Nonplanar Substrates Research Articles

Super anti‐impact silicone elastomer with shell‐less shear thickening fluid droplets in matrix

AbstractA soft and stretchable safeguarding silicone rubber is obtained by embedding large amount of shell‐less shear thickening fluid (STF) droplets into polydimethylsiloxane (PDMS) matrix through the synergistic process of emulsification and polymerization. Feeding time and temperature are optimized to generate the efficient STFs with 72.2 wt% SiO2 and high thickening viscosity of 6340 Pa·s. The embedding process and the evolution of the shell‐less STF droplets in PDMS matrix are explored by both optical and scanning electronic microscopes. The influence of the STF content on the mechanical and anti‐impact performance of the composites is explored through tensile tests and drop hammer tests. The STF content could be as much as 75 wt%, which enhances not only the softness and stretchability (elongation at break >200%) but also the impact‐protective performance of the silicone rubber. The STF/PDMS composites covering on planar and nonplanar glass substrates demonstrate self‐adaptive protection effect by reducing the force impact peak by 35%, due to the shear thickening and energy absorption of STF in the composites. This study develops a facile and scalable method for the implantation of the STF into polymer matrix, extending the applications of STF/PDMS composites in varied fields.

Scanning Acoustic Microscopy Characterization of Cold-Sprayed Coatings Deposited on Grooved Substrates

AbstractThe effect of non-planar substrate surface on homogeneity and quality of cold-sprayed (CS) deposits was studied by scanning acoustic microscopy (SAM). Fe coatings were cold-sprayed onto Al substrates containing artificially introduced grooves of square- and trapezoid-shaped geometries, with flat or cylindrical bottoms. The Al substrates were either wrought or cold-sprayed, to comprehend their prospective influence on the Fe coatings buildup. SAM was then used to assess morphological properties of the materials from the cross-view and top-view directions. The microstructure below the surface of the studied samples was visualized by measuring the amplitudes of the reflection echoes and the velocity of the ultrasonic waves. The SAM analysis revealed that the regions of coating imperfections around the grooves are larger than what is suggested by standard scanning electron microscopy (SEM) observations. Furthermore, we found that the seemingly non-influenced coating regions that appear perfectly homogeneous and dense in SEM do, in fact, possess heterogeneous microstructure associated with the individual CS nozzle passes.

Conductivity and Flexibility Enhancement of Aerosol-Jet-Printed Sensors Using a Silver Nanoparticle Ink with Carbon Nanotubes

Efforts to miniaturize and customize electronic devices have attracted considerable amounts of attention in many industrial fields. Recently, due to its innovative printing technology with the capability of printing fine features onto non-planar substrates without masks, aerosol jet printing (AJP) is emerging as a promising printed-electronics technology capable of meeting the requirements of various advanced electronic applications. In this research, a novel manufacturing process based on AJP is proposed in order to fabricate highly flexible and conductive customized temperature sensors. To improve the flexibility and conductivity of the printed tracks, a silver nanoparticle/carbon nanotubes composite ink is developed. Customized temperature sensors are then designed and fabricated based on the optimized process parameters of AJP. It was found that the CNTs served as bridges to connect silver nanoparticles and defects, which could be expected to reduce the contact resistivity and enhance the flexibility of the printed sensor.

In Situ Smoothing of Facets on Spalled GaAs(100) Substrates during OMVPE Growth of III-V Epilayers, Solar Cells, and Other Devices: The Impact of Surface Impurities/Dopants.

One possible pathway toward reducing the cost of III-V solar cells is to remove them from their growth substrate by spalling fracture, and then reuse the substrate for the growth of multiple cells. Here we consider the growth of III-V cells on spalled GaAs(100) substrates, which typically have faceted surfaces after spalling. To facilitate the growth of high-quality cells, these faceted surfaces should be smoothed prior to cell growth. In this study, we show that these surfaces can be smoothed during organometallic vapor-phase epitaxy growth, but the choice of epilayer material and modification of the various surfaces by impurities/dopants greatly impacts whether or not the surface becomes smooth, and how rapidly the smoothing occurs. Representative examples are presented along with a discussion of the underlying growth processes. Although this work was motivated by solar cell growth, the methods are generally applicable to the growth of any III-V device on a nonplanar substrate.

Interaction of atmospheric pressure helium plasma jet with non-planar substrates: path selectivity of surface ionization wave

Most surfaces treated by atmospheric pressure plasma jets (APPJs) in practical applications are notably three-dimensional. However, non-planar surfaces exhibit a diverse array of geometries, such as variations in curvature, roughness, and texture, complicating the prediction of surface ionization waves (SIWs) propagation behavior across varied surface shapes, in the absence of sufficient experimental data. In this study, we made measurements of APPJ interactions with the non-planar substrates using the spatio-temporal resolved image method. Non-planar substrates encompassed wavy surfaces, arrayed hemispheres, and randomly textured raised surfaces. We tracked the morphology and velocity of SIW propagation over these surfaces. The results indicate that the SIW propagation on non-planar surfaces is significantly influenced by surface geometry and displays path selectivity, i.e. the SIW tends to propagate along valleys. The average propagation velocity of the SIW increases with the increasing radius of the wavy surface, as well as with the increased height of the arrayed hemispheres. This is attributable to the surface geometry constraining the dispersion of the SIW, causing it to concentrate and propagate in a singular direction. Moreover, the surface geometry markedly affects the distribution of the plasma treatment area, with the plasma inclined to enter valleys (where the light emission is significantly stronger than that of peaks) and to closely adhere to hemispherical surfaces. These patterns suggest a potential positive impact on treating skin surfaces such as pores, reducing bacteria in wrinkles, and addressing pimples.

Photonic curing for innovative fabrication of flexible metal oxide optoelectronics

Flexible optoelectronics, based on non-planar substrates, hold promise for diverse applications such as wearables, health monitors, and displays due to their cost-effective manufacturing methods. Despite the superior properties of metal oxides, the challenge of processing them at high temperatures incompatible with plastic substrates necessitates innovative annealing approaches. Photonic curing, which delivers microsecond to millisecond broadband (200–1500 nm) light pulses on a sample, emerges as a viable solution. Depending on the optical properties, the targeted film absorbs the radiant energy resulting in rapid heating while the transparent substrate absorbs a minimal amount of light and remains at ambient temperature. The light intensity can be high, but since the light pulse is short, the total energy absorbed by the sample remains low and will not damage the plastic substrate. This perspective explores the innovative application of photonic curing to fabricate flexible metal oxide optoelectronics, including thin-film transistors, metal–insulator–metal devices, solar cells, transparent conductors, and Li batteries, emphasizing the conversion of sol–gel precursors to metal oxides. However, this technique was initially developed for sintering metal nanoparticles to conductive patterns and poses intriguing challenges in explaining its mechanism for metal oxide conversion, especially considering the limited absorption of visible light by most sol–gel precursors. The review delves into UV-induced photochemistry, common flexible metal-oxide optoelectronic components, and non-intuitive distinctions between photonic curing and thermal annealing. By elucidating the distinctive role of photonic curing in overcoming temperature-related challenges and advancing the fabrication of flexible metal oxide optoelectronics, this perspective offers valuable insights that could shape the future of flexible optoelectronics.

Controlling Electrodeposition in Nonplanar High Areal Capacity Battery Anodes via Charge Transport and Chemical Modulation.

Controlling the morphological evolution of electrochemical crystal growth in battery anodes is of fundamental and practical importance, particularly towards realizing practical, high-energy batteries based on metal electrodes. Such batteries require highly reversible plating/stripping reactions at the anode to achieve a long cycle life. While conformal electrodeposition and electrode reversibility have been demonstrated in numerous proof-of-concept experiments featuring moderate to low areal capacity (≤3 mA h/cm2) electrodes, achieving high levels of reversibility is progressively challenging at the higher capacities (e.g., 10 mA h/cm2), required in applications. Nonplanar, "3D" electrodes composed of electrically conductive, porous substrates are conventionally thought to overcome trade-offs between reversibility and capacity because they hypothetically "host" the electrodeposits in an electronically conducting framework, providing redundant pathways for electron flow. Here, we challenge this hypothesis and instead show that a nonplanar substrate with moderate electrical conductivity (ideally, with an electrical conductance similar to the ionic conductance of the electrolyte) and composed of a passivated cathode-facing surface efficiently regulates electro-crystallization. In contrast, an architecture with a high intrinsic electrical conductivity or with a high electrical conductivity coating on the front surface results in dominantly out-of-plane growth, making the 3D architecture in effect function as a 2D substrate. Using Zn as an example, we demonstrate that interconnected carbon fiber substrates coated by SiO2 on the front and Cu on the back successfully ushers electroplated Zn metal into the 3D framework at a macroscopic length scale, maximizing use of the interior space of the framework. The effective integration of electrodeposits into the 3D framework also enables unprecedented plating/stripping reversibility >99.5% at high current density (e.g., 10 mA/cm2) and high areal capacities (e.g., 10 mA h/cm2). Used in full-cell Zn||NaV3O8 batteries with stringent N/P ratios of 3:1, the substrates are also shown to enhance cycle life.

Fabrication Aspects and Performance Characterization of α-Al2O3/AlPO4 Based Sandwich Configuration Flow Channel Inserts and Coatings for High Temperature Liquid Metal Applications

Abstract Liquid metals (LMs) exhibit several key characteristics justifying their utilization as coolants and breeders for nuclear fusion reactors and advanced fission reactors. In fusion reactors, the LMs confront an exorbitantly high flow retarding force, due to the magneto-hydro-dynamics (MHD) effect, imposing significant demands on the pumping power and designs of ancillary coolant systems. Corrosion of structural materials leading to activated corrosion products and coolant chemistry control are some of the vital issues common to both fusion and fission reactors employing liquid lead (Pb) and its alloys. To address these concerns, different technological solutions such as flow channel inserts (FCIs) and high temperature compatible corrosion resistant coatings are being investigated to provide a chemical and/or electrical isolation between the LM and structural material for advanced reactors. In this study, three different prototype geometries (circular, square, and 90 deg bend) of steel-insulator-steel sandwich FCIs are fabricated for fusion reactor applications and an extensive characterization of the electrical insulation is performed over an operating temperature range of 100 °C–600 °C. Welding trials and pneumatic pressure tests up to 10 kg/cm2 (g) are performed on the assemblies to validate the electrical and mechanical integrity over typical fusion reactor operational regime. This paper presents detailed fabrication aspects along with quantitative estimations of insulation filling density, electrical insulation performance and, for the first time, a detailed systematic study of insulation degradation resulting from the combined effects of tungsten inert gas (TIG) welding, exposure to pressure and machining operations on these FCIs. The paper also provides critical details derived from the metallurgical examinations and visual observations from the destructive tests executed on the prototypes. Further, from an implementation perspective toward Lead-cooled Fast Reactors (LFRs), a preliminary feasibility assessment of the α-Al2O3/AlPO4 coating is performed through thin film deposition trials on planar and non-planar substrates followed by mechanical characterizations, such as coating thickness, surface roughness, adhesion strength and microhardness. Metallurgical analyses are presented and discussed to assess Pb ingress after 700 h of continuous exposure to molten Pb alloy at 300 °C–400 °C.

Investigation of thermal stress effects during annealing of hafnia-made thin film using molecular dynamics simulations

Hafnia or hafnium oxide is a high-κ dielectric material with paramount importance in the realm of semiconductor devices. Recent advancements in 3D device structures require a few nanometer-thick conformal films on non-planar substrates. During the fabrication stage, the annealing process of thin films has been discovered to mitigate delamination issues at the film-substrate interface. However, it has been observed that the residual stress, which emerges as the film cools to room temperature, may lead to delamination. In this study, we propose an idealized atomistic model to mimic the critical region of a 3D-NAND structure, to get insights into the effect of thermal stress and delamination during the annealing of hafnia-made thin film. We employ molecular dynamics simulation using charge-optimized many-body potential (COMB) to perform heating and cooling simulations for different thicknesses of the hafnia layer. Our results suggest that, during heating, as the annealing temperature increases, the severity of delamination decreases. At extremely low thickness of the hafnia layer, delamination does not occur. However, significant delamination is observed during the cooling process, especially when the high temperature gradient is high.

A reproducible extrusion printing process with highly viscous nanoparticle inks

Abstract Printing of functional materials such as nanoparticle inks is a class of additive fabrication techniques complementary to standard subtractive electronics fabrication techniques such as pcb technology on pcb level or silicon based microelectronics on integrated circuit level. To date the majority of digital printing processes for (micro)electronics is inkjet based. Moreover aerosol jet based printing also establishes itself for printing on non-planar substrates and for materials with higher viscosities. A material deposition technique available since decades and mainly used for dispensing of adhesives and sealing materials is fluid-filament printing. It allows to cover a wide range of materials and viscosities and thus, also holds potential for additive manufacturing of electronics. In this paper we systematically study the influences on fluid filament printing both theoretically taking into account ink and equipment tolerances and experimentally using mainly standard dispensing equipment and two commercial screen printing inks. At the end of the paper we derive recommendations for reproducible printing of conductive lines and pads and give an outlook to printing 2.5D structures.

Antireflective coatings of chitin nanofibers on glass fabricated through electric field deposition

Due to their wide variety of practical applications, antireflective coatings have been studied intensively. In this paper, we developed a novel approach to fabricate antireflective coatings on glass substrate by using charged chitin nanofibers (ChNFs) and electric field deposition. The ChNFs were obtained via ultrasonic treatment of the modified chitin through partial deacetylation, esterification and esterification followed partial deacetylation (dual modification), respectively. The ChNF coatings prepared by applying electric field deposition and using aqueous dispersions of the dual modified ChNFs had antireflective capacity. The effects of electric field intensity, electric field application time and ChNF dispersion concentration on antireflective capacity of the ChNF coatings were studied. The coating obtained by applying 55 V electric field for 5 min and using the dispersion of the dual modified ChNFs with concentration of 0.05 wt% yielded increase in transmittance of a glass substrate (∼ 2.4% at wavelength of 550 nm). The results of this study demonstrate that electric field deposition is a high efficiency and low cost approach to prepare antireflective coatings on large size and nonplanar substrates with charged nanofibers.

Innovative process to obtain thin films and micro-nanostructured ZrN films from a photo-structurable ZrO2 sol-gel using rapid thermal nitridation

Zirconium nitride (ZrN) is widely used in many industrial sectors for its outstanding performances including its mechanical properties, high chemical and thermal stability. Associated with its plasmonic behavior, these properties make ZrN a suitable candidate for optical applications at high temperature or in extreme environments. The authors present an innovative, easy-to-use and rapid process for producing ZrN thin films from a photo-structurable ZrO2 sol-gel using a rapid thermal nitridation (RTN) process. In this process, a ZrO2 sol-gel layer is converted into a ZrN thin film in a few minutes by rapid thermal annealing (RTA) under ammonia gas. Compared to physical or chemical vapor deposition, usually used to produce ZrN thin films, the advantages of the sol-gel method include suitability for non-planar and large substrates and the possibility of nanotexturing of crystallized ZrN surfaces in considerably less time, at a larger scale and at a lower cost. The ZrO2 and ZrN thin films were characterized by Raman spectroscopy, X-ray diffraction and Transmission Electron Microscopy, to confirm complete nitridation. The optical, electrical and tribological properties were also investigated. Finally, the nitridation method was also used on structured ZrO2 layers and showed the versatility of the process e.g. enabling the production of micro-nanostructured ZrN films without using any etching techniques.

Measurement of the bonding energy via non-planar direct bonding

An accurate measurement of the bonding energy of an interface is important in many areas of applied research. We present a novel method for measuring the bonding energy, which is based on the principle of non-planar direct bonding, i.e., direct bonding of originally planar wafers onto non-planar substrates. We discuss in detail the advantages and disadvantages compared to the commonly used double cantilever beam method. To demonstrate the practical relevance, by using the example of glass wafers, the evolution of the bonding energy during different de-bonding steps is investigated, focusing on how the surface shape variations and the surface roughness affects water stress corrosion. We find that the bonding energy in the corroded state is not affected by the original surface shape variations and mid-spatial frequency range roughness, anymore. A molecular mechanism to explain this phenomenon is proposed.

Development of New Magnetron Sputter Deposition Processes for Laser Target Fabrication

Magnetron sputter deposition is an enabling technology for laser target fabrication. Solutions are readily available for the deposition of most sub-micron-thick elemental films on planar substrates. However, major challenges still remain for the development of robust deposition processes in regimes of ultrathick (over μm) coatings and nonplanar substrates. These challenging deposition regimes are directly relevant to laser target applications, including both sphero-cylindrical hohlraums and spherical ablators for inertial confinement fusion (ICF) targets. Understanding underlying physical mechanisms for a specific material system is crucial for process development, given the overall complexity of the deposition process, its nonlinear dependence on deposition parameters, and a very large process space, often precluding conventional process optimization approaches. Here, we describe our approach to developing new deposition processes and give practical advice with examples of new results from our ongoing studies of glassy boron carbide ceramics for next-generation ICF ablators and nonequilibrium gold-tantalum alloys for hohlraums for magnetized ICF schemes. Emphasis is given to two major challenges of ultrathick coatings related to achieving process stability and reducing residual stress.

Machine Learning Enables Process Optimization of Aerosol Jet 3D Printing Based on the Droplet Morphology.

Aerosol jet printing (AJP) is a promising noncontact direct ink writing technology that enables flexible and conformal electronic devices to be fabricated onto planar and nonplanar substrates with higher resolution and less waste. Despite possessing many advantages, the limited electrical performance of microelectronic devices caused by the poor printing quality is still the greatest hurdle to overcome for AJP technology. With the motivation to improve the printing quality, a novel hybrid machine learning method is proposed to analyze and optimize the AJP process based on the deposited droplet morphology in this study. The proposed method consists of classic machine learning approaches, including space-filling-based experimental design, clustering, classification, regression, and multiobjective optimization. In the proposed method, a two-dimensional (2D) design space is fully explored using a Latin hypercube sampling approach for experimental design, and a K-means clustering approach is employed to reveal the cause-effect relationship between the deposited droplet morphology and printed line characteristics. Following that, an optimal operating window with respect to the deposited droplet morphology is identified using a support vector machine to ensure the printing quality in a design space. Finally, to achieve high-controllability and sufficient-thickness droplets, Gaussian process regression is adopted to develop the process model of droplet geometrical properties, and the deposited droplet morphology is optimized under dual conflicting objectives of customizing the droplet diameter and maximizing droplet thickness. Different from previous printing quality optimization approaches, the proposed method enables a systemic investigation on the formation mechanisms of printed line characteristics, and the printing quality is fundamentally optimized based on the deposited droplet morphology. Moreover, data-driven-based characteristics can help the proposed approach serve as a guideline for printing quality optimization in other noncontact direct ink writing technologies.

Smart Polymer Surfaces with Complex Wrinkled Patterns: Reversible, Non-Planar, Gradient, and Hierarchical Structures.

This review summarizes the relevant developments in preparing wrinkled structures with variable characteristics. These include the formation of smart interfaces with reversible wrinkle formation, the construction of wrinkles in non-planar supports, or, more interestingly, the development of complex hierarchically structured wrinkled patterns. Smart wrinkled surfaces obtained using light-responsive, pH-responsive, temperature-responsive, and electromagnetic-responsive polymers are thoroughly described. These systems control the formation of wrinkles in particular surface positions and the reversible construction of planar-wrinkled surfaces. This know-how of non-planar substrates has been recently extended to other structures, thus forming wrinkled patterns on solid, hollow spheres, cylinders, and cylindrical tubes. Finally, this bibliographic analysis also presents some illustrative examples of the potential of wrinkle formation to create more complex patterns, including gradient structures and hierarchically multiscale-ordered wrinkles. The orientation and the wrinkle characteristics (amplitude and period) can also be modulated according to the requested application.

Multi-axis two photon polymerization machine and software concept for the manufacturing of aspheric lenses on non-planar substrates

Multi-axis two photon polymerization machine and software concept for the manufacturing of aspheric lenses on non-planar substrates

Reflow transfer for conformal three-dimensional microprinting.

From microcircuits to metamaterials, the micropatterning of surfaces adds valuable functionality. For nonplanar surfaces, incompatibility with conventional microlithography requires the transfer of originally planar micropatterns onto those surfaces; however, existing approaches accommodate only limited curvatures. A microtransfer approach was developed using reflowable materials that transform between solid and liquid on demand, freely stretching to yield transfers that naturally conform down to nanoscale radii of curvature and arbitrarily complex topographies. Such reflow transfer helps generalize microprinting, extending the reach of precision planar microlithography to highly nonplanar substrates and microstructures. With gentle water-based processing, reflow transfer can be applied to a range of materials, with microprinting demonstrated onto metal, plastic, paper, glass, polystyrene, semiconductor, elastomer, hydrogel, and multiple biological surfaces.

Aerosol jet printing polymer dispersed liquid crystals on highly curved optical surfaces and edges

We demonstrate a new technique for producing Polymer Dispersed Liquid Crystal (PDLC) devices utilising aerosol jet printing (AJP). PDLCs require two substrates to act as scaffold for the Indium Tin Oxide electrodes, which restricts the device geometries. Our approach precludes the requirement for the second substrate by printing the electrode directly onto the surface of the PDLC, which is also printed. The process has the potential to be precursory to the implementation of non-contact printing techniques for a variety of liquid crystal-based devices on non-planar substrates. We report the demonstration of direct deposition of PDLC films onto non-planar optical surfaces, including a functional device printed over the 90° edge of a prism. Scanning Electron Microscopy is used to inspect surface features of the polymer electrodes and the liquid crystal domains in the host polymer. The minimum relaxation time of the PDLC was measured at 1.3 ms with an 800 Hz, 90 V, peak-to-peak (Vpp) applied AC field. Cross-polarised transmission is reduced by up to a factor of 3.9. A transparent/scattering contrast ratio of 1.4 is reported between 0 and 140 V at 100 Hz.

Conformal laser printing and laser sintering of Ag nanoparticle inks: a digital approach for the additive manufacturing of micro-conductive patterns on patterned flexible substrates

ABSTRACT The laser induced forward transfer and sintering of metal nanoparticle inks has been proven a key enabling technology for flexible electronics. Nevertheless, many challenges concerning the conformal processing of non-planar substrates incorporating thermally sensitive layers are yet to be addressed. In this work, we study the behaviour of conformal laser printing of silver nanoparticle inks on patterned samples comprising sensitive underlying structures, by correlating the laser sintering powers employed to the undesired effects on the adjacent interfaces. The latter include demanding surface topographies with periodic patterns and micro-components exhibiting aspect ratio in the nano to 100-micron scale. We investigate the contribution of crucial processing parameters, such as the per pulse energy, repetition rate and the pulse to pulse spatial and temporal overlap to the overall result. The demonstrated results validate the versatility of laser processing which can offer application specific solutions on different use cases involving multilayered and multimaterial electronics.