Lenward Seals

Rapid, reversible, sensitive porous silicon gas sensor

The development of a sensitive porous silicon (PS) gas sensor which utilizes photoluminescence induced electroless metallization as a means of obtaining a highly efficient electrical contact has been demonstrated for the detection of HCl, NH3, and NO at the 10 ppm level. The problem of spreading resistance (kΩ–MΩ) is overcome as low resistance contacts ∼20–100 Ω are made to the mesoporous PS structure through electroless gold plating. The response of this device, which operates at a bias voltage of 1–10 mV, is rapid and reversible.

Patterned Metallization of Porous Silicon from Electroless Solution for Direct Electrical Contact

The excitation of the triplet exciton leading to the long-lived photoluminescence characteristic of a porous silicon (PS) surface has been used to selectively enhance the highly efficient, controlled, and patterned plating of copper and silver metal from electroless solutions. The basis of this method lies in the use of the long-lived excited state to promote an enhanced reduction at the PS surface. Excited fluorophors, created at the PS surface, using a Xe arc lamp or HeNe laser, exhibit an interaction and reduction capability absent without optical pumping. The thickness of the metal deposit is proportional to the time and intensity of exposure and the contact resistance can be made less than 500 Ω.

Formation of ferromagnetic Ni/SiO2 nanospheres

Abstract Dispersed SiO 2 nanospheres have been nickel-plated using an electroless-plating solution. Magnetic resonance (MR) experiments have been performed on these samples. The MR signals demonstrate the presence of Ni +2 and Ni +3 paramagnetic centers, which are most easily seen below 40 K, and ferromagnetic metallic Ni, which can be readily seen above 40 K. The MR results also indicate only the presence of paramagnetic Ni +3 in a dried sample of the Ni-plating solution that does not contain any SiO 2 nanospheres. These results suggest that an interfacial reaction at the surface of the SiO 2 nanospheres leads to the formation of ferromagnetic Ni, which deposits onto the spheres and forms a Ni/SiO 2 nanosphere composite.

On the Correlation of Aqueous and Nonaqueous In Situ and Ex Situ Photoluminescent Emissions from Porous Silicon Evidence for Surface‐Bound Emitters

Porous silicon samples were prepared by anodizing p-doped Si(100) substrates in both aqueous (HF/H 2 O, HF/CH 3 OH, HF/CH 3 OH/H 2 O, HF/C 2 H 5 OH/H 2 O) and nonaqueous (MeCN/HF) media. The time-dependent porous silicon photoluminescence (PL) was monitored during the etch (in situ) and after removal from the etch solution (ex situ). Correlation of the ex situ and in situ PL indicates that the composition of the etchant solution plays an extremely important role in the onset, time-dependent intensity, and lifetime of the emission, both in and out O solution. The effect of etchant solution additives (ethylene glycol, CH 3 OH, C 2 H 5 OH, NaF, HCl, and NaCl) on the porous silicon PL both during and following the etching cycle, was also determined. The distinct and different correlations found between aqueous and nonaqueous etchants provide insights into the mechanism of PL. These results, when considered in the context of quantum chemical modeling, strongly suggest surface-bound silicon oxyhydride moieties as the source of the porous silicon PL.

Formation of Ni/SiO 2 and Ag/SiO 2 Nanosphere Composites

SiO 2 nanospheres have been produced via a high temperature evaporation process and they have been Ni or Ag plated using electroless plating solutions. These samples were examined by Atomic Force Microscopy (AFM) and Magnetic Resonance (MR). The initial SiO 2 nanospheres were about 30 nm in diameter, and the Ni plating layer resulted in a 25nm thick metallic Ni coverage, while the Ag coverage was estimated to be in the 150 nm range. In the case of the Ni/SiO 2 nanosphere composites, the MR signals show the presence of Ni +2 and Ni +3 paramagnetic centers, seen below 40K, and ferromagnetic metallic Ni, which is seen above 40K. The dried Ni plating solution (with no SiO 2 ) shows only the presence of paramagnetic Ni +3 . These results suggest that an interfacial reaction at the surface of the SiO 2 nanospheres leads to the formation of ferromagnetic Ni, which deposits onto the spheres and forms a ferromagnetic Ni/SiO 2 nanosphere composite. In the case of the Ag/SiO 2 nanosphere composites, no MR signal is seen from the non-magnetic Ag, but strong paramagnetic behavior has been noted for Co +2 , which originates from the plating solution.