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Metallic inclusions and graphite-bearing fractures in diamond

Smith et al., 2016 - Photo Credit: Evan Smith

Laboratories and Instrumentation

Fourier-Transform Infrared Spectroscopy (FTIR)

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Department of Geosciences, University of Padova

The ThermoFischer Nicolet Ni10 FTIR spectrometer at the University of Padova (above). An FTIR map of a diamond showing the distribution of A-centers (N2 defects) (right).

By using FTIR spectroscopy, we can measure the amount, and at what frequency, infrared light that is absorbed by different functional groups in the sample. For example, absorption due to C-C bonds in diamond give rise to the intrinsic diamond absorption pattern at approximately 2600 - 1600 cm-1. FTIR is also capable of detecting vacancies and impurities in diamond such and N, B and H and gives us information about how such impurities are configured to form defects in the crystal structure of diamond. For example, the 3107 cm-1 peak (as seen in the type IaA and IaB spectra to the left) is due to H impurities, specifically C-H stretching associated with the VN3H defect which involves a vacancy, three N atoms and a H atom.  

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Elemental Analyzer - Isotope Ratio Mass Spectrometer (EA-IRMS) 

EA-IRMS Padova

Department of Geosciences, University of Padova

Using this EA - IRMS system, precise elemental and isotopic measurements of highly refractory minerals, such as diamond, can be made. This is done by first pyrolyzing the diamond to produce a sample-derived gas which is then analyzed to evaluate the isotopic composition of various stable isotopes, such as hydrogen.

By better understanding the H, N and C isotopic composition of different types of diamonds we can further constrain the composition and source of diamond forming media. Moreover, evaluating the isotopic variability within individual diamonds and/or across growth zones may lead to important realizations about the different mechanisms related to diamond nucleation and growth.

The Thermo Scientific EA Isolink Delta Q  Isotope Ratio Mass Spectrometer system located at the University of Padova, Department of Geosciences.

Micro-Raman Spectroscopy

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Micro-Raman spectroscopy is used to study the vibrational modes and structural properties of materials. A sample is illuminated with laser light which is scattered through interaction with different functional groups in the sample. By measuring the frequency and intensity of the scattered light we can determine the composition and structure of the sample material. Raman spectroscopy can be used to identify different mineral inclusions in diamond which have implications for the conditions and mechanisms of diamond genesis and growth.

Department of Geosciences, University of Padova

The Witec alpha 300R Raman Spectrometer + Zeiss microscope attachment located at the University of Padova, Department of Geosciences.

Single Crystal X-Ray Diffraction (SCXRD)

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Department of Geosciences, University of Padova

SCXRD works by bombarding a single crystal with X-rays and measuring the pattern of diffracted beams to determine the three-dimensional arrangement of atoms in the crystal lattice and the precise positions of individual atoms (a set of xyz atom coordinates). We will use SCXRD to collect crystallographic data (e.g. unit cell parameters) of mineral inclusions in diamond. Such data allows one to use the methods of elastic geobarometry to calculate approximate temperatures, pressures and depths of diamond formation. Analysis of the crystallographic orientation of mineral inclusions determined by SCXRD, allows one to make inferences regarding the timing of diamond formation with respect to mineral inclusions, e.g. did the inclusion minerals form before, during, or after the host diamond? 

The Rigaku-Oxford single crystal diffractometer equipped with a micro X-ray source and no-noise detector 200 K Pilatus (Dectris) capable of analyzing mineral inclusions 30-40 microns in size. Located at the University of Padova, Department of Geosciences.

SEM - Cathodoluminescence (CL)

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CL analyses of crystals involves directing a beam of high-energy electrons onto the surface of the crystal, causing it to emit light. By analyzing the spectral and spatial characteristics of the emitted light, information about the crystal's composition, defects, and structure can be obtained with high spatial resolution. CL can be performed to assess diamond growth zones and to assist in locating SIMS analysis spots within specific growth zones.

The TESCAN S9000G GMU FEG-FIB scanning electron microscope (Oxford Instruments) equipped with a panchromatic cathodoluminescence (CL) detector and EDX, WDS, EBSD, and a FIB, located at the University of Padova, Department of Geosciences.

Department of Geosciences, University of Padova

Diamond Polishing Bench

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Department of Geosciences, University of Padova

Using our custom-built diamond polishing bench, we are able to doubly-flat polish diamonds with a wide range of sizes (cm to micron) and morphologies (e.g. octahedral, cuboid, irregular fragments, etc.) for analysis. The bench is equipped with both diamond-impregnated and plain steel scaifes (polishing wheels) and allows for a jewelry-grade surface polish if needed. Diamonds are mounted in "pots" which are then fastened to a "tang" to allow the polishing angle and pressure to be controlled by the user. Diamonds should be polished along the "soft direction" i.e. on the (110) face, where the atomic density is relatively less. Therefore, careful examination of the morphology of each diamond is required prior to polishing to ensure the sciafe is not damaged. 

The diamond polishing bench with central scaife (polishing wheel), stationary and motorized tang stages, RPM controller, and dust extraction unit.

Our post-doc Maxwell Day doubly-flat polishing a  0.5mm diamond fragment for FTIR analysis.

Videographer: Davide Novella

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