Alloying of Pd thin films with Nb(001)

Annealing at elevated temperatures (1000–1600 K) of at least 10 ML thick Pd films deposited on Nb(0 0 1) has been found to result in a substrate capped by a pseudomorphic monolayer of Pd. This 1 ML thick Pd cap layer was characterised with a combination of UPS and DFT-calculations. UPS, RHEED and AES show that this cap layer protects the Nb(0 0 1) surface against (oxygen) contamination, which is a well known problem of Nb substrates. AES sputter profiling indicates that a major part of the Pd material in excess of the pseudomorphic monolayer is dissolved in the Nb lattice just below the surface. XPD shows that these dissolved Pd atoms occupy substitutional sites in the substrate. The analysis of the XPS-anisotropy also provides some information about the concentration and positions of the Pd and Nb atoms in the alloyed samples

Lithium Transport through Ultrathin Silicon Layers

This contribution presents non-destructive measurements of lithium transport parameters (diffusivity, permeability) in nanometer sized silicon layers done by a novel neutron reflectometry (NR) based approach [4]

Epitaxial growth of ultrathin palladium films on Re{0001}

Ultrathin bimetallic layers create unusual magnetic and surface chemical effects through the modification of electronic structure brought on by low dimensionality, polymorphism, reduced screening, and epitaxial strain. Previous studies have related valence and core-level shifts to surface reactivity through the d-band model of Hammer and Nørskov, and in heteroepitaxial films this band position is determined by competing effects of coordination, strain, and hybridization of substrate and overlayer states. In this study we employ the epitaxially matched Pd on Re{0001} system to grow films with no lateral strain. We use a recent advancement in low-energy electron diffraction to expand the data range sufficiently for a reliable determination of the growth sequence and out-of-plane surface relaxation as a function of film thickness. The results are supported by scanning tunneling microscopy and X-ray photoemission spectroscopy, which show that the growth is layer-by-layer with significant core-level shifts due to changes in film structure, morphology, and bonding

Gold and silver diffusion in germanium: a thermodynamic approach

Diffusion properties are technologically important in the understanding of semiconductors for the efficent formation of defined nanoelectronic devices. In the present study we employ experimental data to show that bulk materials properties (elastic and expansivity data) can be used to describe gold and silver diffusion in germanium for a wide temperature range (702–1177 K). Here we show that the so-called cBΩ model thermodynamic model, which assumes that the defect Gibbs energy is proportional to the isothermal bulk modulus and the mean volume per atom, adequately metallic diffusion in germanium

Self-diffusion in germanium isotope multilayers at low temperatures

Self-diffusion in intrinsic single crystalline germanium was investigated between 429 and 596 degrees C using (70)Ge/(nat)Ge isotope multilayer structures. The diffusivities were determined by neutron reflectometry from the decay of the first and third order Bragg peak. At high temperatures the diffusivities are in excellent agreement with literature data obtained by ion beam sputtering techniques, while considerably smaller diffusion lengths between 0.6 and 4.1 nm were measured. At lower temperatures the accessible range of diffusivities could be expanded to D approximate to 1x10(-25) m(2) s(-1), which is three orders of magnitude lower than the values measured by sputtering techniques. Taking into account available data on Ge self-diffusion, the temperature dependence is accurately described over nine orders of magnitude by a single Arrhenius equation. A diffusion activation enthalpy of 3.13 +/- 0.03 eV and a pre-exponential factor of 2.54x10(-3) m(2) s(-1) for temperatures between 429 and 904 degrees C are obtained. Single vacancies are considered to prevail self-diffusion in Ge over the whole temperature range

Fundamental experiments on the measurement of Li diffusion in electrochemically lithiated silicon electrodes for lithium

The knowledge of Li diffusion in lithium silicide (LixSi) is nowadays of importance for the Li-ion battery (LIB) research and development community. About twenty times more charge (Li+) can be stored per Si atom (Li3.75Si) than per C atom (LiC6), while carbon is still the main storage material in commercial LIBs. Consequently, huge effort is made to replace carbon by silicon in LIBs. Unfortunately, the diffusion of high amounts of Li+ into silicon during LIB operation is accompanied by a huge volume expansion of up to 400 % leading to a pulverization of the silicon electrode due to stress. Li diffusion in the interior of the electrode plays an important role for a fundamental understanding and for an optimization of application relevant properties like charging/discharging rates, maximum capacity, self-discharge, and cycling stability. This contribution reports about the realization of Li diffusion experiments in electrochemically lithiated amorphous silicon. Li diffusion was investigated at room temperature using the technique of secondary ion mass spectrometry (SIMS) in depth profile and in line scan mode in combination with stable 6Li isotope tracers. Experiments were done on 200 nm thin Si electrodes with a Li+ insertion stage of about 30 % and 80 % of full capacity. SIMS line scan data were successfully obtained, which will allow to measure fast Li diffusion on electrodes over macroscopic distances in the mm range, which is not possible using SIMS depth profiling mode

Evidence for strong Auger electron diffraction in thin metallic films

We deposited \chem{Ag} and \chem{Au} films on a \chem{Nb(100)} surface terminated with a pseudomorphic \chem{Pd} monolayer (ML). Instead of continuously decreasing, the \chem{Pd}-MVV (330\un{eV}) Auger signal received in normal emission from the \chem{Pd} ML increases for the coverage range of 1\un{ML}–2\un{ML} of the deposited \chem{Ag} or \chem{Au}. This increase leads to a \chem{Pd}-MVV (330\un{eV}) Auger signal even stronger than that coming from the uncovered \chem{Pd} substrate. We demonstrate that the forward focusing of the \chem{Pd}-MVV (330\un{eV}) Auger electrons by the growing \chem{Ag} or \chem{Au} film is responsible for this effect. We subsequently show how this phenomenon can be used to determine the absolute thickness of the deposited films, making Auger electron diffraction more useful for film thickness determination than signal damping in Auger electron spectroscopy