Nanopatterning Technique Research Articles

Breakthroughs in photonics 2012: Nano-structuring and nano-fabrication enabled by extreme ultraviolet laser sources

Two- and three-dimensional structures with submicron dimensions, such as photonic crystals, patterned magnetic media, micro- and nano-electromechanical systems (MEMs/NEMs), microfluidics chips, etc., are becoming ubiquitous in multiple applications across many research fields. The necessity to engineer these devices has inspired the development of novel nanofabrication and nano-patterning methods. This review describes major accomplishments in laser-based nano-patterning and nano-fabrication methods. In particular, it focuses on newly developed nano-patterning techniques based on the use of extreme ultraviolet laser light that contributes to the rapid and efficient fabrication of periodic nano-structures.

Robust fabrication and evaluation of nanopattern insert molded parts

Nanopatterning techniques have been developed for optical, magnetic, chemical, biological, and micro/nanoelectronic applications, where the verification of the nanopattern geometry is also critical for quality control of nanoengineered products. Nanopattern insert molding is a new method to produce nanopatterns on polymeric surface with high resolution, good productivity, and low cost. In this study, a disposable polymeric film, made of polyvinyl alcohol (PVA), was used as a stamp for replicating nanopatterns. In addition, a specialized image processing platform was proposed to characterize nanopattern structures, especially circular nanopillars with high accuracy and convenience. Such a tool was used for optimization of nanopattern processing conditions. The “shape dispersity index” was introduced to evaluate the replication quality in more systematic and robust manners.

Monolithic 3D titania with ultrathin nanoshell structures for enhanced photocatalytic activity and recyclability

Titania has attracted considerable interest for use in water purification applications due to its excellent photocatalytic activity. To further improve the efficiency of photocatalysis, numerous nanostructures (i.e. nanoparticles, nanotubes, and nanowires) have been proposed to increase the surface area of titania. Despite the high photocatalytic performance of the nanostructured titania, subsequent difficulties encountered in recollection and reuse of titania inhibit the practical application for water purification systems. Here we successfully fabricate monolithic, three dimensional (3D) nanoshell titania with high uniformity over large areas (~1 × 1 inch(2)) through proximity field nanopatterning (PnP) and low-temperature atomic layer deposition (ALD) techniques. The higher surface area of 3D nanoshell titania increases the photocatalytic performance more than three-fold relative to that of a thin film of equivalent sample size. Also, the monolithic form of titania enables it to be reused without any degradation of photocatalytic activity. The newly developed nanomaterials in this study can serve as an efficient and reusable photocatalyst for water purification systems.

Template-Based Surface Nano-Patterning and Device Applications

Surface nano-patterns on substrates are the fundamental structures of various nano-devices. Template-based surface nano-patterning techniques are highly efficient methods in realizing different surface nano-patterns. The time-saving and low-cost fabrication processes of the UTAM (ultra-thin alumina membranes) template-based surface patterning are highly desirable for industry in fabricating different kinds of nano-devices. This manuscript summarizes the recent advancements in the field of UTAM template based surface nano-patterning, the basic concepts, the general fabrication processes, the structure-related properties, and the device applications of these template-based surface nano-patterning techniques are introduced.

Nanofabrication and plasma polymerization assisted surface modification of a transducer based on localized surface plasmon resonance of gold nanostructure arrays for biosensor applications

The nanofabrication and surface modification of a transducer based on localized surface plasmon resonance (LSPR) of gold nanostructure arrays for biosensing was studied. We used electron beam lithography for the nanopatterning technique, which let us choose LSPR sensor properties by providing immense control over nanostructural geometry. A critical step in the utilization of this transducer is to form a selective biolayer over the gold nanostructures. We applied plasma polymerization and wet chemistry techniques for ethylenediamine (EDA) modification and glutaraldehyde immobilization as intermediate layers, respectively. The gold nanostructure arrays were primarily modified using EDA in order to activate the surface with amine groups that are cross-linked with later added avidin molecules by the help of glutaraldhyde layer residing in between. The success of plasma polymerization was validated with x-ray photoelectron spectroscopy measurements. As a last step, we introduced biotin to the surface (biotin has a high affinity for avidin). We were able to detect the LSPR resonance wavelength shift in the transmission spectra at each step of modification, including the avidin-biotin interaction, which acts as a model for specific molecule detection using LSPR.

Life time evaluation of PDMS stamps for UV-enhanced substrate conformal imprint lithography

UV-enhanced substrate conformal imprint lithography (UV-SCIL) is a large area nano patterning technique which has the potential to find its way into industrial application. A promising application for UV-SCIL exists in the field of high brightness LEDs. Here, a surface patterning can increase the external quantum efficiency and therefore the light output of LEDs significantly. But, before UV-SCIL can be introduced as patterning technique into industrial application, process relevant parameters like the interaction between the PDMS stamp and the UV-curing material as well as the overall life time of PDMS stamps have to be evaluated. Within this work, stamps from different PDMS material compositions with a diameter of 150 mm were fabricated. These stamps were used to perform UV-SCIL with the epoxy based resist Katiobond OM VE 110707 from DELO Industrial Adhesives and it was found that the final resist layer thickness strongly depends on the PDMS material composition, the number of imprints, and the time between two subsequent imprints. This can be explained by diffusion of one or several components of the UV-curing material into the stamps, which influences the life time of the PDMS stamps. With the actual optimum PDMS material composition, 500 UV-SCIL imprints could be successfully performed without any visible degradation.

Metalorganic vapor phase epitaxial growth of (211)B CdTe on nanopatterned (211)Si

AbstractLow‐defect density epitaxial CdTe on Si is very crucial for fabricating high performance HgCdTe IR focal planar arrays on Si. This paper discusses a novel nanopatterning technique to explore defect reduction in CdTe epitaxy on (211)Si. Nanopatterning of full 3″ (211)Si wafers was done by growing a thin layer of thermal SiO2 and patterning by molecular transfer lithography (MxL) based on water‐soluble templates. Conditions for obtaining selective Ge and CdTe were obtained in the temperature range of 575‐675 °C and 505‐520 °C respectively. X‐ray analysis of thin CdTe films grown on these substrates gave wider full‐width half‐maximum (FWHM) values when compared to the layers grown on blanket (non‐patterned) (211)Si, which is attributed to some patterning defects and spurious nucleation on oxide side walls. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Large-area nanostructured substrates for surface enhanced Raman spectroscopy

We demonstrate substantial enhancement of Raman transitions of organic molecules by nanostructured gold-coated substrates at the excitation wavelength of 785 nm and experimentally study the factors that influence the enhancement. The substrates are fabricated by using a robust and cost-effective nanopatterning technique that allows us to create high-density gold- or silver-coated nanopillars simultaneously on the whole surface of a standard silicon wafer.

Fabrication of carbon nanostructures using photo-nanoimprint lithography and pyrolysis

High-throughput synthesis of carbon nanostructures with reproducible shape and dimensions, at desired locations, has been a key challenge for further exploring carbon nanostructures as functional units in various nanodevices. In this work, carbon structures with dimensions from the 50 nano- to micrometer level have been fabricated by carbonizing a photo-nanoimprint lithography patterned resist polymer (AR-UL-01) at high temperature under inert atmosphere. The resulting carbon nanostructures showed significant vertical shrinkage but minimal loss in the lateral direction. Thermal behavior studies of the resist polymer in the pyrolysis cycle indicated gaseous evolution of various byproducts before the formation of solid carbon. Microstructure, elemental composition and resistivity characterization of the nanostructures produced by this process has shown that the carbon derived from a pyrolyzed nanoimprint resist is very similar to the pyrolyzed photoresist carbon from an SU-8 negative-tone photoresist. This simple approach is valuable as a wafer-level carbon nano-patterning technique.

N- and p-Type modulation of ZnO nanomesh coated graphene field effect transistors

Periodic zinc oxide (ZnO) nanomeshes of different thicknesses were deposited on single-layer graphene to form back-gated field effect transistors (GFETs). The GFETs exhibit tunable electronic properties, featuring n- and p-type characteristics by merely controlling the thickness of the ZnO nanomesh layer. Furthermore, the effect of thermal strain on the GFETs from the substrate is suppressed by the ZnO nanomesh, which improves the thermal stability of the GFETs. This nanopatterning technique could modulate the electronic properties of the GFETs effectively.

Flexible subwavelength gratings fabricated by reversal soft UV nanoimprint

We present a replication process, named reversal soft ultraviolet (UV) nanoimprint, to fabricate a high-aspect-ratio flexible subwavelength grating (SWG) on a polyurethane acrylate (PUA). This nanopatterning technique consists of casting, reversal UV imprint, and dry release. The UV curing process of PUA to avoid pattern collapse is investigated. Revalpha film acts as the supporting and sacrificial layer during the whole process due to its special surface energy property. The free-standing PUA structures with a period of 200 nm and a depth of 350 nm can be automatically released from the Revalpha film by heating. The PUA resist is well suited to replicate fine patterns of the mold with high aspect ratio and large area precisely and uniformly for low surface energy and low viscosity. The measured transmittance is compared with the calculation results based on rigorous coupled-wave analysis in the wavelength region ranging from 500 to 800 nm. The experimental results agree well with the theoretical calculations.

A Versatile Nanopatterning Technique Based on Controlled Undercutting and Liftoff

A new low-cost top-down nanolithography technique based on controlled undercutting and liftoff is reported. The method is applicable to a wide selection of inorganic materials (those that can be patterned by dry etching or lift-off) and can create 100-nm sized structures over wafer-sized areas. The method requires only conventional microfabrication processes and is ideal for producing nanowires, rings, and dots. A proof-of-concept experiment is also described for the fabrication of gold-nanowire transparent conducting electrodes, which show excellent optoelectronic properties. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Orienting the Demixion of a Diblock-copolymer Using 193 nm Interferometric Lithography for the Controlled Deposition of Nanoparticles

DUV interferometric lithography and diblock copolymer self-organization have successfully been combined to provide a simple and highly collective nanopatterning technique enabling the organization of nanoparticles over several orders of magnitude, from nanometre to millimetre. The nanostructural changes at the surface of the polymer film after thermal annealing have been monitored by AFM and the process parameters optimized for obtaining a long-range organization of the lamellar domains. In particular, the impact of the annealing conditions and geometric parameters of the substrate patterns have been investigated. The nanopatterns resulting from the lamellar demixion of (PS-b-MMA) were used for a controlled deposition of nanoparticles. The affinity of the hydrophobic particles for the PS block was demonstrated, opening new doors towards the preparation of high-density arrays of nanoparticles with potential applications in data storage.

Nanogap Electrode Fabrication for a Nanoscale Device by Volume‐Expanding Electrochemical Synthesis

A novel nanogap fabrication method using an electrochemical nanopatterning technique is presented. Electrochemical deposition of platinum ions reduces the microgap size to the sub-50-nm range due to the self-limited volume expansion of the electrodes. Additionally, the low crystallinity of platinum reduces the line edge roughness in the electrodes, whereas the high crystallinity of gold increases it. Current compliance, a buffered resistor, and a symmetric deposition strategy are used to achieve high reliability and practicality of nanogap electrodes. As a possible application, an organic thin-film transistor using the nanogap electrodes is also demonstrated.

A Fabrication Method of the Silica-Based Moth-Eye Structures and Its Application to the Organic Light-Emitting Diodes

For the application of moth-eye patterns to practical optical devices, a novel nano-patterning technique, which can fabricate transparent and robust material based nano patterns through a simple process, needs to be developed, because the moth-eye structures are usually exposed to the outer environment. In this study, silica based moth-eye structures were directly fabricated on a glass substrate by the direct hydrogen silsesquioxane (HSQ) printing and annealing technique. The transmittance of the glass substrate was enhanced by 3–4% in the visible range by the silica moth-eye structures and it was confirmed that the light output efficiency of the green organic-light emitting diode (OLED) was enhanced by 7–9% using the encapsulation glass with the silica moth-eye patterns.

Characterization of CMOS programmable multi-beam blanking arrays as used for programmable multi-beam projection lithography and resistless nanopatterning

Multi-beam projection lithography and resistless direct nanopatterning techniques provide decisive advantages compared to existing single electron and ion beam tools. Aperture plate systems (APS) including CMOS addressable programmable blanking arrays serve as pattern generators within these tools. An APS test stand was designed to achieve 0.08 µrad for measuring lateral/angular beamlet movements. For CMOS programmable APS units, providing 43 000 programmable beams, nearest-neighbour cross talk measurements have shown 5.5 µrad influence. This is well below the target spec for the charged particle multi-beam projection technology.

A trans-scaled nanofabrication using 3D diffuser lithography, metal molding and nano-imprinting

This paper describes our proposal and successful demonstration of a trans-scaled nanofabrication using conventional micro-technologies. In order to achieve this, we first performed ‘3D diffuser lithography,’ which is simply conventional contact microlithography with an optical diffuser sheet, to make submicron-sized nanopatterns on a photoresist mold. We then replicated these patterns onto a nickel mold, thereby successfully fabricating nickel nano-tip arrays 300 nm in diameter without the use of any specially-designed nanopatterning equipment or techniques. Then, the conventional thermal nano-imprinting onto a PMMA target was conducted using the fabricated Ni stamp, producing nano-dot arrays in an area of several hundreds of microns per side, where each dot diameter was 700 nm with 5.8% uniformity. The largest size which can accommodate this method depends on the size of the conventional contact lithography tool, which currently extends to several meters, according to contemporary machinery. The proposed method is cost effective for mass production, and can be applied to various fields of nanoscale applications.

Template directed assembly of dynamic micellar nanoparticles

The ability to pattern functional nanoparticle arrays in multiple dimensions will enable future devices which exhibit functions that cannot be realized using unstructured nanoparticle arrays. Here we demonstrate the unique assembly properties of dynamic micellar nanoparticles by combining a top down lithographic nanopatterning technique with a solution-based bottom up self-assembly. The templates for the directed self-assembly of the micelles consisted of arrays of cylindrical recess features fabricated by nanoimprint lithography. Silica was coated on this patterned substrate and subsequently selectively functionalized with a positively charged molecular monolayer (N-(3-Trimethoxysilylpropyl) diethylenetriamine) to regulate the micelle-surface interactions. The self-assembled block co-polymer polystyrene-b-poly(4-vinyl pyridine) (PS480k–PVP145k) micelles were approximately 325nm in diameter in aqueous solutions (pH = 2.5) and 50nm in diameter in the dry state. The average number of micelles assembled per feature increased from less than 1 to 12 with increasing feature diameter in the range of 200nm–1μm. Using a 2D model for maximum packing of circles in circular host features, the effective sphere size of the micelles during assembly was calculated to be 250nm in diameter. Thus, the micelles exhibited three characteristic sizes during assembly, 325nm in bulk solution, 250nm during assembly, and 50nm in the dry state. This dramatic variation in nanoparticle volume during the assembly process offers unique opportunities for forming nanometre scale, multidimensional arrays not accessible using hard sphere building blocks.

Nanofibrillar Patterns by Plasma Etching: The Influence of Polymer Crystallinity and Orientation in Surface Morphology

This manuscript explores the possibility of exploiting polymer morphology (thermal or flow-induced) as materials inherent template, and domain-selective plasma etching as pattern developer, to obtain nanopatterned surfaces with different and controlled geometries, with a particular focus on nanofibrillar patterns. Oxidative plasma treatment of PET films has rendered patterned surfaces with different geometries depending on the crystallinity and orientation of the PET sample and plasma treatment time (or etching ratio). Homogeneous patterns with either randomly distributed or aligned nanofibrils with diameters between 20 and 40 nm and lengths up to 1 μm (after extensive etching) were observed depending on the sample pretreatment. Our results demonstrate the potential of oxidative plasmas as templateless nanopatterning technique and reveal a complex interplay between plasma etching parameters and polymer microstructure driving the pattern formation mechanism. These results open the possibility of fabricatin...

Possibility of Pulsed Electrochemical Processes to Nanofabrication Using Scanning Probe Oxidation

This study demonstrates nano-scale lithography process on localized (100) silicon (p-type) surface using modified AFM apparatuses and controlling methods. AFM-based experimental apparatuses are connected the customized pulse generator that supplies electricity between conductive tip and silicon surface maintaining constant humidity during processes. Then pulse durations are controlled according to various experimental conditions. The pulsed electrochemical reaction within the gap between conductive tip and silicon surface induces the formation of oxide with nano-scale topographies. Various heights and widths of oxides can be created by AFM surface modification according to various pulse durations and applied electrical conditions under humidity environment. In addition, it can be known that oxides are completely removed after sample surface is etched in diluted HF solution, which shows micro/nano-scale grooves can be fabricated after predefined chemical treatment. They are wider than oxides widths and have several nanometer depths. Nano patterning technique from this experiment suggests that pulse electrochemical machining process has bright potential for advancing nano machining technologies.