High-Dose Rate Brachytherapy for Non-Melanoma Skin Cancer

https://digitalcommons.misericordia.edu/medimg_seniorposters/1047/thumbnail.jp

Surface-sensitive spectro-electrochemistry using ultrafast 2D ATR IR spectroscopy

A new method is presented for the combination of spectro-electrochemistry and femtosecond 2D IR spectroscopy. The key concept is based on ultrathin (similar to nm) conductive layers of noble metals and indium-tin oxide (ITO) as working electrodes on a single-reflection attenuated total reflectance (ATR) element in conjunction with ultrafast, multidimensional ATR spectroscopy. The ATR geometry offers prominent benefits in ultrafast spectro-electrochemistry, that is, surface sensitivity for studying electrochemical processes directly at the solvent-electrode interface as well as the application of strongly IR-absorbing solvents such as water due to a very short effective path length of the evanescent wave at the interface. We present a balanced comparison between usable electrode materials regarding their performance in the ultrafast ATR setup. The electrochemical performance is demonstrated by vibrational Stark-shift spectroscopy of carbon monoxide (CO) adsorbed to platinum-coated, ultrathin ITO electrodes. We furthermore measure vibrational relaxation and spectral diffusion of the stretching mode from surface-bound CO dependent on the applied potential to the working electrode and find a negligible impact of the electrode potential on ultrafast CO dynamics

Temperature Dependence of the Structure of Langmuir Films of Normal-Alkanes on Liquid Mercury

The temperature dependent phase behavior of Langmuir films of n-alkanes [CH3(CH2)n−2CH3, denote Cn] on mercury was studied for chain lengths 19 ⩽ n ⩽ 22 and temperatures 15 ⩽ T ⩽ 44 °C, using surface tensiometry and surface x-ray diffraction methods. In contrast with Langmuir films on water, where molecules invariably orient roughly surface normal, alkanes on mercury are always oriented surface parallel and show no long-range in-plane order at any surface pressure. A gas and several condensed phases of single, double, and triple layers of lying-down molecules are found, depending on n and T. At high coverages, the alkanes studied here show transitions from a triple to a double to a single layer with increasing temperature. The transition temperature from a double to a single layer is found to be ∼ 5 °C, lower than the bulk rotator-to-liquid melting temperature, while the transition from a triple to a double layer is about as much below the double-to-single layer transition. Both monolayer and bulk transition temperatures show a linear increase with n with identical slopes of ∼ 4.5 °C/CH2 within the range of n values addressed here. It is suggested that the film and bulk transitions are both driven by a common cause: the proliferation of gauche defects in the chain with increasing temperature.Engineering and Applied Science

Langmuir Films of Normal-Alkanes on the Surface of Liquid Mercury

The coverage dependent phase behavior of molecular films of n-alkanes ($CH_{3}CH_{n−2}CH_3$, denote Cn) on mercury was studied for lengths 10 $\leq$ n $\leq$ 50, using surface tensiometry and surface x-ray diffraction methods. In contrast with Langmuir films on water, where roughly surface-normal molecular orientation is invariably found, alkanes on mercury are always oriented surface-parallel, and show no long-range in-plane order at any surface pressure. At a low coverage a two-dimensional gas phase is found, followed, upon increasing the coverage, by a single condensed layer (n $\leq$ 18), a sequence of single and double layers (19 $\leq$ n $\leq$ 20; n $\geq$ 26), or a sequence of single, double, and triple layers (22 $\leq$ n $\leq$ 24). The thermodynamical and structural properties of these layers, as determined from the measurements, are discussed.Engineering and Applied Science

Plasmonic Substrates Do Not Promote Vibrational Energy Transfer at Solid–Liquid Interfaces

Intermolecular vibrational energy transfer in monolayers of isotopically mixed rhenium carbonyl complexes at solid–liquid interfaces is investigated with the help of ultrafast 2D Attenuated Total Reflectance Infrared (2D ATR IR) spectroscopy in dependence of plasmonic surface enhancement effects. Dielectric and plasmonic materials are used to demonstrate that plasmonic effects have no impact on the vibrational energy transfer rate in a regime of moderate IR surface enhancement (enhancement factors up to ca. 30). This result can be explained with the common image-dipole picture. The vibrational energy transfer rate thus can be used as a direct observable to determine intermolecular distances on surfaces, regardless of their plasmonic properties

Ultrafast Vibrational Energy Transfer in Catalytic Monolayers at Solid–Liquid Interfaces

We investigate the ultrafast vibrational dynamics of monolayers from adsorbed rhenium–carbonyl CO2-reduction catalysts on a semiconductor surface (indium–tin-oxide (ITO)) with ultrafast two-dimensional attenuated total reflection infrared (2D ATR IR) spectroscopy. The complexes are partially equipped with isotope-labeled (13C) carbonyl ligands to generate two spectroscopically distinguishable forms of the molecules. Ultrafast vibrational energy transfer between the molecules is observed via the temporal evolution of cross-peaks between their symmetric carbonyl stretching vibrations. These contributions appear with time constant of 70 and 90 ps for downhill and uphill energy transfer, respectively. The energy transfer is thus markedly slower than any of the other intramolecular dynamics. From the transfer rate, an intermolecular distance of ∼4–5 Å can be estimated, close to the van der Waals distance of the molecular head groups. The present paper presents an important cornerstone for a better understanding of intermolecular coupling mechanisms of molecules on surfaces and explains the absence of similar features in earlier studies

Dipolar colloids in apolar media: direct microscopy of two-dimensional suspensions

Spherical colloids, in an absence of external fields, are commonly assumed to interact solely through rotationally-invariant potentials, u(r). While the presence of permanent dipoles in aqueous suspensions has been previously suggested by some experiments, the rotational degrees of freedom of spherical colloids are typically neglected. We prove, by direct experiments, the presence of permanent dipoles in commonly used spherical poly(methyl methacrylate) (PMMA) colloids, suspended in an apolar organic medium. We study, by a combination of direct confocal microscopy, computer simulations, and theory, the structure and other thermodynamical properties of organic suspensions of colloidal spheres, confined to a two-dimensional (2D) monolayer. Our studies reveal the effects of the dipolar interactions on the structure and the osmotic pressure of these fluids. These observations have far-reaching consequences for the fundamental colloidal science, opening new directions in self-assembly of complex colloidal clusters