EnSol (Norway)

Metal nanoparticles have interesting optical properties, in particular, the localized surface plasmon resonance effect (LSPR), which can be used in a range of applications such as photon detectors, photovoltaics, and biosensors. The theory of LSPR is complex, and hence, it is very important to develop reliable model systems, where the properties of the particles can be investigated under controlled conditions. Important parameters, which influence the frequency and intensity of the LSPR, are size, shape, and spacing of the individual nanoparticles, as well as the metal and the surrounding medium. For applications related to photovoltaics, in particular, it is important to investigate the effect of nanoparticles, covering large areas to mimic realistic operating conditions. Here, the authors present a preparation method and optical investigations of LSPR for large arrays (5 mm × 5 mm) of gold and aluminum nanoparticles ranging in diameter from 44 to 140 nm (corresponding to around 120 million particles). The authors compare and see that the LSPR measurements have a good agreement with previously published results from the literature. These measurements from the literature were mostly performed on much smaller arrays. The authors briefly discuss the effect of depositing the nanoparticles on an indium-tin-oxide-coated glass instead of a bare glass substrates and point out an interesting scanning electron microscopy imaging artifact when measuring the samples deposited directly on nonconductive substrates. A shrinkage effect is seen due to sample charging, causing the measured dimensions to appear smaller than the physical size of the object.

Electron beam lithography (EBL) is a maskless lithography technique used in numerous applications for fabrication of ultrahigh-resolution photolithography masks. The main disadvantage of EBL is that it is time-consuming, requiring the pattern to be written in a successive fashion. Various approaches are used to lower the write time. Throughput-oriented EBL instruments used in industrial applications typically apply a very high acceleration voltage (≥50 kV). However, in many research environments, more cost-effective instruments are used. These tools are usually optimized for high-resolution writing and are not very fast. Hence, they are normally not considered very suitable for writing large-scale structures with high pattern densities, even for limited resolution applications. In this paper, the authors show that a carefully considered optimization of the writing parameters in an EBL instrument (Raith e_LiNE) can improve the writing time to more than 40 times faster than commonly used instrument settings. The authors have applied the optimization procedure in the fabrication of high-precision photolithography masks. Chrome photolithography masks, 15 mm in diameter with a write resolution of 200 nm, were routinely produced during overnight exposures (less than 9 h). The write time estimated by the instrument software for most commonly used settings was close to 14 days. A comparison with conventional chrome masks fabricated using a high-resolution (128 000 dpi) photolithography mask printer showed that our pattern definition is significantly better.