Electrodeposition Behaviors Of Copper, Indium, And Gallium In [BMIM][TfO] Ionic Liquid

Copper, indium, and gallium metal as well as their deposits have a wide application in electronic and information industry. They are also the key components of several important semiconductor compounds, such as In Sb,In As,Ga N,Cu(In,Ga)(S,Se)2. The traditional aqueous systems, used to elecctrodpeosit these three metals and their alloys, are faced with the problems of pollution, safety production, and difficult manipulation etc. Ionic liquid with several special physico-chemical properties is promising to replace aqueous electrodeposition bath, especially for the electrodeposition of the alloy with various kinds, special structures, and excellent performance. As the fundamental study for the preparation of CIGS thin film by electrodeposition, in this thesis the electrodeposition behaviors of copper(II), indium(III), and gallium(III) in 1-butyl-3-methylimidazolium trifluoromethanesulfonate([BMIM][Tf O]) have been systematically investigated by using cyclic voltammetry, rotating disk electrode, and chronoamperometry.Cyclic voltammetry study shows that on the three working electrodes electrochemical windows of [BMIM][Tf O] have the following order: glass carbon electrode(GCE) > Pt electrode > Mo electrode, and the electrochemical windows decrease with the increase of temperature.In the [BMIM][Tf O] ionic liquid gallium(III) ions are discharged by one step on the above three electrodes, with a typical nucleation loop in the voltammograms, and the nucleation overpotential has the following order: GCE > Pt electrode > Mo. The diffusion coefficients of gallium(III) ions at various temperatures are obtained by using rotating disk electrode according to Levich equation, and diffusion activation energy is about 47.15 KJ/mol according to Arrhenius equation. The analysis of current transients and SEM images shows that the nucleation of gallium on both GCE and Mo electrodes at 70℃ is a 3-dimensional instantaneous process. However at 25℃ on GCE it is a 3-dimensional progressive process at 25℃. The values of nucleation parameter No(Crystal nucleus density) obtained by nonlinear fit according to the theoretical equation are much smaller than that obtained from the SEM images, which is related with the aggregation of the nucleus and solution system. The SEM images demonstrate that gallium deposits on Mo substrate have spherical grains. The gallium deposits obtained at 20℃ are smooth and compact at low overpotential, while porous at high overpotential. Higher temperature is beneficial to obtain gallium deposits with bigger grains, however when above the melt point of gallium, temperature almost does not have effect on the morphology of gallium deposits. According to the XRD analysis, the gallium deposits obtained at 60℃ have a weak crystalline.The electroreduction of copper(II) ions is involved with two steps, the redox couple Cu2+/Cu+ and Cu+/Cu0, and the second step may be a process involved with multi-electron and multi-step. The diffusion coefficients of copper(II) ions at various temperatures are also obtained, and they are much bigger than that of gallium(III) ions. The diffusion activation energys of the reaction of Cu2+/Cu+ and Cu2+/Cu0 are 34.72 å'Œ 31.88 KJ/mol, respectively. Copper has a 3-dimenional progressive nucleation on GCE, while has a 3-dimenional instantaneous nucleation on Mo electrode. Copper deposits on Mo substrate consists of spherical grains, and higher overpotential is beneficial to obtain smooth and compact copper deposits with smaller grains. Copper deposits with bigger grains can be obtained at higher temperature. Copper electrodeposits obtained at 70℃ is crystalline state, whose crystal sizes are about 25 nm estimated by Scherrer equation.Indium(III) ions are also discharged by one step on GCE and Mo electrode, with a typical nucleation loop in the voltammograms. The diffusion coefficients of indium(II) ions at 70℃ is 3.93×10-8 cm2/s, which is close to that of gallium(III) ions. The nucleation of indium on both GCE and Mo electrode is 3-dimenional instantaneous process, and indium nucleuses grow preferably on certain crystal face. Grains with several shapes can be found in the indium electrodeposits. Higher overpotential is also beneficial to obtain smooth and compact indium deposits with smaller grains. Octahedral indium particles dispersed evenly on the Mo film substrate can be obtained at low overpotential. Higher temperature is beneficial to obtain indium electrodeposits with bigger grains. Indium deposits obtained at 70℃ is crystalline state, whose crystal sizes are about 79 nm according to Scherrer equation.In addition, indium deposits grow preferably on the(101) surface. Molecular dynamic simulation reveals that the pair of BMIM+ and Tf O- have relative strong interaction with several indium crystal faces, and the binding energy with(111) and(110) is biggest. These results explain why indium particles with several shapes can be grown on Mo film.