Surface Energy Of Substrate Research Articles

Controlled processing of polymer nanoribbons: Enabling microhelix transformations

ABSTRACTFlow‐coated, two‐dimensional polymer ribbon structures undergo a shape‐transformation into a three‐dimensional helix upon their release into a solution. Driven by surface forces and due to geometric asymmetry, the helix radius and spring constant depend upon the ribbon cross‐section dimensions, surface energy, and material elastic modulus. Such spring‐like microhelices offer multiple functionalities combined with mechanical stretching and shape recovery. Fabricating such microhelices requires a sequence of processing steps, beginning with flow‐coating of ribbons on a substrate, followed by etching of a “scum layer” to allow for an independent release into a solution, upon which shape‐transformation occurs. During the deposition‐etch‐release sequence, various control parameters influence the nanoribbon size and geometry, hence the helix properties. The experimental study presented here focuses on the influence of meniscus height, substrate velocity, substrate surface energy, and etch time on nanoribbon size (height and width), scum layer thickness, and helix radius. The results show that meniscus height and contact angle dictate flux toward the meniscus edge and volume available for spatial assembly, allowing control over the aspect ratio of ribbons. We vary the aspect ratio by two orders of magnitude, while maintaining geometric asymmetry needed for helix shape‐transformation. We provide robust scaling for the nanoribbon size and geometry and report the advantages and disadvantages of different parameters, in the control of polymer nanoribbon and helix fabrication. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1270–1278

Polytype control of MoS2 using chemical bath deposition.

Molybdenum disulfide (MoS2) has a wide range of applications from electronics to catalysis. While the properties of single-layer and multilayer MoS2 films are well understood, controlling the deposited MoS2 polytype remains a significant challenge. In this work, we employ chemical bath deposition, an aqueous deposition technique, to deposit large area MoS2 thin films at room temperature. Using Raman spectroscopy and x-ray photoelectron spectroscopy, we show that the deposited MoS2 polytype can be changed from semiconducting 2H MoS2 on hydrophobic -CH3 and -CO2C6F5 terminated self-assembled monolayers (SAMs) to semimetallic 1T MoS2 on hydrophilic -OH and -COOH terminated SAMs. The data suggest that the deposition of MoS2 polytypes is controlled by the substrate surface energy. High surface energy substrates stabilize 1T MoS2 films, while 2H MoS2 is deposited on lower surface energy substrates. This effect appears to be general enabling the deposition of different MoS2 polytypes on a wide range of substrates.

(Invited) Unraveling Synergistic Interactions driving the Chemical Mechanical Planarization Process

Due to the emergence of sub-10 nm technologies, next generation CMP slurry formulations have continued to increase in additive (nanoparticle and chemistry) complexity to meet stringent device specifications. Therefore, it is essential to probe the molecular level interactions at the nanoparticle/slurry chemistry/substrate interface and in turn correlate them to key performance metrics such as removal rate, post CMP defects, planarization efficiency. More specifically, this work has developed a suite of techniques that explore the adsorption/complexation dynamics that evolve during the CMP process. Employing a suite of techniques such as modified atomic force microscopy (AFM), electrochemical quartz crystal nanobalance (EQCN), dynamic contact angle measurements, fluorescence microscopy, pre/post polish characterization of particle properties (size and zeta potential), and in-situ rotating disk electrode open circuit potential measurement the critical static and dynamic mechanisms can be exposed. Correlation of this information gives way to modulation (desired or undesired) of the CMP performance potentially providing tunabilty (process and formulation) at advanced technology nodes to meet stringent electrical, topography, and defect requirements. Furthermore, these methods have shown great promise as a vehicle to probe the molecular level interactions at the nanoparticle/chemistry/ substrate interface. Results have shown excellent correlation to key process performance metrics and have provided insight into relevant surface chemistry changes that impact critical interactions during the CMP process. This presentation will address key interactions through a series of case studies focusing on probing the impact of inhibitor structure on the substrate surface energy relevant to Cu CMP, the role of slurry chemistry on controlling defectivity during STI post-CMP cleaning, and effect of organic additives on the modulation of nanoparticle surface properties to enhance STI CMP performance.

Detailed Characterization of the Effect of Application of Commercially Available Surface Treatment Agents on Textile Wetting Behavior

The change in the wetting behavior of a standard commercially available textile material in response to surface treatment has been thoroughly characterized with conventional laboratory measurement techniques. The characterization was carried out by taking a series of contact angle measurements that allowed for the determination of the corresponding shift in substrate surface energy as a result of the applied treatment. The collected surface energy values were expressed in terms of the spreading parameter S, which was used to describe phase behavior at the substrate/droplet interface. However, these results showed that the use of a coarse parameter S, or even the work of adhesion ( W a ) and the work of cohesion ( W c ) parameters alone did not adequately account for the observed wetting behavior. A proper description of droplet formation on substrate surface was provided only when the interfacial interaction was examined at a more detailed level by involving the individual dispersive ( σ l d , σ s d ) and polar ( σ l p , σ s p ) surface energy components of both the solid and the wetting liquid. The methodology for characterization of interactions between a textile substrate coated with various surface active agents and several functional fluids have been developed. Several practical examples of how this methodology can be applied to describe the substrate surface treatment and the resulting wetting behavior are described herein.

Superhydrophilic Smart Coating for Self-Cleaning Application on Glass Substrate

In general, superhydrophilic coating on glass substrate possesses water contact angle (WCA) below 10° and contains high self-cleaning properties in outdoor environment as compared to noncoated glass substrate panels. In this study, the superhydrophilic coating behavior on glass substrate has been developed. The micro- and nanosized titanium dioxide (TiO2) particles have been utilized to improve the surface roughness, and the polypropylene glycol (PPG) has been utilized to increase the surface energy of glass substrates. The wettability of coating surface shows the coating possess water contact angle (WCA) as low as 5° and suddenly reduce to 0° after 10 s. Superhydrophilic coated glass clearly shows excellent dirt repellent against dilute ketchup solution due to the absence of dirt streak on the glass surface. Meanwhile, the dirt streak is present on the bare glass surface indicating its weak self-cleaning property. The developed superhydrophilic coating on glass substrate was also found to have great antifog property compared to the bare glass substrate. Superhydrophilic surfaces have showed free tiny droplet even at 130°C of hot boiling bath for 10 min and completely dry after 1 min. The superhydrophilic coating surfaces have demonstrated free water streak after impacting with harsh water spraying for 5 min confirming that the superhydrophilic coating on glass substrate is antiwater streak.

Influence of surface treatment on the surface energy of an aluminium substrate

The mechanisms by which adhesion occurs are known. In all cases, the search for an adequate surface condition is decisive in achieving a good adhesion. For this reason, the researches usually work on modifying the surface roughness or improving the thermodynamic characteristics of the surface. The objective on this work is to analyse influence of different attack types (chemical, mechanic, with laser …) which are used to improve surface finish, roughness and surface energy. We have analysed the effects that have produced in the contact angle, measuring the surface energy by the Zisman method. The results revealed that the method of attack has more influence on the value of surface energy than the values of roughness obtained, which can make rethink the type of surface treatment to improve adhesion.

Engineering of Porphyrin Molecules for Use as Effective Cathode Interfacial Modifiers in Organic Solar Cells of Enhanced Efficiency and Stability.

In the present work, we effectively modify the TiO2 electron transport layer of organic solar cells with an inverted architecture using appropriately engineered porphyrin molecules. The results show that the optimized porphyrin modifier bearing two carboxylic acids as the anchoring groups and a triazine electron-withdrawing spacer significantly reduces the work function of TiO2, thereby reducing the electron extraction barrier. Moreover, the lower surface energy of the porphyrin-modified substrate results in better physical compatibility between the latter and the photoactive blend. Upon employing porphyrin-modified TiO2 electron transport layers in PTB7:PC71BM-based organic solar cells we obtained an improved average power conversion efficiency up to 8.73%. Importantly, porphyrin modification significantly increased the lifetime of the devices, which retained 80% of their initial efficiency after 500 h of storage in the dark. Because of its simplicity and efficacy, this approach should give tantalizing glimpses and generate an impact into the potential of porphyrins to facilitate electron transfer in organic solar cells and related devices.

Custom tailoring of conductive ink/substrate properties for increased thin film deposition of poly(dimethylsiloxane) films

The creation of more robust biocompatible printed electronics devices requires an understanding of interactions between conductive inks and substrates to achieve desired printing and functional properties. In this study, we present a water-based conductive ink that can provide a readily achieved thin film deposition on a highly hydrophobic surface such as poly(dimethylsiloxane) (PDMS). We also show that surface treatments with atmospheric plasma can be utilized to tailor the surface energy of hydrophobic substrates to improve the deposition of inks not custom made for such applications. By using a tailored Ag nano-particle ink, we have successfully printed conductive traces onto a hydrophobic (PDMS) substrate without any surface modification. It was also shown that when introducing atmospheric plasma treatment to the PDMS substrate prior to printing with the tailored ink poor printing resulted. The proposed mechanism for the cause of this poor wetting and deposition is an adverse interaction between the ink and PDMS surface caused by surface oxidation resultant of plasma treatment. The results show that the generally accepted rule that a difference between the substrate and ink surface energy of 10 mN/m for good print quality does not necessarily hold true in the case of functional printing.

Vertical Stratification Engineering for Organic Bulk-Heterojunction Devices.

High-efficiency organic solar cells (OSCs) can be produced through optimization of component molecular design, coupled with interfacial engineering and control of active layer morphology. However, vertical stratification of the bulk-heterojunction (BHJ), a spontaneous activity that occurs during the drying process, remains an intricate problem yet to be solved. Routes toward regulating the vertical separation profile and evaluating the effects on the final device should be explored to further enhance the performance of OSCs. Herein, we establish a connection between the material surface energy, absorption, and vertical stratification, which can then be linked to photovoltaic conversion characteristics. Through assessing the performance of temporary, artificial vertically stratified layers created by the sequential casting of the individual components to form a multilayered structure, optimal vertical stratification can be achieved. Adjusting the surface energy offset between the substrate results in donor and acceptor stabilization of that stratified layer. Further, a trade-off between the photocurrent generated in the visible region and the amount of donor or acceptor in close proximity to the electrode was observed. Modification of the substrate surface energy was achieved using self-assembled small molecules (SASM), which, in turn, directly impacted the polymer donor to acceptor ratio at the interface. Using three different donor polymers in conjunction with two alternative acceptors in an inverted organic solar cell architecture, the concentration of polymer donor molecules at the ITO (indium tin oxide)/BHJ interface could be increased relative to the acceptor. Appropriate selection of SASM facilitated a synchronized enhancement in external quantum efficiency and power conversion efficiencies over 10.5%.

Biomaterial surface energy-driven ligand assembly strongly regulates stem cell mechanosensitivity and fate on very soft substrates

Although mechanisms of cell-material interaction and cellular mechanotransduction are increasingly understood, the mechanical insensitivity of mesenchymal cells to certain soft amorphous biomaterial substrates has remained largely unexplained. We reveal that surface energy-driven supramolecular ligand assembly can regulate mesenchymal stem cell (MSC) sensing of substrate mechanical compliance and subsequent cell fate. Human MSCs were cultured on collagen-coated hydrophobic polydimethylsiloxane (PDMS) and hydrophilic polyethylene-oxide-PDMS (PEO-PDMS) of a range of stiffnesses. Although cell contractility was similarly diminished on soft substrates of both types, cell spreading and osteogenic differentiation occurred only on soft PDMS and not hydrophilic PEO-PDMS (elastic modulus <1 kPa). Substrate surface energy yields distinct ligand topologies with accordingly distinct profiles of recruited transmembrane cell receptors and related focal adhesion signaling. These differences did not differentially regulate Rho-associated kinase activity, but nonetheless regulated both cell spreading and downstream differentiation.

The enhanced abrasion resistance of an anti-fingerprint coating on chrome-plated brass substrate by integrating sputtering and atmospheric pressure plasma jet technologies

We demonstrate the procedure of fabricating an anti-fingerprint coating on plated-Cr/brass substrates by the combination of two processes: (1) Sputtering and (2) Atmospheric pressure plasma jet (APPJ). APPJ surface treatment on sputtered-SiOx glue layer on plated-Cr/brass substrate is conducted to improve its surface property to be hydrophilic for chemical bonding with an anti-fingerprint agent (AF-C01). The results show that the surface energy of original substrate are evolving from 44.2 mN/m to 60.8 mN/m and 76.9 mN/m for the sputtered-SiOx film and APPJ-treated SiOx film, respectively. Subsequently, the spin-coating process using a commercialnt (AF-C01 agent for the prepared sample is implemented. The hydrophobicity of anti-fingerprint characteristics for all of the samples with a quite low surface energy around 10.5 mN/m are obtained. For practical evaluation of abrasion behavior, a good abrasion resistance of AF/APPJ-treated SiOx/plated-Cr/brass sample under 1000 g-steel wood loading is evidently obtained from the slow variation of water contact angle value. The results demonstrate that the feasibility of integrating APPJ process on the sputtered-SiOx film for improving the surface properties of chrome-plated brass substrate is practically achieved.

Unified icing theory based on phase transition of supercooled water on a substrate

Lack of knowledge on substrate icing hinders us from predicting the effects of typical substrate properties in icing and anti-icing research. The pattern formation and tip shape of icing on a substrate must be explored to understanding the physics of icing on a substrate. In this paper, the pattern, velocity and tip shape of ice on substrates with different thermal conductivities and surface energies are evaluated in a series of experiments. Experimental results show that as supercooling and thermal conductivity increase, the ice on substrate evolves from a single-needle dendrite to a smooth ice film. In contrast, for free icing the same evolution process can be completed at a higher supercooling than substrate icing. Experimental results on hydrophilic and Plexiglas surfaces demonstrate an abruptly decrease of velocity and Peclet number of ice occurs at approximately 271.6 K, whereas the tip shape of ice does not change obviously; while for free icing this phenomenon is not found. Furthermore, a theoretical analysis on phase transition of substrate icing is performed. It shows that the surface energy of substrates can increase the size of metastable cubic ice and reduce the temperature on the ice tip by 1.5 K compared to free ice, thereby causing the decrease in the velocity and Peclet number of ice. Also the heat conduction of substrates decrease the heat flux in ice growth direction and lead to absolute stability of substrate icing in lower supercooling compared to free icing. In terms of the comparison between free icing and substrate icing, a unified icing theory is proposed to describe the equilibrium icing mode, the non-equilibrium growth state, and the corresponding growth equations. Using this theory, the velocity and pattern of substrate icing with different supercooling, thermal conductivity, and surface energy can be predicted well, as well as these results of free icing.

Wettability of Si and Al–12Si alloy on Pd-implanted 6H–SiC**Project supported by the National Natural Science Foundation of China (Grant Nos. 51572112 and 51172177), the Natural Science Foundation of Jiangsu Province, China (Grant No. BK20151340), the Six Talent Peaks Project of Jiangsu Province, China (Grant Nos. 2014-XCL-002 and TD-XCL-004), the Innovation/Entrepreneurship Program of Jiangsu Province, China (Grant No. [2015]26), and the

SiC monocrystal substrates are implanted by Pd ions with different ion-beam energies and fluences, and the effects of Pd ion implantation on wettability of Si/SiC and Al–12Si/SiC systems are investigated by the sessile drop technique. The decreases of contact angles of the two systems are disclosed after the ion implantation, which can be attributed to the increase of surface energy (σSV) of SiC substrate derived from high concentration of defects induced by the ion-implantation and to the decrease of solid–liquid surface energy (σSL) resulting from the increasing interfacial interactions. This study can provide guidance in improving the wettability of metals on SiC and the electronic packaging process of SiC substrate.

Influence of substrate surface energy and surfactant on crystalline morphology and surface defect density in hydrothermally-grown ZnO nanowires

We investigated the influence of substrate surface energy before seed layer formation on hydrothermally grown zinc oxide (ZnO) nanowires (NWs). The qualities of ZnO NWs prepared by the surface-enhanced growth method with ultraviolet ozone (UVO) treatment were analyzed in terms of crystalline morphology and surface defect density, and were compared with those of ZnO NWs prepared by the conventional bulk-enhanced growth method adopting polyethyleneimine (PEI) as the surfactant in an aqueous growth solution. In both cases, a positive effect on the morphological properties and crystallinity of ZnO NWs was observed; however, the surface-enhanced growth method was more efficient for obtaining hydrothermally grown ZnO NWs with higher aspect ratios and larger surface areas. The ZnO NW growth rate in the surface-enhanced growth method was two times faster than in the conventional bulk-enhanced growth method. Photoluminescence (PL) spectra and time-resolved PL (TR-PL) responses indicated that a high density of oxygen vacancies on ZnO NW surfaces was produced by the surface-enhanced growth method, because highly oriented ZnO NWs can be grown without surface passivation effect, on the contrary with the bulk-enhanced growth method.

Direct, large area growth of few-layered MoS2 nanostructures on various flexible substrates: growth kinetics and its effect on photodetection studies

Even though the chemical vapor deposition approach for synthesizing MoS2 has gained in importance, direct large area growth of MoS2 on flexible substrates remains a challenge. The synthesis of MoS2 has mostly been performed in a vacuum or by thermolysis, requiring elevated temperatures and intricate post-processing techniques. Ease of synthesis of MoS2 on different flexible substrates, using a solution process strategy, would make the potential applications of MoS2 in electronics, optoelectronics and energy storage more viable. In this work we report for the first time the one-step solution-processed growth of MoS2 on various flexible substrates (cellulose paper, Al foil, Cu foil, polyimide, carbon paper, ceramic paper and cotton thread). The growth kinetics of MoS2 is explained in terms of surface energies of substrates and classical theory of nucleation and growth. The growth of MoS2 on these substrates not only yielded different morphologies of MoS2 nanosheets, but also the layers of MoS2 varied, thus confirming the key role of the substrate during the growth process. Finally, photodetection studies performed on MoS2 grown on the flexible substrates suggest that defects introduced during the hydrothermal process play a crucial role in the performance of the photodetector. This study paves the way for simple, large area solution-processed synthesis of MoS2 on various arbitrary substrates, with potential applications in the fields of optoelectronics, medical and energy storage, etc.

Dynamics of faceted thin films formation during vapor deposition

In this study, an anisotropic phase-field model was established to simulate the growth of crystalline thin films during vapor deposition. The formation and evolution of characteristic surface with faceted morphologies were demonstrated, in accordance with the regularly obtained microstructure in the actual experiments. In addition, the influences of deposition parameters, such as the deposition rate and the interfacial energy, on the formation mechanism of the characteristic morphology were also illustrated. While a relatively low surface energy of substrate was regarded, the faceted islands were formed, owing to the anisotropic interfacial energy of thin films. In the condition of a high surface energy of substrate, the layered structures of deposited films were produced, which was corresponding to the Frank–van der Merwe growth mode. As various deposition rates were utilized in the numerical simulations, diverse surface morphologies were developed on the basis of the dominant mechanisms, correlating with the adatom diffusion and the deposition kinetics. According to the calculation results, it was observed that a surface character with flattened morphology was generally driven by the adatom diffusion, while the factor of the deposition kinetics was inclined to roughen the surface of thin films. These numerical simulations enhanced the knowledge of thin film growth and facilitated the progress of the vapor deposition technology for advanced applications.

Interfacial and thermal energy driven growth and evolution of Langmuir-Schaefer monolayers of Au-nanoparticles.

Structures of Langmuir-Schaefer (LS) monolayers of thiol-coated Au-nanoparticles (DT-AuNPs) deposited on H-terminated and OTS self-assembled Si substrates (of different hydrophobic strength and stability) and their evolution with time under ambient conditions, which plays an important role for their practical use as 2D-nanostructures over large areas, were investigated using the X-ray reflectivity technique. The strong effect of substrate surface energy (γ) on the initial structures and the competitive role of room temperature thermal energy (kT) and the change in interfacial energy (Δγ) at ambient conditions on the evolution and final structures of the DT-AuNP LS monolayers are evident. The strong-hydrophobic OTS-Si substrate, during transfer, seems to induce strong attraction towards hydrophobic DT-AuNPs on hydrophilic (repulsive) water to form vertically compact partially covered (with voids) monolayer structures (of perfect monolayer thickness) at low pressure and nearly covered buckled monolayer structures (of enhanced monolayer thickness) at high pressure. After transfer, the small kT-energy (in absence of repulsive water) probably fluctuates the DT-AuNPs to form vertically expanded monolayer structures, through systematic exponential growth with time. The effect is prominent for the film deposited at low pressure, where the initial film-coverage and film-thickness are low. On the other hand, the weak-hydrophobic H-Si substrate, during transfer, appears to induce optimum attraction towards DT-AuNPs to better mimic the Langmuir monolayer structures on it. After transfer, the change in the substrate surface nature, from weak-hydrophobic to weak-hydrophilic with time (i.e. Δγ-energy, apart from the kT-energy), enhances the size of the voids and weakens the monolayer/bilayer structure to form a similar expanded monolayer structure, the thickness of which is probably optimized by the available thermal energy.

Characterisation of platinum nanoparticles deposited on C60 fullerene nanowhiskers

ABSTRACTPlatinum nanoparticles (Pt NPs) with a mean diameter of 2.7 ± 0.8 nm were successfully deposited on C60 fullerene nanowhiskers (C60FNWs) by coaxial arc plasma deposition (CAPD). No correlation was observed between the face-centred cubic (fcc) lattice constant and the diameter of the deposited Pt NPs, while the mean fcc lattice constant of the Pt NPs on C60FNWs was less than that of bulk Pt and significantly different from that of the Pt NPs deposited on graphite particles. The Pt NPs deposited on graphite particles showed larger lattice strains than the Pt NPs deposited on C60FNWs. These results suggest that the strained structure of Pt NPs deposited by CAPD changes depending on the surface energy of the carbon substrate.

Improving partial wetting resolution on flexible substrates for application of polymer optical waveguides

Considering the increasing amount of data for communication and infotainment applications, fabrication of optical networks and bus systems is a challenging task for production engineering. A two-step manufacturing process for polymer optical waveguides is presented. By improving the highly efficient flexographic printing technology by laser functionalization of the printing tool in combination with a subsequent spray application, high-quality waveguides are accomplished. By adjusting the resulting surface energy of the foil substrate in the first fabrication process, the spray application achieved high-aspect ratio waveguides with a low attenuation of 0.2 dB/cm at 850 nm.

Critical Role of Surface Energy in Guiding Crystallization of Solution-Coated Conjugated Polymer Thin Films.

It is well-known that substrate surface properties have a profound impact on the morphology of thin films solution coated atop and the resulting solid-state properties. However, design rules for guiding the substrate selection have not yet been established. Such design rules are particularly important for solution-coated semiconducting polymers, as the substrate-directed thin film morphology can impact charge transport properties by orders of magnitude. We hypothesize that substrate surface energies dictate the thin film morphology by modulating the free energy barrier to heterogeneous nucleation. To test this hypothesis, we systematically vary the substrate surface energy via surface functionalization techniques. We perform in-depth morphology and device characterizations to establish the relationship between substrate surface energy, thin film morphology and charge transport properties, employing donor-acceptor (D-A) conjugated polymers. We find that decreasing the substrate surface energy progressively increases thin film crystallinity, degree of molecular ordering, and extent of domain alignment. Notably, the enhanced morphology on the lowest surface energy substrate leads to a 10-fold increase in the charge carrier mobility. We further develop a free energy model relating the substrate surface energy to the penalty of heterogeneous nucleation from solution in the thin film geometry. The model correctly predicts the experimental trend, thereby validating our hypothesis. This work is a significant step toward establishing design rules and understanding the critical role of substrates in determining morphology of solution-coated thin films.