Quantum size effect directed selective self-assembling of cobalt phthalocyanine on Pb(111) thin films

Adsorption and self-assembly of cobalt phthalocyanine (CoPc) molecules on Pb(111) thin films with a thickness ranging from 10 atomic monolayers (ML) to 20 ML were investigated by using scanning tunneling microscopy and spectroscopy (STM/STS). Unprecedented thickness-selective oscillating adsorption and self-assembly behavior of the molecules on the films were observed. STS measurement reveals that this oscillatory behavior arises from quantum size effect. The strong quantum confinement of electron motion in the Pb films modulates the electronic density of states at the Fermi level (DOS(EF)), leading to preferential adsorption at thicknesses of higher DOS(EF). The work provides an unambiguous evidence for quantum modulation of surface reactivities of a metal thin film.     

Langmuir-Blodgett monolayers of InP quantum dots with short chain ligands

We demonstrate the organization of nearly monodisperse colloidal InP quantum dots at the air/water interface in Langmuir monolayers. The organization of the particles is monitored in situ by surface pressure-surface area measurements and ex situ by AFM measurements on films transferred to mica by Langmuir-Blodgett deposition. The influence of different ligands on the quality of the monolayer formed has been studied. We show that densely packed monolayers with little holes can be formed using short chain ligands like pyridine and pentamethylene sulfide. The advantage of using short chain ligands for electron tunneling to or from the quantum dots is demonstrated using scanning tunneling spectroscopy.     

Topography Structure and Scanning Tunneling Spectrum of Nickel（Ⅱ）-tetraphenylporphyrin Molecules on Au（111）

1 INTRODUCTION Metalloporphyrins are intensively studied for many reasons. They have been comprehensively used in biochemistry, analytical chemistry and so on. They play an important role in biological processes such as oxygen transport photosynthesis and enzyme catalysis. They can act as catalysts[1], and can undergo reversible redox reactions in which the site of electron transfer may be localized on the por- phyrin ring or on the central metal ion. Both reaction types are important in…     

Vibronic transitions in single metalloporphyrins.

Structural and electronic properties of single zinc etioporphyrin molecules adsorbed on Al2O3/NiAl(110) were probed by a low-temperature scanning tunneling microscope (STM). Scanning tunneling spectroscopy (STS) revealed progressions of spectral features corresponding to the vibronic states of individual molecules that depend strongly on the molecular conformations. Vibronic features observed by STS were compared with the results from fluorescence induced by tunneling electrons (tunneling-induced fluorescence, TIF).     

Topography Structure and Scanning Tunneling Spectrum of Nickel(Ⅱ)-tetraphenylporphyrin Molecules on Au(111)

Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) were performed on monolayer film of NiTPP supported on Au(111) under ultrahigh vacuum (UHV) conditions. The constant current STM images show remarkable bias dependence. High resolution STM data clearly show the individual NiTPP molecules and allow easy differentiation between NiTPP and CoTPP reported before. Scanning tunneling spectra, as a function of molecule-tip separation, were acquired over a range of tip motion of 0.42 nm. Spectra do not show the variation in band splitting with tip distance. It appears for molecules such as NiTPP that the average potential at the molecule is essentially the same at the same metal substrate. For molecules of the height of NiTPP, the scanning tunneling spectra should give reliable occupied and unoccupied orbital energies over a wide range of tip-molecule distances.     

HREELS, STM, and STS study of CH(3)-terminated Si(111)-(1x1) surface

An ideally (1x1)-CH(3)(methyl)-terminated Si(111) surface was composed by Grignard reaction of photochlorinated Si(111) and the surface structure was for the first time confirmed by Auger electron spectroscopy, low energy electron diffraction, high-resolution electron energy loss spectroscopy (HREELS), scanning tunneling microscopy (STM), and scanning tunneling spectroscopy (STS). HREELS revealed the vibration modes associated to the CH(3)-group as well as the C-Si bond. STM discerned an adlattice with (1x1) periodicity on Si(111) composed of protrusions with internal features, covering all surface terraces. The surface structure was confirmed to be stable at temperatures below 600 K. STS showed that an occupied-state band exists at gap voltage of -1.57 eV, generated by the surface CH(3) adlattice. This CH(3):Si(111)-(1x1) adlayer with high stability and unique electronic property is prospective for applications such as nanoscale lithography and advanced electrochemistry.     

Adsorption of atomic hydrogen on ZnO(1010): STM study

The adsorption of atomic hydrogen on a single crystal ZnO(1010) surface has been studied by scanning tunneling microscopy (STM) under ultrahigh vacuum conditions at room temperature and at elevated temperatures. High resolution STM images indicate that a well-ordered (1x1) H adlayer is formed on the ZnO(1010) surface. The STM data strongly indicate that the hydrogen adsorbs on top of the oxygen atoms forming hydroxyl species. Scanning tunneling spectroscopy (STS) studies reveal a H atom induced metallization at room temperature. In contrast to the clean surface for the hydrogen-covered surface distinct defects structures consisting of missing O and Zn atoms could be identified.     

Direct and indirect causes of Fermi level pinning at the SiO/GaAs interface

The correlation between atomic bonding sites and the electronic structure of SiO on GaAs(001)-c(2x8)/(2x4) was investigated using scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and density functional theory (DFT). At low coverage, STM images reveal that SiO molecules bond Si end down; this is consistent with Si being undercoordinated and O being fully coordinated in molecular SiO. At approximately 5% ML (monolayer) coverage, multiple bonding geometries were observed. To confirm the site assignments from STM images, DFT calculations were used to estimate the total adsorption energies of the different bonding geometries as a function of SiO coverage. STS measurements indicated that SiO pins the Fermi level midgap at approximately 5% ML coverage. DFT calculations reveal that the direct causes of Fermi level pinning at the SiO GaAs(001)-(2x4) interface are a result of either local charge buildups or the generation of partially filled dangling bonds on Si atoms.     

Electronic structures of one-dimensional metal-molecule hybrid chains studied using scanning tunneling microscopy and density functional theory

The electronic structures of self-assembled hybrid chains comprising Ag atoms and organic molecules were studied using scanning tunneling microscopy (STM) and spectroscopy (STS) in parallel with density functional theory (DFT). Hybrid chains were prepared by catalytic breaking of Br-C bonds in 4,4″-dibromo-p-terphenyl molecules, followed by spontaneous formation of Ag-C bonds on Ag(111). An atomic model was proposed for the observed hybrid chain structures. Four electronic states were resolved using STS measurements, and strong energy dependence was observed in STM images. These results were explained using first-principles calculations based on DFT.     

Iridium–Titanium Textured Electrodes: Production and Investigation by Electrochemical Scanning Tunneling Microscopy and Spectroscopy

A technique for the production of perfect thin-layered Ir coatings on inert Ti supports is developed. The highly textured coatings have some potential uses. Local topography and energy nonuniformness of the surface of such Ir electrodes are studied by electrochemical scanning tunneling microscopy (ESTM) and scanning tunneling spectroscopy (STS). In situ STM images of Ir–Ti textured electrodes with axial texture (111) are obtained with an atomic resolution at potentials of 0.3 to 1.2 V, in 0.05 M H₂SO₄ as well. Energy states of surfaces of Ir–Ti textured electrodes are studied with an atomic resolution using in situ STS by distance and voltage. Dependences of the tunneling current on the tunneling voltage and the tunneling-gap width are measured at Ir-surface potentials of 0.3 to 1.2 V. Effective potential barrier for the electron tunneling is estimated at different potentials of Ir.     

Mechanism of electrochemical charge transport in individual transition metal complexes

We used electrochemical scanning tunneling microscopy (STM) and spectroscopy (STS) to elucidate the mechanism of electron transport through individual pyridyl-based Os complexes. Our tunneling data obtained by two-dimensional electrochemical STS and STM imaging lead us to the conclusion that electron transport occurs by thermally activated hopping. The conductance enhancement around the redox potential of the complex, which is reminiscent of switching and transistor characterics in electronics, is reflected both in the STM imaging contrast and directly in the tunneling current. The latter shows a biphasic distance dependence, in line with a two-step electron hopping process. Under conditions where the substrate/molecule electron transfer (ET) step is dominant in determining the overall tunneling current, we determined the conductance of an individual Os complex to be 9 nS (Vbias = 0.1 V). We use theoretical approaches to connect the single-molecule conductance with electrochemical kinetics data obtained from monolayer experiments. While the latter leave some controversy regarding the degree of electronic coupling, our results suggest that electron transport occurs in the adiabatic limit of strong electronic coupling. Remarkably, and in contrast to established ET theory, the redox-mediated tunneling current remains strongly distance dependent due to the electronic coupling, even in the adiabatic limit. We exploit this feature and apply it to electrochemical single-molecule conductance data. In this way, we attempt to paint a unified picture of electrochemical charge transport at the single-molecule and monolayer levels.     

STM/STS observation of polyoxoanions on HOPG surfaces: the wheel-shaped [Cu20Cl(OH)24(H2O)12(P8W48O184)]25- and the ball-shaped [{Sn(CH3)2(H2O)}24{Sn(CH3)2}12(A-PW9O34)12]36-

A combination of scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) techniques have been performed on the wheel-shaped [Cu20Cl(OH)24(H2O)12(P8W48O184)]25- and the ball-shaped [{Sn(CH3)2(H2O)}24{Sn(CH3)2}12(A-PW9O34)12]36- deposited on highly oriented pyrolytic graphite surfaces. Small, regular molecule clusters, as well as separated single molecules, were observed. The size of the molecules is in agreement with the data determined by X-ray crystallography. In STS measurements, we found a rather large contrast at the expected location of the Cu metal centers in our molecules, i.e., the location of the individual Cu ions in their organic matrix is directly addressable by STS.     

Recent progress in probing atomic and molecular quantum coherence with scanning tunneling microscopy

Quantum coherent physics and chemistry concern the creation and manipulation of an excited-state manifold that contains the superposition and entanglement of multiple quantum levels. Electromagnetic waves such as light and microwave can be used to generate and probe different quantum coherent phenomena. The recent advances in scanning tunneling microscopy (STM) techniques including ultrafast laser coupled STM and electron spin resonance STM combine electromagnetic excitation with tunneling electron detection, bringing the investigation of quantum coherence down to the atomic and molecular level. Here, we survey the latest STM studies of different quantum coherent phenomena covering molecular vibration, electron transfer, surface plasmon resonance, phonon, spin oscillation, and electronic transition, and discuss the state and promise of characterizing and manipulating quantum coherence at the atomic or molecular scale.     

TiO2表面电子结构及其光催化活性

利用ＨＣｌ和ＨＣｌＯ４对不同方法制备的ＴｉＯ２进行了表面修饰,发现经强酸修饰后ＴｉＯ２的光催化活性有明显提高,其中ＨＣｌ的修饰效果好于ＨＣｌＯ４。     

STM and STS of coronene on HOPG 0001 in UHV - adsorption of the smallest possible graphite flakes on graphite

The adsorption of the aromatic molecule hexabenzobenzene (coronene) on an HOPG(0001) surface was investigated under UHV conditions by means of variable temperature scanning tunneling microscopy (STM) and spectroscopy (STS). Imaging on a mesoscopic scale showed a distribution of coronene islands. These islands are mobile on the surface and can be pinned at step-edges. Zooming in on areas apart from the islands reveals an hexagonal arrangement of coronene molecules in a closed layer. Submolecular resolved molecules consist of bright spots with varying intensity. This variation in intensity is explained with the commensurability of the adlayer. STS investigations were performed for various tip-sample distances, adjusted by the tunneling current setpoint. A gap can be seen for every setpoint, but its width is dependent on the setpoint. The gap for the largest tip-sample distance and therefore the smallest tip-sample interaction is compared with the theoretical value.     

Nanoscale electrocrystallisation of Sb and the compound semiconductor AlSb from an ionic liquid

Aluminium antimonide nanoclusters with an apparent band gap energy of 0.92 +/- 0.2 eV have been electrodeposited from the neutral ionic melt AlCl3-1-butyl-3-methylimidazolium chloride {AlCl3-[C4mim]+Cl-} at room temperature and have been characterized in-situ by electrochemical scanning tunneling microscopy (STM) and spectroscopy (STS).     

Initial growth of lutetium(III) bis-phthalocyanine on Ag(111) surface

The adsorption of lutetium(III) bis-phthalocyanine (LuPc(2)) on Ag(111) was investigated using scanning tunneling microscopy and spectroscopy (STM/STS). A comprehensive study was carried out toward understanding the driving mechanism responsible for the formation of the first and second monolayers (MLs). In both MLs, the adsorbed molecules are found to exhibit different in-plane orientations arranged according to a "chess-board" like pattern. Highly resolved STM images allowed an exact determination of the corresponding angle mismatch, which differs for the first and second MLs. The tunneling transport through individual molecules reveals a negative differential resistance (NDR) effect detectable within the current-voltage curves. The corresponding density of states (DOS) representation is consistent with a resonant tunneling mechanism sustained by the valence band (VB) states close to the Fermi energy (E(F)) recorded via highly resolved ultraviolet photoemission spectroscopy (UPS).     

Geometric and Electronic Behavior of C60 on PTCDA Hydrogen Bonded Network

Self-assembled supramolecular networks are promising spacer layer for electronic decoupling from the metal substrate.However,the mechanism behind of how the intrinsic electronic structure of spacer layers affects the adsorbate is still unclear.Here a hydrogen bonded network composed of n-type semiconducting molecules 3,4,9,10-perylene-tetracarboxylic-dianhydride(PTCDA)is prepared under ultra-high vacuum to serve as a spacer layer for functional organics C60 on Au(111).The geometric and electronic information of C60 was investigated by scanning tunneling microscopy and scanning tunneling spectroscopy(STM/STS)at 5 K.Effective decoupling from the metal surface yields an energy gap of 3.67 eV for C602nd,merely considering the HOMO-LUMO peak separation.The broadening of resonance peaks in STS measurements however indicates unneglected interlayer interactions in this hetero-organic system.Moreover,we scrutinize the nucleation sites of C60 on PTCDA layer and attribute this to the decreased diffusion capability on a less dense molecular arrangement possessing inhomogeneous spatial distribution of unoccupied molecular orbitals.     

Rectification in Supramolecular Zinc Porphyrin/Fulleropyrrolidine Dyads Self‐Organized on Gold(111)

Self‐assembled donor/acceptor dyads are of current interest as they are biomimetic to the natural photosynthetic conversion system. Herein, we present an ultrahigh‐vacuum scanning tunneling microscopy and scanning tunneling spectroscopy (UHV‐STM/STS) study of ex situ self‐assembled supramolecular dyads consisting of fulleropyrrolidines (PyC₂C₆₀) axially ligated to zinc(II) tetraphenylporphyrin (ZnTPP), self organized on a 4‐aminothiophenol (4‐ATP) self‐assembled monolayer on gold(111). These dyads show both bias‐polarity‐dependent apparent height in STM images and highly rectifying behavior in tunneling spectroscopy. First‐principles density functional theory calculations clarify the conformational and electronic properties of the 4‐ATP/ZnTPP/PyC₂C₆₀ system. Interestingly, we find easier tunneling for electrons moving from the acceptor side of the dyads to the donor side, in the inverse‐rectifying sense with respect to previously reported molecular rectifiers. Such behavior cannot be explained as an elastic resonant tunneling process, but it can by using a model based on the Aviram–Ratner mechanism.     

核壳结构AgInS2@ZnS量子点的合成及荧光性能

合成了一种新型核壳结构的AgInS₂@ZnS量子点并研究了其荧光性能. AgInS₂@ZnS的合成包括以变性牛血清白蛋白(dBSA)为稳定剂水相法构建AgInS₂核以及形成ZnS壳两部分. 考察了配方和工艺条件对该量子点荧光性能的影响, 并采用X射线粉末衍射(XRD)等手段对制备的纳米粒子进行了表征. 结果表明, AgInS₂@ZnS是一种核壳结构的纳米物质, 其粒径介于5~7 nm之间, 荧光量子产率达35.3%.