Symposium PM3 : Science-Enabled Advances in Materials- and Manufacturing-Technologies

Additive manufacturing (AM) of metal components is a rapidly growing advanced manufacturing paradigm that promises unparalleled flexibility in the production of parts with complex geometries. However, the extreme processing conditions create inhomogeneous materials that can include intense localized compositional gradients, elongated microstructures, pronounced crystallographic texture, highly anisotropic local and macroscopic stresses that approach the flow stress, and unexpected crystalline phases. Substantial post processing is typically required to achieve useable mechanical properties, but position-dependent variations within the part and life-cycle issues such as fatigue and corrosion greatly complicate part qualification. The route to qualification of AM materials requires close control of the build process (including open-architecture instrumentation, design of experiment predictions and processing feedback loops), world-leading in situ and ex situ characterization and modeling of the as-built and post-processed microstructure and stresses, and rigorous characterization and modeling of the in-service environment material behavior. I will describe our work on AM Inconel 625, ATI 718Plus and 17-4 steel. Finally, I will describe our progress in establishing the Additive Manufacturing Benchmark Test Series (AM-Bench), a continuing series of highly controlled benchmark tests for additive manufacturing that will allow modelers to test their simulations against rigorous, highly controlled additive manufacturing benchmark test data.

Ti alloys find extensive use in the aerospace industry due to their high strength, light weight and excellent corrosion resistance. While there has been significant experimental work on Ti and its alloys spanning decades, a fundamental understanding of point defects and interfaces in Ti has to be developed for the design of next generation of Ti alloys. Here, we present the results of such a study. We have carried out a complete computational analysis to determine formation energies of point defects including vacancies, self-interstitials, and interstitial and substitutional impurities/dopants using density functional theory driven genomics. We consider a broad range of elements as impurities and show that the atomic size and the electronegativity of the impurity play significant roles in determining its position in the Ti lattice. Furthermore, we employ ab initio thermodynamics to develop surface phase diagrams of Ti in the presence of oxygen. These maps provide crucial information on the Ti-TiO_x interface and the surface energy at a given partial pressure of oxygen and temperature.

Additive manufacturing is rising in popularity for the past few years due to its wide potentials application in various areas. In this work, we demonstrate that the phase field crystal (PFC) model can be applied to identify and predict the microstructures during the solidification of the metals in additive manufacturing. Compared with the conventional phase field (PF) model which introduces spatially uniform fields, PFC model is a comparatively new model which introduces a thermodynamic free energy scalar that is minimized by periodic atomic densities and is also rotationally invariant. In this work, PFC model has been used to simulate the crystal growth during the solidification process of additive manufacturing. The starting point of each simulation is a number of already solidified seeds at various lattice orientations and distances from each other. The results revealed the columnar structure of the build metal, which matches the real growth in additive manufacturing experiment. Furthermore, the effect of ambient temperature and seed-seed distance has been investigated. It was observed that the grain growth speed increased when the ambient temperature is lower, which is in line with our conventional thought. Finally, the formation of crystal defects during the process was recorded and the resulted long-range stresses were calculated using the eigenstresses theory.

Several advanced technological applications (aerospace, automotive, energy production, infrastructure, etc.) currently provide major driving forces for optimized alloy development. Increasingly, these employ engineering materials-by-design approaches applied to various new manufacturing technologies. However, to move from an empirical design approach to a fully mechanistic one, a full understanding must be developed in each case of the sequence of precipitate phase formation and evolution that underlies the desired mechanical properties for optimized component performance. For example, metal components produced by additive manufacturing (AM) often exhibit fine dendritic microstructures and elemental segregation due to the rapid solidification in the build process, which without homogenization would adversely affect the materials performance. Furthermore, AM as-built products also frequently exhibit significant internal residual stress distributions that need to be annealed out along with post-build solutionizing and ageing treatments. Due to the far-from-equilibrium nature of AM, these heat treatments can produce unexpected phase formation, or have other effects that need to be better understood if the promise of AM is to be fully realized. Using a high-temperature sample heating stage with state-of-the-art X-ray synchrotron based small-angle and ultra-small-angle X-ray scattering (SAXS and USAXS) to provide real-time microstructure information, together with simultaneous wide-angle X-ray scattering (WAXS) as a sensitive probe for detecting emerging structural phases, the microstructural and structural evolution of precipitate and carbide formation can be followed during actual homogenization, stress relieving, ageing or solutionizing treatments. Such experimental observations under in operando conditions can be directly compared with the predictions of thermodynamic models to provide input for optimized materials-by-design efforts in new alloy development. The potential of such studies is illustrated by recent results obtained from aluminum and titanium based aerospace alloys, nickel superalloys, and advanced steels.

Cellular materials in nature have been a source of inspiration for engineers. These structures consist of gas-filled pores throughout the solid body while maintaining high strength at relatively low densities. These materials can also offer high stiffness, improved impact absorption, and thermal and acoustic insulation. Conventional processing routes to fabricate cellular structures constrain part geometry (mostly limited to planar geometry) and material selection. These limitations often hinder their widespread application preventing a designer from tailoring part mesostructure as well as its geometry for specific design purpose(s). There is an increasing interest in addressing these limitations using additive manufacturing technologies. While many of metal additive manufacturing techniques are being employed commercially, they often suffer from the detrimental effects of high-temperature processing, such as large residual stresses, poor mechanical properties, unwanted phase transformations and part distortion.
In the present investigation, low temperature additive manufacturing called cold spraying is investigated as a potential method to fabricate metallic cellular structures. In cold spray, solid metal particles of micron size range are accelerated by supersonic gas flow in a De Laval nozzle. In this process, the energy for bonding is provided in the form of kinetic energy rather than heat. Therefore, high temperatures and its detrimental effects are avoided. A new workspace, ‘sub-critical’ impact condition, is explored to fabricate porous structures made of titanium alloy for biomedical applications. The effect of support structure, particle size, deposition parameter (temperature) and deposition kinetics (gun traverse speed) on the microstructure are investigated.
The results show that spray parameters can be tuned for certain porosity, and yet retain sufficient strength. The elastic modulus and compressive yield strength of 30% porous structure were 4383±45 and 483±40 MPa respectively. Post heat treatment could change the mechanical behavior of cellular structures by modifying interparticle bindings, giving more design space to modulate properties. In vitro human mesenchymal stem cells (hMSCs) were used to evaluate the biocompatibility of the structure. Cell viability was analyzed using two color fluorescent staining. Cell morphology and surface topography were also analyzed. The results show promise in producing personalized scaffolds for tissue regeneration applications.

Advanced materials that operate in safety-critical environments are often subject to rigorous processing and inspection procedures that largely eliminate “extrinsic” defects, such as stray oxides or pores, to maximize properties such as fatigue. The nature of the microstructural "neighborhoods" that result in fatigue crack initiation has been studied in detail in both low cycle and high cycle fatigue in the nickel-base alloy René 88DT. Protocols for acquisition of large 3-D microstructural volumes of the order of mm³ with the TriBeam femtosecond laser-based tomography approach are reviewed. The probability of encountering the critical combination of features in a given volume of material is considered along with implications for modeling of fatigue life.

Fatigue remains to be a critical and challenging issue for engineers and scientists. During cyclic loading, the stress state and structure of the material are evolving, which results in a dynamic problem with many variables to consider. Given the vast microstructure variations in structural engineering materials, it poses a problem of how the uncertainty in the microstructure propagates to variability in the fatigue response of the material. Of greater interest to our community, is how do we account for the uncertainty in defect/microstructure distributions within our material in our life predictions and analysis. The focus of this talk will be an overview of research efforts to understand, model, and verify activities for crack nucleation resulting from persistent slip bands. Results from in situ fatigue experiments, in the form of (i) concurrent digital image correlation and electron backscatter diffraction and (ii) high energy x-ray diffraction microscopy, are discussed to map strain evolution relative to the materials microstructure. Finally, we note that as a result of fatigue life limitations in gas turbine applications, many components are overdesigned leading to increased weight and lower operating temperatures of the engine. Thus, significant energy efficiency benefits exist with better fatigue life prognosis.

The severe plastic deformation process has emerged as a technique for producing materials with a ultra-fine grain microstructure and hence enhanced mechanical properties [1]. Large strain extrusion machining has been demonstrated as a severe plastic deformation process and it affords a simultaneous shape- and dimension-control of extrusion in the deformation process for producing ultra-fine grained chips with required geometry [1].
In this study, a finite element model is developed for the large strain extrusion machining of Inconel 718 with our proposed constitutive model to analyse the effect of process parameters, i.e., the chip compression ratio and tool-chip friction, on the deformation and also effective strain distribution along the chip. The modified Zerilli-Armstrong [2] model based on the concept of dislocation mechanics is utilized in this study. The modified Zerilli-Armstrong model [2] was developed for predicting elevated temperature flow behaviour and so necessary corrections were made to this model to make it suitable for the entire range of machining conditions. The proposed new constitutive relationship is incorporated into a finite element model of orthogonal machining process built using ABAQUS/Explicit platform. The effectiveness of the proposed material model is validated by comparing the cutting force predictions for the continuous chip formation of Inconel 718 during orthogonal machining process with the experimental values available in literature. The predictions are in good agreement with experimental results with an error less than 8 % and therefore the proposed constitutive relationship accurately models the material behaviour of Inconel 718.
Until now only strain hardening was considered in the finite element analysis of large strain extrusion machining process because of the low cutting speeds typically employed but in this study strain rate and temperature effects were also considered by using the proposed material model. The simulations show that in contrast to conventional machining large plastic strains can be realized in large strain extrusion machining by changing the chip compression ratio. The variation of effective strain with friction-coefficient shows that an increase in friction results in a considerable increase in effective strain over a small region of the chip along the tool-chip interface. Analysis of this effective strain distribution shows that the chip underwent increased inhomogeneous deformation with a larger friction coefficient. The finite element modeling presented in this effort will facilitate the designing of both process-parameters and fixtures for the large strain extrusion machining process through predictions of important parameters like chip compression ratio.

References
1.Moscoso, Ravi Shankar, Mann, Compton, & Chandrasekar, J. Mater. Res, 22 (1) 201–05, 2007.
2.Dipti, Sumantra, Utpal, Bhaduri & Sivaprasad, Mater. Sci.Eng: A, 526 (1):1–6, 2009.

Corresponding author:[email protected]

Large strain extrusion machining is one of the severe plastic deformation processes used to produce ultra-fine-grained and nanocrystalline materials. This process employs a suitable constraint at the location of chip formation such that the machining and extrusion occur simultaneously [1]. The present effort attempts to adopt this method to produce ultra-fine-grain microstructure from Ti-6Al-4V alloy due to its widespread applications in aerospace, biomedical and marine sectors. The formation of saw-tooth chips due to shear localization during machining restrains the use of this alloy for the production of chips possessing ultra-fine-grain microstructure. Shear localization has been suppressed in this effort by suitably modifying the crystallographic grain orientation of the workpiece by cold-rolling prior to machining. The preferential alignment of grains in the cold-rolled workpiece leads to continuous chip formation during unconstrained machining. In addition, further imposition of strains for improving microstructure refinement is affected by the large strain extrusion machining process.

Ti-6Al-4V plates, cold-rolled to a reduction of 47% prior to cutting, were subjected to large strain extrusion machining using a HAAS CNC milling machine at a cutting speed of 0.8 m/min and depth of cut of 100 μm. The cutting tool comprised of a tungsten carbide insert brazed on the tool holder with a rake angle of 5^o and a relief angle of 7^o. Large strain extrusion machining setup in this paper employs a cutting tool attachment fixture with a slot that acts as a constraint for the chip resulting from the machining process. The gap in the slot is same as the final chip thickness that is governed by the chip compression ratio (set at 1.4 in this effort). The suppression of shear localization is triggered by modifying the initial workpiece texture by cold-rolling in this effort rather than using small compression ratio of 0.6 as reported in [2].

Machining was along the normal direction - rolling direction (ND-RD) plane with the cutting velocity directed along the rolling direction. Longitudinal sections of the resulting foils were polished and etched to reveal the microstructure using optical microscopy. The microstructure of the foil comprises elongated α and β grains that are a manifestation of the large strains imposed in the severe plastic deformation process. The Vickers hardness values of the as-received bulk, cold-rolled bulk and the foil were 335 ±10 HV, 347±7 HV and 376±6 HV respectively. Hardness of the foil is about 12% more than the as-received bulk material, which can be attributed to microstructure refinement.

Reference
[1] Saldana, Swaminathan, Brown, Moscoso, Mann, Compton & Chandrasekar, ASME J. of manuf. sci. & engg., 132:1-12, 2010
[2] Sagapuram, Yeung, Guo, Mahato, M’Saoubi, Compton, Trumble & Chandrasekar. CIRP Annals-Manuf. Tech., 64(1):49-52, 2015

Corresponding author: Balkrishna.C.Rao, [email protected], +91 044 22574660

A lower critical solution transition (LCST) has been frequently observed in block copolymer systems. Most previous studies on LCST phenomena have been focused on their peculiar behaviors. Here we for the first time show that LCST behaviour appears in PEO-PPO-PEO triblock copolymer / carbon precursor mixture system and propose a novel synthetic route via the LCST that enables facile fabrication of multi-hierarchical carbon monoliths. Our approach is to structure the gel-phased mixture with 3D printed mold at the macro-scale, to structure-direct the carbon precursor with block copolymer self-assembly at the nano-scale, and to form graphitic carbons with carbonization process. As evidenced by structure analyses, the carbon monoliths have a well-controlled multi-hierarchical structure ranging from angstroms to centimeters. Finally, the underlying physics of the LCST behavior in the mixture of PEO-PPO-PEO triblock copolymer and carbon precursor is revealed by molecular dynamics simulations.

The high cost and time expended typically in the successful deployment of new materials into high performance commercial products is attributable to multiple factors. The most significant of these factors include the heavy reliance on experiments, the persisting disconnect between multiscale experiments and multiscale models, the lack of a broadly accessible data and knowledge infrastructure that can support the implementation of a holistic systems approach, and the lack of a suitable framework for facilitating and enhancing the critically needed cross-disciplinary collaborations. The emerging discipline of Materials Data Science and Informatics (MDSI) promises to address these key technology gaps. The potential benefits to the materials innovation enterprise that could accrue from an aggressive adoption of the novel concepts and toolsets offered by MDSI are examined. A specific vision for a modern, data-centered, materials innovation ecosystem is expounded that can potentially leverage these recent advances.
A central factor for the very large materials development and certification cycles is the lack of a mathematically rigorous framework for communicating the core materials knowledge to design/manufacturing, and creating effective two-way couplings between these domains. From this perspective, it becomes essential to embrace and adopt the definition of “materials knowledge” as essentially the hierarchical (i.e., multiscale) process-structure-property (PSP) linkages of high value to design/manufacturing. In other words, in an effort to move towards the goals listed earlier, we would strive to organize, formulate and express all materials insights (both legacy as well as new) into one of two forms: (i) process-structure (PS) linkages and (ii) structure-property (SP) linkages. PS linkages aim to capture the details of material structure evolution as a function of the process parameters (capturing the process history), while SP linkages aim to express the properties (characteristics of materials response) as a function of the material structure. It should be noted that material structure plays an important role in both sets of linkages. Indeed, herein lays the main challenge for the task described above. The mathematical descriptions of both “process” and “property” require relatively low dimensional representations compared to the “material structure”. The very large number of variables involved in quantifying the material structure poses significant challenges to conventional approaches in formulating PSP linkages, and demands a new data-driven paradigm.

The Center for PRedictive Integrated Structural Materials Science (PRISMS) is a major Materials Genome Initiative effort creating a unique scientific framework for accelerated predictive materials science. There are three key elements of this framework. This first is a suite of high performance, open-source integrated multi-scale computational tools for predicting microstructural evolution and mechanical behavior of structural metals. The second is The Materials Commons, a knowledge repository and virtual collaboration space for curating, archiving and disseminating information from experiments and computations. The third element of the PRISMS framework is set of integrated scientific “Use Cases” in which these computational methods are tightly linked with advanced experimental methods to demonstrate the ability of the PRISMS framework for improving our predictive understanding of magnesium alloys, in particular precipitate evolution and the influence of microstructure on monotonic and cyclic mechanical behavior. This talk will review the Center’s progress, plans and opportunities for collaboration. Approaches for incorporating the PRISMS framework into the development of new materials and manufacturing processes will be described.

Novel applications in self-sintering powders for additive manufacturing, self-healing composites for energy and aviation, micro-soldering and microwelding in electronics and micro-catheters in medicine have motivated interest in nanostructured reactive materials (nanoheaters), such as Ni-Al multilayers, releasing instantaneous, localized precise amounts of heat upon thermal or electrical ignition. Their batch fabrication by vacuum sputtering is presently replaced by new scalable manufacturing methods such as continuous-feed ball milling. Recent work in computational and experimental material science establishes the self-propagating high-temperature synthesis (SHS) conditions of thermal and diffusion transport in such multi-scale, self-similar (packed globular and/or percolating lamellar) optimal material structures. However, science-based computational modeling of nanoheater structures manufactured by ball milling and their dynamic dependence on processing conditions is a recent development, enabling novel nanoheater manufacturing routes using bimetallic foil and thermite powder raw materials. Thus, the objective of this research is to illustrate the underlying high-rate stochastic micro-mechanics during ball milling of multi-material, multi-layered particulate structures such as Ni-Al nanoheaters.

Computational modeling of the evolving structure of a representative particulate during its random collisions with the balls and vial walls, its contact and joining with adjacent powders and clusters, and its deformation and growth is initiated by a descriptive statistical formulation of Brownian-like impact kinetics. The structural model of the particulate consists of monometallic domains described by warped ellipsoidal primitives, on which solid mechanics science-based surface contact is implemented through Hertz theory, and volume deformation via Castigliano strain energy methods. The simulation transforms ideal elastic stress/strain fields and work in this first step into energetically equivalent frictional slip and plastic yield deformations, along with joining of the primitives at a second step. Two yield and friction parameters of the model are calibrated experimentally via tensile testing of lap-joint strength of ball-milled Ni-Al multilayer foils to match the simulated energies. The model-predicted particulate structures during Ni-Al powder tests are compared with experimental micrographs at various stages of ball milling, and validated through the fractal dimension values of the respective 2D sections. The results establish a mechanics principles-based computational tool for manufacturing process and material optimization.

Pneumatic tyres in the automotive industry are composites of an elastomer combined with carbon black, other additives, and reinforced with steel. New designs have focused on improving wet traction, noise reduction, and irregular tread wear. However development has been limited by the strength of the major reinforcement material; steel wire. Improving mechanical properties of steel wires, particularly strength will not only enable implementation of new designs but will reduce the amount of steel required in a tyre, permitting weight savings leading to better fuel economy.

A processing route to render the steel microstructure better for wire drawing and augment strength in the drawn structure has been investigated. Forming a fine pearlite interlamellar spacing improves drawability and increases ultimate tensile strength (UTS), hence steel rods are transformed from austenite to pearlite in salt baths ~540°C; forming finer pearlite with lower transformation temperatures. However, interruption of the drawing procedure to carry out the patenting step slows down the manufacturing process increasing the opportunity cost and lowers potential output. Moreover incurring additional costs due maintaining elevated temperatures (~1000-900°C) to first austenitise the steel before quenching it into a salt bath to obtain a fine pearlite microstructure. The patenting procedure not only serves to restore ductility to enable further drawing but produces a microstructure with higher capacity for strength increases. Therefore, the ability to restore ductility during the drawing process and increase strength is commercially attractive and presents the potential to improve drawability. Authors have suggested the application of electric current to cold worked metal reduces residual stress [1] by the interaction of the current with forest dislocations, causing redistribution of dislocations to positions of low energy. This treatment therefore promising in tackling the aforementioned challenge.

To begin to investigate the influence of electric current treatment in improving the drawability of plain carbon steels, the mechanical properties for rods of composition 0.81C 0.70Mn 0.23Si wt.% at diameters 4.09 and 3.00 mm dry drawn from 10.00 mm are characterised. The total number of passes for 4.09 and 3.00 mm diameter rods are 7 and 10 respectively resulting in true strains of 1.79 and 2.41. Samples are treated with electric currents in between the two drawing stages of 4.09 and 3.00 mm, and tested at both stages in tension, torsion and reverse bends along with control samples for comparison. The applied currents are pulsed at a frequency of 100 Hz with each pulse being approximated by a square wave of width 80μs and modest current densities of 7.96 Amm^-2. Thus the influence of electric current on the drawability of plain carbon steel rod is assessed at two stages of reduction.

[1] Y. Z. Zhou et al. J. Mater. Res., 2000, 15, 1056–1061.

In metal forming, the combination of materials engineering and innovative press technology offers the opportunity of enhanced formability and influenced component properties. In the considered case, the new press technology of cushion-ram pulsation (CRP) interacts with hot sheet metal forming and advanced tool design. This kind of novel thermomechanical treatment becomes significantly relevant with regard to the production of high-strength structural parts of complex shape.

Well-described hot stamping processes, for instance, combine metal forming of austenitized steel with rapid cooling. Thus the hot sheet metal is formed into its final shape while simultaneously increasing in strength due to quenching as a result of martensitic transformation.

Innovative press technology, such as servo lead screw presses, enhances forming processes substantially by adjusted forming parameters: servo electric drives provide flexible defined motion profiles of ram and cushion. This allows for various combinations of acceleration, motion, and temporary stops of the forming tool.

The focused superposition of rapid cooling of austenitized steel and precise pulsating forming results in optimized forming capacity as well as in influenced component properties. An analysis is conducted regarding the influence of a step-by-step deep drawing process of manganese-boron steel 22MnB5, using a pulsating ram-cushion motion, and a simultaneous cooling process. From the perspective of materials technology, the stops occurring in step-by-step forming provide sufficient time for softening and recovery of forming properties. Furthermore, the desired microstructure can be set by distinctive cooling rates. The final component properties and the related enhanced formability can only be adjusted by simultaneously combining step-by-step forming and controlled cooling. This kind of thermomechanical treatment consists primarily in the intelligent superposition of materials- and press technology.

In order to examine the newly developed process in more detail, FE simulation is applied by using the software Simufact Forming V13. Thus, relevant process and material parameters can be determined, for example stress and strain states, strain rates, holding periods, and cooling rates. The considered values are required for profound experiments using the forming simulator BAEHR DIL 805 A/D. Forming properties at defined forming temperatures are examined as well as the softening behaviour of the material at forming due to pulsating ram and cushion motion. The experimental results of forming and softening behaviour at distinctive temperatures provide a basis for an optimized forming-temperature-time window in the combined processes of step-by-step hot sheet metal forming and simultaneous cooling.

Bearings are among the most important components in a variety of machines. To improve the service life and reliability of bearings is important, especially in aircraft and space vehicles. A successful treatment on the inner surface of a tubular structure is the basis of the bearing’s performance enhancement, since fractures usually occur on the inner ring, outer ring of the bearings. Only when the treating capabilities are fulfilled and controllable, can a bearing surface structure improvement be applicable.
A new treating method to conduct surface mechanical attrition treatment (SMAT) on the inner surface of a tubular structure was developed. SMAT is an effective advanced technology for metal material’s mechanical and physical properties improvement. This treating method created a nano-crystallized layer on the metal surface which can effectively improve the strength of the original metal material while maintaining the material’s ductility at a certain level. Computational dynamic simulations and statistical tools were used to implement this research, defining an optimal outline of the reflector to attain more effective impacts. Stainless steel 304 tubes were treated, measured and analyzed to evaluate the effect of this treating method. The micro-hardness distributions were compared with the finite element analysis (FEA) results. The information showed that inner surface treatment can effectively improve the materials’ properties by changing their surface structures. The reported treating method also was applied on processing the inner ring of bearings. The surface hardness and the cross-sectional hardness remarkably upgraded, which are critical to the fatigue performance of bearings. The results proved that this treating method has good performance and value in practical application.

Carbon nanotubes (CNTs) have been recognized as potential candidate for reinforcements in lightweight metals. A composite consisting of CNTs embedded in an Al-matrix might work as an ultra-low-resistive material with the potential of having a room-temperature resistivity far below Al, Cu and Ag. While several advances have been made in developing Al-CNT composites, three major challenges: (1) interfacial bond strength between CNT and the Al matrix, (2) homogeneous dispersion of the CNTs in the Al matrix and impurity (CNTs) scattering centers, continue to limit progress in Al-CNT composites. Several conventional methods including powder metallurgy, melting and solidification, thermal spray and electrochemical deposition have been used to process Al and CNT to form composites. We present both experimental and theoretical results that address these challenges and demonstrate the fabrication of easily drawable Al-CNT composites into 1.0mm diameter wires We observed for the first time ~10 to 26% ± 2% reduction in the electrical resistivity of Al-CNT composite using CNT-hybrid as reinforcement and an inductive melting technique that takes advantage of the induced eddy current in the melt to provide in-situ stirring.

A magnetic soft actuator made of nickel nanoparticles blended with polydimethylsilocane (PDMS) was 3D printed (robocasted) to ultimately test magnetically-driven locomotion. The designed PDMS robotic framework was robocasted using a multi-nozzle colloidal gel deposition system. The nickel powder consisted of up to 40 wt% in the printable gel, and did not change the viscosity and modulus of the gel significantly. This soft material with pre-blended nickel particles was incorporated into the assembly of a soft robot, and its locomotion driven by magnetic field was tested. The application of an external magnetic field generated torque on the magnetic actuator and, thus, produced deformation of the robot’s framework. A variety of PDMS structures were 3D-printed with two actuation principles adapted in this research: (1) the shift of the center of the gravity introduced crawling and (2) the deformation-associated potential energy restore and release caused jumping.

The goal of this research is to fabricate near-net shape isotropic (Nd)₂Fe₁₄B-based (NdFeB) bonded magnets using a 3D printing process to compete with conventional injection molding techniques used for bonded magnets. Additive manufacturing minimizes the waste of critical materials and allows for the creation of complex shapes and sizes. We have chosen both the binder jetting and big area additive manufacturing processes. High performance bonded magnets were produced. We will report in detail about our success with additive manufacturing. This study provides a new pathway for preparing near-net shape bonded magnets for various magnetic applications.

The pronounced textures of rolled pure titanium cause strong anisotropy of mechanical properties and have detrimental influence on working and shaping properties. The relationship between texture and mechanical properties anisotropy of pure titanium has been investigated in this study. The pure titanium after hot rolling and cold rolling were investigated to clarify the effect of process on the texture and mechanical properties. Results show the anisotropy of mechanical properties of pure titanium was closely related to the crystallographic texture. Hot-rolled titanium sheet exhibits strong anisotropy of mechanical properties due to the {10-10}<11-20> and {11-20}<10-10>. The {10-10}<11-20> and {11-20}<10-10> texture were suppressed and (0002) basal texture were developed after cold rolling and annealing treatment, the anisotropy in the yield strength decreased and R-value increased. CSC's 0.6mm titanium sheets equip with the outstanding forming ability and pass the roof forming test. CSC‘s 0.6mm titanium sheets have been used for the architectural material of National Taiwan Normal University, International Kang Chiao school and Taipei great dome.

Using paraffin as the phase change material, expanded graphite as the carrier, carbon fiber as the heat transfer enhancement filler, using the good adsorbability of expanded graphite and the high thermal conductivity of carbon fiber, the three element phase change composites of the carbon fiber/paraffin/expanded graphite were prepared. The effects of the filler＇content and size on the thermal conductivity and heat transfer enhancement about three element phase change composites were investigated. The results showed that the thermal conductivity of the three element phase change composites was determined by the size and content of the carbon fiber, the thermal conductivity of the composites were increased with the increasing of carbon fiber content, and were decreased with the increasing of carbon fiber size, the effect of heat transfer enhancement was greatly enhanced with the increasing of carbon fiber content about three element phase change composites. The phase change latent heat becomes smaller with the increasing of carbon fiber content in composites, the phase temperature decrease slightly and phase transition in advance.
KEY WORDS： three element phase change composite, carbon fiber, thermal conductivity, heat transfer enhancement

A molybdenum carbide coating on the surface of graphite fibers prepared by molten salts method was proposed to improve the interfacial bonding and thermal properties of short graphite fiber/Al composites. The graphite fiber/Al composites were fabricated by vacuum pressure infiltration of Mo₂C-coated graphite fibers with pure aluminum. The characteristics of Mo₂C coating were analyzed and the microstructures as well as thermal properties of the obtained graphite fiber/Al composites were investigated. The results indicated that the strengthened interfacial adhesion between graphite fiber and aluminum matrix as well as improved thermal properties including enhanced thermal conductivity and reduced thermal expansion were achieved by the Mo₂C coating. The in-plane thermal conductivity of 60 vol.% Mo₂C-coated graphite fiber/Al composite was 221 W m^-1 K^-1 enhanced by 92% over that of uncoated composite and the coefficient of thermal expansion was 6.1×10^-6 K^-1 which was suitable for electronic substrate materials.

Nano-structured ferritic stainless steel (Fe-18Cr-xSi) was developed by a combination of mechanically alloying (MA) and spark plasma sintering (SPS) process. SPS was carried out in vacuum at three different temperatures at a fixed holding time and an applied pressure of 50 MPa. Potentiodynamic Polarization (PDP), Linear Polarization (LPR) and Electrochemical Impedance Spectroscopy (EIS) were used to study the effect of sintering temperature on the electrochemical properties of newly developed nanostructured ferritic Fe-18Cr-2Si alloy in acidic solution. The results showed that with increasing sintering temperature, corrosion resistance was increased in terms of pitting potential (E_pit), passive current density (i_p) and polarization resistance (Rp). The improved corrosion resistance was found to be closely related with the densification of the sintered alloys.

This paper presents the development of the designed Quantum Chemical Technology by the company "Nanoamorph Technology". Also presented some unique properties of nano amorphous metals (not-alloy) obtained by this technology. It is shown that as a result of nano amorphous metals application as fillers to create polymer nanocomposites based on various matrices, wear resistance and other properties in some cases increase to 9-12 times.

Cu-Mo alloys are of interest due to their excellent thermal and electrical conductivity, and good fatigue resistance. To date, even though physical (e.g. mechanical alloying, vapor deposition, rapid solidification) and chemical (e.g. co-precipitation, sol-gel) methods have been utilized for Co-Mo film synthesis, few reports have been published for fabricating Cu-Mo films by electrodeposition and none, to the best of the authors’ knowledge as nanowires. Molybdate ions currently cannot be fully reduced in aqueous electrolyte without a codepositing element, referred to as induced codeposition. Typically iron group elements, e.g. Ni, induce best molybdate reduction to zero valence state Mo. Cu has been recognized as also inducing the molybdate reduction reaction, but at a much lower extent. In this work, a new method of combining template electrodeposition and copper displacement reaction was developed for synthesizing Cu-Mo nanowires with a small amount of nickel or iron. Ni-Mo or Fe-Ni-Mo nanowire segments were first electrodeposited into nanopores of polycarbonate membranes, to induce the reduction of molybdate. Next, the membrane was dipped into a low pH copper solution to etch the Ni component, or Fe-Ni component, in the axial direction, and at the same time displace these elements with copper. Nanowires were inspected at different length scales (optical microscopy, SEM and TEM) and the average composition determined by x-ray fluorescence. Results demonstrate that an axial displacement reaction of copper is beneficial for obtaining uniform and integrated Cu-Mo nanowires. Additionally, percentage of Mo in the as-prepared Cu-Mo nanowires can be easily modulated by adjusting the initial Ni-Mo and Fe-Ni-Mo components to reach 20 wt%.

Perovskite-type oxides, the general formula LnFeO₃ (Ln-La, Pr, Gd)), have distorted orthorhombic perovskite structure where FeO₆ as a rotary tilted polyhedron fills the empty space left around the Ln group. There is a mixed valence state of Fe²⁺/Fe³⁺ originated from the 3d iron ions in LnFeO₃ resulted by anion deficiency, making LnFeO₃ material with prominent electrical and magnetic properties for various applications for example, such as catalyst, sensor and magneto-optic materials etc.
One important area of research aimed the reducing energy consumption in the synthesis of the perovskite phase. Perovskite could be synthesized by heating the corresponding metal oxides in a stoichiometric ratio. The main difficulty in obtaining single-phase LnFeO₃ is the presence of undesired phases of Ln₃Fe₅O₁₂ and Fe₃O₄. Moreover, the garnet phase (Ln₃Fe₅O₁₂) is thermodynamically more stable than LnFeO₃.
For increasing the chemical reaction rate and temperature of synthesis, a various routes of soft-chemistry (for example glycine-nitrate combustion reaction, sol-gel, co-precipitation method, hydrothermal treatment etc.) are used.
In the present work, an ultrasonic aerosol spray pyrolysis method was developed to prepare micron-sized granules. This method is an effective technique to prepare particles with a wide range of compositions of controllable size from micrometer to submicrometer range. Also, a homogeneous composition of its products, easy controllability, and short production times are the additional advantages of this process.
The precursor solutions were prepared by dissolving a stoichiometric amount of salt nitrates (La(NO₃)₃/ Fe(NO₃)₃; Gd(NO₃)₃/Fe(NO₃)₃; Pr(NO₃)₃/Fe(NO₃)₃) in distilled water. Nitrate solutions were atomized using an ultrasonic nebulizer with a resonant frequency of 1.7 MHz.
The aerosol stream was introduced into the horizontal quartz reactor at 650- 850 ^oC by nitrogen flow. The obtained particles were collected onto glass filter. The flow rate of nitrogen used as a carrier gas was fixed at 5 ml/min. The residence time of drops in the hot zone of the furnace was 3 seconds.
The obtained powders consisted of microspheres - 0.1-2 µm in the diameter containing 20-50 nm nanoparticles of La-Fe-O phases.
Phase transitions in the system Ln-Fe-O (Ln-La, Pr, Gd) were analyzed in the wide temperature range (400-600 ^oC) to obtain single-phase samples and study their crystallinity.
It was shown that the complex approach allows to obtain single-phase LnFeO₃ with submicron grain size and spherical micromorphology.

Among the transition-metal- oxides cobalt-spinels receive large attention in the scientific community because of their potential applications in Li-ion batteries, thermistors, solid-oxide fuel-cells, magnetic recording, microwave and RF devices [1,2]. In the present work we report a detailed study of the micro-Raman spectroscopy of inverse and normal-spinel cobalt-oxides Co₂TiO₄ and Co₃O₄, respectively, along with their composites. A series of solid solutions of Co₃O₄ + x wt%Co₂TiO₄ was synthesized by standard ceramic solid-state- reaction method over a whole range of the compositions 0 ≤ x ≤ 100%. Changes occurring in the crystal structure and temperature dependence of Raman modes were examined. For the lower and intermediate compositions (x <30 wt%), five Raman-active modes were recognized at 689, 618, 518, 480, and 195 cm_-1 which are associated with A_1g, E_g and 3F_2g phonon symmetries (Fig. 1). Conversely, pure Co₂TiO₄ exhibits anomalously broad Raman-spectrum without any signatures of ‘F_2g’ mode. At low-temperatures (20 K ≤ T ≤ 300 K) the A_1g peak of Co₂TiO₄ shifts to high frequency side with clear anomalies across 20 K and 40 K associated with the magnetic compensation temperature and ferrimagnetic Néel temperature, respectively. Peculiarities of such low-temperature Raman spectra in consonance with the magnetic and crystal structure of both the spinels Co₂TiO₄, Co₃O₄ will be presented.

Three-dimensional structures in nanometer scale has a lot of potentials in its applications in wide range of areas, including but not limited to photonics and sensors. However, their wider applications have been limited due to slow and expensive fabrication methods and limitations in morphologies. In this study, block copolymer self-assembly is utilized in effort to design a novel fabrication method for a variety of metallic nanostructures. Block copolymers are known to generate uniform and periodic patterns and are usually used to fabricate high-resolution patterns in two dimensions. However, when given three-dimensional confinement and sufficient mobility, certain block copolymers are known to form structures that cannot be seen in typical two-dimensional conditions. To induce such effect, PS-b-PDMS(polystyrene-block-polydimethylsiloxane) and PS-b-P2VP(polystyrene-block-poly(2-vinylpyridine)) block copolymers are placed in a template that provides a 3-dimensional cylindrical confinement and annealed in solvent vapor for self-assembly. Theoretical simulations show various morphologies, such as rings, rolled perforated lamellae, and double helix, can be formed depending on the relative size of the confinement to the polymer chain length. Accordingly, an appropriate template fabrication method was devised to have controllable pore sizes to induce the controlled formation of different morphologies. Through selective etching process, the polymer chains are used as structural directing agents, applicable for a range of metals. This method will provide a novel method that allows swift, inexpensive, and scalable fabrication of various 3-dimensional nanostructures using block copolymer.

Here we report the synthesis, modeling, and measured results for Germanium Telluride (GeTe) phase changing nanomaterial based inks and electronics devices. The synthesis of the nanoparticles begins with dissolving germanium (II) iodide and trioctylphosphine oxide (TOPO) in trioctylphosphine (TOP) and tellurium separately under an argon or nitrogen atmosphere, followed by material injection, nucleation, growth, purification, and suspension steps at NG NEXT Lab. These nanomaterial inks were successfully developed and demonstrated typical particle sizes of < 50 nm in diameter, with viscosity at around 1 centipoise. Next the ink was printed using a Fujifilm Multi-material inkjet printer. A layer thickness of around 300 nm was deposited after 8 passes of printing in a fully printed coplanar waveguide (CPW) test cell. Detailed experimental results demonstrated more than 5 orders of magnitude of changes in resistivity for the GeTe ink based device. The measured and observed fundamental material behaviors also include clearly observed threshold voltage and current snapback region. A Poole-Frenkel Conduction electronic model is next used to simulate the carrier hopping and direct tunneling effects for the 3D printed phase change material (PCM). The simulated results are compared with measured results to offer invaluable insight and understanding of the synthesized and printed GeTe nanomaterial devices. These early results indicated that 3D Aerosol Jet printed PCM materials are potentially a game changer for future low cost, fast turnaround time, and fully reconfigurable wireless communication, radar and phased array electronics systems. To our knowledge, this is the first reported experimental results for GeTe synthesized nanomaterial electronic switching devices based on Inkjet additive 3D printing technology. Other latest 3D printed nanomaterial research progresses at NG Next will be also presented, which include study results on 3D printed polymer materials, electronics devices, and 4-D (time variant) configurable phased array antennas.

In the past decade, printed electronics technology has received an increased interest due to its simplicity, low cost, and flexibility. Printed electronics technology is an attractive alternative to conventional photolithography and has been applied in many electronic devices such as flexible displays, wearable electronics and solar cells. Conventionally, metallic nano-inks made with silver nanoparticles (NPs) has been widely employed because of their excellent conductivity, stability and sintering efficiency. Recently, Cu nanoparticle inks (NP-inks) have been studied for printed electronics due to its low cost compared to Ag NPs. However, most copper nanoparticles are covered with an oxide shell and cannot be sintered by conventional sintering method such as thermal sintering.
To solve these problem, we previously developed a flash light sintering method combined with poly(N-vinylpyrrolidone) (PVP) functionalization of Cu nanoparticles. Flash light sintering method can instantly reduce the copper oxide shell and sinter Cu nanoparticles at room temperature and under ambient condition in a few milliseconds without damaging the substrate. For these reasons, flash light sintering technology has been employed to fabricate copper electrode patterns on polymer substrates such as polyethylene and polyimide. However, flash light sintering method has a limitation on application for several substrates such as silicon wafer with high thermal conductivity. In the flash light sintering process, the temperature of Cu film should reach certain level for melting and well necking of copper nanoparticles while flash light irradiates on the Cu film. However, when Cu NP-ink on the silicon wafer substrate is irradiated by flash light, the heat converted from light energy is rapidly conducted to substrate, so that Cu film is not able to keep sufficient latent heat for phase changing.
To overcome these limitations, in this work, a method to fabricate Cu electrode patterns on the silicon wafer using a flash light was developed for crystalline silicon solar cells. In order to improve Cu film characteristics such as electrical conductivity and adhesion, Cu NP-inks for flash light sintering on silicon solar cells were fabricated and optimized. Furthermore, it was found that bimodal copper NP-ink could enhance the packing density and electrical conductivity of Cu films. Meanwhile, the flash light irradiation conditions such as irradiation energy, pulse number, pulse duration, and pulse gap were optimized for enhancing electrical characteristics of the Cu film. From this study, it was demonstrated that Cu electrode patterns with high electrical conductivity were successfully obtained even on the silicon wafer substrate with high thermal conductivity using flash light sintering method. Therefore, it is expected that flash light sintering method developed in this work can be widely used in various applications and industries.

Recently, printed electronics technique received tremendous attention for manufacturing electronic devices. Since this technique needs simple process (i.e. printing, sintering, and inspection process), it has benefits such as simplicity, low-cost, flexibility, and short process time. Printed electronics generally uses noble metallic nanoparticles (NPs) such as Au and Ag. However, they are too expensive to be commercialized for real-applications. Therefore, Cu NPs have been emerging as an alternative material because of their low-cost and high electrical conductivity which is similar with that of Ag. However, Cu NPs form oxide shell even at room temperature, and it cannot be sintered under ambient condition. For this reason, conventional thermal sintering needs inert gas chamber and reducing agent for sintering it. Also, it requires long time process (60 min) and induces a damage on the flexible polymer substrate due to its high temperature process (over 300 ^oC). As a result, this method is not appropriate to sinter Cu NPs.
In this respect, a flash light sintering method was studied to solve above problems. In the flash light sintering method, the xenon lamp irradiates intensive visible light in few milliseconds, and then the metallic NPs were sintered in short time. Also, this method could reduce oxide shell of Cu NPs by combining binder like poly(N-vinylpyrrolidone) (PVP) and sinter Cu NPs in room temperature and ambient condition. Furthermore, its short process time enable non-damaging of flexible substrates after sintering process. Previous studies were mostly focused on enhancing electrical conductivity of sintered Cu electrode. However, high adhesion strength should be also satisfied for the application of sintered Cu electrodes. Accordingly, systematic study considered both electrical conductivity and adhesion strength has been needed.
In this work, two different sizes of Cu NPs (40 nm and 100 nm in diameter) were employed to improve electrical conductivity and adhesion strength. Several Cu nano-inks were fabricated and printed with various mixing ratios, and then subsequently sintered by flash light sintering method. The flash light sintering condition was investigated with various parameters (irradiation energy and pulse number) to optimize sintering condition. Also, in-depth study about sintering mechanism of bimodal Cu NPs was performed by using real-time measurement of sheet resistance during a sintering process. The sintered Cu nano-ink films were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). From these results, it was found that optimal ratio of 40 nm to 100 nm NPs is 25:75 wt%, and multi-pulse sintered Cu nano-ink film (pulse duration: 1 ms, off-time: 3 ms, pulse number: 4, and irradiation energy: 6 J/cm²) exhibited the lowest resistivity of 10.3 µΩ●cm and 5B adhesion level among all the cases.

Recently, a tremendous interest in printed electronics has been increasing. Printed electronics refers to the application of printing technologies for the fabrication of electronic circuits and devices. Printed electronics techniques present a low-cost solutions to the production of electronic devices. Currently, novel nanotechnology-based inks made with metals such as Au and Ag have excellent conductivity, stability and sintering efficiency. However, these noble metals are too expensive. For this reason, copper nanoinks have considerable attention as a low-cost alternative to silver or gold nanoinks for printed electronics. However, most copper nanoparticles are covered with an oxide shell and cannot be sintered by thermal sintering under ambient conditions.
To solve these problems, we previously developed a flash light sintering method combined with poly (N-vinylpyrrolidone) (PVP) functionalization of copper nanoparticles. Flash light sintering method can instantly reduce the copper oxide shell and sinter copper nanoparticles at room temperature and under ambient condition in a few milliseconds without damaging the substrate. Moreover, it is possible to sinter a large area of Cu nanofilm using flashes from a xenon lamp.
In this work, the effect of the thickness of a copper oxide-shell on flash light sintering of Cu nanoparticles (NPs) was investigated. The electrical properties of Cu NP-ink films with various oxide-shell thicknesses were examined by measuring the sheet resistance. Furthermore, the amount of PVP in the Cu NP-ink was varied to reduce the copper oxide-shell efficiently and enhance the flash light sintering of the Cu NPs. Also, to investigate the reduction and sintering phenomena of Cu NPs with respect to the copper oxide shell thickness, the sheet resistances of the Cu films were measured in real-time using an in-situ resistance measuring system during the flash light sintering process. The results of this study established the maximum allowable thickness of the copper oxide shell that allows flash light sintering of Cu NPs, the results also provide the optimal amount of PVP in Cu NP-ink for a particular copper oxide shell thickness.

Semiconductors are promising materials for mid-IR transmission due to their favorable optical properties and room temperature stability. A ‘Rod in tube’ method was utilized to fabricate glass-cladded germanium-core fibers in a laboratory-fabricated mini draw tower at 1000°C. Electron microscopy studies were carried out to study the diffusion of cladding components into the semiconductor core. Optical characterization was performed over a wide range of wavelengths. The results of elemental diffusion into the core and their relation to the wavelength dependent optical transmission losses will be presented.

Semiconductor core optical fibers have brought new light to integrated photonics and optoelectronics as new solutions to that not possibly solved by on-chip devices. Crystalline semiconductors, such as silicon and germanium in particular, have superior optical and electronic properties, therefore, high purity and single crystallinity of these silicon and germanium cores are much sought after to realize superior in-fiber device performances. However, high-quality, small core (microns to submicron) single crystal fibers have not been available. Typically, crystalline semiconductor core fibers are made through either a molten core drawing technique [1] or by deposition of amorphous semiconductors into silica capillaries at low temperatures via high-pressure chemical vapor deposition (HPCVD), [2] followed by high temperature thermal annealing. [3] But the optical losses of these fibers are still relatively high. Although the quality of the as-drawn crystalline Si optical fibers have been improved through a post-laser processing using a CO₂ laser, [4] there is still space for improvement in terms of the optical losses and further reducing the core size for potential nonlinear optical applications. Here, we present novel results of fabricating single crystal silicon and germanium core fibers through crystallizing amorphous silicon and germanium fibers using a 488nm continuous wave argon ion laser. [5] These fibers have extremely low optical propagation losses (more than one orders of magnitude lower than the best ever reported) and photoresponsivity close to bulk.

The laser wavelength was chosen so that the glass cladding is transparent and only the semiconductor cores are effectively heated. Moreover, continuous wave other than pulsed laser was considered in order to reduce the cooling rate of the melted silicon and germanium. HPCVD was used to produce the amorphous fibers before laser heating. During the laser crystallization processing, a series of amorphous silicon (1.7 μm core diameter) and germanium fibers (5.6 μm core diameter) were scanned through the focused laser beam. We employed X-ray diffraction, Raman spectroscopy and transmission electron microscopy to characterize the crystallized fibers, and performed finite element modeling to understand the formation of these single crystal fibers. Optical transmission and optoelectronic properties characterizations indicate that these fibers could be useful for nonlinear optics, infrared waveguiding [6] and all-in-fiber devices.

This work is supported by the Penn State NSF-MRSEC Center for Nanoscale Science.

References
1. Ballato et al. Opt. Express 16, 18675 (2008)
2. Sazio et al. Science 311, 1583 (2006)
3. Chaudhuri et al. ACS Photonics, 3, 378-384 (2016)
4. Healy et al. Adv. Optical. Mater., 4 (7), 1004-1008 (2016)
5. Ji et al. Adv. Optical Mater., DOI: 10.1002/adom.201600592 (2016)
6. Ji et al. Opt. Express 22 (23), 28459 (2014)

In order to make use of the shape- and size-dependent properties of colloidal semiconductor nanocrystals (NCs) it is necessary to synthesize them with homogeneous shape and narrow size distribution. Controlling these parameters during colloidal synthesis is facilitated significantly by understanding the NCs’ early stages of formation, since size and shape are determined during this phase.

Monitoring the nucleation of the NCs, which happens rapidly at the very beginning of their synthesis, and their subsequent growth requires the ability to make size-dependent measurements very quickly after initiating a reaction between their precursors as well as at different points later in time. Suitable time-resolved characterization techniques are UV/VIS absorption spectroscopy and X-ray scattering.

Commercial stopped-flow devices,^[1,2] as well as liquid free jets,^[3] have been reported as suitable tools for in-situ studies of semiconductor NC nucleation and growth kinetics. These devices however are either limited to reactions occurring at low temperatures (stopped-flow), or have very limited observable growth times (free jets).

We have designed and implemented a continuous-flow device, which allows the conduction of colloidal high-temperature (200-400 °C) NC syntheses, combined with the possibility of performing in-situ time-resolved characterization of the synthesized NCs. For this purpose, the device is equipped with a UV/VIS absorption spectrometer and an X-ray flow-cell to allow simultaneous detection of optical spectra as well as small and wide angle X-ray scattering. By coupling a series of custom-made delay growth ovens of different lengths, it is possible to study the growth kinetics.

In our contribution we present the results from our UV/VIS absorption studies of the nucleation and growth of CdSe NCs, as well as the results from SAXS and WAXS studies at the European Synchrotron Research Facility. Based on these results we propose a growth mechanism of CdSe NCs based on a series of magic-sized clusters.


1) A. L. Brazeau et al., J. Phys. Chem. C 2009, 113, 20246.
2) M. Tiemann et al., ChemPhysChem, 2005, 6, 2113.
3) W. Schmidt et al., J. Am. Chem. Soc., 2010, 132, 6822.

Atomic calligraphy is a microelectromechanical systems (MEMS) based method of nanomanufacturing that has the potential to be higher throughput and more versatile than conventional methods. It relies on a MEMS device that can position a dynamic stencil of shadow mask with nanometer precision. The power of this method is its scalability. Thousands of stencils can be milled into a single positioner and thousands of positioners can be fabricated on a single chip. By scaling in this manner a 10⁶-10⁸ increase in throughput can be achieved without sacrificing resolution. Clogging of the stencils limits the life time of the device. Joule heating of the stencils prevents clogging of the stencil and extends the lifetime of the device. Precise alignment of the chip to the substrate is require to get optimum resolution. A system has been developed that uses piezo stages and contact alignments to precisely align the chip to the substrate. Here we present on these methods and demonstrate initial results.

Using spatial and interfacial control, the micro-sized silicon waste from wafer slurry could greatly increase its retention potential as a green resource for silicon-based anode in lithium ion batteries (LIBs). Through step by step spatial and interfacial control, the cyclability of recycled waste gains potential performance from its original poor retention property. In the stages of spatial control, the stabilizers of active, inactive and conductive additives were mixed into a slurry for maintaining the architecture and the conductivity of electrode. In addition, a fusion electrode modification of interfacial control combines electrolyte additive and technique of double-plasma enhanced carbon shield (D-PECS) to convert the chemical bond states and to alter the formation of solid electrolyte interphases (SEIs) in the first cycle. With this modification, the resistances of SEIs and charge transfer decrease substantially from 88.4 to 34.5 ohms and 40.3 to 9.9 ohms, respectively. Furthermore, the formed SEIs switch its morphology from random wrapping to smooth plateau, and the expansion thickness of electrodes reduce from 21 to 14.5 μm after the first cycle. Finally, the depth profiles of chemical composition from external into internal electrode illustrate that the fusion electrode modification not only forms a boundary to balance the interface between internal and external electrodes, but also inhibits the SEIs formation, relating the stabilization of micro-sized Si electrode. Through the modification of spatial and interfacial control, the performance of micro-sized Si waste electrode can be boosted from its serious capacity degradation (100 cycles with 5 mAh/g) to potential retention (200 cycles with 1100 mAh/g), meeting the requirements for facile and cost-effective in industrial production.

We propose a extremely robust and easily patternable silver nanowires (AgNWs) electrodes on copy paper. Using an auxiliary adhesion layer and a simple laminating dry transfer, AgNWs can be easily transferred to paper as well as various substrates. For dry transfer, AgNWs is chemically reduced by reducing agent, floated on water, and lifted by a hydrophobic film.[1] Using the film and lamination process, AgNWs are dry-transferred to the pattern-printed copy paper using laser jet printer and embedded in toner without becoming wet or causing damage of substrate. The intercalated toner layer between the AgNWs and substrate enhances adhesion between AgNWs and substrate, not only improving high foldability of the electrodes, but also facilitating selective patterning of the AgNWs with micrometer scale resolution. Using the proposed process, extremely robust electronics based on copy paper are fabricated, such as a printed circuit board for a 7-segments display, portable heater, and capacitive touch sensor, demonstrating the applicability of the robust AgNWs-based electrodes to paper electronics.

[1] Ahn, J.; Seo, J.-W.; Kim, J. Y.; Lee, J.; Cho, C.; Kang, J.; Choi, S.-Y.; Lee, J.-Y. Self-Supplied Nano-Fusing and Transferring Metal Nanostructures via Surface Oxide Reduction. ACS Appl. Mater. Interfaces 2016, 8 (2), 1112–1119.

Electron beam-target interaction during pulsed electron beam ablation (PEBA) is a complex process, which comprised of heating, phase changes, and removal of a fine fraction from the target surface. Thin film deposition during PEBA is significantly influenced by many factors such as power density, beam energy, background gas pressure, and target to substrate distance. Beam-target interaction can be considerably affected by heat source as it acts as the basis for the thermal behavior of the target. To find out, we have analyzed the effect of two different heat sources on the maximum temperature of the target surface. The first heat source considered in this study is based on a Monte Carlo approach to estimate the absorbed energy distribution along the electrons penetration depth in the target. The second heat source is based on experimental measurements to describe the decaying energy of the electrons beneath the target surface. A one-dimensional thermal model based on a two-stage heat conduction equation is presented to study the influence of the heat source on the ablation of a graphite target. The surface temperature, surface recession velocity, ablation depth, and ablated mass per unit area are estimated by the model. The preliminary findings show that the beam source terms used seem to have a marginal effect on the ablation performance of the electron beam.

Ultrafast laser offers the advantages of reduced recast/microcracks and minimized heat affected zones around ablation section due to its ultra-short pulse durations and ultra-high power densities, which is obviously different from melting region caused by long-pulse laser and can considerably increase the fabrication precision and quality eventually.
By manipulating the spatial shape of ultrafast laser pulses either, the electron excitation processes during laser-material interactions can be precisely controlled. As a result, high-quality, high-aspect-ratio, high-efficient micro/nano-fabrication method can be achieved, for example: we proposed to: 1) control the spatial distribution of electron density by spatially shaping the femtosecond laser pulses, with which metallic nanowires with a minimum width of 56 nm (~1/13 of the wavelength) can be fabricated; 2) adjust optical near-field distribution and the corresponding electron generation on fabricated material surface, by which the periods, orientations and structures of the surface ripples can be effectively adjusted. Also, high-quality microholes with a diameter of 1.6 μm and an aspect ratio of 330:1 are fabricated by a spatially shaped single femtosecond laser pulse. It takes 42 min to fabricate 251,001 holes in a 1 cm × 1 cm area, which is very uniform in size and shape. Meanwhile, A multiscale measurement system (from femtosecond scale to second scale) is developed for revealing the multiple time scale fundamentals during femtosecond laser material interactions, including the femtosecond-scale propagation of a laser pulse, picosecond-scale generation/evolution of laser-induced plasma, nanosecond-scale plasma ejection/expansion, and microsecond-scale hole formation.

There is much interest in using femtosecond laser pulses for precise and thermal-damage-free material removal for numerous scientific, medical and industrial applications. A major limitation arises from the low speeds at which material can be ablated, in addition to the complexity of the required laser technology. Much of the complexity in laser design is due to high pulse energy threshold required for efficient ablation (~100 µJ pulses with <10 ps duration, kHz-level repetition rates and thus, mostly based on solid state laser technology). It is not possible to scale up the ablation rate simply by increasing pulse energy, which is limited by shielding effects or the repetition rate, which requires higher average power, which leads to collateral damage from heat accumulation.

Here, in order to circumvent this limitation, we adapt ablation cooling, a technique routinely used in aerospace engineering since the 1950s [1] – thermal energy contained in the ablated portion is removed with the ablated mass, thus reducing average temperature of the remaining material. We access this new regime by applying extremely high repetition rate pulses (GHz-range) to ablate the target material before the residual heat deposited by previous pulses diffuses away from the targeted region [2]. Experimental results obtained with 9 different materials indicate that we are able to increase the ablation efficiency by an order of magnitude, despite reducing individual pulse energies by ~1000 times, to sub-µJ levels, while simultaneously reducing thermal effects. We also show thermal-damage-free removal of brain tissue at 2 mm³/min and dentine at 3 mm³/min.
References:
[1] Sutton, G. P. & Biblarz, O. Rocket propulsion elements. (Wiley, 2011).
[2] Kerse, C., et al., “Ablation-cooled material removal with ultrafast bursts of pulses,” accepted for publication in Nature.

Pulsed electron beam ablation (PEBA) has proven to be a promising and powerful technique for the growth of high quality thin films. Pulsed electron beam film deposition consists of many physical processes including target material heating, target ablation, plasma plume expansion, and film growth on a substrate. Plasma plume expansion into a vacuum or an ambient gas is a fundamental issue in PEBA as the quality of thin films deposited onto the substrate depends on the composition, energy and density of particles ejected from the target. In the present study, gas-dynamics equations are solved to investigate plasma expansion induced by interaction of a nanosecond electron beam pulse (~100 ns) with a graphite target in an argon atmosphere at reduced pressure. The effect of the electron beam efficiency and power density on plume expansion is assessed. The temperature, pressure, velocity and density profiles of the plasma plume are numerically simulated in time and as a function of spatial dimension. The preliminary results show a rich variety of behaviors. The model is validated by comparing some of the obtained simulation results with experimental data available in the literature.

Fiber-reinforced composites possess a unique combination of strength, stiffness, and low density that makes them well suited to a wide variety of applications including structural materials for aircraft and wind turbines. However, fabrication of these materials is a time and energy intensive process that requires hours of high-temperature curing, driving up cost of production and limiting their scope of application. Frontal polymerization (FP) uses a propagating reaction wave driven by an exothermic polymerization reaction to quickly convert liquid monomer to solid polymer. Here we report the use of FP to rapidly fabricate fiber-reinforced composites of polydicyclopentadiene and carbon fiber. We demonstrate control of frontal velocity and pot life by altering the monomer and catalyst chemistry. Additionally, the effects of the fiber reinforcement on frontal dynamics are explored. The use of FP enables curing of fiber-reinforced composites in <2 min with minimal input energy. The FP of these composite materials may significantly reduce their cost and facilitate their use in a greater variety of applications.

Nanoscale grain coalescence in metal thin film, which companies the sintering and densification of nanoparticles, is a technology widely used in nanofabrication, such as nanowelding, modification of thin film properties, and self-assembly of 3D nanostructures. Various techniques have been achieved to trigger grain coalescence by applying energy to the thin film. However, there is a great challenge to control the performance of grain coalescence because ofthe difficulty in applying right amount of heat on nano-grains. A plasma triggered grain coalescence process offers the possibility to precisely control the phase and morphology of the grain coalescence. Here, we systematically investigated the mechanism of plasma triggered grain coalesced and utilized it to achieve the self-assembly of 3D nanostructures. The grain coalescence triggered in this process is due to the exothermic energy generated by plasma etching of Si. The effects of plasma power and the flow rates of gases on controlling the morphologies of grain coalescence have been studied. In addition, by balancing the isotropic/ anisotropic substrate etching profile and the etching rate, it is possible to simultaneously release 2D structures and induce sufficient surface tension force, generated by grain coalescence, to achieve the self-assembly of 3D nanostructures.

Plasmonic materials and devices aim to exploit the unique optical properties of metallic nanostructures to enable routing and manipulation of light at the nanoscale. Lately this field has enabled exciting applications in the areas of chemical and biomedical sensing, information and communication technologies, solar energy harvesting, lighting, cancer treatment, optical encoding of information and surface decorations among others.
A significant challenge in delivering the aforementioned devices is the materials’ preparation method. So far, efforts have been dominated by various techniques like nanolithography, ion beam nanofabrication, atomic layer deposition, pattern transfer, and template stripping. However, while these techniques can deliver an unrivalled particle monodispersity, they are rather complex, demanding multiple steps, long processing times and/or the use of toxic agents. An alternative, less complex, fabrication and patterning scheme is that of laser annealing (LA): an ultra-fast and macroscopically cold process that provides freedom of design and fast processing times. These characteristics are well suited for large-scale low-cost manufacturing of materials and devices and also enable the use of inexpensive flexible substrates, a prerequisite for roll-to-roll (R2R) processing which is becoming nowadays the manufacturing route of choice for many emerging applications.
The research methodology pursued involves the sequential tuning of the laser wavelength into resonance with two different physical absorption processes: the interband transitions of the metal’s d-electrons (UV frequencies), or the LSPR of the metal particles (visible frequencies). We use an excimer laser (193 and/or 248 nm) for the former and a Nd:YAG laser with an optical parametric oscillator unit (532nm and/or 633nm) for the latter. We demonstrate that each absorption process selectively targets the melting and re-solidification of different particle size groups, which under certain circumstances can lead to nearly monodispersed nanoparticle arrays. We call this process Modification of Nanoparticle Arrays by Laser Induced Self-Assembly (MONA-LISA). To get insight into the heating dynamics involved during UV and/or Vis LA, we performed optical and heat transport calculations and obtained the spatial absorption profile as well as the transient temperature profile at each nanoparticle. These resulted into recipe maps that can facilitate the design of plasmonic templates with predefined morphology onto various substrates. Recent scanning electron microscopy images and optical reflectance spectroscopy measurements on LA Ag films are discussed in light of these findings.

Polyelectrolyte microcapsules are fabricated by one-step microfluidic approach in an all aqueous condition. We use two immiscible, aqueous polymer solutions with an interfacial tension that is large enough to generate water-in-water (W/W) drops. Using these W/W drops as templates, we fabricate polyelectrolyte microcapsules based on the interfacial complexation of oppositely charged polyelectrolytes. The shell thickness of those polyelectrolyte microcapsules is nearly independent of the polymer concentration and molecular weight. We characterize the encapsulation efficiency of those microcapsules. The positively charged molecules is being released right after encapsulation, and the release of negatively charged molecules is significantly prolonged because of attractive electrostatic interactions in these polyelectrolyte microcapsules. Furthermore, we demonstrate the application of these polyelectrolyte microcapsules in encapsulation and release of proteins without impairing their activities. Our platform enables a one-step encapsulation and should benefit wide range of applications requiring encapsulation and sustained release of molecules in aqueous environments.

In recent decades, significant effort has been made to develop diagnostic devices conform to the ASSURED criteria (affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free and deliverable) as defined by the World Health Organization.[i] Emergence of microfluidic devices with their outstanding characteristics such as the ability to process microscale liquids, being rapid, simple and cost-effective has a great impact on diagnostics and public health. However, the fabrication of chip based devices has limited uptake in point-of-care diagnostic applications.[ii] Recently, various yarn and textiles have attracted a great deal of attention as potential low-cost substrates within microfluidic and biosensor applications.[iii] These inexpensive, wearable and broadly available multi-filament materials have several properties that support their application in simple, scalable and mass producible microfluidic analytical devices. Fibres are flexible, reusable, difficult to break or tear accidentally, and easy to convert into 3D structures via traditional techniques such as knitting, weaving or sewing to form sophisticated fluid transport devices. These advantages make them a very good candidate as a novel platform to achieve the ASSURED diagnostic device goals. Although thread-based microfluidic devices offer a range of advantages in portable diagnostics, producing reproducible 3D functionalized textile-based microfluidic devices is still challenging.

The wide variety of fibrous materials and composite formulations available opens new possibilities for exploitation of specific surface interactions, providing a plethora of opportunities over the next few years in the generation of low-cost thread-based biosensing and diagnostic devices. In this study, for the first time, 3D knitted and braided structures have been developed and the migration of fluorescent analytes under the influence of an electric field monitored across a range of novel textile assemblies. Sample heating, as result of the Joule effect, is a significant consequence when electric field is applied. If thermal conductivity of the material is low, temperature gradients in cross- and axial- stream directions during separation may result in separation variability during electrofluidic processes. Herein, we formulated and fabricated liquid crystal graphene oxide (LCGO) and low density polyethylene (LDPE) composite fibres combined with commercially available polyester threads in order to minimize Joule heating effects. Additionally, the thermally conducting LCGO/LDPE composite fibres were introduced into 3D polyester knitted structures, and temperature and current were measured for a range of graphene loadings.

We are living through the convergence of biology, polymers, cognitive science, nano enabled science& engineering and digital media. Together, they constitute much of the early 21^st century technological development in applied material science, fabrication and manufacture which, when coupled to creative and environmentally sound design fundamentals, provide a pathway for innovative natural material product platforms. In particular, polysaccharide nanomaterials that can drive new applications through processing solutions that can meet compelling human centred needs in sustainability, resilience, health, transportation and consumer goods.
This paper presents results from laboratory and semi-tech experimental investigations recently carried out exploring how nanoscalar dispersed materials, in particular, micro and nano-fibrillated cellulose can create significant improvements to the resilient and sustainable production of bulk paper pulp and furthermore can be shown to enhance the performance characteristics in the case of structured paper and board products (mechanical, printable and visual). The work of the P³i group at Northumbria School of Design explores Printable, Paintable , Programmable materials capable of exhibiting intelligence where viable product outcomes include the basis for smarter material systems or ‘more for less’ material systems with the potential to enhance sustainable manufacture without loss of performance.
We describe both the creation and incorporation of nanoscalar cellulose into paper pulp compositions and the resulting physical and quality characteristics obtained as a function of the dispersed phase concentration of nanocellulosic fibrils introduced into the paper pulp network and discuss how this influences mechanical performance in terms of Young’s Modulus and shear strength.This is significant because being able to reduce paper mass (and associated evaporative –energy load) while improving paper performance allows for scalable production of paper that has a significantly reduced environmental footprint, and is especially relevant as new paper formulations will remain a key ‘soft’ material with multiple uses over the coming decades through battery technology, electronics based on paper and advances in interactive consumer goods packaging.
Finally our exploratory studies in Design:STEM natural ‘soft’ material systems has necessarily required close multidisciplinary collaboration between both academe researchers and a global consumer products partner which is actively seeking out innovative material solutions to reduce material burden and energy load in its continuous manufacturing processes.

Recently, development trends of electronic devices have become flexibility, miniaturization, low operating power and multifunctionality. The electrode, one of the most important component of electronic devices should have good feasibility and lattice misfit with working layer. Nowadays physical vapor deposition(PVD) method such as sputtering and pulsed laser deposition(PLD) was used to deposit electrode on substrate or working layer. Deposition of electrode using PVD method, however, has significant challenge both fundamental research and industrial points of view. In the case of fundamental research view, the nanocrystal properties could be widely tuned by adapting the size, shape and defect control in the nanocrystals. Second, films for the electrode would be preferred fabricating via inexpensive processes such as solution processes including spin-coating and drop drying.
In this work, we demonstrate and investigate piezoelectric nanogenerators consist of (Na0.5K0.5)NbO3 (NKN) energy generating materials and metal electrode made of Ag nanocrystals prepared by colloidal method. A highly uniform Ag single nanocrystals were well developed as well as to keep the dispersivity as colloidal solution. Ag electrode have been deposited on polyethersulfone(PES) substrate using spin-coating and randomly oriented perovskite-structured NKN thin films have been grown on Ag/PES substrate via radio frequency magnetron sputtering. The metal-insulator-metal (Pt-NKN-Ag) structured nano generators poled under an electric field of 100kV/cm and the electrical properties were successfully performed under regular bending motion.
This approach offers more effective method of fabricating thin films for electronic devices prepared by nanocrystals with high degree of control wherein size and defect could be engineered in synthesis stage.

Printed circuit board (PCB) is composed of multiple layers of copper and insulator sheets, and works as a support to connect electric components. A lot of approaches have been studied for thermosetting polymers as a candidate material. Since these PCB materials are required to have functions of physical stability and electrical insulation, epoxy resin is good candidate due to its mechanical strength and commercial availability. Epoxy preforms also display excellent solubility in normal organic solvents to impregnate on to PCB surface and strong adhesion to a copper foil during the process. However, single epoxy resin has limited insulating properties to meet required demands with enhanced workloads possibly due to the presence of free hydroxyl groups, relatively high polar group, during thermal polymerization which is believed a leading cause of reduction in insulation property. As other candidates as insulating materials, thermosetting polymers including polycyanate and dicyclopentadiene were reported. Recently, benzoxazine gains interests as a new generation of electrical insulating materials since inherent hydroxyl groups are strongly bonded by internal hydrogen interactions and their functions as a polar group are not expected to be serious as those in epoxy resins. Polymerization of benzoxazine was carried out by heat treatment with catalyst-free condition generating no by-product. Herein, we have focused on dissipation factor because it is an important value as applied frequency is getting higher in the field of insulating materials. In this study, along with benzoxazine, silica nanoparticle was introduced to improve mechanical stability and electrical insulation properties. Using silica nanoparticle, epoxy/benzoxazine hybrid film were prepared having ultra-low dissipation and superior mechanical stability. To prepare hybrid films, monobenzoxazine and linear polybenzoxazine were employed to compare their properties. For monobenzoxazine based hybrid film, optimized amount of epoxy resin was added to overcome brittle nature of benzoxazine. Lower dissipation factor was obtained (~ 0.005 frequency/10 GHz) as composition of epoxy resin decreased, however, decreased epoxy portion resulted in poor mechanical stability. On the contrary, linear polybenzoxazine and silica hybrid film displayed improved physical stability without epoxy resin but showed limitation of adhesion to copper layer possibly due to insufficient polar functional groups. Finally, hybrid films based on epoxy resin and linear polybenzoxazine showed enhanced adhesion to copper foil and excellent electrical insulation property (dissipation factor = ~ 0.006).

Transparent and conducting electrodes (TCEs) are an essential part of various optoelectronic devices such as touchscreens, displays, photovoltaics, and so on. With the recent emerging of flexible or wearable devices, its bendability and stretchability became additional requirements, which cannot be satisfied by traditional oxide-based transparent conducting materials. Among several approaches for the production of highly flexible TCEs, metal-mesh-based structures have been actively investigated because of excellent performances and reliabilities. Nevertheless, the fabrication of mesh or grid structures with a sub-micron line width is generally complex and cumbersome. Here, we introduce an extremely facile process for the fabrication of metal mesh patterns embedded in flexible substrate. Our strategy is based on sub-micron replication and area-selective lift-off process using the novel principle of solvent-assisted delamination of deposited metal thin films, which selectively occurs at predefined locations. Our fabrication process is simple, convenient, and cost-effective in that it does not require any lithography/etching steps or sophisticated facilities. These transparent electrodes composed of Ag nanomesh have outstanding optical and electrical properties (e.g. sheet resistances of 0.45Ω/sheet at 88% transmittance or 2.46 Ω/sheet at 93% transmittance depending on the width and height of mesh patterns), which are markedly superior to other flexible TCEs such as graphene or silver nanowires. The excellent structural stability of embedded mesh patterns enables to achieve its high aspect ratio, and as a result, its resistance can be significantly lowered without compromising optical transparency. Moreover, there was no noticeable change of resistance or transparency for over 1,000 repeated bending cycles with a bending radius of 5 mm, which confirms the outstanding bendability and reliability of our embedded transparent electrodes.

Lithium iron phosphate (LiFePO₄) is a widely used material for lithium ion batteries, due to its stability and lower toxicity compared to other commonly used cathode materials (i.e. LiCoO₂). This has resulted in a large number of developed methods to synthesize LiFePO₄, including: hydrothermal, solid state, spray pyrolysis, and coprecipitation. Although LiFePO₄ is known to be an environmentally friendlier material, many of the methods by which it’s synthesized are not as ecologically benign. Energy intensive methods such as solid state synthesis require high temperatures to completely synthesize the material. At an attempt to create a more sustainable synthesis process, we propose a method in which an ionic liquid in combination with water is used as the synthesis medium. This opens up the possibility of recycling and reusing the ionic liquid for subsequent synthesis.
Ionic liquids, known for their unique properties of a high boiling point and a liquid state at room temperature, have been used in the past as a synthesis medium for LiFePO₄, and an alternative to aqueous solutions. Due to the insolubility of chosen precursors (FeSO_{4 *}7H₂O and Li₃PO₄) in our ionic liquid (1-ethyl-3-methylimidazolium trifluoromethanesulfonate), we propose a mixture of deionized water and ionic liquid to increase solubility of precursors.
In this work, we provide an overview of the varying effects of DI water to ionic liquid ratio, reaction time, temperature dependence and partial concentration of precursors. Specifically, we explore how the aforementioned factor affects the morphology, crystallinity, and electrochemical properties of synthesized LiFePO₄.
Synthesis is conducted in a controlled environment inside of a tube furnace under varying parameters. Electrochemical properties of the synthesized material are characterized by coin cell testing, cyclic voltammetry (two electrode system), and electrical impedance spectroscopy. Morphology and size distribution are characterized using scanning electron microscopy. Crystallinity is analyzed through x-ray diffraction.

Acrylate grouting material has been widely used in dams, tunnels and other underground buildings. This paper introduces the basic components of acrylate grouting material, then the reaction mechanism and dynamics of gelation process are discussed based on the theory of free radical polymerization. By measuring the relationship between gelation time and the concentration of initiator ammonium persulfate, the chain termination of free radical is confirmed to be single-base termination reaction. The gelation time is inversely proportional with the concentration of initiator and is directly proportional to the natural logarithm of the ratio of the initial concentration [M]₀ and a time component concentration [M] of the acrylate monomer. The quantitative relation between them was derived. The result has a guiding significance on the material design and the gelation control of acrylate grouting material.

According to increasing consumption of nano-fiber, Electrospinning technique has attracted much attention because the nanofibers which was made from electrospinning has smaller diameter than other technique and can be produced using various types of polymers and solvents. However, the rate of electrospinning always has limitation to produce a huge amounts of nano-fiber in industrial field. The electrospinning which uses syringe produces the nano-fiber in the rate of 0.5g/h because the technique uses the polymer solution which was traveled from one spinet only. To overcome the limitation, multi-needle electrospinning which has a number of spinet and needleless electrospinning which includes cylinder, coil, and ball types was reported. Here, we introduce an advanced method for the mass-production of electrospinning using rotating helically probed cylinder without syringe. The rotating drums impregnating several needles on surface are connected with DC power supplier, and the polymeric solution is located under the rotating drums. The positive voltage are applied on the needles, and the rotating drum is rotated with desired rpm. Polymer droplet will be formed on end of each needles, and Taylor cones are generated on each needles when positive voltage is applied. This can provide clear morphology of nanofibers using various polymers and increased producing rate in lower supplied voltage.

Humic substances (HS) are major components of the natural organic matter (NOM) in soil and water. Particularly, HS affect the chemistry, cycling and bioavailability of chemical elements in soil. Regarding their structure, they are complex and heterogeneous mixtures of polydispersed materials formed by biochemical and chemical reactions during the decay and transformation of plant and microbial remains (a process called humification). Plant lignin and its transformation products, as well as polysaccharides, proteins, lipids, nucleic acids, etc., are important components taking part in this process. HS are highly chemically reactive, yet recalcitrant with respect to biodegradation. Humic substances can interact with several nutrients and toxic metals, which can be more available to organisms or actually sequestered so as to reduce their toxicity or beneficial value. The mechanisms of many of these interactions are unclear. That is a result of our lack of knowledge of the structural components of humic substances. In addition, HS are efficient fluorescent materials and can be divided into three main fractions: humic acids (HA), fulvic acids (FA) and humin. Fulvic acids are soluble in water at all pH; HA are insoluble at low pH and Humin is insoluble at all pH values. Fractal theory has been considered an alternative tool to explain the conformation of molecular aggregates. The presence of fractal models indicates that the system may be decomposed in parts, each part being a copy of the whole. In the present work, a drop of different HS materials was dried on a glass surface and its suspended molecules were deposited in a typical dendritic-like fashion during the evaporation process. Confocal laser scanning microscopy (CLSM), equipped with spectral analysis, Fluorescence Lifetime Imaging (FLIM) and two-photon (2P) excitation, was employed to quantify the formation of dendritic deposits in real time and to access a new variety of HS fluorescence states related to structural changes and molecular aggregation. Image methodologies were developed to enhance the viewing of fractal patterns, and observe variations in HS concentration and organization along the area of the original drop, with features that cannot be perceived in a usual image analysis. The fluorescence spectral shape and position correlate well to HS concentration, to the HA or FA fraction and to the fractal morphology. The fluorescence decay time became longer with the decrease HS aggregates along the dendritic structures, which corresponds to HS emission and decay time features in a less concentrated environment. These results suggest that HS arrangement in such fractal structures is based on a well-organized environment that ensures different level of interaction between the molecules. In addition, the variety of HS fluorescence states accessed by two-photon excitation can allow an even broader optical characterization of soil materials and their fractal properties.

Typically, composites are lightweight, and high strength and hence are attractive for use in aerospace, automotive applications. For most of the aerospace applications, laminated composites serve as a primary load carrying structure and are subjected to a variety of loadings including transverse impact and fatigue loadings. The typical laminated composites are weak in the transverse direction. Since laminated composites are weak in transverse direction, when these laminates are subjected to transverse loading, most of the time interlaminar failure occurs in the form of delaminations. Conventional methods of preventing delaminations include improving the design and improving the matrix properties. Although, improving the composite design suppress delaminations to some extent, a substantial amount of compromise with other properties like increase of resin volume fraction, degradation of inplane properties, voids, distortion in fibers and laminate, an increase of cost or process complexities are common. The present day researchers are more focused on improving matrix by nanomaterials such as Carbon Nano Tube(CNT), though the cost is hampering its potential for an industrial prospect. Electrospun nanofibers are being considered as a cheap alternative for vapor grown CNTs and other nanomaterials which involve complex fabrication and application methods in the field of interlaminar reinforcement for polymer matrix composites. Most of the aerospace quality composites are manufactured using prepreg due to the higher percentage of fiber volume fraction and hence higher mechanical properties. Although, nanomaterials have been recognized as a major advancement for improvement of composite material properties, there has been very little effort to fabricate prepregs using nanofibers. The current research focuses on the challenges involved in the fabrication of nanofiber enhanced prepregs and process difficulties and possible solutions for fabricating electrospun nanofiber overlaid prepregs. The effects of heat treatment on electrospun nanofiber overlaid woven fabric on the mechanical properties of both glass and carbon are investigated. A novel technique is proposed for manufacturing of nanofiber engineered prepregs.

Organic thin film transistors (OTFTs) can provide low-cost flexible electronics via large-area and high-volume manufacturing. Among the many factors that govern circuit design, the aspect ratio of channel width to length (W/L) serves as a tunable scaling factor for drain current. In this work, we develop methods for obtaining multiple aspect ratios for circuit design using printing of solution processed electronic materials onto flexible substrates. We combine high-speed doctor blade and surface energy patterning to demonstrate arrays of OTFTs that are later integrated to form circuits. In the surface energy patterning process, a hydrophobic self-assembled monolayer of fluoroalkylsilane is deposited on a plastic substrate, and plasma etching is used to create hydrophilic regions. Then, the desirable ink is patterned on the hydrophilic regions using doctor blading [1]. The aspect ratio of the source and drain (SD) features are increased by controlling the ink volume of the bottom electrode (PEDOT:PSS). By optimizing the printing conditions, we increase the SD features to 450 µm width and demonstrate an array of devices with aspect ratios of 7:1 µm and 3:1 µm. The patterned semiconductor island also contributes to the control of aspect ratio values. The semiconductor (small molecule diF-TES ADT:PTAA) is patterned on top of the SD features to fabricate devices with channel widths ranging from 100 to 350 µm. A dielectric layer (amorphous fluoropolymer) is used as the gate insulator. Devices with smaller aspect ratio show an average mobility of 0.5 cm² V/s, whereas devices with larger aspect ratio show an average mobility around 0.8 cm² V/s due to their crystal structure. In order to get larger aspect ratios, we use interdigitated source and drain design. This provides the advantage of having control over the channel width by connecting the discrete fingers to make source and drains and get the desired aspect ratio from 3:1 to 50:1. We utilize screen-printing to interconnect devices and demonstrate simple circuits such as enhancement-load inverters. Using larger aspect ratio OTFT as driver transistor and smaller aspect ratio for the load transistor, we show increase in k factor ratios (higher gain) and smaller noise margins as expected compared to inverters with the same geometries for driver and load transistors.
References:
[1] Pierre, A., Sadeghi, M., Payne, M. M., Facchetti, A., Anthony, J. E. and Arias, A. C. (2014), All-Printed Flexible Organic Transistors Enabled by Surface Tension-Guided Blade Coating. Adv. Mater., 26: 5722–5727. doi:10.1002/adma.201401520

Interference lithography has proven to be a useful technique for generating periodic sub-diffraction limited nanostructures. Interference lithography can be implemented by exposing a photoresistpolymer to laser light using a two-beam arrangement or more simply a one beam configuration based on a Lloyd'sMirrorInterferometer. For typical photoresist layers, an anti-reflection coating must be deposited on the substrate to prevent adverse reflections from cancelling the holographic pattern of the interfering beams. For silicon substrates, such coatings are typically multilayered and complex in composition. By thinning the photoresist layer to a thickness well below the quarter wavelength of the exposing beam, we demonstrate that interference gratings can be generated without an anti-reflection coating on the substrate. We used ammonium dichromate doped polyvinyl alcohol as the positive photoresist because it provides excellent pinhole free layers down to thicknesses of 40nm, and can be cross-linked by a low-cost single mode 457nm laser, and can be etched in water. Gratings with a period of 320nm and depth of 4nm were realized, as well as a variety of morphologies depending on the photoresist thickness. This simplified interference lithography technique promises to be useful for generating periodic nanostructureswith high fidelity and minimal substrate treatments.

Magneto-active elastomers (MAEs) are mixtures of magnetically sensitive filler and a hyperelastic matrix material such as silicone elastomer. Historically, MAEs have been fabricated with hard magnetic particulates with low aspect ratios with respect to the easy magnetic axis. When a magnetic field is applied to MAEs with high magnetic anisotropy, particles tend to align with the direction of the field. However, these particles cannot rotate freely within the elastomer, therefore distributed torque at the particulate level is created throughout the material causing macroscopic deformation. MAEs have seen use recently as distributed actuators utilizing this magnetic torque. Consequently there is need to develop a means of producing MAEs with increasing magnetic anisotropy to aid torque production.

Previous studies have used plate-like barium hexaferrite particles with magnetization normal to the plate, with desired aspect ratios equal to or less than one. This research proposes the fabrication of MAEs from hard magnetic fibers with high aspect ratios, rather than hard magnetic particles, to increase remanent and saturation magnetizations. Recent studies suggest that while squareness ratios of 0.8 are not uncommon in hard-magnetic particulate MAEs, these values could be improved with highly aligned magnetic fibers possibly through the coherence in stray fields.

For this work, two sets of MAEs will be studied. The first will be traditional hard-magnetic MAEs fabricated using 325 mesh M-type Barium Hexaferrite particles (BAM) in Sylgard 184 silicone elastomer. These MAEs will be cured in the presence of a ~1T magnetic field to align the particles. The second set of MAEs will be fabricated using the same BAM particles, however these particles will be first used to form aligned fibers through a magnetic drawing procedure. The drawing procedure produces fibers by exposing a particle-matrix mixture to a 0.110 T field for 20 minutes. The material will then be heat treated within the magnetic field, to cure the fibers. The length of the fibers will range from 2 - 5 mm. Next, those fibers will be placed in pure elastomer resin and cured in the presence of a magnetic field to align the fibers with the elastomer resin.

The magnetic properties of the all MAEs will be determined by vibrating sample magnetometry. From the resulting hysteresis loops, the remanent magnetization, saturation magnetization and squareness ratio will be determined and compared to MAEs made with particles. Characterization of the distribution of magnetization will also be conducted to assess alignment.

After BAM fibers can be produced, a future goal is to four-dimensionally (4D) print active structures with embedded BAM fibers. By using 4D printing, magnetic material can be fabricated in arbitrary geometries and magnetic orientation for applications as biosensors, MEMS devices, micro- or macroscale embedded actuators, and tailored electromagnetic devices.

Reducing the cost of lithium-ion batteries (LIBs) is a major effort by the LIBs industry. This work proposes a synthesis method to decrease the production cost for LiFePO_4, by synthesizing the material through an open-air environment solid state reaction. In our approach, iron phosphate (FePO₄) powder is preheated to eliminate moisture. Once dried, the FePO₄ is mixed with lithium acetate (CH₃COOLi), and the mixture is heated in a tube furnace. The solid state reaction is conducted in an open air environment. In order to minimize the oxidation of the formed LiFePO₄, an optimized tube reaction vessel is utilized during synthesis. X-ray Diffraction (XRD) and Energy Dispersive Spectroscopy (EDS) are used to characterize the crystal structure and chemical composition of the synthesized material. Furthermore, scanning electron microscopy (SEM) characterization shows the grain size of the formed LiFePO₄ to be in the range of 200 nm to 600 nm. The synthesized LiFePO₄ is assembled into a half coin cell. The cycleability and performance under different C-rates are tested using an Arbin tester

There is currently much research in the area of wireless optical commutations and indoor free space optics with hopes to improve the data rates of the current wireless network. Optical communications can reach speeds upwards of 10Gb/s which will be able to run in parallel with current data speeds. Many of the models for this system involve a centralized light source that has the capability to delivers light to many transmitters via optical fibers. The light from the fiber is then collimated through a lens system and steered to a target using a spatial light modulator (SLM).
Microelectromechanical systems (MEMS) are a growing industry and are currently being used for many applications, including optical communication. We have developed an electrothermal tip-tilt varifocal micromirror with the capability of steering a beam of light ±30°, compared to most SLM systems which are limited to approximately ±10°. In addition, the varifocal capability of the mirror allows us to tune the spot size of the beam rather than using a fixed diameter. Using a microelectromechanical (MEMS) mirror not only increases the steering range, but the size of the device also opens up the possibility of creating a micro transmitter and receiver that can be installed in devices such as a laptop or a phone. This would allow for device-to-device communication rather than limiting communication to only router-to-device. In this work we take advantage of our mirror’s large focal range and investigate using the mirror to couple with a cleaved single mode optical fiber without additional optics. Using 1550nm light, we optimized the fiber coupling, characterized the beam properties with regards to the mirror angle and radius of curvature, and performed bit error rate testing on the device. By implementing this fiber coupling, we simplify the system by removing lenses which has potential benefits such as manufacturing.

Squaraines (SQ) have shown great promise as materials for organic photovoltaics (OPV) due to their high absorbance in the near infra-red and the ability to manipulate their aggregation in thin films. In order to further improve the efficiency of SQ OPV devices, though, it is necessary to gain a more in-depth understanding of the active layer from both a physical and chemical point of view.
In this work, for a variety of squaraines, we correlate solution absorption and solid state absorption from films of accurately determined thickness (AFM) to arrive at a relationship between solid state absorptivity and solution state extinction coefficient. We further spectroscopically determine (i) the relative populations of aggregates and monomers in thin films of SQ blended with PCBM, and (ii) the number of SQ molecules in each aggregate complex. This increased understanding of the aggregation of SQ not only allows for rapid quality testing through quick thin film absorption measurement, but also, after comparison with computational simulation and power conversion efficiency data, allows us to consider how chemical tuning within a homologous series of squaraines might lead to an optimized active layer material.

The low surface interfacial free energy, high flexibility, optical transparency and chemical inertness and durability have made Polydimethylsiloxane (PDMS) a primary structural material for bioMEMS, microfluidic and other biomedical devices. However, the low thermal conductivities have severely restricted the performance of these devices and also hindered PDMS from many potential applications.
In this research, PDMS/Nickel (Ni) composites with embedded Ni spherical particle columns were studied for thermal conductivity enhancement. The volume fraction of Ni particles ranged from 2 to 20% while the strength of the applied magnetic field was fixed at 0.45 Tesla. The distribution and morphology of the column structures were quantitatively analyzed using optical microscope, scanning electron microscope (SEM) and digital image processing. A reusable 3ω measurement technique was applied to measure the effective thermal conductivity of PDMS/Ni composites in the parallel direction to the magnetic field. The measured thermal conductivity was compared with the prediction from a finite element model built on the observed microscopic structures. Under a static magnetic field, Ni particles align parallel to the field forming columns. The results illustrated that the diameter of Ni columns increased with increasing particle volume fraction while the center to center spacing between columns did not change substantially under the fixed magnetic strength. The magnetically aligned particle columns significantly enhanced the thermal conductivity of PDMS compared to the randomly distributed particles by about two-fold. However, the point contacts between magnetically aligned spherical fillers are the major limiting factor for the further improvement of thermal conductivity.

Surface of highly ordered pyrolytic graphite (HOPG) is reformed by using ambient plasma. The HOPG film shows various pore structures after the plasma treatment, indicating improved electrochemical properties for supercapacitor applications because of increase of the surface area. We also compare water effect on the film during the plasma treatment. Water might protect HOPG surface from the plasma and provide oxygen functional groups onto it, resulting in lower infected pores and higher impedance compared with them of HOPG film without water. Ambient plasma, therefore, could be considered as an economic and effective method for sample reformations.

Precision molding is a replicative production method for the mass production of complex glass optics in high precision. In contrast to the traditional material removal process, such as grinding and polishing, the surface as well as the entire shape of the optical component is created by deforming glass at elevated temperatures using precise molding tools with optical surfaces. The molded glass components present high shape accuracy and surface finish after the molding process, therefore no further processing is required. During the molding process, the glass is heated in the molding tool up to above Tg, then pressed into desired shape and cooled down to approximately 200 °C. The precision glass molding is therefore a complex thermo-mechanical process, in which the glass lens undergoes uneven cooling speed and stress distribution. These lead to several drawbacks on the molded glass optics, such as form deviation, index drop and fracture. In this study, FEM simulation was employed in order to achieve preliminary understanding of the molding process. The FEM model included viscoelasticity behavior of glass material (stress-relaxation, structure-relaxation and thermos-rheological simplicity), as well as thermodynamics model of the molding machine. In the form of a case study of a real molding example, the form deviation, index drop and fracture of the molded glass optic were predicted in advance of the molding experiment by means of the numerical calculation of thermal shrinkage, volume change and stress distribution respectively. The good agreement between simulation results and molding experiment results proves the accuracy of the developed FEM model.

The aim of this project is to use statistical modeling to predict, understand, and control how low-temperature microwave-radiation (MWR) assisted growth impacts the crystallinity and composition of ceramic thin films. Traditionally, ceramic films are crystallized using high temperature (> 500 °C) processes inside furnaces. These temperatures lead to high energy demands and limit the substrates available for film growth, as many polymeric substrates decompose at temperatures above 200 °C. Despite these limitations, no new manufacturing technology for low-temperature synthesis of crystalline ceramic thin films has been developed. We have demonstrated that crystalline anatase-phase Titanium Dioxide (TiO₂) thin films can be grown at temperatures as low as 150 °C through the selective heating of a conducting layer (e.g, metal, indium doped tin oxide or ITO) by MWR.

MWR is able to selectively heat the ITO layer by coupling energy to its molecules through polarization and conduction, promoting film crystallization and growth. We’ve successfully crystallized anatase TiO₂ films at 150 °C in 60 minutes, whereas conventionally grown anatase requires a 2 hour sintering step at 450 °C. This marks a significant decrease in energy consumption, as heating the microwave solution to 150 °C uses only 0.18% of the energy as heating a furnace to 450 °C, and demonstrates the advantages of MWR-assisted heating reported previously: reduced temperatures and reaction time, and improved product yield when compared with conventional synthesis routes.

The potential of MWR-assisted synthesis as an energy effective thin film manufacturing technology hinges on our ability to reliably control the crystallinity of the resultant films both spatially in the x,y plane and along the thickness (z) dimension. The most uniform and crystalline films occurred at an optimal convergence of MWR power, solution temperature, and reaction time, although several other independent variables can be controlled to impact crystallinity, such as power ramp rate and solution concentration. To determine how these variables influence the resulting films, we use a regression quadratic and sequential experimental design to create an evolving map for film growth and characterization. Preliminary results indicate that there is an ideal solution concentration range for optimized growth, and that slower power ramp rates lead to more uniform, crystalline films even at temperatures below 140 °C.

Scaling up the manufacturing process of MWR-assisted synthesis remains a challenge, but would create new opportunities and applications for a variety of ceramic materials, including complex perovskite oxides. Increasing understanding and control of the relationship between process parameters and film properties, which is the goal of this statistical model, is a crucial step in understanding the mechanisms behind MWR-assisted synthesis and applying this technique to other material systems and larger scale manufacturing.

We report the detection of noncentrommetry in the family of HRTiO₄ (R = rare earths) layered perovskites having a Ruddlesden-Popper structure, one formerly understood to possess center of symmetry^1,2,3,4. Symmetry breaking arises from the type of oxygen octahedral rotations, a mechanism that is not active in simple ABO₃ perovskites. In addition, we discovered a competition between oxygen octahedral rotations and sliding of the octahedral perovskite blocks at the OH layers. For the smaller rare earth ions, R = Eu, Gd, Dy, which favor octahedral rotations, noncentrosymmetry is present but the sliding at the OH layer is absent. For the larger rare earth ions, R = Nd and Sm, the octahedral rotations are absent, but in order to optimize the hydrogen bonding, sliding of the octahedral blocks at the OH layers occurs. This study reveals a new improper mechanism for inducing noncentrosymmetry in layered oxides, and chemical-structural effects related to rare earth ion size and hydrogen bonding that can turn this mechanism on and off. We are also able to construct a complete phase diagram of temperature versus rare earth ionic radius for the HRTiO₄ family.

Reference:
(1) Nishimoto, S.; Matsuda, M.; Harjo, S.; Hoshikawa, A.; Kamiyama, T.; Ishigaki, T.; Miyake, M. J. Solid State Chem. 2006, 179, 1892–1897.
(2) Nishimoto, S.; Matsuda, M.; Harjo, S.; Hoshikawa, A.; Kamiyama, T.; Ishigaki, T.; Miyake, M. J. Eur. Ceram. Soc. 2006, 26, 725–729.
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Ultrahigh gas permeation barriers are required as encapsulation for organic light emitting diodes, organic photovoltaics as well as Perovskite solar cells. Up to now, the fabrication of thin film barriers on temperature sensitive substrates such as polymer foils is still challenging. So far, ALD has been shown as the only deposition technique to prepare single layers with extremely low water permeation rates, which are suitable for OLED encapsulation, due to high film quality. In conventional ALD, two gaseous precursors are usually sequentially exposed to the substrate in an evacuated reaction chamber by pulsing. Inert gas purging inhibit gas phase reactions by removing precursor excess and reaction byproducts. As ALD is based on self-limiting surface reactions, it can provide pinhole-free and conformal coatings even on three-dimensional substrates. However, conventional ALD is subject to low deposition rates and expensive vacuum technology. Consequently, very recently it has been proven that spatial ALD can overcome those drawbacks. As opposed to conventional ALD the precursors as well as the purge gases are continuously introduced into a specially designed deposition head. The ALD characteristic film growth is realized by moving the substrate through spatially separated reaction zones. During the deposition process the precursor bubblers, the gas flow rates as well as the substrate temperature and velocity are in an equilibrium state. This allows us to determine the amount of precursor materials which are needed for saturated growth condition as well as for the total material yield.
Trimethylaluminium (TMA) as well as bisdiethylaminosilan (BDEAS) were used as metal precursors and ozone as co-reactant to deposit Al₂O₃ and SiO₂ films. In general, amorphous Al₂O₃ films can provide very low water vapor transfer rates (WVTR) in a range between 10^-5 to 10^-6 g/(m²×d). However, under tough aging conditions such as 70 °C and 70% relative humidity respectively, alumina is easily corroded within few hours, resulting in totally losing its barrier performance. An embedded thin SiO₂ layer within the alumina film, however, is able to extent the degradation time. The WVTR can be dramatically reduced by three orders of magnitude, due to a sufficient reduction of the alumina corrosion. Surprisingly, we also found that alumina can be stabilized when silicon is inserted into the bulk material, making the films more resistive against corrosion. Those SiAl_xO_y films were prepared with a precursor sequence of BDEAS/ozone/TMA/ozone per ALD cycle cycle and analyzed with infrared spectroscopy. Interestingly, at 100 °C process temperature a relatively high growth per cycle (GPC) of 0.225 nm/cycle was achieved whereas the GPC of the Al₂O₃ and SiO₂ single layers were only 0.16 and 0.013 nm/cycle respectively. It is obvious that TMA behaves as a reducing agent for BDEAS.

VO₂ is an extremely interesting thermochromic material due to its reversible phase transition from a low-temperature monoclinic semiconductor to a high-temperature tetragonal metal. High modulation of infrared transmittance and electrical and thermal conductivity makes VO₂-based films a suitable candidate for numerous applications such as self-tunable infrared filters, temperature sensing devices, smart windows with automatically varied solar transmission or control of heat fluxes in cars.
This contribution deals with properties of VO₂ thin films in a wide temperature range from -30 to 100 °C. The films (75-100 nm thick) were prepared by high-power impulse magnetron sputtering (up to 5 kWcm^-2 in a pulse) of V in Ar+O₂ plasma, and the desired elemental composition was achieved using a pulsed reactive gas (O₂) flow control. Under these conditions the films grow out of a highly ionized flux of film-forming particles with many metal ions, which allowed us to prepare densified crystalline thermochromic VO₂ without any substrate bias voltage and at a low deposition temperature of 250 °C (compared to the state of the art of >=400 °C) [1]. This e.g. facilitates depositions on sensitive substrates (such as polymers) and insulating substrates (such as glass), and consequently significantly increases the application potential of this material. In addition to (i) the aforementioned advance in manufacturing, the novelty of this contribution is further based on (ii) the wide measurement temperature range considered and (iii) the low thermochromic transition temperature of around 50 °C (compared to the most frequently cited value of 68 °C).
The films were primarily characterized using a spectroscopic ellipsometer equipped with a heat/cool stage. The characterization included both (i) temperature-dependent measurements at a selected wavelength and (ii) spectroscopic measurements at selected temperatures. The optical constants were fitted using a description of VO₂ by the Cody-Lorentz oscillator combined with Lorentz oscillators. Moreover, the optical constants were used to predict the transmittance of glass coated by VO₂ of various thicknesses. The most important results from the application point of view include (i) the aforementioned low transition temperature of around 50 °C, (ii) very low (for VO₂) room-temperature extinction coefficient (e.g. 0.10 at 550 nm, leading to a high predicted transmittance in the visible region) and (iii) high modulation of the predicted transmittance in the infrared region (e.g. 39% at -30°C, 30% at the room temperature and 3% above the transition temperature at a wavelength of 2000 nm for a 100 nm film thickness). The results are important for the design of thermochromic coatings, and pathways for their preparation under simplified industry-friendly conditions, for various technological applications.

[1] J. Houska et al., Appl. Surf. Sci., submitted (2016)

Developing novel and efficient method to fabricate micro-sized metallic or oxide structures has attracted great research interest, as such process is involved in manufacture of various devices including microelectromechanical systems, printed circuit boards, and wire bonds in integrated circuits. Among all possible methods for microfabrication, electrodeposition has the advantages of low cost, availability at room temperature and high scalability. However, current techniques using electrodeposition to fabricate metallic or oxide structures generally have the deposition process conducted in bulk electrolyte, hence requiring the substrate that the structure is deposited onto to be masked. Methods that do not require the masking procedure have also been developed, but improvement was limited in terms of reduction in complexity and increase in product quality. In this paper, we will present a novel approach to fabricate metallic or oxide micro-structures. By combining the concept of additive manufacturing and confined electrodeposition, the newly developed system can fabricate structures in a single step, therefore achieving higher simplicity and efficiency.
The method involves the extrusion of a small volume of electrolyte through a conductive nozzle onto a conductive substrate, while at the same time a voltage is applied across the nozzle and substrate. This causes electrodeposition of metal or oxide from the electrolyte at the gap between the nozzle and substrate. With aid of a computer-controlled motion system, the nozzle is swept across the substrate, performing the extrusion and electrodeposition at various locations to eventually fabricate a structure of the material. 2D patterns of primarily Cu₂O have been successfully fabricated using the method with single sweep at one location, and factors including deposition voltage, sweeping speed, and surface profile of substrate that affect performance of the system have been investigated. We have also observed that, by increasing the number of sweeps at the same location, patterns of Cu or Cu₂O with higher thickness can be obtained. Therefore, there is good potential that the method can also be utilized to fabricate 3D structure of metals and oxides. In addition, by switching the polarity between the nozzle and substrate, patterned etching or anodization should also be feasible with the proposed system.

Nanoscale process integration demands novel nano-patterning techniques in compliance with the requirements of next generation devices. Conventionally, top-down subtractive (etch) or additive (deposition/lift-off) processes in conjunction with various lithography techniques is employed to achieve film patterning, which become increasingly challenging due to the ever-shrinking mis-alignment requirements. To reduce the complexity burden of lithographic alignment in critical fabrication steps, self-aligned processes such as selective deposition and selective etching might provide attractive solutions. Area-selective atomic layer deposition (AS-ALD) has attracted immense attention in recent years for self-aligned accurate pattern placement with sub-nanometer thickness control.
Here, we demonstrate a methodology to achieve AS-ALD by using inductively couple plasma (ICP) grown C₄F₈ polymer film as hydrophobic blocking layer for selective deposition. Our approach has been tested for metal-oxide materials including ZnO, Al₂O₃, and HfO₂. Contact angle, X-ray photoelectron spectroscopy, spectroscopic ellipsometer, and scanning electron microscopy measurements were performed to investigate the blocking ability of plasma polymerized C₄F₈ layers against ALD-grown metal-oxide films. Characterizations carried out revealed that effective ZnO blocking on C₄F₈ can be achieved up to more than 100 ALD cycles, resulting in selective growth of ~15 nm thick films. Initial nucleation has been observed for 136-cycle ZnO films and additional ALD cycles eventually led to growth on C₄F₈ layer at conventional GPC values. On the other hand, although no complete blocking is observed, a rather slow nucleation has been observed for HfO₂ growth on C₄F₈ coated surfaces up to 100 growth cycles, while C₄F₈ layer deposited under the present conditions has been found to be ineffective in blocking Al₂O₃ growth. By exploiting this inhibition feature of C₄F₈ layer, ZnO patterning has been performed on two and three-dimensional micro and nano-scale patterned C₄F₈/Si substrates. The robust albeit rather simple and straightforward technique presented in this work overcomes various challenges associated with previous methods of AS-ALD and provides an alternative route towards nano-patterning using AS-ALD.

Controlling the lateral dimensions of thin films by patterning is an essential requirement for microelectronics industry for continuous device miniaturization. Conventionally, thin film patterning is achieved by photolithography which includes several processing steps. During the atomic layer deposition (ALD) process, film nucleation is critically dependent on the surface chemistry of the substrate which makes it possible to achieve area-selective ALD (AS-ALD) by chemically modifying the substrate surface. Local modification of substrate surface opens up possibilities to achieve lateral control over film growth in addition to robust thickness control during ALD process. AS-ALD offers numerous advantages in transistor fabrication such as reduction of the lithography steps required, elimination of complicated etching processes, and minimization of expensive and poisonous reagent use.
In this work, we report detailed investigation to select the most compatible polymer among poly(methyl methacrylate) (PMMA), polyvinylpyrrolidone (PVP), and octafluorocyclobutane (C₄F₈) for AS-ALD of TiO₂. TiO₂ was grown at 150 °C using tetrakis(dimethylamido) titanium (TDMAT) and H₂O as titanium and oxygen precursors, respectively. PMMA and PVP were deposited using spin coating and C₄F₈ was grown using inductively coupled plasma (ICP) deposition tool. Contact angle, scanning electron microscope (SEM), spectroscopic ellipsometer, and X-ray photoelectron spectroscopy (XPS) measurements were performed to investigate the effectiveness of polymer layers for AS-ALD process of TiO₂. TiO₂ was grown with different number of growth cycles (maximum = 1200 cycles) on PMMA, PVP and C₄F₈. PMMA revealed successful growth inhibition upto the maximum inspected growth cycles. PVP was able to block TiO₂ growth upto 300 growth cycles and C₄F₈ revealed no inhibition capability. Finally, mm, μm, and nm scale patterned deposition of TiO₂ is demonstrated using a PMMA masking layer that has been patterned using e-beam lithography. Additionally, we used the selectively grown TiO₂ layers as an etch mask layer to create deep trench structures inside Si. SEM, EDX line scan, EDX elemental mapping, and XPS elemental mapping measurements revealed successful patterning of TiO₂ features. AS-ALD of TiO₂ demonstrated in the present work offers a novel approach to fabricate close packed nanopatterns for various device architectures without any complex etching or liftoff processes.

The development of an efficient method for controlling micro/nanostructured metal oxide would facilitate the further improvement of a diverse range of applications. Herein, we present a newly-developed method for the precise manipulation of micro/nanostructured metal oxides via structure-guided combustion waves (SGCWs), which are produced in hybrid composite films containing core-micro/nanostructured materials and chemical fuels. SGCWs implement instantaneous phase-surface-structure transformation using thermal-chemical-electrical energy conversion in the hybrid composite, as the chemical compositions of metal oxides are preserved or controlled to produce functional materials. In this work, the phase and structure transformation via SGCWs are investigated in Co-doped ZnO nanostructures and copper oxide microstructures. SGCWs at the surfaces of Co₃O₄–ZnO multipod nanostructures (deep brown in color) enable direct phase transformations to newly formed CoO–ZnO_1−x nanoparticles (olive green in color). Such oxygen-release mechanism from Co-doped ZnO significantly affects the SGCWs velocity, and forms lattice defect that interrupt the charge-carrier movements inside the nanostructures. Moreover, the precise characterization of the structural and chemical transitions in the copper oxide microstructures and chemical fuels confirm that the SGCWs in the layered composites of Cu/Cu₂O/CuO microparticle-based films and the chemical fuel layers yield the direct synthesis of Cu(OH)₂ flower-like structures and nanowires at the surfaces. SGCWs in such micro/nanostructured metal oxides can form the high temperature (650 C-900 C) and fast mass diffusion in cm-scale during short time interval (0.1-1 sec), which are driving factors for unique transformations. The SGCWs can be applied as a newly developed one-step, fast, low-cost, large-scale approach for the synthesis of diverse functional micro/nanostructures.

Additive Manufacturing (AM), otherwise known as three-dimensional (3D) printing, is a growing technology area comprised of a spectrum of processes that allow production of solid objects of virtually any shape from information obtained from a digital object. These days, AM processes drive major innovations in areas such as engineering, manufacturing, art, education and medicine. In general, AM processes use additive approaches where materials are applied in successive layers to produce a final part, differing from traditional subtractive manufacturing techniques that rely on the removal of materials by methods such as cutting or milling. AM processes are not necessarily new. They were introduced commercially in the 90’s for the manufacture of complex metal parts and have almost a 30-year history for plastics, mainly due to prototyping efforts that drove the development of multiple commercial products using techniques from stereo-lithography to laser-based powder based fusion processes.
The global market size for AM products is expanding at a rapid pace. Even though the manufacturing costs for AM remain higher compared to common processes, significant reduction in efficiency and logistics in the coming years would make AM approaches attractive for specific cases, especially via reduction of tooling costs, design freedom and reduction in assembly requirements. High demanding applications such as medical, aerospace, oil and gas exploration, military and defense, and semiconductor applications will benefit directly from the expected growth of AM.
Due to the growing number of polymeric resins that are becoming available as a consequence of developments of new processes and technological advancements in AM, there is specific need for the understanding of the structure and property relationships for polymers commercially targeting AM technologies. In this talk we provide a series of examples where polymeric systems are used in the production of parts for high demanding applications using various AM processes. Specifically, developments of high-performance thermoplastics for high demanding engineering applications, as well as comparison to other common polymers used in traditional AM processes will be discussed to highlight the relevance of polymer structure in the final properties of an AM part.
We present an in depth study of the morphological changes observed in selected high performance polymer resins when subjected to conditions typically found in common AM processes, including powder bed fusion processes such as Selective Laser Sintering (SLS), as well as extrusion-based approaches such as Fused Deposition Modeling (FDM). We conclude that the fundamental understanding of the resulting structure of these polymers when processed using conventional AM processes is crucial and necessary for the development of new technologies and future complex processing techniques.

Stereolithography is an additive manufacturing technique that uses selective photoirradiation to cure a liquid resin of photopolymerizable material. By repeating this process, layer-by-layer, a solid object forms. Compared to other additive manufacturing techniques, stereolithography is attractive because of its rapid build speed, micron resolution, and scalability. The main limitation to stereolithography is the lack of compatible materials, particularly elastomeric materials. The viscosity requirements of the liquid pre-polymer resin during processing limit most current stereolithography resins to those comprised of monomeric and oligomeric acrylates and epoxies. Consequently, these materials are highly crosslinked and glassy at room temperature, therefore exhibiting ultimate strains below 90% and limiting technical applications. Herein we report the rapid fabrication of high-resolution silicone (polydimethylsiloxane) based elastomeric devices via stereolithography. Click chemistry permits rapid photopolymerization and facile tuning of mechanical properties by controlling the crosslink density and degree of polymerization. From this elastomeric system, we can directly fabricate different complaint machines.

3D printing technologies have been of growing interest and presented compelling opportunities in various areas. Among them, fused filament fabrication (FFF) 3D printing is dominant in consumer hobbyist arenas since it is a cost-effective process with simple set-up. In FFF, the polymer is melted then extruded through the print head and deposited to a substrate layer by layer. It requires thermoplastic materials, which are melt-processible but poor in mechanical properties (especially when loaded perpendicular to the layer deposition plane), often making FFF unfavored in commercial 3D printing. Crosslinked polymers, also called thermosets, usually have better performance in terms of thermal stability and chemical resistance, as well as better mechanical properties. These qualities make the thermosets desirable for many engineering applications. However, most thermosets are chemically crosslinked and not melt-processible once the crosslinks are introduced into the network. Therefore, reversibly-crosslinked polymers could be a great solution to improve the interlayer adhesion between layers within FFF printed parts and their mechanical properties while maintaining the melt-processibility.

In this presentation, we will be discussing our work on developing novel melt-processible thermosetting polymers for 3D printing, enabled by reversible Diels-Alder chemistry. Two polymer systems will be covered: 1) a blend of acrylic-based linear polymers with pendant furan groups and bismaleimide crosslinkers, and 2) crosslinked polymers comprising multi-furan monomers and multi-maleimide monomers. We will also discuss our approaches to modify the traditional FFF printer and make it adaptive to the novel materials we develop.

Stereolithography (SLA) is an additive manufacturing method whereby patterned light is used to cure a pre-polymer resin layer by layer into a finished part. Today, virtually all resins for SLA rely on acrylate chemistry to cure quickly following exposure to light. However, acrylates are not well known for mechanical strength. Efforts to improve the strength of SLA parts involve acrylate-functionalizing oligomers of epoxides or urethanes or by curing interpenetrating networks of acrylates and urethanes or epoxides. While this has improved the toughness and dimensional stability over pure acrylate systems, neither method is capable of producing parts with toughness comparable to engineering polymers such as Nylon. The answer to producing high performance 3D printed parts lies in the use of novel chemistries to ensure fast print times, minimal shrinkage, and high toughness.
We report the use of thiol-isocyanate polymers as a complete replacement for acrylate-based stereolithography resins. Thiourethanes cure at rates similar to acrylates when exposed to light using novel photo-latent bases. Photopolymerization is possible under light sources already used in the 3D printing industry. These materials benefit from extensive hydrogen bonding, which results in integrated stress-strain curves of over 110 MJ/m3. This represents an order of magnitude improvement over the mechanical performance of current acrylate-based SLA resins. A wide range of possible materials properties are achieved due to the click nature of the thiol-isocyanate reaction. By simply manipulating the monomer choice it is possible to achieve rigid glassy materials with heat deflection temperatures over 100 °C or soft elastic polymers with sub-ambient glass transitions. The polymerization reaction is not oxygen inhibited due to the anionic reaction mechanism, allowing for new 3D printer geometries which are impossible or impractical when using acrylate photopolymers.

Additive manufacturing has the potential to transform traditional manufacturing through the ability to produce customized parts with complex internal geometries that are impossible to create through conventional means. However, parts made using 3D printing techniques such as stereolighography (SLA) and fused filament fabrication (FFF) are frequently unsuitable for industrial end-use applications due to poor mechanical and thermal performance. Both techniques suffer from mechanical anisotropy in the printed parts, where the part performs well in-line with the print direction but is fragile when stressed perpendicular to the printed layers. Each of these problems stem from the fact that the polymer systems used today are not optimized for additive manufacturing, merely adapted for it. We report the use of innovative new chemistries that produce tough, mechanically isotropic parts via both SLA and FFF.
By using novel thiol-based chemistries we have demonstrated SLA printed resins that retain > 90% of their x-axis toughness (23 MJ/m³) in the z-axis (21 MJ/m³). Other resins in this family are capable of extreme toughness, with integrated areas under tensile stress-strain curves over 110 MJ/m³. This represents an increase in toughness over existing resins by one order of magnitude. Innovative self-healing resins have been developed for FFF processes that are 235% more mechanically isotropic compared to current FFF filaments such as PLA. We have demonstrated the ability to print large, geometrically complex parts with these resins. The isotropic toughness of these resins enables industry to employ additive manufacturing for high performance end-use applications.

There is great interest in polymers based additive manufacturing (a.k.a. 3D printing) because of its potential to transform production of low volume parts and its ability to customize via digital and imaging technologies. Yet there are significant barriers slowing the widespread adoption of these technologies including part strength, dimensional control, and speed of production. Our approach is to develop a fundamental understanding of polymers based AM by integrating in-situ monitoring of the non-equilibrium process, ex-situ materials testing and molecular modeling.

Here we examine fused filament fabrication (FFF) with the goal of understanding the factors that control the strength of the weld between layers, which is well recognized as the limiting factor in ultimate part strength. In FFF, a thermoplastic filament is extruded though a rastering nozzle to building a 3-dimensional object. We examine the roles played by the temperature profile, the nozzle shear rate and the polymer viscoelasticity. This approach first requires development of thermal imaging methods to properly ascertain the polymer temperature profile during welding and development of fracture strength methods to isolate fracture to the weld zone. We use this data to construct an effective weld time.

We compare these results to our simple model of the non-isothermal extrusion process to explore the effects that typical printing conditions and material rheology have on the conformation of a polymer melt. In particular, we incorporate both stretch and orientation using the Rolie-Poly constitutive equation to examine the melt structure as it flows through the nozzle, the subsequent alignment with the build plate and the resulting deformation due to the fixed nozzle height, which is typically less than the nozzle radius.

In this presentation, we demonstrate that Additive Manufacturing (3D printing) is a viable approach to rapidly prototype personalised fins for surfboards [1]. Surfing is an iconic sport that is extremely popular in coastal regions around the world. The manufacturing of commercial surfboard fins is based on injection molding. This mold making process is very expensive for one-off designs; hence, they are only used for running vast numbers of standard hydrofoil fins. While this approach works for the masses, it does not offer any room for creating custom fins. In contrast, our fins are designed for the individual user. We use computer aided design and 3D printing utisiling a wide range of composite materials, e.g. ABS, carbon fibre, fibre glass and amorphous thermoplastic polyetherimide resins (ULTEM). The mechanical properties of 3D printed and commercial fins were characterised using a custom-build setup for evaluating flexibility and modulus values. The mechanical properties of the 3D fins were found to be comparable to commercial fins. Computational fluid dynamics (CFD) was used to calculate of longitudinal (drag) and tangential (turning) forces, which are important for surfboard manoeuvrability, stability and speed. A commercial tracking system (9 sensors + GPS) was used to trace and evaluate the performance of 3D printed fins under real-world conditions (i.e. surfing waves). This data showed that the surfing performance of 3D printed fins is similar to commercial fins. In summary, we have used materials science and CFD modeling to drive the development of Additive Manufacturing of 3D printed fins for surfboards.

[1] See https://youtu.be/96Zysk7WgVs

As vehicles become increasingly lightweighted to improve fuel economy, there will be greater need for recycling these alloys. Recycling the alloys will save energy (re-melting is far less energy-intensive than primary smelting) while lowering the cost of lightweight alloys. For high-value recycling, it is imperative to sort accurately to maintain the specific properties the material was alloyed to demonstrate. The state-of-the-art sorting methods are spectroscopic – they are expensive and have a fundamentally low signal-to-noise ratio for light elements, necessitating integration times of more than a minute. Long measurement times and high costs limit the economic incentive for recycling. We present a fast, accurate, and inexpensive alloy detection method based on a simple electrochemical mechanism.