Ionic Liquids Can Permanently Modify Porous Silicon Surface Chemistry

Abstract

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.

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

“…The synthesis and characterization details on the 20 conventional ILs compiled within Table are available in a previous publication . The following alkene-terminal ILs (Table ) were prepared as described below: 1-butyl-3-vinyl­imidazolium bis­(tri­fluoro­methyl­sulfonyl)­imide ([BVIm]­[Tf 2 N]), 1-allyl-3-vinyl­imidazolium bis­(tri­fluoro­methyl­sulfonyl)­imide ([AVIm]­[Tf 2 N]), 1-allyl-3-methyl­imidazolium bis­(tri­fluoro­methyl­sulfonyl)­imide ([AMIm]­[Tf 2 N]), 1-(hex-5-en-1-yl)-3-methyl­imidazolium bis­(tri­fluoro­methyl­sulfonyl)­imide ([HeMIm]­[Tf 2 N]), and 1-(dec-5-en-1-yl)-3-methyl­imidazolium bis­(tri­fluoro­methyl­sulfonyl)­imide ([DeMIm]­[Tf 2 N]).…”

“…Photoluminescence emission (PLE) measurements were carried out using an epi-photoluminescence multispectral imaging microscope (488 nm excitation, 490 nm dichroic filter, 565 nm long pass filter, 3.5 s exposure time, liquid crystal tunable filter scanned from 620 to 850 nm at a 10 nm step size, and 1 × 1 binning). Additional experimental details on PL-based IL spot intensity profiles can be found in our previous work …”

“…Each FT-IR spectrum was baseline corrected and normalized at 620 cm –1 (crystalline mode Si–Si stretch) to correct for differences between pSi chips and account for multiple reflections . Further details on FT-IR spectral acquisition can be obtained from our previous report . Measurements were carried out between 295–298 K.…”

“…After a 5 h hydrosilylation, the IL/pSi microarray was decoupled from the flow cell and immersed in 40 mL of anhydrous DCM (15 min) to remove unreacted alkene-terminated IL. The printed pSi microarrays were then stored as described previously …”

“…In earlier work, we employed 20 structurally distinct ILs, comprising both hydrophobic and hydrophilic examples, for the printing of IL microarrays onto the surface of as-prepared, hydrogen-passivated porous silicon (ap-pSi) via contact pin printing (CPP) . Following microarray printing, each IL spot was investigated and characterized using photoluminescence emission (PLE) and Fourier-transform infrared (FT-IR) imaging.…”