Frequently Asked Questions
Preparing your proposal
Below we give some information to help the users plan their experiment. All times given are only guidelines! For more information on the end-station, sample holders, in-situ preparation system, please look at the Endstations page. If there are still open questions, do not hesitate in contacting the beamline scientist.
How many shifts to ask?
That will depend on what is there to measure, as explained in the questions below. As a general guideline, for normal experiments that do not require any in-situ sample preparation, between 9 to 15 shifts is commonly allocated, depending on the complexity of the experiment. For experiments involving in-situ sample preparation normally 15 to 17 shifts is adequate. For sample preparation shifts look at the next item below.
How is the shift counting for sample preparation?
Beamtimes requiring in-situ sample preparation are scheduled, if possible, such that the sample preparation system can be accessed off-line a few days during the week preceding the beamtime. These preparation shifts do not count on the total proposal shift request. The shift request concerns only the actual beamtime.
How are the shifts defined?
One shift corresponds to 8 hours. The three shifts in the day are officially defined in the schedule as 7:00-15:00, 15:00-23:00, 23:00-7:00 (of next day).
How long does a measurement take?
One single energy scan takes around 3 minutes. However, dichroic measurements involve repeating these measurements for different polarization and applied field direction. In order to acquire good statistics, a dichoism measurement will take between 40 minutes up to 3 hrs, depending how strong the dichroic signal is.
One element specific magnetization curve takes at least one hour. This is the time for a full loop (field ramping in both directions). One curve is often enough, but since problems with baseline drifting might occur which cause curves not matching perfectly, the measurement of 2 or 3 curves is sometimes needed.
The time described above should be multiplied by the number of samples, absorption edges, temperature, geometries (in-plane, out-of-plane) one intends to measure. Besides, for changing and stabilizing in different temperatures one should count about 1/2 hr time. The time for sample changing is explained in the next question.
In the beginning of an experiment a few steps are needed to setup the measurements as: aligning the sample in the beam, finding best compromise of beamline settings in terms of energy resolution and flux. For that, an additional time of 1/2 shift (~4hrs) should be counted in addition to the measurement time.
How long takes the sample transfer?
There are several steps involved in sample transfer. Please, refer to the End-station sketch for more information on the different chambers cited here. The standard sample holder accomodates around 3 samples of 5x5mm. For in-situ sample preparation a 'Omicron' plate type sample holder is used, where only one substrate can be mounted.
The sample holder is first loaded in the load-lock and up to two sample holders can be loaded at the same time. The load-lock is then pumped down. This is the step which takes the longest time. We normally do it overnight (a minimum pumping of 5 hrs is required) so the first samples should be mounted on the day before starting the experiment. After the load-lock is pumped the process of transfering the sample holder from the load-lock to the cryostat takes about 5-10 minutes only. However, the sample insert MUST be at room temperature for sample transfer. The process of warming up to room temperature and cool down to base temperature (2K) takes 2 hours in average. This time should be added for every sample holder transfer required.
The transfer chamber (see End-station sketch) has a 'parking' stage where up to 5 sample holders can be mounted. This is an intermediate chamber where sample holders coming from the load-lock or from the in-situ sample preparation can be kept under vacuum while another sample holder is being measured. This chamber is kept at high vacuum, from 5e-10mbar to 1e-8mbar.
Which samples and which elements can be measured?
Our sample holders so far accomodate only solid samples. We can measure thin films, single crystals or powder samples. The working energy range of the beamline is 400eV to 1800eV. This range covers, for example, K-edges of O, F, N; L3,2 edges of Sc to Zn, the M3,2 edges of Mo to Pd; M5,4 edges of La to Lu. For checking if your element has an edge we can reach please check it in the CXRO website and consult the beamline scientist whether this edge has a strong enough resonance.