59 results found
Vitale V, Atalar K, Mostofi AA, et al., 2021, Flat band properties of twisted transition metal dichalcogenide homo- andheterobilayers of MoS2, MoSe2, WS2 and WSe2, 2D Materials, Vol: 8, ISSN: 2053-1583
Twisted bilayers of two-dimensional materials, such as twisted bilayergraphene, often feature flat electronic bands that enable the observation ofelectron correlation effects. In this work, we study the electronic structureof twisted transition metal dichalcogenide (TMD) homo- and heterobilayers thatare obtained by combining MoS$_2$, WS$_2$, MoSe$_2$ and WSe$_2$ monolayers, andshow how flat band properties depend on the chemical composition of the bilayeras well as its twist angle. We determine the relaxed atomic structure of thetwisted bilayers using classical force fields and calculate the electronic bandstructure using a tight-binding model parametrized from first-principlesdensity-functional theory. We find that the highest valence bands in thesesystems can derive either from $\Gamma$-point or $K$/$K'$-point states of theconstituent monolayers. For homobilayers, the two highest valence bands arecomposed of monolayer $\Gamma$-point states, exhibit a graphene-like dispersionand become flat as the twist angle is reduced. The situation is morecomplicated for heterobilayers where the ordering of $\Gamma$-derived and$K$/$K'$-derived states depends both on the material composition and also thetwist angle. In all systems, qualitatively different band structures areobtained when atomic relaxations are neglected.
Goodwin Z, Klebl L, Vitale V, et al., 2021, Flat bands, electron interactions and magnetic order in magic-angle mono-trilayer graphene, Physical Review Materials, ISSN: 2475-9953
Starting with twisted bilayer graphene, graphene-based moir\'e materials haverecently been established as a new platform for studying strong electroncorrelations. In this paper, we study twisted graphene monolayers on trilayergraphene and demonstrate that this system can host flat bands when the twistangle is close to the magic-angle of 1.16$^\circ$. When monolayer graphene istwisted on ABA trilayer graphene (denoted AtABA), the flat bands are notisolated, but are intersected by a dispersive Dirac cone. In contrast, graphenetwisted on ABC trilayer graphene (denoted AtABC) exhibits a gap between flatand remote bands. Since ABC trilayer graphene and twisted bilayer graphene areknown to host broken symmetry phases, we further investigate magic-angle AtABC.We study the effect of electron-electron interactions in AtABC using bothHartree theory, and an atomic Hubbard theory to calculate the magnetic phasediagram as a function of doping, twist angle and perpendicular electric field.Our analysis reveals a rich variety of magnetic orderings, includingferromagnetism and ferrimagnetism, and demonstrates that a perpendicularelectric field makes AtABC more susceptible to magnetic ordering.
Goebel A, Rubio A, Lischner J, 2021, Light-Induced Charge Transfer from Transition-Metal-Doped Aluminum Clusters to Carbon Dioxide, JOURNAL OF PHYSICAL CHEMISTRY A, Vol: 125, Pages: 5878-5885, ISSN: 1089-5639
Lu Q, Martins H, Kahk JM, et al., 2021, Layer-resolved many-electron interactions in delafossite PdCoO2 from standing-wave photoemission spectroscopy, COMMUNICATIONS PHYSICS, Vol: 4, ISSN: 2399-3650
Klebl L, Goodwin Z, Mostofi AA, et al., 2021, Importance of long-ranged electron-electron interactions for the magnetic phase diagram of twisted bilayer graphene, Physical Review B, Vol: 103, Pages: 1-7, ISSN: 2469-9950
Electron-electron interactions are intrinsically long ranged, but many models of strongly interacting electrons only take short-ranged interactions into account. Here, we present results of atomistic calculations including both long-ranged and short-ranged electron-electron interactions for the magnetic phase diagram of twisted bilayer graphene and demonstrate that qualitatively different results are obtained when long-ranged interactions are neglected. In particular, we use Hartree theory augmented with Hubbard interactions and calculate the interacting spin susceptibility at a range of doping levels and twist angles near the first magic angle to identify the dominant magnetic instabilities. At the magic angle, mostly antiferromagnetic order is found, while ferromagnetism dominates at other twist angles. Moreover, long-ranged interactions significantly increase the twist angle window in which strong correlation phenomena can be expected. These findings are in good agreement with available experimental data.
Roman Castellanos L, Hess O, Lischner J, 2021, Dielectric engineering of hot carrier generation by quantized plasmons in embedded silver nanoparticles, The Journal of Physical Chemistry C: Energy Conversion and Storage, Optical and Electronic Devices, Interfaces, Nanomaterials, and Hard Matter, Vol: 125, Pages: 3081-3087, ISSN: 1932-7447
Understanding and controlling properties of plasmon-induced hot carriers is a key step toward next-generation photovoltaic and photocatalytic devices. Here, we uncover a route to engineering hot-carrier generation rates of silver nanoparticles by designed embedding in dielectric host materials. Extending our recently established quantum-mechanical approach to describe the decay of quantized plasmons into hot carriers we capture both external screening by the nanoparticle environment and internal screening by silver d-electrons through an effective electron–electron interaction. We find that hot-carrier generation can be maximized by engineering the dielectric host material such that the energy of the localized surface plasmon coincides with the highest value of the nanoparticle joint density of states. This allows us to uncover a path to control the energy of the carriers and the amount produced, for example, a large number of relatively low-energy carriers are obtained by embedding in strongly screening environments.
Liang X, Goodwin ZAH, Vitale V, et al., 2020, Effect of bilayer stacking on the atomic and electronic structure of twisted double bilayer graphene, Physical Review B, Vol: 102, Pages: 155146 – 1-155146 – 12, ISSN: 2469-9950
Twisted double bilayer graphene has recently emerged as an interesting moiré material that exhibits strong correlation phenomena that are tunable by an applied electric field. Here we study the atomic and electronic properties of three different graphene double bilayers: double bilayers composed of two AB stacked bilayers (AB/AB), double bilayers composed of two AA stacked bilayers (AA/AA), as well as heterosystems composed of one AB and one AA bilayer (AB/AA). The atomic structure is determined using classical force fields. We find that the inner layers of the double bilayer exhibit significant in-plane and out-of-plane relaxations, similar to twisted bilayer graphene. The relaxations of the outer layers depend on the stacking: atoms in AB bilayers follow the relaxations of the inner layers, while atoms in AA bilayers attempt to avoid higher-energy AA stacking. For the relaxed structures, we calculate the electronic band structures using the tight-binding method. All double bilayers exhibit flat bands at small twist angles, but the shape of the bands depends sensitively on the stacking of the outer layers. To gain further insight, we study the evolution of the band structure as the outer layers are rigidly moved away from the inner layers, while preserving their atomic relaxations. This reveals that the hybridization with the outer layers results in an additional flattening of the inner-layer flat band manifold. Our results establish AA/AA and AB/AA twisted double bilayers as interesting moiré materials with different flat band physics compared to the widely studied AB/AB system.
Song W, Stein Scholtis E, sherrel P, et al., 2020, Electronic Structure Influences on the Formation of the Solid Electrolyte Interphase, Energy and Environmental Science, ISSN: 1754-5692
Kahk J, Lovelock K, Kuusik I, et al., 2020, Frontier orbitals and quasiparticle energy levels in ionic liquids, npj Computational Materials, Vol: 6, Pages: 1-7, ISSN: 2057-3960
Room temperature ionic liquids play an important role in many technological applications and a detailed understanding of their frontier molecular orbitals is required to optimize interfacial barriers,reactivity and stability with respect to electron injection and removal. In this work, we calculate quasiparticle energy levels of ionic liquids using first-principles many-body perturbation theory within the GW approximation and compare our results to various mean-field approaches, including semilocal and hybrid density-functional theory and Hartree-Fock. We find that the mean-field results depend qualitatively and quantitatively on the treatment of exchange-correlation effects, while GW calculations produce results that are in excellent agreement with experimental photoelectron spectra of gas phase ion pairs and ionic liquids. These results establish the GW approach as a valuable tool for understanding the electronic structures of ionic liquids.
Tsai H-Z, Lischner J, Omrani AA, et al., 2020, A molecular shift register made using tunable charge patterns in one-dimensional molecular arrays on graphene, Nature Electronics, Vol: 3, Pages: 598-603, ISSN: 2520-1131
The ability to tune the electronic properties of molecular arrays is an important step in the development of molecule-scale electronic devices. However, control over internal device charge distributions by tuning interactions between molecules has proved challenging. Here, we show that gate-tunable charge patterning can occur in one-dimensional molecular arrays on graphene field-effect transistors. One-dimensional molecular arrays are fabricated using an edge-templated self-assembly process that allows organic molecules (F4TCNQ) to be precisely positioned on graphene devices. The charge configurations of the molecular arrays can be reversibly switched between different collective charge states by tuning the graphene Fermi level via a back-gate electrode. Charge pinning at the ends of the molecular arrays allows the charge state of the entire array to be controlled by adding or removing an edge molecule and changing the total number of molecules in an array between odd and even integers. Charge patterns altered in this way propagate down the array in a cascade effect, allowing the array to function as a charge-based molecular shift register. An extended multi-site Anderson impurity model is used to quantitatively explain this behaviour.
Goodwin Z, Vitale V, Liang X, et al., 2020, Hartree theory calculations of quasiparticle properties in twisted bilayer graphene, Physical Review B: Condensed Matter and Materials Physics, Vol: 2, ISSN: 1098-0121
A detailed understanding of interacting electrons in twisted bilayer graphene(tBLG) near the magic angle is required to gain insights into the physicalorigin of the observed broken symmetry phases including correlated insulatorstates and superconductivity. Here, we present extensive atomistic Hartreetheory calculations of the electronic properties of tBLG in the (semi-)metallicphase as function of doping and twist angle. Specifically, we calculatequasiparticle properties, such as the band structure, density of states (DOS)and local density of states (LDOS), which are directly accessible inphotoemission and tunnelling spectroscopy experiments. We find thatquasiparticle properties change significantly upon doping - an effect which isnot captured by tight-binding theory. In particular, we observe that thepartially occupied bands flatten significantly which enhances the density ofstates at the Fermi level and explains the experimentally observed Fermi levelpinning. We predict a clear signature of this band flattening in the LDOS inthe AB/BA regions of tBLG which can be tested in scanning tunnelingexperiments. We also study the dependence of quasiparticle properties on thedielectric environment of tBLG and discover that these properties aresurprisingly robust as a consequence of the strong internal screening. Finally,we present a simple analytical expression for the Hartree potential whichenables the determination of quasiparticle properties without the need forself-consistent calculations.
Stepanov P, Das I, Lu X, et al., 2020, Untying the insulating and superconducting orders in magic-angle graphene, Nature, Vol: 583, Pages: 375-378, ISSN: 0028-0836
The coexistence of superconducting and correlated insulating states in magic-angle twisted bilayer graphene1-11 prompts fascinating questions about their relationship. Independent control of the microscopic mechanisms that govern these phases could help uncover their individual roles and shed light on their intricate interplay. Here we report on direct tuning of electronic interactions in this system by changing the separation distance between the graphene and a metallic screening layer12,13. We observe quenching of correlated insulators in devices with screening layer separations that are smaller than the typical Wannier orbital size of 15 nanometres and with twist angles that deviate slightly from the magic angle of 1.10 ± 0.05 degrees. Upon extinction of the insulating orders, the vacated phase space is taken over by superconducting domes that feature critical temperatures comparable to those in devices with strong insulators. In addition, we find that insulators at half-filling can reappear in small out-of-plane magnetic fields of 0.4 tesla, giving rise to quantized Hall states with a Chern number of 2. Our study suggests re-examination of the often-assumed 'parent-and-child' relation between the insulating and superconducting phases in moiré graphene, and suggests a way of directly probing the microscopic mechanisms of superconductivity in strongly correlated systems.
Berens J, Bichelmaier S, Fernando NK, et al., 2020, Effects of nitridation on SiC/SiO(2)structures studied by hard X-ray photoelectron spectroscopy, JOURNAL OF PHYSICS-ENERGY, Vol: 2, ISSN: 2515-7655
Li L, Zhang J, Myeong G, et al., 2020, Gate-tunable reversible rashba-edelstein effect in a few-layer graphene/2H-TaS2 heterostructure at room temperature., ACS Nano, Vol: 14, Pages: 5251-5259, ISSN: 1936-0851
We report the observation of current-induced spin polarization, the Rashba-Edelstein effect (REE), and its Onsager reciprocal phenomenon, the spin galvanic effect (SGE), in a few-layer graphene/2H-TaS2 heterostructure at room temperature. Spin-sensitive electrical measurements unveil full spin-polarization reversal by an applied gate voltage. The observed gate-tunable charge-to-spin conversion is explained by the ideal work function mismatch between 2H-TaS2 and graphene, which allows for a strong interface-induced Bychkov-Rashba interaction with a spin-gap reaching 70 meV, while keeping the Dirac nature of the spectrum intact across electron and hole sectors. The reversible electrical generation and control of the nonequilibrium spin polarization vector, not previously observed in a nonmagnetic material, are elegant manifestations of emergent two-dimensional Dirac Fermions with robust spin-helical structure. Our experimental findings, supported by first-principles relativistic electronic structure and transport calculations, demonstrate a route to design low-power spin-logic circuits from layered materials.
Goodwin Z, Vitale V, Corsetti F, et al., 2020, Critical role of device geometry for the phase diagram of twisted bilayer graphene, Physical Review B: Condensed Matter and Materials Physics, Vol: 101, Pages: 1-8, ISSN: 1098-0121
The effective interaction between electrons in two-dimensional materials can be modified by their environment, enabling control of electronic correlations and phases. Here, we study the dependence of electronic correlations in twisted bilayer graphene (tBLG) on the separation to the metallic gate(s) in two device configurations. Using an atomistic tight-binding model, we determine the Hubbard parameters of the flat bands as a function of gate separation, taking into account the screening from the metallic gate(s), the dielectric spacer layers, and the tBLG itself. We determine the critical gate separation at which the Hubbard parameters become smaller than the critical value required for a transition from a correlated insulator state to a (semi)metallic phase. We show how this critical gate separation depends on twist angle, doping, and the device configuration. These calculations may help rationalize the reported differences between recent measurements of tBLG's phase diagram and suggest that correlated insulator states can be screened out in devices with thin dielectric layers.
Castellanos LR, Kahk JM, Hess O, et al., 2020, Generation of plasmonic hot carriers from d-bands in metallic nanoparticles, Journal of Chemical Physics, Vol: 152, ISSN: 0021-9606
We present an approach to master the well-known challenge of calculating the contribution of d-bands to plasmon-induced hot carrier rates in metallic nanoparticles. We generalize the widely used spherical well model for the nanoparticle wavefunctions to flat d-bands using the envelope function technique. Using Fermi’s golden rule, we calculate the generation rates of hot carriers after the decay of the plasmon due to transitions either from a d-band state to an sp-band state or from an sp-band state to another sp-band state. We apply this formalism to spherical silver nanoparticles with radii up to 20 nm and also study the dependence of hot carrier rates on the energy of the d-bands. We find that for nanoparticles with a radius less than 2.5 nm, sp-band state to sp-band state transitions dominate hot carrier production, while d-band state to sp-band state transitions give the largest contribution for larger nanoparticles.
Aghajanian M, Schuler B, Cochrane KA, et al., 2020, Resonant and bound states of charged defects in two-dimensional semiconductors, Physical Review B: Condensed Matter and Materials Physics, Vol: 101, Pages: 1-6, ISSN: 1098-0121
A detailed understanding of charged defects in two-dimensional semiconductors is needed for the development of ultrathin electronic devices. Here, we study negatively charged acceptor impurities in monolayer WS2 using a combination of scanning tunneling spectroscopy and large-scale atomistic electronic structure calculations. We observe several localized defect states of hydrogenic wave function character in the vicinity of the valence band edge. Some of these defect states are bound, while others are resonant. The resonant states result from the multivalley valence band structure of WS2, whereby localized states originating from the secondary valence band maximum at Γ hybridize with continuum states from the primary valence band maximum at K/K′. Resonant states have important consequences for electron transport as they can trap mobile carriers for several tens of picoseconds.
Titanium oxynitride enables a range of plasmonic and optoelectronic functionality using long-lived photo-generated hot carriers. We explore the time scale of hot carriers in TiN and their use in photochemical reduction and Schottky detectors.
Goodwin Z, Corsetti F, Mostofi A, et al., 2019, Attractive electron-electron interactions from internal screening in magic angle twisted bilayer graphene, Physical Review B: Condensed Matter and Materials Physics, Vol: 100, ISSN: 1098-0121
Twisted bilayer graphene (tBLG) has recently emerged as a new platform for studying electroncorrelations, the strength of which can be controlled via the twist angle. Here, we study the effectof internal screening on electron-electron interactions in undoped tBLG. Using the random phaseapproximation, we find that the dielectric response of tBLG drastically increases near the magicangle and is highly twist-angle dependent. As a consequence of the abrupt change of the Fermivelocity as a function of wave vector, the screened interaction in real space exhibits attractiveregions for certain twist angles near the magic angle. Attractive interactions can induce chargedensity waves and superconductivity and therefore our findings could be relevant to understand themicroscopic origins of the recently observed strong correlation phenomena in undoped tBLG. Theresulting screened Hubbard parameters are strongly reduced and exhibit a non-linear dependence onthe twist angle. We also carry out calculations with the constrained random phase approximationand parametrize a twist-angle dependent Keldysh model for the resulting effective interaction.
Dal Forno S, Lischner J, 2019, Electron-phonon coupling and hot electron thermalization in titanium nitride, Physical Review Materials, Vol: 3, ISSN: 2475-9953
We have studied the thermalization of hot carriers in both pristine and defectivetitanium nitride (TiN) using a two-temperature model. All parameters of this model,including the electron-phonon coupling parameter, were obtained from rst-principlesdensity-functional theory calculations. The virtual crystal approximation was used todescribe defective systems. We nd that thermalization of hot carriers occurs on muchfaster time scales than in gold as a consequence of the signi cantly stronger electronphonon coupling in TiN. Speci cally, the largest thermalization times, on the order of200 femtoseconds, are found in TiN with nitrogen vacancies for electron temperaturesaround 4000 K.
Kahk JM, Lischner J, 2019, Accurate absolute core-electron binding energies of molecules, solids and surfaces from first-principles calculations, Physical Review Materials, Vol: 3, ISSN: 2475-9953
Core-electron x-ray photoelectron spectroscopy is a powerful technique for studying the electronicstructure and chemical composition of molecules, solids and surfaces. However, the interpretationof measured spectra and the assignment of peaks to atoms in specific chemical environments is oftenchallenging. Here, we address this problem and introduce a parameter-free computational approachfor calculating absolute core-electron binding energies. In particular, we demonstrate that accurateabsolute binding energies can be obtained from the total energy difference of the ground state anda state with an explicit core hole when exchange and correlation effects are described by a recentlydeveloped meta-generalized gradient approximation and relativistic effects are included even forlight elements. We carry out calculations for molecules, solids and surface species and find excellentagreement with available experimental measurements. For example, we find a mean absolute errorof only 0.16 eV for a reference set of 103 molecular core-electron binding energies. The capability tocalculate accurate absolute core-electron binding energies will enable new insights into a wide rangeof chemical surface processes that are studied by x-ray photoelectron spectroscopy.
Goodwin ZAH, Corsetti F, Mostofi AA, et al., 2019, Twist-angle sensitivity of electron correlations in moiré graphene bilayers, Physical Review B, Vol: 100, ISSN: 2469-9950
Motivated by the recent observation of correlated insulator states and unconventional superconductivity in twisted bilayer graphene, we study the dependence of electron correlations on the twist angle and reveal the existence of strong correlations over a narrow range of twist angles near the magic angle. Specifically, we determine the on-site and extended Hubbard parameters of the low-energy Wannier states using an atomistic quantum-mechanical approach. The ratio of the on-site Hubbard parameter and the width of the flat bands, which is an indicator of the strength of electron correlations, depends sensitively on the screening by the semiconducting substrate and the metallic gates. Including the effect of long-ranged Coulomb interactions significantly reduces electron correlations and explains the experimentally observed sensitivity of strong-correlation phenomena on twist angles.
Roman Castellanos L, Hess O, Lischner J, 2019, Single plasmon hot carrier generation in metallic nanoparticles, Communications Physics, Vol: 2, ISSN: 2399-3650
Hot carriers produced from the decay of localized surface plasmons in metallic nanoparticles are intensely studied because of their optoelectronic, photovoltaic and photocatalytic applications. From a classical perspective, plasmons are coherent oscillations of the electrons in the nanoparticle, but their quantized nature comes to the fore in the novel field of quantum plasmonics. In this work, we introduce a quantum-mechanical material-specific approach for describing the decay of single quantized plasmons into hot electrons and holes. We find that hot carrier generation rates differ significantly from semiclassical predictions. We also investigate the decay of excitations without plasmonic character and show that their hot carrier rates are comparable to those from the decay of plasmonic excitations for small nanoparticles. Our study provides a rigorous and general foundation for further development of plasmonic hot carrier studies in the plasmonic regime required for the design of ultrasmall devices.
Zhang J, Guan M, Lischner J, et al., 2019, Coexistence of Different Charge-Transfer Mechanisms in the Hot-Carrier Dynamics of Hybrid Plasmonic Nanomaterials, NANO LETTERS, Vol: 19, Pages: 3187-3193, ISSN: 1530-6984
Lischner J, 2019, Multiscale modelling of charged impurities in two-dimensional materials, Computational Materials Science, Vol: 160, Pages: 368-373, ISSN: 0927-0256
Charged impurities influence functional properties of two-dimensional materials and a detailed theoretical understanding of charged defects is required to enable a rational design of defect-engineered nanomaterials for applications in ultrathin devices. To achieve this goal, we have developed multiscale approaches that combine atomistic first-principles theories, such as density-functional theory, with coarse-grained continuum models, such as effective mass models. This allows us to model large supercells which are required to accurately describe the slow decay of the screened defect potential and the defect-induced changes in the electronic properties of the two-dimensional host material. I will describe the results of our multiscale calculations for charged defects in doped graphene and in transition-metal dichalcogenide monolayers which have revealed novel mechanisms for controlling and tuning the electronic structure of two-dimensional materials.
Regoutz A, Ganose AM, Blumenthal L, et al., 2019, Insights into the electronic structure of OsO2 using soft and hard x-ray photoelectron spectroscopy in combination with density functional theory, Physical Review Materials, Vol: 3, ISSN: 2475-9953
Theory and experiment are combined to gain an understanding of the electronic properties of OsO2, a poorly studied metallic oxide that crystallizes in the rutile structure. Hard and soft valence-band x-ray photoemission spectra of OsO2 single crystals are in broad agreement with the results of density-functional-theory calculations, aside from a feature shifted to high binding energy of the conduction band. The energy shift corresponds to the conduction electron plasmon energy measured by reflection electron energy loss spectroscopy. The plasmon satellite is reproduced by many-body perturbation theory.
Kahk JM, Lischner J, 2018, Core electron binding energies of adsorbates on Cu(111) from first-principles calculations, Physical Chemistry Chemical Physics, Vol: 20, Pages: 30403-30411, ISSN: 1463-9076
Core-level X-ray Photoelectron Spectroscopy (XPS) is often used to study the surfaces of heterogeneous copper-based catalysts, but the interpretation of measured spectra, in particular the assignment of peaks to adsorbed species, can be extremely challenging. In this study we present a computational scheme which combines the use of slab models of the surface for geometry optimization with cluster models for core electron binding energy calculation. We demonstrate that by following this modelling strategy first principles calculations can be used to guide the analysis of experimental core level spectra of complex surfaces relevant to heterogeneous catalysis. The all-electron ΔSCF method is used for the binding energy calculations. Specifically, we calculate core-level binding energy shifts for a series of adsorbates on Cu(111) and show that the resulting C1s and O1s binding energy shifts for adsorbed CO, CO2, C2H4, HCOO, CH3O, H2O, OH, and a surface oxide on Cu(111) are in good overall agreement with the experimental literature.
Kennes DM, Lischner J, Karrasch C, 2018, Strong correlations and d+id superconductivity in twisted bilayer graphene, Physical Review B, Vol: 98, Pages: 1-4, ISSN: 2469-9950
We compute the phase diagram of twisted bilayer graphene near the magic angle where the occurrence of flat bands enhances the effects of electron-electron interactions and thus unleashes strongly correlated phenomena. Most importantly, we find a crossover between d+id superconductivity and antiferromagnetic insulating behavior near half filling of the lowest electron band when the temperature is increased. This is consistent with recent experiments. Our results are obtained using unbiased many-body renormalization group techniques combined with a mean-field analysis of the effective couplings. We provide a qualitative understanding by considering the competition between Fermi-surface nesting and van Hove singularities.
Wong D, Wang Y, Jin W, et al., 2018, Microscopy of hydrogen and hydrogen-vacancy defect structures on graphene devices, Physical review B: Condensed matter and materials physics, Vol: 98, ISSN: 1098-0121
We have used scanning tunneling microscopy (STM) to investigate two types of hydrogen defect structures on monolayer graphene supported by hexagonal boron nitride (h−BN) in a gated field-effect transistor configuration. The first H-defect type is created by bombarding graphene with 1-keV ionized hydrogen and is identified as two hydrogen atoms bonded to a graphene vacancy via comparison of experimental data to first-principles calculations. The second type of H defect is identified as dimerized hydrogen and is created by depositing atomic hydrogen having only thermal energy onto a graphene surface. Scanning tunneling spectroscopy (STS) measurements reveal that hydrogen dimers formed in this way open a new elastic channel in the tunneling conductance between an STM tip and graphene.
Zhang J, Hong H, Zhang J, et al., 2018, New Pathway for Hot Electron Relaxation in Two-Dimensional Heterostructures, NANO LETTERS, Vol: 18, Pages: 6057-6063, ISSN: 1530-6984
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