High Vacuum Scanning Tunneling Microscopy Research Articles

On-Surface Synthesis of Fused Anthracenyl Porphyrin Derivatives

For the last fifteen years, on-surface synthesis became an extremely popular and powerful method to fabricate nanostructures which otherwise would not have been accessible by conventional wet organic syntheses. The syntheses, realized in the chamber of high vacuum scanning tunneling microscope (STM), permitted the fabrication and the characterization of atomically defined nanostructures such as polycyclic aromatic hydrocarbons (PAH), graphene nanoribbons or 2D covalent networks.1 Among the organic molecules studied by STM, porphyrins are of particular importance because of their electronic and optical properties. Initial studies were mainly devoted to the supramolecular organization of porphyrins and porphyrin derivatives on surface and it is only in 2004 that noble metal surfaces were used as catalytic surface to perform reactions on the porphyrin cores.2 Since then, examples of open-shell porphyrin derivatives3 and conjugated oligomers4 were reported.While the synthesis of fused bis- and tetra-4,5-bis-(2,4,6-trimethylphenoxy)anthracen-9-yl porphyrins containing Ni(II) was reported by Anderson about 10 years ago,5 the formation π-extended porphyrin bearing unsubstituted anthracenyl moieties were never achieved. The formation of such compounds became possible by on-surface synthesis. Herein, we report on the synthesis of fused bis- and tetra-anthracenylporphyrin derivatives via the cyclodehydrogenation the parent meso-substituted molecules on a catalytic Au(111) surface.6 Depending on the annealing temperature, anthracenylporphyrins with the four anthracene fully linked to the porphyrin core or over-oxidized porphyrin in which the anthracene are connected two by two in 2-2’ position were observed by STM (Figure 1). Figure 1. STM images of the fused tetra-anthracenylporphyrins and related porphyrin structures References Clair, S.; de Oteyza, D. G. Chem. Rev. 2019, 119, 4717-4776.Fox, S.; Boyle, R. W. Chem. Commun. 2004, 1322-1323.a) Sun, Q.; Mateo, L. M.; Robles, R.; Ruffieux, P.; Lorente, N.; Bottari, G.; Torres, T.; Fasel, R. J. Am. Chem. Soc. 2020, 142, 18109-18117; b) Zhao, Y.; Jiang, K.; Li, C.; Liu, Y.; Xu, C.; Zheng, W.; Guan, D.; Li, Y.; Zheng, H.; Liu, C.; Luo, W.; Jia, J.; Zhuang, X.; Wang, S. J. Am. Chem. Soc. 2020, 142, 18532-18540.a) Mateo, L. M.; Sun, Q.; Liu, S.-X.; Bergkamp, J. J.; Eimre, K.; Pignedoli, C. A.; Ruffieux, P.; Decurtins, S.; Bottari, G.; Fasel, R.; Torres, T. Angew. Chem., Int. Ed. 2020, 59, 1334-1339; b) Mateo, L. M.; Sun, Q.; Eimre, K.; Pignedoli, C. A.; Torres, T.; Fasel, R.; Bottari, G. Chem. Sci. 2021, 12, 247-252.a) Davis, N. K. S.; Thompson, A. L.; Anderson, H. L. Org. Lett. 2010, 12, 2124-2127; b) Davis, N. K. S.; Thompson, A. L.; Anderson, H. L. J. Am. Chem. Soc. 2011, 133, 30-31.Baljozović, M. et al., in preparation Figure 1

Probing Local Electronic Structures of Au–PbS Metal–Semiconductor Nanodumbbells

Probing electronic structure of metal–semiconductor heterostructures at the local scale is important both from the fundamental and technological point of views. Here, we report on the nanoscale probing of electronic structures of gold–lead sulfide nanodumbbells using ultra high-vacuum scanning tunneling microscopy and spectroscopy techniques. A single lead sulfide nanorod shows delocalization of both conduction and valence bands along the length of the nanorod. The electronic structure of the lead sulfide nanorod is significantly altered upon formation of metal contacts at the tips of lead sulfide nanorod in the form of nanodumbbells. The nanodumbbell shows partial delocalization of the conduction band along the length while the valence band is localized to the semiconductor region of the nanodumbell. Comparison of the tunneling spectra of the pristine nanorod and nanodumbbell reveals n-type behavior of the nanodumbbell owing to the perturbation of energy levels of pristine nanorod by metal contacts donating the electrons to the semiconductor section.

Higher order reconstructions of the Ge(001) surface induced by a Ba layer

Structural properties of Ba-induced reconstructions on a Ge(001) surface, based on atomic-resolution ultra high-vacuum scanning tunneling microscopy measurements, are discussed. It is shown that while the Ba - Ge layer, which fully covers the surface, is dominated by a phase with an internal 2 × 3 periodicity, it also includes portions of higher order 2 × 6 and 4 × 3 surface reconstructions, always accompanied by 1D protrusions embedded into the dominating phase. Modelling the observed higher order structures, using the elementary cell of the 2 × 3 phase calculated within the density functional theory, is shown to reproduce the experimental data very well. As such the higher order reconstructions can be treated as local defects of the dominating 2 × 3 phase.

Are Two Better Than One? A New Approach for Multidentate Grafting of Peptides to a Gold Substrate

Abstract Multidentate binding of two helical hexapeptides to a gold surface was obtained by introducing in the peptide chain a non ribosomial amino acid, i.e. the 4-amino-1,2-dithiolane-4-carboxylic acid (Adt) residue, a C α -tetrasubstituted α-amino acid bearing a heterocyclic side chain characterized by a disulfide group. The two peptides, mainly formed by strongly helicogenic C α -tetrasubstituted α-amino acids, were both functionalized at the N-terminus by a ferrocenoyl (Fc) group, but differ in the number of Adt residues included in the peptide chain: the former (Fc6Adt2) contains two Adt residues at positions 1 and 4, while its analog (Fc6Adt1) contains a single Adt at position 4, since the Adt at position 1 is substituted by an α-amino isobutyric acid (Aib) residue. This peptide design allowed us to explore the different electrochemical properties and morphologies shown by the two peptide layers immobilized on a gold surface by two (Fc6Adt2) or a single (Fc6Adt1) bidentate linker, respectively. The electrochemical activity of the ferrocenoyl probe embedded in the peptide film was characterized by cyclic voltammetry, chronoamperometry and square wave voltammetry, while the binding and the morphology of the peptide layers were studied by X-ray photoelectron spectroscopy (XPS) and ultra high vacuum scanning tunneling microscopy (UHV-STM), respectively. Significant differences were observed in the electron transfer (ET) properties of the two peptides investigated, which emerge from the diverging morphology achieved by the peptide layers on the gold surface. It was found that while a standing-up configuration of the peptide layer, realized by a single bidentate linkage, maximizes the ET efficiency, a lying down configuration (two Adt linkages) allows for precise positioning of Fc in the proximity of a gold surface.

Magnetization reversal of ferromagnetic nanoparticles induced by a stream of polarized electrons

The remagnetization of ferromagnetic Fe3O4 nanoparticles of several thousand cubic nanometers by spin-polarized current is investigated. For this purpose, magnetite nanoparticles are synthesized and deposited on a conductive nonmagnetic substrate. The remagnetization is conducted in high-vacuum scanning tunneling microscope (STM). The STM tip from magnetized iron wire constitutes one electrode while the ferromagnetic nanoparticle on the graphite surface represents the second electrode. The measured threshold value of remagnetization current (Ithresh=9nA) is the lowest value of current at which remagnetization occurs. The change in nanoparticle magnetization is detected by the effect of giant magnetic resistance, specifically, the dependence of the weak polarized current (I<Ithresh) on the mutual directions of magnetization of the electrodes. The results indicate essential difference with available literature data on the influence of polarized current on magnetic moment of small ferromagnetic nanoclusters. The peculiarities of size dependence of the observed effects are explained.

Change in the magnetic moment of a ferromagnetic nanoparticle under polarized current

The magnetization reversal of a ferromagnetic Fe3O4 nanoparticle with a volume of the order of several thousands of cubic nanometers under the influence of spin-polarized current has been investigated on a high-vacuum scanning tunneling microscope, where one of the electrodes is a magnetized iron wire needle and the second electrode is a ferromagnetic nanoparticle on a graphite substrate. The measured threshold current of magnetization reversal, i.e., the lowest value of the current corresponding to the magnetization reversal, is found to be Ithresh ≈ 9 nA. A change in the magnetization of a nanoparticle is revealed using the giant magnetoresistance effect, i.e., the dependence of the weak polarized current (I < Ithresh) on the relative orientation of the magnetizations of the electrodes.

The transition from 3C SiC (1 1 1) to graphene captured by Ultra High Vacuum Scanning Tunneling Microscopy

In this paper we clarify the transformation mechanism of 3C-SiC into graphene upon thermal decomposition, by a combination of high resolution Scanning Tunneling Microscopy (STM) images and first principle calculations. We studied the transition from 3C-SiC to graphene by high temperature annealing of C-terminated 3C SiC(111)/Si(111) samples in Ultra High Vacuum. By using STM we were able to observe very clear atomic resolution images of the transition from SiC (√3×√3)R30° to a new intermediate stage SiC 32×√3R30° (very close to the graphene (2×2) reconstruction) after annealing at 1250°C. We also obtained images of the transformation of the intermediate structure into a (1×1) monolayer graphene, caused by further sublimation of atoms in the subsurface layer. We have interpreted the results by using Density Functional Theory – Local Density Approximation calculations, which give full account of the SiC (√3×√3)R30° reconstruction, but fail to describe the SiC 32×√3R30° structure due to its incommensurability with the 3C-SiC(111) lattice.

Molecular Interface Formation in Titanyl Phthalocyanine–C60 Monolayer Films

Molecular interfaces have been prepared in titanyl phthalocyanine (TiOPc)–C60 monolayer films on Ag(111) and characterized with ultra high vacuum–scanning tunneling microscopy. Two distinct TiOPc monolayer phases, namely, a hexagonal phase and a honeycomb phase, were first generated as molecular-film substrates for C60 growth. Both TiOPc monolayer structures rearrange upon C60 adsorption, yielding films with nanophase-separated TiOPc and C60 domains and a new cocrystalline TiOPc2(C60)1 honeycomb network. Kinetic access to the cocrystalline network is most facile from the hexagonal TiOPc monolayer, producing extended domains. Detailed models for emergent structural phases and molecular interfaces are presented. Mechanisms for C60-induced rearrangements are developed from coverage-dependent measurements.

Scanning tunneling spectra for the etched surface of p-type HgCdTe

PDF HTML阅读 XML下载 导出引用 引用提醒 液相外延p型碲镉汞表面区与腐蚀凹坑的不同扫描隧道谱特征 DOI: 作者: 作者单位: 上海大学理学院物理系和微结构实验室,上海市上大路号,上海大学理学院物理系和微结构实验室,上海市上大路号,上海大学理学院物理系和微结构实验室,上海市上大路号,上海大学理学院物理系和微结构实验室,上海市上大路号,上海大学理学院物理系和微结构实验室,上海市上大路号,上海大学理学院物理系和微结构实验室,上海市上大路号 作者简介: 通讯作者: 中图分类号: 基金项目: 上海市重点学科建设无线电物理专项基金（S30105） Scanning tunneling spectra for the etched surface of ptype HgCdTe Author: Affiliation: Dept of Physics and Laboratory for Microstructures,Shanghai University,Dept of Physics and Laboratory for Microstructures,Shanghai University,Dept of Physics and Laboratory for Microstructures,Shanghai University;China,Dept of Physics and Laboratory for Microstructures,Shanghai University,China,Dept of Physics and Laboratory for Microstructures,Shanghai University,Dept of Physics and Laboratory for Microstructures,Shanghai University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:利用超高真空扫描隧道显微镜对经过溴甲醇溶液腐蚀处理的液相外延碲镉汞材料进行了表征.发现经过腐蚀处理（3%浓度，2.5 min）的样品表面出现高密度的凹坑结构，凹坑深度约几十纳米，横向尺度在几十到几百纳米之间.扫描隧道谱测量表明，腐蚀样品表面平坦区呈现较大表观带隙，需考虑针尖诱导的能带弯曲效应，而凹坑区在零偏压区的扫描隧道谱线则近似为线性变化，说明该区域包含较高的带隙态并直接参与隧穿，从而掩盖了带隙信息. Abstract:Ultrahigh vacuum scanning tunneling microscopy（STM） and spectroscopy （STS）were used to characterize Hg1-xCdxTe grown by liquidphase epitaxy (LPE) method. The sample was etched with 3% Brominemethanol in 2.5 minutes. The STM images display submicrometersized pit structures with depths ranging from a few tens to a few hundreds nanometers. The scanning tunneling spectra show a larger apparent gap than the energy band gap of the bulk material due to the tipinduced band bending effect. In contrast, the scanning tunneling spectra of the pits show a finite slope through zero volt, implying the contribution of high density of band gap states which blur out the band gap information. 参考文献 相似文献 引证文献

Graphene domain boundaries on Pt(111) as nucleation sites for Pt nanocluster formation

The growth of Pt nanoclusters on a graphene layer on Pt(111) was studied with ultra high vacuum scanning tunneling microscopy. Different periodicities in the moiré patterns of the graphene layer are observed corresponding to different orientations with respect to the Pt(111) lattice. Various graphene orientations are possible because of a relatively weak graphene–Pt interaction. Following Pt deposition onto the graphene-covered surface, small Pt nanoclusters are observed to preferentially form along the moiré domain boundaries. The weak interaction of graphene with Pt(111) leads to a weak corrugation in the superlattice compared to other transition metals, such as Ru, but it is found even this weak corrugation is sufficient to serve as a template for the formation of mono-dispersed one-dimensional Pt nanocluster chains. These Pt nanoclusters are relatively stable and only undergo agglomeration at annealing temperatures above 600K.

Playing with Peptides: How to Build a Supramolecular Peptide Nanostructure by Exploiting Helix···Helix Macrodipole Interactions

A novel method to build bicomponent peptide self-assembled monolayers (SAMs) has been developed, by exploiting helix···helix macrodipole interactions. In this work, a peptide-based self-assembled monolayer composed of two helical peptides was immobilized on a gold surface. Specifically, a pyrene-containing octapeptide, devoid of any sulfur atom (A8Pyr), and a hexapeptide, functionalized at the N-terminus with (S,R) lipoic acid, for binding to gold substrates (SSA4WA) via a Au-S linkage, have been employed. Both peptides investigated attain a helical structure, because they are almost exclusively formed by strongly folding inducer C(α)-tetrasubstituted α-amino acids. We demonstrate that the two peptides generate a stable supramolecular nanostructure (a densely packed bicomponent peptide monolayer), where A8Pyr is incorporated into the SSA4WA palisade by exploiting helix···helix macrodipole interactions. The presence of both peptides on the gold surface was investigated by spectroscopic and electrochemical techniques, while the morphology of the monolayer was analyzed by ultra high-vacuum scanning tunnelling microscopy. The composition of the bicomponent SAM on the surface was studied by a combination of electrochemical and spectroscopic techniques. In particular, the amount of Au-S linkages from the sulfur-containing peptides was quantified from reductive desorption of the peptide-based SAM, while the amount of A8Pyr was estimated by fluorescence spectroscopy. The antiparallel orientation of the A8Pyr and SSA4WA peptide chains minimizes the interaction energy between the helix dipoles, suggesting that this kind of electrostatic phenomenon is the driving force that stabilizes the bicomponent SAM.

STM and XPS investigations of bismuth islands on HOPG

The growth of bismuth thin films on highly oriented pyrolitic graphite (HOPG) was studied using ultra high vacuum (UHV) scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The locations of the main XPS peaks, and also the plasmon energy, are in good agreement with results recorded on bulk bismuth. The shape of the Bi 4f doublet, as well as the well developed Fermi edge, indicates the metallic character of the deposited film. One of the observed shoulders is identified with a quantum-well subband characteristic of thin bismuth films. There is no evidence for the existence of Bi–C bonds, consistent with weak bonding between the Bi islands and the HOPG. The height of the islands and their crystallographic orientation were investigated as a function of surface coverage. The Bi islands grow with the (110) plane parallel to the substrate. The observed heights (3, 5, 7, 9 ML) indicate that the preferred crystal structure involves paired layers on an intermediate mono-atomic Bi layer. There is evidence both for and against the Black Phosphorus like allotrope, and the nature of both the layer pairing and the intermediate layer are yet to be resolved. The islands exhibit stripes oriented along the < 1 1 ¯ 0 > axis of the Bi crystal, which is a fast growth direction due to the existence of strongly bonded zig-zag chains of atoms. The surface unit cell and the parameters of the rhombohedral bulk unit cell are estimated based on atomic resolution images. In the case of 2 ML stripes on top of a 5 ML base, the expansion of the outer atomic rows was estimated at 27%. Asymmetries in the growth of the islands are observed. Based on low coverage depositions at reduced substrate temperatures, it is proposed that there is a second fast growth direction corresponding to preferential attachment of atoms to one of the faces of the asymmetric, rhombic cross-section of the (110) crystal.

Subphthalocyanine-based nanocrystals

Ultra high vacuum scanning tunnelling microscopy revealed chlorosubphthalocyanine to self-organize into discrete well-defined bilayer and trilayer triangular nanocrystallites when evaporated onto a Cu(111) surface.

The structure and properties of the Si nanostructures on an HOPG surface

The morphology, electronic structure, and optical properties of self-assembled silicon nanostructures grown on the surface of Highly Oriented Pyrolytic Graphite (HOPG) by molecular beam epitaxy were studied by ultra high vacuum (UHV) scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS) in situ, and by Raman spectroscopy ex situ. At coverages of less than 1 monolayer (ML), the formation of monolayered silicon nanoislands with an atomic structure similar to that of graphene was observed.

Adsorption of a single molecule of a diarylethene photochromic dye on Cu(111)

On the route to single (large) molecule unimolecular chemistry, the adsorption of a photochromic dithienylethene dye on Cu(111) at a submonolayer level has been studied by Ultra High Vacuum-Scanning Tunneling Microscopy at Low Temperature. This technique has shown that the observed adsorbed molecule's shape is compatible with an helical conformation but has also revealed a surrounding electronic corrugation due to the perturbed surface states. Careful examination of the standing wave pattern indicated that only a part of the molecule is indeed interacting with the metallic substrate. Geometric considerations were used to infer that the bridging ethene moiety could be responsible for the electronic scattering. Scanning Tunneling Spectroscopy has shown a substantial amount of charge transfer from the surface to the adsorbate. The hypothesis that this precise double bond is a reactive locus toward charge transfer processes is confirmed by the electrochemical results: this double bond is indeed reduced upon coulometric reduction on glassy carbon. Furthermore, the use of a copper cathode strongly facilitates the reduction since a +0.6 V shift was recorded.

Creation and study of 2D and 3D carbon nanographs

The technology of nanowhiskers growth in the scanning electron microscope vacuum chamber have been applied for the creation of 2D and 3D carbon wireframe nanosystems (CWNS). The probability of electron transition has been calculated within simple quantum graph (quantum network) model. For the purpose of research of CWNS electron state density investigation it is proposed to grow CWNS on the tungsten tip apex and to measure current–voltage characteristics I(V) of Au plate – vacuum gap – CWNS W tip tunneling junction in the ultra high vacuum scanning tunneling microscope. Experiments show that proposed methodic approach gives adequate I(V) dependencies for metallic and semiconductor nanowhiskers at the room temperature. For detection of the peculiarities at I(V) tunneling junction characteristics caused by quantum graphs it is required to carry out measurements at low temperature conditions.

Exploring the F16CoPc/Ag(110) Interface Using Scanning Tunneling Microscopy and Spectroscopy. Part 1: Template-Guided Adlayer Structure Formation

Adsorption of cobalt(II) hexadecafluoro-phthalocyanine (F16CoPc) onto a silver (110) surface, prepared by organic molecular beam epitaxy (OMBE) is investigated using ultra high vacuum scanning tunneling microscopy (UHV STM) operating at 40 K. The asymmetry of the metal substrate is found to act as a template for the organic adlayer that grows preferentially along the [110] crystallographic axis leading to the formation of commensurate structures with well-defined pinning centers. A line-to-line epitaxy is observed where the difference in interpinning line spacing superimposes the development of two different structures: oblique and square. Structural models are proposed and discussed for both adsorbate lattices where the first one is strongly sustained by the molecular self-assembly at the defect proximity and especially at the domain boundaries where a mirror structure is induced.

STM images of a large organic molecule adsorbed on a bare metal substrate or on a thin insulating layer: Visualization of HOMO and LUMO

An isomer of the methylterrylene molecule was adsorbed both on Cu(111) and on a NaCl bilayer deposited on Cu(111) and imaged by ultra high vacuum scanning tunneling microscopy at low temperature (5 K). On the bare metal surface, the STM images do not reveal any intramolecular resolution and do not depend on the applied tunnel bias. On the contrary, the images acquired at specific bias voltages for the molecule on the salt layer show a striking similarity with the spatial distribution of the electronic probability density in the highest occupied molecular orbital (HOMO) and in the lowest unoccupied molecular orbital (LUMO) of free methylterrylene. They are well reproduced by elastic scattering quantum chemistry calculations. These data provide a direct view of the hyperconjugative interaction between the methyl group and the frontier orbitals of terrylene.

Formation of dense nitroxide radical layers on the Au(1 1 1) substrate for ESN-STM measurement

Ultra high vacuum scanning tunnelling microscopy and electron paramagnetic resonance spectroscopy were used to investigate ISL and TEMPOL piperidine nitroxides molecules deposited on the Au(1 1 1) substrate by the drop-cast method. The STM results suggest that both compounds form dense layers on Au(1 1 1) with high molecular mobility observed during imaging process. High resolution STM topographies of both compounds suggest a well-defined molecular order which can be ascribed to the presence of self-assembly mechanism during layers formation. The EPR results indicated that both compounds deposited on the Au(1 1 1) substrate were not reduced retaining their paramagnetic properties. The significance of the results obtained in the field of single spin detection is briefly outlined.

A local view on hyperconjugation

Abstract Two isomers of the methylterrylene molecule were adsorbed on a NaCl bilayer deposited on Cu(1 1 1) and imaged by ultra high vacuum scanning tunneling microscopy at low temperature (5 K). The images acquired for specific bias voltages show a striking similarity with the spatial distribution of the electronic probability density in the highest occupied molecular orbital (HOMO) and in the lowest unoccupied molecular orbital (LUMO) of free methylterrylene. They are well reproduced by elastic scattering quantum chemistry calculations. These data provide a direct view of the hyperconjugative interaction between the methyl group and the frontier orbitals of terrylene.