Ion-beam mixing of metal-semiconductor eutectic systems

Luminescence study of silicon nanostructures prepared by ion beam mixing

The roles of ion irradiation for crystalline growth and internal stresses in Ni films prepared by the ion beam and vapor deposition method were studied. Ni films were prepared on Si〈100〉 wafers by evaporation of Ni metal and simultaneous irradiation with inert gas ions, Ne, Ar, Kr, and Xe. The energies of inert gas ions were changed in the range of 0.5–10.0 keV. Transport ratios of vaporized Ni atoms to inert gas ions to substrates were kept at 15. Ion beam current densities and ion irradiation directions were fixed at 40 μA/cm2 and perpendicular to the substrate surface, respectively. From the x-ray analyses, crystallinities and preferred orientation were changed by ion irradiation conditions. On the other hand, internal stresses were also changed from compressive to tensile depending on ion energies and ion species. It is understood that the variations of crystalline growth and internal stresses in Ni films were caused by the difference of nuclear and electronic energy transfer abilities of irradiating ions.

Current–voltage (I–V) and capacitance–voltage (C–V), measurements were combined with Auger electron spectroscopy (AES) to study the effects of heat treatment on Au–Ge Schottky contacts to n-type GaAs in the temperature range below the Au–Ge eutectic point (∼360 °C). Upon deposition and heat treatment of the contacts, the data showed two distinct stages of transformation at the metal–semiconductor interface. In the first stage a small fraction of Ge atoms, formed an interface layer with an effective n-type doping of one order of magnitude higher than the initial doping of the epitaxial layer and resulted in a current transport mechanism consistent with thermionic-field emission (TFE). In the second stage, while the effective interface doping remained the same, a substantial reduction of the barrier height from φb (TFE)=0.75 eV at 250 °C heat treatment to φb (TFE)=0.34 eV at 300 °C heat treatment was evident and was attributed to the increased disorder at the interface resulting from the indiffusion of the remainder large fraction of Ge (and Au) atoms. The effects of heat treatment appeared to predominantly increase the disorder rather than the doping at the emerging ‘‘heterointerface.’’

Interface modification using high energy (MeV) ion beam mixing

Study of ion beam mixing in Pt/Co bilayer by ion beam analysis

In this work, we present the results of modification of absorption band gap of Silicon nanoclusters (Si-nc) prepared by ion beam mixing on pre-irradiated fused silica. 30 keV Ar+ ions at fluences of 5 x 10(16) to 4 x 10(17) cm(-2) were used to create defects in fused silica glass before introducing Si atoms in the substrate. Si was introduced in the substrates by ion beam mixing using 30 keV Ar+ ions at fluence 1 x 10(17) cm(-2). From UV-Vis absorption spectra, band-gap of Si-nc has been determined for samples prepared at different ion beam-mixing parameters. The absorption edge shifts towards higher energies and size of the silicon nanoclusters decreases with an increase in ion beam fluence used for pre-mixing irradiation.

5 - Ion beam joining of similar and dissimilar materials

Ion beam modification of MoS x films on metals

The effects of reactive I+ ion beams, derived from a source of solid elemental I, on In-containing compound semiconductors have been investigated using transmission electron microscopy. The results are compared with the effects produced by beams of Ar+ and Xe+ inert gas ions. It is shown that the surface accumulation of metallic In due to the disproportionation normally associated with ion milling of these materials can be eliminated by the use of I+ ion beams. Transmission electron microscope specimens in cross-sectional configuration are used to demonstrate the excellent results which may be obtained by I+ ion milling of InP and InSb.

This thesis presents the use of superconductivity as a structural probe for studying amorphous and metastable materials. The characteristics of the superconducting state which facilitate its use as a probe are explained, followed by a description of some of the properties of the materials studied. The superconducting measurements performed were critical current, transition temperature and upper critical field. Materials prepared by rapid quench from the melt, sputter deposition and ion beam mixing were studied. The critical current measurements performed on liquid quenched materials reflect three pinning mechanisms. Crystalline inclusions in otherwise amorphous (Mo0.6Ru0.4)80Si10B10 produced a dramatic increase in critical current. The pinning in purely amorphous (Mo0.6Ru0.4)82B18 was shown to be affected by pinning by surface roughness on the sample edges. This contribution can be eliminated by a proper sample geometry and electropolish treatment. The bulk pinning in purely amorphous (Mo0.6Ru0.4)82B18 was shown to first decrease and then increase as a function of annealing time. This reflects the disappearance of quenched in inhomogeneous strains and excess volume defects followed by the growth of an inhomogeneity such as compositional phase segregation during an anneal. The upper critical field was measured for liquid quenched (Mo0.6Ru0.4)1-xBx for x = 0.12, 0.18 and 0.22 both before and after an anneal. The annealed samples exhibited greater transition widths and more curvature in the Hc2(T) curves than the unannealed samples which are evidence for a growth of inhomogeneities upon annealing. Measurements on sputter deposited (Mo0.6Ru0.4)82B18 were performed on samples sputtered in low (5 µm) and high (75 µm) Ar pressure, The material sputtered in low Ar pressure had a greater drop in Tc than the liquid quenched material and a pinning profile which exhibited a peak near Hc2. The sample sputtered in high Ar pressure was very inhomogeneous as evidenced by transition width and flux pinning force profile. Measurements were performed on ion beam mixed Mo55Ru45. The structure consisted of an amorphous matrix with crystalline inclusions. The pinning profile was characteristic of a strong pinning mechanism. The pinning force decreased then increased as a function of ion beam dose. This reflects the destruction of the remnants of the original structure followed by the formation of an inhomogeneity such as σ-MoRu or Xe gas bubbles during ion beam irradiation.

The problem of allergies arising from the presence of Ni in alloys used for decorative objects coming into contact with the skin has become increasingly important over the past five to ten years. As an alternative, "white bronze" has been shown to be an effective solution even from an aesthetic point of view. This work investigates the corrosion behaviour of copper treated with two different techniques: electroplating and ion beam mixing. To this end copper has been electroplated with a thin (0.3 and 0.04 µm) coating of white bronze (Cu 66, Sn 23, Zn 10, Pb 1 wt%), the high brightness (as a noble metal) and corrosion resistance of which allow it to be used in decorative industries for jewellery, watches, etc. The bronze coating was ion beam mixed through bombardment with an argon ion beam. The corrosion behaviour of the bronze coatings was compared with that of pure copper through two method of analysis: a) electrochemical analysis, aimed at measuring the corrosion rate in a alkaline solution (pH = 12.4); and b) surface analysis intended to verify the thickness, homogeneity and composition of coatings through Rutherford backscattering spectroscopy (RBS) and scanning electron microscopy (SEM). The implanted bronze electroplated copper showed the best corrosion behaviour. Electrochemical tests showed low corrosion rates and a corrosion mechanism similar to that of more noble coatings.

Critical temperatures for radiation enhanced diffusion and metastable alloy formation in ion beam mixing

Study of ion-beam mixing at a Fe/GaAs interface

Pulsed ion beams for modification of metal surface properties

Measurement of lifetimes of thin carbon stripper foils produced by ion-beam sputtering