All-inkjet-printed organic thin-film transistors take advantage of low-cost fabrication and high compatibility to large-area manufacturing, making them potential candidates for flexible, wearable electronics. However, in real-world applications, device instability is an obstacle, and thus, understanding the factors that cause instability becomes compelling. In this work, all-inkjet-printed low-voltage organic thin-film transistors were fabricated and their stability was investigated. The devices demonstrate low operating voltage (<3 V), small subthreshold slope (128 mV/decade), good mobility (0.1 cm2 V−1 s−1), close-to-zero threshold voltage (−0.16 V), and high on/off ratio (>105). Several aspects of stability were investigated, including mechanical bending, shelf life, and bias stress. Based on these tests, we find that water molecule polarization in dielectrics is the main factor causing instability. Our study suggests use of a printable water-resistant dielectric for stability enhancement for the future development of all-inkjet-printed organic thin-film transistors.

We report a 6,13-Bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene) solution-processed high-voltage organic thin film transistor (HVOTFT) with a large breakdown voltage of |VDS| > 450 V, a three-fold increase from previous results. An offset channel architecture and an organosilane-based self-assembled monolayer (SAM) treatment were used to achieve large breakdown voltages. Solution-processed HVOTFTs will enable novel high-voltage and flexible applications. Reliability of the HVOTFT under high-field stress was studied in the context of threshold and onset to conduction voltages.

In the present study, we analyze the influence of temperature and active layer thickness on the electrical properties of electroluminescent devices comprising a polymeric conductive blend (poly(3,4 ethylenedioxythiophene):polystyrene sulfonate, PEDOT:PSS), an inorganic electroluminescent material (manganese doped zinc orthosilicate, Zn2SiO4:Mn) and an organosilicon material (3-glicidoxypropyltrimethoxysilane, GPTMS), manufactured at different weight ratios of the component materials. The devices were obtained by depositing the active layer by drop-casting onto ITO-coated (RF-sputtering) glass substrates and thermally evaporating gold top electrodes in high vacuum. The results show that 90 wt% Zn2SiO4:Mn is required to observe high electroluminescence from the fabricated devices and that the optimum performance (turn-on voltage of 33 V, luminous efficacy of 24 cd/A and maximum luminance of almost 2000 cd/m2) was achieve for a (9.5/0.5/90) (GPTMS/PEDOT:PSS/Zn2SiO4:Mn) weight ratio. The device turn-on voltage found to be as proportional to the thickness of the active layer, indicating that the electroluminescence occurs by a field-effect mechanism. The temperature variation in the 100-300 K range allowed us to develop a theoretical model for the device operation, where the charge carrier transport in the active layer is well described by the variable range hopping model, with luminous efficacy nearby independent of the temperature.

The bulk heterojunction morphology of organic solar cells widely controls their device efficiency and stability. Structural order and domain size of the donor phase strongly impact the charge separation efficiency, recombination rates, and the hole percolation through the bulk to the electrode. Herewith, we report a comprehensive study on the control of polymeric order already initiated in solution by the introduction of orthogonal solvent additives to the common solution of anthracene containing poly(p-phenylene-ethynylene)-alt-poly(p-phenylene-vinylene) (PPE-PPV) copolymer, bearing statistically substituted linear octyloxy and 2-ethylhexyloxy side-chains in 1:1 ratio along the backbone (AnE-PVstat), and fullerene derivative phenyl-C61-butyric acid methyl ester (PCBM). The first solvent, a 1:1 blend of chlorobenzene and chloroform, had been discovered to promote phase separation in solution and deposited films. This effect could be further enhanced and was precisely controlled by addition of methanol to the common solution in various volume fractions. Thus the ability to transfer the polymer aggregates from the solution into films was applied to solar cells and is investigated in detail.

We report here an experimental study of ultrafast response of the dielectric polarization in (Ba0.8Sr0.2)TiO3 thin films to a strong electric field of a nearly single-cycle THz pulse. The phenomenon of Second Harmonic Generation (SHG) is used as a probe of the polarization in the terahertz pump-optical probe experiment. SHG loops for THz pulses of different amplitudes were obtained. The SHG response is modelled assuming that the ferroelectric material is split into 180-degree domains. It is shown that intuitive model based on forced harmonic oscillator does not fully describe to the observed ultrafast ferroelectric response

Interest in active metamaterial (MM) devices has recently increased due to their potential for tunable, switchable, and scalable optical responses. More specifically, a dynamic, on-chip MM polarizer has applications ranging from material characterization to sensing without the need for cumbersome external filters. This work demonstrates efforts to optimize MM devices for dynamic polarization filtering by combining elements from split-ring resonators, wire-pairs, and fishnet patterns. The polarization grid has been designed to operate under an applied voltage with simulated on/off ratios of 75% and dynamic polarization selectivity of 70%. Samples have been fabricated using epitaxial GaAs on sapphire with various n-type doping concentrations to approximate electrical tuning.

Optical antennas made out of materials with hyperbolic dispersion is an alternative approach to realizing efficient subwavelength scatterers and may overcome limitations imposed by plasmonic and all-dielectric designs. Recently emerged natural hyperbolic material hexagonal boron nitride supports phonon-polariton excitations with low optical losses and high anisotropy. Here we study scattering properties of the hyperbolic-medium (HM) antennas, and in particular, we consider a combination of two types of the particles - HM bars and silicon spheres - arranged in a periodic array. We analyze excitation of electric and magnetic resonances in the particles and effect of their overlap in the array. We theoretically demonstrate that decrease of reflectance from the array can be achieved with appropriate particle dimensions where electric and magnetic resonances of different particle types overlap, and the resonance oscillations are in phase. In this case, generalized Kerker condition is satisfied, and particle dimers in the array efficiently scatter light in the forward direction. The effect can be used in designing metasurfaces based on hexagonal boron nitride scatterers with an application in mid-infrared photonics.

Tunable plasmonic resonances across the visible and near infrared spectra have provided novel ways to develop next-generation nanophotonic devices. Here, by utilizing optothermally controllable phase-changing material (PCM), we studied highly tunable charge transfer plasmon (CTP) resonance modes. To this end, we have designed a two-member dimer assembly including gold cores and Ge2Sb2Te5 (GST) shells in distant, touching, and overlapping conditions. We successfully demonstrated that toggling between amorphous (dielectric) and crystalline (conductive) phases of GST allows for achieving tunable dipolar and CTP resonances along the near-infrared spectrum. The proposed dimer structures can help forming optothermally controlled devices without further morphological variations in the geometry of the design, and having strong potential for advanced plasmon modulation and fast data routing.

A complex mechanism of interfacial oxygen scavenging is revealed by electron energy-loss spectroscopy (EELS) for a resistive switching oxide of SrTiO3 with a scavenging layer of Ta. When Ta thin layer is inserted at one of the interfaces of Pt/SrTiO3/Pt structure, a large reduction of electrical resistance is induced for the structure, and oxygen defects are introduced at the interfacial part of SrTiO3. In the resistance decrease by voltage applications, simultaneous occurrence of oxidation and reduction of Ta scavenging layer is shown by EELS analyses from the low-loss spectra. The EELS and scanning transmission electron microscopy observations demonstrate that oxygen scavenging by Ta layer is an interfacial phenomenon where the redox reactions occur at the whole part of the interface. In addition, Pt electrode of the structure, which is chemically inert for oxidation, is revealed to have significant effects in the scavenging processes.

With a high affinity to carbon comparable to titanium and an electrically conductive carbide, zirconium has potential to form ohmic contact on boron doped diamond. In this work, formation of ohmic contacts on boron doped diamond using zirconium is studied in comparison to titanium. Boron doped diamond epitaxial layers have been grown by microwave plasma enhanced chemical vapour deposition with various B/C ratio. Circular Transmission Line Model structures were fabricated using standard micro-fabrication technologies. Specific contact resistance of fabricated contacts was determined for different boron concentrations and for various annealing temperatures. Ohmic contacts using zirconium are formed after annealing at 400 °C. Specific contact resistance steadily decreases with high temperature annealing down to a value of ca. 1 mΩ.cm2 after annealing at 700 °C for highly boron doped diamond. In comparison, titanium contact fabricated on highly doped diamond appears not stable under high temperature annealing.

The unique electronic structure of diamond and its excellent thermal properties allow a broad range of possible applications; from electron sources to RF electronics. However, knowledge of the surface energy levels is essential to produce efficient, high-quality devices. We investigate the valence band position and resulting negative electron affinity for hydrogen terminated diamond under ambient, low vacuum and ultra-high vacuum (UHV) conditions. There was a -0.5 eV change in valence band position causing a negative electron affinity shift from -1.1 eV under UHV to -0.6 eV in ambient pressure. We compare the photoemission current under each environment to predict the ability of the sample to be used as an electron source. The maximum emission was observed when the sample displayed the largest negative affinity. A scanning photoemission measurement is demonstrated to highlight the superior photoemission yield from the hydrogen terminated diamond surface compared to the stainless steel contact. A scanning Kelvin probe measurement is shown to illustrate a method of analyzing the contact potential difference across the diamond surface. Within high-power RF electronics, devices are likely to be operating at increased temperatures so knowledge of the impact of temperature on the energy levels is important. We study the valence band and Fermi level positions for hydrogen terminated diamond from room temperature (300K) to 425K under low and UHV conditions. The Fermi level moved below the valence band edge at increased temperature, illustrating the effect of the 2D hole gas at the surface. We also analyzed the photoemission characteristics and found an increase in yield with increasing temperature. The measurement techniques used to evaluate the energy levels of diamond: photoemission spectroscopy and Kelvin probe measurements, in ambient and vacuum, allow analysis to be completed in minutes. This offers an initial analysis alternative to elucidate more information and predict performance prior to the more time-consuming full device manufacture and characterization.

Memristors represent an intriguing two-terminal device strategy potentially able to replace conventional memory devices as well as to support neuromorphic computing architectures. Here, we present the resistive switching behaviour of the sustainable and low-cost biopolymer chitosan, which can be extracted from natural chitin present for instance in crab exoskeletons. The biopolymer films were doped with Ag ions in varying concentrations and sandwiched between a bottom electrode such as fluorinated-tin-oxide and a silver top electrode. Silver-doped devices showed an overall promising resistive switching behaviour for doping concentrations between 0.5 to 1 wt% AgNO3. As bottom electrode fluorinated-tin-oxide, nickel, silver and titanium were studied and multiple write and erase cycles were recorded. However, the overall reproducibility and stability are still insufficient to support broader applicability.