Microfabrication Research Articles

Fabrication of Micro- and Nanopillars from Pyrolytic Carbon and Tetrahedral Amorphous Carbon.

Pattern formation of pyrolyzed carbon (PyC) and tetrahedral amorphous carbon (ta-C) thin films were investigated at micro- and nanoscale. Micro- and nanopillars were fabricated from both materials, and their biocompatibility was studied with cell viability tests. Carbon materials are known to be very challenging to pattern. Here we demonstrate two approaches to create biocompatible carbon features. The microtopographies were 2 m or 20 m pillars (1:1 aspect ratio) with three different pillar layouts (square-grid, hexa-grid, or random-grid orientation). The nanoscale topography consisted of random nanopillars fabricated by maskless anisotropic etching. The PyC structures were fabricated with photolithography and embossing techniques in SU-8 photopolymer which was pyrolyzed in an inert atmosphere. The ta-C is a thin film coating, and the structures for it were fabricated on silicon substrates. Despite different fabrication methods, both materials were formed into comparable micro- and nanostructures. Mouse neural stem cells were cultured on the samples (without any coatings) and their viability was evaluated with colorimetric viability assay. All samples expressed good biocompatibility, but the topography has only a minor effect on viability. Two m pillars in ta-C shows increased cell count and aggregation compared to planar ta-C reference sample. The presented materials and fabrication techniques are well suited for applications that require carbon chemistry and benefit from large surface area and topography, such as electrophysiological and -chemical sensors for in vivo and in vitro measurements.

Effects of electron beam irradiation on the friction and work function of the wrinkled graphene

The ability to control the tribological and electrical properties of graphene is critical to the fabrication of micro- and nanoelectromechanical systems (MEMS/NEMS) devices. Due to its high energy, electron beam irradiation has been widely used to adjust the local electrical properties of the graphene, such as inducing local defects or n-type doping. However, whether electron beam irradiation can affect the local tribological properties of wrinkled graphene has not been investigated yet. In this research, we demonstrated that the lateral force signal and the work function of the wrinkled monolayer graphene were affected by the electron beam irradiation.By using Kelvin-probe force microscopy (KPFM) and Raman spectroscopy, we measured the local electrical properties of the wrinkled monolayer graphene and confirmed that the electron-beam exposed area was changed as n-doped graphene. We compared the lateral force signal with surface potential data and concluded that the n-type doping induced by electron beam affected the tribological characteristics. Characterization of the electron-beam exposed wrinkled graphene provides a physical insight that the electrical and tribological characteristics of wrinkled graphene are correlated.

Fabrication of SU-8 photoresist micro–nanofluidic chips by thermal imprinting and thermal bonding

Micro–nanofluidic chips have been widely applied in biological and medical fields. In this paper, a simple and low-cost fabrication method for micro–nano fluidic chips is proposed. The nano-channels are fabricated by thermal nano-imprinting on an SU-8 photoresist layer followed by thermal bonding with a second SU-8 photoresist layer. The micro-channels are produced on the second layer by UV exposure and then thermal bonded by a third layer of SU-8 photoresist. The final micro–nano fluidic chip consists of micro-channels (width of 200.0 ± 0.1 μm and, depth of 8.0 ± 0.1 μm) connected by nano-channels (width of 533 ± 6 nm and, depth of 372 ± 6 nm), which has great potential in molecular filtering and detection.

Frontispiece: Fabrication of Self‐Propelled Micro‐ and Nanomotors Based on Janus Structures

Frontispiece: Fabrication of Self‐Propelled Micro‐ and Nanomotors Based on Janus Structures

Controllable fabrication of polygonal micro and nanostructures on sapphire surfaces by chemical etching after femtosecond laser irradiation

We fabricate two different types of micro and nanostructures with either pyramid-like or tetrahedron-like geometry on the sapphire surface, through the use of thechemical etching process after femtosecond laser irradiation. The distinct features of the structures are measured with both scanning electron microscopy and atomic force microscopy. The dynamic regions for the formation of the two surface structures are experimentally obtained to indicate their tunability by varying the laser average fluence and etching temperature. With the help of discussions and analyses, we propose a model to explain the formation mechanisms of the two kinds of structures, in which the competition between the growth of the alunogen (Al2 (SO4)3·17H2O) crystals and the anisotropic etching rate of the sapphire material plays an important role. In addition, it is confirmed that the tetrahedron-like structures can be used to activate the sapphire substrate for the enhancement of Raman scattering and the hydrophobic properties.

Fabrication of micro-/nano-structured super-hydrophobic fluorinated polymer coatings by cold-spray

A fabrication of superhydrophobic Perfluoroalkoxy Alkane (PFA) coatings on stainless steel surfaces by cold-spray technique has been demonstrated in this work. The in-situ supersonic impact deposition and consolidation of finely divided 20–40 μm powder material yielded hydrophobic thin coatings of PFA which exhibited contact angles of 125° but high roll off angles of 60°. The deposition efficiencies were less than 0.5%, coating was mechanically very fragile and non-uniform. However, the cold-spray deposition efficiency was subsequently increased to almost 15% by performing simple modification of particle surface morphology by introducing organosilane coated nanoceramic layers on the PFA particles and by laser texturing the stainless steel substrate surfaces to form mountain-valley micro-structures. The nanoceramic interlayers formed bridge bonds at the particle-particle interface and laser texturing achieved efficient coating-substrate interlock. The improved coatings exhibited super-hydrophobic character with 160° contact angle and 6° roll-off angle. The superhydrophobicity was seen to be as a result of micro-/nano-structured surface consisting of papillae like structures capped by a layer of hydrophobic nanoceramic. The coating also exhibited excellent water repellency.

Beyond grayscale lithography: inherently three-dimensional patterning by Talbot effect

Abstract There are a growing number of applications where three-dimensional patterning is needed for the fabrication of micro- and nanostructures. Thus far, grayscale lithography is the main technique for obtaining a thickness gradient in a resist material that is exploited for pattern transfer by anisotropic etch. However, truly three-dimensional structures can only be produced by unconventional lithography methods such as direct laser writing, focused ion beam electrodeposition, colloidal sphere lithography, and tilted multiple-pass projection lithography, but at the cost of remarkable complexity and lengthiness. In this work, the three-dimensional shape of light, which is formed by Talbot effect diffraction, was exploited to produce inherently three-dimensional patterns in a photosensitive polymer. Using light in the soft X-ray wavelength, periodic three-dimensional structures of lateral period 600 nm were obtained. The position at which the sample has to be located to be in the Fresnel regime was simulated using an analytical implementation of the Fresnel integrals approach. Exploiting the light shape forming in diffraction effects thus enables the patterning of high-resolution three-dimensional nanostructures over a large area and with a single exposure pass – which would be otherwise impossible with conventional lithographic methods.

Continuous Dual-Track Fabrication of Polymer Micro-/Nanofibers Based on Direct Drawing.

This manuscript proposes a continuous and straightforward method for fabricating suspended micro- and nanodiameter polymer fibers using an automated single-step drawing system. Termed track spinning, the system is based on a simple manual fiber drawing process that is automated by using two oppositely rotating tracks. Fibers are continuously spun by direct contact of polymer solution coated tracks followed by mechanical drawing as the distance between the tracks increases. The device can draw single or multifilament arrays of micro- and nanofibers from many kinds of polymers and solvent combinations. To demonstrate, fibers were pulled from polymer solutions containing polyvinyl acetate (PVAc) and polyurethane (PU). Fiber morphology was smooth and uniform, and the diameter was sensitive to draw length and polymer solution/melt properties. Polymer nanofibers with diameters as small as 450 nm and length of 255 mm were produced. The track spinning method is able to form fibers from high viscosity solutions and melts that are not compatible with some other nanofiber fabrication methods. Further, the setup is simple and inexpensive to implement and nozzleless and does not require an electric field or high-velocity jets, and the tracks can be widened and patterned/textured to enhance fiber yield and manufacturing precision.

Biomimetic fabrication of micro-/nanostructure on polypropylene surfaces with high dynamic superhydrophobic stability

Recently, the biomimetic replication of micro-/nanostructure present on lotus leaves has attracted great interest. Unfortunately, the nanostructure on the surfaces of lotus leaves, which play a critical role in making them superhydrophobic and self-cleaning, are difficult to precisely replicate. Herein, a nickel replica is fabricated by electroless plating and electroplating with natural lotus leaf as natural template. Using the nickel template, lotus leaf-like structure is fabricated on polypropylene (PP) surfaces by injection molding, an industrially feasible technique for fast mass-fabrication. It is demonstrated that the micropapillae on the lotus leaf are successfully fabricated on the PP replica, especially nanohairs with sharp tips and high aspect ratio are developed without additional surface coating or chemical modification. The PP replicas exhibit a highly similar wettability with the lotus leaf. More interestingly, the nanohairs on the PP replica are superior to the nanotubules on the lotus leaf in terms of the dynamic superhydrophobic stability and superhydrophobic thermal durability. Impact droplet exhibits shorter contact time on the PP replica than the lotus leaf. Mechanisms for the functionalities of the nanohairs on the PP replica are analyzed. Such superior properties are expected to have industrial applications, such as anti-icing, microdroplet transfer, and self-cleaning.

Fabrication of three-dimensional TKX-50 network-like nanostructures by liquid nitrogen-assisted spray freeze-drying method

ABSTRACTDesign and fabrication of micro- and nanostructures for energetic materials have attracted more attention recently to improve safety properties and enhance detonation performance. Exploring and developing dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50) with unique microstructures, an emerging high-energy-density material with superior comprehensive properties, is of great significance for the potential applications. In this work, we reported that three-dimensional (3D) TKX-50 network-like nanostructures were designed and fabricated successfully via the liquid nitrogen-assisted spray freeze-drying method. Characterization results suggested 3D TKX-50 network-like nanostructures were constructed by self-assembly of small nanoparticles. Furthermore, a nucleation-and-growth self-assembly formation mechanism of the network-like nanostructures depended on the different concentrations of the aqueous solution of TKX-50 was proposed in detail based on the experimental results. More interestingly, thermal analysis results demonstrated these novel 3D TKX-50 network-like nanostructures are much easier to be activated and have a lower decomposition temperature than the raw material, due to decrease in particle sizes, and the impact sensitivity of 3D TKX-50 network-like nanostructures become more sensitive than that of raw TKX-50. Their friction sensitivity of as-prepared samples is similar to the raw materials. Therefore, this work could provide a new prospect for fabrication and application of TKX-50 nanostructures.

Soft High-Resolution Neural Interfacing Probes: Materials and Design Approaches.

Neural interfacing probes are located between the nervous system and the implanted electronic device in order to acquire information on the complex neuronal activity and to reconstruct impaired neural connectivity. Despite remarkable advancement in recent years, conventional neural interfacing is still unable to completely accomplish these goals, especially in long-term brain interfacing. The major limitation arises from physical and mechanical differences between neural interfacing probes and neural tissues that cause local immune responses and production of scar cells near the interface. Therefore, neural interfaces should ideally be extremely soft and have the physical scale of cells to mitigate the boundary between biotic and abiotic systems. Soft materials for neural interfaces have been intensively investigated to improve both interfacing and long-term signal transmission. The design and fabrication of micro and nanoscale devices have drastically decreased the stiffness of probes and enabled single-neuron measurement. In this Mini Review, we discuss materials and design approaches for developing soft high-resolution neural probes intended for long-term brain interfacing and outline existent challenges for achieving next-generation neural interfacing probes.

Tailoring metallic surface properties induced by laser surface processing for industrial applications

As a simple, reproducible, and pollution-free technique with the potential of integration and automation, laser processing has attracted increasing attention. Laser processing, which includes laser polishing, laser cleaning, and fabrication of laser-induced micro-/nano-structures, has been demonstrated to yield smooth, clean, functional surfaces and effective joining. Laser polishing is an advanced, highly efficient, and ecofriendly polishing technology. This study demonstrated the laser polishing of a selective laser-melted Inconel 718 (IN718) superalloy and a titanium alloy sample. The surface roughnesses Ra and Rz of the IN718 superalloy were respectively reduced from 8 and 33 μm to 0.2 and 0.8 μm, and the Ra of the titanium alloy was reduced from 9.8 μm to 0.2 μm. Moreover, the wear resistance and corrosion resistance of the IN718 were apparently improved. As another surface-related processing method, laser cleaning was used to clean terminal blocks. Almost all the contaminants were removed, as verified by the absence of their chemical compositions and the decreased surface roughness. In addition, a superhydrophobic surface with a contact angle of over 160° and sliding angle of <8° on stainless steel was obtained by laser texturing treatment. These results demonstrate the high potential of laser processing in the scientific, technological, and industrial fields.

Structurally diverse coordination compounds of zinc as effective precursors of zinc oxide nanoparticles with various morphologies

The structurally diverse coordination compounds of zinc were designed and synthesized using two types of building blocks: short‐chain carboxylate ions and hexamethylenetetraamine. They were characterized by X‐ray crystallography, infrared spectroscopy and thermal analysis. The studied compounds were used as precursors for production (via controlled thermal conversion) of zinc oxide nanoparticles. The conversion process was optimized in terms of two parameters (heating rate and maximum temperature). Such an approach, combined with proper design of the precursor structure, allows fabrication of various zinc oxide micro‐ and nanoparticles. The influence of a precursor structure and modifications of conversion parameters on size and morphology of ZnO particles were studied and discussed.

To investigate the determinants of cloud computing adoption in the manufacturing micro, small and medium enterprises

Purpose The purpose of this paper is to identify the critical factors influencing the cloud computing adoption (CCA) in the manufacturing micro, small and medium enterprises (MSMEs) by employing a decision-making trial and evaluation laboratory (DEMATEL) methodology. Design/methodology/approach Through literature review and expert opinions, 30 significant factors were identified, and then a DEMATEL approach was applied for exploring the cause–effect relationship between the factors. Findings The results of study highlighted that five factors, namely, “hardware scalability and standardisation”, “cost (subscription fees, maintenance cost and implementation cost (CS1)”, “innovation”, “installation and up gradation (CS28)”, and “quality of service” were the most significant factors influencing the CCA in the case sector. Research limitations/implications The DEMATEL model was developed by considering expert inputs, and these inputs could be biased which can influence the reliability of the model. This study guides the organisational managers, cloud service providers and governmental organisations in formulating the new policies/strategies or modifying the existing ones for the effective CCA in the case sector. Originality/value For the first time. interdependency between the critical factors influencing CCA was discussed by employing the DEMATEL approach in the Indian manufacturing MSMEs context.

Fabrication of fully suspended pyrolytic carbon string resonators for characterization of drug nano- and microparticles

Pyrolytic carbon is a promising material for fabrication of micro- and nanomechanical sensors due to the possibility to control both structural parameters and properties such as resonance frequency, residual stress and electrical conductivity. Here, we present a novel fabrication process for pyrolytic carbon string resonators suspended over a through-wafer-orifice. The pyrolytic carbon string resonators had a length of 400 μm, a width of 30 μm and a thickness of 700 nm. The string resonators were applied for characterization of nano- and microparticulate drug formulations using two different modes of operation. First, mass sensing on nanograms of nebulized or spray coated paracetamol micro- and nanoparticles was demonstrated. Then, absorption spectra of the drug were obtained by nanomechanical infrared spectroscopy (NAM-IR). Finally, an efficient method for in situ regeneration of the sensor was demonstrated.

Continuously Variable Regulation of the Speed of Bubble-Propelled Janus Microcapsule Motors Based on Salt-Responsive Polyelectrolyte Brushes.

The engineering of self-propelled micro-/nanomotors (MNMs) with continuously variable speeds, akin to macroscopic automobiles equipped with a continuously variable transmission, is still a huge challenge. Herein, after grafting with salt-responsive poly[2-(methacryloyloxy)ethyltrimethylammonium chloride] (PMETAC) brushes, bubble-propelled Janus microcapsule motors with polyelectrolyte multilayers exhibited adjustable speeds when the type and concentration of the counterion was changed. Reversible switching between low- and high-speed states was achieved by modulating the PMETAC brushes between hydrophobic and hydrophilic configurations by ion exchange with ClO4 - and polyphosphate anions. This continuously variable regulation enabled control of the speed in an accurate and predictable manner and an autonomous response to the local chemical environment. This study suggests that the integration of polymer brushes with precisely adjustable responsiveness offers a promising route for motion control of smart MNMs that act like their counterparts in living systems.

Hybrid Machining Process For Microfabrication Of Micro Parts

Abstract Hybrid micro-machining known as a fast-growing technology, which appears to be outperforming traditional processes, and opening new areas of application, has revolutionized microelectronics, medical device manufacturing and many more industries. The hybrid micro-machining processes have the capability to manufacture micro parts with a high degree of accuracy and repetition in almost any material possible. In this paper, concept of hybrid micro-machining process and its working principles as well as several key hybrid micro-machining techniques are reviewed. In order to understand the importance of hybrid micro-machining, future research direction and key challenges associated with hybrid micromachining are unfolded as well.

The Perceived Export Barriers of Micro, Small, and Medium Enterprises: An Analysis from Lesotho-Based Manufacturing Enterprises

Small enterprises represent a large proportion of enterprises in most economies and are a driving force for economic growth. Most small enterprises refrain from exporting due to a number of challenges. The aim of this study was to determine the exporting barriers perceived to constrain exporting from Lesotho-based manufacturing micro, small, and medium enterprises (MSMEs). The study adopted a cross-sectional descriptive design. Data were collected from 162 Lesotho-based manufacturing enterprises through a self-administered questionnaire. Factor analysis revealed three export barrier groupings, namely international, distribution, and financial constraints. The descriptive statistics showed that Lesotho-based manufacturing MSMEs perceive lack of financial resources for market research, lack of financial resources to finance export sales, and lack of excess capacity for exports, all internal to an enterprise-loading under financial barriers as constraints to exporting. The study added to the literature new classes of export barriers. The findings suggest that the government of Lesotho has to put in place mechanisms that can reduce financial constraints to enable MSMEs to contribute as expected.

Fabrication of Different Micro Patterned Arrays by Through Mask Electrochemical Micromachining

Patterned microstructures are among the basic micro features that are indispensable in improving the tribological performance and dependability of various mechanical components especially Micro-Electro-Mechanical Systems (MEMS). Through Mask Electrochemical Micromachining (TMEMM) is a feasible process for fabricating micro-patterned arrays with controlled dimension, location and density by maintaining suitable surface texture. In this paper, appropriate machining parameters along with optimal electrolyte combination have been utilized for achieving patterned arrays in the form of micro-dimples and micro-square features. Low aspect ratio mask made of a negative PR (AZ 4903) is being introduced during TMEMM due to its low cost, availability and chemical resistance. Pattern of micro-holes with an average diameter of 65μm as well as micro-squares with a side length of 65μm imprinted on the mask are being replicated over SS304 substrate with substantial repeatability. The influence of two major Electrochemical Micromachining (EMM) parameters viz. duty cycle and machining time are investigated on the machining accuracy and surface properties of the micro-dimples generated with mask of lean thicknesses. Circular micro-dimples with an undercut of 29.15μm, depth 44.10μm and Ra 0.091μm and square micro-dimples possessing 32.63μm undercut, 40.24μm depth and 0.081μm Ra have been successfully fabricated on SS304 by this process of TMEMM.

(INVITED) Positron annihilation spectroscopy and third harmonic generation studies on MnO mixed lead zirconium silicate glass ceramics

This work is intended to report pertinent studies covering several aspects viz., spectroscopic, higher order non-linear optical studies and positron annihilation spectroscopic studies on lead zirconium silicate glass ceramics admixed with different contents of MnO. Lead zirconium silicate glasses mixed with small contents (up to 1.0 mol%) of MnO were prepared and crystallized by subjecting them to the prolonged heat treatment at crystallization temperature ∼ 830 °C. The structural analysis of the samples carried out using XRD, TEM, EDS and differential scanning calorimetric techniques has suggested that the glass ceramics are entrenched with coagulated poly-crystallites viz., Mn2SiO4, Pb2MnO4 and Pb3Mn7O15 that contain manganese ions in multiple oxidation states. These studies have also suggested that Mn2+ ions occupy octahedral as well as tetrahedral positions and the tetrahedral occupancy is predominant in the glass ceramic sample mixed 0.6 mol% of MnO (M6). Infrared, Raman, optical absorption and photoluminescence spectral investigations have further supported the above conclusions and indicated an increasing rigidity of the glass network (attributed to the enhanced tetrahedral occupancy of manganese ions) with increasing concentration of MnO up to 0.6 mol%. Positron annihilation lifetime spectroscopic studies (carried out with 22Na isotope source of strength 0.1 MBq) suggested the sample M6 contains the lowest magnitude of free volume space. This is attributed to the participation of the maximal concentration of Mn2+ ions in the glass network forming. Non-linear optical (NLO) studies using NIR Er-glass laser (λ = 1540 nm) indicated the highest intensity third harmonic generation (THG) beam in the glass ceramics doped with small contents (∼0.2 mol%) of MnO. Overall analysis of these results suggested that the samples with lower concentrations of MnO possess highly disordered internal structure and facilitated the increase of intensity of THG beam; Hence, such samples may be considered as potential candidates for the applications in the fabrication of various micro sized opto-electronic devices, for example, optical switches, optical cross-connectors, microbolometers, photovoltaics, light sensors etc.