synthesis of nanowires using mesoporous silica · mesoporous silica on copper cobalt grown into the...

Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering CenterThe University of Alabama

Synthesis of Nanowires Using Mesoporous Silica

Martin G. Bakker and Roger Campbell

MINT Center and Department of ChemistryThe University of Alabama


Introduction

There is considerable interest in controlling the sizes and morphologies of particles by growing them inside a host. We are applying this approach using mesoporous silica grown onto electrode films. Mesoporous silica can be precipitated out of a solution containing a lyotropic liquid crystal template. After removal of the liquid crystal template, a porous silica film remains.


Introduction (cont.)

XRD indicates that our films have randomly oriented pores. So the film consists of domains of silica in which the pores within a domain are aligned, but where the pore alignment between neighbouringdomains could be substantially different. This is shown as a cartoon in Figure 2.


Hexagonally Arranged Micelles

Figure 1


Possible Pore Alignments

Figure 2


Experimental

The production of the SBA-15 type silica follows a widely used sol-gel type synthesis. In this reaction, tetraethylorthosilicate is used as the silica source and Pluronic P123 is used as the templating agent. Pluronic P123 is a triblock copolymer that forms hexagonally arranged rod shaped micelles over a wide range of temperature and concentration. The silica films are made by dip coating onto a copper electrode prepared by sputtering a 200 nm layer of copper onto a silicon wafer .


Experimental (Cont.)

The polymer was then removed by washing with isopropanol. The nanowires were then formed by electrochemical deposition from an aqueous plating solution of a metal salt.


Results and Discussion

Figure 3 shows optical microscope images of the silica films and the films with cobalt grown into them. The right hand image clearly shows domains of cobalt growth rather than a continuous cobalt film. This is consistent with the expected random orientation of the silica. XRD(Fig. 4) shows that the mesostructure survives incorporation of the cobalt. EDX(Fig.5) of isolated islands of silica confirms the growth of cobalt into the silica. Further analysis will include TEM to determine exact size and orientation of the nanowires.


Mesoporous Silica on Copper

Cobalt grown into the silica

Silica only

Figure 3


XRD of Cobalt grown into SBA-15 Silica

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.5 1 1.5 2 2.5

2θ, degrees

cps, x

106

Figure 4


EDX of Cobalt Grown Into Mesoporous Silica

Figure 5


Conclusions

Preliminary evidence suggests that it is possible to produce nanowires by electrochemical deposition into the open pores of mesoporous silica. Use of electrodeposition will allow the growth of various multilayers (e.g. Co/Cu/Co) which are of interest for fundamental studies of GMR.


Acknowledgements

The support of this work by the MINT center and by NSF through the MRSEC grant DMR-9809423 is gratefully acknowledged.

synthesis of nanowires using mesoporous silica · mesoporous silica on copper cobalt grown into the...

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