Natural Diamond Crystals Research Articles

Study of Structural Imperfections in Natural Type I Diamonds by High-Resolution X-ray Diffraction Techniques

Results of characterization of defects in natural diamond crystals by high-resolution X-ray diffractometry, absolute integrated intensity (ρ) measurements, topography and diffuse X-ray scattering (DXS) techniques are reported. The samples are 〈111〉 natural diamond platelets of dimensions ~2 × 2 mm with thickness in the range ~0.5–1 mm. A five-crystal X-ray diffractometer in three-crystal configuration as well as a four-crystal diffractometer were employed with Mo Kα1 as the exploring radiation. Infrared absorption measurements showed that the samples belong to type Ia variety and contained varying concentrations of A and B forms of nitrogen aggregates as well as platelets. There were large variations in the values of diffraction curve half-widths (18 to 550′′) and values of ρ (2.4 × 10−5–76 × 10−5 rad) for 111 reflection, showing a wide variation in crystalline perfection. Projection and composite stationary X-ray topographs recorded with different diffraction vectors showed the presence of defects like low-angle boundaries. From the analysis of the observed distribution of diffuse X-ray scattering (DXS), point defect clusters were characterized. The clusters were of interstitial as well as vacancy type. The sizes of the defect clusters (Rcl) were determined to be in the range 40 to 190 nm and the volumes of the defect clusters (Acl) were in the range ~1 × 10−25–28 × 10−25 m3. The defect clusters with sizes reported here could be investigated as the measurements were made close to the reciprocal-lattice points. The platelet size was found to vary inversely with the total concentration of nitrogen.

Ceramics Cutting by Self-Sharpening Edge Technique of Single Crystal Diamond.

Alumina-ceramic materials, with these characteristic heat resistant, anti-wear and anti-corro-sive properties, are used for structural components for automotive, spacecraft and aircraft. These materials are highly brittle, super hard and difficult to be machined. Therefore, the cost of machining alumina-ceramic materials is considerably higher than that of metals. As a result a new cutting method has been developed to achieve lower cost processing of the alumina-ceramic materials. In this cutting process, unfinished natural single crystal octahedral diamond corners can be successfully used as a tool to cut ceramics, when cutting with the sharp edge of diamond corners, it is flattened due to abrasion. The flattened diamond tip is repositioned and the newly formed sharp edge is used to cut again. By repeating the repositioning of the diamond tip, natural diamond crystals can be used tool cut alumina ceramics for a longer period of time.

Auger spectroscopy of hydrogenated diamond surfaces

An energy shift and a change of the line shape of the carbon core-valence-valence Auger spectra are observed for diamond surfaces after their exposure to an electron beam, or annealing at temperatures higher then 950 \ifmmode^\circ\else\textdegree\fi{}C. The effect is studied for both natural diamond crystals and chemical-vapor-deposited diamond films. A theoretical model is proposed for Auger spectra of hydrogenated diamond surfaces. The observed changes of the carbon Auger line shape are shown to be related to the redistribution of the valence-band local density of states caused by the hydrogen desorption from the surface. One-electron calculation of Auger spectra of diamond surfaces with various hydrogen coverages are presented. They are based on self-consistent wave functions and matrix elements calculated in the framework of the local-density approximation and the self-consistent linear muffin-tin orbital method with static core-hole effects taken into account. The major features of experimental spectra are explained.

Boron diffusion into diamond under electric bias

Three natural type IIa diamond crystals were used for forced diffusion of boron. The diffusion was performed under bias otherwise with the same conditions. The boron diffusion coefficient in diamond was found to be 8.4 × 10−15 and 4 × 10−14 cm2/s at 1000 °C, depending on the direction of the electric field. The drift velocity of boron in diamond under 850 V at 1000 °C was found to be about 1.2 × 10−8 cm/s.

Radiation response of p-i-p diodes on diamond substrates of various type: electrical properties of semiconductor-insulator homojunctions

Double-junction p-i-p diodes are fabricated on natural and synthetic diamond crystals and polycrystalline CVD diamond films and subjected to /spl gamma/, e/sup -/ and neutron exposure. Parameters of the radiation induced defects (concentration and energy distribution of donor-like traps) are evaluated from the experimental I-V curves using a technique which is based on a model of thermionic injection of holes into the insulating diamond over p-i potential barrier. The evaluated parameters of the traps are used for 2-D numerical simulation of radiation effects on diamond based p-i(SiO/sub 2/)-p solid state triode.

High-resolution diffuse X-ray scattering study of point defect clusters in natural diamond crystals

High-resolution diffuse X-ray scattering study of point defect clusters in natural diamond crystals

Study of loss in absorption of X-rays in thin natural diamond crystals around Laue diffraction maxima

Study of loss in absorption of X-rays in thin natural diamond crystals around Laue diffraction maxima

Electrical properties of lithium-implanted layers on synthetic diamond

Lithium implantation (40 and 50 keV; doses of 2 × 10 16 and 4 × 10 16 cm −2) has been performed in several synthetic and natural diamond crystals at room temperature (RT) and 850–900 °C (high temperature (HT) implantation). In contrast with the case of the RT implantation, the HT implantation did not result in radiation-induced surface graphitization. The samples implanted at RT and 850 °C were subsequently annealed at 900 °C. Comparison of the electrical properties of the doped crystals shows the dependence of the electrical activation on the annealing temperature. Thermal emf measurements have established that the conductivity is n-type.

Channeling radiation of electrons in natural diamond crystals and their coherence and occupation lengths.

Measurements have been performed at the superconducting Darmstadt electron linear accelerator (S-DALINAC) to investigate systematically channeling radiation produced by bombarding natural diamond crystals with thicknesses of 13, 20, 30, and 55 \ensuremath{\mu}m with electrons at 5.2 and 9.0 MeV. Planar channeling from the (110) and (111) planes was studied for a variety of transitions with respect to their energy, intensity, and linewidth. Axial channeling from the $〈110〉$ axis could be detected as well. It was found that the intensity increases as a function of the crystal thickness, and values up to 7.7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}2}$ photons/esr could be obtained, which is the highest intensity at low electron energies achieved so far. The intensity increases with electron energy as ${\ensuremath{\gamma}}^{\frac{5}{2}}$. The $\frac{1}{e}$ occupation length deduced from the photon yield as a function of the crystal thickness was found to be ${l}_{\mathrm{occ}}\ensuremath{\approx}29 \mathrm{and} 85$ \ensuremath{\mu}m for planar and for axial channeling, respectively. These values are by far the largest ever observed. Comparison with a quantum mechanical theory of channeling radiation exhibits fairly good agreement for the intensity and linewidth provided that contributions caused by electronic scattering and Bloch wave broadening, which actually are largest for diamond, are properly taken into account. It turns out that multiple scattering dominates in the planar case and single scattering for the axial channeling. The coherence length could be deduced to be of the order of 0.7 \ensuremath{\mu}m, which is about a factor of 2 larger than observed before in silicon.

Polycrystalline diamond photoconductive device with high UV-visible discrimination

Planar metal–diamond–metal photoconductive devices have been fabricated from free standing large grain (20–30 μm) polycrystalline thin film diamond. An interdigitated electrode design with spacings of 20 μm was used to produce effective UV photodetecting devices at bias values in the range 0.1–10 V. A methane-air treatment has been used to modify the structures such that unprecedented performance characteristics have been recorded (106 higher response to 200 nm than visible wavelengths, <0.1 nA dark currents); spectral features similar to those observed in natural diamond crystals have been observed indicating that the treatment used led to near ideal electronic characteristics from polycrystalline material.

Direct observation of forward diffracted beam from imperfect and thin natural diamond crystals

A diffracted beam in the forward direction has been directly observed in imperfect (diffraction curve half widths: ∼ 100″ -2- ∼ 300″) and thin (μt sec θ: ∼ 0.1 – ∼ 0.3) type II natural diamond crystals. A five crystal X-ray diffractometer was employed in (+,−,+) setting. The intensity of the forward diffracted beam decreased with the degree of imperfection. However, diffraction curve half width of ∼ 300″ is nearly the limit for observation.

The Effect of Temperature on the Deformation of Diamond Surfaces

ABSTRACTA brief review is given of recently published work on the fracture and plastic flow of natural and synthetic diamond crystals when deformed by softer impressors at elevated temperatures. Under these conditions, a brittle-ductile transition (BDT) temperature for the different types of diamond has been established.In this paper we show that below the BDT temperature, brittle ‘chatter’ cracking on {111} cleavage planes accounts for anisotropic wear provided that the mean contact pressure exceeds about 10 GPa. Above the BDT temperature, titanium diboride sliders develop contact pressures sufficient to cause extensive plastic deformation of the diamond specimens but insufficient to produce cleavage fracture. However, repeated sliding with TiB2 does lead to cumulative plastic flow preceding fatigue type fracture on {110} planes. Using cubic boron nitride and diamond sliders above the BD T temperature leads to a combination of both plastic deformation and {110} cracking. The coefficient offriction is a maximum in <100> and a minimum in <110> directions. and the measured scratch hardness, which confirms that the <100> directions are softer than <110>, is shown to be consistent with the predictions of a resolved shear stress model which was de velopedffor explaining anisotropy in all crystals.

Electrical conductivity of combustion flame synthesized diamond

The electrical conductivity, from room temperature to 1000 °C, of combustion flame synthesized diamond films and free-standing diamond slabs are demonstrated to be up to two orders of magnitude lower than that of type IIa natural diamond crystals. The low conductivity, indicative of high purity, has been achieved at diamond growths rates of 5–10 μm/h, considerably higher than that achievable with other diamond synthesis techniques. These high growth rates have been achieved over areas of 5 cm×5 cm and both thin (10 μm) films on silicon substrates and thick (∼80 μm), free-standing diamond slabs exhibit similar electrical behavior. The high purity of this diamond is attributed to the presence of oxidizing species in the flame ambient which are more effective than hydrogen in removing any nondiamond forms of carbon and other impurities from the growing diamond film.

Characterization of diamond single-crystal substrates and homoepitaxial films

We have continued to investigate different diamond single crystal substrates to assess their suitability for the growth of homoepitaxial diamond. Surface topography and defect microstructure of the resulting films are two important qualifiers for the choice of a suitable substrate. Previously developed methods to prepare plan-view TEM samples from bulk diamond substrates and homoepitaxial films have been employed. This contribution describes some of our most recent observations of the surfaces andmicrostructure of natural and synthetic diamond single crystals and homoepitaxial diamond thin films using SEM and TEM - including spatially resolved cathodoluminescence (CL) results.Figs. 1 and 2 show TEM micrographs taken from a (100) natural type Ila diamond crystal and a (100) synthetic type lb diamond that have been ion milled to electron transparency. The mottled background contrast observed in both images which has been observed previously and is believed to result from the extended ion milling used to produce these thin foils.

Direct observation of diffracted X-ray beam in the forward direction from thin and imperfect natural diamond crystals

Direct observation of diffracted X-ray beam in the forward direction from thin and imperfect natural diamond crystals

Study of crystal defects in natural diamond

To study the crystal defects in diamonds, a specimen of natural diamond crystals selected from northeast China was tested by means of Lang X-ray topography and double-crystal X-ray topography. As a result, several types of crystal defect, such as twin boundaries, dislocations, growth bands and substructures existing in the specimen were found. The morphologies of the twin boundaries have been analysed and a detailed discussion of the determination of its characteristic vectors is given. The distribution characteristics of the various crystal defects as well as their relation to the twin boundaries are presented.

Comparison of electronic transport in boron-doped homoepitaxial, polycrystalline, and natural single-crystal diamond

Hall-effect and resistivity measurements were performed on simultaneously deposited B-doped homoepitaxial and polycrystalline diamond films, as well as a (100)-oriented type-IIb natural diamond crystal, over a temperature range of 140–600 K. At 298 K, the respective Hall mobilities for the homoepitaxial and polycrystalline films were 519 and 33 cm2/V s, while the active carrier concentrations were both approximately 2×1014 cm−3. For the natural diamond, a Hall mobility of 564 cm2/V s and a carrier concentration of 2×1013 cm−3 were measured at room temperature. A comparison of the transport behavior of the three specimens indicates that the electronic properties of diamond grown by chemical vapor deposition are potentially of equal or greater quality than natural diamond and that the transport properties of polycrystalline films are severely degraded by the effects of grain boundaries.

Etch-delineation of defects in diamond by exposure to an oxidizing flame

An experimental study of the etching properties of defects in diamond using propane flame exposure in air is presented. Both natural diamond crystals and polycrystalline diamond films were exposed to a flame for an optimum time of 3–4 s. This process topographically delineates defects in diamond via an accelerated etch rate at defect sites. Using transmission electron microscopy (TEM) to determine the exact nature and density of defects present in the diamond, we have found a direct correlation between topographical delineation observed by scanning electron microscopy (SEM) and the defect structure observed by TEM.

High quality homoepitaxial growth of diamond films

High quality diamond films have been grown by hot-filament-assisted and microwave-plasma-assisted chemical vapour deposition on (100) natural diamond crystal for a range of temperatures from about 700 to 1000°C. Pure diamond pyramidal growth structures and crystallites were obtained at high temperatures while smooth transparent films were grown between 750 and 850°C. Both types of film give a low channelling yield with Rutherford backscattering spectroscopy, comparable with single-crystal diamond with no mismatch feature, and no graphite peak by Raman spectroscopy.

X-ray diffraction imaging of man-made and natural diamond

Natural diamond crystals, intended for use as substrates for chemical vapor deposition growth of homoepitaxial diamond films and man-made diamond crystals have been studied by X-ray diffraction imaging (topography) using the National Institute of Standards and Technology materials science X-ray beam line at the National Synchrotron Light Source. An examination of type Ia, type IIa and type IIb natural crystals has shown that, in general, type Ia material is less strained with a better-defined microstructure and with less variation among samples. The type II samples show a large degree of variation in residual strain and a disrupted microstructure resulting from a large number of crystalline imperfections. The high temperature, high pressure process for growth of man-made diamond yields crystals that are almost always superior to commercially available natural material.