Combining Time-Dependent Density Functional Theory and the ΔSCF Approach for Accurate Core-Electron Spectra.

Spectroscopies that probe electronic excitations from core levels into unoccupied orbitals, such as X-ray absorption spectroscopy and electron energy loss spectroscopy, are widely used to gain insight into the electronic and chemical structure of materials. To support the interpretation of experimental spectra, we assess the performance of a first-principles approach that combines linear-response time-dependent density (TDDFT) functional theory with the Δ self-consistent field (ΔSCF) approach. In particular, we first use TDDFT to calculate the core-level spectrum and then shift the spectrum such that the lowest excitation energy from TDDFT agrees with that from ΔSCF. We apply this method to several small molecules and find encouraging agreement between calculated and measured spectra.

Generation of plasmonic hot carriers from d-bands in metallic nanoparticles.

We present an approach to master the well-known challenge of calculating the contribution of d-bands to plasmon-induced hot carrier rates in metallic nanoparticles. We generalize the widely used spherical well model for the nanoparticle wavefunctions to flat d-bands using the envelope function technique. Using Fermi's golden rule, we calculate the generation rates of hot carriers after the decay of the plasmon due to transitions either from a d-band state to an sp-band state or from an sp-band state to another sp-band state. We apply this formalism to spherical silver nanoparticles with radii up to 20 nm and also study the dependence of hot carrier rates on the energy of the d-bands. We find that for nanoparticles with a radius less than 2.5 nm, sp-band state to sp-band state transitions dominate hot carrier production, while d-band state to sp-band state transitions give the largest contribution for larger nanoparticles.

Laboratory-based high pressure X-ray photoelectron spectroscopy: A novel and flexible reaction cell approach.

The last 10-15 years have witnessed a resurgence in the application of high pressure X-ray photoelectron spectroscopy, mainly through the development of new electron energy analyser designs and the utilization of high-brilliance synchrotron radiation sources. To continue this expansion of the technique, it is crucial that instruments are developed for the home-laboratory, considering that this is where the vast majority of traditional ultra-high vacuum (UHV) X-ray photoelectron spectroscopy is performed. The research presented here introduces a new addition to the field, an instrument capable of performing spectroscopy measurements from UHV to high pressure (25 mbar), achieved using a retractable and modular reaction cell design. The ease of use, stability (of analyser, X-ray source, and gas delivery, etc.), and overall capability of the instrument will be demonstrated.

A versatile photoelectron spectrometer for pressures up to 30 mbar.

High-pressure photoelectron spectroscopy is a rapidly developing technique with applications in a wide range of fields ranging from fundamental surface science and catalysis to energy materials, environmental science, and biology. At present the majority of the high-pressure photoelectron spectrometers are situated at synchrotron end stations, but recently a small number of laboratory-based setups have also emerged. In this paper we discuss the design and performance of a new laboratory based high pressure photoelectron spectrometer equipped with an Al Kα X-ray anode and a hemispherical electron energy analyzer combined with a differentially pumped electrostatic lens. The instrument is demonstrated to be capable of measuring core level spectra at pressures up to 30 mbar. Moreover, valence band spectra of a silver sample as well as a carbon-coated surface (graphene) recorded under a 2 mbar nitrogen atmosphere are presented, demonstrating the versatility of this laboratory-based spectrometer.