Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe limits of Near Field Immersion Microwave Microscopy evaluated by imaging bilayer graphene Moir{e} patterns
64
0
0.0
(
0
)
Added by
Gilberto Medeiros-Ribeiro
Publication date
2020
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
Molecular and atomic imaging required the development of electron and scanning probe microscopies to surpass the physical limits dictated by diffraction. Nano-infrared experiments and pico-cavity tip-enhanced Raman spectroscopy imaging later demonstrated that radiation in the visible range can surpass this limit by using scanning probe tips to access the near-field regime. Here we show that ultimate resolution can be obtained by using scanning microwave imaging microscopy to reveal structures with feature sizes down to 1~nm using a radiation of 0.1~m in wavelength. As a test material we use twisted bilayer graphene, which is not only a very important recent topic due to the discovery of correlated electron effects such as superconductivity, but also because it provides a sample where we can systematically tune a superstructure Moire patterns modulation from below one up to tens of nanometers. By analyzing the tip-sample distance dynamics, we demonstrate that this ultimate 10$^8$ probe-to-pattern resolution can be achieved by using liquid immersion microscopy concepts and exquisite force control exerted on nanoscale water menisci.
rate research
Read More
Strain-induced lattice mismatch leads to moir{e} patterns in homobilayer transition metal dichalcogenides (TMDs). We investigate the structural and electronic properties of such strained moir{e} patterns in TMD homobilayers. The moir{e} patterns in strained TMDs consist of several stacking domains which are separated by tensile solitons. Relaxation of these systems distributes the strain unevenly in the moir{e} superlattice, with the maximum strain energy concentrating at the highest energy stackings. The order parameter distribution shows the formation of aster topological defects at the same sites. In contrast, twisted TMDs host shear solitons at the domain walls, and the order parameter distribution in these systems shows the formation of vortex defects. The strained moir{e} systems also show the emergence of several well-separated flat bands at both the valence and conduction band edges, and we observe a significant reduction in the band gap. The flat bands in these strained moir{e} superlattices provide platforms for studying the Hubbard model on a triangular lattice as well as the ionic Hubbard model on a honeycomb lattice. Furthermore, we study the localization of the wave functions corresponding to these flat bands. The wave functions localize at different stackings compared to twisted TMDs, and our results are in excellent agreement with recent spectroscopic experiments [1].
The electronic structure of bilayer graphene is investigated from a resonant Raman study using different laser excitation energies. The values of the parameters of the Slonczewski-Weiss-McClure model for graphite are measured experimentally and some of them differ significantly from those reported previously for graphite, specially that associated with the difference of the effective mass of electrons and holes. The splitting of the two TO phonon branches in bilayer graphene is also obtained from the experimental data. Our results have implications for bilayer graphene electronic devices.
In stacks of two-dimensional crystals, mismatch of their lattice constants and misalignment of crystallographic axes lead to formation of moir{e} patterns. We show that moir{e} superlattice effects persist in twisted bilayer graphene with large twists and short moir{e} periods. Using angle-resolved photoemission, we observe changes in valence band topology across large parts of the Brillouin zone, including vicinity of the saddle point at M and across over 3 eV from the Dirac points. We also detect signatures of potential secondary Dirac points in the reconstructed dispersions. For twists $theta>21.8^{circ}$, scattering of electrons in one graphene layer on the potential of the other leads to intervalley coupling and minigaps at energies above the gap due to cone anti-crossing, usually considered the only low-energy feature due to interlayer coupling. Our work demonstrates robustness of mechanisms which enable engineering of electronic dispersions of stacks of two-dimensional crystals by tuning the interface twist angles.
Rotational misalignment of two stacked honeycomb lattices produces a moire pattern that is observable in scanning tunneling microscopy as a small modulation of the apparent surface height. This is known from experiments on highly-oriented pyrolytic graphite. Here, we observe the combined effect of three-layer moire patterns in multilayer graphene grown on SiC ($000bar{1}$). Small-angle rotations between the first and third layer are shown to produce a double-moire pattern, resulting from the interference of moire patterns from the first three layers. These patterns are strongly affected by relative lattice strain between the layers. We model the moire patterns as a beat-period of the mismatched reciprocal lattice vectors and show how these patterns can be used to determine the relative strain between lattices, in analogy to strain measurement by optical moire interferometry.
Surface plasmons are collective oscillations of electrons in metals or semiconductors enabling confinement and control of electromagnetic energy at subwavelength scales. Rapid progress in plasmonics has largely relied on advances in device nano-fabrication, whereas less attention has been paid to the tunable properties of plasmonic media. One such medium-graphene-is amenable to convenient tuning of its electronic and optical properties with gate voltage. Through infrared nano-imaging we explicitly show that common graphene/SiO2/Si back-gated structures support propagating surface plasmons. The wavelength of graphene plasmons is of the order of 200 nm at technologically relevant infrared frequencies, and they can propagate several times this distance. We have succeeded in altering both the amplitude and wavelength of these plasmons by gate voltage. We investigated losses in graphene using plasmon interferometry: by exploring real space profiles of plasmon standing waves formed between the tip of our nano-probe and edges of the samples. Plasmon dissipation quantified through this analysis is linked to the exotic electrodynamics of graphene. Standard plasmonic figures of merits of our tunable graphene devices surpass that of common metal-based structures.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
