We have fabricated organic thin-film transistors and integrated circuits using pentacene as the active material. Devices were fabricated on glass substrates using low-temperature ionbeam sputtered silicon dioxide as the gate dielectric and a doublelayer photoresist process to isolate devices. These transistors have carrier mobility near 0.5 cm 2 /V-s and on/off current ratio larger than 10 7. Using a level-shifting design that allows circuits to operate over a wide range of threshold voltages, we have fabricated ring oscillators with propagation delay below 75 s per stage, limited by the level-shifting circuitry. When driven directly, inverters without level shifting show submicrosecond rise and fall time constants.

We describe a hybrid pixel array detector (EMPAD -electron microscope pixel array detector) adapted for use in electron microscope applications, especially as a universal detector for scanning transmission electron microscopy. The 128 × 128 pixel detector consists of a 500 µm thick silicon diode array bump-bonded pixel-by-pixel to an application-specific integrated circuit (ASIC). The in-pixel circuitry provides a 1,000,000:1 dynamic range within a single frame, allowing the direct electron beam to be imaged while still maintaining single electron sensitivity. A 1.1 kHz framing rate enables rapid data collection and minimizes sample drift 2 distortions while scanning. By capturing the entire unsaturated diffraction pattern in scanning mode, one can simultaneously capture bright field, dark field, and phase contrast information, aswell as being able to analyze the full scattering distribution, allowing true center of mass imaging. The scattering is recorded on an absolute scale, so that information such as local sample thickness can be directly determined. This paper describes the detector architecture, data acquisition (DAQ) system, and preliminary results from experiments with 80 to 200 keV electron beams.Key words: pixel array detector (PAD), STEM, high dynamic range, mixed mode pixel array detector (MMPAD), electron microscope pixel array detector (EMPAD)

BiFeO 3 thin films have been deposited on ͑001͒ SrTiO 3 substrates by adsorption-controlled reactive molecular-beam epitaxy. For a given bismuth overpressure and oxygen activity, single-phase BiFeO 3 films can be grown over a range of deposition temperatures in accordance with thermodynamic calculations. Four-circle x-ray diffraction reveals phase-pure, epitaxial films with rocking curve full width at half maximum values as narrow as 29 arc sec ͑0.008°͒. Multiple-angle spectroscopic ellipsometry reveals a direct optical band gap at 2.74 eV for stoichiometric as well as 5% bismuth-deficient single-phase BiFeO 3 films.

We report a solvent-induced phase transition in pentacene thin films, from a “thin film” phase to a bulk-like phase. X-ray diffraction indicates that as-deposited thermally evaporated pentacene films consist mainly of (001)-oriented pentacene with an elongated (001) plane spacing of 15.5±0.1 Å, and a minor amount with a (001) plane spacing of 14.5±0.1 Å. When such films are exposed to solvents such as acetone, isopropanol, or ethanol, the plane spacing of the entire layer shifts abruptly from the elongated (001) plane spacing to the bulk value and this shift is accompanied by a macroscopic change in film morphology. While molecular ordering is maintained as indicated by x-ray diffraction, thin film transistor performance is severely degraded, most likely as a result of the morphological changes in the film.

A far ultraviolet ͑UV͒ spectroscopic ellipsometer system working up to 9 eV has been developed, and applied to characterize high-K-dielectric materials. These materials have been gaining greater attention as possible substitutes for SiO 2 as gate dielectrics in aggressively scaled silicon devices. The optical properties of four representative high-K bulk crystalline dielectrics, LaAlO 3 , Y 2 O 3-stabilized HfO 2 (Y 2 O 3) 0.15-(HfO 2) 0.85 , GdScO 3 , and SmScO 3 , were investigated with far UV spectroscopic ellipsometry and visible-near UV optical transmission measurements. Optical dielectric functions and optical band gap energies for these materials are obtained from these studies. The spectroscopic data have been interpreted in terms of a universal electronic structure energy scheme developed form ab initio quantum chemical calculations. The spectroscopic data and results provide information that is needed to select viable alternative dielectric candidate materials with adequate band gaps, and conduction and valence band offset energies for this application, and additionally to provide an optical metrology for gate dielectric films on silicon substrates.