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Research Papers

J. Micro Nano-Manuf. 2016;4(3):031001-031001-8. doi:10.1115/1.4033680.
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A two-pass microrolling-based texturing (μRT) process was utilized to improve the hydrophobicity of aluminum surfaces. Square micropillars were fabricated on aluminum sheets by two mutually orthogonal forming passes by a roller pretextured with microgrooves. Subsequently, the droplet contact angle was measured to evaluate the hydrophobicity of the surface. Results show that surfaces with μRT-imprinted textures have higher contact angles than nontextured surfaces indicating improved hydrophobicity. Furthermore, the process has led to the creation of hierarchical valleylike features on top of each of the micropillars caused by the pile-up effect during the forming process. It was hypothesized that such hierarchical features positively contribute to the improved hydrophobicity of the surface. This hypothesis was validated by testing surfaces with a similar hierarchical textured pattern produced by laser-induced plasma micromachining (LIPMM). The effects of various aspects of texture geometry including surface area-to-volume ratio and groove aspect ratio on the surface contact angle and the anisotropy of the contact angles were investigated.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2016;4(3):031002-031002-10. doi:10.1115/1.4033709.

A computational model to investigate the flushing of electric discharge machining (EDM) debris from the interelectrode gap during the spray-EDM process is developed. Spray-EDM differs from conventional EDM in that an atomized dielectric spray is used to generate a thin film that penetrates the interelectrode gap. The debris flushing in spray-EDM is investigated by developing models for three processes, viz., dielectric spray formation, film formation, and debris flushing. The range of spray system parameters including gas pressure and impingement angle that ensure formation of dielectric film on the surface is identified followed by the determination of dielectric film thickness and velocity. The debris flushing in conventional EDM with stationary dielectric and spray-EDM processes is then compared. It is observed that the dielectric film thickness and velocity play a significant role in removing the debris particles from the machining region. The model is used to determine the spray conditions that result in enhanced debris flushing with spray-EDM.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2016;4(3):031003-031003-9. doi:10.1115/1.4033820.

The purpose of this paper is to make a comparative study on the process capabilities of the two branches of the powder injection molding (PIM) process—metal injection molding (MIM) and ceramic injection molding (CIM), for high-end precision applications. The state-of-the-art literature does not make a clear comparative picture of the process capabilities of MIM and CIM. The current paper systematically characterizes the MIM and CIM processes and presents the process capabilities in terms of part shrinkage, surface replication, tolerance capability, and morphological fidelity. The results and discussion presented in the paper will be useful for thorough understanding of the MIM and CIM processes and to select the right material and process for the right application or even to combine metal and ceramic materials by molding to produce metal–ceramic hybrid components.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2016;4(3):031004-031004-7. doi:10.1115/1.4033742.
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In spite of the great progress made toward addressing the challenge of particle contamination in nanomanufacturing, its deleterious effect on yield is still not negligible. This is particularly true for nanofabrication processes that involve close proximity or contact between two or more surfaces. One such process is Jet-and-Flash Imprint Lithography (J-FIL™), which involves the formation of a nanoscale liquid film between a patterned template and a substrate. In this process, the presence of any frontside particle taller than the liquid film thickness, which is typically sub-25 nm, can not only disrupt the continuity of this liquid film but also damage the expensive template upon contact. The detection of these particles has typically relied on the use of subwavelength optical techniques such as scatterometry that can suffer from low throughput for nanoscale particles. In this paper, a novel mechanics-based method has been proposed as an alternative to these techniques. It can provide a nearly 1000 × amplification of the particle size, thereby allowing for optical microscopy based detection. This technique has been supported by an experimentally validated multiphysics model which also allows for estimation of the loss in yield and potential contact-related template damage because of the particle encounter. Also, finer inspection of template damage needs to be carried out over a much smaller area, thereby increasing throughput of the overall process. This technique also has the potential for inline integration, thereby circumventing the need for separate tooling for subwavelength optical inspection of substrates.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2016;4(3):031005-031005-10. doi:10.1115/1.4033861.
OPEN ACCESS

Motheye antireflective coatings (ARCs) are based on periodic or stochastic features with dimensions below the wavelength of visible light which can be used to produce a gradient index of refraction between air and the substrate. In this work, two silica nanoparticle-based motheye ARCs of similar optical performance, but different physical structures, were deposited on glass and characterized for mechanical behavior to provide insights into the mechanisms for abrasion resistance in these films. Optical and mechanical performances were evaluated in light of the mechanical properties and physical structure of the films using models for describing the mechanical behavior of the films. The results show that the three-layer coating was found to have better abrasion resistance than a simple single layer coating largely due to better crack nucleation resistance and scratch resistance. The simple single-layer film showed better crack propagation resistance than the three-layer film due to the existence of nanoparticles (NPs) throughout the cross section of the film. The three-layer film appears to have higher work of adhesion based on exhibiting better delamination and spallation resistance.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2016;4(3):031006-031006-10. doi:10.1115/1.4033924.

Laser surface melting is being increasingly used as a method of surface polishing steels and other alloys, but understanding the effect of this process on the microstructure and properties is still incomplete. This work experimentally explores several basic questions about how the surface microstructure and properties of S7 tool steel change during a pulsed laser micromelting (PLμM) process. Evaluations of the microstructure and hardness suggest that diffusion-controlled processes such as melt homogenization and surface back-tempering are relevant during rapid microscale laser melting and that the laser parameters and process planning contribute to determining the final surface hardness. The results also suggest that some influence can be exerted over the final hardness obtained from laser surface melting by changing the processing parameters.

Topics: Lasers , Melting , Tool steel
Commentary by Dr. Valentin Fuster

Technical Brief

J. Micro Nano-Manuf. 2016;4(3):034501-034501-6. doi:10.1115/1.4033710.

A suitable tooling strategy is identified to enable mass production of a microreactor baseplate via injection moulding. A bottom grooved micromixer design suitable for micromilling of a tool insert is developed. To identify suitable polymer and process parameters, injection moulding simulations are performed. Mesh generation is described; two approaches of gate description as well as mould temperature control in simulation software are discussed. Three materials are examined from the injection moulding point of view, polystyrene (PS), cyclic olefin copolymer (COC), and polyether ether ketone (PEEK). A microreactor baseplate is produced by injection moulding of PS.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2016;4(3):034502-034502-6. doi:10.1115/1.4033683.
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Silver nanoparticles were electrodeposited from 0.3 M oxalic acid electrolyte on a pure aluminum working electrode under silver ion concentration-limited condition. A silver wire was held in a glass tube containing 1.0 M KCl solution as the counter electrode. Ion exchange between the glass tube and the main electrodeposition bath through a capillary was driven by the overpotentials as high as 10 V supplied by an electrochemical workstation. Due to the reaction between chlorine anion and silver cation to form AgCl solid at the Ag/AgCl electrode, the silver ion concentration-limited condition holds in the electrolyte. It is found that silver grows at the aluminum working electrode to form nanoparticles with an average size of about 52.4 ± 13.6 nm. With the increasing of the deposition time, the silver nanoparticles aggregate into clusters. The silver particle clusters are separated with approximately 112.6 ± 19.7 nm due to the hydrogen bubble-induced self-assembling, which is shown by the confined deposition of silver on a gold coating. The surface roughness of the aluminum substrate leads to the reduced uniformity of silver nanoparticle nucleation and growth.

Commentary by Dr. Valentin Fuster

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