Synthesis and characteristics of a solution-processable fullerene derivative for n-type organic field-effect transistors

A fullerene molecule, C60TH2-DcB, was prepared by Prato reaction which provides better product yields and purity compared with the reaction for the synthesis of [60]methanofullerene analogues. The C60TH2-DcB is readily soluble in common organic solvents and shows good thermal properties. Field-effect transistors fabricated by solution processing exhibit good n-channel characteristics with a maximum mobility of 1.5 × 10⁻³ cm² V⁻¹ s⁻¹ with a threshold voltage of 11 V and on/off current ratio of 1.0 × 10⁵.     

Porous polypyrrole/polymethylmethacrylate composite film prepared by vapor deposition polymerization of pyrrole and its application for ammonia detection

A simple method has been developed to fabricate porous polypyrrole/polymethyl methacrylate composite films. The synthesis procedures include the vapor deposition polymerization of pyrrole on the composite films of polymethyl methacrylate and ferric hydroxide bis(1,4-bis(2-ethylhexyl) sulfosuccinate), successively, washing the obtained composite films with methanol. Scanning electron microscopic and microscopic Raman spectral studies indicated that the pores had an average size of about 5 μm and they were uniformly dispersed in the whole films. The electrical conductivities of the composite films were measured to be in the range of 10^− 3 to 10^− 2 S cm^− 1. The porous composite films showed electroactivity, and the sensors based on them exhibited high sensitivity and fast response to ammonia gas.     

Construction of new iodide selective electrodes based on bis(trans-cinnamaldehyde)1,3-propanediimine(L) zinc(II) chloride [ZnLCl2] and bis(trans-cinnamaldehyde) 1,3-propanediimine(L) cadmium(II) chloride [CdLCl2]

New plasticized PVC membranes iodide selective electrodes have been prepared by incorporating bis(trans-cinnamaldehyde)1,3-propanediimine zinc(II) chloride [ZnLCl2] and bis(trans-cinnamaldehyde) 1,3-propandiimine cadmium(II) chloride [CdLCl2] on the surface of graphite disk electrodes. At optimum value of variables the proposed electrodes have selective response to iodide with respect to a number of inorganic and organic anions with near-Nernstian slopes of − 60 ± 1.9 and − 58.5 ± 1.9 mV/decade of iodide concentration over the range 1.0 × 10^− 6-1.0 × 10^− 1 M with detection limits of 4.0 × 10^− 7 and 3.0 × 10^− 7 M for the electrodes based on [ZnLCl₂] and [CdLCl₂], respectively. The electrodes based on both ionophores have response times of about (6 s), with stable reproducible response during 2 months, while their responses is independent of pH over the range 2.5-10.5. The proposed electrodes successfully have been applied for evaluation of iodide ion content in real samples with complicated matrices including water and pharmaceutical samples.     

The influences of substrate temperature on ambipolar organic heterojunction transistors

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/V s for hole and 1.04 × 10⁻² cm²/V s 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.     

Determination of charge carrier mobility of hole transporting polytriarylamine-based diodes

Hole transport properties of three different side chain poly(triarylamines) have been determined by means of the analysis of steady-state current-voltage characteristics using co-planar diode structures. The interpretation is based on space-charge limited models with field-dependent mobility. Mobilities between ~ 10^− 8 and 10^− 6 cm² V^− 1 s^− 1 are obtained. The highest mobility is achieved for poly(tetraphenylbenzidine) devices and the lowest for poly(triphenylamine) devices. Electron-rich methoxy substituents increase the mobility of poly(triphenylamine)s. A comparison of the mobility values with those obtained using organic field-effect transistors is also given.     

A novel urea biosensor based on zirconia

Electrochemically deposited biocompatible zirconia (ZrO₂) film on gold coated glass electrodes has been utilized for the fabrication of urea biosensor. The prepared ZrO₂ films and bioelectrodes have been characterized using Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and electrochemical techniques, respectively. The urea biosensor, fabricated by immobilizing mixed enzyme [urease (Urs) and glutamate dehydrogenase (GLDH)] on this nanobiomaterial, shows linearity up to 40 mg dL^− 1 of analyte (urea) and sensitivity of 0.071 μA/(mM cm^− 2) with stability up to 4 months when stored at 4 °C. The low value of Michaelis-Menten constant (K_m) estimated using Hans plot as 0.5 mM indicates enhancement in the affinity and/or activity of enzyme attached to this nanostructured biocompatible matrix.     

Flexible organic field-effect transistors and complementary inverters based on a solution-processable quinoidal oligothiophene derivative

We report on the fabrication and characterization of ambipolar organic field-effect transistors based on the solution-processable quinoidal oligothiophene [QQT(CN)4] and using a new fluorinated polymer (AL-X601) with a dielectric constant of 3.1 as dielectric material layer. As-prepared devices show ambipolar transport with hole and electron field-effect mobilities of 6 × 10⁻² and 5 × 10⁻³ cm²/V s respectively as well as an on and off state current ratio higher than 10³. Influence of a thermal annealing on the device performances was investigated and was found to lead to a majority carrier type conversion from a p-type to an n-type dominant behavior. QQT(CN)4 based field-effect transistors and complementary inverters fabricated on flexible substrates and using Al-X601 as gate dielectric material show high performance and good mechanical stability.     

Demonstration of logic AND device using a split-gate pentacene field effect transistor

We report on the fabrication and performance of pentacene-based split-gate field effect transistors (FETs) on doped Si/SiO₂ substrates. Several transistors with split gate structures were fabricated and demonstrated AND logic functionality. The transistor’s functionality was controlled by applying either 0 or − 10 V to each of the gate electrodes. When − 10 V was simultaneously applied to both gates, the transistor was conductive (ON), while any other combination of gate voltages rendered the transistor highly resistive (OFF). A significant advantage of this device is that AND logic devices with multiple inputs can be built using a single pentacene channel with multiple gates. The p-type carrier mobility of charge within the pentacene active layer of these transistors was about 10^− 5 cm²/V-s. We attribute the low value of mobility primarily to the sharp contours of the pentacene film between the drain and the source contacts and to defects in the pentacene film. The average charge density was 1.4 × 10¹² holes/cm². Despite low mobility, the devices operated at lower drain-source (V_DS) and gate-source (V_GS) voltages as compared with previously reported pentacene based FETs.     

Organic field-effect transistors with thermal-cured polyacrylate gate dielectric films

Chemically and thermally stable, durable, thermal-cured polyacrylates having a hydrophobic nature, which were prepared by mixing polyacrylate having reactive sites and functional-anhydride, exhibit good insulation properties and high breakdown voltage (> 4.0 MV/cm) as a dielectric. Plastic-based organic thin-film transistors with the thermal-acryl dielectric layer showed typical current-voltage characteristics; the field-effect mobility was calculated to be 0.22 cm² V^− 1 s^− 1, while the threshold voltage was approximately − 8 V. It has been found that thin dielectric layers gave higher field-effect mobility.     

Amorphous oxide channel TFTs

Thin film transistors (TFTs) using amorphous oxides of post-transition metals: indium, gallium, and zinc for the channel materials are fabricated with radio-frequency magnetron sputtering methods for the deposition of the channel and the gate insulator layers, at room temperature with no high-temperature post-deposition annealing process. The TFTs operate as n-channel field-effect transistors with various structures of top/bottom gate and top/bottom source-and-drain contact including the inverse-stagger types, and with various materials for the gate insulators, the electrodes, and the substrates. The TFTs having smoother channel interfaces show the better performance at the saturation mobility beyond 10 cm² V^− 1 s^− 1 and the on-to-off current ratio over 10⁸ than the rough channel interfaces. The ring oscillator circuits operate with five-stage inverters of the top-gate TFTs or the inverse-stagger TFTs. Organic light-emission diode cells are driven by a simple circuit of the TFTs. It is also found by a combinatorial approach to the material exploration that the TFT characteristics can be controlled by the composition ratio of the metals in the channel layers. The amorphous oxide channel TFTs fabricated with sputtering deposition at low temperature could be a candidate for key devices of large-area flexible electronics.     

Device based on the coupling of an organic light-emitting diode with a photoconductive material

We have realized a device based on the coupling of an organic light-emitting diode (with tri(8-hydroxyquinoline)aluminium for light emission) as an input unit with a photoconductive material as an output unit. Various photoconductive materials like pentacene, Cu-phtalocyanine and fullerene were investigated under green light illumination with an emission peak at 550 nm. Photocurrent measurements versus light intensity and bias voltage (applied between two 50 μm distant indium-tin oxide bottom electrodes for the current to flow through the materials) were realized at room temperature a photocurrent gain around 4 is obtained when the materials are subjected to a luminance of about 5000 cd/m² and for bias voltage of − 50 V. Besides, it was shown that to obtain a device with a fast photocurrent response by switching the light off and on, it is necessary to apply a bias voltage higher than − 200 V in these conditions, the gain is multiplied by a factor of 3.     

Solution-processed zinc tetrabenzoporphyrin thin-films and transistors

Thin-films and organic field-effect transistors fabricated from a solution-processable precursor of zinc tetrabenzoporphyrin (ZnTBP) are reported. Amorphous, insulating precursor films were deposited by spin-casting and thermally converted into polycrystalline, semiconducting thin-films comprising grains on the order of 5 μm in diameter. Thin-film X-ray diffraction indicates a monoclinic unit cell with molecules arranged in a herringbone pattern, which in conjunction with optical and atomic force microscopy indicate a thin-film with grains comprised of randomly oriented ZnTBP aggregates. Optical absorption measurements display broad absorption with bands characteristic of a D_4h symmetric porphyrin molecule. Organic field-effect transistors displayed field-effect mobilities on the order of 10^− 2 cm²/V s and ON-/OFF-current ratios exceeding 10².     

Conductive thin film multilayers of gold on glass formed by self-assembly of multiple size gold nanoparticles

Highly conductive thin films of gold have been fabricated on glass substrates by the deposition of gold nanoparticles of two different diameters. A deposition sequence, alternating between 2.6-nm and 12-nm diameter particles, was used whereby the 2.6-nm particles served to fill in the gaps created by the assembly of the larger 12-nm diameter particles. The resulting thin films, with thicknesses of less than 35 nm, displayed high conductivities, yet were fabricated in substantially fewer deposition cycles than required by previous methods. Analysis of surface morphology performed by atomic force microscopy and scanning electron microscopy showed that the high conductivity is the result of a less porous surface structure than can be achieved through the layering of a single size nanoparticle. Conductivity analysis was performed by 4-point probe with resistivities of 5.00 ± 0.4 × 10^− 6 Ω m for 5 layers and 4.49 ± 0.2 × 10^− 6 Ω m for the 6-layer films.     

Contact resistance variation in top-contact organic thin-film transistors with the deposition rate of Au source/drain electrodes

We investigated the effect of the deposition rate of Au source/drain electrodes on the contact resistance of the top-contact organic thin-film transistors (OTFTs). For the formation of source/drain contacts, Au was thermally deposited at the different rates of 0.5, 1.0, 5.0, and 13.0 Å/s. With increasing the Au deposition rate, the contact resistance extracted at the gate voltage of − 30 V could be reduced from 14 × 10⁶ to 2.4 × 10⁶ Ω, resulting in the characteristic improvements of the top-contact OTFT. It is also found that the contact resistance significantly affects the off-state currents of the device having the short channel length of 10 μm. The control of the deposition rate of source/drain electrodes is suggested to optimize the contact properties of the top-contact OTFTs as well as the device performance.     

All-organic polymer-dispersed liquid crystal light-valves integrated with electroactive anthraquinone-2-sulfonate-doped polypyrrole thin films as driving electrodes

All-organic PDLC (polymer-dispersed liquid crystal) light-valves using all-polymer conductive substrates containing thin films of polypyrrole doped with anthraquinone-2-sulfonate (AQSA⁻) as the driving electrodes were fabricated in this study. The all-polymer conductive substrates were prepared under ambient conditions by in situ depositing polypyrrole thin films on blank flexible poly(ethylene terephthalate), or PET, substrates from aqueous media in which oxidative polymerization of pyrrole was taking place. The obtained flexible all-polymer conductive substrates were semi-transparent with cohesive coatings of AQSA⁻-doped polypyrrole thin films (thickness ∼55 nm). The all-polymer flexible conductive substrates had sheet resistivity ∼40 kΩ □ ⁻¹and T% transparency against air ∼78% at 600 nm. The light-valves fabricated using the above all-polymer conductive substrates showed ∼50% transparency against air at 600 nm when 4 V μm⁻¹ electric field was applied.     

Multicomponent oxide thin-film transistors fabricated by a double-layer inkjet printing process

In this work we report on the fabrication and characterization of multicomponent metal oxide thin-film transistors with a double-layer inkjet printing process. Both the active area and source-drain electrodes of the devices are printed with inks based on metal salt precursors to form Ga₂O₃-In₂O₃-ZnO and In₂O₃-SnO respectively. Electrical characterization has shown that the devices' performance, apart from the active area composition, can also be affected by the printing drop spacing. In general, devices printed with Ga:In:Zn 2:4:1 composition present the highest field effect mobility (~ 1.75-3 cm² V⁻¹ s⁻¹). More stable devices with improved switching, but with a compromise over field effect mobility (~ 0.5-0.9 cm² V⁻¹ s⁻¹) were obtained for the 2:4:2 composition.     

L-Aspartic acid/L-cysteine/gold nanoparticle modified microelectrode for simultaneous detection of copper and lead

This paper presents an electrochemical microsensor for simultaneous detection of copper (II) and lead (II) using an l-aspartic acid/l-cysteine/gold nanoparticle modified microelectrode. The microelectrode was fabricated by Micro Electro-Mechanical System technique. The complex of gold nanoparticles (AuNPs) and amino acid with carboxyl group was used as the selective ligand for metal ions. The microelectrode was firstly modified with AuNPs to increase the sensitive area of the working electrode. Subsequently, the AuNPs/gold electrode was modified with l-cysteine and then covalently linked with a monolayer of l-aspartic acid using glutaraldehyde. Electrochemical analysis of metal ions was achieved by using square wave voltammetry without stirring. The microsensor exhibited an excellent linear range from 5 μg L^− 1 to 2000 μg L^− 1 with the limit of detection of 1 μg L^− 1. This metal ion detection method based on l-aspartic acid/l-cysteine/gold nanoparticle modified microelectrode is simple, sensitive and it could be used for electrochemical analysis of copper (II) and lead (II).     

Enhancement-mode thin film transistor with nitrogen-doped ZnO channel layer deposited by laser molecular beam epitaxy

The thin film transistors (TFTs) based on nitrogen doped zinc oxide (ZnO) were investigated by laser molecular beam epitaxy. The increase of ZnO films' resistivity by nitrogen doping was found and applied in enhancement mode ZnO-TFTs. The ZnO-TFTs with a conventional bottom-gate structure were fabricated on thermally oxidized p-type silicon substrate. Electrical measurement has revealed that the devices operate as an n-channel enhancement mode and exhibit an on/off ratio of 10⁴. The threshold voltage is 5.15 V. The channel mobility on the order of 2.66 cm² V^− 1 s^− 1 has been determined.     

Improved performance of fluorinated copper phthalocyanine thin film transistors using an organic pn junction: Effect of copper phthalocyanine film thickness

We have investigated the effect of film thickness of copper phthalocyanine (CuPc) on improving fluorinated copper phthalocyanine (F₁₆CuPc) thin film transistor (TFT) performance with an organic pn junction. Electron field-effect mobility is exponentially enhanced up to 2.0 × 10^− 2 cm² V^− 1 s^− 1 with increasing of CuPc film thickness, and then unchanged when the CuPc thickness is over the saturation thickness (3 monolayers). The charge carrier density at the interface of F₁₆CuPc/CuPc decreases the total TFT resistance, which leads to the increase of mobility. Threshold voltage is suppressed with increasing CuPc films. On the other hand, larger current on/off ratio is obtained when islanded CuPc films are formed on the surface of F₁₆CuPc films. Therefore, employing an organic pn junction is an effective and simple method to fabricate high performance of n-channel transistors for practical applications.     

Electrochemical studies of cystine modified self-assembled monolayer for Escherichia coli detection

An electrochemical DNA biosensor based on cystine modified self-assembled monolayer (cys-SAM) onto gold electrode (AuE) has been fabricated for Escherichia coli (E. coli) detection. This biosensing electrode has been characterized using scanning electron microscopy (SEM), FT-IR spectroscopy, cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). Under the optimum conditions, this DNA biosensor can be used to detect complementary target DNA concentration in the range of 1 × 10^− 6 M to 1 × 10^− 20 M within 60 s of hybridization time at 25 °C and has been found to be stable for about four months when stored at 4 °C.