Vapor-phase Deposition Process Research Articles

Phosphorescent PdII-PdII Emitter-Based Red OLEDs with an EQEmax of 20.52.

Three dinuclear Pd(II) complexes (1, 2, and 3) with intense red phosphorescence at room temperature are here synthesized using strong ligand field strength compounds. All three complexes are characterized by nuclear magnetic resonance, high-resolution mass spectrometry, and elemental analyses. Complexes 2 and 3 are characterized by single-crystal X-ray diffraction. The crystalline data of 2 and 3 reveal complex double-layer structures, with Pd-Pd distances of 2.8690(9) Å and 2.8584(17) Å, respectively. Furthermore, complexes 1, 2, and 3 show phosphorescence at room temperature in their solid states at the wavelengths of 678, 601, and 672nm, respectively. In addition, they show phosphorescence at 634, 635, and 582nm, respectively, in the 2wt.% (PMMA) films, and phosphorescence at 670, 675, and 589nm, respectively, in the deoxygenated CH2Cl2 solutions. Among three complexes, complex 1 shows red emission at 634nm with phosphorescent quantum yield Ф = 67% in the 2wt.% PMMA film. Furthermore, complex 1-based organic light-emitting diode is fabricated using a vapor-phase deposition process, and their maximum external quantum efficiency reaches 20.52%, which is the highest percentage obtained by using the dinuclear Pd(II) complex triplet emitters with the CIE coordinates of (0.62, 0.38).

Controlling Superhydrophobicity on Complex Substrates Based on a Vapor-Phase Sublimation and Deposition Polymerization.

The superhydrophobic properties of material surfaces have attracted significant research and practical development in a wide range of applications. In the present study, a superhydrophobic coating was fabricated using a vapor-phase sublimation and deposition process. This process offers several advantages, including a controllable and tunable superhydrophobic property, a dry and solvent-free process that uses well-defined water/ice templates during fabrication, and a coating technology that is applicable to various substrates, regardless of their dimensions or complex geometric configurations. The fabrication process exploits time-dependent condensation to produce ice templates with a controlled surface morphology and roughness. The templates are sacrificed via vapor sublimation, which results in mass transfer of water vapor out of the system. A second vapor source of a polymer precursor is then introduced to the system, and deposition occurs upon polymerization on the iced templates, replicating the same topologies from the iced templates. The continuation of the co-current sublimation and deposition processes finally renders permanent hierarchical structures of the polymer coatings that combine the native hydrophobic property of the polymer and the structured property by the sacrificed ice templates, achieving a level of superhydrophobicity that is tunable from 90° to 164°. The experiments demonstrated the use of [2,2]paracyclophanes as the starting materials for forming the superhydrophobic coatings of poly(p-xylylenes) on substrate surfaces. In comparison to conventional vapor deposition of poly(p-xylylenes), which resulted in dense thin-film coatings with only a moderate water contact angle of approximately 90°, the reported superhydrophobic coatings and fabrication process can achieve a high water contact angle of 164°. Demonstrations furthermore revealed that the proposed coatings are durable while maintaining superhydrophobicity on various substrates, including an intraocular lens and a cardiovascular stent, even against harsh treatment conditions and varied solution compositions used on the substrates.

Wafer-Scale High-Detectivity Near-Infrared PbS Detectors Fabricated from Vapor Phase Deposition

The commercialization of uncooled lead-salt photoconductive (PbX PC) detectors has been restricted by the low-yield of standard chemical bath deposition (CBD) manufacturing technology. As an iterative solution, herein, a novel vapor phase deposition (VPD) route is demonstrated by fabricating the 3 in. wafer-scale uniform PbS sensitized films with high detectivity. The morphological evolution suggests that the self-assembled rod-like microstructure, which is dominated by the I2/PbS flux ratio in the VPD process, is the key to triggering the near-infrared (NIR, 1–3 μm) response of the PbS-sensitized films. The maximum peak detectivity of VPD-PbS NIR detector of 1.9 × 1011 cm Hz1/2 W–1 is achieved after optimizing the sensitization-condition dependence of PbS detector’s performance. The high performance of wafer-scale VPD-PbS PC detectors, which attains the same performance as standard CBD-PbS detectors, manifests that the VPD technology opens up a new avenue to the industrialization of uncooled lead-salt PC detectors.

Lead Selenide Thin Films and Uncooled Midinfrared Detectors by Vapor Phase Deposition.

The broad application of lead selenide (PbSe)-based uncooled midinfrared (MIR) detectors has been hindered by the nonuniformity of wafer-level films prepared by the conventional chemical bath deposition (CBD) method. Herein, using a vapor phase deposition (VPD) approach, we demonstrate the deposition of 3 in. wafer-scale uniform PbSe thin films with thicknesses of up to 1.5 μm. To trigger the MIR response, the as-grown films were sensitized at an elevated temperature in an oxygen-iodine atmosphere. We discovered that the key to spark off the MIR response of the PbSe detector originated from the self-assembled rodlike microstructures in the thin films, which can be controlled by the I2/PbSe flux ratio in the VPD process. At room temperature, the thin film detector exhibits an excellent optoelectronic performance, with detectivity up to 2.4 × 109 cm Hz1/2 W-1 achieved under optimized conditions. Our results show that the VPD method opens up a new avenue to the industrialization of uncooled lead-salt MIR detectors.

Controlling the asymmetry of densified and porous hybrid coatings based on vapor sublimation and deposition

Interface coating technology is important to render altered surface properties for materials while replacing undesired original properties. We herein introduce an asymmetric and hybrid coating comprising controlled structural and chemical properties in one coating layer synthesized in simple steps by a vapor-phase sublimation and deposition process. The synthesis of the hybrid coating is based on acknowledging that the adsorption-limited and diffusion-limited polymerization of poly (p-chloro-xylylene) is shown to vary the final coating form factor into a densified thin film and porous structure of poly (p-chloro-xylylene), respectively. The current study enables the manipulation of the two mechanisms at the solid/vapor interface by utilizing ice templates on material substrates with confined and designable configurations as well as locations, and the proposed fabrication process produces asymmetric and hybrid coatings in one transformation step from the arranged ice templates to the substrates. Demonstrations of such advanced hybrid coatings include side-by-side and/or layer-by-layer arrangement of dense/porous films of poly (p-chloro-xylylene) in horizontal and vertical layouts, as well as particulate and organized structural configurations to address the dense/porous combination, and finally, combined structural and chemical properties with define compartments in one coating layer. Most importantly, these hybrid coatings are synthesized utilizing simple mechanisms in simple steps regardless of the complication of the design of the asymmetry configuration, and the fabrication process uses environmentally-friendly water as a template together with the subsequent dry and clean vapor-phase sublimation and deposition process, in which no solvent, initiator, or catalyst is needed. The proposed hybrid coating technology is expected to attract unlimited applications across multidisciplinary fields in materials science.

Improved Cycling Stability of LiNi0.8 Co0.1 Mn0.1 O2 Cathode Material via Variable Temperature Atomic Surface Reduction with Diethyl Zinc.

High-Ni-rich layered oxides [e.g., LiNix Coy Mnz O2 ; x> 0.5, x+ y+ z= 1] are considered one of the most promising cathodes for high-energy-density lithium-ion batteries (LIB). However, extreme electrode-electrolyte reactions, several interfacial issues, and structural instability restrict their practical applicability. Here, a shortened unconventional atomic surface reduction (ASR) technique is demonstrated on the cathode surface as a derivative of the conventional atomic layer deposition (ALD) process, which brings superior cell performances. The atomic surface reaction (reduction process) between diethyl-zinc (as a single precursor) and Ni-rich NMC cathode [LiNi0.8 Co0.1 Mn0.1 O2 ; NCM811] material is carried out using the ALD reactor at different temperatures. The temperature dependency of the process through advanced spectroscopy and microscopy studies is demonstrated and it is shown that thin surface film is formed at 100°C, whereas at 200°C a gradual atomic diffusion of Zn ions from the surface to the near-surface regions is taking place. This unique near-surface penetration of Zn ions significantly improves the electrochemical performance of the NCM811 cathode. This approach paves the way for utilizing vapor phase deposition processes to achieve both surface coatings and near-surface doping in a single reactor to stabilize high-energy cathode materials.

Wear and surface finish studies on CVD coated tungsten carbide indexable inserts

The present work aims at studying of the different types of wear occurring in cemented carbide indexable inserts. Chemical Vapour Deposition (CVD) coated tungsten carbide inserts were selected for the experimentation. Coating was brought about by vapor phase deposition process (CVD). TiN, TiC & Al2O3 coated grades were considered, as they are presently in wide commercial applications. Experiments have been conducted to study the flank wear, crater wear, nose deformation, built up edge formation etc., using R&D facilities at Kennametal India Ltd., Bengaluru. Experiments were conducted to compare surface finish at different feeds and different machining time. Studies indicated that the wear development and wear progression is very much slower in coated grades compared to uncoated grades. Surface finish is comparatively good in case of coated grades which are inferred using SEM. At low cutting speeds the existence of TiC Coating increases the life of the tool. Diffusion occurs as the cutting speed is increased, resulting in a high temperature, necessitating the use of a glaze that is both thermally and chemically stable (Al2O3). Wear analysis is an essential part of cutting tool application in order to assess the performance of coated layers as well as coating process. To measure the wear resistance of the material Pin on disc method is used. Wear analysis were carried out to study all the three types of wear. Experiments were conducted to record flank wear, crater wear, and Built-Up-Edge (BUE) in plain turning of EN8 alloy steel in CNC high powered lathe. Studies were extended to compare tool life of coated grades with uncoated grades. The results of the different stages of the experiments were recorded and discussed in the current study.

Parylene-Based Porous Scaffold with Functionalized Encapsulation of Platelet-Rich Plasma and Living Stem Cells for Tissue Engineering Applications.

A scaffold was fabricated to synergistically encapsulate living human adipose-derived stem cells (hASCs) and platelet-rich plasma (PRP) based on a vapor-phase sublimation and deposition process. During the process, ice templates were prepared using sterile water as the solvent and were used to accommodate the sensitive living cells and PRP molecules. Under controlled processing conditions, the ice templates underwent vapor sublimation to evaporate water molecules, while at the same time, vapor-phase deposition of poly-p-xylylene (Parylene, USP Class VI highly biocompatible) occurred to replace the templates, and the final construction yielded a scaffold with Parylene as the matrix, with simultaneously encapsulated living hASCs and PRP molecules. Evaluation of the fabricated synergistic scaffold for the proliferation activities toward the encapsulated hASCs indicated significant augmentation of cell proliferation contributed by the PRP ingredients. In addition, osteogenic activity in the early stage by alkaline phosphatase expression and later stage with calcium mineralization indicated significant enhancement toward osteogenetic differentiation of the encapsulated hASCs, which were guided by the PRP molecules. By contrast, examinations of adipogenic activity by lipid droplet formation revealed an inhibition of adipogenesis with decreased intracellular lipid accumulation, and a statistically significant downregulation of adipogenic differentiation was postulated for the scaffold products when compared to the osteogenetic results and the control experiments. The reported fabrication method featured a clean and simple process to construct scaffolds that combined delicate living hASCs and PRP molecules inside the structure. The resultant synergistic scaffold and the selected commercially available hASCs and PRP are emerging as tissue engineering tools that provide multifunctionality for tissue repair and regeneration.

Vapor-phase deposition-based self-assembled monolayer for an electrochemical sensing platform

Vapor-phase deposition was investigated to prepare electrochemically stable self-assembled monolayers (SAMs) since the promising coating technology can improve the surface functionality for electrochemical biosensors. In our experiments, mercaptopropionic acid (MPA)–Au SAMs in vapor-phase deposition were compared with those in the liquid-phase process, and their electrochemical properties were interrogated by measuring cyclic voltammetry and impedance spectroscopy. As a result, Au–MPA SAMs prepared in a vapor-phase process exhibited much higher electrochemical stability than those in a liquid-phase process. Furthermore, parameters in the vapor–phase deposition process were optimized for reproducible impedance signals, and the as-prepared Au–MPA SAMs under the conditions were adopted for detecting target IgE. It would pave the way for the development of a highly reproducible electrochemical bio-sensing platform.

Uniform Polypyrrole Layer-Coated Sulfur/Graphene Aerogel via the Vapor-Phase Deposition Technique as the Cathode Material for Li-S Batteries.

The practical application of Li-S batteries is hampered because of their poor cycling stability caused by electrolyte-dissolved lithium polysulfides. Dual functionalities such as strong chemical adsorption stability and high conductivity are highly desired for an ideal host material for the sulfur-based cathode. Herein, a uniform polypyrrole layer-coated sulfur/graphene aerogel composite is designed and synthesized using a novel vapor-phase deposition method. The polypyrrole layer simultaneously acts as a host and an adsorbent for efficient suppression of polysulfide dissolution through strong chemical interaction. The density functional theory calculations reveal that the polypyrrole could trap lithium polysulfides through stronger bonding energy. In addition, the deflation of sulfur/graphene hydrogel during the vapor-phase deposition process enhances the contact of sulfur with matrices, resulting in high sulfur utilization and good rate capability. As a result, the synthesized polypyrrole-coated sulfur/graphene aerogel composite delivers specific discharge capacities of 1167 and 409.1 mA h g-1 at 0.2 and 5 C, respectively. Moreover, the composite can maintain a capacity of 698 mA h g-1 at 0.5 C after 500 cycles, showing an ultraslow decay rate of 0.03% per cycle.

Fabrication of Asymmetrical and Gradient Hierarchy Structures of Poly-p-xylylenes on Multiscale Regimes Based on a Vapor-Phase Sublimation and Deposition Process

An elegant and precise method to fabricate asymmetrical structures and/or gradient structures was developed based on a vapor-phase sublimation and deposition process. The fabricated materials exhib...

Grafted Nanofilms Promote Dropwise Condensation of Low-Surface-Tension Fluids for High-Performance Heat Exchangers

Summary We have designed grafted polymer coatings using initiated chemical vapor deposition (iCVD), a solvent-free, substrate-independent, vapor-phase deposition process, that are capable of stable dropwise condensation of low-surface-tension fluids. Our iCVD coatings effectively increase the vapor-side heat transfer coefficient of the condenser, are stable under industrial environments, and can be applied in a scalable fashion. We explore how tuning the grafting of these iCVD films can minimize the contact angle hysteresis and impact droplet shedding and ultimately heat transfer performance. We measure a 4- to 8-fold enhancement in vapor-side heat transfer coefficients on a variety of substrates including industrially relevant heat exchanger metals such as steel and titanium. We demonstrate that iCVD can be applied to tubular geometries, which allows for direct translation to shell-and-tube heat exchangers, used across industries. Finally, we estimate the overall cycle efficiency improvement our coatings can provide to such processes using an example organic Rankine cycle.

Designing CdS/Se heterojunction as high-performance self-powered UV-visible broadband photodetector

A Se nanorod film is successfully synthesized on a hydrothermally grown CdS layer through a facile vapor phase deposition process, forming a n-CdS/p-Se heterojunction. By virtue of the narrow direct bandgap and large absorption coefficient in UV-visible range of CdS and Se, the integrated CdS/Se photodetector exhibits excellent self-powered behavior in a wide spectral range. In particular, the heterojunction device shows a high photoresponse under weak light irradiation (500 nm, 1.08 μW/cm2) with a large on-off ratio (9 × 103), high responsivity (40 mA/W) and detectivity (1.3 × 1013 Jones), and fast response speed (rise time 2 μs and decay time 22 ms).

Vapor phase deposition of fluoroalkyl trichlorosilanes on silicon and glass: Influence of deposition conditions and chain length on wettability and adhesion forces

Vapor phase deposition (VPD) of a homologous series of fluoroalkyl silanes (FAS), containing 3 to 10 carbon atoms in a molecule, on silicon and glass substrates was investigated. Two deposition procedures were compared: 1) VPD carried out at atmospheric pressure, where silanization reactions occur in an unrestricted presence of FAS vapors and atmospheric water and 2) VPD carried out under evacuated conditions. Significant differences between topographies of the coatings obtained in the two VPD processes were found, suggesting that silanization conditions highly influenced molecular packing densities of the coatings. This, in turn, was considered to influence the trends in the acid-base (AB) component of surface free energy (SFE), macroscopic work of water-substrate adhesion and locally measured adhesion forces on these surfaces. The AB interactions were found to significantly influence wetting and adhesive properties of coatings obtained from short chain precursors by atmospheric pressure VPD (AP-VPD). Wettability and adhesive force on coatings from longer chain precursors deposited by AP-VPD and on coatings from the whole range of tested FAS precursors deposited in low-pressure VPD (LP-VPD) were found to be predominantly governed by dispersive interactions. Correlations between locally measured adhesive force and macroscopic work of adhesion were found. Considering the net effect of FAS deposition procedure on the adhesive force strength, LP-VPD was found to more effectively reduce adhesive force on Si substrates, and both deposition methods were found to be equally effective on glass substrates. Advantages and disadvantages of both deposition methods were highlighted, with references to their most suitable applications.

Surface‐Modified Mesh Filter for Direct Nucleic Acid Extraction and its Application to Gene Expression Analysis

Rapid and convenient isolation of nucleic acids (NAs) from cell lysate plays a key role for onsite gene expression analysis. Here, this study achieves one-step and efficient capture of NA directly from cell lysate by developing a cationic surface-modified mesh filter (SMF). By depositing cationic polymer via vapor-phase deposition process, strong charge interaction is introduced on the surface of the SMF to capture the negatively charged NAs. The NA capturing capability of SMF is confirmed by X-ray photoelectron spectroscopy, fluorescent microscopy, and zeta potential measurement. In addition, the genomic DNAs of Escherichia Coli O157:H7 can be extracted by the SMF from artificially infected food, and fluorescent signal is observed on the surface of SMF after amplification of target gene. The proposed SMF is able to provide a more simplified, convenient, and fast extraction method and can be applied to the fields of food safety testing, clinical diagnosis, or environmental pollutant monitoring.

A Plasmonic Colloidal Photocatalyst Composed of a Metal–Organic Framework Core and a Gold/Anatase Shell for Visible‐Light‐Driven Wastewater Purification from Antibiotics and Hydrogen Evolution

Porous coordination polymers (PCP) or metal- organic frameworks (MOF) are promising materials for the generation of photocatalytically active composite materials. Here, a novel synthesis concept is reported, which permits the formation of PCP/MOF-core-Au/anatase-shell materials. These materials are photocatalysts for wastewater purification and hydrogen generation from water under visible-light illumination. MIL-101 (Cr) is utilized as the core material, which directs the size of the core-shell compound and ensures the overall stability. In addition, its excellent reversible large molecule sorption behavior allows the materials synthesis. The crystalline anatase shell is generated stepwise under mild conditions using titanium(IV) isopropoxide as a precursor. The high degree of control of the vapor phase deposition process permits the precise anatase shell formation. The generation of plasmonic active gold particles on the TiO2 shell leads to an efficient material for visible-light-driven photocatalysis with a higher activity than gold-decorated P25 (Degussa).

Broadband nanophotonic waveguides and resonators based on epitaxial GaN thin films

We demonstrate broadband, low loss optical waveguiding in single crystalline GaN grown epitaxially on c-plane sapphire wafers through a buffered metal-organic chemical vapor phase deposition process. High Q optical microring resonators are realized in near infrared, infrared, and near visible regimes with intrinsic quality factors exceeding 50 000 at all the wavelengths we studied. TEM analysis of etched waveguide reveals growth and etch-induced defects. Reduction of these defects through improved material and device processing could lead to even lower optical losses and enable a wideband photonic platform based on GaN-on-sapphire material system.

β-Hydrogen Elimination Mechanism in the Absence of Low-Lying Acceptor Orbitals in EH2(t-C4H9) (E = N-Bi).

The β-hydrogen elimination reactions of group 15 alkyl compounds at the example of EH2(t-C4H9) (element E = N-Bi) were investigated and compared to the group 13 example of GaH2(t-C4H9). With the aid of extensive density functional theory based analysis of atomic and electronic structures at the transition state, we can derive three distinct reaction classes. The gallium compound follows the well-known β-hydride route with participation of an empty p orbital at the metal in a concerted, synchronous fashion, exhibiting a low barrier. For compounds with group 15 elements, we find highly nonsynchronous reactions with high reaction barriers. In the case of nitrogen, a proton-like H atom is transferred via attack of the nitrogen nonbonding electron pair. For the heavier homologues (P-Bi), E-Cα bond breaking occurs first and the H atom does not carry charge at the transition state. The reaction barrier in group 15 homologues is thus determined by the E-Cα bond strength down the group. The results enable a rationale for ligand design for precursors involved in chemical vapor-phase deposition processes because a good ligand needs to stabilize the positive charge at Cα.

Vapor-phase preparation of gold nanocrystals by chloroauric acid pyrolysis

We report that gold nanocrystals can be prepared from vapor phase using chloroauric acid (HAuCl4) as the precursor. By tuning the vapor-phase deposition parameters, the size and space distribution of the gold nanocrystals can be well controlled on substrates. Systematic control experiments demonstrate that intermediate AuCl and AuCl3 products pyrolyzed from HAuCl4 play an essential role in this vapor-phase deposition process. Compared to conventional wet-chemical synthesis process, vapor-phase process enables direct deposition of gold nanoparticles on solid substrates with better coverage and uniformity, which may find applications in surface-enhanced Raman scattering and plasmon-enhanced photocatalysis.

Simple and Reliable Method to Incorporate the Janus Property onto Arbitrary Porous Substrates

Economical fabrication of waterproof/breathable substrates has many potential applications such as clothing or improved medical dressing. In this work, a facile and reproducible fabrication method was developed to render the Janus property to arbitrary porous substrates. First, a hydrophobic surface was obtained by depositing a fluoropolymer, poly(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl methacrylate) (PHFDMA), on various porous substrates such as polyester fabric, nylon mesh, and filter paper. With a one-step vapor-phase deposition process, termed as initiated chemical vapor deposition (iCVD), a conformal coating of hydrophobic PHFDMA polymer film was achieved on both faces of the porous substrate. Since the hydrophobic perfluoroalkyl functionality is tethered on PHFDMA via hydrolyzable ester functionality, the hydrophobic functionality on PHFDMA was readily released by hydrolysis reaction. Here, by simply floating the PHFDMA-coated substrates on KOH(aq) solution, only the face of the PHFDMA-coated substrate in contact with the KOH(aq) solution became hydrophilic by the conversion of the fluoroalkyl ester group in the PHFDMA to hydrophilic carboxylic acid functionality. The hydrophilized face was able to easily absorb water, showing a contact angle of less than 37°. However, the top side of the PHFDMA-coated substrate was unaffected by the exposure to KOH(aq) solution and remained hydrophobic. Moreover, the carboxylated surface was further functionalized with aminated polystyrene beads. The porous Janus substrates fabricated using this method can be applied to various kinds of clothing such as pants and shirts, something that the lamination process for Gore-tex has not allowed.