Wetting and superhydrophobic properties of PECVD grown hydrocarbon and fluorinated-hydrocarbon coatings

Wetting characteristics of micro-nanorough substrates of aluminum and smooth silicon substrates have been studied and compared by depositing hydrocarbon and fluorinated-hydrocarbon coatings via plasma enhanced chemical vapor deposition (PECVD) technique using a mixture of Ar, CH₄ and C₂F₆ gases. The water contact angles on the hydrocarbon and fluorinated-hydrocarbon coatings deposited on silicon substrates were found to be 72° and 105°, respectively. However, the micro-nanorough aluminum substrates demonstrated superhydrophobic properties upon coatings with fluorinated-hydrocarbon providing a water contact angle of ∼165° and contact angle hysteresis below 2° with water drops rolling off from those surfaces while the same substrates showed contact angle of 135° with water drops sticking on those surfaces. The superhydrophobic properties is due to the high fluorine content in the fluorinated-hydrocarbon coatings of ∼36 at.%, as investigated by X-ray photoelectron spectroscopy (XPS), by lowering the surface energy of the micro-nanorough aluminum substrates.     

Surface modification of doped ZnO thin films

Effects of photo-assisted electrodeless and ion RF-sputter etching on the structural and optical properties of sputtered ZnO:Al thin films were investigated. Photo-assisted electrodeless etching was appropriate for getting “smooth” surfaces and ion RF-sputter etching by high power has significantly modified the surface roughness with an increase of the light diffuse transmittance.     

Behaviour of discontinuous gold films on SrTiO3 substrates under annealing

Morphological changes of thin, discontinuous gold films on SrTiO₃ substrates, resulting from evaporation in the temperature range of 1143-1278 K, have been investigated by means of scanning electron microscopy (SEM) and atomic force microscopy (AFM). If the gold covered fraction of the surface is small, the evaporation kinetics can be related to the desorption of adatoms. Measuring the density of the gold beads and the time dependence of the effective thickness of the film as calculated from the diameter of the beads, the following parameters have been determined: the surface diffusion length of the gold adatoms, , the mass transfer surface diffusion coefficient, and the evaporation flux, .     

Factors affecting phase and height contrast of diblock copolymer PS-b-PEO thin films in dynamic force mode atomic force microscopy

Asymmetric PS-b-PEO block copolymer exhibits well-ordered cylindrical morphology with nanoscale domain sizes due to microphase separation. Since the PS and PEO blocks have large stiffness difference, this polymer system represents an ideal candidate for studies of the phase contrast behavior in atomic force microscopy (AFM). In this paper, PS-b-PEO films are investigated under different scanning conditions using two different atomic force microscopes. It is found that the phase contrast of the film can be well described in terms of energy dissipation, though the exact phase image may also depend on the scanning parameters (e.g., the repulsive versus attractive regimes) as well as the settings of the microscope. Height variation on sample surface does not have significant effect on phase contrast. However, in order to obtain true topography of the polymer film, care has to be taken to avoid damage to the sample by AFM. Under certain conditions, true topography can be obtained during the first scan in spite of the surface-damaging forces are used.     

Formation of AlN layer on (1 1 1)Al substrate by ammonia nitridation

AlN layers were formed on (1 1 1)Al substrates at a temperature below the melting point of Al using preheated ammonia in vacuum. The effect of the removal of the surface oxides on the substrate in the process was investigated. It was found that treatment using a buffered HF solution and subsequent annealing in vacuum was effective for obtaining a clean Al substrate surface. It was clarified that the removal of the surface oxides is required for the nitridation of Al substrates at a low temperature below the melting point of Al.     

Electronic structure and shearing in nanolaminated ternary carbides

We have studied shearing in M₂AlC phases (M=Sc,Y,La,Ti,Zr,Hf,V,Nb,Ta,Cr,Mo,W) using ab initio calculations. We propose that these phases can be classified into two groups based on the valence electron concentration induced changes in C₄₄. One group comprises M=V B and VIB, where the C₄₄ values are approximately 170 GPa and independent of the corresponding MC. The other group includes M=IIIB and IVB, where the C₄₄ shows a linear dependency with the corresponding MC. This may be understood based on the electronic structure: shear resistant bands are filled in M₂AlC phases with M=V B and VIB, while they are not completely filled when M=IIIB and IVB. This notion is also consistent with our stress-strain analysis. These valence electron concentration induced changes in shear behaviour were compared to previously published valence electron concentration induced changes in compression behaviour [Z. Sun, D. Music, R. Ahuja, S. Li, J.M. Schneider, Phys. Rev. B 70 (2004) 092102]. These classification proposals exhibit identical critical valence electron concentration values for the group boundary. However, the physical mechanisms are not identical: the classification proposal for the bulk modulus is based on MC-A coupling, while shearing is based on MC-MC coupling.     

Thresholds for radioemission under the initially cold electron beam interaction with a plasma

Generation of electromagnetic radiation under interaction of initially monoenergetic beam with collisionless plasma is studied experimentally. The threshold for EM radiation is found to be determined by the “indirect” collapse of beam excited Langmuir waves.     

Observation of triangle pits in PbSe grown by molecular beam epitaxy

PbSe thin films on BaF₂ (1 1 1) were grown by molecular beam epitaxy with different selenium beam flux. Evolution of PbSe surface morphologies with Se/PbSe beam flux ratio (R_f) has been studied by atomic force microscopy and high-resolution X-ray diffraction. Growth spirals with monolayer steps on PbSe surface are obtained using high beam flux ratio, R_f ≥ 0.6. As R_f decreases to 0.3, nano-scale triangle pits are formed on the surface and the surface of PbSe film changes to 3D islands when R_f = 0. Glide of threading dislocations in 〈1 1 0〉{1 0 0}-glide system and Pb-rich atom agglomerations are the formation mechanism of spiral steps and triangle pits. The nano-scale triangle pits formed on PbSe surface may render potential applications in nano technology.     

Effects of deposition temperature and thickness on the structural properties of thermal evaporated bismuth thin films

Bismuth (Bi) thin films of different thicknesses were deposited onto Si(1 0 0) substrate at various substrate temperatures by thermal evaporation technique. Influences of thickness and deposition temperature on the film morphologies, microstructure, and topographies were investigated. A columnar growth of hexahedron-like grains with bimodal particle size distribution was observed at high deposition temperature. The columnar growth and the presence of large grains induce the Bi films to have large surface roughness as evidenced by atomic force microscopy (AFM). The dependence of the crystalline orientation on the substrate temperature was analyzed by X-ray diffraction (XRD), which shows that the Bi films have completely randomly oriented polycrystalline structure with a rhombohedral phase at high deposition temperature (200 °C) and were strongly textured with preferred orientation at low deposition temperatures (30 and 100 °C).     

First principles study of the electronic structures of erbium silicides with non-frozen 4f treatment

The electronic structures (especially 4f states) of hexagonal and tetragonal erbium silicides are investigated within density functional theory. Contrary to previous theoretical studies on these compounds, Er 4f electrons are treated as valence state electrons, explicitly taking into account the on-site Coulomb interactions. Total energy calculations show that the relaxed hexagonal ErSi_1.7 is more stable than the tetragonal structure, consistently with related experimental observations. The calculated total density of states of the hexagonal ErSi_1.7 agrees well with the experimental valence-band spectrum in a wide energy range from 0 to 12 eV below the Fermi level. In addition, our study indicates that the occupied 4f states in erbium silicides can also locate in the energy range of 0–4.0 eV below the Fermi energy, much different from the prediction of the previously adopted Er ion model.