Novel Dynamic Viscoelastic Measurements of Polyurethane Copolymer Melts and Their Implication to Tack Results

Summary: A series of polyurethane multiblock copolymers with different proportions of hard segments (urethane) to soft segments (polyadipate of hexane‐1,6‐diol), are investigated. Dynamic viscoelastic functions of homogeneous melts in the terminal zone are determined. For the first time, entanglement modulus values of such copolymers are reported, which allows estimation of the packing length. These parameters do not vary with changing the hard‐to‐soft segment ratio, a result that is explained by a compensating effect of the chain architecture. For samples of similar molecular weight, the relaxation time of the terminal zone increases as the hard‐to‐soft segment ratio augments. The adhesives obtained from PUR solutions show a correlation between the elastic modulus and the debonding stress‐strain curves in tack experiments.

The storage modulus of the adhesives as a function of frequency at 70 °C.     

Resonant tunneling in crossed electric and magnetic fields: A tool for investigating extreme hot electron effects

We have investigated the current/voltage characteristic of resonant tunneling structures with wide well regions (80nm). We observe 25 oscillations in the current-voltage characteristic associated with resonances in the quantum well as the structure is biased to 1.0V. With the application of modest transverse magnetic fields, we see a weakening and shift of these oscillations to higher energies. We will describe how the oscillations reveal extreme hot-electron effects in the quantum well with electron mean free paths in excess of 100nm at energies approaching 1eV, and describe a theory for the phase shift which gives information on the effective mass high in the conduction band.     

All-solid-state diode-pumped modelocked Cr:LiSAF laser

A diode-pumped Cr:LiSrAlF/sub 6/ laser has been modelocked for the first time using a multiquantum well absorber in an external cavity to yield CW trains of picosecond pulses.<>     

Low-threshold electrically pumped vertical-cavity surface-emitting microlasers

The authors present vertical-cavity electrically driven lasers with three GaInAs quantum wells and diameters of several mu m exhibiting room-temperature pulsed current thresholds as low as 1.3 mA with 958 nm output wavelength.<>     

Effect of strain on microwave noise characteristics in In/sub 0.52/Al/sub 0.48/As/In/sub x/Ga/sub 1-x/As (0.53

Chough  K.B. Hong  W.-P. Florez  L. Song  J.I. 《Electronics letters》1993,29(15):1338-1340

Effects of etch depth and ion implantation on surface emitting microlasers

The authors fabricated low threshold In/sub 0.2/Ga/sub 0.8/As surface emitting microlasers having various etch depths and sizes. Comparison of electrical and optical properties was made between deep etched (deeper than the active layer) and shallow etched (shallower than the active layer) microlasers. Shallow etched microlasers were F-ion implanted to limit current spreading. The ion implanted shallow etched samples, when larger than about 5 mu m across, show improved room temperature CW characteristics with lower resistances and lower operating voltages than the deep etched microlasers.<>     

Grafted GaAs detectors on lithium niobate and glass opticalwaveguides

The integration of a GaAs MSM (metal-semiconductor-metal) detector with LiNbO₃ and glass optical waveguides is discussed. A 250-nm thick GaAs detector layer was fabricated using a recently reported liftoff technique and subsequently grafted onto the waveguide chip. Proof of the optical interaction between the waveguide and its grafted detector was provided by the total absorption of 633 nm of guided light within a distance of ~1 mm from the leading edge of the GaAs layer and by the presence of a photocurrent at the detector terminals. It is suggested that the grafting technique will prove useful in the design of new and cost-effective optoelectronic devices     

Resonant tunneling through magnetic edge states

Resonant magneto-tunneling of electrons through AlGaAs/GaAs/AlGaAs double barrier structures is investigated for samples with different quantum well widths (300–800Å) and barriers (130–200Å). In a strong transverse magnetic field, resonant tunneling is quenched, and a new set of resonances appear at low bias. These resonances are interpreted as due to tunneling between the edge states on either side of the first barrier. The edge states are the quantum mechanical analog of the classical skipping orbits.