Focused Ion Beam Lithography Research Articles

Microphotonic parabolic light directors fabricated by two-photon lithography

We have fabricated microphotonic parabolic light directors using two-photon lithography, thin-film processing, and aperture formation by focused ion beam lithography. Optical transmission measurements through upright parabolic directors 22 μm high and 10 μm in diameter exhibit strong beam directivity with a beam divergence of 5.6°, in reasonable agreement with ray-tracing and full-field electromagnetic simulations. The results indicate the suitability of microphotonic parabolic light directors for producing collimated beams for applications in advanced solar cell and light-emitting diode designs.

Influence of Patterned Concave Depth and Surface Curvature on Anodization of Titania Nanotubes and Alumina Nanopores

Vertically aligned TiO(2) nanotube and Al(2)O(3) nanopore arrays have been obtained by pattern guided anodization with uniform concave depths. There are some studies about the effect of surface curvature on the growth of Al(2)O(3) nanopores. However, the surface curvature influence on the development of TiO(2) nanotubes is seldom studied. Moreover, there is no research about the effect of heterogeneous concave depths of the guiding patterns on the anodized TiO(2) nanotube and Al(2)O(3) nanopore characteristics, such as diameter, growth direction, and termination/bifurcation. In this study, focused ion beam lithography is used to create concave patterns with heterogeneous depths on flat surfaces and with uniform depths on curved surfaces. For the former, bending and bifurcation of nanotubes/nanopores are observed after the anodization. For the latter, bifurcation of a large tube into two smaller tubes occurs on concave surfaces, while termination of existing tubes occurs on convex surfaces. The growth direction of all TiO(2) nanotubes is perpendicular to the local surface and thus is different on different facets of the same Ti foil. At the edge of the Ti foil where two facets meet, the nanotube growth direction is bent, resulting in a large stress release that causes the formation of cracks.

Controlled Density Patterning of Tolylterpyridine-Tagged Oligonucleotides

An efficient surface anchoring strategy of tolylterpyridine-tagged DNA single strands (ssDNA-ttpy) synthesized on gold electrodes is reported. The method is based on exchange reactions between Fe(II)bis-terpyridine complexed SAMs and ssDNA-ttpy, and allows efficient hybrydization of the cDNA strands. Moreover, by using low-current focused ion beam lithography, micropatterned arrays are obtained, homogeneously covered with ssDNA-ttpy. The surface adsorption kinetics of ssDNA-ttpy, as well as its hybridization efficiency, was monitored by in situ quartz crystal microbalance with dissipation monitoring (QCM-D) technique. The effective confinement of the ssDNA-ttpy at the micrometer level has been monitored by time of flight secondary ion mass spectrometry (ToF-SIMS) and ellipsometric surface imaging experiments, providing laterally resolved chemical and topographic mapping.

Optical field-enhancement in metal nanoparticle arrays contacted by electron beam induced deposition

We study the impact of optical field-enhancement effects on the optoelectronic properties of metal nanoparticle arrays. Applying a focused ion beam lithography in combination with an electron beam induced deposition technique we pattern electrical contacts in a way that they give rise to an electromagnetic field-enhancement. The field-enhancement is directly observed in an enhanced photoconductance of the arrays. Finite-difference time-domain simulations verify that an antenna effect is responsible for the observed increase in the photoconductance.

Glass carbon surface modified by the fluorine ion irradiation

Application of nano and micro fabrication techniques in industry requires solution to some crucial problems. One of the significant problems is the sticking interface between mold surface and imprinted polymer. In this study, we report a solution to the sticking interface problem by modification of nano imprinting mold using fluorine ion implantation. After the fluorine implantation, anti sticking layer appeared on the nano imprinting mold surface. After the implantation, a mold made from glass like carbon was patterned by focused ion beam lithography. The pattern was made up of word “TIRI”. The line width was varied with 300 nm, 500 nm, and 1 μm. The line depth was about 200 ∼ 300 nm. The average depth of implanted fluorine was approximately 90 nm. After imprinting, the resin was removed from the mold by mechanical lift-off process. Transferred pattern was observed and confirmed by a scanning electron microscope (SEM) and an atomic force microscope (AFM). The pattern transferred from mold to resin was found to be successful.

The rapid prototyping of textured amorphous surfaces for the graphoepitaxial deposition of CdTe films using focused ion beam lithography

Cadmium telluride films deposited on amorphous substrates exhibit a grain structure characterized by [111]-oriented grains, but where the in-plane grain orientation is randomized due to the absence of epitaxy. Here, we explore the viability of promoting an in-plane grain alignment through graphoepitaxy. Fifteen different substrate surface textures were fabricated using focused ion beam lithography. This approach allows for the side-by-side deposition of surface textures where both the areal extent and depth of the surface features are varied in a systematic manner. CdTe films deposited overtop these textures show grain structures with dramatic variations, revealing that particular length scales have the most pronounced effect on the grain structure.

Magnetization reversal in Pt/Co(0.5 nm)/Pt nano-platelets patterned by focused ion beamlithography

Arrays of ultrathin Pt/Co(0.5 nm)/Pt nano-platelets with lateral sizes ranging from 30 nm to1 µm have been patterned by focused ion beam (FIB) lithography under a weakGa + ion fluence. From polar magneto-optical Kerr microscopy it is demonstrated thatnano-platelets are ferromagnetic with perpendicular anisotropy down to a size of50 nm. The irradiation process creates a magnetically soft ring at the nano-plateletperiphery in which domain nucleation is initiated at a low field. The magnetizationreversal in nano-platelets can be interpreted using a confined droplet model. All ofthe results prove that ultimate FIB patterning is suitable for preparing discretemagnetic recording media or small magnetic memory elements and nano-devices.

Focused Ion Beam Lithography and Anodization Combined Nanopore Patterning

In this study, focused ion beam lithography and anodization are combined to create different nanopore patterns. Uniform-, alternating-, and gradient-sized shallow nanopore arrays are first made on high purity aluminum by focused ion beam lithography. These shallow pore arrays are then used as pore initiation sites during anodization by different electrolytes. Depending on the nature of the anodization electrolyte, the nanopore patterns by focused ion beam lithography play different roles in further pore development during anodization. The pore-to-pore distance by focused ion beam lithography should match with that by anodization for guided pore development to be effective. Ordered and heterogeneous nanopore arrays are obtained by the focused ion beam lithography and anodization combined approach.

Gradient and alternating diameter nanopore templates by focused ion beam guided anodization

Ordered arrays of anodic alumina nanopores with uniform pore diameters have been fabricated by self-organized anodization of aluminum. However, gradient or alternating diameter nanopore arrays with designed interpore distances have not been possible. In this study, focused ion beam lithography is used to fabricate hexagonally arranged concaves with different diameters in designed arrangements on aluminum surfaces. The patterns are then used to guide the further growth of alumina nanopores in the subsequent oxalic acid anodization. Gradient and alternating nanopore arrangements have been attained by FIB patterning guided oxalic acid anodization. The fundamental understanding of the process is discussed.

Unique nanopore pattern formation by focused ion beam guided anodization

The fabrication of ordered porous templates in large areas with sophisticatedpatterns beyond mono-sized pores in hexagonal packing remains a great technicalchallenge. Conventional anodization cannot overcome this limitation and a newapproach needs to be sought. This study is focused on designing pore patterns insquare and hexagonal arrangements via focused ion beam lithography with varyinginterpore distances in order to form organized pore arrays with more sophisticatedpatterns. The results demonstrate that the small pores from the anodization can bemeshed with the larger pores from the focused ion beam lithography and unique,complicated nanopore patterns can be created. Large pore patterns that cross the grainboundaries are also made possible with the guidance of the pores from focused ionbeam lithography. A fundamental pore pattern formation mechanism is proposed.

Direct-write Focused Ion Beam Lithography

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

The fabrication of ordered arrays of exchange biasedNi/FeF2 nanostructures

The fabrication of ordered arrays of exchange biasedNi/FeF2 nanostructures by focused ion beam lithography is reported. High qualitynano-elements, with controlled removal depth and no significant re-deposition,were carved using small ion beam currents (30 pA), moderate dwell times (1 µs) and repeated passages over the same area. Two types of nanostructureswere fabricated: square arrays of circular dots with diameters from125 ± 8 to500 ± 12 nm and periodicitiesranging from 200 ± 8 to1000 ± 12 nm, and square arraysof square antidots (207 ± 8 nm in edge length) with periodicities ranging from300 ± 8 to1200 ± 12 nm. The arrays were characterized using scanning ion and electron microscopy, and atomicforce microscopy. The effect of the patterning on the exchange bias field (i.e., the shift inthe hysteresis loop of ferromagnetic Ni due to proximity to antiferromagneticFeF2) was studied using magneto-transport measurements. These high quality nanostructuresoffer a unique method to address some of the open questions regarding the microscopicorigin of exchange bias. This is not only of major relevance in the fabrication andminiaturization of magnetic devices but it is also one of the important proximityphenomena in nanoscience and materials science.

Single-defect photonic crystal cavity laser fabricated by a combination of laser holography and focused ion beam lithography

Large-scale, high-throughput fabrication of photonic crystal (PC)-based devices was achieved by using a combination of laser holography (for background PC generation) and focused ion beam lithography (for defect formation). An array of InP-based square-lattice PC lasers with a single air-hole defect was fabricated by this combined lithography. The resultant lasers consistently exhibited two lasing modes, which were identified as quadrupole and dipole modes on the basis of their spectral and polarization properties. The high cavity Q-factor (∼2200) and low laser threshold (∼0.25 mW) indicated that the laser quality was comparable to that of the PC lasers formed by electron-beam lithography.

Amorphous silicon and silicon nitride channel optical waveguides

AbstractIn this work we report on the characterisation of multimode rectangular ridge waveguides fabricated by Plasma Enhanced Chemical Vapor Deposition and anisotropic etching using different cores, consisting of hydrogenated amorphous silicon and amorphous silicon nitride. The propagation losses have been measured at several wavelengths by an end‐fire coupling set‐up and compared to intrinsic absorption of the core materials.Two‐dimensional photonic crystal structures have been carved onto the channel waveguides by Focused Ion Beam lithography demonstrating the possibility to fabricate complex optical elements merging the consolidated amorphous silicon growth technology with ion‐beam nanomachining. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Large area direct-write focused ion-beam lithography with a dual-beam microscope

The authors have investigated the performance of focused ion-beam (FIB) direct-write lithography for large area (multiple write-field) patterning in an FEI Nova Nanolab 600 dual-beam microscope. Their system is configured with a 100 nm resolution X-Y stage and a RAITH ELPHY LITHOGRAPHY control interface, with its own integrated 16 bit DAC pattern generator and software. Key issues with regard to configuration, process parameters, and procedures have been addressed. Characterization of stitching errors, pattern repeatability, and drift were performed. Offset lithography (multiple exposures with offset write fields) and in-field registration marks were evaluated for correcting stitching errors, and a test microfluidic device covering an area of 1×1.4 mm2 was successfully fabricated. The authors found that by using a combination of offset lithography and in-field registration mark correction methods, the stitching errors can be kept well below 100 nm. They also found that due to higher beam deflection speed provided by the electrostatic scanning in FIB systems versus the wide-spread electron-beam systems with electromagnetic scanning, FIB lithography can be just as fast as electron-beam lithography for typical mill depths down to about 200–500 nm (material dependent). This opens the door for a large suite of applications for materials where pattern transfer is difficult or impossible by reactive methods.

Surface patterning nanoparticle-based arrays

In this study, focused ion beam lithography is used to pattern different size and shape island arrays on silicon wafers. Cavity arrays of inverse shapes are then made on silicone mold surfaces by polymerization. After that, Al2O3 nanoparticle-based island arrays are created by a surface feature transfer and freeze casting process using an Al2O3 colloidal suspension. The effects of silicone mold surface wettability and freezing rate on the Al2O3 nanoparticle pattern quality are investigated. The results show that coating the silicone mold surface with a 10 nm thick Au–Pt layer makes the Al2O3 nanoparticle suspension more wetting on the mold surface and also likely reduces the dry Al2O3 nanoparticle adhesion to the mold surface. Freezing rate should be lower than 1 °C/min to avoid cracks or loose Al2O3 nanoparticle packing in the freeze cast features. When these factors are properly controlled, the reported patterning process allows reproduction of micron-size feature arrays from Al2O3 nanoparticle suspensions. The studied approach should be applicable to most nanoparticle-based materials and open numerous opportunities for direct-device fabrication.

Multiscale 3D Patterning of Nanoparticle Assemblies for Plasmonic Devices

AbstractWe have developed a novel strategy for elaborating composite plasmonic nanomaterials in a well controlled manner. Combining several techniques commonly used in microelectronic engineering, namely sputtering deposition, thermal oxidation, ultra low energy ion implantation, focused ion beam lithography, thermal or laser annealing, we have obtained 3D patterned optical layers. Their spatial and spectral responses take benefit of optical interference, plasmonic resonance effects and coupling between excitations in both near and far field regime. Moreover these structures show high level of uniformity, reproducibility and stability, and they preserve flat and chemically uniform surfaces.

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.

Shadow Overlap Ion-beam Lithography for Nanoarchitectures

Precisely constructed nanoscale devices and nanoarchitectures with high spatial resolution are critically needed for applications in high-speed electronics, high-density memory, efficient solar cells, optoelectronics, plasmonics, optical antennas, chemical sensors, biological sensors, and nanospectroscopic imaging. Current methods of classical optical lithography are limited by the diffraction effect of light for nanolithography, and the state of art of e-beam or focused ion beam lithography limit the throughput and further reduction less than few nanometers for large-area batch fabrication. However, these limits can be surpassed surprisingly by utilizing the overlap of two shadow images. Here we present shadow overlap of ion-beam lithography (SOIL), which can combine the advantages of parallel processing, tunable capability of geometries, cost-effective method, and high spatial resolution nanofabrication technique. The SOIL method relies on the overlap of shadows created by the directional metal deposition and etching angles on prepatterned structures. Consequently, highly tunable patterns can be obtained. As examples, unprecedented nanoarchitectures for optical antennas are demonstrated by SOIL. We expect that SOIL can have a significant impact not only on nanoscale devices, but also large-scale (i.e., micro and macro) three-dimensional innovative lithography.

Bipolar resistive switching performance of the nonvolatile memory cells based on (AgI)0.2(Ag2MoO4)0.8 solid electrolyte films

Resistive switching memory cells with polycrystalline (AgI)0.2(Ag2MoO4)0.8 (AIMO) solid electrolyte films as storage medium were fabricated on SiO2/Pt/Ti/Si substrates by using pulse laser deposition technique and focused ion beam lithography. X-ray diffraction, scanning electron microscopy, and energy dispersive x-ray analysis have been employed to investigate the structure, the surface morphology, and the composition of AIMO thin films. The Ag/AIMO/Pt memory cells with sandwich structure exhibit stable, reproducible, and reliable resistive switching characteristics. The ratio of resistance between high resistance states and low resistance states can reach ∼105. Moreover, the low resistance is ∼500 Ω at a compliance current of 0.5 mA, which is favorable to reduce the power dissipation of the entire circuit. The switching-on mechanism has been discussed and the metallic conduction characteristic has also been verified. The fast response speed and the good retention properties further indicate that polycrystalline AIMO thin film is a potential candidate for the next generation nonvolatile memory.