Three‐dimensional nanofabrication of polystyrene by focused ion beam

Abstract

SummaryFocused ion beam micromachining provides a maskless and resistless technique for prototyping of structures from thermoplastic polymers, an example being the production of polystyrene microcantilevers with potential applications as micro/nanoelectromechanical systems sensors and actuators. The applicability of FIB technology is, however, often restricted by the damage created by high energy gallium ion bombardment and local beam heating, which can affect the desired properties and limit the minimum achievable size of the fabricated structure. To investigate the ion-induced damage and determine the limitations of the technique for polymer nanofabrication, we have exposed thin polystyrene film to the ion beam at varying ion doses, ion energies and specimen temperatures. Ion doses ranging from 10 16 to 10 18 ions cm −2 show significant gallium implantation, redeposition of sputtered material and chemical degradation in the polymer. Raman results show that the local heating in polymer during milling is severe at room temperature, damaging the aromatic carbon bonding (C = C) in particular. These observations are supported by the results of a beam heating model and Monte Carlo simulations. The chemical degradation caused by local beam heating is found to be significantly reduced by cooling the specimen to −25 • C during milling. This is consistent with observations that reversible and repeatable thermal actuation of a fabricated polystyrene-platinum microcantilever is only observed when the cantilever is prepared at low temperature milling. Using this cooling approach, polymer structures can be fabricated with dimensions as low as 200 nm and still retain a sufficient volume of material unaffected by the ion beam.

Far‐reaching geometrical artefacts due to thermal decomposition of polymeric coatings around focused ion beam milled pigment particles

“…However, this process can introduce molecular scale changes that are detectable using transmission electron microscope (Kim et al ., ), cause local cracking of the polymer (Olea‐Mejía et al ., ), and even sufficient morphological instabilities to severely deform the geometry FIB‐prototyped nanostructures (Schmied et al ., , ; Orthacker et al ., ). For pure polymers the thermal damage localized to the ion beam impact area can be minimized using cryogenic cooling, low current milling and smart navigation of the ion beam (Kim et al ., , Bassim et al ., , Lee et al ., , Olea‐Mejía et al ., , Schmied et al ., , , Orthacker et al ., ). In the latter approach the ion beam exposure pattern is altered from the common pixelated line‐by‐line raster to increase the time in‐between re‐exposure of individual points.…”

“…Dual beam instruments that combine focused ion beam with a scanning electron microscope (FIB-SEM) are extensively used for characterization of various materials ranging from semiconductors to biological tissue (Stevie et al, 2005;Volkert & Minor, 2007;Bassim et al, 2014), but have not been applied to analysis of organic corrosion barrier coatings. In the past, FIB-SEM has been used for site specific cross sectioning and/or lamella extraction for transmission electron microscope imaging (White et al, 2001;Lins et al, 2002;Loos et al, 2002;Beach et al, 2005;Brunner et al, 2006Brunner et al, , 2008Brostow et al, 2007;Kawahara et al, 2008;Martínez et al, 2008;Wong et al, 2010;Firpo et al, 2015;Qin et al, 2015), destructive tomography (Kato et al, 2007;Lin et al, 2012;Olea-Mejía et al, 2012) and nanofabrication (Aubry et al, 2002;Niihara et al, 2005;Lee et al, 2012;Schmied et al, 2012;Orthacker et al, 2014;Schmied et al, 2014) of polymers and polymeric composites. Out of these examples, only a few studies have been dedicated to characterization of pristine organic coatings and paints (Lins et al, 2002;Brunner et al, 2006Brunner et al, , 2008Brostow et al, 2007;Lin et al, 2012;Chen et al, 2013;Doutre et al, 2014).…”

FIB-Etching of Polymer/Metal Laminates and its Effect on Mechanical Performance

“…This technique was successfully used to prepare crosssections of polymer/metal interfaces (Faber et al, 2014). FIB is not supposed to introduce strain into the material near the interface (Kim et al, 2011;Lee et al, 2011Lee et al, , 2012Bassim et al, 2012;Schmied et al, 2012;Rivera et al, 2013). In FIB a focused beam of 30 keV Ga + ions is used to sputter material.…”

In situ transmission electron microscopy studies of the kinetics of Pt-Mo alloy diffusion in ZrB2 thin films

“…Previous studies have shown that FIBinduced Ga segregates onto the surface in the form of spherical droplets. [24][25][26][27][28][29] Within an hour of annealing at T a $ 773 K, most of the smaller Ga droplets disappear from the transparent regions of the sample via Ostwald ripening and are absorbed by larger droplets located at the thicker ends of the sample. 30 In situ annealing at higher temperatures T a between 1073 and 1173 K are carried out in the double C s -corrected Link€ oping FEI 80-300 Titan 3 scanning TEM (STEM) equipped with EDS and EELS spectrometers.…”