Samples

   1) Size: depends on the measurement you want to do

        a) samples which are homogenous on > 10 micron scale should be done in microARPES or PEEM before nanoARPES is attempted.

        b) nanoARPES samples should be at least a few hundred nm to a micron size.

    2) Insulating: samples that are insulating such as WS2 do not work unless there is a conductive path directly to the place where the probe beam is applied.  That is, side-contacting such insulating materials DOES NOT WORK. They must be deposited onto a conductive substrate, or top-contacted everywhere with a sufficiently thin conductor (like graphene).  If samples must be deposited on insulators, then these should be thin enough and themselves contacted everywhere underneath by a conductor. 

    3) Contacting: Samples that need one contact can readily achieve this by attaching a contact (lithographically, or by silver painting) that can be connected electrically to the sample holder.  We are currently commissioning a sample stage with up to 8 contacts for in operando measurements. Drawings of the contacting sample holder are shown in the figures below.  We have typically attached contacts to the heads of the 8 central screws via silver epoxy or wire wedge bonding.  Samples are held down typically by strapping down with wire attached at 4 threaded holes at the periphery, held in place by screws.  The best mounting practices are still being developed so please check with the beamline scientists before proceeding with mounting to get the latest information.

We have recently commissioned an adaptor for our sample holder, based on the JEDEC MS-004-CD standard.  Users should purchase as many as they like, and these are mounted at the beamline onto our adaptor holder, pictured below.  These carriers are available from many vendors, but we have found that those by Kyocera part number PB-34428 are the only fully non-magnetic ones and are the only ones we recommend.  The only vendor we have found is Evergreen Semiconductor.  

Multi-contact in operando sample holder platform

We developed an 8-contact sampleholder that may be used as a platform for developing complex in operando devices for ARPES spectromicroscopy. Both nanoARPES and microARPES have been outfitted with docks that can accept these sample holders.

A Keysight/Agilent 34970A Data aquisition/switching unit is used to multiplex the 8 holder contacts into the I/O connections of two Keithly 2450 SMUs.  The assignment of contacts to function is arbitrary and can be directed to the correct SMU channels through a graphical software interface at the beamline.  For more details, refer to the transport measurements page.