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1.
Ferroelectric BaTiO3 thin films with a thickness of 10 monolayers (ML) were epitaxially grown on SrTiO3(0 0 1) substrates by very slow deposition using molecular beam epitaxy (MBE). The investigations were carried out by two growth methods: (i) codeposition and (ii) alternate deposition of the metal elements in an oxygen atmosphere. In situ observation of reflection high-energy electron diffraction confirmed that an epitaxial cube-on-cube structure was prepared. After the deposition, X-ray diffraction measurements were carried out. The 10-ML-thick BaTiO3 films were highly c-axis oriented single crystals with good film quality.  相似文献   

2.
A calculation model for determination of the shapes of the constant force surfaces and profiles of lateral forces for the case of the AFM tip scanning the closely packed lattice in contact mode is proposed. Atomic relaxation is taken into account in this model. The existence of breaks on constant force surfaces, which was predicted earlier in an approximation of the fixed lattice, is confirmed. It is shown that due to non-zero atomic mobility, breaks appear for smaller scanning forces than assumed earlier. The shapes of the continuous constant force surfaces and profiles of lateral force components are computed. These results may be used for diagnostics of point defects on the surface.  相似文献   

3.
We examined the surface properties of platinum (Pt) thin films exposed to oxygen and argon plasma treatments and compared them to as-deposited Pt films. The surface wetting properties, refractive index and extinction coefficient of the Pt films were monitored as a function of time after different plasma treatments. Surfaces treated with an oxygen plasma were dramatically different from as-deposited Pt, whereas argon plasma treated surfaces were similar to as-deposited films. X-ray photoelectron spectroscopy confirmed the formation of platinum oxide on films treated with an oxygen plasma, while such oxide diminished after argon plasma treatment. Surface morphology studied with atomic force microscopy indicated a strong dependence of the surface roughness of the Pt films on the power and duration of the argon plasma used for the treatment. Based on these studies, an oxygen plasma treatment followed by a brief low-power argon plasma etch was developed for the purpose of regenerating clean and metallic Pt surfaces, and at the same time providing the smoothest possible surface morphology.  相似文献   

4.
A concave-shaped surface has been prepared in a 6H–SiC(0 0 0 1) substrate by mechanical grinding. As a consequence, the different crystallographic planes building up the 6H–SiC polytype are cut under continuously changing polar angles in all azimuthal directions. Through hydrogen etching, this curved surface breaks up into a whole set of surfaces vicinal to the initial 6H(0 0 0 1) orientation. The local structural reorganisation after hydrogen etching has been studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Two types of local bond environments are present at the step edges leading to a strong anisotropy in the surface etching with hydrogen. As a result, the distribution of the terrace width and the step heights varies with the azimuthal angle and reflects the sixfold symmetry of the bulk crystal. For most azimuthal directions, an alternation of large and small terraces, separated by steps of 0.75 nm heights (height of half the 6H polytype, three bilayers) is observed and only for well defined azimuthal directions, equally spaced terraces separated by steps of 1.5 nm height (one unit cell of 6H–SiC, six bilayers) are found. In addition, the polar variations have been studied by taking various line-scans along the concave-shaped surface with AFM. It seems that for polar angles above 3°, step bunching of several SiC steps occurs whereas below 3° the bimodal terrace width distribution is observed.  相似文献   

5.
Ultra-thin Ag films on the Au(1 1 1) surface were prepared via overpotential deposition (OPD) in the presence of Pb2+ ions. By carrying out repetitive Pb adlayer underpotential deposition (UPD) and stripping cycles during Ag bulk deposition, the two-dimensional growth of Ag films was significantly enhanced in high OPD. The Ag monolayer sample was made by comparing the voltammetry curves, in which the signatures for Pb adlayer UPD on Au(1 1 1) changed to that on Ag(1 1 1). As demonstrated by the X-ray specular reflectivity measurements, nearly complete monolayer and bilayer films can be made with optimized deposition procedures. On subatomic scale, however, we found that these films have significant higher root-mean-square displacement amplitudes than those underpotentially deposited Ag monolayer and bilayer on either Au(1 1 1) or Pt(1 1 1).  相似文献   

6.
Surface morphologies of nanocrystalline TiO2 thin films were studied by analyzing the surface profile of AFM images using wavelet transform method. Based on characterizing the fractal feature and computing the image details at different orientations and resolutions, the surface textures of nanocrystalline TiO2 thin films before and after chemical treatment were examined. The results reveal that titanium isopropoxide treatment leads to an increase of surface roughness. The related mechanism of modification of the microstructure by chemical treatment associated with the improvement of the photocurrent response is discussed.  相似文献   

7.
The present work deals with the electrochemical formation of superlattice structures on n-type (1 0 0) InP in HCl solutions. The superlattices consist of a stack of two layers with alternating high and low porosity on n-type material obtained by changing the anodizing current or the potential periodically in HCl solutions. The superlattice structures were characterized by scanning electron microscopy. The pore morphology and structure depend strongly on the electrochemical conditions. For anodization with low currents (e.g., 1 or 10 mA) or at low potentials (e.g., 1.5 VAg/AgCl), a porous layer with a facet-like structure was formed. For higher currents or potentials, such as 50 or 100 mA or 3 VAg/AgCl, respectively, a tree-like structure with random and/or tangled branches was observed. Finally, samples anodized at 5 VAg/AgCl, show a porous layer with a regular array of straight pores. The morphology and structure of the stacks of the porous layers can be controlled in the nanometer range, depending on the electrochemical conditions.  相似文献   

8.
The morphology of electrochemically deposited Pd films on the Pt(0 0 1) electrode surface has been examined through the combination of cyclic voltammetry (CV) and in situ surface X-ray scattering (SXS). Analysis of SXS measurements has indicated that the Pd grows via pseudomorphic island formation, with the partial occupation of successive layers occurring at a first layer occupation of 0.8 ML. Further Pd deposition sees the formation of larger islands built onto the now complete monolayer, characteristic of pseudomorphic Stranski–Krastanov (SK) growth. In the HUPD potential region the effect of CO on the surface expansion of the multilayer Pd film is negligible. In the hydrogen evolution region, however, the effect of the adsorption of CO has been shown to produce surface normal expansion and in-plane disorder of the Pd film. It is suggested that hydrogen permeation into the Pd film is enhanced on the CO-poisoned surface.  相似文献   

9.
In this paper, we focus on better understanding tapping-mode atomic force microscopy (AFM) data of soft block copolymer materials with regard to: (1) phase attribution; (2) the relationship between topography and inside structure; (3) contrast-reversal artifacts; (4) the influence of annealing treatment on topography. The experiments were performed on the surface of poly(styrene–ethylene/butylene–styrene) (SEBS) triblock copolymer acting as a model system. First, by coupling AFM with transmission electron microscopy (TEM) measurements, the phase attribution for AFM images was determined. Secondly, by imaging an atomically flat SEBS surface as well as an AFM tip-scratched SEBS surface, it was confirmed that the contrast in AFM height images of soft block copolymers is not necessarily the result of surface topography but the result of lateral differences in tip-indentation depth between soft and hard microdomains. It was also found that there is an enlarging effect in AFM images on the domain size of block copolymers due to the tip-indention mechanism. Thirdly, based on the tip-indention mechanism, tentative explanations in some detail for the observed AFM artifacts (a reversal in phase image followed by another reversal in height image) as function of imaging parameters were given. Last, it was demonstrated that the commonly used annealing treatments in AFM sample preparation of block copolymers may in some cases lead to a dramatic topography change due to the unexpected order-to-order structure transition.  相似文献   

10.
Ge (1 0 0) wafers were implanted with 100 keV Mn+ ions with a dose of 2 × 1016 ions/cm2 at different temperatures, ranging from 300 to 573 K. The surface morphology of implanted samples, analyzed with scanning electron microscopy and atomic force microscopy measurements, reveals for the 300-463 K implant temperature range the formation of a surface swelled and porous film, containing sponge-like structures. On the contrary, samples implanted in the 513-573 K temperature range present an atomically flat surface, with a roughness less than 1 nm, indicating that crystalline order has been preserved. X-ray photoemission spectroscopy depth profiling measurements indicate the presence of adsorbed oxygen in the porous layer of lower-temperature implanted samples, as well the presence of a large Mn concentration below the expected end of range for impinging ions. Mn and O concentrations at anomalously great depths are maximum in the 413 K implanted sample, indicating that the phenomenon of ion beam induced porosity is best favored at a well defined temperature.  相似文献   

11.
J.M. Kim  T. Ohtani 《Surface science》2004,549(3):273-280
High-resolution single molecular near-field fluorescence images were observed by scanning near-field optical/atomic force microscopy (SNOM/AFM). We modified the SNOM/AFM for both high-resolution fluorescence imaging and high-resolution topographic imaging. The imaged fluorophore, Alexa 532, is prepared with a poly-methyl-methacrylate (PMMA) film coating. A fluorescence resolution of 25 nm was obtained with a simultaneous topographic image of a flat surface. A sample prepared with a lower PMMA concentration exhibited a rough surface in the micro area. The results for the flat surface indicated that the fluorescence resolution is worst in the rough surface sample, that the maximum fluorescence intensities for the individual fluorophore are similar, and that the decay rate is faster. Thus, we concluded that the morphological effect is an important factor in fluorescence image resolution and the apparent lifetimes of the fluorescence molecules.  相似文献   

12.
D. Kaminski 《Surface science》2005,575(3):233-246
Using surface X-ray diffraction, we have determined the structure of three different sub-monolayer phases of Bi on Cu(1 1 1). In contrast to an early report, we find that at a coverage of 1/3 monolayer a substitutional surface alloy is formed with a (√3 × √3)R30° unit cell. For increasing coverage, de-alloying occurs, leading to an overlayer structure at a coverage of 0.5 ML in which the Bi atoms form zigzag chains. The surface contains three domains of this phase. Finally, at a slightly higher coverage of 0.53 ML, the unit cell is compressed in one direction, leading to a uniaxial-incommensurate phase with three rotational domains.The structure determination includes relaxations in the topmost layers and therefore allows a detailed comparison of the most important bond distances. This shows that an increased charge density of the Cu(1 1 1) surface is the main driving force for the different phases.  相似文献   

13.
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.  相似文献   

14.
The adsorption of germanium on Ag(1 1 0) has been investigated by scanning tunnelling microscopy (STM), as well as surface X-ray diffraction (SXRD). At 0.5 germanium monolayer (ML) coverage, Low Energy Electron Diffraction (LEED) patterns reveals a sharp c(4 × 2) superstructure. Based on STM images and SXRD measurements, we present an atomic model of the surface structure with Ge atoms forming tetramer nano-clusters perfectly assembled in a two-dimensional array over the silver top layer. The adsorption of the germanium atoms induces a weak perturbation of the Ag surface. Upon comparison with results obtained on the (1 1 1) and (1 0 0) faces, we stress the role played by the relative interactions between silver and germanium on the observed surface structures.  相似文献   

15.
The structure of ultrathin Mo films on SrTiO3(1 0 0) was studied by in situ reflection high-energy electron diffraction (RHEED). A different structure was observed for films less than 20 Å thick than for thicker films. These films were epitaxial and had a metastable structure. Thicker films had the dimensions of equilibrium bcc Mo(1 1 0). Relaxation processes transformed the metastable Mo into bcc Mo, resulting in the following orientation relationships between Mo and SrTiO3: (1 1 0)[0 0 1]bcc Mo ∥ (1 0 0)[0 0 1]SrTiO3 and (1 1 0)[1 1 1]bcc Mo ∥ (1 0 0)[0 1 1]SrTiO3. The formation of such specific orientations is related to transformations via the Bain and Needle Path, respectively.  相似文献   

16.
Molecular orientations of pentacene ultrathin films grown on SiO2 substrates were studied without the influence of the atmosphere by vacuum atomic force microscopy (V-AFM) and near edge X-ray absorption fine structure (NEXAFS). The experimental processes from deposition of pentacene to characterization of films were performed under vacuum condition without exposure to the atmosphere. V-AFM and NEXAFS measurements showed that pentacene molecules tend to grow on SiO2 surface with their molecular long axes perpendicular to the substrate surfaces (standing-mode) irrespective of preparation procedure of SiO2 substrate.  相似文献   

17.
The very first stages of the growth of NiO on Cu(1 1 1) is examined on a microscopic scale. The paper focuses on the morphological and structural characterization of nanostructures formed in the 0-1 Å thickness range. Ultra-thin NiO films, obtained through evaporation of a Ni rod under an oxygen atmosphere were grown at 550 K. In the early stages of the growth the oxide film morphology shows 10-30 nm large, monolayer high, islands with a partial incorporation of metallic Ni in the first Cu(1 1 1) surface plane. The first layer is formed by an epitaxial atomic layer exhibiting a STM contrast similar to the one observed on adsorbed oxygen on Cu(1 1 0). A NiO cluster nucleation and coalescence mechanism is proposed in order to explain the formation of the second NiO layer. A α-Ni2O3 hexagonal phase, or a structural distortion of the NiO(1 1 1)()R30° structure could both explain the complex LEED patterns.  相似文献   

18.
The dynamic behavior of steps involved in the relaxation of sharp corners in microfabricated structures on crystalline surfaces have been studied. We find that during the early stages of relaxation of slightly tapered trenches on Si(0 0 1), wide (1 1 0) terraces perpendicular to the substrate are formed near the corners of the trench sidewalls. The evolution of a step profile around the corner region, where step density abruptly changes, is analyzed using one-dimensional step models. It is found that, in case that mass transport occurs through surface diffusion, the preexisting steps on the trench sidewall are accumulated in the corner region, and extensive terraces are formed near the corners.  相似文献   

19.
The orientational phase diagram and morphology of the Eu-adsorbed Si(1 0 0) surface miscut by 0.4° have been studied by low-energy electron diffraction and scanning tunneling microscopy. We demonstrate that the original double-domain configuration with single-layer steps on the Si(1 0 0) substrate can be drastically broken at 0.4 monolayer (ML) of Eu. At this coverage, the ordered domain pattern formed by topographically non-equivalent terraces with Eu-induced 2 × 3 and “2 × 1” (so-called “wavy” structure) reconstructions is found, while no orthogonal 3 × 2 and “1 × 2” domains are observed. A model of the single-domain surface is proposed. The origin of the double- to single-domain transition found for the Eu/Si(1 0 0) system is discussed.  相似文献   

20.
Surfaces of 6H-SiC(0001) homoepitaxial layers deposited on vicinal (3.5° off (0001) towards [11 0]) and on-axis 6H---SiC wafers by chemical vapour deposition have been investigated using ultra-high vacuum scanning tunneling microscopy. Undulating step configurations were observed on both the on-axis and the vicinal surfaces. The former surface possessed wider terraces than the latter. Step heights on both surfaces were 0.25 nm corresponding to single bilayers containing one Si and one C layer. After annealing at T>1100°C for 3–5 min in UHV, selected terraces contained honeycomb-like regions caused by the transformation to a graphitic surface as a result of Si sublimation. A model of the observed step configuration has been proposed based on the observation of the [ 110] or [1 10] orientations of the steps and energetic considerations. Additional deposition of very thin (2 nm) SiC films on the above samples by gas source molecular beam epitaxy was performed to observe the evolution of the surface structure. Step bunching and growth of 6H---SiC layers and formation of 3C---SiC islands were observed on the vicinal and the on-axis surfaces, respectively, and controlled by the diffusion lengths of the adatoms.  相似文献   

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