tuu D  3 ,7-dA!dHHdFd<9P<9P9|v<v<v< t D  3 -w.dA!dHHd Fdr,.Yr,.Yuuu   xHH(F(HH(d':rpae`;ccnainmodsv9&!tcohove/O2) 9P 1.la0Eoyrcnǝpj78fj1cctU7ppirh792h303F>$dmh403h703#h413h713Q聺nu \ ;snpi QQ0Qr  STANDARD OPERATING PROCEDURE for the Vacuum Generator's Model HB501 Scanning Transmission Electron Microscope  Authored by: Jeffrey H. Butler  I. Scope uu0Qr Within the limitations imposed by sample preparation capabilities, the HB501 STEM is the finest microanalytical instrument in the world; equipped with a field emission electron source as well as a host of detector systems (bright field, conventional dark field, high angle annular dark field, energy dispersive x-ray spectrometry, secondary electron, electron energy loss spectrometry and diffraction array CCDs) the STEM can obtain both chemical and structural information from nanometer sized volumes of matter.   The STEM routinely uses ultra-high voltages to accelerate electrons. Although there are adequate safeguards which prevent the high voltage from turning "on" under unsafe circumstances, it is important to emphasize that the high voltage circuitry (especially the high voltage generator tank) should never be removed nor attempted to be serviced by anyone who is not an authorized Vacuum Generator's representative.  The STEM is an ultra-high vacuum (UHV) instrument. Maintaining good vacuum is essential to its continued proper operation. Unfortunately, unlike the situation for the high voltage circuitry, the HB501 has essentially no built in safety precautions which prevent destruction of the UHV. Thus all vacuum problems should only be dealt with by qualified experts.  Consequently this is a very sophisticated not to mention expensive (>$700K) instrument and its operation according to this and/or any other referenced procedures should only be attempted by designated individuals who fulfill both the legal and the training requirements. QQ0Qr II. Safety uu0Qr Emergency Shutdown Procedure :  This procedure must be permanently posted on the STEM main control panel. 1. Press all three (3) red power ("off") buttons on console. 2. Close gun isolation valve (#1). (marked with  black tape) 3. Close column diffusion pump valve (#2). ( yellow tape) 4. Close airlock diffusion pump valve (#3)). ( green tape)  Report emergency to EMS (ext. 2366), and to Jeff Butler (ext. 5061) or Gary M. Brown (ext. 2387); during off-hours, contact Jeff Butler (713-428-7765) or Gary M. Brown (713-424-9219).  Safety Concerns :  Must be registered with Texas state Bureau of Radiation Control as a qualified service representative for radiation producing equipment. This is almost always taken care of by the instrument manufacturer, but in the rare case of the STEM (the only one in Texas and built in England with no U.S. stationed service representative), VG has no registration with the Texas Bureau. This situation was solved for us by registering Jeff Butler with the state as a capable VG service engineer (with VG's endorsement). Subsequently, any service conducted on the STEM by anybody (even VG engineers) legally must be done in Jeff Butler's presence.  %2. Must be registered with Industrial Hygiene (exts. 2446 / 5124) as a radiation producing source. IH will monitor the radiation production: Continuously, by dosimeter mounted on the column near the sample chamber (the film is changed monthly). Periodically, IH should perform semi-annual Geiger counter checks. Aperiodically, following the dismantling of any part of the electron column (c.f. "Equipment Service"). OPERATORS - 1. Must register with Industrial Hygiene (exts. 2446 / 5124) so any exposure to radiation can be monitored as part of the operator's medical records. The operator has open access to these records. 2. Must wear dosimeter film badge and ring whenever operating the STEM. 3. Must annually attend "X-ray Safety Course" offered by IH. SERVICE REPRESENTATIVES - Z Z   The STEM is classified as an x-radiation source and as such it, its operators, and its service representatives must comply with numerous regulations which govern the safe operation of such equipment:  STEM - 1. Must be registered with the Texas state Bureau of Radiation Control, who must be kept informed of the STEM's whereabouts and operational status at all times. If this -2- instrument is moved from L121 the state must be notified. This can be done by contacting Industrial Hygiene (exts. 2446 / 5124). Z Z@0   SUMMARY   OF   HB5Ol   STEM   OPERATION *  *For all operating instructions not included here, refer to the VG manuals. 1.  STANDBY  CONDITION The HB501 will normally be found in the following condition: Electronics console OFF, EDS computer ON, DPOS monitor OFF, EDS monitor OFF Gun isolation valve closed Backing pump ON, set to CONTINUOUS Roughing pump ON Prep chamber gate valve closed Specimen chamber < 10-8 Torr. Gun chamber < 5 X 10-11 Torr. Grigson coils IN Sample from previous session in stage 2.  TO  OBTAIN  A  BEAM 2.1 Check Freon pressure (must not fall below 3 psi). 2.2 Switch ON three power systems on console (insure lens supplies come on). @@8 D   Equipment Service :  1) As stated above (c.f. "Safety Concerns"), any change in the location or operational status of the STEM must be reported to the Texas Bureau of Radiation Control via Industrial Hygiene. 2) Following the dismantling of any part of the electron column, IH must monitor the -3- level of radiation in the vicinity of the instrument. This inspection must be performed before the instrument can be brought back into routine service. QQ0Qr III. Equipment uu0Qr A set of instrumentation manuals which includes detailed descriptions (all the way down to circuit diagrams) of all of the STEM components is located near the instrument.  QQ0Qr IV. Operating Procedures uu0Qr Due to the complexity of its operation, even the most expert STEM user can benefit from the following "checklist" procedures. However, these "quick-reference" guides can only be understood by well-trained users. Essentially all of the procedures included here are intended to supplant the corresponding sections of the "official" operating manual. But the reader is still referred to the manual for any procedures not specifically included in this set. F QQ0Qr V. Calculations uu0Qr This document is not intended to provide any guidlines for understanding the underlying principles nor interpretation of data obtained from the STEM instrument. For a comprehensive review the reader is referred to:  Introduction to Analytical Electron Microscopy , edited by J. J. Hren, J. I. Goldstein and D. C. Joy, Plenum Press, New York, 1979, and  Principles of Analytical Electron Microscopy , edited by D. C. Joy, A. D. Romig and J. I. Goldstein, Plenum Press, New York, 1986. 2.3 Flash tip, starting at "1", and then at the following intervals: 1.5, 2, 3, 4, 4.5, 5. Wait 10 sec. between flashes. 2.4 Set EHT to 20 kV and ON. Increase HT to desired value (usually 100 kV) waiting 30 sec. between steps. 2.5 Open gun isolation valve SLOWLY AT FIRST, checking gun vacuum.  CHECK  THE  TIP  VOLTAGE  IS  OFF  WHENEVER  GUN  ISOLATION  VALVE  IS  BEING  OPENED . 2.6 Set backing pump ALL THE WAY TO AUTOMATIC.  DO  NOT  LEAVE  BACKING  PUMP  SWITCH  IN  CENTER  (OFF)  POSITION . Roughing pump OFF. 2.7 Switch on tip voltage.   NOT TO EXCEED 3.6 kV . (CHECK THAT GUN ISOLATION VALVE IS OPEN BEFORE TURNING ON TIP VOLTAGE.) Z 3.3 Insert objective aperture. OL WOBBLER ON. Center objective aperture mechanically until DF image rotates about center of screen at 50KX. Note feature at screen center. Mag down to 5 or 10 KX. TV scan rate OFF. OL WOBBLER OFF. Set time base to 1 ms line speed and 500 ms frame speed. Position locate spot over feature previously noted at 50KX. This marks the optical axis of the OL. 3.4 Insert and center (over locate spot) smallest SAD aperture. Focus on SAD with C2. Correct condenser astigmatism ( NOT at TV scan rate). Refocus image of specimen with OL. !3.14 Correct objective astigmatism.  NOTE :  LENS SETTINGS   For  normal specimen height  (flat grid): AEM MODE - Condenser Lens #2: 6 on coarse: 6.5 on fine (at this setting, the SAD aperture is focused onto plane of specimen). Objective Lens: approx. 12 to 15 on coarse. HIGH RESOLUTION MODE - Condenser Lens #2: 8 on coarse; 5 on fine Objective Lens: approx. 11 to 14 on coarse. If your specimen is high (low) the objective lens will focus at a lower (higher) setting.  4.  CONDENSER  LENS  ALIGNMENT (After column bakeout) 4.1 Ensure gun is well aligned as per instructions 5.4 - 5.9. If gun is not aligned, the complete procedure of 5 must be performed before proceeding to here. 4.2 Upon reaching this point in the alignment procedure, the optical axes of the gun lens and objective lens are coincidental. We now will mechanically translate and tilt C2 (and Cl) until it (they) also fulfill this criterion. Experience has shown the conventional "lead reversal" technique of condenser alignment to be slow and cumbersome. A faster and more accurate method using the DPOS is described here. 4.10 Increase C2 through focus until the shadow image expands back into a disk. Now translate the disk back through the center marker (i.e. say "1-1/2 times" the way to the center, or "overshoot" the marker) and tilt the center of the disk back to the DPOS marker. 4.11 Decrease C2 through focus (i.e. go to a "underfocus" position) until the shadow image expands back into a disk. Translate the disk 1/2 way to the center and tilt the rest of the way. 4.12 Repeat 4.10 and 4.11 until the shadow image can be brought from minimum C2 current to maximum while remaining centered on the DPOS marker the whole time. 4.13 Test C2 alignment by repeating 4.12 for a wide range of objective lens settings. The shadow image should expand and contract about the center marker for all cases. If it does not, check the position of the center marker again with C2 OFF, as in 4.4. Make sure that the VOA is  OUT . 4.14 Switch off C2 and repeat 4.6 - 4.13 for C1. 4.15 Test C1 and C2 alignment by repeating 4.12 for a wide range of C1 settings. 4.16 The column is now aligned. Proceed to 3 for the final fine alignment. 5.  GUN  ALIGNMENT (After gun bakeout) 5.1 Alignment philosophy is that the objective lens is always fixed (translationally) in the stage. Thus the gun must be translated and tilted in order to sight along the fixed objective lens axis. Once the gun is aligned and locked into this position, all other lenses and apertures which are inserted must be centered to coincide with the established optical axis. o C1, C2 OFF 1 ms line speed, 500 ms frame speed [time base]. "OBJECT ALIGN" [alignment-shift] at normal setting if known; if not, then "zeroed". Electrical "SHIFT" [alignment-shift] "zeroed". "GUN ALIGN" [alignment-shift] OFF (The gun lens has made this set of controls redundant.) "BEAM SELECTOR" [magnification-diffraction] i.e. Grigson coils on NORMAL and "zeroed". "GUN ALIGNMENT" SHIFT and TILT [EHT & TIP Control] controls "zeroed" (i.e. @ "5.0") GUN LENS" COARSE and FINE [EHT & TIP Control] set to minimum value (i.e. @ "0.0") "NORMAL/ALIGN" [on column] switch set to ALIGN. z5.5 Although the initial, rough gun alignment can, in principle, be accomplished with the use of the DPOS, experience has shown the use of the ADF to be more accurate, hence it is the only method discussed here.   NOTE : When mechanically adjusting the gun lens, C1 or C2, always slacken the adjustment keys completely off after each adjustment - this minimizes "backlash" effects. Tighten the keys down only after the final adjustment has been made. 5.6 Increase the ADF gain until an illuminated "circle" appears on the screen. Center this area on the screen using only the gun translate keys.   NOTE : The user will notice that, when the gun lens is set to a minimum or low value, the tilt keys have very little effect on the illumination pattern. As the gun lens current increases the influence of gun tilt becomes correspondingly greater. 5.9 Repeat 5.8 until the gun lens can be brought from 0 through focus to maximum while the illuminated area remains centered on the screen the whole while, changing only in brightness. Do not yet tighten the translation and tilt keys, as this is only the rough alignment step. 5.10 Objective Alignment. Now we use the "OBJECT ALIGN" [Alignment-Shift] to tilt the beam into coincidence with the objective lens axis.   NOTE : The "OBJECT ALIGN" settings are a function of the pole pieces --- i.e. they should remain constant unless the pole pieces have been changed. If these values are known from a previous alignment, enter these settings and skip to 5.19. 5.11 Cancel "LOW MAG" mode. 5.12 Set gun lens coarse to achieve maximum brightness on the BF screen. 5.13 Insert the 100 m objective aperture and form an image (BF and DF) with only the (normalized) objective lens. 5.14 Align the objective aperture as precisely as possible by wobbling the objective lens and positioning the aperture for minimum image movement in the ADF image at 50 KX. Wobbler OFF. 5.15 Focus the objective lens as well as possible on an easily recognizable feature. With a line speed no faster than 1 ms, center the feature using only the mechanical specimen shifts. x5.16 Ensure that the "NORMAL/ALIGN" switch [on column] is set to ALIGN. (This allows the lens current leads to be removed without EHT and ELECTRONIC OPTICS power shutdown.) Switch OFF the OBJECTIVE lens and reverse the direction of current flow by inserting the lens reversal lead into SK5 (side of column). 5.17 Switch on the OBJECTIVE lens, normalize it and refocus on the feature. If the feature has moved relative to the center of the CRT scan, bring it halfway back to the center of the screen with the "OBJECT ALIGN" [Alignment-Shift] coils, and the remaining distance back with the mechanical X and Y shifts. U5.22 Insert the VOA and monitor the beam current incident upon it using the electrometer. Maximize the current by observing the electrometer signal in conjunction with the [video level-2] monitor. 5.23 When the current is maximized, the gun lens has focussed the beam onto the VOA. Since the beam crossover is desired to be just beneath (before) the differential pumping aperture, normalize the gun lens and set it 2 coarse clicks over the maximum current setting. Record the gun lens setting and continue to use this value until the next alignment from the gun up. REMOVE THE VOA!  5.1 With the tip emitting, adjust the camera gain and lens aperture until illumination is visible on the monitor. At this stage you will probably see part of a circular illumination which is "cusped". Using the gun  shifts  it should be possible to remove the cusp to obtain a symmetrical disk of illumination which has a brighter perimeter. The magnification of this image is adjustable by varying the objective lens current. 5.2 increase the gun lens current and use the gun lens  tilts  to retain symmetry in the illumination. Continue to increase the gun lens current until the gun lens is focussed at the differential pumping aperture. At this point the illumination becomes highly abberated but nevertheless still retains recognizable features which can be used to finely adjust the gun lens  tilts. It can be very helpful to make adjustments to the brightness at this stage to reveal otherwise hidden detail. 5.8 Repeat steps 5.6 & 5.7 until there is no appreciable deviation from a symmetrical illumination as the gun lens excitation is varied over its normal operating range, i.e. from just above DPA focus to maximum. V SPECIMEN CHANGE IN THE HB501 1. Turn the tip off. 2. Close the column isolation valve. 3. Turn all PMT's off. 4. Set specimen shift control to "Change". Wait for the red light to come on.  This is the most important step of all. 5. Fill the LN2 reservoirs on both diffusion pumps. 6. Turn on the chamber viewing lamp by depressing the button on the lamp housing. Note that the console EHT power must be on to do this. 7. Withdraw the Grigson coils from the column by rotating the lever fully back and allowing the lock mechanism to slip into place. 8. Ensure that good vacuum exists in the column and the prep chamber. The prep chamber vacuum should be in the 10-7 range. 9. Fully open the gate valve between the prep chamber and the column. 10. Set the selector for the specimen arm to the outermost position. 11. Unlock the set screw on the lateral advance knob for the specimen arm. Watching through the viewing glass, slowly advance the arm into the column until it comes to a complete stop. The set screw on the lateral movement knob should now be retightened. 12. Set the specimen arm selector to the innermost position by pulling outward and rotating 90 degrees simultaneously. The knob will then click into its inner position. The specimen arm can now be moved vertically. 13. Watch through the view glass and lower the specimen arm until it comes to a complete stop and has engaged the specimen holder. To eliminate wobble, maintain a slight outward tension on the knob while raising and lowering the arm. 14. Now reverse steps 10 through 13 to remove the specimen from the column. 15. Close the prep chamber gate valve. 16. Close the isolation valve for the specimen chamber diffusion pump. 17. Close the valve for the EDS port roughing line. 23. Wearing clean gloves, either lint-free cotton or powder-free latex, position the specimen holder in the brass mounting jig. It will fit only one way. Lock the holder into the base using the screw-tightened tabs. 24. Rotate the two knurled screws clockwise until a positive stop is reached. This moves the goniometer gimbal into a horizontal plane. 25. Insert the push rod into the bottom of the base and lock. 26. Remove the grid retaining ring from the top of the specimen holder using the threaded end of the specimen changing tool. 27. Remove the grid from the holder and replace with a new grid. The sample (carbon- coated) side of the grid should in the up position. In the microscope, the sample will then be facing down and in the proper position for EDS. 28. Replace the grid retaining ring. Position it so that the gap in the retaining ring matches the gap in the goniometer ring. This allow a path for X-rays to reach the EDS detector. 34. Close the roughing valve and open the specimen chamber diffusion pump valve. The valve should be opened slightly at first. The ion gauge may kick off but will shortly come on again as the vacuum recovers. The valve can be opened more until it is fully open. 35. Pump on the specimen until the vacuum is in the 10-7 range. 36. Carefully open the specimen chamber isolation valve while watching the column vacuum. If any major change occurs in the column vacuum, close the valve immediately. 37. Steps 10 through 15 can now be performed to insert the specimen into the column and return the specimen arm to its resting position. The sample will be ready for examination when the column vacuum is adequate. 2.8 Switch Display(s) and Detector(s) ON. 2.9 Select condenser lens current(s) to suit mode of operation. (Note the beam is -A2- focussed on the SAD when C2 6.6 and C1 is turned off.) 2.10 Adjust ELS analyzer current ZERO to maximize signal on screen, adjusting BF detector gain as necessary. 3.  COLUMN & SPECTROMETER FINE ALIGNMENT (Daily)   3.1 Open analyzer slit (clockwise looking upwards). 3.2 Switch on CL(S) and OL. Focus image with OL and no objective or detector apertures (entrance aperture only). Switch on C2 WOBBLER; set scan to TV rate. Use gun lens electrical TILTS until BF image rotates about center of screen at 50KX. C2 WOBBLER OFF. 23.5 Switch to SA mode. Remove objective aperture, DPOS screen and ADF detector. 3.6 Select largest ELS entrance aperture. Close ELS analyzer slit. 3.7 Adjust ELS analyzer X and Y FOCUS, CORRECTOR, and ZERO until triangular aberration figure is obtained. 3.8 Center ELS aberration figure on locate spot using Grigson ('BEAM SELECTOR") coils. 3.9 Insert and center ADF detector, ELS entrance and collector apertures on triangular ELS aberration figure. 3.10 Insert objective aperture, remove SAD aperture and switch back to imaging ("M1") mode. 3.11 Re-center objective aperture as per instruction 3.3. Locate spot OFF. 3.12 OL WOBBLER still ON, minimize BF image movement using Grigson coils, then WOBBLER OFF. -A3- 3.13 OPTIONAL: If used, now is the time to insert and center the DPOS. 4.3 Switch OFF Cl and C2. Remove objective aperture. Select "SPOT" mode and 2KX magnification. 4.4 Insert the DPOS and observe the shadow image as the objective lens coarse control is changed. It will expand and contract about a point (the optical axis of the objective lens). 4.5 Center the hole in the DPOS on this point. Set the objective lens to a nominal operating value, say about 12 - 14 on the "COARSE" control. 4.6 Minimize C2 current and switch it ON. The position of the shadow image disk on the DPOS should not change. 4.7 Increase the C2 current until the shadow image disk moves off the center of the -A4- marker (hole). 4.8 Completely slacken all 8 mechanical translate and tilt keys for C2. Bring the shadow image 1/2 way to the center marker with the translate keys and the rest of the way to the center with the tilts. 4.9 Repeat 4.7 and 4.8 until C2 focuses the shadow image down to the smallest possible disk. ,5.2 Remove the gun lens radiation shielding (only necessary for protection against tip flashover) in order to access the gun lens mechanical tilts. 5.3 Place a sufficiently heavy object over the radiation shield's "dead man's" switch and power up the microscope as per instructions 2.1- 3.1, inclusive. -A5- 5.4 Establish-the following initial conditions: All apertures OUT (except entrance aperture to prevent burning scintillator). Magnification (M1) set to 2000X. "LOW MAG" selected (20X is the very lowest mag in the STEM).   NOTE : If no illuminated area can be seen after the ADF signal has been increased; turn the tip OFF, loosen the 4 translation keys and take the gun completely through its travel in both directions. Then approximately center (1/2 the travel in both directions) the translation keys, turn the tip on and begin 5.6 again. 5.7 Set the locate spot to mark the center of the illuminated area. NOTE: The "darkish" circle within the illuminated area is the shadow of the hole in the ADF. There is no need to re-center the ADF, however, as subsequent translation and tilt will cause movement of this shadow. -A6- 5.8 Increase the gun lens current until the illuminated area moves off center. Translate and tilt the gun to re-center this area on the locate spot. 5.18 Repeat 5.16 - 5.17 until the feature remains approximately centered upon reversal at 50 KX mag. Make sure the lens reversal lead is out on the final repetition. Set the "NORMAL/ALIGN" switch [on column] back to NORMAL. -A7- 5.19  Gun  Fine  Alignment - Now the gun lens electrical "SHIFT'' and "TILT" [EHT & TIP control] will be adjusted so the beam from the gun sights precisely along the objective lens optical axis. 5.20 Remove the objective aperture and return to "LOW MAG" (X20) mode. 5.21 Repeat steps 5.6 - 5.9, but now tighten the adjustment keys after the final adjustment has been made. (Tighten only enough that backlash does not become severe.) 5.24 Cancel "LOW MAG" mode. Form an image using only the objective lens but with the gun lens set as in 5.23. Insert the 100 micron objective aperture and center it by wobbling the dark field image as in 5.14. 5.25 Reduce the tip extraction voltage and note the direction of image movement. Shift the image in the same direction using the electrical "X and Y SHIFT" [EHT & TIP control] controls and then return the image to its initial position with the electrical "X and Y TILT" [EHT & TIP control] controls. 5.26 Repeat 5.25 until there is no image movement with extraction voltage change at 100 KX magnification. 5.27 Proceed to condenser lens alignment, 4.1 - 4.16. w -A8- 5.  ALTERNATIVE  GUN  ALIGNMENT (After gun bakeout) This method (provided to us by Andy Waye; VG Microscopes, Ltd.) describes an alternative to the above 5 for the alignment of the VG HB501 STEM with FEG2100 source condenser (gun) lens using the Diffraction Pattern Observation Screen. Starting conditions: Operating vacuum in the gun and column. All apertures out. Objective lens only on, all other lenses off. DPOS in, all other detectors out. G un isolation valve open. Final operating voltage switched on. S pot mode with spot at screen center. Maximum magnification. TV camera on.   NOTE : During this alignment procedure it will be necessary to make appropriate adjustments to the TV camera gain and the camera aperture to maintain sensible intensity on the screen. = 5.3 Insert the virtual objective aperture and monitor the beam current. 5.4 By adjusting the gun lens excitation and the  electrical  shifts and tilts maximize the current on the VOA. 5.5 Note the gun lens excitation and return the electrical shifts and tilts to zero (5.0 on the pot dials). 5.6 Now overfocus the gun lens to maximize excitation . The image obtained will resemble the original "lens off" image, and again, symmetry can be obtained by use -A9- of the gun  shifts .   5.7 Decrease the gun lens excitation to the differential aperture focus position (c.f. 5.5) using the gun lens  tilts maintain symmetry. Alternatively reduce the excitation to a position just above DPA focus. This may be quicker, easier and accurate enough.  -B2- 18. Open the main valve on the helium cylinder in the foyer. Increase the pressure on the second stage of the regulator to approximately 20-50 psi. A safety relief valve in the line between the cylinder and the microscope maintains the line pressure at approximately one atmosphere. A hissing noise can be heard near the cylinder as this happens. 19. Ensure that the roughing valve to the prep chamber is closed. 20. Open the two gas inlet valves and back-fill the prep chamber to atmospheric pressure with helium. 21. Using a 13-mm wrench, remove the lower, outermost flange from the prep chamber. 22. Align the specimen changing tool with the exposed bolts on the open flange, noting that the arrow labeled "Column" is pointing in the right direction. Gently raise the sliding block so that it comes in contact with the base of the specimen holder. Continue to raise until a positive stop is reached. Now lower the block containing the specimen holder and remove from the microscope. =29. Reverse steps 23 through 25 to prepare the specimen holder for replacement in the microscope. 30. Place a new copper gasket or an O-ring on the flange plate. Take great care when removing the old copper gasket not to scratch the knife edge on the flange. 31. Reverse steps 21 and 22 to replace the specimen holder on the specimen arm and properly tighten the nuts on the flange. -B3- 32. Close the gas inlet valves. 33. Open the specimen chamber roughing valve and pump on the chamber for approximately 15 minutes. The vacuum should read near 10-2 torr. d<8d L&$$ "p$3ddubdptd$$S- $#xUP$%$'Y(P$*$.I\0$3I$_!$69;$b@>Me4g4$@$kL DF4EcGIn&L rPTxHH(F(HH(d'