4 research outputs found
Growth of High-Mobility Bi<sub>2</sub>Te<sub>2</sub>Se Nanoplatelets on hBN Sheets by van der Waals Epitaxy
The electrical detection of the surface states of topological
insulators
is strongly impeded by the interference of bulk conduction, which
commonly arises due to pronounced doping associated with the formation
of lattice defects. As exemplified by the topological insulator Bi<sub>2</sub>Te<sub>2</sub>Se, we show that via van der Waals epitaxial
growth on thin hBN substrates the structural quality of such nanoplatelets
can be substantially improved. The surface state carrier mobility
of nanoplatelets on hBN is increased by a factor of about 3 compared
to platelets on conventional Si/SiO<sub><i>x</i></sub> substrates,
which enables the observation of well-developed Shubnikov-de Haas
oscillations. We furthermore demonstrate the possibility to effectively
tune the Fermi level position in the films with the aid of a back
gate
Thermoelectric Limitations of Graphene Nanodevices at Ultrahigh Current Densities
Graphene is atomically thin, possesses excellent thermal
conductivity,
and is able to withstand high current densities, making it attractive
for many nanoscale applications such as field-effect transistors,
interconnects, and thermal management layers. Enabling integration
of graphene into such devices requires nanostructuring, which can
have a drastic impact on the self-heating properties, in particular
at high current densities. Here, we use a combination of scanning
thermal microscopy, finite element thermal analysis, and operando scanning transmission electron microscopy techniques to observe
prototype graphene devices in operation and gain a deeper understanding
of the role of geometry and interfaces during high current density
operation. We find that Peltier effects significantly influence the
operational limit due to local electrical and thermal interfacial
effects, causing asymmetric temperature distribution in the device.
Thus, our results indicate that a proper understanding and design
of graphene devices must include consideration of the surrounding
materials, interfaces, and geometry. Leveraging these aspects provides
opportunities for engineered extreme operation devices
Thermoelectric Limitations of Graphene Nanodevices at Ultrahigh Current Densities
Graphene is atomically thin, possesses excellent thermal
conductivity,
and is able to withstand high current densities, making it attractive
for many nanoscale applications such as field-effect transistors,
interconnects, and thermal management layers. Enabling integration
of graphene into such devices requires nanostructuring, which can
have a drastic impact on the self-heating properties, in particular
at high current densities. Here, we use a combination of scanning
thermal microscopy, finite element thermal analysis, and operando scanning transmission electron microscopy techniques to observe
prototype graphene devices in operation and gain a deeper understanding
of the role of geometry and interfaces during high current density
operation. We find that Peltier effects significantly influence the
operational limit due to local electrical and thermal interfacial
effects, causing asymmetric temperature distribution in the device.
Thus, our results indicate that a proper understanding and design
of graphene devices must include consideration of the surrounding
materials, interfaces, and geometry. Leveraging these aspects provides
opportunities for engineered extreme operation devices
Impact of Spin-Entropy on the Thermoelectric Properties of a 2D Magnet
Heat-to-charge conversion efficiency of thermoelectric
materials
is closely linked to the entropy per charge carrier. Thus, magnetic
materials are promising building blocks for highly efficient energy
harvesters as their carrier entropy is boosted by a spin degree of
freedom. In this work, we investigate how this spin-entropy impacts
heat-to-charge conversion in the A-type antiferromagnet CrSBr. We
perform simultaneous measurements of electrical conductance and thermocurrent
while changing magnetic order using the temperature and magnetic field
as tuning parameters. We find a strong enhancement of the thermoelectric
power factor at around the Néel temperature. We further reveal
that the power factor at low temperatures can be increased by up to
600% upon applying a magnetic field. Our results demonstrate that
the thermoelectric properties of 2D magnets can be optimized by exploiting
the sizable impact of spin-entropy and confirm thermoelectric measurements
as a sensitive tool to investigate subtle magnetic phase transitions
in low-dimensional magnets