bluuebunny/crossref_metadata_2025 huggingface dataset:
Carrier Propagation Dependence on Applied Potentials in Pentacene Organic Field Effect Transistors Investigated by Impedance Spectroscopy and Electrical Time-of-Flight Techniques
Authors: Lin Jack , Weis Martin , Taguchi Dai , Manaka Takaaki , Iwamoto Mitsumasa
Published: April 2011

Transient measurements of impedance spectroscopy and electrical time-of-flight (TOF) techniques were used for the evaluation of carrier propagation dependence on applied potentials in a pentacene organic field effect transistor (OFET). These techniques are based on carrier propagation, thus isolates the effect of charge density. The intrinsic mobility which is free from contact resistance effects was obtained by measurement of various channel lengths. The obtained intrinsic mobility shows good correspondence with steady-state current–voltage measurement's saturation mobility. However, their power law relations on mobility vs applied potential resulted in different exponents, suggesting different carrier propagation mechanisms, which is attributable to filling of traps or space charge field in the channel region. The hypothesis was verified by a modified electrical TOF experiment which demonstrated how the accumulated charges in the channel influence the effective mobility.
Computational Study on Carrier Injection in Ca/Poly(9,9'-dioctylfluorene) Interface by Using Quantum Chemistry and Monte Carlo Methods
Authors: Yamashita Itaru , Onuma Hiroaki , Nagumo Ryo , Miura Ryuji , Suzuki Ai , Tsuboi Hideyuki , Hatakeyama Nozomu , Endou Akira , Takaba Hiromitsu , Kubo Momoji , Miyamoto Akira
Published: April 2011

Control of electron injection barriers at the interface of a cathode/light-emitting polymer is a key factor to improve the device properties of polymer light-emitting diodes. In this study, to investigate the relationship between electron injection and the structure of the interface, we carried out the simulation of carrier injection for the interface model of Ca/poly(9,9'-dioctylfluorene) (PDOF) by using tight-binding quantum chemistry and Monte Carlo simulations. We found that the height of electron injection barriers strongly depends on the interfacial structure; the distance between Ca atoms and aromatic rings of PDOF. The carrier injection property is discussed on the basis of the interaction between C 2p and Ca 4p orbitals.
Grain Boundary Effect on Charge Transport in Pentacene Thin Films
Authors: Weis Martin , Gmucová Katarína , Nádaždy Vojtech , Majková Eva , Haško Daniel , Taguchi Dai , Manaka Takaaki , Iwamoto Mitsumasa
Published: April 2011

We report on charge transport properties of polycrystalline pentacene films with variable average grain size in the range from 0.1 to 0.3 µm controlled by the preparation technology. We illustrate with the organic field-effect transistors decrease of the effective mobility and presence of traps with decrease of the grain size. Analysis of the charge transfer excitons reveals decrease of the mobile charge density and the steady-state voltammetry showed significant increase of oxygen- and hydrogen-related defects. We also briefly discuss accumulation of the defects on the grain boundary and show relation between the defect density and grain boundary length.
Direct Probing of Carrier Behavior in Electroluminescence Indium–Zinc-Oxide/N,N '-Di-[(1-naphthyl)-N,N '-diphenyl]-(1,1'-biphenyl)-4,4'-diamine/Tris(8-hydroxy-quinolinato)aluminum(III)/LiF/Al Diode by Time-Resolved Optical Second-Harmonic Generation
Authors: Taguchi Dai , Zhang Le , Li Jun , Weis Martin , Manaka Takaaki , Iwamoto Mitsumasa
Published: April 2011

By using electric-field-induced second-harmonic generation (EFISHG) measurement, we probed charging and discharging in an α-NPD/Alq3 organic light-emitting diode [α-NPD, N,N '-di-[(1-naphthyl)-N,N '-diphenyl]-(1,1'-biphenyl)-4,4'-diamine; Alq3, tris(8-hydroxy-quinolinato)aluminum(III)] while electroluminescence response was monitored. The EFISHG measurement showed that excessive positive charges accumulated at the α-NPD/Alq3 interface in the charging process, accompanying electroluminescence (EL) radiation, and the accumulated excess positive charges disappeared in the discharging process before the EL decayed. Note that the EL radiation was smooth and strong under the high voltage application, while the EL decayed in a similar way. The Maxwell–Wagner model analysis showed no-dependence of the accumulated excessive positive charge on the applied external voltage, suggesting that electrons and holes injected from the opposite electrodes for EL radiation balanced at the interface. The EFISHG measurement will be useful as a direct way to probe carrier behaviors in organic EL devices.
A Proposal of High Performance and Highly Fabricable Complementary Organic Thin Film Transistor Structure
Authors: Sugawara Akira , Wada Yasuo , Ishikawa Yoshinori , Toyabe Toru
Published: April 2011

A complementary organic thin film transistor (COTFT) structure is proposed, which would make it possible to realize high performance and highly fabricable organic integrated circuits. The structure is based on single organic semiconductor layer, with high electron carrier concentration region (n+) at the n-channel OTFT source/drain contact areas, and high hole carrier concentration region (p+) at the p-channel ones. The COTFT characteristics are analyzed by an OTFT devices simulator, Toyo University Organic Thin Film Transistor Advanced Simulator (TOTAS), which makes it possible to derive drain current–drain voltage (I
d–V
d) characteristics, potential distribution and electron/hole concentration distribution by solving Poisson's equation and current continuity equation. It is found that both n- and p-channel transistors exhibit almost the same I
d–V
d characteristics when n+ and p+ are both 1020 cm-3, and independent of p between 1012 cm-3 and 1015 cm-3. In addition, top contact COTFT and bottom contact one also exhibit almost the same I
d–V
d characteristics if the same device parameters are employed. Therefore, the COTFT structure proposed here would be quite suitable for practical applications, because of its high performance and fabricability.
Diffuser Micropump Structured with Extremely Flexible Diaphragm of 2-µm-thick Polyimide Film
Authors: Liu Yingwei , Komatsuzaki Hiroki , Duan Zongfan , Imai Satomitsu , Nishioka Yasuhiro
Published: April 2011

A miniaturized diffuser/nozzle micropump with extremely thin (only 2.1 µm in thickness) polyimide (PI) membranes was fabricated on a 60-µm-thick Si wafer using simple photolithography processes. The diameter of the diaphragm was 2 mm, and the chamber depth was 60 µm. The micropump was functioned by deforming the membranes with alternating air pressure. The ethanol flow rate of the micropump was over 400 nl/min at 2.5 Hz with an actuated pressure of 5 kPa. The measured flow rate was relatively higher than those of previously reported micropumps with a similar chamber volume owing to the large deflection (over 40 µm) of the PI membrane. The micropump processing issues of plasma induced damage to the PI membrane during Si chamber etching and the behaviors of the static and dynamic deflections of the PI membrane was also discussed. On the basis of the advantages of photolithography processes and the good performance of the micropump, it is expected that the micropump can be fabricated on silicon integrated circuit chips.
Fabrication of Sol–Gel Alumina Dielectric for Low-Voltage Operating Pentacene Transistor
Authors: Han Keon-kook , Seo Soonmin
Published: April 2011

We present a sol–gel based aluminum oxide dielectric for low-voltage organic thin film transistor that is stable and robust. The solution-processed dielectric does not cause hysteresis and the device with the dielectric is stable in that there is no threshold voltage shift when subjected to bias stress. With easy control of the dielectric thickness, the low voltage operating device can be made insensitive to fluctuations in off state voltage.
Optical Properties of Siloxene Films Prepared by High-Temperature Heat Treatment from Thin Films of Polysilane Containing Anthryl Groups
Authors: Tachibana Hiroaki , Mizuno Toya , Ishibe Satoko
Published: April 2011

We report the synthesis of linear and network polysilanes containing anthryl groups and the optical properties of the thin films by heat treatments. We observe the shift to a lower energy of the absorption edge in UV–visible absorption spectra of the thin films, when the polysilane films were heated at 500 °C. This behavior is interpreted in terms of the formation of network siloxene films by the dissociation of anthryl groups from silicon structures and the accompanying incorporation of oxygen into the silicon structures. The addition of UV irradiation before heating enhances the spectral changes caused by heat treatment. It is shown that a vacuum degree during heating and backbone structures of polysilanes affect the formation of the network siloxene structures by heat treatment.
High-Efficiency Electrophosphorescence Red Organic Light-Emitting Diodes Using a Thin 1,3-Bis[2-(2,2'-bipyridin-6-yl)-1,3,4-oxadiazol-5-yl]benzene Cleaving Layer in an Ir-Complex-Doped Emitter Layer
Authors: Chen Chin-Hsiang , Wang Kuo-Run , Tsai Yu-Hsuan , Yen Shuo-Fu , Su Peng-Yin , Cheng Chung-Fu
Published: April 2011

The authors demonstrate a considerable increase in the current efficiency of Ir(piq)2(acac)-doped phosphorescent red organic light-emitting diodes (OLEDs) in which a thin 1,3-bis[2-(2,2'-bipyridin-6-yl)-1,3,4-oxadiazol-5-yl]benzene (Bpy-OXD) layer acts as a cleaving layer. When a 5 nm Bpy-OXD layer divides the emitting layer (EML) into two sub-EMLs, the Ir(piq)2(acac)-doped phosphorescent red OLEDs show significantly increased luminance and current efficiency (a maximum luminance of 9830 cd/m2, corresponding to a current efficiency of 4.36 cd/A) compared with the conventional phosphorescent red OLEDs without this thin Bpy-OXD cleaving layer. We can attribute this improvement mainly to the balance of carrier injection in the double emitting layer and increased the utilization rate of the excitons.
Polarization Analyzing Image Sensor with On-Chip Metal Wire Grid Polarizer in 65-nm Standard Complementary Metal Oxide Semiconductor Process
Authors: Shishido Sanshiro , Noda Toshihiko , Sasagawa Kiyotaka , Tokuda Takashi , Ohta Jun
Published: April 2011

A polarization analyzing complementary metal oxide semiconductor (CMOS) image sensor with a fine on-chip metal wire grid polarizer in the 65-nm standard process is presented. The extinction ratio is an important characteristic for a polarizer that depends largely on the feature size of the metal wire grid pitch and the fabrication CMOS process. To improve the extinction ratio, we designed and fabricated a sensor chip in the 65-nm process. The design rules of the 65-nm process realize the fine metal wire grid pitch compared with the wavelength of visible light. Improvement of extinction ratio is expected by such a fine structure. With the fabricated sensor, an extinction ratio greater than 40 was achieved. The difference between the measured value and the simulation value of the extinction ratio, and pixel crosstalk of the fabricated sensor are discussed.
Compact Electrochemical System Using On-Chip Sensor Electrodes and Integrated Devices
Authors: Yamazaki Tomoyuki , Ikeda Takaaki , Ishida Makoto , Sawada Kazuaki
Published: April 2011

We report a compact electrochemical sensing system to implement cyclic voltammetry. This type of sensor needs a working electrode, counter electrode, and reference electrode, all of which were integrated on a single chip. The electrochemical system also needs a potentiostat and an input voltage-generating circuit, which were developed using on-chip active devices and a few discrete passive components. This is the first sensor system incorporating electrode-side input voltage generation for electrochemical measurements using an on-chip operational amplifier, which replaces a bulky external voltage controller. A continuous cyclic voltammetry measurement was conducted with a well-studied ferricyanide solution to demonstrate the operation of the intelligent sensor chip. A clear peak was observed and linearity to the target chemical concentration was obtained between the peak height and concentration of the ferricyanide solution. With potential for mass production and small size, this sensor chip could be the best candidate to realize point-of-care testing. This sensor chip is a milestone of a fully integrated electrochemical sensor chip.
Amperometric Electrochemical Sensor Array for On-Chip Simultaneous Imaging: Circuit and Microelectrode Design Considerations
Authors: Hasegawa Junichi , Uno Shigeyasu , Nakazato Kazuo
Published: April 2011

We propose a switching circuit and an electrode design for measuring multiple microelectrode currents at high speed. Our goal is to realize two-dimensional (2D) imaging of analyte distributions by amperometry. In the proposed amperometric sensor circuit, each electrode is connected to two switches. During measurement, the potential of all electrodes is fixed, the steady-state current is maintained, and the switching is carried out while maintaining the steady-state current. A current buffer circuit was fabricated, its the characteristics were evaluated. The time course of the electrochemical current of an electrolyte was measured using the current buffer circuit. We have also proposed a microelectrode structure to suppress the expansion of the diffusion layer over the microelectrode array. Each electrode has a steady-state current, which is amplified by a redox cycle, and the time to reach the steady state is reduced to about 1/10 of that required by a single microelectrode. The relation between the characteristic lengths of the electrode geometry and the current gain is presented.
Fabrication of High-Sensitivity Polycrystalline Silicon Nanowire Field-Effect Transistor pH Sensor Using Conventional Complementary Metal–Oxide–Semiconductor Technology
Authors: Chen Hou-Yu , Lin Chia-Yi , Chen Min-Cheng , Huang Chien-Chao , Chien Chao-Hsin
Published: April 2011

High-sensitivity polycrystalline silicon (poly-Si) nanowire field-effect transistor (NW FET) pH sensors using top-down and self-aligned fabrication approaches involving the conventional complementary metal–oxide–semiconductor (CMOS) process are reported. For the top-down NW FET, the shrinkage due to reoxidation enables the nanowire width to be scaled to 40 nm without requiring the use of extra lithography equipment, and this improves the electrical uniformity and the performance of the sensors. The surface-ionic coupling operation of this buried-channel field-effect sensor exhibits superior pH sensitivity (threshold voltage shift > 100 mV/pH) as compared to the surface-channel ion-sensitive FET (ISFET). In addition, we report a novel method for fabricating self-aligned, vertical-channel, poly-Si nanowire sensors. The resulting 65-nm self-aligned vertical-channel poly-Si device was found to be feasible for independent-gate bias control, thus enabling its possible integration in very-large-scale integration (VLSI) circuits. Both the abovementioned approaches enable the manufacture of nanowire devices on a large-scale integrated (LSI) circuit using only CMOS manufacturing processes; this provides a high sensitivity, compact and cost-efficient biosensor systems-on-a-chip application.
Effects of CF4Plasma Treatment on pH and pNa Sensing Properties of Light-Addressable Potentiometric Sensor with a 2-nm-Thick Sensitive HfO2Layer Grown by Atomic Layer Deposition
Authors: Chin Chi-Hang , Lu Tseng-Fu , Wang Jer-Chyi , Yang Jung-Hsiang , Lue Cheng-En , Yang Chia-Ming , Li Sheng-Shian , Lai Chao-Sung
Published: April 2011

We investigated the effect of the carbon tetrafluoride (CF4) plasma treatment on pH and pNa sensing characteristics of a light-addressable potentiometric sensor (LAPS) with a 2-nm-thick HfO2film grown by atomic layer deposition (ALD). An inorganic CF4plasma treatment with different times was performed using plasma enhance chemical vapor deposition (PECVD). For pH detection, the pH sensitivity slightly decreased with increasing CF4plasma time. For pNa detection, the proposed fluorinated HfO2film on a LAPS device is sensitive to Na+ions. The linear relationship between pNa sensitivity and plasma treatment time was observed and the highest pNa sensitivity of 33.9 mV/pNa measured from pNa 1 to pNa 3 was achieved. Compared with that of the same structure without plasma treatment, the sensitivity was improved by twofold. The response mechanism of the fluorinated HfO2LAPS is discussed according to the chemical states determined by X-ray photoelectron spectroscopy (XPS) analysis. The analysis of F 1s, Hf 4f, and O 1s spectra gives evidence that the enhancement of pNa sensitivity is due to the high concentration of incorporated fluorine in HfO2films by CF4plasma surface treatment.
Reference Electrode–Insulator–Nitride–Oxide–Semiconductor Structure with Sm2O3 Sensing Membrane for pH-Sensor Application
Authors: Wang Jer-Chyi , Lu Tseng-Fu , Shih Hui-Yu , Yang Chia-Ming , Lai Chao-Sung , Kao Chyuan-Haur , Pan Tung-Ming
Published: April 2011

We investigate a reference electrode–insulator–nitride–oxide–semiconductor (RINOS) structure with a Sm2O3 sensing membrane and using silicon nitride as the charge trapping layer for pH detection. The proposed RINOS device with the oxide–nitride–oxide (ONO) structure exhibits a high pH sensitivity (larger than the ideal Nernst response, ∼59 mV/pH) owing to hydrogen ion adsorption by the trapped electrons within the embedded Si3N4 layer when applying a stress voltage. As the applied voltage and time increase, pH sensitivity increased. The possible sensing mechanism based on charge attraction was demonstrated using schematic band diagrams. To improve the retention of an increased sensitivity, an additional SiO2 layer as a blocking layer between the Sm2O3 and Si3N4 films to form the RIONOS device was proposed. Compared with the conventional electrolyte–insulator–semiconductor (EIS) structure, the proposed RIONOS device can be used to detect ultra small pH variations owing to its high pH-sensing response.
Sensitivity Improvement of Biosensors Using Si Ring Optical Resonators
Authors: Fukuyama Masataka , Amemiya Yoshiteru , Abe Yosuke , Onishi Yuto , Hirowatari Anna , Terao Kei , Ikeda Takeshi , Kuroda Akio , Yokoyama Shin
Published: April 2011

We have been demonstrating label-free detection of a variety of antigen–antibody reactions using Si ring optical resonators. Although the detection of biomarkers for the diagnosis of diseases generally requires high sensitivity of the order of 10-9 g/ml, the detection sensitivity of our device is currently of the order of 10-6 g/ml. In this paper, we show that the sensitivity of 10-9 g/ml will be possible by adopting the following four strategies: (1) use of slot-type waveguides with light wavelength of 1.3 µm, (2) improvement of quality factor Q of the ring resonator by smoothing the surface roughness, (3) specific adsorption of the bioreceptor protein to the resonator surface, and (4) maintaining temperature within ±0.005 °C. We have also proposed the on-chip temperature compensation method without the need for temperature control of the sample. By combining the proposed approaches, the sensitivity of the biosensor will be improved by a factor of >100, thus realizing practical application of our Si ring biosensor.
Magnetic Field Dependence of Quadrupolar Splitting and Nuclear Spin Coherence Time in a Strained (110) GaAs Quantum Well
Authors: Ishihara Jun , Ono Masaaki , Sato Genki , Matsuzaka Shunichiro , Ohno Yuzo , Ohno Hideo
Published: April 2011

We investigated the magnetic field dependence of quadrupolar splitting and phase relaxation time of nuclear spins in an n-GaAs/AlGaAs (110) quantum well (QW) by optically detected nuclear magnetic resonance (NMR). The NMR spectra show large quadrupolar splitting induced by an internal field gradient in the QW epilayer. At lower magnetic fields, the quadrupolar splitting become much enhanced, resulting in the appearance of the second order magnetic field dependence of the quadrupole interaction in the NMR spectra. It is also shown that the intrinsic coherence time and the effective coherence time for resonant transitions become shorter as a result that the energy splitting between the two levels becomes small and incoherent transition is occurred by irradiation of an rf magnetic field.
Interface Properties of Ag and Au/Graphene Heterostructures Studied by Micro-Raman Spectroscopy
Authors: Entani Shiro , Sakai Seiji , Matsumoto Yoshihiro , Naramoto Hiroshi , Hao Ting , Maeda Yoshihito
Published: April 2011

We have studied the influence of the interface formation of graphene with noble metals (Ag and Au) on its vibrational properties by using confocal micro-Raman spectroscopy. The interactions at the metal/graphene interface are investigated by comparing the results from two different regions, the heterostructure and pristine graphene regions, with and without noble metals on the same graphene sheet. In Ag/graphene, the Raman signal intensity was increased by the surface enhanced Raman scattering process, and the enhanced signals are found to be composed of the broadened D and G peak components emitted from the Ag/graphene interface. The precise evaluation of graphene-layer-number-dependence of the D and G bands revealed that the disordered graphitic carbons were adhered on the glass substrate during the sample preparation by the micromechanical cleavage method. In the 2D band, no obvious peak shift induced by the heterostructure formation was observed in Ag/graphene, whereas a large shift (more than ∼15 cm-1) was observed at Au/single layer graphene. This is considered to be due to the difference in the amount of the doped carriers in graphene between two heterostructures.
Simple Fabrication Technique for Field-Effect Transistor Array Using As-Grown Single-Walled Carbon Nanotubes
Authors: Aikawa Shinya , Einarsson Erik , Inoue Taiki , Xiang Rong , Chiashi Shohei , Shiomi Junichiro , Nishikawa Eiichi , Maruyama Shigeo
Published: April 2011

A carbon nanotube field-effect transistor (CNT-FET) is a promising candidate for future electronic devices; however, its fabrication process is still challenging. We propose a simple fabrication technique for CNT-FET arrays using as-grown single-walled CNTs (SWNTs) as the gate channel. In this study, a hydrophobic self-assembled monolayer (SAM) was used to restrict the catalyst-supporting area after the fabrication of an electrode array. Since it is known that droplets are trapped at rough edges of a hydrophobic surface, the deposition of a liquid-based catalyst, followed by alcohol catalytic chemical vapor deposition (ACCVD) produced SWNTs that grew only at the corners of electrode edges. The current–voltage (I–V) characterization of FETs with a 40 µm channel width showed that 98% of the fabricated devices were electrically connected and more than 50% were functional FETs (I
ON/I
OFF > 102).
Ellipsoidal Band Structure Effects on Maximum Ballistic Current in Silicon Nanowires
Authors: Mori Nobuya , Minari Hideki , Uno Shigeyasu , Hattori Junichi
Published: April 2011

We have calculated the maximum ballistic current density in circular-shaped silicon nanowires (SiNWs) to investigate the validity and limitation of an isotropic in-plane effective-mass approximation, which is often used for analyzing circular-shaped SiNW transistors. We compare the exact elliptic model with three types of isotropic approximations, based on arithmetic, harmonic, or geometric means. The ground subband level is found to be well approximated in the harmonic mean model. For the maximum current density, all the models give the exact value in the quantum limit at smaller radius. The geometric mean model approaches the exact elliptic model for larger radius. In an intermediate region, the harmonic mean model gives the smallest error compared to the other isotropic models.
Performance Investigation on p-Type Si-, Ge-, and Ge–Si Core–Shell Nanowire Schottky Barrier Transistors
Authors: Pu Jing , Sun Lei , Han Ru-Qi
Published: April 2011

In this paper, we investigate the working mechanism of p-channel Schottky barrier Ge–Si core–shell nanowire transistors and then study the impact factors on the device performance of Schottky barrier transistors using Si-, Ge-, and Ge–Si core–shell nanowires as channels. For Ge–Si core–shell channel devices, most holes tunnel at the source near the heterojuction and transport in the Ge core region. Ge channel devices can provide the largest drive current and core–shell devices have the smallest sub-threshold slope among above three types of transistors. It is also found that core–shell device's conductive currents vary a little when fixing Ge core radius and changing Si shell thickness, and core–shell devices' normalized drain current can be greatly enhanced by reducing nanowires' radius or increasing core radius. Moreover, the drivability of core–shell devices is insensitive to both silicide/channel and germanide/channel barrier heights, which will further relax the requirement for contact materials.
In situ Observation of Polycrystalline Silicon Thin Films Grown Using Aluminum-Doped Zinc Oxide on Glass Substrate by the Aluminum-Induced Crystallization
Authors: Jung Mina , Okada Atsushi , Saito Takanobu , Suemasu Takashi , Chung Chan-Yeup , Kawazoe Yoshiyuki , Usami Noritaka
Published: April 2011

We present the impact of Al-doped ZnO (AZO) layer of polycrystalline silicon (poly-Si) thin films grown at different annealing temperatures using aluminum-induced crystallization (AIC). In situ observation revealed that the increase of crystallized fraction was fast in poly-Si films grown with AZO layer compared to those without AZO. It is explained that the roughness of interface between Si and Al by introducing AZO layer was increased, which contributes to enhancement of diffused Si concentration into Al layer. Those results were also quantitatively demonstrated by calculating of Si concentration diffused into the Al layer. Therefore, we exhibit that controlling interface roughness is shown to be important to determine the growth rate of poly-Si thin films.
Theoretical Study on Effect of SiC Crystal Structure on Carrier Transfer in Quantum Dot Solar Cells
Authors: Hirose Sho , Yamashita Itaru , Nagumo Ryo , Miura Ryuji , Suzuki Ai , Tsuboi Hideyuki , Hatakeyama Nozomu , Endou Akira , Takaba Hiromitsu , Kubo Momoji , Miyamoto Akira
Published: April 2011

Quantum dot (QD) solar cells are proposed as high-efficiency solar cells. However, their reported conversion efficiencies have been lower than half of the ideal value. To improve their efficiency, the optimization of their cell structure in terms of various parameters, e.g., dot size, interdot distance, type of materials, and QD/bulk interface structure, is necessary. In this paper, we focused on the most important factor for the improvement in the conversion efficiency of Si/SiC type QD solar cells and investigated the effect of the atomistic structure of the QD/bulk interface on carrier transfer by tight-binding simulation. We constructed models of Si/SiC systems and analyzed the effect of QD/bulk interface defects on their electronic structure and carrier transfer properties. It was suggested that electrons trapped at the QD/bulk interface and the type of SiC crystal structure affect electron transfer.
Multiscale Simulation of Dye-Sensitized Solar Cells Considering Schottky Barrier Effect at Photoelectrode
Authors: Onodera Mari , Nagumo Ryo , Miura Ryuji , Suzuki Ai , Tsuboi Hideyuki , Hatakeyama Nozomu , Endou Akira , Takaba Hiromitsu , Kubo Momoji , Miyamoto Akira
Published: April 2011

The effect of the TiO2/transparent conducting oxide (TCO) interface in a photoelectrode of a dye-sensitized solar cell (DSSC) on its cell performance was investigated using our multiscale simulator, in which we had added a calculation of the voltage loss derived from the Schottky barrier height (SBH) at the TiO2/TCO interface to our previous simulator. We treated the TiO2/TCO interface as a series connection of a Schottky diode of metal/n-type semiconductor. The thermionic-emission theory was applied to describe the electron transfer and the voltage loss at the TiO2/TCO interface. The accuracy of the prediction of the current density–voltage (J–V) characteristics of a DSSC employing the cis-dithiocyanato-bis(2,2'-bipyridyl-4,4'-dicarboxylic acid)-ruthenium(II) (N3 dye) was improved compared with that obtained by our previous simulator. The effects of the SBH on the open circuit voltage (V
OC) and the maximum power output (P
max), as well as the J–V characteristics, of the DSSC were discussed. Our results suggest that a TCO with the SBH≤0.5 is suitable for a DSSC.
Material Research on High-Quality Passivation Layers with Controlled Fixed Charge for Crystalline Silicon Solar Cells
Authors: Tachibana Tomihisa , Sameshima Takashi , Iwashita Yuta , Kiyota Yuji , Chikyow Toyohiro , Yoshida Haruhiko , Arafune Koji , Satoh Shin-ichi , Ogura Atsushi
Published: April 2011

We evaluated the three types of composition spread passivation layer, i.e., Al2O3–HfO2, HfO2–Y2O3, and Al2O3–Y2O3 systems, by combinatorial pulsed laser deposition to evaluate and control the fixed charge, while interface states were kept constant with a SiO2 interlayer. The flat-band voltage of the capacitance–voltage (C–V) curves was shifted widely from positive to negative by changing the composition. The calculated fixed charge in the Y2O3 was positive while those in the HfO2 and Al2O3 were negative. In the Al2O3–Y2O3 system, the fixed charge was significantly varied between -2.7 and 1.3×1012 cm-2 with composition spread. The maximum negative charge was found in the Al2O3 layer with a slight amount of Y2O3, while the maximum positive charge was realized with almost pure Y2O3. The fixed charge modifications were also found in the Al2O3–HfO2 and HfO2–Y2O3 systems. Additional oxidation after layer deposition also modified the fixed charge properties. The largest negative fixed charge of -3.1×1012 cm-2 was found in approximately HfO2:Y2O3=1:1 after the annealing process, while the largest positive charge of 1.3×1012 cm-2 was found for Y2O3 with Al2O3 incorporation. The passivation layers with controlled fixed charge can be promising materials for the high-quality passivation layer in crystalline silicon solar cells.
Surface Morphology and Device Performance of CuInS2 Solar Cells Prepared by Single- and Two-Step Evaporation Methods
Authors: Fukamizu Shohei , Kondo Toshihiro , Oda Yusuke , Minemoto Takashi , Takakura Hideyuki
Published: April 2011

Absorbers of CuInS2 (CIS) solar cells are fabricated by several processes and a 11.4% efficiency CIS solar cell is reported. However, this value is lower than the theoretically expected value, possibly owing to the roughness of the CIS surface. In this study, we attempted to realize smoother CIS films using a new two-step evaporation method. As a first step, Cu-rich CIS films were deposited at a low substrate temperature of 50 °C and were annealed at 500 °C. As a second step, In and S were sequentially deposited on the annealed films to control the compositional ratio to In-rich. The deposited film showed a smoother surface than the film deposited by the single-step evaporation of Cu, In, and S. The CIS solar cell formed using the two-step evaporation method showed a higher open-circuit voltage. This should be due to the smoother film surface, which reduced the p–n junction area of the device.
Stonebraker on data warehouses
Authors: Stonebraker Michael
Published: April 2011

The
Communications
Web site, http://cacm.acm.org, features more than a dozen bloggers in the BLOG@CACM community. In each issue of
Communications
, we'll publish selected posts or excerpts.

twitter

Follow us on Twitter at http://twitter.com/blogCACM

http://cacm.acm.org/blogs/blog-cacm

Data warehouses are not only increasing in size and complexity, but also in their importance to business. Michael Stonebraker shares 10 key ideas on the topic.
Sorting through photos
Authors: Savage Neil
Published: April 2011

Teaching computers to understand pictures could lead to search engines capable of identifying and organizing large datasets of visual information.
I, domestic robot
Authors: Goth Gregory
Published: April 2011

With recent advances in laser rangefinders, faster algorithms, and open source robotic operating systems, researchers are increasing domestic robots' semantic and situational awareness.
Data optimization in developing nations
Authors: Hoffmann Leah
Published: April 2011

Artificial intelligence and machine learning could expand access to health care, improve the quality of education, and respond effectively to natural disasters in the developing world.
Online advertising, behavioral targeting, and privacy
Authors: Goldfarb Avi , Tucker Catherine E.
Published: April 2011

Studying how privacy regulation might impact economic activity on the advertising-supported Internet.
An interview with Steve Furber
Authors: Fitzpatrick Jason
Published: April 2011

Steve Furber, designer of the seminal BBC Microcomputer System and the widely used ARM microprocessor, reflects on his career.
Weapons of mass assignment
Authors: McKenzie Patrick
Published: April 2011

A Ruby on Rails app highlights some serious, yet easily avoided, security vulnerabilities.
The one-second war
Authors: Kamp Poul-Henning
Published: April 2011

Finding a lasting solution to the leap seconds problem has become increasingly urgent.
Brain-computer interfaces for communication and control
Authors: McFarland Dennis J. , Wolpaw Jonathan R.
Published: April 2011

The brain's electrical signals enable people without muscle control to physically interact with the world.
The future of microprocessors
Authors: Borkar Shekhar , Chien Andrew A.
Published: April 2011

Energy efficiency is the new fundamental limiter of processor performance, way beyond numbers of processors.
Proving program termination
Authors: Cook Byron , Podelski Andreas , Rybalchenko Andrey
Published: April 2011

In contrast to popular belief, proving termination is not always impossible.
Puzzled: Games, roles, turns
Authors: Winkler Peter
Published: April 2011

Welcome to three new puzzles. Solutions to the first two will be published next month; the third is (as yet) unsolved. In each, the issue is how your intuition matches up with the mathematics.
Evaluation of Haptic HTML Mappings Derived from a Novel Methodology
Authors: Kuber Ravi , Yu Wai , O’Modhrain M. Sile
Published: April 2011

As levels of awareness surrounding accessibility increase, designers often look towards using nonvisual technologies to make existing graphical interfaces (e.g. Web pages) more inclusive. As existing haptic design guidance is not targeted to the specific needs of blind Web users, inappropriate touchable representations of graphical objects may be developed and integrated with Web interfaces, thereby reducing the quality of the browsing experience. This paper describes the evaluation of haptic HTML mappings that were developed using a participatory-design based technique, and presented using the Logitech Wingman force-feedback mouse. Findings have shown that participants were able to identify objects presented haptically, and develop a structural representation of layout from exploring content. Participants were able to perform a range of Web-based tasks that were previously found to be difficult for some blind users when using a screen reader alone. The haptic HTML mappings are presented, along with recommendations for their application derived from a validation study. The design guidance presented offers a standard reference tool for Web designers wanting to develop an accessible browsing application, using the benefits offered by a force-feedback mouse.
Identifying Behavioral Strategies of Visually Impaired Users to Improve Access to Web Content
Authors: Lunn Darren , Harper Simon , Bechhofer Sean
Published: April 2011

The World Wide Web is a predominantly visual media for presenting and disseminating information. As such, visually impaired users, who access content through audio interaction, are hindered as the Web is not designed with their needs in mind. To compensate for this, visually impaired users develop behavioral strategies to cope when access to the content becomes challenging. While tools exist to aid visually impaired users in accessing the Web, they tend to focus on adapting content to meet the needs of the device rather than the user. Therefore, to further improve Web access an understanding of the behavioral strategies users employ is required. To achieve this, studies of eleven visually impaired Web users were conducted. The data from these sessions were analyzed to develop a framework for identifying strategies that users may employ when they face difficulties accessing the content. Using data for twenty visually impaired users obtained from an independent study, the framework was validated and shown to be flexible and accurate enough to be applicable to multiple data sources. An analysis of the coping strategies identified from the framework revealed six abstract patterns of coping. These patterns were used as the basis for developing behavior-driven transcoding that transformed static Web documents into interactive content by allowing users to navigate between key elements of the page through a consistent set of key presses. Results obtained from a user evaluation of the transcoding support the use of behavior-driven transcoding as a mechanism for improving access to Web content when compared to existing transcoding techniques. This result allows the coping strategies framework to be used as a foundation for further understanding of the strategies visually impaired users employ on Web sites and the transformations required to allow the Web to be accessible to those users.
Child-centered interaction in the design of a game for social skills intervention
Authors: Tan Jean Lee , Goh Dion Hoe-Lian , Ang Rebecca P. , Huan Vivien S.
Published: April 2011

In this article we describe the CALSIUM framework to elicit children's contributions and perspectives in the design of an online game for enhancing social skills of children. This study advocates a participatory design approach that emphasizes the active involvement of users at the early part of the design process. The children play-tested the game prototype and participated in focus group discussions. Using storyboarding, a low-fidelity prototyping technique, they developed design concepts and ideas which were translated into design directions for the development of the game. The data collected were used to glean insights into the likes and dislikes of children and to analyze the opportunities and challenges in engaging children as users, testers, informants, and design partners. Besides stretching children's creativity and critical thinking on the game design, the children's cognitive understanding of social knowledge was enhanced, evident from the design artifacts produced.
DevilTyper
Authors: Ho Chien-Ju , Wu Chen-Chi , Chen Kuan-Ta , Lei Chin-Laung
Published: April 2011

CAPTCHA is an effective and widely used solution for preventing computer programs (i.e., bots) from performing automated but often malicious actions, such as registering thousands of free email accounts or posting advertisement on Web blogs. To make CAPTCHAs robust to automatic character recognition techniques, the text in the tests are often distorted, blurred, and obscure. At the same time, those robust tests may prevent genuine users from telling the text easily and thus distribute the cost of crime prevention among all the users. Thus, we are facing a dilemma, that is, a CAPTCHA should be robust enough so that it cannot be broken by programs, but also needs to be easy enough so that users need not to repeatedly take tests because of wrong guesses.

In this article, we attempt to resolve the dilemma by proposing a human computation game for quantifying the usability of CAPTCHAs. In our game, DevilTyper, players try to defeat as many devils as possible by solving CAPTCHAs, and player behavior in completing a CAPTCHA is recorded at the same time. Therefore, we can evaluate CAPTCHAs' usability by analyzing collected player inputs. Since DevilTyper provides entertainment itself, we conduct a large-scale study for CAPTCHAs' usability without the resource overhead required by traditional survey-based studies. In addition, we propose a consistent and reliable metric for assessing usability. Our evaluation results show that DevilTyper provides a fun and efficient platform for CAPTCHA designers to assess their CAPTCHA usability and thus improve CAPTCHA design.
Large-scale displays for public spaces---constellation of departure
Authors: Sato Munehiko , Suzuki Yasuhiro , Nishizaka Shinya , Torigoe Yusuke , Izumihara Atsushi , Hiyama Atsushi , Nishimura Kunihiro , Tanikawa Tomohiro , Hirose Michitaka
Published: April 2011

The use of large visual displays in public spaces such as large buildings has become increasingly popular. Public art can make use of the characteristics and context of the site. However, it is difficult to install new displays in existing buildings because of the large, rigid hardware associated with such displays. In this article, we describe a robust, lightweight, low-profile, and fully restorable display system that can be easily and quickly installed for use in existing public buildings. We considerably reduced the number of physical components and the system weight with our proposed method, which can be optimized for any planned content. We describe the technical design and implementation of the display system and discuss some of its applications for public audiences. We then report a three-month field trial that we conducted at an airport terminal building. We discuss the advantages and effectiveness of this system in light of the field trial results.
Secretoneurin stimulates the production and release of luteinizing hormone in mouse LβT2 gonadotropin cells
Authors: Zhao E. , McNeilly Judy R. , McNeilly Alan S. , Fischer-Colbrie Reiner , Basak Ajoy , Seong Jae Young , Trudeau Vance L.
Published: April 2011

Secretoneurin (SN) is a functional secretogranin II (SgII)-derived peptide that stimulates luteinizing hormone (LH) production and its release in the goldfish. However, the effects of SN on the pituitary of mammalian species and the underlying mechanisms remain poorly understood. To study SN in mammals, we adopted the mouse LβT2 gonadotropin cell line that has characteristics consistent with normal pituitary gonadotrophs. Using radioimmunoassay and real-time RT-PCR, we demonstrated that static treatment with SN induced a significant increment of LH release and production in LβT2 cells in vitro. We found that GnRH increased cellular SgII mRNA level and total SN-immunoreactive protein release into the culture medium. We also report that SN activated the extracellular signal-regulated kinases (ERK) in either 10-min acute stimulation or 3-h chronic treatment. The SN-induced ERK activation was significantly blocked by pharmacological inhibition of MAPK kinase (MEK) with PD-98059 and protein kinase C (PKC) with bisindolylmaleimide. SN also increased the total cyclic adenosine monophosphate (cAMP) levels similarly to GnRH. However, SN did not activate the GnRH receptor. These data indicate that SN activates the protein kinase A (PKA) and cAMP-induced ERK signaling pathways in the LH-secreting mouse LβT2 pituitary cell line.
Exploration of Heterogeneous FPGA Architectures
Authors: Farooq Umer , Parvez Husain , Mehrez Habib , Marrakchi Zied
Published: April 2011

Mesh-based heterogeneous FPGAs are commonly used in industry and academia due to their area, speed, and power benefits over their homogeneous counterparts. These FPGAs contain a mixture of logic blocks and hard blocks where hard blocks are arranged in fixed columns as they offer an easy and compact layout. However, the placement of hard-blocks in fixed columns can potentially lead to underutilization of logic and routing resources and this problem is further aggravated with increase in the types of hard-blocks. This work explores and compares different floor-planning techniques of mesh-based FPGA to determine their effect on the area, performance, and power of the architecture. A tree-based architecture is also presented; unlike mesh-based architecture, the floor-planning of heterogeneous tree-based architecture does not affect its routing requirements due to its hierarchical structure. Both mesh and tree-based architectures are evaluated for three sets of benchmark circuits. Experimental results show that a more flexible floor-planning in mesh-based FPGA gives better results as compared to the column-based floor-planning. Also it is shown that compared to different floor-plannings of mesh-based FPGA, tree-based architecture gives better area, performance, and power results.
On Stability of Linear Delay Differential Equations under Perron′s Condition
Authors: Diblík J. , Zafer A.
Published: April 2011

The stability of the zero solution of a system of first‐order
linear functional differential equations with nonconstant delay is considered.
Sufficient conditions for stability, uniform stability, asymptotic stability, and
uniform asymptotic stability are established.
Evaluating the Potential of Commercial Forest Inventory Data to Report on Forest Carbon Stock and Forest Carbon Stock Changes for REDD+ under the UNFCCC
Authors: Maniatis Danae , Malhi Yadvinder , Saint André Laurent , Mollicone Danilo , Barbier Nicolas , Saatchi Sassan , Henry Matieu , Tellier Laurent , Schwartzenberg Mathieu , White Lee
Published: April 2011

In the context of the adoption at the 16th Conference of the Parties in 2010 on the REDD+ mitigation mechanism, it is important to obtain reliable data on the spatiotemporal variation of forest carbon stocks and changes (called Emission Factor, EF). A re-occurring debate in estimating EF for REDD+ is the use of existing field measurement data. We provide an assessment of the use of commercial logging inventory data and ecological data to estimate a conservative EF (REDD+ phase 2) or to report on EF following IPCC Guidance and Guidelines (REDD+ phase 3). The data presented originate from five logging companies dispersed over Gabon, totalling 2,240 plots of 0.3 hectares.We distinguish three Forest Types (FTs) in the dataset based on floristic conditions. Estimated mean aboveground biomass (AGB) in the FTs ranges from 312 to 333 Mg ha−1. A 5% accuracy is reached with the number of plots put in place for the FTs and a low sampling uncertainty obtained (± 10 to 13 Mg ha−1). The data could be used to estimate a conservative EF in REDD+ phase 2 and only partially to report on EF following tier 2 requirements for a phase 3.
Metabolomic Characterization of Ovarian Epithelial Carcinomas by HRMAS-NMR Spectroscopy
Authors: Ben Sellem D. , Elbayed K. , Neuville A. , Moussallieh F.-M. , Lang-Averous G. , Piotto M. , Bellocq J.-P. , Namer I. J.
Published: April 2011

Objectives. The objectives of the present study are to determine if a metabolomic study by HRMAS-NMR can (i) discriminate between different histological types of epithelial ovarian carcinomas and healthy ovarian tissue, (ii) generate statistical models capable of classifying borderline tumors and (iii) establish a potential relationship with patient's survival or response to chemotherapy.Methods. 36 human epithelial ovarian tumor biopsies and 3 healthy ovarian tissues were studied using1H HRMAS NMR spectroscopy and multivariate statistical analysis.Results. The results presented in this study demonstrate that the three histological types of epithelial ovarian carcinomas present an effective metabolic pattern difference. Furthermore, a metabolic signature specific of serous (N-acetyl-aspartate) and mucinous (N-acetyl-lysine) carcinomas was found. The statistical models generated in this study are able to predict borderline tumors characterized by an intermediate metabolic pattern similar to the normal ovarian tissue. Finally and importantly, the statistical model of serous carcinomas provided good predictions of both patient's survival rates and the patient's response to chemotherapy.Conclusions. Despite the small number of samples used in this study, the results indicate that metabolomic analysis of intact tissues by HRMAS-NMR is a promising technique which might be applicable to the therapeutic management of patients.