Dynamical Nonlinear Inversion of the Surface Photovoltage at Si(100).

A surface photovoltage (SPV) is observed whenever a doped semiconductor with non-negligible band bending is illuminated by light and charge carriers are excited across the band gap. The sign of the SPV depends on the nature of the doping, the amplitude of the SPV increases with the fluence of the light illumination up to a saturation value, which is determined by the doping concentration. We have investigated Si(100) samples with well-characterized doping levels over a wide range of illumination fluences.

Comparing the Toxicological Responses of Pulmonary Air-Liquid Interface Models upon Exposure to Differentially Treated Carbon Fibers.

In recent years, the use of carbon fibers (CFs) in various sectors of industry has been increasing. Despite the similarity of CF degradation products to other toxicologically relevant materials such as asbestos fibers and carbon nanotubes, a detailed toxicological evaluation of this class of material has yet to be performed. In this work, we exposed advanced air-liquid interface cell culture models of the human lung to CF.

Nanoscale Confinement of Photo-Injected Electrons at Hybrid Interfaces.

A prerequisite for advancing hybrid solar light harvesting systems is a comprehensive understanding of the spatiotemporal dynamics of photoinduced interfacial charge separation. Here, we demonstrate access to this transient charge redistribution for a model hybrid system of nanoporous zinc oxide (ZnO) and ruthenium bipyridyl chromophores. The site-selective probing of the molecular electron donor and semiconductor acceptor by time-resolved X-ray photoemission provides direct insight into the depth distribution of the photoinjected electrons and their interaction with the local band structure on a nanometer length scale.

Real-time interfacial electron dynamics revealed through temporal correlations in x-ray photoelectron spectroscopy.

We present a novel technique to monitor dynamics in interfacial systems through temporal correlations in x-ray photoelectron spectroscopy (XPS) signals. To date, the vast majority of time-resolved x-ray spectroscopy techniques rely on pump-probe schemes, in which the sample is excited out of equilibrium by a pump pulse, and the subsequent dynamics are monitored by probe pulses arriving at a series of well-defined delays relative to the excitation. By definition, this approach is restricted to processes that can either directly or indirectly be initiated by light.

Direct observation of charge separation in an organic light harvesting system by femtosecond time-resolved XPS.

The ultrafast dynamics of photon-to-charge conversion in an organic light-harvesting system is studied by femtosecond time-resolved X-ray photoemission spectroscopy (TR-XPS) at the free-electron laser FLASH. This novel experimental technique provides site-specific information about charge separation and enables the monitoring of free charge carrier generation dynamics on their natural timescale, here applied to the model donor-acceptor system CuPc:C. A previously unobserved channel for exciton dissociation into mobile charge carriers is identified, providing the first direct, real-time characterization of the timescale and efficiency of charge generation from low-energy charge-transfer states in an organic heterojunction.