Force Microscopy In Noncontact Mode Research Articles

Optical and fractal properties of sputter deposited TiO2 films

In this study, TiO2 films were deposited on the glass substrates at different pressures using a DC magnetron sputtering system. The surface topography, fractality, particle size, transparency spectra, and roughness of the deposited films were analyzed through atomic force microscopy in non-contact mode and spectrophotometer (UV–visible) analysis. The Gwyddion open source software was used to analyze the AFM results. The surface morphology, absorption spectra, transparency, and energy band gap of the films were studied through analytical and mathematical relations, including fractal and multifractal dimensions of the films. The pressure influenced the particle size leading to the changes in the surface roughness and fractality of the films. When the working pressure increased above 8 × 10−3 Torr, the nonuniformity in the distribution of surface properties and multifractality increased. Additionally, using optical data and the Tauc’s method, their energy gap was calculated. It was revealed that the TiO2 coatings have a relatively large energy gap of ~ 4 eV, probably due to their small grain size.

The effects of deposition time on the nanoscale patterns of Ag/DLC nanocomposite synthesized by RF-PECVD.

In this study, a stereometric analysis of the three dimensional (3-D) surfaces of the Ag/DLC nanocomposite synthesized by RF-PECVD was performed. Atomic force microscopy in noncontact mode was used to study surface morphology in correlation with multi-parametric statistical analysis. The associated parameters of segmented motifs in conformity with ISO 25178-2:, 2012 have been extracted using MountainsMap® Premium software. The mathematical algorithm computes detached watersheds of hill or dale motifs and determines the maximum and minimum points of motifs. The stereometric analyses with MountainsMap® Premium software provided detailed information on the 3-D surface topography of samples. Fractal analyses revealed the fractal nature of the performed samples is in correlation with the deposition time of samples. Detailed information of manufactured Ag/diamond-like carbon (DLC) nanocomposite is given based on the information about the surface structure, properties, and performance characteristics. The performed analysis allows the high-resolution modeling of Ag/DLC nanocomposite surface microtexture with motif analysis (intrinsic characteristics disclosure and characterization of surfaces fractal), in order to be included in computer interactive simulation algorithms. It was found the fractal dimension decreases with the increase of the deposition times on samples.

English

Diffraction transmission gratings were recorded in AGFA-8E75 film, chemically treated under processes with D-19 + potassium ferrocyanide and a chemical processing technique proposed for PE-2 film to obtain embossed stripes. Holographic structures were measured topographically by the technique of atomic force microscopy in noncontact mode (NC-AFM) and we observe changes in the depths under variations in exposures and used photochemistry. We find that the best performance in terms of relief depth obtained is given by the conventional process which reached depths between 0.15 µm and 0.3 µm for spatial frequencies of the order of 400::500 lp/mm. In this study we evaluated the possibility of obtaining matrices highlighted in silver halide holograms replication processes.

Grain boundary corrosion of the surface of annealed thin layers of gold by OH· radicals

Annealed thin layers of gold with large mono-crystalline areas were treated with OH· radicals generated in an electrochemical Fenton reaction. The morphological changes observed with ex situ atomic force microscopy in non-contact mode and grazing incidence X-ray diffractometry show that the grain boundaries, and generally the non-{111} planes, are the loci of highest reactivity, i.e., the places where the gold dissolution is much faster than on the {111} planes.

NC-AFM Study of the Adsorption of Hexamethoxytriphenylene on KBr(001)

Molecular adsorption studies on atomically clean, well-defined surfaces of bulk insulators are still very scarce and have been restricted to a small number of molecules. In this study, the adsorption of 2,3,6,7,10,11-hexamethoxytriphenylene (HMTP) on KBr(001) was investigated by atomic force microscopy in noncontact mode (NC-AFM) under ultrahigh vacuum at room temperature from submonolayer to multilayer coverage. This molecule is the first member of a new family of molecules, designed and synthesized for adsorption studies on alkali halide surfaces. They were built around a flat aromatic triphenylene core equipped with peripheral polar groups to enhance the interaction of the molecule with the surface in order to limit molecular diffusion at room temperature. Constant-frequency-shift NC-AFM imaging established the following adsorption sequence: The molecules decorate the KBr steps before forming two-molecular-layer-thick islands with a distorted hexagonal arrangement. At higher coverage, a second generation of much taller islands with the structure of the bulk HMTP crystal appears as a consequence of a dewetting transition, driven by the deformation energy accumulated in the first-generation islands during growth. High-resolution images obtained on top of these islands show submolecular contrast. These results will be useful in optimizing the next generation of molecules of this new family.

Influence of substrate morphology on growth mode of thin organic films: An atomic force microscopy study

Morphology of high-vacuum deposited thin films of pentacene and rubrene on annealed vicinal (0001) sapphire surfaces was studied by atomic force microscopy in non-contact mode. Pentacene molecules in the first monolayer form two-dimensional islands with an average height of 1.5nm. The majority of islands nucleate at the steps on the sapphire surface. Surface steps also act as nucleation sites for subsequent monolayers of pentacene. The terrace-and-step morphology of the substrate surface has a larger impact in the case of rubrene thin film growth. Rubrene grows in wire-like structures that follow the direction of the steps. In the case of rubrene films with a nominal thickness of 10nm, the typical widths and heights of the wires are 150 and 25nm, respectively. The separation between the wires is determined by the terrace width on the substrate surface. The difference in the morphology of pentacene and rubrene films may be explained by taking into account different geometries of the two molecules.

Fabrication of rubrene nanowires on vicinal (0 0 0 1) sapphire surfaces

Morphology of high-vacuum deposited rubrene thin films on the annealed (0 0 0 1) vicinal sapphire surfaces was studied by atomic force microscopy in non-contact mode. Atomic force microscopy images of rubrene thin films indicate that a regular array of steps on the sapphire surface acts as a template for the growth of the arrays of rubrene nanosize wires. To further demonstrate that morphological features of a substrate are crucial in determining the morphology of rubrene layers we have grown rubrene on the sapphire surfaces that were characterized by the terrace-and-step morphology with islands. We have found preferential nucleation of rubrene molecules at the intersection between a terrace and a step, as well as around the islands located on terraces.

Roughness of free surfaces of bulk amorphous polymers as studied by x-ray surface scattering and atomic force microscopy

The morphology of free surfaces of polyetherimide (PEI) samples has been characterized using atomic force microscopy in noncontact mode (NC-AFM), x-ray reflectivity (XRR), and x-ray diffuse scattering (XDS). PEI slabs have been prepared by molding pellets onto float glass. In order to characterize the roughness and morphology mathematically, we considered the surfaces as being self-affine with a rms roughness sigma and Hurst coefficient H up to a finite correlation length xi. NC-AFM topographs with sigma = 61 +/- 6.3 Angstrom showed the presence of blobs on the surface having a slight tendency to form clusters. These features are reflected in the height-height correlation function which shows the presence of strong'' short-range (xi(1) = 1064 Angstrom, H-1 = 0.46) and weak long-range (xi(2) = 14537 Angstrom, H-2 = 0.99) correlations. The detection of the specularly reflected contribution in XRR scans only gives access to sigma, the lateral fluctuations being averaged out over the coherence area. Scans in XDS include the detection of the diffuse (off-specular) scattering arising from lateral correlations in the surface fluctuations profile and are hence sensitive to sigma, xi and H. The XDS data have been analyzed by simultaneous fits using the distorted-wave Born approximation up to the first order. Calculations were performed using previously published approximations. Best fits to the experimental data provided strongly different correlations length values (7570 Angstrom less than or equal to xi less than or equal to 1245 Angstrom) indicating that the estimation of the latter by XDS is somewhat ambiguous. This is in agreement with the strong discrepancy between the correlation lengths determined with x rays and NC-AFM, which can be accounted for by the limits of the perturbation theory for interfaces with high rms roughnesses. [S0163-1829(99)04032-1].

Artefacts in non-contact mode force microscopy: the role of adsorbed moisture

Ordered layers of polystyrene spheres have been deposited on mica substrates. Analysis in air by atomic force microscopy, in the non-contact mode, has revealed image artefacts at vacancy sites and at edges of layers. These artefacts cannot be ascribed to the effects of simple convolution of the tip shape with the geometry of the surface features. Instead it is proposed that the origin must be with the interaction. Detailed first-principles calculation of synthetic images, on the assumption of a pure dispersion interaction arising from pairwise summation of R−6 terms, is found to reproduce the expected contours of constant average force gradient, but does not explain the artefacts. Additional results from measurements of force versus distance show that meniscus forces, due to adsorbed moisture, have the appropriate attributes to explain the artefacts — e.g., strength, localisation and hysteresis. The meniscus force has been taken into account; the results from an approximate model give contours of force gradient which are in qualitative agreement with those at artefact locations. It is concluded that the better-than-expected spatial resolution obtained in the non-contact mode can be due to the effects of the meniscus force.

Imaging and manipulation of nanometer-size liquid droplets by scanning polarization force microscopy

Using atomic force microscopy in noncontact mode, we have imaged nanometer-size liquid droplets of KOH water solutions on the surfaces of highly oriented pyrolitic graphite and mica. On graphite the droplets prefer to be adsorbed on atomic step edges. Droplets on the same step tend to be evenly spaced and of similar size. The droplets can be manipulated by the atomic force microscopy tip allowing the controllable formation of droplet patterns on the surface.