nARPES Samples

Substrates

    1) must be conducting (as in all ARPES).  There are two options if the sample substrates must be insulating:

        option a) grow the insulating sample on a conductor.  For example, we cannot measure on pure SrTiO3 (STO) due to charging, but we have successfully measured thin films on 18 unit cells of insulating STO grown on doped STO.  Similarly BN chunks in the thickness range of 10 nm are ideal substates for thin films.

        option b) top-contacting the insulatng overlayer and connecting to the sample holder

    2) must be flat enough.  This assessment depends on the thickness of the film of interest. 

 Examples that DON'T WORK are:

        monolayer material on top of 300 nm SiO2. The monolayers will conform to the substrate and spoil the angular resolution.  Graphene and monolayer TMDs do not work. The graphene bands are completely smeared away. The TMD bands are recognizable but heavily broadened.  Multilayers may be successful depending on material stiffness and interaction to the oxide.  Four layers of graphene on such SiO2 leads to recognizable, but still heavily broadened bands.  We suspect that TMD quad layers would give acceptable results but it is likely that the interface layer in such systems is distorted.

    similar to above, Bulk insulators such as MgO, Al2O3, glass, TiO2, etc DO NOT WORK

Examples that WORK for 2D Exfoliation are:

   ~20nm BN flake on top of  native oxide (typically few nm) SiO2 on Si makes a good flat, and sufficiently conducting substrate.  The SiO2 surface can be prepared by simply solvent cleaning of as-shipped wafers, or else by HF etching followed by H2O2 treatment.

    graphene on glass (as sold economically by Graphene Supermarket).  From the point of view of conductivity these are excellent, however the samples are still to rough to meet the flatness needs for direct deposition of 2D materials.  ~20 nm BN flake as above makes a good intermediary flat layer.