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Editorial

J. Micro Nano-Manuf. 2013;1(1):010201-010201-1. doi:10.1115/1.4023753.

It is my pleasure to present the inaugural issue of the Journal of Micro- and Nano-Manufacturing (JMNM). The mission of this new journal is to disseminate original theoretical and applied research in the areas of micro- and nanomanufacturing to researchers in academia, national laboratories, as well as researchers and developers in industry.

Commentary by Dr. Valentin Fuster

Research Papers

J. Micro Nano-Manuf. 2013;1(1):011001-011001-10. doi:10.1115/1.4023161.

Directional dry adhesives are inspired by animals such as geckos and are a particularly useful technology for climbing applications. Previously, they have generally been manufactured using photolithographic processes. This paper presents a micromachining process that involves making cuts in a soft material using a sharp, lubricated tool to create closely spaced negative cavities of a desired shape. The machined material becomes a mold into which an elastomer is cast to create the directional adhesive. The trajectory of the tool can be varied to avoid plastic flow of the mold material that may adversely affect adjacent cavities. The relationship between tool trajectory and resulting cavity shape is established through modeling and process characterization experiments. This micromachining process is much less expensive than previous photolithographic processes used to create similar features and allows greater flexibility with respect to the microscale feature geometry, mold size, and mold material. The micromachining process produces controllable, directional adhesives, where the normal adhesion increases with shear loading in a preferred direction. This is verified by multi-axis force testing on a flat glass substrate. Upon application of a post-treatment to decrease the roughness of the engaging surfaces of the features after casting, the adhesives significantly outperform comparable directional adhesives made from a photolithographic mold.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2013;1(1):011002-011002-8. doi:10.1115/1.4023160.

We present an approach for producing complex nanoscale patterns by integrating computer-aided design (CAD) geometry processing with an atomic force microscope (AFM) based nanoindentation process. Surface modification is achieved by successive nanoindentation using a vibrating tip. By incorporating CAD geometry, this approach provides enhanced design and patterning capability for producing geometric features of both straight lines and freeform B-splines. This method automatically converts a pattern created in CAD software into a lithography plan for successive nanoindentation. For ensuring reliable lithography, key machining parameters including the interval of nanoindentation and the depth of nanogrooves have been investigated, and a proper procedure for determining the parameters has been provided. Finally, the automated nanolithography has been demonstrated on poly methylmethacrylate (PMMA) samples. It shows the robustness of complex pattern fabrication via the CAD integrated, AFM based nanoindentation approach.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2013;1(1):011003-011008-8. doi:10.1115/1.4023757.

In order to improve the tribological properties of thermomechanically highly stressed surfaces such as cylinder liners, microdimples are produced by fly-cutting kinematics along the functional surface. The structures are used to hold back lubricant but also to increase the hydrodynamic pressure, which is built up between the sliding friction partners. For that, machining strategies for the pattern generation in cylindrical components are developed as well as a mathematical model of the microdimple arrangement and distribution. The tribological performance of the machined microdimples is analyzed by means of ring-on-disk experiments. At low sliding speeds the friction coefficient can be decreased clearly by microdimples. This indicates the potential for low-speed or reciprocating tribosystems like cylinder liners. This potential is quantified by motor driven experiments and the comparison between structured and nonstructured cylinder liners. A honed (fine) liner with additional microdimples along the interstice area shows friction losses up to 19% compared to standard honed nonstructured cylinder liner.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2013;1(1):011004-011004-6. doi:10.1115/1.4023755.

Interdisciplinary research efforts have started focusing on the development of multiscale models and development of designer multiscale surfaces exhibiting specific properties at different scales for a specific purpose. With the rapid evolution of these new engineered surfaces for microelectromechanical systems (MEMS), microfluidics, etc., there is a strong need for developing tools to measure and characterize these surfaces at different scales. In order to obtain all meaningful details of the surface at various required scales, one is left with the only option of measuring the surface using multiple technologies using a combination of instruments. The majority of hardware-based approaches focus on the development of systems housing multiple technologies/capabilities into a single frame. These systems enable the user to obtain different surface maps using various technologies, but the user does not readily have the ability to combine all the obtained data into one single dataset. The effective approach toward multiscale measurement and characterization would be to use the individual measurement tools and finding a method to relate the individual coordinate systems and use an offline virtual tool to unify, manipulate, segment, merge, and retrieve data. Shape primitives and focus-based fusion strategies cannot be used as every data point in the data sets under consideration has to be treated as essentially at optimal focus. A multiscale data fusion strategy results in edge effects on nonplanar and high aspect ratio surfaces. An optimized fusion strategy, the “FWR method,” for the surface metrology domain is proposed where the subimages obtained from discrete wavelet frame (DWF) were separated into three regimes—form, waviness, and roughness—and fusion was not performed on subimages in the form regime. This approach effectively eliminates the edge effects. Individual data-point-level fusion was successfully demonstrated on Fresnel microlens array surface data as a case study of a nondirectional engineered surface with high aspect ratio.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2013;1(1):011005-011005-8. doi:10.1115/1.4023531.

Micropart manipulation is an active research area encompassing a wide array of fields and applications. As the size of the parts to be manipulated by an automated system decreases, the dominant forces are different compared to macroscale ones. Thus, for accurately modeling and evaluating the motion dynamics of a micropart, microscale forces and their effects must be considered. This manuscript employs a nanomicroscale friction model based on the Kogut–Etsion model that along with microscale forces considers surface roughness and material hardness properties to identify the acceleration threshold that would cause a micropart to start sliding on a carrier surface or vertically detach from the carrier surface during gripperless manipulation in a dry environment. The microscale forces change significantly as a function of the surface roughness of the two contacting surfaces. The results indicate that there will always be critical acceleration values below which no sliding or detachment takes place. Also, for the same model parameters, the sliding acceleration is smaller than the detachment acceleration for softer materials and larger for harder materials. The sliding acceleration threshold is more sensitive to hardness changes at smaller surface roughness values as compared to larger surface roughness values. The material hardness has no effect on the detachment acceleration for the same surface roughness values. The knowledge of the acceleration thresholds and their relative magnitudes could be advantageously employed for the development of gripperless manipulation approaches for microcomponent or microdevice handling or for the development of microconveyor platforms for controlled micropart translocation.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2013;1(1):011006-011006-9. doi:10.1115/1.4023756.

Pulsed laser micro polishing (PLμP) has been shown to be an effective method of polishing micro metallic parts whose surface roughness can approach the feature size. Laser pulse duration in the PLμP process is an important parameter that significantly affects the achievable surface finish. This paper describes the influence of laser pulse duration on surface roughness reduction during PLμP. For this purpose, near-infrared laser pulses have been used to polish Ti6Al4V at three different pulse durations: 0.65 μs, 1.91 μs, and 3.60 μs. PLμP at longer pulse durations resulted in dominating Marangoni convective flows, yet significantly higher reductions in the average surface roughness were observed compared to the short pulse duration regime without convection.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2013;1(1):011007-011007-9. doi:10.1115/1.4023287.

This paper presents a comprehensive transient model of various phenomena that occur during laser ablation of TiC target at subnanosecond time-steps. The model is a 1D numerical simulation using finite volume method (FVM) on a target that is divided into subnanometric layers. The phenomena considered in the model include: plasma initiation, uniform plasma expansion, plasma shielding of incoming radiation, and temperature dependent material properties. It is observed that, during the target heating, phase transformations of any layer occur within a few picoseconds, which is significantly lower than the time taken for it to reach boiling point (~ns). The instantaneous width of the phase transformation zones is observed to be negligibly small (<5nm). In addition, the width of the melt zone remains constant once ablation begins. The melt width decreases with an increase in fluence and increases with an increase in pulse duration. On the contrary, the trend in the ablation depth is exactly opposite. The plasma absorbs about 25–50% of the incoming laser radiation at high fluences (20-40J/cm2), and less than 5% in the range of 5-10J/cm2. The simulated results of ablation depth on TiC are in good agreement at lower fluences. At moderate laser fluences (10-25J/cm2), the discrepancy of the error increases to nearly ±7%. Under prediction of ablation depth by 15% at high fluences of 40J/cm2 suggests the possibility of involvement of other mechanisms of removal such as melt expulsion and phase explosion at very high fluences.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2013;1(1):011008-011008-9. doi:10.1115/1.4023532.

In the metal injection molding (MIM) process, fine metal powders are mixed with a binder and injected into molds, similar to plastic injection molding. After molding, the binder is removed from the part, and the compact is sintered to almost full density. Though able to create high-density parts of excellent dimensional control and surface finish, the MIM process is restricted in the size of part that can be produced, due to gravitational deformation during high-temperature sintering and maximum thickness requirements to remove the binding agents in the green state. Larger parts could be made by bonding the green parts to a substrate during sintering; however, a primary obstacle to this approach lies in the sinter shrinkage of the MIM part, which can be up to 20%, meaning that the MIM part shrinks during sintering, while the conventional substrate maintains its dimensions. This behavior would typically inhibit bonding and/or cause cracking and deformation of the MIM part. In this work, we present a structure of micro features molded onto the surface of the MIM part, which bonds, deforms, and allows for shrinkage while bonding to the substrate. The micro features tolerate plastic deformation to permit the shrinkage without causing cracks after the initial bonds are established. In a first series of tests, bond strengths of up to 80% of that of resistance welds have been achieved. This paper describes how the authors developed their proposed method of sinter bonding and how they accomplished effective sinter bonds between MIM parts and solid substrates.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2013;1(1):011009-011009-8. doi:10.1115/1.4023290.

Carbon nanotube (CNT) based polymeric composites exhibit high strength and thermal conductivity and can be electrically conductive at a low percolation threshold. CNT nanocomposites with polystyrene (PS) thermoplastic matrix were injection-molded and high shear stress in the flow direction enabled partial alignment of the CNTs. The samples with different CNT concentrations were prepared to study the effect of CNT concentration on the cutting behavior of the samples. Characterizations of CNT polymer composites were studied to relate different characteristics of materials such as thermal conductivity and mechanical properties to micromachining. Micro-end milling was performed to understand the material removal behavior of CNT nanocomposites. It was found that CNT alignment and concentrations influenced the cutting forces. The mechanistic micromilling force model was used to predict the cutting forces. The force model has been verified with the experimental milling forces. The machinability of the CNT nanocomposites was better than that of pure polymer due to the improved thermal conductivity and mechanical characteristics.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2013;1(1):011010-011010-10. doi:10.1115/1.4023286.

Due to its light weight, high creep, and wear resistance, magnesium metal matrix composites (Mg-MMCs) with nanosized reinforcements are promising for various industrial applications, especially those with high volume fractions of reinforcements. The machinability of Mg-MMCs and related cutting process modeling are important to study. In this paper, an analytical cutting force model is developed to predict cutting forces of Mg-MMC reinforced with SiC nanoparticles in micromilling process. This model is different from previous ones by encompassing the behaviors of nanoparticle reinforcements in three cutting scenarios, i.e., shearing, ploughing, and elastic recovery. By using the enhanced yield strength in the cutting force model, three major strengthening factors are incorporated, including load-bearing effect, enhanced dislocation density strengthening effect, and Orowan strengthening effect. In this way, material properties, such as the particle size and volume fraction as significant factors affecting the cutting forces, are explicitly considered. To validate the model, experiments based on various cutting conditions using two types of end mills (diameters as 100 μm and 1 mm) were conducted on pure Mg, Mg-MMCs with volume fractions of 5 vol. %, 10 vol. %, and 15 vol. %. The experimental results show a good agreement with the predicted cutting force value.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2013;1(1):011011-011011-6. doi:10.1115/1.4023159.

Carbon nanotube (CNT)-based piezoresistive strain sensors have the potential to outperform traditional silicon-based piezoresistors in MEMS devices due to their high strain sensitivity. However, the resolution of CNT-based piezoresistive sensors is currently limited by excessive 1/f or flicker noise. In this paper, we will demonstrate several nanomanufacturing methods that can be used to decrease noise in the CNT-based sensor system without reducing the sensor's strain sensitivity. First, the CNTs were placed in a parallel resistor network to increase the total number of charge carriers in the sensor system. By carefully selecting the types of CNTs used in the sensor system and by correctly designing the system, it is possible to reduce the noise in the sensor system without reducing sensitivity. The CNTs were also coated with aluminum oxide to help protect the CNTs from environmental effects. Finally, the CNTs were annealed to improve contact resistance and to remove adsorbates from the CNT sidewall. The optimal annealing conditions were determined using a design-of-experiments (DOE). Overall, using these noise mitigation techniques it is possible to reduce the total noise in the sensor system by almost 3 orders of magnitude and increase the dynamic range of the sensors by 48 dB.

Commentary by Dr. Valentin Fuster

Technical Briefs

J. Micro Nano-Manuf. 2013;1(1):014501-014501-6. doi:10.1115/1.4023162.

We show that a commercial microwave oven can be used after growth to increase alignment of carbon nanotubes (CNTs) and reduce their resistance as thermal and electrical interface materials. Forests of multiwall CNTs were grown directly on both sides of aluminum foils by thermal chemical vapor deposition (CVD) and subsequently exposed to a microwave treatment in air. Scanning electron micrographs revealed enhanced vertical alignment of CNTs after postgrowth microwave treatment. The microwave treatment creates an electric field near the CNT growth substrate that aligns the CNTs orthogonally to the growth substrate. Microwaved CNT forests produced increased mechanical stiffness by approximately 58%, and reduced thermal and electrical contact resistances by 44% and 41%, respectively, compared to as-grown forests. These performance changes are attributed to an increase in the real contact area established at the CNT distal ends because of the enhanced forest alignment. This conclusion is consistent with several prior observations in the literature. This work demonstrates a facile method to enhance the alignment of CNTs grown by thermal CVD without the use of in situ plasma or electric field application.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2013;1(1):014502-014502-3. doi:10.1115/1.4023288.

Superhydrophobicity in nature is the result of multiscale (hierarchical) roughness which consists of nano-asperities superimposed on micrometer scale roughness. A low-cost superhydrophobic surface was prepared by depositing soot on Vaseline coated glass substrates. The surface was rapidly prepared without any sophisticated fabrication facilities. The surface exhibited a remarkably high water contact angle of 161 deg and a roll-off angle of 3 deg. Atomic force microscopy (AFM) of the surface was done which revealed a very rough surface. The roughness features with nano-asperities superimposed on micrometer scale roughness enhance the water repellency. The micrometer scale peaks on the surface support the water droplet in a Cassie–Baxter state with the nano-asperities sheltering a composite interface below the droplet. The work of adhesion for the surface was also low at 18 nJ. The study will enable easy preparation of a cost effective superhydrophobic surface.

Commentary by Dr. Valentin Fuster

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