Surface Review and Letters

Damage on the mask surface caused by charging effect during plasma etching process continues to attract much attention currently. For example, the round shape of holes can be changed into hexagonal shape. In our previous paper, the reason for this phenomenon has been explained through a particle simulation approach [P. Zhang et al., Plasma Sci. Technol. 15 (2013) 570]. However, it has been observed that the round shape of holes in a mask can also be etched into an asymmetric shape due to factors such as nonuniform plasma source, inclination or vibration of sample platform, etc. This work further aims to explore the charging effect when the round-shaped holes in a mask have been changed into asymmetric-shaped ones by particle simulation method. The distribution of electric field produced by electrons was calculated for different shaped isolated holes (round, hexagonal and asymmetric shapes) in a mask as well as various heights from the mask surface. It is found that the field strength reaches its maximum around a hole edge and presents uniform distribution for the round hole and nonuniform distribution for the hexagonal- and asymmetric-shaped holes. The nonuniform electric field distribution can affect the trajectories of ions falling on the mask surface, further enhancing the asymmetry of the mask hole shape. Additionally, the charging effect on a mask of asymmetric holes aligned in a hexagonal array is also studied. It is found that due to the alignment of holes, the charging effect is quite different from the case in an isolated hole.

Indium-doped cadmium oxide nanocrystals are examined using experimental and theoretical techniques. Raman, UV–Vis, and XRD facilities are used to examine Indium-doped CdO nanostructures with three doping ratios 2%, 4% and 6% weight percentages. Density functional theory (DFT) is used to check and compare lattice constants, energy gaps, and Raman vibrational properties. The presently suggested cages for the cubic rock-salt structured clusters adopted by CdO are called cuboids. These cuboids are investigated in bare, and hydrogen surface passivated cases. Experimental results of In-doped CdO show an increase of lattice constants and energy gap. The same trend is observed using density functional theory calculations. The experimental longitudinal optical Raman peak at 556cm${}^{-1}$ encounters blue shifting to 561.5 cm${}^{-1}$ at 6% weight percentages In doping. This result is in the same trend using DFT calculations of In-doped CdO hydrogen passivated tetracuboid molecular cluster that shifted from 510.2cm${}^{-1}$ to 531.3cm${}^{-1}$ upon In doping. No Burstein–Moss effect is observed by the theoretical model.

The gas response of metal oxide-based sensors depends strongly on its adsorption properties. To explore the potential sensing capability of pristine and nitrogen modified TiO₂/graphene oxide (GO) heterostructures, the adsorption of NO₂ molecule on the N-doped nanocomposites was investigated using density functional theory (DFT) calculations. Six possible configurations were simulated based on the estimated adsorption energies. The binding sites were located over the oxygen, doped nitrogen and five-fold coordinated titanium atoms of TiO₂. The electronic properties including atomic Mulliken population, projected density of states and molecular orbitals were investigated in detail. The N–O bonds of the NO₂ molecule were significantly increased after the adsorption process. The adsorption of NO₂ molecule on the N-doped nanocomposite is more energetically favorable than the adsorption on the undoped one. The results suggest that NO₂ chemisorbs on the considered nanocomposites. Mulliken population analysis reveals a noticeable charge transfer from the nanocomposite to the molecule, which indicate that NO₂ acts as a charge acceptor. Molecular orbital calculations show that the highest occupied molecular orbitals (HOMOs) of the studied systems were mainly localized on the adsorbed NO₂ molecule. The significant overlaps in the projected density of states (PDOS) spectra of the interacting atoms confirm the formation of chemical bonds between them. There is a direct relationship between the results of charge transfer and sensing responses. N-doped nanocomposites have better sensing response than the undoped ones. The results highlight the possibility to develop innovative highly efficient NO₂ sensors based on novel TiO₂/GO nanocomposites.

We present a theoretical investigation of wetting and prewetting phenomena in a nematic-disk like droplet under a concentric anchoring configuration. Our theoretical model is based on Landau–de Gennes free energy together with a quadratic surface energy. By using the Maxwell construction, we numerically solve the Euler–Lagrange differential equation. The occurrence of boundary layer transition is summarized in the phase diagram scanned by temperature and surface potential. We find that prewetting phenomenon disappear below a critical droplet size and critical temperature.

Density functional theory combined with Gibbs free energy calculations is used to study the sensing behavior of tin dioxide (SnO${}_2)$ clusters towards chlorine gas molecules. Studied SnO₂ clusters’ results show the known property of tin dioxide being an oxygen-deficient semiconductor with the preferred stoichiometry SnO${}_{1.8}$. The kind of reactions that result in sensing Cl₂ molecules is investigated. These include oxygen replacement, chlorine molecule dissociation and van der Waals attachment. Oxygen replacement shows an increase in energy gap which is the case experimentally. Optimum sensing operating temperature towards Cl₂ molecules that results from the intersection of the highest SnO₂ adsorption and desorption Gibbs free energy lines is at 275^∘C in agreement with the experimentally measured temperature of 260^∘C.

This research work focuses about fabrication and investigation on the influence of Titanium Carbide (TiC)-graphite particles reinforcement in wear behavior of Aluminium Matrix Composites (AMC). The stir casting technique was used to fabricate AMC reinforced with various weight percentage of TiC and graphite particles. Wear tests were conducted by using pin-on-disc wear testing machine. The hardness of the hybrid composites were recorded on the test specimen. The worn out surfaces of composites were analyzed using Scanning Electron Microscope (SEM). Results reveal that the presence of TiC and graphite particles improved the wear resistance. The wear of composite is primarily due to delamination and abrasion. The graphite particles serve as the solid lubricant on the wear of composite. The hardness of composite is improved with the decrease in weight percentage of graphite. SEM images reveal that the reinforcement particles in the matrix are homogeneously distributed. Also, worn-out surfaces of the composite were studied to observe wear track and wear mechanisms like plowing grooves, crack or cutting, and fragmentation.

This study concentrates more on biocomposite as a matrix, a derivative of Cashew Nut Shell Liquid (CNSL), and its development of Cardanol Resin (CR), along with coconut shell Particle (CSP) as a filler, obliging the environmental concerns as a mandatory one due to the pressure from the consumer, which forces manufacturing sector to seek some other alternative, as lucrative one is for betterment of the humanity also, thereby such sophistication of “green” composite with much potential application can easily thrive on. In this mix, the particle size (25, 50 and 75$\mu$m) and particle loading (0, 10, 20, 30 and 40%) on the CR were reinforced with CSP polymer matrix through compression molding. This is the assessed impact of morphological Scanning Electron Microscopy (SEM), while particles load on mechanical properties such as tensile strength, flexural strength, impact strength and the hardness. They can also see the absorption of water. While doing so, it has been clearly observed that the tensile strength and flexural strength values expanded up to 30% of particle content, for all particle sizes of the particles and afterward, we could note that it diminished for higher particle content. Experimental results indicated that the maximum tensile strength and flexural strength of 30% of CSP/CR composite increase for 25, 50 and 75$\mu$m by 31, 25 and 19% with that of 46, 37 and 27%, respectively, as compared with those of neat CR. The expansion of CSP in composite expanded the hardness and the % of water absorption. Scanning Electron Microscopy (SEM) of the composite surfaces demonstrates that there are genuinely better interfacial connection and appropriation between coconut shell particles and CR matrix.

Electroless nickel coatings containing Mo possess higher thermal stability in comparison with the binary alloy variants. In a quest to achieve enhanced thermal stability of Ni–B coatings, Mo is incorporated to obtain a ternary Ni–B–Mo coating. The coatings are deposited on AISI 1040 steel and characterized using energy dispersive X-ray (EDX) analysis, X-ray diffraction method and scanning electron microscope. The coatings are observed to lie in the mid-B range with amorphous structure in as-deposited condition. On heat treatment, precipitation of crystalline Ni and its borides is observed. The typical cauliflower-like surface morphology of the deposits could be observed in scanning electron micrographs. Microhardness measurements reveal the enhanced thermal stability of Ni–B–Mo coatings. Tribological behavior of Ni–B–Mo coatings at room and elevated temperatures (100^∘C, 300^∘C and 500^∘C) is observed on a pin-on-disc type tribo-tester by varying the applied normal load (10–50N) and rotational speed of the counterface disc (60–100rpm). The purpose of the present work is to observe the tribological behavior and associated tribo-mechanisms at different temperatures under dry sliding condition. In general, the wear of the coatings increases with an increase in applied normal load and speed at room temperature, 100^∘C and 300^∘C. At 500^∘C, the wear increases with load but with speed it first increases up to 80rpm and then decreases. The COF does not show a similar behavior like the wear with varying load and speed at different temperatures. Instead, it is controlled by the accompanying wear mechanisms, formation of oxide debris and oxide layers of Ni and Mo. The worn surface of the coatings is examined using scanning electron microscope and EDX analysis. Back scattered images of wear tracks of Ni–B–Mo coatings at the highest levels of load (50N) and speed (100rpm) at different temperatures further reveal the oxide formation and tribochemical reactions.

Zn${}_{0.9}$Se:Co${}_{0.1}$ thin films were deposited on sapphire (Al₂O₃) substrates in argon atmosphere at various gas pressures by pulsed laser deposition. Influence of argon pressure on the thickness, surface morphology, crystal structure and optical properties of the thin films were investigated by various diagnosis tools. It was found that these physical properties were correlated to the argon pressure and appeared like a mutation between the pressure of 2Pa and 4Pa. As the deposition pressure changed from 2Pa to 4Pa, the collision probability between ablated species and argon molecule was increased, which resulted in the transformation of the deposition type from sputter effect to adsorption effect and the mutation of film thickness and structure. These in turn influence the transmission range and band gap of the films. All of the results suggest that the ambient pressure is a very important factor to the deposition of Zn${}_{0.9}$Se:Co${}_{0.1}$ films by PLD.

Hydrogenated silicon carbonitride (SiCN:H) thin films were deposited by sputtering of silicon carbide target in hydrogen-doped argon and nitrogen atmospheres. The properties of the SiCN:H films were analyzed by scanning electron microscopy with energy dispersive spectrometer, atomic force microscope, Fourier transform infrared spectroscopy, X-ray diffraction and fluorescence spectrophotometer. No distinct crystal was formed in the SiCN:H films as-deposited and annealed at 600^∘C and 800^∘C. The SiCN:H films were mainly composed of Si–N, Si–C, Si–O, C–C, C–N, C$\equiv$N, N–H_n bonds and SiC_xN_y network structure. The strong blue photoluminescence observed from the SiCN:H film annealed at 600^∘C was attributed to SiC_xN_y network structure.

Micro-arc oxidation coatings were fabricated on 7E04 aluminum alloy substrates by micro-arc oxidation (MAO) in the electrolytes with the graphite addition varying from 0 to 8g/L (0, 2, 4, 6, 8g/L). The effect of graphite concentration on the surface morphologies, micro-hardness, thickness, phase composition and corrosion resistance of coatings was investigated. With the graphite powder concentration increasing, the oxidation voltage decreased gradually and the thickness of coatings firstly dropped down and then went up. It is found that the size of micro-pores and sintered discs declined with increase of graphite concentration. The XRD results indicated that MAO coatings mainly consisted of $\gamma$-Al₂O₃, $\theta$-Al₂O₃, SiO₂ and a little $\alpha$-Al₂O₃. The corrosion resistance of coatings was improved with the addition of graphite powder. The study reveals that the appropriate graphite powder in the electrolytes is essential to promote the performance of the coatings.

Heavy metal pollution endangers seawater and there is urgent need for the development of effective detectors that can provide warning of heavy metal pollution. Anodic stripping voltammetry is applicable for the detection of heavy metal pollution in sea water, but it suffers from two problems that are associated with the mercury electrode used: one is insufficient sensitivity and the other is secondary pollution caused by toxic mercury. In this work, we employed boron-doped diamond electrode as an alternative to mercury electrode for the detection of heavy metals. The BDD electrode was fabricated and its electrochemical properties were ascertained. The results of this work showed that: (1) the electrode prepared has a wide electrochemical window (4.2 V) and low background current ($3\pm 2\mu$A). (2) multiple heavy metals (Pb${}^{2+}$, Cd${}^{2+}$, Zn${}^{2+}$ and Cu${}^{2+}$) in seawater samples are detected simultaneously with the optimized electrode, with high sensitivity and good repeatability. (3) the repeatability of the detection meets the values stipulated in the national standard. The detection period is less than 15min, and in situ monitoring of heavy metals in seawater can be achieved by automatic sampling and wireless data transmission.

Cerium mononitride (CeN) film was fabricated by dual ion beam sputtering deposition method on silicon wafer. The oxidization process of CeN film was monitored by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The results showed that, when the CeN film was exposed to ambient atmosphere, bubbles appeared on the film surface rapidly and then the surface flaked off to powders. Meanwhile, the CeN film changed from polycrystalline to amorphous. XPS analysis indicated that the CeN was oxidized to Ce₂O₃ initially, and then further oxidized to CeO₂. These results indicated that the CeN film degraded easily in ambient atmosphere, exhibiting little or no passivation.

Based on primary range $R$, relationships among parameters of secondary electron yield $\delta$ and the processes and characteristics of secondary electron emission (SEE) from negative electron affinity (NEA) semiconductors, the universal formulas for $\delta$ at $0.1\mathrm{\text{keV}}\le E_{\mathrm{\text{p}}}\le 10\mathrm{\text{keV}}$ and at $10\mathrm{\text{keV}}\le E_{\mathrm{\text{p}}}\le 100\mathrm{\text{keV}}$ for NEA semiconductors were deduced, respectively; where $E_{\mathrm{\text{p}}}$ is incident energy of primary electron. According to the characteristics of SEE from NEA semiconductors with $2\mathrm{\text{keV}}\le E_{\mathrm{\text{pmax}}}\le 5\mathrm{\text{keV}}$, $R$, deduced universal formulas for $\delta$ at $0.1\mathrm{\text{keV}}\le E_{\mathrm{\text{p}}}\le 10\mathrm{\text{keV}}$ and at $10\mathrm{\text{keV}}\le E_{\mathrm{\text{p}}}\le 100\mathrm{\text{keV}}$ for NEA semiconductors and experimental data, special formulas for $\delta$ at 0.5$E_{\mathrm{\text{pmax}}}\le E_{\mathrm{\text{p}}}\le 10E_{\mathrm{\text{pmax}}}$ of several NEA semiconductors with $2\mathrm{\text{keV}}\le E_{\mathrm{\text{pmax}}}\le 5\mathrm{\text{keV}}$ were deduced and proved to be true experimentally, respectively; where $E_{\mathrm{\text{pmax}}}$ is the $E_{\mathrm{\text{p}}}$ at which $\delta$ reaches maximum secondary electron yield. It can be concluded that the formula for $B$ of NEA semiconductors with $2\mathrm{\text{keV}}\le E_{\mathrm{\text{pmax}}}\le 5\mathrm{\text{keV}}$ was deduced and could be used to calculate $B$, and that the method of calculating the 1/$\alpha$ of NEA semiconductors with $2\mathrm{\text{keV}}\le E_{\mathrm{\text{pmax}}}\le 5\mathrm{\text{keV}}$ is plausible; where $B$ is the probability that an internal secondary electron escapes into vacuum upon reaching the surface of emitter, and 1/$\alpha$ is mean escape depth of secondary electron.

In this work, aluminum/titanium carbide (Al/TiC) surface composite has been fabricated by friction stir processing using a novel modular Direct Particle Injection Tool (DPI–FSP). The tool has a unique feature wherein the TiC particles have been transferred from the tool itself by spring adjusted plunger movement into the matrix. The microstructural observations from optical and scanning electron microscope (SEM)-EDS results revealed the homogeneous distribution of particles in the stirred zone (SZ) and the thickness of the formed surface composite layer (SCL) is approximately 0.34mm. X-ray diffraction results confirmed that the particles are reinforced in the aluminum matrix, and no intermetallics have been formed in the composite. The microhardness of composite was increased from 68 to 135Hv, and the impact test results showed that the toughness was almost comparable to that of the base metal.

Needle-shaped nanostructured tris(8-hydroxyquinoline) aluminum nanowires (Alq₃) have been obtained by annealing Alq₃ amorphous films at 150^∘C which is lower than the glass transition temperature of Alq₃ (172^∘C). The growth of Alq₃ nanowires is attributed to the migration and stacking of Alq₃ molecules which acquire thermal energy from the annealing process. X-ray diffraction analysis and scanning electronic microscopy spectra show that the Alq₃ nanowires are composed of the well-known $\alpha$-phase Alq₃. The intensity of the photoluminescence spectra firstly increases and then decreases as the annealing time increases, along with a spectral blue shift. The optical transmittance spectra of the annealed Alq₃ films show a smaller average absorption in the visible range and a wider optical bandgap compared with that of the amorphous films, as a result of the decrease of $\pi$ overlapping in the Alq₃ molecules.