NanoWiki

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====== Description ======

The FEI NanoSEM is a Schottky field emitter SEM that has very high resolution down to low accelerating voltages, thanks to the UHR immersion mode in which the focussing field(gradient) extends below the pole piece of the final lens so that the specimen can be placed 'in' the lens at very small working distance.

The resolution at 15 kV is 1 nm (1.3 was measured in the acceptance test) and 1.8 nm at 1 kV (2.0 nm was measured in the acceptance test). The resolution in STEM mode is sub-1 nm!

The NanoSEM has a mechanical stage with motorized x, y, z and rotation, manual tilt from -10 to +90 degrees is possible. The stage is tilt-eucentric at a working distance of 5.000 mm. The stage travel is 50 mm in X and Y direction. Accuracy is 100-200 nm. Available working distance is 1-25 mm, minimum working distance depends on accelerating voltage (1 mm at 1 kV, 4.6 mm at 15 kV)

The system has a HV (specimen chamber pressure is below 1e-6 mbar) mode and a LOWVAC mode where the chamber pressure can be up to 1.5 mbar. In the LOWVAC mode degassing specimen can be observed, and for chemical processing and avoiding charging (in the case of a nonconducting specimen) water or an auxilary gas can be introduced in the sample chamber (pressure can be set in the control software). When the chamber pressure is 1.5 mbar, the final lens is pumped by the drag stage of the TMP, the aperture pumped to 1e-6 mbar by the TMP, pressure in the lower IGP is 1e-8 mbar and the FEG source is still kept at 1e-10 mbar by a series of apertures! In the HV mode the vacuum can be improved by using a cryo-can (an LN2 cryopump) to reduce contamination.

Detectors are a standard ETD with variable bias, a backscatter detector, a TTL-S/B detector, a LVD gaseous detector for low vacuum, a CRT/LVD detector with a larger PLA, a GAD/BSD backscatter detector and a STEM detector (bright and dark field) for transmission mode. The ETD counts secondaries (having a low kinetic energy and only escaping from the specimen if they are created near the surface) and backscattered electrons (that interact with a nucleus and 'bounce' back at near incident beam energy) at positive bias, if a sufficient negative bias is applied the secondaries can't reach the ETD). The backscatter detector has a larger backscatter yield than the ETD. At very low working distances in the UHR immersion mode the yield of the normal detectors will drop, in this case the in-lens detector is used (the electrons spiral into the lens, are accelerated away from the lens axis and detected. Depending on bias, secondary (plus backscatter) or backscatter electrons are counted. At high pressures electrons collide with the gas before reaching any detector, the gaseous detector accelerates the electrons so that in 1 mean free path the ionization energy of the gas is reached: the a collision avalanche in the gas acts as the amplifier (too high potentials creating sparks or a continuous discharge must be avoided of course). The STEM detector has multiple segments so that Z-contrast, bright and dark field are available. A CCD camera with infrared LED illumination is present in the vacuum chamber so that the stage, specimen and their position with respect to the final lens, detectors etc. can be observed continously.

The system has place for 2 GIS's. Currently a Pt deposition GIS is mounted. It is configured for use at eucentric height (5mm). When the GIS needle is inserted it drives to a position 75 um above eucentric height and 100 um to the side of the beam center. The GIS can heat a substance and when a valve is opened it injects gas onto the substrate at the beam incidence point. The gas can be used for EBID or etching.

A cryo-transfer system is mounted that allows a sample to be cryo-fixated by rapid cooling to 77K and subsequently be transferred to the SEM via the cryo-transfer system's loadlock. In the loadlock a sputtering source is present.

A manipulator to mount single carbon nanotubes onto various substrates has been developed.

====== Safety ======
===== For yourself and others =====
   * NEVER make a technical modification to the instrument (consult [[Marcel Hesselberth]] if you need to)
   * The SEM is equipped with UPS's, very high voltages are always present
   * The SEM contains toxic substances. MSDS's are present in the SEM room
   * When the beam is on X-rays are produced, never open the loadlock in this case

===== For the instrument =====
   * The final lens polepiece is made of a soft alloy. **The smallest scratch or dust particle on the polepiece will result in uncorrectable astigmatism.** Some detectors can be mounted onto this polepiece. **If the polepiece is scratched it must be replaced, replacement cost is 30000 euro.**
   * Use the 'elephant' to correctly set the stub height; **use a software or hardware stage limit for protection**
   * When changing Z, if you realize you made a mistake you can **hit the Escape key to stop stage motion.** Be prepared to do this!
   * ALWAYS wear **POWDERFREE gloves** when working in the specimen chamber
   * Changing a detector can be done only after this has been demonstrated to you **by [[Marcel Hesselberth|me]]**
   * **Be very careful when special detectors are mounted**, i.e. do not use GIS and use caution with tilt and Z
   * The SEM does not know what your specimen looks like. If your imaging plane is below the highest point of the specimen (ie when imaging an AFM cantilever from the side), setting the working distance to 1 mm will drive the highest point of the specimen into the final lens. If you regularly image such specimen, always use a dedicated specimen stub (have the workshop machine it if necessary) and use the Z limit for protection!
   * After switching on the HV, **link Z to FWD**
   * UHR mode switches on a strong immersion field. **A magnetic specimen will damage the system in UHR mode**
   * **ONLY tilt at eucentric height** with a single small stub in the center (not with the multi stub holder), use the CCD image for guidance (be sure it's not paused)
   * Use **extreme caution** when the touch alarm is not enabled (ie when you use the picoammeter)
   * Before inserting a GIS needle, **verify that you are at eucentric height**
   * Be careful not to switch off the electron source (if you have supervisor rights)
   * **Never push the 'Shutdown' button** on the microscope server. I consider the presence of this button a bug because it allows everyone to switch off the source.
   * **DO NOT switch on chamber illumination lamp** when HV and detectors are on, scintillator detectors will be damaged
   * **Make sure prep vacuum and airlock vacuum are OK** when operating the loadlock
   * In normal operation, the xT microscope server must always run. If it stops, restart it immediately and check source current (should be around 200 uA)
   * If the system has gone to the emergency shutdown mode, the UPS will keep powering the IGP's for 2 hours. **A SEM administrator must restart the electron gun within that amount of time**, otherwise FEI service has to come. Warn [[Marcel Hesselberth|Marcel]] (room 609a, phone 0646 29 59 00 or 071 5 222 679)
   * Prepare and mount samples on the preparation table. **No liquids** (solvents and other chemicals, silver/carbon paint, coffee and other beverages) are placed on the SEM column or the terminal table.
   * **It is TOTALLY, UNDER ALL CONDITIONS forbidden to change the state of the control PC.** You are not allowed to save a single file there, install a program, put in a CD, floppy or USB stick, it is not even allowed to change an icon on the desktop! All you do there is double click on the microscope server if necessary, start the User Interface and operate it. Data is saved via a share in the users/yourname directory that has been created on the data PC
   * It is equally forbidden to install software on the data PC. You can fetch your data via the share on the network. If you need a software package to be installed on the data PC (for analysis, electron scattering simulations etc.) contact [[Marcel Hesselberth|]].
   * **Contamination of the vacuum chamber must be avoided** at all cost! Treat all SEM parts (including stubs) as UHV components. 'Dirty' activities like deposition or LOWVAC SEM must be announced before in the reservation system and registered in the logbook.

===== For your data =====
Technical backups of the user PC will be made periodically. There are no arrangements with system management to do a full periodic backup right now, so you are responsible for backing up your own data, this can be changed by request.

====== Manual ======

It is necessary to follow the 'NanoSEM intro' before starting. This will typically take an hour or two (but is depending on your SEM experience) and will enable you to use the SEM in HV mode for imaging. Your software account will be created and you will get NanoSEM access to the reservation system.

If you want to use the system for special applications and need to use a GIS, change detectors or do any other activity that requires more tools than the Allen key for stub mounting it is necessary to follow an 'application intro'. Contact [[Marcel Hesselberth]] in this case.

  - Possibly contaminating activities (deposition, wet mode) must be announced in the reservation system
  - Before starting, fill out the logbook
  - Prepare your sample on the preparation table, mount it on a stub
  - Click 'Vent'
  - Make sure CCD (bottom right screen) is unfrozen. 
  - Mount the stub onto the stage, use the elephant to set a safe height
  - Keep an eye on CCD when closing the chamber
  - Click 'Pump'
  - Wait until a 1e-5 mbar is reached
  - Choose HV and spot
  - Click 'HV' to turn on the beam.
  - Adjust contrast and brightness
  - Focus (on the highest point of the sample) at a magnification > 2000 times
  - Link Z to FWD
  - Drive sample up to 10-15 mm, check CCD, keep finger above 'ESC-key'
  - Focus well at a magnification >2000 times
  - Link Z to FWD again
  - Drive sample up to the working height, check CCD, be prepared to hit 'Esc'
  - Set eucentric if necessary (see below)
  - LOCK Z-axis. Now you can switch to single-view.
  - You are in search mode, go to the feature of interest
  - Increase magnification
  - Switch to UHR mode (for a nonmagnetic sample)
  - Focus, correct astigmatism, lens alignment
  - Collect data
  - Fill in logbook before venting
  - Go to QUAD-view, unlock Z
  - When ready, click 'Vent' (High voltage, detectors and pumps are automatically switched off, stage drives down in a safe way), be prepared to hit 'ESC'
  - Remove your specimen stub
  - Call next user or pump down (don't keep chamber vented for a significant amount of time)
  - At the end of the day, switch off the displays
  - Go to your PC and transfer the data

If the SEM will not be used for a while (say, more than 2 days), go to standby mode by stopping the microscope, exiting the microscope server and shutting down the control PC (BUT DO NOT PRESS 'SHUTDOWN' button in the microscope server)

If you want to tilt or use a GIS, you need to set eucentric height. For tilting it is handy so set eucentric very accurately, it is done as follows:
  - Make sure Z and FWD are linked accurately and set 5.000 mm FWD at 0 tilt
  - Focus at M>2000 and move a feature of the sample to the center crosshair
  - Tilt about 5 degrees
  - The feature may move away a bit, bring it back by carefully adjusting Z
  - Go to 0 tilt and repeat this procedure for the maximum tilt you want to achieve
  - You now have the eucentric condition

If the microscope computer crashes:
  - restart computer
  - start the "XT microscope server" program
    * all 3 indicators on the right must be green, if not, call Marcel
  - press "start"
  - check if ALL indicators below become green (initialized), in case not, call Marcel
  - start UI, check pressure.

====== Deposition rates ======

Always deposit at eucentric height!
(below eucentric height the deposition rate is very low. Driving the GIS needle in above eucentric will cause a collision between the needle and the specimen!)

^ Material ^  Date     ^ Sample ID ^ Process parameters                         ^ Measured with  ^ Result         ^ Rate  ^
| Pt       | 20050415  | Pt1 (Marcel) | Spot 5, 50% overlap, 1000 passes, 1 us dwell  | AFM            | | -     |
|Pt        | 20050601  | Pt (Christianne)| Spot 4, 50% overlap, 248932 passes, 1 us dwell, Vol per Dose = 0.0178 um3/nC, Z-size = 500 nm | nanoSEM (43 degrees tilt) |  thickness: 495 nm (+/- 20 nm)   | -|