Peptide-based nanostructures derived from natural amino acids are superior building blocks for biocompatible devices as they can be used in a bottom-up process without the need for expensive lithography. A dense nanostructured network of l,l-diphenylalanine (FF) was synthesized using the solid-vapor-phase technique. Formation of the nanostructures and structure-phase relationship were investigated by electron microscopy and Raman scattering. Thin films of l,l-diphenylalanine micro/nanostructures (FF-MNSs) were used as the dielectric layer in pentacene-based field-effect transistors (FETs) and metal-insulator-semiconductor diodes both in bottom-gate and in top-gate structures. Bias stress studies show that FF-MNS-based pentacene FETs are more resistant to degradation than pentacene FETs using FF thin film (without any nanostructures) as the dielectric layer when both are subjected to sustained electric fields. Furthermore, it is demonstrated that the FF-MNSs can be functionalized for detection of enzyme-analyte interactions. This work opens up a novel and facile route toward scalable organic electronics using peptide nanostructures as scaffolding and as a platform for biosensing.

The effect of polarization modulation of the gate dielectric on the performance of metal-oxidesemiconductor field-effect transistors has been investigated for more than a decade. However, there are no comparable studies in the area of organic field-effect transistors (FETs) using polymer ferroelectric dielectrics, where the effect of polarization rotation by 90 • is examined on the FET characteristics. We demonstrate the effect of polarization rotation in a relaxor ferroelectric dielectric, poly(vinylidene fluoride trifluorethylene (PVDF-TrFE), on the performance of small molecule based organic FETs. The subthreshold swing and other transistor parameters in organic FETs can be controlled in a reversible fashion by switching the polarization direction in the PVDF-TrFE layer. X-ray diffraction and electron microscopy images from PVDF-TrFE reveal changes in the ferroelectric phase and domain size, respectively, upon rotating the external electric field by 90 •. The structural changes corroborate density-functional theoretical studies of an oligomer of the ferroelectric molecule in the presence of an applied electric field. The strategies enumerated here for polarization orientation of the polymer ferroelectric dielectric are applicable for a wide range of polymeric and organic transistors.

Articles you may be interested inLow-voltage organic field-effect transistors based on novel high-κ organometallic lanthanide complex for gate insulating materials AIP Advances 4, 087140 (2014); 10.1063/1.4894450Enhanced performance of ferroelectric-based all organic capacitors and transistors through choice of solvent Appl. Phys. Lett.Surface modification of a ferroelectric polymer insulator for low-voltage readable nonvolatile memory in an organic field-effect transistor Ferroelectric dielectrics, permitting access to nearly an order of magnitude range of dielectric constants with temperature as the tuning parameter, offer a great platform to monitor the changes in interfacial transport in organic field-effect transistors (OFETs) as the polarization strength is tuned. Temperature-dependent transport studies have been carried out from pentacene-based OFETs using the ferroelectric copolymer poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) as a gate insulating layer. The thickness of the gate dielectric was varied from 20 nm to 500 nm. By fits to an Arrhenius-type dependence of the charge carrier mobility as a function of temperature, the activation energy in the ferroelectric phase is found to increase as the thickness of the PVDF-TrFE layer decreases. The weak temperature-dependence of the charge carrier mobility in the ferroelectric phase of PVDF-TrFE may be attributed to a polarization fluctuation driven transport, which results from a coupling of the charge carriers to the surface phonons of the dielectric. By comparing single layer PVDF-TrFE pentacene OFETs with stacked PVDF-TrFE/inorganic dielectric OFETs, the contribution from Fr€ ohlich polarons is extracted. The temperature-dependent mobility of the polarons increases with the thickness of the PVDF-TrFE layer. Using a strongly coupled polaron model, the hopping lengths were determined to vary between 2 Å and 5 Å . V C 2015 AIP Publishing LLC. [http://dx.

the amorphous silicon benchmark of 1 cm 2 Vs −1 , application of organic FETs in displays and sensors have now become a reality. Organic FETs differ from metal oxide semiconductor FET (MOSFET) in several ways; most organic FETs operate in the accumulation region compared to the inversion operating region of MOSFETs. The metal-semiconductor and the semiconductor-dielectric interfaces play a vital role in charge transport properties. In particular, the dielectric interface is notorious for charge trapping. As a result, achieving intrinsic transport in the organic semiconductor layer in FET architectures is very challenging. Using the same organic semiconductor film (either evaporated or solution processed) but different dielectric layers may yield order of magnitude differences in FET carrier mobilities. On the other hand, ultrapure organic single crystals such as rubrene, grown from vapor phase, have shown intrinsic FET mobilities higher than 20 cm 2 Vs −1 . [2] Since the charge accumulation is directly proportional to the dielectric capacitance (C), where; κ being the dielectric constant, ε 0 the permittivity of free space, A the area of the capacitor, and d the thickness of the dielectric, a high value of the dielectric capacitance is required for lowering the operating voltage of FETs. Low-operating voltage FETs, therefore, demand high κ dielectrics, which are more difficult to achieve with polymeric materials compared to inorganic dielectric materials due to their inherently low κ values. Facile methods of preparing polymer dielectrics by appropriate choice of solvents result in thin (well below 100 nm) and pinhole-free films for low-operating voltage FETs. [3,4] Polymer ferroelectrics with higher values of κ compared to non-ferroelectric polymers allow an alternate route toward boosting the capacitance values in FETs. Poly(vinylidene fluoride) (PVDF) ferroelectric polymer and its copolymer such as PVDF trifluorethylene (PVDF-TrFE) with κ > 8 at room temperature have been extensively used in memory and pressure sensing applications. [5][6][7][8][9] Naturally, such dielectrics also provide a route toward low-operating voltage FETs. The vast range of work has utilized PVDF and its copolymers as a gate dielectric in organic FETs. [10][11][12][13] Design of PVDF with carbon quantum dots has opened applications in nanogenerators where the mechanical energy may be efficiently converted to electricity. [14] More recently, PVDF copolymers have been used with charge-modulated organic FETs for multimodal Polymer ferroelectrics are playing an increasingly active role in flexible memory application and wearable electronics. The relaxor ferroelectric dielectric, poly(vinylidene fluoride trifluorethylene (PVDF-TrFE), although vastly used in organic field-effect transistors (FETs), has issues with gate leakage current especially when the film thickness is below 500 nm. This work demonstrates a novel method of selective poling the dielectric layer. By using solutionprocessed 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-p...

It has been shown that the use of a ferroelectric dielectric in 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) field-effect transistors (FETs) results in a negative coefficient of carrier mobility, a signature of a band-like transport, above a certain temperature [A. Laudari and S. Guha, Phys. Rev. Appl. 6, 044007 (2016)]. Along with spontaneous polarization, polymer ferroelectric dielectrics offer a platform for tuning interfacial transport in FETs as their dielectric constant may vary nearly by an order of magnitude with temperature. In this work, we explore a variety of organic and inorganic dielectrics with varying dielectric constants on the temperature-dependent transport properties of TIPS-pentacene organic FETs to obtain a comprehensive insight into the role of energetic disorder and trap states. In particular, a high κ dielectric, Al2O3, shows an activated transport throughout the temperature regime, whereas the ferroelectric copolymer poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE), with comparable and even higher values of κ compared to Al2O3, above 200 K shows a very different behavior. Additionally, the external poling condition of the PVDF-TrFE dielectric plays a role. We attribute the band-like negative coefficient of carrier mobility, observed at high temperatures, in TIPS-pentacene FETs with unpoled PVDF-TrFE to a polarization fluctuation process and explore this phenomenon using the concept of transport energy.