Organic Field-Effect Transistors with a Bilayer Gate Dielectric Comprising an Oxide Nanolaminate Grown by Atomic Layer Deposition.

We report on top-gate OFETs with a bilayer gate dielectric comprising an Al2O3 /HfO2 nanolaminate layer grown by atomic layer deposition and an amorphous fluoro-polymer layer (CYTOP). Top-gate OFETs display average carrier mobility values of 0.9 ± 0.2 cm2/(V s) and threshold voltage values of -1.9 ± 0.5 V and high operational and environmental stability under different environmental conditions such as damp air at 50 °C (80% relative humidity) and prolonged immersion in water at a temperature up to 95 °C.

Systematic reliability study of top-gate p- and n-channel organic field-effect transistors.

We report on a systematic investigation on the performance and stability of p-channel and n-channel top-gate OFETs, with a CYTOP/Al2O3 bilayer gate dielectric, exposed to controlled dry oxygen and humid atmospheres. Despite the severe conditions of environmental exposure, p-channel and n-channel top-gate OFETs show only minor changes of their performance parameters without undergoing irreversible damage. When correlated with the conditions of environmental exposure, these changes provide new insight into the possible physical mechanisms in the presence of oxygen and water. Photoexcited charge collection spectroscopy experiments provided further evidence of oxygen and water effects on OFETs. Top-gate OFETs also display outstanding durability, even when exposed to oxygen plasma and subsequent immersion in water or operated under aqueous media. These remarkable properties arise as a consequence of the use of relatively air stable organic semiconductors and proper engineering of the OFET structure.

Stable organic field-effect transistors for continuous and nondestructive sensing of chemical and biologically relevant molecules in aqueous environment.

The use of organic field-effect transistors (OFETs) as sensors in aqueous media has gained increased attention for environmental monitoring and medical diagnostics. However, stable operation of OFETs in aqueous media is particularly challenging because of electrolytic hydrolysis of water, high ionic conduction through the analyte, and irreversible damage of organic semiconductors when exposed to water. To date, OFET sensors have shown the capability of label-free sensing of various chemical/biological species, but they could only be used once because their operational stability and lifetime while operating in aqueous environments has been poor, and their response times typically slow. Here, we report on OFETs with unprecedented water stability. These OFETs are suitable for the implementation of reusable chemical/biological sensors because they primarily respond to charged species diluted in an aqueous media by rapidly shifting their threshold voltage. These OFET sensors present stable current baselines and saturated signals which are ideal for detection of low concentration of small or large molecules that alter the pH of an aqueous environment. The overall response of these OFET sensors paves the way for the development of continuous chemical/biological nondestructive sensor applications in aqueous media.

Room temperature observation of size dependent single electron tunneling in a sub-2 nm size tunable Pt nanoparticle embedded metal-oxide-semiconductor structure.

In this paper we report size dependent single electron tunneling behavior at room temperature in a metal-oxide-semiconductor structure with uniformly sized Pt nanoparticles embedded in an Al(2)O(3) dielectric. The sub-2 nm size Pt nanoparticles sandwiched between the Al(2)O(3) layers are deposited by a unique tilted target sputter deposition technique which produces metal nanoparticles as small as 0.5 nm with narrow size distributions at room temperature. The charging behavior of these nanoparticles shows clear single electron tunneling peaks due to the Coulomb blockade effect. Moreover, the average single electron addition energy and height of the single electron tunneling current strongly depend on the size of the Pt nanoparticle. These controllable single electron tunneling behaviors suggest a new route for fabrication of single electron devices.

Entropy driven spontaneous formation of highly porous films from polymer-nanoparticle composites.

Nanoporous materials have become indispensable in many fields ranging from photonics, catalysis and semiconductor processing to biosensor infrastructure. Rapid and energy efficient process fabrication of these materials is, however, nontrivial. In this communication, we describe a simple method for the rapid fabrication of these materials from colloidal dispersions of Polymethyl Silsesquioxane nanoparticles. Nanoparticle-polymer composites above the decomposition temperature of the polymer are examined and the entropic gain experienced by the nanoparticles in this rubric is harnessed to fabricate novel highly porous films composed of nanoparticles. Optically smooth, hydrophobic films with low refractive indices (as low as 1.048) and high surface areas (as high as 1325 m(2) g(-1)) have been achieved with this approach. In this communication we address the behavior of such systems that are both temperature and substrate surface energy dependent. The method is applicable, in principle, to a variety of nanoparticle-polymer systems to fabricate custom nanoporous materials.