Flexible Polyethylene Terephthalate Substrate Research Articles

Ultrafast carrier and phonon dynamics in thin films of bismuth telluride on a flexible substrate

Thin films of topological insulators (TIs) possess exotic nonlinear optical properties such as strong light-matter interaction, broadband spectral sensitivity, thickness-dependent tunable bandgap, higher harmonic generation, etc. Due to the presence of metallic surface states with Dirac fermions and an insulating bulk band in TI, they are projected to be a viable material for studying novel physics, resulting in exciting new properties and technologies. The peculiar electron-phonon interactions at the surface have been linked to various unexpected physical features of topological insulators. Although electron behaviour in topological insulators has been extensively investigated on non-flexible substrates, electron-phonon interactions at TI bulk and surfaces states are less well known on a flexible substrate. Because of its potential uses in wearable devices, communications, sensors, and other fields, there is a significant need for the manufacture of high performance flexible optoelectronic responses employing novel exotic materials. In this paper, we preformed ultrafast pump-probe method to explore TI (Bi2Te3) thin films on a flexible PET (polyethylene terephthalate) substrate. We studied the dynamics of Bi2Te3 thin films' hot carrier relaxation progression and coherent phonon behaviour using transient absorbance measurements. Thickness-dependent low-frequency coherent acoustical phonon oscillations are observed in 10 nm thick films, and the changes vanish for 25 nm thick films, and high-frequency optical phonon oscillations are absent in our work. Subpicosecond range of time constant for the photon excitation, diffusion, carrier thermalization, and relaxation are reported. Longer characteristics time was observed for 25 nm film as compared to 10 nm film, and its variation has been discussed here. The thickness-dependent coherent acoustic phonon oscillating in the terahertz frequency range has been experimentally calculated. The film's terahertz frequency response varies with its thickness, allowing it to be employed in future terahertz applications based on flexible topological insulator thin films.

Directional and Polarized Lasing Action on Pb‐free FASnI3 Integrated in Flexible Optical Waveguides

AbstractIn this work, high‐quality FASnI3 (FA, formamidinium) lead‐free perovskite thin films are successfully incorporated in a flexible polyethylene terephthalate (PET) substrate to demonstrate amplified spontaneous emission (ASE) and lasing. The waveguide (WG) consists of polymethylmethacrylate(PMMA)/FASnI3 bilayer deposited on a PET substrate and is properly designed to allow single‐mode propagation at the photoluminescence wavelength. This geometry optimizes the excitation of the emitting FASnI3, enhances the light−matter interaction in the semiconductor thin film, provides a preferable direction for the emitted light and allows its direct outcoupling for on‐chip or fiber‐optic applications. As far as the authors know, ASE and random lasing are obtained for the first time in a flexible‐based WG integrating a highly efficient lead‐free perovskite. The high quality of the deposited films and the optimized design of the structure result in an extremely low ASE/lasing threshold in the range of 1 µJ cm−2, which is only ten times higher than that measured in the same PMMA/FASnI3 structure deposited on a rigid substrate (Si/SiO2). More interestingly, these WGs exhibit a strong polarization anisotropy for the outcoupled ASE/lasing light with a preferable transverse electric polarization. This work is the base for the future development of ecofriendly, flexible, and efficient photonic devices.

Thickness dependent resistive switching behaviors in Ta2O5 layer at low temperature: Towards flexible, invisible, cryo-electronic applications in aerospace

The role of Ta2O5 resistive switching (RS) layer thickness on transparent resistive random-access memories (TRRAMs) is systematically investigated. Ta2O5 TRRAMs (t-TRRAMs) exhibits not only high optical transmittance (82%) in the visible region but also bipolar resistive switching behavior with RON/ROFF ratio of ≈103, SET voltage of (0.37 ± 0.08)V, RESET voltage of -(2.83 ± 0.42)V, good endurance of ≈103 cycles and retention over 104s at room temperature (RT) as well as 80 °C. The temperature-dependent RS properties for t-TRRAMs are experimentally validated from low temperature (150 K) to elevated temperature (333 K). Furthermore, t-TRRAMs are implemented on ITO-coated flexible polyethylene terephthalate (PET) substrates. The flexible t-TRRAMs demonstrate RON/ROFF ratio of ≈102, reasonable endurance of ≈500 cycles, and retention over 104s at RT. The experimental results indicate that t-TRRAMs can be a potential candidate for flexible, invisible, cryo-electronic applications.

Ultrasensitive Graphene-Based Nanobiosensor for Rapid Detection of Hemoglobin in Undiluted Biofluids.

Detection of hemoglobin (Hb), a critical part of the biological system that is responsible for oxygen transportation, is of great significance on clinical diagnosis of various diseases. Particularly, time-efficient Hb detection under nanomole levels has drawn much attention in recent years. Herein, we present a graphene field effect transistor (GFET)-based aptameric nanobiosensor for rapid detection of Hb in undiluted biofluids including serum and urine and for the first time use polyethylenimine (PEI), a kind of comparatively low-cost polymer consisting of numerous amino groups, which can be directly linked with the anchor molecule without any pretreatment as the graphene surface passivation agent. Experimental results indicate the PEI-modified graphene aptameric nanobiosensor can respond to the Hb concentration change in a few minutes (6-8 min) with estimated detection limits of 10.6 fM in 1× PBS, 14.2 fM in undiluted serum, and 11.9 fM in undiluted urine, respectively. Further, considering the potential use of our sensor for implantable and wearable applications, we also examine the sensing performance of the sensor fabricated on an ultrathin flexible polyethylene terephthalate (PET) substrate. The Hb detection results are almost invariable even after 100 cycles of cyclic extension by 120% or 100 cycles of bending with a radius of 1 mm. Hence, our sensor holds great potential for accurate monitoring of nanomole levels of Hb in clinical applications.

Large-Scale Preparation of Silver Nanowire-Based Flexible Transparent Film Heaters by Slot-Die Coating.

Highly flexible silver nanowire-based transparent conductive films (AgNWs TCFs) were large-scale fabricated by slot-die coating AgNWs inks on a flexible polyethylene terephthalate (PET) substrate, and further fabricated into a transparent film heater. Appropriate flow rate, coating speed, and AgNWs concentration allow the construction of the 15 cm × 15 cm AgNW TCFs with a sheet resistance (Rs) of less than 20 Ω/sq, a transmittance (T) at 550 nm higher than 95%, and a haze less than 3.5%. The resultant AgNW TCFs heater possesses high uniformity and superior mechanical stability and can reach a Joule heating temperature of 104 °C with a voltage of 12 V. The slot-die coating method has great potential for large-scale production of AgNW based film heaters promisingly used in window defrost and deicer systems.

Characterization of Piezoelectric Properties of Ag-NPs Doped PVDF Nanocomposite Fibres Membrane Prepared by Near Field Electrospinning.

In this study, Near-field electrospinning (NFES) technique is used with a cylindrical collector to fabricate a large area permanent piezoelectric micro and nanofibers by a prepared solution. NFES requires a small electric field to fabricate fibers Objective: The objective of this paper to investigate silver nanoparticle (Ag-NP)/ Polyvinylidene fluoride (PVDF) composite as the best piezoelectric material with improved properties to produced tremendously flexible and sensitive piezoelectric material with pertinent conductance Methods: In this paper, we used controllable electrospinning technique based on Near-field electrospinning (NFES). The process parameter for Ag-NP/PVDF composite electrospun fiber based on pure PVDF fiber. A PVDF solution concentration of 18 wt.% and 6 wt.% silver nitrate, which is relative to the weight of PVDF wt.% with 1058 μS conductivity fibers, have been directly written on a rotating cylindrical collector for aligned fiber PVDF/Ag-NP fibers are patterned on fabricated copper (Cu) interdigitated electrodes were implemented on a thin flexible polyethylene terephthalate (PET) substrate and Polydimethylsiloxane (PDMS) used as a package to enhance the durability of the PVDF/ Ag-NP device. A notable effect on the piezoelectric response has been observed after Ag-NP addition, confirmed by XRD characterization and tapping test of Ag-NP/PVDF composite fiber. The morphology of the PVDF/Ag-NP fibers and measure diameter by scanning electron microscopy (SEM) and Optical micrograph (OM), of fiber. Finally, a diameter of PVDF/Ag-NP fibers up to ~7 μm. The high diffraction peak at 2θ = 20.5˚ was investigated by X-ray diffraction (XRD) in the piezoelectric crystal β-phase structure. Further addition of silver nanoparticles (Ag- NPs) in the PVDF solution resulted in enhancing the electromechanical conversion of the fibers from ~0.1 V to ~1 V. In conclusion, we can say that confirmed and validated the addition of Ag-NP in PVDF could enhance the piezoelectric property by using NFES technique with improved crystalline phase content can be useful for a wide range of power and sensing applications like biomedical devices and energy harvesting, among others.

Solution-Processed Titanium Dioxide Ion-Gated Transistors and Their Application for pH Sensing

Titanium dioxide (TiO2) is an abundant metal oxide, widely used in food industry, cosmetics, medicine, water treatment and electronic devices. TiO2 is of interest for next-generation indium-free thin-film transistors and ion-gated transistors due to its tunable optoelectronic properties, ambient stability, and solution processability. In this work, we fabricated TiO2 films using a wet chemical approach and demonstrated their transistor behavior with room temperature ionic liquids and aqueous electrolytes. In addition, we demonstrated the pH sensing behavior of the TiO2 IGTs with a sensitivity of ∼48 mV/pH. Furthermore, we demonstrated a low temperature (120°C), solution processed TiO2-based IGTs on flexible polyethylene terephthalate (PET) substrates, which were stable under moderate tensile bending.

Organic bulk heterojunction solar cells spin-coated in ambient environment on flexible and glass substrates

Organic solar cells based on Poly (3-hexylthiophene) [6,6]-phenyl C61-butyric acid methyl ester (P3HT-PCBM) were fabricated in standard architecture by spin-coating on glass and on flexible polyethylene terephthalate (PET) substrates in ambient laboratory environment. In addition to the conventional DC characterization, impedance spectroscopy was used in order to study the capacitive behavior of the devices and obtain their electrical parameters. In combination with the electrical characterization methods, laser-beam-induced current (LBIC) measurements were used as a non-destructive method of mapping the photocurrent distribution and analyzing local device failures and macroscopic defects (shunts, dark spots, defects). The results of the study can be used to develop guidelines for the development and design of P3HT:PCBM solar cells in ambient environment.

Structural, optical and electrical investigation of low-temperature processed zinc oxide quantum dots based thin films using precipitation-spin coating on flexible substrates

Undoped zinc oxide quantum dots (ZnO QDs) solution with ∼4 nm average particle size was synthesized via precipitation technique and spin coated on bare polyethylene terephthalate (PET) and indium tin oxide (ITO) coated PET flexible substrates at low temperature to obtain thin films. The structural, optical and electrical properties of the films were demonstrated by using XRD, FESEM, UV–Visible and Hall Effect. Both films exhibited preferred (101) orientation with slightly better crystallinity on bare PET. Film on ITO coated PET substrate has granular structure with grain size and surface roughness of 4.55 nm and 4.50 nm, respectively. Films showed high visible transmittance with calculated optical band gap of 3.31 eV and 3.35 eV; and refractive index 2.26 and 2.24 respectively, indicating a red shift in the ZnO/ITO/PET in comparison to ZnO/PET. Resistivity of 1.2 × 10−3 Ω cm was achieved with ZnO/ITO/PET electron mobility that surpassed reported hydrothermally synthesized ZnO QDs.

Fabrication of high-quality flexible transparent conductive thin films with a Nb2O5/AgNWs/Nb2O5 sandwich structure

Different sandwich structures of flexible transparent conductive thin film (TCFs) composed of Nb2O5 layers and Ag nanowires (AgNWs) have been prepared onto flexible polyethylene terephthalate (PET) substrate at room temperature to develop an indium-free TCF. The AgNWs are synthesized by a modified polyol method and inserted into the Nb2O5 layers that are prepared by radio frequency magnetron sputtering. The optical and electrical properties can be modified by changing the number of spin-coating cycle of AgNW suspension. At optimized condition, we achieve a flexible Nb2O5/AgNWs/Nb2O5 sandwich thin film with a low sheet resistance of 9.61 Ω/square and a high optical transmittance of 84.3%. Meanwhile, the resistance remains nearly constant after 30 tape tests, suggesting a strong adhesion to the PET substrate. The sandwich thin films show high long-term stability to oxidation, humid heat, and chemicals compared with that of AgNW networks, which can be attributed to the effective covering of Nb2O5 layer on the AgNWs. In addition, the Nb2O5/AgNWs/Nb2O5 sandwich thin films show good stability after repeated bending. This Nb2O5/AgNWs/Nb2O5 sandwich thin film can therefore serve as a high-performance transparent conductive electrode for numerous flexible electronic devices.

Preparing Copper Nanoparticles and Flexible Copper Conductive Sheets.

Nanotechnology is used in a wide range of fields, including medicine, cosmetics, and new material development, and is one of the most popular technologies in the field of flexible electronic products. For the present work, the chemical reduction method with environmentally friendly reducing agents was used to synthesize copper nanoparticles (CuNPs) with good dispersibility. The CuNPs were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and ultraviolet–visible spectrophotometry (UV–vis). After the CuNPs were formed, the solvent, polymers, and additives were added to form copper ink. Finally, the prepared copper inks were applied to flexible polyethylene terephthalate (PET) substrate under low sintering temperature and the effects of sintering time and different concentrations of sintering agent on resistivity were investigated. The results show that the copper nanoparticles synthesized by secondary reduction were smaller, more uniform, and better dispersed than those formed by primary reduction. Ethylene glycol has reducing effects under high temperatures; therefore, the CuNPs formed using the mixed solvent were small and well dispersed. The copper ink was applied on the PET substrate, treated with a formic acid aqueous solution, and sintered at 130 °C for 60 min, and its resistivity was about 1.67 × 10−3 Ω cm. The proposed synthesizing method is expected to have potential applications in the flexible electronic products field.

Trained laser-patterned carbon as high-performance mechanical sensors

We describe the mechanical properties of turbostratically graphitized carbon films obtained by carbon laser-patterning (CLaP) and their application as bending or mechanical pressure sensors. Stable conductive carbonized films were imprinted on a flexible polyethylene terephthalate (PET) substrate by laser-induced carbonization. After initial gentle bending, i.e. training, these sponge-like porous films show a quantitative and reversible change in resistance upon bending or application of pressure in normal loading direction. Maximum response values of ΔR/R0 = 388% upon positive bending (tensile stress) and −22.9% upon negative bending (compression) are implicit for their high sensitivity towards mechanical deformation. Normal mechanical loading in a range between 0 and 500 kPa causes a response between ΔR/R0 = 0 and −15%. The reversible increase or decrease in resistance is attributed to compression or tension of the turbostratically graphitized domains, respectively. This mechanism is supported by a detailed microstructural and chemical high-resolution transmission electron microscopic analysis of the cross-section of the laser-patterned carbon.

Solution process formation of high performance, stable nanostructured transparent metal electrodes via displacement-diffusion-etch process

Transparent electrodes (TEs) with high chemical stability and excellent flexibility are critical for flexible optoelectronic devices, such as photodetectors, solar cells, and light-emitting diodes. Ultrathin metal electrode (thickness less than 20 nm) has been a promising TE candidate, but the fabrication can only be realized by vacuum-based technologies to date, and require tedious surface engineering of the substrates, which are neither ideal for polymeric based flexible applications nor suitable for roll-to-roll large-scale manufacture. This paper presents high-performance nanostructured transparent metal electrodes formation via displacement–diffusion-etch (DDE) process, which enables the solution-processed sub-20-nm-thick ultrathin gold electrodes (UTAuEs) on a wide variety of hard and soft substrates. UTAuEs fabricated on flexible polyethylene terephthalate (PET) substrates show a high chemical/environmental stability and superior bendability to commercial flexible indium–tin-oxide (ITO) electrodes. Moreover, flexible organic solar cells made with UTAuEs show similar power conversion efficiency but much enhanced flexibility, in comparison to that of ITO-based devices.

UVA and solar driven photocatalysis with rGO/TiO2/polysiloxane for inactivation of pathogens in recirculation aquaculture systems (RAS) streams

In this study TiO2/polysiloxane(SiBi) thin films modified with different concentrations of graphene oxide (GO) were prepared by ink-jet printing on flexible polyethylene terephthalate (PET) substrates. Prepared coatings were characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), Raman and water contact angle measurements. During photocatalytic tests strong change of color of prepared coatings modified with GO was observed. XPS analysis of thin films after photocatalytic tests suggests that reduction of GO took place. Prepared coatings were studied for inactivation of microorganisms naturally occurring in aquaculture water under UVA and natural solar irradiation. Effect of rGO concentration in prepared coating on inactivation of target bacteria Aeromonas hydrophila and Citrobacter gillenii was evaluated under UVA irradiation. Aeromonas hydrophila was more sensitive to photocatalytic inactivation in comparison with Citrobacter gillenii. Higher photocatalytic inactivation of target microorganisms was attributed to thin films with concentration of rGO 1 and 5%. The rGO/TiO2/SiBi 5% were further tested for inactivation of Aeromonas salmocida, Serratia fonticola strain and Lactococcus lactis strain under natural solar light. Solar photocatalysis slightly enhanced inactivation of Aeromonas salmocida and Serratia fonticola strain, while opposite was observed for Lactococcus lactis strain.

Green Solvent‐Processed Hemi‐Isoindigo Polymers for Stable Temperature Sensors

AbstractA series of donor‐acceptor polymers, namely PTEB, PMEB, PEEB, and PPEB, are designed and synthesized for temperature sensing. The polymers are composed of hemi‐isoindigo as the acceptor unit, 3,3″‐bis(dodecyloxy)‐2,2″‐bithiophene as the donor unit, and thiophene as the spacer unit. Carbamate solubilizing side chains are used to increase the solubility of the polymers in a green solvent anisole. Furthermore, the carbamate side chains can be thermally removed to form solvent‐resistant polymers PTNB, PMNB, PENB, and PPNB, respectively. The removal of carbamate side chains also helps to elevate the highest occupied molecular orbital energy level of the polymer, thereby promoting p‐doping. PMNB, PENB, and PPNB films are doped with 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) and used for fabricating temperature sensors on flexible polyethylene terephthalate substrates. The sensors exhibit high temperature coefficient of resistance (TCR) of up to −1.92 (±0.125)% °C−1 at 20–60 °C. This is the highest TCR achieved to date for resistor‐type temperature sensors using a non‐composite single conductive polymer. High sensitivity, green solvent processability, and mechanical flexibility make these temperature sensors promising for use in low‐cost, ubiquitous applications.

A no-hysteresis TIPS–pentacene:polystyrene blend-based organic field effect transistor by extruded direct ink writing and the application in a resistive load inverter circuit

Organic field effect transistors (OFETs), with the active layer made from 6,13-bis(triisopropylsilylethinyl) pentacene:polystyrene blend films, were fabricated on rigid (glass) and flexible (polyethylene terephthalate) substrates using a motor-controlled extrusion-based Direct Ink Writing printing method.

Development of Reciprocating Inkjet System for Printed Electronic Devices

Reciprocating inkjet system (RIS) is an additive manufacturing technology in which drops are formed on a substrate by extruding liquid ink from ink chamber via the reciprocating movement of a micro needle. Depending on the diameter of the micro needle, RIS is capable of a small amount drop (approx. 1 pl) with a wide range of viscosity (1~300,000mPa.s) levels, unlike a piezoelectric inkjet printing which can perform only 1-15mPa.s. Also, RIS is capable of printing inks with various drop sizes (10µm to 1000µm). This wide range of printable ink viscosity is attributed to both the mechanical extrusion mechanism adopted in the method, and the size controllability associated with the micro-needle diameter. Furthermore, the printing frequency of RIS is typically limited to 1-20 Hz which is considerably lower than that of conventional inkjet printing, (1-10kHz) because the micro needle must move in a reciprocating manner through mechanical movement. Although the slow frequency is at times problematic for some applications, the controllability of the high-resolution drop sizes is beneficial in applications such as the repair of open circuits, solder paste dropping for interconnections and all kinds of substrates. This paper, therefore, focuses on the development of RIS wherein printing process parameters (needle diameter, needle moving velocity, distance from substrate, and reciprocating frequency of inkjet head) are optimized. Moreover, the RIS is utilized to print fine conductive patterns on a flexible polyethylene terephthalate (PET) substrate for the fabrication of printed sensor which are analyzed by optical characterization. The results are then documented and discussed along with the conclusions drawn.

Simulation and lithographic fabrication of a triple band terahertz metamaterial absorber coated on flexible polyethylene terephthalate substrate

A triple band metamaterial absorber in the terahertz range, incorporating a three closed circle ring resonator, was designed and fabricated on flexible polyethylene terephthalate “PET” substrate. The proposed design was investigated theoretically and experimentally. Computer simulation technology “CST” was used to study the designed structure, while lithography technique was used to fabricate the absorber and terahertz time-domain spectroscopy was utilized to measure the reflectivity. Results showed the presence of three intensive peaks at the resonance frequencies of ‘0.43, 0.61, and 0.88 THz’, which correspond to the absorptivity of 98%, 91%, and 98%, respectively. The sensitivity of the three peaks was found to be ‘70.5, 133, and 149.5 GHz/RIU’, respectively. The parametric studies and field distributions were analysed. Furthermore, the proposed design exhibited polarization insensitivity for both transverse electric “TE” and transverse magnetic “TM” modes from 00 to 900. It was concluded that the proposed design can be specifically viable for some important applications such as ‘THz’ images, filtering, biological sensing, and optical communications.

A Triband Slot Patch Antenna for Conformal and Wearable Applications

With the rapid development of wireless communication technology and the Internet of Things (IoT), wireless body area networks (WBAN) have been thriving. This paper presents a triband patch antenna with multiple slots for conformal and wearable applications. The proposed antenna operates at 5.8, 6.2, and 8.4 GHz. The antenna was designed with a flexible polyethylene terephthalate (PET) substrate, and the corresponding conformal tests and on-body performance were conducted via simulation. The antenna demonstrated promising gain and acceptable fluctuations when applied on curvature surfaces. The specific absorption rate (SAR) for on-body simulation also suggests that this antenna is suitable for wearable applications.

Numerical Study on Broadband Antireflection of Moth-Eye Nanostructured Polymer Film with Flexible Polyethylene Terephthalate Substrate

The application of moth-eye nanostructured polymer film on the flexible polyethylene terephthalate (PET) substrate is an effective way to improve its antireflection (AR) performance. However, many factors affect the AR properties of the moth-eye structure in the actual manufacturing process. Moreover, the antireflection research based on PET substrate has been relatively lacking compared with the silicon substrate. In this paper, we simulate and analyze the AR performance of the moth-eye nanostructured polymer film on PET substrate by using the finite-difference time-domain method within the wavelength range of 400–1100 nm. Simulation results show that the parabola-shaped moth-eye structure (PSMS) can suppress the Fresnel reflection significantly. Moreover, the height and filling ratios are the dominant factors that affect the AR performance of PSMS. Additionally, the base diameter, residual layer thickness, and the refractive index of PSMS polymer film also affect the reflectivity of PET slightly. As a result, an optimal PSMS with base diameter of 400 nm, height of 300 nm, and the hexagonal close-packed arrangement is appropriate, and the solar-weighted reflectivity of PET can be suppressed to 0.21%, which shows a prominent advantage over the bare PET (≈6%). Therefore, this research has promising potential for improving the optical performance of optoelectronic devices by using nanostructured polymer materials.