An investigation on focused electron/ion beam induced degradation mechanisms of conjugated polymers

Abstract

Irradiation damage, caused by the use of beams in the electron microscopes, leads to undesired physical/chemical material property changes or uncontrollable modification of structures that are being processed. Particularly, soft matter such as polymers or biological materials is highly susceptible and very much prone to react on irradiation by electron and ion beams. The effect is even higher when materials are subjected to energetic species such as ions that possess high momentum and relatively low mean path due to their mass. Especially when Ga(+) ions (used as the ion source in Focused Ion Beam (FIB) instruments) are considered, the end-effect might even be the total loss of the material's properties. This paper will discuss the possible types of degradation mechanisms and defect formations that can take place during ion and electron beam irradiation of the conjugated polymers: e.g. polyfluorene (PF) and poly-3-hexylthiophene (P3HT) thin films. For the investigation of the irradiation induced degradation mechanisms in this study, complementary analytical techniques such as Raman Spectroscopy (RS), Infrared Spectroscopy (IR), Electron Energy Loss Spectroscopy (EELS), Atomic Force Microscopy (AFM), and Fluorescence Microscopy including Photoluminescence (PL) and Electroluminescence (EL) Microscopy were applied.

Three‐dimensional nanofabrication of polystyrene by focused ion beam

“…The pristine polystyrene exhibits a typical Raman spectrum (Palm, 1951), in which the peaks that appear between 2800 and 3200 cm −1 are attributed to the carbon–hydrogen (CH, CH 2 ) bonds, whereas the peaks below 2000 cm −1 are ascribed to the carbon–carbon aromatic bonds (benzene ring). The depth of penetration is typically less than 1 μm (depends primarily on the wavelength of the laser source and the absorption of the light by the sample), thus making this technique highly suitable for the damage analysis caused by ion bombardment (Sezen et al ., 2009; Sezen et al ., 2011).…”

“…The authors have recently been using this technique for the production of free‐standing polystyrene–platinum bimorph cantilever thermal microactuators for MEMS/NEMS applications (Lee et al ., 2011). These applications may, however, be limited by the creation of unwanted morphological and chemical modifications in the polymers due to variations in the surface structure of the polymer film (Ektessabi & Sano, 2000; Niihara et al ., 2005; Sezen et al ., 2009; Kim et al ., 2011; Sezen et al ., 2011). Critical issues in polymer micro/nanofabrication using the ion beam include direct sputtering and indirect thermal evaporation of surface atoms/molecules, depletion of main components of the polymer such as carbon, hydrogen, oxygen, etc., rearrangement of chemical bonds and cross‐linking, and incorporation of ions into the film (Ektessabi & Sano, 2000).…”

“…Possible routes to minimize the damage caused by the ion beam include milling the polymers at cryogenic temperatures (e.g. −150°C) to reduce local heating (Niihara et al ., 2005; Sezen et al ., 2009; Kim et al ., 2011; Sezen et al ., 2011), applying an electrically conductive coating or using an electron flood gun against ion charging (Stokes et al ., 2007) or removing the polymer at a faster rate using water vapour (Kochumalayil et al ., 2009a, b).…”

Visualizing cellulase activity

“…Likewise, beam damage on delicate matter can produce artifacts and sample damage (Allison et al, 2010; Imai et al, 2003; Peckys et al, 2011). This can be delayed by using a low temperature sample stage, which, however, requires special equipment for a rapid sample freezing in order to prevent ice formation within the specimen (Clegg and Collyer, 1991; Sezen et al, 2009, 2011). Finally, the lack of capability to visualize dynamic processes and the non‐environmental conditions required (i.e., vacuum) further limits the application of TEM in following the structural dynamics of enzymatic cellulose degradation.…”

Mask‐free prototyping of metal‐oxide‐semiconductor devices utilizing focused electron beam induced deposition

“…As a viable way of overcoming these challenges, direct writing techniques have been implemented over the last years. Focused ion beam induced deposition (FIBID) has already been used to deposit electrical contacts on Si NW transistors directly at room temperature . However, this technique suffers from serious drawbacks.…”