The University of Tennessee, Knoxville

Joint Institute for Advanced Materials


About the Ion Mill

Image reproduced with courtesy of Gatan, Inc.

New technologies and developments in new materials require changes in ion milling techniques to enhance sample quality and high-resolution TEM results. Gatan's Precision Ion Polishing System (PIPS) continues to be an industry standard for TEM sample preparation. To enhance the performance and capabilities of the PIPS, a liquid nitrogen (LN2) cooling system is used.

PIPS instructions

Part 1 Starting Up the PIPS

  1. Turn on the power to the PIPS. Press the upper portion of the main power switch. The diaphragm (DP) and turbomolecular drag pumps (MDP) will start and the digital display on the left side of the front panel will light up. The (amber) DP High indicator will come on and stay on until the backing pressure drops below 12 Torr.
  2. After about 15 minutes, the MDP indicator will light up (green) indicating the MDP has reached 60% running speed. Work chamber pressure appears on the analog meter.
  3. Once the chamber pressure is < 5 x 10^-4 Torr, turn on the gas-valve switches for both guns.
  4. Rotate the gas-flow control knobs CW to the fully closed position, then back them off 3 full turns. This process will purge the guns.
  5. While waiting for the guns to purge, check the following:
    • The specimen mount is in the raised position. Press the upper part of the airlock control switch to raise the specimen mount if it is on the lowered position.
    • The airlock cover is in place and the airlock chamber is evacuated. If the vent LED is illuminated, the airlock is vented. Evacuate the airlock chamber by pressing the VAC button while rotating the airlock cover to make sure the O-ring is well seated.
    • Periodically press the DP Test button to monitor the backing pressure (should be <10 Torr) as the airlock chamber is evacuated. The pressure will be displayed on the Beam Energy digital display (center display).

Part 2 Raising the Specimen Mount/Piston

Specimens are mounted either on a Gatan DuoPost or a single-sided specimen post. The specimen post plugs into a specimen mount located at the top of the Whisperlok piston. The following procedure assumes the piston/specimen mount is in the work chamber.

  1. Raising the specimen Mount/Piston. This will raise the specimen mount/piston into the airlock to allow specimen loading. The piston will not rise immediately but waits for the specimen mount to rotate to its reference or home position. The piston then rises and seals off the work chamber from the airlock chamber.
  2. Vent the airlock chamber by holding down the Vent button. Once vented, the airlock’s cover can be removed and a new specimen post can be inserted or an old one removed. A special pair of angled tweezers is supplied to facilitate this operation.

Part 3 Lowering the Specimen Mount/Piston

  1. Replace the airlock cover.
  2. Press the VAC button. Rotate the airlock cover to be sure the airlock O-ring is properly seated.
  3. Hold down the VAC button and press the DP Test button. Reading the backing pressure on the Beam Energy digital display when the DP button is pressed.
  4. Once the airlock chamber pressure reaches the preset level, the green VAC light will illuminate.
  5. Press the airlock control switch to lower the specimen mount/piston. If the airlock piston will not go down, check the following things:
    • The vent LED must be off. If the Vent LED is On, the airlock is still at atmospheric pressure. Evacuate the airlock.
    • The rotation control is in the On position. At the Off position, the rotate motor is not rotating so the piston will not lower.

Part 4 Rotating Specimens

  1. The specimen can be rotated in a CCW direction by a variable DC motor. The rotation speed can be varied from zero (off) through 6 rpm using the rotation speed control on the front panel. The motor drives a bevel gear mounted to the Whisperlok piston. The gear automatically disengages when the specimen is raised.
  2. Mounted to the bevel gear, as part of the ion beam modulator, is an encoded plate enabling the piston’s rotational angle to be referenced so that the piston rotates to the home position each time the piston is raised.

Part 5 Purging the Ion Guns

  1. HV to the ion guns must be OFF.
  2. Switch OFF the right gas control switch.
  3. Switch ON the left gas control switch. Adjust the left needle valve to raise the chamber pressure to 1x 10^-4 Torr.
  4. Switch OFF the left gas control switch.
  5. Switch ON the right gas control switch. Adjust the right needle valve to raise the chamber pressure to 1x 10^-4 Torr.
  6. Switch on both guns and purge for about 15 minutes. Turn OFF both left and right gas switches and turn ON HV. Confirm maximum beam current of <5 microAmps is obtained for each gun with an accelerating voltage of 5.0 keV.

Part 6 Adjusting Gun Gas Flow

  1. Turn off the gas-valve switch for the left gun and work only with the right gun.
  2. Set the rotate speed control dial to 3 rpm.
  3. Be sure the beam modulator is turned off.
  4. Press the VAC button to evacuate the airlock chamber.
  5. Toggle the airlock control button to LOWER. This lowers the piston to its working position.
  6. Set the HV timer to 30 minutes and press START. Scroll with the UP Arrow button to set the interval. Press the Start/Stop button to start the timer.
  7. Adjust the ion gun voltage control until the beam energy display indicates 5.0 keV.
  8. Adjust the right needle valve. Rotate the needle valve CCW until the chamber pressure just enters the 10^-4 region. Slowly rotate the needle valve CW to reach the peak current.
  9. Operating range. Rotate the needle back CCW until the current drops by ~10% to 15% of its maximum value (if peak current is 45 microAmps, focused current is is 38-40 microAmps. This completes the gas-flow adjustment of the right gun.
  10. Repeat this procedure for the left gun. Turn off the right gun gas-valve switch and repeat for the left gun.
  11. Be sure both gas-valve switches are turned back on when adjustment to both guns is completed.

Part 7 Beam Alignment

  1. Rotate both gun knobs to align the gun angles at 10? Top. When Properly aligned at 10?, there will be no need to realign the guns at any other angle.
  2. Turn off the gas-flow switch for the left gun and work only with the right gun.
  3. Turn on the rotate speed control and set it at position 3 on the dial.
  4. Evacuate the airlock chamber and lower the piston to its working position.
  5. Set the HV timer to 30 minutes. Scroll with the Up Arrow button to set the interval. Press the Start/Stop button to start the timer.
  6. Adjust the ion gun voltage control until the beam energy display indicates 5.0keV.
  7. Vary the gas-flow control (CW and CCW) and note the change in the beam profile. While viewing the alignment screen, adjust the gas flow until the beam width is a minimum. If gas flow is increased too much, the pressure in the gun will become too high to support a discharge and the ion beam will turn off.
  8. Adjust the z-alignment drive screw (vertical adjust). While viewing the beam crossing the screen, use the tool provided to adjust the z-alignment drive screw.
  9. Adjust the x-alignment drive screw (horizontal adjust). Adjust the drive screw to center the beam over the center hole in the screen.
  10. Adjust the gas-flow control until the beam is slightly larger than the width of the center hole.
  11. Switch off the gas valve switch for the right gun and repeat the preceding steps for the left gun.
  12. After completing this procedure for each gun, turn on the gas-valve switch to both guns and view both beams on the screen. If the two beams do not precisely intersect the screen center, the “x” drive requires further adjustment. Once both lines intersect at the screen center and they appear sharp and bright across the screen diameter, then beam alignment is complete.

Part 8 Using the Digital Process Timer

Setting the time base. Timing intervals from 0.1 sec to 23 hr 59 min can be set using four user-selectable programming time bases.

Time Bases

Code     Time Base
0              000.1-999.9 Seconds
1              00:01-59:59 Minutes:Seconds
2              0001-9999 Seconds
3              00.01-23.59 Hours:Minutes

  1. Turn off the main power switch.
  2. Press Down Arrow button while turning on the main power switch. Release the Down Arrow button once the display comes up.
  3. Use the Up Arrow button to select the desired code. A number from 0-3 will appear corresponding to the codes in the above table. Use the Up Arrow button to select the desired code.
  4. Turn off the main power switch and wait 2 seconds.
  5. Turn on the main power switch.

The timer will now remain in the new time base unless reprogrammed.

 


 

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