We demonstrate controllable shift of the threshold voltage and the turn-on voltage in pentacene thin film transistors and rubrene single crystal field effect transistors (FET) by the use of nine organosilanes with different functional groups. Prior to depositing the organic semiconductors, the organosilanes were applied to the SiO2 gate insulator from solution and form a self assembled monolayer (SAM). The observed shift of the transfer characteristics range from -2 to 50 V and can be related to the surface potential of the layer next to the transistor channel. Concomitantly the mobile charge carrier concentration at zero gate bias reaches up to 4 × 10 12 /cm 2 . In the single crystal FETs the measured transfer characteristics are also shifted, while essentially maintaining the high quality of the subthreshold swing. The shift of the transfer characteristics is governed by the built-in electric field of the SAM and can be explained using a simple energy level diagram. In the thin film devices, the subthreshold region is broadened, indicating that the SAM creates additional trap states, whose density is estimated to be of order 1 × 10 12 /cm 2 .

Sacrificial bonds and hidden length in structural molecules and composites have been found to greatly increase the fracture toughness of biomaterials by providing a reversible, molecular-scale energy-dissipation mechanism. This mechanism relies on the energy, of order 100 eV, needed to reduce entropy and increase enthalpy as molecular segments are stretched after being released by the breaking of weak bonds, called sacrificial bonds. This energy is relatively large compared to the energy needed to break the polymer backbone, of order a few eV. In many biological cases, the breaking of sacrificial bonds has been found to be reversible, thereby additionally providing a "self-healing" property to the material. Due to the nanoscopic nature of this mechanism, single molecule force spectroscopy using an atomic force microscope has been a useful tool to investigate this mechanism. Especially when investigating natural molecular constructs, force versus distance curves quickly become very complicated. In this work we propose various types of sacrificial bonds, their combination, and how they appear in single molecule force spectroscopy measurements. We find that by close analysis of the force spectroscopy curves, additional information can be obtained about the molecules and their bonds to the native constructs.

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We identify the dynamics of an atomic force microscope (AFM) in order to design a feedback controller that enables faster image acquisition at reduced imaging error compared to the now generally employed proportional integral differential (PID) controllers. First, a force model for the tip–sample interaction in an AFM is used to show that the dynamic behavior of the cantilever working in contact mode can be neglected for control purposes due to the relatively small oscillation amplitude of the cantilever in response to a defined topography step. Consequently, the dynamic behavior of the AFM system can be reduced to the behavior of the piezoelectric scanner making the design of a model based controller for the AFM possible. Second, a black box identification of the scanner of a commercial AFM (Nanoscope IIIa, Digital Instruments) is performed using subspace methods. Identification yields a mathematical model of the scanner which allows us to design a new controller utilizing H∞ theory. Finally, this controller is implemented on an existing AFM and operated in contact mode. We demonstrate that such an H∞-controlled AFM system, while scanning at rates five times faster than conventional PID-controlled systems, operates with reduced measurement error and allows scanning at lower forces.

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