Resolution Scanning Tunneling Microscopy Research Articles

Visualization of electronic states on atomically smooth graphitic edges with different types of hydrogen termination

The relation between electronic structure and hydrogen content at the edges of nanosized holes (nanoholes) in graphite single layer is studied by means of atomically resolved scanning tunneling microscopy and first-principles calculations. Repeatable production of nanoholes with predominantly zigzag hydrogenated edges was realized by bombardment of the top graphene layer of graphite with low-energy (100 eV) Ar${}^{+}$ ions and its further treatment (etching) in an atomic hydrogen environment. Two main types of nanohole zigzag edge, with a striking contrast to each other, are identified: (i) monohydrogenated zigzag edge supporting edge-localized $\ensuremath{\pi}$ state on its boundary; (ii) zigzag edge with repeating two monohydrogenated sites and one dihydrogenated site, without features of the edge-localized state and characterized by a prominent standing wave pattern. Absence of the localized state at a general (chiral) hydrogenated graphitic edge consisting of a mixture of zigzag and armchair fragments is also discussed.

Assessment of the resolution of scanning tunneling microscope with a tip of a boron-doped diamond

The assessment of the resolution of scanning tunneling microscope when operated in the scanning mode has been made based on the analysis of the tunneling current on parameters of diamond tip-sample system. The scanning parameters and accuracy of supporting the constant tunneling current by the system of the instrument feedback, at which the presence of the atomic resolution is possible in the case of a single channel of tunneling, have been defined. An alternative (in respect to the best known publications) explanation of the hexagonal structure of the pyrolytic graphite surface observed with atomic resolution has been suggested. The problem of multichannel tunneling caused by the presence of several nanoprotrusions in the diamond probe test zone that initiate tunneling and impair the resolution of a scanning tunneling microscope is discussed.

Electronically Nonalloyed State of a Statistical Single Atomic Layer Semiconductor Alloy

Using atomically and momentum resolved scanning tunneling microscopy and spectroscopy, we demonstrate that a two-dimensional (2D) √3 × √3 semiconducting Ga-Si single atomic alloy layer exhibits an electronic structure with atomic localization and which is different at the Si and Ga atom sites. No indication of an interaction or an electronic intermixing and formation of a new alloy band structure is present, as if no alloying happened. The electronic localization is traced back to the lack of intra alloy bonds due to the 2D atomically confined structure of the alloy overlayer.

Focus on vacuum and cryogenics

Focus on vacuum and cryogenics

Nanomanipulation and nanofabrication with multi-probe scanning tunneling microscope: From individual atoms to nanowires

The wide variety of nanoscale structures and devices demands novel tools for handling, assembly, and fabrication at nanoscopic positioning precision. The manipulation tools should allow for in situ characterization and testing of fundamental building blocks, such as nanotubes and nanowires, as they are built into functional devices. In this paper, a bottom-up technique for nanomanipulation and nanofabrication is reported by using a 4-probe scanning tunneling microscope (STM) combined with a scanning electron microscope (SEM). The applications of this technique are demonstrated in a variety of nanosystems, from manipulating individual atoms to bending, cutting, breaking carbon nanofibers, and constructing nanodevices for electrical characterizations. The combination of the wide field of view of SEM, the atomic position resolution of STM, and the flexibility of multiple scanning probes is expected to be a valuable tool for rapid prototyping in the nanoscience and nanotechnology.

Orbital selective coupling between Ni adatoms and graphene Dirac electrons

We investigate the coupling of Ni monomers and trimers to graphene by means of atomically resolved scanning tunneling microscopy (STM). The precise adsorption site of the adatoms is determined experimentally. STM images reveal characteristic nodal structures above the Ni adatoms and trimers on graphene. First-principles calculations combined with symmetry considerations explain our experimental results by an orbitally controlled interaction of the adatoms and clusters with the Dirac electrons in graphene.

STM Self-Calibration Technique Based on Image Stitching

Scanning tunneling microscope (STM) has several advantages, such as high resolution, and is wildly used. Piezoelectric scanner brings the horizontal resolution of STM up to 0.1 nm, and is it derived by piezoelectric ceramic. Piezoelectric scanner has piezoelectric ceramic’s character. So, piezoelectric scanner output must be calibrated at regular intervals. Graphite atom arrange in a special manner. In the same layer, the distance between adjacent atoms is the same, 0.25nm. This feature can be used to measure length and calibrate small scale scanning. For the 512 × 512 resolution image, the maximum scan range that can distinguish atoms is 30nm2. More large area of atomic image needs to use image stitching technology. By image stitching, small scale scanning, less than 1μm can be calibrated.

Effects of Immersion Temperature on Self-Assembled Monolayers of Octanethiol on Au(111)

Self-assembled monolayers (SAMs) of 1-octanethiol (OT) on Au(111) surfaces, prepared at immersion temperatures between 300K and 363K in a sealed stainless steel chamber, were studied by scanning tunneling microscopy (STM). An oblique (√3×√3)R30° OT-SAM structure was observed below 348K, whereas a superstructure (3×√7)R11° covered the gold surfaces at 363K. The highly resolved STM images permitted assignment of four symmetry-inequivalent OT molecules per 8.7×7.6Å2 unit cell at 363K. Differences in the topographical heights of the molecules were attributed to the binding of OT sulfur head groups at different adsorption sites on Au(111). This structure was not observed in stirring reflux at a high temperature, which indicates a higher pressure (>1atm) in the chamber may be one of crucial factors for structural transition. As the immersion temperature increased, a lower density of vacancy islands and a higher fraction of island area were observed.

Growth and Atomic-Scale Characterizations of Graphene on Multifaceted Textured Pt Foils Prepared by Chemical Vapor Deposition

The synthesis of centimeter-scale uniform graphene on Pt foils was accomplished via a traditional ambient pressure chemical vapor deposition (CVD) method. Using scanning electron microscopy (SEM) and Raman spectroscopy, we reveal the macroscopic continuity, the thickness, as well as the defect state of as-grown graphene. Of particular importance is that the Pt foils after CVD growth have multifaceted texture, which allows us to explore the substrate crystallography effect on the growth rate and the continuity of graphene. By virtue of atomically resolved scanning tunneling microscopy (STM), we conclude that graphene grows mainly in registry with the symmetries of Pt(111), Pt(110), and Pt(100) facets, leading to hexagonal lattices and striped superstructures. Nevertheless, the carbon lattices on interweaving facets with different identities are connected seamlessly, which ensure the graphene growth from nanometer to micrometer levels. With these results, another prototype for clarifying the preliminary growth mechanism of the CVD process is demonstrated as an analogue of graphene on Cu foils.

Monolayered adatom aggregation induced by metallofullerene molecules on Cu(100)

The adsorption and self-assembly of Gd@C 82 molecules on Cu(100) surface have been investigated using scanning tunneling microscopy (STM). The metallofullerene molecules in the assemblies showed two characteristic apparent heights in the STM images. STM manipulation and spectroscopy was performed and revealed the formation of Cu adatom islands underneath the Gd@C 82 molecules. The monolayered Cu aggregates were resulted from the adatom–molecule complexation, which is supported by density functional theory (DFT) calculations that show charge transfer and electrostatic interactions between Gd@C 82 and adatoms. In addition, sub-molecularly resolved STM images demonstrated the structural and orientational ordering of Gd@C 82 assemblies upon thermal annealing. DFT calculations demonstrated that Gd atom located at the lower part of the carbon cage is a favored adsorption configuration for Gd@C 82 molecules adsorbed on Cu(100).

Imaging an Ionic Liquid Adlayer by Scanning Tunneling Microscopy at the Solid|Vacuum Interface

Structure formation in an ionic liquid adlayer: First molecularly resolved scanning tunneling microscopy images of an ionic liquid adlayer ([Py1,4]+ [FAP]− (see image)), evaporated on a Au(111) surface, resolve a molecular pattern at 210 K with a distinct short range order, indicating a 2D solid, while at room temperature, the mobility of the adlayer is too high to resolve molecular features, as expected for a 2D liquid.

STM and AFM high resolution intramolecular imaging of a single decastarphene molecule

Single decastarphene molecules, adsorbed on Cu(1 1 1) and on a bilayer of NaCl/Cu(1 1 1) are imaged by a combination of low temperature scanning tunneling microscopy (STM) and dynamic atomic force microscopy in the non-contact mode (nc-AFM). This dual imaging technique provides the intramolecular electron density maps of the frontier molecular orbitals via the STM images and the atomic scale skeleton via its constant-height frequency shift nc-AFM images. Recording both images at the same time opens the way to exactly locate the valence states electronic density map of the imaged molecule on its atomic scale skeleton.

Comparative study of the nature of chemical bonding of corrugated graphene on Ru(0001) and Rh(111) by electronic structure calculations

Recently, atomic resolved scanning tunneling microscopy investigations revealed that, depending on the substrate (Ni(111), Ru(0001), Ir(111), Pt(111), Rh(111)), graphene overlayer might present regular corrugation patterns, with periodically repeated units of a few nanometers. Variations of the interactions at the interface and the modulation of the local electronic properties are associated with the exact atomic arrangement of the carbon pairs with respect to the metal atoms of the substrate. Better understanding of the atomic structure and of the chemical bonding between graphene and the underlying transition metal is motivated by the fundamental scientific relevance of such systems, but it is also crucial in the perspective of possible applications. With the present work, we propose model systems for the two interfaces showing the most pronounced corrugation patterns, i.e. graphene/Ru(0001) and graphene/Rh(111). Our goal is to understand the nature of the interactions by means of electronic structure calculations based on Density Functional Theory. Our simulations qualitatively reproduce very well experimental results such as the STM topographies and the electrostatic potential maps, and quantitatively provide the closest agreement that has been published so far. The detailed analysis of the electronic structure at the interface highlights similarities and differences by changing the supporting transition metal. Our results point to a fundamental role of the hybridization between the π orbitals of graphene with the d band of the metal in determining the specific corrugation of the adsorbed monolayer. It is shown that differences in the response of the graphene electronic structure to the interaction with the metal can hinder the hybridization and lead to substantially different structures.

Giant Mesoscopic Spin Hall Effect on the Surface of Topological Insulator

We study mesoscopic spin Hall effect on the surface of a topological insulator with a step-function potential by using the McMillan method commonly used in the study of superconductor junctions. In the ballistic transport regime, we predict a giant spin polarization induced by a transverse electric current with parameter suitable to the topological insulator thin film Bi(2)Se(3). The spin polarization oscillates across the potential boundary with no confinement due to the Klein paradox, and should be observable in a spin resolved scanning tunneling microscope.

In Situ Observation of Water Dissociation with Lattice Incorporation at FeO Particle Edges Using Scanning Tunneling Microscopy and X-ray Photoelectron Spectroscopy

The dissociation of H2O and formation of adsorbed hydroxyl groups on FeO particles grown on Au(111) were identified with in situ X-ray photoelectron spectroscopy (XPS) at water pressures ranging from 3 × 10(-8) to 0.1 Torr. The facile dissociation of H2O takes place at FeO particle edges, and it was successfully observed in situ with atomically resolved scanning tunneling microscopy (STM). The in situ STM studies show that adsorbed hydroxyl groups were formed exclusively along the edges of the FeO particles with the O atom becoming directly incorporated into the oxide crystalline lattice. The STM results are consistent with coordinatively unsaturated ferrous (CUF) sites along the FeO particle edge causing the observed reactivity with H2O. Our results also directly illustrate how structural defects and under-coordinated sites participate in chemical reactions.

Epitaxial growth of a silicene sheet

Using atomic resolved scanning tunneling microscopy, we present here the experimental evidence of a silicene sheet (graphenelike structure) epitaxially grown on a close-packed silver surface [Ag(111)]. This has been achieved via direct condensation of a silicon atomic flux onto the single-crystal substrate in ultrahigh vacuum conditions. A highly ordered silicon structure, arranged within a honeycomb lattice, is synthesized and present two silicon sublattices occupying positions at different heights (0.02 nm) indicating possible sp2-sp3 hybridizations.

ChemInform Abstract: Direct Visualization of Chirality in Two Dimensions

AbstractReview: 24 refs.

Self-Assembled 1-Octadecanethiol Monolayers on Graphene for Mercury Detection

We report studies on surface modification of graphene with 1-octadecanethiol and its application as heavy metal sensors. The alkanethiol molecules can self-assemble into large-scale highly ordered monolayers on single-layer graphene regardless of the roughness of graphene surfaces inherited from the underlying amorphorous silicon oxide (SiO2) dielectric substrates. Atomically resolved scanning tunneling microscopy imaging of modified graphene sheets on SiO2 was conducted to reveal configuration details of the self-assembled structure. Functionalization of graphene field effect transistors (Gra-FETs) with 1-octadecanethiol was realized and successfully explored for mercury(II) (Hg2+) detection at 10 ppm.

Defect Structure of Ultrathin Ceria Films on Pt(111): Atomic Views from Scanning Tunnelling Microscopy

Atomically resolved scanning tunnelling microscopy (STM) images have been obtained on ultrathin films of CeO2(111) supported on Pt(111). The ultrathin films were grown in two ways, by reactive deposition in an oxygen atmosphere and by postoxidation of Ce/Pt surface alloys. STM results are compared with previously reported high-temperature STM and noncontact atomic force microscopy (NC-AFM) images of the native CeO2(111) surface. The similarity between these images is striking and allows a number of defects and adsorbates in our ultrathin film to be assigned. Moreover, the similarity in structure between the native oxide and the ceria ultrathin film indicates that it is an excellent topographic mimic of the native oxide.

Probing Electronic Superexchange Coupling at Isolated Poly-p-phenylene Molecules

Superexchange coupling in poly-p-phenylene molecular wires was probed using scanning tunneling microscopy/spectroscopy at cryogenic temperatures. The coupling strength was characterized by measuring the energy splitting between the molecular states constructed by symmetric and antisymmetric dimerization of molecular fragments' orbitals. The results confirm the theoretically predicted exponential decay behavior of the superexchange coupling on a single-molecule level. A decay constant of 0.10 +/- 0.02 A(-1) was obtained. Owing to the high spatial resolution of scanning tunneling microscopy, the molecules' internal states (e.g., molecular conformation) as well as external states (e.g., interaction with foreign atoms or molecules) were elucidated with atomic precision at the mean time of characterizing the superexchange coupling. This method provides a new approach to quantify how intramolecular charge transfer is influenced by molecular conformation and interaction with the surroundings.