Solution-processed n-type fullerene field-effect transistors prepared using CVD-grown graphene electrodes: improving performance with thermal annealing

Solution-processed organic field effect transistors (OFETs) have generated significant interest as key elements for use in all-organic electronic applications aimed at realizing low-cost, lightweight, and flexible devices.

The origin of excellent gate-bias stress stability in organic field-effect transistors employing fluorinated-polymer gate dielectrics

Tuning of the energetic barriers to charge transfer at the semiconductor/dielectric interface in organic field-effect transistors (OFETs) is achieved by varying the dielectric functionality. Based on this, the correlation between the magnitude of the energy barrier and the gate-bias stress stability of the OFETs is demonstrated, and the origin of the excellent device stability of OFETs employing fluorinated dielectrics is revealed.

Test of prototype ITER vacuum ultraviolet spectrometer and its application to impurity study in KSTAR plasmas

To optimize the design of ITER vacuum ultraviolet (VUV) spectrometer, a prototype VUV spectrometer was developed. The sensitivity calibration curve of the spectrometer was calculated from the mirror reflectivity, the grating efficiency, and the detector efficiency. The calibration curve was consistent with the calibration points derived in the experiment using the calibrated hollow cathode lamp. For the application of the prototype ITER VUV spectrometer, the prototype spectrometer was installed at KSTAR, and various impurity emission lines could be measured. By analyzing about 100 shots, strong positive correlation between the O VI and the C IV emission intensities could be found.

Colloidal nanocrystals with inorganic halide, pseudohalide, and halometallate ligands

We investigate simple halides and pseudohalides as an important class of inorganic ligands for nanocrystals (NCs) in solution phase ligand exchange. These short, robust, and easy to model ligands bind to the NC surface and provide electrostatic stabilization of NC dispersions in N-methylformamide. The replacement of organic ligands on NCs with compact halide and pseudohalide ligands greatly facilitates electronic communication between NCs. For example, a high electron mobility of μ ≈ 12 cm(2) V(-1) s(-1) has been observed in thin films made of I(-)-capped CdSe NCs. We also studied charge transport properties of thin films based on the pseudohalide N3(-)-capped InAs NCs, suggesting the possibility of obtaining "all III-V" NC solids. In addition, we extend the surface chemistry of halometallates (e.g., CH3NH3PbI3), which can stabilize colloidal solutions of lead chalcogenide NCs. These halide, pseudohalide, and halometallate ligands enrich the current family of inorganic ligands and can open up more opportunities for applications of NCs in the fields of electronics, optoelectronics, and thermoelectrics.

High-performance organic complementary inverters using monolayer graphene electrodes

Chemical vapor deposition-grown graphene has been an attractive electrode material for organic electronic devices, such as organic field-effect transistors (OFETs), because it is highly conductive and provides good oxidation and thermal stability properties. However, it still remains a challenge to demonstrate organic complementary circuits using graphene electrodes because of the relatively poor performance of n-type OFETs. Here, we report the development of high-performance organic complementary inverters using graphene as source/drain electrodes and N, N'-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C13) and pentacene as n- and p-type organic semiconductors, respectively. Graphene electrodes were n-doped via the formation of NH2-terminated self-assembled monolayers that lowered the work function and the electron injection barrier between the graphene and PTCDI-C13. Thermal annealing improved the molecular packing among PTCDI-C13 groups on the graphene surface, thereby increasing the crystallinity and grain size. The thermally annealed PTCDI-C13 OFETs prepared using n-doped graphene electrodes exhibited a good field-effect mobility of up to 0.43 cm2/(V s), which was comparable to the values obtained from other p-type pentacene OFETs. By integrating p- and n-type OFETs, we successfully fabricated organic complementary inverters that exhibited highly symmetric operation with an excellent voltage gain of up to 124 and good noise margin.

Temperature-dependent Hall and field-effect mobility in strongly coupled all-inorganic nanocrystal arrays

We report on the temperature-dependent Hall effect characteristics of nanocrystal (NC) arrays prepared from colloidal InAs NCs capped with metal chalcogenide complex (MCC) ligands (In2Se4(2-) and Cu7S4(-)). Our study demonstrates that Hall effect measurements are a powerful way of exploring the fundamental properties of NC solids. We found that solution-cast 5.3 nm InAs NC films capped with copper sulfide MCC ligands exhibited high Hall mobility values over 16 cm(2)/(V s). We also showed that the nature of MCC ligands can control doping in NC solids. The comparative study of the temperature-dependent Hall and field-effect mobility values provides valuable insights concerning the charge transport mechanism and points to the transition from a weak to a strong coupling regime in all-inorganic InAs NC solids.

Bi(1)-(x)Sb(x) alloy nanocrystals: colloidal synthesis, charge transport, and thermoelectric properties

Nanostructured Bi1-xSbx alloys constitute a convenient system to study charge transport in a nanostructured narrow-gap semiconductor with promising thermoelectric properties. In this work, we developed the colloidal synthesis of monodisperse sub-10 nm Bi1-xSbx alloy nanocrystals (NCs) with controllable size and compositions. The surface chemistry of Bi1-xSbx NCs was tailored with inorganic ligands to improve the interparticle charge transport as well as to control the carrier concentration. Temperature-dependent (10-300 K) electrical measurements were performed on the Bi1-xSbx NC based pellets to investigate the effect of surface chemistry and grain size (∼10-40 nm) on their charge transport properties. The Hall effect measurements revealed that the temperature dependence of carrier mobility and concentration strongly depended on the grain size and the surface chemistry, which was different from the reported bulk behavior. At low temperatures, electron mobility in nanostructured Bi1-xSbx was directly proportional to the average grain size, while the concentration of free carriers was inversely proportional to the grain size. We propose a model explaining such behavior. Preliminary measurements of thermoelectric properties showed a ZT value comparable to those of bulk Bi1-xSbx alloys at 300 K, suggesting a potential of Bi1-xSbx NCs for low-temperature thermoelectric applications.

Self-organizing properties of triethylsilylethynyl-anthradithiophene on monolayer graphene electrodes in solution-processed transistors

Graphene has shown great potential as an electrode material for organic electronic devices such as organic field-effect transistors (FETs) because of its high conductivity, thinness, and good compatibility with organic semiconductor materials. To achieve high performance in graphene-based organic FETs, favorable molecular orientation and good crystallinity of organic semiconductors on graphene are desired. This strongly depends on the surface properties of graphene. Here, we investigate the effects of polymer residues that remain on graphene source/drain electrodes after the transfer/patterning processes on the self-organizing properties and field-effect characteristics of the overlying solution-processed triethylsilylethynyl-anthradithiophene (TES-ADT). A solvent-assisted polymer residue removal process was introduced to effectively remove residues or impurities on the graphene surface. Unlike vacuum-deposited small molecules, TES-ADT displayed a standing-up molecular assembly, which facilitates lateral charge transport, on both the residue-removed clean graphene and as-transferred graphene with polymer residues. However, TES-ADT films grown on the cleaned graphene showed a higher crystallinity and larger grain size than those on the as-transferred graphene. The resulting TES-ADT FETs using cleaned graphene source/drain electrodes therefore exhibited a superior device performance compared to devices using as-transferred graphene electrodes, with mobilities as high as 1.38 cm(2) V(-1) s(-1).

A Study on the Reactive Compatibilization of a PBT/LCP Blend: Catalyst Effect

The in situ compatibilization of poly(butylene terephthalate) (PBT) with liquid crystalline polymer (LCP) via catalyzed transesterification reaction was examined through thermal, rheological, morphological and mechanical studies. The addition of catalyst, dibutyltindilaurate, was found to promote the transesterification between PBT and LCP. Maintenance of high vacuum environment was required to produce the high molecular weight copolymers in the reactor, which, acting at the interface, diminished the size of the dispersed phase (LCP) and enhanced interfacial adhesion that led to an early increase of the flexural strength. Flexural strength was reduced after long time reaction due to the chain scission. Transesterification confirmed by NMR spectroscopic analysis played a major role in the interchange process.

High-performance triethylsilylethynyl anthradithiophene transistors prepared without solvent vapor annealing: the effects of self-assembly during dip-coating

Solution-processable small-molecule organic semiconductors have recently attracted significant attention for use as the active channel layers in organic field-effect transistors due to their good intrinsic charge carrier mobility and easy processability. Dip-coating is a good method for optimizing the film morphology and molecular ordering of the small-molecular semiconductors because the drying speed can be quantitatively controlled at the air-solution-substrate contact line. Here, we report the preparation of highly crystalline triethylsilylethynyl-anthradithiophene (TES-ADT) crystal arrays that exhibit an excellent field-effect mobility (up to 1.8 cm(2)/(V s)) via an optimized one-step dip-coating process. High-quality TES-ADT crystals were grown without solvent vapor annealing postprocessing steps, which were previously thought to be essential for improving the morphology, crystallinity, and electrical characteristics of TES-ADT thin films. An interesting correlation between the optimal pull-out rate and the self-assembly tendencies of some soluble acene semiconductors was observed, and the origin of the correlation was investigated. Our work demonstrates an alternative simple approach to achieving highly crystalline TES-ADT thin films, and further proposes a prospective method for optimizing the formation of thin films via the molecular self-assembly of soluble acenes.

Disability in atypical parkinsonian syndromes is more dependent on memory dysfunction than motor symptoms

BACKGROUND

There is a gap in the systematic description and investigation of functional disability in corticobasal syndrome (CBS) and progressive supranuclear palsy (PSP). Additionally, the relations between disability, apraxia, cognitive and behavioural changes are not well understood in atypical parkinsonian syndromes.

METHODS

Fifty patients were included in this study (CBS = 18; PSP = 11), including a subgroup of primary progressive aphasia-nonfluent variant (PPA-nfv = 21) who were used as a control group given the clinic-pathological overlap. Functional disability (basic and instrumental activities of daily living), general cognition and behavioural changes were evaluated at baseline, with a subgroup of patients being reassessed after 16 months.

RESULTS

The corticobasal syndrome group had the most marked disability in basic activities in comparison to progressive supranuclear palsy and primary progressive aphasia-nonfluent variant. Longitudinal decline was marked for all three groups. In a linear regression examining factors behind functional disability in CBS and PSP, memory dysfunction emerged as the main factor (48.5%), followed by apraxia (14.9%) and atypical parkinsonian symptoms (9.6%).

CONCLUSIONS

Memory dysfunction is the most important factor in functional disability in CBS and PSP, which has to be taken into consideration in disease management, prognosis and planning of services to fully address patients' and families' needs.