Annealing and doping-dependent magnetoresistance in single layer poly(3-hexyl-thiophene) organic semiconductor device

We compare the current density–voltage (J–V) and magnetoconductance (MC) response of a poly(3-hexyl-thiophene) (P3HT) device (Au/P3HT(350 nm)/Al) before and after annealing above the glass transition temperature of 150 °C under vacuum. There is a decrease of more than 3 orders of magnitude in current density due to an increase of the charge injection barriers after de-doping through annealing. An increase, approaching 1 order of magnitude, in the negative MC response after annealing can be explained by a shift in the Fermi level due to de-doping, according to the bipolaron mechanism. We successfully tune the charge injection barrier through re-doping by photo-oxidation. This leads to the charge injection and transport transitioning from unipolar to ambipolar, as the bias increases, and we model the MC response using a combination of bipolaron and triplet-polaron interaction mechanisms.     

Photoacoustic Thermal Characterization of Porous Rare-Earth Phosphate Ceramics

The laser induced non-destructive photoacoustic technique has been employed to measure the thermal diffusivity of lanthanum phosphate ceramics prepared by the sol–gel route. The thermal diffusivity value was evaluated by knowing the transition frequency between the thermally thin to thermally thick region from the log–log plot of photoacoustic amplitude versus chopping frequency. Analysis of the data was carried out on the basis of the one-dimensional model of Rosencwaig and Gersho. The present investigation reveals that the sintering temperature has great influence on the propagation of heat carriers and hence on the thermal diffusivity value. The results were interpreted in terms of variations in porosity with sintering temperature as well as with changes in grain size.     

Global optimization of case-based reasoning for breast cytology diagnosis

Case-based reasoning (CBR) is one of the most popular prediction techniques in medical domains because it is easy to apply, has no possibility of overfitting, and provides a good explanation for the output. However, it has a critical limitation – its prediction performance is generally lower than other AI techniques like artificial neural networks (ANN). In order to obtain accurate results from CBR, effective retrieval and matching of useful prior cases for the problem is essential, but it is still a controversial issue to design a good matching and retrieval mechanism for CBR systems. In this study, we propose a novel approach to enhance the prediction performance of CBR. Our suggestion is the simultaneous optimization of feature weights, instance selection, and the number of neighbors that combine using genetic algorithms (GA). Our model improves the prediction performance in three ways – (1) measuring similarity between cases more accurately by considering relative importance of each feature, (2) eliminating useless or erroneous reference cases, and (3) combining several similar cases represent significant patterns. To validate the usefulness of our model, this study applied it to a real-world case for evaluating cytological features derived directly from a digital scan of breast fine needle aspirate (FNA) slides. Experimental results showed that the prediction accuracy of conventional CBR may be improved significantly by using our model. We also found that our proposed model outperformed all the other optimized models for CBR using GA.     

Spectroscopic characterizations of Er doped LaPO4 submicron phosphors prepared by homogeneous precipitation method

Hexagonal shaped LaPO₄ submicron particles doped with various concentrations of Er were successfully prepared by homogenous precipitation method using metal nitrates and ammonium phosphate. Particles of approximate particle size 125 nm and size distribution of 85 nm are obtained with good crystallinity. After heat treatment at 1200 °C for 2 h, the particles are characterized for their various optical properties such as absorption, emission, fluorescence decay and optical band gap. Optical absorption and emission data are numerically analyzed with the help of Judd–Ofelt model to evaluate various radiative spectral properties such as radiative decay rates, radiative quantum yield, emission cross-section and fluorescence branching ratios of various emission transitions. Though the radiative quantum yield of 1554 nm emission approaches the theoretical limit of 100%, the experimentally measured quantum yield is only 11% at 12 W/cm² at 980 nm excitation power density in 2% Er doped LaPO₄.     

Student perception and usage of an automated programming assessment tool

Automated assessment systems are gaining popularity within computer programming courses. In this paper we perform an empirical evaluation of Mooshak, an online judge that verifies program correctness, in order to determine its usefulness in classroom settings. In particular, we provide a detailed study on how students use the tool, analyze their opinions and critiques about it, and measure other features like its capability to reduce dropout rates. The experience was carried out within a course on algorithm design and analysis where we collected information through several questionnaires and data generated by the tool during the course. Among the main findings we highlight: (1) the usage of the tool was adequate in relation to students’ own testing; (2) its feedback needs to be richer in order to improve its acceptance among students; and (3) there was no statistical evidence to claim Mooshak reduced the dropout rate.     

Molecular design of deep blue fluorescent emitters with 20% external quantum efficiency and narrow emission spectrum

A thermally activated delayed fluorescent (TADF) emitter, 2,7-bis(9,9-dimethylacridin-10(9H)-yl)-9,9-dimethyl-9H-thioxanthene 10,10-dioxide (DMTDAc), was developed as a deep blue TADF emitter using a rigid 9,9-dimethyl-9H-thioxanthene 10,10-dioxide (DMTD) acceptor and an acridine donor. The rigid DMTD acceptor narrowed emission spectrum of DMTDAc by interlocking two phenyl units of diphenylsulfone. A deep blue TADF device with an external quantum efficiency close to 20% with a deep blue color coordinate of (0.15,0.13) was provided using the DMTDAc TADF emitter.     

Fabrication of high-efficiency multilayered organic light-emitting diodes by a film transfer method

In this paper, we report the fabrication of small-molecule-based thin-film layers with a thickness of several tens of nanometers on a release layer by bar coating and subsequent stacking onto other organic layers by the developed film transfer method using driving belts and rollers as a prototype roll-to-roll technique. We use novel thermally activated delayed fluorescence (TADF) materials in this process, achieving multilayered organic light-emitting diodes (OLEDs) with high external quantum efficiency (EQE), which is comparable to those of OLEDs prepared by conventional vacuum deposition. The developed film transfer method shows great potential to realize OLEDs with high efficiency at low cost.     

Dependence of Pt(II) based phosphorescent emitter orientation on host molecule orientation in doped organic thin films

We report that the molecular orientation of a disk-shaped Pt(II) complex dopant in organic thin films is linearly proportional to the orientation of the host molecules. We ascribe this relationship to the parallel alignment of the Pt complex with the host molecules induced by a π-π interaction. This would be caused by their planar and conjugated structure, indicating that the intermolecular interaction and steric effect play an important role. This finding can be applied to obtain a horizontal emitter orientation, resulting in highly efficient OLEDs based on Pt(II) complexes.     

Conductive amorphous hydrocarbon film for bio-sensor formed by low temperature neutral beam enhanced chemical vapor deposition

Amorphous hydrocarbon (aCH) material is receiving plenty of attention due to its possible wide application. However, one hurdle facing this application is that high temperature is required to express conductivity of aCH, e.g., post annealing or deposition at high temperature. To form a conductive aCH on a substrate controlled below room temperature, we have developed a neutral beam enhanced chemical vapor deposition (NBECVD) method to control a hydrocarbon molecular structure that has a large conjugated system with delocalized π electrons in film. For material gas, we prepared toluene. As a result, we obtained a highly conductive carbon on a Si substrate with −50 °C using only toluene by optimizing the state of disassociated material gas. From an evaluation of film structure, a polycyclic aromatic hydrocarbon molecular structure was grown and contained in film because NBECVD could avoid irradiating UV to the Si substrate during deposition. Thus, an excited large conjugated chain structure generated by toluene in plasma could be maintained and polymerized on the Si substrate. Furthermore, the conductive aCH film could work as electrode in solution by electrochemical examination. Additionally, we found that nitrogen doped into conductive aCH could increase the working current of an electrode.     

Preparation of in situ grown silicon carbide nanofibers radially onto carbon fibers and their effects on the microstructure and flexural properties of carbon/carbon composites

Silicon carbide nanofibers (SiCNFs) used as the second reinforcements of carbon/carbon composites were grown radially on the carbon fiber surface. The microstructure of SiCNFs and their effects on the microstructure and flexural properties of C/C composites were investigated. Results show that there are many defects such as twin crystals and stacking faults in SiCNFs which were grown by catalytic chemical vapor deposition. During the same process, the skin region of carbon fiber has changed. Several SiC layers are formed and the arrangement of the graphite layers around SiC layers is more orderly. In the next chemical vapor infiltration, due to the induction of SiCNFs, the middle textural pyrocarbon were formed firstly and then is the high textural pyrocarbon. The existence of SiCNFs also contributes to the three-phase interface between pyrocarbon, SiCNFs and carbon fibers, resulting in a good bond between carbon fiber and matrix. Those structural changes lead the better flexural properties of SiCNF–C/C composites compared with C/C composites.