Electrodeposition of Lanthanum Thin Films

Yitzhak Snow, Tyler Pounds, Stephen Farias, Robert C. Cammarata, Jonah Erlebacher

Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States

INTRODUCTION:

We designed a system to electrochemically deposit smooth

lanthanum films from an ionic liquid.

Lanthanum compounds have a number of significant applications.

We demonstrate the first smooth electrochemically deposited

lanthanum film, although monocrystalline lanthanum films have

been reported [1].

Electrochemical deposition provides a scalable method to produce

conformal films at low processing temperatures. In addition, the

process allows for the synthesis of materials directly into a

nanostructured form, which could provide improved materials

performance [2].

We report electrochemical synthesis of La2O3 thin films, using ionic

liquid electrolytes to extend the potential window and minimize

oxidation of lanthanum during deposition. The reported

electrochemical deposition technique may also be a viable

processing technique for producing other lanthanum compounds.

RESULTS:

Through electrochemical deposition,

the bottom end of the wire was coated

in a film (Fig. 2,3,4). EDAX analysis

(Fig. 1, Table 1) determined the

elemental composition. Lanthanum

makes up 22.08% of the analyzed

specimen, by weight.

The bromine is present due to its

function as the anion in ionic liquid

that serves as the electrolyte, resulting

in high concentrations in the film. The

oxygen is present in part because

lanthanum reacts readily with air,

forming La2O3. The silver seen is the

substrate.

CONCLUSIONS :

This work has shown the feasibility of electrochemical

deposition to create thin films of lanthanum and lanthanum

compounds. This could allow for the creation of

thermoelectric and other materials with increased control over

the nanostructure. Although the lanthanum films are prone to

rapid oxidation, they have still been created using these

techniques.

In the future, increased control over oxygen and in the

electrochemical cell should allow for the creation of metallic

lanthanum, rather than an oxide. It remains to be determined at

what stage of the reaction the oxidation takes place.

In addition, addition of other ions to the electrolyte should

allow for their co-deposition with lanthanum, allowing for the

creation of lanthanum compounds.

By using a nanostructured aluminum oxide substrate as the

working electrode, electrochemical films can be manufactured

in a nanostructure quickly and simply. Nanostructured films of

lanthanum and lanthanum compounds could have improved

properties compared to the bulk material.

REFERENCES:

1. Legeai, S., Diliberto, S., Stein, N., Boulanger, C., Estager,

J., Papaiconomou, N., & Draye, M. (2008). Room-

temperature ionic liquid for lanthanum electrodeposition.

Electrochemistry Communications, 10(11), 1661-1664.

2. Chi, S. I. C., Farias, S. L., & Cammarata, R. C. (2013,

January). A Novel Approach to Synthesize Lanthanum

Telluride Thermoelectric Thin Films in Ambient

Conditions. In MRS Proceedings (Vol. 1543, pp. 113-118).

Cambridge University Press.

METHODS/ MATERIALS:

The goal was to design a system in which lanthanide films could be

electrochemically deposited. The ionic liquid, 1-ethyl-3-

methylimidazolium bromide (EMIM-Br), was prepared in house

according to the reaction scheme shown.

EDAX ZAF Quantification

(Standardless)

Element Normalized

SEC Table : Default

Element Wt % At %

Br L 39.84 16.7

La L 22.08 5.33

C K 18.92 52.76

Ag L 5.82 1.81

O K 5.12 10.73

N K 4.39 10.5

Ni L 3.82 2.18

Total 100 100

Table 1 EDAX analysis of film

Figure 1 EDAX peaks, showing the presence of lanthanum

SEM images of lanthanum oxide films electrochemically deposited on a silver

wire. Magnifications of;

250x (Figure 2, left, 500x (Figure 3, middle), 1000x (Figure 4, bottom)

ACKNOWLEDGEMENTS:

Johns Hopkins department of Materials Science and

Engineering

Hopkins Extreme Materials Institute

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Cyclic Voltammetry of Ionic Liquid Electrolyte

Ionic Liquid with 0.4g Lanthanum

Ionic Liquid with no Lanthanum

Figure 6 CV curves for IL with and without lanthanumFigure 5 Design of 3 electrode cell configuration

used to deposit the lanthanum films.

FUTURE WORK:

Although lanthanum films can be consistently deposited, the

primary problem with the current procedure is the constant

oxidation of the lanthanum films. To avoid this, more control

will be needed to eliminate water from the reaction

environment. This would mean the dehydration of the

lanthanum salt, complete drying of the ionic liquid, and better

control over the humidity in the atmosphere of the reaction

cell. All of these steps have been worked on in some capacity,

with varying degrees of success.

Mixed under Ar+

Ionic liquids are necessary for lanthanum deposition, because the in

an aqueous solution, the water would undergo electrolysis before

lanthanum ions would be reduced. In addition, the oxygen dissolved

in the water would immediately react with the lanthanum, since

lanthanum reacts spontaneously and rapidly with even small

quantities of oxygen. EMIM-Br has a low oxygen solubility and a

low melting temperature (~75° C). The ionic liquid was kept under

argon, beginning with the synthesis of the liquid, and continuing

through the addition and deposition of lanthanum. This was achieved

by blowing argon gas into the reaction cell at a positive pressure.

The ionic liquid was melted and kept at a constant 90° C using a

water bath, in the setup shown (Fig. 5).

Approximately 0.5 g of lanthanum nitrate hexahydrate, La(NO3)3,

was added to about 10 ml of the ionic liquid, where it separates into

La3+ and (NO3)-. A three electrode system was used, with a Ag/AgCl

reference electrode, a platinum counter electrode, and a silver wire

working electrode. Cyclic voltammetry (Fig. 6) determined the

presence of a deposition peak at approximately -1.5 volts with

respect to the reference. A potentiostatic deposition was then run for

five minutes at -1.5 volts with respect to the reference. Upon the

completion of the deposition, the wire was analyzed in an SEM

using LEI detection, with EDAX to characterize the elemental

composition.