Time-resolved soft X-ray core-level photoemission spectroscopy at 880 °C using the pulsed laser and synchrotron radiation and the pulse heating current
Copper adsorption on Ru(0001) has been studied by synchrotron radiation. The clean Ru 3d 5/2 spectra were found to consist of two components with a binding energy shift of 400 meV. The component with the lower binding energy represents the first layer of ruthenium atoms. Adsorption of copper gives rise to core level shifts of the Ru 3d 5/2 components, which were studied as a function of Cu coverage. Experiments were carried out with copper coverages varying from the submonolayer range up to two monolayers of copper. The binding energy of the Cu 2p 3/2 level was measured by X-ray photoemission spectroscopy.
AbstractTime-resolved photoelectron spectroscopy can give insights into carrier dynamics and offers the possibility of element and site-specific information through the measurements of core levels. In this paper, we demonstrate that this method can access electrons dynamics in PbS quantum dots over a wide time window spanning from pico- to microseconds in a single experiment carried out at the synchrotron facility BESSY II. The method is sensitive to small changes in core level positions. Fast measurements at low pump fluences are enabled by the use of a pump laser at a lower repetition frequency than the repetition frequency of the X-ray pulses used to probe the core level electrons: Through the use of a time-resolved spectrometer, time-dependent analysis of data from all synchrotron pulses is possible. Furthermore, by picosecond control of the pump laser arrival at the sample relative to the X-ray pulses, a time-resolution limited only by the length of the X-ray pulses is achieved. Using this method, we studied the charge dynamics in thin film samples of PbS quantum dots on n-type MgZnO substrates through time-resolved measurements of the Pb 5d core level. We found a time-resolved core level shift, which we could assign to electron injection and charge accumulation at the MgZnO/PbS quantum dots interface. This assignment was confirmed through the measurement of PbS films with different thicknesses. Our results therefore give insight into the magnitude of the photovoltage generated specifically at the MgZnO/PbS interface and into the timescale of charge transport and electron injection, as well as into the timescale of charge recombination at this interface. It is a unique feature of our method that the timescale of both these processes can be accessed in a single experiment and investigated for a specific interface.
ABSTRACTSynchrotron x-ray pulses from the Cornell High Energy Synchrotron Source
(CHESS) have been used to carry out nanosecond resolution measurements of
the temperature distrubutions in Ge during UV pulsed-laser irradiation. KrF
(249 nm) laser pulses of 25 ns FWHM with an energy density of 0.6 J/cm2 were
used. The temperatures were determined from x-ray Bragg profile measurements
of thermal expansion induced strain on <111> oriented Ge. The data
indicate the presence of a liquid-solid interface near the melting point,
and large (1500-4500°C/pm) temperature gradients in the solid; these Ge
results are analagous to previous ones for Si. The measured temperature
distributions are compared with those obtained from heat flow calculations,
and the overheating and undercooling of the interface relative to the
equilibrium melting point are discussed.
ABSTRACTSynchrotron x-ray pulses have been used to make nanosecond resolution time-resolved x-ray diffraction measurements on silicon during pulsed laser annealing. Thermal expansion analysis of near-surface strains during annealing has provided depth dependent temperature profiles indicating >1100°C temperatures and diffraction from boron implanted silicon has shown evidence for near-surface melting. These results are in qualitative agreement with the thermal melting model of laser annealing.
ABSTRACTWe studied the poly [2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV)/LiF/Al interface by angle-dependent X-ray photoemission spectroscopy (XPS). The changes in the C1s, O 1s, Al 2p core level spectra, and the evolution of O to C and Li to F atomic ratios at different photoelectron take-off angles were carefully analyzed. A reduced oxygen concentration with a LiF layer at the interface suggests that LiF can help reduce the oxidation of Al. The interface was found rich in Li+ ions, some of which might be attached to MEH-PPV to form “N type” doping. The electron injection layer consists of Li+doped MEH-PPV, LiF, Al oxides, and metallic Al.
A method for studying pico to microsecond time-resolved core-level spectroscopy used to investigate electron dynamics in quantum dots