Polymer Film Thickness Research Articles

Printing 2D Conjugated Polymer Monolayers and Their Distinct Electronic Properties

AbstractRecently, 2D monolayer films of conjugated polymers have gained increasing attention owing to the preeminence of 2D inorganic films that exhibit unique optoelectronic and mechanical properties compared to their bulk analogs. Despite numerous efforts, crystallization of semiconducting polymers into highly ordered 2D monolayer films still remains challenging. Herein, a dynamic‐template‐assisted meniscus‐guided coating is utilized to fabricate continuous, highly ordered 2D monolayer films of conjugated polymers over a centimeter scale with enhanced backbone π–π stacking. In contrast, monolayer films printed on solid substrates confer upon the 1D fiber networks strong alkyl side‐chain stacking at the expense of backbone packing. From single‐layers to multilayers, the polymer π‐stacks change from edge‐on to bimodal orientation as the film thickness reaches ≈20 nm. Spectroscopic and cyclic voltammetry analysis reveals an abrupt increase in J‐aggregation and absorption coefficient and a decrease in bandgap and highest occupied molecular orbital level until critical thickness, possibly arising from the straightened polymer backbone. This is corroborated by an abrupt increase in hole mobility with film thickness, reaching a maximum of 0.7 cm2 V−1 s−1 near the critical thickness. Finally, fabrication of chemical sensors incorporating polymer films of various thicknesses is demonstrated, and an ultrahigh sensitivity of the ≈7 nm thick ultrathin film (bilayers) to 1 ppb ammonia is shown.

A Self-Healing Nanofiber-Based Self-Responsive Time-Temperature Indicator for Securing a Cold-Supply Chain.

Perishable foods at undesired temperatures can generate foodborne illnesses that present significant societal costs. To certify refrigeration succession in a food-supply chain, a flexible, easy-to-interpret, damage-tolerant, and sensitive time-temperature indicator (TTI) that uses a self-healing nanofiber mat is devised. This mat is opaque when refrigerated due to nanofiber-induced light scattering, but becomes irreversibly transparent at room temperature through self-healing-induced interfibrillar fusion leading to the appearance of a warning sign. The mat monitors both freezer (-20 °C) and chiller (2 °C) successions and its timer is tunable over the 0.5-22.5 h range through control of the polymer composition and film thickness. The thin mat itself serves as both a temperature sensor and display; it does not require modularization, accurately measures localized or gradient heat, and functions even after crushing, cutting, and when weight-loaded in a manner that existing TTIs cannot. It also contains no drainable chemicals and is attachable to various shapes because it operates through an intrinsic physical response.

Влияние толщины субмикронных пленок электроактивных полимеров на токи термостимулированной деполяризации

Abstract The results of studying the thermally stimulated depolarization currents in thin films of polydiphenylenephthalide (PDP) with a thickness of 20 nm to 1.4 μm under a constant stress in a structure with an insulating dielectric layer are presented. Nonmonotonic behavior of the dependence of the activation energy of charge carrier trapping sites and the relaxation of the space charge on the thickness of PDP polymer films is found. A correlation between the change in the supramolecular structure of the films and the above parameters is established. The obtained results are interpreted using the theory of thermally stimulated discharge in short-circuit heterogeneous structures.

Preparation of fluorinated/silanized polyacrylates amphiphilic polymers and their anticorrosion and antifouling performance

A series of fluorinated/silanized polyacrylates amphiphilic polymers were successfully synthesized by changing its fluorinated groups content (CFP) and then thoroughly characterized. A modified corrosion resistance (RSd) that takes the polymer film thickness into account was proposed to evaluate the anticorrosion performance of the polymers. The results show that the thermal stability of all polymers is high with the decomposition temperature being higher than 330 °C, and the RSd larger than 108 Ωcm2 μm−1 even after immersion in 3.5 wt% NaCl static solution for 7 d. Meanwhile, almost all the polymer’s water contact angle, surface smoothness, Rsd and antifouling performance (except for the adsorption of HFg on the polymer of CFP being ca. 26.7 wt%) increase with the increment of CFP, whereas CFP has negligible influence on polymer’s glass transition temperature. Furthermore, the polymer of CFP being ca. 15.4 wt% exhibits the lower adsorption and the maximum removal of both BAS and HFg proteins.

Nanoscale Block Copolymer Self‐Assembly and Microscale Polymer Film Dewetting: Progress in Understanding the Role of Interfacial Energies in the Formation of Hierarchical Nanostructures

AbstractBlock copolymer (BCP) self‐assembly (SA) can be exploited for next‐generation lithography for the advanced nanopatterning of surfaces with versatile nanoscale features. To render BCP‐SA suitable for the creation of tailored surface patterns, a fundamental understanding of interfacial interactions is crucial. This progress report gives an overview on the interplay of BCP microscale film thickness modulation and nanoscale microphase separation during BCP‐SA. Light is shed on the role of interfacial energies in both events. Microscale processes determining the topography of BCP films, i.e., hole/island formation and dewetting into droplets, are presented. Nanoscale microphase separation into energetically favorable pattern orientations in dependency on the polymer film thickness and influenced by surface polarities are discussed critically. Finally, examples are shown in which the combination of microscale dewetting and nanoscale microphase separation are exploited to create hierarchical nanostructures from BCPs. An outlook is given presenting successful applications of both mechanisms on prepatterned surfaces in order to control position and morphology of the hierarchical nanostructures. This approach is particularly promising for the creation of advanced surface architectures.

PLASMA PARAMETERS AND COMPOSITION IN CF4 + O2 + Ar AND CHF3 + O2 +Ar IN REACTIVE ION ETCHING PROCESSES

The comparative analysis of both CF4+O2+Ar and CHF3+O2+Ar plasma systems under the typical conditions of reactive ion etching of silicon and silicon-based compounds was carried out. The data on internal plasma parameters, plasma chemistry as well as the steady-state plasma composition were obtained using a description of Langmuir probe diagnostics and 0-dimensional (global) plasma modeling. As a presented in the literature, both experimental and modeling procedures were carried out at constant total gas pressure, input power, bias power. The obtained results allowed one 1) to figure out the influence of oxygen on steady-state densities of plasma active species through the kinetics of both electron-impact and atom-molecular reactions; 2) to understand the features of fluorine atoms and fluorocarbon radicals kinetics which determine chemical activity and polymerization ability of plasmas in respect to treated surfaces; 3) to perform the model-bases analysis of heterogeneous process kinetics (etching, polymerization, polymer destruction) which determine the overall etching regime and output parameters. It was found that the substitution of argon for oxygen in both gas mixtures 1) results in monotonic increase in fluorine atom density; 2) is accompanied by decreasing polymerization ability of a gas phase and 3) causes the rapid (by about two orders of magnitude at ~ 20% О2) decrease in fluorocarbon polymer film thickness with the higher values for CHF3+O2+Ar system.

First-Principles Calculation of Physical Tensors of α-Diisopropylammonium Bromide (α-DIPAB) Molecular Ferroelectric Crystal

We report accurate calculations of tonsorial elements of α-Diisopropylammonium bromide (α-DIPAB) molecular ferroelectric crystal. In particular, elastic, piezoelectric and dielectric tensors were calculated using Vienna ab initio simulation package (VASP) within the framework of density functional (DFT) theory. The determination of above parameters allows an accurate description of the energy landscape for modeling of realistic devices at finite temperatures. We determine the major physical tensors in energy expansion of total energy per volume of un-deformed crystal to provide experimentalists with valuable information for designing and fabrication of pyroelectric detectors, capacitors, piezoelectric ferroelectric memories, display devices, electro-optic devices, and ultrasound transducers based on α-DIPAB. The spontaneous polarization P_s was calculated using Berry phase approach and found to be 22.64 μC⁄〖cm〗^2 in agreement with reported theoretical value. The dynamical Born effective charge tensor is reported for all atoms in the unit cell of α-DIPAB to get a deeper insight into the bonding network. The neighboring layers of DIPA molecules were found to be strongly crenelated due to the strong short-ranged electrostatic repulsion between Br sites in the DIPAB crystal structure. The organization of species in DIPA molecular layer as well as in the bromine “stitching” layer is essential for accurate calculation of DIPAB elastic properties. Having understood the actual network bonding in α-DIPAB, we calculated the components of the elastic moduli tensor. Our results indicate that a Young’s modulus of 10-180 GPa and a shear modulus of 4-26 GPa were found. Thus, α-DIPAB phase has a great potential to be a terrific candidate for flexible electronic device applications. The value of the principle component of electronic contribution to the static dielectric tensor of α-DIPAB is found to be ≈ 2.5, i.e. 50% smaller than that in typical perovskite-based ferroelectrics. Therefore, α-DIPAB is anticipated to exhibit creative materials' innovations. It offers highly customized features for specific applications, including insulation on polymer thick film conductive inks in the manufacture of membrane switches and flex circuits. Furthermore, clamped-ion piezoelectric tensor is calculated. Our results indicate a reasonable piezoelectric response of this polar crystal making it a low cost attractive candidate for piezoelectric applications.

Understanding Film Thickness‐Dependent Block Copolymer Self‐Assembly by Controlled Polymer Dewetting on Prepatterned Surfaces

AbstractBlock copolymer (BCP) lithography is a versatile bottom‐up approach for the creation of regular nanoscale patterns on large surface areas. The pattern morphology evolving during the microphase separation of a BCP is strongly dependent on the polymer film thickness. Thus, surface wetting as well as interfacial energies between polymer and substrate determine the polymer behavior, however, the complex interplay of those effects is not yet fully understood. In this work, a model describing the film thickness dependence of BCP self‐assembly on prepatterned surfaces is proposed. Polymer dewetting on nanohole‐patterned surfaces is controlled using different prepattern dimensions, polymer amounts, and microphase‐separation temperatures. This is found to allow for a precise local film thickness modulation and thus allows to guide BCP self‐assembly into arrays of tailored hierarchical nanoarchitectures. Analytical calculations of the total surface free energies of the microphase‐separated polymer of different film thicknesses confined inside nanoholes confirm the model. The insights contribute to the understanding of fundamental processes in polymer dewetting and BCP self‐assembly and allow for the controlled creation of advanced hierarchical nanostructures on large areas for applications in optics, plasmonics, and biomedical devices.

Parameters of Plasma and Way of Etching Silicon in a CF4 + CHF3 + O2 Mixture

The effect of the CF4/CHF3 ratio in a CF4 + CHF3 + 9% O2 mixture on the parameters of the gaseous phase and kinetics of etching of silicon under the conditions of low-pressure inductively coupled plasma is investigated. It was found that substitution of CF4 by CHF3 at constant external parameters of the plasma (1) leads to a change of the temperature (average energy) and density of the electrons; (2) causes a decrease of the fluorine atom density followed by the majority of the molecules of HF; and (3) stimulates an increase of the rate of deposition and thickness of the fluorocarbon polymer film. By the analysis of the way of etching of silicon with the use of the calculated data on the fluxes of active particles, it was found that the observed change of the etching rate can be explained by heterogeneous reactions with the involvement of O, H, and HF. It was assumed that the process of etching silicon proceeds in the mode of limitation by the flux of chemically active particles F + HF and is characterized by the effective probability depending on the thickness of the fluorocarbon polymer film.

Tapered copolymers of styrene and 4‐vinylbenzocyclobutene via carbanionic polymerization for crosslinkable polymer films

ABSTRACTWell‐defined polystyrene homopolymers with surface‐adhesive triethoxysilyl end group were synthesized via living carbanionic polymerization, epoxide end‐functionalization and subsequent hydrosilylation with triethoxysilane. Grafting‐to performance of polymers with various molecular weight (Mn = 3000–14,000 g mol−1) to a silicon surface was examined in dependence of reaction time, polymer concentration, solvent and number of alkoxysilyl end groups. Crosslinkable polymers for surface modification were synthesized by statistical carbanionic copolymerization of 4‐vinylbenzocyclobutene (4‐VBCB) and styrene, followed by epoxide end‐functionalization and triethoxysilane modification (Mn = 4000–14,000 g mol−1). The copolymers were characterized by 1H‐NMR, THF‐SEC, and matrix‐assisted laser desorption and ionization time‐of‐flight mass spectrometry. In situ 1H‐NMR kinetic studies in cyclohexane‐d12 provided information regarding the monomer gradient in the polymer chains, with styrene being the more reactive monomer (rs = 2.75, r4‐VBCB = 0.23). Thin polymer films on silicon wafers were prepared by grafting‐to surface modification under conditions derived for the polystyrene homopolymer. The traceless, thermally induced crosslinking reaction of the benzocyclobutene units was studied by DSC in bulk as well as in 3–6 nm thick polymer films. Crosslinked films were analyzed by atomic force microscopy, ellipsometry, and nanoindentation, showing smooth polymer films with an increased modulus. © 2019 The Authors. Journal of Polymer Science published by Wiley Periodicals, Inc. J. Polym. Sci. 2020, 58, 181–192

S-Nitrosothiol Plasma-Modified Surfaces for the Prevention of Bacterial Biofilm Formation.

The development of novel strategies for the prevention of bacterial infections is of utmost importance because of the exponential growth in the number of patient morbidity related to nosocomial and chronic infections. Nitric oxide (NO) is known to be a potent inhibitor of bacterial growth and adhesion to surfaces. Here, we develop an antibiofilm coating that possesses S-nitrosothiol NO donors via plasma polymerization (PP) for biofilm prevention applications. Cell culture dishes of four different film thicknesses ranging from 125 to 1000 nm were coated via PP using a thiol monomer. The thiol functionality on the substrates was converted to S-nitrosothiol NO precursors using tert-butyl nitrite. The successful conjugation of thiol and subsequent formation of S-nitrosothiol functionalities on the substrates were confirmed using X-ray photoelectron spectroscopy and UV-vis analysis. These coatings are capable of releasing NO over 2 days, and the NO loading is tunable by the polymer film thickness. The antibiofilm activity of the surfaces was assessed using Gram-negative bacteria, Pseudomonas aeruginosa. Higher film thickness (and hence, higher NO loading) demonstrate better antibiofilm activity, and the best performing coating shows 81 and 60% inhibition of bacterial attachment to the surface after exposure to bacterial culture solution for 24 and 36 h, respectively. Overall, the NO-releasing plasma-modified surfaces present a potential viable strategy to inhibit bacterial biofilm formation.

Complete Protection of O2-Sensitive Catalysts in Thin Films.

Energy conversion schemes involving dihydrogen hold great potential for meeting sustainable energy needs, but widespread implementation cannot proceed without solutions that mitigate the cost of rare metal catalysts and the O2 instability of biological and bioinspired replacements. Recently, thick films (>100 μm) of redox polymers were shown to prevent O2 catalyst damage but also resulted in unnecessary catalyst load and mass transport limitations. Here we apply novel homogeneous thin films (down to 3 μm) that provide protection from O2 while achieving highly efficient catalyst utilization. Our empirical data are explained by modeling, demonstrating that resistance to O2 inactivation can be obtained for nonlimiting periods of time when the optimal thickness for catalyst utilization and current generation is achieved, even when using highly fragile catalysts such as the enzyme hydrogenase. We show that different protection mechanisms operate depending on the matrix dimensions and the intrinsic catalyst properties and can be integrated together synergistically to achieve stable H2 oxidation currents in the presence of O2, potentially enabling a plethora of practical applications for bioinspired catalysts under harsh oxidative conditions.

Investigation of Electrochemical Mechanisms in Redox-Active Polymer Thin-Films

Thin-film redox-active polymers, such as polyaniline and polythiophene, exhibit high rate energy storage, and have recently been demonstrated for their utility in electrochemical desalination. In order to improve the effectiveness of redox-active polymer films for electrochemical desalination, we need to understand the fundamental electrochemical mechanisms occurring in these materials. In particular, we are interested in understanding how the deposition technique impacts the polymer structure and in turn the type and quantity of ions binding to the film under applied potential in aqueous solutions. Furthermore, investigating the influence of thickness of these polymer films can further the understanding of their electrochemical mechanisms and rate capabilities. Here, we deposit thin-film redox-active polymers using nitrogen and sulfur heterocyclic monomers, and demonstrate control over the polymer film thickness from 1 – 20 nm by tuning the deposition parameters. We characterize rate capability of charge storage of the polymer films over this thickness range, and employ a range of characterization techniques, including electrochemical quartz crystal microbalance (EQCM), to study the fundamental electrochemical mechanisms at play in aqueous solutions. Mechanistic and performance studies are carried out in aqueous solutions containing various cations (e.g. Li+, Na+, K+) and anions (e.g. SO4 2-, Cl-, Br-). The insights from this study will help to inform the development of thin-film polymers for enhanced electrochemical desalination. Figure 1

Molecularly imprinted electrochemical impedance sensor for sensitive dibutyl phthalate (DBP) determination

An efficient approach that integrates a molecularly imprinted conducting polymer, polypyrrole (PPY) with a sensitive electrochemical impedance sensing platform for the quantification of dibutyl phthalate (DBP) was presented. The molecular imprinting process was employed by one-pot step by the electrochemical polymerization of the pyrrole which enabled control of polymer film thickness, easy adherence of the polymer layers on the sensing substrate and simplicity of the fabrication. Molecular imprinted polymer (MIP) modified surfaces were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). EIS technique was carried out as a detection method since DBP molecules are electrically insulative and non-electroactive. In the molecular imprinting process, each step was optimized and the linear response was obtained in the range between 0.01–1.0 μM of DBP concentrations with a low detection limit as 4.5 nM under optimized conditions. Also, the relative standard deviation (RSD) was calculated as 5.21% for six different electrodes which were prepared independently. The developed sensor provided useful platform for rapid, simple and inexpensive detection of DBP.

Determining Water Sorption and Desorption in Thin Hydrophilic Polymer Films by Thermal Treatment

Knowledge of dry thickness of polymer films is required to determine the areal density of polymeric grafts and the degree of swelling of polymer networks and surface-anchored polymer assemblies. Because hydrophilic polymer films absorb water at ambient conditions and retain it, it is challenging to establish accurate dry thickness in such systems. Here we report on determining water uptake by chargeable/charged polymer films by monitoring the coefficient of thermal expansion (CTE) and thermo-optic coefficient (TOC) using ellipsometry. Knowing accurate amount of moisture in polymer films is needed for numerous applications, including, humidity and temperature sensors, polymer nanoreactors, lubricating coatings, antibacterial surfaces, and many others.

Fabrication and characterisation of novel nanofiltration polymeric membrane

A novel composite membrane was obtained by combining the products of ion-tracking and electrospinning processes. Swift heavy ions generated from a cyclotron were used to irradiate polyethylene terephthalate (PET) polymer film of thickness 23 µm to create latent tracks which were then chemically etched in an alkaline solution, to produce track-etched membrane. Magnetron sputtering was then used to deposite titanium (Ti) on the membrane to produce PET-TM with Ti thickness of ˜45 nm. Polyamide 6 nanofibres (PA6-nfs) or polyacrylonitrile nanofibres (PAN-nfs) were directly electrospun upon the Ti coated PET-TM using an electrospinning process. The average fibre diameter of PA6-nfs or PAN-nfs was 52 ± 9.8 nm or 354 ± 40 nm, respectively. The track-etched membrane, the nanofibres and the novel composite membrane were characterised using SEM, TEM, TGA, ATR-FTIR and adsorption/desorption of nitrogen techniques. The results confirmed the fabrication of nanofibre coated track-etched composite membrane.

Novel NIR-absorbing benzotrithiophene-based copolymers for organic photovoltaics

Three benzotrithiophene (BTT)-based copolymers were designed and synthesized by engineering alkyl chains on BTT and incorporating them into DPP or DFBT as acceptors. These polymers were fully characterized and the devices fabricated from these polymers were investigated for the correlation of polymer structures with photovoltaic performances. The molecular weight (Mn) and PDI of P1–P3 were measured as being in the range of 28.4–51.4 kDa and the range of 1.3–1.6, respectively. The thermal stability of the polymers as decomposition temperatures at 5% weight loss was found to be between 354 and 377 °C. The absorption spectra of P1, P2, and P3 as a film or in solution covered a broad range of wavelengths, extending to the NIR region. The absorption spectrum of P1 as a film displays the most red-shifted absorption maximum (λmax) at 799 nm, whereas P2 and P3 showed maxima at 716 nm and 653 nm, respectively. The HOMO levels of P1, P2, and P3 were found to be −5.25, −5.16, and −5.23 eV, respectively, through electrochemical parameters. After being optimized by polymer concentration, additive concentration, and film thickness, the average PCEs of the devices fabricated from the polymer blends were measured as 3.12% for P1, 0.13% for P2, and 0.70% for P3. AFM study revealed that addition of DIO to the blend film of P1 brought a dramatic change in its morphology, from a big granular structure to a smooth and nano-scale phase separation, leading to greatly improving the PCE. However, DIO addition to P2 and P3 did not have a positive effect on the blend film morphologies, which still remained rough and aggregated, leading to inferior PCEs. These AFM results proved the close correlations between the polymer blend morphologies and the corresponding device performances.

Gas-phase chemistry and etching mechanism of SiNx thin films in C4F8 + Ar inductively coupled plasma

In this study, we investigated the etching characteristics of non-stoichiometric SiNx thin films in C4F8 + Ar inductively coupled rf (13.56 MHz) plasma. The SiNx etching rates together with SiNx/Si and SiNx/SiO2 etching selectivities were measured as functions of the gas pressure (4–10 mTorr, or 0.53–1.33 Pa), input power (700–1000 W), bias power (100–400 W), and C4F8/Ar mixing ratio (0%–75% Ar). Data on internal plasma parameters and plasma chemistry as well as steady-state plasma composition were obtained by both Langmuir probe diagnostics and zero-dimensional plasma modeling. The etching mechanism of SiNx was analyzed through the relationship between the measured etching rates and model-predicted fluxes of active species (F atoms, CFx radicals, and positive ions). It was confirmed that within the given range of input process conditions, the SiNx etching process 1) appears in the steady-state etching regime, 2) exhibits the features of ion-assisted chemical reactions in the neutral-flux-limited mode, and 3) is influenced by the thickness of the fluorocarbon polymer film. It was shown that the influence of input process parameters on the effective probability of SiNx + F chemical reaction may be adequately characterized by the fluorocarbon radicals/fluorine atoms and fluorocarbon radicals/ion energy flux ratios.

Tuning Channel Architecture of Interdigitated Organic Electrochemical Transistors for Recording the Action Potentials of Electrogenic Cells

AbstractOrganic electrochemical transistors (OECTs) have emerged as versatile electrophysiological sensors due to their high transconductance, biocompatibility, and transparent channel material. High maximum transconductances are demonstrated facilitating the extracellular recording of signals from electrogenic cells. However, this requires large channel dimensions and thick polymer films. These large channel dimensions lead to low transistor densities. Here, interdigitated OECTs (iOECTs) are introduced, which feature high transconductances at small device areas. A superior device performance is achieved by systematically optimizing the electrode layout regarding channel length, number of electrode fingers and electrode width. Interestingly, the maximum transconductance (gmax) does not straightforwardly scale with the channel width‐to‐length ratio, which is different from planar OECTs. This deviation is caused by the dominating influence of the source–drain series resistance Rsd for short channel devices. Of note, there is a critical channel length (15 µm) above which the channel resistance Rch becomes dominant and the device characteristics converge toward those of planar OECTs. Design rules for engineering the performance of iOECTs are proposed and tested by recording action potentials of cardiomyocyte‐like HL‐1 cells with high signal‐to‐noise ratios. These results demonstrate that interdigitated OECTs meet two requirements of bioelectronic applications, namely, high device performance and small channel dimensions.

Precise Generation of Selective Surface-Confined Glycoprotein Recognition Sites.

Since glycoproteins have become increasingly recognized as key players in a wide variety of disease processes, there is an increasing need for advanced affinity materials for highly selective glycoprotein binding. Herein, for the first time, a surface-initiated controlled radical polymerization is integrated with supramolecular templating and molecular imprinting to yield highly reproducible synthetic recognition sites on surfaces with dissociation constants (KD) in the low micromolar range for target glycoproteins and minimal binding to nontarget glycoproteins. Importantly, it is shown that the synthetic strategy has a remarkable ability to distinguish the glycosylated and nonglycosylated forms of the same glycoprotein, with a >5-fold difference in binding affinity. The precise control over the polymer film thickness and positioning of multiple carbohydrate receptors plays a crucial role in achieving an enhanced affinity and selectivity. The generated functional materials of unprecedented glycoprotein recognition performance open up a wealth of opportunities in the biotechnological and biomedical fields.