Soft x-ray spectroscopy of high pressure liquid.

We describe a new experimental technique that allows for soft x-ray spectroscopy studies (∼100-1000 eV) of high pressure liquid (∼100 bars). We achieve this through a liquid cell with a 100 nm-thick SiN membrane window, which is sandwiched by two identical O-rings for vacuum sealing. The thin SiN membrane allows soft x-rays to penetrate, while separating the high-pressure liquid under investigation from the vacuum required for soft x-ray transmission and detection.

Surface Enhanced Raman Spectroscopy of Organic Molecules on Magnetite (Fe3O4) Nanoparticles.

Surface-enhanced Raman spectroscopy (SERS) of species bound to environmentally relevant oxide nanoparticles is largely limited to organic molecules structurally related to catechol that facilitate a chemical enhancement of the Raman signal. Here, we report that magnetite (Fe3O4) nanoparticles provide a SERS signal from oxalic acid and cysteine via an electric field enhancement. Magnetite thus likely provides an oxide substrate for SERS study of any adsorbed organic molecule.

Cooperative and competitive adsorption of amino acids with Ca²⁺ on rutile (α-TiO₂).

The interactions of biomolecules such as amino acids with mineral surfaces in the near-surface environment are an important part of the short and long-term carbon cycles. Amino acid-mineral surface interactions also play an important role in biomineralization, biomedicine, and in assembling the building blocks of life in the prebiotic era. Although the pH effects during adsorption of amino acids onto mineral surfaces have been studied, little is known about the effects of environmentally important divalent cations.

Speciation of L-DOPA on nanorutile as a function of pH and surface coverage using surface-enhanced Raman spectroscopy (SERS).

The adsorption configuration of organic molecules on mineral surfaces is of great interest because it can provide fundamental information for both engineered and natural systems. Here we have conducted surface-enhanced Raman spectroscopy (SERS) measurements to probe the attachment configurations of DOPA on nanorutile particles under different pH and surface coverage conditions. The Raman signal enhancement arises when a charge transfer (CT) complex forms between the nanoparticles and adsorbed DOPA.