Quantitative characterization of carrier injection across metal–organic interfaces using Bardeen theory

We have investigated the contact between a metal and an organic/polymeric (o/p) material and we have introduced a relation for carrier injection using Bardeen theory. A series of narrow barriers is considered in the semiconductor side to account for the localized nature of the carriers in the o/p material. As an application of the model, we have calculated the hopping rate of carriers in terms of the contact parameters. Also, we have discussed the hopping of carriers deep into the organic dielectric. Finally, we have explored the hopping rate in practical contacts between polyfluorene-based polymers and different electrodes.     

An enhanced cost-aware mapping algorithm based on improved shuffled frog leaping in network on chips

The Journal of Supercomputing - Network on chip (NoC) has been of great interest in recent years. However, according to the recent studies, high communication cost has been raised as the one most...     

Nanoscale conjugated-polymer light-emitting diodes

We use e-beam lithography to pattern an indium tin oxide (ITO) electrode to create arrays of conjugated-polymer LEDs, each of which has a hole-injecting contact limited to 100 nm in diameter. Using optical microscopy, we estimate that the electroluminescence from a 100 nm diameter LED comes from a region characterized by a diameter of approximately 170 nm. This apparent broadening occurs due to current spreading within a PEDOT:PSS layer which was included to aid hole injection.     

Effect of seed layers on low-temperature,chemical bath deposited ZnO nanorods-based near UV-OLED performance

Low-temperature wet chemical bath deposition (CBD) method is one of the most efficient and least hazardous solution-based techniques which is widely employed to grow ZnO NRs. In CBD method, a seed layer is usually deposited on the substrate. In this paper, high quality ZnO and aluminum doped ZnO (AZO) seed layers are sputtered on the indium tin oxide (ITO) coated glass. In continue, aligned ZnO NRs are grown on the AZO and ZnO seed layers via CBD technique. The effect of the growth time and seed layer on the physical properties of as-grown ZnO NRs are investigated. According to the results, the seed layer plays an essential role on the growth orientation and growth rate of the ZnO NRs. The ZnO NRs grown on AZO seed layer are more aligned rather than ZnO seed layer due to their higher texture coefficients. The relative photoluminescence (PL) intensity ratio of near band emission (NBE) to deep level emission (DLE) (I_NBE/I_DLE) for the ZnO NRs grown on AZO and ZnO seed layers are calculated as 7.45 and 2.62, respectively. To investigate the performance of the as-grown ZnO NRs, near ultraviolet organic light-emitting diodes (UV-OLEDs) using ZnO NRs array as n-type material and poly [2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene-vinylene] (MEH-PPV) conjugated polymer as p-type material have been fabricated. The total concentration of traps ($N_t$), the characteristic energies ($E_t$) and the turn-on voltages for the devices with the structures of ITO/AZO/ZnO NRs/MEH-PPV/Al (device A) and ITO/ZnO/ZnO NRs/MEH-PPV/Al (device B) are attained 7.65 × 10¹⁶ and 7.75 × 10¹⁶ cm^?3, 0.232 and 0.206 eV, 23 and 21 V, respectively. Moreover, based on the electroluminescence (EL) spectra, the NBE peaks for device A and B are obtained nearly in the wavelengths of 382 and 388 nm, respectively. Finally, various charge carrier transportation processes of prepared UV-OLEDs have been studied, systematically.     

Observations of backgate impedance dispersion in GaAs isolationstructures

Low frequency reactive, resonant and negative resistance effects have been observed in backgate current flow in monolithic GaAs integrated circuits. Comparisons have been made between structures prepared by MBE on undoped buffer layers at high and low temperatures and by ion implantation. The study employed GaAs MESFETs which were similarly prepared on the three substrates. Backgate admittance spectroscopy measurements were performed between adjacent isolated n-type mesa structures on the different isolation materials in the range 10 Hz to 10 kHz, at temperatures ranging from 80 K to 340 K. In the case of the ion implanted and normally buffered structures the form of the susceptance frequency spectra depended on cathode size, dc bias and temperature and could include capacitive relaxation as well as inductive and capacitive behaviors separated by a resonance. The form of the variation of the conductance was closely associated and frequently included a frequency region within which there was negative small signal resistance. These effects were not present when the buffer layer was prepared at low temperatures. The results are summarized to make explicit the requirements of an explanatory model     

Iranian Medical Universities in SCIE: evaluation of address variation

Patenting and licensing is not only a significant method of university knowledge transfer, but also an important indicator for measuring academic R&D strength and knowledge utilization. The methodologies of quantitative and qualitative analysis, including a special patent h-index indicator to assess patenting quality, were used to examine university patenting worldwide. Analysis of university patenting from 1998 to 2008 showed a significant overall global increase in which Chinese academia stands out: most of the top 20 universities in patenting in 2008 were in China. However, a low rate of utilization of Chinese academic patents may have roots in: (1) university research evaluation system encourages the patent production more, rather than the utilization; (2) problems in the formal mechanisms for university technology transfer and licensing, (3) industry’s limited expectation and receptive capabilities and/or (4) a mismatch between the interests of the two institutional spheres. The next action to be taken by government, university and industry in China will be to explore strategies for improving academic patent quality and industry take-up.     

Autoclave‐assisted synthesis of AgNPs in Z. officinale extract and assessment of their cytotoxicity,antibacterial and antioxidant activities

In this study, the authors synthesised silver nanoparticles (AgNPs) using autoclave as a simple, unique and eco‐friendly approach. The effect of Zingiber officinale extract was evaluated as a reducing and stabiliser agent. According to transmission electron microscopy results, the AgNPs were in the spherical shape with a particle size of ∼17 nm. The biomedical properties of AgNPs as antibacterial agents and free radical scavenging activity were estimated. Synthesised AgNPs showed significant 1,1‐diphenyl‐2‐picryl‐hydrazyl free radical scavenging. Strong bactericidal activity was shown by the AgNPs on Gram‐positive and Gram‐negative bacteria. A maximum inhibition zone of ∼14 mm was obtained for epidermidis at a concentration of 60 μg/ml for sample fabricated at 24 h. The AgNPs also showed a significant cytotoxic effect against MCF‐7 breast cancer cell lines with an half maximal inhibitory concentration value of 62 μg/ml in 24 h by the MTT assay. It could be concluded that Z. officinale extract can be used effectively in the production of potential antioxidant and antimicrobial AgNPs for commercial application.Inspec keywords: nanoparticles, cancer, organic compounds, antibacterial activity, particle size, microorganisms, silver, visible spectra, ultraviolet spectra, biomedical materials, biochemistry, nanofabrication, free radicals, nanomedicine, toxicology, cellular biophysics, transmission electron microscopyOther keywords: unique approach, eco‐friendly approach, zingiber officinale, reducing agent, stabiliser agent, transmission electron microscopy results, antibacterial agents, free radical scavenging activity, synthesised AgNPs, 1‐diphenyl‐2‐picryl‐hydrazyl free radical scavenging, strong bactericidal activity, antimicrobial AgNPs, autoclave‐assisted synthesis, antioxidant activities, cytotoxic effect, silver nanoparticles, autoclave, time 24.0 hour     

Quality enhancement of AZO thin films at various thicknesses by introducing ITO buffer layer

Due to the simultaneously superior optical transmittance and low electrical resistivity, transparent conductive electrodes play a significant role in semiconductor electronics. To enhance the electrical properties of these films, one approach is thickness increment which degrades the optical properties. However, a preferred way to optimize both electrical and optical properties of these layers is to introduce a buffer layer. In this work, the effects of buffer layer and film thickness on the structural, electrical, optical and morphological properties of AZO thin films are investigated. Al-doped zinc oxide (AZO) is prepared at various thicknesses of 100 to 300 nm on the bare and 100 nm-thick indium tin oxide (ITO) coated glass substrates by radio frequency sputtering. Results demonstrate that by introducing ITO as a buffer layer, the average values of sheet resistance and strain within the film are decreased (about 76 and 3.3 times lower than films deposited on bare glasses), respectively. Furthermore, the average transmittance of ITO/AZO bilayer is improved nearly 10% regarding single AZO thin film. This indicates that bilayer thin films show better physical properties rather than conventional monolayer thin films. As the AZO film thickness increases, the interplanar spacing, d₍₀₀₂₎, strain within the film and compressive stress of the film in the hexagonal lattice, decreases indicating the higher yield of AZO crystal. Moreover, with the growth in film thickness, carrier concentration and optical band gap (E_g) of AZO film are increased from 4.62?×?10¹⁹ to 8.21?×?10¹⁹ cm^?3 and from 3.55 to 3.62 eV, respectively due to the Burstein-Moss (BM) effect. The refractive index of AZO thin film is obtained in the range of 2.24–2.26. With the presence of ITO buffer layer, the AZO thin film exhibits a resistivity as low as 6?×?10^?4 Ω cm, a sheet resistance of 15 Ω/sq and a high figure of merit (FOM) of 1.19?×?10⁴ (Ω cm)^?1 at a film thickness of 300 nm. As a result, the quality of AZO thin films deposited on ITO buffer layer is found to be superior regarding those grown on a bare glass substrate. This study has been performed over these two substrates because of their significant usage in the organic light emitting diodes and photovoltaic applications as an enhanced carrier injecting electrodes.     

Large area Ag-TiO2 UV radiation sensor fabricated on a thermally oxidized titanium chip

A Schottky-type ultraviolet (UV) light sensor is fabricated on a thermally oxidized titanium chip. The device is of Ag-TiO₂-Ti structure, and the Schottky junction between silver and rutile is formed subsequent to the vacuum deposition of silver on the thermally grown rutile layer by a controlled thermal annealing in air. The device operates at −300 mV biasing established between silver and titanium electrodes. The dark reverse current of this diode increases four orders of magnitude when illuminated with UV light (355 nm) of 10 μW/mm² intensity. The device is almost insensitive to visible light and requires no filtering when used for ambient UV level detection. The operation mechanism of the device is described by photonic electron-hole pair generation in the carrier depleted titanium dioxide layer adjacent to the silver electrode. The electrode-to-electrode distance is 1 μm only affording much faster performance compared to photoconductive UV detectors fabricated based on titanium dioxide; the response and recovery times of the device are 10 ms and 17 ms, respectively. At its standby mode, a 1 mm² active area device consumes less than 10 pW of electric power. Sensors with sensitive areas as large as ∼10 mm² are easy to fabricate. The fabricated devices are rugged, resistant to UV degradation, and cost effective.     

Pricing Internet services: proposed improvements

Flat-rate pricing appeals to Internet users and service providers because of its simplicity and predictability. However, congestion is the inevitable consequence of flat-rate pricing because Internet users who pay a fixed access fee have no incentive to limit their network usage. Future applications that require timely delivery of data will require mechanisms for allocating network resources that give consumers choices in services and prices while allowing service providers to recover their costs. We examine the proposed improvements in Internet pricing that are designed to increase its economic efficiency and support the deployment of new applications that require a better quality of service than the Internet currently offers