Surface evolution of thermoelectric material KCu_(4)Se_(3) explored by scanning tunneling microscopy

Novel two-dimensional thermoelectric materials have attracted significant attention in the field of thermoelectric due to their low lattice thermal conductivity.A comprehensive understanding of their microscopic structures is crucial for driving further the optimization of materials properties and developing novel functional materials.Here,by using in situ scanning tunneling microscopy,we report the atomic layer evolution and surface reconstruction on the cleaved thermoelectric material KCu_(4)Se_(3) for the first time.We clearly revealed each atomic layer,including the naturally cleaved K atomic layer,the intermediate Se^(2-)atomic layer,and the Se^(-)atomic layer that emerges in the thermodynamic-stable state.Departing from the maj ority of studies that predominantly concentrate on macroscopic measurements of the charge transport,our results reveal the coexistence of potassium disorder and complex reconstructed patterns of selenium,which potentially influences charge carrier and lattice dynamics.These results provide direct insight into the surface microstructures and evolution of KCu_(4)Se_(3),and shed useful light on designing functional materials with superior performance.

A Highly Stable Electrochemical Scanning Tunneling Microscope

We demonstrate a home-built electrochemical scanning tunneling microscope （ECSTM）. The ECSTM exhibits highly stable performance. The drifting rates in XY and Z directions of the ECSTM are about 67 and 55.6 pm/min, respectively. Moreover, a specially designed scanner unit successfully solves the well-known problem of large leakage current in high humidity atmosphere. The mechanical structure of the ECSTM is described in detail. The excellent performances of the system are demonstrated by the measured STM images （in copper sulfate solution）, including clean and well-ordered large area morphology of Au（111） and the atomically resolved image of highly oriented pyrolytic graphite.

Compact Scanning Tunneling Microscope with Large Scale Searching Capability for Mmultidisciplinary Applications

We present the design and performance of a home-built scanning tunneling microscope （STM）, which is compact （66 mm tall and 25 mm in diameter）, yet equipped with a 3D atomic precision piezoelectric motor in which the Z coarse approach relies on a high simplic-ity friction-type walker （of our own invention） driven by an axially cut piezoelectric tube. The walker is vertically inserted in a piezoelectric scanner tube （PST） with its brim laying at on the PST end as the inertial slider （driven by the PST） for the XZ （sample plane） motion. The STM is designed to be capable of searching rare microscopic targets （defects, dopants, boundaries, nano-devices, etc.） in a macroscopic sample area （square millimeters） under extreme conditions （low temperatures, strong magnetic elds, etc.） in which it ts. It gives good atomic resolution images after scanning a highly oriented pyrolytic graphite sample in air at room temperature.

A Simple,Compact and Rigid Scanning Tunneling Microscope

We present a homebuilt scanning tunneling microscope(STM)which employs an inner-wall polished sapphire guiding tube as a rail for the scanner to form a short tip-sample mechanical loop.The scanner is mounted on a square rod which is housed in the guiding tube and held by a spring strip.The stiff sapphire guiding tube allows the STM body to be made in a simple,compact and rigid form.Also the material of sapphire improves the thermal stability of the STM for its good thermal conductivity.To demonstrate the performance of the STM,high quality atomic-resolution STM images of high oriented pyrolytic graphite were given.

Vibration Compensation for Scanning Tunneling Microscope

The influence of vibration is already one of main obstacles for improving the nano measuring accuracy.The techniques of anti-vibration,vibration isolation and vibration compensation become an important branch in nano measuring field.Starting with the research of sensitivity to vibration of scanning tunneling microscope(STM),the theory,techniques and realization methods of nano vibration sensor based on tunnel effect are initially investigated,followed by developing the experimental devices.The experiments of the vibration detection and vibration compensation are carried out.The experimental results show that vibration sensor based on tunnel effect is characterized by high sensitivity,good frequency characteristic and the same vibratory response characteristic consistent with STM.

BAINITE STRUCTURE IN Cu-Zn-Al ALLOY OBSERVED BY SCANNING TUNNELING MICROSCOPE

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Scanning Tunneling Microscopic and Scanning Tunneling Spectroscopic Studies of Nanocrystalline CdSe Thin Film

Nanocrystalline CdSe thin film prepared by chemical solution deposition was imaged in air with a scanning tunnelling microscope(STM). Scanning tunnelling current spectroscopy(STS) was taken at a fixed tip - sample separation. Tunnelling current(i) - voltage(v) curve and differential conductance spectrum show an n-type schottky rectifying behaviour and yield a direct measure of band gap energy. An increase of bandgap energy (1.8 - 2.1eV) was measured indicating energy quantization of this particular thin film.,

Scanning tunnelling microscope studies of growth of RuO2（110） thin layer on Ru（0001）

This paper reports that the growth of RuO2（110） thin layer growth on Ru（0001） has been investigated by means of scanning tunnelling microscope （STM）. The STM images showed a domain structure with three rotational domains of RuO2（110） rotated by an angle of 120°. The as-grown RuO2（110） thin layer is expanded from the bulk-truncated RuO2（110） due to the large mismatch between RuO2（110） and the Ru（0001） substrate. The results also indicate that growth of RuO2（110） thin layer on the Ru（0001） substrate by oxidation tends first to formation of the Ru-O （oxygen） chains in the [001] direction of RuO2 （110）.

FABRICATION OF THE TIP FOR ELECTROCHEMICAL SCANNING TUNNELING MICROSCOPY

A nover technique for the fabrication of the tip for e tectrochemical scanning tunneting microscopy(ECSTM)is presented. The curvature radius of the fabricated tip is smatter than 1 μM. Faradaic leakage current is tess than 0.1nA in the sotution of 1 mol/L NaCl. The atomic image of highty oriented pyrotytic graphite (HOPG)has been taken using the prepared tip.

Microscopic growth mechanism and edge states of monolayer 1T'-MoTe_(2)

Transition metal ditellurides(TMTDs)have versatile physical properties,including non-trivial topology,Weyl semimetal states and unique spin texture.Controlled growth of high-quality and large-scale monolayer TMTDs with preferred crystal phases is crucial for their applications.Here,we demonstrate the epitaxial growth of 1T'-MoTe_(2) on Au(111)and graphitized silicon carbide(Gr/SiC)by molecular beam epitaxy(MBE).We investigate the morphology of the grown1T'-MoTe_(2) at the atomic level by scanning tunnelling microscopy(STM)and reveal the corresponding microscopic growth mechanism.It is found that the unique ordered Te structures preferentially deposited on Au(111)regulate the growth of monolayer single crystal 1T'-MoTe_(2),while the Mo clusters were preferentially deposited on the Gr/SiC substrate,which impedes the ordered growth of monolayer MoTe_(2).We confirm that the size of single crystal 1T'-MoTe_(2) grown on Au(111)is nearly two orders of magnitude larger than that on Gr/SiC.By scanning tunnelling spectroscopy(STS),we observe that the STS spectrum of the monolayer 1T'-MoTe_(2) nano-island at the edge is different from that at the interior,which exhibits enhanced conductivity.

Combining scanning tunneling microscope (STM) imaging and local manipulation to probe the high dose oxidation structure of the Si(111)-7×7 surface

Understanding the atomistic formation of oxide layers on semiconductors is important for thin film fabrication,scaling down conventional devices and for the integration of emerging research materials.Here,the initial oxidation of Si(111)is studied using the scanning tunneling microscope.Prior to the complete saturation of the silicon surface with oxygen,we are able to probe the atomic nature of the oxide layer formation.We establish the threshold for local manipulation of inserted oxygen sites to be+3.8 V.Only by combining imaging with local atomic manipulation are we able to determine whether inserted oxygen exists beneath surface-bonded oxygen sites and differentiate between sites that have one and more than one oxygen atom inserted beneath the surface.Prior to the creation of the thin oxide film we observe a flip in the manipulation rates of inserted oxygen sites consistent with more oxygen inserting beneath the silicon surface.

Tunneling Electron Induced Fluorescence from Single Porphyrin Molecules Decoupled by Striped-Phase Octanethiol Self-assembled Monolayer

We investigate tunneling electron induced luminescence from isolated single porphyrin molecules that are decoupled by striped-phase self-assembled monolayer of octanethiol from the underneath Au（111） substrate. Intrinsic single-molecule electroluminescence has been realized by such decoupling at both bias polarities. The photon emission intensity acquired from the molecular lobe is found stronger than that from the molecular center. These re- sults provide useful information on the understanding of electroluminescent behavior and mechanism in molecular tunnel junctions.

Heisenberg, uncertainty, and the scanning tunneling microscope

We show by a statistical analysis of high-resolution scanning tunneling microscopy （STM） exper- iments, that the interpretation of the density of electron charge as a statistical quantity leads to a conflict with the Heisenberg uncertainty principle. Given the precision in these experiments we find that the uncertainty principle would be violated by close to two orders of magnitude, if this interpretation were correct. We are thus forced to conclude that the density of electron charge is a physically real, i.e., in principle precisely measurable quantity.

Role of Nanocavity Plasmons in Tunneling Electron Induced Light Emission on and near a Molecule

By using a microscopic quantum model, we study theoretically different roles of nanocavity plasmons in scanning tunneling microscope(STM) induced light emission upon selective initial excitation of molecules or plasmons. The time evolution and spectroscopic properties of the emission from the coupled plasmon-molecule system in each case are studied using time-dependent quantum mater equations. When the STM tip is placed on the molecule to ensure direct carrier injection induced molecular excitation, the major role of the plasmons is to enhance the molecular emission via increasing its radiative decay rate, resulting in sharp molecule-specific emission peaks. On the other hand, when the STM tip is located in close proximity to the edge of the molecule but without direct carrier injection into the molecule, the role of the plasmon-molecule coupling is to cause destructive interferences between the two quantum objects, leading to the occurrence of Fano dips around the energy of the molecular exciton in the plasmonic emission spectra.

Direct Imaging of Molecular Orbitals of Metal Phthalocyanines on Metal Surfaces with an O2-Functionalized Tip of a Scanning Tunneling Microscope

High-resolution scanning tunneling microscope images of iron phthalocyanine and zinc phthalocyanine molecules on Au（111） have been obtained using a functionalized tip of a scanning tunneling microscope （STM）, and show rich intramolecular features that are not observed using clean tips. Ab initio density functional theory calculations and extended Huckel theory calculations revealed that the imaging of detailed electronic states is due specifically to the decoration of the STM tip with O2. The detailed structures are differentiated only when interacting with the highly directional orbitals of the oxygen molecules adsorbed on a truncated, [111]-oriented tungsten tip. Our results indicate a method for increasing the resolution in generic scans and thus, have potential applications in fundamental research based on high-resolution electronic states of molecules on metals, concerning, for example, chemical reactions, and catalysis mechanisms.

Scanning Tunneling Microscope Observations of Non-AB Stacking of Graphene on Ni Films

Microscopic features of graphene segregated on Ni films prior to chemical transfer--including atomic structures of monolayers and bilayers, Moire patterns due to non-AB stacking, as well as wrinkles and ripples caused by strain effects-have been characterized in detail by high-resolution scanning tunneling microscopy （STM）. We found that the stacking geometry of the bilayer graphene usually deviates from the traditional Bernal stacking （or so-called AB stacking）, resulting in the formation of a variety of Moir6 patterns. The relative rotations inside the bilayer were then qualitatively deduced from the relationship between Moir6 patterns and carbon lattices. Moreover, we found that typical defects such as wrinkles and ripples tend to evolve around multi-step boundaries of Ni, thus reflecting strong perturbations from substrate corrugations. These investigations of the morphology and the mechanism of formation of wrinkles and ripples are fundamental topics in graphene research. This work is expected to contribute to the exploration of electronic and transport properties of wrinkles and ripples.

VARIANT STRUCTURES OF DNA OBSERVED BY SCANNING TUNNELING MICROSCOPE

Deoxyribonucleic acid (DNA), as the essential genetic substance in life process, may undergo structural changes in various environments. For instance, the unwinding of the original double helix of DNA could occur after being heated.

Measuring fine molecular structures with luminescence signal from an alternating current scanning tunneling microscope

In scanning tunneling microscopy-induced luminescence(STML),the photon count is measured to reflect single-molecule properties,e.g.,the first molecular excited state.The energy of the first excited state is typically shown by a rise of the photon count as a function of the bias voltage between the tip and the substrate.It remains a challenge to determine the precise rise position of the current due to possible experimental noise.In this work,we propose an alternating current version of STML to resolve the fine structures in the photon count measurement.The measured photon count and the current at the long-time limit show a sinusoidal oscillation.The zero-frequency component of the current shows knee points at the precise voltage as the fraction of the detuning between the molecular gap and the DC component of the bias voltage.We propose to measure the energy level with discontinuity of the first derivative of such a zero-frequency component.The current method will extend the application of STML in terms of measuring molecular properties.

Construction of tunable supramolecular networks studied by scanning tunneling microscopy

In this review we describe a family of organic-based host frameworks which can accommodate guest molecules. The aim of the study is to test the adjustability of this class of mimic structures that may lead to new interesting functions. Emphasis of our research is placed upon four aspects: 1) thermal properties, 2) surface photochemistry, 3) fullerene adsorption, and 4) guest inclusion. It is envisioned that such approach of nanoporous molecular networks might be developed into a new family of useful soft frameworks for studies toward shape-selective catalysis, molecular recognition, self-assembly, and host-guest supramolecular chemistry.