Fabrication Of Functional Devices Research Articles

Harnessing Polar Interactions Tunes the Stability of Ultrathin Polymer Solution Films.

The stability of ultrathin (<100 nm) polymer films is essential in applications like protective coatings. On the contrary, their instability may actually be desirable for the emergence of self-assembled nanoscale patterns utilized in the fabrication of functional devices. Polymer solution films exhibit two distinct kinds of instabilities, viz., dewetting (long-wave) and decomposition (short-wave). Dewetting refers to the rupture of the continuous film to form isolated domains, while decomposition leads to phase separation within the polymer solution. The focus of this work is on leveraging polar interactions between the solute and solvent molecules to tune the stability of the film. A gradient dynamics-based thin film model is developed to investigate pattern formation in a thin polar polymer solution film. The Flory-Huggins theory is suitably modified by introducing a polar interaction parameter that depends upon the concentration of the polymer and the dipole moments of monomer (μ1) and solvent molecules (μ0). A linear stability analysis is performed to determine the characteristic length scale and growth rate of the instabilities. It is shown that the range of concentration space for the occurrence of the decomposition mode is directly affected by the Flory interaction parameter (χ0), μ0, and μ1, thereby serving as control parameters to tune the width of the concentration range. It is further shown that ignoring polar interactions may lead to incorrect predictions of the instability mode, including a complete loss of the decomposition mode. In addition, the long-wave dewetting length scale is found to decrease due to bulk dipolar interactions at higher polymer concentrations. Finally, numerical simulations are carried out to track the nonlinear evolution of the interface and concentration field for both the decomposition and dewetting modes of instability.

Spin coating epitaxial heterodimensional tin perovskites for light-emitting diodes.

Environmentally friendly tin (Sn) perovskites have received considerable attention due to their great potential for replacing their toxic lead counterparts in applications of photovoltaics and light-emitting diodes (LEDs). However, the device performance of Sn perovskites lags far behind that of lead perovskites, and the highest reported external quantum efficiencies of near-infrared Sn perovskite LEDs are below 10%. The poor performance stems mainly from the numerous defects within Sn perovskite crystallites and grain boundaries, leading to serious non-radiative recombination. Various epitaxy methods have been introduced to obtain high-quality perovskites, although their sophisticated processes limit the scalable fabrication of functional devices. Here we demonstrate that epitaxial heterodimensional Sn perovskite films can be fabricated using a spin-coating process, and efficient LEDs with an external quantum efficiency of 11.6% can be achieved based on these films. The film is composed of a two-dimensional perovskite layer and a three-dimensional perovskite layer, which is highly ordered and has a well-defined interface with minimal interfacial areas between the different dimensional perovskites. This unique nanostructure is formed through direct spin coating of the perovskite precursor solution with tryptophan and SnF2 additives onto indium tin oxide glass. We believe that our approach will provide new opportunities for further developing high-performance optoelectronic devices based on heterodimensional perovskites.

Direct Laser Writing Dry Lithography of High‐Resolution Micro‐/Nanostructures in AgSb4Te Thin Film for Tunable Perfect Absorber

Direct laser writing is promising for fabrication of functional structures due to its high speed, low cost, and facile operation. However, high resolution is difficult to be implemented due to wet development‐induced structural collapse. Ag‐doped Sb4Te thin film is proposed for high‐resolution direct laser writing dry lithography. The crystalline structures and binding environment of AgSb4Te thin films are investigated. The dry lithographic characteristics suggest that the developing selectivity of exposed to as‐deposited film is as high as 17 under CHF3/O2 gas and the minimum linewidth of patterns can reach 80 nm via adjusting grating period. Developing selectivity mechanism is ascribed to exposure induced phase separation along with generation of Sb component and Ag7Te4 phases. The Sb component can be readily etched due to the lack of Ag atom protection and then etching of residual Ag7Te4 phase is further promoted while the uniformly distributed Ag atoms in as‐deposited film restrain its etching. In addition, nanohole array is fabricated onto AgSb4Te thin films and tunable absorbance can be realized by adjusting pattern period and phase‐change process. This work may provide a useful guide for the investigation of direct laser writing lithography mechanism and functional device fabrication.

Highly efficient nonlinear vortex beam generation by using a compact nonlinear fork grating

Vortex beams with an orbital angular momentum (OAM) are extremely important in optical trapping, optical micromachining, high-capacity optical communications, and quantum optics. Nonlinear generation of such a vortex beam enables vortex beams to be obtained at new wavelengths, which opens up new possibilities for all-optical switching and manipulation of vortex beams. However, previous nonlinear vortex beam generation suffers from either low efficiency or low-level integration. Here, we use the technique of ultraviolet photolithography-assisted inductively coupled plasma (ICP) etching to realize a compact nonlinear fork grating for high-efficiency nonlinear vortex beam generation. In our experiment, the depth of such a compact nonlinear fork-grating structure can be precisely controlled by etching time. The vortex beams with a topological charge of l = ±1, ± 2, ± 3 can be generated in the far field, and the normalized nonlinear conversion efficiency of such nonlinear vortex beam is 189% W−1cm−2. Our method not only provides an efficient and compact method for nonlinear vortex beam manipulation but also suits for timesaving and large-area nonlinear functional device fabrication.

Vector valley Hall edge solitons in distorted type-II Dirac photonic lattices.

Topological edge states have recently garnered a lot of attention across various fields of physics. The topological edge soliton is a hybrid edge state that is both topologically protected and immune to defects or disorders, and a localized bound state that is diffraction-free, owing to the self-balance of diffraction by nonlinearity. Topological edge solitons hold great potential for on-chip optical functional device fabrication. In this report, we present the discovery of vector valley Hall edge (VHE) solitons in type-II Dirac photonic lattices, formed by breaking lattice inversion symmetry with distortion operations. The distorted lattice features a two-layer domain wall that supports both in-phase and out-of-phase VHE states, appearing in two different band gaps. Superposing soliton envelopes onto VHE states generates bright-bright and bright-dipole vector VHE solitons. The propagation dynamics of such vector solitons reveal a periodic change in their profiles, accompanied by the energy periodically transferring between the layers of the domain wall. The reported vector VHE solitons are found to be metastable.

Nanobridge Stencil Enabling High Resolution Arbitrarily Shaped Metallic Thin Films on Various Substrates

AbstractStencil lithography (SL), which uses a perforated membrane as a reusable shadow mask to locally add material patterns on substrates provides a simple but versatile approach for the fabrication of functional devices on a large variety of substrate materials by physical vapor deposition (PVD). Mechanical stress induced by the accumulation of condensed material on the thin stencil membrane during the PVD step leads to stencil bending and breaking, therefore, suspended stencil membranes with arbitrary openings are, in practice, not possible. Here, a new approach to remedy this limitation is reported by introducing auxiliary bridges in stencils. These bridges prevent the suspended membrane from bending out of plane, thereby enabling aperture openings to have almost arbitrary geometry. These bridges are sufficiently narrow so that they do not entirely block the material deposition by PVD and thus create a continuous material pattern by taking advantage of the blurring effect. The successful metal deposition through the designed nanobridge stencil on a wide range of substrate materials underlines the usability and the versatility of the proposed stencil design. The work presented here provides a versatile fabrication method to produce arbitrarily shaped metal patterns that were previously impossible due to the topological constraints of nanostencils.

Laser-Induced Forward Transferred Optical Scattering Nanosilica for Transparent Displays.

Laser printing has become a promising alternative for large-scale fabrication of functional devices. Here, laser-induced forward transfer (LIFT) of nanosilica was successfully achieved using a lower-cost nanosecond laser with a center wavelength of 1064 nm. To enhance the light absorption of silica, a small amount of graphene oxide (GO) was added to the fumed silica. Investigations were conducted to give an insight into the role of GO in the LIFT process. Pattern deposition was achieved with a minimum line width of 221 μm. The scattering can be tuned from ~2.5% to ~17.5% by changing the laser fluence. The patternable transparent display based on laser transferred nanosilica (LTNS) film was also demonstrated, showing its capability to deliver information on multiple levels. This LIFT based technique promotes fast, flexible, and low-cost manufacturing of scattering-based translucent screens or patterns for transparent displays.

New Metal-Plastic Hybrid Additive Manufacturing for Precise Fabrication of Arbitrary Metal Patterns on External and Even Internal Surfaces of 3D Plastic Structures.

Constructing precise metal patterns on complex three-dimensional (3D) plastic parts allows the fabrication of functional devices for advanced applications. However, it is currently expensive and requires complex processes. This study demonstrates a process for the fabrication of 3D metal-plastic composite structures with arbitrarily complex shapes. A light-cured resin is modified to prepare the active precursor allowing subsequent electroless plating (ELP). A multimaterial digital light processing 3D printer was newly developed to fabricate the parts containing regions made of either standard resin or active precursor nested within each other. Selective 3D ELP processing of such parts provided various metal-plastic composite parts having complicated hollow structures with specific topological relationships with the resolution of 40 μm. Using this technique, 3D devices that cannot be manufactured by traditional methods are possible, and metal patterns can be produced inside plastic parts as a means of further miniaturizing electronics. The proposed method can also generate metal coatings exhibiting improved adhesion of metal to substrate. Finally, several sensors composed of different functional materials and specific metal patterns were designed and fabricated. The present results demonstrate the viability of the proposed method and suggest potential applications in the fields of 3D electronics, wearable devices, and sensors.

Functional Devices from Bottom-Up Silicon Nanowires: A Review.

This paper summarizes some of the essential aspects for the fabrication of functional devices from bottom-up silicon nanowires. In a first part, the different ways of exploiting nanowires in functional devices, from single nanowires to large assemblies of nanowires such as nanonets (two-dimensional arrays of randomly oriented nanowires), are briefly reviewed. Subsequently, the main properties of nanowires are discussed followed by those of nanonets that benefit from the large numbers of nanowires involved. After describing the main techniques used for the growth of nanowires, in the context of functional device fabrication, the different techniques used for nanowire manipulation are largely presented as they constitute one of the first fundamental steps that allows the nanowire positioning necessary to start the integration process. The advantages and disadvantages of each of these manipulation techniques are discussed. Then, the main families of nanowire-based transistors are presented; their most common integration routes and the electrical performance of the resulting devices are also presented and compared in order to highlight the relevance of these different geometries. Because they can be bottlenecks, the key technological elements necessary for the integration of silicon nanowires are detailed: the sintering technique, the importance of surface and interface engineering, and the key role of silicidation for good device performance. Finally the main application areas for these silicon nanowire devices are reviewed.

Charge Transfer in Self-Assembled Fullerene-Tetraphenylporphyrin Non-Covalent Multilayer

Self-assembly of organic molecules is a promising method for generating multilayer systems for fabrication of functional devices. In particular, fullerene (C60) and porphyrin molecules offer a variety of binding modes, including π–π interactions, dipole electrostatic attraction, and hydrogen bonding, to tailor the charge separation and charge recombination limiting device performance. Here, we investigate multilayer systems obtained by the sequential physical vapor deposition of C60 and tetraphenylporphyrin (H2TPP) layers, focusing on the effect of the interfaces on the charge transfer processes. Absorbance spectra indicate noncovalent-like π-stacking, with the increment of fullerene interfaces shifting the porphyrin Soret band toward the blue. Similarly, surface photovoltage measurements in the multilayer systems show that as the number of interfaces increases, so does the photogeneration of charge. Charge separation follows carrier generation given that the recombination time, associated to trap states, decreases. This behavior indicates that the Donor-Acceptor nature of the fullerene-porphyrin bilayer system is conserved, and even enhanced in the multilayer film, and that the number of interfaces aids to the formation of selective paths for charge carrier collection, demonstrating its potential in optoelectronic devices.

3D printing of polyvinylidene fluoride composite films with enhanced electroactive beta-phase for flexible wearable pressure sensors

Following the notable rise of three-dimensional (3D) printing in recent years, its use for the fabrication of functional devices derived from piezoelectric polymers such as poly (vinylidene fluoride), PVDF, has become an active area of research. However, there is still a lot to understand about the structure–property-processing relationship regarding the 3D printing of PVDF-based polymers with an enhanced piezoelectric property, which is closely related to the β-phase crystal structure of the polymer. This paper presents the preliminary results of investigations into the extrusion-based 3D printing of poly(vinylidene fluoride-hexafluoropropylene), PVDF-HFP, a PVDF copolymer. Towards the enhancement of the β-phase content of this copolymer, the study analyzed the influence of two fillers in the form of barium titanate (BaTiO3) and untreated activated carbon (UAC) and considered the effect of two printing parameters on the piezoelectric crystalline structure of the PVDF-HFP. First, composite films of the PVDF-HFP with the fillers were formed via the solvent evaporation casting method. From the characterization of the solvent-cast samples using Fourier Transform Infrared Spectrum (FTIR), a composite consisting of 10.55 wt% BaTiO3 and 0.45 wt% UAC with the matrix of PVDF-HFP was found to produce a superior β-phase content (67%) and it was deployed for syringe-based extrusion-assisted 3D printing. Post-fabrication characterization of the extruded samples was carried out to examine the influence of the 3D printing conditions in the form of printing bed temperature (50, 75, 95) and extrusion speed (10, 15, 25). It was found that the combination of a higher printing bed temperature and a low printing speed further enhanced the β-phase content for the PVDF-HFP composites, yielding a β-phase content of 79.6%. Confirmation of the electromechanical/piezoelectric response of the unpoled strips of printed samples revealed a positive correlation between the externally applied pressure on the printed strips and generated voltage.

A Universal Approach for Room-Temperature Printing and Coating of 2D Materials.

Processing 2D materials into printable or coatable inks for the fabrication of functional devices has proven to be quite difficult. Additives are often used in large concentrations to address the processing challenges, but they drastically degrade the electronic properties of the materials. To remove the additives a high-temperature post-deposition treatment can be used, but this complicates the fabrication process and limits the choice of materials (i.e., no heat-sensitive materials). In this work, by exploiting the unique properties of 2D materials, a universal strategy for the formulation of additive-free inks is developed, in which the roles of the additives are taken over by van der Waals (vdW) interactions. In this new class of inks, which is termed "vdW inks", solvents are dispersed within the interconnected network of 2D materials, minimizing the dispersibility-related limitations on solvent selection. Furthermore, flow behavior of the inks and mechanical properties of the resultant films are mainly controlled by the interflake vdW attractions. The structure of the vdW inks, their rheological properties, and film-formation behavior are discussed in detail. Large-scale production and formulation of the vdW inks for major high-throughput printing and coating methods, as well as their application for room-temperature fabrication of functional films/devices are demonstrated.

In-plane quasi-single-domain BaTiO3 via interfacial symmetry engineering

The control of the in-plane domain evolution in ferroelectric thin films is not only critical to understanding ferroelectric phenomena but also to enabling functional device fabrication. However, in-plane polarized ferroelectric thin films typically exhibit complicated multi-domain states, not desirable for optoelectronic device performance. Here we report a strategy combining interfacial symmetry engineering and anisotropic strain to design single-domain, in-plane polarized ferroelectric BaTiO3 thin films. Theoretical calculations predict the key role of the BaTiO3/PrScO3{({{{{{boldsymbol{110}}}}}})}_{{{{{{bf{O}}}}}}} substrate interfacial environment, where anisotropic strain, monoclinic distortions, and interfacial electrostatic potential stabilize a single-variant spontaneous polarization. A combination of scanning transmission electron microscopy, piezoresponse force microscopy, ferroelectric hysteresis loop measurements, and second harmonic generation measurements directly reveals the stabilization of the in-plane quasi-single-domain polarization state. This work offers design principles for engineering in-plane domains of ferroelectric oxide thin films, which is a prerequisite for high performance optoelectronic devices.

Molecular-Scale Chemical Imaging of the Orientation of an On-Surface Coordination Complex by Tip-Enhanced Raman Spectroscopy.

Metal-organic coordination structures at interfaces play an essential role in many biological and chemical systems. Understanding the molecular specificity, orientation, and spatial distribution of the coordination complexes at the nanometer scale is of great importance for effective molecular engineering of nanostructures and fabrication of functional devices with controllable properties. However, fundamental properties of such coordination systems are still rarely studied directly. In this work, we present a spectroscopic approach on the basis of tip-enhanced Raman spectroscopy (TERS) to investigate cobalt(II) tetraphenyl-porphyrine coordination species on the scale of a single molecule under ambient conditions. Coordination species anchored on gold surfaces modified with pyridine thiol self-assembled monolayers can be spectroscopically distinguished and mapped with ca. 2 nm resolution. In addition, in combination with density functional theory simulations, the adsorption configuration and molecular orientation of the coordination complexes are also revealed using TERS imaging.

Active acoustic absorption device using additive manufacturing technique for normal incident wave

This research presents an application of the additive manufacturing (AM) technology for active acoustic absorption device. Fabrication of functional devices in acoustic system is one of the challenging goals of additive manufacturing technology. In order to achieve this objective, an important step is to test the acoustic performance and characteristics of AM device and make it active from an acoustics point of view. Numerous roadblocks that need to be overcome exist and research activities in this field are rare. Thus this research aims to experimentally observe and utilize the anisotropic absorption coefficients of AM device caused by its anisotropic stiffness characteristics. In addition, this research also proposes the concept of an active acoustic device. Some experiments are carried out to show the validity of the active acoustic device using AM technology.

Assembly and Active Control of Nanoparticles using Polymer Brushes as a Scaffold

Abstract Inorganic nanoparticles are an attractive material that shows unique properties that differ from their bulk counterparts. Assembly of nanoparticles with soft materials is an effective approach to leverage their unusual properties for the fabrication of functional devices. Among the various soft materials, polymer brushes are expected to offer exciting opportunities due to their unique conformational properties. Here, we review research progress in the assembly and active control of gold nanoparticles with polymer brushes as a scaffold.

Directed Self-Assembly of Block Copolymers for the Fabrication of Functional Devices.

Directed self-assembly of block copolymers is a bottom-up approach to nanofabrication that has attracted high interest in recent years due to its inherent simplicity, high throughput, low cost and potential for sub-10 nm resolution. In this paper, we review the main principles of directed self-assembly of block copolymers and give a brief overview of some of the most extended applications. We present a novel fabrication route based on the introduction of directed self-assembly of block copolymers as a patterning option for the fabrication of nanoelectromechanical systems. As a proof of concept, we demonstrate the fabrication of suspended silicon membranes clamped by dense arrays of single-crystal silicon nanowires of sub-10 nm diameter. Resulting devices can be further developed for building up high-sensitive mass sensors based on nanomechanical resonators.

Laser-induced Joining of Nanoscale Materials: Processing, Properties, and Applications

• Current progress of laser joining of multidimensional nanomaterials are reviewed. • Laser joining of homogeneous and heterogenous nanomaterials are summarized. • Mechanism of laser nanojoining and practical applications are discussed. • Challenges and directions for future research in laser nanojoining are proposed. The rapid development of flexible and wearable nanodevices for a variety of commercial applications has identified a pressing need for targeted research on nanomaterials for use as building blocks in the fabrication of functional devices via bottom-up assembly. In the search for new fabrication technology, nanojoining or nanowelding has been selected as a promising method in this bottom-up approach. While there are a number of methods that can be used for nanojoining, laser processing is of interest because laser nanojoining combines high-precision property with a flexible manufacturing platform. In this review we discuss how this technology can be implemented in practical applications and outline the advantages and limitations of laser-induced nanojoining. We emphasize how laser nanojoining introduces reliability and reproducibility to the joining process, and show that this is due to precise control over heat-input in nanoscale dimensions. We also review the ways in which laser nanojoining can be integrated with other commercial fabrication operations in practical applications. To illustrate the flexibility of laser nanojoining, we give a detailed summary of joining involving a wide variety of multidimensional heterogeneous nanomaterials in the form of zero-dimension, one-dimension and two-dimension as well as the hybrid combination of these building blocks. We also discuss how laser processing can be used to generate hybrid materials with new functionalities as electrodes for various devices, optical systems and in functional circuits. The mechanisms and strategies in laser-induced joining of nanomaterials are systematically discussed in this paper along with a review of the properties and applications of the joined nanostructures. We also review some challenges in the implementation of this technology and discuss some possible directions for future research into laser-induced nanojoining.

SiC MOSFET with a Self-Aligned Channel Defined by Shallow Source-JFET Implantation: A Simulation Study

A new concept for SiC MOSFET with a self-aligned channel is presented. The channel is defined by shallow source-JFET implantation into a counter-doped layer. This concept is verified by TCAD device simulations. It is shown that the method is applicable to fabrication of functional devices. The most critical parameter of the process is misalignment between channel and p-shield. Almost no change of electrical current in forward conduction state and the leakage current and electric field in the gate oxide in blocking state is observed for the misalignments below 400 nm.

Flexible PZT-Integrated, Bilateral Sensors via Transfer-Free Laser Lift-Off for Multimodal Measurements.

Fabrication of functional devices that require a high-temperature annealing process on a thin, temperature-sensitive substrate is a long-standing, crucial issue in flexible electronics. Herein, we propose a transfer-free laser lift-off method to directly fabricate lead zirconate titanate (PZT) piezoelectric sensors that commonly undergo a high-temperature annealing (∼650 °C) on ubiquitous flexible substrates, including polyimide (∼300 °C), polyethylene terephthalate (∼120 °C), and polydimethylsiloxane (∼150 °C). The method includes the steps of fabricating sensors, encapsulating a flexible substrate, and peeling off the device by melting the sacrificial PZT layer at the interface with a sapphire glass. The appropriate fluence of laser energy has been figured out to avoid inadequate stripping or damage of the device. In addition, a process window for reliable stripping of the device has been established among the laser fluence and the thickness of the sacrificial layer and the supporting substrate. Furthermore, the capability of the newly proposed technique has been verified and expanded by successfully integrating several sensors that need skillful low-temperature heating treatment on top of a flexible supporting substrate accordingly before stripping. Finally, a PZT-integrated, bilateral multimodal sensor on a PI substrate has been fabricated, and the device demonstrates excellent performance and stability toward perceiving distributed dynamic pressure and temperature stimuli, revealing its high potential for the fabrication of high-performance devices for multimodal sensing applications.