Initiated Chemical Vapor Deposition: A Versatile Tool for Various Device Applications

Advances in device technology have been accompanied by the development of new types of materials and device fabrication methods. Considering device design, initiated chemical vapor deposition (iCVD) inspires innovation as a platform technology that extends the application range of a material or device. iCVD serves as a versatile tool for surface modification using functional thin film. The building of polymeric thin films from vapor phase monomers is highly desirable for the surface modification of thermally sensitive substrates. The precise control of thin film thicknesses can be achieved using iCVD, creating a conformal coating on nano‐, and micro‐structured substrates such as membranes and microfluidics. iCVD allows for the deposition of polymer thin films of high chemical functionality, and thus, substrate surfaces can be functionalized directly from the iCVD polymer film or can selectively gain functionality through chemical reactions between functional groups on the substrate and other reactive molecules. These beneficial aspects of iCVD can spur breakthroughs in device fabrication based on the deposition of robust and functional polymer thin films. This review describes significant implications of and recent progress made in iCVD‐based technologies in three fields: electronic devices, surface engineering, and biomedical applications.

     

Transparente und leitfähige Veredelung von Kunststoffoberflächen

Deposition Techniques for Transparent Conducting Thin‐Films on Glass and Polymer Substrates We report on thin films deposited at atmospheric pressures on glass and polymer substrates with various techniques. The introduced thin‐film materials show intrinsic properties being suitable for different applications while maintaining the principle properties of the substrates themselves (e. g. shape. rigidity/flexibility, transparency). With the main focus on optical and electronic applications the properties of the deposited films can be adjusted by the choice of coating material (e. g. metal oxide, CNT), the film's shape (compact, particulate) and the deposition process itself. We compare deposition and properties of different TCO‐materials with CNT‐based thin film techniques and demonstrate approaches for the integration of these processes in production lines.     

SERS Active Surface in Two Steps,Patterning and Metallization

Robust and reproducible metallized nano/microstructured surfaces of polymeric surfaces have been successfully prepared by direct laser interference patterning (DLIP) of commercial polymeric films followed by sputtering of metallic thin films. The SERS spectra for 2‐thioaniline adsorbed on a structured polycarbonate surfaces covered with a gold or platinum film showed a ca. three order of magnitude enhancement over a flat surface with the same metal film. The method here reported is suitable for mass production of substrates for SERS since large areas (several cm²) can be structured in ca. 1–5 s.     

Luminescent method for measuring the thickness of thin coating films on rough surfaces

Conclusions A luminescent method has been developed for evaluating the thickness of thin transparent luminescent coatings on surfaces of solid bodies by means of an equipment consisting of instruments produced by our industry.The high sensitivity of photomultipliers and the high definition of their luminous beam (of the order of 1 ²) are suitable for measuring the surface of thin films either at separate points, or for plotting their thickness diagrams along a definite path of the tested surface.This method can be recommended for evaluating oil coatings over rough metal surfaces. The method used for this purpose to date has consisted of applying lubricating layers of volatile solvents, with their thickness being evaluated by computation from the concentration of the solution and the area which it covered. This method contributes considerable errors. First, it is assumed that an oil film of a definite thickness is thus produced, whereas even on a smooth surface the oil is distributed nonuniformly, and all the more so on a rough surface. Second, the true area of a rough surface is not known, and it is assumed in calculations that the surface is smooth. These errors can be reduced by using the luminescent method.The same technique can be used for evaluating the distribution of lubricants over a friction path, for testing the uniformity and continuity of certain decorative or insulating coatings, etc.Thus, the measurement of film thicknesses by the luminescent method can be used both in scientific research and in industry.Translated from Izmeritel'naya Tekhnika, No. 9, pp. 27–29, September, 1967.     

Microarchitected Stretching‐Dominated Mechanical Metamaterials with Minimal Surface Topologies

Historically, the creation of lightweight, yet mechanically robust, materials have been the most sought‐after engineering pursuit. For that purpose, research efforts are dedicated to finding pathways to emulate and mimic the resilience offered by natural biological systems (i.e., bone and wood). These natural systems evolved over time to provide the most attainable structural efficiency through their architectural characteristics that can span over multiple length scales. Nature‐inspired man‐made cellular metamaterials have effective properties that depend largely on their topology rather than composition and are hence remarkable candidates for a wide range of application. Despite their geometrical complexity, the fabrication of such metamaterials is made possible by the emergence of advanced fabrication techniques that permit the fabrication of complex architectures down to the nanometer scale. In this work, we report the fabrication and mechanical testing of nature‐inspired, mathematically created, micro‐architected, cellular metamaterials with topologies based on triply periodic minimal surfaces (TPMS) with cubic symmetries fabricated through direct laser writing two‐photon lithography. These TPMS‐based microlattices are sheet/shell‐ and strut‐based metamaterials with high geometrical complexity. Interestingly, results show that TPMS sheet‐based microlattices follow a stretching‐dominated mode of deformation, and further illustrate their mechanical superiority over the traditional and well‐known strut‐based microlattices and microlattice composites. The TPMS sheet‐based polymeric microlattices exhibited mechanical properties superior to other micrloattices comprising metal‐ and ceramic‐coated polymeric substrates and, interestingly, are less affected by the change in density, which opens the door for fabricating ultralightweight materials without much sacrificing mechanical properties.

     

Funktionelle Beschichtungen auf Basis anorganischer Nanosole

Functional coatings on basis of inorganic nanosols The controlled hydrolysis of silicon or metal alkoxides produces nanoparticulate oxide sols which condense to thin transparent gel films on any substrates after coating and drying (so‐called “sol‐gel process”). The co‐hydrolysis and co‐condensation of different alkoxides (chemical modification) as well as the embedding of different additives (physical modification) offers almost unlimited possibilities to vary the properties of nanosols and, therefore, also of the resulting coatings, and to adapt them to the purpose intended. By coating of flexible substrates like textiles, papers or polymer foils it is possible to combine the material protecting functions of the inorganic oxide layer with new functional qualities, e. g. modification of surface energy and charge, alteration of the optical properties, realization of biocompatible and bioactive properties.     

A Template‐Free Method Towards Conducting Polymer Nanostructures

Conducting polymer nanostructures have recently received special attention in nanoscience and nanotechnology because of their highly π‐conjugated polymeric chains and metal‐like conductivity, such that they can be regarded not only as excellent molecular wires, but also as basic units for the formation of nanodevices. Although various approaches, such as hard‐template methods, soft‐template methods, electrospinning technology, and so on are widely employed to synthesize or fabricate conducting polymer nanostructures and their composite nanostructures, each of the currently used methods possess disadvantages. Therefore, finding a facile, efficient, and controlled method of forming conducting polymer nanostructures is desirable. Similar to other nanomaterials, the effect of size (in these cases 1–100 nm) on the properties of the conducting polymer nanostructures must be considered. Electrical measurements of single nanotubes or nanowires are desirable in order to be able to understand the pure electrical properties of conducting polymer nanostructures. Compared with bulk conducting polymers, conducting polymer nanostructures are expected to display improved performance in technological applications because of the unique properties arising from their nanometer‐scaled size: high conductivity, large surface area, and light weight. Thus, it is also desirable to develop promising applications for conducting polymer nanostructures. In accordance with the issues described above, our research focuses on a new synthesis method to form conducting polymer nanostructures and on the related formation mechanism of the resultant nanostructures. The electrical and transport properties of single nanotubes of conducting polymer, measured by a four‐probe method, and promising applications of such template‐free‐synthesized conducting polymer nanostructures as new microwave absorbing materials and sensors guided by a reversible wettability are also of interest. This article reports some of our main results and reviews some important contributions of others.

     

PWB compatible high value integral capacitors by MOCVD

The 1998 National Electronics Manufacturing Technology Roadmap indicates that a capacitance density of 50 nF cm^–2 will be required in 2001 for successful implementation of integral passive technology in the microelectronics packaging industries. Higher permittivity polymer/ceramic nanocomposites have been proven to be a viable option for integral capacitors on printed wiring boards (PWB). Although the nanocomposite materials are in their developmental stage, it is unlikely that this materials system could meet such high capacitance needs and still utilize a large area manufacturable process. In this study, an alternative metal organic chemical vapor deposition (MOCVD) technique has been implemented to deposit TiO₂ thin film dielectrics at temperatures below 180 °C with higher capacitance densities. Two different metal-dielectric-metal type parallel plate capacitor structures have been fabricated on silicon and PWB substrates for relatively high frequency (45 MHz–1 GHz) and low frequency (100 Hz–1 MHz) characterization. Copper was used as the ground and upper electrodes with a 10 nm Cr adhesion layer between the dielectric and the electrodes. Capacitance was measured using a Keithley LCZ meter and a HP4194 impedance gain-phase analzer at the lower frequency range. Specific capacitance as high as 200 nF cm^–2 was achieved at 1 MHz from devices built on silicon substrates and at 100 kHz from devices on PWB substrates. For the first time, thin film TiO₂ on PWB substrates is reported at temperatures below 180 °C using MOCVD.     

Measurement of Thermal Conductivity of TiO2 Thin Films Using 3ω Method

TiO₂ film has been used in many industrial components such as laser filters, protection mirrors, chemical sensors, and optical catalysts. Therefore, the thermal properties of TiO₂ thin films are important in, e.g., reducing the thermal conductivity of ceramic coatings in gas turbines and increasing the laser damage threshold of antireflection coatings. The thermal conductivity of four kinds of TiO₂ thin films, prepared by dc magnetron sputtering, was measured using the 3 method in the temperature range from 80 K to room temperature. The results showed that the thermal conductivity of TiO₂ thin films strongly depends on the thickness and the microstructure of the films. The films with smaller grain size and thinner thickness have smaller thermal conductivities.     

Recent Developments in Controlled Vapor‐Phase Growth of 2D Group 6 Transition Metal Dichalcogenides

An overview of recent developments in controlled vapor‐phase growth of 2D transition metal dichalcogenide (2D TMD) films is presented. Investigations of thin‐film formation mechanisms and strategies for realizing 2D TMD films with less‐defective large domains are of central importance because single‐crystal‐like 2D TMDs exhibit the most beneficial electronic and optoelectronic properties. The focus is on the role of the various growth parameters, including strategies for efficiently delivering the precursors, the selection and preparation of the substrate surface as a growth assistant, and the introduction of growth promoters (e.g., organic molecules and alkali metal halides) to facilitate the layered growth of (Mo, W)(S, Se, Te)₂ atomic crystals on inert substrates. Critical factors governing the thermodynamic and kinetic factors related to chemical reaction pathways and the growth mechanism are reviewed. With modification of classical nucleation theory, strategies for designing and growing various vertical/lateral TMD‐based heterostructures are discussed. Then, several pioneering techniques for facile observation of structural defects in TMDs, which substantially degrade the properties of macroscale TMDs, are introduced. Technical challenges to be overcome and future research directions in the vapor‐phase growth of 2D TMDs for heterojunction devices are discussed in light of recent advances in the field.     

Interfacial adhesion of polymeric adhesive film on different surfaces in the fabrication of polymer photonic devices

One main critical issue in the fabrication of polymer optical devices is the adhesion strength of polymeric layer to the substrate. High adhesion strength is desirable and critical in order to avoid peeling out of polymeric layer from the substrate due to stress generated during fabrication, handling and lifetime. Therefore, the aim of this study is to investigate the interfacial adhesion of polymeric adhesive film on different possible substrate surfaces such as pure silicon wafer, silica on silicon wafer, and thin metal layer (Chromium–Cr) on silicon wafer under different processing conditions. Surface morphology of the substrates before deposition was characterized by atomic force microscope (AFM). Adhesive shear button was made on those substrates by using photolithography process and the interfacial adhesion was measured by using a Dage D2400 shear tester. The effect of exposing in high temperature and typical damp heat condition on the interfacial adhesion was also studied. We found that the best adhesion performance was obtained for the case using Cr thin in all processing conditions, especially under heat treatment and damp heat test. From this study, we suggest that a thin layer of metal film on silicon wafer can be use to improve the adhesion and the reliability of the polymer photonic devices. The oxidized silica on silicon wafer is an alternative choice at the expense of reducing adhesion performance. Moreover, using silica layer has the advantage over Cr layer that one fabrication step can be reduced since the silica layer itself can effectively act as the lower cladding of the devices.     

金属表面均三嗪二硫醇纳米聚合薄膜研究进展

综述了均三嗪二硫醇类化合物纳米聚合薄膜在各种金属基底表面的光聚合、热聚合、蒸发聚合及电化学聚合制备方法及在金属防护、材料间粘接、润滑特性、介电特性、超疏水和作为重金属离子处理剂等方面的应用。对该类化合物在不同金属表面的吸附作用和聚合机理进行了归纳、讨论与分析。提出了通过对该类三嗪二硫醇化合物分子进行改性研究,可在金属表...     

Laser‐Textured Metal Substrates as Photoanodes for Enhanced PEC Water Splitting Reactions

We demonstrate the effect of femtosecond laser structuring of titanium substrates to increase the absorption, photoconversion, and overall photoelectrochemical water splitting (PEC) performance compared to pristine metal substrates, independent of any additional top coat layers. The influence of ultra short laser pulse patterning on PEC efficiency is investigated toward spectroscopic (UV‐Vis), microscopic (SEM), crystallographic (XRD), and compositional (XPS) properties. The beneficial effect of a periodically patterned substrate is attributed to enhanced specific surface area and improved in‐plane light trapping when compared to flat surfaces. Photoanodes for water splitting experiments fabricated by titanium and iron oxide films on laser pre‐patterned Ti substrates are also found to show enhanced PEC efficiency (0.057 mA cm^?2) when compared to unpatterened substrates (0.028 mA cm^?2). The lower absolute PEC efficiencies are due to extreme thin films.

     

Epitaxial Lift‐Off of Centimeter‐Scaled Spinel Ferrite Oxide Thin Films for Flexible Electronics

Mechanical flexibility of electronic devices has attracted much attention from research due to the great demand in practical applications and rich commercial value. Integration of functional oxide materials in flexible polymer materials has proven an effective way to achieve flexibility of functional electronic devices. However, the chemical and mechanical incompatibilities at the interfaces of dissimilar materials make it still a big challenge to synthesize high‐quality single‐crystalline oxide thin film directly on flexible polymer substrates. This study reports an improved method that is employed to successfully transfer a centimeter‐scaled single‐crystalline LiFe₅O₈ thin film on polyimide substrate. Structural characterizations show that the transferred films have essentially no difference in comparison with the as‐grown films with respect to the microstructure. In particular, the transferred LiFe₅O₈ films exhibit excellent magnetic properties under various mechanical bending statuses and show excellent fatigue properties during the bending cycle tests. These results demonstrate that the improved transfer method provides an effective way to compose single‐crystalline functional oxide thin films onto flexible substrates for applications in flexible and wearable electronics.     

High‐Entropy Alloy (HEA)‐Coated Nanolattice Structures and Their Mechanical Properties

Nanolattice structure fabricated by two‐photon lithography (TPL) is a coupling of size‐dependent mechanical properties at micro/nano‐scale with structural geometry responses in wide applications of scalable micro/nano‐manufacturing. In this work, three‐dimensional (3D) polymeric nanolattices are initially fabricated using TPL, then conformably coated with an 80 nm thick high‐entropy alloy (HEA) thin film (CoCrFeNiAl_0.3) via physical vapor deposition (PVD). 3D atomic‐probe tomography (APT) reveals the homogeneous element distribution in the synthesized HEA film deposited on the substrate. Mechanical properties of the obtained composite architectures are investigated via in situ scanning electron microscope (SEM) compression test, as well as finite element method (FEM) at the relevant length scales. The presented HEA‐coated nanolattice encouragingly not only exhibits superior compressive specific strength of ≈0.032 MPa kg^?1 m³ with density well below 1000 kg m^?3, but also shows good compression ductility due to its composite nature. This concept of combining HEA with polymer lattice structures demonstrates the potential of fabricating novel architected metamaterials with tunable mechanical properties.

     

Wetting‐Induced Climbing for Transferring Interfacially Assembled Large‐Area Ultrathin Pristine Graphene Film

Owing to inherent 2D structure, marvelous mechanical, electrical, and thermal properties, graphene has great potential as a macroscopic thin film for surface coating, composite, flexible electrode, and sensor. Nevertheless, the production of large‐area graphene‐based thin film from pristine graphene dispersion is severely impeded by its poor solution processability. In this study, a robust wetting‐induced climbing strategy is reported for transferring the interfacially assembled large‐area ultrathin pristine graphene film. This strategy can quickly convert solvent‐exfoliated pristine graphene dispersion into ultrathin graphene film on various substrates with different materials (glass, metal, plastics, and cloth), shapes (film, fiber, and bulk), and hydrophobic/hydrophilic patterns. It is also applicable to nanoparticles, nanofibers, and other exfoliated 2D nanomaterials for fabricating large‐area ultrathin films. Alternate climbing of different ultrathin nanomaterial films allows a layer‐by‐layer transfer, forming a well‐ordered layered composite film with the integration of multiple pristine nanomaterials at nanometer scale. This powerful strategy would greatly promote the development of solvent‐exfoliated pristine nanomaterials from dispersions to macroscopic thin film materials.     

Deformation and Fracture of Micron‐Sized Metal‐Coated Polymer Spheres: An In Situ Study

In situ imaging and analysis of the mechanical behavior of micron‐sized metal‐coated polymer particles under compression is reported. A nanoindentation set‐up mounted in a scanning electron microscope is used to observe the deformation and fracture of 10 μm polymer spheres with Ni, Ni/Au, Au, and Ag coatings. The spheres fracture in one of two metallization‐dependent modes, brittle, and ductile, depending only on the presence of a nickel layer. The metal coating always fractures parallel to the direction of compression. The mechanical properties up to the point of coating fracture are rate‐dependent due to the viscoelastic polymer core. Metal‐coated polymer spheres are an important composite material in electronics packaging, and this study demonstrates a novel method of evaluating the mechanical properties of particles to tailor them for electronic materials.

     

Rheological characterization and thermal degradation of PTFE

PTFE (¯M _n=5×10⁶), when heated near the melting temperature (335 to 337 C) while in contact with carbon black, is characterized by an effective viscosity and a thermal stability which are orders of magnitude lower than those found in the absence of the contacting high surface area material. The penetration of the PTFE into the porous carbon black occurs by the spreading of a very thin polymer film followed by a thickening of this film with time at temperature until a limiting concentration is reached. The lower the average molecular weight of the PTFE, the more rapidly it penetrates into the porous material. Similar phenomena have been observed with high molecular weight PTFE heated near the melting temperature while contacting high surface area metal blacks or porous sintered metals.     

Corrosion protection by plasma-polymerized coatings

A large volume microwave plasma generator was used for producing thin plasma-polymerized (PP) films as corrosion protection on metal substrates.Through the control of plasma polymerization variables (“monomer” vapour, pressure, power density and substrate temperature), strongly adhering, pinhole-free and highly cross-linked coatings can be deposited on metal surfaces. Numerous monomer-metal combinations were tested and PP films were found to outperform “conventional” polymeric coatings in various corrosive media. Organosilicone films appear to hold particular promise as they have excellent mechanical properties and are stable up to high (>800°C) temperatures. Carbon steel substrates with coatings 2 μ thick were found to withstand a simulated marine environment for periods of several weeks with no trace of corrosion.     

Gate Dielectrics for Organic Field‐Effect Transistors: New Opportunities for Organic Electronics

In this contribution we review the motivations for, and recent advances in, new gate dielectric materials for incorporation into organic thin‐film transistors (OTFTs) for organic electronics. After a general introduction to OTFT materials, operating principles, and processing requirements for optimizing low‐cost organic electronics, this review focuses on three classes of OTFT‐compatible dielectrics: i) inorganic (high‐k) materials; ii) polymeric materials; and iii) self‐assembled mono‐ and/multilayer materials. The principal goals in this active research area are tunable and reduced OTFT operating voltages, leading to decreased device power consumption while providing excellent dielectric/insulator properties and efficient low‐cost solution‐phase processing characteristics.