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The interference of electronic wavefunctions within a Kagome lattice can result in a flat band structure, where low‐energy electrons exhibit highly correlated behavior, facilitating exploration of interactions among intriguing electronic states. However, the inherent high carrier density in most known Kagome materials often hampers the manipulation of these quantum phenomena through conventional means, such as gate voltage. In this work, a unique tunability in the electrical and optoelectronic properties of exfoliated Nb3I8, a 2D semiconductor featuring a “breathing” Kagome lattice is uncovered. Characterization via temperature‐dependent ARPES confirms its semiconducting nature with a flat band structure. Experimental results from bias and gate voltage dependent transport measurements on thin film Nb3I8 transistor devices demonstrate ambipolar conductance. Notably, these findings reveal a broadband photoresponse in the device, spanning from visible to near infrared wavelengths (532 −1100 nm), with the photocurrent showing gate‐dependent characteristics that mirror the dark current's ambipolar nature. This observation marks the first instance of ambipolar transport in a Kagome semiconductor, opening up exciting new avenues for electronic and optoelectronic device development. [ABSTRACT FROM AUTHOR]

Two‐dimensional material‐based field‐effect transistors (2DM‐FETs) are playing a revolutionary role in electronic devices. However, before electronic design automation (EDA) for 2DM‐FETs can be achieved, it remains necessary to determine how to incorporate contact transports into model. Reported methods compromise between physical intelligibility and model compactness due to the heterojunction nature. To address this, quasi‐Fermi‐level phase space theory (QFLPS) is generalized to incorporate contact transports using the Landauer formula. It turns out that the Landauer‐QFLPS model effectively overcomes the issue of concern. The proposed new formula can describe 2DM‐FETs with Schottky or Ohmic contacts with superior accuracy and efficiency over previous methods, especially when describing non‐monotonic drain conductance characteristics. A three‐bit threshold inverter quantizer (TIQ) circuit is fabricated using ambipolar black phosphorus and it is demonstrated that the model accurately predicts circuit performance. The model could be very effective and valuable in the development of 2DM‐FET‐based integrated circuits. [ABSTRACT FROM AUTHOR]

Abstract Two‐dimensional material‐based field‐effect transistors (2DM‐FETs) are playing a revolutionary role in electronic devices. However, before electronic design automation (EDA) for 2DM‐FETs can be achieved, it remains necessary to determine how to incorporate contact transports into model. Reported methods compromise between physical intelligibility and model compactness due to the heterojunction nature. To address this, quasi‐Fermi‐level phase space theory (QFLPS) is generalized to incorporate contact transports using the Landauer formula. It turns out that the Landauer‐QFLPS model effectively overcomes the issue of concern. The proposed new formula can describe 2DM‐FETs with Schottky or Ohmic contacts with superior accuracy and efficiency over previous methods, especially when describing non‐monotonic drain conductance characteristics. A three‐bit threshold inverter quantizer (TIQ) circuit is fabricated using ambipolar black phosphorus and it is demonstrated that the model accurately predicts circuit performance. The model could be very effective and valuable in the development of 2DM‐FET‐based integrated circuits.

The charged forms of π–conjugated chromophores are relevant in the field of organic electronics as charge carriers in optoelectronic devices, but also as energy storage substrates in organic batteries. In this context, intramolecular reorganization energy plays an important role in controlling material efficiency. In this work, we investigate how the diradical character influences the reorganization energies of holes and electrons by considering a library of diradicaloid chromophores. We determine the reorganization energies with the four-point adiabatic potential method using quantum–chemical calculations at density functional theory (DFT) level. To assess the role of diradical character, we compare the results obtained, assuming both closed-shell and open-shell representations of the neutral species. The study shows how the diradical character impacts the geometrical and electronic structure of neutral species, which in turn control the magnitude of reorganization energies for both charge carriers. Based on computed geometries of neutral and charged species, we propose a simple scheme to rationalize the small, computed reorganization energies for both n-type and p-type charge transport. The study is supplemented with the calculation of intermolecular electronic couplings governing charge transport for selected diradicals, further supporting the ambipolar character of the investigated diradicals. [ABSTRACT FROM AUTHOR]

The role of two defects in the ambipolar character of nanocrystalline selenium poor Sb2Se3 is studied. At low temperature, the electrical transport in Sb2Se3 thin films with nm‐sized crystallites and grains is dominated by the ionization of a shallow acceptor, while at high temperature a deep donor is the leading one. The ionization energy of the deep donor agrees with theoretical reports for selenium vacancies. However, the value of the ionization energy of the shallow acceptor is in contradiction with theoretical reports pointing out to an unreported shallow defect. These findings have been confirmed by two independent experimental techniques, Electron Paramagnetic Resonance, and electrical transport as a function of temperature. The mobility of the free carriers has been found not to be limited by grain potential barriers (GPB), in contrast with polycrystalline thin films. Both findings, new shallow acceptor and zero height GPB, constitute advantages for the design of nanostructured Sb2Se3‐based solar cells and other optoelectronic devices. These results not only provide useful information for the growth of nanocrystalline Sb2Se3 thin films with ambipolar transport properties, but also about the complexity of defect physics in low‐symmetry and Q1D semiconductors. [ABSTRACT FROM AUTHOR]

Negative differential resistance (NDR) is an exotic quantum tunneling phenomenon that is exhibited in narrow p‐n junctions with heavy doping concentrations. However, the presence of multiple heterojunctions in a conventional tunneling device often hampers the observance of NDR and a deep understanding of its origin, particularly in 2D van der Waals heterojunctions. Herein, the emergence of quantum tunneling at the charge neutrality point (VCNP) in ambipolar multilayered black phosphorus (BP) transistors without heterojunctions is reported. The nearly identical electron and hole carrier densities at VCNP in the presence of a drain bias (VD) result in a lateral p‐i‐n configuration inside the BP multilayers similar to that in a tunneling field‐effect transistor. The variation of the local carrier density profile and tunneling barrier with VD at VCNP drives a sharp enhancement of the activation energy and local resistance, which consequently allows to observe band‐to‐band tunneling at up to 340 K. The enhancement of the local doping profile along the BP channel and the NDR behavior in the fabricated reconfigurable top‐gate BP device with an h‐BN top‐dielectric provide further evidence for the origin of NDR in 2D ambipolar materials. [ABSTRACT FROM AUTHOR]

Abstract The role of two defects in the ambipolar character of nanocrystalline selenium poor Sb2Se3 is studied. At low temperature, the electrical transport in Sb2Se3 thin films with nm‐sized crystallites and grains is dominated by the ionization of a shallow acceptor, while at high temperature a deep donor is the leading one. The ionization energy of the deep donor agrees with theoretical reports for selenium vacancies. However, the value of the ionization energy of the shallow acceptor is in contradiction with theoretical reports pointing out to an unreported shallow defect. These findings have been confirmed by two independent experimental techniques, Electron Paramagnetic Resonance, and electrical transport as a function of temperature. The mobility of the free carriers has been found not to be limited by grain potential barriers (GPB), in contrast with polycrystalline thin films. Both findings, new shallow acceptor and zero height GPB, constitute advantages for the design of nanostructured Sb2Se3‐based solar cells and other optoelectronic devices. These results not only provide useful information for the growth of nanocrystalline Sb2Se3 thin films with ambipolar transport properties, but also about the complexity of defect physics in low‐symmetry and Q1D semiconductors.

As high-performance organic semiconductors, π-conjugated polymers have attracted much attention due to their charming advantages including low-cost, solution processability, mechanical flexibility, and tunable optoelectronic properties. During the past several decades, the great advances have been made in polymers-based OFETs with p-type, n-type or even ambipolar characterics. Through chemical modification and alignment optimization, lots of conjugated polymers exhibited superior mobilities, and some mobilities are even larger than 10 cm2·V−1·s−1 in OFETs, which makes them very promising for the applications in organic electronic devices. This review describes the recent progress of the high performance polymers used in OFETs from the aspects of molecular design and assembly strategy. Furthermore, the current challenges and outlook in the design and development of conjugated polymers are also mentioned. [ABSTRACT FROM AUTHOR]

The continuous innovation of captivating new organic semiconducting materials remains pivotal in the development of high-performance organic electronic devices. Herein, a molecular engineering by combining sila-annulation with the vertical extension of rylene diimides (RDIs) toward high-mobility organic semiconductors is presented. The unilateral and bilateral sila-annulated quaterrylene diimides (Si-QDI and 2Si-QDI) are designed and synthesized. In particular, the symmetrical bilateral 2Si-QDI exhibits a compact, 1D slipped π-π stacking arrangement through the synergistic combination of a sizable π-conjugated core and intercalating alkyl chains. Combining the appreciable elevated HOMO levels and reduced energy gaps, the single-crystalline organic field-effect transistors (SC-OFETs) based on 2Si-QDI demonstrate exceptional ambipolar transport characteristics with an impressive hole mobility of 3.0 cm 2 V -1 s -1 and an electron mobility of 0.03 cm 2 V -1 s -1 , representing the best ampibolar SC-OFETs based on RDIs. Detailed theoretical calculations rationalize that the larger transfer integral along the π-π stacking direction is responsible for the achievement of the superior charge transport. This study showcases the remarkable potential of sila-annulation in optimizing carrier transport performances of polycyclic aromatic hydrocarbons (PAHs)., (© 2023 Wiley‐VCH GmbH.)

The current study concerns a technique to amplify the gas sensitivity of reduced graphene oxide (rGO)-field-effect transistor (FET) sensor for the detection of very low concentration gaseous species. rGO channel exhibits tunable carrier density with ambipolar transport in FET structure by the change of electrostatic potential through the gate terminal. At low carrier density of channel, the exchange of carriers due to surface adsorption and desorption is significant that eventually enhances the sensitivity of the rGO-FET sensor at a typical gate voltage (VGS). The back-gated rGO-FET sensor was fabricated on p-Si substrate with 90-nm-thick SiO2 layer. The defects, disorders, and morphology of single-layer (major) rGO were characterized with the spectroscopic and microscopic study. The modulation of ambient sensitivity of rGO film was tested in the exposure of different ambient like dry air, argon, oxygen, and a test vapor methanol. 1.95% methanol (at 150 ppm) sensitivity at VGS = 0 V was amplified up to 127.93% at VGS= 5 V and 82.38% at VGS = 13 V where the temperature and drain-to-source voltage (VDS) were 100 °C and 1.4 mV, respectively. [ABSTRACT FROM AUTHOR]

To realize single‐molecule field‐effect transistors, a crucial test for evaluating the integrity of single‐molecule electronics into conventional circuit architectures, remains elusive. Though interfacial effect is widely accepted to be crucially important in electronic devices, rare reports have studied fine control of the interface in single‐molecule transistors. Through molecular engineering, different numbers of methylene groups are incorporated between the diketopyrrolopyrrole (DPP) kernel and anchor groups (AMn‐DPP, n = 0−3), and how the molecule–electrode interface affects the performance of single‐molecule transistors is investigated. Both experimental and theoretical data demonstrate that p‐type charge transport dominates in AM0‐DPP and AM1‐DPP single‐molecule transistors, while AM2‐DPP and AM3‐DPP systems exhibit ambipolar field‐effect behaviors, which is attributed to the HOMO‐pinning effect in AM0‐DPP and AM1‐DPP molecular junctions. Theoretical calculations show that the parity of the methylene number results in two different connection symmetries between the DPP kernel and graphene electrodes, and thus different electronic interactions, leading to different relative molecular energy‐level alignments form those of isolated molecules, which has never been reported before. These results provide crucial information for precise control of the interfaces in molecular junctions, new insight into building multifunctional graphene–organic hybrid electronic devices, and the design of functional organic materials. [ABSTRACT FROM AUTHOR]

Ambipolar transport characteristics of thin film transistors fabricated from nontoxic white light emitting quantum dot complexes (QDCs) are herein reported to exhibit efficient carrier mobilities. The QDCs are synthesized by forming bluish green emitting zinc quinolate complex on the surface of orange emitting Mn2+‐doped ZnS quantum dots (Qdots) using 8‐hydroxyquinoline 5‐sulfonic acid as the chelating ligand. The device exhibits efficient ambipolar transport characteristics with high ION/IOFF ratio of 104 and electron mobility and hole mobility of 2.95 × 10−02 and 1.06 × 10−02 cm2 V−1 s−1, respectively. The subthreshold slope of Qdot complex–integrated thin film transistor increases from that of Mn2+‐doped ZnS Qdot–integrated thin film transistor from 0.35 to 0.79 V dec−1 in p‐field effect transistor (FET) and from 0.59 to 0.97 V dec−1 in n‐FET operations, which annotates an increase in trap state density due to surface complexation of the Qdot. These results suggest that white light emitting QDC can be used as an efficient transport as well as an emissive material, which open up new paradigm for advanced optoelectronic applications. [ABSTRACT FROM AUTHOR]

In the first part of this article, a physics-based surface-potential compact model to describe current–voltage (I–V) relationship in few-layered ambipolar black phosphorus (BP) transistors is presented. The proposed model captures the essential physics of thin-film BP FETs by accounting for the effects of: 1) in-plane band-structure anisotropy in BP, as well as the asymmetry in electron and hole current conduction characteristics; 2) nonlinear Schottky-type source/drain contact resistances; 3) interface traps; 4) ambipolar current conduction in the device using two separate quasi-Fermi levels for electrons and holes; and 5) the effect of temperature on the model parameters. In this article, the model is validated against measured data of back-gated BP transistors with gate lengths of 1000 and 300 nm with the BP thickness of 7.3 and 8.1 nm and for the temperature range of 200–298 K. We also validate the model against numerical TCAD data of BP transistors with channel lengths of 300 and 600 nm and BP thickness of 6 nm. The model is also applied to unipolar 2-D FETs with channel materials, such as MoS2 and WSe2. Compared with prior BP FET models that are mainly suited for near-equilibrium transport and room-temperature operation, the model developed here shows excellent agreement with experimental and numerical data over broad bias and temperature range. [ABSTRACT FROM AUTHOR]

We report a physics-based surface-potential compact model to describe current–voltage (I – V) relationship in a few-layered ambipolar black phosphorus (BP) transistors. To model the device electrostatics, the 2-D density of states of carriers and Fermi–Dirac statistics are used, while carrier transport is described using the drift-diffusion formalism. The model also comprehends the effects of interface traps and voltage-dependent Schottky-type source/drain contact resistances. Compared with prior BP FET models that are mainly suited for near-equilibrium transport and room-temperature operation, the model developed here is applicable over broad bias and temperature range. Validation of the model against measurement data of BP transistors with gate lengths 300–1000 nm and operating temperature from 200–298 K is demonstrated in a companion article. [ABSTRACT FROM AUTHOR]

Applying a drain bias to a strongly gate-coupled semiconductor influences the carrier density of the channel. However, practical applications of this drain-bias-induced effect in the advancement of switching electronics have remained elusive due to the limited capabilities of its current modulation known to date. Here, we show strategies to largely control the current by utilizing drain-bias-induced carrier type switching in an ambipolar molybdenum disulfide (MoS 2 ) field-effect transistor with Pt bottom contacts. Our CMOS-compatible device architecture, incorporating a partially gate-coupled p-n junction, achieves multifunctionality. The ambipolar MoS 2 device operates as an ambipolar transistor (on/off ratios exceeding 10 7 for both NMOS and PMOS), a rectifier (rectification ratio of ∼3 × 10 6 ), a reversible negative breakdown diode with an adjustable breakdown voltage (on/off ratio exceeding 10 9 with a maximum current as high as 10 -4 A), and a photodetector. Finally, we demonstrate a complementary inverter (gain of ∼24 at V dd = 1.5 V), which is highly facile to fabricate without the need for complex heterostructures and doping processes. Our study provides strategies to achieve high-performance ambipolar MoS 2 devices and to effectively utilize drain bias for electrical switching.

Novel co-crystal microwires based on phenothiazine (PTZ) and tetracyanoquinodimethane (TCNQ) have been fabricated using a facile solution method and fully characterized. The microwires had well-defined shapes, smooth surfaces and high crystalline. Moreover, the co-crystal microwires exhibited a significant absorption at wavelengths between 900 and 2400 nm owing to the charge-transfer interaction between PTZ and TCNQ. The prototype field-effect transistor with the bottom-gate was directly constructed, exhibiting typical ambipolar charge transport characteristics. [ABSTRACT FROM AUTHOR]

We report clear room temperature ambipolar transport in ambient-air processed methylammonium lead iodide (MAPbI3) thin-film transistors (TFTs) with aluminum oxide gate-insulators and indium-zinc-oxide source/drain electrodes. The high ionicity of the MAPbI3 leads to p-type and n-type self-doping, and depending on the applied bias we show that simultaneous or selective transport of electrons and/or holes is possible in a single MAPbI3 TFT. The electron transport (n-type), however, is slightly more pronounced than the hole transport (p-type), and the respective channel resistances range from 5−11 and 44−55 MΩ/μm. Both p-type and n-type TFTs show good on-state characteristics for low driving voltages. It is also shown here that the on-state current of the n-type and p-type TFTs is highest in the slightly PbI2-rich and MAI-rich films, respectively, suggesting controllable n-type or p-type transport by varying precursor ratio.

The Seebeck coefficient of both electrons and holes in a family of ambipolar diketopyrrolopyrrole copolymers is investigated using field-effect gated measurements. It is found that at high carrier concentrations the magnitude of the Seebeck coefficients is not strongly dependent on the molecular structure of the backbone within this family of polymers. Additionally, the Seebeck coefficients of electrons and holes have very similar magnitudes showing that electrons and holes experience a similar energetic landscape. Subtle differences in the carrier concentration dependence between the polymers are observed, which are interpreted in terms of different degrees of energetic disorder on the basis of molecular dynamics and electronic structure simulations. [ABSTRACT FROM AUTHOR]

Charge transport rate is one of the key parameters determining the performance of organic electronic devices. In this paper, we used density functional theory (DFT) at the M06-2X/6−31 $$+$$ G(d) level to compute the charge transport rates of nine coronene topological structures. The results show that the energy gap of these nine coronene derivatives is in the range 2.90-3.30 eV, falling into the organic semiconductor category. The size of the conjugate ring has a large influence on the charge transport properties. Incorporation of methyl groups on the rigid core of tetrabenzocoronene and hexabenzocoronene is more conducive to the hole transport of the molecule than incorporating methoxyl groups. The derivatisation of a 'long plate-like' coronene with methoxyl groups facilitates both hole and electron transport. This class of molecules can thus be used in the design of ambipolar transport semiconductor materials. Graphical Abstract:: JCSC-D-16-01407 SYNOPSIS Density functional theory was used to compute the charge transport rates of three series nine coronene topological structures at the M06-2X/6−31+G(d) level. Tetrabenzocoronene (series a) and hexabenzocoronene (series b) could be candidates for a hole-transporting (p-type) organic semiconductor material, and 'long plate-like' coronene topological structures (series c) could be used as an ambipolar transport material. [ABSTRACT FROM AUTHOR]

Two new D−A polymers ( PBTPBF-HH and PBTPBF-TT ) based on (3 E , 7 E )-3,7-bis(4-(2-decyltetradecyl)-4 H -thieno[3,2- b ]pyrrole-5,6-dione)benzo[1,2- b :4,5- b' ]difuran-2,6(3 H ,7 H )-dione and ( E )-2-(2-(thiophen-2-yl)vinyl)thiophene units with different side-chain positions (head-to-head and tail-to-tail) were synthesized, and the side-chain positions were optimized with respect to their planarity, microstructure and performance as organic thin-film transistors. Both the polymers showed broad absorption spectra (covering 400–1600 nm) and remarkably low bandgaps (ca. 0.8 eV). PBTPBF-HH containing head-to-head linkages had a dual texture, in which face-on and edge-on crystallites coexisted. In contrast, PBTPBF-TT containing tail-to-tail linkages mainly exhibited an edge-on texture. Consequently, PBTPBF-TT showed a much higher transport performance than PBTPBF-HH when evaluated using bottom-gate/top-contact organic thin-film transistors. The best mobilities of above 0.80 cm 2 V −1 s −1 and 0.19 cm 2 V −1 s −1 were obtained for hole and electron, respectively, at the optimized thermal annealing and in the presence of a high boiling point additive. Overall, this study showed that a minimal change in their side-chain positions dramatically optimized the planarity, microstructure, π-stacking orientation, and charge transport performance. [ABSTRACT FROM AUTHOR]

Ambipolar dual-gate transistors based on low-dimensional materials, such as graphene, carbon nanotubes, black phosphorus, and certain transition metal dichalcogenides (TMDs), enable reconfigurable logic circuits with a suppressed off-state current. These circuits achieve the same logical output as complementary metal-oxide semiconductor (CMOS) with fewer transistors and offer greater flexibility in design. The primary challenge lies in the cascadability and power consumption of these logic gates with static CMOS-like connections. In this article, high-performance ambipolar dual-gate transistors based on tungsten diselenide (WSe 2 ) are fabricated. A high on-off ratio of 10 8 and 10 6 , a low off-state current of 100 to 300 fA, a negligible hysteresis, and an ideal subthreshold swing of 62 and 63 mV/dec are measured in the p- and n-type transport, respectively. We demonstrate cascadable and cascaded logic gates using ambipolar TMD transistors with minimal static power consumption, including inverters, XOR, NAND, NOR, and buffers made by cascaded inverters. A thorough study of both the control gate and the polarity gate behavior is conducted. The noise margin of the logic gates is measured and analyzed. The large noise margin enables the implementation of V T -drop circuits, a type of logic with reduced transistor number and simplified circuit design. Finally, the speed performance of the V T -drop and other circuits built by dual-gate devices is qualitatively analyzed. This work makes advancements in the field of ambipolar dual-gate TMD transistors, showing their potential for low-power, high-speed, and more flexible logic circuits.

Three copolymers ( P1 , P2 , and P3 ) based on benzodithiophenedione and diketopyrrolopyrrole units were synthesized by Suzuki reaction. The thermal, optical, electrochemical, microstructure, charge transport and phototransistor properties of the copolymers were also investigated. The field-effect performances of the copolymers were optimized by tailoring their structure and using thermal annealing. The three copolymers exhibited ambipolar transport under vacuum, but hole characteristics in air. The optimized copolymer P3 exhibited a balanced hole and electron mobility of 0.022 and 0.028 cm 2 V −1 s −1 , respectively, under vacuum conditions, but hole transport in air with a hole mobility of as high as 0.034 cm 2 V −1 s −1 . Phototransistors based on P3 showed a photocurrent/dark current ratio of 6.4 × 10 3 under near-infrared light illumination (808 nm). This is the first investigation on the field-effect and phototransistor performances of benzodithiophenedione-based copolymers. [ABSTRACT FROM AUTHOR]

Oxygen permeation measurements were performed on dense symmetric samples of Ca 0.5 Sr 0.5 Ti 0.6 Fe 0.15 Mn 0.25 O 3− δ and compared to CaTi 0.6 Fe 0.15 Mn 0.25 O 3− δ in order to assess the influence of the perovskite lattice volume on oxygen permeation. Oxygen flux measurements were performed in the temperature range 700–1000 °C and as function of feed side p O 2 from 10 −2 to 1 bar, and at high pressures up to 4 bar with a p O 2 of 3.36 bar. The O 2 permeability of the Sr-doped sample was significantly lower than that of the Sr-free sample, amounting to 3.9×10 −3 mL min −1 cm −1 at 900 °C for a feed side p O 2 of 0.21 bar. The O 2 permeability of CaTi 0.6 Fe 0.15 Mn 0.25 O 3− δ shows little variation with increased feed side pressures and reaches 1.5×10 −2 mL min −1 cm −1 at 900 °C for a feed side p O 2 of 3.36 bar. This is approximately 1.5 times higher than the O 2 permeability with a feed side p O 2 of 0.21 bar. Furthermore, in order to assess the applicability of CaTi 0.6 Fe 0.15 Mn 0.25 O 3− δ as an oxygen membrane material, creep tests were performed under compressive loads of 30 and 63 MPa, respectively, in air in the temperature range 700–1000 °C; the results indicate a high creep resistance for this class of materials. The measured O 2 permeabilities and creep rates are compared with other state-of-the-art membrane materials and their performance for relevant applications is discussed in terms of chemical and mechanical stability. [ABSTRACT FROM AUTHOR]

We realize and investigate ionic liquid gated field-effect transistors (FETs) on large-area MoS2monolayers grown by chemical vapor deposition (CVD). Under electron accumulation, the performance of these devices is comparable to that of FETs based on exfoliated flakes. FETs on CVD-grown material, however, exhibit clear ambipolar transport, which for MoS2 monolayers had not been reported previously. We exploit this property to estimate the bandgap Δ of monolayer MoS2 directly from the device transfer curves and find Δ ≈ 2.4-2.7 eV. In the ambipolar injection regime, we observe electroluminescence due to exciton recombination in MoS2, originating from the region close to the hole-injecting contact. Both the observed transport properties and the behavior of the electroluminescence can be consistently understood as due to the presence of defect states at an energy of 250-300 meV above the top of the valence band, acting as deep traps for holes. Our results are of technological relevance, as they show that devices with useful optoelectronic functionality can be realized on large-area MoS2monolayers produced by controllable and scalable techniques. [ABSTRACT FROM AUTHOR]

Oxygen permeation measurements are performed on dense samples of CaTi 0.85 Fe 0.15 O 3− δ , CaTi 0.75 Fe 0.15 Mg 0.05 O 3− δ and CaTi 0.75 Fe 0.15 Mn 0.10 O 3− δ in combination with density functional theory (DFT) calculations and X-ray photoelectron spectroscopy (XPS) in order to assess Mg and Mn as dopants for improving the O 2 permeability of CaTi 1− x Fe x O 3− δ based oxygen separation membranes. The oxygen permeation measurements were carried out at temperatures ranging between 700 and 1000 °C with feed side oxygen partial pressures between 0.01 and 1 bar. The O 2 permeability was experimentally found to be highest for the Mn doped sample over the whole temperature range, reaching 4.2×10 −3 ml min −1 cm −1 at 900 °C and 0.21 bar O 2 in the feed which corresponds to a 40% increase over the Fe-doped sample and similar to reported values for x =0.2. While the O 2 permeability of the Mg doped sample was also higher than the Fe-doped sample, it approached that of the Fe-doped sample above 900 °C. According to the DFT calculations, Mn introduces electronic states within the band gap and will predominately exist in the effectively negative charge state, as indicated by XPS measurements. Mn may therefore improve the ionic and electronic conductivity of CTF based membranes. The results are discussed in terms of the limiting species for ambipolar transport and O 2 permeability, i.e., oxygen vacancies and electronic charge carriers. [ABSTRACT FROM AUTHOR]

Recently, rock-salt IV-VI semiconductors, such as Pb1-xSnxSe(Te) and SnTe, have been observed to host topological crystalline insulator (TCI) states.1-7 The nontrivial states have long been believed to exhibit ambipolar field effects and possess massive Dirac Fermions in two-dimension (2D) limit due to the surface hybridization.8,9 However, these exciting attributes of TCI remain previously inaccessible owing to the complicated control over composition and thickness.10,11 Here, we systematically investigate doping and thickness-induced topological phase transitions by electrical transport. We demonstrate the first evidence of the ambipolar properties in Pb1-xSnxSe thin films. Surface gap opening is observed in 10 nm TCI originated from the strong finite-size effect. Importantly, magnetoconductance hosts a competition between weak antilocalization and weak localization, suggesting a strikingly tunable Berry phase evolution and strong electron-electron interaction. Our findings serve as a new probe to study electron behavior and pave the way for further exploring and manipulating this novel 2D TCI phase. [ABSTRACT FROM AUTHOR]

Tetrasubstituted-pyrenes containing peripheral diarylamines (1-4) or fluorenes (5-6) have been synthesized. These compounds are highly fluorescent and possess high morphological stability and thermal stability. Compounds containing peripheral arylamines (1-3) can be used as the hole-transport and green-emitting materials for two-layered electroluminescent devices. Compounds with peripheral fluorenes (5-6) are efficient blue emitters and exhibit ambipolar carrier-transport characteristics with high electron mobilities (10-3-10-2cm2/Vs) and high hole mobilities (>10-3cm2/Vs). Non-doped blue-emitting devices with promising electroluminescent performance (i.e., high efficiency and narrow/saturated emission) can be achieved using fluorene-substituted pyrenes as either the hole-transport/emitting layer or the electron-transport/emitting layer in the two-layered devices. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen permeation in 30% Mo-substituted lanthanum tungsten oxide membranes, La27Mo1.5W3.5O55.5 (LWMo), has been measured as a function of temperature, hydrogen partial pressure gradient, and water vapor pressure in the sweep gas. Transport of hydrogen by means of ambipolar proton–electron conductivity and – with wet sweep gas – water splitting contributes to the measured hydrogen content in the permeate. At 700°C under dry sweep conditions, the H2 permeability in LWMo was mLmin−1 cm-1, which is significantly higher than that for state-of-the-art SrCeO3-based membranes. Proton conductivity was identified as rate limiting for ambipolar bulk transport across the membrane. On these bases it is evident that Mo-substitution is a successful doping strategy to increase the n-type conductivity and H2 permeability compared to nominally unsubstituted lanthanum tungsten oxide. A steady-state model based on the Wagner transport theory with partial conductivities as input parameters predicted H2 permeabilities in good agreement with the measured data. LWMo is a highly competitive mixed proton–electron conducting oxide for hydrogen transport membrane applications provided that long term stability can be ensured. [Copyright &y& Elsevier]

Highlights: [•] The carrier mobility of BTMN and BCMN molecular crystals has been simulated theoretically. [•] The charge transport in both crystals behaves in a “bandlike” manner when the nuclear tunneling effect is considered. [•] BCMN is quite promising ambipolar OFET materials under favorable device conditions. [•] The hole transport is remarkable anisotropic in both crystals. [ABSTRACT FROM AUTHOR]

Two coordination complex emitters as well as host materials Be(PPI)2 and Zn(PPI)2 (PPI = 2-(1-phenyl-1 H-phenanthro[9,10- d]imidazol-2-yl)phenol) are designed, synthesized, and characterized. The incorporation of the metal atom leads to a twisted conformation and rigid molecular structure, which improve the thermal stability of Be(PPI)2 and Zn(PPI)2 with high Td and Tg at around 475 and 217 °C, respectively. The introduction of the electron-donating phenol group results in the emission color shifting to the deep-blue region and the emission maximum appears at around 429 nm. This molecular design strategy ensures that the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) HOMO and LUMO of Be(PPI)2 and Zn(PPI)2 localize on the different moieties of the molecules. Therefore, the two complexes have an ambipolar transport property and a small singlet-triplet splitting of 0.35 eV for Be(PPI)2 and 0.21 eV for Zn(PPI)2. An undoped deep-blue fluorescent organic light-emitting device (OLED) that uses Be(PPI)2 as emitter exhibits a maximum power efficiency of 2.5 lm W−1 with the CIE coordinates of (0.15, 0.09), which are very close to the National Television Standards Committee (NTSC) blue standard (CIE: 0.14, 0.08). Green and red phosphorescent OLEDs (PhOLEDs) that use Be(PPI)2 and Zn(PPI)2 as host materials show high performance. Highest power efficiencies of 67.5 lm W−1 for green PhOLEDs and 21.7 lm W−1 for red PhOLEDs are achieved. In addition, the Be(PPI)2-based devices show low-efficiency roll-off behavior, which is attributed to the more balanced carrier-transport property of Be(PPI)2. [ABSTRACT FROM AUTHOR]

Energy, area, and bandwidth efficient communication primitives are essential to sustain the rapid increase in connectivity among internet-of-things (IoT) edge devices. While IoT edge-sensing, edge-computing, and edge-storage have witnessed innovation in materials and devices, IoT edge communication is yet to experience such transformation. The aging silicon (Si)-based complementary metal-oxide-semiconductor (CMOS) technology continues to remain the mainstay of communication devices where they are used to implement amplitude, frequency, and phase shift keying (amplitude-shift keying [ASK]/frequency-shift keying [FSK]/phase-shift keying [PSK]). Keying allows digital information to be communicated over a radio channel. While CMOS-based keying devices have evolved over the years, their hardware footprint and energy consumption are major concerns for resource constrained IoT communication. Furthermore, separate circuit designs and hardware elements are needed for each keying scheme and achieving multibit modulation to improve bandwidth efficiency remains a challenge. Here, a reconfigurable modulator is introduced that exploits unique ambipolar transport and programmable Dirac voltage in ultrathin MoTe 2 field-effect transistors to achieve ASK, FSK, and PSK modulation. Furthermore, by integrating two programmed MoTe 2 field-effect transistors, multibit data modulation is demonstrated, which improves the bandwidth efficiency by 200%. Finally, a frequency quadrupler is also realized exploiting the unique "double-well" transfer characteristic., (© 2022 Wiley-VCH GmbH.)

After carefully theoretical research, as for the concepts of P- and N- type semiconductors, it is found that there are contradictions between inorganic and polymer semiconductors. Then through the basic concepts of hole and electron, it can be derived that all the polymer semiconductors should have ambipolar transporting characteristics, which has been proved by the subsequently experimental data through the impedance spectroscopy from the common materials. Such general ambipolar transporting properties of polymers are firstly systematically investigated in diode structure, which is closer to their intrinsic properties. The hole can be seen as "electron group of hole", and it is difficult to be quenched than one electron, which can then help to get the common reported data that the number of hole transporting polymers are more popular than that of electron transport. Moreover, the experimental mobility curves mostly show the negative slope, which seems to be opposite to the basic fact that the electric field will accelerate the directional movement of carrier. The concept of carrier segment is then proposed for such negative slope, which is one conjugation projection system. In one carrier segment, the carrier can move freely as in one molecule, which can be accelerated by external electric field. From one carrier segment to another carrier segment, the kinetic energy of carrier could be relaxed by the vibration of carrier segment dipole. If the energy loss from vibration relaxation of carrier segment is larger than the energy increment from the external electric field, the carrier mobility curve will show the whole negative characteristic. Which effect can have the main influence is determined by the molecular structure of polymers. At last, the vibration model of the polymers has been investigated through the IR spectroscopy and the calculation methods. It is showed that the vibration models of P3HT have some special characteristics, which are corresponding to the fact that its slopes of hole and electron mobility curves are contrary to each other. [Display omitted] ● Ambipolar transporting properties of polymers are firstly systematically investigated in diode structure. ● Hole and electron mobilities of Polymers film can be tested by impedance spectroscopy. ● Carrier mobility curves of polymers show the negative slope. ● Carriers can move freely in one carrier segment, which is one conjugation projection system. ● The vibration relaxation of the carrier segment makes the carrier mobility curve have a negative slope. [ABSTRACT FROM AUTHOR]

Abstract: Two acene-based semiconductors were investigated with respect to their performance as n-type materials in organic field-effect transistors. The partially fluorinated ditetracenes (Ditetracen is protected by copywrite through the Patent WO/2007/000268. The patent is property of the Dritte Patentportfolio Beteiligungsgesellschaft mbH & Co. KG.) (DT) were synthesized in a high yield with different degrees of fluorination, one with four and another with two fluorine substituents (named as DT-4F and DT-2F, respectively). Both materials exhibit high thermal stability, with decomposition temperatures above 500°C. Since both materials are supposed to have a lowered LUMO level compared to the non-fluorinated parent DT, n-type operation in thin-film transistors (TFTs) with gold source and drain contacts was expected. TFTs based on DT-2F, however, showed weak ambipolar transport only, which demonstrates insufficient fluorination to switch from hole-dominated to electron-dominated transport. On the other hand, high performance n-type TFTs have been achieved from DT-4F, with electron mobilities up to 1.0cm2/Vs. This result indicates that fluorinated DT material can act as excellent n-type semiconductor for applications in complementary circuits. This is demonstrated in a complementary inverter stage using DT-4F-based TFTs as n-type transistor and a non-fluorinated DT derivative-based TFT as p-type transistor. [Copyright &y& Elsevier]

Two conjugated polymers containing stilbene and fumaronitrile moieties were synthesized to investigate their electronic properties by the existence of electron-withdrawing cyano groups on a vinylene backbone. The cyclic voltammetry investigation and time-dependent density functional theory calculations indicated that the cyano substituents lowered the lowest unoccupied molecular orbital (LUMO) energy level by about 0.65 and 0.63 eV, respectively. The lowering of the LUMO energy levels due to the electron-withdrawing properties of the cyano substituents could enhance electron injection capability. Furthermore, bithiophene-fumaronitrile (donor-acceptor) intermolecular interaction facilitates the self-assembly of the polymer chains. Organic field-effect transistors (OFETs) based on PBTSB without the electron-withdrawing group only exhibit hole transport, while OFETs based on PBTFN with cyano substituents exhibit ambipolar characteristics. The growth of PBTFN crystalline fibrils was observed with increasing annealing temperature, which enhanced hole and electron mobility. A complementary-like inverter using PBTFN with ambipolar properties exhibited good symmetry with an inverting voltage nearly half that of the power supply with a gain of 9 at VDD = 100 V. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 [ABSTRACT FROM AUTHOR]

Abstract: In this work, a modified, lumped element graphene field effect device model is presented. The model is based on the “Top-of-the-barrier” approach which is usually valid only for ballistic graphene nanotransistors. Proper modifications are introduced to extend the model’s validity so that it accurately describes both ballistic and diffusive graphene devices. The model is compared to data already presented in the literature. It is shown that a good agreement is obtained for both nano-sized and large area graphene based channels. Accurate prediction of drain current and transconductance for both cases is obtained. [Copyright &y& Elsevier]

This paper presents a compact model for the current–voltage characteristics of graphene field-effect transistors (GFETs), which is based on an extension of the “virtual-source” model previously proposed for Si MOSFETs and is valid for both saturation and nonsaturation regions of device operation. This GFET virtual-source model provides a simple and intuitive understanding of carrier transport in GFETs, allowing extraction of the virtual-source injection velocity vVS, which is a physical parameter with great technological significance for short-channel graphene transistors. The derived I–V characteristics account for the combined effects of the drain–source voltage VDS, the top-gate voltage VTGS, and the back-gate voltage VBGS. With only a small set of fitting parameters, the model shows excellent agreement with experimental data. It is also shown that the extracted virtual-source carrier injection velocity for graphene devices is much higher than in Si MOSFETs and state-of-the-art III–V heterostructure FETs with similar gate length, demonstrating the great potential of GFETs for high-frequency applications. Comparison with experimental data for chemical-vapor-deposited GFETs from our group and epitaxial GFETs in the literature confirms the validity and flexibility of the model for a wide range of existing GFET devices. [ABSTRACT FROM PUBLISHER]

Abstract: We report a comparative study of optical properties, structure and morphology, field-effect transistor (FET) and solar cell performance between poly(4-(3,4′-dihexyl-2,2′-bithiophen-5-yl)-7-(5′-(9,9-dioctyl-9H-fluoren-2-yl)-3,4′-dihexyl-2,2′-bithiophen-5-yl)benzo[c][1,2,5]thiadiazole) (F8TTBTT), and its predecessor poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2′,2″-diyl) (F8TBT). Compared to F8TBT, F8TTBTT has two more thiophene units incorporated in its monomer structure. Such a modification leads to a reduced optical band gap, improved charge injection and significantly enhanced ambipolar field-effect mobilities reaching 5×10−2 cm2 V−1 s−1 for holes and 4×10−3 cm2 V−1 s−1 for electrons. The enhanced carrier mobilities are most likely a result of an increased backbone planarization and interchain interaction. As a consequence of ambipolar transport, light-emission was observed from the transistor channel during operation. The reduced band gap and improved charge transport make F8TTBTT an interesting candidate also for solar cell applications. Unoptimized solar cells based on F8TTBTT:PCBM blends were found to exhibit power conversion efficiency under AM 1.5 illumination of ∼1.54%. [Copyright &y& Elsevier]

Abstract: Organic heterojunction thin-film transistors are fabricated based on copper phthalocyanine (CuPc) and hexadecafluorophtholocyaninatocopper (F16CuPc) as double active layers, which exhibit typical ambipolar conduction. Several substrate temperatures are utilized to tune film morphology, which results in a remarkable change on the electric characteristics of organic transistors. The highest balanced mobility value of 2.91×10−2 cm2/Vs for hole and 1.04×10−2 cm2/Vs for electron are obtained by depositing F16CuPc at 150°C and CuPc at 200°C, respectively, which are comparable to those conventional single-layer devices. This result demonstrates that the growth conditions of organic heterojunctions play a crucial role in ambipolar devices. [ABSTRACT FROM AUTHOR]

Abstract: N-channel operation of pentacene thin-film transistors with ultrathin poly(methyl methacrylate) (PMMA) gate buffer layer and gold source–drain electrode was observed. We prepared pentacene thin-film transistors with an 8-nm thick PMMA buffer layer on SiO2 gate insulators and obtained electron and hole field-effect mobilities of 5.3×10−2 cm2/(Vs) and 0.21cm2/(Vs), respectively, in a vacuum of 0.1Pa. In spite of using gold electrodes with a high work function, the electron mobility was considerably improved in comparison with previous studies, because the ultrathin PMMA film could decrease electron traps on SiO2 surfaces, and enhance the electron accumulation by applied gate voltages. [Copyright &y& Elsevier]

Despite a large steric bulk of C60, a molecular graphene with a covalently linked C60 pendant [hexabenzocoronene (HBC)-C60; 1] self-assembles into a coaxial nanotube whose wall consists of a graphite-like π-stacked HBC array, whereas the nanotube surface is fully covered by a molecular layer of clustering C60. Because of this explicit coaxial configuration, the nanotube exhibits an ambipolar character in the field-effect transistor output [hole mobility (μh) = 9.7 × 10-7 cm² V-1 s-1; electron mobility (μe) = 1.1 × 10-5 cm² V-1 s-1) and displays a photovoltaic response upon light illumination. Successful coassembly of 1 and an HBC derivative without C60 (2) allows for tailoring the p/n heterojunction in the nanotube, so that its ambipolar carrier transport property can be optimized for enhancing the open-circuit voltage in the photovoltaic output. As evaluated by an electrodeless method called flash-photolysis time-resolved microwave conductivity technique, the intratubular hole mobility (2.0 cm² V-1 s-1) of a coassembled nanotube containing 10 mol % of HBC-C60 (1) is as large as the intersheet mobility in graphite. The homotropic nanotube of 2 blended with a soluble C60 derivative [(6,6)-phenyl C61 butyric acid methyl ester] displayed a photovoltaic response with a much different composition dependency, where the largest open-circuit voltage attained was obviously lower than that realized by the coassembly of 1 and 2. [ABSTRACT FROM AUTHOR]

Abstract: A novel blue emitter, In2Bt, featured with a rigid and coplanar distyryl-p-phenylene backbone flattened by two different bridging atoms (i.e. carbon and sulfur) exhibits high thermal and morphological stability (T g ∼192°C) and ambipolar charge carrier mobilities in the range of 10−4 ∼10−5 cm2 V−1 s−1. OLED device: ITO/PEDOT:PSS (300Å)/α-NPD (200Å)/TCTA (100Å)/In2Bt (200Å)/TPBI (500Å)/LiF (5Å)/Al (1500Å) utilized In2Bt as an emitter gave a maximum brightness as high as 8000cdm−2 (12V) and saturated-blue emission with CIE chromaticity coordinates of (0.16, 0.08), which is very close to the National Television Standards Committee (NTSC) standard blue gives an enlarged palette of colors for color displays. [Copyright &y& Elsevier]