Mass-selected Pt ion deposition in ultrahigh vacuum (UHV) was used to prepare a series of size-selected electrodes with Pt (n ≤ 14) clusters supported on either glassy carbon (GC) or indium tin oxide (ITO). After characterization of the physical properties of the electrodes in UHV, an in situ method was used to study electrocatalytic activity for the oxygen reduction and ethanol oxidation reactions, without significant air exposure. For each reaction studied, there are similarities between the catalytic properties of Pt-containing electrodes and those of nanoparticulate or bulk Pt electrodes, but there are also important differences that provide mechanistic insights. For all systems, strong cluster size effects were observed. For comparison, select experiments were done under identical conditions but with the Pt electrodes exposed to air prior to electrochemical studies, resulting in strong modification/suppression of catalytic activity due to adventitious contaminants. For ethanol oxidation at Pt/ITO, activity varies with size nonmonotonically, by more than an order of magnitude. The sharp size dependence persists during at least 30 to 40 cycles through the Pt redox potential, indicating that processes that would tend to broaden the size distribution are not efficient. All but the least active sizes are substantially more active per mass of Pt, than Pt nanoparticles under the same conditions. The oscillatory dependence of activity on size is anticorrelated with the binding energy of the Pt 4d core level, demonstrating that activity is controlled by the electronic structure of the supported clusters. For oxygen reduction at Pt/ITO, the branching between water and hydrogen peroxide production is strongly dependent on cluster size, with small clusters selectively producing peroxide with high activity. The selectivity appears to be related to the size of the active site, with no obvious correlation to Pt electronic properties. The most unusual effect seen was for Pt/GC, studied under acid conditions appropriate to oxygen reduction. Pt and a few other cluster sizes show "normal" oxygen reduction activity, similar to what is measured for Pt nanoparticles on GC under the same conditions. Many of the small clusters, however, are found to catalyze highly efficient oxidation, by water, of the glassy carbon support, with essentially no overpotential. The high activity for carbon oxidation for many Pt/GC electrodes and the absence of significant carbon oxidation for a GC electrode with Pt nanoparticles raise the question of whether small Pt clusters may be responsible for much of the corrosion observed in Pt/carbon electrodes. This system provides another example where activity for oxidation catalysis is anticorrelated with the Pt core level binding energies, indicating that it is electronic, rather than geometric, structure that limits activity.

Understanding the factors that control electrochemical catalysis is essential to improving performance. We report a study of electrocatalytic ethanol oxidation - a process important for direct ethanol fuel cells - over size-selected Pt centers ranging from single atoms to Pt14. Model electrodes were prepared by soft-landing of mass-selected Ptn(+) on indium tin oxide (ITO) supports in ultrahigh vacuum, and transferred to an in situ electrochemical cell without exposure to air. Each electrode had identical Pt coverage, and differed only in the size of Pt clusters deposited. The small Ptn have activities that vary strongly, and non-monotonically with deposited size. Activity per gram Pt ranges up to ten times higher than that of 5 to 10 nm Pt particles dispersed on ITO. Activity is anti-correlated with the Pt 4d core orbital binding energy, indicating that electron rich clusters are essential for high activity.

Deposition of size-selected Pt n clusters on indium tin oxide (ITO) films in ultrahigh vacuum was used to create electrodes with catalytic sites of controlled size. We report a study of the oxygen reduction reaction (ORR) in 0.1 M HClO 4 at size-selected Pt n /ITO electrodes that were prepared and characterized without exposure to laboratory air. It was found that the ORR onset potential was size-dependent, varying from ∼0.66 V vs NHE for Pt 1 /ITO to ∼0.78 V vs NHE for Pt n (n ≥ 10). The maximum ORR currents per gram of Pt were found to be about an order of magnitude higher than that for ITO with 5 nm Pt particles. The branching ratio between the production of water and hydrogen peroxide in ORR was found to be strongly size-dependent. For 5 nm Pt particles on ITO or for polycrystalline Pt, little H 2 O 2 was produced, but as cluster size was decreased, the H 2 O 2 branching became large, suggesting that small Pt clusters could be useful selective catalysts for H 2 O 2 electrosynthesis. Because there was no obvious correlation of ORR activity with Pt n electronic properties, as probed by photoemission, the effect of size on branching is tentatively attributed to size of the available oxygen binding sites.

We have studied the circular dichroism (CD), in the ultraviolet and visible regions, of the transparent, chiral molecule 1,1’‐Bi‐2‐naphtol (BINOL) in 1.5 μm thick films. The initial transparent film shows an additional negative cotton effect in the CD compared to solution. With time under room temperature the film undergoes a structural phase transition. This goes hand in hand with a cotton effect at the low energy absorption band which inverts with opposite propagation direction of light through the film which is revealed as a polarity reversal of ellipticity (PRE). After completion of the phase transition the film exhibits circular differential scattering throughout the visible range which also shows PRE. The structure change was studied with Raman, microscopy under cross polarization conditions and nonlinear second‐harmonic generation circular dichroism (SHG‐CD). The superposition of the optical activity of individual molecules and isotropy effects makes an interpretation challenging. Yet overcoming this challenge by finding a suitable model structural information can be derived from CD measurements.

Chiroptical methods have been proven to be superior compared to their achiral counterparts for the structural elucidation of many compounds. In order to expand the use of chiroptical systems to everyday applications, the development of functional materials exhibiting intense chiroptical responses is essential. Particularly, tailored and robust interfaces compatible with standard device operation conditions are required. Herein, we present the design and synthesis of chiral allenes and their use for the functionalization of gold surfaces. The self-assembly results in a monolayer-thin room-temperature-stable upstanding chiral architecture as ascertained by ellipsometry, X-ray photoelectron spectroscopy, and near-edge X-ray absorption-fine-structure. Moreover, these nanostructures anchored to device-compatible substrates features intense chiroptical second harmonic generation. Both straight-forward preparation of the device-compatible interfaces along with their chiroptical nature provide major prospects for everyday applications.

Water-soluble ligand protected optically active silver nanostructures were synthesised in a one-step reduction and capping process mediated by thiol-containing biomolecules. The synthesis was performed successfully with d- and l-cysteine and l-glutathione. The chiroptical properties of the obtained nanostructures were investigated by circular dichroism spectroscopy in the ultraviolet and visible wavelength range. They exhibit a g-value of up to 0.7%, which is about one order of magnitude larger compared to particles prepared by citrate reduction followed by a ligand exchange reaction. The structure and composition of the prepared materials were characterised by transmission electron microscopy, energy-dispersive X-ray and X-ray photoelectron spectroscopy. Although these structures do not have a chiral geometry, they show mirror image g-values when capped with d- and l-cysteine. This indicates that the underlying chirality transfer mechanism is based on an electric field polarisation process.

In this work, we present an experimental setup for the in situ and ex situ study of the optical activity of samples, which can be prepared under ultra‐high vacuum (UHV) conditions by second‐harmonic generation circular dichroism (SHG‐CD) over a broad spectral range. The use of a racemic mixture as a qualified reference for the anisotropy factor is described and, as an example, the chiroptical properties of 1.5 μm thick (multilayers) as well as sub‐monolayer thin films of the R‐ and S‐enantiomer of 1,1′‐Bi‐2‐naphthol (BINOL) evaporated onto BK7 substrates were investigated.

The extinction spectra of size-selected, supported Ag20 and Ag55 clusters have been measured with surface cavity ring-down (s-CRD) spectroscopy under ultrahigh vacuum (UHV) conditions. A single plasmonic resonance around 3.2 eV is observed. The reaction with benzenethiol shifts the localized surface plasmon resonance (LSPR) by ≈0.3 eV to lower energies, which is attributed to an increased dielectric function of the surrounding medium as well as to a reduction of the free-electron density inside the silver clusters. The time dependence of the LSPR redshift under exposure to benzenethiol has a double exponential behavior. A rapid redshift is caused by chemisorption of benzenethiol from the gas phase via the formation of a sulfur–silver bond, whereas a slow redshift is caused by additional physisorption of benzenethiol. Comparative studies with benzene, which do not show any chemisorption but show physisorption character on silver, reveal that ≈0.2 eV of the overall redshift can be attributed to an increased dielectric constant of the surrounding medium, whereas a reduction of the free-electron density accounts for ≈0.1 eV of the observed redshift.