Low-Power High-Performance Asymmetrical Double-Gate Circuits Using Back-Gate-Controlled Wide-Tunable-Range Diode Voltage

This paper presents a new power-reduction scheme using a back-gate-controlled asymmetrical double-gate device with robust data-retention capability for high-performance logic/SRAM power gating or variable/dynamic supply applications. The scheme reduces the transistor count, area, and capacitance in the header/footer device and provides a wide range of virtual ground (GND) or supply voltage. Physical analysis and numerical mix-mode device/circuit-simulation results confirm that the proposed scheme can be applied to low-power high-performance circuit applications in 65-nm technology node and beyond. Variable/dynamic supply or GND voltage using the proposed scheme improves read and write margins in scaled SRAM without degrading read and write performance.     

Study of chirp-free operation for guide/antiguide modulator

A method of achieving chirp-free operation of a field-induced guide/antiguide intensity modulator is reported. Both measured and calculated data for chirp-free operation are demonstrated for a 1.15-μm wavelength. In a push-pull mode of operation, the index in the guide and antiguide regions of the modulator change in opposing directions, which can be adjusted such that the resulting phase shift contributions to the guided mode cancel each other, resulting in zero net mode phase shift     

Computer simulation of the human-body effects on acircular-loop-wire antenna for radio-pager communications at 152, 280,and 400 MHz

This paper presents an extensive computer simulation of the influence of the human body on a circular-loop-wire antenna to simulate the pager antenna. The coupled integral equations (CIEs) approach and the method of moments (MoM) are employed for numerical simulation of this antenna-body-coupling problem. The magnetic frill source is used to model the antenna-feeding structure. A realistically shaped full-scale human-body model (1.7 m) is constructed. A small loop antenna (loop radius b=1.7 cm and wire radius a=0.072 cm) of x, y, and z orientation, in free space or proximate to the human body at the top pocket (chest position) or belt level (waist position), is considered. Numerical results of the antenna characteristics and body absorption at 152, 280, and 400 MHz are presented and discussed for radio-paging applications. At 280 MHz, it is found that the real part of the impedance increases about five to ten times, and, hence, the antenna ohmic-loss radiation efficiency increases from 17% (in free space) to 69%, 44.3%, and 58.4%, respectively, for the x-, y-, and z-oriented loops when proximate to the body. The radiation efficiencies, reduced by the body-absorption effect, are 5%, 61%, and 25% for the x-, y-, and z-oriented loops, respectively. For the y-oriented loop, which is found to be the most suitable for paging communications, the antenna efficiencies are almost the same at the two location levels for all frequencies considered. The computed antenna characteristics influenced by the human body; including the input impedance, antenna patterns, cross-polarization field level, radiation efficiencies, and maximum and minimum power gains, are important for the antenna/RF design and the link-budget consideration     

PD/SOI SRAM performance in presence of gate-to-body tunneling current

This paper presents a detailed study on the effects of gate-to-body tunneling current on partially depleted silicon-on-insulator (PD/SOI) CMOS SRAM. It is shown that the presence of gate-to-body tunneling current changes the strength of individual cell transistor in the quiescent (standby) state, thus affecting subsequent write/read operations. The degradation in the "write" performance is shown to be more significant than the degradation in the "read" performance, and the effect is more pronounced at lowered temperature. For the beneficial side, the presence of the gate-to-body tunneling current reduces the initial cycle parasitic bipolar disturb from unselected cells on the same bitline during write/read operation.     

Time-resolved resonance Raman and computational investigation of the influence of 4-acetamido and 4-N-methylacetamido substituents on the chemistry of phenylnitrene

A time-resolved resonance Raman (TR(3)) and computational investigation of the photochemistry of 4-acetamidophenyl azide and 4-N-methylacetamidophenyl azide in acetonitrile is presented. Photolysis of 4-acetamidophenyl azide appears to initially produce singlet 4-acetamidophenylnitrene which undergoes fast intersystem crossing (ISC) to form triplet 4-acetamidophenylnitrene. The latter species formally produces 4,4'-bisacetamidoazobenzene. RI-CC2/TZVP and TD-B3LYP/TZVP calculations predict the formation of the singlet nitrene from the photogenerated S(1) surface of the azide excited state. The triplet 4-acetamidophenylnitrene and 4,4'-bisacetamidoazobenzene species are both clearly observed on the nanosecond to microsecond time-scale in TR(3) experiments. In contrast, only one species can be observed in analogous TR(3) experiments after photolysis of 4-N-methylacetamidophenyl azide in acetonitrile, and this species is tentatively assigned to the compound resulting from dimerization of a 1,2-didehydroazepine. The different photochemical reaction outcomes for the photolysis of 4-acetamidophenyl azide and 4-N-methylacetamidophenyl azide molecules indicate that the 4-acetamido group has a substantial influence on the ISC rate of the corresponding substituted singlet phenylnitrene, but the 4-N-methylacetamido group does not. CASSCF analyses predict that both singlet nitrenes have open-shell electronic configurations and concluded that the dissimilarity in the photochemistry is probably due to differential geometrical distortions between the states. We briefly discuss the probable implications of this intriguing substitution effect on the photochemistry of phenyl azides and the chemistry of the related nitrenes.     

Organic photovoltaics incorporating fulleroisoquinolinones as n-type materials

Fulleroisoquinolinones have been synthesized by palladium-catalyzed annulation of N-alkyl benzamides with C(60). A device incorporating fulleroisoquinolinones and the conjugated polymer P3HT exhibited power conversion efficiency up to 2.3% under AM 1.5G irradiation.     

Hybrid opto-electric manipulation in microfluidics-opportunities and challenges

Hybrid opto-electric manipulation in microfluidics/nanofluidics refers to a set of methodologies employing optical modulation of electrokinetic schemes to achieve particle or fluid manipulation at the micro- and nano-scale. Over the last decade, a set of methodologies, which differ in their modulation strategy and/or the length scale of operation, have emerged. These techniques offer new opportunities with their dynamic nature, and their ability for parallel operation has created novel applications and devices. Hybrid opto-electric techniques have been utilized to manipulate objects ranging in diversity from millimetre-sized droplets to nano-particles. This review article discusses the underlying principles, applications and future perspectives of various hybrid opto-electric techniques that have emerged over the last decade under a unified umbrella.     

Comprehensive studies on an overall proton transfer cycle of the ortho-green fluorescent protein chromophore

Initiated by excited-state intramolecular proton transfer (ESIPT) reaction, an overall reaction cycle of 4-(2-hydroxybenzylidene)-1,2-dimethyl-1H-imidazol-5(4H)-one (o-HBDI), an analogue of the core chromophore of the green fluorescent protein (GFP), has been investigated. In contrast to the native GFP core, 4-(4-hydroxybenzylidene)-1,2-dimethyl-1H-imidazol-5(4H)-one (p-HBDI), which requires hydrogen-bonding relay to accomplish proton transfer in vivo, o-HBDI possesses a seven-membered-ring intramolecular hydrogen bond and thus provides an ideal system for mimicking an intrinsic proton-transfer reaction. Upon excitation, ESIPT takes place in o-HBDI, resulting in a ～600 nm proton-transfer tautomer emission. The o-HBDI tautomer emission, resolved by fluorescence upconversion, is comprised of an instantaneous rise to a few hundred femtosecond oscillation in the early relaxation stage. Frequency analysis derived from ultrashort pulse gives two low-frequency vibrations at 115 and 236 cm(-1), corresponding to skeletal deformation motions associated with the hydrogen bond. The results further conclude that ESIPT in o-HBDI is essentially triggered by low-frequency motions and may be barrierless along the reaction coordinate. Femtosecond UV/vis transient absorption spectra also provide supplementary evidence for the structural evolution during the reaction. In CH(3)CN, an instant rise of a 530 nm transient is resolved, which then undergoes 7.8 ps decay, accompanied by the growth of a rather long-lived 580 nm transient species. It is thus concluded that following ESIPT the cis-proton transfer isomer undergoes cis-trans-isomerization. The results of viscosity-dependent dynamics are in favor of the one-bond-flip mechanism, which is in contrast to the volume-conserving isomerization behavior for cis-stilbene and p-HBDI. Further confirmation is given by the picosecond-femtosecond transient IR absorption spectra, where several new and long-lived IR bands in the range of 1400-1500 cm(-1) are assigned to the phenyl in-plane breathing motions of the trans-proton transfer tautomer. Monitored by the nanosecond transient absorption, the 580 nm transient undergoes a ～7.7 μs decay constant, accompanied by the growth of a new ～500 nm band. The latter is assigned to a deprotonated tautomer species, which then undergoes the ground-state reverse proton recombination to the original o-HBDI in ～50 μs, achieving an overall, reversible proton transfer cycle. This assignment is unambiguously supported by pump-probe laser induced fluorescence studies. On these standpoints, a comparison of photophysical properties among o-HBDI, p-HBDI, and wild-type GFP is discussed in detail.     

Reconsideration on hydrogen bond strengthening or cleavage of photoexcited coumarin 102 in aqueous solvent: a DFT/TDDFT study

In this work, the excited-state hydrogen bonding dynamics of photoexcited coumarin 102 in aqueous solvent is reconsidered. The electronically excited states of the hydrogen bonded complexes formed by coumarin 102 (C102) chromophore and the hydrogen donating water solvent have been investigated using the time-dependent density functional theory method. Two intermolecular hydrogen bonds between C102 and water molecules are considered. The previous works (Wells et al., J Phys Chem A 2008, 112, 2511) have proposed that one intermolecular hydrogen bond would be strengthened and the other one would be cleaved upon photoexcitation to the electronically excited states. However, our theoretical calculations have demonstrated that both the two intermolecular hydrogen bonds between C102 solute and H(2)O solvent molecules are significantly strengthened in electronically excited states by comparison with those in ground state. Hence, we have confirmed again that intermolecular hydrogen bonds between C102 chromophore and aqueous solvents are strengthened not cleaved upon electronic excitation, which is in accordance with Zhao's works.