The effects of strain on STM lithography on HS-ssDNA/Au (1 1 1) surface

Scanning tunneling microscopy (STM) lithography was utilized to investigate a 12-mer HS-ssDNA self-assembled Au (1 1 1) surface. Under low sample bias and high tunneling current, the repeated scanning resulted in the growth of nanostripes. The stripe orientation, the stripe width, and the spacer width between adjacent nanostripes were found to be dependent on their relative locations from dislocation points where two adjacent gold terraces overlap. The stripe and the spacer width also vary with the distance from these points. The results indicate that such stripes may reflect the strain distributions and the release pathway along the Au surfaces. The results also suggest that the presence of HS-ssDNA molecules enhances the lithography processes on the gold surface by acting as force transmitters.     

Adsorption, reaction and desorption of hydrogen on modified Pd(1 1 1) surfaces

The interaction of hydrogen (deuterium) with different modified Pd(1 1 1) surfaces has been investigated. The focus was put on the energy and angel dependence of the desorbing molecules from oxygen covered, potassium covered and vanadium oxide covered surfaces. Conventional adsorption/desorption as well as permeation/desorption experiments were performed. For the oxygen covered surface optimum reaction rates for water production and the energy distribution of the reaction products were determined, both for the reaction of oxygen with molecular hydrogen as well as with atomic hydrogen. Potassium on the surface enhances the activation barrier for hydrogen adsorption resulting in a hyper-thermal desorption flux and a forward focused angular distribution of desorption. Permeation/desorption of deuterium from ultra-thin vanadium oxide films yield mainly thermalized desorbing molecules or slightly hyper-thermal, depending on the oxidation state of the surface oxide.     

Addition reaction and characterization of chlorotris(triphenylphosphine)iridium(I) on silicon(1 1 1) surfaces

Studies were performed to determine the chemical addition of a metal complex molecule, chlorotris(triphenylphosphine)iridium(I), on hydrogen passivated Si(1 1 1) surfaces to form a self-assembled monolayer (SAM). The iridium complex was synthesized prior to chemical addition, for which modified reaction conditions were chosen. Following addition, the silicon surfaces were characterized with X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). The XPS results revealed that the surfaces consisted of the expected elemental percentages and that the iridium has a slightly higher success rate at attaching to oxide-free surfaces. XPS data also strongly indicate that the iridium complex remained intact upon chemisorption and did not decompose during the addition reaction. CV data show a difference between iridium treated surfaces and control samples. Hydrogen passivated wafers with iridium complex were much more conductive than those which were terminated with just an oxide or with an oxide and iridium complex. Furthermore, no free iridium reagent was detected as an additional feature in the current profile, indicating there was no physisorbed layer.     

光条亮度对线结构光测量精度的影响

光条中心的提取精度直接影响线结构光传感器最后的测量精度,而光条亮度是影响提取精度的主要因素。提出了光条中心提取精度的评价方法,通过实验获得光条亮度与光条中心提取精度之间的关系曲线;为了在实际测量中能获得最佳光条亮度(对应最高的提取精度)设计了基于D/A转换的光条亮度自适应调节电路。实验结果表明:光条过暗或过亮都会使线结构光传感器的测量精度降低,在测量不同颜色的表面时通过光条亮度的自适应调节均可获得最高的提取精度。     

Adsorption of amino acids on indium arsenide (1 0 0) surfaces: Assessment of passivation capabilities

Angle-Resolved X-ray Photoelectron Spectroscopy (ARXPS) was used to examine amino acid bonding and oxide removal on InAs(1 0 0) surfaces. Five amino acids were studied, including cysteine, lysine, aspartic acid, glutamic acid and arginine. Observations on the ability of specific functional groups to prevent oxide formation were made by examining the thickness of oxide films on the functionalize surfaces. Amino acids that possessed more than one functional group having resonance were shown to most effectively affect oxide formation. The influence of these groups on the electronic structure of InAs(1 0 0) provides insight into how multifunctional passivation strategies could be beneficial, as well as showing how biological molecules might affect detection when InAs(1 0 0) is used as a platform.     

Thickness dependent stripe structure stability of Ag films on Si(1 1 1)-(4 × 1)-In substrate

The thickness dependent stripe structure stabilization of Ag films on Si(1 1 1)-(4 × 1)-In substrate is thermodynamically considered. It is found that for the stability of the structure, there is a competition between the sum of elastic energy and stacking fault energy in the film and the film-substrate interface energy. The presence of equilibrium of them leads to a critical film thickness. Beyond it, the stripe structure will transform into a flat one. Our prediction for n_c of Ag films shows reasonable agreement with experimental data. In addition, according to the established model, it is predicted that Au could also form the above stripe structure on this substrate with a similar n_c value of Ag.     

Interactions of Lump and Solitons to Generalized (2+1)-Dimensional Ito Systems*

The $(2+1)$-dimensional Ito equation is extended to a general form including some nonintegrable effects via introducing generalized bilinear operators. It is pointed out that the nonintegrable $(2+1)$-dimensional Ito equation contains lump solutions and interaction solutions between lump and stripe solitons. The result shows that the lump soliton will be swallowed or arisen by a stripe soliton in a fixed time. Furthermore, by the interaction between a lump and a paired resonant stripe soliton, the lump will be transformed to an instanton or a rogue wave.     

Surface state lifetime in quasi-one-dimensional oxygen stripes on Cu(1 1 0)

Scanning tunneling spectroscopy data on the lifetime and bottom energy of a surface state band in quasi-one-dimensional stripes are presented as a function of stripe width. The adsorbate system Cu(1 1 0)-p(2 × 1)O has been used to prepare a two-dimensional adsorbate layer and almost defect free quasi-one-dimensional stripes with a width of 3-15 CuO rows, respectively. The onset of an unoccupied surface state band (at 0.56 eV above Fermi-energy on the fully covered surface) has been analyzed with respect to the quasi-particle lifetime at the crossover from two to one dimension. A drastic increase of the onset-width with decreasing stripe width is observed. It can be explained by a decrease of quasi-particle lifetime using a Fabry-Pérot-like model. We obtain a reduction of lifetime from 37 ± 8 fs on the two-dimensional adsorbate layer to 5 ± 1 fs on a three CuO rows wide stripe.     

Magnetization reversal via bloch points nucleation in nanowires and dots: a micromagnetic study

Micromagnetic studies of the reversal of stripe domains in elements of different geometries are reported. Various 2D and 3D codes are used in order to allow comparison between an infinite slab, nanowires and dots. Starting from a saturated state the establishment of stripe domains through the sample is first studied. Contrary to the thin film case, the nucleation of this pattern is not uniform and is very different to the geometry of a wire or an isolated dot. Special attention is paid to the reversal of the core of the vortex (the remnants of inner walls between up and down domains) which requires the insertion of point singularities called Bloch points (BP) either at surfaces or created in a pair depending on the length allowed for the stripe in the corresponding element. The magnetization distribution around the core of the various BP is described in detail as well as the key characteristics of their motion. Finally, some experiments are suggested predicting the behaviour of stripe domains under an applied field.     

Initial stages of oxidation of Cu(1 1 1)

Several surface analysis techniques were combined to study the initial stages of oxidation of Cu(1 1 1) surfaces exposed to O₂ at low pressure (<5 × 10⁻⁶ mbar) and room temperature. Scanning tunneling microscopy (STM) results show that the reactivity is governed by the restructuring of the Cu(1 1 1) surface. On the terraces, oxygen dissociative adsorption leads to the formation of isolated O adatoms and clusters weakly bound to the surface. The O adatoms are located in the fcc threefold hollow sites of the unrestructured terraces. Friedel oscillations with an amplitude lower than 5 pm have been measured around the adatoms. At step edges, surface restructuring is initiated and leads to the nucleation and growth of a two-dimensional disordered layer of oxide precursor. The electronic structure of this oxide layer is characterised by a band gap measured by scanning tunneling spectroscopy to be ∼1.5 eV wide. The growth of the oxide islands progresses by consumption of the upper metal terraces to form triangular indents. The extraction of the Cu atoms at this interface generates a preferential orientation of the interface along the close-packed directions of the metal. A second growth front corresponds to the step edges of the oxide islands and progresses above the lower metal terraces. This is where the excess Cu atoms extracted at the first growth front are incorporated. STM shows that the growing disordered oxide layer consists of units of hexagonal structure with a first nearest neighbour distance characteristic of a relaxed Cu-Cu distance (∼0.3 nm), consistent with local Cu₂O(1 1 1)-like elements. Exposure at 300 °C is necessary to form an ordered two-dimensional layer of oxide precursor. It forms the so-called “29” superstructure assigned to a periodic distorted Cu₂O(1 1 1)-like structure.     

Why the case for clean surfaces does not hold water: Structure and morphology of hydroxylated nickel oxide (1 1 1)

We report an experimental and theoretical analysis of the √3 × √3-R30° and 2 × 2 reconstructions on the NiO (1 1 1) surface combining transmission electron microscopy, X-ray photoelectron spectroscopy, and reasonably accurate density functional calculations using the meta-GGA hybrid functional TPSSh. While the main focus here is on the surface structure, we also observe an unusual step morphology with terraces containing only even numbers of unit cells during annealing of the surfaces. The experimental data clearly shows that the surfaces contain significant coverage of hydroxyl terminations, and the surface structures are essentially the same as those reported on the MgO (1 1 1) surface implying an identical kinetically-limited water-driven structural transition pathway. The octapole structure can therefore be all but ruled out for single crystals of NiO annealed in or transported through humid air. The theoretical analysis indicates, as expected, that simple density functional theory methods for such strongly-correlated oxide surfaces are marginal, while better consideration of the metal d-electrons has a large effect although it is still not perfect.     

Yttrium segregation and surface phases of yttria-stabilized zirconia (1 1 1) surface

Surface segregation of yttria-stabilized zirconia (YSZ) was studied via first-principles computations and thermodynamics. For the cubic YSZ (1 1 1) surface, yttrium can segregate only to a subsurface layer, and these segregation phases are terminated at the surface by defective oxygen layers with honeycomb structure. The segregation is independent of the bulk yttrium concentration at high oxygen partial pressures or low temperatures. At very low oxygen partial pressures and high temperatures there is no surface yttrium segregation and the surface is terminated by O–Zr. Our results provide a reasonable explanation for previous experimental work, and also a framework for extending our understanding of cation segregation in oxide surfaces.     

Ultra thin V2O3 films grown on oxidized Si(1 1 1)

The growth of V₂O₃(0 0 0 1) has been investigated by scanning tunnelling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). Direct evaporation of vanadium onto the Si(1 1 1)-7 × 7 substrate gives rise to massive surface intermixing and consequent silicide formation. In order to obtain the vanadium oxide with good quality, the 7 × 7 surface was initially partially oxidized which leads to a smooth oxygen–silicon surface layer which in turn prevents a complete vanadium–silicon alloy formation. Finally a vanadium oxide film of V₂O₃ stoichiometry was created. The grown film exposes single crystalline areas of stepped surfaces which appear azimuthally randomly-oriented.     

Ge dots on Si (1 1 1) and (1 0 0) surfaces with SiO2 coverage: Raman study

Germanium quantum dots formed on Si (1 1 1) and (1 0 0)-oriented surfaces coated with ultra-thin oxide layers are studied using Raman spectroscopy technique. Some structural properties (height, stoichiometry and mechanical stresses) of the dots were estimated from Raman data. For analysis of the experimental data, the Raman spectra of Ge nanoclusters containing some hundreds of Ge atoms were calculated numerically. The effects of the resonance enhancement of the intensity of Raman scattering in the Ge-nanoclusters–SiO₂–Si system were discussed. The influence of the lateral sizes of Ge nano-clusters on the frequencies of phonons localized in them was studied using numerical simulation. The influence of multi-layer growth on the structure of the Ge quantum dots was investigated.     

Surface and subsurface oxide formation on Ni(1 0 0) and Ni(1 1 1)

The oxidation of Ni(1 0 0) and Ni(1 1 1) at elevated temperatures and large oxygen exposures, typical of the methods used in the preparation of NiO(1 0 0) films for surface studies, has been investigated by medium energy ion scattering (MEIS) using 100 keV H⁺ incident ions. Oxide film growth proceeds significantly faster on Ni(1 1 1) than on Ni(1 0 0), but on both surfaces oxide penetration occurs to depths significantly greater than 100 Å with total exposures of 1200 and 6000 L respectively. The metal/oxide interface is extremely rough, with metallic Ni extending to the surface, even for much thicker oxide films on Ni(1 1 1). On Ni(1 1 1), NiO growth occurs with the (1 0 0) face parallel to the Ni(1 1 1) surface and the close-packed 〈1 1 0〉 directions parallel. On Ni(1 0 0) the MEIS blocking curves cannot be reconciled with a single orientation of NiO(1 0 0) (with the 〈1 1 0〉 directions parallel) on the surface, but is consistent with the substantial orientational disorder (including tilt) previously identified by spot-profile analysis LEED.     

In situ monitoring of nucleation and evolution of Ge nanodots on faintly oxidized Si(1 1 1) surfaces

We have investigated the nucleation and evolution of germanium (Ge) nanodot (ND)s taking place while depositing Ge onto the silicon (Si) (1 1 1) surfaces with ultra-thin Si oxide films by using ultra-high vacuum in situ high-resolution transmission electron microscopy in the profile-imaging geometry. Various types of growth phenomena such as nucleation, growth and coalescence of Ge NDs have successfully been observed. The results show that the growth phenomena of the Ge NDs are dramatically rapid after their size reaches the size of the critical nucleus. The critical nucleus size estimated from a model using the cohesive energy of the Ge NDs has been consistent with observed one.     

An AFM study of the processing of hydrogen passivated silicon(1 1 1) of a low miscut angle

We present atomic force microscopy (AFM) measurements from a passivated silicon crystal miscut by 0.1° and show the etching regime to be significantly different from surfaces with a larger miscut angle. A simple kinetic model is developed to explain the results and is used to derive the optimal etching conditions for nominally flat Si(1 1 1)–(1×1)H. We show that small changes in miscut angle can alter the kinetic steady state and promote the formation of deep etch pits, even on the least stable, miscut surface. Collisions of steps with these pits result in arrays of stable, self-aligned ‘etch hillocks' over micron dimensions. Following preparation, we use AFM to observe the initial growth of native oxide on the Si(1 1 1)–(1×1)H surface, and demonstrate that AFM is a sensitive probe to surface oxidation in the sub-monolayer regime.     

Quasi-one-dimensional structures on the Si(1 1 1) surface induced by Ba adsorption

Ba-induced quasi-one-dimensional reconstructions of the Si(1 1 1) surface have been investigated by low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). While the 3 × ‘2’ surface shows double-periodicity along the stripes in STM images consistent with half-order streaks observed in LEED patterns, no sign of the double-periodicity along the chain direction was detected for the 5 × 1 surface. The 5× stripes in STM images show internal structures with multiple rows. The two rows comprising the boundaries of a 5× stripe in the filled-state STM image are found to have 3a × √3/2 spacing across the stripe. The observation of the successive 3× and 2× spacings between the boundary rows supports a structural model proposed for the Ba-induced 5 × 1 Si reconstruction composed of honeycomb chains and Seiwatz chains. The highest coverage 2 × 8 surface does not reveal a quasi-1D row structure in STM images.     

Formation of and phase transitions in electrodeposited tellurium atomic layers on Au(1 1 1)

Detailed studies of the structures formed by the electrodeposition of atomic layers of Te on Au(1 1 1) surfaces from aqueous solutions were performed using in situ scanning tunneling microscopy (STM), as well as by UHV-EC techniques such as low energy electron diffraction and Auger electron spectroscopy. There are two features in the voltammetry that may be considered underpotential deposition (UPD). However, from the voltammetry, it is clear that the deposition process is kinetically slow, and from this study it appears that several atomic layer structures are actually formed at overpotentials. Prior to deposition, a surface excess of a tellurium oxide species coats the surface. This layer is then converted to a Au(1 1 1)(√3×√3)R30°–Te structure with an array of domain walls, at 1/3 ML. The initial structure appears to have a symmetric array of walls, resulting in a (13×13) periodicity, which then converts to a less symmetric structure where the domain walls form rhombi, with a larger periodicity. During the second UPD feature, the coverage increases, forming a (√7×√13) unit cell at 0.36 ML and then a (3×3) at 0.44 ML. Commensurate with the formation of these higher coverage structures, a roughening transition takes place, where the surface becomes pitted, resulting in about 40% of the surface being covered with single atom deep pits. This process appears to be related to the pits formed in the surfaces of self-assembled monolayers (SAM) of thiols on Au surfaces, and layers of Se and S on Au surfaces. Several theories have been suggested to account for these pits. The model that appears to best explain the pits is based on shrinking of the size of the underlying Au atoms, reconstructing the underlying Au. There also appears to be a high coverage structure, near 0.9 ML, that forms at potentials near where the (3×3) forms, but only by holding the potential for an extended period of time. Subsequent dissolution of this high coverage structure produces domains of disordered Te atoms, which gradually decrease in coverage until the (3×3) is again formed at 0.44 ML.     

化学腐蚀和硫处理对InSb(111)表面的影响

本文应用俄歇电子能谱和X射线光电子能谱对化学腐蚀和硫处理的InSb表面进行了研究。实验中发现经过CP-4腐蚀以后在样品的表面生成了InSb的氧化层,氧化层中的组分是锑的氧化物明显多于铟的氧化物。样品经过硫处理以后能够除去InSb表面的氧化层并且形成硫化物钝化层。 关键词：