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MB-IR

 

This diamond anvil cell can be used in either the infrared studies for probing compositions of materials or in the studies for understanding physical properties under measurable pressure conditions. This instrument, with two brilliant-cut Type IIa anvils each weighing approximately .18 carats with .6 mm culets or pressure bearing surfaces, has superior optical transparency in the UV and IR range than the one with Type Ia anvils.

If pressure-induced effect should be studied, this instrument can generate measurable hydrostatic pressure of 70 kilobars and up (one bar is approximately one atmosphere).

MB-IR Diagram
MB-IR Cell

IR STUDIES

Employed in the FTIR spectrometer or IR microscope, the cell can apply tremendous amounts of pressure to flatten the interest materials, therefore the IR spectra can be obtained. Place the sample on the lower diamond anvil in the plate containing the spindles and then position the top plate, bringing the two halves together. Insert the three Allen cap screws into the top plate and very slowly tighten them with a wrench( No. 10-32) until firm. Observe your sample under magnification for any abnormal situations. Flatten the sample by tightening the screws sequentially in very small increments until the satisfactory thickness of your sample has been achieved.

WARNING - DO NOT APPLY PRESSURE ON THE TWO BARE DIAMOND ANVILS.

The diamond bonded to its mount is in fixed orientation and parallel to the opposite diamond. In spite the instrument has been aligned, routine inspection of the anvils is strongly recommended. The anvils can be cleaned by wiping acetone or alcohol across the working surfaces with a pointed tissue. Do not let the solvent come in contact with the epoxy as it will eventually loosen the bond holding the diamond to its mount. The undersides of the diamond anvils are cleaned by placing a drop of acetone in the aperture and scrubbing with a round toothpick.

The diamond cell can also be attached to a guide plate in the sample compartment of FTIR spectrometer or on the stage of IR microscope.

HIGH PRESSURE STUDIES

A pre-indented gasket is recommended before the hole is drilled. Inconel, a metal foil 0.01" thick, is supplied as gasket materials. Any burrs around the hole should be removed with a rat-tail file or a micro drill bit. The sample, usually a 100 micron die or smaller, with a pressure calibrant and pressure transmitting medium, is loaded and sealed by tightening three Allen cap screws sequentially in very small increments. In order to maintain the alignment and the parallelism of the anvils during the change of the pressure, it is important to monitor the height of the cell. A micrometer then may be used. Be aware that the indented gasket will not remain at the same thickness after altering the pressures. It is also a common phenomenon that the hole will shift around under altered pressure, which may result in the failure of the chamber enclosure if the pressure is not evenly applied to the diamond anvils. Hence, it is always a good idea to re-examine the sample under a microscope each time the pressure has been changed.

The pressure range of this instrument is 70 kilobars and up. One of the techniques for calibrating the pressure is to measure the ruby fluorescence. The pressures can be determined by the frequency shifts of the famous R1 and R2 lines. Using the formula below, one can calibrate the in-situ pressure in diamond anvil cell.

The cell measures 31.5 mm from the base of the triangle to the center of the curvature. The thickness, with the diamonds in place, is 17.5 mm. The steel disc diamond mounts are 12.7 mm in diameter and 3.3 mm thick with cone angle openings underneath. A mounting plate is included with the assembly.

 

 

INSTRUCTIONS

(MB-IR)

The infrared pressure diamond anvil cell can be used in infrared studies for probing composition of materials and in studies for understanding physical properties under measurable pressure conditions.

WARNING: DO NOT APPLY PRESSURE ON THE BARE DIAMOND ANVIL SURFACES.

Store the instrument with a piece of cardboard between the two diamond anvils to prevent abrasions. Anvils should be inspected before and after each use.

GUIDE PLATE ATTACHMENT

The two small non-threaded holes on the face of the lower support (with three spindles) can be used to attach the guide plate in the sample compartment of FTIR spectrometers or on the stage of IR microscopes. The two small threaded holes on the same face are provided for attachments using two #2-56 screws that are not provided.

CLEANING THE ANVILS

The anvils can be cleaned by wiping acetone or alcohol across the working surfaces using tissue paper twisted into a pointed tip. Do not let the solvent come into contact with the epoxy as it will eventually loosen the bond holding the diamond to its mount. The working surfaces can also be cleaned by scraping with a razor blade or with a needle. The undersides of the diamond anvils are cleaned by scrubbing with a round toothpick or placing a drop of acetone into the aperture if necessary.

APPLICATION (I): IR STUDIES>

Failure to follow this procedure may result in damage to the anvils.
  1. Clean the two diamond anvils as instructed above.
  2. Carefully assemble the instrument with fingers. Do not let anvils come in contact with each other. Place instrument on a surface with the triangular plate containing the three spindles facing upward. Place a piece of the sample onto the lower diamond anvil. Then bring the two halves slowly together (refer to Application (III) for liquid samples).
  3. Insert three Allen cap screws into the top plate and slowly turn them with a wrench (No. 10-32) until firm. DO NOT APPLY PRESSURE YET.
  4. Inspect the sample under magnification. Repeat steps 1 through 3 if necessary.
  5. Attach the cell to the guide plate. The guide plate may not be needed if a microscope or a beam condenser is used.
  6. Flatten the sample by tightening the Allen screws sequentially in very small increments of a few degrees per turn. Repeat this step until desired sample thickness is obtained.
  7. Transmit the IR beam through the diamond cell for transmission or absorption measurements.
  8. Disassemble the cell by loosening the screws sequentially in small increments. Store the diamond cell as instructed.

APPLICATION (II): HIGH PRESSURE STUDIES

  1. Clean the two diamond anvils as instructed.
  2. OBSERVING PARALLELISM: Align the red markings and assemble two triangular plates carefully. Insert three Allen cap screws (No. 10-32) into the instrument and turn until firm. Do not apply pressure on anvils yet. Observe the fringe pattern with transmitted white light under magnification. Carefully manipulate the three Allen cap screws until only one light fringe is seen, showing the parallelism of the diamond anvils.
  3. Measure and record the height of the three sides of the instrument with a micrometer for future reference in maintaining parallelism.
  4. Carefully disassemble the instrument.
  5. GASKET PREPARATION: A pre-indented gasket is recommended prior to making the sample chamber hole. Make alignment markings on the gasket and the diamond cell with wax or nail polish for future reference when positioning the gasket. Indent the gasket to half its thickness, then drill a hole as close to the center of the indentation as possible. Remove any rough edges (burrs) around the hole with a rat-tail file or a micro drill bit.
  6. SAMPLE PREPARATION: Cut soft samples into small pieces (e.g. 50 microns die). Harder samples may be polished with fine grit sandpaper and reduced by using a sharpened needle.
  7. LOADING SAMPLE: Support the gasket on the lower anvil with balls of paraffin, noting previous alignment markings.
  8. Level the lower support and load the sample, pressure calibrant (e.g. ruby chips) and pressure transmitting medium (e.g. liquid argon) under magnification. Pressure calibrants such as ruby chips should be distributed evenly around the sample for monitoring hydrostatic pressure conditions. Several attempts may be needed when performing this step. After completing this step, proceed to step 9 immediately.
  9. Assemble the instrument and tighten the three Allen cap screws sequentially in very small increments until a moderate amount of pressure is applied to the gasket. This procedure is needed to ensure the pressure transmitting medium has been successfully loaded.
  10. Observe the chamber hole. Under pressure, the hole will change shape slightly. However, if the hole is significantly deformed, the instrument may have lost the pressure medium. If medium loss is uncertain, apply more pressure by tightening the three Allen screws and observing the sample hole for any changes. Begin the process from step 1 if the pressure medium has been lost. Otherwise, proceed to step 11.
  11. Measure and record the height again as instructed in step 3. The parallelism can be maintained by comparing these measurements with the data obtained earlier in step 3.
  12. PRESSURE CALIBRATION: Ruby fluorescence can be used to calibrate the in-situ pressure. The frequency shifts of the R1 and R2 lines determine the pressure by using the following formula:

    Where Δλ and λ0 are the wavelength (in nm) change under pressure and the wavelength at ambient pressure respectively. Lower case letter b is a parameter, would be 5 or 7.665 corresponds to non-hydrostatic or quasi-hydrostatic pressure respectively. Light sources using an argon ion laser from 488 nm and 514.5 nm lines are commonly used in this technique.
  13. Record the current pressure and begin the experiment.
  14. ALTERING PRESSURE: The pressures can be repeatedly altered by tightening or loosening the three Allen screws. Refer to steps 2, 3, and step 11 for maintaining parallelism. The chamber hole may shift under altered pressures. Turn the Allen cap screw(s) to move the chamber hole toward the opposite direction if the hole is off center to the culet. Notice that turning the screws will change the pressure. Follow this step closely to avoid sample failure.
  15. Calibrate the pressure according to step 12, then continue your experiments.
  16. Disassemble the cell by loosening the screws sequentially in small increments. Store the diamond cell as instructed.

APPLICATION (III): HIGH PRESSURE STUDIES IN THE IR

  1. LIQUID SAMPLES: Clean the diamond anvils as instructed. Choose a non-metal material to make the gasket if pressure is not desired. Avoid the possibility of a chemical reaction between the gasket material and the sample. Proceed directly to step 11.
  2. NON-LIQUID SAMPLES: Clean the diamond anvils as instructed. Preparing the sample for high pressure studies and IR analysis is a critical step. Carefully assemble the instrument with fingers. Do not let anvils come in contact with each other. Place instrument on a surface with the triangular plate containing three spindles facing upward. Place a piece of the sample onto the lower diamond anvil. Then bring the two halves slowly together.
  3. Insert three Allen cap screws into the top plate and slowly turn them with a wrench (No. 10-32) until firm. DO NOT APPLY PRESSURE YET.
  4. Inspect the sample under magnification. Repeat steps 2 through 4 if necessary.
  5. Attach the cell to the guide plate. The guide plate may not be needed if a microscope or a beam condenser is used.
  6. Flatten the sample by turning the three Allen screws sequentially in very small increments of a few degrees per turn. Repeat this step until the desired sample thickness is obtained. Disassemble the instrument and remove the flattened sample from the anvils.
  7. Cut the sample into small pieces (e.g. 50 microns die) from the flattened area by using a sharpened needle. Sandpaper can be used to sharpen the needle.
  8. Store the sample in a safe place for future use.
  9. Clean the diamond anvils again as instructed.
  10. GASKET PREPARATION: A pre-indented gasket is recommended prior to making the sample chamber hole. Make alignment markings on the gasket and the diamond cell with wax or nail polish for future reference when positioning the gasket. Indent the gasket to half its thickness, then drill a hole as close to the center of the indentation as possible. Remove any rough edges (burrs) around the hole with a rat-tail file or a micro drill bit. Note that the gasket may need to be indented and drilled several times to obtain optimal infrared results.
  11. Follow steps 7 through 10 in Application (II) for loading the sample. Follow steps 12 through 15 in Application (II) for calibrating and altering pressure. The crystalline alpha quartz calibrating technique can also be used to calibrate pressure in the infrared and can determine pressure using an FTIR/IR spectrometer. This technique can be found in the following articles:
    1) P.T.T. Wong, F.L. Baudais, and D.J. Moffatt, "Crystalline Quartz as an Internal Pressure Calibrant for High Pressure Infrared Spectroscopy", Applied Spectroscopy, Volume 39, Number 4, Page 733-735, 1985.
    2) P.T.T. Wong, F.L. Baudais, and D.J. Moffatt, "Hydrostatic pressure effects on TO-LO splitting and softening of infrared active phonons in alpha-quartz", Journal of Chemical Physics, 84(2), Page 671-674, 1986.

 

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Last updated: February 04, 2004