Using ultrafast angle-resolved light scattering technique, we were able to trigger photoinduced phase transition processes in V2O3 film grown on a glass substrate. The phase transition is caused by photoacoustic wave in the film and appears as coherent oscillations of scattering signal at various time scales. These processes strongly depend on the size of microstructures constituting the V2O3 film. One of the key findings of our study is the presence of a size dependent phase transition threshold for V2O3 microstructures, where small size structures ( $\tilde <$ 0.5μm) have lowest contribution to the phase transition. The presence of this threshold can be well described by considering uneven internal strain in the films which is one of the key parameters controlling phase transition dynamics in various vanadium oxides.

Ca3Co4O9 (CCO) is a promising material for thermoelectric applications; however, this layered oxide shows a large number of physical features that complicate understanding and systematically improving its properties. A significant component of CCO’s behavior is its magnetotransport properties, particularly in the low temperature region where an incommensurate spin density wave affects its band structure. In order to improve understanding in this area, we perform low temperature magnetoresistance (MR) measurements on a bulk CCO sample. Field-less resistivity measurements confirm the conventional behavior of our sample, with a metal-to-insulator transition at approximately 70 K, and a shoulder indicating ferrimagnetism at 14 K. Resistivity vs. temperature under applied magnetic field show significant MR below around 35 K.

The oxide interface SrTiO3/LaAlO3 supports a 2D electron liquid displaying superconductivity and magnetism, while allowing for a continuous control of the electron density using a gate. Our recent measurements have shown a similar surprising nonmonotonic behavior as function of the gate voltage (carrier density) of three quantities: the superconducting critical temperature and field, the inverse Hall coefficient, and the frequency of quantum oscillations. While the total density has to be monotonic as function of gate, the last result indicates that one of the involved bands has a nonmontonic occupancy as function of the chemical potential. We show how electronic interactions can lead to such an effect, by creating a competition between the involved bands and making their sturcture non-rigid, and thus account for all these effects. Adding Fock terms to our previous Hartree treatment makes this scenario even more generic.

To benefit from the many advantages of organic semiconductors like flexibility, transparency, and small thickness, electronic devices should be entirely made from organic materials. This means, additionally to organic LEDs, organic solar cells, and organic sensors, we need organic transistors to amplify, process, and control signals and electrical power. The standard lateral organic field effect transistor (OFET) does not offer the necessary performance for many of these applications. One promising candidate for solving this problem is the vertical organic field effect transistor (VOFET). In addition to the altered structure of the electrodes, the VOFET has one additional part compared to the OFET – the source-insulator. However, the influence of the used material, the size, and geometry of this insulator on the behavior of the transistor has not yet been examined. We investigate key-parameters of the VOFET with different source insulator materials and geometries. We also present transmission electron microscopy (TEM) images of the edge area. Additionally, we investigate the charge transport in such devices using drift-diffusion simulations and the concept of a vertical organic light emitting transistor (VOLET). The VOLET is a VOFET with an embedded OLED. It allows the tracking of the local current density by measuring the light intensity distribution.

We show that the insulator material and thickness only have a small influence on the performance, while there is a strong impact by the insulator geometry – mainly the overlap of the insulator into the channel. By tuning this overlap, on/off-ratios of 9x105 without contact doping are possible.

Polysilicon complementary metal oxide semiconductor (CMOS) thin film transistors (TFTs) are fabricated on large area, flexible stainless steel foils using novel ink depositions within a hybrid printed/conventional process flow. A self-aligned top gate TFT structure is realized with an additive materials approach to substitute the use of high capital cost ion implantation and lithography processes. Polyhydrosilane-based silicon ink is coated and laser crystallized to form the polysilicon channel. Semiconductor grade P-type and N-type unique dopant ink formulations are screen printed and combined with thermal drive in and activation to form self-aligned doped source and drain regions. A high refractory top gate material is chosen for its process compatibility with printed dopants, chemical resistance, and work function. Steel foil substrates are fully encapsulated to allow for high temperature processing. The resultant materials set and process flow enables TFT electrical characteristics with NMOS and PMOS mobilities exceeding 120 cm2/Vs and 60 cm2/Vs, respectively. On/Off ratios are >107. Reproducibility, uniformity, and reliability data in a production environmental is shown to demonstrate high volume, high throughput manufacturability. The device characteristics and scheme enable NFC (13.56MHz) capable circuits for use in flexible NFC and display-based smart labels and packaging.

By taking advantage of three-terminal capacitance-voltage (TT-CV) measurement, we investigated a formation of trapped charge in pentacene(Pn)-based organic field-effect transistors (OFETs) during the bias stress measurement. The shift of the turn-on voltage in transfer curve correlated well with the increase of trapped charge estimated from TT-CV curves. Moreover, TT-CV measurement revealed that the trapped charges were distributed inhomogeneously at the vicinity of the pentacene/insulator interface, indicating that the current does not obviously affect their formation. Thus we suggested that the trapped charges are formed by keeping Pn molecules as unstable cation (hole state) by the prolonged bias stress.

In this work, we present low temperature flash light based curing of spray coated high-k zirconium oxide (ZrOx) thin film to realize low voltage operated flexible and fully patterned organic thin film transistors (OTFTs). A simple sol-gel technique was followed to prepare ZrOx from a zirconium complex. By spraying the precursor solution onto substrate through shadow mask, a patterned film was obtained. On the other hand subsequent flash light curing of the coated film not only reduced processing time but also allowed us to fabricate device on polymeric flexible substrate. Spectroscopic analysis confirmed formation of ZrOx film from the solution of zirconium complex. Finally as prepared ZrOx was used as gate dielectric layer in OTFT structure to keep operating voltage as low as -3V. Flexible polyethylenetrephthalate (PET) sheet was used as flexible substrate and pentacene was used as organic active layer. Each and every layer was deposited through metal made shadow mask to develop fully patterned OTFT. Field effect mobility and ON/OFF ratio of as fabricated transistor was found to be as high as 1.2 cm2V-1S-1 and 105 respectively.