Flexible Kapton Substrate Research Articles

Enhancing cardiovascular health monitoring: Simultaneous multi-artery cardiac markers recording with flexible and bio-compatible AlN piezoelectric sensors

Continuous monitoring of cardiovascular parameters like pulse wave velocity (PWV), blood pressure wave (BPW), stiffness index (SI), reflection index (RI), mean arterial pressure (MAP), and cardio-ankle vascular index (CAVI) has significant clinical importance for the early diagnosis of cardiovascular diseases (CVDs). Standard approaches, including echocardiography, impedance cardiography, or hemodynamic monitoring, are hindered by expensive and bulky apparatus and accessibility only in specialized facilities. Moreover, noninvasive techniques like sphygmomanometry, electrocardiography, and arterial tonometry often lack accuracy due to external electrical interferences, artifacts produced by unreliable electrode contacts, misreading from placement errors, or failure in detecting transient issues and trends. Here, we report a bio-compatible, flexible, noninvasive, low-cost piezoelectric sensor for continuous and real-time cardiovascular monitoring. The sensor, utilizing a thin aluminum nitride film on a flexible Kapton substrate, is used to extract heart rate, blood pressure waves, pulse wave velocities, and cardio-ankle vascular index from four arterial pulse sites: carotid, brachial, radial, and posterior tibial arteries. This simultaneous recording, for the first time in the same experiment, allows to provide a comprehensive cardiovascular patient's health profile. In a test with a 28-year-old male subject, the sensor yielded the SI = 7.1 ± 0.2 m/s, RI = 54.4 ± 0.5 %, MAP = 86.2 ± 1.5 mmHg, CAVI = 7.8 ± 0.2, and seven PWVs from the combination of the four different arterial positions, in good agreement with the typical values reported in the literature. These findings make the proposed technology a powerful tool to facilitate personalized medical diagnosis in preventing CVDs.

Biologically inspired piezoresistive MEMS acoustic vector sensor for underwater applications

Underwater acoustics has assumed a pivotal role in the detection, navigation, communication, and target identification of ships and submarines. In recent years, advancements in noise reduction from marine vessels have underscored the significance of underwater acoustic vector sensors. This paper presents a novel approach to the design, fabrication, and characterization of a two-dimensional Micro-Electro Mechanical Systems (MEMS) vector acoustic sensor tailored for underwater environments. Traditional underwater acoustic vector sensors often employ doped polysilicon or silicon/germanium sensing films on rigid silicon substrates. The inflexible nature of silicon substrates necessitates labor-intensive and costly chemical-mechanical polishing processes to achieve submicron thickness, often requiring extended clean-room usage. In contrast, this work proposes a simplified, cost-effective, and scalable alternative. The sensor design utilizes reduced graphene oxide (rGO) as the sensing material and Kapton as the substrate, chosen for their unique properties. rGO exhibits high carrier mobility and low intrinsic noise, ensuring clear signals with minimal external interference, thereby improving measurement accuracy in challenging environments. Kapton provides excellent thermal stability, mechanical strength, and chemical resistance, along with superior insulating properties that reduce electrical noise, enhancing the signal-to-noise ratio. The designed vector sensor leverages the piezoresistive transduction principle, incorporating a thin piezoresistive film of rGO on a flexible Kapton substrate via a straightforward drop-casting method. Inspired by the sensory mechanisms of aquatic life, the two-dimensional vector sensor not only detects pressure associated with acoustic signals but also discerns the direction from which these low and ultralow frequency signals originate. The device's performance characteristics, sensitivity, and directivity are comprehensively evaluated through static, dynamic, and acoustic tests conducted in both air and water mediums. Static tests reveal the piezoresistive behavior of rGO under applied displacement, yielding displacement sensitivities of 0.0279 V/mm and 0.0276 V/mm for axial and radial displacements, respectively. Dynamic and acoustic tests demonstrate the sensor's capability to detect low-frequency signals spanning from 0.25 Hz to 200 Hz, exhibiting a smooth and favorable frequency response. In air, the sensor exhibits receiving sensitivities ranging from −15.18 dB to −19.75 dB (X-channel) and −13.67 dB to −16.67 dB (Y-channel). In the underwater environment, these values range from −134.40 dB to −138.93 dB (X-channel) and −131.83 dB to −136.93 dB (Y-channel). Notably, the variation in receiving sensitivity across channels in both air and water is limited to within 6 dB. Furthermore, the device showcases a symmetrical directivity pattern resembling the shape of an "8," with an approximate sensitivity of −136.66 dB, a significant improvement compared to the −165 dB sensitivity of conventional polysilicon underwater vector sensors. These experimental findings affirm the feasibility of the proposed underwater vector sensor, based on the piezoresistive effect and MEMS technology, highlighting its two-dimensional directivity capabilities.

Optical tunability with superlattice hyperbolic metamaterial coatings

Optical tunability is demonstrated with multi-metal hyperbolic metamaterial (HMM) structures on varying substrate surfaces. A systematic uniaxial modeling methodology is adapted from classical approaches to extract the anisotropic permittivity of the films to identify epsilon-near-zero (ENZ) behavior over a wide range of metal volume fractions (φ). The anisotropic model accuracy is quantified by a mean squared error (MSE) with the presented modeling routine resulting in a MSE < 35 for all samples. The optical model thicknesses were verified with transmission electron microscopy (TEM) imaging and measurements. This study also demonstrates the ability to tune the optical responses in the visible-to-infrared frequencies with surface microtexturing and applied strain with HMM coatings on flexible Kapton substrates. Furthermore, the structured films and modeling procedure lay the groundwork for future studies on coupling the anisotropic optical and thermal properties for control over advanced multifunctional thin-film coatings.

Kirigami-inspired organic and inorganic film-based flexible thermoelectric devices with built-in heat sink

Thermoelectric (TE) devices can convert heat to electricity directly, which offers a unique opportunity to realize waste heat recovery. However, conventional TE devices inevitably use heat sinks, which are bulky, rigid and heavy, limiting practical applications. Herein, we propose a fully integrated film-based TE device with intrinsically built-in fins as heat sink in a hexagonal honeycomb device structure, that simultaneously achieves high TE performance and conformability, as confirmed by experiments and modelling. A flexible Kapton substrate with copper electrodes, integrating either carbon nanotube (CNT) veils or bismuth telluride (Bi2Te3) TE ‘legs’, both of n- and p-type, achieved a remarkable specific power of 185.4 nW K−2 for a Bi2Te3-based device and 53.1 nW K−2 for a CNT-based device, thanks to the heat dissipation effect granted by the built-in fins. Besides, the addition of oriented polymer films interconnects, contracting when above their glass transition temperature, allowed a single substrate two-dimensional (2D) TE device to self-fold into a three-dimensional (3D) hexagonal honeycomb structure, with built-in fins, contactlessly and autonomously. The demonstrated shape-programmed kirigami-inspired scalable TE device paves the way for realising self-powered applications comprising hundreds of TE legs with both inorganic (e.g., Bi2Te3) and organic (e.g. CNT veils) TE materials and integrated heat sinks.

Enhanced spin–orbit torques in strained NiFe/Pt bi-layers on flexible substrate

Magnetization manipulation caused by spin–orbit torque is one of the central themes investigated in spintronics domain. The spin–orbit torque efficiencies can be manoeuvred by application of mechanical strain. In this direction, this study furthers the effort in understanding the evolution of spin–orbit torque efficiencies in mechanically strained ferromagnet (FM)/heavy metal(HM) (Ni81Fe19/Pt) bi-layer films on flexible kapton substrate, by the use of spin torque ferromagnetic resonance (ST-FMR) measurement technique. We report a tensile strain induced enhancement in damping-like and field-like spin–orbit torque efficiencies. The effective damping-like spin torque conductivity increased by 42% on the application of 0.312% tensile strain, which is encouraging from the magnetization switching application point of view. In order to investigate the driving factors behind the enhanced damping-like spin torque conductivity, ab-initio calculations were also carried out. Our findings provide insights into the workings of strain in FM/HM bi-layer stack and is a step forward in the implementation of flexible spintronics devices.

Molecular-orientation-dependent magnetic properties of iron phthalocyanine (FePc) thin films and microwires

The development of molecular magnets plays a major role in emerging organic spintronics applications, as it exhibits both semiconducting and magnetic properties. Herein, we report on the molecular-orientation-dependent magnetic properties of iron phthalocyanine (FePc) thin films and microwires. FePc thin films grown on SiO2 and flexible kapton substrates clearly reveal that the morphology is strongly influenced by the substrates and film thickness. Meanwhile, the molecular stacking orientation of FePc thin films can be tuned by 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA) templating layer and film thickness. Magnetic hysteresis loops show that the iron atoms are strongly magnetically coupled into ferromagnetic chains at low temperature with high coercivity at 1000 Oe. The magnetization and susceptibility of FePc thin films are dependent on the molecular orientation, and the Curie–Weiss constant is modulated from 24 ± 2 K K to 35 ± 2 K through the templating effect, in which the molecular stacking orientation changes from standing-up to lying-down arrangement. Furthermore, strong orientation dependent ferromagnetism is also observed in low-dimensional η-FePc microwires, in which the Curie–Weiss constants change from 20 ± 2 K to 35 ± 2 K when magnetic field rotated from short wire axis to long wire axis. The ability to fabricate FePc thin films on flexible substrate with controllable molecular orientation and ferromagnetism makes them promising candidates for flexible spintronic devices.

Study of the sensitivity of moisture-sensitive structures with UV reduction on the basis of ZnO produced by the sol-gel method

A structure based on a thin-film nanocrystalline zinc oxide obtained by the sol-gel method on a flexible Kapton substrate has been developed. It has been established that its electrical resistance increases significantly under the influence of moisture contained in the air. When irradiated with ultraviolet radiation, the resistance of the structure decreases by almost two orders of magnitude. After the UV exposure finish, a long-term process of restoration of electrical conductivity is observed, which is described by the fractional-exponential Kohlrausch function.

Compact hybrid EBG microstrip antenna for wearable applications

Abstract A novel strip line fed, circularly polarized (CP), annular slotted dual band antenna using hybrid electromagnetic band gap (EBG) structure for Global Positioning System (GPS) has been herein designed, analyzed, and investigated for wearable applications. Adjusting the radii of the annular slots on the radiating patch excellent circular polarized (CP) radiation and impedance matching is achieved. The design demonstrates Kapton based flexible, robust, and low-profile solution with permittivity of 3.4 to meet the requirements of wearable applications. Due to the high losses of the animal body, the electromagnetic band gap (EBG) structure is used to reduce back radiation and the effect of frequency detuning. The proposed antenna structure also enhances the front-to-back ratio (FBR) by 10 dB. This antenna with dimensions 0.56λ 0 × 0.4913λ 0 × 0.002λ 0 analyzed using a flexible Kapton substrate. Optimized hybrid EBG structure provides an excellent Specific Absorption Rate (SAR) along with all other antenna parameters, within acceptable for GPS-based wearable applications at 1.13 GHz and 1.157 GHz frequency band. Therefore the proposed antenna is a suitable candidate for GPS-based tracking and wireless body area network (WBAN) applications. The proposed antenna was also tested upon fabrication and the measured results agree with simulated results.

(Digital Presentation) Electrodeposition of Re on Aerosol Jet Printed Metal Seed Layers on Flexible Substrates

Quantum computers (QCs) are expected to run advanced algorithms to solve currently intractable challenges in chemistry simulations, cryptography, medicine, and finance.[1] The Josephson Junction based qubits that power a quantum computer must reside in a cryogenically cooled chamber at 10 mK. Communications with this chip is currently carried out with a chandelier of rigid cables.[2] A flexible cable containing superconducting interconnect lines could in principle simplify the design of QC interconnects and lead to improvement in qubit density and efficiency. We have previously demonstrated the use of aerosol jet printing (AJP) for the patterning of electrodeposited Cu and Ni [3]. We have also recently reported on the development of a water-in-salt method to electrodeposit superconducting Re on evaporated Au on Si substrates. These Re components have a critical temperature above 4.2 K, which makes the superconductivity easily accessible with liquid He cooling[4].We report for the first time the metallization of flexible Kapton substrates with printed Au and Ag nanoparticle inks by aerosol jet printing as the seed for superconductor electrodeposition. Electrodeposition of Re onto the printed structures was performed using the water-in-salt method. ASTM D3359 tests demonstrated that Au has superior adhesion to Kapton, while the Ag seed does not survive rhenium deposition, potentially due to the high internal stress of Re. Further, improved adhesion was demonstrated when Kapton substrates were roughened with 1200 grit sandpaper. Electrodeposited Re on AJP Au seed layer on flexible Kapton substrates, as shown in Figure 1, demonstrated a superconducting transition temperature of 6K. In addition, electrodeposited Re on Au survived 200 cycles of flexure testing under >30 MPa load and 1.2% strain. These efforts demonstrate the proof-of-principle for patterning of superconducting interconnects for the further development of QCs. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. SAND2022-11522 A References [1] F. Bova, A. Goldfarb, and R.G. Melko “Commercial Applications of Quantum Computing.” EPJ Quantum Tech. (2021) 8:2.[2] S. Krinner, S. Storz, P. Kurpiers, P. Magnard, J. Heinsoo, R. Keller, J. Lütolf, C. Eichler & A. Wallraff. “Engineering cryogenic setups for 100-qubit scale superconducting circuit systems.” EPJ Quantum Tech. (2019) 6:2.[3] L. K. Tsui, S. C. Kayser, S. A. Strong, and J. M. Lavin, “High Resolution Aerosol Jet Printed Components with Electrodeposition-Enhanced Conductance.” ECS J. Solid State Sci. Tech. (2021). 10, 047001.[4] W. D. Sides, E. Hassani, D. P. Pappas, Y. Hu, T. S. Oh, Q. Huang “Grain growth and superconductivity of rhenium electrodeposited from water-in-salt electrolytes.” J. App. Phys. (2020). 127, 085301.Figure 1. (a) Photograph of a well adhered Re on Au sample. (b) Superconducting transition data for Re on printed Au on Kapton. Figure 1

Calibration of the Scanning Kelvin Probe By Applied External Potential

The scanning Kelvin probe (SKP) is a device that measures the difference in work function between a sample and probe tip on the instrument, and has proven to be a useful research tool over the past several decades. With this technique, the Volta potential difference, also known as the contact potential difference (CPD), can be determined which can characterize the corrosion, contamination, and coating condition of a surface of interest. The recently developed Field Deployable Scanning Kelvin Probe (FDSKP) allows for a variety of new uses as it allows the SKP technique to be used in a field environment rather than samples or test components being brought to a lab. However, additional challenges come with the increased portability and versatility of the FDSKP, as the set-up and tear down nature of a field deployable unit necessitates a rapid determination that the system is properly set up and functioning. A calibration electrode solves this problem while further demonstrating the underlying connections between electrical potential and the work function as measured by the SKP.The absolute potential difference, also called the Galvani potential (Φ), can be described as the sum of two components: the Volta potential (Ψ) and the dipole potential (χ)1. The Volta potential is directly related to the electrode potential and, therefore, corrosion potential2. This relationship has been used in previous methods of SKP calibration that included relating the Volta potential differences measured by the SKP to the electrode potentials of bare metals and the corrosion potentials of immersed metals3. The effort described here develops a new approach to SKP calibration by applying an external potential onto the calibration electrode surface to further modify the Volta potential and, therefore, the measured Volta potential difference between the polarized sample and the probe tip. The design of the calibration electrode includes flat conductive regions across which a potential can be applied. By applying an external potential to a sample, the measured work function is changed by that amount, thus sharp voltage changes between regions of different applied potential can be observed.The calibration electrode described here is a flexible Kapton substrate with vacuum deposited gold regions produced through a mask and UV lithography fabrication process (Figure 1). Three different geometric designs of matching shapes with a 10 um gap between them are present: bars, wedges, and a puzzle-piece type design. By electrically connecting one region from each of the three designs into two groups, a potential difference could then be applied between the two regions of each design group by means of a potentiostat or battery. With this applied potential, an SKP area scan was performed above the sample. The average work function for each of the two regions was determined. The difference in average work function correlates very well with applied potential across a range of voltage from -1 V to 1 V at steady-state. Similar results were recorded on both coated and uncoated electrodes. As the correlation between observed work function difference and applied potential is very good, this can be used to calibrate an SKP system and demonstrate its proper functioning. A system check can include determining that the measured voltage difference on the calibration electrode matches the applied potential. Additionally, the sharp distinction on the sample between regions of different work function can allow for the calibration and tuning of SKP parameters, such as electrometer and proportional integral derivative (PID), in order to optimize the system’s measurement capability. As SKP techniques move from the lab into the field, a calibration electrode is very useful as it will greatly assist in system set-up and facilitate parameter optimization to allow for better and clearer results. References Grunmeir, G., Juttner, K. and Stratmann, M. (2000) Novel Electrochemical Techniques in Corrosion Research. In R.W. Cahn, P. Haasen & E.J. Kramer (Eds.), Material Science and Technology: Corrosion and Environmental Degradation (Volume I, p. 285-382). Wiley-VCH.Leng, H. Streckel and M. Stratmann “The Delamination of Polymeric Coatings from Steel. Part I: Calibation of the Kelvin Probe and Basic Delamination Mechanism,” Corrosion Science 41 (1999): p. 547-578.B. Cook et al. “Calibration of the Scanning Kelvin Probe Force Microscope under Controlled Environmental Conditions,” Electrochimica Acta 66 (2012), p. 100-105. Figure 1

Functional cyclic bending test for integrated inductors on flexible Kapton substrate

This work presents a method to assess the reliability of integrated inductors on a flexible substrate through a functional cyclic bending test, which consists of a full characterization of these inductors after several bending cycles. Inductors were fabricated through a simple and original technology suitable for use in the heterogeneous integration of radiofrequency and microwave applications. Failure analysis before and after tests have not found any problem related to the use of a flexible substrate. Less than 15 % of the tested inductors failed after the bending tests, indicating the good performance of the fabrication process and a robust method to evaluate the reliability of such components.

A detailed performance analysis of a novel UWB flexible monopole antenna realized with airbrush technique for different technologies

In this article, a detailed performance analysis of a novel flexible monopole antenna with a 141.46% impedance bandwidth in the 2.4–14 GHz ultrawideband (UWB) range is present. The antenna is fabricated on a flexible Kapton substrate with compact geometry for different technology applications under different bending conditions. The airbrush printed technique was preferred due to its advantages such as easy production, conductivity control, and no loss of surface waves. The antenna has dimensions of 82 × 57 × 0.125 mm3 and is fed by a coplanar waveguide transmission line. All necessary antenna simulations are performed using Computer Simulation Technology (CST). According to the positions of identical antennas face to face, face to side, side to side, time-domain analysis is performed for the impact response analysis. The transmission coefficient characteristics (S 21) and the group delay are measured for various bending conditions. Time and frequency domain analyzes show that the proposed UWB antenna has the much-needed stable performance in UWB antenna. The proposed UWB antenna has good performance over the operating spectrum for a flat and bending configuration.

Fabrication of a high-sensitive wearable temperature sensor with an improved response time based on PEDOT:PSS/rGO on a flexible kapton substrate

Fabrication of a high-sensitive wearable temperature sensor with an improved response time based on PEDOT:PSS/rGO on a flexible kapton substrate

Effect of substrate temperature on micro-structural, optical and electrical properties of V2O5 thin films

Vanadium pentoxide (V2O5) thin films have been prepared onto ITO coated flexible Kapton substrates by electron beam evaporation technique. The influence of substrate temperature on the structural, morphological, optical and electrical properties has been investigated. The XRD results reveals that the films prepared at lower temperatures are amorphous in nature and the films prepared at 300 oC is exhibited predominant (001) orientation with an orthorhombic crystal structure. AFM study showed that the grain size varies from 80 nm to 150 nm. The optical studies revealed that the transmittance decreased with increasing substrate temperature. The optical absorption coefficient ‘a’ determined from the experimentally measured transmittance and reflectance data for V2O5 films was found to give a better fit for the exponent n = 3/2 suggesting the direct forbidden transitions with an estimated optical band gap of 2.31 eV for the films prepared at 300 oC. The electrical conductivity has been observed to be increased from 2 x 10-6 S/cm to 3 x 10-2 S/cm by varying temperature from 30 oC to 300 oC. The electrochemical experiments exhibited the discharge capacity of about 60 μAh/(cm2-μm) for the films deposited at 300 oC.

Atomic-Oxygen-Durable and Antistatic α-AlxTiyO/γ-NiCr Coating on Kapton for Aerospace Applications.

Polymers used for the exteriors of spacecraft are always exposed to risks such as atomic oxygen (AO) or electrostatic discharge (ESD) degradation. In this work, an AlxTiyO/NiCr coating with excellent mechanical stability, AO durability, and electrostatic dissipative properties was deposited via ion implantation (IIP), filter cathode vacuum arc (FCVA), and high-power impulse magnetron sputtering (HiPIMS) on a flexible Kapton substrate. Scratch and cycle folding tests indicated good adhesion and toughness of the AlxTiyO/NiCr-coated Kapton, which were due to the gradient structure fabricated by the multitechnology combination. AO exposure tests demonstrated an extremely low erosion yield (Ey = 5.15 × 10-26 cm3 atom-1) of the AlxTiyO/NiCr-coated Kapton, only 1.72% of that observed for pristine Kapton. Moreover, Rutherford backscattering spectrometry (RBS) and Kelvin probe force microscopy (KPFM) results showed that the AlxTiyO/NiCr-coated Kapton has elevated surface electrostatic dissipative properties and sufficient conductivity. The multitechnology combination offers great flexibility for customizing the gradient structure to realize a comprehensive performance improvement. In addition, such a coating has great prospects for aerospace applications.

Selective and electronic detection of COVID-19 (Coronavirus) using carbon nanotube field effect transistor-based biosensor: A proof-of-concept study

In this work, we propose and demonstrate a carbon nanotube (CNT) field-effect transistor (FET) based biosensor for selective detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). CNT FETs were fabricated on a flexible Kapton substrate and the sensor was fabricated by immobilizing the reverse sequence of the RNA-dependent RNA polymerase gene of SARS-CoV-2 onto the CNT channel. The biosensors were tested for the synthetic positive and control target sequences. The biosensor showed a selective sensing response to the positive target sequence with a limit of detection of 10 fM. The promising results from our study suggest that the CNT FET based biosensors can be used as a diagnostic tool for the detection of SARS-CoV-2.

Magnetotransport Properties of Semi-Metallic Bismuth Thin Films for Flexible Sensor Applications

In this paper we describe characterization of semi-metallic bismuth thin films. We prepared bismuth thin films by a deposition of bismuth through thermal evaporation onto flexible Kapton substrates and annealing at temperatures close to the melting point of Bi. We studied the morphology and transport properties of these films. Immediately after the deposition we observed competition between vanishing of the grain boundaries and elastic strain energy, which stabilized at larger thicknesses leading to the grain size of 140 nm. This effect was accompanied by a continuous decrease of resistivity which, however, was larger than for the bulk bismuth. The film annealing at temperatures close to the melting point of Bi led to a 300% increase of magnetoresistance at room temperature and in the magnetic field of 7 T. The in situ resistance measurements allowed us to determine the permissible temperature at which the annealing does not cause the loss of film continuity.

Design of Piezo-Resistive Type Acoustic Vector Sensor using Graphene for Underwater Applications

In recent years as the level of radiated noise of submarine drastically got decreased, the requirement of underwater acoustic sensor has become essential for the detection of low frequency acoustic signal. The latest advancement in the field of underwater sensors is the Micro Electro Mechanical Systems (MEMS) sensor. The major advantage of this sensor being determination of directionality along with the measurement of pressure of an acoustic signal. The biological inspiration behind the design of the sensor was derived from fish lateral line sensing system, with piezoresistive transduction principle to obtain the objective of miniaturization and low frequency signal detection. In this paper, we are reporting the design, simulation of an underwater two-dimensional MEMS acoustic vector sensor which exhibits better sensitivity, flexibility when compared to the traditional acoustic vector sensor. In this work, thin film of piezoresistve material, Reduced Graphene Oxide (Rgo) is taken as pressure sensing element instead of traditional polysilicon material and its performance in terms of sensitivity and directivity is analysed. MEMS acoustic vector sensors using Reduced Graphene Oxide and polysilicon were simulated on flexible kapton and silicon substrate respectively using COMSOL Multiphysics 5.5 vesrion. The simulation results indicates that designed vector sensor based on MEMS technology and piezoresistive effect of rGO on flexible kapton substrate is feasible and possesses better sensitivity of -149.47 dB when compared to the sensitivity of -171.37 dB of polysilicon based traditional acoustic vector sensor. The simulated value of eigen frequency of the sensor is found as around 47Hz, which almost matches with the theoretical value of resonance frequency of the sensor as per the design considerations of the sensor and hence capable of detecting low frequency acoustic signals.

Crack resistance of bismuth ferrite films obtained on a flexible substrate

Ultrathin BiOx and FeOx layers were obtained by Atomic Layer Deposition (ALD) on the surface of a flexible Kapton substrate (poly (4,4’-oxydiphenylene-pyromellitimide)) at a temperature of 250 °C. The layer thickness was 50 - 100 nm. Surface morphology, electrical polarization, and mechanical properties were investigated by Atomic Force Microscope, Piezoelectric Force Microscopy and Force Modulation Microscopy. Chemical analysis was performed by X-ray Photoelectron Spectroscopy, where the formation of Bi2O3 and Fe2O3 phases, as well as intermediate phases in the Bi-Fe-O system, was observed. With a small increase in the Bi content of the film, the BFO / Kapton structure becomes more crack resistant. Modification of the Kapton surface with bismuth and iron oxides showed that such a composition exhibits multiferroic behavior.

Reduced graphene oxide-chitosan flexible nanocomposites for efficient bacteria capture and photothermal ablation

AbstractOne of the major public health concerns today is bacterial infection-associated diseases. Traditional antibacterial therapies are becoming less efficient because frequent and inadequate use of antibiotics has caused mutations in bacteria that led to many antibiotic-resistant bacterial strains. It is, therefore, crucial to develop novel antibacterial materials and strategies that will successfully combat both gram-positive and gram-negative bacteria. In the present study, we will demonstrate a simple and efficient method for bacteria capture and elimination through photothermal ablation. The developed material consists of a flexible Kapton substrate, coated with reduced graphene oxide-chitosan (rGO-CS) thin films. Reduced graphene oxide has strong absorption in the near-infrared (NIR) region, while chitosan has the ability to bind bacteria through electrostatic interactions. The K/rGO-CS device proved to capture and efficiently eradicate both planktonic Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) bacteria after 10 min of NIR (980 nm) irradiation.