Defu Liang

Underpotential Codeposition of Fe–Pt Alloys from an Alkaline Complexing Electrolyte: Electrochemical Studies

The availability of electrochemical growth processes for Fe―Pt alloys may facilitate their integration within microfabrication manufacturing lines and enable novel functionalities in microsystems. In this paper, the electrodeposition of Fe―Pt from slightly alkaline solutions containing citrate, glycine, and amino-nitrite complexes is studied by means of electrochemical quartz crystal microbalance (EQCM) and analytical/structural investigations. Pt is reduced from its amino-nitrite complex while Fe is reduced from Fe 3+ citrate/glycinate complexes through a two-step process. At variance with similar films grown from acidic solutions, the electrolyte is stable over months and the resulting films are smooth, dense, and homogeneous. Most importantly, oxygen incorporation is limited to 1―6 atom %. Significant carbon incorporation from decomposition of the complexants and kinetic trapping during growth is observed. The dependence of alloy composition on applied potential can be explained by assuming underpotential codeposition of iron from a Fe 2+ intermediate; the experimentally determined alloy composition dependence on applied potential was in agreement with an estimate of the redox potential for the Fe 2+ /Fe reaction obtained by EQCM and the reported enthalpy of mixing of the bulk Fe―Pt phase at high temperature.

Electrodeposition of Fe-Pt Films with Low Oxide Content Using an Alkaline Complexing Electrolyte

Electrochemical deposition of equiatomic Fe-Pt from complexing electrolytes provides precise tuning of alloy stoichiometry, enables close control of the growth process, and results in limited oxygen incorporation. The films grow epitaxially on oriented substrates and the low oxygen content favors transformation from the as-deposited cubic to the high anisotropy L1(0) phase and magnetic hardening upon thermal annealing at temperatures (400-450 degrees C) much lower than previously achieved by other plating processes.

Underpotential Codeposition of Cu–Au Alloys

The simultaneous underpotential codeposition of Cu and diffusion-limited overpotential codeposition of Au into Cu―Au alloy films is investigated from sulfuric acid solutions containing high concentrations of cupric ions and low concentrations of tetrachloroaurate ions. These conditions allow Cu to be deposited close to equilibrium, with the Cu fraction thermodynamically limited by the deposition potential. The dependence of the alloy composition on potential is described by a subregular solution alloying model. The average value of the bulk alloy minimum mixing enthalpy of ―6.1 ± 1 kJ/mol obtained from fits to this model agrees with the value of ―6.35 kJ/mol assessed in the literature.

Underpotential Co-deposition of Au–Cu Alloys: Switching the Underpotentially Deposited Element by Selective Complexation

Underpotential deposition and monolayer replacement processes are widely used for the synthesis of core/shell catalysts and heterointerfaces. Conventionally, only the more noble metal can be underpotentially deposited on or replace the less noble metal, limiting the number of accessible material configurations. We show here that the reverse process is possible, using the Au-Cu pair as a model system. By tuning the redox potentials of the two components via use of strong, selective metal ion complexes, Au-Cu alloys could be synthesized at will by (i) conventional underpotential co-deposition, whereby Cu is reduced at underpotential in parallel with the overpotential deposition of Au, or (ii) the reverse process, where Au is reduced at underpotential, while Cu is deposited at overpotential. Selective complexation also draws the redox potential of Au and Cu closer, resulting in co-deposition under activation control for the noble metal and precise alloy composition control by the applied potential, enabling in principle the formation of arbitrary metal or alloy interfaces. The alloys resulting from the two processes exhibit distinct enthalpy of mixing, suggesting different degrees of short-range order and dissimilar atomic configurations. These findings open new perspectives on underpotential deposition phenomena and possibly new synthetic opportunities in electrodeposition.

Structure, Magnetic Properties, and Phase Transformations in Electrodeposited Fe-Rich Fe–Pt Films

Fe rich Fe-Pt films with 56 at.%-75 at.% Fe are electrodeposited from an alkaline solution. A face-centered cubic (111) texture is clearly observed for as-deposited films with <;62 at.% Fe, while a body centered cubic (110) orientation is seen for higher Fe fraction. After annealing in forming gas for 1 h at or above 400 °C, a transformation to a face centered tetragonal (FCT)

Electrodeposition of Ag–Ni films from thiourea complexing solutions

L1_{0}

Fe-Pt magnetic multilayers by electrochemical deposition

phase was observed below 62 Fe at.%. With increasing Fe content, the annealed films show a texture change from (200) to (002); films with <;72% Fe show coercivity

Nanoscale Structuring in Au–Ni Films Grown by Electrochemical Underpotential Co‐deposition

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Electroplating of Fe-Rich NiFe Alloys in Sub-50 nm Lines

kOe while films with Fe above that value show small coercivity. Of particular interest are the 75 at.% films; these show a FCT structure after annealing at or above 450 °C, which differs from the

Phase transformation and magnetic hardening in electrodeposited, equiatomic Fe–Pt films

L1_{0}