18 research outputs found
The hot pick-up technique for batch assembly of van der Waals heterostructures
The assembly of individual two-dimensional materials into van der Waals
heterostructures enables the construction of layered three-dimensional
materials with desirable electronic and optical properties. A core problem in
the fabrication of these structures is the formation of clean interfaces
between the individual two-dimensional materials which would affect device
performance. We present here a technique for the rapid batch fabrication of van
der Waals heterostructures, demonstrated by the controlled production of 22
mono-, bi- and trilayer graphene stacks encapsulated in hexagonal boron nitride
with close to 100% yield. For the monolayer devices we found semiclassical mean
free paths up to 0.9 micrometer, with the narrowest samples showing clear
indications of the transport being affected by boundary scattering. The
presented method readily lends itself to fabrication of van der Waals
heterostructures in both ambient and controlled atmospheres, while the ability
to assemble pre-patterned layers paves the way for complex three-dimensional
architectures.Comment: 32 pages, 6 figures, 34 references, 14 supplementary figure
Graphene mobility mapping
Carrier mobility and chemical doping level are essential figures of merit for graphene, and large-scale characterization of these properties and their uniformity is a prerequisite for commercialization of graphene for electronics and electrodes. However, existing mapping techniques cannot directly assess these vital parameters in a non-destructive way. By deconvoluting carrier mobility and density from non-contact terahertz spectroscopic measurements of conductance in graphene samples with terahertz-transparent backgates, we are able to present maps of the spatial variation of both quantities over large areas. The demonstrated non-contact approach provides a drastically more efficient alternative to measurements in contacted devices, with potential for aggressive scaling towards wafers/minute. The observed linear relation between conductance and carrier density in chemical vapour deposition graphene indicates dominance by charged scatterers. Unexpectedly, significant variations in mobility rather than doping are the cause of large conductance inhomogeneities, highlighting the importance of statistical approaches when assessing large-area graphene transport properties