scholarly journals Direct observation of van der Waals stacking–dependent interlayer magnetism

Science ◽  
2019 ◽  
Vol 366 (6468) ◽  
pp. 983-987 ◽  
Author(s):  
Weijong Chen ◽  
Zeyuan Sun ◽  
Zhongjie Wang ◽  
Lehua Gu ◽  
Xiaodong Xu ◽  
...  
Keyword(s):  
Lattice Structure ◽  
Twist Angle ◽  
Van Der Waals ◽  
Magnetic Semiconductor ◽  
Interlayer Coupling ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Atomic Lattice ◽  
Stacking Order ◽  
The Individual

Controlling the crystal structure is a powerful approach for manipulating the fundamental properties of solids. In van der Waals materials, this control can be achieved by modifying the stacking order through rotation and translation between the layers. Here, we observed stacking-dependent interlayer magnetism in the two-dimensional (2D) magnetic semiconductor chromium tribromide (CrBr3), which was enabled by the successful growth of its monolayer and bilayer through molecular beam epitaxy. Using in situ spin-polarized scanning tunneling microscopy and spectroscopy, we directly correlate the atomic lattice structure with the observed magnetic order. Although the individual monolayer CrBr3 is ferromagnetic, the interlayer coupling in bilayer depends on the stacking order and can be either ferromagnetic or antiferromagnetic. Our observations pave the way for manipulating 2D magnetism with layer twist angle control.

scholarly journals Abnormal conductivity in low-angle twisted bilayer graphene

2020 ◽  
Vol 6 (47) ◽  
pp. eabc5555
Author(s):  
Shuai Zhang ◽  
Aisheng Song ◽  
Lingxiu Chen ◽  
Chengxin Jiang ◽  
Chen Chen ◽  
...  
Keyword(s):  
Density Functional ◽  
Twist Angle ◽  
Van Der Waals ◽  
Density Functional Theory Calculations ◽  
Bilayer Graphene ◽  
Abnormal Behavior ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Van Der Waals Materials ◽  
The Impact

Controlling the interlayer twist angle offers a powerful means for tuning the electronic properties of two-dimensional (2D) van der Waals materials. Typically, the electrical conductivity would increase monotonically with decreasing twist angle owing to the enhanced coupling between adjacent layers. Here, we report a nonmonotonic angle-dependent vertical conductivity across the interface of bilayer graphene with low twist angles. More specifically, the vertical conductivity enhances gradually with decreasing twist angle up to a crossover angle at θc ≈ 5°, and then it drops notably upon further decrease in the twist angle. Revealed by density functional theory calculations and scanning tunneling microscopy, the abnormal behavior is attributed to the unusual reduction in average carrier density originating from local atomic reconstruction. The impact of atomic reconstruction on vertical conductivity is unique for low-angle twisted 2D van der Waals materials and provides a strategy for designing and optimizing their electronic performance.

scholarly journals STM study on the self-assembly of oligothiophene-based organic semiconductors

2011 ◽  
Vol 2 ◽  
pp. 802-808 ◽  
Author(s):  
Elena Mena-Osteritz ◽  
Marta Urdanpilleta ◽  
Erwaa El-Hosseiny ◽  
Berndt Koslowski ◽  
Paul Ziemann ◽  
...  
Keyword(s):  
Organic Semiconductors ◽  
Self Assembly ◽  
Theoretical Calculations ◽  
The Self ◽  
Scanning Tunneling ◽  
Ambient Conditions ◽  
Tunneling Microscopy ◽  
Substitution Pattern ◽  
Electronic Density ◽  
The Individual

The self-assembly properties of a series of functionalized regioregular oligo(3-alkylthiophenes) were investigated by using scanning tunneling microscopy (STM) at the liquid–solid interface under ambient conditions. The characteristics of the 2-D crystals formed on the (0001) plane of highly ordered pyrolitic graphite (HOPG) strongly depend on the length of the π-conjugated oligomer backbone, on the functional groups attached to it, and on the alkyl substitution pattern on the individual thiophene units. Theoretical calculations were performed to analyze the geometry and electronic density of the molecular orbitals as well as to analyze the intermolecular interactions, in order to obtain models of the 2-D molecular ordering on the substrate.

scholarly journals Orientation Ordering and Chiral Superstructures in Fullerene Monolayer on Cd (0001)

Nanomaterials ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 1305
Author(s):  
Yuzhi Shang ◽  
Zilong Wang ◽  
Daxiao Yang ◽  
Yaru Wang ◽  
Chaoke Ma ◽  
...  
Keyword(s):  
Thin Films ◽  
Charge Transfer ◽  
Scanning Tunneling Spectroscopy ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Orientational Disorder ◽  
Temperature Scanning ◽  
Orientation Ordering ◽  
The Individual ◽  
Misorientation Angles

The structure of C60 thin films grown on Cd (0001) surface has been investigated from submonolayer to second monolayer regimes with a low-temperature scanning tunneling microscopy (STM). There are different C60 domains with various misorientation angles relative to the lattice directions of Cd (0001). In the (2√3 × 2√3) R30° domain, orientational disorder of the individual C60 molecules with either pentagon, hexagon, or 6:6 bond facing up has been observed. However, orientation ordering appeared in the R26° domain such that all the C60 molecules adopt the same orientation with the 6:6 bond facing up. In particular, complex chiral motifs composed of seven C60 molecules with clockwise or anticlockwise handedness have been observed in the R4° and R8° domains, respectively. Scanning tunneling spectroscopy (STS) measurements reveal a reduced HOMO–LOMO gap of 2.1 eV for the C60 molecules adsorbed on Cd (0001) due to the substrate screening and charge transfer from Cd to C60 molecules.

Multilayered silicene: the bottom-up approach for a weakly relaxed Si(111) with Dirac surface states

Nanoscale ◽  
2015 ◽  
Vol 7 (38) ◽  
pp. 15880-15885 ◽  
Author(s):  
Huixia Fu ◽  
Lan Chen ◽  
Jian Chen ◽  
Jinglan Qiu ◽  
Zijing Ding ◽  
...  
Keyword(s):  
Scanning Tunneling Microscopy ◽  
First Principles ◽  
Van Der Waals ◽  
Surface States ◽  
Scanning Tunneling ◽  
Diamond Structure ◽  
Tunneling Microscopy ◽  
Bottom Up

Combining first principles investigations and scanning tunneling microscopy, we identify that the presumable van der Waals packed multilayered silicene sheets spontaneously transform into a diamond-structure bulk Si film due to strong interlayer couplings.

STM Nanospectroscopic Study of Defects in Semiconductors

2002 ◽  
Vol 719 ◽  
Author(s):  
Koji Maeda ◽  
Akira Hida ◽  
Yutaka Mera
Keyword(s):  
Continuous Light ◽  
Tunneling Current ◽  
Scanning Tunneling ◽  
Light Illumination ◽  
Tunneling Microscopy ◽  
Bulk Gaas ◽  
Quenching Effect ◽  
Reversible Transformation ◽  
The Individual ◽  
Defects In Semiconductors

AbstractCoupling of scanning tunneling microscopy (STM) with various schemes of optical spectroscopy was found to provide powerful tools for study of crystalline defects in bulk semiconducting solids. The simplest method was applied to a subsurface defect in a bulk GaAs crystal in which the signal was acquired by detecting the change in the tunneling current reflecting a local surface swelling that occurs when the wavelength of the chopped light used for spectroscopic measurements coincides with a photoabsorption spectral peak of the defect. Another scheme using a continuous light of variable wavelength was applied to midgap centers, assigned as arsenic antisite defects, densely populated in low-temperature-grown GaAs epifilms. Experiments at 90K revealed that light illumination causes reversible transformation of the individual defects to a metastable state with an excitation spectrum very close to one observed for the photo-quenching effect of EL2 centers in bulk GaAs.

Twisted charge-density-wave patterns in bilayer 2D crystals and modulated electronic states

2D Materials ◽  
2021 ◽  
Author(s):  
Yaoyao Chen ◽  
Liwei Liu ◽  
Xuan Song ◽  
Han Yang ◽  
zeping Huang ◽  
...  
Keyword(s):  
Charge Density ◽  
Density Wave ◽  
Single Layer ◽  
Interlayer Coupling ◽  
Charge Density Waves ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Atomic Lattices ◽  
Fresh Insight ◽  
2D Crystals

Abstract The twistronics of the atomic-thick two-dimensional (2D) van der Waals materials has opened a new venue to investigate the interlayer coupling. Till now, most studies focus on the twist of atomic lattices and the resulted moiré superstructures, while the reports about the twist of charge density waves (CDW), the superstructures of which are from individual layers are limited. Here, using molecular beam epitaxy, we construct bilayer (BL) 1T-NbSe2 vertical structures. With high resolution scanning tunneling microscopy observations, we identify two cases of CDW twisted stacking with atomic precision. The typical twist angles are 0o and 60o between the 1st and the 2nd layer, although the top Se atomic lattices of these two layers are parallel. Compared to the single layer case, the dI/dV at BL shows an insulator-to-metal transition, with the Hubbard bands shrinking towards the Fermi level (EF ). More intriguingly, interlayer coupling states rise near EF , which are dependent on the CDW twist angles. These findings give fresh insight into the engineering of 2D materials by CDW twisting and are potentially applicable for future nanoelectronic devices.

scholarly journals Lattice reconstruction induced multiple ultra-flat bands in twisted bilayer WSe2

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
En Li ◽  
Jin-Xin Hu ◽  
Xuemeng Feng ◽  
Zishu Zhou ◽  
Liheng An ◽  
...  
Keyword(s):  
Twist Angle ◽  
Transition Metal Dichalcogenides ◽  
Coulomb Repulsion ◽  
Crystal Form ◽  
Scanning Tunneling ◽  
Emergent Properties ◽  
Tunneling Conductance ◽  
Tunneling Microscopy ◽  
Flat Bands ◽  
Wide Range

AbstractMoiré superlattices in van der Waals heterostructures provide a tunable platform to study emergent properties that are absent in the natural crystal form. Twisted bilayer transition metal dichalcogenides (TB-TMDs) can host moiré flat bands over a wide range of twist angles. For twist angle close to 60°, it was predicted that TB-TMDs undergo a lattice reconstruction which causes the formation of ultra-flat bands. Here, by using scanning tunneling microscopy and spectroscopy, we show the emergence of multiple ultra-flat bands in twisted bilayer WSe2 when the twist angle is within 3° of 60°. The ultra-flat bands are manifested as narrow tunneling conductance peaks with estimated bandwidth less than 10 meV, which is only a fraction of the estimated on-site Coulomb repulsion energy. The number of these ultra-flat bands and spatial distribution of the wavefunctions match well with the theoretical predictions, strongly evidencing that the observed ultra-flat bands are induced by lattice reconstruction. Our work provides a foundation for further study of the exotic correlated phases in TB-TMDs.

scholarly journals Local, global, and nonlinear screening in twisted double-layer graphene

2016 ◽  
Vol 113 (24) ◽  
pp. 6623-6628 ◽  
Author(s):  
Chih-Pin Lu ◽  
Martin Rodriguez-Vega ◽  
Guohong Li ◽  
Adina Luican-Mayer ◽  
Kenji Watanabe ◽  
...  
Keyword(s):  
Buffer Layer ◽  
Random Potential ◽  
Electronic Materials ◽  
Twist Angle ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Environmental Disturbances ◽  
Potential Fluctuations ◽  
2D System ◽  
Unique Capability

One-atom-thick crystalline layers and their vertical heterostructures carry the promise of designer electronic materials that are unattainable by standard growth techniques. To realize their potential it is necessary to isolate them from environmental disturbances, in particular those introduced by the substrate. However, finding and characterizing suitable substrates, and minimizing the random potential fluctuations they introduce, has been a persistent challenge in this emerging field. Here we show that Landau-level (LL) spectroscopy offers the unique capability to quantify both the reduction of the quasiparticles’ lifetime and the long-range inhomogeneity due to random potential fluctuations. Harnessing this technique together with direct scanning tunneling microscopy and numerical simulations we demonstrate that the insertion of a graphene buffer layer with a large twist angle is a very effective method to shield a 2D system from substrate interference that has the additional desirable property of preserving the electronic structure of the system under study. We further show that owing to its remarkable nonlinear screening capability a single graphene buffer layer provides better shielding than either increasing the distance to the substrate or doubling the carrier density and reduces the amplitude of the potential fluctuations in graphene to values even lower than the ones in AB-stacked bilayer graphene.

Roughness of electronic interfaces in Ga As p-n multilayers investigated by cross-sectional scanning tunneling microscopy

2002 ◽  
Vol 719 ◽  
Author(s):  
N. D. Jäger ◽  
K. Urban ◽  
E. R. Weber ◽  
Ph. Ebert
Keyword(s):  
Charge Carrier ◽  
Scanning Tunneling Microscopy ◽  
Fermi Energy ◽  
Scanning Tunneling ◽  
Dopant Atom ◽  
Tunneling Microscopy ◽  
Cross Sectional ◽  
Semiconductor Structures ◽  
Dopant Atoms ◽  
The Individual

AbstractWe investigated the roughness of the electronic interfaces of GaAs p-n multilayers using cross-sectional scanning tunneling microscopy. We demonstrate that these interfaces exhibit a much larger roughness than the underlying essentially perfect ‘metallurgical’ interface, due to the individual long range electrostatic screening fields around each dopant atom near the interface and due to a clustering of dopant atoms. The clustering and the inherently connected local lack of dopant atoms gives rise to charge carrier depletion zones extending locally through entire nominally homogeneously doped layers once the layer thickness is close to the cluster dimensions. Thus, local variations in the dopant atom distribution limit the precision of the spatial and energetic positioning of the Fermi energy in nanoscale semiconductor structures.

scholarly journals Atomically-resolved interlayer charge ordering and its interplay with superconductivity in YBa2Cu3O6.81

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Chun-Chih Hsu ◽  
Bo-Chao Huang ◽  
Michael Schnedler ◽  
Ming-Yu Lai ◽  
Yuh-Lin Wang ◽  
...  
Keyword(s):  
Carrier Transport ◽  
Charge Order ◽  
Interlayer Coupling ◽  
Real Space ◽  
Charge Ordering ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Cross Sectional ◽  
Competing Orders

AbstractHigh-temperature superconductive (SC) cuprates exhibit not only a SC phase, but also competing orders, suppressing superconductivity. Charge order (CO) has been recognized as an important competing order, but its microscopic spatial interplay with SC phase as well as the interlayer coupling in CO and SC phases remain elusive, despite being essential for understanding the physical mechanisms of competing orders and hence superconductivity. Here we report the achievement of direct real-space imaging with atomic-scale resolution of cryogenically cleaved YBa2Cu3O6.81 using cross-sectional scanning tunneling microscopy/spectroscopy. CO nanodomains are found embedded in the SC phase with a proximity-like boundary region characterized by mutual suppression of CO and superconductivity. Furthermore, SC coherence as well as CO occur on both CuO chain and plane layers, revealing carrier transport and density of states mixing between layers. The CO antiphase correlation along the c direction suggests a dominance of Coulomb repulsion over Josephson tunneling between adjacent layers.

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