Cyclic Transparent Optical Polymer Research Articles

Determination of Surface Charge Density and Charge Mapping of CYTOP Film in Air using Electrostatic Force Microscopy.

Cyclic transparent optical polymer (CYTOP), a fluoropolymer, finds a plethora of applications in microelectronic devices for sustainable energy harvesting and memory devices. By and large, these devices demand high voltage breakdown, a high dielectric constant, transparency, charge storage, and retention capabilities. Despite many efforts, comprehensive investigation of the charge distribution, retention, and discharge studies conducted on the CYTOP film at the micro-scale remains elusive. Here, we present direct quantification and mapping of surface charge on the CYTOP surface at room temperature using two different modes of advanced surface probe microscopy i.e., Kelvin probe force microscopy (KPFM) and electrostatic force microscopy (EFM). We estimated that the surface charge densities of the CYTOP film using EFM are 1.4 and 3.3 μC/cm2 for the injection of positive and negative charges, respectively. Furthermore, we determined the charge retention time for both injected positive and negative charges. We found that the retention capacity of the negative charges on the CYTOP film is much higher as compared to the positive charges. Moreover, it is also observed that injected negative charges are strongly localized on the CYTOP surface compared to the positive counterpart. Additionally, we demonstrated that charge writing is possible on the CYTOP surface using the AFM conductive tip. These results may find potential applications in energy harvesting, sensing, memory devices, security, and surveillance.

Fatigue test on optical fiber angle sensors based on polymeric materials for flexion–extension applications

Polymer Optical Fiber (POF) and Cyclic Transparent Optical Polymer (CYTOP) based sensors present some advantages related to their light weight, flexibility, and reduced dimensionality for applications in assistive robotics compared to conventional sensors that are rigid and heavy. To ensure adequate functionality, usability, and controllability of the systems over time, the measurements made by the sensors must be maintained in optimal ranges of functionality. Considering that for most robotic assistance applications an adequate range of motion of the limbs is at approximately 80°, this study presents a fatigue test performed on three Polymeric Optical Fiber sensors for angle measurement in this range. The tests were performed on a bending system that generates variations at a frequency of 2 Hz recording the voltage variation. For fatigue measurement each sensor was instrumented into the system and set to perform a total of 40,000 cycles, repeating the tests two times per sensor. The results show that the CYTOP optical fiber-based sensor did not break during the trial; however, it is determined that this type of fiber is more sensitive to light variations in the environment. On the other hand, the other two sensors reached a time of approximately 70 min for a total of 8,360 cycles to rupture. These results have potential usability in characterizing systems incorporating angle sensors to estimate proper system performance.

Influence of gamma and electron radiation on perfluorinated optical fiber material composition

This letter presents a material analysis of the cyclic transparent optical polymer (CYTOP) fiber when exposed to gamma and electron radiation. In this case, the influence of the radiations in the CYTOP material composition is analyzed using the FTIR and Raman spectroscopy, where the latter is applied on two regions of the optical fiber, the core and overcladding. Furthermore, a CYTOP fiber without been exposed to radiation is also tested. Results show that the electron radiation leads to 60% higher variation in the material composition when compared with the gamma radiation in FTIR tests. The Raman spectroscopy indicates that both radiation conditions lead to compositional changes in the CYTOP fiber core, where peaks related − CH3 and aromatic C − H bonds appeared in these conditions. Such effect is not only related to molecular rearrangement, but also thermal effects when the fibers are subjected to gamma and electron radiations.

Performance enhancement of droplet-based electricity generator using a CYTOP intermediate layer

Effective strategies for improving the performance of a droplet-based electricity generator (DEG) remain a challenge. Herein, we propose to introduce an intermediate layer of cyclic transparent optical polymer (CYTOP) by adjusting the thickness, injecting ionized ions into the surface, and increasing the surface area. We observed the positive effects of the introduction of a CYTOP layer on outputs, especially with a greater thickness, surface ionized-air modification and larger surface area, which could promote the practical application of DEG in energy harvesting.

Room temperature processed protective layer for printed silver electrodes.

Low-temperature processed printed silver electrodes pave the way for electrical connections in flexible substrates with reduced energy consumption. Despite their excellent performance and simple process, printed silver electrodes' poor stability limits their applications. This study demonstrates a transparent protective layer without thermal annealing for printed silver electrodes, which maintains its electrical properties for a long period of time. A fluoropolymer, specifically a cyclic transparent optical polymer (CYTOP), was used as a protective layer for silver. The CYTOP is room temperature processable and chemically stable against carboxyl acid. The introduction of the CYTOP film on the printed silver electrodes mitigates the chemical reaction between silver and carboxyl acid, thereby elongating its lifetime. Under heated acetic acid, the printed silver electrodes with a CYTOP protective layer maintained their initial resistance for up to 300 hours, while the electrodes without a protective layer were damaged within a few hours. A microscopic image shows that the protective layer enables printed electrodes to maintain their shape without damage. Hence, the protective layer guarantees the accurate and reliable performance of electronic devices with printed electrodes under actual operating conditions. This research will contribute to designing chemically reliable flexible devices in the near future.

Influence of UV Radiation on Mechanical Properties of Polymer Optical Fibers.

This paper presents an analysis of the mechanical properties of different polymer optical fibers (POFs) at ultraviolet (UV) radiation conditions. Cyclic transparent optical polymer (CYTOP) and polymethyl methacrylate (PMMA) optical fibers are used in these analyses. In this case, the fiber samples are irradiated at the same wavelength, pulse time and energy conditions for different times, namely, 10 s, 1 min, 2 min and 3 min. The samples are tested in tensile tests and dynamic mechanical thermal analysis (DMTA) to infer the variation in the static and dynamic properties of such fibers as a function of the UV radiation condition. Furthermore, reference samples of each fiber (without UV radiation) are tested for comparison purposes. The results show a lower UV resistance of PMMA fibers, i.e., higher variation in the material features in static conditions (Young's modulus variation of 0.65 GPa). In addition, CYTOP fiber (material known for its high UV resistance related to its optical properties) also presented Young's modulus variation of around 0.38 GPa. The reason for this reduction in the moduli is related to possible localized annealing due to thermal effects when the fibers are subjected to UV radiation. The dynamic results also indicated a higher variation in the PMMA fibers storage modulus, which is around 30% higher than the variations in the CYTOP fibers when different radiation conditions are analyzed. However, CYTOP fibers show a smaller operational temperature range and higher variation in the storage modulus as a function of the temperature when compared with PMMA fibers. In contrast, PMMA fibers show higher variations in their material properties when subjected to oscillatory loads at different frequency conditions. Thus, the results obtained in this work can be used as guidelines for the influence of UV radiation in POFs not only for the material choice, but also on the limitations of UV radiation in the fabrication of the grating as well as in sensor applications at UV radiation conditions.

Temperature-Insensitive Curvature Sensor With Plane-by-Plane Inscription of Off-Center Tilted Bragg Gratings in CYTOP Fibers

We demonstrate of an off-centered tilted fiber Bragg grating (FBG) inscribed in cyclic transparent optical polymer (CYTOP) fiber as a curvature sensor. The gratings were inscribed using a femtosecond (fs) laser with the direct write, plane-by-plane method due to its high flexibility and suitability for customization, particularly for the development of a single-peak spectrum in multimode CYTOP fiber. The grating is applied to curvature sensing, where the spectral features, namely the wavelength shift and reflected optical power, are analyzed with respect to the curvature angle on the optical fiber. The off-center and tilted FBG response as a function of the angle is compared with a centered and uniform FBG inscribed in CYTOP fiber using the same inscription method and laser parameters. Results show a significant improvement for the off-center grating when the wavelength shift information is considered and lower optical power sensitivity as a function of the angle with respect to the centered FBG. In addition, the temperature sensitivity differences of the two gratings, enables the development of temperature-insensitive angle sensor using a single off-center tilted FBG.

Postirradiation Transmission Characteristics of CYTOP Fiber Exposed by Gamma Radiation

We investigated offline the evolution of radiation-induced attenuation (RIA) in polymer perfluorinated cyclic transparent optical polymer (CYTOP) optical fiber irradiated with different gamma radiation doses of 1–50 kGy. We considered the wavelength range varying from 800 up to 1750 nm. The RIA spectra measured at different times after irradiation have qualitatively similar shapes. However, quantitatively the RIA evolution significantly depends on the spectral range: in the short-wavelength part, the transmission partly recovers, while in the infrared, at wavelengths above 1300 nm the RIA grows and then saturates becoming permanent. The effects of temperature and photobleaching on RIA dynamics are examined. The ability of the fiber transmission recovery is investigated in the 600–1750-nm range with the use of climatic chamber.

Improved Electrical and Temporal Stability of In-Zn Oxide Semiconductor Thin-Film Transistors With Organic Passivation Layer

Solution-processed In-Zn oxide (IZO) semiconductor thin-film transistors (TFTs) were fabricated with passivation layers of either poly(methyl methacrylate) (PMMA) or cyclic transparent optical polymer (CYTOP). According to the transfer curves obtained on the day of fabrication and after 200 days, the drain-source current of the IZO TFT without a passivation layer decreased by approximately 37 %. For the PMMA-passivated IZO TFT, it decreased by approximately 31 %. The current for the CYTOPpassivated IZO TFT showed significantly lower, only 7 % deterioration. Hence, the CYTOP-passivated IZO TFT exhibited improved electrical stability under long term ambient storage. This was attributed to the difference in the chemical composition of the two polymers, as CYTOP is a fluoropolymer, while PMMA is an ester group containing organic polymer. We show, passivation of the active layer with the proper organic film improves the stability of the high-performance solution-processed IZO TFTs.

Ultra-Flexible Organic Photovoltaics with Low-Temperature Deposited IZTO on a Cyclic Polymer Substrate Having Excellent Mechanical Properties.

In this study, ultra-flexible organic photovoltaics (OPVs) with a new device structure are developed as a power source for ultra-flexible wearable devices with excellent biocompatibility. To fabricate ultra-flexible OPVs with excellent mechanical properties, we develop an ultra-flexible substrate with a bilayer structure based on polymers and transparent conducting oxides. An amorphous perfluorinated polymer (cyclic transparent optical polymer, CYTOP) is introduced as an ultra-flexible substrate by a solution process. An indium zinc tin oxide (IZTO) transparent electrode possessing an amorphous structure is fabricated via pulsed DC magnetron sputtering at room temperature using a target containing 80 atom % In2O3-10 atom % ZnO-10 atom % SnO2. Ultra-flexible OPVs with a one-dimensional (1D) grating pattern are fabricated on the buffer layer and photoactive layer. These OPVs exhibit an increase of 12% in power conversion efficiency (PCE) (maximum PCE: 8.52%) compared to the reference, thereby minimizing reliance on the incident angle of light. In addition, even after 1000 compression/relaxation tests with a compression strain of 33%, the PCE of the ultra-flexible OPVs is maintained up to 94.8% of its initial value.

Characterization and analysis of a POF sensor embedded in different materials: Towards wearable systems for stiffness estimation

This paper presents the development, characterization and analysis of an intensity variation-based polymer optical fiber (POF) force sensor using cyclic transparent optical polymer (CYTOP) fiber through side-coupling light source embedded in different materials. Tests with application of vertical force on the sensor with different supports were performed to analyze the sensor responses when embedded in different materials. In addition, vertical force tests along the fiber were performed to analyze the sensor feasibility of detecting the location of applied force. Results of the force characterization on different materials show that the POF-CYTOP force sensor response is related to elastic modulus of the materials. Using the support I, more flexible (elastic modulus of 18.6MPa), the sensor responses presented a high influence of the light coupling, resulting in an increase of the optical power. In contrast, the responses using the support II (elastic modulus of 1.6GPa), presented a decrease of optical power variation with only a minor increase in the optical power when small forces are applied. This is due to the higher strain in the POF, resulting in optical power decrease due to radiation losses and stress-optical effect. Tests with application of the force along the fiber show that the sensor had different sensitivities for impacts located at different distances of the lateral section, leading to the possibility of estimating the impact location using a multiplexed sensor array. The differences in the sensor’s responses over the different supports show the feasibility of using the proposed sensor system for the stiffness assessment in users, where wearable optical fiber sensors can be employed on the real-time estimation of soft tissues, which finds important applications in rehabilitation as well as wearable robotics control and design.

Discovery of polymer electret material via de novo molecule generation and functional group enrichment analysis

We designed a high-performance polymer electret material using a deep-learning-based de novo molecule generator. By statistically analyzing the enrichment of the functional groups of the generated molecules, the hydroxyl group was determined to be crucial for enhancing the electron gain energy. Incorporating such acquired knowledge, we designed a molecule using cyclic transparent optical polymer (CYTOP; perfluoro-3-butenyl-vinyl ether). The molecule was synthesized, and its surface potential for a 15-μm-thick film is kept at −3 kV for more than 800 h. Its performance was significantly better than all commercialized CYTOP polymer electrets, indicating great potential for its application in vibration-based energy harvesting. Our results demonstrate the application of machine learning in polymer electret design and confirm the combination of molecule generation and functional group enrichment analysis to be a promising chemical discovery method achieved via human–artificial intelligence collaboration.

Bias stress instability in multilayered MoTe 2 field effect transistors under DC and pulse‐mode operation

Here, bias stress instability on multilayered MoTe2 field effect transistors (m-MoTe2 FETs) with encapsulation of hydrophobic polymers (cyclic transparent optical polymer) is systematically investigated under DC and pulse mode operation. During DC mode stress, the threshold voltage shift (ΔVth) under positive bias stress is at least three times larger than that of negative stress due to high hole barrier (∼0.57 eV), compared with electron barrier (∼0.18 eV). However, ΔVth in positive pulse mode stress is significantly reduced with decrease of a duty cycle, as compared with that of negative stress. With isolation from external gas ambient effects such as H2O and O2, shallow electron traps in multilayered MoTe2 field effect transistors are identified as one of strong candidates to cause bias polarity dependency on ΔVth in pulse mode. Moreover, recovery time for traps, involved during positive bias stress, is six times faster than that of negative stress, substantiating that shallow electron traps and their fast detrapping are one of key origins. In practice, optimisation of pulse mode operation via bipolar switching can be potentially utilised for minimisation of device instability during the operation of multilayered MoTe2 field effect transistors devices and their circuits.

Vortex Polymer Optical Fiber with 64 Stable OAM States.

This research introduces a numerical design of an air-core vortex polymer optical fiber in cyclic transparent optical polymer (CYTOP) that propagates 32 orbital angular momentum (OAM) modes, i.e., it may support up to 64 stable OAM-states considering left- and right-handed circular polarizations. This fiber seeks to be an alternative to increase the capacity of short-range optical communication systems multiplexed by modes, in agreement with the high demand of low-cost, insensitive-to-bending and easy-to-handle fibers similar to others optical fibers fabricated in polymers. This novel fiber possesses unique characteristics: a diameter of 50 µm that would allow a high mechanical compatibility with commercially available polymer optical fibers, a difference of effective index between neighbor OAM modes of around 10−4 over a bandwidth from 1 to 1.6 µm, propagation losses of approximately 15 × 10−3 dB/m for all OAM modes, and a very low dispersion for OAM higher order modes (±l = 16) of up to +2.5 ps/km-nm compared with OAM lower order modes at a telecom wavelength of 1.3 µm, in which the CYTOP exhibits a minimal attenuation. The spectra of mutual coupling coefficients between modes are computed considering small bends of up to 3 cm of radius and slight ellipticity in the ring of up to 5%. Results show lower-charge weights for higher order OAM modes.

Solid-State Electron Affinity Analysis of Amorphous Fluorinated Polymer Electret.

In this study, electron trapping phenomena in amorphous polymer electrets were studied using a solid-state electron affinity analysis by means of molecular dynamics simulations parametrized with ab initio calculations. Negatively charged amorphous systems of a cyclic transparent optical polymer (CYTOP) with different end groups were reproduced by molecular dynamics simulations parametrized by density functional theory analysis. Quantum mechanical calculations were performed for electron trapping sites to determine the electron affinity of an isolated molecule. The influence of the amorphous system surrounding the trapping site was considered by accounting for electrostatic interactions with surrounding molecules and multipole induction. A series of analyses were carried out to mimic the conformational diversity of the amorphous system. The calculated solid-state electron affinities were found to adopt a Gaussian-type distribution and were in good accordance with the experimental data for surface potential and thermally stimulated discharge spectra, indicating the reliability of the present analysis for predicting the charging performance of amorphous polymer electrets.

Ultra-Flexible Organic Photovoltaics with Nanograting Patterns Based on CYTOP/Ag Nanowires Substrate.

In this study, we developed a method for fabricating ultrathin polymer substrates that can be used in ultra-flexible organic photovoltaics (OPVs) via a non-vacuum process using cyclic transparent optical polymer. In addition, a Ag nanowire network layer was used as a transparent electrode in a solution process. All processes were conducted on large area via spin coating. The power conversion efficiency (PCE) of the ultra-flexible OPV improved by 6.4% compared to the PCE of the ITO/Glass-based OPV. In addition, the PCE of the OPV increased to 10.12% after introducing nanostructures in the ZnO and photoactive layers. We performed 1000 cycles of compression/relaxation tests to evaluate the mechanical properties of the ultra-flexible OPV, after which, the PCE remained at 67% of the initial value. Therefore, the developed OPV system is suitable as a power source for portable devices.

Perfluorinated fiber material properties following femtosecond laser inscription

This paper presents the materials analysis and comparison of fiber gratings inscribed using the plane-by-plane femtosecond laser method in cyclic transparent optical polymer (CYTOP) fibers at different angles. Specifically, the gratings were inscribed with 0°, 45° and 90° angle in respect to the core's optical axis. The materials molecular structures are investigated through the Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy, which indicate that the changes on the material structure are highly controlled and restricted to the fiber core, as an important benefit of the plane-by-plane inscription method. In order to verify the impact of the grating inscription in the samples' physical properties, thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) are performed. Results show an increase in the degradation temperature in higher inscription angles (90°), whereas there is no significant variation in the polymer glass transition temperature (T g ) between samples. However, the frequency shift on the polymer loss factor monotonically increases with the decrease of the grating angle, i.e., 0° sample shows the largest shift in the loss factor. Regarding the elastic modulus, the 90° inscription angle sample presents the lowest elastic modulus. The results obtained in these analyses provide guidelines on the fabrication and operation limits (in terms of temperature and stress) of POF based devices, including tunable filters and sensors. • Perfluorinated fiber properties after the gratings inscription using femtosecond laser. • Thermal and mechanical analyses on gratings inscribed at different planes. • Infrared and Raman spectroscopies for the analysis of material's structure.

FPI-POFBG Angular Movement Sensor Inscribed in CYTOP Fibers With Dynamic Angle Compensator

We present the development and application of an angular movement sensor based on Fabry-Perot interferometer (FPI) in series with a fiber Bragg grating (FBG) inscribed in cyclic transparent optical polymer (CYTOP) using a femtosecond laser. The FPI was fabricated with UV-curable resin between the CYTOP and a silica pigtail, which provides flexibility and the possibility in situ fabrication. In this case, the FPI is an edge-filter for the FBG response, which presents both wavelength shift and optical power attenuation as the bending angle increases. A dynamic compensator for the material’s viscoelastic response resulted in a six-fold reduction in the sensor’s transient response error. The FPI-POFBG angular movement sensor was validated in knee angle monitoring during gait cycles, where the sensor presented errors as low as 2.5°. This is a low-cost sensor with high flexibility on fabrication and with the capacity of following subtle angle variations, as the ones commonly occurred in gait cycles.

Origin of Off‐State Current in Multilayered MoTe2 Field‐Effect Transistors: Gate‐Induced Drain Leakage and Poole–Frenkel Conduction

Herein, as one of bias‐dependent channel leakage issues in p‐channel multilayered molybdenum ditelluride field‐effect transistors (m‐MoTe2 FETs), anomalous increase in off‐state current is reproducibly observed with increase in drain‐to‐gate voltage (VDG), even after hydrophobic, cyclic transparent optical polymer (CYTOP) encapsulation. For elucidation on the behind mechanism for the phenomena, drain‐ and gate‐bias dependent channel leakage currents are systematically analyzed in the range of temperature 100 to 380 K. Surprisingly, analysis on trap‐assisted indirect tunneling current substantiates that the off‐state current is mainly attributed to gate‐induced drain leakage (GIDL) current associated with band bending in m‐MoTe2 FETs. Moreover, linear slope (0.00163) of ln (IDS/F) versus F1/2 plot and its coincidence with theoretical value (0.00148) identify that thermal emission associated with Poole–Frenkel effect is strongly involved at low drain bias of −1.1 V (e.g., effective barrier height, ϕB ≈ 0.61 eV), whereas GIDL current becomes more predominant at high drain bias of −3.1 V (ϕB ≈ 0.51 eV). Thus, in‐depth understanding on the origin of anomalous leakage current and its systematic validation would be beneficial for the development of novel devices and circuits based on transition metal chalcogenides (TMDCs).

Solution-Processed Flexible Gas Barrier Films for Organic Field-Effect Transistors

The solution-processed gas barrier film was fabricated and used for organic field-effect transistors (OFETs). Organic-inorganic hybrid sol-gel materials and cyclic transparent optical polymer (CYTOP) were used as the bottom and top layers of the barrier films, respectively, to effectively protect against gas permeation through the barrier films. The organic-inorganic hybrid material includes sol-gel precursors and amphiphilic polymers. The conventional sol-gel precursors form siloxane bonds by sol-gel reaction and form densely-packed rigid part in thin films. The alkoxysilane-functionalized amphiphilic polymer in the sol-gel precursor solutions has two hydrophobic segments and a hydrophilic segment. The amphiphilic polymer with reactive alkoxysilane groups at both ends of the hydrophobic segments can be involved in the sol-gel reaction, and they can act as surfactants to surround the conventional precursors stabilizing the nanoparticles formed by the hydrolytic condensation reaction of precursors. The amphiphilic polymer also provides flexibility for hybrid sol-gel thin films. CYTOP was used to introduce hydrophobicity on top of the organic-inorganic hybrid thin films. The barrier films containing the organic-inorganic hybrid and hydrophobic CYTOP layers were applied to OFETs and exhibited notable gas barrier properties, high transparency, and flexibility. The encapsulated OFETs with 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) as an organic semiconductor showed a slight decrease in hole mobility from 0.13 to 0.11 cm2 V-1 s-1, while the OFETs without barrier films showed a mobility decrease from 0.11 to 0.03 cm2 V-1 s-1.