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.

Scanning tunneling microscopy of polymers: A status report

1989 ◽  
Vol 47 ◽  
pp. 330-331
Author(s):  
P.E. Russell ◽  
I.H. Musselman
Keyword(s):  
High Resolution ◽  
Scanning Tunneling Microscopy ◽  
Sample Surface ◽  
Atomic Scale ◽  
Constant Current ◽  
Scanning Tunneling ◽  
Status Report ◽  
Tunneling Microscopy ◽  
Research Issues ◽  
Wide Range

Scanning tunneling microscopy (STM) has evolved rapidly in the past few years. Major developments have occurred in instrumentation, theory, and in a wide range of applications. In this paper, an overview of the application of STM and related techniques to polymers will be given, followed by a discussion of current research issues and prospects for future developments. The application of STM to polymers can be conveniently divided into the following subject areas: atomic scale imaging of uncoated polymer structures; topographic imaging and metrology of man-made polymer structures; and modification of polymer structures. Since many polymers are poor electrical conductors and hence unsuitable for use as a tunneling electrode, the related atomic force microscopy (AFM) technique which is capable of imaging both conductors and insulators has also been applied to polymers.The STM is well known for its high resolution capabilities in the x, y and z axes (Å in x andy and sub-Å in z). In addition to high resolution capabilities, the STM technique provides true three dimensional information in the constant current mode. In this mode, the STM tip is held at a fixed tunneling current (and a fixed bias voltage) and hence a fixed height above the sample surface while scanning across the sample surface.

scholarly journals Imaging and identification of point defects in PtTe2

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
Kuanysh Zhussupbekov ◽  
Lida Ansari ◽  
John B. McManus ◽  
Ainur Zhussupbekova ◽  
Igor V. Shvets ◽  
...  
Keyword(s):  
Point Defects ◽  
Density Functional ◽  
Transition Metal Dichalcogenides ◽  
Density Functional Theory Calculations ◽  
Charge Carrier Mobility ◽  
Scanning Tunneling Spectroscopy ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Recombination Rates ◽  
And Performance

AbstractThe properties and performance of two-dimensional (2D) materials can be greatly affected by point defects. PtTe2, a 2D material that belongs to the group 10 transition metal dichalcogenides, is a type-II Dirac semimetal, which has gained a lot of attention recently due to its potential for applications in catalysis, photonics, and spintronics. Here, we provide an experimental and theoretical investigation of point defects on and near the surface of PtTe2. Using scanning tunneling microscopy and scanning tunneling spectroscopy (STS) measurements, in combination with first-principle calculations, we identify and characterize five common surface and subsurface point defects. The influence of these defects on the electronic structure of PtTe2 is explored in detail through grid STS measurements and complementary density functional theory calculations. We believe these findings will be of significance to future efforts to engineer point defects in PtTe2, which is an interesting and enticing approach to tune the charge-carrier mobility and electron–hole recombination rates, as well as the site reactivity for catalysis.

Using a Moderate Vacuum, Hot/Cryo-Stage Equipped AFM for In-Situ Observation of α-Phase Growth In 60SN40PB Hypoeutectic Solder

1998 ◽  
Vol 4 (S2) ◽  
pp. 316-317
Author(s):  
D. N. Leonard ◽  
P.E. Russell
Keyword(s):  
Surface Science ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Scanning Tunneling ◽  
In Situ Observation ◽  
Atmospheric Conditions ◽  
Tunneling Microscopy ◽  
Wide Range ◽  
Gas Environment

Atomic force microscopy (AFM) was introduced in 1984, and proved to be more versatile than scanning tunneling microscopy (STM) due to the AFM's capabilities to scan non-conductive samples under atmospheric conditions and achieve atomic resolution. Ultra high vacuum (UHV) AFM has been used in surface science applications when control of oxidation and corrosion of a sample's surface are required. Expensive equipment and time consuming sample exchanges are two drawbacks of the UHV AFM system that limit its use. Until recently, no hot/cryo-stage, moderate vacuum, controlled gas environment AFM was commonly available.We have demonstrated that phase transformations are easily observable in metal alloys and polymers with the use of a moderate vacuum AFM that has in-situ heating/cooling capabilities and quick (within minutes) sample exchange times. This talk will describe the results of experiments involving a wide range of samples designed to make use of the full capabilities of a hot/cryo-stage, controlled gas environment AFM.

Sb-terminated InAs(001)-(2×4) and (2×8) studied using scanning tunneling microscopy and ab initio density functional theory

2001 ◽  
Vol 692 ◽  
Author(s):  
William Barvosa-Carter ◽  
Frank Grosse ◽  
James H. G. Owen ◽  
Jennifer J. Zinck
Keyword(s):  
Density Functional Theory ◽  
Scanning Tunneling Microscopy ◽  
Ab Initio ◽  
Density Functional ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Functional Theory ◽  
Subsequent Formation ◽  
Wide Range ◽  
Symmetry Surface

AbstractWe have studied the structure of MBE-grown InAs(001)-(2×4) surfaces exposed to low Sb2 fluxes by scanning tunneling microscopy (STM) and ab initio density functional theory (DFT). Experimentally, we observe an Sb-terminated α2(2×4) phase over a wide range of temperatures (400–510 °C) for low Sb2 flux (<0.1 ML/s), whereas temperature and As2 flux must be carefully controlled to achieve the same As-terminated surface structure. At lower temperatures, we observe indications of an Sb-terminated (2×8) symmetry surface phase, and we report briefly on its proposed structure and stability, as well as its possible role in subsequent formation of the Sb-terminated (1×3) phase found at typical Sb2 fluxes used during heterostructure growth.

Defect-Mediated Growth of YBa2Cu3O7-δ Films

1992 ◽  
Vol 280 ◽  
Author(s):  
D. G. Schlom ◽  
D. Anselmetti ◽  
J. G. Bednorz ◽  
Ch. Gerber ◽  
J. Mannhar
Keyword(s):  
Growth Conditions ◽  
Substrate Material ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Surface Evolution ◽  
Screw Dislocations ◽  
Surface Steps ◽  
Defect Sites ◽  
Wide Range ◽  
Intrinsic Feature

ABSTRACTThe evolution of the surface microstructure of sputtered c-axis oriented epitaxial YBa2Cu3O7-δ films has been monitored by scanning tunneling microscopy (STM). The results indicate that growth is dominated by the incorporation of depositing species at defect sites. These defect sites, which provide energetically favorable positions for accommodating the arriving species, are at ledges—either along growth spirals emanating from screw dislocations, or due to the closely spaced surface steps arising from the macroscopic tilt of the substrate. If the substrate is misoriented sufficiently, the depositing species may diffuse to and be accommodated by these surface steps, without the supersaturation on the terraces attaining a high enough level for two-dimensional nucleation to occur. Under these conditions, growth occurs by step propagation. Otherwise, a high density of screw dislocations (≈109 cm-2) is nucleated during the initial stages of growth, which provides a continual supply of ledge incorporation sites in the vicinity of the depositing species. The surface evolution reported appears to be an intrinsic feature of c-axis oriented YBa2Cu3O7-δ films for a wide range of growth conditions, irrespective of the substrate material or vapor phase deposition method.

Scanning Tunneling Microscopy and Spectroscopy Studies of Single Wall Carbon Nanotubes

1998 ◽  
Vol 13 (9) ◽  
pp. 2380-2388 ◽  
Author(s):  
Teri Wang Odom ◽  
Jin-Lin Huang ◽  
Philip Kim ◽  
Min Ouyang ◽  
Charles M. Lieber
Keyword(s):  
Carbon Nanotubes ◽  
Scanning Tunneling Microscopy ◽  
Single Wall Carbon Nanotubes ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Metallic Behavior ◽  
Single Wall Carbon ◽  
Wide Range ◽  
Theoretical Predictions ◽  
Spectroscopy Studies

Scanning tunneling microscopy and spectroscopy have been used to characterize the atomic structure and tunneling density of states of individual single wall carbon nanotubes (SWNT's) and ropes containing many SWNT's. Analysis of atomically resolved SWNT images shows that the nanotubes consist of a wide range of diameters and helicities with no one structure clearly dominant. Tunneling spectroscopy measurements made simultaneously on atomically resolved SWNT's exhibit semiconducting and metallic behavior that depend predictably on helicity and diameter. In addition the band gaps of the semiconducting tubes were also found to depend inversely on diameter. These results are compared to theoretical predictions, and the implications of these studies as well as important future directions are discussed.

Topographic Comparison of G-Wire DNA Imaged by Hydration Scanning Tunneling and Atomic Force Microscopy as a Function of Humidity

1998 ◽  
Vol 4 (S2) ◽  
pp. 302-303
Author(s):  
D. Janigian ◽  
E. Morales ◽  
T. Muir ◽  
B. Garcia ◽  
J. Vesenka
Keyword(s):  
Relative Humidity ◽  
Self Assembly ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Force Microscopy ◽  
Atomic Force ◽  
Wide Range ◽  
Dna Strands ◽  
Humidity Dependence ◽  
Better Than

The tendency of poly-G oligonucleotides to undergo self-assembly into helical nucleic acid tetramers have been termed G-quartets. Also known as G-wires, these structures retain their crystallographic determined dimensions better than duplex DNA when imaged with the atomic force microscope (AFM). Relative humidity has been known to affect both the resolution and measured height DNA strands on mica. The results below aim to develop a model that can be used to define the mechanical properties of G-wires by scanning probe microscopy investigations. G-wires were examined under a wide range of relative humidity to determine their tolerance to shear forces under the AFM, and to establish imaging conditions for hydration scanning tunneling microscopy (HSTM).The relative humidity dependence of G-wires were taken with 125 μm long, 20 μm wide silicon nitride cantilevers in contact AFM mode (spring constant ∼ 0.4 N/m) (Fig. 1).

scholarly journals On the Structure of Ultrathin FeO Films on Ag(111)

Nanomaterials ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 828 ◽  
Author(s):  
Mikołaj Lewandowski ◽  
Tomasz Pabisiak ◽  
Natalia Michalak ◽  
Zygmunt Miłosz ◽  
Višnja Babačić ◽  
...  
Keyword(s):  
Transition Metal ◽  
Photoelectron Spectroscopy ◽  
Density Functional ◽  
Lattice Mismatch ◽  
Transition Metal Dichalcogenides ◽  
Chemical Properties ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Free Standing ◽  
Preparation Conditions

Ultrathin transition metal oxide films exhibit unique physical and chemical properties not observed for the corresponding bulk oxides. These properties, originating mainly from the limited thickness and the interaction with the support, make those films similar to other supported 2D materials with bulk counterparts, such as transition metal dichalcogenides. Ultrathin iron oxide (FeO) films, for example, were shown to exhibit unique electronic, catalytic and magnetic properties that depend on the type of the used support. Ag(111) has always been considered a promising substrate for FeO growth, as it has the same surface symmetry, only ~5% lattice mismatch, is considered to be weakly-interacting and relatively resistant to oxidation. The reports on the growth and structure of ultrathin FeO films on Ag(111) are scarce and often contradictory to each other. We attempted to shed more light on this system by growing the films using different preparation procedures and studying their structure using scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). We observed the formation of a previously unreported Moiré superstructure with 45 Å periodicity, as well as other reconstructed and reconstruction-free surface species. The experimental results obtained by us and other groups indicate that the structure of FeO films on this particular support critically depends on the films’ preparation conditions. We also performed density functional theory (DFT) calculations on the structure and properties of a conceptual reconstruction-free FeO film on Ag(111). The results indicate that such a film, if successfully grown, should exhibit tunable thickness-dependent properties, being substrate-influenced in the monolayer regime and free-standing-FeO-like when in the bilayer form.

LOCAL ELECTRONIC PROPERTIES OF DOMAIN BOUNDARIES ON c(2 × 2) Fe(001) THIN FILM SURFACES

2006 ◽  
Vol 05 (06) ◽  
pp. 935-942 ◽  
Author(s):  
HIROFUMI OKA ◽  
AGUS SUBAGYO ◽  
KAZUHISA SUEOKA
Keyword(s):  
Bias Voltage ◽  
Surface States ◽  
Scanning Tunneling ◽  
Tunneling Conductance ◽  
Tunneling Microscopy ◽  
Voltage Range ◽  
Domain Boundaries ◽  
Voltage Dependent ◽  
The Difference

Scanning tunneling microscopy (STM) and spectroscopy have been performed on a nanostructure "line-like pattern" appearing on atomically flat terraces of bcc-Fe (001) with a c(2 × 2) reconstructed structure. Atomically resolved STM reveals that the line-like pattern consists of regularly aligned surface atoms that have a similar symmetry to the (1 × 1) structure of Fe (001). The line-like pattern plays a role of domain boundaries of c(2 × 2) domains. The patterns exhibit bias-voltage dependent image contrast in the STM topographic images. In negative sample bias-voltage range the patterns appear lower than the c(2 × 2) domains and higher in positive range. In dI/dV tunneling spectra taken on the patterns a shoulder is observed around +0.2 V. On the other hands, a small salient is distinguished around +0.4 V in the spectra taken on the c(2 × 2) domains. These features are originated from surface states existing on bcc-Fe (001) surfaces with (1 × 1) structure and c(2 × 2) reconstructed structure, respectively. Emergence of the line-like patterns results in the difference of tunneling conductance.

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