as well as quartz needles. No potassium is found in the pyroxene from associated nondiamondiferous rocks. Starting materials in experiments were diamondiferous marble and garnet-pyroxene rock. Experiments were carried out at P = 5.7 GPa and T = 1420° C, and at P = 7.0 GPa and 1700° C using a multi-anvil apparatus with a 300 mm outer diameter of the multi-anvil sphere. The following conclusions can be inferred from the data obtained. Unlike pyroxene in the starting specimens, the newly formed pyroxene is K-depleted, which indicates that the rocks used in the experiments differ in composition from the natural medium of diamond crystallization. The garnets synthesized in experiments with dolomite marble contain up to 4% majorite component, whereas the garnet from the initial rock contains no majorite. These data clearly show that the pressure under which dolomite marbles formed did not exceed 50 kbar. The experimental diamonds are all octahedra, whereas the diamonds in the starting samples were cubes. We believe that the main factor governing the morphology of diamond crystals is the composition of the medium of crystallization. The obtained data suggest that in dolomite marbles and garnet-pyroxene rocks, diamond crystallized from a carbonatite melt in equilibrium with a K-rich fluid.

The growth and morphology of diamond crystals

The growth and morphology of diamond crystals

On the real crystal octahedra.

A real crystal octahedron is defined as any polyhedron bounded, at least, by some of four pairs of parallel planes being in a standard crystallographic orientation with arbitrary distances between them. All the combinatorially non-equivalent shapes (30 in total) are found and characterized by 2-subordination symbols, automorphism group orders and symmetry point groups. The results are discussed with respect to the diamond crystal morphology.

Compositional mapping of the argon–methane–hydrogen system for polycrystalline to nanocrystalline diamond film growth in a hot-filament chemical vapor deposition system

The transition in diamond crystal morphology from well-faceted microcrystalline to nanocrystalline phases as a function of increasing argon (Ar) concentration has been studied in a hot-filament chemical vapor deposition (HFCVD) system. The range of Ar concentration in a Ar–methane–hydrogen mixture that permits well-faceted diamond growth is up to 90%. At a concentration of 95.5%, a marked transition into nanocrystalline diamond phase could be observed. Although no graphitic phases were observed by transmission electron microscope and x-ray diffraction up to 95.5% Ar concentration, Raman analyses revealed a proportionate increase in amorphous carbon content with an increase in Ar concentration. The addition of Ar appears to create an electron-rich gas environment because a plasma can be readily discharged by applying a bias to the sample. Analysis of the plasma by optical emission spectroscopy revealed a linear correlation between Ar addition and the occurrence of C2 dimers in the plasma. Our results identified the narrow Ar-methane-hydrogen composition window that is effective for the growth of thick and smooth nanocrystalline diamond in HFCVD.

Diamond synthesis with a DC plasma jet: control of the substrate temperature

Abstract A substrate cooling assembly has been developed for an independent temperature control, which takes advantage of vaporization heat of water: the water is atomized by compressed air and the droplets vaporize at the back side of the substrate holder. It is reported that it is possible to change the substrate temperature by varying the aerosol water flow rate, which corresponds to altering the cooling power. Consequently, the influence of the substrate temperature on the morphology of diamond crystals can be investigated without affecting the other parameters, especially the distance between the plasma torch and the substrate. Diamond deposition was carried out on silicon substrates placed in a vacuum chamber. The diamond films were analyzed by scanning electron microscopy for morphology.

The diamond growth from Li2CO3, Na2CO3, K2CO3 and Cs2CO3 solvent-catalysts at P=7 GPa and T=1700–1750°C

Abstract In the series of experiments at P =7 GPa and T =1700–1750°C with their duration from 10 min to 18.5 h the processes of diamond spontaneous nucleation and growth on a seeds in the systems Li 2 CO 3 –C, Na 2 CO 3 –C, K 2 CO 3 –C and Cs 2 CO 3 –C were studied using the ‘split-sphere’ type of apparatus (BARS). Diamond formation in such conditions requires more time than in metal–graphite systems. The essential dependence of diamond morphology and nucleation peculiarities on the composition of crystallization medium was established. It is shown that the catalytic activity of alkaline carbonates is determined by the sequence Li 2 CO 3 ≫Na 2 CO 3 >K 2 CO 3 >Cs 2 CO 3 , while the morphology of diamond crystals, synthesized in the carbonates of the sequence, changes regularly from cuboctahedron to octahedron. The maximum size of synthesized crystals reaches 600–700 μm, while the maximum layer, grown on a seed is 400–500 μm. The rate of synthesis reaction and the number of diamond nuclei decrease regularly with the increase of cation radius in the sequence Li + →Na + →K + →Cs + , while the duration of the synthesis inductive period increases simultaneously.

Oxy-acetylene flame chemical vapour deposition of diamond films. Part I: the influence of deposition parameters on diamond morphology

In this work we present an extended characterisation of polycrystalline diamond films grown by the acetylene flame chemical vapour deposition (CVD) method. In the first part, scanning electron microscopy (SEM) is used to study the influence of process parameters on diamond crystal morphology. In the second part, various surface analysis techniques are used to study the effects of process parameters on diamond composition and their relation to morphology. Process parameters, such as the substrate temperature and molar ratio between oxygen and acetylene, are seen to have a great influence on the morphology of the films. With an appropriate choice of parameters it is possible to obtain areas of polycrystalline diamond films with good crystallinity and homogeneous crystal size, which could permit the use of flame CVD as a suitable diamond deposition technique for small area applications.