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We study the effects of the uniaxial tensile strain and shear deformation as well as their combinations on the electronic properties of single-layer black phosphorene. The evolutions of the strain-dependent band gap are obtained using the numerical calculations within the tight-binding (TB) model as well as the first-principles (DFT) simulations and compared with previous findings. The TB-model-based findings show that the band gap of the strain-free phosphorene agrees with the experimental value and linearly depends on both stretching and shearing: increases (decreases) as the stretching increases (decreases), whereas gradually decreases with increasing the shear. A linear dependence is less or more similar as compared to that obtained from the ab initio simulations for shear strain, however disagrees with a non-monotonic behaviour from the DFT-based calculations for tensile strain. Possible reasons for the discrepancy are discussed. In case of a combined deformation, when both strain types (tensile/compression + shear) are loaded simultaneously, their mutual influence extends the realizable band gap range: from zero up to the values respective to the wide-band-gap semiconductors. At a switched-on combined strain, the semiconductor-semimetal phase transition in the phosphorene is reachable at a weaker (strictly non-destructive) strain, which contributes to progress in fundamental and breakthroughs., Funding Agencies|National Academy of Sciences of Ukraine [0120U102265]; Armed Forces of Ukraine; [0122U002396]

In this work, we present an investigation of the electronic states in a series of thermally activated delayed fluorescence (TADF) exciplexes formed with the popular electron-transport compound TpBpTa and hole-transporting TCTA, TAPC, TPD10, TPD, and NPB. We rationalize the photophysical behavior of exciplexes by using computational methods and demonstrate that the reason for the commonly observed temporal red shift in the time-resolved spectra is related to the distribution of molecular conformations, thus CT energy, in film. We also use spectrally resolved thermoluminescence (SRTL) measurements to give insight into the trapping phenomena in exciplex blends. The results demonstrate that trapped charge carriers in the majority of studied exciplexes recombine through the luminescent intermolecular CT state. In addition, we report OLED devices using the said exciplexes in the emissive layer. The best performance is obtained with the TCTA:TpBpTa and TAPC:TpBpTa exciplexes showing maximum external quantum efficiencies (EQEs) of 8.8% and 7.2%, respectively., Funding Agencies|National Science Center in Poland [2018/31/N/ST4/03459]; Swedish Research Council [2018-05973]; Ministry of Education and Science of Ukraine [0121U107533]; [2020-04600]

Objective. Electric stimulation delivered by implantable electrodes is a key component of neural engineering. While factors affecting long-term stability, safety, and biocompatibility are a topic of continuous investigation, a widely-accepted principle is that charge injection should be reversible, with no net electrochemical products forming. We want to evaluate oxygen reduction reactions (ORR) occurring at different electrode materials when using established materials and stimulation protocols. Approach. As stimulation electrodes, we have tested platinum, gold, tungsten, nichrome, iridium oxide, titanium, titanium nitride, and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate). We use cyclic voltammetry and voltage-step amperometry in oxygenated versus inert conditions to establish at which potentials ORR occurs, and the magnitudes of diffusion-limited ORR currents. We also benchmark the areal capacitance of each electrode material. We use amperometric probes (Clark-type electrodes) to quantify the O-2 and H2O2 concentrations in the vicinity of the electrode surface. O-2 and H2O2 concentrations are measured while applying DC current, or various biphasic charge-balanced pulses of amplitude in the range 10-30 mu C cm(-2)/phase. To corroborate experimental measurements, we employ finite element modelling to recreate 3D gradients of O-2 and H2O2. Main results. All electrode materials support ORR and can create hypoxic conditions near the electrode surface. We find that electrode materials differ significantly in their onset potentials for ORR, and in the extent to which they produce H2O2 as a by-product. A key result is that typical charge-balanced biphasic pulse protocols do lead to irreversible ORR. Some electrodes induce severely hypoxic conditions, others additionally produce an accumulation of hydrogen peroxide into the mM range. Significance. Our findings highlight faradaic ORR as a critical consideration for neural interface devices and show that the esta

H2O2 plays a significant role in a range of physiological processes where it performs vital tasks in redox signaling. The sensitivity of many biological pathways to H2O2 opens up a unique direction in the development of bioelectronics devices to control levels of reactive-oxygen species (ROS). Here a microfabricated ROS modulation device that relies on controlled faradaic reactions is presented. A concentric pixel arrangement of a peroxide-evolving cathode surrounded by an anode ring which decomposes the peroxide, resulting in localized peroxide delivery is reported. The conducting polymer (poly(3,4-ethylenedioxythiophene) (PEDOT), is exploited as the cathode. PEDOT selectively catalyzes the oxygen reduction reaction resulting in the production of hydrogen peroxide (H2O2). Using electrochemical and optical assays, combined with modeling, the performance of the devices is benchmarked. The concentric pixels generate tunable gradients of peroxide and oxygen concentrations. The faradaic devices are prototyped by modulating human H2O2-sensitive Kv7.2/7.3 (M-type) channels expressed in a single-cell model (Xenopus laevis oocytes). The Kv7 ion channel family is responsible for regulating neuronal excitability in the heart, brain, and smooth muscles, making it an ideal platform for faradaic ROS stimulation. The results demonstrate the potential of PEDOT to act as an H2O2 delivery system, paving the way to ROS-based organic bioelectronics.

Ultrathin devices are rapidly developing for skin-compatible medical applications and wearable electronics. Powering skin-interfaced electronics requires thin and lightweight energy storage devices, where solution-processing enables scalable fabrication. To attain such devices, a sequential deposition is employed to achieve all spray-coated symmetric microsupercapacitors (mu SCs) on ultrathin parylene C substrates, where both electrode and gel electrolyte are based on the cheap and abundant biopolymer, cellulose. The optimized spraying procedure allows an overall device thickness of approximate to 11 mu m to be obtained with a 40% active material volume fraction and a resulting volumetric capacitance of 7 F cm(-3). Long-term operation capability (90% of capacitance retention after 10(4) cycles) and mechanical robustness are achieved (1000 cycles, capacitance retention of 98%) under extreme bending (rolling) conditions. Finite element analysis is utilized to simulate stresses and strains in real-sized mu SCs under different bending conditions. Moreover, an organic electrochromic display is printed and powered with two serially connected mu-SCs as an example of a wearable, skin-integrated, fully organic electronic application., Funding Agencies|European Research Council (ERC) under the European Unions Horizon 2020 research and innovation programEuropean Research Council (ERC) [949191]; city council of Brno, Czech Republic

H2O2 plays a significant role in a range of physiological processes where it performs vital tasks in redox signaling. The sensitivity of many biological pathways to H2O2 opens up a unique direction in the development of bioelectronics devices to control levels of reactive-oxygen species (ROS). Here a microfabricated ROS modulation device that relies on controlled faradaic reactions is presented. A concentric pixel arrangement of a peroxide-evolving cathode surrounded by an anode ring which decomposes the peroxide, resulting in localized peroxide delivery is reported. The conducting polymer (poly(3,4-ethylenedioxythiophene) (PEDOT), is exploited as the cathode. PEDOT selectively catalyzes the oxygen reduction reaction resulting in the production of hydrogen peroxide (H2O2). Using electrochemical and optical assays, combined with modeling, the performance of the devices is benchmarked. The concentric pixels generate tunable gradients of peroxide and oxygen concentrations. The faradaic devices are prototyped by modulating human H2O2-sensitive Kv7.2/7.3 (M-type) channels expressed in a single-cell model (Xenopus laevis oocytes). The Kv7 ion channel family is responsible for regulating neuronal excitability in the heart, brain, and smooth muscles, making it an ideal platform for faradaic ROS stimulation. The results demonstrate the potential of PEDOT to act as an H2O2 delivery system, paving the way to ROS-based organic bioelectronics., Funding Agencies|European Research Council (ERC) under the European Unions Horizon 2020 research and innovation programEuropean Research Council (ERC) [850622, 949191]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation; Swedish Foundation for Strategic Research (SSF)Swedish Foundation for Strategic Research; MEYS CR [LM2018110]

Objective. Vagus nerve stimulation (VNS) is a promising approach for the treatment of a wide variety of debilitating conditions, including autoimmune diseases and intractable epilepsy. Much remains to be learned about the molecular mechanisms involved in vagus nerve regulation of organ function. Despite an abundance of well-characterized rodent models of common chronic diseases, currently available technologies are rarely suitable for the required long-term experiments in freely moving animals, particularly experimental mice. Due to challenging anatomical limitations, many relevant experiments require miniaturized, less invasive, and wireless devices for precise stimulation of the vagus nerve and other peripheral nerves of interest. Our objective is to outline possible solutions to this problem by using nongenetic light-based stimulation. Approach. We describe how to design and benchmark new microstimulation devices that are based on transcutaneous photovoltaic stimulation. The approach is to use wired multielectrode cuffs to test different stimulation patterns, and then build photovoltaic stimulators to generate the most optimal patterns. We validate stimulation through heart rate analysis. Main results. A range of different stimulation geometries are explored with large differences in performance. Two types of photovoltaic devices are fabricated to deliver stimulation: photocapacitors and photovoltaic flags. The former is simple and more compact, but has limited efficiency. The photovoltaic flag approach is more elaborate, but highly efficient. Both can be used for wireless actuation of the vagus nerve using light impulses. Significance. These approaches can enable studies in small animals that were previously challenging, such as long-term in vivo studies for mapping functional vagus nerve innervation. This new knowledge may have potential to support clinical translation of VNS for treatment of select inflammatory and neurologic diseases., QC 20230113

Implantable devices for the wireless modulation of neural tissue need to be designed for reliability, safety and reduced invasiveness. Here we report chronic electrical stimulation of the sciatic nerve in rats by an implanted organic electrolytic photocapacitor that transduces deep-red light into electrical signals. The photocapacitor relies on commercially available semiconducting non-toxic pigments and is integrated in a conformable 0.1-mm(3) thin-film cuff. In freely moving rats, fixation of the cuff around the sciatic nerve, 10 mm below the surface of the skin, allowed stimulation (via 50-1,000-mu s pulses of deep-red light at wavelengths of 638 nm or 660 nm) of the nerve for over 100 days. The robustness, biocompatibility, low volume and high-performance characteristics of organic electrolytic photocapacitors may facilitate the wireless chronic stimulation of peripheral nerves. An organic electrolytic photocapacitor transducing deep-red light into electrical signals and implanted within a thin cuff around the sciatic nerve of rats allows for wireless electrical stimulation of the nerve for over 100 days.

We show abrupt changes in the electronic properties of graphene with different types of binding to oxygen. Whereas oxygen bonded to the basal plane in the form of functional groups p-type dopes graphene, we prove that substitutional (i.e. in-plane) oxygen n-type dopes it. Moreover, we determine that impurity scattering potentials introduced by these substitutional atoms are notably larger than those of conventional donors, e.g. nitrogen. Both facts ultimately result in a conduction asymmetry in the system with holes being scattered more strongly than electrons. These findings provide essential insights into the impact of oxygen in carbon nanomaterials such as graphene oxide, oxidized carbon nanotubes or novel two-dimensional pi-conjugated organic frameworks, promising compounds for a wide range of applications including flexible electronics, catalysis, energy storage or biomedicine., Funding Agencies|Danish National Research FoundationDanmarks Grundforskningsfond [DNRF103]; EU Graphene Flagship Core 2 [785219]; EU Graphene Flagship Core 3 [785219]; Villum Young Investigator Program [19130]; Programma per Giovani Ricercatori-Rita Levi Montalcini 2017; NAS of Ukraine [0120U102265]; Provincial Council of Gipuzkoa [2021-CIEN-000070-01]; Basque Department of Education [PIBA-2020-1-0014]; VinnovaVinnova [201902878]; Spanish Ministry of Science and InnovationSpanish Government [PID2019-107338RB-C66]; European Union (EU) through Horizon 2020 (FET-Open project SPRING Grant) [863098]; MICINN Ramon y Cajal program [RYC2019-028443-I]

Energy storage technology incorporating conducting polymers as the active component in electrode structures, in part based on natural materials, is a promising strategy toward a sustainable future. Electronic and ionic charge transport in poly(3,4-ethylenedioxythiophene) (PEDOT) provides fundamentals for energy storage, governed by volumetric PEDOT:counterion double layers. Despite extensive experimental investigations, a solid understanding of the capacitance in PEDOT-based nanocomposites remains unsatisfactory. Here, we report on the charge storage mechanism in PEDOT composited with cellulose nanofibrils (termed as "power paper") from three different perspectives: experimental measurements, density functional theory atomistic simulations, and device-scale simulations based on the NernstPlanck-Poisson equations. The capacitance of the power paper was investigated by varying the film thickness, charging currents, and electrolyte ion concentrations. We show that the volumetric capacitance of the power paper originates from electrostatic molecular double layers defined at atomistic scales, formed between holes, localized in the PEDOT backbone, and their counterions. Experimental galvanostatic cycling characteristics of the power paper is well reproduced within the electrostatic Nernst-PlanckPoisson model. The difference between the specific capacitance and the intrinsic volumetric capacitance is also outlined. Substantial oxygen reduction reactions were identified and recorded in situ in the vicinity of the power paper surface at negative potentials. Purging of dissolved oxygen from the electrolyte leads to the elimination of currents originating from the oxygen reduction reactions and allows us to obtain well-defined electrostatic-capacitive behavior (box-shaped cyclic voltammetry and triangular galvanostatic charge-discharge characteristics) at a large operational potential window from -0.6 V to +0.6 V. The obtained results reveal that the fundamental charge storage, Funding Agencies|Swedish Energy AgencySwedish Energy Agency [43561-1]; Wallenberg Wood Science Center

The UV-to-IR transitions in p-doped poly(3-hexylthiophene) (P3HT) with alkyl side chains and polar polythiophene with tetraethylene glycol side chains are studied experimentally by means of the absorption spectroscopy and computationally using density functional theory (DFT) and tight-binding DFT. The evolution of electronic structure is calculated as the doping level is varied, while the roles of dopant ions, chain twisting, and pi-pi stacking are also considered, each of these having the effect of broadening the absorption peaks while not significantly changing their positions. The calculated spectra are found to be in good agreement with experimental spectra obtained for the polymers doped with a molybdenum dithiolene complex. As in other DFT studies of doped conjugated polymers, the electronic structure and assignment of optical transitions that emerge are qualitatively different from those obtained through earlier "traditional" approaches. In particular, the two prominent bands seen for the p-doped materials are present for both polarons and bipolarons/polaron pairs. The lowest energy of these transitions is due to excitation from the valence band to a spin-resolved orbitals located in the gap between the bands. The higher-energy band is a superposition of excitation from the valence band to a spin-resolved orbitals in the gap and an excitation between bands., Funding Agencies|Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation; Swedish Research CouncilSwedish Research Council [2016-05990, 2018-03824]; National Science Foundation (DMREF program)National Science Foundation (NSF)NSF - Directorate for Computer & Information Science & Engineering (CISE) [DMR-1729737]; Advanced Functional Material Center at Linkoping University

Implementing the quantum-mechanical Kubo-Greenwood formalism for the numerical calculation of dc conductivity, we demonstrate that the electron transport properties of a graphene layer can be tailored through the combined effect of defects (point and line scatterers) and strains (uniaxial tension and shear), which are commonly present in a graphene sample due to the features of its growth procedure and when the sample is used in devices. Motivated by two experimental works (He X. et al. Appl. Phys. Lett., 104 (2014) 243108; 105 (2014) 083108), where authors did not observe the transport gap even at large (22.5% of tensile and 16.7% of shear) deformations, we explain possible reasons, emphasizing on graphenes strain and defect sensing. The strain- and defect-induced electron-hole asymmetry and anisotropy of conductivity, and its nonmonotony as a function of deformation suggest perspectives for the strain-defect engineering of electrotransport properties of graphene and related 2D materials., Funding Agencies|Deutsche Forschungsgemeinschaft (DFG)German Research Foundation (DFG) [Phi81/41600]; National Research Foundation of Ukraine [Phi81/41600]; NAS of Ukraine [0120U102265]

The capacitance of conducting polymers represents one of the most important material parameters that in many cases determines the device and material performances. Despite a vast number of experimental studies, the theoretical understanding of the origin of the capacitance in conducting polymers remains unsatisfactory and appears even controversial. Here, we present a theoretical method, based on first principle capacitance calculations using density functional theory (DFT), and apply it to calculate the volumetric capacitance of two archetypical conducting polymers: poly(3,4-ethylene dioxythiophene) (PEDOT) and polypyrrole (PPy). Our aim is to achieve a quantitate description of the volumetric capacitance and to provide a qualitative understanding of its nature at the atomistic level. We find that the volumetric capacitance of PEDOT and PPy is approximate to 100 F cm(-3) and approximate to 300 F cm(-3), respectively, which is within the range of the corresponding reported experimental results. We demonstrate that the capacitance of conducting polymers originates from charges stored in atomistic Stern layers formed by counterions and doped polymeric chains. The Stern layers have a purely electrostatic origin, since the counterions do not form any bonds with the atoms of the polymeric chains, and no charge transfer between the counterions and conducting polymer takes place. This classifies the conducting polymers as double-layer supercapacitors rather than pseudo-capacitors. Further, we analyze contributions to the total capacitance originating from the classical capacitance C-C and the quantum capacitance C-Q, respectively, and find that the latter provides a dominant contribution. The method of calculations of the capacitance developed in the present paper is rather general and opens up the way for engineering and optimizing the capacitive response of the conducting polymers., Funding Agencies|Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation; Swedish Research CouncilSwedish Research Council [2016-05990, 2017-04474]; Swedish Energy AgencySwedish Energy Agency [43561-1]; Wallenberg Wood Science Center; Advanced Functional Material Center at Linkoping University

The possibility of inducing a sizeable energy gap in the electronic structure of a graphene layer is still one of the biggest and most debated challenges in graphene electronics. Despite promising theoretical results, some experimental studies report the absence of a bandgap even in highly mechanically strained graphene. In this paper, we address the main reasons for these discrepancies and study the influence of uniaxial tensile and shear strains as well as their combinations on the eventual bandgap opening in monolayer graphene. Deformation-dependent bandgap diagrams are constructed over a wide range of the strain tensor parameters of up to 26%, which is close to predicted graphene breaking point. The use of a combination of shear strain and uniaxial tensile deformations is found to be the easiest way for bandgap opening and tuning. The results of our numerical calculations demonstrate that shear strains can induce a bandgap of up to 4eV at the largest elastic deformations, while a combination of shear and uniaxial strains can provide an energy gap of up to 6eV that is substantially higher than for some materials (including silicon) typically used in nanoelectronic devices. The numerically obtained findings are carefully contrasted with other results available in the literature., Funding Agencies|National Research Fund of Ukraine [F78/39535 (PhiF78/184-2018), PhiF81/41600]; National Academy of Sciences of Ukraine [KPiKBK 6541230-1A]; DFGGerman Research Foundation (DFG) [PhiF81/41600]