Nanomoulding of Functional Materials, a Versatile Complementary Pattern Replication Method to Nanoimprinting

Summary

We describe a nanomoulding technique which allows low-cost nanoscale patterning of functional materials, materials stacks and full devices. Nanomoulding can be performed on any nanoimprinting setup and can be applied to a wide range of materials and deposition processes.

Abstract

We describe a nanomoulding technique which allows low-cost nanoscale patterning of functional materials, materials stacks and full devices. Nanomoulding combined with layer transfer enables the replication of arbitrary surface patterns from a master structure onto the functional material. Nanomoulding can be performed on any nanoimprinting setup and can be applied to a wide range of materials and deposition processes. In particular we demonstrate the fabrication of patterned transparent zinc oxide electrodes for light trapping applications in solar cells.

Introduction

Nanopatterning has gained tremendous importance in many fields of nanotechnology and applied sciences. Pattern generation is the first step and may be accomplished by top-down approaches such as electron-beam lithography or bottom-up approaches based on self-assembly methods such as nanosphere lithography or block copolymer lithography ¹. As important as pattern generation is pattern replication. Besides photolithography, nanoimprinting (Figure 1) has emerged as a promising alternative in particular suitable for high-throughput large-area nanoscale patterning at low cost ^2-4. While photolithography requires a patterned ma....

Protocol

1. Mould Fabrication

We use our home-built nanoimprinting setup for the fabrication of the negative mould following Ref. ⁶, but any alternative nanoimprinting setup will work fine. Alternatively a functionalized polydimethylsiloxane (PDMS) mould might also work.

1. Fabricate or buy a suitable master carrying the nanoscale pattern to be transferred. In principle, any master suitable for nanoimprinting will do the job. We use a textured ZnO layer on a glass sheet (Schott, AF32 eco, 41 mm x 41 mm x 0.5 mm) deposited as described in 3.1 as a master structure to illustrate the method.
2. Apply an anti-adhesion layer on....

Results

Figure 3 summarizes some illustrative examples of nanomoulded structures. A ZnO master structure grown by CVD on glass is shown in (a). The corresponding nanomoulded ZnO replica is shown in (d). Comparison of the local height (g) and angle (j) histograms extracted from AFM images reveal the high fidelity of the nanomoulding process. Analogous results are shown for a one-dimensional grating fabricated by interference lithography (b,e,h,k) and anodically textured aluminum (c,f,i,l).

Discussion

Nanomoulding allows the transfer of nanopatterns on arbitrary functional materials. Comparison of the individual processing steps in Figure 1 and 2 reveals the close relationship between nanomoulding and nanoimprinting. The major difference between nanomoulding and nanoimprinting is the additional material deposition step in Figure 2e. The remaining process flow is identical. Nanomoulding can therefore be performed on any available nanoimprinting setup.

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Nanoimprinting resin	Microresist	Ormostamp
(1H, 1H, 2H, 2H-Perfluoroctyl)-trichlorsilane, anti-adhesion agent	Sigma Aldrich	448931-10G
Glass slides	Schott	AF32 eco	0.5 mm
Polyethylennaphtalate (PEN) sheets	Goodfellow	ES361090	0.125 mm
(C2H5)2Zn	Akzo Nobel
Ag sputter target 4N	Heraeus	81062165
B2H6, SiH4, H2, B(CH3)3, PH3, CH4, CO2	Messer
EQUIPMENT
Nanoimprinting system	Home-built
LP-CVD system	Home-built
PVD system	Leybold	Univex 450 B
PE-CVD reactor	Indeotec	Octopus I
SEM	JEOL	JSM-7500 TFE
AFM	Digital Instruments	Nanoscope 3100