Modern spintronics involves the development of clean low-dimensional electronic systems with the goal of coherent control of spin transport for quantum-based computation. Graphene is an ideal platform towards this goal, thanks to its potential to embed exceptionally high-quality electronic transport. In this thesis, we report the observation of efficient and tunable spin injection in high-quality and fully-encapsulated graphene, enabled by van der Waals heterostructures with one-dimensional (1D) contacts. The nanoscale-wide 1D contacts offer a sizeable and gate-tunable contact resistance, allowing spin injection both at room and at low temperature, with the latter exhibiting spin injection efficiency comparable with standard two-dimensional (2D) tunnel contacts. This architecture prevents significant doping from the contacts within the graphene channel, a problem inherent to standard 2D contacts, allowing us to routinely achieve high-quality channels with mobilities up to approx. 130,000 cm2V-1s-1, which remains constant within a range of technologically relevant carrier densities, and electron mean free paths comparable with the dimensions of the channel, which may indicate that the device is in a quasi-ballistic spin transport regime. Electrical control of cooling and heating is of considerable interest in the electronics industry. The study of thermoelectric effects in 2D heterostructures may deliver a technology to these important applications. Recently, thermoelectric effects in graphene have been studied when fabricated on SiO2, Boron Nitride (hBN) substrates and fully hBN encapsulated. However, when the graphene and hBN are aligned the Density of States (DoS) is modified; thermoelectrics in such structures has not been studied to date. In this thesis, we report the use of thermoelectric measurements as a complementary characterisation of 2D materials electronic band structure. Additionally, we show extra features around the secondary Dirac points of the thermopower, for an aligned device, which are different from that of the non-aligned device. The trends for the primary feature and these secondary features with respect to the device temperature has the potential to lead to novel technologies.
|Date of Award||6 Jan 2021|
- The University of Manchester
|Supervisor||Irina Grigorieva (Supervisor) & Ivan Vera Marun (Supervisor)|
- one-dimensional contacts