Mineralogy and Crystallography
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Stepper Motor Control Software:

Fortran-based software to control stepper motors. Download .

 

Single-crystal Diffractometers: back to top

We have two operating single-crystal diffractometers: one is an automated Picker mostly for high-pressure work, and the other is a Bruker X8 Apex diffractometer equipped with a 4K Apex II CCD detector for general crystallographic studies. Both provide Mo radiation. The Picker was obtained from Charlie Burnham's lab at Harvard in 1997 and has been extensively rebuilt. Automation is accomplished with in-house software, providing the flexibility to attack a problem from any configuration. It operates under Eulerian geometry and uses a point detector preceeded by both a cylindrical and a double-slit collimator.
Installation of software/hardware instructions.
The Bruker X8 was provided to the lab by a private donor with matching funds from the College of Science. It represents Bruker's state-of-the-art small lab diffractometer. It runs under Kappa geometry with a full suite of Bruker software for data analysis.

 

The Orienter: back to top

This is the simple-minded name that we gave to a machine that we built to orient crystals. It is a rebuilt P4 with Kappa geometry that was completely stripped of all electronics and hardware related to diffraction. New motors and controllers were assembled and the machine operates through an in-house Windows dialog box application. The orientation matrix of a sample is obtained on the X8, then the sample is transferred to the Orienter. The user chooses two crystallographic axes that are oriented 90 deg from each other and the crystal is rotated into that orientation. The crystal can then be fixed to any sort of holder. We use titanium pins and orient along the axis of the pin and the perpendicular direction indicated by a fudicial mark on the side of the pin. Image

 

Electron Microprobe: back to top

We use the Cameca SX-50 at the Department of Lunar and Planetary Sciences, managed by Ken Domanik. Link

 

Motor Drivers: back to top

Motors on diffractometers need to be moved. We are working on Windows algorithms for this. Here is some info on using our Single code to run motors for translation devices.

 

Single-crystal Diffractometer Shutter: back to top

We have designed and built a new shutter for a Picker diffractometer. Images and details of the shutter can be examined.

 

Powder Diffractometer: back to top

We have a Bruker D8 Advance using Cu radiation with both a scintillation detector as well as an energy dispersive one to handle fluorescent material. It operates and interfaces with Bruker software and the ICDD database. Image

 

Raman Spectrometers: back to top

We have two Raman spectrometers. They are used to examine the vibrational spectroscopy of minerals, as well as a means to mesure the pressure in diamond anvil cells.
One is an open access instrument built on an optical table by Alex Goncharov and Victor Struzhkin. Image. It uses a tunable 100 mW Ar-ion laser (usually at 514.532 nm) and a Jobin Yvon Spex HR 460 spectometer equipped with a liquid nitrogen cooled Princeton Instruments 1152 x 256 pixel CCD detector. We prefer a 1200 groves mm-1 grating centered at 530.4 nm and collect data with Roper Instruments Winspec/32 software. This instrument is capable of producing good polarized and oriented spectra of minerals. Samples can be oriented onto a goniometer stage and rotated precisely into position and spun at speeds up to 720 degrees per sec. The open access of the geometry of the instrument provides the ability to integrate any research environment with Raman spectroscopy.
The other spectrometer is a Thermo Nikolet Almega microRaman system. Image. It is a fully integrated, black-box type machine with simple-to-use controls and searching software. We modified the sample stage to permit the investigation of thicker samples. It uses an Olympus microscope. The polarization of the laser is mixed. It operates with two choices of wavelength for the lasers, 532 and 785 nm. and the beam intensity can be easily varied.

 

Diamond Anvil Cells: back to top

Single-crystal X-ray diffraction and Raman spectroscopy experiments at high-pressures are conducted with a sample that is inclosed in a four-post diamond anvil cell as illustrated .

 

Gas Loading Apparatus: back to top

We have a machine to load the four-post diamond anvil cells with gas to about 2.5 kbar. The main purpose is to load helium as a pressure medium since it remains quasi-hydrostatic to the highest pressures.

 

Miscellaneous Items: back to top

We have run some Raman measurements on moissanite to compare with diamonds for use in a diamond anvil cell. The images demonstrate that moissanite is not a suitable anvil for Raman experiments at high pressures.

 

 

© 2004 all rights reserved
Contact downs@geo.arizona.edu with any suggestions or corrections

 

The University Of Arizona Department Of Geosciences Mineralogy and Crystallography Professor Robert T Downs