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New approaches to nanofabrication: molding, printing, and other techniques.

Nanoimprint lithography (NIL) is a nonconventional lithographic technique for high-throughput patterning of polymer nanostructures at great precision and at low costs. Unlike traditional lithographic approaches, which achieve pattern definition through the use of photons or electrons to modify the chemical and physical properties of the resist, NIL relies on direct mechanical deformation of the resist material and can therefore achieve resolutions beyond the limitations set by light diffraction or beam scattering that are encountered in conventional techniques. This Review covers the basic principles of nanoimprinting, with an emphasis on the requirements on materials for the imprinting mold, surface properties, and resist materials for successful and reliable nanostructure replication.

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Nanoimprint Lithography: Methods and Material Requirements**

This thesis explores transport phenomena in nanochannels on a chip. Fundamental nanofluidic ionic studies form the basis for novel separation and preconcentration applications for proteomic purposes. The measurements were performed with 50-nm-high 1D nanochannels, which are easily accessible from both sides by two microchannels. Nanometer characteristic apertures were manufactured in the bonded structure of Pyrex-amorphous silicon – Pyrex, in which the thickness of the amorphous silicon layer serves as a spacer to define the height of the nanochannels. The geometry of the nanometer-sized apertures is well defined, which simplifies the modeling of the transport across them. Compared to biological pores, the present nanochannels in Pyrex offer increased stability. Fundamental characteristics of nanometer-sized apertures were obtained by impedance spectroscopy measurements of the nanochannel at different ionic strengths and pH values. A conductance plateau (on a log-log scale) was modeled and measured, establishing due to the dominance of the surface charge density in the nanochannels, which induces an excess of mobile counterions to maintain electroneutrality. The nanochannel conductance can be regulated at low ionic strengths by pH adjustment, and by an external voltage applied on the chip to change the zeta potential. This field-effect allows the regulation of ionic flow which can be exploited for the fabrication of nanofluidic devices. Fluorescence measurements confirm that 50-nm-high nanochannels show an exclusion of co-ions and an enrichment of counterions at low ionic strengths. This permselectivity is related to the increasing thickness of the electrical double layer (EDL) with decreasing salt concentrations, which results in an EDL overlap in an aperture if the height of the nanochannel and the thickness of the EDL are comparable in size. The diffusive transport of charged species and therefore the exclusion-enrichment effect was described with a simple model based on the Poisson-Boltzmann equation. The negatively charged Pyrex surface of the nanometer characteristic apertures can be inversed with chemical surface pretreatments, resulting in an exclusion of cations and an enrichment of anions. When a pressure gradient is applied across the nanochannels, charged molecules are electrostatically rejected at the entrance of the nanometer-sized apertures, which can be used for separation processes. Proteomic applications are presented such as the separation and preconcentration of proteins. The diffusion of Lectin proteins with different isoelectric points and very similar compositions were controlled by regulating the pH value of the buffer. When the proteins are neutral at their pI value, the diffusion coefficient is maximal because the biomolecules does not interact electrostatically with the charged surfaces of the nanochannel. This led to a fast separation of three Lectin proteins across the nanochannel. The pI values measured in this experiment are slightly shifted compared to the values obtained with isoelectric focusing because of reversible adsorption of proteins on the walls which affects the pH value in the nanochannel. An important application in the proteomic field is the preconcentration of biomolecules. By applying an electric field across the nanochannel, anionic and cationic analytes were preconcentrated on the cathodic side of the nanometer-sized aperture whereas on the anodic side depletion of ions was observed. This is due to concentration polarization, a complex of effects related to the formation of ionic concentration gradients in the electrolyte solution adjacent to an ion-selective interface. It was measured that the preconcentration factor increased with the net charge of the molecule, leading to a preconcentration factor of > 600 for rGFP proteins in 9 minutes. Such preconcentrations are important in micro total analysis systems to achieve increased detection signals of analytes contained in dilute solutions. Compared to cylindrical pores, our fabrication process allows the realization of nanochannels on a chip in which the exclusion-enrichment effect and a big flux across the nanometer-sized aperture can be achieved, showing the interest for possible micro total analysis system applications. The described exclusion-enrichment effect as well as concentration polarization play an important role in transport phenomena in nanofluidics. The appendix includes preliminary investigations in DNA molecule separation and fluorescence correlation spectroscopy measurements, which allows investigating the behavior of molecules in the nanochannel itself.

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Transport phenomena in nanofluidics

Data Reduction And Error Analysis For The Physical Sciences

Dielectric polymer nanocomposites are rapidly emerging as novel materials for a number of advanced engineering applications. In this Review, we present a comprehensive review of the use of ferroelectric polymers, especially PVDF and PVDF-based copolymers/blends as potential components in dielectric nanocomposite materials for high energy density capacitor applications. Various parameters like dielectric constant, dielectric loss, breakdown strength, energy density, and flexibility of the polymer nanocomposites have been thoroughly investigated. Fillers with different shapes have been found to cause significant variation in the physical and electrical properties. Generally, one-dimensional and two-dimensional nanofillers with large aspect ratios provide enhanced flexibility versus zero-dimensional fillers. Surface modification of nanomaterials as well as polymers adds flavor to the dielectric properties of the resulting nanocomposites. Nowadays, three-phase nanocomposites with either combination of fillers...

Recent Progress on Ferroelectric Polymer-Based Nanocomposites for High Energy Density Capacitors: Synthesis, Dielectric Properties, and Future Aspects.

We report advances in nanoimprint lithography, its application in nanogap metal contacts, and related fabrication yield. We have demonstrated 5nm linewidth and 14nm linepitch in resist using nanoimprint lithography at room temperature with a pressure less than 15psi. We fabricated gold contacts (for the application of single macromolecule devices) with 5nm separation by nanoimprint in resist and lift-off of metal. Finally, the uniformity and manufacturability of nanoimprint over a 4in. wafer were demonstrated.

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Fabrication of 5 nm linewidth and 14 nm pitch features by nanoimprint lithography

In this article we report on the fabrication of subwavelength antireflection structures on silicon substrates using a trilayer resist nanoimprint lithography and liftoff process. We have fabricated cone-shaped nanoscale silicon pillars with a continuous effective index gradient, which greatly enhances its antireflective performances. Our measurements show that the two-dimensional subwavelength structure effectively suppresses surface reflection over a wide spectral bandwidth and a large field of view. A reflectivity of 0.3% was measured at 632.8 nm wavelength, which is less than 1% of the flat silicon surface reflectivity.

Fabrication of large area subwavelength antireflection structures on Si using trilayer resist nanoimprint lithography and liftoff

A key issue in nanoimprint lithography (NIL) is determining the ultimate pitch resolution achievable for various pattern shapes and their critical dimensional control. To this end, we demonstrated the fabrication of 6 nm half-pitch gratings and 0.04 µm2 cell area SRAM metal interconnects with 20 nm line half-pitch in resist by NIL. The mould for the 6 nm half-pitch grating was fabricated by cleaving a GaAs /Al0.7Ga0.3As superlattice grown on GaAs with molecular beam epitaxy, and selectively etching away the Al0.7Ga0.3As layers in dilute hydrofluoric acid. The mould for the 0.04 µm2 SRAM metal interconnects was fabricated in silicon dioxide using 35 kV electron beam lithography with polystyrene as a negative resist and a reactive ion etch with the resist as mask. Imprints from both moulds showed excellent fidelity and critical dimension control.

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6 nm half-pitch lines and 0.04 νm 2 static random access memory patterns by nanoimprint lithography

We developed a hybrid nanoimprint-soft lithography technique with sub-15 nm resolution. It is capable of patterning both flat and curved substrates. The key component of the technology is the mold, which consists of rigid features on an elastic poly(dimethylsiloxane) (PDMS) support. The mold was fabricated by imprinting a reverse image onto the PDMS substrate using a UV-curable low-viscosity prepolymer film. Patterns with sub-15-nm resolution were faithfully duplicated on a flat substrate without applying external pressure. Gratings at 200 nm pitch were also successfully imprinted onto the cylindrical surface of a single mode optical fiber with a 125 microm diameter.

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Haixiong Ge

Papers

Fabrication of 5 nm linewidth and 14 nm pitch features by nanoimprint lithography

Fabrication of large area subwavelength antireflection structures on Si using trilayer resist nanoimprint lithography and liftoff

6 nm half-pitch lines and 0.04 νm 2 static random access memory patterns by nanoimprint lithography

Hybrid Nanoimprint−Soft Lithography with Sub-15 nm Resolution

Top-down fabrication of shape-controlled, monodisperse nanoparticles for biomedical applications.