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Fused filament fabrication (FFF) has become a preferred method for additive manufacturing due to its cost-effectiveness and flexibility. However, the parts built using FFF process suffer from lower mechanical strength compared to that fabricated using traditional method. In this work, an in-process laser heating method was presented to heal residual stress, therefore improve mechanical behavior along in-plane direction. The enhancement in tensile strength and elongation of fabricated samples with the utilization of laser heating have been demonstrated. In addition, models and hypothesis on the transformation of microstructure were proposed and verified by experimental data. With the utilization of laser pre-deposition heating, tensile strength of printed polyether ether keton (PEEK) part along in-plane direction increased by 11.4%, thus reached 93.5% that of the bulk material property. The fracture behavior was also altered from brittle to stretchable with visible necking effect, backed up with both tensile curve and scanning electron microscope images independently.

Material extrusion-based polymer 3D printing, one of the most commonly used additive manufacturing processes for thermoplastics and composites, has drawn extensive attention due to its capability and cost effectiveness. However, the low surface finish quality of the printed parts remains a drawback due to the nature of stacking successive layers along one direction and the nature of rastering of the extruded tracks of material. In this work, an in-process thermal radiation-assisted, surface reflow method is demonstrated that significantly improves the surface finish of the sidewalls of printed parts. It is observed that the surface finish of the printed part is drastically improved for both flat and curved surfaces. The effect of surface reflow on roughness reduction was characterized using optical profilometry and scanning electron microscopy (SEM), while the local heated spot temperature was quantified using a thermal camera.

Fused Filament Fabrication (FFF) 3D printing provides an effective solution for fabrication of custom components at affordable cost and in short time. Nevertheless, relative to the conventional methods, the anisotropic properties exhibited by FFF 3D printed parts cause the mechanical strength to be less satisfactory. In order to resolve the problem, we propose an in-process laser local pre-deposition heating (LLPH) method, which is capable of enhancing thermal relaxation at inter-layer interface and reinforcing inter-layer adhesion, that ultimately resulted in an increase in tensile strength along the build direction. This improvement in tensile strength of the build parts with in-process laser power has been demonstrated in this manuscript. Besides, the subsequent relevance with polymer relaxation, reptation and entanglement has been discussed. As verified by mechanical testing, tensile strength was improved by 350% compared to control sample and 99.5% isotropy was achieved (build-direction strength divided by in-plane strength) with the application of laser. Scanning Electron Microscope was used to make observation of isotropic behavior at inter-layer interface.

Metal forming is often performed at elevated temperatures, typically above the recrystallization temperature of metals, which results in a reduction in yield stress during forming. Similar reduction in yield stress can also be achieved by simultaneous application of ultrasonic energy during deformation. The resulting softening of metals causes a reduction in the forming forces and increased ductility. A thorough understanding of the effect of ultrasonic energy irradiation during deformation on the microstructure is lacking which seems to be inhibiting wider adoption of ultrasonic energy in more manufacturing processes. In this manuscript, a detailed analysis of the microstructure of aluminum 6061 alloy and copper, which have identical Faced-Center Cubic crystal structure but different stacking fault energies, has been presented. Focus has been placed on the differences between their microstructure evolution behaviors after deformation under simultaneous application of ultrasonic energy. These differences have been distinctly highlighted using Electron Backscatter Diffraction (EBSD) and TEM analysis. EBSD analysis revealed assistance to subgrain formation due to ultrasonic energy. It was also observed that due to lack of dynamic recovery, copper underwent discontinuous dynamic recrystallization (DDRX) during ultrasonic energy assisted deformation. On the other hand, the recrystallization mechanism in Al6061 alloy was found to be geometric dynamic recrystallization (gDRX). The insights obtained in this work potentially advance the understanding of mechanisms governing microstructure evolution during ultrasonic energy assisted deformation and establish analogy between the mechanisms governing thermomechanical processing and ultrasonic energy assisted deformation.

Industrial robots, as mature and high-efficient equipment, have been applied to various fields, such as vehicle manufacturing, product packaging, painting, welding, and medical surgery. Most industrial robots are only operating in their own workspace, in other words, they are floor-mounted at the fixed locations. Just some industrial robots are wall-mounted on one linear rail based on the applications. Sometimes, industrial robots are ceiling-mounted on an X-Y gantry to perform upside-down manipulation tasks. The main objective of this paper is to describe the NeXus, a custom robotic system that has been designed for precision microsystem integration tasks with such a gantry. The system tasks include assembly, bonding, and 3D printing of sensor arrays, solar cells, and microrobotic prototypes. The NeXus consists of a custom designed frame, providing structural rigidity, a large overhead X-Y gantry carrying a 6 degrees of freedom industrial robot, and several other precision positioners and processes. We focus here on the design and precision evaluation of the overhead ceiling-mounted industrial robot of NeXus and its supporting frame. We first simulated the behavior of the frame using Finite Element Analysis (FEA), then experimentally evaluated the pose repeatability of the robot end-effector using three different types of sensors. Results verify that the performance objectives of the design are achieved.

Acoustoplastic Metal Direct-write (AMD), a recently demonstrated metal direct manufacturing technique, uses acoustic energy to enable deformation and deposition of voxels of fully dense material from metal filaments. Voxel by voxel, this technique is capable of creating high density (> 99.5%) metal parts at room temperature and in ambient conditions without post-processes. To understand the microstructure evolution of the component during the fabrication process, Electron Backscatter Diffraction (EBSD) analysis was performed on three successive layers in a built part. No significant effect of the deposition of additional material was observed on the lower layers. Hence, by manipulating the microstructure of each voxel during deposition process, the microstructure of the bulk of the component can be potentially controlled.

Fused Filament Fabrication (FFF) 3D printing has become an effective way to fabricate custom parts at low cost and fast speed. However, due to anisotropic properties of FFF 3D printed parts, their mechanical strength is unsatisfactory compared to those of parts made using traditional methods. To address this issue, an in-process laser local pre-deposition heating (LLPH) method is reported to increase thermal relaxation at inter-layer interface, for improvement of inter-layer adhesion, and therefore tensile strength in the build direction. The effect of laser power on tensile strength, and in-depth investigation of polymer relaxation, reptation and entanglement are presented. 178% increase in tensile strength and an isotropy value of 82.8% (build-direction strength divided by build-plane strength) were achieved. Isotropic behavior at inter-layer interface was observed using Scanning Electron Microscope.

Fused filament fabrication (FFF) technology has been a cost-effective option in the additive manufacturing industry. It, however, still faces drawbacks in terms of tolerance, accuracy, surface finish and material property anisotropy that prevent it from applications in engineering production environment. To address the issue of material property anisotropy, authors had reported an in-process laser local pre-deposition heating (LLPH) method to increase the inter-layer interface temperature during FFF printing. As a result, interpenetrating inter-layer diffusion is achieved to a larger extent, and thereby higher part strength in the build direction is achieved. In the current work, a detailed analysis of the temperature history of the inter-layer interface with and without LLPH method has been presented. The effect of increase in the thermal bonding potential due to the use of LLPH method on the interlayer bond toughness and the peak flexural strength of the components has been presented. A 77% increase in the interlayer bond toughness has been demonstrated.

It is now well established that simultaneous application of acoustic energy during deformation results in lowering of stresses required for plastic deformation. This phenomenon of acoustic softening has been used in several manufacturing processes, but there is no consensus on the exact physics governing the phenomenon. To further the understanding of the process physics, in this manuscript, after-deformation microstructure of aluminium samples deformed with simultaneous application of kilohertz range acoustic energy was studied using Electron-Backscatter Diffraction analysis. The microstructure shows evidence of acoustic energy enabled dynamic recovery. It is found that the subgrain sizes increase with an increase in acoustic energy density applied during deformation. A modified Kocks-Mecking (KM) model for crystal plasticity has been used to account for the observed acoustic energy enabled dynamic recovery. Using the modified KM model, predicted stress versus strain curves were plotted and compared with experimental results. Good agreements were found between predictions and experimental results. The manuscript identifies an analogy between microstructure evolution in hot deformation and that in acoustic energy assisted deformation.

In this work the process of Acoustoplastic Metal Direct-write (AMD) is introduced for the first time. Millimeter-scale 3D aluminum articles were printed to demonstrate the process feasibility. Evidence of process-induced inter-layer and intra-layer mass transport resulting in metallurgical bonding across voxels was obtained. During voxel formation, a process temperature rise of 5 ° Celsius from a process ambient temperature of 25 ° Celsius was recorded. In addition, acoustic energy-induced microstructural changes during process were observed in the material. The work presented here not only demonstrates the feasibility of a new non-melt fusion room temperature metal 3D printing approach—capable of producing metals with more than 99 percent density—but also presents both observational study and an initial theoretical basis upon which a new athermal microstructural transformation process may be understood

Material extrusion-based 3D printing processes have shown importance in the overall development of the field of additive manufacturing and displayed tremendous potential to becoming a cross-cutting tool for research, engineering, developmental work in a wide array of disciplines. In the context of the Fused Deposition Modeling (FDM, one form of Materials extrusion-based 3D printing), one of the main process issues lies in the property anisotropy of parts built using this method, even with process optimization. To address this issue, we report a near-IR laser-based pre-deposition heating method to locally heat up the region of an existing layer near the nozzle before an extrudate comes in contact with the heated region. This in-process approach raises the inter-layer interface temperature to above the critical temperature to increase the interpenetrating diffusion, and therefore the inter-layer bond strength. A 50% increase in the inter-layer bond strength in parts built with this approach is demonstrated. The in-process pre-deposition local heating approach reported here represents an effective means to increase the inter-layer bond strength, and property isotropy of FDM parts. Further, this approach is capable of real-time monitoring and controlling of temperatures at the inter-layer and inter-filament interfaces across the entire volume of a built part, allowing control of the physics of the FDM process to achieve desired mechanical properties.

One of the fundamental issues in the Fused Filament Fabrication (FFF) additive manufacturing process lies in the mechanical property anisotropy where the strength of the FFF-3D printed part in the build-direction can be significantly lower than that in other directions. The physical phenomenon that governs this issue is the coupled effect of macroscopic thermal mechanical issues associated with the thermal history of the interface, and the microscopic effect of the polymer microstructure and mass transfer across interfaces. In this study it was found that the use of 34.4 kHz ultrasonic vibrations during FFF-3D printing results in an increase of up to 10% in the interlayer adhesion in Acrylonitrile Butadiene Styrene (ABS), comparing the printing in identical thermal conditions to that in conventional FFF printing. This increase in the interlayer adhesion strength is attributed to the increase in polymer reptation due to ultrasonic vibration-induced relaxation of the polymer chains from secondary interactions in the interface regions.

Concentrated solar power plants (CSPs) are gaining momentum due to their potential of power generation throughout the day for base load applications in the desert regions with extremely high direct normal irradiance (DNI). Among various types of the CSPs, solar tower power technologies are becoming the front runners especially in the United States and around the world with the possibility to compete with traditional power generation technologies in terms of efficiency and levelized cost of electricity (LCOE). A bibliometric analysis of the publications on the CSP systems and components since 1990 shows a total of 6400+ publications and reveals an exponential growth due to reasons that CSP systems promises a lot of potential as the future large scale power source for varied applications. This review consolidates the benefits and challenges of the CSP technologies particularly in the desert regions. Thorough literature analysis as well as the meteorological data projects the trend that the CSP systems would become a reality in the Middle East and North Africa (MENA), Australia, Southwestern region of the United States, Southwestern part of China and China/Mongolia border with high direct normal irradiance. However, enormous amount of support and capital investments are needed for making these CSP systems realistic as there is not much power grid network in existence. It is evident that there are multiple challenges specifically in water consumption, materials design and development for the optimum heat transfer fluid, thermal energy storage and receiver subsystems in addition to commercial viability and environmental impacts. Each of the challenges is discussed in detail and suggestions are made to address the challenges.

There is a strong motivation to explore the possibility of harnessing solar thermal energy around the world, especially in locations with temperate weather. This review discusses the current status of heat transfer fluid, which is one of the critical components for storing and transferring thermal energy in concentrating solar power systems. Various types of heat transfer fluids including air, water/steam, thermal oils, organic fluids, molten-salts and liquid metals are reviewed in detail, particularly regarding the melting temperature, thermal stability limit and corrosion issues. Stainless steels and nickel based alloys are the typical piping and container materials for heat transfer fluids. Stability of the stainless steels and alloys while in contact with heat transfer fluids is very important for the longevity of concentrating solar power systems. Corrosion properties of stainless steels and nickel based alloys in different heat transfer fluids are discussed in terms of corrosion rates.

A numerical model was developed to capture the charge-mass transport in electrochemical nanomanufacturing processes based on mixed-conducting solid electrolyte material systems. This model was verified by the matching of numerical predictions and experimental measurements of process parameters. The model was also used to predict parameters affecting ionic current flow, and to study the temporal and spatial transport properties of solid electrolyte silver sulfide during an electrode dissolution process. Conditions in which phase separation could occur in silver sulfide were found. Enhanced transport properties due to confinement in lateral dimensions were also observed through the developed model.

A new solid-state electrochemical patterning technique was applied to fabrication of high-resolution silver bowtie antennas and hexagonal arrays. These silver nanofeatures were used to investigate the relation among surface enhanced Raman scattering (SERS) enhancement factor (EF), extinction, local electromagnetic (EM) field maxima of the features. It is found that spectral extinction property or the plasmonic resonance of a given SERS substrate alone is not sufficient for determining optimal EF; the number of points of high local EM field, or ‘hot spots’, and the distribution of those high-field spots, too, play a role. Copyright © 2014 John Wiley & Sons, Ltd.

The 3D Thermal modeling utilizes a Finite Differencing heat alteration method augmented with empirical boundary conditions is employed to develop 3D thermal model for the integration of thermoelectric modules with proton exchange membrane fuel cell stack. Hardware-in-Loop was designed under pre-defined drive cycle to obtain fuel cell performance parameters along with anode and cathode gas flow-rates and surface temperatures. The fuel cell model is used to conjugate the experimental boundary conditions with the Finite Differencing code, which implemented heat generation across the stack to depict the chemical composition process. The structural and temporal temperature contours obtained from this model are in compliance with the actual recordings obtained from the infrared detector and thermocouples. The model is harmonized with thermo-electric modules with a modeling strategy, which enables optimize better temporal profile across the stack. This study presents the improvement of a 3D thermal model for proton exchange membrane fuel cell stack along with the interfaced thermo-electric module. The model provided a virtual environment using a model-based design approach to assist the design engineers to manipulate the design correction earlier in the process and eliminate the need for costly and time consuming prototypes.

As AM technologies become increasingly recognized, manufacturing industries have started to consider AM as one of the enabling technologies that will transform the paradigm of manufacturing. In aerospace industries, companies have embraced AM in the belief that it will become critical to their competitiveness. In biomedicine industries, AM is considered to be the most promising manufacturing technology to achieve customized medicine and treatment in the future. In addition, with digitalized information exchange and process management, AM is also regarded integral to the so-called “Industry 4.0” revolution, which enables intelligent and agile manufacturing via the integration with various tools including internet of things and machine–human connectivity and interactions.

Additive manufacturing (AM) or three-dimensional (3D) printing is the process of creating 3D objects or products, layer by layer, from a 3D digital model. The 3D digital model can be created from CAD, CT, MRI, or laser scanning. AM is the reverse process of traditional manufacturing technologies, such as machining, in which one starts with a block of material and subsequently, the material is removed in a subtractive process forming the final desired part.

The metallic powder bed fusion (PBF) marketplace has been growing rapidly in the second decade of the twenty-first century. The technology has been incorporated into design, engineering, and manufacturing. This chapter will provide insight into the current status of the global 3D printing marketplace with emphasis on additive manufacturing activities and how they are impacting the global supply base. 3D printing will have a major influence on global supply chain logistics and traditional supply chain establishments.

The idea of producing a 3 dimensional object layer by layer came about long before the development of ideas around additive manufacturing. The first concept patented can perhaps be traced back to Peacock for his patented laminated horse shoes in 1902. Half a century later in 1952, Kojima demonstrated the benefits of layer manufacturing processes. A number of additional patents and demonstrations took placed in the time period of 60–80 s that further solidified the idea of producing a 3 dimensional object using a layer wide approach and in the meantime set the stage for introduction and development of processes based on this principle to produce physical prototypes.

A series of steps goes into the process chain required to generate a useful physical part from the concept of the same part using additive manufacturing processes.

Frequency dependence in phonon surface scattering is a debated topic in fundamental phonon physics. Recent experiments and theory suggest such a phenomenon, but an independent agreement between the two remains elusive. We report low-temperature dependence of thermal conductivity in silicon nanowires fabricated using a two-step, metal-assisted chemical etch. By reducing etch rates down to 0.5 nm/s from the typical100 nm/s, we report controllable roughening of nanowire surfaces and selectively focus on moderate roughness scales rather than the extreme scales investigated previously. This critically enables direct comparison with perturbation-based spectral scattering theory. Using experimentally characterized surface roughness, we show that a multiple scattering theory provides excellent agreement and explanation of the observed low-temperature dependence of rough surface nanowires. The theory does not employ any fitting parameters. A 5-10 nm roughness correlation length is typical in metal-assisted chemical etching and resonantly scatters dominant phonons in silicon, leading to the observed ~T(1.6-2.4) behavior. Our work provides fundamental and quantitative insight into spectral phonon scattering from rough surfaces. This advances applications of nanowires in thermoelectric energy conversion.

Silicon is an excellent transparent material for building IR micro-optical elements such as holographic and blazed gratings, and curvilinear micro-lenses. Shaping this material in 3D with mirror quality finish and single-digit microscale resolution is challenging due to its brittleness and high-melting point. To achieve these patterning characteristics, electron-beam grayscale lithography is typically selected to pattern a 2.5D feature onto a resist thin-film. Subsequently, the film features are transferred into the underlying silicon substrate by deep-reactive ion etching (DRIE) [1]. Small variations in the resist thickness lead to large shape distortions and reduced patterning repeatability. Further, the direct-write nature of e-beam lithography provides for slow throughput. Developing an alternative, parallel and scalable method to nanopatterning silicon with 2.5D geometrical control may impact emerging areas such as the design of sub-wavelength photonic and micro-optic elements for silicon photonics applications. Micro and nanoscale patterning of inorganic semiconductors (e.g. Silicon) requires traditional micromachining processes such as plasma-assisted etching (e.g. DRIE) and wet-etching (e.g. KOH etching). Neither of the aforementioned processes offer the capability to control the geometry in 3D with resolution in the nanoscale range. Thus, it is desirable to develop a low-temperature, low-stress and ambient approach to nanostructuring silicon in 3D. Wet etching approaches are good candidates for achieving such goal because they bypass the need for high-temperature processing and stressing materials beyond the elastic limit. Yet, they still rely on lithographical steps and offer limited sidewall control, restricting the scope of features it can produce. In recent literature, catalyst-based wet etching processes such as metal-assisted chemical etching (MACE) have been shown to pattern high-aspect ratio structures in semiconductors [2–3]. Some researchers have achieved control over the etch profile and etching direction, generating a limited set of interesting 3D objects [4–6]. The degrees of freedom in MACE patterning are still highly constrained due to limited control of the catalyst motion. Additionally, thin-film based MACE relies on intermediate 2D masking steps to pattern the catalyst which are often lithographical. Thus, this indirect approach to patterning silicon increases lead time and processing costs. In this paper, Mac-imprint, a direct imprint configuration of MACE, is introduced to overcome these fundamental barriers. It relies on the use of a catalytic stamp immersed in the etchant and brought against a silicon chip to selectively dissolve it at contact points. Stamps can be reused multiple times to pattern substrates with lifetimes that are dependent solely on its chemical and mechanical degradation. This process is inherently non-lithographic and occurs at room temperature. As a demonstration of its high-resolution capabilities, silicon wafers were patterned with a sinusoidal wave whose pitch and amplitude were 1 μm and 250 nm, respectively. The patterned surface RMS error from the ideal surface was measured to be 13 nm. The key drawback of this approach is the generation of porous defects near the vicinity of the contact interface between stamp and substrate. Its spatial distribution is qualitatively discussed in the context of the diffusion model of MACE [7].

Semiconductor nanowires have potential applications in photovoltaics, batteries, and thermoelectrics. We report a top-down fabrication method that involves the combination of superionic-solid-state-stamping (S4) patterning with metal-assisted-chemical-etching (MacEtch), to produce silicon nanowire arrays with defined geometry and optical properties in a manufacturable fashion. Strong light emission in the entire visible and near infrared wavelength range at room temperature, tunable by etching condition, attributed to surface features, and enhanced by silver surface plasmon, is demonstrated.

Self-similar Sierpinski carpet fractals were fabricated using a new nanopatterning technique, i.e. solid-state superionic stamping (S4), to study the effect of feature size on plasmon-enhanced Raman scattering. A real-time Raman image showing electromagnetic (EM) field enhancement contrast is demonstrated. The effects were studied and explained in the context of modes of surface plasmon excitation. Additionally, we find that the EM field enhancement supported by the fractals extends further spatially as compared to continuous Ag surfaces. Copyright © 2010 John Wiley & Sons, Ltd.

Cathodoluminescence spectroscopy has been performed on silver nanoparticles in a scanning electron microscopy setup. Peaks appearing in the visible range for particles fabricated on silicon substrate are shown to arrive from excitation of out-of-plane eigenmodes by the electron beam. Monochromatic emission maps have been shown to resolve spatial field variation of resonant plasmon mode on length scale smaller than 25 nm. Finite-difference time-domain numerical simulations are performed for both the cases of light excitation and electron excitation. The results of radiative emission under electron excitation show an excellent agreement with experiments. A complete vectorial description of induced field is given, which complements the information obtained from experiments.

In this letter we demonstrate the possibility of using the solid ionic conductor Ag2S for the fabrication of sub-100 nnm features in a Cu film. We also evaluate the physical properties of the Cu–Ag2S interface through an electroimpedance spectroscopy study. Cu meander lines of 60 nm in width were obtained and the screening length and the surface adatom concentration of Cu on the interface were also evaluated to be 20 nm and 1012/cm2 respectively.

Artificially engineered metamaterials have emerged with properties and functionalities previously unattainable in natural materials. The scientific breakthroughs made in this new class of electromagnetic materials are closely linked with progress in developing physics-driven design and novel parallel fabrication methods. For example, a smooth superlens has been demonstrated with 30-nm imaging resolution, or 1/12 of the corresponding wavelength, far below the diffraction limit. Similarly, a photoswitchable optical negative-index material has been printed, showing a remarkable tuning range of refractive index in the communication wavelength. New frontiers are being explored as intrinsic limitations challenge the scaling of microwave metamaterial designs to optical frequencies. These novel metamaterials promise an entire new generation of passive and active optical elements, such as paper-thin superlenses and modulators.

Planning for the operation of a railway system is a very complicated task. At the center stage of this planning work is timetabling. In this work we present TrainWorld, a powerful, sophisticated software system that, among other capabilities, is able to solve for high-quality timetables for real-sized, complicated railways. Testing with Taiwan Railways Administration (TRA) data demonstrates the ability of TrainWorld in solving for real-world timetables. The TRA system has 224 stations, approximately three-quarters of the 1085Km railway are double-tracked, and the rest are single-tracked. The system offers close to 1000 daily services in its 18-hour operation hours. Some busy stations carry more than 280 services a day, resulting in an eight-minute average headway between trains. TrainWorld is able to solve a timetable for such a system in approximately 70 hours, and the result is close to the real timetable.Copyright © 2013 by ASME

Railway system operation is a very complicated task and must be supported by the coordination of several systems including engineering, transportation, locomotive maintenance and management, ticket system and passengers service, etc. Ideally, a modern railway enterprise information system should be an integrated, consisted, and site-opened database to support railway system operation. However, multiple isolated applications instead of one integrated enterprise information system are often formed due to historical factors such as independent departments, budgetary constraint and application requirements diversification. Take Taiwan Railways Administration (TRA) as an example, four major departments have their own support systems and databases that store critical planning and operational data. Those systems are isolated and can hardly communicate with each other. As a result, most cross-systems information analyses or data reference for decision making are done manually, which significantly affect the organizational efficiency of TRA. To address the aforementioned issues, a railway decision support platform (RDSP) for integrating the legacy systems (databases) is proposed in this paper. RDSP is designed to be a railway enterprise information system that supports the critical functions of data warehouse and decision support. Furthermore, RDSP is built by integrating the existing legacy systems rather than by building it from scratch. A data bridging system (HDBS) including four modules are design and implemented, input module for connecting the external data sources, output module for exporting integrated report or dumping data by predefined criteria for other systems, configuration module with a web-based user interface for setting up the periodic operations of data input or output tasks, and DB connection module for connecting external databases. Various types of railway system data are designed in RDSP schema and collected, including facilities, timetable, train services records, tickets, centralized traffic control (CTC) system records, and automatic train protection (ATP) system records. RDSP provides a system framework to integrate many isolated island-style databases that currently exist in TRA, and can form a cross-enterprise database that serves as the primary and only data platform. To demonstrate the efficacy of the RDSP, a spatiotemporal ticket-selling analysis report, a train delay cause analysis report, and a timetable planning software (TrainWorld) are designed on top of it. In the future, RDSP will play a major supportive role in infrastructure maintenance, operations, decision support, and planning.

We report the fabrication of degenerately doped silicon (Si) nanowires of different aspect ratios using a simple, low-cost and effective technique that involves metal-assisted chemical etching (MacEtch) combined with soft lithography or thermal dewetting metal patterning. We demonstrate sub-micron diameter Si nanowire arrays with aspect ratios as high as 180:1, and present the challenges in producing solid nanowires using MacEtch as the doping level increases in both p- and n-type Si. We report a systematic reduction in the porosity of these nanowires by adjusting the etching solution composition and temperature. We found that the porosity decreases from top to bottom along the axial direction and increases with etching time. With a MacEtch solution that has a high [HF]:[H2O2] ratio and low temperature, it is possible to form completely solid nanowires with aspect ratios of less than approximately 10:1. However, further etching to produce longer wires renders the top portion of the nanowires porous. (Some figures may appear in colour only in the online journal)

In this paper, we report direct patterning of metal nanostructures using an embossed solid electrochemical stamp. Microforming of solid superionic stamps using Si templates-analogous to polymer patterning in nano-imprint lithography-is explored. Silver sulfide (Ag2S)-a superionic conductor with excellent micro-forming properties-is investigated as a candidate material. Important parameters of the superionic stamp, including mechanical behavior, material flow during forming, and feature recovery after embossing are studied. Excellent feature transferability during embossing as well as etching is observed. To illustrate the capability of this approach silver nano-antennas with gaps 6 mm is also demonstrated. Embossing based metal patterning allows fabrication beyond two-dimensional nanofabrication and several patterning schemes are reported., 11 pages (double spaced), 7 figures, 1 table, continuation of work submitted to MRS Spring 2009

Electrochemical dissolution of ionic species into a solid is an area of great interest in several fields including nanoscale patterning and energy storage. Such dissolution is strongly influenced by several factors e.g., work function difference, dislocation density, grain size, and number of grain boundaries. These parameters are strongly influenced by mechanical deformation of the ionic conductor. Here we characterize such a system of silver (Ag) and silver sulfide (Ag2S), where incorporation of Ag into the solid ionic conductor, Ag2S, is dramatically influenced by mechanical deformation. We show more than three-fold dissolution rate enhancement when the polycrystalline conductor is compressed to one-third of its original size. We attribute this enhancement to increased dislocation density which is supported by the high current densities observed during dissolution. Additionally, reduced electronic currents suggest most of this contribution comes from increased reaction at the metal-conductor interface. Our studies have important applications in areas involving ionic transport including direct metal patterning and energy storage technology.

We report a top-down fabrication method that involves the combination of superionic-solid-state-stamping (S4) patterning with metal-assisted-chemical-etching (MacEtch), to produce silicon nanowire arrays with defined geometry and optical properties in a manufacturable fashion.

We describe in this chapter development of plasmonic optical antennas for light concentration and near-field enhancement. A set of bow tie nanoantennas are fabricated and characterized with optical and electron excitation methods. Optical spectroscopy of these subwavelength antennas displays pronounced extinction peaks at resonant wavelength, showing total extinction cross sections as much as 10 times of their physical dimensions. On the other hand, coherent excitation of the bow tie antennas allows tuning the peak wavelength of the scattered light by changing the periodicity. Under dark-field microscopy, we observed the scattered waves from arrays of different bow tie antennas in complete visible spectrum. The local resonant modes of the bow tie antennas are also probed by focused electrons. Such cathodoluminescence spectroscopy reveals the fine details of enhanced field on the optical nanoantennas at resolution down to 20 nm. Finally, we show examples of surface-enhanced Raman spectroscopy on the nanoantennas. Effective designs based on local enhancement and radiation engineering of the plasmonic optical antennas would promise revolutionary changes in highly compact and integrated photonics for photon energy conversion, adaptive sensing, and image processing.

The recent growth in optoelectronics, nanoelectronics, nanooptics, and chemical and biological sensing has been fueled by the ability to fabricate nanostructures with ever smaller features. However, several significant constraints still remain in terms of cost, limited pattern size, processing conditions, pattern flexibility, and so on. Fabrication of features as small as 50 nm at ambient conditions with high pattern flexibility and low cost remains a serious challenge. Here we report a new solid-state electrochemical imprinting process that is carried out at ambient conditions, requires nominal pressure and very low electric potential, eliminates any liquid electrolytes, shows very high reproducibility, and promises the capability to scale up for large area patterning while retaining a significant cost advantage. Through combination of the best merits of nanoimprint lithography, micro forming, and the solid-state electrochemical imprinting technique, S4, (recently introduced by Hsu et al., Nano Lett., 2007, 7, 446; and Schultz et al., J. Vac. Sci. Techol. B, 2007, 25, 2419), we show a very high pattern flexibility to create nano-scale metallic features.As a first step, we use a micro-forming-like embossing process to engrave nano-scale features onto a solid electrolyte tool surface using an e-beam fabricated Si mold. Silver sulfide, Ag2S, is used as a solid electrolyte because of its favorable mechanical properties for micro forming and its excellent electrochemical properties. This ionic compound is ductile and has a relatively low yield stress at 80MPa. Followed by embossing, the patterned solid electrolyte surface is then used to carry out the S4 process, creating a negative image on a metallic substrate. This process eliminates the costly Focused Ion Beam milling used by Hsu et al. to create features on the electrolyte tool. It is also highly favorable for large-area patterning as well as mass-production of metallic substrates restricted only by the capability to fabricate the mold at first step. The embossed solid-electrolyte tool surface can be easily trimmed off with a microtome; the tool can then be re-used for embossing and patterning metallic substrates.Using this process we demonstrate the ability to fabricate silver nanostructures with features 30 sq. mm. Such large scale fabrication is highly desired for applications like biomimetics and patterning for superhydrophobic surfaces.

The pressing need for energy conversion devices with higher efficiency and the pursuit for nano-scale sensing have called for intense research in the use of plasmonic nanostructures. In this work, we discuss fabrication and characterization of bowtie antennas with gaps down to 10 nm for optical frequencies. With structures as simple as equilateral triangles, we observed an extinction cross section of ten times the geometrical cross section, which is twice the value previously reported. Finally, we measured the scattering profile of a series of bowtie antennas with increased size using confocal microscopy.