Accepted Manuscripts

Yancheng Wang, Dai Xue and Deqing Mei
J. Micro Nano-Manuf   doi: 10.1115/1.4038675
This paper develops a novel standing surface acoustic wave (SAW) device with three-pair of interdigital transducers (IDTs) to fabricate the patterned microstructure arrays with the assistance of ultraviolet (UV) polymerization. The working principle, structural design, and fabrication of the SAW device are presented. Then experimental setup was conducted to investigate the fabrication process and method of the patterned microstructure arrays on a thin photosensitive polymer surface. By adjusting the input wavelength and working voltage and selecting the pairs of IDTs, several types of patterned microstructure arrays, such as linear undulate and latticed undulate with different surface morphologies, could be fabricated. For the application of the microstructure arrays, L929 mouse fibroblasts are cultured on the surface with linear undulate microstructure arrays. Preliminary results showed that the cells aligned well with the direction of the patterned surface and can enhance the cell culturing. Therefore, by using the developed SAW device with the assistance of UV polymerization is an effective method to fabricate the patterned microstructure arrays, which may have great potential in the applications of biomedical and/or microelectronic fields.
TOPICS: Manufacturing, Surface acoustic waves, Ultraviolet radiation, Polymerization, Biomedicine, Fibroblasts, Wavelength, Structural design, Polymers, Transducers
Technical Brief  
Joon Hyong Cho and Michael Cullinan
J. Micro Nano-Manuf   doi: 10.1115/1.4038676
This paper presents graphene growth on Pt thin films deposited with four different adhesion layers: Ti, Cr, Ta, and Ni. During the graphene growth at 1000 oC using conventional Chemical Vapor Deposition method, these adhesion layers diffuse into and alloy with Pt layer resulting in graphene to grown on different alloys. This means that each different adhesion layers induces a different quality and number of layer(s) of graphene grown on the Pt thin film. This paper presents the feasibility of graphene growth on Pt thin films with various adhesion layers and the obstacles needed to overcome in order to enhance graphene transfer from Pt thin films. Therefore, this paper address one of the major difficulties of graphene growth and transfer to the implementation of graphene in NEMS/MEMS devices.
TOPICS: Thin films, Graphene, Platinum, Adhesion, Alloys, Chemical vapor deposition, Microelectromechanical systems, Nanoelectromechanical systems
Pedram Parandoush, Hanxiong Fan, Xiaolei Song and Dong Lin
J. Micro Nano-Manuf   doi: 10.1115/1.4038669
Bioceramics with porous microstructure has attracted intense attention in tissue engineering due to tissue growth facilitation in the human body. In the present work, a novel manufacturing process for producing hydroxyapatite (HA) aerogels with a high density shell inspired by human bone microstructure is proposed for bone tissue engineering applications. This method combines laser processing and traditional freeze casting in which HA aerogel is prepared by freeze casting and aqueous suspension prior to laser processing of the aerogel surface with a focused CO2 laser beam that forms a dense layer on top of the porous microstructure. Using the proposed method, HA aerogel with dense shell was successfully prepared with a microstructure similar to human bone. The effect of laser process parameters on surface and cross-sectional morphology and microstructure was investigated in order to obtain optimum parameters and have a better understanding of the process. Low laser energy resulted in fragile surface with defects and cracks due to low temperature and inability of laser to fully melt the surface while high laser energy caused thermal damage both to surface and microstructure. The range of 40-45 W laser power, 5 mm/s scanning speed, spot size of 1 mmm and 50 % overlap in laser scanning the surface yielded the best surface morphology and micro structure in our experiments.
TOPICS: Lasers, Surface engineering, Bone, Shells, Casting, Manufacturing, Carbon dioxide lasers, Fracture (Materials), Biological tissues, Tissue engineering, Damage, Engineering systems and industry applications, Low temperature, Density
Xiuqing Hao, Hanlong Li, Xiaolu Song, Liang Li and Ning He
J. Micro Nano-Manuf   doi: 10.1115/1.4038629
The micro/nano textured cemented carbide surface of different wettability was produced by laser scanning and fluorinated treatment. The tribological properties of the un-textured, oleophobic and oleophilic micro/nano textured surface were investigated experimentally including the effects of crank speed and contact pressure by a reciprocating friction and a wear tester. For all tested surfaces, the friction coefficient of the surface decreased as both the increasing crank speed and contact pressure increased. Compared to the un-textured surface, the friction coefficient of the micro/nano textured surface was significantly decreased, being sensitive to the wettability of the surface. Besides, the tribological properties of the oleophobic micro/nano textured surface were superior to the oleophilic micro/nano textured surface under the same experimental conditions. The improvement in tribological properties of the oleophobic micro/nano textured surface could be attributed to the low wettability, which was beneficial to rapid accumulation of the lubricating oil on the surface.
TOPICS: Tribology, Lasers, Friction, Pressure, Wear, Lubricating oils
Technical Brief  
Buddhika Jayasena and Shreyes Melkote
J. Micro Nano-Manuf   doi: 10.1115/1.4038606
Molecular Dynamics (MD) simulations are used to gain insights into the process conditions that cause separation of graphene layers from a highly ordered pyrolytic graphite (HOPG) source in a polydimethylsiloxane (PDMS) stamp assisted mechanical exfoliation process. Specifically, the effects of selected exfoliation process parameters and pre-existing defects, such as layer discontinuities in the graphite source, on the exfoliation process are investigated. The results show that exfoliation of individual and few layer graphene requires delicate control of the normal force applied to the HOPG by the PDMS stamp. The study also shows that defects (e.g. discontinuities) in the HOPG have a significant impact on the thickness of separated layers and the layer separation force. The insights derived from this study are expected to be very useful in the development of a low-cost, scalable, large area graphene production process.
TOPICS: Molecular dynamics, Plasma desorption mass spectrometry, Graphene, Graphite, Separation (Technology), Manufacturing, Simulation, Engineering simulation
Lu Lu, Erina Baynojir Joyee and Yayue Pan
J. Micro Nano-Manuf   doi: 10.1115/1.4038574
To date, several Additive Manufacturing technologies have been developed for fabricating smart particle-polymer composites. Those techniques can control particle distributions to achieve gradient or heterogeneous properties and functions. Such manufacturing capability opened up new applications in many fields. However, it is still widely unknown how to design the localized material distribution to achieve desired product properties and functionalities. The correlation between micro-scale material distribution and macroscopic composite performance needs to be established. In our previous work, a novel Magnetic-field-assisted Stereolithography (M-PSL) process was developed, for fabricating magnetic particle-polymer composites. In this work, we focused on the study of magnetic-field-responsive particle-polymer composite design with the aim of developing guidelines for predicting the magnetic-field-responsive properties of the composite. Micro-scale particle distribution parameters, including particle loading fraction, magnetic particle chain structure, microstructure orientation, and particle distribution patterns, were investigated. Their influences on the properties of particle-polymer liquid suspensions and properties of the 3D printed composites were characterized. By utilizing the magnetic anisotropy properties of the printed composites, motions of the printed parts could be actuated at different positions in the applied magnetic field. Physical models were established to predict magnetic properties of the composite and trigger distance of fabricated parts. The predicted results agreed well with the experimental measurements, indicating the effectiveness of predicting macroscopic composite performance using micro-scale distribution data, and the feasibility of using the developed physical models to guide multi-material and multi-functional composite design.
TOPICS: Composite materials, Microscale devices, Magnetic particles, Additive manufacturing, Particulate matter, Polymers, Design, Magnetic fields, Manufacturing, Stereolithography, Anisotropy, Parallel strand lumber, Chain
Guest Editorial  
Yayue Pan
J. Micro Nano-Manuf   doi: 10.1115/1.4038575
TOPICS: Manufacturing
Technical Brief  
Chi Zhou, Guanglei Zhao and Dong Lin
J. Micro Nano-Manuf   doi: 10.1115/1.4038452
As an emerging and effective nano-manufacturing technology, the directional freezing based 3D printing can form 3-Dimensional (3D) nano-structures with complex shapes and superior functionalities, and thus has received ever increasing publicity in the past years. One of the key challenges in this process is the proper heat management, since the heat induced melting and solidification process significantly affects the functional integrity and structural integrity of the printed structure. A novel approach for heat prediction out of modeling and optimization is introduced in this study. Based on the prediction, we propose a heuristic tool path planning method. The simulation results demonstrate that the tool path planning highly affects the spatial and temporal temperature distribution of the being printed part and the optimized tool path planning can effectively improve the uniformity of the temperature distribution which will consequently enhance the performance of the fabricated nano-structures.
TOPICS: Nanomaterials, Freezing, Path planning, Additive manufacturing, Heat, Temperature distribution, Nanostructures , Optimization, Solidification, Shapes, Simulation results, Melting, Modeling, Nanomanufacturing
Xiaoming Yu, Meng Zhang and Shuting Lei
J. Micro Nano-Manuf   doi: 10.1115/1.4038453
Photopolymerization enables the printing of three-dimensional (3D) objects through successively solidifying liquid photopolymer on 2D planes. However, such layer-by-layer process significantly limits printing speed, because a large number of layers need to be processed in sequence. In this paper, we propose a novel 3D printing method based on multiphoton polymerization using femtosecond Bessel beam. This method eliminates the need for layer-by-layer processing, and therefore dramatically increases printing speed for structures with high aspect ratios, such as wires and tubes. By using unmodulated Bessel beam, a stationary laser exposure creates a wire with average diameter of 100 µm and length exceeding 10 mm, resulting in an aspect ratio > 100:1. Scanning this beam on the lateral plane fabricates a hollow tube within a few seconds, more than 10 times faster than using the layer-by-layer method. Next, we modulate the Bessel beam with a spatial light modulator (SLM) and generate multiple beam segments along the laser propagation direction. Experimentally observed beam pattern agrees with optics diffraction calculation. This 3D printing method can be further explored for fabricating complex structures, and has the potential to dramatically increase 3D printing speed while maintaining high resolution.
TOPICS: Polymerization, Additive manufacturing, Printing, Lasers, Wire, Photopolymers, Resolution (Optics), Optics, Diffraction
Yachao Wang, Jing Shi, Shiqiang Lu and Weihan Xiao
J. Micro Nano-Manuf   doi: 10.1115/1.4038454
Graphene possesses many outstanding properties, such as high strengths, light weight, making it an ideal reinforcement for metal matrix composite (MMCs). Meanwhile, fabricating MMCs through laser assisted additive manufacturing (LAAM) has attracted much attention in recent years due to the advantages of low waste, high precision, short production lead time, and high flexibility. In this study, graphene reinforced aluminum alloy AlSi10Mg is fabricated using selective laser melting. Composite powder is prepared using high-energy ball milling. Room temperature tensile tests are conducted to evaluate the tensile properties. Scanning electron microscopy (SEM) observations are conducted to investigate the microstructure and fracture surface of obtain composite. It is found that adding GNPs significantly increases porosity and therefore deteriorates material tensile performance. The relationship between porosity and material strength are numerically investigated. Taking into consideration the strength reduction caused by large porosity, the strengthening effect of GNPs turns out to be significant, which reaches 60.2 MPa.
TOPICS: Lasers, Melting, Mechanical properties, Graphene, Porosity, Metal matrix composites, Composite materials, Aluminum alloys, Weight (Mass), Temperature, Strength (Materials), Fracture (Materials), Tensile strength, Additive manufacturing, Fracture (Process), Scanning electron microscopy, Ball milling
Nilabh K Roy, Obehi G Dibua, William Jou, Feng He, Jihoon Jeong, Yaguo Wang and Michael Cullinan
J. Micro Nano-Manuf   doi: 10.1115/1.4038455
A high electrical and thermal conductivity coupled with low costs make copper (Cu) an enticing alternative to aluminum for fabrication of interconnects in packaging applications. To tap into the benefits of the ever-reducing size of transistors, it is required to increase the input/output (I/O) pin count on electronic chips and thus minimize the size of chip to board interconnects. Laser sintering of Cu nanoparticle (NP) inks can serve as a promising process for developing these micron sized, 3D interconnect structures. However, the exact processing windows for Cu NP sintering are not well known. Therefore, this paper presents an extensive experimental investigation of the sintering processing window with different lasers including femtosecond (fs), nanosecond (ns) and continuous-wave (CW) lasers. The dependence of the processing window on Cu layer thicknesses and laser exposure durations has also been investigated. A simplified model to estimate optimum laser sintering windows for Cu NPs using pulsed lasers is presented and the predicted estimates are compared against the experimental results. Given the simplicity of the model, it is shown to provide good estimates for fluence required for the onset of sintering and the processing window for good sintering of Cu NPs.
TOPICS: Copper, Lasers, Waves, Nanoparticles, Sintering, Inks, Thermal conductivity, Fluence (Radiation measurement), Transistors, Packaging, Manufacturing, Aluminum
Jingzhou Zhao and Xiaochun Li
J. Micro Nano-Manuf   doi: 10.1115/1.4038433
Thermal drawing from a preform recently emerges as a scalable manufacturing method for the high volume production of continuous metal micro wires for numerous applications. However no model can yet satisfactorily provide effective understanding of core diameter and continuity from process parameters and material properties during thermal drawing. In this paper, a long wavelength model is derived to describe the dynamics of a molten metal micro-jet entrained within an immiscible, viscous, nonlinear free-surface extensional flow . The model requires numerical data (e.g. drawing force and cladding profile) be measured in real-time. Examination of the boundary conditions reveals that the diameter control mechanism is essentially volume conservation. The flow rate of molten metal is controlled upstream while the flow velocity is controlled downstream realized by solidification of the molten metal. The dynamics of the molten metal jet are found to be dominated by interfacial tension, stress in the cladding, and pressure in the molten metal. Taylor's conical fluid interface solution [1] is found to be a special case from this model. A dimensionless capillary number Ca=2Fa/(?A(0)) is suggested to be used as the indicator for the transition from continuous mode (i.e. viscous stress dominating) to dripping mode (i.e. interfacial tension dominating). Experimental results showed the existence of a critical capillary number Ca_cr, above which continuous metal microwires can be produced, providing the first ever quantitative predictor of the core continuity during preform drawing of metal microwires.
TOPICS: Metals, Fibers, Manufacturing, Wavelength, Preforms, Flow (Dynamics), Surface tension, Dynamics (Mechanics), Cladding systems (Building), Stress, Materials properties, Fluids, Solidification, Boundary-value problems, Pressure, Wire
Yong X. Gan, Ann D. Chen, Jeremy Gan and Kevin R. Anderson
J. Micro Nano-Manuf   doi: 10.1115/1.4038432
In this work, an electrohydrodynamic casting approach was used to manufacture a carbon nanofiber composite material containing bismuth telluride (Bi2Te3) particles. A 10% polyacrylonitrile (PAN) polymer solution was taken as the precursor to generate nanofibers. Bismuth telluride micro particles were added into the polymer solution. The particle-containing solution was electrohydrodynamically cast onto a substrate to form a PAN-based nanofiber composite mat. High temperature heat treatment on the polymeric matrix composite mat in hydrogen atmosphere resulted in the formation of a micro particle loaded carbon nanofiber composite material. Scanning electron microscopic (SEM) analysis was conducted to observe the morphology and reveal the composition of the composite material. Energy conversion functions in view of converting heat into electricity, electromagnetic wave energy into heat, and photon energy into electricity were shown. Strong Seebeck effect, hyperthermia and photovoltaics of the composite mat were found. In addition, the potential applications as sensors were discussed.
TOPICS: Composite materials, Casting, Electrohydrodynamics, Carbon, Nanofibers, Microparticles, Polymer solutions, Particulate matter, Heat, Photons, Electrons, Sensors, Heat treating (Metalworking), Energy conversion, Wave energy, Photovoltaics, Hydrogen, High temperature, Thermoelectricity
Keivan Ahmadi
J. Micro Nano-Manuf   doi: 10.1115/1.4038434
An Output-Only Modal Analysis (OMA) approach is presented to obtain the direct Frequency Response Function (FRF) at the tip of the tool in micromilling setups. White noise input is provided using acoustic excitation and the resulting vibrations are measured using a Laser Doppler Vibrometer (LDV). Auto Regressive identification is used to extract the natural frequencies and damping ratios of the structural modes of the milling setup, and mass-sensitivity analysis is used to obtain modal stiffness values. The accuracy of the tool tip FRFs that are constructed using OMA is verified by comparing them against the FRFs that are measured using impulse hammer tests. The direct FRF at the tool tip is an essential component in predicting and avoiding excessive and unstable vibrations in milling operations. The presented approach provides a practical method for the direct measurement of the tool tip FRF in micromilling where the application of traditional hammer tests is not possible.
TOPICS: Micromilling, Modal analysis, Hammers, Vibration, Milling, Stiffness, White noise, Laser Doppler vibrometers, Frequency response, Impulse (Physics), Damping, Excitation, Acoustics
Hagen Mueller, Tobias Groezinger, Sascha Weser, Wolfgang Eberhardt and Andre Zimmermann
J. Micro Nano-Manuf   doi: 10.1115/1.4038320
Reliability aspects are crucial for the success of every technology in industrial application. Regarding interconnect devices, several methods are applied to evaluate reliability of conductor paths like accelerated environmental tests. Especially Molded Interconnect Devices (MID) which enable versatile applications with 3D circuitry on 3D shaped injection molded thermoplastic parts are often under particular stress, e.g. as component of a housing. In this study a new test method for evaluating the flexural fatigue strength of conductor paths produced by the laser based LPKF-LDS® technology is presented. For characterization of test samples a test bench for flexural fatigue test was built up. A result of the flexural fatigue test is a characteristic Woehler curve of the metal layer system. Applying this new test method, essential influencing parameters on the reliability of MID under mechanical load can be identified. So the metal layer system as well as the geometric parameters of the metal layer is crucial for the performance. Furthermore test specimens are tested under different types of mechanical load, i. e. tensile stress and compressive stress. For a holistic view on reliability of MID experimental results are discussed and supported by simulations. An important finding of the study is the advantage of nickel-free layer systems in contrast to the Cu/Ni/Au layer system which is often used in MID technology.
TOPICS: Fatigue strength, Reliability, Metals, Stress, Fatigue testing, Tension, Engineering simulation, Compressive stress, Nickel, Lasers, Simulation
Tahseen Jwad, Sunan Deng, Haider Butt and Stefan Dimov
J. Micro Nano-Manuf   doi: 10.1115/1.4038097
Fresnel zone plates (FZPs) have been gaining a significant attention by industry due to their compact design and light weight. Different fabrication methods have been reported and used for their manufacture but they are relatively expensive. This research proposes a new low-cost one-step fabrication method that utilises nanosecond laser selective oxidation of titanium coatings on glass substrates and thus to form TiO2 nano-scale films with different thicknesses by controlling the laser fluence and the scanning speed. In this way phase-shifting FZPs was manufactured where the TiO2 thin-films acted as a phase shifter for the reflected light while the gain in phase depended on the film thickness. A model was created to analyse the performance of such FZPs based on the scalar theory. Finally, phase-shifting FZPs were fabricated for different operating wavelengths by varying the film thickness and a measurement setup was built to compare experimental and theoretical results. A good agreement between these results was achieved and an FZP efficiency of 5.5% to 20.9% was obtained when varying the wavelength and the oxide thicknesses of the zones.
TOPICS: Thin films, Manufacturing, Plates (structures), Lasers, Film thickness, Wavelength, Scalars, Weight (Mass), Fluence (Radiation measurement), Design, Nanoscale phenomena, oxidation, Titanium, Coatings, Glass
Deepak Patil, S. Aravindan, Mishi Kaushal Wasson, P. Vivekanandan and P. V. Rao
J. Micro Nano-Manuf   doi: 10.1115/1.4038093
The method for fast fabrication of superhydrophobic surfaces was proposed to resist the formation of biofilm ofEscherichia coli (E.coli) and Staphylococcus aureus (S. aureus) for orthopedic and dental implants. Laser beam machining with nanosecond pulsed laser (Nd:YAG) was used to fabricate pit structure on Grade-5 Ti-6Al-4V alloy followed by annealing (at 3000C with different time scales) in order to reduce the transition time from hydrophilic to superhydrophobic surface generation. Field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) techniques were used to characterize the textured samples. The surface wettability of plain and textured samples was measured by the sessile drop method using goniometer. The biofilm formation was quantitatively and qualitatively evaluated by crystal violet binding assay and field emission scanning electron microscopy respectively. The biofilm formation is observed on plain (hydrophilic) surface for both the types of bacteria, whereas significantly less biofilm formation is observed on the laser textured (superhydrophobic) surfaces. The proposed methodhelps in reducing the risk of infection associated with implants without using cytotoxic bactericidal agents.
TOPICS: Manufacturing, Titanium alloys, Lasers, Scanning electron microscopy, Electron field emission, Laser beam machining, Orthopedics, Bacteria, Risk, Alloys, X-ray diffraction, Annealing, Crystals

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