Improved hole-injection contact for top-emitting polymeric diodes

In this letter, an efficient hole-injection contact was achieved for the top-emitting polymeric light-emitting diodes (PLEDs). The anode has a structure of metal/molybdenum oxide/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS). It has been found that hole injection was significantly improved by inserting a thin layer of MoO3 between aluminum and PEDOT:PSS. An ultraviolet photoelectron spectroscopy (UPS) was used to investigate the change of work function, and photovoltaic measurement confirmed that the improved hole injection is due to the reduction of barrier height, resulted from the addition of transition metal oxide. PEDOT:PSS layer was found necessary in anode structure to further enhance the hole injection and electroluminance efficiency. A peak power efficiency of 11.42lm∕W was achieved at current density of 1.2mA/cm2 for the white emission top-emitting PLEDs

Evaluating e-portfolio Using by Learning Stages: A Case Study in an Interdisciplinary Program

This study conducts an investigation of posts in the e-portfolio platform of the program: “The interdisciplinary training program for talented college students in science.” Participants in this program were supposed to show their learning portfolios on this platform. Among the 2150 registered students, we randomly selected 126 students who have made at least 3 posts to become the target sample. By identifying the learning stages and posting styles shown by their posts, we find that students are mostly in the surface learning stages and weak in completing their learning portfolios. The results suggest that more strategies should be learned in e-portfolio use. In addition, some related issues about learning performance are also discussed

A simple circuit realization of the tent map

We present a very simple electronic implementation of the tent map, one of the best-known discrete dynamical systems. This is achieved by using integrated circuits and passive elements only. The experimental behavior of the tent map electronic circuit is compared with its numerical simulation counterpart. We find that the electronic circuit presents fixed points, periodicity, period doubling, chaos and intermittency that match with high accuracy the corresponding theoretical valuesComment: 6 pages, 6 figures, 10 references, published versio

Finite temperature Casimir effect for massive scalar field in spacetime with extra dimensions

We compute the finite temperature Casimir energy for massive scalar field with general curvature coupling subject to Dirichlet or Neumann boundary conditions on the walls of a closed cylinder with arbitrary cross section, located in a background spacetime of the form $M^{d_1+1}\times \mathcal{N}^n$, where $M^{d_1+1}$ is the $(d_1+1)$-dimensional Minkowski spacetime and $\mathcal{N}^n$ is an $n$-dimensional internal manifold. The Casimir energy is regularized using the criteria that it should vanish in the infinite mass limit. The Casimir force acting on a piston moving freely inside the closed cylinder is derived and it is shown that it is independent of the regularization procedure. By letting one of the chambers of the cylinder divided by the piston to be infinitely long, we obtain the Casimir force acting on two parallel plates embedded in the cylinder. It is shown that if both the plates assume Dirichlet or Neumann boundary conditions, the strength of the Casimir force is reduced by the increase in mass. Under certain conditions, the passage from massless to massive will change the nature of the force from long range to short range. Other properties of the Casimir force such as its sign, its behavior at low and high temperature, and its behavior at small and large plate separations, are found to be similar to the massless case. Explicit exact formulas and asymptotic behaviors of the Casimir force at different limits are derived. The Casimir force when one plate assumes Dirichlet boundary condition and one plate assumes Neumann boundary condition is also derived and shown to be repulsive.Comment: 28 pages, 4 figure

The Effect of ePortfolio Satisfaction on Students’ Learning Motivation and Internet Self-efficacy

This study aims to investigate the effect of e-Portfolio satisfaction on students’ learn­ing motivation and Internet self-efficacy toward the use of e-Portfolio. The data collected for this study occurred over 3 months. Participants were 450 students taking the course of common at an university. The counting of 443 questionnaires was received. The findings revealed that there were positive correlations between learning motivation, Internet self-efficacy, and e-Portfolio satisfac­tion. For gender, the result showed that there were no significant Internet self-efficacy differences between gender. Besides, there were the significant differences in learning motivations and in Internet self-efficacy between the two groups. Furthermore, the multistep regression analysis in­dicated that the learning motivation was the significant predictor of Internet self-efficacy, and In­ternet self-efficacy was the significant predictor of e-Portfolio satisfaction. Based on the findings, educators and researchers needed to pay attention to these influences and take these factors into consideration in e-Portfolio. The study concludes by assessing the overall gains and shortcomings of the reform effort toward using the e-Portfolio to help student self-learning

Origin of photomultiplication in C60 based devices

In this manuscript, the origin of the photomultiplication effect was studied in C60 based devices by evaluating the wavelength dependent external and internal quantum efficiencies under various biases. The effect of materials with disordered structures on the photomultiplication effect was determined by intentionally integrating both ordered and disordered material structures into one organic solar cell device with a configuration of indium tin oxide/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS)∕pentacene∕C60 fullerene/bathocuproine (BCP)/Al. Our results show that both the disordered structure of C60 and the charge trapping effect at the C60∕PEDOT:PSS interface contribute to the photomultiplication effect. By studying the C60-only single layer device, the charge trapping sites are identified to be at the C60 and PEDOT:PSS interface. The interfacial traps behave as an electronic valve that enables a significant increase in electron injection, which causes the photomultiplication phenomena. Quantitative comparisons indicate that photomultiplication induced by C60 disordered structure is much less significant than that by charge trapping at the interface

Spectroscopy of vibrational modes in metal nanoshells

We study the spectrum of vibrational modes in metal nanoparticles with a dielectric core. Vibrational modes are excited by the rapid heating of the particle lattice that takes place after laser excitation, and can be monitored by means of pump-probe spectroscopy as coherent oscillations of transient optical spectra. In nanoshells, the presence of two metal surfaces results in a substantially different energy spectrum of acoustic vibrations than for solid particles. We calculated the energy spectrum as well as the damping of nanoshell vibrational modes. The oscillator strength of fundamental breathing mode is larger than that in solid nanoparticles. At the same time, in very thin nanoshells, the fundamental mode is overdamped due to instantaneous energy transfer to the surrounding medium

Bose-Einstein condensation and superfluidity of dilute Bose gas in a random potential

We develop the dilute Bose gas model with random potential in order to understand the Bose system in random media such as 4He in porous glass. Using the random potential taking account of the pore size dependence, we can compare quantitatively the calculated specific heat with the experimental results, without free parameters. The agreement is excellent at low temperatures, which justifies our model. The relation between Bose condensation and superfluidity is discussed. Our model can predict some unobserved phenomena in this system.Comment: 9 pages, 11 figures, accepted for publication in Phys. Rev.

Preparation of atomically clean and flat Si(100) surfaces by low-energy ion sputtering and low-temperature annealing

Si(100) surfaces were prepared by wet-chemical etching followed by 0.3-1.5keV Ar ion sputtering, either at elevated or room temperature. After a brief anneal under ultrahigh vacuum conditions, the resulting surfaces were examined by scanning tunneling microscopy. We find that wet-chemical etching alone cannot produce a clean and flat Si(100) surface. However, subsequent 300eV Ar ion sputtering at room temperature followed by a 973K anneal yields atomically clean and flat Si(100) surfaces suitable for nanoscale device fabrication.Comment: 13 pages, 3 figures, to be published in Applied Surface Scienc