Hybrid nanocolloids by shadow growth

Abstract

Nanoparticles containing shape-engineered functional materials hold immense promise for applications due to their unique electronic, optical, magnetic, and catalytic properties [1]. However, a number of functional materials are not only difficult to fabricate with nanoscale features, but are also prone to corrosion in solution. While nanocolloids synthesized by chemical means have been proposed for various medical applications, there are, to the best of our knowledge, no commercial in vivo uses yet, as chemically synthesized complex nanoparticles are not chemically stable in solution [2]. In 2013, our group has reported a generic wafer-scale 3D nanofabrication scheme by combining two techniques, namely block copolymer micelle nanolithography (BCML) with glancing angle deposition (GLAD) [3]. This “nanoGLAD” scheme allows the design of 3D hybrid nanomaterials since it permits the control over both the shape and material composition at the nanoscale. In order to obtain solutions of Co, Ni, Cu, Ag, etc. nanocolloids, which are in general not chemically stable in solution, additional steps are needed to protect the materials against corrosion. Here, we introduce an advanced nanoGLAD scheme in conjunction with atomic layer deposition (ALD), which can protect the nanocolloids from the outside environment.[4] The challenge is to ensure complete encapsulation by an appropriate shell layer without defects. In particular the wafer-facing side of the colloids is not shielded from ALD. The scheme we present overcomes this limitation and encapsulates the nanocolloid in an oxide shell. Since such physically grown oxide layer is chemically inert, the core-shell geometry grown by our scheme dramatically increases the colloidal stability. We present Co magnetic nanocolloids that without the protective layer corrode within hours in an acidic environment, but that are stable for weeks and in some cases even months when grown by the scheme we present here. Entirely new applications are possible including plasmonic sensing with Cu,[4] Mg,[5] Ag-Ti,[6], Au-Pd,[7] and nanorheology with Au-Fe[8] hybrid nanoparticles in aqueous solutions, which will be also discussed in this presentation.

Keywords

3D nanofabrication, hybrid nanocolloids, physical shadow growth

References

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