the diode was consisted of printed inorganic layers of Si and NbSi 2 microparticles with an organic binder. [ 8 ] Because the operational frequency of the diode scales with its charge-transporting properties, the realization of the UHF rectifi er based on organic materials has been a challenge. Recently, a rectifi er with a 3 dB frequency reaching an impressive 700 MHz in terms of voltage was demonstrated, but its voltage output ( V out ) at 1 GHz was only 0.31 V for an AC input signal with 2 V amplitude. [ 9 ] In order to achieve ultrahigh frequency performance organic rectifi ers, which commonly consist of diodes and capacitors, it is important to achieve high charge carrier injection effi ciency and mobility within the organic semiconductor layer. Even if the work function of a metal electrode is selected to match the highest occupied molecular orbital (HOMO) level of an organic semiconductor, the formation of an adversely aligned dipole or other (e.g., oxide) interface layer can lead to a hole injection barrier, limiting charge injection. [ 10,11 ] Self-assembled monolayers (SAMs) represent one good candidate for ensuring effi cient charge injection by specifi cally tuning the metal work function. [12][13][14][15] Interfacial charge trapping can also sometimes help. [ 16 ] The permanent dipole moment of suitably selected SAM molecules changes the effective metal work function, reducing the charge injection barrier. SAMs may also be used to enhance the properties of gate dielectric layers in organic thin fi lm transistors (TFTs). [ 17,18 ] In addition to SAM-based metal work function tuning, surface energy characteristics are also altered by the SAM functional groups. This in turn can modify the subsequent deposition of organic semiconductor layers. In particular, pentacene grain formation, one of the important factors determining pentacene thin fi lm mobility, is much affected by substrate surface energy. The SAM molecule functional groups can be selected to lower the surface energy, thereby enhancing molecular packing and improving mobility. [ 19 ] Studies have shown that the orientation of pentacene deposited on Au is different to that deposited on SAM-treated Au. [20][21][22] The effect that such structural differences have on electrical characteristics for transport in the vertical direction (normal to the fi lm plane) has not been investigated to any great extent; the great majority of studies have focused on in-plane transport within TFT structures. [23][24][25] In this study, we investigated vertical diode structures instead of TFTs and as a result of the understanding gained we were able to fabricate ultrafast pentacene rectifi ers with V out = 3.8 V at 1 GHz and with a 3 dB frequency, in terms of voltage, of 1.24 GHz, the highest value reported to date. [ 8 ] Conjugated organic molecules such as pentacene, demonstrate strong electron-vibrational mode coupling with a dependence on orientation. This allows us to use Raman spectroscopy as a probe for molecular orientation. [ 26 ] Here, For automatic det...

Numerous conjugated oligoacenes and polythiophenes are being heavily studied in the search for high-mobility organic semiconductors. Although many researchers have designed fused aromatic compounds as organic semiconductors for organic thin-film transistors (OTFTs), pyrene-based organic semiconductors with high mobilities and on-off current ratios have not yet been reported. Here, we introduce a new pyrene-based p-type organic semiconductor showing liquid crystal behavior. The thin film characteristics of this material are investigated by varying the substrate temperature during the deposition and the gate dielectric condition using the surface modification with a self-assembled monolayer, and systematically studied in correlation with the performances of transistor devices with this compound. OTFT fabricated under the optimum deposition conditions of this compound, namely, 1,6-bis(5'-octyl-2,2'-bithiophen-5-yl)pyrene (BOBTP) shows a high-performance transistor behavior with a field-effect mobility of 2.1 cm(2) V(-1) s(-1) and an on-off current ratio of 7.6 × 10(6) and enhanced long-term stability compared to the pentacene thin-film transistor.

We synthesized and characterized polystyrene brushes on a silicon wafer using surface-initiated atom transfer radical polymerization. The thickness of the polymer brush was controlled by adjusting the reaction time. We investigated monomer conversion as well as the molecular weight and density of the polymer brushes. When the monomer conversion reached 100%, the number-average molecular weight and film thickness reached 135,000 and 113 nm, respectively. The estimated densities of the synthesized polystyrene brushes were in the range 0.34-0.54 chains/nm2, high enough to be categorized in the "concentrated brush" regime. The synthesized polymer brush was used as an insulating layer in an organic thin-film transistor. Organic thin-film transistors were fabricated using pentacene as an active p-type organic semiconductor and a polystyrene brush on a SiO2 layer as a gate dielectric. The pentacene based organic thin-film transistor with the polystyrene brush exhibited a field-effect mobility microFET of 0.099 cm2/(V x s).

We show the existence of a new class of astrophysical objects where the self-gravity of the dust is balanced by the force arising from shielded electric fields on the charged dust. The problem of equilibrium dust clouds is formulated in terms of an equation of hydrostatic force balance together with an equation of state. Because of the dust charge reduction at high dust density, the adiabatic index reduces from two to zero. This gives rise to a mass limit M AS for the maximum dust mass that can be supported against gravitational collapse by these fields. If the total mass M D of the dust in the interstellar cloud exceeds M AS , the dust collapses, while in the case M D < M AS , equilibrium may be achieved. The physics of the mass limit is similar to the Chandrasekhar's mass limit for compact objects, such as white dwarfs and neutron stars.

A gigahertz‐operable pentacene rectifier enabled by controlled film formation using a self‐assembled monolayer (SAM) is demonstrated by Kang et al. in article number 1500282. Pentacene deposited on SAM‐treated Au forms an ordered structure, thereby exhibiting much improved electrical characteristics, in contrast with a disordered pentacene structure on bare Au. Moreover, SAM treatment lowers the charge injection barrier, which further improves the device performance.