Y. Huttel

Generation of Nanoparticles with Adjustable Size and Controlled Stoichiometry: Recent Advances

We present a bottom-up fabrication route based on the sputtering gas aggregation source that allows the generation of nanoparticles with controllable and tunable chemical composition while keeping the control of the cluster size. We demonstrate that the chemical composition of the particles can be monitored by the individual adjustment of the working parameters of the magnetrons inserted in a gas aggregation zone. Such control of the parameters leads to a fine control of the ion density of each target material and hence to the control of the chemical composition of the nanoparticles. In particular, we show through X-ray photoemission, atomic force microscopy, and high-resolution transmission electron microscopy that it is possible to generate bimetallic (AgAu) and trimetallic (AgAuPd) alloy nanoparticles with well-defined and tunable stoichiometries from three targets of pure Ag, Au, and Pd. The proposed route for the generation of nanoparticles opens new possibilities for the fabrication of nanoparticles using a physical method that, for some applications, could be complementary to the chemical methods.

Epitaxial growth of AlN on sapphire (0 0 0 1) by sputtering: a structural, morphological and optical study

We report on the growth conditions dependence of the morphology and structural quality of epitaxial AlN thin films deposited by normal incidence reactive sputtering. The crystallographic quality is increased for higher concentrations of nitrogen in the plasma during the deposition process. Also the presence of an intermediate AlN buffer is found to reduce the stress induced by the substrate and to enhance the quality of the subsequent AlN deposit; the morphology and roughness of the surface of the deposit depend on the deposition temperature of the buffer layer. From spectroscopic ellipsometry measurements we deduce and present the evolution of the refractive index and extinction coefficient with the wavelength for AlN deposits obtained under different growth conditions.

Nanopatterning of carbonaceous structures by field-induced carbon dioxide splitting with a force microscope

We report a tip-based nanofabrication method to generate carbon nanopatterns. The process uses the field-induced transformation of carbon dioxide gas into a solid material. It requires the application of low-to-moderate voltages ∼10–40 V. The method allow us to fabricated sub-25 nm dots and it can be up scaled to pattern square centimeter areas. Photoemission spectroscopy shows that the carbon is the dominating atomic species of the fabricated structures. The formation of carbon nanostructures and oxides by atomic force microscope nanolithography expands its potential by providing patterns on the same sample with different chemical composition.

Cobalt nanoparticles deposited and embedded in AlN: Magnetic, magneto-optical, and morphological properties

We present a structural, morphological, magnetic, and magneto-optical study of cobalt nanoparticles deposited on 50A AlN∕c-sapphire substrates and embedded in an AlN matrix. The dependence of the properties of Co nanoclusters deposited on AlN with growth temperature and amount of deposited Co are studied and discussed. Also we directly compare the properties of as grown and AlN embedded Co nanoclusters and show that the AlN matrix has a strong impact on their magnetic and magneto-optical properties.

Low‐energy Ar+ ion bombardment‐induced modification of surface atomic bond lengths on InP(100) wafer

We report the first direct measurement of surface interatomic bond distance modifications due to ion bombardment. The experiments were performed using low energy Ar+ ion on a InP(100) surface by photoemission x‐ray absorption fine structure. The structural changes are sputtering time dependent and result in first (P–In) and second (P–P) surface bond distances relaxation approaching the bulk values. It suggests that, prior to bond breaking, the Ar+ ion beam first stretches atomic bond lengths during a precursor stage, with small energy and momentum transfer. This work brings new insights into the knowledge of ion sputtering various micromechanisms which is relevant for surface preparation.

Aspect-ratio and lateral-resolution enhancement in force microscopy by attaching nanoclusters generated by an ion cluster source at the end of a silicon tip

One of the factors that limit the spatial resolution in atomic force microscopy (AFM) is the physical size of the probe. This limitation is particularly severe when the imaged structures are comparable in size to the tips apex. The resolution in the AFM is usually enhanced by using sharp tips with high aspect ratios. In the present paper we propose an approach to modify AFM tips that consists of depositing nanoclusters on standard silicon tips. We show that the use of those tips leads to atomic force microscopy images of higher aspect ratios and spatial resolution. The present approach has two major properties. It provides higher aspect-ratio images of nanoscale objects and, at the same time, enables to functionalize the AFM tips by depositing nanoparticles with well-controlled chemical composition.

O 1s investigation of SiO2/Si interface formation using an alkali metal promoter

Abstract We have investigated the role of pre-adsorbed potassium in the promotion of silicon surface oxidation by core level and valence band photoemission experiments using AlKα (1,486.6 eV) and ZrMζ (151.4 eV) X-ray lines. We dose between 10 +15 and 10 +18 oxygen molecules onto a Si(100)2 × 1 surface modified by a K overlayer. Under these conditions the oxidation rate of silicon is enhanced by about 3 to 4 orders of magnitude with formation of a silicon oxide layer having high oxidation states (Si 3+ ) at room temperature. The alkali metal catalyst is removed by thermal annealing (at about 600°C), leading to the formation of a SiO 2 /Si interface at lower temperatures than by direct thermal oxidation. The O 1s core level line clearly displays two components which suggests that the oxygen atoms have different bond configurations including binding to the substrate and the adsorbate, as also indicated by the corresponding valence band results. Interestingly, the respective intensities of the O 1s components behave very differently upon increasing oxygen exposure. The Si related component grows proportionally to the logarithm of the number of dosed oxygen molecules, whereas the K related one is already saturated at the smallest dose and yields a constant value for the whole exposure range. This feature demonstrates that the potassium atoms do not “store” oxygen, but only a small fraction of oxygen atoms is bound weakly to the catalyst. The micromechanisms of promotion will be described and compared to the latest state-of-the-art ab initio theoretical calculations using the local density functional approach.

Angle-resolved photoemission study and first principles calculation of the electronic structure of GaTe

The electronic band structure of GaTe is calculated by numerical atomic orbital density-functional theory, in the local-density approximation. In addition, the valence-band dispersion along various directions of the GaTe Brillouin zone is determined experimentally by angle-resolved photoelectron spectroscopy. Along these directions, the calculated valence-band structure is in good concordance with the valence-band dispersion obtained by these measurements. It is established that GaTe is a direct-gap semiconductor with a band gap located at the Z point, that is, at a Brillouin-zone border in a direction perpendicular to the layers. The valence-band maximum shows a marked p-like behavior, with a pronounced anion contribution. The conduction band minimum arises from states with a comparable s- p-cation and p-anion orbital contributions. Spin-orbit interaction appears to especially alter the dispersion and binding energy of states of the topmost valence bands lying at

Interface magnetic properties of epitaxial Fe-InAs heterostructures

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Capping layer effects in the structure and composition of Co nanoparticle ultrathin films

Spin-orbit interaction favors a hybridization of the topmost