Random phase mask as a model of a rough surface: Part II. Experiment

Artificial roughness was created on sample surfaces by etching through a two-dimensional orthogonal grating with a stochastic distribution of square "defects" of size. "Defects" depth was varied from 0.02 μm up to 1.005 μm. The experimental dependences of the scattering of polarized light were studied on four types of surface roughness for two materials: quartz and aluminum. The defect sizes of the random phase mask were 25 × 25 μm and 2.5 × 2.5 μm. The impacts of the sizes and density of artificial defects of rough surfaces on the polarization of reflected light were investigated by multiple-angle-of-incidence (MAI) ellipsometry at a wavelength of 0.63 μm.     

Preparation and characterization of NaSm9(SiO4)6O2 powders with infrared absorptive properties

NaSm₉(SiO₄)₆O₂ powders were synthesized by mild hydrothermal method at 180 °C for 24 h. The infrared optical properties and structure of the obtained powders were characterized. There existed two narrow and sharp absorptive bands near 943 cm^− 1 (10.6 μm). The band at 938 cm^− 1 was assigned to the stretching vibrations of SiOSm groups connecting to Q¹ species and the band at 989 cm^− 1 was attributed to the stretching vibrations of SiOSm groups linking with Q⁰ species. The reflectivity was lower than 1% from 900 to 1200 nm and reached the minimum of 0.46% at 1073 nm. The prepared powders exhibit potential to act as a new kind of absorptive material for the infrared light of 10.6 μm and 1.06 μm.     

Artificial petal surface based on hierarchical micro- and nanostructures

In this paper, we present an artificial rose petal composed of hierarchical micro- and nanostructures on a polymethyl methacrylate surface. The petal effect implies that the surface has a high adhesion force in spite of being in a super-hydrophobic state, while the lotus effect implies that the surface has a low adhesion force when it is in a super-hydrophobic state. We have fabricated four different types of surfaces, namely, smooth, nanostructured, microstructured, and hierarchically micro-nanostructured surfaces. Microstructures and nanostructures have a quadrangular pyramid shape (one-side length: 15 ± 2 μm, height: 10.6 ± 1 μm) and a circular bump shape (diameter: 130 ± 10 nm, height: 100 ± 10 nm), respectively. The four types of surfaces are also chemically treated with trichlorosilane in order to reduce the surface energy. The contact angles of the smooth, nanostructured, microstructured, and hierarchically micro-nanostructured surfaces are measured to be 104° ± 2°, 112° ± 2°, 138° ± 4°, and 159° ± 2° after the chemical treatment. In the case of the super-hydrophobic micro-nanostructured surfaces, water droplets remain attached to the surface, even when the surface is turned upside down.     

Synthesis and characterization of electrolyte-grade 10%Gd-doped ceria thin film/ceramic substrate structures for solid oxide fuel cells

In the present research, spray pyrolysis technique is employed to synthesize 10%Gd-doped ceria (GDC) thin films on ceramic substrates with an intention to use the "film/substrate" structure in solid oxide fuel cells. GDC films deposited on GDC substrate showed enhanced crystallite formation. In case of NiO-GDC composite substrate, the thickness of film was higher (~ 13 μm) as compared to the film thickness on GDC substrate (~ 2 μm). The relative density of the films deposited on both the substrates was of the order of 95%. The impedance measurements revealed that ionic conductivity of GDC/NiO-GDC structure was of the order of 0.10 S/cm at 500 °C, which is a desirable property for its prospective application.     

Self-healing of surface cracks in mortars with expansive additive and crystalline additive

This research studies the self-healing potential of cement-based materials incorporating calcium sulfoaluminate based expansive additive (CSA) and crystalline additive (CA). Mortar specimens were used throughout the study. At the age of 28 days, specimens were pre-cracked to introduce a surface crack width of between 100 and 400 μm. Thereafter, the specimens were submerged in water to create a self-healing process. The experimental results indicated that the mixtures with CSA and CA showed favorable surface crack closing ability. The optimal mix design was found to be a ternary blend of Portland cement, 10 wt.% CSA and 1.5 wt.% CA, by which a surface crack width up to about 400 μm was completely closed, and the rate of water passing was dropped to zero within 28 days. It was hypothesized that the amount of leached Ca²⁺ from the matrix plays an important role on the precipitation of calcium carbonate which is the major healing product. The analyses showed that those specimens with CSA/CA additions released more Ca²⁺ than that control specimen. Moreover, those specimens with additives had higher pH value which would favor calcium carbonate precipitation.     

Study of alumosilicate porcelains: Sol-gel preparation, characterization and erosion evaluated by gravimetric method

In this paper, the sol-gel synthesis and characteristic properties of kalsilite-type alumosilicates (KAlSiO₄ and K_0.5Na_0.5AlSiO₄) are reported. The polycrystalline powders were characterized by thermal analysis (TG/DTA), powder X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). Single-phase kalsilite oxides have been obtained after annealing precursor gels for 5 h in the temperature range of 750-850 °C. It was demonstrated that crystallinity of the samples slightly depends on the temperature of annealing. From the results obtained, it could be concluded that the KAlSiO₄ solids are composed of the volumetric plate-like grains with no regular size (from 5 μm to 30 μm at 750 °C and around 5-50 μm at 850 °C). Larger crystallites for mixed potassium-sodium kalsilite have formed (from 10 μm to 80 μm at 750 °C and >100 μm at 850 °C) in comparison with potassium kalsilite samples). The erosion of obtained dental porcelain samples stored in saliva, beer and Coca-Cola was compared.     

Essential work of fracture and failure mechanisms of polypropylene-clay nanocomposites

The fracture behavior of polymer nanocomposites (PNCs) based on a polypropylene with organo-modified clays (2 wt.%) and different coupling agents was studied by means of essential work of fracture (EWF). The PNC microstructure was characterized by clay particle dispersion at the micron scale (>1 μm) and sub-micron scale (200 nm to 1 μm), with good intercalation and partial exfoliation (<100 nm). Tensile testing showed significant improvements (+25-50%) corresponding to nanoparticle reinforcement effects. Fracture surfaces revealed that fracture occurred by void initiation at larger clay particles, followed by void growth and coalescence as the surrounding matrix stretched into ligaments. EWF improvements (+20%) were noted for PNCs that had fewer micron scale particles and showed higher tensile improvements. Toughness improvements were attributed to higher voiding stresses and improved matrix resistance attributed to finer, more oriented clay nanoparticles.     

Optical switches based on CdS single nanowire

CdS nanowires have been synthesized by a composite-hydroxide-mediated approach. The characterization of the nanowire with X-ray diffraction, scanning electron microscopy, and transmission electron microscopy indicated a single-crystalline hexagonal structure growing along direction with length up to 100 μm. The UV-visible reflection spectrum demonstrated a band gap of 2.36 eV. A strong light emission centered at 543 nm was observed under different excitation wavelengths of 300, 320, 360 and 400 nm, which was further confirmed by a bright fluorescent imaging of a single CdS nanowire. The photocurrent response based on a single CdS nanowire showed distinct optical switch under the intermittent illumination of white light. The rise and decay time were less than 1.0 and 0.2 s, respectively, indicating high crystallization with fewer trap centers in the CdS nanowires. It is possible that the undesirable trapping effects on grain-boundaries for photoconductors could be avoided thanks to the single-crystalline nature of the CdS nanowires.     

Two step deposition method with a high growth rate for ZnO nanowire arrays and its application in photovoltaics

We present an approach for the growth of ZnO nanowire arrays with a length of up to 30 μm on fluorine doped tin oxide substrates with a growth rate of 20 μm per hour. The growth was carried out in a vapor phase transport setup at a temperature of 600 °C. To achieve an aligned growth on fluorine doped tin oxide substrates we used wet-chemically grown nanowire arrays with typical length of 2 to 3 μm as a seeding layer. Additionally the nanowire arrays were used as electrodes for the manufacturing of dye sensitized solar cells and the best achieved efficiencies were 1.83% at 10 mW/cm² and 1.47% at 100 mW/cm².     

Biodegradable polyurethane composite scaffolds containing Bioglass® for bone tissue engineering

Five types of solid and porous polyurethane composites containing 5–20 wt.% of Bioglass® inclusions were synthesized. Porous structures were fabricated by polymer coagulation combined with the salt-particle leaching method. In-vitro bioactivity tests in simulated body fluid (SBF) were carried out and the marker of bioactivity, e.g. formation of surface hydroxyapatite or calcium phosphate layers upon immersion in SBF, was investigated. The chemical and physical properties of the solid and porous composites before and after immersion in SBF were evaluated using different techniques: Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA) and Thermogravimetric Analysis (TGA). Moreover the surface structure and microstructure of the composites was characterised by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM), respectively. Mercury intrusion porosimetry, SEM and microtomography (μCT) were used to determine pore size distribution and porosity. The fabricated foams exhibited porosity >70% with open pores of 100–400 μm in size and pore walls containing numerous micropores of <10 μm. This pore structure satisfies the requirements for bone tissue engineering applications. The effects of Bioglass® addition on microstructure, mechanical properties and bioactivity of polyurethane scaffolds were evaluated. It was found that composite foams showed a higher storage modulus than neat polyurethane foams. The high bioactivity of composite scaffolds was confirmed by the rapid formation of hydroxyapatite on the foam surfaces upon immersion in SBF.     

Surface characterization of plasma-treated and PEG-grafted PDMS for micro fluidic applications

The contact angle measurements have shown that polydimethyl siloxane (PDMS) surfaces treated by air plasma can recover up to about 40% of its hydrophobic nature in less than 20 min of air exposure. Therefore, poly(ethylene glycol) (PEG) silane was grafted after plasma treatment to permanently change the PDMS surface as hydrophilic in nature for micro fluidic application. The surface chemistry of plasma-treated and PEG-grafted PDMS substrate has been studied using X-ray photoelectron spectroscopy (XPS). The proportion of carbon atoms as C-Si and hydrocarbon decreased for both plasma-treated as well as PEG-grafted PDMS surfaces. The plasma treatment had increased the proportion of carbon atoms as CO and C(O)OX in C1s, whereas grafting of PEG silane decreased the proportion of C(O)OX and an increase in C-OX and CO functionalities. This is due to the interaction of OCH₃ on Si (in PEG silane) with C-OX and C(O)OX on plasma-treated PDMS by covalent bonding. Therefore, an increase in CO and C-OX functionalities and relative decrease in C(O)OX is expected. The plasma treatment of micro channels had increased the fluid velocity by a factor or four and similar measurements were observed in PEG grafted micro channel in PDMS chip. This indicates that the fluid velocity depends on the hydrophilic nature of substrate. The effect of nature of fluids on the fluid velocity in PDMS-based micro channel was also studied. It was observed that the fluid velocity was decreased with decreasing the pH values of the fluid.     

Effects of the cryogenic cooling on the fatigue strength of the AISI 304 stainless steel ground components

For environmental considerations, the substitution of the conventionally used oil-based grinding fluids has nowadays become strongly recommended. Although several alternatives have been proposed, cryogenic cooling by liquid nitrogen is the non-polluting coolant that has been given relatively more attention because of its very low temperature. In this investigation, in order to contribute to developing this promising cooling mode, its beneficial effects on the ground surface integrity of the AISI 304 stainless steel and their consequences on the fatigue lifetime are explored. Results of this investigation show that grinding under cryogenic cooling mode generates surfaces with lower roughness, less defects, higher work hardening and less tensile residual stresses than those obtained on surfaces ground under oil-based grinding fluid. These surface enhancements result into substantial improvements in the fatigue behaviour of components ground under this cooling mode. An increasing rate of almost 15% of the endurance limit at 2 × 10⁶ cycles could be realized. SEM analyses of the fatigue fracture surfaces have shown that the fatigue cracks observed on the specimens ground under cryogenic cooling are shorter (i.e., 30-50 μm) than those generated under oil-based cooling mode (i.e., 150-200 μm). The realized improvements in the surface integrity and in the fatigue behaviour are thought to be related to the reduction of the grinding zone temperature observed under cryogenic cooling, as no significant differences between the grinding force components for both cooling modes have been observed.     

Comparison of dry etching of PMMA and polycarbonate in diffusion pump-based O2 capacitively coupled plasma and inductively coupled plasma

We report a comparison of dry etching of polymethyl methacrylate (PMMA) and polycarbonate (PC) in O₂ capacitively coupled plasma (CCP) and inductively coupled plasma (ICP). A diffusion pump was used as high vacuum pump in both cases. Experimental variables were process pressure (30-180 mTorr), CCP power (25-150 W) and ICP power (0-350 W). Gas flow rate was fixed at 5 sccm. An optimized process pressure range of 40-60 mTorr was found for the maximum etch rate of PMMA and PC in both CCP and ICP etch modes. ICP etching produced the highest etch rate of 0.9 μm/min for PMMA at 40 mTorr, 100 W CCP and 300 W ICP power, while 100 W CCP only plasma produced 0.46 μm/min for PMMA at the same condition. For polycarbonate, the highest etch rates were 0.45 and 0.27 μm/min, respectively. RMS surface roughnesses of PMMA and PC were about 2-3 nm after etching. Etch selectivity of PMMA over photoresist was 1-2 and that of PC was less than 1. When ICP power increased from 0 to 350 W, etch rates of PMMA and PC increased linearly from 0.47 to 1.18 μm/min and from 0.18 to 0.6 μm/min, while the negative self bias slightly reduced from 364 to 352 V. Increase of CCP power raised both self bias and PMMA etch rate. PMMA etch rates were about 3 times higher than those of PC at the same CCP conditions. SEM data showed that there was some undercutting of PMMA and PC after etching at 300 W ICP, 100 W CCP and 40 mTorr. The results also showed that the etched surface of PMMA was rough and that of PC was relatively smooth.     

Three-body abrasion on wear and frictional performance of treated betelnut fibre reinforced epoxy (T-BFRE) composite

This work aims to investigate the wear and frictional behaviour of a new epoxy composite based on treated betelnut fibres subjected to three-body abrasion using different abrasive particle sizes (500 μm, 714 μm and 1430 μm) and sliding velocities (0.026–0.115 m s⁻¹) at constant applied load (5 N) using a newly developed Linear Tribo Machine. The worn surfaces of the composite were studied using scanning electron microscope. The work revealed that the predominant wear mechanism of treated betelnut fibre reinforced epoxy (T-BFRE) composite sliding against grain sands was plastic deformation, pitting and pullout of betelnut fibres. The composite exhibited higher values in frictional coefficient when it was subjected against coarse sand. Besides, the abrasive wear of the composite is depending on the size of abrasive particles and sliding velocity. Higher weight loss is noticed at high sliding velocities. The specific wear rate for the composite subjected to three different sand particles follow the order of: coarse > grain > fine sands respectively.     

The characteristics of sub-10 nm gate-length erbium-silicided n-type Schottky barrier metal-oxide-semiconductor field-effect-transistors

10 and 6 nm erbium-silicided n-type Schottky barrier metal-oxide-semiconductor field-effect transistors (SB-MOSFETs) were manufactured. The manufactured 10 nm n-type SB-MOSFET showed a large on/off current ratio (> 10⁶) with low leakage current less than 10^− 5 μA/μm due to the existence of the robust Schottky barrier between source and channel region. The saturation currents were 550 and 320 μA/μm when drain and gate voltages were 2 V and 3 V, for the 10 and 6 nm erbium-silicided n-type SB-MOSFETs, respectively. The manufactured SB-MOSFETs exhibited superior short channel characteristics due to the existence of Schottky barrier between source and channel region.     

Nanostructured surface changes of Ti-35Ta-xZr alloys with changes in anodization factors

The purpose of this study was to investigate the changes of the nanostructured surface of Ti-35Ta-xZr alloys for dental application resulting from changes in anodization factors. TiO₂ nanotubes were formed on Ti-35Ta-xZr alloys by anodization in H₃PO₄-containing NaF solutions. Anodization was carried out using a scanning potentiostat. Microstructures of the alloys were examined by optical microscopy (OM), field emission scanning electron microscopy (FE-SEM) and x-ray diffraction (XRD). Microstructures of the Ti-35Ta-xZr alloys were changed from α" phase to β phase, and morphologies changed from a needle-like to an equiaxed structure, with increasing Zr content. As the Zr content increased from 3 to 7 to 15 wt.%, the average thickness of the TiO₂ nanotubes increased from 4.5 μm to 6.1 μm to 9.0 μm. When the anodizing potential was increased from 3 V to 10 V, the thickness of the nanotube layers increased from about 0.5 μm to 9.5 μm. As the anodization time increased from 30 min to 180 min at 10 V, the nanotube thickness increased from 4 μm to 9.5 μm. The amorphous oxide phase in the nanotubes transformed to anatase and rutile phases of TiO₂ by heat treatment above 300 °C.     

Spark plasma sintered tantalum carbide-carbon nanotube composite: Effect of pressure, carbon nanotube length and dispersion technique on microstructure and mechanical properties

TaC-4 wt.% CNT composites were synthesized using spark plasma sintering. Two kinds of CNTs, having long (10-20 μm) and short (1-3 μm) length, were dispersed by wet chemistry and spray drying techniques respectively. Spark plasma sintering was carried out at 1850 °C at pressures of 100, 255 and 363 MPa. Addition of CNTs leads to an increase in the density of 100 MPa sample from 89% to 95%. Short CNTs are more effective in increasing the density of the composites whereas long CNTs are more effective grain growth inhibitors. The longer CNTs are more effective in increasing the fracture toughness and an increase up to 60% was observed for 363 MPa sample. Hardness and elastic modulus are found to increase by 22% and 18% respectively for 100 MPa samples by addition of long CNTs. Raman spectroscopy, SEM and TEM images indicated that the CNTs were getting transformed into flaky graphitic structures at pressure higher than 100 MPa.