[Show abstract][Hide abstract] ABSTRACT: We report a novel method for stable doping of carbon nanotubes (CNT) based on methods of molecular self assembly. A conformal growth of a self-assembled monolayer of fluoroalkyl tri-chloro-silane (FTS) at CNT surfaces results in a strong increase of the sheet conductivity of CNT electrodes by 60-300%, depending on the CNT chirality and composition. The charge carrier mobility of undoped partially aligned CNT films was independently estimated in a field-effect transistor geometry (similar to 100 cm(2) V-1 s(-1)). The hole density induced by the FTS monolayer in CNT sheets is estimated to be similar to 1.8 x 10(14) cm(-2). We also show that FTS doping of CNT anodes greatly improves the performance of organic solar cells. This large and stable doping effect, easily achieved in largearea samples, makes this approach very attractive for applications of CNTs in transparent and flexible electronics. (C) 2014 AIP Publishing LLC.
[Show abstract][Hide abstract] ABSTRACT: Fundamental studies of intrinsic charge transport properties of organic semiconductors are often hindered by charge traps associated with static disorder present even in optimized single-crystal devices. Here, we report a method of surface functionalization using an inert non-conjugated polymer, perfluoropolyether (PFPE), deposited at the surface of organic molecular crystals, which results in accumulation of mobile holes and a 'trap healing' effect at the crystal/PFPE interface. As a consequence, a remarkable ultralow-noise, trp-free conduction regime characterized by intrinsic mobility and transport anisotropy emerges in organic single crystals, and Hall effect measurements with an unprecedented signal-to-noise ratio are demonstrated. This general method to convert trap-dominated organic semiconductors to intrinsic systems may enable the determination of intrinsic transport parameters with high accuracy and make Hall effect measurements in molecular crystals ubiquitous.
Nature Material 10/2013; 12(12). DOI:10.1038/nmat3781 · 36.50 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The origin of the bias stress effect related only to semiconductor properties is investigated in "air-gap" organic field-effect transistors (OFETs) in the absence of a material gate dielectric. The effect becomes stronger as the density of trap states in the semiconductor increases. A theoretical model based on carrier trapping and relaxation in localized tail states is formulated. Polar molecular vapors in the gap of "air-gap" OFETs also have a significant impact on the bias stress effect via the formation of bound states between the charge carriers and molecular dipoles at the semiconductor surface.
[Show abstract][Hide abstract] ABSTRACT: A novel vacuum lamination approach to fabrication of high-performance single-crystal organic field-effect transistors has been developed. The non-destructive nature of this method allows a direct comparison of field-effect mobilities achieved with various gate dielectrics using the same single-crystal sample. The method also allows gating delicate systems, such as n -type crystals and SAM-coated surfaces, without perturbation.
[Show abstract][Hide abstract] ABSTRACT: Integration of organic and inorganic electronic materials is one of the emerging approaches to achieve novel material functionalities. Here, we demonstrate a stable self-assembled monolayer of an alkylsilane grown at the surface of graphite and graphene. Detailed characterization of the system using scanning probe microscopy, X-ray photoelectron spectroscopy, and transport measurements reveals the monolayer structure and its effect on the electronic properties of graphene. The monolayer induces a strong surface doping with a high density of mobile holes (n > 10(13) cm(-2)). The ability to tune electronic properties of graphene via stable molecular self-assembly, including selective doping of steps, edges, and other defects, may have important implications in future graphene electronics.