A5031129890- Graphene research and applications
- Quantum and electron transport phenomena
- 2D Materials and Applications
- Molecular Junctions and Nanostructures
- Carbon Nanotubes in Composites
- Semiconductor Quantum Structures and Devices
- Chalcogenide Semiconductor Thin Films
- Topological Materials and Phenomena
- Electron and X-Ray Spectroscopy Techniques
- Surface and Thin Film Phenomena
- Diamond and Carbon-based Materials Research
- Force Microscopy Techniques and Applications
- Advanced Electron Microscopy Techniques and Applications
- Organic and Molecular Conductors Research
- Thermal properties of materials
- Spectroscopy and Quantum Chemical Studies
- MXene and MAX Phase Materials
- Boron and Carbon Nanomaterials Research
- Thermal Radiation and Cooling Technologies
- Mechanical and Optical Resonators
- Quantum, superfluid, helium dynamics
- Nanowire Synthesis and Applications
- Quantum Information and Cryptography
- Plasmonic and Surface Plasmon Research
- Microfluidic and Capillary Electrophoresis Applications
University of Arizona
2016-2025
Oak Ridge National Laboratory
2018
Northwestern University
2014
Delft University of Technology
2003-2007
Harvard University
2000-2005
University of California, Santa Barbara
2001-2005
Harvard University Press
2003
Centre d'Études Scientifiques et Techniques d'Aquitaine
2002
Commissariat à l'Énergie Atomique et aux Énergies Alternatives
2002
Van der Waals heterostructures comprise a new class of artificial materials formed by stacking atomically-thin planar crystals. Here, we demonstrate band structure engineering van heterostructure composed monolayer graphene flake coupled to rotationally-aligned hexagonal boron nitride substrate. The spatially-varying interlayer atomic registry results both in local breaking the carbon sublattice symmetry and long-range moir\'e superlattice potential graphene. This interplay between short-...
We describe the realization of van der Waals (vdW) heterostructures with accurate rotational alignment individual layer crystal axes. illustrate approach by demonstrating a Bernal-stacked bilayer graphene formed using successive transfers monolayer flakes. The Raman spectra this artificial possess wide 2D band, which is best fit four Lorentzians, consistent Bernal stacking. Scanning tunneling microscopy reveals no moiré pattern on graphene, and spectroscopy as function gate voltage constant...
According to electronic structure theory, bilayer graphene is expected have anomalous properties when it has long-period moir\'e patterns produced by small misalignments between its individual layer honeycomb lattices. We realized crystals with accurately controlled twist angles smaller than 1 degree and studied their using scanning probe microscopy electron transport. observe conductivity minima at charge neutrality, satellite gaps that appear carrier densities for degree, tunneling...
The rise of two-dimensional (2D) materials research took place following the isolation graphene in 2004. These new 2D include transition metal dichalcogenides, mono-elemental sheets, and several carbide- nitride-based materials. number publications related to these emerging has been drastically increasing over last five years. Thus, through this comprehensive review, we aim discuss most recent groundbreaking discoveries as well opportunities remaining challenges. This review starts out by...
In minimally twisted bilayer graphene, a moiré pattern consisting of AB and BA stacking regions separated by domain walls forms. These are predicted to support counterpropogating topologically protected helical (TPH) edge states when the gapped. We fabricate designer crystals with wavelengths longer than 50 nm demonstrate emergence TPH on wall network scanning tunneling spectroscopy measurements. observe double-line profile walls, only occurring Our results practical flexible method for...
Scanning a charged tip above the two-dimensional electron gas inside gallium arsenide/aluminum arsenide nanostructure allows coherent flow from lowest quantized modes of quantum point contact at liquid helium temperatures to be imaged. As width is increased, its electrical conductance increases in steps 2 e(2)/h, where e charge and h Planck's constant. The angular dependence on each step agrees with theory, fringes separated by half wavelength are observed. Placing so that it interrupts...
We carried out scanning tunneling spectroscopy measurements on exfoliated monolayer graphene ${\text{SiO}}_{2}$ to probe the correlation between its electronic and structural properties. Maps of local density states are characterized by electron hole puddles that arise due long-range intravalley scattering from intrinsic ripples in random-charged impurities. At low energy, we observe short-range intervalley which attribute lattice defects. Our results demonstrate properties influenced...
Combining atomically-thin van der Waals materials into heterostructures provides a powerful path towards the creation of designer electronic devices. The interaction strength between neighbouring layers, most easily controlled through their interlayer separation, can have significant influence on properties these composite materials. Here, we demonstrate unprecedented control over interactions by locally modifying separation graphene and boron nitride, which achieve applying pressure with...
The field of graphene research has developed rapidly since its first isolation by mechanical exfoliation in 2004. Due to the relativistic Dirac nature charge carriers, is both a promising material for next-generation electronic devices and convenient low-energy testbed intrinsically high-energy physical phenomena. Both these branches require facile fabrication clean so as not obscure intrinsic properties. Hexagonal boron nitride emerged substrate it insulating, atomically flat provides...
We study the response of graphene to high-intensity, 50-femtosecond laser pulse excitation. establish that has a high (∼3 × 1012 Wcm−2) single-shot damage threshold. Above this threshold, single cleanly ablates graphene, leaving microscopically defined edges. Below we observe laser-induced defect formation leading degradation lattice over multiple exposures. identify modification processes through in-situ Raman microscopy. The effective lifetime chemical vapor deposition grown under...
Optical reflectivity contrast provides a simple, fast and noninvasive method for characterization of few monolayer samples two-dimensional materials. Here we apply this technique to measure the thickness thin flakes hexagonal Boron Nitride (hBN), which is material increasing interest in nanodevice fabrication. The optical shows strong negative peak at short wavelengths zero dependent wavelength. varies linearly 1-80 layers hBN, permits easy calibration thickness. We demonstrate applicability...
Controlling the flow of charge neutral interlayer exciton (IX) quasiparticles can potentially lead to low loss excitonic circuits. Here, we report unidirectional transport IXs along nanoscale electrostatically defined channels in an MoSe2–WSe2 heterostructure. These results are enabled by a lithographically triangular etch graphene gate create potential energy "slide". By performing spatially and temporally resolved photoluminescence measurements, measure smoothly varying IX structure high...
Abstract Interlayer excitons (IXs) in MoSe 2 –WSe heterobilayers have generated interest as highly tunable light emitters transition metal dichalcogenide (TMD) heterostructures. Previous reports of spectrally narrow (<1 meV) photoluminescence (PL) emission lines at low temperature been attributed to IXs localized by the moiré potential between TMD layers. We show that IX PL are present even when is suppressed inserting a bilayer hexagonal boron nitride (hBN) spacer compare doping,...
We present a lithography-free technique for fabrication of clean, high quality graphene devices. This is based on evaporation through hard Si shadow masks, and eliminates contaminants introduced by lithographical processes. demonstrate that devices fabricated this have significantly higher mobility values than those obtained standard electron beam lithography. To obtain ultra-high devices, we extend to fabricate suspended samples with mobilities as 120 000 cm2/(V·s).
We report scanning tunneling microscopy (STM) and spectroscopy (STS) measurements of monolayer bilayer WSe$_2$. measure a band gap 2.21 $\pm$ 0.08 eV in WSe$_2$, which is much larger than the energy photoluminescence peak indicating large excitonic binding energy. additionally observe significant electronic scattering arising from atomic-scale defects. Using Fourier transform STS (FT-STS), we map versus momentum dispersion relations for Further, by tracking allowed forbidden channels as...
For quantum technologies based on single excitons and spins, the deterministic placement control of a exciton is long-standing goal. MoSe2-WSe2 heterostructures host spatially indirect interlayer (IXs) which exhibit highly tunable energies unique spin-valley physics, making them promising candidates for information processing. Previous IX trapping approaches involving moir\'e superlattices nanopillars do not meet technology requirements energy tunability. Here, we use nanopatterned graphene...
The stacking order degree of freedom in trilayer graphene plays a critical role determining the existence an electric field tunable band gap. We present spatially-resolved tunneling spectroscopy measurements dual gated Bernal (ABA) and rhombohedral (ABC) stacked devices. demonstrate that while ABA remains metallic, ABC exhibits widely gap as function field. However, we find charged impurities underlying substrate cause substantial spatial fluctuation size. Our work elucidates microscopic...
Fast carrier cooling is important for high power graphene based devices. Strongly coupled optical phonons play a major role in the relaxation of photoexcited carriers graphene. Heterostructures and hexagonal boron nitride (hBN) have shown exceptional mobility saturation current, which makes them ideal applications, but effect hBN substrate on mechanisms not understood. We track hot photo-excited graphene-hBN heterostructures using ultrafast pump-probe spectroscopy. find that cool down four...