Microgroove Arrays Research Articles

Research on wafer-level SiC microgroove array process via integrated molding-etching process

Silicon carbide (SiC) microgroove arrays (MGAs) play a pivotal role as optical components in modern optical engineering. This paper introduces an innovative approach for the fabrication of MGAs on hard materials. This method integrates hot embossing (HE) and inductively coupled plasma (ICP), utilizing polydimethylsiloxane (PDMS) as the intermediary mold due to its excellent demolding performance and shape replication qualities. The process involves transferring the MGAs from the Ni-P master mold to the PDMS mold, followed by replication onto the photoresist surface by hot embossing. Subsequently, the MGAs on the photoresist mask is etched into the hard substrate material using ICP etching. For efficient customization of MGAs, a reliable geometrical model based on angular dependence theory is developed to assist in selecting process parameters and designing masks. The correlation between etching selectivity and characteristic dimension is elucidated. Experimental results demonstrate that the sidewall angle decreases with higher selectivity and increases with a greater sidewall angle on the patterned mask. Plasma etching reveals unaffected areas in convex corners and the forming errors in concave corners, highlighting a high angular dependence of the etch rate. Moreover, minimizing microdefects can be achieved by optimizing process parameters and reducing etch time.

Impact of process parameters on the flow behavior and filling accuracy of photoresist in hot embossing for microgroove array

Hot embossing is a cost-effective and efficient method for fabricating micro-nano structures. However, challenges arise from the flow behavior and rebound phenomena of photoresists during hot embossing, leading to issues with filling accuracy and subsequently degrading optical properties. Therefore, elucidating the impact of process parameters on filling accuracy in hot embossing is crucial. Initially, a polydimethylsiloxane (PDMS) soft mold was fabricated by replicating microgroove arrays from a nickel-phosphorus (Ni-P) mold, which was produced using ultra-precision fly-cutting techniques. Subsequently, the microgroove morphology from the PDMS soft mold was transferred onto the photoresist surface through hot embossing. A numerical model for photoresist filling accuracy was established and experimentally validated. The filling mechanism of photoresist in hot embossing was elucidated. Polymer viscoelasticity decreased with increasing temperature, substantially enhancing filling accuracy, followed by a gradual decrease due to rebound phenomena. Additionally, higher embossing forces enhanced the filling ratio, but excessive pressure led to the deformation of the soft mold. Process parameters were optimized through numerical simulation and experimentation, achieving processing errors at the hundred-nanometer level and a filling ratio of 97.3 %.

Forming mechanism of a novel shape-surface integrated incremental sheet forming process for fabricating parts with enhanced surface functionality

Metallic components with surface microfeatures are increasingly used in aerospace, automotive and other applications due to their drag-reducing properties. In this situation, we proposed a novel shape-surface integrated incremental sheet forming (S2-ISF) process to achieve the simultaneous fabrication of both surface microfeatures and desired geometric shape. It was found that an increase in the forming angle was most effective in improving the formation of microgroove array, followed by the step size, the spindle speed and the feed rate. Moreover, when the forming angle is constant, the step size and microgroove pitch increase linearly. Compared to the as-received sheet, the yield strength is increased by more than 20% after the S2-ISF process. Moreover, we observed that the increase of forming angle in the S2-ISF process has promoted grain deformation and grain fragmentation, which is favorable for the formed part to obtain more uniform and finer grains. The grain size distribution along the thickness direction shows the characteristics of ‘coarse in the middle and fine at both ends’. Finally, we found that the formed parts with different microgroove pitch from the S2-ISF process have the significant enhancement on the hydrophobicity and anti-friction property. When microgroove pitch is 155.5 μm, the surface contact angle of formed part improved from 70.65° to 101.39°, and the wear volume of formed part decreases from 4.89 × 10−3 mm3 to 3.65 × 10−3 mm3. This work provides a solution for the efficient and economical fabrication of three-dimensional thin-walled parts with microgroove array to enhance surface functionality.

Research on production of microgroove arrays on TiAl intermetallic alloy by micro milling

TiAl intermetallic alloy is a superior lightweight material with excellent performance, and its micro features or components have promising applications in manufacturing fields. In this work, an investigation of micro milling of microgroove arrays on TiAl alloy was studied. The effects of cutting parameters including the feed per tooth (fz) and depth of cut ( ap) on the milling force, surface morphology, surface roughness and burr size of the micro-slots were investigated. The wear types and mechanisms of the micro end mills were also studied. The results showed that the optimal cutting parameters were fz = 3.5 μm/z and ap = 4 μm, which provided the best surface roughness Sa of 152 nm, top-burr heights on up- and down-milling sides of 19 and 19.5 μm respectively. Using the optimized cutting parameters, microgrooves with a width of 500 μm, aspect ratio of 5 and array period of 10 were fabricated successfully. Surface topography, dimensional accuracy and perpendicularity of the microgroove arrays were characterized. Results demonstrated that an increase in the microgroove number, microgroove edge chipping as well as burrs of the entrance and exit increased gradually. The dimensional error between the obtained width and the designed width of the microgroove was less than 2%, and the slope of the sidewalls reached more than 89°. The wear mechanisms of the micro end mills were abrasive wear and adhesive wear, and wear types were coating delamination, cutting edge chipping, and tool nose breakage.

A novel micro-rolling & incremental sheet forming hybrid process: Deformation behavior and microstructure evolution

Thin-walled metal parts with functional micro-featured surface have broad application prospects in the fields of resistance reduction, noise reduction, etc. In this study, a novel micro-rolling & incremental sheet forming hybrid process (μR-ISF) is proposed to fabricate thin-walled metal parts with microgroove arrays. An analytical model which relates the rolling force and microgroove depth in the micro-rolling stage was first established. Then, the formation mechanism of microgroove morphology during both micro-rolling stage and macro-shape forming stage are investigated. After the micro-grooved sheet being incrementally formed, a significant reduction (between 21% to nearly 60%) is occurred in the depth of both transverse and longitudinal grooves compared to the flat sheet. Meanwhile, the width of transverse grooves decreases slightly by about 10% on average, while the width of longitudinal microgrooves increases significantly by more than 30% on average. After micro-rolling, 85°{101¯2} tensile twins appear on the micro-grooved sheet and the percentage of 65°{112¯2} compressive twins increases. After incremental forming, the percentage of low-angle grain boundaries and the density of geometrically necessary dislocations in the formed part increase significantly, and the grain size distribution becomes more uniform. The present work provides a new strategy for the fabrication of 3D metal thin-walled components with surface micro-features.

An investigation on the adhesion of dual-scale micro-nano composite structure on the surface of aluminum

Adhesion is a crucial characteristic of hydrophobic surfaces that significantly impacts their practical applications. This paper proposes an innovative method for preparing a dual-scale micro-nano composite structure surface by combining mechanical ruling and anodic oxidation, which demonstrates great potential in enhancing hydrophobic surface properties. Through the analysis of the influence of micro-groove depth on the adhesion of hydrophobic surfaces, it has been discovered that micro-groove dimensions can be used to control surface adhesion while maintaining hydrophobicity, without complex chemical modifications. These findings present a promising approach for tailoring the properties of hydrophobic surfaces to suit specific applications. Compared with the single-scale micro-groove array structures, the surface roughness of the dual-scale micro-nano composite structures is significantly increased, and the contact angle of the water droplet is significantly increased. At the same time, the hydrophobicity and adhesion of the surface of the dual-scale micro-nano composite structures were analyzed. The results show that after anodizing, the contact angle of the dual-scale micro-nano composite structure surface increases, and the surface adhesion can be controlled by adjusting the structural parameters of the micro-groove and the anodizing process parameters, to ensure that the surface presents hydrophobic property while realizing the controllable adhesion of the hydrophobic surface. In this paper, dual-scale micro-nano composite structures fabricated by the composite method have achieved hydrophobic properties, and the surface adhesion can be effectively controlled by adjusting the processing parameters. This method has certain reference significance for the preparation of the controllable adhesive hydrophobic surface and lays a foundation for the further study of the controllable adhesive hydrophobic surface.

Feasibility study on ultraprecision micro-milling of the additively manufactured NiTi alloy for generating microstructure arrays

Nickel-titanium (NiTi) alloy has unique functional properties in medical and microelectronics products. Recently, additive manufacturing has become an attractive way of fabricating NiTi alloy. However, the study of generating microstructure arrays on additively manufactured (AMed) NiTi alloy surfaces remains unclear. Motivated by this, this study proposes the ultraprecision micro-milling (UMM) process to generate microstructure arrays and perform a systematic investigation. First, selective laser melting, as a popular additive manufacturing way, was utilized to fabricate the AMed NiTi alloy. Then, the UMM process was carried out to machine these samples. After the machining experiments, a mirror surface with a surface roughness of 0.014 μm can be acquired, which demonstrates the good machinability of the AMed NiTi alloy. Moreover, the micro-groove array and micro-pillar array with low machining errors were machined on the AMed NiTi alloy surfaces, which verifies the effectiveness of the proposed machining process. The corresponding cutting forces, tool conditions, and chip morphologies were studied to fully understand the machining mechanism of the AMed NiTi alloy. Besides, the surface wettability of microstructure arrays was also quantitatively analyzed. Therefore, this study provides a facile and effective machining process for generating microstructure arrays on the AMed NiTi alloy surfaces.

Structured microgroove columns as a potential solution to obtain perfectly ordered particle beds

We report on a novel concept to produce ordered beds of spherical particles in a suitable format for liquid chromatography. In this concept, spherical particles are either positioned individually (single-layer column) or stacked (multi-layer column) in micromachined pockets that form an interconnected array of micro-grooves acting as a perfectly ordered chromatographic column. As a first step towards realizing this concept, we report on the breakthrough we realized by obtaining a solution to uniformly fill the micro-groove arrays with spherical particles. We show this can be achieved in a few sweeps using a dedicated rubbing approach wherein a particle suspension is manually rubbed over a silicon chip. In addition, numerical calculations of the dispersion in the newly introduced column format have been carried out and demonstrate the combined advantage of order and reduced flow resistance the newly proposed concept has over the conventional packed bed. For fully-porous particles and a zone retention factor of k’’ = 2, the hmin decreases from hmin = 1.9 for the best possible packed bed column to around hmin = 1.0 for the microgroove array, while the interstitial velocity-based separation impedance Ei (a direct measure for the required analysis time) decreases from 1450 to 200. The next steps will focus on the removal of occasional particles remaining on the sides of the micro-pockets, the addition of a cover substrate to seal the column and the subsequent conduction of actual chromatographic separations.

High-temperature silicon carbide material with wicking and evaporative cooling functionalities fabricated by femtosecond laser surface nano/microstructuring

A multifunctional silicon carbide (6H–SiC) material with efficient wicking and evaporative cooling performances in a temperature range of 23–180 °C is created through hierarchical surface nano/microstructuring by a femtosecond laser. The elaborated hierarchical surface structure is an array of nanotextured microgrooves that includes structural features in a range between about 15 nm and 140 μm, integrating benefits from micro- and nanoscale physics of capillarity and thermodynamics. The spatiotemporal dynamics of both water spreading and temperature field obtained by optical and infrared imaging show the excellent wicking and evaporative cooling functionalities of the created material. The range of applications of the developed multifunctional 6H–SiC material includes the technologies for enhancing power generation efficiency, waste heat recovery, and cooling high-heat-flux Si- and SiC-based electronic devices. The application of the created material in cooling technologies for power generation can result in substantial fuel savings and global reduction in greenhouse gas emissions.

Enhancing Anticorrosion Resistance of Aluminum Alloys Using Femtosecond Laser-Based Surface Structuring and Coating.

We report a robust two-step method for developing adherent and anticorrosive molybdenum (Mo)-based coatings over an aluminum (Al) 6061 alloy substrate using a femtosecond (fs) laser. The fs laser nanostructuring of Al 6061 alloy in air gives rise to regular arrays of microgrooves exhibiting superhydrophilic surface properties. The microstructured surface is further coated with an Mo layer using the fs-pulsed laser deposition (fs-PLD) technique. The combination of the two femtosecond laser surface treatments (microstructuring followed by coating) enabled the development of a highly corrosion-resistant surface, with a corrosion current of magnitude less than that of the pristine, the only structured, and the annealed alloy samples. The underlying mechanism is attributed to the laser-assisted formation of highly rough hierarchical oxide structures on the Al 6061 surface along with post heat treatment, which passivates the surface and provide the necessary platform for firm adhesion for Mo coating. Our results reveal that the corrosive nature of the Al-based alloys can be controlled and improved using a combined approach of femtosecond laser-based surface structuring and coating.

Theoretical and numerical investigation of micro-textures fabrication by ultrasonic surface rolling process

Surface texturing is a potential approach to achieving excellent surface performance. To realize high precision and efficiency in micro-texturing fabrication, a surface texturing method utilizing an ultrasonic surface rolling process is proposed. Firstly, the feasibility and geometric controllability of micro-texture preparation using ultrasonic surface rolling process are analyzed. Then, a contact theory model of ultrasonic rolling texturing process is established, which can describe the geometric relationship of the micro-texturing generation region. Based on the elastic–plastic theory, simulations of single-pass and multi-pass ultrasonic rolling texturing processes are developed to elucidate the formation and strengthening mechanism of micro-textures, and further characterize the effects of ultrasonic rolling machining parameters on micro-textures. A series of validation tests of ultrasonic rolling texturing are implemented on AISI 5140 steel. Simulation and experimental results show that the ultrasonic surface rolling process can fabricate micro-groove arrays with the periodic distribution. The validity of the theoretical and finite element models is confirmed by the comparison results. It is demonstrated that the ultrasonic rolling texturing process is a feasible and efficient way to fabricate controllable micro-textures.

Robust Packaging of Vertically Aligned Graphite Substrate by Copper Micro-Rib Structuring

Vertically aligned graphite substrate (VGS)-copper packaging was renowned for improving the robustness against the thermal gradient loading by using micro texturing. The micro-groove array with a line width of 50 μm and a pitch of 100 μm was formed into the VGS by controlling the line depth with the use of fast-rate oxygen plasma etching. Three micro-grooved VGS specimens were wet-plated to fill these microgrooves with copper deposits and to cover the VGS surfaces. The nearly full-deposited VGS-Copper specimens were subjected to a severe thermal transient loading test. The simply Cu-covered package and shallow rib-structured VGS-Cu packages were damaged to delaminate at their interfaces. The VGS-Cu package with the copper rib structure with a height of 50 μm experienced no delamination. This rib-structured VGS-copper package with high rib height had sufficient robustness against the severe thermal transients even with the proof of homogeneous thermal spreading capacity.

Enhancement of frictional properties of Ni-MoS2 self-lubricating composite coatings by microgroove arrays

The self-lubricating Ni-MoS2 composite coating deposited on a stainless-steel (SS) surface with microgroove arrays are prepared and detailed characterized in this paper. Laser surface texturing (LST) and electrochemical deposition (ECD) are carried out successively to fabricate such composite coating. Compared with the Ni-MoS2 coating deposited directly on the non-LST substrate, the coefficient of friction (COF) of the Ni-MoS2 coating on the microtextured substrate is reduced from 0.17 to 0.14, the wear volume is decreased by 21%, the average depth of wear track is decreased by 61%, the running-in time is significantly minimized to 1/11, and the lifetime is remarkable increased. The excellent frictional properties can be attributed to the influence of the microtexture on the growth pattern of Ni-MoS2 coating, as well as the synergistic lubrication effect between texture and the Ni-MoS2 structure.

Research on surface quality and tool wear of micro-groove array machined by a novel micro-milling cutter

Research on surface quality and tool wear of micro-groove array machined by a novel micro-milling cutter

Steerable drops on heated concentric microgroove arrays

Guided drop transport is of great importance in various water and thermal management technologies. Unidirectional drop transport on a hot surface has been widely developed, but a bidirectional reversal is still challenging. Here, we report a steerable transport of drop impinging on heated concentric microgroove arrays, on which the directionality of drop transport is dictated by the drop boiling modes. In the transition boiling state, the driving force originated from the Laplace pressure difference rendered by the microgrooves, which enables the drop rebounding towards the center of curvature. While in the film boiling state, a net force towards the opposite side is generated between the grooves and the penetrated liquid, that drives the drop far away from the center of curvature. Our experimental and theoretical results uncover that the lateral displacement is controlled by both the Weber number and off-center distance. These findings strengthen our fundamental understanding of drop impact dynamics at high temperatures and are essential for effective cooling of hot-spot cores and drop sieving.

Bioinspired microgroove arrays with drag reduction and hydrophobic properties

Reducing energy consumption is one of the most effective ways to solve the problem of energy shortage. In this work, nature-inspired paint microgroove arrays with different periods were fabricated using a one-step laser ablation method. A wind tunnel experiment was performed at two wind speeds, 27.7 and 33.3 m/s, to collect drag force data on smooth and structured paint coatings. The results showed that microgroove arrays oriented perpendicular to the flow direction were beneficial to drag reduction, and a drag reduction rate of up to 7.2% was obtained. Meanwhile, the microgroove arrays induced by laser ablation changed the wettability of the paint surface to hydrophobicity. The contact angle shows a slightly decreasing trend with an increase in the periodic scale. Furthermore, the anticorrosion properties of these microgrooves make them advantageous in harsh environments. The fabricated drag-reducing paint microstructures, with the features of self-cleaning and durability, have the potential to be applied on vehicles to realize speed improvement and energy saving.

Controllable hydrophilic titanium surface with micro-protrusion or micro-groove processed by femtosecond laser direct writing

Smart surfaces with switchable wettability have aroused enormous interest, due to their multifunction in chemistry, biology and medicine. In this paper, a controllable hydrophilic titanium surface with either micro-protrusion or micro-groove is processed by femtosecond laser. The relationship between laser processing parameters of defocus value (Df), scanning speed (Vs), power (Po) and the shape/size of structures are systematically studied. Results show that Df and Vs mainly affect the shape of structures, while Vs and Po influence size. The surface structures can change from micro-groove to micro-protrusion, for the first time, by adjusting processing parameters. After laser processing, morphology and chemical composition are analyzed. It is found that the oxygen content in the middle area of micro-protrusion is higher than the recast layer of micro-groove. The formation mechanism can be attributed to the photo-thermal effect and Marangoni convection effect. Furthermore, the surface roughness and contact angle (CA) measurement results show that the surface roughness of micro-groove array is greater than micro-protrusion array, while micro-protrusion array can promote hydrophilicity compared with micro-groove array. Moreover, the micro-protrusion array with high scanning interval (△) can maintain the hydrophilicity better than micro-groove array even after 90 days. The selected area modification of femtosecond laser processing can potentially be applied to improve biological activity in titanium implants.

Fabrication and pool boiling performance assessment of microgroove array surfaces with secondary micro-structures for high power applications

Microstructure surface is an effective method to improve the boiling performance and has the feasibility of application in solving the heat dissipation problem of high-power electronics. This study develops microgroove array surfaces with secondary micro-structures (MSs) by two perpendicular electrical discharge machining processes to further maximize the boiling performance. Wavy electrodes composed of copper and tin foils with varying thickness and quantity are prepared to fabricate MSs with different structural parameters, and it is confirmed that the enhancement ratio of MSs on boiling performance increases with the increase of number and width of secondary microgrooves. The wall superheats at the onset of nucleate boiling of MSs are 45.3%–62.1% lower than that of smooth copper plate, and an outstanding critical heat flux of 2592.4 kW/m2 with a maximum heat transfer coefficient of 138.6 kW/m2∙oC are achieved. The greatly enhanced boiling performance is attributed to the microgroove arrays and the secondary micro-structures, i.e., micro fins, ablation craters, and micropillars, which provide more nucleation sites and larger heat transfer area. Finally, the cell performance enhancement of concentrated photovoltaics using the nucleate boiling of MSs as thermal management solutions is evaluated as an example of its potential applications.

Enhancement of Frictional Properties of Ni-Mos2 Self-Lubricating Composite Coatings by Microgroove Arrays

Enhancement of Frictional Properties of Ni-Mos2 Self-Lubricating Composite Coatings by Microgroove Arrays

Suspended Palladium/Polymer Bilayer for High-Contrast and Fast Hydrogen Sensors.

Hydrogen sensing is extremely essential for hydrogen-related applications due to the explosibility of hydrogen gas (H2). Here, we first present a high-contrast and fast optical hydrogen sensor, which is a partially suspended Pd/PMMA bilayer on a PDMS substrate with a microgroove array on the surface. The suspended structure reduces constraints from the substrate on the Pd film, leading to a large wrinkling amplitude and fast response rate during hydrogenation. The PMMA film can protect the Pd film from the poisonous impurities in the air and improve the flexibility of the bilayer. When exposed to 4% H2 mixed with air, the reflectance of the sensor drops down from 43 to 4% at 600 nm wavelength, in which the corresponding reflectance contrast, defined as the ratio of the reflectances before and after exposure to hydrogen, is 10.75. Such a high reflectance variation results from the light scattering induced by the wrinkling of the suspended Pd/PMMA bilayer during hydrogenation. Meanwhile, the sensor has a fast response that the reflectance can decrease from 43 to 33% within 0.6 s. Moreover, the sensor shows good recyclability and hydrogen selectivity. These excellent performances suggest that our suspended Pd/PMMA bilayer has great potential for practical hydrogen detection.