M. Maenhoudt

Photoinduced enhancement of superconductivity

We show clear and conclusive experimental evidence for the enhancement of superconductivity in GdBa2Cu3Ox and YBa2Cu3Ox thin films by photoexcitation. Upon laser illumination the critical temperature increases while the resistivity of the material decreases. The relaxation back to the original state is very slow, of the order of days at room temperature. The existence of this effect opens the possibility of fabricating weak‐link devices with in situ tunable superconducting characteristics.

Controlled preparation of oxygen deficient YBa2Cu3Ox films

We describe a simple method based on the oxygen pressure‐temperature phase diagram to prepare oxygen deficient YBa2Cu3Ox thin films. Systematic critical temperature and x‐ray diffraction experiments clearly show that films with different oxygen contents (6.6≤x≤7) are obtained in a controlled, reproducible, and reversible way.

Growth of particle-free YBa2Cu3O7 films by off-axis sputtering

Abstract The preparation of good YBa 2 Cu 3 O 7 thin films is often hindered by the production of non-stoichiometric particles which degrade the superconducting properties of the layer. A systematic study of films prepared by off-axis single target magnetron sputtering shows that the presence of copper-rich particles dramatically decreases the critical current density but does not affect the critical temperature. The formation of these particles can be avoided by carefully adjusting the position of the substrate with respect to the target. Films without off-stoichiometric particles have excellent superconducting properties.

Implantation temperature dependent distribution of NiSi2 formed by ion beam synthesis in silicon

The formation and distribution of NiSi2 in (111) silicon by Ni‐ion implantation with a fluence of 1.1×1017 cm−2 and an energy of 90 keV is studied as a function of the temperature during implantation. For temperatures below 200 °C, a buried layer of NiSi2 precipitates is formed. Increasing the temperature gradually from 200 to 350 °C leads first to the formation of a double buried NiSi2 layer which with increasing temperature evolves into an epitaxial NiSi2 surface layer. A tentative model to explain for the observed anomalous behavior is presented.

Simultaneous synthesis of well-separated buried and surface silicides using a single ion implantation step

An unusual Ni distribution with two completely separated buried and surface silicide layers has been observed after Ni ion implantation in Si(111) kept at a temperature of 300 °C, with a dose of 1.1×1017/cm2 and at a fixed energy of 90 keV. RBS/channeling, AES, and cross‐sectional TEM have been used to study this phenomenon as a function of the substrate temperature and Co co‐implantation. A model is presented, based on the diffusion of the transition metal, the defect annealing during the implantation, and the gettering power of the surface and the end of range defects.

Photoexcitation effects in YBa2Cu3Ox

Abstract We show through photoexcitation experiments carried out on YBa 2 Cu 3 O x c-axis oriented films that photoinduced phenomena are not restricted to insulating samples. Superconducting films with critical temperatures varying between 2 K and 40 K show a clear enhancement of the superconducting transition after illumination. The increase in T c is accompanied by a corresponding decrease in the resistivity ρ, and an increase in the Hall coefficient R H , indicative of an increased carrier density. Furthermore, the carrier mobility is also affected by illumination.

Relation between the Hall angle slope and the carrier density in oxygen-depleted YBa2Cu3Ox films

Abstract A detailed study of the Hall angle cotθ H in YBa 2 Cu 3 O x epitaxial thin films with various oxygen contents clearly shows the existence of a linear relation between the slope of cotθ H versus T 2 and the carrier density. The zero-temperature intercept C =cotθ H ( T =0 K) and the mobility at room temperature change substantially for an oxygen content x ≈6.6, indicating that both effects are closely related.

YBa2Cu3Ox: a natural multilayer system with tunable anisotropy

The authors report on magnetoresistivity rho ab( theta ,H,T) measurements below Tc in YBa2Cu3Oxn films with differing oxygen content x. The observed variations in the angular and field dependence of rho ab with reduced x indicate a gradual dimensional crossover from an anisotropic 3D to a quasi-2D behaviour. The increasing anisotropy is related to a decrease of the coupling between the Cu2O2 bilayers when oxygen is removed from the Cu1Ox chain-planes.

Ion beam synthesis of buried and surface nickel silicides during a single implantation step

Abstract An unusual Ni distribution with two completely separated buried and surface silicide layers has been observed after Ni ion implantation in Si(111) kept at a temperature of 300°C, with a dose of 1.1 × 10 17 /cm 2 and at a fixed energy of 90 keV. The Ni profile and its substrate temperature dependence, its dose dependence and the influence from the preceding Co implantation were studied by RBS, AES and TEM. A model based on the diffusion of the transition metal, defect annealing during the implantation, and the gettering power of the surface and the end-of-range defects is presented.

Ion beam synthesis of heteroepitaxial Si/CoxNi1-xSi2/Si(111) structures

Heteroepitaxial Co x Ni 1-x Si 2 layers with good crystalline quality (χ min =3.5%) have been formed by ion beam synthesis. For a sample with x = 0.66, we found that this ternary silicide layer contains 11% type B and 89% type A orientation. The TEM investigation reveals that the type B component is mainly located at the interfaces with a thickness of only a few monolayers. XRD studies of the same sample show that the strain of the type B component is smaller than that of the type A component and this is probably the reason for such a unique distribution of the type B component in the epilayer. RBS/channeling, AES, TEM, XRD and resistivity measurements have been used in this study.