Codeposition Of Metals Research Articles

Columnar and Subsurface Silicide Growth with Novel Molecular Beam Epitaxy Techniques

ABSTRACTMolecular beam epitaxy of silicides is conventionally carried out at temperatures ≤500°C, with stoichiometric Si:metal flux ratios or deposition of pure metal. We have found novel growth modes for epitaxial CoSi2 at high temperatures coupled with Si-rich flux ratios or low deposition rates. In the first of these modes, codeposition of metal and Si at 600-800°C with excess Si leads to the formation of epitaxial silicide columns surrounded by single-crystal Si. During the initial stages of the deposition, the excess Si grows homoepitaxially in between the silicide, which forms islands, so that the lateral growth of the islands is confined. Once a template layer is established by this process, columns of silicide form as a result of selective epitaxy of silicide on silicide and Si on Si. This growth process allows nanometer control over silicide particles in three dimensions. In the second of these modes, a columnar silicide seed layer is used as a template to nucleate subsurface growth of CoSi2. With a 100 nm Si layer covering CoSi2 seeds, Co deposited at 800°C and 0.01 nm/s diffuses down to grow on the buried seeds rather than nucleating surface silicide islands. For thicker Si caps or higher deposition rates, the surface concentration of Co exceeds the critical concentration for nucleation of islands, preventing this subsurface growth mode from occurring. Using this technique, single-crystal layers of CoSi2 buried under single-crystal Si caps have been grown.

Epitaxy of metal silicides

Abstract Epitaxial growth of the silicon-rich metal silicides NiSi 2 , CoSi 2 and IrSi 3 is reviewed. Codeposition of metals and silicon at low substrate temperatures is shown to alleviate the main problem associated with solid phase epitaxy using metal deposition alone, i.e. the nucleation controlled reaction to the silicide in question. NiSi 2 is an exception since owing to an epitaxial precursor phase the interfacial energies are lowered sufficiently, so that for thin films nucleation is no longer a problem. The growth of high quality CoSi 2 /Si superlattices is shown to be feasible by combining the codeposition technique with silicon MBE. Excellent electrical properties of epitaxial CoSi 2 films is demonstrated, remaining metallic down to a thickness of 10 A. Surface scattering in Si/CoSi 2 /Si heterostructures is nearly eliminated, CoSi 2 thicker than 35 A showing bulk residual resistivities. Such heterostructures have been applied to the fabrication of the permeable base transistor (PBT), using low pressure vapour phase epitaxy for the last overgrowth step after patterning. Device performance is found to be superior to any overgrown silicon PBT reported to date.

Zerovalent metal polymer composites. I. Metallized beads

AbstractBinding of a noble metal salt, e.g., PdCl to a functional ligand on a polymer surface, e.g., amine, quaternary ammonium, sulphonic acid, followed by reduction to zerovalent state and subsequent reductive deposition of transition metal ions, such as copper, nickel, and cobalt, provides a sequence of events leading to controlled zerovalent metal polymer composites. Metallization of submicron and larger beads are described. Large amounts of metal can be incorporated. The metallized beads retain the shape of the starting beads, even at high bonding of metal. They adapt the properties of the metal, e.g., magnetic properties. The submicron particles are sensitive to hydrolysis. Multicomponent systems, such as multimetallic beads, are provided by additive codeposition of metal ions, or by codeposition of metal and dye. Direct deposition of metal to preimmobilized dye ligands is also possible, leading to magenta, cyan, or yellow metallic beads, with no adverse influence on the magnetic properties. Further deposition of noble metals by subtractive deposition on active metal surfaces is also described. Submicron latices can be immobilized by coating on polyester‐based films, e.g., KODAK ESTAR base, and then activated with palladium and metallized to form highly conductive film surfaces.

Underpotential deposition and its relation to the anomalous deposition of metals in alloys

It has been long known that the codeposition of metals as alloys can often lead to reduction of the less noble coponent ion at potentials more positive than can be predicted from thermodynamic considerations only...

The influence of hydrolysis on the deposition and CO-DE-position of iron-group metals (Fe, Co, Ni) at the dropping mercury electrode

The deposition and co-deposition of iron(II), cobalt(II) and nickel(II) ions were studied polarographically in weakly acid (pH 3–5.5) solutions. Variation of pH in this region does not affect the waves. By adding oxygen to the solution, high pH values were generated at the electrode surface (O 2 + 2 H 2O + 4 e → 4 OH −) leading to hydrolysis of the discharging metal ions. Hydrolysis not only reduces the concentration of the discharging species due to Me 2+ + 2 OH − → Me(OH) 2 ↓ but also leads to adsorption of hydroxides at the interface. Chronopotentiometric measurements showed that about 3 · 10 −10 moles/cm 2 Fe(OH) 2 are adsorbed at the electrode. Hydrolysis changes the rate of single metal discharge only slightly, but has a strong effect on the co-deposition of metals. The discharge of one metal can be suppressed by the presence of a second iron-group metal. Ferrous ions cause the strongest suppression followed by cobaltous ions. The same sequence (Fe 2+ > Co 2+ > Ni 2+) is found in the suppression of Tl + discharge. This sequence is interpreted on the basis of adsorption measurements.

Zur elektrokristallisation von Legierungen und zu ihrer phasenstruktur

In the electrolytic codeposition of metals a deposit is sometimes formed, which is in contradiction to the phase diagram. In certain cases one obtains a single phase of mixed crystals, in other cases two phase alloys, which include one pure component. The reasons for this behaviour were studied in the present work. Experimental results obtained with the systems copper—lead, copper—bismuth, copper—thallium, copper—nickel and silver—copper show that the phase structure of an alloy can be predicted from a comparison of the electrochemical parameters of the alloy deposition (overvoltage) with the quantities characterizing the kinetics of the formation of a new phase (work of formation of new nuclei).In the present investigation the composition of the oversaturated mixed crystals was found to depend on the cathodic overvoltage. This suggests that the cause of the formation of metastable deposits in electrocrystallization is the increased energy of the atoms discharged at a high overvoltage.

The Codeposition of Metals of the Same Valence in Acid Solutions

We investigated the thermal behavior of dislocation loops formed in a CH3O-multielement-molecular-ion-implanted epitaxial silicon (Si) wafer by real-time cross-sectional tunneling electron microscopy observation with in situ heating. We found that the CH3O-ion-implantation-induced faulted Frank dislocation loops (FDLs) shrink at a low rate at the beginning of heat treatment (1st stage), and then the shrinkage rate rapidly increased (2nd stage), resulting in the dissolution of the defects. The activation energies for the shrinkage of FDLs in the 1st and 2nd stages were found to be 2.94±0.31 and 4.95±0.25 eV, respectively. The shrinkage behavior in the 1st stage is the desorption of C and O atoms that segregated along the edge of an FDL because of the interaction between the CH3O-ion-implantation-induced FDL and the segregated impurities. On the other hand, the 2nd stage corresponds to the desorption of Si atoms from FDLs and its migration. Our experimental results suggest that thermal stability of the dislocation loop is determined by the kind of segregated impurities around the dislocation loop.