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Dibenzo[n]phenacenes (DBnP, n = 5–7) were applied to the active layers of p-channel FETs and their effective mobilities were evaluated to demonstrate that C2h-symmetrical DB6P showed superior performance to the C2v-symmetrical homologues.

The application of an electric field can be a new technique to control the electronic properties of two-dimensional materials. In a conventional double-gate structure, an ionic liquid is used in th...

The [10]phenacene and [11]phenacene molecules have been synthesized using a simple repetition of Wittig reactions followed by photocyclization. Sufficient amounts of [10]phenacene and [11]phenacene were obtained, and thin-film FETs using these molecules have been fabricated with SiO2 and ionic liquid gate dielectrics. These FETs operated in p-channel. The averaged measurements of field-effect mobility, <μ>, were 3.1(7) × 10−2 and 1.11(4) × 10−1 cm2 V−1 s−1, respectively, for [10]phenacene and [11]phenacene thin-film FETs with SiO2 gate dielectrics. Furthermore, [10]phenacene and [11]phenacene thin-film electric-double-layer (EDL) FETs with ionic liquid showed low-voltage p-channel FET properties, with <μ> values of 3(1) and 1(1) cm2 V−1 s−1, respectively. This study also discusses the future utility of the extremely extended π-network molecules [10]phenacene and [11]phenacene as the active layer of FET devices, based on the experimental results obtained.

The transport properties of 3,10-ditetradecylpicene ((C14H29)2-picene) and [6]phenacene thin-film field-effect transistors (FETs) on Si and plastic substrates are reported, in which SiO2 and parylene are used as gate dielectrics, respectively. These devices show p-channel normally-off FET characteristics. A μ value of 1.34 cm2 V−1 s−1 is obtained in the (C14H29)2-picene thin-film FET, where 500 μm thick polyethylene terephthalate (PET) and 1 μm thick parylene are used as the substrate and gate dielectric, respectively. Moreover, excellent FET performance is obtained in the (C14H29)2-picene thin-film FET using a high-k gate dielectric, ZrO2, which is formed on a 350 μm thick PET substrate, showing p-channel normally-off FET properties and low voltage operation. The μ value reaches 6.31 cm2 V−1 s−1 in the FET device. The FET properties of N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDIC8) thin-film FETs formed on PET are also reported, showing n-channel normally-off FET characteristics. We report a bias stress effect on flexible [6]phenacene thin film FETs that are fabricated on a PEN substrate. Two types of experiments are performed for investigating the bias stress effect on FETs, and the bias stress effect under light irradiation is very different from that under no irradiation. This difference is well explained based on the hole-filling of trap states by electron excitation. We show the characteristics of a complementary MOS inverter (CMOS), constituting a [6]phenecene thin-film FET (p-channel) and a PTCDIC8 thin-film FET (n-channel) formed on the PET and PEN substrates, i.e., a flexible CMOS inverter. The maximum gain reaches 300. Furthermore, we report low-voltage operation for the flexible CMOS inverter, where ZrO2 is used as the gate dielectric. Through this study, we have achieved the fabrication of flexible thin-film FETs with a high μ and low voltage operation, and flexible CMOS inverters with a high gain as well as low operation voltage. This study could provide a basis for future practical/human-compatible electronic devices.

Dibenzo[n]phenecenes (DBnPs, n = 5-7) were conveniently synthesised through Mallory photocyclization as the key step. Effective mobilities of single-crystal field-effect transistors of DBnPs were evaluated to demonstrate that C2h-symmetrical DB6P shows higher performance than C2v-symmetrical DB5P and DB7P.

Organic field-effect transistors (FETs) can be applied to radio-frequency identification tags (RFIDs) and active-matrix flat-panel displays. For RFID application, a cardinal functional block is a ring oscillator using an odd number of inverters to convert DC voltage to AC. Herein, we report the properties of two ring oscillators, one formed with [6]phenacene for a p-channel FET and N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) for an n-channel FET, and one formed with 3,10-ditetradecylpicene ((C14H29)2-picene) for a p-channel FET and PTCDI-C8 for an n-channel FET. The former ring oscillator provided a maximum oscillation frequency, fosc of 26 Hz, and the latter a maximum fosc of 21 Hz. The drain–drain voltage, VDD, applied to these ring oscillators was 100 V. This may be the first step towards a future practical ring oscillator using phenacene molecules. The values of field-effect mobility, μ in the p-channel [6]phenacene FET and n-channel PTCDI-C8 FET, which form the building blocks in the ring oscillator with an fosc value of 26 Hz, are 1.19 and 1.50 × 10−1 cm2 V−1 s−1, respectively, while the values in the p-channel (C14H29)2-picene FET and n-channel PTCDI-C8 FET, which form the ring oscillator with an fosc of 21 Hz, are 1.85 and 1.54 × 10−1 cm2 V−1 s−1, respectively. The μ values in the p-channel FETs are higher by one order of magnitude than those of the n-channel FET, which must be addressed to increase the value of fosc. Finally, we fabricated a ring oscillator with ZrO2 instead of parylene for the gate dielectric, which provided the low-voltage operation of the ring oscillator, in which [6]phenacene and PTCDI-C8 thin-film FETs were employed. The value of fosc obtained in the ring oscillator was 24 Hz. In this ring oscillator, the VDD value applied was limited to 20 V. The durability of the ring oscillators was also investigated, and the bias stress effect on the fosc and the amplitude of the output voltage, Vout are discussed. This successful operation of ring oscillators represents an important step towards the realization of future practical integrated logic gate circuits using phenacene molecules.

Picene derivatives incorporating imide moieties along the long-axis direction of the picene core (C

The synthesis of a hexacyclic fused polyheteroaromatic system, namely carbazolo[2,1-a]carbazole, via a simple two-step route is reported. Additionally, the characterization of its electronic structure is described, corresponding to a very stable molecule that is also transparent to visible light. Solid state packing is determined by X-ray diffraction analysis which, in combination with the computational calculation of the charge transfer parameters, reveals an adequate molecular arrangement to achieve a low anisotropic environment for charge transport. This π-conjugated system is used as an organic semiconductor for the fabrication of thin film and single crystal organic field-effect transistors (OFETs). Furthermore, the evaluation of different gate dielectrics results in transistors with very good hole mobilities and low operating voltages. In agreement with these results, carbazolo[2,1-a]carbazole becomes one of the best organic semiconductors belonging to the family of carbazole-based azaphenacenes.

In this chapter, field-effect transistors (FETs) are reported using π-conjugated hydrocarbon molecules (polycyclic hydrocarbons). The p-channel FET properties are recorded for the FETs using polycyclic aromatic hydrocarbons. Currently, the highest field-effect mobility (μ) that polycyclic hydrocarbon FETs reach is 21 cm2 V−1 s−1 for 3,10-ditetradecylpicene, which is one of phenacene-type molecules. Thus, the recent FETs of polycyclic hydrocarbons show excellent FET characteristics, suggesting that the materials are promising as active layers for future practical organic FET devices. In this chapter, the recent advancement of the FETs using polycyclic hydrocarbons are reported completely, in particular the FETs using extended π-conjugated hydrocarbon molecules, such as phenacene, and the FETs using fullerene molecules are also reported. Furthermore, intercalation chemistry of the π-conjugated hydrocarbon molecules is reported, which facilitates realization of novel physical properties, such as superconductivity and ferromagnetism.

‘Aromatic hydrocarbon’ implies an organic molecule that satisfies the (4 n + 2) π-electron rule and consists of benzene rings. Doping solid aromatic hydrocarbons with metals provides the superconductivity. The first discovery of such superconductivity was made for K-doped picene (K x picene, five benzene rings). Its superconducting transition temperatures ( T c ’s) were 7 and 18 K. Recently, we found a new superconducting K x picene phase with a T c as high as 14 K, so we now know that K x picene possesses multiple superconducting phases. Besides K x picene, we discovered new superconductors such as Rb x picene and Ca x picene. A most serious problem is that the shielding fraction is ⩽15% for K x picene and Rb x picene, and it is often ∼1% for other superconductors. Such low shielding fractions have made it difficult to determine the crystal structures of superconducting phases. Nevertheless, many research groups have expended a great deal of effort to make high quality hydrocarbon superconductors in the five years since the discovery of hydrocarbon superconductivity. At the present stage, superconductivity is observed in certain metal-doped aromatic hydrocarbons (picene, phenanthrene and dibenzopentacene), but the shielding fraction remains stubbornly low. The highest priority research area is to prepare aromatic superconductors with a high superconducting volume-fraction. Despite these difficulties, aromatic superconductivity is still a core research target and presents interesting and potentially breakthrough challenges, such as the positive pressure dependence of T c that is clearly observed in some phases of aromatic hydrocarbon superconductors, suggesting behavior not explained by the standard BCS picture of superconductivity. In this article, we describe the present status of this research field, and discuss its future prospects.

Field-effect transistors (FETs) have been fabricated with thin films of a series of 2,9-dialkylated phenanthro[1,2-b:8,7-b′]dithiophene derivatives (Cn-PDTs). The FET characteristics of Cn-PDT thin-film FETs with an SiO2 gate dielectric as well as high-k gate dielectrics were recorded, and the dependence of the field-effect mobility, μ, on the number (n) of carbon atoms in the alkyl chains was investigated, showing that the 2,9-didodecylphenanthro[1,2-b:8,7-b′]dithiophene (C12-PDT) thin-film FET displays superior properties, with μs as high as 1.8 cm2 V−1 s−1 for the SiO2 gate dielectric and 2.2 cm2 V−1 s−1 for the HfO2 gate dielectric. The average μ values, 〈μ〉, reach 1.1(5) and 1.8(6) cm2 V−1 s−1, respectively, for the SiO2 and ZrO2 gate dielectrics. Low-voltage operation, showing an absolute average threshold voltage 〈|Vth|〉 of ∼11 V, was implemented, together with the above high 〈μ〉 of ∼2 cm2 V−1 s−1. Also, a flexible FET was fabricated with a parylene gate dielectric. The results of this study show the potential of the C12-PDT molecule for application in a high-performance transistor.

A new phenacene-type molecule with five fused aromatic rings was synthesized: 2,7-didodecylphenanthro[2,1-b:7,8-b′]dithiophene ((C12H25)2-i-PDT), with two terminal thiophene rings. Field-effect transistors (FETs) using thin films of this molecule were fabricated using various gate dielectrics, showing p-channel normally-off FET properties with field-effect mobilities (μ) greater than 1 cm2 V−1 s−1. The highest μ value in the thin-film FETs fabricated in this study was 5.4 cm2 V−1 s−1, when a 150 nm-thick ZrO2 gate dielectric was used. This implies that (C12H25)2-i-PDT is very suitable for use in a transistor. Its good FET performance is fully discussed, based on electronic/topological properties and theoretical calculations.

Many chemists have attempted syntheses of extended π-electron network molecules because of the widespread interest in the chemistry, physics and materials science of such molecules and their potential applications. In particular, extended phenacene molecules, consisting of coplanar fused benzene rings in a repeating W-shaped pattern have attracted much attention because field-effect transistors (FETs) using phenacene molecules show promisingly high performance. Until now, the most extended phenacene molecule available for transistors was [8]phenacene, with eight benzene rings, which showed very high FET performance. Here, we report the synthesis of a more extended phenacene molecule, [9]phenacene, with nine benzene rings. Our synthesis produced enough [9]phenacene to allow the characterization of its crystal and electronic structures, as well as the fabrication of FETs using thin-film and single-crystal [9]phenacene. The latter showed a field-effect mobility as high as 18 cm2 V−1 s−1, which is the highest mobility realized so far in organic single-crystal FETs.

Novel [6]phenacenes (fulminenes) with two long alkyl chains at the axis positions were synthesized. This short synthesis comprises the following three steps: (1) ruthenium-catalyzed direct C–H bond arylation; (2) conversion of directing groups by Wittig reaction; and (3) bismuth- or gold-catalyzed cyclization of vinyl ether. Organic field-effect transistor devices fabricated with a thin film of 3,11-di(tetradecyl)fulminene exhibited typical p-channel normally-off properties.

Field-effect transistors (FETs) with single crystals of a new phenacene-type molecule, [8]phenacene, were fabricated and characterized. This new molecule consists of a phenacene core of eight benzene rings, with an extended π-conjugated system, which was recently synthesized for use in an FET by our group. The FET characteristics of an [8]phenacene single-crystal FET with SiO2 gate dielectrics show typical p-channel properties with an average field-effect mobility, 〈μ〉, as high as 3(2) cm2 V−1 s−1 in two-terminal measurement mode, which is a relatively high value for a p-channel single-crystal FET. The 〈μ〉 was determined to be 6(2) cm2 V−1 s−1 in four-terminal measurement mode. Low-voltage operation was achieved with PbZr0.52Ti0.48O3 (PZT) as the gate dielectric, and an electric-double-layer (EDL) capacitor. The 〈μ〉 and average values of absolute threshold voltage, 〈|Vth|〉, were 1.6(4) cm2 V−1 s−1 and 5(1) V, respectively, for PZT, and 4(2) × 10−1 cm2 V−1 s−1 and 2.38(4) V, respectively, for the EDL capacitor; these values were evaluated in two-terminal measurement mode. The inverter circuit was fabricated using [8]phenacene and N,N′-1H,1H-perfluorobutyldicyanoperylene-carboxydi-imide single-crystal FETs. This is the first logic gate circuit using phenacene molecules. Furthermore, the relationship between μ and the number of benzene rings was clarified based on this study and the previous studies on phenacene single-crystal FETs. Transistors fabricated using the single crystals of [8]phenacene | Request PDF. Available from: https://www.researchgate.net/publication/279312106_Transistors_fabricated_using_the_single_crystals_of_8phenacene [accessed Mar 08 2018].

This article reviews new superconducting phases of carbon-based materials. During the past decade, new carbon-based superconductors have been extensively developed through the use of intercalation chemistry, electrostatic carrier doping, and surface-proving techniques. The superconducting transition temperature T c of these materials has been rapidly elevated, and the variety of superconductors has been increased. This review fully introduces graphite, graphene, and hydrocarbon superconductors and future perspectives of high-T c superconductors based on these materials, including present problems. Carbon-based superconductors show various types of interesting behavior, such as a positive pressure dependence of T c. At present, experimental information on superconductors is still insufficient, and theoretical treatment is also incomplete. In particular, experimental results are still lacking for graphene and hydrocarbon superconductors. Therefore, it is very important to review experimental results in detail and introduce theoretical approaches, for the sake of advances in condensed matter physics. Furthermore, the recent experimental results on hydrocarbon superconductors obtained by our group are also included in this article. Consequently, this review article may provide a hint to designing new carbon-based superconductors exhibiting higher T c and interesting physical features.

Correction for ‘Transistor application of new picene-type molecules, 2,9-dialkylated phenanthro[1,2-b:8,7-b′]dithiophenes’ by Yoshihiro Kubozono et al., J. Mater. Chem. C, 2015, 3, DOI: 10.1039/c4tc02413c.