Large Surface Roughness Research Articles

Sequentially Coated Wavy Nanowire Composite Transparent Electrode for Stretchable Solar Cells.

Recent advances in fabricating stretchable and transparent electrodes have led to various techniques for establishing next-generation form-factor optoelectronic devices. Wavy Ag nanowire networks with large curvature radii are promising platforms as stretchable and transparent electrodes due to their high electrical conductivity and stretchability even at very high transparency. However, there are disadvantages such as intrinsic nonregular conductivity, large surface roughness, and nanowire oxidation in air. Here, we introduce electrically synergistic but mechanically independent composite electrodes by sequentially introducing conducting polymers and ionic liquids into the wavy Ag nanowire network to maintain the superior performance of the stretchable transparent electrode while ensuring overall conductivity, lower roughness, and long-term stability. In particular, plenty of ionic liquids can be incorporated into the uniformly coated conducting polymer so that the elastic modulus can be significantly lowered and sliding can occur at the nanowire interface, thereby obtaining the high mechanical stretchability of the composite electrode. Finally, as a result of applying the composite film as the stretchable transparent electrode of stretchable organic solar cells, the organic solar cell exhibits a high power conversion efficiency of 11.3% and 89% compared to the initial efficiency even at 20% tensile strain, demonstrating excellent stretching stability.

Research on AlN thin film microstructure processing technology based on ultra-thin cantilever beam structure

Aiming at the problem of poor solution selection ratio when the AlN film and porous silicon sacrificial layer are released in the ultra-thin cantilever structure and at the problem of large surface roughness after AlN graphing, the wet corrosion process parameters were optimized, and the influence of different corrosive fluids and corrosion times on the surface roughness of AlN and the influence on the etching rate of AlN were studied, and different process parameters were selected for experiments. According to the experimental results, a suitable microstructure processing method was selected to effectively reduce the surface roughness of AlN and improve the integrity of the AlN film and the reliability and yield of the cantilever structure when the sacrificial layer is released. The microstructure fabrication of AlN films in ultra-thin cantilever structures enables the fabrication of ultra-micro-force sensors, accelerometers, acoustic sensors, and other devices.

Preparation of high performance MgO ceramic filter and its interaction with molten steel: Effect of porous MgO powder

In this study, two kinds of MgO ceramic filters were prepared by using porous magnesia powder and fused magnesia powder as raw material, respectively. The microstructures, mechanical properties and purification efficiency on the molten steel of two MgO ceramic filters were investigated by mercury porosimetry measurement, SEM, EDS and immersion test with molten steel, etc. The results demonstrate that compared with the filter FM prepared from the fused magnesia powder, the rheological property of the slurry of the filter PM was improved via the finer and uniformly distributed nano-sized Mg(OH)2 particles generated by the hydration of the porous magnesia powder, which not only optimized the macropore structure but also promoted the growth of the sintering neck between the microparticles of the skeleton. Therefore, the MgO filter skeleton with a microporous structure was obtained, which elevated the strength and thermal shock resistance of the filter PM. According to the immersion tests with the molten steel, both filters significantly reduced the number of inclusions with size < 5 µm2 in the molten steel as well as their total oxygen contents, and the filter PM had better purification efficiency than the filter FM. The reason for the better purification efficiency of the filter PM was related to its smaller micro-sized pores, larger surface roughness, and certain high-temperature liquid phase in their skeletons. In general, the porous magnesia powder resulted in higher compressive strength, better thermal shock resistance and superior purification efficiency on the molten steel of the filter compared with the fused magnesia powder.

Flexible Film Bulk Acoustic Resonator Based on Low-Porosity β-Phase P(VDF-TrFE) Film for Human Vital Signs Monitoring.

P(VDF-TrFE) is a promising material for flexible acoustic devices owing to its good piezoelectric performance and excellent stretchability. However, the high density of internal pores and large surface roughness of the conventional P(VDF-TrFE) results in a high propagation attenuation for acoustic waves, which limits its use in flexible acoustic devices. In this paper, a novel method based on two-step annealing is proposed to effectively remove the pores inside the P(VDF-TrFE) film and reduce its surface roughness. The obtained P(VDF-TrFE) film possesses excellent characteristics, including a high breakdown strength of >300 kV/mm, a high-purity β-phase content of more than 80%, and high piezoelectric coefficients (d33) of 42 pm/V. Based on the low-porosity β-phase P(VDF-TrFE) film, we fabricated flexible film bulk acoustic resonators (FBARs) which exhibit high sharp resonance peaks. The pressure sensor was made by sandwiching the FBARs with two PDMS microneedle patches. Heartbeat and respiration rate monitoring were achieved using the pressure sensor. This work demonstrates the feasibility of high-performance flexible piezoelectric acoustic resonators based on low-porosity P(VDF-TrFE) films, which could see wider applications in the wearable sensors for both physical and chemical sensing.

Nanosphere-structured hierarchically porous PVDF-HFP fabric for passive daytime radiative cooling via one-step water vapor-induced phase separation

Growing demand for efficient and economical cooling for indoor as well as outdoor applications, especially personal cooling in outdoor environments, is a major global challenge today. Currently, tailored optical structures with spectral selectivity are being used as cooling strategies. However, developing these photonic structures generally requires sophisticated multi-step manufacturing processes and use of multiple solvents which limits their acceptability for large-scale production and cost-effectiveness. Therefore, for the first time, herein we report the fabrication of nanosphere-structured hierarchically porous poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) fibrous fabric via a facile one-step electrospinning process based on water vapor-induced phase separation (WVIPS) technique using single solvent. The fabricated fabric with interconnected nanospheres structure and hierarchically porous fibers possessed large roughness and high specific surface area. Cooling performance of the fabricated PVDF-HFP fabrics was evaluated using skin simulators to mimic human body. The as-prepared PVDF-HFP fabric exhibits a superior average solar reflectance (∼93.7 %) and infrared emittance (∼91.9 %), yielding a temperature drop of ∼19.8 °C and ∼13.2 °C compared to the bare skin simulator and the one covered with cotton fabric, respectively, under solar intensity of ∼950 W m−2. Additionally, excellent hydrophobicity and adsorption make designed fabrics potentially suitable materials for not only radiative cooling but also for waterproof and filtration applications.

Combined polishing process of a sapphire aspherical component based on temperature-controlled magnetorheological processing.

In view of the problems of large surface roughness and low removal efficiency caused by the existing sapphire processing process, a combined polishing process based on temperature control computer controlled optical surfacing-magnetic rheology is proposed. The polishing removal mechanism of sapphire material polishing and the law of processing surface roughness change are studied. The optimal process parameters are obtained by designing the orthogonal experiments. Under this parameter, a sapphire aspherical component with good surface quality is obtained, and the temperature has a significant amount of influence on the removal efficiency. Finally, the optimum temperature of sapphire material under magnetorheological polishing was determined to be 75°C. The results greatly improve the manufacturing efficiency of high sapphire surface quality.

Simulation of realistic speckle fields by using surface integral equation and multi-level fast multipole method

This report presents a speckle simulator which calculates rigorously speckle fields with full randomization from rough surfaces. To achieve this, surface integral equation (SIE) method accelerated via multilevel fast multipole method (MLFMM) is implemented. Among several linear formulations to combine the electric and magnetic field integral equations, we demonstrate that one is most suitable for dielectric rough surfaces and one for metallic rough surfaces. As examples, silver and silicon rough surfaces are simulated at a wavelength of 500 nm. To investigate speckles from extended areas, silicon rough surfaces with a size of 30×30 µm2 and two million unknowns are calculated. Based on the resultant speckle fields, speckle contrast, angular speckle-correlation and transverse autocorrelation function of intensity in the van Cittert-Zernike zone are further calculated and known relations versus surface roughness are manifested, indicating that sufficient statistic surface information is encoded in the speckle fields. The SIE-MLFMM method with the suitable formulation proves to be an efficient rigorous simulation tool for relatively large rough surface problems and would enable more profound numerical studies for speckle involved optical metrologies.

Highly efficient spin current source using BiSb topological insulator/NiO bilayers

BiSb is a topological insulator with both giant spin Hall effect and high electrical conductivity, which are important for ultralow power spin–orbit-torque magnetoresistive random access memory. However, when a ferromagnetic (FM) thin film is deposited on top of BiSb, large surface roughness and diffusion of Sb out of the BiSb layer into the FM layer results in a much smaller effective spin Hall angle In this work, we show that by inserting a NiO layer between BiSb and Co, we can significantly improve of BiSb and induce perpendicular magnetic anisotropy at the NiO/Co interface. We obtained a large = 10.3 for the BiSb bottom layer at the NiO layer thickness of 3 nm, which is comparable to the best of BiSb top layer studied so far. Our study shows that BiSb/NiO bilayers are promising for integration of BiSb to SOT-MRAM.

Synthesis of Ti6Al4V/SrFHA Composites by Microwave-Assisted Liquid Phase Deposition and Calcination.

The feasibility of synthesis of Ti6Al4V/SrFHA (Ca9.37Sr0.63(PO4)6F2) composites via coating strontium and fluorine co-doped HA to Ti6Al4V substrate by microwave-assisted liquid phase deposition and calcination was evaluated, with a focus on the effect of the deposition temperature from 30 °C to 70 °C. The outcomes demonstrate that strontium and fluorine can be successfully doped into HA to form a SrFHA coating with modified micromorphology which is deposited on the alloy. When the deposition temperature was 50 °C, the coating with the largest uniform continuous SrFHA coverage was obtained. After calcination, the adhesion strength and Vickers microhardness of the Ti6Al4V/SrFHA composite increased from 0.68 MPa and 323 HV to 2.41 MPa and 329 HV, respectively, with a decrease in the water contact angle from 10.88° to 7.24°, exhibiting enhancement of both mechanical properties and wettability. Moreover, the composite obtained at the deposition temperature of 50 °C exhibited good bioactivity based on the simulate body fluid (SBF) test. On account of the above features primarily as a result of the combined effect of the co-doping of strontium and fluorine, high crystallinity of SrFHA, large surface roughness, and formation of the titanium oxide transition layer, the Ti6Al4V/SrFHA composite shows great potential in dental implantology.

Optical Humidity Sensor Based on CdSe/ZnS Quantum Dots Modified by Porous Silica

AbstractUltra‐sensitive optical humidity sensors based on nanomaterials play important roles in the fields of science and industry. The related research has been reported, however, the underlying physical mechanism is still unclear. In order to clarify this point, and further improve the sensing performance, herein, optical humidity sensor based on porous silica/quantum dots (PS/QDs) hybrid nanoarchitecture has been developed. PS is selected to enhance emission of QDs due to its large surface roughness, which can improve light utilization. Under optimized conditions, the emission from the hybrid PS/QDs can be enhanced 6.5 times compared with the as‐grown QDs. With the increase of relative humidity from 20% to 80%, the hybrid PS/QDs demonstrate excellent response, wide sensing range, fast response time (22–40 s), good selectivity, and repeatability. Based on laser spectroscopy, the sensing mechanism is ascribed to the passivation of the surface defects by water molecules, which results in enhanced emission. This work provides a simple and low‐cost method to fabricate humidity sensors and shows promising applications in environmental detection.

Design of large-area metasurfaces for the mid-IR and suited for CMOS-compatible fabrication by masked lithography

The use of masked UV (i-line) lithography in a MEMS foundry for CMOS-compatible fabrication of large-area metasurface-based absorbers for the mid-infrared is demonstrated. The challenges are in: (a) the limited number of acceptable metals, (b) the thickness tolerance of the layers used in the CMOS process, and (c) the imaging capabilities of i-line lithography as compared to e-beam. The claimed throughput advantage with manageable distortion of masked lithography and the suitability of the layers used in a CMOS-compatible process in the fabrication of mid-IR absorbers was tested. Issues investigated are: (a) the impact of aluminium as the preferred metal in the MIM patch on the plasmonic response, (b) the influence of SiO2 as preferred dielectric material, (c) the effect of corner rounding and horizontal-vertical bias of the masked lithography and (d) measures that can be taken during the design phase to mitigate any such detrimental effect. Based on the findings, disk-shaped patches are identified as the most suitable for shape-tolerant design. Metasurfaces with a unit-cell side-length of 3μm were fabricated over a chip area larger than 105μm2. Measurements do confirm that (a) aluminium is a suitable CMOS-compatible material for mid-IR metamaterial absorber fabrication, (b) a large surface roughness results in widening of the absorption peaks and (c) the typical layer thickness tolerance used in a MEMS foundry is also acceptable for mid-IR metasurface fabrication. Masked lithography limits the minimum design wavelength to about 3.5μm, while the surface roughness Rq ~ 5nm results in a bandwidth up to FWHM = 400nm.

The Importance of Electrochemically Active Surface Area in the Corrosion Behavior of Additively Manufactured 316L Stainless Steel

Surfaces of additively manufactured (AM) stainless steel (SS) by fusing metallic powders are known to be much rougher than those produced by conventionally fabrication methods. The measured surface roughness (Sa or Sq) can range from a few to tens of microns depending on the build angle. Recent studies have shown that the large surface roughness associated with printing conditions makes the AM SS surfaces susceptible to localized corrosion and open-circuit corrosion [1, 2]. Sa or Sq have also long been used to characterize the corrosion behavior of traditionally manufactured metals [3]. However, the open-circuit corrosion rate of the traditional metals has been mainly studied in the submicron-scale surface roughness, and some results have showed that changes in the roughness of hundreds of nanometers or more have little effect on the change in the corrosion rate [4]. In addition, when applied to AM materials, no consistent correlation between the pitting breakdown potential (Eb) and surface roughness has been observed.In this study, the dependence of the corrosion behavior on the electrochemically active surface area of AM 316L SS, defined as the total area of the curvilinear surface that is exposed to the electrolyte, has been explored. The localized corrosion susceptibility was evaluated under full immersion in 3.5 wt% NaCl solution through potentiodynamic polarization for testing articles with different surface roughness. While no correlation to Sa or Sq was displayed, the Eb values showed a clear statistical trend with respect to the electrochemically active surface area: the lager the active surface area, the smaller the Eb. The observed correlation fits well with a previously reported stochastic pitting model on metal surfaces [5]. In addition, by normalizing linear polarization resistance and electrochemical impedance spectra with the electrochemically active surface area, it can be confirmed that the as-printed surface roughness of AM 316L SS did not have a significant effect on the change of the open-circuit corrosion phenomenon under static immersion conditions. Our results suggest that electrochemically active surface area is an appropriate parameter to characterize the corrosion behavior of AM metal surfaces.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Prediction and Control of Product Shape Quality for Wire and Arc Additive Manufacturing

Abstract Wire and arc additive manufacturing (WAAM) has become an economically viable option for fast fabrication of large near-net shape parts using high-value materials in the aerospace and petroleum industries. However, wide adoption of WAAM technologies has been limited by low shape accuracy, high surface roughness, and poor reproducibility. Since WAAM part quality is affected by a multitude of factors related to part geometries, materials, and process parameters, experimental characterization or physics-based simulation for WAAM process optimization can be cost prohibitive, particularly for new part designs. As an effective alternative, data-analytical approaches have been developed for prescriptive modeling and compensation of shape deviations in 3D printed parts. However, WAAM faces a unique challenge of large shape deviation and high surface roughness at the same time. Accurate prediction and control of WAAM part quality require process-meaningful error decomposition under geometric measurement uncertainties. We propose a generalized additive modeling approach to separate global geometric shape deformation from surface roughness. Under this statistical framework, tensor product basis expansion is adopted to learn both the low-order shape deformation and high-order roughness patterns. The established predictive model enables optimal geometric compensation for product redesign to reduce shape deformation from the target geometry without altering process parameters. Experimental validation on WAAM manufactured cylindrical walls of various radii shows the effectiveness of the proposed framework.

Effect of large scale roughness of block ramps on dissolved oxygen efficiency in water

Abstract Block ramps are generally characterized by super critical flow over the ramps, and the presence of roughness lying on the surface of the block ramps induces excessive turbulence, which causes some turbulent energy dissipation and air entrainment. Aeration in a block ramp is caused by the intensity of turbulence created in the water flow by surface roughness of the block ramp and hydraulic jump downstream of block ramp. Macro or large-scale roughness like boulders, as a protruding element on surface of block ramp, could increase intensify turbulence and flow aeration along block ramps. This paper presents an experimental investigation of the dissolved oxygen efficiency in block ramps with slopes of 1:3, 1:5 and 1:7, on which large-scale granular materials with different arrangement patterns were glued. Comparison of results indicated that, for both free and ramp hydraulic jumps, the block ramps with a slope of 1:3 and large-scale roughness increase the dissolved oxygen efficiency almost 20% above that of the similar smooth block ramps. By reducing of the slope of block ramps to 1:5, the dissolved oxygen efficiency of the block ramps with large surface roughness became 3 and 19% for free and ramp hydraulic jumps, respectively. However, the block ramps with 1:7 slope had corresponding dissolved oxygen efficiency of 19 and 32%, respectively. Furthermore, installation of large scale roughness with the structured arrangement have better performance to increase dissolved oxygen (DO) in comparison with the interlocked large-scale roughness.

Influence of Build Angle and Polishing Roughness on Corrosion Resistance of 316L Stainless Steel Fabricated by SLM Method.

Metal parts formed by laser additive manufacturing methods usually have large surface roughness, which affects the corrosion resistance of the parts. This study reported the reason for and mechanism of the large surface roughness of 316L stainless steel samples manufactured by selective laser melting (SLM) at different build angles. Through the study, the reason for the large top surface roughness (average surface roughness is 15.3 ) is due to the molten channel structure formed on the surface. The large side surface roughness (average surface roughness is 19.1 ) is due to the incomplete fused particles adhering to the surface. Through electrochemical experiments, the influence of the build angle and polishing treatment on the corrosion resistance of the sample was studied. The different roughness of the top and side surfaces results in different corrosion resistances (the top surface pitting potential is 0.317 and the side surface pitting potential is 0.148 ), and polishing can improve the surface corrosion resistance of specimens by reducing the surface roughness, especially for the side surface (from 0.148 to 0.351 ). Therefore, parts manufactured by SLM can be post-treated to reduce roughness and improve surface corrosion resistance.

Diamond Chisel Utilization and Effect of Feeding on Surface Roughness of AISI 1045 Steel

Shape and surface roughness of a product, when it is produced by a lathe, plays an important role because of its friction, wear, lubrication systems, and others. In each workpiece, the result of the machining process has a certain shape and surface roughness such as shiny, smooth, and rough surfaces. The machining process determines the surface roughness at a certain level, where the surface roughness is used as a reference for product evaluation. Machining the surface roughness of a product does not have a small value, but sometimes a product requires a large surface roughness value according to its function. Keywords: Feeding, surface roughness, AISI 1045, diamond chisel.

The Effect of Surface Roughness of Magnetic Particles on the Electromagnetic Wave Absorbing Performance of Fe3O4/Multiwalled Carbon Nanotubes Hybrids

AbstractRecently, for electromagnetic wave (EMW) absorption materials, a considerable literature has testified the significant role of structures, composition, morphologies and interface in the enhancement of absorbing properties. However, far too little attention has been paid to the intensive research of surface morphology of Fe3O4 particles. The objective of this paper is to research the influence of Fe3O4 morphology on absorbing performance of Fe3O4/Multiwalled Carbon Nanotubes (MWCNTs) hybrids. The morphology of Fe3O4 particles was adjusted by the templating agent content of NH4HCO3 and NH4Ac in hydrothermal process. Of importance, we proposed to quantify the difference of Fe3O4 morphology by surface roughness. The surface roughness of three Fe3O4 particles are characterized by atomic force microscopes (AFM), which were 13.1 nm, 21.3 nm and 32.4 nm, respectively. The three absorbing hybrids were prepared via blending Fe3O4 particles with MWCNTs, and the minimum reflection loss (RLmin) of the three hybrids were −24.89 dB, −30.88 dB and −41.00 dB, respectively. The results indicated that the Fe3O4 with larger surface roughness tends to exhibit better EMW absorbing performance. It can be inferred that the greater roughness of Fe3O4 particles is an important factor to enhance EMW absorbing properties of Fe3O4/MWCNTs hybrids.

Soft machining-induced surface and edge chipping damage in pre-crystalized lithium silicate glass ceramics

Soft machining is a key procedure in fabrication of high-strength lithium-based silicate glass ceramic (LS) restorations. This paper reports on the diamond machining-induced surface and edge chipping damage in two pre-crystalized LS materials: pre-crystallized lithium metasilicate/orthophosphate glass ceramic (Pre-LS, IPS e.max CAD) and pre-crystallized zirconia-containing lithium metasilicate glass ceramic (Pre-ZLS, Vita Suprinity). Indentation techniques were used to measure the material mechanical properties. Soft machining was conducted using a robotic controlled apparatus mimicking dental CAD/CAM machining processes at different removal rates and enabling in-process force measurement. Machined surface roughness was assessed using 3D confocal optical profilometry in terms of the average and maximum surface heights. Scanning electron microscopy was used to assess diamond tool and machined surface and edge morphology. Soft machining of both materials was dominated by brittle fracture mixed with localized ductile flow. However, the higher brittleness index of Pre-ZLS than Pre-LS yielded higher degrees of machining-induced conchoidal fractures in Pre-ZLS in comparison with irregular fractures in Pre-LS. Thus, much larger surface roughness and deeper edge chipping damage were produced in Pre-ZLS than Pre-LS. Machining forces for Pre-ZLS were significantly smaller than Pre-LS, due to the lower machinability index associated with a complex relation of the mechanical properties as well as less debris adhesion for Pre-ZLS than Pre-LS. Further, increased material removal rates resulted in significantly increased machining forces, maximum surface roughness and fracture, and edge chipping damage in both Pre-ZLS and Pre-LS materials. Therefore, optimization of soft machining processes needs to be practiced to achieve accepted surface and edge quality at balanced removal rates.

Enhanced luminescence property of GaN-based LEDs with p-InGaN cap layer grown on p-GaN surface

The influence of a p-In0.06Ga0.94N cap layer grown on p-GaN on the device performance of GaN-based light-emitting diodes (LEDs) was investigated. Compared to conventional p-GaN LED structure, the light output power of p-InGaN/GaN structure LED was enhanced by 20% and the operating voltage decreased from 3.81 to 3.29 V under 20 mA injection current. Based on surface morphology and electrical analysis, these improvements were mainly attributed to the higher light extraction efficiency and lower contact resistence. It was observed that V-shaped pits appearing on the surface of p-InGaN increased surface roughness, resulting in higher extraction efficiency. After molten KOH etching to p-InGaN layer, the V-shaped pits became bigger, further increasing surface roughness. The larger surface roughness further increased light output power from 20% to 44%. In addition, the forward voltage under 20 mA increased from 3.29 V to 3.41 V which indicated etching process decreased the surface ohmic contact.

Improvement of the Effective Spin Hall Angle by Inserting an Interfacial Layer in Sputtered BiSb Topological Insulator (Bottom)/Ferromagnet With In-Plane Magnetization

The topological insulator BiSb is promising for spin-orbit torque applications thanks to its high electrical conductivity and giant spin Hall effect. Previous works have reported a large spin Hall angle for BiSb deposited on top of a ferromagnetic layer with perpendicular magnetic anisotropy. However, since BiSb has large surface roughness, obtaining a large spin Hall angle in BiSb (bottom)/ferromagnet (FM) is more challenging than in FM/BiSb (top) structures, especially when the FM layer is very thin. Here, we investigate the role of an interfacial layer on the effective spin Hall angle in BiSb (bottom)/FM with in-plane magnetization deposited by magnetron sputtering on sapphire substrates. We showed that inserting an interfacial layer with optimized thickness helps improve the effective spin Hall angle. We achieved a relatively high effective spin Hall angle of 1.7 in BiSb (bottom)/Ru 1 nm/Co 1 nm/Pt 1 nm structure.