G. Petö

Lateral growth of titanium silicide over a silicon dioxide layer

If a silicon dioxide step on a single crystal of silicon covered with titanium is annealed, then, following vertical growth on the silicon part, lateral growth of titanium silicide takes place over the oxide layer. In the temperature range 750–950 °C this lateral growth of Ti–silicide was found to be a linear function of the square root of the annealing time. The activation energy of the lateral growth was found to be 1.89 eV. During lateral growth the Ti–silicide forms a deep spike in the silicon crystal at the SiO2 step.

Electronic structure and catalytic properties of transition metal nanoparticles: The effect of size reduction

Size reduction of metal particles results in the formation of nanoparticles having short-range order and metastable state.Modeling of the nanoparticles can be obtained by various approaches. The major arrangement is the use of a model support on which metal nanoparticles can be created in a controlled way. Another approach is the use of amorphous alloy as precursor in which the ensemble of active sites (normally small metal nuclei embedded into amorphous matrix) is created.The modeling will be illustrated through the paper using SiO2/Si(100) on which several transition metals will be deposited by pulsed laser deposition. Ultraviolet photoelectron spectroscopic technique as well as transmission electron microscopic technique will be utilized in characterization of the samples. CO chemisorption and CO oxidation as test reaction will be applied to show the connection between catalytic behavior and electronic properties or morphology of nanoparticles.

Pressure dependent formation of small Cu and Ag particles during laser ablation

Abstract In this paper the possibility of application of laser ablation in inert gas atmosphere for deposition of nanosized particles is examined. Cu and Ag were deposited by laser ablation in 0–10 mbar Ar atmosphere. The samples were characterized by TEM and XPS. It was found that below 1 mbar for Cu and 2 mbar for Ag, island like thin film formation occurs. In Cu above 1 mbar lonely nanoparticles with diameters of 3–4 nm as well as large cluster aggregates were found, instead of the islands. This morphology remained unchanged up to 10 mbar. On the contrary, in Ag at 5 mbar individual particles with sizes of 4–6 nm were observed instead of the aggregates or islands. At 10 mbar the number of the 4–6 nm particles strongly decreased, and particles in the size range of 10 nm became dominant. The observed results may be related to the different decelerating rate of the evaporated Cu and Ag atoms in the Ar atmosphere.

Thickness‐dependent formation of Gd‐silicide compounds

Gd‐silicide phases were investigated by x‐ray diffraction. The results showed that not only one phase exists in a Gd thin‐film and silicon substrate reactions. The first phase formed was hexagonal GdSi≊1.7, the second orthorhombic GdSi2. The ratio of the two phases depends on temperature of the heat treatment, and at a given temperature and time of annealing, a dependence of the thickness of the evaporated Gd layer was found. At ∼100‐nm Gd thickness the dominant phase was orthorhombic GdSi2, at ∼250 nm hexagonal GdSi≊1.7. In the 300–1000‐nm interval orthorhombic GdSi2 was the main component again. Rutherford backscattering analysis showed that the phases were found mixed within the layer. This thickness‐dependent formation could be described with a simple model proposed by Gosele and Tu [J. Appl. Phys. 53, 3252 (1982)].Gd‐silicide phases were investigated by x‐ray diffraction. The results showed that not only one phase exists in a Gd thin‐film and silicon substrate reactions. The first phase formed was hexagonal GdSi≊1.7, the second orthorhombic GdSi2. The ratio of the two phases depends on temperature of the heat treatment, and at a given temperature and time of annealing, a dependence of the thickness of the evaporated Gd layer was found. At ∼100‐nm Gd thickness the dominant phase was orthorhombic GdSi2, at ∼250 nm hexagonal GdSi≊1.7. In the 300–1000‐nm interval orthorhombic GdSi2 was the main component again. Rutherford backscattering analysis showed that the phases were found mixed within the layer. This thickness‐dependent formation could be described with a simple model proposed by Gosele and Tu [J. Appl. Phys. 53, 3252 (1982)].

Electronic structure of Ag nanoparticles deposited on Si(1 0 0)

Nanosize silver particles were prepared by argon ion sputtering of an island-like silver film deposited by pulsed laser evaporation onto Si(1 0 0). The changes in the electronic structure related to particle size were observed by photoelectron spectroscopy during sputtering. The changes in the valence band induced by size reduction were dominated by a strong decrease in the lowest binding energy peak of the Ag 4d band, while other structures at higher binding energies remained unchanged. This redistribution of the d-states in the valence band seems to be common for noble metal nanoparticles.

Laser ablation induced formation of nanoparticles and nanocrystal networks

Using experimental data on morphology of nanophase materials prepared by pulsed laser ablation in an inert gas atmosphere, we present a phenomenological description of their condensation process. According to our idea, in high enough background pressure a shock wave is initiated by collisions between gas and target atoms, which slows down and spatially confines the plume, while it is effectively cooled by further collisions. Thus, the plume becomes highly supersaturated and the condensed phase of the target material starts to develop via homogeneous nucleation. Later on, still in a very limited volume, nanoparticles grow via complete or incomplete coalescence forming compact objects or large networks. The pressure threshold for gas phase condensation is intimately related to the collisional energy loss characteristics of the particular gas-target combination as well as to the thermophysical properties of the target.

Epitaxy of orthorhombic gadolinium disilicide on 〈100〉 silicon

Epitaxial orthorhombic GdSi2 was grown by in situ vacuum annealing of a 50‐nm Gd layer on 〈100〉 silicon. The epitaxy was proved by x‐ray diffraction, electron diffraction, and ion channeling measurements. The lattice mismatch between the orthorhombic GdSi2 and 〈100〉 silicon substrate was found to be 4%.

Epitaxy of GdSi≊1.7 on 〈111〉Si by solid phase reaction

Epitaxial hexagonal GdSi≊1.7 was grown by in situ vacuum annealing of 50 and 250 nm Gd layers on 〈111〉 silicon. The epitaxy was investigated by x‐ray and electron diffraction measurements.

Formation of GdSi2 under UHV evaporation and in situ annealing

GdSi2 was prepared under ultrahigh vacuum conditions. Prior to processing, a clean interface was produced using diluted HF dipping. It is pointed out that the ‘‘critical temperature’’ for formation published earlier is probably an artifact and correlation between the interface native oxide and the critical temperature is established.

Divalent Mn in calcium hydroxyapatite by pulse laser deposition.

Pulse laser deposition (PLD) was used to deposit Mn containing calcium hydroxyapatite (HAMn). The PLD process ensures that the composition of the target and the deposited layer is the same. In some cases additional effort should be made to preserve some volatile components, namely OH. This was ensured by water steam supply. Calcium hydroxyapatite deposited by this method has the same properties as the target in respect to lattice parameters and valence state of Mn, which ensures the fixation between hard tissue and metal implants. This fact makes PLD grown HAMn layer covering implants to be improved for practical use.