Nanoporous silicon, commonly recognized for its photoluminescent properties, has gained attention as a new energetic
material capable of energy density more than twice that of TNT. The addition of an oxidizer solution to inert nanoporous
silicon results in an exothermic reaction when heat, friction, or focused light is supplied to the system. The energetic
material can be integrated alongside microelectronics and micro-electro-mechanical systems (MEMS) for on-chip
applications. This integration capability, along with the potential for large energetic yield, makes nanoporous energetic
silicon a viable material for developing novel MEMS Safing and Arming (S&A) technologies. While ignition of
nanoporous energetic silicon has been demonstrated for the purpose of propagation velocity measurements using a YAG
laser, in this paper we show optical ignition for potential integration of the energetic with a miniaturized S&A device.
Ignition is demonstrated using a 514nm laser at 37.7mW and a power density of 2.7kW/cm2 at a stand-off distance of
23cm. Raman spectroscopy verifies that significant stress in porous silicon is produced by a laser operating near the
power density observed to ignite porous silicon. Lastly, we integrate the nanoporous energetic silicon with a MEMS
S&A, and demonstrate transfer to a firetrain consisting of one primary and one secondary explosive using a thermal
initiator to ignite the nanoporous energetic silicon.
Interface chemistry can be implemented to modulate the aggregation and dispersion of nanoparticles in a colloidal
solution. In this experimental study, we demonstrate the controlled aggregation of superparamagnetic magnetite
nanoparticles in organic and aqueous solutions. With decrease in solution pH, individual nanoparticles (12-14 nm)
reproducibly cluster to form ~52 nm monodisperse aggregates in toluene. Spin-spin (T2) proton relaxation
measurements of the micellated clusters before and after aggregation show a change in the molar relaxation rate from
303 sec-1mol-1 to 368 sec-1mol-1 for individual and clustered nanoparticles, respectively. DNA-mediated aggregation of
micellated nanoparticles in the colloidal solution is also demonstrated where the number of single-stranded DNA per
particle determines the ultimate size of the nanoparticle aggregate.
We have studied the corrosion of phosphorus-doped polySi when contacted to a gold metallization layer and exposed to various hydrofluoric acid (HF) based chemistries, including mixtures with HCl, C2H6O, H2O, NH4F, Triton-X-100, as well as vapor-based HF. Here, we utilize optical-, electron-, and atomic-force-microscopy, optical interferometry, as well as instrumented indentation ("nanoindentation") to characterize test and reference specimens exposed to the various HF solutions. These measurements provide information concerning the appearance, roughness, physical dimensions, hardness, elastic modulus, and reverse phase transformation activity of the various polysilicon specimens. In general, some of the chemistries produced time-dependent darkening or "staining" visibly seen on free surfaces, roughening and attack at grain boundaries, nano-scale pitting of the free surfaces, decrease in thickness, decrease in hardness and mechanical modulus, and diminished elbow and reverse excursion activity for those silicon specimens electrically connected to metal. Change in performance is attributed to the formation of a galvanic cell during the HF immersion, and the corresponding damage driven by an anodic current. The results here can be used to explain previous work, which focused on the change in performance of designated MEMS diagnostic structures.