A gate-quality dielectric system for SiGe metal-oxide-semiconductordevices

The authors present a high-quality dielectric system for use with Si_1-xGe_x alloys. The system employs plasma-enhanced chemical vapor deposited (PECVD) SiO₂ on a thin (6-8-nm) layer of pure silicon grown epitaxially on the Si_1-x Ge_x layer. The buffer layer and the deposited oxide prevent the accumulation of Ge at the oxide-semiconductor interface and thus keep the interface state density within acceptable limits. The Si cap layer leads to a sequential turn-on of the Si_1-xGe_x channel and the Si cap channel as is clearly observed in the low-temperature C-V curves. The authors show that this dual-channel structure can be designed to suppress the parasitic Si cap channel. The MOS capacitors are also used to extract valence-band offsets     

Hydroxamic acids and their derivatives—III Preparation of esters of pivalohydroxamic acid and their use in peptide synthesis

Reaction of N-protected amino acids with pivalonitrile oxide affords “active esters” which are useful in peptide syntheses.     

High temperature superconductivity in bismuth-alkaline earth-copper-oxygen system

Electrical resistivity measurements of a series of compounds in the bismuth-alkaline earth-copper-oxygen system have been carried out. Several compositions (BiSrCaCu₂O _x , BiSrCaCu₃O _x , Bi₂Sr₂CaCu₄O _x and Bi₄Sr₃Ca₃Cu₈O _x ) showed superconducting onset temperatures in the range 90–130 K, though none of them showedT _cf(R=0) above 77 K. ExtrapolatedT _cf of three compounds are in the range 72–75 K. All compounds are multiphasic.     

Redundancy in Barlow-Wu Structures

An expression is derived for the increase in stochastic performance of a continuum structure of the Barlow-Wu type when each component of a subset is replicated once. If a single component is to be replicated, criteria are given for selecting the component so as to maximize the system performance for series and parallel structures. A series of upper bounds is derived for the increase in terms of the critical importance of the replicated component.     

Preconcentration of iodide from saline water samples and determination by the catalytic method

A method is described for the determination of nanogram levels of iodide in saline water samples. The interfering chloride, present in milligram levels, is eluted out of a column of a strong anion exchanger, retaining the iodide quantitatively. The iodide is then recovered from the column with 2 M ammonium nitrate solution. The determination is carried out by the catalytic method based on the reduction of Ce(IV) by As(III) in presence of iodide. The arresting method was found to be more sensitive. The method can be easily adapted in a field laboratory, with accuracy comparable with neutron activation analysis.     

Demonstration of a p-channel BICFET in the GexSi1-x/Si system

Operational bipolar inversion-channel field-effect transistors (BICFETs) based on the Ge_xSi_1-x/Si system are discussed. The 300 K current gain of β=365 at a current density of J_c=2.5×10⁴ A/cm² is the highest value reported for any BICFET to date. The use of a double-heterojunction inversion channel eliminates the collector offset voltage. The present devices are limited by the channel resistance, so that performance improvements are expected for laterally-scaled-down devices     

Effects of periodic masker interruption on the intelligibility of interrupted speech

When listeners hear a target signal in the presence of competing sounds, they are quite good at extracting information at instances when the local signal-to-noise ratio of the target is most favorable. Previous research suggests that listeners can easily understand a periodically interrupted target when it is interleaved with noise. It is not clear if this ability extends to the case where an interrupted target is alternated with a speech masker rather than noise. This study examined speech intelligibility in the presence of noise or speech maskers, which were either continuous or interrupted at one of six rates between 4 and 128 Hz. Results indicated that with noise maskers, listeners performed significantly better with interrupted, rather than continuous maskers. With speech maskers, however, performance was better in continuous, rather than interrupted masker conditions. Presumably the listeners used continuity as a cue to distinguish the continuous masker from the interrupted target. Intelligibility in the interrupted masker condition was improved by introducing a pitch difference between the target and speech masker. These results highlight the role that target-masker differences in continuity and pitch play in the segregation of competing speech signals.     

Total synthesis of brevenal

This Article describes the total synthesis of the marine ladder toxin brevenal utilizing a convergent synthetic strategy. Critical to the success of this work was the use of olefinic-ester cyclization reactions and the utilization of glycal epoxides as precursors to C-C and C-H bonds.