Surface Review and Letters

In order to arrange directionally, multi-wall carbon nanotubes (MWCNTs) are functionalized with ferromagnetic cobalt on the surface via the electroless plating method. The uniform and continuous cobalt coating was received in pH $=$ 9 at 45${}^{\circ }$C for 30min. It is found that the hydroxyl and carbonyl groups could be successfully introduced on the surface of raw MWCNTs after treated in boiling nitric acid that would provide the active points for cobalt deposition. The diameters of the cobalt (Co)-coated MWCNTs increase to 20–50nm from 8–15nm of purified ones. As a result of nanoscale cobalt coating, MWCNTs show strong ferromagnetism at room temperature. The Co-coated MWCNT respond to magnetic field susceptibly in the distilled water and arrange themselves in the direction of the applied magnetic field up to 1T. The hysteresis curve results show that the coercivity of Co-MWCNTs is 1285.2 Oe, which is about four times that of cobalt powder itself.

Multilayer diamond-like carbon film with germanium buffer layers, which was composed of several thick DLC layers and thin germanium island “layers” and named as Ge-DLC film, was prepared on the germanium substrate by ultraviolet laser. The Ge-DLC film had almost same surface roughness as the pure DLC film. Hardness of the Ge-DLC film was above 48.1GPa, which was almost the same as that of pure DLC film. Meanwhile, compared to the pure DLC film, the critical load of Ge-DLC film on the germanium substrate increased from 81.6mN to 143.8mN. Moreover, Ge-DLC film on germanium substrates had no change after fastness tests. The results showed that Ge-DLC film not only kept high hardness but also had higher critical load than that of pure DLC film. Therefore, it could be used as practical protective films.

In this paper, galvanized steel substrates were pre-treated in $\gamma$-(2,3-epoxypropoxy)propyl trimethoxy silane solutions containing salts ((NH${}_4{)}_2$TiF₆, K₂ZrF₆ and NaVO${}_3)$ and SiO₂. The surface microstructures of the coated substrates were evaluated by scanning electron microscopy (SEM). The anti-corrosion performance of the modified silane film applied on galvanized steel substrates was evaluated by potentio-dynamic polarization (Tafel) and electrochemical impedance spectroscopy (EIS). The electrochemical results reveal that the addition of salts ((NH${}_4{)}_2$TiF₆, K₂ZrF₆ and NaVO${}_3)$ may produce a more stable and protective fluoride combined with their oxides in the silane layer. The results also reveal that the addition of the SiO₂ nanoparticles reinforced the barrier properties of the silane films and imparted its corrosion inhibition ability.

The plasma electrolytic borocarbonitriding (PEB/C/N) process on pure iron was carried out in 25% borax solution with glycerine and carbamide additives under different discharge time at 360V. The morphology and structure of PEB/C/N hardened layers were analyzed by SEM and XRD. The hardness profiles of hardened layers were measured by microhardness test. Corrosion behavior of PEB/C/N layers was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Their wear performance was carried out using a pin-disc friction and wear tester under dry sliding test. The PEB/C/N samples mainly consisted of $\alpha$-Fe, Fe₂B, Fe₃C, FeN, FeB, Fe₂O₃ and Fe₄N phases, and the Fe₂B phase was the dominant phase in the boride layer. It was found that the thickness of boride layer increased with the discharge time and reached 14$\mu$m after 60min treatment. The microhardness of the boride layer was up to 2100HV, which was much higher than that of the bare pure iron (about 150HV). After PEB/C/N treatment, the corrosion resistance of pure iron was slightly improved. The friction coefficient of PEB/C/N treated pure iron decreased to 0.129 from 0.556 of pure iron substrate. The wear rate of the PEB/C/N layer after 60min under dry sliding against ZrO₂ ball was only 1/10 of that of the bare pure iron. The PEB/C/N treatment is an effective way to improve the wear behavior of pure iron.

A novel method named soak sacrificial layer ultrasonic method (SSLUM) has been presented for optimizing the surface roughness of the microchannels of polymethyl methacrylate (PMMA)-based microfluidic chips. CO₂ laser was used for ablative microchannels on the PMMA sheet, and the effects of key parameters including laser power, laser ablation speed and solution concentration on the surface roughness of microchannels were estimated and optimized by SSLUM. The experimental observation demonstrates that the surface roughness results mainly from the residues on the channel wall, which are produced by the bubbles movement and bursting. The research results show that the surface roughness can be improved effectively by using SSLUM. In our experiment, the best value was Ra $=$ 110nm with laser power 12W, laser ablation speed 10mm/s, the solution concentration 75%, and the time of ultrasonic vibration 25min. SSLUM is proven to be an effective, simple and rapid method for optimizing the surface roughness of microchannels of microfluidic chips.

Nowadays, composites are used in different parts of industries and it is one of the most important subjects. The most widely used reinforcements in metal matrix composites are Al₂O₃ and SiC fibers and particles which may be used in cutting-edge functional and structural applications of aerospace, defense, and automobile industries. Depending on the type of powder used, composite materials are difficult to machine by conventional cutting tools and methods. The most appropriate way for machining of these composites is electro discharge. For the reason of improving the surface quality, tool wear rate and material removal rate and reducing the cracks on the surface, Al₂O₃ powder was used. In this study, the effect of input parameters of EDM such as voltage, pulse current, pulse on-time and pulse off-time on output parameters like material removal rate, tool wear rate and surface roughness in both conditions of the rotary tool with powder mixed dielectric EDM and the stationary tool excluding powder mixed dielectric were investigated. The critical parameters were identified by variance analysis, while the optimum machining parameter settings were achieved via Taguchi method. Results show that using of powder mixed dielectric and rotary tool reduce the tool wear rate, surface roughness and the cracks on the surface significantly. It is found also that using of powder mixed dielectric and rotary tool improve the material removal rate due to improved flushing action and sparking efficiency. The analysis of variance showed that the pulse current and pulse on-time affected highly the MRR, TWR, surface roughness and surface cracks.

Homoepitaxial growth film for (001), (110) and (111) Ni substrates is investigated by means of molecular dynamics (MD) simulation. Embedded atom method (EAM) is considered to represent the interaction potential between nickel atoms. The simulation is performed at 300K using an incident energy of 0.06eV. In this study, the deposition process is performed periodically and the period, $n$, is relative to a perfect layer filling. The coverage rate of the actual expected level, $L_{(n)}$, can be considered a determinant for thin-film growth of nickel. The $L_{(n)}$ level is the most filled level during the deposition on (001) substrate, while it is the less filled one in the case of (111) substrate. Moreover, the upper level is the one which is responsible for the surface roughness and the appearance time of an upper layer may also be a factor influencing the surface roughness. The deposition on (111) substrate induces the most rigorous surface with a rapid appearance time of the upper layers. The $L_{(n-1)}$ layers are almost completely filled for all substrates. The $L_{(n-2)}$ and lower layers are completely filled for (001) and (110) substrates while for (111) substrate the completely filled layers are $L_{(n-3)}$ and lower ones.

The electronic band structure, density of states (DOS) and interlayer interaction in Li-intercalated graphene bilayers are studied by means of density functional theory (DFT) calculations. It has been found that for a pristine bilayer, the relative shift of graphene layers from AB stacking configuration, pertinent to a bulk graphite, to AA configuration results in the opening of the bandgap at Fermi level, so that the bilayer becomes a semiconductor. The Li intercalation of the graphene bilayer significantly increases the density of states at Fermi level, which can be considered as an increased metallicity. The electronic density in the space between graphene layers also substantially increases and leads to related increase of the interlayer interaction. We hope that the obtained results of calculations will be useful for various applications of Li-intercalated graphene layers in nanoelectronics.

Holmium (Ho)-doped AlN thin films of thicknesses 60, 90 and 300 nm were grown in pure nitrogen atmosphere via RF magnetron sputtering. The deposited thin films were irradiated with protons at a dose of 5$\times$10${}^{14}$ ions/cm² and the effects of irradiation on structural, magnetic and electrical characteristics of thin films were investigated. Rutherford backscattering spectroscopy (RBS) confirmed the presence of Al, N and Ho in prepared samples. X-ray diffraction analysis showed that crystallinity of the thin films was enhanced after irradiation and thicker films were more crystalline. Atomic force microscopy (AFM) revealed that the surface roughness and porosity of the thin films were increased after irradiation. Magnetic measurements showed that diamagnetic AlN:Ho thin films can be transformed into paramagnetic and ferromagnetic ones via suitable irradiation. The increase in carrier concentrations after irradiation was responsible for tuning the electrical and magnetic characteristics of thin films for applications in various high voltage microelectronic and magnetic devices.

In this article, Magnetohydrodynamic (MHD) squeezing flow between two parallel disks is considered. The upper disk is taken to be solid and the lower one is permeable. Soret and Dufour effects are measured to explore the thermal-diffusion and diffusion-thermo effects. Governing PDEs are converted into system of ODEs with the support of suitable similarity transforms. Homotopy analysis method (HAM) has been employed to obtain the expressions for velocity, temperature and concentration profiles. Effects of different emerging parameters such as squeezing number $S$, Hartman number $M$, Prandtl number Pr, Eckert number Ec, dimensionless length $\delta$ and Schmidt number Sc on the flow are also discussed with the help of graphs for velocity, temperature and concentration. The local Nusselt and Sherwood numbers along with convergence of the series solutions are presented with the help of graphs. From the results obtained, we observed that the physical quantities like skin friction coefficient increases with increasing value of Hartmann number $M$ in the blowing case $(A<0)$ whereas a fall is observed in the suction case $(A>0)$. However, the rate of heat transfer at upper wall increases with increasing values of Dufour number Du and Soret number Sr for both the suction $(A>0)$ and blowing flow $(A<0)$, whereas, for the larger values of Dufour number Du and smaller values of Soret number Sr, a rapid fall is observed in Sherwood number Sh for both the suction $(A>0)$ and blowing $(A<0)$ cases. A numerical solution is obtained by employing Runge–Kutta method of order four (RK-4) to check the validity and reliability of the developed algorithm. A well agreement is found between both the solutions.

The wear behavior of nanostructured hypoeutectic Fe${}_{94.3}$B${}_{5.7}$ alloy was investigated in comparison with coarse grained counterpart. The friction coefficient of the Fe${}_{94.3}$B${}_{5.7}$ alloy changed slightly with grain size. While the wear rate decreased as the grain size decreased to nano scale. Both Fe₂O₃ and Fe₂SiO₄ oxides were found on the worn surfaces in the nanostructured Fe${}_{94.3}$B${}_{5.7}$ alloy, but only a few oxide films were observed for the coarse grained counterpart. These results suggested that the nanostructured eutectic was conducive to forming oxide films on the worn surface of the Fe${}_{94.3}$B${}_{5.7}$ alloy, and improved the wear resistance.

The synergism of CeCl₃ (Ce) with cysteine (Cys) on the corrosion of P110 carbon steel in 3% NaCl solutions was investigated by electrochemical methods and surface analysis. The results showed that CeCl₃ and cysteine do little to inhibit the corrosion of carbon steel, but the combination of CeCl₃ with cysteine has obvious synergistic effect on the corrosion of carbon steel and the corrosion inhibition efficiency was improved significantly. The potentiodynamic polarization curves indicated that the mixture of CeCl₃ and cysteine acts as a cathodic inhibitor. Scanning electron microscope (SEM) and Infrared (IR) reflection spectra showed the synergistic inhibition effect was formed by the complexes between rare earth Ce(III) ion and amino acid.

For lithium–ion batteries, the composite silicon-based electrodes can prevent from losing electrical contact and hence retain the capacity over many cycles. To uncover the adhesion mechanism on the interface formed by the copper foil and the thin silicon coatings during the cold gas dynamic spraying (CGDS) at the microscopic level, the first-principle calculations are performed to investigate the interface properties between them. The ideal work of adhesion, fracture toughness and the interface electronic properties are analyzed. It is found that all the atoms on the interface have vertical displacements, and covalent and ionic bonds are formed between the interfacial Cu and Si atoms which increases the bonding strength. However, the ideal work of adhesion on the interface is lower than one of the Cu bulk and Si bulk, so that fracture would be easier to take place on the interface.

The photoelectrochemical cell attracts attention worldwide due to conversion of optical energy into electricity, production of hydrogen through water splitting and use in photodetector and photo-sensor applications. We have been working on the photochemical cell based on regioregular polyhexylthiophenes hybrid-structured films for photoelectrochemical and photovoltaic applications. This paper discusses the hybrid film studies on regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) with 2D molybdenum disulfide (MoS₂) for photoelectrochemical cell. The hybrid P3HT/MoS₂ films deposited over indium tin oxide (ITO)-coated glass plate or n-type silicon substrates were characterized using FTIR, UV/vis, electrochemical and scanning electron microscopy (SEM) techniques. The optical measurements showed a higher absorption magnitude with low reflection properties of P3HT/MoS₂ hybrid films revealing a superior photocurrent compared to both P3HT and MoS₂ films. The P3HT/MoS₂ hybrid-based photoelectrochemical cell yielded a short-circuit current ($I_{\mathrm{\text{sc}}}$) of 183.16$\mu \mathrm{\text{A}}\cdot {\mathrm{\text{cm}}}^{-2}$, open-circuit voltage ($V_{\mathrm{\text{oc}}}$) of 0.92V, fill factor (FF) of 25% and power conversion efficiency ($\eta$) of 0.18% under the light intensity of 242W$\cdot {\mathrm{\text{m}}}^{-2}$. The estimated power conversion efficiency and fill factor are comparable to organic-based photovoltaic devices.