Hybrid FIB milling strategy for the fabrication of plasmonic nanostructures on semiconductor substrates

The optical properties of plasmonic semiconductor devices fabricated by focused ion beam (FIB) milling deteriorate because of the amorphisation of the semiconductor substrate. This study explores the effects of combining traditional 30 kV FIB milling with 5 kV FIB patterning to minimise the semiconductor damage and at the same time maintain high spatial resolution. The use of reduced acceleration voltages is shown to reduce the damage from higher energy ions on the example of fabrication of plasmonic crystals on semiconductor substrates leading to 7-fold increase in transmission. This effect is important for focused-ion beam fabrication of plasmonic structures integrated with photodetectors, light-emitting diodes and semiconductor lasers.

Plasmonic junctions with cucurbit[5]uril 'glue': fabrication of precise sub-nm junctions in gold nanoparticle assemblies

Aggregation of gold nanoparticles with rigid cucurbit[5]uril molecules generates fixed inter-particle separations of 0.91 nm. These nanoparticle assemblies possess discrete plasmonic modes which elucidate nanoscale growth and serve as molecular-recognition based SERS substrates.

Fabrication and optical properties of gold nanotube arrays

Arrays of gold nanotubes with polypyrrole cores were grown on glass substrates by electrodeposition into thin film porous alumina templates. Measurements of optical transmission revealed strong extinction peaks related to plasmonic resonances, which were sensitive to the polarization state and angle of incidence. On prolonging the electrodeposition of gold, the polypyrrole core became fully encapsulated and this had a dramatic effect on the optical properties of the arrays, which was rationalized by finite element simulation of the local field intensities resulting from plasmon excitation.

The controlled fabrication and geometry tunable optics of gold nanotube arrays

Arrays of vertically aligned gold nanotubes are fabricated over several square centimetres which display a geometry tunable plasmonic extinction peak at visible wavelengths and at normal incidence. The fabrication method gives control over nanotube dimensions with inner core diameters of 15–30 nm, wall thicknesses of 5–15 nm and nanotube lengths of up to 300 nm. It is possible to tune the position of the extinction peak through the wavelength range 600–900 nm by varying the inner core diameter and wall thickness. The experimental data are in agreement with numerical modelling of the optical properties which further reveal highly localized and enhanced electric fields around the nanotubes. The tunable nature of the optical response exhibited by such structures could be important for various label-free sensing applications based on both refractive index sensing and surface-enhanced Raman scattering.

Fabrication and optical properties of large-scale arrays of gold nanocavities based on rod-in-a-tube coaxials

Centimeter sized arrays of gold coaxial rod-in-a tube cavities have been fabricated using anodized aluminum oxide as a template. The etching process used to create the cavities enables the production of extremely small gaps between tube and rod, on the order of 5 nm, smaller than those created by standard fabrication techniques. Normal incidence spectroscopy reveals two extinction peaks in the visible and near infrared wavelength range associated with resonant plasmonic modes excited in the structure. Numerical simulations show that the modes are associated with in-phase and out-of-phase hybridization of transverse dipolar excitations in the nanorod and in the tube.

Mask assisted fabrication of nanoislands of BiFeO3 by ion beam milling

We report on a low-damage method for direct and rapid fabrication of arrays of epitaxial BiFeO3(BFO) nanoislands. An array of aluminium dots is evaporated through a stencil mask on top of an epitaxial BiFeO3 thin film. Low energy focused ion beam milling of an area several microns wide containing the array-covered film leads to removal of the bismuth ferrite in between the aluminium-masked dots. By chemical etching of the remaining aluminium, nanoscale epitaxial bismuth ferrite islands with diameter ∼250 nm were obtained. Piezoresponse force microscopy showed that as-fabricated structures exhibited good piezoelectric and ferroelectric properties, with polarization state retention of several days.

Virtual metrology enabled early stage prediction for enhanced control of multi-stage fabrication processes

Semiconductor fabrication involves several sequential processing steps with the result that critical production variables are often affected by a superposition of affects over multiple steps. In this paper a Virtual Metrology (VM) system for early stage measurement of such variables is presented; the VM system seeks to express the contribution to the output variability that is due to a defined observable part of the production line. The outputs of the processed system may be used for process monitoring and control purposes. A second contribution of this work is the introduction of Elastic Nets, a regularization and variable selection technique for the modelling of highly-correlated datasets, as a technique for the development of VM models. Elastic Nets and the proposed VM system are illustrated using real data from a multi-stage etch process used in the fabrication of disk drive read/write heads. © 2013 IEEE.