Link between O2SiH infrared band amplitude and porous silicon photoluminescence during ambient O3 oxidation

Controlling Microarray Feature Spreading and Response Stability on Porous Silicon Platforms by Using Alkene-Terminal Ionic Liquids and UV Hydrosilylation

In an attempt to develop reversible sensors based on ionic liquid/porous silicon (IL/pSi) platforms, we introduce an approach using task-specific, alkene-terminal ILs (AT-ILs) for direct grafting to the hydrogen-passivated as prepared-pSi (ap-pSi) surface via UV-hydrosilylation to address previous shortcomings associated with IL pattern impermanence (i.e., spread). By employing photoluminescence emission (PLE) and Fourier-transform infrared (FT-IR) imaging measurements, we demonstrate that the covalent grafting of AT-ILs onto the ap-pSi surface via photochemical hydrosilylation not only mitigates such feature spreading but also greatly improves PLE pattern stability. Significantly, we have discovered that, upon hydrosilylation, the resulting contact pin printed IL features remain stable to repeated challenges by toluene vapors, demonstrating the utility of AT-IL hydrosilylation for producing high-fidelity microarray features on pSi toward robust optical sensory microarrays.

Oxygen backed silicon hydride in correlation with the photoluminescence of silicon nano-crystals

Converting silicon hydride (–SiH) to oxygen backed silicon hydride (–OSiH) on porous silicon leads to a shift in the wavelength of photoluminescence (PL) maximum from 670 to 605 nm, corresponding to an increase of 0.2 eV on emission energy.

Contact Pin-Printing onto Porous Silicon for Creating Microarrays with High Chemical Diversity

We explore the size and spatial microheterogeneity of contact pin-printed spots formed on porous silicon (pSi). Glycerol was contact printed at room temperature onto as-prepared, hydrogen-passivated pSi (ap-pSi) using 50 or 200 µm diameter solid pins. The pSi was then subjected to a strong oxidizing environment (gaseous O₃) and washed to remove the glycerol masks. The glycerol-free regions were converted to oxidized pSi (ox-pSi); the glycerol-coated regions were protected from O₃, but not entirely. The final array is described as circularly shaped "ap-pSi" regions on a field of ox-pSi. When comparing the areas outside and inside the glycerol-masked pSi spots, one finds dramatic differences in the Si-O-Si, SiH_x (x = 1-3) and O_ySiH_x (y, x = 1-3) levels with a spatially dependent continuum of compositions across the spot diameter. Experimental conditions could be adjusted to tune the final ap-pSi spot diameter and edge widths from 90 µm to 520 µm and 20 µm to 130 µm, respectively. The resulting ap-pSi spot diameter is explained by using molecular kinetic theory and time-dependent glycerol imbibement into the pSi within a one-dimensional Darcy's law model.

Ionic Liquids Can Permanently Modify Porous Silicon Surface Chemistry

To develop ionic liquid/porous silicon (IL/pSi) microarrays we have contact pin-printed 20 hydrophobic and hydrophilic ionic liquids onto as-prepared, hydrogen-passivated porous silicon (ap-pSi) and then determined the individual IL spot size, shape and associated pSi surface chemistry. The results reveal that the hydrophobic ionic liquids oxidize the ap-pSi slightly. In contrast, the hydrophilic ionic liquids lead to heavily oxidized pSi (i.e., ox-pSi). The strong oxidation arises from residual water within the hydrophilic ILs that is delivered from these ILs into the ap-pSi matrix causing oxidation. This phenomenon is less of an issue in the hydrophobic ILs because their water solubility is substantially lower.

An in-depth study linking the infrared spectroscopy and photoluminescence of porous silicon during ambient hydrogen peroxide oxidation

We carefully tailored a porous silicon (pSi) surface by oxidation with hydrogen peroxide (H2O2) to determine the time-dependent changes in nanocrystallite surface chemistries (e.g., Si-O-Si, SiH(x) [x = 1, 2], OySiH [y = 2, 3], and SiOH/H2O) and their influence on the pSi photoluminescence (PL). The relationship between infrared band amplitudes and PL intensity were evaluated under H2O2 and O3 (previously studied) oxidation. The pSi surface composition under O3 and H2O2 oxidation conditions tended to, save the O(y)SiH (y = 2, 3) species, approach similar values at the longest oxidation times studied, but they took very different paths in reaching these end points. Furthermore, the pSi surface compositions that exhibit maximum/minimum PL under each oxidant are very different.