Graphene Quantum Sheet Catalyzed Silicon Photocathode for Selective CO2 Conversion to CO

The reduction of carbon dioxide (CO₂) into chemical feedstock is drawing increasing attention as a prominent method of recycling atmospheric CO₂. Although many studies have been devoted in designing an efficient catalyst for CO₂ conversion with noble metals, low selectivity and high energy input still remain major hurdles. One possible solution is to use the combination of an earth‐abundant electrocatalyst with a photoelectrode powered by solar energy. Herein, for the first time, a p‐type silicon nanowire with nitrogen‐doped graphene quantum sheets (N‐GQSs) as heterogeneous electrocatalyst for selective CO production is demonstrated. The photoreduction of CO₂ into CO is achieved at a potential of ?1.53 V versus Ag/Ag⁺, providing 0.15 mA cm^?2 of current density, which is 130 mV higher than that of a p‐type Si nanowire decorated with well‐known Cu catalyst. The faradaic efficiency for CO is 95%, demonstrating significantly improved selectivity compared with that of bare planar Si. The density functional theory (DFT) calculations are performed, which suggest that pyridinic N acts as the active site and band alignment can be achieved for N‐GQSs larger than 3 nm. The demonstrated high efficiency of the catalytic system provides new insights for the development of nonprecious, environmentally benign CO₂ utilization.     

Surface leakage current analysis of ion implanted ZnS-passivated n-on-p HgCdTe diodes in weak inversion

Effects of fixed charge on R₀A value of ZnS-passivated x=0.3 HgCdTe n-on-p diode are explained as a shunt resistance that affects current-voltage (I-V) and dynamic resistance-voltage (Rd-V) characteristics. The fixed charge of 1×10¹¹/cm² to 2 × 10¹¹/cm² which is usually obtained with ZnS passivation makes the surface weakly inverted and reduces HgCdTe diode R₀A value owing to the short generation lifetime of HgCdTe substrate. The gate-controlled diode and specially fabricated diode are used to explain the surface leakage current in the weak inversion and charge sheet model is used to explain the characteristics. It is found that the surface leakage current by the inverted channel in the weak inversion can reduce R₀A more than other currents such as the generation current and tunneling current which are usually used to explain the surface leakage current of HgCdTe diode.     

Board-level reliability of Pb-free solder joints of TSOP and various CSPs

To evaluate various Pb-free solder systems for leaded package, thin small outline packages (TSOPs) and chip scale packages (CSPs) including leadframe CSP (LFCSP), fine pitch BGA (FBGA), and wafer level CSP (WLCSP) were characterized in terms of board level and mechanical solder joint reliability. For board level solder joint reliability test of TSOPs, daisy chain samples having pure-Sn were prepared and placed on daisy chain printed circuit board (PCB) with Pb-free solder pastes. For CSPs, the same composition of Pb-free solder balls and solder pastes were used for assembly of daisy chain PCB. The samples were subjected to temperature cycle (T/C) tests (-65/spl deg/C/spl sim/150/spl deg/C, -55/spl deg/C/spl sim/125/spl deg/C, 2 cycles/h). Solder joint lifetime was electrically monitored by resistance measurement and the metallurgical characteristics of solder joint were analyzed by microstructural observation on a cross-section sample. In addition, mechanical tests including shock test, variable frequency vibration test, and four point twisting test were carried out with daisy chain packages too. In order to compare the effect of Pb-free solders with those of Sn-Pb solder, Sn-Pb solder balls and solder paste were included. According to this paper, most Pb-free solder systems were compatible with the conventional Sn-Pb solder with respect to board level and mechanical solder joint reliability. For application of Pb-free solder to WLCSP, Cu diffusion barrier layer is required to block the excessive Cu diffusion, which induced Cu trace failure.     

A higher order FDTD method in Integral formulation

We present a fourth-order (4, 4) finite-difference time-domain (FDTD)-like algorithm based on the integral form of Maxwell's equations. The algorithm, which is called the integro-difference time-domain (IDTD) method, achieves its fourth-order accuracy in space and time by taking into account the spatial and temporal variations of electromagnetic fields within each computational cell. In the algorithm, the electromagnetic fields within each cell are represented by space and time integrals (or integral averages) of the fields, i.e., the electric and magnetic fluxes (D,B) are represented by the surface-integral average, and the electric and magnetic fields (E,H) by the line and time integral average. In order to relate the integral average fields in the staggered update equations, we have obtained constitutive relations for these fields. It is shown that the IDTD update equations combined with the constitutive relations are fourth-order accurate both in space and time. The fourth-order correction terms are represented by the modified coefficients in the update equations; the numerical structure remains the same as the conventional second-order update equations and more importantly does not require the storage of field variables at the previous time steps to obtain the fourth-order accuracy in time. Furthermore, the Courant-Friedrichs-Lewy (CFL) stability criteria of this fourth-order algorithm turns out to be identical to the stability limits of conventional second-order FDTD scheme based on differential formulation.     

2D Image Construction from Low Resolution Response of a New Non‐invasive Measurement for Medical Application

This paper presents an application of digital signal processing to data acquired by the radio imaging method (RIM) that was adopted to measure moisture distribution inside the human body. RIM was originally developed for the mining industry; we are applying the method to a biomedical measurement because of its simplicity, economy, and safety. When a two‐dimensional image was constructed from the measured data, the method provided insufficient resolution because the wavelength of the measurement medium, a weak electromagnetic wave in a VHF band, was longer than human tissues. We built and measured a phantom, a model simulating the human body, consisting of two water tanks representing large internal organs. A digital equalizer was applied to the measured values as a weight function, and images were reconstructed that corresponded to the original shape of the two water tanks. As a result, a two‐dimensional image containing two individual peaks corresponding to the original two small water tanks was constructed. The result suggests the method was applicable to biomedical measurement by the assistance of digital signal processing. This technique may be applicable to home‐based medical care and other situations in which safety, simplicity, and economy are important.     

An Analytical Framework for Imperfect DS‐CDMA Closed‐Loop Power Control over Flat Fading

This letter presents an analytical framework for a performance analysis of the imperfect direct‐sequence code division multiple access (DS‐CDMA) closed‐loop power control (CLPC) loop with loop delay, channel estimation error, and power control command bit error as the parameters under a Rayleigh flat fading environment. The proposed model is verified through a comparison between analytical results and simulation ones.     

A 1-V 10.7-MHz switched-opamp bandpass /spl Sigma//spl Delta/ modulator using double-sampling finite-gain-compensation technique

A 1 V switched-capacitor (SC) bandpass sigma-delta (/spl Sigma//spl Delta/) modulator is realized using a high-speed switched-opamp (SO) technique with a sampling frequency of up to 50 MHz, which is improved ten times more than prior 1 V SO designs and comparable to the performance of the state-of-the-art SC circuits that operate at much higher supply voltages. On the system level, a fast-settling double-sampling SC biquadratic filter architecture is proposed to achieve high-speed operation. A low-voltage double-sampling finite-gain-compensation technique is employed to realize a high-resolution /spl Sigma//spl Delta/ modulator using only low-DC-gain opamps to maximize the speed and to reduce power dissipation. On the circuit level, a fast-switching methodology is proposed for the design of the switchable opamps to achieve a switching frequency up to 50 MHz. Implemented in a 0.35-/spl mu/m CMOS process (V/sub TP/=0.82 V and V/sub TN/=0.65 V) and at 1 V supply, the modulator achieves a measured peak signal-to-noise-and-distortion ratio (SNDR) of 42.3 dB at 10.7 MHz with a signal bandwidth of 200 kHz, while dissipating 12 mW and occupying a chip area of 1.3 mm/sup 2/.     

Thermally Controlled,Patterned Graphene Transfer Printing for Transparent and Wearable Electronic/Optoelectronic System

Graphene has been highlighted as a platform material in transparent electronics and optoelectronics, including flexible and stretchable ones, due to its unique properties such as optical transparency, mechanical softness, ultrathin thickness, and high carrier mobility. Despite huge research efforts for graphene‐based electronic/optoelectronic devices, there are remaining challenges in terms of their seamless integration, such as the high‐quality contact formation, precise alignment of micrometer‐scale patterns, and control of interfacial‐adhesion/local‐resistance. Here, a thermally controlled transfer printing technique that allows multiple patterned‐graphene transfers at desired locations is presented. Using the thermal‐expansion mismatch between the viscoelastic sacrificial layer and the elastic stamp, a “heating and cooling” process precisely positions patterned graphene layers on various substrates, including graphene prepatterns, hydrophilic surfaces, and superhydrophobic surfaces, with high transfer yields. A detailed theoretical analysis of underlying physics/mechanics of this approach is also described. The proposed transfer printing successfully integrates graphene‐based stretchable sensors, actuators, light‐emitting diodes, and other electronics in one platform, paving the way toward transparent and wearable multifunctional electronic systems.     

A management architecture for client‐defined cloud storage services

Cloud service providers offer virtual resources to users, who then pay for as much as they use. High‐speed networks help to overcome the limitation of geographical distances between clients and cloud servers, which encourage users to adopt cloud storage services for data backup and sharing. However, users use only a few cloud storage services because of the complexity of managing multiple accounts and distributing data to store. In this paper, we propose the client‐defined management architecture (CLIMA) that redefines a storage service by coordinating multiple cloud storage services from clients. We address practical issues of coordinating multiple cloud service providers using a client‐based approach. We implement a prototype as a realization of CLIMA, which achieves both reliability and privacy protection using erasure code and higher performance by optimally scheduling data transmission. We use our prototype to evaluate the benefits of CLIMA on commercial cloud storage service providers. Finally, CLIMA empowers clients to increase the manageability and flexibility of cloud storage services. Copyright © 2015 John Wiley & Sons, Ltd.     

Pulsed laser annealing of single-crystal and ion-implanted semiconductors

The dynamic characteristics of both single-crystal and ion-implanted semiconductor layers annealed by a pulsed high-power laser beam is examined analytically for the first time by means of a parametrized perturbation method. The laser-induced lattice temperature rise is explicitly related to the laser beam parameters as well as the semiconductor properties. Specifically, the temperature in the annealed semiconductor is characterized in terms of the ambipolar diffusion length of hot, excess charge carriers, the optical attenuation coefficient of the medium, and the operating laser power, and the threshold pulse energy for surface melting is calculated for the case of silicon devices. It is shown that the pulse energy required for the onset of surface melting is sensitively dependent on the optical absorption coefficient, decreases significantly with increasing pulse intensity, and increases remarkably with increasing diffusion length of excess charge carriers.