Jairo Velasco Jr.

University of California, Santa Cruz, Physics, Faculty Member

Followers

Following

Co-authors

Public Views

I am a condensed matter physicist trained in low temperature electron transport at high magnetic fields and in scanning tunneling microscopy (STM). I am also an expert in device fabrication based on 2D layered materials.

Research in 2D materials is rewarding because it explores both purely scientific and fundamental engineering questions. Uniquely, these materials host different types of exotic ground states that emerge because of correlated phenomena, and also have the potential for enabling new technologies that may transform our everyday lives. Within this context my lab will pursue three directions:

(i) Development of novel device types using ultra-clean fabrication techniques.
(ii) Characterization of these devices at the nanoscale with a combined low temperature scanning tunneling microscope (STM) and transport measurement scheme that also has optical capabilities.
(iii) Manipulation of the electronic structure of these devices by surface modification techniques, deliberate substrate coupling, and light.
Supervisors: Professor Jeanie Lau and Professor Mike Crommie

less

Zhejiang University

Damghan University

Joaquín Fernández Rossier

University of Alicante / Universidad de Alicante

zhenyuan zhang

Rutgers, The State University of New Jersey

sadegh aghaei

Markus Morgenstern

Moshe Ben Shalom

The University of Manchester

InterestsView All (7)

Uploads

Papers by Jairo Velasco Jr.

Visualization and Manipulation of Bilayer Graphene Quantum Dots with Broken Rotational Symmetry and Nontrivial Topology

Nano Letters, Nov 23, 2020

Electrostatically defined quantum dots (QDs) in Bernal stacked bilayer graphene (BLG) are a promi... more Electrostatically defined quantum dots (QDs) in Bernal stacked bilayer graphene (BLG) are a promising quantum information platform because of their long spin decoherence times, high sample quality, and tunability. Importantly, the shape of QD states determine the electron energy spectrum, the interactions between electrons, and the coupling of electrons to their environment, all of which are relevant for quantum information processing. Despite its importance, the shape of BLG QD states remains experimentally unexamined. Here we report direct visualization of BLG QD states by using a scanning tunneling microscope. Strikingly, we find these states exhibit a robust broken rotational symmetry. By using a numerical tight-binding model, we determine that the observed broken rotational symmetry can be attributed to low energy anisotropic bands. We then compare confined holes and electrons and demonstrate the influence of BLG's nontrivial band topology. Our study distinguishes BLG QDs from prior QD platforms with trivial band topology.

Download

$Research paper thumbnail of A boron nitride - graphene - C$_{60}$ heterostructure$

A boron nitride - graphene - C$_{60}$ heterostructure

Bulletin of the American Physical Society, Mar 5, 2015

Berkeley-We have fabricated a new van-der-Waals heterostructure composed by BN/graphene/C 60. We ... more Berkeley-We have fabricated a new van-der-Waals heterostructure composed by BN/graphene/C 60. We performed transport measurements on the preliminary BN/graphene device finding a sharp Dirac point at the neutrality point. After the deposition of a C 60 thin film by thermal evaporation, we have observed a significant n-doping of the heterostructure. This suggests an unusual electron transfer from C 60 into the BN/graphene structure. This BN/graphene/C 60 heterostructure can be of interest in photovoltaic applications. It can be used to build devices like p-n junctions, where C 60 can be easily deposited in defined regions of a graphene junction by the use of a shadow mask. Our results are contrasted with theoretical calculations.

Download

Surface states and quasiparticle interference in Bernal and rhombohedral graphite with and without trigonal warping

Physical review, Oct 13, 2021

We use an exact analytical technique [Phys. Rev. B 101, 115405 (2020), Phys. Rev. B 102, 165117 (... more We use an exact analytical technique [Phys. Rev. B 101, 115405 (2020), Phys. Rev. B 102, 165117 (2020)] to recover the surface Green's functions for Bernal (ABA) and rhombohedral (ABC) graphite. For rhombohedral graphite we recover the predicted surface flat bands. For Bernal graphite we find that the surface state spectral function is similar to the bilayer one, but the trigonal warping effects are enhanced, and the surface quasiparticles have a much shorter lifetime. We subsequently use the T-matrix formalism to study the quasiparticle interference patterns generated on the surface of semi-infinite ABA and ABC graphite in the presence of impurity scattering. We compare our predictions to experimental STM data of impurity-localized states on the surface of Bernal graphite which appear to be in a good agreement with our calculations.

Download

Direct Visualization of Native Defects in Graphite and Their Effect on the Electronic Properties of Bernal-Stacked Bilayer Graphene

Nano Letters, Aug 20, 2021

Graphite crystals used to prepare graphene-based heterostructures are generally assumed to be def... more Graphite crystals used to prepare graphene-based heterostructures are generally assumed to be defect free. We report here scanning tunneling microscopy results that show graphite commonly used to prepare graphene devices can contain a significant amount of native defects. Extensive scanning of the surface allows us to determine the concentration of native defects to be 6.6 10 8 cm-2. We further study the effects of these native defects on the electronic properties of Bernal-stacked bilayer graphene. We observe gate-dependent intravalley scattering and successfully compare our experimental results to T-matrix-based calculations, revealing a clear carrier density dependence in the distribution of the scattering vectors. We also present a technique for evaluating the spatial distribution of short-scale scattering. A theoretical analysis based on the Boltzmann transport equation predicts that the dilute native defects identified here are an important extrinsic source of scattering, ultimately setting the mobility at low temperatures.

Download

$Research paper thumbnail of Direct growth of single- and few-layer MoS$_{\mathrm{2}}$ on h-BN by CVD method$

Direct growth of single- and few-layer MoS$_{\mathrm{2}}$ on h-BN by CVD method

Bulletin of the American Physical Society, Mar 18, 2016

and LBNL-As a promising candidate for the next-generation electronics, large-scale single-and few... more and LBNL-As a promising candidate for the next-generation electronics, large-scale single-and few-layer molybdenum disulfide (MoS 2) grown by CVD method is an important advancement towards technological implementation of this material. However, the choice of substrate can significantly affect the performance of MoS 2 based devices. An attractive insulating substrate or mate for MoS 2 (and related materials such as graphene) is hexagonal boron nitride (h-BN). Stacked heterostructures of MoS 2 and h-BN have been produced by manual transfer methods, but a more efficient and scalable assembly method is needed. Here we demonstrate the direct growth of single-and few-layer MoS 2 on h-BN by chemical vapor deposition (CVD) method. The growth mechanisms for single-and few-layer samples are found to be distinct, and for single-layer samples low relative rotation angles (<5) between the MoS 2 and h-BN lattices prevail. In addition, MoS 2 directly grown on h-BN maintains its intrinsic 1.89 eV bandgap. Our CVD synthesis method presents a viable path towards high-quality MoS 2 based field effect transistors in a controllable and scalable fashion.

Download

Giant orbital magnetic moments and paramagnetic shift in artificial relativistic atoms and molecules

Nature Nanotechnology, Mar 1, 2023

Massless Dirac fermions have been observed in various materials such as graphene and topological ... more Massless Dirac fermions have been observed in various materials such as graphene and topological insulators in recent years, thus offering a solid-state platform to study relativistic quantum phenomena. Single quantum dots (QDs) and coupled QDs formed with massless Dirac fermions can be viewed as artificial relativistic atoms and molecules, respectively. Such structures offer a unique platform to study atomic and molecular physics in the ultra-relativistic regime. Here, we use a scanning tunneling microscope to create and probe single and coupled electrostatically defined graphene QDs to unravel the unique magnetic field responses of artificial relativistic nanostructures. Giant orbital Zeeman splitting and orbital magnetic moment up to ~70 meV/T and ~600 are observed in single graphene QDs. While for coupled graphene QDs, Aharonov-Bohm oscillations and strong Van Vleck paramagnetic shift (~20 meV/T 2) are observed. Such properties of artificial relativistic atoms and molecules can be leveraged for novel magnetic field sensing modalities.

Download

Quasiparticle interference patterns in bilayer graphene with trigonal warping

Physical Review B

We calculate the form of quasiparticle interference patterns in bilayer graphene within a lowener... more We calculate the form of quasiparticle interference patterns in bilayer graphene within a lowenergy description, taking into account perturbatively the trigonal warping terms. We introduce four different types of impurities localized on the A and B sublattices of the first and the second layer, and we obtain closed-form analytical expressions both in real and Fourier spaces for the oscillatory corrections to the local density of states generated by the impurities. Finally, we compare our findings with recent experimental and semi-analytical T-matrix results from arXiv:2104.10620 and we show that there is a very good agreement between our findings and the previous results, as well as with the experimental data.

Download

Persistent and reversible electrostatic control of doping in graphene/hexagonal boron nitride heterostructures

Journal of Applied Physics, 2020

Since its first application as a substrate for graphene field effect transistors (FETs), hexagona... more Since its first application as a substrate for graphene field effect transistors (FETs), hexagonal boron nitride (hBN) has become a prominent component in two-dimensional (2D) material devices. In addition, hBN has been shown to host defects that can be manipulated to change the electronic properties of adjacent 2D materials. Despite the wide use of such defect manipulations, no focused efforts have been made to further the understanding of defect excitations and their influence in graphene/hBN FETs. In this study, we explore the effect of high electric fields (∼10V/nm) on graphene/hBN FETs and find that persistent and reversible shifts in graphene's charge neutrality point (CNP) occur. By increasing the applied electric field and temperature of our device, we find that this CNP shift is enhanced. With this insight, we propose a mechanism that explains these observations based on Poole–Frenkel emissions from defects in hBN. Finally, we show that such an effect may be suppressed ...

Download

$Research paper thumbnail of Direct CVD Growth of Monolayer Graphene on Exfoliated BN on SiO $ _ {2} $$

Direct CVD Growth of Monolayer Graphene on Exfoliated BN on SiO $ _ {2} $

Download

Imaging electrostatically confined Dirac fermions in graphene quantum dots

Nature Physics, 2016

Electrostatic confinement of charge carriers in graphene is governed by Klein tunnelling, a relat... more Electrostatic confinement of charge carriers in graphene is governed by Klein tunnelling, a relativistic quantum process in which particle-hole transmutation leads to unusual anisotropic transmission at p-n junction boundaries 1-5. Reflection and transmission at these boundaries a ect the quantum interference of electronic waves, enabling the formation of novel quasi-bound states 6-12. Here we report the use of scanning tunnelling microscopy to map the electronic structure of Dirac fermions confined in quantum dots defined by circular graphene p-n junctions. The quantum dots were fabricated using a technique involving local manipulation of defect charge within the insulating substrate beneath a graphene monolayer 13. Inside such graphene quantum dots we observe resonances due to quasi-bound states and directly visualize the quantum interference patterns arising from these states. Outside the quantum dots Dirac fermions exhibit Friedel oscillation-like behaviour. Bolstered by a theoretical model describing relativistic particles in a harmonic oscillator potential, our findings yield insights into the spatial behaviour of electrostatically confined Dirac fermions. Quantum confinement in graphene has previously been accomplished through lithographically patterned structures 14-17 , graphene edges 18 , and chemically synthesized graphene islands 19-22. These systems, however, are either too contaminated for direct wavefunction visualization or use metallic substrates that prevent electrostatic gating. Electron confinement in graphene has also been induced through high magnetic fields 23 and supercritical impurities 24 , but these methods are unwieldy for many technological applications. An alternative approach for confining electrons in graphene relies on using electrostatic potentials. However, this is notoriously difficult because Klein tunnelling renders electric potentials transparent to massless Dirac fermions at non-oblique incidence 1-5. Nevertheless, it has been theoretically predicted that a circular graphene p-n junction can localize Dirac electrons and form quasi-bound quantum dot states 6-11. A recent tunnelling spectroscopy experiment 12 revealed signatures of electron confinement induced by the electrostatic potential created by a charged scanning tunnelling microscope (STM) tip. However, since the confining potential moves with the STM tip, this method allows neither spatial imaging of the resulting confined modes nor patterning control of the confinement potential.

Download

Nanospot angle-resolved photoemission study of Bernal-stacked bilayer graphene on hexagonal boron nitride: Band structure and local variation of lattice alignment

Physical Review B, 2019

Hexagonal boron nitride (hBN) is the supporting substrate of choice for two-dimensional material ... more Hexagonal boron nitride (hBN) is the supporting substrate of choice for two-dimensional material devices because it is atomically flat and chemically inert. However, due to the small size of mechanically exfoliated hBN flakes, electronic structure studies of 2D materials supported by hBN using angle-resolved photoemission spectroscopy (ARPES) are challenging. Here we investigate the electronic band structure of a Bernal-stacked bilayer graphene sheet on a hexagonal boron nitride (BLG/hBN) flake using nanospot ARPES (nanoARPES). By fitting high-resolution energy vs. momentum electronic band spectra, we extract the tight-binding parameters for BLG on hBN. In addition, we reveal spatial variations of the alignment angle between BLG and hBN lattices via inhomogeneity of the electronic bands near the Fermi level. We confirmed these findings by scanning tunneling microscopy measurements obtained on the same device. Our results from spatially resolved nanoARPES measurements of BLG/hBN heterostructures are instrumental for understanding experiments that utilize spatially averaging techniques such as electronic transport and optical spectroscopy.

Download

Comprehensive Electrostatic Modeling of Exposed Quantum Dots in Graphene/Hexagonal Boron Nitride Heterostructures

Nanomaterials

Recent experimental advancements have enabled the creation of tunable localized electrostatic pot... more Recent experimental advancements have enabled the creation of tunable localized electrostatic potentials in graphene/hexagonal boron nitride (hBN) heterostructures without concealing the graphene surface. These potentials corral graphene electrons yielding systems akin to electrostatically defined quantum dots (QDs). The spectroscopic characterization of these exposed QDs with the scanning tunneling microscope (STM) revealed intriguing resonances that are consistent with a tunneling probability of 100% across the QD walls. This effect, known as Klein tunneling, is emblematic of relativistic particles, underscoring the uniqueness of these graphene QDs. Despite the advancements with electrostatically defined graphene QDs, a complete understanding of their spectroscopic features still remains elusive. In this study, we address this lapse in knowledge by comprehensively considering the electrostatic environment of exposed graphene QDs. We then implement these considerations into tight b...

Download

Determination of the trigonal warping orientation in Bernal-stacked bilayer graphene via scanning tunneling microscopy

Physical Review B

The existence of strong trigonal warping around the K point for the low energy electronic states ... more The existence of strong trigonal warping around the K point for the low energy electronic states in multilayer (2) graphene films and graphite is well established. It is responsible for phenomena such as Lifshitz transitions and anisotropic ballistic transport. The absolute orientation of the trigonal warping with respect to the center of the Brillouin zone is however not agreed upon. Here, we use quasiparticle scattering experiments on a gated bilayer graphene/hexagonal boron nitride heterostructure to settle this disagreement. We compare Fourier transforms of scattering interference maps acquired at various energies away from the charge neutrality point with tight-binding-based joint density of states simulations. This comparison enables unambiguous determination of the trigonal warping orientation for bilayer graphene low energy states. Our experimental technique is promising for quasi-directly studying fine features of the band structure of gated two-dimensional materials such as topological transitions, interlayer hybridization, and moiré minibands.

Download

Visualizing the Effect of an Electrostatic Gate with Angle-Resolved Photoemission Spectroscopy

Nano Letters

Electrostatic gating is pervasive in materials science, yet its effects on the electronic band st... more Electrostatic gating is pervasive in materials science, yet its effects on the electronic band structure of materials has never been revealed directly by angle-resolved photoemission spectroscopy (ARPES), the technique of choice to non-invasively probe the electronic band structure of a material. By means of a state-of-the-art ARPES setup with sub-micron spatial resolution, we have investigated a heterostructure composed of Bernal-stacked bilayer graphene (BLG) on hexagonal boron nitride and deposited on a graphite flake. By voltage biasing the latter, the electric field effect is directly visualized on the valence band as well as on the carbon 1s core level of BLG. The band gap opening of BLG submitted to a transverse electric field is discussed and the importance of intralayer screening is put forward. Our results pave the way for new studies that will use momentum-resolved electronic structure information to gain insight on the physics of materials submitted to the electric field effect.

Download

Visualization and Control of Single-Electron Charging in Bilayer Graphene Quantum Dots

Nano letters, Aug 8, 2018

Graphene p-n junctions provide an ideal platform for investigating novel behavior at the boundary... more Graphene p-n junctions provide an ideal platform for investigating novel behavior at the boundary between electronics and optics that arise from massless Dirac Fermions, such as whispering gallery modes and Veselago lensing. Bilayer graphene also hosts Dirac Fermions, but they differ from single-layer graphene charge carriers because they are massive, can be gapped by an applied perpendicular electric field, and have very different pseudospin selection rules across a p-n junction. Novel phenomena predicted for these massive Dirac Fermions at p-n junctions include anti-Klein tunneling, oscillatory Zener tunneling, and electron cloaked states. Despite these predictions there has been little experimental focus on the microscopic spatial behavior of massive Dirac Fermions in the presence of p-n junctions. Here we report the experimental manipulation and characterization of massive Dirac Fermions within bilayer graphene quantum dots defined by circular p-n junctions through the use of sc...

Download

Photoinduced doping in heterostructures of graphene and boron nitride

by Salman Kahn, C. Nosiglia, Jairo Velasco Jr., and T. Taniguchi

The design of stacks of layered materials in which adjacent layers interact by van der Waals forc... more The design of stacks of layered materials in which adjacent layers interact by van der Waals forces 1 has enabled the combination of various two-dimensional crystals with different electrical, optical and mechanical properties as well as the emergence of novel physical phenomena and device functionality 2-8 . Here, we report photoinduced doping in van der Waals heterostructures consisting of graphene and boron nitride layers. It enables flexible and repeatable writing and erasing of charge doping in graphene with visible light. We demonstrate that this photoinduced doping maintains the high carrier mobility of the graphene/ boron nitride heterostructure, thus resembling the modulation doping technique used in semiconductor heterojunctions, and can be used to generate spatially varying doping profiles such as p-n junctions. We show that this photoinduced doping arises from microscopically coupled optical and electrical responses of graphene/boron nitride heterostructures, including optical excitation of defect transitions in boron nitride, electrical transport in graphene, and charge transfer between boron nitride and graphene.

Download

Fabrication of Gate-tunable Graphene Devices for Scanning Tunneling Microscopy Studies with Coulomb Impurities

by Salman Kahn, Youngkyou Kim, and Jairo Velasco Jr.

Journal of Visualized Experiments, 2015

Owing to its relativistic low-energy charge carriers, the interaction between graphene and variou... more Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees of freedom to control electronic devices. In particular, the behavior of graphene&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s charge carriers in response to potentials from charged Coulomb impurities is predicted to differ significantly from that of most materials. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) can provide detailed information on both the spatial and energy dependence of graphene&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s electronic structure in the presence of a charged impurity. The design of a hybrid impurity-graphene device, fabricated using controlled deposition of impurities onto a back-gated graphene surface, has enabled several novel methods for controllably tuning graphene&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s electronic properties.(1-8) Electrostatic gating enables control of the charge carrier density in graphene and the ability to reversibly tune the charge(2) and/or molecular(5) states of an impurity. This paper outlines the process of fabricating a gate-tunable graphene device decorated with individual Coulomb impurities for combined STM/STS studies.(2-5) These studies provide valuable insights into the underlying physics, as well as signposts for designing hybrid graphene devices.

Characterization and manipulation of individual defects in insulating hexagonal boron nitride using scanning tunnelling microscopy

by Jairo Velasco Jr., Salman Kahn, and Chad Germany

Defects play a key role in determining the properties and technological applications of nanoscale... more Defects play a key role in determining the properties and technological applications of nanoscale materials and, because they tend to be highly localized, characterizing them at the single-defect level is of particular importance. Scanning tunnelling microscopy has long been used to image the electronic structure of individual point defects in conductors1, semiconductors2, 3, 4 and ultrathin films5, 6, 7, 8, 9, but such single-defect electronic characterization remains an elusive goal for intrinsic bulk insulators. Here, we show that individual native defects in an intrinsic bulk hexagonal boron nitride insulator can be characterized and manipulated using a scanning tunnelling microscope. This would typically be impossible due to the lack of a conducting drain path for electrical current. We overcome this problem by using a graphene/boron nitride heterostructure, which exploits the atomically thin nature of graphene to allow the visualization of defect phenomena in the underlying bulk boron nitride. We observe three different defect structures that we attribute to defects within the bulk insulating boron nitride. Using scanning tunnelling spectroscopy we obtain charge and energy-level information for these boron nitride defect structures. We also show that it is possible to manipulate the defects through voltage pulses applied to the scanning tunnelling microscope tip.

Download

Nanoscale Control of Rewriteable Doping Patterns in Pristine Graphene/Boron Nitride Heterostructures

by Jairo Velasco Jr., Salman Kahn, and Juwon Lee

Nanoscale control of charge doping in two-dimensional (2D) materials permits the realization of e... more Nanoscale control of charge doping in two-dimensional (2D) materials permits the realization of electronic analogs of optical phenomena, relativistic physics at low energies, and technologically promising nanoelectronics. Electrostatic gating and chemical doping are the two most common methods to achieve local control of such doping. However, these approaches suffer from complicated fabrication processes that introduce contamination, change material properties irreversibly, and lack flexible pattern control. Here we demonstrate a clean, simple, and reversible technique that permits writing, reading, and erasing of doping patterns for 2D materials at the nanometer scale. We accomplish this by employing a graphene/boron nitride heterostructure that is equipped with a bottom gate electrode. By using electron transport and scanning tunneling microscopy (STM), we demonstrate that spatial control of charge doping can be realized with the application of either light or STM tip voltage excitations in conjunction with a gate electric field. Our straightforward and novel technique provides a new path toward on-demand graphene p−n junctions and ultrathin memory devices. KEYWORDS: Graphene/boron nitride heterostructures, scanning tunneling microscopy, p−n junctions, boron nitride defects L ocal control of charge doping in 2D systems allows for the study of new classes of phenomena that include electronic lensing, 1,2 Klein tunneling, 3,4 ultrathin light emitting diodes, 5−7 and in situ tunable plasmonic platforms. 8 The fabrication of nanostructures exhibiting such doping, however, requires sophisticated lithography procedures that compromise sample quality and do not yield flexible control of doping patterns, 9−14 thus hampering advancement in these areas. Some progress has been made in patterning buried GaAs/AlGaAs heterojunctions via a lithography-free conducting AFM tip-based technique 15 although only for a single dopant polarity. For more open graphene/BN heterostructures, it has been shown that illumination via visible light causes defect charge migration within the BN layer, thus shifting the graphene charge neutrality point (CNP) 16 and inducing doping. Currently, however, there is no understanding of how such defect charge migration varies spatially at the nanoscale and whether it might be exploited as a tool for developing new 2D devices. Here we address these issues directly via a new scheme that combines optical and local electric field excitation of defect charge in a BN insulator overlaid with graphene. This permits us to write, read, and even erase doping patterns at the nanoscale. Unlike other tip-based patterning methods, 15 this new technique allows direct wave function mapping of 2D devices and control over local doping polarity. Figure 1 shows two different schemes that we used for creating our rewritable doping patterns in a graphene/BN heterostructure supported by an SiO 2 /Si substrate and contacted by gold/chrome electrodes. A backgate voltage V g applied to the doped Si substrate permits global tuning of the graphene doping level, while local modification is achieved by excitation (via photons or DC electric field) of electrons (holes) from donor-like

Download

Fabrication of Gate-tunable Graphene Devices for Scanning Tunneling Microscopy Studies with Coulomb Impurities

by Jairo Velasco Jr. and Youngkyou Kim

Journal of Visualized Experiments, 2015

Owing to its relativistic low-energy charge carriers, the interaction between graphene and variou... more Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees of freedom to control electronic devices. In particular, the behavior of graphene&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s charge carriers in response to potentials from charged Coulomb impurities is predicted to differ significantly from that of most materials. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) can provide detailed information on both the spatial and energy dependence of graphene&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s electronic structure in the presence of a charged impurity. The design of a hybrid impurity-graphene device, fabricated using controlled deposition of impurities onto a back-gated graphene surface, has enabled several novel methods for controllably tuning graphene&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s electronic properties.(1-8) Electrostatic gating enables control of the charge carrier density in graphene and the ability to reversibly tune the charge(2) and/or molecular(5) states of an impurity. This paper outlines the process of fabricating a gate-tunable graphene device decorated with individual Coulomb impurities for combined STM/STS studies.(2-5) These studies provide valuable insights into the underlying physics, as well as signposts for designing hybrid graphene devices.

Visualization and Manipulation of Bilayer Graphene Quantum Dots with Broken Rotational Symmetry and Nontrivial Topology

Nano Letters, Nov 23, 2020

Download

$Research paper thumbnail of A boron nitride - graphene - C$_{60}$ heterostructure$

A boron nitride - graphene - C$_{60}$ heterostructure

Bulletin of the American Physical Society, Mar 5, 2015

Download

Surface states and quasiparticle interference in Bernal and rhombohedral graphite with and without trigonal warping

Physical review, Oct 13, 2021

Download

Direct Visualization of Native Defects in Graphite and Their Effect on the Electronic Properties of Bernal-Stacked Bilayer Graphene

Nano Letters, Aug 20, 2021

Download

$Research paper thumbnail of Direct growth of single- and few-layer MoS$_{\mathrm{2}}$ on h-BN by CVD method$

Direct growth of single- and few-layer MoS$_{\mathrm{2}}$ on h-BN by CVD method

Bulletin of the American Physical Society, Mar 18, 2016

Download

Giant orbital magnetic moments and paramagnetic shift in artificial relativistic atoms and molecules

Nature Nanotechnology, Mar 1, 2023

Download

Quasiparticle interference patterns in bilayer graphene with trigonal warping

Physical Review B

Download

Persistent and reversible electrostatic control of doping in graphene/hexagonal boron nitride heterostructures

Journal of Applied Physics, 2020

Download

$Research paper thumbnail of Direct CVD Growth of Monolayer Graphene on Exfoliated BN on SiO $ _ {2} $$

Direct CVD Growth of Monolayer Graphene on Exfoliated BN on SiO $ _ {2} $

Download

Imaging electrostatically confined Dirac fermions in graphene quantum dots

Nature Physics, 2016

Download

Nanospot angle-resolved photoemission study of Bernal-stacked bilayer graphene on hexagonal boron nitride: Band structure and local variation of lattice alignment

Physical Review B, 2019

Download

Comprehensive Electrostatic Modeling of Exposed Quantum Dots in Graphene/Hexagonal Boron Nitride Heterostructures

Nanomaterials

Download

Determination of the trigonal warping orientation in Bernal-stacked bilayer graphene via scanning tunneling microscopy

Physical Review B

Download

Visualizing the Effect of an Electrostatic Gate with Angle-Resolved Photoemission Spectroscopy

Nano Letters

Download

Visualization and Control of Single-Electron Charging in Bilayer Graphene Quantum Dots

Nano letters, Aug 8, 2018

Download

Photoinduced doping in heterostructures of graphene and boron nitride

by Salman Kahn, C. Nosiglia, Jairo Velasco Jr., and T. Taniguchi

Download

Fabrication of Gate-tunable Graphene Devices for Scanning Tunneling Microscopy Studies with Coulomb Impurities

by Salman Kahn, Youngkyou Kim, and Jairo Velasco Jr.

Journal of Visualized Experiments, 2015

Characterization and manipulation of individual defects in insulating hexagonal boron nitride using scanning tunnelling microscopy

by Jairo Velasco Jr., Salman Kahn, and Chad Germany

Download

Nanoscale Control of Rewriteable Doping Patterns in Pristine Graphene/Boron Nitride Heterostructures

by Jairo Velasco Jr., Salman Kahn, and Juwon Lee

Download

Fabrication of Gate-tunable Graphene Devices for Scanning Tunneling Microscopy Studies with Coulomb Impurities

by Jairo Velasco Jr. and Youngkyou Kim

Journal of Visualized Experiments, 2015

Owing to its relativistic low-energy charge carriers, the interaction between graphene and variou... more Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees of freedom to control electronic devices. In particular, the behavior of graphene&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s charge carriers in response to potentials from charged Coulomb impurities is predicted to differ significantly from that of most materials. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) can provide detailed information on both the spatial and energy dependence of graphene&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s electronic structure in the presence of a charged impurity. The design of a hybrid impurity-graphene device, fabricated using controlled deposition of impurities onto a back-gated graphene surface, has enabled several novel methods for controllably tuning graphene&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s electronic properties.(1-8) Electrostatic gating enables control of the charge carrier density in graphene and the ability to reversibly tune the charge(2) and/or molecular(5) states of an impurity. This paper outlines the process of fabricating a gate-tunable graphene device decorated with individual Coulomb impurities for combined STM/STS studies.(2-5) These studies provide valuable insights into the underlying physics, as well as signposts for designing hybrid graphene devices.

Interaction-induced gapped state in charge neutral bilayer graphene

Jairo Velasco Jr.

Uploads

Papers by Jairo Velasco Jr.

Log In