Dynamic probe of ZnTe(110) surface by scanning tunneling microscopy

Abstract

The reconstructed surface structure of the II–VI semiconductor ZnTe (110), which is a promising material in the research field of semiconductor spintronics, was studied by scanning tunneling microscopy/spectroscopy (STM/STS). First, the surface states formed by reconstruction by the charge transfer of dangling bond electrons from cationic Zn to anionic Te atoms, which are similar to those of IV and III–V semiconductors, were confirmed in real space. Secondly, oscillation in tunneling current between binary states, which is considered to reflect a conformational change in the topmost Zn–Te structure between the reconstructed and bulk-like ideal structures, was directly observed by STM. Third, using the technique of charge injection, a surface atomic structure was successfully fabricated, suggesting the possibility of atomic-scale manipulation of this widely applicable surface of ZnTe.     

Active nanocharacterization of nanofunctional materials by scanning tunneling microscopy

Abstract

Recent developments in the application of scanning tunneling microscopy (STM) to nanofabrication and nanocharacterization are reviewed. The main focus of this paper is to outline techniques for depositing and manipulating nanometer-scale structures using STM tips. Firstly, the transfer of STM tip material through the application of voltage pulses is introduced. The highly reproducible fabrication of metallic silver nanodots and nanowires is discussed. The mechanism is thought to be spontaneous point-contact formation caused by field-enhanced diffusion to the apex of the tip. Transfer through the application of z-direction pulses is also introduced. Sub-nanometer displacement pulses along the z-direction form point contacts that can be used for reproducible nanodot deposition. Next, the discovery of the STM structural manipulation of surface phases is discussed. It has been demonstrated that superstructures on Si(001) surfaces can be reverse-manipulated by controlling the injected carriers. Finally, the fabrication of an atomic-scale one-dimensional quantum confinement system by single-atom deposition using a controlled point contact is presented. Because of its combined nanofabrication and nanocharacterization capabilities, STM is a powerful tool for exploring the nanotechnology and nanoscience fields.     

Active nanocharacterization of nanofunctional materials by scanning tunneling microscopy

Recent developments in the application of scanning tunneling microscopy (STM) to nanofabrication and nanocharacterization are reviewed. The main focus of this paper is to outline techniques for depositing and manipulating nanometer-scale structures using STM tips. Firstly, the transfer of STM tip material through the application of voltage pulses is introduced. The highly reproducible fabrication of metallic silver nanodots and nanowires is discussed. The mechanism is thought to be spontaneous point-contact formation caused by field-enhanced diffusion to the apex of the tip. Transfer through the application of z-direction pulses is also introduced. Sub-nanometer displacement pulses along the z-direction form point contacts that can be used for reproducible nanodot deposition. Next, the discovery of the STM structural manipulation of surface phases is discussed. It has been demonstrated that superstructures on Si(001) surfaces can be reverse-manipulated by controlling the injected carriers. Finally, the fabrication of an atomic-scale one-dimensional quantum confinement system by single-atom deposition using a controlled point contact is presented. Because of its combined nanofabrication and nanocharacterization capabilities, STM is a powerful tool for exploring the nanotechnology and nanoscience fields.     

Identification of molecular flipping of an asymmetric tris(phthalocyaninato) lutetium triple-decker complex by scanning tunneling microscopy/spectroscopy

The assembling behavior and electronic properties of asymmetric tris(phthalocyaninato) lutetium tripledecker sandwich complex molecules (Lu₂Pc₃) on highly oriented pyrolytic graphite (HOPG) surfaces have been studied by scanning tunneling microscopy/spectroscopy (STM/STS) methods. Phase transitions were observed at different bias polarities, involving an ordered packing arrangement with fourfold symmetry at negative bias and an amorphous arrangement at positive bias. Molecular switching behaviour for individual Lu₂Pc₃ molecules was reported here according to the bias-polarity-induced flipping phenomena and the peak shift in dI/dV versus V curves at different voltage scanning directions. The sensitive response of the strong intrinsic molecular dipole to an external electric field is proposed to be responsible for molecular switching of Lu₂Pc₃ at the solid/liquid interface. This article is published with open access at Springerlink.com     

Boron surface phase on Si(111): atomic structure and Si overgrowth studied by scanning tunneling microscopy and work function measurement

Surface reconstructions of boron (B) on silicon (Si) have been well known for several years. One reconstruction of special interest to us is the so called R30° boron surface phase (BSP) on Si(111). This reconstruction can occur in two different forms, one with B located on T₄ lattice sites (B-T₄), the second one with B residing in S₅ sites (B-S₅) directly underneath a Si adatom in a T₄ site. The two forms of the R30° reconstruction are expected to exhibit completely different properties due to their different chemical binding. In this paper we present work function measurements of these surface phases which clearly show their distinctively different behaviour and allow the determination of the temperature at which the boron atoms migrate from the T₄ sites to the S₅ sites. Furthermore, STM results concerning the overgrowth of BSPs with Si films of variable thicknesses and its effect on the BSP itself are shown.     

Pairing insights in iron-based superconductors from scanning tunneling microscopy

Scanning tunneling microscopy (STM) has made tremendous progress in the study and understanding of both classical and unconventional superconductors. This has motivated a rapidly growing effort to apply the same techniques to the iron-based high-T_c superconductors since their discovery in 2008. Five years have brought exciting advances in imaging and spectroscopic investigation of this new class of materials. In this review, we focus on several recent STM contributions to the identification of the gap symmetry and pairing glue. We highlight the unique capabilities and challenges still ahead for STM studies of iron-based superconductors.     

Sub-molecular features of single proteins in solution resolved with scanning tunneling microscopy

Scanning tunneling microscopy (STM) can be used to image individual biological molecules, such as proteins, in vacuum or air. This requires sample dehydration and thus may not reflect the native state of the molecule. Extensive efforts have been made to image single proteins in solution using STM; however, the images have revealed only round or oval shapes with no sub-molecular details. Here, we present the sub-molecular features of streptavidin proteins under physiological conditions using a homebuilt low-leakage-current and highstability liquid phase STM. The N-lobe, C-lobe, and C-terminal tail of the epidermal growth factor receptor kinase domains were also resolved in solution. Our results demonstrate that the structure, morphology, and dynamics of a protein molecule can be examined under physiological conditions by the STM.

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Lyocell基炭纤维表面微结构的STM研究

采用SEM揭示出Lyocell基炭纤维(LCF)表面比粘胶基炭纤维(RCF)表面光滑,而后者粗糙的表面上还存在裂纹和沟槽,这也是导致RCF强度偏低的一个原因。尝试利用扫描隧道显微镜(STM)的原子级分辨率来研究LCF的表面微结构。在500nm×500nm观测范围内,发现了由25nm宽,150nm长的条状微结构组成的约150nm2大小的沿纤维轴呈近乎45°角排列的块状结构;并测得LCF表面碳原子间距离为0.331nm,结果表明Lyocell基炭纤维表面尚未形成完整的碳网六元环结构。     

Under-surface observation of thin-film alumina on NiAl(100) with scanning tunneling microscopy

Scanning tunneling microscopy (STM) was used to investigate the oxide structures underlying the surface of alumina thin-film grown on NiAl(100). At a bias voltage (on the sample) below 2.0 V, STM topography images of the alumina layer beneath the surface were obtained. A probe with depth of 2-8 Å was readily attained. The under-surface observation shows that the film consists of stacked layers of alumina whereas the layered alumina unnecessarily comprises entire θ-Al₂O₃ unit cells. The lattice orientation of the upper alumina layer differs from that of the lower one by 90° — the newly grown oxide structurally matching the horizontal oxide rather than the lower oxide. The results indicate a growth process competing with the typical mode of epitaxial growth for the growth of alumina film.     

Temperature‐Dependent Tip‐Induced Motion of Ga Adatom on GaAs (110) Surface

The temperature‐dependent tip‐induced‐motion of a Ga adatom on a GaAs (110) surface is experimentally demonstrated using scanning tunneling microscopy (STM). The surface adsorption energy profile obtained by first‐principle electronic structure calculations reveals that the origin of the Ga motion observed at 78 K is attributable to the tip‐induced Ga adatom hopping between the most stable potential minima among the three local minima, whereas that observed at 4.2 K is attributable to the tip‐induced hopping and sliding motions through the next stable minima as well as the most stable minima. Furthermore, it is shown that a slight progressive modification of the adatom motion observed only at 4.2 K resulting from repeated STM line scans is consistent with the overall picture taking account of the heating of the adatom owing to the tip current.     

Cerium oxide layers on Pt(111): a scanning tunneling microscopy study

Ultrathin epitaxial layers of cerium oxide were prepared by oxidation of layers of an ordered Pt–Ce surface alloy on top of a Pt(111) single crystal. They consist of low-dimensional CeO₂ islands. Atomically resolved scanning tunnel microscopy (STM) images indicate a surface structure of the fluorite-type CeO₂(111) 1×1 phase and the presence of surface defects.     

Reversible hydrogenation and bandgap opening of graphene and graphite surfaces probed by scanning tunneling spectroscopy

The effects of hydrogenation on the topography and electronic properties of graphene and graphite surfaces are studied by scanning tunneling microscopy and spectroscopy. The surfaces are chemically modified using an Ar/H(2) plasma. By analyzing thousands of scanning tunneling spectroscopy measurements it is determined that the hydrogen chemisorption on the surface of graphite/graphene opens on average an energy bandgap of 0.4 eV around the Fermi level. Although the plasma treatment modifies the surface topography in an irreversible way, the change in the electronic properties can be reversed by moderate thermal annealing and the samples can be hydrogenated again to yield a similar, but slightly reduced, semiconducting behavior after the second hydrogenation.     

基于SPM技术的纳米信息存储薄膜的研究进展

扫描探针显微技术SPM可以在原子或分子尺度上对表面进行表征和修饰，应用SPM技术可以在薄膜表面形成纳米级的信息点阵，特别适合发展超高密度的信息存储，是一种非常有希望代替传统磁存储，光存储的纳米级存储技术，本文介绍了纳米信息存储薄膜的研究进展，并对其制备技术和读写机制进行了初步的探讨。     

A comparison of different carbon filaments on the nanometer and atomic scales by scanning tunneling microscopy

Scanning tunneling microscopy (STM) has been employed as a tool to elucidate the structural differences between carbon nanotubes (CNTs) and carbon nanofibers (CNFs) at the nanometer and atomic scales. As opposed to the seamless, virtually defect-free structure of CNTs that was visualized by STM at both scales, CNFs displayed a fragmented graphitic conformation (nanographites), where the nanographitic domains were below 2-3 nm in lateral size. Thus, STM is proposed as a suitable technique to discriminate these two types of carbon nanostructures.