Novel mesoscale defect structure on NiO(1 0 0) surfaces by atomic force microscopy

Cleaved NiO(1 0 0) surfaces were imaged with atomic force microscopy (AFM) to determine defect concentrations and morphology. Random 〈0 1 0〉 and 〈0 0 1〉 oriented steps, which have been previously characterized, were the most common defect observed on the cleaved surface and formed with step heights in multiples of 2.1 Å, the Ni-O nearest-neighbor distance, and terrace widths in the range of 25-100 nm. In addition, the surface showed novel mesoscale (∼0.5-2 μm) square pyramidal defects with the pyramid base oriented along 〈1 0 0〉 symmetry related directions. Upon etching, the pyramidal defects converted to more stable cubic pits, consistent with (1 0 0) symmetry related walls. The square pyramidal pits tended to cluster or to form along step edges, where the weakened structure is more susceptible to surface deformations. Also, a small concentration of square pyramidal pits, oriented with the base of the pyramid along 〈0 1 1〉, was observed on the cleaved NiO surfaces. For comparison purposes, chemical mechanical polished (CMP) NiO(1 0 0) substrates were imaged with AFM. Defect concentrations were of comparable levels to the cleaved surface, but showed a different distribution of defect types. Long-ranged stepped defects were much less common on CMP substrates, and the predominant defects observed were cubic pits with sidewalls steeper than could be accurately measured by the AFM tip. These defects were similar in size and structure to those observed on cleaved NiO(1 0 0) surfaces that had been acid etched, although pit clustering was more pronounced for the CMP surfaces.     

氧化镍位于510～610 nm的激光诱导荧光光谱 (cited: 1)

采用激光诱导荧光技术在510～650 nm研究了超声射流冷却下的氧化镍光谱,观测了55个振转谱带. 通过转动分析发现激发态的同位素位移、振转间隔和转动常数都表现出高度的不规则性,26个[Ω=0,1]-X³∑^-₀的跃迁谱带被暂时归属为5个振动序列. 此外实验中还观测了部分谱带的色散谱和寿命.     

Non-contact atomic force microscopy imaging of TiO2(100) surfaces

Atomically resolved non-contact fm mode atomic force microscopy images have been obtained from TiO₂(100) surfaces. The 1×1 surface is observed, as well as the 1×3 phase previously imaged with STM. The morphology of the latter reconstruction consists of (110) microfacets. An additional reconstruction with 1×3 symmetry is observed, which is assigned to a phase intermediate between the 1×1 and 1×3-microfacet terminations.     

Study on orientation mechanisms of poly(vinylidenefluoride-trifluoroethylene) molecules aligned by atomic force microscopy

We have developed a molecular orientation control technique for polymers utilizing contact-mode atomic force microscopy (AFM). In this paper, we studied the molecular alignment mechanism of this technique by applying it to poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)). The resultant alignment and formed crystal size were strongly dependent on the temperature during the modification. They also depended on the scan line spacing of the modification. These results made the alignment mechanism clear. The obtained molecular alignment was stable against the heat treatment even at the temperatures just below T_m.     

Observation of the V2O5(001) surface using ambient atomic force microscopy

Constant force images of the V₂O₅(001) surface were recorded in ambient conditions with atomic force microscopy. All images exhibit the 11.5 Å × 3.5 Å. periodicity expected for a bulk terminated surface. However, images reveal differences from the ideal structure. The experimental results are interpreted in terms of preferential adsorption sites for water molecules. Because these sites are thought to influence the catalytic properties of the surface, their characterization is an important step towards understanding how the atomic-scale structure of a surface influences its properties.     

Imaging of atomic-scale structure of oxide surfaces and adsorbed molecules by noncontact atomic force microscopy

Atom-resolved images of a TiO₂(110)-(1×1) surface and individual formate and acetate ions adsorbed on the surface were obtained by noncontact atomic force microscopy (NC-AFM) in ultrahigh vacuum. In contrast to previous scanning tunneling microscopic studies imaging five-fold coordinated Ti atoms, outermost atoms of bridge-bound oxygen ridges of the surface were resolved as protruding rows by NC-AFM. High-resolution image of the surface revealed that the bridging oxygen atoms on terraces ordered in a (1×1) periodicity. Randomly distributed point and multiple defects of oxygen atoms were also imaged as dark spots. The (2×1) overlayer of formate and acetate ions were resolved as ordered bright spots. Dispersed formate ions at a low coverage were also observed as bright spots between the bridging oxygen ridges along the [001] direction.     

Confocal Raman imaging and atomic force microscopy of the surface reaction of NO2 and NaCl(100) under humidity

Polarized confocal Raman imaging combined with non‐contact atomic force microscopy (AFM) was used to study the three‐dimensional evolution of the NaCl(100) surface during its reaction with NO₂ at low pressure as a function of relative humidity (RH) from 0% to nearly 80%. Sea salt particles containing NaCl as the main constituent are believed to be the major source of reactive tropospheric chlorine and nitrate fallouts. At an RH of 0%, the reaction of dry NO₂ generates surface conversion to NaNO₃ monolayer capping the NaCl(100) surface and releases NOCl. The subsequent exposure of this NaNO₃ layer to RH below ∼45% induces the formation of rare NaNO₃ tetrahedral crystals less than 0.5 µm in size. The crystallization occurs through two‐dimensional NO₃⁻ migration under the H₂O monolayer regime. After another subsequent exposure to RH above 45% and below 75%, supermicrometric NaNO₃ rhombohedral plates were obtained under the H₂O multilayer regime. On the other hand, the simultaneous exposure of NaCl(100) to NO₂ and H₂O below ∼45% RH rapidly generates numerous submicrometric NaNO₃ tetrahedra on the NaCl(100) surface. The dramatic increase of NaNO₃ production in the presence of water vapour is explained by the formation of HNO₃ and its easy reaction with the NaCl(100) surface. For RH above 45% and below 75%, the tetrahedra evolve to rhombohedral plates of supermicrometric size. The exposure of NaCl(100) to NO₂/H₂O mixtures under RH above 75% induces the coexistence of both solid‐state NaNO₃ and dissolved NO₃⁻ in droplets. Copyright © 2008 John Wiley & Sons, Ltd.     

Au(110)表面结构和氧原子吸附的第一性原理研究

用密度泛函理论(DFT)研究了金属Au(110)表面结构以及氧原子的吸附状态.计算得到Au(110)-(1×2)缺列再构表面原子的弛豫分别是-15.0%(Δd₁₂/d₀)和-1.1%(Δd₂₃/d₀),表面能为52.7 meV/²,功函数Φ=5.00 eV;Au(110)-(1×3)缺列再构表面的Δd_{1 关键词： 缺列再构Au(110)表面 STM图像 氧原子吸附}     

Imaging polycrystalline and smoke MgO surfaces with atomic force microscopy: a case study of high resolution image on a polycrystalline oxide

Atomic force microscopy in contact, non-contact and in high resolution modes have been used to image MgO powder samples, obtained at different degree of sintering, starting from Mg(OH)₂ decomposition or obtained in form of smoke. From high resolution AFM images of MgO smoke, the lattice periodicity on regular surfaces has been revealed for the first time, under ambient conditions. The high surface perfection of the microcrystals has been further confirmed by HRTEM analysis. To obtain more information on the local structure of the single faces, in terms of type and distribution of the surface active sites, the adsorption of a simple probe molecule (CO) on such surfaces has been investigated by means of FTIR spectroscopy.     

Ultra smooth NiO thin films on flexible plastic (PET) substrate at room temperature by RF magnetron sputtering and effect of oxygen partial pressure on their properties

Transparent p-type nickel oxide thin films were grown on polyethylene terephthalate (PET) and glass substrates by RF magnetron sputtering technique in argon + oxygen atmosphere with different oxygen partial pressures at room temperature. The morphology of the NiO thin films grown on PET and glass substrates was studied by atomic force microscope. The rms surface roughnesses of the films were in the range 0.63-0.65 nm. These ultra smooth nanocrystalline NiO thin films are useful for many applications. High resolution transmission electron microscopic studies revealed that the grains of NiO films on the highly flexible PET substrate were purely crystalline and spherical in shape with diameters 8-10 nm. XRD analysis also supported these results. NiO films grown on the PET substrates were found to have better crystalline quality with fewer defects than those on the glass substrates. The sheet resistances of the NiO films deposited on PET and glass substrates were not much different; having values 5.1 and 5.3 kΩ/□ and decreased to 3.05, 3.1 kΩ/□ respectively with increasing oxygen partial pressure. The thicknesses of the films on both substrates were ∼700 nm. It was also noted that further increase in oxygen partial pressure caused increase in resistivity due to formation of defects in NiO.     

In situ observation on Au(1 0 0) surface in molten EMImBF4 by electrochemical atomic force microscopy (EC-AFM)

The Au(1 0 0) surface structure in contact with 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF₄) has been observed using electrochemical atomic force microscopy (EC-AFM) under an electrochemically controlled potential. The AFM images, taken in EMImBF₄ in the potential range from −0.6 to 0.2 V vs. Ag/Ag(I), shows a fourfold symmetry with the distance between protrusions of ≈0.30-0.32 nm. This structure agrees well with the ideal surface structure of Au(1 0 0)-(1 × 1) and it is very similar to that previously obtained in a sulfuric acid aqueous solution.     

Effect of chain length on the adhesion behaviour of n-alkanethiol self-assembled monolayers on Au(111): An atomic force microscopy study

The effect of chain length on the adhesion behaviour of n-alkanethiols CH₃(CH₂)_nSH, wheren = 5, 6, 7, 9, 10, 11, 14 and 15 has been followed by carrying out pull-off force measurement using atomic force microscopy (AFM). The self-assembled monolayers on Au(111) surface has been characterized by reflection absorption infra-red spectroscopy (RAIRS) and contact mode AFM. It is observed that the work of adhesion is independent of thiol chain length though the standard deviation is high for short chain length thiol-based monolayers. This may be attributed to the relatively more deformable nature of the short chain thiol films due to their heterogeneity in the monolayer structure than the long chain ones. This, in turn, increases the contact area/volume between the AFM tip and the monolayer, and hence the force of adhesion. However, in the presence of water, the force of adhesion is lower than that observed in air reflecting the effects of capillary forces/polar components associated with the surface energy.     

Atomic resolution noncontact atomic force and scanning tunneling microscopy of TiO2(110)-(1 x 1) and - (1 x 2): simultaneous imaging of surface structures and electronic states

We present simultaneous imaging of TiO2(110)-(1 x 1) and - (1 x 2) using noncontact atomic force microscopy (NC-AFM) and scanning tunneling microscopy (STM). The surface topography was imaged under NC-AFM feedback, while the surface electronic states were imaged by STM. The image contrasts of NC-AFM and STM were antiphase in (1 x 1) and in phase in (1 x 2). The uppermost oxygen and Ti atoms underneath were, respectively, imaged by NC-AFM and STM. The NC-AFM image contrast was close to the true surface topography in (1 x 2), but reduced in (1 x 1).     

The interplay between surface micro-topography and -mechanics of type I collagen fibrils in air and aqueous media: An atomic force microscopy study

Calf skin type I collagen fibrils were regenerated from acidic solution and imaged with contact mode atomic force microscopy in air, water, and buffer solution. When imaged in air at a contact force of 20-150 nN, collagen fibrils exhibited a distinct transverse banding pattern with a period of 65 nm, consisting of high ridges and shallow grooves. The force dependence of the images suggests that such banding pattern is attributed to the transverse contraction of the fibril upon dehydration during sample preparation, which reflects the tangential mass density across the fibril. Imaging in water and phosphate buffer solution at a contact force of 15-80 nN revealed hydrated collagen fibrils with smooth surfaces. The rigidity of the collagen fibrils decreased considerably upon hydration. Scanning the cantilever tip in an aqueous medium at a contact force of 90-280 nN enabled us to probe subunit arrangement in the bulk region of the collagen fibril. The results indicate that the molecular assembly in the hydrated fibril is akin to that in the intact form. The image resolution was improved by stabilizing the collagen molecules through crosslinking with glutaraldehyde, which served to resolve microfibril-like structure on the fibril surface. Received 28 March 2000 and Received in final form 15 June 2001     

Crystalline structure of the Au(1 1 1) surface revealed by stereographic intensity DEPES maps

The intensity of elastically backscattered electrons at the primary electron beam energy 1.9 keV was used to obtain a stereographic map of Au(1 1 1) by means of the directional elastic peak electron spectroscopy (DEPES). An experimental result is compared with the theoretical data obtained by using multiple scattering calculations (MS) performed for both not-reconstructed and model-reconstructed clusters. The lateral lattice misfit of the first layer leads to quantitative changes of theoretical intensities showing a sensitivity of DEPES to the short atomic chain axial order. This comparison proves that a main contribution of the experimental contrast originates from a higher background level. Moreover an anisotropy of the inelastic mean free path is discussed in the paper.     

Preparation and characterization of n-type conductive (Al, Co) co-doped ZnO thin films deposited by sputtering from aerogel nanopowders

Highly transparent, n-type conducting ZnO thin films were obtained by low temperature magnetron sputtering of (Co, Al) co-doped ZnO nanocrystalline aerogels. The nanoparticles of ∼30 nm size were synthesized by a sol-gel method using supercritical drying in ethyl alcohol. The structural, optical and electrical properties of the films were investigated. The ZnO films were polycrystalline textured, preferentially oriented with the (0 0 2) crystallographic direction normal to the film plane. The films show within the visible wavelength region an optical transmittance of more than 90% and a low electrical resistivity of 3.5 × 10⁻⁴ Ω cm at room temperature.     

第一性原理研究氧空位对Ag在MgO(001)面吸附的影响

采用基于密度泛函理论的第一性原理研究方法,应用Vienna Ab-initio Simulation Package (VASP),计算了氧空位对Ag原子在MgO(001)面吸附的影响．通过成键过程中电荷密度的变化以及电荷转移的讨论,从原子尺度上分析了MgO(001)面空位点Fs和Fs+对其吸附、聚集与成核属性的影响以及吸附的能量属性.结果表明,相对清洁的MgO表面而言,Ag原子吸附在O空位时,能够更牢固地与MgO表面结合,并吸引更多的Ag原子聚集在一起,形成一个个独立的Ag原子岛.     

Comparative Study of Tribological Properties of Polyphenylene Sulfide (PPS), Polyethersulfone (PES), and Polysulfone (PSU)

The tribological properties of polyphenylene sulfide (PPS), polyethersulfone (PES) and polysulfone (PSU), which have similar molecular structures, were investigated using an end-face contact tribometer and a reciprocating tribometer. The thermomechanical behavior of the polymers was analyzed using dynamic mechanical analysis (DMA). PPS exhibited a maximum friction coefficient with increasing load and sliding speed, while the friction coefficients of PES and PSU decreased only slightly. The wear rate of PPS was much lower than that of PES and PSU under high loads and speeds. It is suggested that the main factors influencing the friction and wear properties of the neat polymers are their condensed state and heat resistance. Amorphous PES and PSU showed liquid-like behavior and very low friction when the frictional surface was in the molten-flow state. The macromolecular crystals of crystallizable PPS give it some solid-like behavior and load-carrying capacity; hence PPS exhibited lower wear than PES and PSU.     

Cu(100) (2×22)R45°-O的表面结构与电子态的密度泛函研究

用第一性原理的总能计算研究了Cu(100))面的表面结构、弛豫以及氧原子的(2×22)吸附状 态.计算给出了Cu(100) (2×22)R45°-O吸附表面的结构参数，并得到了上述结构下氧吸附 的Cu(100)表面氧原子和各层Cu原子的电子态密度.计算得到的吸附表面功函数为4.58 eV ，与清洁Cu(100)表面功函数(～4.53 eV)几乎相同.吸附氧原子与最外层铜原子之间的垂直 距离约为0.02 nm，其能带结构体现出一定的金属性，同时由于Cu-O的杂化作用在费米能以 下约6.4 eV附近出现了局域的表面态.可以认为，在Cu(100) (2×22)R45°的氧吸附表面结 构下，吸附氧原子和衬底之间的结合主要来源于表面最外层铜原子与氧原子的相互作用. 关键词： Cu(100)(2×22)R45°-O表面 缺列再构 表面电子态