Surface Review and Letters

The surface modification mechanism of polyvinyl chloride (PVC) by ozonation was investigated to study the selective hydrophilization of PVC surface among other plastics. Infrared analysis confirmed the increase of hydrophilic groups. XPS analysis revealed that the increase was due to the structural change in chlorine group in PVC to hydroxylic acid, ketone, and carboxylic groups by ozonation. This chemical reaction by ozone could occur only for polymers with chlorides in its structure and resulted in the selective hydrophilization of PVC among various polymers.

The processes of nickel electrodeposition on Pt/Si(100) substrate from an aqueous sulfate, Watts, and chloride solution have been studied using electrochemical techniques and atomic force microscopy (AFM). It was found that hydrogen evolution reaction (HER) was shifted more cathodically and the nickel electrodeposition obeys to inhibition process, caused by adsorbed species in surface substrate. At early stage of the deposition chronoamperometric results were compared with Sharifker and Hills theoretical model. The nucleation was in agreement with progressive mode followed by 3D diffusion growth mechanism. The nucleation is generally slow at low over potentials, in all studied baths. AFM images show distribution nickel clusters, with different sizes.

Dipole–exchange spin waves (SWs) are studied in ferromagnetic nanostructures with spherical geometries such as spheres, part spheres, and spherical shells, both individually and in finite-sized arrays. A microscopic theory is used based on a spin Hamiltonian, which incorporates the short-range exchange and long-range magnetic dipole–dipole interactions, as well as an external magnetic field applied in any direction. Our theory is advantageous for describing the dynamical properties of inhomogeneously magnetized samples, and the use of phenomenological boundary conditions is avoided. Numerical results are deduced for the frequencies of the discrete SW modes and their dependence on the radius, spacing between particles, applied field, etc. Applications are made to Permalloy Fe₁₉Ni₈₁ and alloy Co₈₀Ni₂₀ nanoparticles with their sizes varying from 10 to 100 nm. Through a Green function theory, the spatial distributions and spectral intensities of the SWs are also deduced. The mode-mixing (hybridization) effects on the SW branches are found to be important, depending on the particle sizes and geometries.

To bridge the structure gap, electrochemical reactions can be studied in flow cells with nm-sized catalyst particles deposited or fabricated on the cell walls. The understanding of the role of mass transport in such cells is now limited. To clarify the likely effects in this field, we analyze the simplest reaction scheme including intermediate desorption, readsorption, and subsequent reaction and show how the net rate of the formation of intermediate can be influenced by its diffusion in the liquid phase. With certain approximations, we derive analytical results describing reaction and diffusion near catalyst particles and in more remote regions in the simplest 1D case and more complex 2D and 3D situations.

In this work, Ni₈₀Fe₂₀/Cu composite wires of length 50 mm, consisting a Cu core of diameter 100 μm, coated with a layer of Ni₈₀Fe₂₀, were produced by RF magnetron sputtering. To obtain a uniform coating, the wires were spun during sputtering by a homemade system. The results showed that the spinning speed might affect the maximum MI ratio and the magnetic properties. The MI ratio of the sputtered wires increases with the wire spinning speed in the magnetron sputtering. The film thickness had a significant effect on the magnitude and the optimum frequency of the giant magneto-impedance effect. The maximum MI ratio can reach about 247.4% for the specimen with a Ni₈₀Fe₂₀ coating thickness of 2.81 μm at 400 kHz. This large MI effect, obtained at such low frequency range, was correlated with the electromagnetic interaction between the inner core and the magnetic coating.

Recently, gold nanoparticles (AuNPs) were reported to increase the specificity and efficiency of the polymerase chain reaction (PCR). In this paper, we tested the enhancement of AuNPs with five different sizes on the specificity of two-round PCR. The results showed that, except 5.02 nm AuNPs, the AuNPs that could achieve the similar enhancement happened to have nearly the same total surface area. The surface effect seems to be the key factor of nanogold-assisted PCR.

Patterning materials on hydrophobic polymer substrates have extensive applications in fabricating flexible devices at low cost, while the low transfer efficiency encumbers its advance. This paper provides a facile route to transfer materials onto hydrophobic polymer substrates with high efficiency by operating in organic solvent atmosphere. Under the assistance of condensed organic solvent layer on the substrate, bovine serum albumin (BSA) are desirably transferred onto untreated hydrophobic polymer substrates, such as poly(dimethylsiloxane) (PDMS), polystyrene (PS), and poly(ethylene terephthalate) (PET) as a proof-of-concept experiment. Moreover, the combination of this method with stepwise contraction and adsorption nanolithography (SCAN) was also demonstrated as an alternative way to further miniaturize patterns prepared by other methods.

The oscillatory behavior during partial oxidation of methane was studied by the Monte Carlo simulation with Langmuir–Hinshelwood mechanism and oxide formation and removal. The well-developed reaction rate oscillations can be observed when the CH₄ adsorption probability varies in a small window. The oscillation window is very sensitive to the variation of reaction temperature. When the temperature increases, the window for sustained oscillation becomes narrow and has an obvious shift. In the meantime, the oscillation period tends to become small and the amplitude decreases. When the temperature increases to a certain value, the oscillations will disappear.

Possibility of cubic structures in small manganese (Mn) clusters has been studied using the linear combination of Gaussian orbitals (LCGO) method. Local spin density approximation is adopted for the exchange correlation potential. Both high-spin and low-spin states are found for Mn₁₃ and Mn₁₉ clusters with the face-centered cubic symmetry; however, no equilibrium lattice constant could be found. For Mn₉ and Mn₁₅ clusters with the body-centered cubic symmetry, only high-spin states are found. No equilibrium lattice constant could be found for bcc Mn₉; however, a weak possibility of bcc structure in Mn₁₅ is found. The calculated magnetic moment of Mn₁₅ is, however, found to be too large compared with the experimental result.

Nanocomposite nc-ZrCN/a-C:H(N) films were prepared by filtered cathodic vacuum arc technique using the C₂H₂ and N₂ gas as the precursor. The effect of the C₂H₂ and N₂ flow rate on the microstructure, internal stress, phase composition, and mechanical properties of nanocomposite nc-ZrCN/a-C:H(N) films has been investigated by glancing incidence X-ray diffraction (GIXRD), surface profiler, and X-ray photoelectron spectroscopy(XPS). It was revealed that the C₂H₂ and N₂ flow rate affected the structure, Zr content, and internal stress of the films significantly. Furthermore, XRD pattern indicated the presence of the ZrCN crystalline grains in the range of 3–10 nm, and the deconvolution results for XPS spectra showed that the film mainly was constituted by Zr–C, C=C(sp2) and C–C(sp3) bonds.

The effects of the roughness of ZnS underlayer on the microstructure, optical, and electrical properties of nanometer Ag thin film have been investigated in this paper. Nanometer Ag thin films in glass/ZnS/7.5 nm Ag/30 nm ZnS stacks have been deposited and analyzed. In the stacks, the underlayers of ZnS have been sputtered with various thicknesses to generate various surface roughnesses. The X-ray diffraction (XRD) has been used to study the crystal structure of Ag films. The surface topography and the roughness of ZnS underlayer have been analyzed by atomic force microscopy. The sheet resistant will become larger as the increasing of the roughness. The optical constants can be derived by fitting the transmission and reflectance spectrum. From optical constants comparison of Ag films, with the surface of the stack becoming rougher, it was found that the refractive index will increase but the extinction coefficient will decrease.

The MoS₂ particles were coated with polystyrene and can be written as PS/MoS₂ hereinafter. Ni–PS/MoS₂ coatings and Ni–MoS₂ coatings were produced by PC electrodeposition technique. The surface morphology of Ni–PS/MoS₂ coating was examined and compared with those of Ni–MoS₂ coating. The effect of particle concentrations on the volume percent of particles incorporated in the coatings was investigated. And the microhardness of coatings was also investigated. Results show that the surface morphology of Ni–PS/MoS₂ coating is regular and the thickness of coating is uniform. The introduction of MoS₂ to coatings caused dendritic growth. The surface morphology of Ni–MoS₂ coating is irregular. With the same particles concentration in bath, the volume percent of PS/MoS₂ particles incorporated in the composite coatings was higher than those of MoS₂ particles; and the microhardness of Ni–PS/MoS₂ coating was higher than those of Ni–MoS₂ coating.

Ce-doped Bi₂Ti₂O₇ thin films have been successfully prepared on P-type Si substrates by a chemical solution deposition method. The structural properties of the films were studied by X-ray diffraction. The phase of Ce-doped Bi₂Ti₂O₇ was more stable than that of Bi₂Ti₂O₇ without Ce substitution. The films exhibited good insulating properties at room temperature. The dielectric constant of the films annealed at 700°C at 100 kHz was 168 and the dissipation factor was 0.038. All these results showed that Ce-doped Bi₂Ti₂O₇ thin films could be used as storage capacitors in DRAM and MOS.

There exists an optimal amount of solvent (generally water) that can be added to the slurry phase reaction between solid reactants; the reactivity and efficiency of such reactions are different from those without solvent or those with large amount of solvent. Obviously, the solvent plays a crucial role in the process of the reaction, and it is the key to the understanding of unique reactivity and high efficiency of such slurry phase reactions. The water molecule absorbed on the surface of solid reactants, which is called bound water, has uniquely different properties compared with bulk water. Surface hydroxylation resulting from bound water greatly influences the chemical activity of the surface, which could be playing a role as catalyst or as the initialization point for further reactions, so that the reactants can react easily and fast under a simple reaction condition.

Ceramic coatings have been synthesized on 6063 aluminum alloy by micro-arc oxidation (MAO) technique. The effects of current intensity on the chemical and mechanical properties of MAO coatings have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), micro-hardness test, adhesion measurement, and friction and wear tests. The fabricated samples consist mainly of α-Al₂O₃ and γ-Al₂O₃ phases. SEM results show that the surface of the prepared coatings is dense except some pores distributed over the coating surface. Mechanical measurements show that these kinds of samples have high hardness, excellent adhesion, and high friction resistance. The coating consists of a thin buffer layer at the metal surface followed by a relatively compact inner layer and finally a higher porous ceramic layer. Meanwhile, there is a nonuniform distribution of hardness for the samples in the plane parallel to the substrate.

TiC-based wear resistant coating was prepared by plasma spraying using reconstituted composite powders doped with ultra-fine carbide. Phase composition and microstructure of as-sprayed coating were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) utilizing backscattered imaging mode (BSE), and electron probe micro-analysis. Wear test was performed by using a ring-on-block tester under dry sliding condition. Results show that the coating adheres well to the substrate and no delamination appears. TiC content underwent pronounced reduction because of oxidation, reaction, and physical loss. Reactions between TiC and Mo and probably between dissociated C and Mo lead to the formation of Mo₂C. Wear resistance of NiCrMo–TiC coating is about 4–8 times higher than that of substrate under different applied force. This work shed light on the reconstitution of spraying powder doped with ultra-fine reinforce phase particles, and the present results are important for the preparation of nano-doped TiC-based coatings.

An improved chemical bath deposition (CBD) technique has been provided to prepare zinc sulfide (ZnS) thin films on glass substrates deposited at 80–82°C using a mixed aqueous solution of zinc sulfate, ammonium sulfate, thiourea, hydrazine hydrate, and ammonia at the alkaline conditions. Both the traditional magnetic agitation and the substrates vibration by hand frequently were done simultaneously during the deposition. The substrates vibration reduced the formation and residence of gas bubbles on the glass substrates during growth and resulted in growth of clean ZnS thin films with high quality. Ammonia and hydrazine hydrate were used as complexing agents. It is found that hydrazine hydrate played an important role in growth of ZnS films. The structure and microstructure of ZnS films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV-vis spectroscopic methods. The XRD showed a hexagonal structure. The formed ZnS films exhibited good optical properties with high transmittance in the visible region and the band gap value was estimated to be 3.5–3.70 eV.

The critical thickness of structural transition from a tetragonal structure to a normal bulk structure for epitaxial ultrathin films deposited on the metallic and semiconductor substrates is thermodynamically considered. It is found that equilibrium between the elastic energy of the tetrahedral structure and the film–substrate interface energy is present when a critical thickness is reached. The predictions of the critical thickness are in agreement with the experimental results of films.

The properties of the cotton fabric with water-repellence finishing by sol method with the hexadecyltrimethoxysilane as additive were observed. The cotton fabrics were immersed in the prepared sols with double dip and double nip dried at 90°C, annealed at 160°C for 3 min. The water repellence and the physical properties such as gas permeability, bending properties, beetling properties, tensile strength, elongation at break, abrasion resistance, and anti-crease properties of the cotton fabrics were investigated. The results showed that anti-crease and tensile strength were improved. However, the abrasion resistance of the cotton fabrics decreased in some way. Both the bending and beetling properties measurement proved that the handle of the treated cotton fabrics changed stiffness. For the dyed fabrics by the water-repellent finishing, the hue was slightly changed, the deeper color was achieved. There is no adverse effect for treated fabric by water-repellent finishing on the fastness.

The formation of a minimum ice unit (MIU) and ice crystal is simulated. The simulation indicates that an MIU is made up of 10 H₂O molecules, and the MIU shows a four-hexagon cage structure. On the basis of simulation, we can calculate that 1 mol ice crystal contains 2 mol hydrogen bonds, and 16.67% hydrogen bonds should be broken during water fusion at 0°C. A total of 12.5% hydrogen bonds should be broken when 1 mol water is heated from 0°C to 100°C, and 70.83% hydrogen bonds should be broken when 1 mol water is vaporized into steam at 100°C. A total of 8.33% volume contract during water fusion at 0°C can also be calculated according to the MIU simulation in this paper.

The electrochemical formation and reduction of O-layers on gold (111) films in 1 m sulfuric acid under different potentiodynamic routines are investigated utilizing in situ scanning tunneling microscopy. The surface dynamics is interpreted considering the anodic and cathodic reaction pathways recently proposed complemented with concurrent relaxation phenomena occurring after gold (111) lattice mild disruption (one gold atom deep) and moderate disruption (several atoms deep). The dynamics of both oxidized and reduced gold topographies depends on the potentiodynamic routine utilized to form OH/O surface species. The topography resulting from a mild oxidative disruption is dominated by quasi-2D holes and hillocks of the order of 5 nm, involving about 500–600 gold atoms each, and their coalescence. A cooperative turnover process at the O-layer, in which the anion ad-layer and interfacial water play a key role, determines the oxidized surface topography. The reduction of these O-layers results in gold clusters, their features depending on the applied potential routine. A moderate oxidative disruption produces a surface topography of hillocks and holes several gold atoms high and deep, respectively. The subsequent reduction leads to a spinodal gold pattern. Concurrent coalescence appears to be the result of an Ostwald ripening that involves the surface diffusion of both gold atoms and clusters. These processes produce an increase in surface roughness and an incipient gold faceting. The dynamics of different topographies can be qualitatively explained employing the arguments from colloidal science theory. For 1.1 V ≤ E ≅ E_pzc weak electrostatic repulsions favor gold atom/cluster coalescence, whereas for E < E_pzc the attenuated electrostatic repulsions among gold surfaces stabilize small clusters over the substrate producing string-like patterns.

Localization of surface plasmons polariton is reviewed in the context of experiments and modeling of near-field optical images. Near-field imaging of elastic (in-plane) surface plasmon scattering is discussed, and approaches for the correct image interpretation are outlined. Nonlinear effects related to localized surface plasmons are pressented. Surface plasmon localization opens up numerous possibilities for application in biosensing, nanophotonics, and in general in the area of surface optics properties.

Au/Cu thin films (33–320 nm thickness) were deposited by thermal evaporation on p-type silicon (100) substrates. Two groups of these bimaterial films were alloyed into a vacuum oven by diffusion. The first group was prepared with 24% Au atomic concentration (i.e. 33, 96, 158, 224, and 320 nm as AuCu total thickness). The second group was prepared changing the Au atomic concentration from 10% to 90%, with 10% Au steps and similar total thickness (100 nm). Prepared alloys were characterized with atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and collinear four-probe techniques in order to obtain their morphology, stoichiometry, crystalline structure, and electrical resistivity, respectively. Particularly, electrical resistivity presented abrupt changes with the atomic concentration and the annealing temperature with important differences as compared with pure Au and Cu thin films.

This paper reports the π–A isotherm and spectroscopic characterizations of mixed Langmuir and Langmuir–Blodgett films of a nonamphiphilic thiophene derivative, namely, 2,5-Bis (5-tert-butyl-benzoxazolyl)-thiophene (BBOT) molecules, mixed with polymethyl methacrylate (PMMA) and stearic acid (SA). The π–A isotherms and molefraction vs. area per molecule studies indicate some repulsive interaction between sample (BBOT) and matrix (PMMA or SA) molecules. At higher surface pressure in the SA mixed BBOT Langmuir monolayer, a phase transition occurs, which has been revealed by π–A isotherm studies. UV-vis absorption and fluorescence spectroscopic studies confirm this phase transition and closer association of BBOT molecules. Spectroscopic studies of LB films lifted at higher surface pressure clearly confirm the presence of dimmers and higher-order n-meric sites.

Porous silicon (PS) layers have been prepared from n-type silicon wafers of (100) orientation. SEM, FTIR, and PL have been used to characterize the morphological and optical properties of PS. The influence of varying light illumination in the anodizing solution, on structural and optical properties of PS, has been investigated. It is observed that pore size increases with light illumination level, attains maximum for 17.5 mW/m² and then decreases. The PL spectrum peak shifts toward the higher energy side, which supports the quantum confinement effect in PS. The FTIR shows that the Si–H_n peaks are observed at the surface of the PS layer and these chemical species also give raise the PL in PS.

The inhibitive effect of 2,3-diaminonaphthalene (2,3-DAN) for corrosion of aluminum in 1 M HCl was investigated using hydrogen evolution technique at 30 and 40°C. Quantum chemical calculation results showed that 2,3-DAN molecule possessed planar structure with a number of active centers, which aided the adsorption process. The Mulliken charge density, the highest occupied molecular orbital (HOMO), and the lowest unoccupied molecular orbital (LUMO) were found mainly focused around nitrogen atoms and the cyclic of the benzene as well. The presence of 2,3-DAN molecules in the corrosive medium (1 M HCl solution) inhibits the corrosion process of aluminum and as the concentration of 2,3-DAN increases the inhibition efficiency also increases but decreases with rise in temperature. The corrosion inhibition of 2,3-DAN was discussed in terms of blocking of the Al surface by adsorption of the molecules of the inhibitor at the active centers. It was found that the adsorption of 2,3-DAN onto the Al surface followed the Langmuir adsorption isotherm and 2,3-DAN adsorbed on Al surface probably by physisorption. The proposed physisorption mechanism was supported by the calculated values of E_a, Q_ads, and ΔG_ads.

An infrared CO₂ laser was used for regional heating to study the heating effect on hot filament chemical vapor deposition of diamond-like carbon formation on Si(100) face substrates. The substrate surface temperature was about 450–500°C. The power of the laser called low, medium, and high raised the temperature of the substrate locally by 25, 45, and 55°C, respectively. At medium laser power, at the central laser beam region, a narrow Raman peak centered at 1438 cm^-1 was detected. It can be concluded that this region has good-quality DLC. This moderate high-frequency peak corresponds to a fourfold-rotation-symmetry atom in an amorphous carbon network from the tight-binding molecular dynamics simulation of Wang and Ho.

The tribo-performance of a new engineering composite material based on coconut fibers was investigated. In this work, coconut fibers reinforced polyester (CFRP) composites were developed. The tribo-experiments were conducted by using pin-on-disc machine under dry and wet sliding contact condition against smooth stainless steel counterface. Worn surfaces were observed using optical microscope. Friction coefficient and specific wear rate were presented as a function of sliding distance (0–0.6 km) at different sliding velocities (0.1–0.28 m/s). The effect of applied load and sliding velocity was evaluated. The results showed that all test parameters have significant influence on friction and wear characteristics of the composites. Moreover, friction coefficient increased as the normal load and speed increased, the values were about 0.7–0.9 under dry contact condition. Meanwhile, under wet contact condition, there was a great reduction in the friction coefficient, i.e. the values were about 0.1–0.2. Furthermore, the specific wear rates were found to be around 2–4 (10^-3) mm³/Nm under dry contact condition and highly reduced under wet condition. In other words, the presence of water as cleaner and polisher assisted to enhance the adhesive wear performance of CFRP by about 10%. The images from optical microscope showed evidence of adhesive wear mode with transition to abrasive wear mode at higher sliding velocities due to third body abrasion. On the other hand, optical images for wet condition showed less adhesive wear and smooth surfaces.