Magnetic-Field-Induced Level Crossing and the Spin Dynamics of Excitons in Zn1?xMnxTe/ZnTe Quantum Wells

Magnetic-field-induced level crossing and the spin dynamics of excitons in a Zn_1–x Mn _x Te/ZnTe single quantum well are studied. The circularly-polarized photoluminescence (PL) shows that the down spin branch of the Zn_1–x Mn _x Te exciton overlaps with both the up and down spin branches of the ZnTe exciton at a crossing field (H _c) of 4 T, due to the giant Zeeman shift of Zn_1–x Mn _x Te. The PL intensities and lifetimes in each layer become gradually equal toward H _c, which shows the mixing of wavefunctions of the excitons generated in each layer. Above H _c, each branch of the spin-polarized exciton separates again. The lifetimes of the spin-polarized exciton PL reflect the spin-flip relaxation in ZnTe and the spin mixing between Zn_1–x Mn _x Te and ZnTe layers.     

Magnetic-Field-Induced Level Crossing and the Spin Dynamics of Excitons in Zn1−x Mn x Te/ZnTe Quantum Wells

Magnetic-field-induced level crossing and the spin dynamics of excitons in a Zn_1?x Mn _x Te/ZnTe single quantum well are studied. The circularly-polarized photoluminescence (PL) shows that the down spin branch of the Zn_1?x Mn _x Te exciton overlaps with both the up and down spin branches of the ZnTe exciton at a crossing field (H _c) of 4 T, due to the giant Zeeman shift of Zn_1?x Mn _x Te. The PL intensities and lifetimes in each layer become gradually equal toward H _c, which shows the mixing of wavefunctions of the excitons generated in each layer. Above H _c, each branch of the spin-polarized exciton separates again. The lifetimes of the spin-polarized exciton PL reflect the spin-flip relaxation in ZnTe and the spin mixing between Zn_1?x Mn _x Te and ZnTe layers.     

Layered‐Herringbone Polymorphs and Alkyl‐Chain Ordering in Molecular Bilayer Organic Semiconductors

Production and control of 2D self‐organized layers of π‐conjugated molecules is a fundamental issue in organic electronics devices. This study reports that an intralayer polymorphic transformation is apparently observed in a bilayer‐type layered‐herringbone packing of a series of 2‐mono‐alkylated‐benzothieno[3,2‐b][1]benzothiophenes (mono‐C_n‐BTBTs) with the change in the substituted alkyl‐chain length, n. Slight variation in the intermolecular arrangement in the single‐crystal films is investigated with reasonable sensitivity via polarized optical absorption spectroscopy through the excitonic interactions between neighboring π‐electron cores. A clear polymorphic transition is observed based on the features of the in‐plane optical anisotropy with the change in the chain length between n = 7 (or less) and 8 (or more). A unique phase separation of the polymorphs is also observed in the films produced using a mixed solution with molecules having different n: the respective polymorphic phases appear separately, either as single molecular bilayers or multibilayer‐stacked films owing to geometrical frustration. The results indicate that the intralayer packing motif is predetermined by the competition and balance between the intermolecular core–core and chain–chain interactions. These findings pave the way for rational designing of organic molecules with considerably high layered crystallinity, and thus, of efficient carrier transport in organic thin‐film transistors.     

Gait generation and change of direction for the underactuated three-legged robot

This paper describes a three-legged robot that consists of one actuated leg and two passive legs. The active leg has a knee joint and an ankle joint. The passive legs have no knee joint, although they have a passive ankle joint respectively. The passive leg part and the actuated leg part are linked by a hip part. The robot behavior is passive while the robot is supported by its passive legs and swings the actuated leg part. Generally, in the event that an actuator or a transmitting mechanism fails, robots cannot apply torques to the joint. We therefore took up a walking robot with passive knee joints not only for the energy-efficient walking but also with a view to making ambulation failsafe in case of mechanical failures.     

A 30-μA data-retention pseudostatic RAM with virtually staticRAM mode

A 1-Mb (128K×8) pseudostatic RAM (PSRAM) is described. A novel feature of the RAM is the inclusion of a virtually static RAM (VSRAM) mode, while being fully compatible with a standard PSRAM. The RAM changes into the VSRAM mode when the RFSH pin is grounded, even in active cycles. The RAM can be used either as a fast PSRAM of 36-ns access time or as a convenient VSRAM of 66-ns access time. The typical operation current and data-retention current are 30 mA at 160-ns cycle time and 30 μA, respectively. In order to achieve high-speed operation, low data-retention current, and high reliability, the RAM uses delay-time tunable design, a current-mirror timer, hot-carrier resistant circuits, and an optimized arbiter. These technologies are applicable to general advanced VLSIs     

A 9-ns HIT-delay 32-kbyte cache macro for high-speed RISC

A 32-kB cache macro with an experimental reduced instruction set computer (RISC) is realized. A pipelined cache access to realize a cycle time shorter than the cache access time is proposed. A double-word-line architecture combines single-port cells, dual-port cells, and CAM cells into a memory array to improve silicon area efficiency. The cache macro exhibits 9-ns typical clock-to-HIT delay as a result of several circuit techniques, such as a section word-line selector, a dual transfer gate, and 1.0-μm CMOS technology. It supports multitask operation with logical addressing by a selective clear circuit. The RISC includes a double-word load/store instruction using a 64-b bus to fully utilize the on-chip cache macro. A test scheme allows measurement of the internal signal delay. The test device design is based on the unified design rules scalable through multigenerations of process technologies down to 0.8 μm     

Wavelength division two-way fibre-optic transmission experiments using micro-optic duplexers

Experimental two-way transmission of high-speed digital pulse signals over a single 10 km optical fibre line has been realised at 800 nm band, employing newly developed small size and low-loss micro-optic duplexers, AlGaAs d.h. lasers of different emission wavelengths, a spliced graded-index high-silica fibre and Si-a.p.d.s.     

12-channel parallel optical-fiber transmission using a low-drivecurrent 1.3-μm LED array and a p-i-n PD array

Twelve-channel 14-Mb/s/channel 1-km parallel optical-fiber transmission using a 1×12 low-drive-current 1.3-μm light-emitting diode (LED) linear array and an InGaAs p-i-n photodiode linear array, with the LED drive current as low as 12 mAp-p/channel, is discussed. No receiver sensitivity degradation has been observed under simultaneous 12-channel operation. The skew was less than 6 ns after transmission through a 1-km-long 12-channel optical-fiber cable, which was sufficiently small for 14-Mb/s parallel transmission     

Spectral chirping suppression using modified DFB-DC-PBH LD

A chirping suppression scheme is proposed and demonstrated using a modified DFB-DC-PBH LD. This scheme is effective both for sinusoidal modulation and for pulse modulation. The chirping is suppressed to one tenth in 100 MHz sinusoidal modulation and one fifth in 2 Gbit/s pulse modulation.