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Polymer filaments represent the fundamental materials employed in fused filament fabrication additive manufacturing. This paper uses an innovative nondestructive evaluation technique for gauging the elastic properties of these polymer filaments. The method hinges on acoustic wave scattering theory, wherein a polymer filament is immersed in water and exposed to an incident acoustic wave. The waves scattered from the cylinder contain crucial information concerning the elastic properties of the filament. To extract these properties, an inverse method is applied which compares the resonance frequencies of the scattered signal with those anticipated based on a theoretical model. To improve the performance of this method in identifying the resonance frequencies, the derivative of the unwrapped phase within the backscattered pressure spectrum is analyzed. This is an advantageous approach as it can be equally applied to both experimental and theoretical pressure spectra, simplifying the task of identification of resonance frequencies considerably. The method's effectiveness is exemplified through its application to an aluminum rod followed by its application to two polymer filaments. Comparing the elastic constants of the polymer filaments determined through the proposed method with values reported in the literature underscores the method's capability to accurately measure the elastic constants of polymer filaments. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles (MNPs) in a suspension have been shown to change resistance by an order of magnitude based on an applied field. We have prepared the MNPs samples with matrices of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PDOT:PSS) or H2O, and Co MNPs and carried out the magnetoresistive measurements. A switch-based model is used to understand the mechanism for the change in resistance. We further propose devices for memory based on MNPs. Building blocks for these devices are then fabricated using additive manufacturing techniques and measurements of change in resistance under the influence of a magnetic field are conducted. Niche applications of additive manufacturing techniques to the fabrication of these devices are proposed. The device uses MNPs suspended in a soft matter matrix. The application of a magnetic field is used to move the MNPs to or away from electrical contacts. Depending on the change of position of the MNPs, a connection is either made or broken, which can act as a 1 or a 0. The measured change in resistance observed in such devices is more than an order of magnitude depending on the matrix solution. The proposed device and its manufacturing process could be feasible for magnetic memory and in-memory computing devices on any flexible substrates. [ABSTRACT FROM AUTHOR]

Physical models can help improve solar cell efficiency during the design phase and for quality control after the fabrication process. We present a data-driven approach to inverse modeling that can predict the underlying parameters of a finite element method solar cell model based on an electroluminescence (EL) image of a solar cell with known cell geometry and laser scribed defects. For training the inverse model, 75 000 synthetic EL images were generated with randomized parameters of the physical cell model. We combine 17 deep convolutional neural networks based on a modified VGG19 architecture into a deep ensemble to add uncertainty estimates. Using the silicon solar cell model, we show that such a novel approach to data-driven statistical inverse modeling can help apply recent developments in deep learning to new engineering applications that require real-time parameterizations of physical models augmented by confidence intervals. The trained network was tested on four different physical solar cell samples, and the estimated parameters were used to create the corresponding model representations. Resimulations of the measurements yielded relative deviations of the calculated and the measured junction voltage values of 0.2% on average with a maximum of 10%, demonstrating the validity of the approach. [ABSTRACT FROM AUTHOR]

Radio-frequency (RF) micro-electro-mechanical-system (MEMS) switches are widely used in communication devices and test instruments. In this paper, we demonstrate the structural design and optimization of a novel RF MEMS switch with a straight top electrode. The insertion loss, isolation, actuator voltage, and stress distribution of the switch are optimized and explored simultaneously by HFSS and COMSOL software, taking into account both its RF and mechanical properties. Based on the optimized results, a switch was fabricated by a micromachining process compatible with conventional IC processes. The RF performance in the DC to 18 GHz range was measured with a vector network analyzer, showing isolation of more than 21.28 dB over the entire operating frequency range. Moreover, the required actuation voltage was about 9.9 V, and the switching time was approximately 33 μs. A maximum lifetime of 109 switching cycles was obtained. Additionally, the dimension of the sample is 1.8 mm × 1.8 mm × 0.3 mm, which might find application in the current stage. HIGHLIGHTS: • A new type of top electrode for a switch is proposed in this paper. The sample size is 1.8 mm × 1.8 mm × 0.3 mm. The design was miniaturized to make it easy to integrate. • The switch has a lower drive voltage (9.9 V) and a faster response time, so that the switching time was increased to 33 μs. In addition, the isolation was greater than 21.28 dB over the operating frequency range, achieving excellent RF performance. • A micro-machining process compatible with the traditional integrated circuit process was used to manufacture the switch, and the design realized high reliability. The maximum lifetime of the switch is 109 cycles. [ABSTRACT FROM AUTHOR]

A fundamental problem in the direct manufacturing of flexible devices is the low melting temperature of flexible substrates, which hinders the development of flexible electronics. Proposed here is an electron-cyclotron-resonance sputtering system that can batch-fabricate devices directly on flexible substrates under a low temperature by virtue of the polariton energy transfer between the plasma and the material. Flexible graphene nanosheet-embedded carbon (F-GNEC) films are manufactured directly on polyimide, polyethylene terephthalate, and polydimethylsiloxane, and how the substrate bias (electron energy), microwave power (plasma flux and energy), and magnetic field (electron flux) affect the nanostructure of the F-GNEC films is investigated, indicating that electron energy and flux contribute to the formation of standing graphene nanosheets in the film. The films have good uniformity of distribution in a large size (17 mm × 17 mm), and tensile and angle sensors with a high gauge factor (0.92) and fast response (50 ms) for a machine hand are obtained by virtue of the unique nanostructure of the F-GNEC film. This work sheds light on the quantum manufacturing of carbon sensors and its applications for intelligent machine hands and virtual-reality technology. HIGHLIGHTS: • Graphene nanosheet films are manufactured directly on flexible substrates at a low temperature due to polariton energy transfer. • Tensile and angle sensors with a high gauge factor (0.92) and fast response (50 ms) for a machine hand are obtained. • This work sheds light on the quantum manufacturing of carbon sensors and its applications for intelligent machine hands. [ABSTRACT FROM AUTHOR]

Phase Change Memory (PCM) is a leading candidate for next generation data storage, but it typically suffers from high switching (RESET) current density (20–30 MA/cm2). Interfacial Phase Change Memory (IPCM) is a type of PCM using multilayers of Sb2Te3/GeTe, with up to 100× lower reported RESET current compared to the standard Ge2Sb2Te5-based PCM. Several hypotheses involving fundamentally new switching mechanisms have been proposed to explain the low switching current densities, but consensus is lacking. Here, we investigate IPCM switching by analyzing its thermal, electrical, and fabrication dependencies. First, we measure the effective thermal conductivity (∼0.4 W m−1 K−1) and thermal boundary resistance (∼3.4 m2 K GW−1) of Sb2Te3/GeTe multilayers. Simulations show that IPCM thermal properties account only for an ∼13% reduction of current vs standard PCM and cannot explain previously reported results. Interestingly, electrical measurements reveal that our IPCM RESET indeed occurs by a melt-quench process, similar to PCM. Finally, we find that high deposition temperature causes defects including surface roughness and voids within the multilayer films. Thus, the substantial RESET current reduction of IPCM appears to be caused by voids within the multilayers, which migrate to the bottom electrode interface by thermophoresis, reducing the effective contact area. These results shed light on the IPCM switching mechanism, suggesting that an improved control of layer deposition is necessary to obtain reliable switching. [ABSTRACT FROM AUTHOR]

Noble-metal-based surface-enhanced Raman spectroscopy (SERS) substrates can be employed as catalysts capable of generating hot electrons to drive chemical reactions of target molecules adsorbed on their surface. However, the localized surface plasmons excited from pure noble metals generally exhibit relatively low hot-electron utilization efficiency with the reactants owing to charge carrier recombination. This problem can be solved by integrating heterogeneous structures with the noble metal. Herein, we describe the fabrication of bifunctional SERS substrates by constructing Au@Ag, Au@Ag2S, and Au@SiO2 core-shell nanoparticles and evaluate the effects of the three heterostructures (Au cores encapsulated by shells composed of metal, semiconductor, or insulator) on the hot-electron transfer efficiency by in situ monitoring of the catalytic dimerization of p-nitrophenol to form p,p′-dimercaptoazobenzene under 632.8 nm laser illumination. The developed SERS strategy opens up new opportunities for exploring hot-electron-induced reactions as well as providing a useful reference for photocatalyst selection. [ABSTRACT FROM AUTHOR]

We investigated the effects of nitrogen doping in amorphous carbon layers on the diffusion of fluorine atoms based on density functional theory calculations. For N doping at both substitutional and interstitial sites, the F atom binds to the surrounding C atoms rather than the N atom during structural relaxation due to the electrostatic repulsion between N and F atoms. Furthermore, the diffusion barriers associated with the F atom passing by the N atom are extremely large (5.19 eV for substitutional N doping and 4.77 eV for interstitial N doping), primarily due to the electrostatic repulsion originating from the strong electronegativities of both atoms. The results clearly show that N doping increases the diffusion barrier of the F atom, thereby suppressing the diffusion of the F atom. The findings provide information about the role of N doping in amorphous carbon layers and yield insights for improving the fabrication processes of future integrated semiconductor devices. [ABSTRACT FROM AUTHOR]

Scalable fabrication of atomically thin hexagonal boron nitride (h-BN) films is highly important for the future implementation of this two-dimensional dielectric in various applications. In this contribution, we report on systematical growth experiments of few-layer thick h-BN, synthesized by molecular beam epitaxy (MBE), on crystalline Ni films deposited on MgO(111). The samples are studied using scanning electron microscopy, atomic force microscopy, Raman spectroscopy, and synchrotron-based grazing incidence diffraction. Growth parameters for the realization of continuous h-BN films with high structural quality are presented and discussed. Additionally, our study also aims at gaining insight into the nucleation and growth behavior of h-BN on the Ni surface, which is crucial for achieving further improvement in terms of crystal quality and thickness homogeneity of h-BN layers grown not only by MBE but also by other methods. [ABSTRACT FROM AUTHOR]

In this work, we theoretically investigate the material and transport properties of strained chevron graphene nanoribbons (CGNRs) which can be easily synthesized by the bottom-up fabrication technology. Because of the unique atomic structures, the energy and pressure of the CGNRs vary asymmetrically along compressive and tensile strains. Under the two strain directions, the CGNRs' bandgaps and carrier effective masses in the conduction band minimum and the valence band maximum are all reduced. The transport properties are promoted accordingly, except some negative differential conductance behaviors caused by energy state localizations. When the tensile strains exceed a criterion value, the C–C bonds in the inner sides of the CGNR corners will be broken in sequence. Meanwhile, the CGNRs can restore their initial unstrained states rapidly when the strains are removed. However, if the broken bonds are saturated by foreign atoms, such as H, a novel kind of stable carbon structure will be obtained. The investigations suggest possible applications of strain engineered CGNRs in transport devices. [ABSTRACT FROM AUTHOR]

The generation of a rectifying metal-semiconductor contact forms a charge depletion layer in the semiconductor surface. The resulting space charge leads to a surface band bending and the formation of a Schottky barrier. The present study introduces an unconventional method to measure and monitor the surface band bending during metal atom deposition by recording the displacement current between the metal and the semiconductor. Magnesium atoms are evaporated at 130 K onto hydrogen-passivated p-Si(001) surfaces. During deposition, the time-dependent reverse current in the diode is detected. A sharp current peak of a few nA can be attributed to the displaced charge when the first monolayers of the Mg film are formed. The currents are proportional to the number of Mg atoms impinging onto the surface. Integrating the observed displacement currents over time yields the total space charge densities at the interface between 8 and 23 nC/cm 2. This is in excellent agreement with the calculated value for a Schottky barrier of 0.5 eV and assuming flatband condition for hydrogen-passivated Si(001) surfaces. [ABSTRACT FROM AUTHOR]

In spite of being known since a century ago, high operational voltage and low sound pressure level have limited wide applications of thermophones. In recent years, utilizing graphene in thermophones has been proposed as an attractive solution, which is benefiting from high electrical and thermal conductivity and inherent high surface area, to enhance the heat transfer and lowering the required electrical input power. In this paper, a laser-scribed graphene (LSG) layer is utilized to realize graphene-based thermophones, which provide a considerably high sound pressure level of about 80 dB (Pin = 0.6 W). Furthermore, a layer of carbon nanotubes (CNTs) is incorporated on the prepared LSG sheets, which benefits from both randomly oriented CNTs over the surface of reduced graphene oxide (rGO) sheets and suspended CNTs, which act like heat exchanger nano-fins on rGO sheets and efficient heat generators, respectively. The input voltage for CNT/LSG based thermophones is measured 7 times lower than the prepared LSG samples, in order to generate the same sound pressure level (75 dB). The achieved sound pressure, normalized to the input power, has increased about 80 dB by incorporating CNTs which entitles the proposed structure as a promising candidate for novel thermophones. [ABSTRACT FROM AUTHOR]

In order to know the threshold quantity of the zinc interstitials that contributes to an increase in carrier concentration in the Al-doped ZnO (AZO) films and their effect on the overall microstructure and optoelectronic properties of these films, in this work, Zn-rich-AZO and ZnO thin films are fabricated by adding excess zinc (from a zinc metallic target) during their deposition in RF magnetron sputtering and are then investigated using a wide range of experimental techniques. All these films are found to grow in a ZnO hexagonal wurtzite crystal structure with strong (002) orientation of the crystallites, with no indication of Al2O3, metallic Zn, and Al. The excessively introduced zinc in these AZO and/or ZnO films is found to increase the shallow donor level defects (i.e., zinc interstitials and oxygen-related electronic defect states), which is found to significantly increase the carrier concentration in these films. Additionally, aluminum is seen to enhance the creation of these electronic defect states in these films, thereby contributing more to the overall carrier concentration of these films. However, carrier mobility is found to decrease when the carrier concentration values are higher than 4 × 1020 cm−3, because of the electron-electron scattering. Whereas the optical band gap of the ZnO films is found to increase with increasing carrier concentration because of the Burstein-Moss shift, these decrease for the AZO films due to the band gap narrowing effect caused by excess carrier concentration. [ABSTRACT FROM AUTHOR]

Lens fabrication by droplet evaporation has attracted a lot of attention since the fabrication approach is simple and moldless. Droplet position accuracy is a critical parameter in this approach, and thus it is of great importance to use accurate methods to realize the droplet position alignment. In this paper, we propose an electrohydrodynamic (EHD) assisted droplet alignment method. An electrostatic force was induced at the interface between materials to overcome the surface tension and gravity. The deviation of droplet position from the center region was eliminated and alignment was successfully realized. We demonstrated the capability of the proposed method theoretically and experimentally. First, we built a simulation model coupled with the three-phase flow formulations and the EHD equations to study the three-phase flowing process in an electric field. Results show that it is the uneven electric field distribution that leads to the relative movement of the droplet. Then, we conducted experiments to verify the method. Experimental results are consistent with the numerical simulation results. Moreover, we successfully fabricated a crater lens after applying the proposed method. A light emitting diode module packaging with the fabricated crater lens shows a significant light intensity distribution adjustment compared with a spherical cap lens. [ABSTRACT FROM AUTHOR]

Cuprous (Cu2O) and cupric (CuO) oxide thin films have been deposited by radio frequency magnetron sputtering with two different oxygen partial pressures. The as-deposited copper oxide films were subjected to post-annealing at 300 °C for 30 min to improve the microstructural, morphological, and optical properties of thin films. Optical absorption studies revealed the existence of a large number of subgap states inside CuO films than Cu2O films. Cu2O and CuO thin film transistors (TFTs) were fabricated in an inverted staggered structure by using a post-annealed channel layer. The field effect mobility values of Cu2O and CuO TFTs were 5.20 × 10−4 cm2 V−1 s−1 and 2.33 × 10−4 cm2 V−1 s−1, respectively. The poor values of subthreshold swing, threshold voltage, and field effect mobility of the TFTs were due to the charge trap density at the copper oxide/dielectric interface as well as defect induced trap states originated from the oxygen vacancies inside the bulk copper oxide. In order to study the distribution of the trap states in the Cu2O and CuO active layer, the temperature dependent transfer characteristics of transistors in the temperature range between 310 K and 340 K were studied. The observed subgap states were found to be decreasing exponentially inside the bandgap, with CuO TFT showing higher subgap states than Cu2O TFT. The high-density hole trap states in the CuO channel are one of the plausible reasons for the lower mobility in CuO TFT than in Cu2O TFT. The origin of these subgap states was attributed to the impurities or oxygen vacancies present in the CuO channel layer. [ABSTRACT FROM AUTHOR]

Superhydrophilic–superhydrophobic patterned surfaces constitute a branch of surface chemistry involving the two extreme states of superhydrophilicity and superhydrophobicity combined on the same surface in precise patterns. Such surfaces have many advantages, including controllable wettability, enrichment ability, accessibility, and the ability to manipulate and pattern water droplets, and they offer new functionalities and possibilities for a wide variety of emerging applications, such as microarrays, biomedical assays, microfluidics, and environmental protection. This review presents the basic theory, simplified fabrication, and emerging applications of superhydrophilic–superhydrophobic patterned surfaces. First, the fundamental theories of wettability that explain the spreading of a droplet on a solid surface are described. Then, the fabrication methods for preparing superhydrophilic–superhydrophobic patterned surfaces are introduced, and the emerging applications of such surfaces that are currently being explored are highlighted. Finally, the remaining challenges of constructing such surfaces and future applications that would benefit from their use are discussed. HIGHLIGHTS: •The fundamental theories of surface wettability are introduced to explain the spreading of a droplet on a solid surface. •The methods for constructing superhydrophilic–superhydrophobic patterned surfaces are described regarding hierarchical structure fabrication, chemical modification, and wettability patterning. •The emerging applications of such surfaces are highlighted, including droplet arrays, cell arrays, biosensors, microfluidic systems, and environmental protection. • The remaining challenges of preparing such surfaces and future applications that would benefit from their use are discussed. [ABSTRACT FROM AUTHOR]

We developed a simple and controllable nanogap fabrication method called "activation." In the activation technique, electromigration is induced by a field emission current passing through the nanogaps. Activation enables the electrical properties of Ni nanogaps in a vacuum to be controlled and is expected to be applicable to Au nanogaps even in ambient air. In this study, we investigated the activation properties of Au nanogaps in ambient air from a practical point of view. When activation was performed in ambient air, the tunnel resistance of the Au nanogaps decreased from over 100 TX to 3.7 Mτ as the preset current increased from 1 nA to 1.5 μA. Moreover, after activation in ambient air with a preset current of 500 nA, the barrier widths and heights of the Au nanogaps were estimated using the Simmons model to be approximately 0.5 nm and 3.3 eV, respectively. The extracted barrier height is smaller than that of 4.6 eV resulting from activation in a vacuum and much lower than the work function of bulk Au. This difference implies the presence of atmospherically derived moisture or contamination adsorbed on the nanogaps. These results suggest that activation can be utilized for Au nanogap fabrication even in ambient air. [ABSTRACT FROM AUTHOR]

Nanostructured bimetallic reactive multilayers can be conveniently produced by ball milling of elemental powders. This research explores the non-equilibrium microscale conductive thermal transport in ball-milled particulate fractal structures during fabrication, arising from heat dissipation by bulk plastic deformation and surface friction. Upon impactor collisions, temperature increments are determined at interface joints and domain volumes using Green's functions, mirrored by source images with respect to warped ellipsoid domain boundaries. Heat source efficiency is calibrated via laboratory data to compensate for thermal expansion and impactor inelasticity, and the thermal analysis is coupled to a dynamic mechanics model of the particulate fracture. This thermomechanical model shows good agreement with the fractal dimensions of the observed microstructure from ball milling experiments. The model is intended to provide a comprehensive physical understanding of the fundamental process mechanism. In addition, the model could serve as a realtime thermal observer for closed-loop process control, as well as for interfacial diffusion and reaction analysis during ball milling. [ABSTRACT FROM AUTHOR]

This paper reports a previously unreported anomaly that occurs when attempting to perform deep, highly anisotropic etches into fused silica using an Inductively-Coupled Plasma (ICP) etch process. Specifically, it was observed that the top portion of the etched features exhibited a substantially different angle compared to the vertical sidewalls that would be expected in a typical highly anisotropic etch process. This anomaly has been termed as "faceting." A possible explanation of the mechanism that causes this effect and a method to eradicate it has been developed. Additionally, the method to eliminate the faceting is demonstrated. It is theorized that this faceting is a result of the interaction of the electro-potential electrical fields that surround the patterned nickel layers used as a hard mask and the electrical fields directing the high-energy ions from the plasma to the substrate surface. Based on this theory, an equation for calculating the minimum hard mask thickness required for a desired etch depth into fused silica to avoid faceting was derived. As validation, test samples were fabricated employing hard masks of thicknesses calculated based on the derived equation, and it was found that no faceting was observed on these samples, thereby demonstrating that the solution performed as predicted. Deep highly anisotropic etching of fused silica, as well as other forms of silicon dioxide, including crystalline quartz, using plasma etching, has an important application in the fabrication of several MEMS, NEMS, microelectronic, and photonic devices. Therefore, a method to eliminate faceting is an important development for the accurate control of the dimensions of deep and anisotropic etched features of these devices using ICP etch technology. [ABSTRACT FROM AUTHOR]

This report describes the fabrication, characterization, and transfer of ultra-compact thin-film magnetless Faraday rotators to silicon photonic substrates. Thin films of magnetization latching bismuth-substituted rare-earth iron garnets were produced from commercially available materials by mechanical lapping, dice polishing, and crystal-ion-slicing. Eleven-lm-thick films were shown to retain the 45° Faraday rotation of the bulk material to within 2° at 1.55 lm wavelength without repoling. Anti-reflection coated films evince 0:09 dB insertion loses and better than -20 dB extinction ratios. Lower extinction ratios than the bulk are ascribed to multimode propagation. Significantly larger extinction ratios are predicted for single-mode waveguides. Faraday rotation, extinction ratios, and insertion loss tests on He-ion implanted slab waveguides of the same material yielded similar results. The work culminated with bond alignment and transfer of 7 μm-thick crystal-ion-sliced 50×480 μm² films onto silicon photonic substrates. [ABSTRACT FROM AUTHOR]

A method for generating high quality multilayer blazed gratings using ion beam assisted deposition is proposed and analyzed with numerical simulations. Conventional fabrication methods for multilayer blazed gratings are limited by unwanted smoothing of the surface profile during multilayer deposition. By contrast, we demonstrate that our proposed method is capable of producing gratings that retain a nearly ideal blazed grating profile after the deposition of an arbitrary number of layers. Through numerical analysis, we establish the conditions in which this procedure produces a high quality multilayer blazed grating. These gratings would be suitable for use in the extreme ultraviolet or soft X-ray regime. We also discuss how the control parameters may be selected to optimize the gratings formed in an experiment. [ABSTRACT FROM AUTHOR]

Conventional machining of metallic glass is a challenge due to its amorphous nature and inherent brittleness. This work investigates the non-conventional machining of Zr-based metallic glass, Vitreloy-1, using laser processing with a Yb-fiber laser and an electro-jet milling (EJM) process. Grooves were fabricated using these techniques in Vitreloy disks of 1.5 mm thickness to study the machining behavior. The grooves formed with the laser were smooth, although there was observation of dross at the groove edges, which was selectively removed through the EJM process. On the other hand, the EJM process was found to produce dross-free grooves; however, it caused leaching of zirconium from the groove zone, which was understood from the elemental maps obtained using the scanning electron microscope. A comparison of the laser grooving and EJM grooving process was also carried out using Vickers micro-indentation. Indentations made close to the groove edge in laser grooved samples developed shear bands but the same were absent in the EJM grooved samples. Since shear banding tendency is an indicator of the inherent toughness of the metallic glass, the laser grooving technique is found more suitable for nonconventional machining of metallic glass. [ABSTRACT FROM AUTHOR]

Laser material deposition (LMD) is a laser-based additive manufacturing process that is widely used for fabrication, diversification, and repair of parts in various industries. LMD processes can be distinguished by the form of the filler material. In terms of availability, storage, safe handling, and price, filler material in wire form often has advantages over powdered materials. In this work, the influence of tool path planning on the deposition accuracy and the process stability of LMD with coaxial wire feed is studied. The laser beam and wire are arranged coaxially to each other, with the wire being fed through the inside of an annular shaped laser beam without any shadowing. While the process is completely directionally independent, the stability is linked to the wire feed rate, laser power, and process feed rate. Additionally, the ratio between the wire and the laser beam diameter affects the stability. Movement of the wire inside the annular beam may result in shadowing and process abort. Changes in the working distance (defocusing) lead to changes in the beam diameter, which affects the process stability. This can result in imperfections, i.e., bonding defects, or pores in the tracks and layers that will add up in the built components and must be avoided for imperfection-free three-dimensional geometries. On even surfaces, the geometry of the deposited tracks is controlled by changing the laser power, the wire feed speed, and the process speed. When building three-dimensional parts, critical points of the tool path planning are acute angled corners and crossing points. In the experiments, boundaries for the process stability in critical points are established and track geometries are compared to previous results. Furthermore, different strategies for the avoidance of material accumulation at the start, end, and crossing points are investigated. The different approaches are discussed, and finally an outlook for further use and possible applications is given. [ABSTRACT FROM AUTHOR]

Joining of materials, with a strong bearing on the manufacturing industry, has remained an active area of research for decades. The demand for the fabrication of a variety of miniature components has placed more emphasis, in particular, on the welding of thin materials. Welding of thin materials is a challenging task, and more so if they are foils of dissimilar materials, as even a tiny weld flaw invariably can lead to a rapid blemishing of the job. Aluminum with its good thermal and electrical properties, low specific weight, and low cost is often considered a preferred material in many applications. In this communication, the authors present the result of a feasibility study of laser-assisted welding of stainless steel (AISI 304) and pure aluminum foils. A repetitive single-mode nanosecond fiber laser was used to carry out the weld in the lap joint configuration. Welding between the foils was done in the weld brazing mode. Electron microscopy, microhardness measurements, and tensile testing were carried on the weld to evaluate its microstructural and mechanical properties. In the course of welding, stainless steel remained in solid state, while aluminum underwent localized melting over a narrow zone at the interface. The use of very short duration repetitive laser pulses with lower heat input restricted the bulk diffusion of elements across the interface and thereby the generation of the intermetallic compound/second phase with minimum Heat Affected Zone and almost no distortion. This study establishes a nanosecond laser-assisted welding technique as an option for microwelding between stainless steel and aluminum foil. [ABSTRACT FROM AUTHOR]

For the prediction of residual distortions of high-performance steel alloy parts induced by laser melting deposition (LMD), two efficient simulation methods are developed, which are the improved thermal-mechanical coupled method and the multiscale method. In the improved thermal-mechanical coupled method, the detailed loading process of the moving laser heat source is omitted, and the deposited coarse blocks are used to divide the LMD parts, which can improve the efficiency of mechanism exploration for the LMD process. Based on the eight-layer line deposition model, the length range of the deposited coarse blocks that can improve the computational efficiency under the premise of accuracy is explored, which is 5–8 mm. The distortion of the substrate after printing two-layer multipath part by pragmatic deposition strategies is accurately predicted by this method, which is consistent with the experimental measurement. The deviation between the predicted maximum distortion and the actual value is only 0.8%. Furthermore, a multiscale method based on the inherent strain method is also adopted. The two simulation methods are used to predict the distortion of the substrate after depositing pragmatic square frame structure. The deviations of the maximum distortion predicted by the improved thermal-mechanical coupled method and the multiscale method are 5.2% and 4.3%, respectively. The time-consuming of the multiscale method is only 2.8% of the former. For the direct prediction of distortion results of large-sized LMD parts in engineering, the advantages of the multiscale method are significant. [ABSTRACT FROM AUTHOR]

Wave-permeable materials with certain metallic film patterns are of importance for electromagnetic wave transportation. Laser processing showed obvious advantages when fabricating such materials. The article studied the etching effects of key laser parameters on Al-coated composite materials. It is found that (1) a balance of etching quality and efficiency could be obtained when the operating laser energy density is about five to eight times that of the ablation threshold; (2) the effects of the laser focal spot size and the pulse overlap are interrelated to decide machining precision; and (3) the laser scanning trajectory affects the appearance of the etched surface, possibly due to the fiber bundle braided direction. The findings could benefit similar wave-permeable materials laser processing. [ABSTRACT FROM AUTHOR]

While the process of metal induced crystallization (MIC) is widely used in the fabrication of thin film electronic devices, its application to the field of thermoelectrics is fairly new. Especially, its implementation in the field of the classic thermoelectric material SiGe could lead to a low cost approach by combining the benefits of low thermal budget, self-doping, and thin film and sputter deposition compatibility. In this work, samples consisting of SiGe/Al multilayers deposited on aluminum oxide based substrates have been prepared. Special emphasis was put on the ratio of Al to SiGe and the resulting changes in transport properties during annealing. On one hand, a certain amount of Al is needed to ensure a complete MIC process for the SiGe, but on the other hand, an excess of Al results in a metallic system with low thermoelectric efficiency. In-situ characterization during annealing of the samples was carried out via x-ray diffraction, electrical resistivity, and Seebeck measurements. [ABSTRACT FROM AUTHOR]

In this work, Electro-Inductive wave (EIW) propagation phenomenon is employed in order to introduce a polarization rotation capability in a rectangular patch antenna. The EIW propagation phenomenon is used to master the field distribution within the rectangular patch, and hence, to change the polarization of a patch antenna, which is shown to change from linear to circular polarization. EIW propagation is supported by a chain of Complementary Split Ring Resonators printed in a rectangular patch antenna at specific locations. This principle of operation is demonstrated with the design, fabrication, and measurement of antenna prototypes. Experimental results confirm numerical analysis, providing a simple antenna configuration with polarization variation capabilities, extendable to multiple configurations, in radiated waves as well as in guided wave phenomena. [ABSTRACT FROM AUTHOR]

The organic permeable base transistor is a vertical transistor architecture that enables high performance while maintaining a simple low-resolution fabrication. It has been argued that the charge transport through the nano-sized openings of the central base electrode limits the performance. Here, we demonstrate by using 3D drift-diffusion simulations that this is not the case in the relevant operation range. At low current densities, the applied base potential controls the number of charges that can pass through an opening and the opening is the current limiting factor. However, at higher current densities, charges accumulate within the openings and in front of the base insulation, allowing for an efficient lateral transport of charges towards the next opening. The on-state in the current-voltage characteristics reaches the maximum possible current given by space charge limited current transport through the intrinsic semiconductor layers. Thus, even a small effective area of the openings can drive huge current densities, and further device optimization has to focus on reducing the intrinsic layer thickness to a minimum. [ABSTRACT FROM AUTHOR]

The role of the inversion layer on injection and recombination phenomena in light emitting diodes (LEDs) is here studied on a multilayer (ML) structure of silicon nanocrystals (Si-NCs) embedded in SiO2. Two Si-NC LEDs, which are similar for the active material but different in the fabrication process, elucidate the role of the non-radiative recombination rates at the ML/substrate interface. By studying current- and capacitance-voltage characteristics as well as electroluminescence spectra and time-resolved electroluminescence under pulsed and alternating bias pumping scheme in both the devices, we are able to ascribe the different experimental results to an efficient or inefficient minority carrier (electron) supply by the p-type substrate in the metal oxide semiconductor LEDs. [ABSTRACT FROM AUTHOR]

Microscopic Fourier-transform infrared (FT-IR) spectra are measured for a Cu/low-k interconnect structure using polarized IR light for different widths of low-k spaces and Cu lines, and for different heights of Cu lines, on Si substrates. Although the widths of the Cu line and the low-k space are 70 nm each, considerably smaller than the wavelength of the IR light, the FT-IR spectra of the low-k film were obtained for the Cu/low-k interconnect structure. A suitable method was established for measuring the process-induced damage in a low-k film that was not detected by the TEM-EELS (Transmission Electron Microscope-Electron Energy-Loss Spectroscopy) using microscopic IR polarized light. Based on the IR results, it was presumed that the FT-IR spectra mainly reflect the structural changes in the sidewalls of the low-k films for Cu/low-k interconnect structures, and the mechanism of generating process-induced damage involves the generation of Si-OH groups in the low-k film when the Si-CH3 bonds break during the fabrication processes. The Si-OH groups attract moisture and the OH peak intensity increases. It was concluded that the increase in the OH groups in the low-k film is a sensitive indicator of low-k damage. We achieved the characterization of the process-induced damage that was not detected by the TEM-EELS and speculated that the proposed method is applicable to interconnects with line and space widths of 70 nm/70 nm and on shorter scales of leading edge devices. The location of process-induced damage and its mechanism for the Cu/low-k interconnect structure were revealed via the measurement method. [ABSTRACT FROM AUTHOR]

A rolling-based printing approach for transferring arrays of patterned micro- and nano-structures directly from rigid fabrication substrates onto flexible substrates is presented. Transfer-printing experiments show that the new process can achieve high-yield and high-fidelity transfer of silicon nanomembrane components with diverse architectures to polyethylene terephthalate substrates over chip-scale areas (>1 x 1 cm²) in <0.3 s. The underlying mechanics of the process are investigated through finite element simulations of the contact and transfer process. These mechanics models provide guidance for controlling the contact area and strain in the flexible substrate during transfer, both of which are key for achieving reproducible and controlled component transfer over large areas. [ABSTRACT FROM AUTHOR]

In this study, a combination of electrospinning and laser texturing is introduced as a novel method for increasing the biocompatibility of metal implants. Besides having a rough laser treated surface, the implant benefits from the high porosity and better wettability of an electrospun fibrous structure, which is a more favorable environment for cell proliferation. Titanium samples were patterned using a nanosecond laser beam and were placed as collectors in an electrospinning machine. They were then soaked in simulated body fluid for four weeks. Energy Dispersive X-ray and X-Ray Diffraction results indicate significantly more hydroxyapatite formation on laser treated samples with nanoscale fibers deposited on their surface. This shows that having a laser treated surface underneath the fibrous layer can improve short-term biocompatibility even before degradation of fibers. The thermal conductivity of the electrospun layer, measured using a Hot Disk Transient Plane Source instrument and computer code, was shown to be considerably lower than that of titanium and very close to bone. The presence of this layer can therefore be beneficial in making the implant more compatible to a biological medium. In case of dental implants, it was shown that this layer can act as a thermal barrier while a hot beverage is consumed and it can decrease the temperature rise by about 60%, which avoids any possible damage to newly formed cells during the healing period. [ABSTRACT FROM AUTHOR]

A structure featuring vertical directional coupling of long-range surface plasmon polaritons between strip waveguides at λ = 1.55 μm is investigated with the aim of producing efficient elements that enable optical multilayer routing for 3D photonics. We have introduced a practical computational method to calculate the interaction on the bent part. This method allows us both to assess the importance of the interaction in the bent part and to control it by a suitable choice of the fabrication parameters that helps also to restrain effects due to fabrication issues. The scheme adopted here allows to reduce the insertion losses compared with other planar and multilayer devices. [ABSTRACT FROM AUTHOR]

Carbon nanotube thin film transistors (CNT-TFTs) are promising candidates for future high performance and low cost macro-electronics. However, most of the reported CNT-TFTs are fabricated in small quantities on a relatively small size substrate. The yield of large scale fabrication and the performance uniformity of devices on large size substrates should be improved before the CNT-TFTs reach real products. In this paper, 25 200 devices, with various geometries (channel width and channel length), were fabricated on 4-in. size ridged and flexible substrates. Almost 100% device yield were obtained on a rigid substrate with high out-put current (>8 μA/μm), high on/off current ratio (>105), and high mobility (>30 cm²/V·s). More importantly, uniform performance in 4-in. area was achieved, and the fabrication process can be scaled up. The results give us more confidence for the real application of the CNT-TFT technology in the near future. [ABSTRACT FROM AUTHOR]

The Ni contact layer was deposited on semi-insulating 4H-SiC substrate by magnetron sputtering. The as-deposited samples were treated by rapid thermal annealing (RTA) and KrF excimer laser thermal annealing (LTA), respectively. The RTA annealed sample is rectifying while the LTA sample is Ohmic. The specific contact resistance (ρc) is 1.97 × 10-3 Ω·cm2, which was determined by the circular transmission line model. High resolution transmission electron microscopy morphologies and selected area electron diffraction patterns demonstrate that the 3C-SiC transition zone is formed in the near-interface region of the SiC after the as-deposited sample is treated by LTA, which is responsible for the Ohmic contact formation in the semi-insulating 4H-SiC. [ABSTRACT FROM AUTHOR]

This work analyzes carrier transport, the relaxation of non-equilibrium charge, and the electronic structure of fluorinated graphene (FG) films with graphene quantum dots (GQDs). The FG films with GQDs were fabricated by means of chemical functionalization in an aqueous solution of hydrofluoric acid. High fluctuations of potential relief inside the FG barriers have been detected in the range of up to 200 mV. A phenomenological expression that describes the dependence of the time of non-equilibrium charge emission from GQDs on quantum confinement levels and film thickness (potential barrier parameters between GQDs) is suggested. An increase in the degree of functionalization leads to a decrease in GQD size, the removal of the GQD effect on carrier transport, and the relaxation of non-equilibrium charge. The study of the electronic properties of FG films with GQDs has revealed a unipolar resistive switching effect in the films with a relatively high degree of fluorination and a high current modulation (up to ON/OFF~104-105) in transistor-like structures with a lower degree of fluorination. 2D films with GQDs are believed to have considerable potential for various electronic applications (nonvolatile memory, 2D connections with optical control and logic elements). [ABSTRACT FROM AUTHOR]

By hybrid integration of plasmonic and dielectric waveguide concepts, it is shown that nearly perfect coherentabsorption can be achieved in a co-propagating coupler geometry. First, the operating principle of the proposed device is detailed in the context of a more general 2 × 2 lossy coupler formalism. Then, it is shown how to tune the device in a wide region of possible working points, its broadband operation, and the tolerance to fabrication uncertainties. Finally, a complete picture of the electromagnetic modes inside the hybrid structure is analyzed, shining light onto the potentials which the proposed device holds in view of classical and quantum signal processing, nonlinear optics, polarization control, and sensing. [ABSTRACT FROM AUTHOR]

This paper presents simulation, fabrication, and characterization of single-element ultrahigh frequency (100–300-MHz) needle ultrasonic transducers based on 0–3 composite Pb(Zr0.52Ti0.48)O3 (PZT) films prepared by using composite ceramic sol-gel film and sol-infiltration technique. The center frequency of the developed transducer at 300-MHz was the highest frequency of PbTiO3 ceramic-based ultrasonic transducers ever reported. Furthermore, a brief description of the composite model was followed by the development of a new expression for predicting the longitudinal velocity, the clamped dielectric constant, and the complex electromechanical coupling coefficient kt of these films, which is very important in ultrasonic transducer design. Moreover, these parameters are difficult to obtain by measuring the frequency dependence of impedance and phase angle because of the weak signal of the previous 0–3 composite films transducer (>100 MHz). The modeling results show that the Cubes model with a geometric factor n=0.05 fits well with the measured data. This model will be helpful for developing the 0–3 composite systems for ultrahigh frequency ultrasonic transducer design. [ABSTRACT FROM AUTHOR]

Nano-patterned ferroelectric materials have attracted significant attention as the presence of two or more thermodynamically equivalent switchable polarization states can be employed in many applications such as non-volatile memory. In this work, a simple and effective approach for fabrication of highly ordered poly(vinylidene fluoride–trifluoroethylene) P(VDF-TrFE) nanodot arrays is demonstrated. By using a soft polydimethylsiloxane mold, we successfully transferred the 2D array pattern from the initial monolayer of colloidal polystyrene nanospheres to the imprinted P(VDF-TrFE) films via nanoimprinting. The existence of a preferred orientation of the copolymer chain after nanoimprinting was confirmed by Fourier transform infrared spectra. Local polarization switching behavior was measured by piezoresponse force microscopy, and each nanodot showed well-formed hysteresis curve and butterfly loop with a coercive field of ~62.5 MV/m. To illustrate the potential application of these ordered P(VDF-TrFE) nanodot arrays, the writing and reading process as non-volatile memory was demonstrated at a relatively low voltage. As such, our results offer a facile and promising route to produce arrays of ferroelectric polymer nanodots with improved piezoelectric functionality. [ABSTRACT FROM AUTHOR]

We study several parasitic effects on the implementation of a Josephson radiation comb generator based on a dc superconducting quantum interference device (SQUID) driven by an external magnetic field. This system can be used as a radiation generator similarly to what is done in optics and metrology, and allows one to generate up to several hundreds of harmonics of the driving frequency. First we take into account how the assumption of a finite loop geometrical inductance and junction capacitance in each SQUID may alter the operation of the devices. Then, we estimate the effect of imperfections in the fabrication of an array of SQUIDs, which is an unavoidable source of errors in practical situations. We show that the role of the junction capacitance is, in general, negligible, whereas the geometrical inductance has a beneficial effect on the performance of the device. The errors on the areas and junction resistance asymmetries may deteriorate the performance, but their effect can be limited to a large extent by a suitable choice of fabrication parameters. [ABSTRACT FROM AUTHOR]

During the laser-powder bed fusion process on aluminum alloys, instabilities such as spatter ejections result from the laser-matter interaction. These spatters create a variety of defects and affect the mechanical properties of the final parts. To help in understanding this phenomenon, a global method was developed, combining experimental study and image analysis. This system provides statistic information on spatter population (radius, velocity, direction, and emission rate), and the idea of pollutant spatter is defined. Four aluminum alloys are compared. The results show that the oxygen content in the fabrication chamber has no effect on the spatter ejection dynamic. The spatter velocity, angle of ejection, and size increase with intensity. Also, significant differences are noticed between the different alloys. [ABSTRACT FROM AUTHOR]

Fabrication technologies for the semiconductor industry have enabled ever smaller electronic components but now face a fundamental limit in their assembly. As the components get smaller and smaller, the difficulty of assembly increases. At the same time, the number of components per circuit board area is growing, as is the case with LED displays. This in turn calls for an increasing assembly rate. The conventional pick-and-place method can handle approximately 25–30 thousand dies per hour but has increasing limitations when component dimensions are reduced below 150 μm edge length. Laser-induced forward transfer is used as a potential alternative for an assembly of semiconductor components. This technique allows to transfer semiconductor components with an edge length of less than 150 μm to a target substrate. The current process is contactless, damage-free, and has sufficient placement accuracy. If this process is combined with the property of high-pulse repetition rates, it is possible to significantly increase the assembly rate of semiconductor components compared to the current limitations. The aim of this study is to characterize the flight properties of silicon semiconductor components of various dimensions in a laser-driven transfer process using optical imaging methods. This method allows to analyze velocity, the direction of fall, and acceleration of falling components. The results can be used to analyze the transfer behavior of various component sizes and to make estimates of the stability of the transfer process. [ABSTRACT FROM AUTHOR]

Nowadays, customized optomechanics for complex optical setups are increasingly manufactured additively using the polymer-based process of fused filament fabrication. In this article, a kinematic polymer mirror holder is demonstrated, in which the mirror is imprinted and thus fixed against misalignment. Furthermore, the necessary spring system and ball joint are manufactured in a single printing process. This mirror holder can then be embedded into an also printed cage system. Mirror mounts made of different polymers are examined and compared with each other. The mechanical stress induced into the imprinted optic is determined. Regarding the 3D-printed spring system, the angular alignment range as well as the load limits are defined. The reproducibility of the mirror's angular position and the long-term stability together with the influence of thermal cycling is determined. The results will be compared with a conventional, subtractive manufactured metallic optomechanic. [ABSTRACT FROM AUTHOR]