Selectively accessing the hotspots of optical nanoantennas by self-aligned dry laser ablation.

Plasmonic nanostructures serve as optical antennas for concentrating the energy of incoming light in localized hotspots close to their surface. By positioning nanoemitters in the antenna hotspots, energy transfer is enabled, leading to novel hybrid antenna-emitter-systems, where the antenna can be used to manipulate the optical properties of the nano-objects. The challenge remains how to precisely position emitters within the hotspots.

Polymer-metal coating for high contrast SEM cross sections at the deep nanoscale.

In scanning electron microscopy (SEM), imaging nanoscale features by means of the cross-sectioning method becomes increasingly challenging with shrinking feature sizes. However, obtaining high quality images, at high magnification, is crucial for critical dimension and patterned feature evaluation. Therefore, in this work, we present a new sample preparation method for high performance cross-sectional secondary electron (SE) imaging, targeting features at the deep nanoscale and into the sub-10 nm regime.

Fundamental understanding of chemical processes in extreme ultraviolet resist materials.

New photoresists are needed to advance extreme ultraviolet (EUV) lithography. The tailored design of efficient photoresists is enabled by a fundamental understanding of EUV induced chemistry. Processes that occur in the resist film after absorption of an EUV photon are discussed, and a new approach to study these processes on a fundamental level is described.

Atomic layer deposition for spacer defined double patterning of sub-10 nm titanium dioxide features.

The next generation of hard disk drive technology for data storage densities beyond 5 Tb/in will require single-bit patterning of features with sub-10 nm dimensions by nanoimprint lithography. To address this challenge master templates are fabricated using pattern multiplication with atomic layer deposition (ALD). Sub-10 nm lithography requires a solid understanding of materials and their interactions.

Investigation of phonon coherence and backscattering using silicon nanomeshes.

Phonons can display both wave-like and particle-like behaviour during thermal transport. While thermal transport in silicon nanomeshes has been previously interpreted by phonon wave effects due to interference with periodic structures, as well as phonon particle effects including backscattering, the dominant mechanism responsible for thermal conductivity reductions below classical predictions still remains unclear. Here we isolate the wave-related coherence effects by comparing periodic and aperiodic nanomeshes, and quantify the backscattering effect by comparing variable-pitch nanomeshes.

Toward an integrated device for spatiotemporal superposition of free-electron lasers and laser pulses.

Free-electron lasers (FELs) currently represent a step forward on time-resolved investigations on any phase of matter through pump-probe methods involving FELs and laser beams. That class of experiments requires an accurate spatial and temporal superposition of pump and probe beams on the sample, which at present is still a critical procedure. More efficient approaches are demanded to quickly achieve the superposition and synchronization of the beams.

Low temperature dry etching of chromium towards control at sub-5 nm dimensions.

Patterned chromium and its compounds are crucial materials for nanoscale patterning and chromium based devices. Here we investigate how temperature can be used to control chromium etching using chlorine/oxygen gas mixtures. Oxygen/chlorine ratios between 0% and 100% and temperatures between -100 °C and +40 °C are studied.

Resist Materials for Extreme Ultraviolet Lithography: Toward Low-Cost Single-Digit-Nanometer Patterning.

Extreme ultraviolet lithography (EUVL) is the leading technology for enabling miniaturization of computational components over the next decade. Next-generation resists will need to meet demanding performance criteria of 10 nm critical dimension, 1.2 nm line-edge roughness, and 20 mJ cm(-2) exposure dose.

Complex Materials by Atomic Layer Deposition.

Complex materials are defined as nanostructured materials with combinations of structure and/or composition that lead to performance surpassing the sum of their individual components. There are many methods that can create complex materials; however, atomic layer deposition (ALD) is uniquely suited to control composition and structural parameters at the atomic level. The use of ALD for creating complex insulators, semiconductors, and conductors is discussed, along with its use in novel structural applications.

Harnessing entropic and enthalpic contributions to create a negative tone chemically amplified molecular resist for high-resolution lithography.

Here we present a new resist design concept. By adding dilute cross-linkers to a chemically amplified molecular resist, we synergize entropic and enthalpic contributions to dissolution by harnessing both changes to molecular weight and changes in intermolecular bonding to create a system that outperforms resists that emphasize one contribution over the other. We study patterning performance, resist modulus, solubility kinetics and material redistribution as a function of cross-linker concentration.

Low-temperature plasma etching of high aspect-ratio densely packed 15 to sub-10 nm silicon features derived from PS-PDMS block copolymer patterns.

The combination of block copolymer (BCP) lithography and plasma etching offers a gateway to densely packed sub-10 nm features for advanced nanotechnology. Despite the advances in BCP lithography, plasma pattern transfer remains a major challenge. We use controlled and low substrate temperatures during plasma etching of a chromium hard mask and then the underlying substrate as a route to high aspect ratio sub-10 nm silicon features derived from BCP lithography.

Obtaining nanoimprint template gratings with 10 nm half-pitch by atomic layer deposition enabled spacer double patterning.

A strategy for fabricating nanoimprint templates with sub-10 nm line and 20 nm pitch gratings is demonstrated, by combining electron beam lithography and atomic layer deposition. This is achieved through pitch division using a spacer double-patterning technique. The nanostructures are then replicated using step-and-repeat ultra-violet assisted nanoimprint lithography.

A route for fabricating printable photonic devices with sub-10 nm resolution.

A novel and robust route for high-throughput, high-performance nanophotonics-based direct imprint of high refractive index and low visible wavelength absorption materials is presented. Sub-10 nm TiO2 nanostructures are fabricated by low-pressure UV-imprinting of an organic-inorganic resist material. Post-imprint thermal annealing allows optical property tuning over a wide range of values.

Plasmon resonance tuning in metallic nanocavities.

Nanocavities fabricated in a metallic surface have important and technologically useful properties of complete light absorption and strong field enhancement. Here, we demonstrate how a nanometerthick alumina deposition inside such a cavity can be used to gain an exquisite control over the resonance wavelength. This process allows achieving a precise control over the spectral response and is completely reversible allowing many tuning attempts to be made on a single structure until the optimum performance is achieved.

Super-selective cryogenic etching for sub-10 nm features.

Plasma etching is a powerful technique for transferring high-resolution lithographic masks into functional materials. Significant challenges arise with shrinking feature sizes, such as etching with thin masks. Traditionally this has been addressed with hard masks and consequently additional costly steps.

High aspect ratio sub-15 nm silicon trenches from block copolymer templates.

High-aspect-ratio sub-15-nm silicon trenches are fabricated directly from plasma etching of a block copolymer mask. A novel method that combines a block copolymer reconstruction process and reactive ion etching is used to make the polymer mask. Silicon trenches are characterized by various methods and used as a master for subsequent imprinting of different materials.

Sub-20 nm laser ablation for lithographic dry development.

Pattern collapse of small or high aspect ratio lines during traditional wet development is a major challenge for miniaturization in nanolithography. Here we report on a new dry process which combines high resolution resist exposure with selective laser ablation to achieve high resolution with high aspect ratios. Using a low power 532 nm laser, we dry develop a normally negative tone methyl acetoxy calix(6)arene in positive tone to reveal sub-20 nm half-pitch features in a ∼100 nm film at aspect ratios unattainable with conventional development with ablation time of 1-2 s per laser pixel (∼600 nm diameter spot).

Single digit nanofabrication by step-and-repeat nanoimprint lithography.

A novel strategy for fabricating nanoimprint templates with sub-10 nm patterns is demonstrated by combining electron beam lithography and atomic layer deposition. Nanostructures are replicated by step-and-repeat nanoimprint lithography and successfully transferred into functional material with high fidelity. The process extends the capacity of step-and-repeat nanoimprint lithography as a single digit nanofabrication method.

Sub-10 nm nanofabrication via nanoimprint directed self-assembly of block copolymers.

Directed self-assembly (DSA) of block copolymers (BCPs), either by selective wetting of surface chemical prepatterns or by graphoepitaxial alignment with surface topography, has ushered in a new era for high-resolution nanopatterning. These pioneering approaches, while effective, require expensive and time-consuming lithographic patterning of each substrate to direct the assembly. To overcome this shortcoming, nanoimprint molds--attainable via low-cost optical lithography--were investigated for their potential to be reusable and efficiently template the assembly of block copolymers (BCPs) while under complete confinement.

Interface segregating fluoralkyl-modified polymers for high-fidelity block copolymer nanoimprint lithography.

Block copolymer (BCP) lithography is a powerful technique to write periodic arrays of nanoscale features into substrates at exceptionally high densities. In order to place these features at will on substrates, nanoimprint offers a deceptively clear path toward high throughput production: nanoimprint molds are reusable, promote graphoepitaxial alignment of BCP microdomains within their topography, and are efficiently aligned with respect to the substrate using interferometry. Unfortunately, when thin films of BCPs are subjected to thermal nanoimprint, there is an overwhelming degree of adhesion at the mold-polymer interface, which compromises the entire process.

Step and repeat UV nanoimprint lithography on pre-spin coated resist film: a promising route for fabricating nanodevices.

A step and repeat UV nanoimprint lithography process on pre-spin coated resist film is demonstrated for patterning a large area with features sizes down to sub-15 nm. The high fidelity between the template and imprinted structures is verified with a difference in their line edge roughness of less than 0.5 nm (3σ deviation value).

Formation of bandgap and subbands in graphene nanomeshes with sub-10 nm ribbon width fabricated via nanoimprint lithography.

We fabricated hexagonal graphene nanomeshes (GNMs) with sub-10 nm ribbon width. The fabrication combines nanoimprint lithography, block-copolymer self-assembly for high-resolution nanoimprint template patterning, and electrostatic printing of graphene. Graphene field-effect transistors (GFETs) made from GNMs exhibit very different electronic characteristics in comparison with unpatterned GFETs even at room temperature.

Nanoimprint-induced molecular stacking and pattern stabilization in a solution-processed subphthalocyanine film.

We present a systematic study on the thermal nanoimprinting of a boron subphthalocynamine molecule, 2-allylphenoxy-(subphthalocyaninato)boron(III) (SubPc-A), which represents a class of attractive small-molecular weight organic compounds for organic-based photovoltaics (OPV). The final equilibrium imprinted feature profile strongly depends on the imprinting temperature. The highest feature aspect ratio (or contrast) occurs at a specific window of imprinting temperatures (80-90 degrees C).

Self-collimation of light over millimeter-scale distance in a quasi-zero-average-index metamaterial.

Inspired by the concept of complementary media, we experimentally demonstrate that an engineered metamaterial made of alternating, stripe layers of negatively refracting (photonic crystals) and positively refracting (air) materials strongly collimates a beam of near-infrared light. This quasi-zero-average-index metamaterial fully preserves the beam spot size throughout the sample for a light beam traveling through the metamaterial a distance of 2 mm-more than 1000 times the input wavelength lambda=1.55 microm.

Electrostatic force assisted exfoliation of prepatterned few-layer graphenes into device sites.

We present a novel fabrication method for incorporating nanometer to micrometer scale few-layer graphene (FLG) features onto substrates with electrostatic exfoliation. We pattern highly oriented pyrolytic graphite using standard lithographic techniques and subsequently, in a single step, exfoliate and transfer-print the prepatterned FLG features onto a silicon wafer using electrostatic force. We have successfully demonstrated the exfoliation/printing of 18 nm wide FLG nanolines and periodic arrays of 1.