Improving performance of polymer photovoltaic devices using an annealing-free approach via construction of ordered aggregates in solution

Low crystalline order has been proved to be one of the main hindrances for achieving high performance devices based on thin films composed of crystallizable polymer. In this work, we use a facile method to substantially improve crystallinity of poly(3-hexylthiophene) (P3HT) in its pure or composite film via the construction of ordered precursors in the solution used for thin film deposition. These improvements have been confirmed by bright-field transmission electron micrography, electron diffraction, UV-Vis absorption and wide-angle X-ray diffraction.

Weak epitaxy growth and phase behavior of planar phthalocyanines on p-sexiphenyl monolayer film

We systematically investigated the weak epitaxy growth (WEG) behavior of a series of planar phthalocyanine compounds (MPc), i.e., metal-free phthalocyanine (H2PC), nickel phthalocyanine (NiPc), copper phthalocyanine (CuPc), zinc phthalocyanine (ZnPc), iron phthalocyanine (FePc); cobalt phthalocyanine (CoPc), grown on a p-sexiphenyl (p-6P) monolayer film by selected area electron diffraction (SAED) and atomic force microscopy (AFM). Two types of epitaxial relations, named as incommensurate epitaxy and commensurate epitaxy, were identified between phthalocyanine compounds and the substrate of the p-6P film.

Carbon nanotube/gold nanoparticles/polyethylenimine-functionalized ionic liquid thin film composites for glucose biosensing

A novel glucose biosensor based on immobilization of glucose oxidase (GOD) in thin films of polyethylenimine-functionalized ionic liquid (PFIL), containing a mixture of carbon nanotubes (CNT) and gold nanoparticles (AuNPs) and deposited on glassy carbon electrodes, was developed. Direct electrochemistry of glucose oxidase in the film was observed, with linear glucose response up to 12 mM. The PFIL-stabilized gold nanoparticles had a diameter of 2.4 +/- 0.8 nm and exhibited favorable stability (stored even over one month with invisible change in UV-vis spectroscopic measurements).

Weak Epitaxy Growth of Copper Hexadecafluorophthalocyanine (F16CuPc) on p-Sexiphenyl Monolayer Film

Weak epitaxy growth (WEG) behavior and mechanism of copper hexadecafluorophthalocyanine (F16CuPc) on p-sexiphenyl (p-6P) monolayer film were investigated by atomic force microscopy (AFM), selected area electron diffraction (SEAD), and wide-angle X-ray diffraction (WAXD). High-quality F16CuPc films with high order, large size, and molecular-level smoothness were obtained successfully by WEG method. It was identified that there exists incommensurate epitaxial relation between highly oriented F16CuPc and p-6P films. The geometrical channels of p-6P monolayer surface induce the nucleation and growth of F16CuPc molecules.

Synthesis and Characterization of Coil-Rod-Coil Triblock Copolymers Comprising Fluorene-Based Mesogenic Monodisperse Conjugated Rod and Poly(ethylene oxide) Coil

A series of coil-rod-coil triblock copolymers (i.e., F3T8EO8, F3T8EO17, F3T8EO45, and F3T8EO125) with a mesogenic monodisperse conjugated oligomer comprising 3 fluorene, 8 thiophene, and 2 phenyl units as the rod and poly(ethylene oxide) (PEO) as the coil were synthesized. A reference compound, that is F3T8ME2, with the identical rod but without PEO was also prepared for comparison. The volume fraction of PEO (f(PEO)) was 0, 0.16, 0.28, 0.50, and 0.73 for F3T8ME2, F3T8EO8, F3T8EO17, F3T8EO45, and F3T8EO125, respectively. It was found that the introduction of PEO into the triblock copolymers encouraged the formation of H-type aggregation and f(PEO)-dependent highly ordered mesophases while f(PEO) < 0.73. For F3T8ME2, only nematic mesophase was observed. In contrast, F3T8EO8 and F3T8EO17, with f(PEO) of 0.16 and 0.28, respectively, are smectic A (SA) mesomorphism.

Study on the Single Crystals of Poly(3-octylthiophene) Induced by Solvent-Vapor Annealing

Needle-like single crystals of poly(3-octylthiophene) (P3OT) have been prepared by tetrahydrofuran-vapor annealing. The morphology and structure of the crystals were characterized with optical microscopy, scanning electron microscopy, atomic force microscopy, transmission electron microscopy, and wide-angle X-ray diffraction. It is observed that the P3OT molecules are packed with the backbones parallel to the length axis of the crystal and the alkyl side chains perpendicular to the substrate. The field effect transistor based on the P3OT single crystal exhibited a charge carrier mobility of 1.54 x 10(-4) cm(2)/(Vs) and on/off current ratio of 37, and the molecular orientation of the crystal is ascribed to account for the device performance. The time-dependent morphological evolution demonstrated that the crystals underwent Ostwald ripening when annealed.

Synthesis and characterization of monodisperse oligo(fluorene-co-bithiophene)s

A series of monodisperse oligo(9,9-di-n-octylfluorene-co-bithiophene)s (OFbTs) with molecular lengths of up to 19.5 nm and molecular weights up to 7025 g mol(-1) has been synthesized by a divergent/convergent approach involving Stille coupling reactions. Stille coupling is quite efficient in preparing this class of oligomers, and even the molecule with nine fluorene units and eight bithiophene units (F9Th16) can be synthesized in a yield as high as 70%. Because of easy functionalization of the thiophene ring at its alpha position, no additional protecting group allowing activation for further reaction is necessary. However, the synthetic routes must be optimized to eliminate contamination of the targeting compounds with the homocoupling product of the organotin reagents. Synthesis of the longest oligomer F13Th24 in a relative large quantity is limited by its low yield due to the pronounced ligand-exchange side reactions of the starting materials and reaction intermediates. All oligomers longer than F4Th6 are nematic mesomorphs and exhibit enhanced glass transition temperature and clearing point with increasing molecular length, as revealed by differential scanning calorimetry and polarizing optical microscopy.

Creation of a complex butterfly attractor using a novel Lorenz-type system

A novel Lorenz-type system of nonlinear differential equations is proposed. Unlike the original Lorenz system, where the chaotic dynamics remain confined to the positive half-space with respect to the Z state variable due to a limiting threshold effect, the proposed system enables bipolar swing of this state variable. In addition, the classical set of parameters (a, b, c) controlling the behavior of the Lorenz system are reduced to a single parameter, namely a. Two possible modes of operation are admitted by the system; switching between these two modes results in the creation of a complex butterfly chaotic attractor. Numerical simulations and results from an experimental setup are presented

Carbon nanotubes as materials in nanotechnology

Carbon nanotubes (CNTs) are hollow tubes of sp2-hybridised carbon with diameters of the order of nanometres. Due to their unique physical properties, which include ballistic transport and high mechanical strength, they are of significant interest for technological applications. The electronic properties of CNTs are of particular interest for use as gas sensors, interconnect materials in the semi-conductor industry and as the channel material in CNT based field effect transistors. The primary difficulty associated with the use of CNTs in electronic applications is the inability to control electronic properties at the growth stage; as grown CNTs consist of a mixture of metallic and semi-conducting CNTs. Doping has the potential to solve this problem and is a focus of this thesis. Nitrogen-doped CNTs typically have defective structures; the usual hollow CNT structure is replaced by a series of compartments. Through density functional theory (DFT) calculations and experimental results, we propose an explanation for the defective structures obtained, based on the stronger binding of N to the growth catalyst in comparison to C. In real electronic devices, CNTs need to be contacted to metal, we generate the current-voltage (IV) characteristics of metal-contacted CNTs considering both the effect of dopants and the structure of the interface region on electronic properties. We find that substitutionally doped CNTs produce Ohmic contacts and that scattering at the interface is strongly influenced by structure. In addition, we consider the effect of the common vacancy defects on the electronic properties of large diameter CNTs. Defects increase scattering in the CNT, with the greatest scattering occurring for the largest defect (555777). We validate the independent scattering approximation for small diameter CNTs, which enables mean free paths in large diameter CNTs to be calculated, with a smaller mean free paths found for larger defects.

Development of inversion-mode and junctionless Indium-Gallium-Arsenide MOSFETs

This PhD covers the development of planar inversion-mode and junctionless Al2O3/In0.53Ga0.47As metal-oxidesemiconductor field-effect transistors (MOSFETs). An implant activation anneal was developed for the formation of the source and drain (S/D) of the inversionmode MOSFET. Fabricated inversion-mode devices were used as test vehicles to investigate the impact of forming gas annealing (FGA) on device performance. Following FGA, the devices exhibited a subthreshold swing (SS) of 150mV/dec., an ION/IOFF of 104 and the transconductance, drive current and peak effective mobility increased by 29%, 25% and 15%, respectively. An alternative technique, based on the fitting of the measured full-gate capacitance vs gate voltage using a selfconsistent Poisson-Schrödinger solver, was developed to extract the trap energy profile across the full In0.53Ga0.47As bandgap and beyond. A multi-frequency inversion-charge pumping approach was proposed to (1) study the traps located at energy levels aligned with the In0.53Ga0.47As conduction band and (2) separate the trapped charge and mobile charge contributions. The analysis revealed an effective mobility (μeff) peaking at ~2850cm2/V.s for an inversion-charge density (Ninv) = 7*1011cm2 and rapidly decreasing to ~600cm2/V.s for Ninv = 1*1013 cm2, consistent with a μeff limited by surface roughness scattering. Atomic force microscopy measurements confirmed a large surface roughness of 1.95±0.28nm on the In0.53Ga0.47As channel caused by the S/D activation anneal. In order to circumvent the issue relative to S/D formation, a junctionless In0.53Ga0.47As device was developed. A digital etch was used to thin the In0.53Ga0.47As channel and investigate the impact of channel thickness (tInGaAs) on device performance. Scaling of the SS with tInGaAs was observed for tInGaAs going from 24 to 16nm, yielding a SS of 115mV/dec. for tInGaAs = 16nm. Flat-band μeff values of 2130 and 1975cm2/V.s were extracted on devices with tInGaAs of 24 and 20nm, respectively

On the adsorption of hexaammineruthenium (III) at anionic self-assembled monolayers

The binding of the electroactive hexaammineruthenium (III) complex ions to anionic self-assembled monolayers (SAMs) has been investigated by means of chronocoulometry and ac voltammetry. From chronocoulometric data recorded in 10-2 M LiClO4 containing different [Ru(NH3)6]3+ concentrations, we have established the adsorption isotherm of [Ru(NH3)6]3+ on a compact monolayer of 2-mercaptobenzimidazole-5-sulfonate (MBIS) self-assembled on Au(1 1 1). The data were satisfactorily fitted to the linearized Langmuir adsorption isotherm and a binding constant of 4.0 (±0.4) × 106 M-1 has been determined. The electrostatic binding of [Ru(NH3)6]3+ to a dilute PNA-DNA monolayer formed after hybridization on a PNA-modified gold electrode by self-assembly from a mixed solution of mercaptobutan-1-ol and PNA oligonucleotides has been studied by ac voltammetry. The admittance of the PNA-modified electrode after hybridization with complementary DNA was measured in 0.01 M Tris-HCl buffer containing different [Ru(NH3)6]3+ concentrations. Based on these data, a binding constant of [Ru(NH3)6]3+ to the surface-confined PNA-DNA duplex was derived from the Langmuir isotherm and amounts to 2.9 (±0.3) × 105 M-1. As the interactions between [Ru(NH3)6]3+ and the immobilized PNA-DNA hybrids on the gold surface are essentially electrostatic, the adsorption of the highly charged cationic redox complex at low concentrations to the negatively charged PNA-DNA modified surface is in large competition with other monovalent cations present in the electrolyte at higher concentrations. The influence of competing sodium cations was thus studied by adding different NaCl concentrations in the 0.01 M Tris-HCl electrolyte. © 2008 Elsevier Ltd. All rights reserved.

Ferroelectric hafnium oxide: A CMOS-compatible and highly scalable approach to future ferroelectric memories

With the ability to engineer ferroelectricity in HfO2 thin films, manufacturable and highly scaled MFM capacitors and MFIS-FETs can be implemented into a CMOS-environment. NVM properties of the resulting devices are discussed and contrasted to existing perovskite based FRAM.

New SR drive with integrated charging capacity for plug-in hybrid electric vehicles (PHEVs)

Plug-in hybrid electric vehicles (PHEVs) provide much promise in reducing greenhouse gas emissions and, thus, are a focal point of research and development. Existing on-board charging capacity is effective but requires the use of several power conversion devices and power converters, which reduce reliability and cost efficiency. This paper presents a novel three-phase switched reluctance (SR) motor drive with integrated charging functions (including internal combustion engine and grid charging). The electrical energy flow within the drivetrain is controlled by a power electronic converter with less power switching devices and magnetic devices. It allows the desired energy conversion between the engine generator, the battery, and the SR motor under different operation modes. Battery-charging techniques are developed to operate under both motor-driving mode and standstill-charging mode. During the magnetization mode, the machine's phase windings are energized by the dc-link voltage. The power converter and the machine phase windings are controlled with a three-phase relay to enable the use of the ac-dc rectifier. The power converter can work as a buck-boost-type or a buck-type dc-dc converter for charging the battery. Simulation results in MATLAB/Simulink and experiments on a 3-kW SR motor validate the effectiveness of the proposed technologies, which may have significant economic implications and improve the PHEVs' market acceptance

A potentiometric biosensor for rapid on-site disease diagnostics

Quantitative point-of-care (POC) devices are the next generation for serological disease diagnosis. Whilst pathogen serology is typically performed by centralized laboratories using Enzyme-Linked ImmunoSorbent Assay (ELISA), faster on-site diagnosis would infer improved disease management and treatment decisions. Using the model pathogen Bovine Herpes Virus-1 (BHV-1) this study employs an extended-gate field-effect transistor (FET) for direct potentiometric serological diagnosis. BHV-1 is a major viral pathogen of Bovine Respiratory Disease (BRD), the leading cause of economic loss ($2 billion annually in the US only) to the cattle and dairy industry. To demonstrate the sensor capabilities as a diagnostic tool, BHV-1 viral protein gE was expressed and immobilized on the sensor surface to serve as a capture antigen for a BHV-1-specific antibody (anti-gE), produced in cattle in response to viral infection. The gE-coated immunosensor was shown to be highly sensitive and selective to anti-gE present in commercially available anti-BHV-1 antiserum and in real serum samples from cattle with results being in excellent agreement with Surface Plasmon Resonance (SPR) and ELISA. The FET sensor is significantly faster than ELISA (<10 min), a crucial factor for successful disease intervention. This sensor technology is versatile, amenable to multiplexing, easily integrated to POC devices, and has the potential to impact a wide range of human and animal diseases.

Nanosensor for assessing the risk of a cardiovascular disease

The incidence of cardiovascular diseases (CVD) has been increasing according to the European and global statistics. Thus, the development of new analytical devices, such as biosensors for assessing the risk of CVD could become a valuable approach for the improvement of healthcare service. In latest years, the nanotechnology has provided new materials with improved electronic properties which have an important contribution in the transduction mechanism of biosensors. Thus, in this thesis, biosensors based on field effect transistors with single-walled carbon nanotubes (NTFET) were developed for the detection of C-reactive protein (CRP) in clinical samples, that is, blood serum and saliva from a group of control patients and a group of CVD risk patients. CRP is an acute-phase protein, which is commonly known as the best validated biomarker for the assessment of CVD, the single-walled carbon nanotubes (SWCNT) were applied as transduction components, and the immunoreaction (interaction between the CRP antigen and the antibodies specific to CRP) was used as the mechanism of molecular recognition for the label-free detection of CRP. After the microfabrication of field effect transistors (FET), the screening of the most important variables for the dispersion of SWCNT, the assemblage of NTFET, and their application on standard solutions of CRP, it was found that NTFET respond accurately to CRP both in saliva and in serum samples, since similar CRP levels were found with the NTFET and the traditional methodology (ELISA technique). On the other hand, a strong correlation between salivary and serum CRP was found with NTFET, which means that saliva could be used, based on non-invasive sampling, as an alternative fluid to blood serum. It was also shown that NTFET could discriminate control patients from CVD risk patients, allowing the determination of a cut-off value for salivary CRP of 1900 ng L-1, which corresponds to the well established cut-off of 3 mg L-1 for CRP in serum, constituting an important finding for the possible establishment of a new range of CRP levels based on saliva. According to the data provided from the volunteer patients regarding their lipoprotein profile and lifestyle factors, it was concluded that the control and the CVD risk patients could be separated taking into account the various risk factors established in literature as strong contributors for developing a CVD, such as triglycerides, serum CRP, total cholesterol, LDL cholesterol, body mass index, Framingham risk score, hypertension, dyslipidemia, and diabetes mellitus. Thus, this work could provide an additional contribution to the understanding of the association of biomarkers levels in serum and saliva samples, and above all, cost-effective, rapid, label-free, and disposable NTFET were developed, based on a noninvasive sampling, for the assessment of CVD risk, thus constituting a potential point-of-care technology.