Stefan Harrer

Room Temperature Nanoimprint Lithography Using Molds Fabricated by Molecular Beam Epitaxy

We have demonstrated single-step room temperature nanoimprint lithography (RTNIL) using polystyrene (PS, average molecular weights ranging from 13 to 97 kg/mol) as the imprint polymer layer on a silicon substrate for imprinting rectangular line patterns with varying aspect ratios, ranging from 11 to 500 nm wide. To accomplish this demonstration, we designed and built a tool that controllably pressed a mold into a stationary imprint sample applying imprint pressures between 280 and 700 MPa. The molds used in these experiments were GaAs/AlGaAs sandwich structures fabricated by molecular beam epitaxy (MBE) that we cleaved and selectively etched afterward in order to generate 3-D grating structures with nanometer resolution on their edges. We fabricated positive and negative molds comprising single- line as well as multiline patterns with different aspect ratios and linewidths between 9 and 300 nm.

Planar Nanogap Electrodes by Direct Nanotransfer Printing

Planar nanogap electrodes of predetermined spacing are fabricated using direct high-resolution metal nanotransfer printing on a solid substrate (see image). A GaAs/AlGaAs heterostructure featuring a nanoscale groove on a cleaved plane is the mold. Successful transfer experiments yield sectioned metal thin films with gap separation down to about 10 nm having excellent electrical properties.

Patterning Poly(3-Hexylthiophene) in the Sub-50-nm Region by Nanoimprint Lithography

We use thermal and room temperature nanoimprint lithography (NIL) for directly patterning the photoactive polymer poly(3-hexylthiophene-2,5-diyl) (P3HT) in the sub-50-nm region. Different types of molds were used to directly imprint the desired structures into P3HT thin films. Good pattern transfer is achieved independent of the presence of other underlying polymer layers or the type of substrate incorporated. Further, we discuss the future application of this technology to the fabrication of ordered heterojuction organic photovoltaic devices and demonstrate that the NIL process involved does not damage the polymer or alter its chemical or electrical properties.

Technology Assessment of a Novel High-Yield Lithographic Technique for Sub-15-nm Direct Nanotransfer Printing of Nanogap Electrodes

We have demonstrated direct nanoscale transfer printing (nTP) of PdAu lines from a hard mold onto a hard substrate at room temperature without employing any flexible buffer layers or organic adhesion promoters or release agent layers. PdAu was evaporated onto the mold surface, and a Ti layer was deposited on top of the PdAu layer. By pressing the mold against a Si/SiO2 substrate, the PdAu/Ti sandwich structure was directly transferred onto the SiO2 surface. The molds used in these experiments were GaAs/AlGaAs sandwich structures fabricated by molecular beam epitaxy that we cleaved and selectively etched afterwards in order to generate 3-D grating structures with nanometer resolution on their edges. We fabricated positive multiline molds with different aspect ratios, linewidths between 15 and 100 nm, and spacings between lines ranging from 5 to 70 nm. We also fabricated negative single-line molds with a positive supporting structure comprising a single 16-nm-wide groove feature. The experiments revealed that direct hard-on-hard transfer of nanoscale structures from a mold onto a substrate can be used to fabricate PdAu gaps with widths down to 9 nm. We also performed electronic measurements on transfer patterns and demonstrated that transferred structures can be used as electrodes, which are electrically isolated by these gaps. Since isolation characteristics of gaps improved with decreasing gap length, we partitioned longer gap segments into multiple shorter ones by focused ion beam lithography and conventional optical lithography in combination with wet chemical or plasma etching of the mold or the substrate, respectively. In this paper, we give a detailed description of all technological aspects of the developed direct nTP technique, including mold preparation, patterning efficiency, short reduction techniques, and yield.

Advances in Nanoimprint Lithography

Challenges and issues of Nanoimprint Lithography (NIL) are addressed and discussed. In particular, imprinting properties of an innovative epoxy-based polymer have been investigated, which can be used for combined thermal and ultraviolet nanoimprinting (TUV-NIL) processes aiming at high-throughput nanoimprint lithography. Our recent progress in developing a new room-temperature nanoimprint (RTNIL) tool for the sub-10-nm region is shown.

Nanoimprint Lithography for Optical Components

Nanoimprint lithography (NIL) is a new technique for lithographic patterning of nanostructures, which has advantages of high resolution, high throughput and low cost. This technique is presenting great opportunities for innovation and discovery in many engineering and scientific areas, such as electronic, optoelectronic and magnetism. We will show how the combination of different NIL techniques can lead to the realization of optical components such as waveguide gratings, sub-wavelength gratings, wavelength filters and photonic crystals, which in turn can lead to the design of optical devices with enhanced performance.

Deposition of PdAu Thin Films Sectioned by Sub-15-Nm Gaps on Silicon Using Direct Nanotransfer Printing

We have demonstrated direct nanoscale transfer printing of PdAu lines from a hard mold onto a hard substrate at room-temperature without employing any flexible buffer layers or organic adhesion promoters or release agent layers. The molds used in these experiments were GaAs/AlGaAs sandwich structures fabricated by molecular-beam epitaxy that we cleaved and selectively etched afterwards in order to generate 3D grating structures with nanometer resolution on their edges. We fabricated positive multi-line molds with different aspect ratios, linewidths between 15 nm and 100 nm, and spacings between lines ranging from 9 nm to 70 nm. PdAu was evaporated onto the mold surface, and a titanium layer was deposited on top of the PdAu layer. By pressing the mold against a Si/SiO2 substrate the Ti/PdAu sandwich structure was directly transferred onto the SiO2 surface. The experiments revealed that direct hard-on-hard transfer of nanoscale structures from a mold onto a substrate can be used to fabricate PdAu gaps with widths of down to 9 nm.