Determination of the interface energy level alignment of a doped organic hetero-junction using capacitance–voltage measurements

A simple method based on capacitance–voltage (C–V) measurements is reported to determine the interface energy level alignment at the junction of 15 mol% Cs₂CO₃ doped 4,7-diphenyl-1,10-phenanthroline (BPhen) and 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HATCN) fabricated under high vacuum. The junction properties, such as the depletion layer thickness, built-in potentials and vacuum level shift were calculated with simple Mott–Schottky and Poisson’s equations with the boundary condition of a continuous electric flux density using the information from the C–V data. The interface energy level alignment determined by this method is well matched with the one determined using the in situ ultraviolet photoemission spectroscopy (UPS) and X-ray photoemission spectroscopy (XPS) experiments performed under ultra-high vacuum. This method can be applied to other semiconductor junctions such as the organic p–n homojunctions and heterojunctions with known energy levels, as long as the metal/semiconductor contact is Ohmic without referring to the photoemission spectroscopies. Moreover, the energy level alignment determined by the C–V measurement gives a more realistic result since the films for the measurements are formed under high vacuum which is a normal device fabrication environment rather than under ultra high vacuum.     

Effect of Different Quantum Well Structures on the Output Power Performance of GaN-Based Light-Emitting Diodes

We investigated the effect of two different quantum well (QW) structures having different indium contents on the optical performance of fully packaged GaN-based light-emitting diodes (LEDs). Dual-spectrum QW LEDs exhibit ～4% higher external quantum efficiency (at 350 mA) than single-spectrum QW LEDs. However, the two types of LEDs exhibit similar efficiency droop behavior. For both types of LEDs, the output power decreases with increasing junction temperature. When the junction temperature exceeds 70°C, the dual-spectrum QW LEDs exhibit lower output power than the single-spectrum QW LEDs. The wavelength dependence of the output power (at 350 mA) of single-spectrum QW LEDs shows that the LEDs with shorter wavelengths experience more rapid optical degradation than the LEDs with longer wavelengths. Based on the wavelength- and junction-temperature-dependent output power, the droop behavior of the dual-spectrum QW LEDs is described and discussed.     

Energetic distribution of interface states extracted from photo-conductance of organic thin film transistors

In this paper, a new method is introduced to obtain the energetic distribution of the interface states (density of states; DOS) extracted from the photo-conductance of organic thin film transistors (OTFTs) which exhibit varied transfer characteristics under illumination with different photon energies. The method was applied to pentacene OTFTs, and the results were compared with existing data. The major findings were not only the existence of the well-known peaks of DOS at 1.82 eV (free exciton of pentacene), and at 1.49 eV (extrinsic exciton due to dihydropentacene) but also new peaks were found at 1.25 eV, 1.29 eV, 1.31 eV, and 1.35 eV in the mid-gap. The new peaks were strongly enhanced under exposure to oxygen, and thus seem to be related to the defects associated with the presence of oxygen.     

Versatile threshold voltage control of OTFTs via discontinuous pn-heterojunction formation

We demonstrate the versatility of the threshold voltage control for organic thin-film transistors (OTFTs) based on formation of discontinuous pn-heterojunction on the active channel layer. By depositing n-type dioctyl perylene tetracarboxylic diimide molecules discontinuously onto base p-type pentacene thin films (the formation of the discontinuous pn-heterojunction), a positive shift of the threshold voltage was attained which enabled realizing a depletion-mode transistor from an original enhancement-mode pristine pentacene transistor. Careful control of the threshold voltage based on this method led assembling a depletion-load inverter comprising a depletion-mode transistor and an enhancement-mode transistor connected in series that yielded tunable signal inversion voltage approaching 0 V. In addition, the tunability could be applied to improve the program/erase signal ratio for non-volatile transistor memories by more than 4 orders of magnitude compared to reference memory devices made of pristine pentacene transistors.     

Encapsulation of lead-free Sn/Zn/Bi solder alloy particles by coating with wax powder for improving oxidation resistance

An encapsulation treatment of lead-free Sn/Zn/Bi solder powder was investigated for improving the oxidation resistance. Sn-8mass%Zn-3mass%Bi alloy particles were coated with a wax (12-hydroxystearic acid) powder by means of a dry mechanical treatment method using a ball mill. In order to determine the optimum operating conditions of the ball mill in the wax-coating treatments, the compressive energy required for deforming a single Sn/Zn/Bi alloy particle was measured with an unconfined compression tester and the mechanical energy applied to the alloy particles in the ball mill was estimated using the results of the compression test. The optimum operating conditions were determined based on both the applied energy and the flowability of solder pastes, and the wax-coated alloy particles maintaining the spherical shape were obtained under the conditions. The wettability test and the solder balling test for the solder pastes containing the wax-coated alloy particles stored at room temperature in air were carried out to evaluate the oxidation resistance performance. The wax-coated alloy particles had an excellent wettability compared with the original alloy particles, and the oxidation resistance of the Sn/Zn/Bi solder powder was improved by the encapsulation treatment.     

Blind adaptive decorrelating detector for DS-CDMA systems:auxiliary-vector detector

A blind adaptive decorrelating detector is proposed which consists of two vectors: one is the pre-assigned spreading code of the desired user and the other is orthogonal to it. The orthogonal vector is adjusted adaptively to minimise the multiple access interference (MAI). This blind adaptive detector requires no more knowledge than does the conventional single-user receiver. Simulation results show that the obtained performance is close to that of the decorrelator     

Failure analysis of video processor defined as No Fault Found (NFF): Reproduction in system level and advanced analysis technique in IC level

This paper has studied the video processors for Flat Panel Display (FPD) which is defined as No Fault Found (NFF) among field failures. NFF phenomenon of video processor was the initial feature of field failure and showed Composite Video Broadcast Signal (CVBS) noise but it worked properly after some hours. NFF phenomenon has been a rising issue in the field of electronic device and the system recently. Highly Accelerated Life Testing (HALT) method has been used to reproduce field failure symptom. Modulated exciting technique has been applied as stress profile. Through the above, it was possible to reproduce the symptom which is the same as the field failure. Fault isolation and the defect was detected through the Advanced failure analysis method such as backside polishing, PEM, OBIRCH, and SEM. And it explains the defect and suggests the stress factor which can cause the defect.     

On the sources of methane to the los angeles atmosphere

We use historical and new atmospheric trace gas observations to refine the estimated source of methane (CH(4)) emitted into California's South Coast Air Basin (the larger Los Angeles metropolitan region). Referenced to the California Air Resources Board (CARB) CO emissions inventory, total CH(4) emissions are 0.44 ± 0.15 Tg each year. To investigate the possible contribution of fossil fuel emissions, we use ambient air observations of methane (CH(4)), ethane (C(2)H(6)), and carbon monoxide (CO), together with measured C(2)H(6) to CH(4) enhancement ratios in the Los Angeles natural gas supply. The observed atmospheric C(2)H(6) to CH(4) ratio during the ARCTAS (2008) and CalNex (2010) aircraft campaigns is similar to the ratio of these gases in the natural gas supplied to the basin during both these campaigns. Thus, at the upper limit (assuming that the only major source of atmospheric C(2)H(6) is fugitive emissions from the natural gas infrastructure) these data are consistent with the attribution of most (0.39 ± 0.15 Tg yr(-1)) of the excess CH(4) in the basin to uncombusted losses from the natural gas system (approximately 2.5-6% of natural gas delivered to basin customers). However, there are other sources of C(2)H(6) in the region. In particular, emissions of C(2)H(6) (and CH(4)) from natural gas seeps as well as those associated with petroleum production, both of which are poorly known, will reduce the inferred contribution of the natural gas infrastructure to the total CH(4) emissions, potentially significantly. This study highlights both the value and challenges associated with the use of ethane as a tracer for fugitive emissions from the natural gas production and distribution system.     

Analysis of kimchi microflora using denaturing gradient gel electrophoresis

A polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) technique was used to determine the microfloral composition during the fermentation of kimchi, a traditional Korean fermented vegetable food. The kimchi was fermented at 10 degrees C or 20 degrees C for 30 or 20 days, respectively. DGGE of the partially amplified 16S rDNA was performed and the most intense bands sequenced. The application of this culture-independent molecular technique determined that the lactic acid bacteria Weissella confusa, Leuconostoc citreum, Lactobacillus sakei, and Lactobacillus curvatus were the main microorganisms responsible for kimchi fermentation.