Light-emitting transistor structures based on semiconducting polymers and inorganic nanoparticles

One of the new directions in organic electronics is the development of light-emitting organic field-effect transistors, which combine the light-emitting properties of organic light-emitting diodes and the switching properties of organic field-effect transistors. Optical and electronic properties of novel nanocomposite materials based on semiconducting polymers and inorganic nanoparticles and designed for applications in organic electronics devices were investigated. Light-emitting organic field-effect transistors with composite active layers based on the soluble semiconducting polymers PFO and MEH-PPV and ZnO nanoparticles and having asymmetric electrodes (Al and Au) that inject electrons into ZnO and holes into PFO and MEH-PPV were prepared and investigated. The data are interpreted in the context of the possibility of organic field-effect transistors based on PFO: ZnO and MEH-PPV: ZnO composite films to work in both the unipolar regime and the ambipolar regime. It is shown that the mobility of charge carriers in light-emitting organic field-effect transistors based on PFO: ZnO at 300 K reaches ～0.02 for electrons and ～0.03 cm²/(V s) for holes, increasing with an increase in the concentration of nanoparticles up to ～2 cm²/(V s), a value that is comparable to the maximum mobility values for conducting polymers. Light-emitting organic field-effect transistors based on PFO: ZnO and MEH-PPV: ZnO emit light in the green and orange ranges of the optical spectrum, respectively, their electroluminescence intensities rising with an increase in either the negative bias or the positive bias at the source-drain and the gate as well as with an increase in the concentration of ZnO nanoparticles. The results indicate that light-emitting organic field-effect transistors based on soluble conjugated polymers and semiconducting ZnO nanoparticles are examples of multifunctional devices whose production technology is compatible with the modern ink-jet printing technology of organic electronics.     

Charge transport in fibre-based perylene-diimide transistors: effect of the alkyl substitution and processing technique

We report a comparative study on the self-assembly from solution and electrical characterization of n-type semiconducting fibres obtained from five different perylenebis(dicarboximide) (PDI) derivatives. In particular we investigated the role of the nature of the alkyl chain covalently linked to the N,N' sites of the PDI in modulating the molecular solubility and aggregation capacity. We explored the morphologies of the self-assembled architectures physisorbed on dielectric surfaces and in particular how they can be modified by tuning the deposition and post-deposition procedures, i.e. by modulating the kinetics of the self-assembly process. To this end, alongside the conventional spin-coating, solvent vapour annealing (SVA) and solvent induced precipitation (SIP) have been employed. Both approaches led to fibres having widths of several hundred nanometres and lengths up to tens of micrometres. SVA formed isolated fibres which were tens of nanometres high, flat, and tapered at the ends. Conversely, SIP fibres exhibited nearly matching heights and widths, but organized into bundles. Despite these morphological differences, the same intermolecular packing is found by XRD in each type of structure, albeit with differing degrees of long-range order. The study of the electrical characteristics of the obtained low dimensional nano-assemblies has been accomplished by fabricating and characterizing organic field-effect transistors.     

Active polymer nanofibers for photonics,electronics, energy generation and micromechanics

Active polymer nanofibers for opto- and nano-electronics benefit from low cost and versatile fabrication processes and exhibit an unequaled flexibility in terms of chemical composition, physical properties and achievable functionality. For these reasons, they have rapidly emerged as powerful tool for nanotechnologies and as building blocks of a wide range of devices. Both bottom up and top down nanofabrication concepts were developed to produce nanofibers made of conjugated or other functional polymers and blends. This article summarizes and reviews the chemico-physical and functional requirements for polymer nanofibers to be used in opto- and nanoelectronics, as well as recent advances in various promising device architectures, such as light emitting and photovoltaic devices, photodetectors, field-effect transistors, piezo- and thermoelectric generators, and actuators. The outlook of functional polymer nanofibers and of devices based on them is also outlined and discussed.     

Contact Resistance and Trap Density of Oligoaniline Field-Effect Transistor

The characteristics of metal-oxide-semiconductor field-effect transistors (MOSFETs) fabricated with 16-mer oligoaniline (16ANI) as semiconducting layer have been investigated. It is found that the contact resistance can be reduced three orders of magnitude by modifying the interface between metal electrode and organic material. Hence the field-effect mobility of modified 16ANI MOSFET can be increased by four times. The mobility can be further improved in the subsequent thermal treatment process. It is found that the field-effect mobility rather depends on trap density than on contact resistance.     

Device and circuit-level performance of carbon nanotube field-effect transistor with benchmarking against a nano-MOSFET

ABSTRACT: The performance of a semiconducting carbon nanotube (CNT) is assessed and tabulated for parameters against those of a metal-oxide-semiconductor field-effect transistor (MOSFET). Both CNT and MOSFET models considered agree well with the trends in the available experimental data. The results obtained show that nanotubes can significantly reduce the drain-induced barrier lowering effect and subthreshold swing in silicon channel replacement while sustaining smaller channel area at higher current density. Performance metrics of both devices such as current drive strength, current on-off ratio (Ion/Ioff), energy-delay product, and power-delay product for logic gates, namely NAND and NOR, are presented. Design rules used for carbon nanotube field-effect transistors (CNTFETs) are compatible with the 45-nm MOSFET technology. The parasitics associated with interconnects are also incorporated in the model. Interconnects can affect the propagation delay in a CNTFET. Smaller length interconnects result in higher cutoff frequency.     

Novel optoelectronic devices based on single semiconductor nanowires (nanobelts)

ABSTRACT: Semiconductor nanowires (NWs) or nanobelts (NBs) have attracted more and more attention due to their potential application in novel optoelectronic devices. In this review, we present our recent work on novel NB photodetectors, where a three-terminal metal-semiconductor field-effect transistor (MESFET) device structure was exploited. In contrast to the common two-terminal NB (NW) photodetectors, the MESFET-based photodetector can make a balance among overall performance parameters, which is desired for practical device applications. We also present our recent work on graphene nanoribbon/semiconductor NW (SNW) heterojunction light-emitting diodes (LEDs). Herein, by taking advantage of both graphene and SNWs, we have fabricated, for the first time, the graphene-based nano-LEDs. This achievement opens a new avenue for developing graphene-based nano-electroluminescence devices. Moreover, the novel graphene/SNW hybrid devices can also find use in other applications, such as high-sensitivity sensor and transparent flexible devices in the future.     

Molecular aggregation–performance relationship in the design of novel cyclohexylethynyl end-capped quaterthiophenes for solution-processed organic transistors

The synthesis and characterization of cyclohexylethenyl end-capped quaterthiophenes is reported. Additionally, an investigation of the performance of organic field-effect transistors based on these quaterthiophenes in view of the relationship between the solid-state (or aggregate) order and the electronic performance is described. UV–vis absorption measurements revealed that the quaterthiophene with an asymmetrically substituted cyclohexylethynyl end-group induced the formation of H-type aggregates, whereas the quaterthiophene with a symmetrically substituted cyclohexylethynyl end-groups favored the formation of J-type aggregates. Two-dimensional grazing-incidence wide-angle X-ray scattering studies were performed to support the molecular structure-dependent packing of films of the new quaterthiophenes. Solution-processed quaterthiophenes were tested as the active layers of p-type organic field-effect transistors with a bottom gate/top contact geometry. The field-effect mobility of devices that incorporated asymmetric quaterthiophene molecules was quite high, exceeding 0.02 cm²/V s, due to H-aggregation and good in-plane ordering. In contrast, the field-effect mobility of devices that incorporated symmetrical quaterthiophenes, was low, above 5 × 10^?4 cm²/(V s), due to the formation of J-aggregates and poor in-plane ordering. A comparison of the symmetrical and asymmetrical quaterthiophene derivatives revealed that the molecular aggregation-dependent packing, determined by the cyclohexylethynyl end groups, was responsible for influencing the organic field-effect transistor performance.     

Determination of the amino acid tryptophan in protein fibres

Tryptophan can be used as an indicator amino acid for the photostability of proteins. The analysis of tryptophan and its degradation products is hampered by their instability in oxidative or strongly acidic media, or light. Various methods were employed to quantify tryptophan in wool and other protein fibres such as silk and human hair. Acid, alkaline and enzymatic methods were used to hydrolyse protein fibres. The amino acid tryptophan in wool and other protein fibres was determined by a colorimetric method, by amino acid analysis and by reversed-phase HPLC. The different analytical methods were compared with regard to their results. The colorimetric method (p-dimethylamino-benzaldehyde) proved to give reliable results for the tryptophan content in wool and unpigmented protein fibres. This method can be used also for wool dyed with acid, metal complex or reactive dyes or for pigmented keratin fibres after correction for a blank sample. Interference between dye and colorimetric reagent also have to be evaluated.     

Organic nanofibers integrated by transfer technique in field-effect transistor devices

The electrical properties of self-assembled organic crystalline nanofibers are studied by integrating these on field-effect transistor platforms using both top and bottom contact configurations. In the staggered geometries, where the nanofibers are sandwiched between the gate and the source-drain electrodes, a better electrical conduction is observed when compared to the coplanar geometry where the nanofibers are placed over the gate and the source-drain electrodes. Qualitatively different output characteristics were observed for top and bottom contact devices reflecting the significantly different contact resistances. Bottom contact devices are dominated by contact effects, while the top contact device characteristics are determined by the nanofiber bulk properties. It is found that the contact resistance is lower for crystalline nanofibers when compared to amorphous thin films. These results shed light on the charge injection and transport properties for such organic nanostructures and thus constitute a significant step forward toward a nanofiber-based light-emitting device.     

Doping dependent crystal structures and optoelectronic properties of n-type CdSe:Ga nanowries

Although CdSe nanostructures possess excellent electrical and optical properties, efforts to make nano-optoelectronic devices from CdSe nanostructures have been hampered by the lack of efficient methods to rationally control their structural and electrical characteristics. Here, we report CdSe nanowires (NWs) with doping dependent crystal structures and optoelectronic properties by using gallium (Ga) as the efficient n-type dopant via a simple thermal co-evaporation method. The phase change of CdSe NWs from wurtzite to zinc blende with increased doping level is observed. Systematical measurements on the transport properties of the CdSe:Ga NWs reveal that the NW conductivity could be tuned in a wide range of near nine orders of magnitude by adjusting the Ga doping level and a high electron concentration up to 4.5 × 10(19) cm(-3) is obtained. Moreover, high-performance top-gate field-effect transistors are constructed based on the individual CdSe:Ga NWs by using high-κ HfO(2) as the gate dielectric. The great potential of the CdSe:Ga NWs as high-sensitive photodetectors and nanoscale light emitters is also exploited, revealing the promising applications of the CdSe:Ga NWs in new-generation nano-optoelectronics.     

Processing a mixture of short-cut SVM and Kapron fibres into plastics by injection molding

Conclusions -- The possibility has been demonstrated of processing a mixture of short-cut Kapron fibres and SVM fibres into plastics by extrusion and injection molding. Preliminary mixing of the reinforcing filler with the matrix fibres at the stage of cutting makes it possible to ensure a stable ratio of the components and to eliminate the need for using metering devices in introducing the filler into the melt.-- The plastics obtained have high physico-mechanical and antifrictional properties and can be used as constructional materials.VNIIPV (Mytischi). Translated from Khimicheskie Volokna, No. 5, pp. 51–52, September–October, 1992.     

Fabrication of regular arrays of organic crystalline needles using creases formed on oxidized poly(dimethylsiloxane) surfaces

In this study, creases are regularly self-assembled on the oxidized surface of poly(dimethylsiloxane) by swelling-induced buckling instability. These creases are then used as templates for the regular arrangement of crystalline needles. The solution of an organic compound is confined in the aligned creases and dried to generate a crystalline needle in each crease. Thus, the orientation of the crystalline needles and their two-dimensional position could be controlled. The organic compounds used in this study are anthraquinone and 9,10-dibromoanthracene, among which the latter is an organic semiconducting material. It is expected that the method proposed in the study can be used to fabricate regular arrays of organic semiconducting crystalline needles or nanowires that can be used as elements of electronic devices such as organic field-effect transistors and chemical sensors. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47736.     

The characterization and application of p-type semiconducting mesoporous carbon nanofibers

The microstructures of mesoporous carbon nanofibers were characterized by scanning electron microscopy, transmission electron microscopy, nano-Raman, nitrogen adsorption-desorption and optical transmission. They possessed a high specific surface area 840 m² g⁻¹ and a 1.07 eV band gap. All mesoporous carbon nanofiber network can act as the channel material in p-type field-effect transistor devices with field-effect mobilities over 10 cm²/V s. Furthermore, mesoporous carbon nanofiber network exhibits better sensitivity and faster response to NO₂ gas than that of carbon nanotubes, which makes it a promising candidate as poisonous gas sensing nanodevices.     

Effect of atomic layer deposition temperature on the performance of top-down ZnO nanowire transistors

This paper studies the effect of atomic layer deposition (ALD) temperature on the performance of top-down ZnO nanowire transistors. Electrical characteristics are presented for 10-μm ZnO nanowire field-effect transistors (FETs) and for deposition temperatures in the range 120°C to 210°C. Well-behaved transistor output characteristics are obtained for all deposition temperatures. It is shown that the maximum field-effect mobility occurs for an ALD temperature of 190°C. This maximum field-effect mobility corresponds with a maximum Hall effect bulk mobility and with a ZnO film that is stoichiometric. The optimized transistors have a field-effect mobility of 10 cm²/V.s, which is approximately ten times higher than can typically be achieved in thin-film amorphous silicon transistors. Furthermore, simulations indicate that the drain current and field-effect mobility extraction are limited by the contact resistance. When the effects of contact resistance are de-embedded, a field-effect mobility of 129 cm²/V.s is obtained. This excellent result demonstrates the promise of top-down ZnO nanowire technology for a wide variety of applications such as high-performance thin-film electronics, flexible electronics, and biosensing.     

One-Dimensional Nanostructures and Devices of II–V Group Semiconductors

The II–V group semiconductors, with narrow band gaps, are important materials with many applications in infrared detectors, lasers, solar cells, ultrasonic multipliers, and Hall generators. Since the first report on trumpet-like Zn₃P₂ nanowires, one-dimensional (1-D) nanostructures of II–V group semiconductors have attracted great research attention recently because these special 1-D nanostructures may find applications in fabricating new electronic and optoelectronic nanoscale devices. This article covers the 1-D II–V semiconducting nanostructures that have been synthesized till now, focusing on nanotubes, nanowires, nanobelts, and special nanostructures like heterostructured nanowires. Novel electronic and optoelectronic devices built on 1-D II–V semiconducting nanostructures will also be discussed, which include metal–insulator-semiconductor field-effect transistors, metal-semiconductor field-effect transistors, and p–n heterojunction photodiode. We intent to provide the readers a brief account of these exciting research activities.     

In vitro hydrolytic degradation of centrifugally spun polyhydroxybutyrate–pectin composite fibres

BACKGROUND: Centrifugal spinning is a novel fibre‐forming process that readily permits the incorporation of additives while avoiding the thermal damage often associated with conventional melt spinning. Centrifugal spinning of a viscous solution of poly(3‐hydroxybutyrate) (PHB) mixed with pectin was used to fabricate a range of fibres containing different concentrations of this biologically active agent. The influence of this blending on fibre morphology and in vitro degradation in an accelerated hydrolytic model at 70 °C and pH of 10.6 is reported. RESULTS: Blending influenced the physiochemical properties of the fibres, and this significantly affected the degradation profile of both the fibre and its PHB constituent. A greater influence on degradation was exerted by the type of pectin and its degree of esterification than by variations in its loading. CONCLUSION: Centrifugal spinning permits the fabrication of composite fibrous matrices from PHB and pectin. Incorporation of the polysaccharide into the fibres can be used to manipulate degradation behaviour and demonstrates a model for doping of matrices with active biological constituents. The unique features of the centrifugal spinning process, as illustrated by the structure of the fibres and the degradation profiles, suggest possible applications of centrifugally spun biopolymers as wound scaffolding devices and in tissue engineering. Copyright © 2009 Society of Chemical Industry     

Raman spectroscopy of Kevlar fibres during deformation—Caveat emptor

It has been demonstrated that when aromatic polyamide fibres such as Kevlar 49 are subjected to mechanical deformation, significant frequency shifts are obtained for the peak position of the 1610 cm^?1 Raman band using both 632·8 nm and 488 nm laser radiation. Two earlier reports of the deformation of fibres in a 488 nm argon ion laser beam reported no such frequency shifts. It has been shown that this wavelength of laser light can degrade Kevlar fibres. This causes premature failure of the fibres through chain scission and the fibres break at low strains before significant levels of stress or strain can be achieved. Hence, the previous conflicts can be resolved and it has been demonstrated that simultaneous Raman spectroscopy and mechanical deformation is a powerful method of following the micromechanics of fibre deformation.     

Dyeing properties of polyamide super-microfibre with disperse dyes

The dyeing properties of polyamide super-microfibres and conventional fibres dyed with disperse dyes have been studied by measuring the adsorption isotherm, the rate of dye uptake, the time of half-dyeing and the amount of equilibrium adsorption. The thermodynamic analysis shows that the adsorption isotherms of super-microfibres follow a Langmuir sorption model. The kinetic results show that super-microfibres have a faster dyeing rate and a higher equilibrium dye uptake compared to conventional fibres. This can be explained by the greater surface area and dye capacity of the super-microfibres. The wash and light fastness properties of the super-microfibres dyed with disperse dyes are lower than conventional fibres.     

Solar energy conversion with tunable plasmonic nanostructures for thermoelectric devices

The photothermal effect in localized surface plasmon resonance (LSPR) should be fully utilized when integrating plasmonics into solar technologies for improved light absorption. In this communication, we demonstrate that the photothermal effect of silver nanostructures can provide a heat source for thermoelectric devices for the first time. The plasmonic band of silver nanostructures can be facilely manoeuvred by tailoring their shapes, enabling them to interact with photons in different spectral ranges for the efficient utilization of solar light. It is anticipated that this concept can be extended to design a photovoltaic-thermoelectric tandem cell structure with plasmonics as mediation for light harvesting.     

Influence of the ratio of gate length to drain-to-source distance on the electron mobility in AlGaN/AlN/GaN heterostructure field-effect transistors

ABSTRACT: Using measured capacitance-voltage curves with different gate lengths and current-voltage characteristics at low drain-to-source voltage for the AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) of different drain-to-source distances, we found that the dominant scattering mechanism in the AlGaN/AlN/GaN HFETs is determined by the ratio of gate length to drain-to-source distance. For the devices with small ratio (here less than 1/2), the polarization Coulomb field scattering dominates the electron mobility. However, for the devices with large ratio (here more than 1/2), the LO phonon scattering and interface roughness scattering are dominant. The reason is closely related to the polarization Coulomb field scattering.