Nanopatterned Films Research Articles

Hybrid organic/GaN photonic crystal light-emitting diode

Periodically nano-patterned organic films incorporating color converting light-emitting polymers have been integrated onto InGaN/GaN light-emitting diodes (LEDs). Polarized and strongly modified hybrid LED emission is observed due to the photonic crystal effect of the nano-pattern. Emission characteristics are appropriate for various applications, and fast modulation capability with an optical −3 dB bandwidth of 168 MHz is demonstrated.

Fabrication and characterization of nanopatterned poly(ethylene oxide) thin films prepared from precursors formed in solution

Poly(ethylene oxide) (PEO) films with uniform nanopatterns were prepared by spin-coating dilute solutions containing crystallized PEO precursors onto silicon wafers. To form the precursors in solution, the PEO solutions were heated and incubated at 18°C with stirring for 6h. The blocky PEO stripes are uniformly distributed over the films and are arranged inside grain boundaries that form simple closed curves with distorted hexagonal shapes. In addition, an ordered silicon oxide stripe pattern was fabricated by using a nanopatterned PEO thin film as a template.

Total absorption of TM polarized light in a 100 nm spectral band in a nanopatterned thin a-Si film

We report a leaky-mode resonant absorber fashioned as one-dimensional nanopatterned ultra-thin films. This simple structure exhibits optical absorbance of ∼66% in the 300-750 nm wavelength band, which is an ∼60% increase relative to a comparable planar reference structure. The transverse-magnetic (TM) polarized light in the ∼460-560 nm band is nearly totally absorbed. Applying a backside metal reflector raises the absorbance farther to ∼73%.

Nanopatterned Protein Films Directed by Ionic Complexation with Water-Soluble Diblock Copolymers.

The use of ionic interactions to direct both protein templating and block copolymer self-assembly into nanopatterned films with only aqueous processing conditions is demonstrated using block copolymers containing both thermally responsive and pH responsive blocks. Controlled reversible addition-fragmentation chain-transfer (RAFT) polymerization is employed to synthesize poly(N-isopropylacrylamide-b-2-(dimethylamino)ethyl acrylate) (PNIPAM-b-PDMAEA) diblock copolymers. The pH-dependent ionic complexation between the fluorescent protein, mCherry, and the ionic PDMAEA block is established using dynamic light scattering (DLS) and UV-Vis spectroscopy. DLS shows that the size of the resulting coacervate micelles depends strongly on pH, while UV-Vis spectroscopy shows a correlation between the protein's absorption maximum and the ionic microenvironment. Zeta potential measurements clearly indicate the ionic nature of the complex-forming interactions. Spin casting was used to prepare nanostructured films from the protein-block copolymer coacervates. After film formation, the lower critical solution temperature (LCST) of the PNIPAM blocks allows the nanomaterial to be effectively immobilized in aqueous environments at physiological temperatures, enabling potential use as a controlled protein release material or polymer matrix for protein immobilization. At pH 9.2 and 7.8, the release rates are at least 10 times faster than that at pH 6.4 due to weaker interaction between protein and PNIPAM-b-PDMAEA (PND) diblock copolymer. Due to the ionic environment in which protein is confined, the majority of the protein (80%) remains active, independent of pH, even after having been dehydrated in vacuum and confined in the films.

Surface modified nano-patterned SU-8 pillar array optically transparent super-hydrophobic thin film

We report the fabrication and characterization of a porous nano-patterned SU-8 high aspect ratio pillar array as a transparent super-hydrophobic thin film. A 250 µm thick SU-8 layer was backside exposed through a glass substrate to form an array of high aspect ratio tapered pillars with angles in the range of 3°–5°. The SU-8 pillar array was plasma treated to form nano-porous surfaces, and then subsequently coated with fluorocarbon (FC) or Parylene-C film. Static contact angles and optical transmittance of various surface conditions such as with and without plasma treatment, Parylene-C versus FC, were tested and results were compared. Among various surface treated SU-8 pillar arrays, the plasma-treated nano-porous FC-coated SU-8 pillar array showed the highest static contact angle of 161°. It was found that the optical transmittance at around 530 nm for the nano-porous FC-coated SU-8 pillar array was approximately 65%, while the bare SU-8 film was approximately 95%. These nano-patterned transparent polymer films could be used in various water-repellent applications.

Domain Formation in Nano-patterned PZT Thin Films

ABSTRACTIn this work, reactive magnetron-sputtered Pb(Zr,Ti)O3thin films were used to fabricate well-ordered nanodot arrays by means of nanosphere lithography (NSL). NSL is based on a two-step etch process by means of, firstly adjusting the diameter of polystyrene spheres in the self-assembled polymeric nanosphere mask using reactive ion etching, and secondly transferring the mask to the substrate by ion milling with adjusted heights. Hence, structures with different aspect ratios can be fabricated.Piezoresponse force microscopy was used as the inspection tool on both non-patterned and patterned films. Both the topography and polarization out of plane and in plane was deduced in this mode. Grains of nanodots with low aspect ratio form domain structures comparable to domains in non-patterned films. In contrast to that, nanodots with a higher aspect ratio form particular structures. The in-plane amplitude images show mostly a bisectioned domain assembly, while the out-of-plane amplitude images show in some cases more complex structures like “c”-shaped domains or multi-domains around a center domain.The patterning of the ferroelectric material was shown to affect the formation of ferroelectric domains. The initial polycrystalline, randomly-ordered films are re-oriented and show domain structures depending on nanodisc diameter and aspect ratio. This may enable tailoring of ferroelectric materials in their piezoelectric and pyroelectric properties by patterning.

In-situ magnetic nano-patterning of Fe films grown on Cu(100)

Metastable paramagnetic face-centered cubic (fcc) Fe films grown on a Cu(100) single crystal at room temperature can be transformed to the ferromagnetic body-centered cubic (bcc) structure by ion irradiation. We have employed this technique to write small ferromagnetic patches by Ar+ irradiation through a gold coated SiN mask with regularly arranged 80-nm diameter holes, which was placed on top of the as-prepared fcc Fe films. Nanopatterning was performed on both 8-monolayer (ML) Fe films grown in ultrahigh vacuum as well as 22-ML films stabilized by dosing carbon monoxide during growth. The structural transformation of these nano-patterned films was investigated using scanning tunneling microscopy. In both 8 and 22-ML fcc Fe films, the bcc needles are found to protrude laterally out of the irradiated part of the sample, limiting the resolution of the technique to a few 10 nm. The magnetic transformation was confirmed by magnetic force microscopy.

High quality nano-patterned thin films of the coordination compound {Fe(pyrazine)[Pt(CN)4]} deposited layer-by-layer

An optimised procedure was developed for the layer-by-layer deposition of the Hofmann clathrate-like coordination compound {Fe(pyrazine)[Pt(CN)4]} either as continuous or as nano-patterned thin films. Characterization of the thickness and topography of the thin films by atomic force microscopy (AFM) and by surface plasmon resonance (SPR) spectroscopy, which also yields the layer's refractive index and losses, are reported. We found that the films are of good optical quality and the results of both AFM and SPR experiments are in good agreement with the theoretical predictions of the films thicknesses.

Comprehensive Survey for the Frontier Disciplines

Organic light-emitting device (OLED) technology shows tremendous commercial applications in communication, information, display, and lighting. It has been one of the most attractive projects in optoelectronic information field over the last decade. However, the internal efficiency is quite different from the external efficiency, and to some extent, a low external efficiency restrictes the development and application of OLEDs. The light out-coupling has been improved by a number of different techniques through the modification of device architecture. In this paper we present various light out-coupling techniques that have been implemented to enhance the external efficiency of OLEDs. Various OLED device modification techniques, e.g., micro-lens array, photonic crystal structure, nano-patterned and nanoporous films, and microcavity technique, have been reviewed and discussed. Finally, some perspectives on light out-coupling techniques are proposed.

Pattern-Definable and Low Cost Fabrication of Nanopatterned Conducting Polymer Film on Flexible Substrates

This study reports the pattern definable and low cost fabrication of nanopatterned conducting polymer film on flexible substrates. Noble nanopatterned polymer hard template was fabricated by using nanoimprint lithography (NIL) and used for electropolymerization of conducting polymer. Conducting polymer was electrochemically deposited on the template and transferred over to flexible substrates. Eventually conducting polymer films with various nanopatterns were fabricated on flexible substrates. High pattern definability was achieved by nanoimprinted polymer template, which was molded from lithographically fabricated stamp. Low cost fabrication was accomplished due to low cost NIL, reusable polymer templates, and low material consumption of electrodeposition. The electrodeposited films were transferred using double sided tape. Because the templates are made of flexible polymer, the transfer bonding method applied in this study is adaptable to both wafers and flexible polymer substrates. The fabricated nanopatterned conducting polymer film can be applied to gas sensors, super capacitors, super wetting films, and neuron interfaces due to its characteristic of high surface to volume. For an illustrative application, the gas sensing properties of films were tested. The result showed enhanced sensing characteristic with nanopatterned film, which are attributed to the high surface to volume ratio of nanopatterned films.

Resonant Andreev transmission in two-dimensional array of SNS junctions

We present an experimental study of transport properties of a large two-dimensional array of superconductor–normal-metal–superconductor (SNS) junctions comprised of the nanopatterned superconducting film, ensuring that NS interfaces of our SNS junctions are highly transparent. We find the anomalously high charge transmission at certain applied voltages commensurate with the magnitude of the gap in superconducting islands. This indicates the nonlocal nature of the charge transfer in multiply connected SNS systems. We propose the mechanism of the correlated transmission of Cooper pairs in large arrays of SNS junctions based on the combined action of the proximity effect and the simultaneous Andreev conversion processes at many NS-interfaces.

Effects of array arrangements in nano-patterned thin film media

In this work, the effect of different arrays arrangements on the magnetic behaviour of patterned thin film media is simulated. The modeled films consist of 80×80 cobalt grains of uniform diameter (20 nm) distributed into two different array arrangement: hexagonal (triangular) or square arrays. In addition to that, for each array arrangement, two cases of anisotropy orientations, random and textured films are considered. For both array arrangements and media orientations, hysteresis loops at different array separation ( d) were simulated. Predictions show that for closely packed films, the shearing effects on the magnetization loop are much larger for the square array arrangement than the hexagonal one. According to these predictions, the bit switching field distribution in interacting 2D systems is much narrower for the hexagonal array arrangement. This result could be very important for high-density magnetic recording where a narrow bit switching field distribution is required.

Simulations of parallel and transverse remanences in textured nano-patterned thin film media

In this work the effects of dipolar coupling on the distribution of effective orientations in textured nano-patterned media is simulated. The modelled films consist of 50×50 cobalt grains of uniform diameters ( D=20 nm) arranged in hexagonal (triangular) arrays. The grains easy axes are distributed according to a Gaussian texture function with a standard deviation of 30° about the texture direction. For different array separations ( d), the distribution of anisotropy orientations is extracted from the simulated parallel M rp( β) and transverse M rt( β) remanence curves where β is the angle by which the film is rotated. For the non-interacting case, predictions show that, M rt( β)=d M rp( β)/d β which is consistent with Shrikman and Treves theory whereas for the interacting case, M rt( β) is deviated from d M rp( β)/d β. The extracted distribution of effective orientations is found to become narrower as the array separation is decreased which is due to dipolar-induced texturing effects.

Magnetism in nanopatterned graphite film

Using first-principles calculations, we show that nanopatterned graphite films (NPGFs) can exhibit magnetism in analogy to graphene-based nanostructures (GBNs). In particular, graphite films with patterned nanoscale triangular holes and channels with zigzag edges all have ferromagnetic ground states. The magnetic moments are localized at the edges with a behavior similar to that of GBNs. Our findings suggest that the NPGFs form a unique class of magnetic materials.

Polymer Brushes on Periodically Nanopatterned Surfaces

Structural properties of polymer brushes tethered on a periodically nanopatterned substrate are investigated by computer simulations. The substrate consists of an alternating succession of two different types of equal-width parallel stripes, and the polymers are end-tethered selectively on every second stripe. Three distinct morphologies of the nanopatterned brush have been identified, and their range of stability has been determined in terms of a single universal parameter that combines the grafting density, the polymer length, and the stripe width. We propose scaling relations for the average brush height and for the architectural properties of the outer surface of the nanopatterned brush under good solvent conditions. Our analysis provides guidelines for fabricating well-defined and tunable nanopatterned polymeric films.

Electroless Deposition of Metals on Nanopatterns of Organosilane SAMs

Hybrid metal-organic architectures can be fabricated at the nanoscale using guided self-assembly on well-defined organic scaffolds to produce layered nanostructures. We have developed a new chemical approach to fabricate nanopatterns of metal nanostructures via electroless metal deposition of nanopatterned silane thin films. First, a surface with different functionalities is prepared with engineered nanopatterns of adhesive and resistive silanes. Next, the organosilane nanopatterns are used as a foundation for site-selective electroless deposition of metals such as iron oxide.

Thermal stability and corrosion resistance of the magnetic anisotropy in ultrathin nanopatterned films

We addressed the thermal stability and corrosion resistance of the magnetic anisotropy of surface-step atoms in nanopatterned ultrathin Fe/Ag(001) films. The step-induced anisotropy was remarkably stable, in ultrahigh vacuum, for flashing temperature up to 520 K, but showed no resistance to atmospheric oxidation. Capping the nanopatterned films with ultrathin chromium overlayers allowed to preserve the magnetic anisotropy due to step atoms while extending its thermal stability to above 670 K and greatly enhancing its resistance under oxidizing atmospheric environment.

Nanopatterned collagen tubes for vascular tissue engineering

Nanopatterned (330 nm wide channels) type I collagen films were prepared by solvent casting on poly(dimethyl siloxane) (PDMS) templates. These films were rolled into tubular constructs and crosslinked. Tubular constructs were incubated under cell culture conditions for 28 days and examined by stereomicroscopy and scanning electron microscopy (SEM) for the integrity of the structure. The nanopatterned films were also seeded with human vascular smooth muscle cells (VSMCs) and examined after immunostaining with fluorescence microscopy and SEM to assess the cell phenotype and alignment on the nanopatterns on the films.

Reflow dynamics of thin patterned viscous films

This letter presents a study of viscous smoothening dynamics of a nanopatterned thin film. Ultrathin film manufacturing processes appearing to be a key point of nanotechnology engineering and numerous studies have been recently led in order to exhibit driving parameters of this transient surface motion, focusing on time scale accuracy method. Based on nanomechanical analysis, this letter shows that controlled shape measurements provided much more detailed information about reflow mechanism. Control of reflow process of any complex surface shape, or measurement of material parameter as thin film viscosity, free surface energy, or even Hamaker constant are therefore possible.

Design of Reversible Cross-Linkers for Step and Flash Imprint Lithography Imprint Resists

Progress in the semiconductor manufacturing industry depends upon continuous improvements in the resolution of lithographic patterning through innovative materials development and frequent retooling with expensive optics and radiation sources. Step and Flash Imprint Lithography is a low-cost, nanoimprint lithography process that generates nanopatterned polymeric films via the photopolymerization of low-viscosity solutions containing cross-linking monomers in a transparent template (mold). The highly cross-linked imprint materials are completely insoluble in all inert solvents, which poses a problem for reworking wafers with faulty imprints and cleaning templates contaminated with cured imprint resist. Degradable cross-linkers provide a means of stripping cross-linked polymer networks. The controlled degradation of polymers containing acetal- and tertiary ester-based cross-linkers is demonstrated herein. The viscosity and dose to cure are presented for several prepolymer formulations, along with imprint resolution and tensile modulus results for the cured polymers. Optimum conditions for de-cross-linking and stripping of the cross-linked polymers are presented, including demonstrations of their utility.