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last update 15/02/2010
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 Troubleshooting 

  1. Vacuum related
  2. Sample transfer
  3. Apertures
  4. Imaging related
  5. Evaporators
  6. Software related

  1. Vacuum related
    • What are the approximate pressures during normal operation?
      Under normal operation conditions both the main chamber (MCH) and column (COL) is in the low to mid 10-10 mbar range. The preparation chamber (PCH) is usually somewhere between high 10-9 and low 10-8 mbar.

    • What are the interlock settings in the microscope chamber?
      The COL and MCH pressures are used as interlock triggers with the set points at 5.10-7 and 2.10-5 mbar, respectively. There is no interlock for the PCH pressure, so one needs to be careful opening the PCH-MCH valve. The detailed interlock settings are as follows:

      HV Off Alarm On Bakeout Max
      MCH 2.10-5 mbar 5.10-6 mbar 5.10-6 mbar
      COL 5.10-7 mbar 5.10-8 mbar 5.10-6 mbar

    • What happens when the pressure is too high?
      If the interlock is triggered, the HV rack turns itself off. There are two possibilities at this point: either the chamber is vented completely, or the pressure rised temporarily above the set point and came back down afterwards. The first situation is very severe and the resulting damage may be considerable. In the latter situation, i.e. the pressure was temporarily above the interlock set point, the biggest concern is the stress on the e-gun filament due to its uncontrolled switching and to a disharge in the MCP detector. In this case, to bring the microscope back in operation, follow these steps:
      • leave everything turned off!! Make sure that the problem with the pressure is resolved, and the pressure has recovered its normal value.
      • set the filament to zero, by turning its knob all the way counter clockwise.
      • the MCP (Channel plate) voltage supply must be off at this time. Turn the knobs of both the MCP and the phosphor screen to zero (V0 and Va).
      • (of course only if the pressure is good) turn on the HV power supply, by pushing the corresponding (big circular) green button.
      • the lenses should be back at their normal operating values.
      • turn ON the MCP supply. Increase the MCP and phosphor screen voltages in the following order: phosphor screen (Va) to 2 kV, then MCP (V0) to 1.3 kV, and then phosphor screen (Va) to 5.5 kV.
      • increase the filament current very slowly from zero to 1.75 A. This should take at least 5 minutes. Do it in 0.2 A steps every minute or so.

    • Can I turn off the MCH ion gauge?
      No!! Turning of the gauge will trigger the interlock and turn off the HV rack, as explained in the previous item. Actually there is a way to turn it off without triggering the interlock, but to do this, there has to be absolutely someone from the beamline personnel present. Note that the PCH gauge can be turned off without any problems, as it is not interlocked.



    • What is the procedure to do an experiment involving gases?
      There are two leak valves connected to the MCH, one of which is used for oxygen. Whatever is the gas used, the advisable thing to do is to turn on the MCH turbo, wait until it reaches good pressure, open its valve to MCH, and close the valve of the MCH ion pump in order not to contaminate it.

    • How do I turn on the MCH turbo?
      At the moment, the MCH turbo is backed up by the Pfeiffer turbo station. Normally, the MCH turbo (which is under the table, more or less below the e-gun) is kept switched off in order to reduce vibrations, and the valves connecting it to MCH and to the airlock turbo are kept closed. To start the MCH turbo, do the following:
      • First of all, check all the valves. Both turbo-MCH (manual) and turbo-backing (pneumatic) valves should be closed. When switched off, the turbo is always kept under static vacuum (probably in the mbar range).
      • Switch ON the primary (membrane) pump of the Pfeiffer station. Pump only with the membrane pump for 5-10 minutes. To do so, set parameter 23 (MOTOR TMP) OFF on the Pfeiffer station.
      • When the backing pressure is a few mbar, open the turbo-backing valve by pushing the "open" button on its interlock box.
      • Start the backing turbo (Pfeiffer) by setting parameter 23 (MOTOR TMP) ON.
      • When the pirani gauge placed behind the turbo is underrange (UR), start the turbo by pushing the ON button on its controller. Once it reaches full speed (660 Hz) its power consumption should be below 20 Watts.
      • Wait at least an hour before opening the turbo-MCH valve.

    • What is the highest gas partial pressures that can be used during experiments?
      Depends on the gas. For example with oxygen, in principle one can go upto mid-10-6 mbar range staying below the interlock setting. However, it is likely that a short bake-out is needed in order to recover the chamber pressure back to its normal level after this type of exposure. As for other gases, such as NO2, it should be discussed with the beamline personnel.

    • How do I close the valve between the MCH and COL?
      The valve between MCH and COL is controlled by a linear feedthrough, and it is very delicate. One should tighten it very very gently!!! The close position is around 0.4 and the open position around 0.15 on the linear feedthrough marker.

    • What does the "E03" message displayed on the MCH gauge controller?
      Don't worry, this just means that the pressure is below the range of the gauge. This message appears for low 10-10 mbar.


  2. Sample transfer (More information can be found on the page concerning the sample transfer procedures).

  3. Apertures
    • Which apertures do I need to worry about?
      The field-limiting aperture, the contrast aperture and the energy slit are the most commonly used ones during microscope operation. For special cases, one may also want to place the illumination aperture in order to limit the incident electron beam dimensions.

    • How do I insert the contrast aperture?
      The best way is to do this with the electron beam. Align the sample, and stay in the LEEM mode with the grabber preview on in order to get a live picture of the sample. Set the field-of-view to 10 microns. Then simply insert the contrast aperture by moving it with its linear feedthrough. Once you see a bit of light, you can adjust to maximize the intensity, using the two knobs placed above and below the feedthrough. If you don't see any intensity at all, the best is to go to LEED mode, and place the contrast aperture on the (0,0) spot. Before switching to LEED, remember to put in the field-limiting aperture and "close" the Wehnelt, i.e. turn down the e-gun emission current to zero.

    • How do I insert the field-limiting aperture?
      Again, the best way is to do this with the electron beam. Align the sample, and stay in the LEEM mode with the grabber preview on in order to get a live picture of the sample. Set the field-of-view to 10 microns. Then simply insert the aperture by moving it with its linear feedthrough. You should see in order 3 apertures from big to small. If you do not see any light at all, go to a larger field-of-view (e.g. 30 microns) and try again. If still nothing, remove the aperture completely and check whether there is still light on the detector.

    • How do I insert the energy slit?
      Do this with the electron beam on and stay in the LEEM mode with the grabber preview on in order to get a live picture of the sample. Choose the field-of-view which you want to use in the experiment. Then simply move in the linear stage at the top of the analyser chamber until light appears. Make sure to move it slowly. Otherwise one may get discharges in the analyzer. There are two slits: the first selects an energy resolution of 0.6 eV, the second 0.3 eV. Adjust the slit position so that the field of view appears homogeneously illuminated. Note that changing the electron emission current slightly displaces the electron beam at the dispersive plane, so try to place the energy slit always using the same emission current.

    • What are the approximate positions of the apertures?
      The apertures are placed using linear feedthroughs. The approximate settings on the feedthrough markers are given in the table below:

      C. APR. F. LIM. APR. ENG. SLIT
      POS1 15 mm (100 um) 15 mm (20 um) 4 mm (OUT)
      POS2 18 mm (30 um) 18 mm (5 um) 10 mm (LARGE)
      POS3 21 mm (20 um) 21 mm (2 um) 16 mm (SMALL)



  4. Imaging related
    • I am following the alignment instructions, but I don't see the beam at all, why?
      Check that the HV is turned on and at 18 kV. If the HV is ok, and the emission from the e-gun is above zero (~ 0.02 microAmps), then check that all the apertures are out of the way. Check if the grabber is on, so there is live picture on the screen. Try moving the focus further out, lowering the objective value down to 1250 mA. If the beam still does not appear, the problem is most likely in the illumination section. For the alignments of the corresponding lenses, ask for help from beamline personnel!

    • How do I turn on the high voltage?
      The HV controls are shown below in figure 1. Under normal circumstances, you never have to touch the interlock or the power supply ON/OFF buttons. The high voltage is simply ramped up using the "HV Adjust" button shown in the figure. Note that to increase the voltage, one has to first enable the HV, by pressing the small green square button, labelled as "HV enable" in the figure. Unfortunately this enable button does not work very well, and it needs to be pressed a couple of times before actually getting set (also note that its green LED never comes on). Close to 18 kV, use the "HV Fine Adjust" button in order to set the voltage precisely at -18000 volts.


      Figure.1 High voltage controls.

    • What do I do if the high voltage turns OFF on its own?
      Possibly there was a discharge between sample and objective or one in the analyzer. A discharge can be identified by a sudden increase in the pressure. If the discharge is strong, the start voltage gets automatically set to 500V. To recover, in LEEM2000 program click "Refresh all supplies" under "Tools" menu. The red square button must be lit. Push it to turn it off. Set the HV knob to zero. Push the small square green button next to it to enable back the HV (Not the big circular green button, which is the HV power supply button!). Then slowly ramp up the HV to 18 kV, watching carefully the pressures. If the start voltage was not set to 500 V, simply press the red button off, push the green button on, and ramp up the HV (Note that the small green enable -square- button does not work well, and one may need to push it few times before the HV is actually enabled). The HV may fail also due to an increase in the leakage current between sample and objective, rather than an arc. In order to deal with this situation, you need to increase the maximum allowed current between sample and ground. Do this by turning the knob corresponding to the max current by 0.1 steps (in units given on the knob) and then check out whether HV fails again. Stop increasing the "current max" as soon as HV does not fail anymore. Do not go above 3.0, and anyway report this problem to the beamline personnel. Increasing the "max. current" may result in the destruction of your sample, in case a strong arc occurs and the max. current threshold is set too high.

    • Which settings are accessed manually on the HV rack?
      Under normal operation conditions, the user of the microscope needs to control manually the sample heating supply (the filament current, bombardment voltage, and the maximum emission current), and the Wehnelt voltage to increase/reduce the emission from the e-gun source.

    • How high can I heat the sample while imaging?
      It is advisable to stay below 800C, which corresponds to about 14 mV thermocouple voltage.

    • What happens if I switch to LEED without putting the field limiting aperture in?
      Most likely the intensity will be too high, and there will be permanent damage on the channel plate detector (i.e. burned spots). Imagine that the e-beam size 80 microns, which is 40 times larger than the area used for doing LEED. There will be 3 orders of magnitude higher intensity than usual! Please consider that the detector is very expensive (14.000 euros!!) and delivery times are rather long.

    • What can I do if the photon beam is unstable?
      Drifts in the illumination can have different causes, most likely a variation in the sample temperature. If you can exclude this possibility, it is good idea to check the Elettra beam stability thourgh the Elettra beam position monitor .



  5. Evaporators
    • Which type of evaporators are used in the microscope chamber?
      We use most commonly the Omicron e-beam evaporators. The Au evaporator currently mounted on the chamber is made by Elmitec and is rather similar to the Omicron. There are also home-made evaporators for Cu and Pb, which have presently neither cooling nor shutter, but all the same they work well with the pressure in the 10-10 mbar range.

    • How do I connect the water lines?
      The water lines are connected to the main line behind the microscope chamber. For the appropriate connectors and tubes, please contact the beamline personnel.

    • What is the significance of the temperature reading on the Omicron controller?
      The reading on the Omicron controller shows the temperature on the cooling body (i.e. the so called "shroud"), and it should be around room temperature under normal operation conditions. If you see that it rises when filament is on, check whether there is water circulation. Otherwise, this option is only useful during degassing after bakeout.

    • What are the rough settings for the Au evaporator?
      The Au evaporator is operated around 2.60 A, 500 V, 25 mA emission current for evaporation, which corresponds to a crucible temperature of about 1020 C. At this setting, the evaporation rate will be roughly a monolayer every several minutes. Note that, as opposed to the Omicron evaporator, the temperature reading is on the Au crucible, and it can be used as a calibration parameter.



  6. Software related
    • Which software do I need to use to operate the microscope?
      All user operations can be performed through the program UMEASURE (previously called GUI). Umeasure interfaces to three separate programs, which actually do the real work: BCS Java (for beamline controls), LEEM2000 (for microscope controls), and UVIEW (both for data acquisition and display). The necessary funcionality of all three programs are reproduced within Umeasure. In addition to the basic controls Umeasure provides powerful (jython) macros which implement more involved data acquisition procedures such as imaging XPS, XAS, XMCD, etc.

    • How do I start Umeasure?
      The necessary files are placed in a folder called "Umeasure Batchfiles" on the control computer (currently pnano5). In order to start Umeasure nameserver, Uview and LEEM2000 should be up and running, and the CORBA interface should be available (CCBRIDGE). The steps to follow are:
      • run nameserver (by double-clicking).
      • run uview2002. This will automatically start LEEM2000 and CCBridge.
      • run umeasure.

    • How do I name the data files?
      The data files are automatically named and saved according to the convention of Umeasure. Each acquisition (a scan, a single image, etc) is saved in a separated folder with a name generated according to the date and a running index for that day. All data folders are collected in the folder for that day, which is located in the monthly folder:
      d:/ data / yyyy_mm / yyyy_mm_dd / yyyy_mm_dd_xxx_suffix
      "xxx" is the index and "suffix" is a label to denote the type of acquisition. Currently the available suffixes and their meanings are:

      Suffix Meaning
      IMG single image
      MOV movie, sequence
      REFOC mirror scan
      IV I(V) scan
      WKF work function scan
      XPS imaging photoemission scan
      XAS imaging absorption scan
      XMCD imaging dichroism
      UNDSCAN undulator scan
      CFG configuration file

    • What is the data format?
      The images are saved as 16-bit tif files. Each acquisition is accompanied by a series of text files recording the state of the microscope, the beamline along with the acquisition details. In addition to the configuration info, there is another text file (suffix "trace") which have auxiliary information corresponding to each image such as temperature, pressure, etc.

    • How do I view the data after acquisition?
      Any image processing software capable of viewing tif16 will do. We use Igor, taking advantage of the comprehensive macros developed at this beamline. The macros are collected under a common file called "speleem_imageanalysis.ipf", which is freely avaiable to everyone.

    • How do I analyse the data?
      As mentioned in the previous item there is a comprehensive image processing software developed at the Nanospectroscopy beamline. The Igor macro "speleem_imageanalysis.ipf" has all the functionality to perform most of the data analysis work.

    • How do I view the ROI scan during acquisition?
      Up to four region-of-interests (ROI) can be chosen in Uview. The average intensity within each ROI is communicated to Umeasure during scan and is displayed in a window.

    • How to reboot the BCS?
      If BCSJava or any browser cannot communicate with the BCS, the BCS http server has to be restarted or rebooted: please follow the instructions listed here.

    • When I try to open a valve, I get a message like "..insufficient priviliges.."
      Possibly, another branchline (French or FEL) is controlling the BCS. Try to contact someone from the other branches.

    • When I try to open a valve, I get a message related to "..cooling.."
      Probably the monochromator cooling water pressure is outside the set limits. Contact someone from the beamline personnel for further troubleshooting.