STM studies on porphyrins Otsuki, Joe
Coordination chemistry reviews,
10/2010, Letnik:
254, Številka:
19
Journal Article
Recenzirano
Porphyrins are promising components to be used in molecular electronics due to their rich electronic/photonic properties. Preparation of supramolecular architectures of porphyrins on solid surfaces ...would constitute a basis for further development toward molecular circuitry or other constructs for molecular electronics applications. Assemblies on surfaces can be probed with scanning tunneling microscopy (STM) at submolecular resolutions to reveal the arrangements and conformations of molecules on an individual molecule basis. The electronic characteristics within a single porphyrin molecule can also be probed by means of the same technique. This review summarizes the status quo of STM studies on porphyrins on surfaces with regard to their assemblies, structures, and electronic properties at the single molecule level.
Recently, several research groups have reported the growth of germanene, a new member of the graphene family. Germanene is in many aspects very similar to graphene, but in contrast to the planar ...graphene lattice, the germanene honeycomb lattice is buckled and composed of two vertically displaced sub-lattices. Density functional theory calculations have revealed that free-standing germanene is a 2D Dirac fermion system, i.e. the electrons behave as massless relativistic particles that are described by the Dirac equation, which is the relativistic variant of the Schrödinger equation. Germanene is a very appealing 2D material. The spin-orbit gap in germanene (~24 meV) is much larger than in graphene (<0.05 meV), which makes germanene the ideal candidate to exhibit the quantum spin Hall effect at experimentally accessible temperatures. Additionally, the germanene lattice offers the possibility to open a band gap via for instance an externally applied electrical field, adsorption of foreign atoms or coupling with a substrate. This opening of the band gap paves the way to the realization of germanene based field-effect devices. In this topical review we will (1) address the various methods to synthesize germanene (2) provide a brief overview of the key results that have been obtained by density functional theory calculations and (3) discuss the potential of germanene for future applications as well for fundamentally oriented studies.
Scanning Tunneling Microscopy/Spectroscopy
In article number 2300413, Shern‐Long Lee and co‐workers summarize recent scanning tunneling microscopy/spectroscopy (STM/STS) studies of 3D ...nanoarchitectures based on the supramolecular assembly of functionalized molecules at the liquid‐solid interface. The authors highlight several molecular systems with an emphasis on unique characteristics and electronic properties, providing insights into the designs of supramolecular architectures with increasing complexity and desired functionality.
Two-dimensional black phosphorus (BP) has sparked enormous research interest due to its high carrier mobility, layer-dependent direct bandgap and outstanding in-plane anisotropic properties. BP is ...one of the few two-dimensional materials where it is possible to tune the bandgap over a wide energy range from the visible up to the infrared. In this article, we report the observation of a giant Stark effect in electrostatically gated few-layer BP. Using low-temperature scanning tunnelling microscopy, we observed that in few-layer BP, when electrons are injected, a monotonic reduction of the bandgap occurs. The injected electrons compensate the existing defect-induced holes and achieve up to 35.5% bandgap modulation in the light-doping regime. When probed by tunnelling spectroscopy, the local density of states in few-layer BP shows characteristic resonance features arising from layer-dependent sub-band structures due to quantum confinement effects. The demonstration of an electrical gate-controlled giant Stark effect in BP paves the way to designing electro-optic modulators and photodetector devices that can be operated in a wide electromagnetic spectral range.
We report a molecular investigation of a cobalt phthalocyanine (CoPc)‐catalyzed CO2 reduction reaction by electrochemical scanning tunneling microscopy (ECSTM). An ordered adlayer of CoPc was ...prepared on Au(111). Approximately 14 % of the adsorbed species appeared with high contrast in a CO2‐purged electrolyte environment. The ECSTM experiments indicate the proportion of high‐contrast species correlated with the reduction of CoIIPc (−0.2 V vs. saturated calomel electrode (SCE)). The high‐contrast species is ascribed to the CoPc‐CO2 complex, which is further confirmed by theoretical simulation. The sharp contrast change from CoPc‐CO2 to CoPc is revealed by in situ ECSTM characterization of the reaction. Potential step experiments provide dynamic information for the initial stage of the reaction, which include the reduction of CoPc and the binding of CO2, and the latter is the rate‐limiting step. The rate constant of the formation and dissociation of CoPc‐CO2 is estimated on the basis of the in situ ECSTM experiment.
Imaging the electrocatalytic process: The cobalt‐phthalocyanine‐catalyzed CO2 reduction reaction is investigated by electrochemical scanning tunneling microscopy at the molecular scale. The molecular processes of the reaction, including the reduction of CoII, the binding of CO2, and the subsequent process, are revealed.
Germanene, a 2D honeycomb structure similar to silicene, has been fabricated on Al(111). The 2D germanene layer covers uniformly the substrate with a large coherence over the Al(111) surface atomic ...plane. It is characterized by a (3 × 3) superstructure with respect to the substrate lattice, shown by low energy electron diffraction and scanning tunnelling microscopy. First-principles calculations indicate that the Ge atoms accommodate in a very regular atomic configuration with a buckled conformation.
Single-layer black phosphorus (BP), or phosphorene, is a highly anisotropic two-dimensional elemental material possessing promising semiconductor properties for flexible electronics. However, the ...direct bandgap of single-layer black phosphorus predicted theoretically has not been directly measured, and the properties of its edges have not been considered in detail. Here we report atomic scale electronic variation related to strain-induced anisotropic deformation of the puckered honeycomb structure of freshly cleaved black phosphorus using a high-resolution scanning tunneling spectroscopy (STS) survey along the light (x) and heavy (y) effective mass directions. Through a combination of STS measurements and first-principles calculations, a model for edge reconstruction is also determined. The reconstruction is shown to self-passivate most dangling bonds by switching the coordination number of phosphorus from 3 to 5 or 3 to 4.
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•STM lithography with silicon layers removal is realized on Si(1 0 0)-2×-Cl.•Voltage pulse leads to the formation of pits by removing one or two silicon layers.•The typical etched pit ...has a lateral size of 1–2 nm and a depth of 1–5 Å.•Pits can contain chlorine vacancies.
We report the realization of STM-based lithography with silicon layers removal on the chlorinated Si(1 0 0)-2 × 1 surface at 77 K. In contrast to other STM lithography studies, we were able to remove locally both chlorine and silicon atoms. Most of the etched pits have a lateral size of 10–20 Å and a depth of 1–5 Å. In the pits in which the STM image with atomic resolution is obtained, the bottom is mainly covered with chlorine. Some pits contain chlorine vacancies. Mechanisms of STM-induced removal of silicon and chlorine atoms on Si(1 0 0)-2 × 1-Cl are discussed and compared with the well-studied case of STM-induced hydrogen desorption on Si(1 0 0)-2 × 1-H. The results open up new possibilities of the three-dimensional local etching with STM lithography.
The chemical bond is of central interest in chemistry, and it is of significance to study the nature of intermolecular bonds in real‐space. Herein, non‐contact atomic force microscopy (nc‐AFM) and ...low‐temperature scanning tunneling microscopy (LT‐STM) are employed to acquire real‐space atomic information of molecular clusters, i.e., monomer, dimer, trimer, tetramer, formed on Au(111). The formation of the various molecular clusters is due to the diversity of halogen bonds. DFT calculation also suggests the formation of three distinct halogen bonds among the molecular clusters, which originates from the noncovalent interactions of Br‐atoms with the positive potential H‐atoms, neutral potential Br‐atoms, and negative potential N‐atoms, respectively. This work demonstrates the real‐space investigation of the multiple halogen bonds by nc‐AFM/LT‐STM, indicating the potential use of this technique to study other intermolecular bonds and to understand complex supramolecular assemblies at the atomic/sub‐molecular level.
A real‐space investigation of the multiple halogen bonds by the non‐contact atomic force microscopy (nc‐AFM)/low‐temperature scanning tunneling microscopy (LT‐STM) technique is demonstrated. Due to the noncovalent interactions of Br‐atom with the H‐atom, Br‐atom and N‐atom, three distinct types of halogen bonds form and are investigated in real‐space. This work suggests AFM/STM as a powerful technique to study the nature of intermolecular bonds at the sub‐molecular level.
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