Soft Bath Research Articles

Tunable electroluminescence from low‐threshold voltage LED structure based on electrodeposited Zn1−xCdxO‐nanorods/p‐GaN heterojunction

AbstractViolet light‐emitting diode (LED) structures based on Cd‐alloyed zinc oxide (Zn1−xCdxO) nanorods (NRs)/p‐GaN heterojunction have been fabricated by epitaxial electrodeposition at low temperatures in an aqueous soft bath followed by a mild thermal annealing. The ultraviolet (UV) room‐temperature emission peak at around 397 nm with a full width at half‐maximum (FWHM) of 10 nm observed from pure ZnO‐NRs/p‐GaN at room temperature was shifted to 417 nm with FWHM of 14 nm by employing a Zn0.92Cd0.08O‐NRs/p‐GaN heterojunction. The emission threshold voltage was low at about 5.0 V and the electroluminescence (EL) intensity rapidly increased with the applied forward‐bias voltage. The emission wavelength increased with the Cd content in the alloy. The EL physics mechanism in LED structures of the heterojunctions is discussed.

Morphology of crystalline Nylon-610 membranes prepared by the immersion-precipitation process: competition between crystallization and liquid–liquid phase separation

Nylon-610 membranes were prepared at 25°C by direct immersion of various dope solutions into either formic acid/water or 1-octanol bath. Depending on the dope and bath conditions, the precipitated membranes demonstrated characteristics derived from crystallization and/or liquid–liquid phase separation during the precipitation process. As a good dope solution was immersed in a harsh bath, e.g., water, precipitation occurred initiated by liquid–liquid phase separation. The formed membrane exhibited a cellular structure similar to that commonly observed in amorphous membranes. Alternatively, when a metastable dope (with respect to crystallization) was immersed in a soft bath containing a substantial amount of formic acid, crystallization dictated the precipitation process to yield bi-continuous, particulate membranes. Membranes with extensive macrovoids were observed, in the event that the dope contained a large amount of solvent. In the latter case, precipitation took place immediately after immersion, consistent with Strathmann and Smolder’s results for several membrane forming systems. In addition, skinless microporous membranes were prepared by precipitation of the dope solutions in a 1-octanol bath, in which precipitation occurred slowly and the formed membrane was composed of “sheaf-like” crystallites that interlocked into a homogeneous bi-continuous network.

Formation of crystalline EVAL membranes by controlled mass transfer process in water–DMSO–EVAL copolymer systems

The effect of solvent content in the coagulation bath on the formation of poly(ethylene-co-vinyl alcohol) (EVAL) membranes by isothermal immersion–precipitation in water–dimethylsulfoxide (DMSO)–EVAL system has been investigated. As a homogeneous EVAL dope is immersed in a harsh bath, e.g., water, instant precipitation occurs initiated by the liquid–liquid demixing process. The formed membrane exhibits an asymmetric morphology with extensive finger-like macrovoids, similar to that observed in most amorphous polymeric membranes. On the other hand, if precipitation takes place in a soft bath containing a substantial amount of solvent, crystallization, rather than liquid–liquid demixing, starts to dominate and a skinless, bi-continuous, particulate membrane becomes the precipitated product. The immersion–precipitation process for the present system has been modeled as a ternary mass transfer problem. The calculated diffusion trajectories and concentration profiles illustrate reasonably the membrane morphologies formed in various immersion conditions.