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Review Article

J. Micro Nano-Manuf. 2018;6(4):040801-040801-10. doi:10.1115/1.4041615.
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Opto-thermophoretic manipulation is an emerging field, which exploits the thermophoretic migration of particles and colloidal species under a light-controlled temperature gradient field. The entropically favorable photon–phonon conversion and widely applicable heat-directed migration make it promising for low-power manipulation of variable particles in different fluidic environments. By exploiting an optothermal substrate, versatile opto-thermophoretic manipulation of colloidal particles and biological objects can be achieved via optical heating. In this paper, we summarize the working principles, concepts, and applications of the recently developed opto-thermophoretic techniques. Opto-thermophoretic trapping, tweezing, assembly, and printing of colloidal particles and biological objects are discussed thoroughly. With their low-power operation, simple optics, and diverse functionalities, opto-thermophoretic manipulation techniques will offer great opportunities in materials science, nanomanufacturing, life sciences, colloidal science, and nanomedicine.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2018;6(4):040802-040802-20. doi:10.1115/1.4041934.

The paper provides an overview of high-resolution electrohydrodynamic (EHD) printing processes for general applications in high-precision micro/nanoscale fabrication and manufacturing. Compared with other printing approaches, EHD printing offers many unique advantages and opportunities in the printing resolution, tunable printing modes, and wide material applicability, which has been successfully applied in numerous applications that include additive manufacturing, printed electronics, biomedical sensors and devices, and optical and photonic devices. In this review, the EHDs-based printing mechanism and the resulting printing modes are described, from which various EHD printing processes were developed. The material applicability and ink printability are discussed to establish the critical factors of the printable inks in EHD printing. A number of EHD printing processes and printing systems that are suitable for micro/nanomanufacturing applications are described in this paper. The recent progresses, opportunities, and challenges of EHD printing are reviewed for a range of potential application areas.

Commentary by Dr. Valentin Fuster

Research Papers

J. Micro Nano-Manuf. 2018;6(4):041001-041001-10. doi:10.1115/1.4041508.

Higher temperature assisted processing of silicon, such as heat-assisted diamond turning, is often being considered to improve surface integrity. At higher temperatures and under mechanical loading and unloading, caused by a moving tool, silicon deforms plastically often in association with occurrence of phase transformations. This paper investigates such phase transformations in rotational scratching of single crystal (100) p-type silicon with a conical diamond tool under various furnace-controlled temperatures ranging from room temperature (RT) to 500 °C and at scratching speeds comparable to that used in the diamond turning process (1 m/s). Phase transformation study, using Raman spectroscopy, at various crystal orientations, shows differences in phases formed at various temperatures when compared to that reported in indentation. The tendency to form phases is compared between scratched and diamond turned surfaces at RT, and also with that reported at low scratching speeds in the literature. Analytical indenting-based pressure calculations show that at higher temperatures, phase transformations can happen in silicon at significantly lower pressures. Analysis of depths of the scratched groove indicates that at temperatures beyond a certain threshold, plastic deformation and significant elastic recovery may be causing shallow grooves. Abrasive wear coefficients are thus seen to decrease with the increase in temperatures. This study is expected to help tune heat-assisted diamond turning conditions to improve surface formation.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2018;6(4):041002-041002-12. doi:10.1115/1.4041531.

A three-dimensional (3D)-virtual calibration and visual servo are implemented for augmented reality (AR)-assisted peg-in-hole microassembly operations. By employing 3D model and ray casting, the 3D coordinates on virtual mating rod correspondent to the two-dimensional (2D) virtual image points are extracted. The detecting and tracking of image feature points for calibration is carried out by the proposed algorithm of regional template matching (TM) and scanning with edge fitting (RTM-SEF). For achieving subpixel error between the feature points in real and virtual images, a coarse-fine virtual calibration method is proposed. In regard to the image viewed by the real and virtual cameras, a calibrated virtual camera is utilized to track the mating rod. A visual servo control law including coarse and fine tuning is proposed to ensure sub-pixel error between the most important feature point in the real and virtual images. The AR technology is mainly employed in the alignment between micropeg and mating hole for inserting a micropeg of diameter 80 μm with length 1–1.4 mm into a mating rod with 100 μm hole.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2018;6(4):041003-041003-8. doi:10.1115/1.4041532.

We report the tuning of surface wetting through sacrificial nanoimprint lithography (SNIL). In this process, grown ZnO nanomaterials are transferred by imprint into a metallic glass (MG) and an elastomeric material, and then etched to impart controlled surface roughness. This process increases the hydrophilicity and hydrophobicity of both surfaces, the Pt57.5Cu14.7Ni5.3P22.5 MG and thermoplastic elastomer (TPE), respectively. The growth conditions of the ZnO change the characteristic length scale of the roughness, which in turn alters the properties of the patterned surface. The novelty of this approach includes reusability of templates and that it is able to create superhydrophilic and superhydrophobic surfaces in a manner compatible with the fabrication of macroscopic three-dimensional (3D) parts. Because the wettability is achieved by only modifying topography, without using any chemical surface modifiers, the prepared surfaces are relatively more durable.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2018;6(4):041004-041004-9. doi:10.1115/1.4041668.

One of the limitations of commercially available metal additive manufacturing (AM) processes is the minimum feature size most processes can achieve. A proposed solution to bridge this gap is microscale selective laser sintering (μ-SLS). The advent of this process creates a need for models which are able to predict the structural properties of sintered parts. While there are currently a number of good SLS models, the majority of these models predict sintering as a melting process which is accurate for microparticles. However, when particles tend to the nanoscale, sintering becomes a diffusion process dominated by grain boundary and surface diffusion between particles. As such, this paper presents an approach to model sintering by tracking the diffusion between nanoparticles on a bed scale. Phase field modeling (PFM) is used in this study to track the evolution of particles undergoing sintering. Changes in relative density are then calculated from the results of the PFM simulations. These results are compared to experimental data obtained from furnace heating done on dried copper nanoparticle inks, and the simulation constants are calibrated to match physical properties.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Micro Nano-Manuf. 2018;6(4):044501-044501-5. doi:10.1115/1.4041509.

Due to its excellent quality, fused silica has been widely used in various industrial applications. The nonlinear absorptive nature of ultrafast laser pulses enables the induction of morphological changes within the bulk transparent materials. In this study, the interior modification of fused silica is induced by a picosecond pulsed laser, and the relationship between processing parameters and the modification geometry is demonstrated. Three different patterns are identified according to the geometric characteristics of the modification. Furthermore, a simple experiment-based model considering the incubation effect is put forward to predict picosecond pulse-induced morphological changes in fused silica.

Commentary by Dr. Valentin Fuster

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