1D Edge Contacts to 2D Material Heterostructures
Publicerad
Författare
Typ
Examensarbete för masterexamen
Program
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Graphene has been in the focus of research in many fields of applications due to its
unique properties. In particular, the 2D nature, low charge carrier concentration and
high mobility of carriers are promising properties for the use in magnetic Hall sensors.
At the same time, low spin-orbit coupling and negligible hyperfine interactions make
it interesting for spin-polarized electron transport. However, single graphene layer,
if unprotected, is prone to defects introduced during fabrication processes and also
defects due to interfaces with other insulators or contact materials. These factors
would inevitably lead to decrease of graphene device performance. By encapsulating
graphene in hexagonal boron nitride (h-BN), another insulating atomically flat twodimensional
(2D) material with superior interface properties with graphene, one
can fabricate heterostructures for robust and high-performance devices. Utilizing
one-dimensional (1D) edge contacts to graphene sheet in such devices based on
2D materials would also allow to minimize contacts-induced degradation of channel
properties.
The graphene/h-BN heterostructures for studied devices were prepared both by
exfoliation from bulk crystals and by transfer of CVD-grown materials over large
area. After patterning the 2D heterostructures, 1D edge contacts were fabricated
by means of electron or laser beam lithography and electron beam evaporation of
metals. In these devices, proof-of-concept for batch fabrication of Hall elements on
large area all-CVD h-BN/graphene/h-BN heterostructures is demonstrated. Such
1D edge contacts of ferromagnetic materials to graphene/h-BN heterostructures are
also explored for spin injection into graphene in devices with novel design.
The findings described in this thesis allow to advance the graphene Hall elements
fabrication technology towards large-scale, industry-compatible manufacturing and
lay basis for understanding and further optimization of the phenomena that drive
and influence the operation of graphene spin-based devices with novel design involving
1D edge contacts.
Beskrivning
Ämne/nyckelord
graphene, hexagonal boron nitride, 2D materials, van der Waals heterostructures, 1D edge contacts, Hall sensors, nonlocal spin valve, local Hall effect