Surface Review and Letters

Al₂O₃ coatings were prepared on T6-tempered Al6061 alloys substrate under a hybrid voltage (AC 200 V–60 Hz and DC 260 V value) by plasma electrolytic oxidation (PEO) in 30 min. The effects of different electrolytes on the abrasive behaviors of the coatings were studied by conducting dry ball-on-disk wear tests. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate the coating microstructure. XRD analysis results show that the coatings mainly consist of α- and γ-Al₂O₃, and some mullite and AlPO₄ phase in Na₂SiO₃ and Na₃PO₄ containing electrolytes, respectively. The wear test results show that the coatings which were PEO-treated in Na₃PO₄ containing electrolyte presented the most excellent abrasive resistance property.

We investigated the properties of inorganic–organic hybrid thin films prepared by sol–gel reaction. Sol solutions were synthesized by using two kinds of nanosized boehmite and methyltrimethoxysilane (MTMS) in variation with the amount of MTMS at different reaction times. Boehmite nano sol of spherical and fibrous shapes was used as inorganic material, and MTMS was used as organic material. The morphology of boehmite nano sol powder was observed by transmission electron microscopy. Coating sols were prepared from boehmite sol and MTMS by sol–gel reaction. Physical and chemical properties of thin films prepared from boehmite and MTMS sols were investigated. Surface hydrophobicity, roughness, thickness, thermal resistance and electrical resistivity of boehmite/MTMS thin films were investigated.

Hydrogenated amorphous and nanocrystalline silicon thin films were grown on porous anodic alumina substrates using electron cyclotron resonance-chemical vapor deposition technique from argon, hydrogen and silane gas composition. The structural characterization of the deposited hydrogenated silicon films were performed by scanning electron microscopy, Raman spectroscopy, and X-ray diffraction studies. The results revealed that mixed amorphous/nanocrystalline silicon phases with specific novel morphology were obtained on textured surfaces. The evolution of the film on ripple-like surface exhibited amorphous dominant structure, however, the film deposited on tipped/ribbed surface consisted of amorphous and nanocrystalline phases composite. The growth process strongly depends on the textured substrate pattern, which influences on the nanostructure shapes and crystallinity.

We have deposited MgB₂ thin films on the carbon fiber by hybrid physical–chemical vapor deposition (HPCVD) method which is known as the most effective technique for depositing MgB₂ thin films without pore formation. By adopting carbon fiber as substrate and gas phase reaction between diborane (B₂H₆) gas and Mg vapor for MgB₂ formation, core-shell structured MgB₂/C composite fiber could be synthesized. The high quality of the prepared MgB₂ fibers was confirmed with scanning electron microscopy (SEM), and the critical temperature (T_c) of the sample deposited at 590°C and 12 sccm flow rate of B₂H₆ was measured at ~40 K. The microstructures of MgB₂ layer was characterized using transmission electron microscopy (TEM). The bright-field TEM images showed MgB₂ with the grain size of several nanometers. The MgB₂ thin film showed highly dense microstructure without pore and well-connected to the carbon fiber interface. High-resolution TEM (HRTEM) images and scanning transmission electron microscopy (STEM) revealed the presence of interface phase between MgB₂ thin films and carbon fiber.

In this paper, the retrogression and reaging (RRA) behavior and corrosion properties of Sc-containing Al–Zn–Mg–Cu alloy were observed. The dependence of the mechanical properties and corrosion resistance on the heat treatment condition was measured by hardness, tensile, C-ring and conductivity testing. The retrogression time for recovery of the yield strength of the alloy subjected to T6 treatment was 20 min at 200°C of retrogression temperature, which was longer than that of Al7075 alloy. The results of electrical conductivity and C-ring tests showed that the stress corrosion cracking (SCC) resistance in Sc-containing alloy treated for 20 min at 200°C was improved. These study results demonstrated the ability of the Sc-containing alloy to extend the retrogression time and thereby improve the SCC resistance and mechanical properties.

We investigated the optimal method of application and the anticorrosive abilities of Zn, Al, and Zn + 15%Al spray coatings in protecting stainless steel 304 (STS304) in sea water. If a defect such as porosity or an oxide layer, causes STS304 to be exposed to sea water, and the thermal spray coating material will act as the cathode and anode, respectively. The Tafel experiments revealed that Al-coated specimens among applied coating methods had the lowest corrosion current densities. As the corrosion potential decreases with increasing corrosion current density, we estimated the characteristics and lifetime of the protective thermal spray coating layer in the galvanic cell formed by the thermal spray coating layer and STS304.

Cu seed layer was deposited by chemical vapor deposition using new Cu precursor, Cu(dmamb)₂. The Cu layers still need the barrier layer to prevent the diffusion, so Ta and Ti were used for the barrier layer on Si(100). Low temperature (LT) copper buffer layer was introduced and the effect of the buffer on the Cu films was investigated. The grown Cu layers were analyzed using FESEM, XRD, and four point probe measurement. The Cu seed layers were successfully deposited using Cu(dmamb)₂ precursor. Better thickness uniformity was obtained in the Cu films with the LT Cu buffer, which lowered the electrical resistivity.

A thermopile sensor composed of 196 pairs of p–n thin film legs was processed on a glass substrate by using successive electrodeposition of the n-type Bi–Te and the p-type Sb–Te thin films. The 5.3-μm thick Bi–Te film, electrodeposited at a constant voltage of -50 mV in the 50-mM electrolyte with the Bi/(Bi + Te) mole ratio of 0.5, exhibited a Seebeck coefficient of -67 μV/K. The 5.2-μm thick Sb–Te film, electrodeposited at a constant voltage of 20 mV in the 70-mM solution with the Sb/(Sb + Te) mole ratio of 0.9, possessed a Seebeck coefficient of 63 μV/K. The thermopile sensor exhibited the sensitivities of 13.1 mV/K with temperature differences smaller than 9 K and of 27.3 mV/K with temperature differences larger than 9 K respectively, across the hot and cold ends.

This work illustrates how the separation of a semiconductor wafer into individual devices occurs during conventional mechanical dicing. In situ examinations indicate that the final separation of the wafer takes place before the dicing blade has fully penetrated its active surface. Thus, it was predicted that mechanical dicing-induced damage in the separated device patterns would be due to other mechanical actions rather than the grinding action between the diamond particles embedded in the blade and the wafer. Based on the in situ examinations, it was experimentally tested how manipulating the revolving speed of the dicing blade affected the prevention of dicing-induced damage to device patterns. The experimental results show that among various mechanical actions, the impact stress due to the revolving action of the blade could be the most possible candidate for damage in the device pattern on the final uncut semiconductor wafer.

The fracture strength of LOC (lead-on-chip) packages was measured through three-point bending tests. Metallurgical examination shows that failure in an LOC package begins at a pre-existing flaw in the form of a scratch on the bottom surface of the plastic-encapsulated silicon chip. The flexural strength of LOC packages was estimated as a function of the geometry of the grinding-induced scratches on the back surface of the chips. The major conclusion is that the fracture strength of the plastic package, including the silicon chip, can be enhanced up to 80% by changing its scratch marks from 0°, running parallel to its lateral direction, to 90°, running parallel to its longitudinal direction.

The growth of the TiO₂ thin films coated on the polypropylene beads was analyzed experimentally in a rotating cylindrical plasma chemical vapor deposition (PCVD) reactor. The precursors for the thin films were generated by plasma reactions, and they deposited on the polypropylene beads to become the uniform thin films. The TiO₂ thin films grow more quickly on the polypropylene beads by increasing the mass flow rate of TTIP, or the rotation speed of the reactor. The smaller number of polypropylene beads in the reactor increases the growth rate of the thin films. The high-quality TiO₂ thin films can be coated on particles uniformly by using the rotating cylindrical PCVD process. The particles coated with high-quality TiO₂ thin films can be applied to the removal of air and water pollutants by a photodegradation reaction of TiO₂.

Microstructural evolution and fracture behavior of zirconia (ZrO₂)-based thermal barrier coatings (TBCs) were investigated under thermal exposure. New ZrO₂ granule with 8 wt.% yttria (Y₂O₃) with a deformed hollow morphology was developed through a spray drying process and employed to prepare TBCs. The thermal exposure tests were conducted at 1210°C with a dwell time of 100 h till 800 h. The residual stress at the interface between top coat and thermally grown oxide (TGO) layer was measured using a nanoindentation technique before and after thermal exposure. Vertical cracks on the top coat were newly formed and interlamellar cracks at the interface were enhanced after the thermal exposure of 800 h. Especially, partial delamination was observed at the interface after the thermal exposure of 800 h in TBC samples tested. The microstructural evolution in the top coat could be defined through load–displacement curves, showing a higher load or a less displacement after the thermal exposure of 800 h. The stress state was strongly dependent on the TGO geometry, resulting in the compressive stresses at the "valleys" or the "troughs," and the tensile stresses at the "crests" or peak areas, in the ranges of -500 to -75 MPa and of +168 to + 24 MPa, respectively. These stress terms incorporated with resintering during thermal exposure affected the mechanical properties such as hardness and elastic modulus of the top coat.

Anti-reflection layers made from sub-wavelength structures or nanostructure arrays have been extensively studied due to the high demand of the solar cell markets and the use of consuming electronics such as plane displays, glasses, prisms, videos, and the monitors of the camera. Conventionally, this anti-reflection layer was fabricated by multilayer films deposition through sputtering, wet-coating or sol-gel. However, these methods have several disadvantages such as process instability, high cost and high temperature procedure.

In the current study, fabrication methods of UV curing and nano-imprinting processes are proposed to produce large-area polymer sheets with sub-wavelength structures (SWS). Porous anodic alumina (PAA) mold of nano-holes was used to fabricate SWS on a PET sheet with UV photoresists of refractive index of 1.53 by roll-to-roll processing. The reflectance of SWS on PET decreases from 9.39 to 4.25% at the wavelength of 550 nm. The contact angle changes from 78.1° to 103.2°. The porous anodic alumina mold was also used to imprint a PMMA film and SWS were obtained by hot embossing at different temperatures. The reflectance changes from 4.25 to 2.16% at the wavelength of 550 nm after nano-imprinting. A successful low cost approach to produce large-area polymer sheets with SWS is obtained by both UV curing and nano-imprinting processes.

We investigated the interaction of varied plasma power with ultralow-κ Toluene–TEOS hybrid plasma-polymer thin films, as well as changes in electrical and mechanical properties with various mixture ratios of toluene and TEOS (tetraethoxysilane). Using the plasma enhanced chemical vapor deposition (PECVD) method, organic–inorganic hybrid polymer thin films were deposited on silicon(100) substrates under 150°C of wall temperature and a ratio of TEOS to toluene. Toluene and TEOS were utilized as organic and inorganic precursors, and hydrogen and argon were used as bubbler and carrier gases, respectively. In order to compare the differences in the electrical and the mechanical properties of plasma polymerized thin films, we grew the hybrid polymer thin films under 30 W of RF (radio frequency using 13.56 MHz) power with various ratios of toluene to TEOS. The as-grown polymerized thin films were first analyzed by Fourier Transform Infrared (FT-IR) spectroscopy, and Atomic Force Microscopy (AFM). The results of FT-IR showed that the hybrid polymer thin films were totally fragmented and polymerized with increasing RF power. AFM showed that polymer films with smooth surface could be grown under various deposition conditions. An impedance analyzer was utilized for the measurements of capacitance values for dielectric constants and the thin films were analyzed for hardness and Young's modulus using a nanoindenter.

The particles, suspended in the electrolyte, can be co-deposited with metal. The co-deposition behaviors of WC and Co-coated WC particles on nickel matrix were investigated. Many operating parameters that influence on the quantity of incorporated particles, including current density, bath agitation and electrolyte composition were investigated. The co-deposition of particles during electroplating depends on the rate of metal deposition and on the flux of particles to the film surface. The growth rate of the metal film is determined by the current density, whereas the flux of particles to the electrode surface is dependent on the particle size, particle concentration in solution, the electrode rotation rate, the particle diffusion coefficient, and the electrode geometry. The kinetic parameters in the co-deposition were calculated from the experimental results. Co-coated WC particles were easily incorporated in the matrix than WC particles from the calculated and experimental results.

Novel three-dimensional (3D) branched nanotubes of sodium niobate (NaNbO₃) were produced by a multi-step reaction, which involves the synthesis of Nb₂O₅ branched nanowires and subsequently treating these precursors in alkali solution. XRD and SEM have been used to analyze current products. All the obtained nanobranches exhibited tubular structure, which was induced by nanoscale Kirkendall effect and surface diffusion. This work demonstrates a simple and efficient pathway to design hierarchical and complex hollow nanostructures, which are expected to have important applications, such as sensors and photocatalysts.

In this work, two types of electrodeposited Ni–Fe/insulator/Cu composite wires, namely Ni–Fe/seed layer/glass coated copper wire (Composite Wire A), and Ni–Fe/seed layer/sputtered SiO2/Cu (Composite Wire B), have been fabricated and their giant magneto-impedance effects have been investigated. With different implementations of the insulator layer, the magneto-impedance effect of Composite Wire A, whose insulator layer is cast from the melt Pyrex, is significantly higher than that of Composite Wire B with an insulator of sputtered SiO₂ layer. The profile of the insulator layer, as well as the thickness of magnetic layer and the diameter of the conductive core, greatly influences the interaction between the magnetic layer of Ni–Fe and the copper core, as shown in their giant magneto-impedance (GMI) effects. The maximum MI ratios obtained from Composite Wires A and B are 226% at 800 kHz when H_ext = 0.87 Oe, and 95% at 1 MHz when H_ext = 0 Oe, respectively. The Composite Wire A is a promising candidate for the sensing element of high sensitivity sensors to very weak magnetic field. For Composite Wire B, further improvement on its GMI effect and sensing performance requires optimization of its geometric parameters and the deposition conditions.

Hierarchical alveolate structures in nano- to microscale were fabricated on both aluminum and stainless steel substrates via a chemical etching. On aluminum surfaces, sharp edged caves and plateaus were found. On stainless steel substrate, fine papillae stand on protuberances. These surfaces exhibit super-hydrophobic properties after the fluorination treatment, their water contact angles are 158° and 160°, respectively, with the contact angle hysteresis of about 5°. The roll off angle is about 5°. Ice melting behaviors on a plate of aluminum super-hydrophobic surface were compared with those on a hydrophilic one, their difference shows that the new feature of super-hydrophobic surface could be expected.

In the past decade, the development of nanoelectronics and nano-optics has attracted much interest in surface nanostructuring of semiconductor materials. The irradiation of a microlens array by a laser beam generates many focused light spots, which can act as a direct writing tool on photo-polymer materials. This maskless surface nanostructuring technique enables thousands to millions of identical nano-features to be patterned in a couple of laser pulses. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images show that nano-features were patterned uniformly on the substrate surface, which suggests a versatile way of parallel surface nanostructuring over a large area. The simulation results of the energy flux distribution at the focal plane of the microlens arrays will also be discussed.