Analytical study of KOH wet etch surface passivation for III-nitride micropillars.

III-Nitride micropillar structures show great promise for applications in micro light-emitting diodes and vertical power transistors due to their excellent scalability and outstanding electrical properties. Typically, III-Nitride micropillars are fabricated through a top-down approach using reactive ion etch which leads to roughened, nonvertical sidewalls that results in significant performance degradation. Thus, it is essential to remove this plasma etch induced surface damage. Here, we show that potassium hydroxide (KOH) acts as a crystallographic etchant for III-Nitride micropillars, preferentially exposing the vertical <11¯00> m-plane, and effectively removing dry etch damage and reducing the structure diameter at up to 36.6 nm/min. Both KOH solution temperature and concentration have a dramatic effect on this wet etch progression. We found that a solution of 20% AZ400K (2% KOH) at 90°C is effective at producing smooth, highly vertical sidewalls with RMS surface roughness as low as 2.59 nm, ideal for high-performance electronic and optoelectronic devices.

Developing a Functional Poly(dimethylsiloxane)-Based Microbial Nanoculture System Using Dimethylallylamine.

Here, a novel poly(dimethylsiloxane) (PDMS)-based microbial culture system was investigated. Bacteria were encapsulated in functional and semipermeable membranes, mimicking the cell microenvironment and facilitating mass transport for interrogating microbial dynamics, thereby overcoming one of the major challenges associated with commercially available PDMS such as Sylgard 184. The hydrophobic nature and lack of control in the polymer network in Sylgard 184 significantly impede the the tunability of the transport and mechanical properties of the material as well as its usage as an isolation chamber for culturing and delivering microbes. Therefore, a novel PDMS composition was developed and functionalized with dimethylallylamine (DMAA) to alter its hydrophobicity and modify the polymer network. Characterization techniques including NMR spectroscopy, contact angle measurements, and sol-gel process were utilized to evaluate the physical and chemical properties of the newly fabricated membranes. Furthermore, the DMAA-containing polymer mixture was used as a proof of concept to generate hydrodynamically stable microcapsules and cultivate Escherichia coli cells in the functionalized capsules. The membrane exhibited a selective permeability to tetracycline, which diffused into the capsules to inhibit the growth of the encapsulated microbes. The functionality achieved here with the addition of DMAA, coupled with the high-throughput encapsulation technique, could prove to be an effective testing and diagnostic tool to evaluate microbial resistance, growth dynamics, and interspecies interaction and lays the foundation for in vivo models.