Surface Review and Letters

Tailoring pore-creating method to fit the various demands of different researchers is the frontier issue in the research of electrode capacitance of boron-doped diamond (BDD). Two critical factors in achieving the desired capacitance are the pore size and shape. This work compares the characteristics and applicability of various pore-creating methods, and reveals the influence mechanism of factors such as surface area, size and shape of the pore, on the capacitance of BDD electrodes. Obtained results could facilitate researchers to develop a personalized pore-creating method to achieve the desired capacitance.

The gradient fine-grained oxygen-boosting layer was prepared on equal channel angular processing (ECAP)-treated titanium with thermal oxidation and oxygen boost diffusion process, and tribological properties were systematically characterized. Results show that the as-prepared boosting layer consists of surface coarse-grained region, and inner fine-grained region. The corresponding thickness and mechanical properties further increase compared to those of virgin titanium. The oxygen-boosting layer reveals excellent anti-wear properties, the dominant wear mechanism of which is abrasive.

The corrosion hindrance impact of Syzygium aromaticum fruit extract has been analyzed on mild steel (MS) corrosion in 0.5M H₂SO₄ by utilizing weight reduction estimations, potentiodynamic polarization estimations and electrochemical impedance spectroscopy (EIS) procedures. This Eugenol- and Eugenol-acetate-containing extract diminishes the corrosion rate of MS in acidic medium. The greatest corrosion restraint effectiveness was observed at 500mg/L inhibitor concentration in 0.5M H₂SO₄. The adsorption of Syzygium aromaticum extract on the surface of MS has been analyzed by utilizing atomic force microscopy (AFM), scanning electron microscopy (SEM) study and spectroscopic strategies.

The finite element method (FEM) is employed to analyze the residual stress distribution of bi-layer (a-SiC $+$ diamond) film system, and the adhesion enhancement mechanism of a-SiC interlayer is further investigated. The influence of a-SiC interlayer on the surface topography of WC-Co substrate is taken into consideration by adopting a 3D surface topography model agreeing with the Atomic Force Microscope (AFM) characterization of a-SiC interlayer. For the sake of comparison, the stress distribution of a diamond film with no interlayer is also simulated. The simulation analysis reveals that the residual stress distribution is much more homogeneous after employing the a-SiC interlayer, which is supposed to be of great importance to the adhesion enhancement of diamond films. Afterwards, the diamond films with and without a-SiC interlayer are fabricated on WC-Co substrates. Raman mapping is carried out to measure the real residual stress distribution of as-fabricated a-SiC diamond films, which is in accordance with the simulation results. Moreover, the a-SiC interlayered diamond film exhibits better adhesion than the diamond film with no interlayer in adhesion evaluation, which can be ascribed to the more homogeneous residual stress distribution and better interfacial bonding after introducing the a-SiC interlayer.

Geometric and electronic properties of nitric oxide adsorption on W_mMo_n ($m+n\le$ 6) clusters have been systematically calculated by density functional theory (DFT) at the generalized gradient approximation (GGA) level for ground-state structures. NO molecule prefers top site with nitrogen-end bridging a tungsten atom for W${}_{1,2}$Mo${}_{1,2,3}$ and W₃Mo₂ clusters. While NO tends to locate on the hollow site for WMo₅, W₂Mo₄ and W₃Mo₃ clusters, and dissociation of NO molecule happens on W₃Mo, N–O bond lengths expand in accordance with the variation of adsorption energy with the increasing number of tungsten atoms, originating from metal $\to {\pi }^{\ast }$ back-donation. Electron transfer occurs among 4d state of Mo, 5d state of W, 2p state of N and 2p state of O.

The microstructures of AA4045/AA3003Mod./AA4045 aluminum-brazed sheet were observed and determined by stereoscopic digital microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectrometer (EDS). The corrosion process of the brazed sheet in the exfoliation corrosion (EXCO) solution was investigated by electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN) techniques. The results showed that the brazed sheet was composed of the Al-Si eutectic zone, the precipitates-free zone (PFZ), the band of dense precipitates zone (BDP) and the core material. With the immersion time increased, the capacitive time constant in EIS plot changed from one time constant through two unclear time constants to two clear time constants, and then went back to two unclear time constants again. The maximum relative energy in energy distribution plot (EDP) changed from small scales through middle scales to large scales, and then went back to middle scales. The corrosion process could be divided into four stages: the dissolution of the eutectic $\alpha$-Al in the resolidified clad in the form of pitting corrosion; the corrosion of the primary $\alpha$-Al grain boundaries in the form of intergranular corrosion (IGC); the corrosion of the BDP zone in the form of exfoliation corrosion; and the corrosion of the core material in the form of IGC.

Room temperature scanning tunneling microscopy was used to investigate the adsorption of a dye molecule, iron-phthalocyanine (FePc), on ZnO(0001). Submolecular resolution reveals the orientation of molecules with respect to crystallographic directions of the surface. Upon adsorption, the molecular symmetry is reduced. First-principles calculations trace these observations to a strong molecule-substrate bond, which induces deformations of the molecule.

Titanium oxide (TiO₂) film was deposited by rectification factor (RF) magnetron sputtering technique on glass substrates and p-Si (111) wafers to fabricate n-TiO₂/p-Si heterojunction devices for the investigation of material and device properties, respectively. The structural, surface morphology, optical and electrical properties of TiO₂ film were characterized by means of scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), UV–visual (UV–Vis) spectral and dark current-voltage (I–V) measurement analyses. The deposited film layer was found to be homogeneous structure with crack-free surface. The bandgap value of TiO₂ film was determined as 3.6eV and transmission was around 65–85% in the spectral range of 320–1100nm. The conductivity type of the deposited film was determined as n-type by hot probe method. These values make TiO₂ film a suitable candidate as the n-type window layer in possible diode applications. TiO₂ film was also deposited on p-Si (111) wafer to obtain Al/n-TiO₂/p-Si/Al heterojunction device structure. The dark I–V characteristic was studied to determine the possible conduction mechanisms and diode parameters.

Herein, the results of a study focused on graphene in activation and cross-linking reactions with hydrazine are reported. The method provides an approach to the preparation of graphene-based materials, in this case, with a preset distance between individual layer and a relatively low ratio between the Raman $G$ and $D$ bands — $D$ peak intensity/$G$ peak intensity ($I_D$/$I_G$), ca. 1.81 (for unmodified High Strength Metallurgical Graphene${}^{\text{®}}$ (HSMG${}^{\text{®}}$ [Trade mark number: 013391669; Office for Harmonization in the Internal Market]), this ratio is 0.16). A 3D structure was created without a substrate (e.g. Si, SiO₂ or polymer). This method allows for the preparation of a 3D graphene structure without the $\pi$–$\pi$ interactions between individual layers.

In this paper, the enhancement of NiCrBSi coatings by adding Cr₃C₂ were investigated. The NiCrBSi coatings with different additions of Cr₃C₂ were produced by laser cladding. The microstructure, hardness and wear resistance of the coatings were studied by optical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness tester and M-200 wear tester. It is found that the main phases in the coatings are $\gamma$-Ni, Cr${}_{23}$C₆ and Cr₇C₃, and they also contain a small amount of CrB, Ni₄B₃ and Ni₃Si₂. Moreover, with the increase of Cr₃C₂ addition, the microhardness and wear resistance of coatings are obviously improved. When the addition of Cr₃C₂ is 20%, the wear resistance of the coating is the best, and the wear resistance of the coating increased by 191.2% than that of the Cr₃C₂-free coating. The wear resistance of coating decreases when the addition of Cr₃C₂ reaches 30%.

The electrochemical migration (ECM) behavior of Sn-3.0Ag-0.5Cu solder alloy under thin electrolyte layers was investigated using a technique based on the coupling of in situ electrochemical measurements and optical observation. Results showed that the mean time to failure first increased and then decreased as thickness of the electrolyte layer increased, the maximum value was present at 200$\mu$m. The higher the bias voltage applied, the faster was the rate of dendrite growth. And, Sn leaded the ECM of SAC305 solder alloy. Mechanisms relevant have been proposed to explain the ECM behavior of Sn-3.0Ag-0.5Cu solder alloy.

This paper proposes the modified mechanical and mathematical modeling of lead zirconium titanate (PZT) sensor based on the PZT constitutive relation in order to solve the complicated boundary condition and stress situation of PZT sensor due to the effect of adhesive-layer damping. The experimental study on the surface-bonded PZT sensor is chosen to carry out the correctness of the proposed models. The results show that the PZT sensor modeling is simplified to three types. When the amplitude of harmonic force is constant, the greater the excitation frequency, the more sensitive the output voltage is, the easier the signal acquisition is. At a certain frequency, the voltage output is proportional to the force amplitude. The larger the area or thickness of PZT, the greater the output voltage is, the more sensitive the signal output is. The output voltage is in quadratic relation to the bonding thickness. Furthermore, the smaller the output voltage, the greater the damping is. The signal loss is about 25.82%. The signal acquisition effect of the PZT square wafer is better than that of circular wafer under the same area of PZT sensor. The research achievements reveal the sensing mechanisms and validate the efficiency of the developed model and effectively simulate and detect direct piezoelectric rule of PZT sensor.

This paper studies the effect of anisotropic surface tension on the morphological stability of deep cellular crystal in directional solidification by using the matched asymptotic expansion method and multiple variable expansion method. We find that the morphological stability of deep cellular crystal growth with anisotropic surface tension shows the same mechanism as that with isotropic surface tension. The deep cellular crystal growth contains two types of global instability mechanisms: the global oscillatory instability, whose neutral modes yield strong oscillatory dendritic structures, and the low-frequency instability, whose neutral modes yield weakly oscillatory cellular structures. Anisotropic surface tension has the significant effect on the two global instability mechanisms. As the anisotropic surface tension increases, the unstable domain of global oscillatory instability decreases, whereas the unstable domain of the global low-frequency instability increases.

Low wear resistance and high sensitivity to fretting fatigue (FF) damage limit the application of titanium alloys. In order to improve its wear resistance, surface plasma Zirconium (Zr) alloying is a candidate through solution strengthening with its property of infinite solid solution with $\alpha$–Ti and $\beta$–Ti. In this work, the plasma Zr metallurgy technique was used to improve the FF resistance of Ti6Al4V alloy combined with shot peening (SP), which is different from the combined treatments of the surface modification with high hardness and SP, and may explain the impacts of ductility and strength in improving FF resistance. The results indicate that the Zr metallurgy layer is composed of a Zr–Ti solid solution with low surface hardness and density, which induce the reduction of the fretting wear (FW) resistance and FF resistance of the Ti6Al4V alloy. Instead, when SP was used as the post treatment, the FW and FF behavior of the titanium alloy were increased obviously after prior plasma Zr metallurgy, especially to high cycle fatigue. This indicates that residual stress introduced by SP is beneficial for improving both FW and resistance.

In this work, the growth mechanism of nickel-plated coating on primer-modified poly(ethylene terephthalate) (PET) sheets was investigated systematically. Results showed the surface structure of primer-modified PET sheets would chemisorb Sn and Pd, which are used as the catalyst for the electroless nickel plating. Nickel particles were formed on the plated PET surface. The crystal preferential orientation transformed from (200) plane to (111) plane and nickel particles grew with the increase of thickness of plated coating. The growth of nickel particles mainly included lateral growth and vertical growth. Cracks and then shed were formed in the nickel coating when the thickness exceeded about 228nm.

The corrosion behavior of as-cast AZ91C magnesium alloy was studied by performing friction stir processing (FSP) and FSP followed by solution annealing and then aging. Phase analysis, microstructural characterization, potentiodynamic polarization test and immersion tests were carried out to relate the corrosion behavior to the samples microstructure. The microstructural observations revealed the breakage and dissolution of coarse dendritic microstructure as well as the coarse secondary $\beta$-Mg${}_{17}$Al${}_{12}$ phase which resulted in a homogenized and fine grained microstructure (15$\mu$m). T6 heat treatment resulted in an excessive growth and dispersion of the secondary phases in the microstructure of FSP zone. The potentiodynamic polarization and immersion tests proved a significant effect of both FSP and FSP followed by T6 on increasing the corrosion resistance of the cast AZ91C magnesium alloy. Improve in corrosion resistance after FSP was attributed to grain refinement and elimination of segregations and casting defects which makes more adhesive passive layer. Increase in volume fraction of precipitations after T6 heat treatment is determined to be the main factor which stabilizes the passive layer at different polarization values and is considered to be responsible for increasing the corrosion resistance.