D. Decanini

Nanoscale Magnetic Domains in Mesoscopic Magnets

The basic magnetic properties of three-dimensional nanostructured materials can be drastically different from those of a continuous film. High-resolution magnetic force microscopy studies of magnetic submicrometer-sized cobalt dots with geometrical dimensions comparable to the width of magnetic domains reveal a variety of intricate domain patterns controlled by the details of the dot geometry. By changing the thickness of the dots, the width of the geometrically constrained magnetic domains can be tuned. Concentric rings and spirals with vortex configurations have been stabilized, with particular incidence in the magnetization reversal process as observed in the ensemble-averaged hysteresis loops.

λ3/1000 Plasmonic Nanocavities for Biosensing Fabricated by Soft UV Nanoimprint Lithography

Arrays of plasmonic nanocavities with very low volumes, down to λ(3)/1000, have been fabricated by soft UV nanoimprint lithography. Nearly perfect omnidirectional absorption (3-70°) is demonstrated for the fundamental mode of the cavity (λ ≃ 1.15 μm). The second-order mode exhibits a sharper resonance with strong angular dependence and total optical absorption when the critical coupling condition is fulfilled (45-50°, λ ≃ 750 nm). It leads to high refractive index sensitivity (405 nm/RIU) and figure of merit (∼21) and offers new perspectives for efficient biosensing experiments in ultralow volumes.

Study of large area high density magnetic dot arrays fabricated using synchrotron radiation based x‐ray lithography

Large area arrays of dots have been patterned in Au/Co/Au(111) sandwiches with ultrathin Co layers (0.6 to 2 nm) and a perpendicular easy magnetization axis. Dot dimensions down to 0.2 μm have been achieved using x‐ray lithography, with either positive resist and direct ion beam etching or a lift‐off process with aluminum mask. Both processes have been tested against the damages they induce to the fragile structure of the samples. The magneto‐optical effects and magnetization reversal processes in the arrays have been characterized versus Co thickness, dot dimension, and lattice aspect ratio. For high quality samples, the domain walls propagation mechanism that drives magnetization reversal in as‐grown films is drastically modified in dot arrays, leading to a large increase of the coercive field with dot diameter reduction, together with changes in the shape of the hysteresis loops.

Metal nanostructures prepared by template electrodeposition

Abstract Template electrodeposition, by which is meant electrodeposition in natural or artificial holes in an insulating layer on a conducting substrate, offers an inexpensive route to the fabrication of patterned metal films, in some cases with structures that cannot be produced by any other method. For example, we show that it is possible to prepare nanowires of Co–Cu granular alloy by template electrodeposition in porous aluminium oxide, and that the GMR of the wires increases, as expected, on annealing. As another example, we have fabricated arrays of multilayered μm-diameter dots using a resist layer patterned by X-ray lithography as the template – here a useful feature of electrodeposition is that it is selective, occurring only in the template holes, and not on the surface of the resist layer. Finally, we show one extension of the technique beyond magnetic materials, presenting initial results for the structure and transport properties of Pb nanowires, which are not only superconducting, but may also be grown as single-crystals.

Permalloy cylindrical submicron size dot arrays

Abstract Arrays of cylindrical permalloy dots of diameter varying from 88 to 200 nm were fabricated using high-resolution X-ray and electron beam lithography techniques. Reduction of the diameter induces a drastic modification of the magnetisation reversal process. For single domain dots, interdot dipolar coupling plays an important role for the global stable state. Magnetic force microscopy and alternating gradient magnetometry results are presented and discussed.

Spin-wave quantization and dynamic coupling in micron-size circular magnetic dots

We report on the observation of spin-wave quantization in square arrays of micron-size circular magnetic Ni80Fe20 dots by means of Brillouin light-scattering spectroscopy. For a large wave-vector interval several discrete, dispersionless modes with a frequency splitting of up to 2.5 GHz were observed. The modes are identified as magnetostatic surface spin waves laterally quantized due to in-plane confinement in each single dot. The frequencies of the lowest observed modes decrease with increasing distance between the dots, thus indicating an essential dynamic magnetic dipole interaction between the dots at small interdot distances.

50‐nm x‐ray lithography using synchrotron radiation

A technology of proximity x‐ray lithography has been developed to replicate patterns of sub‐100‐nm feature size using synchrotron radiation. Process modeling has been done in advance in order to optimize the mask absorber thickness. It is shown that with tungsten absorber, a 0.3 μm thickness is the most desirable for 50 nm linewidth processing. Masks compatible with a Karl Suss stepper have been fabricated using 50 keV electron‐beam lithography and reactive ion etching techniques. As a result, well‐defined 50‐nm‐wide isolated W lines and small gratings of period down to 100 nm have been fabricated. Then they have been replicated under proximity condition using Super ACO synchrotron radiation. We present details of a replication procedure with gap settings down to 5 μm and show how sub‐100 nm structures can be 1:1 printed into both poly (methylmethacrylate) (PMMA) and (8.5%) MAA/PMMA resists. Finally, the results are analyzed in terms of a scaling rule to evaluate the resolution limit as a function of prox...

Fabrication of three-dimensional photonic structures with submicrometer resolution by x-ray lithography

We report on the fabrication of diamond-like photonic structures in PMMA resist and their use as porous templates for transferring three-dimensional patterns to metals or dielectrics. Following the original “three drilling holes” approach first proposed by Yablonovitch, we used three consecutive exposures of PMMA resist to an x-ray beam through a triangular lattice of holes. A submicronic patterning was thus obtained in thick PMMA layers (>6 μm). Optical characterizations of 1.3 μm period templates showed a well-defined photonic gap in the midinfrared. The pattern transfers from the PMMA templates to a metal (copper) and a high refractive index dielectric (titania) were achieved by the electrodeposition and sol–gel filling techniques, respectively. Three-dimensional metallic structures of 1.3 μm lattice constant were obtained with extreme regularity over a thickness of ∼6 μm, thereby providing a way to build submicrometer photonic band gap materials for optical wavelengths.

A 100‐nm patterned x‐ray mask technology based on amorphous SiC membranes

A mask technology based on amorphous SiC membranes and stress minimized W and Au absorbers has been developed to reach 100‐nm critical linewidth pattern. Using low temperature techniques, plasma‐enhanced chemical vapor deposition and rf triode sputtering, very smooth large membranes (45×45 mm2 with a surface roughness <5 nm) have been produced. Two absorber technologies have been developed: gold electroplating in a cyanide bath and tungsten rf sputtering with subsequent dry etching. Induced film stresses were investigated as a function of the absorber microstructure and minimized by a fine adjustment of the deposition parameters. With a new process, based on a single patterned resist layer, we succeeded in transfering patterns with linewidth down to 100 nm. To demonstrate the dimensional quality of the x‐ray masks, x‐ray exposures have been performed under synchrotron radiation at Super‐ACO:150‐nm‐wide line and 450‐nm‐wide space gratings have been obtained in 1.7‐μm‐thick PMMA resist by contact printing. ...

Highly parallel mix-and-match fabrication of nanopillar arrays integrated in microfluidic channels for long DNA molecule separation

We report on a mix-and-match method based on a combination of soft UV nanoimprint lithography, contact optical lithography, and reactive-ion-etch techniques, which is applicable for high throughput manufacturing of nanostructure integrated microfluidic devices. We demonstrate the integration of high density and high aspect ratio nanopillars into microfluidic channels as electrophoresis sieving matrices. As a result, λ DNA and T4 DNA can be separated within a few minutes. By changing the pattern design, the device could be used for separation of other types of molecules.