Fabricating Metallic Nanoclusters for Electronic, Photonic and Medical Applications

By AZoNano

Table of Contents

Introduction
DPN Technology
Fabrication of Metallic Nanoclusters
Image Analysis of Nanoclusters
Conclusion
About NanoInk

Introduction

Recent developments in nanomaterials research have resulted in the design, production and characterization of novel materials such as nanotubes, nanoparticles and nanoclusters. The unique optical, chemical and electronic properties of these materials make them ideal candidates for applications in the fields of electronics, medicine and photonics.

NanoInk uses its Dip Pen Nanolithography (DPN) technology for the deposition of materials with nanoscale precision to fabricate metallic nanoclusters. This application note discusses the application of DPN for printing metallic ions in a block copolymer carrier directly to designated locations on a surface. The printed surface then undergoes heat treatment for the decomposition of the polymer and oxidization of the metal ions, resulting in the formation of metal oxide nanocluster arrays over large areas.

Dip Pen Nanolithography Technology

Dip Pen Nanolithography (DPN) is an established nanofabrication technique that uses a sharp tip to deposit materials onto a surface. Besides creating small feature sizes, NanoInk's robust DPN systems can provide rapid and versatile design of feature geometry. It is possible to scale up the fabrication process to pattern hundreds to thousands of features in a comparatively shorter time with the help of a NanoInk custom designed multiple-tip cantilever pen array.

Fabrication of Metallic Nanoclusters

Mirkin et al. has shown the ability of using polymer carrier by leveraging the efficacy of gold ions in its work. An aqueous solution of the block copolymer poly (2-vinyl pyridine-b-ethylene oxide) (P2VP-PEO) was used as a carrier for transporting metal ions onto substrate. The application of a polymer as a delivery matrix helps achieving feature sizes that are much smaller than the size of the originally deposited droplet. This can be achieved through the removal of each printed microdroplet’s organic components utilizing either a post-deposition oxygen plasma or heat treatment step. This feature size reduction technique is capable of achieving reductions of more than 90% compared to the size of the original printed droplet if the concentration of the printing mixture metal ions is low.

NanoInk's nanofabrication tool (either the NLP 2000 System or the DPN 5000 System) equipped with a NanoInk 12-pen tip cantilever array (M-type) was used for the deposition of sub-micron sized droplets of a mixture of metal salt in P2VP-PEO over a SiO2 substrate. The next process was the heat treatment of the patterned surface for polymer decomposition and metal ion oxidation. Metallic nanocluster fabrication process is schematically represented in figure 1.

Figure 1. Schematic depicting the process of metallic nanocluster fabrication. (Top) Metal salts are printed on the substrate using a block co-polymer carrier. (Bottom) Printed substrate is heat treated to remove carrier and reduce the salt to its metal or metal oxide form.

Coating the DPN cantilever pen arrays using different metal ion/block co-polymer mixtures was the first step in the printing process. This was done by sinking the cantilevers into an inkwell reservoir containing polymer/ion material. The rate of material transfer between instrument pen tip and substrate surface can be increased by raising the humidity level of the DPN system. The patterns produced in the DPN printing process were designed to have dense arrays of metal active sites with regular separations between features. The arrayed samples were then put on a hotplate at a temperature of 360 °C for 2 hours.

Image Analysis of Nanoclusters

After the heat treatment process, image analysis was conducted on multiple platforms to verify the configuration and composition of nanoclusters. Powder XRD spectrums were used for determining the composition of any material left on the surface after the heat treatment of nickel nitrate and iron nitrate nanoclusters. Atomic force microscopy (AFM) images of different DPN-deposited metal oxide nanoclusters are illustrated in figure 2.

Figure 2. AFM images of various DPN-deposited metal oxide nanoclusters formed after heat treatment.

Creating a sample that generates a powerful XRD signal was the first step in the XRD spectrum analysis. Although DPN can print arrays at high density in the X and Y planes, the height of the Z sample is only a few nanometers, thus the amount of remaining material on the substrate is very limited for subsequent XRD spectrum analysis. Since identical conditions were employed in the creation of DPN arrays and XRD analysis samples, the XRD spectra obtained was reckoned as the representative of the spectra that would be formed by the arrays themselves. Results from powder XRD analysis are presented in figure 3. Strong peaks characterizing anti-ferromagnetic nickel oxide and iron oxide were noted. The work also produced similar data from cobalt, gold, iridium, and chromium ion nanoclusters. The data confirmed that there were no traces of polymer. However, the oxidation of cobalt ions produced nanoclusters within the original droplet’s diameter.

Figure 3. Powder XRD spectra of iron and nickel nanoclusters fabricated on an SiO2 surface using DPN

Conclusion

The DPN nanofabrication technique is a very reliable process for nanocluster formation in regular arrays on silicon oxide surface. It can handle the deposition of various transition metals that together boast a variety of oxidation states.

About NanoInk

NanoInk, Inc. is an emerging growth technology company specializing in nanometer-scale manufacturing and applications development for the life sciences, engineering, pharmaceutical, and education industries. Using Dip Pen Nanolithography® (DPN®), a patented and proprietary nanofabrication technology, scientists are enabled to rapidly and easily create micro-and nanoscale structures from a variety of materials on a range of substrates. This low cost, easy to use and scalable technique brings sophisticated nanofabrication to the laboratory desktop. Headquartered in the Illinois Science + Technology Park, north of Chicago, NanoInk currently has several divisions including the NanoFabrication Systems Division, the Nano BioDiscovery Division, the NanoProfessor® Division and the NanoGuardian™ Division. For more information on products and services offered by NanoInk, Inc., visit www.nanoink.net.

This information has been sourced, reviewed and adapted from materials provided by NanoInk.

For more information on this source, please visit NanoInk.

Date Added: Jan 18, 2013 | Updated: Jun 11, 2013
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