Thermoelectric properties of nano-bulk bismuth telluride prepared with spark plasma sintered nano-plates

The pursuit for a high-performance thermoelectric n-type bismuth telluride-based material is significant because n-type materials are inferior to their corresponding p-type materials in highly efficient thermoelectric modules. Herein, to improve the thermoelectric performance of an n-type Bi₂Te₃, we prepared Bi₂Te₃ nano-plates with a homogeneous sub-micron size distribution and thickness range of about a few tens of nanometers. This was achieved using a typical nano-chemical synthetic method, and the prepared materials were then spark plasma sintered to fabricate n-type nano-bulk Bi₂Te₃ samples. We observed a significant enhancement of the anisotropic electrical transport properties for the nano-bulk sample with a higher power factor along the in-plane direction (24.3?μW?cm^?1?K^?2 at 300?K) than that along the out-of-plane direction (8.1?μW?cm^?1?K^?2 at 300?K). However, thermal transport properties were insensitive along the measured direction for the nano-bulk sample. We used a dimensionless figure of merit ZT to calculate the thermoelectric performance. The results showed that the maximum ZT value of 0.69 was achieved along the in-plane direction at 440?K for the nano-bulk n-type Bi₂Te₃ sample, which was however smaller than that of the previously reported n-type samples (ZT of 1.1). We believe that a further enhancement of the ZT value in the fabricated nano-bulk sample could be accomplished by effectively removing the surface organic ligand of the Bi₂Te₃ nano-plate particles and optimizing the spark plasma sintering conditions, maintaining the nano-plate morphology intact.     

True nature of active layers in organic solar cells fabricated by sequential casting of donor and acceptor layers

The operation characteristics of nominal bilayer (BL) organic solar cells (OSCs), the active layers (ALs) of which consisted of sequentially casted bottom P3HT donor and top ICBA acceptor layers, resembled those of OSCs with bulk heterojunction (BHJ) ALs. Optical analysis and device simulations showed that such resemblance can be attributed to a similarity in the micromorphology of ALs; as‐deposited BL‐type ALs transformed spontaneously into BHJ‐type ALs. The inclusion of P3HT nanowires (NWs) in the donor layers resulted in different AL micromorphology and consequently a larger power conversion efficiency. Separate assessment of the exciton generation and charge–carrier transport and/or extraction showed that the contribution of P3HT NWs was more prominent in optical effects.

     

Generalized passivity-based chaos synchronization

In this paper, a new passivity-based synchronization method for a general class of chaotic systems is proposed. Based on the Lyapunov theory and the linear matrix inequality （LMI） approach, the passivity-based controller is presented to make the synchronization error system not only passive but also asymptotically stable. The proposed controller can be obtained by solving a convex optimization problem represented by the LMI. Simulation studies for the Genesio-Tesi chaotic system and the Qi chaotic system are presented to demonstrate the effectiveness of the proposed scheme.     

Experimental study of critical heat flux enhancement during forced convective flow boiling of nanofluid on a short heated surface

Enhancements of nucleate boiling critical heat flux (CHF) using nanofluids in a pool boiling are well-known. Considering importance of flow boiling heat transfer in various practical applications, an experimental study on CHF enhancements of nanofluids under convective flow conditions was performed. A rectangular flow channel with 10-mm width and 5-mm height was used. A 10 mm-diameter disk-type copper surface, heated by conduction heat transfer, was placed at the bottom surface of the flow channel as a test heater. Aqueous nanofluids with alumina nanoparticles at the concentration of 0.01% by volume were investigated. The experimental results showed that the nanofluid flow boiling CHF was distinctly enhanced under the forced convective flow conditions compared to that in pure water. Subsequent to the boiling experiments, the heater surfaces were examined with scanning electron microscope and by measuring contact angle. The surface characterization results suggested that the flow boiling CHF enhancement in nanofluids is mostly caused by the nanoparticles deposition of the heater surface during vigorous boiling of nanofluids and the subsequent wettability enhancements.     

Effective Multiplexing Method for Conditional Access System in Terrestrial DMB

This letter proposes a conditional access system (CAS) suitable for use in terrestrial digital multimedia broadcasting (T‐DMB), based on an effective multiplexing method to provide encrypted T‐DMB services. Specifically, the proposed multiplexing method for a CAS is designed to reduce the additional bit rate while assuring easy access to the designated encrypted services. Finally, the performance of the implemented CAS is confirmed through implementation and a broadcasting experiment under various service environments.     

Theoretical and Experimental Studies of Bending of Inorganic Electronic Materials on Plastic Substrates

This paper describes materials and mechanics aspects of bending in systems consisting of ribbons and bars of single crystalline silicon supported by sheets of plastic. The combined experimental and theoretical results provide an understanding for the essential behaviors and for mechanisms associated with layouts that achieve maximum bendability. Examples of highly bendable silicon devices on plastic illustrate some of these concepts. Although the studies presented here focus on ribbons and bars of silicon, the same basic considerations apply to other implementations of inorganic materials on plastic substrates, ranging from amorphous or polycrystalline thin films, to collections of nanowires and nanoparticles. The contents are, as a result, relevant to the growing community of researchers interested in the use of inorganic materials in flexible electronics.     

A 1.1 GHz 12 μA/Mb-Leakage SRAM Design in 65 nm Ultra-Low-Power CMOS Technology With Integrated Leakage Reduction for Mobile Applications

A low-power, high-speed SRAM macro is designed in a 65 nm ultra-low-power (ULP) logic technology for mobile applications. The 65 nm strained silicon technology improves transistor performance/leakage tradeoff, which is essential to achieve fast SRAM access speed at substantially low operating voltage and standby leakage. The 1 Mb SRAM macro features a 0.667 mum² low-leakage memory cell and can operate over a wide range of supply voltages from 1.2 V to 0.5 V. It achieves operating frequency of 1.1 GHz and 250 MHz at 1.2 V and 0.7 V, respectively. The SRAM leakage is reduced to 12 muA/Mb at the data retention voltage of 0.5 V. The measured bitcell leakage from the SRAM array is ~2 pA/bit at retention voltage with integrated leakage reduction schemes.     

A High-Power CMOS Switch Using A Novel Adaptive Voltage Swing Distribution Method in Multistack FETs

A high-power CMOS switch using a novel adaptive voltage swing distribution method in a multistack field-effect transistor (FET) scheme is proposed. The proposed adaptive voltage swing distribution method in multistack FETs is very effective in preventing unwanted channel formation with low control voltage supply in OFF-state FETs. This, in turn, increases power-handling capability when a large-signal voltage swing is applied. In the proposed CMOS switch, the behavior of the voltage swing in OFF-state multistack FETs shows a difference with respect to the level of input voltage swing. The characteristics of voltage swing distribution and leakage channel formation in the CMOS switch is fully analyzed with incorporation of the novel adaptive voltage swing distribution method into a three-stacked nMOS Rx switch in a standard 0.18-mum triple-well CMOS process. In addition, linearity of the proposed technique is verified through the measurement data of the single-pole double-throw switches that employ the proposed technique in the Rx switch. Two different types of configurations are implemented and characterized at the Rx switches, which consist of four-stacked nMOS devices, to demonstrate the method of minimizing voltage stress issues on one of the multistacked FETs. Layout consideration was also taken to prevent interference between leakage signals at the substrate. The measured performance of the proposed design shows an input 0.3-dB compression point of 33.5 dBm at 1.9 GHz. To the best of our knowledge, this is the highest power-handling capability of a CMOS switch in a standard CMOS process ever reported. The insertion losses of the Tx and Rx switches are 1.6 and 1.9 dB, respectively, at 1.9 GHz. The isolation of the Tx and Rx switches is around 20 and 30 dB, respectively, at 1.9 GHz.     

Electron holography study for two-dimensional dopant profile measurement with specimens prepared by backside ion milling

The visualization of two-dimensional dopant profiles and the quantitative analysis of the built-in potential across the p-n junction, DeltaV(p-n), by electron holography were carried out with specimens prepared from the backside ion milling method combined with the focused ion beam technique. It was possible to obtain dopant profiling of the large field of view with low surface damage and gradually changed thickness. From the quantitative analysis using the phase information of electron holography and the thickness information of electron energy-loss spectroscopy, DeltaV(p-n) was estimated to be about 0.78 V assuming that the thickness of the dead layer on both surfaces is 50 nm, which is to show the difference of within 12% from the calculated value. It demonstrates that the backside ion milling method is a very promising specimen preparation technique for the reliable and quantitative analysis of dopant profiling with electron holography.     

Diversity eigenbeamforming for coded signals

Transmit antenna diversity without feedback has been widely investigated for various wireless communication systems. Especially, space-time codes are extensively studied to exploit the spatial diversity induced by multiple transmit antennas. Apart from these approaches, there can be different methods that provide a diversity gain using multiple antennas with conventional channel coding. In this paper, diversity eigenbeamforming is studied to exploit the spatial diversity when the channel covariance matrix is available at the transmitter. Diversity eigenbeamforming is based on eigenmode (of the spatial covariance matrix) switching that converts the spatial diversity into the temporal diversity which is exploited by channel coding. Optimized diversity eigenbeamforming is considered to take into account the spatial correlation. In addition, the trade-off between diversity and multiplexing gains is addressed. It is shown that the diversity eigenbeamforming can achieve optimal trade-off for the case of one receive antenna. Although, for simplicity, binary phase shift keying (BPSK) is used to derive diversity eigenbeamforming, any higher-order modulation scheme can also be used with diversity eigenbeamforming.