Smooth Surface Profile Research Articles

(Invited) III-Nitride Ultraviolet LEDs and Lasers for Applications in Biology and Medicine

Ultraviolet (UV) light emitters with large-energy photons are being developed for emerging biology and medicine applications such as sterilization, water/air purification, and medical treatments, as a replacement for mercury vapor lamps. Solid-state UV light-emitting diodes (LEDs) and lasers based on wide bandgap III-Nitrides offer compact sizes, wavelength tuning, long lifetimes, and sustainability over mercury vapor lamps. While visible LEDs and lasers with longer emission wavelengths find widespread commercial uses for solid-state lighting and display, UV emitters with AlGaN heterostructures struggle with poor external quantum efficiencies of typically less than 10%, which drop further when wavelengths get shorter. Therefore, it is extremely challenging to realize high-efficiency UV emitters despite the demand for compact UV light source, especially for disinfection and sterilization from the pandemic as those high-energy photons can break DNA/RNA bonds and deactivate virus/bacteria. Here, I will discuss our recent developments toward realization of high-efficiency UV LEDs and lasers.To enhance the radiative recombination rate (R sp) from the AlGaN quantum well (QW) active region, we had pursued novel QW design to overcome issues from the existence of valence subbands crossover. Specifically, the arrangement of the three energy-degenerate valence subbands - heavy hole (HH), light hole (LH), and the crystal-field split-off hole (CH) bands for high Al-content and low Al-content AlGaN QWs are completely different. The ordering of the valence bands strongly affects the optical matrix element via the oscillator strength, as well as the direction of the photon emission. Our work has proposed promising solution on the use of delta-QW design to address the valence subbands crossover issue, in order to significantly boost up the R sp. In addition, to enhance the extraction efficiency of UV emitters, we demonstrated the realization and characterization of top-down fabricated, electrically driven UV micropillar array LEDs emitting at 286 nm with a narrow, 9 nm linewidth and output power densities up to 35 mW/cm2. Top-down fabrication allows for formation of perfectly uniform arrays of micropillars with easily tunable diameter and pitch, which cannot be achieved with epitaxially grown nanowires without the use of selective area epitaxy. Dry etch damage induced surface losses were avoided through the use of a two-step etch process combining a Cl dry etch and a hydroxyl-based wet etch to form the micropillar arrays. We also revealed that the unique inverse-taper profile of our micropillars could produce significant enhancements in the extraction efficiency with the increased taper angle. Lastly, our developed III-Nitride wet etch by the use of hydroxyl-based chemicals such as potassium hydroxide (KOH) investigated the effects of temperature, concentration, and the damage recovery aspects of hydroxyl etching of III-Nitride nano and micro structures, leading to important smooth surface profiles for micropillar/nanowire LEDs and optimized mirror facets for ridge-emitting UV lasers.

Rapid Algorithmic Blade Design Applying Machine Learning From Shape Optimization to Satisfy Multidisciplinary Constraints

Abstract This paper presents a new, rapid, flexible approach for turbine blade section design combining algorithmic and inverse techniques to enable automatic generation of blade sections guaranteed to conform to multidisciplinary requirements, with the aim of accelerating turbomachinery design iterations. The approach links a base algorithm to parametrize and generate blade section geometry conforming to structural and manufacturability constraints such as section area, trailing edge radius, and exit wedge angle with a 2D cfd solver to calculate surface isentropic Mach number profile for aerodynamic performance evaluation. To achieve blade sections with smooth surface and lenticular Mach number profile concave up on the pressure side and concave down on the suction side, the base algorithm is tuned by a surrogate inverse model trained by machine learning from pre-generated tuning data obtained by case-by-case shape optimization for a range of design conditions. A weighted objective function is applied to quantify both geometric and aerodynamic quality of blade sections for the optimization. Shape optimization improves output section quality by 54–87% compared to the untuned algorithm. Aerodynamically, suction-side flow separation is eliminated in the optimized sections, giving 70% less pressure loss compared to the untuned algorithm for the best cases. Across all conditions spanning the examined design space, the surrogate model successfully captures most of this improvement, yielding blade sections of similar quality to explicit optimization sufficient to meet the geometric and aerodynamic requirements for design. Furthermore, section quality is preserved even if imposed structural and manufacturability constraints are perturbed within typical margins, guaranteeing blade sections that are always viable for practical use. Blade sections from the surrogate-tuned algorithm are output within minutes, eliminating the time-intensiveness of existing manual or case-by-case design approaches.

Inverse scattering of periodic surfaces with a superlens.

We propose a scheme for imaging periodic surfaces using a superlens. By employing an inverse scattering model and the transformed field expansion method, we derive an approximate reconstruction formula for the surface profile, assuming small amplitude. This formula suggests that unlimited resolution can be achieved for the linearized inverse problem with perfectly matched parameters. Our method requires only a single incident wave at a fixed frequency and can be efficiently implemented using fast Fourier transform. Through numerical experiments, we demonstrate that our method achieves resolution significantly surpassing the resolution limit for both smooth and non-smooth surface profiles with either perfect or marginally imperfect parameters.

Detailed investigations on structural, spectroscopic, and optoelectronic properties of Ethyl Nile Blue thin films

Here, we highlight the interrelation between constitutional and spectroscopical properties of Ethyl Nile Blue thin films. The deposited films are amorphous with a homogenous and smooth surface profile. Spectrophotometrically, films show high IR transparency with intense UV and visible light absorption. Moreover, ENB films exhibit an indirect energy gap and Urbach energy ∼2.77 eV and 63 meV, respectively. The dispersion behavior of the films is inspected in correspondence to the single-effective-oscillator model. Referring to the thermal emissivity and the surface resistance characteristics of ENB film, impressive IR features have been discovered displaying the validity of ENB film in IR thermal emission applications. The nonlinear properties of ENB film like nonlinear optical susceptibility, nonlinear refractive index, and nonlinear absorption coefficient are evaluated. Comparison of the optical parameters of ENB and other conjugated organic dyes, it is highly recommended to possess high potentiality in UV–visible optoelectronics and optical switching applications.

Comprehensive design method of a soft multifocal contact lens with NURBS.

This study presents a comprehensive method for designing a multifocal contact lens (MCL) with Snell's law and non-uniform rational B-spline (NURBS) curves. Instead of using thin lens approximation, general mathematical formulas have been developed to achieve the accurate coordinates of points on the anterior lens surface profile of the MCL to meet various given optical power distributions. Then the NURBS curve is adjusted to fit these data points to obtain the smooth front lens surface profile. This method not only improves the accuracy of the optical power profiles of MCLs but also reduces the spherical aberration in near/distance optical zones. The experimental results show that the power profiles of soft MCLs agree with those of the simulation results and original design requirements. The proposed method has been proven for the MCL design, and it can be feasibly applied in complex optical lens designs.

Fabrication of Perforated PDMS Microchannel by Successive Laser Pyrolysis.

Poly(dimethylsiloxane) has attracted much attention in soft lithography and has also been preferred as a platform for a photochemical reaction, thanks to its outstanding characteristics including ease of use, nontoxicity, and high optical transmittance. However, the low stiffness of PDMS, an obvious advantage for soft lithography, is often treated as an obstacle in conducting precise handling or maintaining its structural integrity. For these reasons, a Glass-PDMS-Glass structure has emerged as a straightforward alternative. Nevertheless, several challenges are remaining in fabricating Glass-PDMS-Glass structure through the conventional PDMS patterning techniques such as photolithography and etching processes for master mold. The complicated techniques are not suitable for frequent design modifications in research-oriented fields, and fabrication of perforated PDMS is hard to achieve using mold replication. Herein, we utilize the successive laser pyrolysis technique to pattern thin-film PDMS for microfluidic applications. The direct use of thin film at the glass surface prevents the difficulties of thin-film handling. Through the precise control of photothermal pyrolysis phenomena, we provide a facile fabrication process for perforated PDMS microchannels. In the final demonstration, the laminar flow has been successfully created owing to the smooth surface profile. We envision further applications using rapid prototyping of the perforated PDMS microchannel.

Advances in Laser Additive Manufacturing of Ti-Nb Alloys: From Nanostructured Powders to Bulk Objects.

The additive manufacturing of low elastic modulus alloys that have a certain level of porosity for biomedical needs is a growing area of research. Here, we show the results of manufacturing of porous and dense samples by a laser powder bed fusion (LPBF) of Ti-Nb alloy, using two distinctive fusion strategies. The nanostructured Ti-Nb alloy powders were produced by mechanical alloying and have a nanostructured state with nanosized grains up to 90 nm. The manufactured porous samples have pronounced open porosity and advanced roughness, contrary to dense samples with a relatively smooth surface profile. The structure of both types of samples after LPBF is formed by uniaxial grains having micro- and nanosized features. The inner structure of the porous samples is comprised of an open interconnected system of pores. The volume fraction of isolated porosity is 2 vol. % and the total porosity is 20 vol. %. Cell viability was assessed in vitro for 3 and 7 days using the MG63 cell line. With longer culture periods, cells showed an increased cell density over the entire surface of a porous Ti-Nb sample. Both types of samples are not cytotoxic and could be used for further in vivo studies.

Surface modification of ultrahigh strength 300M steel under supercritical carbon dioxide (scCO2)-assisted grinding process

300M steel has been widely utilized in the manufacturing processes of functional parts served in harsh environments. The properties of the parts’ surface layer induced by the grinding process are of great importance for the service performance, which can be determined by the input parameters of processing. This paper carried out evaluation of surface modification of 300M steel material under the scCO2-assisted grinding process. To further enhance the understanding of this processing design, the generation of surface modification with dry and flood techniques were also compared. The surface morphology, surface roughness, microstructure evolution, work hardening and surface residual stresses were recorded. The mechanism of grain refinement and the substructure of the martensite lath has been revealed. It was found that the scCO2-assisted grinding processes are responsible for smoother surface profile compared to the dry and flood techniques. Meanwhile, the machined surface roughness was maintained at a stable lower level as the grinding depth increases, proving the great superiority of scCO2 medium for improving the productivity and process sustainability. The grains in the superficial layer have been noticeably refined after grinding operation while it presents deeper refinement with scCO2-assisted grinding process. Meanwhile, nanocrystalline and carbide precipitation were clearly found on the refined layer with scCO2 medium, the crystal defects are mainly the combination of dislocation tangles (DTs), dislocation walls (DWs) and dislocation cells (DCs), and the stacking fault was observed to be the substructure for the lath martensite except the dislocation with TEM analysis. The designed scCO2-assisted grinding contributes to higher work hardening and compressive stresses compared to dry and flood methods.

Material and Si-based diode analyses of sputtered ZnTe thin films

Structural, optical, and electrical properties ZnTe thin films grown by magnetron sputtering technique were studied by X-ray diffraction, atomic force microscopy, Raman spectroscopy, and electrical conductivity measurements. Structural analyses showed that ZnTe thin films grown on soda–lime glass substrates have a cubic crystalline structure. This crystalline nature of the films was also discussed in terms of Raman active modes. From atomic force microscopy images, the smooth and dense surface profile was observed. The conductivity of the film at room temperature was measured as 2.45 × 10−4 (Ω cm)−1 and the temperature dependency of conductivity showed Arrhenius behavior. The dark conductivity profile was modeled by thermionic emission mechanism and activation energies were extracted. In addition, the conductivity values indicated an increasing behavior with illumination intensity applied between 20 and 115 mW/cm2. The heterojunction diode was generated by sputtering ZnTe film on n-Si wafer substrate and the rectification behavior was evaluated to determine the main diode parameters.

Application of FDM technology to reduce aerodynamic drag

Purpose The purpose of this paper is to analyze the aerodynamic improvements obtained in a wing section with a NACA 0018 airfoil manufactured using the fused deposition modeling (FDM) technique with regard to a smooth surface made by milling. The creation of micro-riblets on the surface of the airfoil, due to the deposition of the material layer by layer, improves the general aerodynamic performance of the parts, provided that the riblets are parallel to the flow line. The incidence of the thickness of the thread deposited in each layer – to be the variable on which the geometry of the riblets is based – was studied. Design/methodology/approach The wing section was designed using 3D software. Three different models were designed by rapid prototyping, using additive and subtractive manufacturing. Two of the profiles were manufactured using FDM varying the thickness of the layer to be able to compare the aerodynamic improvements. The third model was manufactured using a subtractive rapid prototyping machine generating a smooth surface profile. These three models were tested inside the wind tunnel to be able to quantify the aerodynamic efficiency according to the geometry and the riblets size. Findings The manufacture of an aerodynamic profile using FDM provides, in addition to the lightness and the ability to design parts with complex geometries, an improvement in the aerodynamic efficiency of 10 per cent compared with profiles with a smooth surface. Practical implications With the aerodynamic advantage gained through the use of FDM positions, the additive manufacturing serves as an excellent alternative for the manufacture of lightweight aerodynamic parts, with low structural loading and with low Reynolds number (∼5·105). This technological advantage would be applied to the UAV (unmanned aerial vehicle) industry. Originality/value The study carried out in this article demonstrates that the use of FDM as a manufacture process of end-used parts that are subject to movement generates an additional advantage that had not been considered. The additive manufacturing allows us to directly manufacture riblets by creating the necessary surface so as to reduce the aerodynamic drag.

Surface improvement of laser solid forming Inconel 718 by electrochemical machining

Surface improvement of laser solid forming Inconel 718 by electrochemical machining was investigated. Microstructure observation shows that there exists a fiber texture and the ⟨001⟩ direction is parallel to the build direction. Furthermore, the alloying elements of Nb, Mo, and Ti are rich in interdendritic regions, and γ/Laves eutectic phase and γ/carbides eutectic phase are located in the interdendritic regions. Besides, the surface morphologies are wavy due to the overlapping of the scanning tracks and the stacking effect between deposited layers. Electrochemical results show that the top surface requires less time to obtain a smooth surface profile than the side surface due to their original surface profiles difference and the less volume of the bulges on the top surface. The numerical simulation indicates that the uneven surface profiles become smooth owing to the fact that the surface peaks dissolve faster than the surface depressions. These results provide an insight into improving the surface quality of the as-deposited Inconel 718.

Effect of screw thread length on stiffness of proximal humerus locking plate constructs: A finite element study

Plate-based treatment of proximal humerus fractures is associated with a high risk of complications such as screw perforation into glenohumeral joint. Smooth and threaded pegs were developed with the hope of minimising these risks. No consensus exists onto which threading profile achieves stiffest bone-plate construct. This study investigated the biomechanical effect of five percentages of threading on individual humeral head screws on a bone-plate construct. A finite element model simulating a two-part proximal humerus fracture treated with a Spatial Subchondral Support plate was developed and validated against in vitro biomechanical tests. The proportion of the humeral head screw length that was threaded was varied between 0%-100% in 25% increments. A 5-mm cantilever varus displacement was applied and the required load (F5) was calculated. Full (100%) threading achieved the stiffest construct for all six screws. Fully threading all smooth pegs at once increased F5 by 18%. Threading did not increase F5 equally in all screws. Inferior three plate screws exhibited a larger increase in stiffness than superior three. Most of the mechanical benefits of threading in inferior three screws can be achieved by using threaded pegs (50% threading) while the superior three screws need to be fully threaded. In practice, the smooth surface profile may also offer additional mechanical benefits if implanted with longer lengths and larger diameters. Threading is an effective way of increasing the varus bending stiffness of proximal humerus plates constructs.

РОЗРОБКА ВИСОКОЕФЕКТИВНОЇ СУДНОВОЇ СИСТЕМИ ОЧИЩЕННЯ ПОВІТРЯ ВІД КРАПЛИННОЇ ВОЛОГИ

It is investigated one of the directions of increasing the technical, economic and environmental characteristics of engines and power plants by air cleaning as a working fluid of condensed moisture. Prospective methods of aerosol medium separation with the help of gradient intensification of transfer processes in boundary layers of multifunctional surfaces are also investigated. Multifunctional surfaces include surfaces with a coefficient of compactness more than 2000 m2/m3, characterized by improved heat exchange and separating properties. A characteristic feature of the developed separating profiles is the combination of a waveform part with flat input and output elements. In the assembly, the separating profiles form the curved channels with a number of successive confuser and diffuser elements. In diffusor elements, there are separating zones with the gas reverse flow. The liquid film resulting from the droplets deposition, falling into these zones, is influenced by the vortices effect that counteracts the film motion in the direction of the main flow and facilitates its flow under the action of gravity. The investigations of gas dynamics and deposition coefficients of the separation profile were performed. The coefficient of droplets deposition for flow rates of 5, 10, 15, 20 m/s in separating profiles with a radius of 5, 10, 15, 20, 25 mm was calculated. It was determined that vortex zones provide full removal of captured water from the smooth surface profile up to the airspeed of 5 m/s. Excess of this speed leads to the removal of part of the water from the vortex zones. Drainage elements are provided for preventing secondary flooding of the flow in flat sections of the separation profile. Design solutions and a generalized scheme of the ship system of air cleaning of condensed moisture for the air flow from 20 to 2000 m3/h were developed. The introduction of filters based on gradient technologies will increase the reliability, the life of the marine power equipment and its elements. This will contribute to the creation of high-efficiency energy-saving technologies and efficient design solutions for a wide range of gradient marine power plant separators.

Improving flexural strength and toughness of geopolymer mortars through additively manufactured metallic rebars

Abstract This paper presents the results of an experimental study on the flexural reinforcement of a geopolymer mortar through additively manufactured metallic rebars. A mortar employing a geopolymer binder with low calcium content fly ash is reinforced with Ti6Al4V rebars additively manufactured though electron beam melting. The effectiveness of reinforcements realized with rebars featuring either smooth or rough surface profiles is studied through three-point bending tests and post-test microscopy analysis. The given experimental results highlight micro and macroscale pullout failure mechanisms in specimens reinforced with rebars showing cylindrical embossments on the lateral surface, which remarkably improve the flexural strength and the interfacial bond strength of the analyzed mortar. The role played by the surface roughness of the reinforced elements on the bond-slip response of the matrix-rebar interface is highlighted, while drawing comparisons with available literature results on cement mortars.

Evaluation of RBD palm stearin as alternative lubricant for cold forward extrusion process

A rapid growth in awareness level over environmental problems have brought researchers to find a substitute lubricant to reduce the use of mineral based lubricants. In this paper, the lubrication performance of RBD palm stearin was evaluated in order to be utilized as alternative lubricant for metal forming lubricant. Commercial paraffinic mineral oil VG460 and VG95 were used for comparison purposes. The experiment was conducted using cold work extrusion apparatus that consists of taper die (made of tool steel SKD11) and a pair of billet (made of pure aluminium A1100). The results obtained from these experiments showed that RBD palm stearin can reduce extrusion load, produce a lower surface roughness value and have smooth surface profile compared to commercial paraffinic mineral oils. It is demonstrated that RBD palm stearin have promising lubrication performance and can be considered as alternative lubricant in metal forming process.

Characterization of Carbon Black Filled PDMS-Composite Membranes for Sensor Applications

This paper describes the characterization of conductive PDMS (CPDMS) composites. Composite have been achieved by filling the PDMS with CarbonBlack (CB). Two different methods were used to prepare the CPDMS composites: (A) direct mixing of CB with PDMS (CB-PDMS); (B) dissolving of CB in methanol before mixing with PDMS (CB-Methanol-PDMS). At a certain critical CB concentration, called percolation threshold, the membranes get conductive. Membranes of CPDMS (thickness ≈ 100µm) have been fabricated. CPDMS membranes of method (B) show a smoother surface profile as membranes of method (A). By means of a two–point resistivity measurement, the electrical resistance of CPDMS membranes was measured. With an increase of the CB concentration, the resistance decreases. Membranes of method (B) show a low percolation threshold and a low surface resistivity. Effects of pressure and temperature on the membrane resistance were investigated, too. Around the percolation threshold, the resistance shows the highest sensitivity on pressure and temperature variations. The Young’s modulus of CPDMS membranes exponentially increase with an increase of the CB concentration.

Wet chemical etching of ZnO films using NH x -based (NH4)2CO3 and NH4OH alkaline solution

In this paper, we deposited ZnO thin films by RF magnetron sputtering at room temperature from un-doped targets. Wet chemical etching of ZnO films in (NH4)2CO3 and NH4OH solutions were examined. For comparison, hydrochloric acid was also used as an etchant. The NH x -based alkaline solutions provide well-controlled etching rate, and smooth surface and sidewall profiles. Although NH x -based alkaline solution etch rates for ZnO were relatively low, they were enhanced with the use of a H3O stabilizer. In this case, the NH4OH solution went from reaction-dominant mode to diffusion-dominant mode, which is beneficial for smooth surface morphology.

Dyeing of Wool and Cotton Fabrics with Leaves of Apple (Malus Domestica) Tree

ABSTRACTIn this study, apple leaves were used to dye wool and cotton fabrics. Effects of mordant type and dyeing technique on color yield and fastness properties were investigated. The selected dyed fibre sample surfaces were observed using a scanning electron microscope (SEM). Color strength (K/S) values of the dyed fabrics were between 0.53 and 20.56. Washing and rubbing fastness results of the dyed fabrics were moderate/high. The SEM images of the naturally dyed fabrics demonstrated a smooth surface profile. We have concluded that apple leaf is suitable for the natural dyeing of wool fabrics.

Rheological analysis of ceramic pastes with ethyl cellulose for screen-printing

Pastes of ceramic particles are used in many industrial applications such as in printed electronic products and solid oxide fuel cells. Ethyl cellulose (EC), a polymer component in the paste, is very useful to control the rheological properties of the pastes for screen printing. In this study, to prepare ceramic La0.6Sr0.4Ti0.3Fe0.7O3−δ (LSTF) pastes, EC was mixed with an organic solvent, ethylene glycol monobutyl ether acetate, and LSTF powder. The effects of EC and LSTF particle contents were investigated on the rheological properties of the pastes, using shear, stress, frequency-dependence, and a 3-step recovery tests. The recovery ratio of the pastes in the 3-step tests was found to depend strongly on their EC and LSTF particle contents, decreasing at higher contents due to the formation of a strong network. We also investigated the microstructure and surfaces of thick films fabricated through screen-printing, and confirmed that pastes with a low recovery ratio and high viscosity afford smooth surface profiles.

Single shot interferogram analysis for optical metrology.

We report a novel constrained optimization method for single shot interferogram analysis. The unknown test wavefront is estimated as a minimum L2-norm squared solution whose phase is constrained to the space spanned by a finite number of Zernike polynomials. Using a single frame from standard phase shifting datasets, we demonstrate that our approach provides a phase map that matches with that generated using phase shifting algorithms to within λ/100 rms error. Our simulations and experimental results suggest the possibility of a simplified low-cost high quality optical metrology system for performing routine metrology tests involving smooth surface profiles.